NITROBENZENE PRODUCTION

 

 

 

 

 

by

SARAH RASHEED Ghayeb

Jumada II 1430

June 2009

AL- Nahrain University

College of Engineering

Chemical Engineering Department

A Final Year Project Submitted to the Department of Chemical

Engineering in the Engineering of Nahrain University in

Partial Fulfillment of the Requirements for the Degree Bachelors in Scienece of Chemical Engineering

I

 

Abstract

Nitrobenzene or caswell No. 600 chemical material use in the

manufacture of various plastic monomers and polymers, rubber chemicals,

drugs, pesticides, soaps, and as a solvent in petroleum refining and

manufacture of cellulose ethers and cellulose acetate…ect

The production capacity of nitrobenzene 70000 ton/year, this capacity

was take as rough estimation for the requirements of our country.

Nitrobenzene is manufacture commercially by the direct nitration of

benzene using a mixture of nitric acid and sulfuric acid, many processes for

this manufacture but the more safety, economic and lower capital cost is the

continuous isothermal nitration process.

In this project material balance, energy balance, design of the nitrator,

settler, heat exchanger and distillation column, process control, plant

location & Toxicity and Effect of Nitrobenzene.

II

 

List of Contents

Content Page

Abstract I

List of Content II

List of Figures VI

List of Tables VII

Nomenclature VIII

Chapter One: Introduction

1.1 History 1

1.2 Specification of Nitrobenzene 2

1.3 Identity 4

1.4 Physical Properties 4

1.5 Chemical Properties 5

1.6 Uses 11

1.7 Nitrobenzene Derivative 12

Chapter Two: Production Methods of Nitrobenzene

2.1 General 14

2.2 Batch Process 16

2.3 Tubular Reactor Process 17

2.4 Continuous Process 18

2.4.1 Adiabatic continuous process 19

2.4.2 Isothermal continuous process 21

III

 

2.5 Non-Industrial Sources 21

2.6 Process Selection 23

2.7 Description of the Selected Process 23

Chapter Three: Material Balance

3.1 General Information 27

3.2 Material Balance on Nitrator 28

3.3 Separator Material Balance 30

3.4 Washing Process Material Balance 30

3.4.1 1st Washing Process Material Balance 32

3.4.2 2nd Washing Process Material Balance 32

3.5 Reconcentrator Material Balance 35

3.6 Distillation Material Balance 38

Chapter four: Energy Balance

4.1 Energy Balance on Nitrator 42

4.2 Separator Energy Balance 46

4.3 Energy Balance on Evaporator 48

4.4 Washing Process Energy Balance 52

4.4.1 1st Washing process Energy Balance 52

4.4.2 2nd Washing process Energy Balance 54

4.5 Distillation Energy Balance 57

IV

 

Chapter Five: Equipment Design

5.1 Nitrator Design 64

5.2 Settler Design 77

5.3 Heat Exchanger Design 82

5.4 Distillation Design 90

Chapter Six: Control System

6.1 Introduction 104

6.2 Control of Nitrator 105

6.3 Settler Control 107

6.4 Vaporizer Control 108

6-5 Heat Exchanger Control 109

6.6 Distillation column control 110

Chapter Seven: Plant Layout

7.1 Site Considerations 113

7.2 Site Layout 116

7.3 Plant Layout 118

7.4 Utilities 119

7.5 Environmental Consideration 120

7.6 Waste Management 120

7.8 Nitrobenzene Plant Location

122

V

 

Chapter Eight: Toxicity and Effects of Nitrobenzene

8.1 General 123

8.2 Effects on humans 124

8-3  Effects on organisms in the environment 125

8.4 Hazard and risk evaluation 126

8.5 Industrial safety 128

References 129

Appendixes

Appendix A: Physical Properties A-1

Appendix B: Equilibrium Data B-1

VI

 

List of Figures

Figure No. Title page

1-1 Reduction products of nitrobenzene 6

1-2 Key intermediates derived from nitrobenzene 13

2-1 production of Nitrobenzene- continuous process 19

2-2 Flow sheet for the production of nitrobenzene adiabatically

20

2-3 Atmospheric reactions generating and removing nitrobenzene

22

2-4 Typical continuous Nitrobenzene Process 26

4-1 Process Flow Diagram 63

5-1 Vapor-Liquid Equilibrium diagram (Isothermal) at 70oC

91

6-1 Nitrator Control 106

6-2 Settler control 107

6-3 Settler control 107

6-4 vaporizer control 108

6-5 Heat Exchanger control 109

6-6 Temperature pattern control 111

6-7 Composition control 111

6-8 Composition control 112

7-1 A typical site plant 118

VII

 

List of Tables

Table NO. Title Page

1-1 Specification for technical-Grade Nitrobenzene 3

1-2 Specifications for Distilled-grade Nitrobenzene (mirbane oil)

3

1-3 Some Physical Properties of Nitrobenzene 5

1-4 Reduction products of nitrobenzene 7

1-5 Type and estimated consumption of nitrobenzene in Western Europe in 1994

11

2-1 nitrobenzene production capacities in European countries in 1985

15

3-1 Material Balance on Nitrator 29

3-2 Material balance on separator 31

3-3 Material Balance on 1st Washing Unit 33

3-4 Material Balance on 2nd Washing Unit 35

3-5 Material Balance on Reconcentrator 38

3-6 Material Balance on Distillation 39

3-7 Overall Material Balance 40

3-8 all Streams of Material Balances 41

4-1 all Streams of Energy Balances 62

VIII

 

Nomenclature

Symbol Definition Unit

Aa Active Area m2

Aap Area under Apron m2

Ac Distillation Column Area m2

Ad Downcomer Area m2

Ah Hole Area m2

Ai Area or the Interface m2

Am Clearance Area under Downcomer m2

An Net Area m2

Ao Heat Transfer Area m2

Ap Total Area available for perforation m2

As Cross flow Area m2

a Blade Width m

b Baffle Width m

C Corrosion Allowance mm

Co Orifice Coefficient -

cp Specific heat KJ/Kg.mol.K

D Diameter m

DA Agitator Diameter m

Db Bundle Diameter m

Deff Effective Column Diameter m

IX

 

de Equivalent Diameter m

dh Diameter of Hole mm

di Inside Tube Diameter m

dm Diameter of Manholes mm

do Outside Tube Diameter m

dp Droplet Diameter µm

FC Flow Controller -

FLV Liquid Vapor Factor -

Ft Correction factor for ∆TLm -

FW Wind Load N/m

f Material Tensile Strength N/mm2

Gt Mass Velocity of the Fluid Tube Side Kg/m2.s

Gs Mass Velocity of the Fluid Shell Side Kg/m2.s

HA Height of agitator m

HL Height of the nitrator content m

hap Height of bottom edge of the apron above the plate

mm

hb Downcomer back-up mm

hbc Clear liquid back-up mm

hd Pressure drop through the tray plate mm Liquid

hdc Head loss in downcomer mm Liquid

hi Inside (tube) Heat Transfer coefficient W/m2.oC

hid Inside tube foaling coefficient W/m2.oC

ho outside (shell) Heat Transfer coefficient W/m2.oC

X

 

hod Outside tube foaling coefficient W/m2.oC

how Weir Crest (height of the liquid over weir) mm Liquid

hr Residence Head s

hT Total Height of Distillation Column m

ht Total plate drop head mm

hv Heat transfer to vessel W/m2.oC

hw Weir Height mm

J Joined Efficiency -

jf Friction Factor -

Kf Thermal Conductivity W/m.oC

LC Level Control -

Lc Continuous phase Volumetric flowrate m3/s

Lm Liquid mass flowrate Kg/s

Ln Liquid mass flowrate Kg/s

LW Weir Length m

lB Baffle spacing mm

lp Hole Pitch mm

Ms Bending moment at any plane N.m

m Mass flowrate Kg/s

N Agitator Speed rps

Np Power Number -

Np Number of passes -

Nt Number of Tubes -

P Pressure Design N/mm2

.

XI

 

PA Shaft Power W

Pch Sugden’s Parachor -

Pt Pitch mm

Pw Wind Pressure (Load per unit area) N/m2

r Blade Length m

S Distance measured from the free end m

T Temperature of the fluid in shell side oC

TC Temperature Controller -

TM Measuring Element -

t Temperature of the fluid in tube side oC

tr Residence time s

Uo Overall Heat Transfer coefficient W/m2.oC

uc Velocity of Continuous phase m/s

ud Settling velocity through hole m/s

uf Flooding Velocity m/s

uh Vapor Velocity through Hole m/s

umin Actual minimum Velocity of the Vapor m/s

ut Linear Velocity of the Fluid flow in Tube m/s

uv Corrected Flooding Vapor Velocity m/s

V Volume of Nitrator m3

Vm Vapor mass flowrate Kg/s

Vn Vapor mass flowrate Kg/s

XII

 

Greek Notation

µ Viscosity Pa.s

µc Viscosity of the Continuous phase Pa.s

µd Viscosity of the dispersed phase Pa.s

µw Viscosity at the wall Temperature Pa.s

τ Residence Time min

νo Initial Volumetric flowrate m3/hr

σ Surface Tension mJ/m2

ρ Density Kg/ m3

ρc Density of the Continuous phase Kg/ m3

ρd Density of the dispersed phase Kg/ m3

λ Latent Heat KJ/Kg.mol

∆TLm Mean Logarithm Temperature oC

∆Tm Mean Temperature Difference oC

∆Pt Pressure Drop in Tube Side pa

∆Ps Pressure Drop in Shell Side pa

XIII

 

Dimensionless Groups

Nu = h d /K Nusselt Number

Pr = cp µ / K Prandtle Number

Re = ρ u d / µ Reynolds Number

 

 

 

Chapter One Introduction

 

 

 

 

 

 

 

 

1

 

Chapter One

Introduction

1.1 History

The earliest aromatic nitro compounds were obtained by MITSCHERLISH

in 1834 by treating hydrocarbons derived from coal tar with fuming acid [1, 2,

&3]. By 1835 LAURENT was working on the nitration of naphthalene, the most

readily available pure aromatic hydrocarbon at that time. DALE reported on

mixed nitro compounds derived from crude benzene at the 1838 annual meeting

of the British Association for the Advancement of Science. Not until 1845,

however, did HOFMANN and MUSPRATT report their systematic work on the

nitration of benzene to give mono- and dinitrobenzenes by using a mixture of

nitric and sulfuric acids [1].

The first small-scale production of nitrobenzene was carefully distilled to

give a yellow liquid with a smell of bitter almonds for sale to soap and perfume

manufacturers as “essence of mirbane.”[1]

The number of naturally occurring nitro aromatic compounds is small; the

first to be recognized was chloramphenicol, an important compound extracted

from cultures of a soil mold Steptomyces venezuelas and identified in 1949 [1].

This discovery stimulated investigations into the role of nitro group in

pharmacological activity, following the earlier (1943) discvery of the

antibacterial activity of nitrofuran derivatives. Many synthetic pharmaceuticals

and agrochemicals contain nitro aromatic groups, although the function of the

nitro group is often obscure [1].

The choice of nitro compounds covered here is influenced strongly by

their commercial application of compounds in the 1981 European core

2

 

Inventory. Most nitro compounds, or their derivatives, are intermediates for

colorants, agrochemicals, pharmaceuticals, or other fine chemicals with a few

major volume outlets for synthetic materials and explosives [1].

1.2 Specifications of Nitrobenzene

Nitrobenzene [98-95-3](oil of mirbane),C6H5NO2, is colourless to pale

yellow oily liquid with on odour resembling that of bitter almonds or "shoe

polish." Depending on the purity, its color varies from pale yellow to yellowish

brown [2 & 3].

Product specifications have been developed for technical-grade

nitrobenzene and for distilled-grade nitrobenzene, also called mirbane oil. An

example of a typical set of specification used by a major manufacturer of

nitrobenzene is given in Tables 1-1 and 1-2. Equivalent specifications are usually

negotiated between manufactures and major customers. Specification on

technical-grade nitrobenzene often is drawn up as an internal quality standard

since most nitrobenzene is converted captively to aniline. The type of aniline

process used and certain design details of the plant can result in small changes in

the specifications deemed necessary for technical-grade nitrobenzene. The

presence of small amounts of water is little consequence in the operation of

aniline plants; water is formed in process in the catalytic hydrogenation of

nitrobenzene and is a required reactant in the Bechamp process. However, sulfur

is known to be catalyst poison in the catalytic hydrogenation of nitrobenzene,

and dinitrobenzene and dinitrophenol are thought to form tarlike deposits on the

catalysts. The level of sulfur in technical-grade nitrobenzene is controlled

through specifications on its level in the feedstock benzene. Nitrophenols are

3

 

easily removed to a level of below 10 ppm through an alkaline wash. The

fraction of dinitrobenzene found in commercial nitrobenzene plants is usually

well below 100 ppm, and at this low level dinitrobenzene can be tolerated as a

minor impurity of the nitrobenzene fed to an aniline plant [4].

Mirbane oil is produced by purification of technical-grade nitrobenzene

through distillation. Trace contamination by aniline plant to the nitrobenzene

plant. Again, specifications for distilled-grade nitrobenzene are usually

negotiated between the manufacturer and major customers. Through distillation

it is possible to further reduce the fraction of low and high boiling impurities in

technical-grade nitrobenzene [4].

Table 1-1 Specification for technical-Grade Nitrobenzene [4]

Table 1-2 Specifications for Distilled-grade Nitrobenzene (mirbane oil) [4]

Appearance Clear yellow oil free from visible water and boiling at approximately 211oC at 760 mmHg pressure

Distillation range (5-95Ml) 0.5oC (maximum)

Crystallization point 5.5oC (minimum)

Specific gravity (15.5/15.5oC) 1.208 – 1.211

Aniline content 0.0075% (maximum)

Appearance Pale yellow oil with a characteristic order. It may be slightly hazy owing to the presence of small globules of free water

Water content 0.5% (maximum) Specific gravity (15.5/15.5oC) 1.206-1.209 Dinitrobenzene content 0.1% (maximum) Low-boiling impurities (benzene + aliphatic hydrocarbons) 0.25% (maximum)

Sulfur- containing impurities (CS2 + nitrothiophene +elementary sulfur) 2.5 ppm (maximum, as sulfur)

4

 

 

Common name: nitrobenzene

Chemical formula: C6H5NO2

Chemical structure:

Relative molecular mass: 123.11

CAS name: nitrobenzene

IUPAC name: nitrobenzene

CAS registry number: 98-95-3

NIOSH RTECS DA6475000

Synonyms: nitrobenzol, mononitrobenzol, MNB, C.I. solvent black 6, essence of mirbane, essence of myrbane, mirbane oil, oil of mirbane, oil of myrbane, nigrosine spirit soluble B

1.4 Physical properties

Nitrobenzene is a colorless to pale yellow oily liquid with an odor

resembling that of bitter almonds or "shoe polish." It has a melting point of 5.7

°C and a boiling point of 211°C. Its vapor pressure is 20 Pa at 20°C, and its

solubility in water is 1900 mg/liter at 20°C. It represents a fire hazard, with a

flash point (closed cup method) of 88°C and an explosive limit (lower) of 1.8%

by volume in air [3].

1.3 Identity [5]

5

 

Table 1-3 Some Physical Properties of Nitrobenzene [1,2,3&5]

Mp.oC 5.58 Bp.oC 210.9 Viscosity pa.sec 1.900599219*10-3 Thermal conductivity W/moC 0.14473 Surface tension (20oC) mN/m 43.35 Specific heat J/goC At 25 oC At 30 oC

1.473 1.418

Latent heat of fusion J/g 94.1 Latent heat of vaporization J/g 331 Heat of combustion (at constant volume)MJ/mol

3.074

Flash point (closed cup) oC 88

Auto ignition temperature oC 482 Explosive limit in air (93 oC)vol% 1.8 Vapor pressure pa At 20 oC At 25 oC At 30 oC

20 38 47

Solubility in water mg/liter At 20 oC At 25 oC

1900 2090

Solubility in organic solvent Freely soluble in ethanol, acetone, ether Density (25oC)Kg/m3 1198.484586

1.5 Chemical properties

Nitrobenzene reactions involve substitutions on the aromatic ring and reactions

involving the nitro group. Under electrophilic conditions, the substitution occurs at a

slower rate than for benzene, and the nitro group promotes meta substitution.

Nitrobenzene can undergo halogenations, sulfonation, and nitration, but it does not

undergo Friedel-Crafts reactions. Under nucleophilic conditions, the nitro group

promotes ortho and para substitution [2].

6

 

The reduction of the nitro group to yield aniline is the most commercially

important reaction of the nitrobenzene. Usually the reaction is carried out by the

catalytic hydrogenation of nitrobenzene, either in the gas phase or in solution, or by

using iron borings and dilute hydrochloric acid (the Bechamp process). Depending on

the conditions, the reduction of nitrobenzene can lead to variety of products. The

series of reduction products is shown in figure 1-1 Nitrosobenzen, N-

phenylhydroxylamine, and aniline are primary reduction products. Azoxybenzene is

formed by the condensation of nitrosobenzene and N-phenylhdroxylamine in alkaline

solutions, and azoxybenzene can be reduced to form azobenzene and

hydrazobenzene. The reduction products of nitrobenzene under various conditions are

given in Table 1-4 [2].

Figure 1-1 Reduction products of nitrobenzene [1, 2&14]

7

 

Table 1-4 Reduction products of nitrobenzene [2]

The process used most commonly for the manufacture of aniline is the catalytic

hydrogenation of nitrobenzene which has largely replaced the older Bechamp

process. In this latter process nitrobenzene reacts with iron and water in the presence

of small amounts of hydrochloric acid to form aniline, iron oxide, and hydrogen. The

chemistry of the two nitrobenzene-based aniline processes is described through the

following stoichiometric equations [4]:

C6H5NO2 + 3H2 C6H5NH2 + 2H2O 1.1

C6H5NO2 +3 Fe + 4 H2O C6H5NH2 +Fe(OH)2 + FeO + Fe (OH)3 + 0.5H2 1.2

Nitration, which is introduction of nitro group or the NO2 group into the

molecule, is achieved by bringing mixed acid and the compound to be nitrated into

intimate contact under vigorous agitation. Care must be taken to remove the heat of

nitrating. The acid left on completion of the nitration reaction is called spent acid. In

benzene nitration of the reaction is heterogeneous; benzene and nitrobenzene have

Reagent Product

Fe, Zn or Sn + HCL aniline

H2 + metal catalyst + heat (gas phase or

solution)

aniline

SnCL2 + acetic acid aniline

Zn + NaOH hydrazobenzene, azobenzene

Zn + H2O N-phenylhydroxylamine

Na3AsO3 azoxybenzene

LiALH4 azoxybenzene

Na2S2O3 + Na3PO4 Sodium phenylsulfamate, C6H5NHSO3Na

CU/SiO2

HCL/Fecl

8

 

very low solubility in the mixed and spent acids. The overall stoichiometry for the

reaction of benzene and nitric acid to form nitrobenzene and water is

+ HNO3 + H2O

Sulfuric acid is a catalyst in the nitration reaction and does not enter directly into the

stoichiometry of Equation 1.3. The role of sulfuric acid is two fold: it acts as a

dehydrating agent by absorbing the water formed in the nitration reaction and it is

responsible for the dissociation of nitric acid and through which the reactive species,

the nitronium ion, is formed. The positively charged nitronium ion, NO2, reacts with

the aromatic compound by electrophilic attack to form a positively charged complex.

This complex breaks down fast through reaction of the proton with an anion such as

HSO4. The reaction mechanism is described through the following stoichiometric

equations[4]: 

NO2

H2SO4 ∆Ho = -34.825 Kcal/g.mol 1.3

-

9

 

Equations 1.4 to 1.7 add up to Equation 1.3. The rate-controlling reaction is that

of Equation 1.5. The rate of nitration reaction is a function of many variables, but

most importantly it is a function of sulfuric acid strength, which is capable of

changing the rate by several orders of magnitude. The steep increase of the nitration

rate with the sulfuric acid strength is generally though to be due to the parallel

increase in the concentration of the nitronium ion in the mixed acid. It is the

nitronium ion which is the reactive species in the rate-controlling Equation 1.5 [4].

The nitronium ion is also present in strong nitric acid, and benzene can be nitrated

using nitric acid alone. The incentive for this process is that it would eliminate the

sometimes costly disposal or reconcentration of the spent sulfuric acid. No

commercial plant appears to be operating using a nitric acid only process. Of concern

would be the fact that mixtures of nitric acid and benzene or nitrobenzene can be

detonated [4].

The main by-products formed in commercial nitrobenzene plants are

dinitrobenzene (C6H4 (NO2)2), dinitrophenol (C6H3OH (NO2)2), and picric acid

(C6H2OH (NO2)2). The fraction of dinitrobenzene obtained is usually well below 100

ppm, but can reach a few hundred ppm if the nitration is accidentally operated with

excess nitric acid. The introduction of nitro groups into the benzene ring lowers the

electron density, thereby impeding electrophilic attack. Substantial rates of

conversion to dinitrobenzene are possible only at high spent acid strengths.

Furthermore, commercial nitrobenzene plants usually operate with excess benzene

which will consume most of the nitric acid well before significant quantities of

dinitrobenzene can be formed [4].

A possible but not proven mechanism is the one where the nitronium ion becomes

attached to the benzene ring through one of its oxygen atoms instead of the nitrogen

10

 

atom, the product being phenol and the nitrosyl ion, NO+. The phenol then reacts with

nitric acid, possibly through a complex between the nitrosyl ion and the phenol, to

form nitrophenol and nitrous acid, HNO2. The one-to-one molar ratio between

nitrophenol and nitrous acid is confirmed through experiment. Nitrophenol is further

nitrated to dinitrophenol and picric acid. The rates for this di- and trinitration are

relatively fast; there is usually only a trace of mononitrophenol found in the crude

nitrobenzene. The stoichiometry of the reactions is shown in the following equations

[2]:

Other by-products are formed from trace impurities in the benzene feedstock or in

the recycle sulfuric acid. There is also the possibility that very small amounts of

11

 

benzene and nitrobenzene undergo other reactions. Most of these by-products are

removed in the washing stage of the process together with the nitrophenols. The yield

loss caused by these side reactions is negligible. Of more concern is the fast that

some of these trace impurities from surface-active compounds which can

oceasionally lead to the formation of stable emulsions in the washing section [4].

1.6 Uses

Nitrobenzene is used primarily in the production of aniline, but it is also used as

a solvent and as an ingredient in metal polishes and soaps. In the USA, around 98%

of nitrobenzene produced is converted into aniline; the major use of aniline is in the

manufacture of polyurethanes. Nitrobenzene is also used as a solvent in petroleum

refining, as a solvent in the manufacture of cellulose ethers and cellulose acetate

(around 1.5%), in Friedel-Crafts reactions to hold the catalyst in solution (it dissolves

anhydrous aluminium chloride as a result of the formation of a complex) and in the

manufacture of dinitrobenzenes and dichloroanilines (around 0.5%). It is also used in

the synthesis of other organic compounds, including acetaminophen [3].

According to the BUA (1994), nitrobenzene is used in Western Europe for the

purposes shown in Table 5-1 [5].

Table 5-1 Type and estimated consumption of nitrobenzene in Western

Europe in 1994

Main application areas or chemical manufacture

Nitrobenzene consumption (tones/year) in Western Europe

Aniline 380 000m-Nitrobenzenesulfonic acid 5 000m-Chloronitrobenzene 4 300 Hydrazobenzene 1 000

12

 

Dinitrobenzene 4 000 Others (solvents, dyes) 4 000 Total 398 300

Dunlap (1981) reported that most of the production of aniline and other

substituted nitrobenzenes from nitrobenzene go into the manufacture of various

plastic monomers and polymers (50%) and rubber chemicals (27%), with a

smaller proportion into the synthesis of hydroquinones (5%), dyes and

intermediates (6%), drugs (3%), pesticides and other specialty items (9%) [5].

Past minor uses of nitrobenzene included use as a flavouring agent, as a

solvent in marking inks and in metal, furniture, floor and shoe polishes, as a

perfume, including in perfumed soaps, as a dye intermediate, as a deodorant and

disinfectant, in leather dressing, for refining lubricating oils and as a flavouring

agent. It is not known whether it may still be used in some countries as a solvent

in some consumer products (e.g., shoe polish) [5].

The 22,680 metric ton of nitrobenzene left was used to produce a variety

of other products, such as para-aminophenole [123-30-8] (PAP) and nigrosine

dyes. The U.S. producers of PAP are Mallinckrodt, Inc., Rho^ne-Poulene, and

Hoechst Celanese, with combined production capacities > 35,000 metric tons (as

of may 1995). Mallinckrodt is the largest producer, with over 50% of capacity.

PAP primarily is used as an intermediate for acetaminophen [103-90-2] [2].

1.7 Nitrobenzene Derivatives

• 2,5-dichloronitobenzene • 2,5-dimethoxynitrobenzene • Dinitrobenzene • O-nitrobenzene

13

 

• M-nitrobenzenesulfonic acid, sodium salt • O-nitrochlorobenzene • P-nitrochlorobenzene • M-nitrochlorobenzene [15]. • 1,3,5-Trinitrobenzene • 1, 3-Dinitrobenzene [1].

Figure 1-2 Key intermediates derived from nitrobenzene

 

 

 

Chapter Two Production Methods of

Nitrobenzene

14

Chapter Two

Production Methods of Nitrobenzene

2.1General

World production of nitrobenzene in 1994 was estimated at 2 133 800

tones; about one-third was produced in the USA [5].

In the USA, there has been a gradual increase in nitrobenzene production,

with the following production/demand amounts, in thousands of tones, reported:

73 (1960), 249 (1970), 277 (1980), 435 (1986), 533 (1990) and 740 (1994).

Based on increased production capacity and increased production of aniline (the

major end-product of nitrobenzene), it is likely that nitrobenzene production

volume will continue to increase [5].

Production of nitrobenzene in Japan was thought to be around 70 000

tones in 1980 and 135 000 tones in 1990. Patil & Shinde (1989) reported that

production of nitrobenzene in India was around 22 000 tones per year [5].

Nitrobenzene is produced at two sites in the United Kingdom with a total

capacity of 167 000 tones per year. It has been estimated that a maximum of

115 400 tones of aniline was produced in the United Kingdom in 1990. If it is

assumed that 98% of the nitrobenzene in the United Kingdom is used to make

aniline, then the total amount of nitrobenzene used in the United Kingdom would

be around 155 600 tones per year [5].

15

Capacities for nitrobenzene production are available for several Western

European countries and are shown in Table 3-1 Production for Western Europe

was reported as 670 000 tones in 1990 [5].

Table 2-1 nitrobenzene production capacities in European countries in 1985

Nitrobenzene is manufactured commercially by the direct nitration of

benzene using a mixture of nitric acid and sulfuric acid [2, 4, 7, &8].

This commonly is referred to as mixed acid or nitrating acid. Because two

phases are formed in the reaction mixture and the reactants are distributed

between them, the rate of nitration is controlled by mass transfer between the

phases as well as by chemical kinetics. The reaction vessels are acid-resistant,

glass-lined steel vessels equipped with efficient agitators. By vigorous agitation,

the interfacial area of the heterogeneous reaction mixture is maintained as high

as possible, thereby enhancing the mass transfer of reactants. The reactors

contain internal cooling coils which control the temperature of the highly

exothermic reaction [2&3].

Nitrobenzene can be produced by either a batch or continuous process

[2&3].

Country Capacity (tones) Belgium 200 000Germany 240 000 Italy 18 000 Portugal 70 000Switzerland 5 000 United Kingdom 145 000USA 434 000 Japan 97 000

16

2.2Batch process

With a typical batch process, the reactor is charged with benzene, then the

nitrating acid (56-60 wt % H2SO4, 27-32 wt% HNO3, and 8-17 wt % H2O) is

added slowly below the surface of benzene. The temperature can be raised to

about 90oC toward the end of reaction to promote completion of reaction. The

reaction mixture is fed into a separator where the spent acid settles to the bottom

and is drawn off to be refortified. The crude nitrobenzene is drawn from the top

of the separator and washed in several steps with a dilute base, such as sodium

carbonate, sodium hydroxide, magnesium hydroxide, etc, and then water.

Depending upon the desired purity of the nitrobenzene, the product can be

distilled. Usually a slight excess of benzene is used to ensure that little or no

nitric acid remains in the spent acid. The batch reaction time generally is 2-4

hours, and typical yields are 95-98 wt % based on benzene charged [2].

Based on yield of 1000 kg of nitrobenzene, material requirements for the process

are as follows [3]

Quantity, kg Material 650 Benzene 720 Sulfuric acid 520 Nitric acid 110 Water 10 Sodium carbonate

The separation of the nitrobenzene is accomplished in large conical-

bottomed lead tanks, each capable of holding one or more charges. The nitrator

charges are permitted to settle here for 4-12 hr, when the spent acid is drawn off

from the bottom of the lead tanks and delivered to the spent-acid tanks for

additional settling or for treatment with benzene next to be nitrated, in order to

17

extract the residual nitrobenzene. The nitrobenzene is then delivered to the

neutralizing house [9].

The neutralizing tub may be either a large lead conical-shaped tub

containing an air-spider, which is used for agitating the charge of nitrobenzene

during the washing process, or a standard cast-iron kettle similar to the nitrator

with sleeve-and –propeller agitation. The neutralizing vessel is prepared with a

"heel" of warm water, which is delivered from an adjacent vat, and the

nitrobenzene is blown into it. The charge is thoroughly agitated and warmed with

live stream for 30 min, or until neutral to congo, and then allowed to settle for a

similar period. The supernatant acid water is then run off through side outlets

into a labyrinth where practically all the enmeshed nitrobenzene will settle out.

The charge is now given a neutralizing wash at 40-50oC with a warm sodium

carbonate solution, until alkaline to phenolphthalein [9].

2.3 Tubular Reactor process

Most homogeneous gas-phase flow reactor is tubular [19]. The nitrator

also can be designed as a tubular reactor, e.g., a tube-and-shell heat exchanger

with appropriate cooling, involving turbulent flow. Generally, with a tubular

reactor, the reaction mixture is pumped through the reactor in a recycle loop and

aportion of the mixture is withdrawn and fed into the separator. A slight excess

of benzene usually is fed into the nitrator to ensure that the nitric acid in the

nitrating acid is consumed to the maximum possible extent and to minimize the

formation of dinitrobenzene. The temperature of nitrator is maintained at 50-

100oC by varying the amount of cooling. The reaction mixture flows from the

nitrator into a separator or centrifuge where it is separated into two phases [2].

18

The tubular reactor [i.e., plug-flow reactor (PFR)] is relatively easy to

maintain (no moving parts), and it usually produces the highest conversion per

reactor volume of any of the flow reactors. The disadvantage of the reactor and

hot spots can occur when the reaction is exothermic. The tubular reactor is

commonly found either in the form of one long tube or as one of a number of

shorter reactors arranged in a tube bank [10].

2.4 Continuous process

A typical continuous process for the production of the nitrobenzene is

given in Figure 2. Benzene and the nitrating acid (56-65 wt % H2SO4, 20-26 wt

% HNO3, and 15-18 wt % water) are fed into the nitrator, which can be a stirred

cylindrical reactor with internal cooling coils and external heat exchangers or a

cascade of such reactors [2].

The basic sequence of operations for a continuous process is the same as that for

a batch process; however for a given rate of production, however, for a given

rate of production, the size of the naitrators is much smaller in the continuous

process. A 0.114-m3 (30-gal) continuous nitrator has roughly the same

production capacity as a 5.68-m3 (1500-gal) batch reactor [3].

The nitration in continuous process can take place with elimination of

heat of reaction, e.g. adiabatically, or isothermally [11].

19

2.4.1 Adiabatic Continuous Process

The processes where the heat of nitration is used to directly boil off water,

benzene and nitrobenzene from the nitrator [4]. An adiabatic nitration process

was developed for the production of nitrobenzene. This method eliminated the

need to remove the heat of reaction by excessive cooling. The excess heat can be

used in the sulfuric acid reconcentration step. An additional advantage of this

method is the reduction in reaction times to 0.5-7.5 minutes. The nitration step is

carried out at higher than usual temperatures 120-160oC. because excess benzene

is used, the higher temperature allows water to be removed as a water-benzene

azeotrope. The water is separated and the benzenephase, containing

approximately 8 %nitrobenzene, is recycled back into the reactor. The dry

sulfuric acid is then reused continuously [2].

The adiabatic process integrates nitration with sulfuric acid concentration,

thus using the heat of nitration to reconcentrate the spent sulfuric acid. This is

Figure 2-1 production of Nitrobenzene- continuous process [1]

20

achieved by circulating a large volume of sulfuric acid through the nitrators,

absorbing the heat of nitration without undue temperature rise. the spent acid is

then flash concentrated under vacuum [4].

One observes that the nitrobenzene stream from the separator is used to

heat the benzene feed. However, care must be taken so that the temperature

never exceeds 190oC, where secondary reactions could result in an explosion.

One of the safety precaution is the installation of relief valves that will rupture

before the temperature approaches 190oC, thereby allowing a boil-off of water

and benzene, which would drop the reactor temperature [10].

Figure 2-2 Flow sheet for the production of nitrobenzene adiabatically

21

2.4.2 Isothermal Continuous Process

The isothermal process is different from the adiabatic process only in the

nitration section. In the isothermal process, typically a minimum of 2 nitrators in

series is used with up to 4 nitrators in large plants. Spent acid and crude

nitrobenzene are usually separated through gravity settlers, but in some designs

centrifugal separation is used. The spent acid is stripped free of dissolved

nitrobenzene and nitric acid either by steam srripping or through benzene

extraction-prenitration. It is then either reconcentrated and recycled or

discharged, often for use in phosphate rock digestion. Spent acid stripping is

sometimes omitted in small plants; yield losses and emissions of nitrobenzene

and nitrogen oxide must then be tolerated [4].

2.5 Non-Industrial Sources

Nitrobenzene has been shown to be emitted from a multiple-hearth sewage

sludge incineration unit in the USA. The unit consisted of 12 hearths and

operated at a rate of 13–15 tones per hour, with a maximum temperature of 770

°C at the sixth hearth. Nitrobenzene was monitored at the scrubber inlet and

outlet. The concentrations measured were 60 µg/m3 at the scrubber inlet

(corresponding to an emission of 3.2 g/h) and 16 µg/m3 at the scrubber outlet

(corresponding to an emission of 0.9 g/h). The scrubber reduced the nitrobenzene

concentration by 71% [5].

The levels of nitrobenzene in air have been measured at five hazardous

waste landfills and one sanitary landfill in New Jersey, USA. Samples were

collected over a 24-h period at five locations within each landfill. Mean levels

22

measured in the five hazardous waste landfills were 0.05, 0.65, 2.7, 1.0 and 6.6

µg/m3. The maximum level recorded was 51.8 µg/m3. At the sanitary landfill,

nitrobenzene was below the detection limit (0.25 µg/m3) at all locations [5].

Nitrobenzene has been shown to be formed from the atmospheric reactions

of benzene in the presence of nitrogen oxides. The reaction is thought to be

initiated by hydroxyl radicals. Nitrobenzene, once formed, reacts quite slowly in

the atmosphere; this could therefore provide a major source of atmospheric

nitrobenzene, although it has not been possible to quantify this source. Atkinson

et al. (1987) reported that aniline is slowly oxidized to nitrobenzene by ozone.

These reactions are summarized in Figure 2-3 [5].

Figure 2-3 Atmospheric reactions generating and removing nitrobenzene

23

2.6 Process Selection

A continuous nitration process generally offers lower capital costs and

more efficient labor usage than a batch process; thus, most, if not all, of the

nitrobenzene producers use continuous processes [2&3].

In contrast to the batch process, a continuous process typically utilizes a

lower nitric acid concentration and, because of the rapid and efficient mixing in

the smaller reactors, higher reaction rates are observed [3].

The continuous nitration can take place with elimination of heat of

reaction, e.g. isothermally, or adiabatically [11].

In adiabatic process, the heat of reaction is not dissipated by cooling

during the process, but instead is subsequently used for evaporating the water of

reaction, so that a sulfuric acid suitable for recirculation obtained. One factor

common to all the processes which have been proposed for this purpose is that

they require new installations of special corrosion-resistant materials to

accommodate the high process temperatures (up to 145oC.) and they also require

considerably more stringent safety measures. This offsets the potential

advantages of these processes [12].

The isothermal processes such that considerable economic and ecological

advantages are obtained over the state-of-the-art [12].

2.7 Description of the Selected Process

The production of nitrobenzene by subjecting benzene to isothermal nitration

with a mixture of nitric acid and sulfuric acid [9], concentrated sulfuric acid has

24

two functions: it reacts with nitric acid to form the nitronium ion, and it absorbs

the water formed during the reaction, which shifts the equilibrium to the

formation of nitrobenzene [4, 8, 13, &14]

A charge of benzene into a nitrator (a slight excess of benzene is added to

avoid nitric acid in the spent acid [1, 2, &3]), then slowly feeding in a mixed

nitrating acid (60 wt. % H2SO4, 25 wt. % HNO3, 15 wt. % H2O [2&14]), and

thereafter digesting the reaction mixture in the same vessel. Since the addition of

the mixed acids requires several hours in order to avoid uncontrollable rises in

temperature, and the digestion period requires several more hours, the apparatus

used, particularly the nitrator, has to be large in order to provide a high

production rate, and constant operator surveillance must be maintained. In

addition, an explosion hazard is present at the start of any run due to the large

unreacted charge in the nitrator [15].

The temperature in the nitrator is held at 50oC [2, 3, 16&17], governed by

the rate of feed of benzene. Reaction is rapid in well-stirred and continuous

nitration vessels. The reaction must be cooled to keep it under control. Good heat

transfer can be assured by the use of jackets, coils, and good agitation in the

25

nitration vessel [16]. Nitration vessels are usually made of stainless steel,

although cast iron stands up well against mixed acids [16&18].

It then enters a separator tank from which a portion of spent acid is

removed from bottom, and the crude nitrobenzene is drawn off the top of the

separator [18].

The removed of spent acid (sulfuric acid & water) is enter to evaporator in

order to concentrating the sulfuric acid with fresh sulfuric acid (98 wt. % [4])

and then with fresh nitric acid (64 wt. % [4]) to the nitrator [12].

The crude nitrobenzene (nitrobenzene, benzene, sulfuric acid &water) is

drawn from the top of the separator and is wash with the sodium carbonate in

order to remove sulfuric acid from crude nitrobenzene, fellowing by final

washing with calcium sulfate (anhydrite) to remove the water from react the

calcium sulfate with water to formed calcium sulfate (Gypsum) [2,12,&14]. The

product is topped in still to remove benzene and give pure product (96-99 wt. %)

[1,2 & 3].

26  

nitrator Acid separation 1st washing 2nd washing Distillation

Sulfuric acid reconcentration

(Evaporator)

CaSO4 Na2CO3

Crude nitrobenzene

Spent acid Nitrobenzene NaSO4

H2CO3

Gypsum Fresh sulfuric acid

98 wt. %

Nitrating acid

Benzene

Benzene Nitric acid

64wt. %

H2O

Fig. 2-4 Typical continuous nitrobenzene process

 

 

Chapter Three Material Balance

 

27

Chapter Three

Material Balance

Note: Data necessary in appendix A.

3.1 General Information

Main Reaction

C6H6 + HNO3 C6H5NO2 +H2O … (3.1)

Capacity = 70000 ton/year [5]

Year = 300 working day

= 233.333333 ton/day

= 9722.222222 Kg/day

= 78.9718188 Kg.mol/hr

No nitric acid remains in the spent acid [2&14]

Conversion = 100 % [2&14,1&4]

From stoichiometry:

Benzene required = 78.97183188 Kmol/hr

Water formed = 78.97183188 Kg.mol/hr

Required nitric acid = 78.97183188 Kg.mol/hr

H2SO4

28

3.2 Material Balance on Nitrator

Usually a slight excess of benzene (3.24 wt %) is used to ensure that little or

no nitric acid remains in the spent acid [2, 4, 16&21].

Wt. of benzene = 78097183188 * 78.11 = 6168.489788 Kg/hr

Wt. of benzene excess = 6168.489788 * 0.0324 = 199.8590691 Kg/hr

Total wt. of benzene input = 6168.489788 + 199.8590691

Total wt. of benzene input = 6368.348857 Kg/hr

Total nitric acid input = 78.97183188 * 63.02= 4976.804845 Kg/hr

Nitrating acid composition H2SO4 60 wt %, HNO3 25 wt %, & H2O 15 wt %

[2&21].

Total weight of nitrating acid = = 19907.21938 Kg/hr

Wt. of sulfuric acid input =

Wt. of sulfuric acid input = 11944.33163 Kg/h

Wt. of water input = = 2986.082907 Kg/hr

Wt. of water formed = 78.97183188 * 18.02 = 1423.07241 Kg/hr

Nitrator

3

4

5

29

Water output in Stream 5 = 2986.082907 + 1423.07241

Water output in Stream 5 = 4409.155317 Kg/hr

Table 3-1 Material Balance on Nitrator

Component

[Kg/hr]

[Kg/hr]

[Kg/hr]

C6H6 - 6368.348857 199.8590691

HNO3 4976.804845 - -

H2SO4 11944.33163 - 11944.33163

H2O 2986.082907 - 4409.155317

C6H5NO2 - - 9722.222222

Total

19907.21938

6368.348857

26275.56824

26275.56824

3 4 5

30

3.3 Separator Material Balance

1 wt % of total acid solution (sulfuric acid + water) will goes with crude

nitrobenzene [16].

Stream 5 Acid solution input to separator = 4409.155317 + 11944.33163

= 16353.48695 kg/hr

Stream 7 (Crude Nitrobenzene) = excess BZ.+ N.B. + 1 wt. % of acid solution

Excess BZ. = 199.8590691 Kg/hr

N.B. = 9722.222222 kg/hr

Wt. of acid solution in stream 7 = 0.01 * 16353.48695 = 163.5348695 Kg/hr

Wt. % sulfuric acid in acid solution = * 100 = 73.03843924 %

Wt. % water in acid solution = 26.96156076 %

this above acid wt% is the same for stream 6 & stream 7.

Wt. of sulfuric acid in stream 7= 163.5348695 * 0.73038439

Aid Separation

5 7

6

31

Wt. of sulfuric acid in stream 7 =119.4433163 Kg/h

Wt. water in stream 7 = 163.5348695 * 0.2696156076 = 44.09515532 Kg/hr

Stream 6 (spent acid) = water + sulfuric acid

99 Wt % of total acid solution will goes in stream 6(spent acid).Wt. of spent

acid = 16353.48695 * 0.99 = 16189.95208 Kg/hr = stream 6

Wt. of sulfuric acid in spent acid = 16189.95208 * 0.7303843924

Wt. of sulfuric acid in spent acid = 11824.88831 Kg/hr

Wt. of water in spent acid = 16189.9520 * 0.2696156076

Wt. of water in spent acid = 4365.063767 Kg/hr

Table 3-2 Material balance on separator

Component

[Kg/hr]

[Kg/hr]

[Kg/hr]

C6H6 199.8590691 - 199.8590691

HNO3 - - -

H2SO4 11944.33163 11824.88831 119.4433163

H2O 4409.155317 4365.063767 44.0915532

C6H5NO2 9722.222222 - 9722.222222

Total

26275.56824

16189.95208

10085.61616

26275.56824

6 75

32

3.4 Washing Process Material Balance

3.4.1 1st Washing process Material Balance

Na2CO3 + H2SO4 Na2SO4 + H2CO3

From stoichiometry

Mole of Na2CO3 input in stream 8 = mole of sulfuric acid in stream 7

Mole of sulfuric acid in stream 7 =

Mole of sulfuric acid in stream 7 = 1.217815215 Kg.mol/hr

Wt. of Na2SO4 input = 1.217815215 * 106.00

Wt. of Na2SO4 input = 129.0884128 Kg.mol/hr = stream 8

Mole of Na2SO4 = 1.217815215 Kg.mol/hr

Wt. of Na2SO4 = 1.217815215 * 142.05

Wt. of Na2SO4 = 172.9906513 Kg/hr

1st Washing

Na2CO3

7

9

10

8

33

Mole of H2CO3 = 1.217815215 Kg.mol/hr

Wt. of H2CO3 = 1.217815215 * 62.03

Wt. of H2CO3 = 75.4510778 Kg/hr

Wt. of water input in stream 7 = wt. of water output in stream 9

Wt. of water input in stream 7 = 44.0915532 Kg/hr

Table 3-3Material Balance on 1st Washing Unit

Component

[Kg/hr]

[Kg/hr]

[Kg/hr]

[Kg/hr]

C6H6 199.8590691 - - 199.8590691

HNO3 - - - -

H2SO4 119.4433163 - - -

H2O 44.0915532 - - 44.0915532

C6H5NO2 9722.222222 - - 9722.222222

Na2CO3 - 129.0884128 - -

Na2SO4 - - 172.9906513 -

H2CO3 - - 75.4510778 -

Total

10085.61616 129.0884128 248.5317291 9966.172836

10214.70457 10214.70457

7 8 10 9

34

3.4.2 2nd Washing process Material Balance

CaSO4 + 2H2O CaSO4.2H2O

Wt. of water input in stream 10 = 44.0915532 Kg/hr

Mole of water input in 10 = = 2.446812053 Kg

From stoichiometry

Mole of CaSO4 = 1.223406027 Kg.mol/hr

Wt. of CaSO4 = 1.223406027 * 136.14 = 166.5544965 Kg/hr = stream 11

Mole of CaSO4.2H2O = 1.223406027 Kg.mol/hr

Wt. of CaSO4.2H2O = 1.223406027 * 172.18

Wt. of CaSO4.2H2O = 210.6460497 Kg/hr = stream 12

11

10

12

13

2nd Washing

CaSO4.2H2O

(Gypsum)

CaSO4

35

Table 3-4 Material Balance on 2nd Washing Unit

Component

[Kg/hr]

[Kg/hr]

[Kg/hr]

[Kg/hr]

C6H6 199.8590691 - - 199.8590691

HNO3 - - - -

H2SO4 - - - -

H2O 44.0915532 - - -

C6H5NO2 9722.222222 - - 9722.222222

CaSO4 - 166.5544965 - -

CaSO4.2H2O - - 210.6460497 -

Total

9966.172836

166.5544965

210.6460497

9922.0812

10132.72733 10132.72734

3.5 Reconcentrator Material Balance

12 10 11

Sulfuric acid

reconcentration

H2O

1

18

2

3 1

166

2nd mixing point

1st mixing point

13

36

The concentrated of nitric acid added in stream 1 is 64wt. %, and the

concentrated of sulfuric acid added in stream 2 is 98 wt. % [4].

Material balance on nitric acid

Stream of fresh nitric acid = stream 1

0.64 stream 1 = 0.25 stream 3

Stream 1 = = 7776.25757 Kg/hr

Wt. of nitric acid input in stream 1 = 0.64 * 7776.25757

= 4976.804845 Kg/hr

Wt. of water in stream1 = 0.36 * 7776.25757 = 2799.452725 Kg/hr

Material balance on sulfuric acid

Stream of fresh sulfuric acid = stream 2

Amount of sulfuric acid input in stream 2 equal to amount that consumed in

1st washing process = 119.4433163 Kg/hr

Stream 2 = = 121.880935 Kg/hr

Wt. of water in input in stream 2 = 121.880935 * 0.02 = 2.4376187 Kg/hr

Material balance on water that must be removed

Total wt. of water input = 2799.452725 + 2.4376187

= 2801.890344 Kg/hr

Wt of water in stream 17 (after reconcentrator)

= wt. of water in nitrating acid – total wt. of water input

37

= 2986.082907 - 2801.890344 = 184.1925633 Kg/hr

Wt. of water must be removed in stream17

= wt. of water in spent acid (stream 6) – water after reconcentrator in

stream17

= 4365.063767 - 184.1925633

= 4180.871204 Kg/hr = stream 16

Material balance on reconcentrator

Stream 6 = stream 16 + stream 17

Stream 17 = 16189.95208 - 4180.871204= 12009.08088 Kg/hr

Wt. of water in stream 17 = 184.1925633 Kg/hr

Wt of sulfuric acid in stream 17 = 12009.08088 - 184.1925633

Wt of sulfuric acid in stream 17 = 11824.88831 Kg/hr

Material balance on 1st mixing point

Stream 17 + stream 2 = stream 18

Stream 18 = 12009.08088 + 121.880935= 12130.96182 Kg/hr

Wt. of water in stream 18 = 184.1925633 + 2.4376187

Wt. of water in stream 18 =186.630182 Kg/hr

Wt. of sulfuric acid in stream 18 = 12130.96182 + 186.630182

Wt. of sulfuric acid in stream 18 = 11944.33163 Kg/hr

38

Table 3-5 Material Balance on Reconcentrator

component

[Kg/hr]

[Kg/hr]

[Kg/hr]

[Kg/hr]

[Kg/hr]

[Kg/hr]

[Kg/hr]

HNO3 - - - - - 4976.804845 4976.804845

H2SO4 11824.88831 - 11824.88831 11944.33163 119.4433163 - 11944.33159

H2O 4365.063767 4180.871204 184.192563 186.6301817 2.4376187 2799.452725 2986.082907

Total 16189.95208 4180.871204 12009.08088 12130.96181 121.880935 7776.25757 19907.21934

3.6 Distillation Material Balance

Stream 13 = 97722.081291 Kg/hr

Benzene in stream 13 = 199.8590691 Kg/hr

Nitrobenzene in stream 13 = 9722.222222 Kg/hr

Purity between 96 – 99 wt. % [2 & 14]

17 1816 1 26 3

Distillation

13

14

15

39

Select purity = 99 wt. %

Stream 15 (bottom) = = 9820.426487 Kg/hr

Benzene in stream 15 = 9820.426487 - 9722.222222

Benzene in stream 15 = 98.20426486 Kg/hr

Benzene in stream 14 (top) = 199.8590691 – 98.20426486

= 101.6548042 Kg /hr

Table 3-6 Material Balance on Distillation

Component

[Kg/hr]

[Kg/hr]

[Kg/hr]

C6H6 199.8590691 101.6548042 98.20426486

C6H5NO2 9722.222222 - 9722.222222

Total

9922.081291

101.6548042 9820.426987

9922.081291

13 14 15

40  

3.7 Overall Material Balance

Table 3-7 Overall Material Balance

In ( Kg/hr) Out (Kg/hr)

[Kg/hr]

[Kg/hr]

[Kg/hr]

[Kg/hr]

[Kg/hr]

[Kg/hr]

[Kg/hr]

[Kg/hr]

[Kg/hr]

[Kg/hr] C6H6 - - 6368.348857 - - - - - 101.6548042 98.20426486 HNO3 4976.804845 - - - - - - - - - H2SO4 - 119.4433163 - - - - - 4180.871204 - - H2O 2799.452725 2.376187 - - - - - - - -

C6H5NO2 - - - - - - - - - 9722.222222 Na2CO3 - - - 129.0884128 - - - - - - H2CO3 - - - - - 75.4510778 - - - - Na2SO4 - - - - - 172.9906513 - - - - CaSO4 - - - - 166.5544965 - - - - -

CaSO4.2H2O - - - - - - 210.6460497 - - -

Total

7776.25757 121.880935 6368.348857 129.0884128 166.5544965 248.5317291 210.6460497 4180.871204 101.6548042 9820.426987 14562.13027 14562.13027

8 11 4 9 15 2 12 1 14 16 Stream

No.Comp.

41  

Table 3-8 all Streams of Material Balances

  

[Kg/hr]

[Kg/hr]

[Kg/hr]

[Kg/hr]

[Kg/hr]

[Kg/hr]

[Kg/hr]

[Kg/hr]

[Kg/hr]

[Kg/hr]

[Kg/hr]

[Kg/hr]

[Kg/hr]

[Kg/hr]

[Kg/hr]

[Kg/hr]

[Kg/hr]

[Kg/hr]

C6H6 - ‐ - 6368.348857 199.8590691 ‐  199.8590691 - - 199.8590691 - - 199.8590691 101.6548042 98.20426486 - - -

HNO3 4976.804845   4976.804845 - - ‐  - - - - ‐ ‐ - - - - - -

H2SO4 - ‐  11944.33163 - 11944.33163 11824.88831  119.4433163 - - - ‐ - - - - 11824.88831 11944.33163

H2O 2799.452725 119.4433163  2986.082907 - 4409.155317 4365.063767  44.0915532 - - 44.0915532 ‐ ‐ - - - 4180.871204 184.192563 186.6301817

C6H5NO2 - 2.4376187  - - 9722.222222 ‐  9722.222222 - - 9722.222222 ‐ ‐ 9722.222222 - 9722.222222 - - -

Na2CO3 - ‐ 

-

-

  

-

129.0884128 - - ‐ ‐ - - - - - -

H2CO3 - ‐  - - - - - 75.4510778 - ‐ ‐ - - - - - -

Na2SO4 - ‐  - - ‐  - - 172.9906513 - - - - - - - - -

CaSO4 - ‐  - - ‐  - - - - 166.5544965 - - - - - - -

CaSO4.2H2O - - - - - - - - - - 210.6460497 - - - - - -

Total 7776.25757 121.880935 19907.21938 6368.348857 26275.56824

16189.95208 10085.61616 129.0884128 248.5317291 9966.172836 166.5544965 210.6460497 9722.0812 101.6548042 9820.426987 4180.871204 12009.08088 12130.96181

COMP.

Stream NO.

1 2 3 4 5 6 7 8 11109 12 13 14 15 16 17 18

 

 

 

Chapter Four Energy Balance

42  

Chapter Four

Energy Balance

 

 

Note: Data necessary in appendix A.

4.1 Energy Balance on Nitrator

C6H6 + HNO3 C6H5NO2 + H2O

∆Hr = -146948.0527 KJ/Kg.mol

Qr = * -146948.0527 = -11604756.91 KJ/hr

Q3 = * ∆Hi * ni

∆Hi = cpi dT

Qr = ∆HHNO3 = 131.250 (325.15 – 298.15) – (323.152 – 298.152) + *10-3 (325.153 – 298.153) = 2745.87058 KJ/Kg.mol

H2SO4

5

4

H.W 70oC

3

H.W60oC

C.w30oC

C.W 30oC

43  

QHNO3 = *2745.87058 = 216846.4298 KJ/hr

∆HH2O = 32.243 (323.15 – 298.15) + *10-3(323.152-298.152) + *10-5

(323.153-298.153) – *10-9(323.154-298.154)

∆HH2O = 843.7765567 KJ/Kg.mol

QH2O = * 843.7765567 = 139,821.6844 KJ/hr

∆HH2SO4 = 139.1(50-25) + * (502-252) = 3623.65625 KJ/Kg.mol

QH2SO4 = * 3623.65625 = 441294.3716 KJ/hr

Q3 = 216846.4298 + 139,821.6844 + 441294.3716 = 797962.4858 KJ/hr

Q4 = ∆H4 * nBZ.

∆H4 = -33.917 (303.15-298.15) + *10-1(303.152-298.152) – *10-4

(303.153-298.153) + *10-8(303.154-298.154) = 416.7382512

Q4 = * 416.7382512 = 33976.886 KJ/hr

Q5 = * ∆Hi * ni

∆Hi = cpi dT

∆HBZ. = -33.917 (323.15-298.15) + *10-1(323.152-298.152) –

*10-4(323.153-298.153) + *10-8(323.154-298.154)

KJ/Kg.mol 

44  

∆HBZ. = 2160.861183 KJ/Kg.mol

QBZ. = * 2160.861183 = 5528.96818 KJ/hr

∆HH2SO4 = 139.1(50-25) + * (502-252) = 3623.65625 KJ/Kg.mol

QH2SO4 = * 3623.65625 = 441294.3716 KJ/hr

∆HH2O = 32.243 (323.15 – 298.15) + *10-3(323.152-298.152) + *10-5

(323.153-298.153) – *10-9(323.154-298.154)

∆HH2O = 843.7765567 KJ/Kg.mol

QH2O = * 843.7765567 = 206456.2648 KJ/hr

∆HN.B. = 295.3 (323.15-298.15) – (323.152-298.152) + *10-3

(323.153-298.153) = 4580.779561 KJ/Kg.mol

QN.B. = * 4580.779561 =361752.5534 KJ/hr

Q5 = 5528.96818 + 441294.3716 + 206456.2648 + 361752.5534

Q5 = 1015032.158 KJ/hr

The over all heat balance around nitrator

Heat input + Heat generation = Heat out + Heat accumulation

Q3+ Q4- Qr = Q5 + Qcooling

Qcooling = 797962.4858 + 33976.886 + 11604765.9 – 1015032.158

0.0 S.S

45  

Qcooling = 11,421,664.11 KJ/hr

Qcooling = QJacketed + QCoil

QJacketed = 0.75 Qcooling & QCoil = 0.25 Qcooling [explanatory note in chapter five]

QJacketed = 0.75*11,421,664.11 = +8,566,248.085 KJ/hr

QCoil = 0.25*11,421,664.11 = 2,855,416.028 KJ/hr

Water inter jacket at T=30oC and leaves at T=65oC.

QJacketed = ∆HH2O * n H2O

∆HJacketed =32.243 (338.15 -303.15) + *10-3 (338.152-303.152) + *10-5

(338.153-303.153) – *10-9 (338.154-303.154)

∆HJacketed = 188.206832 KJ/Kg.mol

n H2O = = 7,209.391374 Kg.mol/hr

mjacket = 129,913.2326 Kg/hr flow rate of water in jacket

Water inter coil at T=30oC and leaves at T=70oC.

∆Hcoil = 32.243 (34315 -303.15) + *10-3 (343.152-303.152) + *10-5

(343.153-303.153) – *10-9 (343.154-303.154)

∆Hcoil = 1353.828196 KJ/Kg.mol

ncoil = = 2,109.142088 Kg.mol/hr

mcoil = 38,006.74043 Kg/hr flow rate of water in coil

. 

. 

46  

4.2 Separator Energy Balance

Assume perfect insulated system, so there is no energy loose through system.

Q5 = 1015032.158 KJ/hr

Q6 = * ∆Hi * ni

∆Hi = cpi dT

∆HH2SO4 = 139.1(50-25) + * (502-252) = 3623.65625 KJ/Kg.mol

QH2SO4 = * 3623.65625 = 436881.4277 KJ/hr

∆HH2O = 32.243 (323.15 – 298.15) + *10-3(323.152-298.152) + *10-5

(323.153-298.153) – *10-9(323.154-298.154)

∆HH2O = 843.7765567 KJ/Kg.mol

Separator 

5

7 6

47  

QH2O = * 843.7765567 = 204391.7023 KJ/hr

Q6 = 436881.4277 + 204391.7023 = 641273.13 KJ/hr

Q7 = * ∆Hi * ni

∆Hi = cpi dT

∆HBZ. = -33.917 (323.15-298.15) + *10-1(323.152-298.152) – *10-4

(323.153-298.153) + *10-8(323.154-298.154)

∆HBZ. = 2160.861183 KJ/Kg.mol

QBZ. = * 2160.861183 = 5528.96818 KJ/hr

∆HH2SO4 = 139.1(50-25) + * (502-252) = 3623.65625 KJ/Kg.mol

QH2SO4 = * 3623.65625 = 4412.943716 KJ/hr

∆HH2O = 32.243 (323.15 – 298.15) + *10-3(323.152-298.152) + *10-5

(323.153-298.153) – *10-9(323.154-298.154)

∆HH2O = 843.7765567 KJ/Kg.mol

QH2O = * 843.7765567 = 2064.562649 KJ/hr

∆HN.B. = 295.3 (323.15-298.15) – (323.152-298.152) + *10-3

(323.153-298.153) = 4580.779561 KJ/Kg.molQN.B. = *

4580.779561 =361752.5534 KJ/hr

48  

Q7 = 5528.96818 + 4412.943716 +2064.562649 + 361752.5534

Q7 = 373759.0279 KJ/hr

4.3 Energy Balance on Evaporator

Q6 = 641273.13 KJ/hr

∆H16 = 32.243 (373.15 – 298.15) + *10-3(323.152-298.152) + *10-5

(373.153-298.153) – *10-9(373.154-298.154) + 40683

∆H16 = 2545.822066 + 40683 = 43228.82207 KJ/Kg.mol

Q16 = * 43228.82207 = 10029641.36 KJ/hr

Q17 = * ∆Hi * ni

∆Hi = cpi dT

6

17 Out 17 In

2

18

1 3 16

250oCSteam 250oC 3973000 pa

HNO3 64wt. %

H2SO4 98 wt.%

49  

∆HH2SO4 = 139.1(100-25) + * (1002-252) = 11163.28125 KJ/Kg.mol

QH2SO4 = * 11163.28125 = 1345886.562 KJ/hr

∆HH2O = 32.243 (373.15 – 298.15) + *10-3(323.152-298.152) + *10-5

(373.153-298.153) – *10-9(373.154-298.154) + 40683

∆HH2O = 43228.82207 KJ/Kg.mol

QH2O = * 43228.82207 = 441866.1228 KJ/hr

Q17 = 1345886.562 + 441866.1228 = 1,787,752.684 KJ/hr

Q6 + QSteam = Q16 + Q17

QSteam = Q16 + Q17 - Q6

QSteam = 10029641.36 + 1,787,752.684 + 641273.13 = 11,176,120.91 KJ/hr

mSteam = = 6,512.131986 Kg/hr

nsteam = 361.383573 Kg.mol/hr

Heat Exchanger Energy Balance

. 

Cooling water 30oC

 

100oC

65.5 oC

50oC

1717

50  

Q17(In H.Ex.) = 1,787,752.684 KJ/hr

∆HH2SO4 = 139.1(65.5-25) + * (65.52-252) = 5,919.256238 KJ/Kg.mol

QH2SO4 = * 5,919.256238 = 713,674.4704 KJ/hr

∆HH2O = 32.243 (338.65 – 298.15) + *10-3(338.652-298.152) + *10-

5(338.653-298.153) – *10-9(338.654-298.154)

∆HH2O = 1,369.293843 KJ/Kg.mol

QH2O = * 1,369.293843 = 13,996.32311 KJ/hr

Q17(Out..Ex.) = 713,674.4704 + 13,996.32311 = 727,643.7935 KJ/hr

Q17(In H.Ex.) = Q17(Out..Ex.) + Qcooling

Qcooling = Q17(In H.Ex.) - Q17(Out..Ex.)

Qcooling = 1,787,752.684 - 727,643.7935 = 1,060,108.891 KJ/hr

∆HCooling = 32.243 (323.15 – 303.15) + *10-3(323.152-303.152) +

*10-5(323.153-303.153) – *10-9(323.154-303.154)

∆HCooling = 675.3912584 KJ/Kg.mol

nCooling = = 1,569.621871 KJ/hr

mCooling = 28,284.58611 Kg/hr

Energy Balance on 1st. mixing point

Because high concentration of H2SO4 added (98wt.%) the heat of mixing is

Zero p.433, figure (12.17) [26].

. 

51  

Q2 = * ∆Hi * ni

∆Hi = cpi dT

∆HH2SO4 = 139.1(30-25) + * (302-252) = 716.93625 KJ/Kg.mol

QH2SO4 = * 716.93625 = 873.0958735 KJ/hr

∆HH2O = 32.243 (303.15 – 298.15) + *10-3(303.152-298.152) + *10-

5(303.153-298.153) – *10-9(303.154-298.154)

∆HH2O = 168.3852983 KJ/Kg.mol

QH2O = * 168.3852983 = 22.77797736 KJ/hr

Q2 = 873.0958735 + 22.77797736 = 895.8738509 KJ/hr

Q18= Q17(Out..Ex.) + Q2

Q18 = 727,643.7935 + 895.8738509 = 728,539.6673 KJ/hr

Q18 =[ *139.1(T-25) + * (T2-252)] +[ *

32.243 (T – 298.15) + *10-3(T2-298.152) + *10-5 (T3-298.153) –

*10-9(T4-298.154) ]

Find T18 by trial & error

T18 = 65.15oC

Note

Heat of mixing of HNO3 not takes under consideration.

∆Hdil.(mix.) = 11,864.53747 KJ/Kg.mol (5.104) [21].

52  

4.4 Washing Process Energy Balance

4.4.1 1st Washing process Energy Balance

Na2CO3 + H2SO4 Na2SO4 + H2CO3

∆Hro = -699.65 – 1413.891 + 1131.546

∆Hro = -170.485 KJ/g.mol

∆Hro = -170,485 KJ/Kg.mol

∆Hr = ∆Hro + ∆HProduct - ∆HReactant

∆HNa2CO3 = 111.08 ∆T

∆HNa2CO3 = 111.08 * (30 – 25) = 555.4 KJ/Kg.mol

∆HH2SO4 = 139.1(50-25) + * (502-252) = 3,623.65625 KJ/Kg.mol

∆HH2CO3 = 126.1128611 ∆T

∆HNa2SO4 = 128.229 ∆T

∆HProduct - ∆HReactant = 126.1128611 ∆T + 128.229 ∆T - 3,623.65625 - 555.4

∆HProduct - ∆HReactant = 254.3418611 ∆T – 4,179.05625

∆Hr = -170,485 + 254.3418611 ∆T – 4,179.05625

∆Hr = -174,664.0563 + 254.3418611 ∆T

Qr = [-174,664.0563 + 254.3418611 ∆T]

Qr = 1.217815215 [-174,664.0563 + 254.3418611 ∆T]

Qr = -212,708.5452 + 309.7413883 ∆T

Q7 = 373759.0279 KJ/hr

53  

∆H8 = 111.08 * (30 – 25) = 555.4 KJ/Kg.mol

Q8 = * 555.4 = 676.374704 KJ/hr

Q9 = * ∆Hi * ni

∆Hi = cpi dT

∆HNa2SO4 = 128.229 ∆T

∆HH2CO3 = 126.1128611 ∆T

Q9 = [ * 128.229 ∆T] + [ * 126.1128611 ∆T]

Q9 = 156.1592272 ∆T + 153.5821611∆T

Q9 = 309.7413883 ∆T

Q10 = ∆HMixture * ni

∆HMixture = cpMixture dT

cp10 = cpMixture = 277.604511 - 0.823102128 ∆T + 1.594487804*10-3∆T2 + 2.067652194*10-9∆T3

∆H10 = ∆HMixture = 277.604511 ∆T - ∆T2 + *10-3

∆T3 + *10-9∆T4

∆HMixture = ∆H10 = 277.604511 ∆T - 0.411551064 ∆T2 + 5.314959347*10-4

∆T3 + 5.169130485 *10-10 ∆T4

Q10 = 83.97733129 [277.604511 ∆T - 0.411551064 ∆T2 +5.314959347*10-4

∆T3 + 5.169130485 *10-10 ∆T4

54  

Q10 = 23,312.48936 ∆T – 34.56096004 ∆T2 + 0.04463361 ∆T3 + 4.340897832 * 10-8 ∆T4

Heat input + Heat generation = Heat out + Heat accumulation

Q7 + Q8 - Qr = Q9 + Q10

373759.0279 + 676.374704 – (-212,708.5452 + 309.7413883 ∆T)

= 309.7413883 ∆T + 23,312.48936 ∆T – 34.56096004 ∆T2 + 0.04463361 ∆T3 + 4.340897832 * 10-8 ∆T4

587,143.9477 = 23,931.97214 ∆T - 34.56096004 ∆T2 + 0.04463361 ∆T3 + 4.340897832 * 10-8 ∆T4

This equation above is solved by trial and error until the right hand equals the left hand.

T = 62.88295021 oC

Q7 = 373759.0279 KJ/hr

Q8 = 676.3475704 KJ/hr

Q9 = 11,733.91759 KJ/hr

Q10 = 563,676.1122 KJ/hr

Qr = - 200,974.6276 KJ/hr

4.4.2 2nd Washing process Energy Balance

CaSO4 + 2H2O CaSO4.2H2O

∆Hro = -2,024.021 + (2* 286.025) + 1,435.097

∆Hro = -16.874 KJ/g.mol

∆Hro = -16,874 KJ/Kg.mol

0.0 S.S

55  

∆Hr = ∆Hro + ∆HProduct - ∆HReactant∆HH2O = 32.243 (336.0329502 – 298.15) +

*10-3 (336.0395022-298.152) + *10-5(336.03295023-298.153) -

*10-9 (336.03295024-298.154)

∆HH2O = 1,280.433889 KJ/Kg.mol

∆HCaSO4 = 99.73 (30 – 25)

∆HCaSO4 = 498.65 KJ/Kg.mol

∆HCaSO4.2H2O = 186.149 ∆T

∆HProduct - ∆HReactant = 186.149 ∆T - 498.65 – (2* 1,280.433889)

∆HProduct - ∆HReactant = 186.149 ∆T - 3,059.517779

∆Hr = -16,874 + 186.149 ∆T - 3,059.517779

∆Hr = -19,933.51778 + 186.149 ∆T

Qr = [-19,933.51778 + 186.149 ∆T]

Qr = -24,386.78579 + 227.7358085∆T

Q10 = 563,676.1122 KJ/hr

∆H11 = 99.73 (30 – 25)

∆H11 = 498.65 KJ/Kg.mol

Q11 = * 498.65 = 610.0514153 KJ/hr

∆H12 = ∆HGypsum = 186.149∆T

Q12 = * 186.149 ∆T

Q12 = 227.7358085 ∆T

56  

Q13 = ∆HMixture * ni

∆HMixture = cpMixture dT

Cp13=cpMixture = 284.968122 – 0.847861952 ∆T+ 1.642023363 *10-3∆T2 + 2.237621333 *10-9∆T3

∆HMixture =284.968122 ∆T - ∆T2 + *10-3 ∆T3 +

*10-9 ∆T4

∆HMixture = ∆H13 =284.968122 ∆T - 0.423930976 ∆T2 + 5.47341121*10-4

∆T3 + 5.594053333 *10-10 ∆T4

Q13 = 81.53051923 [284.968122 ∆T - 0.423930976 ∆T2 + 5.47341121*10-4

∆T3 + 5.594053333 *10-10 ∆T4]

Q13 = 23,233.59895 - 34.56331259∆T2 + 0.044625005 ∆T3 + 4.560860728 *10-8 ∆T4

Heat input + Heat generation = Heat out + Heat accumulation

Q10 + Q11- Qr = Q12 + Q13

563,676.1122 + 610.0514153 – (-24,386.78579 + 227.7358085∆T) = 227.7358085 ∆T + 23,233.59895 - 34.56331259∆T2 + 0.044625005 ∆T3 + 4.560860728 *10-8 ∆T4

588,672.9494 = 23,789.07057 ∆T- 34.56331259∆T2 + 0.044625005 ∆T3 + 4.560860728 *10-8 ∆T4

This equation above is solved by trial and error until the right hand equals the left hand.

T= 63.33466274 oC

Qr -15,656.61038 KJ/hr

Q12 = 10,646.90855 KJ/hr

0.0 S.S

57  

Q13 = 567,379.1321 KJ/hr

4.5 Distillation Energy Balance

From calculation of bubble point at feed finds T13 (OUT H.EX.) = 192.1oC, & find T= 200.87oC at bottom section.

Heat Exchanger Energy Balance

Q13(IN H.EX.) = 567,379.1321 KJ/hr

13 IN 13 Out

14

15

63.335oC 192.1oC

80.1oC

200.87oC

Steam 250oC

63.334 oC Steam 210oC

192.1oC

13 In 13 Out

R D

58  

Q13 (OUT H.EX.) = * ∆Hi * ni

∆Hi = cpi dT

∆HBZ. = ∆HLiquid + λ + ∆HVapoure

∆HLquid = cpi dT

∆HLiquid = -33.917 (353.25-298.15) + *10-1(353.252-298.152) –

*10-4(353.253-298.153) + *10-8(353.254-298.154)

∆HLiquid = 5,012.048424 KJ/Kg.mol

λ = 30,781 KJ/Kg.mol

∆HVapour = cpi dT

∆HVapoure = 8.314 [ -0.206 (465.25 – 353.25) + * 10-3 * (465.252 –

353.252) – * 10-6 (465.253 – 353.253)

∆HVapoure = 12,607.37459 KJ/Kg.mol

∆HBZ = 5,012.048424 + 30,781+ 12,607.37459 = 48.42302 KJ/Kg.mol

QBZ. = * 48.42302 = 123,841.5502 KJ/hr

∆HN.B. = 295.3 (465.25-298.15) – (465.252-298.152) + *10-3

(465.253-298.153) = 34,706.15308 KJ/Kg.mol

QN.B. = * 34,706.15308 = 2,740,808.486 KJ/hr

Q13 (OUT H.EX.) = 123,841.5502 + 2,740,808.486 = 2,864,650.036 KJ/hr

59  

Q13(IN H.EX.) + QHeating = Q13 (OUT H.EX.)

QHeating = Q13 (OUT H.EX.) - Q13(IN H.EX.)

QHeating = 2,864,650.036 - 567,379.1321= 2,279,270.904 KJ/hr

QHeating = m * ( hg2 – hg1)

m = = 765,756.968 Kg/hr

Distillation Energy Balance

Q13 (OUT H.EX.) + QReboiler = Q14 + Q15 + QCondencer

Material Balance on Condenser

R = Reflux ratio =

Rm = [ – α ]

α = poBZ./ Po

N.B

α = = 19.54121672

Rm = [ –19.54121672 *

Rm = 1.1718560223

Ractual = 1.2 Rm

Ractual = 2.062272268

V = L + D

L = Ractual * D

. 

. 

60  

L = 2.062272268 * 101.6548042

L = 209.6398836 Kg/hr

L = 2.68390582 Kg.mol/hr

V = 209.6398836 + 101.6548042

V = 311.2946878 Kg/hr

V = 3.985337189 Kg.mol/hr

QCondencer = V λBZ.

QCondencer = 3.985337189 * 30,781

QCondencer = 122,672.664 KJ/hr

Q14 = ∆HBZ. * ni

∆HBZ. = -33.917 (353.25-298.15) + *10-1(353.252-298.152) –

*10-4(353.253-298.153) + *10-8(353.254-298.154)

∆HBZ. = 5,012.048424 KJ/Kg.mol

Q14 = QBZ. = * 5,012.048424 = 6,522.83704 KJ/hr

Q15 = * ∆Hi * ni

∆Hi = cpi dT

∆HBZ. = ∆HLiquid + λ + ∆HVapoure

∆HLquid = cpi dT

∆HLiquid = -33.917 (353.25-298.15) + *10-1(353.252-298.152) –

61  

*10-4(353.253-298.153) + *10-8(353.254-298.154)

∆HLiquid = 5,012.048424 KJ/Kg.mol

λ = 30,781 KJ/Kg.mol

∆HVapour = cpi dT

∆HVapoure = 8.314 [ -0.206 (474.02 – 353.25) + * 10-3 * (474.022 –

353.252) – * 10-6 (474.02– 353.253)

∆HVapoure = 13,716.10935 KJ/Kg.mol

∆HBZ = 5,012.048424 + 30,781+ 13,716.10935 = 49,509.15778 KJ/Kg.mol

QBZ. = * 49,509.15778 = 62,245.68482 KJ/hr

∆HN.B. = 295.3 (474.02-298.15) – (474.022-298.152) + *10-3

(474.023-298.153) = 36,925.461 KJ/Kg.mol

QN.B. = * 36,925.461 = 2,916,071.298 KJ/hr

Q15 = 62,245.68482 + 2,916,071.298 = 2,978,316.983 KJ/hr

Q13 (OUT H.EX.) + QReboiler = Q14 + Q15 + QCondencer

QReboiler = Q14 + Q15 + QCondencer - Q13 (OUT H.EX.)

QReboiler = 6,522.83704 + 2,978,316.983 +122,672.664 - 2,864,650.036

QReboiler = 242,862.4479 KJ/hr

62  

Table 4-1 all Streams of Energy Balances

[KJ/hr]

[KJ/hr]

[KJ/hr]

[KJ/hr]

[KJ/hr]

[KJ/hr]

[KJ/hr]

[KJ/hr]

[KJ/hr]

[KJ/hr]

[KJ/hr]

[KJ/hr]

[Kg/hr]

[KJ/hr]

[KJ/hr]

[KJ/hr]

[KJ/hr]

[KJ/hr]

[KJ/hr]

[KJ/hr]

C6H6 - - - 33976.886 5528.96818 - - - - 8567.670381 - - 8676.50917 123841.5502 6522.83704 62245.68484 - - - -

HNO3 43435.94798 - 216846.4298 - - - - - - - - - - - - - - - - -

H2SO4 - 873.0958735 441294.3716 - 441294.3716 436881.4277 4412.943716 - - - - - - - - - - 713647.4704 714329.4225

H2O 26159.21003 22.77797736 139821.6844 - 206456.2648 204391.7023 2064.562649 - - 3132.981073 - - - - - - 10029641.36 441866.1228 13996.32311 14055.2733

C6H5NO2 - - - - 361752.5534 - 361752.5534 - - 551975.5477 - - 558702.6315 2740808.486 - 2916071.298 - - - -

Na2CO3 - - - - - - - 676.3745704 - - - - - - - - - - - -

H2CO3 - - - - - - - - 5915.772227 - - - - - - - - - - -

Na2SO4 - - - - - - - - 5818.145361 - - - - - - - - - - -

CaSO4 - - - - - - - - - - 610.0514153 - - - - - - - - -

CaSO4.2H2O - - - - - - - - - - - 10646.90855 - - - - - - - -

Total 69595.15801 895.8738509 797962.4858 33976.886 1015032.158 641273.13 373759.0279 676.3745704 11733.91759 563676.1992 610.0514153 10646.90855 567379.1321 2864650.036 6522.83704 2978316.983 10029641.36 1787752.684 727643.7935 728384.6957

Pressure atm 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

Temperature

oC 30 30 50 30 50 50 50 30 62.88295021 62.88295021 30 63.33466274 63.33466274 192.1 80.1 200.87 100 100 65.5 65.15

1 2 3 4 5 6 7 8 11 109 1214 15

17 IN

1817

OUT

Stream NO.

COMP.

16 13IN

17 out

63  

                    

Feed Benzene

Nitrator

3

Vaporizer

Settler

Distillation Column

Product N.B

Washing Tank 1nd

Washing Tank 2st

Cooling

Heater

Production of Nitrobenzene

Figure 4-1 Process Flow Diagram

 

 

 

1

2

18

17 17

5

7

7

8

9

10

10

11

12

13

13 13

14

15

6

4

 

 

 

Chapter Five Equipment Design

64

Chapter Five

Equipment Design

Note: Data necessary in appendix A.

5.1 Nitrator Design

A simple stirred tank reactor is used, sized to give sufficient residence

time, and provided with sufficient agitation to promote dispersion of the organic

phase [4].

Good heat transfer can be assumed by use external jacket & internal coil.

Nitration vessel made of stainless steel (18Cr/8 Ni) (316) [4&16].

Calculation of Nitrator volume

Residence time = τ = 10 min [29]

τ = 0.166666666 hr

τ =

νo = stream 3 + stream 4

νo = [ + + + ]

νo = 20.37924292 m3/hr

V = τ * νo

V = 0.166666666 * 20.37924292

65

V = 3.396540473 m3 = 897.1088536 gal

This volume is very satisfied and very close to reference [16].

Added 10% to the volume of nitrator for safety and increase the efficiency

of mixing.

V = 3.396540473 * 1.1

V = 3.73619452 m3

D =

D = 2.181070978 m

Agitator Design

According to figure (9-16) [30] illustrated the relationship between vessel

volume and viscosity, so selected turbine impeller (disk mounted flat blade

turbine).

DA = D/3

DA = 2.181070978/3 = 0.727023659 m

HA = D/3

HA = 2.181070978/3 = 0.727023659 m

r = D/4

r = 2.181070978/4 = 0.545267744 m

a = 2.181070978/5 = 0.436214195 m

HL = D = 2.181070978 m

66

Also use four symmetric baffles

b = width of baffle = D/10

b = 2.181070978/10 = 0.2181070978 m

Calculation the shaft power required to drive the an agitator

The shaft power required to operate the stirrer can be calculated by the

following equation [31]:

PA = NP* ρ * N3 *D5A

NP = Power Number, determined from figure (9.7)[31].

Re =

2.181

0.218

2.181

0.70.73

67

Assume the agitator rotation per minute (N) = 100 rpm =1.67 rps.

Re =

Re = 8.074454885 * 104 [is very suitable]

NP = 5

PA = 5 * 1173.870615 * (1.67)3 * (0.727023659)5

PA = 5,519.239048 watt = 5.519239048 Kwatt

Design the Jacket around Nitrator

The jacket is used to cool the nitrator content and keep temperature at

50oC. Select dimple jacket, assume the spacing between jacket and vessel wall is

100mm and the jacket is fitted with a spiral baffle, the pitch between the spirals

is 200mm.

The jacket is fitted to the nitrator section and extend to a height of 80% from the

height of the nitrator.

HJacket = 0.80 * 2.181070978 = 1.744856782 m

The baffle forms continuous spiral chanel section 100mm * 200mm.

Number of spirals = height of jacket / pitch

Number of spirals = = 8.72428391 9

Cross- sectional area of channel = 100 * 200 * 10-6 = 0.02m2

68

de = = 133.333mm

length of channel = 9 * * 2.181070978 = 61.66832905 m

From Energy Balance:

mJacket = 129,913.2326 Kg/hr

Physical properties of water at mean temperature = 47.5oC as fellows

[32]:

Cp= 4.174 KJ/Kg.oC, ρ = 989.25 Kg/m3, µ = 5.755 * 10-4, pr = 3.74 &

K = 0.64225.

u = *

u = 1.823958001m/s

Nu = 0.023 Re0.8 Pro.33 [ ]0.14

Water is not viscose so neglect viscosity correction term.

Nu = 0.023 Re0.8 Pro.33

Re =

Re = = 62,867.15905

.

69

Re = 4.180355498 * 105

Nu = 0.023 * (418,035.5498)0.8 * (3.74)0.33

Nu = 1,116.21033

Nu =

hj = = 5,376.659075 W/m2.oC

∆p = 8 jf ( ) ( )

jf = 2* 10-3 from figure (12.24) [23].

∆p = 8 * (2 * 10-3) ] * ]

∆p = 12,177.17195 pa = 1.767PSI < 10 PSI (acceptable)

Design the Coil inside the Nitrator

Diameter of pipe of coil = D/30

Diameter of pipe of coil = = 0.072702365 m

Not found pipe diameter 72.7mm in standerd, so take outside diameter standard

steel pipe as 76.1mm, wall thickness as 3.65mm [34]

Inside diameter = di = do + 2Lw

70

di = 76.1- 3.65 = 68.8mm

Physical proprieties of vessel content at 50oC as fellows [22, 23, 28&33]:

Kav. = 0.326087319, ρav. = 1,425.7889 Kg/m3, µav. = 2.228013388 *10-3 pa.s &

cpav. = 1.947772473 KJ/Kg.k

The heat transfer coefficient of vessel can be calculated from equation below:

= C [ ] a [ ]b [ ]c

C,a,b,c are constants according to type of agitator and surface type (coil or

jacket)

C = 1.1, a = 0.62, b = 0.33, c = 0.14 [23]

Neglect the viscosity correction term.

= 1.1 [ ] 0.62

[ ]

hv = 4,269.214368 W /m2.oC

Tube side

hi = 4200 (1.35 + 0.02 t) ut0.8 / di

0.2

t = = 50oC

71

A = di2

A = * (68.8)2

A = 3717.635083 mm2

u = * *

u = 2.869804254 m / s

hi = 4200 (1.35 + 0.02 (50)) (2.869804254)0.8 / (68.8)0.2

hi = 9,841.95296 W / m2. oC

= + + + *

Kw = 16.3 for stainless steel [32].

= + + + *

= 7.705482183 * 10-4

Uo = 1,297.777318 W/m2.oC

Q = Uo Ao ∆T

From Energy Balance:

Qcoil = 2,855,416.028 KJ /hr = 793,171.1189 J/s

72

Ao = = 15.27941481 m2

Length of tube =

Length of tube = = 63. 910491481m

Assume Number of turns = 19 turns

Diameter of turn= = 1.090535489m 1m

Mechanical Design [23&30]

Calculation of the cylindrical part

Thickness of cylindrical part of Nitrator can be calculated directly from

equation bellow:

t = + C

J = 0.85, f = 175N/mm2, C = 1mm

P= 1.1*1 =1.1atm = 0.1114575N/mm2

t = + 1

t = 1.817438078mm 2mm

73

Calculations of the Reactor cover thickness

Thickness of the cover can be calculated from:

t =

J = 1[The cover consist of one piece]

t =

t = 0.694606292mm

Calculations of the Height of cover

The height of cover (distance from the head of reactor to the tangent line)

can be calculated by knowing the major &minor axis.

Rs = a2/b , Rs = Di = 2.181070978 m

2a = major axis = Do

Do = Di + 2(thickness)

Do = 2.181070978 + 2(1.817438078*10-3)

Do = 2.184706233 m

2b = minor axis = 2h

h = height of head from tangent line

a = 2.184706233/2 = 1.092353117m

b = a2/Rs

74

b = 1.0923531172/2.184706233 = 0.546176558 m

h = 0.546176558 m height of cover

Calculation of the volume of Nitrator

V = 0.05Di3 + 1.65 t D2

V = 0.05* 2.1810709783 + 1.65 * 0.694606292*10-3 * 2.1810709782

V = 0.524227513 m3

Over all volume of Nitrator = volume of cylindrical part + volume of covers

VTotal = 3.73619452 + 2(0.524227513)

VTotal = 4.784649546 m3

Overall length of reactor = length of cylindrical part + 2*length of cover

LTotal = 2.181070978 + 2* 0.546176558

LTotal = 3.273424094 m

Calculation of the weight of Nitrator

Wv = 240 Cv Dm (Hv + 0.8 Dm) t

Cv = 1.08, factor to account weight of nozzles

Dm = Di + t

Dm = 2.181070978 + 1.817438078*10-3 = 2.182888416 m

Hv = Di = 2.181070978 m

Wv = 240 * 1.08 * 2.182888416 (2.181070978 + 0.8 * 2.182888416)

75

Wv = 2222.130942 Kg

Design the supporting of Nitrator

The reactor supporting legs depend mainly on the weight of Nitrator and

material inside.

Wv = 2222.130942 Kg

Weight of material inside = 26,275.56824 Kg

Total weight of Nitrator = 2222.130942 + 26,275.56824 = 28,497.69918 Kg

Density of stainless steel (18% Cr, 8% Ni) = 7,817 Kg/m3 [32].

Each support bear weight of =

Each support bear weight of = = 7,124.424796 Kg

The volume of one leg support = = 0.911401405 m3

For supporting leg L/D = 8

V = D2L

V = D2 (8D) =2 D3

D = = 0.525424043m

76

L = 8* 0.525424043 = 4.203392345m

Wind load

The effect of the wind on tall vessels (over 50m) although the calculation

about this small effect is made.

Wind load = Fw = Pw * Deff

Pw = 1280 N/m2

Deff = Do = 2.184706233 m

Fw = 1280 * 2.184706233 = 2,796.423978 N/m

Bending moment at any plane = Ms = Fw / 2 *S2

S = Di = 2.181070978m

Ms = * (2.181070978)2 = 6,645.304084N.m

The Nitrator does not consider tall vessel so the effect of wind is not high.

77

5.2 Settler Design [23]

Design of Settler (Decanter) to separate a crude nitrobenzene from a spent acid

(heavy phase).

Crude nitrobenzene flow rate (stream 7) = 10,085.61616 Kg/hr

Spent acid flow rate (stream 6) = 16,189.95208 Kg/hr

ρd(Croude Nitrobenzene) = 1,173.870615 Kg/m3 [22,28&33].

ρC(Spent Acid) = 1,582.722727 Kg/m3 [22,28&33].

µd(Croude Nitrobenzene) = 1.280716063 * 10-3 pa.s

µc (Spent Acid) = 2.81813726 * 10-3 pa.s

Take dd = 150µm (droplet diameter)

ud =

ud =

ud = -1.779029395 * 10-3 m/s (rising)

As the flow rate is small, use a vertical cylindrical vessel.

LC = * = 2.84143826 * 10-3 m3/s

78

ud > uc ( the decanter vessel is sized on the basis that the velocity of the

continuous phase must be less than settling velocity of the droplets of the

dispersed phace) [23].

Ai = Lc/uc

Ai = = 1.597184548 m2

Ai =

r = = 0.71302148 m

Diameter of vertical cylinder = 1.426048961 m

Take the height as twice the diameter, a reasonable value for a cylinder.

Height = 2.852085922 m

Take the dispersion as 10 percent of the height =0.285208592 m

Check the residence time of the droplets in the dispersion band

= = 160.3169644 s = 2.671949407 min

This is satisfactory , atime of 2-5 min is normally recommended.

Check the size of the spent acid (continuous, heavy phase) droplets that

could be entrained with the crude Nitrobenzene (light phase).Velocity of the

Velocity crude Nitrobenze phase = * *

79

Velocity crude Nitrobenze phase = 1.494254608 * 10-3 m/s

dd = (stock’s law)

dd =

dd = 9.267388216 * 10-5 m = 92.67388216 µm ( which is very satifactory; below

150µm).

Piping Arrangement

To minimize entrainment by the jet of the liquid entering the vessel, the

inlet velocity for a decanter should keep below 1m/s.

Flow-rate = *

Flow-rate = 5.22803863 * 10-3 m3/s

Area of pipe = = 5.22803863 * 10-3 m2

Pipe diameter = = 0.081587655 m = 81.587655 mm say

88.9 diameter of the standerd steel pipe [34].

Take the position of the interface as half-way up the vessel and the light

liquid off-take as at 90 percent of the vessel height.

80

Z1 = 0.9 * 2.852085922 = 2.56687733 m

Z3 = 0.5 * 2.852085922 = 1.42604296 m

Z2 =

Z2 = + 1.426042961

Z2 = 2.272174706 m

Proposed Design

Crude N.B

Spent Acid Z3 = 1.4 m Z1 = 2.6 m Z2 =2 m

Heavy liquid

take off

Liquid- light

take off

D = 1.4 m

81

Mechanical Design

The material of construction used is stainless steel [4], select stainless steel

(18 Cr / 8 Ni) (304) which is corrosion resistance.

Calculation of the Thickness of Decanter

Thickness of the decanter can be calculated directly from equation bellow:

t = + C

J = 0.85, f = 145N/mm2, C = 1mm, D = 1.426 * 103mm

P= 1.1*1 =1.1atm = 0.1114575N/mm2

t = + 1

t = 1.645072183 mm 2mm less than 7mm so that take the thickness 6mm [23]

Calculation the thicness of domed ends:

Select the ellipsodial heads

t =

t =

t = 0.644838821mm 0.645mm

82

5.3 Heat Exchanger Design [23]

The heat exchanger which is used as cooller to cool the spent acid from vaporizer from 100oC to 65.5 by using cold water.

water is corrosive more than Spent acid, so assign to tube side.

Operating Condition

Temperature of a hot spent acid inputT1 = 100oC

Temperature of a cold spent acid outputT1 = 65.5oC

Temperature of a cold water input t1 = 30oC

Temperature of a hot water input t2 = 50oC

Cooling water

t1 =30oC hot water

t2=30oC

Spent Acid

T1=100oC

Spent Acid

T2=65.5oC

T1=100oC

T2=50oC T2=65.5oC

t1=30oC

∆T1 {

}∆T2

83

t1 = 30 °C

t2 = 50 °C

T2 = 65.5 °C

T1 =100 °C

The hot spent acid & cold water passed counter currently ( more efficient

than co-current).

From energy balance:

QCooling = 1,060,108.891 KJ/hr = 294.4746919 KWatt

mH2O = 28,284.58611 Kg/hr = 7.856829475 Kg / s

Mean Temperature Difference (∆Tm)

( ) ( )

( )( )12

21

1221

lntTtT

tTtTTlm

−

−−−−

=∆

( ) ( )( )( )

CTlmo33696435.42

305.6530100ln

305.6550100=

−−

−−−=∆

∆Tm = Ft ∆Tlm

Use one shell and two tube passes.

R = ( T1 – T2 ) / ( t2 – t1 )

S = ( t2 – t1 ) / ( T1 – t1)

R = (100 – 65.5) / ( 50 –30)= 1.725

S = ( 50 – 30 ) / (100 – 30 ) = 0.285714285

From figure (12.19) [23] at R = 1.725 & S = 0.285714285 → Ft = 0.95

∆Tm = 0.95 * 42.33696435 = 40.22011613oC

From table (12-1) [23] choose U = 800 W/m2.oC.

.

84

Provisional area

Q = U A ∆Tm

A = = 9.151971708 m2

Pipe Dimension

Choose 20mm o.d, 16mm i.d, 4.88m long tube table (12.3) [23]

Allowing for tube sheet thicness, take L = 4.83m, material of construction Cupro-Nickel.

Area of one tube = π do L

Area of one tube = π* 20*10-3 * 4.83 * 10-3= 0.30347785 m2

Number of tubes = Nt = A / At

Number of tubes = 9.151971708 / 0.30347785 = 30.15696763 30 tube

Use 1.25 Triangular pitch, this type of pitch is more efficient than rectangular

pitch.

Db = bundle diameter = do (Nt / k1 ) 1/n1

From table (12-4) [23], k1 = 0.24, n1= 2.207

Db = 20 * (30 / 0.249)1/2.207

Db = 175.3490987 mm

Use a split-ring floating head type, assume clearance = 30mm

Shell diameter; Ds = 175.3490987+ 30 = 205.3490987 mm

Pt

Flow

Triangular Pitch

85

Tube – Side Coefficient

Mean temperature = (30 + 50) /2 =40°C

Physical properties of water at mean temperature [32]:

Cp = 4.174kJ/kg.°C, ρ = 992.04 kg/m3, µ = 6.556 * 10-4 pa.s, Kf =0.6328 W/m °C , Pr = 4.334.

tube cross-sectional area = π di2 /4 = π (16)2 /4 = 201.0619296 m2

tube per pass = 30 / 2 = 15

total flow area = At = 15 * 201.0619296 * 10-6 = 3.015928947 * 10-3 m2

Mass velocity (G) = mH2O/At

Mass velocity (G) = 7.856829475/ 3.015928947*10-3

Mass velocity (G) = 2,605.110934kg/m2.s

Water linear velocity = 2,605.110934 / 992.04 = 2.626014005 m/s

Re = ρ ut d /µ

Re = 992.04 * 2.626014005 * 16 * 10-3 / 6.556 * 10-4 = 6.357805817 * 104

hi = 4200 (1.35 + 0.02 t) ut0.8 / di

0.2

hi = 4200 ( 1.35 + 0.02 (40)) (2.626014005)0.8 / (16)0.2

hi = 11,227.97364 W/m2.oC

or

( ) 14.033.0 /PrRe whf

ii Jk

dhµµ=

Negiect (µ/µw) 0.14

From Figure (12.23)[23], jh = 3.1×10-3

.

86

hi = (0.6328/16 * 10-3) ( 3.1 * 10-3) (6.357805817 * 104) (4.334) 0.33

hi = 12,647.03674W/m2 °C

take the lower value hi = 11,227.97364 W/m2.oC

calculation of tube teperature

hi (tw – t) = U (T – t)

11,227.97364 (tw – 40) = 800 (82.75 – 40)

tw = 43.03245965oC 43 oC

µw = 6.199243243 * 10-4 pa.s at 43 oC

[ ]0.14 = [ ]0.14 = 1.007864243 1[no correction factor

needed]

Shell – Side Coefficient

Choose baffle spacing = lB = 0.2Ds [23]

lB = 0.2 * 205.3490987 = 41.06981914mm

tube pitch = 1.25 do = 1.25 (20) = 25mm

As =

As = = 1.686730069*10-3m2

mspent acid = 12,009.08088 Kg/hr = 3.3358558 Kg/s

Gs = = 1977.705776 Kgde = ( pt2 – 0.917 do )

.

87

de = (252 – 0.917 * 202 ) = 14.201 mm

all physical properties at 82.75oC of spent acid [24, 28&32]:

Cp = 1.590330869 kJ/kg.°C

ρ = 1,748.959499 kg/m3

µ = 5.376377382 * 10-3 pa.s

Kf =0.401408274 W/m °C

Pr = 2.130055474

Re = = = 5.223851997 * 103

Choose 25 percent baffle cut, from figure ( 12.29) [23], jh = 2.4 * 10-2

hs = jh Re pr1/3 [ ]0.14

Negiect (µ/µw) 0.14

hs = * 2.4 * 10-2 * ( 5223.851997) * ( 2.130055474)1/3

hs = 4,559.6671 W /m2.oC

Calculation of the Shell Temperature

hS (T–Tw) = U (T – t)

4,559.6671 (tw – 40) = 800 (82.75 – 40)

tw = 75.24945243oC 75.25 oC

88

µw = 6.077856682* 10-3 pa.s at 75.25 oC

[ ]0.14 = [ ]0.14 = 0.982977327 1[no correction factor

needed]

Checking for over all Heat Transfer Coefficient

The value of over heat transfer coefficient must be checked and the new value of U must be greater than assumed value (800 W/ m2.oC).

hid

dhd

dk

dddhhU i

o

idi

o

w

ioo

odoo

112

)/ln(111++++=

Kw = 50 W / m .oC (for curpo-Nikel) [32].

Take the foaling coefficient as 6000 W/ m2.oC [23].

= + + + * + *

= 7.28006325 * 10-4

Uo = 1,373.614614 W/ m2.oC (Above the assumed value of 800 W/ m2.oC)

Calculation of Pressure Drop

Tube Side

Pressure drop in the tube side can be calculated from equation below, the pressure drop calculated must be smaller than 10 psi.

∆Pt = Np [ 8jf + 2.5]

jf = 3 * 10-3 from figure (12.24) [23].

89

∆Pt = 2[ 8 * 3 * 10-3 * + 2.5]

∆Pt = 66,666.10822 pa = 9.671766996 psi < 10 psi ( acceptable).

Shell Side

∆Ps = 8jf

us = GS /ρ = 1977.705776 / 1748.959499 = 1.130789922 m/s

from figure (12.30) [23], at Re = 5.223851997 * 103 → jf = 5.7 * 10-3

∆Ps = 8* 5.7 * 10-3 *

∆Ps = 75,096.10397 pa = 10.89477156 psi considered suitable not mor large than

10 psi .

Input and Output Manholes

Diameter of manholes is given in equation below:

dm = 282 m0.52 ρ-0.37

Manhol for Input Hot Spent Acid

dm = 282 * ( 3.3358558)0.52 * ( 1,748.959499)-0.37

dm = 33.30338513 mm

Manhol for Input Cold Water

dm = 282 * ( 7.856829475)0.52 * (992.04)-0.37

dm = 64.13010051 mm

.

90

5.4 Distillation Design [23,30&35]

Comp.

Feed Top Bottom

Wt.% Mol.% Wt.% Mol.% Wt.% Mol.%

C6H6 2.014285745 3.31381848 100 100 1 1.567082484

C6H5NO2 97.98571425 96.86168152 - - 99 98.43291752

TemperatureoC 192.1 80.1 200.87

Vapor-liquid equilibrium data for Benzene-Nitrobenzene [36]: (see appendex B)

X Y 0 0

0.05 0.451 0.1 0.759

0.15 0.923 0.2 0.957

0.25 0.969 0.3 0.975

0.35 0.981 0.4 0.985

0.45 0.988 0.5 0.989

0.55 0.99 0.6 0.992

0.65 0.994 0.7 0.995

0.75 0.996 0.8 0.996

0.85 0.997 0.9 0.999

0.95 0.999 1 1

91

Benzene Vapor M

ole Fraction 

0 0.2 0.4 0.6 0.8 1

0

0.2

0.4

0.6

0.8

1

Figure 5-1 Vapor-Liquid Equilibrium diagram (Isothermal) at 70oC

R = 2.062272268

Intercept = = = 0.326554895 0.33

From equilibrium curve by Mc cabe-Tiele method find the number of stages equal 3.

Number of theoretical plate = 3 + 1 = 4

Benzene Liquid Mole Fraction

92

assume column efficiency of 60 percent. Take reboiler as equivalent to one stage.

No. of real stages = = 5

Estimate base pressure

Assume 100mm water, pressure drop per plate.

column pressure drop = 100 * 10-3 * 1000 * 9.81 * 5 = 4905 pa

top pressure, 1 atm = 101.325 * 103 pa

bottom pressure drop = 101.325 * 103 + 4905 = 106,230 pa = 106.230 Kpa

Column Diameter

At Top of the Column

Top temperature = 80.1 oC = 353.25 K

Top pressure = 101.325 * 103 pa

L

V

n

nLV V

LF

ρρ

=

From material Balance:

Ln = 209.6398836 Kg/hr = 0.058233301Kg/s

Vn = 311.2946878 Kg/hr = 0.086470746 Kg/s

RTMwtP

V

.=ρ

ρV = = 2.694828052 Kg/m3

ρL = 815.0831896 Kg/m3 at 80.1 oC [28].

93

FLV = = 0.038722801

Take plate spacing 0.45 [ The plate spacing is reduced to avoid the problem of

supporting a tall, slender column] [30].

From figure (11.29) [23] at FLV = 0.038722801 and plate spacing = 0.45,

K1 = 7.5 * 10-2

Correction for surface tension

σ = * 10-12

pch for Benzene = ( 4.8 * 6) + ( 17.1 * 6) = 131.4

σ = * 10-12

σ = 3.488266696 mJ/m2 = 3.488266696 * 10-3 J/m2

(K1)correct = [σ / 20 * 10-3 ]0.2 * K1

(K1)correct = [3.488266696 * 10-3]0.2 * 7.5 * 10-2

(K1)correct = 0.013081

uf = (K1)correct

4

4

94

uf = 0.013081 = 0.227120984 m/s

for design a value of 80-85 percent of the flooding velocity should be used.

uv = 0.85 * uf

uv = 0.85 * 0.227120984 = 0.193052836 m/s

maximum volumetric flow-rate =

maximum volumetric flow-rate = = 0.032087667 m3/s

An = = 0.16621184 m2

At first trial take downcomer area as 12 percent of total.

Ac = = = 0.188877091 m2

Dc = = 0.490393497 m 0.5 m

At Bottom of the Column

Top temperature = 200.87 oC = 474.02 K

Top pressure = 106.230 Kpa

L

V

m

mLV V

LF

ρρ

=

From material Balance:

95

Lm = Vm + stream 15

Vm = Vn = 0.086470746 Kg/s

Stream 15 = 9,820.426487 Kg/ hr = 2.727896246 Kg/s

Lm = 0.086470746 + 2.727896246 = 2.814366992 Kg/s

ρL(mix.) = 1002.856487 Kg/m3 at 200.87 oC [28]

ρV(mix.) =

Mwt. av. = 122.4048129 Kg/Kg.mol

ρV(mix.) = = 3.229930538 Kg/m3

FLV = = 1.847096398

From figure (11.29) [23] at FLV =1.847096398 and plate spacing = 0.45,

K1 = 1.8 * 10-2

Correction for surface tension

σ = * 10-12

pch for Benzene = ( 4.8 * 6) + ( 17.1 * 6) = 131.4

ρV BZ. = = 0.032994305 Kg/m3

ρL BZ. = 656.0793695 Kg/m3

4

96

σBZ. = * 10-12

σ BZ. = 1.483518856mJ/m2 = 1.483518856 * 10-3 J/m2

pch for Nitrobenzene = (4.8*6) + ( 17.1*5) + (12.1*1) + (20*2) = 166.8

ρV BZ. = = 3.266436233Kg/m3

ρL N.B = 1,008.377286 Kg/m3

σN.B = * 10-12

σN.B = 3.49273426 mJ/m2 = 3.439273426*10-3 J/m2

σmix. = (1.483518856 * 10-3 * 0.01567082484) + (3.439273426*10-3 * 0.9843291752) = 3.408625139 * 10-3 J/m2

(K1)correct = [σ / 20 * 10-3 ]0.2 * K1

(K1)correct = [3.408625139*10-3]0.2 * 7.5 * 10-2

(K1)correct = 0.012635206

uf = (K1)correct

uf = 0.013081 = 0.219920976m/s

for design a value of 80-85 percent of the flooding velocity should be used.

uv = 0.85 * uf

4

4

97

uv = 0.85 *0.219920976 = 0.186932829 m/s

maximum volumetric flow-rate =

maximum volumetric flow-rate = = 0.026207778 m3/s

An = = 0.140198909 m2

At first trial take downcomer area as 12 percent of total.

Ac = = = 0.159316942 m2

Dc = = 0.450387201 m

So we will take column diameter Dc = 0.490393497 m 0.5 m

Provisional Plate Design

Column diameter Dc = 0.5 m

Column area Ac = 0.19634954 m2

Downcomer area Ad = 0.12 Ac = 0.12*0.19634954 = 0.03561944 m2

Net area An =Ac - Ad = 0.19634954 - 0.03561944 = 0.172787595 m2

Active area Aa = Ac- 2Ad = 0.19634954 – 2* 0.03561944 = 0.14922565 m2

Holes area Ah = take 10 percent Aa as first trial

Ah = 0.1 * Aa

Ah = 0.1 * 0.14922565

Ah = 0.014922565 m2

98

Weir length from figure (11.31) [23], at Ad/ Ac = 12 → lw = 0.76 Dc

lw = 0.76 * 0.5 =0.38 m

Take: weir height hw = 50mm

Hole diameter dh = 5 mm

Plate thickness = 5 mm

Check weeping

how = 750 [ ]2/3

maximum liquid rate = 2.814366992 Kg/s

maximum how = 750 [ ]2/3 = 28.44243839 mm Liquid

minimum liquid rate, at 70 percent turn down.

minimum liquid rate = 2.81436699 * 0.7 = 1.970056894 Kg/s

minimum how = 750 [ ]2/3 = 22.42326516 mm Liquid

At minimum rate hw + how = 50 + 22.42326516 = 72.42326518 mm

From fig (11.30) [23], K2 = 30.6

uh min. =

uh min. = = 6.810578219 m/s

actual minimum vapour velocity = minimum vapour rate / Ah

99

actual minimum vapour velocity = 0.7 * 0.02607778 / 0.014922562

actual minimum vapour velocity = 1.22937613m/s < 6.810578219 m/s

So minimum operating rate below weep point, so reduced the hole area.

Second Trial

Take: dh = 4.167 mm

Ah = 0.02 Aa = 0.02 * 0.14922565 =2.984513 * 10-3m2

uh min. = = 5.21179869 m/s

actual minimum vapour velocity = 0.7 * 0.02607778 / 2.984513 * 10-3

actual minimum vapour velocity = 6.116390178m/s > 5.21179869 m/s

So minimum operating rate will be well above weep point.

Plate Pressure Drop

Dry plate drop

Maximum vapor velocity through holes

uh =

uh = = 8.737700255 m/s

hd = 51 [ ]2 [ ]

from figure (11.39) [23], at Ah / AP Ah / Aa =0.03,

plate thicness / hole diameter = 5 / 4.167 = 1.2

100

Co = 0.81

hd = 51 [ ]2 [ ] = 19.30499388 mm Liquid

hr = = = 12.46439562 mm Liquid

Total Plate Pressure Drop

ht = hd + ( hw + how ) + hr

ht = 19.30499388 + (50 + 28.4424389) + 12.46439562

ht = 110.2118279 mm liquid

100mm was assumed to calculate the base pressure. The calculation could

be repeated with a revised estimate but the small change in physical properties

will have little effect on the plate design. 110.219279 mm per plate is considered

acceptable.

Downcomer Liquid back-up

Downcomer pressure loss

Take hap = hw - 10 = 50 – 10 = 40 mm

Aap = hap lw = Am

Aap = 40 * 10-3 * 0.38 = 0.0152 m2

hdc = 166 [ ]2

hdc = 166 * [ ]2 = 5.65854496 mm

101

hb = ( hw + how ) + ht + hdc

hb = (50 + 28.4424389) + 110.2118279 + 5.65854496

hb = 194.3128113 mm = 0.1943128112 m

hb < ½ (tray spacing + wier hight)

0.1943128112 m < ½ (0.45 + 0.05)

0.2632 m < 0.25 m

So tray spacing acceptable.

Check Residence Time

tr =

tr =

tr = 1.631438149s < 3 sec ( not satifactory)

Check Entrainment

uv = = 0.15167627 m/s

percentage flooding =

percentage flooding = * 100 = 68.96853282%

from figure ( 11-29) [23], ψ =0.03 well bellow 0.1, satifactory

plate Layout

use sieve plate. Allow 50mm unperforated strip round plate edge;

102

50mm wide callming zones.

Perforated Area

From figure (11.32) [23],

At lw / Dc = 0.76

θo = 99o

α = 180 o – 99o =81o

mean length of unperforated edge strip

= (0.5 –0.01)( π / 180 * 81) = 0.636172512 m

Area of unperforated edge strips = 0.636172512 * 50 * 10-3

Area of unperforated edge strips = 0.031808625 m2

Area of calming zones = 2 (0.05) * ( 0.38 – 2 * 0.05) = 0.028 m2

Ap = active area – unperforated edge strip area – calming area

Ap = 0.14922565 – (0.031808625 + 0.028 ) = 0.089416724 m2

At (Ah/ Ap) = 2.984513*10-3/ 0.089416724 = 0.03337757

From fig. (11.33) [23]

lp/dh = 4

lp = 4 * 4.167 = 16.668 mm (pitch).

Number of holes

Area of one hole = (π/4) dh2

= (π/4) (0.004167) 2

= 1.363756653*10-5 m2

α

θ

50 mm

50 mm

lw= 0.38 D = 0.5 m

103

Number of holes = hole area / area of one hole

Number of holes = 2.984513*10-3/ 1.363756653*10-5

Number of holes = 219 holes

Total Height of Distillation Column

hT = (Tray Spacing * No. plate) + thicness of plate

hT = (0.45 * 5) + 0.005 = 2.255m

 

 

Chapter Six Control System

 

104  

Chapter Six

Control System

6.1 Introduction

Instruments are provided to monitor the key process variables during plant

operation. They may be incorporated in automatic control loops, or used for the

manual monitoring of the process operation. They may also be part of an

automatic computer data lagging system. Instruments monitoring critical process

variables will be fitted with automatic alarms to alert the operators to critical and

hazardous situations.

The primary objectives of the designer when specifying instrumentation

and control schemes are:

1. Safe plant operation:

a) To keep the process variables within known safe operation limits.

b) To detect dangerous situations as they develop and to provide alarms

and automatic shut-down systems.

c) To provide interlocks and alarms to prevent dangerous operating

procedures.

2. Production rate:

To achieve the design product out put.

3. Product quality:

To maintain the product composition within specified quality standards.

4. Cost:

105  

To operate at the lowest production cost, commensurate with the other

objectives.

6.2 Control of Nitrator

Nitration reactions must be considered potentially hazardous. This is

because of heat of nitration is substantial but also because further heat release

is possible through nitric acid oxidation if the reaction gets out of hand. An

incident is reported where a batch nitrobenzene plant caught fire after the belt

drive of an agitator slipped, and unreacted benzene and nitric acid were

allowed to accumulate without adequate cooling. Great care has to be taken to

properly design the control system for a nitration plant and to properly size

the pressure relief system, which serves as last resort [4].

In the isothermal process, nitric acid and benzene are fed in a fixed molar

ratio of C6H6 / HNO3, usually about 1.05. The sulfuric acid rate is matched in

proportion to give a spent acid strength of about 70% H2SO4. Temperature in

the nitrator is controlled by throttling the cooling water flow rate to the

nitratar. High temperature switches will shut off the feeds and open the

cooling water valve wide. A low speed or power switch on the nitrator

agitator will also shut off all feeds. The level in the nitrator is set by gravity

overflow [4].

Control of the adiabatic process also requires control of the benzene and

nitric acid feed in affixed molar ratio. No direct temperature is required since

sulfuric acid is the heat sink of the process. The temperature is controlled by

controlling the sulfuric acid circulation rate. Safty interlocks must be

provided to shut the process safely in the case of failure of sulfuric acid

circulation. Control of the acid concentrator, in particular of the sulfuric acid

106  

strength produced, must be integrated with the nitration section [4], figure 6-1

illustrated the control of isothermal nitrator [23].

Figure 6-1 Nitrator Control

LC

TC TC

FC

FC

FC

FC

Feed

107  

6.3 Settler Control

Decanter are normally designed for continuous operation, the position of the

interface can be controlled, with or without the use of the instruments, by use of

the siphon take-off for the heavy liquid [23].

Figure 6-2 Settler control

Feed

LC

Heavy liquid

Liquid- light

Crude N.B

Spent Acid

Heavy liquid take off

Liquid- light take off

Feed

Figure 6-3 Settler control

108  

6.4 Vaporizer Control

Level control is often used for vaporizers; the controller controlling the

steam supply to the heating surface, with the liquid feed to the vaporizer on flow

control, as shown in figure 6-4. An increased the feed results in an automatic

increase in steam to the vaporizer to vaporize the increased flow and maintain

the level constant [23].

Figure 6-4 vaporizer control

Feed

Trap

Steam

TC

LC

109  

6-5 Heat Exchanger Control

Exchangers do not always require special temperature control. Since their

purpose in a process is to provide the maximum recovery of heat, there is reason

to restrict their performance by the use of controls [22].

When a fluid is cooled in an exchanger, it usually passes through a cooler and

its temperature is controlled by a flow adjustment of the water. It is not possible

to control both the flow quantities and the outlet temperatures of both streams

passing through an exchanger at the exchanger itself, since one adjustable quality

must always be present. Thus, if the outlet temperatures of both streams are to be

controlled and the flow or temperature of one stream may vary, the flow or outlet

temperature of the other stream must also vary [22].

Most of the problems of exchanger instrumentation are encountered when the

two streams are of unequal size, the one being very much larger than other [22].

If the heat exchanger is between two process streams whose flows are fixed,

by-pass control will have to be used, figure 6-5 shows the control of heat

exchanger [23].

Figure 6-5 Heat Exchanger control

TC

110  

6.6 Distillation column control

The primary objective of distillation column control is to maintain the

specified composition of the top and bottom products, and any side streams;

correcting for the effects of Disturbances in:

1. Feed flow-rate, composition and temperature.

2. Steam supply pressure.

3. Cooling water pressure and header temperature.

4. Ambient conditions, which cause changes in internal reflux

The compositions are controlled by regulating reflux flow and boil-up. The

column overall material balance must also be controlled; distillation columns

have little surge capacity (hold-up) and the flow of distillate and bottom product

(and side-streams) must match the feed flows. Column pressure is normally

controlled at a constant value [23].

The use of variable pressure control to conserve energy, Feed temperature

is not normally controlled, unless a feed preheater is used. Temperature is often

used as an indication of composition. The temperature sensor should be located

at the position in the column where the rate of change of temperature with

change in composition of the key component is a maximum [23].

Near the top and bottom of the column the change is usually small. Top

temperatures are usually controlled by varying the reflux ratio and bottom

temperatures by varying the boil-up rate. If reliable on-line analyzers are

available they can be incorporated in the control loop, but more complex control

equipment will be needed [23].

111  

Figure 6-6 Temperature pattern control

With this arrangement interaction can occur between the top and bottom

temperature controllers, figure 6-5 [23].

Figure 6-7 Composition control.

Reflux ratio controlled by a ratio controller, or splitter box, and the bottom

product as a fixed ratio of the feed flow, figure 6-6 [23].

112  

Figure 6-8 Composition control

Top product take-off and boil-up controlled by feed; figure 6-7 [23].

 

 

 

Chapter Seven Plant Layout

113  

Chapter Seven

Plant Layout

7.1 Site Considerations [23]

The location of the plant can have a crucial effect on the profitability of a

project, and the scope for future expansion. Many factors must be considered

when selecting a suitable site, and only a brief review of the principal factors will

be given in this chapter. The principle factors to consider are:

1) Marketing area

For materials that are produced in bulk quantities; such as cement, mineral

acids, and fertilisers, where the cost of the product per tonne is relatively low and

the cost of transport a significant fraction of the sales price, the plant should be

located close to the primary market. This consideration will be less important for

low volume production, high-priced products; such as pharmaceuticals.

In an international market, there may be an advantage to be gained by

locating the plant within an area with preferential tariff agreements; such as the

European Community (EC).

2) Raw materials

The availability and price of suitable raw materials will often determine

the site location. Plants producing bulk chemicals are best located close to the

source of the major raw material; where this is also close to the marketing area.

114  

3) Transport

The transport of materials and products to and from the plant will be an

overriding consideration in site selection. If practicable, a site should be selected

that is close to at least two major forms of transport: road, rail, waterway (canal

or river), or a sea port. Road transport is being increasingly used, and is suitable

for local distribution from a central warehouse. Rail transport will be cheaper for

the long-distance transport of bulk chemicals. Air transport is convenient and

efficient for the movement of personnel and essential equipment and supplies,

and the proximity of the site to a major airport should be considered.

4) Availability of labor

Labor will be needed for construction of the plant and its operation.

Skilled construction workers will usually be brought in from outside the site

area, but there should be an adequate pool of unskilled labor available locally;

and labor suitable for training to operate the plant. Skilled tradesmen will be

needed for plant maintenance. Local trade union customs and restrictive

practices will have to be considered when assessing the availability and

suitability of the local labor for recruitment and training.

5) Utilities (services)

Chemical processes invariably require large quantities of water for cooling

and general process use, and the plant must be located near a source of water of

suitable quality. Process water may be drawn from a river, from wells, or

purchased from a local authority. At some sites, the cooling water required

can be taken from a river or lake, or from the sea; at other locations cooling

towers will be needed. Electrical power will be needed at all sites.

Electrochemical processes that require large quantities of power; for example,

115  

aluminium smelters, need to be located close to a cheap source of power. A

competitively priced fuel must be available on site for steam and power

generation.

6) Environmental impact, and effluent disposal

All industrial processes produce waste products, and full consideration

must be given to the difficulties and cost of their disposal. The disposal of toxic

and harmful effluents will be covered by local regulations, and the appropriate

authorities must be consulted during the initial site survey to determine the

standards that must be met. An environmental impact assessment should be

made for each new project, or major medication or addition to an existing

process.

7) Local community considerations

The proposed plant must fit in with and be acceptable to the local

community. Full consideration must be given to the safe location of the plant so

that it does not impose a significant additional risk to the community. On a new

site, the local community must be able to provide adequate facilities for the plant

personnel: schools, banks, housing, and recreational and cultural facilities.

8) Land (site considerations)

Sufficient suitable land must be available for the proposed plant and for

future expansion. The land should ideally be flat, well drained and have suitable

load-bearing characteristics. A full site evaluation should be made to determine

the need for piling or other special foundations.

116  

9) Climate

Adverse climatic conditions at a site will increase costs. Abnormally low

temperatures will require the provision of additional insulation and special

heating for equipment and pipe runs. Stronger structures will be needed at

locations subject to high winds (cyclone/hurricane areas) or earthquakes.

10) Political and strategic considerations

Capital grants, tax concessions, and other inducements are often given by

governments to direct new investment to preferred locations; such as areas of

high unemployment. The availability of such grants can be the overriding

consideration in site selection.

7.2 Site Layout [23]

The process units and ancillary buildings should be laid out to give the

most economical flow of materials and personnel around the site. Hazardous

processes must be located at a safe distance from other buildings. Consideration

must also be given to the future expansion of the site. The ancillary buildings

and services required on a site, in addition to the main processing units

(buildings), will include:

1. Storages for raw materials and products: tank farms and warehouses.

2. Maintenance workshops.

3. Stores, for maintenance and operating supplies.

4. Laboratories for process control.

5. Fire stations and other emergency services.

117  

6. Utilities: steam boilers, compressed air, power generation, refrigeration,

transformer stations.

7. Effluent disposal plant.

8. Offices for general administration.

9. Canteens and other amenity buildings, such as medical centres.

10. Car parks.

When roughing out the preliminary site layout, the process units will

normally be sited first and arranged to give a smooth flow of materials through

the various processing steps, from raw material to final product storage. Process

units are normally spaced at least 30 m apart; greater spacing may be needed for

hazardous processes.

The location of the principal ancillary buildings should then be decided.

They should be arranged so as to minimize the time spent by personnel in

travelling between buildings. Administration offices and laboratories, in which a

relatively large number of people will be working, should be located well away

from potentially hazardous processes. Control rooms will normally be located

adjacent to the processing units, but with potentially hazardous processes may

have to be sited at a safer distance.

The sitting of the main process units will determine the layout of the plant

roads, pipe alleys and drains. Access roads will be needed to each building for

construction, and for operation and maintenance.

Utility buildings should be sited to give the most economical run of pipes

to and from the process units.

118  

Cooling towers should be sited so that under the prevailing winds the

plume of condensate spray drifts away from the plant area and adjacent

properties. The main storage areas should be placed between the loading and

unloading facilities and the process units they serve. Storage tanks containing

hazardous materials should be sited at least 70m (200ft) from the site boundary.

A typical plot plant is shown in figure 7-1.

Figure 7-1 A typical site plan

7.3 Plant Layout

The economic construction and efficient operation of a process unit will

depend on how well the plant and equipment specified on the process flow-sheet

is laid out.

The principal factors to be considered are:

1. Economic considerations: construction and operating costs.

119  

2. The process requirements.

3. Convenience of operation.

4. Convenience of maintenance.

5. Safety.

6. Future expansion.

7. Modular construction.

7.4 Utilities [23]

The word “Utilities” is now generally used for the ancillary services

needed in the Operation of any production process. These services will normally

be supplied from Central site facility; and will include:

1. Electricity.

2. Steam, for process heating.

3. Cooling water.

4. Water for general use.

5. Demineralised water.

6. Compressed air.

7. Inert-gas supplies.

8. Refrigeration.

9. Effluent disposal facilities.

120  

7.5 Environmental Consideration [23]

All individuals and companies have a duty of care to their neighbors, and

to the environment in general. In the United Kingdom this is embodied in the

Common Law. In addition to this moral duty, stringent controls over the

environment are being introduced in the United Kingdom, the European Union,

the United States, and in other industrialized countries and developing countries.

Vigilance is required in both the design and operation of process plant to

ensure that legal standards are met and that no harm is done to the environment.

Consideration must be given to:

1. All emissions to land, air, water.

2. Waste management.

3. Smells.

4. Noise.

5. The visual impact.

6. Any other nuisances.

7. The environmental friendliness of the products.

7.6 Waste Management [23]

Waste arises mainly as byproducts or unused reactants from the process,

or as off- specification product produced through mis-operation. There will also

be fugitive emissions from leaking seals and flanges, and inadvertent spills and

discharges through mis-operation. In emergency situations, material may be

121  

discharged to the atmosphere through vents normally protected by bursting discs

and relief values.

The designer must consider all possible sources of pollution and, where

practicable, select processes that will eliminate or reduce (minimize) waste

generation.

Unused reactants can be recycled and off-specification product

reprocessed. Integrated processes can be selected: the waste from one process

becoming the raw material for another. For example, the otherwise waste

hydrogen chloride produced in a chlorination process can be used for

chlorination using a different reaction; as in the balanced, chlorination-

oxyhydrochlorination process for vinyl chloride production. It may be possible to

sell waste to another company, for use as raw material in their manufacturing

processes. For example, the use of off-specification and recycled plastics in the

production of lower grade products, such as the ubiquitous black plastics bucket.

Processes and equipment should be designed to reduce the chances of mis-

operation; by drains, and pumps should be sited so that any leaks flow into the

plant effluent collection system, not directly to sewers. Hold-up systems, tanks

and ponds, should be provided to retain spills for treatment. Flanged joints

should be kept to the minimum needed for the assembly and maintenance of

equipment.

When waste is produced, processes must be incorporated in the design for its

treatment and safe disposal. The following techniques can be considered:

1. Dilution and dispersion.

122  

2. Discharge to foul water sewer (with the agreement of the appropriate

authority).

3. Physical treatments: scrubbing, settling, absorption and adsorption.

4. Chemical treatment: precipitation (for example, of heavy metals),

neutralization.

5. Biological treatment: activated sludge and other processes.

6. Incineration on land, or at sea.

7.8 Nitrobenzene Plant Location

Based on these previous factors which are required in nitrobenzene

manufacturing plant, I select AL- Basrah as plant location in a place at which the

wind pass through the plant must not hit the cities and inter to the goverarate

because nitrobenzene plant causing ambient air pollutant which may effected on

people negatively this location will provide to the plant utilities which need since

it near the river and Shatt AL-Arab which also contain a large harbor which we

can use it for export purposes. The foundation of the refinery in Basrah “AL

Rumela Refinery” which provide low cost of transport requirement, also labors

and local community which satisfied the labor requirement.

 

 

Chapter Eight Toxicity and Effects of

Nitrobenzene  

123  

Chapter Eight

Toxicity and Effects of Nitrobenzene

8.1 General

Nitrobenzene is very toxic substance; the maximum allowable

concentration for nitrobenzene is 1 ppm or 5 mg/m3. It was exposed for eight

hours to 1 ppm nitrobenzene in the working atmosphere, about 25 mg of

nitrobenzene would be absorbed, of which about one-third would be by skin

absorption and the remainder by inhalation. The primary effect of nitrobenzene

is the conversion of hemoglobin to methemoglobin; thus the conversion

eliminates hemoglobin from the oxygen-transport cycle. Exposure to

nitrobenzene may irritate the skin and eyes. Nitrobenzene affects the central

nervous system and produces fatigue, headache, vertigo, vomiting, general

weakness and in some cases unconsciousness and coma. There generally is a

latent period of 1-4 hours before signs or symptoms appear. Nitrobenzene is a

powerful methemoglobin former, and cyanosis appears when the methemoglobin

level reaches 15%. Chronic exposure can lead to spleen and liver damage,

jaundice, and anemia. Alcohol ingestion tends to increase the toxic effects of

nitrobenzene; thus alcohol in any form should not be ingested by the victim of

nitrobenzene poisoning for several days after the nitrobenzene poisoning or

exposure. Impervious protective clothing should be worn in areas where risk of

splash exists. Ordinary work clothes that have been splashed should be removed

immediately, and the skin washed thoroughly with soap and worm water. In

areas of high vapor concentration (>1 ppm), full face mask with organic-vapor

124  

consters or air-supplied respirators should be used. Clean work clothing should

be worn daily, and showering after each shift should be mandatory [2&3].

With respect to the hazards of fire and explosion, nitrobenzene is

classified as modrate hazard when exposed to heat or flame. Nitrobenzene is

classified by the ICC as a class-B poisonous liquid [2&3].

8.2 Effects on Humans

Nitrobenzene is toxic to humans by inhalational, dermal and oral

exposure. The main systemic effect associated with human exposure to

nitrobenzene is methaemoglobinaemia [5].

Numerous accidental poisonings and deaths in humans from ingestion of

nitrobenzene have been reported. In cases of oral ingestion or in which the

patients were apparently near death due to severe methaemoglobinaemia,

termination of exposure and prompt medical intervention resulted in gradual

improvement and recovery. Although human exposure to sufficiently high

quantities of nitrobenzene can be lethal via any route of exposure, it is

considered unlikely that levels of exposure high enough to cause death would

occur except in cases of industrial accidents or suicides [5].

The spleen is likely to be a target organ during human exposure to

nitrobenzene; in a woman occupationally exposed to nitrobenzene in paint

(mainly by inhalation), the spleen was tender and enlarged [5].

Neurotoxic symptoms reported in humans after inhalation exposure to

nitrobenzene have included headache, confusion, vertigo and nausea. Effects in

125  

orally exposed persons have also included those symptoms, as well as apnoea

and coma [5].

8-3 Effects on Organisms in the Environment 

  Nitrobenzene appears to and an 8-day lowest-observed-effect

concentration of 1.9 mg/litre for the blue-green be toxic to bacteria and may

adversely affect sewage treatment facilities if present in high concentrations in

influent. The lowest toxic concentration reported for microorganisms is for the

bacterium Nitrosomonas, with an EC50 of 0.92 mg/litre based upon the inhibition

of ammonia consumption. Other reported values are a 72-h no-observed-effect

concentration of 1.9 mg/litre for the protozoan Entosiphon sulcatum alga

Microcystis aeruginosa [5].

For freshwater invertebrates, acute toxicity (24- to 48-h LC50 values)

ranged from 24 mg/litre for the water flea (Daphnia magna) to 140 mg/litre for

the snail (Lymnaea stagnalis). For marine invertebrates, the lowest acute toxicity

value reported was a 96-h LC50 of 6.7 mg/litre for the mysid shrimp (Mysidopsis

bahia). The lowest chronic test value reported was a 20-day NOEC of 1.9

mg/litre for Daphnia magna, with an EC50, based on reproduction, of 10 mg/litre

[5].

Freshwater fish showed similar low sensitivity to nitrobenzene. The 96-h

LC50 values ranged from 24 mg/litre for the medaka (Oryzias latipes) to142

mg/litre for the guppy (Poecilia reticulata). There was no effect on mortality or

behaviour of medaka at 7.6 mg/litre over an 18-day exposure [5].

126  

8.4 Hazard and Risk Evaluation

Methaemoglobinaemia and subsequent haematological and splenic

changes have been observed in exposed humans, but the data do not allow

quantification of the exposure–response relationship. In rodents,

methaemoglobinaemia, haematological effects, testicular effects and, in the

inhalation studies, effects on the respiratory system were found at the lowest

doses tested. Methaemoglobinaemia, bilateral epididymal hypospermia and

bilateral testicular atrophy were observed at the lowest exposure level studied, 5

mg/m3 (1 ppm), in rats. In mice, there was a dose-related increase in the

incidence of bronchiolization of alveolar walls and alveolar/bronchial

hyperplasia at the lowest dose tested of 26 mg/m3 (5 ppm). Carcinogenic

response was observed after exposure to nitrobenzene in rats and mice:

mammary adenocarcinomas were observed in female B6C3F1 mice, and liver

carcinomas and thyroid follicular cell adenocarcinomas were seen in male

Fischer-344 rats. Benign tumours were observed in five organs. Studies on

genotoxicity have usually given negative results [5].

Although several metabolic products of nitrobenzene are candidates for

cancer causality, the mechanism of carcinogenic action is not known. Because of

the likely commonality of redox mechanisms in test animals and humans, it is

hypothesized that nitrobenzene may cause cancer in humans by any route of

exposure [5].

Exposure of the general population to nitrobenzene from air or drinking-

water is likely to be very low. Although no no-observed-adverse-effect level

could be derived from any of the toxicological studies, there is a seemingly low

127  

risk for non-neoplastic effects. If exposure values are low enough to avoid non-

neoplastic effects, it is expected that carcinogenic effects will not occur [5].

Acute poisonings by nitrobenzene in consumer products have occurred

frequently in the past. Significant human exposure is possible, due to the

moderate vapour pressure of nitrobenzene and extensive skin absorption.

Furthermore, the relatively pleasant almond smell of nitrobenzene may not

discourage people from consuming food or water contaminated with it. Infants

are especially susceptible to the effects of nitrobenzene [5].

There is limited information on exposure in the workplace. In one

workplace study, exposure concentrations were of the same order of magnitude

as the lowest-observed-adverse-effect levels in a long-term inhalation study.

Therefore, there is significant concern for the health of workers exposed to

nitrobenzene [5].

Nitrobenzene shows little tendency to bioaccumulate and appears to

undergo both aerobic and anaerobic biotransformation. For terrestrial systems,

the levels of concern reported in laboratory tests are unlikely to occur in the

natural environment, except possibly in areas close to nitrobenzene production

and use and areas contaminated by spillage [5].

Using the available acute toxicity data and a statistical distribution

method, together with an acute: chronic toxicity ratio derived from data on

crustaceans, the concentration limit for nitrobenzene to protect 95% of

freshwater species with 50% confidence may be estimated to be 200 µg/litre.

Nitrobenzene is thus unlikely to pose an environmental hazard to aquatic species

at levels typically reported in surface waters, around 0.1–1 µg/litre. Even at

128  

highest reported concentrations (67 µg/litre), nitrobenzene is unlikely to be of

concern to freshwater species [5].

There is not enough information to derive a guideline value for marine

organisms [5].

8.5 Industrial Safety

• Storage precaution: store in a refrigerator or in a cool, dry place [37].

• Skin contact: Flood all areas of body that have contacted the substance

with water. Don’t wait to remove contaminated clothing; do it under the

water stream. Use soap to help assure removal. Isolate contaminated

clothing when removed to prevent contact by others [37].

• Inhalation: leave contaminated area immediately; breathe fresh air.

Proper respiratory protection must be supplied to any rescuers. If

coughing, difficult breathing or any other symptoms develop, seek

medical attention at once, even if symptoms develop many hours after

exposure [37].

• Eye contact: remove any contact lenses at once. Flush eyes well with

copious quantities of water or normal saline for at least 20-30 minutes.

• Ingestion: if convulsions are not present, give a glass or two of water or

milk to dilute the substance. Assure that the person’s airway is

unobstructed and contact a hosnital or poison center immediately for

advice on wiether or not to induce vomiting [37].

129  

References

1- Ullmann’s Encyclopedia of Industrial Chemistry, 2005 Wiley-VCH Verlag

GmbH & Co. KGaA.

2- Krik and Othmer, “Encyclopedia of Chemical Technology”, Vol.17, 4th Ed.,

p (133-152).

3- Krik and Other, “Encyclopedia of Chemical Technology”, Vol.15, 3rd Ed., p

(917-932).

4- John J.Mcketta, “Encyclopedia of Chemical Processing & Design”, Vol. 31,

p. (165-188).

5- http:// Whqlibdoc.Who.int / ech / who.EH.C.230.

6- www. Technology bank.dupont.com.

7- “ Hydrocarbon Processing”, Vol.58,1979, NO.11

8- “Hydrocarbon Processing”, 1978.

9- P.H.Grogins, “Unit Process Organic Synthesis”, fifth edition.

10- H.Scott Fogler, “Elements of Chemical Reaction Engineering”.

11- U.S.pat. 7,326,816 B2 (Feb. 5, 2008).

12- U.S.pat. 4,772,757 (Sep.20, 1988).

13- Sami Matter & Lewis Hatch, “From Hydrocarbon to Petrochemicals”.

14- Sami Matter & Lewis F. Hatch, (2000), “Chemistry of petrochemicals

Processes”, 2nd.

15- U.S.pat. 2,773,911 (Dec.11, 1956).

16- James G. Speight, “Chemical & Process Design Handbook”.

17- Austin, G.T., (1984), “Shreve’s Chemical Process Industries”, 5th Ed., p.

(772).

18- SEP Handbook, “Petrochemical & Downstream Projects”.

19- Robert H. Perry (1997), “Perry’s Chemical Engineer’s Handbook”, 7th Ed.

130  

20- John A. Dean, (1999), “Lange’s Handbook of Chemistry”, Fifteenth Edition,

McGraw-Hill, INC.

21- David R. Lide, (2000-2001), “CRC Handbook of Chemistry & Physics”,

editor-in-chief.

22- Donald Q. Kern, (2005), “Process Heat Transfer”, Twelfth reprint 2005.

Tata McGraw-Hill Edition.

23- Coulson & Richardson’s, (2005), “Chemical Engineering Design”, Vol.6,

Fourth Edition.

24- David M. Himmelblau, (1989), “Basic Principles & Calculation in Chemical

Enginnring”, Fifth Edition.

25- Jack Winnick, (1997), “Chemical Engineering Thermodynamics”, John

Wily & Sons, Inc.

26- J M Smith & H C Van Ness, (2003), “Introduction to Chemical Engineering

Thermodynamics”, Sixth Edition, Tata McGraw-Hill Publishing Company

Limited.

27- Reid & Prausintz, (1987), “The Properties of Gases & Liquids”, Fourth

Edition.

28- Chemicad 6.0.1 Program.

29- Stanley M. Walas, (1990), “Chemical Process Equipment Selection &

Design”, Butterworth-Heinemann Series in Chemical Engineering.

30- H. R. Backhurts & J. H. Harker, (1973) “Process Design”, Heinemamm

Education Books.

31- Brodkey & Hershey, (1988), “Transport Phenomena”, McGraw-Hill Book

Company.

32- Holman, (1981), “Heat Transfer”, 5th edition, McGraw Hill.

33- Coulson & Richardson’s, (1999), “Chemical Engineering”, Vol.1, Sixth

Edition.

131  

34- Alan S. Foust, (1980), “Principles of Unit Operation”, Second Edition.

35- Coulson & Richardson’s, (2002), “Chemical Engineering”, Vol.2, Fifth

Edition.

36- Shuzo Ohe, (1989), “Vapor-Liquid Equilibrium Data”.

37- Lawrence H. Keith & Douglas B. Walters, “Compendium of Safety Data

Sheets for Research & Industrial Chemicals”, Part III.

 

 

 

Appendixes

A-1  

Appendix A

Physical Properties

1- General Properties [19,20,21,22,23,24,25,26,27&28]

Comp. Mwt. [Kg /Kg.mol]

B.P [oC]

∆Hof

(298.15K) [KJ /g.mol]

λ [KJ / Kg.mol]

C6H6 (L) 78.11 80.1 49.1 30781 HNO3 (L) 63.02 - -173.230 - H2SO4 (L) 98.08 - -811.32 - H2O (L) 18.02 100 -285.840 40683

C6H5NO2 (L) 123.11 210.9 12.500 - Na2CO3 (c) (Soda Ash)

106 - -1131.546 -

H2CO3 (aq) 62.03 - -699.65 - Na2SO4 (c) 142.05 - -1413.891 - CaSO4 (c) 136.14 - -1432.7 -

CaSO4.2H2O(c) (Gypsum)

172.18 - -2024.021 -

2- Specific Heat Capacity

A- Specific Heat Capacity of Liquid [KJ / Kg.mol.K] [23&28]

Cp = A + BT + CT2 + DT3

Comp. A B C D C6H6 (L) -33.917 4.743 * 10-1 -3.017 * 10-4 7.130 * 10-9

HNO3 (L) 131.250 -0.1219 0.1704 *10-3 - H2O (L) 32.243 1.923 * 10-3 1.055 * 10-5 -3.596 *10-9

C6H5NO2 (L) 295.3 -0.8907 1.705 * 10-3 -

A-2  

Specific Heat Capacity of Sulfuric acid [KJ / Kg.mol.oC] [24]

Cp = A + BT

Comp. A B H2SO4 (L) 139.1 0.1559

B- Specific Heat Capacity of Crystals [19,20,21,24&25]

Comp. Cp [KJ / Kg.mol.oC] Na2CO3 (c) (Soda Ash) 111.08

Na2SO4 (c) 128.229 CaSO4 (c) 99.73

CaSO4.2H2O(c) (Gypsum) 186.149

C- Specific Heat Capacity of Carbonic acid (predicted) [24]

Cp = K (Mwt.) a

For Acids: K = 0.91, a = -0.152

Cp =0.91* (63.03)-0.152

Cp = 0.485921283 cal /g.oC = 126.1128611 KJ /Kg.mol.oC

D- Specific Heat Capacity of Vapor [KJ / Kg.mol.K] [26]

Cpig / R = A + BT + CT2 + DT-2

Comp. A B C

C6H6 (V) -0.206 39.064*10-3 -13.301*10-6

H2O (V) 3.470 1.450*10-3 0.121*10+5

A-3  

4- Density of Liquids , [Kg.mol / m3][28]

ρ =

Comp. A B C D Range Temperature

KC6H6 (L) 1.0259 0.26666 562.05 0.28394 279-562 HNO3 (L) 1.5943 0.2311 520 0.1917 232-373 H2SO4 (L) 0.8322 0.19356 925 0.2857 284-364 H2O (L) 5.4590 3.0542*10-1 6.4713*102 8.1*10-2 273-333

C6H5NO2 (L) 0.69123 0.24124 719 0.28135 279-719

5- Viscosity of Liquids, [pa.s][28]

µ = exp. [A + B/T + C LnT + DTE] [28]

Comp. A B C D E Range Temperature

K C6H6 (L) 7.5117 294.68 -2.794 - - 279-545 HNO3 (L) 96wt.%

-28.886 1940 2.678 - - 240-356

H2SO4 (L) 98wt.%

-179.84 10694 24.611 - - 284- 367

H2O (L) -51.964 3.6706*103 5.7331 -5.349*10-29 10 273-643 C6H5NO2 (L) -34.557 2611.3 3.4283 - - 273-481

µ H2SO4 (60wt.%) = 3.65*10-3 pa.s at 50 oC figure (14) [22]

µ HNO3 (60wt.%) = 1.47*10-3 pa.s at 50 oC figure (14) [22].

A-4  

6- Thermal Conductivity of Liquids, [W / m.oC]

K = A + BT + CT2 + DT3

Comp. A B C D Range Temperature

K C6H6 (L) 0.23444 -0.00030572 - - 279-413 HNO3 (L) 96wt.%

0.12107 0.0005383 - - 233-433

H2SO4 (L) 98wt.%

0.014247 0.0010763 - - 283-371

H2O (L) -0.4267 0.00569 -8.0065*10-6 1.815*10-9 273-633 C6H5NO2 (L) 0.1869 -0.0001305 - - 283-371

6-Vapor Pressure of liquids using Antoine’s Equation, [mmHg]

Ln po = A - [23]

T = Temperature in K

Comp. A B C Range Temperature

oC C6H6 (L) 15.9008 2788.51 -52.36 7-104

Log po = A - [25]

T = Temperature in oC

Comp. A B C Range Temperature

oC C6H6 (L) 7.1156 1746.6 201.8 134-211

C6H5NO2 (L) 6.90565 1211.033 220.79 8-103

B-1  

Appendix B

Equilibrium Data

XY data for Benzene / Nitrobenzene NRTL Bij Bji Alpha Aij Aji Cij Cji Dij Dji 659.89 -263.35 0.311 0.00 0.00 0.00 0.00 0.00 0.00 Mole Fractions T Deg C P atm X1 Y1 Gamma1 Gamma2 Phi1 Phi2 210.635 1.000 0.00000 0.00000 1.416 1.000 1.000 1.000 151.914 1.000 0.10000 0.82031 1.376 1.001 1.000 1.000 126.933 1.000 0.20000 0.93286 1.340 1.005 1.000 1.000 112.693 1.000 0.30000 0.96616 1.303 1.013 1.000 1.000 103.357 1.000 0.40000 0.98015 1.261 1.031 1.000 1.000 96.798 1.000 0.50000 0.98727 1.214 1.063 1.000 1.000 92.010 1.000 0.60000 0.99139 1.162 1.123 1.000 1.000 88.401 1.000 0.70000 0.99406 1.108 1.228 1.000 1.000 85.524 1.000 0.80000 0.99603 1.057 1.418 1.000 1.000 82.944 1.000 0.90000 0.99781 1.017 1.778 1.000 1.000 80.129 1.000 1.00000 1.00000 1.000 2.529 1.000 1.000

B-2  

رشكر و التقدي

الحمد هللا على ما انعم، و صالته و سالمه على رسوله االمين المبعوث رحمة للعالمين و :بعد

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محاولة تطبيق جميع المواد الدراسية فيه ، و آذللك الدعم المعنوي المستمر الذي و

.ساعدني بشكل آبير في تقوية ارادتي على اتمام هذا العمل

ة النهرين على تعاملهم االآثر من جامعشكر و تقدير الى موظفي المكتبة المرآزية .اي آلل او ملل ن الرائع مع الطلبة دو

 

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