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Prediction of Thermodynamic Properties of Industrially important

Polymers

CL 445 –Supervised learning II Project report

Submitted By: Rishikesh Awale

Roll No: 10D020009

Project Guide: Professor Jhumpa Adhikari

Submitted on: 28th April 2014

Department of Chemical Engineering, IIT Bombay

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Abstract

This project report starts with detailed literature survey of polystyrene and styrene comprising of

all the aspects right from their discovery, various routes of production with all process

considerations & process flow sheets, properties(chemical, physical, mechanical, optical,

thermal and electrical),Product specifications, end uses and Global demand and supply for the

product. The report also briefly emphasises separation of ethylbenzene and styrene by extractive

distillation using sulfolane and Ionic liquid such as 4-methyl-N-butylpyridinium

tetrafluoroborate ([4-mebupy]-[BF4]) and provides VLE data for ethylbenzene and styrene with

both extracting agents mentioned here. The concept of TraPPE-United Atom model is also given

which is used to evaluate total potential energy of system of particles.Lastly introduction to

Gibbs ensemble Monte Carlo simulation technique from statistical thermodynamic point of view

is given where three types of “Monte Carlo moves” meant to satisfy three conditions of

equilibrium between vapour and liquid of a pure substance / multicomponent mixture namely:

Internal equilibrium within each phase, equality of pressure between the two phases and equality

of Chemical potential of each component in both phases are explained.

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Certification

Department of Chemical Engineering

Indian Institute of Technology, Bombay

The project report entitled "Prediction of Thermodynamic Properties of Industrially important

Polymers" prepared by Rishikesh Awale (Roll No.10D020009) may be accepted for being

evaluated.

Date: April 28, 2014 Signature of student

Name of the Guide:

Signature of Guide:

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Index

S. No Topic Page No

1 Chapter 1 - Literature survey of Polystyrene 6

1.1 Introduction 6

1.2 Structure 6

1.3 Production 6

1.4 Polystyrene continuous production PFD(Bulk polymerization process) 7

1.5 Chemistry of free radical polymerisation of styrene 9

1.6 Properties of polystyrene 12

1.7 Uses of polystyrene 14

2 Chapter 2- Literature survey of Styrene 15

2.1 Introduction 15

2.2 Production 15

2.3 Catalytic dehydrogenation of ethyl benzene 15

2.4 PFD of ethyl benzene dehydrogenation process 18

2.5 Process equipments 19

2.6 Process flowsheet description 20

2.7 Ethyl benzene hydroperoxide process 20

2.8 PFD of Propylene oxide process 21

2.9 Process flowsheet description 22

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S. No Topic Page No

2.10 Ethyl benzene and styrene separation 23

2.11 VLE data for ethyl benzene styrene mixture at different pressures 24

2.12 Antoine equation parameters for ethyl benzene styrene and sulfolane 24

2.13 Worldwide Demand and Scenario of Styrene 25

2.14 Global styrene supply and demand 26

2.15 Styrene global consumption by application 26

2.16 Styrene global supply demand and balance 26

2.17 Uses of styrene 27

2.18 Industrial specifications of styrene 27

3 Chapter 3- Prediction of thermodynamic properties using molecular

simulations

28

3.1 Trappe united atom model 28

3.1 Phase equilibria and coexistence using Gibbs ensemble Monte Carlo method 30

3.2 Particle transfer within a box 31

3.3 Volume exchange among the two phases 31

3.4 Exchange of particles between two boxes 32

35 List of Tables and Figures 33

36 List of references 34

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Literature survey

Introduction

Polystyrene is an important synthetic vinyl polymer widely produced commercially by free

radical vinyl polymerization of monomer styrene, a liquid hydrocarbon produced by

dehydrogenation of ethyl benzene. It is a hard transparent (when not added with colourful

additives) and relatively brittle plastic material used worldwide and finds its applications in

packaging, electric and electronic appliances, construction, automobiles, plastic furnitures.

Historically [1] it is said to be discovered by a German chemist named Eduard Simon when he

first separated it from natural resins. But it was another German organic Chemist, Hermann

Staudinger who found it that polystyrene is made up of long chains of styrene molecules.

Structure

Polystyrene being a polymer of styrene has continuous long chain of styrene (CH2=CHC6H5)

fragments as its repeating unit. The carbon atoms are linked to one another by covalent bonds.

Every alternate carbon atom in the chain has benzene ring attached to it.

Phenyl group present in polymer chain is responsible for some important properties exhibited by

polystyrene and it is only because of these properties polystyrene finds wide range of

applications in our daily life.

The bulky phenyl group attached to polymer chain does not allow rotation about carbon-carbon

single bonds and that is the reason why polystyrene is a hard material.

Another important aspect of presence of phenyl group is that a systematic close packed

crystalline arrangement is not possible because of which polystyrene is a transparent compound.

Production

At commercial scale Polystyrene is manufactured by addition polymerization of styrene in

presence of an inert organic solvent.1, 2- Dichloroethane is one of the most commonly used

solvent for this. There are other alternate organic solvents also such as carbon tetra chloride,

ethyl chloride, benzene, toluene, ethyl benzene methylene dichloride which can be used.

The different methods for production of polystyrene available are [3]:

Fig 1 [2]

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1. Solution (bulk) polymerization:

Solution (bulk) polymerization is also known as mass polymerization in the industry. Majority

of all polystyrene produced universally follows this method. The common solvents used in this

process are the styrene monomer and ethyl benzene. Mass polymerization process can take place

in two modes, batch and continuous, of which continuous is the most preferred. In batch

polymerization conversion of monomer up to 80% is achievable but the problem of temperature

control, periodic maintenance of reactor vessels is also present. Therefore worldwide,

polymerization of styrene in continuous mode is preferred. From continuous production of

polystyrene conversion up to 85 % is obtained

Feed for the first reactor is 50 weight percent styrene monomer, 100 ppm water (on the basis of

styrene amount in kgs ), 2000 ppm boron trifluoride (gas phase, on the basis of styrene amount

in kgs) and the organic solvent chosen . The initiator solution is prepared by mixing 1.5% by

weight boron trifluoride gas into the organic solvent containing 280 ppm water. This solution is

continuously prepared in a holding vessel and the effluent of this vessel continuously enters in

all the reactors.The polymerization reaction releases heat, not in large amount but still the

temperature must not go beyond 70oC , the condition at which average molecular weight of

polymer formed decreases that is why the reactors are jacketed with continuous supply of

cooling agent through them.

The process flow diagram for continuous process of polystyrene:

Initiator

Styrene

Cooling water in

reactor jacket

Cooling water

Separator

Solvent

Polystyrene

Fig 2

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2. Suspension polymerization

Essential requirements for suspension polymerization are:

Initiator, suspending agent, Stabilizing agent, Catalyst and Polymerization Temperature

Initiators: The initiators generally used are benzoyl peroxide and t-butyl hydro peroxide.

Stabilizing agent: To keep the drops at proper size, a stabilizing agent is added. The stabilizing

agents are often insoluble inorganic such as calcium carbonate, calcium phosphates or bentonite

clay. They are present in small amount than the suspending agents. Their concentration in the

suspension is between 0.01-0.5percent of monomer charged.

Catalyst: A catalyst is used to control the reaction rate. The catalysts are usually Peroxides. The

most common ones are benzoyl, diacetyl, lauroyl, caproyl and tert-butyl. Their concentration

varies from 0.1-0.5% of the monomer charged. The ratio of monomer to dispersing medium is

between 10 and 40%.

Polymerization temperature: Polymerization of styrene occurs at temperature range of 90-95oC

In suspension polymerization method we can get polymers of higher average molecular weight.

In this process styrene drops of size range 0.15-0.50 mm in diameter are formed with the help of

an appropriate suspending agent such as partially hydrolysed polyvinyl acetate, inorganic

phosphates or magnesium silicates in aqueous medium. Polymerization reaction takes place in

these small suspended drops providing large surface contact area per unit volume of reactor

solution. Moreover a stabilizing agent for stabilizing size of drops must also be added. Styrene

and water are preheated and then sent as feed into the batch reactor the dispersing and stabilizing

agent and the catalyst without any preheating are charged from top into the reactor. Typical

water to monomer ratios is 1:1 to 3:1.The last and important step is the separation of water from

polystyrene and other organic compounds which is done by physical separation of water from

organic phase in a decanter the organic phase is later dried and passes through devolatilizer so

that the polystyrene gets rid of the volatile compounds in it and is formed in pellets which can be

conveniently stored and packed.

3. Emulsion polymerization- In this method styrene drops of microscopic size are

suspended in aqueous medium with stabilizing and suspending agents added into the mixture.

This method is not commercially used for making polystyrenes is used only when certain

monomeric additives are added along with monomer to make speciality polymer(high impact

grades of polystyrene).

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Chemistry of free radical polymerisation of styrene

In free radical polymerization of styrene ,styrene monomers continuously link to each other

through active centre sites formed after their addition to radicals of initiators (such as Benzoyl

peroxide )and the active centre site subsequently moves to the other side of the polymer

molecule’s chain with the help of a chain transferring agent such as butyl mercaptan to which

new monomer molecules then links.The polymer chain is terminated when the active chain

centre is detached from it by combination reaction.

The overall process that makes one complete chain of polymer takes place in the following

mentioned stages:

1. Initiation-This is the preliminary step of polymerization in which first free radicals of

initiator are generated either via homolysis in which thermal or any other kind of energy

such as light energy is supplied to break the single bond present in initiator molecule to

give duplicate free radicals or via heterolysis in which reactive free radicals are formed

by electron transfer between initiator and the other ion .These free radicals later add to

monomer molecule as per following scheme:

I R*+R* , I represents Initiator molecule and R* is the free radical of the initiator

R*+MRM* Addition of Free radical to monomer molecule

2. Propagation-In this stage monomer gets attached to the active chain end formed in the

previous step of chain initiation between radical and monomer resulting in the formation

of new active site to which new monomer molecule can link in to ways either in head to

head or head to tail orientation.

Propagation:

R1*+M R2*

R2*+M R3*

Rn*+M Rn+1*

~CH2-CH* + CH2=CH ~CH2-CH -CH2-CH

* Head to tail

Ph Ph Ph Ph

~CH2-CH* +CH2=CH ~CH2-CH -CH-CH2

* Head to head

Ph Ph Ph Ph

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3. Transfer-In this step the active polymer chain site is transferred to another molecule to

facilitate further monomer linking at active site of molecule. Chain transfer in case of

styrene polymerization is not feasible without addition of a suitable chain transfer agent

such as Butyl mercaptan.

Rn* + ZY RnY + Z* ZY is the chain transfer agent

The active chain can be transferred to polymer, monomer, and reaction medium or to the

chain transfer agent itself. The average molecular weight of the polymer increases if the

monomer holds the new active chain site.

4. Termination-This is the last stage in polymerization of polymeric chain carried from the

previous step of chain transfer. Now the active chain centre no longer exists on polymeric chain

and links to new monomer unit. After this the same steps from initiation to termination take

place and several polymeric units (chains) are formed thus. In case of polystyrene termination

via combination reaction is prevalent.

Rn*+Rm* Pn+m Combination reaction

Rn*+Rm* Pn + Pm Disproportionation reaction

Properties of Polystyrene [4]

Chemical properties

1. Polystyrene is an inert and stable chemical.

2. It is soluble in a few organic solvents that contain acetone.

3. It is highly flammable compounds and gives yellowish orange flame on burning.

4. Upon oxidation forms carbon dioxide and water vapour like other hydrocarbons do.

5. Polystyrene polymers get degraded on exposure to sunlight, due to photo oxidation.

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Physical properties

1. It is transparent, hard and brittle material like glass

2. It is highly elastic

3. Specific gravity of polystyrene is 1.03-1.06 g/cm3

4. Polystyrene is a non-Newtonian fluid and its viscosity depends on the rate of deformation it

experiences.

Mechanical properties

1. Young’s Modulus 3000-3600 MPa

2. Tensile strength 30-60 MPa

3. Shear Modulus 1400 MPa

4. Crystal form of polystyrene exhibits low impact strength.

Optical Properties

1. Polystyrene when not added with rubber while its processing is transparent plastic

polymer

2. Refractive index is 1.58 to 1.59

3. Transmittance is 88-90%

4. Haze % is 0.1 to 1.1

Thermal properties

1. Polystyrene has glass transition temperature of 1000C.

2. Specific heat capacity 1250J/kgK

3. Thermal conductivity 0.14 W/mK

4. Coefficient of thermal expansion(linear) in temperature range 20-100oC is 120μm/mK

Electrical properties

1. Dielectric strength 20 MV/m

2. Dielectric constant 2.5

3. Resistivity > 1016

ohm*cm

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Thermodynamic Data of Styrene [5],[6]

CAS Registry Number: 100-42-5

IUPAC name:poly (1-phenylethene-1, 2-diyl)

Chemical Formula: C8H8

Molecular weight: 104.1491

Melting point:-30.6oC

Boiling point:145.15 oC

Gas phase thermochemistry data

Quantity Value Units References

∆Hfo(gas) 146.9+1.0 kJ/mol Prosen and Rossini,

1945

∆Hfo(gas) 151.5 kJ/mol Landrieu, Baylocq, et

al., 1929

∆Hfo(gas) 131.5 +4.0 kJ/mol N/A

∆Hfo(gas) -15.1 kJ/mol Moureu and Andre,

1914

Phase change data

Quantity Value Units Method Reference

Tboil 419. ± 2. K AVG N/A

Quantity Value Units Method Reference

Tfus 241. ± 8. K AVG N/A

Quantity Value Units Method Reference

Ttriple 242.47 K N/A Pitzer, Guttman, et al., 1946

Ttriple 242.47 K N/A

Guttman, Westrum, et al.,

1943

Ttriple 242.47 K N/A Guttman, 1943

Quantity Value Units Method Reference

ΔvapH°

43.93 ±

0.42 kJ/mol V

Pitzer, Guttman, et al.,

1946, 2

ΔvapH° 43.5 kJ/mol N/A Prosen and Rossini, 1945

Table 2

Flammable limits in air = 1.1-6.1 vol %

Flash point = 31.1 oC

Auto ignition temperature = 490 oC

Table 1

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Antoine Equation Parameters

log10(P)=A−(B/(T+C))

P=vapour pressure(bar) &T=Temperature(K)

Temperature

(K) A B C Reference

305.6 - 355.34 4.0593 1459.9 -59.551

Chaiyavech and van Winkle,

1959

303.07 -

417.92 4.21948 1525.1 -56.379 Dreyer, Martin, et al., 1955

Table 3

Enthalpy of fusion

ΔfusH

(kJ/mol)

Temperature

(K) Reference

10.964 242.27 Warfield and Petree, 1961

10.949 242.27

Pitzer, Guttman, et al., 1946,

3

10.95 242.47 Guttman and Westrum, 1943

10.95 242.47

Lebedev, Lebedev, et al.,

1985

10.95 242.3 Domalski and Hearing, 1996

Table 4

Entropy of fusion

ΔfusS

(J/mol*K)

Temperature

(K) Reference

45.32 242.27 Warfield and Petree, 1961

45.16 242.27

Pitzer, Guttman, et al., 1946,

3

45.16 242.47 Guttman and Westrum, 1943

45.2 242.47

Lebedev, Lebedev, et al.,

1985

Condensed phase thermochemistry data

Quantity Value Units Method Reference

ΔfH°liquid 103.4 ± 0.92 kJ/mol Ccb Prosen and Rossini, 1945

ΔfH°liquid 108 kJ/mol Ccb Landrieu, Baylocq, et al., 1929

ΔfH°liquid 87.6 ± 4.0 kJ/mol Ccb N/A

ΔfH°liquid -58.6 kJ/mol Ccb Moureu and Andre, 1914

Quantity Value Units Method Reference

ΔcH°liquid -4390. ± 60. kJ/mol AVG N/A

Table 5

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Quantity Value Units Method Reference

S°liquid 240.5 J/mol*K N/A Warfield and Petree, 1961

S°liquid 237.57 J/mol*K N/A Pitzer, Guttman, et al., 1946

S°liquid 237.6 J/mol*K N/A Guttman and Westrum, 1943

Table 6

Constant pressure heat capacity of liquid

Cp,liquid (J/mol*K)

Temperature

(K) Reference

183.2 298.15 Lebedev, Lebedev, et al., 1985

182.6 298.16 Warfield and Petree, 1961

235.6 298 Kurbatov, 1950

182.84 298.15 Pitzer, Guttman, et al., 1946

179.9 298.5 Smith and Andrews, 1931

Table 7

Uses

1. Used for making disposable cutleries

2. Casing of electronic appliances including computers audio and video cassettes are

made from polystyrene

3. Plastic furnitures

4. Essential element of the material used in making soundproof walls

5. Test tubes, petri dishes, trays for conducting tissue cultures are made from polystyrene

6. It is also used in making high impact strength projecting elastomers such as styrene-

butadiene-styrene (SBS) and styrene-isoprene-styrene (SIS) rubber.

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Styrene

Introduction- It is an aromatic liquid hydrocarbon majorly produced from ethyl benzene in bulk

amounts especially for manufacture of polystyrene an important plastic polymer. It was first

made in mid-1930s by Dow Chemical ltd [7]. It can also be used for manufacture of various

polymers and resins such as Acrylonitrile Butadiene Styrene (ABS), Styrene Butadiene rubber

(SBR), Styrene Butadiene latex and fibreglass.

Production

There are two major industrial processes by which styrene can be manufactured

1. Catalytic dehydrogenation of ethyl benzene [8]

2. Ethyl benzene hydro peroxide process [9]

1. Catalytic dehydrogenation of ethyl benzene

90% of worldwide production of styrene takes place by employing this process in which the raw

material used are ethyl benzene and steam (not reactant). Ethyl benzene in vaporised from is

used as reactant and the steam should be superheated. Catalyst for this process contains 84.3%

iron as Fe2O3, 2.4% chromium as Cr2O3 and 13.3% potassium as K2CO3 .Two or three adiabatic

fixed bed reactors connected in series provided with inter stage heating by superheated steam are

employed for the process. The reaction is highly endothermic in nature and that’s why large

amount of heat is to be supplied to the reactor for dehydrogenation of ethyl benzene to occur.

Main reaction taking place:

Dehydrogenation of ethyl benzene in presence of superheated steam is the desired reaction

chemical equation for this is as below:

C6H5CH2CH3 C6H5CH=CH2 + H2

Besides these there are always other side reactions taking place at higher reactor

temperatures.The dominant side reaction is hydrogenolysis of ethyl benzene producing toluene

and methane:

Fig 3

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C6H5CH=CH2 + 2 H2 C6H5CH3 + CH4

Following are the less dominant side reactions:

C6H5CH2CH3 C6H6 + C2H4

C6H5CH2CH3 8 C + 5 H2

The last reaction produces carbon which deactivates the catalyst by blocking active catalyst sites

and thereby reduces conversion of ethylbenzene so introduction of superheated steam into the

reactor enables removal of carbon from catalyst because the steam itself reacts with carbon on

surface of catalyst and converts it into CO2 and H2.

Addition of steam offers following advantages [10]

1. Steam added provides heat required for the reaction

2. Steam reduces the partial pressure of ethyl benzene and thus helps in shifting the main

reaction in forward equilibrium direction

3. Steam reduces coke formation by reacting with carbon deposited on catalyst surface formed as

a result of decomposition of methane at higher temperatures and converting it to form carbon

dioxide and hydrogen

Role of steam in enhancing equilibrium conversion of Ethylbenzene can be understood

graphically as follows

The operating conditions for reactor are,

Temperature=600-650oC

Pressure<=1bar.

Figure 4

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Steam to ethyl benzene ratio: 10-15

Conversion in the first reactor is around 35% and overall conversion of ethyl benzene up to 65%

is achieved with 90% yield.

Important consideration for process: Since styrene is operated at low temperatures

(~700C) at in the separation process, there is a risk of polymerization. To prevent that,

inhibitors are used in the distillation train. The inhibitors are mainly aromatic compounds

with nitro-, amino- or hydroxyl groups. Since, most of the inhibitors are coloured

compounds; they are not used for the final purification. Instead 4-tert-Butylcatechol

(TBC) is used [9]. Distillations are also carried under vacuum conditions to prohibit

polymerization.

Figure 5

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Process flow-diagram (Adiabatic process) [9]

Furnace

Fresh EB

Rec

ycle

d E

B

Superheated steam

Water

Ste

am

F

BR

-1

FB

R-2

Compressor

H

X-1

H

X-2

H

X-3

C

oo

ling

Wat

er

Phase

Separator

Compressor

Off-gas

C

on

den

sate

Benzene + Toluene

Distillation column

1

EB recovery column Styrene purification column

column

Figure 6

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Process Equipments

Furnace: The furnace is used to convert steam/water into superheated steam.

Reactors (FBR-1 and FBR-2): For better yields, interaction between reactants and

catalyst must be high. Fluidised beds provide the best solid-gas interaction, but they also

significantly increase the pressure drop. Since the operating pressures are low, high

pressure drop has to be avoided. Hence a fixed bed reactor is used. Commercial catalyst

beds have a radial flow direction, with gases moving outwards. This ensures proper

distribution of gases through the bed and also decreases the pressure drop since the path

followed by gases is shorter as compared to axial flow. Both reactors: FBR-1 and FBR-2

are to be operated at 630°C and pressure less than atmospheric as Δng > 0 (more moles

produced). The FBR-1 is proposed to be operated at 500mmHg and the second reactor,

FBR-2 at 300 mmHg considering the pressure drops after moving through pipes.

HX-1: The first heat exchanger is a typical shell and tube heat exchanger with the

product stream going in the shell side and steam through the tubes.

HX-2: The second heat exchanger is exactly like the first one.

HX-3: The third heat exchanger is a partial condenser that converts with water going

through the tubes and the mixture passing through the shell side.

Phase Separator: A three phase separator is used to remove water and gases from the

product stream. The gas is mainly hydrogen, the by-product of the dehydrogenation

reaction. Hydrogen is removed from the separator and used as a heat source to produce

steam. Some gas is sent back to the separator to maintain the pressure in the separator.

The liquid gets separated into organic and aqueous phases. Water from the separator is

removed as condensate and reused to produce steam. Glass wool is used to remove any

liquids entrained in the vapour phase as the presence of liquids will decrease the

efficiency of gas compressor due to clogging.

Distillation Column: After removing hydrogen and water, the product stream consists

only of SM, EB, benzene, toluene and minor impurities. This stream is then separated

into SM+EB and Benzene + Toluene using a distillation column exploiting the

significant differences in their boiling points which are 145 0C, 136

0C, 80.1

0C and

110.6 0C respectively.

EB Recovery column: Since the boiling points of SM and EB are close, separation

requires a lot of stages. Perry’s Handbook suggests using bubble cap tray column, 2.6

feet diameter and 19.7 in tray spacing. This column would require 34 trays. Hence, most

industrial plants prefer to use a packed column. With a packed column a smaller column

height can provide effective separation equivalent to 70-100 theoretical trays. Structured

stainless steel packing is used in the column. The EB recovered is recycled back to the

reactor. The distillate temperature is to be used as 1300C (EB boiling point) and the

raffinate temperature as 1460C (Styrene Boiling point). This range is to ensure that EB is

by large in vapour phase and not styrene.

Styrene Purification column: SM is further purified to achieve 99.7% purity as per the

industry standards set by ASTM. The distillate temperature is to be maintained around

146 0C which is the boiling point of styrene.

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Process Flow-sheet Description

First of all the fresh and recycled EB are mixed with superheated steam (coming from the

furnace) and the resulting mixture is passed axially through the first reactor labelled as (FBR-

1).The output mixture from FBR- is heated to the requisite temperature by a heat exchanger

(HX-1) because the reaction is endothermic and has brought down temperature of the reaction

mixture. For further conversion of ethylbenzene this mixture is later passed through the second

reactor labelled as (FBR-2).To keep the styrene and ethylbenzene mixture as liquid mixture so

that we can separate them in distillation tower later, it is compressed to a higher pressure so that

none of these two starts boiling. It’s now passed through the shell side of a second heat

exchanger labelled as (HX-2) where the output steam from HX-1 is passed through the tubes.

This results in the steam getting heated and the mixture losing heat. This heat exchanger works

as an economizer that produces steam which is sent in the furnace to make superheated steam

and this superheated steam is sent into the first reactor. The mixture which lost heat by making

steam is now sent to the third heat exchanger (HX-3), which is a partial condenser. Cooling

water is used to partially condense the product stream. The mixture loses heat and all the

condensable components (SM, EB, Benzene, Toluene, steam) get condensed into liquid form,

while the non-condensable components (H2, CO, CO2) remain as is. The 3-phase separator

separates the mixture into gas, organic and aqueous phase. The organic phase is sent forward for

separation by distillation. A series of distillation columns are used to separate Benzene +

Toluene, EB (which is recycled), industrial grade SM and ta

Ethyl benzene hydro peroxide process

This process accounts for less than 10 % worldwide production of styrene. . It produces

propylene oxide (PO) along with Styrene (SM) and the process is called POSM. The global

demand of PO is 2/10 of SM but via POSM 4/10 of PO is produced. Since, the SM production

via this method can’t be increased alone, the local PO demand dictates the profitability of this

method. This process is not available for licensing.

There are three steps in the process:

Oxidation Step: Air is bubbled through liquid EB in a series of reactors with decreasing

temperatures from 150 to 130 0C. This converts EB to EB hydroperoxide.

Epoxidation Step: This reaction is carried out in liquid phase, with temperature ranging

from 100-130 0C and a catalyst of soluble molybdenum naphthanate/silica gel. This gives

α-phenylethanol and Propylene Oxide (PO).

Dehydration Step: The dehydration of α-phenylethanol in the presence of a dehydrating

agent like Al2O3 gives SM.

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Reactions taking place:

Reaction 1: Oxidation of Ethyl Benzene to Ethyl Benzene hydro Peroxide

C6H5C2H5 + O2 →C6H5CH(OOH)CH3

C6H5C2H5 + ½O2 → C6H5CH(CH3)OH

C6H5C2H5 + x O2 → acids + C6H5CO(CH3)

Reaction 2: Reaction of Propylene with EBHP to give Propylene Oxide and MBA

C6H5CH(OOH)CH3 + C3H6 → C6H5CH(CH3)OH + C3H6O

Reaction 3: Hydrogenation of Acetophenone (ACP) to Methyl Benzyl Alcohol [MBA] to enrich

MBA

C6H5CO(CH3) + H2 → C6H5CH (CH3)OH

Reaction 4: Dehydration of Methyl Benzyl Alcohol to give Styrene[SM]

C6H5CH(CH3)OH → C6H5CH = CH2 + H2O

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Process flow diagram of styrene manufacture by Propylene oxide process

Air

EBHP (90%)

MBA

ACP

EB

13%

conversion 13%

Conversion

Propylene PO

MBA

ACP

EB

13%

conversi

on

PO

Crude

PO

Purified

Direct Oxidation Catalytic

Epoxidation Caustic Wash

Ethyl-Benzene

Fresh

Ethyl-Benzene MBA, ACP, EB

MBA

H2

Ethyl-Benzene

Recovery Column

MBA

ACP SM

MBA

ACP

MBA

ACP

Dehydration

Al2O3

SM

refining/Caustic

Wash

Styrene Monomer

ACP Hydrogenation

Figure 7

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Process flow-sheet description

The raw material ethyl benzene is oxidised at 130oC and 0.2MPa pressure to ethyl benzene

hydro peroxide in a series of reactors maintained at temperatures decreasing from 150 to 130oC

in which air is continuously bubbled at bottom in liquid column of ethyl benzene fed

continuously inside from top in to the reactor. Later the EBH formed is made to react with

propylene in presence of molybdenum or titanium catalyst to produce α-phenyl ethanol and

propylene oxide. This mixture when dehydrated at 250oC and low pressures over acidic catalyst

such as Al2O3 produces crude styrene which is finally further purified from oxygenates that act

as poison for catalyst of styrene polymerisation. An additional reaction to convert Acetophenone

(ACP), a side product during the oxidation of EB, is hydrogenated to MBA for better recycling

and higher production of styrene.EB is oxygenated to give the three products at 206-275 kPa and

140°C - 150°C. The conversion is around 13%. The Selectivity towards EBHP is around 90%

while the other products amount to the remaining 10%. Since, only 13% conversion is achieved,

Ethyl benzene is recovered back for reuse. EBHP is then reacted with Propylene at 95°C –

130°C and 2500-4000 kPa, in presence of titanium catalyst over silica (SiO2) support catalyst.

Conversion of around 95% is achieved with selectivity of 92-95% Propylene Oxide. Propylene

Oxide is then separated out from the product stream. The rest of the product stream is treated

with caustic wash to neutralize acids. In the presence of Acids, the Methyl Benzyl Alcohol

[MBA] gets converted to styrene which readily polymerised at the given condition. Ethyl

Benzene is then recovered from the stream as only 13% was earlier converted.The rest of the

stream with MBA and ACP is then carried ahead. MBA from the stream is dehydrated in

presence Al2O3 to give styrene monomer. ACP from the stream is also hydrogenated to MBA in

Reaction set-3 and then fed back to improve overall styrene yield.

Ethyl benzene and styrene separation [11]

The relative volatility for VLE mixture of styrene and ethyl benzene has value ~ 1.3-1.4 because

boiling points of these two compounds are quite close. Therefore fractional distillation for

separating out these compounds from each other either requires large reboiler duty or vaccum

conditions inside distillation column. Either of these are high energy/power consuming options

but are still in practice at commercial scale. Besides these the distillation towers are required to

have around 100 trays to achieve higher purity of styrene as finished product. Current Research

on extractive distillation of styrene-ethyl benzene mixture reveals that sulfolane can be added to

this mixture and can increase the value of relative volatility from 1.3 -1.4 to 2.2 thereby easing

the separation of components. A further research study shows that sulfolane can be replaced with

Ionic liquid such as 4-methyl-N-butylpyridinium tetrafluoroborate ([4-mebupy]-[BF4]).This new

extracting agent increases the value of relative volatility of styrene ethyl benzene VLE mixture

24 | P a g e

up to 2.7-2.8 .The advantages of ILs are that they are chemically and thermally stable at

temperatures close to 100oC and have low vapour pressure at these temperatures.

VLE data for styrene ethyl benzene mixture at different pressures [12]

5 kPa 10 kPa 20 kPa

T x1 y1 T x1 y1 T x1 y1

332.3 0.026 0.037 348.2 0.026 0.037 366 0.026 0.036

332.1 0.051 0.074 347.9 0.051 0.073 365.7 0.05 0.07

331.5 0.089 0.126 347.6 0.084 0.118 365.4 0.084 0.114

330.5 0.181 0.245 346.6 0.178 0.239 364.5 0.176 0.233

329.5 0.264 0.346 345.7 0.281 0.36 363.5 0.279 0.35

329.1 0.349 0.44 344.7 0.376 0.466 362.5 0.374 0.455

327.9 0.475 0.569 344 0.478 0.565 361.8 0.476 0.558

327 0.571 0.658 343.2 0.574 0.656 360.9 0.575 0.653

326.3 0.676 0.752 342.4 0.67 0.739 360 0.667 0.735

325.5 0.784 0.841 341.5 0.775 0.828 359.2 0.774 0.824

325 0.877 0.91 341.1 0.834 0.874 358.8 0.834 0.871

324.5 0.938 0.953 340.3 0.937 0.951 358 0.937 0.949

Table 8

Table 8

Antione Equation Parameters for Styrene, Ethyl-benzene and Sulfolane

Component T(K) Ai Bi Ci

Ethyl-benzene 324-364 20.8051 3211.78 -63.05

Styrene 332-373 21.1275 3453.58 -58.5

Sulfolane 391.2-559.2 21.9503 5193.41 -61.76 Table 9

=

Pisat

represents saturation pressure of component i at temperature T

25 | P a g e

Worldwide Demand and Supply Scenario of styrene[13]

The demand for styrene has since shifted towards the manufacture of polystyrene. In 2010, the

worldwide consumption of styrene was approximately 25 million tonnes, of which more than

half was for the production of polystyrene .The demand for styrene is expected to grow at 0.8%

in Asian markets.

The global consumption for styrene monomer is driven by polystyrene demand. The global

demand for styrene in 2010 was approximately 25million tonnes/year, 61% of which was for

polystyrene production. Since the Asia-Pacific region (not including China) is a net importer of

styrene, it would be profitable to establish a plant in this region. The demand for styrene in Asia-

Pacific was 7.3million tonnes/year in 2010 and has been growing at 0.8%/year. The total

capacity achievable by plants in Asia-Pacific is 9million tonnes. However, in recent years the

demand for styrene has seen steady increase due to higher production of polystyrene and EPS.

The global utilization rate is predicted to increase from 80% in 2010 to as high as 93% by 2017.

Figure 8

26 | P a g e

Based on the annual consumption growth rate of 0.8%, the consumption of styrene in Asia-

Pacific will be 7.71millon by the year 2017. So to balance this 0.41million tonne increase in

consumption, the total capacity needs to be increased by 0.5million tonnes assuming that the

plant operates at 80% utilization. Hence, a plant capacity of 100,000-500,000 tonnes/year is a

feasible option.

IOCL has set up a 220,000 tonnes/year capacity SBR plant in Panipat and a recently closed

BASF plant in Thane had a capacity 100,000 tonnes/year. Hence, we set the plant capacity to

200,000 tonnes/year.

Figure 9

Figure 10

27 | P a g e

Uses

Styrene based products are used extensively in rubber, plastic, insulation, fibreglass and

packaging

Polystyrene - It is the main polymer of styrene. It is a thermoplastic- thus making it

mouldable above a temperature and solidifies when cooled. They are used for packaging

of several goods example: CD-covers, jewellery cases etc.

ABS (Acrylonitrile Butadiene Styrene) - It mainly is known for its strength and shock

absorbing nature. Used in golf club heads, car bumper heads, protective gears,

refrigerator liners, medical devices, small household appliances and luggage etc.

SBR (Styrene Butadiene Rubber) - On account of its elastic properties, it is used in

making vehicle tires, shoe heels and soles etc.

SB latex - It is a water emulsion of styrene-butadiene co-polymer Particles. Mainly used

for paper coating, carpet backing, wood lamination

Product Industrial specifications [14]

Content Unit Specification

Purity wt% Min. 99.70

Benzene Content wt% Max. 1

Ethylene Benzene ppm 500 max.

Colour Pt-Co Haze units Max. 10

Inhibitor Content mg/kg 10-20

Polymers Content mg/kg Max. 10

Aldehydes (Benzaldehyde) wt% Max 0.32

Peroxides Content (as H2O2) mg/kg Max. 100

Table 10

28 | P a g e

Prediction of Thermodynamic properties using molecular simulations

Styrene of high purity as finished product cannot be obtained unless the efficient ways of

separating it from unconverted reactants and side products of the process are known.Styrene has

to separated from ethylbenzene in plants producing styrene. The difference in boiling points of

these chemicals is only 9oC and therefore direct fractional distillation will require large no of

trays and high reboiler duty therefore extractive distillation if adopted will make separation

process more economic. Knowledge of VLE data and activity coefficients is essential for

designing and operating distillation process as it reveals nature of interactions among the species

in liquid and vapour phases to be separated and deviations from ideality.

Molecular simulations are the better means for estimating thermodynamic properties

comparatively more accurately experimentally for systems containing multiple phases of pure or

multicomponent mixture in equilibrium. The overall interaction energy of system of molecules

of pure or multicomponent mixture is described in terms of an appropriate conservative force

field.

TraPPE –UA [16]

TraPPE refers to transferable potentials for phase Equilibria.Phase equilibrium behavoir,

deviation from ideality of solutions are all attributed to the nature of intermolecular interactions

(forces) among atoms/molecules in solution.These intermolecular ineteractions can be described

by conservative force fields one which is widely used for molecular modelling and simulation is

United atom force field model. TraPPE United atom force models groups carbon and hydrogen

atoms bonded to it together as a pseudo atom i.e. C, CH, CH2, CH3 and CH4 are all one

interaction site in the system. By 'transferable' we mean that the force field parameters such as

epsilon and sigma in LJ potential model for a given interaction site (pseudo atom)should be

same when used for different molecules (e.g., identical parameters should be used for the methyl

group present in, say, n-hexane, 1-hexene, or 1-hexanol) and that the force field should be same

for different state points (e.g., pressure, temperature, or composition) and for different

properties (e.g., thermodynamic, structural, or transport).

The total potential energy of the system is divided into two parts:

1. Bonded - This accounts for intramolecular interactions between pseudo atoms within a

molecule itself.

2. Non-bonded- This accounts for intermolecular interactions between pseudo atoms present on

different molecules and pseudo atoms within a molecule if these are separated by four or more

bonds.

29 | P a g e

Bonded interactions are further of 3 types

(i) 1-2 interaction in which interaction sites connected through a common bond are

considered, the bond length is assumed to be fixed.

There are 7 such interactions which exist between pseudo atoms located at 1 and 2,2 and

3,3 and 4,4 and 5,5 and 6,6 and 1,1 and 7 & 7 and 8.Schematic of 1-2 interaction is as below:

A B

(ii) 1-3 interaction in which interaction sites separated by two bonds at the two ends of V-

shaped network which bends about the location of central pseudo atom are considered.

There are 9 such V shaped network under harmonic bonding potential formed by pseudo atoms

located at 1,2,3; 2,3,4; 3,4,5; 4,5,6; 5,6,1; 6,1,2; 6,1,7; 2,1,7; and 1,7,8 locations

A C

B

(iii) 1-4 interactions also called dihedral interactions in which the interaction sites separated

by three chemical bonds forming a network (shown below) which is under torsion about central

bond are considered.

A D

B C

The angle between the planes containing pseudo atoms A, B, C and B, C, D is called dihedral

angle and this angle changes by virtue of interaction between pseudo atoms A and D.

Pseudo atoms located at 2, 3, 4, 5 & 6 are CH groups in benzene ring

Pseudo atom located at 1 is Carbon atom in benzene ring

Pseudo atom located at 7 is CH group of substituted alkene group

Pseudo atom located at 8 is CH2 group of substituted alkene group

Figure 11

Figure 12

30 | P a g e

Phase equilibria and coexistence using Gibbs ensemble Monte Carlo method [15]

Gibbs ensemble method is one of the computationally most efficient and simple systematic

method used for obtaining VLCCs (Vapour liquid coexistence curves) from VLE data obtained

from simulation results for pure substances or multicomponent mixtures helpful in predicting

their important thermodynamic properties.

The macroscopic system which consists of liquid and its vapour is checked for equilibrium by

first taking out two microscopic regions from each phase in separate fictional boxes and

applying acceptance criteria for following mentioned moves which are meant for satisfying

conditions for Vapour liquid equilibrium:

1. Trial move to displace a randomly selected particle in one of the boxes from its initial

location to new coordinates. This trial move is intended for condition of internal

equilibrium within each box

2. Trial move to exchange volume among the two boxes in such a way that the total volume

of the two boxes remains fixed. This trial move is intended for condition of equality of

pressure between two phases.

3. Trial move to transfer a particle from one box to the other. This trial move is intended for

condition of equality of chemical potentials of each component in all phases

Let the Temperature, Total Volume and Total Number of particles in a system of pure substance

present partially in liquid and vapour phase be T, V and N respectively.

Then the expression for partition function [15] for the overall system is as follows:

QNVT=

∑ (

)

∫

∫ [ ( )] ∫

[ ( )]

Λ is the thermal de Broglie wavelength given as Λ=

√

β=

, ξ1 and ξ2 are the scaled coordinates of the particles in vapour and liquid phase

respectively and U1(N1) and U2(N2) represent potential energy of vapour and liquid phase

If V1 and N1 are the volume and number of particles of vapour phase then volume and number of

particles of liquid phase will be V-V1 and N-N1 respectively.

The probability of finding configuration of system [15] in above mentioned state is:

P (N1, V1; N, V, T) ∝

exp (N1lnV1+N2lnV2- βU1 (N1)-βU2 (N2))

Keeping this expression in mind we will later see the acceptance criterias in Gibbs ensemble

method for ascertaining conditions of vapour liquid equilibrium.

31 | P a g e

Particle transfer within a box

When a particle in vapour phase initially at location for which total potential energy of the

vapour phase is Ui is randomly picked and located to new coordinates for which total potential

energy of the vapour phase is say Uf then the change in potential energy of the vapour system

is ∆U= Uf-Ui .

Using the probability density function [15] which we had mentioned earlier:

P (N1, V1; N, V, T) ∝

exp (N1lnV1+N2lnV2- βU1 (N1)-βU2 (N2))

Probability distribution of initial configuration given above is:

Pi ∝

exp (N1lnV1+N2lnV2- βU1i (N1)-βU2i (N2)) ………………… (1)

Similarly Probability distribution of final configuration given above is:

Pf ∝

exp (N1lnV1+N2lnV2- βU1f (N1)-βU2i (N2)) …………………. (2)

Dividing equation (1) with equation (2) we get relative probability for transition from initial

configuration to final configuration as:

= [exp (-β(U1f (N1)- U1f (N1))]

= [exp (-β(∆U)]

If sign of ∆U is positive then a random number is generated in [0,1] and the move is accepted

only if random number generated is less than exp(-β∆U) otherwise not accepted. In case ∆U is

negative the probability of transition of particle to new location is 1 as exponent of a negative

number is always greater than or equal to 1 and probability can at max be equal to 1.

Volume Exchange among the two boxes

Let us assume that the initial and final volumes of vapour phase are Vi and Vf respectively then

the change in volume is ∆V= Vf- Vi

Let total potential energy of the vapour phase before and after volume change is Ei and Ef then

change in potential energy of vapour phase is ∆U= Uf-Ui

Using the probability density function [12] which we had mentioned earlier:

P (N1, V1; N, V, T) ∝

exp (N1lnV1+N2lnV2- βU1 (N1)-βU2 (N2))

Probability density corresponding to initial configuration where volume of vapour phase is Vi

and energy Ei is:

32 | P a g e

Pi ∝

exp (N1lnV1+N2lnV2- βU1i (N1)-βU2i (N2)) [U1i (N1) + U2i (N2) =Ui]

……….(1)

Similarly for final configuration where volume of vapour phase is Vf and total energy Ef

probability density is:

Pf ∝

exp (N1lnV1+N2lnV2- βU1f (N1)-βU2f(N2)) [U1f(N1) + U2f(N2)=Uf]

……….(2)

Dividing equation (1) with equation (2) we see relative probability for transition from initial

configuration to final configuration as:

= [

]

N1[

]

N-N1exp[-β(Ef -Ei)]

Particle exchange between two boxes

In this last trial move of Gibbs ensemble Monte Carlo simulation a particle is randomly picked

and transferred to another box after randomly picking the box from which particle will be

transferred. For transfer of particle from vapour phase to liquid phase the relative probability for

occurrence of this event is:

( ) ( )

( )

( ) ( ( )) ( )

exp[-β(Ef-Ei)]

Therefore the probability that particle from vapour phase will go to liquid phase is

( )

( ) exp[-β(Ef-Ei)] if Ef-Ei is positive and 1 if its negative

Similarly for transfer of particle from liquid to vapour phase the probability is

( )( )

( )( )exp[-β(Ef-Ei)] if Ef-Ei is positive and 1 if its negative

33 | P a g e

List of Figures and Tables in report

Fig 1-Chemical structure of polystyrene

Fig 2-Flow sheet of solution polymerization of styrene

Fig 3-Chemical structure of styrene

Fig 4-Effect of presence of steam on equilibrium conversion of ethylbenzene versus

Temperature

Fig 5- Equilibrium conversion of ethylbenzene versus Temperature for two different pressures

Fig 6- Process flow diagram for catalytic dehydrogenation of ethylbenzene

Fig 7- Process flow diagram for propylene oxide process

Fig 8 -Yearly global styrene demand and capacity variation

Fig 9-Styrene global consumption by application

Fig 10-Styrene global supply demand and balance

Fig 11- Location of pseudo atoms in styrene molecule

Fig 12 - Four molecule dihedral network in styrene

Table 1 – Gas phase thermochemistry data of styrene

Table 2 – Phase change data

Table 3 – Antoine equation parameters for styrene

Table 4 – Enthalpy of fusion

Table 5-Entropy of fusion

Table 6-Condensed phase thermochemistry data

Table 7-Constant pressure heat capacity of liquid styrene

Table 8-VLE data for styrene ethylbezene mixture at different pressures

Table 9-Antione Equation Parameters for Styrene, Ethyl-benzene and Sulfolane

Table 10-Industrial specifications for styrene

34 | P a g e

List of References:

[1] http://inventors.about.com/od/pstartinventions/a/styrofoam.htm

[2] http://www.nature.com/srep/2013/130826/srep02502/fig_tab/srep02502_F1.html

[3] Polystyrene: Synthesis Production and Application by J.R. Winsch

[4] http://www.boedeker.com/polyst_p.htm

[5] http://webbook.nist.gov/chemistry/

[6] http://www.styrenemonomer.org/2.2.html &

http://www.chemicalbook.com/ChemicalProductProperty_EN_CB3415111.htm

[7] Ullmann's Encyclopedia of Industrial Chemistry

[8] Arno Behr, Styrene Production from Ethylbenzene. Universitat Dortmund

[9] http://www.sbioinformatics.com/design_thesis/Styrene/Styrene_Methods-2520of-

2520Production.pdf

[10] Chemical process technology 2nd

edition Jacob A Moulin et al

[11] Journal of chemical and engineering data Mark T. G. Jongmans et al

[12] Journal of chemical and engineering data Isobaric Low-Pressure VaporLiquid Equilibrium

Data for Ethylbenzene + Styrene + Sulfolane and the Three Constituent Binary Systems By

Mark T. G. Jongmans et al

[13] Styrene: 2013 World Market Outlook and Forecast up to 2017, merchant research

and consulting ltd.

[14] ASTM, Designation: D2827− 13 Standard Specifications for Styrene Monomer

[15] Introduction to Molecular Simulation and Statistical Thermodynamics by Berend Smit

Daan Frenkel.

[16] https://www.chem.umn.edu/groups/siepmann/trappe/united_atom.php