University of Texas at Austin Michigan Technological University1

Environmental Assessment During Process Synthesis - Chapters 7 and 8

David T. Allen

Department of Chemical Engineering

University of Texas

University of Texas at Austin Michigan Technological University2

Software explorationGreen Chemistry Expert System

TOPIC AREAS• Green Synthetic Reactions - search a database for alternatives• Designing Safer Chemicals - information on chemical classes• Green Solvents/Reaction Conditions - alternative solvents / uses

- solvent properties

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Software demonstration Green Chemistry Expert System

search Green Synthetic Reactions for adipic acid references

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Adipic Acid SynthesisTraditional vs. New

Traditional Route - from cyclohexanol/cyclohexanone Cu (.1-.5%)

C6H12O+ 2 HNO3 + 2 H2O C6H10O4 + (NO, NO2, N2O, N2) V (.02-.1%)

92-96% Yield of Adipic Acid

• Carbon - 100%• Oxygen - 4/9 x 100 = 44.4%• Hydrogen - 10/18 x 100 = 55.6%• Nitrogen - 0%

Product Mass = (6 C)(12) + (10 H)(1) + (4 O)(16) = 146 g

Reactant Mass = (6 C)(12) + (18 H)(1) + (9 O)(16) + (2 N)(14) = 262 g

Mass Efficiency = 146/262 x 100 = 55.7%

global warmingozone depletion

hazardous

Davis and Kemp, 1991, Adipic Acid, in Kirk-Othmer Encyclopedia of Chemical Technology, V. 1, 466 - 493

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New Route - from cyclohexene Na2WO4•2H2O (1%)

C6H10 + 4 H2O2 C6H10O4 + 4 H2O [CH3(n-C8H17) 3N]HSO4 (1%)

90% Yield of Adipic Acid

• Carbon - 100%• Oxygen - 4/8 x 100 = 50%• Hydrogen - 10/18 x 100 = 55.6%

Product Mass = (6 C)(12) + (10 H)(1) + (4 O)(16) = 146 g

Reactant Mass = (6 C)(12) + (18 H)(1) + (8 O)(16) = 218 g

Mass Efficiency = 146/218 x 100 = 67%

Adipic Acid SynthesisTraditional vs. New

Sato, et al. 1998, A “green” route to adipic acid:…, Science, V. 281, 11 Sept. 1646 - 1647

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Maleic Anhydride SynthesisBenzene vs Butane - Mass Efficiency

Benzene Route (Hedley et al. 1975, reference in ch. 8) V2O5

2 C6H6 + 9 O2 2 C4H2O3 + H2O + 4 CO2

(air) MoO3

95% Yield of Maleic Anhydride from Benzene in Fixed Bed Reactor

Butane Route (VO)2P2O5

C4H10 + 3.5 O2 C4H2O0 + 4 H2O (air)

60% Yield of Maleic Anhydride from Butane in Fixed Bed Reactor

Mass Efficiency = 2(4)(12) + 3(2)(16) + 2(2)(1)

2(6)(12) + 9(2)(16) + 2(6)(1) (100) = 44.4%

Mass Efficiency = (4)(12) + (3)(16) + (2)(1)

(4)(12) + 3.5(2)(16) + (10)(1) (100) = 57.6%

Felthouse et al., 1991, “Maleic Anhydride, ..”, in Kirk-Othmer Encyclopedia of Chemical Technology, V. 15, 893 - 928

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Maleic Anhydride SynthesisBenzene vs Butane - Summary Table

Chapter 8Material

Stoichiometry 1 $/lb 2 TLV 3 TW 4 Persistence 5

Air Water (d) (d)

logBCF 5

Benzene Process

Benzene [71-43-2]

Maleic Anhydride

-1.19

1.00

0.184

0.530

10

0.25

100

----

10

1.7

10

7x10-4

1.0

----

Butane Process

Butane [106-97-8]

Maleic Anhydride

-1.22

1.00

0.141

0.530

800

0.25

----

----

7.25

1.7

----

7x10-4

----

----

1 Rudd et al. 1981, “Petroleum Technology Assessment”, Wiley Interscience, New York2 Chemical Marketing Reporter (Benzene and MA 6/12/00); Texas Liquid (Butane 6/22/00)3 Threshold Limit Value, ACGIH - Amer. Conf. of Gov. Indust. Hyg., Inc. , www.acgih.org4 Toxicity Weight, www.epa.gov/opptintr/env_ind/index.html and www.epa.gov/ngispgm3/iris/subst/index.html5 ChemFate Database - www.esc.syrres.com, EFDB menu item

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Maleic Anhydride SynthesisBenzene vs Butane - Tier 1 Assessment

Benzene Route

Butane Route

(TLV Index)

Environmental Index (non - carcinogenic) = | i | (TLVi ) 1

i

TLV Index = (1.19)(1 / 10) + (1.0)(1 / .25) = 4.12

TLV Index = (1.22)(1 / 800) + (1.0)(1/ .25) = 4.00

Where i is the overall stoichiometric coefficient of reactant or product i

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EPA Index

Environmental Index (carcinogenic) = | i | (Maximum toxicity weight)i i

Benzene Route

Butane Route

EPA Index = (1.19)(100) + (1.0)(0) = 119

EPA Index = (1.22)(0) + (1.0)(0) = 0

Maleic Anhydride SynthesisBenzene vs Butane - Tier 1 Assessment

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Identifying and estimating air emissions and other releases from process units

1. Identify waste release sources in process flowsheets

2. Methods for estimating emissions from chemical processes

3. Case study - Benzene to Maleic Anhydride process evaluation

Chapter 8

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Benzene to MA Process

AP-42, Chapter 6, section 6.14, Air CHIEF CD, www.epa.gov/ttn/chief/airchief.htm

V2O5

2 C6H6 + 9 O2 ----------> 2 C4H2O3 + H2O + 4 CO2

MoO3

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1. Waste streams from process units

2. Major equipment - vents on reactors, column separators, storage tanks, vacuum systems, ..

3. Fugitive sources - large number of small releases from pumps, valves, fittings, flanges, open pipes, ..

4. Loading/unloading operations

5. Vessel clean out, residuals in drums and tanks

6. Secondary sources - emissions from wastewater treatment, other waste treatment operations, on-site land applications of waste, ..

7. Spend catalyst residues, column residues and tars, sludges from tanks, columns, and wastewater treatment, …

8. Energy consumption - criteria air pollutants, traces of hazardous air pollutants, global warming gases,

Typical waste emission sources from chemical processes - Ch 8

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1. Actual measurements of process waste stream contents and flow rates or indirectly estimated based on mass balance and stoichiometry. (most preferred but not always available at design stage)

2. Release data for surrogate chemical or process or emission factors based on measured data

3. Mathematical models of emissions (emission correlations, mass transfer theory, process design software, etc.)

4. Estimates based on best engineering judgement or rules of thumb

Process release estimation methods

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Waste stream summaries based on past experience

1. Hedley, W.H. et al. 1975, “Potential Pollutants from Petrochemical

Processes”, Technomics, Westport, CT

2. AP-42 Document, Chapters 5 and 6 on petroleum and chemical industries,

Air CHIEF CD, www.epa.gov/ttn/chief/airchief.htm

3. Other sources

i. Kirk-Othmer Encyclopedia of Chemical Technology, 1991-

ii. Hydrocarbon Processing, “Petrochemical Processes ‘99”, March 1999.

Emission estimation methods: based on surrogate processes

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Emission Factors - major equipment

Average Emission Factors for Chemical Process Units Calculated from the US EPA L&E Database

Process Unit EFav ; (kg emitted/103 kg throughput)

Reactor Vents 1.50

Distillation Columns Vents 0.70

Absorber Units 2.20

Strippers 0.20

Sumps/Decanters 0.02

Dryers 0.70

Cooling Towers 0.10

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Emission factors - fugitive sources; minor equipment

Ei (kg i / yr) mi EFav Ns 365

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Emission factors - criteria pollutants from energy

consumption

Ei (lb i / yr) EFav(lb i / 103gal) ED(Btu / yr)

HV(Btu / 103 gal) BEAP-42, Chapter 1, section 1.3, Air CHIEF CD, www.epa.gov/ttn/chief/airchief.htm

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Emission factors - CO2 from energy consumption

Ei (lb i / yr) EFav(lb i / 103gal) ED(Btu / yr)

HV(Btu / 103 gal) BE

AP-42, Chapter 1, section 1.3, Air CHIEF CD, www.epa.gov/ttn/chief/airchief.htm

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Software Tools

Storage tanks

TANKS 4.0 - program from EPA - www.epa.gov/ttn/chief/tanks.html

Wastewater treatment

WATER8 - on Air CHIEF CD - www.epa.gov/ttn/chief/airchief.html

Treatment storage and disposal facility (TSDF) processes

CHEMDAT8 - on Air CHIEF CD

Emission correlations/models - storage tanks and waste treatment

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Tier 2 environmental assessment indexes

1. Energy: [total energy (Btu/yr)] / [production rate (MM lb/yr)]

2. Materials: [raw materials (MM lb/yr)] / [production rate (MM lb/yr)]

3. Water: [process water (MM lb/yr)] / [production rate (MM lb/yr)]

4. Emissions: [total emissions and wastes (MM lb/yr)] / [production rate (MM lb/yr)]

5. Targeted emissions: [total targeted emissions and wastes (MM lb/yr)] / [production rate (MM lb/yr)]

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Benzene to MA Process

AP-42, Chapter 6, section 6.14, Air CHIEF CD, www.epa.gov/ttn/chief/airchief.htm

V2O5

2 C6H6 + 9 O2 ----------> 2 C4H2O3 + H2O + 4 CO2

MoO3

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Air emission and releases sources:Benzene to MA Process

Source Identification

1. Product recovery absorber vent

2. Vacuum system vent

3. Storage and handling emissions

4. Secondary emissions from water out, spent catalyst, fractionation column residues

5. Fugitive sources (pumps, valves, fittings, ..)

6. Energy consumption

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Uncontrolled Air emission / releasesBenzene to MA Process (lb/103 lb MA)

Release Source

i Methods used

MaleicAnhydride(MA)

Benzene Xylene CriteriaPollutants

CO2 Tars andoxygenates

Venting fromstorage tanks

1 0.03 0.14

Absorber columnvent 2

100 700 (CO) 972 20

Vacuum systemvent 2

0.02 0.02

FugitiveEmissions

3 0.2 0.2 0.1

Loading/unloadingoperations

4 0.2 2.0

Wastes fromvacuum columns

5 3.8 26.5

Energy useemissions

6 5.3 562

Total 4.2 102.3 0.1 705 1,534 46.5

1 Vertical fixed-roof tank; surrogate for MA is PCE; Tanks 4.0 program from EPA – www.epa.gov/ttn/chief/tanks/html2 Hedley et al. 1975. Potential Pollutants from Petrochemical Processes. Technomic, West Port, CT AP-42 chapter 6 section 6.14, Air CHIEF CD, www.epa.gov/ttn/chief/airchief.htm3 Typical chemical industry emission factor from Berglund and Hansen, 1990.4 Equation 8.3-4, chapter 8, Green Engineering textbook.5 Hedley et al. 1975. Potential Pollutants from Petrochemical Processes. Technomic, West Port, CT6 AP-42, Chapter 1, section 1.3, Table 1.3-11, Air CHIEF CD, www.epa.gov/ttn/chief/airchief.htm

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Benzene to MA Process Conclusions from emissions summary

1. Chemical profile:

CO2 > CO > benzene > tars-oxygenates > MA

2. Toxicity profile:

Benzene > MA > CO > tars-oxygenates > CO2

3. Unit operations profile:

Absorber vent > energy consumption > vacuum system vent

- Pollution prevention and control opportunities are centered

on benzene, the absorber unit, and energy consumption -

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Emission Mechanisms; Fixed Roof Tank

LTOTAL = LSTANDING + LWORKING

Roof Column

Vent

T

P

LiquidLevel

- Weather, paint color/quality

- Weather

- liquid throughput, volume of tank

Vapor pressure of liquid drives emissions

Pollution prevention - Storage Tanks

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Storage tank comparison -TANKS 4.0 program

Storage Tank Type Vertical Internal Domed External

Fixed Roof Floating Roof Floating Roof

Annual Emissions (lb)

White Paint 337.6 66.2 42.8

Grey (Medium) Paint 489.1 85.1 52.4

Heated (White) 313.5

Poor (Grey/Medium) 509.7 81.0 51.5

Gaseous waste stream flowsheet • Toluene emissions only • 100 kgmole/hr absorber oil rate • 15,228.5 gallon tank for each comparison

Pollution prevention strategies • replace fixed-roof with floating-roof tank • maintain light-colored paint in good condition • heat tank to reduce temperature fluctuations

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Fugitive Sources -pollution prevention techniques