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Environmental Assessment During Process Synthesis - Chapters 7 and 8

Environmental Assessment During Process Synthesis - Chapters 7 and 8 . David T. Allen Department of Chemical Engineering University of Texas. Software exploration Green Chemistry Expert System. TOPIC AREAS • Green Synthetic Reactions - search a database for alternatives

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Environmental Assessment During Process Synthesis - Chapters 7 and 8

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  1. Environmental Assessment During Process Synthesis - Chapters 7 and 8 David T. Allen Department of Chemical Engineering University of Texas

  2. 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

  3. Software demonstration Green Chemistry Expert System search Green Synthetic Reactions for adipic acid references

  4. 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% hazardous global warming ozone depletion Davis and Kemp, 1991, Adipic Acid, in Kirk-Othmer Encyclopedia of Chemical Technology, V. 1, 466 - 493

  5. Adipic Acid SynthesisTraditional vs. New 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% Sato, et al. 1998, A “green” route to adipic acid:…, Science, V. 281, 11 Sept. 1646 - 1647

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

  7. Maleic Anhydride SynthesisBenzene vs Butane - Summary Table 1 Rudd et al. 1981, “Petroleum Technology Assessment”, Wiley Interscience, New York 2 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.org 4 Toxicity Weight, www.epa.gov/opptintr/env_ind/index.html and www.epa.gov/ngispgm3/iris/subst/index.html 5 ChemFate Database - www.esc.syrres.com, EFDB menu item

  8. Maleic Anhydride SynthesisBenzene vs Butane - Tier 1 Assessment Benzene Route Butane Route Where i is the overall stoichiometric coefficient of reactant or product i

  9. Maleic Anhydride SynthesisBenzene vs Butane - Tier 1 Assessment Benzene Route Butane Route

  10. Chapter 8 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

  11. Benzene to MA Process V2O5 2 C6H6 + 9 O2 ----------> 2 C4H2O3 + H2O + 4 CO2 MoO3 AP-42, Chapter 6, section 6.14, Air CHIEF CD, www.epa.gov/ttn/chief/airchief.htm

  12. Typical waste emission sources from chemical processes - Ch 8 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,

  13. Process release estimation methods 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

  14. Emission estimation methods: based on surrogate processes 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.

  15. 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

  16. Emission factors - fugitive sources; minor equipment

  17. Emission factors - criteria pollutants from energy consumption AP-42, Chapter 1, section 1.3, Air CHIEF CD, www.epa.gov/ttn/chief/airchief.htm

  18. Emission factors - CO2 from energy consumption AP-42, Chapter 1, section 1.3, Air CHIEF CD, www.epa.gov/ttn/chief/airchief.htm

  19. Emission correlations/models - storage tanks and waste treatment 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

  20. 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)]

  21. Benzene to MA Process V2O5 2 C6H6 + 9 O2 ----------> 2 C4H2O3 + H2O + 4 CO2 MoO3 AP-42, Chapter 6, section 6.14, Air CHIEF CD, www.epa.gov/ttn/chief/airchief.htm

  22. 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

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

  24. 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 -

  25. Pollution prevention - Storage Tanks Emission Mechanisms; Fixed Roof Tank LTOTAL = LSTANDING + LWORKING Vent Vapor pressure of liquid drives emissions DT DP Liquid Level - Weather, paint color/quality - Weather - liquid throughput, volume of tank Roof Column

  26. Storage tank comparison -TANKS 4.0 program 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

  27. Fugitive Sources -pollution prevention techniques

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