1. University of Texas at AustinMichigan Technological University 1 Module 4: Environmental Evaluation and Improvement During Process Synthesis - Chapters 8 and 9 David R. Shonnard Department of Chemical Engineering Michigan Technological University

2. University of Texas at AustinMichigan Technological University 2 Module 4: Outline l Educational goals and topics covered in the module l Potential uses of the module in chemical engineering courses l Identify and estimate emissions from process units - Chapter 8 l Pollution prevention strategies for process units - Chapter 9 After the Input-Output structure is established, an environmental evaluation during process synthesis can identify large sources of waste generation and release; directing the attention of the designer to pollution prevention options within the process

3. University of Texas at AustinMichigan Technological University 3 Module 4: Educational goals and topics covered in the module Students will: l estimate air emissions and other releases from process units after developing a preliminary process flowsheet, using software and hand calculations l have a better understanding of the mechanisms for pollutant generation and release from process units l become familiar with practical pollution prevention strategies for process units

4. University of Texas at AustinMichigan Technological University 4 Module 4: Potential uses of the module in chemical engineering courses Mass/energy balance course: criteria pollutant emissions from energy consumption emission of global change gases from energy consumption calculate emission factors from combustion stoichiometry Continuous/stagewise separations course: evaluate environmental aspects of mass separating agents Design course: pollution prevention strategies for unit operations Reactor design course: environmental aspects of chemical reactions and reactors pollution prevention strategies for chemical reactors

5. University of Texas at AustinMichigan Technological University 5 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

6. University of Texas at AustinMichigan Technological University 6 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. Spent 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, Module 4: Typical waste emission sources from chemical processes - Ch 8

7. University of Texas at AustinMichigan Technological University 7 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 a 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 Module 4: Process release estimation methods

8. University of Texas at AustinMichigan Technological University 8 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. Module 4: Emission estimation methods: based on surrogate processes

9. University of Texas at AustinMichigan Technological University 9 Module 4: Emission Factors - major equipment

10. University of Texas at AustinMichigan Technological University 10 Module 4: Emission factors - fugitive sources; minor equipment

11. University of Texas at AustinMichigan Technological University 11 Module 4: Emission factors - criteria pollutants from energy consumption AP-42, Chapter 1, section 1.3, Air CHIEF CD, www.epa.gov/ttn/chief/airchief.htm

12. University of Texas at AustinMichigan Technological University 12 Module 4: Emission factors - CO 2 from energy consumption AP-42, Chapter 1, section 1.3, Air CHIEF CD, www.epa.gov/ttn/chief/airchief.htm

13. University of Texas at AustinMichigan Technological University 13 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 Module 4: Emission correlations/models - storage tanks and waste treatment

14. University of Texas at AustinMichigan Technological University 14 Module 4: Benzene to MA Process AP-42, Chapter 6, section 6.14, Air CHIEF CD, www.epa.gov/ttn/chief/airchief.htm V 2 O 5 2 C 6 H 6 + 9 O 2 ----------> 2 C 4 H 2 O 3 + H 2 O + 4 CO 2 MoO 3

15. University of Texas at AustinMichigan Technological University 15 Module 4: 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

16. University of Texas at AustinMichigan Technological University 16 Process data for energy consumption 0.15 lb fuel oil equivalent per lb Maleic Anhydride product fuel oil #6 in a Normally Fired Utility Boiler 1% sulfur Boiler efficiency included in the energy usage data Module 4: emissions from energy consumption: Criteria pollutants (SO 2, SO 3, NOx, CO, PM) AirCHIEF Demonstration

17. University of Texas at AustinMichigan Technological University 17 Module 4: emissions from energy consumption: continued

18. University of Texas at AustinMichigan Technological University 18 Module 4: Uncontrolled Air emission / releases Benzene to MA Process (lb/10 3 lb MA)

19. University of Texas at AustinMichigan Technological University 19 Module 4: Flowsheet evaluation - n-butane to maleic anhydride Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 15, pp. 893-927. 1991

20. University of Texas at AustinMichigan Technological University 20 Module 4: Uncontrolled Air emission / releases n-butane to MA Process (lb/10 3 lb MA)

21. University of Texas at AustinMichigan Technological University 21 Module 4: 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)]

22. University of Texas at AustinMichigan Technological University 22 Module 4: Benzene to MA Process Conclusions from emissions summary 1. Chemical profile: CO 2 > CO > benzene > tars-oxygenates > MA 2. Toxicity profile: Benzene > MA > CO > tars-oxygenates > CO 2 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 -

23. University of Texas at AustinMichigan Technological University 23 Module 4: Chapter 9 Pollution prevention strategies for process units 1. Material choices for unit operations 2. Pollution prevention for chemical reactions and reactors 3. Separation units: reducing energy consumption and wastes 4. Preventing pollution for storage tanks and fugitive sources 5. Case study applications - VOC recovery/recycle: effect of MSA choice on energy consumption Maleic anhydride from n-butane: MA yield vs reaction temperature

24. University of Texas at AustinMichigan Technological University 24 Module 4: Important issues regarding pollution prevention for unit operations 1. Material selection: fuel type, mass separating agents (MSAs), air, water, diluents, heat transfer fluids 2. Operating conditions: temperature, pressure, mixing intensity 3. Energy consumption: high efficiency boilers, operation of units to minimize energy usage 4. Material storage and fugitive sources: storage tank choices and equipment monitoring and maintenance 5. Waste generation mechanisms: understanding this will lead to pollution prevention strategies

25. University of Texas at AustinMichigan Technological University 25 Example Problem: Calculate the annual uncontrolled SO 2 emissions to satisfy a steam energy demand of 10 8 Btu/yr with a boiler efficiency of.85 assuming Fuel Oil #6, #2, and Natural Gas. Module 4: Pollution prevention through material selection - fuel type

26. University of Texas at AustinMichigan Technological University 26 Module 4: Pollution prevention through material selection - water pretreatment to prevent 10 kg sludge/kg ppt RCRA waste Reverse Osmosis

27. University of Texas at AustinMichigan Technological University 27 Module 4: Pollution prevention through material selection - reactor applications 1. Catalysts: that allow the use of more environmentally benign raw materials that convert wastes to usable products and feedstocks products more environmentally friendly - e.g. RFG / low S diesel fuel 2. Oxidants: in partial oxidation reactions replace air with pure O 2 or enriched air to reduce NOx emissions 3. Solvents and diluents : replace toxic solvents with benign alternatives for polymer synthesis replace air with CO 2 as heat sinks in exothermic gas phase reactions

28. University of Texas at AustinMichigan Technological University 28 Module 4: Pollution prevention for chemical reactors 1. Reaction type: series versus parallel pathways irreversible versus reversible competitive-consecutive reaction pathway 2. Reactor type: issues of residence time, mixing, heat transfer 3. Reaction conditions: effects of temperature on product selectivity effect of mixing on yield and selectivity

29. University of Texas at AustinMichigan Technological University 29 1st Order Irreversible Parallel Reactions Module 4: Pollution prevention for chemical reactions High Conversion t > 5(k p + k w ) -1 High Selectivity k p >> k w Selectivity Independent of residence time

30. University of Texas at AustinMichigan Technological University 30 Module 4: Pollution prevention for chemical reactions 1st Order Irreversible Series Reactions High Conversion t > 5 k p -1 High Selectivity k p >> k w Selectivity dependent on residence time

31. University of Texas at AustinMichigan Technological University 31 Reversible Series Reactions CH 4 + H 2 O  CO + 3H 2 Steam reforming of CH 4 CO + H 2 O  CO 2 + H 2 R = CH 4 P = CO W = CO 2 Separate and recycle waste to extinction Module 4: Pollution prevention for chemical reactions

32. University of Texas at AustinMichigan Technological University 32 Module 4: Pollution prevention - reactor types 1. CSTR: not always the best choice if residence time is critical 2. Plug flow reactor: better control over residence time temperature control may be a problem for highly exothermic reactions 3. Fluidized bed reactor : if selectivity is affected by temperature, tighter control possible 4. Separative reactors: remove product before byproduct formation can occur: series reactions

33. University of Texas at AustinMichigan Technological University 33 Module 4: Pollution prevention - reaction temperature 1st Order Irreversible Parallel Reactions For E p > E w, E p was set to 20 kcal/mole and E w to 10 kcal/mole. for E p > E w, E p = 20 kcal/mole E w to 10 kcal/mole for E w > E p, E p = 10 kcal/mole E w to 20 kcal/mole E = activation energy

34. University of Texas at AustinMichigan Technological University 34 Module 4: Pollution prevention - mixing effects Irreversible 2nd order competitive-consecutive reactions Y = yield = P/A o Y exp = expected yield  = mixing time scale Increased mixing will increase observed yield AoAo BoBo CSTR

35. University of Texas at AustinMichigan Technological University 35 Module 4: Pollution prevention - other reactor modifications 1. Improve Reactant Addition: premix reactants and catalysts prior to reactor addition add low density materials at reactor bottom to ensure effective mixing 2. Catalysts: use a heterogeneous catalyst to avoid heavy metal waste streams select catalysts with higher selectivity and physical characteristics (size, porosity, shape, etc.) 3. Distribute flow in fixed-bed reactors 4. Heating/Cooling: use co-current coolant flow for better temperature control use inert diluents (CO 2 ) to control temperature in gas phase reactions 5. Improve reactor monitoring and control

36. University of Texas at AustinMichigan Technological University 36 Module 4: Pollution prevention - for separation devices 1. Choose the best technology: take advantage of key property differences (e.g. volatility for distillation) 2. Choose the best mass separating agent: consider operability, environmental impacts, energy usage, and safety 3. Separation Heuristics combine similar streams to minimize the number of separation units separate highest-volume components first remove corrosive and unstable materials early do the most difficult separations last do high-purity recovery fraction separations last avoid adding new components to the separation sequence avoid extreme operating conditions (temperature, pressure)

37. University of Texas at AustinMichigan Technological University 37 Module 4: Pollution prevention - example of mass separating agent choice HYSYS  Flowsheet Absorber oil recycle Absorber Vent; 90% recovery of VOC Conditions for simulations 1. 10-stage columns, 2. 10 ˚C approach temperature for heat integration, 3. absorber temperature = 32 ˚C MSA Screening 1. 857 chemicals 2. Hansen Sol. Par. 11.8   d  22 0   p  9.3 0   h  11.2 3. T bp > 220 ˚C 4. T mp < 26 ˚C 5. 23 chemicals remain

38. University of Texas at AustinMichigan Technological University 38 Module 4: Pollution prevention - results of mass separating agent choice

39. University of Texas at AustinMichigan Technological University 39 Emission Mechanisms; Fixed Roof Tank L TOTAL = L STANDING + L WORKING Roof Column Vent  T  P Liquid Level - Weather, paint color/quality - Weather - liquid throughput, volume of tank Vapor pressure of liquid drives emissions Module 4: Pollution prevention - Storage Tanks

40. University of Texas at AustinMichigan Technological University 40 Module 4: Storage tank comparison - TANKS 4.0 Demonstration Gaseous waste stream flowsheet ; pg 37 Toluene emissions only 516,600 gal/yr flowrate of toluene 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

41. University of Texas at AustinMichigan Technological University 41 Module 4: Fugitive Sources - pollution prevention techniques

42. University of Texas at AustinMichigan Technological University 42 Module 4: Flowsheet evaluation - maleic anhydride from n-butane Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 15, pp. 893-927. 1991

43. University of Texas at AustinMichigan Technological University 43 Principal Reaction 1. C 4 H 10 + 3.5O 2  C 4 H 2 O 3 + 4H 2 O-  H R,1 = 1.26x10 6 kJ/kmole 2. C 4 H 10 + 4.5O 2  4CO + 5H 2 O-  H R,2 = 1.53x10 6 kJ/kmole 3. C 4 H 10 + 6.5O 2  4CO 2 + 5H 2 O-  H R,3 = 2.66x10 6 kJ/kmole Activation EnergiesRate Equations E 1 /R = 8,677 K E 2 /R = 8,663 K E 3 /R = 8,940 K Module 4: Reaction rate parameters - Maleic anhydride from n-butane Schneider et al. 1987, “Kinetic investigation and reactor simulation…”, Ind. Eng. Chem. Res., Vol. 26, 2236-2241

44. University of Texas at AustinMichigan Technological University 44 Module 4: Fixed-bed reactor section - 100 MM tons/yr maleic anhydride process

45. University of Texas at AustinMichigan Technological University 45 Module 4: Case Study - reactor temperature: Maleic anhydride from n-butane

46. University of Texas at AustinMichigan Technological University 46 Module 4: Summary/Conclusions 1. Methodologies/software tools - process synthesis : emission factors surrogate process information from historical sources emission estimation software: TANKS 4.0, AirCHIEF 7.0, process simulator packages, Tier 2 environmental assessment 2. Case studies: VOC recovery/recycle from a gaseous waste stream - effects of MSA choice on energy consumption Maleic anhydride from n-butane - effect of reaction temperature on conversion, MA yield, MA selectivity