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Chapter 8

Chapter 8. Part 0 – Hierarchical Design Procedures. Hierarchy of Decisions. Example Hydrodealkylation of Toluene. Purge H 2 , CH 4. H 2 , CH 4. Benzene. Toluene. Dipheny1. Input-Output Structure of the Flowsheet. 5. Purge H 2 , CH 4. H 2 , CH 4. 1. 3. Process. Benzene

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Chapter 8

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  1. Chapter 8 Part 0 – Hierarchical Design Procedures

  2. Hierarchy of Decisions

  3. Example Hydrodealkylation of Toluene

  4. Purge H2 , CH4 H2 , CH4 Benzene Toluene Dipheny1 Input-Output Structure of the Flowsheet

  5. 5 Purge H2 , CH4 H2 , CH4 1 3 Process Benzene Diphenyl 2 4 Toluene Production rate = 265 Design variables: FE and x Component 1 2 3 4 5 H2 FH2 0 0 0 FE CH4 FM0 0 0 FM + PB/S Benzene 0 0 PB0 0 Toluene 0 PB/S 0 0 0 Diphenyl 0 0 0 PB(1 - S)/(2S) 0 Temperature 100 100 100 100 100 Pressure 550 15 15 15 465 where S = 1 - 0.0036/(1 -x)1.544 FH2=FE + PB(1 + S)/2S FM = (1 - yFH)[FE + PB(1 + S)/S]/ yFH FG = FH2 + FE FIGURE 5.2-1 . Stream table Tier 1 Environmental Performance Tools!

  6. Gas recycle Purge H2 , CH4 Benzene H2 , CH4 Reactor system Separation system Toluene Dipheny1 Toluene recycle Recycle Structure of the Flowsheet

  7. Vapor recovery system Purge H2 , CH4 H2 , CH4 Reactor system Phase split Toluene Benzene Liquid separation system Dipheny1 Simplified Flowsheet for the Separation System

  8. Toluene feed ENERGY INTEGRATION

  9. LEVEL 2 DECISIONS: 1 ) Should we purify the feed streams before they enter the process? 2 ) Should we remove or recycle a reversible by-product? 3 ) Should we use a gas recycle and purge stream? 4 ) Should we not bother to recover and recycle some reactants? 5 ) How many product streams will there be? 6 ) What are the design variables for the input/output structure? What economic trade-offs are associated with these variables? Products & By products PROCESS Feeds       OR Purge Products & By products PROCESS Feeds      

  10. Purge H2 , CH4 Reactor Separation System H2 , CH4 Benzene Toluene Diphenyl LEVEL 2

  11. LEVEL 3 DECISIONS 1 ) How many reactors are required ? Is there any separation between the reactors ? 2 ) How many recycle streams are required ? 3 ) Do we want to use an excess of one reactant at the reactor inlet ? Is there a need to separate product partway or recycle byproduct ? 4 ) Should the reactor be operated adiabatically or with direct heating or cooling ? Is a diluent or heat carrier required ? What are the proper operating temperature and pressure ? 5 ) Is a gas compressor required ? costs ? 6 ) Which reactor model should be used ? 7 ) How do the reactor/compressor costs affect the economic potential ?

  12. LEVEL 3 : purge reactor separator products feeds Liquid ? Liquid / Vapor ? Vapor ?

  13. LEVEL 4 : 1 ) Liquid LEVEL 3 reactor liquid separation system liquid products feeds Liquid recycle

  14. purge LEVEL 4 : 2 ) Liquid / Vapor Vapor Recovery system vapor gas recycle vapor 35C Phase Split liq. liq. reactor liquid separation system liquid products feeds Liq. recycle LEVEL 3

  15. purge LEVEL 4 : 3 ) Vapor Vapor Recovery system vapor gas recycle 35C Phase Split liquid liquid vapor reactor liquid separation system products feeds Liquid recycle LEVEL 3

  16. RULES FOR PLACING THE VAPOR RECOVERY SYSTEM 1 ) Place the vapor recovery system on the purge stream if significant amounts of valuable materials are being lost in the purge. 2 ) Place the vapor recovery system on the gas-recycle stream if materials that are deleterious to the reactor operation (catalyst poisoning, etc.) are present in this stream or if recycling of some components degrades the product distribution. 3 ) Place the vapor recovery system on the flash vapor stream if both 1 ) and 2 ) are valid. 4 ) Do not use a vapor recovery system if neither 1 ) nor 2 ) are important.

  17. TYPE OF VAPOR RECOVERY SYSTEM 1 ) Condensation - low. T and/or high P 2 ) Absorption 3 ) Adsorption 4 ) Membrane separation 5 ) Reaction ADJUST MATERIAL BALANCE ?

  18. DECISION IN SYNTHESIZING LIQUID SEPARATION SYSTEM 1. How should light ends be removed, if they might contaminate the product ? 2. What should be the destination of light end ? 3. Do we recycle components that from azeotropes with reactants, or do we split the azeotropes ? 4. What separations can be made by distillation ? 5. What sequence of columns do we use ? 6. How should we accomplish separations if distillation is not feasible ?

  19. P2 Rationale • Some of the decisions made at each level might change the streams leaving the process. Some of the exit streams may cause pollution problems. • If we can make decisions that do not introduce exit streams to the flowsheet that have environmental impacts, the P2 goal is achieved.

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