Hierarchy of Decisions

1. Hierarchy of Decisions

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

3. LEVEL 3 DECISIONS • How many reactors are required ? Is there any separation between the reactors ? • How many recycle streams are required ? • 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 ? • 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 ? • Is a gas compressor required ? costs ? • Which reactor model should be used ? • How do the reactor/compressor costs affect the economic potential ?

4. 範例 　　產製苯的程序之反應路徑如下： 以上的反應合適操作條件為　　　　　 ，500 psia， 故設計一個反應系統即可。 Q1: 程序中應該要有幾個反應系統？ 若決定好的反應途徑中，有個別反應須操作在不同的操作條件或使用不同觸媒，則必須分別設計反應系統，若無以上情況則可使用一個反應系統。

5. Q1: Number of Reactor Systems If sets of reactions take place at different T and P, or if they require different catalysts, then we use different reactor systems for these reaction sets. For example, Acetone  Ketene + CH4 Ketene  CO + 1/2C2H4 700C, 1atm Ketene + Acetic Acid  Acetic Anhydride 80 C, 1atm

6. Destination Codes and Component Classifications Destination code Component classifications 1. Vent Gaseous by-products and feed impurities 2. Recycle and purge Gaseous reactants plus inert gases and/or gaseous by-products 3. Recycle Reactants Reaction intermediates Azeotropes with reactants (sometimes) Reversible by-products (sometimes) 4.None Reactants-if complete conversion or unstable reaction intermediates 5.Excess - vent Gaseous reactant not recovered or recycles 6.Excess - vent Liquid reactant not recovered or recycled 7.Primary product Primary product 8.Fuel By-products to fuel 9.Waste By-products to waste treatment should be minimized A ) List all the components that are expected to leave the reactor. This list includes all thecomponentsinfeedstreams, and allreactantsandproductsthatappearinevery reaction. B ) Classify each component in the list according to Table 5.1-3 and assign a destination code to each. C ) Order the components by their normal boiling points and group them with neighboring destinations. D ) The number of groups of all but the recycle streams is then considered to be the number of product streams.

7. Q2: Number of Recycle Streams EXAMPLE HDA Process ComponentNBP , CDestination H2 -253 Recycle + Purge Gas Recycle CH4 -161 Recycle + Purge Gas Recycle Benzene 80 Primary Product Toluene 111 Recycle Liquid Recycle Diphenyl 255 By-product Compressor CH4 , H2(Purge) (Gas Recycle) Benezene (PrimaryProduct) Reactor Separator (Feed)H2 , CH4 (Feed) Toluene Diphenyl (By-product) Toluene (Liquid Recycle)

8. Q2: Number of Recycle Streams EXAMPLE Acetone Ketene + CH4700C Ketene  CO + 1/2C2H41atm Ketene + Acetic Acid Acetic Anhydride 80 C, 1atm ComponentNBP, CDestination CO -312.6 Fuel By-product CH4 -258.6 “ C2H4 -154.8 “ Ketene -42.1 Unstable Acetone 133.2 Reactant Acetic Acid 244.3 Reactant Acetic Anhydride 281.9 Primary Product CO , CH4 , C2H4 (By-product) Acetic Acid (feed) Acetone (feed) R1 R2 Separation Acetic Anhydride (primary product) Acetic Acid (recycle to R2) Acetone (recycle to R1)

9. Q3: Reactor Inputs and Outputs 3.1 Feed Excess Reactants • shift product distribution • force another component to be close to complete conversion • shift equilibrium Therefore, molar ratio of reactants entering reactorshould be treated as a design variable!

11. Type 3 Multiple reactions in series producing byproducts shift product distribution ex. CH3 + H2 + CH4 excess 5:1 2+ H2 Type 4 Mixed parallel and series reactions  byproducts shift product distribution ex. CH4 + Cl2  CH3Cl + HCl Primary excess 10:1 CH3Cl + Cl2 CH2Cl2+ HCl CH2Cl2+ Cl2  CHCl3 + HCl Secondary CHCl3 + Cl2  CCl4 + HCl O O O O O

14. Some of the decisions involve introducing a new component (inert) into the flowsheet, e.g. adding a new component to shift the product distribution, to shift the equilibrium conversion, or to act as a heat carrier. This will require that we also remove the component from the process and this may cause a waste treatment problem. Example Ethylene production C2H6= C2H4 +H2Steam is usually used as the C2H6 + H2 = 2CH4diluent. Example Styrene Production EB = styrene +H2 EB  benzene +C2H4Steam is also used. EB + H2 toluene + CH4

15. 3.3 Remove Product during Reaction to shift equilibrium + product distribution Type 1(b): single reversible reaction: ex. 2SO2 + O2= 2SO3 H2O H2O SO2 REACT ABSORB REACT ABSORB O2 + N2 H2SO4 H2SO4 Type 3: multiple reactions in series  byproduct FEED  PRODUCT remove PRODUCT = BYPRODUCT remove .

16. 3.4 Recycle Byproduct to shift equilibrium + product distribution CH3 + H2 + CH4 2 = + H2 O O O O O

17. Q4: Reactor Operation 4.1 Setting Reactor Temperature T   k   V  Single Reaction : - endothermic AHAP ! - exothermic * irreversible AHAP ! * reversible continuously decreasing as conversion increases.  Multiple Reaction max. selectivity T  400C  Use of stainless steel is severely limited ! T  260C  High pressure steam ( 40~50 bar) provides heat at 250-265 C T  40C  Cooling water Temp 25-30C

23. Arrangements for fixed-bed reactor

24. Arrangements for fixed-bed reactor

25. Arrangements for fixed-bed reactor

26. Arrangements for fixed-bed reactor

28. Odecrease in the number of moles AHAP

29. Quick Calculations to establish recycle material balance - Example: HDA process in which toluene is limiting reactant (to be done first ) yPH RG Purge , PG FG, yFH H2 , CH4 Benzene , PB reactor separator FT FT ( 1-X ) PD Toluene Diphenyl LEVEL 3 FT ( 1-X ) LEVEL 2 always valid for limiting reactant when there is complete recovery and recycle of the limiting reactant

30. Quick calculations to establish recycle material balance -Example: HDA process in which H2 is the other reactant(Next ) molar ratio extra design variable Note that details of separation system have not been specified at this level. Therefore, we assume that reactants one recovered completely.

31. Q5: Compressor Design and Cost Whenever a gas-recycle stream is present, we will need a gas- recycle compressor. Covered in “Unit Operation (I)”

32. Q6: Reactor Models Q7: Reactor Design and Costs Covered in “Reactor Design and Reaction Kinetics”

33. Economic Potential at Level 3 Note, $ $ EP3=EP2-annualized costs of reactors -annualized costs of compressors 2  106 1  106 0.2 0.4 0.6 $/year 0 0.1 0.3 0.5 0.7 -1  106 -2  106   does not include any separation or heating and cooling cost