HW Help. How do you want to run the separation? Safety Issues? Ease of Processing

Transcription

1 HW Help Perform Gross Profitability Analysis on NaOH + CH4 --> Na+CO+H NaOH+C-->Na+CO+1/H NaOH+1/ H-->Na+HO NaOH + CO Na+CO+1/H How do you want to run the reaction? NaOH - Solid, Liquid or Gas T for ΔGrxn = (-) Is this T going to give you S,L or G Can P influence S,L or G? How do you want to run the separation? Safety Issues? Ease of Processing

2 HW Help Perform Gross Profitability Analysis on NaOH + CH4 --> Na+CO+H NaOH+C-->Na+CO+1/H NaOH+1/ H-->Na+HO NaOH + CO Na+CO+1/H How do you want to run the reaction? NaOH - Solid, Liquid or Gas T for ΔGrxn = (-), rxn is exo or endo? Is this T going to give you S,L or G? Can P influence S,L or G? Density MP( C) BP( C) ΔHvap H -53 CH4-161 CO -19 C.6 3,550 4, kj/mol NaOH , kj/mol Na kj/mole Tmax=1150ºC How do you want to run the separation? Safety Issues? Ease of Processing

3 Reactor Design for Selective Product Distribution Sieder, et.al. Chapter 15 Terry A. Ring Chemical Engineering University of Utah

4 Onion Model of Process Design

5 Overview Parallel Reactions A+B R (desired) A S Series Reactions A B C(desired) D Independent Reactions A B (desired) C D+E Series-Parallel Reactions A+B C+D (desired) A+C E Mixing, Temperature and Pressure Effects

6 Examples Ethylene Oxide Synthesis CH =CH + O CO + H O O CH =CH + O CH -CH (desired)

7 Examples Diethanolamine Synthesis N CH HOCH NH CH HOCH CH CH O desired NH CH HOCH NH CH HOCH CH CH O NH CH HOCH NH CH CH O 3 \ / \ / 3 \ / ) ( ) ( ) ( ) ( + + +

8 Examples Butadiene Synthesis, C 4 H 6, from Ethanol O H H C CHO CH H C H CHO CH OH H C O H H C OH H C

9 Examples Maleic Anhydride Synthesis C 6 H 6 + 9/ O C 4 H O 3 + CO + H O C 4 H O O 4 CO + H O C 6 H / O 6 CO + 3 H O

10 Rate Selectivity Parallel Reactions A+B R (desired) A+B S Rate Selectivity S D/U = r r D U = k k D U C ( α A D α U ) ( β C B D β U ) (α D - α U ) >1 make C A as large as possible (β D β U )>1 make C B as large as possible (k D /k U )= (k od /k ou )exp[-(e A-D -E A-U )/(RT)] E A-D > E A-U T E A-D < E A-U T

11 Reactor Design to Maximize Desired Product

12 Maximize Desired Product Series Reactions A B(desired) C D Plug Flow Reactor Optimum Time in Reactor

13 Fractional Yield CH 3 CH OH ( g) + 5 CH 3CHO + O 1 O CO CH CHO + H 3 + H O O (k /k 1 )=f(t)

14 Real Reaction Systems More complicated than either Series Reactions Parallel Reactions Effects of equilibrium must be considered Confounding heat effects All have Reactor Design Implications Use Optimizer in Aspen + to evaluate Reactor Design

15 Reactor Heat Effects Sieder Chapter 15 Terry A. Ring Chemical Engineering University of Utah

16 Problems Managing Heat effects Optimization Make the most product from the least reactant

17 Reaction Heat Heuristics 1-High exothermic heat of reaction: Consider using excess reactant, inert diluents or cold shots of reactant. Consider them early on in the design -Lower exothermic heat of reaction: Use heat exchanger on/in reactor. Or use intercoolers between adiabatic reaction stages. 3-High endothermic heat of reaction: Consider use of excess reactant, inert diluents or hot shots. Consider them early on in the design. 4-Lower endothermic heat of reaction: Use heat exchanger on/in reactor. Or use interheaters between adiabatic reaction stages.

18 Managing Heat Effects Reaction Run Away Exothermic Reaction Dies Endothermic Preventing Explosions Preventing Stalling

19 Single Equilibrium aa +bb rr + ss K eq = a a r R a A a a s S b B Equilibrium Reactor- Temperature Effects = exp G RT o rxn a i activity of component I Gas Phase, a i = φ i y i P, φ i= = fugacity coefficient of i Liquid Phase, a i = γ i x i exp[v i (P-P is ) /RT] γ i = activity coefficient of i V i =Partial Molar Volume of i, d Van t Hoff eq. ln dt K eq = H RT o rxn

20 Kinetic Reactors - CSTR & PFR Temperature Effects Used to Size the Reactor Used to determine the reactor dynamics Reaction Kinetics r j k( T ) = = k dc o dt j = k( T ) E exp RT A i= 1 C C αi i

21 Equilibrium and Kinetic Limits Increasing Temperature Increases the Rate Equilibrium Limits Conversion

22 PFR no backmixing Used to Size the Reactor V = F ko X k dx r Space Time = Vol./Q 0 Outlet Conversion is used for flow sheet mass and heat balances k

23 CSTR complete backmixing Used to Size the Reactor V = F ko X r k k Outlet Conversion is used for flow sheet mass and heat balances

24 Temperature Profiles in a Reactor Exothermic Reaction

25 Reactor with Heating or Cooling Q = UA ΔT Reactor is a Shell and Tube (filled with catalyst) HX

26 Best Temperature Path

27 Optimum Inlet Temperature Exothermic Rxn

28 Various Reactors, Various Reactions

29 Managing Heat Effects Reaction Run Away Exothermic Reaction Dies Endothermic Preventing Explosions Preventing Stalling

30 Reactor with Heating or Cooling Q = UA ΔT

31 Inerts Addition Effect

32 Managing Heat Effects Reaction Run Away Exothermic Reaction Dies Endothermic Preventing Explosions Preventing Stalling

33 Inter-stage Cooler Lowers Temp. Exothermic Equilibria

34 Inter-stage Cold Feed Lowers Temp Lowers Conversion Exothermic Equilibria

35 Optimization of Desired Product Reaction Networks Heuristic 7 Maximize yield, moles of product formed per mole of reactant consumed Maximize Selectivity Number of moles of desired product formed per mole of undesirable product formed Maximum Attainable Region see discussion in Chap t. 6 SS&L. Reactors and bypass Reactor sequences

36 Engineering Tricks Reactor types Multiple Reactors Mixtures of Reactors Bypass Recycle after Separation Split Feed Points/ Multiple Feed Points Diluents Temperature Management

37 Reactor Problem on Previous Design I Final Exam

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42 Feed Temperature, ΔH rxn Heat Balance over Reactor Adiabatic Cooling Adiabatic Q = UA ΔT lm

43 Aspen Kinetics This is from Aspen Help

44 Aspen Units - Rate=kT n e [- E/RT]πC i α i Rate Units i When Rate Basis is Cat (wt), substitute sec kg catalyst for sec m 3 in each expression above. For either rate basis, the reactor volume or catalyst weight used is determined by the reactor where the reaction occurs.