this project is due may 11



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For this study, the following is your list of gaseous and vapor species with abbreviations: Let CH3COCH3 ≡ A, CH2CO ≡ B, C ≡ . CH3, H ≡ . H, E ≡ C2H6, G ≡ H2, N ≡ CH4 Here are your reactions and rates: NOTE: M = third body (any molecule)

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MEMORANDUM To: ChE 349 Class Date: March 30, 2020 (assigned) The Chemistry From: Prof. Barat Re: Term Project (v.1b) Due: May 5, 2020 Years ago, an important precursor to acrylic acid (CH2=CHC=OOH), a key organic building block for many useful products, was ketene (CH2=C=O). One way to make ketene was the vapor-phase pyrolysis of acetone (CH3C=OCH3). Pyrolysis means heating in the absence of oxygen. The overall endothermic reaction is: CH3COCH3  CH2CO + CH4 Jeffreys (1964) claimed the rate is 1st order in acetone vapor. The following elementary gas phase mechanism can explain this dependence and the products: CH3COCH3 ⇔ CH3C.O + .CH3 CH3C.O  CH2CO + .H .H + .CH + M  CH + M 3 4 The symbol M represents a third body – any species in the reacting vapor. The “dot” species like .H are free radicals. A pseudo steady-state hypothesis (PSSH) analysis (not shown here) of this 3-step mechanism consistent with the observed rate data reveals that the slow step is the forward direction of the first step. This suggests collapsing the first two steps into an effective single step: CH3COCH3  CH2CO + .CH3 + .H The presence of .H and .CH3 radicals can give rise to carbon deposition (coke) through a complex set of rapid reactions not shown here. To acknowledge the potential of this undesirable byproduct formation, three other elementary reactions are added below. The C2H6 potentially can react further to form coke. .CH + .CH + M  C H + M 3 3 2 6 .H + .CH + M  CH + M 3 4 .H + .H + M  H + M 2 Your Reactions and Kinetics For this study, the following is your list of gaseous and vapor species with abbreviations: Let CH3COCH3 ≡ A, CH2CO ≡ B, C ≡ .CH3, H ≡ .H, E ≡ C2H6, G ≡ H2, N ≡ CH4 Here are your reactions and rates: NOTE: M = third body (any molecule) 1 AB+C+H r1 = k1CA (1) H+C+MN+M r2 = k2CHCCCM (2) C+C+ME+M 𝑟𝑟3 = 𝑘𝑘3 𝐶𝐶𝐶𝐶2 𝐶𝐶𝑀𝑀 (3) H+H+MG+M  34222  k1 = 8.2E14 exp −  sec-1  T  𝑟𝑟4 = 𝑘𝑘4 𝐶𝐶𝐻𝐻2 𝐶𝐶𝑀𝑀 (4) Source: Jeffreys (1964)  298 1.8 k2 = 1.1E20  cm6/mole2-sec  T  Source: NIST  298  7.0  1390  k3 = 6.1E23  exp−  cm6/mole2-sec  T   T  Source: NIST  298  k 4 = 2.2 E15  cm6/mole2-sec  T  Source: NIST T = absolute temperature (K) Thermodynamics Mean heat capacities: c pj (J/mole-K) All species in the gas or vapor phase. Standard heats of formation (Tref = 298 K): ∆H ofj (kJ/mole) CH2CO CH3COCH3 CH4 .H C2H6 Symbol B A N H E c pj 83 163 71 21 117 o -61 -217 -75 218 -84 ∆H fj .CH 3 C 60 146 H2 G 30 0 NOTE: Account for the dependence of ∆𝐻𝐻𝑟𝑟𝑟𝑟 with temperature using 𝑐𝑐̅𝑝𝑝𝑝𝑝 values. Reactor The reactor is a PFR with pure A feed at To, Po. The pressure drop is assumed to be small enough to ignore. External heat transfer gives the needed heat input. 2 Next are key data for your analysis. • • • • • • FAo = 0.1 mole/s V = 1000000. cm3 To = 350 K Po = 0.2-2.0 atm Ua = 0.001 J/cm3-s-K Ta = 900 K (pure A feed) (range) Your Tasks • Prepare and run a computer simulation of species balances and energy balance for a Base Case where Po = 1 atm. For the Base Case, prepare the following plots: o Conversion XA and T vs. V on the same graph (use both primary and secondary axes) o FA, FB, and FN vs. V on the same graph o FE and FG vs. V on the same graph o FH and FC vs. V on the same graph (use both vertical axes for clarity) • Run a series of sensitivity cases where the only parameter you change is the pressure Po (see range above). Prepare a plot of XA vs. Po. Make sure you run a sufficient number of cases to get a smooth graph. • Prepare a Project Memo according to the guidelines below. • Scan your memo as a PDF, and email to Prof. Barat via Canvas email. References • Jeffreys, G. V., A Problem in Chemical Engineering Design: The Manufacture of Acetic Anhydride, 2nd ed. (London: Institution of Chemical engineers, 1964). • NIST - Project Memo Format Your Term Project industrial memo should contain the following sections: o Cover page  Including your name and affiliation  Executive summary (like an abstract) - strong bottom line statement o Short problem statement  Objectives 3    Major constraints Key assumptions Species and Energy Balances o Sample solution printout from your equation solver – must include a listing of the equations solved and used o Results and Discussion  Required plots (see Your Tasks)  Brief discussion of each, especially the impact of pressure o Conclusions Term Project Grading Rubric Term Project Grade Sheet – Spring 2020 Date Due: May 5 Student Name: Reporting Format: Memo Date Submitted: Item Requirements No. Technical Base Case 1 Plot: XA and T vs. V 2 Plot: FA, FB, and FN vs. V 3 Plot: FE and FG vs. V 4 Plot: FH and FC vs. V Sensitivity 5 Plot: XA vs. Po Memo 6 Cover page 7 Short problem statement 8 Sample solution printout from solver (including equations used) 9 Result and Discussion 10 Conclusions 11 General memo quality Sub-Totals Total Score (max 44 “Project” points) Poor Fair 1 2 Good Excellent 3 4 Instructor Comments: 4 ...
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