Final Exam 2008 - UNIVERSITY OF CALIFORNIA Department of...

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UNIVERSITY OF CALIFORNIA Department of Chemical Engineering and Materials Science ECH51 Material Balances Practice Final Exam (On the final exam there will 4-5 problems; extra problems are included in the practice exam) Prof. B. G. Higgins Winter 2008 Given for Exam: Total Mass Balance (1) t H t L r „ V + H t L r H v - w L ÿ n A = 0 Axiom I: Species Balance (molar form) (2) t H t L c A V + H t L c A H v A - w L ÿ n A = H t L R A V, A = 1,2,…,N Axiom II: (3) A = 1 MW A R A = 0 In order to get partial credit for a problem you must show your reasoning and intermediate calculations based on Axioms I and II above Problem 1 This problem deals with the hydrodealkylation of aromatics by reaction with hydrogen to form the parent aromatic compound. The potential reactions are converting toluene ( C 6 H 5 CH 3 ) to benzene ( C 6 H 6 ), xylene ( C 6 H 4 H CH 3 L 2 ) to toluene ( C 6 H 5 CH 3 ), and pseudocumene ( C 6 H 3 H CH 3 L 3 , called C 9 ) to xylene ( C 6 H 4 H CH 3 L 2 ). In this particular application a reformate stream #1 consisting of 5% benzene, 20% toluene, 35% xylene and 40% C 9 is fed to a reactor with a hydrogen stream #2. Stream #2 has 5 mol H 2 per mol of stream #1. The
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conversion of toluene is 80%, the conversion of xylene is 74% and the conversion of C 9 is 70%. The product stream #3 contains toluene, benzene, xylene pseudocumene, hydrogen, methane H CH 4 L as well as a small amount, 0.1% diphenyl ( H C 6 H 5 L 2 ) as a consequence of a side reaction. (i) Determine the constraints on the rates of productions R i for this system. (ii) Select a suitable control volume and write down the species balances.
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