17-Lect-MultipleRxns0

17-Lect-MultipleRxns0 - 1 Chemical Reaction Engineering -...

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Unformatted text preview: 1 Chemical Reaction Engineering - Musgrave Multiple Reactions Lecture 17 - Page 1 Outline: 1. Definitions (Fogler 6.1) 2. Parallel Reactions (Fogler 6.2) Next Time: (Fogler 6.3) 1. Maximizing the Desired Product in Series Rxns (Fogler 6.3) Reactants Products E D E H rxn P(E) Fraction of N A that has sufficient energy to surmount barrier at temperature T ~exp(-E/kT) Higher Temps Chemical Reaction Engineering - Musgrave Multiple Reactions Lecture 17 - Page 2 The active reaction pathways in a reaction system can involve: A B + C A D A B C A + B C + D A + C D A B + C D E + F Parallel Reactions : Reactions that compete for the same reactant Series Reactions : Reactions where products react Complex Reactions : Reactions that both compete and where products react Independent Reactions : Reactions where reactants nor products react with each other C 2 H 2 + O 2 2CO 2 + 2H 2 O C 2 H 2 + O 2 C 2 H 2 O C 2 H 2 O + NH 3 HOC 2 H 4 NH 2 HOC 2 H 4 NH 2 + EO (HOC 2 H 4 ) 2 NH (HOC 2 H 4 ) 2 NH + EO (HOC 2 H 4 ) 3 N C 2 H 5 OH C 2 H 4 + H 2 O C 2 H 5 OH CH 3 CHO + H 2 C 2 H 4 +CH 3 CHO C 2 H 6 + H 2 O C 2 H 6 C 2 H 4 + H 2 C 6 H 14 C 3 H 8 + C 3 H 6 Type of Multiple Rxns: General Form: Example: 2 Chemical Reaction Engineering - Musgrave Multiple Reactions Lecture 17 - Page 3 Multiple reactions can produce both desired and undesired products: Parallel Reactions : Series Reactions : A D A U A D U k D k U k D k U For either case we want k D /k U to be large so that a maximum amount of desired product is produced, and a minimum amount of undesired byproduct is produced. The larger k D /k U is the more selective the reaction. The competition between formation of D and U is described by the branching ratio k D /k U . Although the reaction doesnt branch, the ratio k D /k U describes how quickly the desired product transforms into undesired product. Chemical Reaction Engineering - Musgrave Multiple Reactions Lecture 17 - Page 4 The ratio of the rate of formation of D to U is the instantaneous selectivity S D/U : Series Reactions : A D A U A D U r D r U r D r U The more selective the reaction, the less need for separation. Parallel Reactions : Instantaneous selectivity is high when ratio of rates of formation of D to U is high. Instantaneous selectivity is high when subsequent transformation of U is slower than formation of D. Chemical Processes Separations Separations Raw Materials Final Product The overall selectivity: and in a batch reactor: S D / U = r D r U S D / U = F D F U S D / U = N D N U 3 Chemical Reaction Engineering - Musgrave Multiple Reactions Lecture 17 - Page 5 For parallel rxns in a CSTR: S D / U = F D F U = r D V r U V = r D r U = S D / U For sequential rxns in a CSTR: S D / U = F D F U = r D r U ( ) V r U V = S D / U 1 A D A U A D U k D k U k D k U F A0 F D , F U V =...
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This note was uploaded on 04/25/2010 for the course CHEN 4330 taught by Professor Staff during the Spring '08 term at Colorado.

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17-Lect-MultipleRxns0 - 1 Chemical Reaction Engineering -...

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