lecture 17 - CHE 349, Lecture 25 CHE 349: Kinetics and...

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CHE 349: Kinetics and Reactor Design Lecture 25 Jing Wu 350 Tiernan Department of Chemical Engineering ± jingwu@adm.njit.edu ² 973-642-7064 CHE 349 - Lecture 25 by Jing Wu 2 Assignment Important Sections of Chapter 10 Sec. 10.1-10.3 Reivew HW10.3, HW10-4, HW10-11. HW 10-10 (will go over in class) Carefully Read 10.3.3, so that you can derive the rate limiting desorption case. CHE 349 - Lecture 25 by Jing Wu 3 The Langmuir-Hinshelwood Approach • It consists of first assuming a sequence of steps in the reaction. A choice must be made between such mechanisms as molecular or atomic adsorption, and single- or dual-site reaction. • Rate laws are written for the individual steps as shown in the preceding section, assuming that all steps are reversible. • A rate-limiting step is postulated and steps that are not rate-limiting are used to eliminate all coverage- dependent terms. CHE 349 - Lecture 25 by Jing Wu 4 Dissociative Adsorption Limits Rapid H 2 + 2S 2H S N 2 + S N 2 S N 2 S + S 2N S Rate-limiting N S + H S NH S + S NH 3 S NH 3 + S NH S + H S H 2 N S + S H 2 N S + H S NH 3 S + S Rapid 3H 2 + N 2 2NH 3
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CHE 349 - Lecture 25 by Jing Wu 5 Surface Reaction Limited Mechanism NO CO + N CO 2 1 2 + Rapid CO + S CO S NO + S NO S NO S + CO S CO 2 + N S + S Rate-limiting Rapid N S + N S N 2 S N 2 S N 2 +S CHE 349 - Lecture 25 by Jing Wu 6 Synthesizing a Rate Law, Mechanism, and Rate-Limiting Step C+S C SB S + P B + S k A k -A k s k -s k D k -D Figure 10-10 on 604 CHE 349 - Lecture 25 by Jing Wu 7 = = C S C v C A AD C K C C P k r r ' The rate of adsorption: = S P S B S C S S K P C C k r The surface reaction rate:
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lecture 17 - CHE 349, Lecture 25 CHE 349: Kinetics and...

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