Exercise 6 Text

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INDUSTRIAL ORGANIC CHEMISTRY – EXERCISE 6 Methanol synthesis: development of the rate equations Methanol can be synthetizing upon a Cu/ZnO/Al2O3 catalyst using a mixture of carbon monoxide, carbon dioxide and hydrogen. Generally speaking, the kinetic mechanism can be based on two different reactions: the methanol synthesis from CO2 (1) and the reverse water gas shift reaction (2). COଶ+3Hଶ →CHଷOH+HଶO (1) COଶ+Hଶ →CO+HଶO (2) The following reaction scheme comprises several elementary steps which have to be considered for the synthesis of methanol and for the reverse water gas shift reactions. Vanden Bussche and Froment, Journal of Catalysis 161, 1–10 (1996) It is required to derive the reaction rates for the two reactions according to a Langmuir–Hinshelwood- Hougen-Watson (LLHW) model. The following assumptions can be employed: 1. Hydrogen and carbon dioxide adsorb dissociatively 2. All the active sites are equivalent 3. O*, H2O* and H* are the only adsorbate present on the surface in non-negligible amount 4. The rate determining step of the methanol synthesis is the hydrogenation of the formate (HCO2**) 5. The rate determining step of the reverse water gas shift is the dissociative adsorption of CO2 A set of kinetic measurements obtained in an annular laboratory reactor are available for the determination of the kinetic constants. It is asked to evaluate the kinetic constants of the methanol synthesis and of the reverse water gas shift, given following assumptions: 1. The laboratory reactor is isothermal and isobaric 2. Negligible internal and external transport limitations 3. The adsorption constants are taken from literature Reactor data: Catalyst weight [g] 13.5 Packed bed density [g/cm3] 1.322 Catalytic bed length [mm] 40.0 Reactor OD [mm] 19.0 Reactor ID [mm] 6.00…