A mathematical modeling study on the intensification of the water-gas shift reaction

Low temperature water gas shift (WGS) reaction is modeled over a CuO/ZnO/Al2O3 catalyst in the presence of a ZIF-7 membrane. Upon validation of the model with the literature-based experimental data, effects of the flow arrangement, sweep gas type and flow rate, pressure and gas hourly space velocity (GHSV) on CO conversion are analyzed and permeated H2 flow rate is determined at different pressures. During the parameter analysis, performance of ZIF-7 membrane is also compared with a Pd-Ag membrane under the same reaction conditions. Ultimately, it is found that the best performance corresponding to 98% CO conversion is observed at 800 h-1 GHSV, and 10 bar with 1.072 mol.h-1 co-current steam flow used as the sweep gas. Employing steam as the sweep gas resulted in significant CO conversion improvement and co-current arrangement is found to be essential for keeping the temperature profile isothermal. Moreover, ZIF-7 shown significantly better performance than Pd-Ag membrane due to the reverse permeation of steam in ZIF-7 reactor. Low temperature WGS reaction model is followed by a ZIF-7 membrane microreactor model that involved Pt-CeO2 catalyst. After the validation of reactor model and kinetics, similar parameter analysis also performed for ZIF-7 membrane microreactor. Effects of sweep type and molar flow rate, pressure and residence time are investigated. Also, the same model is run in a mode that reflects the conventional two adiabatic consecutive reactors that operates over Fe/Cr (First reactor) and CuO/ZnO/Al2O3 (Second reactor), and the data gathered are compared with the single reactor Pt-CeO2 data. Parameter analysis shown that at 10 bar, using steam as the sweep gas at 10 times of the retentate inlet flow rate in co–current flow is the most beneficial and 100% conversion can be achieved as the residence time is increased to 35.55 g.h/mol. Moreover, comparison studies shown that single unit membrane reactor with 11.85 g.h/mol residence time at 400°C result in a superior performance (94.54% CO conversion) compared to the conventional reactor model.