Boreskov Institute of Catalysis of the Siberian Branch of Russian ...

OP-III-7SIMULATION STUDIES OF A MEMBRANE WATER-GAS SHIFTREACTOR UNDER NON-ISOTHERMAL CONDITIONSM. Esperanza Adrover, Eduardo López, Daniel O. Borio, Marisa N. PederneraPlanta Piloto de Ingeniería Química (Universidad Nacional del Sur - CONICET), Camino LaCarrindanga km. 7 - 8000 Bahía Blanca – Argentina. e-mail: mpedernera@plapiqui.edu.arIntroduction: Hydrogen production processes and their subsequent purification stepshave been extensively studied in the last two decades for fuel-cell feeding. Reforming orpartial oxidation of hydrocarbons or alcohols have been reported as the main routes to obtainthe required hydrogen. In most cases, the CO content also evolving from the productionreactor has to be reduced to avoid the poisoning of the fuel-cell anode catalyst. The water-gasshift reaction (WGSR) is selected to accomplish this task, with the additional effect ofincreasing the H 2 production. This moderately exothermic reaction is strongly controlled bychemical equilibrium. An attractive alternative to increase the CO conversion is the use ofmembrane reactors (MR) to provoke an equilibrium displacement by the selective permeationof hydrogen from the reaction medium [1-2].Many studies have been reported concerning water-gas shift membrane reactors (WGS-MR) [3]. In the vast majority of them isothermal operation has been considered. Thisassumption is reasonable in low-scale (laboratory) equipment due to the high relationstransfer area / reaction volume under use. Nevertheless, when several membrane tubes areinstalled in parallel inside a shell through where the sweep gas flows, the hypothesis ofisothermal-operation could be no more realistic. In a previous publication, a theoretical studyof the influence of thermal effects on a WGS-MR performance is carried out for differentconfigurations of the sweep-gas flow on the reactor shell (co and counter-current) [4]. Thepresent contribution presents results regarding the effect of the operating pressure and thesweep-gas flowrate on the performance of the WGS-MR. A 1-D, pseudohomogeneousmathematical model has been selected to represent the reactor operation under adiabaticconditions (energy transfer between process and permeate streams only due to the permeationflow). A comparison with a conventional fixed-bed reactor (CR, without H 2 permeation) isalso reported.Results and discussion: The operation of a WGS-MR to process the outlet of a 1kW thmethanol reformer was analyzed. 30 membrane tubes of 8mm I.D. and 150 mm length,located in parallel, have been selected. Simulations show a strong influence of the operatingpressure (P) for a constant sweep gas pressure of 1 atm, flowing co-currently with the processgas. In fact, higher pressures lead to an appreciable increase of the CO conversion (X CO ) dueto higher H 2 permeation flows and enhanced equilibrium displacement. This increase in X COis also associated to higher thermal effects. To show this phenomenon, Figure 1 reportsconversion-temperature trajectories for both the membrane reactor and the conventionalfixed-bed reactor. The increment of temperature in the membrane reactor when comparing103