A CATALYTICALLY ACTIVE MEMBRANE REACTOR FOR FAST, HIGHLY EXOTHERMIC, HETEROGENEOUS GAS REACTIONS - A PILOT-PLANT STUDY

Membrane reactors have been frequently studied because of their abilit y to combine chemical activity and separation properties into one devi ce. Due to their thermal stability and mechanical strength, ceramic me mbranes are preferred over polymeric ones, but small transmembrane flu xes obstruct a widespread industrial use of a membrane reactor. Conseq uently, a bench-scale membrane reactor with a tubular, macroporous mem brane (d(p) 780 nm) was developed in order to attain increased fluxes. A cooling pipe was concentrically placed inside the tubular membrane to remove heat from the membrane surface, so the present membrane reac tor was suitable to conduct exothermic reactions. As a model reaction, the heterogeneous oxidation of carbon monoxide over platinum, with se parated feed of carbon monoxide and oxygen, was performed in the prese nt setup. First, the present membrane reactor was characterized by the determination of the transport parameters, structure parameters of th e membrane and the external transfer coefficients. Subsequently fluxes of the reactants and products were measured over a wide range of proc ess conditions. Especially the influence of a transmembrane pressure d ifference was studied extensively. Furthermore overall conversion of c arbon monoxide was measured under various process conditions, and the results were compared with the simulations of a simplified, overall re actor model. From the results of the present investigation, it could b e concluded that the application of a pressure difference over the mem brane turned out to be a major process control parameter. It increases the product yield and preferentially directs the fluxes toward one si de of the membrane. It was shown that even for macroporous catalytic m embranes substantial pressure differences are allowed without any slip of unconverted reactants through the membrane. Furthermore, high degr ees of conversion were observed in the present setup, and the simulati ons of the overall reactor model were in reasonable agreement with the experimental data, The overall model contained no adjustable paramete rs. From this study, the catalytically active, ceramic membrane reacto r with separated feed of reactants turned out to be highly flexible an d easy to control.