Evaluation of palladium-impregnation on the performance of a Vycor glass catalytic membrane reactor

This paper analyzes the effect of palladium-impregnation sites on the performance of catalytically active, tubular porous Vycor® glass (trademark of Corning Glass Works) membrane reactors. The preferred site of palladium deposition onto the glass membrane was varied according to the method of impregnation as determined by EDX, SEM, and BET analysis. Catalytically active membranes synthesized by the adsorption of palladium nitrate onto Vycor glass (PM1) exhibited palladium deposited preferentially at the inner and outer surface of the glass tube. In contrast, membranes synthesized by the reaction of palladium allyl chloride dimer with hydrogen peroxide-treated Vycor glass (PM2) exhibited a more uniform deposition of palladium throughout the membrane wall. The dehydrogenation of cyclohexane to benzene was used as the test reaction to evaluate PM1, PM2, and unimpregnated Vycor glass in a membrane reactor. For all evaluations, 0.5 wt.% Pd/Al₂O₃ catalyst granules were packed into the bore of the tubular membrane reactor. Cyclohexane conversion was increased in each evaluation beyond predetermined equilibrium values, and conversion increased with increasing sweep shell flowrate. However, the performance of PM1 and PM2 varied significantly from both each other and Vycor glass. PM1 demonstrated increases in conversion from an equilibrium value (determined in a fixed bed reactor) of 30% to over 75%; under identical reaction conditions, unimpregnated Vycor glass membranes increased conversion to approximately 65%. PM2 demonstrated increases in cyclohexane conversion to only 39%.