MEASURING CONVERSIONS IN DEHYDROGENATION REACTIONS - WITH THE AID OF A PD-AG MEMBRANE

A useful method is introduced for the determination of H-2 partial pre ssure in a gas mixture to estimate conversions in selective dehydrogen ation reactions by applying a palladium-silver (Pd-23 wt % Ag) membran e. The membrane is connected downstream of the dehydrogenation reactor and operated at the same temperature and pressure as the reactor. In this method, the tubular membrane outlet is closed, allowing H-2 to di ffuse through the membrane wall until an equilibrium is established be tween the H-2 pressure and the H-2 partial pressure in a gas mixture i nside and outside the membrane, respectively. Dehydrogenation conversi ons of methylcyclohexane to toluene in a packed-bed reactor calculated from the observed H-2 pressures inside the closed membrane were very close to those obtained by gas chromatographic analysis at 593-643 K, 15 bar, and liquid hourly space velocities of 1.9-5.2 h(-1). Additiona l measurements with gas mixtures of H-2-N-2 confirmed the reliability of the method.