Reactions of methanol over catalytically active alumina membranes

The reactions of methanol over catalytically active alumina membranes are described in this paper. Alumina membranes showed very active properties for the decomposition of methanol. The selectivity to formaldehyde showed a maximum of 15% at 450°C. There was a preferential distribution of the products at both sides of the membrane reactor as a result of the different diffusion paths which resulted in different contact times with the catalyst. Oxygen supplied to the reactor from the side of the support (methanol entered the reactor from the side of the top-layer) at low partial pressures (ca. 5% of methanol), although it did not affect the reaction, could extend the life-time of the membrane catalyst by more than three times. No interaction between methanol and oxygen occurred in the membranes due to the existence of Knudsen transport of the gases. The reactant configuration and the mode of operation of the membrane reactor appeared to have an influence on its performance. Comparative experiments with fixed-bed reactors with the same catalyst (γ-Al2O3) showed specific reaction rates (per gram of catalyst) which were ten times lower than those achieved in the membrane reactor. This is probably because the active surface accessible to the reactants per gram of catalytic material is higher in the membrane than in the powder form of the catalyst