Evaluation of a tubular nano-composite ceramic membrane for hydrogen separation in methane steam reforming reaction

Tubular silica/alumina membranes with three different thicknesses of selective layer (75-100 nm) were successfully applied as membrane reactors for simultaneous production and purification of hydrogen. BET analysis indicated a decreasing trend in membrane characteristics by adding successive layers, which is well in agreement with the graded structure of the substrate. These membranes showed a high permeance of 5-11 x 10(-7) mol m(-2) s(-1) Pa-1 and good separation factor of 20-300 at various temperatures (773-1073 K) in an equimolar mixture of H-2, CH4, CO, and CO2. The reactor performance of the membranes was evaluated for the methane steam reforming (MSR) reaction - using a conventional nickel/alumina catalyst with 10 wt% of nickel on the alumina support - in the reaction temperature range of 773-1073 K and pressure range of 1-10 bar. X-ray diffraction measurements of the catalyst showed a good dispersion of nickel on the alumina substrate. The reactor results showed an increasing trend for H-2 yield between 3.8-30 x 10(-6) mol g(-1) with both increasing temperature and pressure, but CH4 conversion decreased about 30% with increasing pressure from 1 to 10 bar. These results also indicate higher values of hydrogen yield and methane conversion in comparison to the equilibrium conditions for all membranes even up to 35% by increasing either temperature or pressure.