Disk membranes generated from high-purity natural clinoptilolite mineral rock have shown promising hydrogen separation performance. To scale up production of these types of membranes for industrial gas separation, a coating strategy was devised. A mixture of natural clinoptilolite and aluminum silicate was deposited on the inner surface of porous stainless steel tubes by the slip casting technique. Phase composition and morphology of the coating materials were investigated using X-ray diffraction. The performance was evaluated for a range of gases using single gas permeation tests at different temperatures and pressures. Introduction of the second layer significantly improved the performance of the membrane system. The experiments on the double-layered membranes measured a hydrogen permeance of 1.65 Â 10 À7 mol Á m À2 Á s À1 Á Pa À1 at 300 8C. H 2 /CO 2 and H 2 /C 2 H 6 single gas selectivity was 10.2 and 8.45 respectively at 25 8C and feed pressure of 110 kPa. These results show that natural zeolite coated stainless steel tubular membranes have high potential for large-scale gas separation at high temperature requirements.

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Single and multicomponent gas permeation tests were used to evaluate the performance of metal-supported clinoptilolite membranes. The efficiency of hydrogen separation from lower hydrocarbons (methane, ethane, and ethylene) was studied within the temperature and pressure ranges of 25–600 °C and 110–160 kPa, respectively. The hydrogen separation factor was found to reduce noticeably in the gas mixture compared with single gas experiments at 25 °C. The difference between the single and multicomponent gas results decreased as the temperature increased to higher than 300 °C, which is when the competitive adsorption–diffusion mechanism was replaced by Knudsen diffusion or activated diffusion mechanisms. To evaluate the effect of gas adsorption, the zeolite surface isotherms of each gas in the mixture were obtained from 25 °C to 600 °C. The results indicated negligible adsorption of individual gases at temperatures higher than 300 °C. Increasing the feed pressure resulted in a higher separation efficiency for the individual gases compared with the multicomponent mixture, due to the governing effect of the adsorptive mechanism. This study provides valuable insight into the application of natural zeolites for the separation of hydrogen from a mixture of hydrocarbons.

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Propane dehydrogenation was carried over a commercial Pt-Sn/ -Al 2 O 3 catalyst at atmospheric pressure and reaction temperatures of 580, 600, and 620 ı C and WHSV of 11 h 1 in an experimental tubular quartz reactor. Propane conversions were measured for catalyst time on stream of up to nine days. The amounts of coke deposited on the catalyst were measured after one, three, six, and nine days on stream using a thermogravimetric differential thermal analyzer (TG-DTA) for each reaction temperature. The coke formation kinetics was successfully described by a coke formation model based on a monolayer-multilayer mechanism. In addition, catalyst deactivation was presented by a time-dependant deactivation function. The kinetic order for monolayer coke formation was found to be two, which would support a coke formation step involving two active sites. The kinetic order for multilayer coke formation was found to be zero. The activation energy for monolayer coke formation was found to be 29.1 kJ/mol, which was lower than the activation energy of about 265.1 kJ/mol for multilayer coke formation indicating that the presence of metals can promote coke formation on the catalyst surface.