Investigation on isobutane dehydrogenation in fluidized bed membrane reactors

The aim of the present study was to prepare a palladium composite membrane tube possessing exclusive selectivity to hydrogen and to investigate the performance of it in a fluidized bed membrane reactor where isobutene was formed by the dehydrogenation of isobutane. Isobutene has recently received considerable attention because of the increasing demand for methyl tertiary butyl ether (MTBE) and ethyl tertiary butyl ether (ETBE), as additives for gasoline to increase the octane number.In the ELP (electroless plating) studies, porous glass tube was used as support. Synthesized Al(OH)3 gel was forced to the surface of the tube by applying vacuum. Vacuum application on the support took 1 hour and after that support was heated at 550oC to obtain the transformation of Al(OH)3 structure to ? -Al2O3. Loading of alumina on the support was performed two times. Al/Si ratio was 5.65 (by mass) after two modification processes. Activation was done by dipping the modified support into acidic SnCl2 solution, PdCl2 solution and pure water in sequence. Six plating studies were carried out on the same support at a bath temperature of 35oC and in a pH range of 10-11. Surface compositions on Al, Si, Pd basis after sixth plating step were %98.46 Pd, %1.36 Si, %0.18 Al and plating thickness of 130 ? m was determined. It was investigated how modification with alumina and plating studies effected pore size distribution of the support by using physisorption and mercury porosimetry data. It was observed that pores having an average diameter of 7 nm increased after sixth plating step. Dehydrogenation reaction of isobutane was carried out on pure Cr2O3 catalyst placed in the synthesized membrane tube. The minumum fluidization velocity was determined experimentally as 1.5 cm/s at 17oC for the catalyst with mean diameter of 84 ? m. Experiments were carried out at superficial gas velocities of 1.7 times the minumum fluidization velocity. In the experimental runs, a small pressure difference (0.005 atm) between membrane tube inside and outside was created and reactor temperature was kept at 450oC. It was shown that isobutane conversion to isobutene obtained in fluidized bed membrane reactor was 1.5 times higher than the equilibrium value.