Low temperature catalytic dehydrogenation of methylcyclohexane assisted with pore fill type palladium membrane reactor.

Artur Gora
Institute of Advanced Industrial Science and Technology, Research Center for Compact Chemical Process 4-2-1, Nigatake, Miyagino-ku, Sendai 983-8551/Institute of Catalisis, Polish Academy of Sciences 30 239 Kraków, Niezapominajek 3, Poland

*David A. Pacheco Tanaka
Institute of Advanced Industrial Science and Technology, Research Center for Compact Chemical Process 4-2-1, Nigatake, Miyagino-ku, Sendai 983-8551

*Fujio Mizukami
Institute of Advanced Industrial Science and Technology, Research Center for Compact Chemical Process 4-2-1, Nigatake, Miyagino-ku, Sendai 983-8551

*Toshishige M. Suzuki
Institute of Advanced Industrial Science and Technology, Research Center for Compact Chemical Process 4-2-1, Nigatake, Miyagino-ku, Sendai 983-8551

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     Last modified: April 30, 2006

Abstract
The main problem for the use of hydrogen as a clean energy source is the difficulty in creating of a distribution infrastructure for safe and cost-effective transport and storage. Storage methods currently used (liquefied hydrogen, metal hydrides, compressed hydrogen gas, carbon sorption) are too expensive and do not meet the performance requirements of future applications. The use of unsaturated compounds such as toluene (TOL), which can store hydrogen in the form of methylcyclohexane (MCH), has been shown to be potentially feasible for both mobile and stationary applications. MCH is a liquid and it can be stored and transported in existing oil tanks and ships.
The reversible reaction of dehydrogenation of MCH to toluene, and in general all dehydrogenation reactions of paraffin to aromatic compounds, is highly endothermic and strongly restricted by thermodynamic equilibrium. The ability of the dehydrogenation catalyst placed inside membrane tube combined with the selective removal of hydrogen permeation through the membrane shift the reaction towards the product side. Palladium membrane has been already shown to be promising candidates for this process in temperatures above 523K. However at lower temperatures the hydrogen embrittlement due to hydrogenation dehydrogenation cycling and α–β phase transformation of palladium crystals limit the membrane durability. To avoid this limitation, pore filled membrane, in which palladium nanoparticles are packed in the intermediate space of alumina layer has been used. The biggest advantage of this membrane is that it can work continuously at lower temperatures range (323-473K).
Present paper deals with dehydrogenation of methylocyclohexane to toluene at low temperature with the use of pore filled membrane. The newly constructed membrane reactor was tested for 600 hours in different reaction conditions and was shown to work effectively in low temperature range without decline of membrane selectivity and permeability properties. In comparison to non-membrane system observed conversion of MTC to TOL was about 70% higher in the temperature range 323-423K and the reaction yield reached almost 95% at 423K.