Applications of hydrogenation and dehydrogenation on noble metal catalysts

摘要

Hydrogenation and dehydrogenation on Pd- and Pt- catalysts are encountered inmany industrial hydrocarbon processes. The present work considers the development ofcatalysts and their kinetic modeling along a general and rigorous approach. The first partdeals with the kinetics of selective hydrogenation, more particularly of the C3 cut of athermal cracking unit for olefins production. The kinetics of the gas phase selectivehydrogenation of methyl-acetylene (MA) and propadiene (PD) over a Pd/?-aluminacatalyst were investigated in a fixed bed tubular reactor at temperatures 60 - 80 oC and apressure of 20 bara. Hougen-Watson type kinetic equations were derived. The formationof higher oligomers slowly deactivated the catalyst. The effect of the deactivating agenton the rates of the main reactions as well as on the deactivating agent formation itselfwas expressed in terms of a deactivation function multiplying the corresponding rates atzero deactivation. Then, the kinetic model was plugged into the reactor model to simulate an industrial adiabatic reactor. In the second part the production of hydrogenfrom hydrocarbons was investigated. In both cyclohexane and decalin dehydrogenations,conversions higher than 98% could be obtained over Pt/?-alumina catalyst at temperatureof 320 and 340 oC, respectively, with no apparent deactivation for 30 h and with co-feedof H2 in the feed. Except for H2 and trace amounts of side cracking products, less than0.01%, benzene was the only dehydrogenated product in cyclohexane dehydrogenation.In the case of decalin dehydrogenation, partially dehydrogenated product, tetralin, wasalso formed with selectivity lower than 5%, depending on operating conditions. Arigorous Hougen-Watson type kinetic model was derived, which accounted for both thedehydrogenation of cis- and trans- decalin in the feed and also the isomerization of thetwo isomers. Jet A is the logic fuel in the battlefields. The dehydrogenation of Jet A canproduce H2 for military fuel cell application. Although the H2 production is lower thanthat of steam/autothermal reforming, it eliminates the needs of high temperature andproduct separation operation.