Kinetics of the reactions of the light alkenes over SAPO-34

Many petrochemical processes produce light olefin byproducts that can be used to produce propene. This study reports the kinetics of the reactions of ethene, propene and n-butene isomers over a SAPO-34 catalyst at 450 degrees C and different space velocities and discusses suitable modes of reaction to maximize propene yield. The shape selectivity of SAPO-34 prevented the formation of i-butene and high alkenes. When a single alkene (ethene, propene, or n-butene) was used as the reactant, the other alkenes were rapidly produced by dimerization and cracking such that the final compositions of the light alkenes were close to the equilibrium composition, with propene as the main species. Hydrogen transfer reactions to form an alkane from an alkene were slower than alkene inter-conversion. A kinetic model for alkene inter-conversion was deduced. Experimental and simulation results indicated that a lower partial pressure of the reactant gave increased propene yield when ethene was the feed. (C) 2008 Elsevier B.V. All rights reserved.