Selective hydrogenation of 1,3-butadiene in mixture with isobutene on a Pd/ [formula omitted]-alumina catalyst in a semi-batch reactor

Abstract

Butene isomers ( C 4 ) are obtained in the refinery as by-products of the steam cracking of naphtha and light gas oil. The C 4 isomers contain a large fraction of butadiene. Butadiene is separated from this fraction by extractive distillation to produce a raffinate stream. However, the raffinate stream contains traces of butadiene (up to approximately 1%). For this stream to be used for isooctane production via the dimerization of isobutene and the hydrogenation of isooctene in a catalytic distillation column, the butadiene present in this stream should be removed, as it would otherwise poison the dimerization catalyst. The butadiene present in this stream may be removed by selective hydrogenation. This paper describes a kinetic study of the liquid-phase selective hydrogenation of 1,3-butadiene present in a mixture with isobutene using a Pd / α - Al 2 O 3 catalyst in a semi-batch reactor. Experimental results revealed that Pd / α - Al 2 O 3 was highly selective for the hydrogenation of butadiene in the presence of isobutene. The catalyst did not show any appreciable deactivation. Hydrogenation of butadiene produced 1- and 2-butenes and n -butane. A very detailed reactor model, incorporating internal diffusion inside the catalyst particles was developed to interpret the experimental results. A kinetic model for the selective hydrogenation on the catalyst was developed by using simplified versions of the Langmuir–Hinshelwood mechanism. The estimated model parameters described the experimental data accurately. The hydrogenation reaction was found to be severely limited by the diffusion rate of hydrogen in the catalyst particle.