A process for the production of propylene from the metathesis of ethylene and 2-butene is disclosed wherein a mixed C.sub.4 stream is first treated to enrich and separate the 2-butene from 1-butene and isobutene by isomerization of 1-butene and concurrent fractional distillation of the 2-butene and isobutene to provide the 2-butene feed the metathesis with ethylene. In addition the mixed C.sub.4 stream may be treated to remove mercaptans and dienes prior to 2-butene enrichment.