an improved butane isomerization process which decreases the rate of catalyst deactivation is disclosed . a normal butane feed stream which contains small amounts of isobutylene is passed through a polymerization zone wherein the isobutylenes are converted into heavier hydrocarbons . the polymerization zone effluent is passed into the deisobutanizer column in which the isomerization zone effluent is separated for the recovery of the product isobutane . heavy hydrocarbons are removed as a net bottoms stream and the remaining fresh feed components become part of the normal butane recycle stream removed from the deisobutanizer as a sidecut stream .