Patent ID: 7638675
Filing Date: 2009-12-29
Classification: C07C

Abstract:
1. A process for isomerizing a normal butane-containing isomerization feed containing at least 50 mass-% normal butane to provide an isomerate comprising isobutane comprising: (a) isomerizing the isomerization feed under isomerization conditions including the presence of isomerization catalyst to provide an isomerization effluent containing normal butane but in a concentration less than that in the feedstock; (b) distilling at least a portion of the isomerization effluent to provide a lower boiling fraction containing isobutane and lighter paraffins wherein at least 80 mass-% of the lower boiling fraction is isobutane and a higher boiling, normal butane-containing fraction containing normal butane and at least 10 mass-% isobutane; (c) contacting at least a portion of the normal butane-containing fraction from step (b) with a retentate-side of a selectively permeable sieving membrane under conditions including sufficient membrane surface area and pressure differential across the membrane to provide a retentate fraction containing at least 80 mass-% isobutane, and to provide across the membrane at a permeate-side, a permeate fraction having an increased concentration of normal butane, wherein the sieving membrane has a C (d) withdrawing from step (c) the retentate fraction; (e) recycling at least a portion of the permeate fraction of step (c) to step (a) as a portion of the isomerization feed.