Patent ID: 7638674

Claim:
A process for isomerizing a feedstock comprising paraffins having between 5 and 6 carbon atoms wherein at least 15 mass-percent of the feedstock is linear paraffin to provide an isomerate comprising isomerized paraffins comprising: a. isomerizing the feedstock under isomerization conditions including the presence of isomerization catalyst to provide an isomerization effluent containing linear paraffins 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 dimethylbutanes and lighter paraffins and a higher boiling normal hexane-containing fraction containing normal hexane, methylpentanes, dimethylbutanes and methylcyclopentane, c. contacting at least a portion of the normal hexane-containing fraction from step b with a retentate-side of a selectively permeable sieving membrane under conditions including sufficient sieving membrane to provide a retentate fraction of the side stream that has an increased concentration of methylcyclopentane and dimethylbutanes, and to provide across the sieving membrane at a permeate-side, a permeate fraction having an increased concentration of normal hexane and methyl pentanes, said permeate fraction containing at least 75 mass-percent of the normal hexane contained in the normal hexane-containing fraction contacted with the sieving membrane wherein the sieving membrane has a C 6 Permeate Flow Index of at least 0.01 and a C 6 Permeate Flow Ratio of at least 1.25:1, d. withdrawing from step c the retentate fraction; and e. recycling at least a portion of the permeate fraction of step (c) to step (a).