Patent ID: 7638676
Filing Date: 2009-12-29
Classification: C07C,C10G

Abstract:
1. A process for isomerizing a feedstock comprising paraffins having between 5 and 7 carbon atoms wherein at least about 15 mass-percent of the feedstock is linear paraffin to provide an isomerate comprising: a. isomerizing a feedstock under isomerization conditions including the presence of isomerization catalyst to provide an isomerization effluent containing linear paraffins including normal hexane 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, a higher boiling fraction containing normal hexane and methylpentanes, and a bottoms stream containing normal hexane and heavies, wherein the higher boiling fraction contains less than about 75 mass percent of the normal hexane subjected to distillation in this step b, and the bottoms stream contains at least about 25 mass percent of the normal hexane subjected to distillation in this step b, c. contacting at least a portion of the bottoms stream 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 of the bottoms stream that has a reduced concentration of normal hexane, and to provide across the membrane at a permeate-side, a permeate fraction having an increased concentration of normal hexane, said permeate fraction containing at least about 50 mass-percent of the normal hexane contained in the bottoms stream contacted with the membrane, wherein the sieving membrane has a C d. passing at least a portion of the permeate fraction of step c to step a.