Patent ID: 7485768

Claim:
A continuous process for upgrading a naphtha boiling range feedstock containing at least isopentane, normal pentane and hydrocarbons having 6 carbon atoms to provide a gasoline fraction stream having a reduced vapor pressure and a pentane fraction stream having reduced isopentane content comprising: a. fractionating by distillation a stream which is at least a portion of the feedstock to provide (i) higher boiling fraction stream containing normal pentane and hydrocarbon having 6 carbons atoms and a reduce mole ratio of isopentane to normal pentane as compared to that of the feedstock, and (ii) lower boiling fraction steam containing isopentane and up to about 15 mole percent normal pentane based on total pentane in said fraction; b. subjecting lower boiling fraction stream to isomerization conditions to provide an isomerate stream containing between about 20 and 40 mole percent normal pentane based upon total pentanes and hydrocarbon by-products containing 4 and fewer carbon atoms; c. recycling at least a portion of the isomerate stream to step (a); d. removing hydrocarbons having up to 4 carbon atoms from said isomerate stream; and e. fractionating the higher boiling fraction stream by distillation hydrocarbons having 6 carbon atoms contained in the feed stream from normal pentane to provide; i. normal pentane-containing lower boiling fraction stream containing at least about 93 mole percent of the normal pentane provided for the distillation, and ii. higher boiling fraction stream containing hydrocarbons having 6 carbon atoms and a RVP of up to about 50 kPa, wherein said lower boiling fraction stream of step (a) contains at least about 80 mole percent of the isopentane contained in the aggregate of the feed stream and the recycle stream of step (c) and step (a) has a Refining Efficiency Index of at least 75.