light straight run naphtha gas oil condensate light raffinates light reformate light hydrocarbons field butanes and straight run distillates having distillation end points of about 77 u00b0 c 170 u00b0 f and containing substantial quantities of c 4 c 6 paraffins preferably the effluent from the isomerization zone will contain a substantial amount of c 4 hydrocarbons c 4 hydrocarbons concentration of at least 3 mol are desired and c 4 hydrocarbon concentration in the range of from 5 to 20 mol are preferred the c 4 hydrocarbons in the effluent may be present in the feed entering the isomerization zone or produced by cracking reactions within the isomerization zone the feed stream may also contain low concentrations of unsaturated hydrocarbons and hydrocarbons having more than 6 carbon atoms the concentration of these materials should be limited to 10 wt for unsaturated compounds and 20 wt for heavier hydrocarbons in order to restrict hydrogen consumption and cracking reactions hydrogen is admixed with the feed to the isomerization zone although no net hydrogen is consumed in the isomerization reaction the isomerization zone will have a net consumption of hydrogen often referred to as the stoichiometric hydrogen requirement which is associated with a number of side reactions that occur these side reactions include saturation of olefins and any remaining aromatics cracking and disproportionation hydrogen in excess of the stoichiometric amounts for the side reactions is maintained in the isomerization zone to provide good stability and conversion by compensating for variations in feedstream compositions that alter the stoichiometric hydrogen requirements and to prolong catalyst life by suppressing the side reactions side reactions left unchecked reduce conversion and lead to the formation of carbonaceous compounds i e coke that foul the catalyst it has been found to be advantageous to minimize the amount.