Process for separating normal paraffins from hydrocarbons mixtures

Claim 1

In an isobaric process for separating normal paraffins from non-normal hydrocarbons in a gas oil-containing vapor feedstream by (1) the selective adsorption of normal paraffins by passage of said feedstream through a molecular sieve adsorbent bed, (2) cocurrent purge with n-hexane to sweep out void space vapor containing a high concentration of non-normal hydrocarbons from the effluent end of the bed, (3) countercurrent purge with n-hexane to desorb normal paraffin adsorbate from the bed, (4) recovery of n-hexane from said separated normal paraffins and non-normal hydrocarbons, and (5) recycling of said n-hexane for purging and desorbing of said bed and to dilute the gas oil-containing feedstream for adsorption at less than 700° F., the improvement comprising diluting said gas oil-containing feedstream with cocurrent purge effluent as a source of n-hexane used to enable said selective adsorption to be carried out at less than 700° F. without capillary condensation, wherein the initial portion of the cocurrent purge effluent containing essentially non-normal hydrocarbon is not employed for said feedstock dilution, and the remaining portion of said cocurrent purge effluent comprising about the last 10% to 80% of the total cocurrent purge effluent is used as a source of n-hexane for said feedstream dilution purposes, whereby the equipment size and energy consumption for processing of said recycle n-hexane are reduced and the utilization of said adsorbent and the efficiency of the adsorption process can be enhanced.