Constant pressure separation of normal paraffins from hydrocarbon mixtures

Claim 1

In an isobaric process for separating normal paraffins from non-normal hydrocarbons in a feed stream containing between 10 and 40 mol percent normal paraffins having 10 to 25 carbon atoms and non-normal hydrocarbons by (1) the selective adsorption of normal paraffins by passage of said feed stream 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 of said bed, the improvement comprising diverting a portion of the desorption effluent from said countercurrent purge step as a source of said n-hexane used for cocurrent purge, the quantity of said countercurrent purge effluent diverted as cocurrent purge being that necessary to achieve a desired degree of separation of said normal paraffins and non-normal hydrocarbons and comprising from about 2.5 to about 5 bed volume voids, whereby the equipment size and energy consumption for the processing of said recycle n-hexane is reduced, without need to increase the adsorbent bed size to adsorb the additional normal paraffins introduced to the bed with the desorption effluent used as cocurrent purge gas.