Adsorption process

An improved process for using three molecular sieve adsorbent beds to effect the resolution of a continuous flow of a vapor-phase hydrocarbon feed mixture containing normal paraffins and non-normal paraffin hydrocarbons into an adsorbate product fraction comprising normal paraffins and a raffinate product fraction comprising non-normal paraffin hydrocarbons, which process comprises repeated sequential performance of the following steps:

• step one, in which
• the feed mixture is passed through a first adsorbent bed,
• effluent is withdrawn from the first bed and passed through a second adsorbent bed
• a continuous flow of eluent is passed through a third adsorbent bed,
• adsorbate product is withdrawn as an effluent from the third bed, and
• raffinate product is withdrawn as an effluent from the second bed;
• step two, in which
• the feed mixture is passed through the second bed,
• the eluent flow is divided into a desorption eluent stream, which contains between 50 and 95 volume percent of the eluent flow, and a purge eluent stream, which contains between 5 and 50 volume percent of the eluent flow,
• the purge eluent stream is passed through the first bed,
• the desorption eluent stream is passed through the third bed,
• effluent is withdrawn from the first bed and is passed through the second bed,
• adsorbate product is withdrawn as effluent from the third bed, and
• raffinate product is withdrawn as effluent from the second bed;
• step three, in which
• the feed mixture is passed through the second bed,
• effluent is withdrawn from the second bed and passed through the third bed,
• the eluent flow is passed through the first bed,
• adsorbate product is withdrawn as an effluent from the first bed, and
• raffinate product is withdrawn as an effluent from the third bed;
• step four, in which
• the feed mixture is passed through the third bed,
• the eluent flow is divided into a desorption eluent stream, which contains between 50 and 95 volume percent of the eluent flow, and a purge eluent stream, which contains between 5 and 50 volume percent of the eluent flow,
• the purge eluent stream is passed through the second bed,
• the desorption eluent stream is passed through the first bed,
• effluent is withdrawn from the second bed and is passed through the third bed,
• adsorbate product is withdrawn as effluent from the first bed, and
• raffinate product is withdrawn as effluent from the third bed;
• step five, in which
• the feed mixture is passed through the third bed,
• effluent is withdrawn from the third bed and passed through the first bed,
• the eluent flow is passed through the second bed,
• adsorbate product is withdrawn as an effluent from the second bed, and
• raffinate product is withdrawn as an effluent from the first bed;
• and
• step six, in which
• the feed mixture is passed through the first bed,
• the eluent flow is divided into a desorption eluent stream, which contains between 50 and 95 volume percent of the eluent flow, and a purge eluent stream, which contains between 5 and 50 volume percent of the eluent flow,
• the purge eluent stream is passed through the third bed,
• the desorption eluent stream is passed through the second bed,
• effluent is withdrawn from the third bed and is passed through the first bed,
• adsorbate product is withdrawn as effluent from the second bed, and
• raffinate product is withdrawn as effluent from the first bed.