Method for the removal of polymer from a purge medium in a monoolefin adsorption - desorption separation process

In a process for the separation of hydrocarbons in a vapor feed stream containing straight-chain and branched-chain monoolefin having from four to six carbon atoms inclusive comprising:

• as an adsorption step,
• passing said vapor feed stream into one end of an adsorber containing molecular sieve having a pore diameter of about 5 Angstroms and having adsorbed thereon a straight-chain paraffin hydrocarbon;
• and
• obtaining from the other end of said adsorber a first effluent fluid stream exiting in vapor phase comprising branched-chain monoolefin, branched-chain polyolefin, and straight-chain paraffin hydrocarbon;
• as a copurge step,
• passing a first vapor purge stream containing straight-chain paraffin hydrocarbon into said one end of said adsorber;
• and
• obtaining from said other end of said adsorber a second effluent fluid stream exiting in vapor phase comprising branched-chain monoolefin, branched-chain polyolefin, and straight-chain paraffin hydrocarbon;
• as a countercurrent purge step,
• passing a second vapor purge stream containing a straight-chain paraffin hydrocarbon into said other end of said adsorber;
• and
• obtaining from said one end of said adsorber a third effluent fluid stream exiting in vapor phase comprising straight-chain monoolefin, branched-chain polyolefin, and straight-chain paraffin hydrocarbon;
• wherein the partial pressure of the straight-chain paraffin hydrocarbon content of said first and second vapor purge streams is greater than the partial pressure of the straight-chain monoolefin content of the vapor feed stream and wherein said molecular sieve is partially loaded with straight-chain paraffin hydrocarbon during all of said adsorption, copurge and countercurrent purge steps;
• and
• separating said branched-chain monoolefin from said branched-chain polyolefin and said straight-chain paraffin hydrocarbon in said first and second effluent fluid streams, said separation providing a fourth effluent fluid stream comprising branched-chain polyolefin and straight-chain paraffin hydrocarbon;
• separating said said straight-chain monoolefin from said branched-chain polyolefin and said straight-chain paraffin hydrocarbon in said third effluent fluid stream, said separation providing a fifth effluent fluid stream comprising branched-chain polyolefin and straight-chain paraffin hydrocarbon;
• the improvement in which comprises:
• (a) recycling said fifth effluent fluid stream comprising branched-chain polyolefin and straight-chain paraffin hydrocarbon for use in said first and second purge streams without separation of said branched-chain polyolefin from said straight-chain paraffin hydrocarbon in said fifth effluent fluid stream;
• (b) introducing at least a portion of said fourth effluent fluid stream into a separation unit for separating said branched-chain polyolefin from said straight-chain paraffin hydrocarbon and obtaining from said separation unit a sixth effluent fluid stream comprising straight-chain paraffin hydrocarbon and a seventh effluent fluid stream comprising branched-chain polyolefin;
• and
• (c) recycling said sixth effluent fluid stream comprising straight-chain paraffin hydrocarbon for use in said first and second purge streams.