Method and system for light olefin separation
A process is provided for separation of light olefins and paraffins and particular for the separation of propylene and propane comprising sending at least one olefin/paraffin stream to a distillation column and a membrane unit to produce an olefin stream comprising at least 92 mol % olefin. In an embodiment of the invention where the membrane unit is placed downstream from the column which can produce propylene streams at polymer grade of over 99.5 mol % propylene.
1. A process for separation of olefin and paraffin mixtures comprising sending at least one hydrocarbon stream to a distillation column to produce an upper stream more concentrated in olefin than said at least one hydrocarbon stream and a bottom stream more concentrated in paraffin than the at least one hydrocarbon stream and sending a portion of said upper stream in vapor phase comprising 72-90% olefin to a membrane unit to separate said upper stream into a permeate stream in vapor phase comprising at least 99 mol % olefin and a retentate stream in vapor phase comprising paraffin, wherein the portion of the upper stream is recycled to the distillation column after condensation, wherein said membrane unit comprises a plurality of membranes which are facilitated transport membranes comprising a solid nonporous polymer matrix layer on top of a nanoporous support membrane.
2. The process of claim 1 wherein said facilitated transport membranes comprise metal ions incorporated into said nonporous polymer matrix layer and nanopores on a skin layer surface of said nanoporous support membrane.
3. The process of claim 1 wherein said at least one hydrocarbon stream comprise at least two streams comprising different concentrations of olefin.
4. The process of claim 1 wherein said permeate stream comprises about 99.8 mol % olefin.
5. The process of claim 1 wherein at least a portion of said retentate stream is recycled to said distillation column to separate said retentate stream into a paraffin stream and an olefin stream.
6. The process of claim 1 wherein said hydrocarbon stream comprises C3 or C4 olefin and paraffin hydrocarbons.
7. The process of claim 1 wherein said olefin is propylene, wherein said paraffin is propane, and wherein said hydrocarbon stream comprises propylene and propane hydrocarbons.
8. The process of claim 1 wherein said olefin is ethylene, wherein said paraffin is ethane, and wherein said hydrocarbon stream comprises ethylene and ethane hydrocarbons.
9. The process of claim 1 wherein said olefin is C4 olefin, wherein said paraffin is C4 paraffin, and wherein said hydrocarbon stream comprises C4 olefin and C4 paraffin hydrocarbons.
10. The process of claim 1 wherein the upper stream contains <0.05% C4 olefins in the total olefins.
11. The process of claim 1 wherein the permeate stream is compressed and then condensed with cooling water.
12. The process of claim 5 wherein at least a portion of the retentate stream is condensed to liquid before recycling to the distillation column.
13. The process of claim 11 wherein the condensation of the upper stream not sent to the membrane is done via heat exchange with the distillation column bottom material supplying heat duty for the reboiler.
14. The process of claim 11 wherein at least a portion of the retentate stream is returned to the distillation column below the point of return of the upper stream that is not sent to the membrane.