Relating to propylene oxide purification
View Patent ↗A method of separating impurities from impure PO, the method comprising distilling impure PO in a distillation zone to provide distillate PO of enhanced purity, wherein heat is provided to the distillation zone by a bottoms reboiler and by an intermediate reboiler, the intermediate reboiler providing heat at a lower temperature than the bottoms reboiler. A suitable distillation system is also disclosed.
1. A method of separating impurities from impure propylene oxide, the method comprising distilling impure propylene oxide in a distillation zone to provide distillate propylene oxide of enhanced purity, wherein heat is provided to the distillation zone by a bottoms reboiler and by an intermediate reboiler, the intermediate reboiler providing heat at a lower temperature than the bottoms reboiler.
2. The method of claim 1 , wherein the heat provided by the intermediate reboiler is from a heat source having a temperature in the range of from 80° C. to 180° C.
3. The method of claim 1 , wherein the heat provided by the intermediate reboiler is taken directly or indirectly from a process stream cooled as part of a process of producing propylene oxide.
4. The method of claim 3 , wherein the heat provided by the intermediate reboiler is from flash steam generated by cooling of a process stream as part of a process of producing propylene oxide.
5. The method of claim 1 , wherein the bottoms reboiler inputs heat to a bottoms region of the distillation zone and the intermediate reboiler inputs heat to an upper region of the distillation zone.
6. The method of claim 5 , wherein the upper region of the distillation zone comprises a plurality of at least 10 consecutive theoretical trays having tray temperatures that differ by at most 40° C.
7. The method of claim 6 , wherein the temperature of said plurality of trays is in the range of from 50 to 120° C.
8. The method of claim 5 , wherein the intermediate reboiler inputs heat at a reference tray of the upper region having a temperature which is at least 50° C. lower than the maximum temperature of the bottoms region, the reference tray being a lowermost one of a plurality of at least 10 consecutive theoretical trays in the upper region, said plurality of trays having tray temperatures that differ by at most 40° C.
9. The method of claim 1 , wherein the intermediate reboiler, or a combination of intermediate reboilers, assumes at least 25% of overall reboiler duty.
10. The method of claim 1 , wherein the impure propylene oxide is distilled by extractive distillation.
11. The method of claim 1 , wherein the distillate propylene oxide comprises at least 99.5% w/w propylene oxide.
12. A distillation system for separating impurities from impure propylene oxide, the system comprising:
a structure defining a distillation zone having an inlet for impure propylene oxide, a distillate outlet for purified propylene oxide, and one or more outlets for streams enriched in impurities;
a bottoms reboiler for providing heat to the distillation zone at a first temperature; and
an intermediate reboiler for providing heat to the distillation zone at a second temperature lower than the first temperature.
13. The distillation system of claim 12 wherein the distillation zone comprises: at most 15 theoretical trays between a bottoms reboiler input and an intermediate reboiler input into the distillation zone; and at least 10 theoretical trays above the intermediate reboiler input.
14. The distillation system of claim 12 , wherein the distillation zone comprises an inlet for extractive distillation solvent located above the inlet for impure propylene oxide, and a bottoms outlet for extractive distillation solvent enriched in impurities.