Propylene oxide recovery from propylene by extractive distillation with an alcohol-ketone-hydrocarbon solvent

Claim 2

A process for continuously separating propylene oxide and propylene, each in a high state of purity, from a crude propylene oxide obtained by the catalytic epoxidation of propylene with an organic hydroperoxide and containing said propylene oxide in admixture with propylene, water, and organic impurities comprising the hydrocarbon, alcohol, and ketone corresponding to said organic hydroperoxide, consisting essentially of a. extractively distilling said crude propylene oxide in a first extractive distillation zone by the addition of an extractive solvent mixture as a separate stream, obtained originally from within the system, under controlled extractive distillation conditions resulting in the formation of a vapor overhead product comprising only part of said propylene and water while willfully retaining a substantial part of said propylene in the liquid bottom product; b. extractively distilling the liquid bottom product from said first extractive distillation zone in a second extractive distillation zone by the addition to said second zone of an additional quantity of said extractive solvent mixture as a separate stream, likewise originally obtained from within the system, separating a vapor overhead product comprising the remainder of said propylene and water from a liquid bottom product comprising propylene oxide, said solvent mixture, and organic impurities; c. fractionating said second extractive distillation zone bottom product in a separate fractionating zone, thereby separating a vapor overhead comPrising substantially pure propylene oxide from a liquid fraction comprising said organic impurities; and d. passing at least a part of said liquid fraction from said fractionating zone to said first and second extractive distillation zones to be used therein as said solvent mixture obtained from within the system.

Claim 3

The process in accordance with claim 3 wherein said organic hydroperoxide is an aralkyl hydroperoxide.

Claim 4

The process in accordance with claim 3 wherein said organic hydroperoxide is ethylbenzene hydroperoxide.

Claim 5

The process in accordance with claim 3 wherein the temperature within reboilers of said extractive distillation and fractionating zones may be as high as 230* C.

Claim 6

The process in accordance with claim 3 wherein a progressively decreasing pressure range is maintained in said extractive distillation and fractionating zones in the direction of flow.

Claim 7

The process in accordance with claim 3 wherein the temperature maintained at the top stages of the rectifying sections of the first and second extractive distillation zones are about 60* to about 116* and about 49* to about 94* C., respectively.

Claim 8

The process in accordance with claim 3 wherein said extractive solvent mixture employed in said extractive distillation zones is obtained from within the system by flashing said liquid fraction from said fractionating zone, and thereafter condensing the overhead vapor product from said flash.

Claim 9

The process in accordance with claim 3 wherein said extractive solvent mixture is added to the top stage of each of said first and second extractive distillation zones.