Process for fractionation of a gaseous mixture employing side stream withdrawal, separation, and recycle

Claim 2

A process for fractionating a gaseous mixture by distillation in a fractionating column wherein, during distillation, at least two components of the gaseous mixture are present in a sufficient concentration to form a substantially azeotropic mixture in the absence of a preventative step, said process comprising withdrawing a side stream fluid from the column during fractionation, and separating said side stream fluid so as to remove preferentially at least a portion of one of the components of the substantially azeotropic mixture and recycling resultant depleted side stream to said fractionating column at a point below the point of withdrawal of said side stream.

Claim 3

A process according to claim 1, wherein said side stream fluid is withdrawn, height-wise, from approximately the middle of the column.

Claim 4

A process according to claim 1, wherein said separating of said side stream is conducted by a physical or chemical scrubbing step.

Claim 5

A process according to claim 1, wherein said separating of said side fluid is conducted by diffusion on semipermeable membranes.

Claim 6

A process according to claim 1, wherein the gaseous mixture to be fractionated contains an acid gas and a hydrocarbon.

Claim 7

A process according to claim 5, wherein the acid gas proportion of the depleted side stream fluid is at most 5%.

Claim 8

A process for fractionating a gaseous mixture by distillation in a fractionating column, said gaseous mixture consisting essentially of about 5-20% methane, about 50-90% carbon dioxide, and about 2-10% ethane, wherein, during distillation, CO 2 is present in the fractionating column in a sufficient concentration to freeze out as a solid under distillation conditions in the column in the absence of a preventive step, said process comprising fractionating the mixture to obtain a methane-enriched overhead and a CO 2 enriched bottoms fraction, withdrawing a sidestream liquid from the column during fractionation, said sidestream liquid being withdrawn at a point where ethane is enriched in the liquid and where CO 2 is present in a lower concentration than in the bottoms fraction, and separating said sidestream liquid so as to remove preferentially the CO 2 and recycling resultant CO 2 -depleted stream further enriched in ethane to said fractionating column, said depleted stream having a higher dissolving capacity for CO 2 than the stream withdrawn.

Claim 9

A process for fractionating a gaseous mixture by distillation in a fractionating column, said gaseous mixture consisting essentially of about 5-20% methane, about 50-90% carbon dioxide, and about 2-10% ethane, wherein, during distillation, CO 2 is present in the fractionating column in a sufficient concentration to freeze out as a solid under distillation conditions in the column in the absence of a preventive step, said process comprising fractionating the mixture to obtain a methane-enriched overhead and a CO 2 enriched bottoms fraction, withdrawing a sidestream liquid from the column during fractionation, said sidestream liquid being withdrawn at a point where ethane is enriched in the liquid and where CO 2 is present in a lower concentration than in the bottoms fraction, and separating said sidestream liquid so as to remove preferentially the CO 2 and recycling resultant CO 2 -depleted stream further enriched in ethane to said fractionating column, said depleted stream having a higher dissolving capacity for CO 2 than the stream withdrawn.

Claim 10

A process according to claim 7, wherein said separating of said sidestream is conducted by diffusion on semipermeable membranes.

Claim 11

A process according to claim 7, wherein the gaseous mixture to be fractionated is a CO 2 -containing motive gas recycled from tertiary oil recovery, and the gas enriched in CO 2 recovered from the bottom of said fractionating column is employed as motive gas in said tertiary oil recovery.

Claim 12

A process according to claim 9, wherein said separating of said sidestream is conducted by diffusion on semipermeable membranes.

Claim 13

A process according to claim 9, wherein the stream enriched in CO 2 recovered as bottoms from said fractionating column, is combined with another stream enriched in CO 2 , the latter being removed from said side stream fluid.

Claim 14

A process according to claim 7, wherein the enriched ethane stream is recycled into the column above the point of withdrawal.

Claim 15

A process according to claim 12, wherein the withdrawn sidestream is separated by semi-permeable membranes to remove both carbon dioxide and methane selectively from the sidestream, thereby obtaining an enriched stream of ethane which is recycled into the column.

Claim 16

A process according to claim 7, wherein the sidestream is withdrawn from the column at the zone of the highest ethane concentration therein.

Claim 17

A process according to claim 14, wherein the enriched ethane stream is recycled into the column above the point of withdrawal.