Recovery of volatile organic compounds from gas streams

A method for recovering one or more volatile compounds contained in admixture with one or more low-boiling gases which comprises:

• (a) compressing a gaseous mixture comprising said one or more volatile organic compounds and one or more low-boiling gases to a pressure of at least 30 psia;
• and cooling, partially condensing, and separating the resulting compressed mixture at a first temperature to yield a first vapor and a first condensate stream;
• (b) further cooling said first vapor stream to a second temperature to yield a second stream containing mixed vapor and condensate, and separating the mixed stream into a second vapor and a second condensate stream having a first initial freezing point, said second vapor stream comprising said one or more low-boiling gases having a substantially reduced concentration of said volatile organic compounds;
• and
• (c) cooling said second vapor stream to a third temperature by indirect heat exchange with a first cold recirculating liquid which is cooled in turn by indirect heat exchange with a first stream of vaporizing liquid nitrogen to yield a third mixed stream containing vapor and condensate, and separating the third mixed stream into a third vapor and a third condensate stream having a second initial freezing point, said third vapor stream comprising said one or more low-boiling gases substantially free of residual volatile organic compounds;
• wherein said second temperature is controlled at a temperature above said first initial freezing point of said second condensate stream and said third temperature is controlled at a temperature of -40.degree. to -100.degree. F. which is above said second initial freezing point of said third condensate stream, whereby operation of steps (a), (b), and (c) at a pressure of at least 30 psia allows condensation at higher temperatures than those possible at a pressure below 30 psia, thereby reducing refrigeration requirements for said cooling and the probability of freezing in said second and third condensate streams.