Method and apparatus for the separation of C4 hydrocarbons from gaseous mixtures containing the same

C4 hydrocarbons are separated from a gaseous mixture containing the same and lower hydrocarbons and hydrogen, by cooling such a gaseous mixture (45) to a temperature between -60 DEG F. and +32 DEG F. until a portion of the C4 hydrocarbons is condensed. The mixture of gas and liquid C4 hydrocarbons thus produced is phase separated in a first phase separation (53), and the liquid from this first phase separation is withdrawn as C4 hydrocarbons product (69). Gas from the first phase separation (53) is further cooled(47) until substantially all of the remaining C4 hydrocarbons are condensed but not the hydrogen. The latter material is subjected to a second phase separation (75), and liquid from the second phase separation (77) is withdrawn as liquid C4 hydrocarbons product (69). Vapor from the second phase separation (75) is withdrawn and expanded isentropically in a first expansion engine (81) to produce a mixture of liquid and vapor, which is subjected to a third phase separation (85), and liquid from the third phase separation (85) is withdrawn as liquid C4 hydrocarbons product (69). A portion of vapor separated in the third phase separation (85) is expanded isentropically in a second expansion engine (137), and refrigeration from vapor from the second expansion engine (137) is recovered by indirect heat exchange (47) with the first-mentioned mixture (45). Gas separated in the third separation (85) is cooled to produce a mixture of gas and liquid, which is phase separated (103 or 123). Gas from the latter phase separation is expanded isentropically in the second expansion engine (137), and refrigeration from material from second expansion engine (137) is also recovered by indirect heat exchange (99) with gas separated in the third phase separation (85).