Dehydrocyclodimerization process

A process for the recovery of hydrogen from the effluent stream of a hydrogen-producing hydrocarbon conversion process which comprises the steps of:

• (a) separating a reaction zone effluent stream, which comprises hydrogen and a mixture of C.sub.1 -C.sub.7 hydrocarbons, into a vapor phase first process stream, which comprises hydrogen and C.sub.1 -C.sub.3 hydrocarbons, and a condensate stream, which comprises C.sub.6 -plus hydrocarbons, in a first vapor-liquid separation zone;
• (b) passing the condensate stream into a fractionation zone in which a C.sub.6 -plus product of the hydrocarbon conversion process is recovered;
• (c) compressing the first process stream to a pressure above about 300 psig;
• (d) passing the first process stream into a membrane separation zone in which the first process stream is contacted with semi-permeable membrane which selectively allows the permeation of hydrogen and thereby producing a hydrogen-rich product stream which is removed from the process and a vapor phase second process stream which comprises C.sub.1 -C.sub.3 hydrocarbons;
• (d) forming a vapor phase third process stream, which comprises methane, and a liquid phase fourth process stream, which comprises ethane and propane by partially condensing the second process stream by indirect heat exchange against a cooling medium followed by vapor-liquid separation in a second vapor-liquid separation zone at a pressure above about 300 psig;
• (e) flashing the fourth process stream to a substantially lower pressure and thereby forming a vapor phase sixth process stream, which comprises methane, and a liquid phase fifth process stream, which comprises propane, with the fourth and fifth process streams being substantially cooler than the second process stream;
• (f) employing the fifth process stream as at least a part of the previously referred to coolant medium used to partially condense the second process stream;
• and
• (g) withdrawing the fifth process stream and the sixth process stream from the process.

A process for the separation of the effluent stream of a dehydrocyclodimerization process which comprises the steps of:

• (a) partially condensing a vapor phase dehydrocyclodimerization reaction zone effluent stream, which comprises hydrogen, methane, ethane, propane, butane, benzene, toluene and xylene, and separating the resultant fluids in a first vapor-liquid separation zone into a vapor phase first process stream, which comprises hydrogen and C.sub.1 -C.sub.7 hydrocarbons, and a condensate stream which comprises benzene, toluene and xylenes;
• (b) passing the condensate stream into a fractionation zone, and recovering benzene, toluene and xylenes from the fractionation zone;
• (c) compressing the first process stream to a pressure above about 430 psig;
• (d) removing benzene from the first process stream in an absorption zone;
• (e) passing the first process stream into a membrane separation zone in which the first process stream is contacted with a hydrogen selective permeation membrane under membrane separation conditions, and thereby producing a hydrogen-rich effluent stream which is removed from the process and a vapor phase second process stream, which comprises methane, ethane and propane;
• (f) forming a vapor phase third process stream comprising methane and a liquid phase fourth process stream, comprising ethane and propane, by partially condensing the second process stream by indirect heat exchange against a coolant medium followed by vapor-liquid separation in a second separation zone operated at a pressure above about 400 psig;
• (g) flashing the fourth process stream to substantially lower pressure and thereby forming a vapor phase sixth process stream comprising methane, and a liquid phase fifth process stream, which comprises propane, with the fifth and sixth process streams being substantially cooler than the second process stream;
• and
• (h) employing the fifth process stream as at least a part of the previously referred to coolant medium used to partially condense the second process stream.