HYDROCRACKING WITH SEPARATION OF RECYCLE HYDROGEN BY MEMBRANE

摘要

Efficient utilization of hydrogen in a hydrocracking system is obtained by recovering in a first gas-liquid separation zone hydrogen by gas-liquid separation of hydrocrackate at a pressure of at least about 75 percent of the pressure in the hydrocracking zone, and recovering in a second gas-liquid separation zone hydrogen from the separated liquid phase from the first gas-liquid separation zone, said second gas-liquid separation zone being at a pressure less than 75 percent of the pressure in the first gas-liquid separation zone and at conditions sufficient to provide a separated vapor phase containing at least about 50 volume percent of hydrogen and having a hydrogen partial pressure of at least about 20 atmospheres. At least a portion of the separated vapor phase from the second gas-liquid separation zone is contacted with the feed side of a polymeric membrane exhibiting a high selectivity to the permeation of hydrogen as compared to the permeation of methane. The opposite side, i.e., permeate side, of the membrane is maintained at a pressure sufficiently below the pressure on the feed side of the membrane such that the ratio of the total pressure on the feed side to total pressure on the permeate side of the membrane is at least about 3:1 to permeate hydrogen to the permeate side of the membrane and provide a hydrogen permeate having a concentration of hydrogen greater than the concentration of hydrogen in the separated vapor phase contacting the membrane. At least a portion of the hydrogen permeate is recycled to the hydrocracking zone. Thus, the second gas-liquid separation zone co-acts with the polymeric membrane separation to provide a highly useable, recovered hydrogen stream in the hydrocracking system.