TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: (b) includes cooling at least a portion of the effluent stream in multiple stages and reducing the pressure of the effluent stream.The treatment comprises water washing or amine scrubbing to remove at least a part of the hydrogen sulfide from the effluent stream.The process further involves compressing the feed stream prior to passing the feed stream across the feed side.The compressing results in condensation of a liquid hydrocarbon fraction which is removed from the feed stream prior to passing the feed stream across the feed side.Preferred Apparatus: The reactor comprises a hydrotreater, hydrocracker, an isomerization unit, catalytic reformer, or hydrodealkylation unit.Preferred Hydrocarbon: The light hydrocarbon additionally includes methane, ethane, or at least a 3C hydrocarbon.The permeate stream having a hydrogen concentration of at least about 1.5 (preferably 2) times lower than the feed stream is recirculated to step b) and is subjected to further separation treatment.The residue stream has a hydrogen concentration of not more than 5 (preferably not more than 2) higher than the feed stream and is recirculated to the reactor loop without recompression.    TECHNOLOGY FOCUS - POLYMERS - Preferred Membrane: The polymeric membrane comprises silicone rubber, super-glassy polymer or a polyamide-polyether block copolymer. WIDER DISCLOSURE - A reactor apparatus containing a reactor loop, the phase separation equipment and the membrane separation unit containing a contaminant-selective membrane is also disclosed.    EXAMPLE - A computer calculation was performed to stimulate the treatment of a typical off gas stream comprising hydrogen (74.5%), methane (17.5%), ethane (6.5%) and propane (1.5%) from a phase separator of a hydrocracker process. The treatment process was carried out with no gas discharged through optional purge line such that all the stream was send to the membrane unit. The off gas stream from the phase separator had a flow rate of 50 mm scfd at 50degrees C and at a pressure of 1800 psia. The calculation was carried out to produce a total hydrocarbon removal of about 1500 lb/h. A comparative calculation was performed such that the membrane unit was unselective. The results for test/comparative were as follows: the purge in the case of test removal was about 2500 lb/h of hydrocarbons with the loss of 300 lb/h of hydrogen i.e. 40% hydrogen loss. As a result the hydrogen concentration in the recycle stream was increased from 74.5 - 75.2%. The purge in the case of comparative removal w as about 2500 lb/h hydrocarbons (methane (1302 lb/h), ethane (907 lb/h), and propane (307 lb/h)) from the loop with a concentration loss of about 700 lb/h of hydrogen.