Patent ID: 7947117

Claim:
A membrane process for the purification of hydrogen contained in a synthesis gas from steam reforming a petroleum fraction or natural gas comprising modifying a two stage water gas shift (WGS) process comprising a high temperature stage and a low temperature stage so as to obtain a synthesis gas containing less than 5000 ppm of CO, said modifying comprising eliminating the low temperature stage and passing the synthesis gas mixture from high-temperature WGS stage, containing more than 5,000 ppm of CO, into a system comprising three membrane separation units (U 1 , U 2 , U 3 ), whereby said membrane process comprises the following stages: The synthesis gas mixture to be processed ( 1 ) from the high temperature WGS stage is introduced into a first membrane separation unit (U 1 ), from which there is extracted: A first permeate ( 3 ) that consists essentially of hydrogen that is sent into a third membrane separation unit (U 3 ), after recompression, A first retentate ( 4 ) that is introduced into a second membrane separation unit (U 2 ) from which there is extracted: A second permeate ( 5 ), which, after recompression, is recycled to the inlet of the first separation unit (U 1 ) in a mixture with the flow to be processed ( 1 ), and A second retentate ( 7 ); from the third membrane separation unit, there is extracted: A third retentate ( 9 ) that is recycled to the inlet of the first membrane separation unit (U 1 ) in a mixture with said mixture to be processed ( 1 ), A third permeate ( 10 ) that comprises hydrogen with at least 98% purity and that contains at most 150 ppm of CO.