Laboratory tests of a membrane for H2 /CH4 separation gave a permeate composition of 80 percent H, and a residue of 42 percent H, when the feed had 50 percent H2 and the feed and permeate absolute pressures were 100 and 151bf /in.2 . The permeate flow was 20 percent of the feed flow.
(a) What is the membrane selectivity?
(b) About what permeate composition would have been obtained if a vacuum had been used on the downstream side?