Hydrogen purification using a SAPO-34 membrane

A SAPO-34 membrane separated CO2/H2 and H2/CH4 mixtures at feed pressures up to 1.7 MPa. Strong CO2 adsorption inhibited H2 adsorption and decreased H2 permeances significantly, especially at low temperatures, so that CO2 preferentially permeated and CO2/H2 selectivities were higher at low temperatures. At 253 K, CO2/H2 separation selectivities were greater than 100 with CO2 permeances of 3 × 10−8 mol m−2 s−1 Pa−1. The CO2/H2 separation exceeded the upper bounds (selectivity–permeability plot) for polymer membranes. The SAPO-34 membrane separated H2 from CH4 because CH4 is close to the SAPO-34 pore size and has a lower diffusivity than H2. The H2/CH4 separation selectivity had a small maximum with temperature, and decreased slightly with feed pressure and CH4 feed concentration.