Scale-up of SAPO-34 membranes for CO2/CH4 separation

High flux SAPO-34 membranes on porous, tubular stainless steel supports with CO2/CH4 separation selectivities greater than 200 were scaled up from 5 cm length to 25 cm (a factor of 7.5 increase in membrane area). The preparation of the 25-cm membranes required a more dilute synthesis gel and shorter crystallization times to avoid excess build-up of zeolite crystals at the bottom of the membrane tubes. These changes yielded 25-cm membranes with similar permeances and selectivities to those of the 5-cm membranes. Aluminum sources, gel compositions, and synthesis procedures were systematically investigated to lower the membrane cost, optimize the separation performance, and obtain good reproducibility. The CO2 permeances of the 25-cm membranes were approximately 5 × 10−7 mol/(m2 s Pa) at 295 K for a feed pressure of 138 kPa and a 50/50 feed.