Optimization of pressure‐vacuum swing adsorption processes for nitrogen rejection from natural gas streams using a nitrogen selective metal organic framework

A vanadium(II/III) metal–organic framework (MOF), V 2 Cl 2.8 (btdd), that is selective to N 2 over CH 4 was recently discovered. Process optimizations were performed to determine the performance of this MOF to reach the pipeline transport purity of 96 mol% CH 4 . Two cycles were considered: the basic three‐step cycle and the Skarstrom cycle. First, the three‐step cycle was considered with a wide range of operating conditions. Three inlet compositions (55/45, 80/20, and 92/8 mol% CH 4 /N 2 ), three process temperatures (30, 40, and 50°C) and a range of adsorption pressures (100–500 kPa) were considered. A detailed process model in tandem with machine learning‐aided optimization was employed to determine the optimal set of operating conditions. The three‐step cycle was unable to meet the 96 mol% CH 4 purity requirement in most cases studied. However, the Skarstrom cycle was able to meet the 96 mol% CH 4 purity requirement in all cases studied. The maximum recovery, at a purity of 96 mol%, was at 84.2% for the Skarstrom cycle with a methane feed composition of 80 mol% at 50°C and an adsorption pressure of 100 kPa. For the Skarstrom cycle, at a feed temperature of 50°C, an adsorption pressure of 100 kPa and a feed methane composition of 92 mol%, the productivity could be as high as 21.18 tonnes per day CH 4 m −3 at a recovery of 73%. The achievable recovery‐productivity values were comparable to a carbon molecular sieve process reported in the literature at similar operating conditions.