Dual-stage vacuum pressure swing adsorption for green hydrogen recovery from natural gas grids

Purification of green hydrogen (GH) from natural gas grids (NGG) can be expensive and challenging through a single-step Pressure Swing Adsorption (PSA) process due to the low H-2 concentration in the grid (<20 % v/v). Herein, we report for the first time the design of a dual-stage vacuum pressure swing adsorption process (DS-VPSA) to purify H-2 blended in NGG with a synergy action of two types of adsorbents: a Carbon Molecular Sieve 3K-172 (CMS) in stage 1 and zeolite 13X in stage 2. In Stage 1, the CMS kinetically separates H-2 from CH4, pre-concentrating H-2 from 20 % to over 50-60 % (v/v), followed by Stage 2, where a thermodynamic separation with zeolite 13X achieves a final product with a high H-2 purity content (>99 % v/v). A mathematical model is developed in Aspen adsorption, where numerical simulations are performed to establish the best operating conditions of the global DS-VPSA. A parametric study is also conducted to optimize performance parameters such as recovery, purity, productivity, and specific energy. The results indicate that it is possible to achieve a final H-2 product with a purity of 99.97 % (fuel cell grade), a recovery of 67 %, and productivity of 1.60x10(-2) kg(H2)/kg(ads)/hr, and a total specific energy consumption of 10.06 MJ/kg(H2), which is a significant achievement reported so far.