Hydrogen recovery from off-gases with nitrogen-rich impurity by pressure swing adsorption using CaX and 5A zeolites

Many studies in the literature about pressure swing adsorption (PSA) hydrogen purification deal with the recovery of hydrogen from off-gases where nitrogen concentration in the feed mixture is usually below 5 %. Practical examples of hydrogen-containing off-gases with higher nitrogen concentration are total hydrocarbon reforming off-gas, and coke oven gas. In this work, the separation performance of CaX and 5A zeolites in the hydrogen recovery from these gases by PSA is compared using a simulation tool called PSASIM. Reciprocal diffusion time constants and adsorption isotherms of nitrogen, methane and carbon monoxide in CaX zeolite measured experimentally are included. Simulations show that, with a feed pressure of 3 bar, CaX yields higher hydrogen recovery than 5A zeolite for the same product purity (above 99.7 %) with both feed gases. CaX removes nitrogen better than 5A zeolite, although it is worse for removing carbon monoxide and methane. The hydrogen recovery can be increased notably (from about 65 % to above 90 %) by including a rinse step in the PSA cycle while maintaining high hydrogen product purity.