Extraction of natural hydrogen from a natural gas probe by LaNi4.8Al0.2 metal hydride

Abstract

Natural hydrogen can be considered as a low-carbon energy resource. Impurities are frequently present in natural hydrogen and developed commercial hydrogen purification technologies are not adapted to extract hydrogen from low-grade feedstocks. Metal hydride selectively absorb hydrogen from gas mixtures and could be used for efficient purification of hydrogen, including its extraction from low-grade mixtures, including natural gas/hydrogen blends. We present results of reactor scale experimental investigations of natural hydrogen extraction from a probe of concentrated natural gas - NG (4 % of H₂) from of the Kovyktinskoye gas and condensate field using a metal hydride reactor with 1 kg of LaNi_4.8Al_0.2. The metal hydride bed was easily activated in pure hydrogen, reaching the full capacity of 150 stL (1.33 wt%) in 3 cycles. Metal hydride absorbed hydrogen from the NG probe fed into reactor at 2 MPa. Purity of desorbed natural hydrogen was 98.6–99.0 %. Nevertheless, the probe contained different sulfur species that are poisonous for metal hydrides. Exposure to the NG sample has led to poisoning of the MH bed in 1 cycle, capacity fell to 36 stL and desorption pressure decreased by six times. We were able to reactivate the MH bed by pure H₂ to 100 stL capacity in 5 cycles and to almost full capacity in 10+ cycles. We conclude, that the metal hydride purification is suitable for hydrogen extraction, though sulfur has to be removed from the feed for concentrations less than 1 ppm and preferably below a few ppb.