Sequential hydrogen production system from formic acid and H2/CO2 separation under high-pressure conditions

Abstract

Hydrogen (H₂) production from formic acid (FA) is highly attractive as a sustainable energy source from the interconversion between CO₂ and FA. Dehydrogenation of FA at high pressures has advantages over a reaction at atmospheric conditions for the separation of H₂ and CO₂ due to the reaction and the volumetric energy density of H₂. We demonstrated the continuous production of high-pressure H₂ by catalytic decomposition of FA, and subsequent separation of H₂ and CO₂ from FA decomposition gas (H₂ : CO₂ = 1 : 1) using the phase change phenomenon at low temperatures while maintaining high pressure. An iridium aqua complex coordinated with a bidentate pyridyl-imidazoline ligand catalyzed the dehydrogenation of FA with high efficiency at a pressure as high as 153 MPa. The Ir catalyst was found to be stable under continuous addition of neat FA at high pressures. The generation time and rate of high-pressure H₂ were controlled by feeding neat FA to the aqueous reaction system. Using our combined system, more than 99 mol% of H₂ (96 mol% of purity) and 94 mol% of CO₂ (99 mol% of purity) were separately obtained from FA as a gas and liquid, respectively, under the high-pressure conditions without any mechanical compression.