Biomass–formic acid–hydrogen conversion process: sustainable production of formic acid from biomass using greenhouse gas†

Abstract

Sustainable green hydrogen production processes and efficient hydrogen storage methods are highly sought after to advance the hydrogen economy. Recently, a biomass–formic acid–hydrogen conversion process, which combines the formic acid production process from biomass with a formic acid dehydrogenation process, has been developed to address the two critical issues in the hydrogen field. Traditionally, inorganic acid reactants have been used to increase formic acid production during biomass treatment. In this study, we utilized a greenhouse gas as a heterogeneous acid reactant to replace toxic strong acid reactants. A formic acid yield of 36.18% was achieved using lignocellulose biomass under 30 bar CO₂ pressure, with 11 wt% H₂O₂ at 170 °C for 3 h, which is comparable to the yields reported in biomass conversion studies employing sulfuric acid, highlighting the competitiveness of this greener approach. We used a carbonic acid reactant instead of inorganic acid reactants, advancing the development of a sustainable formic acid production process. Various herbaceous biomass types (corn and wheat stover) were tested in the hydrolysis–oxidation system using CO₂ gas and H₂O₂. Formic acid yields (17.43 and 20.45%) were lower when herbaceous biomass was used than when red pine was used. Finally, formic acid derived from biomass was converted to hydrogen gas in a dehydrogenation system using a Pd heterogeneous catalyst at room temperature. This process eliminates the use of harmful inorganic acids while contributing to significant carbon reduction. Carbon emission analysis results show that this process can achieve a net carbon reduction of 5.83 tons of CO₂ per ton of hydrogen produced. This approach not only supports carbon-neutral hydrogen production but also demonstrates high scalability potential, making it a viable solution for meeting global sustainability targets at an industrial scale.