화학공학소재연구정보센터
Energy & Fuels, Vol.32, No.9, 10008-10015, 2018
Releasing Hydrogen at High Pressures from Liquid Carriers: Aspects for the H-2 Delivery to Fueling Stations
Hydrogen fueling stations require multiple stages of compression to achieve the pressure needed to refuel hydrogen fuel cell electric vehicles at 700 bar. The physical compression equipment constitutes a large share of the total investment cost of hydrogen fueling stations. Hydrogen carriers, i.e., materials that carry either physisorbed or chemisorbed H-2, provide an alternate approach to transport and deliver higher densities of hydrogen to the fueling station at lower pressures. Additionally, some liquid phase hydrogen carriers (LPHCs) are defined by thermodynamic properties that allow H-2 release at elevated pressure, thus providing an opportunity to reduce the number of compressors at the fueling station. This study compares a series of LPHCs and evaluates the approach of using aqueous solutions of formic acid (FA) to deliver high volumetric densities of H-2 to fueling stations and provide a first step of compression. While hydrogen release from most liquid carriers will provide hydrogen slightly above ambient pressure at high temperatures, hydrogen release from the decomposition of FA can provide hydrogen at pressures of several hundred bars at moderate temperatures. A challenge of formic acid is that the high pressure hydrogen is accompanied by 1 equivalent of carbon dioxide and thus requires subsequent separation and purification operations. Nevertheless, formic acid has the advantage of being liquid, which simplifies its handling and provides a continuous supply to a release unit. Furthermore, the energy demand for hydrogen release from FA is lower than for most alternative hydrogen carrier materials.