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Keywords:

  • CO2 hydrogenation;
  • Energy storage;
  • Fischer-Tropsch synthesis;
  • Renewable liquid fuel;
  • Reverse water-gas shift

Abstract

The substitution of fossil fuels by renewable energy sources is needed to decrease greenhouse gas emissions, especially CO2. Wind and solar power are today considered as attractive alternatives for electric power generation, but are not suitable for providing base load. Thus, efficient storage of electrical energy is inevitable. Liquid hydrocarbons (HCs) exhibit an excellent volumetric energy density and offer various opportunities for storing electric energy. They can be produced by CO2 and renewable H2 (generated by water electrolysis) in a two step process. The first step is generation of syngas by reverse water-gas shift (RWGS) at elevated temperatures; the second step comprises the production of liquid hydrocarbons by Fischer-Tropsch (FT) synthesis. The experiments on RWGS with a commercial Ni-catalyst show that a CO2 conversion of around 80 % can be reached at 800 °C within a very short residence time of less than < 0.1 s. The experiments on FTS with Fe as catalyst and syngas containing different amounts of CO2 indicate that the influence of CO2 on CO conversion and product selectivities (including net CO2 production by water-gas shift) is insignificant if the inlet partial pressures of H2 and CO are kept constant. If CO is substituted by CO2, less HCs are formed, the water-gas shift is repressed, and methane selectivity increases.