Process for the methanation of carbon dioxide from gas mixtures after separation by selective reversible adsorption

摘要

A method is proposed for separating carbon dioxide (CO2) from combustion exhaust gases of fossil fuels for the purpose of conversion into methane (CH4) by conveying the gas mixture through an adsorption tube with an adsorbent having a strong CO2 rejection, as opposed to the main components Nitrogen and water. When they have left the adsorption tube, the CO2 stored therein is backwashed with hydrogen gas (H2) and passed directly to a catalytic reactor for conversion to methane by the known Sabatier method. For a complete reaction, an excess of H2 is required and the resulting H2 + CH4 reaction mixture is passed to a fuel cell for removal of H2 for conversion to direct current and water, while CH4 leaves the fuel cell unchanged and ready for further use, e.g. B. is available as energy storage or for feeding into the natural gas network. The process is in principle a cycle process in which H2 and CO2-containing waste gases are fed in and leaves only CH4 as the reaction product, provided that the hydrogen required for the process is produced by electrolysis of water with electricity from so-called renewable energy sources. In this case, the by-products of the process remain in the system: electrical direct current from the fuel cell is recycled to the water electrolysis as well as the resulting water in the fuel cell and the oxygen produced during the electrolysis is fed inversely into the fuel cell as a reaction gas. If the produced methane is burned for energy recovery, the resulting climate-damaging CO2 as exhaust gas can also be reintroduced into the process and thus the inventive method is climate-neutral and energy-efficient, since the described separation of CO2 isothermal and without pressure changes. The separation of CO2 from exhaust gases carried out by the process according to the invention is an integral part of the overall system consisting of the known components electrolyzer, catalytic reactor and fuel cell.