METHANATION TECHNOLOGIES FOR PRODUCING SYNTHETIC RENEWABLE METHANE

Abstract

Methanation, or the generation of synthetic methane through the combination of carbon dioxide and hydrogen, has been attracting more and more attention of researchers and energy scientists in recent years due to the fact that the development of an effective and economically feasible technology for the implementation of this process will allow solving a number of energy and environmental problems. First, it is the accumulation of excess renewable electricity from solar and wind power plants by using it in the creation of another energy-intensive product, namely synthetic natural gas, which removes the problem of coordinating unstable sources of electricity with energy networks. Secondly, methanation becomes another technology for enriching biogas and turning it into biomethane, which will allow it to be used through existing gas networks and contribute to solving the problem of natural gas shortage. The development and improvement of methanation technologies are engaged in many organizations of the world - Germany, Denmark, France, the USA, Japan and others. Research is conducted in two main directions: catalytic methanation and biological methanation. In the first direction, methanation is carried out through the Sabatier reaction using catalysts. The problems of such methanation are: the development of catalysts with high activity, selectivity and resistance to the heat of reaction, the provision of optimal reaction modes, in particular temperature and pressure, through the use of various methods of reactor cooling, control of the reaction mechanism, the use of three-phase reactors, changing their structure, and so on. Biological methanation is carried out using of biological methanogens - so-called archaea, which act as a kind of catalyst. The methanation is carried out either directly in the biomass anaerobic digestion reactor (in-situ methanation) or in a separate reactor into which biogas and hydrogen are fed separately (ex-situ methanation). One of the main problems of in-situ methanation is the simultaneous provision of optimal conditions for both acetoclastic and hydrogenotrophic methanogens. This problem is solved by ex-situ methanation, in which the optimal conditions for anaerobic digestion and methanation processes are provided separately. It is clear that optimal conditions are also provided for biomethanation of pure CO2 and H2, when the «broth» for archaea is created separately. A comparison of catalytic and biological methanation technologies shows that catalytic methanation provides higher energy efficiency and requires much smaller reactor sizes than biological methanation for the same methane yield. However, the latter has a higher resistance to harmful impurities than the catalytic one.