Methanation of Carbon Dioxide

Abstract

The ever growing use of renewable sources of energy led to a need for energy storage. Mainly due to the intermittency nature of applications like solar and wind. In addition, the need for regulation of the greenhouse gases led to the development of carbon capture and storage applications. Thus, the combination of those two factors accelerated the production of renewable fuels (called also solar fuels). Renewable fuels is a power-to-x solution of storing the surplus electric energy produced from renewable sources, via multiple steps processes. Hence, solar fuels can contribute immensely in a lorg-term, large-scale energy storage solution. Those fuels are synthetic hydrocarbon that derive from hydrogen (produced from renewables) and the CO2 captured. Some possible fuels are methanol, methane and liquid hydrocarbons. Amongst, those, methane is the most promising solution. It can be synthesized with a single reaction, it has high energy density and can be easily distributed. The methanation of CO2 is an exothermic catalytic reaction and takes place in multiple fixed bed reactors in row. In order for this renewable methane to be used as SNG, high purity levels are required. Hence, novel techniques are researched to achieve the necessary purity of methane in fewer process steps. The present study focuses on one of those techniques called separation enhanced methanation of CO2. The principle behind this technique is the removal, in situ, of the vapor produced by the reaction, to increase the conversion of reactants. This topic is approached experimentally. A fixed bed reactor built in house is used for the experiments. For the hydrogenation ofCO2 a nickel catalyst is used, coupled with two different zeolites (3A and 4A) for the adsorption ofwater vapor. Initially, the pure catalyst’s performance was tested. Subsequently, the combinations of catalyst-zeolites (physical mixture) followed to determine the enhancement of the process. Two GHSV were applied in the experiments, for different temperatures in the range of 200±C-360±C. Also, different combinations of catalyst-zeolite 4A were deployed, regarding the size of the catalyst particles. Fromthe results, it was concluded that the proximity of the catalytic sites to the zeolites surface plays the most dominant role in the performance of the process. This proximity is linked to the average particle size and the uniformity of the bed. The highest conversion rates were achieved in the range of 260±C to 280±C, with values of up to 98,5% of conversion.