Synthetic natural gas production through biogas methanation using a sorption-enhanced reaction process

Abstract

Using CO2 from biogenic sources to produce fuels is one of the most attractive applications in climate change mitigation, as it leads to the replacement of fossil fuels and contributes to the circular economy. By this means, the primary purpose of this paper is to design a biogas methanation process to produce synthetic natural gas (SNG) suitable to be fed into the gas grid. In this way, a SERP process was proposed in which the equilibrium is overcome by eliminating the co-produced water using a selective adsorbent, such as zeolite 3A. For this purpose, two different catalysts were (NiAl2O3 and Ni5A) and compared with a commercial catalyst. First, the catalytic performance of the three catalysts was studied in an experimental setup, discarding the Ni5A catalyst due to its lower reaction yields. Subsequently, a sorption-enhanced reaction process (SERP) was designed by simulation using the experimental kinetic data obtained and a theoretical model of reaction/adsorption cycles design. The PSASIM software, previously registered by the research group, was used for the simulation. The proposed process consisted of three main stages: a first reaction/adsorption stage where the biogas was upgraded to SNG with the corresponding water adsorption by the catalyst/adsorbent, and a second and third stages (purge and rinse) where the retained water in the adsorbent is desorbed and eliminated from the process. The process variables studied were temperature and biogas composition fed to the process. Finally, at 488 K and a residual waste biogas composition (55–60 % CH4), CO2 conversions of 99.55 % and selectivities towards methane of 99.99 % were achieved using NiAl2O3-zeolite3A mixture. In addition, the purity of the methane produced was 98.6 % molar in the product.