Biogas upgrading through CO2 methanation in a polytropic - distributed feed fixed bed reactor
P. Durán, Pablo Aragüés-Aldea, Rodrigo González-Pizarro, V.D. Mercader, F. Cazaña, Eva Francés, J.Á. Peña, J. Herguido
Abstract
Methanation of the CO2 contained in a biogas stream has been experimentally analyzed in a fixed bed reactor with a Ni-Mn catalyst, evaluating the effect of feeding reactants distributed throughout the bed. The performance of different feeding configurations (conventional cofeeding and others implying a lateral distribution of one of the reactive streams) has been analyzed for different nominal temperatures T (250 - 400 ºC) and weight-related space velocities WHSV (47.71 - 6.63 gCO2 gcat-1 h-1), always keeping a H2: CO2 ratio of 4:1, and a CH4:CO2 ratio of 7:3. For identical WHSV, the lateral biogas distribution (Poly-Biogas feeding configuration) always showed the best results in terms of activity (higher conversion at the same temperature) and selectivity (lower selectivity to CO in iso-conversion). These better results agree with what was observed in a previous work in methanation of CO2 (i.e., without methane in the feed). In that work, CO2 was distributed along the catalytic bed by several lateral feeds (Poly-CO2). When T was kept constant and WHSV was varied, the reactor fed with distributed biogas (Poly-Biogas), again confirmed its higher efficiency and better selectivity for biogas upgrading (i.e., higher CH4 content). Furthermore, by adopting a Poly-Biogas (or poly-CO2) feeding configuration, a more homogeneous temperature profile was achieved along the bed avoiding the severity of hot spots appearance. In contrast, the lateral distribution of hydrogen (Poly-H2) always led to similar or worse results than those for the conventional co-feeding configuration.