Biogas upgrading through CO2 methanation in a multiple-inlet fixed bed reactor: Simulated parametric analysis

Abstract

A simulation of the catalytic CO₂ methanation reaction was carried out, evaluating the effect of reactants distributed feeding throughout the bed. The main operational parameters were studied in a multiple-inlet reactor to test their effect on conversions and, most importantly, on selectivities towards both CO and CH₄ as reaction products. The analyzed parameters were, firstly, the number of feeding points (N) and the dosage degree of reactants, followed by temperature (T), partial pressures of reactants (H₂:CO₂ ratios), and the composition of a sweetened biogas as feeding stream (CH₄:CO₂ ratios). It is confirmed that a distribution of biogas through several side inlets improves selectivities to the desired CH₄ product, over other feeding configurations. The effect of distributing reactants becomes intensified when the number of lateral feedings increases. This observation supports the experimental trends already proven in previous works. Regarding main operation parameters such as temperature and H₂:CO₂ molar ratio, the analysis confirmed that their influence on selectivities acts just as predicted at low conversions. However, when these conversions become higher the space velocity (WHSV) is the most important factor for selectivities. Finally, no significant changes in reaction performance were obtained when modifying the biogas CH₄:CO₂ ratio in the broad range of methane concentrations from 55 v% to 70 v%.