Biogas-to-methane conversion via sorption-enhanced methanation: experimental evaluation of reactor configuration strategies

Producing synthetic natural gas (SNG) from renewable sources is crucial for decarbonising the energy system, as it provides a storable, dispatchable energy carrier that complements intermittent renewable electricity while enabling the substitution of fossil-derived natural gas through existing storage and distribution infrastructures. This study employed the sorption-enhanced methanation (SEM) process to upgrade biogas to high-purity methane, using a commercial Ni-based catalyst and an LTA zeolite (4 A). Experiments were conducted in a TRL-3 laboratory-scale fixed-bed reactor under three configurations, namely conventional, polytropic (poly-H2 and poly-biogas) and stratified beds. The conventional configuration yielded the best overall performance, achieving 100 vol%. CH4 purity, full CO2 conversion and 100% selectivity under optimal conditions (225 °C, 9.5 bar and a H2/CO2 feed ratio of 4:1). Polytropic feeding reduced hot spots, but limited H2O adsorption. This resulted in shorter pre-breakthrough times (24 min) and lower CH4 purities (96.7–99.2 vol%.). The stratified configuration yielded similar conversions, but suffered from higher local temperatures (up to 287 °C) and shorter breakthrough times (26 min). Optimization of regeneration conditions confirmed complete zeolite recovery using a PSA step of 30 min with a purge flow of 400 Nl/h. Stability tests over 11 cycles demonstrated that the catalyst–adsorbent system maintained its kinetic and adsorptive properties, supporting the robustness of the SEM process. Overall, these findings validate SEM as a promising, scalable strategy for producing renewable methane from biogas.