(562c) Ex-Situ and in-Situ Biogas Purification in a Novel Hybrid Electrolyzer for Biomethanation to Enable Power-to-Gas Facilities

Among various available energy storage technologies power-to-gas approaches are promising, as they turn excess electricity into carbon-neutral fuel gases like renewable natural gas (RNG, i.e., CH₄) or hydrogen (H₂). Provided with sufficient purity, RNG has the unique advantage of allowing the usage of preexisting gas grids for storage and distribution. H₂ from water electrolysis, that is still requires substantial investments in distribution infrastructure, is also projected to play indispensable roles in future energy systems.

Biomethanation in waste treatment facility is a promising power-to-gas technology which converts H₂ and CO₂ into pipeline ready and carbon-neutral CH₄. However, its application for biogas upgrading is still in a nascent stage due to limited mass transfer of gaseous substrates to the waterborne methanogens and the ineffective co-injection of CH₄ (55-65% of biogas) into the biomethanation reactor, causing reduced feed gas residence times and large reactor volumes. A novel hybrid electrolyzer has been demonstrated to be technically and economically viable to provide stoichiometric ratio of H₂ and CO₂ (in HCO₃^- form ) for biomethanation. It enables small footprint biomethanation by concurrently produces H₂ and partitions biogas (a mixture of CH₄ and CO₂) into pipeline ready CH₄ and aqueous HCO₃^-, thus entirely avoiding CH₄ intrusion in the biomethanation reactor and maximizing feedstock transfer to the methanogens, respectively. Results demonstrate that the novel electrolyzer can purify real biogas (67.8% CH₄ and 32.2% CO₂) up to a CH₄ purity of 98.2%, while simultaneously delivering H₂ and HCO₃^- at a molar ratio for biomethanation (4 H₂ + CO₂ → CH₄ + 2 H₂O). In this presentation, engineering design and performance to purify biogas and produce H₂ with ex-situ and in-situ CO₂ capture in the hybrid electrolyzer will be discussed.