Physico-chemical elimination of unwanted CO2, H2S and H2O fractions from biomethane

Abstract

Biomethane, the principal component of biogas, is one of the major alternatives to fossil fuel. Reducing the amount of carbon dioxide (CO₂), hydrogen sulfide (H₂S) and water (H₂O) content from their mixture with methane (CH₄) in biogas is necessary for ensuring their practical applications as fuels and the minimum methane (CH₄) content is stipulated to be 95%. Herein, a facile process for the combined removal of CO₂, H₂S and H₂O by using two different sets of purifying mixtures including calcium hydroxide (Ca(OH)₂) + activated carbon + silica gel for experiment T1 and Ca(OH)₂ + zero-valent iron (Fe⁰) + sodium sulphate (Na₂SO₄) for experiment T2 is presented. The CO₂ concentration was reduced from 33% in raw biogas to 2.65 and 4.8% in biogas treated in T1 and T2, respectively. The corresponding H₂S concentration falls from 365 ppm to 14 and 29 ppm, while H₂O content decreased from 5% to 0.03 and 0.87%. As a result of this physico-chemical minimization of the unwanted gas fraction, the overall biomethane concentration increased from 62% in raw biogas to 97.55 and 95.02% in the purified gas after the accomplishment of the purification process by experiments T1 and T2, respectively. We propose that this purification method can be applied in a small farmland or rural area to obtain purified biomethane.