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

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.