Sulfur recycle in biogas production: Novel Higee desulfurization process using natural amino acid salts

In this work, a desulfurization method using natural amino acid salts (AAS), which can be green prepared by biological fermentation, is proposed to remove H₂S from raw biogas. Biogas purification and fertilizer production can be simultaneously achieved to close sulfur recycle. The reaction kinetic characteristics of H₂S absorption with three kinds of AAS, including potassium β-alaninate (PA), potassium sarcosinate (PS) and potassium l-prolinate (PP) are first studied. Kinetic parameters including orders of reaction, rate constants, pre-exponential factors and activation energies are given. AAS absorbent exhibits good potential for biogas desulfurization. Higee (high gravity) technology is utilized to intensify H₂S removal. The effects of operating conditions on H₂S removal efficiency are investigated and PP shows the best desulfurization performance. The phytotoxicity of AAS and amino acid salt sulfide (AASS) is assessed by the germination index of mungbean seeds. PP and its salt sulfide (PPS) show relatively low phytotoxicity and their allowable agricultural feeding concentrations are below 0.08 M and 0.04 M, respectively. The desulfurization method demonstrates a green route for biogas purification to achieve sulfur recycle.