Novel Non-aqueous Amine Solvents for Biogas Upgrading

Reducing the CO 2 and H 2 S contents of biogas is a prerequisite to raise its quality to that of natural gas. The chemical capture of carbon dioxide was accomplished with non-aqueous single 2-amino-2-methyl-1-propanol (AMP), 2-( tert -butylamino)ethanol (TBMEA), 2-(isopropylamino)ethanol (IPMEA), and N -methyl-2,2′-iminodiethanol (MDEA), with their 1:1 blends dissolved in either an ethylene glycol/1-propanol mixture or single diethylene glycol monomethyl ether. The gas mixtures used contain either 15 or 40% CO 2 in air, sometimes added with 50 ppm H 2 S. We designed two different experimental procedures: (1) separate experiments of CO 2 absorption and desorption aimed at selecting the most efficient amines and (2) continuous cycles of CO 2 absorption (20 °C) and desorption (90–95 °C) featuring CO 2 removal efficiency in the range of 89–96%. The CO 2 /amine/alcohol equilibria were analyzed by 13 C nuclear magnetic resonance (NMR) spectroscopy, which allowed us to identify and quantify the carbonated species in solution originated from both amine and alcohol carbonatation. In some continuous cycles of CO 2 absorption, H 2 S was selectively captured by aqueous H 2 O 2 and separated as either elemental sulfur or CaSO 4 .