Synthesis, Solubilities, and Cyclic Capacities of Amino Alcohols for CO2 Capture from Flue Gas Streams

Amines that have been widely used in post combustion CO2 capture processes are monoethanolamine (MEA), diethanolamine (DEA) and N-methyldiethanolamine (MDEA). If used individually, these solvents have their limitations, and efforts to resolve these have produced formulated solvents consisting of blends of amines and some chemical additives. The advantages derivable from amine blends are also limited to commercially available individual amines. It is therefore desirable to synthesize new amines or amino alcohols that could incorporate the advantages of amine blends in the same molecule or provide new materials for blending in a formulated solvent. Recently, such amino alcohols have been synthesized based on an approach of rational molecular design and synthesis. This involved a systematic modification of the structure of amino alcohols by an appropriate placement of substituent functional groups, especially the hydroxyl function, relative to the position of the amino group. Some of the resulting amino alcohols were 4-(diethylamino)-2-butanol (Reg 1); 4-(piperidino)-2-butanol (Reg 2); 4-propylamino-2-butanol (Reg 3) and 4-(ethyl-methyl-amino)-2-butanol (Reg 4). The performance of these amino alcohols in aqueous solutions in terms of solubility of CO2 and cyclic capacity were compared with those of aqueous MEA using tests conducted at temperatures of 40, 60 and 80 degrees C at CO2 partial pressures of 15 and 100 kPa. All the listed amino alcohols provided a much higher CO2 absorption capacity than MEA with Reg 3 showing the highest absorption capacities at all the temperature considered. The cyclic capacity (derived as the difference between the solubilities at 40 and 80 degrees C) of the listed solvents were also much higher than that for MEA with Reg 4 showing the highest cyclic capacity. These characteristics result in a much higher CO2 absorption and a much less energy consumption for absorbent regeneration, such as in CO2 stripping, compared to conventional amines.