Investigation on vapour–liquid equilibrium ( <scp>VLE</scp> ) solubility of <scp> CO ₂ </scp> in aqueous solutions of amino sugars

Abstract Amino sugars, which are candidate CO 2 ‐capturing solvents, react reversibly with CO 2 , thereby setting up vapour–liquid equilibrium (VLE). Knowing equilibrium data is useful for designing gas–liquid contactors for CO 2 absorption. In this work, VLE data for two amino sugars, glucosamine (GA) and N‐methyl‐D‐glucamine (NMG), was measured and reported at 303, 308, and 313 K using a high‐pressure VLE setup for the first time. The equilibrium CO 2 partial pressure was high (up to 1500 kPa). The molarity of sugar in the aqueous solution was in the 0.5–1.25 M range. It was found that the CO 2 loading capacity of NMG was much higher than that of GA. For instance, 1.25 M NMG loaded 1.066 mol/mol at 303 K and 1500 kPa CO 2 partial pressure. Using regression, empirical equations were developed to predict VLE data for GA and NMG. To enable comparison, VLE trials were also performed using two amines, monoethanolamine (MEA) and 2‐amino‐2‐methyl‐1‐propanol (AMP), and an amino acid salt potassium glycinate (PG). It was found that CO 2 solubility (α, mol/mol) in NMG was comparable to that in MEA and higher than that in PG. Besides, it was also found that CO 2 was most soluble in AMP. The effect of promoter addition on the loading capacity at T = 308 K was studied too. The value of CO 2 solubility in GA solution (1 M) at = 1450 kPa was α = 0.298 mol CO 2 /mol amino sugar. It improved to α = 0.46 mol/mol in GA/NMG (1/0.5 M) mixtures. Similarly, the CO 2 solubility in NMG solution (0.75 M) at = 250 kPa was α = 0.76 mol CO 2 /mol amino sugar. It improved to 0.94 and 0.93 mol/mol in NMG/PZ and NMG/AMP (0.75/0.25 M) mixtures (here, PZ denotes piperazine). In this way, this work provided new and useful VLE data for individual and blended sugar solutions.