Investigation on vapour–liquid equilibrium (VLE) solubility of CO2 in aqueous solutions of amino sugars

Amino sugars, which are candidate CO₂-capturing solvents, react reversibly with CO₂, thereby setting up vapour–liquid equilibrium (VLE). Knowing equilibrium data is useful for designing gas–liquid contactors for CO₂ 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 CO₂ partial pressure $\left(P_{C{O}_2}^{*}\right)$ 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 CO₂ 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 CO₂ 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 CO₂ solubility (α, mol/mol) in NMG was comparable to that in MEA and higher than that in PG. Besides, it was also found that CO₂ was most soluble in AMP. The effect of promoter addition on the loading capacity at T = 308 K was studied too. The value of CO₂ solubility in GA solution (1 M) at $P_{C{O}_2}^{*}$ = 1450 kPa was α = 0.298 mol CO₂/mol amino sugar. It improved to α = 0.46 mol/mol in GA/NMG (1/0.5 M) mixtures. Similarly, the CO₂ solubility in NMG solution (0.75 M) at $P_{C{O}_2}^{*}$ = 250 kPa was α = 0.76 mol CO₂/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.