Enhancement of the Absorption of CO₂ in Alkaline Buffers by Organic Solutes:  Relation with Degree of Dissociation and Molecular OH Density

Absorption of CO2 in a wetted-wall column by 0.5 M Na2CO3/0.5 M NaHCO3 buffer with and without various concentrations of saccharose, fructose, glucose, formaldehyde, glycerin, methanol, or ethanol was measured under conditions in which the reaction of CO2 was of pseudo-first-order. For the purposes of comparison, experiments were also carried out with arsenite in both buffer and pure water. For all of these solutes, the absorption enhancement factor increased with solute concentration. Rate constants kc for the overall reaction were obtained by fitting Danckwerts' expression for absorption to the experimental data, and correlation of kc with solute concentration then afforded rate constants kcat for the catalyzed reactions. For each solute, an empirical correlation was found between the absorption enhancement factor and Hatta numbers calculated from the rate constant for the uncatalyzed reaction and from k = kcat[cat]. The notion that the enhancement of absorption by acid−base reaction is facilitated by dipole−dipole interaction between the solutes and CO2 is supported by an empirical correlation relating kcat to the degree of dissociation of the solute and the density of OH groups in the solute molecule.