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

Abstract

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 k c for the overall reaction were obtained by fitting Danckwerts' expression for absorption to the experimental data, and correlation of k c with solute concentration then afforded rate constants k cat 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 = k cat[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 k cat to the degree of dissociation of the solute and the density of OH groups in the solute molecule.

Influence of Selected Saccharides on the Precipitation of Calcium-Vaterite Mixtures by the CO2 Bubbling Method

“…When saccharides are components of solutions, the shortening of reaction time is most probably caused by the increase of the CO 2 absorption rate. Vasquez et al [36] reported the enhancement of CO 2 adsorption rate in alkaline buffers when fructose, glucose, or sucrose was added to the solutions. The increase in CO 2 mass transfer from the gas phase to the liquid phase was related to the number of hydroxyl groups in the solute molecules and for the solution containing sucrose was higher than for solutions with glucose of fructose.…”

Biomimetic Catalysis of CO2 Hydration: A Materials Perspective

“…Hence most of these catalysts have been evaluated for their activities at pH > 10. The molecules tested were acetaldehyde hydrate, acetate, arginine, arsenite, ,− arsenious acid, boric acid, ,, butyl chloral hydrate, chloral hydrate, chloral alcoholate, diacetyl hydrate, hypobromous acid, hypochlorous acid, , copper sulfate, ethanol, formaldehyde, ,, fructose, germanic acid, , glucose, glycerin, glycine, glyoxal hydrate, methanol, phosphate, , phosphite, proline, rhodium hydride, methylene glycol, saccharose, sarcosine, selenic acid, , silicic acid, , vanadium­(V) oxide, telluric acid, , sodium acetate, sodium bisulfate, sodium orthovanadate and zinc sulfate . Most of these inorganic chemicals have different oxidation states depending on pH .…”

Enhancement of the Absorption of CO2 in Alkaline Buffer Solutions: Joint Action of Two Enhancers

“…Once the gas−liquid exposure time t e and the total contact area A have been calculated as described previously, the overall pseudo-first-order rate constant k c can be obtained by fitting eq 2 to the experimental data, and the enhancement factor E and Hatta number Ha can be calculated: …”

“…The concentrations used, which for each individual catalyst are within the range used in the previous study, are listed in Table together with the corresponding values of relevant concentration-dependent physical properties. The experimental procedure and the reactor, a wetted-wall column, were exactly as reported previously 2 Physical Properties of a Solution of CO 2 Absorption Enhancers in 0.5 M Sodium Carbonate/0.5 M Sodium Bicarbonate Buffer, with the Corresponding Values of k c , the Overall Rate Constant for the Reaction of CO 2 , at 298.1 K [saccharose] (kmol/m 3 )[arsenite] (kmol/m 3 )[formaldehyde] (kmol/m 3 )ρ (kg/m 3 )μ ×10 3 (kg/(m·s)) C e × 10 3 (kmol/m 3 ) D × 10 9 (m 2 /s) k c (1/s) 0.073 0.005 1081.9 1.403 18.78 1.47 5.35 0.073 0.010 1081.9 1.403 18.78 1.47 6.87 0.073 0.015 1081.9 1.403 18.78 1.47 8.39 0.146 0.005 1091.8 1.533 18.21 1.37 8.31 0.146 0.0075 1091.8 1.533 18.21 1.37 9.05 0.146 0.010 1091.8 1.533 18.21 1.37 9.79 0.146 0.0125 1091.8 1.533 18.21 1.37 10.53 0.146 0.015 1091.8 1.533 18.21 1.37 11.28 0.219 0.005 1102.1 1.668 17.75 1.27 11.25 0.219 0.010 1102.1 1.668 17.75 1.27 12.71 0.219 0.015 1102.1 1.668 17.75 1.27 14.16 0.094 0.27 1093.7 1.490 18.60 1.40 10.46 0.146 0.18 1091.8 1.534 18.21 1.36 10.00 0.146 0.27 1100.9 1.575 18.21 1.33 11.51 0.146 ...…”

“…In our earlier study of CO 2 absorption in wetted-wall column by alkaline 0.5 M/0.5 M sodium carbonate/bicarbonate buffers containing an absorption catalyser, sodium arsenite, formaldehyde, glycerin, methanol, ethanol, saccharose, glucose, or fructose, we found that k cat , the rate constant for the reaction involving the catalyst, depended on two characteristics of the catalyst, its degree of dissociation, δ = K a /( K a + [H + ]), and its mass density of OH groups, β = mN OH / M , where N OH is the number of OH groups per molecule of catalyst, M is its molecular mass, and m is the molecular mass of the OH group: …”