Water-lean absorbents have potential applications for energy-efficient CO 2 capture. In this work, the chemical kinetics of the reaction between carbon dioxide (CO 2 ) and potassium prolinate (ProK) in ethanol, ethylene glycol and water solvents was measured in a stirred cell reactor with a stable gas-liquid interface at temperatures from 275.2 to 285.2 K and ProK molar concentrations up to 2.0 M. The experiments were performed under the pseudo-first-order regime to determine the overall kinetic rate constant ( k ov ) using two-film theory. The results showed that the reaction rates in each polar solvent increase considerably as the increasing ProK concentrations and temperatures. The reaction order was found to be in the range of 1.4–2.0 with respect to ProK concentration, depending on the solvents used. The kinetic results for the reaction in ethanol were also interpreted based on zwitterion mechanism and termolecular mechanism. The calculated from the two proposed models match well with the experimental data.
Water-lean phase change amino acid salt (AAS) has provided a promising solution to energy-efficient CO 2 capture. In this work, novel phase behaviors (liquid–liquid-solid and liquid–liquid) of potassium prolinate (ProK)-2-butoxyethanol (EGBE)-water system (P-E-H) were investigated to improve the CO 2 capture performance. Distribution of phase-forming compositions and CO 2 absorbed among the phases, regeneration efficiency of CO 2 -rich solutions and cyclic capacity were discussed in details, varying the ProK concentration and the mass ratio of EGBE to water (E to H). Phase splitting points were observed to be close to the saturated state under the absorption conditions. For liquid–liquid-solid systems, with decreasing the mass ratio of E to H, volume fraction of the solid phase and the captured CO 2 in ProH + –HCO 3 − species decreases. Desorption conditions were optimized for the CO 2 -rich slurry to form a homogenous liquid after blending with top liquid phase (MWTP) for absorbent reuse, where about 1.0–1.5 times higher desorption efficiency and cyclic capacity in comparison with aqueous 30 mass% MEA. Stability of capture performance and system compositions during eight runs of continuous absorption-phase separation-slurry desorption indicates the 40P-35E-25H absorbent excellent recyclability.
Potassium prolinate + water + ethanol (ProK/W/Eth) solution has potential use as a liquid-to-solid phase-changing absorbent for energy-efficient CO2 capture process. In this study, the equilibrium solubility of CO2 in ProK/W/Eth solutions was measured in a stirred equilibrium cell at a temperature range from 293 to 343 K and CO2 partial pressures up to 200 kPa. Density and viscosity were also measured at temperatures from 293 to 333 K and ProK molality up to 6.09 mol·kg–1 ethanol. Moreover, the CO2 loading and cyclic capacity were compared with aqueous monoethanolamine (MEA) and aqueous ProK solution. The solubility data were well-represented using a Soft model with AAD within 8.0%. The data of density and viscosity were also correlated with empirical models. The predicted results matched well the experimental data with AAD within 0.37% for density and 1.38% for viscosity.
High energy consumption for aqueous amine-based CO 2 capture process is still a major drawback limiting its commercial deployment. Most of heat is used for water vaporization during solvent regeneration for CO 2 stripping. Development of phase-changing solvents is an attractive energy-efficient method to reduce energy requirement. In this work, we have proposed potassium prolinate (ProK)/ethanol solution as a novel non-aqueous absorbent. Its physical properties and the rate of CO 2 absorption were investigated and compared with the aqueous ProK systems. Phase behaviours during CO 2 absorption and partition of CO 2 absorbed between liquid and solid phases were characterized. The main species in solid precipitates were identified as bicarbonate and proline salts by 13 C NMR and XRD. Moreover, the regenerated absorbents can remain relatively stable after absorption-desorption cycles.
Phase change solvents are attractive energy-efficient absorbents for carbon dioxide (CO 2 ) capture due to CO 2 -rich phase formation. Potassium prolinate + water + ethanol (ProK/W/Eth) solution has shown good capture characteristics as a promising one in our previous work. In this work, absorption rate of CO 2 , solubility of N 2 O, and heat of absorption for ProK/W/Eth solution were investigated using a stirred cell reactor and a CPA201 reaction calorimeter and these results were also compared with the aqueous ProK and 30 mass% MEA solutions. Using ethanol as a solvent can substantially increase the CO 2 physical solubility and the absorption rate of CO 2 in ProK/W/Eth solutions is far higher than that in aqueous 30 mass% MEA solutions especially at a low CO 2 loading range. Solid precipitation, obtained from the liquid-to-solid phase change absorption, was analyzed by 13 C NMR and DSC-TGA. The enthalpy change for ProK/W/Eth solutions at various CO 2 loading was also discussed.
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