Enhancement of kinetic rates of CO₂ in aqueous solutions of piperazine and methyldiethanolamine with addition of sulfolane

Abstract

Measurements of kinetics rates of CO 2 in aqueous solutions of methyldiethanolamine (MDEA), piperazine (PZ), and mixtures of (MDEA + PZ), (PZ + sulfolane) and (MDEA + sulfolane) were carried out using the stopped flow technique, and reported in terms of pseudo-first-order rate constants (k 0 ). When possible, the second-order reaction rate constants (k 2 ) were regressed from the data. Experiments were performed over new concentration ranges of (10-60), (200-800), (200-800, 10-40), (10-40, 10-200), and (200-800, 10-200) mol/m 3 for the above-mentioned five systems, respectively, and at temperatures varying from (298.15-313.15 K). When sulfolane was added to the amine solution, pseudo-firstorder rate constants in the mixed solvents were higher than in aqueous MDEA and PZ solutions at all temperatures. The kinetic rates were highest at 298.15 K and decreased at higher temperatures for aqueous (MDEA + sulfolane) solutions but increased with temperature for aqueous (PZ + sulfolane) systems. Reaction orders for both PZ and MDEA were practically one at all sulfolane concentrations and temperatures. The base catalysis mechanism was used to regress very well data for aqueous MDEA and (MDEA + sulfolane + water) and the termolecular mechanism was used for (PZ + sulfolane + water) system. Both the zwitterion and termolecular models were able to fit the experimental data for the aqueous PZ system well. Finally, the termolecular and a hybrid model based on the combination of the Zwitterion and base catalysis mechanisms were able to successfully correlate the experimental data for the mixed aqueous (MDEA + PZ) systems.

Elucidation of Operating Parameters Influencing the Ultrasonic-Assisted Absorption of Bulk CO2 Using Unpromoted and Promoted Methyldiethanolamine

“…As the viscosity decreases, the intermolecular spacing expands, giving the CO 2 molecules access to more space between the solvent molecules near the gas–liquid interface. This reduces the mass transfer resistance to CO 2 diffusion through the liquid, favoring CO 2 transportation from gas to liquid phase and subsequently raising the absorption rate. − However, it should be noted again that the favorable effect of temperature is limited since the chemical reactions during the CO 2 absorption process are inherently exothermic. The results also imply that, at a low temperature of 30 °C, the CO 2 absorption rate by promoted MDEA was around 4 times higher than the unpromoted condition.…”