An Optimization Study of Carbon Dioxide Absorption into the Aqueous Solution of Monoethanolamine and Tetrabutylphosphonium Methanesulfonate Hybrid Solvent Using RSM-CCD Methodology

Abstract

The main purposes of this project are to assess and to optimize the solubility of carbon dioxide (CO2) in an aqueous 30 wt% monoethanolamine-tetrabutylphosphonium methanesulfonate (MEA-[TBP][MeSO3]) new hybrid solvent. In this study, the viscosity and density of aqueous MEA-[TBP][MeSO3] hybrid solvents containing different amounts of [TBP][MeSO4] were determined. Meanwhile, Fourier Transform-Infrared (FT-IR) Spectroscopy was used to determine the presence of carbamate in aqueous MEA-[TBP][MeSO3] to prove that CO2 was absorbed by aqueous MEA-[TBP][MeSO3]. Response Surface Methodology (RSM) based on central composite design (CCD) was used to design the experiments and explore the effects of three independent parameters on the solubility of CO2 in aqueous MEA-[TBP][MeSO3]. The three independent parameters are concentration of [TBP][MeSO3] (2–20 wt.%), temperature (30–60 °C) and pressure of CO2 (2–30 bar). The experimental data was found to fit a quadratic equation using multiple regressions and analyzed using analysis of variance (ANOVA). The final empirical equation in terms of actual factors was deducted as mol fraction = 0.5316 − (2.76 × 10−4)A − (8.8 × 10−4)B + (8.48 × 10−3)C + (2.9 × 10−5)AB + (2.976 × 10−6)AC + (5.5 × 10−5)BC − (8.4 × 10−5)A2 − (3.3 × 10−5)B2 − (1.19 × 10−4)C2, whereby A = ionic liquid ([TBP][MeSO3]) concentration, B = temperature and C = CO2 pressure. An attempt was made to perform the experiments for solubility of CO2 in aqueous MEA-[TBP][MeSO3] to validate the removal of CO2 predicted by RSM. Based on a validation study, the experimental data showed a percentage error between 0.6% and 2.11% as compared to the predicted value of CO2 removal by RSM.

Experimental and Mathematical Modelling of Factors Influencing Carbon Dioxide Absorption into the Aqueous Solution of Monoethanolamine and 1-Butyl-3-methylimidazolium Dibutylphosphate Using Response Surface Methodology (RSM)

“…They also describe the ‘salting-out effect’, where adding salt into aqueous MEA reduces the solubility of carbamate in the solution. The same behavior of decreasing CO 2 solubility with an increasing IL concentration was reported in previous publications [ 25 , 34 ]. Despite the reduced CO 2 solubility from the effect of reduced water which was replaced by ILs, the presence of IL may help in saving energy during the regeneration process due to its lower heat capacity as compared to the heat capacity of water [ 6 , 22 ].…”

“…Meanwhile, an increase in the concentration of (BMIM)(DBP) increases the internal resistance in the mixture, which in turn increases the viscosity of the hybrid solvent. A similar observation was reported by Xu et al, Khan et al and Zainul Anuar et al, where the viscosity of the hybrid solvent of aqueous MEA and IL increased greatly when the concentration of IL increased [ 22 , 24 , 25 ].…”

“…It was also found that the solubility of CO 2 in the hybrid solvent measured at a temperature of 30 °C and a pressure of 30 bar slightly decreased with increasing of the (BMIM)(DBP) concentration. A similar trend was reported for other hybrid solvents; MEA-(TBP)(MeSO 3 ) by Zainul Anuar et al, MEA-(C 2 OHmim)(DCA) and MEA-(BMIM)(DCA) by Xu et al, MDEA-(N 11 )(Gly) by Feng et al and MDEA-PZ-(BMIM)(OTf) by Khan et al [ 8 , 22 , 25 , 27 ].…”

“…The experimental value of a 0.599 mole fraction of CO 2 was in agreement with the predicted value estimated by RSM within a 95% confidence interval. It was also found that the CO 2 solubility in the aqueous 30 wt% MEA-(BMIM)(DBP) under optimum conditions was slightly lower than the solubility of CO 2 in another reported hybrid solvent, i.e., MEA-(TBP)(MeSO 3 ) hybrid solvent [ 25 ].…”

Optimization of novel nonaqueous hexanol‐based monoethanolamine/methyl diethanolamine solvent forCO2absorption

“…Setameteekul et al 43 employed a similar factorial RSM design to model and optimize the mass transfer coefficient in two systems with aqueous MEA and aqueous MEA/MDEA solvents, respectively. Anuar et al 44 used a CCD‐RSM to model a novel hybrid solvent with 30‐wt% MEA‐tetrabutylphosponium methanesulfonate. Independent variables such as concentration, pressure, and temperature are evaluated, and the RSM‐based model is evaluated against the experimental results.…”