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.