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Optimization and Characterization of an Amino Acid Ionic Liquid and Polyethylene Glycol Blend Solvent for Precombustion CO2 Capture: Experiments and Model Fitting

Usman, Muhammad, Huang, Huang, Li, Jun, Hillestad, Magne, Deng, Liyuan
Industrial & Engineering Chemistry Research 2016 v.55 no.46 pp. 12080-12090
absorbents, absorption, amino acids, carbon dioxide, industrial applications, ionic liquids, models, polyethylene glycol, solubility, temperature, thermal stability, vapor pressure, viscosity
Amino acid ionic liquids are green solvents with low toxicities and properties suitable for precombustion CO₂ capture, such as high CO₂ absorption, good thermal stability, and negligible vapor pressure. However, their high viscosities and relatively high costs have hampered their industrial applications. In this work, we systematically studied the amino acid ionic liquid tetrabutylphosphonium glycinate ([P₄₄₄₄][Gly]) and its blends with the low-cost and less viscous cosolvent poly(ethylene glycol) (PEG400). The concentration of the blend solvent was optimized with respect to CO₂ solubility, regeneration efficiency, and cyclic capacity. The solubilities of CO₂ in [P₄₄₄₄][Gly], PEG400, and their blends of four different concentrations were measured experimentally in the temperature range of 60–140 °C and up to a pressure of 17 bar. The results showed that the CO₂ solubility increased with increasing ionic liquid concentration in the blend and decreased with increasing temperature. The optimum CO₂ absorption was determined to occur at 30 wt % of [P₄₄₄₄][Gly] in the blend. The regeneration study of the 30 wt % [P₄₄₄₄][Gly]–70 wt % PEG400 blend for three cycles verified its reusability in the process and confirmed that the reaction between [P₄₄₄₄][Gly] and CO₂ can be reversed at 140 °C. The CO₂ absorption capacity of the blend absorbent was found to be up to a loading of 1.23 mol of CO₂/mol of absorbent. The parameter fitting of the experimental data using empirical correlations was evaluated, and these correlations were developed in particular to predict the blend solvent of an amino acid ionic liquid–PEG400 system based on the ionic liquid concentration and temperature.