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 ([P-4444][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 [P-4444] [Gly], PEG400, and their blends of four different concentrations were measured experimentally in the temperature range of 60-140 degrees 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 [P-4444] [Gly] in the blend. The regeneration study of the 30 wt % [P-4444] [Gly]-70 wt % PEG400 blend for three cycles verified its reusability in the process and confirmed that the reaction between [P-4444] [Gly] and CO2 can be reversed at 140 degrees 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.