An environmentally friendly deep eutectic solvent for CO2 capture

A leading cause of global warming is the increase of carbon dioxide (CO₂) emissions due to anthropogenic activities which prompts an urgent need for substantial reduction. Recently, CO₂ absorption in deep eutectic solvents (DESs) has attracted scientific attention, because of their adaptability compared to traditional ionic liquids and aqueous amine solutions. This study employs the heating method to synthesize DESs using tetrapropylammonium bromide (TPAB) and formic acid (Fa) with molar ratios of TPAB-Fa (1:1) and TPAB-Fa (1:2). Absorption experiments by static method quantified CO₂ solubility in the DESs under varied pressures and temperatures. TPAB-Fa (1:2) at 25.0 °C was the most efficient with the CO₂ solubility of 0.218. Thermodynamic modeling was performed by employing the nonrandom two liquids activity coefficient model and the Peng-Robinson equation of state for the liquid and gas phases, respectively. The Henry's law constant was determined from experimental data. CO₂ physical absorption was confirmed via nuclear magnetic resonance (NMR) and Fourier-transform infrared (FT-IR) analyses. TPAB-Fa (1:2), as the superior DES, exhibited regeneration efficiency of 99% after five absorption/desorption cycles.