Experimental Evaluation of CO2 Absorption and Thermophysical Properties of TBAB-Based Deep Eutectic Solvents with Amine and Acid Donors

Carbon dioxide emissions from fossil fuel burning remains a severe environmental challenge that needs to be addressed. Deep eutectic solvents (DESs) have emerged as promising alternatives to conventional alkanolamines for CO2 capture applications due to their lower volatility and reduced corrosion potential. In this work, two tetrabutylammonium bromide (TBAB)-based systems were synthesized using different hydrogen bond donors: 2-amino-2-methyl-1-propanol (AMP) at a 1:1 molar ratio and p-toluenesulfonic acid (PTSA) at a 1:2 molar ratio. FTIR spectroscopic analysis confirmed that TBAB-AMP (1:1) forms a true DES through hydrogen bonding interactions, whereas TBAB-PTSA (1:2) undergoes proton transfer to form an ionic salt. CO2 solubility measurements were conducted using the pressure drop method up to 15 bar at 30 °C. The TBAB-AMP system exhibited a CO2 uptake of 0.194 mol CO2/mol DES at 14.7 bar, approximately 2.5-fold higher than the TBAB-PTSA system, which achieved 0.079 mol/mol at 14.5 bar. Critical and thermophysical properties were estimated using the modified Lydersen–Joback–Reid, Lee–Kesler, and Haghbakhsh group-contribution methods. Viscosity measurements conducted from 30 to 50 °C revealed that TBAB-AMP exhibited significantly lower viscosity, ranging from 163 to 46 mPa·s, compared to TBAB-PTSA, which showed viscosity values between 536 and 155 mPa·s. The superior CO2 capture performance of the amine-functionalized DES was attributed to favorable hydrogen-bonding interactions, lower viscosity, which enabled better mass transfer, and enhanced chemical affinity toward CO2 through carbamate formation.