Abstract
Amine absorption (or amine scrubbing) is currently the most established method for CO2 capture; however, it has environmental shortcomings and is energy-intensive. Deep eutectic solvents (DESs) are an interesting alternative to conventional amines. Due to their biodegradability, lower toxicity and lower prices, DESs are considered to be “more benign” absorbents for CO2 capture than ionic liquids. In this work, the CO2 absorption capacity of choline-chloride/levulinic-acid-based (ChCl:LvAc) DESs was measured at different temperatures, pressures and stirring speeds using a vapour–liquid equilibrium rig. DES regeneration was performed using a heat treatment method. The DES compositions studied had ChCl:LvAc molar ratios of 1:2 and 1:3 and water contents of 0, 2.5 and 5 mol%. The experimental results showed that the CO2 absorption capacity of the ChCl:LvAc DESs is strongly affected by the operating pressure and stirring speed, moderately affected by the temperature and minimally affected by the hydrogen bond acceptor (HBA):hydrogen bond donator (HBD) molar ratio as well as water content. Thermodynamic properties for CO2 absorption were calculated from the experimental data. The regeneration of the DESs was performed at different temperatures, with the optimal regeneration temperature estimated to be 80 °C. The DESs exhibited good recyclability and moderate CO2/N2 selectivity.
Highlights
Renewable electricity production methods are still not an alternative to the burning of fossil fuels, irrespective of their progressive advances
Visual inspection of Figure 2 seems to indicate that, overall, the hydrogen bond acceptor (HBA):hydrogen bond donator (HBD) molar ratio and the water content both have a small effect on the CO2 absorption capacity in ChCl:LvAc
The temperature trend observed for the ChCl:LvAc Deep eutectic solvents (DESs) agrees with the results reported in the literature for other DESs [7,30,31]
Summary
Renewable electricity production methods are still not an alternative to the burning of fossil fuels, irrespective of their progressive advances. Anthropogenic emissions of greenhouse gases (GHGs) are anticipated to continue increasing in the coming decades, with anthropic CO2 expected to remain one of the primary reasons behind climate change. Over the last six decades, the concentration of CO2 in the atmosphere has been increasing dramatically, reaching a value of approximately 418 ppm in June 2021 [1]. Amine absorption is currently the most applied and established method for CO2 capture [2]. The method utilises conventional amines (typically monoethanolamine, MEA), which have environmental shortcomings and consume a lot of energy to regenerate the solvent [3]. Deep eutectic solvents (DESs) are among the favourable alternatives to substitute conventional amines for CO2 capture and have some advantages when compared to ionic liquids
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