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The purpose of this paper is to identify firstly the most important solvent characteristics in the CO2 capture process and secondly to determine how they contribute to the total cost of CO2 separation and analyze the economic feasibility of current deep eutectic solvents (DESs) in literature. A rate-based modeling approach was adopted to simulate pre-combustion CO2 capture. The effects of the flow model and the number of segments were investigated for the Selexol process. Different mass transfer correlations due to Bravo et al. (1985), Billet and Schultes (1993) and Hanley and Chen (2012) were adopted for the rate-based models and compared with the equilibrium modelling approach. Subsequently, property and process models were developed for a mixture of decanoic acid and menthol, in equal quantities. A physical property study was conducted with this DES. The CO2 solubility is found to be very important in all rate-based models, as expected, but properties such as the surface tension, thermal conductivity, heat capacity and volatility had a minor influence on the absorption performance. The solvent viscosity strongly affects the mass transfer rate when using the Hanley and Chen (2012) correlations, whereas it plays only a small role in the other two sets of correlations. Using a high CO2 solubility as criterion, two mixtures of allyl triphenylphosphonium bromide (ATPPB) and diethylene glycol (DEG) were screened out from literature. The conventional Selexol process was set as the benchmark for the evaluation of the performances of these DESs. The optimum capture cost for Selexol process is 27.22, 26.66 and 30.84 $2018/tonne CO2 for the adopted correlations, respectively. When employing two of the three studied mass transfer correlations, the estimated process costs for a capture process using this DES can be similar to the costs of the Selexol process. However, when the liquid viscosity strongly affects the mass transfer rate, as is the case when using the Hanley and Chen (2012) correlations, the Selexol process remains more economical. This strongly indicates the need for further experimental and modelling studies on mass transfer rates in absorption columns (with higher viscosity liquids) to help directing the development of suitable DESs for pre-combustion CO2 capture.

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Hydrophobic deep eutectic solvents (DESs) have been designed as effective solvents for precombustion CO2 capture by using a conductor-like screening model for real solvents (COSMO-RS). Reliable CO2 solubilities in various compounds and binary solvents were estimated. We have developed new DESs from 38 selected, nature-derived, hydrophobic, and CO2 affinitive compounds. The possibilities of any two of these substances to form DESs were assessed from predicted activity coefficients, followed by an estimation of the CO2 solubilities of the theoretically feasible DESs. 58 promising hypothetical DESs were screened out. Subsequently, eight DESs were successfully prepared and characterized. Most of these DESs have a density larger than 1.0 g/mL at 298.15 K. The DESs have a similarly low volatility as decanoic acid–menthol (1:2) and are thermally stable below 420 K. Vanillin-4-oxoisophorone (1:3) and methyl salicylate-4-oxoisophorone (1:1) have been identified to be very promising for precombustion capture, showing comparable CO2 solubility and viscosity to the well-known, conventionally used Selexol solvent.

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