Process Simulation and Economic Analysis of Pre-combustion CO2 Capture With Deep Eutectic Solvents

Abstract

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.

Sodium Hexanoate and Dodecanoate Salt-Based Eutectic Solvents: Density, Viscosity, and Kamlet–Taft Parameters

“…However, the viscosity values of NaC6-based ESs are similar to that of hydrophobic ammonium salt-based DESs (265.26 mPa·s) . On the other hand, the viscosity of NaC12-based ESs is of the same order of magnitude of that obtained for ESs composed by menthol/C10 (20.32 mPa·s) …”

“…20 On the other hand, the viscosity of NaC12-based ESs is of the same order of magnitude of that obtained for ESs composed by menthol/ C10 (20.32 mPa•s). 36 The density and viscosity of other sodium salt-based DESs, such as NaCl/ethylene glycol (1:16), NaBr/ethyleneglycol (1:6), and NaI/ethylene glycol (1:4), have also been reported and are listed in Table S6 of the Supporting Information. 26 Despite the much higher proportions of HBAs present in these DESs than in the sodium alkanoate-based ESs studied in this work, a comparison can be established.…”

Development of Natural Hydrophobic Deep Eutectic Solvents for Precombustion CO2 Capture

“…The larger density of our new DESs brings about a longer residence time in the absorber when the solvent is applied for precombustion capture, slightly intensifying the process. 6 Even more exciting, due to the weak interaction strength between the constituents of these new DESs, except for vanillin−4-oxoisophorone (1:3), all viscosities of the newly developed DESs are less than 10 cP at 298.15 K, which is quite beneficial to achieve fast mass transfer during gas absorption. Take vanillin−4-oxoisophorone (1:3) as an example.…”

“…Considering that the boiling point for all DES constituents are above 220 °C (Table S12), the newly developed DESs have a much lower volatility compared to conventional solvents like methanol and toluene. For the DESs, it is much more important to have a relatively low viscosity than it is to have a very low solvent volatility …”

“…Their hydrophobicity and tunable physicochemical properties made them promising for CO 2 physical absorption. 6 In fact, before gas enters the Selexol unit, the dehydration of the feed gas is required, 7 water accumulation in the absorbent can cause a detrimental effect on the absorption capacity and metal corrosion. The use of hydrophobic solvents not only prevents water accumulation but also allows operation at higher absorption temperatures.…”