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.
Highlights
In order to control and reduce anthropogenic greenhouse gas emissions, especially CO2, CO2 capture from fossil fuel power plants is getting great attention
This result is consistent with the results reported in the paper by Trapp et al (2015), who performed a similar equilibrium and rate-based modelling step
A rate-based modeling approach was adopted to evaluate the effectiveness of various pre-combustion CO2 capture strategies based on deep eutectic solvents (DESs) absorption
Summary
In order to control and reduce anthropogenic greenhouse gas emissions, especially CO2, CO2 capture from fossil fuel power plants is getting great attention. There are four major technical routes to capture CO2 from power plants, viz. Precombustion, oxy-fuel, post-combustion and chemical looping combustion. Pre-combustion CO2 capture is associated with the integrated gasification combined cycle (IGCC) and has been considered as a feasible way by separating CO2 from H2. Since the CO2 partial pressure in the flue gas is relatively high, it is quite common to use physical absorption for the CO2 capture (Ban et al, 2014). Among the various technologies for CO2 capture, some of the physical absorption based technologies are relatively mature (Burr and Lyddon, 2008). The Selexol process is a bulk carbon dioxide absorption technique that applies a mixture of dimethyl ether polyethylene glycols (DEPG) as solvent, with formula CH3O(C2H4O)nCH3, where n ranges from 2 to 9
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