Literature sharing: Study on the influence of operating parameters on the CO2 absorption behavior of choline chloride-monoethanolamine eutectic solvent and its aqueous solution
Literature Sharing
Effect of Running Parameters on Absorption Behavior of Choline Chloride-Monoethanolamine Eutectic Solvent and Its Aqueous Solution CO 2
Abstract
The effects of absorption pressure and temperature on the absorption capacity and rate of CO 2 in a choline chloride-monoethanolamine eutectic solvent (ChCl-MEA DES) were evaluated in this study. Mixing water into ChCl-MEA DES as a method to improve the absorption behavior of CO 2 was also investigated. Equilibrium experiments were performed in a batch reactor and the data were analyzed using response surface method (RSM). The results showed that the primary mode of absorption of CO 2 by ChCl-MEA DES was physical absorption . The maximum absorption capacity of CO 2 obtained in this study is 0.379 mol-CO 2 /mol-DES (10 bar, 40 ° C), using DES and 50% v water for absorption. Compared to pure DES, it was found that mixing up to 50% v of water almost doubles the absorption capacity of CO 2 of ChCl-MEA DES. The study of the absorption rate of CO 2 by ChCl-MEA DES found that it is mainly positively affected by pressure and water content, but not much affected by temperature . It was found that the CO2 absorption rate of ChCl-MEA DES containing 50% v water was on average twice that of pure DES. It was also found that water content up to 50% v did not change the mechanism by which ChCl-MEA DES absorbs CO 2 .
Research Background
1. When syngas is used as a chemical feedstock, it is often necessary to remove CO 2 to achieve the desired syngas composition. Removing excess CO 2 will enable syngas to be used in more advanced applications with more stringent gas composition requirements.
The absorption process of polyethylene glycol dimethyl ether and low-temperature methanol must be carried out at a low temperature of about -60 ° C, which requires complex equipment and a large amount of energy consumption. Therefore, it is of great significance to develop CO 2 absorbers that can be used under milder operating conditions and can be effectively regenerated.3. The industrial application of DES requires overcoming its high viscosity.
Experimental results
Figure 1 Graphical representation of experimental design results based on Box-Behnken DoE and response
As can be seen from Figure 1, water content has a positive effect on CO 2 absorptivity; temperature has a negative effect on CO 2 absorptivity; pressure has a positive effect on CO 2 absorptivity. These observations are consistent across all data points within the study range.
Figure 2 Surface diagram of CO 2 absorption capacity and water content, initial pressures at 40 ° C (a), 60 ° C (b) and 80 ° C (c)
By comparing Figures 2 (a), (b) and (c), it is possible to evaluate the effect of temperature on the absorption capacity of CO 2 within the study range. It can be seen that the absorption capacity of CO 2 decreases with temperature. While an increase in the initial operating pressure results in an increase in the absorption capacity of CO 2 . This is due to the fact that the viscosity of water is lower than that of ChCl-MEA DES at a given temperature. Therefore, the presence of a large amount of water will make it easier for the pressure to drive the contact between CO 2 and DES, resulting in a higher absorption capacity of CO 2 . These results show that the absorption behavior of CO 2 by ChCl-MEA DES is consistent with the behavior of physical absorbers, that is, the absorption capacity is proportional to the partial pressure of the absorbed gas. The mechanism of amine solution occurs through chemical reaction, and its absorption performance increases with increasing temperature, while pressure has little effect on absorption capacity. The absorption capacity of CO 2 per mole of DES increases with increasing water content in DES. In Figure 2a, at the same initial pressure, DES with 50% v water has an absorption capacity of 206-0.379 mol-CO 2 /mol-DES, which is on average about 1.5 times that of DES with 25% v water and almost twice that of pure DES (0% v water). The same trend can also be observed in Figures 2 (b) and (c), indicating that this effect applies over the entire temperature range of the study. This does not mean that the same volume of solvent with more water will dissolve more CO 2 . On the contrary, it shows that per mol of DES, when placed in a solution containing more water, can dissolve more CO 2 than when placed in pure DES without water. When comparing the total amount of CO 2 dissolved in an equal volume of solvent, pure DES still dissolves more CO 2 than DES with a high water content.
The presence of water facilitates mass transfer and diffusion of DES, making it easier for DES molecules in aqueous solutions to come into contact with and dissolve CO 2 . This in turn allows more DES molecules in aqueous solutions to participate in CO 2 absorption than molecules in pure DES.
Figure 3 Surface diagram of CO 2 absorbency with water content and initial pressure
As shown in Figure 3, the pressure uniformly increases from 5 bar to 10 bar, and the CO 2 absorbency of DES with 0% v, 25% v, and 50% v water content increases by about 0.753 molCO 2 /kmol-DES • s, indicating that pressure affects DES in the same way regardless of water content. This may mean that while higher water content contributes to DES diffusion and provides more CO 2 and DES contact, the absorption mechanism remains unchanged. This suggests that DES is able to remain stable and intact when mixed with water up to 50% v.
In Figure 3, the larger slope of the initial pressure side indicates that increasing the initial operating pressure of the absorption system will provide a better effect than increasing the water content to increase the CO 2 absorption rate. But increasing the system pressure is usually more complex. Therefore, consider increasing the DES water content as an alternative method to increase the absorption rate of the absorber CO 2 .
CONCLUSION: The absorption of CO 2 by ChCl-MEA DES and its aqueous solution is positively affected by the initial operating pressure and negatively affected by temperature. These results are consistent with predictions that the dominant mode of absorption of CO 2 by ChCl-MEA DES is physical absorption. Studies of the absorption rate of CO 2 by ChCl-MEA DES have found that it is positively affected by pressure and water content, but these two factors do not interact to produce a synergy effect.
Research and innovation points
1. Evaluate the absorption capacity and kinetics of CO 2 at different operating pressures and temperatures, and the absorption effect of CO 2 after mixing with water.
2. Select the response surface method to analyze the interaction between single factors and multiple factors.
3. Analyze the gas after absorption equilibrium to verify the selectivity of the absorber.
Original link
Article Source:
WIBOWO H, LIAO W, ZHOU X, et al. Study on the effect of operating parameters towards CO2 absorption behavior of choline chloride - Monoethanolamine deep eutectic solvent and its aqueous solutions [J]. Chemical Engineering and Processing - Process Intensification, 2020, 157:108142.
Original link:
https://www.sciencedirect.com/science/article/pii/S0255270120306048
