Xiaoyan Ji

Carbon Dioxide Capture with Ionic Liquids and Deep Eutectic Solvents : A New Generation of Sorbents

High cost and high energy penalty for CO2 uptake from flue gases are important obstacles in large-scale industrial applications, and developing efficient technology for CO2 capture from technical and economic points is crucial. Ionic liquids (ILs) show the potential for CO2 separation owing to their inherent advantages, and have been proposed as alternatives to overcome the drawbacks of conventional sorbents. Chemical modification of ILs to improve their performance in CO2 absorption has received more attention. Deep eutectic solvents (DESs) as a new generation of ILs are considered as more economical alternatives to cope with the deficiencies of high cost and high viscosity of conventional ILs. This Review discusses the potential of functionalized ILs and DESs as CO2 sorbents. Incorporation of CO2 -philic functional groups, such as amine, in cation and/or anion moiety of ILs can promot their absorption capacity. In general, the functionalization of the anion part of ILs is more effective than the cation part. DESs represent favorable solvent properties and are capable of capturing CO2 , but the research work is scarce and undeveloped compared to the studies conducted on ILs. It is possible to develop novel DESs with promising absorption capacity. However, more investigation needs to be carried out on the mechanism of CO2 sorption of DESs to clarify how these novel sorbents can be adjusted and fine-tuned to be best tailored as optimized media for CO2 capture.

Screening of deep eutectic solvents (DESs) as green CO2 sorbents: from solubility to viscosity

Deep eutectic solvents (DESs) as ionic liquid (IL) analogues show great potential for CO2 capture. They exhibit favorable solvent properties and are considered to be economical alternatives to conventional ILs. In this study, we prepare 35 DESs and screen them in terms of their CO2 solubility and viscosity, both crucial factors to be considered when designing efficient CO2 sorbents. The influence of salt and HBD type and structure, as well their molar ratio on the CO2 solubility and viscosity of the DESs is investigated. The viscosity and CO2 solubility of the DESs are compared with those of other DESs and conventional ILs. 15 DESs, which exhibit comparable CO2 absorption capacity to choline chloride–urea DESs, glycerol DESs and fluorinated ILs, are chosen as the promising ones. The viscosities of the selected DESs are below 200 mPa s and are lower than those of choline chloride-based DESs. Since the viscosity of the DESs is relatively high, on a par with those of conventional ILs, the effect of water as a co-solvent is investigated in order to decrease the viscosity. The addition of water to the glycerol-based DESs improves the kinetics of absorption by decreasing the viscosity, thus increasing the CO2 absorption capacity. Dry or aqueous DESs that demonstrate a high sorption capacity and low viscosity are chosen for additional analysis and characterization, and further functionalization will be carried out in the future to improve their sorption capacity.

A hybrid perturbed-chain SAFT density functional theory for representing fluid behavior in nanopores: Mixtures

The perturbed-chain statistical associating fluid theory (PC-SAFT) density functional theory developed in our previous work was extended to the description of inhomogeneous confined behavior in nanopores for mixtures. In the developed model, the modified fundamental measure theory and the weighted density approximation were used to represent the hard-sphere and dispersion free energy functionals, respectively, and the chain free energy functional from interfacial statistical associating fluid theory was used to account for the chain connectivity. The developed model was verified by comparing the model prediction with molecular simulation results, and the agreement reveals the reliability of the proposed model in representing the confined behaviors of chain mixtures in nanopores. The developed model was further used to predict the adsorption of methane-carbon dioxide mixtures on activated carbons, in which the parameters of methane and carbon dioxide were taken from the bulk PC-SAFT and those for solid surface were determined from the fitting to the pure-gas adsorption isotherms measured experimentally. The comparison of the model prediction with the available experimental data of mixed-gas adsorption isotherms shows that the model can reliably reproduce the confined behaviors of physically existing mixtures in nanopores.

Methodology of non-equilibrium thermodynamics for kinetics research of CO 2 capture by ionic liquids

In this paper, the methodology of non-equilibrium thermodynamics is introduced for kinetics research of CO2 capture by ionic liquids, and the following three key scientific problems are proposed to apply the methodology in kinetics research of CO2 capture by ionic liquids: reliable thermodynamic models, interfacial transport rate description and accurate experimental flux. The obtaining of accurate experimental flux requires reliable experimental kinetics data and the effective transport area in the CO2 capture process by ionic liquids. Research advances in the three key scientific problems are reviewed systematically and further work is analyzed. Finally, perspectives of non-equilibrium thermodynamic research of the kinetics of CO2 capture by ionic liquids are proposed.

Process simulation and energy optimization for the pulp and paper mill

A process integration model is developed based on mixed integer linear programming. The analysis is carried out using the reMIND software in combination with the commercial optimization software CP ...

Modelling interfacial properties of ionic liquids with ePC-SAFT combined with density gradient theory

Highlights Combination of ePC-SAFT with density gradient theory Calculation of interfacial properties of pure ILs in broad temperature range Quantitative predictions of surface tensions for ILs not used in κ parameter fitting ABSTRACT In this work, density gradient theory (DGT) was combined with electrolyte perturbed-chain (ePC)-SAFT to model the interfacial properties of pure imidazolium-based ionic liquids (ILs). The ePC-SAFT pure-component parameters for the IL-ions were taken from literature for the modelling of density and chemical potential of the pure ILs in the bulk phase. The calculated results were used as inputs for modelling surface tension using DGT. The influence parameters for DGT were obtained from the fitting of the experimental surface tensions. Application of anion-specific influence parameters linearised with the molecular weight of the IL-cation allowed to model surface tensions of pure ILs in a broad temperature range within experimental uncertainty. Surface tensions of ILs which have not been used for the fitting of the influence parameter were predicted in quantitative agreement with experimental data. DGT+ePC-SAFT was further used to predict the interfacial density profile of pure ILs.

Confinement Phenomenon Effect on the CO2 Absorption Working Capacity in Ionic Liquids Immobilized into Porous Solid Supports

In this work, the CO2 absorption working capacity and solubility in ionic liquids immobilized into porous solid materials (substrates) were studied both experimentally and theoretically. The CO2 absorption working capacity in the immobilized ionic liquids was measured experimentally. It was found that the CO2 absorption working capacity and solubility increased up to 10-fold compared to that in the bulk ionic liquids when the film thickness was nearly 2.5 nm in the [HMIm][NTf2] immobilized in the P25. Meanwhile, a new model was proposed to describe the Gibbs free energy of CO2 in the immobilized ionic liquids, and both macro- and microanalyses of the CO2 solubility in the confined ionic liquids were conducted. The theoretical investigations reveal that the substrate has a crucial effect on the gas solubility in the ionic liquid immobilized into the substrates, and the model performance was approved with a consideration of the substrate effect.

Choline-Based Deep Eutectic Solvents for Mitigating Carbon Dioxide Emissions

Global warming is a critical issue facing human beings due to greenhouse gas emissions, especially CO 2 emissions. Mitigating CO 2 emissions by Carbon capture and storage (CCS) has become a hot topic today. CO 2 separation is a crucial step in CCS and is an energy-intensive process. Ionic liquids (ILs) as green solvents have gained tremendous attention for use as liquid absorbents for CO 2 separation. However, the high price, toxicity, and poor biodegradability limit the application of ILs. Recently, deep eutectic solvents (DESs) based on choline chloride (ChCl) (i.e., choline-based DESs) were proposed as a new type of ILs but with additional advantages in cost, environmental impact, and synthesis. To promote the application of choline-based DESs in CO 2 separation, the research work on the microstructure and physicochemical properties of choline-based DESs as well as the water effect were surveyed and compared with traditional ILs. The potential applications of choline-based DESs in CO 2 separation and the challenges were further analyzed. It is shown that choline-based DESs are promising for use as liquid absorbents for CO 2 separation, and the performance of ChCl/urea (1:2) is better than that for other choline-based DESs. However, uncertainties and bottlenecks still exist, and further study on the microstructure and properties needs to be carried out from experimental measurements to model developments.

Modeling mass transfer of CO2 in brine at high pressures by chemical potential gradient

To investigate long-term CO2 behavior in geological formations and quantification of possible CO2 leaks, it is crucial to investigate the potential mobility of CO2 dissolved in brines over a wide range of spatial and temporal scales and density distributions in geological media. In this work, the mass transfer of aqueous CO2 in brines has been investigated by means of a chemical potential gradient model based on non-equilibrium thermodynamics in which the statistical associating fluid theory equation of state was used to calculate the fugacity coefficient of CO2 in brine. The investigation shows that the interfacial concentration of aqueous CO2 and the corresponding density both increase with increasing pressure and decreasing temperature; the effective diffusion coefficients decrease initially and then increase with increasing pressure; and the density of the CO2-disolved brines increases with decreasing CO2 pressure in the CO2 dissolution process. The aqueous CO2 concentration profiles obtained by the chemical potential gradient model are considerably different from those obtained by the concentration gradient model, which shows the importance of considering non-ideality, especially when the pressure is high.