Highly Efficient and Reversible SO2 Capture by Surfactant-Derived Dual Functionalized Ionic Liquids with Metal Chelate Cations

Treatment and Resource Utilization of Gaseous Pollutants in Functionalized Ionic Liquids

With the rapid development of science, technology, and the economy of human society, the emission problem of gas pollutants is becoming more and more serious, which brings great pressure to the global ecological environment. At the same time, the natural resources that can be exploited and utilized on Earth are also showing a trend of exhaustion. As an innovative and environmentally friendly material, functionalized ionic liquids (FILs) have shown great application potential in the capture, separation, and resource utilization of gaseous pollutants. In this paper, the synthesis and characterization methods of FILs are introduced, and the application of FILs in the treatment and recycling of gaseous pollutants is discussed. The future development of FILs in this field is also anticipated, which will provide new ideas and methods for the treatment and recycling of gaseous pollutants and promote the process of environmental protection and sustainable development.

Multiobjective Evaluation of Amine-Based Absorbents for SO2 Capture Process Using the pK a Mathematical Model

The screening of high-efficiency and low-energy consumption absorbents is critical for capturing SO₂. In this study, absorbents with better performance are screened based on mechanism, model, calculation, verification, and analysis methods. The acidity coefficient (pK _a) values of ethylenediamine (EDA), piperazine (PZ), 1-(2-hydroxyethyl)piperazine (HEP), 1,4-bis(2-hydroxyethyl)piperazine (DIHEP), and 1-(2-hydroxyethyl)-4-(2-hydroxypropyl)piperazine (HEHPP) are calculated by quantum chemical methods. A mathematical model of the SO₂ cyclic absorption capacity per amine (α_c) in the amine-based SO₂ capture process is built based on the electroneutrality of the solution. Another model of desorption reaction heat (Q _des) is also built based on the van't Hoff equation. Correspondingly, α_c and Q _des of the above five diamines are calculated and verified with the experimental data. The results show that α_c of the diamine changes with the increase in the pK _a value, and the increase in the pK _a value directly leads to changes in Q _des. The order of α_c of the above five diamines is EDA > PZ > HEHPP > HEP > DIHEP, and the order of Q _des is EDA > PZ > HEHPP > DIHEP > HEP. The multiobjective analysis between α_c and Q _des suggests that it is not advisable to simply pursue a higher α_c while ignoring Q _des. The compound quaternary system absorbent has a wider range of α_c than the single ternary absorbent, which is the direction of absorbent development. This study is expected to strengthen absorbent screening for the amine-based SO₂ capture process from flue gas.

Metal chloride anion based ionic liquids: synthesis, characterization and evaluation of performance in hydrogen sulfide oxidative absorption

Three metal chloride anion based ionic liquids (MCABILs) were synthesized and characterized for high conversion of hydrogen sulfide (H2S).

Capture of Acidic Gases from Flue Gas by Deep Eutectic Solvents

Up to now, many kinds of deep eutectic solvents (DESs) were investigated for the capture of acidic gases from flue gases. In this review, non-functionalized and functionalized DESs, including binary and ternary DESs, for SO2, CO2 and NO capture, are summarized based on the mechanism of absorption, physical interaction or chemical reaction. New strategies for improving the absorption capacity are introduced in this review. For example, a third component can be introduced to form a ternary DES to suppress the increase in viscosity and improve the CO2 absorption capacity. DESs, synthesized with halogen salt hydrogen bond acceptors (HBAs) and functionalized hydrogen bond donors (HBDs), can be used for the absorption of SO2 and NO with high absorption capacities and low viscosities after absorption, due to physicochemical interaction between gases and DESs. Emphasis is given to introducing the absorption capacities of acidic gases in these DESs, the mechanism of the absorption, and the ways to enhance the absorption capacity.

Metal-Based Ionic Liquids in Oxidative Desulfurization: A Critical Review

Ionic liquids (ILs) as novel functional desulfurization materials have attracted increasing attentions. Metal-based ionic liquids (MILs) are classified into three types of metal chloride ILs, metal oxide ILs, and metal complex ILs based on the definition and basic structure of MILs in this critical review. On the basis of the properties of ILs such as structure designability, super dissolution performance, good thermal and chemical stability, nonflammability, and wide electrochemical window, MILs exhibit unique advantages on hydrophobicity, oxidation performance, and Brönsted-Lewis acidity. Therefore, MILs possess both the absorption and oxidation centers for the intramolecular adsorption and oxidation to improve the oxidative desulfurization (ODS) process. During the novel nonaqueous wet oxidative desulfurization process (Nasil), H₂S can be oxidized into elemental sulfur with hydrophobic MILs, which can be regenerated by oxygen for recycle, to solve the problems of low sulfur capacity, low sulfur quality, and severe secondary pollution in the aqueous Lo-Cat wet oxidative desulfurization process. Another outstanding feature of MILs in ODS is biomimetic catalysis, which has the function of activating molecular oxygen and improving the oxidation performance. Metal oxide ILs and metal complex ILs are used in combination with hydrogen peroxide or oxygen with the existing water to generate a Fenton-like reaction to convert hydrophobic organic sulfur or SO₂ into hydrophilic sulfoxide/sulfone or sulfur acid, respectively. However, the corrosion of Cl^- to the equipment and emulsification phenomenon in the extraction process of sulfoxide/sulfone separation still need further study. Furthermore, the promising strategies to construct highly efficient and green desulfurization processes for large-scale applications are provided.

Simultaneous Removal of NO and SO2 from Flue Gas Using [Bmim]2FeCl4/Sulfolane Binary Mixtures

NO and SO2 are the major pollutants of coal combustion. As superior absorbents, ionic liquids are environmentally friendly, are reusable, and can clean flue gases, such as CO2, SO2, and NO x . However, NO and SO2 absorption with low concentration in flue gases under normal conditions is rarely studied. In this work, [Bmim]2FeCl4 was synthesized and mixed with sulfolane for NO and SO2 removal from flue gas. The investigated concentrations of NO and SO2 were 1100 and 2500 ppm, respectively, which are close to real fuel gas conditions. Results showed that 30 wt % [Bmim]2FeCl4/sulfolane mixture performed the best absorption behavior. The presence of SO2 could promote NO absorption by [Bmim]2FeCl4/sulfolane mixture. The 30 wt % [Bmim]2FeCl4/sulfolane mixture had removal efficiencies of 93.6 and 76.2% for NO and SO2, respectively. This mixture also showed great reusability for NO and SO2 after six cycles of absorption. Fourier transform infrared (FTIR) spectrum indicated that SO2 and NO removal by [Bmim]2FeCl4/sulfolane binary mixture was due to the chemical reaction between NO and [Bmim]2FeCl4 and the physical absorption between SO2 and sulfolane.

SO2 absorption in pure ionic liquids: Solubility and functionalization

The SO₂ solubility in ionic liquids and absorption mechanisms with different functionalities, including ether, halide, carboxylate, dicarboxylate, thiocynate, phenol, amino, azole groups, etc., are presented in this review. Strategies of improving SO₂ capture with low binding energy and the separation performance from CO₂ are also concluded. Generally, moderate basicity is favourable for enhancing SO₂ capacity and the water (below 6 wt%) effect on absorption is indefinite but generally slight. Introducing electron-withdrawing substituents such as nitrile, halogen, aldehyde and carboxylic groups are proposed to decrease the chemical absorption enthalpy between ionic liquid and SO₂ in order to reduce regeneration power consumption. Although it is promising, the absorption enthalpy is still much higher than the physisorption performance especially of the ether-functionalized ones. The biocompatible choline-based, betaine-based, and amino acid ionic liquids have clear trends to be applied in SO₂ capture due to their biodegradability, nontoxicity and easy accessibility. Generally, comparing to the traditional solvents, ionic liquids have made great improvement in SO₂ capacity, however, the high viscosity and desorption energy are two main obstacles for SO₂ absorption and separation. Molecular simulations have been applied to reveal the absorption regimes involving the roles of basic functionalities and physical interactions especially the hydrogen bonds, which could be referred for structure designing of the available ionic liquids with readily fluid characteristics and absorption ability.

Exploration of tetra-branched multiple-site SO2 capture materials

Efficient exploration of the configuration space of the reaction complexes consisting of multi-branched structures and SO₂ molecules.

The role of cations in the interactions between anionic N-heterocycles and SO2

Our study shows that cation plays a more important role in the interactions between anionic N-heterocycles and SO2 than in the NHC-CO2 case. The adducts of NHC, SO2 and cation often exhibit multiple stable configurations with close energies rather than the only reported "CO2-sandwiched" planar NHC-CO2-cation structure. The structural diversity makes the models omitting cation inappropriate for predicting the SO2 capture products, which also leads to less clear trends of the cation effects than those observed in the CO2 case. The detailed cation effects are discussed in the text.

Designing tri-branched multiple-site SO2 capture materials

Tri-branched species with multiple isolated reactive sites are proposed for high and uniform SO₂ capture.

Computer-Assisted Design of Imidazolate-Based Ionic Liquids for Improving Sulfur Dioxide Capture, Carbon Dioxide Capture, and Sulfur Dioxide/Carbon Dioxide Selectivity

A new strategy involving the computer-assisted design of substituted imidazolate-based ionic liquids (ILs) through tuning the absorption enthalpy as well as the basicity of the ILs to improve SO₂ capture, CO₂ capture, and SO₂ /CO₂ selectivity was explored. The best substituted imidazolate-based ILs as absorbents for different applications were first predicted. During absorption, high SO₂ capacities up to ≈5.3 and 2.4 molSO2  mol_IL^-1 could be achieved by ILs with the methylimidazolate anions under 1.0 and 0.1 bar (1 bar=0.1 MPa), respectively, through tuning multiple N⋅⋅⋅S interactions between SO₂ and the N atoms in the imidazolate anion with different substituents. In addition, CO₂ capture by the imidazolate-based ILs could also be easily tuned through changing the substituents of the ILs, and 4-bromoimidazolate IL showed a high CO₂ capacity but a low absorption enthalpy. Furthermore, a high selectivity for SO₂ /CO₂ could be reached by IL with 4,5-dicyanoimidazolate anion owing to its high SO₂ capacity but low CO₂ capacity. The results put forward in this work are in good agreement with the predictions. Quantum-chemical calculations and FTIR and NMR spectroscopy analysis methods were used to discuss the SO₂ and CO₂ absorption mechanisms.

Effect of alkyl and halide moieties on the absorption and stratification of SO2 in tetrabutylammonium halide aqueous solutions

To explore the interactions between SO₂ and tetraalkylammonium halide, the effects of temperature, concentration, length of alkyl chain, and halide anion on the solubility of SO₂ in tetraalkylammonium halide aqueous solutions were investigated.

Active chemisorption sites in functionalized ionic liquids for carbon capture

Carbon capture with site-containing ionic liquids is reviewed with particular attention on the activation and design of the interaction sites.

Highly efficient and reversible SO2 capture by halogenated carboxylate ionic liquids

Several halogenated carboxylate ionic liquids were developed for SO₂ capture. Both enhanced capacity, improved desorption, and reversibility of ionic liquids can be achieved via adding halogen sulfur interaction between halogen on the anion and SO₂.