Chemical similarity of dialkyl carbonates and carbon dioxide opens an avenue for novel greenhouse gas scavengers: cheap recycling and low volatility via experiments and simulations

Global warming linked to the industrial emissions of greenhouse gases may be the end of mankind unless it is adequately and timely handled. To prevent irreversible changes to the climate of the Earth, numerous research groups are striving to develop robust CO₂ sorbents. Dialkyl carbonates (DACs) and CO₂ exhibit obvious chemical similarities in their structure and properties. The degrees of oxidation of all atoms composing DACs and CO₂ are identical resulting in very similar nucleophilicities and electrophilicities of all interaction centers. While both compounds possess relatively high partial atomic charges on their polar moieties, the molecular geometries prevent tight binding of the head groups. The computed DAC-DAC binding energies are ∼40 kJ mol^-1, whereas the effect of the alkyl chain length is marginal. The phase transition points and shear viscosities of DACs are very low. We herein hypothesize and numerically rationalize that DACs represent noteworthy physical sorbents for CO₂ thanks to the similar sorbent-CO₂ and sorbent-sorbent interaction energies. By reporting in silico-derived sorption thermodynamics at various conditions, spectral and structural properties, and experimentally derived CO₂ capacities and recyclabilities, we highlight the mutual affinity of DACs and CO₂. Indeed, the experimentally determined CO₂ sorption capacity of 0.88 mol% (diethyl carbonate) at 278.15 K and 30 bar is competitive. The unprecedentedly low DAC-CO₂ binding energies, ∼14 kJ mol^-1, suggest a low-cost desorption process and outstanding recyclability of the sorbent. We also note that DACs possessing long alkyl chains (butyl, hexyl, octyl) exhibit negligible volatilities, while preserving the liquid aggregate state over a practically important temperature range. The reported results may foster the development of a new class of CO₂ scavengers with possibly quite peculiar characteristics.

New water-based nanocapsules of poly(diallyldimethylammonium tetrafluoroborate)/ionic liquid for CO2 capture

Encapsulated ionic liquids as green solvents for CO₂ capture are reported in this work. We present a novel combination of water-based poly(ionic liquid) and imidazolium-based ionic liquids (Emim[X]). Poly(diallyldimethylammonium tetrafluoroborate)/Emim[X] capsules were developed for the first time using Nano Spray Dryer B-90. Capsules were characterized by FTIR, SEM/EDX, TEM, TGA, DSC, CO₂ sorption, and CO₂/N₂ selectivity, CO₂ sorption kinetic and recycling were also demonstrated. Comparing the capsules reported in this work, the combination of poly(diallyldimethylammonium tetrafluoroborate) and the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate (P[DADMA]/BF₄) showed great potential for CO₂ capture and CO₂/N₂ separation, providing higher results (53.4 mg CO₂/g; CO₂/N₂ selectivity: 4.58).

Designing silica xerogels containing RTIL for CO2 capture and CO2/CH4 separation: Influence of ILs anion, cation and cation side alkyl chain length and ramification

CO₂ separation from natural gas is considered to be a crucial strategy to mitigate global warming problems, meet product specification, pipeline specs and other application specific requirements. Silica xerogels (SX) are considered to be potential materials for CO₂ capture due to their high specific surface area. Thus, a series of silica xerogels functionalized with imidazolium, phosphonium, ammonium and pyridinium-based room-temperature ionic liquids (RTILs) were synthesized. The synthesized silica xerogels were characterized by NMR, helium pycnometry, DTA-TG, BET, SEM and TEM. CO₂ sorption, reusability and CO₂/CH₄ selectivity were assessed by the pressure-decay technique. Silica xerogels containing IL demonstrated advantages compared to RTILs used as separation solvents in CO₂ capture processes including higher CO₂ sorption capacity and faster sorption/desorption. Using fluorinated anion for functionalization of silica xerogels leads to a higher affinity for CO₂ over CH_4. The best performance was obtained by SX- [bmim] [TF₂N] (223.4 mg CO₂/g mg/g at 298.15 K and 20 bar). Moreover, SX- [bmim] [TF₂N] showed higher CO₂ sorption capacity as compared to other reported sorbents. CO₂ sorption and CO₂/CH₄ selectivity results were submitted to an analysis of variance and the means compared using Tukey's test (5%).

Supported ionic liquids as highly efficient and low-cost material for CO2/CH4 separation process

Physical immobilization of ionic liquids (ILs) in solid materials appears as an interesting strategy for the development of new sorbents for CO₂ separation from natural gas. In this work the effect of physical immobilization of two ionic liquids with different anions (bmim[Cl] and bmim[OAc]) on two mesoporous supports (commercial silica SBA-15 and silica extracted from rice husk) was evaluated for CO₂ separation from natural gas by experimental determination of CO₂ sorption, CO₂/CH₄ selectivity and sorption kinetics. Results showed that the pure supports present the greatest CO₂ sorption capacity when compared to immobilized ILs. However, CO₂ removal efficiency improves considerably in the CO₂/CH₄ mixture when ILs are immobilized in these supports. The best selectivity results were obtained for supports immobilized with the IL bmim[Cl] and values increased for SIL-Cl by 37% and SBA-Cl 51% when compared with their respective supports. The contribution of SIL-Cl (3.03 ± 0.12) to separation performance (CO₂/CH₄) is similar to SBA-Cl (3.29 ± 0.39). ILs supported also presented fast sorption kinetics when compared to pure ILs thus being an interesting alternative in the search for highly efficient and low-cost separation processes.