Synthesis of cyclic carbonate from vinyl cyclohexene oxide and CO2 using ionic liquids as catalysts

Synthesis of cyclic carbonate from 4-vinyl-1-cyclohexene-1,2-epoxide (VCHO) and carbon dioxide was investigated without using any solvent in the presence of ionic liquid as a catalyst. Ionic liquids based on 1-alkylmethylimidazolium salts of different alkyl groups (ethyl, butyl, hexyl, octyl) and different anions (Cl⁻, BF₄⁻, PF₆⁻) were used as catalysts. The conversion of VCHO was affected by the structure of the imidazolium salt ionic liquids; the ones with the cations of bulkier alkyl chain length and with more nucleophilic anion showed better reactivity. Reaction temperature, carbon dioxide pressure, and zinc halide cocatalyst enhanced the addition of CO₂ to VCHO. Semi-batch operation with continuous supply of carbon dioxide showed higher VCHO conversion than batch operation did.     

Ionic liquids for CO2 capture—Development and progress

Innovative off-the-shelf CO₂ capture approaches are burgeoning in the literature, among which, ionic liquids seem to have been omitted in the recent Intergovernmental Panel on Climate Change (IPCC) survey. Ionic liquids (ILs), because of their tunable properties, wide liquid range, reasonable thermal stability, and negligible vapor pressure, are emerging as promising candidates rivaling with conventional amine scrubbing. Due to substantial solubility, room-temperature ionic liquids (RTILs) are quite useful for CO₂ separation from flue gases. Their absorption capacity can be greatly enhanced by functionalization with an amine moiety but with concurrent increase in viscosity making process handling difficult. However this downside can be overcome by making use of supported ionic-liquid membranes (SILMs), especially where high pressures and temperatures are involved. Moreover, due to negligible loss of ionic liquids during recycling, these technologies will also decrease the CO₂ capture cost to a reasonable extent when employed on industrial scale. There is also need to look deeply into the noxious behavior of these unique species. Nevertheless, the flexibility in synthetic structure of ionic liquids may make them opportunistic in CO₂ capture scenarios.     

Effects of imidazolium salts as cocatalysts on the copolymerization of CO2 with epoxides catalyzed by (salen)CrCl complex

Imidazolium salts, most of which are room temperature ionic liquids (ILs), have been introduced as effective and tunable cocatalysts in the copolymerization of CO₂ with epoxides catalyzed by (salen)Cr^IIICl complex for the first time. Effects of imidazolium salts with different alkyl chains as well as with different anions on the copolymerization were investigated. The results showed that the copolymerization was influenced obviously by the property of anion. In addition, the cation of imidazolium salts with longer alkyl chain length such as n-dodecyl (TOF, 242.5 h⁻¹, carbonate linkages > 99%) displays better activities and selectivity in the copolymerization as compared with N-MeIm (TOF, 72.5 h⁻¹, carbonate linkages 94%). These results are instructive for further design of task-specific ILs as effective cocatalysts to improve the copolymerization of CO₂ with epoxides.     

CO2 absorption and regeneration of alkali metal-based solid sorbents

Potassium-based sorbents were prepared by impregnation with potassium carbonate on supports such as activated carbon (AC), TiO₂, Al₂O₃, MgO, SiO₂ and various zeolites. The CO₂ capture capacity and regeneration property were measured in the presence of H₂O in a fixed-bed reactor, during multiple cycles at various temperature conditions (CO₂ capture at 60 °C and regeneration at 130–400 °C). Sorbents such as K₂CO₃/AC, K₂CO₃/TiO₂, K₂CO₃/MgO, and K₂CO₃/Al₂O₃, which showed excellent CO₂ capture capacity, could be completely regenerated above 130, 130, 350, and 400 °C, respectively. The decrease in the CO₂ capture capacity of K₂CO₃/Al₂O₃ and K₂CO₃/MgO, after regeneration at temperatures of less than 200 °C, could be explained through the formation of KAl(CO₃)₂(OH)₂, K₂Mg(CO₃)₂, and K₂Mg(CO₃)₂·4(H₂O), which did not completely converted to the original K₂CO₃ phase. In the case of K₂CO₃/AC and K₂CO₃/TiO₂, a KHCO₃ crystal structure was formed during CO₂ absorption, unlike K₂CO₃/Al₂O₃ and K₂CO₃/MgO. This phase could be easily converted into the original phase during regeneration, even at a low temperature (130 °C). Therefore, the formation of the KHCO₃ crystal structure after CO₂ absorption is an important factor for regeneration, even at the low temperature. The nature of support plays an important role for CO₂ absorption and regeneration capacities. In particular, the K₂CO₃/TiO₂ sorbent showed excellent characteristics in CO₂ absorption and regeneration in that it satisfies the requirements of a large amount of CO₂ absorption (mg CO₂/g sorbent) and fast and complete regeneration at a low temperature condition (1 atm, 150 °C).     

Ionic liquid as reaction medium for the synthesis and crystallization of a metal-organic framework: (BMIM)2[Cd3(BDC)3Br2] (BMIM = 1-butyl-3-methylimidazolium, BDC = 1,4-benzenedicarboxylate)

An ionic liquid, 1-butyl-3-methylimidazolium bromide, is used as reaction medium for the synthesis and crystallization of a coordination polymer, (BMIM)₂[Cd₃(BDC)₃Br ₂] (1) (BMIM = 1-butyl-3-methylimidazolium, BDC =  1,4-benzenedicarboxylate), which forms an anionic two-dimensional framework with the imidazolium cations located between the layers. This compound is thermally stable up to ca. 340 °C and exhibits blue emission in solid state at room temperature. Other characterizations by IR and UV–visible spectra are also described.     

Evaluation of CO2 permeation through functional assembled mono-layers: Relationships between structure and transport

CO₂ transport through functional assembled mono-layers was evaluated in relation to H₂O and nonpolar gases such as CH₄, O₂, N₂. Membranes based on Pebax^®2533 were functionalised by incorporating chemical compounds containing free hydroxyl, N-alkyl sulphonamide, bulky benzoate groups. The effects of both the chemical nature and concentration of the modifier on the gas transport were reported, respectively. The permeability coefficients of different penetrating chemical species were compared, evidencing the higher affinity of the layers to water vapour and carbon dioxide, due to favourable interactions between polar moieties and penetrant. The condensability of the penetrant directed the permeability of the species considered and was responsible for the high solubility selectivity between H₂O and CO₂ (i.e. , DH₂O/D₂CO=0.6, SH₂O/S₂CO=11.4 at 25 °C for Pebax/KET 50/50 w/w). An increase in polar moieties resulted in enhanced permeability and selectivity with respect to the pure polymer. In contrast, the functionalised polymer was not capable to discriminate between the smallest penetrants such as O₂ and N₂, with consequent decrease in the ideal selectivity (P₂CO/O₂, P₂CO/N₂). The functional layers exhibited permeability and selectivity covering broad ranges of values.     

New findings in the catalytic activity of zinc glutarate and its application in the chemical fixation of CO2 into polycarbonates and their derivatives

A heterogeneous zinc glutarate (ZnGA) catalyst and its derivatives were prepared from various zinc and glutarate sources. The hydrothermal reaction between zinc perchlorate hexahydrate and glutaronitrile afforded ZnGA single crystals (sc-ZnGA), with a monoclinic lattice unit cell and a P2/c space group, as determined by X-ray single-crystal structural analysis. The structural details of the ZnGA catalyst are crucial in helping to elucidate its activity in the copolymerization reactions between carbon dioxide (CO₂) and alkylene oxides. X-ray absorption studies provided direct evidence that CO₂ and propylene oxide (PO) are reversibly adsorbed onto the Zn ion centers on the ZnGA surface. Compared to CO₂, PO was found to insert more easily into the Zn–O bond of the ZnGA catalyst, suggesting that the ZnGA-catalyzed copolymerization is initiated by PO rather than CO₂. The activity of the ZnGA catalyst in the copolymerization of CO₂ and PO was found to depend on the zinc source used, and its ability to produce a catalyst of large surface area and high crystallinity (≥77%). Modification of the glutarate ligand with electron-donating or withdrawing substituents failed to enhance the ZnGA catalyst activity further, indicating that glutarate is the best ligand for the Zn metal ion to achieve a high catalytic activity in the CO₂ copolymerization with PO. The ZnGA-catalyzed copolymerization was further optimized to maximize the yield of alternating poly(propylene carbonate), and also extended to the terpolymerization of CO₂ and PO with δ-valerolactone (VL). Terpolymers with high molecular weights and yields could be obtained by adjusting the PO/VL feed ratios. In addition, the terpolymers were found to exhibit excellent enzymatic and biological degradability.     

Preparation of high surface area CaCO3 by reacting CO2 with aqueous suspensions of Ca(OH)2: Effect of the addition of sodium polyacrylate

High surface area CaCO₃ was produced through the reaction between CO₂ and an aqueous suspension of Ca(OH)₂ with the addition of an additive, sodium polyacrylate. The surface area of CaCO₃ prepared was affected markedly by the amount of additive and the solution pH when adding the additive. The CaCO₃ with the highest surface area (87.7 ± 1.3 m²/g) was obtained under the conditions that the initial Ca(OH)₂ concentration was 2.4 wt.%, the amount of sodium polyacrylate added was 0.2 wt.%, and the solution pH at which the additive was added was in the range of 11.4-11.1. The high surface area CaCO₃ also had a high pore volume. The CaCO₃ was highly reactive toward SO₂, and a conversion of 0.95 was achieved when it was sulfated at 950 °C and 4000 ppm SO₂ in air for 1 min. Prior calcination reduced the reactivity of this high surface area CaCO₃.     

3-Amino-2-cyano-imidoacrylate ligands and their zinc complexes for the copolymerisation of CO2 and epoxides: Living character and temperature optimisation

Zinc acetate complexes with 3-amino-2-cyano-imidoacrylate ligands exhibit high activities and selectivities in the copolymerisation of carbon dioxide and cyclohexene oxide to give aliphatic polycarbonates. In temperature optimisation experiments, temperatures around 90 °C were found to be ideal combining minimal formation of the cyclic carbonate side product with optimal catalytic activity. The living character of the polymerisation was shown by studying molecular weights of the polycarbonates at different levels of monomer conversion.     

Ionic liquid–polymer electrolyte for amperometric solid-state NO2 sensor

A new ionic liquid–polymer electrolyte was successfully tested in the planar amperometric solid-state sensor sensitive towards nitrogen dioxide. The electrolyte consists of 1-butyl-3-methylimidazolium hexafluorophosphate (BMIPF₆) and poly(ethylene glycol) methyl ether methacrylate (PEGMEMA) in the ratio 57:43 mol.% and exhibits ionic conductivity 1.6 × 10⁻⁴ S cm⁻¹ at 20 °C, high electrochemical stability (over 4 V on gold or glassy carbon) and thermal stability (over 230 °C). The analyte, gaseous nitrogen dioxide in air, was determined using the electrochemical reduction at −900 mV vs. Pt/air on gold minigrid indicating electrode with Pt/air as a reference electrode. The sensor response is linear in the NO₂ concentration range 0.3–1.1 ppm and is reproducible and long-term stable.     

Study of the BMIM-PF6: Acetonitrile binary mixture as a solvent for electrochemical studies involving CO2

A series of binary mixtures ranging from 0 vol.% to 100 vol.% CH₃CN in BMIM-PF₆ were investigated to identify an optimum ratio for use in electrochemical studies involving CO₂. Density, viscosity and conductivity were measured for the range of binary mixtures and compared to previously published data. The electrochemistry of a model compound, azobenzene, was studied as well. The data indicated that a binary mixture containing 15–20 vol.% (approximately 0.5 mol fraction) CH₃CN in BMIM-PF₆ was optimal for electrochemistry, and FTIR of CO₂ saturated solutions demonstrated that the solubility of CO₂ in the 15–20% CH₃CN mixtures was only about 10% lower than that seen in the neat BMIM-PF₆.     

CO2 reforming of CH4 over nanocrystalline zirconia-supported nickel catalysts

Mesoporous nanocrystalline zirconia with high-surface area and pure tetragonal crystalline phase has been prepared by the surfactant-assisted route, using Pluronic P123 block copolymer surfactant. The synthesized zirconia showed a surface area of 174 m² g⁻¹ after calcination at 700 °C for 4 h. The prepared zirconia was employed as a support for nickel catalysts in dry reforming reaction. It was found that these catalysts possessed a mesoporous structure and even high-surface area. The activity results indicated that the nickel catalyst showed stable activity for syngas production with a decrease of about 4% in methane conversion after 50 h of reaction. Addition of promoters (CeO₂, La₂O₃ and K₂O) to the catalyst improved both the activity and stability of the nickel catalyst, without any decrease in methane conversion after 50 h of reaction.     

Supercritical CO2-assisted preparation of ibuprofen-loaded PEG-PVP complexes

Stoichiometric ratios of poly(ethylene glycol) (PEG, M_w = 400) with poly(vinylpyrrolidone) (PVP, M_w = ±3.1 × 10⁴ and M_w = 1.25 × 10⁶ M_w) were prepared from ethanol cast solutions and in supercritical CO₂. The complex formation was studied via glass transition (T_g) analysis obtained from differential scanning calorimetry (DSC) thermograms. PEG-PVP blends were also loaded with ibuprofen. The molecular dispersion of ibuprofen, mechanism of interaction, the effect of CO₂ pressure and temperature and ageing of blends were also analysed with DSC, attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray diffraction (XRD). T_g analysis indicated that supercritical CO₂ can facilitate the formation of stoichiometric PEG-PVP complexes. Processing of PEG-PVP blends with ibuprofen results in the molecular dispersion of ibuprofen mainly bonded to PVP carbonyl groups, without significant disruption of the PEG-PVP complex. Increasing process pressure results in extraction of some PEG fractions. Post-processing ATR-FTIR shifts in ibuprofen-PEG-PVP complexes is greater with supercritical CO₂ processing. These shifts are mainly attributed to atmospheric moisture absorption. Overall it was shown that, ibuprofen-loaded PEG-PVP complexes can be prepared from supercritical CO₂ processing showing similar characteristics to such complexes prepared from solution casting.     

CO2 reforming of CH4 over stabilized mesoporous Ni-CaO-ZrO2 composites

Mesoporous Ni-CaO-ZrO₂ nanocomposites with high thermal stability were designed and employed in the CO₂/CH₄ reforming. The nanocomposites with appropriate Ni/Ca/Zr molar ratios exhibited excellent activity and prominent coking resistivity. The Ni crystallites were effectively controlled under the critical size for coke formation in such nanocomposites. It was found that low Ni content resulted in high metal dispersion and good catalytic performance. Moreover, the basicity of the matrices improved the chemisorption of CO₂ and promoted the gasification of deposited coke on the catalyst.     

Promoting effects of CO2 on dehydrogenation of propane over a SiO2-supported Cr2O3 catalyst

The effects of carbon dioxide on the dehydrogenation of C₃H₈ to produce C₃H₆ were investigated over several Cr₂O₃ catalysts supported on Al₂O₃, active carbon and SiO₂. Carbon dioxide exerted promoting effects only on SiO₂-supported Cr₂O₃ catalysts. The promoting effects of carbon dioxide over a Cr₂O₃/SiO₂ catalyst were to enhance the yield of C₃H₆ and to suppress the catalyst deactivation.     

利用二氧化碳和甲基丙烯酸缩水甘油酯制备环碳酸酯的研究

以含有环氧基团和双键结构的甲基丙烯酸缩水甘油酯(GMA)与二氧化碳为原料合成用于制取新型环保材料非异氰酸酯聚氨酯的中间体环碳酸酯(DOMA),考察了催化剂、反应温度、压力、以及时间等反应条件对产物DOMA收率的影响,并对原料和产物通过TGA、红外进行分析,对产物通过碳谱、氢谱进行结构表征,表明在溶剂存在下,以四丁基溴化铵与碘化锌为共催化剂,在温度为110℃、压力为1.2MPa下反应4 h,产物DOMA收率可达75.6%。     

Separation of CO2 from flue gas using electrochemical cells

Past research with high temperature molten carbonate electrochemical cells has shown that carbon dioxide can be separated from flue gas streams produced by pulverized coal combustion for power generation. However, the presence of trace contaminants, i.e., sulfur dioxide and nitric oxides, will impact the electrolyte within the cell. If a lower temperature cell could be devised that would utilize the benefits of commercially-available, upstream desulfurization and denitrification in the power plant, then this CO₂ separation technique can approach more viability in the carbon sequestration area. Recent work has led to the assembly and successful operation of a low temperature electrochemical cell. In the proof-of-concept testing with this cell, an anion exchange membrane was sandwiched between gas-diffusion electrodes consisting of nickel-based anode electrocatalysts on carbon paper. When a potential was applied across the cell and a mixture of oxygen and carbon dioxide was flowed over the wetted electrolyte on the cathode side, a stream of CO₂ to O₂ was produced on the anode side, suggesting that carbonate/bicarbonate ions are the CO₂ carrier in the membrane. Since a mixture of CO₂ and O₂ is produced, the possibility exists to use this stream in oxy-firing of additional fuel.From this research, a novel concept for efficiently producing a carbon dioxide rich effluent from combustion of a fossil fuel was proposed. Carbon dioxide and oxygen are captured from the flue gas of a fossil-fuel combustor by one or more electrochemical cells or cell stacks. The separated stream is then transferred to an oxy-fired combustor which uses the gas stream for ancillary combustion, ultimately resulting in an effluent rich in carbon dioxide. A portion of the resulting flow produced by the oxy-fired combustor may be continuously recycled back into the oxy-fired combustor for temperature control and an optimal carbon dioxide rich effluent.     

Effect of CO2, HCO3 and CO3 on oxygen reduction in anion exchange membrane fuel cells

The effect of carbonate and bicarbonate anions on the oxygen reduction reaction was investigated in four alkaline solutions (pH ∼ 14) on a Pt disk type electrode with varying concentrations of carbonate and bicarbonate. The addition of carbonate and bicarbonate had two primary effects on the observed voltammetric behavior: i) The Tafel slope shifts positive with increasing carbonate/bicarbonate concentration, indicating that the carbonate anions may compete for surface adsorption sites; and ii) The dissolved oxygen concentration and diffusion coefficient are depressed with increasing anion concentration. Finally, adding CO₂ to the cathode stream of an anion exchange membrane fuel cell caused an improvement in the device performance under fully hydrated conditions, suggesting that the fuel cell was operating at least partially under the carbonate cycle.     

Absorption of CO2 and subsequent viscosity reduction of an acrylonitrile copolymer

Acrylonitrile (AN) copolymers (AN content greater than about 85 mol%) are traditionally solution processed to avoid a cyclization and crosslinking reaction that takes place at temperatures where melt processing would be feasible. It is well known that carbon dioxide (CO₂) reduces the glass transition temperature (T_g) and consequently the viscosity of many glassy and some semi-crystalline thermoplastics. However, the ability of CO₂ to act as a processing aid and permit processing of thermally unstable polymers at temperatures below the onset of thermal degradation has not been explored. This study concentrates on the ability to plasticize an AN copolymer with CO₂, which may ultimately permit melt processing at reduced temperatures. To facilitate viscosity measurements and maximize the CO₂ absorption, a relatively thermally stable, commercially produced AN copolymer containing 65 mol% AN was investigated in this research. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) indicated that CO₂ significantly absorbs into and reduces the T_g of the AN copolymer. Pressurized capillary rheometry indicated that the magnitude of the viscosity reduction is dependent on the amount of absorbed CO₂, which correlates directly to the T_g reduction of the plasticized material. Up to a 60% viscosity reduction was obtained over the range of shear rates tested for the plasticized copolymer containing up to 6.7 wt% CO₂ (31 °C T_g reduction), corresponding to as much as a 30 °C equivalent reduction in processing temperature. A Williams-Landel-Ferry (WLF) analysis was used to estimate the viscosity reduction based on the T_g reduction (and corresponding amount of absorbed CO₂) in the plasticized AN copolymer, and the predicted viscosity reduction based on using the universal constants was 34-85% higher than measured, depending on the amount of absorbed CO₂. Van Krevelen's empirical solubility relationships were used to calculate the expected absorbance levels of CO₂, and found to be highly dependent on the choice of constants within the statistical ranges of error of the Van Krevelen relationships.     

CO2和CH3OH直接合成碳酸二甲酯催化剂研究进展

碳酸二甲酯是一种绿色的有机合成中间体,由CO2直接合成碳酸二甲酯备受关注。本文介绍了CO2和CH3OH直接合成碳酸二甲酯的各种催化剂,分析了催化剂的优缺点,探讨了催化反应的机理。同时介绍了合成碳酸二甲酯的新技术和新方法。最后指出了由CO2直接合成碳酸二甲酯的研究趋势。