Homogeneous Phase Copolymerizations of Vinylidene Fluoride and Hexafluoropropene in Supercritical Carbon Dioxide

Copolymerizations of vinylidene fluoride (VDF) and hexafluoropropene (HFP) were carried out in homogeneous phase with supercritical carbon dioxide up to complete VDF conversion using conventional peroxide initiators. The HFP monomer feed ratios, f_HFP, were varied between 0.65 and 0.20. Depending on f_HFP amorphous or semi‐crystalline copolymers were obtained. f_HFP also determines the minimum pressure required to allow for homogeneous phase reactions. For example, HFP‐rich copolymerizations in 70 wt.‐% CO₂ at 100 °C require a pressure of around 500 bar. Further, bulk copolymerizations in homogenous phase were feasible for f_HFP = 0.65 at 900 bar up to complete VDF conversion. Copolymerizations in the presence of perfluorinated hexyl iodide carried out at 75 °C gave access to low dispersity polymers. Due to homogeneous phase conditions the use of any surfactants or fluorinated cosolvent is avoided.

     

Novel Source of Trifluoromethyl Radical As Efficient Initiator for the Polymerization of Vinylidene Fluoride

A persistent perfluoroalkyl radical (PPFR), perfluoro‐3‐ethyl‐2,4‐dimethyl‐3‐pentyl, is shown to be a good source of •CF₃ radicals and a useful radical capable of initiating the polymerization of vinylidene fluoride (VDF). NMR characterizations of the resulting PVDF homopolymers showed that polymerization of VDF was exclusively initiated by •CF₃ radicals. The addition of •CF₃ radical onto VDF was regioselective leading to CF₃‐CH₂‐CF₂‐PVDF and the CF₃ end‐group acted as an efficient label to assess the molecular weights by ¹⁹F NMR spectroscopy. Various [PPFR]₀/[VDF]₀ initial molar ratios lead to CF₃–PVDF–CF₃ of different molecular weights. When that ratio decreased, both the molecular weights and the thermostability of these PVDFs increased, showing less defects of chaining and higher crystallinity.     

Hydrogenolysis of dichlorotetrafluoroethane isomeric mixtures for obtaining 1.1.1.2 - tetrafluoroethane

1.1.1.2 - Tetrafluoroethane was prepared from isomeric mixture of dichlorotetrafluoroethanes through selective hydrogenolysis of CF₃  CCl₂F catalyzed by Pd/C. The other isomer CClF₂  CClF₂ appeared more stable to hydrogenolysis and at most it was converted at a low degree to the monohydrogenated derivative CHF₂CClF₂.Influence of the three meaningful operating parameters was definided on the basis of a statistical testing program.The mathematical elaboration of the experimental data allowed to define some relations, by which it is possible to foresee conversion of CF₃CCl₂F, yield in CF₃CH₂F end concentration of reaction products, such as CF₃CH₃, CF₃CH₂F, CF₃ CHClF end CClF₂CHF₂ versus the above reported operating parameters.     

Trends and perspectives for the technological and commercial development of fluorine chemicals

1.1.1.2 - Tetrafluoroethane was prepared from isomeric mixtures of dichlorotetrafluoroethanes through selective hydrogenolysis of CF₃CCl₂F catalyzed by Pd/C. The other isomer CClF₂CClF₂ appeared more stable to hydrogenolysis and was only converted partially to the monohydrogenated derivative CHF₂CClF₂.The Influences of the three most important operating parameters were defined on the basis of a statistical, testing program.The mathematical elaboration of the experimental data allowed definition of the relationships by which it is possible to foresee conversion of CF₃CCl₂F, yield of CF₃CH₂F and concentration of reaction products, such as CF₃CH₃, CF₃CH₂F, CF₃CHClF and CClF₂CHF₂ in terms of the above parameters.     

Visible-Light Photosynthesis of CHF2/CClF2/CBrF2-Substituted Ring-fused Quinazolinones in Dimethyl Carbonate

With eco-friendly and sustainable CO₂-derived dimethyl carbonate as the sole solvent, the visible-light-induced cascade radical reactions have been established as a green and efficient tool for constructing various CHF₂/CClF₂/CBrF₂-substituted ring-fused quinazolinones.     

Synthesis and characterization of fluorinated telomers containing vinylidene fluoride and hexafluoropropene from 1,6‐diiodoperfluorohexane

The synthesis of original fluorinated (co)telomers containing vinylidene fluoride (VDF) or VDF and hexafluoropropene (HFP) was achieved by radical telomerizations and (co)telomerizations of VDF (or VDF and HFP) in the presence of 1, 6‐diiodoperfluorohexane via a semisuspension process. tert‐Butyl peroxypivalate (TBPPi) was used as an efficient thermal initiator. The numbers of VDF and VDF/HFP base units in the (co)telomers were determined by ¹⁹F and ¹H NMR spectroscopy. They ranged from 10 to 190 VDF base units. Fluorinated telomers of various molecular weights (1200–12,600 g/mol) were obtained by the alteration of the initial [1,6‐diiodoperfluorohexane]₀/[fluoroalkenes]₀ and [TBPPi]₀/[fluoroalkenes]₀ molar ratios. The thermal properties of these fluorinated (co)telomers, such as the glass‐transition temperature and melting temperature, were examined. As expected, these telomers exhibited good thermal stability. They were stable at least up to 350 °C. The compounds containing more than 30 VDF units were crystalline, whereas all those containing VDF‐co‐HFP were amorphous with elastomeric properties, whatever the number was of the fluorinated base units. The structures of I–(VDF)_n–R_F–(VDF)_m–I and I–(HFP)_x(VDF)_n–R_F–(VDF)_m(HFP)_y–I (co)telomers were obtained, and the defects of the VDF chain and the ? CH₂CF₂I and ? CF₂CH₂I functionalities were studied successfully (where R_F = C₆F₁₂). The functionality in the iodine atoms was modified: the higher the VDF content in the telomers, the lower the normal end functionality (? CH₂CF₂I) and the higher the reversed extremity (? CF₂CH₂I). In addition, the percentage of defects increased when the number of VDF units increased. The molecular weights and molecular weight distributions of different telomers and cotelomers were also studied. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1470–1485, 2006     

Fluorinated block copolymers containing poly(vinylidene fluoride) or poly(vinylidene fluoride‐co‐hexafluoropropylene) blocks from perfluoropolyethers: Synthesis and thermal properties

PFPE‐b‐PVDF and PFPE‐b‐poly(VDF‐co‐HFP) block copolymers [where PFPE, PVDF, VDF, and HFP represent perfluoropolyether, poly(vinylidene fluoride), vinylidene fluoride (or 1,1‐difluoroethylene), and hexafluoropropylene] were synthesized by radical (co)telomerizations of VDF (or VDF and HFP) with an iodine‐terminated perfluoropolyether (PFPE‐I). Di‐tert‐butyl peroxide (DTBP) was used and was shown to act as an efficient thermal initiator. The numbers of VDF and VDF/HFP base units in the block copolymers were assessed with ¹⁹F NMR spectroscopy. According to the initial [PFPE‐I]₀/[fluoroalkenes]₀ and [DTBP]₀/[fluoroalkenes]₀ molar ratios, fluorinated block copolymers of various molecular weights (1500–30,300) were obtained. The states and thermal properties of these fluorocopolymers were investigated. The compounds containing PVDF blocks with more than 30 VDF units were crystalline, whereas all those containing poly(VDF‐co‐HFP) blocks exhibited amorphous states, whatever the numbers were of the fluorinated base units. All the samples showed negative glass‐transition temperatures higher than that of the starting PFPE. Interestingly, these PFPE‐b‐PVDF and PFPE‐b‐poly(VDF‐co‐HFP) block copolymers exhibited good thermostability. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 160–171, 2003     

Thermal expansion of polymers submitted to supercritical CO2 as a function of pressure

Interactions of polymers with compressed supercritical CO₂ has been studied by using pressure‐controlled scanning calorimetry (PCSC). Global cubic thermal expansion coefficients (α_{pol‐g‐int}) for medium density polyethylene (MDPE) and poly(vinylidene fluoride) (PVDF) saturated with supercritical CO₂ have been determined at 352.4 K over the pressure range from 0.1 MPa to 100 MPa. In both cases, the isotherms of global α_{pol‐g‐int} exhibit minima near 20 MPa. At pressures below the minimum, α_{pol‐g‐int} for the PVDF–CO₂ system are higher than for the MDPE–CO₂ system, while at pressures above the minimum the opposite was observed. This proves that incorporation of CO₂ in PVDF is stronger than in MDPE. The appearance of the minimum is attributed to the action of compressed CO₂ molecules, which at higher pressures are forced to enter deep inside the interstitial or other voids in the polymer and cause their mechanical distension, which must be associated with an endothermic effect. The measurements have been performed on polymers used for fabrication of pipelines. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44:185–194, 2006     

Improving the Capture of CO2 by Substituted Monoethanolamines: Electronic Effects of Fluorine and Methyl Substituents

The influence of electronic and steric effects on the reaction between CO₂ and monoethanolamine (MEA) absorbents is investigated using computational methods. The pK_a of the alkanolamine, the reaction enthalpy for carbamate formation, and the hydrolytic carbamate stability are important factors for the efficiency of CO₂ capture. The steric and electronic effects of CH₃, CH₂F, CHF₂, CF₃, F, dimethyl, difluoro, and bis(2‐trifluoromethyl) substituents at the α carbon of MEA on this reaction are investigated. Density functional theory (DFT) (B3LYP, M06‐2X, M08‐HX and M11‐L) and ab initio methods [spin component‐scaled second‐order Møller‐Plesset theory (SCS‐MP2), G3], each coupled with solvent models [conductor‐like polarizable continuum model (CPCM) and universal solvation models (SM8 and SMD)], are shown to yield accurately calculated pK_a values of the substituted MEAs. Specifically, G3, SCS‐MP2, and M11‐L methods coupled with the SMD and SM8 solvation models perform well with a mean unsigned error (MUE) of only 0.15, 0.24 and 0.25 pK_a units, respectively. SCS‐MP2 is used to calculate the reaction enthalpy for carbamate formation and the carbamate stability towards hydrolysis. With the introduction of β‐fluoro substituents (especially the CH₂F moiety) the reaction enthalpy for the formation of carbamates can be fine‐tuned to be less exothermic than that using the unsubstituted MEA. This implies a reduced energy requirement for the solvent‐regeneration step in the post‐combustion carbon‐capture method, which is currently the energy‐limiting step in efficient CO₂ capture. β‐Fluoro‐substituted MEAs are also shown to form less stable carbamates than MEA. Thus, β‐fluoro‐substituted MEAs display a great potential for the use in the post‐combustion carbon‐capture process. Finally, a clear correlation is observed between the gas‐phase basicity and the tendency to form carbamates. This allows for the rapid prediction of which species will be formed experimentally, and thus the CO₂‐absorbing capacities of alkanolamines can be estimated.     

Synthesis of poly(vinylidene fluoride)‐b‐poly(styrene sulfonate) block copolymers by controlled radical polymerizations

Block copolymers based on poly(vinylidene fluoride), PVDF, and a series of poly(aromatic sulfonate) sequences were synthesized from controlled radical polymerizations (CRPs). According to the aromatic monomers, appropriate techniques of CRP were chosen: either iodine transfer polymerization (ITP) or atom transfer radical polymerization (ATRP) from PVDF‐I macromolecular chain transfer agents (CTAs) or PVDF‐CCl₃ macroinitiator, respectively. These precursors were produced either by ITP of VDF with C₆F₁₃I or by radical telomerization of VDF with chloroform, respectively. Poly(vinylidene fluoride)‐b‐poly(sodium styrene sulfonate), PVDF‐b‐PSSS, block copolymers were produced from both techniques via a direct polymerization of sodium styrene sulfonate (SSS) monomer or an indirect way with the use of styrene sulfonate ethyl ester (SSE) as a protected monomer. Although the reaction led to block copolymers, the kinetics of ITP of SSS showed that PVDF‐I macromolecular CTAs were not totally efficient because a limitation of the CTA consumption (56%) was observed. This was probably explained by both the low activity of the CTA (that contained inefficient PVDF‐CF₂CH₂? I) and a fast propagation rate of the monomer. That behavior was also noted in the ITP of SSE. On the other hand, ATRP of SSS initiated by PVDF‐CCl₃ was more controlled up to 50% of conversion leading to PVDF‐b‐PSSS block copolymer with an average number molar mass of 6000 g·mol^?1. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Nickel Fluorocarbene Metathesis with Fluoroalkenes

Alkene metathesis with directly fluorinated alkenes is challenging, limiting its application in the burgeoning field of fluoro‐organic chemistry. A new nickel tris(phosphite) fluoro(trifluoromethyl)carbene complex ([P₃Ni]=CFCF₃) reacts with CF₂=CF₂ (TFE) or CF₂=CH₂ (VDF) to yield both metallacyclobutane and perfluorocarbene metathesis products, [P₃Ni]=CF₂ and CR₂=CFCF₃ (R=F, H). The reaction of [P₃Ni]=CFCF₃ with trifluoroethylene also yields metathesis products, [P₃Ni]=CF₂ and cis/trans‐CFCF₃=CFH. However, unlike reactions with TFE and VDF, this reaction forms metallacyclopropanes and fluoronickel alkenyl species, resulting presumably from instability of the expected metallacyclobutanes. DFT calculations and experimental evidence established that the observed metallacyclobutanes are not intermediates in the formation of the observed metathesis products, thus highlighting a novel variant of the Chauvin mechanism enabled by the disparate four‐coordinate transition states.     

Correlations between microstructure and crystallization of the fluorinated terpolymer of tetrafluoroethylene,hexafluoropropylene, and vinylidene fluoride

Random THV terpolymers consisting of tetrafluoroethylene (TFE), hexafluoropropylene (HFP), and vinylidene fluoride (VDF) are viable alternatives to polytetrafluoroethylene (PTFE) combining excellent chemical stability and thermoplastic processability. Although the properties of THV may be modified by crystallization, little is known on how crystallization is influenced by the chain microstructure of THV. We analyzed the chain microstructure of THV‐221G by solid‐state ¹⁹F NMR spectroscopy under fast magic angle spinning, revealing that THV‐221G contains 43.8 mol % TFE, 46.0 mol % VDF, and 10.2 mol % HFP. Sequence analysis revealed that the TFE units are preferentially located next to other TFE units. The HFP units, which are obstacles to crystallization because of their bulky CF₃ side groups, are preferentially located next to VDF units. WAXS measurements correspondingly revealed the presence of THV‐221G crystals with PTFE‐like packing and of further THV‐221G crystal populations with widened d‐spacings caused by the incorporation of certain amounts of HFP units into the THV‐221G crystals. Under confinement imposed by the cylindrical nanopores of self‐ordered alumina, the THV‐221G melting point decreased with decreasing pore diameter. Although direct impingement of the growing THV‐221G crystals on the pore walls is unlikely, the geometric confinement limits the access of growing THV‐221G crystals to crystallizable THV‐221G chain segments. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1402–1408     

Multiscale Computational Study on the Adsorption and Separation of CO2/CH4 and CO2/H2 on Li+‐Doped Mixed‐Ligand Metal–Organic Framework Zn2(NDC)2(diPyNI)

The quantum mechanics (QM) method and grand canonical Monte Carlo (GCMC) simulations are used to study the effect of lithium cation doping on the adsorption and separation of CO₂, CH₄, and H₂ on a twofold interwoven metal–organic framework (MOF), Zn₂(NDC)₂(diPyNI) (NDC=2,6‐naphthalenedicarboxylate; diPyNI=N,N′‐di‐(4‐pyridyl)‐1,4,5,8‐naphthalenetetracarboxydiimide). Second‐order Moller–Plesset (MP2) calculations on the (Li⁺–diPyNI) cluster model show that the energetically most favorable lithium binding site is above the pyridine ring side at a distance of 1.817 Å from the oxygen atom. The results reveal that the adsorption capacity of Zn₂(NDC)₂(diPyNI) for carbon dioxide is higher than those of hydrogen and methane at room temperature. Furthermore, GCMC simulations on the structures obtained from QM calculations predict that the Li⁺‐doped MOF has higher adsorption capacities than the nondoped MOF, especially at low pressures. In addition, the probability density distribution plots reveal that CO₂, CH₄, and H₂ molecules accumulate close to the Li cation site. The selectivity results indicate that CO₂/H₂ selectivity values in Zn₂(NDC)₂(diPyNI) are higher than those of CO₂/CH₄. The selectivity of CO₂ over CH₄ on Li⁺‐doped Zn₂(NDC)₂(diPyNI) is improved relative to the nondoped MOF.     

Measurements and modeling of cloud point behavior for polypropylene/n-pentane and polypropylene/n-pentane/carbon dioxide mixtures at high pressure

The phase behavior of polypropylene (PP) in n-pentane and n-pentane/carbon dioxide solvent mixtures has been studied using a high-pressure variable volume view cell. Cloud point pressures for polypropylene (M_w=50,400) in near-critical n-pentane were studied at temperatures ranging from 432 to 470 K for polymer concentrations of 1 to 15 mass%. Furthermore, cloud point pressures for polypropylene (M_w=95,400) in near-critical n-pentane were studied at temperatures ranging from 450 to 465 K for polymer concentrations of 1 to 8 mass%. Cloud point pressures were also measured for PP (M_w=200,000, 3 mass%) in n-pentane at temperatures ranging from 450 K to 465 K. The cloud point pressures for PP (M_w=50,400) in n-pentane/CO₂ mixtures were determined for PP concentrations of 3.0 mass% and 9.7 mass% with CO₂ solvent concentrations ranging from 12.6 mass% to 42.0 mass% at temperatures ranging from 405 K to 450 K. All of the experimental cloud point isopleths were relatively linear with approximately the same positive slope indicating LCST behavior. The experimental cloud point pressures were relatively insensitive to the concentration and molecular weight of polypropylene. At a given temperature, the cloud point pressure of the PP/n-pentane/carbon dioxide system increased almost linearly with increasing carbon dioxide solvent concentration (for carbon dioxide concentrations less than 30 mass%). The Sanchez–Lacombe (SL) equation of state was used to model the experimental data.     

Synthesis and characterization of N,N‐diethyldithiocarbamate complexes of 2‐alkoxycarbonylethyltin trichloride

N,N‐Diethyldithiocarbamate complexes of 2‐alkoxycarbonylethyltin trichloride, ROCOCH₂CH₂ SnCl_3?x[S₂CNEt₂]_x (R = CH₃ ( a ); CH₃CH₂ ( b ); CH₂?CHCH₂ ( c ); CH₃CH₂CH₂ ( d ); CH₃CH₂CH₂CH₂ ( e ); x = 1 ( 1 ), 2 ( 2 )) were synthesized and characterized by means of elemental analysis, IR, and NMR (¹H, ¹³C and ¹¹⁹Sn) spectra. The crystal structure of 1b (i.e. R = CH₃CH₂, x = 1) was determined and shows that the tin atom adopts a distorted octahedral geometry with both a five‐membered chelate ring, formed via carbonyl coordination to tin, and a four‐membered chelate ring, formed by the bidentate dithiocarbamate. The spectral data and ab initio calculations indicate that intramolecular carbonyl‐oxygen to tin coordination in 1a–1e persists, but not in 2a–2e , owing to the preference of the dithiocarbamate ligands to chelate the tin centre. Copyright © 2005 John Wiley & Sons, Ltd.     

High‐resolution solid‐state NMR study of the domain structure and molecular motion in drawn films of a vinylidene fluoride and trifluoroethylene copolymer with 73 mol % vinylidene fluoride

The heterogeneous higher order structure and molecular motion in a single crystalline film of a vinylidene fluoride (VDF) and trifluoroethylene (TrFE) copolymer with 73 mol % VDF was investigated with the ¹H–¹³C cross‐polarization/magic‐angle spinning NMR technique. A transient oscillation was observed in plots of the ¹³C peak intensity versus the contact time for the CH₂, CHF, and CF₂ groups. On the basis of the extended cross‐relaxation theory of spin diffusion, we determined that the oscillation behavior was caused by the TrFE‐rich segments in the chain and that the crystal consisted of VDF‐rich and TrFE‐rich domains. The former had TrFE‐rich segments in VDF and TrFE fractions of 0.24 and 0.27, respectively, and the latter had VDF‐rich segments in a VDF fraction of 0.49. The spin–lattice relaxation time T_1ρH in the rotating frame for each group was minimal in the three temperature regions of β, α_b, and α_c (↑) on heating and in the two temperature regions of α_1D and α_c (↓) on cooling. The α_c (↑) and α_c (↓) processes depended on the first‐order ferroelectric phase‐transition regions on heating and cooling, respectively. The motional modes for the other processes were confirmed by the T_1ρH minimum behavior of the VDF and TrFE groups in the TrFE‐rich domain and the VDF‐rich segments in the VDF‐rich domain. The β and α_b processes were attributed to the flip–flop motion of the TrFE‐rich segments and the competitive motion of the TrFE‐ and VDF‐rich segments in the ferroelectric phase, respectively. The α_1D process was due to the one‐dimensional diffusion motion of the conformational defects along the chain in the paraelectric phase, accompanied by the trans and gauche transformation of the VDF conformers of ttg⁺tg^? and g⁺tg^?tt. The effect of the competitive motion of the TrFE‐rich segment on the thermal stability of the VDF‐rich segment in the chain near the Curie temperature was examined. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1026–1037, 2002     

Kinetics of the iodine transfer polymerization of vinylidene fluoride

The kinetics of the iodine transfer polymerization (ITP) of vinylidene fluoride (VDF) was achieved in the presence of three different chain‐transfer agents (CTAs): 1‐iodoperfluorohexane (C₆F₁₃I), 1‐iodo‐2H,2H‐perfluorooctane (C₆F₁₃CH₂CF₂I), and 1,1,2,2‐tetrafluoro‐3‐iodopropane (HCF₂CF₂CH₂I). ITPs of VDF carried out in the presence of C₆F₁₃I and C₆F₁₃CH₂CF₂I showed the following: (1) a linear increase in DP_n versus α_VDF, which evidenced the controlled character of ITP, although the polydispersity indices were slightly high (ca 1.5), and (2) theoretical DP_n values close to the targeted ones. In contrast, neither of these statements was observed for the ITP of VDF in the presence of HCF₂CF₂CH₂I achieved under the same conditions, even if the synthesized oligomers could be reactivated. Although the C_Tr values of C₆F₁₃I and C₆F₁₃CH₂CF₂I were close (i.e., 7.7 at 75 °C), that of HCF₂CF₂CH₂I was lower (0.3 at 75 °C). The percentages of ? CF₂I and ? CH₂I functionalities were also assessed, and in the course of the reaction, a reduction of ? CF₂I end groups was noted. Then, the mechanism of the ITP of VDF was proposed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5763–5777, 2006     

Properties of 2,2,2‐Trifluoroethanol/Water Mixtures: Acidity,Basicity, and Dipolarity

In this report, we focus our attention on the characterization of 2,2,2‐trifluoroethanol(TFE)/H₂O mixtures and describe their intrinsic parameters; i.e., solvent acidity (SA), solvent basicity (SB), and solvent dipolarity/polarizability (SPP), by the probe/homomorph‐couple method for a range of mixtures from 0–100% (v/v) TFE. Variation of these parameters is not linear and has a singular and unpredictable behavior depending on the precise composition of the mixture. Based on these parameters, we describe the TFE‐induced changes in some physical properties; i.e., viscosity (η), partial molar volume (V?), density (ρ), dielectric constant (ε), vapor pressure (p_v), and spectroscopic properties; i.e., NMR chemical shifts (δ(¹H)) of TFE Me group for all molar fractions studied. In addition, by means of CD studies, we report that formation of the secondary structure, as percentage of helical content, θ, of a polypeptide, poly(L ‐lysine), in several TFE/H₂O mixtures is adequately described by these mixture parameters. SA, SB, and SPP of TFE/H₂O mixtures provide an excellent tool for the interpretation of formation and stability of intramolecular H‐bonds, and, thus, of secondary structures in polypeptides.     

Decomposition Mechanism of Fluorinated Compounds in Water Plasmas Generated Under Atmospheric Pressure

Decomposition mechanism of HFC-134a, HFC-32, and CF₄ in water plasmas at atmospheric pressure has been investigated. The decomposition efficiency of 99.9% can be obtained up to 3.17 mol kWh⁻¹ of the ratio of hydrofluorocarbon (HFC) feed rate to the arc power and 1.89 mol kWh⁻¹ of the ratio of perfluorocarbon (PFC) feed rate to the arc power. The species such as H₂, CO, CO₂, CH₄, and CF₄ were detected from the effluent gas of both PFC and HFC decomposition. However, CH₂F₂ and CHF₃ were observed only in the case of HFC decomposition. The HFC and PFC decomposition generate CH₂F, CHF_{x (x:1–2)}, and CF_{y (y:1–3)} radicals, then those radicals were subsequently oxidized by oxygen, leading to CO and CO₂ generation in the excess oxygen condition. However, when there is insufficient oxygen available, those radicals were easily recombined with fluorine to form by-product such as CH₂F₂, CHF₃, and CF₄.     

Carbon Dioxide Capture and Release by Anions with Solvent‐Dependent Behaviour: A Theoretical Study

Recently, Clyburne and co‐workers [Science, 2014 , 344, 75–78] reported the novel synthesis of the elusive cyanoformate anion, NCCO₂^?. The stability of this anion is dependent on the dielectric constant of the local environment (polarity‐switchable solvent): it is stable in low‐polarity media and unstable in high‐polarity solvents; hence, capturing and then releasing CO₂. The possibility of extending such behaviour to other anions is explored herein. Specifically, the CO₂ capture process is studied for 26 anions in the gas phase and 3 distinct solvents (water, tetrahydrofuran, and toluene) by using the polarisable continuum model. Calculations are performed with the M06‐2X and B3LYP‐D3 density functionals and the aug‐cc‐pVTZ basis set. The design of new CO₂ complexes with the anion, which can be formed or destroyed on demand by changing the solvent, is possible; the results for the alkoxylate and thiolate anions are especially promising. The nature of the substituents connected to the atom that bonds to CO₂ in the anion is crucial in modulating the relative stability of the products—a key point for reversibility in the CO₂ capture process. A moderate interaction for the anion–CO₂ adduct—about 10 kcal mol^?1 relative free energy with respect to the isolated reactants in the gas phase—and a relevant effect in the dielectric constant of the local environment are also key ingredients to achieve solvent dependency.