Search

Copyright of China Tropical Medicine is the property of China Tropical Medicine Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Under the control of the Montreal Protocol and its amendments, hydrofluorocarbons (HCFCs) are used as temporary substitutes for ozone-depleting substances, such as chlorofluorocarbons, and are regulated for consumption and production. China plans to phase out HCFCs by 2030, and HCFC-22 (CHClF2) is currently the most abundant HCFC in the atmosphere. This study measures the vertical profiles and total columns of atmospheric HCFC-22 from January 2017 to December 2022, based on the mid-infrared solar spectra recorded by the ground-based high-resolution Fourier transform infrared (FTIR) spectrometer at the Hefei remote sensing station. The HCFC-22 total columns over Hefei increased from 2017–2018 and gradually decreased in 2018–2022, with an annual variation rate of 5.98% and −1.02% ± 0.02%, respectively. Compared with the ACE-FTS satellite independent dataset, the FTIR data indicate good consistency with the ACE-FTS data at a 5–25 km altitude, with an average relative difference of −4.38 ± 0.83% between the vertical profiles. HCFC-22 emissions in the Yangtze River Delta from 2017 to 2022 are estimated, derived from measured total columns combined with the Lagrangian transport model and the Bayesian inversion technique. In the Yangtze River Delta, HCFC-22 emissions were high in 2017, with a value of 33.3 ± 16.8 kt, and decreased from 2018 to 2022, with a minimum of 27.3 ± 13.6 kt in 2022 during the observations. [ABSTRACT FROM AUTHOR]

The IR transmittance spectrum of an isotopic mixture of chlorodifluoromethane (CHF2Cl, Ereon-22) with a 33% fraction of 13C and a natural ratio of chlorine isotopes was measured in the frequency range 1400–740 cm–1 with a resolution of 0.001 cm–1 at a temperature of 20°C. An ab initio calculation of the structure and sextic potential energy surface and surfaces of the components of the dipole moment has been carried out by the electronic quantum-mechanical method of Moller–Plesset, MP2/cc-pVTZ. Then the potential was optimized by replacing the harmonic frequencies with the frequencies calculated by the electronic method of coupled clusters, CCSD(T)/aug-cc-pVQZ. The fundamental and combination frequencies were calculated using the operator perturbation theory of Van Vleck (CVPTn) of the second and fourth order (n = 2, 4). Resonance effects were modeled using an additional variational calculation in the basis up to fourfold VCI excitation (4). The average prediction error for the fundamental frequencies of the 12C isotopologues was ~1.5 cm–1. The achieved accuracy made it possible to reliably predict the isotopic frequency shifts of the 13C isotopologues. It is shown that the strong Fermi resonance ν4/2ν6 dominates in the 12C isotopologues and is practically absent in 13C. The literature assumption [Spectrochim. Acta A, 44:553] about the splitting of ν1(CH) due to the resonance ν1/ν2 + ν7 + ν9 is confirmed. The coefficients of the polyadic quantum number are determined. The analysis made it possible to carry out a preliminary identification of the centers of the vibrational-rotational bands of isotopologues 13CHF235Cl and 13CHF237Cl in the spectrum of the mixture in preparation for individual analyzes of the vibrational-rotational structures of individual vibrational transitions. [ABSTRACT FROM AUTHOR]

Under the control of the Montreal Protocol and its amendments, hydrofluorocarbons (HCFCs) are used as temporary substitutes for ozone-depleting substances, such as chlorofluorocarbons, and are regulated for consumption and production. China plans to phase out HCFCs by 2030, and HCFC-22 (CHClF2) is currently the most abundant HCFC in the atmosphere. This study measures the vertical profiles and total columns of atmospheric HCFC-22 from January 2017 to December 2022, based on the mid-infrared solar spectra recorded by the ground-based high-resolution Fourier transform infrared (FTIR) spectrometer at the Hefei remote sensing station. The HCFC-22 total columns over Hefei increased from 2017–2018 and gradually decreased in 2018–2022, with an annual variation rate of 5.98% and −1.02% ± 0.02%, respectively. Compared with the ACE-FTS satellite independent dataset, the FTIR data indicate good consistency with the ACE-FTS data at a 5–25 km altitude, with an average relative difference of −4.38 ± 0.83% between the vertical profiles. HCFC-22 emissions in the Yangtze River Delta from 2017 to 2022 are estimated, derived from measured total columns combined with the Lagrangian transport model and the Bayesian inversion technique. In the Yangtze River Delta, HCFC-22 emissions were high in 2017, with a value of 33.3 ± 16.8 kt, and decreased from 2018 to 2022, with a minimum of 27.3 ± 13.6 kt in 2022 during the observations.

Chlorodifluoromethane (HCFC-22) is one of the air pollutants that destroy the ozone layer and warm the earth. In order to degrade HCFC-22, the catalytic hydrolysis method is currently the most effective environmental technology. Herein, we prepare solid acid MoO3/ZrO2 and solid base MgO/ZrO2 catalysts for the degradation of HCFC-22, with a particular focus on revealing the effects of the catalyst preparation methods, calcination temperatures, and hydrolysis temperatures on the hydrolyzation and hydrolysis rates of HCFC-22. The catalysts are characterized by XRD, N2 isothermal adsorption–desorption, and NH3-TPD. The results show that the solid acid (base) MoO3(MgO)/ZrO2 catalysts have strong catalytic activity for the degradation of HCFC-22, while the catalytic activity of the solid acid MoZr is better than that of the solid base MgZr catalyst and the hydrolysis rate can reach more than 90%. The water vapor generates B-acid centers on the MoO3(MgO)/ZrO2 framework and promotes the hydrolysis of HCFC-22 to HF and HCl. [ABSTRACT FROM AUTHOR]

Chlorodifluoromethane (HCFC-22) is one of the air pollutants that destroy the ozone layer and warm the earth. In order to degrade HCFC-22, the catalytic hydrolysis method is currently the most effective environmental technology. Herein, we prepare solid acid MoO3/ZrO2 and solid base MgO/ZrO2 catalysts for the degradation of HCFC-22, with a particular focus on revealing the effects of the catalyst preparation methods, calcination temperatures, and hydrolysis temperatures on the hydrolyzation and hydrolysis rates of HCFC-22. The catalysts are characterized by XRD, N2 isothermal adsorption–desorption, and NH3-TPD. The results show that the solid acid (base) MoO3(MgO)/ZrO2 catalysts have strong catalytic activity for the degradation of HCFC-22, while the catalytic activity of the solid acid MoZr is better than that of the solid base MgZr catalyst and the hydrolysis rate can reach more than 90%. The water vapor generates B-acid centers on the MoO3(MgO)/ZrO2 framework and promotes the hydrolysis of HCFC-22 to HF and HCl.

The deuteriodifluoromethyl group (CF2D) represents a challenging functional group due to difficult deuterium incorporation and unavailability of precursor reagents. Herein, we report the use of chlorodifluoromethane (ClCF2H) gas in the continuous flow deuteriodifluoromethylation and gem‐difluoroalkenylation of aldehydes. Mechanistic studies revealed that the difluorinated oxaphosphetane (OPA) intermediate can proceed via alkaline hydrolysis in the presence of D2O to provide α‐deuteriodifluoromethylated benzyl alcohols or undergo a retro [2+2] cycloaddition under thermal conditions to provide the gem‐difluoroalkenylated product. [ABSTRACT FROM AUTHOR]

Tetrafluoroethylene (TFE) and hexafluoropropylene (HFP) are the most common monomers for the synthesis of fluoropolymers at industrial scale. Currently, TFE is produced via multistep pyrolysis of chlorodifluoromethane (R22), resulting in a high energy demand and high amounts of waste acids, mainly HCl and HF. In this study, a new chlorine-free process for producing TFE and HFP in a microreactor is presented, starting from partially fluorinated alkanes obtained from electrochemical fluorination (ECF). In the microreactor, high conversion rates of CHF3, which is used as a surrogate of partly fluorinated ECF streams, and high yields of fluoromonomers could be achieved. The energy saving and the environmental impact are shown by a life cycle assessment (LCA). The LCA confirms that the developed process has economical as well as ecological benefits, and is thus an interesting option for future industrial production of fluoroalkenes. [ABSTRACT FROM AUTHOR]

An effective protocol for the difluoromethylation of tosylhydrazone compounds under mild conditions is disclosed via a transition‐metal‐free pathway; ClCF2H is almost quantitatively converted under the set conditions. In this transformation, the process in which tosylhydrazones are decomposed to lead to diazo species has been completely suppressed. This transformation enables tosylhydrazones as efficient difluorocarbene scavengers and the corresponding difluoromethylated products were obtained in good yields with high functional‐group tolerance. [ABSTRACT FROM AUTHOR]

Highlights • Explosion of R22 and R600a was adequately prevented by critical explosion parameters. • Explosion behavior of R22 and R600a at high pressure and temperature was identified. • An appropriate mathematical model was selected for explosion study. Abstract At normal pressure, the refrigerant R-22 (chlorodifluoromethane) does not exhibit explosion behaviour at 30.0, 60.0, 90.0, and 120.0 °C in a 20-L apparatus. However, an increase in the pressure to 10.0 bar at room temperature caused an explosion (lower explosion limit, 16.4 vol%), and maximum explosion pressure occurred at a refrigerant concentration of 40 vol% at 10.0 bar. Thus, R-22 can change from being non-flammable to flammable with an increase in pressure. The explosion limit of the refrigerant R-600a (isobutane) can be changed by increasing the pressure and temperature, thereby increasing the explosion risk. Experimental studies have revealed that the explosion limit of R-600a is 1.5–9.0 vol% at room temperature. This limit is consistent with that specified previously and that predicted here, demonstrating that the experimental data are reliable. This study provides useful information for safer refrigerant design involving R-22 and R-600a at a high pressure and temperature. [ABSTRACT FROM AUTHOR]

Successful laser treatment of selected dermatoses such as hemangiomas requires thermally induced damage to blood vessels while protecting the epidermis. We present and test a procedure in a rabbit liver tissue model that utilizes cryogen spray cooling during continuous Nd:YAG laser irradiation to induce deep photocoagulation necrosis while protecting superficial tissues from thermal injury. Gross and histologic observations are consistent with calculated thicknesses of protected and photocoagulated tissues and demonstrate the feasibility of inducing spatially selective photocoagulation when cryogen spray cooling is used in conjunction with laser irradiation. This procedure may be useful in the thermal treatment of some pathological conditions for which it is desired that deep photocoagulation be induced while protecting superficial tissues.

Poly (lactic acid) (PLA) is typical biocompatible polymer, and is widely used in drug delivery application. For the production of polymeric microspheres loaded with the pharmaceutical, the supercritical fluid technology using carbon difoxide (CO 2 ) is favor because of non-toxic nature. In this work, the phase behaviors of PLA in various supercritical solvents such as dimethyl ether (DME), CO 2 , chlorodifluoromethane (HCFC-22), difluoromethane, trifluoromethane (HFC-23), 1,1,1,2-tetrafluoroethane, 1,1-difluoroethane are described by PC-SAFT model. One binary interaction parameter without considering temperature-dependency is used over a wide range of temperature and pressure. CO 2 shows the poorest solubility, while HCFC-22 and DME show the highest solubility. The predicted cloud-point pressure shows the increasing tendency with an increase of PLA's molecular weight. In addition, the pressure-temperature isopleths for the dl-PLA/CO 2 solutions with DME, HCFC-22, and HFC-23 as a cosolvent are investigated. The predicted results for three ternary systems with PC-SAFT model show a good agreement with experimental data. [ABSTRACT FROM AUTHOR]

A method for the radical chlorodifluoromethylation of (hetero)arenes using chlorodifluoroacetic anhydride is reported. This operationally simple protocol proceeds under mild photochemical conditions with high functional group compatibility and complements the large body of literature for the trifluoromethylation of (hetero)arenes. Introduction of the chlorodifluoromethyl motif enables rapid diversification to a wide array of aromatic scaffolds. This work showcases the chlorodifluoromethyl group as an attractive entryway to otherwise synthetically challenging electron-rich difluoromethyl(hetero)arenes. Furthermore, facile conversion of the CF2Cl moiety into the corresponding aryl esters, gem-difluoroenones, and β-keto-esters is demonstrated. [ABSTRACT FROM AUTHOR]

Infrared laser conversion of chlorodifluoromethane (CF2HCl) enriched in 13C to 31%, to dibromodifluoromethane (CF2Br2) with the same enrichment has been studied. Optimum conditions have been found, and effective laser synthesis of macroscopic amounts (1 g) of CF2Br2 has been carried out. IR absorption spectra of synthesized CF2Br2 with a 13C concentration of 31% have been recorded. The 13C isotope shifts of the ν1, ν6, and ν8 modes have been measured. [ABSTRACT FROM AUTHOR]

Indoor air quality (IAQ) in schools is a matter of concern because children are most vulnerable and sensitive to pollutant exposure. Conservation of energy at the expense of ventilation in heating, ventilation, and air conditioning (HVAC) systems adversely affects IAQ. Extensive use of new materials in building, fitting, and refurbishing emit various pollutants such that the indoor environment creates its own discomfort and health risks. Various schools in Kuwait were selected to assess their IAQ. Comprehensive measurements of volatile organic compounds (VOCs) consisting of 72 organic compounds consisting of aliphatic (C3–C6), aromatic (C6–C9), halogenated (C1–C7), and oxygenated (C2–C9) functional groups in indoor air were made for the first time in schools in Kuwait. The concentrations of indoor air pollutants revealed hot spots (science preparation rooms, science laboratories, arts and crafts classes/paint rooms, and woodworking shops/decoration rooms where local sources contributed to the buildup of pollutants in each school. The most abundant VOC pollutant was chlorodifluoromethane (R22; ClF2CH), which leaked from air conditioning (AC) systems due to improper operation and maintenance. The other copious VOCs were alcohols and acetone at different locations due to improper handling of the chemicals and their excessive uses as solvents. Indoor carbon dioxide (CO2) levels were measured, and these levels reflected the performance of HVAC systems; a specific rate or lack of ventilation affected the IAQ. Recommendations are proposed to mitigate the buildup of indoor air pollutants at school sites. Implications: Indoor air quality in elementary schools has been a subject of extreme importance due to susceptibility and sensibility of children to air pollutants. The schools were selected based on their surrounding environment especially downwind direction from the highly industrialized zone in Kuwait. Extensive sampling from different sites in four schools for comprehensive VOCs and CO2were completed for an extended period of over a year. Different hot spots were identified where leaked refrigerant and inadequate handling of laboratory solvents contributed to the high VOCs in the respective locations. CO2levels reflected HVAC performance and poor ventilation. A list of recommendations has been proposed to eradicate these high levels of air pollution. [ABSTRACT FROM AUTHOR]

[Display omitted] • The study of dichloromethane under a weak electric field has been carried out for the first time. • The study of potential energy surface was carried out to do further research on dissociation property of dichloromethane. • The degradation of dichloromethane under a certain electric field was verified for the first time. • Concerted dissociation in the dichloromethane molecule was found and calculated for the first time. Chlorodifluoromethane (HCFC-22) is a kind of greenhouse gas, the study of its properties and dissociation methods is of great value to reduce its pollution. Based on the density functional theory (DFT), the structure, spectra and dissociation characteristics of HCFC-22 gas molecules under applied electric field (0 V·nm−1–12.856 V·nm−1) are discussed at the 6–311 G++ (d, p) level. The results all show that HCFC-22 molecule is more easily dissociated under an external electric field. The dissociation characteristic of the molecule is as follow: the dissociation barrier decreases gradually with the increase of external electric field. In addition, the UV–Vis spectrum of HCFC-22 is redshifted and the excitation energy decreases gradually under the action of external electric field. The results of this study provide theoretical support for the application of electric field to degrade HCFC-22 molecules, which can help solve the problem of air pollution. [ABSTRACT FROM AUTHOR]

An apparatus based on the “static-analytic” method was designed and commissioned. The apparatus was tested by measuring vapour-liquid equilibrium data for the binary system of carbon dioxide + chlorodifluoromethane at 273.15 K. There is excellent agreement between the experimental data and previous measurements reported in the literature. New experimental vapour-liquid equilibrium data were also measured for the binary systems of ethylene + chlorodifluoromethane at five temperatures, viz. (273.15, 293.15, 313.15, 333.15, and 353.15) K. At the same temperatures (excluding 273.15 K) the critical points of the binary mixtures were also experimentally determined. The experimental data for this binary system were accurately correlated using the Peng–Robinson Equation of State utilizing the Wong–Sandler mixing rule coupled with the Non-Random Two-Liquid (NRTL) activity coefficient model. [ABSTRACT FROM AUTHOR]

The phase equilibrium behavior data are presented for three kinds of commercial polymer-bonded explosive (PBX) elastomers in chlorodifluoromethane (HCFC22). $$\hbox {Levapren}^{{\textregistered }}$$ ethylene- co-vinyl acetate (LP-EVA), $$\hbox {HyTemp}^{{\textregistered }}$$ alkyl acrylate copolymer (HT-ACM), and $$\hbox {Viton}^{{\textregistered }}$$ fluoroelastomer (VT-FE) were used as the PBX elastomers. For each elastomer + HCFC22 system, the cloud point (CP) and/or bubble point (BP) pressures were measured while varying the temperature and elastomer composition using a phase equilibrium apparatus fitted with a variable-volume view cell. The elastomers examined in this study indicated a lower critical solution temperature phase behavior in the HCFC22 solvent. LP-EVA showed the CPs at temperatures of 323 K to 343 K and at pressures of 3 MPa to 10 MPa, whereas HT-ACM showed the CPs at conditions between 338 K and 363 K and between 4 MPa and 12 MPa. For the LP-EVA and HT-ACM elastomers, the BP behavior was observed at temperatures below about 323 K. For the VT-FE + HCFC22 system, only the CP behavior was observed at temperatures between 323 K and 353 K and at pressures between 6 MPa and 21 MPa. As the elastomer composition increased, the CP pressure increased, reached a maximum value at a specific elastomer composition, and then remained almost constant. [ABSTRACT FROM AUTHOR]

In this study, the Boyle temperature of 174 substances are predicted using the cubic and volume – translated cubic equations of state. In this regard, the Peng - Robinson (PR), Soave – Redlich – Kwong (SRK), volume – translated Peng – Robinson (VTPR), volume – translated Soave – Redlich – Kwong (VTSRK) and Patel – Teja – Valderrama (PTV) equations of state are used. The Boyle temperature is calculated for different polar, non – polar and associating substances including alkanes, cycloalkanes, alkenes, aromatics, ethers, esters, ketones, refrigerants, halogens, amines and water. The obtained results are compared with the results of other known correlations published so far, such as Tsonopoulos, Meng – Duan and Estrada – Torres et al. equations. For better understanding, the second virial coefficient and the Zeno line (unit compressibility) are also calculated and compared with the available experimental data. The results show that PR, VTPR and PTV have lower average temperature difference between EoSs and Tsonopoulos or Meng – Duan correlations. The dependency of the reduced Boyle temperature ( T B / T C ) as functions of the Pitzer's acentric factor ( ω ), hydrocarbon chain length ( N C ) and the reduced dipole moment ( μ R ) has been also studied. [ABSTRACT FROM AUTHOR]

Herein, we present the development of a continuous-flow process for a difluoromethylation with difluorocarbene as the reactive reagent. The difluoromethylated product is a key intermediate during the synthesis of eflornithine, a pharmaceutical that is on the World Health Organization's Model List of Essential Medicines. The developed procedure uses inexpensive and commercially available chlorodifluoromethane (CHF2Cl, Freon 22) as difluorocarbene source. Deprotonation of CHF2Cl with NaOH in a biphasic mixture of organic solvent-water generates the carbene. A fast subsequent reaction of the difluorocarbene with the substrate generates the desired product with excellent selectivity. [ABSTRACT FROM AUTHOR]

Trifluoromethane (R23), a ubiquitous byproduct of chlorodifluoromethane (R22) synthesis, is one of the most potential greenhouse gases. The encouraged approach is thermal oxidation to process the vent gas by the clean development mechanism (CDM). Though such an approach could avoid the adverse environmental impacts, it will result in a great economic loss that includes not only the incineration cost but also the waste resource of R23. R23 is valuable as a refrigerant, fire suppression agent, and plasma etchant (purity: 99.999 mol %). In this work, the distillation-pressure swing adsorption (DIST-PSA) process was employed to concentrate R23 from 88% to 99.999% in the vent gas economically. Dynamic breakthrough experiments were performed to predict the adsorbent separation performance. Results indicated the coconut activated carbon (SAC-1) is appropriate material for R23 and R22 separation. The SAC-1 has a high separation factor value for R22 and R23 under the experimental conditions. Afterward, the DIST-PSA hybrid system was studied by process simulation and their energy consumption was analyzed. According to the comprehensive analysis, the best performance is obtained with a feed composition of 88% R23/12% R22 for the PSA unit. Process simulation predicts R23 recovery, purity, and energy consumption, respectively, of 69.52%, 99.9993% and 99.59 kJ·kg-1 R23. Overall, our studies have revealed that coupling a PSA unit with distillation is a feasible and promising technique to separate high-purity R23 efficiently and economically in the R22 synthesis industries. [ABSTRACT FROM AUTHOR]

The reaction of chlorodifluoromethane (R-22) with sodium methoxide produces difluoromethoxymethane, an alternative refrigerant with low ozone depleting potential. In this study a kinetic model of the dehydrochlorination process was identified, based on rate data obtained from a semi-batch gas–liquid reactor. The reaction was studied at a reaction temperature of 283–303 K, R-22 inlet partial pressures of 40.5–60.8 kPa and initial sodium methoxide concentrations between 1.5 and 2.5 mol·dm −3 . The products obtained were difluoromethoxymethane and trimethyl orthoformate as well as sodium chloride and fluoride salts. The reaction proceeds via a three step mechanism, initiated by an α -elimination and involving a difluoromethylene intermediate. The elimination step has an identified pre-exponential factor of 1.18 × 10 4 dm 3 ·mol −1 ·min −1 and activation energy of 15.54 kJ·mol −1 . The reaction yielding the target compound has a pre-exponential factor of 1.15 × 10 8 dm 3 ·mol −1 ·min −1 and activation energy of 47.67 kJ·mol −1 . The byproduct formation reaction has a pre-exponential factor of 8.25 × 10 1 (dm 3 ·mol −1 ) 2 ·min −1 and activation energy of 12.75 kJ·mol −1 . In a semi-batch system the reaction is strongly inhibited by the formation and accumulation of precipitated sodium salts. This feature was incorporated into the reaction model using an inhibition term. [ABSTRACT FROM AUTHOR]

The most widely used hydrochlorofluorocarbon (HCFC) commercially since the 1930s has been chlorodifluoromethane, or HCFC-22, which has the undesirable effect of depleting stratospheric ozone. As this molecule is currently being phased out under the Montreal Protocol, monitoring its concentration profiles using infrared sounders crucially requires accurate laboratory spectroscopic data. This work describes new high-resolution infrared absorption cross sections of chlorodifluoromethane over the spectral range 730-1380 cm-1, determined from spectra recorded using a high-resolution Fourier transform spectrometer (Bruker IFS 125HR) and a 26 cm pathlength cell. Spectra of chlorodifluoromethane/dry synthetic air mixtures were recorded at resolutions between 0.01 and 0.03 cm-1 (calculated as 0.9/MOPD; MOPD denotes the maximum optical path difference) over a range of temperatures and pressures (7.5-762 Torr and 191-295 K) appropriate for atmospheric conditions. This new cross-section dataset improves upon the one currently available in the HITRAN (HIgh-resolution TRANsmission) and GEISA (Gestion et Etude des Informations Spectroscopiques Atmosphériques) databases; in particular it provides coverage over a wider range of pressures and temperatures, has more accurate wavenumber scales, more consistent integrated band intensities, improved signalto- noise, is free of channel fringing, and additionally covers the ν2 and ν7 bands. [ABSTRACT FROM AUTHOR]

Chlorodifluoromethane (CHClF 2 , HCFC-22) is a widely used refrigerant and foaming agent that is not only an ozone-depleting substance (ozone depletion potential (ODP), 0.04) but also a greenhouse gas (global warming potential (GWP), 1780). A comprehensive historical emission inventory for 1990–2014 was produced using a bottom-up method, and a projection through to 2050 was made for China. The results demonstrated that historical emissions increased sharply from 0.2 Gg/yr in 1990 to 127.2 Gg/yr in 2014. Room air-conditioners (RACs), industrial and commercial refrigeration (ICR), and extruded polystyrene (XPS) were three primary emission sources, and accounted for an average of 95.4% of the total emissions over the period studied. The percentage of global HCFC-22 emissions originating from China significantly increased from 0.1% in 1990 to 31.6% in 2012, with an average growth rate of 1.4% per year. Under the Montreal Protocol phasing-out (MPPO) scenario, future emissions were expected to reach a peak of 133.5 Gg/yr in 2016 and then continuously decline to 10.2 Gg/yr in 2050. The accumulative reduction for 2015–2050 would be 5533.8 Gg (equivalent to 221.4 CFC-11 -eq Gg and 9850.1 CO 2 -eq Tg), which is approximately equivalent to the total CO 2 emission for China in 2012 (9900 Tg) (Olivier et al., 2013), compared with the no Montreal Protocol scenario (NMP). Under the MPPO scenario, two cases were analyzed to explore the future emission ranges in China. A comparison between the two cases implied that the choice of emission reduction policy will have a considerable impact on HCFC-22 emissions. [ABSTRACT FROM AUTHOR]

The R22 refrigerant widely used in refrigerating and air conditioning devices is invariably released to the atmosphere due to reasons such as breakdown and/or translocation. As the sales of new devices operating with R22 are decreasing gradually, refrigerants of such available devices should be changed with the ones that are not depleting the ozone layer. In this paper, the amount of consumed energy, cooling capacity and COP values of R417A, R422A, R422D and R424A, which can be used as alternatives to R22, were determined experimentally for a split type air conditioning device at the ambient temperatures of 35, 38 and 41 °C. Basically, COP values of all HFC refrigerants were found to be smaller than that of R22. It was noted that the most suitable refrigerating fluid was R424A, which can be used instead of R22, since the COP of R424A was smaller than that of R22 by 2.5% only at an ambient temperature of 41 °C. [ABSTRACT FROM AUTHOR]

A formulation of the classical nucleation theory (CNT) is developed for bubble nucleation in a binary system composed of a liquid solvent and a dissolved gas. The theoretical predictions are compared to the experimental nucleation data of four binary mixtures, i.e. diethylether – nitrogen, propane – carbon dioxide, isobutane – carbon dioxide, and R22 (chlorodifluoromethane) – carbon dioxide. The presented CNT formulation is found to improve the precision of the simpler theoretical method of Ward et al. [J. Basic Eng. 92 (10), 71–80, 1970] based on the weak-solution approximation. By analyzing the available experimental nucleation data, an inconsistency in the data reported by Mori et al. [Int. J. Heat Mass Transfer, 19 (10), 1153–1159, 1976] for propane – carbon dioxide and R22 – carbon dioxide is identified. [ABSTRACT FROM AUTHOR]

Fluoroform (HFC-23), the unavoidable byproduct of chlorodifluoromethane (HCFC-22) synthesis, is one of the most potent greenhouse gases. The general approach to incinerate the vent gas, though avoids the adverse environmental impacts, is a waste of HFC-23, which is valuable as refrigerant and plasma etchant. In this work, membrane process was coupled with distillation to separate high purity HFC-23 from the vent gas economically. Theoretical analysis and experimental tests were conducted to find the applicable membrane materials. The results indicated that the rubbery PDMS, with higher selectivity and gas permeation coefficients, was superior to the glassy PI for HFC-23 separation. PDMS thin-film composite membranes were prepared and characterized. In the actual permeation tests with industrial vent gas at 30 °C and 0.55 MPa, the as-prepared PDMS composite membranes behaved with selectivity α F22/F23 = 3.2 and permeation rate J F22 = 661 GPU, respectively. Afterwards, the cascaded membrane systems with different stage number were studied by process simulation and their economic feasibility was analyzed. Briefly according to the economic data, the 4-stage cascade structure is the optimal configuration to couple with distillation unit. For a 50 kt/a synthesis plant, the 4-stage process can efficiently refine HFC-23 to a purity as high as 99.5 mol%, with a specific cost of 70 USD t −1 and an extra gross profit of 3.8 × 10 6 USD a −1 . However, taking the process complexity into account, the 3-stage cascaded process, although exhibited slightly lower economic performance, is more suitable in industry. Overall, our studies have revealed that coupling PDMS membrane unit with distillation is a feasible and promising technique to separate high purity HFC-23 efficiently and economically in the HCFC-22 synthesis industries. [ABSTRACT FROM AUTHOR]

The method for difluoromethylation of parent azoles, namely pyrrole, 1,2,3-triazole, 1,2,4-triazole and tetrazole was developed. Difluorometylation of pyrrole and 1,2,3-triazole was performed by action of chlorodifluoromethane. Sodium chlorodifluoroacetate was used as a difluoromethylation agent for 1,2,4-triazole and tetrazole. N-Difluoromethyl derivatives of pyrrole, 1,2,3- and 1,2,4- triazoles were synthesized in moderate to good yields in a multigram scale. N-difluoromethyltetrazole was obtained in a low yield. [ABSTRACT FROM AUTHOR]

Trifluoromethane (CHF3, HFC-23), with a 100-year global warming potential (GWP) of 12400, is regulated under the Kyoto Protocol. HFC-23 emissions in East Asia, especially in China, are currently thought to represent the majority of global HFC-23 emissions. This study provides both a bottom-up emission inventory and the multiannual top-down estimate of HFC-23 emissions in East Asia during 2007–2012. The new bottom-up inventory yields improved simulated HFC-23 mixing ratios compared to previous bottom-up inventories. The top-down estimate uses inverse modeling to further improve the model-measurement agreement. Results show that China contributed 94–98% of all HFC-23 emissions in East Asia. Annual a posteriori emissions from China were around 6.3 Gg/yr during the period 2007–2010 after which they increased to 7.1 ± 0.7 Gg/yr in 2011 and 8.8 ± 0.8 Gg/yr in 2012. For the first time, this study also provides a top-down estimate of HFC-23/HCFC-22 (chlorodifluoromethane, CHClF2) coproduction ratios in non-CDM (Clean Development Mechanism) HCFC-22 production plants as well as in all HCFC-22 production plants in China. [ABSTRACT FROM AUTHOR]