CFC Alternatives Research Articles

Fluorochemicals biodegradation as a potential source of trifluoroacetic acid (TFA) to the environment

The anthropogenic release of trifluoroacetic acid (TFA) into the environmental media is not limited to photochemical oxidation of CFC alternatives and industrial emissions. Biological degradation of some fluorochemicals is expected to be a potential TFA source. For the first time, we assess if the potential precursors [6:2 fluorotelomer alcohol (6:2 FTOH), 4:2 fluorotelomer alcohol (4:2 FTOH), acrinathrin, trifluralin, and 2-(trifluoromethyl)acrylic acid (TFMAA)] can be biologically degraded to TFA. Results show that 6:2 FTOH was terminally transformed to 5:3 polyfluorinated acid (5:3 FTCA; 12.5 mol%), perfluorohexanoic acid (PFHxA; 2.0 mol%), perfluoropentanoic acid (PFPeA; 1.6 mol%), perfluorobutyric acid (PFBA; 1.7 mol%), and TFA (2.3 mol%) by day 32 in the landfill soil microbial culture system. 4:2 FTOH could remove multiple –CF2 groups by microorganisms and produce PFPeA (2.6 mol%), PFBA (17.4 mol%), TFA (7.8 mol%). We also quantified the degradation products of TFMAA as PFBA (1.3 mol%) and TFA (6.3 mol%).Furthermore, we basically analyzed the biodegradation contribution of short-chain FTOH as raw material residuals in commercial products to the TFA burden in the environmental media. We estimate global emission of 3.9–47.3 tonnes of TFA in the period from 1961 to 2019, and project 3.8–46.4 tonnes to be emitted from 2020 to 2040 via the pathway of 4:2 and 6:2 FTOH biodegradation (0.6–7.1 and 0.6–7.0 tonnes in China, respectively). Direct evidence of the experiments indicates that biodegradation of fluorochemicals is an overlooked source of TFA and there are still some unspecified mechanisms of TFA production pathways.

The contribution of fluoropolymer thermolysis to trifluoroacetic acid (TFA) in environmental media

The source of trifluoroacetic acid (TFA) has long been a controversial issue. Fluoropolymer thermolysis is expected to be a potential anthropogenic source except for CFC alternatives. However, its TFA yield and contributions have rarely been reported more recently. In this study, we investigated the thermal properties of three kinds of fluoropolymers, including poly (vinylidene fluoride-co-hexafluropropylene) (PVDF-HFP), poly (vinylidene fluoride-co-chlorotrifluoroethylene) (PVDF-CTFE) and poly (tetrafluoroethylene) (PTFE). A laboratory simulation experiment was then performed to analyze the TFA levels in the thermolysis products and hence to examine the TFA yields of these fluoropolymers. Thermolysis of these fluoropolymers occurred in the temperature ranges from ∼400 °C to ∼650 °C, with the peak weight loss rate at around 550–600 °C. TFA could be produced through fluoropolymer thermolysis when being heated to 500 °C and above. Average TFA yields of PTFE, PVDF-HFP and PVDF-CTFE were 1.2%, 0.9% and 0.3%, respectively. Furthermore, the contribution of fluoropolymer thermolysis and CFC alternatives to rainwater TFA in Beijing, China was evaluated by using a Two-Box model. The degradation of fluoropolymers and HCFCs/HFCs could explain 37.9–43.4 ng L−1 rainwater TFA in Beijing in 2014. The thermolysis of fluoropolymers contributed 0.6–6.1 ng L−1 of rainwater TFA, accounting for 1.6–14.0% of the TFA burden from all the precursors which were considered here.

Ionic liquid-assisted hydroalkoxylation of hexafluoropropene with 2,2,2-trifluoroethanol: A mechanistic consideration

CF 3CHFCF 2OCH 2CF 3 (1,1,2,3,3,3-hexafluoropropyl- 2 ′ , 2 ′ , 2 ′ -trifluoroethylether), one of the third generation CFC alternatives, was obtained in high yield and selectivity from the hydroalkoxylation reaction of hexafluoropropene with 2,2,2-trifluoroethanol conducted in the presence of a catalytic system consisting of a potassium salt and an ionic liquid, 1-butyl-3-methylimidazolium chloride ([BMIm]Cl). The formation of commonly observed olefinic side products in the hydroalkoxylation catalyzed by potassium salts was greatly reduced by the co-presence of [BMIm]Cl. Theoretical calculations and mechanistic studies suggested that potassium ion is largely responsible for the formation of olefinic side products.

The evaluation of time variation global warming effects, TWPA and CWP, for CFC alternatives

Evaluations methods of global warming are presented by considering the direct warming effect of chemical compounds and of decomposed compounds, warming effect due to the formation of troposphere ozone, and the cooling effect due to the decomposition of stratosphere ozone. It is easy to take account the stabilization of global warming gases concentration in the atmosphere, as those methods can conduct the time variations analysis. The methods are named Total Warming Prediction Analysis (TWPA) and Composite Warming Potential (CWP). The evaluation of Mobile Air Conditioning refrigerant is presented as an example of application of our method.

Environmental assessment of CFC alternatives: Rate constants for the reactions of OH radicals with fluorinated compounds

The rate constants for the reactions of OH radicals with CF 3OCHFCF 3, and CF 3CHFCF 3 have been measured over the temperature range 250–430 K. Kinetic measurements have been carried out using the flash photolysis, and laser photolysis methods combined, respectively, with the laser induced fluorescence technique. The influence of impurities in the samples has been investigated by using gas chromatography. No sizable effect of impurities was found on the measured rate constants of these fluorinated compounds, if the purified samples were used in the measurements. The following Arrhenius expressions were determined: k(CF 3OCHFCF 3) = (4.39 ± 1.38) × 10 −13 exp[−(1780 ± 100)/ T] cm 3 molecule −1 s −1, and k(CF 3CHFCF 3) = (6.19 ± 2.07) × 10 −13 exp[−(1830 ± 100)/ T] cm 3 molecule −1 s −1.

Constructing a selection environment: competing expectations for CFC alternatives

While the concept of the ‘selection environment’ is one that is widely used, it is perhaps not that well understood. This paper examines in detail the context in which selection decisions are made through the study of the adoption of alternatives to CFCs. In doing so, close attention is paid to the differing expectations that are offered regarding what adoption of particular technologies means. Different expectations involve different interpretations of the wider (regulatory) context and users will further interpret them in light of their own experience and needs. Hence, the selection environment that faces users is one constructed of competing expectations and interpretations. If we are to better understand selection decisions this process of construction and interpretation needs to be more closely examined.

From complex fluorides to CFC alternatives — an account of fluorine chemistry at Glasgow

Advances in the areas of complex fluorides, high-oxidation state fluorides, perfluorocarbon ligand complexes, solvated cations and radiotracer catalytic studies made in the city of Glasgow are described.

Reinvestigation of Flammability Limits Measurement of Methane by the Conventional Vessel Method with AC Discharge Ignition

The flammability limits of methane have been reinvestigated by using the AC discharge ignition method. This work has partly been motivated by the necessity of evaluating the flammability characteristics of CFC alternatives. In the study, the effects of spark duration time and spark gap on the flammability limits of methane have extensively been explored. The resulting flammable range tends to become wide if the spark duration time is too long and/or the spark gap is too large. The effects of inadequate spark duration time and spark gap are exaggerated if the height of the experimental vessel is too small. As a result, the spark duration time of 0·1–0·2 sec combined with the spark gap of 6–8 mm has been found to make an optimum condition for the correct measurement of the flammability limits by the AC discharge ignition method.

Halogen exchange reactions for CFC alternatives.

Highly active catalysts are required for the conversion of CF3CH2Cl to the CFC-alternative refrigerant, CF3CH2F, by HF vapour under heterogeneous conditions. Chromia impregnated with a very low level of zinc(II) is a superior catalyst precursor to chromia alone. The behaviour of prefluorinated chromia and prefluorinated chromia containing zinc(II) or nickel(II) towards fluorine-18 labelled HF indicates that two types of labile surface fluoride are present, only one of which is catalytically active. Proposals are made to account for the role of ZnII and NiII.

Rapidly Increasing Concentrations of CFC Alternatives (HFC-134a, HCFC-141b, and HCFC-142b) in the Atmosphere as Observed in Hokkaido and Antarctica

Abstract Sharply increasing trends were observed for recent atmospheric concentrations of CFC alternatives by GC/MS analysis of samples collected in Hokkido, Japan and Syowa Station, Antarctica. These trends were consistent with those calculated based on the world production/release statistics for HFC-134a and HCFC-141b, but inconsistent for HCFC-142b, suggestive of some inaccurate release estimations.

HEAT PUMP DRYERS: RESEARCH AND DEVELOPMENT NEEDS AND OPPORTUNITIES

ABSTRACT As some previous research works on heat pump dryers (HPD) gave contradictory results, there is a need to review and identify R&D needs and opportunities in HPD. It was found that mathematical modeling cannot ignore the interdependence of the heat pump working fluid and the process air of the dryer. The performances of various HPD configurations with respect to all operating varibles need further investigation. A well defined mathematical model of combined dryer-drying material characteristic is required for the system modeling. The relative specific drying cost and relative useful energy were introduced as the dryer selection criteria. The role of the heat pump in the HPD system, CFC alternatives and non-conventional heat pump cycles using air or steam as working fluids deserve further investigation.

Fire extinguishers: A case study of CFC replacements

In some well-known TEWI (total equivalent warming impact) analyses of CFC alternatives, global warmer emissions in production have not been considered. The authors show that TEWI can be affected significantly by these production emissions, which suggests they should be considered in some TEWI analyses. The paper describes a TEWI analysis for one production sequence, that which leads from chloroform to tetrafluoroethylene and thence to HFC-227ea, a fire extinguishing agent. Numerous other commercial products stem from this sequence as well, including refrigerants, polymers and surfactants—these are summarised in the paper. Particular emphasis is placed on describing the production sequence and its global warming parameters to show that these can indeed be estimated from published information. The TEWI profile is presented at the close.

Chemistry of waste minimization

Introduction. Waste minimization - the industrial approach. The development and impact of environmental legislation on the chemical industry. The use of solid supports and supported reagents in liquid phase organic reactions. Phase transfer catalysis. Polymer supported synthesis. Industrial synthesis of optically active compounds. CFC alternatives and new catalytic methods of synthesis. Hydrogen peroxide in clean processes. Sonochemistry in waste minimization. Electrochemical aspects of chemical waste minimization. Solvent selection. Polymer recycling. Methods of metal capture from effluent. Chemical destruction using supercritical water. The use of catalysis in the manufacture of fine chemicals and chemical intermediates.

Performance of Carbon Black-Containing Polyurethane Foam in Domestic Refrigerators

The North American appliance industry has been challenged to meet stringent federal standards for energy consumption using CFC alternatives, which generally increase thermal conductivity of a foam. After a period of evaluating several options, the industry has, for the most part, settled on hydrochloro-fluorocarbon, HCFC-141b, as a substitute for CFC-11. Studies have shown that appliance foam systems using carbon black in conjunction with HCFC-141b lower k-factors by 6-9% both in panels and in cabinets. Recent efforts in this area have demonstrated that this approach not only lowers k-factors but can provide benefits to reduce energy consumption of refrigerator cabinets. Preliminary evaluation of carbon black-containing foams based on HCFC-141b had shown that the material processed well in cabinets and had no effect on linear appearance. No modifications to the foam processing equipment was necessary. Since black dispersions are relatively higher in viscosity compared to conventional isocyanates, a process study was conducted to understand flow behavior and maximize foam performance in cabinets. Handmix work was extended to cyclopentane systems. Studies have shown that improvements of 7-9% in k-factors can be obtained in foams containing carbon black. This work demonstrates the versatility of using carbon black with different blowing agents. The use of carbon black provides an additional means of improving thermal insulation of polyurethane foam produced with current technologies.

The thermal conductivity of CFC alternatives HFC-125 and HCFC-141b in the liquid phase

The liquid thermal conductivities of the CFC alternatives, HFC-125, and HCFC-141b measured by a transient hot-wire apparatus with one bare platinum wire are reported in the temperature ranges from 193 to 333 K (HFC-125, CHF2, CF3) and from 193 to 393 K (HCFC-141b,CCI2F-CF3), in the pressure ranges from 2 to 30 MPa (HFC-125) and from 0.1 to 30 MPa (HCFC-141b), respectively. The results have been estimated to have an accurancy of ±0.5%. The liquid thermal conductives obtained have been correlated by a polynomial of temperature and pressure which can represent the experimental results within the standard deviations of 0.49% for HFC-125 and 0.46% for HCFC-141b, respectively.

ACTIVE HEAT TRANSFER ENHANCEMENT BY UTILIZING ELECTRIC FIELDS

Active heat transfer enhancement techniques utilizing electric fields have been the subject of active research in recent years. These studies have used various kinds of fluids, including CFC alternatives. In this review, the effects of electric fields on heat transfer enhancement have been fundamentally and systematically explained from the viewpoint of electrohydrodynamics (EHD) that treats the interactions among electric fields, flow fields, and temperature fields. These interactions have been divided into three categories, namely, gas phase EHD interactions, liquid phase EHD interactions, and interfacial EHD interactions. In this review, the mechanism behind Corona wind generated by Corona discharge has been chosen as a typical gas phase EHD phenomenon, and its enhancement effects on convective heat transfer have been explained. An EHD liquid jet ejected through a ring electrode in the opposite direction of a plate electrode with a velocity on the order of 1 m/s was chosen as the representative liquid phase EHD phenomenon. The convective heat transfer from the plate electrode was enhanced by a factor of 100 due to the forced convection and the turbulence of the EHD jet. The active local EHD generation of turbulence was explained fundamentally. The EHD effects on condensation and boiling were chosen as the representative interfacial EHD phenomena and these mechanisms were explained both theoretically and experimentally. In addition, the EHD defrosting phenomena was explained. Heat transfer can be enhanced over a factor of 5 by electrohydrodynamically removing the condensate from the condensation surface and by using EHD pseudo-dropwise condensation. Furthermore, nucleate boiling heat transfer was increased by a factor of 50 over that given using the same system without electric fields. This increase was due to the EHD effects on the active movement and deformation of the boiling bubbles. In conclusion, the characteristics of active heat transfer enhancement techniques utilizing electric fields and the future potential of electric field effects on thermal engineering problems were described to show that the practical application of these EHD active heat transfer enhancement techniques would be effective for heat transfer control, microscale heat transfer techniques, and energy conservation and global environmental protection problems.

Molecular Precursors to Functional Materials

ABSTRACTThe design of molecular precursors to materials for catalysis will be described. Aluminum fluoride is an important catalytic material for fluorocarbon transformations which are key to the production of CFC alternatives. Catalytic activity is closely related to the crystalline phase of the bulk AIF3 and we show how this phase chemistry can be precisely controlled using molecular precursors to produce pure known phases and also to extend to previously unknown phases. A similar approach to vanadyl phosphate oxidation catalysts will be described where cluster chemistry can be invoked to generate isolated fragments of a catalyst's structure and then used either to explore mechanism or be used as precursors to functional catalyst materials. The underlying themes of controlled molecular precursor synthesis, resultant processability and eventual easy conversion to useful materials are emphasized throughout.

The Use of Alternative Blowing Agents in Polyurethane Foams-a Comparison Between Experimental and Predicted Ageing

Accelerated ageing tests have been the industry standard for many years. With the introduction of CFC alternatives these accelerated ageing tests have become questionable. This paper describes how the ageing of foams, based on the novel blowing agents, can be predicted. The comparison of an «experimental data set» with a «calculated data set» shows the accuracy and reliability of the method presented in this paper. The calculated data set is generated via the determination of fundamental foam physical properties and an ageing calculation model. The two most important facton are the effective diffusion constant and the initial cell gas composition. The influence of temperature on both the effective diffusion constants and gas content is determined

Thermochemistry of possible degradation pathways for compounds CF 3 CHXY(X, Y = H, F, Cl) using AM1 and MNDO semiempirical methods

Heats of reaction for individual steps in various pathways for the oxidative degradation of two-carbon-containing CFC alternatives with the general formula CF 3CHXY (X and Y = H, F, Cl) are evaluated from heats of formation calculated using the AM1 and MNDO semiempirical MO methods. The implications for possible mechanism for degradation of these hydrochlorofluorocarbons or hydrofluorocarbons in the troposphere or in the stratosphere are discussed.

Critical heat flux measurements in a round tube for CFCs and CFC alternatives

Critical heat flux (CHF) measurements have been conducted for HFC-134a, HCFC-123, HCFC-22, CFC-12 and CFC-11 in a multi-fluid loop. The test pressures are up to 2 MPa (corresponding to water equivalent pressure of 7–10 MPa) and mass fluxes from 1000 to 4000 kg m −2 s −1. The heated length is adjustable from 0.5 to 1 m, the I.D. of the tubular test section is 4.2 mm, and the critical quality varies from 0.07 to 0.6. The parametric trends of test results are examined and the test results show good agreement with existing CHF prediction methods. It also provides confirmation that CFC alternatives such as HFC-134a, HCFC-123 and HCFC-22 can be used with confidence as reliable CHF modelling fluids.