Replacements For Chlorofluorocarbons Research Articles

Self-, N 2- and O 2-broadening of pure rotational transitions of HFC-134a

Because of their lower depleting effect on the ozone in the atmosphere, there has been much recent interest in the fluorinated hydrocarbons as replacements for chlorofluorocarbons and hydrochlorofluorocarbons. Since data on the broadening of rotational lines are required for quantitative monitoring of trace compounds in the atmosphere (especially broadening by collision with N 2 and O 2), self- and pressure-broadening of rotational transitions of CF 3CFH 2 have been studied and the self-, N 2- and O 2-broadening coefficients evaluated. In particular, we have analyzed the line shape of the following b type transitions: J=10 0,10←9 1,9 and J=10 1,10←9 0,9 degenerate doublet, J=15 1,15←14 0,14 and J=20 0,20←19 1,19. The source frequency modulation technique has been employed to record the spectra of the rotational transitions investigated.

Theoretical calculation of heat of formation for a number of moderate sized fluorinated compounds

Hydrofluorocarbons (HFCs) and hydrofluoroethers (HFEs) are considered to be potential replacements for chlorofluorocarbons (CFCs). The values of heat of formation have been calculated by using both the bond additivity corrected MP2 method (BAC-MP2/6-31G ∗∗) and atom additivity corrected MP2 method (AAC-MP2/6-31G ∗∗) for moderate sized HFCs and HFEs for which the literature values are not available. The reliability of the calculated values by these methods has been examined by comparing them with the values obtained with G2 and G2MP2 methods as well as with the literature values for a set of 42 simpler molecules.

A review of environmental hazards and adsorption recovery of cleaning solvent hydrochlorofluorocarbons (HCFCs)

Hydrochlorofluorocarbons (HCFCs) are being used as interim replacements for chlorofluorocarbons (CFCs) that cause significant stratospheric ozone depletion and global warming relating to the greenhouse effect. HCFCs under commercial uses such as cleaning solvents include HCFC-123 (2,2-dichloro-1,1,1-trifluoroethane), HCFC-141b (1,1-dichloro-1-fluoroethane), HCFC-225ca (3,3-dichloro-1,1,1,2,2-pentafluoropropane), and HCFC-225cb (1,3-dichloro-1,1,2,2,3-pentafluoropropane). From the environmental, ecological, and regulatory points of view, it is important to limit and control the emissions of these cleaning solvents from the surface finishing processes. Adsorption technology has been utilized for many years to recover organic vapors by using carbon-based or zeolite-based adsorbent. This article aims to introduce these HCFCs in terms of physiochemical properties, commercial uses, and environmental hazards (i.e., stratospheric ozone depletion, global warming, and health & safety). Further, the main studies on the adsorption isotherm and desorption methods of these HCFCs by various adsorbents (i.e., granular activated carbon, activated carbon fiber, and hydrophobic zeolite) are reviewed in this paper.

Heat-transfer mechanisms in polyurethane rigid foam

Polyurethane closed-cell rigid foams have been widely used as insulants in the building and refrigeration industry and also for district heating pipes. It is the special combination of excellent insulation performance and the mechanical stability due to the foaming process which makes this material very attractive for these applications. The replacement of chlorofluorocarbons, which have been banned as blowing agents since 1993, by hydrocarbons in Europe caused a decrease in the insulation capability of polyurethane rigid foams. The additional global requirement to reduce energy losses also adds an incentive to search for potential substances which would improve the thermal performance of rigid foams. To overcome this problem the heat transfer within polyurethane rigid foams via the polymer matrix, enclosed gas, and thermal radiation was examined in various independent experiments. Most importantly, it was observed that the potential to reduce the thermal conductivity of polyurethane rigid foams is higher than had been predicted.

Optimizing Drug Delivery to the Lung: Design of a CFC-Free Corticosteroid Metered-Dose Aerosol System

The mandatory replacement of chlorofluorocarbons (CFCs) with ozone–friendly propellants, such as hydrofluoroalkanes (HFAs), has provided an opportunity to optimize aerosol design and improve drug delivery to pulmonary tissue. Asthma is an inflammatory disorder of the lungs that appears to affect both small and large airways, so ideally, inhaled corticosteroid should reach both central and peripheral sites. This review considers the development of an aerosol system containing beclomethasone dipropionate in hydrofluoroalkane–134a (HFA) propellant (Qvar™, 3M Health Care, Loughborough, UK) designed to target medication delivery throughout the bronchopulmonary tree and to improve the therapeutic ratio (topical efficacy: systemic safety), thereby offering potential clinical benefits to asthma patients.

Why some solvents are given VOC exempt status by the EPA and what the future holds

Hydrofluorocarbons (HFCs) are being used as replacements for chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) that cause significantly stratospheric ozone depletion and global warming. HFCs under commercial uses as cleaning solvents in the electronic components, blowing agent in the foamed plastics, refrigerant in the air conditioning units and refrigerators, fire suppression agent in the fire protection, propellant in the metered dose inhalers (MDIs), and dry etching agent in the semiconductor manufacturing. Among these HFCs, 1,1,1,2-tetrafluoroethane (HFC-134a) is the most widely used one. From the environmental, ecological, and health points of view, it is urgent to mitigate and control the emissions of these HFCs from a diversity of commercial applications and industrial processes. This article aims to introduce these HFCs in commercial uses and environmental hazards (i.e., global warming, photochemical potential, flammability safety, environmental partition and ecotoxicity). Further, the updated data on the human toxicity, occupational exposure and health risk of these HFCs (esp., HFC-134a) are addressed in this review paper.

Induction of micronuclei formation in preimplantation mouse embryos after maternal treatment with 2-bromopropane

We examined effects of 2-bromopropane (2-BP), a chlorofluorocarbon replacement, on mouse embryonic mutagenicity. 2-BP was administered to pregnant mice intraperitoneally (i.p.) (300, 600, 900, and 1800 mg/kg) during the early preimplantation period. On day 3 of gestation, micronuclei (MN) frequency and embryo cell number were determined. 2-BP induced a dose-related significant increase in MN frequency and a treatment-related decrease in embryo cell number. Furthermore, the cell numbers were significantly smaller in the MN-positive embryos by two-way ANOVA taking it into account an interactive effect between 2-BP dose and the presence or absence of MN. A simultaneous decrease in cell number and increase in MN frequency may reflect an embryonic developmental disadvantage resulting from maternal treatment with 2-BP. Further study is needed to establish how 2-BP contributes to postimplantation embryonic development.

CFC phase out

The latest meeting of governmental parties to the Montreal Protocol on Substances that Deplete the Ozone Layer took measures to further restrict chlorofluorocarbons (CFCs), hydrochloro‐fluorocarbons (HCFCs) developed as a replacement for CFCs but also harmful to the stratospheric ozone layer, and other ozone‐depleting chemicals.At the meeting, held in Beijing, China in early December, the parties agreed to provide $440 million in new contributions to the Protocol's Multilateral Fund for the Implementation of the Montreal Protocol (MFMP), which encourages reducing the production and use of ozone‐depleting chemicals and supports adopting ozonefriendly technologies. The fund has spent more than $1 billion since 1991.

Degradation of Hydrohalocarbons and Brominated Compounds by Methane- and Propane-Oxidizing Bacteria

Concern over the use of chemicals that potentially contribute to ozone depletion and the greenhouse effect has led to a ban on chlorofluorocarbons (CFCs) and potential limitations on the use of methyl bromide and other brominated fumigants. The objective of this work was to test naturally occurring aerobic microorganisms for the ability to degrade brominated fumigants and the hydrohalocarbons that have been developed to replace CFCs. The bacterial strains used in this study degraded a significant percentage of the hydrohalocarbons and brominated fumigants tested, which were present at high substrate levels. Degradation was often rapid and complete. Ion chromatog raphy results indicated the stoichiometric release of halogens for several of the compounds tested. Many of the compounds were readily biodegradable at high concentrations and were metabolized by all of the strains tested, while others were more recalcitrant. The presence of these microorganisms in the environment may represent a natural sink for some of these compounds; however, the high substrate and bacterial concentrations used in this study were chosen for bioreactor development. Information about the biodegradability of these compounds may make it easier to choose the most ecologically safe CFC replacements and fumigants.

Adsorption properties and breakthrough model of 1,1-dichloro-1-fluoroethane on activated carbons

Hydrochlorofluorocarbons (HCFCs), among the major replacements for chlorofluorocarbons (CFCs) and chlorinated solvents, are now considered to the prime contribution to the stratospheric ozone depletion. This paper reports the adsorption equilibrium of 1,1-dichloro-1-fluoroethane (HCFC-141b) vapor in air streams on the commercial activated carbons PCB and BPL, which were made from coconut shell and bituminous coal, respectively, at 283, 293, 303, and 313 K. The experimental results show that within the experimental conditions, the adsorption capacities of the two adsorbents for HCFC-141b in dry air streams can be well-fitted by the Langmuir, Freundlich, and Dubinin–Radushkevich (D–R) adsorption equations. The physical properties of the adsorbents are consistent with the isotherm parameters obtained from the adsorption results. In addition, available experimental data of adsorption breakthrough at 283 K were used in conjunction with the Yoon and Nelson model to generate theoretical breakthrough curves based on the obtained values of parameters. In each case, calculated theoretical breakthrough curves are in agreement with corresponding experimental data.

Drug–surfactant–propellant interactions in HFA-formulations

The required replacement of chlorofluorocarbon (CFC) with hydrofluoroalkane (HFA) propellants has challenged formulators of pressurized metered dose inhalers in several major respects. Conventional (CFC soluble) surfactants are effectively insoluble in the major CFC replacement candidates, HFA 134 and HFA 227ea, in the absence of co-solvents. While these ethane and propane derivatives have comparable boiling points and vapor pressures to dichlorodifluoromethane (CFC 12), their increased polarity demands that formulators use either alternative (soluble) surfactants, or co-solvents along with traditional surfactants, in order to stabilize pressurized suspension products. The use of either approach is complicated by the existence of many competing patents and the fact that the science in the area is empirical; predictive theoretical approaches are frustrated by the lack of an adequate database. Technical developments in this area must also take into account the need to avoid crystal growth and/or adhesion of micronized, suspended drugs to internal container surfaces, problems which may be catalyzed by some combinations of surfactant type/concentration, vehicle(s) and physical form/type(s) of drug substance. For some drugs, it appears simpler to use co-solvents with HFA propellants to dissolve the drug, avoiding the need for suspension stabilization. This article presents an overview of the present state of the art with respect to the formulation of MDIs.

Recovery of seven kinds of cfc and cfc replacements on high‐surface area activated carbon

The adsorption isotherms, the constants of the Dubinin—Radushkevich plots, and the constants of the Langmuir plots of chlorofluorocarbon (CFC) and CFC replacements on high‐surface area activated carbon were investigated to estimate the recovery efficiency of CFC and CFC replacements. The adsorption and desorption of HFC134a on a high‐surface area activated carbon was much easier than that of CFC 113 and the CFC replacements. The recovery efficiency of CFC replacements depends on the hydrogen atoms in molecule. It is possible that the saturated amount adsorbed in the pores or on the surface of the activated carbon could be evaluated by the Ws constant of the the Langmuir equation and the Wo constant of the Dubinin‐Radushkevich equation. The a constant of the Langmuir equation and the BEo constant of the Dubinin‐Radushkevich equation depend on the molecular composition.

Adsorption Equilibrium of 1, 1-Dichloro-1-fluoroethane (HCFC-141b) on a Hydrophobic Zeolite

Of the major replacements for chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs) are now accepted as being prime contributors to stratospheric ozone depletion. As a consequence, the development of adsorbents capable of adsorbing and recovering specific HCFCs has received great attention. This paper describes an investigation of the adsorption equilibrium of 1, 1-dichloro-1-fluoroethane (HCFC-141b) vapour on a commercial hydrophobic zeolite. The corresponding Henry, Freundlich and Dubinin–Radushkevich (D–R) equilibrium isotherms have been determined and found to correlate well with the experimental data. Based on the Henry adsorption isotherms obtained at 283, 303 and 313 K. thermodynamic properties such as the enthalpy, free energy and entropy of adsorption have been computed for the adsorption of HCFC-141b vapour on the adsorbent. The results obtained could be useful in the application of HCFC adsorption on the hydrophobic zeolite studied.

Trifluoroacetic acid levels in 1994–1996 fog, rain, snow and surface waters from California and Nevada

Trifluoroacetic acid (TFA) is an atmospheric breakdown product of the chlorofluorocarbon replacements HCFC-123, HCFC-124, and HFC-134a. Due to its low Henry's law constant, TFA will partition into the various aqueous phases that occur throughout the environment. TFA was detected and measured in fog, rain, snow, and surface water obtained in 1994–1996 from several locations in California and Nevada. Fog and rain samples contained 31 – 3779 ng 1 −1 TFA. Snow samples taken in more remote areas had 51 – 584 ng 1 −1. Surface water varied from 55 ng 1 −1 – 41 μg 1 −1 depending on type and location. Washout of TFA from the lower atmosphere was observed in both rain and fog samples. There was a trend toward decreasing TFA in precipitation samples taken at later stages during a single storm event, indicating cleansing of TFA from the lower atmosphere by precipitation. The magnitude of TFA levels suggest that formation in the environment from HCFC and HFC degradation is occurring more rapidly than expected, or that alternate sources of TFA exist.

Atmospheric lifetimes of selected fluorinated ether compounds

Abstract Atmospheric lifetimes have been estimated for a selection of ethers, the latter representing a class of compounds being considered as replacements for chlorofluorocarbons. The estimates are based on laboratory measurements of rate constants for the reaction of the OH radical with the ethers, and a comparison with the behaviour of methyl chloroform in the atmosphere. The lifetimes for the ethers ranged from a few hours to half a year, significantly lower than those of chlorofluorocarbons and other replacements being considered.

The replacement of CFCS in refrigeration equipment by environmentally benign alternatives

The replacement of chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) is of prime importance since these refrigerants make up the vast majority of the working fluids used by the refrigeration industry and suitable alternatives must be found. A number of suitable pure fluids were considered to establish their properties and, in the case of flammable fluids, a risk analysis was carried out in order to assess their safety. The properties of their mixtures were calculated and suitable equations and p-h charts presented. Compressor lubricants have had to be changed since the majority of the CFC and HCFC replacements are hydrofluorocarbons (HFCs). Typically, HFCs are immiscible in the traditional mineral oils and thus a new generation of synthetic oils (usually polyol ester based) have been produced. The properties of these oils have been investigated and various models, including a modified Flory-Huggins equation, have been used to describe their solubility in refrigerants. The effects of refrigerant/oil solubility of the pure refrigerants and their mixtures on system performance have also been analysed and, in the case of refrigerant mixtures, there is a possibility of a composition change due to the differential solubility which influences performance. Finally, compact plate heat exchangers were found to be excellent heat exchangers for the refrigeration industry, provided that it is remembered that there are control and capacity variation limitations associated with their use. The falling film evaporator is studied in detail and there is a possibility that it will fulfill its potential. Compressors tested with alternative refrigerants have shown (in the case of R407c, a replacement for R22) a deterioration in performance with decreasing evaporator temperature when compared to that of R22, while some of the flammable refrigerants may require larger compressors than the CFC and HCFC counterparts, due to their smaller mass flow rates.

Transport and fate of trifluoroacetate in upland forest and wetland ecosystems.

Although trifluoroacetate (TFA), a breakdown product of chlorofluorocarbon replacements, is being dispersed widely within the biosphere, its ecological fate is largely unknown. TFA was added experimentally to an upland, northern hardwood forest and to a small forest wetland ecosystem within the Hubbard Brook Experimental Forest in New Hampshire. Inputs of TFA were not transported conservatively through these ecosystems; instead, significant amounts of TFA were retained within the vegetation and soil compartments. More TFA was retained by the wetland ecosystem than by the upland forest ecosystem. Using simulation modeling, TFA concentrations were predicted for soil and drainage water until the year 2040.

Replacement of chlorofluorocarbons at the DOE gaseous diffusion plants: An assessment of global impacts

Three gaseous diffusion plants (GDPs) for enriching uranium maintain a large inventory of chlorofluorocarbon-114 (CFC-114) as a coolant. To address the continued use of CFC-114, an ozone-depleting substance, the U.S. Department of Energy (DOE) considered introducing perfluorocarbons (PFCs) by the end of 1995. These PFCs would not contribute to stratospheric ozone depletion but would be larger contributors to global warming than would CFC-114. The paper reports the results of an assessment of the global impacts of four alternatives for modifying GDP coolant system operations over a three-year period beginning in 1996. The overall contribution of GDP coolant releases to impacts on ozone depletion and global warming were quantified by parameters referred to as ozone-depletion impact and global-warming impact. The analysis showed that these parameters could be used as surrogates for predicting global impacts to all resources and could provide a framework for assessing environmental impacts of a permanent coolant replacement, eliminating the need for subsequent resource-specific analyses.

Adsorption of inhalational anesthetics and hydrochlorofluorocarbons on activated carbons as a biological model.

Chlorofluorocarbon (CFC) replacements have recently been used for their lower stability and because they have carbon-hydrogen bonds, which means that their atmospheric lifetime is expected to be much shorter than those of CFCs. The adsorption properties of 1,1,2-trichloro-1,2,2-trifluoroethane (CFC113) and its replacement compounds, 1,1-dichloro-2,2,2-trifluoroethane (HCFC123), 1,1-dichloro-1-fluoroethane (HCFC141b), and 1,1-dichloro-1,2,2,3,3-pentafluoropropane (HCFC255ca) on four kinds of activated carbons were investigated. The amount of CFC and HCFCs adsorbed on the activated carbon was concluded to depend upon the number of chloride and carbon atoms in their molecules. The adsorption isotherms of inhalational anesthetics (halothane, chloroform, enflurane, isoflurane, and methoxyflurane) on the activated carbon were measured to evaluate the action mechanism of inhalational anesthesia. The adsorption isotherms of CFC, HCFC, and the inhalational anesthetics were fitted to the Freundlich equation. The Freundlich constant N was well correlated with the minimum alveolar concentration (MAC) of the inhalational anesthetic: 1 MAC means that 50% of the patients will not move during a surgical operation. The adsorption mechanism of inhalational anesthetics on the surface of the activated carbon is concluded to be similar to the adsorption mechanism on a nerve cell. The anesthesia of CFC replacements can be estimated by the Freundlich constant N of the adsorption isotherms.

Physiologically based pharmacokinetic analysis of the concentration- dependent metabolism of halothane

1. Previous studies with the halothane analogue and chlorofluorocarbon replacement 2,2-dichloro-1,1,1-trifluoroethane (HCFC-123) have shown that there are concentration dependent, sex-specific differences in the rate of uptake during inhalation exposure in rat. Since it is well established that there are sex-specific differences in the control of enzyme activity in drug metabolism, male and female rats were exposed by inhalation to halothane concentrations ranging from 500 to 4000 ppm. 2. A physiologically based pharmacokinetic model describing the concentration dependent reduction in uptake and metabolism of halothane in male and female rats was developed. The in vivo metabolic rate constants obtained were : for male rats, Km 0 4 mg litre (2 03 mu mol litre) and Vmaxc 9 2 mg kg h (46 6 mu mol kg h); for female rats, Km 0 4 mg litre (2 03 mu mol litre) and Vmaxc 10 2 mg kg h (51 7 mu mol kg h) . 3. An equation describing the concentration-dependent decrease of hepatic metabolism of halothane successfully simulated the gas-uptake data. Simulation of cumulative urinary excretion of the major metabolite, trifluoroacetic acid, required introduction of a proportionality constant to limit the extent of reduction of halothane metabolism to 20% of the amountofenzyme activity. Good simulation of urinary excretion data was achieved, which was interpreted to indicate that, when only 20% of the enzyme is inactivated, the rate of enzyme resynthesis was adequate to replenish enzyme activity within 24 h. 4. A rapidly reversible, non-biological inactivation mechanism called 'physical toxicity' is discussed as a possible explanation of concentration-dependent gas uptake.