Liquids CFCs

The major advantage of these agents is that they become gaseous at well-defined temperatures and controlled rates, providing product quality and contributing to some improved performance characteristics. However, the effect of CFCs on the environment is under debate. These liquids, odorless and innocuous as they are, are linked to the ozone hole in the stratosphere. The industry is searching for feasible, environmentally and economically acceptable alternatives. Production levels of CFCs have been frozen and gradual phase-out is underway (8). 

The earliest polyurethane foams were water (COj) blown. In the late 1950s CFC-11 was discovered to be an excellent blowing agent for polyurethane foams, especially low-density foams, fhe development of the Ozone Depletion Theory in the late 1970s and its further refinement in the 1980s linked CFCs to a reduction of ozone in the upper atmosphere. As a result of the concern of such ozone reduction causing an increase in ultraviolet (UV) radiation at ground level the world community produced the Montreal Protocol on Substances that Deplete the Ozone Layer in late 1987 (9). 

Up to the present time, many communities and nations are accelerating the phase-out of CFCs by shortening the original timetable of the Montreal Protocol and taxing the use of CFCs. Currently the use of CFCs is limited to 1986-usage levels. It is hoped that two of the major candidates to replace CFC-11, HCFC-141b and HCFC-123, will be fully commercialized by 1993 (9). 

At the Polyurethanes World Congress in Nice, France in 1991 it was reported that the Montreal Protocol was approved by 93 nations in June 1990, and that suppliers have been scrambling to meet its mandate of complete phase-out of CFCs by the year 2000. It was brought out at 

Chemical Fonnula CQjF CQjFj CajFCH, CHCljCFj CF3CH2F 

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Converting the liquid CFC to a gas (i.e. boiling) is analogous to putting energy into a kettle, and watching the water boil off as steam. 

CFC number Formula CAS Registry Number Molecular weight Boiling point, °C Melting point, °C Liquid density, g/mL at °C Liquid refractive index, at°C Critical temp, °C Critical pressure, MPa "... 

The products are available as tablets, capsules, liquids (in the form of solutions, suspensions, emulsions, gels, or injectables), creams (usually oil-in-water emulsions), ointments (usually water-in-oil emulsions), and aerosols, which contain inhalable products or products suitable for external use. Propellants used in aerosols include chlorofluorocarbons (CFCs), which are being phased out. Recently, butane has been used as a propellant in externally applied products. The major manufactured groups include ... 

A liquid chlorine tank was kept cool by a refrigeration system that used CFCs. In 1976 the local management decided to use ammonia instead. Management w as unaware that ammonia and chlorine react to form explosive nitrogen trichloride. Some of the armnonia leaked into the chlorine, and the nitrogen trichloride that was formed exploded in a pipeline... 

With Midgley pacing up and down behind him, Henne prepared their first CFC compound, dichlorodifluoromethane, later called R-12 for Refrigerant-12. The compound looked promising. Under pressure, it liquefied readily, an important property since the cyclical refrigeration process depended on the compound s continually condensing back into a liquid to... 

Groundwater age at each NGMP site has been assessed using multiple tracers. Tritium was analyzed in a 1 L unfiltered unpreserved sample using 70-fold electrolytic enrichment prior to ultra-low level liquid scintillation spectrometry (Morgenstern Taylor 2005). Samples for analysis of CFCs and SF6 (125 ml and 1 L, respectively) were collected in strict... 

The CFC is initially a liquid because of intermolecular interactions (of the London dispersion type). Imagine that the interactions involves 4 kJ of energy but cooling the cheese to 5 °C we liberate about 6 kJ of energy it should be clear that more energy is liberated than is needed to overcome the induced dipoles. We say that... 

This method (EPA 1664) is a liquid-liquid extraction gravimetric procedure that employs n-hexane as the extraction solvent, in place of 1,1,2-trichloroethane (CFC-113) and/or 1,2,2-trifluoroethane (Freon-113), for determination of the conventional pollutant oil and grease. Because the nature and amount of material determined are defined by the solvent and by the details of the method used for extraction, oil and grease method-defined analytes are used. The method may be modified to reduce interferences and take advantage of advances in instrumentation provided that all method equivalency and performance criteria are met. However, n-hexane is a poor solvent for high-molecular-weight petroleum constituents (Speight, 1999, 2001). Thus, the method will produce erroneous data for samples contaminated with heavy oils. 

When a vehicle is parked in the sunlight on a hot summer day, the temperature inside can approach 55°C. One company has patented a non-CFC propelled aerosol that can be sprayed inside a vehicle to reduce the temperature to 25°C within seconds. The spray contains a mixture of two liquids 10% ethanol, C2H5OH, and 90% water by mass. 

Several groups have investigated the effect of surfactants on emitted droplet size. In the early work performed by Polli et al., the surfactant sorbitan trioleate decreased the MM AD of the CFC dexamethasone suspension when added to the formulation (52). A suspension of terbutaline in a CFC system containing sorbitan trioleate surfactant was shown to have little change in emitted particle size when either 2.8 or 14mg/mL of surfactant was added (53). Interestingly, the surfactant had a significant effect on the obscuration (droplet concentration) of the laser diffraction instrument used to determine particle size. Surfactants may lead to an increase in MMAD due to decreased evaporation rates from aerosol droplets. This may occur because of their tendency to associate at the air liquid interface (54). 

Prior to their current phase-out, chlorofluorocarbons (CFCs) were widely used as processing solvents for various materials. CFCs were well suited for many medical applications owing to their high solvency, nonflammability, good materials compatibility, and low toxicity. The uses for CFCs include a silicone deposition solvent, a fluoropolymer dispersion liquid, and processing solvents. However, the Montreal Protocol phase-out of ozone-depleting substances has required that alternative dispersants and solvents be found. Limitations of most available alternatives include flammability, low volatility, poor solvency, and poor materials compatibility. 

Estimate the molar volume Vt of dichlorodifluoromethane CC12F2 (also called freon-12 or CFC-12) (a) from its liquid density and (b) with the element contribution method by Fuller (Table 18.2). 

The liquid viscosity has been measured tor acetone from - CfC.w lor OKK from [Pg.44]

Chlorofluorocarbons (CFCs) are manufactured by reacting hydrogen fluoride and carbon tetrachloride in the presence of a partially fluorinated antimony pentachloride catalyst in a continuous, liquid-phase process. 

By blending CFCs, it is possible to achieve appropriate vapor pressure, solvency and liquid density. However, CFCs have been linked with the depletion of the stratospheric ozone layer and will be phased out in accordance with the Montreal Protocol on Substances that Deplete the Ozone Layer . Current substitutes are the hydrofluoroalkanes (HFAs), e.g. 1,1,1,2-tetrafluoroethane (HFA-134a) and 1,1,2,3,3,3-heptafluoropropane (HFA 227) (Table 10.3). 

There are liquid PBAs that are volatile and change from a liquid to a gaseous state when heated to the plastic processing temperatures. They are short-chain chlorinated and fluorinated aliphatic hydrocarbons (CFCs). Although they can be used over a wide temperature range and at low (atmospheric) pressures, they have been gradually discontinued due to their role in the reduction of stratospheric ozone.249 Other PBAs are reviewed in Table 8.2. 

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