Chlorofluorocarbon fluids

Approximately 50% of the demand for tetrachloroethylene is in the dry-cleaning industry where about 80% of all dry cleaners use it as their primary cleaning agent. Use as a feedstock for chlorofluorocarbon production accounts for 30% of current demand. Metal cleaning and miscellaneous appHcations represent 12 and 8% of demand, respectively. The miscellaneous appHcations include such varied uses as transformer insulating fluid, chemical maskant formulations, and as a process solvent for desulfurizing coal. 

Cleaning Supercritical fluids such as CO9 are being used to clean and degrease quartz rods used to produce optical fibers, produc ts used in the fabrication of printed circuit boards, oily chips from machining operations, and precision bearings in militaiy applications, and so on. Here, CO9 replaces convention chlorocarbon or chlorofluorocarbon solvents. 

The introduction of the chlorofluorocarbon (CFC) fluids in the early 1930s marked the incepuon of the halofluorocarbon industry. Both in terms of tonnage produced and product value, the CFCs have dominated the organofluorocarbon industry and have provided the feedstocks for the development of other fluorocarbon products such as poly(tetrafluoroethylene). 

The two SCFs most often studied—CO2 and water—are the two least expensive of all solvents. CO2 is nontoxic and nonflammable and has a near-ambient critical temperature of 31. UC. CO2 is an environmentally friendly substitute for organic solvents including chlorocarbons and chlorofluorocarbons. Supercritical water (Tc = 374°C) is of interest as a substitute for organic solvents to minimize waste in extraction and reaction processes. Additionally, it is used for hydrothermal oxidation of hazardous organic wastes (also called supercritical water oxidation) and hydrothermal synthesis. (See also Sec. 15 for additional discussion of supercritical fluid separation processes.)... 

At issue is a group of man-made chemicals called chlorofluorocarbons (CFCs), which are used as the refrigeration fluids (Freon) in the air-conditioning and refrigeration units of automobiles, homes, and industry and which, in the past, were used as the pressure gas in spray cans of paint, deodorants, and so forth. There are a number of compounds containing... 

Freon is a commercial trademark for a series of fluorocarbon products used in refrigeration and air-conditioning equipment, as aerosol propellants, blowing agents, fire extinguishing agents, and cleaning fluids and solvents. Many types contain chlorine as well as fluorine, and should be called chlorofluorocarbons (CFCs) [85,86]. 

Hexachlorobutadiene is used as a chemical intermediate in the manufacture of rubber compounds (ERA 1982d). Lesser quantities of hexachlorobutadiene are used as a solvent, a fluid for gyroscopes, a heat transfer liquid, hydraulic fluid, and as a chemical intermediate in the production of chlorofluorocarbons and lubricants (ERA 1980 lARC 1979 Verschueren 1983). Small quantities are also used as a laboratory reagent (ERA 1982d). In the international market, Russia is reported to be one of the major users of hexachlorobutadiene, where it is used as a fumigant on grape crops. 

Some halogen compounds have been too reactive for the health of people and the planet. They can destroy healthy cells and attack the Earths atmosphere in the same active way that they kill germs or break down wood into paper. For instance, chlorofluorocarbon (or CFC) compounds used to be popular cooling chemicals in refrigerators and air conditioners and in the gas that pushed hairspray and deodorant out of aerosol cans. CFCs are now widely banned because they destroy Earths atmosphere. Chlorine is also part of the insect killer DDT, a dry cleaning fluid, and the compounds called PCBs. All of these products are now banned or used rarely because they have been linked to pollution and health problems like cancer and liver disease. 

The temperatures on the envelope where pn = 0 are called inversion temperatures, Tt. At any given pressure, up to a maximum pressure, a given gas exhibits two inversion temperatures. The Joule-Thomson effect is important in refrigeration and in the liquefaction of gases. Modern refrigeration uses the larger effect of the evaporation of working fluids such as the chlorofluorocarbons. 

Supercritical fluid chromatography (SFC) is a column chromatographic technique in which a supercritical fluid is used as a mobile phase. A supercritical fluid is a gas or liquid brought to a temperature and a pressure above its critical point. The first report of SFC dates back to 1962 when Kesper et al. [1] used supercritical fluid chlorofluorocarbons as a mobile phase for the separation of metal porphyrins. It was not until the early 1980s that an important breakthrough of the technique occurred. This was the introduction of capillary SFC and the availability of commercial instrumentation. These became major factors in the recent rise in popularity of SFC. According to the latest estimation, approximately 100 SFC articles are published in major journals every year. 

Supercritical fluid technology has been widely used in extraction and purification processes in the food and pharmaceuticals industryPl 1 1 and for techniques such as supercritical fluid chromatography. Recently, there has been a significant increase in interest of the use of sub- as well as supercritical (SC) carbon dioxide as a substitute for chlorofluorocarbons (CFCs) for a variety of specific and specialized applications t in which the choices of enviromnentally acceptable alternatives are quite limited. 

In addition to the process benefits, there are cost and environmental benefits associated with the supercritical process. The supercritical fluid process has low operating energy costs when compared to other alternative solvent processes and the cost of the carbon dioxide used to supply the system is orders of magnitude less than the purchase costs of chlorofluorocarbons, especially with the added taxes imposed by the federal government. In addition, carbon dioxide is a more environmentally friendly material and does not have the disposal costs associated with other alternatives. 

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