These compounds are in general chemically unreactive, nontoxic and nonflammable. In addition these substances have been widely used as refrigerants, propellants for aerosols and blowing agents. Although CFCs have properties that make them excellent solvents, and useful in many other applications, they are now widely known to decompose in the stratosphere under the influence of high energy UV radiation UV-C.
This prevents most of the HCFC molecules from rising into the stratosphere where they too would act to deplete the ozone layer. Because of the many negative environmental effects of VOCs and halogenated solvents, finding alternatives to these solvents is important. Carbon dioxide pesents an option to the VOCs and halogenated solvents and offers many advantages in its use as a solvent.
Carbon dioxide is nonflammable, nontoxic, and chemically unreactive and it is also available as a cheaply recovered byproduct from the production of ammonia and from natural gas wells. However, carbon dioxide has other negative environmental effects. After using carbon dioxide as a solvent it can be recovered and reused by simply allowing the supercritcal or liquid carbon dioxide to be converted to a gas, capturing the gaseous carbon dioxide, and leaving the less volatile impurities behind.
Compared with organic solvents or water, its enthalpy of vaporization is considerably lower. Another consderation when assessing carbon dioxide as a replacement for less environmentally friendly solvents, is the source of the CO 2. As indicated previously, carbon dioxide is produced as a waste product of ammonia production and from natural gas wells and can be recovered from these processes.
Thus, no additional carbon dioxide need be produced, and the carbon dioxide that would normally be vented into the atmosphere from these processes, can actually be captured and put to good use. Many of these factors contribute to carbon dioxide being a green alternative to VOCs and halogenated organic compounds. As indicted above carbon dioxide is a gas at room temperature and atmospheric pressure.
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Supercritical fluids have properties of both a gas and a liquid. Although carbon dioxide has polar bonds it is a nonpolar molecule since the dipoles of the two bonds cancel one another. Surfactants are substances that increase the solubility of one substance in another. Soaps and detergents are common surfactants that enable nonpolar substances like oil and grease to be emulsified and washed away with the polar solvent water.
From our everyday experiences, we know that oil and water do not mix, that is they are insoluble in each other. They are insoluble in each other because oil is nonpolar and water is polar and the rule of thumb for solubility is "like dissolves like". In other words, polar solvents disolve polar solutes, and nonpolar solvents dissolve nonpolar solutes.
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A surfactant is a molecule that contains a polar portion and a nonpolar portion. By having both polar and nonpolar groups within the same molecule, a surfactant can interact with both polar and nonpolar molecules, thereby increasing the solubility of two otherwise insoluble substances.
In water, surfactant molecules tend to cluster into a spherical geometry with their nonpolar ends on the inside of the sphere and their polar ends on the outside.
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The polar ends are on the outside so they can interact with the polar solvent water. These clusters are called micelles and an example is shown in Figure 4. In , Joseph M. DeSimone of the University of North Carolina and North Carolina State University published his discovery that polymers such as those shown in Figure 5 are soluble in liquid or supercritical fluid CO 2 3. Murphy and R. Riggan, Noyes Data Corp.
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This book contains details of 14 different analysis procedures covering different compounds or groups of compounds in air. Specific guidance is given on the determination of selected toxic compounds in ambient air. Each method is self-contained including pertinent literature citations. Nelson and S-L. Wevill, Noyes Data Corp. Like many Noyes Data Corporation books, this one is the combination of two reports written for the U.
Both reports were prepared for the U. EPA by the above-noted authors who are members to the Radian Corporation. Part I of the book gives background information on the issue of stratospheric ozone degradation and an overview of technically feasible methods for reducing CFCs in aerosol products without adverse effect on human life and health, military preparation and the economy. Part II actually the second of the two reports discusses industry experience in converting to alternative formulations. Detailed non-CFC formulations are provided for 28 categories of aerosol products.
Special equipment may be needed to include these formulations in aerosol containers and the need is discussed along with a variety of alternative dispensing devices. Advantages to, and drawbacks of, these devices are discussed in detail and examples of consumer products which have successfully utilized these alternative products are given.
Food and Drug Administration. Introduction The use of Chlorofluorocarbons CFCs in categories of aerosol propellant use considered "nonessential" was banned in the U. An aerosol was defined as a package consisting of a self-pressurized, non-returnable container constructed of metal, glass, or plastic that contains a fluid product and that is fitted with a valve for expelling the product as a spray, liquid, gas, foam, powder, or paste. The report of that study is summarized in this document. The EPA report lists CFG aerosol applications exempted and excluded by the regulations and provides the rationale for those cases.
Technically feasible methods for reducing CFCs in these aerosol products are suggested. Formulation options for a number of products that currently use regulated CFCs are presented, as are the factors considered in developing the alternative formulations. Conclusions are presented for seven categories of aerosol uses in which CFCs are most difficult to eliminate, and partial or interim reformulations of some categories to decrease CFG use are noted.
Possible CFC reductions, based on several scenarios, are shown. Elements of the proposed CFC reduction plan are compared with the scheduled reductions called for by the Montreal Protocol, and additional studies on aerosol formulation are recommended. Tho 14 applications shown in Table 1 were exempted because they required a CFC propellant for reasons of safety, health, or national security.
Some CFC aerosol applications were excluded from the regulation because they contain propellant only; that is, the propellant is the sole ingredient and may be considered the product itself.
If the CFC serves any purpose other than as the propelling agent, the CFC is deemed an active ingredient and the product is also excluded from regulation. Table 2 lists such excluded CFC aerosol applications.
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The rationale for exempting specific essential uses of CFC aerosols is examined. The 14 specific applications listed in Table 1 are discussed, as are specific excluded applications such as skin chillers used for medical purposes and nonregulated applications. Approximately 28 product types and groups have been or are being produced in aerosol formulas that contain CFCs. Background data on each product or product group are provided, including how the CFC component functions. Industry's interest in preserving the CFC ingredient s is explained.
The primary reasons for requesting exempted status were the unavailability of substitutes, the long delays while obtaining approval from the FDA, solvency and purity profiles especially for CFC uses , life-saving potential of the product, and regulations in hospitals, aircraft organizations, etc.
During the to transition period, no nonflammable liquid propellant alternatives to CFCs were lexicologically approved and commercially available for use. As may be anticipated, some exempted, or excluded, products are no longer in use or have been replaced with ones that contain alternative propellants. However, inhalant and solvent type products are steadily growing in sales volume. Some have a relatively greater potential than others for stratospheric ozone depletion.