Propellant for Sprays

Chlorofluorocarbons (CFCs) come in many forms, including those used as propellants for spray cans and for refrigeration (freon). They were banned as being potentially harmful to the ozone layer of the atmosphere. In 1987 an international agreement was signed by about 90 nations to reduce the use of CFCs by 50% by the year 2000. This did not seem adequate, so in 1990 a new treaty called for the elimination of the use of all CFCs by industrial nations. Some third world countries (e.g., China, India, Russia, and Mexico) still make and sell CFCs, some of which are smuggled into the United States. 

The simplest of the ethers would be ether that has the simplest hydrocarbon backbones attached those backbones are the radicals of the simplest hydrocarbon, methane. Therefore, the simplest of the ethers is dimethyl ether, whose formula is CH3OCH3. Dimethyl is used because there are two methyl radicals, and "di-" is the prefix for two. This compound could also be called methyl methyl ether, or just plain methyl ether, but it is better known as dimethyl ether. It is an easily liquified gas that is extremely flammable, has a relatively low ignition temperature of 66°F, and is used as a solvent, a refrigerant, a propellant for sprays, and a polymerization stabilizer. 

Use Refrigerant, solvent, extraction agent, propellant for sprays, chemical reaction medium, catalyst and stabilizer in polymerization. 

The compounds in question are halogenated hydrocarbons, for example, CFCI3 and CF2CI2. These have had widespread use in ordinary life as refrigerants and propellants for spray cans. The compounds are gases or volatile hquids at usual temperatures, so when released they quickly mix with air. In contrast to most organic com-poimds they are very stable, resisting oxidation by O2 for periods of years or decades. Once in the atmosphere, some of the molecttles eventually find their way to the stratosphere, where Cl atoms are liberated by photochemical reactions and react with O3 to destroy it ... 

Dimethyl Ether Another potential alternative fuel is dimethyl ether (DME, CH3OCH3), presently used as an aerosol and propellant for spray paints and agricultural chemicals and cosmetics and a potential diesel fuel replacement [58, 59]. The storage and handling of DME is similar to standard propane DME can be stored as a liquid at 0.6 MPa in standard propane tanks, and it throttles to a gas at atmospheric pressure. This is similar to the fuel... 

Many gases dissolve in fats and make good propellants. However, most are flammable or toxic, or they react with the fats. Other possible propellants, such as the propane used in hairsprays or in Freon, also cause intoxication when they dissolve in the fats around nerve cells. These substances are not used, since their flammability, safety, cost, or taste makes them less desirable than nitrous oxide for spray cans of whipping cream. 

Inhaled substances may be associated with practices and equipment that may lead to suffocation. Commonly abused inhalants include model glue, spray paints, cleaning fluids, gasoline, liquid typewriter correction fluid, and aerosol propellants for deodorants or hair sprays. Most inhalants produce a rapid high that resembles alcohol intoxication. If sufficient amounts are inhaled, nearly all solvents and gases produce a loss of sensation, and even unconsciousness. Adverse effects may include severe organ damage. 

CFCs gained a lot of attention in the 1980s for their role in damaging the ozone layer. CFCs are synthetic alkanes with chlorine and fluorine attached. They were widely used as refrigerants and propellants (in spray cans) for many decades until scientists realized they were harming the planets atmosphere and possibly changing its climate. 

Freon-12 is used principally as a refrigerant, as a propellant for producing aerosol spray, and in some military applications which are classified... 

VAPORIZED PROPELLANTS. For injectors which produce a very finely atomized spray which vaporizes completely within a short distance from the injector, the gas in the combustion chamber can be considered as a homogeneous mixture of combustibles. Hence the weight of unreacted propellant at any point in the chamber is equal to the total weight of combustibles minus the weight previously reacted ... 

This ester-type anesthetic also contains benzocaine and is prepared in a polyethylene glycol base with flavoring agents added. It is available as a liquid, gel, or spray. The propellant for the spray is A 70. 

Carbon dioxide and other compressed gases such as nitrogen and nitrous oxide are used as propellants for topical pharmaceutical aerosols. They are also used in other aerosol products that work satisfactorily with the coarse aerosol spray that is produced with compressed gases, e.g., cosmetics, furniture polish, and window cleaners. ... 

Dimethyl ether may be used as an aerosol propellant for topical aerosol formulations in combination with hydrocarbons and other propellants. Generally, it cannot be used alone as a propellant owing to its high vapor pressure. Dimethyl ether is a good solvent and has the unique property of high water solubility, compared to other propellants. It has frequently been used with aqueous aerosols. A coarse, wet, spray is formed when dimethyl ether is used as a propellant. 

Another important commercial application of CFCs has been in the aerosol field as a propellant for a wide variety of products. Personal products such as anti-perspirants and hair sprays account for ca. 85% of this use. The characteristic stability, nonflammability, low toxicity, and lack of odor provide a unique combination of properties desirable for propellants. 

Later on, a number of patents were filed (158-165) that described techniques for spraying different compounds onto various substrates. In these processes the solid of interest is suspended in a liquid carrier, and a compressed gas is added to the suspension. Then, the mixture is sprayed onto the surface to be coated. In some cases the compressed gas plays two roles, acting as a propellant and also as a solvent. Most of these processes were patented by... 

Dichlorodifluoromethane and other Freons were once used for many commercial applications as refrigerants for air conditioners and refrigerators as an aerosol propellant for hair sprays, insecticides, paints, adhesives, and cleaners ... 

At the time, they seemed to be ideal coolants for refrigerators. By 1935, the first self-contained home air-conditioning units and eight million new refrigerators in the United States used CFCs as coolants. In addition to their use as refrigerants, CFCs were also used in plastic foams and as propellants in spray cans. 

The solvents in pump sprays are limited to alcohol-water mixtures and are, therefore, not as complex as the solvent-propellant mixtures of aerosols. Generally, ethyl alcohol is the primary solvent, and water the secondary solvent. In some cases, small quantities of propanols or even glycols are also used. The solvent and, of course, the pump spray system largely determine the spray characteristics of a given product, and spray characteristics are very important to the functional character of the product [54]. The solvent-propellant systems of today s hydrocarbon aerosol hairsprays used outside the United States generally consist of alcohol combined with hydrocarbons such as isobutene, butane, or propane and virtually no water. For low-VOC systems, dimethyl ether is the propellant of choice. For additional details on aerosol propellants for hairsprays, see the previous discussion on VOC propellants and the article by Root [53].The solvent-propellant in both aerosol and pump sprays contains the VOC and presents the apparent environmental problem. As stated, the CARB regulations for 1999 of 55% VOC present the target that has stimulated research and development in this area. 

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