CFC propellant

MDI technology has utilized chlorofluorocar-bons (CFCs) as propellants. CFC-containing MDIs... 

There are two general types of formulations. First, the micronized active ingredient may be suspended in liquefied propellants (CFCs or HFAs). This group makes up the most common type of MDI. Second, the drug may be dissolved in a mixture of CFCs or HFAs and ethanol, forming a solution. Less than 25% of MDI products are formulated as solutions developed over 50 years ago. 

Storage and handling of the propellants (CFCs and HFAs), types of filters, transfer piping, and storage tanks should be standardized. Any observations of the appearance of the propellants should be recorded. The supplier s specifications should be reviewed. 

Table 9 Physical properties of propellants (CFCs and HFAs)...

In general, MDI formulations can take the form of either suspensions or solutions. Traditionally the preferred route has been to formulate a suspension of the micronized drug substance in the liquid propellant (CFC or HFA). In some cases, additional excipients (e.g., surfactants and/or cosolvents) have been added to improve the quality of the dispersion. The various MDI formulation options are described in detail later together with a description of some of the alternative options for the input drug substance. 

Marketed MDIs usually contain either CFCs or, more recently, HFCs as propellants. CFC-containing MDIs contain CFC-12 and CFC-11 and sometimes CFC-114. HFCs 134a and 227 have been developed as replacements for CFCs and are used in newer MDIs. In addition, some preliminary work has been conducted with MDIs using hydrocarbons as propellants. 

Although the initial focus was on CFCs, used at the time for aerosol propellants (CFC-11 and -12), blowing agents (CFC-114), cleaners for electronics (CFC-113) and refrigerants (CFC-115), amendments to the Montreal Protocol have led to the control of such common solvents as carbon tetrachloride and 1,1,1-tri-chloroethane, which were used in very large quantities. 

Hydrocarbons have, for the most part, replaced CFCs as propellants. Most personal products such as hair sprays, deodorants, and antiperspirants, as well as household aerosols, are formulated using hydrocarbons or some form of hydro-carbon—halocarbon blend. Blends provide customized vapor pressures and, if halocarbons are utilized, a decrease in flammabiUty. Some blends form azeotropes which have a constant vapor pressure and do not fractionate as the contents of the container are used. 

In 1976 the United States banned the use of CFCs as aerosol propellants. No further steps were taken until 1987 when the United States and some 50 other countries adopted the Montreal Protocol, specifing a 50% reduction of fully halogenated CFCs by 1999. In 1990, an agreement was reached among 93 nations to accelerate the discontinuation of CFCs and completely eliminate production by the year 2000. The 1990 Clean Air Act Amendments contain a phaseout schedule for CFCs, halons, carbon tetrachloride, and methylchloroform. Such steps should stop the iacrease of CFCs ia the atmosphere but, because of the long lifetimes, CFCs will remain ia the atmosphere for centuries. 

In 1990, approximately 115,000 t of CFCs were used as propellants, which represents a 58% decrease from the 1986 level. Most of this market... 

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 ... 

During the 1980s, it became recognized that chlorofluorocarbons (CFCs), widely used as aerosol propellants, are damaging the ozone layer, and aerosol manufacturers were asked to use other propellants. Some... 

Ever) year our planet is bombarded with enough energy from the Sun to destroy all life. Only the ozone in the stratosphere protects us from that onslaught. The ozone, though, is threatened by modern life styles. Chemicals used as coolants and propellants, such as chlorofluorocarbons (CFCs), and the nitrogen oxides in jet exhausts, have been found to create holes in Earth s protective ozone layer. Because they act as catalysts, even small amounts of these chemicals can cause large changes in the vast reaches of the stratosphere. 

A typical example of the interaction between hypothesis and experiment is the story of the work that resulted in worldwide concern over the depletion of the ozone layer in the stratosphere. These studies led to the awarding of the 1995 Nobel Prize for Chemistry to Paul Crutzen, Mario Molina, and F. Sherwood Rowland. Figure FT provides a schematic view of how this prize-winning research advanced. It began in 1971 when experiments revealed that chlorofluorocarbons, or CFCs, had appeared in the Earth s atmosphere. At the time, these CFCs were widely used as refrigerants and as aerosol propellants. Rowland wondered what eventually would happen to these gaseous compounds. He carried out a theoretical analysis, from which he concluded that CFCs are very durable and could persist in the atmosphere for many years. 

C05-0071. Freons (CFCs) are compounds that contain carbon, chlorine, and fluorine in various proportions. They are used as foaming agents, propellants, and refrigeration fluids. Freons are controversial because of the damage they do to the ozone layer in the stratosphere. A 2.55-g sample of a particular Freon in a 1.50-L bulb at 25.0 °C has a pressure of 262 torr. What is the molar mass and formula of the compound ... 

CFC, chlorofluorocarbon propellant HFA, hydrofluoroalkane propellant MDI, metered-dose inhaler. 

Propellants may be of a number of different types CFCs, hydrofluoroalkanes (HFAs), or alkanes. The composition impacts upon performance. A numerical system is employed to identify fluorinated propellants. The rules governing this numbering system allow the molecular structure to be derived from the numerical descriptor. The rules may be listed as follows ... 

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