Chlorofluorocarbon propellants ozone-depleting

In the early 1990s, chlorofluorocarbon refrigerants and propellants were largely replaced by hydrofluorocarbons and hydrochlorofluorocarbons in order to reduce stratospheric ozone depletion. The hydrochlorofluorocarbons and hydrofluorocarbons, unlike the older chlorofluorocarbons, are unstable in the... 

The currently marketed MDIs may look similar to the devices that were first developed by Riker in 1950. However, due to the replacement of the ozone-depleting chlorofluorocarbon (CFC) propellants with HFA propellants, virtually all of the components of the MDI have been altered. In 1987, the Montreal Protocol was drawn up, leading to the eventual phase-out of CFC propellants. MDIs contain-... 

The replacement of chlorofluorocarbon (CFC) propellants with the non-ozone-depleting hydrofluorocarbons (HFCs) merit mention for two reasons. First, it illustrates how environmental impact can be an important selection criterion at a time when green issues are high profile. Second, HFCs were developed and evaluated for safety and delivery capability by a consortium of pharmaceutical companies, with costs shared and evaluation programs defined by prior agreement between end-users and propellant manufacturers. Such collaboration could be employed usefully in the future to develop novel excipients for delivery or targeting. The benefits would undoubtedly accrue to all. 

Pharmaceutical inhalation aerosols are widely used for treatment of diseases such as asthma and chronic bronchitis. There are three basic types of aerosol products the propellant-driven metered-dose inhalers, the dry powder inhalers, and the nebulizers. Because of the ozone-depleting and greenhouse effects of the chlorofluorocarbon (CFG) propellants, interest in the dry powder aerosols has risen in recent years. 

Raoult s law is important because it allows the calculation of vapour pressure from a knowledge of the composition of the solution. The requirement of the Montreal Protocol in 1989 for the replacement of chlorofluorocarbon (CFG) propellants in pressurised metered-dose inhalers with hydrofluoroalkanes (HFAs), because of the ozone-depleting... 

It is important to know whether molecules being released in the lower atmosphere can reach the stratosphere and affect the amount of ozone in it. Certain types of air pollution give rise to radicals that catalyze ozone depletion. A radical is a chemical species that contains an odd (unpaired) electron, and it is usually formed by the rupture of a covalent bond to form a pair of neutral species. One pressing concern involves chlorofluorocarbons (CFCs)—compounds of chlorine, fluorine, and carbon used as refrigerants and as propellants in some aerosol sprays. CFCs are nonreactive at sea level but can photodissociate in the stratosphere ... 

The most significant developments in metered-dose inhaler technology to occur since the early 1990s have been the introduction of hydrofluoroalkane (HFA) systems as alternatives to chlorofluorocarbon (CFC) systems [174]. This has largely been caused by the link between the use of CFC systems and ozone depletion in the upper atmosphere [152,175]. Albuterol and beclomethasone have been reformulated in HFA products, but as yet the CFC products are still subject to an annually renewable medical exemption. The Food and Drug Administration has recently published its position on alternative propellant formulations, which should initiate the phase-out of CFCs [176]. In the meantime, a number of generic CFC products of albuterol have been manufactured. The opportunity for reformulation of products as they come of patent is likely to increase research and development in this area in the near future. New formulation opportunities will also arise from these developments, including solutions [177], micellar [178,179], and microemulsion [180]. 

Strong circumstantial evidence implicates synthetic chlorofluorocarbons (CFCs)— alkanes in which all the hydrogens have been replaced by fluorine and chlorine, such as CFCI3 and CF2CI2—as a major cause of ozone depletion. These gases, known commercially as Freons , have been used extensively as cooling fluids in refrigerators and air conditioners. They were also once widely used as propellants in aerosol... 

Measurements over the last several decades have indicated a rapid decrease of stratospheric ozone. This decrease has been most drastic over Antarctica, where the ozone layer is now almost completely absent (Figure 11.17). Stratospheric ozone over the rest of the planet has decreased at a rate of about 6% each year. Each year, we are exposed to increasing levels of harmful UV radiation that are linked with skin cancer and other health issues. While many factors contribute to ozone depletion, it is believed that the main culprits are compounds called chlorofluorocarbons (CFCs). CFCs are compounds containing only carbon, chlorine, and fluorine. In the past they were heavily used for a wide variety of commercial applications, including as refrigerants, propellants, in the production of foam insulation, as fire-flghting materials, and many other useful applications. They were sold under the trade name Freons. ... 

While less harmful to the environment than CFCs, hydro-chlorofluorocarbons (HCFCs) are stiU ozone-depleting (they are classified as Class II ozone-depleters) and will be phased out by 2020. Hydrofluorocarbons appear to have little or no ozone-depleting effect and are replacing CFCs and HCFCs in refrigerants and aerosol propellants. 

Hydrocarbon propellants, e.g., propane, isobutane, butane, are the most commonly used in mousses. These are insoluble in the mousse concentrate therefore, vigorous shaking of the can before use is required to properly disperse the propellants. Most products use a blend of two or more hydrocarbons. The more volatile the propellant blend, the faster a foam structure is formed and the less dense it is. An exception to this is the use of hydrofluorocarbon 152A [75-37-6] (HFC), which has partial solubility in mousse concentrates and a high volatility. The high volatility creates an immediate foam structure but the partial solubility leads to a creamy, dense foam. HFC is not an ozone depleting propellant as are its cousins the chlorofluorocarbons (CFCs). 

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. 

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