Hydrofluorocarbons, chlorofluorocarbon replacement

Production of hydrogen fluoride from reaction of Cap2 with sulfuric acid is the largest user of fluorspar and accounts for approximately 60—65% of total U.S. consumption. The principal uses of hydrogen fluoride are ia the manufacture of aluminum fluoride and synthetic cryoHte for the Hall aluminum process and fluoropolymers and chlorofluorocarbons that are used as refrigerants, solvents, aerosols (qv), and ia plastics. Because of the concern that chlorofluorocarbons cause upper atmosphere ozone depletion, these compounds are being replaced by hydrochlorofluorocarbons and hydrofluorocarbons. 

A leader in the refrigerants industry, we manufacture and supply customers with economical chlorofluorocarbon (CFC) replacements and non-ozone depleting hydrofluorocarbon (HFC) refrigerants for automotive, home, commercial and transportation uses. In the Americas and Asia, you can find these products under the Genetron name and in Europe and the Middle East under Honeywell Refrigerants. 

As you know, most countries are phasing out certain refrigerants to lessen damage to the ozone layer. The chemicals being phased out are chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). Replacements are hydrofluorocarbons (HFCs) and certain blends. The DuPont web site (www.dupont.com) gives the handy Table I of recommended replacement refrigerants for various applications. 

Hydrofluorocarbon-134a or 1,1,1,2-Tetrafluoroethane (HFC-134a) has been developed as a replacement for fully halogenated chlorofluorocarbons because, compared with chlorofluorocarbons, its residence time in the atmo... 

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... 

Hydrofluorocarbons (HFCs), including 1,1,1,2-tetrafluoroethane (HFC-134a), have been developed as alternatives to chlorofluorocarbons (CFCs), which are known to contribute to the breakdown of ozone to oxygen in the stratosphere. HFCs do not contribute to the destruction of stratospheric ozone, but some HFCs have global warming potential. They primarily serve as replacements for CFCs in refrig... 

In this chapter, recent advances in our understanding of catalytic fluorination under heterogeneous conditions are surveyed from the standpoint of catalyst properties, including developments based on the use of mixed metal fluorides having different structural types, and reaction mechanisms. Much of the newer work has been the result of the need to replace chlorofluorocarbons (CFCs) by alternatives, hydrofluorocarbons (HFCs) or, more controversially, hydrochlorofluorocarbons (HCFCs), following adoption of the Montreal and successor Protocols [2,3]. Where relevant, aspects of catalytic hydrogenolysis, where fluorides have been used as replacement supports in the conventional palladium/carbon catalysts, and isomerization reactions are included. 

As described above, the non-oxidative substitution of chlorine by activated fluorine is one of the most important synthetic routes from the industrial point of view. In these reactions, a C—Cl is replaced by a C—F bond using an appropriate fluorinating agent such as HF. Among all technically-relevant catalysed halogen exchange reactions, synthesis of chlorofluorocarbons, hydrochlorofluorocarbons, and hydrofluorocarbons performed according Eqn. (1) are doubtless the most important processes. 

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. 

Alkyl halides are widely used as refrigerants. Unhl the late 1980s, alkyl halides called chlorofluorocarbons (CFCs) were widely used in refrigerators and air-conditioning systems. Because of their potential to damage Earth s ozone layer, CFCs have been replaced by HFCs, hydrofluorocarbons, which contain only hydrogen and fluorine atoms bonded to carbon. One of the more common HFCs is 1,1,2-trifluoroethane, also called R134a. 

Selective dehydrochlorination of chlorofluorocarbons (CFCs) is a very important environmental issue, and the need to replace these detrimental, ozone-depleting compounds by benign hydrochlorofluorocarbons (HCFCs) and/or hydrofluorocarbons (MFCs) has stimulated intensive work on the subject [172-182]. Palladium has been the most extensively investigated catalytic metal in this reaction, but the moderate selectivity for CH2F2 exhibited by Pd/Si02 (40%) can be significantly increased, up to 95%, with a 20-40 at%. Au addition [180], and, in Pd/C, from 70% to 90% with Au addition [181,182]. 

With chlorofluorocarbons, CFCs, now phased out of use due to their ozone-depleting effects, traditional naphthenic and paraffinic mineral oils used in refrigeration lubricants are being replaced by polyol ester oils. The main reason for the replacement is that traditional mineral oils are immiscible with the more polar hydrofluorocarbons, HFCs, which have replaced CFCs [58]. 

Tetrafluoroethane (hydrofluorocarbon-134a or HFC-134a, b.p. -25°C), which was developed as a replacement for the chlorofluorocarbons that were banned because of ozone-depleting effects, is approved in the UK for the production of natural food flavor extracts. It can be applied to optimize the extraction of plant materials and provides an environmental advantage, as well as health and safety benefits [55,56]. 

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