Читать книгу Concise Handbook of Fluorocarbon Gases - Sina Ebnesajjad - Страница 25

Development of fluorine chemistry allowed economically viable fluorinated chemicals and polymers to be produced during the first half of 20^th century. The first commercial fluorine products of any kind go back to 1930’s, developed to meet the evolving industrial needs for compounds such as new refrigerants. The traditional agents used in refrigeration included ammonia, carbon dioxide, sulfur dioxide, hydrocarbons and methyl chloride. These refrigerants suffered from shortcomings including toxicity, flammability, instability and poor efficiency in the refrigeration cycle. Consequently, the challenges in the development of new agents consisted of the following characteristics:

1 Non-flammable

2 Good thermal stability

3 Low toxicity

4 Atmospheric boiling point of -40°C to 0°C

5 Refrigeration cycle efficiency

Some of the early patents described methods using rather exotic compounds to produce fluorocarbons [3, 4]. Simpler preparation methods have been described for the reaction of hydrofluoric acid with halocarbons (chlorine and bromine) using a catalyst [5].

Fluorocarbon in this book refers an acyclic alkane hydrocarbon in which all or some of hydrogen atoms have been replaced with fluorine (Table 2.1). An acyclic alkyl has the general formula C_nH_2n+1. Some chlorine or bromine atoms may also be present in the molecule. Depending on the structure of chemical compound, fluorocarbon consists of chlorofluorocarbon (CFC), hydrochlorofluorocarbon (HCFC), hydrofluorocarbon (HFC) and hydrofluoroolefin (HFO). All except HFO have been the targets for obsolescence under Montreal Protocol and its amendments. Major fluorocarbon applications include refrigerants, blowing, agents (foam), solvents, aerosol propellants and fire extinguishers.

Chlorofluorocarbons contain Carbon and some combination of Fluorine and Chlorine atoms. They were the original fluorocarbons developed in the 1930’s. Hydrochlorofluorocarbons contain Hydrogen, Chlorine, Fluorine, and Carbon atoms; they were quickly developed and commercialized after the enactment of the Montreal Protocol. Hydrofluorocarbons contain Hydrogen, Fluorine, and Carbon (no chlorine) known as the third generation of fluorocarbons.

Hydrobromofluorocarbons contain Hydrogen, Bromine, Fluorine, and Carbon atoms. Perfluorocarbons contain Fluorine, Carbon, and Bromine atoms, and some contain Chlorine and/or Hydrogen atoms.

Table 2.1 Examples of various acyclic alkane fluorocarbons.

Compound	Chemical formula	Form
Hexane	CH3-CH3	Alkane
Perfluorohexane	CF3-CF3	Perfluorinated
2-bromo-2-chloro-1,1,1- trifluoroethane (Halothane)	CF3-CHBrCl	Fluorobromochlorinated
1,2-dichloro-1,1,2-trifluoroethane	CClF2-CHClF	Hydrochlorofluorocarbon
1,1,2-Trifluoroethane	CHF2-CH2F	Hydrofluorocarbon

Hydrobromofluorocarbons contain Hydrogen, Bromine, Fluorine, and Carbon atoms. Perfluorocarbons contain Fluorine, Carbon, and Bromine atoms, and some contain Chlorine and/or Hydrogen atoms.

To avoid repeating the rather long chemical names of fluorocarbons a system has been devised to use codes for each of them. Oak Ridge National Laboratory [6] has provided the designations of fluorocarbon codes (Section 2.2.1).