Haloalkane

Hydrofluorocarbons ( HFCs) are fluorinated derivatives of hydrocarbons. The fluorocarbons between the partially halogenated fluorocarbons ( HFCs) and the fully halogenated fluorocarbons ( HFCs) are distinguished. Are HFCs completely fluorinated ( ie no hydrogen atoms more), then this is called perfluorocarbons or hydrofluorocarbons, perfluorocarbons.

Properties

Low molecular weight gases HFCs are ( up to about six carbon atoms), or volatile liquids. You are - with the exception of fluorine methane CH3F and Difluoromethane CH2F2 - only slightly soluble in water; with increasing chain length and degree of fluorination decreases solubility. Fully fluorinated representatives have by their stability, a significant lifetime in the atmosphere; they are decomposed only in the ionosphere.

Some important low molecular weight fluorinated hydrocarbons and their properties:

(GWP ) of 100 years

Use

Tetrafluoromethane (CF4 ) in the atmosphere is partially of natural origin. Larger emissions come from the production of primary aluminum. The gas is used in plasma etching, the ions are CF3 and CF2 formed. Fluorinated derivatives of hydrocarbons, ethane and propane (C2, C3 ) are used as the refrigerant. Often azeotropic and zeotropic mixtures of different types are used in order to optimize the properties. Some higher molecular weight fluorinated hydrocarbons (C6 - C8 ) can be used as a cleaner. The most important technical fluorocarbon tetrafluoroethylene is used as starting material for the production of polytetrafluoroethylene (PTFE, Teflon ®).

Further, often patented, mixtures are used, such as R 407c, indicating a 25 % in the mass ratio R125 / R32 23% / 52 % R134a mixed product. These mixtures are designed to replace so dangerous or prohibited pure products as well as possible, at best, with the same technical characteristics.

Impact on the environment

The fluorocarbons in the atmosphere affect the climate. They contribute to global warming (greenhouse effect), since the molecules absorb the heat radiation from the earth's surface. The global warming potential of each fluorinated hydrocarbons is very different and is about a factor of 100-15000 than that of carbon dioxide. In contrast to the CFC the fluorinated hydrocarbons have no ozone depletion potential, and were therefore used as a substitute refrigerant in phasing out CFC refrigerants.

In the European F- Gas Regulation (published on 14 June 2006 ) been taken out of refrigeration systems are measures to reduce refrigerant emissions. This is in contrast to the CFC- Halon Prohibition Ordinance is not a prohibition on use, but by higher requirement to the execution and maintenance of refrigeration systems to the leakage rates are reduced. The Regulation provides that regular leak tests are performed by trained personnel, and the result is logged understandable. In 2011, to be checked whether the objectives of the regulation are met or other use restrictions must be imposed.

Since car air conditioners type of construction have very high leakage rates, greater restrictions were adopted for these systems. From 1 January 2011, only F- gases must be used with a global warming potential of less than 150 or there must be alternative refrigerants are used. When HFC is only the refrigerant R152a (1,1- difluoroethane, global warming potential of 124 ) into consideration. One of the most promising alternatives represents the natural refrigerant carbon dioxide, the relevant contributes with a global warming potential of exactly one CO2 equivalent only when a major emission sources ( combustion of carbon in power plants and engines) to the greenhouse effect. It has already been tested in numerous vehicles and has proven to be energy-efficient solution.

Standardize

EN 378-1 (2000): Refrigerating systems and heat pumps; Safety and environmental requirements - Part 1: Basic requirements, definitions, classification and selection criteria.

Haloalkane

Properties

Use

Impact on the environment

Standardize

Further Reading