Ecological replacements of ozone-depleting substances

Halogenated aliphatic hydrocarbons have appeared in the natural environment in steadily increasing amounts over several decades as a consequence of their growing use, chiefly as refrigerant, foam blowing agent and solvent, prompted by their unique properties and low cost. It is recognised that anthropogenic emissions of the above compounds, which are referred to as ozone-depleting substances (ODS's), are partly responsible for depletion of the stratospheric ozone layer and the so-called greenhouse effect. The photo decomposition of halogenomethanes in the stratosphere produces significant amounts of chlorine atoms, leading to the decay of atmospheric ozone, which allows increased levels of biologically damaging UV radiation to reach the Earth's surface. The discovery of the above phenomenon has initiated efforts towards the withdrawal of ODS. Nowadays, it is accepted that fully halogenated chlorofluorocarbons (CFC's) are the main source of the chlorine that is eroding Earth's protecting ozone, and their role is of great Global concern. In spite of the fact production CFCs has been banned since 01.01.1995 and their use prohibited since 01.01.1996, the depletion of stratospheric ozone will continue because large amounts of these class compounds are still in use. Therefore, the recovery and subsequent destruction of the CFCs still in use is a logical next step, in particular the conversion of the CFC's into useful products is a challenging task. At present CFCs are being replaced by hydrochlorofluorocarbons (HCFC's) and in perspective by hydrofluorocarbons (HFC's), before better replacements are found. The environmental impact of CFC replacements is considered in terms of their ozone depletion potential (ODP), global warming potential (GWP) and ability to form noxious degradation products.