A major application of photochlorination is the production of chloroparaffins. Mixtures of complex composition consisting of several chlorinated paraffins are formed. Chlorinated paraffins have the general sum formula CHCl and are categorized into three groups: Low molecular weight chlorinated paraffins are short chain chloroparaffins (SCCP) with 10 to 13 carbon atoms, followed by medium chain chloroparaffins (MCCP) with carbon chain lengths of 14 to 17 carbon atoms and long chain chlorinated paraffins (LCCP), owing a carbon chainwith more than 17 carbon atoms. Approximately 70% of the chloroparaffins produced are MCCPs with a degree of chlorination from 45 to 52%. The remaining 30% are divided equally between SCCP and LCCP. Short chain chloroparaffins have high toxicity and easily accumulate in the environment. The European Union has classified SCCP as a category III carcinogen and restricted its use.
In 1985 the world production was 300,000 tonnes; since then the production volumes are falling in Europe and North America. In China, on the other hand, production rose sharply. China produced more than 600,000 tonnes of chlorinated paraffins in 2007, while in 2004 it was less than 100,000 tonnes.
The quantum yield for the photochlorination of n-heptane is about 7000, for example. In photochlorination plants, the quantum yield is about 100. In contrast to the thermal chlorination, which can utilize the formed reaction energy, the energy required to maintain the photochemical reaction must be constantly delivered.
The presence of inhibitors, such as oxygen or nitrogen oxides, must be avoided. Too high chlorine concentrations lead to high absorption near the light source and have a disadvantageous effect.