Pyrolysis produces gas, liquid and solid char, the relative proportions of which depend upon the method of pyrolysis and the operating conditions of the pyrolysis reactor, chiefly the rate of heating, the operating temperature and residence time within the pyrolysis reactor.

 

Long residence times and low heating rates are typical of processes such as charcoal manufacture, effectively converting the majority of the carbon present in the feedstock into elemental carbon.

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As residence time reduces and heating rate increases, the proportion of liquid produced increases as there is sufficient heat in the system to boil off any compounds formed by the breaking of polymer chains. Very short residence times and high temperatures give conditions very similar to those encountered in the gasification process, and consequently produce more gas.

 

For the purposes of conversion of plastic into oil products, maximisation of liquids production is desirable, as this will give a material which can be easily transported and refined. This is achieved by so-called ‘fast’ pyrolysis, with residence times of less than 2 seconds, rapid heating and temperatures of around 500°C.

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The liquids produced vary depending on the purification strategy employed by the technology supplier. Generally, the liquid produced by the pyrolysis unit will have a wide boiling point range and include some entrained char.

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