Pyrolysis the way forward for plastics

PROBLEMS with Cardiff’s waste if China stops recycling it?

Surely this is an opportunity for the city to make money out of waste plastics and waste food by reducing them to oils and carbon using pyrolysis?

Nearly 20 years ago, while trying to encourage inward investment in Wales, I learned about industrial pyrolysis from a Bristol-based manufacturer of pyrolysis equipment.

Ever since then I have wondered why Cardiff doesn’t use this method of waste disposal. In pyrolysis the plastics are transformed into oils and carbon black, while metals separate out.

Anhydrous pyrolysis can also be used to produce liquid fuel similar to diesel from plastic waste, with a higher cetane value and lower sulphur content than conventional diesel.

Using pyrolysis to extract fuel from end-of-life plastic is a second-best option after recycling, is environmentally preferable to landfill, and can help reduce dependency on fossil fuels and geoextraction.

Pyrolysis is a recycling technique which converts plastic waste into fuels, monomers, or other valuable materials by thermal and catalytic cracking processes. It allows the treatment of mixed, unwashed plastic wastes.

For many years research has been carried out on thermally converting waste plastics into useful hydrocarbon liquids such as crude oil and diesel fuel. Recently the technology has matured to the point where commercial plants are now available.

Pyrolysis recycling of mixed waste plastics into generator and transportation fuels is seen as the answer for recovering value from unwashed, mixed plastics and achieving their desired diversion from landfill. Scheirs and Kaminsky, (2006), inter alia, provide an overview of the science and technology of pyrolysis of waste plastics.

They describe the types of plastics that are suitable for pyrolysis recycling, the mechanism of pyrolytic degradation of various plastics, characterisation of the pyrolysis products and details of commercially mature pyrolysis technologies.

Their book also covers co-pyrolysis technology, including: waste plastic/ waste oil, waste plastics/coal, and waste plastics/rubber. (Feedstock Recycling and Pyrolysis of Waste Plastics into Diesel and other Fuels).

Pyrolysis of scrap or waste car tyres is preferable to disposal in landfill and allows the high energy content of the tyre to be recovered as fuel. Using tyres as fuel produces the same energy as burning oil and 25% more energy than burning coal.

An average car tyre is made up of 50–60% hydrocarbons, resulting in a yield of 38–56% oil, 10–30% gas and 14–56% carbon char. The oil produced is largely composed of benzene, diesel, kerosene, fuel oil and heavy fuel oil, while the produced gas has a similar composition to natural gas.

Peter Sunman

Cardiff