A Leeds academic has developed a new method of tyre disposal that could add millions of pounds in value to the rubber mountains dotted across the globe.
Paul Williams, senior lecturer in the department of fuel and energy at the University of Leeds, has modified a process known as pyrolysis, which involves the degradation of the tyre using heat, but without oxygen. Rather than burn, the rubber breaks down to produce an oil and gas, leaving a residual carbon and the steel casing of the tyre - all of which can be recycled.
Dr Williams's research, funded by the Engineering and Physical Sciences Research Council, has produced significant increases in high-value chemical yields from the derived oil, which may add as much as £1 per tyre to the commercial value of the pyrolysis process.
The oil produced during pyrolysis contains valuable chemical compounds such as benzene, toluene, xylene and limonene, widely used in the chemical industry in the manufacture of rubber, insecticides, pharmaceuticals and explosives.
But the quantity of the chemicals produced by the standard pyrolysis process has not been sufficient to offset its cost.
Dr Williams's patented process involves passing the gases evolved from pyrolysed tyres through a secondary catalytic reactor. This reduces the amount of oil obtained, but increases the concentration of certain chemical compounds within it - in some cases by as much as 40 times.
About 180 million scrap tyres are produced each year in the European Union and 150 million in the United States. There is an estimated stockpile of 3 billion tyres awaiting disposal. There are more than 121 million tyres on vehicles in Britain, with about 38 million worn tyres replaced each year. About 26 per cent are used as retreads and 46 per cent recycled as reclaimed materials or incinerated for energy recovery.
The tyre mountains are potentially dangerous as each tyre equates to ten litres of fuel oil, and even landfilled tyres can ignite. Tyre fires can be almost impossible to extinguish and emit atmospheric and water-borne pollutants. An EU ruling will ban the disposal of whole tyres in landfill sites by 2003 and shredded tyres by 2006.
But the volume of scrap tyres being produced means that current recycling methods are not enough. "Pyrolysis has been around for a long time but it has not taken off as an alternative treatment technology, due in part to the lack of commercial return. Refining the pyrolysis method with catalysis offers the opportunity to profit from what is regarded as a waste product, and one that is expensive to dispose of responsibly," Dr Williams said.
Dr Williams is developing a commercial strategy for the catalysis process, supported by technology transfer company Leeds Innovations.