Recycle those scrap tyres
27 Jul 2001
An innovation by a British scientist may spark a renewed interest in the environmentally-friendly but little-used recycling process of pyrolysis - and help to reduce the growing mountain of scrap tyres awaiting disposal around the world.
Pyrolysis 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 Paul Williams, of the Department of Fuel and Energy at the University of Leeds (UK) 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, which are widely used in the chemical industry particularly in the manufacture of rubber, insecticides, pharmaceuticals and explosives. However, the quantity of the chemicals produced by the standard pyrolysis process has not been sufficient to offset the cost of the treatment.
Dr Williams' new 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 as much as 40 times.
Scrap tyres present an enormous environmental problem. Approximately 180 million scrap tyres are produced each year in the European Union, and 150 million in the US alone - with an estimated stockpile of 3000 million tyres awaiting disposal. Apart from being an obvious eyesore when stockpiled, they also present a fire hazard. A typical car tyre equates to ten litres of fuel oil, and even landfilled tyres can ignite. Once ignited, such fires can be almost impossible to extinguish and emit atmospheric and water-borne pollutants.
An EC ruling will ban the disposal of whole tyres in landfill sites by 2003 and shredded tyres by 2006. With the increasing emphasis on the environment and sustainability, recycling rather than disposal is becoming the preferred treatment route. However, the sheer volume of scrap tyres being produced means that current recycling methods (for example retreading the tyres or 'crumbing' the rubber for play and sports surfaces) are simply not enough.
Dr Williams believes that his methods could lead to a renewed interest in pyrolysis as a commercially attractive, as well as environmental attractive solution to the problem of scrap tyre disposal.
'Pyrolysis has been around for a long time,' he said, 'but it has not taken off as an alternative treatment technology, due in part to the lack of commercial return on the derived products. 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 is developing a commercial strategy for the catalysis process, supported by technology transfer company Leeds Innovations.
