Pyrolysis turns scrap tyres into oil and gas

An innovative British scientist, Dr Paul Williams, 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 UK.

Every year, 1000m tyres are manufactured worldwide, each lasting for approximately 50,000km. In Britain, over 38m worn tyres are replaced each year with only 46 per cent recycled as reclaimed materials or incinerated for energy recovery. The three most common ways to recycle scrap tyres are retreading, use as fuel in cement kilns, and 'crumbing' which involves shredding the tyres for use as sports or childrens' play area surfaces.

Oil extraction
Williams, based in the Department of Fuel and Energy at the University of Leeds, has been working on pyrolysis which involves the degradation of a tyre using heat, but without oxygen. Rather than burning, 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.

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, pharmaceuticals and explosives. However, the quantity of the chemicals produced by the standard pyrolysis process had not previously been sufficient to offset the cost of the treatment.

Williams' new patented process involves passing the gases evolved from pyrolysed tyres through a secondary catalytic reactor which 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.

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 or 'crumbing' the rubber for play and sports surfaces, are simply not enough.

Williams believes that his methods could lead to a renewed interest in pyrolysis as a commercially attractive, as well as environmentally attractive solution to the problem of scrap tyre disposal. "Pyrolysis has been around for a long time," he says, "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."


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