Pyrolysis turns scrap tyres into oil and gas

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.”