Alternative tire recycling options continually
Recycling tires by grinding them
down to crumb rubber — whether it is to be used as fuel
or as feedstock for new production — is a mature technology
with proven markets, and promising new products and markets are
A Different View
Research continues on other ways to recycle tires, some
more promising than others. Most involve some form of devulcanization
— breaking the sulfur bonds that help vulcanized rubber
hold its shape, a characteristic that also prevents recyclers
from melting tires down and remolding them into new products.
Another promising process —
pyrolysis — involves breaking tires down beyond the rubber,
to the hydrocarbon gases, carbon black and oil that the rubber
is made from. The process also liberates the steel in tires for
recycling. The hydrocarbon gases can be sold, but they are usually
burned to fuel the pyrolysis process.
Thermal reclaim process: The oldest form of devulcanization
— patented in 1858 — is also the least promising.
Thermal devulcanization involves exposing rubber to high temperatures
for an extended period of time to break the sulphur bonds. The
process also breaks the polymer chains themselves, severely degrading
the value of the rubber. The process also presents environmental
and public health risks and is rarely used today.
Mechanical devulcanization: This
process used rollers, mixers and extruders to mechanically "chew"
away at the sulfur bonds. It produces good results but is not
yet economically viable.
Devulcanization with ultrasound:
Early efforts using ultrasound to break the sulfur bonds in vulcanized
rubber were encouraging.
Bacterial devulcanization: Rubber
is ground to a powder, then suspended in a liquid full of sulfur-eating
bacteria such as thilbacillus, rodococcus and sulfolobus. The
process is technically viable but complex, and therefore too expensive.
The technique uses heat, in the absence of oxygen, to
speed up the decomposition of organic material. Theoretically,
the oils, carbon black and scrap steel can be sold, and the hydrocarbon
gases released through pyrolysis can either be sold or used as
fuel at the pyrolysis plant.
But the tire pyrolysis techniques
used today produce mixed quality oils and carbon black that can
be difficult to market. The gas is a low to moderate BTU methane
that is difficult to store.
Because of those quality issues,
no tire pyrolysis plants have been in sustained production in
the United States or anywhere else in the world. Research continues,
however, for a technology that will make tire pyrolysis commercially
— Courtesy of Ohio Department
of Natural Resources