A researcher in the United Kingdom may have come up with an answer to an old problem: what to do with the millions of tires that are discarded annually.
Old tires are a huge problem they're dumped, they're buried, they're piled into mile-high mountains. If you stacked all the stockpiled and landfilled waste tires in the United States on top of each other, they would reach the moon. Lay them end to end and they would encircle the globe more than 140 times.
It's estimated that more than 2 million tires are discarded annually in the European Union, and another 270 million in the United States. An estimated 3 billion are stockpiled, awaiting disposal in the U.S. Dumping in the open creates an eyesore that may result in accidental fires with high pollution emissions or breeding ground for mosquitoes and home to vermin.
Coming up with a way to get rid of all these tires has been the focus of researchers for years. Playgrounds and parking lots have been paved with them, sneakers made with them, equipment built with them. But past strategies have been either limited in terms of the numbers of tires that can be used, not very cost effective, or both.
The oil and gas tied up in the mountains of scrap tires have long been targeted as a possible replacement source of fossil fuels. Tires can yield up to 60 percent of their weight as fuel oil, but the relatively low price of refined crude makes tire-derived fuel products economically unappealing.
Dr. Paul Williams, an energy researcher at University of Leeds, has developed a process he believes will tip the scales toward a greener future for the billions of waste tires awaiting disposal across the world. Williams has taken a technique known as pyrolysis, which has been around for a while, and taken it one step further. Pyrolysis is the degradation of the rubber of the tire using heat in the absence of oxygen.
"Pyrolysis produces a carbon, oil and gas as well as the residual steel in the tire. The problem with the technology taking off is the fact that there is no real demand for the end products," said Williams.
"Our research is looking at two areas to upgrade the carbon left after pyrolysis and to upgrade the oil to produce a chemical feedstock instead of merely a fuel, thereby making the process more economically viable."
The carbon produced through pyrolysis is low grade and can only be used in low grade applications such as carbon black filler for plastic pipes, conveyor belts and plastic shoes.
"Our work has taken the carbon and activated it using steam and carbon dioxide at high temperatures of about 900 C. The activated carbon that is produced has a high surface area and therefore can be used in higher grade applications such as cleaning up polluted waste waters from industry or industrial flue gases. The activated carbons have a much higher commercial value."
"We are also working on upgrading the oil. We have fractionated the oil to produce an oil where the high-value chemicals such as benzene, xylene, toluene and limonene are in much higher concentration. Therefore the oil has a higher value because it can be used as a chemical feedstock instead of just burning the oil for energy."
Much of this value comes from a chemical called limonene, a versatile substance that industry cannot get enough of. It can be turned into solvents, resins, fragrances and is even used as a straight, green swap for ozone-destroying CFCs.
Pyrolysis is not a complete replacement, it's just part of the mix of different processes that will provide the solution to the tire problem.
Williams' work is funded by a grant from the United Kingdom's Engineering and Physical Sciences Research Council. He is working closely with several commercial enterprises and expects the process to be commercially available within a few years.