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The Elusive Dream Of Tire Recycling

Undeterred by past failures, companies pursue high-tech approaches for raw material recovery

by Michael McCoy
April 20, 2015 | A version of this story appeared in Volume 93, Issue 16

Hot Mess
A carbon black recovery facility in Germany.
Credit: CCT
Pyrolysis of shredded tires happens in circular beds at CCT’s plant in Germany.

In 2009, a company called SNRG Corp. announced the purchase of an advanced rubber devulcanization technology. The firm said it would use the process to build a facility in Houston to extract 80 million lb of recycled rubber per year from scrap tires.

“The technology being acquired by the company is unique, proven, and ready for commercial production,” SNRG proclaimed.

The Houston plant was never built, nor were most of the facilities trumpeted over the years as being able to turn the environmental problem of old tires into valuable raw materials.

Undeterred, a new batch of companies is embarking on a fresh round of projects intended to extract devulcanized rubber or carbon black from spent tires. The backers of these projects insist they have solved the technological and economic problems that hobbled high-tech tire recycling in the past.

Thankfully, the huge mountains of bald tires that blighted the American landscape in the 1970s and ’80s no longer exist. Only about 75 million scrap tires languish in piles today, down from close to 1 billion in 1990, according to the Rubber Manufacturers Association (RMA).

Still, old tires continue to be generated in prodigious volumes. In the U.S. alone, about 230 million car and truck tires are discarded every year, says RMA, which gathers detailed statistics on the topic. And one notorious tire pile, outside Denver, still holds close to 30 million tires.

Although tires are almost half rubber, the rubber can’t simply be melted down and reused as many polymers can be. That’s because the rubber is vulcanized—cross-linked with sulfur in a process invented by Charles Goodyear in 1839. Vulcanization imparts needed mechanical properties but is not easily reversed.

Almost 96% of the scrap tires created in 2013 did find markets, RMA says. More than half of them were burned for their energy content in electric utility boilers, paper mills, and cement kilns. About a quarter were ground into so-called crumb rubber, which is added to asphalt or used in playgrounds and sports surfaces.

But proponents of devulcanization and carbon black recovery argue that incineration and playground surfaces are stopgap measures that don’t adequately capture the value of the useful materials in scrap tires.

Sam Visaisouk, chief executive officer of Tyromer, a Canadian developer of devulcanization technology, notes that the market for the 20-mesh crumb-sized rubber used in playgrounds is already oversupplied. And backers of alternative technologies claim that some countries are looking to outlaw tire-derived fuel on environmental grounds.

Where Old Tires Go
Burning for energy value is the largest U.S. use for scrap tires. SOURCE: Rubber Manufacturers Association
Graphic showing the uses of scrap tires.
Burning for energy value is the largest U.S. use for scrap tires. SOURCE: Rubber Manufacturers Association

At present, the most advanced commercial-scale tire recycling in the U.S. is practiced by Lehigh Technologies. The Tucker, Ga.-based firm uses cryogenic milling to break down end-of-life tires and other postindustrial rubber into micrometer-scale powders as small as 300 mesh. Last September, Lehigh raised $8 million from investors including the Japanese synthetic rubber maker JSR.

Lehigh operates what it calls the world’s largest micronized rubber powder facility, with 140 million lb per year of capacity. Depending on the application, Lehigh says, the recycled rubber can be added to new products in amounts of up to 40%.

According to CEO Alan Barton, Lehigh is enjoying annual sales growth rates of 30%. Customers, the firm says, include six of the world’s top 10 tire manufacturers, which have incorporated the firm’s micronized rubber into more than 250 million tires to date. Barton expects JSR to help Lehigh make inroads in Europe and Asia and eventually set up manufacturing in those regions.

Where They Could Go
Graphic showing uses of scrap tires being advertised by tire-recycling companies.
New companies see opportunity in alternative uses for scrap tires. SOURCE: C&EN

Visaisouk and others seeking to develop tire-recycling technologies don’t begrudge Lehigh its success to date. “The problem is so big there will be more than one solution,” Visaisouk says.

Still, he says, even when finely ground, vulcanized rubber such as Lehigh’s can generally be incorporated into new tires and other rubber products at only a few percent without affecting performance. Vulcanization is a thermosetting process that renders rubber unable to be remelted and reused at high concentrations.

Many breakthroughs have been proclaimed over the years in the pursuit of devulcanization. “Since the day Charles Goodyear discovered vulcanization, people have been trying to reverse it,” says Michael Blumenthal, a former RMA vice president who now runs the scrap tire management company MarShay.

Goodyear Tire & Rubber itself revealed in 1999 that it had patented a devulcanization process based on the solvent 2-butanol. In the laboratory, Goodyear said, the process recovered up to 80% of the rubber in a used tire, but it was never commercialized.

A 90-page report commissioned in 2004 by the state of California found companies and institutions offering roughly 25 mechanical, chemical, ultrasonic, microwave, and biological techniques for devulcanizing rubber. But the report also found reliable information hard to come by and no plants operating at commercial scale.

“All things considered under current and likely near-term future conditions,” the report concluded, “devulcanization faces an uphill struggle to be competitive with virgin rubber.”

Tyromer’s solution is to use supercritical carbon dioxide to rapidly swell rubber’s molecular framework, preferentially elongating the sulfur bonds for easy cleavage by shear force inside an extruder. The Canadian firm claims that new tires or other rubber goods can contain up to 20% of its devulcanized rubber without affecting performance.

Visaisouk was in New Jersey recently to receive a piece of imported equipment that has since been shipped to Tyromer’s site in Waterloo, Ontario. He expects the firm’s plant to be running by May 1 with a capacity to devulcanize more than 6 million lb per year of crumb rubber.

His eventual goal is to sell similar systems to crumb rubber producers looking to market a higher-value product. Visaisouk also claims to be working with two of the top four tire companies to incorporate Tyromer’s product into their tires. But like other executives in the field, he says he can’t name names.

Another Canadian firm, Phoenix Innovation Technology, opened an 8 million-lb-per-year plant in a Montreal suburb last fall to manufacture a devulcanized product it calls regenerated rubber. “We break 60% of the sulfur bonds with minimal damage to the rubber,” says Phoenix CEO Stephen Murphy.

Phoenix accomplishes this, according to Murphy, by carefully controlling temperature and shear force in its regenerator via infrared temperature sensors and a customized cooling system. The resulting rubber can be used in tire applications such as tractor and mining vehicle tires and in nontire applications such as conveyor belts, he says.

The idea of devulcanizing rubber back to its original form has an elegant simplicity, but the reality is complex, MarShay’s Blumenthal cautions. Tires contain a mixture of natural, styrene-butadiene, butyl, and polybutadiene rubbers plus carbon black, antioxidants, stearates, and other materials. Breaking carbon-sulfur bonds across that range of ingredients without damaging the polymer isn’t easy.

That’s why another cohort of companies is focused on recovering carbon black, a tire-reinforcing agent that is created by the incomplete combustion of an aromatic oil mist in a hot gas stream. The result is a finely divided carbon powder that is incorporated into tires at up to 30% by weight.

In February, officials from a company called Delta-Energy announced plans to build a $45 million carbon black recovery facility on the site of a former International Paper plant in Natchez, Miss. Delta-Energy is a 2005 spin-off of the RJ Lee Group, a materials characterization and industrial forensics firm that employs more than 250 scientists.

William Cole, Delta-Energy’s vice president of product management, explains that his company started as an internal materials science challenge at RJ Lee. Scientists there developed a catalytic pyrolysis technique that decomposes shredded tires into carbon solids and a hydrocarbon liquid that petrochemical companies can use as a raw material.

Delta-Energy started producing carbon-black-like products in 2008 at a small facility in North Dakota. The equipment was recently relocated to Mississippi, where it will complement the larger facility planned for the site. “Natchez puts us strategically closer to our suppliers and customers,” Cole says.

A German tire-recycling company, Pyrolyx, wants to get even closer to supplies. In February, it announced plans to build a tire pyrolysis facility in Hudson, Colo., on the site of the largest U.S. tire dump.

Based in Munich, Pyrolyx has developed a process for continuous recovery of carbon black from shredded tires. It is in the midst of merging with another German firm, Carbon Clean Tech (CCT), which has operated a 10 million-lb-per-year recovered carbon black facility in Stegelitz, Germany, since 2012. Unlike Pyrolyx, CCT uses a batch process.

After the merger is complete, Pyrolyx plans to build a continuous-process plant at the Stegelitz site, according to Ulrich Sattler, the firm’s chief operating officer. In addition, Pyrolyx has signed a letter of intent with CH2E, the owner of the Hudson tire dump, to build what it says will be the world’s largest recovered carbon black plant right next door.

Both Sattler and Cole acknowledge that their product isn’t exactly the same as virgin carbon black. CCT’s material, for example, includes a broader distribution of particle sizes and may contain some ash. But both executives say their products can work as well as the original. “We can supplement or completely replace,” Cole says.

Given the tire industry’s desire to become more sustainable, executives from tire-recycling companies of all stripes say the time is right for recycled raw materials. Yet they also admit they must overcome a healthy amount of skepticism regarding the technological and economic viability of their processes.

The tire industry executives who are in a position to strike agreements with recycling firms have seen their share of past failures, Tyromer’s Visaisouk acknowledges. “Senior people have been burned in the past by believing devulcanization works,” he says. “ ‘It’s too good to be true,’ is what everyone tells me.”

Indeed, Blumenthal, the former RMA executive, has seen plenty of hype and failure during his 30 years in the scrap tire industry. For now he is reserving judgment on the new technology. “I can’t say that it won’t work,” he says. “What I can say is that in the past it has not worked.”

Still, Blumenthal holds out the possibility that technology and economics will eventually come together to make advanced tire-recycling technology a reality. “At some point in the future,” he says, “someone is going to figure out how to make this work.”  


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