Popular Science, Oct 1994 v245 n4 p62(4) Mired in tires. (junk tires) Mariette DiChristina. Brief Summary: Hundreds of millions of junked tires are stockpiled in US landfills alone, and another 250 million are added each year. Innovative ways to convert recycle junked tires without harming the environment are discussed. Full Text: COPYRIGHT Times Mirror Magazines Inc. 1994 If environmental menaces were judged by the numbeers, junkeed tires would be near the top of the heap. Some three billion tires now languish in U.S. landfills, stockpiles, and illegal dumps. Another 250 million join them every year - one for nearly every man, woman, and child in the country. If you could stack them, the tires would stretch 142,000 miles high - more than halfway to the moon. Tires contribute as much to municipal solid waste as do disposable diapers. Unlike yeaterday's news and aging rock stars, tires don't just fade away. Today's radial tires last twice as long as biasply one made 20 years ago. Built to endure from the first test kick through a lifetime of potholes and peel-outs, an average of 40,000 miles of driving, tires could take centuries to degrade naturally. In the meantime, they are a nuisance: Tires harbor stagnant water and become breeding grounds for disease-carrying mosquitoes and rats. In landfills, they capture explosive methane gas and "float" upward - sometimes shooting to the surface with tremendous force. And they burn in spectacular, stinking fires that can't be fought with only water. When seven million tires went up in smoke a decade ago in Winchester, Va., they burned for more than nine months and oozed 690,000 gallons of oil. Several years ago, a New Jersey tire blaze beneath an elevated highway melted the asphalt. Retreading is, of course, a cheap, low-energy way to put retired tires back to work. Whole tires also can be used to create artificial reefs, dock bumpers, planters, swings, and even energy-efficient house walls. But only 23 percent of U.S. scrap tires are reused in any way, many of them exported, says the EPA. The rest are increasingly being banned from overcrowded landfills: Seventeen states forbid tires in landfills entirely, while 14 more permit only shredded treads. "Ban them and you just get big piles elsewhere," says Michael Blumenthal, executive director of the Scrap Tire Management Council in Washington. "The longer you wait, the bigger the problem." The world's largest pile is in Westley, Calif., where an estimated 34 million scrap tires await the millennium. Covering about 160 acres, the pile reaches six stories high in spots. In southern Connecticut, the owners of the 30-acre Tire Pond are stashing tires underwater - avoiding problems with mosquitoes and fire. The 140-foot-deep pond, a former clay pit, has 15 million tires and is only half fall. Ducks paddle along its rubber shoreline. Like the tire piles themselves, however, the potential solutions are legion. If there's no backyard use for a bald tire, it can be burned as fuel or chopped up and incorporated into new products like hockey pucks, mud flaps, and springy floor pavers. Most intriguing of all options are technologies that break tires into their reusable chemical components. Why has it been so hard to get tire recycling on the right track? For an answer, you have to look behind the treads. From the tiniest tricycle wheel to the monsters that roll tractors, tires have similar ingredients. They typically combine several types of natural and synthetic rubber, fabric, steel, and carbon black (a sooty ingredient also found in shoe soles, inks, sealants, and paints). Each of these ingredients must be recycled separately, unlike recycling, say, an aluminum can. Complicating matters - and making simple tire remolding impossible - is that tire rubber is vulcanized. The sulfur and carbon in the rubber bond inseparably during manufacturing. So, in contrast to that aluminum can, old tires can't easily be made into new ones. "Think of [rubberl as an egg," says Helen Patrauskas of Ford. "Before you cook it, you can make all sorts of things. But once the egg is hardboiled - similar to what happens when making a tire - your only option is egg salad." That's why a process marketed by Titan Technologies of Albuquerque, N.M., is so promising: Developed partly with research grants from Sandia National Laboratories, the Titan system reduces tires to their components. And unlike pyrolysis - a costly, long-known alternative that vaporizes scrap tires at more than 1,000[degrees]F- Titan's process works within an oven-heat range that Betty Crocker would find familiar. The temperature stays around 450[degrees]F, so the end products are not degraded or burned away as with pyrolysis. "Just as fried eggs turn black if you turn the heat up too hot, so will oils from tires," says inventor Floyd Wallace of Lansing, Mich. The key to Wallace's low-temperature process: seven proprietary metallic and inorganic catalysts. In Wallace's machine, shredded tires are first preheated to about 200[degrees]F to remove moisture. Augers then move the chips through a hotter stainless-steel chamber that is about 200 feet long. Along the way, the chips react with the catalysts to create hydrocarbon vapors, carbon black, and ash. In the final step, the vapors are condensed to derive oils that can be used as home heating fuel or to lighten heavier oils, and the remaining gases are sent back through the system. During tests at a pilot plant, each 20-pound auto tire yielded about a gallon of oil, six pounds of carbon black, three pounds of steel, and a half pound of ash. The system also recovered about 25 cubic feet of methane gas per tire, which is used to power the machinery. Two Titan plants opened this summer in Korea. Oils could also function as a tire solvent. Texaco, for one, is experimenting with dissolving shredded tires in oil at 700[degrees]F. This creates a light oil that can be refined into diesel gas, heating fuel, and other chemicals. The process also produces a smaller amount of heavy fuel oil. And University of Wyoming engineers are "co-recycling" scrap tires and waste oil in a two-step thermal process that yields gases and oils. A patented system from Avraam I. Isayev, a polymer engineer at the University of Akron, uses sound as wee as heat to break down the chemical bonds in tires: Tire crumbs are heated to about 400[degrees]F, then blasted with 20,000 cycles per second of ultrasonics (just above the highest frequency the human ear can discern) and compressed at pressures up to several thousand pounds per square inch. "The rubber goes in solid and within milliseconds becomes a highly viscous fluid, like bread dough," says Isayev. With additional curative agents, he says, the doughy material can be molded into new products. A prototype machine handles 50 pounds of tires per hour; Isayev aims to increase that to several thousand pounds per hour. Though promising, these new technologies for breaking down tires remain costly. And they may not be able to handle the sheer volume of tires. Instead, many tire experts pin hopes on incineration. Lafarge Inc. in Whitehall, Pa., for example, is among the 22 U.S. cement kilns that burn tires for supplementary fuel. Electric-utility power plants, paper manufacturers, and other industries also burn tires. As fuel, you could do far worse than to use tires. Each pound of tire provides 12,000 to 16,000 Btu-slightly higher than the same weight of coal. One million tires can replace the equivalent of 500 truck loads of coal, according to Goodyear, the world's largest manufacturer of rubber products. Tires also burn cleaner. That same one million tires used as fuel in place of coal would reduce carbon-dioxide emissions by 19.5 percent, Goodyear claims. Leftover tire ash, which is essentially unusable, in other processes, is actually a bonus in kilns, says Terry Dengler of Lafarge. There, the ash becomes part of the cement; the iron oxide from the steel in tires improves the cement's strength, says Dengler, and saves the company the trouble of adding it. In Whitehall, Lafarge has been burning 2,000 scrap tires a day for about a year. The tires supply 30 percent of one kiln's fuel. At the plant, tires ride a ski-lift-like "hanger" to the kiln. Near the kiln entry, incoming dirt-encrusted tires have coated everything with a thick layer of dust, like a haunted house. But the, automated machinery's noise is enough to wake the dead. Walk beside the cylindrical kiln, where interior temperatures reach 3,700[degrees]F, and its radiated heat suggests a miniature hell on earth. Beyond breaking down or burning tires are ways to turn tire pieces into new products. So-called rubber-modified asphalt, for instance, can hold a lot of old tires: A mile of roadway 36 feet wide and three inches thick uses 16,000 chopped tires. The 1991 Intermodal Transportation Efficiency Act requires that five percent of federally financed asphalt laid in any state must contain rccycled rubber; in 1997, the minimum will rise to 20 percent. A tire road will last twice as long as regular asphalt, says the National Solid Wastes Management Association in Washington, although it is more difficult to recycle and may cost more to maintain. Vehicles that roll along, those roads will also contain the broken bits of old tires. Syntene of Richmond, Ind., mixes powdered tires with other plastics in a patented process. One tire produces 250 brake-pedal pads, containing at least 50 percent scrap tires. The pads should be available on Ford models by year's end. Ford may eventually. use the recycled tire material in other pedal pads, carpet backing, splash guards, and, weather seals. Chrysler and National Rubber Co. of Canada are also teaming up to make steering shaft seals and fender liners with ground tire rubber. These new products will only make a small dent in the U.S. tire pile. Says Jack Zimmer of Goodyear: "You can only make so many swings and roadways with old tires," Even burning rubber can reach a point of no return; when tires exceed 30 percent of kiln fuel, for example, their chemistry adversely alters the cement's curing process. So ultimately, says Zimmer, "We'll need a combination of many, ideas." Article A16101163