In recycling, cold is getting hot.

The idea behind cryogenic cleaning of plastic waste isn't new. Cryogenics have long been used as a means of pulverizing rubber and scrap tires. Probably the earliest use of cryogenics for separation was in recovering chrome from ABS automotive parts nearly 10 years ago.

The principle is that at very low temperatures, like-200 to-300 F, plastic becomes brittle and shatters, incidentally releasing glue, paper and some other contaminants, and killing bacteria in both the product and the waste. "When you reach the glass-transition stage, you can even separate the different materials in multilayer thermoformed packages," says Tom Tomaszek, president of North American Plastics Recycling Corp. in Fort Edward, N.Y.

The big disadvantage of cryogenic processing has been cost. It requires use of liquid nitrogen or carbon dioxide ([CO.sub.2]), which is said to add 2-4[cents]/lb to cleaning costs for post-consumer plastics. But now with heightened pollution concerns, cryogenics may be more of a bargain because it uses no caustic cleaners and nearly no water.

For the past two years, two separate entrepreneurial ventures in Texas and Michigan have been developing cryogenic cleaning units specifically for post-consumer plastics waste. Both companies say no washing stage or other cleaning material is needed to produce cleaner flake than is possible with most water-wash systems. Some potential customers, however, say mild detergent and warm-water wash at the float-sink separation stage are still necessary.

A LIQUID-NITROGEN SYSTEM

Modern Machinery of Beaverton Inc., a small privately held builder of thermoforming and other plastics machinery in Beaverton, Mich., has sold two of its three-chamber liquid-nitrogen systems--a 500-lb/hr "dry" unit delivered in May 1990 and a 2000-lb/hr "wet" unit, incorporating flotation separation of HDPE and PET--both to Secondary Polymers Ltd. in Detroit. The smaller system was essentially a prototype and is currently being rebuilt (the impactor wore out in May). Secondary hopes to have the 2000-lb production line running by July. The 2000-lb cryogenic unit measures roughly 20 ft lon x 10 ft wide x 14 ft high. It has been processing PET soda bottles and base cups 20 hr/day at Modern's plant since mid-January and showing no accelerated wear from the nitrogen, says Modern's director of marketing Edward Whitehouse. Modern will next build a 500-lb model for its own use.

Modern sells machines outright, without license. Liquid nitrogen can be obtained from various suppliers, though Modern recommends Airco Gases in Murray Hill, N.J. Cryogenic cleaning costs about 4[cents]/lb for nitrogen, says Modern's president and co-owner Larry Richardson, "But that's all it cost--there's no water to buy or dispose of and no chemicals."

Richard Plastics, a recycler based in Roosevelt, N.Y., almost bought on e of Modern's units for its new 15-million-lb/yr plant in Trenton, N.J., expected to be running by year end. Ricard's v.p. and former owner Steve Edelson says he is still considering a cryogenic unit. But purchase was delayed when Ricard itself was acquired last year by Resource Recycling Technology Inc. of Binghamton, N.Y., which wanted known technology for the new plant. Edelson says Modern's cryogenic system is "a very efficient way to liberate basecups and labels," but the remaing PET flake still needs a mild detergent wash afterward to remove residual content. Edelson also notes "downside risks" to cryogenics: "You're obligated to maitain a tremendous supply of liquid nitrogen. And this is all untried technology--we don't know what -200 F will do to machinery over a period of time." Nonetheless, Edelson says he planned Ricard's new recycling line with space availabe to permit a cryogenic unit to be installed later.

Modern's two commercial models, Cryclean 2000 (2000 lb/hr) and Cryclean 500 (500 lb/hr) use "a lot of electronics for speed control and metering of materials coming into the chamber and through various cleaning steps inside it," Modern's Richardson says. Controls are off-the-shelf components; software is proprietary.

Modern's system starts with a bale breaker and conveyor. Modern says it builds all auxiliary equipment except the granulators, which pregrind to 0.5-in. flake. Flake is siloed and auger-fed into the cryogenic unit. All other material conveying is by air pressure. In the cryogenic chamber, material is shot at high speed through a series of size-reduction steps (rotating-paddle impactor and conventional knife granulator). Dirt is removed as a powder at temperatures of -200 F, leaving clean, 1/8-in. to 3/16-in. flake, which needs drying only to remove moisture of condensation.

This flake is smaller and more uniform than typical flake made by grinding and washing, and generally isn't pelletized, but goes directly into blow molded multilayer bottles, Richardson says. Stuart Kay, president of Secondary Polymers, says he expects to get a premium price for the flace because no chemicals were used (he sells natural HDPE flake for about 33[cents]/lb).

A 2000-lb/hr "wet" system with water separation of HDPE from PET and two dewatering units costs $400,000 without granulator. (CIRCLE 50)

THE TEXAS ALTERNATIVE

Western Envirronmental Technologies, Inc., Lewisville, Texas, a privately held R&D company with a small commercial bottle-blowing operation, built its pilot cryogenic line two and a half years ago and has run product trials for over a year.

Western also signe an agreement with Environmental Products Corp., Fairfax, Va., an operator of bottle-return machines, and could deliver a 2000-lb/hr recycling system to Envipco in the Los Angeles area in four months, says Western's president and co-owner Kurt Ruppman. The line will include bale breaking, grinding, aspiration of dirt and paper, cryogenic unit, air separation of dirt, flotation/separation of PET from HDPE, dryers, and metal separation. Material will come from Envipco's reverse-vending machines in California.

Western's pilot cryogenic unit is a cylinder about 10 ft long x 3 ft in diam. x 5 ft high and runs at 1200 lb/hr. Feeding at every stage is computer controlled and self-adjusting. Granulator rate is controlled by an ammeter, so if the grinder exceeds a certain amp level, the conveyor stops. From the granulator, material is fed by auger to the cryogenic unit.

The cryogenic unit was built over two years ago with R&D support from ITW Signode, Glenview, Ill., which uses recycled PET in strapping. Signode also supported a nine-month test completed last December of nitrogen cost, separation of aluminum and other contaminants, and cleanliness of flake. A Signode source says the tests showed "cryogenics technology [if properly utilized] is an economically viable approach to producing a superior recycled product."

Ruppman says he has also built a larger cryogenic unit for 5000 lb/hr to enlarge his own in-house system. A 2000 lb/hr polyolefin processing line costs under $500,000. A 2000 lb/hr PET line costs $700,000 including extra dryers and $110,000 for metal separation equipment from Carpco Inc., Jacksonville, Fla. (CIRCLE 51)

FIRST COMMERCIAL INTEREST

Most commercial interest in cryogenics has come from PET recyclers. Wellman Inc. in Johnsonville, S.C., is said to have run tests with Modern's equipment and to have looked at cryogenic processing from Ruppman and Air Products and Chemicals Inc., Allentown, Pa., two years ago.

But Western says it has also put HDPE motor-oil bottles, PS foam, and mixed curbside plastics through its system. Western ran mixed oil bottles for Exxon Chemical Co., Houston, which is investigating technology to recycle them. Exxon's new business development/recycling manager for packaging materials Jack Spencer says cryogenic technology "may be able to do a pretty good clean-up of oil bottles, but overall cost isn't fully understood." (Secondary Polymers says Modern's system cannot run oil bottles.)

WHAT ARE OPERATING COSTS?

Ruppman says the average cost of cleaning plastics with his cryogenic method is 8 cents/lb, including electricity, capital cost depreciated over five years, building, labor, utilities and packaging. Mixed plastics cost 7 cents/lb to process, about 1.5-2 cents of it for nitrogen. PET costs roughly 8 cents/lb to process cryogenically because it requires colder temperatures and more nitrogen. (Nitrogen ranges from 30 cents/100 cu ft for over 10,000 gal to $1/cu ft for small tanks.) According to a source at Graham Packaging Co., York, Pa. (formerly Sonoco Graham Co.), conventional water washing is still 1-2 cents/lb cheaper.

Modern's Whitehouse says operating costs for a Cryclean 500 wet line are 5 cents/lb, reckoning labor at $10/hr, electricity at 9 cents/kwh, and not counting depreciation or other nonoperating costs. A 2000 lb/hr wet line costs 3 cents/lb on the same basis. Both include 2-2.5 cents/lb for nitrogen.

Still, cryogenic cleaning is obviously getting a second look from some good-sized companies. Particularly because cryogenic separation leaves neat, dry residue that packs in gaylords and can be landfilled. With water washing, even though some recyclers filter water for several reuses, eventually the water must be changed, and bleach, detergent, pesticide, paint thinner, and other bottle contents go into sewers or a nearby river. Most water-wash recyclers also reject oil bottles, which are landfilled to avoid disposal problems.

PATENT QUESTIONS

The patent situation concerning cryogenic recycling is also a bit unclear. Modern received "a broad patent" on its process last December, covering "both equipment and process for any plastics material," Richardson says. "Another company could use a cryogenic system, but if they tried to market it, we'd take them to court."

Western's Ruppman says he filed a method patent application in late April for both process and machinery. He says his process is "180 degrees from what everybody thinks we're doing," and utilizes nitrogen in a different manner from other systems.

The holder of many cryogenic patents is Air Products, said to control some 70% of the cryogenic grinding market. Air Products' patents are mostly equipment-related for grinders, including tunnels and a screw conveyor. A few are process patents for cryogenic grinding and separation of tires. Many patents have already passed the 17-year limit and expired, says Air Products industry manager for rubber and plastics David Taschler. (In Air Products' Applied Research and Development Lab in Trexlertown, Pa., Ruppman ran what was probably the first cryogenic separation of post-consumer plastic in 1987.)

Air Products has another interest in plastic recycling besides its cooperative agreement with Western. Air Products is entering an alliance with Micron Powder Systems, a Summit, N.J.-based member of the Hosokawa Micron Group, to develop joint cryogenic separation systems for industrial plastic scrap like telephone cable. "We haven't targeted post-consumer PET specifically, but equipment from Micron Powder and Air Products could be used," Taschler says. (CIRCLE 57)