Expanding automotive recycling to include plastics
As much as 80%, by weight, of the material in every U.S. car is recycled after it reaches the junkyard. Now, researchers and car manufacturers are going after the plastics that currently end up in landfills.
When a car reaches the end of its useful life, its rusted or crumpled remains often travel much further than the nearest junkyard. Vehicle dismantlers recover usable parts for resale or remanufacture. The remaining hulk goes to a shredding facility, where the ferrous and nonferrous metals are collected for recycling. The rest of the shredded scrap—known as shredder residue or fluff—consists largely of plastics and rubber, and somewhere between 3 and 4.5 million tons of it winds up in U.S. landfills every year, according to industry statistics. As carmakers integrate more and more lightweight plastics into vehicles to increase their fuel efficiency, a cost-effective, technically efficient process for separating and recovering the numerous different plastics types used in cars is becoming increasingly important, agree researchers in both the U.S. and Europe.
Now, a mechanical recycling technology developed at Argonne National Laboratory (ANL) as part of a Cooperative Research and Development Agreement (CRADA) with U.S. carmakers and the plastics industry could bring some of this junked material back into the marketplace. The technology could also prove useful in the EU, where an End-of-Life Vehicle (ELV) [96KB PDF] directive went into effect in January, requiring that a minimum of 85% of vehicles be reused or recovered (including energy recovery) and at least 80% be reused or recycled. By 2015, the ELV directive stipulates, 95% must be reused or recovered and 85% reused or recycled. A stakeholder consultation on ELV [764KB PDF] targets that took place in November 2005 cited an urgent need for increased plastics recovery through better separation processes.
“If we had plastic or composite cars, they’d be very light and fuel-efficient, but you’d have to cover Nebraska and Kansas with them” when they reach the end of their useful life, says Joe Carpenter, a technology development manager for the U.S. Department of Energy’s FreedomCAR and Vehicle Technologies Program. “So we have to find a way to recycle these [plastic] materials economically, so that when the newer, advanced plastics materials come along, we’ll have an infrastructure in place that can handle them.”
At ANL’s large-scale pilot plant, shredder residue goes through two processes. First, a bulk separation process sorts the material into four main categories. The mixed-plastics concentrate includes polypropylene, polyethylene, ABS (acrylonitrile-butadiene-styrene), nylon, polyvinyl chloride, polyester, and other plastics. The second category, polyurethane foams, includes materials that are mixed into these foams, such as PBDE (polybrominated diphenyl ether) flame retardants. The other categories are residual metals and the mixture of particles smaller than 0.25 inches in diameter—including iron oxides, other oxides, fibers, glass, and dirt—known in the industry as “fines”. Bassam Jody, an ANL engineer and the project’s manager, says that from there, the plastic-rich stream becomes the feed for a six-stage froth flotation process during which individual plastic types are extracted. Jody explains that the materials in the plastic polymer concentrate are mixed with a patented solution that has a combination of specific gravity, surface tension, and pH that allows air bubbles to stick to one type of targeted plastic but not the others. The plastics that catch the air bubbles float, while the others sink and are moved on to the next separation tank. The patent lists the University of Chicago, which manages ANL, as the assignee.
So far, the process has proved successful in extracting the polyethylene and polypropylene, which are the predominant plastic formulations in today’s junked cars, Jody says. Subsequent tests have shown that the recovered materials are of sufficient quality to be molded into new car parts. Now, the researchers are working on getting other plastics out of the mix.
“The economics are promising, but we really want to recover some of the other plastics from the polymer concentrate,” says Ed Daniels, director of ANL’s energy systems division. “We’re working to determine how much material is actually recoverable and the quality at which we can recover each of the different polymers from the concentrate.”
With a design capacity of up to 2 tons per hour on the mechanical separation system and a 1000-pound-per-hour capacity on the froth flotation system, ANL’s pilot plant is the largest facility anywhere for investigating shredder residue recovery, according to Jody. And the technology appears to have an edge over other types of mechanical separation techniques like hydrocyclones, says Gerald Winslow, DaimlerChrysler Corp.’s representative on the U.S. Council for Automotive Research’s Vehicle Recycling Partnership, which is part of CRADA. These other methods “cause different density separation of individual plastics, but when it comes to separating individual families of plastics, such as polypropylene, together with all of the density differences and variations based on the components in which the plastics were used, ANL’s froth flotation probably offers the best advantage for effective recovery,” he notes.
Possible showstoppers, however, are the substances of concern—PCBs in particular—that consistently show up in shredder residue, Jody says. Although PCBs have not been used in U.S. cars since the 1970s, they are nonetheless found in the residue. This is because all sorts of other waste products that can contain PCBs—such as old home appliances, transformers, light fixtures, and construction and demolition debris—get shredded up along with cars. As a result, the contaminant can get distributed throughout shredder residue.
Currently, U.S. EPA regulations stipulate that shredder residue can go into standard landfills as long as the PCB content is less than 50 parts per million (ppm), Winslow explains. If, however, the recovered plastics go back into commerce, they must be essentially PCB-free, with levels of less than 2 ppm.
Tests of a commercially available plastics washing technology on the recovered plastics will be conducted in March, according to Jody. If the plastics come out cleansed of PCBs, ANL’s method for recycling polypropylene and polyethylene will be available for commercialization, he adds.
