ES&T EUROPEAN N E W S
Industry Invests in Reusing Plastics
T
he two most common methods of recycling plastic waste are material recycling, in which plastics are regranulated and reused as solids, and energy recycling, in which the plastics are incinerated with energy recovery. H o w e v e r , w i t h t h e a d v e n t of tougher European legislation on packaging waste recycling, especially in Germany, polymer producers have been snowing increasing interest in developing another option: feedstock recycling. Feedstock recycling turns plastics back into a basic chemical feedstock—short chain hydrocarbons, or synthesis gas—and reuses these to make brand new chemical products such as polyolefins or ammonia. It differs from material recycling, therefore, because material recycling does not involve breaking down the polymers. One of the advantages of feedstock recycling, say its proponents, at least for reuse in plastics applications, is that the recycled material is as good as new, with none of the concerns about hygiene or structural properties that material recycling can present. The idea, and some of the technology, is not entirely new. The Japanese, for example, did research in the 1970s, mainly to find a way of recovering relatively pure industrial scrap locally. The new European focus, however, is on taking mixed plastics from m u n i c i p a l solid waste, preferably with a minimum of cleaning and sorting. One German company, Veba, already has a commercial-scale plant running. A handful of other companies are planning or running pilot-scale operations. The most recent development was the announcement in November by BP Chemicals that it had put together a consortium of European petrochemical companies to help develop its polymer cracking techn o l o g y . P e t r o f i n a , DSM, ElfAtochem, and Enichem will participate in a pilot plant being built at BP's Grangemouth, Scotland, site. BP's process, aimed at recycling 16 A
Environ. Sci. Technol., Vol. 28, No. 1, 1994
BY A N D R E W
MILLER
postconsumer packaging waste, heats ground-up plastics and converts them to hydrocarbons that can be reprocessed into virgin plastics in existing plants. The process takes place in a fluidized bed reactor at temperatures of 400—600 °C and just above atmospheric pressure, without a catalyst. The polymers are broken into short chains and vaporized, emerging from the top of the reactor and leaving solid impurities such as metal fillers behind. The vapor is cooled to produce the liquid feedstock and a light gas, which can be burned to provide all the energy needed for the reactor. Chlorine produced is neutralized in a proprietary process. So far, the company has been working at the lab scale (1-20 kg/h) on a standard test feed composed of 80% polyethylene and polypropylene, 15% polystyrene, 3% polyethylene terephthalate (PET), and 2% polyvinyl chloride (PVC). John Brophy, general manager for corporate research at BP Chemicals, says he hopes the process will eventually take up to 10% PVC. The liquid product behaves like naphtha in a steam cracker, and like waxy distillate in a fluid catalytic cracker, Brophy e x p l a i n s . The yield, on a weight basis, is about 85%. BP estimates that in current market conditions, for a small commercial plant of 25,000 tons/year, the cost of recycling would be about $100-200 higher per ton of waste plastic than the market value of the product, which would be approximately that of naphtha. Veba, meanwhile, has been recycling used plastics into synthetic crude oil since 1992 at a hydrogénation unit that was originally built in 1981 to turn coal into liquid hydrocarbons. Unlike the gas-phase BP process, the Veba plant, at Bottrop in Germany, uses a liquid-phase process in which vacuum residue from a nearby oil refinery is mixed with the waste plastics. Hydrogénation occurs at 450-490 °C under a
hydrogen partial pressure of 150250 psi and is followed by a separation step to remove impurities and hydrotreatment with a standard fixed bed catalyst. Initially, the plant used expensive, finely ground particles (< 1 mm) of plastic, but this year Veba built a feed preparation unit that depolymerizes and liquefies plastics, which can then be fed to the hydrogénation unit. Also in Germany, BASF is at the point of applying for a patent on a thermal cracking process, developed over the past three years, and expects to build a pilot plant in mid-1994. The process takes mixed plastics waste. BASF is already talking to plastics collection companies about obtaining p o s t c o n s u m e r waste through the German recycling system. Norway's Norsk Hydro, meanwhile, is studying technology for turning mixed plastics into synthesis gas for ammonia production. The major emphasis of the project, according to company Vice-President for Petrochemicals Hallstein Gravrak, is on the liquefaction and depolymerization of plastics in a heated extruder, rather than on a degradative process. The liquid would then be used as feedstock for partial oxidation in a gasifier. So far, Norsk Hydro has been testing a pilot plant in Germany with sorted plastic fractions, but Gravrak says the goal is to take mixed plastics. The Norwegian company is talking to another company about collaborating on the pilot scale testing, which is likely to continue for another year or so. Although feedstock recycling is seen in Europe as another option for coping with increasingly strict legislation on plastics waste, people involved caution against seeing it as the ultimate panacea. It is costly, and other recycling methods have their own advantages.
Andrew Miller is the editor of Chemistry & Industry in London.
0013-936X/94/0927-16A$04.50/0 © 1993 American Chemical Society
