Post-consumer Plastics

Landfill has in the past been the main way of dealing with domestic waste and some industrial packaging. It has a number of important disadvantages. 

Available holes in the ground have become increasingly scarce and, for political reasons, landfill levies are set to rise sharply in all developed countries during the next decade since municipal waste has to be transported over ever increasing distances with associated wastage of energy and increase in final cost. 

Domestic and industrial wastes contain a variety of toxic materials (heavy metals and organic chemical wastes) that can leach from unprepared landfills. The modern trend is to line the landfill with an impervious film of plastic (sanitary landfill) to contain water soluble leachates (Chapter 2, pages 30-32). 

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APPR Assoc, of Post-consumer Plastics Recyclers... 

Commercial plastics polymerisation is akin to making pig s ears out of silk purses, albeit usually useful porcine ears from very worn out handbags. What were once valuable polymers are turned into generally less valuable monomers. The regenerated monomers and small chemicals from polymerisation of post-consumer plastics have no particular moral authority or intrinsic grace compared to chemicals derived from non-recycling sources. To be successful, commercial polymerisation must make economic sense in ways that are understood by those who invest dear money into capital assets. 

Post-consumer plastic waste recycling is discussed with special reference to feedstock recycling, the advantages it has over mechanical recycling, and the techniques involved. Chemolysis and thermolysis are explained, and... 

USE OF REFUSE DERIVED FUEL ENHANCED WITH POST-CONSUMER PLASTICS FOR THE PRODUCTION OF ELECTRICAL ENERGY BY THE GASIFICATION PROCESS... 

Results are presented of studies undertaken in Italy by SAFI and Replastic of the gasification of refuse derived fuel enriched with post-consumer plastics for the production of electrical energy and gas for use in cement making. 11 refs. 

The use of plastics as an energy source was demonstrated on a commercial scale at ICl Materials plastics manufacturing site in Dumfries, UK. This paper covers the preparation and use of pre- and post-consumer plastics as supplementary fuels in a circulating fluidised bed boiler specially designed for co-combustion with coal. Full emissions data on the 15% mixtures of individual plastics with coal are given, together with calculations of thermal efficiencies. Measurements by an independent body (British Coal Research Establishment) confirmed that the co-combustion of coal and plastic reduces some emissions compared with coal alone. Thermal efficiencies of around 80% were achieved and this heat was used effectively during the production of plastics. 7 refs. 

Brief details are given of two proposed resolutions on the subject of pyrolysis of waste plastic. The first states that pyrolysis and other methods of chemically reprocessing post-consumer plastics is a suitable way of diverting waste from landfills. The second resolution, supported by environmentalists, states that pyrolysis only recovers plastic s energy value, and should not be viewed as recycling. 

Examples of mixed post-consumer plastic waste by the combination of a three-stage sink-float method and selective flotation have been presented. The appropriate conditions, e.g., wetting agents, frother, depressant, and pH condition, are of importance (122). 

S. Pongstabodee, N. Kunachitpimol, and S. Damronglerd, Combination of three-stage sink-float method and selective flotation technique for separation of mixed post-consumer plastic waste, Waste Manage. (Oxford), 28(3) 475—483,2008. 

The high consumption of plastics in developed countries (over 50 million tons in the year 2001 and an increase of 4% year-1 is expected) explains the great interest for exploitation of post-consumer plastics. Taking into account that the environmental regulations prohibit their exploitation by combustion, thermal decomposition or pyrolysis is one of the procedures for recycling plastic with best perspectives for obtaining feedstock and fuel. 

In spite of the major effort in this field in the last 30 years, the development at industrial scale of post-consumer plastic pyrolysis has considerable uncertainties concerning the selection of the more suitable technology. The more developed technology in the literature is the bubbling fluidized bed reactor [1-5] where the fused plastic coats the inert particles (sand). Nevertheless, the operation at large scale in this reactor presents problems of defluidization, due to particle agglomeration provoked by fusion of particles coated with plastic [4]. 

One approach to reduce the contaminant levels consists in reusing the wasted plastic as the core of the new material. Residues of pesticides or harmful contaminants may limit recycling of plastics as a result of their potential toxicity. Utilisation of post-consumer plastics for pharmaceutical or food-contact applications is forbidden, and multilayer food packaging materials manufactured using functional barriers are subjected to strict regulations [9, 40, 41]. 

W. Ding, J. Liang, and L.L. Anderson, Thermal and catalytic degradation of high-density polyethylene and commingled post-consumer plastic waste. Fuel Process. Technol., 51, 47 (1997). 

Huber, M., and Franz, R. (1997). Studies on contamination of post-consumer plastics from controlled resources for recycling into food packaging applications. Deutsche lebensmittel-Rundschan 93(10), 328-331. (In Franz, R., and Welle, F. (2003). Recycling packaging materials. Ch. 23. In "Novel Food Packaging Teclmiques" (R. Ahvenainen, ed.), pp. 497-518. Woodhead, CRC Press, Boca Raton, FL). 

In this chapter the technical as well as legislative aspects of mechanical (secondary) recycling of post-consumer plastics will be described. For packaging materials containing a certain amount of PCR plastics the most important point is the migration of the suspicious compounds from the polymer. 

Feedstock/feed stream Post-consumer plastics used as raw materials for recycling. 

The problem with post-consumer plastics is their immense variety and widespread application. One tonne of plastics can be converted into either 20000 two-litre drinks bottles or 120000 carrier bags Collecting, sorting, baling, and transporting such numbers of lightweight materials is a tremendous task, with typical cost levels as shown in Table 1.10. 

Although direct liquefaction of waste plastic looked promising, problems associated with impurities (paper, aluminum, etc.) and chlorine derived from PVC caused operational difficulties. Consequently, it currently appears that the first step of any feedstock recycling process for waste plastics or tires should be pyrolysis, which allows much easier separation of solid impurities and chlorine. Research on pyrolysis of post-consumer plastic has been carried out by Kaminsky and co-workers [17, 18], Conrad Industries [19, 20], and Shah et al. [21]. Shah et al. [21] conducted pyrolysis experiments on relatively dirty post-consumer waste plastic obtained from the DSD. The pyrolysis oils were then subjected to hydroprocessing to convert them into high-quality transportation fuels (gasoline, kerosene, diesel). 

Transportation fuel. For mixed post-consumer plastic (PCP) that contains significant amounts of paper, inorganics, and chlorine, the best approach appears to be pyrolysis followed by hydroprocessing. Batch mode pyrolysis at 600°C, followed by thermal or... 

Plastics have become the material of choice in the modem world and their applications in the industrial field are continually increasing. Presently plastics are manufactured for various uses such as consumer packaging, wires, pipes, containers, bottles, appliances, electrical/electronic parts, compnters and automotive parts. Most post-consumer plastic products are discarded and end up as mixed plastic municipal waste. The disposal of this waste has become a major social concern. 

A distinct advantage of plastic pyrolysis into fuels as a means of recycling is its ability to handle mixed and unwashed plastics. Post-consumer plastics are often commingled and contaminated with extraneous materials such as soil, dirt, aluminium foils, paper labels and food remnants. While soil, dirt and glue can be removed from post-consumer plastics by washing, this is a fairly expensive operation and it leads to secondary waste streams... 

Flnidized-bed processes are either bnbbling or internally circulating. The fluidized-bed reactor is very versatile for the pyrolysis of polyolefins. Nevertheless one of the problems with fluidized-bed pyrolysis of post-consumer plastics relates to the stickiness of the sand particles (the fluidization medium) that becomes coated with fused plastic. In order to solve these problems, new reactors have been proposed, snch as the conical spouted bed, the conical rotary reactor, a sphere circnlation reactor and a reactor with mechanical particle stirring. 

Researchers at the Chehalis facility carried out 18-months of parametric study to assess the Conrad recycling process [9]. Their objective was to identify process bottlenecks, develop operating parameters and begin to assess product value and markets. For the initial experiments a base feed mixture of 60 20 20 high-density polyethylene, polypropylene and polystyrene (HDPE PP PS) was used as representative of the major constituents found in post-consumer plastic streams. 

Any post-consumer plastic stream will contain some halogens in the form of polyvinyl chloride, polyvinylidene chloride, brominated flame retardants, halogenated additives, food waste, or salt. Therefore, two issues must be considered. First, the gas stream resulting from the depolymerization of plastics must be scrubbed to remove any halogenated gases to satisfy emissions controls. Second, halogens in the liquid product must be minimized to increase its value and marketability. Therefore the Conrad process has been developed. It is a robust process unit that can accommodate a variable feedstream and produce a consistent product, free of nonhydrocarbon impurities by low feed preparation costs. 

Poly(ethylene terephthalate), PET, has become one of the major post-consumer plastic wastes. PET products do not present a direct threat to the environment, but they do pose a problem of considerable concern due to the huge amount of solid waste produced [1]. The disposal of this waste together with its low bio-degradability and photo-degradability, now represents a serious challenge for industrial countries worldwide. 

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