Plastics fraction of municipal solid waste

Another approach for overcoming the problems posed by conventional cracking catalysts has been disclosed recently by Reverse et al. [101]. In this case, direct cracking is performed by using as catalyst a molten bed of pure metal or a metal mixture (mainly lead, zinc, tin) at a temperature of 460-550°C wherein the waste polymer is loaded inside the reactor at a certain depth. The authors point out that the products are indeed a result of the combination of both thermal and catalytic cracking. The catalyst composition may also include some acidic component such as metal silicates, metal carbonates and their mixtures. The process can be applied to pure and mixed polymers (PE, PET, PP, PVC), as well as to the plastic fraction of municipal solid wastes. 

A simpler solution to the problem of paper contamination is to allow for a paper component in the plastics fraction and to use a processing method which can disintegrate the cellulose fibers into small fragments such that they act as particulate fillers in the plastics. Such a method has been developed at Chalmers University of Technology (the CUT-method) making it possible to reprocess both the plastics fraction of municipal solid waste (PFMW) and a number of different industrial plastic waste materials contaminated with paper. " ... 

An Ecoprofile is an assessment of the environmental and resource impacts of a waste disposal process. This paper describes ecoprofiles for six different ways of disposing the plastic fraction in municipal solid waste -two material recycling processes that include separation of the plastic waste, material recycling without separation of the plastic waste, pyrolysis, incineration with heat recovery, and landfill. 17 refs. 

Plastics are a significantly larger fraction of municipal solid waste by volume than they are by weight. Is it more accurate to look at the solid waste burden by weight or by volume Why ... 

With increased use of plastics in consumer applications environmental concerns relating to these materials are beginning to be raised. For instance, a particularly visible plastics-related environmental problem is that of municipal solid waste disposal. With about 30% of the plastics production used in packaging, it is not surprising to find a significant and growing fraction of plastics in the municipal solid waste and in urban litter streams. Consumer awareness and sensitivity to the environmental impact of solid waste has never been at a higher... 

In the municipal solid waste streams in 1999, plastics amounted to about 10.5% by weight of the 459.8 billion pounds of municipal solid waste (55). The waste plastic collected from the solid waste stream is a contaminated, assorted mixture of a variety of plastics. This makes their identification, separation, and purification very challenging. In the plastic waste stream, polyethylene forms the largest fraction, which is followed by PET. 

Chemical composition of waste plastic cracking products depends on shares of the individual polymers (PE, PP, PS) in the feed and process parameters. This fact decides the technological application of the final products. Important products of the cracking process, both petroleum fractions and waste plastics, are coke residues. Coke residue yield increases considerably, up to 10 wt%, in cracking of municipal and industrial waste plastics since they contain various inorganic impurities and additives. It can be applied as solid fuel, like brown coal. In the fluid cracking the solid residue is continuously removed from the process by combustion in a regenerator section. 

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