Municipal waste plastics pyrolysis

T. Bhaskar, M. A. Uddin, K. Murai, J. Kaneko, K. Hamano, T. Kusaba, A. Muto and Y. Sakata, Comparison of thermal degradation products from real municipal waste plastic and model mixed plastics. J. Analytical and Applied Pyrolysis, 70, 579-587, (2003). 

The pyrolysis process for waste recycling is frequently done at larger scale than analytical pyrolysis. However, analytical pyrolysis studies are performed independently for the understanding and the optimization of such processes [10,16-19]. Also, model mixtures can be used in parallel with real samples. For example, the comparison of thermal degradation products from real municipal waste plastic and model mixed plastics can help understand the compounds generated in waste incinerators. In one such study [20], analytical pyrolysis of real municipal plastic waste obtained from Sapporo, Japan and model mixed plastics was carried out at 430 °C in atmospheric pressure by batch operation. The chlorinated hydrocarbons found in degradation liquid products of poly(ethylene)/poly(propylene)/ poly(styrene)/poly(vinyl chloride) and other polymeric mixtures were monitored. It was determined that the presence of poly(ethylene terephthalate), in addition to chlorinated plastics in the waste, facilitates... 

Poly(ethylene terephthalate) (PET) is used for bottles, carpets, and food packaging and is a very common waste polymer. It comprises 11.7% of the municipal waste plastic in Western Europe. Due to the fact that over 90% of all PET is used in packaging (in particular drink bottles because of its gas barrier characteristics) the majority of PET becomes waste within less than a year of production [1]. This plastic is commonly seen in studies attempting to derive porous carbons from plastic wastes due to the relatively higher residue that remains after its pyrolysis. A complete section in the review is allocated to PET due to its relative popularity for AC production. 

The production of plastics also involves the use of potentially harmful chemicals under the name of stabilizers or colorants. Many of these stabilizers/additives have not undergone environmental risk assessment and their impact on human health and the environment is currently uncertain and doubtful. Phthalates, as additives, are widely used in the manufacturing of PVC products, and risk assessments of the effects of phthalates on the environment are currently being carried out. Recent research for the Community Recycling Network casts doubt on whether pyrolysis and gasification are the right processes for dealing with the residual municipal waste. 

In addition, the presence additional chlorinated compounds in the PET mixed plastics such as 3P/PVC/PET and MWP were found to be chlorine derivatives of benzoic acids. Kulesza and German [36] reported the influence of poly(vinyl chloride) on poly(ethylene terephthalate) pyrolysis. They reported that the chloroesters of terephthalic and benzoic acids were found with PVC and PET mixtures (1 1). In our present investigation, the PVC/PET ratio was 1 1 and contains the other plastics such as PE, PP and PS. The ratio of mixed plastics PP PE PS PVC PET was 3 3 3 1 1 and this composition was prepared are similar to the real municipal waste from Sapporo, Japan. 2-Methyl benzoylchloride was identified as one of the additional chlorinated hydrocarbons observed in 3P/PVC/PET and MWP degradation than 3P/PVC degradation chlorinated hydrocarbons. The other chlorinated hydrocarbons could not be identified in 3P/PVC/PET and MWP degradation. It is evident from the studies that the new chlorine compounds obtained due to the presence of PET in plastic samples in either model mixed on MWP. 

Waste materials such as municipal solid waste, scrap tires, and waste plastics have traditionally been placed in sanitary landfills. However, with landfill space rapidly decreasing in the United States and worldwide, an alternative disposal method for these waste materials becomes imperative. The recycling of solid wastes is a challenging problem, with both economic and environmental constraints. Recently, two broad approaches have been attempted to reclaim solid wastes. The first approach relies on thermal or catalytic conversion of waste materials into fuel and valuable chemical feedstocks. Examples of this approach include gasification, pyrolysis, depolymerization, and liquefaction. The second approach relies on the physical recovery of valuable ingredients in the waste materials. 

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. 

Increase in thermal process temperature up to 685-715°C in a fluidized-bed system (Hamburg University Pyrolysis Process-HUPP) and application of a mixture of municipal plastic wastes resulted mainly in gaseous products, over 41 wt%, of which olefins constituted 15%, and aromatic (BTX)-containing liquid products [14], Considerably better results from the point of view of C2 and C3 olefins yield were obtained in other experiments. The application of steam as fluidization agent instead of circulation pyrolysis gas enabled an increase of C2-C3 olefins yield from 48 to 60%, accompanied by decrease in BTX yield from 24 to 11 wt% [15],... 

Table 11.3 shows the yield of gas, oil/wax and char from the fixed bed pyrolysis of the main polyalkene plastics, polyethylene and polypropylene, found in municipal solid waste [7-15], Table 11.4 shows the gas, oil/wax and char from the pyrolysis of other plastics [7-9, 14-17], All of the plastics produced an oil/wax and gas and in some cases a char. The product yield related directly to the type of plastic, the reactor type... 

The pyrolysis of mixtures of single plastics and real-world plastic derived from municipal solid waste has been investigated by several researchers and the yield of gas, oiFwax... 

Meszaros [53] reported the pyrolysis of municipal plastic waste (MPW) containing 3% of PVC in an auger kiln reactor (Com-ad recycling process). Lime was used in order... 

A detailed study on scavenging HCl by calcium-based sorbents (Ca-C sorbent, consisting of 90 wt% of CaCOs and 10 wt% of phenol resin) during or after pyrolysis has been completed recently by Bhaskar et al. [36] and is planned for technical application at a municipal plastic waste pyrolysis plant at Mizushima, Japan. Calcium-based scavenging is a strategy already followed in industry and studied deeply for fluidized-bed pyrolysis of thermoplastics by Sinn and Kaminsky [37-39]. 

Patent US 6,152,306 describes a whole plant for the reduction of municipal solid waste, including plastics. The plant is said to include a microwave reduction chamber in which pyrolysis presumably occurs. However the document did not contain any detail regarding the chemical reactions or the mechanisms involved [123]. 

Other materials in waste that is thermally processed also were studied by pyrolytic techniques, typically with the purpose of regenerating the monomers or of obtaining other useful small molecules. For example, pyrolytic studies were performed for the evaluation of the possibilities for re-utilization of nylon carpet waste [7], the recycling of thermoset polymeric composites [8], the recovery of methyl methacrylate from poly(methyl methacrylate) waste [9], as well as for other raw material recovery from pyrolysis of plastic waste [10]. The results of incineration of various other types of waste also were studied at model scale [11, 12). These studies were applied to specific waste materials associated with the manufacturing process or to municipal solid waste [13-15)... 

Copyrolysis of municipal solid waste (MSW) has led to a good separation when coupled to GC/MS. MSW is usually mainly composed of plastic residues (e.g., from packaging) and organic matter. During incineration of MSW each component may have a positive or negative influence on the thermal behavior of the others. Therefore, pyrolysis can also be envisaged as a tool for analyzing... 

---