Poly incineration products

Another development is due to the interest in polychlorodibenzofurans, spurred by their occurrence as environmental contaminants. Polychloro-phenols are manufactured in large amounts (150,000 tons per annum) and find a wide range of uses. The usual method of manufacture involves the hydrolysis of chlorobenzenes, and side reactions, favored by high temperature, can lead to the production of polychlorodibenzofurans and poly-chlorodibenzo-p-dioxins. The Seveso incident is well known." Polychloro-biphenyls are also widely used industrial chemicals, particularly in heat exchange systems, and their pyrolysis leads to the formation of polychloro-dibenzofurans. Polychlorodibenzofurans have also been detected in the fly ash and flue gases of incinerators and industrial heating plants. The most toxic of the polychlorodibenzofurans are 2,3,7,8-tetra-, 1,2,3,7,8-penta-, and 2,3,4,7,8-pentachlorodibenzofuran, and an extensive literature exists on the environmental pollution and the results of human exposure to these substances. A particularly tragic example of the latter occurred in 1968 in the Fukuoka prefecture of Japan after consumption of rice oil contaminated with a commercial polychlorobiphenyl. 

Organic polymers can also be incinerated as a means of disposal, (a) What products are formed on combustion of polyethylene (b) What products are formed on combustion of polyethylene terephthalate (c) Are these reactions exothermic or endothermic (See Sections 6.4 and 29.3 for related reactions.) (d) Propose a reason why HOPE and PET must be separated from poly(vinyl chloride) prior to incineration. 

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... 

Polychlorodibenzo-p-dioxins (PCDDs) and poly-chlorodibenzofurans (PCDFs) are mostly produced by incineration, although they are also a waste product of the pulp/paper and chemical manufacturing industries (Duarte-Davidson et al. 1997).There are potentially 75 PCDD and 135 PCDF congeners (see Fig. 7.17), but PCDDs from most biological samples contain only the tetra- to octachloro congeners with 2,3,7,8 chlorination the absence of the other congeners has been attributed to rapid metabolism and excretion (Ahlborg... 

Pyrolysis has been used to examine the types of air pollutants that might be generated from various types of waste plastic materials during incineration or thermal decomposition in landfills. One such study " used GC and GC/MS to examine the products that were formed when two kinds of widely used plastic wrapping film (made of poly(vinylidene chloride)) were pyrolyzed. 

An ideal way to recycle waste plastics is to remelt them and form new products directly, bnt this process is usually possible only in the case of rather homogeneous waste streams. With heterogeneous plastic-containing waste streams, however, because other processing steps would be required, landfilling and incineration are the most favored disposal methods from an economic point of view. These disposal processes can lead to environmental problems, especially in the case of halogen-containing plastics snch as poly (vinyl chloride) (PVC). 

---