Polychlorinated dibenzodioxins combustion

Polychlorinated dibenzodioxins and dibenzofurans (PCDD/Fs), in contrast to other chlorinated chemicals, have never been commercially manufactured nor are of any benefit or known use. PCDD/Fs are ubiquitous contaminants, which are released as byproducts of incomplete combustion or as impurities in chemical processes, and that their levels in the environment are increasing. 

Warnatz J, Maas U, Dibble RW (1996), Combustion Physical and Chemical Fundamentals, Modeling and Simulation, Experiments, Pollutant Formation . Springer, Berlin Zoller W, Ballschmiter K (1986), Fresenius Z. Anal. Chem. 323 19-23.. .Formation of polychlorinated dibenzodioxins and dibenzofurans by heating chlorophenols and chlorophenates at various temperatures"... 

United States because they build up in the environment and can cause harmful health effects, they are still in use in many other countries. Polychlorinated dibenzodioxins and polychlorinated dibenzofurans (dioxins) (Fu et ah, 2003) consist of 210 different compounds that have similar chemical properties (Bhandari and Xia, 2005). This class of compounds is persistent, toxic, and bioaccumulative. They are generated as by-products during incomplete combustion of chlorine containing wastes such as municipal solid waste, sewage sludge, and hospital and hazardous wastes (Bhandari and Xia, 2005). PCBs were widely used in the past and now contaminate many industrial and natural areas. 

Polychlorinated dibenzodioxins and polychlorinated dibenzofurans (PCDDs/PCDFs), polycyclic aromatic hydrocarbons (PAHs), and polychlorinated biphenyls (PCBs) are now ubiquitous in the environment. Their occurrence in indoor air mainly results from the frequent use of chemical products such as paints, glue, sealants, fire retardants and wood protection agents up to the mid-1980s. Furthermore, PCDDs/PCDFs and PAHs are always formed to some extent during incomplete combustion processes. A list of possible sources is given in Table 1.4-1. 

Because PCB molecules have two benzene rings or 12 carbon atoms as well as some chlorine atoms, they wUl bum at high temperatures when ignited. The main danger from a PCB fire is not the PCB itself, but the formation of extremely toxic byproducts of combustion, such as polychlorinated dibenzodioxins, polychlorinated dibenzofurans, and hydrogen chloride gas, which often produce immediate respiratory effect. The formation of dioxins and furans... 

Polychlorinated dibenzodioxins and furans (PCDD/Fs) are persistent, bioaccumulative toxic by-products of incomplete combustion—whether manmade or natural—and certain chemical processes. 2,3,7,8-tetrachlorodibenzodioxin (TCDD) is the most toxic of the family of 210 compounds. 

Despite the research progress mentioned above, none of the above techniques has been widely adopted commercially for environmental remediation applications due to one or more limitations of each method. For example, incineration of concentrated chlorinated organic compounds requires special treatments to remove the HCl generated. HCl corrodes the equipment if not removed. In addition, incineration of PCBs and other chlorinated organics often produces more toxic compounds (e.g. dioxins) if it is not carefully controlled. Thus, Erickson et al (87) reported that combustion of PCBs leads to the formation of small amounts of the most highly toxic polychlorinated dibenzofurans (PCDFs) and polychlorinated dibenzodioxins (PCDDs). Moreover, disposal of chlorinated solvents, neat PCBs, and related chemicals by... 

Direct thermal combustion represents the conventional technology for the destruction of chlorinated organic compounds. However, besides the very high temperatures (>1000 °C), this route has the typical disadvantage of generating more toxic by-products, such as the polychlorinated carcinogenic and environmentally persistent dibenzodioxins and polychlorinated dibenzofiirans [57]. 

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