Chemistry chlorine

The chemistry of chlorine, as well as other halogens, plays an important role in combustion and in a number of industrial processes. The reactions of chorine and chlorinated hydrocarbons are important in incineration of hazardous chemical wastes, which frequently contain these compounds. Also fuels such as biomass may contain significant amounts of chlorine. In biomass combustion, chlorine interacts with sulfur and alkali metals, a chemistry that has considerable implications for aerosol formation, deposit formation, and corrosion but is rather poorly understood. 

Because of the implications for atmospheric chemistry, chlorine reactions have been studied extensively at low temperatures. Despite the growing interest in incineration of toxic chemical waste involving chlorinated hydrocarbons, studies at high temperatures are still limited. Current mechanisms for high-temperature applications rely to a significant extent on extrapolation of low temperature data [355]. 

As an example of the chlorine chemistry, consider the chlorination of methane. The chlorination reaction, which proceeds at temperatures above 1200 K, consists of two main stages [285], The first involves formation of methyl chloride (CH3CI) from methane. It is initiated by dissociation of a chlorine molecule, 

This sequence corresponds to the exothermic overall reaction CH4 + CI2 CH3CI + HC1. Depending on reaction conditions, the chlorination may continue, converting methyl chloride to dichloromethane (CH2CI2) in another exothermic chain reaction, 

The second stage involves pyrolysis of the primary products CH3CI and CH2CI2. In this stage, higher hydrocarbons are formed through recombination reactions such as 

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Chlorine Chemistry Comicil (CCC), 270 Chlorine dioxide, 38 Chlorine trifluoride, 38 Chlomiephos, 38 Chlomiequat chloride, 38 Chloroacetaldhyde, 38 Chloroacetic acid, 38 2-Chloroacetophenone, 38 Chloroacetyl chloride, 38 Chloroanihnes, 39 Chlorobenzene, 39... 

The starting material for all industrial chlorine chemistry is sodium chloride, obtained primarily by evaporation of seawater. The chloride ion is highly stable and must be oxidized electrolytically to produce chlorine gas. This is carried out on an industrial scale using the chlor-alkali process, which is shown schematically in Figure 21-15. The electrochemistry involved in the chlor-alkali process is discussed in Section 19-. As with all electrolytic processes, the energy costs are very high, but the process is economically feasible because it generates three commercially valuable products H2 gas, aqueous NaOH, and CI2 gas. 

Terrence Collins is the Thomas Lord Professor of Chemistry at Carnegie Mellon University who contends that the dangers of chlorine chemistry are not adequately addressed by either academe or industry, and alternatives to chlorine and chlorine processors must be pursued. He notes, Many serious pollution episodes are attributable to chlorine products and processes. This information also belongs in chemistry courses to help avoid related mistakes. Examples include dioxin-contaminated 2,4,5-T, extensively used as a peacetime herbicide and as a component of the Vietnam War s agent orange chlorofluorocarbons (CFCs) polychlorinated biphenyls (PCBs the pesticides aldrin, chlordane, dieldrin, DDT, endrin, heptachlor, hexachlorobenzene, lindane, mirex, and toxaphene pentachlorophe-... 

Ball HA, Reinhard M (1984) In Jolley RL, Bull RJ, Davis WP, Katz S, Roberts MH Jr, Jacobs VA (eds) Water chlorination chemistry, environmental impact and health effects. Lewis Publishers, Chelsea, MI, vol 5, pp 1505... 

Copaken J. 1990. Trihalomethanes Is swimming pool water hazardous. In Water chlorination Chemistry, Environmental Impact and Health Effects, volume 6. Chelsea, MI Lewis Publishers, Inc. 

Taylor DH, Pfohl RJ Effect of chlorine dioxide on neurobehavioral development of rats. In Bull RJ, Davis WP, Katz S, et al. (eds) Water Chlorination, Chemistry, Environmental Impact, and Health Ejfects, Vol 5, pp 355-364. Chelsea, MI, Lewis, 1985... 

Carlton BD, Smith MK. 1985. Reproductive effects of alternate disinfectants and their by-products. Water chlorination chemistry, environmental impact and health effects. In Proceedings of the fifth conference on water chlorination- environmental impact and health effeets, Williamsburg, Virginia, June 3-8, 1984. Chelsea, MI Lewis Publishers, Inc., 295-305. 

After the first reports of this phenomenon, major field campaigns were launched, which clearly established a relationship between ozone destruction and chlorine chemistry. For example, Fig. 1.8 shows simultaneous aircraft measurements of ozone and the free radical CIO as the plane flew toward the South Pole. As it entered the polar vortex, a relatively well-contained air mass over Antarctica, 03 dropped dramati-... 

Other species that can initiate this sulfur oxidation chemistry are N03 (discussed in Chapter 7.D.1) and ClJ. The latter radical anion is formed in sea salt particles when atomic chlorine is generated and reacts with chloride ion. In addition, Vogt et al. (1996) have proposed that oxidation of SO2- by HOC1 and HOBr in sea salt particles may be quite important. Table 8.13 summarizes the aqueous-phase chlorine chemistry that occurs in sea salt particles and Table 8.14 the oxidation of S(IV) by reactive chlorine and bromine species in solution. 

TABLE 8.13 Some Aqueous-Phase Chlorine Chemistry... 

Although there has been some controversy over whether there is indeed a true ozone deficit problem (e.g., Crutzen et al., 1995), a combination of measured concentrations of OH, HOz, and CIO with photochemical modeling seems to indicate that it may, indeed, exist (Osterman et al., 1997 Crtuzen, 1997), although the source of the discrepancy remains unclear. Measurements of CIO in the upper stratosphere have found concentrations that are much smaller (by a factor of 2) than predicted by the models (e.g., Dessler et al., 1996 Michelsen et al., 1996). Because of the chlorine chemistry discussed later, model overestimates of CIO will also result in larger predicted losses of 03 and hence smaller concentrations. 

Analogous to chlorine chemistry, the formation of bromine nitrate represents the major short circuit in its ozone destruction cycle ... 

In Section C.3, we saw that gas-phase chlorine chemistry in the stratosphere is inextricably intertwined with bromine chemistry. Because of this close interrelationship, altering the concentrations of only one of the halogens (e.g., through controls) may not have the proportional quantitative result that might be initially expected. We explore in this section in more detail the role of brominated organics in stratospheric ozone destruction and the interrelationship with chlorine chemistry. 

HOBr also serves to couple bromine and chlorine chemistry in an indirect manner. Thus, photolysis of HOBr generates increased OH concentrations, which then cause a faster recycling of HC1 back into chlorine atoms (Lary et al., 1996 Randeniya et al., 1996a,b Tie and Brasseur, 1996). Lary et al. (1996) estimated that the lifetime of HC1 can be reduced by as much as a factor of three through this effect and suggest that the unexplained rapid rise in OH reported by Salawitch et al. (1994) at dawn may be due to the photolysis of HOBr formed overnight rather than of a nitrogen species such as HONO. 

Sander, S. P., R. R. Friedl, and J. S. Francisco, Experimental and Theoretical Studies of Atmospheric Inorganic Chlorine Chemistry, in Progress and Problems in Atmospheric Chemistry, Advanced Series in Physical Chemistry (J. R. Barker, Ed.), Vol. 3, pp. 876-921, World Scientific, Singapore, 1995. 

K. R. Chan, Chlorine Chemistry on Polar Stratospheric Cloud Particles in the Arctic Winter, Science, 261, 1130-1134 (1993a). 

Chandra, S C. H. Jackman, and E. L. Fleming, Recent Trends in Ozone in the Upper Stratosphere Implications for Chlorine Chemistry, Geophys. Res. Lett., 22, 843-846 (1995). 

Reinhard Joas studied process engineering and business management, graduating with a doctorate on the economic and ecological aspects of chlorine chemistry. He is the founder and managing director of BiPRO and advises the European Commission, the European Parliament, the Ministries of Environment and Economy as well as business companies and associations on technical, ecological and economic issues. 

At that time (1994-96), I had research support for a project on estrogenic compounds funded by the Chemical Manufacturers Association (CMA) my only official contact with the association was Ann Mason, Director of Scientific and Regulatory Affairs (Chlorine Chemistry Council, CMA), who asked for a yearly report. My opinions on the endocrine disruptor hypothesis have been based on analysis of scientific publications and have been consistent prior to, during, and after the research (not personal) support from the CMA. 

Wilcox, P. Denny, S. In Water Chlorination Chemistry, Environmental Impact and Health Effects Jolley, R. L. Bull, R. J. Davis, W. P. Katz, S. ... 

In this chapter we discuss the detailed chemistry of selected high-temperature processes where gas-phase reactions are important. Most research on gas-phase reactions has been motivated by environmental issues in atmospheric chemistry or in combustion. Significant advances in the detailed understanding of fuel-oxidation chemistry, as well as nitrogen, sulphur, and chlorine chemistry, have allowed development of modeling tools that can be used for design purposes for a number of combustion and industrial processes. 

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