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Source: Chang and Allen (1997).

Source: Chang and Allen (1997).

have developed basic material and energy flow models of over 400 chemical processes associated with the production of more than 200 chemical products (Rudd et al. 1981), describing a complex web of chemical manufacturing technologies.

An understanding of material flows in these networks can be used at a variety of levels. First, the material flow networks can be used simply to identify potential users and suppliers of materials, and to identify networks of processes that are strategically related. For example, for the types of networks shown in Figures 32.6 and 32.7, it would be useful to have lists of processes that produce and consume hydrochloric acid. A partial list is given in Table 32.4; such lists are useful in identifying potential material exchange network.

Once consumers and producers of the target chemicals are identified, material and energy flow models can be used to construct networks. The network that makes the most sense depends on the features that are to be optimized. Analyses have been performed to identify networks that minimize energy consumption (Sokic, Cvetkovic and Trifunovic 1990; Sokic, Zdravkovic and Trifunovic 1990), the use of toxic intermediates (Yang 1984; Fathi-Afshar and Yang 1985) and chlorine use (Chang and Allen 1997). Other analyses have considered the response of networks to perturbations in energy supplies (Fathi-Afshar et al. 1981) and restrictions on the use of toxic substances (Fathi-Afshar and Rudd 1981). Regardless of the application, however, the material flow model of the chemical manufacturing web provides the basic information necessary to identify and optimize networks of processes.

Yet another use of comprehensive material flow models is in the evaluation of new technologies (Chang and Allen 1997). Consider once again the case of chlorine use in chem-

Figure 32.8 A summary of chlorine flows in the European chemical industry Table 32.4 Partial list of processes that produce or consume hydrochloric acid

Processes that consume hydrochloric acid

Chlorobenzene via oxychlorination of benzene

Chloroprene via dimerization of acetylene

Ethyl chloride via hydrochlorination of ethanol

Glycerine via hydrolysis of epichlorohydrin

Methyl chloride via hydrochlorination of methanol

Perchloroethylene via oxychlorination of ethylene dichloride

Trichloroethylene via oxychlorination of ethylene dichloride

Processes that produce hydrochloric acid

Adiponitrile via chlorination of butadiene Benzoic acid via chlorination of toluene Carbon tetrachloride via chlorination of methane

Chloroform via chlorination of methyl chloride

Ethyl chloride via chlorination of ethanol

Methyl chloride via chlorination of methane

Perchloroethylene via chlorination of ethylene dichloride Phenol via dehydrochlorination of chlorobenzene Trichloroethylene via chlorination of ethylene dichloride

Note: *Such lists are useful in identifying potential material exchange networks.

ical manufacturing. Rather than generating complex networks involving HCl and molecular chlorine, it might be preferable to use a chemistry that converts waste HCl into molecular chlorine. Several processes have been proposed and three are listed in Table 32.5. These processes will only be successful if they can compete with the re-use of by-product HCl, in the types of networks described in Figures 32.6 and 32.7. Data on material and

Table 32.5 Processes for reducing chlorine use in chemical manufacturing

Process description

Chlorine via electrolysis of hydrogen chloride (Ker-Chlor process) Chlorine via oxidation of hydrogen chloride (CuCl2 catalyst Chlorine via oxidation of hydrogen chloride (HNO3 catalyst)

Source: Chang and Allen (1997).

energy flows in the chemical manufacturing web can again be used to assess the competitiveness of new chemical pathways, such as the technologies listed in Table 32.5.

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