Insights into the Formation and Profile of Chlorinated Polycyclic Aromatic Hydrocarbons during Chlorobenzene and Chloroethylene Manufacturing Processes

Abstract

Chlorinated polycyclic aromatic hydrocarbons including chlorinated naphthalenes and congeners with three to five rings are ubiquitous atmospheric pollutants. Congener profiles and formation mechanisms from typical chemical manufacturing have not been researched extensively. We measured the concentrations of 75 chlorinated naphthalenes and 18 chlorinated polycyclic aromatic hydrocarbons in raw materials, intermediates, products, and bottom residues from chemical plants producing monochlorobenzene and chloroethylene by different techniques. The findings confirmed that these chemical manufacturing processes are newly identified sources of atmospheric emissions of these compounds. More-chlorinated naphthalenes were formed from chloroethylene production than from monochlorobenzene production, which could be explained by the higher temperatures in the former process. Successive chlorination appeared to be an important formation pathway of polychlorinated naphthalenes according to their congener profiles and was supported by quantum chemical calculations of electrophilic chlorination on various positions of naphthalene. Chlorinated polycyclic aromatic hydrocarbons were more likely to be formed during the production of monochlorobenzene than chloroethylene. Moreover, we suggested that ring rearrangement and ring coupling are important transformation reactions between polychlorinated naphthalenes and chlorinated polycyclic aromatic hydrocarbons.

Formation and Inventory of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans and Other Byproducts along Manufacturing Processes of Chlorobenzene and Chloroethylene

“…As for POPs in chloroethylene products, polychlorinated naphthalenes (1.1–2.6 ng/mL) and hexachlorobutadiene (71–396 ng/mL) were detected in chloroethylene products, , which were also higher than PCDD/Fs (0.21–1.2 ng/mL) in chloroethylene detected in this research. However, the TEQ of PCDD/Fs in monochlorobenzene (6.8 pg TEQ/mL) and chloroethylene (6.8–19 pg TEQ/mL) products were higher than the TEQ of polychlorinated naphthalenes in monochlorobenzene (0.080 pg TEQ/mL) and chloroethylene (0.080–1.1 pg TEQ/mL) products . The TEQ of PCDD/Fs was also higher than the TEQ of chlorinated biphenyls in dichlorobenzene products .…”

“…Therefore, those POPs, especially those of higher concentrations such as HCBDs, 33 need to be further concerned during the chemical manufacturing processes. 23,34,35 The characteristic chemicals found in the bottom residue samples from the different processes (Figure 2) allowed us to speculatively identify the side reactions that produced the byproducts while the main reaction occurred (Figure 3). In process A, five side reactions were tentatively identified, including dearomatization, chlorination of chlorobenzenes, chlorination of chlorophenols, chlorination of biphenyls, and polyphenyl growth (Figure 3a).…”

“…Besides PCDD/Fs, polychlorinated biphenyls and polychlorinated naphthalenes were screened-out in the chlorobenzene production related samples; polychlorinated naphthalenes, pentachlorobenzene, hexachlorobenzene, and hexachlorobutadiene were screened-out in chloroethylene production related samples, which have been listed in the Annex C of the Stockholm Convention as unintentional produced POPs. Therefore, those POPs, especially those of higher concentrations such as HCBDs, need to be further concerned during the chemical manufacturing processes. ,, …”

“…The identification of 1,2,3,4,5-pentachloro-6-(2,2-dichloroethenyl)­benzene suggested that ring growth reactions occurred (Figure c). This may have caused the formation of chlorinated polyaromatic hydrocarbons …”

Metal-Catalyzed Formation of Organic Pollutants Intermediated by Organic Free Radicals

“…4 The chlorine substituent positions are important indicators of the mechanisms through which chlorinated pollutants form, and the distribution pattern of congeners with different chlorine substituent positions can be used to identify the mechanisms through which pollutants formed. 34 We used pentachlorophenol (PCP), which has chlorine atoms occupying all of the hydrogen substituent positions on the phenol ring, as a precursor to study the chlorination/dechlorination mechanisms involved in catalysis of different metal compounds. CuO, ZnO, α-Al 2 O 3 , and γ-Al 2 O 3 , which have distinct crystal structures, were used as catalysts.…”