Dioxin and furan formation on CuCl 2 from chlorinated phenols with one Ortho chlorine

Abstract

The formation of chlorinated dibenzo-p-dioxins (CDDs) and dibenzofurans (CDFs) on CuCl2 particlesfrom four phenols with one ortho chlorine was studied in a flow reactor over the temperature range 300 to 450°C and contrasted with gas-phase results between 500 and 700°C. Heated nitrogen gas streams containing 7/8% oxygen, 1.7% benzene vapor, and equal amounts of 2-chlorophenol 2,3-dichlorophenol, 2,3,5-trichlorophenol, and 2,3,4,5-tetrachlorophenol vapor (450 ppmv, each) were passed through a particle bed containing 0.5% (mass) CuCl2: the nominal gas particle contact time was 0.3 s. CDD/F product yields of greater than 1% phenol conversion were observed between 350 and 425°C. Unlike gas-phase CDD/F formation, formation on CuCl2 favored CDDs over CDFs, and CDDs were formed predominantly with loss of one chlorine atom. While total CDD/F yields varied significantly with temperature, CDD/F isomer distributions did not. Thus, isomer patterns may provide a fingerprint for CDD/F formation from phenol precursors. Based on results of experiments with single phenol precursors, phenol precursors were assigned to all CDD/F products 2,3,4-Trichlorophenol was found to have the greatest propensity to form CDDs, whereas 2,3-dichlorophenol and 2,3,4,5-tetrachlorophenol were found to have the greatest propensity to form CDFs. Similar to gas-phase CDD/F formation, these results on CuCl2 suggest that chlorine substitution at phenol meta sites favors CDF formation, whereas chlorine substitution at ortho and para sites favors CDD formation.