Microcontaminants in pentachlorophenol synthesis. 2. Effects of catalyst identity, concentration, and addition strategy

Polychlorinated dibenzodioxins (PCDDs.) and dibenzofurans (PCDFs) are undesired byproducts that form as microcontaminants during the synthesis of pentachlorophenol. Using catalyst concentrations below 0.25 wt% leads to a marked increase in the toxic equivalent (TEQ) concentration of PCDDs and PCDFs in the pentachlorophenol product. With a catalyst concentration of 0.5 wt %, the TEQ concentration in the product was largely insensitive to the catalyst identity (AlCl₃ vs FeCl₃) and to the catalyst addition strategy (adding all at once or adding it incrementally). These results suggest that the microcontaminant-forming reactions are not catalyzed by the Lewis acid, which catalyzes the desired chlorination reaction. Thus, one must examine other process or reaction variables to identify the means to influence the microcontaminant level in pentachlorophenol.