Microcontaminants in Pentachlorophenol Synthesis. 3. Effect of Temperature and Chlorine Flow Rate at End of Run

Polychlorinated dibenzodioxins (PCDDs) and dibenzofurans (PCDFs) are undesired byproducts that form as microcontaminants during the synthesis of pentachlorophenol. In temperature-programmed, laboratory-scale synthesis, most of the microcontaminant toxicity forms near the end of the run and while the molten pentachlorophenol product cools and solidifies. Terminating the chlorine feed to the reactor before the end of the run, where some tetrachlorophenol remains, prevented the formation of microcontaminants in high concentrations in the final product. Therefore, it appears that the microcontaminant-forming reactions that occur near the end of the run are inhibited by creating chlorine starvation conditions in the reaction system. In a commercial implementation of this strategy, it may also be beneficial to purge the reactor contents with an inert gas after stopping the chlorine flow to remove the residual chlorine.