Reaction pathways in pentachlorophenol synthesis. 1. Temperature-programmed reaction

Pentachlorophenol, a wood preservative for nonresidential applications, contains parts per million levels of dibenzodioxins and dibenzofurans with six or more chlorine atoms. There is interest in reducing the levels of these microcontaminants in pentachlorophenol. We conducted pentachlorophenol synthesis reactions in the laboratory to demonstrate the ability to mimic the commercially practiced temperature-programmed synthesis and to identify an operating region where mass-transfer limitations were effectively eliminated. The laboratory system was operated in a temperature-programmed fashion and produced pentachlorophenol with a yield and microcontaminant content similar to those of the commercially produced material. The experiments also revealed a stirring rate, number of gas spargers, and chlorine flow rate that enabled the laboratory-scale reaction to proceed in the kinetics-controlled regime. Results indicated that microcontaminant formation was low until near the end of the run where the microcontaminant levels increased greatly with modest increases in temperature and pentachlorophenol yield. Additionally, the presence or absence of mass-transfer limitations had little influence on the effect of temperature on the pentachlorophenol yield and micrcontaminant level.