Gas phase catalytic hydroprocessing of trichlorophenols

The catalytic hydrodechlorination of four trichlorophenol (TCP) isomers (2, 3,5-TCP, 2,3,6-TCP, 2,4,5-TCP and 2,4,6-TCP) was studied in the gas phase u sing an Ni/SiO2 catalyst over the temperature range 473 K less than or equa l to T less than or equal to 573 K. The catalyst was 100% selective in remo ving chlorine(s), leaving the hydroxyl group and benzene ring intact. Dechl orination proceeds via stepwise and concerted routes and the relative impor tance of each is dependent on the nature of the isomer where steric rather than resonance effects appear to determine the ultimate product distributio n. Dechlorination efficiency is quantified in terms of phenol yield, chlori ne removal rate and the ultimate partitioning of chlorine in the parent org anic or product inorganic host. The reaction pathways, with associated pseu do-first order rate constants, for the conversion of 2,3,6-TCP and 2,4,6-TC P are presented. The effect of time and temperature on process selectivity is discussed and the nature of catalyst deactivation is considered. (C) 200 0 Society of Chemical Industry.