WCl6 chemical transformations occurring during pyrolysis and steam activation of coals plus WCl6 mixtures

Different concentrations of WCl6 have been added to three kinds of coking c oals before their pyrolysis. The rank of the coal and mainly the volatile m atters removed during the heat treatment are of great influence on the tran sformations of tungsten hexachloride. It first reacts with oxygen present i n the starting coal to transform into WO2.9 between ambient and 550 degrees C. From 550 degrees C to 750 degrees the trioxide is reduced to WO2 and a fraction reacts with Ca to form CaWO4 as shown by X-ray diffraction. The to tal amount of W introduced in the initial mixture is recovered in the resul ting green-coke and the total amount of chlorine is removed as HCl. After s team activation, WO2 is oxidised into W24O68. (C) 2000 Kluwer Academic Publ ishers.