Devolatilization of coal and zinc chloride: impregnated coal in a nitric oxide atmosphere. [Effects of ZnCl/sub 2/ on volatility; 10 refs]

Zinc chloride is known to be an effective coal hydrogenation catalyst when impregnated in small amounts on the coal surface or when mixed with coal in amounts in excess of the coal. The mechanism of interaction of zinc chloride is not understood. Previously reported studies have shown that zinc chloride and other metal halides suppress the evolution of tar and gases during pyrolysis of coal in nitrogen atmospheres. This was shown to be due to the dehydrogenation of hydroaromatic structures in the coal at temperatures below the onset of pyrolysis reactions. This reaction is accompanied by other structural changes in the coal. These experiments have been extended to nitric oxide-nitrogen atmospheres. Nitric oxide is a free-radical scavenger and is known to alter the pyrolysis behavior of coal. Thermogravimetric analysis of coal in a flow system of nitrogen and nitric oxide (NO/sub N2/ = 0.1) shows a decrease in the devolatilization of the coal in the temperature range 200-650/sup 0/C as compared to coal heated in a nitrogen atmosphere. Above 650/sup 0/C there is pronounced oxidation in the presence of nitric oxide. Coal samples impregnated with zinc chloride show a greater suppression of volatility over this temperature range. Similar results aremore » observed in isothermal experiments. The total suppression of volatility for the zinc chloride-impregnated sample in nitric oxide is approximately the sum of the separate effects of zinc chloride and of nitric oxide. This indicates that the interaction of zinc chloride with coal does not involve free-radicals.« less