COAL LIQUEFACTION WITH MOLYBDENUM CATALYSTS

Coal liquefaction experiments have been carried out in a stirred autoclave under nitrogen. Tetralin was employed as solvent, and the catalyst, when used, was ammonium heptamolybdate (impregnated on coal) or stannous chloride (powdered). Production of pentane-soluble oil was higher in the runs with catalyst, but net hydrogen transfer from tetralin to coal was less when catalyst was used. Coal and powdered stannous chloride exhibited a marked synergistic effect on the dehydrogenation of tetralin. A free radical mechanism was suggested to explain this effect, and model experiments with bibenzyl (but no coal) gave results that were consistent with this mechanism. An apparent synergistic effect of coal and impregnated ammonium heptamolybdate was shown to be attributed simply to improved distribution (higher surface area) of the impregnated catalyst, the coal acting as a high-area support.;One of the most effective ways of employing a small amount of ammonium heptamolybdate for coal liquefaction is to impregnate the catalyst onto powdered coal in a preliminary step. However, this is cumbersome and expensive. The liquefaction of a West Virginia coal has been studied in the presence of ammonium heptamolybdate catalyst added in the form of microcapsules. Average diameter of the polymeric microcapsules was about 6 micrometers. Autoclave testing of the catalytic effect on liquefaction showed, both for coal conversion and hydrogen consumption, that at 450(DEGREES)C the microencapsulated catalyst is at least as good as ammonium heptamolybdate pre-impregnated on the coal and far better than powdered ammonium heptamolybdate. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI.;Comparison of the results from autoclave experiments (under nitrogen) with those from tubing bomb experiments (under air) indicated major differences in coal conversion and hydrogen transfer. The conversion was 62% in the autoclave and 81% in the tubing bomb, and the hydrogen transfer was 0.7% in the autoclave and 2.93% in the tubing bomb, when 1% of Mo (based on coal) was impregnated on coal in a preliminary step. These differences are attributed to: (a) The more extensive dissociation reaction in the autoclave, which depletes the hydrogen-donor quality of the solvent, just at surface of the coal where an impregnated catalyst is located; and (b) the lower value of P(,H(,2)) built up in the autoclave; the ratio of coal dissolution is known to drease with drease in hydrogen pressure.