Two-Stage Catalytic Coliquefaction of Coal and Waste Tire

Abstract

Two-stage catalytic liquefaction of coal and waste tire was studied using two bituminous coals, Blind Canyon and Illinois No. 6, and a sub-bituminous coal, Wyodak. The tire sample was a mixture of waste, recycled tires. In the first stage, the tire was liquefied separately at 350 or 400 °C under N 2 or H 2 to obtain tire oil. In the second stage, each coal was liquefied, in turn, with tire oil at 350-450 °C and 1000 psi of H 2 (cold) using various tire-oil/coal ratios. A few second-stage runs were carried out with coal and vacuum-pyrolized tire oil obtained from a commercial source. Some of the second-stage runs were catalytic. For these, a ferric-sulfide-based catalyst was impregnated in situ in the coal. In general, the use of tire oil shows an improvement in coal conversion. In the absence of catalyst, the effects are similar with tire oils prepared under different conditions. With the catalyst, the increase upon adding tire oil is greatest when the tire oil is prepared at 400 °C in a hydrogen atmosphere. A synergistic effect can be quantified by adding to the conversion (or oil yield) for catalyst plus coal the increase in conversion (or oil yield) observed when tire oil is added to coal in the absence of catalyst and comparing this number to the conversion (or oil yield) when the feed is coal plus tire oil plus catalyst. In general, the improvements are most pronounced at the higher temperatures of the second stage and at higher ratios of tire oil to coal. For all three coals, the effects of tire oil are greater than those due to the whole tire in single-stage coliquefaction, especially with a catalyst present at high tire-oil/coal ratios. A kinetic analysis shows that the thermal reactions of coal and tire oil have lower activation energies in the second stage of two-stage liquefaction compared to those in single-stage liquefaction. A similar effect is noted for the catalytic reactions, at least for the bituminous coals. This indicates that two-stage liquefaction is beneficial, particularly at mild temperatures in the second stage. Further, the activation energies for the synergistic rate constants are higher for the catalytic reactions than for the thermal reactions, indicating that diffusion effects in the coal may be important in the noncatalytic processes.