Mechanism of coal hydrogenation—liquefaction; Effect of temperature and coal particle size

The effect of coal particle size, hydrogen pressure and temperature on the extent of coal conversion in an entrained flow reactor is presented. Coal hydrogenation is done by feeding dry coal with ZnCl 2 catalyst into a continuous stream of hydrogen. The hydrogen-coal stream enters a long, small internal-diameter reactor (coiled tube reactor) controlled at about 500°C and 12.4 MPa hydrogen. At these conditions the coal particles become plastic and sticky. The hydrogen provides the energy to force the sticky coal particles through the reactor. Conversion of 85% of the coal to liquids and gases is easily attained. A physical mechanism is presented based on the unreacted-core-shrinking model. This mechanism aids in the explanation of the effect of process variables on reaction rates. Projections beyond the range of the variables studied are presented. These projections indicate that the pressure of coal liquefaction processes may be reduced by (1) the use of dry coal particles and (2) the reduction of the particle size. Significant reaction rates may be attained at pressures as low as 0.7 MPa by proper adjustment of particle size and temperature.