Direct liquefaction of soft brown coal from the Kosovo Basin

Abstract

The behaviour of Kosovo Basin (Yugoslavia) soft brown coal was studied during a direct liquefaction process by catalytic hydrogenation. A stream of hydrogen was passed through a tetralin dispersion of the pulverized coal in the presence of commercial extruded hydrogenating-desulphurizing cobalt-molybdenum/alumina catalyst. The experiments were carried out in the temperature range between 365 and 440°C at 13.5 and 15.0 MPa, the reactants being kept at selected stationary working conditions for 1-8 hrs. The yields of liquid products soluble in n-heptane (light oils), asphaltenes (n-heptane insoluble liquid products) and the solid coal residue served as a basis for the estimation of coal reactivity and for the calculation of total coal conversion. The liquid product yields varied substantially depending on the reaction temperature and the residence time. The total conversion under most of the applied reaction conditions was found to be around 80%, the highest (-86%) being observed with the longest, 8 h residence time. Various types of grains of modified coal and newly formed types of coal grains, as well as mineral matter were identified by micropetrographic analysis, indicating the release of gases in the initial stages of hydrogenation and the formation of semi-coke and coke by the polymerization of liquid products in the later reaction stages.