The formation of liquid products such as BTX and tar from the pyrolysis of coal was reviewed from a chemical point of view. First, the dissociation of bonds in coal during heat treatment was discussed. Polymethylene and/or oxymethylene bridges play important roles for the tar formation, because of their relatively low bond energies. The radicals produced in the above stage should be stabilized by hydrogen supplied either from other parts of coal molecule or from ambient atmosphere to yield liquid products. The factors which affect the final product yields were discussed. The secondary reaction of primary volatile matter is essential in this respect. The temperature, heating rate, residence time, coal particle size, gas pressure and minerals in coal all influence the secondary reaction. A molecular model of a bituminous coal and the reaction model during pyrolysis were proposed
