Production of light aromatics from coal hydrogenates

The production of light monoaromatic hydrocarbons by thermal cracking of pre-hydrogenated polyaromatics has been studied. Results are presented for the pyrolysis of 1,2-di hydronaphthalene, perhydronaphthalene and perhydroindan between 700 and 900°C at atmospheric pressure in a stream of nitrogen as the inert carrier gas and with a residence time of 0.5 s in the reactor. The cracking of decalin, perhydronaphthalene, gives high yields (up to 30% by weight) of BTX, more than 20% ethylene and 15–20% methane. In contrast, the pyrolysis of 1,2-dihydronaphthalene or of tetralin resulting from only partial hydrogenation of naphthalene, gives very small yields of benzene and other light aromatics. The main reaction is dehydrogenation and the re-formation of naphthalene. It has been shown that the complete hydrogenation of naphthalene makes it possible to break one of the two rings between 750 and 850°C and to produce simultaneously significant amounts of ethylene and light aromatics. The same phenomena have been observed in the pyrolysis of perhydroindan and other completely hydrogenated polyaromatic compounds. It can be concluded that complete hydrogenation causes the stability of the rings, which is characteristic of polyaromatics, to disappear. The industrial interest of the results obtained lies in the simultaneous production of light aromatics and ethylene from perhydropolyaromatic compounds formed by the hydrogenation of coal.