The extent to which coal liquefaction catalysts promote the cleavage of aliphatic bridges was investigated. Bibenzyl was chosen as a model to represent an ethyl bridge between two aromatic centers. An initial screening of catalysts showed that Co molybdate on SiO/sub 2/-promoted Al/sub 2/O/sub 3/, WS/sub 2/, LiCl-SnCl/sub 2/, SnCl/sub 2/ promoted with NH/sub 4/Cl, ZnCl/sub 2/, and SbCl/sub 3/ were all inactive as catalysts. FeCl/sub 3/ caused the bibenzyl to undergo a disproportionation reaction yielding benzene plus a tarry substance. AlCl/sub 3/ brought about a complete conversion of bibenzyl to benzene, toluene, and ethylbenzene as the primary products and lesser amounts of cyclohexane- and diphenyl-type derivatives, as well as a tarry substance. p-Toluenesulfonic acid was found to decompose but did not cause the formation of products from bibenzyl. More extensive experiments were then performed with AlCl/sub 3/. Product yields and distributions as a function of temperature, H/sub 2/ pressure, and catalyst concentration were determined. Participation of benzene, the solvent, in these reactions was also investigated. Bibenzyl conversion and the yields of toluene and ethylbenzene were a strong function of temperature and catalyst concentration but not of H/sub 2/ pressure. The yield of cyclohexane derivatives increased with pressure. This suggested that the H/sub 2/ needed to form toluene and ethylbenzene is derived from the reactant or solvent but not from dissolved H/sub 2/. Conversely, the formation of cyclohexane derivatives does involve the consumption of dissolved H/sub 2/. Plausible mechanisms are discussed.
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