Thermal Hydrodealkylation of Alkylbenzenes in the Presence of Methanol or Water

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The thermal hydrodealkylation of alkylbenzenes and alkylphenols were carried out in hydrogen in the presence and absence of methanol. The methanol solution of alkylbenzenes and alkylphenols was injected into the reactor at 850 C for 1 h. For the reaction in the presence of methanol in H2, the yields of benzene increased, and the condensed products and carbon decreased compared with the results of the reaction in H2 without methanol. For the reaction of xylenes, the benzene yield was somewhat lower and the toluene yield was higher than those of the reaction of ethylbenzene. Therefore, the C2-fragment or C2-side chain should play an important role in producing condensed aromatics such as naphthalene, indene, etc.In the reactions of cresols and ethylphenols at 850 C in the presence or absence of methanol, benzene was the most abundant product in all the reactions. Dehydroxylation also occurred in addition to hydtodealkylation. For the reaction in H2 with methanol, the benzene yield increa … More sed for o-cresol and o-ethylphenol, and decreased for m-cresol and m-ethylphenol while the toluene yield slightly increased compared with the results from the reactions without methanol.In order to examine the reaction mechanism, the reaction of dueterated toluene in the presence of methanol was carried out at 750 C.Benzene having no deuterium and toluene having 1-to 5-deutrium were detected after the reaction. These results suggest that the benzyl radical produced initially from thermal cracking of toluene may react with hydrogen radical from methanol decomposition to produce phenyl radical which subtracts from hydrogen of toluene or hydrogen to produce benzene.In the presence of water the reaction did not accelerate effectively because of no decomposition of water.Thermal hydrodealkylation and dehydroxylation reactions in hydrogen in the presence of methanol were confirmed by the reaction of alkylbenzenes and alkylphenols.It is suggested that a suitable catalyst may lower the reaction temperature and the amount of condensed products. Less