Thermal Hydrodealkylation of Alkylbenzenes in the Presence of Methanol or Water

在甲醇存在和不存在的情况下，烷基苯和烷基酚在氢气中进行了热氢脱烷基化反应。将烷基苯和烷基酚的甲醇溶液在850℃下反应1h，与在无甲醇的氢气中反应相比，在有甲醇存在的氢气中反应，苯产率增加，缩合产物和碳减少。对二甲苯反应，苯产率略低于乙苯反应，甲苯产率高于乙苯反应。在850℃下甲酚和乙基酚在甲醇存在或不存在时的反应中，苯是最丰富的产物。除糖基脱烷基化外，还发生了脱羟基作用。在氢气中与甲醇反应，苯产率增加…与不加甲醇的反应相比，邻甲酚和邻乙基苯酚的选择性较高，间甲酚和间乙基苯酚的选择性较低，而甲苯产率略有增加。为了探讨反应机理，在750℃下进行了甲苯在甲醇存在下的反应，反应后检测到不含氚的苯和1~5-氚的甲苯。这些结果表明，甲苯热裂解产生的苯基自由基可能与甲醇分解产生的氢自由基反应生成苯基，再减去甲苯的氢或氢气生成苯。在有水的情况下，由于没有水的分解，该反应不能有效地加速反应。烷基苯和烷基酚在甲醇存在下的热加氢脱烷基化和脱羟基反应证实了烷基苯和烷基酚在氢气中的反应，表明合适的催化剂可以降低反应温度和缩合产物的数量。较少

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