Dealkylation of alkylphenols in phenol oil on acid zeolites

Abstract

The majority of the phenolic compounds in coal tar are alkyl-substituted phenols. To overcome the difficulty of separation, zeolites catalyzed dealkylation of alkylphenols was studied in a slurry-bed reactor. ZSM-5 displayed higher catalytic performance than other zeolites within a group of acidic zeolites with various topologies (including SAPO-34, ZSM-23, MCM-22, USY, and Mordenite). The yield of phenol gradually increased together with the zeolite acidity, but the types and yields of byproducts also increased in step with it. The pore size of the zeolites was a significant influence at similar acidity. The micropore of ZSM-5 inhibited some bimolecular processes, decreasing disproportionation/transalkylation as a result of transition state shape selection. In this study, the reaction paths of alkylphenols were investigated, based on the composition of products catalyzed by different zeolites, the distribution of products under different conditions, and the reaction process of various alkylphenols. Reaction process of alkylphenols included dealkylation, isomerization, disproportionation, transalkylation, and C-C cracking. Dealkylation took the place of isomerization as the primary reaction when the reaction temperature exceeded 350 °C. Disproportionation, transalkylation, and C-C cracking were exacerbated by excessive temperature. In addition, excessive reaction time and pressure can exacerbate side reactions, alkylphenols yields and coke deposition.