The effects of in situ-produced hydrogen on catalytic upgrading of lignite pyrolysis volatiles over ZSM-5 zeolites to produce light aromatics

Abstract

The introduction of in situ hydrogen donors to obtain a high H/Ceff ratio is an effective way to upgrade coal pyrolysis volatiles to light aromatics. In this study, the influence of different in-situ hydrogen suppliers in catalytic reforming of coal pyrolysis vapors was explored. The abilities of active hydrogen donation were greatly corresponded to structures of hydrogen donors. Isopropanol showed the best catalytic performance due to the release of a large amount of active α-H as a result of negative inductive effect of hydroxyl. Whereas tertbutanol showed the poorest catalytic performance owing to the lack of α-H. Meanwhile, the effect of in-situ hydrogen production via steam reforming with different alcohols on light aromatic yields was investigated. The highest BTEXN yield was obtained under in-situ hydrogen production from isopropanol steam reforming. Two circumstances of hydrogen supply were further compared. Relatively higher BTEXN yield was presented in the reaction of methanol steam reforming than that of using methanol solely. However, higher BTEXN yield was contrarily obtained from sole isopropanol as a hydrogen donor despite lower H2 production was gained compared to the case of isopropanol steam reforming. The fact was probably ascribed that high electron-withdrawing effect of hydroxyl for isopropanol promoted the cleavage of α-C-H bond and favored the transfer of active hydrogen to reactants over acid sites.