Title : Selective conversion of methanol to para-xylene over Zn doped core-shell zeolite catalyst
Abstract:
p-Xylene is the most important isomer of xylenes for chemical industries since it can be converted into terephthalic acid which is one of the precursors of polyethylene terephthalate (PET). Currently, p-xylene has been mainly produced from petroleum resources through multistep processes including reaction and separation processes. There is a serious problem in these processes; petroleum resources will be exhausted in the future. Furthermore, there is another problem that separation of p-xylene from xylenes needs huge energy due to the repetitive adsorptive separation and isomerization. Thus, more simple processes to produce p-xylene from nonpetroleum resources is strongly desirable. Direct p-xylene synthesis from methanol is one of the most promising candidates to solve both problems.
In this study, We designed Zn ion doped ZSM-5/silicalite-1 core-shell zeolite catalyst (Zn/ZSM-5/S). We confirmed that the prepared catalyst was the Zn doped core-shell zeolite by XRD, XPS, ICP, N2 adsorption measurements and FE-SEM observations. On methanol to para-xylene (MTpX) over the core-shell catalyst, p-xylene yield was 40.7 C-mol% and para-selectivity (para-xylene selectivity in xylene isomers) was higher than 99 C-mol% owing to suppressing the undesired isomerizations of xylenes on the acid sites on the external surfaces, which substantially exceeds the other results reported in the literature. In addition to the high yield and selectivity of p-xylene, the coke deposition rate of the fabricated core-shell catalyst was slower than conventional zeolite due to suppressing the extreme coke formation by the acid sites on the external surfaces, which leads to prolonged catalyst lifetime.
Hence, this work disclose that Zn doped core-shell zeolite catalyst showed excellent catalytic performances on MTpX, which provides the new direction for the production of p-xylene via sustainable routes.
