Collaborative Effect of Zinc and Phosphorus on the Modified HZSM-5 Zeolites in the Conversion of Methanol to Aromatics
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Collaborative Effect of Zinc and Phosphorus on the Modified HZSM‑5 Zeolites in the Conversion of Methanol to Aromatics Hu Li1 · Xue‑Gang Li1 · Wen‑De Xiao1 Received: 19 February 2020 / Accepted: 16 August 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract In this work, the cooperative effect of Zn and P modification on the pore structure and acid properties of HZSM-5 and its catalytic performance in methanol catalytic dehydration to aromatic process were investigated. N H3-TPD and Py-IR tests reveal that introducing P and Zn can significantly decrease the acidic strength and increase the Lewis/Brönsted acid ratio of HZSM-5, which is beneficial for the aromatization of methanol rather than the hydrogen transfer reaction. Meanwhile, P doping also enlarges the pore size of HZSM-5, enhancing the coke resistance and the formation of xylene and C 9+ aromatics. Compared to the ones modified by Z nSO4 and Zn(NO3)2, HZSM-5 modified by Z n3(PO4)2 exhibits higher aromatics selectivity and lower paraffin generation, with better durability in long term operation. Furthermore, excessive Zn and P loading will result in negative impact on aromatics selectivity, and the optimal loading of ZnO and P 2O5 are about 1% and 2%, respectively; higher reaction temperature and lower Si/Al lead to higher aromatics selectivity. Graphic Abstract
Keywords Methanol to aromatics · Methanol conversion · HZSM-5 · Phosphorus modification · Zinc modification Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10562-020-03360-3) contains supplementary material, which is available to authorized users. * Wen‑De Xiao [email protected] 1
School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, 800 Dong‑Chuan Road, Shanghai 200240, China
1 Introduction Nowadays, methanol has become a new feedstock for hydrocarbon production to alleviate the dependence on petroleum resources, since it can be produced from coal, natural gas and biomass through synthesis gas (CO + H2) [1]. By employing different zeolite catalysts, several methanol-to-hydrocarbon
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(MTH) processes have been proposed, such as methanol-toolefins (MTO), methanol-to-propylene (MTP), methanol-togasoline (MTG) and methanol-to-aromatics (MTA), among which MTO and MTP have been successfully commercialized with a capacity of million tons of methanol consumed per year [2–5]. The target products of MTA process are light aromatics such as benzene, toluene, and xylene (BTX), which is an effective aromatics synthesis route due to the high mass yield (~ 90%) [6]. HZSM-5 s modified by metal oxides are the dominant catalysts used in MTA due to their good catalytic activity resulting from the cooperative effect of its zeotype and acidity [7]. Over acid sites, methanol is firstly dehydrated and converted into olefins via repeated methylation and cracking of olefins or aromatics as the hydrocarbon pool dual-cycle mechanism [8, 9]. These olefins are converted into aromatics
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