Methanol Conversion on SAPO-34 Catalysts Synthesized by Tri-templates
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Methanol Conversion on SAPO-34 Catalysts Synthesized by Tri-templates Liping Ye1, a, Fahai Cao1, b, Weiyong Ying1, c, *, Dingye Fang1, d, Qiwen Sun2, e 1 Engineering Research Center of Large Scale Reactor Engineering and Technology, Ministry of Education; State Key Laboratory of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, China 2 State Key Laboratory of Coal Liquefaction and Coal Chemical Technology, Shanghai 201203, China a [email protected], [email protected], [email protected], [email protected], e [email protected] Keywords: template; SAPO-34; DEA; TEAOH; TEA; MTO Abstract. The effect of different combinations of a new tri-templating agent TEAOH/DEA/TEA, namely tetraethyl ammonium hydroxide (TEAOH)/diethylamine (DEA)/triethylamine (TEA), on the catalytic performance of SAPO-34 was investigated in MTO conversion. It was found that SAPO-34 and SAPO-5 are competing phases at TEA concentrations higher than 40 %. Pure SAPO-34 with high crystallinity, large BET surface area and small crystal size (0.8~1.4μm) was obtained at a low TEA concentrations. The combination of TEAOH/DEA/TEA strongly governed the acidity of crystals. TEAOH:DEA:TEA=0.67:0.67:0.67 gave an economical catalyst active in MTO reaction with 100 % methanol conversion, 89.39 % ethylene and propylene selectivity, a longest lifetime and a high coke capability of 24.2 wt %. 1. INTRODUCTION The introduction of silicon atoms in AlPO frameworks (SAPO) leads to the appearance of Brönsted acidity relevant for acid catalyzed reactions such as methanol-to-olefins (MTO), n-alkane cracking and hydrocracking, oxidative dehydrogenation of alkanes and so on. An increased public attention has been focused on MTO process on account of the high crude oil price and the public awareness of the need for obtaining fuels from alternative sources (such as coal, nature gas and biomass) [1]. SAPO-34, with excellent performance in MTO conversion [2], is one of the candidates for commercial applications. The principle of the generation of protonic acidity of SAPOs, as known to all, may be explained by the introduction of Si in a theoretical framework of AlPO4. In fact, three potential mechanisms of Si substitution were proposed [3]. Si may replace Al (SM1), P (SM2), or Al-P pairs (SM3). As the formation of Si-O-P bonds is unlikely, such bonds formed in SM2 and 3 have to be modified by the replacement of P by Si. This gives rise to isolated silicon Si(4Al) and siliceous islands Si(nAl, 4-nSi, 0
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