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晶种法合成SAPO-34分子筛研究
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摘要
SAPO-34分子筛是MTO反应最理想的催化剂,但是通常合成SAPO-34的水热法存在诸多问题(合成时间长、模板剂用量大、能耗高等)~[1,2]。本实验通过向晶化液中加入晶种的方法来解决以上问题。研究结果表明:在低模板剂用量下(TEA/Al_2O_3=2.0),若未加晶种,合成产物是SAPO-34和SAPO-5的混合物,但是加入27.7%(以晶化液中SiO_2重量计)自制晶种后,SAPO-5分子筛杂晶消失,SAPO-34分子筛的结晶度明显提高。SEM图表明晶种法合成的产物形貌为立方体,平均晶粒粒度1-2μm,但粒度分布都不均匀。通过对比,发现焙烧后的晶种更有利于合成粒度较小的分子筛,降低SAPO-34分子筛的弱酸量和强酸量。在MTO反应中,采用焙烧的晶种合成的SAPO-34分子筛催化寿命最长,低碳烯烃选择性高达94.3%。
SAPO-34 is the best zeolite for methanol-to-olefins(MTO) reaction,but the preparation is limited with long crystallization time,large amount of template and high energy consumption,etc~([1,2]).In this research,these problems were solved by the addition of seeds.The experiments showed that if the amount of template was reduced(TEA/Al_2O_3=2.0) and the preparation was absence of seeds,the product would be a mixture of SAPO-34 and SAPO-5,but high-crystallinity SAPO-34 molecular sieves could be prepared under the condition of seed/SiO_2=0.277.The SEM image shows that the morphology of SAPO-34 is cube with the uneven partical size of about 1-2μm,and calcined seed is beneficial to prepare small crystal SAPO-34 molecular sieves with less acid amount,the product showed the longest lifetime and exceptional selectivity to light olefins of 94.3%in MTO reaction.
引文
[1]Yang,G J;Wei,Y X;Xu,S T;Chen,J R.J.Phys.Chemis C.2013,117:8214.
    [2]H Imai;N Hayashida;T Yokoi;T Tatsumi.Micropor.Mesopor,Mater.2014,196:341

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