Effect of Si/Al ratio of SAPO-34 on reactivity and coke composition in methanol to olefins reaction

doi:10.11949/j.issn.0438-1157.20150842

Abstract

Abstract:

In order to investigate the effect of Si/Al ratio of SAPO-34 on the reactivity and coke composition in the methanol to olefins reaction, a series SAPO-34 samples with different Si/Al ratio were prepared with controlling the composition of the synthesis gel. The total acidity, acid strength and the distribution of acid sites of these samples were characterized. The results showed that the amount of close acid sites increased with increasing Si/Al ratio of SAPO-34. The influences of the Si/Al ratio of SAPO-34 on the performances in the reaction of methanol to olefins were investigated. The result showed close acid sites were the main active sites for hydrogen transfer and oligomerizations which increased the selectivity of by-product propane and coke, as a result the life time and the selectivity of olefins decreased. The dissolved coke were analyzed using in-situ thermogravity combined with mass spectrometry and gas chromatography mass spectrometry,the results showed that the close acid sites accelerated the generation of anthracene, phenanthrene, naphthalene, and other polycyclic aromatic products in the cage of SAPO-34, which led the blockage of the product diffusion channel and rapid deactivation of SAPO-34.

Key words: methanol to olefins, molecule sieve, catalysis, activity, close acid, deactivation

摘要：

为了研究硅铝比对甲醇制烯烃反应性能及积炭组成的影响,控制合成中的原料配比制备了一系列不同硅铝比的SAPO-34分子筛。对合成的SAPO-34分子筛上的总酸量、酸强度和酸中心的分布进行了表征,发现成对的酸性位点随硅铝比的增大而增加。在固定床反应器中,系统地研究了SAPO-34分子筛的硅铝比对MTO反应性能的影响。由于成对的酸性中心是氢转移、低聚和成环的主要活性中心,能够增加副产物丙烷选择性及焦炭的生成速率,降低SAPO-34催化剂的烯烃选择性和催化剂的寿命。反应失活分析表明,在350℃、常压、空速为10 h^-1的条件下,催化剂可用一级反应失活方程描述,失活与硅铝比的3次方呈正比。采用原位热重质谱分析结合溶炭色谱质谱联用分析,发现硅铝比较高的SAPO-34分子筛笼内萘及其同系物乃至蒽、菲等稠环芳烃产物的生成速度较快,堵塞产物扩散的通道,导致催化剂的快速失活。

关键词: 甲醇制烯烃, 分子筛, 催化, 活性, 成对酸中心, 失活

CLC Number:

TQ028.8

CUI Yu, WANG Yao, WEI Fei. Effect of Si/Al ratio of SAPO-34 on reactivity and coke composition in methanol to olefins reaction[J]. CIESC Journal, 2015, 66(8): 2982-2989.

崔宇, 王垚, 魏飞. SAPO-34分子筛硅铝比对甲醇制烯烃反应性能及积炭组成的影响[J]. 化工学报, 2015, 66(8): 2982-2989.

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