超强碱催化剂载体结构对丙烯二聚生成4-甲基-1-戊烯反应性能影响的研究

Influence of support structure of superbase catalyst on dimerization of propylene to 4-methyl-1-pentene

负载碱金属K固体超强碱为催化丙烯二聚生成4-甲基-1-戊烯(4MP1)过程的催化剂,该反应过程中催化剂载体发挥着不可忽视的作用,本工作系统地研究了4MP1生成过程中催化剂载体的作用及不同载体性能的影响规律。采用压汞仪、扫描电子显微镜(SEM)等手段对载体物质的比表面积、孔径分布等孔道结构进行表征。结果表明,当二聚反应的目标产物是4MP1时,以K_(2)CO_(3)为载体负载碱金属K所制备的催化剂具有较好的4MP1选择性,达87.38%;各载体表现出的催化性能差异主要是因为不同载体的孔道结构会产生内扩散阻力,影响丙烯二聚反应的产物分布;针对丙烯二聚反应路径及4MP1异构化反应,丙烯二聚高选择性生成4MP1应首选具有低比表面积、较大孔径、孔径分布窄的物质作为载体。

The catalyst support is an important part of the load-type catalyst.As an active substance with good dispersibility in the skeleton,it can not only increase the strength of the catalyst but also serve as an active center.In addition,the pore structure and specific surface area of the support also have a great influence on the catalytic performance of the catalyst.Therefore,it is necessary to study the structure of the catalyst support.In the catalytic dimerization of propylene to produce 4-methyl-1-pentene(4MP1),4MP1 is a thermodynamically unstable product,which is extremely easy to be converted into other thermodynamically more stable byproducts.Moreover,the distribution of propylene dimerization products is complex,and the equilibrium conversion rate of each reaction is close to 100%,with a high degree of spontaneity.Therefore,in order to improve the selectivity of 4MP1,a suitable catalyst system should be selected.Solid base catalyst has been widely used in the dipolymerization of propylene to 4MP1 because of its high selectivity and ability to inhibit isomerization.Alkali metal K was supported by alkali metal carbonate,alkali metal bicarbonate,alkaline earth metal carbonate,and alumina of different crystalline forms to prepare solid superbase catalysts for propylene dimerization to 4MP1.The role of catalyst support in the process of 4MP1 formation and the influence of different support properties were systematically summarized.The specific surface area and pore diameter distribution of the carrier material were characterized by a mercury injection meter and scanning electron microscope(SEM).The results showed that the internal diffusion resistance was caused by the pore structure of different carriers,which affected the product distribution of the propylene dimerization reaction.When the target product of the dimerization reaction was 4MP1,the catalyst prepared by using K_(2)CO_(3) as the support to support alkali metal K had a good 4MP1 selectivity,up to 87.38%.For the propylene dimerization reaction path and 4MP1 isomerization reaction,the material with low specific surface area,large pore diameter,and narrow pore diameter distribution should be preferred as the carrier for the high selectivity of propylene dimerization 4MP1.