ZSM-35分子筛酸性对正丁烯异构化反应性能的影响

ACID CHARACTERIZATION OF ZSM-35 ZEOLITES AND EFFECT ON n-BUTENE ISOMERIZATION

为了详尽定性和定量分析ZSM-35分子筛孔道内部和外部的酸中心,对在不同焙烧晶化条件下制备的3种ZSM-35分子筛样品(编号分别为GNJ,GNX,GW)采用NH3-TPD和吸附不同探针分子的31P MAS NMR谱进行表征,并在微反装置上对3种样品进行催化正丁烯异构化反应性能评价。结果表明:ZSM-35分子筛中Brnsted酸酸量远多于Lewis酸酸量,且不同制备方法得到的ZSM-35分子筛Brnsted酸强度与酸量不同;GNJ主要有1种弱Brnsted酸中心,GW有3种不同强度的Brnsted酸中心,较弱的Brnsted酸中心在孔道内部和外部均有分布,较强的两种Brnsted酸中心主要分布在孔道内部;GNX有两种不同强度的Brnsted酸中心,在孔道内部和外部均有分布,且GNX的Brnsted酸酸量高于GNJ和GW;催化正丁烯异构化反应时,ZSM-35分子筛的中强Brnsted酸中心是异丁烯生成的必要酸中心,且中强Brnsted酸中心更有利于异丁烯的生成,因此制备具有合适的中强Brnsted酸强度和酸分布的ZSM-35分子筛有利于正丁烯异构化反应的进行。

In order to determine qualitatively and quantitatively the internal and external acid sites of the ZSM-35 zeolites,three types of ZSM-35 samples(GNJ,GNX,GW)prepared under different crystallization and calcination conditions were characterized using NH3-TPD and 31P MAS NMR of adsorbing different probe molecules.Simultaneously the selectivity and activity of the isomerization of n-butene on different catalysts were analyzed.The results showed that the amount of Brnsted acid site in ZSM-35 zeolites were much more than Lewis acid site,the acid strength and amount on ZSM-35 zeolites were different according to preparation methods.GNJ had a kind of weak Brnsted acid,GW had three kinds of Brnsted acid sites of different strengths,the weaker Brnsted acid sites were distributed inside and outside the channel and the stronger two kinds of Brnsted acid sites were mainly distributed inside the channel.GNX had two kinds of Brnsted acid sites of different strengths,which were distributed inside and outside the channel.Brnsted acid amount of GNX was more than the other two samples.When catalyzing the isomerization of n-butene,it was found that the medium strong Brnsted acid site was an essential acidic site for isobutene formation and it was more conducive to the formation of isobutylene.Therefore,the preparation of ZSM-35 molecular sieve with appropriate suitable medium-strong Brnsted acid strength and acid distribution was beneficial to the progress of the n-butene isomerization reaction.