纳米晶堆积ZSM-5沸石的合成、改性及其催化烯烃转化性能

Synthesis,Modification and Catalytic Properties of Aggregated ZSM-5 Zeolite Nanocrystals for Olefin Conversion

在不添加介孔模板剂的情况下,通过水热合成法直接合成具有纳米晶堆积形貌的多级结构ZSM-5沸石。通过氨水水热处理、浸渍法引入镧和磷的组合改性方法调变纳米晶堆积HZSM-5沸石的酸性质,进而改善其催化1-己烯异构化和催化重汽油降烯烃的性能。结果表明:与HZSM-5沸石相比,采用0.4%质量分数氨水水热处理,负载3%质量分数La2O3和0.5%质量分数磷的方法组合改性HZSM-5后,可以降低沸石的弱酸、强酸和Bronsted酸(B酸)酸量以及B酸和Lewis酸(L酸)的酸量比值,提高中强酸酸量及其比例,体现出优异的烯烃异构化性能;用于1-己烯转化反应,产物中烯烃体积分数仅为1.8%,异构烷烃的质量收率高达44.8%,比工业催化剂高出17.8百分点;在催化重汽油降烯烃反应中,产物中异构烷烃和芳烃体积分数高于工业催化剂,且辛烷值损失更小。

Here,aggregated ZSM-5 zeolite nanocrystals were directly synthesized by the hydrothermal synthesis method without using any mesopore templates.The combination modification methods for the prepared ZSM-5 zeolite were developed via the introduction of hydrothermal treatment with ammonia solution and impregnation of La and P elements,in order to adjust the acidic properties of zeolite and then to improve the catalytic performance of the 1-hexene isomerization and olefin reduction of heavy FCC gasoline,respectively.After the modification of bulk HZSM-5 zeolite with hydrothermal treatment using 0.4%mass fraction ammonia solution and the impregnation of 3%mass fraction La2O3 and 0.5%mass fraction phosphorus,the amount of weak acid,strong acid,Bronsted acid(B acid)and the ratio of B acid amount to Lewis acid(L acid)amount decreased,and the amount and fraction of medium-strong acid in total acid increased.The modified ZSM-5 exhibits good catalytic performance in olefin isomerization.For the conversion of 1-hexene,the volume fraction of olefin in the product is only 1.8%,and the yield of iso-paraffin is as high as 44.8%,which is 17.8 percentages higher than that of the industrial catalyst.Moreover,the volume fractions of iso-alkane and aromatics of gasoline over the prepared catalyst are higher than those of industrial catalysts,and the loss of octane number is also smaller in the olefin reduction of heavy FCC gasoline.