不同焙烧工艺下FER结构HZSM-35分子筛催化剂的正丁烯异构化反应

Isomerization of n-butene on HZSM-35 zeolite catalyst with FER structure under different calcination processes

采用水热合成法制备合适硅铝比的FER结构HZSM-35分子筛,并在晶化过程中加入模板剂(CHA)、结构导向剂(SDA),考察了一步法、两步法焙烧工艺对纯晶相FER结构HZSM-35分子筛结构及性能的影响,并评价了在反应压力0.5 MPa、反应温度330℃、质量空速4~6 h^(-1)条件下,2种焙烧工艺所制得FER结构HZSM-35分子筛催化剂在醚后碳四原料的正丁烯异构化反应中的催化活性及稳定性。结果表明:不同焙烧工艺对FER结构HZSM-35分子筛的酸性质和孔结构、以及相应催化剂的活性和稳定性的影响较大;采用两步法焙烧工艺制得含SDA的FER结构HZSM-35分子筛的孔体积、比表面积及总酸量的增量均大于一步法制得的,使其孔径结构更有利于正丁烯骨架异构化;加入SDA制得的FER结构HZSM-35分子筛的结晶度达到98%,远高于无SDA参与制得的83%,而且两步法焙烧工艺所得含SDA分子筛的结晶度较焙烧前基本无变化;当异丁烯选择性达到90%时,在一步法焙烧工艺制得含SDA的FER结构HZSM-35分子筛催化剂作用下的反应需200 h,而在相应两步法焙烧制得催化剂作用下的反应只需20 h,即后者大大缩短了正丁烯异构化反应的有效起活时间。

HZSM-35 zeolite with FER structure was synthesized by the hydrothermal method,and the template agent(CHA)and structure guide agent(SDA)were added during the crystallization process,then the effects of one-step and two-step calcination processes on the structure and properties of HZSM-35 zeolite with pure crystalline FER structure were investigated.Under the conditions of reaction pressure at 0.5 MPa,reaction temperature at 330℃,and mass space velocity at 4-6 h^(-1),the catalytic activity and stability of the FER structure HZSM-35 zeolite catalysts prepared by such above two kinds of calcination processes were evaluated for n-butene isomerization in C4 post-ether feedstock.The results showed that different calcination processes had great effects on the acidity,pore structure,activity and stability of HZSM-35 zeolite with FER structure.The increments of pore volume,specific surface area and total acid content of FER structure HZSM-35 zeolite containing SDA prepared by two-step calcination process were greater than that prepared by one-step calcination process,which made their pore size structure more favorable to isomerize n-butene skeleton.The crystallinity of FER structure HZSM-35 zeolite prepared with SDA was 98%,which was much higher than 83%of that without SDA,moreover,the crystallinity of zeolite containing SDA obtained by the two-step calcination process remained basically unchanged in comparison with that of before calcination.When the selectivity of iso-butene reached 90%,it would take 200 h for the reaction of FER structure HZSM-35 zeolite catalyst containing SDA prepared by one-step calcination process,however that reaction of the corresponding zeolite catalyst prepared by two-step calcination process just took 20 h,namely,the latter greatly shortened the effective activation time of n-butylene isomerization.