分级晶化合成SAPO-34分子筛及其催化性能的研究

为调控SAPO-34分子筛的粒径,提高其甲醇制低碳烯烃(MTO)的催化性能,采用分级晶化方式将晶化过程分为四级,依次合成并分离出各级SAPO-34分子筛产品。测定各级产品的平均粒度,并进行XRD,SEM,NMR表征以及MTO催化性能评价,结果表明:相比于相同条件下传统方法制备的SAPO-34分子筛,分级晶化产品的总收率较高,平均粒径较小,MTO反应单程寿命较长,乙烯选择性略高;随分级晶化的进行,SAPO-34分子筛的平均粒径逐渐减小,硅取代磷和铝的SMⅢ机理发生的比例逐渐增大,体系中依次出现了Si(1Si,3Al)和Si(2Si,2Al)结构,粒径较小的三级产品与粒径较大的二级产品在甲醇转化率大于99%时单程寿命和双烯收率均相当。

SYNTHESIS OF SAPO-34 MOLECULAR SIEVE BY INTERMITTENT CRYSTALLIZATION AND ITS EFFECT ON CATALYTIC PERFORMANCE

In order to control the particle size of SAPO-34 molecular sieve and improve its catalytic performance for conversion of methanol to light olefins (MTO), the crystallization process was divided into four sections in sequence and four SAPO-34 molecular sieve samples were obtained. The samples were characterized by XRD, SEM, NMR, particle size analysis and catalytic performance evaluation. The results showed that compared with the one stage continuous process, the total yield of the samples by the intermittent crystallization is higher, the average particle size is smaller, the life time in MTO reaction is longer, and the yield of ethylene is higher than that of the conversional continuous crystallization. The particle size of the samples decreases and the proportion of SM III mechanism where the silicon atom replaces phosphorus and aluminum atoms increases as the intermittent crystallization continues and the structure of Si (1Si, 3Al) and Si (2Si, 2Al) is observed in second and third stages, respectively. The lifetime and the olefin yields (ethylene and propylene) of the samples with smaller particle size from the third stage and the samples with larger particle size from the second stage are the same.