SAPO-34分子筛的合成及甲醇制烯烃催化性能

Synthesis and MTO Catalytic Performance of SAPO-34

以三乙胺为模板剂,系统研究了合成凝胶中硅、磷酸及水含量对SAPO-34分子筛晶化及甲醇制烯烃(MTO)催化性能的影响.结果表明,Si对SAPO-34的形成具有结构导向作用,只有当n(SiO2)∶n(Al2O3)≥0.25时才可以得到纯相SAPO-34分子筛.随着凝胶中Si含量增大,合成样品中出现氧化铝物种,使结晶度及比表面积逐渐下降,催化稳定性降低.凝胶n(P2O5)∶n(Al2O3)和n(H2O)∶n(Al2O3)对SAPO-34的合成和催化性能也有很大影响.当n(P2O5)∶n(Al2O3)=1.1∶1,n(H2O)∶n(Al2O3)=36∶1时,合成样品具有较高的比表面积及较为理想的(P+Si)/Al摩尔比和适宜的酸性,单程寿命达到520 min.在此基础上研究了焙烧条件对SAPO-34分子筛催化性能的影响,结果表明,SAPO-34在流动的空气气氛中焙烧8 h得到的样品比焙烧10 h的样品残留了更多的模板剂,且部分残留的模板剂以二烯烃的形式存在,催化寿命明显比焙烧10 h的样品长,达到580 min.

Effects of n（SiO2）∶n（Al2O3）,n（P2O5）∶n（Al2O3） and n（H2O）∶n（Al2O3） in the synthesis gel on the crystallization of SAPO-34 were systematically studied with triethylamine as a templating molecule for the purpose of improving its catalytic performance in methanol to olefin（MTO） reaction.Pure SAPO-34 phase can only be synthesized with the synthesis gel having a n（SiO2）∶n（Al2O3） larger than 0.25,demonstrating the structure-directing role of Si.Nevertheless,a further increase in the Si content in the synthesis gel led to not only the formation of Al2O3 but also the decrease in the crystallinity,surface area and catalytic stability of SAPO-34.The n（P2O5）∶n（Al2O3） and n（H2O）∶n（Al2O3） in the synthesis gel also significantly influenced the crystallization and catalytic performance of SAPO-34.When n（P2O5）∶n（Al2O3） and n（H2O）∶n（Al2O3） were 1.1 and 36,respectively,the synthesized sample with a n（P＋Si）∶n（Al） close to 1 showed high surface area and appropriate acidity,resulting in a catalytic lifetime of 520 min without lowering olefin selectivity.The catalytic performance of SAPO-34 is also highly dependent on its calcination conditions.The sample calcined at 550 ℃ for 8 h in flowing air showed a much higher catalytic stability（its catalytic lifetime reached 580 min） than the sample calcined for 10 h under the same conditions as a result of different hydrocarbon residuals kept in SAPO-34 after calcination.