碱处理制备高硅多级孔ZSM-5催化MTP反应

High Silicon Hierarchical ZSM-5 Zeolite Prepared by Alkaline Treatment Catalyzed MTP Reaction

以水热法合成母体硼硅沸石(BS),然后使用氢氧化钠(NaOH)溶液单独处理以及氢氧化钠和十六烷基三甲基溴化铵(CTAB)混合溶液处理,并在碱溶液中加入铝源,制备一系列高硅多级孔ZSM-5分子筛样品(命名为BHZ-A和BHZ-AB系列样品)。采用XRD、SEM、ICP、Ar物理吸附、NH3-TPD和热重分析等手段表征样品的孔结构和酸性质等,并提出了CTAB的保护作用:在碱处理过程中,CTAB抑制NaOH的脱硅作用从而保护分子筛不被过度刻蚀。在压力0.1 MPa、温度743 K、水/醇摩尔比为1/1和甲醇质量空速为3 h^(-1)条件下,采用固定床反应器评价BHZ(含B的H型ZSM-5)分子筛样品催化甲醇制丙烯(MTP)反应72 h的性能。结果表明:通过碱处理制备得到的高硅多级孔ZSM-5分子筛的强酸量是影响其MTP反应性能和积炭的主要因素,由于BHZ-0.1A和BHZ-0.1AB样品具有丰富的介孔和合适的酸性,其MTP反应性能优异,丙烯选择性均约为50%,积炭量均约为1.5%。

The parent boron-silicon zeolite was synthesized by hydrothermal method,and then treated with NaOH solution alone or NaOH and hexadecyl trimethyl ammonium bromide(CTAB)mixed solution;moreover,a series of high silicon hierarchical ZSM-5 samples(BHZ-A and BHZ-AB series samples)were prepared by adding Al source in the alkaline solution.The pore structure and acid properties of the samples are characterized by XRD,SEM,ICP,Ar adsorption-desorption,NH 3-TPD and thermogravimetric analysis.The protective effect of CTAB is proposed as below:CTAB inhibits the desilication of NaOH to protect the zeolite from excessive etching during alkaline treatment.The performance of BHZ(H-type ZSM-5 containing B)molecular sieve sample in methanol to propylene(MTP)reaction for 72 hours was evaluated on a fixed bed reactor under pressure of 0.1 MPa,reaction temperature of 743 K,H_(2)O/CH_(3)OH molar ratio of 1/1,and methanol MHSV of 3 h^(-1).The results show that the strong acid content of the high silicon hierarchical ZSM-5 zeolite prepared by alkali treatment is the main factor affecting its performance in MTP reaction and coke deposition.Boasting of rich mesopores and suitable acidity,BHZ-0.1A and BHZ-0.1AB samples exhibit excellent performance in MTP reaction,with the propylene selectivity and carbon deposition of about 50%and 1.5%respectively.