Synthesis And Modification Of SAPO-34 Molecular Sieve Catalyst For Methanol-to-Olefin Reaction

The light olefins, especially ethylene and propylene, are indispensable basic raw materials for modern chemical industry. They are generally produced by the crude oil cracking process, which is greatly dependent on the petroleum resources. So people are searching for methods to replace the conventional oil route to get light olefins. One of these is the methanol-to-olefin process (MTO), because methanol can be obtained from multiple sources, such as coal, natural gas and biomass, and by using methanol as starting material, olefins can be produced without the involvement of oil. It is of great significance to develop the MTO process, especially for China which is abundant of coal and lack of oil. And China has made considerable progress in the research and industrialization of MTO technology.The key technology of MTO process is the research and development of catalyst, which is demanded to give high methanol conversion and high light olefin selectivity. Due to its weak acidity and small pore, the SAPO-34 molecular sieve is supposed to be one of the most excellent catalysts.In this dissertation, the MTO reaction conditions including reaction temperature, pressure, methanol concentration and liquid hourly space velocity (LHSV) were firstly investigated, and the optimal reaction condition was as the follows:50% aqueous methanol as feedstock,400℃,1.5 h-1 LHSV, and atmospheric pressure.SAPO-34 molecular sieve was synthesized by hydro thermal method and the synthetic conditions as well as the gel compositions are studied. Pure SAPO-34 crystals can be synthesized as the following conditions:crystallized at 80～200℃for 24 h-48 h under dynamic condition. The suitable gel composition was as follows:SiO2:Al2O3:P2O5: Morpholine:H2O=1.0:1.0:(0.8～1.2):(2.0～3.0):(30-90). The as synthesized SAPO-34 showed excellent catalytic activity in MTO reaction.The multiple template hydrothermal systems were studied by using triethylamine (TEA) and morpholine (MOR) as template in the synthesis of SAPO-34. Catalysts synthesized by bi-template showed higher catalytic activity than that synthesized by single template. With TEA/MOR=3:1, selectivity to ethylene reached 48%, and the overall selectivity of light olefins reached 87.9%.Metal modification of SAPO-34 was also studied. The effect of different metals was compared in large scope including Fe, Mn, La, Ce, Zn, Co and so on. It turned out that the Mn, Ce and La modified SAPO-34 exhibited high selectivity to light olefins. The influence of modification methods was also investigated. And as a result, the wet impregnation method presents better catalytic performance than incipient-wetness impregnation method and ion exchange method. Selectivity to ethylene of catalyst synthesized by wet impregnation method had increased 10% compared with unmodified catalyst. And catalyst modified by ion exchange method had shorter induction period in the MTO process.