分子筛对甲醇制轻烯烃反应烃类产物选择性的影响

采用XRD、SEM、XRF、BET、NH₃-TPD等方法表征USY、Beta、ZSM-5、ZSM-22、SAPO-41和SAPO-34分子筛的物相、组成、结构和酸性，并采用脉冲微反技术考察这些分子筛催化甲醇转化反应活性及烃类产物选择性随反应温度的变化。结果表明，三维十二元环的USY和Beta分子筛的甲醇转化催化活性最高，其次为二维十元环的ZSM-5分子筛，一维十元环的ZSM-22分子筛最低。分子筛的孔结构与孔径尺寸具有择形效应，与反应温度共同影响高选择性烃类产物的碳链长度。大孔分子筛在反应温度450℃以下时的C₄ 烃选择性最高；在反应温度400℃以上时，中孔ZSM-5、ZSM-22和SAPO-41分子筛的C₃烃选择性最佳，小孔SAPO-34分子筛的C₃烃和C₂烃选择性最高。随着反应温度升高，高选择性烃产物的碳数降低。ZSM-5和SAPO-34分子筛是特别适合于甲醇制丙烯和乙烯的择形催化剂，这2种分子筛在催化选择性方面还具有优异的升温特性，在400~550℃范围，随着反应温度升高，产物中乙烯和丙烯的总选择性提高，副产物中丙烷、C₄、C₅和C₆₊烃的选择性降低，甲烷选择性略有增加。

Effect of Molecular Sieves on Hydrocarbon Selectivity in Methanol to Olefin Reaction

Molecular sieves, such as USY, Beta, ZSM-5, ZSM-22, SAPO-41 and SAPO-34, were characterized by means of XRD, SEM, XRF, BET and NH₃-TPD to analyze physico-chemical properties such as phase, composition, pore structure and acidity parameters. The catalytic performances of these molecular sieves in methanol to olefin (MTO) reaction, such as catalytic activity, hydrocarbon selectivity, were evaluated with micro-pulse feed reactor experimental technology. The results showed that catalytic activity of USY, Beta molecular sieves with three-dimensional 12-ring opening were higher than those of ZSM-5 with two-dimensional 10-ring opening and ZSM-22 with one-dimensional 10-ring opening in MTO reaction. Pore structure and pore size of molecular sieves determined hydrocarbon selectivity in methanol conversion product due to shape-selective effects, for example, majority of hydrocarbon product was C₄ with USY and Beta molecular sieves of 12-ring opening as catalyst at reaction temperature below 450℃, while above 400℃, that was C₃ with ZSM-5, ZSM-22 and SAPO-41 of 10-ring opening, and C₃, C₂ with SAPO-34 of 8-ring opening as catalyst. Meanwhile, carbon number of majority of hydrocarbon product decreased with the reaction temperature rising. The suitable shape-selective catalysts for MTP (methanol-to-propylene) is ZSM-5, and for MTO is SAPO-34, and both of them have desirable rising-temperature characteristics. The total selectivity of ethylene and propylene increased with reaction temperature rising in the range of 450-550℃, side-product selectivity of propane, C₄, C₅ and C₆₊ hydrocarbons decreased sharply, and of methane increased slightly.