【作者】 丁春华；

【导师】 王祥生；

【作者基本信息】 大连理工大学 ， 工业催化， 2007， 博士

【摘要】 对二甲苯是基本有机化工原料，主要用于生产对苯二甲酸（PTA）和对苯二甲酸二甲酯（DMT）。甲苯（T）甲醇（M）烷基化合成高浓度对二甲苯是增产对二甲苯的一条新工艺路线。本论文从分子筛类型和载体的选择、成型、改性以及反应条件等方面探讨了影响催化剂活性、对位选择性和稳定性的因素，分析了催化剂孔结构和表面酸性对催化剂择形性和积炭的影响。考察了微米HZSM-5、纳米HZSM-5和HMCM-22分子筛的物化性能和催化甲苯甲醇烷基化性能。结果表明，与HZSM-5相比，HMCM-22的活性更高，但易导致甲苯的深度烷基化反应。经氧化物改性后，纳米HZSM-5的对位选择性更高。因此，纳米ZSM-5是制备甲苯甲醇选择烷基化催化剂的适宜母体。分别以Al₂O₃、SiO₂、Al₂O₃／RE₂O₃及SiO₂／RE₂O₃为载体，与纳米ZSM-5挤条成型，并采用浸渍法进行改性研究。结果表明，采用Al₂O₃／RE₂O₃复合载体时，催化剂成型简便，载体含量为10～15 wt％Al₂O₃和10 wt％RE₂O₃时，成型的纳米ZSM-5经3 wt％SiO₂、5～10wt％P₂O₅和3 wt％MgO改性后用于甲苯甲醇烷基化反应，其选择性和稳定性都较好。水热处理研究表明，水热处理后纳米HZSM-5分子筛催化剂的酸量下降，酸强度降低，骨架铝脱除，形成大量二次孔，孔口收缩。Al₂O₃／RE₂O₃复合载体可以抑制水热处理过程中酸中心的过度消除和深度脱铝。酸强度在+2．27≤H₀≤+4．8之间的酸对甲苯甲醇烷基化反应起主要作用，催化剂活性与总酸量之间没有对应关系。分子筛类型、晶粒大小及载体不同，经水热处理后催化剂的酸性变化、孔分布和催化性能差别很大。Al₂O₃／RE₂O₃复合载体成型纳米HZSM-5经700℃水热处理后表现出甲苯甲醇烷基化活性和选择性均提高的特点，与分子筛类型、晶粒大小和载体密切相关。考察了甲苯甲醇烷基化过程中添加水对改性ZSM-5催化剂积炭和催化性能的影响。在反应体系中添加适量的水可以提高甲苯转化率、对二甲苯选择性和催化剂的稳定性；随着H₂O／M摩尔比的提高，催化剂的积炭速率降低，积炭量下降，水在甲苯甲醇烷基化反应中能有效抑制积炭生成，延长催化剂的寿命。对Al₂O₃／RE₂O₃复合载体（占分子筛比例为15 wt％的Al₂O₃和10 wt％的RE₂O₃）成型的纳米ZSM-5催化剂，采用3 wt％SiO₂、5 wt％P₂O₅和3 wt％MgO复合改性后用于甲苯甲醇烷基化合成对二甲苯，在常压、460℃、T／M=2 mol／mol、2h^-1（WHSV，T+M）、H₂／（T+M）=8 mol／mol，H₂O／（T+M）=8 mol／mol的反应条件下，经500 h长运转，甲苯转化率在20～35％之间（平均值为30．70％），对二甲苯选择性在83～90％之间（平均值为85．92％）。该催化剂的再生性能和放大制备性能良好，具有一定工业应用前景。更多还原

【Abstract】 Para-Xylene is an important essential organic material for the petrochemical industry, and it is mainly used to produce terephthalic acid （PTA） and terephthalates （DMT）. Toluene （T） alkylation with methanol （M） to produce para-Xylene with high concentration is a new technologic route to increase para-Xylene. The influence factors on activity, para-selectivity and stability of catalysts are investigated from aspects such as the type of zeolites and binders, modification, reaction conditions and so on. The effect of pore structure and acid sites on the selectivity and coking of catalysts is analyzed in this work.The physicochemical property and the catalytic performance for toluene alkylation with methanol of microscale HZSM-5, nanoscale HZSM-5 and HMCM-22 are studied. The results indicate that HMCM-22 can result in further alkylation of toluene more easily comparing to HZSM-5 zeolites. The catalytic performance of modified MCM-22 and nanoscale ZSM-5 catalysts for toluene alkylation with methanol is compared. It is found that nanoscale ZSM-5 is easier to get high para-selectivity. Therefore, nanoscale ZSM-5 is a better parent zeolite for toluene alkylation with methanol.Nanoscale HZSM-5 is bounded with binders such as Al₂O₃, SiO₂, Al₂O₃/RE₂O₃ and SiO₂/RE₂O₃, respectively, and the modification of bounded nanoscale HZSM-5 catalysts is studied. The catalysts bounded with different binders all show good stability during alkylation of toluene with methanol. The nanoscale HZSM-5 catalysts bounded with Al₂O₃/RE₂O₃ as binder show better stability when the para-selective is high after modification with oxides. As the content of Al₂O₃ is higher, the coking of the catalyst is faster and the stability of the catalyst is lower. The nanoscale HZSM-5 catalysts which are bounded with 10-15 wt% Al₂O₃ and 10 wt% RE₂O₃ have better general properties. It can be concluded from the results of modification with oxides that the para-selectivity of nanoscale ZSM-5 can be improved with the decrease of acid strength and the ratio of Bronsted acid sites to Lewis acid sites. The catalysts impregnated with 3 wt% SiO₂, 5-10 wt% P₂O₅ and 3 wt% MgO show better catalytic properties for toluene alkylation with methanol.For the nanoscale ZSM-5 zeolite studied in this work, the total amount of acid sites decreases significantly and strong acid sites almost totally disappear with the hydrothermal treatment temperature higher than 500℃. High temperature hydrothermally dealuminated nanoscale ZSM-5 zeolite catalyst results in high catalytic activity for the alkylation of toluene with methanol and improves para-selectivity especially when the catalyst is treated at 700℃, but the catalytic activity is very low for alkylation of ethylbenzene with ethanol. It can be suggested that only a small part of the acid with acid strength +2.27≤H₀≤+4.8 seems to contribute to the alkylation of toluene with methanol. The crystal size, appropriate acid strength and right B/L acid site ratio of the steamed nanoscale ZSM-5 may be responsible for achieving the maximal values of both toluene conversion and para-xylene selectivity in toluene alkylation with methanol.The coking and catalytic properties of modified ZSM-5 zeolite catalysts by introducing water into the reactor as cofeed along with the toluene/methanol feed during the alkylation reaction are studied. When appropriate water is introduced during toluene alkylation with methanol, all the toluene conversion, para-xylene selectivity and stability are increased; coking is restrained and the age of catalyst is prolonged; the coking speed and coke quantity are decreased with increased H2O/M. But both the toluene conversion and para-xylene selectivity are lower than that in conditions without water introducing.For nanoscale ZSM-5 catalysts bounded with Al₂O₃/RE₂O₃ （15 wt% Al₂O₃ and 10 wt% RE₂O₃） as binder, after modification with 3 wt% SiO₂, 5 wt% P₂O₅ and 3 wt% MgO, the toluene conversion can be maintained between 20-35% （average is 30.70%） for 500 hours on-stream with para-xylene selectivity higher than 83% （average is 85.92%） during toluene alkylation with methanol at atmospheric pressure, 460℃, molar ratio of Toluene/Methanol=2, 2 h^-1 （WHSV of the mixture of toluene and methanol）, molar ratio of H₂/（Toluene and Methanol）=8 mol/mol and molar ratio of H₂O/（Toluene and Methanol）=8 mol/mol. The properties of the regeneration and magnified preparation of this catalyst are favorable. Therefore, it is showed potential in application in industry.更多还原