【作者】 张小兵；

【导师】 谢克昌； 李忠；

【作者基本信息】 太原理工大学 ， 化学工程与技术， 2010， 博士

【摘要】 气-液-固三相浆态床合成甲醇工艺具有传热效率好、可采用富CO合成气、单程转化率高、尾气不循环或少循环、在线更换催化剂以及操作负荷弹性大等特点,适合大规模生产甲醇,并且特别适宜用于以煤气化为基础的多联产系统中的化工产品联产。但是目前该工艺所采用的催化剂基本为经破碎加工而成的工业用固定床合成甲醇CuO/ZnO/Al₂O₃催化剂,稳定性较差,失活速率快,未能工业化应用。在前人研究的基础上,本论文系统地对共沉淀法制备浆态床用CuO/ZnO/Al₂O₃催化剂的工艺条件进行了研究,首次采用了喷雾干燥成型工艺,获得了高稳定性和高活性的粉状催化剂,并且对催化剂及其前驱物的结构进行了深入表征和分析,阐明了催化剂结构与性能的关系。获得的主要结论如下:1、沉淀与老化过程是影响CuO/ZnO/Al₂O₃催化剂前驱体物相组成及结晶程度并进而影响催化剂微观结构的主要因素。在本论文考察的条件范围内,催化剂前驱体的物相主要以孔雀石（Cu₂（CO₃）（OH）₂）和类孔雀石（（Cu, Zn）₂（CO₃）（OH）₂）为主。随着沉淀与老化温度的升高或老化时间的延长,前驱体中各物相的结晶度逐渐增加。在70℃沉淀并80℃老化1.0 hr条件下所制备的催化剂前驱体具有适当的结晶程度,于350℃下焙烧4.0 hr所得催化剂中CuO微晶的平均粒径较小（4.50 nm）,催化剂的比表面积（BET,98.6 m²/gcat）和孔径分布在58 200 A范围内的比例（53.8 %）均最大。在240℃、4.0 MPa、H2/ CO /CO₂ = 92/36/7和空速为810 ml/gcat·h条件下,甲醇的时空收率和催化剂的失活率分别达到了153.3 g/kgcat·h和1.44 %/d。2、焙烧过程对CuO/ZnO/Al₂O₃催化剂的微观结构也有较大影响。随着焙烧温度的升高或者焙烧时间的延长,催化剂中CuO微晶的平均粒径逐渐增加,催化剂的比表面积以及孔径分布在58 200 A范围内的比例呈先增大后减小的趋势。70℃沉淀并80℃老化1.0 hr后制备的前驱体经350℃焙烧2.0 hr后所得催化剂中CuO微晶的平均粒径较小（3.41 nm）,催化剂的比表面积（BET,122.2 m²/gcat）和孔径分布在58 200 A范围内的比例（67.6 %）均最大。在240℃、4.0 MPa、H₂/ CO /CO₂ = 92/36/7和空速为810 ml/gcat·h条件下,甲醇的时空收率和催化剂的失活率分别达到了172.2 g/kgcat·h和0.43 %/d。3、喷雾干燥有利于催化剂稳定性的进一步提高。在其它条件均相同的情况下,225℃喷雾干燥所制备催化剂中CuO微晶的平均粒径最小（3.47 nm）,催化剂的比表面积（BET,114.5 m²/gcat）和孔径分布在58 200 A范围内的比例（68.1 %）均最大。在240℃、4.0 MPa、H2/ CO /CO₂ = 92/36/7和空速为810 ml/gcat·h条件下,甲醇的时空收率和催化剂的失活率分别达到了166.7 g/kgcat·h和0.16 %/d。与常规干燥下制备催化剂的时空收率（172.2 g/kgcat·h）与失活率（0.43 %/d）相比,活性基本相当,稳定性大幅提高,而且失活率已低于文献报道的最低值0.18%/d。4、外观形貌是导致喷雾干燥成型所制备的催化剂稳定性较好的最主要原因。在225℃进行喷雾干燥所制备的催化剂与常规干燥制备的催化剂相比,二者在CuO微晶的平均粒径、比表面积和孔径分布在58 200 A范围内的比例等微观结构特征上基本保持了一致,不同的是喷雾干燥成型所制备催化剂的外观形貌呈现了均匀细小的、平均粒径为71μm的球形颗粒状,而常规干燥所制备的催化剂的外观形貌则呈现了平均粒径为118μm的无规则颗粒状。5、XPS表征表明,催化剂中Cu元素的电子结合能向低位移越大,受周围元素的影响越强,催化剂的活性与稳定性越好;与之相反,Zn和Al元素的电子结合能向低位移越小,受周围元素的影响越弱,催化剂的活性与稳定性越好。6、CuO/ZnO/Al₂O₃催化剂在催化合成气合成甲醇反应前,CuO被还原为Cu0;反应后催化剂的Cu0微晶的平均粒径越小,越分散,其催化活性与稳定性越好。更多还原

【Abstract】 The liquid-phase methanol synthesis process has many advantages such as high reaction heat transfer rates, suitable for CO-rich syngas, high conversion per pass, no or less circulation of tail gas, replacement of catalyst on-line, flexible on operational load, etc., is suitable for large-scale production of methanol and especially for being involved in the coal-based integrated gasification combined cycle. But the catalyst used was mostly the crashed commercial CuO/ZnO/Al₂O₃ catalyst for fixed-bed methanol synthesis process, and has not been commercially popularized until now because of its poor stability. On the researches of the predecessors, the co-precipitation process of the CuO/ZnO/Al₂O₃ catalyst for liquid-phase methanol synthesis was systematically studied in this dissertation. Spray-drying process was introduced in co-precipitation process for the first time and powdery CuO/ZnO/Al₂O₃ catalyst with both of high stability and activity was obtained. The structures of the catalyst and its precursor were characterized and analyzed, and relations between structure and performance of the catalyst were discussed. The main results were as follows:1. The precipitation and aging procedures were the main influencing factors of the phase composition and crystalinity of the precursor and the micro structure of the CuO/ZnO/Al₂O₃ catalyst. Along with the temperature increment of precipitation and aging and the time extending of aging, the crystalinity of phases in the precursors enhanced gradually. The precursor was mainly composed of malachite （Cu₂（CO₃）（OH）₂） and zinc malachite （（Cu, Zn）₂（CO₃）（OH）₂） under the conditions investigated in this dissertation. The precursor obtained under the conditions of precipitating at 70℃and aging at 80℃for 1.0 hr had proper crystalinity, and the mean diameter of CuO crystallite （4.50 nm） in the resulted CuO/ZnO/Al₂O₃ catalyst was smaller, both of its BET surface （98.6 m²/gcat） and proportion of pore diameter （53.8 %） between 58 and 200 ? were the largest among the catalysts prepared in the investigation of precicitation and aging precedure. The space time yield and deactivation rate of the catalyst had reached up to 153.3 g/kgcat·h and 1.44 %/d respectively under the reaction conditions of 240℃、4.0 MPa、H₂/ CO /CO₂ = 92/36/7 and space velocity 810 ml/gcat·h.2. The calcination procedure will influence the micro structure of the CuO/ZnO/Al₂O₃ catalyst as well. Along with the temperature increment and time extending of calcination, The mean diameter of CuO crystallite increased gradually, and both of the BET surface and proportion of pore diameter between 58 and 200 ? increased at first and then decreased. Under the conditions of precipitating at 70℃, aging at 80℃for 1.0 hr and calcining at 350℃for 2.0 hrs, the mean diameter of CuO crystallite （3.41 nm） in the catalyst was smaller, both of the BET surface （122.2 m²/gcat） and proportion of pore diameter （67.6 %） between 58 and 200 A of the catalyst were the largest among the catalysts prepared in the investigation of calcination precedure. The space time yield and deactivation rate of the catalyst had reached up to 172.2 g/kgcat·h and 0.43 %/d respectively under the reaction conditions of 240℃、4.0 MPa、H2/ CO /CO₂ = 92/36/7 and space velocity 810 ml/gcat·h.3. The spray drying procedure was beneficial for the stability of the CuO/ZnO/Al₂O₃ catalyst. Under the conditions of spray drying at 225℃and the other preparation conditions same as conventional drying, the mean diameter of CuO crystallite （3.47 nm） in the catalyst was the smallest, both of the BET surface （114.5 m2/gcat） and proportion of pore diameter （68.1 %） between 58 and 200 A of the catalyst were the largest among the catalysts prepared in the investigation of spray drying precedure. The space time yield and deactivation rate of the catalyst had reached up to 166.7 g/kgcat·h and 0.16 %/d respectively under the reaction conditions of 240℃、4.0 MPa、H₂/ CO /CO₂ = 92/36/7 and space velocity 810 ml/gcat·h. Comparing with the catalyst obtained with conventional drying procedure, the space time yield of the two catalysts are equivalent, but the stablility of the catalyst that spray-dried is much better, and the deactivating rate of the catalyst is lower than the lowest value （0.18 %/d） reported in the published literatures.4. The reason for the catalyst spray dried with better stability was that its morphology was different from the catalysts conventionally dried. Comparing the catalyst spray dried at 225℃with the catalyst conventionally dried, their micro structures such as mean diameter of CuO crystallite, BET surface and proportion of pore diameter between 58 and 200 A were equalent with each other, but the morphology of the two catalysts were different. The catalyst spray dried was homogeneous sphere with mean diameter 71μm and the catalyst conventionally dried was irregular shape with mean diameter 121μm.5. The XPS measurement shows that the stability and activity of the catalyst will be better when the binding energy of Cu element shifts more to lower value, and the binding energy of Zn and Al element shift less to lower value.6. In the atmosphere of syngas for methanol synhesis, the state of the Cu element in the Cu/ZnO/Al₂O₃ catalyst prepared in this study was metal copper, and the activity and stability of the catalyst will be better when the mean diameter of the metal copper crystallite within the used catalyst was smaller.更多还原