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环己醇和环己酮(KA油)是制备尼龙所需材料己二酸和己内酰胺的重要中间体,也可用作油漆、农药和染料等的溶剂以及染色和褪光丝的均化剂等.工业上制取KA油的方法主要为苯酚加氢法、环己烯水合法和环己烷氧化法,其中环己烷氧化法最为普遍,是非常重要的工业过程.为获得适宜的KA油选择性,工业上普遍采用Co盐为催化剂,将环己烷氧化单程转化率控制在5.0%以下,从而使得产物选择性达到70%以上.该环己烷氧化制KA油过程不仅生产效率较低,而且所用均相催化剂因分离困难而不能重复使用.因此,当前关于环己烷氧化反应催化剂的研究均是围绕多相催化剂进行.氧气选择性氧化环己烷反应因具有更高的原子经济性而逐渐成为环己烷氧化法制KA油研究中最具挑战性的课题.该反应是自由基机理,而Co~(2+),Cr~(3+),Mn~(2+)和Ce~(2+)等金属离子可以促进自由基链反应,因此含有这些金属的多相催化剂被广泛用于该反应.另一方面,AlPO-n系列分子筛由于具有特殊的孔结构和一定的表面酸性,在催化反应中显示出较大的应用潜力.如果进行杂原子掺杂,通过改变分子筛骨架的电荷平衡,可以有效提高其表面酸性.例如磷酸硅铝分子筛(SAPO-5)具有中等强度的酸性和良好的择形性,因而作为固体酸催化剂广泛用于乙醇脱水、甲醇制烯烃、丙烯聚合和苯乙烯环氧化等反应,表现出较高的选择性和良好的稳定性.本文以传统均相Co盐催化剂的多相化为出发点,制备了Co掺杂SAPO-5与分子筛催化剂(Co-SAPO-5),考察了Co掺杂量对催化剂结构、表面性质以及氧气选择性氧化环己烷反应性能的影响.结果表明,一部分Co进入分子筛骨架,同时有少量Co以氧化钻形式高度分散在SAPO-5表面.Co掺杂对SAOP-5催化剂比表面积没有显著影响,但可使其孔体积减小.相反,Co掺杂可以提高SAOP-5分子筛表面B酸性位数量和总酸量.活性测试结果表明,环己烷转化率随着Co-SAPO-5催化剂中Co含量的增加而增加,但KA油选择性在转化率高于6.3%时急剧下降.还考察了反应温度、反应时间、初始氧气压力和催化剂用量对Co-SAPO-5分子筛催化剂性能的影响,得到了最优反应条件.以Co-SAPO-5-0.2(Co/Si摩尔比为0.2)分子筛为催化剂时,KA油总收率最高可达7.8%.另外,Co-SAPO-5催化剂在环己烷氧化反应中显示出很好的稳定性,Co-SAPO-5-0.2催化剂套用6次后活性几乎没有变化.
Cyclohexanol and cyclohexanone (KA oil) are important intermediates of adipic acid and caprolactam used in the preparation of nylon. They are also used as solvents for paints, pesticides and dyes, leveling agents for dyeing and fading filaments and the like. The KA oil is mainly prepared by the methods of phenol hydrogenation, cyclohexene hydration and cyclohexane oxidation, among which cyclohexane oxidation is the most common and is a very important industrial process. To get suitable KA oil selection Co, salt is widely used as a catalyst in industry and the conversion rate of cyclohexane oxidation is controlled below 5.0%, so that the selectivity of the product is over 70% .The oxidation of cyclohexane to KA oil not only has low production efficiency, And the homogeneous catalyst used can not be reused because of the difficulty of separation.Therefore, the current studies on cyclohexane oxidation catalysts are all carried out around heterogeneous catalysts.The oxygen selective oxidation of cyclohexane due to its higher atomic economy Has become the most challenging topic in the research of KA oil by cyclohexane oxidation.The reaction is a free radical mechanism, and the reaction of Co ~ (2 +), Cr ~ (3 +), Mn ~ (2+) and Ce ~ 2+) and other metal ions can promote free radical chain reaction, and therefore contain this On the other hand, AlPO-n series zeolites show great potential in catalytic reactions due to their special pore structure and certain surface acidity.If heteroatoms Doping can effectively improve the surface acidity by changing the charge balance of the molecular sieve framework, for example, the silicate-aluminophosphate molecular sieve (SAPO-5) has moderate acidity and good shape selectivity and is widely used as a solid acid catalyst for dehydration of ethanol , Methanol to olefins, propylene polymerization and styrene epoxidation reactions, showing high selectivity and good stability.In this paper, the traditional homogeneous Co salt catalyst heterogeneity as the starting point, prepared Co-doped SAPO -5 and molecular sieve catalyst (Co-SAPO-5), the effects of Co doping amount on the structure, surface properties and oxygen selectivity of cyclohexane were investigated. The results showed that a part of Co entered into the molecular sieve framework, Co was highly dispersed on the surface of SAPO-5 by the oxidized diamond.Co doping had no significant effect on the specific surface area of SAOP-5 catalyst, but decreased its pore volume.Co-doping, on the other hand, increased SAOP-5 The number of acidic sites on the surface of molecular sieve B and the total acid amount.The activity test results showed that the cyclohexane conversion increased with the increase of Co content in Co-SAPO-5 catalyst, but KA oil selectivity was higher than 6.3% The reaction temperature, the reaction time, the initial oxygen pressure and the amount of catalyst on the performance of Co-SAPO-5 molecular sieve catalyst were investigated.The optimal reaction conditions were obtained.Using Co-SAPO-5-0.2 Ratio of 0.2) zeolite catalyst, the total yield of KA oil up to 7.8%. In addition, Co-SAPO-5 catalyst showed good stability in cyclohexane oxidation, Co-SAPO-5-0.2 There was almost no change in the activity of the catalyst after 6 applications.