【作者】 赵司旗；

【导师】 连奕新； 方维平； 韩保平；

【作者基本信息】 厦门大学 ， 化学工程， 2018， 硕士

【摘要】 苯乙烯主要用于生产合成橡胶、聚氨酯等一系列聚合材料,是非常重要的有机原料。乙苯脱氢制苯乙烯作为一种最主要的工业生产路径,其核心技术是选择具有高活性、高选择性及性能稳定的Fe-K-Ce系催化剂。相较于传统的乙苯脱氢工艺,甲苯甲醇侧链烷基化制苯乙烯工艺具有能耗低、成本低、反应条件温和等优势,是当前比较热门的研究方向。本文首先通过制备一系列Fe-K-Ce系催化剂,考察不同制备方法和钾源的选择对催化剂乙苯脱氢性能的影响;其次,探索不同金属改性的13X分子筛对甲醇甲苯侧链烷基化反应制备苯乙烯的影响。研究表明:采用四种制备方法制备均能产生催化剂活性相前驱体—多铁酸钾K2Fe22034的晶相,差别在于其结晶度不同。对比反应前后催化剂的表征结果可知,两次煅烧法制备的催化剂中CeO₂的晶粒更小,含有较多的晶格氧,酸碱中心密度适中,且制备的催化剂具有较强的抗积碳能力。因此,采用两次锻烧法制备Fe-K-Ce系乙苯脱氢催化剂效果最佳,乙苯转化率达到72%,苯乙烯选择性达到92.7%。且通过优化反应条件发现,乙苯脱氢活性对反应温度的变化非常敏感,适度提高反应温度能明显提高乙苯转化率和苯乙烯收率。为了进一步优化助剂钾,制备了一系列不同K源的催化剂。评价结果表明,由K2CO₃、KOH及KNO₃制备的催化剂乙苯脱氢性能较好,转化率均在72%左右。而采用钾霞石和黄腐酸钾制备的催化剂中较难形成活性相前驱体—多铁酸钾K2Fe22034的晶相,因而乙苯脱氢活性明显较低,其中K2CO₃是较为适宜的钾源。另一方面,通过不同金属盐对13X分子筛进行表面改性,应用于甲醇甲苯侧链烷基化反应。研究发现,金属改性均对13X分子筛骨架结构造成了不同程度的破坏,同时还调变了其酸碱性。其中,Mg能够中和部分弱酸,而Zn和Zr会增强催化剂的酸性。Zn和Cu改性的催化剂甲苯转化率较高,但是苯乙烯选择性明显较低;Mg和Zr改性的催化剂甲苯转化率较低,但是目标产物选择性较高。如何通过表面酸碱性调变,提高甲苯转化率、苯乙烯选择性有待进一步探索。更多还原

【Abstract】 Styrene is a basic and important chemical raw material in organic processes,which has been applied to synthesize a series of polymeric materials such as rubber and polyurethane.Styrene is industrially produced by dehydrogenation of ethylbenzene on Fe-K-Ce based catalysts,which should have high activity,selectivity,and stability.Compared to this traditional process,methylation of toluene by methanol is an energy saving,low cost,and mild reaction.Due to more surplus toluene and methanol,this methylation reaction has also become a hot research field.In this work,the effect of preparation method on the ethylbenzene dehydrogenation performance of Fe-K-Ce based catalysts was investigated and then the influence of metallic promoters was explored for methylation of toluene over modified 13X zeolite catalysts.The formation of crystal phase of potassium ferrate(K₂Fe₂₂O₃₄)is not sensitive to the preparation processes,while its crystallinity is different.After comparison of characteristics of the fresh and used catalyst,it was found that the crystals of CeO₂ after two-step calcinations method are smaller and the lattice oxygen is abundant.The density of the acid-base centers is also moderate;The catalyst has the strong resistance to coke formation.Therefore,the two-step calcinations method is suitable for preparation of Fe-K-Ce based catalysts,at an ethylbenzene conversion of 72%,with a styrene selectivity to 92.7%.After optimization of operation parameters,the dehydrogenation activity increased with the reaction temperature increasing.In order to optimize potassium,different potassium precursor was investigated further based on two-step calcination method.The results show that the dehydrogenation activities over the catalysts prepared from K₂CO₃,KOH and KNO₃ are better,and the conversions of ethylbenzene are 72%.While the catalysts prepared by potassium nepheline and potassium fulvic acid have detrimental effect on the formation of K2Fe22O₃4,the dehydrogenation activity was significantly reduced.So the K₂CO₃ is a suitable precursor.The surface of 13X molecular sieves were modified by different metal salts and used in the alkylation reaction of methanol to toluene side chains.The framework of the 13X zeolite was damaged varying degrees by adding of different metal promoter.Simultaneously,the acid-base centers were also modified depending on metal promoter.Mg neutralized part of weak acids,while Zn,Zr enhanced the acidity of support.The toluene conversion increased,while the selectivities to ethylbenzene and styrene is lower over the Zn and Cu modified catalysts.On the contrary,the toluene conversion decreased with the high selectivity to desired product over the Mg and Zr modified catalysts.How to improve toluene conversion and styrene selectivity through surface acid-alkaline modulation needs further exploration.更多还原