【作者】 张晨；

【导师】 宋春山； 郭新闻；

【作者基本信息】 大连理工大学 ， 催化化学与工程， 2010， 博士

【摘要】 2,6-二甲基萘(2,6-DMN)是一种合成高性能聚合物的重要原料,由于其工业化制备过程复杂,生产成本高,导致其下游产品价格较高。本论文以沸石分子筛为催化剂,2-甲基萘(2-MN)甲基化一步法合成2,6-DMN以降低其生产成本。系统研究了不同改性方法对催化剂反应性能的影响,得到如下结论：研究了硅酯液相沉积和水蒸汽处理对HZSM-5的催化性能的影响。发现调变催化剂的孔道对提高2,6-／2,7-DMN比值作用并不显著,最有效的手段是降低催化剂的酸强度。2,6-DMN的异构化主产物是1,6-DMN,而非2,7-DMN。抑制1,6-DMN的生成可以有效提高2,6-DMN的选择性。由于KNO3溶液改性对催化剂的孔结构影响较小,同时能够有效的抑制强酸中心。因此,可在KNO3改性分子筛上得到较高2-MN转化率以及2,6-／2,7-DMN比值。然而KNO3的引入导致催化剂活性位利用率降低,稳定性变差。通过水热处理配合酸洗对催化剂扩孔,增强了反应物和产物孔道内的扩散效果,提高了催化剂上活性位的利用率,有效缓解催化剂的失活；再引入钾离子可保持催化剂较高的初始活性,同时催化剂的稳定性以及目的产物的选择性均有明显的提高；2,6-DMN的选择性达到63%,2,6-／2,7-DMN比值约为2.5,2,6-DMN的收率可达12%。磷酸氢铵改性可以提高2,6-DMN的选择性,改善催化剂稳定性,但降低了2,6-／2,7-DMN比值。量化计算结果表明催化剂酸性增强抑制2,6-DMN生成,磷酸盐的引入增强了分子筛的弱酸的酸强度。因此,磷酸盐改性不利于提高2,6-／2,7-DMN比值。NH4F改性可使HZSM-5脱铝。随着焙烧温度的升高,脱铝程度逐渐加深,导致骨架铝降低,非骨架铝以及氟铝络合物逐渐增加。在NH4F改性纳米HZSM-5过程中,随着焙烧温度的升高,催化剂的初始活性逐渐降低,但是稳定性得到有效的改善。尤其当焙烧温度为500℃时效果最佳,催化剂上2-MN转化率在反应6小时内始终保持在15%左右。NH4F的引入有效的提高了2,6-DMN的选择性和2,6-／2,7-DMN比值。NH4F改性微米HZSM-5作用效果与改性纳米HZSM-5作用效果基本一致：改性对催化剂有脱铝的作用,可降低催化剂的酸中心的数量和强度,有效抑制2-MN的异构化,提高2,6-DMN的选择性和催化剂的稳定性。但微米HZSM-5上二甲基萘的选择性略高于纳米HZSM-5。NH4F改性后继续添加SrO,2,6-DMN选择性可达65%,而1-MN选择性低于10%,2-MN的转化率在反应6小时中始终保持在10%左右,催化剂的稳定性得到改善。改性催化剂反应结果表明,弱酸中心为催化2-MN甲基化反应的催化活性中心;而强酸中心则会增加副反应发生的几率,加速催化剂的失活,通过改性降低强酸中心的强度,可提高目的产物的选择性以及催化剂的稳定性。更多还原

【Abstract】 2,6-Dimethylnaphthalene(2,6-DMN) is starting material to synthesize high performance polymeric material. Since the process of 2,6-DMN synthesis is very complex, its down-stream product price is very high. Therefore, looking for a efficient synthesis route of 2,6-DMN has become a very important subject. In this dissertation we tried to use HZSM-5 as catalyst to synthesize 2,6-DMN by methylation of 2-methylnaphthalene(2-MN).The effects of steam treatment and TEOS modification of HZSM-5 zeolite were examined on the physico-chemical properties, catalytic selectivity and activity in synthesis of 2,6-DMN. Based on the characterization and reaction results, it can be concluded that adjusting acidic property of HZSM-5 catalyst has more desirable impact on shape-selective methylation of 2-MN than optimizing pore channel and pore mouth of the catalyst. Tailoring acidic characteristics is more important than spatial control for distinguishing between 2,6-DMN and 2,7-DMN. Therefore, how to optimize acidic characteristics is a key factor for improving the ratio of 2,6-DMN to 2,7-DMN in methylation of 2-MN with methanol for the synthesis of 2,6-DMN.According to the above conclusion, we choose KNO3 to modify HZSM-5 to improve the performance of catalyst in this reaction. XRD patterns showed that the structure of zeolite framework was scarcely damaged after potassium modification. NH3-TPD profiles indicated acidity decreased in the K-modified HZSM-5. The modification also resulted in mild desilication of the HZSM-5 framework. Introduction of suitable amount of potassium can improve selectivity to 2,6-DMN. Stability of zeolite, however, was ruined by introduction of potassium. Recovering acidity method that was used on KZSM-5 proved that suitable number of acidic sites is beneficial for improving selectivity of desired product.Hydrothermal treatment followed by HCl leaching improved the stability of catalyst. The increasing of selectivity to the desired product mainly came from the decreasing of acid sites and the slight enlargement of pore channel of HZSM-5. The integrated modified catalyst took the advantages of excellent stability of hydrothermal treatment HZSM-5 and high selectivity over potassium modified HZSM-5 at high conversion of 2-MN. The selectivity and yield of 2,6-DMN can reached about 65% and 10% respectively. Ratio of 2,6-/2,7-DMN achieved as high as 2.5, conversion of 2-MN can be kept at 19% within 6 hrs of time on stream. This superior catalytic property should be attributed to reasonably adjusting acid properties and pore dimension of catalyst.NH4F modification caused dealumination of HZSM-5. Over nano HZSM-5, the best catalytic performance of modified catalyst was obtained at 500℃calcinations temperature. This improvement should be attributed to the removal of strong acid sites. The similar trend was achieved on the micro HZSM-5. Integrated modification on HZSM-5 with NH4F and SrO could optimizes catalytic performance much better than introduction of the two modification methods onto the HZSM-5 alone. Over the modified HZSM-5 catalyst, the selectivity of 2,6-DMN can reach 64% and the conversion of 2-MN can keep at 9% for 6 hrs, and the ratio of 2,6-/2,7-DMN can reach 2.0更多还原