Shape-selective Methylation Of 2-methylnaphthalene Into 2,6-dimethylnaphthalene Over Modified ZSM-5 Zeolite Catalysts

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...