Preparation And Modification Of Modified Nano - Sized ZSM - 5 Molecular Sieve

In this thesis, nanosized ZSM-5 zeolites were synthesized by seed-induced method. The structures and acidic properties of the catalysts were characterized by means of XRD, N2 physical adsorption and desorption, SEM, NH3-TPD and Py-IR. The influence of reaction temperature, weight hour space velocity (WHSV), flow rate of carrier gas and reaction pressure on the catalytic performance of nanosized ZSM-5 zeolite in the aromatization of 1-hexene was investigated in a flowing type fixed bed microreactor. The optimized technologic conditions were as follows:reaction temperature 480℃, WHSV 2.0 h-1, flow rate of carrier gas Qn2= 75 ml/min, reaction pressure P= 0.5 Mpa.By seed-induced in-situ synthesis, Ga and Zn were introduced into the framework of nano-ZSM-5 zeolite; the structural and acidic characteristics were investigated in an effort to study the effect of heteroatom contents and heteroatom type on the catalyst structure, acidity and catalytic activity in the aromatization of 1-hexene. The results showed that the introduction of Ga and Zn both could improve the strength of Lewis acid; reduce the strength of Brenstedacid and the value of B/L. However, the former amount of Brensted acid sites was increased while the latter was on the contrary. Besides, the introduction of Zn resulted in a wider range of B/L. In the aromatization reaction of 1-hexene, the introduction of Ga and Zn also improved the selectivity for aromatizing and stability of catalyst, and Ga-HNZ5 and Zn (4:6) Al-HNZ5 had the highest selectivity, respectively. But the difference was that the former had a higher C6-C8 aromatics selectivity, and the later had a higher selectivity of C9 aromatics.In order to investigate the effect of the concentration of NaOH solution on the structure, acidity and catalytic performance of aromatization reaction, the samples Zn(4:6)Al-HNZ5 was treated with different concentrations of NaOH solution respectively. The results revealed that the treatment of nano-ZSM-5 zeolite of Zn isomorphous replacement with appropriate concentration of NaOH solution can effectively elute the amorphous species so as to improve the diffusion performance, and the adjusted acidity could promote the aromatization process.Nanosized ZSM-5 zeolite of aluminosilicate and gallosilicate were modified by Zn via impregnation method. The influence of the Zn-loading on the structure, acidity and catalytic performance of aromatization reaction was investigated. The experiment results showed that Zn-modification can increase the strength and amount of Lewis acid sites while reduce Br(?)nsted acid sites; the aluminosilicate and gallosilicate nano-ZSM-5 zeolites of 2.0 wt.% and 1.0 wt.%Zn showed excellent aromatization selectivities of 61.6% and 66.8%, respectively.Aromatization performances of different feedstocks over aluminosilicate, gallosilicate and ZnZSM-5 catalysts were investigated. Feedstocks with high ratio of hydrocarbon had higher aromatization selectivity, however, the presence of alkane would reduce the aromatization activity; after the treatement, aromatics content of FCC gasoline were increased by 25.2%,33.9% and 35.3%. What’s more, the Motor octane was raised to 95.9, and nano-ZSM-5 zeolites which modified by Ga and Zn isomorphic replacement showed a higher reaction stability co Mpared with aluminosilicate nano-ZSM-5 zeolite.