Preparation Of Supported Molecular Sieve Catalysts And It's Ethylene Oligomerization Performance

As an important petrochemical feedstock, a-olefins are conformed to be the perfect matrix of PAO which is the basal component of IV lubricating oil used in various kinds of advanced and sophisticated machines or equipments. Nowdays, ethylene oligomerization is the widest and most advanced method to produce a-olefins. The technologies which are industrialized, such as the process of Chevron, BP Amoco, Shell and so on, all utilize homogenious method which is studied and improved continuously for more than a half century. Nevertheless, these processes have the advantage of good selectivity of a-olefins and high activity, they also exhibit the faults of difficulting separation between products and catalyst and handling of waste catalyst. These faults are difficult to overcome and lead to the result of high cost and go against environmental protection and energy saving. Therefor, it is significant to explore the processes of heterogenous catalyst, such as molecular sieve catalysts studied in this work,to overcome the faults mentioned above.Al-MCM-41 molecular sieve catalysts with good degree of crystallinity and high degree of order are prepared in the medium of ammonia by hydrothermal synthesis method, using cetyltrimethylammonium bromide(CTABr) as structural template agent, tetraethyl orthosilioate(TOES) as silica source, AlCl3·6H2O as aluminia source. Using ion-exchanged method, metal-supported MCM-41 molecular sieve catalysts are prepared and its ethylene oligomerization activity is tested in continuous flow micro-fixed-bed reactor.The results of ctalysts preparition show that samples with good degree of crystallinity and high degree of order can be obtained under the conditons that the ratio of raw material is at n(CTABr):n(SiO2):n(AlCl3):n(NH3):n(H2O)=0.3:1:(0-0.05):(5-10), the crystallizing time is 72 h at 120℃, and the temperature of baking is at 550℃for 5 hour. And these samples possess high specific surface area of 975.8 m2/g,high specific pore volume of 0.91 ml/g and narrow pore distribution between 2.5-3.5nm. However, with the decline of n(Si)/n(Al), the degree of crystallinity and order are decreased. Besides, M-MCM-41(M:Ni, W, Cr and so on) are prepared as the same way as Al-MCM-41, Characterization suggests they still keep the feature of ordered hexagonal mesoporous structure.Metal-supported MCM-41 molecular sieve catalysts M-MCM-41are tested in ethylene oligomerization and the results of reacts turn out that Cr-MCM-41,Al-MCM-41 and Ni/Al-MCM-41 have oligomerization activity and Ni/Al-MCM-41 catalyst is the best one. To sum up, the optimal catalytic activity of Ni/Al-MCM-41 is at the conditions of 250℃,3.0MPa,1.25h-1 (WHSV) and the n(Si/Al) ratio at 75. Besides, the catalyst activity can be measured up to 11.83 g(g-Cat-h)-1 and selectivity of a-olefins can be to 20.66%. Finally, we show the mechanism of ethylene oligomerization on the supported molecular sieves according to experiment results.This work is an great meaningful exploration and experience for heterogenous ethylence oligomerization study to obtain a-olefins.