Synthesis Of One-dimensional Mesoporous Material MCM-41 And Its Application In Olefin Oligomerization

With the rapid development of the petrochemical industry,olefin oligomerization,as an important industrial reaction,is an effective way to produce engine fuels,detergent raw materials,lubricants,plasticizers and other chemicals.At present,most of the catalysts for olefin oligomerization are homogeneous catalysts.However,homogeneous catalysts have problems such as difficult separation of products and catalysts,strong corrosiveness to reaction equipment,and large environmental pollution.Compared with homogeneous catalysts,heterogeneous catalysts have attracted extensive attention from researchers due to their low cost,strong reproducibility,and easy separation of products.Based on the self-characteristics of the one-dimensional ordered mesoporous silicon material MCM-41 and combined with the advantages of heterogeneous catalysis,the research goal of this subject is to obtain a high-performance heterogeneous olefin oligomerization catalyst.Using 1-decene and ethylene as raw materials,the acidity controllable olefin oligomerization catalyst has been developed.The influence law of olefin oligomerization reaction factors was explored,and the reaction mechanism in the olefin oligomerization process was clarified,thereby providing a new theoretical basis and technical guidance for the preparation of olefin oligomerization catalysts.This paper aims at the design and preparation of high-performance olefin oligomerization heterogeneous catalysts.The chemically modified ordered mesoporous silicon material MCM-41 is used as a catalyst to improve the catalytic activity and stability of the olefin oligomerization reaction by adjusting the acidity of the catalyst and/or the distribution of metal active sites.The specific work is as follows:First,the Al-MCM-41-X catalyst(X stands for different ratios of silicon to aluminum),with a highly ordered mesoporous structure,high crystallinity,high specific surface area and different acidity was successfully synthesized at room temperature based on a typical sol-gel soft template method,and used in the 1-decene oligomerization reaction.By controlling the content of added aluminum,the acidity of the catalyst can be precisely controlled.The results showed that the Al-MCM-41-15catalyst with a reaction temperature of 230 ~oC and an initial nitrogen pressure of 2.0MPa for 6 hours and a total acid concentration(Br?nsted acid+Lewis acid)of 172?mol/g has the best catalytic performance.The olefin conversion rate was 70.4%,and the selectivity of the oligomerization product was 96.7%.The results of five consecutive cycles of the catalyst showed that the conversion rate of 1-decene and the selectivity of oligomerization products remained relatively stable.The catalysts before and after the reaction were analyzed by Py-IR,FTIR and XRD.The results showed that the acidic sites and structure of the Al-MCM-41-15 catalyst did not change significantly.Second,the active sites of nickel are loaded onto different positions of the one-dimensional mesoporous material Al-MCM-41-15 through wet impregnation loading(IWI),ion exchange loading(IE),and physical mixing loading(PM),and used in the ethylene oligomerization reaction.The catalysts prepared by wet impregnation support and ion exchange method support both have high reaction activity in the initial stage of the reaction,and the ethylene conversion rate is close to about 95%.However,as the reaction progressed,the catalyst prepared by the ion exchange method was more severely deactivated.After 84 h of reaction,the ethylene conversion rate was only52.7%,while the ethylene conversion rate of the catalyst prepared by the wet impregnation method could still reach 76.5%.In addition,it was found that the optimal loading of nickel active sites was 2.5 wt%.Third,based on the self-designed heterogeneous Ni/Al-MCM-41-X bifunctional catalyst to catalyze the ethylene oligomerization reaction.Al-MCM-41-X supports with different acidities were prepared by aluminization treatment,and the nickel active sites were loaded onto the Al-MCM-41-X supports by ordinary impregnation method.The nickel-based bifunctional Ni/Al-MCM-41-X catalysts with different acidity were prepared.The results show that the Ni/Al-MCM-41-X bifunctional catalyst has a highly ordered one-dimensional mesoporous structure and adjustable acidity,and exhibits excellent reaction performance.In addition,nickel active sites and acidic sites are both key factors for activating the ethylene oligomerization reaction.The optimal reaction results can be obtained by adjusting the balance between acidic sites and nickel active sites,with up to 96%ethylene conversion and 95%selectivity for even-numbered carbon oligomerization products.Through precise control of acid sites,it is found that the increase of Lewis acid sites and Br?nsted acid sites can effectively improve the catalytic activity of the catalyst.When the optimal reaction performance is obtained,the Lewis acid site and Br?nsted acid site concentrations of the Ni/Al-MCM-41-X bifunctional catalyst are 237?mol/g and 53?mol/g,respectively.