Study On The Performance Of The Modified Montmorillonite Supported Cobalt Catalyst Slurry Bed

In recent years,facing the increased oil import dependence and the serious problem of environmental pollution,Fischer-Tropsch（FT）synthesis has drawn much attention of researchers around the world.FT synthesis is one of the best ways to produce fuels without sulfur,nitrogen,and aromatics from coal and biomass-derived syngas.Therefore,FT synthesis is considered as the new solution to deal with the energy crisis and increase energy supply.However,the product distribution of FT synthesis following the Anderson-Schulz-Flory（ASF）regulation,the product of FT synthesis contains complicated chemical and fuel composition,including olefin,alkane（C1-C100+）and other chemicals.Thus,how to develop and design the catalystwith high activity and selectivity for synthesizing the target products plays a significant role in both theoretical studies and industrial production.The assembling reactive metal and solid acid into a bifunctional catalyst is an effective strategy to increase the selectivity of target products.Due to the abundance,environmental compatibility,adjustable acidity and porous structure of montmorillonite（MMT）,the pillared MMT and acid activated MMT have been studied as a support for FT synthesis in the fixed bed reactor in the previous research in our laboratory.However,it is well known that the CO conversion and product distribution of FT synthesis will be influenced by the reactor types due to the different heat and mass transfer process.In this paper,based on the previous work in our group,the composition,layer spacing,porous structure and acidity of montmorillonite were modified by the method of pillaring with metal oxides and acid activation.And the modified montmorillonite supported Co catalyst was prepared via the incipient impregnation method.Moreover,the catalytic performance of FT synthesis was investigated in the slurry bed reactor.The main results are summarized as follows:（1）By using thethe Na-type montmorillonite（Na-MMT）as a matrix,AlC13,ZrClO2,3-aminopropyltrimethoxysilane,tetraethoxysilane and butyl titanate were used as precursors,a series of pillared MMT（PILC）by different oxides and mixed oxides were successfully prepared.It is indicated that the physicochemical properties of the PILC can be highly affacted by the ingredient of the pillaring oxides.Compared with the single oxide MMT,theSi/Al-PILC,Si/Zr-PILC,and Si/Ti-PILC catalysts showed higer surface area.Furthermore,acidic sites of the catalyst showed an increased trend after the introduction of the pillaring oxide.The results of FT synthesis in the slurry bed reactor indicated that the selectivity of C5-C18 over mixed oxides pillared MMT is higher than that over single oxide pillared MMT.The Co/Si-Zr-MMT showed the highest selectivity of C5-C18,which can be attributed to the higher amount of acidic sites and acidic strength.Moreover,the selectivity of CH4 and C2-C4 decreased in compared with the results in the fixed bed reactor in our previous work.（2）The activated MMT（H-MMT）was prepared via HNO₃solution with varied temperatures.The Co-based catalysts were prepared via the incipient impregnation method,by which using cobalt nitrate as the precursor.The results revealed that the structure and acidic sites of on the surface of H-MMTs were changed after the acidic activation by HNO₃.It is indicated that the acidic activation conditions can significantly affect the extent of acidic sites.The interaction between pillared MMT and Co can be influenced by the porous structure,composition,and acidic properties of pillared MMT.Similar with the results in the fixed bed reactor in our previous work,the CO conversion and product selectivity can be influenced by the acid activation conditions.The CH4 selectivity decreased with the increase of temperature of acid activation,which can be attributed to the formation of mesopores and macropores.However,the amount of acidic sites decreased clearly,which result in selectivity of Ci9+ increased.And isomerization,the amount of catalytic hydrogenation product is significantly reduced,normal are significantly increased.And the amount of isomerization and catalytic hydrogenation products is also reduced,normal paraffins increased significantly.