Research On The Application Of Mesoporous Alumina-carbon Material In The Dehydration Reaction Of Ethanol

Compared with traditional petroleum steam cracking to produce ethylene,ethanol dehydration has the advantages of low energy consumption,high atomic economy and easy separation of products,which meets the production requirements of my country’s green chemistry.γ-Al₂O₃ is a commonly used ethanol dehydration catalyst.The weak acid sites on its surface are beneficial to the ethanol dehydration reaction,but there are many by-products and the target product has low selectivity.The carbon material has the advantages of similar chemical inertness on the surface,high specific surface area,good hydrophobicity and high olefin selectivity.Compared withγ-Al₂O₃,the similar chemical inertness of the carbon material is beneficial to inhibit the side reaction of ethanol dehydration.Taking advantage of the acidic active sites of the alumina material and the inertness of the surface of the carbon material,this paper uses the solvent volatilization co-assembly method to synthesize an alumina-carbon composite material for ethanol dehydration.（1）Phenolic resin was used as carbon source,F127 was used as surfactant,and the chelate formed by aluminum nitrate and acetylacetone was used as aluminum source.Alumina-carbon composite was synthesized by solvent volatilization co-assembly method.After ammonia treatment,the second calcination was carried out to obtain NH₃-x AM catalyst（NH₃-means calcined after treatment with ammonia water,x is the mass fraction of alumina,AM is the abbreviation of aluminum mesoporous carbon）.The influence of alumina content in NH₃-x AM catalyst on the performance of ethanol dehydration reaction was investigated.The characterization results show that the catalysts NH₃-5AM,NH₃-10AM,and NH₃-15AM present a similar flake structure,and the flakes are connected to each other to form abundant macroporous voids,which helps the diffusion of reactants and products;temperature programmed desorption（NH₃-TPD）indicates oxidation aluminum-carbon composite catalyst in the presence of carbon to produce more weak acid sites,reducing the surface acid sites of Al₂O₃,helps generate ether.Under the conditions of ethanol feed rate of 0.004 m L/min,carrier gas Ar flow rate of 36 m L/min,WHSV_C2H5OH=2.4 h^-1,the selectivity of the catalyst NH₃-10AM to ether is 90%in the temperature 350～400 ^oC range of～100%,and its yield is between 20%～40%,it was attributed to that the addition of carbon increased the specific surface area of the catalyst and provided more active sites for weak acids,which contributed to the formation of diethyl ether.（2）Chapter respectively Al₂O₃/C composites,Al₂O₃ and carbon as a carrier for the metal precursor copper nitrate,deposition-precipitation method to prepare the catalyst Cu/Al₂O₃/C,Cu/Al₂O₃ and Cu/C.The catalyst was characterized by XRD,TEM,and TPD,and the influence of the pore structure and acid strength of the copper-based catalyst on the catalytic performance was analyzed.Copper-based catalysts（Cu/Al₂O₃/C,Cu/Al₂O₃ and Cu/C）were applied to the ethanol dehydration catalytic reaction,and the influence of the pore structure and acid strength of the three copper-based catalysts on the catalytic performance of the ethanol dehydration reaction was investigated.The catalyst Cu/Al₂O₃/C shifted to higher binding energy,indicating that the electron cloud density of copper in the catalyst Cu/Al₂O₃/C has decreased,there may be a strong interaction between Cu and Al₂O₃/C,and part of the copper is fixed by the alumina in the Al₂O₃/C carrier.The results of NH₃-TPD showed that the number of weak acid sites and medium to strong acid sites of the catalyst Cu/Al₂O₃/C were 674.2 and 729.4μmol/g_cat.,respectively,and the acidity of the catalyst Cu/Al₂O₃ were 860.6 and 1619.9μmol/g_cat.,respectively.Compared with the catalyst Cu/Al₂O₃,it can be seen that the amount of weak acid and medium strong acid in the catalyst Cu/Al₂O₃/C has been reduced,indicating that the addition of carbon reduces the amount of strong acid and weak acid in the carrier.These three catalysts were used in the ethanol dehydration reaction,and the results showed that the catalyst Cu/Al₂O₃/C basically converted the reactants at a reaction temperature of 450 ^oC,and the selectivity to the product ethylene was as high as 98%.The catalyst Cu/Al₂O₃/C was significantly higher than the catalyst Cu/Al₂O₃ and Cu/C,which is due to the small copper nanoparticles,large active surface area,but has a more suitable strong acid and weak,two active sites for ease of dehydration of ethanol reaction.Meanwhile,the catalyst Cu/Al₂O₃/C by cycling stability test experiments,after 48 hours the catalyst Cu/Al₂O₃/C conversion rate remains substantially constant ethanol dehydration reaction,the product selectivity to ethylene was maintained at 98%,has good cycle stability.