Study On MgO/SBA-15 Catalysts For The Synthesis Of 1,3-butadiene From Ethanol

1,3-Butadiene,as an important fundamental chemical raw material in the field of chemical industry,has been applied in the synthetic rubber industry,and is predominantly obtained via the extractive distillation from C₄ steam cracker fractions.With the worldwide rapid depletion of non-renewable resources such as fossil,combined with the urgent need for energy in the world economy,and the increased awareness for environmental protection,a new and sustainable route is expected to replace the traditional production route for butadiene.Therefore,the technologically matured and widely used technology for the ethanol production form biomasses gives a strong support by providing raw materials to the so called“ethanol method”in the production of butadiene as well as makes firm foundation for the industration of this route.In this study,the preparation conditions of the MgO/SBA-15 catalysts and the optimization of the reaction temperature as well as the catalytic performances,stability and anti-carbon ability of samples were investigated.The function of acid and base sites of the due catalysts and mechanism in the ethanol transforming into butadiene process were also investigated.The results of the experiments shown that the catalysts prepared using solvent impregnation method,with Mg（NO₃）₂·6H₂O being the precursor,under the calcination temperature of 500℃,were well in spreading MgO species onto the inner micropores of SBA-15,forming the Mg-O-Si moieties by the strong interaction between MgO and SBA-15.Much more weak and medium strength acidity as well as moderate basicity were formed as consequence.It was found that the catalytic perfoemance,stability and anti-carbon ability of the caralyst sample prepared with SBA-15 being the support were superior to that of those prepared with traditional silicas.The best catalytic performance was reached with ethanol and acetaldehyde mix conversion being 55.85%and butadiene selectivity of 80.15%under the condition of the reaction temperature,the feed space velocity and the acetaldehyde ratio being 350℃,2.64 h^-11 and 3.5/1,respectively.The adition of some amount of acetaldehyde in feed can boost the butadiene selectivity to a large extent.While the the formation of ethylene and ether was effectively suppressed.It was found that there existed competitive adsorption on the surface of the catalysts between ethanol and acetaldehyde moleculars in gas phase.And the acetaldehyde molecules were more likely to adsorb and occupy the active center of the catalyst,transforming into the important intermediate-butanel via aldol condensation process,which in return,inhibited the formation of the dehydration products.The results of poisoning of acid and base sites shown that the the optimum acid sites for the production of butadiene in the MgO/SiO₂ system were the moderate-strength acid sites,corresponding to the NH₃ desorption temperature range of 200³00℃;and base sites with moderate basicity,corresponding to the CO₂ desorption temperature range of 150²50℃,which the Mg-O-Si bonds can be account for.Moreover,the formation of ethylene was mainly catalyzed by the strong acid sites of the catalysts.The Activity of strong basicity in aldol condensation of acetaldehyde was high enough,that,at the initial stage of the reaction,those sites were actually deactivated by the heavier compounds formed by mltimerization of acetaldehyde and other intermediates.