Study Of Catalyzed Hydrogenolysis Reaction Of Cellulose Over Ni-W-Cu/MgAl₂O₄

Lignocellulose is a renewable resource that can fix carbon.The main product of catalytic hydrogenolysis from lignocellulose is ethylene glycol.In this paper,the hydrogenolysis of cellulose were studied catalyzed by the Ni-W-Cu/MgAl₂O₄catalysts which were prepared by isovolume impregnation method with magnesium aluminum spinel（MgAl₂O₄）as carrier,aiming to provide theoretical basis for the development of cellulose hydrogenolysis.The main research contents are as follows:An analytical method was developed to determine the composition of cellulose hydrolysis products by high performance liquid chromatography（HPLC）equipped with refractive index detector.The composition of the cellulose hydrolysis products was qualitative analysis by comparing with standard samples.The results showed that the products contained ethylene glycol,1,2-propanediol,glycerol,glucose,erythritol and sorbitol.The standard curves were calibrated with the standards of the above components.The results showed that the peak areas of all the components of the hydrogenolysis products showed good linearity with the standards,since the correlation coefficients were all above 0.996.The relative deviations of the precision and reproducibility experiments were 0.29-0.81%and0.47-1.05%,respectively,with the relative errors of the spiked recovery experiments 0.12-1.63%.The product distribution of cellulose hydrolysis reaction was determined by the previously established analytical method.The main product of cellulose hydrogenolysis was found to be ethylene glycol（2.39 g/L）,and the reaction pathway of cellulose hydrogenolysis was tentatively deduced.The optimum method and conditions for the preparation of the catalysts were determined.The carrier（MgAl₂O₄）was prepared by sol-gel method and the loaded multifunctional Ni-W-Cu/MgAl₂O₄ catalysts were prepared by isovolume impregnation method.The effects of Ni,W and Cu loadings and Mg/Al on the catalytic activity of Ni-W-Cu/MgAl₂O₄ were studied by single-factor experiments.The structure and physicochemical properties of the prepared catalysts were characterized by XRD,XPS,Py-IR and TEM techniques.The results showed that the optimal preparation conditions of Ni-W-Cu/MgAl₂O₄ catalysts were obtained as follows:the loadings of Ni,W and Cu were 5 wt.%,15 wt.%and 15 wt.%,respectively,and the Mg/Al ratio was 1/3.The results showed that the addition of Ni,W and Cu not only promoted the formation of more L acid sites which was beneficial for the hydrolysis of cellulose to glucose,but also improved the reduction of Ni species.Moreover,5Ni-15W-15Cu/MgAl₂O₄（1:3）exhibited more acid amount and obtained more oxygen vacancies.the loadings of Ni,W and Cu on the re-cycled catalyst were tested using inductively coupled plasma emission spectroscopy.As a result,the ethylene glycol yield remained essentially constant when cycled three times.No significant change in Ni loading and Cu when cycled six times,while the loading of tungsten decreased significantly from 16.0%to12.8%.The reaction conditions of 5Ni-15W-15Cu/MgAl₂O₄（1:3）catalyzed hydrogenolysis of lignocellulose were investigated.The effects of the conditions of reaction temperature,reaction pressure,reaction time and catalysts amount on the reaction of cellulose and sugarcane bagasse pith for the production of ethylene glycol were investigated by single-factor experiments.The results showed that the optimum conditions for the preparation of ethylene glycol from cellulose were:reaction temperature of 245℃,hydrogen pressure of 3.0 MPa,reaction time of2.0 h,and catalysts amount of 0.3 g,and the yield of ethylene glycol was 53.1%under these conditions;the optimum conditions for the preparation of ethylene glycol from sugarcane bagasse pith were:reaction temperature of 245℃,hydrogen pressure of 5.0 MPa,and reaction time of 2.0 h,and the yield of ethylene glycol was 30.3%.A kinetic model for the hydrogenolysis reaction of cellulose over Ni-W-Cu/MgAl₂O₄ catalyst was established.A first-order cascade reaction kinetic model and a shrinking core model were established,and the kinetic data were regressed and analyzed using the Levenberg-Marquart method with 1STOPT 5.0programming.The experimental and calculated values of both models were in good agreement,and the activation energies of both models were also in good agreement,indicating that the simplified first-order cascade kinetic model has been able to describe the hydrogenolysis reaction of cellulose over Ni-W-Cu/MgAl₂O₄ catalyst well.The hydrolysis of cellulose was the controlling step of the reaction rate,and high temperature facilitated the hydrolysis of cellulose to glucose.