Study On Improving Selectivity Of Glucose In Cellulose Hydrolysis

Cellulose biomass has a high value of utilization and a vast application prospect,but its chemical properties are stable.Therefore,solid acid catalysts are often used to catalyze the hydrolysis of cellulose.However,products of the cellulose hydrolysis are complex.In this paper,a combination method of experiments and computational chemistry was used to improve the selectivity of glucose in cellulose hydrolysis:First,a new kind of catalyst was proposed by the deprotonation of silanol groups without using any acid precursor to achieve the hydrolysis of cellulose.Pyridine adsorption FTIR(Fourier Transform Infrared)showed that no Bronsted acid site was found on the catalyst surface.And the pH test showed that the aqueous dispersion of this catalyst at room temperature did not have any acidity.The result of DFT(Density Functional Theory)calculation shows that the providing of hydrogen ions by silanols is an endothermic process,and the activation energy is 0.926 eV.Therefore,silanol groups will deprotonize when the environment reaches a certain temperature.Under the optimal condition,the maximum products total yield was 50.74%.Among them,the selectivity of glucose is 95.1%and the yields of 5-HMF(5-Hydroxymethylfurfural)and furfural are relatively low.This indicates that further conversion of glucose to 5-HMF and furfural does not occur with this catalyst.In order to improve the selectivity of glucose in cellulose hydrolysis catalyzed by traditional acid catalysts,benzene ring was used to modify the surface of the catalyst to realize the process that glucose left the catalyst surface spontaneously.The results of in situ infrared adsorption showed that the adsorption of glucose was significantly weakened after catalyst was modified.In the hydrothermal experiments,the sulfonated catalyst modified by benzene showed a diminishing effect on the degradation and conversion of glucose compared with the unmodified one.When using the benzene-modified solid acid catalyst to hydrolyze cellulose,the glucose yield was 55.11%and the glucose selectivity was 95.98%.When using the unmodified catalyst,the glucose yield was only 29.53%and the glucose selectivity was 82.33%.This indicates that benzene ring can improve the selectivity of glucose for traditional sulfonic acid catalysts.The results of molecular dynamics calculations showed that the adsorption energy for glucose on the unmodified catalyst is-19.61 kcal/mol.When the catalyst was modified by benzene,the adsorption for glucose on the catalyst becomes weaker and the adsorption energy decreases to-14.37 kcal/mol.These changes are caused by the steric effect of the benzene ring.In summary,the methods of preparing silica hydroxyl catalyst and using benzene ring to modify the surface of catalyst were proposed to improve the selectivity of glucose in cellulose hydrolysis.And these two methods provide a new idea for the application of cellulose hydrolysis.The silicon hydroxyl groups on the catalyst surface are spontaneously generated by calcination from silicon source.At the same time,no acidic precursor was used to introduce acidity during the preparation of the catalyst.This has less polluting than traditional acidic catalyst preparation methods.The modification method can improve the selectivity of glucose for traditional sulfonic acid catalyst in cellulose hydrolysis,and explores the potential of application for traditional sulfonic acid solid acid catalyst.