| Vanillin（4-hydroxy-3-methoxybenzaldehyde）is in great demand as a widely used fragrance.At present,in industry,guaiacol is used as raw material,which is condensed with glyoxylic acid under alkaline conditions,and then undergoes oxidative decarboxylation to produce vanillin.However,this process has problems such as toxic raw materials,complex reactions and corrosiveness.People have focused their research on natural macromolecular lignin rich in benzene ring structure and tried to use it as a raw material to explore a green and efficient catalytic system for the preparation of vanillin by oxidizing lignin to solve the problems of poor product quality and environmental pollution in the production of vanillin,which open up a new way for the efficient utilization of lignin.In this thesis,vanillyl alcohol and 4-methylguaiacol,which are small molecule model compounds of lignin,were used as raw materials,and a series of catalytic systems were designed for the preparation of vanillin by alkali-free oxidation of lignin model compounds with high catalytic performance from the perspectives of solvent and catalyst.N-propanol,water/n-octane/n-propanol microemulsion were used as solvent,and bimetal supported Co-Pd/C was used as catalyst.The effects of the type of solvent,the type and proportion of the active component in the catalyst,reaction temperature,time,pressure and other conditions were investigated,and the optimal oxidation conditions were obtained.Under the optimal oxidation conditions,the conversion rate of vanillyl alcohol was 94.68%,and the selectivity of vanillin was98.35%,the conversion rate of 4-methylguaiacol was 95%,and the selectivity of vanillin was 83.33%.The results were analyzed by TEM,XPS,XRD,H2-TPR and other techniques.The results showed that the bimetallic synergy in the catalyst and the dispersion and morphology of active metals were the keys to the efficient oxidation of vanillin.This study provides a technical reserve for the preparation of vanillin from lignin. |
PDF Full Text Request