Catalytical Conversion Of Wheat Strawto Furfural Derivatives

Wheat Straw is an abundant waste of agricultural production and treated as important biomass resources. Cellulose and hemicelluloses, which are major compositions of wheat straw, can be converted to representative chemical intermediates such as 5-hydroxymethylfurfural (5-HMF), furfural, levulinic acid and so on. These compounds contain active reactive groups of hydroxyl methyl and aldehyde which can be used in synthesizing of high polymer materials with high value-added. However, cellulose and hemicelluloses are not completely used due to the lack of green solvent with the property of low cost and good solvability. Besides, the short of suitable, high catalytic efficiency and recoverable solid-acid catalyst hinders the preparation of 5-HMF and furfural which causes the problem of low conversion efficiency and high cost. Considering these issues, we employed inorganic molten salt hydrates as solvent to dissolve cellulose and hemicelluloses in situ. And converting of furfural derivatives with inorganic acid and solid-acid catalyst was studied. Some results were presented below:In the zinc chloride molten salt hydrates, high temperature and low solid-to-liquid ratio promoted wheat straw dissolution. At the optimum condition (100℃,2wt%), the dissolution rate of carbohydrate was 95.33%.At the optimum condition(140℃,0.9 wt% HC1,1 h), the conversion rates of HMF and furfural was 74.62 mol% and 87.88 mol%, respectively.The influence of different molar ratio of Cr, Ti and Si and calcination temperature on catalytic conversion of carbohydrate in wheat straw to 5-HMF and furfural by synthesizing of SO42-/CrO2-TiO2-SiO2 solid catalyst. The highest efficiency of solid acid catalyst was achieved when the molar ratio of Cr, Ti and Si was 3:4:1 and the calcination temperature was 500℃. The highest yields of 5-HMF and furfural reached to 83.63% and 89.46%, respectively when 6 wt% catalysts were added.At last, we studied the impact of cycle index of solid-acid catalyst on yields of furfural derived products and regenerated the inactivated catalyst. The results indicated that the catalytic efficiency decreased significantly with the increase of cycle index. The yields of furfural derivatives reduced to less than 15% and the catalyst was deactivation when the cycle index reached to 7. The activity of catalyst was recovered after treatment of high temperature burning, acid impregnation and calcination. After which, the yields of 5-HMF and furfural were higher than that of two times recycling of the catalysts, indicating the achievement of the purpose of the catalyst recycling.This study proposed a system of high dissolving capacity, environmentally friendly and price moderate to convert and utilize wheat straw. It is of great significance in development and utilization with high added value of biomass resources.