Conversion Of Hemicelluose Into Furfural Using Inorganic Salt Catalysts

With the accessible oil fields are becoming depleted and CO2emissions from fossil fuel are affecting the earth's climate, the most imminent result that awaits mankind is the tremendous crisis of energy if we remain dependent on the fossil resources. Hence, much research is being devoted to exploring non-fossil carbon energy resources. Among these, the lignocellulosic refining technology with lignocellulose as raw materials is considered as a promising alternative program. Furfural, an important platform compound, which can be directly converted into biofuels or many down-stream products through further reaction, has become the focus of scientists.The effects of different metal chlorides on conversion of xylose into furfural in toluene/water system at140?160?were studied first in this paper. Based on the above research, aluminum chloride was chosen as catalyst. The response surface methodology was used to determine the effects of independent variables, including reaction temperature, reaction time, concentration of aluminum trichloride and xylose concentration, liquid solid ratio on the conversion of xylose and corncob. Meanwhile, the first order reaction model were developed to explain the relationship between the reaction rate constants and reaction temperature and AICl3concentrations, and the kinetic parameters were obtained. Finally, the mechanism of conversion of corncob into furfural catalyzed by AICl3in biphasic system was discussed.Through the above research, the main conclusions were summarized as follows:(1) Compared with no catalyst loading, all the tested chlorides could converse xylose into furfural, the amphoteric metal chloride AICl3and transition metal chloride CrCl3had better catalytic performances. The kinetic study results showed that the ratio of rate constants beween formation and decomposition of furfural catalyzed by AICl3was greater than that catalyzed by CrCl3, which indicated that the catalytic activity of AICl3was better than that of CrCl3.(2) The independent variables including reaction temperature, reaction time and concentration of AICl3had a significant effect on dehydration of xylose into furfural. With the reaction temperature and concentration of AICl3increasing,the xylose conversion could be promoted and the furfural yield should be improved respectively. The maximum predicted furfural yield was46.51%when the temperature, reaction time, AICl3concentration and the initial xylose concentration were149.71?,112.79min, O.lmol·L-1and0.35mol·L-1, respectively. Under these conditions, the xylose conversion was nearly100%. With the first order kinetic equation, the evaluated activation energies of formation and decomposition reaction of furfural were110.76kJ·mol-1,158.38kJ-mol"1, respectively.(3) AICl3was an effective catalyst for corncob hydrolysis into furfural in biphasic system. The surface response analysis for corncob conversion indicated that reaction temperature and AICl3concentration were highly significant term. A furfual yield of52.66%could be achieved at temperature of177?, time of78.38min, AlC13concentration of0.08mol·L-1and the solid liquid ratio of0.15g·L-1.Kinetic study showed that the activation energy of furfural formation was less than xylose formation with AICl3as catalyst, and with increasing concentration of AICl3, the activation energy of furfural formation decreased. When the concentration of AICl3were0.06mol·L-1,0.10mol·L-1,0.14mol·L-1, the activation energies of the conversion xylose into furfural were95.87kJ·mol'1,78.91kJ·mol-1and75.68kJ·mol-1, respectively. The XRD and SEM analysis of corncob before and after hydrolysis showed that AICl3could effectively break the structure of fibrous tissue and promote the hydrolysis of corncob.(4) Above all, the mechanism of hydrolysis of corncob hemicellulose into furfural catalyzed by AICl3in biphasic system was discussed. It can be devided into two parts. On the one hand, hydrogen ions from aluminum ions hydrolysis in water, could improve the formation of xylose. On the other hand, the coordination effect between metal center of AICl3and oxygen atom of xylose molecule could isomerize xylose into xylulose, then remove three molecules of water to form furfural.