Reaction Kinetics of Xylose to Furfural Catalyzed by Sulfuric Acid Systems

Furfural yields from dehydration of xylose in conventional production processes catalyzed by sulfuric acid were limited to fifty percent because of side reactions. In the past, there are some researches about increasing furfural production rate and yield, such as addition of chromium ions (III) or sodium chloride respectively in acidic reaction media. In this study, reaction kinetics of furfural production from pure xylose in a homogeneous catalyst with chromium ions (III) and sodium chloride in sulfuric acid solution has been studied under a batch reaction system. Experimental designs and statistical analysis were used to find optimal concentrations of the catalysts for furfural production. In this research, the synergetic effect of simultaneous addition of sulfuric acid, chromium sulfate (III) and sodium chloride on catalytic property has been found, which can increase the furfural production rate substantially. In addition, the results about effects of reaction temperature showed that the activation energy of the major reaction is higher than side reactions; therefore, furfural selectivity and yield can increase at higher reaction temperature. When the reaction was in the solution with 2.5mM sulfuric acid, 5ppm chromium sulfate(III) and 5wt% sodium chloride at 200℃ high temperature, the value of the ratio between main reaction rate and side reaction rate k1/k2 (furfural selectivity) can reach 3.95. Reaction kinetics of xylose solution, produced from agricultural wastes (wood-chip) in real pretreatment processes developed by Institute of Nuclear Energy Research, have also been studied. Compared with the results of pure xylose at the same reaction conditions, lower reaction rates and higher side reaction rate of furfural degradation were found. Furfural selectivity and yield decreased significantly. It demonstrated that the reaction may be influenced by impurities contained in wood-chip xylose solution. The analysis of the composition of the impurities in wood-chip xylose solution was carried out. It was found that only glucose can increase the degradation rate of furfural. Thence, there were still other unknown impurities in wood-chip xylose solution affecting reaction rates. Moreover, the value of selectivity k1/k2 decreased as the reaction temperature increased. When the reaction was in the solution with 50mM sulfuric acid, 3.27ppm chromium sulfate(III) and 5wt% sodium chloride at 160℃, the value of k1/k2 (furfural selectivity) was only at 2.36.