The role of xylulose as an intermediate in xylose conversion to furfural: insights via experiments and kinetic modelling

An experimental work has been performed to study the relevance of xylulose as an intermediate in xylose conversion to furfural in aqueous solution. The furfural formation was investigated at the temperature range from 180 to 220 °C during non-catalyzed and acid-catalyzed conversion of xylose in a stirred microwave-assisted batch reactor. The separate experiments on xylulose and furfural conversions were carried out under similar conditions. The maximum furfural yields obtained from xylose were 48 mol% and 65 mol% for the non-catalyzed and the acid-catalyzed processes, respectively. It was shown that the furfural yield is significantly lower from xylulose than from xylose. Furthermore, the effects of initial xylose concentration and the formation of xylulose were investigated in a mechanistic modeling study. A new reaction mechanism was developed taking into account the xylulose formation from xylose. Based on the experimental results and the proposed reaction model, it was concluded that xylose isomerization to xylulose with subsequent furfural formation is not a primary reaction pathway. The obtained kinetic parameters were further used for plug flow reactor simulations to evaluate furfural yields achievable by an optimized continuous operation.