半纤维素六碳糖转化为5-羟甲基糠醛的动力学

Kinetic of conversion of hemicellulose hexose to 5-hydroxymethylfurfural

选取甘露糖和半乳糖两种典型半纤维素六碳糖作为模化物,考察其在水相中较宽温度（100~200℃）和时间（10~240min）范围内的降解行为。实验结果表明,较高的反应温度能提高六碳糖的转化率和5-羟甲基糠醛（HMF）的产率;在200℃时甘露糖和半乳糖生成的HMF最高产率分别为26.82%和22.86%,乙酰丙酸（LA）的产率低于3%;半乳糖因容易异构化生成塔格糖而非果糖,导致其HMF产率较低。采用六碳糖平行生成HMF和Humin,随后HMF平行生成的LA和Humin的反应模型对六碳糖降解动力学进行分析,揭示了六碳糖的类型对HMF和Humin生成机制的影响。此外,针对六碳糖生成的Humin的Van Krevelen图和FTIR谱图进行分析进一步发现,Humin是通过脱水聚合生成的呋喃环基聚合物,同时其结构特征与单糖类型紧密相关。

The conversion of mannose and galactose to 5-hydroxymethylfurfural（HMF） was investigated under aqueous conditions at a wide range of temperature（100~200℃）and time（10~240min）without catalyst.The results showed that higher temperature favored the decomposition of hexoses and increased the yield of HMF.At 200℃,the maximum yields of HMF for mannose and galactose were 26.82% and 22.86%,respectively,and their levulinic acid（LA）yields were at a low level below 3%.The lower yield of HMF from galactose because isomerization to tagatose is easier than that to fructose.A reaction model that hexose firstly decomposed to HMF and Humin,followed by the degradation of HMF to LA and Humin,was used to analyze the reaction kinetics.The model predicted the experiment results well.The obtained kinetic parameters revealed the varied mechanisms of HMF and Humin formation from different types of hexose.Finally,structural characterization of the Humins based on the Van Krevelen diagram and FTIR spectra showed that the Humins were furanic polymers formed by dehydration and condensation, and their structure were closely related to monosaccharide types.