果糖低温快速热解制备5-羟甲基糠醛的机理研究

提出了一种利用果糖低温快速热解制备5-羟甲基糠醛(HMF)并联产糠醛(FF)副产物的方法。通过Py-GC/MS(快速热解-气相色谱/质谱联用)实验,研究果糖快速热解的产物分布特性以及温度对HMF生成的影响。结果表明,HMF是果糖低温快速热解的最主要产物,在350 ℃下可获得最大产率,在250 ℃下可获得最高纯度,相对峰面积含量高达81.2%。此外,通过密度泛函理论计算,研究果糖热解形成HMF的五条可能反应途径。计算结果表明,果糖热解形成HMF的能量最优途径为路径1,即果糖首先发生C2位羟基与C1位氢的脱水,再发生C3位羟基与C1位羟基氢的脱水,最后发生C4位羟基与C5位氢的脱水而形成HMF。

Reaction mechanism of low-temperature fast pyrolysis of fructose to produce 5-hydroxymethyl furfural

Low-temperature fast pyrolysis of fructose offered a promising way to produce 5-hydroxymethyl furfural (HMF) together with furfural (FF) as an important by-product. In this work, pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) measurements were performed to investigate the product distribution from fast pyrolysis of fructose; the effects of pyrolysis temperature on the HMF formation behaviors were considered. The results indicated that HMF is the predominant product from the fast pyrolysis of fructose; the product mixture with highest content of HMF (81.2%, determined by the gas chromatography peak areas) is obtained at 250 ℃, while the maximal yield of HMF is achieved at 350 ℃. Five possible pathways of HMF formation from fructose were considered by density functional theory (DFT). The DFT calculation results suggested that pathway 1 is most energetically favored, i.e. fructose molecule first undergoes a dehydration process by losing -OH at C2 and -H at C1 and then it is subjected to subsequent dehydrations involving -OH at C3 and -H of hydroxyl group at C1 as well as -OH at C4 and -H at C5, to form HMF.