水热液化制备5-羟甲基糠醛的碳稳定同位素分馏研究

Carbon Stable Isotope Fractionation of 5-Hydroxymethylfurfural from Hydrothermal Liquefaction

对比了不同碳稳定同位素组成原料在水热液化制备5-羟甲基糠醛(5-HMF)过程中碳稳定同位素分馏特征,研究原料的碳稳定同位素组成对5-HMF产率的影响。结果表明:木薯淀粉水热液化制备的5-HMF的最大产率为33.90%,高于玉米淀粉的29.93%,杨木纤维素(P-C)最大产率为31.00%,高于玉米秸秆纤维素(CS-C)的30.76%,竹粉和杨木的最大产率分别为13.00%和13.80%,高于玉米秸秆和玉米芯(分别为11.60%和12.53%)。在反应时间为15 min时,不同原料的反应速率如下:木薯淀粉0.301 g/(L·min)大于玉米淀粉0.128 g/(L·min),P-C为0.513 g/(L·min)大于CS-C的0.386 g/(L·min),竹粉0.133 g/(L·min)大于杨木0.124 g/(L·min),大于玉米芯0.117 g/(L·min),大于玉米秸秆0.097 g/(L·min)。δ_(^(13)C)值较小的原料(木薯淀粉、P-C、杨木、竹粉)反应过程中的δ_(^(13)C)值在反应初期的变化速率大于δ_(^(13)C)较大的原料(玉米淀粉、CS-C、玉米秸秆和与玉米芯)。水热过程中存在稳定同位素动力学效应,^(13)C同位素较富集的原料参与反应需要的能量更多,反应速率慢,5-HMF的产率低。液化过程中结构简单的原料稳定同位素分馏影响较大;液化程度越大,δ_(^(13)C)的变化程度越大。

In this work, the carbon isotopic fractionation characteristics of feedstocks with different stable carbon isotopic compositions during hydrothermal liquefaction for preparation of 5-hydroxymethylfurfural( 5-HMF) were compared, and the effect of carbon stable isotope composition of raw materials on the yield of 5-HMF was studied. The results showed that the maximum yield of tapioca starch was 33.90%, which is higher than those of corn starch(29.93%), poplar cellulose(P-C,31.00%), and corn straw cellulose(CS-C,30.76%), respectively. The maximum yields of bamboo flour and poplar were 13.00% and 13.80%, which were higher than those of corn straw(11.6%) and corn cob(12.53%), respectively. At the reaction time of 15 min, the reaction rate of different raw materials: tapioca starch 0.301 g/(L·min) was greater than corn starch 0.128 g/(L·min), poplar cellulose 0.513 g/(L·min) was greater than corn straw cellulose 0.386 g/(L·min), and bamboo powder 0.133 g/(L·min) was greater than poplar 0.124 g/(L·min),which was greater than corn cob 0.117 g/(L·min) and greater than corn straw 0.097 g/(L·min). In the reaction process, the change rate of δ_(^(13)C)value of raw materials with smaller δ_(^(13)C)value(cassava starch, poplar cellulose, poplar and bamboo powder) in the initial stage of reaction was greater than that of raw materials with larger δ_(^(13)C)value(corn starch, corn straw cellulose, corn straw and corn cob). There was a stable isotope kinetic effect in the hydrothermal liquefaction process. The^(13)C isotope required more energy to participate than the enriched raw materials in the reaction, the reaction rate was slow, and the yield of 5-HMF was low. In the process of liquefaction, the stable isotope fractionation of raw material with a simple structure has a great influence. The greater degree of liquefaction, the greater degree of change of δ_(^(13)C).