小麦秸秆水热预处理半纤维素降解动力学研究

doi:10.11949/0438-1157.20200053

摘要/Abstract

摘要：

水热预处理是木质纤维素原料高效能源转化的主要工艺流程之一，但是以小麦秸秆为原料的水热预处理的反应路径与反应机理仍有研究不足之处, 制约该预处理过程的优化及实际生产应用。本文以小麦秸秆为研究对象，实验研究了木质纤维素水热预处理过程反应动力学。研究发现，在水热预处理过程中，小麦秸秆的主要降解过程是半纤维素降解产生低聚木糖、木糖以及糠醛的过程，半纤维素在水热过程中几乎完全降解。随着预处理温度的升高，水解液中低聚木糖和木糖的浓度降低，而糠醛的浓度增加；随着保温时间的延长，低聚木糖与木糖的浓度先增加后减小，糠醛的浓度会趋于稳定。根据实验结果提出反应路径并拟合获得动力学速率常数和反应活化能，所获的动力学模型可以很好地解释反应物浓度的变化，与实验数据吻合良好。该模型可以为小麦秸秆水解预处理系统的设计提供参考。

关键词: 小麦秸秆, 水热预处理, 半纤维素, 低聚木糖, 木糖, 糠醛

Abstract:

Hydrothermal pretreatment is one key process for efficient energy conversion of lignocellulose raw materials. However, the reaction path and reaction mechanism of hydrothermal pretreatment using wheat straw as raw materials are still insufficiently studied, limiting the optimization of the pretreatment process and the real-world application. In this paper, wheat straw was used as the research object, and the reaction kinetics of hydrothermal pretreatment of lignocellulose was experimentally studied. It was found that the degradation of hemicellulose to xylooligosaccharide, xylose, and furfural is the main degradation process in the hydrothermal pretreatment process. In addition, the concentration of xylooligosaccharide and xylose in the hydrolysate decreased with the increase of pretreatment temperature, while the concentration of furfural increased. The concentration of xylooligosaccharide and xylose in the hydrolysate first increased and then decreased with the incubation time, and the concentration of furfural tended to be stable with the incubation time. According to the experimental results, a new reaction path was proposed, and the kinetic rate constant and the activation energy of the reaction were obtained. The obtained kinetic model can well explain the changes in the concentration of the reactants, which was in a good agreement with the experimental data. This model can provide guidance for the design of wheat straw hydrolysis pretreatment system.

Key words: wheat straw, hydrothermal pretreatment, hemicellulose, xylooligosaccharides, xylose, furfural

中图分类号:

X 712

张晗,付乾,廖强,夏奡,黄云,朱贤青,朱恂. 小麦秸秆水热预处理半纤维素降解动力学研究[J]. 化工学报, 2020, 71(7): 3098-3105.

Han ZHANG,Qian FU,Qiang LIAO,Ao XIA,Yun HUANG,Xianqing ZHU,Xun ZHU. Study on degradation kinetics of hemicellulose in wheat straw hydrothermal pretreatment[J]. CIESC Journal, 2020, 71(7): 3098-3105.

图/表 6

图1 动力学模型

Fig1 Kinetic model

图2 水热预处理后固体剩余物质量及化学组分含量

Fig.2 Mass and chemical composition of solid residues after hydrothermal pretreatment

图3 水解液中低聚木糖、木糖以及糠醛的浓度

Fig.3 Concentration of xylooligosaccharide, xylose and furfural in hrdrolysate

表1 不同温度下水热预处理过程的动力学速率常数

Table 1 Kinetic rate constants of hydrothermal pretreatment at different temperatures

温度/℃	k₁/min^-1	k₂ /min^-1	k₃ /min^-1	k₄ /min^-1	k₅/min^-1	F_f
180	0.8829	0.0056	0.0775	0.0259	0.01525	0.7207
190	1.4368	0.0116	0.1123	0.0571	0.02	0.7927
200	1.8948	0.0151	0.2779	0.1963	0.0245	0.8668
210	2.2731	0.0207	0.3858	0.3443	0.031	0.8872
220	2.7416	0.0413	0.5124	0.505	0.0497	0.9596

表2 指前因子与反应活化能

Table 2 Frequency factors and activation energy

速率常数	指前因子	活化能/(kJ·mol^-1)	R²
k₁	13.49	50.86	0.946
k₂	17.44	84.95	0.956
k₃	22.23	93.33	0.949
k₄	34.73	144.21	0.959
k₅	9.54	51.83	0.953

图4 lnki和T-1的Arrhenius图

Fig.4 Arrhenius plots of lnkiversusT-1

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