Research progress on lignocellulose pretreatment technology

doi:10.16085/j.issn.1000-6613.2019-0704

Abstract

Abstract:

Fuel ethanol conversion by lignocellulose generally requires raw materials pretreatment, enzymatic hydrolysis and fermentation processes. The efficiency of direct enzymatic hydrolysis of cellulosic biomass is very low due to the complex chemical structure of the lignocellulosic materials. Generally, appropriate pretreatment is necessary before enzymatic hydrolysis is carried out in order to break the dense structure of substrate, increase the surface area of the cellulose and improve the subsequent cellulase accessibility. Based on the analysis of common pretreatment techniques for lignocellulose, this paper focused on three relatively efficient pretreatment techniques: microwave-assisted ionic liquid pretreatment, two-stage deep eutectic solvents pretreatment and FeCl₃ pretreatment. Their strengths and weaknesses were analyzed. Microwave-assisted ionic liquid pretreatment can effectively deconstruct lignin and hemicellulose, destroy the crystalline region of cellulose, and facilitate subsequent enzymatic hydrolysis. However, microwave heating process will decompose ionic liquid and carbonize some substrates, which will reduce the effect of pretreatment. Two-stage DES pretreatment can effectively improve the enzymatic hydrolysis efficiency, but the residual DES in the raw material after pretreatment may inhibit the cellulase and microorganisms in the subsequent reaction. FeCl₃ pretreatment can effectively destroy the ether bond and partial ester bond between lignin and carbohydrate, and remove hemicellulose from the substrate, while less degradation of lignin and cellulose. Finally, the paper prospected the development trend of lignocellulose pretreatment technology.

Key words: lignocellulose, pretreatment, microwave-assisted ionic liquid, two-stage DES, Ferric trichloride

摘要：

木质纤维素转化燃料乙醇一般需要经过原料预处理、酶水解和发酵过程。由于木质纤维原料化学结构复杂、直接酶解效率非常低，一般在酶水解之前需要进行适当的预处理以打破其致密结构，增加纤维表面积，提高后续纤维素酶的可及性。预处理程度直接影响纤维底物后续酶水解的效果。本文在木质纤维素常用预处理技术分析的基础上，重点讨论了3种相对高效的预处理技术：微波辅助离子液体预处理、两阶段深度共熔溶剂（DES）预处理和氯化铁预处理技术，分析了它们的优势、不足及发展现状。文中指出微波辅助离子液体预处理可有效解构木质素和半纤维素，破坏纤维素结晶区域，利于后续酶解，但微波加热过程会使离子液体分解和部分底物碳化。两阶段DES预处理可有效提高酶水解效率，但是预处理后原料中残留的DES可能会对后续反应中纤维素酶和微生物产生抑制作用。氯化铁预处理可有效破坏木质素与碳水化合物间的结合键，脱除底物中的半纤维素，而对木质素和纤维素降解较少，具有很好的发展前景。由于单一预处理技术的局限性，寻求低成本高效的联合预处理技术将是未来重点发展的方向。

关键词: 木质纤维素, 预处理, 微波辅助离子液体, 两阶段深度共熔溶剂, 氯化铁

CLC Number:

Yunqi CAO,Xianli XIE,Zhenqiang GUO,Yanyan WANG,Yunyun LIU,Aimin WU,Yu ZHAO. Research progress on lignocellulose pretreatment technology[J]. Chemical Industry and Engineering Progress, 2020, 39(2): 489-495.

曹运齐,解先利,郭振强,王严严,刘云云,吴蔼民,赵于. 木质纤维素预处理技术研究进展[J]. 化工进展, 2020, 39(2): 489-495.

Figures/Tables 4

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预处理技术	作用机理	优点	缺点
机械粉碎	破坏纤维素结晶结构，降低其结晶度	减小颗粒尺寸，降低结晶度，增加比表面积，提高基质浓度	能耗大，成本高
稀酸预处理	水解纤维素，除去半纤维素	提高半纤维素水解糖得率	腐蚀设备，有抑制物，酸须回收，成本高
碱预处理	破坏组分之间的结合键，分解部分半纤维素，降低纤维素聚合度和结晶度，脱除木质素	润胀纤维素，降低结晶度，提高酶解效率，室温下进行	存在试剂回收、中和、洗涤等问题
水热法	溶出半纤维素，去除部分木质素	增大纤维素与酶的接触面积，无需化学试剂，酶解效率高	水解产物复杂，还原糖得率不高，进料液固比较大
氨爆破	破坏纤维素结构，提高半纤维素降解率	破坏纤维素结晶结构，提高纤维素酶解可及性，抑制物少	氨回收能耗及成本高，难推广
蒸汽爆破	水解半纤维素，增大纤维素孔隙率	预处理时间短，能耗低，无污染，酶解效率高，应用较广泛	产生抑制性产物，洗涤导致多糖得率降低
生物法	除去木质素和部分半纤维素，提高纤维素酶解糖化率	作用条件温和，能耗低，无污染	效率低，预处理时间长，难以实现工业化生产

预处理技术	作用机理	优点	缺点
机械粉碎	破坏纤维素结晶结构，降低其结晶度	减小颗粒尺寸，降低结晶度，增加比表面积，提高基质浓度	能耗大，成本高
稀酸预处理	水解纤维素，除去半纤维素	提高半纤维素水解糖得率	腐蚀设备，有抑制物，酸须回收，成本高
碱预处理	破坏组分之间的结合键，分解部分半纤维素，降低纤维素聚合度和结晶度，脱除木质素	润胀纤维素，降低结晶度，提高酶解效率，室温下进行	存在试剂回收、中和、洗涤等问题
水热法	溶出半纤维素，去除部分木质素	增大纤维素与酶的接触面积，无需化学试剂，酶解效率高	水解产物复杂，还原糖得率不高，进料液固比较大
氨爆破	破坏纤维素结构，提高半纤维素降解率	破坏纤维素结晶结构，提高纤维素酶解可及性，抑制物少	氨回收能耗及成本高，难推广
蒸汽爆破	水解半纤维素，增大纤维素孔隙率	预处理时间短，能耗低，无污染，酶解效率高，应用较广泛	产生抑制性产物，洗涤导致多糖得率降低
生物法	除去木质素和部分半纤维素，提高纤维素酶解糖化率	作用条件温和，能耗低，无污染	效率低，预处理时间长，难以实现工业化生产

DES	纤维素溶解度/%	半纤维素溶解度/%	木质素溶解度/%
CU	3.0	12.5	16.7
CO	2.9	8.6	9.4
MP	2.4	1.8	2.7

DES	纤维素溶解度/%	半纤维素溶解度/%	木质素溶解度/%
CU	3.0	12.5	16.7
CO	2.9	8.6	9.4
MP	2.4	1.8	2.7

预处理	残留物回收率/%	残留物组分质量分数/%			酶解残留物糖产率/%
预处理	残留物回收率/%	纤维素	半纤维素	木质素	葡萄糖	木糖
CU（12h）	72.4	43.7	22.1	13.9	48.4	30.4
MP（12h）	73.9	45.0	22.3	15.7	47.4	22.8
MP-CU（6h）	60.5	54.6	18.1	10.8	52.6	20.1
CU-MP（6h）	65.3	49.8	21.4	14.3	47.7	24.8
CO（4h）	58.2	52.6	1.5	23.7	72.9	4.0
CU（4h）	74.1	43.2	24.5	15.0	47.5	28.0
CO-CU（2h）	54.9	60.7	2.8	17.8	89.8	7.3
CU-CO（2h）	52.1	63.5	3.8	24.2	71.7	7.5
未处理样品	100	35.1	20.6	22.6	24.8	7.9