氯化胆碱类低共熔溶剂对木质纤维素分离及其利用的研究进展

柳静, 王昌梅, 赵兴玲, 吴凯, 尹芳, 杨红, 杨斌, 梁承月, 张无敌

中国农学通报. 2023, 39(33): 156-164

PDF(1175 KB)
PDF(1175 KB)
中国农学通报 ›› 2023, Vol. 39 ›› Issue (33) : 156-164. DOI: 10.11924/j.issn.1000-6850.casb2022-0835
生物质能源

氯化胆碱类低共熔溶剂对木质纤维素分离及其利用的研究进展

作者信息 +

Lignocellulose Separation and Utilization Based on Choline Chloride Eutectic Solvents: A Review

Author information +
History +

摘要

为了去除木质纤维素固有复杂抗性结构,实现木质纤维素原料的高效利用,研究人员不断开发新的木质纤维素预处理技术。低共熔溶剂(Deep Eutectic Solvents, DESs)作为一种绿色溶剂,具有成本低、制备简单、热稳定性好、可设计性等优势,在促进木质纤维素原料预处理、原料酶解转化方面有着较好的应用潜力,得到了研究者们的广泛关注和认可。本研究在查阅国内外研究现状和研究成果的相关报道基础上,综述了氯化胆碱DESs的合成及性质,预处理木质纤维素的作用机理,对木质纤维素酶解效果及转化为生物乙醇的相关研究,指出不同氢键供体、不同的预处理条件对原料的木质素去除率及葡萄糖产量有很大影响,认为DESs预处理木质纤维素极大提高了后续纤维素酶解过程的糖化率,并对DESs预处理机理、循环使用、工艺参数优化方面提出了展望。

Abstract

In order to remove the inherent complex resistance structure of lignocellulose and achieve efficient utilization of lignocellulose, new lignocellulosic pretreatment technologies have been improved continuously. As green solvents, Deep Eutectic Solvents (DESs) have the advantages of low cost, simple preparation, thermal stability, and designability. They have great application potential in promoting the pretreatment of lignocellulose and enzymatic hydrolysis, and have received widespread attention. Based on the analysis and summary of the research status and achievements at home and abroad, the research progress of synthesis and properties of DESs, pretreatment mechanism, enzymatic hydrolysis, and bioethanol conversion were discussed. It was pointed out that different hydrogen bond donors and different pre-treatment conditions had a significant impact on the lignin removal rate and glucose yield. It was believed that pretreatment of lignocellulose with DESs could greatly improve the saccharification rate. Prospects for DESs pretreatment mechanism, recycling, and process parameter optimization were proposed.

关键词

低共熔溶剂 / 木质纤维素 / 酶解 / 生物乙醇

Key words

deep eutectic solvents / lignocellulose / enzymolysis / bioethanol

引用本文

导出引用
柳静 , 王昌梅 , 赵兴玲 , 吴凯 , 尹芳 , 杨红 , 杨斌 , 梁承月 , 张无敌. 氯化胆碱类低共熔溶剂对木质纤维素分离及其利用的研究进展. 中国农学通报. 2023, 39(33): 156-164 https://doi.org/10.11924/j.issn.1000-6850.casb2022-0835
LIU Jing , WANG Changmei , ZHAO Xingling , WU Kai , YIN Fang , YANG Hong , YANG Bin , LIANG Chengyue , ZHANG Wudi. Lignocellulose Separation and Utilization Based on Choline Chloride Eutectic Solvents: A Review. Chinese Agricultural Science Bulletin. 2023, 39(33): 156-164 https://doi.org/10.11924/j.issn.1000-6850.casb2022-0835

0 引言

在能源短缺和环境保护的双重压力下,世界能源格局发生了深刻变革,发展可再生清洁能源已经成为各国学者研究的重点。木质纤维素是自然界中储量最丰富的可再生资源,来源广泛且易获取,然而实际利用率却并不高。木质纤维素既可以转化为能源燃料,也可以进一步加工为各种高附加值产品。构成木质纤维素的三大组分分别是纤维素(35%~50%)、半纤维素(20%~35%)及木质素(10%~30%)[1,2],各组分之间通过共价键和非共价键相互链接,构成了极其复杂的网状结构,难以直接利用。预处理是生物精炼过程中的关键步骤,约占整个生物精炼过程总成本的40%[3]。近年来,科学家们围绕木质纤维素原料的组成成分对其进行处理转化,以求实现高值化利用。其中,纤维素和半纤维素经过转化生成糖类,再经过生物转化得到液体燃料,木质素通过转化为化工产品能应用于不同领域。
围绕木质纤维素的预处理问题,国内外研究人员先后对各种预处理方法进行深入研究,并进行广泛评价,如酸处理法、碱处理法、有机溶剂处理法、离子液体处理法、生物处理法等[4-5],都能够有效将纤维素、半纤维素和木质素三组分进行分离。然而这些方法各有利弊:酸碱预处理法提取出的纤维素纯度高,易于酶解,但容易对设备造成一定程度的损坏,其他组分作为废液处理会污染环境且造成资源浪费;湿法氧化处理会造成半纤维素的大量流失,降低工艺的经济性;有机溶剂预处理条件较为温和,但处理步骤繁琐,存在安全隐患,溶剂难回收等问题;由于离子液体处理法成本高、毒性大、不可回收性和不可生物降解性,其工业化应用受到限制;生物法处理周期长且成本高,难以达到工业化的要求[6]。为实现生物质资源的高值化利用,探究一种绿色高效预处理方法是本领域亟待攻克的技术难题[6]
低共熔溶剂(Deep eutectic solvents,DESs)是一种新型的绿色溶剂,与离子液体相比,具有原料来源广泛、容易制备、低毒性及可生物降解等优势[7]。自ABBOTT[8]等首次合成DESs以来,因其选择性溶解多糖和木质素的特点,被广泛应用于木质纤维素原料分离提取[9-10]。ZHANG等[11]使用氯化胆碱和甘油合成DES预处理玉米芯,木质素去除率达到71.3%。CHEN等[12]使用氯化胆碱/乙二醇预处理柳枝稷,木质素去除率可以达到54%。VALLARI[13]用氯化胆碱分别与丙二酸、甘油、乳酸合成DESs,预处理甘蔗渣。研究表明,氯化胆碱/乳酸对甘蔗渣木质素去除率达到81.6%,酶解糖化效率提高至98.5%。
然而,DESs预处理过程是一个复杂的反应体系,预处理的效果受到许多因素的影响,如DESs的性质、预处理温度、预处理时间等。MASSAYEV[14]用PCA和PLS分析方法研究了影响DESs预处理效果的变量。结果显示,最显著的变量是强度因子、溶剂类型、粒度、搅拌强度和氢键供体。目前,DESs在木质纤维素领域的研究范围逐渐扩大,对于其将生物质资源预处理并有效加工成可持续的生物燃料少有报道。基于目前的研究现状,本研究在概述DESs的性质和预处理机理的基础上,从不同预处理的条件和不同氢键供体方面阐明了DESs预处理对木质纤维素酶解及发酵产乙醇的影响,为木质纤维素的高效利用提供研究方向。

1 DESs的合成及性质

1.1 DESs的合成

低共熔溶剂(DESs)是氢键供体(Hydrogen Bond Donors, HBDs)与氢键受体(Hydrogen Bond Acceptors, HBAs)以固定摩尔比,在一定的温度和环境压力下,通过分子间氢键作用形成的共晶混合物。合成DESs的方法有加热法、研磨法和旋转蒸发法[15]。DESs的一般表达式为Cat+X-zY,其中Cat+表示阳离子基团包括铵、磷或锍阳离子;X-代表路易斯碱,通常是卤素阴离子;Y表示路易斯酸或布朗斯特酸;z表示与阴离子相互作用的分子数量[16]。DESs中使用的氢键供体HBDs(乳酸、甲酸、甘油等)和氢键受体HBA(氯化胆碱,ChCl),能够提供和接受质子,它们之间能够形成氢键[17]。这类DESs容易制备,且绝大多数可生物降解,价格低廉,与咪唑盐类离子液体有相似的理化性质,可以被用来代替离子液体[16]

1.2 DESs的性质

1.2.1 凝固点和熔点

大多DESs的熔点都低于150℃,并低于其单一组分。ABBOTT等[18]认为凝固点主要取决于胆碱盐与氢键供体的晶格能大小、相互结合方式以及其形成液相过程中的熵变。HBAs和HBDs之间氢键的形成促进电荷离域化使得熔点低于单个组分[19]。胆碱类DESs的熔点为固体组分熔化形成DESs时的特定温度,决定了其适用温度的下限。DESs熔点受到HBAs/HBDs摩尔比、HBDs选择、制备方法等的影响。DESs熔点的降低程度与HBDs和HBAs间形成的氢键键能大小密切相关,通过设计合适的HBAs/HBDs摩尔比,可以得到该DESs的最低共熔点[20]

1.2.2 密度

通常,大多数DESs表现出比水更高的密度,并且受温度及其组分结构、比例等情况的影响。温度升高可以增大分子动能和分子间距,提高分子流动性,进而使DESs体积增大,DESs密度得到降低[21]。ZHAO等[22]制备了20组胆碱类DESs,研究发现HBDs中羧基的存在和溶剂中不同程度的氢键提高了DESs的密度。聂文洁[23]运用分子动力学模拟研究了ChCl/乙二醇、ChCl/丙二醇、ChCl/丁二醇溶剂的性质和结构特性,发现密度随着温度呈现线性变化。

1.2.3 黏度

DESs的黏度是工业应用中的关键参数,与常规离子液体相比,胆碱类DESs的黏度比分子流体和高温熔融盐都要大[24],且受温度的影响较大。升高温度可使DESs分子获得足够的动能来克服分子间作用力,实现运动自由,分子间范德华力和氢键相互作用也随之减弱,DESs黏度可以得到降低。DAI等[25-26]发现,当温度从20℃升高至40℃,ChCl/葡萄糖黏度可降低67%。
DESs的高黏度会阻碍热量以及反应过程中的传质,降低预处理过程的效率。DESs具有吸湿性,可以从空气中和木质纤维素材料中吸收水分。YANG等[27]发现ChCl/尿素可以从空气中吸收水分来降低黏度和电化学窗口,SHAUKAT等[28]发现水分的存在会降低DESs的黏度。ABBOTT等[29]采用空穴理论研究ChCl与羧酸形成的DESs时发现,黏度受离子的流动性和空穴效应的影响。DESs各组分间的氢键网络、范德华力、静电作用等也大大降低了溶剂的流动性。研究还发现,添加适量的水能够显著降低DESs的黏度并增大其溶解度[30]。在实际应用中,可以考虑通过优化流动性来降低DESs黏度,如在制备DESs过程中增加水分进行组分调节,可降低反应体系的黏度,优化反应机制,提高反应速率。

1.2.4 电导率

大多数DESs具有弱导电性(常温下<1 mS/cm),DESs的电导率大小与温度有关。将电导率与温度的关系用Arrhenius方程拟合:lnσ = lnσ0-/RT,lnσ随T-1线性降低,即电导率随温度升高而增大[31]。电导率与DESs黏度同样有关。ABBOTT等[18]对电导率和黏度的活化能进行比较,发现ChCl摩尔比在30%~70%时,电导率与黏度的倒数是呈线性相关[19]

1.2.5 极性与pH

DESs的极性对用作工业有机溶剂的环保替代品非常重要。大多数的DESs是极性溶液,具有高极性和氢键接受能力的DESs可以更容易地分解生物质以去除木质素。研究表明,DESs可以通过提供合适的极性来增强预处理过程中的反应活性[32-33]
DESs的酸碱性是非常重要的物理化学性质。DESs中的HBDs和HBAs决定了溶剂的pH值。HAYYAN等[34]以果糖作为HBD,与ChCl合成DESs,研究了HBD对DESs中pH值的影响,发现HBD摩尔比的增加会导致DESs的pH值升高。ABBOTT等[35]证明,向ChCl/甘油混合物中添加氯离子会降低DESs的酸度,并将混合物的pH值变为碱性。此外,DESs的pH值受温度影响较大。随着温度的升高,DESs的pH值线性降低[36]。SKULCOVA等[36]发现醇基DESs的pH值随温度升高缓慢下降,而羧基DESs的pH值温度升高急剧下降。
部分DESs的物理化学性质总结如表1所示。
表1 部分DESs的物理化学性质
DESs 熔点/℃ 黏度/Pa.S 密度/(g/cm3) 表面张力/(mN/N) 电导率/(S/m) 参考文献
ChCl/尿素(1:2) 12 0.75(25℃) 1.25 52.00 0.075(25℃) [37]
ChCl/丙三醇(1:2) -36.15 0.26(25℃) 1.18 -- 0.105(25℃) [37]
ChCl/乙二醇(1:2) -66.01 0.037(25℃) 1.12 48.91 0.761(25℃) [38]
ChCl/1,4-丁二醇(1:3) -32 0.14(25℃) 1.06 47.17 0.164(25℃) [38]
ChCl/草酸(1:1) 34 -- -- -- -- [16]
ChCl/苹果酸(1:1) -- 3.34(25℃) -- 65.68 0.0036 [39,40]
ChCl/乙酰苯 (1:2) -- -- -- 41.86 -- [40]

2 DESs对木质纤维素预处理机理

2012年,FRANCISCO等[41]合成出多种DESs用于加工木质纤维素,首次证实了DESs对木质纤维素类生物质的增溶能力[42]
由于具有较强的氢键形成能力,DESs对木质纤维原料中各组分具有选择性或者优先溶解性,过程相对简单温和[43]。除了破坏连接木质素半纤维素的共价键和连接木质素纤维素的氢键外,DESs对木质素的生物质分馏主要依赖于木质素中芳基醚(C-O键)和碳-碳键(C-C键)的裂解[40]。DESs对木质素有着较强的溶解能力,并且在溶解过程中几乎不破坏木质素的骨架结构,只是在一定程度上使木质素发生降解,生成部分甲氧基[44]。LYNAM等[45]制备了5种DESs(ChCl/甲酸、ChCl/乳酸、ChCl/乙酸、甜菜碱/乳酸、脯氨酸/乳酸)用于溶解碱木质素、木聚糖和纤维素的混合物模拟生物材料,通过测定溶解度(见表2)发现在60℃时就能够溶解木质素,对纤维素和木聚糖几乎不溶解。DESs预处理木质纤维素的效果与预处理时间、预处理温度、HBDs类型的不同而有显著差异,下面对各因素进行讨论。
表2 木质纤维素不同组分在部分DESs中的溶解度
DESs 摩尔比 木质素溶解度/% 木聚糖溶解度/% 纤维素溶解度/% 参考文献
ChCl/甲酸 1:2 14 <1 <1 [45]
ChCl/乳酸 1:10 13 <5 <3
ChCl/乙酸 1:2 12 <1 <1
甜菜碱/乳酸 1:2 9 <1 <1
脯氨酸/乳酸 1:3.3 9 <1 <1

2.1 时间对DESs预处理效果的影响

木质纤维素的预处理效果与预处理时间密切相关。熊龙[46]以构树木粉为原料,在140℃下,采用ChCl/乳酸(摩尔比为1:2)分别经过1、2、3、4 h预处理,处理后纤维素含量明显增加。与未处理组相比,4个时间下的残余物回收率随着处理时间的增加而逐渐降低。可能的原因是乳酸是中强酸,随着处理时间的延长和羧酸基团的剧烈作用,原料发生焦化[11]。解先利[47]等用ChCl/乙醇胺对甘草渣进行预处理,经过不同时间预处理后(1、2、3、4 h),发现半纤维素和木质素在预处理4 h后去除率相对较高。

2.2 温度对DESs预处理效果的影响

根据范特霍夫定律和阿伦尼乌斯(Arrhenius)公式,化学反应的速率会随着温度的变化而变化,进而影响到预处理的效果。酸性和碱性的DESs预处理木质纤维素原料还受到温度的影响。杨宇辰等[48]分别合成了ChCl/草酸、ChCl/甲酸、ChCl/乳酸、ChCl/乙二醇、ChCl/甘油5种DESs体系,对玉米芯进行预处理,研究发现预处理后的固体物质回收率随着反应温度的升高而下降。对于碱性DESs也同样存在这样的现象。Procentese等[49]制备ChCl/尿素(80℃和115℃)和ChCl/咪唑(80、115℃和150℃)两种碱性DESs对玉米芯进行预处理,研究发现木质素去除率随着温度的升高而增加。
熊龙[46]发现随着DESs预处理温度的上升,残余物中纤维素含量由36.31%增加到73.20%,木聚糖含量先降低然后保持在3.83%,而木质素含量降低幅度不大。这是因为在预处理过程中,随着温度升高,反应的速率加快,促进了木质素的去除,加之半纤维素和非结晶区纤维素大分子部分转化为低分子量可溶性产物,导致残渣回收率降低,与LI等[50]的报道结果一致。因此,纤维素纯度越高、残余物的回收率越低成为了一个预处理的普遍现象。
同时,温度升高会影响DESs体系中氢键网路,导致体系中部分分子脱离氢键束缚,进行自由扩散,从而降低DESs体系的黏度,增强DESs溶剂的渗透性[23],从而破坏木质素、半纤维素和纤维素之间形成的复杂氢键网络,溶解生物质的部分木质素、半纤维素和纤维素。GUO等[51]制备了ChCl/甲酸、ChCl/1,4-丁二醇、甜菜碱/乳酸三种DESs,分别在80℃、100℃、120℃进行预处理,研究发现木质素去除率均随温度的升高而增大[52]。但是预处理温度升高,纤维素损失率也会增加。熊龙[46]的研究中发现新随着预处理温度从140 ℃升至180℃,残余物回收率由78.40%下降到30.10%,纤维素损失率由1.36%提高39.32%,木聚糖去除率高达95.18%,当温度为170℃和180℃时,木质素去除率和酶解消化率几乎没有变化,这可能是原料在DESs预处理中多糖的大量损失,反而影响到酶解作用[48]。多名学者的研究也证实了当木质素去除率达到较高程度后,进一步的木质素脱除并不会促进后续酶解作用,并且木质素的全部去除并非是提高酶解消化率的最优途径[53]。此外,也有研究发现随着预处理温度升高,木质素的去除率反而降低。YU等[54]制备的ChCl/甲酸(摩尔比为1:6)用于草药残留物预处理,预处理温度为从100℃增加至120℃时,木质素去除率反而降低。由此可知,木质素的去除效果受DESs的组成成分及其摩尔比、反应条件等多种因素的影响[52]。因此,木质素去除率、酶解效率与预处理温度之间的关系是进一步研究的重点。

2.3 HBDs的选择对预处理效果的影响

在胆碱类DESs中,预处理的效果很大程度上与HBDs的选择有关(见表3)。基于多元醇组成的DESs体系,羟基的数量与木质素去除能力有关。HBDs中羟基越多,DESs木质素去除率就越低。HOU[55]制备不同醇基的DESs对稻草秸秆进行预处理时发现,预处理效率和纤维素酶消化率由高到低依次为:ChCl/乙二醇>ChCl/甘油>ChCl/木糖醇。原因在于更多羟基的存在会形成更强的分子间氢键,其稳定性更强,黏度更高,这需要更多的能量来弱化氢键结构,降低其黏度,从而有利于渗透到木质纤维素中并与之相互作用[25]
表3 不同种类DESs对木质素的分离效果
原料 DESs 摩尔比 预处理条件 木质素去除率/% 参考文献
小麦秸秆 ChCl/单乙醇胺 1:2 90 ℃,12 h 81.0 [59]
小麦秸秆 ChCl/二乙醇胺 1:8 90 ℃,12 h 73.5
小麦秸秆 ChCl/甲基二乙醇胺 1:10 90 ℃,12 h 44.6
小麦秸秆 ChCl/乙酰胺 1:2 90 ℃,12 h 3.4
小麦秸秆 ChCl/尿素 1:2 70 ℃,12 h 76.4
小麦秸秆 ChCl/单乙醇胺 1:6 110 ℃,12 h 87.7
玉米芯 ChCl/尿素 1:2 80 ℃,15 h 40.0 [50]
玉米芯 ChCl/咪唑 3:7 115 ℃,15 h 70.0
玉米芯 ChCl/咪唑 3:7 150 ℃,15 h 88.0
玉米芯 ChCl/咪唑 3:7 120 ℃,4 h 11.1
核桃壳 ChCl/乳酸 1:2 145 ℃,6 h 64.3 [60]
桃核 ChCl/乳酸 1:2 145 ℃,6 h 70.2
油棕空果壳 ChCl/苹果酸 1:1 120 ℃,8 h 22.9 [58]
油棕空果壳 ChCl/柠檬酸 1:1 120 ℃,8 h 20.6
油棕空果壳 ChCl/甲酸 1:2 120 ℃,8 h 61.9
油棕空果壳 ChCl/甲酸 1:5 120 ℃,8 h 25.0
油棕空果壳 ChCl/乙酸 1:2 120 ℃,8 h 28.0
油棕空果壳 ChCl/乙酸 1:5 120 ℃,8 h 40.0
油棕空果壳 ChCl/丙酸 1:2 120 ℃,8 h 20.4
油棕空果壳 ChCl/丁酸 1:2 120 ℃,8 h 14.3
油棕空果壳 ChCl/琥珀酸 2:1 120 ℃,8 h 10.7
玉米芯 ChCl/乙二醇 1:2 90 ℃,24 h 87.6 [11]
玉米芯 ChCl/丙三醇 1:2 90 ℃,24 h 71.3
玉米芯 ChCl/丙三醇/聚乙二醇 1:2:1 60 ℃,2 h 62.9 [61]
稻草 ChCl/乙二醇 1:1 120 ℃,3 h 28.7 [55]
稻草 ChCl/1,2-丙二醇 1:1 120 ℃,3 h 32.9
稻草 ChCl/1,3-丙二醇 1:1 120 ℃,3 h 34.2
杨木 ChCl/乳酸 1:2 170 ℃,4 h 49.2 [62]
ChCl与羧酸组成的DESs体系,木质素去除能力与溶剂pKa值密切相关。DESs组分的pKa值与解离原子的电子位置和质子溶剂化自由能相关,即溶剂中的pKa值代表给出质子能力和溶剂体系内氢键强弱情况[56]。pKa值越低,溶剂的酸性就越强。FRANCISCO[57]的研究发现,由于半纤维素对酸较为敏感,pKa值增大,体系酸度减弱,木聚糖的去除率降低[55]。酸性的DESs体系在去除木聚糖和木质素方面表现出显著的效果,同时还能保证大部分纤维素的完整性[53]。酸性HBDs官能团的选择对于DESs体系也是至关重要的。在酸的官能团方面,TAN[58]研究了官能团类型对木质素提取效果的影响,HBDs中存在的羟基、双键、短烷基链和单羧酸结构有利于木质素的提取。值得探究的是,烷基或吸电子基团的存在也会影响酸基DESs体系的性能。较长烷基链酸构成的DESs体系,由于酸的空间位阻较大,显著减少了生物质与DESs之间的相互作用。
碱基DESs体系主要含有胺和酰胺基团,以此作为HBDs,对木质素的去除率较为显著。同时,木质素去除效果与DESs的碱性强弱也有关,DESs的碱性越强,木质素去除率就越高。赵峥等[59]选用几种不同碱性DESs对小麦秸秆进行预处理,研究发现三种乙醇胺基DESs木质素去除率依次为:ChCl/乙醇胺、ChCl/二乙醇胺、ChCl/甲基二乙醇胺。木质素去除效果与其pH值相对应,当pH值大于10时,木质素的去除效率显著增加。碱性DESs中HBDs中氨基数量也与木质素去除能力有关。HOU等[55]制备不同的酰胺基DESs对稻草秸秆进行预处理,发现DESs的预处理效率和纤维素酶消化率由高到低依次为:ChCl/甲酰胺>ChCl/尿素>ChCl/盐酸胍。可能是由于HBDs中氨基数量越多,在溶剂体系中形成的氢键越多,因此没有足够量的游离和活性基团与生物质各组分相互作用,导致预处理的效果不佳。

3 DESs预处理对纤维素素酶解效果的影响

木质素、半纤维素的存在以及纤维素的结晶情况对酶水解过程有着紧密联系[63]。在酶解过程中,木质素作为阻止纤维素酶水解纤维素的物理屏障。通常,满意的水解性能取决于半纤维素和木质素的有效去除。ZHOU等[64]指出纤维素转化率与木聚糖和木质素的去除率呈正相关(R2>0.77)。通常,含有酸基的DESs在糖化方面比醇解和酰胺基DESs更有优势,能有效提高酶解效率。TIAN等[65]指出,具有双键、羟基、短烷基链和单羧酸结构的DESs在生物质馏分上表现更佳。杨宇辰[48]等发现草酸和甲酸与ChCl组成的DESs溶剂在100℃预处理玉米芯后能获得最高的酶水解率,分别为55.87%和47.54%,乳酸与ChCl组成的DESs预处理玉米芯后酶水解率由80℃的36.90%提高至140℃时的94.11%,葡萄糖回收率也由34.35%提高至85.00%。ZULKEFLI等[66]将氯化物-乙二醇(EAC:EG)用于油棕树干(OPT)纤维预处理,葡萄糖产量为74%。HOU等[55]将ChCl/草酸和ChCl/尿素用于水稻秸秆纤维预处理,葡萄糖产量达到90.2%。杨露敏[67]以甘蔗渣为原料进行DESs预处理,发现ChCl和草酸的组合木聚糖去除率最高,达到93.9%;ChCl和乳酸组合的DES木质素去除效果最好达到83.6%。
由于酶在多元醇基DESs中显示出优异的稳定性,具有多元醇基DESs在生物质回收糖能力方面具有较好潜力。PROCENTESE等[68]使用ChCl/甘油和ChCl/乙二醇预处理农业食品废物,结果表明,从食品废物中可获得大约217kt/年的总可发酵糖。虽然多元醇基DESs在糖化方面表现优异,然而由于缺乏酸度,在木质素和木聚糖去除效果上低于酸基DESs。因此,部分研究学者采取将醇基的DESs与酸结合后来提高其性能。GUO等[69]使用ChCl/甘油与硅钨酸辅助预处理奇岗,其中酶解效率可达到97.3%,在12 h内葡萄糖产率为80%。值得注意的是,单独使用ChCl/甘油时仅去除1.6%的木质素和5.3%的木聚糖,而引入杂多酸后,木质素和木聚糖的去除率显著提高,分别上升至89.5%和58.5%。CHEN等[70]通过酸化含水DES(ChCl/甘油,含0.9%H2SO4)将柳枝稷分馏成木质素、富含木糖的预处理水解物和富含纤维素的纸浆,其中富含纤维素的纸浆酶水解可实现89%的葡萄糖产率。
为降低生产成本,在工业化生产中若采用预处理后直接进行酶解,需要评估纤维素酶对DESs溶剂的适应性。GUNNY等[71]合成了ChCl/甘油、ChCl/乙二醇、ChCl/丙二酸三种DESs用于评价纤维素酶的稳定性,结果显示在10%(v/v)的ChCl/甘油和ChCl/乙二醇酶解体系中,纤维素酶活能够保持其90%以上的活性,而在含有丙二酸的DES的24 h内,活性降低了60%。WAHLSTROM等[72]比较了三种里氏木霉纤维素酶(纤维素二糖水解酶Cel7A、纤维素内切酶Cel5A和Cel7B)以及一种里氏木霉木聚糖酶Xyn11在3种高浓度DESs溶液中的稳定性,发现ChCl/甘油(1:1)对纤维素酶具有高度稳定性,酶的活性变化较小,但预处理效率有限。王冬梅[73]观察了ChCl/甲酸残留量对纤维素酶活性的影响,当残留量低于2%时,糖化6 h纤维素酶活性不受影响。KUMAR等[74]研究了ChCl/甘油、ChCl/1,2-丙二醇、ChCl/乙二醇等DESs对纤维素酶活性影响,发现在高浓度下(DESs添加量为30%),对纤维素酶活性无明显抑制。在ChCl/甘油、ChCl/1,2-丙二醇添加量为10%的浓度体系中,对克拉维孢菌NRRL Y-50464的生长速率、糖消耗和乙醇生产没有影响,而10%(v/v)的ChCl/乙二醇抑制并延迟了微生物的细胞生长。
这些研究表明一些DESs对纤维素酶活性的影响较小,且与纤维素酶具有良好的相容性,生物质预处理糖化一步法工艺是可行的,可在一定程度上控制生产成本。为了更好地利用DESs,还需进行纤维素酶对DESs的耐受限度、抑制机理方面开展进一步深入研究。

4 DESs预处理对乙醇产量的影响

利用木质纤维素原料生产乙醇最早是1910年由Heinerch等[75]通过酸水解木材和发酵得到的,至今已有上百年的时间。目前,常规的木质纤维素生产乙醇的工艺包括原料预处理、酶水解、乙醇发酵和分离提纯等步骤。经 DESs预处理后的木质纤维素对生物发酵过程并无明显的抑制作用,然而利用DESs预处理后的木质纤维素为原料进行乙醇生产的研究并不多。
GUO等[69]利用ChCl/甘油预处理的奇岗进行半同步糖化发酵,获得了81.8%的乙醇产率,发酵效率高达97.3%,是未预处理的8倍。KUMAR等[74]使用ChCl/甘油预处理后的稻草进行水解发酵,可获得226.7 g/L的最大还原糖,并且还原糖可以有效的发酵成乙醇。
近年来,也有研究人员将利用预处理后的木质纤维素生产丁醇,也获得较好的成果。CHEN等[76]利用乙二醇/ChCl体系在酸性条件下预处理柳枝稷,葡萄糖产率达到86.2%,经过芽孢杆菌发酵后2,3-丁二醇产量为90.2 g/L。XU[77]等利用ChCl/甲酸体系对玉米秸秆进行预处理,半纤维素和木质素的脱除率分别为66. 2%、23.8%,酶解后葡萄糖产率达到99%,发酵所得丁醇浓度为5.63 g/L。这些研究成果证明了从木质素纤维素原料制备生物燃料过程中,DESs预处理木质纤素是一种有前景的工艺技术。

5 展望

DESs凭借其独特的物化性质,在处理木质纤维素方面展现了独特的优势,不仅被成功应用于生物质组分分离,还推动木质纤维素转化为生物燃料[78]。但目前DESs的研究与应用尚处于初级阶段,其工业化利用还需突破以下几个方面的问题。
(1)DESs研究机理方面,前期的研究主要集中在DESs组成成分对预处理机理及效果的影响,还需对DESs理化性质方面(如黏度、电导率、密度、表面张力等)进行探究,为DESs的实际应用提供理论指导。
(2)基于DESs的可设计性理念,辅助分子模拟手段,设计针对不同来源的木质纤维素DESs,以提高目标产物得率。
(3)进一步研究DESs的可回收性和再利用性。开发DESs回收新技术工艺,提高回收利用率,降低产业化成本。溶剂的可回收性和重复使用性决定了DESs预处理生物质的工艺可行性。
(4)预处理条件进一步优化。通过探究预处理条件(如DESs用量、时间、温度)与纤维素酶的协同效应,减少纤维素酶的使用,降低生产成本。在生物质精炼工艺中,预处理阶段约占总成本的40%,其中水解阶段为整个工艺带来较大成本,如果纤维素酶可以实现回收或者再利用,可以大大降低生产成本。
随着研究的不断深入,DESs在木质纤维素原料预处理方面会逐步实现高效化、低能耗。通过充分利用DESs预处理技术的优势,探索生物质原料可持续转化为生物燃料或更多种类的高附加值产品,降低成本,提高生产工艺的经济可行性,减少对化石燃料的依赖。

参考文献

[1]
AGRAWAL R, VERMA A K, SATLEWAL A, et al. Application of nanoparticle-immobilized thermostable beta-glucosidase for improving the sugarcane juice properties[J]. Innovative food science & emerging technologies, 2016, 33:472-482.
[2]
WANG Y T, FAN C F, HU H Z, et al. Genetic modification of plant cell walls to enhance biomass yield and biofuel production in bioenergy crops[J]. Biotechnology advances, 2016, 34(5):997-1017.
Plant cell walls represent an enormous biomass resource for the generation of biofuels and chemicals. As lignocellulose property principally determines biomass recalcitrance, the genetic modification of plant cell walls has been posed as a powerful solution. Here, we review recent progress in understanding the effects of distinct cell wall polymers (cellulose, hemicelluloses, lignin, pectin, wall proteins) on the enzymatic digestibility of biomass under various physical and chemical pretreatments in herbaceous grasses, major agronomic crops and fast-growing trees. We also compare the main factors of wall polymer features, including cellulose crystallinity (CrI), hemicellulosic Xyl/Ara ratio, monolignol proportion and uronic acid level. Furthermore, the review presents the main gene candidates, such as CesA, GH9, GH10, GT61, GT43 etc., for potential genetic cell wall modification towards enhancing both biomass yield and enzymatic saccharification in genetic mutants and transgenic plants. Regarding cell wall modification, it proposes a novel groove-like cell wall model that highlights to increase amorphous regions (density and depth) of the native cellulose microfibrils, providing a general strategy for bioenergy crop breeding and biofuel processing technology.Copyright © 2016 Elsevier Inc. All rights reserved.
[3]
HALDAR D, PURKAIT M K. A review on the environment-friendly emerging techniques for pretreatment of lignocellulosic biomass: mechanistic insight and advancements[J]. Chemosphere, 264(Part2):128523.
[4]
YAO F P, TIAN D, SHEN F, et al. Recycling solvent system in phosphoric acid plus hydrogen peroxide pretreatment towards a more sustainable lignocellulose biorefinery for bioethanol[J]. Bioresource technology, 2019, 275:19-26.
Pretreating lignocellulosic biomass by phosphoric acid plus hydrogen peroxide (PHP) was integrated with recovering concentrated phosphoric acid (CPA), lignin, and treating phosphorus (P) wastewater. Results indicated no significant effects on cellulose recovery was observed by promoting ethanol addition, but CPA and lignin recovery were improved to 80.0% and 23.3%, respectively. Increasing water addition did not greatly affect CPA recovery (80.0-80.4%), and lignin recovery (22.8-23.6%). Consequently, the ratio of 11:1 (ethanol/PHP solution) and 4:1 (water/de-ethanol liquor) were suggested for solid/liquid separation and lignin precipitation. Average 86.0% CPA was recycled for pretreatment (≥11 runs) with average 96.3% cellulose-glucose conversion. A specially-developed biochar from crab shell was efficient on P removal with maximal adsorption capacity of 261.6 mg/g. Pretreating 1.0 kg wheat straw by 1.1 kg CPA harvested 155.0 g ethanol, 45.0 g high purity lignin and 4.9 kg P-rich biochar fertilizer. Recovering CPA, biochar-fertilizer and lignin, and P wastewater treatment made PHP pretreatment towards more sustainable and cleaner.Copyright © 2018 Elsevier Ltd. All rights reserved.
[5]
ZHANG K, PEI Z J, WANG D H. Organic solvent pretreatment of lignocellulosic biomass for biofuels and biochemicals: a review[J]. Bioresource technology, 2016, 199:21-33.
Lignocellulosic biomass represents the largest potential volume and lowest cost for biofuel and biochemical production. Pretreatment is an essential component of biomass conversion process, affecting a majority of downstream processes, including enzymatic hydrolysis, fermentation, and final product separation. Organic solvent pretreatment is recognized as an emerging way ahead because of its inherent advantages, such as the ability to fractionate lignocellulosic biomass into cellulose, lignin, and hemicellulose components with high purity, as well as easy solvent recovery and solvent reuse. Objectives of this review were to update and extend previous works on pretreatment of lignocellulosic biomass for biofuels and biochemicals using organic solvents, especially on ethanol, methanol, ethylene glycol, glycerol, acetic acid, and formic acid. Perspectives and recommendations were given to fully describe implementation of proper organic solvent pretreatment for future research. Copyright © 2015 Elsevier Ltd. All rights reserved.
[6]
余燕燕, 李以琳, 楼雨寒, 等. 低共熔溶剂解离木纤维时木质素缩合对纤维素酶解的影响[J]. 林业工程报 2021, 6(6):101-108.
[7]
张斌斌. NADES预处理对水稻秸秆酶解效果及机制的研究[D]. 湘潭: 湘潭大学, 2019.
[8]
ABBOTT A P, CAPPER G, DAVIES D L, et al. Novel solvent properties of choline chloride/urea mixtures[J]. Chemical Communications, 2003, 1:70-71.
[9]
李利芬, 吴志刚, 梁坚坤, 等. 共熔溶剂在木质纤维类生物质研究中的应用[J]. 林业工程学报, 2020, 5(4):20-28.
[10]
董艳梅, 安艳霞, 马阳阳, 等. 深度共熔溶剂预处理木质纤维素生物质研究进展[J]. 化工进展, 2021, 40(3):1594-1603.
木质纤维素生物质转化为生物燃料或化工产品一般需经历预处理、酶解及发酵过程,因其复杂的化学结构,在酶解前通常进行预处理以破坏其致密结构,提高酶与纤维素的可及性。深度共熔溶剂(DES)是一类新型的“绿色”溶剂,具有制备简单、价格低廉、性质可调、可生物降解、可循环使用等优势,可有效去除木质素组分,同时保留大部分纤维素,在生物质预处理方面具有巨大的潜力。本文介绍了DES的构成、分类及理化性质,总结了DES预处理对生物质组分的影响,并对预处理效果的影响因素如底物和DES的类型、溶剂黏度、温度、生物载量、微波及超声波辅助工艺和两阶段处理工艺等方面进行分析,探讨了DES和生物的相容性,最后针对DES存在的问题及缺点,提出了理性设计和大规模利用DES的机遇与挑战,本文可为实现生物质的低成本预处理和高价值利用提供新的思路。
[11]
ZHANG C W, XIA S Q, MA P S. Facile pretreatment of lignocellulosic biomass using deep eutectic solvents[J]. Bioresource Technology, 2016, 219:1-5.
[12]
CHEN Z, BAI X, LUSI A, et al. High-solid lignocellulose processing enabled by natural deep eutectic solvent for lignin extraction and industrially relevant production of renewable chemicals[J]. Acs sustainable chemistry & engineering, 2018, 6(9):12205-12216.
[13]
CHOURASIA VR, PANDEY A, PANT KK, et al. Improving enzymatic digestibility of sugarcane bagasse from different varieties of sugarcane using deep eutectic solvent pretreatment[J]. Bioresource technology, 2021, 337:125480.
[14]
SALIM M, LEE K M. Evaluation of deep eutectic solvent pretreatment towards efficacy of enzymatic saccharification using multivariate analysis techniques[J]. Journal of cleaner production, 2022, 360:132239.
[15]
赵冰怡. 深度共熔溶剂的制备、性质及其应用于芦丁萃取的研究[D]. 广州: 华南理工大学, 2016.
[16]
SMITH E L, ABBOTT A P, RYDER K S. Deep eutectic solvents (DESs) and their applications[J]. Chemical reviews, 2014, 114(21):11060-11082.
[17]
竹源, 齐本坤, 梁欣泉, 等. 有机酸及多元醇类低共熔溶剂预处理木质纤维素研究进展[J]. 应用化工, 2021, 50(10):2786-2796.
[18]
ABBOTT A P, CAPPER G, DAVIES D L, et al. Preparation of novel, moisture-stable, Lewis-acidic ionic liquids containing quaternary ammonium salts with functional side chains[J]. Chemical communications, 2001, 19:2010-2011.
[19]
张盈盈, 陆小华, 冯新, 等. 胆碱类低共熔溶剂的物性及应用[J]. 化学进展, 2013, 25(6):881-892.
[20]
谢宜彤, 郭鑫, 吕艳娜. 低共熔溶剂在木质纤维原料溶解及其组分分离中的研究进展[J]. 林产化学与工业, 2019, 39(5):11-18.
[21]
GARCIA G, APARICIO S, ULLAH R, et al. Deep eutectic solvents: physicochemical properties and gas separation applications[J]. Energy & fuels, 2015, 29(4):2616-2644.
[22]
ZHAO B Y, XU P, YANG F X, et al. Biocompatible deep eutectic solvents based on choline chloride: characterization and application to the extraction of rutin from sophora japonica[J]. ACS Sustainable chemistry & engineering, 2015, 3(11):2746-2755.
[23]
聂文洁, 王剑飞, 赵贯甲, 等. 氯化胆碱类低共熔溶剂结构与性质的分子动力学研究[J]. 四川大学学报(自然科学版), 2022, 59(3):1-9.
[24]
ABBOTT A P, CAPPER G, DAVIES D L, et al. Ionic liquid analogues formed from hydrated metal salts[J]. Chemistry-a european journal, 2004, 10:3769-3774.
A dark green, viscous liquid can be formed by mixing choline chloride with chromium(III) chloride hexahydrate and the physical properties are characteristic of an ionic liquid. The eutectic composition is found to be 1:2 choline chloride/chromium chloride. The viscosity and conductivity are measured as a function of temperature and composition and explained in terms of the ion size and liquid void volume. The electrochemical response of the ionic liquid is also characterised and it is shown that chromium can be electrodeposited efficiently to yield a crack-free deposit. This approach could circumvent the use of chromic acid for chromium electroplating, which would be a major environmental benefit. This method of using hydrated metal salts to form ionic liquids is shown to be valid for a variety of other salt mixtures with choline chloride.
[25]
DAI Y T, VAN SPRONSEN J, WITKAMP G J, et al. Natural deep eutectic solvents as new potential media for green technology[J]. Analytica chimica acta, 2013, 766(5):61-68.
[26]
DAI Y T, WITKAMP G J, VERPOORTE R, et al. Tailoring properties of natural deep eutectic solvents with water to facilitate their applications[J]. Food chemistry, 2015, 187(15):14-19.
[27]
DU C L, ZHAO B Y, CHEN X B, et al. Effect of water presence on choline chloride-2urea ionic liquid and coating platings from the hydrated ionic liquid[J]. Scientific reports, 2016, 6:1-14.
Krabbe disease (KD) is a neurodegenerative disorder caused by the lack of β- galactosylceramidase enzymatic activity and by widespread accumulation of the cytotoxic galactosyl-sphingosine in neuronal, myelinating and endothelial cells. Despite the wide use of Twitcher mice as experimental model for KD, the ultrastructure of this model is partial and mainly addressing peripheral nerves. More details are requested to elucidate the basis of the motor defects, which are the first to appear during KD onset. Here we use transmission electron microscopy (TEM) to focus on the alterations produced by KD in the lower motor system at postnatal day 15 (P15), a nearly asymptomatic stage, and in the juvenile P30 mouse. We find mild effects on motorneuron soma, severe ones on sciatic nerves and very severe effects on nerve terminals and neuromuscular junctions at P30, with peripheral damage being already detectable at P15. Finally, we find that the gastrocnemius muscle undergoes atrophy and structural changes that are independent of denervation at P15. Our data further characterize the ultrastructural analysis of the KD mouse model, and support recent theories of a dying-back mechanism for neuronal degeneration, which is independent of demyelination.
[28]
SHAUKAT S, BUCHNER R. Densities, viscosities [from (278.15 to 318.15) K], and electrical conductivities (at 298.15 K) of aqueous solutions of Choline Chloride and Chloro-Choline Chloride[J]. Jouranal of chemical and engineering date, 2011, 56(12):4944-4949.
[29]
ABBOTT A P, HARRIS R C, RYDER K S. Application of hole theory to define ionic liquids by their transport properties[J]. Journal of Physical Chemistry B, 2007, 111(18):4910-4913.
[30]
张盈盈, 陆小华, 冯新, 等. 胆碱类低共熔溶剂的物性及应用[J]. 化学进展, 2013, 25(6):882-893.
[31]
张欢欢, 刘玉婷, 李戎, 等. 新型低共熔溶剂的制备、表征及物性研究[J]. 化学通报, 2015, 78(1):73-79.
[32]
OMAR K A, SADEGHI R. Physicochemical properties of deep eutectic solvents: a review[J]. Journal of molecular liquids, 2022, 360(15):119524.
[33]
PANDEY A, MANKAR A R, AHMAD E. Deep eutectic solvents: a greener approach towards biorefineries[M]. Biomass, biofuels, biochemicals, Elsevier, 2021:193-219.
[34]
HAYYAN A, MJALLI F S, AINASHEF I M. Fruit sugar-based deep eutectic solvents and their physical properties[J]. Thermochimica acta, 2012, 541(10):70-75.
[35]
ABBOTT A P, ALABDULLAH S S M, AL-MURSHEDI A Y M. Brønsted acidity in deep eutectic solvents and ionic liquids[J]. Faraday discuss, 2018, 206:365-377.
Despite the importance of ionic liquids in a variety of fields, little is understood about the behaviour of protons in these media. The main difficulty arises due to the unknown activity of protons in non-aqueous solvents. This study presents acid dissociation constants for nine organic acids in deep eutectic solvents (DESs) using standard pH indicator solutes. The pK value for bromophenol blue was found by titrating the DES with triflic acid. The experimental method was developed to understand the acid-base properties of deep eutectic solvents, and through this study it was found that the organic acids studied were slightly less dissociated in the DES than in water with pK values between 0.2 and 0.5 higher. pK values were also determined for two ionic liquids, [Bmim][BF] and [Emim][acetate]. The anion of the ionic liquid changes the pH of the solution by acting as a buffer. [Emim][acetate] was found to be more basic than water. It is also shown that water significantly affects the pH of ionic liquids. This is thought to arise because aqueous mixtures with ionic liquids form heterogeneous solutions and the proton partitions into the aqueous phase. This study also attempted to develop an electrochemical pH sensor. It was shown that a linear response of cell potential vs. ln a could be obtained but the slope for the correlation was less than that obtained in aqueous solutions. Finally it was shown that the liquid junction potential between two reference electrodes immersed in different DESs was dependent upon the pH difference between the liquids.
[36]
SKULCOVA A, RUSS A, JABLONSKY M., et al. The pH behavior of seventeen deep eutectic solvents[J]. Bioresources, 2018, 13:5042-5051.
[37]
ABO-HAMAD A M. HAYYAN, ALSAADI M A, et al. Potential applications of deep eutectic solvents in nanotechnology[J]. Chemical engineering journal, 2015, 273:551-567.
[38]
TANG B, ROW K H. Recent developments in deep eutectic solvents in chemical sciences[J]. Monatshefte für chemie - chemical monthly, 2013, 144(10):1427-1454.
[39]
FRANK E, DOUGLAS M, ABBOTT A P. Electrodeposition from ionic liquids || physical properties of ionic liquids for electrochemical applications[M]. Weinheim: Wiley-VCH, 2008:83-123.
[40]
ABBOTT A P, BOOTHBY D, CAPPER G, et al. Deep dutectic solvents formed between choline chloride and carboxylic acids:  versatile alternatives to ionic liquids[J]. Journal of the american chemical society, 2004, 126(29):9142-9147.
[41]
FRANCISCO M, BRUINHORST AVD, KROON M C. New natural and renewable low transition temperature mixtures (LTTMs): screening as solvents for lignocellulosic biomass processing[J]. The royal society of chemistry, 2012, 14:2153-2157.
[42]
刘仲洋, 谭丽萍, 刘同军. 低共熔溶剂体系促进木质纤维素酶解效率的研究进展[J]. 齐鲁工业大学学报, 2020, 34(2):5-12.
[43]
陈子澍, 赵子暄, 张绍蒙, 等. 季铵盐/酰胺类低共熔溶剂的制备及其对纤维素的溶解性能[J]. 林产化学与工业, 2018, 38(5):3-99.
[44]
张成武. 低共熔溶剂预处理木质纤维素的研究[D]. 天津: 天津大学, 2016.
[45]
LYNAM J G, KUMAR N, WONG M J. Deep eutectic solvents’ ability to solubilize lignin, cellulose, and hemicellulose; thermal stability; and density[J]. Bioresource technology, 2017, 238:684-689.
[46]
熊龙. 低共熔溶剂预处理中木质素结构的变化及对纤维素酶影响的研究[D]. 武汉: 湖北工业大学, 2021.
[47]
解先利, 刘云云, 余强, 等. 低共熔溶剂预处理提高甘草渣酶解效果优化[J]. 化工进展, 2022, 41(3):1349-1356.
近年来,低共熔溶剂(deep eutectic solvent,DES)以易制备、成本低、易回收等优势,在生物质预处理方面受到广泛关注。本研究以氯化胆碱为氢键受体,乙醇胺为氢键供体,合成DES,研究了不同温度、时间和固液比预处理条件对中药渣组分和酶解效果的影响。结果表明:固液比1∶20、120℃、预处理4h后原料中木质素去除率达到78.42%,纤维素回收率为83.89%。随后对不同条件下所得底物进行酶水解,反应96h后发现,较优条件下所得底物酶解效率为78.57%,较未处理中药渣(30.40%)提高了1.58倍。类分形动力学分析表明,预处理温度对酶解效果影响最大。SEM、XRD和FTIR检测发现,预处理后底物形貌、结晶指数和官能团变化有利于酶解效果的提高。
[48]
杨宇辰, 鄢贵龙, 杨依晶, 等. 氯化胆碱类低共熔溶剂处理对玉米芯的影响[J]. 食品工业, 2022, 43(1):194-198.
[49]
PROCENTESE A, JOHNSON E, ORR V, et al. Deep eutectic solvent pretreatment and subsequent saccharification of corncob[J], Bioresource technology, 2015, 192:31-36.
Ionic liquid (ILs) pretreatment of lignocellulosic biomass has attracted broad scientific interest, despite high costs, possible toxicity and energy intensive recycling. An alternative group of ionic solvents with similar physicochemical properties are deep eutectic solvents (DESs). Corncob residues were pretreated with three different DES systems: choline chloride and glycerol, choline chloride and imidazole, choline chloride and urea. The pretreated biomass was characterised in terms of lignin content, sugars concentration, enzymatic digestibility and crystallinity index. A reduction of lignin and hemicellulose content resulted in increased crystallinity of the pretreated biomass while the crystallinity of the cellulose fraction could be reduced, depending on DES system and operating conditions. The subsequent enzymatic saccharification was enhanced in terms of rate and extent. A total of 41 g fermentable sugars (27 g glucose and 14 g xylose) could be recovered from 100g corncob, representing 76% (86% and 63%) of the initially available carbohydrates.Copyright © 2015 Elsevier Ltd. All rights reserved.
[50]
LI L F, YU L P, WU Z G, et al. Delignification of poplar wood with lactic acid-based deep eutectic solvents[J]. Wood research, 2019, 64(3):507-522.
[51]
Guo Z W, LING Z, WANG C, et al. Integration of facile deep eutectic solvents pretreatment for enhanced enzymatic hydrolysis and lignin valorization from industrial xylose residue[J]. Bioresource technology, 2018, 265:334-339.
In this study, a novel biomass pretreatment process using three kinds of deep eutectic solvents (DESs) was developed to improve saccharification efficiency and lignin valorization. The major components of xylose residue including cellulose and lignin fractions were released, recovered and utilized. Pretreatment with betaine/lactic acid system at 120 °C for 2 h was found to be the optimal conditions with prominently increased enzymatic digestibility (from 55.3% to 96.8%). The efficient conversion was mainly ascribed to the significant delignification efficiency of 81.6% after betaine/lactic acid pretreatment, which caused incompact structure and corrosive surface of treated xylose residue. The recoverable lignin had high purity, low molecular weight (630-2040 g/mol) and polydispersity (1.07-1.76). Based on the comprehensive analysis, the one-pot DESs system provides us a facile and effective approach for whole components valorization of lignocellulosic materials.Copyright © 2018 Elsevier Ltd. All rights reserved.
[52]
陈鑫东, 熊莲, 黎海龙, 等. 低共熔溶剂在木质纤维素预处理促进酶水解效率的研究进展[J]. 新能源进展, 2019, 7(5):415-422.
[53]
KISHIMOTO T, URKI Y, UBUKATA M. Easy synthesis of β-O-4 type lignin related polymers[J]. Organic biomolecular chemistry, 2005, 3(6):1067-1073.
[54]
YU Q, ZHANG A, WANG W, et al. Deep eutectic solvents from hemicellulose-derived acids for the cellulosic ethanol refining of Akebia' herbal residues[J]. Bioresource technology, 2018, 247:705-710.
Here, the potential use of herbal residues of Akebia as feedstock for ethanol production is evaluated. Additionally, five deep eutectic solvents from hemicellulose-derived acids were prepared to overcome biomass recalcitrance. Reaction temperatures had more significant influences on solid loss and chemical composition than the molar ratios of choline chloride (ChCl) to derived acids. Glycolic acid resulted in the maximum levels of lignin, xylan and glucan removal, which were 60.0%, 100% and 71.5%, respectively, at 120°C with a 1:6M ratio of ChCl-glycolic acid. In contrast, ChCl-formic acid resulted in the greatest level of glucan retention, at 97.8%, with a lignin removal rate of 40.7% under the same pretreatment conditions. Moreover, ChCl loading could significantly enhance the selectivity of carboxylic acid for lignin dissolution. A 98.0% level of subsequent enzymatic saccharification and a 100% ethanol yield were achieved after ChCl-formic acid pretreatments of Akebia' herbal residues.Copyright © 2017 Elsevier Ltd. All rights reserved.
[55]
HOU X D, LI A L, LIN K P, et al. Insight into the structure-function relationships of deep eutectic solvents during rice straw pretreatment[J]. Bioresource technology, 2018, 247:261-267.
[56]
GROSS K C, SEYBOLD P G, HADAD C M. Comparison of different atomic charge schemes for predicting pKa variations in substituted anilines and phenols[J]. International journal of quantum chemistry, 2002, 90(1):445-458.
[57]
FRANCISCO M, VAN DEN BRUINHORSTA A, KROON M C. Low-transition-temperature mixtures (LTTMs): a new generation of designer solvents[J]. Angewandte chemie -international edition, 2013, 52(11):3074-3085.
[58]
TAN Y T, NGOH G C, CHUA A S M. Effect of functional groups in acid constituent of deep eutectic solvent for extraction of reactive lignin[J]. Bioresource technology, 2019, 281:359-366.
In this study, acidic deep eutectic solvents (DES) synthesized from various organic carboxylic acid hydrogen bond donors were applied to lignocellulosic oil palm empty fruit bunch (EFB) pretreatment. The influence of functional group types on acid and their molar ratios with hydrogen bond acceptor on lignin extraction were evaluated. The result showed presence of hydroxyl group and short alkyl chain enhanced biomass fractionation and lignin extraction. Choline chloride:lactic acid (CC-LA) with the ratio of 1:15 and choline chloride:formic acid (CC-FA) with 1:2 ratio extracted more than 60 wt% of lignin. CC-LA DES-extracted lignin (DEEL) exhibited comparable reactivity with technical and commercial lignin based on its phenolic hydroxyl content (3.33-3.72 mmol/g). Also, the DES-pretreated EFB comprised of enriched glucan content after biopolymer fractionation. Both DES-pretreated EFB and DEEL can be potential feedstock for subsequent conversion processes. This study presented DES as an effective and facile pretreatment method for reactive lignin extraction.Copyright © 2019. Published by Elsevier Ltd.
[59]
ZHAO Z, CHEN X Y, ALI M F, et al. Pretreatment of wheat straw using basic ethanolamine-based deep eutectic solvents for improving enzymatichydrolysis[J]. Bioresource technology, 2018, 263:325-333.
[60]
ZHANG K, SUN Q, WEI L, et al. Characterization of lignin streams during ionic liquid/hydrochloric acid/formaldehyde pretreatment of corn stalk[J]. Bioresource technology, 2021, 331:125064.
[61]
XUE B, YANG Y, TANG R. Efficient dissolution of lignin in novel ternary deep eutectic solvents and its application in polyurethane[J]. International journal of biological macromolecules, 2020, 164(1):480-488.
[62]
周敏姑, 郭英杰, 郝子越, 等. 氯化胆碱-乳酸低共熔溶剂预处理对杨木酶水解特性的影响[J]. 西北农林科技大学学报(自然科学版), 2020, 48(12):55-63.
[63]
OH Y, PARK S, JUNG D, et al. Effect of hydrogen bond donor on the choline chloride-based deep eutectic solvent-mediated extraction of lignin from pine wood[J]. International journal of biological macromolecules, 2020, 165,Part A(15):187-197.
[64]
ZHOU X L, HUANG T J, LIU J, et al. Recyclable deep eutectic solvent coupling sodium hydroxide post-treatment for boosting woody/herbaceous biomass conversion at mild condition[J]. Bioresource technology, 2021, 320(Part A):124327.
[65]
TIAN D, CHANDRA R P, LEE J S, et al. A comparison of various lignin-extraction methods to enhance the accessibility and ease of enzymatic hydrolysis of the cellulosic component of steam-pretreated poplar[J]. Biotechenology for biofuels, 2017, 10:157.
[66]
ZULKEFLI S, ABDULMALEK E, ABDUL RAHMAN M B. Pretreatment of oil palm trunk in deep eutectic solvent and optimization of enzymatic hydrolysis of pretreated oil palm trunk[J]. Renewable energy, 2017, 107:36-41.
[67]
杨露敏. 深度共熔溶剂结构性质对甘蔗渣预处理效率的影响研究[D]. 广州: 广州工业大学, 2020.
[68]
PROCENTESE A, RAGANATI F, OLIVIERI G, et al. Deep Eutectic solvents pretreatment of agro-industrial food waste[J]. Biotechnology for biofuels, 2018, 11:37.
Background: Waste biomass from agro-food industries are a reliable and readily exploitable resource. From the circular economy point of view, direct residues from these industries exploited for production of fuel/chemicals is a winning issue, because it reduces the environmental/cost impact and improves the eco-sustainability of productions.Results: The present paper reports recent results of deep eutectic solvent (DES) pretreatment on a selected group of the agro-industrial food wastes (AFWs) produced in Europe. In particular, apple residues, potato peels, coffee silver-skin, and brewer's spent grains were pretreated with two DESs, (choline chloride-glycerol and choline chloride-ethylene glycol) for fermentable sugar production. Pretreated biomass was enzymatic digested by commercial enzymes to produce fermentable sugars. Operating conditions of the DES pretreatment were changed in wide intervals. The solid to solvent ratio ranged between 1:8 and 1:32, and the temperature between 60 and 150 degrees C. The DES reaction time was set at 3 h. Optimal operating conditions were: 3 h pretreatment with choline chloride-glycerol at 1:16 biomass to solvent ratio and 115 degrees C. Moreover, to assess the expected European amount of fermentable sugars from the investigated AFWs, a market analysis was carried out. The overall sugar production was about 217 kt yr(-1), whose main fraction was from the hydrolysis of BSGs pretreated with choline chloride-glycerol DES at the optimal conditions.Conclusions: The reported results boost deep investigation on lignocellulosic biomass using DES. This investigated new class of solvents is easy to prepare, biodegradable and cheaper than ionic liquid. Moreover, they reported good results in terms of sugars' release at mild operating conditions (time, temperature and pressure).
[69]
GUO Z W, ZHANG Q, YOU T, et al. Heteropoly acids enhanced neutral deep eutectic solvent pretreatment for enzymatic hydrolysis and ethanol fermentation of Miscanthus x giganteus under mild conditions[J]. Bioresource technology, 2019, 293:122036.
[70]
CHEN Z, REZNICEK W D, WAN C. Deep eutectic solvent pretreatment enabling full utilization of switchgrass[J]. Bioresource technology, 2018, 263:40-48.
In this study, an acidified, aqueous DES comprising choline chloride: glycerol (ChCl:Gly) was used to fractionate switchgrass into three major streams under a relatively mild condition: cellulose-rich pulp, lignin, and xylose-rich liquor. The pulp showed good digestibility with about 89% glucose yield. The solvent can be recycled successfully and reused for at least four more pretreatment cycles while maintaining its pretreatment capability. The solvent recycling also improved the lignin recovery from the pretreatment liquor. Lignin recovered from different pretreatment cycles had the β-O-4 bonds preserved, and shared similar structures with native lignin. Using the pretreatment liquor as a substrate, the oleaginous yeast Rhodotorula toruloides produced 18.7 g/L biomass with lipid and carotenoid titers of 8.1 g/L and 15.0 mg/L, respectively. Overall, this study demonstrated a green process integrating chemical and biological methods toward full utilization of lignocellulosic biomass.Copyright © 2018 Elsevier Ltd. All rights reserved.
[71]
GUNNY A A N, ARBAIN D, NASHEF E M, et al. Applicability evaluation of deep eutectic solvents-cellulase system for lignocellulose hydrolysis[J]. Bioresource technology, 2015, 181: 297-302.
Deep Eutectic Solvents (DESs) have recently emerged as a new generation of ionic liquids for lignocellulose pretreatment. However, DESs contain salt components which tend to inactivate cellulase in the subsequent saccharification process. To alleviate this problem, it is necessary to evaluate the applicability of the DESs-Cellulase system. This was accomplished in the present study by first studying the stability of cellulase in the presence of selected DESs followed by applicability evaluation based on glucose production, energy consumption and kinetic performance. Results showed that the cellulase was able to retain more than 90% of its original activity in the presence of 10% (v/v) for glycerol based DES (GLY) and ethylene glycol based DES (EG). Furthermore, both DESs system exhibited higher glucose percentage enhancement and lower energy consumption as compared to diluted alkali system. Among the two DESs studied, EG showed comparatively better kinetic performance. Copyright © 2015 Elsevier Ltd. All rights reserved.
[72]
WAHLSTROM R, HILTUNEN J, MARIAH P, et al. Comparison of three deep eutectic solvents and 1-ethyl-3-methylimidazolium acetate in the pretreatment of lignocellulose: effect on enzyme stability, lignocellulose digestibility and one-pot hydrolysis[J]. RSC Advances, 2016, 6:68100-68110.
[73]
王冬梅, 刘云. 低共熔溶剂(DES)分级分离木质纤维素组分新技术[J]. 北京化工大学学报, 2018, 45(6):40-47.
[74]
KUMAR A K, PARIKH B S, SHAH E, et al. Cellulosic ethanol production from green solvent-pretreated rice straw[J]. Biocatalysis and agricultural biotechnology, 2016, 7:14-23.
[75]
陈洪章. 纤维素生物技术[M]. 北京: 化学工业出版社, 2005.
[76]
ZHU C, BAI X L, LUSI A, et al. High-solid lignocellulose processing enabled by natural deep eutectic solvent for lignin extraction and industrially relevant production of renewable chemicals[J]. ACS sustainable chemistry & engineering, 2018, 6(9):12205-12216.
[77]
XU G C, DING J C, HAN R Z, et al. Enhancing cellulose accessibility of corn stover by deep eutectic solvent pretreatment for butanol fermentation[J]. Bioresource technology, 2016, 203:364-369.
[78]
汝娟坚, 张远, 卜骄骄, 等. 低共熔溶剂在电沉积金属及其合金方面的研究进展[J]. 科学技术创新, 2019, 20:191.

基金

云南师范大学研究生科研创新基金“低共熔溶剂预处理玉米秸秆的研究”(YJSJJ21-A06)
云南省万人计划产业技术领军人才项目“有机废弃物能源回收与资源化利用关键技术研发及示范”(20191096)
云南省国际科技合作专项“中国昆明——老挝万象可再生能源推广与示范科技创新中心”(202003AF140001)
昆明市国际(对外)科技合作基地“昆明-万象创新中心”(GHJD-2020026)
PDF(1175 KB)

文章所在专题

热点综述

804

Accesses

0

Citation

Detail

段落导航
相关文章

/