酸性助水溶剂制备木质纳米纤维素及功能应用研究进展

木质纳米纤维素因具有制备工艺简单、环境友好、成本效益高等特点而在各领域受到广泛关注,其制备与应用已成为相关领域的研究热点。然而,木质纤维组分间的聚集结构和复杂的化学键(醚健、酯键等)结合形成了抗解聚屏障,需要对其进行预处理破除屏障。酸性助水溶剂体系具有溶解选择性高、产物易分离、可循环利用等优点,是一种高效环保的绿色预处理工艺,是木质纳米纤维素制备及高值化利用的重要预处理方法。本文首先介绍了酸性助水溶剂的概念及作用机理,综述了酸性助水溶剂体系制备木质纳米纤维素的方法及性能,讨论了木质纳米纤维素的功能化应用进展,最后总结了酸性助水溶剂体系存在的不足,并对其今后的研究方向进行了展望。     

酶解木质素的碱催化温和水热降解

针对木质素相对分子质量大、空间位阻大、反应活性低、难于利用的缺点,以氢氧化钠作催化剂对酶解木质素进行温和水热降解。研究了反应条件对降解木质素产率的影响,并以红外光谱（FT-IR）、核磁共振谱（¹H NMR）、凝胶渗透色谱（GPC）来表征降解木质素产物。优化后的水热降解条件为反应温度200℃,反应时间120 min,氢氧化钠与木质素的质量比值为0.2,木质素的质量分数为8%,此条件下降解木质素的产率为71%。FT-IR分析表明,在温和的水热降解条件下,木质素的芳环结构得以保留。¹H NMR分析结果表明,水热降解使木质素的部分醚键断裂,酚羟基增多。GPC分析表明,木质素相对分子质量明显下降,证明在此过程中木质素发生了降解。     

超临界CO2萃取脱除甘蔗渣木质素的研究

采用超临界CO₂萃取技术,研究了萃取条件对甘蔗渣木质素脱除规律的影响,设计正交试验方案得出纸浆得率、综纤素维含量、Klason木质素含量,进一步得出脱木质素率,以确定最优条件.结果表明,温度是影响超临界CO₂脱除木质素的最主要因素.在180 ℃、 20 MPa下,用1,4-二氧六环2 mL作夹带剂反应60 min,脱木质素率达到79.61%.用GC-MS 对不同温度下超临界CO₂萃取液的分析以研究在超临界CO₂下甘蔗渣中木质素的溶出规律,结果表明,木质素的降解不仅发生在芳基醚键这种大分子的断裂,还导致了苯环上甲氧基的断裂.且在高温作用下,还会导致甘蔗渣中其它碳水化合物、纤维素和半纤维素的降解.     

甲醇降解碱木质素

采用超临界甲醇法将碱木质素降解为小分子芳香族化合物,考察了反应温度、反应时间和溶剂中水含量对降解反应的影响。碱木质素被降解为约21种单环芳香族化合物,其中7～11种为主要组分,多为以愈创木基结构为主的芳香族衍生物。产物中非酚型组分较稳定,不易发生进一步反应,且随着反应时间的延长,其所占比例不断增大,而酚型组分稳定性较差,易发生进一步反应。碱木质素降解反应速率的突变发生在250～280℃,温度越高,反应速率越大。水的存在有利于醚键的断裂和酚型组分的生成。在水体积分数为50%的甲醇-水共溶剂体系中,2-甲氧基-4-乙基苯酚的选择性最好,其在产物中的质量分数达48.6%。碱木质素的醚键在反应中全部断裂,四氢呋喃不溶物中主要是以缩合结构为主的木质素残片和再聚合产物。     

甲醇汽油互溶性影响的研究

本文分析了甲醇一汽油体系中水含量、温度、汽油组成等因素对其互溶性的影响，论述了助溶剂的作用机理与助溶剂的选择。水含量越高、温度越低则互溶性越差，反之亦然。醇类助溶剂助溶效果强于酯类、醚类等助溶剂，复配助溶剂助溶效果强于单组份助溶剂。     

低共熔溶剂协同酸性二氧六环预处理杨木及其酶水解特性的探究

以杨木为原料,采用低共熔溶剂(DES)协同酸性二氧六环进行预处理,研究盐酸浓度、预处理时间和预处理温度对杨木酶水解特性的影响。结果表明,当盐酸质量分数为1%,反应温度为110℃,时间为70 min时,酶水解得率为69.75%,纤维素保留率为73.66%、半纤维素和木质素脱除率分别为72.61%和48.71%。协同预处理在保留纤维素的同时,可显著提高杨木中半纤维素和木质素的脱除率。同时,预处理能够大大提高杨木的结晶度,破坏杨木的致密结构,影响其热稳定性,进而有效提高纤维素酶水解得率。     

亚临界水中离子液体催化蔗渣液化残渣分析

分别采用FT-IR、SEM对亚临界水中酸性功能化离子液体催化蔗渣液化残余物的主要成分及其表面形貌进行系统的分析,并对其与酸性离子液体催化剂的酸强度、反应温度、反应时间等工艺条件之间的关联规律进行了详细探讨。结果表明,蔗渣液化后的残渣主要是由木质素、难降解或部分降解的芳香类化合物组成;酸性越强、反应温度越高,蔗渣的液化程度越高,结构破坏得越彻底,液化残渣表面越粗糙。     

巨龙竹有机溶剂木质素提取及结构表征

为表征巨龙竹木质素化学结构,在温和条件下连续采用二氧六环和二甲基亚砜抽提竹材原料,得到竹材木质素组分。红外光谱、凝胶色谱和核磁共振分析结果表明,巨龙竹木质素属于典型的禾草类木质素,其大分子由对羟基苯丙烷(H)、愈创木基丙烷(G)和紫丁香基丙烷(S)三种基本结构单元组成;巨龙竹木质素大分子的主要联接键为β-O-4'醚键、β-β'和β-5'碳-碳键;在巨龙竹木质素大分子中,苯丙烷结构单元侧链γ位碳与对香豆酸存在化学键联接,形成对香豆酸酯。     

秸秆中木质素对其超低酸水解过程的影响

以湖北稻草秸秆为研究对象,研究了超低酸水解木质纤维素的适宜条件,测定了适宜条件下的超低酸法水解15种不同种类秸秆的纤维素及半纤维素的转化率、还原糖得率及结晶度的变化。实验结果表明:秸秆投料量3 g、硫酸投料量45 mL(硫酸质量分数0.05%)、搅拌转速500 r/min、反应温度210 ℃、反应时间10 min为适宜的水解条件。对15种不同种类秸秆的水解结果统计得到,随着秸秆中木质素含量的增大,纤维素和半纤维素的转化率都逐渐降低,还原糖得率逐渐降低;通过SEM和X衍射分析水解前后的木质纤维素结构,得到了木质素影响水解过程的方式:1)木质素含量越大,纤维素的结晶度越大,纤维素的非晶化越困难,从而影响了纤维素的水解;2)原木质素不溶于反应体系且在酸性条件下相对稳定,富木质素层的木质素阻碍反应物与产物扩散,使富木质素层内的纤维素、半纤维素水解速率降低;3)木质素含量越高,木质纤维素的富木质素层越厚、强度越大,水解时难以从颗粒表面脱落,进一步降低水解速率。     

NHPI催化分子氧氧化α—O—4型木质素模型分子

以苄基苯基醚为模型分子,氧气为氧化剂,考察了N-羟基邻苯二甲酰亚胺(NHPI)对分子氧氧化木质素醚键(α-O-4)的催化作用和多种可溶性过渡金属盐的助催化作用,探究了NHPI和硝酸铜用量、反应温度、反应时间和氧气分压对反应的影响。结果表明:NHPI催化分子氧氧化苄基苯基醚生成苯甲醛和苯酚,在可溶性的钴、锰、镍和铜盐中,铜盐对NHPI的助催化作用最好。在NHPI/Cu(NO3)2催化下,当氧分压高于0.5 MPa时,苄基苯基醚的氧化反应对氧气为0级。过高温度会加剧目标产物苯甲醛和苯酚的深度氧化。优化的工艺条件为,以乙酸为溶剂,n(苄基苯基醚)∶n(NHPI)∶n(硝酸铜)=1.0∶0.2∶0.02,氧气分压为1.0 MPa时,在110℃下反应15h,苄基苯基醚的转化率为37.2%。     

Structure and Reactivity of Spruce Mechanical Pulp Lignins Part II. Organosolv Fractionation of Lignins in a Flow-Through Reactor

Various spruce mechanical pulps were subjected to delignification with ethanol-water (1 : 1, v / v ) containing 0.1 M acetic acid at 175°C in a flow- through reactor. A thermomechanical pulp (TMP) and the corresponding samples derived from its bleaching (BTMP) and yellowing ( YBTMP ) treatments were delignified to a similar extent, about 70% of delignification degree, as compared with spruce wood. A series of five successive lignin fractions was recovered from each pulp sample and then characterized by various analytical methods. Large structural variations were observed within these fractions. The number of phenolic structures appeared to be an important factor influencing the dissolution of lignins in the ethanol-water medium. These lignin fractions were found to be different in the amount of β-aryl ether structures and in the relative importance of main carbon-carbon bonding patterns. The results are discussed in relation to the lignin fractionation in the flow-through reactor.     

Investigation of the effects of ternary deep eutectic solvent composition on pretreatment of sorghum stover

Biomass-derived deep eutectic solvents (DESs) have been introduced as promising pretreatment and fractionation solvents because of their mild processing conditions, easy synthesis, and green solvent components from biomass. In recent DES studies, solvent-based third constituents like water, ethanol, and others improve the processibility of typical binary DESs. However, the impacts of these components are not well understood. Here, two solvent-based constituents, including water and ethylene glycol, were applied to 3,4-dihydroxybenzoic acid (DHBA)-based DES system for improving the conversion efficiency of cellulose-rich fraction and the properties of lignin fraction. Chemical composition, enzymatic digestibility, degree of polymerization of cellulose and physicochemical properties of lignin were used to evaluate the impact of each third constituent on biomass processing. Ternary ChCl-DHBA DESs exhibited better performances in delignification, fermentable sugar production, and preservation of β-O-4 ether linkage in lignin compared with binary ChCl-DHBA DES.     

定量~(13)C-NMR谱表征蔗渣碱木素结构

从蔗渣纸浆黑液中制出纯蔗渣碱木素，然后测定其定量13C-NMR谱．图谱分析表明，蔗渣碱木素主要由紫丁香基，愈创木基和对羟苯基三种丙烷结构单元组成，其中未绩合的紫丁香基、愈创木基和对羟羊基含量比为2.2：1．0：1．4．蔗渣碱术素结构单元间主要以β-O－4烷基芳基醚键连接，也有一定量的非环状α-醚键存在．蔗渣碱木素中，相当部分对香豆酸类结构并非通过酯键而是通过醚键或碳双键连接于芳核上．     

Delignification Mechanism During High-Boiling Solvent Pulping. V. Reaction of Nonphenolic β- O -4 Model Compounds in the Presence and Absence of Glucose

Abstract

Nonphenolic β-aryl ether model compounds, veratrylglycerol-β-guaiacyl ether (1) and its α-ethyl ether (2) were treated in 70% aqueous 1,4-butanediol solutions at 180°C. The reactivity of compound 2 was higher than that of compound 1. Benzyl ether formation with 1,4-butanediol was observed. This suggests the high reactivity of lignin–carbohydrate complex with benzyl ether type under HBS pulping conditions. On the other hand, guaiacol was not detected in the reaction mixture. This indicates that β-aryl ether in nonphenolic structures is inert to HBS pulping conditions. Addition of glucose and acetic acid enhanced the benzyl ether formation with 1,4-butanediol, but not cleavage of β-aryl ethers.     

ENHANCEMENT OF SOLUBILITY AND MASS-TRANSFER COEFFICIENT OF 1,2-DIHYDROXY-9,10-ANTHRAQUINONE (ALIZARIN) THROUGH HYDROTROPY

The effect of hydrotropes potassium p-toluene sulfonate (KPTS), citric acid, and nicotinamide on the solubility and mass-transfer coefficient of 1,2-dihydroxy-9,10-anthraquinone (alizarin) was studied. Solubility studies were carried out under a wide range of hydrotrope concentrations (0 to 3.0 mol·L^?1) and different system temperatures (303 to 333 K). It was observed that the solubility and mass-transfer coefficient of alizarin increases with an increase in hydrotrope concentration and system temperature. The maximum enhancement factor, the ratio of the value of solubility in the presence and absence of a hydrotrope, was determined for all experiments under study. The effectivity of hydrotropes was measured by the determination of the Setschenow constant, K_s. The order of effectiveness of various hydrotropes based on K_s values is potassium p-toluene sulfonate > citric acid > nicotinamide.     

乙酰溴法对小兴安岭碱法杨木黑液提取物成分的研究

衍生化后的还原裂解(DFRC)法作为木质素结构解析的新方法,可以对碱法杨木黑液提取物中大分子结构的β-O-4醚键和α芳基醚键实施选择性的高效断裂.实验采用DFRC法对碱法萃取的杨木木质素进行降解,通过GC及GC-MS,分析研究了小兴安岭碱法杨木黑液提取物的成分和结构.结果表明:碱法杨木黑液提取物中主要包括4类化合物:B...     

Oxygen Delignification Chemistry and Its Impact on Pulp Fibers

Abstract

Two southern pine kraft pulps with kappa numbers of 30.0 (SW1-0) and 48.0 (SW2-0) were oxygen delignified by 30–60% by varying the reaction temperature (78–110°C) and charge of sodium hydroxide (1.6–4.4%). O-bleachability was found to be correlated to the incoming kappa number and charge of sodium hydroxide employed. In general, a lower charge of caustic and a higher brownstock kappa number improved pulp bleachability. The residual lignin in the brownstocks and O-delignified kraft pulp samples was isolated and characterized by ¹³C and ³¹P NMR. ¹³C NMR analysis of the residual lignin samples indicated that the post-oxygen delignified pulps were enriched with α-carbonyl groups and carboxylic acid groups. The content of β-O-aryl structures was increased by 23–36% depending on the extent of oxygen delignification. The post-oxygen delignified pulps were also shown to have increased substituted aryl carbons. ³¹P NMR indicated that the relative content of condensed phenolic units increased by 9–20% after the oxygen delignification, depending on the severity of the O-stage. This observation was probably due to the accumulation or formation of 5,5-biphenyl structures in the process. The physical strength properties of brownstock and post-oxygen delignified pulps were assessed in terms of zero-span strength, tensile strength, tear strength, and burst strength. Oxygen delignification led to a slight increase in the curls and kinks of the pulp fibers. The O-stage was shown to cause a 4.8–15.6% decrease in zero-span strength. In contrast, oxygen delignification increased tensile strength. This result could be explained as the improvement of fiber bonding after the oxygen bleaching.     

Effect of hydrotropes on solubility and mass transfer coefficient of lauric acid

A comprehensive investigation on the solubility and mass transfer coefficient enhancement of lauric acid through hydrotropy has been undertaken. The solubility and mass transfer studies were carried out using hydrotropes such as sodium cumene sulfonate, sodium p-xylene sulfonate and sodium p-toluene sulfonate under a wide range of hydrotrope concentrations (0 to 3.0 mol/L) and different system temperatures (303 to 333 K). The effectiveness of hydrotropes was measured in terms of Setschnew constant K _s and reported for all hydrotropes used in this study. The solubility data are also fitted in a polynomial equation as the function of hydrotrope concentration.     

Delignification of intact biomass and cellulosic coproduct of acid‐catalyzed hydrolysis

The kinetics of acid‐catalyzed hemicellulose removal and also alkaline delignification of oat hull biomass were investigated. All three operational parameters namely, catalyst concentration (0.10–0.55 N H₂SO₄), temperature (110–130°C), and residence time (up to 150 min) affected the efficiency of hemicellulose removal, with 100% of hemicellulose removed by appropriate selection of process parameters. Analysis of delignification kinetics (in the temperature range of 30–100°C) indicated that it can be expressed very well by a two‐phase model for the crude biomass and also for the hemicellulose‐prehydrolyzed material. The application of acid‐catalyzed prehydrolysis improved the capacity of lignin dissolution especially at lower temperatures (30 and 65°C) and accelerated the dissolution of lignin. This acceleration of delignification by prehydrolysis was possible at all levels of temperature in the bulk phase; however, results were more significant at the lower temperatures in the terminal phase. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1783–1791, 2015     

ATR-FTIR Measurement of Biomass Components in Phosphonium Ionic Liquids

Abstract

Qualitative and quantitative measurements of biomass components dissolved in the phosphonium ionic liquids (ILs), trihexyltetradecylphosphonium chloride ([P66614]Cl) and tributylmethylphosphonium methylsulphate ([P4441]MeSO₄), are obtained using attenuated total reflectance-FTIR. Absorption bands related to cellulose, hemicelluloses, and lignin dissolution monitored in situ in biomass-IL mixtures indicate lignin dissolution in both ILs and some holocellulose dissolution in the hydrophilic [P4441]MeSO₄. The kinetics of lignin dissolution reported here indicate that while dissolution in the hydrophobic IL [P66614]Cl appears to follow an accepted mechanism of acid catalyzed β-aryl ether cleavage, dissolution in the hydrophilic IL [P4441]MeSO₄ does not appear to follow this mechanism and may not be followed by condensation reactions (initiated by reactive ketones). The measurement of lignin dissolution in phosphonium ILs based on absorbance at 1510 cm^?1 has demonstrated utility. When coupled with the gravimetric Klason lignin method, ATR-FTIR study of reaction mixtures can lead to a better understanding of the delignification process.