Aluminiumchlorid‐katalysierter Organosolv‐Aufschluss von Buchenholz

The Organosolv pulping is a process to separate lignocellulosic biomass into its components cellulose, hemicellulose and lignin. Usually this process is catalyzed by Brønsted acids. In this work the Brønsted acid is replaced by the Lewis acid aluminum chloride. Much less aluminum chloride is needed to achieve similar pulp properties like high cellulose recovery, high hemicellulose and lignin removal. Also aluminum chloride catalyzes the degradation of xylose to the important basic chemicals furfural and lactic acid.     

A new approach for the production of cellulose acetate: Acetylation of mechanical pulp with subsequent isolation of cellulose acetate by differential solubility

A heretofore uninvestigated approach to the production of cellulose acetate, the acetylation of whole wood pulp with subsequent isolation of the cellulose derivative by differential solubility, is described. The mechanical pulp used was produced by refining aspen wood chips with a disc refiner. Two conventional acetylation techniques, the fibrous and solution process, were employed to acetylato all components of the pulp. The cellulose acetate was isolated from the acetylated lignin and hemicellulose by dissolving in dichloromethane/methanol (9:1, v/v). The advantage of this new approach is that the high cost involved in using an extensively purified dissolving pulp are avoided. Both acetylation techniques yielded a product that was about 84% cellulose acetate. The remaining acetylated components were lignin and hemicellulose. The yield of cellulose acetate, based on the cellulose content of the original pulp and the product, was 75–80%.     

Tetrahydrofurfuryl Alcohol (THFA) Pulping of Rice Straw

Abstract

A 80–95% solution of tetrahydrofurfuryl alcohol (THFA) added with 0.15–0.5% catalytic hydrochloric acid (HCl) was used to pulp rice straw. The pulping conditions applied for organosolv digestions of the straw at atmospheric pressure and 120°C cooking for 4 h. The characteristics of the digestion, chemical properties of the resulting pulp, and the handsheet physical properties were evaluated. As for the pulp yields, the method has high delignification specificity, at kappa number 20, the yield was ca. 60%, about 15–20% higher than the traditional alkaline pulping method. Furthermore, with increasing THFA concentrations, efficacies of delignification also increased. Increasing the catalyst dosage also caused an increase in delignification. Delignification rate of 120°C cooking are not so appreciable, but high yield were retained. If cooking temperatures were increased to 130 and 150°C, although even higher delignification rates were achievable, the yield decreased as well. During the cooking the dissolution of carbohydrate was low, at most 23%, consisting of mostly hemicelluloses, which was as high as 78% of the dissolved carbohydrates. The optimal conditions of the THFA/HCl cooking applied 95% THFA, 0.50% HCl, temperature of 120°C, and cooking time of 240 min. Residue lignin in the resulting pulp was low, and can be bleached to high brightness easily with a conventional bleaching sequence. If, however, energy and operation efficiency was a primary consideration, then a procedural heating scheme could be employed. The physical properties of the THFA pulp handsheets were inferior to those of the kraft pulp. The main reason was the damage to cellulose sustained during the acidic cooking condition.     

Alkaline Pre-treatment of Hardwood Chips Prior to Delignification

Abstract

Hardwood (Betula pendula) chips were extracted having alkaline aqueous solutions with varying chemical charges (1, 2, 3, 4, 6, and 8% of NaOH on wood), treatment times (30, 60, 90, and 120 minutes), and temperatures (130°C and 150°C). The total amount of material removed was in the range 2.1–16.5% of the original dry feedstock. This fraction was characterized in terms of carbohydrates and their degradation products (mainly aliphatic carboxylic acids together with some furanoic compounds), lignin, and extractives. Low alkali charges (1–4% of NaOH) were not sufficient to neutralize all the acids formed (mainly acetic acid from the acetyl groups of xylan). In contrast, an increase in alkali charge (6% and 8% of NaOH) more intensively facilitated the alkali-catalyzed degradation reactions of polysaccharides to various hydroxy acids, which were then typically present as one of the main constituents in the dissolved organic matter, along with other aliphatic carboxylic acids (acetic and formic acids), lignin, extractives, and carbohydrates.     

从糠醛渣中提取纤维素的工艺

以甲酸和过氧化氢作溶剂,采用Milox三段法提取糠醛渣中的纤维素,将蒸煮与碱性过氧化氢漂白过程相结合,实现了木质素和纤维素分离的无氯漂白工艺,考察了甲酸用量、过氧化氢用量、提取温度和提取时间对糠醛渣中纤维素提取效果的影响。实验结果表明：当甲酸用量为80 mL,过氧化氢用量为14 mL,三段反应温度和时间分别为80 ℃反应2.5 h、95 ℃反应2.5h以及抽滤后加入新鲜溶剂在80 ℃再反应2.5 h,糠醛渣纤维素的得率是41.92%,纤维素的含量为85.09%,木质素含量为3.22%。由此可见该工艺优于其它工艺结果,能够更好地提高糠醛渣的应用价值。     

植物纤维原料及纸浆中的木素―碳水化合物复合体

造纸工业中所用的木质纤维原料主要是由纤维素、半纤维素和木素组成的。纤维聚合物之间存在相互作用。研究证明,在木材和纸浆中,部分木素和碳水化合物发生化学键联接形成木素―碳水化合物复合体结构。文章着重介绍了复合物中三种重要化学键的键型;结合前人的研究成果,综述了云杉木、杨木、麦草以及各种针叶木浆和阔叶木浆中的木素―碳水化合物复合体(LCC);此外,对LCC的形成机理和蒸煮过程中形成新LCC的可能性加以阐述。     

甲酸―盐酸体系下木质纤维素的组分分离

研究了常压下甲酸―盐酸体系中木屑的溶解规律,结合酸回收和碱沉方法实现了木屑的组分分离。经酸体系处理后的剩余物主要成分为纤维素,滤液经酸回收和碱沉后得到的沉淀是木质素,半纤维素全部水解。实验确定了最佳分离条件:在甲酸―盐酸(体积比3∶1)体系中,溶解温度为60℃,溶解时间为180min,液固比为10∶1,在此条件下,木屑的溶解率可达48.8%,木质素收率为23.2%。通过FTIR、XRD及NMR等方法对溶解后及甲酸回收后剩余物质的结构进行了分析确证。     

木素的存在对纤维素水解反应性能及其产物结构的影响

对木素含量为0.9％—8.3％的速生杨硫酸盐浆进行了X—射线分析研究。利用多相水解方法测定了其反应性能。研究结果确定,浆中结晶纤维素含量取决于木素脱出程度并随着木素含量的降低而增加。木屑和浆中的纤维素结晶度相当高,而在脱木素过程中只呈微小变化。木素存在于多相水解反应过程中起着阻碍纤维素水解的作用,降低其反应速度常数。基于研究结果,提出了木素与纤维素结晶部分外表面联结的结论.并探讨了这种联结键的可能形式。     

Beyond waste: Transforming wheat straw into oxygen and UV-resistant cellulose films

Regenerated cellulose membrane is a biomaterial obtained by activating, dissolving, solidifying, and regenerating cellulose powder using solvents of different polarities. It has the characteristics of high oxygen resistance and high strength. However, its low water vapor barrier and single function limit its application. In order to improve the water resistance of regenerated cellulose membranes and endow them with UV resistance, lignin was extracted from waste wheat straw using formic acid method. The extracted formic acid lignin (FAL) was added to the cellulose solution to prepare a series of regenerated lignocellulosic membranes (RC-FAL) with different lignin contents. The results indicate that lignin can not only improve the water vapor barrier, tensile strength, and water resistance of the film, but also enhance the oxygen barrier and UV absorption of the film. Compared with pure cellulose film, the contact angle of lignocellulose film can be increased by 66.2%, the UV absorption rate can reach 100%, and the oxygen transmission coefficient has no significant effect. In this paper, a new kind of biological packaging material with high oxygen resistance, strong ultraviolet absorption, and water resistance was prepared by recycling waste wheat straw, it has a broad application prospect in the industrial production of packaging materials.     

Sustainable Production of Levulinic Acid from the Cellulosic Fraction of Pinus Pinaster Wood: Operation in Aqueous Media Under Microwave Irradiation

The fractionation of the structural components of lignocellulosic biomass (cellulose, hemicelluloses, and lignin) and the separate utilization of the resulting fractions for specific purposes, according to the philosophy of biorefineries, enables the development of sustainable processes for biomass utilization. In this work, Pinus pinaster wood was subjected to aqueous processing to remove water-soluble extractives and hemicelluloses, and the resulting solid was subjected to pulping with HCl-catalyzed acetic acid solutions (Acetosolv method). The pulp was employed as a substrate for levulinic acid manufacture by reaction in acidic media under microwave irradiation. The effects of the major operational variables (temperature, reaction time, and acid concentration) on the levulinic acid yield were established by statistical modeling of experimental data. Operating under the best reaction conditions (at 191.2°C for 18.9 min in aqueous media containing 1.10% HCl), the levulinic acid yield accounted for 56.4% of the stoichiometric value.     

Fractionation and Characterization of Wood Cell Wall Components of Fagus crenata Blume Using LiCl/DMSO Solvent System

Abstract

The fractionation of wood cell wall components was achieved by the application of the LiCl/DMSO solvent system developed in our previous study. Various soluble and insoluble fractions were prepared from beech milled wood by extractions with DMSO containing different amounts of lithium chloride (LiCl) for the study of a lignin-carbohydrate complex (LCC). Nitrobenzene oxidation (NO) analyses demonstrated that the lignin in the soluble fractions always has lower yields of NO products consisting of syringaldehyde + syringic acid (S_y) and vanillin + vanillic acid (V_a). The syringyl ratios, S_y/(S_y+V_a), were also lower than in insoluble fractions. Accordingly, lignins with lower syringyl ratios are better soluble than those with higher syringyl ratios. The former is typical in the primary wall and the latter in the secondary wall. Solubilization of glucan is significantly dependent on the LiCl concentration in DMSO. In the absence of LiCl, only about 6% of glucan was found in the soluble fraction, but about 40% of lignin and xylan were solubilized. The additional 40% of lignin and xylan became soluble together with glucan solubilization, which increased at 3% LiCl concentration. However, a fraction amounting to 13% (based on the whole wood) still remained as a residue under these conditions. Glucan solubilization could not be the reason for this observation as ball-milled cellulose is soluble in 3% LiCl/DMSO. It is likely that strong interactions between lignin and carbohydrates prevent solubilization of this fraction, which has never been isolated and analyzed in previous studies.     

Why Acid pH Increases the Selectivity of the Ozone Bleaching Processes

The influence of pH on pulp properties was studied by the kinetic analysis of ozone bleaching of Eucalyptus Kraft pulp. The crystallinity of the pulps was also evaluated by XRD. The rate constants of delignification and chromophore removal decreased with the increase in pH, while the rate constant of cellulose degradation increased. The selectivity of the process was 6 times higher at pH 2.5 than at pH 10. There was a portion of lignin inaccessible that cannot be removed by ozone, even at high doses, promoting a strong cellulose degradation. At high ozone doses and acid pH, the ozone reacted primarily with the crystalline portions of the cellulose, while at alkaline pH it reacted indiscriminately with amorphous and crystalline cellulose.     

Steam-explosion pretreatment of olive cake

Olive cake was processed by steam-explosion under different steam conditions, followed by fractionation to separate the main components. In the water-soluble fraction, the main compounds were carbohydrates. Glucose represented a significant part of the total monosaccharide content, especially under conditions of mild severity, followed by arabinose, but the solubilization of sugars occurred predominantly in the oligomeric fraction. Mannitol was also found in significant amounts (1.5%), similar to that in the initial material. In the ethyl acetate extract, low molecular weight phenols were identified, the most aboundant being hydroxytyrosol, which is present in the olive pulp. Hydroxytyrosol is abundant and has great antioxidant activity, reaching 149 mg/100 g of dry olive cake. The procedure used in this study obtained all the hydroxytyrosol residual present in the by-product. The constitutive polymers were quantified in the insoluble fraction, and the sugar composition showed that cellulose was associated with a high proportion of xylans and other polysaccharides rich in arabinose and galactose. This cellulose was nearly amorphous, as it was highly susceptible to hydrolytic enzymes. The extractables in dilute alkali (not true lignins) increased as steaming became more severe; the residual “lignin” in this fraction decreased. Enzymatic hydrolysis of the insoluble fraction using a cellulolytic complex was also studied. The slight increase in the extent of saccharification was not proportional to the high alkaline delignification. However, when the residues were efficiently delignified with chlorite treatment, the susceptibility to enzymatic hydrolysis greatly increased.     

Fractional and structural characterization of ball-milled and enzyme lignins from wheat straw

Ball-milled and enzyme lignins were extracted with 90 and 50% dioxane–water from 6 days ball-milled wheat straw, and subsequently cellulase-treated straw residues, respectively. The crude lignin preparations were purified using a two-step precipitation method instead of the traditional ether precipitation procedure, and fractionated into pure milled lignin (PML), pure enzyme lignin (PEL), hemicellulose-rich milled lignin (HRML), lignin-rich enzyme lignin (LREL), and solubilized lignin during enzyme treatment (SLET) fractions. The five lignin fraction were studied using spectroscopic and degradative tecyhniques. The PML and PEL fractions showed very low content of associated polysaccharides (2.36–2.86%). The PML is mainly composed of β-O-4 ether bonds in the lignin structural units. The less common β-5 and β-β carbon–carbon linkages are also present. The results obtained also indicated that the lignins in wheat straw cell walls appeared to be very closely associated to p-coumaric and ferulic acid, and glucuronic acid or 4-O-methylglucuronic acid. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1633–1641, 1998     

The dependence of char and carbon yield on lignocellulosic precursor composition

A set of lignocellulosic precursors of widely varying composition was pyrolyzed under argon at 15°C/min to 500°C. Variation in the total mass and carbon yields among precursors was found to be due to variation in composition, i.e. distribution of the main organic components (lignin, holocellulose and extractives). Simple models for total mass and carbon yields of the precursors allowed determination by multiple regression analysis of the total mass and carbon yield of the components pyrolyzing in their native state in the lignocellulosic matrix. The component yields thus estimated were compared to results observed in studies of isolated components, such as reagent-grade cellulose. The char yield from lignin (53%) was found to be three times that of cellulose (18%) because of the higher initial carbon content in lignin (63 vs 44%) as well as the higher carbon yield (76 vs 40%).     

Developments in Ozone-Based Bleaching of Pulps

ABSTRACT

This paper summarizes the review of developments in the area of ozone-based elemental chlorine free (ECF) and total chlorine free (TCF) bleaching of wood and non-wood pulps. Focused areas of review are reaction mechanism of ozone with carbohydrates and lignin, effect of process conditions maintained during ozone bleaching on pulp properties, effect of using different cellulose protectors, effect of alkaline extraction after ozone bleaching of pulps, effect of ozone bleaching on final bleached pulp properties, ECF and TCF bleaching sequences used along with ozone for of wood and non-wood pulps, and commercial scale utilization of ozone for pulp bleaching.     

Characteristics of hemicellulose,cellulose and lignin pyrolysis

The pyrolysis characteristics of three main components (hemicellulose, cellulose and lignin) of biomass were investigated using, respectively, a thermogravimetric analyzer (TGA) with differential scanning calorimetry (DSC) detector and a pack bed. The releasing of main gas products from biomass pyrolysis in TGA was on-line measured using Fourier transform infrared (FTIR) spectroscopy. In thermal analysis, the pyrolysis of hemicellulose and cellulose occurred quickly, with the weight loss of hemicellulose mainly happened at 220–315 °C and that of cellulose at 315–400 °C. However, lignin was more difficult to decompose, as its weight loss happened in a wide temperature range (from 160 to 900 °C) and the generated solid residue was very high (∼40 wt.%). From the viewpoint of energy consumption in the course of pyrolysis, cellulose behaved differently from hemicellulose and lignin; the pyrolysis of the former was endothermic while that of the latter was exothermic. The main gas products from pyrolyzing the three components were similar, including CO₂, CO, CH₄ and some organics. The releasing behaviors of H₂ and the total gas yield were measured using Micro-GC when pyrolyzing the three components in a packed bed. It was observed that hemicellulose had higher CO₂ yield, cellulose generated higher CO yield, and lignin owned higher H₂ and CH₄ yield. A better understanding to the gas products releasing from biomass pyrolysis could be achieved based on this in-depth investigation on three main biomass components.     

木质纤维素甲酸预处理及其组分分离

以玉米芯为研究对象,提出了常压中温条件下甲酸预处理木质纤维素组分分离的工艺. 在该体系中半纤维素迅速发生水解,大部分木质素被溶解,而纤维素基本不发生水解,经固液分离和甲酸回收实现了玉米芯全组分分离. 考察了预处理温度、时间和甲酸浓度对玉米芯各组分分离效果及水解产物(可溶性糖)含量的影响规律,结果表明,随着反应的进行,甲酸溶液中可溶性糖和木质素量先迅速增大,随后趋于平衡;在50~75℃间对各组分分离的影响不明显. 综合考虑分离效果和成本,选择最佳反应温度为60℃,处理时间为3 h,甲酸浓度为88%(w). 在该条件下,纤维素、半纤维素和木质素回收率分别可达91.4%, 88.5%和63.7%.     

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.     

The influence of temperature on the yields of compounds existing in bio-oils obtained from biomass samples via pyrolysis

The influence of temperature on the compounds existing in liquid products obtained from biomass samples via pyrolysis were examined in relation to the yield and composition of the product bio-oils. The product liquids were analysed by a gas chromatography mass spectrometry combined system. The bio-oils were composed of a range of cyclopentanone, methoxyphenol, acetic acid, methanol, acetone, furfural, phenol, formic acid, levoglucosan, guaiacol and their alkylated phenol derivatives. Thermal depolymerization and decomposition of biomass structural components, such as cellulose, hemicelluloses, lignin form liquids and gas products as well as a solid residue of charcoal. The structural components of the biomass samples mainly affect the pyrolytic degradation products. A reaction mechanism is proposed which describes a possible reaction route for the formation of the characteristic compounds found in the oils. The supercritical water extraction and liquefaction partial reactions also occur during the pyrolysis. Acetic acid is formed in the thermal decomposition of all three main components of biomass. In the pyrolysis reactions of biomass: water is formed by dehydration; acetic acid comes from the elimination of acetyl groups originally linked to the xylose unit; furfural is formed by dehydration of the xylose unit; formic acid proceeds from carboxylic groups of uronic acid; and methanol arises from methoxyl groups of uronic acid