Comparison of hydrothermal,hydrotropic and organosolv pretreatment for improving the enzymatic digestibility of bamboo

Pretreatment is the crucial step to disrupt the recalcitrant structure of lignocellulosic biomass for improving the enzymatic hydrolysis efficiency. Typically, hydrothermal, organosolv and hydrotropic pretreatments are environmentally benign and effective methods. In this work, effects of hydrothermal, organosolv and hydrotropic pretreatments on improving enzymatic hydrolysis of bamboo were comprehensively compared. Hydrotropic pretreatment was more effective in removal lignin and xylose from bamboo fiber cell wall. However, the surface coverage by lignin and extractives were dramatically displaced during organosolv pretreatment as investigation by X-ray photoelectron spectroscopy. After pretreatments, the crystallinity of cellulose in pretreated substrates has a significant reduction, and pores were exposed on fiber surface. The residual content of acetyl and phenolic groups in hydrotropic pretreated substrates is lower than organosolv pretreated substrates. In order to deeply assess the delignification of pretreatments, the isolated lignins obtaining from pretreatments process were characterized by Fourier transform infrared spectroscopy also. It was revealed that hydrotropic lignin contained more phenolic hydroxyl group and syringyl units than organosolv lignin. Compared to hydrothermal and organosolv pretreatment, cellulase adsorption capacity of pretreated substrates was notably improved by hydrotropic pretreatment, which indicating the better enzyme accessibility of cellulose. Eventually, the maximum glucose yield was obtained from hydrotropic pretreated substrates.     

Towards quantitative catalytic lignin depolymerization

The products of base-catalyzed liquid-phase hydrolysis of lignin depend markedly on the operating conditions. By varying temperature, pressure, catalyst concentration, and residence time, the yield of monomers and oligomers from depolymerized lignin can be adjusted. It is shown that monomers of phenolic derivatives are the only primary products of base-catalyzed hydrolysis and that oligomers form as secondary products. Oligomerization and polymerization of these highly reactive products, however, limit the amount of obtainable product oil containing low-molecular-weight phenolic products. Therefore, inhibition of concurrent oligomerization and polymerization reactions during hydrothermal lignin depolymerization is important to enhance product yields. Applying boric acid as a capping agent to suppress addition and condensation reactions of initially formed products is presented as a successful approach in this direction. Combination of base-catalyzed lignin hydrolysis with addition of boric acid protecting agent shifts the product distribution to lower molecular weight compounds and increases product yields beyond 85%.     

溶出温度对乙醇木质素超临界解聚特性影响研究

通过控制溶出温度(160、180和200℃),制备了三种毛竹乙醇木质素EOL(EOL-160、EOL-180和EOL-200),并采用红外光谱仪(FT-IR)、凝胶渗透色谱(GPC)和热重分析(TG)分别对乙醇木质素的官能团、分子量分布及热稳定性进行了分析;采用微型高温高压反应釜,在超临界乙醇体系,进行三种乙醇木质素的解聚实验,通过气相色谱/质谱联用仪(GC/MS)及FT-IR对解聚产物进行分析,探讨乙醇木质素特性对其超临界乙醇环境解聚产物组成的影响规律。结果表明,随着溶出温度的升高,乙醇木质素溶出率呈上升趋势。EOL-160、EOL-180和EOL-200三种乙醇木质素在超临界条件解聚液相产物主要成分分别为对乙基苯酚、2,6-二甲氧基苯酚和4-羟基-3-甲氧基-苯甲酸酯。     

Studies on polymers and composites from lignin and fiber derived from sugar cane

Sugarcane fiber (i.e. bagasse) lignin has a larger fraction of aromatics unsubstitution in the ortho position than hardwood or softwood lignin and hence has the greater ability to be derivatized. Furthermore, organosolv lignin has a higher purity than sulfonated and kraft lignins. This work examines the purification of organosolv lignin derived from bagasse and the physico‐chemical properties of the lignin and lignin‐phenol formaldehyde (PF) resin coatings, and composites. The wetability tests have shown that lignin and lignin‐PF resin films are effective water barrier coatings, though the contact angles of lignin‐PF resin films were considerably less than the wax films. The overall mechanical properties (i.e. peak stress, peak strain and modulus) of the bagasse fiber composites were lower than the values obtained with the composites without the inclusion of bagasse fiber. Copyright © 2007 John Wiley & Sons, Ltd.     

Effect of Lignin Structure Characteristics on the Performance of Lignin Based Phenol Formaldehyde Adhesives

As the second most abundant biopolymer, lignin remains underutilized in various industrial applications. Various forms of lignin generated from different methods affect its physical and chemical properties to a certain extent. To promote the broader commercial utilization of currently available industrial lignins, lignin sulfonate (SL), kraft lignin (KL), and organosolv lignin (OL) are utilized to partially replace phenol in the synthesis of phenol formaldehyde (PF) adhesives. The impact of lignin production process on the effectiveness of lignin-based phenolic (LPF) adhesives is examined based on the structural analysis of the selected industrial lignin. The results show that OL has more phenolic hydroxyl groups, lower molecular weight, and greater number of reactive sites than the other two types of lignins. The maximum replacement rate of phenol by OL reaches 70% w/w, resulting in organosolv lignin phenolic (OLPF) adhesives with a viscosity of 960 mPa·s, a minimal free formaldehyde content of 0.157%, and a shear strength of 1.84 MPa. It exhibits better performance compared with the other two types of lignin-based adhesives and meets the requirements of national standards.     

Organosolv Fractionation of Birch Sawdust: Establishing a Lignin-First Biorefinery

The use of residual biomass for bioconversions makes it possible to decrease the output of fossil-based chemicals and pursue a greener economy. While the use of lignocellulosic material as sustainable feedstock has been tried at pilot scale, industrial production is not yet economically feasible, requiring further technology and feedstock optimization. The aim of this study was to examine the feasibility of replacing woodchips with residual sawdust in biorefinery applications. Woodchips can be used in value-added processes such as paper pulp production, whereas sawdust is currently used mainly for combustion. The main advantages of sawdust are its large supply and a particle size sufficiently small for the pretreatment process. Whereas, the main challenge is the higher complexity of the lignocellulosic biomass, as it can contain small amounts of bark and cambium. Here, we studied the fractionation of birch sawdust by organosolv pretreatment at two different temperatures and for two different durations. We evaluated the efficiency of fractionation into the three main fractions: lignin, cellulose, and hemicellulose. The cellulose content in pretreated biomass was as high as 69.2%, which was nearly double the amount in untreated biomass. The obtained lignin was of high purity, with a maximum 4.5% of contaminating sugars. Subsequent evaluation of the susceptibility of pretreated solids to enzymatic saccharification revealed glucose yields ranging from 75% to 90% after 48 h but reaching 100.0% under the best conditions. In summary, birch sawdust can be successfully utilized as a feedstock for organosolv fractionation and replace woodchips to simplify and lower the costs of biorefinery processes.     

Green and Efficient Processing of Cinnamomum cassia Bark by Using Ionic Liquids: Extraction of Essential Oil and Construction of UV‐Resistant Composite Films from Residual Biomass

There is significant interest in the development of a sustainable and integrated process for the extraction of essential oils and separation of biopolymers by using novel and efficient solvent systems. Herein, cassia essential oil enriched in coumarin is extracted from Cinnamomum cassia bark by using a protic ionic liquid (IL), ethylammonium nitrate (EAN), through dissolution and the creation of a biphasic system with the help of diethyl ether. The process has been perfected, in terms of higher biomass dissolution ability and essential oil yield through the addition of aprotic ILs (based on the 1‐butyl‐3‐methylimidazolium (C₄mim) cation and chloride or acetate anions) to EAN. After extraction of oil, cellulose‐rich material and free lignin were regenerated from biomass–IL solutions by using a 1:1 mixture of acetone–water. The purity of the extracted essential oil and biopolymers were ascertained by means of FTIR spectroscopy, NMR spectroscopy, and GC‐MS techniques. Because lignin contains UV‐blocking chromophores, the oil‐free residual lignocellulosic material has been directly utilized to construct UV‐light‐resistant composite materials in conjunction with the biopolymer chitosan. Composite material thus obtained was processed to form biodegradable films, which were characterized for mechanical and optical properties. The films showed excellent UV‐light resistance and mechanical properties, thereby making it a material suitable for packaging and light‐sensitive applications.     

Isolation options for non-cellulosic heteropolysaccharides (HetPS)

The isolation of non-cellulosic heteropolysaccharides (HetPS) from barley husks (Hordeum spp.) and yellow poplar wood chips (Liriodendron tulipifera) was accomplished using mild steam explosion followed by extraction with water and ultrafiltration. The generally low yields, low purity, and low degree of polymerization (DP) improved when the HetPS were isolated following either alkali extraction of hammermilled or disk-refined biomass, or from holocellulose preparations generated by the conventional chlorite method or by organosolv delignification. Several purification methods were examined including precipitation using methanol; treatment with hydrogen peroxide (H₂O₂) or activated carbon (C) followed by precipitation with methanol; and H₂O₂-treatment followed by ultrafiltration. The isolation protocols were judged based on product yield, xylan content, and DP. The results indicate that, although steam explosion is effective in removing HetPS from the fiber source, virtually none remain in polymeric form. By contrast, alkali extraction succeeds in separating polymeric HetPS from the fiber source; and HetPS purity increases and polydispersity decreases with fiber prehydrolysis and delignification. Significant processing difficulties were attributed to the intimate association of HetPS with lignin which was effectively disrupted by acid-catalyzed pretreatment and treatment with H₂O₂. Ultrafiltration of H₂O₂-treated HetPS solutions represents the best procedure for isolating a xylan-rich polymer in high yield, with high DP and with high purity. Aqueous HetPS solutions can be spray- or freeze-dried into powderous products.     

Comparison of hot-water extraction and steam treatment for production of high purity-grade dissolving pulp from green bamboo

The performance of hot-water extraction (HWE) and steam treatment (ST), followed by kraft pulping were compared for production of high purity-grade dissolving pulp from green bamboo. With the same prehydrolysis intensity (represented by the P-factor), the fractionation efficiency of HWE is far lower than that of ST. Because of lower removal of non-cellulosic components, the solid residue from HWE (even at approximately double the prehydrolysis intensity, P-factor = 1,379) required more active alkali (AA) during kraft pulping to obtain a cellulose purity equivalent to that achieved by the ST (P-factor = 756)-kraft process. To reach equivalent hemicellulose removal, HWE required more severe intensity than ST. However, FTIR and SEM characterizations of solid residue confirmed that intensified HWE resulted in significant lignin condensation. Antagonistic effects of hemicellulose removal and lignin condensation extent on subsequent kraft pulping were therefore more apparent in HWE than that in ST. Under the same kraft pulping conditions, lignin condensation from a severely intensified HWE process (P-factor = 2,020) caused greater cellulose yield and viscosity loss than that found for ST. Finally, at a given residual pentosan or lignin content, the cellulose yields from all HWE-kraft pulps were about 3 % lower than those from ST-kraft pulps. Consequently, based on an optimally setup chlorine dioxide bleaching stage, a cellulosic pulp with alpha-cellulose content of 97.6 % and viscosity of 927 mL/g was successfully produced from a ST-kraft pulp (P-factor = 756, AA = 19 %).     

Strategies to enhance the enzymatic hydrolysis of pretreated softwood with high residual lignin content

Pretreatment of Douglas-fir by steam explosion produces a substrate containing approx 43% lignin. Two strategies were investigated for reducing the effect of this residual lignin on enzymatic hydrolysis of cellulose: mild alkali extraction and protein addition. Extraction with cold 1% NaOH reduced the lignin content by only approx 7%, but cellulose to glucose conversion was enhanced by about 30%. Before alkali extraction, addition of exogenous protein resulted in a significant improvement in cellulose hydrolysis, but this protein effect was substantially diminished after alkali treatment. Lignin appears to reduce cellulose hydrolysis by two distinct mechanisms: by forming a physical barrier that prevents enzyme access and by non-productively binding cellulolytic enzymes. Cold alkali appears to selectively remove a fraction of lignin from steam-exploded Douglas-fir with high affinity for protein. Corresponding data for mixed softwood pretreated by organosolv extraction indicates that the relative importance of the two mechanisms by which residual lignin affects hydrolysis is different according to the pre- and post-treatment method used.     

Structural features and thermal degradation properties of various lignin macromolecules obtained from poplar wood (Populus albaglandulosa)

Four different lignins obtained from poplar wood (milled wood lignin: ML, organosolv lignin: OL, ionic liquid lignin: IL and Klason lignin: KL) were subjected to several types of chemical/thermal analyses to compare their structural features and thermal decomposition properties. The ML, OL, IL and KL yield from poplar wood was 5.5, 3.9, 5.8, 19.5 wt%, respectively. Functional group analysis revealed that during the OL and KL extraction processes, the condensation reaction involved with phenolic hydroxyl groups of lignins significantly prevailed, which led to a highly condensed OL and KL structure. Thermogravimetric analysis (TGA) results showed that OL and KL thermal stability was much higher than that of ML and IL. The derivatization followed by reductive cleavage (DFRC) data showed that the thermal stability was highly associated with the frequency of arylglycerol-β-aryl ether (β-O-4) linkages in the lignin polymers. Pyrolysis-GC/MS (Py-GC/MS) analysis confirmed that acetic acid and several types of phenolic compounds were the main lignin pyrolysis products. The maximum sum of ML (13.8 wt%), OL (9.9 wt%) and IL (11.8 wt%) pyrolysis products was obtained at the pyrolysis temperature of 600 °C, whereas KL (1.6 wt%) was significantly lower due to its high thermal stability and condensation degree. The S- and G-type pyrolysis products (S/G) ratio varied from 1.61 to 1.93 for ML, 2.28 to 5.28 for OL, 2.06 to 2.86 for IL and 1.40 to 2.20 for KL, depending on the pyrolysis temperature, which ranged between 400 °C and 700 °C.     

Size-exclusion chromatography of the soluble lignin products from hydrogen peroxide brightening of mechanical pulps

The molar mass distributions and yields of soluble lignin degradation products formed during the alkaline hydrogen peroxide brightening of spruce mechanical pulp have been determined. These distributions depend on pH, the extent to which the pulp was subjected to solvent extractions, H₂O₂ concentration and reaction time. At and below pH 11, there is an excellent correlation between the brightness and b values on pulp and the amounts of residual peroxide and lignin derived products in solution. Brightening reactions lead primarily to products with intermediate molecular mass values between 1500 and 6000. During multistage brightening, the products formed are initially those with high ionizable phenolic hydroxyl and low carbohydrate contents, and carbonyl-containing moieties. NMR and UV spectroscopic analysis show that products formed include lignin and carbohydrate-containing species. The lignin-originating products from the later stages contain a lower relative concentration of ionizable phenolic groups and more visible-absorbing and carbohydrate-containing species. Brightness and b gains during multistage brightening were exponential with product yield.     

Microwave-assisted extraction of phenolics from Canarium album L. and identification of the main phenolic compound

Microwave-assisted extraction (MAE) was applied in the extraction of phenolics from Canarium album L. Effects of various conditions including the solvent, solvent to material ratio, microwave power and irradiation time on extraction yield of phenolics were investigated. In terms of the optimal conditions of MAE, it was concluded that 70% (v/v) of ethanol was the proper extraction solvent, the solvent to material ratio was 10 : 1 (mL : g), and the microwave power and irradiation time were 600 W and 15 s, respectively. Compared with normal stirring extraction and ultrasound-assisted extraction, the MAE of phenolics from C. album L. was more time efficient and gave a high extraction rate. More than 1.2% extraction yield was achieved with MAE, and the purity of the phenolics in the extract product was up to 25%. In addition, by ultraviolet-visible (UV) spectrometry and electrospray ionised mass spectrometry (ESI/MS), the main phenolic compound in the extract product was identified as gallic acid.     

Catalyzed sulphite and semichemical pulping

Very high yield sulphite pulps were produced by cooking black spruce wafers in pulping liquors at pH 7 or 10, containing 0.1% (on O.D. wood) of soluble anthraquinone (SAQ). These pulps had better strength properties relative to controls prepared without SAQ, breaking length and burst index being greater, on average, by 20%. Other improvements included: increased pulping rate, lower lignin contents at comparable pulp yields, and higher carbohydrate content at the same level of residual lignin in pulp (this resulted in an increase of total pulp yield by 2%). Results of cooks in liquors ranging in pH from 4 to 10, and under variable conditions of time (20–60 min) and temperature (120–160°C) suggested that: firstly, AQ does not act as a pulping catalyst at pH 4, and secondly, the sulphonate contents of AQ-catalyzed pulps are lower than those of the uncatalyzed controls. In the light of the lower sulphonate content, the higher strength is unexpected.     

次烟煤与木质素共热溶物的液化及其Ni-Mo-S/Al2O3催化剂循环利用性能

对神府次烟煤与木质素共热溶得到的四种具有不同热溶产率的热溶物进行元素分析、红外光谱、同步荧光光谱等表征,对四种热溶物和神府原煤的加氢液化性能进行比较,并进行了催化剂在热溶物液化过程的循环利用性能研究。结果表明,神府煤热溶物较同一温度得到的神府煤与木质素共热溶物具有更多的芳香组分和四环及其以上的多环芳烃。热溶物较神府原煤在液化时具有更高的转化率和油收率。在催化剂Ni-Mo-S/Al₂O₃作用下,热溶物在液化过程中几乎全部转化,并具有很高的油收率,且神府煤与木质素共热溶物较神府煤热溶物具有更高的油收率。在神府煤与木质素共热溶物的液化过程中,催化剂Ni-Mo-S/Al₂O₃表现出优异的可循环利用性能,经过四次循环利用后没有观察到催化剂表面的炭沉积现象。     

Production of Terephthalic Acid from Corn Stover Lignin

Funneling and functionalization of a mixture of lignin‐derived monomers into a single high‐value chemical is fascinating. Reported herein is a three‐step strategy for the production of terephthalic acid (TPA) from lignin‐derived monomer mixtures, in which redundant, non‐uniform substitutes such as methoxy groups are removed and the desired carboxy groups are introduced. This strategy begins with the hydro‐treatment of corn‐stover‐derived lignin oil over a supported molybdenum catalyst to selectively remove methoxy groups. The generated 4‐alkylphenols are converted into 4‐alkylbenzoic acids by carbonylation with carbon monoxide. The Co‐Mn‐Br catalyst then oxidizes various alkyl chains into carboxy groups, transforming the 4‐alkylbenzoic acid mixture into a single product: TPA. For this route, the overall yields of TPA based on lignin content of corn stover could reach 15.5 wt %, and importantly, TPA with greater than 99 % purity was obtained simply by first decanting the reaction mixture and then washing the solid product with water.     

DMEAD: a new dialkyl azodicarboxylate for the Mitsunobu reaction

Di-2-methoxyethyl azodicarboxylate (DMEAD) is prepared in 65% yield in two steps as a crystalline solid. Use of DMEAD in the Mitsunobu reaction of a variety of alcohols with pronucleophiles results in good yields of the products under sufficient stereospecificity of inversion, as conventional diisopropyl azodicarboxylate (DIAD) does. Isolation of the product is, however, much easier with DMEAD than that with DIAD, because the hydrazine produced from DMEAD is highly hydrophilic and is completely separable by a simple extraction into neutral water. Purification of the organic layer, after separation of the other by-product, triphenylphosphane oxide, by filtration, easily provides high purity of the product in a good yield. Concentration of the water layer yields the hydrazine, which can be reused for the preparation of DMEAD. One-step removal of the two by-products by the aqueous extraction was also possible when trimethylphosphane and DMEAD were employed.     

生物质三组分热裂解行为的对比研究

在热天平上对比研究了生物质中的纤维素、半纤维素和木质素三种主要组分的热失重规律。结果表明，作为半纤维素模型化合物的木聚糖热稳定性差，在217℃～390℃发生明显分解；纤维素热裂解起始温度最高，且主要失重发生在较窄温度区域，固体残留物仅为6.5%；木质素表现出较宽的失重温度区域，最终固体残留物高达42%。在红外辐射机理试验台上对比研究了三组分热裂解产物随温度的变化规律。三组分热裂解生物油产量随温度变化先升后降。纤维素生物油产量在峰值上最高，但纤维素生物油热稳定性差，高温时挥发分的二次分解最明显；木聚糖和木质素生物油产量较低，表现出较好的热稳定性。三组分热裂解焦炭产量随温度升高而降低，最终纤维素热裂解焦炭产量为1.5%，而木聚糖和木质素分别为22%和26%。三组分热裂解气体产物随温度升高而增长，但在气体组成分布上因三组分的结构上的差异而不同。     

Understanding the Nonproductive Enzyme Adsorption and Physicochemical Properties of Residual Lignins in Moso Bamboo Pretreated with Sulfuric Acid and Kraft Pulping

In this work, to elucidate why the acid-pretreated bamboo shows disappointingly low enzymatic digestibility comparing to the alkali-pretreated bamboo, residual lignins in acid-pretreated and kraft pulped bamboo were isolated and analyzed by adsorption isotherm to evaluate their extents of nonproductive enzyme adsorption. Meanwhile, physicochemical properties of the isolated lignins were analyzed and a relationship was established with non-productive adsorption. Results showed that the adsorption affinity and binding strength of cellulase on acid-pretreated bamboo lignin (MWLa) was significantly higher than that on residual lignin in pulped bamboo (MWLp). The maximum adsorption capacity of cellulase on MWLp was 129.49 mg/g lignin, which was lower than that on MWLa (160.25 mg/g lignin). When isolated lignins were added into the Avicel hydrolysis solution, the inhibitory effect on enzymatic hydrolysis efficiency of MWLa was found to be considerably stronger than that with MWLp. The cellulase adsorption on isolated lignins was correlated positively with hydrophobicity, phenolic hydroxyl group, and degree of condensation but negatively with surface charges and aliphatic hydroxyl group. These results suggest that the higher nonproductive cellulase adsorption and physicochemical properties of residual lignin in acid-pretreated bamboo may be responsible for its disappointingly low enzymatic digestibility.     

碱木质素超/亚临界乙醇体系解聚机理研究

采用微型高温高压反应釜,在超/亚临界乙醇体系,进行麦草碱木质素的解聚实验,通过扫描电子显微镜(SEM)、气相色谱/质谱联用仪(GC/MS)及红外光谱仪(FT-IR)对解聚产物进行分析,探讨大分子结构的解聚机理。结果表明,碱木质素在乙醇临界点条件(240℃,7.2 MPa)解聚获得最低残焦得率,数值为16.5%。碱木质素在亚临界乙醇体系解聚过程,碱木质素熔融形成直径1.0-2.0μm的微球分散于乙醇中,结构单体间少量醚键和苯环侧链Cα均裂断裂,形成酚类、酯类、酮类和酸类产物;碱木质素在超临界乙醇体系解聚过程,熔融微球直径明显缩小,解聚时发生大量结构单体间醚键、苯环侧链Cα断裂及酯类产物的二次分解反应,解聚产物中酯类产物含量(11.94%)降低,酚类产物得率(52.14%)提高。