麦草碱木质素的微波辅助液化降解

研究了微波辅助条件下液化剂、催化剂、反应温度和反应时间对麦草碱木质素进行液化降解制备生物油收率的影响,并利用红外光谱(FT-IR)、气相色谱质谱联用仪(GC-MS)和核磁共振氢谱(1H-NMR)对产物进行表征。结果表明,微波辅助下以甲醇为液化剂,硫酸铁为催化剂液化降解碱木质素可以显著缩短液化反应时间,在160℃相对较低液化温度下反应5 min,生物油的收率达到55.22%。液化降解后的木质素残渣结构变化少,表明木质素降解产物的重新聚合的几率低,碱木质素反应原料可以回收再利用以提高原料利用率。生物油主要为单酚类物质,其中,S型、G型和H型单体的含量分别为57.72%、25.28%和8.98%。核磁共振氢谱中β-O-4键和C-C键质子峰的存在说明生物油中含有部分的二聚体和低聚体酚类化合物。     

Microwave assisted liquefaction of wheat straw alkali lignin for the production of monophenolic compounds

The microwave assisted liquefaction process of wheat straw alkali lignin was investigated to obtain monophenolic compounds as the precursor of bio-fuel. It is found that the total yield of monophenolic compounds is significantly improved under microwave irradiation, reaching 15.77%under a relatively mild liquefaction condition of 10 wt% H2SO4 as the catalyst, 10 wt% phenol as the hydrogen-donor reagent at 120?C for40 min. Compared with conventional thermal liquefaction process, microwave irradiation promotes the cleavage of C–C bonds, which gives an extra 29% of Caryl–Cα bond cleavage, and increases the yield of monophenolic compounds from 0.92% to 13.61% under the same conditions.The excessive temperature and prolonged time under microwave irradiation will promote the recondensation of degraded lignin fragments, so the key to obtain high yield of monophenolic compounds is to avoid the recondensation reaction. The selected solid catalyst promotes the dissociation of methoxy groups, and the addition of phenol into liquefaction can only slightly improve the yield of monophencolic compounds.     

Characterization of hemicelluloses isolated with tetraacetylethylenediamine activated peroxide from ultrasound irradiated and alkali pre-treated wheat straw

Post-treatment with 2% H₂O₂-0.2% tetraacetylethylenediamine (TAED) at pH 11.8 for 12 h at 48 °C solubilized 27.1-28.1% of the original hemicelluloses and 43.3-46.2% of the original lignin from the ultrasound irradiated and alkali pre-treated wheat straw. It was found that the bleaching activator TAED forms peracetic acid with hydroperoxide anion in aqueous alkali and improves the brightness of the solubilized hemicelluloses. Xylose was a predominant sugar in all the hemicellulosic preparations, comprising 72.0-73.1% of the total sugars. Arabinose (13.4-13.9%) and glucose (6.7-7.9%) were detected as the second and third major neutral sugar constituents. In addition, the hemicelluloses also contained a noticeable amount of 4-O-methyl-d-glucuronic acid (6.0-7.0%) together with a small amount of galactose (4.3-4.9%) and minor quantities of rhamnose (1.5-1.8%) and mannose (0.5-0.8%). Furthermore, the hemicellulosic preparations obtained by TAED activated peroxide extraction showed a relatively lower content of associated lignin (3.8-4.4%), but a higher molecular weight (34,210-40,310 g mol⁻¹). No significant differences in the structural features such as oxidation of the hemicelluloses by TAED were observed as compared to those obtained by alkaline peroxide without bleaching activator.     

Ethanol production from steam-explosion pretreated wheat straw

Bioconversion of cereal straw to bioethanol is becoming an attractive alternative to conventional fuel ethanol production from grains. In this work, the best operational conditions for steam-explosion pretreatment of wheat straw for ethanol production by a simultaneous saccharification and fermentation process were studied, using diluted acid [H₂SO₄ 0.9% (w/w)] and water as preimpregnation agents. Acid-or water-impregnated biomass was steam-exploded at different temperatures (160–200°C) and residence times (5, 10, and 20 min). Composition of solid and filtrate obtained after pretreatment, enzymatic digestibility and ethanol production of pretreated wheat straw at different experimental conditions was analyzed. The best pretreatment conditions to obtain high conversion yield to ethanol (approx 80% of theoretical) of cellulose-rich residue after steam-explosion were 190°C and 10 min or 200°C and 5 min, in acid-impregnated straw. However, 180°C for 10 min in acid-impregnated biomass provided the highest ethanol yield referred to raw material (140 L/t wheat straw), and sugars recovery yield in the filtrate (300 g/kg wheat straw).     

Characterisation of degraded organosolv hemicelluloses from wheat straw

Treatment of the dewaxed wheat straw with acetic acid-H₂O (65/35, v/v), acetic acid-H₂O (80/20), acetic acid-H₂O (90/10), formic acid-acetic acid-H₂O (20/60/20), formic acid-acetic acid-H₂O (30/60/10), methanol-H₂O (60/40), and ethanol-H₂O (60/40) using 0.1% HCl as a catalyst at 85 °C for 4 h degraded 42.4, 58.7, 70.0, 65.1, 76.5, 14.2, and 22.2% of the original hemicelluloses and 78.2, 80.0, 88.2, 89.4, 94.1, 23.5, and 37.4% of the original lignin, respectively. It was found that substantial hemicelluloses and lignin were degraded during the treatment with organic acids. The optimum condition for degradation of hemicelluloses was found to use a mixture of formic acid-acetic acid-H₂O (30/60/10), which yielded 76.5% of the original hemicelluloses from wheat straw. Xylose was a major constituent in all the degraded hemicellulosic preparations. Glucose and arabinose appeared in noticeable amounts. Uronic acids, principally 4-O-methyl-d-glucuronic acid occurred in a small amount. Galactose, mannose, and rhamnose were present as minor components. In comparison, the five degraded hemicellulosic preparations isolated during the treatment with organic acids were more linear and partially acetylated, whereas the two acidic alcohol-degradable hemicelluloses were more branched. The FT-IR and liquid-state ¹³C NMR analyses revealed that the organosolv treatments under the acidic conditions substantially degraded the hemicellulosic polymers as shown by their lower molecular weights ranging between 8480 and 18,940 g mol⁻¹. The thermal stability of the hemicellulosic preparations, degraded during the aqueous organic acids, was lower than that of the hemicellulosic preparations, degraded during the aqueous alcohols.     

Examination of manufacturing porous plate materials from wheat straw

The role of parameters of a barothermal processing wheat straw in the hydrolysis of polysaccharides and also their influence on the process of manufacturing porous plate materials were studied.     

Nitrobenzene oxidation of fractions of cotton-plant dioxane lignin

Summary Analysis of the products of alkaline nitrobenzene oxidation of lignin fractions has confirmed their chemical inhomogeneity and has shown that in the various fractions the amounts of condensed syringly and guaiacyl structures differed markedly.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii No. 1, pp. 82–84, January–February, 1979.     

Isolation of individual fractions of dioxane lignin from kenaf stems and their study

Summary 1. Three fractions of dioxane lignin have been isolated from kenaf stems of the variety Uzbekskii-15-74 by stepwise extraction with aqueous dioxane containing HCl.2. On the basis of the results of elementary and functional analyses, semiempirical formulas of all the fractions have been derived, and their IR and UV spectra have been recorded.3. It has been shown that an increase in the time of extraction leads to a rise in the molecular weight of the fractions and to a decrease in their degree of polydispersity.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 637–641, September–October, 1978.     

Nitration of lignin isolated from spruce wood by mechanical grinding

Summary 1. The nitration of spruce lignin obtained by mechanical grinding has been carried out with nitric acid in an anhydrous medium under heterogeneous and homogeneous conditions. Fractionation of the nitrolignin has been carried out and the elementary and functional composition of the fractions has been determined; the mean semi-empirical formulas of the C₉ structures have been calculated for both fractions. It has been shown that, depending on the nitration conditions, from one to two nitro groups enter the C₆-C₃ structural element of nitrolignin and, with an excess of HNO₃, nitrate groups as well.The fall in the content of OCH₃ groups corresponds to the content of phenolic hydroxyl groups in the initial MGL and can be explained by the demethylation of the guaiacyl structures of the lignin on nitration.Khimiya Prirodnykh Soedinenii, Vol. 2, No. 1, pp. 58–65, 1966     

Elucidation of the complex molecular structure of wheat straw lignin polymer by atmospheric pressure photoionization quadrupole time-of-flight tandem mass spectrometry

Wheat straw lignin was extracted using the novel CIMV procedure which selectively separates the cellulose, hemicelluloses and lignin. Solid-state (13)C NMR experiments using cross polarization/magic angle spinning (CP/MAS) were carried out on the extracted wheat straw lignin and some structural indices were revealed. Atmospheric pressure photoionization mass spectrometry (APPI-MS) has proven to be a powerful analytical tool capable of ionizing small to large lignin oligomers, which cannot be ionized efficiently by atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI). The APPI mass spectra of the extracted wheat straw lignin were recorded in the positive and negative ion modes. Positive ion mode APPI-MS indicated the exact presence of 39 specific oligomeric ions. Negative ion APPI-MS indicated the additional presence of at least 18 specific oligomeric ions. The structural characterization of this novel and complete series of 57 specific related oligomers was achieved by calculating the exact molecular masses measured by high-resolution quadrupole time-of-flight mass spectrometry (QqToF-MS). Some oligomeric species photoionized in both the positive and negative ion modes to form the respective protonated and deprotonated molecules. Low-energy collision-induced dissociation tandem mass spectrometric analyses performed with a QqToF-MS/MS hybrid instrument provided unique dissociation patterns of the complete series of novel precursor ions. These MS/MS analyses provided diagnostic product ions, which enabled us to determine the exact molecular structures and arrangement of the selected 57 different related ionic species.     

Molecular characterization of arabinoxylans from hull-less barley milling fractions

Arabinoxylans were prepared from different hull-less barley milling fractions (bran, shorts and flour). The yields of hull-less bran arabinoxylan (HBB-AX), shorts arabinoxylan (HBS-AX) and flour arabinoxylan (HBF-AX) were 8.42%, 4.08% and 2.13% respectively. Sugar composition analysis showed that arabinose and xylose were the main sugars. HBF-AX had the highest Ara/Xyl ratio, followed by HBS-AX and HBB-AX. Size exclusion chromatography analysis (HPSEC) showed that HBF-AX had the highest molecular weight, followed by HBS-AX and HBB-AX, which had the lowest molecular weight. Aqueous solutions of HBB-AX, HBS-AX and HBF-AX had higher molecular weight(Mw) than in 0.5 mol/L NaOH and 1.0 mol/L NaOH. Dynamic light scattering analysis (DLS) showed that HBB-AX, HBS-AX and HBF-AX had existed in two states in distilled water, 0.5 mol/L NaOH, 1.0 mol/L NaOH, and DMSO/H?O (90/10), an unaggregated state and an aggregated state, with the latter predominating.     

Uranium removal from aqueous solutions by wood powder and wheat straw

The influence of initial uranium concentration, solution pH, contact time and adsorbent mass was investigated for removal of uranium from aqueous solutions by pine wood powder and wheat straw using a batch technique. The maximum removal efficiency of uranium achieved at pH 8 and 7 for pine wood powder and wheat straw, respectively. Langmuir and Freundlich adsorption isotherms and three kinetic models of adsorption including; Elovich, Lagergren pseudo-first and Lagergren pseudo-second order were used to describe the adsorption mechanisms. The uranium sorption onto wood and wheat straw powders followed a Freundlich isotherm. The kinetic studies showed that the data fitted very well to the pseudo-second order model in the studied concentration range of uranium for both adsorbents. Uranium desorption from loaded adsorbents also studied using batch techniques as a function of desorptive reagent, desorption time and desorptive reagent concentration. The results of the experiment indicated that the optimum desorption efficiency of uranium for wood powder and wheat straw occurred in 5 min shaking time, using 1.5 M HNO₃ and 2 M Na₂CO₃ solutions, respectively.     

麦草半纤维素的快速热裂解实验研究

采用管式炉反应器在550℃~850℃进行了半纤维素的高温快速热裂解实验,以了解其热裂解产物分布及热解规律。结果表明,半纤维素热解三相产物中,气体产物产率最大且随着温度的升高而增加,其主要成分为H₂、CO、CO₂、CH₄ 以及小分子烃类。液相产物中主要是酸类、醇类、呋喃、环戊烯酮类化合物,以及苯酚等芳香化合物,其产率随着温度的升高无明显变化。而焦炭产率则随着温度的升高而降低,且其中残留有大量的有机化合物如醇类、酮类及脱水糖等。     

Wheat straw lignin extraction with bio-based solvents using enabling technologies

Two bio-based solvents, natural deep eutectic solvents (NaDESs) and γ-valerolactone (GVL), have been used under microwave (MW), and ultrasound (US) irradiation to design an efficient and sustainable process for wheat straw delignification and have been compared with the traditional alkali procedure. Best delignification (45%) was achieved with a three-component NaDES (lactic acid/glycerol/choline chloride) under MW irradiation (at 120 °C in 30 min), with solid/liquid ratio of 1:50. A GVL/water mixture (8:2) also gave an efficient delignification (27%) under US irradiation (40 kHz, 200 W) at 50 °C for 60 min. Analytical pyrolysis (Py) coupled with GC/MS/FID, provides valuable information on the extracts’ chemical profile. DPPH and Folin–Ciocalteu tests highlighted the efficiency of MW- and US-assisted extraction as well as the extracts quality. The highest antioxidant activity for the NaDES extracts was obtained under US irradiation.     

Structure and morphology of cellulose in wheat straw

The structure and morphology of cellulose extracted from wheat were studied. It was found that the extraction process is effective and hemicelluloses and lignin can be extracted completely. Cellulose in wheat straw was identified as cellulose I allomorph with low crystallinity and the crystallinity of cellulose from different parts of the wheat straw has little difference. There was no metastable cellulose I crystalline modification found in wheat straw; only the more stable cellulose I crystalline modification existed. Cellulose chains in the epidermis of wheat straw were observed with their orientation along the growth direction of wheat straw, while those in parenchyma were observed with almost no preferred orientation. There are two kinds of morphologies on the surface of wheat straw. One is the fiber structure with fibrils of about 5 m diameter, and the other is the fiber structure with serration morphology at the edge of the fiber, with which the fibers are connected together. The diameter of the latter one is about 10 m. The vascular bundles consist of circular rings while spiral structure cellulose backbones covered with thin cellulose film were also observed.     

Ozone pretreatment and fermentative hydrolysis of wheat straw

Principles of the ozone pretreatment of wheat straw for subsequent fermentation into sugars are investigated. The optimum moisture contents of straw in the ozonation process are obtained from data on the kinetics of ozone absorbed by samples with different contents of water. The dependence of the yield of reducing sugars in the fermentative reaction on the quantity of absorbed ozone is established. The maximum conversion of polysaccharides is obtained at ozone doses of around 3 mmol/g of biomass, and it exceeds the value for nonozonated samples by an order of magnitude. The yield of sugar falls upon increasing the dose of ozone. The process of removing lignin from the cell walls of straw during ozonation is visualized by means of scanning electron microscopy.