Molecular Characteristics of Kraft-AQ Pulping Lignin Fractionated by Sequential Organic Solvent Extraction

Kraft-AQ pulping lignin was sequentially fractionated by organic solvent extractions and the molecular properties of each fraction were characterized by chemical degradation, GPC, UV, FT-IR, (13)C-NMR and thermal analysis. The average molecular weight and polydispersity of each lignin fraction increased with its hydrogen-bonding capacity (Hildebrand solubility parameter). In addition, the ratio of the non-condensed guaiacyl/syringyl units and the content of β-O-4 linkages increased with the increment of the lignin fractions extracted successively with hexane, diethylether, methylene chloride, methanol, and dioxane. Furthermore, the presence of the condensation reaction products was contributed to the higher thermal stability of the larger molecules.     

Modified Kraft Pulping of Bagasse: Infrared Spectroscopy of Lignin

Abstract

The infrared spectroscopy of precipitated lignin from waste black liquors of bagasse pulping with kraft sulfite pulping process was investigated. Also the effect of anthraquinon and methanol addition in the soda, kraft and kraft-sulfite pulping liquor on the infrared specra of the precipitated lignin was studied. The presence of methanol in the pulping liquor causes an increase in the degradation as well as increase in the carboxylic group in the precipitated lignin. Also, the phenolic hydroxyl group in case of kraft lignin is higher than soda lignin. Presence of sulfite in the kraft-sulfite pulping liquor produces lignin hydroxyl groups.     

Improvement of the oxidation stability of biodiesel as prepared by supercritical methanol method with lignin

An antioxidation effect of lignin‐derived products in biodiesel prepared using supercritical methanol (300°C/20 MPa) with molar ratio between rapeseed oil and methanol of 1:42 was studied. It was found that lignin could be decomposed to low molecular compounds that have a free radical‐trapping effect after supercritical methanol treatment. However, longer treatment time decreased the antioxidation effect of the lignin‐derived compounds. Rapeseed biodiesel prepared by supercritical methanol method at 300°C/20 MPa for 20 min with a small amount of added lignin showed an induction period longer than 6 h at 110°C in a Rancimat test. In addition, it was found that lignin had a catalytic effect in biodiesel production using the supercritical methanol method without significantly affecting other fuel properties of the prepared biodiesel. Thus, the study proved that lignin addition provides an inexpensive and technically acceptable way to improve the oxidation stability of biodiesel prepared by the supercritical methanol method with satisfactory fuel properties.     

Immobilized laccase on magnetic nanoparticles for enhanced lignin model compounds degradation

As a natural aromatic polymer, lignin has great potential but limited industrial application due to its complex chemical structure. Among strategies for lignin conversion, biodegradation has attracted promising interest recently in term of efficiency, selectivity and mild condition. In order to overcome the issues of poor stability and non-reusability of enzyme in the biodegradation of lignin, this work explored a protocol of immobilized laccase on magnetic nanoparticles (MNPs) with rough surfaces for enhanced lignin model compounds degradation. Scanning electron microscope with energy dispersive spectrometer (SEM-EDS), flourier transformation infrared spectroscopy (FTIR) and thermal gravimetric analysis (TGA) were utilized to characterize the immobilization of laccase. The results showed a maximum activity recovery of 64.7% towards laccase when it was incubated with MNPs and glutaraldehyde (GA) with concentrations of 6 mg·ml^-1 and 7.5 mg·ml^-1 for 5 h, respectively. The immobilized laccase showed improved thermal stability and pH tolerance compared with free laccase, and remained more than 80% of its initial activity after 20 days of storage at 4 ℃. In addition, about 40% residual activity of the laccase remained after 8 times cycles. Gas chromatography-mass spectrometry (GC-MS) was utilized to characterize the products of lignin model compound degradation and activation, and the efficiency of immobilized laccase was calculated to be 1-5 times that of free laccase. It was proposed that the synergistic effect between MNPs and laccase displays an important role in the enhancement of stability and activity in lignin model compound biodegradation.     

Immobilized laccase on magnetic nanoparticles for enhanced lignin model compounds degradation

As a natural aromatic polymer, lignin has great potential but limited industrial application due to its complex chemical structure. Among strategies for lignin conversion, biodegradation has attracted promising interest recently in term of efficiency, selectivity and mild condition. In order to overcome the issues of poor stability and non-reusability of enzyme in the biodegradation of lignin, this work explored a protocol of immobilized laccase on magnetic nanoparticles(MNPs) with rough surfaces for enhanced lignin model compounds degradation.Scanning electron microscope with energy dispersive spectrometer(SEM-EDS), flourier transformation infrared spectroscopy(FTIR) and thermal gravimetric analysis(TGA) were utilized to characterize the immobilization of laccase. The results showed a maximum activity recovery of 64.7% towards laccase when it was incubated with MNPs and glutaraldehyde(GA) with concentrations of 6 mg·ml~(-1) and 7.5 mg·ml~(-1) for 5 h, respectively. The immobilized laccase showed improved thermal stability and pH tolerance compared with free laccase, and remained more than 80% of its initial activity after 20 days of storage at 4 ℃. In addition, about 40% residual activity of the laccase remained after 8 times cycles. Gas chromatography–mass spectrometry(GC–MS) was utilized to characterize the products of lignin model compound degradation and activation, and the efficiency of immobilized laccase was calculated to be 1–5 times that of free laccase. It was proposed that the synergistic effect between MNPs and laccase displays an important role in the enhancement of stability and activity in lignin model compound biodegradation.     

Delignification Mechanism During High-Boiling Solvent Pulping. IV. Effect of a Reducing Sugar on the Degradation of Guaiacylglycerol-β-guaiacyl Ether

Abstract

A phenolic β-O-4 type lignin model compound, guaiacylglycerol-β-guaiacyl ether was treated with 70 wt% aqueous 1,3-butanediol solution in the presence of glucose at 160–200°C to investigate the effect of reducing sugars on the degradation of lignin during high-boiling solvent (HBS) pulping. Addition of glucose increased the formation of guaiacol, coniferyl alcohol, and its γ-ethers, and decreased the formation of radical coupling compounds dramatically. These results suggest that reducing sugars may stabilize phenoxy radicals formed by homolysis of phenolic β-ethers. The kinetic studies also revealed that the disappearance of the β-ether model compound was enhanced substantially by the presence of glucose, which suggests that in addition to homolysis of the β-ether, a reducing sugar-assisted β-ether cleavage may be involved under the conditions used.     

Demethylation and Nitration of Lignin

Abstract

The formation of methanol during treatment of wood meal with nitrogen dioxide is favored by the presence of oxygen and suppressed by addition of sodium sulfate. With 0.5% of added nitrogen dioxide large amounts of methanol were produced at 70°C when kraft lignin was impregnated with 0.5M nitric acid. A markedly increased formation of methanol and nitro groups in the lignin occurred when sodium nitrate was added. At low acidity the effect of sodium nitrate was insignificant. In a solution which was 0.5 molal with respect to nitric acid and 0.8 molal with respect to sodium nitrate, appreciable amounts of methanol and nitro groups were produced even when no nitrogen dioxide was added. This is explained by a generation of nitrogen dioxide from nitric acid in a autocatalytic process favored by high concentrations of nitrate and hydrogen ions.     

Methanol formation from methane partial oxidation in CH4–O2–NO gaseous phase at atmospheric pressure

The reaction condition for high yield of methanol in a gaseous reaction between methane and oxygen in the presence of NO at atmospheric pressure was explored. Methane partial oxidation without NO (CH₄–O₂) gave only 1% conversion of methane at 966 K. The addition of NO led to a remarkable increase in methane conversion and to high selectivity to C₁-oxygenates. The conversion of methane attained 10% at 808 K in the presence of NO (0.5%) where the selectivities to methanol and formaldehyde were 22.1 and 24.1%, respectively. Nitromethane and carbon oxides were also observed in the product gas. The amount of nitromethane was almost equal and/or near to that of initial NO. The carbon monoxide produced was several times higher than carbon dioxide. Influences of NO concentration, ratio of methane to oxygen, water vapor, and dilution with helium gas on product distribution were measured. Low concentration of NO (0.35–0.55%) was favorable for methanol formation. High selectivity to methanol was obtained at low value of the ratio of methane to oxygen (2.0–3.0) or low concentration of dilution gas (<16%). The NO₂ added promoted methane partial oxidation and selectivity to methanol. Therefore, it was assured that NO_x promoted the formation of CH₃√ and CH₃O√ in the gas phase reaction for CH₄–O₂–NO.     

On the formation of degradation products from the pyrolysis of tall oil fatty acids with kraft lignin

Mixtures of tall oil fatty acids and kraft lignin from southern pine wood were pyrolyzed at 160 C and 280 C with or without exclusion of oxygen. In addition to fatty acids of various chain lengths and aromatic degradation products from lignin, a number of homologousn-alkylbenzenes were formed (ca. 1.5%) and characterized by gas chromatography-mass spectrometry. The possible ways of formation of the latter from fatty acids are discussed briefly.     

Fundamental Study of Relative Delignification Efficiencies (III): Organosolv Pulping Systems

Reactions of l-(4-guaiacyl)-2-(O-guaiacyl)-l,5-pentanediol (1) provide relative rates of pulping reactions that involve quinone methides (QMs). Model 1 was reacted under soda, kraft, soda/anthrahydroquinone (AHQ), and sulfite conditions in the presence of various water/alcohol media. All alkaline reactions displayed the same lignin model disappearance rate, verifying that QM formation was the rate-determining step. Alcohol addition had the following effect on increasing the paryl ether cleavage of model 1: no increase for methanol addition to soda, kraft, and alkaline SO₃ ^?2 systems; small increase for isopropanol addition to neutral sulfite and acid bisulfite systems; large increase for methanol addition to the soda/AHQ system. In the latter case, the amount of enhancement correlated with the level of methanol present; other solvent/water media exhibited a similar response as methanol. Several hypotheses relating to electron transfer (radical) chemistry are postulated for the observed synergism between the solvent and AHQ.     

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。     

漆酶-助剂体系催化氧化具有α-苄基氢的木素模型物

研究了漆酶—助剂体系催化氧化具有等基氢不同结构的木索非酚型和酚型模型化合物，结果表明非酚型具有苄醇结构的木素模型化合物能发生α位脱氢氧化，但此氧化反应是有限度的，氧化的结果主要生成芳香醛，没有发现进一步被氧化成芳香酸。而具有Cα和Cβ双键的化合物，α位的氢却很稳定，不能被氧化。酚型的本素模型化合物在漆酶的催化反应体系中发生聚合。     

桉木光诱导氧化降解研究

本文研究了尾叶桉（Eucalyptusurophylla）木粉在光照射下其木素和多聚糖的变化行为．研究表明，在光照射下木素及木素结构单元中的甲氧基含量降低，多聚糖含量降低，铜价升高．UV分析可知，木素光降解产物中羰基或与苯环共轭的乙烯双键结构较多．经GC－MS分析鉴定出尾叶桉SCMP浆40种低分子量木素光氧化降解产物，其中丁香基型占58．10％，愈疮木基型占18．75％，其它占21．93％，主要降解产物包括丁香醛、2－羟基－3－丁香基丙酸、3，4－二羟基苯甲酸,2－丁香基乙醇、丁香酸、丁香酸和香兰素等.另外也研究了光降解过程中木素自由基变化行为。ESR分析测定表明，光照射产生的自由基在纯的氮气或二氧化碳中相对稳定，在空气或氧气中游离基迅速衰减，从而证实光诱导氧化作用是木材或富含木素化学机械浆光降解的重要作用。     

木质素在超临界甲醇和乙醇溶剂中液化过程分析

通过研究木质素分别在超临界甲醇和乙醇溶剂中的液化过程，分析反应温度（260～340℃）及反应时间（0～120min）对木质素在两种溶剂中的转化率、生物油收率及其组分差异的影响。实验表明，木质素在超临界乙醇中的转化率及产物收率均高于甲醇。当反应温度340℃，反应时间60min，木质素在超临界乙醇中的转化率和生物油收率比在甲醇中分别提高了16.23%和11.54%，残渣收率降低了16.23%。通过GC-MS和FTIR对生物油和残渣分析，发现生物油组分中芳香族化合物相对含量较高，在甲醇和乙醇溶剂中分别达到66.13%和58.84%；随着反应时间的延长，甲醇溶剂中残渣的醚键官能团逐渐增强，而在乙醇溶剂中则先增强后减弱。分析认为在木质素降解过程中，超临界乙醇和甲醇均可产生氢自由基作为供氢体，攻击木质素及其大分子片段中的官能团，同时使液化产物中的活性片段减活，减弱重聚合反应，从而更利于芳烃产物的生成。而甲醇在液化过程中容易与木质素断键产生的苯酚中间体发生脱氢缩合反应，通过醚键聚合产生长链芳香族化合物，形成残渣，降低生物油收率。     

Ozonation Reactions of Monomer and Dimer Lignin Models: Influence of a Catalytic Amount of a Manganese Cyclam Derivative on the Ozonation Reaction

This work focuses on the study of the reactivity of ozone with lignin models such as vanillin and dehydro-di-isoeugenol (DHDIE) in methanol solution. The primary by-products formed are characterized by Gas Chromatography - Mass Spectrometry (GC-MS) and possible mechanisms for the formation of these by-products are suggested. In the presence of a catalytic amount of a manganese tetraazamacrocyclic complex, other degradation derivatives are identified during DHDIE ozonation, proving that the complex induces a different reactivity of ozone towards the model.     

木质素与含磷阻燃剂对环氧树脂固化物阻燃性能的影响

利用不同质量比的木质素、苯酐（PA）、环氧树脂（EP）、2-（二苯基磷酰基）琥珀酸（DPPOSA）共固化制备出一系列环氧树脂固化物,采用极限氧指数测试、UL-94垂直燃烧评级测试、锥形量热仪热释放速率和总热释放量测试、空气条件下的热重分析测试和扫描电镜对环氧固化物进行测试和分析。当EP为90.0%、PA为6.5%、DPPOSA为2.0%、木质素为1.5%时制备的环氧固化物（P-12）的热稳定性能和阻燃性能得到了明显的改善。阻燃性能测试表明：其极限氧指数（LOI）达到34.6%,垂直燃烧测试通过UL-94的V-0级,热释放速率和热释放总量也有效降低;热降解测试结果表明：DPPOSA和木质素的加入可以使材料的降解时间提前,成炭能力增强;扫描电镜结果显示：添加DPPOSA和木质素的环氧固化物燃烧后形成连续、均一、紧密的炭层,进一步证明DPPOSA和木质素的加入使环氧固化物的成炭能力得到增强。     

Catalysts for Direct Methanol Fuel Cells

The activity of in house prepared carbon-supported Pt-Ru catalysts for methanol oxidation and carbon-supported RuSe for the oxygen reduction reaction in direct methanol fuel cells (DMFCs) was investigated. The composition of Pt-Ru/C was varied both in terms of weight loading (ratio of total metal content to carbon) as well as the ratio of Pt to Ru. The measurements were carried out in a half cell arrangement in sulphuric acid at various temperatures. The weight loading and ratio of Pt to Ru were varied in order to find out the optimum weight loading of precious metal and the temperature dependence of Pt to Ru ratio on methanol oxidation reaction. It has been found that there exists an optimum in the weight loading at 60 wt.% for carbon-supported Pt-Ru catalyst towards its maximum mass activity. While 1:1 Pt to Ru ratio exhibits a higher activity than 3:2 Pt:Ru above 60 °C, 3:2 ratio exhibits a higher activity at lower temperature. It has been observed that RuSe is inactive towards methanol and it is realised that RuSe is a potential candidate as methanol tolerant oxygen reduction catalyst. The activity of carbon supported RuSe for oxygen reduction reaction (ORR) was tested in sulphuric acid in the presence of methanol. Even though the mass specific activity of the RuSe catalyst is somewhat lower than that of Pt/C, the surface activity of carbon-supported RuSe is superior than that of carbon supported Pt which indicate the unfavourable size distribution of RuSe/C catalyst.     

Effect of Soda-Additive Pulping on Molecular Characteristics of Residual Pulp Lignin

The soda-additive pulps of pine wood were compared to corresponding soda and kraft pulps in respect to the macromolecular properties of the residual pulp lignins. Results of measurements of number and weight—average molecular weights as well as branching parameters show that the presence of additives such as anthraquinone, methanol and O₂—pretreatment significantly causes the breaking of cross-links in the pulp lignin. On the other hand, ethylenediamine and hydroeulfide ion contribute mainly to extensive lignin degradation. The influence of used additives on the condensation reactions of the residual lignin has also been studied.     

Synergetic effects of graphene platelets and carbon nanotubes on the mechanical and thermal properties of epoxy composites

A remarkable synergetic effect between the multi-graphene platelets (MGPs) and multi-walled carbon nanotubes (MWCNTs) in improving the mechanical properties and thermal conductivity of epoxy composites is demonstrated. Stacking of individual two-dimensional MGPs is effectively inhibited by introducing one-dimensional MWCNTs. Long and tortuous MWCNTs can bridge adjacent MGPs and inhibit their aggregation, resulting in a high contact area between the MGP/MWCNT structures and the polymer matrix. Scanning electron microscope images of the fracture surfaces of the epoxy matrix showed that MWCNT/MGP hybrid nanofillers exhibited higher solubility and better compatibility than individual MWCNTs and MGPs did. The tensile strength of GD400-MWCNT/MGP/epoxy composites was 35.4% higher than that of the epoxy alone, compared to only a 0.9% increase in tensile strength for MGP/epoxy composites over the epoxy compound. Thermal conductivity increased by 146.9% using GD400-MWCNT/MGP hybrid fillers and 23.9% for MGP fillers, compared to non-derivatised epoxy.     

碱木质素的微波氧化降解(英文)

The effects of oxidant dosage,oxidation temperature and time on the degradation of soda lignin by hydrogen peroxide with and without the presence of microwave irradiation were investigated.It is found that the oxidative degradation of lignin includes the cleavage of ether bond inβ-O-4 structure,the partial destruction of aromatic ring,and the re-condensation of the degraded lignin.Compared to the conventionally heated oxidation of lignin,the microwave irradiation efficiently facilitates the degradation of the lignin with high molecular weight and the re-condensation of that with low molecular weight at a low oxidant dosage,low oxidation temperature,or a short oxidation time,which leads to the formation of the degraded lignin with narrower molecular weight distribution and lower molecular weight.Additionally,the lignin degraded in the presence of microwave irradiation has the characteristics of higher content of phenolic hydroxyl group,lower content of methoxyl group,and lower degree of condensation,which enhances the reactivity of lignin.Therefore,the oxidative degradation of lignin assisted by microwave irradiation may be a new pretreatment approach for efficiently utilizing the soda lignin.