Analysis of progress of oxidation reaction during oxygen-alkali treatment of lignin 2: significance of oxidation reaction of lignin during oxygen delignification

The progress of lignin oxidation during oxygenalkali bleaching of pulp was evaluated by the method based on the difference between permanganate consumption of original pulp and that of the mixture of pulp and effluent after oxygen-alkali bleaching. By low-consistency oxygen bleaching of softwood kraft pulp, the permanganate consumption decreased very little. When the kappa number of the pulp was halved (from 25.4 to 13.4), the decrease in permanganate consumption of 1 g pulp was only 1.22ml of 0.02mol/l potassium permanganate. This value was smaller than that obtained for the oxygen-alkali treatment of a corresponding amount of isolated residual lignin, 6.40ml. This was not due to the slow oxidation of lignin in pulp but to the formation of permanganate-consuming substances from carbohydrates. Those newly formed substances cannot be oxidized by oxygen-alkali treatment. Taking these facts into account, lignin originally present in pulp was found to be oxidized well. Reduction of carbonyl groups in carbohydrates prevented the formation of such substances.Part of this paper was presented at the 10th ISWPC, Yokohama, June 1999; and at the 43rd Lignin Symposium, Fuchu, October 1998     

Analysis of progress of oxidation reaction during oxygen-alkali treatment of lignin I: method and its application to lignin oxidation

A new method is applied to evaluate the progress of the oxidation reaction of lignin during oxygen-alkali treatment. This method employs the difference in permanganate consumption of the sample before and after the oxygen-alkali treatment as an indication for the lignin oxidation. When kraft lignin and residual lignin isolated from unbleached softwood kraft pulp were subjected to oxygen-alkali treatment up to 6000min, the progress of the oxidation expressed by this method was separated into clearly distinguished three phases. During the first and second phases, the progress of oxidation was well correlated to the loss of methoxyl group and to the decrease in the yield of nitrobenzene oxidation products. The addition of Mn⁺ to the oxygen-alkali treatment depressed oxidation during the second phase partly and that during the third phase almost completely. Calculations based on the change in the permanganate consumption revealed that the oxidation during the first phase corresponded to 4.2 electrons abstracted from one lignin structural unit on average. The oxidation process by oxygen-alkali treatment was hypothetically attributed to the direct reaction between molecular oxygen and the phenolic unit of lignin, which mainly took place during the first phase, and to the autooxidation-type oxidation during the second and third phases.Part of this paper was presented at the 9th ISWPC, Montreal, June 1997; and at the 42nd Lignin Symposium, Sapporo, October 1997     

Oxidative cleavage of lignin aromatics during chlorine bleaching of kraft pulp

Methanol liberation and methoxyl loss during chlorine bleaching of softwood kraft pulp were quantitatively investigated to estimate the degree of structural modification of lignin aromatics. An increase in the chlorine multiple led to enhanced methoxyl loss from lignin. Our result, using pH-adjusted chlorine water (pH 5.7), by which chlorination under oxidation-favorable conditions was achieved, strongly supported the importance of the oxidation reaction by chlorine during delignification and lignin degradation. It was also suggested that methanol can be produced not only via catalytic hydrolysis by chlorine but via oxidative cleavage of the ether bond as well. The infrared spectrum of chlorolignins suggested that chlorine oxidation can open aromatic rings to muconic acid derivatives without cleaving ether bonding of the methoxyl group. No straight relation between the methoxyl content and the kappa number of chlorinated pulps was shown. The methoxyl content of bleached kraft pulps subjected to successive chlorination and alkali extraction showed a good relation with the kappa number. This means that almost all the portions of the oxidatively modified lignin structure were successfully removed during these treatments, and the aromatic structures of residual lignin in chlorinated and alkali-extracted pulps were thought to remain intact.Part of this paper was presented at the 46th Annual Meeting of the Japan Wood Research Society, Kumamoto, April 1996; the 10th International Symposium on Wood and Pulping Chemistry, Yokohama, June 1999; and the 67th Pulp and Paper Research Conference, Tokyo, June 2000     

The effect of lignin on the bending properties and fixation by cooling of wood

To clarify the effects of lignin on the fixation of bending deformation by cooling, cooling set for delignified woods with various lignin residues were investigated to compare with mechanical and dynamic viscoelastic properties. Bending tests showed that steep reductions occurred in the modulus of elasticity and modulus of rupture with delignification during the initial stage of delignification. The dynamic viscoelastic measurements revealed that the peak temperature of tan δ due to micro-Brownian motion of lignin was reduced with delignification, and the peak disappeared in the temperature range of 5°–100°C for the specimens that had lost more than 21% of their weight. On the other hand, no clear change in residual set was found in the range of 0%–15% of weight loss in spite of a marked reduction in lignin content. Subsequently, set decreased steeply for the specimens delignified beyond 15% of weight loss. It was suggested that cooling set is not determined solely by lignin content but is influenced by changes in the quality of lignin due to delignification. Lignin quality affects the balance of the elastic potential to recover from deformation and its viscosity, which is an indication of resistance against flow. Part of this report was presented at the 57th Annual Meeting of the Japan Wood Research Society, Hiroshima, August 2007     

Evaluation of the extent of the oxidation reaction during chlorine bleaching of pulp

A modified method was developed to evaluate how much chlorine is consumed by the oxidation reaction during the chlorine bleaching process. This evaluation is, in principle, based on the sum of chloride produced during the chlorination stage (C-stage) and produced during alkali treatment of both the C-stage effluent and the chlorinated pulp. Results obtained by this method proved that about 50%–75% of chlorine was consumed by the oxidation reaction during chlorine bleaching, depending on the reaction condition of chlorination. Even under a reaction condition that is not favorable to an oxidation reaction (low pH), approximately three electrons were abstracted from one lignin structural unit by chlorine bleaching. This result provides additional evidence for our recent observation that lignin is extensively oxidized during chlorine bleaching even when pure chlorine without any chlorine dioxide substitution was used.Part of this paper was presented at the 40th Lignin Symposium. Tsukuba, Japan, October 12, 1995     

Spectral analysis of the successive degradation process of kraft lignin by alkaline oxygen treatment

Softwood kraft lignin was subjected to alkaline oxygen treatment in a fundamental study of lignin degradation. Two different spectral changes were observed in the time course of ultraviolet-visible spectra along with the progress of the treatment. These spectral changes could be recognized as proceeding along certain temporal functions that were based on second-order decays with different halflives. The spectral changes were defined as “fast change” and “slow change.” The fitting studies on the amount of total protons on the unsaturated and aromatic systems, the amount of unconjugated phenolic substructure determined by differential ionization spectra, and the amount of methoxyl group with temporal functions showed that two reaction types (formation of muconate derivatives and ortho-quinone derivatives) can be expected as the major modification types occurring during fast change. The fitting study of the time course of infrared attenuated total reflectance (ATR) spectra gave corresponding infrared ATR spectral features of fast and slow changes. The occurrence of the formation of muconate derivatives by fast change was strongly supported by the spectral feature of fast change. On the other hand, it is suggested that the aromatic structure of lignin was further degraded during slow change. In addition, formation of resistant phenolic substructures is suggested as another possible modification type occurring by fast change. Parts of this article were presented at the 13th International Symposium on Wood, Fiber, and Pulping Chemistry, Auckland, New Zealand, May 2005     

Infrared spectroscopic study of alkaline oxygen treatment of lignin with ATR technique in aqueous state 1: method for determining quantitative spectra of oxygen-degraded lignin

For the fundamental study of oxygen delignification of kraft pulp, structural changes of kraft lignin during alkaline oxygen treatment were investigated with the use of infrared measurement with attenuated total reflectance (ATR) technique. In the neutralized reaction mixture of alkaline oxygen-treated kraft lignin, there is a significant amount of NaCl, so that the spectral changes of water due to the coexistence of NaCl was investigated, and how to remove the huge absorption of NaCl solution is discussed. Sodium vanillate–NaCl solutions were employed as model solutions for the reaction mixture. Partial least square (PLS) regression was applied for the prediction of NaCl concentration, and the spectrum of NaCl solution was subtracted from the spectrum of sodium vanillate–NaCl solution as background measurement. This allowed us to obtain the vanillate spectra free from the absorption of NaCl solution. In addition, the mathematical method for reconstructing the spectrum of NaCl solution is discussed. The spectrum of NaCl solution is reconstructed as the linear combination of basic spectra calculated by singular value decomposition (SVD), and it was subtracted from that of the sodium vanillate–NaCl solution. By this procedure, the vanillate spectra were also obtained quantitatively, as has been demonstrated in PLS regression study. It was also confirmed that the quantitative spectra of high molecular weight fraction of alkaline oxygen-treated kraft lignin were obtained by the use of this reconstruction technique.Parts of this report were presented at the 52nd Annual Meeting of the Japan Wood Research Society, Gifu, Japan, April 2002 and the 12th International Symposium on Wood and Pulping Chemistry, Madison, USA, June 2003     

Ultraviolet microspectrophotometric investigation of the distribution of lignin in Prunus jamasakura differentiated on a three-dimensional clinostat

To examine the effect of gravity on lignin content and deposition in plant cells, we used ultraviolet (UV) microspectrophotometry and chemical methods to investigate the secondary xylem of Prunus jamasakura grown on a three-dimensional (3D) clinostat, which simulates microgravity. The stem of the 3D-clinostat specimens elongated with bending and the width of their secondary phloem increased. The UV absorbance of the 3D-clinostat specimens at 278 nm was higher than that of the control specimens, which were grown on the ground, in the wood fiber cell corner middle lamella, compound middle lamella, and fiber secondary wall; the UV absorbance in the vessel secondary wall did not differ between the specimens. The lignin content in the stem, including the bark, of the 3D-clinostat specimens, as determined using an acetyl bromide method, was less than that of the control specimens. In the specimens that differentiated on a 3D clinostat, the amount of lignin in the wood fibers increased, while the proportion of the lignified xylem in the stem decreased relative to control values.     

Application of cationic polymer prepared from sulfuric acid lignin as a retention aid for usual rosin sizes to neutral papermaking

Cationic polymers that acted as the retention aids for usual rosin sizes in neutral papermaking were prepared from sulfuric acid lignin (SAL), one type of acid lignin. To convert SAL to the cationic polymer (MP-SAL), SAL was phenolated and then treated by the Mannich reaction to introduce the amino groups. In the MP-SAL single system, MP-SAL exhibited high sizing effectiveness in neutral papermaking with the rosin emulsion size. However, MP-SAL showed no sizing effectiveness when soap rosin size was used. MP-SAL showed increased sizing effectiveness as the pK _a of the introduced amino group increased. From this and comparison of the sizing degrees of MP-SAL and polyethylenimine, which possesses a linear structure, it was suggested that the sizing effectiveness was not only affected by the charge density and molecular weight, but also by the basicity of the introduced amino groups and the molecular structure of the retention aid. In the alum–MP-SAL dual system, alum and MP-SAL synergistically enhanced the sizing effectiveness in the rosin emulsion sizing at neutral pH. In turn, this allowed a decrease in the MP-SAL dosage and resulted in a small decrease in brightness.Part of this report was presented at the 48th Lignin Symposium, October 2003, Fukui     

Immunohistochemical localization of enzymes related to lignin biosynthesis in the primary xylem of hybrid aspen

We have investigated the spatial regulation of the accumulation of enzymes involved in the biosynthesis of shikimate and lignin during differentiation of primary xylem from the apical meristem via procambium in hybrid aspen (Populus sieboldii x Populus grandidentata). Immuohistochemical staining revealed that, in the top part of shoots, lignification began in a single or just a few adjacent vessel elements and subsequently spread to neighboring cells. The spatial localization of 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase (DAHPS), which is one of the key enzymes in the shikimate pathway, was tightly correlated with the cell-specific deposition of lignin in the primary xylem. We also found that the spatial localization of enzymes in the general phenylpropanoid pathway and in the lignin-specific pathway was closely associated with the cell-specific deposition of lignin and the accumulation of DAHPS. Our data suggest that enzymes that act in the shikimate, general phenylpropanoid, and lignin-specific pathways are initially produced and function coordinately in a single or a few adjacent elements at the start of primary xylem development.     

Contribution of lignin to the reactivity of wood in chemical modifications I: influence of delignification on acetylation

In order to examine the contribution of wood components to the acetylation of wood, we acetylated wood meal that had been partially delignified. The results were analyzed in terms of the reaction kinetics. The first-order rate equation was successfully adjusted to the weight gain data. The rate constant for acetylation initially increased with progress of lignin elimination and then turned to decrease; the apparent activation energy showed the reverse tendency and ranged from about 90 to 130 kJ/mol. These results suggest that lignin elimination brings not only separation of lignin but also drastic change of the chemical and/or physical structure in the residual lignin, and this affects the reactivity of wood meal as a whole. The ultimate weight gain estimated by the regression of the rate equation showed a minimum when lignin was moderately eliminated, which was explained in terms of enhanced reactivity of lignin and lower accessibility for holocellulose than predicted. The equilibrium moisture content had a maximum when lignin was moderately eliminated. This tendency is the opposite of that observed for the ultimate weight gain, and suggests that the sites for acetylation do not always correspond to those for moisture adsorption. Part of this report was presented at the 54th Annual Meeting of the Japan Wood Research Society, Sapporo, August 2004     

Mechanical properties of wood in an unstable state due to temperature changes,and analysis of the relevant mechanism VI: dielectric relaxation of quenched wood

To analyze the effects of lignin on the destabilization of wood due to quenching, we examined the dielectric properties of untreated and delignified wood before and after quenching at 20°C from 50 Hz to 100 MHz. For untreated wood, the inflection points of log ε′ and log σ vs log f and the peak of log(tan δ) vs log f were attributed to interfacial polarization before quenching, and the location of the inflection point shifted to a higher frequency with increasing moisture content because of changes in the water cluster. After quenching, the inflection points of log ε′ and log σ and the peak of log(tan δ ) shifted to higher frequency; however, the values of log ε′, log σ recovered to those before quenching with the passage of time. For delignified wood, dielectric relaxation was observed at a higher frequency than for untreated wood irrespective of quenching. It was inferred that the mobility of water molecules was influenced by the cluster surroundings because of increased number of adsorption sites in hemicellulose. Moreover, after quenching, the recovery process did not change greatly over time; it was shown that the matrix structure was affected more by quenching with the loss of lignin.     

Contribution of lignin to the reactivity of wood in chemical modifications II: influence of delignification on reaction with vaporous formaldehyde

Participation of lignin in the reaction between vapor-phase formaldehyde and wood was examined by using gradually delignified wood meal. A fi rst-order rate equation was successfully applied to the weight gain data. From the estimated reaction parameters such as rate constant, k, and ultimate weight gain, a, the reactivity toward formaldehyde was discussed among wood components, and compared with that for acetylation. k decreased monotonously with progress of the elimination of lignin, suggesting that the reaction rate of lignin is dominant over that of whole wood, and the decrease in the ratio of lignin retarded the reaction of wood as a whole. On the other hand, a increased with decreasing lignin content. This may be attributable to the enhanced reactivity of the remaining lignin due to some structural changes and to the increase in the number of reactive sites in polysaccharides as a result of their exposure accompanying the elimination of lignin. The dependencies of k and a on the lignin content were not similar to the case for acetylation, probably because of the difference in the reaction phase. In vapor-phase formaldehyde treatment, the remaining lignin reacts as it is, whereas in liquid-phase acetylation it would undergo rearrangement or swelling of the structure in the reaction solution.     

Synthesis of β-O-4 type oligomeric lignin model compound by the nucleophilic addition of carbanion to the aldehyde group

A synthetic method for obtaining lignin oligomer that contains only the β-O-4 structure is described in detail. This method consists of three reaction steps: (1) the synthesis of t-butoxycarbonylmethyl vanillin (2), (2) the nucleophilic addition oligomerization of compound 2, and (3) the reduction of the oligomeric β-hydroxyl ester. In the first step, compound 2 was synthesized from vanillin in 96.8% yield. In the second step, compound 2 was oligomerized with commercial lithium diisopropylamide (LDA) to obtain oligomeric β-hydroxyl ester (3) in 87.2% yield; the repeating units of this oligomer were joined only by β-O-4 linkages as confirmed by nuclear magnetic resonance (NMR) spectroscopy. In the third step, the oligomeric β-hydroxyl ester (3) was reduced with LiAlH₄ to give compound 4 in 42.4% yield. On the basis of NMR, matrix-assisted laser desorption ionization time-of-flight mass spectrometry, and gel permeation chromatography analyses of compound 4, it was concluded that compound 4 was an oligomeric lignin model compound containing only β-O-4 interunit linkages. The number average degree of polymerization (DPn) of obtained compound 4 was about 7.0 (M _w/M _n = 1.42). Using this oligomeric lignin model compound, conventional degradation and analytical methods will give new information.     

Ultrastructure of the S2 layer in relation to lignin distribution inPinus radiata tracheids

The ultrastructure of the S₂ layer in relation to its lignin distribution was examined using transmission electron microscopy in the tracheids ofPinus radiata. The S₂ layer had a striated appearance at low magnification. Observations at higher magnifications showed lignin to be distributed inhomogeneously in this layer, appearing as a mosaic of electron-dense and electron-lucent regions. These regions are scattered, showing a pattern of often interconnecting sinuous features in a predominantly radial profile. The significance of these features of the S₂ layer is discussed, particularly in relation to the available information from recent ultrastructural observations on the appearance of cellulose microfibrils and the pattern of their distribution in the S₂ layer using rapid freeze-deep etching in conjunction with transmission electron microscopy. Predictions are made as to the likely distribution and arrangement of cellulose microfibrils in the S₂ layer based on the pattern of lignin distribution observed in this layer.     

湖南省2001—2010年能源类碳排放特征

以湖南省2001年碳排放情况为基准,对湖南省10年来能源碳排放量进行分析。结果表明:全省能源碳排放量呈逐年上升趋势,排放量主要集中在第二产业,单位GDP碳排放量低于全国水平。在此基础上,提出了湖南省实施低碳排放的对策和建议。