A Method for Evaluating Lignin Mobility Distributions Obtained by Capillary Zone Electrophoresis

Abstract

The profile of the mobility distribution of lignin-containing samples depends on type of sample. To facilitate comparison, a procedure for determining the average mobility (μ_av), i.e. the average charge density, of lignin is presented. The procedure is applied to black liquor (Sb), isolated dissolved lignin (Sd) and isolated residual (Sr) lignin samples, obtained from flow-through kraft cooks of softwood. The μ_av of the isolated lignin samples is compared with the concentration of phenol and carboxyl groups and relative molecular size. As the cook proceeds the μ_av for a particular type of lignin sample increases, reflecting an increase in average charge density. The μ_av, measured at pH 12, decreases in the order Sd>Sb>Sr, except at the end of the cook, when the average charge densities of the Sb and Sr samples are similar. Associations between lignin and carbohydrate fragments are proposed to cause the lower mobility of black liquor compared to isolated dissolved lignin. Characterisations performed at pH 10 indicate that the isolated dissolved lignin samples may have a higher pK_a in the middle of the cook than the other samples.     

BEHAVIOR OF EUCALYPTUS GLOBULUS LIGNIN DURING KRAFT PULPING. II. ANALYSIS BY NMR,ESI/MS,AND GPC

ABSTRACT

Residual and dissolved lignin from different phases of kraft delignification of Eucalyptus globulus wood were isolated and characterized by 1D and 2D ¹H NMR, ¹³C NMR, Electrospray Ionization Mass Spectrometry (ESI/MS), and gel permeation chromatography (GPC). During the temperature rise period, below 70°C, about 20% of the lignin was dissolved without significant structural changes. Above 70°C, the lignin suffered significant degradation/fragmentation in the cell wall prior to dissolution. The lignin ether-linked syringyl units were the most susceptible to alkaline degradation. Through the course of pulping, the residual lignin (RL) revealed a gradual increase of aliphatic moieties of unknown structure, as well as a decrease of native structures such as phenylcoumaran and pino-/syringaresinol lignin units. A significant decrease of the β-O-4 structures content in RL was detected only at the final cooking temperature. The lignin dissolved in the black liquor (BL) consisted of highly branched oligomers with rather low molecular weight (average mass 800–1000 u). A part of BL (about 30%) was chemically linked to carbohydrates and possessed a large molecular weight distribution (500–4000 u). BL showed a progressive decrease in β-O-4 and pino-/syringaresinol structures and formation of enol ether and stilbene structures. The GPC analyses showed a continuous decrease of the molecular weight of both the residual and dissolved lignins during the pulping process, particularly in the residual stage.     

Molecular Mass Distribution of Lignin from the Alkaline Pulping of Hardwood,Softwood, and Wheat Straw

Abstract

The behavior of lignin during kraft (hardwood, softwood, and wheat straw) and soda-AQ (wheat straw) pulping was studied, mainly in terms of delignification degree and molecular mass distribution (MMD). In the initial delignification phase (at 140°C for 15–60 min), a prominent part of the dissolved softwood kraft lignin (18–25 g/L, MM mostly > 3,000 Da) was found in the liquid phase of chip cavities, rather than in the external bulk black liquor (5–7 g/L, MM mostly < 3,000 Da). The maximum weight average MM values ( _w) of the soluble lignin under conventional cooking conditions were detected for the kraft softwood (4,100 Da), and kraft birch (3,400 Da) when the degree of delignification was 65–75%, corresponding to a residual lignin content of 5–10%. The maximum _w of the dissolved wheat straw kraft (5,050 Da) and soda-AQ (5,900 Da) lignins was clearly higher than that of wood-based kraft lignins (2,950–4, 100 Da).     

BEHAVIOR OF EUCALYPTUS GLOBULUS LIGNIN DURING KRAFT PULPING. I. ANALYSIS BY CHEMICAL DEGRADATION METHODS

ABSTRACT

Eucalyptus globulus wood was subjected to kraft pulping, reaching different extents of delignification. The residual and dissolved lignins were isolated by soft acidolysis and acidic precipitation, respectively, and submitted to analysis of residual sugars and methoxyl groups, as well as to analysis by nitrobenzene and permanganate oxidation and thioacidolysis. Results from both residual and dissolved lignins analyses indicated that in the initial phase of pulping there is a preferential removal of lignin enriched in guaiacylpropane (G) and p-hydroxyphenylpropane (H) units, which is highly condensed and bonded with polysaccharides, predominantly with xylan. During the bulk and residual phases of pulping, lignin enriched in syringylpropane (S) units is progressively removed, leading to the increase of S/G ratio of black liquor lignin. After a purification step of dissolved lignins, two fractions with distinct levels of carbohydrates and with different structural features were obtained. The overall results were interpreted in terms of the topochemistry of the kraft pulping process.     

Organosolv delignification of white‐ and brown‐rotted Eucalyptus grandis hardwood

Sound (undecayed control) and fungally‐pretreated wood samples were submitted to organosolv delignification. The cooking liquor used was methanol/water (78:22 v/v) containing CaCl₂ and MgSO₄ each at a concentration of 25 mmol dm⁻³. The cooking process was performed at 180 °C for reaction times varying from 5 to 100 min. Despite some differences in the lignin removal pattern, pseudo‐first order kinetic models permitted a prediction of delignification rate constants for all experiments. All biodegraded samples provided higher delignification rate constants than the undecayed control (2.0 × 10⁻²min⁻¹ for the undecayed control and, for example, 14.2 × 10⁻²min⁻¹ for the sample decayed by Trametes versicolor for 2.5 months). Biodegraded samples also presented significantly increased xylan removal rates. The type of biodegradation affected the behavior of wood samples under organosolv pulping. The highest delignification and xylan removal rate constants were observed in the sample decayed by T versicolor for 2.5 months (17% weight loss). However, high delignification and xylan removal rate constants were also observed in the sample decayed by Punctularia artropurpurascens for only 0.5 months (1.2% weight loss). Data obtained from a single fungal species pretreatment or data from all fungal pretreatments indicated that there is no clear correlation between the delignification constants and the wood weight or component losses. This lack of correlation suggested that the structure of residual polymers in decayed wood affects the delignification process in the organosolv pulping more than the removal extent of each individual component. © 2000 Society of Chemical Industry     

Delignification of Pinus taeda wood chips treated with Ceriporiopsis subvermispora for preparing high‐yield kraft pulps

Pinus taeda wood chips were treated with the white‐rot fungus Ceriporiopsis subvermispora in 20‐dm³ bioreactors for periods varying from 15 to 90 days. Decayed samples, non‐inoculated controls and extractive‐free wood samples were submitted to kraft pulping using 25% of sulfidity and different active alkali concentrations in the cooking liquor. Cooking reactions were carried out isothermally at 170 °C. Residual lignin contents of pulps prepared from biotreated wood chips were lower than those observed in pulps from the undecayed control. Delignification kinetic studies showed that the initial delignification phase was accelerated and shortened by the fungal pretreatment. At a cooking time fixed before the end of the bulk delignification phase, the fungal pretreatment provided pulps with significantly lower kappa numbers or pulps with a fixed kappa number were obtained by reducing the amount of active alkali added to the liquor. Pulps of kappa 80 were obtained both from the undecayed control cooked with 20.8% of active alkali and from the 15‐day‐biotreated sample cooked with only 15% of active alkali. The biopulping benefits were neither proportional to the extent of the biodelignification nor to the biological removal of some specific wood component. DFRC‐determination (derivatization followed by reductive cleavage) of the amount of aryl–ether linkages in residual lignins of biotreated samples indicated an extensive depolymerization during the initial stages of biodegradation, which suggested that bio‐depolymerized lignin was easily released during the first stages of cooking, resulting in a faster and shorter initial delignification phase. © 2002 Society of Chemical Industry     

麦草氨法制浆工艺及动力学

1 INTRODUCTION Under the pressure of rising consumption on wood resource, more attention has been paid to using non-wood raw materials in papermaking industry. Pulping on non-wood fiber material is expected to increase from 7%—8% at the present to 10%—15% in 2010 in the world[1]. Non-wood material, particularly wheat straw, are exploited as the main raw material for papermaking in China because of the limited wood resource with a forest coverage of only 13.94%[2]. The main problem that …     

Characterization of Residual Lignins Isolated from Unbleached and Semibleached Softwood Kraft Pulps

Abstract

Residual lignins in an unbleached and a semibleached softwood (Pinus taeda L.) kraft pulp were isolated by enzymatic hydrolysis of polysaccharides in the pulps. After purification, the residual lignins were characterized. A dissolved lignin was also isolated from the alkaline extraction spent liquor by acidification and characterized.

Results of the characterization indicate that extensive degradation of residual lignin in kraft pulp occurred during the first two stages of bleaching. The results also strongly support the previous finding that stable covalent linkages between residual lignins and carbohydrates in pulp any be the most probable cause for the residual lignins to resist delignification during kraft pulping and prebleaching.     

Investigation of the Chemistry of Oxygen Delignification of Low Kappa Softwood Kraft Pulp using an Organic/Inorganic Chemical Selectivity System

Abstract

Oxygen delignification (OD) of low kappa softwood kraft pulp was examined in two steps without inter‐stage washing as part of an overall program to evaluate the efficiency of a selectivity enhancement system consisting of phenol and magnesium sulfate. Black liquor carryover in the reaction system did not substantially affect delignification and the selectivity of these OD reactions. The residual lignins from both the original pulp and oxygen‐delignified pulp with and without the phenol/MgSO₄ selectivity enhancement system were prepared and characterized using NMR spectroscopy. The effluent lignins after oxygen delignification were also prepared and characterized. The lignin characterizations provided the basis for the rationalization of the selectivity observed. A significant finding of this study was that the phenol/MgSO₄ system in the oxygen delignification reaction appeared to hinder phenolic guaiacyl unit condensation. It also appeared to enrich the levels of p‐hydroxyphenyls in the residual lignin.     

Nitrogen containing additives in soda pulping of bagasse pith

Unbleached soda pulp was prepared from Egyptian bagasse pith by varying the alkali concentration and the time of heating at the boiling point of the liquor under atmospheric pressure. A linear relationship was observed between the dissolved pith and the dissolved lignin. Pulping with alkali concentration higher than 10% but not exceeding 16% was more effective, since more delignification took place with lower dissolved pith percentage. p- And m-nitrobenzoic acids and also hydroxylamine hydrochloride had a slight or no effect on the yield of the pulps. The alkali solubility percentage of the pulps prepared in the presence of any of the additives was lower than the control pulp. The delignification was enhanced more on the addition of hydroxylamine hydrochloride than p-nitrobenzoic acid, while m-nitrobenzoic acid seemed to have no effect. The yield of the pulps thus prepared, as determined by weighing, showed lower values than those determined by a chemical method. The soda delignification rate was shown to be proportional to the amount of unremoved lignin and the concentration of alkali in the liquor. The delignification reaction was found to follow approximately first-order kinetics.     

Characterization of Dissolved Kraft Lignin by Capillary Zone Electrophoresis

This report presents a method to characterize underivatized lignin by Capillary Zone Electrophoresis (CZE), in which separation is achieved by differences in mobility due to differences in the charge-to-size ratios of the solutes.

A comparison has been made between the separation of lignin by CZE and earlier studies¹ regarding the size and phenolic content of dissolved lignin. The samples were isolated at different times from a flow-through kraft cook and characterized by CZE in an alkaline solution. The resulting electropherograms show a molecular mobility distribution. The molecular mobility distribution of each fraction is in good agreement with its molecular size distribution and phenolic content. As the cook proceeds, the mobility of the lignin fragments increases with increasing phenolic content. Although the molecular size distribution shows a slight increase in molecular weight at the end of the cook according to Size Exclusion Chromatography (SEC), this does not seem to affect the mobility distribution.

The change in mobility distribution may be a useful new parameter to be used in lignin characterization, as the dissolution of lignin is influenced by the number of ionized groups and by the size of the lignin fragments.     

硫酸盐制浆过程中硫的分布与变化规律

本文研究了兴安落叶松硫酸盐制浆过程中流在蒸煮液、溶出木素和残余木素中的分布及变化情况。结果表明，蒸煮过程中蒸煮液的活性碱和硫化钠浓度不断下降，硫化度则不断上升，活性碱与硫化钠的消耗主要发生在初始脱水素阶段．溶出木素的含硫量在初始脱木素阶段量最高，随着蒸煮反应的进行，其百分含量逐渐下降，但绝对量却不断上升。蒸煮结束时，约占总用硫量1／5的硫与溶出木素结合在一起。木片或纸浆的含硫量与木素的硫化速率和残余木素的含量密切相关。在残余脱木素阶段，残余木素的硫化对木素的说除已没有促进作用。     

The Influence of the Bleaching Medium on Caustic Extraction Efficiency (II): Oxidized Lignin Solubility

Abstract

Caustic extractions performed with >50% ethanol solutions severely hindered lignin removal from chlorine dioxide (D₀) treated pulps. In this study, we show that the alkali solubility of an isolated D₀ lignin decreased as the concentration of ethanol in the medium was increased from 50 to 75%. In addition, the amount of dissolved lignin in the alkaline extraction effluents approached its solubility limit when the medium contained more than 50% ethanol. These results indicate that alkaline extractions of D₀-stage pulps with ethanol-rich media were limited by the lower solubility of ionized lignin fragments in these solutions as compared to water. An empirical solubility parameter analysis predicted that non-ionized D₀ lignins should be more soluble in ethanol than in water. Indeed, delignification with an acid extraction stage was improved when the water was replaced with ethanol.     

The Influence of Sulfidity in Kraft Pulping on the Nature of Residual Lignin

The influence of sulfidity in kraft pulping of Norway spruce chips on the characteristics of residual lignin has been examined at two levels 25 and 40%. Comparing with the reference kraft cook at similar kappa number, the high sulfidity pulp lignin displayed a significantly lower phenolic hydroxyl group content, and a lower response to O₂ delignification, but it gave a slightly higher yield of nitrobenzene oxidation products, and was more responsive to a neutral sulfite treatment.     

Kinetics of Wheat Straw Delignification in Soda and Kraft Pulping

Kraft and soda delignification kinetics of wheat straw, Triticum aestivum, have been studied as a function of OH “concentration, HS” concentration, and temperature. It was found that about 90% of the lignin is dissolved in the rapid initial phase. The rates of delignification in the bulk and residual phases were found to be similar to those of birch wood, Betula pubescens. The amount of residual phase lignin was found to be considerably less than in birch or spruce, Picea abies, and it was affected by the same factors, A model that accurately describes the delignification of wheat straw was derived.     

Characterization of Lignins from Organosolv Pulping According to the Organocell Process,Part 2. Residual Lignins

Abstract

Residual lignins were isolated from cooking residues obtained from 20 1 batch cookings of spruce chips by either ball-milling or enzymatic treatment. The lignins were characterized in terms of yield, elemental composition, polysaccharide moieties and functional groups and compared with the corresponding dissolved lignins.

The residual lignins generally proved to be less changed than the dissolved lignins. They show considerable adherence to cellulose and xylose portions. Aliphatic OH groups were found to decrease remarkably towards the end of the cook, which was explained by the formation of new lignin-lignin and lignin-polysaccharide bonds as well as by side chain degradation.

Lignin methylation by methanolic liquor was almost negligible.     

Laser-Induced Fluoresence of Lignins with Excitation from 457 to 621 Nanometers

Laser-induced fluorescence has been used to examine changes in lignin and black liquor during the course of kraft pulping. When excited with a laser at 457 and 488 nm, lignin samples isolated during the course of pulping, purified, and redissolved in alkali exhibited increasing fluorescent emission intensity. This may be explained by changes in lignin structure during pulping. At higher excitation wavelengths, differences between samples diminished. Black liquors showed decreasing fluorescent intensity with increasing pulping. We attribute this behavior to the increase in optical density of the liquors as cooking time proceeds. The optical density increases with cooking time proceeds. The optical density increases with cooking time because greater amounts of lignin and other materials dissolve from the wood and enter the black liquor.     

蒸煮液的物理化学特征及在制浆过程中的行为 Ⅱ.木素对蒸煮液的表面张力的影响

通过加入木素自制黑液及取自一个连续等温蒸煮过程的黑液的数据比较,研究了木素对蒸煮液的表面张力的影响。结果显示,木素起着表面活性剂的作用使蒸煮液的表面张力降低。但木素对实际取得的黑液的表面张力的影响要大于人工自制的,其主要原因是前者还含有木材的其它成分,如半纤维素及脂肪酸。黑液表面张力的主要成分是Lifshitz-van der Waals引力 γLLW,其次是Lewis酸碱反应力γLAB。     

Tailoring the molecular and thermo–mechanical properties of kraft lignin by ultrafiltration

This study has shown that ultrafiltration allows the selective extraction from industrial black liquors of lignin fraction with specific thermo‐mechanical properties, which can be matched to the intended end uses. Ultrafiltration resulted in the efficient fractionation of kraft lignin according to its molecular weight, with an accumulation of sulfur‐containing compounds in the low‐molecular weight fractions. The obtained lignin samples had a varying quantities of functional groups, which correlated with their molecular weight with decreased molecular size, the lignin fractions had a higher amount of phenolic hydroxyl groups and fewer aliphatic hydroxyl groups. Depending on the molecular weight, glass‐transition temperatures (T_g) between 70 and 170°C were obtained for lignin samples isolated from the same batch of black liquor, a tendency confirmed by two independent methods, DSC, and dynamic rheology (DMA). The Fox–Flory equation adequately described the relationship between the number average molecular masses (M_n) and T_g's‐irrespective of the method applied. DMA showed that low‐molecular‐weight lignin exhibits a good flow behavior as well as high‐temperature crosslinking capability. Unfractionated and high molecular weight lignin (M_w >5 kDa), on the other hand, do not soften sufficiently and may require additional modifications for use in thermal processings where melt‐flow is required as the first step. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40799.     

Pulping with organic acids: 3-acetic acid pulping of Bagasse

Bagasse was subjected to acetic acid pulping; the effects of the addition of 0.5% H₂SO₄ to the pulping solutions (50, 70 and 90% acetic acid) and varying the liquor ratio, on pulp yield, delignification %, pentosan content and strength properties of the pulps obtained were evaluated. Addition of H₂SO₄ improved the delignification but at the expense of yield and pentosan content. The breaking length and burst deteriorated, whereas the tear was slightly improved. Raising the liquor ratio from 5:1 to 10:1 also reduced the strength properties of the pulps. Delignification of Casuarina was easier than bagasse. IR studies of the acetic acid lignins obtained from both raw materials showed that Casuarina lignins contained more syringyl nuclei than bagasse lignin; the latter resembled softwood lignins. Addition of H₂SO₄ to bagasse changed the syringyl-deficient to guaiacyl-deficient lignin. A relationship was found between the ease of delignification for both raw materials and the relative intensity of the bands corresponding to syringyl groups.