Assessment of potential approaches to improve Eucalyptus globulus kraft pulping yield

The main goal of this work is to study the potential approaches to improve polysaccharides retention during Eucalyptus globulus kraft pulping. The addition of anthraquinone to kraft pulping leads to the highest pulp yield while the addition of urea promotes lower depolymerization of polysaccharides (higher pulp viscosity), but does not have a significant effect on yield. The early interruption of kraft cooking followed by oxygen delignification is a reliable approach to increase pulp yield, particularly when pulping is interrupted at the end of the faster and more selective kinetic regime (bulk phase). Yield loss during oxygen delignification is considerably lower than that incurred in the last phase of kraft pulping. Pulping with OH^?/HS^? charge profiling, carried out with liquor injection in three different phases leads to a yield increase. However, this increase results from a lower total alkali charge applied when profiling pulping is compared to standard pulping conditions, rather than to alkali profiling. Standard kraft pulping with different active alkali (AA) charges demonstrated that this operational variable is determinant for pulp yield and viscosity. Pulping experiences with lower AA (14%) resulted in a higher and almost constant pulp viscosity and in a higher pulp yield, assigned to improved retention of both cellulose and xylan. During the last stage of pulping, cellulose content decreases, this being mainly responsible for the decrease of pulp yield, while xylan content is almost constant, a feature attributed to the peculiar structure of this E. globulus's hemicellulose. Copyright © 2007 Society of Chemical Industry     

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     

Isothermal Reaction Kinetics of Kraft Delignification of Douglas-Fir

Kraft delignification of Douglas-fir (Pseudotsuga menziesii) wood meal was carried out under an instantaneous isothermal condition with a liquor-to-wood ratio of 50 to investigate the effects of reaction temperature and chemical concentration on the rate of delignification. The temperatures studied were in the range of 120 to 175°C. Three levels of [HO^?l] and three levels of [HS^?l] concentrations were investigated. In each case an efficient mechanical agitation of the pulping liquor was maintained and the delignification was extended to reach its completion. Using a nonlinear regression analysis on the delignification results, a single kinetics equation was resolved to describe the effect of temperature and chemical concentration on the rates of delignification for the initial, bulk, and final phases. This equation also revealed that the amounts of lignin removed due to the chemical reactions in the initial, bulk, and final phases were 18.8, 71.4, and 3.8%, respectively. About 6% of the total lignin was dissolved into the pulping solution before any significant chemical reaction occurred to the lignin core. The activation energies of delignification reactions in the initial, bulk, and final phases were 85.8, 123.8, and 110.0 kJ/mole, respectively. The Ln(pre-exponential factors) were 22.5, 30.5, and 23.4 m^?l1 for the initial, bulk, and final phases, respectively. The rate of delignification was strongly affected by the presence of [HO^?l] in the bulk and final phases. Whereas, [HS^?l] had a significant effect on the rate of delignification only in the bulk phase. These chemical effects were also quantified.     

Development of Mathematical Models for Describing Organosolv Pulping Kinetics of Fungally Pretreated Wood Samples

Abstract

Eucalyptus grandis wood samples decayed by white- and brown-rot fungi were cooked at 180°C for 5 to 100 min with methanol/water (78:22 v/v) containing 25 mM of CaCl₂ and 25 mM MgSO₄. Mathematical models for describing organosolv pulping kinetics of the fungally pretreated samples were developed to estimate delignification constants, and also rate constants for xylan and wood mass solubilization. These models had high R² values and were able to predict pulp yield, as well as lignin and xylan contents during the process at 99% confidence level. Delignification of undecayed control samples had a rate constant of 2.0 × 10^?2 min^?1 for the bulk phase. Most decayed samples presented delignification constants higher than those of the control. Some decayed samples exhibited an additional delignification phase at the beginning of the process, which was characterized by a low solubilization rate. These samples required insertion of an additional term in the model to represent this phase.     

Suitability of Hybrid Willow as a Source of Pulp

Hybrid willow (Salix spp.) is a potential source of pulp as demonstrated by its fibre morphology, chemical composition and pulping kinetics. Fibre length and cell wall thickness measurements on one and two years old clones ranged from 0·49 mm to 0·70 mm and 2·5 μm to 3·6 μm respectively. Fibre length variation by annual growth layer varied from 0·5 mm in the first growth layer to about 1·1 mm in the last growth layer and the maximum growth rate occurred in the first two to three years for fourteen years old clones. The clones were producing more fibre fraction as indicated by volumetric composition. The UV absorptfvities of milled wood lignin was found in the range of 12·17 -14·31 Lg^?1cm^?1 at 278 nm and the presence of syringyl and guaiacyl lignin was observed. ¹³C-NMR results of acetylated milled wood lignin showed clonal structural variations during lignification process and the Klason lignin content of one and two years old clones ranged from 20·8% to 26·1%. Bulk kraft delignification of mature wood resulted in 5–6% higher yield than juvenile wood from the same clone and the pulping activation energy ranged from 98 kJ.mol^?1 to 120 kJ.mor^?1.     

Formic acid/acetone‐organosolv pulping of white‐rotted Pinus radiata softwood

Organosolv pulping of fungally pretreated samples of Pinus radiata was evaluated. A screening study using five white‐rot fungi indicated that Ceriporiopsis subvermisopora and Punctularia artropurpurascens were the most selective ones for lignin degradation. These fungi were further cultured in bioreactors containing 2.5 kg of wood chips. Fungally‐pretreated samples were delignified by formic acid/acetone (7:3) at 150 °C. Pulping kinetics and strength properties of the resulting unbleached pulps were evaluated. Delignification rates and xylan solubilization rates were higher for the decayed samples than for the undecayed control, except for the sample biotreated with P artropurpurascens for 30 days. C subvermispora proved appropriate for treating the wood samples before organosolv pulping, since pretreatment with this fungus resulted in faster wood delignification and pulps with lower residual lignin. Increases in tensile index ranging from 3% to 22% were observed for most pulps prepared from biotreated samples, independently both of the fungal species used in the pretreatment and of the extent of the wood biodegradation expressed as wood weight loss. However, tear and burst indexes and brightness were lower than or similar to those of pulps prepared from the undecayed control. © 2000 Society of Chemical Industry     

Ethanol‐based pulping from Cynara cardunculus L

A non‐conventional pulping process based on the delignification of cardoon (Cynara cardunculus L) in ethanol–water mixtures has been studied to evaluate its pulping potential and to establish the optimum pulping conditions for this lignocellulosic material. The variables analyzed were the concentration of ethanol in the cooking liquor, the pulping time and temperature. Variable optimization was performed by a central composite design. High viscosity, low kappa number and acceptable screened yield were used as pulp quality criteria to optimize cooking conditions. Pulps having low kappa numbers and viscosities greater than 900 cm³/g^?1 were obtained. The total pulp yield was low compared with wood pulping due to the high contents of extractives and ash in cardoon. The amount of rejects in the pulp is of importance, especially for pulps with a high kappa number. The most suitable pulping conditions were 188 °C, 135 min and 50% (w/w) ethanol concentration. In these conditions the kappa number of the pulp was around 26, the pulp viscosity greater than 1100 cm³ g^?1 and a screened pulp yield of about 31% was obtained. Copyright © 2005 Society of Chemical Industry     

Rapid Hydrothermolysis of Poplar Wood: Comparison of Sapwood,Heartwood, Bark,and Isolated Lignin

Abstract

Rapid hydrothermolysis at 350°C of poplar sapwood, heartwood and bark, as well as the lignin extracted from the sapwood and heartwood, gives oil and water soluble fractions whose chemical analysis is correlated with the nature of the feed stock. Results from cellulose and Douglas fir are included, and the poplar bark and heartwood lignin are shown to give an ether soluble oil that consists mainly of guaiacyl units while the sapwood product is mainly syringyl. However, the chloroform soluble oil from both sapwood and heartwood was mainly syringyl with the additional presence of carbohydrate derived material in the heartwood oil. The acetone-only soluble residue from sapwood was shown by pyrolysis mass spectrometry to be mainly cellulose derived while that from heartwood was mainly from lignin. Thus there is a fundamental difference in the behaviour of the poplar sapwood and heartwood that may arise from different distributions of the guaiacyl and syringyl units, and of the binding to the cellulose. The origin of the rapid hydrothermolysis products with respect to the major wood components is discussed. An empirical approach to the calculation of the lignin content based on the rapid hydrothermolysis fractions is presented.     

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.     

The Potential of Hydrothermally Pretreated Industrial Barks From E. globulus as a Feedstock for Pulp Production

This study focused on the use of industrial eucalyptus globulus bark as an alternative fiber source for bleached pulp and paper production. Bark has high extractives and ash contents (7.7% and 3.5%, respectively) but a mild hydrothermal pretreatment was tested, decreasing its values to 2.8% and 2.4%, respectively. Untreated and pretreated bark were kraft pulped at 15% and 20% (as Na₂O) active alkali conditions. The pretreatment improved delignification when using low active alkali; kappa number 25.4 vs 17.5, and shives 3.1% vs 0%, respectively, with untreated and pretreated bark. The pretreatment resulted in a lower chemical demand to obtain pulps with similar yield and kappa number. It was possible to produce bleached pulps with good handsheet optical, physical, and mechanical properties with slightly lower values than those of industrial eucalypt wood pulps; e.g., brightness > 85% vs 87%, tear index > 4.2 vs 5.6 mn.m².g^?1, tensile index > 62 vs 69 n.m.g^?1 for bark and wood pulps, respectively.     

Formation and Reaction of Coniferyl Alcohol During Alkaline Pulping

The formation and subsequent disappearance of coniferyl alcohol during kraft and soda-AQ (anthraquinone) pulping of western hemlock wood meal have been studied under isothermal condition. At 140°C, the amount of coniferyl alcohol generated increases to a sharp maximum (0.4% of total lignin in kraft and 1.9% in soda-AQ pulping) and then declines rapidly to low values. It was found that the disappearance of coniferyl alcohol was mainly due to condensation with other components of dissolved lignin. Nearly identical activation energies, 125 kJ mole^?1 for kraft and 128 kJ mole^?1 for soda-AQ pulping, were derived from the initial rates of coniferyl alcohol formation, conforming closely with the value 121 kJ mole^?1 for the cleavage of phenolic β-ether model compounds in the kraft process.     

枫香树材硫酸盐法蒸煮历程

研究了枫香树材硫酸盐法蒸煮过程中木素、戊聚糖和纸浆得率的变化。结果表明,枫香硫酸盐法蒸煮脱木素可分为以下三个阶段:第一阶段,升温到155℃,属于初始脱木素阶段,木素脱除率达到22.5%左右,戊聚糖溶出30.16%,得率为70.48%;第二阶段,从155℃开始到165℃保温60 min,属于大量脱木素阶段,木素脱除率达93.74%,戊聚糖溶出48.31%,得率为47.43%;第三阶段,从165℃保温60 min后到蒸煮末期,属于残余脱木素阶段,木素脱除率达到98%左右,戊聚糖溶出51.04%,得率为43.87%。     

Base‐catalyzed organosolv pulping of jute

Jute fibers were pulped using a novel caustic soda and ethanol–alkali (EtOH–NaOH) pulping process with the aim of minimizing problems associated with conventional chemical pulping. The effects of reaction conditions on the pulp yield, degree of delignification and selected physical properties were evaluated. The results indicate that adding ethanol to the conventional soda process was effective for improving both delignification and the physical properties of jute pulps. It was found that the delignification proceeded more rapidly and more selectively with ethanol–alkali than with alkali alone, giving higher yields at a given kappa number. Strength properties were markedly improved. The greatest values for burst (5.8 kPa m² g^?1) and tensile strength (68 N m g^?1) were obtained at 175 °C and 2.5 h reaction time. Copyright © 2003 Society of Chemical Industry     

Soda Pulping of Hardwoods Catalyzed by Anthraquinone and Methyl Substituted Anthraquinones

Abstract

Black liquor gasification (BLG) as well as the recovery of lignin and other organic compounds from pulping black liquor would be aided if an efficient sulfur‐free pulping process could be developed. This has provided new impetus for research on soda pulping with redox catalysts instead of sodium sulfide that is presently used in the kraft process. Soda/anthraquinone (AQ) pulping afforded white birch (Betula papyrifera) and sugar maple (Acer saccharum) pulps with equal if not superior strength to kraft pulps. However, the delignification rate was significantly lower for soda/AQ pulping. When AQ was replaced by 2‐methylanthraquinone (2‐MAQ) a delignification rate only slightly lower than that of kraft pulping was obtained at the same effective alkali (EA). At a kappa number of ～20, a soda/2‐MAQ pulp was produced from sugar maple at a higher yield (1.2% on chips) than for a kraft pulp. 2‐MAQ was synthesized, as a powder, at 75% yield using an AlCl₃–mediated Friedel‐Crafts reaction that is one of the methods used for commercial production of AQ.     

Brightness Improvement Of Douglas Fir Thermomechanical Pulp By Edta And Ascorbic Acid Treatments On Chips

This investigation studies the use of Douglas fir wood as feedstock for thermomechanical pulp (THP). Douglas fir wood extractives include flavonoids and other polyphenolic compounds, which make the pulp susceptible to discolouration. Pulp darkening is promoted by the formation of metal-chelates and phenolic oxidation products. The effectiveness of various wood pretreat- ments to prevent the discoloration of polyphenolic extractives in Douglas fir wood was investigated in lab-scale experiments. Iron- mediated brightness losses (up to 5.1% ISO) could be prevented by wood pretreatment with 0.2% EDTA. Treatment of wood meal slurries at temperature levels comparable to those applied in thermo- mechanical pulping caused wood discoloration due to polyphenol oxidation. The brightness losses could be reduced by the addition of 0.5% ascorbic acid. The anti-oxidizing agent was more effective with sapwood compared to heartwood. EDTA pretreatment allowed an increase in the proportion of heartwood from 12% to 39% (w/w) that could be tolerated as feedstock for the production of dithionite bleached TMP with a brightness of 60% ISO. Wood chip impregnation with both EDTA and ascorbic acid only proved advantageous over EDTA alone in Douglas fir samples consisting almost exclusively of sapwood.     

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.     

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     

Aspen Knots,a Rich Source of Flavonoids

Abstract

Hydrophilic extractives in heartwood, sapwood, and knots of three aspen species were analyzed by gas chromatography, gas chromatography‐mass spectrometry, and high‐performance size‐exclusion chromatography. The amounts of flavonoids were considerably higher in the knots relative to the stem wood. Flavonoids identified were dihydrokaempferol, naringenin, kaempferol, catechin, and taxifolin. In addition, glycosides of dihydrokaempferol, naringenin, and kaempferol were identified by mass spectrometry and shown to be glucosides by enzymatic hydrolysis by β‐D‐glucosidase. Dihydrokaempferol and its glucoside dominated in all knot samples although there were variations in the amounts and composition of the extractives. The total amounts of flavonoids varied between 11 and 43 mg/g in Populus tremula, 12 and 62 mg/g in Populus tremuloides and 47 and 82 mg/g in Populus grandidentata. The aspen knots were found to be a rich source of bioactive flavonoids.     

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.     

Effect of lignin on mechanical,biodegradability, morphology,and thermal properties of polypropylene/polylactic acid/lignin biocomposite

ABSTRACT

The effects of lignin on mechanical, biodegradability, morphology, and thermal properties of PP/PLA/lignin were investigated. PP/PLA/lignin film were manufactured by adding PP, PLA, lignin and compatibilizer into rheomix at 200°C, at 70?rev?min^?1 for 30?minthen pressed using Hydraulic Hot Press at 200°C–210°C, at 6 bar for 20?min. The functional groups of PP/PLA/lignin were analyzed using FTIR. The surface morphology, mechanical properties and thermal stability was measured by SEM, tensile strenght and TGA respectively. TThe FTIR intensity of vibration peak of –CH₃?cm^-1 from PP/lignin and PP/PLA/lignin at 997–993, 1458–1451 and 2966–2904?cm^-1 was lower than neat PP. The addition of lignin into PP/lignin, PLA/lignin and PP/PLA/lignin can reduce tensile strength and elongation at break. The thermal stability PP/PLA/lignin was lower than the PP/lignin but higher compared to PP/PLA biocomposites. The biodegradability of PP/PLA/lignin biocomposites was two times higher than that of PP/lignin.