Eucalyptus Kraft Pulp Research Articles

An Approach to Industrial Application: Influence of Black Liquor and pH on Xylanase Efficiency in Bleaching of Eucalyptus Kraft Pulp

To obtain a more realistic appraisal of the potential efficiency of xylanases in the industrial bleaching, the influence of pH and the presence of black liquor (measured as COD) on the bleaching efficiency of two commercial xylanases was studied at high temperature. These pH’s, CODs, and temperatures are close to those used in the storage tower of the B fiber line in Jacareí unit of Fibria (Brazil). The pulp samples obtained after each bleaching stage were analyzed for kappa number, brightness, viscosity, and hexenuronic acid content, and so were the effluents for COD, TOC, color, turbidity, and pH after the enzymatic stage. On the basis of the results, the xylanases were found to increase pulp brightness in the treatment involving the most unfavorable conditions (viz. high COD and pH). However, an initial COD above 9 kgO2 t−1 and/or a pH higher than 9.5 detracted from their bleaching efficiency. The effect on the kappa number and hexenuronic acids content of the pulp was apparent immediately after the enzymatic stage, and the most marked increase in brightness was observed after the chlorine dioxide stage.

The final bleaching of eucalypt kraft pulps with hydrogen peroxide: relationship with industrial ECF bleaching history and cellulose degradation

AbstractBACKGROUND: The process of chemical pulp bleaching is based for the most part in chlorine dioxide within elemental chlorine free (ECF) technologies. The use of greener alternatives such as bleaching with hydrogen peroxide (P stage) is not widely used owing to selectivity concerns related to transition metal‐catalyzed decomposition reactions. Even at the final stage where peroxide is recognized to boost brightness and improve the brightness stability of the bleached pulp, cellulose degradation often overcomes these advantages. This paper presents the results of studies intended to optimize final peroxide bleaching performance considering two standard ECF industrial bleaching sequences: the conventional DED and the ECF‐light OQ(PO)D (stages name: D—chlorine dioxide; E—alkaline extraction; O—oxygen; Q—chelation, (PO)—hydrogen peroxide pressurized with oxygen).RESULTS: The addition of sodium diethylenetriaminepentaacetate (DTPA) was the most effective option in terms of DED pulp bleachability and selectivity with hydrogen peroxide, as well as in terms of brightness reversion. As regards the OQ(PO)D pulp, a blend of DTPA and magnesium was the most beneficial in those properties.CONCLUSIONS: The choice of the best hydrogen peroxide stabilizer, among the different tested combinations of magnesium and chelants (EDTA and DTPA) studied, in terms of pulp bleachability, bleaching selectivity and brightness reversion is dependent on the impact of the previous bleaching stages on metallic nature and content. The pulp Mg/(Fe + Cu) ratio was highlighted as a process parameter controlling cellulose degradation in peroxide bleaching. Copyright © 2010 Society of Chemical Industry

Chemical components of bleached eucalypt kraft pulp effluent COD and treatment removal efficiency during normal mill operation and maintenance shutdowns

In order to meet increasingly strict Brazilian COD emissions limits, mills must understand the components that contribute to effluent COD, how these vary between normal mill operation and maintenance shutdowns, and how this variation affects treatment efficiency. To this end, primary and secondary effluents from a Brazilian bleached eucalypt kraft pulp mill activated sludge system were analyzed for COD, lignin, extractives, carbohydrates and AOX over a sixth month period that included two general maintenance shutdowns and four months of normal operation. Primary effluent presented significantly different compositions during periods of normal operation and mill shutdowns. During normal operation, the main components of effluent COD (909 mg/l average) were carbohydrates, followed by lignin. However, the lignin fraction was the main component of secondary effluent COD during both normal operation and mill shutdowns. Higher removal efficiencies for COD carbohydrates and AOX were observed during normal operation compared to shutdowns, while no difference in removal efficiencies of lignin and extractives was observed. Carbohydrate removal efficiency was significantly lower in one of the parallel treatment lines. The different removal efficiencies reflect not only variations in effluent composition, but possibly differences in system operational control which should be explored in greater detail.

Performance of new and commercial xylanases for ECF and TCF bleaching of eucalyptus kraft pulp

Since xylanases can differ widely in their bleaching efficiency, the performance of one new and two commercial xylanases was evaluated in an eucalyptus kraft pulp following XD (X: xylanase; D: chlorine dioxide) and XP (P: hydrogen peroxide) sequences. The new xylanase did not show a significant bleach boosting effect but increased the hexenuronic acid (HexA) removal by 10% after the D stage. The two commercial xylanases behaved in a different way, being one of them (XC) the most effective in increasing delignification (9%) and brightness (3%ISO). Its effectiveness was related to its greater action on releasing the xylan polymer, thus producing also a strong decrease in the HexA contents during the enzymatic stage (15%). All xylanases produced morphological changes in the fibre surfaces, but only with XC cracks and holes that improved the diffusion of reactives were observed. Finally, the best bleaching results were obtained with the XD sequence and therefore, a complete bleaching sequence XDEopD1 (Eop: alkaline extraction with oxygen and peroxide) was carried out with the best enzyme.

Biobleaching of eucalypt kraft pulp with a two laccase-mediator stages sequence

A new biobleaching sequence, with two enzymatic stages based on the application of laccase-mediator systems, was tested (L 1EL 2QPo) in order to increase the effectiveness of enzyme delignification on eucalypt kraft pulp. Different synthetic – 1-hydroxybenzotriazole (HBT) and violuric acid (VA) – and natural – syringaldehyde (SyAl) – mediators were used in the laccase stages and the biobleached pulp were compared in terms of chemical, optical and physico-mechanical properties. The pulp bleached with HBT or VA showed similar delignification (64.1% and 65.9% respectively) and optical properties (86.4% and 86.1% ISO brightness respectively) than an industrial TCF pulp (68.3% delignification and 84.8% ISO brightness). SyAl improved these properties in a lower extent (56.71% delignification and 80.52% ISO brightness). Regarding physico-mechanical properties of pulp, the biobleaching sequence had no a negative effect, even some slight improvements were observed in very specific cases.

Delignification of eucalypt kraft pulp with manganese-substituted polyoxometalate assisted by fungal versatile peroxidase

Oxidation of the manganese-substituted polyoxometalate [SiW11MnII(H2O)O39]6− (SiW11MnII) to [SiW11MnIII(H2O)O39]5− (SiW11MnIII), one of the most selective polyoxometalates for the kraft pulp delignification, by versatile peroxidase (VP) was studied. First, SiW11MnII was demonstrated to be quickly oxidized by VP at room temperature in the presence of H2O2 (Km=6.4±0.7mM and kcat=47±2s−1). Second, the filtrate from eucalypt pulp delignification containing reduced polyoxometalate was treated with VP/H2O2, and 95–100% reoxidation was attained. In this way, it was possible to reuse the liquor from a first SiW11MnIII stage for further delignification, in a sequence constituted by two polyoxometalate stages, and a short intermediate step consisting of the addition of VP/H2O2 to the filtrate for SiW11MnII reoxidation. When the first ClO2 stage of a conventional bleaching sequence was substituted by the two-stage delignification with polyoxometalate (assisted by VP) a 50% saving in ClO2 was obtained for similar mechanical strength of the final pulp.

The assessment of chromophores in bleached cellulosic pulps employing UV-Raman spectroscopy

UV-Resonance Raman (UV-RR) coupled with UV–visible Diffuse Reflectance (UV–vis DR) spectroscopy was applied to a solid-state study of chromophores in Eucalyptus globulus kraft cellulosic pulps bleached by chlorine dioxide and hydrogen peroxide. The UV-RR spectra were acquired at 325 nm laser beam excitation, which was shown to be appropriate for selective analysis of chromophore structures in polysaccharides. The proposed approach allowed the monitoring of chromophores in pulps and to track the extent of polysaccharide oxidation. However, precaution was suggested while performing a quantitative analysis of chromophores at the characteristic band of ∼1600 cm −1 because of charge transfer complexes (CTCs) that exist in the pulp. These CTCs can affect the intensity of the aforementioned band by diminishing the conjugate state in the chromophore moieties. The amount of carbonyl and carboxyl groups in polysaccharides correlated with the intensity of the band at 1093 cm −1. The analysis of UV-RR spectra revealed xylan as an important source of chromophores in eucalypt kraft pulp.

Molybdo-vanado-phosphate heteropolyanion catalyzed pulp ozonation in acetone/water solution. Part 1. Effect of process variables

The effect of solvent and catalyst concentration, pH and ionic strength on ozone bleaching of commercial eucalypt kraft pulp in acetone–water solution in the presence of Keggin-type heteropolyanion [PMo7V5O40]8− (HPA-5) has been examined and compared with conventional (solvent/catalyst free) ozonation systems. The solvent content and medium acidity were found to be the principal factors affecting ozonation efficiency. Increase in acetone concentration from 6% to 60% (w/w) led to gain in pulp brightness by 20.6% and delignification degree by 28.4%. Within the operative pH 1–2 range required for ozonation, the increase in pulp brightness by 7.6% and delignification degree by 18.1% was observed with acidity change from pH 1 to 2. The HPA-5 concentration of 1mM was found to be optimal for effective pulp ozonation in acetone solution. The role of the Donnan effect was examined. Increase in ionic strength (cation concentration) up to 0.25M caused significant bleaching improvement.

Optimization of Treatments for the Conversion of Eucalyptus Kraft Pulp to Dissolving Pulp

Eucalyptus wood is known worldwide for its use in the production of kraft pulps and dissolving pulps. In our previous study, the feasibility of using a eucalyptus kraft pulp as a dissolving pulp was investigated. It was demonstrated that a kraft pulp subjected to a sequence of treatments that included enzymatic treatments using a xylanase and a monocomponent endoglucanase and, an alkali extraction, accomplished the requirements of a commercial dissolving pulp in terms of cellulose reactivity and hemicellulose content. Nevertheless, the low degree of polymerization and the presence of cellulose II showed that the combination of treatments had to be optimized. As a result, the parameters involved in the sequence of treatments were examined as well as their influence in the production of dissolving pulps. Furthermore, new sequences were tested. It was noticed that by decreasing the concentration of alkali in the alkali extraction stage, no cellulose II formed at short reaction times (10 min.) and that the degree of polymerization was increased. On the other hand, the cellulose reactivity and the hemicellulose content were barely affected. Moreover, a high pulp consistency (10%) led to an inhomogeneous mixture and the stirring effect was slightly noticeable.

Initiating ECF bleaching sequences of eucalyptus kraft pulps with Z/D and Z/E stages

Abstract Ozone bleaching is a common practice in pulping, and also of eucalyptus, where it is usually applied in combination with bleaching sequences based on oxygen, hydrogen peroxide, or chlorine dioxide. Ozone has been proven to be a highly efficient and competitive bleaching chemical in terms of delignification efficiency, low costs, and reducing ecological impact. The objective of the present work was to evaluate technology with ozone/alkaline extraction (Z/E) and ozone/chlorine dioxide (Z/D) for bleaching of eucalyptus kraft pulp. Primarily, the impact of these bleaching steps on refinability and quality of pulp should be investigated. As reference, the sequence D*(EP)D (hot chlorine dioxide, extraction in presence of hydrogen peroxide, chlorine dioxide) was selected, which is considered as the state-of-the-art bleaching in elemental chlorine free (ECF) bleaching technology. Various bleaching sequences with ozone in their first step (Z/D(EP)DP, Z/D(EP)DD, Z/EDP, Z/EDD and A*Z/EDP) were found to provide kraft pulps of similar brightness and in similar yield as the reference sequence D*(EP)D. The kappa number, viscosity, and the contents of glucose and xylose, and hexenuronic acid of the pulps were also similar. In addition, the Z sequences resulted in a substantial reduction of the total chlorine dioxide consumption (more than 30.3% in all cases). The A*Z/EDP sequence, which proved to be the most efficient, yielded 87.5% ClO2 reduction. The studied bleaching sequences also resulted in substantially improved brightness reversal with regard to the reference sequence. The sequence A*Z/EDP was also the most efficient as regards the removal or organochlorines (OX) from the pulp and their reduction in the effluents (AOX). Ozone bleaching sequences improved paper strength, especially with the A*Z/EDP sequence.

Effect of different coupling agents on the browning of cellulose–polypropylene composites during melt processing

The effects of two coupling agents on the discoloration of cellulose/polypropylene composites during melt processing have been investigated. Composites of polypropylene, coupling agent and bleached eucalyptus Kraft pulp were produced by compounding in a twin-screw extruder. The coupling agents were maleic anhydride-grafted polypropylene (MAPP) and polyethylenimine (PEI). The discoloration was measured using standard colorimetry and the discoloration was investigated using diffuse reflectance (FTIR and UV–Visible) spectroscopy. Both MAPP and PEI increase the browning, but the two mechanisms are clearly different. PEI reacts with carbonyl compounds produced in the cellulose degradation to form new chromophores; however, no specific discoloration processes were detected in composites made with MAPP. In this case, the detrimental effect on the discolouration was related to the increased frictional degradation.

Obtaining low-HexA-content cellulose from eucalypt fibres: Which glycosil hydrolase family is more efficient?

Four new bacterial xylanases from different glycosyl hydrolase families (11, 10 and 5) were evaluated for hexenuronic acid (HexA) removal capacity and bleach boosting ability of a eucalypt kraft pulp. The family 11 xylanase was the most effective in enhancing HexA removal and also in increasing delignification and brightness. A very innovative point was that a xylanase from family 5 was applied in pulp bleaching for the first time, showing a notable contribution to pulp bleachability. On the contrary, the family 10 xylanases did not modify kappa number or brightness. A remarkable effect was that the tested xylanases reduced pulp HexA content. The effects produced by the different xylanases in pulp properties were closely related with the effects observed in the effluent properties. The effluents from enzymatic treatments showed the dissolved xylans and xylooligosaccharides branched with HexA, as well as lignin. In addition, a simple tool to assess the boost bleaching ability of a xylanase treatment was also used.

The role of xylanases and laccases on hexenuronic acid and lignin removal

The variation of the contents in hexenuronic acids (HexA) and lignin in eucalyptus kraft pulp during sequences with the laccase–mediator treatment with or without xylanase pretreatment was studied. The laccase–HBT system (HBT: 1-hydroxybenzotriazole) initially oxidized lignin alone but altered cellulose in the pulp as well after some time. Once all accessible lignin was removed, the system acted on HexA. As a result, the laccase–mediator treatment reduced the HexA content of the pulp, especially if a xylanase pretreatment was applied before. A previously unseen effect was observed here: HexA removal was found to depend on the laccase and HBT doses, but not on the reaction time. In addition, the xylanase pretreatment was found to strongly boost the effects of the laccase–HBT system by facilitating their access to HexA without affecting the lignin content.

Some effects of bleached kraft pulp mill effluents on aquatic organisms – a review.

Paper is still the prime carrier of information and it is information that reduces uncertainty in decision making. Despite the promises of the paperless office ushered in by the computer age it is obvious to everyone that the reverse seems true. We need paper and it costs money to produce and buy. There are strong economic arguments driving the current interest by the pulp and paper industry in Australia but like many development projects the financial balance sheet of profit and loss are more easily understood than some of the intangible impacts of such investments. This paper describes, from the available literature, some of the effects of water borne wastes from pulp mills on fish and other aquatic organisms in other parts of the world. Firstly the pulping processes that create the pollutants will be described, followed by a brief documentation of the characteristics of the wastes involved. The effects on aquatic life will be described and, finally, some comments on the Commonwealth Government’s recently released Environmental Guidelines for New Bleached Eucalypt Kraft Pulp Mills will be provided.

Polyoxometalate catalyzed ozonation of chemical pulps in organic solvent media

Polyoxometalate (POM) catalyzed ozonation of chemical pulps in organic solvent media was found to be particularly effective and selective environmentally benign bleaching approach providing a way for substantial increase in pulp brightness, viscosity and degree of delignification in comparison with other ozone-based bleaching techniques. A series of tested low-boiling polar aprotic and protic organic solvents showed a well-defined capacity for ozonation improvement in the presence of Keggin-type heteropolyanion [PMo 7V 5O 40] 8− (HPA-5). Even moderate solvent proportion of 6% (w/w) in the reaction solution caused additional gain in brightness up to 3.4% ISO with simultaneous increase in pulp viscosity up to 8.8% and lignin removal up to 18.9% after HPA-5 catalyzed ozonation (0.8% O 3; 0.5 mM HPA), as compared with the control solvent-free process. An aqueous acetone solution was found to be the preferred reaction medium in terms of pulp brightening and delignification. Under optimized conditions, the POM-catalyzed ozonation of eucalypt kraft pulp in acetone/water solution showed remarkable brightness improvement by 15.1% ISO with additional lignin removal by 39.4% and increase in intrinsic viscosity by 3% in comparison with pulp bleached in water media.

Thermal and spectroscopic analyses on the molecular interaction between eucalyptus kraft pulp components and offset printing inks

Thermal and infrared spectroscopic analyzes were carried out in order to study the kind of interaction between the anatomical components of the bleached eucalyptus kraft pulp with offset inks. A Bauer-McNett fiber classifier was used in order to obtain the anatomical components of the pulp, separately. The determinations of the enthalpy of the processes occurring in the samples of inks and pulp, as well as the enthalpy of these components interactions were obtained by Differential Scanning Calorimetry. In the interaction between pulp and offset ink, the reduced enthalpy values of the endothermic peak were interpreted as due to the released energy for adhesion of the ink pigment to the substratum. The low enthalpy value, 58 to 121 cal.g -, ¹indicated that the settling of the ink occurs by physical interactions. The pulp fraction enriched with vessel elements caused a higher energy release during the adherence of the pigment into the pulp.

Influence of operation conditions on laccase-mediator removal of sterols from eucalypt pulp

The way how sterols, the main lipophilic compounds present in eucalypt kraft pulp, are eliminated by an enzymatic stage using the laccase-mediator system was evaluated. With this purpose laccase-mediator stage (L) was applied on an Eucalyptus globulus pulp under different operation conditions following a three-variable (laccase dose, mediator dose and reaction time) sequential statistical plan, to optimise the removal of sterols. The decrease in pulp sterol content during the enzymatic treatment was related to the decrease in kappa number and to brightness increase, as well as with the increase in some oxidation products of sitosterol (namely 7-oxositosterol and stigmasta-3,5-dien-7-one). The increase in reaction time from 1 to 5 h strongly reduced the sterol content, while no more sterols were eliminated during the 5–7 h period. Increasing the laccase dose from 1 to 20 U g −1 of pulp produced a high reduction in pulp sterols, whereas the increase in mediator (1-hydroxybenzotriazole) dose (from 0.5 to 2.5% of pulp weight) had only a slight influence in removing sterols. Therefore, at 16 U g −1 laccase dose, 0.5% mediator dose, 4 h of reaction, practically all the sterols were removed. Finally, it was demonstrated that sterols were more sensitive to a L stage (practically 100% of sterols were eliminated) than to a chlorine dioxide stage (54% of sterols eliminated).

Polymeric Branched Flocculant Effect on the Flocculation Process of Pulp Suspensions in the Papermaking Industry

This paper presents the effect of the structure of cationic polyacrylamides (CPAMs) on flocculation of pulp suspensions and floc properties. A focused beam reflectance measurement (FBRM) probe was used to monitor flocculation, deflocculation, and reflocculation processes in real time. To carry out the study, 1% elemental chlorine free (ECF) eucalyptus kraft pulp containing 20% ground calcium carbonate (GCC) was used. Results show that the effect of the CPAM structure depends on charge density and polymer dose. Floc size does not always decrease with branching degree, whereas floc stability and reflocculation ability increased when highly charged and branched CPAM was used. These findings indicate that the use of highly branched CPAMs with very high molecular weight is very promising as a retention aid method to improve the papermaking process.

Mass transfer and thermodynamic aspects of sodium desorption from eucalyptus kraft pulp by acidification using carbon dioxide

The thermodynamics and mass transfer aspects associated with the use of CO 2 for the acidification, particularly for the removal of Na + from pulp fibres, were studied. The acidifications with CO 2 and with H 2SO 4 were carried out in a stirred tank reactor under different temperatures, agitation speeds, concentrations of CO 2 and H 2SO 4 and treatment times. The CO 2 acidification of pulp was found to be very fast at Re > 10 4 and N p of 4, and reached equilibrium within 5 min. The volumetric mass transfer coefficient, k L a, of the CO 2 acidification was found to be in the range of 0.0005–0.0083 s −1. Thermodynamically, the CO 2 acidification was achievable only at pH > 4. The extent of the resultant Na + exchange increased with the acidification time, agitator speed and CO 2 flow rate. Under similar experimental conditions, the extent of Na + desorption by CO 2 acidification was found to be slightly lower than that achieved by sulfuric acidification. The equilibrium distribution of Na + in the solution and the fibre phase can be estimated using a model based on the Donnan theory.

Are the pulp fiber wall surface layers the most resistant ones towards bleaching

The residues of the wood cell wall compound middle lamella affect the composition of the relevant pulp fiber surface layers and influence the fibers’ bleachability. The objective of the present work was to separate the eucalyptus kraft and birch organosolv pulp fiber wall surface layers by hydromechanical peeling and to proceed with enzyme boosted bleaching of the separated fiber wall layers. The initial content of lignin and heteroaromatic compounds (“false” lignin) was determined by chemical methods and UV-spectra. The separated fiber wall surface layers representing the residues of the primary wall P and outer layer S1 of the secondary wall, as well as the main part of the secondary wall were exposed to the bleaching sequence peroxide-xylanase treatment-alkaline extraction-peroxide (P1-X-E-P2). brightness measurements revealed significant distinctions between the preparations. The final brightness of the main part of eucalyptus kraft pulp fibers reached 67%, while the brightness of the surface layers attained only 50% ISO. Similar results were obtained for birch organosolv pulp. It was concluded that the main reason for the described phenomena is the discordant chemical composition of the different fiber wall layers.