Bleaching Of Hardwood Kraft Pulp Research Articles

Effects of residual phenolic compounds on xylanase-assisted ClO2 bleaching of hardwood kraft pulp

In both pulping and bleaching processes, lignin in the pulp fiber is degraded into smaller molecules that need to be rinsed away. However, despite the installation of automatic washing equipment, the small phenolic compounds among other lignin degradation products can hardly be completely removed from the brownstock. Among the myriad of small phenolic compounds degrading from lignin, some are water-soluble and highly reactive with bleaching reagents. To understand the impact of residual phenolic compounds from black liquor on pulp bleaching, six monomeric phenolic model compounds were tested in this study. Catechol and vanillin showed inhibitory effects on xylanase activity, while catechol, vanillin, and guaiacol interfered with the delignification reaction in the chlorine dioxide (D) and alkaline extraction (E) stages of the bleaching sequence, thereby preserving the integrity of cellulose in the pulp. Because the efficiency of xylanase and bleaching reagents is hindered by the presence of these phenolic compounds, higher operational cost and more bleaching reagents are needed, which are incompatible with modern environmental policies in the world. Nonetheless, the presence of remaining soluble phenolic compounds in the brownstock can improve the bleaching selectivity important for the production of high-quality pulp with less-degraded cellulose chains.

How do xylanase and hot acid stages differ at enhancing elemental chlorine-free bleaching of hardwood kraft pulp?

Hardwood kraft pulp contains relatively high hexenuronic acid content which increases unnecessary consumption of bleaching chemicals and has negative effects on pulp brightness stability. Hexenuronic acid can be partly removed by an enzyme treatment or a hot acid treatment. The difference between enzyme and hot acid stages on removing hexenuronic acid and enhancing hardwood kraft pulp ECF bleaching has been investigated. A typical hot acid stage removed more than 60% of hexenuronic acid but only saved about 20% of chlorine dioxide to achieve 84% ISO, while xylanase treatment only removed 12% of hexenuronic acid but saved approximately 40% of chlorine dioxide to achieve the same brightness target. In addition to a slight reduction of hexenuronic acid, fiber ultrastructure analysis reveals that enzyme pretreatment removed hemicellulose layer which was originally present on the fiber surface. The removal of “barrier” xylan increases fiber accessibility to bleaching chemicals and decreases the diffusion resistance of delignification during bleaching.

Minimizing Viscosity Loss during Totally Chlorine-Free Bleaching of Hardwood Kraft Pulp

By applying increasing amounts of ozone (Z stage bleaching) on eucalyptus oxygen-delignified pulps, it was observed that both lignin and hexenuronic acids (HexA) are attacked early during the treatment. While the HexA were progressively removed, however, the oxidized lignin tended to stay in the pulp. An acidic stage (A stage) at pH 3 and a temperature of 90 to 95°C removed a high proportion of the HexA, which eventually reduced the ozone requirement. In spite of the negative impact of the A stage on the DP of cellulose, totally chlorine-free sequences containing A led to pulps of higher viscosity. Increasing the temperature in A to 120°C did not seem to have an effect other than increasing the rate of the hydrolysis reactions. A very efficient metal removal was observed when a chelating agent was added in A (AQ). Some trials showed that splitting the Z stage in a ZEZE-like process (E for alkaline extraction) minimized the impact on pulp viscosity, and that AQPZE-like sequences can reach a quality comparable to some commercial elemental chlorine-free (ECF) pulps.

Hydrogen peroxide bleaching of hardwood kraft pulp with adsorbed birch xylan and its effect on paper properties

The adsorption of xylan on pulp fibers improves the strength properties of paper. However, the optical properties are decreased significantly. The objective of our research was to bleach hardwood kraft pulp with adsorbed birch xylan by hydrogen peroxide and study the effect of bleaching parameters on paper properties. The bleaching parameters studied included bleaching temperature, time, initial pH as well as MgSO4 dosage. The optical properties (whiteness, brightness, opacity) and physical properties (tensile index, tearing index, bulk) of handsheets made from the pulp bleached with different process variables were measured. The results showed that better optical properties were obtained with higher bleaching temperature, longer bleaching time, and more MgSO4 dosage. Bleaching from an initial pH of 11 provided the highest brightness value. On the other hand, strength properties were improved with decreasing of the bleaching temperature, and increasing the initial pH and MgSO4 dosage. The relationship between strength properties and bleaching time varied depending on bleaching temperature. According to the results, both good mechanical properties and optical properties could be achieved when the operating parameters were controlled properly. Therefore hydrogen peroxide bleaching was proved to be a suitable method for bleaching hardwood kraft pulp with adsorption of birch xylan.

Xylanase production by Paenibacillus campinasensis BL11 and its pretreatment of hardwood kraft pulp bleaching

Production of a single component 41 kDa xylanase from Paenibacillus campinasensis BL11 was conducted under various pH and temperature at the shake flask level. Alternative carbon and nitrogen sources were also evaluated. Up to 10.5 IU/mL and 29.39 IU/mg specific activity of xylanase in crude extract was obtained at 24 h, 37 °C, pH 8. In addition, same level of xylanase productions was also obtained on rice husk and rice straw at 2 days of incubation. Relative xylanase activities of 56.8% and 51.9% were found after 4 h incubation in pH 7 and pH 9 at 65 °C, respectively. Xylanase pretreatments (2.5 IU per gram of oven-dry pulp) increased brightness (as much as 4.4 and 3.9%) and viscosity (as much as 0.5 and 0.3 cP) of pulp after full chlorine dioxide bleaching for untreated and oxygen delignified hardwood kraft pulp. Increased benefits of pretreatment were found with increasing xylanase dosage and pretreatment time.

On the theoretical basis for the low bleaching chemical requirement of hot chlorine dioxide bleaching of hardwood kraft pulp

Article On the theoretical basis for the low bleaching chemical requirement of hot chlorine dioxide bleaching of hardwood kraft pulp was published on January 1, 2004 in the journal Nordic Pulp & Paper Research Journal (volume 19, issue 1).

Oxidized Derivatives of Lipophilic Extractives Formed during Hardwood Kraft Pulp Bleaching

Summary The structural changes of E. globulus wood extractives during bleaching with chlorine dioxide (D), oxygen (O), ozone (Z) and hydrogen peroxide (P) were studied. The detailed characterisation of the extractive derivatives detected in the partially bleached D, O, P and Z pulps was achieved by performing reactions of pure reference compounds with the different bleaching agents. The results show that the unsaturated sterols and fatty acids are extensively degraded during chlorine dioxide and ozone bleaching and only partially degraded during oxygen and hydrogen peroxide bleaching. The corresponding saturated extractives as well as the long chain aliphatic alcohols and ω-hydroxyfatty acids were stable during bleaching. The main oxidation products of β-sitosterol and oleic and linoleic acids, including one chlorinated derivative of linoleic acid, were identified here for the first time in E. globulus bleached pulps and bleaching filtrates.

Operating Experience of ECF Bleaching with Xylanase Treatment

Yonago mill of Oji Paper produces approximately 1, 200 tons of hardwood pulps per day at 85-86% ISO brightness for coated paper products.Xylanase treatment with on-site enzyme production was introduced into the hardwood kraft pulp bleaching process (C-E/O-dnD) in October 1998. A thermostable xylanase from a microorganism. Bacillus sp. S-2113, that we isolated through screening was selected for use in this process. The xylanasecontaining culture was applied to the bleaching process without removing the bacterial cells from the culture medium. Therefore. xylanase treatment process could be operated economically. Introducing xylanase treatment was allowed to reduce bleaching chemicals, so chemical cost was lower than before.In Novenber 2000, the bleaching process was converted to ECF one (D0-E/O-dnD). As a result, effluent AOX and chloroform emissions have decreased significantly. It is recognized that introducing xylanase treatment is allowed to reduce bleaching chemicals in ECF bleaching process, too.

On-Site Production of Xylanase and its Application on Hard Wood Kraft Pulp Bleaching

Xylanase treatment with on-site enzyme production was introduced into the hardwood kraft pulp bleaching process (C-E/O-dnD) at Yonago mill in October, 1998.A thermostable xylanase from a microorganism, Bacillus sp.S-2113, that we isolated through screening was selected for use in this process.The xylanase-containing culture was applied to the bleaching process without removing the bacterial cells from the culture medium.Two years have passed since the xylanase treatment operation, with onsite enzyme production, was begun, and so far, this operation has been working well.The ECF bleaching sequence will start operation within the year 2000in Yonago mill.The effects of enzyme bleaching in the ECF bleaching process are expected to be even greater then.

Application of a Catalyst in Peroxide Bleaching of Eucalyptus Kraft Pulp

Summary A binuclear [Mn(III)Mn(IV)(μ-O)2(μ-CH3COO)L](ClO4−)2 complex with L = 1,2 Bis-(4,7-dimethyl-1,4,7-triazacyclonon-1-yl)-ethane, described as a selective catalyst in hydrogen peroxide bleaching of softwood pulps, was tested in hardwood kraft pulp bleaching. The catalyst application gave rise to a higher consumption of peroxide which resulted in higher pulp brightness. The delignification improvement caused by the catalyst was shown to be much lower compared to catalysed peroxide bleaching of softwood kraft pulp. In contrast to the results of softwood pulp bleaching no selectivity improvements could be found when using the catalyst in bleaching of eucalyptus kraft pulp.

Extraction in aqueous two-phase systems of alkaline xylanase produced by Bacillus pumilus and its application in kraft pulp bleaching

The aim of this work was to extract and to purify xylanase, produced by Bacillus pumilus from the crude fermentation broth, using aqueous two-phase systems (ATPS). The xylanase was extracted by partitioning in ATPS composed of phosphate and polyethylene glycol (PEG). The effect of tie-line length, PEG molecular mass and NaCl concentrations upon the purification factors and yields of xylanase were investigated by statistical design. The best system studied was that containing 22% PEG6000, 10% K 2HPO 4 and 12% NaCl with a purification factor of 33 and a 98% yield of enzyme activity. This system was also used for continuous extraction in a pulsed caps column. Subsequently, the xylanase from the crude fermentation broth was tested in hardwood kraft pulp bleaching.

The Application of Xylanase on Hardwood Kraft Pulp Bleaching and its Operating Experience

Enzyme bleaching was introduced to the process (C-E/O-dnD) for bleaching of hardwood kraft pulp in Yonago mill in October, 1998. This is the first case in which an enzyme has been steadily applied for pulp bleaching in Japan. A thermostable xylanase from a microorganism that we isolated through screening was selected for use in this process. This microorganism, Bacillus sp. S-2113, produces two extracellular xylanases, XP1 and XP2. Expansion of the scale of enzyme production from the laboratory-scale to the mill-scale has been accomplished. It was found that hardwood kraft pulp is effective as a xylanase inducer in the case of this microorganism. The xylanase-containing culture can be applied to the bleaching process without removing the bacterial cells from the culture medium. After the enzyme bleaching process, the microorganism is killed by the bleaching chemicals used in the next step of the bleaching process. The pulp used in the culture medium is returned to the fiber line. Furthermore, because the quantity of enzyme used (the culture) is relatively low, there is no adverse influence on the quality of the pulp. One year has passed since the enzyme bleaching operation, with on-site enzyme production, was begun, and so far, this operation has been working well.The ECF bleaching sequence will start operation within the year 2000 in Yonago mill. The effects of enzyme bleaching in the ECF bleaching process are expected to be even greater then.

Hydrolysis of xylans by enzyme systems from solid cultures of Trichoderma harzianum strains.

Xylanase activity was isolated from crude extracts of Trichoderma harzianum strains C and 4 grown at 28 degree C in a solid medium containing wheat bran as the carbon source. Enzyme activity was demonstrable in the permeate after ultrafiltration of the crude extracts using an Amicon system. The hydrolysis patterns of different xylans and paper pulps by xylanase activity ranged from xylose, xylobiose and xylotriose to higher xylooligosaccharides. A purified ss-xylosidase from the Trichoderma harzianum strain released xylose, xylobiose and xylotriose from seaweed, deacetylated, oat spelt and birchwood xylans. The purified enzyme was not active against acetylated xylan and catalyzed the hydrolysis of xylooligosaccharides, including xylotriose, xylotetraose and xylopentaose. However, the enzyme was not able to degrade xylohexaose. Xylanase pretreatment was effective for hardwood kraft pulp bleaching. Hardwood kraft pulp bleached in the XEOP sequence had its kappa number reduced from 13.2 to 8.9 and a viscosity of 20. 45 cp. The efficiency of delignification was 33%.

Bleaching of Hardwood Kraft Pulp with Manganese Peroxidase from Phanerochaete sordida YK-624 without Addition of MnSO(inf4)

In vitro bleaching of an unbleached hardwood kraft pulp was performed with partially purified manganese peroxidase (MnP) from the fungus Phanerochaete sordida YK-624 without the addition of MnSO(inf4) in the presence of oxalate, malonate, or gluconate as manganese chelator. When the pulp was treated without the addition of MnSO(inf4), the pulp brightness increased by about 10 points in the presence of 2 mM oxalate, but the brightness did not significantly increase in the presence of 50 mM malonate, a good manganese chelator. Residual MnP activity decreased faster during the bleaching with MnP without MnSO(inf4) in the presence of malonate than in the presence of oxalate. Oxalate reduced MnO(inf2) which already existed in the pulp or was produced from Mn(sup2+) by oxidation with MnP and thus supplied Mn(sup2+) to the MnP system. The presence of gluconate, produced by the H(inf2)O(inf2)-generating enzyme glucose oxidase, also improved the pulp brightness without the addition of MnSO(inf4), although treatment with gluconate was inferior to that with oxalate with regard to increase of brightness. It can be concluded that bleaching of hardwood kraft pulp with MnP, using manganese originally existing in the pulp, is possible in the presence of oxalate, a good manganese chelator and reducing reagent.

In Vitro Bleaching of Hardwood Kraft Pulp by Extracellular Enzymes Excreted from White Rot Fungi in a Cultivation System Using a Membrane Filter

To clarify the role of excreted extracellular enzymes during long-term incubation in a pulp biobleaching system with white rot fungi, we developed a cultivation system in which a membrane filter is used; this membrane filter can prevent direct contact between hyphae and kraft pulp, but allows extracellular enzymes to attack the kraft pulp. Phanerochaete sordida YK-624 brightened the pulp 21.4 points to 54.0% brightness after a 5-day in vitro treatment; this value was significantly higher than the values obtained with Phanerochaete chrysosporium and Coriolus versicolor after a 7-day treatment. Our results indicate that cell-free, membrane-filtered components from the in vitro bleaching system are capable of delignifying unbleached kraft pulp. Obvious candidates for filterable reagents capable of delignifying and bleaching kraft pulp are peroxidase and phenoloxidase proteins. The level of secreted manganese peroxidase activity in the filterable components was substantial during strain YK-624 in vitro bleaching. A positive correlation between the level of manganese peroxidase and brightening of the pulp was observed.

Demethylation and delignification of kraft pulp by Trametes versicolor laccase in the presence of 2,2?-azinobis-(3-ethylbenzthiazoline-6-sulphonate)

Bleaching of hardwood kraft pulp by Trametes versicolor was accompanied by release and accumulation of methanol, which was produced by demethylation of the pulp. A partial demethylation of the pulp was observed with isolated laccase I from T. versicolor. The extent of demethylation by laccase was increased to the level released by the fungus by addition of 2,2′-azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS). Methanol release by the laccase/ABTS combination was followed by slower kappa reduction. Both methanol release and kappa reduction were dependent on laccase and ABTS concentrations. The fungus did not produce a stable equivalent of ABTS during bleaching, because extracellular culture fluid from bleaching cultures gave only the same methanol release from pulp as laccase I. Pulp viscosity, an indicator of cellulose chain length, was decreased only slightly by laccase. Thus the enzyme in the presence of ABTS, unlike the fungus, specifically attacks lignin.

Effect of polydimethylsiloxane oxygen carriers on the biological bleaching of hardwood kraft pulp by Trametes versicolor

Improving the availability of oxygen by adding polydimethylsiloxanes (PDMS) oxygen carriers to Trametes versicolor cultures increased pulp brightening. The presence of the oxygen carriers in cultures of T. versicolor with hardwood kraft pulp increased the growth rate of the fungus, but not the ultimate biomass yield. The PDMS also stimulated brightening of hardwood kraft pulp by it T. versicolor immobilized in polyurethane foam. A threefold increase in the oxygen uptake rate in T. versicolor cultures with PDMS was observed. This increase can be explained by elevated oxygen transfer rate and attributed to the surfactant properties of PDMS.

Biological bleaching of hardwood kraft pulp using Trametes (Coriolus) versicolor immobilized in polyurethane foam

Incubation of hardwood kraft pulp (HWKP) in agitated aerated cultures of the white-rot fungus Trametes versicolor increases pulp brightness and decreases its residual lignin content. A consequence of this biobleaching with whole cultures is that the resulting pulp also contains fungal biomass (up to ca. 10% (w/w)). In this report culture conditions for the immobilization of T. versicolor on polyurethane foam and bleaching of HWKP with the immobilized fungus are described. The major advantage of using immobilized fungus to bleach HWKP is that the fungal biomass can be separated from the pulp after treatment, resulting in a biologically bleached pulp free of fungal mycelium. From an analysis of pulp samples bleached with free and foam-immobilized mycelium, we conclude that fungal biomass in pulp treated with free mycelium accounts for up to 25% of the reduction in pulp viscosity (indication of cellulose chain length) whereas the zero span breaking length (indication of fibre strength) is not significantly affected by the presence of the fungus. Immobilization of the fungus on polyurethane foam also allows the repeated use of the same fungal biomass to bleach successive batches of pulp, either immediately or after storage at 4°C.

Viscosity‐enhancing bleaching of hardwood kraft pulp with xylanase from a cloned gene

The idea of removing lignin from kraft pulp with ligninolytic microorganisms has been around for some time.' More recently, a peroxidase has been described2 which, in the presence of low concentrations of peroxide, might depolymerize lignin and, in combination with an extraction, thereby bleach kraft pulp. An alternative approach is based on reports that residual lignin in unbleached kraft pulp is linked to hemi~ellulose~ and that cleavage of this linkage will allow lignin to be r e l e a ~ e d . ~ Hydrolysis of the lignin-hemicellulose linkage would have to be specific, in order to prevent deterioration of pulp qualities, e.g. viscosity, due to cellulose hydrolysis . 5 Ideally, the ligninhemicellulose linkage itself should be the only one cleaved. In hardwoods, the linkage is mainly betwen lignin and xylan, possibly through arabinose side chain^.^ We recently produced clones of E . coli capable of endoxylanase or P-xylosidase production in the absence of cellulase,8,' which could find potential application in lignincarbohydrate cleavage, especially for hardwood kraft pulps where xylan is the predominant hemicellulose, and can even be redeposited on the pulp during cooking. We now describe experiments which demonstrate that lignin removal can, indeed, be aided by treatment with xylanase from a cloned system, and that the resulting pulp retains viscosity as well as the required strength properties.