Oxygen-delignified Kraft Pulp Research Articles

Efeito da extração alcalina na redução do número Kappa no branqueamento ECF

The acid hydrolysis stage (A HT ) used in bleaching sequences of pulp, has as its main objective, the degradation of hexenuronic acids which are present in the pulp and can affect its brightness, reversal of brightness, among others. Despite the benefit of using the acid hydrolysis stage, the pH of this stage is not the most adequate, but when it comes to the degradation of lignin, it is more reactive in alkaline medium. Therefore, the present work sought to study an improvement in the bleaching process by the addition of an alkaline extraction stage after A HT stage, obtaining the best possible use of the chlorine dioxide stage. In this study, oxygen-delignified Kraft pulp from eucalyptus was used. Different ECF (Elemental Chlorine Free) bleaching sequences were performed in the pulp: D 0 (E+P)D 1 , A HT D 0 (E+P)D 1 , A HT /ED 0 (E+P)D 1 and A HT ED 0 (E+P)D 1 .As a result, the inclusion of a simple alkaline stage after the acid hydrolysis indicate a positive effect on the bleaching sequence, with a significant reduction in the consumption of chlorine dioxide. The inclusion of simple alkaline extraction also allowed the reduction of the kappa number and increased brightness, with a reduction of 0.3 points in the average Kappa number and a 1.3% ISO increase in brightness, analyzed after alkaline extraction with hydrogen peroxide of the sequence A HT /ED 0 (E+P)D 1 when compared to the one without simple alkaline extraction.

Comparison of the Ability of Several White-rot Fungi to Biobleach Acacia Oxygen-delignified Kraft Pulp

Previous screening analyses demonstrated that the in vivo biobleaching activities of the white-rot fungi Irpex lacteus KB-1.1 and Lentinus tigrinus LP-7 are higher than those of Phanerochaete chrysosporium and Trametes versicolor. The purpose of the current study was to examine the production of extracellular enzymes of these four white-rot fungi grown on three types of low-cost media containing agricultural and forestry waste, and to evaluate the ability of the produced extracellular enzymes to biobleach Acacia oxygen-delignified kraft pulp (A-OKP). The biobleaching activity of extracellular fractions of I. lacteus, L. tigrinus, T. versicolor, and P. chrysosporium cultures was the most pronounced after 3 days of incubation with Acacia mangium wood powder supplemented with rice bran and 1% glucose (WRBG) with resultant Kappa number reduction of 4.4%, 6.7%, 3.3%, and 3.3%, respectively. Therefore, biobleaching ability of I. lacteus and L. tigrinus have been shown to be higher than of T. versicolor and P. chrysosporium, both in vivo and in vitro.

A pronounced improvement of the kappa number reduction and pulp properties associated with the use of extracellular enzymes secreted by selected fungal strains

A combination of extracellular enzymes secreted by Irpex lacteus KB-1.1 and Lentinus tigrinus LP-7 showed promising results in the reduction of kappa number of Acacia oxygen-delignified kraft pulp (A-OKP) in previous studies. However, the observed Kappa number reduction was low, and the bleaching process required further optimization. In the current study, the A-OKP was treated with a combination of extracellular enzymes of I. lacteus and L. tigrinus, with a subsequent alkaline peroxide extraction, which significantly improved the Kappa number reduction. The maximum achieved Kappa number reduction was 26%. The effects of static incubation and sterilization of the extracellular enzymes on biobleaching process were evaluated. Compared with a static biobleaching, biobleaching with shaking shortened the required incubation time required from 3 to 1 d. The utility of extracellular enzymes was tested with and without sterilization; no significant differences in Kappa number reduction, brightness, and physical properties of the pulp were observed. The physical properties of all pulp samples were improved following the enzymatic treatment. Furthermore, a low-cost medium containing wood powder supplemented with rice bran and palm sugar (WRBP) was used for the production of enzymes for biobleaching of A-OKP.

BIOMIMETIC TCF BLEACHING OF PULP BY SIMPLE INORGANIC COMPLEXES OF CUPRIC/COBALT ACETATE

Oxygen delignified kraft pulp from eucalyptus (E. urophylla × E. grandis) was catalytically pretreated in aerobic condition using ammonium persulfate in present of catalists like cupric acetate and/or cobalt acetate in acetic acid-water solution, i. e. S2O8 2- -Cu 2+ , S2O8 2- -Co 2+ and S2O8 2- -(Cu 2+ +Co 2+ ). Final bleached pulp after pretreatment with the three catalytic systems showed higher delignification (23.45%, 21.85% and 19.63% respectively), better optical properties (82.93, 82.18 and 81.92% ISO brightness respectively) and pulp viscosity (787, 791 and 762 mL/g respectively; mL/g: intrinsic viscosity unit of pulp) than the control pulp (14.12% delignification, 77.33% ISO brightness and 746 mL/g viscosity). S2O8 2- -Cu 2+ and S2O8 2- -Co 2+ showed similar reduction in hydrogen peroxide consumption (61.91%, 62.48%), and S2O8 2- -(Cu 2+ +Co 2+ ) showed a greater reduction in hydrogen peroxide consumption than the two treatments (83.05%). Some improvements in tensile and tear strength of the resulting pulp were observed. The new sequence also yields composite effluents with larger percentage of lignin aromatic compounds compared to the control.

Biobleaching of Acacia kraft pulp with extracellular enzymes secreted by Irpex lacteus KB-1.1 and Lentinus tigrinus LP-7 using low-cost media

The white-rot fungi Irpex lacteus KB-1.1 and Lentinus tigrinus LP-7 have been shown in previous studies to have high biobleaching activity in vivo. The aim of this study was to investigate the activities and stabilities of extracellular enzymes, prepared from I. lacteus and L. tigrinus culture grown in three types of economical media of agricultural and forestry wastes, for biobleaching of Acacia oxygen-delignified kraft pulp using kappa number reduction as an indicator of delignification. After 3 days of incubation, the extracellular enzymes preparations from I. lacteus and L. tigrinus cultures in media of Acacia mangium wood powder supplemented with rice bran and addition 1 % glucose (WRBG), resulted in significant decrease of 4.4 and 6.7 %, respectively. A slightly higher kappa number reduction (7.4 %) was achieved with the combine extracellular enzymes from I. lacteus and L. tigrinus. One of the strategies for reducing the cost of enzyme production for treatment processes in the pulp and paper industry is the utilization of agricultural and forestry waste. Thus, WRBG has potential as a culture medium for producing stable lignolytic enzymes simply and economically.

FT-Raman, FT-infrared and NIR spectroscopic characterization of oxygen-delignified kraft pulp treated with hydrogen peroxide under acidic and alkaline conditions

The effects of bleaching treatment of oxygen-delignified softwood kraft pulp with hydrogen peroxide under acidic and alkaline conditions were studied using standard technological techniques and spectroscopic analytical methods: near-infrared (NIR), Fourier-transform infrared (FTIR) and Fourier-transform (FT) Raman spectroscopies. Among the three tested spectroscopic techniques, NIR analysis appeared to be the most appropriate in terms of possible technological applications. The use of NIR spectroscopy combined with multivariate data analysis allowed to create models for pulp bleaching monitoring based on CIE L*a*b* measurements. Near-infrared and FTIR spectroscopic studies allowed differentiating between the effects of the acidic and alkaline peroxide bleaching stages, but failed in relation to the delignification process. The most representative bands in the FTIR and FT-Raman spectra in terms of delignification and chromophore removal exhibited no correlation with standard technological measurement results.

Decolorization of oxygen-delignified bleaching effluent and biobleaching of oxygen-delignified kraft pulp by non-white-rot fungus Geotrichum candidum Dec 1

Decolorization of oxygen-delignified bleaching effluent (abbreviated as OBE) and biobleaching of oxygen-delignified kraft pulp (OKP) were conducted using a non-white rot fungus Geotrichum candidum Dec 1 (abbreviated as Dec 1) which has ability to decolorize various synthetic dyes and molasses. Dec 1 decolorized up to 77% of OBE for 6 days. In addition, Dec 1 increased the brightness of OKP from 47.8% to 51.2% and decreased the kappa value of OKP from 12.4 to 10.4 points during a 6-day incubation period at a 25% of pulp-concentration. At 2% pulp-concentration, the brightness of OKP increased by 13% and the kappa value of OKP decreased by 4 points only for a 3-day incubation period. When the decolorized OBE was used for bleaching of OKP, the brightness of OKP increased to 62.7% under the shaking culture to a 2% pulp-concentration using culture fluid of decolorized OBE. It was revealed that Dec 1 is a potential to apply for decolorization of wastewater and biobleaching of pulp in paper-mills.

Multistage oxygen delignification of high-kappa pine kraft pulp with peroxymonosulfuric acid (Px)

Abstract In the present study the advantages of multistage oxygen delignification was explored in comparison with a single-stage process at the same level of total caustic charge. A pine kraft pulp with kappa number of 65 (Kn65) was bleached with the focus on the effect of NaOH-charge distribution on Kn, pulp yield, and selectivity of oxygen delignification. The effect of initial chelation with ethylenediaminetetraacetic acid (EDTA) and interstage pulp treatment with peroxymonosulfuric acid (Px) were also investigated. It is shown that the chelated pulp with high Kn may be delignified in three stages to Kn15, but at an unacceptable reduction in pulp viscosity and yield. In contrast, interstage treatment of the chelated pulp with Px at a total charge of 2% active oxygen (based on pulp) in combination with three stages of oxygen delignification enables Kn reduction to about 15 at acceptable viscosity and total yield advantage of about 0.5% (based on wood) compared to an oxygen-delignified kraft pulp with Kn24 derived from the same pine wood chips.

Salen copper (II) complex encapsulated in Y zeolite: An effective heterogeneous catalyst for TCF pulp bleaching using peracetic acid

Cu(salen) and NaY encapsulated complexes, were synthesized by the “impregnation” (Cu(salen)/Y-IM) and flexible ligand “ship-in-a-botttle” (Cu(salen)/Y-SB) method. The resulting compounds were characterized by XRD, FTIR, DR UV–vis, BET. The encapsulated complexes show structural properties and chemical behaviour which is different from those of the neat complex. The catalytic bleaching by Cu(salen) and encapsulated Cu(salen) was tested for the eucalyptus oxygen delignified kraft pulp using peracetic acid as an oxidant. Influence of catalysis on TCF (total chlorine free) bleaching viz. delignification, property of bleached pulp was studied. Under the catalytic conditions, the encapsulated copper complexes exhibit enhanced activity or selectivity compared to the neat complex. The reasons for the enhanced activity of Cu(salen) upon encapsulation in NaY are reported by UV–vis techniques. The catalytic performance of encapsulated complex could be attributed to the formation of copper–hydroperoxide species.

Recombinant manganese peroxidase (rMnP) from Pichia pastoris. Part 2: Application in TCF and ECF bleaching

AbstractThe recombinant manganese peroxidase (rMnP) produced from the yeastPichia pastorishas been investigated in totally chlorine free (TCF) and elemental chlorine free (ECF) bleaching sequences for improving the bleachability of kraft pulps. In TCF bleaching, oxygen delignified hardwood kraft pulp was treated with rMnP, followed by a sequence combining a chelating and alkaline peroxide bleaching stage. The inclusion of the enzymatic treatment significantly improved the pulp brightness to a level that is difficult to obtain by chemical bleaching alone. Furthermore, the treatment with rMnP resulted in energy savings during pulp refining with PFI mill with a slight improvement in pulp strength properties such as tensile index and burst index. In ECF bleaching, a significant reduction in chlorine dioxide consumption was obtained. A three-stage rMnP treatment combined with alkaline extraction, followed by DED bleaching sequence for hardwood kraft pulp (HWKP) or DEDED bleaching sequence for softwood kraft pulp (SWKP), reduced the total effective chlorine by 41% and 32% for HWKP and SWKP, respectively, compared with the conventional bleaching sequences without enzymatic treatment. The strength properties of the enzyme-treated pulp were also slightly better than that of the control pulp. Further reductions in the consumption of total effective chlorine were obtained when a xylanase pretreatment was incorporated into the bleaching sequence before the repeated rMnP treatment.

Screening of white rot fungi for biobleaching of Acacia oxygen-delignified kraft pulp

To reduce the levels of chlorine-based chemicals in Acacia kraft pulp, we sought to isolate white rot fungus strains that could be used for biobleaching. For this purpose, we collected 600 fungal sources from Indonesia and subjected them to a three-step screening method. The first step involved culturing the strains on Acacia mangium wood powder, guaiacol and agar (WGA) medium. Of the 600 sources, 258 strains grew on WGA medium and generated a red color. The second step revealed that 31 of the 258 strains could degrade extractive-free A. mangium wood powder. The third step examined the ability of the strains to bleach A. mangium oxygen-delignified kraft pulp (A-OKP) under various pH conditions and showed that five strains could biobleach A-OKP at pH 5, 6, and 8. In contrast, the biobleaching abilities of Trametes versicolor and Phanerochaete chrysosporium, which served as standards, were much lower than those of the five new strains, particularly at pH 8. These five strains may be useful for biobleaching of A-OKP.

Differences in residual lignin properties betweenBetula verrucosaandEucalyptus urograndiskraft pulps

By comparing the ultrastructural features of two oxygen delignified hardwood kraft pulps (Eucalyptus urograndis and Betula verrucosa), we have demonstrated a marked difference in their residual lignin properties. In this study, properties such as crystallinity and crystal size of cellulose, molecular weights, carboxyl group contents, and carbohydrate compositions of the two kraft pulps were compared. The examined pulps were in our observations relatively similar. A significant difference, however, was observed in the size exclusion chromatography measurements, which indirectly suggested that a significant portion of residual lignin in eucalyptus pulp was associated with cellulose. Birch pulp, in contrast, exhibited a more conventional tendency for hardwood pulps: lignin mainly associated with hemicelluloses.

Characterization of Fiber Carboxylic Acid Development during One-Stage Oxygen Delignification

This study examines the changes in fiber carboxylate content during a series of one-stage oxygen delignification experiments using a southern United States pine kraft pulp. The carboxylic acid content of the oxygen-delignified pulps before and after holocellulose pulping was determined to establish the distribution of acid groups in lignin and pulp carbohydrates. The carboxylic acid content in residual lignin were also examined and compared with the holocellulose results in an attempt to decouple the responses from residual lignin and carbohydrate. It was found that oxygen-delignified kraft pulps exhibited an initial 4%−13% increase in total fiber carboxylic acid content in the first 10−30 min, followed by a steady state or slight decrease. In contrast, the holocellulose of oxygen-delignified pulps exhibited an initial 6%−8% decrease in carboxylic acid content in the first 10 min, followed by a small increase and then a slow decline. The residual lignin isolated from these pulps showed an initial 37% carboxylic acid content rise in the first 10 min, followed by a rapid drop and then a further slow increase at 100 °C with 2.5% NaOH and 800 kPa of O2. The characteristic kappa numbers for the maximum carboxylic acid content were observed in the range of 19−24 for the oxygen-delignified fibers and the corresponding holocellulose, and ∼25 for the residual lignin of oxygen-delignified pulps under experimental conditions. Overall, acid groups in the residual lignin significantly affect the total fiber carboxylic acid content in the initial phase, whereas acid groups in the carbohydrate fraction control the total fiber carboxylic acid behavior in the remaining phases. The optimal conditions for obtaining a pulp with high carboxylic acid content, under the conditions studied, were observed to be 100 °C with 2.5% NaOH and 800 kPa of oxygen.

Evaluation of chloroform formed in process of kraft pulp bleaching mill using chlorine dioxide

Chloroform formation, balance, and discharge were estimated in a kraft pulp mill that used an elemental chlorine-free (ECF) bleaching line with chlorine dioxide as well as an effluent treatment process. This was achieved by collecting and analyzing discharge water and air samples that contained measurable levels of chloroform. Chloroform formation in ECF bleaching of hardwood oxygen-delignified kraft pulp (LOKP) was estimated to be 2.07–5.34 g/pulp air-dried ton (adt), and approximately 30% of the chloroform produced was discharged to bleaching effluents. Chloroform in the effluents was not decomposed by activated sludge, and more than 97% was emitted to the air by volatilization. It is suggested that chloroform formation in Japanese LOKP bleaching mills can be decreased to 16–42 t/year with a production of 8 million adt pulp by introducing ECF bleaching into all mills. This is a considerable fall from the chloroform discharge from ECF and chlorine bleaching mills in Japan that was estimated to be approximately 1000 t for the 1999 fiscal year.

Surface Characterization of Unbleached and Oxygen Delignified Kraft Pulp Fibers

The chemical and morphological surface properties of different unbleached and oxygen delignified softwood kraft pulp fibers were evaluated by using different ESCA and SEM techniques. The results of the different techniques have revealed that the surface of unbleached and oxygen delignified kraft pulp fibers has a higher content of lignin and in some cases also extractives, in comparison with the bulk of the fibers. However, the amount of lignin obtained on the fiber surfaces differs substantially from one technique to another. The mercurization technique (mercurization followed by the determination of mercury by ESCA) gave about three to five times lower values on the surface coverage of lignin, in comparison with the normal ESCA procedure. Good correlation between the surface coverage of lignin and the total amount of lignin was obtained for all techniques, however, the best correlation was obtained for the mercurization technique. The results also show that the total and surface charges of the unbleached and oxygen delignified pulp fibers decreased with a decrease in kappa number and that the extent of fibrillation increased with a decrease in kappa number.

Oxygen Degradation and Spectroscopic Characterization of Hardwood Kraft Lignin

A series of sweet gum kraft pulps with initial kappa numbers ranging from 29 to 13.6 was subjected to oxygen delignification employing 1.00 and 4.00% charges of caustic. The O-delignified pulps were characterized according to lignin content, pulp yield, and viscosity. In addition, residual lignin samples were isolated from the kraft brownstock and the post-oxygen-delignified kraft pulps, along with the corresponding O-effluents. The structural changes of these lignins during oxygen delignification were investigated using UV spectroscopy and advanced NMR techniques. Differential UV spectra indicated that lignins isolated from oxygen-delignified kraft pulp and its effluent were significantly reduced at λmax 260, 280, and 370 nm in comparison to the brownstock lignins. These changes in absorbance are attributed to the degradation of phenolic and stilbene structures during oxygen delignification. 31P NMR lignin data revealed that the primary sites of oxidation during an O-stage were syringyl and guaiacyl phen...

Interaction between divalent metal ions and oxygen-delignified kraft pulps

Interaction between divalent metal ions and oxygen-delignified kraft pulps

Acid-base properties of oxygen-delignified kraft pulps

The acid-base properties of oxygen-delignified kraft pulps have been investigated in 0.02 and 0.10 mol/L (Na)Cl-media at 25 degreesC. The measurements have been performed with high precision potent ...

Scanning probe microscopy and enhanced data analysis on lignin and elemental-chlorine-free or oxygen-delignified pine kraft pulp

Fibres from conventional pine kraft pulp (KP), oxygen-delignified KP (KPO) and elemental-chlorine-free (ECF) bleached KP were characterized by scanning probe microscopy (SPM). The surface morphology of lignin isolated from the respective pine KP was studied. The data analysis of the phase-shift data measured by using different tapping mode imaging parameters enabled the study of both the surface amphiphility and stiffness as a function of delignification. The average phase-shift values were observed to correlate to the respective kappa values, when imaging with small tapping amplitude (30 nm), referred to the capability of SPM to follow local amphipilic (adhesion) differences on a wood fibre surface. The roughness (standard deviation) of the average phase-shift values was taken as a measure of the sample homogeneity. The mean morphological roughness was observed to increase with decreasing bulk lignin concentration. The surface of lignin appeared mainly granular but occasionally some linear structures were observed. The surface roughness of different fractions of flow-through residual lignin samples correlated quite well to the molar mass of the respective fraction. Each grain contained hundreds of lignin molecules. Most of the lignin samples were homogeneous as regards friction and phase-contrast images. The surface of the nondelignified pine KP was typically granular. ECF delignification was more effective than oxygen delignification in removing this granular phase. The decrease in the relative amount of the granular phase correlated to a decreasing kappa value of the pulp. The granular phase is thus suggested to correspond to lignin, but it cannot be ruled out that small amounts of hemicellulose, extractives or a mixture of these components are embedded in this phase. The surface concentration of the granular phase of the KPO samples was, according to the phase-contrast images, clearly higher than the bulk lignin concentration, as indicated by the corresponding kappa values.

Oxidation of lignin in eucalyptus kraft pulp by manganese peroxidase from Bjerkandera sp. strain BOS55

The white rot fungus Bjerkandera sp. strain BOS55 was shown in previous studies to cause high levels of kraft pulp bleaching and delignification under culture conditions in which manganese peroxidase (MnP) occurs as the dominant oxidative enzyme. In this study, the MnP of Bjerkandera was isolated and tested in vitro with eucalyptus oxygen-delignified kraft pulp (ODKP) based on measuring the reduction in kappa number as an indicator of lignin oxidation. The MnP preparation applied at 60 U/g pulp for 6 h caused a significant decrease of 11–13% in the kappa number in the ODKP under optimal conditions compared to parallel-incubated controls lacking enzyme. The effects of MnP dosage, Mn 2+ concentration, organic acid buffer selection, pH and H 2O 2 addition were evaluated. The optimal Mn 2+ concentration range for lignin oxidation in ODKP was 100–500 μM. In the presence of low oxalate concentrations (0.3–2 mM), the Bjerkandera MnP also significantly reduced the kappa number of ODKP by 6% without any Mn. This observation is in agreement with the fact that purified Bjerkandera MnP has Mn-independent activities. Under incubation conditions with added Mn 2+, buffers composed of metal-complexing organic acids provided two-fold better kappa number reductions compared to the inert acetic acid. The optimal H 2O 2 dosage was found to be 0.017 μmol/min ml when added as semi-continuous pulses (every 30 min) or 0.2 μmol/min ml when generated continuously by glucose oxidase. Excess H 2O 2 caused severe inactivation of MnP during the incubations. Factors that improved the turnover of the enzyme, such as Mn 2+ and metal-chelating acids, stabilized MnP against rapid inactivation.