Sulfuric acid bleaching of kraft pulp II: Behavior of lignin and carbohydrate during sulfuric acid bleaching

The purpose of this study was to investigate the behavior of lignin and carbohydrates in kraft pulps during sulfuric acid bleaching. Beech kraft pulp and red pine kraft pulp were bleached with dilute sulfuric acid at pH 1.3 with addition of sodium nitrate and sodium nitrite at 100°C for 1 h. The pulps were then extracted with aqueous sodium hydroxide solution at 70°C for 1 h. Lignin and carbohydrates in the acid effluents and the alkali effluents were analyzed. The carbohydrate compositions of unbleached and bleached kraft pulps were also determined. The residual lignin in kraft pulp was degraded to a molecular size similar to that of milled wood lignin during sulfuric acid bleaching without additives, and it was further degraded to a much smaller molecular size during sulfuric acid bleaching with additives. It was found that the amount of carbohydrate dissolved in the bleach effluents were only about 1 of the dry weight of the kraft pulp under these bleaching conditions. The carbohydrates dissolved during bleaching were mostly of hemicellulose origin.Part of this report was presented at the 8th International Symposium on Wood and Pulping Chemistry, Helsinki, July 1995     

甲脒亚磺酸漂白废旧新闻纸脱墨浆

采用甲脒亚磺酸(FAS)对废旧新闻纸脱墨浆进行了单段漂白实验,探讨了FAS用量、NaOH和FAS用量比、浆浓、漂白温度和时间对纸浆漂白的影响。结果表明:废旧新闻纸脱墨浆采用单段FAS漂白,其最佳工艺条件为FAS用量0.6%,NaOH用量0.3%,浆浓5%,温度70℃,时间60 min,纸浆白度可达57.9%SBD。     

Characterisation of pulp demethylation during chlorine dioxide bleaching

Summary The methoxyl loss from softwood kraft pulp during chlorine dioxide treatment can be accounted for by methanol and the methoxyl content of dissolved organic material in the bleach filtrate. This was established by a methoxyl group mass balance made at different bleaching times. It was found that ClO₂ rather than the in-situ generated hypochlorous acid is mainly responsible for the methanol formation. It was shown that fully methylated pulp is hardly demethylated by ClO₂ under industrial ClO₂ bleaching conditions when hypochlorous acid is effectively captured. Furthermore, the rates of formation of methanol and methoxyl group containing dissolved organic material are proportional to each other. The experimental evidence suggest that demethylation and delignification are closely related during ClO₂ treatment of softwood kraft pulp.     

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 2.07–5.34g/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 16–42t/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 1000t for the 1999 fiscal year.     

Sulfuric acid bleaching of kraft pulp 1: Bleaching of hardwood and softwood kraft pulps

To develop a new nonchlorine bleaching technology, hardwood and softwood kraft pulps, before and after oxygen-alkali predelignification, were treated with dilute sulfuric acid solutions (pH 1.0-1.8) at 100°C for 1 h and then extracted with aqueous sodium hydroxide at 70°C for l h. Hardwood kraft pulp was successfully bleached. The delignification selectivity was similar to that seen with oxygen-alkali bleaching; and it was greatly enhanced by the addition of sodium nitrate and sodium nitrite. The sulfuric acid bleaching can replace the presently adopted oxygen and chlorine stages if the additives are allowed. This bleaching process was also effective for oxygen-bleached hardwood kraft pulp, but it was less effective for softwood kraft pulp and oxygen-bleached softwood kraft pulp. The effectiveness of the addition of sodium nitrate and sodium nitrite was more apparent for softwood kraft pulp than for hardwood kraft pulp.Part of this report was presented at the 7th International Symposium on Wood and Pulping Chemistry, Beijing, July 1993     

Screening of wood-rotting fungi for kraft pulp bleaching by the Poly R decolorization test and biobleaching of hardwood kraft pulp byPhanerochaete crassa WD1694

From among 419 wood-rotting fungi 10 were selected by the Poly R decolorization test, and their ability to bleach hardwood kraft pulp was assayed. Of the 10 selected, 6 fungi (i.e.,Phanerochaete crassa WD1694 and F150;Pleurotus pulmonarius PSC-H, PSC-M, and PSC-T;and Pleurotus species A119) showed much higher bleaching ability thanPhanerochaete chrysosponum BKMF1767 orTrametes versicolor WD1670, both of which are well-known high ligninolytic fungi.P. crassa WD1694 had the highest bleaching ability among the selected strains, and it increased the pulp brightness from 28 to 54, with a corresponding decrease in kappa number from 16 to 6 after 10 days of cultivation and alkali extraction. MnP was a predominant ligninolytic enzyme ofP. crassa WD1694 during the biobleaching.This research was presented in part at the 46th Annual Meeting of the Japan Wood Research Society, Kumamoto, April 1996     

Sulfuric acid bleaching of kraft pulp III: reactivity of kraft pulping-resistant structures under acidic conditions

To investigate the bleaching mechanism, a lignincarbohydrate complex (LCC) model compound, a vinyl ether-type lignin model dimer, and a hexeneuronic acid model compound were treated with dilute sulfuric acid of different pHs. Beech kraft pulp and red pine kraft pulp were also treated with dilute sulfuric acid and then extracted with aqueous alkali. The amount of hexeneuronic acid degradation products in acid effluents and lignin dissolved in alkali effluents were determined. It was found that the benzyl ether-type LCC bond and the vinyl ether bond in lignin were effectively cleaved under the pH where sulfuric acid bleaching of kraft pulp was effective. Hexeneuronic acid group was also effectively degraded during sulfuric acid bleaching. In beech kraft pulp bleaching, both lignin removal and hexeneuronic acid removal contributed to the kappa number reduction. In red pine bleaching, the contribution of hexeneuronic acid removal was negligible, and most of the kappa number reduction was achieved by the lignin removal.Part of this report was presented at the 9th International Symposium on Wood and Pulping Chemistry, Montreal, July 1997     

Oxidative cleavage of lignin aromatics during chlorine bleaching of kraft pulp

Methanol liberation and methoxyl loss during chlorine bleaching of softwood kraft pulp were quantitatively investigated to estimate the degree of structural modification of lignin aromatics. An increase in the chlorine multiple led to enhanced methoxyl loss from lignin. Our result, using pH-adjusted chlorine water (pH 5.7), by which chlorination under oxidation-favorable conditions was achieved, strongly supported the importance of the oxidation reaction by chlorine during delignification and lignin degradation. It was also suggested that methanol can be produced not only via catalytic hydrolysis by chlorine but via oxidative cleavage of the ether bond as well. The infrared spectrum of chlorolignins suggested that chlorine oxidation can open aromatic rings to muconic acid derivatives without cleaving ether bonding of the methoxyl group. No straight relation between the methoxyl content and the kappa number of chlorinated pulps was shown. The methoxyl content of bleached kraft pulps subjected to successive chlorination and alkali extraction showed a good relation with the kappa number. This means that almost all the portions of the oxidatively modified lignin structure were successfully removed during these treatments, and the aromatic structures of residual lignin in chlorinated and alkali-extracted pulps were thought to remain intact.Part of this paper was presented at the 46th Annual Meeting of the Japan Wood Research Society, Kumamoto, April 1996; the 10th International Symposium on Wood and Pulping Chemistry, Yokohama, June 1999; and the 67th Pulp and Paper Research Conference, Tokyo, June 2000     

Change in oxidation state of manganese atoms in kraft pulp during biological bleaching with white-rot fungusPhanerochaete sordida YK-624

Change in the oxidation state of manganese atoms in unbleached hardwood kraft pulp (UKP) during the biological bleaching of UKP withPhanerochaete sordida YK-624 was determined by the electron spin resonance (ESR) method. The spectrum of Mn(II), which reveals hyperfine splitting, was not observed in the ESR analysis of UKP, but the spectrum for manganese dioxide was observed. After fungal treatment of UKP withP. sordida YK-624, the spectrum of Mn(II) was detected. The reduction of manganese dioxide was triggered by the increase in NADPH-dependent ferrireductase activity. It is concluded that the manganese dioxide dominant in UKP was reduced byP. sordida YK-624 to Mn(II), which stimulates the production and function of manganese peroxidase.     

Antibody-based assay for galacturonan deesterification on wood pulp fibers during bleaching

Antibodies recognizing galacturonan were used in immunoassays for industrial unbleached and hydrogen peroxide-bleached chemithermomechanical pulp (CTMP). The assays were based on a colorimetric method using specific monoclonal antibody recognition of acidic and methylated homogalacturonan, respectively, on the pulp fiber surfaces. Alkaline phosphatase-conjugated antibodies were linked to the galacturonan specific antibodies, and an alkaline phosphatase substrate (p-nitrophenylphosphate) was used to develop a yellow reaction product that can be followed spectrophotometrically. Together the newly developed immunoassays were able to describe the deesterification, specifically, of surface-localized galacturonan on CTMP, induced by alkaline hydrogen peroxide bleaching. Unbleached CTMP showed relatively more labeling by methylated galacturonan recognizing antibodies, whereas bleached CTMP was relatively more labeled for acidic galacturonan. The increase in negative charge of the bleached pulp was also shown by polyelectrolyte titration; the negative surface charge was 9.3 μeq g⁻¹ in unbleached CTMP and 21.7 μeq g⁻¹ in bleached pulp.     

Evaluation of the extent of the oxidation reaction during chlorine bleaching of pulp

A modified method was developed to evaluate how much chlorine is consumed by the oxidation reaction during the chlorine bleaching process. This evaluation is, in principle, based on the sum of chloride produced during the chlorination stage (C-stage) and produced during alkali treatment of both the C-stage effluent and the chlorinated pulp. Results obtained by this method proved that about 50%–75% of chlorine was consumed by the oxidation reaction during chlorine bleaching, depending on the reaction condition of chlorination. Even under a reaction condition that is not favorable to an oxidation reaction (low pH), approximately three electrons were abstracted from one lignin structural unit by chlorine bleaching. This result provides additional evidence for our recent observation that lignin is extensively oxidized during chlorine bleaching even when pure chlorine without any chlorine dioxide substitution was used.Part of this paper was presented at the 40th Lignin Symposium. Tsukuba, Japan, October 12, 1995     

Decolorization of kraft pulp bleaching effluent by a newly isolated fungus, Geotrichum candidum Dec 1

Kraft pulp bleaching effluent supplemented with glucose was decolorized by a newly isolated fungusGeotrichum candidum Dec 1 (Dec 1) that showed a wide decolorizing spectrum to synthetic dyes. When the glucose concentration in the effluent was 30 g/l, the color removal and the reduction of absorbable organic halogens were 78% and 43% after 7 days culture, respectively. The average molecular weight of colored substances measured by gel filtration chromatography was lowered to less than 3000 from 5600 after 7 days culture. As the contribution of extracellular enzymes such as peroxidase (DyP), manganese peroxidase, and laccase to the decolorization of the kraft pulp bleaching effluent was small, Dec 1 appears to have a different mechanism of decolorizing kraft pulp bleaching effluent when compared with enzymes used to decolorize synthetic dyes.     

The impact of log surface damage caused by harvester Eucalyptus debarking on pulp value recovery

Mechanised harvesting operations are growing in popularity in South Africa, as motor-manual and manual harvesting operations pose significant health and safety risks to workers. Potential damage inflicted by single-grip harvester feed rollers and delimbing knives on the log surface during debranching and debarking of eucalypts may affect chip size distributions during chip production. Chip size is important as it influences pulp quality and recovery in the kraft pulping process. The study investigated the influence of two mechanised debarking treatments in eucalypts (three feed roller passes and five feed roller passes along the stem surface) with feed-roller-induced log surface damage on pulp value recovery. The two mechanised treatments were compared against chips produced from manually debarked logs with no surface damage. In addition, the effect of two log drying periods (one week and two weeks) and three log classes (base, middle and top logs) on chip quality were also analysed. An economic evaluation was conducted to quantify potential recoverable pulp value losses associated with debarking treatments and log drying periods. Logs subject to manual debarking produced significantly less undesired sized chips than both three-pass and five-pass mechanically debarked logs and therefore had significantly greater pulp value recovery. Mechanically debarked logs had a projected pulp value recovery of R62, R86 and R123 less per bone dry tonne of chips produced from base, middle and top logs, respectively, when compared with manually debarked logs with no log surface damage after a one-week log drying period. Mechanically debarked logs also had a projected pulp value recovery of R77, R40 and R59 less per bone dry tonne of chips produced from base, middle and top logs, respectively, when compared with manually debarked logs with no log surface damage after a two-week log drying period. Logs dried for two weeks also produced significantly less under-sized chips than chips produced from one-week-dried logs and therefore had greater pulp value recovery. However, two-week-dried logs produced wood chips with significantly more over-thick chips than logs dried for one week. The volume of undesirable-sized chips produced during chipping increased with decreasing log size.     

Fibre losses during debranching and debarking of Eucalyptus pulp logs using a single-grip harvester

Mechanised harvesting operations are becoming more prevalent in South Africa, with the realisation that motor- manual and manual harvesting operations pose significant health and safety risks to workers. However, the potential damage caused by single-grip harvester feed rollers and delimbing knives on the log surface during debranching and debarking of eucalypts pulp logs may negatively affect fibre recovery as opposed to manually debarked logs, which show little or no log surface damage. Compared with manual debarking, this study investi- gated the influence of two mechanised debarking treatments on wood fibre loss on eucalypt log assortments debarked by harvester head feed rollers and delimbing knives. The two mechanised debarking treatments consisted of three and five feed roller passes along the stem surface. In addition to quantifying the magnitude of this fibre loss, a financial evaluation was done to calculate the value of these losses. The three- and five-pass debarking treatments caused significant fibre losses of 1.425 green tonnes per hectare (gt ha?1) and 2.275 gt ha?1, respec- tively, as opposed to manually debarked logs, which produced no fibre losses. Wood fibre losses in terms of total potential (or available) wood mass for three- and five-pass mechanically debarked trees were 1.06% and 1.70%, respectively. These represent a fibre value loss of R441.75 ha?1 and R705.25 ha?1 for three- and five-pass operations, respectively. For the 6.48 million gt y?1 currently mechanically debarked for the South African pulp and paper industry, this equates to fibre value losses of R21.36 million and R34.10 million annually for three- and five-pass operations, respectively.     

Location and fate of carboxyl groups in aspen alkaline peroxide-impregnated chemithermomechanical pulp fibres during alkaline peroxide bleaching

The origin and kinetic changes of carboxyl groups in aspen chemithermomechanical pulp (CTMP) fibres during alkaline peroxide bleaching were evaluated. The results showed that the major contributors of carboxyl groups in aspen CTMP fibres were the 4-O-methylglucuronic acid, galacturonic acid and the carboxyl groups in oxidized lignin. Alkaline peroxide bleaching could increase the total carboxyl groups, surface charge and dissolved anionic substances. However, the excess degradation by superfluous hydroxide and peroxide could result in the reduction of carboxyl groups in fibres because of the production and dissolution of low-molar-mass substances. The total carboxyl groups from polysaccharides in fibres remained constant, and the increase of carboxyl groups in fibres should result from the carboxyl groups newly formed by the lignin oxidation during peroxide bleaching. Alkaline peroxide bleaching could also result in the removal of a large part of extractives and a small fraction of lignin on the fibre surface.     

Fiber surface characteristics evaluated by principal component analysis

Principal component analysis (PCA) was used to evaluate the results of standard fiber analyses, determinations of charge, electron spectroscopy for chemical analysis (ESCA) measurements, and selective staining of kraft fibers prebleached with oxygen, followed by hydrogen peroxide or ozone. The majority of data variance is explained by the lignin content in fibers and by polarity (hydrophilicity vs hydrophobicity) of functional groups. The lignin determination methods (kappa number, C1 (ESCA), selective staining) gave similar but not equal results, because they measure different parts of lignin. The determination methods of the charged groups (total charge, surface charge, C4 (ESCA), and hexenuronic acids) also gave similar but not equal results. The results of staining by using cationic dyes do not correlate with the quantity of anionic (mainly carboxylic) groups in fibers, regardless of whether the dyes are selective for lignin or hemicellulose. Hydrogen bonding and hydrophobic interactions seem to overrule ionic interactions between dyes and fibers. Therefore, the majority of bonds formed between fibers themselves, as well as between fibers and paper additives, can to a great extent be expected to have the character of hydrogen bonds.     

Modification of softwood kraft pulp with carboxymethyl cellulose and cationic surfactants

An elemental chlorine-free (ECF)-bleached soft-wood kraft pulp was treated first with a carboxymethyl cellulose (CMC, degree of substitution 0.3, 1% on pulp) and then with alkyltrimethylammonium bromides (alkyl chain lengths of C₁₀ to C₁₆). Surprisingly, the treatment with dodecyltrimethylammonium bromide (C₁₂TAB) markedly increased the internal and tensile strengths of the handsheets prepared from the modified pulp. Environmental scanning electron microscopy (ESEM) showed that these properties could be partly explained by the “rope/gum-like” bridges that were formed between the fibers.     

杨树纸浆林造林模式的研究

为优化杨树小径材纸浆林模式,采用多分子的正交试验方法,通过对试验数据的统计分析和比较,筛选出较理想的纸浆林模式为:①立地条件中上等:A2B1C2———美洲黑杨·1666株/hm2·1m×6m·集约经营·6年主伐;A3B1C2———欧美杨·1666株/hm2·1m×6m·集约经营·6年主伐。②立地条件稍差:A2B2C2———美洲黑杨·1111株/hm2·1.5m×6m·集约经营·7年主伐;A3B2C2———欧美杨·1111株/hm2·1.5m×6m·集约经营·7年主伐。     

硫酸盐草浆黑液制粉状活性炭的研究

本文探讨硫酸盐草浆纸厂黑液的治理和利用,提出用酸化法从黑液中沉析木素制取粉状活性炭。大约生产10t草浆可制取1t优质粉状活性炭。同时还含有占总碱量24%的Na_2S可回收。排出的废液即使不再经过处理,其污染程度也已大大降低。