ClO2 Bleaching Research Articles

Influence of Kappa Number on Enhancing Pulp Brightness through Stage D0 with ClO2 Bleaching Process: Environmental Implications and Considerations

<p>Stage D0 in the pulp bleaching process, utilizing Chlorine Dioxide (ClO2), represents a critical phase aimed at improving pulp brightness while simultaneously addressing environmental concerns. This stage enhancement of pulp brightness can made an environmental impact, as excessive usage can lead to harmful emissions and environmental degradation. The amount of ClO<sub>2</sub> used at stage D0 is influenced by the kappa number, the greater the kappa number, the greater the ClO<sub>2</sub> use will be to produce brightness that corresponds to standar. The calculation of ClO<sub>2</sub> usage at stage D0 is carried out after obtaining data related to ClO<sub>2</sub> and the amount of pulp production from DCS (Distribute Control System). Based on the results of calculations and analysis, it can be concluded that the kappa number influences the total use of ClO<sub>2</sub> in stage D0. The more ClO<sub>2</sub> used in the D0 tower will produce pulp with a higher level of brightness.</p>

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.

Cleaner approach for medium consistency eucalyptus slab pulp production using ozone bleaching under turbulent mixing

Eucalyptus slab (ES), a cellulosic waste from wood processing is abundant and can be utilized for the pulping in many wood scarce countries. However, during chlorine dioxide (ClO2) bleaching, which is the current applied bleaching technique for medium consistency eucalyptus slab pulp (MC-ESP), toxic absorbable organic halides (AOX) is still generated, causing pollution to the water environment. Applying ozone gas (O3) to replace ClO2 for MC-ESP bleaching is a promising alternative way since O3 is a clean and powerful oxidizing agent but not producing AOX pollutant. In this work, the influences of the three most important O3-bleaching factors, i.e., O3-concentration, O3-dosage and mixing intensity to the bleaching properties of MC-ESP was systematically evaluated. It was found that increasing of O3-concentration and O3-dosage greatly improved the properties of MC-ESP. Turbulent mixing intensity had a effective effect on improving O3-bleaching of MC-ESP. The high O3-concentration (170 mg/L), 1.0% O3-dosage and 1200 rpm rotational speed were found to be optimum conditions for O3-bleaching of MC-ESP. Under this condition, the brightness, kappa number and viscosity of the pulp obtained were similar or even better than those of the ESP after bleaching with similar or higher ClO2-dosage, however, without generating toxic AOX and with lower pollution load of effluent. This research provided important supports for the development of MC-ESP cleaner production by reducing the pollutant from ClO2 bleaching. Such approach of using wood processing waste as raw material, O3 gas as AOX-free bleaching agent could provide the excellent options for eco-friendly pulp production.

Unraveling the Fate of Lignin from Eucalyptus and Poplar during Integrated Delignification and Bleaching.

Efficient deconstruction of lignocellulose is vitally important for the biorefinery industry because lignin structures play a crucial role in the high value-added conversion of lignin. In this study, an integrated process based on hydrothermal pretreatment (HTP) and Kraft delignification was proposed to deconstruct lignocellulosic biomass. It was found that the HTP not only facilitated the production of xylo-oligosaccharides but also reduced the chemicals dosage of the following delignification. The structural characteristics of lignin obtained from the integrated process were investigated by NMR spectroscopy and gel-permeation chromatography. Additionally, double enzymatic lignins (DELs) isolated from different feedstocks were used as "model lignin" to delineate the structural transformations of lignin during H2 O2 , ClO2 , and O3 bleaching. Significant changes of the lignin structure were observed during the ClO2 bleaching process, including degradation of aromatic rings, enrichment in p-hydroxyphenyl units, and increase of carboxylic groups. A comparison of the structural characteristics of the bleached lignins indicated that HTP benefited the subsequent bleaching process. Enhanced knowledge of lignin chemistry during deconstruction and delignification could provide valuable insight into the current lignocellulose biorefinery.

Effect of microwave-involved ClO2 bleaching on the characteristics of lipophilic extractives of bleached Eucalyptus globulus pulps

The preparation of bleached pulp from Eucalyptus globulus pulp was evaluated after utilizing chlorine dioxide (ClO2) with or without microwave irradiation. The three ClO2-bleaching processes examined were water-bath heating; microwave heating; and microwave pretreatment combined with water-bath heating. These processes were applied to eucalypt pulps that were oxygen-delignified. The effects of the treatments on the levels of lipophilic extractives and properties of the resulting pulps were compared with one another. The microwave-induced treatment had a remarkable effect, leading to an increase in pulp brightness and a decrease in lipophilic extractives when compared with the control (i.e., A). The sample under the condition of microwave pretreatment combined with water-bath heating achieved a higher brightness and reduced lipophilic extractives, which were increased by 45.8% and reduced by 37.4%, respectively. This study demonstrated an effective microwave-pretreated method in ClO2 bleaching process, which provides a promising route for alleviating pitch deposition problems occurring during pulp manufacture.

Evaluating the effectiveness of using ClO2 bleaching as substitution of traditional Cl2 on PCDD/F reduction in a non-wood pulp and paper mill using reeds as raw materials

The effectiveness of ClO2 bleaching as a replacement for conventional Cl2 bleaching, which is intensively practiced in developing countries, to reduce polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in non-wood pulp and paper mills has not been field tested. The first field study was performed to investigate PCDD/F variations when ClO2 bleaching was used as a substitute for conventional Cl2 bleaching in a non-wood pulp and paper mill. It was found that the PCDD/F toxic equivalents (TEQs) in solid and effluent samples were approximately 1.3–14.9 times lower when ClO2 bleaching was used instead of the conventional Cl2 bleaching. 2,3,7,8-Substituted tetrachlorinated dibenzofurans (2,3,7,8-TCDF) were the dominant contributors to total PCDD/F TEQs in samples from the investigated mill when using conventional Cl2 bleaching. The formation amounts of 2,3,7,8-TCDF were reduced from 1.56–2.76 pg TEQ/g to 0.02–0.32 pg TEQ/g in solid samples when ClO2 bleaching was used instead of the conventional Cl2 bleaching. The replacement of Cl2 with ClO2 might decrease the chlorination reactions of dibenzofuran as potential precursors, and thus reduce the formation amounts of 2,3,7,8-TCDF. The results could provide important knowledge for suggesting the best available technique for PCDD/F reduction for non-wood pulp and paper mills in developing countries.

Effects of D0-stage temperature, pH, and kappa factor on chlorine dioxide decomposition and D0-(EP)-D1 bleaching performance for eucalypt pulps

Mills have largely used chlorine dioxide (ClO2) for eucalyptus kraft pulp bleaching. Different mills have observed significant variation in ClO2 demand to reach full brightness (≥90 ISO). These large differences in ClO2 consumption derive from many factors. The most significant include differences in carryover loads and hexenuronic acid (HexA) contents and the level of chlorate formation across bleaching. Handling of pulp with high HexA content and ClO2 losses to chlorate can be minimized by proper operation of the ClO2 stages across the bleach plant. An oxygen delignified eucalyptus kraft pulp with a kappa of 10-12 units contains only 4-6 units actually derived from lignin. This scarce amount of lignin (0.6%-0.9%) is not able to consume high ClO2 doses and, as a consequence, the excess ClO2 applied can end up being converted into chlorate. Hence, proper optimization of ClO2 bleaching stages can save significant amounts of this oxidant. This study focused on optimizing ClO2 bleaching for a typical oxygen delignified eucalyptus kraft pulp of kappa number 11.7. Elemental chlorine free bleaching was carried out with the D0-(EP)-D1 sequence. The following conditions were varied in the D0 stage: temperature, end pH, and kappa factor. The results indicated that maximum ClO2 bleaching efficiency is achieved when minimum chlorate is formed, especially when ClO2 bleaching is adjusted in such a way that residual active chlorine is maintained to a minimum. The most significant variable affecting chlorate formation is pH; however, ClO2 doses (ClO2 concentration) also play a very important role. Chlorate formation is more intense in the D1 stage in relation to the D0 stage. Optimum conditions to run the D0 stage were 90°C, 3.5 pH, and 0.22 kappa factor.

Properties of Enzyme Pretreated Wikstroemia sikokiana and Broussonetia papyrifera Bast Fiber Pulps

Xylanase, pectinase complex, and BL11 pectinase were employed for the pretreatment of gampi and paper mulberry bast fiber pulps prior to chlorine dioxide bleaching. The bleaching efficiencies of the pulps with different enzymatic pretreatments were investigated. Accelerated aging by heat-humidity treatment was also conducted to evaluate yellowing phenomena and to estimate the prevention of brightness reversion (brightness retention) by enzymatic pretreatment. The order of active chlorine required with respect to pretreatment was pectinase complex > xylanase > BL11 pectinase for soda and soda/oxalate gampi pulps and pectinase complex > BL11 pectinase > xylanase for soda and soda/oxalate paper mulberry pulps. Higher brightness retention values were observed for soda/oxalate pulps compared to soda pulps. The brightness retention levels for gampi pulps and mulberry pulps after ClO2 bleaching with enzymatic pretreatment were higher than the levels of ClO2 and NaClO bleaching pulps. Enzymatic treatments were thus able to reduce the usage of ClO2 and to assist in producing photo-stable paper materials for art and artifact-repairing applications. Thus, enzymatic pretreatment of the pulp has the potential to meet world trends and environmental sustainability for pulp and paper industries.

Synergistic Effect of Xylanase and Chemical Bleaching Agent on Bleaching Properties of KP Pulp

Synergistic effect of xylanase and bleaching agent on bleaching properties of KP pulp was investigated. The combination of ClO2 chlorination, alkali extraction and ClO2 bleaching with xylanase was applied. Results showed that X/DED bleaching process could make full use of xylanase, xylan was degraded and the role of bleaching agent was accelerated which enhancing the chemical accessibility of xylanase. The coordination of the two parts improved bleaching effect significantly. But for DX/ED bleaching process, the brightness of bleached pulp treated with different xylanase treating time was very low or a little low, indicating the role of xylanase on pulp was very important for improving bleaching properties, and residual xylanase had little effect on improvement of alkaline extract. Effect of xylanase in ClO2 stage had little effect on bleaching effect of pulp, and brightness are near each other. When xylanase and ClO2 were added together, xylanase almost did not show its role in bleaching, and bleaching result was neat to that of DED process

The Study on Pulping and Papermaking Performance of Banana Stem and Leaf

The chemical composition of various parts of banana stem and leaf were analysed. The soda cooking and kraft cooking process of banana stem were optimized. The bleaching performance of the banana stem pulp was discussed. The results showed that the banana stem and leaf kraft pulp were good fiber material for pulping and papermaking. The brightness of banana stem bleached pulp can reach above 80%ISO through ClO2 bleaching.

Chlorine dioxide bleaching of soda-anthraquinone jute pulp to a very high brightness

Bleaching of soda-anthraquinone jute pulp by chlorine dioxide (ClO2) was studied to reach a target brightness of above 88% for the purpose of using less bleaching chemicals. The performance of either chlorine dioxide or peroxide in the final bleaching to boost brightness was also studied. The experimental results revealed that the final brightness depended on ClO2 charge in the Do and D1 stages. The brightness reversion was lower when the final stage brightening was done by peroxide. The use of Mg(OH)2 in the D1 and D2 stages improved the final brightness due to the formation of less chlorate and chlorite during the Mg(OH)2- based ClO2 brightening stages. The strength properties of pulp bleached by peroxide in the final stage was slightly better than that from ClO2 as the final ClO2 bleaching stage.

Preparation of Hexenuronic Acid to Estimate the Discharge of AOX during ClO2 Bleaching

Preparation of Hexenuronic Acid to Estimate the Discharge of AOX during ClO2 Bleaching

Reduction of AOX by Prolonged ClO2 Bleaching under High Temperature and Acidic pH Conditions

高温，低pH条件下でクラフトパルプを二酸化塩素漂白した場合に，AOX生成量が減少すると報告されているが，その原因について検討した。初段二酸化塩素漂白の温度を70℃から95℃にした時，顕著なAOXの減少が確認された。AOXは，二酸化塩素の還元により生成した塩素のリグニンなどへの置換反応によって生成すると考えられる。リグニンの塩素化には，この置換反応と酸化反応があり，温度が上昇すると置換反応に比べて酸化反応がより促進されるとの知見がある。よって，高温二酸化塩素漂白では，生成した塩素が酸化反応に迅速に消費されることにより，見かけ上置換反応を抑制し，AOXが減少したのではないかと推定する。次に，初段二酸化塩素漂白の漂白時間を15分から90分に延長した場合にも，漂白温度の上昇と同様にAOXを減少させる効果があることを確認した。この二酸化塩素漂白では，同時にヘキセンウロン酸の加水分解を行うため低pH条件に設定されているが，その条件ではリグニンの一部も加水分解される。しかしながら，この条件下で，AOXが減少するために必要となる脱ハロゲン化反応が同時に生じているとは考え難い。そこで，二酸化塩素漂白で生成するとされる数種の有機塩素化合物を酸性水溶液中，95℃で90～120分間加熱したが，AOXの減少を説明できるような脱ハロゲン化や著しい分解は認められなかった。それゆえ，AOX減少のメカニズムを解明するためには，さらなる検討が必要である。

Preparation of Arabinoxylan and its Sorption on Bacterial Cellulose During Cultivation

AbstractThe sorption of arabinoxylan (AX) on bacterial cellulose was investigated by adding AX to the culture medium of Gluconacetobacter xylinus. The starting AX material was produced by alkaline extraction of oat spelts. To investigate the impact of varying AX quality, the residual lignin was reduced by ClO2 bleaching. Furthermore, bleached and unbleached xylans were subjected to xylanase hydrolysis in order to produce fractions of varying molar mass. Of all samples only the water soluble fractions were used for sorption experiments. A reduced molar mass resulted in a lower sorption of AX to the cellulose, while the lignin content increased the sorption of AX on bacterial cellulose. The sorption of AX resulted in a reduction of bacterial cellulose crystallinity and cellulose Iα content. In combined treatments of AX with xyloglucan and β‐glucan no synergistic effect of those polysaccharides on the AX sorption was found.

Development of Phenolic Lignin During ClO2Bleaching of Kraft Pulp

Abstract The development of the phenolic lignin content in kraft pulp during ClO2 bleaching was quantitatively determined by the periodate oxidation method. The effect of hypochlorous acid, an intermediate formed during chlorine dioxide bleaching, was eliminated by addition of sulfamic acid, a scavenger of hypochlorous acid. It was found that the number of free phenolic lignin groups per 100 lignin monomer units decreased from about 29 for unbleached kraft lignin to about 6.5 after 1 minute of ClO2 bleaching. It was also shown that the in-situ generated hypochlorous acid created phenolic hydroxyl groups during chlorine dioxide bleaching. Since it was found that delignification by chlorine dioxide itself was mostly restricted to free phenolic lignin, these findings were used to explain the effect on delignification of addition order of chlorine and chlorine dioxide during bleaching of kraft pulp.

Characterisation of pulp demethylation during chlorine dioxide bleaching

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.