Chlorine Dioxide Bleaching Stage Research Articles

Kinetics of Adsorbable Organic Halogen Formation During the First Chlorine Dioxide Bleaching Stage of Eucalyptus Kraft Pulp

The emission standard for adsorbable organic halogen (AOX) has been adjusted as a mandatory assessment indicator in the papermaking industrial pollutants emission standards of China. To provide a theoretical basis to reduce AOX formation, a kinetic model of the first chlorine dioxide bleaching stage (D0) is presented for elemental chlorine-free (ECF) bleaching of eucalyptus kraft pulp. The kinetics of the D0 stage can be expressed as dW/dt = 314.6e-20.53/RT[H+]0.21[ClO2]0.41K0.98, where the reaction series for lignin, chlorine dioxide dosage, and H+ concentration are 0.98, 0.41, and 0.21, respectively. The reaction activation energy was 20.53 kJ.mol-1. R2 was greater than 0.9, which means that the model was shown to have high prognostic ability and feasibility. In the D0 stage, mostly lignin was removed and the reaction was fast. Much AOX was formed at the beginning of bleaching, and the reaction rate was primarily determined by the lignin content and chlorine dioxide dosage. H+ existed primarily as a catalyst and had little influence on AOX formation. The AOX formation occurs easily, as the reaction activation energy is less than 30 kJ.mol-1.

Xylanase-Aided Chlorine Dioxide Bleaching of Bagasse Pulp to Reduce AOX Formation

Xylanase pretreatment was used to improve the chlorine dioxide bleaching of bagasse pulp. The pulp was pretreated with xylanase, which was followed by a chlorine dioxide bleaching stage. The HexA content of the pulp and the AOX content of the bleaching effluent were measured using UV-Vis and GC-MS methods, respectively. The results showed that a good correlation occurred between HexA and kappa number. HexA content of the pulp decreased significantly after the xylanase pretreatment. The AOX content of the bleaching effluent decreased as HexA was removed from the pulp. It was found that AOX could be reduced by up to 29.8%, comparing XD0 with a D0 stage. Fourier transform infrared spectroscopy (FTIR) was employed to determine the breakage of chemical bonds in the pulp. It revealed that some lignin and hemicellulose were removed after xylanase treatment. The GC-MS results showed that some toxic chloride such as 2,4,6-trichlorophenol could be completely removed after xylanase pretreatment.

Absorbable Organic Halide (AOX) Reduction in Elemental Chlorine-Free (ECF) Bleaching of Bagasse Pulp from the Addition of Sodium Sulphide

A laboratory investigation was developed to confirm and to quantify the reductions in absorbable organic halide (AOX) discharge when sodium sulphide was added during elemental chlorine-free (ECF) bleaching of sugarcane bagasse pulp. After the chlorine dioxide bleaching stage, the pulp was sent directly into the extraction stage without washing. FTIR was employed to determine the breakage of chemical bonds in the pulp, and GC-MS was used to measure the composition of the bleaching effluent. The addition of sodium sulphide caused a reduction in AOX of up to 46.7%. The AOX reduction reached this maximum when the sodium sulphide was added 30 min after the start of the extraction stage and when the pH was higher than 12. FTIR spectroscopy showed that the phenolic lignin of the pulp was degraded by the sodium sulphide and that the syringyl lignin and C-O-C, C=O structure of the pulp holocellulose of the pulp was preserved during the extraction stage. The GC-MS showed that the chlorobenzene and chlorophenol contents decreased noticeably after the addition of sodium sulphide.

Removal of hexenuronic acid by xylanase to reduce adsorbable organic halides formation in chlorine dioxide bleaching of bagasse pulp

Xylanase-aided chlorine dioxide bleaching of bagasse pulp was investigated. The pulp was pretreated with xylanase and followed a chlorine dioxide bleaching stage. The ATR-FTIR and XPS were employed to determine the surface chemistry of the control pulp, xylanase treated and chlorine dioxide treated pulps. The hexenuronic acid (HexA) could obviously be reduced after xylanase pretreatment, and the adsorbable organic halides (AOX) were reduced after chlorine dioxide bleaching. Compared to the control pulp, AOX could be reduced by 21.4–26.6% with xylanase treatment. Chlorine dioxide demand could be reduced by 12.5–22% to achieve the same brightness. The ATR-FTIR and XPS results showed that lignin and hemicellulose (mainly HexA) were the main source for AOX formation. Xylanase pretreatment could remove HexA and expose more lignin, which decreased the chlorine dioxide demand and thus reduced formation of AOX.

Kinetics of AOX Formation in Chlorine Dioxide Bleaching of Bagasse Pulp

In this paper, a kinetic model of the first chlorine dioxide bleaching stage (D0) in an elemental chlorine-free (ECF) bleaching sequence is presented for bagasse pulps. The model is based on the rate of adsorbable organic halogen (AOX) formation. The effects of the chlorine dioxide dosage, the sulfuric acid dosage, and the reaction temperature on the AOX content of wastewater are examined. The reaction of AOX formation could be divided into two periods. A large amount of AOX was formed rapidly within the first 10 min. Ten minutes later, the AOX formation rate significantly decreased. The kinetics could be expressed as: dW⁄dt=660.8•e^(-997.98/T) 〖•[ClO〗_2 ]^0.877•[H2SO4 ]^0.355•W^(-1.065), where W is the AOX content, t is the bleaching time (min), T is the temperature (K), [ClO2] is the dosage of chlorine dioxide (kg/odt), and [H2SO4] is the dosage of sulfuric acid (kg/odt). The fit of the experiment results obtained for different temperatures, initial chlorine dioxide dosages, initial sulfuric acid dosages, and AOX content were very good, revealing the ability of the model to predict typical mill operating conditions.

Comparison of hot-water extraction and steam treatment for production of high purity-grade dissolving pulp from green bamboo

The performance of hot-water extraction (HWE) and steam treatment (ST), followed by kraft pulping were compared for production of high purity-grade dissolving pulp from green bamboo. With the same prehydrolysis intensity (represented by the P-factor), the fractionation efficiency of HWE is far lower than that of ST. Because of lower removal of non-cellulosic components, the solid residue from HWE (even at approximately double the prehydrolysis intensity, P-factor = 1,379) required more active alkali (AA) during kraft pulping to obtain a cellulose purity equivalent to that achieved by the ST (P-factor = 756)-kraft process. To reach equivalent hemicellulose removal, HWE required more severe intensity than ST. However, FTIR and SEM characterizations of solid residue confirmed that intensified HWE resulted in significant lignin condensation. Antagonistic effects of hemicellulose removal and lignin condensation extent on subsequent kraft pulping were therefore more apparent in HWE than that in ST. Under the same kraft pulping conditions, lignin condensation from a severely intensified HWE process (P-factor = 2,020) caused greater cellulose yield and viscosity loss than that found for ST. Finally, at a given residual pentosan or lignin content, the cellulose yields from all HWE-kraft pulps were about 3 % lower than those from ST-kraft pulps. Consequently, based on an optimally setup chlorine dioxide bleaching stage, a cellulosic pulp with alpha-cellulose content of 97.6 % and viscosity of 927 mL/g was successfully produced from a ST-kraft pulp (P-factor = 756, AA = 19 %).

Alkaline Chlorine Dioxide Bleaching Of Cloned Eucalyptus Wood 2012 and Its Environmental Impact

The bleaching chemistry indicates that pH affects the effectiveness of chlorine dioxide treatment and the standard recommendations has been to maintain a final stage pH range for brightening with chlorine dioxide between 3.5 and 4.0. But we used 16% & 17% TAA cooked Clone EH2012 of kappa number 18.7 & 17.4 without Oxygen Delignification (ODL), were bleached in Acidic and Alkaline pH initial chlorine dioxide (DO) stage, followed by Caustic reinforced Hydrogen peroxide (Ep) and final Chlorine dioxide (D1) stage of bleaching. At constant bleaching condition both EH2012 pulps show these alkaline pH bleaching methods can improve the pulp bleachability without affecting pulp strength properties, optical properties, and physical properties and improved effluent characteristics. The Alkaline pH bleached pulp final brightness 84.72 %ISO (16% TAA) and 85.8%ISO (17% TAA) are well compared to Acidic pH final brightness 83.6 %ISO (16% TAA) and 84.6%ISO (17% TAA) initial chlorine dioxide bleaching and followed by extraction reinforced Hydrogen peroxide and final Chlorine dioxide bleaching. Both 16&17% TAA cooked pulps filtrate analysis of the Alkaline pH Do stage, shows lower Colour (14.6 & 15.4%), Total Dissolved Solids (10.7 & 17.9%) and COD (14.2 & 18.0%) than Acidic pH Do bleaching filtrate. Based on results from the Acidic and Alkaline pH bleaching of EH2012 pulp , we found that the optimum pH for initial Do and final D1 chlorine dioxide bleaching stage should be operated with a final pH close to alkaline, when a typical chlorine dioxide charge is applied and its effluent characteristics shows lesser inorganic load when compared to acidic effluent .

Assessment of mixing quality for an industrial pulp mixer using electrical resistance tomography

AbstractThe quality of mixing of a pulp suspension and chlorine dioxide by a static mixer in an industrial chlorine dioxide bleaching stage was evaluated using electrical resistance tomography (ERT) as a function of process operating conditions, including chemical flow rate, suspension flow rate, and suspension mass concentration. The uniformity was quantified by a mixing index based on the coefficient of variation of the individual conductivity values in each image pixel. An increase in the mixing index, indicating lower mixing quality, was observed when the chemical flow rate increased. In addition, the mixing quality decreased with a decrease in suspension flow rate. On the other hand, a decrease in the suspension mass concentration at a constant volumetric suspension flow rate gave better mixing quality. The results show that ERT can be used to evaluate industrial‐scale mixer performance and to monitor the changes in the mixing quality as a function of process operating conditions. The results are in good agreement with those in the literature based on other measurement techniques for similar mixer installations.

Kinetics of the First Chlorine Dioxide Bleaching Stage (D1) of a Hardwood Kraft Pulp

In the present work, kinetic studies were performed to investigate the first chlorine dioxide bleaching stage of a Eucalyptus globulus kraft pulp. The bleaching reaction can be described by an initial short but very fast step, followed by a slower step. The proposed model for the D1 stage is based on both the light absorption coefficient and the chlorine dioxide concentration. A set of two depletion factors for the chlorine dioxide concentration and for the light absorption coefficient was described as a function of temperature for the fast and short steps of the reaction. The longer and slower periods were described by a homogeneous model. A nonlinear relationship between the chlorine dioxide consumption and the decrease in the light absorption coefficient, which is dependent on the extent of delignification but independent of temperature, was also established. Moreover, a linear relationship between the upper brightness limit and the temperature was observed. The fit of the experimental results obtained for different temperatures, initial chlorine dioxide concentrations, and initial light absorption coefficients is very good, revealing the ability of the model to predict typical mill operating conditions.

Application of an amperometric sensor to in-line monitoring of pulp bleaching with chlorine dioxide

Chlorine dioxide is replacing chlorine as the active compound in pulp bleaching in order to reduce the amount of chlorine used in the process and hence also in the waste waters. In bleaching with chlorine dioxide part of the effective bleaching chemical is usually chlorite. The electrochemistry of chlorine dioxide and chlorite at solid electrodes was studied by cyclic voltammetry at different pH values. The observed voltammograms indicated that reduction of chlorine dioxide gives chlorite and oxidation of chlorite gives chlorine dioxide. Both voltammograms were well developed, indicating a reversible process. Both platinum and glassy carbon were used as the working electrode. The dependence of the limiting current of chlorine dioxide and chlorite on pH was studied at both electrodes. The method was tested in the chlorine dioxide bleaching stage D1 in a typical bleaching process. A good correlation was found between the concentrations of chlorine dioxide and chlorite measured by the in-line amperometric method and a standard titrimetric method.

Effects of pH and Peroxide Addition on Corrosion of Type 316L Stainless Steel in Chlorine Dioxide Bleaching Stage Washer Environment

Abstract Localized corrosion behavior of Type 316L stainless steel in chlorine dioxide bleach stage washer environments was investigated by potentiodynamic anodic polarization techniques. The exten...

Manganese in the chlorine dioxide bleaching of kraft pulp

AbstractManganese in the pulp during the bleaching process has a marked effect in reducing the reflectance of the pulp. This effect is most notable in the chlorine dioxide bleaching stage. The effect is variable depending on the stage and solubility of the manganese contamination, the final pH of thc pulp, the filter water used in washing the pulp and other unknown and variable factors. The manganese contamination of unbleached pulp is largely removed in the chlorination stage, but subsequent contamination is more difficult to remove although a final acid wash does improve the reflectance.