Bleaching of eucalyptus kraft pulps with chlorine dioxide: Factors affecting the efficiency of the final D stage

TAPPI Journal ◽  
2012 ◽  
Vol 11 (3) ◽  
pp. 43-53 ◽  
Author(s):  
OLENA SEVASTYANOVA ◽  
ANNBRITT FORSSTRÖM ◽  
EVA WACKERBERG ◽  
MIKAEL E. LINDSTRÖM
Keyword(s):  
Carboxylic Acid ◽  
Chlorine Dioxide ◽  
Ph Value ◽  
Eucalyptus Grandis ◽  
Conductometric Titration ◽  
Kappa Number ◽  
Kraft Pulps ◽  
Factors Affecting ◽  
Hexenuronic Acid ◽  
A Minor

We investigated the bleaching efficiency of the final chlorine dioxide (D2) stage in the D0(EP)D1D2 bleaching sequence, focusing on the effect of pH in relation to the bleaching history of pulp samples. The samples used were unbleached kraft Eucalyptus grandis pulps with kappa no. 14.8 and the same pulp oxygen-delignified to kappa nos. 12 and 9.8. The samples were bleached according to the D0(EP)D1 sequence to a brightness of about 86% ISO and then submitted to the final D2 stage under identical conditions (e.g., chlorine dioxide charge, time, temperature, and final pH). The target final brightness was 90.5% ISO. Changes in the kappa number, brightness, viscosity, and contents of hexenuronic acid, 4-O-methylglucuronic acid, and the total amount of carboxylic acid (COOH) groups in pulps were monitored during the bleaching sequence. The final brightness of eucalyptus kraft pulps increased when the terminal pH of the D2 stage was raised from 3.0 to 6.5. The 90.5% ISO target brightness in the D2 stage was achieved for all pulps within a pH range of 4.5–6.5, but this required adjusting final pH for individual samples. The optimal pH value with respect to pulp viscosity was between 3 and 5. Despite dissimilar conditions applied in previous bleaching stages, the samples after the D1 stage revealed similar residual lignin contents as shown by kappa number analysis. The content of hexenuronic acid in the samples, however, varied broadly, from 2 to 26 mmol/kg. Conductometric titration showed different amounts of carboxylic acid groups in pulps after the D1 stage, of which hexenuronic acid accounted for only a minor part. The variations in the fiber charge resulted from the different bleaching conditions applied before the D2 stage. The fiber charge affected the alkali demand in the final D2 stage, whereas variations in the alkali demand affected the initial pH and associated process kinetics. Lower total fiber charge was found to be beneficial for improved final brightening and viscosity when bleached at higher final pH.

Voltammetric analysis of the bleachability of softwood kraft pulps

Holzforschung ◽  
2004 ◽  
Vol 58 (6) ◽  
pp. 581-587 ◽  
Author(s):  
Robert Bourbonnais ◽  
Loredana Valeanu ◽  
Michael G. Paice
Keyword(s):  
Chlorine Dioxide ◽  
Acid Content ◽  
Black Spruce ◽  
Kappa Number ◽  
Western Hemlock ◽  
Kraft Pulps ◽  
Residual Lignin ◽  
Redox Mediators ◽  
Voltammetric Analysis ◽  
Hexenuronic Acid

Abstract Kraft and oxygen delignified pulps with various kappa numbers were prepared from black spruce and western hemlock chips. The bleachability (ratio of kappa number decrease to chlorine dioxide applied) of the different pulps at the same kappa number varied with both wood furnish and delignification process. Thus, unbleached kappa number alone is not a reliable indicator of bleachability for these pulps. This may be due in part to the variable hexenuronic acid content of the pulps; those with higher ratio of hexenuronic acid content to kappa number (HexA/kappa) are harder to bleach. Voltammetric analysis of the same kraft pulps in the presence of redox mediators was found to measure both the content and reactivity of residual lignin. Peak current ratios of redox mediators correlated with pulp bleachability for all pulps. These ratios may therefore provide a more accurate prediction of bleachability than unbleached kappa number.

Pre-bleaching of kraft acacia pulp

2019 ◽  
Vol 34 (2) ◽  
pp. 165-172 ◽  
Author(s):  
Moinul Haque ◽  
Moumita Nanjiba ◽  
M. Sarwar Jahan ◽  
M. A. Quaiyyum ◽  
M. Zahangir Alam ◽  
...  
Keyword(s):  
Acacia Mangium ◽  
Kappa Number ◽  
Acacia Auriculiformis ◽  
Kraft Pulps ◽  
Oxygen Delignification ◽  
Acid Pretreatment ◽  
Acacia Hybrid ◽  
Pre Treatment ◽  
Hexenuronic Acid ◽  
Peroxyformic Acid

Abstract Kraft pulps from acacia hybrid, Acacia mangium of 8 years old and Acacia auriculiformis of 6, 8 and 10 years old were pre-treated with oxygen, peroxyformic acid and acid treatment prior to bleaching. The kappa number reduction was 52–63 % by oxygen delignification, 31–35 % by peroxyformic acid (PFA) pre-treatment and 11–13 % by acid pre-treatment. Oxygen delignified pulp required less chlorine dioxide charge to reach target brightness. At the consumption of 30 kg ClO2/ton of pulp, the pulp brightness reached to 65–71 % for the untreated pulp, 81–85 % for the oxygen delignified pulp, 81–82 % for the PFA treatment and 79–80 % for acid pre-treated pulp. COD load in bleached effluent was much lower in oxygen delignified pulp. Cold alkali extraction of unbleached and oxygen delignified pulps was also carried out with varying alkali charge to remove hexenuronic acid (HexA) from the pulp. Xylan removal from the pulp was insignificant and resulted in no removal of HexA. Acid pretreatment removed 55.7 % to 17.8 % HexA from acacia hybrid, 57.5 % to 16.3 % from A. auriculiformis of 10 years and 58.6 % to 20.1 % from A. auriculiformis of 6 years old, resulting in improved final pulp brightness.

scholarly journals Impact of dissolved lignin in oxygen delignification and chlorine dioxide stages

TAPPI Journal ◽  
2016 ◽  
Vol 15 (3) ◽  
pp. 167-174 ◽  
Author(s):  
Caroline Wilke ◽  
Niclas Andersson ◽  
Rick Van Fleet ◽  
Akhlesh Mathur ◽  
Ulf Germgard
Keyword(s):  
Chlorine Dioxide ◽  
Laboratory Experiments ◽  
Feedforward Control ◽  
Lignin Content ◽  
Pulp Mill ◽  
Kappa Number ◽  
Oxygen Delignification ◽  
Disturbance Factor ◽  
A Minor ◽  
Different Levels

While carryover of dissolved lignin between stages in the pulp mill fiber line is a well-known problem, it is still typically seen only as a minor disturbance factor or bias in the control of oxygen (O2) delignification and bleaching stages. The present study, however, reveals that it plays a larger role than anticipated, and that it should be properly analyzed in order to correctly control the process stages. This is especially important for the O2 and D0 stages as the lignin content is still high in these positions. The results of the study show that dissolved lignin carried over between stages may have a significant impact on the bleaching chemical consumption and, indirectly, on the pulp quality. Mill investigations have shown very large variations in the dissolved lignin content in the pulp before the oxygen delignification stage and before the D0 stage that have significantly influenced the bleaching chemical demand and, subsequently, the degree of delignification. In order to develop a better understanding of the mechanisms of the dissolved lignin’s reactions, laboratory O2 and D0 experiments with controlled levels of dissolved lignin were conducted. It was anticipated that a better feedforward control could be achieved using an online dissolved lignin measurement, and results from mill trials are presented. Chlorine dioxide laboratory experiments using different levels of carryover (i.e., different dissolved lignin contents) were conducted. It was concluded that the filtrate kappa number provides a relevant measure of the bleach demand due to the dissolved lignin and that, subsequently, the combined fiber and filtrate kappa number provides an appropriate measure for optimum feedforward control of the stages. Mill results support these findings, which show that the chemical consumption is reduced significantly using the total kappa number. The post-D or post-DE kappa number feedback control can most probably be eliminated by using this technology.

Extension of a steady-state chlorine dioxide brightening model for Z-ECF bleaching of softwood kraft pulps

TAPPI Journal ◽  
2021 ◽  
Vol 20 (3) ◽  
pp. 186-197
Author(s):  
BRIAN N. BROGDON ◽  
LUCIAN A. LUCIAN
Keyword(s):  
Steady State ◽  
Linear Relationship ◽  
Chlorine Dioxide ◽  
Current Model ◽  
Kappa Number ◽  
Kraft Pulps ◽  
Current Investigation ◽  
Elemental Chlorine ◽  
Steady State Model ◽  
Ecf Bleaching

Earlier studies developed a steady-state model to predict the brightness and/or bleach consumption during the chlorine dioxide brightening (D1) of softwood pulps produced by conventional elemental-chlorine-free (ECF) sequences. This model relates the chlorine dioxide consumed to the brightness gains predicated upon an asymptotic D1 brightness limit, an incoming D1 pulp brightness, and an equation parameter (β11). The current investigation examines the application of this model to ECF sequences that use ozone delignification (Z-ECF). Literature D1 data from various Z-ECF bleaching studies, which investigated OZ, OD0/Z, and OZ/D0 delignification, were fitted to the model. The β11 parameter was found to be linearly correlated to the entering kappa number. Interestingly, this linear relationship was found to be identical to the relationships observed when modeling the D1 stage for conventional ECF and chlorine-based bleach sequences. Subtle differences in D1 brightening response in the model among the various bleach sequences are reflected by incoming pulp brightness (at the same kappa number). The current model is used to illustrate how alterations to Z-ECF delignification affect D1 brightening and chlorine dioxide consumption.

Ozone bleaching of South African Eucalyptus grandis kraft pulps containing high levels of hexenuronic acids

TAPPI Journal ◽  
2013 ◽  
Vol 12 (8) ◽  
pp. 9-16 ◽  
Author(s):  
JEROME E. ANDREW ◽  
JONAS JOHAKIMU ◽  
NKANYISO E. NGEMA
Keyword(s):  
South African ◽  
Chlorine Dioxide ◽  
Preliminary Investigation ◽  
Eucalyptus Grandis ◽  
Reference Sequence ◽  
Kraft Pulps ◽  
Oxygen Delignification ◽  
Pulp Bleaching ◽  
Brightness Reversion ◽  
Removal Efficiencies

Ozone use in conjunction with chlorine dioxide during pulp bleaching offers several advantages over conventional bleaching sequences that make use of chlorine dioxide only. Despite this, in South Africa, only one mill uses ozone. The current study was a preliminary investigation into the use of ozone in bleaching sequences for kraft pulps produced from South African Eucalyptus grandis wood chips, which typically contained high amounts of hexenuronic acids (HexA). The objective of the study was to compare the performance of ozone to other technologies used to remove HexA, such as acid hydrolysis (A) and hot chlorine dioxide (DHT) stages. Bleaching sequences using chlorine dioxide (i.e., OAD0ED1D2 and ODHTED1D2) were compared to bleaching sequences using ozone (i.e., OZD0ED1 and OAZD0ED1). The results showed that ozone preferentially reacted with HexA in the presence of lignin. When applied after oxygen delignification, ozone had the same HexA removal efficiencies as the A- and DHT- stages at dosages in excess of 0.6%. When used in combination with the A-stage, the HexA removal efficiencies of ozone reached 96%. Consequently, up to 15% savings in the estimated bleaching chemical costs were achieved when the OAZD0(EP)D sequence was used, compared to the standard reference sequence (OAD0ED1D2). The residual HexA in the bleached pulp affected brightness reversion of the pulps, but this was only evident for the bleaching sequences that used chlorine dioxide, not for those that included ozone.

Stoichiometric model of chlorine dioxide delignification of hardwood kraft pulps with oxidant-reinforced extraction effect,

TAPPI Journal ◽  
2013 ◽  
Vol 12 (2) ◽  
pp. 17-26 ◽  
Author(s):  
BRIAN N. BROGDON
Keyword(s):  
Steady State ◽  
Chlorine Dioxide ◽  
Empirical Relationship ◽  
Kappa Number ◽  
Published Data ◽  
Kraft Pulps ◽  
Mathematical Transformation ◽  
Stoichiometric Model ◽  
Hardwood Species ◽  
Steady State Model

A generalized, steady-state model for hardwoods is proposed for predicting bleaching delignification and/or chlorine dioxide (ClO2) consumption for sequences that use oxidant-reinforced extraction. Published data for various hardwood species and mixtures were analyzed to develop the model. The kappa number data from these studies were normalized to their respective pre-D0 kappa number, and the normalized kappa numbers were plotted against the bleach demand. This mathematical transformation allowed for various brownstocks and oxygen-delignified pulps with different kappa numbers to be modeled as a single curve based on an empirical relationship with fitted equation parameters. One of the two equation parameters could be expressed as simple functions of oxidant-reinforced extraction conditions (i.e., peroxide dosage). The model forecasts ClO2 usage reasonably well (±0.20% ClO2 on pulp) for conventional ClO2 delignification with extraction. Attempts to incorporate modified bleaching delignification processes that eliminate hexenuronic acids into the model were unsuccessful; data were insufficient to develop a relationship. This straightforward stoichiometric model contains relatively few fitted parameters to be determined. The model could be used with other steady-state brightening-stage models to predict bleach usage.

The Effects of Chlorination Conditions on the AOX and Chlorinated Phenol Content of Kraft Bleach Plant Wastewaters

1991 ◽  
Vol 24 (3-4) ◽  
pp. 55-63 ◽  
Author(s):  
Paul N. McFarlane ◽  
Robert W. Allison ◽  
Thomas A. Clark ◽  
Keith L. Mackie
Keyword(s):  
Chlorine Dioxide ◽  
Effective Means ◽  
Kappa Number ◽  
Kraft Pulps ◽  
Chlorinated Phenols ◽  
Phenol Content ◽  
Central Composite Experimental Design ◽  
Adsorbable Organic Halide ◽  
Linear Manner ◽  
Central Composite

A central composite experimental design was used to develop models of the yields of Adsorbable Organic Halide (AOX) and chlorophenolic compounds in wastewaters produced by bleaching oxygen delignified kraft pulps. The following five variables were used to control the bleaching conditions: total available chlorine, chlorine dioxide substitution, incoming kappa number, chlorination time and temperature. The total available chlorine and the chlorine dioxide substitution were the most important parameters in all the models developed. The yields (g.tonne−1) of AOX and total chlorophenolic compounds increased linearly with increasing total chlorine application. Elevating the level of chlorine dioxide substitution caused the yield of AOX to decrease linearly while the yield of total chlorophenols diminished in a non-linear manner. Increasing the level of chlorine dioxide substitution at a given total chlorine application is an effective means of reducing the emissions of both AOX and chlorinated phenols.

Stoichiometric model of chlorine dioxide delignification of softwood kraft pulps with oxidant-reinforced extraction

TAPPI Journal ◽  
2012 ◽  
Vol 11 (3) ◽  
pp. 31-39 ◽  
Author(s):  
BRIAN N. BROGDON
Keyword(s):  
Steady State ◽  
Chlorine Dioxide ◽  
Kappa Number ◽  
Extraction Temperature ◽  
Kraft Pulps ◽  
Mathematical Transformation ◽  
Stoichiometric Model ◽  
Steady State Model ◽  
Minimum Number ◽  
Experimental Values

A generalized, steady-state model estimates bleaching delignification and/or chlorine dioxide consumption for sequences that employ oxidant-reinforced extraction. The model is based on Germgård’s stoichiometric expression for the D0E1 sequence, which relates chlorine dioxide uptake to post-extracted kappa number. Germgård’s integrated stoichiometric model was modified to normalize the extracted kappa number to the incoming kappa number. This mathematical transformation allows for various brownstocks and oxygen-delignified pulps with different kappa numbers to be modeled as a single curve whereby its shape is related to the stoichiometric parameter. From analyzing various softwood bleaching studies, it was determined that this stoichiometric parameter could be expressed as a simple function of oxidant-reinforced extraction conditions (e.g., extraction temperature and peroxide dosage). The generalized delignification model forecasts chlorine dioxide usage with small relative error from the experimental values, typically ±3% to ±10%. This model is relatively simple, with a minimum number of equation parameters to determined, and can be used with other steady-state brightening stage models to predict bleach usage.

Effects of lignin chemistry on oxygen delignification performance

TAPPI Journal ◽  
2018 ◽  
Vol 17 (07) ◽  
pp. 373-381 ◽  
Author(s):  
Valeria Juste Gomes ◽  
Hasan Jameel ◽  
Hou-Min Chang ◽  
Robert Narron ◽  
Jorge Colodette ◽  
...  
Keyword(s):  
Molecular Oxygen ◽  
Chemical Properties ◽  
Kappa Number ◽  
Kraft Pulps ◽  
Residual Lignin ◽  
Reactive Site ◽  
Oxygen Delignification ◽  
Hardwood Species ◽  
Hexenuronic Acid ◽  
The Relationship

The present work focused on characterizing the chemical and structural properties of isolated lignin from six hardwoods and their kraft pulps in an attempt to better understand the relationship between lignin’s chemical properties and resultant oxygen delignification performance. Several hardwood samples were cooked under the same conditions with varying alkali charges to obtain unbleached pulps with kappa numbers between 19 and 20. These pulps were then subjected to an oxygen delignification stage. Both processes were evaluated for pulp quality, residual lignin, and O-stage delignification efficiency. The oxygen delignification stage was carried out under fixed conditions and evaluated with regards to kappa number, which was corrected for hexenuronic acid (HexA) contributions.Results revealed that different hardwood species exhibited differing oxygen delignification efficiencies. A high correlation was found between the O-stage delignification efficiency and the content of phenolic groups in the unbleached lignin, which confirmed that free phenolic groups are the reactive site for molecular oxygen attack. When different hardwood species were compared, the HexA contents were not found to affect O-stage delignification efficiencies.

Sign in / Sign up

Export Citation Format

Share Document