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.

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.

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.

scholarly journals Revised steady-state model for chlorine dioxide brightening that considers extraction washer carryover effects

TAPPI Journal ◽  
2016 ◽  
Vol 15 (3) ◽  
pp. 178-185 ◽  
Author(s):  
Brian Brogdon
Keyword(s):  
Steady State ◽  
Chlorine Dioxide ◽  
Kappa Number ◽  
Negative Effects ◽  
Carryover Effects ◽  
Dissolved Solids ◽  
Generalized Model ◽  
Stoichiometric Model ◽  
Steady State Model ◽  
Kappa Value

In an earlier investigation, a generalized model was developed to simulate the first chlorine dioxide (ClO2) brightening stage (D1). That stoichiometric model accurately predicts pulp brightness values for given bleach charges and vice versa for laboratory softwood pulps. The equation parameters are dependent on the kappa number and brightness of the extracted pulp. In this study, the earlier model was refined to include the negative effects of extraction carryover to simulate more realistically a mill’s D1 stage. Extracted pulps that contain washer carryover were found to brighten as if the pulp had a kappa number equal to the sum of the extracted kappa and the kappa value of extraction dissolved solids. If this higher kappa (i.e., apparent or wet kappa) is used in place of the extracted kappa with the D1 model, the equations suitably predicted the bleached brightness for a given bleach charge. The modified expressions were used to quantify the amount of carryover and to calculate carryover bleach consumption for a softwood D0(EOP)D1 fiber line. The mill’s washed pulps were found to have carryover levels of 1.4 kappa units, which was consuming 48% of the total D1 bleach charge. Additional analyses revealed that extraction carryover consumes 2.5-4.6 kg ClO2/ton pulp per kappa unit of carryover when bleaching a pulp to 78% to 84% ISO.

scholarly journals Generalized steady-state model for chlorine dioxide brightening of hardwood kraft pulps

TAPPI Journal ◽  
2017 ◽  
Vol 16 (05) ◽  
pp. 263-272
Author(s):  
Brian Brogdon
Keyword(s):  
Steady State ◽  
Chlorine Dioxide ◽  
Kinetic Studies ◽  
Kraft Pulping ◽  
State Model ◽  
Kraft Pulps ◽  
Steady State Model ◽  
Plant Data ◽  
Pulp Properties ◽  
Hardwood Pulp

A generalized, steady-state model for the first chlorine dioxide brightening (D1) stage is proposed for North American hardwood kraft pulps. The model predicts the post-D1 brightness obtained for a given chlorine dioxide (ClO2) charge based on three equation parameters. Data from laboratory D1 studies were examined with the model to determine the relationships of the parameters to extracted pulp properties. The asymptotic D1 brightness limit at extremely high bleach charges was ~93% ISO for most hardwood pulps. This parameter can be calculated from the limiting light absorption coefficient of D1 kinetic studies (≈ 0.10 m2/kg) and the unbeaten light scattering coefficient of the pulp. A second parameter was linearly correlated to the extracted kappa number of the hardwood pulp. This relationship seems to be affected by the chosen kraft pulping process (e.g., liquor or dissolved solids profiling). The final parameter is the extracted pulp brightness. The hardwood D1 model forecasted the brightness values of laboratory pulps that differ from measured values of ±0.5 to ±0.6 points. Daily averages of bleach plant data for a southeastern U.S. hardwood fiber line were examined with the model. Predictions were generally 0.5 points higher than the measured mill brightness values. This observation implied that the D0(EOP) pulp contained a small amount of extraction washer carryover (~0.4 kappa units on pulp) that was consuming ~1.2 kg ClO2/ton pulp, which was not accounted for in the hardwood D1 model.

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.

Improved steady-state models for chlorine dioxide delignification sequences that include washer carryover effects

TAPPI Journal ◽  
2015 ◽  
Vol 14 (2) ◽  
pp. 93-103 ◽  
Author(s):  
BRIAN N. BROGDON
Keyword(s):  
Steady State ◽  
Chlorine Dioxide ◽  
Control Strategies ◽  
Kappa Number ◽  
Carryover Effects ◽  
Advanced Process Control ◽  
Elemental Chlorine ◽  
Plant Data ◽  
State Models ◽  
Ecf Bleaching

In previous studies, generalized steady-state models were proposed to approximate the chlorine dioxide demand needed for the delignification of softwood and hardwood pulps, where the kappa number entering the bleach plant can fluctuate. However, these expressions neglect the effect of dissolved solids with the stock that originate from incomplete pulp washing. In this study, the original elemental chlorine-free (ECF) models are modified to include the effects of carryover from brownstock or post-oxygen washing. The stoichiometric bleach consumption from carryover, based on its composition, was calculated from various literature sources. The majority of the bleach demand (about 70%) results from the dissolved lignin contained in the brownstock carryover, with the remainder resulting from the inorganic sulfur constituents (e.g., sulfide and thiosulfate). When the effect of brownstock carryover was taken into account, the modified models accurately predicted the amount of chlorine dioxide consumed for a given delignification level (about ±0.1% chlorine dioxide) vs. actual bleach plant data. The improved models can be used to gauge the level of washer carryover entering the bleach plant if this parameter is not regularly monitored by the mill. Additionally, these modified expressions could be integrated into advanced process control strategies for ECF bleaching where the washer carryover or dissolved lignin entrainment is measured with online sensors.

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.

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.

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.

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