Startseite On the nature of the selectivity of oxygen delignification
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On the nature of the selectivity of oxygen delignification

  • Jenny Sjöström , Mikael E. Lindström , Tomas Vikström , Cláudia V. Esteves , Gunnar Henriksson und Olena Sevastyanova EMAIL logo
Veröffentlicht/Copyright: 18. November 2024
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Nordic Pulp & Paper Research Journal
Aus der Zeitschrift Nordic Pulp & Paper Research Journal Band 40 Heft 1

Abstract

This work has focused on oxygen’s role in the delignification process within the context of pulp production. We have investigated the role of oxygen in a complex set of chemical reactions taking place during this process, including both oxidative and non-oxidative reactions. This study explores the impact of pH changes during the oxygen delignification process and the characteristics of the resulting pulps. Additionally, this research examines the effect of oxygen, by comparing conventional oxygen delignification with trials using air and nitrogen. Industrial softwood kraft pulps with a kappa number of 35 were subjected to delignification for 20–120 min under alkaline conditions. The resulting pulps were assessed for kappa number, intrinsic viscosity, fiber charge, and ISO brightness. An important observation from this research is the reduction in lignin molecular weight upon exposure to oxygen and air, suggesting depolymerization reactions facilitated by oxygen species, whereas nitrogen exposure results in less pronounced changes. This finding underscores the impact of oxygen in altering lignin structure, thus informing the selectivity and effectiveness of the delignification process.

Keywords: alkaline extraction; kraft pulp; oxygen delignification; selectivity; alkaline leaching; viscosity

1 Introduction

Oxygen delignification has since its introduction in the 70’s (McDonough 1989; Stratton et al. 2004) become a typical technique for the preparation of bleached and half-bleached kraft pulps. It is normally carried out directly after the brown stock washing and is a cost-efficient way to remove residual lignin from the pulp fibers with relatively high selectivity (Parsad et al. 1994; van Heiningen et al. 2018); although oxygen delignification stages can also be performed later in the bleaching sequence (Brogdon and Lucia 2005).

After the kraft pulping, most lignin has been removed from the fibers; however, some lignin is still present. This residual lignin has a higher content of phenols compared to native lignin and can be broadly divided into two major types. The first type consists of degradation fragments from the kraft pulping that were not transferred to the black liquor during the pulping or washing process; this lignin can be removed by leaching (Li et al. 1997). The second type is lignin molecules covalently attached to the fiber by lignin carbohydrate complexes (LCC), i.e. covalent bonds as ethers and phenyl glycosides (Lawoko et al. 2005; Rööst 2004).

It is believed that the oxygen delignification process involves the oxidation of mainly phenolic groups in lignin, resulting in the formation of muconic acids and other hydrophilic compounds that are highly soluble in alkaline liquor (Asgari and Argyropoulos 1998). Additionally, depolymerizations of lignin macromolecules occur, including the breakage of the 4-O-5 bond, which is usually stable during kraft pulping (Gierer and Imsgard 1977). The possible reaction mechanisms are described in Figure 1.

Figure 1: Lignin degrading and solubilizing oxidation reactions in oxygen delignification.
Figure 1:

Lignin degrading and solubilizing oxidation reactions in oxygen delignification.

Despite that the conditions during oxygen delignification are alkalic and certain cutting of polysaccharide chains by radical mechanisms occur (see Reaction 1), yield loss by peeling is believed to be low, since reducing ends of polysaccharides can be stabilized by oxidations (Samuelsson and Stolpe 1969; Sjöström 1991; van Heiningen et al. 2018), and many ends has undergone stopping reactions already in the kraft pulping (McDonough 1989).

Even if the carbohydrate yield losses during oxygen delignification normally are limited, there is generally a loss of viscosity, i.e., a decrease in the degree of polymerization of the cellulose (Sixta et al. 2006; Tao et al. 2011). This is believed to be due to superoxide anions formed during the oxidation forming aggressive hydroxyl radicals (Guay et al. 2000; Johansson and Ljunggren 1994; Reitberger et al. 2001) according to:

2 O 2 − · + 2   H + → H 2 O 2 + O 2
O 2 − · + Me n + → O 2 + Me ( n − 1 ) +
Reaction 1 Me ( n − 1 ) + H 2 O 2 →  OH · + OH − + Me n +

A major challenge is that O2, the active chemical, has low solubility in water and must be added as a gas. Therefore, the oxygen delignification is carried out in a three-phase system: solid fiber, process liquor, and gas (Hsu and Hsieh 1988). Hence, the reactions are carried out under overpressure with highly enriched oxygen rather than air, as a way to avoid disturbing gas bubbles of nitrogen and argon in the system. The need for overpressure and oxygen manufacture (normally made by chromatography) makes the investment costs for oxygen delignification considerable (Kangas et al. 2014). In modern mills, the oxygen step is usually carried out in two steps, the first one consists of a shorter retention time, lower temperature, and higher oxygen pressure while in the second step, the temperature is increased, and pressure is decreased. This is due to the belief that the reactions occur relatively fast while the mass transfer of the reaction products is slower (Li et al. 1997; Pahlevanzadeh and van Heiningen 2023).

The mechanisms of lignin removal during oxygen delignification are not yet fully understood. It is observed that the formation of muconic acids during lignin degradation reactions consumes alkali, which may reduce lignin solubility. Additionally, lignin molecules that are not covalently bound to carbohydrates, i.e., those not part of lignin-carbohydrate complexes (LCCs), may be removed through a slow leaching process rather than chemical modifications (Li et al. 1997). In light of these observations, our work aims to investigate the selectivity and leaching effects of oxygen delignification, focusing on changes in brightness, kappa number, and viscosity. We examine resulting reaction products, lignin, and pulp, to gain insights into changes in lignin size, molecular structure, and total fiber charge of the resulting fibers.

2 Materials and methods

2.1 Materials

In the study a pulp mix of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies), with a starting kappa number of 35 from Östrand kraft pulp mill, SCA was used. All other chemicals were of analytical grade.

2.2 Oxygen delignification

Industrial softwood kraft pulp was subjected to delignification experiments in steel autoclaves. The pulp, with a starting kappa number of 35 was mixed with chemicals and deionized water to a consistency of 10 % and an alkali charge of 1.8 % on the pulp. MgSO4 was added to reduce the degradation of carbohydrates to a charge of 0.25 % on pulp. The experiments were conducted with three different levels of added oxygen, either 5 bars of oxygen, regular air (atmospheric pressure), or 5 bars of inert nitrogen was introduced to the system (after evacuating the autoclave from the air). After charging the chemicals the autoclaves were immediately rotated in an electrically heated glycerol bath at 95 °C. Delignification time was 20, 40, 60, 80, 100, and 120 min before the reaction was terminated by placing the autoclaves in a cold-water bath. The pulp was separated with a funnel lined with mesh cloth from the filtrate, which was collected for further analysis. The pulp was then washed in a mesh Büchner funnel until the conductivity of the filtrate was below 25 μS cm−1 before one part of the pulp was dried overnight at 40 °C and one part of the pulp was kept in the fridge before analysis.

2.3 Pulp analysis

The kappa number of the dry pulp was measured according to ISO 302:2015, intrinsic viscosity analysis according to ISO 5351:2010, and brightness measurements according to ISO 2470-1:2016 with paper sheets made according to SCAN-CM 11:95. The total fiber charge of wet pulps was calculated according to SCAN-CM 65:02 and the water retention values of dry pulps were analyzed according to SS-ISO 23714:2015, with the modification of using Eppendorf tubes with filter inserts as centrifugal containers. The lignin content of the samples was calculated according to the formula L = k a p p a   n u m b e r * 0.132 100 The degree of polymerization (DP) was calculated according to the formula DP = 1.65[μ]1.11 (Evans and Wallis 1989) where μ is the intrinsic viscosity of the pulp. In addition, the lignin removal due to oxygen delignification was calculated by subtracting the lignin content L removed during the nitrogen reaction from the oxygenated reaction.

2.4 Lignin isolation and analysis

To isolate lignin, H2SO4 was gradually added until the pH reached 2, causing precipitation. The solid was then separated from the liquid through centrifugation. After extracting the supernatant, the pellet was resuspended in a dilute H2SO4 solution and the separation process was repeated, the pellet was then freeze-dried before analysis (Sjöström et al. 2023).

The isolated lignin was analyzed by 31P-NMR spectroscopy to investigate the amount of different functional groups (Argyropoulos et al. 1993; Asgari and Argyropoulos 1998). The steps for conducting 31P-NMR spectroscopy were followed as described in the literature (Meng et al. 2019). Around 30 mg of lignin was dissolved in a mixture of 100 μL DMF and 100 μL pyridine. As an internal standard reagent, Endo-N-hydroxy-5-norbornene-2,3-dicarboximide at 60 mg/mL was used. Chromium (III) acetylacetonate at 5 mg/mL was used as a relaxation reagent. The sample was phosphorylated using 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane and the derivatized sample was dissolved in CDCl3 before the analysis. The 31P NMR experiment was performed with a 90° pulse angle, inverse-gated proton decoupling, and a delay time of 5 s, collecting 256 scans. The data was analyzed with MestReNova© software according to the literature (Meng et al. 2019).

In addition, molecular weight analysis was conducted on the isolated lignins using an Infinity 1,260 instrument (Polymer Standard Services, Germany) that was equipped with UV and RI detectors. The system comprised a PSS 100 Å column, a PSS GRAM 10 000 Å analytical column, and a PSS precolumn. To prepare the samples, 1 mg of lignin was dissolved in 2 ml of eluent consisting of dimethyl sulfoxide with 0.5 % w/w lithium bromide. The filtered samples were then moved to glass vials before analysis. Pullulan standards were used for standard calibration. Baseline correction, comparison with the calibration curve, and calculation of molecular weight and polydispersity index were carried out using the software PSS WinGPC.

3 Results and discussion

To investigate the role of oxygen, laboratory-scale oxygen delignification was performed on softwood kraft pulp using oxygen, air, and inert nitrogen gas for various periods in a range between 20 and 120 min. The filtrate from each reaction was collected and the resulting pH can be seen in Figure 2.

Figure 2: pH profile of the three different reactions, overcharged with oxygen, air, and absence of oxygen (inert nitrogen) over time. The pH was measured in the filtrate collected by filtration from the pulp.
Figure 2:

pH profile of the three different reactions, overcharged with oxygen, air, and absence of oxygen (inert nitrogen) over time. The pH was measured in the filtrate collected by filtration from the pulp.

During the reactions, the pH of the collected filtrate decreased with time in the experiments with oxygen. Approximately at 60 min the pH goes below 10.5 which is a level that is not in favor of the oxidizing reactions (Ljunggren and Johansson 1990). Although the decrease in pH was recorded in the trials with air and nitrogen, the changes were not as significant and even after 120 min were above pH 11.

There are several reasons for the reduced pH of the oxygen delignification reactions such as the oxidizing reactions with lignin, which leads to the formation of muconic acid structures, Figure 1 However, some pH decreases could be observed in the trials with low amounts of oxygen. This can be attributed to the consumption of alkali, in both lignin and carbohydrate reactions (Gierer et al. 2001) i.e., again the formation of carboxylic acids (Figure 1).

3.1 Pulp properties

In a similar fashion to the decrease in pH, the kappa number was also lowered during reactions, with the most significant reduction in the experiments with oxygen (Figure 3). The kappa number provides an estimate of the overall lignin content that remains in the pulp, and it is reasonable to expect a significant decrease when oxygen is present in the system due to the oxidation, solubilization, and extraction of lignin. However, there is still a decrease in the kappa number in autoclaves with less or no oxygen (Figure 3). This could be due to the presence of residual lignin from the pulping stage that did not have sufficient time to diffuse from the fiber before the pulp was washed, i.e., leaching of already soluble lignin (Pahlevanzadeh and van Heiningen 2023). Air has a stronger effect than nitrogen because air contains approximately 20 % O2 which can react with the lignin, making it more soluble. The rate of delignification in the oxygen experiment slows down after 60 min (Kalliola et al. 2011), this could be related to the pH drop discussed in the section above, supporting that the pH is important for sufficient delignification.

Figure 3: Kappa number decrease during three different reactions, overcharged with oxygen, air, and absence of oxygen (inert nitrogen) over time.
Figure 3:

Kappa number decrease during three different reactions, overcharged with oxygen, air, and absence of oxygen (inert nitrogen) over time.

Furthermore, the loss of viscosity was followed during the experiments (Figure 4). Data indicated that the largest viscosity losses were obtained in the samples delignified in the presence of oxygen. Interestingly, the pulp samples delignified in the air at atmospheric pressure had similar viscosity losses as the samples delignified with the oxygen in a pressurized system. When oxygen is present under these conditions, an expected substantial viscosity reduction arises mainly from the action of oxygen radicals, such as the hydroxy radical (Gierer et al. 2001; Huang et al. 2019; Reitberger et al. 2001). Conversely, the limited oxygen condition yielded a reduced viscosity loss, attributing this to the mitigated influence of oxygen radicals. Finally, in the nitrogen autoclave, a comparatively small reduction in viscosity is seen without the contribution of oxygen-derived radicals. Since there is no oxygen in the system, oxidation does not stabilize the reducing ends, increasing the opportunity for peeling reactions. Although the peeling reactions occur more slowly in the oxygen delignification temperature range (Van Loon and Glaus 1997) it could still contribute to viscosity losses. Alkaline hydrolysis is at the studied temperature considered negligible (Davidson 1934; Lai and Sarkanen 1967), however, due to cooked kraft pulp exhibiting a more amorphous behavior, the influence of alkaline degradation and peeling reactions cannot be completely disregarded in either experiment, since more disordered cellulose most likely is more sensitive to alkaline scission (Gentile et al. 1987; Knill and Kennedy 2003).

Figure 4: Loss in intrinsic viscosity of pulp produced from three different reactions; overcharged with oxygen, air, and absence of oxygen (inert nitrogen) over time.
Figure 4:

Loss in intrinsic viscosity of pulp produced from three different reactions; overcharged with oxygen, air, and absence of oxygen (inert nitrogen) over time.

The results indicate that only delignification in the presence of oxygen yields an acceptable level of selectivity. When the viscosity data is plotted against the kappa number, it becomes clear that oxygen treatment results in the most selective delignification, outperforming both air and nitrogen treatments, with nitrogen being the least effective (Figure 5). This suggests that despite oxygen’s tendency also to degrade polysaccharides through radical formation, its rapid delignification process is still advantageous.

Figure 5: Kappa number versus intrinsic viscosity from three different experiments; overcharged with oxygen, air, and absence of oxygen (inert nitrogen) over time.
Figure 5:

Kappa number versus intrinsic viscosity from three different experiments; overcharged with oxygen, air, and absence of oxygen (inert nitrogen) over time.

In Figure 6, an additional selectivity plot illustrates the differences between the various experiments. The natural logarithm of the weight fraction of the original lignin, ln L 0 L Y (where L0 and L are the original and oxygen bleached, respectively, lignin content based on kappa number and Y is the mass yield) was plotted against the number of cellulose chain scissions, 1 D P t − 1 D P 0 (where DP0 and DPt are the degree of polymerization of the original pulp and after oxygen delignification), as previously demonstrated (van Heiningen et al. 2018). The degree of polymerization was calculated according to: DP = 1.65[μ]1.11 (Evans and Wallis 1989). From this plot, the delignification/cellulose degradation ratio can be determined from the slope of the linear trendline. The experiment with a high level of oxygen still exhibited the highest selectivity, but there was no significant difference between the nitrogen and air experiments. These results lead to the conclusion that in the air experiment, the effects of the low levels of oxygen are affecting the carbohydrates to a greater extent compared to the lignin dissolving mechanisms. In Figure 6 the corrected value for oxygen was calculated by subtracting the values from the nitrogen experiment, as well. This was done by subtracting the amount of lignin that was removed by leaching in the nitrogen trial. The selectivity is then increased further.

Figure 6: The natural logarithm of the weight proportion of the initial lignin, (where L0 and Lt are the original and oxygen-bleached lignin content based on kappa number, and Y is the mass yield), against the cellulose chain scission count, with DP0 and DPt representing the degree of polymerization of the initial pulp and after the reactions at each time point.
Figure 6:

The natural logarithm of the weight proportion of the initial lignin, (where L0 and Lt are the original and oxygen-bleached lignin content based on kappa number, and Y is the mass yield), against the cellulose chain scission count, with DP0 and DPt representing the degree of polymerization of the initial pulp and after the reactions at each time point.

Pulp brightness was also measured, and as expected, the delignification with oxygen resulted in significantly higher pulp brightness compared to the delignification with nitrogen and air, with air yielding somewhat better results than nitrogen (Figure 7a). In the experiment with high oxygen level, a higher brightness increase was observed, likely due to the simultaneous processes of lignin oxidation and extraction, as well as lignin bleaching facilitated by the formation of hydrogen peroxide (Kontturi et al. 2005; Lachenal 1996). The bleaching effect of hydrogen peroxide likely played a key role in brightness enhancement. In the experiment with air, an increase in brightness was also observed, though the impacts of hydrogen peroxide and lignin oxidation were less pronounced compared to the oxygen-rich scenario, with lignin leaching still significantly contributing to the brightness improvement. Conversely, the experiment conducted without oxygen completely, probably exhibited brightness enhancement mainly through the leaching of lignin. Nonetheless, for all three experimental setups, the brightness generally correlated with the kappa number (Figure 7b), which indicates that most of the brightness improvement can be attributed to delignification.

Figure 7: Brightness characteristics of pulp under various reaction conditions. (a) Increase in brightness of pulp over time for three different reactions: overcharged with oxygen, overcharged with air, and in the absence of oxygen (inert nitrogen) and (b) relationship between ISO brightness and kappa number for three experimental conditions: overcharged with oxygen, overcharged with air, and in the absence of oxygen (inert nitrogen).
Figure 7:

Brightness characteristics of pulp under various reaction conditions. (a) Increase in brightness of pulp over time for three different reactions: overcharged with oxygen, overcharged with air, and in the absence of oxygen (inert nitrogen) and (b) relationship between ISO brightness and kappa number for three experimental conditions: overcharged with oxygen, overcharged with air, and in the absence of oxygen (inert nitrogen).

In the experiment with high oxygen levels, the pulp showed a slight reduction in its total fiber charge (Figure 8). However, the reduction was not as prominent in the experiments conducted with air and N2. One explanation is that oxidized lignin is removed from the pulp and with it a fraction of the charged groups in the fiber. The results are somewhat unexpected since previous research demonstrated that oxygen delignification has the potential to increase the total fiber charge (Esteves 2022; Esteves et al. 2021). However, it is important to note that the total fiber charge is composed of both charged groups in lignin and charged groups in the carbohydrates. Oxygen delignification involves introducing charged groups via lignin oxidation and carbohydrate-stopping mechanisms, as well as extracting charged groups through carbohydrate degradation and lignin removal. These processes occur simultaneously and a more pronounced lignin extraction can also yield in lower fiber charge (Zhang et al. 2006). The differences can be caused by different process parameters, kraft cooking conditions, and starting material.

Figure 8: Total fiber charge from three different reactions; overcharged with oxygen, air, and absence of oxygen (inert nitrogen) over time.
Figure 8:

Total fiber charge from three different reactions; overcharged with oxygen, air, and absence of oxygen (inert nitrogen) over time.

Finally, water retention values were recorded for the pulp samples delignified under different conditions (Figure 9). The water retention value describes the fiber’s capacity to hold water and have previously been reported to decrease as the total fiber charge decreases (Esteves et al. 2021). The decreased WRV from the starting material could be attributed to delignification and thereby a decreased amount of charged groups remaining in the fiber. Overall, no significant difference was obtained between the reactions.

Figure 9: Water retention values from three different reactions; overcharged with oxygen, air, and absence of oxygen (inert nitrogen) over time.
Figure 9:

Water retention values from three different reactions; overcharged with oxygen, air, and absence of oxygen (inert nitrogen) over time.

3.2 Characteristics of lignin removed from pulp during the delignification process

Lignin extracted from the pulp during the delignification stages was precipitated and analyzed. The lignin analysis aimed to follow the structural and weight-related changes in the extracted lignin over time and with different amounts of oxygen in the system.

Based on the results presented in Table 1, only the lignin extracted during the oxygen delignification trials demonstrates a stable trend towards an increase in the content of carboxylic groups with time. This is in agreement with the suggested mechanisms of the reactions between oxygen and lignin in the pulp during the oxygen delignification step (Asgari and Argyropoulos 1998; Gierer and Imsgard 1977) described in Figure 1.

Table 1:

Functional groups according to 31P-NMR spectroscopy in mmol/g of extracted lignin.

Oxygen 20 min 40 min 80 min 120 min
Aliphatic -OH 1.43 ± 0.020 1.76 ± 0.023 1.62 ± 0.021 1.89 ± 0.019
Condensed phenolics 0.99 ± 0.015 1.01 ± 0.012 0.96 ± 0.022 1.11 ± 0.011
Guaiacyl -OH 0.44 ± 0.021 0.39 ± 0.008 0.37 ± 0.013 0.35 ± 0.005
p-hydroxy phenyl 0.11 ± 0.017 0.11 ± 0.018 0.11 ± 0.013 0.11 ± 0.007
Carboxylic acids 1.18 ± 0.024 1.28 ± 0.021 1.41 ± 0.001 1.44 ± 0.014
Air 20 min 40 min 80 min 120 min
Aliphatic -OH 1.31 ± 0.025 1.65 ± 0.020 1.53 ± 0.02 1.59 ± 0.021
Condensed phenolics 0.93 ± 0.021 1.04 ± 0.012 1.11 ± 0.004 0.97 ± 0.014
Guaiacyl -OH 0.40 ± 0.019 0.43 ± 0.022 0.46 ± 0.023 0.39 ± 0.013
p-hydroxy phenyl 0.09 ± 0.020 0.11 ± 0.018 0.11 ± 0.024 0.10 ± 0.023
Carboxylic acids 1.22 ± 0.023 1.33 ± 0.028 1.21 ± 0.019 1.21 ± 0.012
Nitrogen 20 min 40 min 80 min 120 min
Aliphatic -OH 1.53 ± 0.021 1.45 ± 0.011 1.30 ± 0.027 1.59 ± 0.020
Condensed phenolics 0.94 ± 0.043 1.09 ± 0.022 1.00 ± 0.020 1.02 ± 0.031
Guaiacyl -OH 0.39 ± 0.024 0.44 ± 0.021 0.41 ± 0.023 0.41 ± 0.026
p-hydroxy phenyl 0.10 ± 0.117 0.12 ± 0.013 0.09 ± 0.023 0.11 ± 0.024
Carboxylic acids 1.23 ± 0.02 1.07 ± 0.032 0.96 ± 0.043 1.04 ± 0.02

At the same time, there were either no or minimal alterations in this parameter for the lignin extracted after the experiment with oxygen and nitrogen, respectively. These results support the earlier claim that the lignin removed in experiments with either air or nitrogen was mainly due to leaching and not oxidation reactions between oxygen and lignin.

The weight average molecular mass distribution (Mw) analyzed using SEC, of lignin decreases when exposed to oxygen and air (Figure 10). Based on previous studies (Kalliola et al. 2015), the reduction in molecular weight (MW) indicates that depolymerization reactions (Figure 1) are taking place, which are likely facilitated by oxygen species. The increase in molecular weight after 80 min in the oxygen experiment could be explained by larger fragments requiring a longer time to diffuse from the fibers and the average then shifts towards larger molecules. However, this reduction in molecular size is less pronounced when nitrogen is used, indicating that oxygen plays a critical role in the depolymerization of lignin. Alkaline depolymerization of lignin is proposed to occur in the absence of oxygen.

Figure 10: Weight average molar mass distribution of extracted lignin from three different reactions; overcharged with oxygen, air, and absence of oxygen (inert nitrogen) over time.
Figure 10:

Weight average molar mass distribution of extracted lignin from three different reactions; overcharged with oxygen, air, and absence of oxygen (inert nitrogen) over time.

4 Conclusions

During the oxygen delignification process, a notable decrease in pH level is observed, primarily due to the formation of oxidative structures such as muconic acid, alongside other non-oxidative reactions. The reduction in lignin content is predominantly achieved through oxidation, although a portion of lignin removal also occurs via leaching. The observed loss in viscosity can be ascribed to the effects of oxygen, which likely engages in radical chemistry. Oxygen not only enhances the selectivity of delignification but also appears to accelerate the process, likely due to its facilitation of more rapid initial delignification, which may include the leaching of lignin fractions already soluble.

A key observation from this study is that oxygen significantly contributes to lignin depolymerization during oxygen delignification, as evidenced by the decrease in lignin molecular weight distribution when exposed to oxygen and air. While alkaline depolymerization can occur without oxygen, its presence substantially enhances these reactions, leading to a more efficient breakdown of lignin structures. However, the different oxygen levels during the trials did not affect the fiber’s capacity to hold water. This comprehensive understanding of the mechanisms and effects of oxygen delignification, including the influence of oxygen on lignin molecular size and the interplay between oxidative and leaching processes, provides valuable insights for optimizing the delignification process to improve the efficiency and environmental performance of pulp production.

Corresponding author: Olena Sevastyanova, Department of Fiber and Polymer Technology, School of Chemistry, Health and Biotechnology, Royal Institute of Technology KTH, Teknikringen 56-58, 114 28 Stockholm, Sweden; and Wallenberg Wood Science Centre, Department of Fibre and Polymer Technology, KTH Royal Institute of Technology, Teknikringen 56-58, 114 28 Stockholm, Sweden, E-mail:

Funding source: BioInnovation – a joint initiative by Vinnova (Sweden’s innovation agency), Formas (Swedish governmental research council for sustainable development), and the Swedish Energy Agency

Acknowledgments

The authors would like to thank SCA for their raw material contribution.

  1. Research ethics: Not applicable.

  2. Informed consent: Not applicable.

  3. Author contributions: The authors have accepted responsibility for the entire content of this manuscript and approved its submission.

  4. Use of Large Language Models, AI and Machine Learning Tools: None declared.

  5. Conflict of interest: The authors state no conflict of interest.

  6. Research funding: The work was performed within the strategical innovation program BioInnovation – a joint initiative by Vinnova (Sweden’s innovation agency), Formas (Swedish governmental research council for sustainable development), and the Swedish Energy Agency.

  7. Data availability: The raw data can be obtained on request from the corresponding author.

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Received: 2024-04-12
Accepted: 2024-10-30
Published Online: 2024-11-18
Published in Print: 2025-03-26

© 2024 the author(s), published by De Gruyter, Berlin/Boston

This work is licensed under the Creative Commons Attribution 4.0 International License.

Artikel in diesem Heft

  1. Frontmatter
  2. Biorefining
  3. Fractionation methods of eucalyptus kraft lignin for application in biorefinery
  4. Pulp and paper industry side-stream materials as feed for the oleaginous yeast species Lipomyces starkeyi and Rhodotorula toruloides
  5. Chemical Pulping
  6. Comparing classic time series models and state-of-the-art time series neural networks for forecasting as-fired liquor properties
  7. Optimization of kraft pulping process for Sesbania aculeata (dhaincha) stems using RSM
  8. On the nature of the selectivity of oxygen delignification
  9. Unlocking potential: the role of chemometric modeling in pulp and paper manufacturing
  10. Effects of chemical environment on softwood kraft pulp: exploring beyond conventional washing methods
  11. Bleaching
  12. Variations in carbohydrates molar mass distribution during chemical degradation and consequences on fibre strength
  13. Mechanical Pulping
  14. Energy consumption in refiner mechanical pulping
  15. Paper Technology
  16. Australian wheat and hardwood fibers for advanced packaging materials
  17. Compression refining: the future of refining? Application to bleached kraft eucalyptus pulp
  18. The effect of nanocellulose to coated paper and recycled paper
  19. Interpreting the relationship between properties of wood and pulping & paper via machine learning algorithms combined with SHAP analysis
  20. Hybridization to prepare environmentally friendly, cost-effective superhydrophobic oleophobic coatings
  21. Paper Physics
  22. Characterising the mechanical behaviour of dry-formed cellulose fibre materials
  23. Paper Chemistry
  24. Study on the properties of ground film paper prepared from lactic acid-modified cellulose
  25. Environmental Impact
  26. Characterization of sludge from a cellulose pulp mill for its potential biovalorization
  27. The in situ green synthesis of metal organic framework (HKUST-1)/cellulose/chitosan composite aerogel (CSGA/HKUST-1) and its adsorption on tetracycline
  28. Evaluation of the potential use of powdered activated carbon in the treatment of effluents from bleached kraft pulp mills
  29. Recycling
  30. Waste newspaper activation by sodium phosphate for adsorption dynamics of methylene blue
https://doi.org/10.1515/npprj-2024-0026
Schlagwörter für diesen Artikel
alkaline extraction; kraft pulp; oxygen delignification; selectivity; alkaline leaching; viscosity
Creative Commons
BY 4.0

Artikel in diesem Heft

  1. Frontmatter
  2. Biorefining
  3. Fractionation methods of eucalyptus kraft lignin for application in biorefinery
  4. Pulp and paper industry side-stream materials as feed for the oleaginous yeast species Lipomyces starkeyi and Rhodotorula toruloides
  5. Chemical Pulping
  6. Comparing classic time series models and state-of-the-art time series neural networks for forecasting as-fired liquor properties
  7. Optimization of kraft pulping process for Sesbania aculeata (dhaincha) stems using RSM
  8. On the nature of the selectivity of oxygen delignification
  9. Unlocking potential: the role of chemometric modeling in pulp and paper manufacturing
  10. Effects of chemical environment on softwood kraft pulp: exploring beyond conventional washing methods
  11. Bleaching
  12. Variations in carbohydrates molar mass distribution during chemical degradation and consequences on fibre strength
  13. Mechanical Pulping
  14. Energy consumption in refiner mechanical pulping
  15. Paper Technology
  16. Australian wheat and hardwood fibers for advanced packaging materials
  17. Compression refining: the future of refining? Application to bleached kraft eucalyptus pulp
  18. The effect of nanocellulose to coated paper and recycled paper
  19. Interpreting the relationship between properties of wood and pulping & paper via machine learning algorithms combined with SHAP analysis
  20. Hybridization to prepare environmentally friendly, cost-effective superhydrophobic oleophobic coatings
  21. Paper Physics
  22. Characterising the mechanical behaviour of dry-formed cellulose fibre materials
  23. Paper Chemistry
  24. Study on the properties of ground film paper prepared from lactic acid-modified cellulose
  25. Environmental Impact
  26. Characterization of sludge from a cellulose pulp mill for its potential biovalorization
  27. The in situ green synthesis of metal organic framework (HKUST-1)/cellulose/chitosan composite aerogel (CSGA/HKUST-1) and its adsorption on tetracycline
  28. Evaluation of the potential use of powdered activated carbon in the treatment of effluents from bleached kraft pulp mills
  29. Recycling
  30. Waste newspaper activation by sodium phosphate for adsorption dynamics of methylene blue
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