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Chlorine dioxide is an important and excellent bleaching agent for sulfate pulp. In bleaching, it can be used in two different stages to achieve different purposes. On the one hand, it is an excellent brightening agent, used at the end of the bleaching process to achieve high pulp whiteness with good whiteness stability. On the other hand, chlorine dioxide differs from elemental chlorine in that it can absorb five electrons, thus enhancing its oxidizing power. It also has a strong lignin removal effect, and can be used at the beginning of the bleaching process to remove lignin. Compared to using elemental chlorine alone, or in combination with elemental chlorine dioxide, it has a stronger lignin removal capacity and better delignification selectivity , avoiding severe degradation of cellulose and hemicellulose.
In China, chlorine, hypochlorite, and hydrogen peroxide are the main bleaching agents used for pulp. Bleaching with hypochlorite and chlorine easily produces carcinogenic organochlorides, and hypochlorous acid also oxidizes cellulose, reducing the material's strength. Furthermore, chlorine bleaching results in unstable pulp brightness and a tendency to yellow during storage . When using hydrogen peroxide as a bleaching agent, if the solution contains a large number of metal ions that decompose hydrogen peroxide, up to 65% of the hydrogen peroxide may be ineffectively decomposed during the bleaching process. Chlorine dioxide bleaching overcomes these drawbacks, producing pulp with high brightness, good brightness stability, minimal viscosity reduction, high pulp yield, and very low levels of carcinogenic organochlorides in the bleaching wastewater.
Reducing the amount of elemental chlorine used in the bleaching process, and replacing some or all of the chlorine gas with chlorine dioxide, is an effective measure to reduce pollution in bleaching wastewater . During bleaching, Cl₂ and ClO₂ react with lignin to form organochlorides. However, the reaction between Cl₂ and lignin is mainly a substitution reaction, easily forming polychlorinated phenols. Chlorine dioxide, on the other hand, generally causes lignin to decompose, breaking it down into fragments, thus significantly reducing the content of dioxins and furans in bleaching wastewater. Studies have shown that in bleaching wastewater from low- carbohydrate pulp produced using the ECF process with modified cooking, AOX can be reduced to below 0.15 kg/t oven- dry pulp , chlorophenols can be removed by 98%, and dioxins can be reduced to undetectable levels.
The application of chlorine dioxide has received widespread attention worldwide. Replacing Cl₂ with 100% ClO₂ to produce ECF pulp is currently the main measure adopted by many factories in Europe and North America.
Chlorine dioxide is a widely adopted technology in developed countries for bleaching and brightening pulp. To date, no more ideal alternative has been found that surpasses chlorine dioxide in terms of cost, pulp brightness, strength, and stability. Therefore, the chlorine bleaching method used in pulping will soon be replaced. Chlorine dioxide has a weaker oxidizing power than hypochlorous acid, a commonly used oxidizing bleaching agent, but stronger than chlorine gas. When bleaching pulp, hypochlorous acid simultaneously oxidizes cellulose, reducing the material's strength, while chlorine bleaching reacts with lignin to form chlorinated lignin, resulting in unstable pulp brightness and a tendency to yellow during storage. Chlorine dioxide bleaching overcomes these drawbacks. Bleached pulp exhibits high brightness, high strength, no yellowing, minimal viscosity reduction, good opacity, easy fading of dust spots, high pulp yield, and the absence of carcinogenic organochlorides in the bleaching solution. For difficult-to-bleach pulps such as sulfate wood pulp, chlorine dioxide is currently the best bleaching agent, achieving a brightness of over 90 degrees with minimal damage to fiber strength. For pulp with the same whiteness and strength requirements, chlorine dioxide only needs to be bleached to stage 5, while hypochlorous acid requires at least stage 8 to 9. Chlorine dioxide can exert a good bleaching effect under acidic (pH 3.5 to 5.5), neutral, or alkaline (pH 8.5 to 9.5) conditions.
Chlorine dioxide, as the main bleaching agent in elemental chlorine-free (ECF) sequential bleaching processes, is widely used in pulp mills both domestically and internationally for multi-stage bleaching of wood pulp, bamboo pulp, reed pulp, and wheat ( rice) straw pulp, gradually reducing or replacing hypochlorite bleaching . Compared with traditional chlorine and sodium hypochlorite bleaching, the main advantages of chlorine dioxide can be summarized as follows:
(1) Selective removal of lignin. Chlorine dioxide has a low oxidation potential, and pulp bleaching has a strong selectivity for lignin, which can break the ether bonds of lignin and open the benzene ring, making it soluble in dilute alkaline solution. It causes less damage to cellulose and hemicellulose, resulting in high bleached pulp yield, high mechanical strength, and good whiteness stability. The strength of the pulp is significantly improved, and the resin content in the pulp is low.
(2) Chlorine dioxide has strong oxidizing power and high bleaching efficiency. 1 kg of chlorine dioxide is equivalent to the oxidizing power of 2.63 kg of hypochlorite, and it works best in weak acid media.
rotten pulp during papermaking .
(4) The wastewater has a low load, which greatly reduces the toxic and carcinogenic organic halides (AOX), reduces wastewater treatment costs, and reduces water consumption in papermaking.
(5) Bleaching waste paper pulp with chlorine dioxide is easier than bleaching chemical pulp with chlorine dioxide. It requires less dosage, can be carried out under neutral or alkaline conditions, is not greatly affected by temperature, and has a very short processing time, generally only 5 minutes.
(6) It can eliminate fluorescent whitening agents in waste paper pulp. Even a small amount of chlorine dioxide can significantly reduce the fluorescence of waste paper pulp, while even with a large increase in the amount of fluorescent inhibitor, it is difficult to reduce the pulp fluorescence to the level achieved with a small amount of chlorine dioxide. Fluorescent inhibitors reduce the apparent whiteness of the pulp, resulting in a significant loss of pulp whiteness. Chlorine dioxide reacts rapidly to destroy the molecular structure of fluorescent whitening agents, and the reaction occurs at an alkaline pH (compared to an acidic pH during non-chlorine dioxide bleaching). Practical experience has shown that no increase in corrosion has been observed.
(7) It can reduce the acidity, color and sodium chloride content of bleaching wastewater. Bleaching loss is reduced , yield is increased, and COD of intermediate wastewater is reduced.
(8) Bleaching pulp with chlorine and hypochlorite as bleaching agents produces wastewater containing large amounts of the carcinogen dioxin, while bleaching can greatly reduce the emission of carcinogens. In recent years, due to increasingly stringent environmental protection requirements, this discovery has prompted us to consider using bleached pulp more.
Given these advantages, chlorine dioxide has become the mainstream bleaching agent for chemical pulp bleaching. Currently, more than 90% of chemical pulp worldwide is bleached using chlorine dioxide.
3.2.1.5 Chlorine dioxide bleaching process conditions
The basic process conditions for chlorine dioxide bleaching include the amount of chlorine dioxide used, the pH of the medium, the slurry concentration, the temperature, and the time.
(1) The production cost of chlorine dioxide is relatively high, and it is usually used as a supplement to bleaching after the CE stage (chlorination-alkali treatment). The general dosage is 0.7% to 2.0%, and when it is used to replace chlorine in the chlorination stage , the dosage is 0.1% to 1.5%.
(2) As mentioned above, bleaching is carried out under weak acid conditions, so the oxidizing ability can be fully utilized. Therefore, the pH is generally controlled in the range of 3.5 to 5.5.
(3) Increasing the pulp concentration in bleaching is beneficial to improving the production capacity of the equipment and saving steam consumption. For the currently used mixing equipment, the pulp concentration for bleaching is 10% to 12%.
(4) Temperature and time react quickly with the pulp. 75% of the pulp is consumed in the first 5 minutes of the reaction. The reaction slows down afterward. Therefore, in industrial production, a bleaching temperature of 60-70℃ and a bleaching time of 3 hours are generally used.
Chlorine dioxide is an excellent bleaching agent for sulfate pulp. It can be used as a whitening agent at the end of the bleaching process to achieve high and stable whiteness. Furthermore, due to its ability to gain five electrons and its strong oxidizing power, it can efficiently remove lignin at the beginning of the process. Compared to using elemental chlorine alone or a mixture of chlorine and chlorine dioxide, its delignification ability and selectivity are stronger, reducing the degradation of cellulose and hemicellulose.
Chlorine dioxide has a wide range of applications. Currently, it is used both domestically and internationally for pulp and fiber bleaching; treatment of drinking water, industrial wastewater, hospital sewage, and industrial circulating cooling water; disinfection, sterilization, and algae removal in poultry slaughtering, indoor sanitation, and beer manufacturing; oil extraction; food preservation; poultry and livestock production; aquaculture; and plant preservation.
In 2026, the Ministry of Agriculture and Rural Affairs will focus on the prevention and control of livestock and poultry diseases such as African swine fever and porcine reproductive and respiratory syndrome (PRRS). Disinfection and disease prevention are crucial during the peak spring breeding season. Traditional disinfectants have shortcomings such as strong irritation, residues, and susceptibility to environmental influences. Chlorine dioxide is highly efficient, safe, and has a broad-spectrum bactericidal effect, making it suitable for large-scale farming. Xiuba has been deeply involved in this field for over forty years, and its products are adapted to various farming scenarios, making it the preferred choice for disease prevention and disinfection.
Soy sauce and vinegar are essential daily condiments, and the hygiene control throughout the entire process directly affects product quality and food safety. With the continuous improvement of hygiene standards in the food industry, safe and residue-free professional disinfection is particularly important. Shandong Huashi Pharmaceutical's Xiuba chlorine dioxide disinfectant powder AB agent can be customized to meet the needs of each stage of production, building a reliable hygiene protection barrier for soy sauce and vinegar production.
In 2026, food safety supervision in the food processing industry was upgraded. Wet starch products, with their high moisture content and susceptibility to spoilage, urgently require additive-free preservation solutions. Chlorine dioxide is safe, has good sterilization effects, leaves no residue, does not react with starch, and can preserve the original taste and nutrition of the product, providing a new preservation technology path for wet starch processing.
With the implementation of new food regulations in 2026, rice cakes, due to their multiple production stages and high moisture content, are susceptible to microbial contamination and spoilage. Traditional disinfection methods suffer from residue issues or limitations in their application scenarios. Food-grade chlorine dioxide, however, leaves no residue, has a broad sterilization range, and is highly adaptable to various scenarios, meeting the disinfection needs of the entire rice cake production process.
Secondary water supply tanks in high-rise buildings are a crucial link in residents' water supply. Without long-term disinfection, they are prone to the growth of harmful microorganisms. National regulations stipulate that they must be cleaned and disinfected at least twice a year. Chlorine dioxide, due to its safety, lack of residue, and excellent disinfection effect, has become the mainstream disinfectant in this scenario, complying with relevant regulations for drinking water disinfection.
The dairy fermentation industry has long been plagued by bacteriophage contamination, with traditional control methods proving largely ineffective. The implementation of the new national standard for fermented milk in September 2025 further raised production hygiene standards. Xiuba chlorine dioxide disinfectant can precisely eliminate bacteriophages, creating a three-dimensional disinfection barrier encompassing air, surfaces, and pipelines, meeting the requirements of the new national standard and GMP, and building a solid defense for safe dairy production.
With the implementation of the new "Technical Specifications for the Production of Prepackaged Drinking Water" in 2026, the disinfection standards for bottled water production have been upgraded. Chlorine dioxide disinfectant meets the requirements of the new regulations and plays an important role in the disinfection of the entire bottled water production process. It has excellent sterilization effect, is safe and harmless, and has a wide range of applications, which can achieve safety assurance for the entire production chain.
As essential daily condiments, the hygiene control of the entire production and processing process of soy sauce and vinegar directly determines product quality and food safety. With the continuous upgrading of food production hygiene standards, how to achieve safe, effective, and residue-free disinfection and sterilization in all stages of soy sauce and vinegar brewing and processing has become an important issue for ensuring the quality of condiment production. As a result, the construction of professional hygiene protection barriers has become a focus of attention in the industry.
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