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Chlorine dioxide bleaching technology is widely used worldwide due to its unique oxidizing properties and advantages such as low wastewater color and low levels of harmful substances. Theoretically , ClO₂ has an effective chlorine content as high as 263%, while ordinary bleaching powder has an effective chlorine content of no more than 42%, bleaching powder concentrate has an effective chlorine content of 60%–75%, and sodium chlorite has a theoretical effective chlorine content of 157%. Comparatively, ClO₂ has a much higher bleaching efficiency. The oxidation potential of ClO₂ lies between that of pigments and impurities attached to fibers and that of cellulose. When bleaching silk fabrics and pulp , it can oxidize and remove pigments and impurities without interacting with or damaging the fibers. Therefore, ClO₂ is suitable for bleaching high-strength, high-brightness high-grade pulp. In traditional bleaching agents, chlorine and hypochlorous acid have higher oxidation potentials than cellulose itself. Over time, the fibers themselves are oxidized, leading to fiber quality deterioration. The bleached pulp fails to meet the strength and brightness requirements for producing high-grade paper. Furthermore, it generates potent pollutants such as chlorophenols and chloramines, which have teratogenic or carcinogenic effects, seriously endangering fish and other aquatic life and polluting the ecological environment. However, in the past decade, no toxic chlorinated organic compounds have been found in the ClO₂ bleaching process. It has not only improved paper quality and competitiveness but also significantly reduced environmental pollution.

Since the world's first pulp and paper mill using ClO₂ to bleach pulp in 1946, countries with advanced pulp and paper technology have largely replaced CEH (chlorination-alkali treatment-hypochlorite bleaching) or CEHH (chlorination, alkali treatment, and two-stage calcium hypochlorite bleaching) pulp bleaching with ClO₂ . In the late 1950s, in developed Western pulp and paper countries, chlorine dioxide was already the most common bleaching agent for chemical pulps. Currently, developed countries have switched to using chlorine dioxide as a pulp bleaching agent. The use of chlorine dioxide to bleach pulp in China's paper industry is still in its early stages, but its vast market potential holds immense promise. Due to the rapid growth in domestic paper sales, production cannot meet demand, and imports are increasing year by year. This huge market potential indicates that China's paper industry is a sunrise industry in the 21st century. Manufacturing high-quality, high-grade paper requires advanced production processes; therefore, chlorine dioxide bleaching technology will gradually be applied and promoted in China.

Decades ago, other countries began exploring the use of ClO₂ to bleach pulp. In paper bleaching, the substitution rate of chlorine dioxide for chlorine gas can reach over 70%. Currently, almost all pulp in North America, Western Europe, and Japan is bleached using chlorine dioxide. Chlorine dioxide also has a strong ability to bleach fibers and textiles. Using chlorine dioxide to bleach fibers or textiles results in soft fibers, prevents yellowing, does not damage the fibers, and does not generate new contaminants.

Research on chlorine dioxide in my country started relatively late. However, with the continuous expansion of the chlorine dioxide application market, many water treatment plants and paper mills are increasingly aware of its bactericidal, algae-killing, and pulp bleaching properties. Domestic chlorine dioxide preparation technology is now very mature and its production cost is lower than that of foreign equipment, resulting in significant economic and social benefits in many fields. Among domestic paper mills currently using chlorine dioxide for pulp bleaching, the increased economic benefits from improved physical properties of bleached pulp and higher paper quality are considerable. More importantly, the adoption of elemental chlorine-free (ECF) bleaching technology significantly reduces organic halides (AOX) in bleaching wastewater, while also providing substantial environmental benefits by reducing wastewater color and acidity.

Historically, China's pulp production lines were relatively small, primarily using chlorine and hypochlorite as bleaching agents, with common bleaching processes including H₂, HH, and CEH. Until the mid-1990s, the Chinese government invested in and built several large-scale chemical pulp mills in Zhalantun (Inner Mongolia), Shaowu (Fujian), Heda (Guangxi), Fenghuang (Guangxi), and Ya'an (Sichuan). At that time, their designed pulping capacity was mostly around 50,000 tons per year. These pulp production lines imported chlorine dioxide generation systems from abroad, making them among the earliest enterprises in China to adopt chlorine dioxide bleaching. After the turn of the 21st century, China's pulp and paper industry experienced rapid development, with the construction of a large number of large-scale pulp production lines with an annual output of over 100,000 tons. These newly built pulp production lines almost entirely adopted chlorine dioxide bleaching technology.

Table 3-18 Some enterprises in my country currently using chlorine dioxide bleaching

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For newly built pulp mills, chlorine dioxide bleaching is an excellent choice. Furthermore, with increasing national and corporate attention to bleaching wastewater pollution, particularly the control of organochlorine emissions, more and more existing pulping production lines will adopt chlorine dioxide bleaching. We can expect that chlorine dioxide bleaching technology will see increasing application in China's paper industry in the future .

Most of the existing enterprises in my country with chlorine dioxide production capabilities have adopted oxygen delignification technology. This is the most typical design for bleaching processes. From a cost perspective, many enterprises currently use a combination of chlorine dioxide and chlorine, known as the D/C stage. The combination of approximately 30%–50% chlorine dioxide and chlorine effectively demonstrates the protective effect of chlorine dioxide on fibers and its selective destruction of lignin chromophores. This significantly improves the strength and brightness of pulp compared to using 100% chlorine, although the content of organic chlorides in the wastewater is higher than with 100% chlorine dioxide. Not only newly built plants, but also existing bleaching production lines can be retrofitted to incorporate chlorine dioxide bleaching. Various small-scale chlorine dioxide generators developed for small-scale pulping production lines are currently in the trial and promotion stage and are expected to enter the market soon. Small-scale chlorine dioxide generators are typically inexpensive and require less investment, making them particularly suitable for the technical retrofitting of older small pulping lines.