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Advantages And Disadvantages Of Pulp Bleaching

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About 5 to 10% of non-wood pulp comes from agricultural residues. This is produced by soda pulping. The most available agricultural crops among these are wheat straw and bagasse. Pulping using the soda process is limited to easily pulp materials such as straw and some hardwoods but is not a primary process 25). Reduction of carbohydrate degradation during the pulping process can be achieved by using anthraquinone as an additive. The soda-AQ process can also utilize the same mechanical recovery that is used for kraft pulping. 3.5 Production of dissolving pulp Dissolving pulp (DP) is a high-grade cellulose pulp that has a very high content of cellulose with low contents of hemicelluloses and lignin. DP is used as a material for viscose rayon, cellophane, chemical additives, and other cellulose derivatives. …show more content…

The approaches for pulp bleaching can be classified into three groups as follows: elemental chlorine, elemental chlorine-free (ECF), and totally chlorine free (TCF) bleaching. Elemental chlorine pulp bleaching was once widely used by most existing bleaching plants. This process uses chlorine (Cl2) and hypochlorite to brighten the pulp. Currently, hypochlorite is no longer used and chlorine has been replaced with chlorine dioxide as a bleaching agent in elemental chlorine-free bleaching (ECF). Totally chlorine-free (TCF) bleaching utilizes agents such as oxygen, peracetic acid, ozone, and peroxide without using chlorine. TCF eliminates chlorine pollutants in the wastewater stream. Efficient extraction is very important in the first stage of the bleaching process. For example, about 30–50% of lignin is removed before alkaline extraction. Sodium hydroxide is the most efficient agent for reducing the kappa number of pulp. Around 80 to 90% of the lignin is removed after alkaline extraction31). 3.5.4 Bleaching

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