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Effect of mixing on peroxymonosulfate generation Shaharuzzaman, Mohammad

Abstract

Efficient generation of pulping and bleaching chemicals is essential to economic production of pulp. In some cases the success of a proposed process will depend on whether the key chemical can be generated economically at an industrial scale. Peroxymonosulfate (PMS, Na₂S0₅) has shown to be an effective and selective TCF bleaching agent for both delignification and brightness development. The commercial production of PMS is achieved by reacting concentrated H₂SO₄ with 70% H2O2. Conversion is limited to 70% by equilibrium, and production costs are high for commercial bleaching applications. With the increase of oxygen delignification throughout the world, a cheaper method to generate alkaline PMS is desired. This is because an acidic PMS stage, if placed between two alkaline oxygen treatments, would require additional alkali to reach the required bleaching pH. The additional cost of the added alkali would significantly increase the total cost associated with use of acidic PMS. PMS can also be generated by the oxidation of sodium sulfite with oxygen or air in alkali media. This shows promise as an economic alternative for basic PMS generation. Past generation of PMS in the laboratory was limited to 20% yield and 3.8 g/L Na₂S0₅. However, the reaction is mixing-sensitive and optimization of mixing and reaction conditions allow both the yield and chemical concentration to be increased. The effects of key parameters (feed-time, energy dissipation rate, sodium sulfite concentration, reactant volume ratio, oxygen pressure and temperature) were verified in a number of different batch reactors (medium-intensity, P[sub HT], high-intensity, rotor-stator). The addition time of sodium sulfite (feed time) was found to affect both the PMS yield and concentration. For very short feed times (

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