Pulp and paper applications
The most highly used bleaching agents today for the pulp and paper industry are hydrogen peroxide and sodium chlorate. Hydrogen peroxide is used for all types of pulp production while sodium chlorate is used only in the production of chemical pulp.
In the process of manufacturing mechanical pulps, i.e., stone wood ground pulp (SWG), thermo mechanical pulp (TMP), chemi thermo mechanical pulp (CTMP) and alkaline peroxide mechanical pulp (APMP), hydrogen peroxide plays a key role in the development of the optical properties. Hydrogen peroxide remains the principal bleaching agent of mechanical pulps. Applied alone or in combination with other bleaching agents, it ensures optimal whitening performance.
Sodium chlorate is the principal bleaching agent on elemental chlorine free (ECF) sequences, whereas hydrogen peroxide is the leading chemical in total chlorine free (TCF). In both these bleaching processes, these products are the key agents to ensure a high degree of brightness while minimizing the impact of effluents.
Sodium chlorate is an on-site generator for chlorine dioxide. Chlorine dioxide is an efficient delignification and bleaching agent in ECF bleaching sequences for all types of chemical pulp, kraft or sulfite. It enables ECF pulps, with high and stable brightness together with excellent mechanical properties, to be obtained with minimum cost and high yield.
Moreover, waste water from ECF pulps giving a level of aquatic toxicity much lower than that of conventional processes based on chlorine, ECF process has become a best available technology (BAT) and has obtained an enviable position of the most widespread in the world of chemical pulp bleaching.
Hydrogen peroxide is used as a bleaching agent, alone or in combination with others oxidizing or reducing agents, in the pulping stage of recovered and recycled papers, ensuring therefore a very high degree of brightening effect.