Nowadays, bleaching sequences for ECF (Elemental Chlorine Free) or TCF (Totally Chlorine Free) pulps became basic technologies for pulp bleaching stemmed from the chemical crushing of long or short fibers.
The production of bleached pulp reached an advanced technological stage and a concern on
sustainability which has motivated researches and system applications on water closing circuits,
minimizing the effluent discharges, placing off course the used water to closed circuits of treatment and reuse. Those processes are being possible due to the combination of hydrogen peroxide and chlorine dioxide in the ECF bleaching processes, and from the combination of hydrogen peroxide with oxygen and ozone in the TCF bleaching sequences.
The control of metals and the removal of impurities through more efficient washings favor the stability and the efficiency of Hydrogen peroxide in the bleaching stages, making its application possible in terms of pressure and higher temperature in obtaining products with physical and chemical properties that add value and meet the needs of the countless customers in the bleaching pulp producing industries in several continents.
In the bleaching of mechanical pulp the attainment of high productivity, brightness and physical properties, have made the hydrogen peroxide the most efficient feasible bleaching agent to be used. In the important and increasing industry of paper reuse for tissues production, the hydrogen peroxide also adds value and collects properties to the final product, enabling the attainment of high brightness with less need of virgin fibers.
Bleaching of Chemical Pulp
The bleaching of chemical pulp distinguishes by its multiple stages. Basically, after it had been cooked it results even in two predelignifying oxidative stages, a delignifying stage followed by an oxidative extraction and a bleaching one.
The hydrogen peroxide is a versatile product that can be applied in all phases depending only on the control of the application conditions. In alkaline means and in adequate conditions the Hydrogen peroxide releases
the perhydroxyl (HOO-) ion, which is extremely selective and keeps the physical properties of pulp.
This way, we present the three most important applications of the Hydrogen peroxide in pulp:
- In the extraction, (Ep) or (Eop), the hydrogen peroxide removes the substances partially oxidized by the delignifying product applied in a previous stage;
- At the end of the bleaching, one stage (P) or (PO) conceives high and steady brightness;
- In the double predelignifying stages, the usage of Hydrogen peroxide enables short stages of bleaching with low discharges of the COD (Chemical Oxygen Demand).
In integrated plants, a final alkaline stage with Hydrogen peroxide results in a low use of chemical products and power in the refining.
The advanced technology that makes the high efficiency in cooking feasible, better performance in washing stages with good control of process in the application of the acid lixiviation, improved the alkaline stages with the Hydrogen peroxide. Pressurized stages (PO) or with high consistency (P*) reach excellent results with low use of Hydrogen peroxide when compared with the medium consistency stages, low temperatures and atmospheric conditions.
The field for the application of different technologies enlarged in the use of Hydrogen peroxide with the replacement of chlorine gas and its derivatives, reducing the AOX (absorbable organic halides), the COD, and also the brightness reversion.
For being a liquid product, of easy transportation and handling, the hydrogen peroxide allows production increase without the need of investment in equipment for generation of other oxidizing compounds.
Sequences for bleaching with high brightness values, low reversion grades, productive, of ensured quality and environmental commitment, like: A D PO D; D Eop D P; A Z Q PO; Q Z D PO, that only become possible with the application of hydrogen peroxide.
High Yield Pulp Bleaching
For high brightness, the alkaline bleaching process is indispensable in the production of the mechanical pulp. In the SGW, TGW, TMP, BCTMP, APMP and APP, the process increases the brightness, improves the mechanical properties, reduces brightness reversion and keeps the high yield.
Hydrogen peroxide and the bleaching liquor, composed mainly by caustic soda and a metal chelating, are applied in the paper pulp to guarantee the correct homogenizing and reaction efficiency made during average or high consistency in the bleaching tower, with time e temperature of the process previously determined.
The yields of the physical properties and on bleaching, that can vary from 5 to more than 20 points, depending on the type of mechanical pulp and of the process conditions.
Bleaching of Paper Scraps
This product is also characterized by one or two steps of bleaching. The pulp to be bleached presents diverse characteristics in function of its achievement, and it might be rich in chemical pulp (white prints), pulps of high yield (newspapers, magazines, cards) and inorganic loads from the alkaline gluing of papers.
The hydrogen peroxide can be used in many steps of the process, aiming to the improving of fiber properties and bleaching yield. The application points can on pulper, where it can also act as a decontaminating agent; at the disperger step or bleaching tower.
PERÓXIDOS DO BRASIL has specialized technicians for the application of hydrogen peroxide in the process of pulp and paper, counting with a laboratory for simulating the complete bleaching sequences and other complimentary analyses.
The correct and safe handling of hydrogen peroxide is part of PERÓXIDOS DO BRASIL Responsible Care politic, and as consequence, we put at our clients disposal our services of technical support, evaluation of existing storage tanks; projects and safety training, including lectures and a CD that’s distributed upon request.