Versatile bleaching and anti-slime agents
Pulp and Paper
Evonik supplies the sustainable chemicals persulfates, hydrogen peroxide, and peracetic acid used in the pulp and paper industry, which have been specially developed to meet the different needs of the pulp and paper industry.
Hydrogen peroxide for pulp bleaching and paper recycling
In the pulp and paper industry hydrogen peroxide is frequently applied as a versatile bleach for chemical pulp, mechanical pulp bleaching (as the only or as the dominant bleaching chemical) as well as in paper recycling with printing ink removal (de-inking). The bleaching conditions can be adjusted within a wide range to suit equipment limitations and temperature level.
In the bleaching of Kraft pulp, the internationally most important pulp type, hydrogen peroxide is an important bleaching agent within a multi-stage process. Alkaline conditions are required to generate the active bleaching species from hydrogen peroxide, the perhydroxyl anion. Consequently, extraction stages can be used for peroxide addition to boost the effects on extraction and brightness. The application of hydrogen peroxide allows top brightness levels with improved brightness stability, optimized economy through savings in the total chemicals required, low residue of halogenated compounds both in pulp (OX) and in effluent (AOX) and low effluent color. Hydrogen peroxide is applied as the exclusive bleaching agent in sulfite pulp brightening. In single or two-stage processes it allows bleaching to full brightness.
Mechanical pulp, generated by the conventional ground-wood process or modern refining technology (TMP or CTMP, and APMP processes), is bleached with hydrogen peroxide to achieve very high brightness levels. Yield and fiber properties are kept on a very high level. The conventional approach is the application of hydrogen peroxide together with caustic soda as alkali source, sodium silicate for stabilization and buffering and a chelant for the sequestering of heavy metals in the wood pulp. Hydrogen peroxide gives high brightness and high brightness stability against aging and yellowing, moderate effluent load and good biodegradability.
In paper recycling the removal of printing ink is the most important objective when the fibers are reused in the manufacture of printing papers or tissue grades. Brightness and color removal are secondary targets. Fiber brightening is achieved mainly with hydrogen peroxide. The alkaline conditions of the repulping of wastepaper are ideally suited for a simultaneous application of hydrogen peroxide. Small amounts of hydrogen peroxide are sufficient to improve brightness and prevent alkaline yellowing. In post bleaching steps, e.g. in a disperser, the brightness is further improved.
For pulp and paper applications Evonik recommends the use of our standard hydrogen peroxide grade.
Slime formation in paper machines can result in high costs. This requires the application of anti-slime agents. Typical anti-slime agents are bromium-, organic sulfur- and quaternary ammonium compounds, as well as aldehydes. The application of PERACLEAN® represents an environmentally benign alternative to the current chemistry. After the disinfection, it decomposes into harmless residues, i.e. water, oxygen and acetic acid.
In highly organic loaded water circuits of paper mills bacteria can produce unwanted smell which negatively impacts the final paper quality or the environment. In such cases, PERACLEAN® can be used as a biocide and strong oxidizer for odor control.
High brightness in TCF and ECF pulps can be achieved by using PERACLEAN® in a post-bleaching stage. Advantages of post-bleaching with PERACLEAN® are
- Higher brightness
- Good brightness stability and no yellowing
- Cleaner pulp
- Lower consumption of other biocides
- Stand-by solution with limited investment costs
In many paper mills there is a need to disinfect the water system to prevent microbial contamination of fibrous material in the circulating water. Polysaccharides, which are leached from the pulp, act as nutrients for microbial growth and result in formations of microbial or semi-chemical slimes. These cause critical failures in papermaking and reduction in the quality of paper, resulting in overall losses. The uncontrolled growth of slimes can cause breakages of paper and, as a consequence, stop the entire production process.
Solutions of PERACLEAN® peracetic acid have been proved to be an effective bio-film remover in water systems and are used as an environmentally benign oxidizing biocide in the pulp and paper industry.
The addition of HYPROX® hydrogen peroxide in effluent is a useful tool to prevent odors and anaerobic conditions.
Hydrogen peroxide has been used successfully as a reducing agent for the conversion of sodium chlorate to chlorine dioxide (ClO2) for large scale use in the pulp and paper industry. Hydrogen peroxide has a faster rate of reaction than methanol and thus is a viable alternative if additional ClO2 production is required. Evonik’s H-Pure (patented) hydrogen peroxide for ClO2 generation is specially formulated to eliminate foaming when it is used for ClO2 generation which can significantly increase ClO2 capacity.
H-Pure increased ClO2 capacity 37% when compared to our competitors ClO2 grade hydrogen peroxide. Partial substitution of methanol with H-Pure can also yield an incremental increase in ClO2 capacity as well. Hydrogen peroxide also eliminates byproduct Cl2 formation when producing ClO2.
We are a leading supplier of persulfates as a pulping agent for paper products containing wet strength resin. Sodium hypochlorite has historically been used to break down wet strength paper products. This generated free chlorine, which could lead to organic halide by-products and corrosion.
Persulfate salts, on the other hand, are environmentally friendly, halogen-free chemicals used in the paper industry. They can be applied to oxidize the waterproof resin for the reprocessing of broke or offset paper.
