BLEACHING: PHOSPHONATE IMPROVES BLEACHING
By Pulp & Paper Canada
By Pulp & Paper Canada
QUEBEC, QC — Dequest can save your mill US$1 to $8/admt of pulp, said Brad McCann, National Market Manager, Industrial Products, Solutia Canada. Dequest is a phosphonate (or phosphonic acid), a mult…
QUEBEC, QC — Dequest can save your mill US$1 to $8/admt of pulp, said Brad McCann, National Market Manager, Industrial Products, Solutia Canada. Dequest is a phosphonate (or phosphonic acid), a multi-functional metal-ion controlling agent, and an ‘excellent hydrogen peroxide stabilizer,’ the company says. The product sequesters metal ions, and can replace sodium silicate in bleaching.
“The metals have negative effects (in the pulp bleaching process). We need to chelate or take out the metals,” McCann said.
Metals react with hydrogen peroxide and can cause the paper to yellow. “You have to have a high pH to prevent reversion which is the yellowing of paper, “said McCann.
McCann addressed an audience of about 30 at a press conference and symposium held at the Muse du Qubec, on February 25.
The change in bleaching conditions in pulping systems has fueled the interest and demand for a product like Dequest. “The application for the pulp and paper industry has taken a long time,” said Jacques Verspeek, the business director for Dequest worldwide. “In the past, water was not an issue,”said Verspeek. The amount of water used now is an issue, and closing systems increases chemical concentrations.
“Now (mills) are cutting back on water…. The concentration of the metals in the systems is what makes Dequest interesting,” Verspeek said. The increased use of hydrogen peroxide also contributes.
Applications of Dequest were discussed in the symposium. Dr. Mohini Sain, UQTR’s pulp and paper research centre, showed that a partial replacement of sodium silicate with a Dequest-derived product could be a viable alternative for deinking mills. An optimization of sodium silicate, phosphonate, and caustic charges will be needed to maximize brightness gain in the deinking process.
Stan Heimburger, Heimburger & Co., showed that improved stabilization of hydrogen peroxide during bleaching of high-yield, recycled and chemical pulps can be achieved by the addition of modified organophosphonates. He reported some of the benefits that can be realized by optimizing the effect of an organic stabilizer as higher brightness, higher residual, lower kappa number, higher fibre strength, lower operating costs and lower variability in final product specifications.
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