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Mitigation of Pulp and Paper Effluent Color and Mill Smells

It appears to be clear that great benefits can be delivered to the pulp and paper (P&P) industry by small molecule catalytic activation of hydrogen peroxide. By “great benefits”, we mean industrial changes that promise to ameliorate or remove environmental concerns while improving profitability.

TAML® catalysts are one-time-use small molecule catalysts that can improve peroxide pulp bleaching. In addition, the catalysts also offer a new process for treating the effluent from any chlorine-based (D, C, H) bleaching that is contaminated with “color” and chlorinated lignin fragments called collectively “AOX” for “absorbable organic halogen’. AOX is chlorinated material than can be captured on activated carbon. The picture below illustrates where the color and AOX contaminants arise.

Wood pulp consists of two polymers, primarily cellulose, the material used for making white paper, and 2–6% colored lignin. Bleaching seeks to remove the lignin from the cellulose. Worldwide, the P&P industry is currently using chlorine dioxide as its principal bleaching agent. Chlorine dioxide oxidatively breaks lignin away from the solid cellulose in two forms, little fragments and big fragments. The fast majority of lignin solubilized by bleaching is in the form of little fragments. These are than digested by bacteria and other organisms in artificial oxidation lakes before the effluent is ejected to a natural water body such as a river, lake or ocean. However, the big lignin fragments where the color resides are too large to be digested by the microorganisms. The color is recalcitrant and ends up staining natural waterways and changing the flux of light absorbed by aquatic ecosystems.

Dominant Wood Pulp Bleaching Technology — “Elemental Cl-free” ClO2

diagram of pulp bleaching with ClO2

“Bleaching” is breaking the colored lignin away from the solid pulp to leave white cellulose. TAML® catalysts activate hydrogen peroxide to provide a superfast totally chlorine free method for bleaching wood pulp with very high selectivity.

Our industrial collaborators, PAPRO New Zealand, Ltd., have shown that TAML®/peroxide removes 56% of the color and 36% of the adsorbable organic halogen (AOX) from a softwood bleach plant effluent. We have achieved higher color reductions with effluent streams from North American mills.

This effluent treatment process is a major breakthrough that is unprecedented in its performance and ease of execution. The technology requires small amounts of peroxide and miniscule quantities of TAML® activator (ca. 500 nM) and the process proceeds rapidly at room temperature. The industrial researchers concluded: “Overall, the system appears to show significant potential for the treatment of pulp and paper effluent streams, especially for the removal of color and AOX. The system is robust to fluctuations in operating conditions, needs very low levels of activator and operates under conditions that should be easy to reproduce in mill applications.”