Mimicking haloperoxidase assisted pulp bleaching through slow addition of hypochlorous acid

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Kemian tekniikan korkeakoulu | Master's thesis
Biomass Refining
Degree programme
Master's Programme in Chemical, Biochemical and Materials Engineering
Bleaching is a chemical process in which the pulp is further treated to reach the final product requirements, most commonly with brightness improvement. Bleaching stage and sequence design is a recurring multi-objective multi-variable optimization problem, where the industry is still searching for greener methods without trading off the final product properties and economics. Current trend is increasing the number of stages and utilizing catalytic agents along to aid bleaching performance without increasing the total chemical load. The former research work on the topic suggests utilization of tertiary amine catalysts and ligninolytic enzymes are promising to be further investigated for commercialization. Latest literature on this is reported by Novozymes, where they have concluded haloperoxidase is promising to further continue the pre-commercialization stage. In this thesis, the enzymatic kinetics are mimicked to perform a pseudo-haloperoxidase bleaching stage. This is performed by adding the hypochlorous acid in a continuous manner, which has never been mentioned in the prior literature on bleaching to our knowledge. Along this, two new catalysts, CM-DABCO and CEM-DABCO that are developed in Aalto University, are utilized in the experiments along DABCO as the control. The objective of this research is to figure out if the proposed system could mimic the outcome achieved by Novozymes, and if the new catalysts would be beneficial. This research involves recently found or novel analytical techniques such as UV-Raman aided HexA content determination and co-existing active chemical titration. The findings of this study show that the proposed system is comparable with Novozymes research regarding ISO brightness improvement when the chemical charges are not considered. Pseudo Hap stage over-performed the Novozymes case in terms of kappa number and HexA content reduction excluding the effect of chemical charges. Thus, the outcomes of this thesis point out probable deviation from Novozymes case, in terms of equilibrium chemistry and half reaction intermediates.
Vuorinen, Tapani
Thesis advisor
Isaza Ferro, Estefania
haloperoxidase, enzymatic bleaching, pseudo, slow addition, mimic, hypochlorous acid
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