The Haloperoxidase-DABCO System: exploring a Novel Method of Enzymatic Pulp Bleaching

I denne afhandling undersøges en ny enzymatisk proces til blegning af cellulosepulp og fjernelse af hexenuronic acid (HexA). I processen indgår en haloperoxidase (Hap) og en tertiær amin (DABCO) der testes på oxygen-delignificeret eukalyptus kraft pulp. Ved at køre processen ved konstant pH (pH 4,5; 60°C) sås en øget lyshed samt en god respons på peroxid-alkalisk ekstraktion hvor mere end 80% HexA fjernelse opnået, uden at cellulose strukturen blev nedbrudt. I et optimeret, men ikke-bufret system, blev Hap/DABCO-systemet sammenlignet med en ikke-enzymatisk HOCl behandling, og en mindre effekt af Hap/DABCO-systemet blev fundet. På samme niveau af lyshed var HOCl behandlingen overlegen i forhold til reduktion af HexA og kappanummer. Hydrogenperoxid og ikke kun den enzymatiske oxidation kan være medvirkende til blegningen under Hap/DABCO behandling. Organochlor-dannelse blev målt og vurderet at være meget højere end reference-behandlinger med chloridoxid. Det blev konkluderet, at problemet med dannelse af organochlor skal løses før en fremtidig anvendelse af Hap/DABCO teknologien.
A novel approach for cellulosic pulp bleaching and hexenuronic acid (HexA) removal using a haloperoxidase (Hap) and a tertiary amine catalyst (DABCO) was tested on oxygen-delignified eucalypt kraft pulp. In a buffered system (pH 4,5, 60°C), high brightness gain, good response to peroxide-reinforced alkaline extraction and more than 80% HexA removal were achieved, while preserving cellulose integrity. In an optimized, but non-buffered system, Hap/DABCO was compared to the non-enzymatic HOCl treatment and an inferior performance of the former was found. At the same brightness level, HOCl treatment performed superior in terms of HexA and kappa number reduction. Hydrogen peroxide was proposed as most likely playing a role in contributing to the brightening during Hap/DABCO treatment. Organochlorine formation was measured and found to be much higher than reference chlorine dioxide treatments. It was concluded that the problem of organochlorine formation must be solved for this technology to be used in the future.