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Soft ECF-bleaching of softwood pulp
2011 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

The aim of bleaching is to increase the brightness of the pulp by reducing the amount of the residual lignin and to provide the pulp with specific physicochemical properties. It is known that the brightness of the pulp depends on its ability to reflect the light, which can be reached by discoloration of the coloring agents contained in the unbleached pulp or by their removal. The coloring agents are generally different chromophoric groups in the residual lignin whose properties strongly depend on the method of pulp cooking, nature of wood and the bleaching agents. The subjects of the research were softwood kraft pulp after oxygen-alkali treatment (Kappa number 10-14) and softwood kraft pulp without oxygen-alkali treatment (Kappa number 30). In the present work, softwood kraft pulp samples were bleached according to the following schemes: HO—A—P—D—P(a) and A—P—D—P(a), where HO – Oxygen-alkaline treatment stage; A –Acidic bleaching stage where sulphuric acid or sulphuric dioxide water is used as a reagent; P – Alkaline bleaching stage where hydrogen peroxide is used as a reagent; D – Acidic bleaching stage where chlorine dioxide is used as a reagent; P(a) – Acidic bleaching stage where hydrogen peroxide is used as a reagent. The pulp stiffness and brightness were determined to illustrate the efficiency of the acid-catalytic activation of pulp. The dependences of the delignification degree and hydrogen peroxide conversion on time according to the scheme H0 — A—P were defined. The pulp viscosity and paper mechanical characteristics such as breaking length and tear resistance as well as chemical oxygen demand (COD) of bleaching filtrates were estimated. The results provided better understanding of elemental chlorine free bleaching (ECF-bleaching) with low chlorine dioxide consumption (“soft” ECF bleaching). Moreover, a conclusion was made that “soft” ECF-bleaching was the most optimal process because it was more environmentally friendly than ECF and cheaper than total chlorine free (TCF) bleaching.

Place, publisher, year, edition, pages
Keyword [en]
Physics Chemistry Maths
Keyword [sv]
Fysik, Kemi, Matematik
URN: urn:nbn:se:ltu:diva-43801Local ID: 1a1262aa-4016-4c7f-a9a1-e52f874a23e5OAI: diva2:1017043
Subject / course
Student thesis, at least 30 credits
Educational program
Chemical Engineering, master's level
Validerat; 20110207 (anonymous)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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