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You are here : Home > Training > EFPG Days > 11- Effect and future of the bleaching chemicals (slides 1-8)

Last update : September 12, 2003

			Third Session : Bleaching
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					XI - Effect and future of the bleaching chemicals (slides 1-8) Dominique Lachenal (EFPG)

A - Bleaching chemistry (slides 1-8)

	1 - Introduction During cooking, lignin is either depolymerized (Kraft process) or made hydrophilic (sulphite process). As a consequence:     Residual lignin in kraft pulp is not sufficiently depolymerized to become soluble   Residual lignin in sulphite pulp is not enough sulphonated to become soluble Bleaching chemistry can be summarized by the grafting of COOH on lignin.				2 - Lignin in kraft process Lignin in wood Lignin in kraft pulp Dissolved lignin during bleaching

	3 - Lignin in sulphite process Lignin in wood Lignin in sulfite pulp Dissolved lignin during bleaching				4 - Bleaching general reaction All the bleaching chemicals give the same global reaction on lignin, as shown by the following figure: This global reaction is an oxidation involving four electrons per aromatic ring.

	5 - Bleaching with chlorine dioxide Chlorine is formed and is responsible for part of the delignification.				6 - Bleaching with chlorine

	7 - Bleaching with ozone Hydrogen peroxide is formed. Its contribution to delignification is not known.				8 - Bleaching with oxygen

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