Condensation reactions during kraft pulping

Fig. 7 -29. Examples of condensation reactions during alkali and kraft pulping (Gierer, 1970).

Condensation reactions of lignin have been mentioned 22) in connection with sulfite pulping as being responsible for color formation. However, most of the likely condensation reactions occurring during a kraft cook do not lead directly to chromophore formation. One potential condensation reaction which would give a chromophore is the formation of a chalcone (XIX) from vanillin and acetoguaiacone, both of which have been isolated by Enkvist 12) from black liquor. 

Condensation Reactions A variety of condensation reactions are known to occur in alkaline pulping. Since carbon-to-carbon linkages are formed between lignin entities, it has been proposed that as a result of condensation reactions, lignin dissolution is retarded, particularly during the terminal phases of kraft pulping. 

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