Salient Reactions in Lignin During Pulping and Oxygen Delignification, 2000 Pulping / Process & Product Quality Conference Proceedings

D. S. Argyropoulos, L. Akim, B. Ahvazi--This paper describes our efforts focused at defining the formation of the various condensed moieties in lignin as they emerge during conventional kraft, EMCC R , soda and oxygen delignification conditions. Overall, a new perspective with regard to the abundance of such units, their formation profiles and their reactivity is presented. More specifically, the paper initially focuses at our efforts aimed at defining the formation of diphenylmethanes in softwood milled wood lignin under kraft and soda pulping conditions. This information provided additional evidence supporting the fact that modern modified cooking technologies alter the structure of residual kraft lignin beneficially. The role and fate of the newly discovered structures of dibenzodioxocins is also discussed and their significance toward pulping and bleaching operations emphasized. Finally, the fate and role of the condensed phenolic structures under oxygen delignification conditions is discussed. Our conclusions do not point to a single factor as being responsible for the limits confronting oxygen delignification. Amongst the major factors impeding the effectiveness of oxygen delignification are: (i) the accumulation of unreactive 5-5’ biphenyl structures forming from ring opening reactions of dibenzodioxocins and via phenoxy guaiacyl radical coupling reactions between the liquor and the fiber and (ii) the accumulation of considerably less reactive p-hydroxyphenyl structures.