The possibility of controlling formation and cleavage reactions of HexA during kraft pulping, 2006 Engineering, Pulping, and Environmental Conference

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During kraft pulping, the side groups in the xylan backbone, 4-O-methyl-D-glucuronic acid (MeGlcA), are partly converted to hexenuronic acid (HexA). Simultaneously, degradation reactions of these side groups take place. In this study, the activation energies(Ea)for these reactions were determined during kraft pulping of birch from constant composition cook. The results show that Ea of bulk delignification (118kJ/mol, in accordance with earlier studies) is similar to that of HexA formation (129kJ/mol) and MeGlcA degradation (120kJ/mol), but it is lower than that of HexA degradation (141kJ/mol). The differences in activation energie simply a possibility of controlling the HexA and MeGlcA content in xylan by cooking temperature. This study demonstrated that this is indeed the case for the dissolved xylan, where as pulp xylan is not markedly affected by a change in cooking temperature.