Quantification method for hydrogen peroxide formation during oxygen delignification of kraft pulp

The addition of phenylglyoxylic acid provided a method to quantify hydrogen peroxide formation during oxygen delignification of kraft pulp. Phenylglyoxylic acid is readily cleaved by hydrogen peroxide with the result that relatively stable benzoic acid is formed that can be analysed in the pulping liquor by gas chromatography. In addition, phenylglyoxylic acid improved the selectivity by hindering the homolytic cleavage of hydrogen peroxide into the selectivity decreasing hydroxyl radical. The analysed amounts of benzoic acid showed a relatively high amount of hydrogen peroxide formation after 30 min delignification. This correlated with improved selectivity between 10 and 30 min delignification, where non-oxidised structures in the liquor start to oxidise, generating hydrogen peroxide and shielding the pulp from carbohydrate degrading oxygen species. Diluting the oxygen delignification with industrial liquor did not affect the selectivity favourably. A radical scavenger, dipicolinic acid, also failed to improve selectivity during the oxygen stage.