Studies on the Ozonation of Structural Elements in Residual Kraft Lign Ins

Abstract

In order to elucidate the main reactions of ozone with residual lignins in softwood kraft pulps, model compounds representing conjugated structures (styrenes and stilbenes) and structures of the biaryl, diary] ether and diarylmethane types have been treated with this oxidant. The oxidation mixtures were analyzed using HPLC and GC techniques and the main components were identified by 'H NMR and mass spectrometry. Formation of the degradation products is interpretod in terms of known mechanisms of ozonation. A comparison between the reaction rates reveals that the structural types studied in this work can be arranged according to their ease of ozonation in the following order: stilbenes > stv-renes > phenolic structures > muconic acid type intermediates (from the opening of aromatic rings) > non-phenolic structures >> aromatic aldehydes (from the degradation of conjugated structures). The advantages connected with the use of ozone as deligni-fying reagent are briefly discussed in the light of the results obta ined.