The effect of autocatalyzed ethanol pulping on lignin characteristics

The development of phenolic hydroxyl and carbonyl groups and the changes in the molecular weight of lignin during the autocatalyzed ethanol-water pulp ing of Eucalyptus globulus wood was modeled. The models were developed usin g a response surface method and were employed to study the influence of coo king temperature, cooking time and ethanol concentration on lignin characte ristics. The functional groups content was found to increase as the cooking time was risen and the concentration of ethanol in the pulping liquor was reduced. These cooking conditions lead to a more extensive cleavage of the bonds between lignin units due to the longer treatment, higher temperature and increased acidity of the pulping liquor. The cleavage of lignin bonds r esulted in the occurrence of new functional groups and a reduction in ligni n molecular weight. The steady decrease in molecular weight with the intens ity of cooking conditions indicates that lignin condensation does not play an important role under the conditions studied.