Abstract:

The pyrolysis characteristics of black 1iquor solid were studied via thermogravimetric analysis , and the effect of heating rate on the pyrolysis characteristics was investigated , followed by a comparison with that of alkali lignin. The results show that (1) the pyrolysis of black liquor consists of 4 stages , with two peaks of rapid weight loss respectively in the low- and high -temperature ranges; (2) the polysaccharides , aliphatic carboxylic acids and alkali metal salts in black liquor have certain effects on the pyrolysis characteristics of black liquor; (3) the pyrolysis of alkali lignin , which begins early and lasts for a long period , includes 4 stages , namely , the dehydration , the water holding , the rapid weight loss and the slow weight loss stages; and (4) there are some differences in the pyrolysis characteristics between black liquor and alkali lignin. Moreover , according to the analysis of pyrolysis process by means of Coats-Redferen method and based on the calculated kinetic parameters of black liquor and al- kali lignin pyrolysis at different heating rates , it is found that the reaction order of black liquor pyrolysis is 4 at the organic pyrolysis region , and that the activation energy and frequency factor in the decomposition increase slightly with the heating rate.

Key words: black liquor, alkali lignin, pyrolysis, thermogravimetric analysis