Thermogravimetric behavior of black liquors and their organic constituents

The slow thermal degradation of various black liquors and their organic components (lignin, aliphatic carboxylic acids, extractives and polysaccharides) was investigated by thermogravimetry in the temperature range 25–700 °C under an inert nitrogen atmosphere and at a heating rate of 20 °C/min.
Oven-dried samples of pine and birch black liquors from kraft and soda-anthraquinone pulping were tested. Similar tests with black liquor components were carried out both in the absence and in the presence of alkali. In all cases, the mass loss occurred primarily in the temperature range 250–500 °C.
The thermograms of the various black liquors were very similar even though there were significant differences in the thermograms of the individual black liquor components.
The possible roles of the individual components in the thermal degradation of black liquor are discussed.
During the thermogravimetric runs, the formation of the most prominent gaseous products, carbon dioxide and carbon monoxide, was monitored by Fourier transforminfrared analysis.