Influence of dissolved lignin on the combustion properties of softwood and hardwood kraft black liquors

Relationships between the chemical structure of the dissolved lignin and the combustion properties (burning time and swelling) of the corresponding pine (Pinus sylvestris) and birch (Betula verrucosa/B. pubescens) kraft black liquors were studied. In each case, the lignin fraction was primarily characterized in the terms of total content, amount of "monomers", average molecular mass, and molecular-mass distribution. The fraction was also separated and characterized by NMR spectroscopy (i.e., determination of different hydroxyl groups) and elemental analysis. Tn addition, further data on the chemical structure were obtained by analyzing liquid chromatographically the degradation products formed from lignin with CuO oxidation. Statistical analysis indicated several linear correlations between the structural parameters of lignin and the combustion properties of the corresponding black liquors. Finally, a multivariate data analysis of chemical and combustion data was performed.