Characterization of Hardwood Soda-AQ Lignins Precipitated from Black Liquor through Selective Acidification

In the development of integrated biorefinery process alternatives to produce value-added by-products, various black liquors from sulfur-free pulping processes offer potential feedstocks for recovering their main chemical constituents, lignin and aliphatic carboxylic acids. In this study, lignin fractions were obtained from silver birch (Betula pendula) soda-anthraquinone black liquor by carbonation (pH to about 8.5) or by acidification (pH to about 2) with H2SO4 after carbonation or directly. These fractions were characterized by Fourier transform infrared (FTIR), ultraviolet (UV), energy dispersive X-ray fluorescence (ED XRF), and 13C nuclear magnetic resonance (13C NMR) spectroscopy. In addition, the molecular weight distributions of these lignin fractions were determined. All the experimental data clearly suggested that only small differences between the precipitated lignins existed, and thus, their equal chemical utilization seems possible.