Spectroscopic comparison of lignin separated by electrolysis and acid precipitation of wheat straw soda black liquor

Abstract

Electrolysis experiments were carried out with wheat straw soda black liquor. Organics from black liquor were electrodeposited at the anode. These organics were studied for their FTIR and NMR spectra and compared with those separated by acid precipitation of black liquor. The electrodeposited organics were found to be chemically distinct from those obtained by the acidification of the black liquor. Notably, they differed in the characteristic features of the aromatic part from hitherto known lignin formulations as revealed by the absence of signals for quaternary aromatic carbon between δ 129 and δ155 ppm in their 13C NMR spectra and higher proportion of aromatic protons in their 1H NMR spectra. The hydroxyl environment was also found to be different by the shift in O H stretching band to higher frequency. Other significant differences were noted in the FTIR and NMR spectra of the electrodeposited solids from those of acid precipitated solids.