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Abstract: Electrolysis experiments were carried out with wheat straw soda black liquor with stainless steel (SS) electrodes. Electroactive lignin anions were found to form complex with the iron in the matrix of the SS anode surface to form a solid deposit. The deposits were examined with SEM and found to be in the form of irregular small granular mass. The granular solids so obtained were characterized with Energy Dispersive X-ray (EDX) analysis, TEM, XRD, and Selected Area Electron Diffraction (SAED) techniques. The electrodeposited lignin contained an unusually high iron to carbon atomic ratio. The granules varied in size from 1 to 1.5μm, with each granule itself made up of individual particles of different size and shape. The solids were amorphous in nature as confirmed by their XRD and SAED analyses. [Copyright &y& Elsevier]

Abstract: Lignin samples were separated from soda black liquor of wheat straw and bagasse by electrolysis and also by acid precipitation. These were compared for their thermochemical characteristics by 1H NMR, TGA and DTA analyses. Lignins separated by electrolysis were found to have only 11–12 methoxyl groups per hundred phenylpropane units compared to 36–38 groups for acid precipitated lignins. They also had larger proportion of aromatic hydrogen and higher carbon to hydrogen ratio than acid precipitated lignins. All the lignin samples underwent a low temperature endothermic expulsion of adsorbed moisture. The distinctly exothermic nature of the thermal decomposition of acid precipitated lignins was missing for electrolytically separated lignins. Under comparable conditions, lignins separated by electrolysis could yield more amount of char compared to acid precipitated lignins. [Copyright &y& Elsevier]

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 δ155ppm 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 Oing 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. [Copyright &y& Elsevier]

Abstract: Cathodic hydrogen evolution reaction and the reactions at the anodic counter electrode have been studied for black liquor electrolysis using standard electrochemical methods. These are compared with alkaline water electrolysis as control. In black liquor electrolysis the hydrogen evolution is found to be kinetically facile with exchange current densities of 2.194mA/cm2, and 9.856mA/cm2 for wheat straw black liquor and eucalyptus black liquor, respectively, in comparison to 1.075mA/cm2 for alkaline water. The cathodic Tafel slopes are −112.8, −116.9, and −135.3mV/dec for alkaline water, wheat straw black liquor, and eucalyptus black liquor, respectively. The activation overpotential for hydrogen evolution is significantly lower for black liquor electrolysis. Black liquor electrolysis shows additional anodic electroactivity in a potential window of −0.2 to 0.2V, well shifted from the region of oxygen evolution reaction. This reaction follows a sluggish one electron oxidative charge transfer as revealed by cyclic and square wave voltammograms. The anodic charge transfer coefficient is slightly higher than 0.5. Black liquor electrolysis could produce hydrogen with a much lower inter-electrode potential with the exclusion of gaseous products being formed at the anode. This can have significant bearing on the energy efficiency of the process. [Copyright &y& Elsevier]