Hydrothermal conversion of commercial lignin to carbonaceous materials

Abstract

Commercial lignin is a by-product of pulping and the emerging bio-refinery industries. Herein, we report the hydrothermal treatment (HTT) or conversion (HTC) of three commercial types of lignin to carbonaceous materials. HTC of lignin was carried out in an autoclave in the presence of water at temperature and pressure of approximately 300 °C and 1000 psi respectively. Morphological, physical and chemical properties of parent lignin and their hydrothermally derived carbonaceous materials were characterized by X-ray diffraction, scanning electron microscopy (SEM), thermogravimetric analysis, elemental composition, Fourier-transform infrared and Raman spectroscopies (FTIR). This study demonstrated differences in the morphology of carbons from the three lignin types. SEM analysis showed that hydrothermally derived carbonaceous materials from Mascoma lignin contained spherical particles with diameters ranging from 50 to 250 nm whereas that from ammonium and sodium lignosulfonate lignins contained similar particles but were highly agglomerated. The better characteristics of the post-HTT Mascoma carbon vis-a-vis post-HTT ammonium and sodium carbons are also evident in the results obtained from X-ray diffraction, thermo-gravimetric analysis, and FTIR spectroscopy. Thus, carbonaceous materials can be obtained from low-value commercial lignins via HTT and their properties are influenced by the type of lignin.