Lignin based future catalysts for hydrogen production

Biochar is a promising catalyst for hydrogen production in the biomass gasification process. Based on preliminary results, it seems possible to regulate the formation conditions (heating rate, process temperature, reaction time) of biochar from thermochemical processes applied to lignin in such a way as to produce materials that maintain some of the typical functional groups of lignin, particularly in terms of oxygen-containing functionalities, and that can therefore be appropriately modified for the production of higher value-added products. Lignin-based biochar has been investigated using different technical lignins in order to understand, based on their functional characteristics, which ones could be opportunely functionalized to be used as a catalyst in gasification processes. Four different technical lignins, namely two different kraft lignins and two different organosolv lignins, were tested; for comparison, lignosulfonate lignin and alkali lignin, both, were also studied. Biochars from the various lignins have been obtained by vacuum pyrolysis using a new heating system with a heating rate of 700°C per minute. Samples were heated up to 600°C, and temperature was held for 2 minutes; the process is suitable to avoid possible side reactions, as well as condensation reactions and formation of unwanted products. Biochar so obtained was characterized by specific surface and porosity analysis, thermogravimetric analysis, elemental analysis, scanning electron microscopy and nuclear magnetic resonance. Liquid and gaseous fractions formed during the thermal processes were analysed by a gas chromatograph coupled to a mass spectrometer. During the pyrolysis process, phenolic compounds and/or AHs can be produced, showing promising applications in biochemical intermediates and biofuel additives. From the preliminary results, lignosulphonate and alkaline lignins seem to be the most reluctant to react, highlighting an unsuitability for the formation of a functionalizable biochar. Furthermore, the high sulfur content present in lignosulfonate lignin and also in the derived biochar makes it less suitable for its use as a starting material for catalysts development. Differently, the technical lignins appear to be the most promising lignins in the production of functionalizable biochar. Tga analysis on pyrolytic biochar shows a great thermal stability at 600 °C compared to their precursor lignins and BET and NMR studies show biochar structures easily malleable to the insertion of catalytically active metals.