Towards Liquid Fuels from Lignin

Abstract: The solubility of Lignoboost lignin was compared with softwood lignin precipitated from filtered black liquor and explained by Hilebrand as well as Hansen solubility parameters theory. The ability to dissolve efficiently lignin rises as the hydrogen bonding capacities together with the polarity of the solvents increases; similarly, their solubility parameter, according to Hildebrand, lay within the range between twelve and fourteen. Lower molecular weight lignin obtained by ultrafiltration is definitely more soluble than lignin obtained by Lignoboost process, especially at higher concentration.   In addition, viscosity measurements show that solutions obtained from low molecular weight lignin are always less viscous than Lignoboost solutions. The gap in viscosity, between two lignins, becomes even higher at high concentration. The relationship between molecular weight of lignin and viscosity has been demonstrated by SEC analysis and application of Mark–Houwink–Sakurada equation.   By ash content evaluation it has been possible to find out the most efficient conditions to lower salts formation when lignin is burnt. Several washes carried on with cold and acidic water have decreased the amount of ash to a value lower than 0,5% of dry weight.   The effect of methanol fractionation on the molecular weight and its distribution of Lignoboost lignin has been investigated showing phase separation. The heavy and high lignin content fraction shows a pseudoplastic behaviour; however, its viscosity at low shear rate is too high to be interesting in a fuel production context and because the high volatility of methanol.