Pyrolysis of LignoBoost lignin in ZnCl2-KCl-NaCl molten salt media: Insights into process-pyrolysis oil yield and composition relations

Depolymerization of lignin by pyrolysis has been identified as a viable route to produce renewable fuels and biobased platform chemicals. Herein we report the pyrolysis of LignoBoost lignin in a molten salt consisting of ZnCl2-KCl-NaCl (60:20:20 mol ratio) in a g-scale reactor set-up with a focus on the liquid phase yields and composition. The effects of relevant process parameters such as temperature (250-450 degrees C), reaction time (10-50 min), and N2 flow rate (10-30 mL min -1) on the product yields were elucidated using design of experiments. The highest bio-oil yield was 47.1 wt% (450 degrees C, 10 min) and the yield of organics in the bio-oil at this condition was 24 wt% (on lignin intake), the remainder being water. The latter is considerably higher than found for an experiment at similar conditions without salt (16 wt%). Temperature and reaction time were shown to have the largest effects on bio-oil yield. Prolonged reaction times resulted in higher amounts of gas phase components (H2, CO2) and water, and a reduced amount of solid products. Statistical analyses and validation experiments showed that the experimental product yields are in good agreement with the predicted values from the model. The properties and molecular composition of the liquid products were determined using various analytical techniques and reveal that the presence of a molten salt during pyrolysis has a positive influence on the composition of the liquid phase like a higher level of depolymerization and higher selectivity to aromatic and phenolic monomers compared to thermal pyrolysis.