Kinetic study and effect of flash pyrolysis temperature of kraft lignin on the yield of aromatic compounds

The growth in global energy demand and the urge to reduce CO2 emission make renewable sources viable alternatives to replace fossil fuels and petrochemicals. Black liquor, a by-product of pulp industry, has been mostly burned to generate energy. Nevertheless, its pyrolysis is an alternative valorization route for obtaining valuable aromatics. The present study aims the energetic characterization of kraft lignin, evaluation of the kinetics of commercial alkaline lignin as a standard model, and the study of the renewable aromatics yield obtained from flash pyrolysis of kraft lignin at 400, 500 and 600 degrees C. The kinetic study shows an increasing apparent activation energy up to 760 degrees C, with a maximum value of 338.2 kJ mol(-1). The reaction order greater than one for 35-840 degrees C reinforces the bimolecular mechanism degradation. The main pyrolysis products were phenolics and aromatics with methoxy groups. The highest amount of phenolics, toluene, and p-xylene was obtained at 600 degrees C. Results show that lignin has low energetic potential for thermochemical processes due to the low content of volatiles (45.64%) and ash (21.6%), and low calorific value (15 MJ kg(-1)). Despite low volatile content, the results show kraft lignin is a renewable alternative source with potential to generate building blocks.