Study of the primary pyrolysis of Kraft lignin at high heating rates: Yields and kinetics

The primary pyrolysis of Kraft lignin was studied in a Pyroprobe 1000 apparatus. Experiments were carried out at a nominal heating rate of 20 degrees C ms(-1) over a range of temperatures between 450 and 900 degrees C and for several pyrolysis times (1-30 s). The evolution with temperature of the main gaseous and volatile products was analysed. A mathematical model that takes into account physical phenomena (heat transfer limitations in the heating and cooling stages), the kinetics of thermal decomposition and the endothermic character of the reaction was developed to explain the experimental data. In the kinetic analysis, the C function model for primary decomposition was used. This model assumes that lignin is formed by a large number of fractions, each one of which begins to decompose at a characteristic temperature.