Multi-step devolatization kinetics of Klason lignin isolated from beech wood and agro-industrial wastes

Lignin decomposition is of paramount importance for the formulation of biomass pyrolysis mechanisms useful for the development and optimization of the pyrolysis technology. In this study the decomposition behavior of residual lignin in torrefied woods is found to roughly coincide with that of the Klason isolated samples, which thus can be used as reliable model compounds. Previous kinetic models for the Klason and the pseudo-component lignin in beech wood are compared. A correlation is observed between the kinetic and the thermogravimetric parameters. The analysis is used as the initial basis for the formulation of a more accurate three-step kinetic model over the temperature range 300–973 K. Three main decomposition zones of the curves for beech wood Klason lignin are identified and described by activation energies of 61, 147 and 113 kJ/mol and corresponding reaction orders in the range 2–3.4. The active pyrolysis zone of Klason lignin isolated from two agricultural residues (olive pomace, wheat straw) is reached at lower temperatures and exhibits higher peak rates compared to the wood counterparts, but three- step kinetics can again be used with small variations on the estimated parameters.