Acetosolv pulping of pine wood. Kinetic modelling of lignin solubilization and condensation

Experiments of delignification of Pinus pinaster wood by acetic acid at atmospheric pressure showed that acetic acid concentration is a primary factor in the process and that high concentrations (90%) significantly improve the delignification degree. The kinetics of the process were satisfactorily explained by a model of consecutive first-order reactions corresponding to lignin solubilization followed by lignin condensation and reprecipitation onto the lignocellulosic matrix, hydrolysis of α-aryl ether bonds being the dominant reaction of the delignification process. The selectivity of the lignin dissolution was practically independent of operating conditions. When the degree of delignification reached a value around 90% the selectivity decreased considerably due to lignin condensation.