Development of mathematical models for describing organosolv pulping kinetics of fungally pretreated wood samples

Eucalyptus grandis wood samples decayed by white- and brown-rot fungi were cooked at 180 degrees C for 5 to 100 min with methanol/water (78:22 v/v) containing 25 mM of CaCl2 and 25 mM MgSO4. Mathematical models for describing organosolv pulping kinetics of the fungally pretreated samples were developed to estimate delignification constants, and also rate constants for xylan and wood mass solubilization. These models had high R-2 values and were able to predict pulp yield, as well as lignin and xylan contents during the process at 99% confidence level. Delignification of undecayed control samples had a rate constant of 2.0 x10(-2) min(-1) for the bulk phase. Most decayed samples presented delignification constants higher than those of the control. Some decayed samples exhibited an additional delignification phase at the beginning of the process, which was characterized by a low solubilization rate. These samples required insertion of an additional term in the model to represent this phase.