The kinetics of Organosolv delignification of black cottonwood in aqueous methanol was studied in the temperature ränge 130-210°C using 0.00 to 0.05 M sulfuric acid äs catalyst. The bulk delignification phase followed pseudo-first order kinetics with an activation energy of 19.2 kcal/mol (80.3 kJ/mol) suggesting the cleavage of benzyl ether linkages to be the rate determining reaction. At low catalyst concentrations (< 0.02 M sulfuric acid), the bulk rate constant of deashed cottonwood is nearly proportional to the catalyst concentration. When the delignification was carried out in a flow-through reactor, the rate constant was increased by a factor of 1.8 probably äs a consequence of the solubility properties of Organosolv lignins. At any level of delignification, the flow-through reactor produces holocellulose fibers with higher DP values than the batch reactor. The molecular weights of isolated flow-through reactor lignins are substantially higher than those found for the batch reactor lignins, e.g. M w = ~ 50000 versus -9500.

SynopsisThe study of the effect of thickness on the mass uptake is shown to be quite helpful in the understanding of the complexities of polymer/organic penetrant sorption behavior. Isothermal diffusion results for methanol, acetone, and carbon tetrachloride in polycarbonate plates and films of various thicknesses ranging from 12 mils (0.030 cm) to l/4 in. (0.633 cm) are presented. The diffusion is purely Fickian only in the case of methanol, which is a poor solvent for polycarbonate and has a low level of saturation in it (0.06 g/g). Methanol does not lead to a detectable swelling or any appreciable crystallization of the polymer during the diffusion process. Acetone and carbon tetrachloride are much better solvents and lead to much higher saturation levels; they crystallize polycarbonate, and their mass uptake is anomalous. The diffusion of carbon tetrachloride exhibits initially a case I1 diffusion behavior followed for thicker plates by an intermediate behavior between case I1 and Fickian diffusion. The anomalous diffusion in the case of acetone appears to be associated primarily with surface effects.