Delignification Rate of White Birch Chips During Ethanol-Water Cooking in a Stirred Batch Reactor with Rapid Liquor Displacement

摘要

A digester was modified to perform as a stirred batch reactor with rapid liquor displacement in order to study the delignification kinetics of white birch in an ethanol-water system. The ethanol-water solution pumped into the reactor contained acetic acid at a concentration comparable to that found during batch cooking with ethanol-water. The high flow rate of pulping liquor ensured that the increase in acetic acid concentration due to hydrolysis of the hemicellulose was relatively small. Variation in acetic acid feed concentration did not have a significant effect on pulp delignification, bringing into question the term "autocatalyzed" solvent pulping normally used for ethanol-water cooking. Therefore, delignification may be mostly the result of high-temperature uncatalyzed hydrolysis of lignin ether linkages by water. The ethanol in the system would then serve to dissolve the lignin fragments. To verify this hypothesis, the ethanol concentration was varied, as were cooking time and temperature. The lignin removal rate was determined by UV analysis of the extracted liquor. The pulp was characterized by measurement of the kappa number, viscosity and pulp yield.