KINETICS AND MASS-TRANSFER FOR SUPERCRITICAL FLUID EXTRACTION OF WOOD

Rates of extraction of lignin from white fir sapwood with supercritical tert-butyl alcohol were measured dynamically in a continuous-flow system. The extraction rate increased with temperature and pressure but was independent of particle size and flow rate for our experimental conditions. A model is presented for the supercritical reaction-extraction process, accounting for the reaction of solid lignin in the particle, intraparticle diffusion, and external mass transfer of lignin derivatives. For the reaction in the particle, two parallel first-order reactions for the degradation of two lignin types satisfactorily represent the data. The kinetic parameters for the reaction were estimated from the model analysis. Model simulations supported the experimental results, which showed the extraction process was not affected by the mass transfer. © 1990, American Chemical Society. All rights reserved.