Extraction of lignin from wood with supercritical alcohols

Abstract

Extraction of lignin from samples of white fir sapwood with supercritical t-butanol and isopropanol is examined. Experiments were carried out with a continuous flow system to study the effect of temperature and pressure on the dynamic response of the extraction process. Plots of concentration as a function of time were obtained by measuring the absorbance of the lignin/ t-butanol extract effluent at 280 nm over an extraction time of 100 minutes or longer. The total effluent was analyzed to determine the amount of lignin extracted. Increasing the temperature dramatically increased the fraction of lignin extracted. Increased pressure also showed increased yields. Subcritical temperatures resulted in very low yields compared to supercritical temperatures. Additional analysis examined changes in porosity of wood residues extracted with supercritical isopropanol and t-butanol. Porosity and pore volume increased during the extraction process. Most pores were in the range 1–20 μm, and extraction increased the number of these pores.