High-pressure delignification of Eucalyptus Wood by 1,4-Dioxane-CO2 Mixtures

Abstract

High-pressure reactive extraction of Eucalyptus globulus wood was undertaken. Extractions were carried out with CO2 + 1,4-dioxane mixtures at 170 bar pressure at temperatures of 160–180 °C. The influence of temperature, extraction time, composition of the fluid mixture, and flow rate on the extraction were investigated. In the range of temperatures studied, only a small increase in lignin and hemicellulose extraction is observed when temperature is increased. At 180 °C, the degradative extraction of cellulose starts, but at lower temperatures, cellulose losses are small. The selectivity of the extraction depends upon the composition of the extracting mixture. CO2-rich fluid mixtures extract hemicellulose preferentially and total hemicellulose removal can be achieved. Maximum delignification was obtained by extraction with pure dioxane with 75% of the lignin initially present in wood being removed. Selectivity towards lignin vs. hemicellulose extraction increases with increasing flow rate until a plateau is reached.