Green liquor extraction of hemicelluloses from southern pine in an Integrated Forest Biorefinery

Loblolly Pine chips were extracted with fresh green liquor solutions containing sufficient alkalinity to approximately neutralize the acids released upon treatment of the chip-liquor mass at elevated temperatures of 170, 180 and 190 °C for various times. The components of green liquor extracts were then quantified using high pressure anion exchange chromatography and UV spectrophotometer. The time–temperature effect on the extracted yields including the wood weight loss of wood chips after extraction could be well described by the H-factor approach. Sugar components were all found in their polymeric forms in the liquor. About 2.5–3% of wood mass was extracted as total sugars at an H-factor of about 4000. In general, mannose showed lower extraction than xylose. With increasing chemical charge, arabinoglucuronoxylan and galactoglucomannan extracts decreased, whereas dissolved lignin increased. Cellulose showed a minimum dependence on H-factor and chemical charge. The total sugar showed an inverse proportionality to the final liquor pH that rapidly dropped from alkali to the neutral in the very early stages of extraction and leveled off slowly reaching the acid region. Significant difference between total organic yield and the weight loss provides a possible evidence for the presence of significant amount of low molecular weight dissolved organics that were not accounted for.