The Isolation of Kraft Lignin from Black Liquor during Korean Red Pine Kraft Pulping and Evaluation of the Isolated Kraft Lignin

The lignin precipitation from the black liquor of the kraft pulping of Korean red pine was conducted to evaluate the effects of the pH conditions on the efficiency of the precipitation and the properties of the precipitated lignin. The sulfuric acid was added to the black liquor for adjusting pH. The lower pH condition resulted in the higher amount of precipitated lignin, which was evaluated by using UV spectrophotometer. The significant increase of the lignin yield was observed between pH 4-5. However, the purity of the precipitated lignin was increased at the higher pH condition. The changes in the properties of the precipitated lignin depending on the pH condition of precipitation were indirectly evaluated with the changes in the phenolic hydroxyl group contents in the lignin structure by using the differential spectrum from the UV spectrum. The contents of the phenolic hydroxyl group of each precipitated lignin were not significantly changed.