PREPARATION OF HIGH-PURITY SULFATE LIGNIN FROM SPENT BLACK LIQUOR USING ULTRAFILTRATION AND DIAFILTRATION PROCESSES

The paper presents investigations concerning the ultrafiltration proce ss of black liquor using ultrafiltration polyacrylonitrile membranes. The above membranes proved useful in the process of concentration and fractionation of these liquors. As a result, concentrates enriched wit h macromolecular post-sulphate lignin were obtained. Raising the trans membrane pressure, the sulphate lignin concentrates of high purity lev el were obtained (purity level higher than 88%). Further purity increa se of the sulphate lignin is possible through raising the volumetric p ermeate flow yield to 90% (deep concentration), although the average p ermeate flux is then decreasing. Alternatively higher purity of the co ncentrates can be obtained by complementing the ultrafiltration proces s with dialfiltration, i.e., by removing residual impurities with an e xtra amount of water added in the process. The obtained results are re liable enough to recommend ultrafiltration as a production method for the preparation of sulphate lignin concentrates.