Ultrafiltration of kraft cooking liquors from a continuous cooking process

摘要

Two cooking liquors and a black liquor were fractionated by ultrafiltration.The liquors were withdrawn from different stages in a kraft pulp mill employing continuous digestion.The ultrafiltration was performed at 90deg C with two ceramic membranes with cut-offs of 5 kDa and 15 kDa.Only small differences in membrane performance were observed when concentrating the three liquors to 90 volume reduction.The average flux was 551/m~2 h for the 5 kDa membrane and about 1151/m~2 h for the 15 kDa membrane.The concentration of lignin was on average 230 and 155 g/L in the retentate from the 5 kDa and 15 kDa cut-off membranes.The ash content was reduced from 37-40 g/g total dry solids to 20-30 g/g after ultrafiltration.