Ultrafiltration of Lignin rock from black liquor obtained from a South African kraft mill.
Kekana, Paul Thabo.
MetadataShow full item record
This study focused on investigating the possibility of extracting lignin from black liquor generated from South African Kraft mill black liquors. Although ultrafiltration has been applied successfully and widely to extract lignin from black liquor it was expedient to conduct this study and apply the technique to black liquor generated from a South African Kraft mill since the structure and the composition of lignin varies mainly as a function of their origin (softwoods, hardwoods or herbaceous crops) but also of several factors such as growth conditions, harvesting and drying of the lignocellulosic biomass. The main hypothesis in this study therefore is that ultrafiltration could be used effectively as a technique to extract lignin from black liquor generated from South African Kraft mill black liquor. In addition, simulations can be performed to elucidate the fouling mechanism by which the flux decline experimental data conforms to. The test protocol in this work commenced with finding the optimum membrane cut-off size at which the retention of lignin and decline in flux could be studied. The ultrafiltration feasibility tests were performed later in batch mode. In this study batch ultrafiltration tests were conducted to investigate the effects of operating pressure, stirring rate and feed concentration on the extent of lignin retention and permeate flux. Results showed that retention of lignin increased with increase in operating pressure, feed concentration and stirring rate but decreased with increase in molecular cut-off size of the membrane. Permeate flux on the other hand increased with an increase in pressure, stirring rate and molecular cut-off size of the membrane but decreased with increase in feed concentration. The flux decline experimental data was modelled by applying the solute mass balance for a stirred cell and by assuming that fouling mechanism is described by the intermediate blocking model. The main achievements in this study are: - The extraction of lignin from black liquor was successfully carried out by ultrafiltration on a bench scale using a stirred cell and extraction efficiencies as high as 86% could be achieved depending on the experimental conditions - The flux decline results were modelled by applying the experimental data to the intermediate blocking model This study was concluded with recommendations to perform more tests in order to - Study the retention of lignin by ultrafiltration using ceramic membranes in a continuous pilot plant setup - Investigate generation of activated carbon from the precipitated lignin - Characterize the activated carbons and compare them to commercial samples - study the potential of using the activated for water purification - Develop models for the activity and performance of the carbons.