Ultrafiltration of Lignin rock from black liquor obtained from a South African kraft mill.
Date
2015
Authors
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Abstract
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.
Description
Master of Science in Chemical Engineering . University of KwaZulu-Natal, Howard College 2015.
Keywords
Theses--Chemical engineering., Lignin--South Africa., Sulfate waste liquor., Sulfate pulping process., Ultrafiltration., Polymers., black liquor., kraft mill.