Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The goal of this study is to produce cellulose acetate (CA) hollow-fine-fibre membranes with
good water flux performance in the 95 – 96% salt retention range for brackish water
desalination from first principles. First, the acceptable range of fibre dimensions was
determined by means of a collapse pressure calculation using the elastic buckling pressure
equation (thin shell assumption). Second, the pressure drop across the fibre wall in the
hollow-fine fibre was determined by using the Hagen-Poiseuille equation, in order to
determine how this would affect the chosen fibre dimensions. It was determined that the
acceptable range of fibre dimensions was 222 – 247 m, and the wall thickness was 50 m.
Fibres with these dimensions exhibited a high resistance to brackish water operating pressure
of 20 – 25 bar, without collapse. The pressure drop calculations of these dimensions showed
a sufficiently low pressure drop across the fibres.
A dry-wet spinning technique was used for the preparation of the hollow-fine-fibre
membranes. Hollow-fine fibres were spun using CA dissolved in a suitable solvent and
non-solvent mixture comprising acetone and formamide.
The effects of the dope composition and spinning parameters such as solvent to non-solvent
ratio, bore fluid ratio, take-up speed, dope extrusion rate and heat treatment on the membrane
morphology and performance were investigated. The spun fibres showed a good
morphological structure, with no macrovoids (sponge-like structure), which is favourable for
reverse osmosis (RO) applications. The hollow-fine-fibre membranes showed a good
brackish water desalination performance within brackish water operating conditions.
Statistical analysis was used to generate a fabrication formulation for producing cellulose
acetate hollow-fine-fibre membrane for brackish water desalination with improved salt
retention and flux. A three-level three-factor factorial was used to the study of the effect of
spinning parameters (solvent to non-solvent ratio, bore fluid ratio and air gap distance).
A regression equation was successfully established and was used to predictably produce
membranes with good performance within the limits of the factors studied. RO performance
of these hollow-fine-fibre membranes was good: The salt retention ranged from 96 to 98%
and the permeate flux ranged from 60 to 46 L/m2.d (2 000 ppm, NaCl, 20 bar, 24 oC). / AFRIKAANSE OPSOMMING: Die studie het ten doel gehad om selluloseasetaat holveselmembrane vanaf eerste beginsels
vir brakwaterontsouting te ontwikkel. Die ontsoutingsvlakke van die membrane moet tussen
95 en 96% lê met ’n aanvaarbare waterproduksievermoë. Aanvaarbare deursneë vir die
holvesels is eerstens bepaal deur platval-berekeninge met behulp van die inmekaarvouvergelyking
uit te voer (dunwand aanname). Hierna is drukval oor die wand van die holvesel
met behulp van die Hagen-Poiseuille vergelyking bepaal ten einde vas te stel hoe dit die
gekose dimensies sal beïnvloed. Daar is vasgestel dat vesel deursneë tussen 222 en 247 um
met ’n 50 um wand aanvaarbaar is. Vesels met hierdie dimensies het ’n hoë weerstand teen
inval getoon by brakwater opereringsdrukke tussen 20 en 25 bar.
’n Droë-nat spintegniek is in die voorbereiding van die holveselmembrane gebruik. Holvesel
membrane is met ’n selluloseasetaat stroop gespin wat uit ’n oplosmiddel (asetoon) en nieoplossmiddel
(formamied) bestaan het.
Die effek van die spinstroop samestelling en spinparameters soos die oplosmiddel tot nieoplosmiddel
verhouding, lumen-vloeistof verhouding, opneemspoed, spinstroop ekstrusie
tempo en hittebehandeling op membraan morfologie en werkverrigting is ondersoek. Die
gespinde vesels toon ’n sponsagtige struktuur sonder die teenwoordigheid van enige mikroleemtes
wat voordelig is vir tru-osmose toepassings. Die holvesel membrane het aanvaarbare
brakwater ontsoutings werkverrigting.
Statistiese analise is gebruik in die generasie van produksieformulasies vir die produksie van
brakwater ontsoutingsmembrane met verbeterde retensie en vloed. ’n Drie-vlak driefaktoriaal
ontwerp is tydens die studie gebruik om die effek van spinparameters (oplosmiddel
tot nie-oplosmiddel verhouding, lumen vloeistof verhouding, en lug-gaping) te ondersoek. ’n
Regressie vergelyking is suksesvol daargestel en gebruik om voorspelbaar membrane met
goeie werkverrigting binne die limiete van die studie te produseer. Die tru-osmose
werkverrigting van die membrane was goed: die sout retensie het tussen 96 en 98% gelê en
die permeaatvloed tussen 60 en 46 L/m2.d (2 000 ppm NaCl, 20 bar, 24oC).
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/4253 |
| Date | 03 1900 |
| Creators | Tawari, Akram |
| Contributors | Bradshaw, S. M., Jacobs, E. P., University of Stellenbosch. Faculty of Engineering. Dept. of Process Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
| Format | 110 p. : ill. |
| Rights | University of Stellenbosch |
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