Thesis (MScIng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Recent years have seen the development of various treatment methods for the purification
of industrial waste waters due to the increased demand for reduced pollutant
effluents. Aqueous waste streams containing toxic organic compounds are of special
interest, since conventional treatment methods such as biological waste treatment
can not always be used. Other popular treatment methods are often ineffective.
Catalytic oxidation of organic wastes has been investigated since the 1960s with
varying degrees of success. A major problem associated with this method is the high
temperatures and pressures required to improve the activation energies involved.
Electrochemical oxidation has become a popular method in the literature of treating
these wastes, since the applied voltage determines the activation energy, and
therefore the process can often be performed at ambient conditions.
This thesis investigates the capability of a unique reactor system in the treatment
of these wastes. The reactor utilises proton-exchange membrane technology to eliminate
the requirement of conductivity in treated waste streams; thus the membrane
serves as a solid electrolyte. The reactor system has therefore been referred to as a
solid-polymer-electrolyte reactor. Novel metal oxide anodes are responsible for the
oxidation of the organic molecules. These metal oxide catalysts show promise in the
treatment of a wide variety of organic wastes. A SnO2 catalyst doped with ZrO2 is
used as anode in this study. Dopants are added to the catalyst to improve properties
such as catalytic activity and conductivity.
Kinetic data was obtained on a wide range of values for the chosen experimental
parameters (current density and flow rate). Phenol, an organic molecule often referred
to in the literature as model contaminant due to its resistance to oxidation,was also used as contaminant in this study. The use of the reactor system in the disinfection
of water containing selected pathogens, were included in the experimental
work. This kinetic data served in the development of a simple model of the process,
and provided the basis for a full analysis regarding potential scale-up and economic
feasibility.
A requirement of the study was the accurate determination of the various oxidation
breakdown products of phenol. This led to the refinement of an HPLC analytical
method in order to quantitatively determine these products.
The full analysis showed that the current reactor system would not be economically
viable — mainly due to very long reactor lengths required for the complete
removal of all organic material. Both mass transfer and charge transfer at the chosen
experimental conditions influenced the electrochemical oxidation of phenol. High
pressure drops, causing low flow rates in the reactor, accounted for this because of
the narrow flow channels required in the reactor. Some catalyst deactivation was
also suspected to affect the overall reaction, but the full extent of the deactivation
was not investigated thoroughly.
There is still room for improvement in the electrochemical oxidation of organic
wastes. The design of the flow channels, a factor that was not investigated, can
significantly improve efficiency. Another aspect that was not investigated was the
catalyst type. The catalyst has been identified in the literature as the main contributing
factor to the success of the oxidation reaction. A wide variety of metal oxide
catalysts are currently being researched and may improve the kinetics of the process
even further. Further improvement needs to be made on the membrane/electrode
assembly to improve current density distribution.
Every improvement of the process in terms of the reactor design and catalyst will
impact on the economics of the process, thus making the process more competitive
with current treatment technologies. / AFRIKAANSE OPSOMMING: In die afgelope paar dekades, is daar ’n wye verskeidenheid metodes ontwikkel wat
gebruik kan word om industri¨ele afvoer strome te behandel. Hierdie ontwikkeling
het plaasgevind as gevolg van die verhoogde eis aan skoner afvoerstrome. Wateragtige
afvoerstrome wat organiese verbindings bevat, is van besonderse belang omdat
hierdie tipe strome soms besonders moeilik kan wees om te behandel. Gebruiklike
metodes is in die meeste gevalle ongeskik vir behandelings-doeleindes. Katalitiese
oksidasie is sedert die 1960’s gebruik, maar hierdie prosesse benodig dikwels ho¨e
drukke en temperature om suksesvol te wees. Elektrochemiese oksidasie het intussen
’n populˆere behandelingsmetode geword, aangesien die aktiveringsenergie vir die oksidasieproses
hoofsaaklik afhanklik is van die aangewende potensiaal en dus kan die
proses by atmosferiese toestande gebruik word.
In hierdie tesis word die geskiktheid van ’n unieke reaktorstelsel vir water-suiwering
ondersoek. Die reaktor gebruik ’n proton-uitruilings-membraan om die behoefte
vir konduktiwiteit in die water uit te skakel. Die membraan dien dus as ’n
tipe soliede elektroliet en as gevolg hiervan word na die reaktorstelsel verwys as ’n
soliede-polimeer-elektroliet reaktor. Nuwe metaal-oksied anodes word in die reaktor
gebruik aangesien hulle belowende resultate toon in die oksidasie van organiese
verbindings. In die navorsing, is ’n SnO2 katalis wat klein hoeveelhede ZrO2 bevat
gebruik. Oksiede soos ZrO2 word dikwels gebruik om die aktiwiteit en konduktiwiteit
van hierdie kataliste te bevorder.
Kinetiese data is oor ’n wye bereik van parameter waardes ingesamel. Die hoof
parameters in die eksperimentele werk was stroom digtheid en vloeitempo. Fenol,
‘n komponent wat volgens die literatuur in hierdie tipe van werk gebruik word, isas die besoedelende komponent gekies. Die doeltreffendheid van die reaktor in die
ontsmetting van water, wat met ’n verskeidenheid skadelike mikro-organismes besmet
is, is ook getoets. ‘n Eenvoudinge model is opgestel m.b.v. die kinetiese data,
waarna ’n volledige analise met betrekking tot grootskaalse bedryf en ekonomiese
uitvoerbaarheid gedoen is.
‘n Vereiste van die studie was om die konsentrasie van die afbreek-produkte
van die oksidasie akkuraat vas te stel. As gevolg hiervan is ‘n ho¨e-druk-vloeistofchromatografie
analitiese metode verfyn.
Die analise het getoon dat die reaktorstelsel nie ekonomies sou wees nie. Een
van die hoofredes hiervoor is die onrealistiese reaktorlengtes wat benodig sou word.
Resultate het getoon dat die reaksie deur beide massa-oordrag en lading-oordrag
be¨ınvloed word. Ho¨e drukvalle in die reaktor wat gelei het tot lae vloeitempo’s was
hiervoor verantwoordelik. Die deaktivering van die katalis be¨ınvloed waarskynlik die
reaksie, maar die deaktiveringsverskynsel is nie ten volle ondersoek nie.
Die reaktorstelsel kan verder verbeter word deur verskeie elemente van die reaktor
te ondersoek. Die ontwerp van die vloeikanale in die reaktor is nie ondersoek nie en
kan die werksverrigting van die reaktor verhoog. Uit die literatuur is gevind dat die
tipe metaaloksied wat as katalis gebruik word, die reaksie direk be¨ınvloed. Dus kan
navorsing wat tans op die kataliste gedoen word nuwe kataliste na vore bring wat
meer doeltreffend sal wees. Laastens, is die huidige membraan/elektrode samestelling
nog oneffektief en kan die reaktor-opstelling dus nog verbeter word.
Elke verbetering wat op die bogenoemde faktore van die reaktor ontwerp verkry
word, sal die ekomoniese uitvoerbaarheid van die proses be¨ınvloed. So, sal die proses
al meer kompeterend met huidige behandelingsmetodes word.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/16292 |
| Date | 04 1900 |
| Creators | Cronje, Martin |
| Contributors | Knoetze, J. H., Sanderson, R. D., University of Stellenbosch. Faculty of Engineering. Dept. of Process Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | xvi, 159 leaves : ill. |
| Rights | University of Stellenbosch |
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