Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: The study of water-in-oil emulsion stability and separation was carried out for this thesis. The
main objectives were as follows: to rank crude oil samples in terms of creating stable emulsions;
to assess the effect of the brine pH on emulsion stability; to investigate the influence of different
organic acids on emulsion stability; and to determine the efficiency of an electric separator in
removing water droplets from a flowing organic liquid.
Seven crude oil samples from different sources such as A, C, H, M, P, U, and V were used to
investigate the water-in-crude-oil emulsion. Two crude oil blends were also used. Brine solution
comprising 4 wt% NaCl and 1 wt% CaCl2 was used. In this study the gravity settling, critical
electric field (CEF) and centrifuge test methods were used to estimate the emulsion stability
created by the crude oil and crude oil blend samples. The experiments were carried out at 60°C.
In the gravity test method, the brine pH, stirring speed, stirring time and water-cut (the fraction
of water in the emulsion) were changed in 2IV-1 factorial design. The parameters for the
centrifuge and CEF test methods were selected on the basis of the gravity test method. The crude
oil samples were ranked in terms of creating stable emulsion in the following order V, U, P, H,
A, M and C. The crude oil blends created more stable emulsions than their respective
constituents. The ranking order of the crude oil samples did not correlate to asphaltenes, resins,
wax or total acid number (TAN). There was a good correlation between the test methods used.
There was an increase and decrease in the brine pH when different crude oil samples were in
contact with the brine. It is believed that the structure of the surfactants present in crude oil may
explain the emulsion-forming characteristics of different crude oil deposits around the world.
To account for the effect of organic acids on emulsion stability, different organic acids were
used. In this case, a mixture of equal volumes of heptane and toluene (here referred to as heptol)
was used as the model for crude oil. The brine solution composition was the same as the one
used in the crude oil experiments. Equal volumes of heptol and brine were mixed for a period of
time and then separated. The brine pH was changed from acidic to basic. In this regard, gas chromatography and liquid chromatography were used to analyse the concentration of the acids
in the brine and heptol samples. It was found that the partitioning coefficient for acids containing
a straight-chain hydrocarbon moiety decreased with an increase in molecular weight. However,
the partitioning coefficient depended on the structure of the acid. The presence of a benzene ring
in the organic acid increased the partitioning coefficient. Organic acids with rings created an
interface layer when the heptol sample was mixed with basic brine solution. This confirmed that
the emulsion of water and crude oil starts with the formation of a film, and it also provides
insight into the formation of naphthenate soap. It is believed that the naphthenic acids that cause
stable emulsions have rings. More organic acids should be tested. It is recommended that the
interaction of asphaltenes, resins and naphthenic acids should be investigated at different pH
levels, temperatures and pressures.
The separation of water droplets from a flowing organic liquid was carried out using a direct
current (d.c.) electric separator. The separator used centrifugal forces and a d.c. electric field to
enhance the removal of water drops from a flowing organic liquid. For this, vegetable oil, crude
oil blend and heptane were used as the continuous phase. The experiments were carried out at
room temperature (for heptane and vegetable oil) and at 70°C (for vegetable oil and crude oil
blend). The flow rate to the separator was kept constant. The separator removed water droplets
from flowing organic liquids. A maximum of 97% (at 100 V)of water droplets was removed
from the heptane liquid; a maximum of 28% (at 100 V) of water droplets was removed from the
vegetable oil at 70°C and 5% (at 100 V) of water droplets was removed from the crude oil blend.
The d.c. electric field enhanced the efficiency of the separator in removing water droplets. The
break-up of the droplets is suspected to decrease the efficiency of the separator. This separator
can easily be installed into existing process lines and does not require much space. However,
further improvements are needed in the design of this separator.
Emulsions created in the petroleum industries are quite complex to deal with. The identification
of the structure of the components in crude oil is a matter that still has to be investigated. An
improvement in the techniques may lead to a better understanding of the cause of the ultra-stable
emulsion encountered in the petroleum and related industries. / AFRIKAANSE OPSOMMING: Die studie van die stabiliteit en skeiding van water-in-olie-emulsies is vir hierdie tesis uitgevoer.
Die hoofdoelstellings was as volg: om ruolie-monsters in terme van die skepping van stabiele
emulsies te klassifiseer; om die effek van die pekel-pH op emulsie-stabiliteit te assesseer; om die
invloed van verskillende organiese sure op emulsie-stabiliteit te ondersoek; en om die
doeltreffendheid van ’n elektriese skeier in die verwydering van waterdruppels uit ’n vloeiende
organiese vloeistof te bepaal.
Sewe ruolie-monsters uit verskillende bronne soos was A, C, H, M, P, U en V gebruik om die
water-in-ruolie-emulsie te ondersoek. Twee ruolie-mengels is ook gebruik. ’n Pekeloplossing
wat 4 wt% NaCl en 1 wt% CaCl2 bevat, is gebruik. In hierdie studie is die gravitasie-afsakkings-,
kritieke elektriese veld- (KEV-) en sentrifuge-toetsmetodes gebruik om die emulsie-stabiliteit te
beraam wat deur die ruolie- en ruolie-mengsel-monsters geskep is. Die eksperimente is teen
60°C uitgevoer. In die gravitasietoetsmetode is die pekel-pH, roertempo en watersnyding (die
fraksie van water in die emulsie) is in ‘n 2IV-1-faktoriaalontwerp ondersoek. Die parameters vir
die sentrifuge- en KEV-toetsmetodes is op grond van die gravitasietoetsmetode resultate gekies.
Die ruolie-monsters is in terme van die skepping van ’n emulsie stabiliteit geklassifiseer in die
volyende orde V, U, P, H, A, M, en C. Die rudie-menysels het meer stabiele emulsies gerorm as
die respektiewe samestellende dele. Die rangorde van emulsie stabiliteit van die ruolie-monsters
het nie met asfaltene, hars, waks of totale suurgetal gekorreleer nie. Daar was ’n goeie korrelasie
tussen die toetsmetodes wat gebruik is. Daar was ’n toename of afname in die pekel-pH wanneer
verskillende ruolie-monsters in kontak met die pekel was. Die aanname is dat die struktuur van
die surfaktante wat in die ruolie teenwoordig is, die emulsievormende karaktereienskappe van
verskillende ruolie-neerslae regoor die wêreld kan verklaar.
Om die effek van organiese sure op emulsie-stabiliteit te verklaar, is verskillende organiese sure
gebruik. In hierdie geval is ’n mengsel van gelyke hoeveelhede heptaan en tolueen (voortaan
verwys na as heptol) as die model vir ruolie gebruik. Die pekeloplossing-samestelling was dieselfde as die een wat in die ruolie-eksperimente gebruik is. Gelyke hoeveelhede heptol en
pekel is vir ’n tydperk gemeng en toe geskei. Die pekel-pH is van suurvormend tot basies
verander. Gaschromatografie en vloeistofchromatografie is gebruik om die konsentrasie van die
sure in die pekel- en heptoloplossings te analiseer. Daar is gevind dat die verdelingskoëffisiënt
vir sure wat ’n reguitketting-koolwaterstofhelfte bevat met ’n toename in molekulêre gewig
afneem. Die verdelingskoëffisiënt het egter van die struktuur van die suur afgehang. Die
teenwoordigheid van ’n benseenring in die organiese suur het die verdelingskoëffisiënt verhoog.
Organiese sure met ringe het ’n tussenvlaklaag geskep toe die heptolmonster met die basiese
pekeloplossing gemeng is. Dit het bevestig dat die emulsie van water en ruolie met die vorming
van ’n vlies begin, en gee ook insig in die vorming van naftenaatseep. Dit blyk dat die
naftenaatsure wat stabiele emulsies veroorsaak, ringe het. Meer organiese sure moet getoets
word. Daar word aanbeveel dat die interaksie van asfaltene, hars en naftenaatsure teen
verskillende pH-vlakke, temperature en drukke getoets word.
Die skeiding van waterdruppels uit ’n vloeiende organiese vloeistof is uitgevoer met behulp van
’n gelykstroom- elektriese skeier. Die skeier het sentrifugiese kragte en ’n wisselstroomelektriese
veld gebruik om die verwydering van waterdruppels uit ’n vloeiende organiese
vloeistof te verhoog. Hiervoor is plantolie, ’n ruoliemengsel en heptaan gebruik as die
deurlopende fase. Die eksperimente is teen kamertemperatuur (vir heptaan en plantolie) en teen
70°C (vir plantolie en ruolie-mengsel) uitgevoer. Die vloeitempo na die skeier is konstant gehou.
Die skeier het waterdruppels uit die vloeiende organiese vloeistowwe verwyder. N’ maksimum
van 97% (by 100 V) van die water drupples is verweider van die heptaan vloeistof; a maksimum
van 28% (by 100 V) van die water druppels was verweider van die plantolie by 70°C en 5% (by
100 V) van die water druppels was verweider van die rudie mengsel. Die gelykstroom- elektriese
veld het die doeltreffendheid van die skeier om waterdruppels te verwyder, verhoog. Daar word
vermoed dat die afbreek van die waterdruppels die doeltreffendheid van die skeier verlaag. Die
skeier kan met gemak in bestaande proseslyne geïnstalleer word en benodig nie veel spasie nie.
Verdere verbeterings is egter nodig ten opsigte van die ontwerp van hierdie skeier.
Emulsies wat in die petroleumbedrywe geskep word, is kompleks om te hanteer. Die
identifikasie van die struktuur van die komponente in ruolie verg verdere ondersoek. ’n Verbetering in hierdie tegnieke kan tot beter begrip lei van die oorsaak van die ultrastabiele
emulsie wat in die petroleum- en verwante bedrywe aangetref word.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/2267 |
| Date | 12 1900 |
| Creators | Andre, Antonio Luzaiadio Buco |
| Contributors | Els, E. R., University of Stellenbosch. Faculty of Engineering. Dept. of Process Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | Unknown |
| Type | Thesis |
| Rights | University of Stellenbosch |
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