Investigation of the stability and separation of water-in-oil emulsion.

Andre, Antonio Luzaiadio Buco (2009-12)

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2009.

Thesis

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.

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