Many advances have been made in the field of emulsions in recent years. Emulsion behavior is largely controlled by the properties of the adsorbed layers that stabilized the oil-water surfaces. The effect of chemical demulsifiers in demulsification of water-in-crude oil emulsions were assessed experimentally. The relative rates of water separation were characterized via graduated beakers. Four groups of demulsifier with different functional groups were used in this work namely amines, polyhydric alcohol, sulphonate and polymer. The effect of alcohol addition on demulsification performance also studied. The results obtained in this study have exposed the capability of chemical demulsifiers in destabilization of water-in-crude oil emulsions. Further works are nevertheless required to provide deeper understanding of the mechanisms involved to facilitate the development of an optimum system applicable to the industry.
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Water is normally present in crude oil reservoirs or is injected as steam to stimulate oil production. Water and oil can mix while rising through the well and when passing through valves and pumps to form in most cases relatively stable dispersions of water droplets in crude oil (w/o), which are usually referred to as oil field emulsions. Formation of these emulsions during oil production is a costly problem, both in terms of chemicals used and due to production losses. Therefore, the breaking of emulsions (destabilization) is necessary in many applications such as environmental technology, painting, coating and petroleum industry. Chemical destabilization is the most widely applied method of treating water-in-oil (w/o) emulsions and involves the use of chemical additives to accelerate the emulsion breaking process. For economic and operational reasons, it is necessary to separate the water completely from the crude oil before transporting or refining them. In petroleum system, asphaltenes and resinous substances comprise a major portion of the interfacially active components of the oil (Sjoblom et al., 1992; Johansen et al., 1989; Urdahl et al., 1992; Corbett and Petrossi, 1978; Shiffert et al., 1984). Anklam (1997) reported that in the oil industry, water comes into contact with crude oil on many occasions, creating emulsions stabilized by various components in the oil, including the asphaltenes and resins. At drilling sites, the recovered oil will contain some water and hydrophilic impurities which need to be removed before shipping and processing. There are many methods for the neutralization and reduction of the emulsifying agent has been used, for example, Hannessey et al. (1995) used the gravity separation, while electrostatic coalescence has used by Bailes et al. (1997), chemical demulsification used by Abdurahman et al. (2006), centrifugal and filtration methods mentioned by Lissant (1983) as techniques used for breaking the emulsion.
The objective of this research is to study the effect of chemical additives on breaking emulsions. Experimental results showed that, addition of alcohol to chemical demulsifiers will highly accelerate the process of emulsion demulsification.
MATERIALS AND METHODS
To accomplish the objective of this study, the crude oil samples were obtained from Petronas Refinery at Melaka. A detailed procedure for the water-in-oil (w/o) emulsions preparation and their procedures including the formation of w/o emulsion, their characteristics and method of preparation are thoroughly described in a previous research by Abdurahman et al. (2006). Here the work merely describes the main experimental steps. Water-in-crude oil emulsions were prepared by dispersing distilled water in crude oil at room temperature with a standard three blade propeller at speed of 1600 rpm. Relevant properties of the crude oil are listed in Table 1. Triton X-100 used beside asphaltenes and resins originally present in the crude oil to stabilize the emulsions. The emulsifying agent was used as received without any further dilution.
|Table 1:||Crude oil analysis|
The prepared emulsions were used to check for w/o or o/w emulsions. All emulsions investigated were found w/o emulsions type (oil continuous phase).
Four chemical demulsifiers were used to perform demulsification tests. These chemicals were; amine groups, polymeric, sulphonate and polyhydric alcohol demulsifiers. The chemical demulsifiers used were listed in Table 2. While the interfacial pressure of various demulsifiers related to the percentage of water and oil separation is presented in Table 3. The ability of these chemicals to destabilize w/o emulsions were evaluated from the volume of water observed in the beaker as follows:
|Table 2:||The chemical additives used in emulsion demulsification tests|
|Table 3:||The interfacial pressure of various demulsifiers related to the percentage of water and oil separation|
RESULTS AND DISCUSSION
Demulsification is the breaking of a crude-oil emulsion into oil and water phases. From a process point of view, the oil producer is interested in two aspects of demulsification; the rate or speed at which this separation takes place and the amount of water left in the crude oil after separation. The stability of the emulsions was determined visually by measuring the water and oil separation from emulsions at 30°C as a function of time. In terms of emulsion characterization, this study used a variety of surfactants to get a high stability for water-in-oil emulsions. Coalescence needs to be minimized to obtain any useful rheological information. In this regard, as shear rate increases, the viscosity decreased. Figure 1, the viscosity data shown in Fig. 1 indicate that the emulsions exhibit Newtonian behavior up to a water content of 20% (this is indicated by constant values of viscosity for all shear rates or a slope of zero). At water cuts above 20%, the slopes of the curves deviate from zero, indicating Non-Newtonian behavior. Also, the Non-Newtonian behavior is pseudoplastic, or shear thinning behavior (i.e., viscosity decrease with increasing shear rates).
pH: Water-phase pH has a strong influence on emulsion stability (Kimbler et al., 1966; Strassner, 1968; Jones et al., 1978). The stabilizing, rigid-emulsion film contains organic acids and bases, asphaltenes with ionizable groups and solids. The pH of water affects the rigidity of the interfacial films. pH also influence the type of emulsion formed. Low pH (acidic), generally produes w/o emulsions, whereas high pH (basic) produces o/w emulsion. Figure 2 shows the effect of pH on emulsion stability. The optimum pH for demulsification is found at 10 without demulsifier. Addition of a demulsifier enhances demulsification after 5 h and the maximum water separation (95% v/v) is achieved after 15 h.
Interfacial Pressure (Ω): The interfacial pressure of demulsification process (Ω) is defined as the difference between the interfacial tension of the oil containing stabilizer/aqueous phase γo and that of the same system when a destabilizer γd is added. The interfacial pressure Ω is calculated from equation Ω = γo - γd, where γo and γd are the interfacial tension between crude oil and synthetic oil field emulsion before and after addition of demulsifier, respectively. Results of this study showed that the higher (Ω) value, the higher the instability of emulsion and vice versa.
|Fig. 1:||Viscosity vs. shear rate of crude oil emulsions|
|Fig. 2:||Effect of pH and demulsifier concentration on emulsion stability|
The interfacial pressure of various demulsifiers related to the percentage of water and oil separation is presented in Table 3. As shown in the Table 3, there is a direct correlation between the interfacial pressure and the percentage of water separation.
Based on the results, the demulsifiers can be divided into three groups. The first group consists of the demulsifiers such as amine group, sulphonate and polyhydric alcohols group which have Ω values ranging from 4.1 to 7.5 which can destabilize the emulsion. The amount of water which can be separated from the emulsion is up to 80%. The second group comprises Polyethylene Glycol (PEG) 600, Polyethylene Glycol (PEG) 1000, AOT, propylamine which have Ω values ranging from 2 to 6 and can partly break the emulsion. The amount of water separated from this group is in the interval of 25 to 67%. The third group consists of poly PO terminated, polyethylene block PEG, polyethylene Oxide (PEO), 100000, trioctylamine, Propylene glycol, PG, ethylene glycol, EG and NaDBS which have Ω values ranging from -8 to 2.8 and could not destabilize the emulsion. The percentage of water separation is less than 15%.Figure 3 and 4 shows some typical results of demulsification experiments conducted to test the influence and performance of the amine group demulsifiers on the crude oil emulsion stability.
|Table 4:||The influence of butanol in enhancing the destabilization process of cru-de oil using oil soluble demulsifiers|
|Fig. 3:||The influence of amine group demulsifiers on crude oil emulsion stability (percentage of water separation)|
|Fig. 4:||The influence of amine group demulsifiers on crude oil emulsion stability (percentage of oil separation)|
Figure 3 and 4 shows separation of water and oil from water-in-oil emulsions as a function of time, respectively. As shown in Fig. 3 and 4, all amine groups showed the water and oil separations. This could be attributed to a very specific interaction between the amine added and the naturally occurring constituents in the interfacial film.
The large agglomerates have a larger sedimentation velocity than the individual particles and require larger forces to hold them at the interface. The equation for sedimentation velocity from Stokes law is:
|Fig. 5:||The influence of butanol in enhancing the oil soluble demulsifiers respect to water separation|
|Fig. 6:||The influence of butanol in enhancing the oil soluble demulsifiers respect to oil separation|
where; vw is the sedimentation velocity, R is the water droplets radius; Pw, Po are the densities of water and oil, respectively; g is the force acting on the system (gravitational) and μo is the viscosity of the continuous (oil). As droplets agglomerate, the density flocs decreases because of entrained continuous phase (oil), but their radius increases, resulting in a higher sedimentation velocity because of the squared dependency on the radius.
Effect of Alcohol Addition on Demulsification Performance
Oil soluble demulsifier: To study the effect of alcohol addition on demulsification performance, this study used three oil soluble demulsifiers; dioctylamine, igepal and aerosol T (AOT) Table 4.
Figure 5 and 6 shows the profiles of water and oil separation from emulsion destabilized by the oil soluble demulsifiers alone as well as adding butanol as enhancement agent. As shown in Figure 5 and 6, the performance of all demulsifiers either water or oil separation can be enhanced by adding alcohol. In general, after 1440 min, the percentage of water separation without adding butanol alcohol is less than 43%. In contrast, destabilization process by adding butanol can improve the water separation ranging from 43 to 48 for dioctylamine, 22 to 54 for igepal and 38 to 47% for AOT, respectively. Our experimental results showed that using butanol alone there were no emulsion destabilization for 24 h, these percentages of separation are smaller than other demulsifiers. It means that butanol does not effect the destabilization if used alone as destabilizer, but they can enhance the destabilization process when used together with a demulsifier. Butanol is grouped into medium chain alcohol that possesses the solubility properties, like slightly soluble in water and more soluble in non-polar or weakly polar compound. It is different from low chain alcohol (C1-C3) which is miscible in water, or long chain alcohol (C7 or more) to be insoluble in water. Dioctylamine is non-polar compound that is not soluble in water because the highly polar water molecules are held to each other by very strong dipole-dipole interaction hydrogen bonds. Its a very weak attractive force between water molecules and the non-polar dioctylamine molecules.
The influence of butanol in enhancing the AOT demulsifier performance shows that the percentage of water separation is less than the oil separation at any time. For example, for 1440 min both percentages of water and oil separation from the emulsion are 47 and 74%, respectively.
Based on results of this study, it can be concluded that, emulsions are characterized by the type of emulsion (W/O or O/W), nature of emulsifying agents present, bulk viscosity and interfacial viscosity. The percentage of water separated is the best indicator of emulsion stability, because it is a measure of the degree of aggregation or flocculation of individual emulsion water droplets and coalescence of aggregated water droplets. Water phase pH it found has a strong influence on emulsion stability.
Four chemical demulsifiers were used to perform demulsification tests. These chemicals were; amine groups, polymeric, sulphonate and polyhydric alcohol demulsifiers. Three oil soluble demulsifiers blended with alcohol and thoroughly investigated their effect on demulsification performance.