- Email: [email protected]
Influence of demulsifier on interfacial film between oil and water
Colloids and Surfaces A: Physicochem. Eng. Aspects 272 (2006) 27–31
Influence of demulsifier on interfacial film between oil and water夽 Wanli Kang a,∗ , Guolin Jing a , Hongyan Zhang a , Mingyuan Li b , Zhaoliang Wu b a
Daqing Petroleum Institute, Daqing, 163318 Heilongjiang, China b Petroleum University, Beijing102249, China
Received 24 July 2004; received in revised form 4 July 2005; accepted 8 July 2005 Available online 16 August 2005
Abstract Demulsification of a synthetic water in oil (W/O) crude oil emulsion was studied by measuring water–oil interfacial properties such as life time and thinning rate of oil film in the presence of various demulsifiers. The results indicated that the interfacial elasticity decreased both the strength and the life time of oil film and film thickness when adding the demulsifiers. The oil film broke when film thickness came to a critical level. As for a demulsifier, the interfacial elasticity was decreased with demulsifier concentration increase, and stayed constant above a critical demulsifier concentration. The rate of dewatering is related to interfacial elasticity. When different demulsifiers were compared, the more the interfacial elasticity was lowered, the more efficient was the dewatering. The mechanism of the different types of demulsifiers was discussed based on the experimental results. The demulsifiers partially replaced the emulsifiers, which led to the interfacial elasticity decreased. The effect of chemical structure of the demulsifiers on water–oil interfacial film was studied. © 2005 Elsevier B.V. All rights reserved. Keywords: Demulsifier; Oil film life; Thinning rate of oil film; Interfacial tension; Interfacial viscosity; Interfacial elasticity; Dewatering rate
1. Introduction
2. Experimental
There have been many studies on stability and demulsification of crude oil emulsions reported by many investigators [1–6]. These studies are more focused on effects of interfacial tension and interfacial viscosity rather than on the oil film life time, the thinning rate of oil film and interfacial elasticity of the film. The demulsification mechanism of demulsifiers is quite complicated, and no demulsifier can be applied to break all kinds of crude oil emulsions [7–9]. In this paper, demulsification of a synthetic emulsion (W/O) is studied by focusing on oil film life time, thinning rate of the film, and interfacial properties between oil and water in the presence of various of demulsifiers.
2.1. Materials
夽 Supported by the Outstanding Youth Science Foundation of Heilongjiang
(J03-11) and NSFC (10172028). ∗ Corresponding author. E-mail address: [email protected] (W.L. Kang). 0927-7757/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2005.07.004
• Crude oil: Daqing Oil Field, PR. China. • Emulsifier: Span 80, Liaoyang Aoke Chemical Company. • Demulsifier: the demulsifiers used were denoted as A, B, C and D. A and B are of the type of phenol-formaldehyde resin polyoxyethylene (EO) polyoxypropylene (PO); C and D of polyoxyethylene polyoxypropylene polymers obtained from Liaoyang Aoke Chemical Company. • NP serials: nonyl phenol polyoxyethylene(4,6,8,10,15), the number represents polyoxyethylene molecule number. • SA serials: phenol-formaldehyde resin polyoxyethylene polyoxypropylene(20,25,30,35,40,45), the number represents weight percent of polyoxyethylene. 2.2. Equipments • Interfacial tensiometer: TX550A, Baovi Corporation, USA. The interfacial tension is determined between
28
W.L. Kang et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 272 (2006) 27–31
chemical solutions and synthetic oil at 45 ◦ C. It reached equilibrium about 60 min at which time interfacial tension values were measured. • CIR-100 interfacial rheometer: Camtel Corporation Britain. CIR-100 Interfacial Rheometer, a stress controller in which there is minimum friction can record mechanical vibratory action, measure interfacial elastic modulus and interfacial viscosity by using a Pt/Ir Du Nouy ring. It can control the change of vibratory swing between −1◦ and +1◦ by using a high-accuracy amplitude sensor. • JI-100A weak electric properties measurement equipment: made in Nankai University. It is used to measure electric capacity and electric resistance of oil film by electric bridge principle. Cm = εS/dm, Cm denotes film electric capacity; S the film area; ε the film dielectric constant, therefore, high Cm value means thin film. 2.3. Procedures A synthetic oil was prepared by mixing purified kerosene and dewatered crude oil in the ratio of 7:3 (v/v) followed by adding treated production water from Daqing Oil Field to make a mode emulsion (ratio of the synthetic oil and the water was 5:4 (v/v)). The amounts (mg/L) of demulsifiers added were based on the volume of the emulsion. The demulsification of the emulsion was carried out by a bottle test at 45 ◦ C. The dewater amount is determined with time. The oil film was prepared in a hole of a Teflon cell wall between twin cells with solution in which electrodes were connected to JI-100A. The device is similar to one used in the artificial bilayers experiment. Testing conditions of oil–water interfacial rheological characteristics were: temperature at 45 ◦ C, under controlled stress mode with low-frequency scanning, referenced comparative samples are kerosene and re-distilled water. Testing procedures were: (1) testing ring is pegged on Interfacial Rheometer; (2) 8 mL water sample is added to sample cup by using syringe; (3) the sample cup was put on the Interfacial Rheometer; (4) the test board was raised to make Du Nouy ring immersed into water sample; (5) the test board was lowered to make testing ring set at water–air interface; (6) oil sample was evenly added to water interface; (7) finally, interfacial shear elastic modulus and interfacial shear viscosity were measured.
Fig. 1. The effect of the demulsifiers on oil film breaking.
film was broken. If there is demulsifier, the Cm value will increase gradually with time and oil film will break gradually. This indicated that demulsifier molecules were adsorbed gradually on oil–water interfacial film and replaced the emulsifiers. That replacement decreased both the strength and the life of oil film and film thickness until it collapsed. The life time of oil film (T) is defined as the time till the Cm value increases suddenly. The life time of oil film also indicates the strength of oil film. The effect of four demulsifiers on oil film life time is shown in Fig. 2, where the life time is plotted against demulsifier concentrations. The breaking rate of oil film was apparently accelerated with the addition of the demulsifiers. This indicates that some of the pre-existing interfacially active components are replaced by the demulsifier at the interface, which reduces the film strength and speeds up the interfacial film thinning. Oil film life time decreased with the increase of demulsifier concentration. When the concentration of demulsifier reached a certain level, film life time reached a plateau. This shows that the demulsifier molecules are adsorbed on the oil film, meanwhile film strength and stability decreased and the rate of oil film thinning and the demulsifying efficiency increased with increase of the demulsifier concentration. When the concentration is increased even more, the
3. Results and discussions 3.1. Effect of demulsifiers on oil–water interfacial film breaking The processes of oil film breaking with/without demulsifiers are shown in Fig. 1, where the oil film thickness, Cm is plotted with time. If there is no demulsifier in the system, the oil film thickness remains constant for a certain time once oil film has formed. The Cm value increased suddenly and oil
Fig. 2. The effect of the demulsifiers concentrations on the oil film life.
W.L. Kang et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 272 (2006) 27–31
Fig. 3. The effect of the different demulsifiers concentrations on the thinning rate of oil film.
demulsifiers are saturated at oil–water interface and the oil film life time remain constant. The effect of demulsifier concentration on the thinning rate of oil film is shown in Fig. 3. The Cm value is the measure of film thickness, so the curve of Cm versus time indicates the change of oil thickness with time. The thinning rate of film is the rate of decreasing film thickness. The rate of oil film thinning of a demulsifier at certain concentration can be expressed by a slope of the Cm–t curve (dCm/dt). With an increase of demulsifier concentration, the slope also increased (Fig. 3), which means that the amount of demulsifier adsorbed on the oil film increases with an increase of demulsifier concentration, and reduces the film strength and increases the rate of oil film thinning. The influence of demulsifier on the demulsifying dewatering efficiency is shown in Fig. 4. After 20 min of adding demulsifier, the dewatering rate (DWR) was calculated by measuring the amount of the emulsified water and freed water. With the increase in demulsifier concentration, the dewatering rate of emulsion increased. If the concentration of demulsifier is above a certain value (for example A concentration: 60 mg/L), the dewatering rate increased slowly with the demulsifier concentration. The demulsifying efficiency is related to oil film life time and thickness and dewatering rate of emulsion. The more oil film life time is reduced and the quicker the oil film thins, the more efficient the dewatering rate of emulsion shows. Analysis of the results showed that the interfacial elasticity decreased and the emulsifiers at the interfacial film were replaced by demulsifiers if they were used in this system, which decreased the strength and the life of oil film as well as film thickness. When the thinning of film thickness came to a critical value, the film broke. The effect of demulsifier concentration on interfacial tension between the synthetic oil–water interface is shown in Fig. 5. The interfacial tension decreased with the increase of demulsifier concentration. When the demulsifier concentration reached a certain level, interfacial tension drastically changed. The water-soluble and oil-soluble demulsifiers can decrease both the interfacial tension (IFT) and the interfacial viscosity (IFV), but the water-soluble demulsifiers C and D can decrease them to much lower level. Comparing the systems with the similar type of demulsifiers (Figs. 4–6),
29
Fig. 4. The effect of different demulsifiers concentrations on dewatering rate.
Fig. 5. The effect of demulsifiers concentrations on interfacial tensions between the synthetic oil–water.
the results indicate that the low IFT and IFV will improve demulsifying efficiency. That is, with the increase of demulsifier concentration, the interfacial tension and the interfacial viscosity decreased and dewatering rate increased. The IFT values are not well correlated with the demulsifying efficiency when comparing the systems with the different types of demulsifiers. All four demulsifiers A, B, C, and D can also decrease the oil–water interfacial elasticity (IFE). The low interfacial elasticity can improve the demulsifying efficiency no matter what types of demulsifiers are used in the emulsions (Figs. 7 and 4). So the interfacial elasticity is a dominant factor in determining the demulsifying efficiency.
Fig. 6. The effect of demulsifiers concentrations on interfacial viscosity between the synthetic oil–water.
30
W.L. Kang et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 272 (2006) 27–31
Fig. 9. The effect of 800 mg/L NP serials on the rate of oil film thinning. Fig. 7. The effect of demulsifiers on interfacial elasticity between the synthetic oil–water.
The interfacial elasticity decreases while the demulsifier is adsorbed and replaces the emulsifier at the interface, which decreases the strength and the life time of oil film as well as the film thickness. When the film thickness reaches a critical value, the film breaks. 3.2. Effect of chemical structures of demulsifiers on interfacial film Fig. 8 shows the effect of NPs polyoxyethylene numbers on dewatering rate of the synthetic emulsion and oil film life time. The dewatering rate of synthetic emulsion increases while oil film life time is shortened with increase of polyoxyethylene numbers. It indicates that there is correlation between NPs polyoxyethylene numbers and film life and demulsification efficiency. The slopes of Cm–t curves for NP series show an ascending trend with the numbers (Fig. 9). This also indicates that adsorption of demulsifiers at interface makes the strength of oil film decrease and the rate of oil film thinning increase. The interfacial tensions of synthetic oil–water decrease with the polyoxyethylene numbers (Fig. 10). The interfacial tension shows the same trends for the demulsifiers with less than 10 of NP as dewatering rate of synthetic emulsion (Figs. 8 and 10). There is no correlation between the two parameters but there is correlation between the interfacial
Fig. 8. The effect of 800 mg/L NP serials on the dewatering rate and oil film life.
Fig. 10. The effect of 800 mg/L NP serials on interfacial tensions between synthetic oil–water.
viscosity and elasticity of synthetic oil–water and the demulsification efficiency with the different NPs polyoxyethylene numbers (Figs. 11 and 8). The molecular structure of NP serials is linear. Its lipophile tail is not changed, but the head chain of polyoxyethylene is curled into water. The molecular average area of absorption at interface increases with the polyoxyethylene numbers. The molecules of demulsifiers adsorped at interface loosely. This leads to the changing of oil film life and interfacial properties. The effect of SA’s polyoxyethylene numbers on oil film life time and dewatering rate is shown in Fig. 12. There seems to be a good correlation between the two parameters on the vertical axis. The peak value of SA’s polyoxyethylene number
Fig. 11. The effect of 800 mg/L NP serials on interfacial viscosity and elasticity between synthetic oil–water.
W.L. Kang et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 272 (2006) 27–31
31
4. Conclusions
Fig. 12. The effect of 800 mg/L SA serials on the dewatering rate and oil film life.
(1) The oil film is stable first, then begins to be broken suddenly without demulsifier. The oil film is thinned gradually with a demulsifier, and finally breaks. There is a good correlation between oil film parameters and dewatering rates. (2) Interfacial viscosity and elasticity are important parameters in evaluating demulsifiers. The correlation between the interfacial tensions and the demulsification efficiency strongly depends on the demulsification system. (3) There is a correlation among NP’s polyoxyethylene numbers and film life and demulsification efficiency. There is a peak ratio and parameters between EO and PO number for different SAs. (4) The demulsification mechanism is that the demulsifiers partially replace the emulsifiers in the oil film, which leads to decrease in the interfacial viscosity and elasticity.
Acknowledgement
Fig. 13. The effect of 800 mg/L SA serials on the thinning rate of oil film.
is 35. Fig. 13 shows the rates of oil film thinning with SA’s polyoxyethylene numbers. It also indicates that there is the best combination of EO and PO number for different SAs. The interfacial tensions and the interfacial viscosity and elasticity with SA’s polyoxyethylene numbers are shown in Fig. 14. There is the same trend with polyoxyethylene numbers. The peak value, 35 is again found. This means that the number 35 is the worst ratio between EO and PO numbers for SA and the interfacial film strength is the strongest. SA serials are the types of multi-branch demulsifiers of phenol-formaldehyde resin polyoxyethylene polyoxypropylene. EO and PO are adsorbed by the way of multi-points at interface. When the ratio of EO and PO reaches a certain level, the interfacial properties are enormously affected.
Fig. 14. The effect of 800 mg/L NP serials on interfacial tensions, viscosity and elasticity of the synthetic oil and water.
We would like to thank Shirahama Keishiro, Professor Emeritus, Saga University; Sara Weaver, an English teacher and Yi Liu, my friend, NM, USA for their helpful revision.
References [1] W.L. Kang, D.M. Wang, Emulsification characteristic and deemulsifiers action for alkaline/surfactant/polymer flooding, SPE72138, 2001, pp. 8–9. [2] W.L. Kang, Y. Liu, B.Y. Qi, G.Z. Liao, Z.Y. Yang, J.C. Hong, Interactions between alkali surfactant/polymer and their effects on emulsion stability, Colloid. Surf. A 175 (1/2) (2000) 243–247. [3] W.L. Kang, X.L. Shan, A.H. Long, J.G. Li, Studies on demulsification mechanism of demulsifier for the three-compound combination flooding effluent emulsions, Chem. J. Chinese Univ. 20 (5) (1999) 759–761. [4] J.J. Qiao, M. Zhan, Study on the mechanism of petroleum emulsion’s breaking effect of interfacial tension on the effectiveness of demulsification, Acta Petrolei Sinica (Petrol. Process.) 15 (2) (1999) 1– 2. [5] Foyeke O. Opawale, Diane J. Burgess, Influence of interfacial properties of lipophilic surfactants on water-in-oil emulsion stability, J. Colloid Sci. 197 (1998) 142–150. [6] R.A. Mohammed, A.I. Bailey, P.F. Luckham, S.E. Taylor, Dewatering of crude oil emulsions. 3. Emulsion resolution by chemical means, Colloid. Surf. A 83 (1994) 261. [7] M.Y. Li, P. Zhen, Study of crude emulsifiable liquid stability. VI. Interfacial film character and crude emulsifiable liquid stability, Acta Petrolei Sinica (Petrol. Process.) 14 (3) (1998) 1–5. [8] J. Sjoblom, H. Sonderlund, S. Lindblad, E.J. Johansen, I.M. Skjarvo, Water-in-crude oil emulsions from the Norwegian continental shelf. Part II. Chemical destabilization and interfacial tensions, Colloid Polym. Sci. 268 (1990) 389–398. [9] L.L. Schramm (Ed.), Petroleum emulsions—basic principles, in: Emulsions: Fundamentals and Applications in the Petroleum Industry, American Chemical Society, Washington, DC, 1992, pp. 1–49.
Influence of demulsifier on interfacial film between oil and water夽 Wanli Kang a,∗ , Guolin Jing a , Hongyan Zhang a , Mingyuan Li b , Zhaoliang Wu b a
Daqing Petroleum Institute, Daqing, 163318 Heilongjiang, China b Petroleum University, Beijing102249, China
Received 24 July 2004; received in revised form 4 July 2005; accepted 8 July 2005 Available online 16 August 2005
Abstract Demulsification of a synthetic water in oil (W/O) crude oil emulsion was studied by measuring water–oil interfacial properties such as life time and thinning rate of oil film in the presence of various demulsifiers. The results indicated that the interfacial elasticity decreased both the strength and the life time of oil film and film thickness when adding the demulsifiers. The oil film broke when film thickness came to a critical level. As for a demulsifier, the interfacial elasticity was decreased with demulsifier concentration increase, and stayed constant above a critical demulsifier concentration. The rate of dewatering is related to interfacial elasticity. When different demulsifiers were compared, the more the interfacial elasticity was lowered, the more efficient was the dewatering. The mechanism of the different types of demulsifiers was discussed based on the experimental results. The demulsifiers partially replaced the emulsifiers, which led to the interfacial elasticity decreased. The effect of chemical structure of the demulsifiers on water–oil interfacial film was studied. © 2005 Elsevier B.V. All rights reserved. Keywords: Demulsifier; Oil film life; Thinning rate of oil film; Interfacial tension; Interfacial viscosity; Interfacial elasticity; Dewatering rate
1. Introduction
2. Experimental
There have been many studies on stability and demulsification of crude oil emulsions reported by many investigators [1–6]. These studies are more focused on effects of interfacial tension and interfacial viscosity rather than on the oil film life time, the thinning rate of oil film and interfacial elasticity of the film. The demulsification mechanism of demulsifiers is quite complicated, and no demulsifier can be applied to break all kinds of crude oil emulsions [7–9]. In this paper, demulsification of a synthetic emulsion (W/O) is studied by focusing on oil film life time, thinning rate of the film, and interfacial properties between oil and water in the presence of various of demulsifiers.
2.1. Materials
夽 Supported by the Outstanding Youth Science Foundation of Heilongjiang
(J03-11) and NSFC (10172028). ∗ Corresponding author. E-mail address: [email protected] (W.L. Kang). 0927-7757/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2005.07.004
• Crude oil: Daqing Oil Field, PR. China. • Emulsifier: Span 80, Liaoyang Aoke Chemical Company. • Demulsifier: the demulsifiers used were denoted as A, B, C and D. A and B are of the type of phenol-formaldehyde resin polyoxyethylene (EO) polyoxypropylene (PO); C and D of polyoxyethylene polyoxypropylene polymers obtained from Liaoyang Aoke Chemical Company. • NP serials: nonyl phenol polyoxyethylene(4,6,8,10,15), the number represents polyoxyethylene molecule number. • SA serials: phenol-formaldehyde resin polyoxyethylene polyoxypropylene(20,25,30,35,40,45), the number represents weight percent of polyoxyethylene. 2.2. Equipments • Interfacial tensiometer: TX550A, Baovi Corporation, USA. The interfacial tension is determined between
28
W.L. Kang et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 272 (2006) 27–31
chemical solutions and synthetic oil at 45 ◦ C. It reached equilibrium about 60 min at which time interfacial tension values were measured. • CIR-100 interfacial rheometer: Camtel Corporation Britain. CIR-100 Interfacial Rheometer, a stress controller in which there is minimum friction can record mechanical vibratory action, measure interfacial elastic modulus and interfacial viscosity by using a Pt/Ir Du Nouy ring. It can control the change of vibratory swing between −1◦ and +1◦ by using a high-accuracy amplitude sensor. • JI-100A weak electric properties measurement equipment: made in Nankai University. It is used to measure electric capacity and electric resistance of oil film by electric bridge principle. Cm = εS/dm, Cm denotes film electric capacity; S the film area; ε the film dielectric constant, therefore, high Cm value means thin film. 2.3. Procedures A synthetic oil was prepared by mixing purified kerosene and dewatered crude oil in the ratio of 7:3 (v/v) followed by adding treated production water from Daqing Oil Field to make a mode emulsion (ratio of the synthetic oil and the water was 5:4 (v/v)). The amounts (mg/L) of demulsifiers added were based on the volume of the emulsion. The demulsification of the emulsion was carried out by a bottle test at 45 ◦ C. The dewater amount is determined with time. The oil film was prepared in a hole of a Teflon cell wall between twin cells with solution in which electrodes were connected to JI-100A. The device is similar to one used in the artificial bilayers experiment. Testing conditions of oil–water interfacial rheological characteristics were: temperature at 45 ◦ C, under controlled stress mode with low-frequency scanning, referenced comparative samples are kerosene and re-distilled water. Testing procedures were: (1) testing ring is pegged on Interfacial Rheometer; (2) 8 mL water sample is added to sample cup by using syringe; (3) the sample cup was put on the Interfacial Rheometer; (4) the test board was raised to make Du Nouy ring immersed into water sample; (5) the test board was lowered to make testing ring set at water–air interface; (6) oil sample was evenly added to water interface; (7) finally, interfacial shear elastic modulus and interfacial shear viscosity were measured.
Fig. 1. The effect of the demulsifiers on oil film breaking.
film was broken. If there is demulsifier, the Cm value will increase gradually with time and oil film will break gradually. This indicated that demulsifier molecules were adsorbed gradually on oil–water interfacial film and replaced the emulsifiers. That replacement decreased both the strength and the life of oil film and film thickness until it collapsed. The life time of oil film (T) is defined as the time till the Cm value increases suddenly. The life time of oil film also indicates the strength of oil film. The effect of four demulsifiers on oil film life time is shown in Fig. 2, where the life time is plotted against demulsifier concentrations. The breaking rate of oil film was apparently accelerated with the addition of the demulsifiers. This indicates that some of the pre-existing interfacially active components are replaced by the demulsifier at the interface, which reduces the film strength and speeds up the interfacial film thinning. Oil film life time decreased with the increase of demulsifier concentration. When the concentration of demulsifier reached a certain level, film life time reached a plateau. This shows that the demulsifier molecules are adsorbed on the oil film, meanwhile film strength and stability decreased and the rate of oil film thinning and the demulsifying efficiency increased with increase of the demulsifier concentration. When the concentration is increased even more, the
3. Results and discussions 3.1. Effect of demulsifiers on oil–water interfacial film breaking The processes of oil film breaking with/without demulsifiers are shown in Fig. 1, where the oil film thickness, Cm is plotted with time. If there is no demulsifier in the system, the oil film thickness remains constant for a certain time once oil film has formed. The Cm value increased suddenly and oil
Fig. 2. The effect of the demulsifiers concentrations on the oil film life.
W.L. Kang et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 272 (2006) 27–31
Fig. 3. The effect of the different demulsifiers concentrations on the thinning rate of oil film.
demulsifiers are saturated at oil–water interface and the oil film life time remain constant. The effect of demulsifier concentration on the thinning rate of oil film is shown in Fig. 3. The Cm value is the measure of film thickness, so the curve of Cm versus time indicates the change of oil thickness with time. The thinning rate of film is the rate of decreasing film thickness. The rate of oil film thinning of a demulsifier at certain concentration can be expressed by a slope of the Cm–t curve (dCm/dt). With an increase of demulsifier concentration, the slope also increased (Fig. 3), which means that the amount of demulsifier adsorbed on the oil film increases with an increase of demulsifier concentration, and reduces the film strength and increases the rate of oil film thinning. The influence of demulsifier on the demulsifying dewatering efficiency is shown in Fig. 4. After 20 min of adding demulsifier, the dewatering rate (DWR) was calculated by measuring the amount of the emulsified water and freed water. With the increase in demulsifier concentration, the dewatering rate of emulsion increased. If the concentration of demulsifier is above a certain value (for example A concentration: 60 mg/L), the dewatering rate increased slowly with the demulsifier concentration. The demulsifying efficiency is related to oil film life time and thickness and dewatering rate of emulsion. The more oil film life time is reduced and the quicker the oil film thins, the more efficient the dewatering rate of emulsion shows. Analysis of the results showed that the interfacial elasticity decreased and the emulsifiers at the interfacial film were replaced by demulsifiers if they were used in this system, which decreased the strength and the life of oil film as well as film thickness. When the thinning of film thickness came to a critical value, the film broke. The effect of demulsifier concentration on interfacial tension between the synthetic oil–water interface is shown in Fig. 5. The interfacial tension decreased with the increase of demulsifier concentration. When the demulsifier concentration reached a certain level, interfacial tension drastically changed. The water-soluble and oil-soluble demulsifiers can decrease both the interfacial tension (IFT) and the interfacial viscosity (IFV), but the water-soluble demulsifiers C and D can decrease them to much lower level. Comparing the systems with the similar type of demulsifiers (Figs. 4–6),
29
Fig. 4. The effect of different demulsifiers concentrations on dewatering rate.
Fig. 5. The effect of demulsifiers concentrations on interfacial tensions between the synthetic oil–water.
the results indicate that the low IFT and IFV will improve demulsifying efficiency. That is, with the increase of demulsifier concentration, the interfacial tension and the interfacial viscosity decreased and dewatering rate increased. The IFT values are not well correlated with the demulsifying efficiency when comparing the systems with the different types of demulsifiers. All four demulsifiers A, B, C, and D can also decrease the oil–water interfacial elasticity (IFE). The low interfacial elasticity can improve the demulsifying efficiency no matter what types of demulsifiers are used in the emulsions (Figs. 7 and 4). So the interfacial elasticity is a dominant factor in determining the demulsifying efficiency.
Fig. 6. The effect of demulsifiers concentrations on interfacial viscosity between the synthetic oil–water.
30
W.L. Kang et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 272 (2006) 27–31
Fig. 9. The effect of 800 mg/L NP serials on the rate of oil film thinning. Fig. 7. The effect of demulsifiers on interfacial elasticity between the synthetic oil–water.
The interfacial elasticity decreases while the demulsifier is adsorbed and replaces the emulsifier at the interface, which decreases the strength and the life time of oil film as well as the film thickness. When the film thickness reaches a critical value, the film breaks. 3.2. Effect of chemical structures of demulsifiers on interfacial film Fig. 8 shows the effect of NPs polyoxyethylene numbers on dewatering rate of the synthetic emulsion and oil film life time. The dewatering rate of synthetic emulsion increases while oil film life time is shortened with increase of polyoxyethylene numbers. It indicates that there is correlation between NPs polyoxyethylene numbers and film life and demulsification efficiency. The slopes of Cm–t curves for NP series show an ascending trend with the numbers (Fig. 9). This also indicates that adsorption of demulsifiers at interface makes the strength of oil film decrease and the rate of oil film thinning increase. The interfacial tensions of synthetic oil–water decrease with the polyoxyethylene numbers (Fig. 10). The interfacial tension shows the same trends for the demulsifiers with less than 10 of NP as dewatering rate of synthetic emulsion (Figs. 8 and 10). There is no correlation between the two parameters but there is correlation between the interfacial
Fig. 8. The effect of 800 mg/L NP serials on the dewatering rate and oil film life.
Fig. 10. The effect of 800 mg/L NP serials on interfacial tensions between synthetic oil–water.
viscosity and elasticity of synthetic oil–water and the demulsification efficiency with the different NPs polyoxyethylene numbers (Figs. 11 and 8). The molecular structure of NP serials is linear. Its lipophile tail is not changed, but the head chain of polyoxyethylene is curled into water. The molecular average area of absorption at interface increases with the polyoxyethylene numbers. The molecules of demulsifiers adsorped at interface loosely. This leads to the changing of oil film life and interfacial properties. The effect of SA’s polyoxyethylene numbers on oil film life time and dewatering rate is shown in Fig. 12. There seems to be a good correlation between the two parameters on the vertical axis. The peak value of SA’s polyoxyethylene number
Fig. 11. The effect of 800 mg/L NP serials on interfacial viscosity and elasticity between synthetic oil–water.
W.L. Kang et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 272 (2006) 27–31
31
4. Conclusions
Fig. 12. The effect of 800 mg/L SA serials on the dewatering rate and oil film life.
(1) The oil film is stable first, then begins to be broken suddenly without demulsifier. The oil film is thinned gradually with a demulsifier, and finally breaks. There is a good correlation between oil film parameters and dewatering rates. (2) Interfacial viscosity and elasticity are important parameters in evaluating demulsifiers. The correlation between the interfacial tensions and the demulsification efficiency strongly depends on the demulsification system. (3) There is a correlation among NP’s polyoxyethylene numbers and film life and demulsification efficiency. There is a peak ratio and parameters between EO and PO number for different SAs. (4) The demulsification mechanism is that the demulsifiers partially replace the emulsifiers in the oil film, which leads to decrease in the interfacial viscosity and elasticity.
Acknowledgement
Fig. 13. The effect of 800 mg/L SA serials on the thinning rate of oil film.
is 35. Fig. 13 shows the rates of oil film thinning with SA’s polyoxyethylene numbers. It also indicates that there is the best combination of EO and PO number for different SAs. The interfacial tensions and the interfacial viscosity and elasticity with SA’s polyoxyethylene numbers are shown in Fig. 14. There is the same trend with polyoxyethylene numbers. The peak value, 35 is again found. This means that the number 35 is the worst ratio between EO and PO numbers for SA and the interfacial film strength is the strongest. SA serials are the types of multi-branch demulsifiers of phenol-formaldehyde resin polyoxyethylene polyoxypropylene. EO and PO are adsorbed by the way of multi-points at interface. When the ratio of EO and PO reaches a certain level, the interfacial properties are enormously affected.
Fig. 14. The effect of 800 mg/L NP serials on interfacial tensions, viscosity and elasticity of the synthetic oil and water.
We would like to thank Shirahama Keishiro, Professor Emeritus, Saga University; Sara Weaver, an English teacher and Yi Liu, my friend, NM, USA for their helpful revision.
References [1] W.L. Kang, D.M. Wang, Emulsification characteristic and deemulsifiers action for alkaline/surfactant/polymer flooding, SPE72138, 2001, pp. 8–9. [2] W.L. Kang, Y. Liu, B.Y. Qi, G.Z. Liao, Z.Y. Yang, J.C. Hong, Interactions between alkali surfactant/polymer and their effects on emulsion stability, Colloid. Surf. A 175 (1/2) (2000) 243–247. [3] W.L. Kang, X.L. Shan, A.H. Long, J.G. Li, Studies on demulsification mechanism of demulsifier for the three-compound combination flooding effluent emulsions, Chem. J. Chinese Univ. 20 (5) (1999) 759–761. [4] J.J. Qiao, M. Zhan, Study on the mechanism of petroleum emulsion’s breaking effect of interfacial tension on the effectiveness of demulsification, Acta Petrolei Sinica (Petrol. Process.) 15 (2) (1999) 1– 2. [5] Foyeke O. Opawale, Diane J. Burgess, Influence of interfacial properties of lipophilic surfactants on water-in-oil emulsion stability, J. Colloid Sci. 197 (1998) 142–150. [6] R.A. Mohammed, A.I. Bailey, P.F. Luckham, S.E. Taylor, Dewatering of crude oil emulsions. 3. Emulsion resolution by chemical means, Colloid. Surf. A 83 (1994) 261. [7] M.Y. Li, P. Zhen, Study of crude emulsifiable liquid stability. VI. Interfacial film character and crude emulsifiable liquid stability, Acta Petrolei Sinica (Petrol. Process.) 14 (3) (1998) 1–5. [8] J. Sjoblom, H. Sonderlund, S. Lindblad, E.J. Johansen, I.M. Skjarvo, Water-in-crude oil emulsions from the Norwegian continental shelf. Part II. Chemical destabilization and interfacial tensions, Colloid Polym. Sci. 268 (1990) 389–398. [9] L.L. Schramm (Ed.), Petroleum emulsions—basic principles, in: Emulsions: Fundamentals and Applications in the Petroleum Industry, American Chemical Society, Washington, DC, 1992, pp. 1–49.