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Optimization of chemical demulsifications of water in crude oil emulsions
Egyptian Journal of Petroleum xxx (xxxx) xxx
Contents lists available at ScienceDirect
Egyptian Journal of Petroleum journal homepage: www.sciencedirect.com
Full Length Article
Optimization of chemical demulsifications of water in crude oil emulsions Olusiji Ayoade Adeyanju a,⇑, Layioye Ola Oyekunle b a b
Department of Chemical and Petroleum Engineering, University of Lagos, Nigeria Department of Petroleum Engineering, Covenant University, Otta, Ogun State, Nigeria
a r t i c l e
i n f o
Article history: Received 17 January 2019 Revised 18 July 2019 Accepted 28 July 2019 Available online xxxx Keywords: Operating parameters Intermolecular interaction Mixing time Optimal conditions Demulsification
a b s t r a c t The instability of the water in crude oil emulsion and separation of the dispersed water as free water are influenced by the emulsion properties and the operating parameters during the demulsification process. This study aims to relate these properties/operating parameters to the amount of separated water. Steps were taken to determine and validate the optimal separations that can be achieved. Six operating parameters were identified through sensitivity analyses to have an energetic effect on percentage water separation. The bottle test method was used on two different samples of water in oil synthetic emulsions (sample A and B from different Nigerian oil fields). Response surface methodology central composite design (RSMCCD) was used to design the experiment, and generate the desired regression equations/ models. Results show that optimum percentage water separations of 93 and 95% (V/V) were achieved with the emulsions A and B respectively using the combination of the optimal variables derived from the model equations. These were improvements from percentage water separations of 80 and 83% (V/V) achieved using the two crude oil samples in their naturally occurring state when the properties of the emulsions were not enhanced to their determined optimal operating conditions. Ó 2019 Egyptian Petroleum Research Institute. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction A high percentage of the world produced crude oils exist in form of emulsions. Most of the emulsions are in the form of water-in-oil (w/o) type. For operational, economic and environmental reasons, there is a need to separate the water from the oil in the water in oil emulsion before their transportation and processing. Previous studies in the field of physical chemistry and surface phenomena had succeeded in the efficient demulsification of water-in-oil emulsion [1,2]. The intermolecular interaction forces in emulsion are active and couple with the surface tension at the phase boundaries makes the liquids inherent in the emulsion to have the tendency of reducing their surface area to the minimum. These made the individual drops to coagulate and form bigger droplets. The coagulation of dispersed water in the continuous oil phase made their separation imminent [3–5]. Therefore any variables/properties of the emulsion that affect the surface tension at the interphase between
Peer review under responsibility of Egyptian Petroleum Research Institute. ⇑ Corresponding author. E-mail addresses: [email protected] (O.A. Adeyanju), layioyekunle@ yahoo.com (L.O. Oyekunle).
the dispersed water phase and the continuous oil phase in the emulsion will influence the rate of water separation from the water in oil emulsion. The basis of this study is to investigate the effect of such parameter on the separated water during the demulsification process.
2. Literature review Different components/surfactants have been identified to be responsible for the emulsion stability, these include asphaltenes, resins and oil soluble organic acids (e.g. naphthenic, carboxylic) and bases. These components also called emulsifiers constitute the interfacial films that surround the dispersed water in the water in oil emulsion [6–8]. Studies show that the instability of the emulsion and separation of the dispersed water as free water are influenced by the emulsion properties and the operating parameters [9]. Fortuny et al., [10] in their study of the effect of salinity, temperature, water content and pH on crude oil emulsion stability concluded that the emulsion containing high water content are characterized by a high rate of demulsification except for crude of high pH and salt contents. The effects of most of the properties of the emulsions on the de-emulsification of different water in oil
https://doi.org/10.1016/j.ejpe.2019.07.002 1110-0621/Ó 2019 Egyptian Petroleum Research Institute. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Please cite this article as: O. A. Adeyanju and L. O. Oyekunle, Optimization of chemical demulsifications of water in crude oil emulsions, Egyptian Journal of Petroleum, https://doi.org/10.1016/j.ejpe.2019.07.002
2
O.A. Adeyanju, L.O. Oyekunle / Egyptian Journal of Petroleum xxx (xxxx) xxx
emulsions are still matters of controversies [11]. Abdulkadir, [12] in an effort of identifying the most effective combination of operating parameters at which an identified demulsifier can be applied through the comparative analysis of different demulsifiers on a Nigerian crude oil concluded that the demulsifier is best applied at a temperature of 60 °C at a concentration of 50 ppm. Different methods are on-going to optimize the demulsifications of crude oil emulsions [13–15].
Table 2 Range of experimental parameters used. Parameters
Range
Temperatures Mixing time of the demulsifier with the crude sample pH of the crude sample Demulsifier concentration Modifier (Methanol) concentration Crude oil salt content
30–70 °C 1–7 min 4.0–12.0 20–140 ppm 20–100 ppm 0.02–0.18 g/ml
3. Materials and methods
Fraction of separated water
3.1. Crude oils properties
¼ Two crude oils (crude oil A and B) with low basic sediments and water (BS&W) of 0.7 and 0.95% respectively were obtained from two different fields flow stations in Southern Nigeria. The bottle test method was used in the evaluation of the percentage of water separated. The properties of the two used crude oils are tabulated in Table 1. 3.2. Chemicals and equipment The demulsifier, acids, alkaline, and alcohol were supplied by Finlab Nigeria Limited, the emulsifier; sodium dodecyl sulphate (SDS) and the commercial demulsifier (Basorol E 2032) were supplied by MON Scientific (Nigeria) Limited. The homogenizer used is the SAMRO SRH60-70 homogenizer manufactured by ShangHai amro homogenizer CO., LTD. 3.3. Emulsion preparation The experimental studies were carried out using synthetic emulsions prepared from crude oils and water samples sourced from the crude oil and water outlets of a heater-treater located in the above mentioned fields flow stations of the southern Nigerian. The emulsion preparation was described in an earlier study [16]. 3.4. Methodology The bottle tests were performed with several 15 ml. of emulsified crude oils at varying operating parameters tabulated in the Table 2 below: The Minital-16 software was used in designing the experiments using the aforementioned operating parameters as the independent variables. A total of ninety (90) experiments were conducted on each of the two (2) crude oils and the response was the fraction of water that separated out of the emulsified crude oil. The percentage of water separated is given as:
Volume of separated water; mL Original v olume of water in the emulsified oil; mL
ð1Þ
4. Results and discussions 4.1. Sensitivity analyses Sensitivity analyses were performed on the water in crude oil de-emulsification process using the aforementioned parameters: Temperature, demulsifier concentration, mixing time, pH, salt concentration and modifier concentration. The analyses help to highlight the impact of each of the parameter change on the demulsification process. These were achieved by varying the input (reference) parameters individually, while the others are kept constants. Fig. 1 shows the results of the sensitivity analyses for each of the operating parameters on percentage water separation. Results show that the percentage water separated increases at the decreasing rate as each of the parameter/variable increases, reaching a peak (maximum/optimum value). The reference operating parameters used for the sensitivity analyses in Fig. 1 were Temperature = 60 °C, demulsifier concentration = 80 ppm, mixing time = 3.5 min, pH = 8, salt content (salinity) = 0.08 g/ml and Modifier concentration = 60 ppm. 4.1.1. Effect of temperature Fig. 1 shows that the amount of separated water increases with the temperature. This is due to increase in the rate of collisions and coalescence of the emulsified water particles in the crude oil, resulting in water droplets separation due to gravity as results of density difference between the coalescence water droplets and the crude oil. Also, increased temperature causes the destabilization of the water-oil interfacial surface that promotes the demulsification of water in the crude oil. The rate of water separated per degree Celsius (°C) rise in temperature decreases from 0.7 to 0.4 V/(V°C) as the temperature varies between 20 and 200% of the reference temperature for crude oil A. This is due to reduction
Table 1 Properties of the two crude oils and their measurement methods. Properties
Experimental Measurement Method
Crude oil sample Oil-A
Oil-B
Gravity at 28 °C, API Pour point, °C Viscosity at 28 °C, cp Salt content, (g/m3) Asphaltene (%) Resin (%) Basic Sediment and Water BS&W (%) Saturated Hydrocarbon (%) Aromatic Hydrocarbon, (%)
ASTM-D5002-16 ASTM-D97-66 ASTM-D445 ASTM-D6470-99 (2015) ASTM-D7-5 (06560) ASTM-D893-69 ASTM-D4007-02
42 29 8.8 18.5 0.21 23.7 0.7
28 22 9.1 15 0.17 17.6 0.95
ASTM-D2786-91 (2016) ASTM-D3238-95 (2015)
38 17.24
29 26.45
Fig. 1. Effect of Different Operating Parameters (variables) on Percentage Water Separated.
Please cite this article as: O. A. Adeyanju and L. O. Oyekunle, Optimization of chemical demulsifications of water in crude oil emulsions, Egyptian Journal of Petroleum, https://doi.org/10.1016/j.ejpe.2019.07.002
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O.A. Adeyanju, L.O. Oyekunle / Egyptian Journal of Petroleum xxx (xxxx) xxx
in the rate of emulsified water collisions as less emulsified waters were available for such collision. 4.1.2. Effect of demulsifier concentrations As the concentration of the commercial demulsifier (Basorol E 2032) increases the percentage of water separated increases due to increase in demulsifier available for the destabilization of oilwater interface medium. The rate of water separation per unit addition of demulsifier was observed to drop for both crude oils, reducing from 0.8 to 0.2 V/(Vppm) and from 0.9 to 0.2 V/(Vppm) for crude oil A and B respectively. This is due to the combined effect of the decrease in the amount of emulsified water available for demulsification process and increases in resistance to the destabilization process at the water-oil interface as a result of the reduction in water to crude oil ratio in the crude oil emulsions. 4.1.3. Effect of mixing time Increasing the time of mixing of the demulsifier with the emulsified crude oil increases the amount of water separated from the water in crude oil emulsion. This is due to an increase in the ability of the demulsifier to gain access to the oil-water interface sustaining the emulsified water in the emulsions, destabilizing it and make the coalescence and separations of emulsified water inevitable. The rate of separated water in respect to time in minute reduces as mixing time increases, reducing from 0.3 to 0.1 V(V/minute) for crude oil A. These inferred that there is optimum stirring/mixing time beyond which the action will results in the creation of more emulsified water and making the rate of water separation increasingly difficult. 4.1.4. Effect of pH The effect of pH on the demulsification process was studied by addition of hydrochloric acid (HCl) or sodium hydroxide (NaOH) (depending on the intended pH) to the water phase prior to emulsion preparation. The Fig. 1 shows that the water in crude oil emulsion achieved the highest stability at both the alkaline and acidic medium, with the emulsion becoming more stable as the alkalinity or acidity increases, as exhibit by the consistent reduction in the percentage of separated water collected from the experiments. The highest instabilities of the emulsified crude oils occur around the neutral pH of 9.0 and 8.0 for crude oil A and B respectively. This is due to the polarity of the water in the alkaline and acidic medium which increased the electrostatic repulsion resulting in the destabilization of the interfacial properties of the water oil emulsion thereby stabilizing the emulsion. 4.1.5. Effect of salt content (salinity) The effect of salt content on the percentage water separation was studied for each of the crude oil by adding between 0.02 and 0.18 g/mL of sodium chloride (NaCl) respectively to each of the aqueous water content prior to their use for emulsion preparation. An equal amount (20 ppm) of the same demulsifier was added to each of the ten prepared samples with varying salts (NaCl) content. The salt seems to aid in the demulsification of the emulsified water in the water in crude oil emulsions. This is in agreement with previous studies [10,12]. The salt ions seem to have an adverse effect on the water-oil interfacial film holding the emulsified water in the water in oil emulsions.
while the short chain alcohol are soluble in water. Hence short chain alcohols is efficient for water separation in water in oil emulsion due to its ability to diffuse through the interfacial film into the emulsified water contained in the continuous oil phase. While the long chain alcohols are preferred in the crude oil in water emulsion. 4.2. Model equations Successful identification of the effects of operating parameters: temperature, demulsifier concentration, modifier (methanol) concentration, pH, salt content and mixing time on the percentage of separated water from each of the water in oil emulsions, warranted the efforts to relate these operating parameters to the percentage water separated for each of the studied crude samples. The six operating parameters were constraints to the ranges stated in Table 2. Minitab-16 software was used to design the experiments, formulate the models (empirical) and analyze the results. A total of ninety (90) experiments organized in factorial design were conducted on each of the two emulsion samples. The response selected for analyses was the percentage of water separated (V/V) from the water in crude oil emulsions given by Eq. (1). For crude oil emulsion prepared from crude oil A, the empirical model equation is given as: W sep ð%Þ ¼ 6:872 þ 0:00346T þ 0:423M t þ 0:465P h þ 0:722Dc þ 0:817Sc þ0:138M c 0:00342T 2 0:0125M 2t 0:0472P 2h 0:00107D2c 0:0251S2c þ 0:00261TDc ð2Þ
where T = temperature (°C), Mt = mixing time (minute), Ph = pH of emulsion, Dc = demulsifier concentration (ppm), Sc = salt content (g/ml), Mc = Modifier concentration (ppm) and Wsep (%) = percentage water separation. The model’s terms in the equations are those that are left after the insignificant variables and interactions have been eliminated. For emulsion prepared from crude oil B, the model equation was given as: W sep ð%Þ ¼ 9:143 þ 0:334T þ 0:404M t þ 0:452P h þ 0:725Dc þ 0:791Sc þ0:133M c 0:00338T 2 0:0138M 2t 0:0441P 2h 0:00116D2c 0:0262S2c þ 0:00279TDc ð3Þ
The statistical analyses show that the model equations for both crude samples were highly significant with very low probability values (P < 0.001) i.e. the probability of incorrect prediction by the model due to experimental error or noise factors is small. In furtherance to the efforts in testing the model validity, the lack of fit results was not statistically significant as the P-values were 0.297 and 0.365 for crude oil A and B respectively. The model affirms the significant influences of the identified properties/variables: temperature, demulsifier concentration, mixing time, salt content, pH, and modifier concentration in the separation of emulsified water from the water in crude oil emulsion judging by their P-values below 0.05. 4.3. Response contour plots
4.1.6. Effect of emulsion modifier Previous studies [16,17] showed that alcohol can be used as a modifier to help in the demulsification process. Alcohols tend to reduce the effectiveness of the interfacial film between the emulsified water and the continuous crude oil phase in the water in oil emulsions. The compositions of the interfacial films are mainly water and oil and the long chain alcohol are soluble in crude oil
The interactive effects of the variables on each other were investigated using the contour plots generated with Minitab-16 software. The two dimensional contour plots were based on the developed models by each crude oil with four variables kept constant at their coded zero levels, while varying the other two variables.
Please cite this article as: O. A. Adeyanju and L. O. Oyekunle, Optimization of chemical demulsifications of water in crude oil emulsions, Egyptian Journal of Petroleum, https://doi.org/10.1016/j.ejpe.2019.07.002
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O.A. Adeyanju, L.O. Oyekunle / Egyptian Journal of Petroleum xxx (xxxx) xxx
Fig. 2. Contour Plots of Percentage Water Separation against Temperature and Demulsifier Concentration.
Fig. 2 shows the interactive effect of the temperature and the demulsifier concentration on each other. The figure shows that as the temperature increases from 0 to 90 °C and demulsifier’s concentration increases from 0 to 250 ppm, more than 80% (V/V) of the emulsified water was separated. At the temperature of between 0 and 62 °C and demulsifiers concentration of between 0 and 100 ppm, the percentage of separated water was less than 15% (V/V). When the temperature was increased to above 62 °C and the demulsifier concentration was raised above 150 ppm there was a tremendous increase in the percentage water separated rising to as much as 85% (V/V). Fig. 3 shows the contours plot of percentage of water separated against mixing time and pH value. It was shown that keeping other variables constant at their hold values, the just a little above 30% of water was separated from the emulsion when the pH values were varied between 1 and 14 and mixing time increased from 1 to 10 min. Thus, confirming the fact that the effects of pH values on the separated water were not as significant as that of temperature and demulsifier concentration. 4.4. Models optimization The model equations were optimized by settling the partial derivatives of the equation to zero with respect to the corresponding variables to determine the stationary variables. Results show that the second derivatives in respect to each of the variables were
negatives an indication that the stationary values were at the maximum points. The optimum values of each variable from the model/regression equation developed from emulsion prepared from crude oil A were evaluated as: T = 87 °C, Mt = 10.5 min, Ph = 8.0, Dc = 254 ppm, Sc = 0.332 g/ml, Mc = 185 ppm producing percentage water separation, Wsep (%) = 97.32%. Similar results of T = 82.2 °C, Mt = 11.8 min, Ph = 7.4, Dc = 268 ppm, Sc = 0.325 g/ml, Mc = 235 ppm were obtain for model equation developed from emulsion prepared from crude oil B, generating an optimum water separation of 98.57%
4.5. Model validation In an effort to validate the optimum water separation generated from the regression equations/models, experiments were conducted with emulsions prepared from crude oil A and B using the generated optimum values of each parameter from the software. Percentage water of 93 and 95% (V/V) was successfully separated from water in oil emulsions prepared from crude oil A and B respectively. The closeness of the percentage water separated from experimental run to the result generated from the model, (differences of 4.44 and 3.62% (V/V) for crude oil A and B respectively) further confirms the effectiveness of the models to relate the percentage water separation to the operating parameters.
Fig. 3. Contour Plots of Percentage Water Separation against pH values and mixing time.
Please cite this article as: O. A. Adeyanju and L. O. Oyekunle, Optimization of chemical demulsifications of water in crude oil emulsions, Egyptian Journal of Petroleum, https://doi.org/10.1016/j.ejpe.2019.07.002
O.A. Adeyanju, L.O. Oyekunle / Egyptian Journal of Petroleum xxx (xxxx) xxx
5. Conclusion It was shown that the emulsions prepared from the two crude oil samples from two petroleum field in southern Nigeria have different model equations that relate the percentage of water separated to the operating/emulsion parameters. The separated water was observed to depend on the operating/emulsion parameters which include: temperature, demulsifier concentration, mixing time, salt content, pH values, and modifier concentration. The temperature, demulsifier concentration and mixing time were observed to predominate the separation process while the effect of pH values, salt content, and modifier concentration was relatively lower. Optimum percentage water separations of 93 and 95% were achieved with the emulsions prepared from crude oil A and B respectively using the combination of the optimal variables generated from the software. This is an improvement from the highest values of 81 and 87% (V/V) separated water achieved from emulsions prepared from crude oil A and B respectively when the designed experiments were performed with emulsions, whose properties were not at the optimum values. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. References [1] A.N. Dimitrov, D.I. Yordanov, P.S. Petkov, Study on the effect of demulsifiers on crude oil and petroleum products, Int. J. Environ. Res. 6 (2) (2012) 435–442. [2] E.D. Shchukin, A.V. Pertsov, E.A. Amelina, A.S. Zelenev, Colloid Surf. Chem. 12 (2001) 583–664, Elsevier.
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[3] Y.G. Frolov, Adsorbed surface layers and thermodynamic aggregation stability of dispersed system, Colloidnyj Zhurnal 57 (2) (1995) 247–251. [4] E.D. Shchukin, The influence of surface-active media on the mechanical properties of materials, Adv. Colloid Interface Sci. 123–126 (2006) 33–47. [5] E.D. Shchukin, A.I. Bessonov, S.I. Kontorovich, I.N. Polukarova, E.A. Amelina, I.N. Burenkova, B. Romanovsky, V, Effects of adsorption-active media on the mechanical properties of catalysts and adsorbents, Colloids Surf. A: Physicochem. Eng. Aspect 282–283 (2006) 287–297. [6] S.L. Kokal, J.I. Al-Juraid, Quantification of various factor affecting emulsion stability: Water cut, Temperature, Asphaltene content, Demulsifier Dosage and Mixing Different Crudes, paper41, SPE Annual Technical Conference and Exhibition, 1999, Houston, USA. [7] D.D. Eley, M.J. Hey, J.D. Symonds, Emulsion of water in asphaltene containing oil, Colloids Surf. 32 (1998) 87. [8] H. Groezin, O.C. Mullins, Asphalthene Molecular Size and Weight by Time resolved Fluorescence Depolarization, in: O.C. Mullins, E.Y. Sheu, A. Hammami, A.G. Marshall (Eds.), Asphalthenes, Heavy oils, and Petroleomics, Springer, New York, 2007, p. 17. [9] S. Poteau, J.F. Argillier, D. Langevin, F. Pincet, E. Perez, Influence of pH on stability and dynamic properties of asphalthenes and other amphiphilic molecules at the oil-water interface, Energy Fuels 19 (2005) 1337–1341. [10] M. Fortuny, C.B.Z. Oliveira, R.L. Melo, M. Nele, R.C. Coutinho, A.F. Santos, Effect of salinity, temperature, water content, and pH on a microwave demulsification of crude oil emulsion, Energy Fuels 21 (2007) 1358–1364. [11] P. Hajivand, A. Vaziri, Optimization of demulsifier formulation for separation of water from crude oil emulsions, Braz. J. Chem. Eng. 32 (2015) 1–20. [12] M. Abdulkadir, Comparative analysis of the effect of demulsifier in the treatment of crude oil, Emulsion 5 (6) (2010). [13] S. Akbari, A. Nour, S. Jamari, A. Rajabi, Demulsification of water-in-crude oil emulsion via conventional heating technology in their optimum conditions, Aust. J. Basic Appl. Sci. 10 (4) (2016) 66–74. [14] M. Balsamo, A. Erto, A. Lancia, Chemical demulsification of model, water-in-oil emulsions with low water content by mean of ionic liquids, Braz. J. Chem. Eng. 34 (1) (2017) 273–282. [15] E. Decola, A. Hall, M. Popovich, H. Dahslett, Assessment of Demulsification and Separation Technologies for use in Offshore Oil Recovery Operation, (2018) Report submitted to the Bureau of Safety and Environmental Enforcement (BSEE) United State Department of Interior, Washington D.C. [16] O.A. Adeyanju, L.O. Oyekunle, Optimum demulsifier formulations for Nigerian crude oil-water emulsion, Egypt. J. Pet. 27 (2018) 657–662. [17] H.N. Abdurahman, M.Y. Rosli, J. Zulkifly, Chemical demulsification of water-incrude oil emulsions, J. Appl. Sci. 7 (2007) 196–201.
Please cite this article as: O. A. Adeyanju and L. O. Oyekunle, Optimization of chemical demulsifications of water in crude oil emulsions, Egyptian Journal of Petroleum, https://doi.org/10.1016/j.ejpe.2019.07.002
Contents lists available at ScienceDirect
Egyptian Journal of Petroleum journal homepage: www.sciencedirect.com
Full Length Article
Optimization of chemical demulsifications of water in crude oil emulsions Olusiji Ayoade Adeyanju a,⇑, Layioye Ola Oyekunle b a b
Department of Chemical and Petroleum Engineering, University of Lagos, Nigeria Department of Petroleum Engineering, Covenant University, Otta, Ogun State, Nigeria
a r t i c l e
i n f o
Article history: Received 17 January 2019 Revised 18 July 2019 Accepted 28 July 2019 Available online xxxx Keywords: Operating parameters Intermolecular interaction Mixing time Optimal conditions Demulsification
a b s t r a c t The instability of the water in crude oil emulsion and separation of the dispersed water as free water are influenced by the emulsion properties and the operating parameters during the demulsification process. This study aims to relate these properties/operating parameters to the amount of separated water. Steps were taken to determine and validate the optimal separations that can be achieved. Six operating parameters were identified through sensitivity analyses to have an energetic effect on percentage water separation. The bottle test method was used on two different samples of water in oil synthetic emulsions (sample A and B from different Nigerian oil fields). Response surface methodology central composite design (RSMCCD) was used to design the experiment, and generate the desired regression equations/ models. Results show that optimum percentage water separations of 93 and 95% (V/V) were achieved with the emulsions A and B respectively using the combination of the optimal variables derived from the model equations. These were improvements from percentage water separations of 80 and 83% (V/V) achieved using the two crude oil samples in their naturally occurring state when the properties of the emulsions were not enhanced to their determined optimal operating conditions. Ó 2019 Egyptian Petroleum Research Institute. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction A high percentage of the world produced crude oils exist in form of emulsions. Most of the emulsions are in the form of water-in-oil (w/o) type. For operational, economic and environmental reasons, there is a need to separate the water from the oil in the water in oil emulsion before their transportation and processing. Previous studies in the field of physical chemistry and surface phenomena had succeeded in the efficient demulsification of water-in-oil emulsion [1,2]. The intermolecular interaction forces in emulsion are active and couple with the surface tension at the phase boundaries makes the liquids inherent in the emulsion to have the tendency of reducing their surface area to the minimum. These made the individual drops to coagulate and form bigger droplets. The coagulation of dispersed water in the continuous oil phase made their separation imminent [3–5]. Therefore any variables/properties of the emulsion that affect the surface tension at the interphase between
Peer review under responsibility of Egyptian Petroleum Research Institute. ⇑ Corresponding author. E-mail addresses: [email protected] (O.A. Adeyanju), layioyekunle@ yahoo.com (L.O. Oyekunle).
the dispersed water phase and the continuous oil phase in the emulsion will influence the rate of water separation from the water in oil emulsion. The basis of this study is to investigate the effect of such parameter on the separated water during the demulsification process.
2. Literature review Different components/surfactants have been identified to be responsible for the emulsion stability, these include asphaltenes, resins and oil soluble organic acids (e.g. naphthenic, carboxylic) and bases. These components also called emulsifiers constitute the interfacial films that surround the dispersed water in the water in oil emulsion [6–8]. Studies show that the instability of the emulsion and separation of the dispersed water as free water are influenced by the emulsion properties and the operating parameters [9]. Fortuny et al., [10] in their study of the effect of salinity, temperature, water content and pH on crude oil emulsion stability concluded that the emulsion containing high water content are characterized by a high rate of demulsification except for crude of high pH and salt contents. The effects of most of the properties of the emulsions on the de-emulsification of different water in oil
https://doi.org/10.1016/j.ejpe.2019.07.002 1110-0621/Ó 2019 Egyptian Petroleum Research Institute. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Please cite this article as: O. A. Adeyanju and L. O. Oyekunle, Optimization of chemical demulsifications of water in crude oil emulsions, Egyptian Journal of Petroleum, https://doi.org/10.1016/j.ejpe.2019.07.002
2
O.A. Adeyanju, L.O. Oyekunle / Egyptian Journal of Petroleum xxx (xxxx) xxx
emulsions are still matters of controversies [11]. Abdulkadir, [12] in an effort of identifying the most effective combination of operating parameters at which an identified demulsifier can be applied through the comparative analysis of different demulsifiers on a Nigerian crude oil concluded that the demulsifier is best applied at a temperature of 60 °C at a concentration of 50 ppm. Different methods are on-going to optimize the demulsifications of crude oil emulsions [13–15].
Table 2 Range of experimental parameters used. Parameters
Range
Temperatures Mixing time of the demulsifier with the crude sample pH of the crude sample Demulsifier concentration Modifier (Methanol) concentration Crude oil salt content
30–70 °C 1–7 min 4.0–12.0 20–140 ppm 20–100 ppm 0.02–0.18 g/ml
3. Materials and methods
Fraction of separated water
3.1. Crude oils properties
¼ Two crude oils (crude oil A and B) with low basic sediments and water (BS&W) of 0.7 and 0.95% respectively were obtained from two different fields flow stations in Southern Nigeria. The bottle test method was used in the evaluation of the percentage of water separated. The properties of the two used crude oils are tabulated in Table 1. 3.2. Chemicals and equipment The demulsifier, acids, alkaline, and alcohol were supplied by Finlab Nigeria Limited, the emulsifier; sodium dodecyl sulphate (SDS) and the commercial demulsifier (Basorol E 2032) were supplied by MON Scientific (Nigeria) Limited. The homogenizer used is the SAMRO SRH60-70 homogenizer manufactured by ShangHai amro homogenizer CO., LTD. 3.3. Emulsion preparation The experimental studies were carried out using synthetic emulsions prepared from crude oils and water samples sourced from the crude oil and water outlets of a heater-treater located in the above mentioned fields flow stations of the southern Nigerian. The emulsion preparation was described in an earlier study [16]. 3.4. Methodology The bottle tests were performed with several 15 ml. of emulsified crude oils at varying operating parameters tabulated in the Table 2 below: The Minital-16 software was used in designing the experiments using the aforementioned operating parameters as the independent variables. A total of ninety (90) experiments were conducted on each of the two (2) crude oils and the response was the fraction of water that separated out of the emulsified crude oil. The percentage of water separated is given as:
Volume of separated water; mL Original v olume of water in the emulsified oil; mL
ð1Þ
4. Results and discussions 4.1. Sensitivity analyses Sensitivity analyses were performed on the water in crude oil de-emulsification process using the aforementioned parameters: Temperature, demulsifier concentration, mixing time, pH, salt concentration and modifier concentration. The analyses help to highlight the impact of each of the parameter change on the demulsification process. These were achieved by varying the input (reference) parameters individually, while the others are kept constants. Fig. 1 shows the results of the sensitivity analyses for each of the operating parameters on percentage water separation. Results show that the percentage water separated increases at the decreasing rate as each of the parameter/variable increases, reaching a peak (maximum/optimum value). The reference operating parameters used for the sensitivity analyses in Fig. 1 were Temperature = 60 °C, demulsifier concentration = 80 ppm, mixing time = 3.5 min, pH = 8, salt content (salinity) = 0.08 g/ml and Modifier concentration = 60 ppm. 4.1.1. Effect of temperature Fig. 1 shows that the amount of separated water increases with the temperature. This is due to increase in the rate of collisions and coalescence of the emulsified water particles in the crude oil, resulting in water droplets separation due to gravity as results of density difference between the coalescence water droplets and the crude oil. Also, increased temperature causes the destabilization of the water-oil interfacial surface that promotes the demulsification of water in the crude oil. The rate of water separated per degree Celsius (°C) rise in temperature decreases from 0.7 to 0.4 V/(V°C) as the temperature varies between 20 and 200% of the reference temperature for crude oil A. This is due to reduction
Table 1 Properties of the two crude oils and their measurement methods. Properties
Experimental Measurement Method
Crude oil sample Oil-A
Oil-B
Gravity at 28 °C, API Pour point, °C Viscosity at 28 °C, cp Salt content, (g/m3) Asphaltene (%) Resin (%) Basic Sediment and Water BS&W (%) Saturated Hydrocarbon (%) Aromatic Hydrocarbon, (%)
ASTM-D5002-16 ASTM-D97-66 ASTM-D445 ASTM-D6470-99 (2015) ASTM-D7-5 (06560) ASTM-D893-69 ASTM-D4007-02
42 29 8.8 18.5 0.21 23.7 0.7
28 22 9.1 15 0.17 17.6 0.95
ASTM-D2786-91 (2016) ASTM-D3238-95 (2015)
38 17.24
29 26.45
Fig. 1. Effect of Different Operating Parameters (variables) on Percentage Water Separated.
Please cite this article as: O. A. Adeyanju and L. O. Oyekunle, Optimization of chemical demulsifications of water in crude oil emulsions, Egyptian Journal of Petroleum, https://doi.org/10.1016/j.ejpe.2019.07.002
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O.A. Adeyanju, L.O. Oyekunle / Egyptian Journal of Petroleum xxx (xxxx) xxx
in the rate of emulsified water collisions as less emulsified waters were available for such collision. 4.1.2. Effect of demulsifier concentrations As the concentration of the commercial demulsifier (Basorol E 2032) increases the percentage of water separated increases due to increase in demulsifier available for the destabilization of oilwater interface medium. The rate of water separation per unit addition of demulsifier was observed to drop for both crude oils, reducing from 0.8 to 0.2 V/(Vppm) and from 0.9 to 0.2 V/(Vppm) for crude oil A and B respectively. This is due to the combined effect of the decrease in the amount of emulsified water available for demulsification process and increases in resistance to the destabilization process at the water-oil interface as a result of the reduction in water to crude oil ratio in the crude oil emulsions. 4.1.3. Effect of mixing time Increasing the time of mixing of the demulsifier with the emulsified crude oil increases the amount of water separated from the water in crude oil emulsion. This is due to an increase in the ability of the demulsifier to gain access to the oil-water interface sustaining the emulsified water in the emulsions, destabilizing it and make the coalescence and separations of emulsified water inevitable. The rate of separated water in respect to time in minute reduces as mixing time increases, reducing from 0.3 to 0.1 V(V/minute) for crude oil A. These inferred that there is optimum stirring/mixing time beyond which the action will results in the creation of more emulsified water and making the rate of water separation increasingly difficult. 4.1.4. Effect of pH The effect of pH on the demulsification process was studied by addition of hydrochloric acid (HCl) or sodium hydroxide (NaOH) (depending on the intended pH) to the water phase prior to emulsion preparation. The Fig. 1 shows that the water in crude oil emulsion achieved the highest stability at both the alkaline and acidic medium, with the emulsion becoming more stable as the alkalinity or acidity increases, as exhibit by the consistent reduction in the percentage of separated water collected from the experiments. The highest instabilities of the emulsified crude oils occur around the neutral pH of 9.0 and 8.0 for crude oil A and B respectively. This is due to the polarity of the water in the alkaline and acidic medium which increased the electrostatic repulsion resulting in the destabilization of the interfacial properties of the water oil emulsion thereby stabilizing the emulsion. 4.1.5. Effect of salt content (salinity) The effect of salt content on the percentage water separation was studied for each of the crude oil by adding between 0.02 and 0.18 g/mL of sodium chloride (NaCl) respectively to each of the aqueous water content prior to their use for emulsion preparation. An equal amount (20 ppm) of the same demulsifier was added to each of the ten prepared samples with varying salts (NaCl) content. The salt seems to aid in the demulsification of the emulsified water in the water in crude oil emulsions. This is in agreement with previous studies [10,12]. The salt ions seem to have an adverse effect on the water-oil interfacial film holding the emulsified water in the water in oil emulsions.
while the short chain alcohol are soluble in water. Hence short chain alcohols is efficient for water separation in water in oil emulsion due to its ability to diffuse through the interfacial film into the emulsified water contained in the continuous oil phase. While the long chain alcohols are preferred in the crude oil in water emulsion. 4.2. Model equations Successful identification of the effects of operating parameters: temperature, demulsifier concentration, modifier (methanol) concentration, pH, salt content and mixing time on the percentage of separated water from each of the water in oil emulsions, warranted the efforts to relate these operating parameters to the percentage water separated for each of the studied crude samples. The six operating parameters were constraints to the ranges stated in Table 2. Minitab-16 software was used to design the experiments, formulate the models (empirical) and analyze the results. A total of ninety (90) experiments organized in factorial design were conducted on each of the two emulsion samples. The response selected for analyses was the percentage of water separated (V/V) from the water in crude oil emulsions given by Eq. (1). For crude oil emulsion prepared from crude oil A, the empirical model equation is given as: W sep ð%Þ ¼ 6:872 þ 0:00346T þ 0:423M t þ 0:465P h þ 0:722Dc þ 0:817Sc þ0:138M c 0:00342T 2 0:0125M 2t 0:0472P 2h 0:00107D2c 0:0251S2c þ 0:00261TDc ð2Þ
where T = temperature (°C), Mt = mixing time (minute), Ph = pH of emulsion, Dc = demulsifier concentration (ppm), Sc = salt content (g/ml), Mc = Modifier concentration (ppm) and Wsep (%) = percentage water separation. The model’s terms in the equations are those that are left after the insignificant variables and interactions have been eliminated. For emulsion prepared from crude oil B, the model equation was given as: W sep ð%Þ ¼ 9:143 þ 0:334T þ 0:404M t þ 0:452P h þ 0:725Dc þ 0:791Sc þ0:133M c 0:00338T 2 0:0138M 2t 0:0441P 2h 0:00116D2c 0:0262S2c þ 0:00279TDc ð3Þ
The statistical analyses show that the model equations for both crude samples were highly significant with very low probability values (P < 0.001) i.e. the probability of incorrect prediction by the model due to experimental error or noise factors is small. In furtherance to the efforts in testing the model validity, the lack of fit results was not statistically significant as the P-values were 0.297 and 0.365 for crude oil A and B respectively. The model affirms the significant influences of the identified properties/variables: temperature, demulsifier concentration, mixing time, salt content, pH, and modifier concentration in the separation of emulsified water from the water in crude oil emulsion judging by their P-values below 0.05. 4.3. Response contour plots
4.1.6. Effect of emulsion modifier Previous studies [16,17] showed that alcohol can be used as a modifier to help in the demulsification process. Alcohols tend to reduce the effectiveness of the interfacial film between the emulsified water and the continuous crude oil phase in the water in oil emulsions. The compositions of the interfacial films are mainly water and oil and the long chain alcohol are soluble in crude oil
The interactive effects of the variables on each other were investigated using the contour plots generated with Minitab-16 software. The two dimensional contour plots were based on the developed models by each crude oil with four variables kept constant at their coded zero levels, while varying the other two variables.
Please cite this article as: O. A. Adeyanju and L. O. Oyekunle, Optimization of chemical demulsifications of water in crude oil emulsions, Egyptian Journal of Petroleum, https://doi.org/10.1016/j.ejpe.2019.07.002
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O.A. Adeyanju, L.O. Oyekunle / Egyptian Journal of Petroleum xxx (xxxx) xxx
Fig. 2. Contour Plots of Percentage Water Separation against Temperature and Demulsifier Concentration.
Fig. 2 shows the interactive effect of the temperature and the demulsifier concentration on each other. The figure shows that as the temperature increases from 0 to 90 °C and demulsifier’s concentration increases from 0 to 250 ppm, more than 80% (V/V) of the emulsified water was separated. At the temperature of between 0 and 62 °C and demulsifiers concentration of between 0 and 100 ppm, the percentage of separated water was less than 15% (V/V). When the temperature was increased to above 62 °C and the demulsifier concentration was raised above 150 ppm there was a tremendous increase in the percentage water separated rising to as much as 85% (V/V). Fig. 3 shows the contours plot of percentage of water separated against mixing time and pH value. It was shown that keeping other variables constant at their hold values, the just a little above 30% of water was separated from the emulsion when the pH values were varied between 1 and 14 and mixing time increased from 1 to 10 min. Thus, confirming the fact that the effects of pH values on the separated water were not as significant as that of temperature and demulsifier concentration. 4.4. Models optimization The model equations were optimized by settling the partial derivatives of the equation to zero with respect to the corresponding variables to determine the stationary variables. Results show that the second derivatives in respect to each of the variables were
negatives an indication that the stationary values were at the maximum points. The optimum values of each variable from the model/regression equation developed from emulsion prepared from crude oil A were evaluated as: T = 87 °C, Mt = 10.5 min, Ph = 8.0, Dc = 254 ppm, Sc = 0.332 g/ml, Mc = 185 ppm producing percentage water separation, Wsep (%) = 97.32%. Similar results of T = 82.2 °C, Mt = 11.8 min, Ph = 7.4, Dc = 268 ppm, Sc = 0.325 g/ml, Mc = 235 ppm were obtain for model equation developed from emulsion prepared from crude oil B, generating an optimum water separation of 98.57%
4.5. Model validation In an effort to validate the optimum water separation generated from the regression equations/models, experiments were conducted with emulsions prepared from crude oil A and B using the generated optimum values of each parameter from the software. Percentage water of 93 and 95% (V/V) was successfully separated from water in oil emulsions prepared from crude oil A and B respectively. The closeness of the percentage water separated from experimental run to the result generated from the model, (differences of 4.44 and 3.62% (V/V) for crude oil A and B respectively) further confirms the effectiveness of the models to relate the percentage water separation to the operating parameters.
Fig. 3. Contour Plots of Percentage Water Separation against pH values and mixing time.
Please cite this article as: O. A. Adeyanju and L. O. Oyekunle, Optimization of chemical demulsifications of water in crude oil emulsions, Egyptian Journal of Petroleum, https://doi.org/10.1016/j.ejpe.2019.07.002
O.A. Adeyanju, L.O. Oyekunle / Egyptian Journal of Petroleum xxx (xxxx) xxx
5. Conclusion It was shown that the emulsions prepared from the two crude oil samples from two petroleum field in southern Nigeria have different model equations that relate the percentage of water separated to the operating/emulsion parameters. The separated water was observed to depend on the operating/emulsion parameters which include: temperature, demulsifier concentration, mixing time, salt content, pH values, and modifier concentration. The temperature, demulsifier concentration and mixing time were observed to predominate the separation process while the effect of pH values, salt content, and modifier concentration was relatively lower. Optimum percentage water separations of 93 and 95% were achieved with the emulsions prepared from crude oil A and B respectively using the combination of the optimal variables generated from the software. This is an improvement from the highest values of 81 and 87% (V/V) separated water achieved from emulsions prepared from crude oil A and B respectively when the designed experiments were performed with emulsions, whose properties were not at the optimum values. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. References [1] A.N. Dimitrov, D.I. Yordanov, P.S. Petkov, Study on the effect of demulsifiers on crude oil and petroleum products, Int. J. Environ. Res. 6 (2) (2012) 435–442. [2] E.D. Shchukin, A.V. Pertsov, E.A. Amelina, A.S. Zelenev, Colloid Surf. Chem. 12 (2001) 583–664, Elsevier.
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[3] Y.G. Frolov, Adsorbed surface layers and thermodynamic aggregation stability of dispersed system, Colloidnyj Zhurnal 57 (2) (1995) 247–251. [4] E.D. Shchukin, The influence of surface-active media on the mechanical properties of materials, Adv. Colloid Interface Sci. 123–126 (2006) 33–47. [5] E.D. Shchukin, A.I. Bessonov, S.I. Kontorovich, I.N. Polukarova, E.A. Amelina, I.N. Burenkova, B. Romanovsky, V, Effects of adsorption-active media on the mechanical properties of catalysts and adsorbents, Colloids Surf. A: Physicochem. Eng. Aspect 282–283 (2006) 287–297. [6] S.L. Kokal, J.I. Al-Juraid, Quantification of various factor affecting emulsion stability: Water cut, Temperature, Asphaltene content, Demulsifier Dosage and Mixing Different Crudes, paper41, SPE Annual Technical Conference and Exhibition, 1999, Houston, USA. [7] D.D. Eley, M.J. Hey, J.D. Symonds, Emulsion of water in asphaltene containing oil, Colloids Surf. 32 (1998) 87. [8] H. Groezin, O.C. Mullins, Asphalthene Molecular Size and Weight by Time resolved Fluorescence Depolarization, in: O.C. Mullins, E.Y. Sheu, A. Hammami, A.G. Marshall (Eds.), Asphalthenes, Heavy oils, and Petroleomics, Springer, New York, 2007, p. 17. [9] S. Poteau, J.F. Argillier, D. Langevin, F. Pincet, E. Perez, Influence of pH on stability and dynamic properties of asphalthenes and other amphiphilic molecules at the oil-water interface, Energy Fuels 19 (2005) 1337–1341. [10] M. Fortuny, C.B.Z. Oliveira, R.L. Melo, M. Nele, R.C. Coutinho, A.F. Santos, Effect of salinity, temperature, water content, and pH on a microwave demulsification of crude oil emulsion, Energy Fuels 21 (2007) 1358–1364. [11] P. Hajivand, A. Vaziri, Optimization of demulsifier formulation for separation of water from crude oil emulsions, Braz. J. Chem. Eng. 32 (2015) 1–20. [12] M. Abdulkadir, Comparative analysis of the effect of demulsifier in the treatment of crude oil, Emulsion 5 (6) (2010). [13] S. Akbari, A. Nour, S. Jamari, A. Rajabi, Demulsification of water-in-crude oil emulsion via conventional heating technology in their optimum conditions, Aust. J. Basic Appl. Sci. 10 (4) (2016) 66–74. [14] M. Balsamo, A. Erto, A. Lancia, Chemical demulsification of model, water-in-oil emulsions with low water content by mean of ionic liquids, Braz. J. Chem. Eng. 34 (1) (2017) 273–282. [15] E. Decola, A. Hall, M. Popovich, H. Dahslett, Assessment of Demulsification and Separation Technologies for use in Offshore Oil Recovery Operation, (2018) Report submitted to the Bureau of Safety and Environmental Enforcement (BSEE) United State Department of Interior, Washington D.C. [16] O.A. Adeyanju, L.O. Oyekunle, Optimum demulsifier formulations for Nigerian crude oil-water emulsion, Egypt. J. Pet. 27 (2018) 657–662. [17] H.N. Abdurahman, M.Y. Rosli, J. Zulkifly, Chemical demulsification of water-incrude oil emulsions, J. Appl. Sci. 7 (2007) 196–201.
Please cite this article as: O. A. Adeyanju and L. O. Oyekunle, Optimization of chemical demulsifications of water in crude oil emulsions, Egyptian Journal of Petroleum, https://doi.org/10.1016/j.ejpe.2019.07.002