Prospects of Bitumen Emulsification using a Hydrophilic Polymeric Surfactant O.S. Alade*1, 2, K. Sasaki1, Y. Sugai1, B. Ademodi2, J. Kumasaka1, M. Nakano3 Resources Production and Safety Engineering Laboratory, Department of Earth Resources Engineering, Kyushu University, Fukuoka, Japan. 1
Petroleum and Petrochemical Engineering Laboratory, Department of Chemical Engineering, Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria. 2
3
Research Center, Japan Petroleum Exploration Co. LTD. (JAPEX), Chiba, Japan.
*13TE1403M@s.kyushu-u.ac.jp or 1oalade@oauife.edu.ng; 2krsasaki@mine.kyushu-u.ac.jp; 3sugai@mine.kyushu-u.ac.jp, 4bademodi@yahoo.com; 5j.kumasaka@mine.kyushu-u.ac.jp; 6masanori.nakano@japex.co.jp Abstract One of the most important factors of the successful production, transportation and utilization of the highly viscous oil such as bitumen is viscosity reduction. Several approaches including emulsification of bitumen as dispersed particle in the continuous aqueous phase containing surfactant have been investigated and practised. However, recent progress in heavy oil emulsification has witnessed the use of polymeric surfactants. The use of this type of surfactants have been supported by observations including the ability to form emulsion which is easy to brake and environmental friendly compared to the low molecular weight surfactants. The present effort therefore seeks primarily to investigate the suitability of a hydrophilic polymeric surfactant in viscosity reduction of the bitumen. It has been observed that the sample of polymeric surfactant employed is able to significantly reduce the viscosity of the original sample of bitumen and stabilized the emulsion formed. Keywords Bitumen Recovery; Emulsion Stability; Emulsion Viscosity; Polymeric Surfactant; Mild Agitation
Introduction The growing global concerns about finding alternative energy sources is not unconnected with the dwindling conventional oil reserve, increasing energy demand and environmental issues. More so, according to Saniere et al (2004), predictions made by a number of prominent bodies, including the US Department of Energy, the international Energy Agency and the World Energy Council are all in agreement with the view that the world energy consumption will continue to increase. Thus, several alternative energy sources have been explored and developed. Among them, heavy oil, extra heavy oil and bitumen have received much attention due to the relative abundance. There exist huge resources of bitumen, extra heavy and heavy oil in place worldwide [2]. However, high viscosity, due to high asphaltene content and/or low API gravity has remained the major issue to overcome in recovery, production and transportation of these resources [3, 4]. Furthermore, during recovery and transportation up to the surface and the subsequent pipeline transportation of heavy oil over a long distance, the major concern remains high viscosity which causes high pressure and increased energy requirement for pumping [5]. Therefore, a key factor to successful production of heavy oil includes searching for environmental friendly, cost effective and efficient ways for viscosity reduction. Viscosity reduction options, including heating, dilution with lighter hydrocarbon, upgrading, core annular flow and dispersion as oil in water emulsion have been practised [1]. Among these methods, significant viscosity reduction of heavy oil/bitumen has been reported using the emulsification method [5]. Generally, apart from the objective for transportation, emulsion and/or emulsification is an important subject of discussion and investigation in the petroleum production field due to its economic effects [6]. Concerning viscosity International Journal of Engineering Practical Research, Vol. 4 No. 1-April 2015 2326-5914/15/01 055-05 Š 2015 DEStech Publications, Inc. doi: 10.12783/ijepr.2015.0401.12
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O.S. Alade, K. Sasaki, Y. Sugai, B. Ademodi, J. Kumasaka, M. Nakano
reduction and to improve mobiltiy what of interest is the oil-in-water emulsion which consists a liquid-liquid dispersed system in which the particles of bitumen are dispersed in continuous water phase. This is mainly achieved using the surface active agent known as surfactant to lower the interfacial tension between the aqueous phase and oil phase which are originally immiscible [7]. However, emulsion resolution after transportation is one of the major concerns over the use of surfactants [8, 9]. In the recent years, a category of hydrophilic polymeric surfactant known as polyvinyl alcohol (PVA) and the derivatives have used in viscosity reduction of heavy oil [9]. Such chemical formulation, compared to the low molecular weight surfactants, have offered advantages in emulsion formation and braking [9]. Environmental advantage [8] has also been reported in favour of them. However, apart from some few cases [8, 9], research efforts utilising this class of surfactant in viscosity reduction of the highly viscous heavy oil and/or bitumen has not received much attention. This therefore informs the present discussion. Thus, the primary objective of this article is to evaluate the viscosity reduction potential of the samples of hydrophilic polymeric surfactant as a surface active agent for bitumen emulsification. Material and Methodology Material Bitumen was sampled from an oil field in Alberta, Canada. The detailed specification of this oil is presented in Table 1. Hydrolysed samples of the polymeric surfactant (PVA-205, PVA-235 and KRE-537) supplied by the Kuraray Co., LTD., Japanwas employed for emulsification. TABLE 1 DETAIL SPECIFICATION OF THE EXPERIMENTAL CONDITIONS
Bitumen Properties Kinematic viscosity @ 50 oC Density @ 15 oC API Emulsification conditions Emulsification temperature Tf (oC) Bitumen content CB (% w/w) Content of aqueous phase (% w/w) Concentration of polymeric surfactant CS (ppm) Mixing speed (AR) (rpm)
Value 6970 mm2/s 1016.4 kg/m3 7.6 40 70 30 5000 500
Experimental Methodology 1)
Emulsification and Stability Tests
Bitumen in water emulsion was formed under the emulsification conditions as presented in Table 1. Preheated sample of bitumen was dispersed in aqueous solution containing CS=5,000ppm (= 0.5%) of the polymeric surfactant using a hot plate with a magnetic stirrer at a low shearing speed (AR) of 500 rpm for 10 minutes. Thus, emulsion containing bitumen content (CB) of 70 % w/w was formed at the average formation temperature Tf = 40oC. Emulsion stability was tested using accelerated settling method. Emulsion samples were centrifuged at 4000 rpm (corresponding to 1434 g) for 10 minutes using a table centrifuge. Stability (⹲) was estimated as a percentage of the fraction of the initial water content in emulsion defined by
Where Wf and Wi stand for water fraction separated as free water and initial water content of the emulsion, respectively. Sample was also taken immediately for particle size analysis using a light microscope interfaced with a computer. The photomicrograph were subsequently analysed for droplet size distribution with the software, ImageJ TM. Average diameter of particles of emulsion was estimated using volume mean diameter (dv) giving as:
Prospects of Bitumen Emulsification using a Hydrophilic Polymeric Surfactant
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where ni is number of the droplets counted as ith diameter of droplet (µ m).
Bitumen: oil phase
Aqueous phase: containing 0.5% PVA
Agitation produced by stirrer
Bitumen particle stabil;ized by PVA particle
Magnetic stirrer and hot plate FIGURE 1. DESCRIPTION OF THE EMULSIFICATION PROCESS
2)
Viscosity Test
The viscosity of emulsion was tested at temperature, Te (oC) between 40 to 75 oC and the shearing rate of 0.14 s-1 using a viscometer (Brookfield DV-I with thermos-cell, spindle number SC4-34). The instrument was calibrated with the appropriate standard fluids before use. Percentage viscosity reduction (µ p) was estimated as µp where µ and µ a are the viscosity of the original sample of bitumen and apparent viscosity of emulsion at temperature Te (oC), respectively. Results and Discussion Emulsion properties including the stability and viscosity and/or rheology have been measured as standards for its quality employed in its recovery and pipeline transportation [10]. Considering these characteristics of emulsion, under the present study, the samples of the hydrophilic polymeric surfactants employed were observed to support emulsification of the bitumen sample in aqueous solution. After mild agitation, bitumen was dispersed as droplet particle of average size of 12 µ m in diameter in the aqueous phase. The stability of this mixture was observed to be appreciable under the stability test employed. Table 2 presents the stability and the particles sizes of some selected samples from the experiments. Sample of emulsion and typical micrographic images are presented in Figure 2. TABLE 2. STABILITY AND THE PARTICLES SIZES OF SOME SELECTED SAMPLES FROM THE EXPERIMENTS
PVA Samples PVA-205 PVA-235 KRE-537
(A)
% Stability (W) 38 45 38
(B)
Particle size (µ m) 12 13 12
(C)
mm 40µ m m FIGURE 2. TYPICAL MICROGRAPHIC IMAGES FROM THE EXPERIMENTS: (A) EMULSION FORMED USING PVA-205, (B) EMULSION FORMED USING PVA-235 AND (C) EMULSION FORMED USING KRE-537.
Moreover, the samples of the polymeric surfactants were also observed to support viscosity reduction of the original bitumen sample. From Figure 3, the viscosity-temperature relationship of the emulsion is compared with that of the original bitumen and emulsion formed by steam condensation. It was observed that the viscosity of the original bitumen was significantly reduced over the range of temperature tested (percentage reduction (µ p) of
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O.S. Alade, K. Sasaki, Y. Sugai, B. Ademodi, J. Kumasaka, M. Nakano
about 90%). In contrast, the viscosity of the steam-bitumen emulsion was observed to increase compared to the original bitumen. Similar observations in viscosity reduction using formulations of polymeric surfactant samples have been previously reported [8] a (PVA-bitumen emulsion) CB = 70% w/w (original bitumen)
8000
a (steam-bitumen emulsion) CB = 78% w/w
Viscosity mPas)
6000
4000
2000
0
30
40
50
60
70
80
90
100
Emulsion Temperature Te (oC) FIGURE 3. VARIATION OF APPARENT VISCOSITY OF PVA-BITUMEN EMULSION µA (MPAS) VS. TEMPERATURE TE (°C) AT SHEARING RATE OF 0.14 S-1 COMPARED WITH THE VISCOSITY OF ORIGINAL BITUMEN AND STEAM-BITUMEN EMULSION
Conclusion The suitability of the employed hydrophilic polymeric surfactant was evaluated and confirmed considering the emulsion stability and the apparent viscosity. Moreover, the main objective of viscosity reduction was achieved through the present study. Another notable observation and/or an advantage were/was the ability of the chemical to assist in dispersion after mild agitation. The stability of the emulsion was also observed to be moderate. These observations are in tandem with the reported merit of the polymeric surfactant as compared with the low molecular weight surfactant [9]. REFERENCES
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Olalekan Alade is a PhD candidate at Department of Earth Resources Engineering, Kyushu University, Japan. He holds B.Tech. from Ladoke Akintola University, Nigeria and M.Sc. (Obafemi Awolowo University) both in Chemical Engineering. His research interest captures application of chemical engineering principles in heavy oil production and transportation. Olalekan Alade is a member of NSChE and SPE. Kyuro Sasaki is a professor of Resources Production and Safety Engineering, Department of Earth Resources Engineering at the Faculty of Engineering, Kyushu University, Japan. He holds B.Eng., M.Eng. and PhD (in Fluids Engineering) from Hokkaido University, Japan. His background is fluid engineering and production engineering, and current research areas include thermal fluids transport phenomena in mineral resources production, system design and numerical modelling in mining and petroleum engineering area. Dr. Sasaki is a member of MMIJ, JAPT, and SPE. Yuichi Sugai is an assistant professor at the Department of Earth Resources Engineering, Kyushu University, Japan. He holds a Ph.D. degree from Tohoku University in earth engineering. He has written and published several technical papers related to petroleum engineering. Bayo Ademodi is an associate professor of Chemical Engineering at Department of Chemical Engineering Obafemi Awolowo University, Nigeria. He studied BSc Chemical Engineering in the Howard University, Washington D.C ., U.S.A. and M.Sc. in Chemical Engineering at the Pennsylvania State University, U.S.A. He obtained PhD degree in Chemical Engineering from Obafemi Awolowo University. He has a vast research experience in the field of petroleum/petrochemical product development and hydrocarbon processing generally. This has won him some consultancy job in Nigeria. He is currently interested in the development of Unit operation for processing Nigerian bitumen and/or heavy oil resources.