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Determination of petroleum sulfonates in crude oil by column-switching anion-exchange chromatography
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Chinese Chemical Letters 19 (2008) 219–222 www.elsevier.com/locate/cclet
Determination of petroleum sulfonates in crude oil by column-switching anion-exchange chromatography Liang Zhao a,b, Xu Long Cao c, Hong Yan Wang c, Xia Liu a, Sheng Xiang Jiang a,* a
Key Laboratory for Natural Medicine of Gansu Province, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China b Graduate School of the Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100039, China c Geological and Scientific Research Institute, Shengli Oilfield, SINOPEC, Dongying 257015, China Received 11 October 2007
Abstract A column-switching anion-exchange chromatography method was described for the separation and determination of petroleum monosulfonates (PMS) and petroleum disulfonates (PDS) in crude oil that was simply diluted with the dichloromethane/methanol (60/40). The high performance liquid chromatography (HPLC) system consisted of a clean-up column and an analytical column, which were connected with two six-port switching valves. Detection of petroleum sulfonates was available and repeatable. This method has been successfully applied to determine PMS and PDS in crude oil samples from Shengli oil field. # 2007 Sheng Xiang Jiang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Petroleum sulfonate; Determination; Anion-exchange chromatography; Column-switching; Crude oil
Petroleum sulfonates are used to reduce the interfacial tension between the oil and water, thereby easing the flow of oil through the rock pores. In order to understand better the flooding behavior of petroleum sulfonates when used in EOR processes, it is necessary to establish reliable and simple techniques and methods for the detection of petroleum monosulfonates (PMS) and petroleum disulfonates (PDS) in crude oil samples. Various methods of high performance liquid chromatography (HPLC) have been developed for determining petroleum sulfonates in hydrophilic samples [1–4]. Many techniques and methods, involving solid-phase extraction, various modes of HPLC, capillary electrophoresis, GC–mass spectrometry, liquid chromatography–mass spectrometry, and flow injection-mass spectrometry methods, etc., have also been employed for the analysis of aromatic sulfonates in aqueous media [5–14]. However, strategies thus far reported were not available for the separation and determination of PMS and PDS at low concentration level in crude oil. This paper describes the separation and determination of PMS and PDS at low concentration level in crude oil by a column-switching anion-exchange chromatography method. Both the purification and separation processes are carried out on two strong anionexchange columns and two six-port switching valves, which provide a unique means for the selective separation of PMS and PDS in crude oil.
* Corresponding author. E-mail address: [email protected] (S.X. Jiang). 1001-8417/$ – see front matter # 2007 Sheng Xiang Jiang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2007.12.015
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L. Zhao et al. / Chinese Chemical Letters 19 (2008) 219–222
Fig. 1. A schematic diagram of the column-switching HPLC system. The arrows indicate the direction of the flow depending on the valve position: dashed line, V1/V2 = II/II (clean-up), bold line, V1/V2 = I/I (analysis) (V1 and V2: six-port switching valve).
1. Experimental Sodium 2-naphthalene sulfonates (2-NS) and sodium 1,5-naphthalene disulfonates (1,5-NDS) were dissolved in methanol and was further diluted in methanol as a series stock solution. Spiked crude oil samples were prepared by addition of the series stock solution to blank crude oil solutions giving the final content of 2-NS of 9.6, 48.0, 96.0, 192.0, 480.0 mg/mL and 1,5-NDS of 8.0, 40.0, 80.0, 160.0, 400.0 mg/mL in crude oil solutions, respectively. The blank crude oil solutions were obtained by weighing 1.0 g of crude oil and in an ultrasonic bath dissolving in 10 mL of dichloromethane/methanol (60/40) to require concentration of 100 mg/mL before the spiked crude oil samples were prepared. The analytical sample was prepared by weighing 1.0 g of crude oil sample from oil field and in an ultrasonic bath dissolving in 10 mL of dichloromethane/methanol (60/40). Three mobile phases were used for the separation: (mobile phase A) dichloromethane; (mobile phase B) methanol–water (60:40); and (mobile phase C) methanol– 0.3 mol/L NaH2PO4 (60:40). All mobile phases flow-rate were 1.0 mL/min. The quantification wavelength was 278 nm and all separations were carried out at room temperature. A schematic diagram of the column-switching HPLC system is show in Fig. 1. The column-switching valves 1 and 2 were placed in position II. Crude oil sample was injected onto the clean-up column. The interfering compounds in the crude oil sample were washed to waste tank by isocratic elution using mobile phase A (100%) at a flow-rate of 1.0 mL/min for 10 min. After on-line purification of the crude oil sample on the clean-up column, the switching valve 1 was shifted to position I and the clean-up column was equilibrated for 10 min by passing through mobile phase B (100%). The switching valve 2 was turned to position I and the analytes enriched on the clean-up column were eluted into the analytical column and separated by gradient elution immediately after valve switching. The gradient begins with mobile phase B (100%) for 5 min. During the 5 to 10 min the concentration of mobile phase B is decreased exponentially from 100 to 0% while the concentration of mobile phase C is increased exponentially from 0 to 100%. Then mobile phase C remained for 10 min in a total elution time of 15 min. 2. Results and discussion Separation of petroleum sulfonates according to the hydrophilic end may be achieved by anion-exchange HPLC. However, it is difficult to separate and analyze PMS and PDS in crude oil, in which a large amount of organic matters can be co-eluted on the analytical column and result in the hump of interference peaks in the chromatogram. Columnswitching techniques, which can regulate the flowing way and composition of mobile phase to eliminate interference and improve selectivity, offer a simple means of rapid analysis of the target compounds in complex mixtures. For online determination of petroleum sulfonates in crude oil samples, it is necessary to choose a clean-up column, which can selectively adsorb petroleum sulfonates rather than the interfering compounds in crude oil samples. In this study, the strong anion-exchange column has been served as the clean-up column for highly selective adsorbing petroleum sulfonates in crude oil. In using dichloromethane as washing solvents, the majority of interfering compounds were
L. Zhao et al. / Chinese Chemical Letters 19 (2008) 219–222
221
Fig. 2. Chromatograms of crude oil samples on the column-switching system.
Fig. 3. Peak 1, 2-NS; peak 2, 1,5-NDS.
quickly eluted while there was strong retention of petroleum sulfonates adsorbed on the clean-up column. The petroleum sulfonates were subsequently transferred to the analytical column and further separation by switching the valve position and with other mobile phase. Fig. 2 shows a chromatogram of blank crude oil on the column-switching system. As demonstrated by the chromatogram, interfering compounds in crude oil have no significant interference on the determination of petroleum sulfonates. Fig. 3 shows the typical chromatogram of crude oil containing 48.0 and 40.0 mg/mL of 2-NS and 1,5-NDS on the column-switching system. As shown, naphthalene sulfontes with different numbers of sulfonic groups are well separated. Fig. 4 shows a chromatogram of real crude oil sample on the columnswitching system. As shown, petroleum sulfonates are separated into monosulfonate and disulfonate groups.
Fig. 4. Peak 1, PMS; peak 2, PDS.
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L. Zhao et al. / Chinese Chemical Letters 19 (2008) 219–222
Table 1 Analytical samples determination Samples
PMS (mg/mL)
PDS (mg/mL)
1 2 3 4
33.4 61.4 179.7 212.3
30.1 55.0 163.9 187.5
The standard calibration curves for spiked crude oil containing 2-NS and 1,5-NDS were linear in the range of 9.6– 480.0 mg/mL and 8.0–400.0 mg/mL with correlation coefficient greater than 0.997 and 0.998, respectively. Recovery was tested by adding three known quantities (in the concentration range of calibration curve) of 2-NS and 1,5-NDS to real sample. The recovery was 92.0–102.9% for 2-NS and 92.6–105.5% for 1,5-NDS. Reproducibility was evaluated by carrying out the determination six times on the same standard solution of 2-NS and 1,5-NDS. The relative standard deviation (RSD) was 3.0% for 2-NS, and 4.3% for 1,5-NDS. The limit of detection for PMS and PDS was set to 10.0 and 12.5 mg/mL in crude oil solutions, which is the lowest concentration of the analytes that can be measured with a coefficient of variation less than 10%. As an application of the proposed method, the determination of petroleum sulfonates in crude oil samples was tried. Four analytical samples were determinated by the column-switching procedure. A typical chromatogram of the samples was obtained on the column-switching system(shown in Fig. 4), and the results of the determination of PMS and PDS in the samples were shown in Table 1. 3. Conclusion A simple and reliable column-switching HPLC method for the determination of petroleum sulfonates in crude oil was developed. The method seems to be advantageous over other methods reported so far in literature in terms of separation efficiency and processing procedure of sample, especially in the case of the crude oil sample because there is great difficulty in processing sample. This method was successfully applied to the determination of concentrations of PMS and PDS in crude oil. Obviously, the column-switching technique described in this paper is applicable to study the flooding performance of petroleum sulfonates used in EOR processes. Acknowledgments We are grateful to the National Nature Science Foundation of China (No. 20675085). We are also grateful to the support from the Program of the Light in China’s Western Region (2003) and the Province Nature Science Foundation of Gansu (No. 3ZS041-A25-23). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]
R.E. Barden, D.A. Jaeger, P.S. Ossip, J. Chromatogr. A 109 (1975) 377. G.R. Bear, C.W. Lawley, R.M. Riddle, J. Chromatogr. A 302 (1984) 65. Y.B. Liu, L. Zhao, L.R. Chen, Chin. J. Oilfield Chem. 4 (1987) 305. S.X. Jiang, L.R. Chen, Chin. J. Anal. Chem. 20 (1992) 677. T. Reemtsma, J. Chromatogr. A 733 (1996) 473. T. Reemtsma, J. Chromatogr. A 1000 (2003) 477. T.P. Knepper, J. Chromatogr. A 974 (2002) 111. A. Rigol, A. Latorre, S. Lacorte, D. Barcelo, J. Chromatogr. A 963 (2002) 265. T. Reemtsma, J. Chromatogr. A 919 (2001) 289. E. Marengo, M.C. Gennaro, V. Gianotti, Chemometr. Intell. Lab. Syst. 53 (2000) 57. R. Loos, M.C. Alonso, D. Barcelo, J. Chromatogr. A 890 (2000) 225. T. Storm, T. Reemtsma, M. Jekel, J. Chromatogr. A 854 (1999) 175. S. Angelino, A.B. Prevot, M.C. Gennaro, E. Pramauro, J. Chromatogr. A 845 (1999) 257. R. Loos, R. Niessner, J. Chromatogr. A 822 (1998) 291.
Chinese Chemical Letters 19 (2008) 219–222 www.elsevier.com/locate/cclet
Determination of petroleum sulfonates in crude oil by column-switching anion-exchange chromatography Liang Zhao a,b, Xu Long Cao c, Hong Yan Wang c, Xia Liu a, Sheng Xiang Jiang a,* a
Key Laboratory for Natural Medicine of Gansu Province, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China b Graduate School of the Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100039, China c Geological and Scientific Research Institute, Shengli Oilfield, SINOPEC, Dongying 257015, China Received 11 October 2007
Abstract A column-switching anion-exchange chromatography method was described for the separation and determination of petroleum monosulfonates (PMS) and petroleum disulfonates (PDS) in crude oil that was simply diluted with the dichloromethane/methanol (60/40). The high performance liquid chromatography (HPLC) system consisted of a clean-up column and an analytical column, which were connected with two six-port switching valves. Detection of petroleum sulfonates was available and repeatable. This method has been successfully applied to determine PMS and PDS in crude oil samples from Shengli oil field. # 2007 Sheng Xiang Jiang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Petroleum sulfonate; Determination; Anion-exchange chromatography; Column-switching; Crude oil
Petroleum sulfonates are used to reduce the interfacial tension between the oil and water, thereby easing the flow of oil through the rock pores. In order to understand better the flooding behavior of petroleum sulfonates when used in EOR processes, it is necessary to establish reliable and simple techniques and methods for the detection of petroleum monosulfonates (PMS) and petroleum disulfonates (PDS) in crude oil samples. Various methods of high performance liquid chromatography (HPLC) have been developed for determining petroleum sulfonates in hydrophilic samples [1–4]. Many techniques and methods, involving solid-phase extraction, various modes of HPLC, capillary electrophoresis, GC–mass spectrometry, liquid chromatography–mass spectrometry, and flow injection-mass spectrometry methods, etc., have also been employed for the analysis of aromatic sulfonates in aqueous media [5–14]. However, strategies thus far reported were not available for the separation and determination of PMS and PDS at low concentration level in crude oil. This paper describes the separation and determination of PMS and PDS at low concentration level in crude oil by a column-switching anion-exchange chromatography method. Both the purification and separation processes are carried out on two strong anionexchange columns and two six-port switching valves, which provide a unique means for the selective separation of PMS and PDS in crude oil.
* Corresponding author. E-mail address: [email protected] (S.X. Jiang). 1001-8417/$ – see front matter # 2007 Sheng Xiang Jiang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2007.12.015
220
L. Zhao et al. / Chinese Chemical Letters 19 (2008) 219–222
Fig. 1. A schematic diagram of the column-switching HPLC system. The arrows indicate the direction of the flow depending on the valve position: dashed line, V1/V2 = II/II (clean-up), bold line, V1/V2 = I/I (analysis) (V1 and V2: six-port switching valve).
1. Experimental Sodium 2-naphthalene sulfonates (2-NS) and sodium 1,5-naphthalene disulfonates (1,5-NDS) were dissolved in methanol and was further diluted in methanol as a series stock solution. Spiked crude oil samples were prepared by addition of the series stock solution to blank crude oil solutions giving the final content of 2-NS of 9.6, 48.0, 96.0, 192.0, 480.0 mg/mL and 1,5-NDS of 8.0, 40.0, 80.0, 160.0, 400.0 mg/mL in crude oil solutions, respectively. The blank crude oil solutions were obtained by weighing 1.0 g of crude oil and in an ultrasonic bath dissolving in 10 mL of dichloromethane/methanol (60/40) to require concentration of 100 mg/mL before the spiked crude oil samples were prepared. The analytical sample was prepared by weighing 1.0 g of crude oil sample from oil field and in an ultrasonic bath dissolving in 10 mL of dichloromethane/methanol (60/40). Three mobile phases were used for the separation: (mobile phase A) dichloromethane; (mobile phase B) methanol–water (60:40); and (mobile phase C) methanol– 0.3 mol/L NaH2PO4 (60:40). All mobile phases flow-rate were 1.0 mL/min. The quantification wavelength was 278 nm and all separations were carried out at room temperature. A schematic diagram of the column-switching HPLC system is show in Fig. 1. The column-switching valves 1 and 2 were placed in position II. Crude oil sample was injected onto the clean-up column. The interfering compounds in the crude oil sample were washed to waste tank by isocratic elution using mobile phase A (100%) at a flow-rate of 1.0 mL/min for 10 min. After on-line purification of the crude oil sample on the clean-up column, the switching valve 1 was shifted to position I and the clean-up column was equilibrated for 10 min by passing through mobile phase B (100%). The switching valve 2 was turned to position I and the analytes enriched on the clean-up column were eluted into the analytical column and separated by gradient elution immediately after valve switching. The gradient begins with mobile phase B (100%) for 5 min. During the 5 to 10 min the concentration of mobile phase B is decreased exponentially from 100 to 0% while the concentration of mobile phase C is increased exponentially from 0 to 100%. Then mobile phase C remained for 10 min in a total elution time of 15 min. 2. Results and discussion Separation of petroleum sulfonates according to the hydrophilic end may be achieved by anion-exchange HPLC. However, it is difficult to separate and analyze PMS and PDS in crude oil, in which a large amount of organic matters can be co-eluted on the analytical column and result in the hump of interference peaks in the chromatogram. Columnswitching techniques, which can regulate the flowing way and composition of mobile phase to eliminate interference and improve selectivity, offer a simple means of rapid analysis of the target compounds in complex mixtures. For online determination of petroleum sulfonates in crude oil samples, it is necessary to choose a clean-up column, which can selectively adsorb petroleum sulfonates rather than the interfering compounds in crude oil samples. In this study, the strong anion-exchange column has been served as the clean-up column for highly selective adsorbing petroleum sulfonates in crude oil. In using dichloromethane as washing solvents, the majority of interfering compounds were
L. Zhao et al. / Chinese Chemical Letters 19 (2008) 219–222
221
Fig. 2. Chromatograms of crude oil samples on the column-switching system.
Fig. 3. Peak 1, 2-NS; peak 2, 1,5-NDS.
quickly eluted while there was strong retention of petroleum sulfonates adsorbed on the clean-up column. The petroleum sulfonates were subsequently transferred to the analytical column and further separation by switching the valve position and with other mobile phase. Fig. 2 shows a chromatogram of blank crude oil on the column-switching system. As demonstrated by the chromatogram, interfering compounds in crude oil have no significant interference on the determination of petroleum sulfonates. Fig. 3 shows the typical chromatogram of crude oil containing 48.0 and 40.0 mg/mL of 2-NS and 1,5-NDS on the column-switching system. As shown, naphthalene sulfontes with different numbers of sulfonic groups are well separated. Fig. 4 shows a chromatogram of real crude oil sample on the columnswitching system. As shown, petroleum sulfonates are separated into monosulfonate and disulfonate groups.
Fig. 4. Peak 1, PMS; peak 2, PDS.
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L. Zhao et al. / Chinese Chemical Letters 19 (2008) 219–222
Table 1 Analytical samples determination Samples
PMS (mg/mL)
PDS (mg/mL)
1 2 3 4
33.4 61.4 179.7 212.3
30.1 55.0 163.9 187.5
The standard calibration curves for spiked crude oil containing 2-NS and 1,5-NDS were linear in the range of 9.6– 480.0 mg/mL and 8.0–400.0 mg/mL with correlation coefficient greater than 0.997 and 0.998, respectively. Recovery was tested by adding three known quantities (in the concentration range of calibration curve) of 2-NS and 1,5-NDS to real sample. The recovery was 92.0–102.9% for 2-NS and 92.6–105.5% for 1,5-NDS. Reproducibility was evaluated by carrying out the determination six times on the same standard solution of 2-NS and 1,5-NDS. The relative standard deviation (RSD) was 3.0% for 2-NS, and 4.3% for 1,5-NDS. The limit of detection for PMS and PDS was set to 10.0 and 12.5 mg/mL in crude oil solutions, which is the lowest concentration of the analytes that can be measured with a coefficient of variation less than 10%. As an application of the proposed method, the determination of petroleum sulfonates in crude oil samples was tried. Four analytical samples were determinated by the column-switching procedure. A typical chromatogram of the samples was obtained on the column-switching system(shown in Fig. 4), and the results of the determination of PMS and PDS in the samples were shown in Table 1. 3. Conclusion A simple and reliable column-switching HPLC method for the determination of petroleum sulfonates in crude oil was developed. The method seems to be advantageous over other methods reported so far in literature in terms of separation efficiency and processing procedure of sample, especially in the case of the crude oil sample because there is great difficulty in processing sample. This method was successfully applied to the determination of concentrations of PMS and PDS in crude oil. Obviously, the column-switching technique described in this paper is applicable to study the flooding performance of petroleum sulfonates used in EOR processes. Acknowledgments We are grateful to the National Nature Science Foundation of China (No. 20675085). We are also grateful to the support from the Program of the Light in China’s Western Region (2003) and the Province Nature Science Foundation of Gansu (No. 3ZS041-A25-23). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]
R.E. Barden, D.A. Jaeger, P.S. Ossip, J. Chromatogr. A 109 (1975) 377. G.R. Bear, C.W. Lawley, R.M. Riddle, J. Chromatogr. A 302 (1984) 65. Y.B. Liu, L. Zhao, L.R. Chen, Chin. J. Oilfield Chem. 4 (1987) 305. S.X. Jiang, L.R. Chen, Chin. J. Anal. Chem. 20 (1992) 677. T. Reemtsma, J. Chromatogr. A 733 (1996) 473. T. Reemtsma, J. Chromatogr. A 1000 (2003) 477. T.P. Knepper, J. Chromatogr. A 974 (2002) 111. A. Rigol, A. Latorre, S. Lacorte, D. Barcelo, J. Chromatogr. A 963 (2002) 265. T. Reemtsma, J. Chromatogr. A 919 (2001) 289. E. Marengo, M.C. Gennaro, V. Gianotti, Chemometr. Intell. Lab. Syst. 53 (2000) 57. R. Loos, M.C. Alonso, D. Barcelo, J. Chromatogr. A 890 (2000) 225. T. Storm, T. Reemtsma, M. Jekel, J. Chromatogr. A 854 (1999) 175. S. Angelino, A.B. Prevot, M.C. Gennaro, E. Pramauro, J. Chromatogr. A 845 (1999) 257. R. Loos, R. Niessner, J. Chromatogr. A 822 (1998) 291.