Adsorption Behavior of Betaine-Type Surfactant on Quartz Sand

(15) studied the adsorption of N-dodecyl betaine (NDB) on silica gel and found that the adsorption of NDB depended upon the content of salt in the sol...
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Adsorption Behavior of Betaine-Type Surfactant on Quartz Sand Na Li,† Guicai Zhang,*,†,‡ Jijiang Ge,† Jin Luchao,† Zhang Jianqiang,† Ding Baodong,† and Haihua Pei† †

Petroleum Engineering College, and ‡State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao 266555, People’s Republic of China ABSTRACT: The betaine-type amphoteric surfactant exhibits excellent ability in reducing oilwater interfacial tension for many kinds of crude oil, but less attention is paid to its adsorption behavior on oil reservoir rock. In this paper, a high-performance liquid chromatography (HPLC) method is established to measure the adsorption of betaine on quartz sand. The mobile phase consists of methanol and water (methanol/water = 90:10 or 85:15 by volume). The column temperature is 40 °C; the flow rate is 1 mL/min; and the sample volume is 20 mL. On the basis of this method, the adsorption of the betaine-type surfactant and sodium dodecyl benzene sulfonate (SDBS) in different conditions was measured and compared. The results indicate that the adsorption of the carboxybetaine-type surfactant and sulfobetaine-type surfactant decreases first and then increases with the increase of the NaCl concentration and reaches relatively low points when the concentration of NaCl is 5 and 1020 wt %, respectively. The adsorption of SDBS increases with the NaCl concentration monotonically, which is at least 50% higher than that of the betaine surfactant when the concentration of NaCl is over 5 wt %. After Ca2+ was added to the solution, the adsorption of the betaine-type surfactant on the quartz sand surface, as the opposite case of SDBS, decreases. Moreover, it is found that the adsorption of betaine on the surface of quartz correspondingly decreases with the increase of pH. These behaviors can be explained by the charges of the betaine-type surfactant molecule and the quartz surface. The investigation is instructive for surfactant selection for enhanced oil recovery (EOR).

1. INTRODUCTION Chemical combination flooding is a tertiary recovery technique developed in the 1980s.1 Since the 1990s, 12 industrial pilot tests have been launched successively in the Daqing, Shengli, and Karamay oilfields in China. These field tests indicate that chemical combination flooding can improve the oil recovery factor by 20%.2 However, this technology still has some deficiencies. One problem is the scaling resulting from the reaction of alkali and the calcium ion in the injection water or formation rock, which interferes with the usual injection and impairs the oil production. Besides, a higher concentration of alkali (0.61.2 wt %) is added to the combination-flooding system with the request of ultra-low interfacial tension (IFT), especially for the oil with a low acid number. However, lots of remaining alkali in the solution may cause a salt-sensitive effect on polymer; therefore, the capability of the combination-flooding system to improve sweep efficiency is weakened. In view of these problems, an alkali-free combinationflooding technique, i.e., surfactantpolymer (SP) flooding, has been developed in recent years in the Shengli and Daqing oilfields. Surfactants usually used in combination flooding are petroleum sulfonate, alkylbenzene sulfonate, sodium dodecyl benzene sulfonate (SDBS), etc.3 It is difficult for these surfactants to reduce the IFT to ultra-low ( CBET-17 > SBET-17. It is easy to understand the effects of Ca2+ on the adsorption of the betaine surfactant from the electrostatic interaction. In comparison to Na+, Ca2+ has a stronger ability to compress the diffuse electric double layer on the quartz surface. Therefore, the electronegativity of the quartz surface is further weakened after 300 mg/L Ca2+ is added to 1% NaCl brine solution, which causes the decrease in the adsorption of the betaine surfactant and the sharp increase in the adsorption of SDBS. When the concentration of Ca2+ in solution is increased from 300 to 500 mg/L, the electronegativity on the surface of quartz is further reduced; accordingly, the adsorption of SDBS, which is a electronegative surfactant, continuously increases, while for the betaine surfactant, its adsorption is lower than that in pure brine but is higher than that in the solution with 1% NaCl and 300 mg/L Ca2+. This

Figure 14. Effect of Ca2+ on the adsorption of SDBS.

behavior is related to the electrostatic interaction macroscopically, while microscopically, it is related to the alternation of the adsorption pattern of the betaine surfactant on the surface of quartz with or without the appearance of Ca2+ in solution. Three patterns about the adsorption of the betaine surfactant on the negatively charged solid have been proposed by Hu et al.12 as follows: when there is no Ca2+, the betaine surfactant is adsorbed on the solid surface through an electrostatic interaction and oriented to the solid surface with the quaternary nitrogen group becoming close to the surface and the anionic group becoming far from the surface. In this case, the stronger negative interaction energies in this system cause the adsorption to occur more easily. When some of the solid surface is covered with Ca2+, an oblique adsorption pattern appears, in which the anionic part of the betaine surfactant is closer to the silica surface as a result of the attraction between Ca2+ and the sulfonate group of the betaine surfactant, while the cationic quaternary ammonium part of the betaine surfactant is attracted by the net negative charge of the surface. As the number of Ca2+ covering the quartz surface continues to increase, the quartz surface would become positively charged. Then, the repulsion between cationic groups and Ca2+ 4435

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with a negative charge declines. In 1996, Chavez et al.31 also found that the adsorption of betaine on Si3N4 and Al2O3 decreased with the increase of pH when the pH of the medium was higher than the isoelectric point. Chavez et al. thought that it was because the hydrated OH ion had a strong ability to bind with positive sites in the betaine molecule at a high pH value, which weakened the electrostatic interaction between betaine and the solid surface. In summary, the adsorption behavoir of the betaine surfactant is obviously different from that of the conventional surfactant (SDBS). With the presence of NaCl and Ca2+ in solution, the adsorption of SDBS always increases and exhibits less resistance to both NaCl and Ca2+. However, for the betaine surfactant, the adsorption decreases first and then increases with the increase of the NaCl concentration. Furthermore, the adsorption of betaine in the presence of Ca2+ in the solution is obviously lower than that without Ca2+. These results show that betaine has excellent resistance to both NaCl and Ca2+. Figure 15. Effect of alkali on the adsorption of CBET-17.

4. CONCLUSION A HPLC method is established to measure the adsorption of betaine. The mobile phase is the mixture of methanol and water (methanol/water = 90:10 or 85:15 by volume); the column temperature is at 40 °C; the flow rate is 1 mL/min; and the sample volume is 20 mL. With the increase of the NaCl concentration, the adsorption of CBET-17 and SBET-17 decreases first and then increases and is relatively low when the concentration of NaCl is 5 and 1020 wt %, respectively. While the adsorption of SDBS increases with the concentration of NaCl monotonically, which is at least 50% higher than those of betaine surfactants when the concentration of salt in the solution is larger than 5 wt %. After Ca2+ is added to the solution of 1 wt % NaCl, the adsorption of betaine on the quartz sand obviously decreases, while the adsorption of SDBS obviously increases. With the increase of alkalinity in the aqueous solution, the adsorption of the betaine surfactant correspondingly decreases. Figure 16. Effect of alkali on the adsorption of SBET-17.

and the attraction between anionic groups and Ca2+ would make the betaine molecule adsorb on the quartz surface in a vertical way. These different adsorption patterns determine varying interaction energies. The results of molecular dynamic simulation indicate that the negative interaction energy is the strongest in the first case and the negative interaction energy in the second case is less than that in the last case.12 This evidence can be used to explain the trend that the adsorption of the betaine surfactant in the solution with 1% NaCl and 300 mg/L Ca2+ is a little less than that when 1% NaCl and 500 mg/L Ca2+ are present in the solution. 3.2.3. Effect of Alkali. The electronegativity of the quartz surface increases with the alkalinity in solution. Therefore, the adsorption of betaine on the quartz surface would also increase according to the explanation mentioned above. However, the results are just the opposite, with the adsorption decreasing after NaOH is added to the solution of 1 wt % NaCl, as shown in Figures 15 and 16. In fact, the anionic part of the betaine surfactant, which may ionize completely in alkalic solution, dominates the electric property of the surfactant with the increase of the pH value in aqueous solution; therefore, its adsorption on the solid

’ AUTHOR INFORMATION Corresponding Author

*Telephone: +8653286981178. E-mail: [email protected]. com.

’ ACKNOWLEDGMENT Financial support from the National Natural Science Foundation of China (51104170), the New Century Excellent Talents Awards Program from the Ministry of Education of China (NECT-07-0846), and the Fok Ying Tung Education Foundation (114016) is gratefully acknowledged. ’ REFERENCES (1) Nelson, R. C.; Lawson, J. B.; Thigpen, D. R.; Stegemeier, G. L. Proceedings of the 1984 Society of Petroleum Engineers (SPE) Enhanced Oil Recovery Symposium; Tulsa, OK, April 1518, 1984; SPE Paper 12672. (2) Gao, S.; Gao, Q. Proceedings of the 2010 Society of Petroleum Engineers (SPE) Enhanced Oil Recovery (EOR) Conference at Oil and Gas West Asia; Muscat, Oman, April 1113, 2010; SPE Paper 127714. (3) Yang, J.; Qiao, W.; Li, Z.; Cheng, L. Fuel 2005, 84, 1607–1611. (4) Li, Y.; He, X.; Cao, X.; Zhao, G.; Tian, X.; Cui, X. J. Colloid Interface Sci. 2007, 307, 215–220. 4436

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