Effect of pH on the stability of crude oil emulsions

doi:10.16085/j.issn.1000-6613.2015.07.007

Abstract

Abstract: The effect of pH on stability of crude oil emulsions was studied. The aggregation and spreading behaviors of resins and asphaltenes on oil-water interface were measured. In addition, the interfacial tension (IFT) and conductivity of model emulsions stabilized by the resin and asphaltene respectively were measured under different pH values. The results indicate that the asphaltenes are easier to aggregate and spread to form high viscoelasticity film than resins. When pH in the acidic range or in the basic range, the IFT both decreases, which enhances the stability and demulsification difficulty of emulsions, and the demulsification experiments are in agreement with it. It has a remarkable change in the stability of resin-stabilized and asphaltene-stabilized emulsions, respectively. When the pH increases from 2 to 10, and their change trends are opposite, pH 2 to 10, the stability of resin-stabilized emulsion increased, the oil-water separation speed slower, the stability of asphaltene-stabilized emulsions decreases, change of the conductivity:0.21—1.8mS/cm. Therefore, when pH < 7, asphaltenes film is strongest, resins film is weakest, the electric dehydrator works normally during the electric dehydration process; however, the results are opposite when pH > 7, all of these demonstrate that the short circuit has a relationship with the change of stability of asphaltenes and resins.

Key words: electric dehydration, crude oil emulsion, short circuit, pH

摘要： 研究了pH值对原油乳状液稳定性的影响, 测定了胶质和沥青质在油水界面上的聚集和铺张情况, 不同pH值下油水界面张力以及胶质和沥青质模拟乳状液的稳定性变化, 并且完成了不同pH值下的乳状液化学破乳以及电场破乳实验。沥青质相对胶质更易在界面上聚集和铺展, 形成高黏弹性的界面膜。pH值为酸性或碱性时都能有效降低油水界面张力, 增加乳状液稳定性, 使其化学破乳脱水困难, 而破乳实验也验证了这一观点。随着pH值从2增加到10, 胶质模拟乳状液和沥青质模拟乳状液稳定性变化大, 变化趋势则刚好相反, 胶质模拟乳状液稳定性增加, 油水分离速度减慢;沥青质模拟乳状液稳定性减弱, 体系电导率0.21～1.8mS/cm。因此pH<7时, 沥青质稳定能力强, 而胶质稳定能力弱, 电脱水过程中电脱装置正常工作;pH>7时, 结果相反, 表明电脱装置短路现象与沥青质、胶质稳定能力变化相关。

关键词: 电脱水, 原油乳状液, 短路, pH值

CLC Number:

DUAN Ming, TAO Jun, FANG Shenwen, SHI Peng, LI Keyi, SONG Xianyu, TAO Tao. Effect of pH on the stability of crude oil emulsions[J]. Chemical Industry and Engineering Progree, 2015, 34(07): 1853-1857.

段明, 陶俊, 方申文, 施鹏, 李珂怡, 宋先雨, 陶滔. pH值对原油乳状液稳定性的影响[J]. 化工进展, 2015, 34(07): 1853-1857.

References

[1] Mohammed R A, Bailey A I, Luckham P F, et al. Dewatering of crude oil emulsions 1. Rheological behavior of the crude oil-water interface [J]. Colloids Surf. A., 1993, 80:223-235.
[2] 石斌龙, 张谋真, 程蝉, 等. TA162824原油破乳剂的复配[J]. 化工进展, 2013, 32(3):678-680.
[3] 姜佳丽, 苟社全, 达建文, 等. 原油破乳研究进展[J]. 化工进展, 2009, 28(2):214-221.
[4] 刘娟, 赵亚溥, 胡斌, 等. 油水乳状液的稳定机理及其化学破乳技术的研究进展[J]. 化工进展, 2013, 32(4):891-897.
[5] Bailes P J, Larkai S K L. Liquid phase separation in pulsed d.c. fields[J]. Trans. IChemE., 1982, 60:115-121.
[6] Allan R S, Mason S G. Effects of electric fields on coalescence in liquid+liquid systems[J]. Trans. Faraday Soc., 1961, 57:2027-2040.
[7] Brown A H, Hanson C. Effect of oscillating electric fields on coalescence in liquid+liquid systems[J]. Trans. Faraday Soc., 1965, 61:1754-1760.
[8] 陈庆国, 梁雯, 宋春辉. 电场强度对原油乳状液破乳脱水的影响[J]. 高电压技术, 2014, 40(1):173-180.
[9] Mousavi S H, Ghadiri M, Buckley M. Electro-coalescence of water drops in oils under pulsatile electric fields[J]. Chem. Eng. Sci., 2014, 120:130-142.
[10] 郭海军, 段明, 张健, 等. 酸化返排液对原油乳状液稳定性的影响[J]. 油田化学, 2008, 25(2):130-132.
[11] 项玉芝. 酸化返排液中分理出的原油脱水时电脱水器跳闸原因及对策[J]. 油田化学, 2003, 20(4):342-344.
[12] 吴泽美, 孙玉民, 史贵生, 等. 酸化后原油电脱水困难原因分析[J]. 长江大学学报:自然科学版, 2011, 8(4):52-53.
[13] Poteau S, Argillier J F, Langevin D, et al. Influence of pH on stability and dynamic properties of asphaltene and other amphiphilic molecules at the oil-water interface[J]. Energy & Fuels, 2005, 19:1337-1341.
[14] Taylor S E. Investigations into the electrical and coalescence behaviour of water-in-crude oil emulsions in high voltage gradients[J]. Colloids Surf., 1988, 29:29-51.
[15] Chen T Y, Mohammed R A, Bailey A I, et al. Dewatering of crude oil emulsions 4. Emulsion resolution by the application of an electric field[J]. Colloids Surf. A, 1994, 83:273-284.