Article pubs.acs.org/IECR
Effect of Rheology Properties of Oil/Water Interface on Demulsification of Crude Oil Emulsions Jun Tao,† Peng Shi,†,‡ Shenwen Fang,†,‡ Keyi Li,† Heng Zhang,† and Ming Duan*,†,‡ †
School of Chemistry and Chemical Engineering, Southwest Petroleum University, Chengdu, Sichuan 610500, China Oil & Gas Field Applied Chemistry Key Laboratory of Sichuan Province, Southwest Petroleum University, Chengdu, Sichuan 610500, China
‡
ABSTRACT: Chemical demulsification is widely used in the petroleum industry to remove water from crude oil all over the world. In this work, the relationship between the rheological properties of oil/water interfacial film and demulsification of crude oil emulsions was investigated. The results showed that the elastic modulus was the critical factor for the dehydration ratio, the emulsions showed high dehydration ratio when demulsifiers reduced the elastic modulus of oil−water film to a certain extent (below 5 mN/m). Correlations between dehydration ratio and equilibrium interfacial tension, dynamic interfacial tension, and loss modulus were also investigated. The results showed no correlation between the interfacial tension (IFT), the loss modulus, and the dehydration ratio. However, correlations were observed between dynamic IFT, loss modulus, and demulsification speed when the demulsifier could reduce the elastic modulus of the oil−water film to MD-3 > blank, which was consistent with the demulsification speed. 3.2. Film Rheology. According to eq 1, the effect of demulsifiers on the dilational modulus of the oil/water interfacial film was measured. The relationship between the dehydration ratio of emulsions and the dilational modulus values is presented in Figure 5. As shown in Figure 5, most of the emulsions were broken effectively when the dilational modulus was ∼6 mN/m. However, the dehydration ratio of MD-4, MD-5, and MD-6 could not be explained well by the dilational modulus data (i.e., the dilational modulus values of
Figure 4. Microscope observation of size of water droplets during the demulsification process.
MD-4, MD-5, and MD-6 were almost the same, but their dehydration ratios were different). Since the dilational modulus could be divided into an elastic modulus component and a loss modulus component, experiD
DOI: 10.1021/acs.iecr.5b00639 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research
shows the relationship between the loss modulus and the dehydration ratio. Obviously, the loss modulus had a poor correlation with demulsifier performance. Nevertheless, as defined in eq 3, the loss modulus is directly proportional to the surface viscosity: the lower the loss modulus, the smaller the surface viscosity. Figure 7 shows the
Figure 5. Effect of dilational modulus on the demulsification of crude oil emulsions.
ments for the elastic modulus andthe loss modulus were conducted. The results are shown in Figures 6a and 6b. Figure
Figure 7. Comparison between loss modulus and the viscosity of oil/ water interfacial film.
relationship between the loss modulus and the surface viscosity, which confirmed this point. The surface viscosity has an important effect on the diffusion and arrangement of demulsifier at the oil/water interface. Generally, low surface viscosity will promote the diffusion and arrangement of demulsifier at the interface. The film then would become thinner and rupture, thus increasing the demulsification speed of crude oil emulsions. Therefore, the loss modulus may be related to the demulsification speed due to the surface viscosity. As shown in Figure 8, the loss modulus does have a relationship
Figure 6. Effect of (a) elastic modulus and (b) loss modulus on the demulsification of crude oil emulsions.
6a shows the relationship between the elastic modulus of emulsions and the dehydration ratio. Obviously, the emulsions showed high dehydration ratios when the elastic modulus of interfacial film was
