Zhao Sui

Effect of Acidic Components on the Dynamic Interfacial Tensions in Surfactant/Alkali/Acidic Crude Oil Systems

The acidic components have been extracted from the crude oil by solvents. The dynamic interfacial tensions (IFTs) in surfactant/alkali/acidic crude oil or the residual oil systems were investigated by spinning drop method. The transient, the minimum and the stable IFT values were obtained. It is shown that the acidic components play an important role in lowering IFTs between the alkaline solutions and the crude oil or affecting IFTs between the surfactant solutions and the crude oil when the ionic strength is low. The minima of dynamic IFTs are affected by both the adsorption-desorption barriers and the concentrations and the ratios of the interfacial active substances on the interfaces.

Adsorption Behavior of Cationic and Zwitterionic Surfactants on Poly(methyl methacrylate)

The wetting behavior of poly(methyl methacrylate) (PMMA) surfaces by aqueous solutions of cationic surfactants, hexadecanol glycidyl ether ammonium chloride (C16PC), hexadecanol polyoxyethylene (3) glycidyl ether ammonium chloride (C16(EO)3PC), and zwitterionic surfactants, hexadecanol glycidyl ether glycine betaine (C16PB) and hexadecanol polyoxyethylene(3) glycidyl ether glycine betaine (C16(EO)3PB), were investigated by sessile drop analysis. The influence of surfactant type and concentration on contact angle was determined. The PMMA surface is modified hydrophobically only slightly at low bulk concentration because the surfactant molecules are parallel to the substrate surface and the hydrophilic groups are close to the surface. However, at high concentration, the surfactant molecules can adsorb onto the PMMA surface through Lifshitz-van der Waals interactions and hydrophilic groups directed towards the bulk phase of solution, which increases the hydrophilic character of the PMMA surface. The contact angles of cationic surfactants show little variation following the insertion of polyoxyethylene units. However, the presence of polyoxyethylene units in the zwitterionic surfactants leads to an obvious decrease of contact angle because of the formation of hemimicelles on the PMMA surface.

Effect of Hydrophobically Modified Polyacrylamide on Interfacial Dilational Rheological Properties of Crude Oil Components

The effect of hydrophobically modified polyacrylamide (HMPAM) on the dilational rheological properties of interfacial films containing acidic components or asphaltenes in petroleum crude oil was investigated by drop shape analysis method. The influence of surface-active component concentration on the dilational rheological behavior was investigated. Experimental results show that the dilational modulus is approximately 100 mN·m-1 for a 1750 mg·L-1 HMPAM solution. This is due to the formation of an interfacial structure by a hydrophobic interaction among HMPAM molecules. As the interfacial film ages, the acidic component molecules adsorb onto the interface and form mixed complexes with the hydrophobic parts of the HMPAM molecules. These interactions reduce the dilational modulus by a fast exchange process and the elasticity of the structure improves because of an enhanced hydrophobic interaction among the HMPAM molecules. For asphaltenes, the nature of the interfacial film is controlled by both the structure of HMPAM and the interfacial complex formed by pure asphaltene molecules because of their relatively larger molecular sizes as well as their strong intermolecular interactions, which leads to a slight decrease in the dilational modulus compared with the pure HMPAM system.

Interfacial Dilational Properties of Tri-Substituted Alkyl Benzene Sulfonates

The dilational rheological properties of five types of surfactants:sodium 3,4-dihexylbenzene sulfonate (66),sodium 3,4-diheptylbenzene sulfonate (77),sodium 2-ethyl-4,5-dihexylbenzene sulfonate (266),sodium 2-propyl4,5-dihexylbenzene sulfonate (366),and sodium 2-butyl-4,5-dihexylbenzene sulfonate (466) at the air-water and decanewater interfaces were investigated by a drop shape analysis method.The influence of hydrophobic chains located at different positions on the benzene ring on the interfacial molecular behavior was investigated.Experimental results showed that the hydrophobic chains that were located at different positions affected the dilational elasticity and dilational viscosity differently.The dilational elasticity appeared to increase with an increase in the length of the hydrophobic group and the dilational viscosity behaved differently.The short alkyl chain (2-4) ortho to the sulfonate group had little influence on the dilational viscosity,while an increase in the long meta alkyl group played an important role in the surface relaxation process,which resulted in higher surface dilational viscosity.The insertion of decane molecules from the oil phase weakened the strong interactions between the meta-alkyl chains and therefore the interfacial dilational parameters were obviously lower than those of the surface.We also found that the interfacial dilational viscosities of a pair of structural isomers,77 and 266,were approximately equal.

Effects of Surfactants on Interfacial Shear Rheological Properties of Polymers for Enhanced Oil Recovery

The effects of surfactants, namely sodium dodecylbenzenesulfonate(SDBS) and hexadecyltrimethylammonium bromide(CTAB), on the interfacial shear rheological properties of partially hydrolyzed polyacrylamide(PHPAM) and hydrophobically modified polyacrylamide(HMPAM) solutions, which are used in oilfields, were studied using a biconical method. The experimental results show that the interfacial shear complex modulus of HMPAM is significantly higher than that of PHPAM, because an interfacial net structure can be formed by HMPAM molecules through hydrophobic interactions. The SDBS and CTAB molecules can form interfacial aggregates with hydrophobic blocks of HMPAM and destroy the interfacial net structure, which results in a significant decrease in the shear modulus with increasing surfactant concentration. At the same time, the properties of the interfacial film change from viscous to elastic. At low SDBS concentrations, the mixed adsorption film formed by PHPAM and a few SDBS molecules has enhanced strength. However, SDBS molecules can displace PHPAM molecules at the interface and weaken the film at higher surfactant concentrations. The cationic surfactant CTAB neutralizes the negative charge on PHPAM, leading to partial curling of the polymer chain, which decreases the film strength. Relaxation measurements confirmed our mechanism involving destruction of the interfacial netstructure of HMPAM by the surfactant.