Interfacial Shear Rheology of Calcium Naphthenate at the Oil/Water Interface and the Influence of pH,Calcium, and in Presence of a Model Monoacid

In this article, the interfacial shear rheological properties of calcium naphthenate with a model tetraacid at the chloroform/xylene-water interface has been investigated as a function of aqueous pH, calcium concentration and monoacid concentration. The experiments are carried out using an interfacial rheology system with an electro commutated motor, direct strain oscillation and a biconical bob geometry. The model tetraacid used, BP10, has previously been shown to have similar bulk and interfacial properties as a narrow group of tetraprotic, so-called Arn acids, and these acids are known to be responsible for formation of hard deposits during oil recovery. A great increase in the elastic modulus was observed around pH 6.2, which is in agreement with observations from oil fields with calcium naphthenate deposition problems. The gel strength and elastic nature is highest around the gelation onset, believed to be due to a bilayer-like conformation of the tetraacid generating a densely packed interface with high cross-linking density and possible film growth. As a function of calcium concentration, both a reduction of the gel strength and slower gel formation was observed when decreasing the calcium concentration from 10 to 4 mM. Myristic acid, a linear C14 fatty acid, was employed as a model for indigenous monoacids and the influence onto the viscoelastic properties of the Ca²⁺-TA film was studied as a function of myristic acid concentration at pH 8.0 and 6.5. A great reduction of both the gel strength and elasticity was obvious in the range of 100 to 1000 higher monoacid than tetraacid concentration. This is however typical indigenous acid concentrations for an acidic crude oil, and may indicate that indigenous monoacids have the ability to act as indigenous inhibitors towards formation of calcium naphthenate. This could explain why some Arn-containing acidic crude oils have deposition problems while others do not. Moreover, all parameters should be taken into account when predicting the deposition risk for a given crude oil, such as concentrations of Ca²⁺, Arn, monoacids and other indigenous acids.     

Model compounds for C80 isoprenoid tetraacids: Part II. Interfacial reactions, physicochemical properties and comparison with indigenous tetraacids

Novel model compounds are desired to study properties of a narrow group of tetrameric acids from crude oil mainly responsible for naphthenate deposition. It is important to make a comparison to find to what degree the model compounds can reflect the properties of the indigenous tetraacids and where there are deviations, before using the model compounds in naphthenate research. A comparison between two synthesised model compounds and indigenous tetraacids has been carried out regarding physicochemical properties including thermal solid state properties, critical micelle concentrations, monolayer properties and interfacial reactions. Of the two studied model compounds, one was observed to form the same cross-linked network with Ca²⁺, a typical feature of the indigenous tetraacids. Interfacial reactions using the pendant drop technique also showed that four different divalent cations could all form this network with the model tetraacid. The film formation was however dependent on the ratio M²⁺/TA. The main deviations were in the solid state, where the model compounds showed crystalline transitions, contrary to the indigenous tetraacids. We conclude that the two different model compounds mimic the indigenous tetraacids well with respect to several of their properties and are suitable for use in naphthenate research.     

环烷酸对油水界面膜流变性质的影响研究

研究了环烷酸对油水界面膜界面张力、弹性模量、损耗模量以及界面膜破裂速率常数的影响,同时对环烷酸与沥青质之间的相互作用进行了测定。结果表明,环烷酸使得原油油水界面张力下降;弹性模量随着环烷酸加量以及振荡频率的增加都分别逐渐增大,并且最终都趋于平衡;在任何振荡频率值时,损耗模量都随着环烷酸加量先增大后减小;当环烷酸加量增加时,界面膜破裂速率常数降低。环烷酸与沥青质之间存在相互作用,随着环烷酸加量的增加,其对沥青质界面膜弹性模量的影响与对原油界面膜弹性模量的影响相似,表明环烷酸主要是通过与沥青质相互作用而促进乳状液稳定性的。     

The chemistry of tetrameric acids in petroleum

This article reviews the properties of a novel class of molecules: the tetrameric acids. These molecules have brought a large interest in petroleum science since the discovery of the family of molecules named ARN in 2004. ARN, which is naturally present in oil, is responsible, by reaction with calcium ion, of the formation of calcium naphthenate deposits; organic deposits that cause irregularities in crude oil production and processing. In order to study the properties of ARN, a model tetrameric acid molecule mimicking some of its properties named BP-10 has been developed in 2008 by Nordgård and Sjöblom and has been extensively used since then.     

短链烷基对多取代烷基苯磺酸盐界面性质的影响

利用悬挂滴方法研究了2,5-二乙基-4-壬基苯磺酸钠(292)、2,5-二丙基-4-壬基苯磺酸钠(393)和2,5-二丁基-4-壬基苯磺酸钠(494)在空气-水表面和正癸烷-水界面的扩张流变性质,考察了时间、界面压、工作频率及体相浓度对扩张弹性和粘性的影响。研究发现,在低表面活性剂浓度条件下,表面吸附膜类似弹性膜,其强度由膜内分子的相互作用决定;高浓度下体相与表面间的扩散交换过程控制表面膜的性质。油分子的插入导致界面吸附分子之间相互作用的削弱,扩散交换过程主导界面膜性质;但随着短链烷基长度增加,油分子的影响变小。表面膜的强度在吸附达到平衡前已经决定,而界面膜在吸附饱和后仍然随界面分子重排而变化。     

Ion‐Specific Self‐Assembly of Low‐Dimension Aggregate Structures of Conjugated Polymer at Two‐Phase Interface

A novel and facile approach to manipulate the morphology of Cu²⁺‐ion‐specific assembly of conjugated polymer by coordinative interaction at an oil–water two‐phase interface is present. The application of increasing importance is the use of π‐conjugated polymers as receptors, exploiting their ability to selectively form complexes, which can obviously change the optical properties in solution and induce the formation of varied solid nano/microstructures. By this method, microtubes are formed through self‐rolling of a strained ionic bilayer film at the oil/water interface.     

Influence of demulsifier on interfacial film between oil and water

Demulsification of a synthetic water in oil (W/O) crude oil emulsion was studied by measuring water–oil interfacial properties such as life time and thinning rate of oil film in the presence of various demulsifiers. The results indicated that the interfacial elasticity decreased both the strength and the life time of oil film and film thickness when adding the demulsifiers. The oil film broke when film thickness came to a critical level. As for a demulsifier, the interfacial elasticity was decreased with demulsifier concentration increase, and stayed constant above a critical demulsifier concentration. The rate of dewatering is related to interfacial elasticity. When different demulsifiers were compared, the more the interfacial elasticity was lowered, the more efficient was the dewatering. The mechanism of the different types of demulsifiers was discussed based on the experimental results. The demulsifiers partially replaced the emulsifiers, which led to the interfacial elasticity decreased. The effect of chemical structure of the demulsifiers on water–oil interfacial film was studied.     

Isolation and Characterization of Naphthenic Acids from a Metal Naphthenate Deposit: Molecular Properties at Oil‐Water and Air‐Water Interfaces

Naphthenic acids from a West African metal naphthenate deposit have been isolated and characterized by infrared (IR), nuclear magnetic resonance (NMR), and Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICR MS). The sample has been shown to comprise a narrow group of 4‐protic naphthenic acids of molecular weight ～1230 Da. The determined mass of 1230.0627 Da suggests a compound with the elemental composition C₈₀H₁₄₂O₈. The NMR data show no sign of carbon‐carbon multiple bonds. Hence, the elemental composition indicates the presence of six saturated hydrocarbon rings. The naphthenic acids have proved to be highly oil‐water (o/w) interfacially active. On elevation of the pH from 5.6 to 9.0, interfacial activity increases gradually due to a higher degree of dissociation of the carboxylic groups. At pH 9.0, the interfacial tension (IFT) between water and toluene‐hexadecane (1–9 vol.) is lowered by ～40 mN/m at concentrations of only 0.0050–0.010 mM naphthenic acid. The time rate of decrease of the IFT (dγ/dt) is also concentration‐dependent, and a well‐defined IFT is attained at long observation periods.

The C₈₀ naphthenic acids form relatively unstable Langmuir monolayers. The stability decreases further with increasing pH as more monomers become dissociated and dissolve into the aqueous phase. The stability is altered upon addition of calcium ions into the subphase due to formation of calcium naphthenate at the surface. In the undissociated state, the acids have a molecular area of ～160 Å²/molecule in the noninteracting region. The high area reflects an extended molecular structure comprising four carboxylic head groups, which are likely to be separated by hydrocarbon chains.     

Interfacial dilational properties of anionic gemini surfactants with polymethylene spacers

The dilational properties of anionic gemini surfactants alkanediyl-α,ω-bis(m-octylphenoxy sulfonate) (C₈C_mC₈) with polymethylene spacers at the water–air and water–decane interfaces were investigated by oscillating barriers and interfacial tension relaxation methods. The influences of oscillating frequency and bulk concentration on the dilational properties were explored. The experimental results show that the linking spacer plays an important role in the interfacial dilational properties. The moduli pass through one maximum for all three gemini surfactants at both water–air and water–decane interfaces. However, the values of moduli at the water–air interface are obviously higher than those at the water–decane interface because the sublayer formed by spacer chains will be destroyed by the insertion of oil molecules. Moreover, with the increase of spacer length, the surface adsorption film becomes more viscous at high concentration, which can be attributed to the process involving the formation of the sublayer. On the other hand, the spacers of the adsorbed C₈C₆C₈ molecules will extend into the oil phase when the interface is compressed. As a result, the interfacial film becomes more elastic with the increase of spacer length at high concentration. The experimental results obtained by the interfacial tension relaxation measurements are in accord with those obtained by the oscillating barriers method.     

原油活性组分油水界面膜扩张粘弹性研究

研究了用超临界萃取分馏法（SFEF）从伊朗重质原油中分离的两个具有不同平均分子量的原油界面活性组分在正癸烷/水界面的扩张粘弹性行为以及温度对体系扩张粘弹性的影响.研究发现平均分子量大的样品能在油水界面形成更为牢固的界面膜.从扩张模量幅度对扩张频率的双对数曲线和扩张模量相角的频率依赖关系可以推断所有实验体系界面膜的主要的弛豫过程不是扩散弛豫,而可能主要是通过吸脱附势垒的弛豫过程.温度对两个样品的扩张粘弹性参数都有强烈的影响.升高温度可以降低膜的强度和粘度,并且改变相角的频率响应.     

Phosvitin-calcium aggregation and organization at the air-water interface

Phosvitin, an egg yolk protein constituted by 50% of phosphorylated serines, presents good emulsifying properties whereas its interfacial properties are not yet clearly elucidated and remain object of discussion. Phosvitin has a high charge density and naturally forms aggregates through phosphocalcic bridges in egg yolk. This high charge density, doubled by this capacity to aggregate, limits the adsorption of the protein at the air-water interface. In this work, we investigated the aggregation impact by calcium ions on the organization of the phosvitin interfacial film using the atomic force microscopy. Phosvitin interfacial films without calcium ions are compared to phosvitin interfacial films formed in the presence of calcium ions in the subphase. We demonstrated that phosvitin is able to anchor at air-water interfaces in spite of its numerous negative charges. In the compression isotherm a transition was observed just before 28 mN/m signifying a possible modification of the interfacial film structure or organization. Calcium ions induce a reorganization towards a greater compaction of the phosvitin interfacial film even at low surface pressure. In conclusion we suggest that, in diluted regime, phosvitin molecules could adsorb by their two hydrophobic extremities exhibiting loops in the aqueous phase, whereas in concentred regime (high interfacial concentration) it would be adsorbed at the interface by only one extremity (brush model).     

Synthesis and evaluation of demulsifiers with polyethyleneimine as accepter for treating crude oil emulsions

Demulsifiers provide an important means of breaking water‐in‐crude oil, which are formed during crude oil exploitation. In present work, twenty polyether copolymers based on polyethyleneimine (PEI) were synthesized. The interfacial properties of the PEI polyethers at the water‐crude oil interface were described by interfacial tension (IFT) and interfacial dilational modulus. The effects of position isomerism, size of intermediate and ratio of ethylene oxide (EO)/propylene oxide (PO) on the demulsification efficiency of these polyethers were studied. The results show that different positions of the EO and PO in copolymers lead to huge difference in both interfacial properties and demulsification performance. Polymers with hydrophilic core and hydrophobic tails (Ex‐mn series) are not efficient on demulsification of water‐in‐oil emulsion whereas polymers with hydrophobic core and hydrophilic tails (Px‐mn series) are. Meanwhile, Px‐mn series show higher IFT and lower interfacial dilational modulus than Ex‐mn series. In the same series, the IFT and interfacial dilational modulus decrease with decreasing EO/PO ratio. In the series with best demulsification performance (P199‐mn series), 60 min water removal rates of the polymers increase with decreasing EO/PO ratio at 65°C. In other words, the longer the hydrophobic blocks of polymers, the stronger the demulsification capacity. The effect of concentration of demulsifier on the demulsification efficiency was also investigated. Copyright © 2015 John Wiley & Sons, Ltd.     

Stability of Water/Crude Oil Systems Correlated to the Physicochemical Properties of the Oil Phase

A characterization of 30 crude oils has been performed to determine the relative level of influence that individual parameters have over the overall stability of w/o emulsions. The crude oils have been analyzed with respect to bulk and interfacial properties and the characteristics of their w/o emulsions. The parameters include compositional properties, acidity, spectroscopic signatures in the infrared and near‐infrared region, density, viscosity, molecular weight, interfacial tension, dilational relaxation, droplet size distribution, and stability to gravitationally and electrically induced separation. As expected, a strong covariance between several physicochemical properties was found. Near‐infrared spectroscopy proved to be an effective tool for crude oil analysis. In particular, we have showed the importance of the hydrodynamic resistance to electrically‐induced separation (static) in heavy crude oil‐water emulsions. A rough estimate of the drag forces and dielectrophoretic forces seemed to capture the difference between the 30 crude oils. Given enough time, water‐in‐heavy oil emulsions could be destabilized even at very low electric field magnitude (d.c.). When droplets approach each other in an inhomogeneous electric field, strong dielectrophoretic forces disintegrate the films and result in coalescence. The relative contribution from film stability to the overall emulsion stability may therefore be very different in a gravitational field compared to that in an electrical field.     

Thickening properties and emulsification mechanisms of new derivatives of polysaccharides in aqueous solution

The thickening properties of aqueous solutions of HHM-HEC (hydrophobically-hydrophilically modified hydroxyethylcellulose) and the emulsification mechanisms of HHM-HEC/water/oil systems were investigated. A dramatic increase in viscosity was observed with increased HHM-HEC concentration in water, caused by aggregation of hydrophobic alkyl chains. At higher concentrations of HHM-HEC (above 0.6 wt%) in water, it forms an elastic gel, which has good thixotropic properties and a high yield value. O/W (oil-in-water) type emulsions were obtained using HHM-HEC, which can emulsify various kinds of oil, including hydrocarbon, silicone, and perfluoropolymethylisopropyl ether. The viscosity of these emulsions depends only upon the oil volume fraction, not on the kind of oil. In addition, the oil particle size in the emulsions remained constant after a certain period because HHM-HEC formed a strong gel network structure and a protective layer, which prevented the emulsion from coalescing. Measurements of interfacial tension revealed that the alkyl chains in HHM-HEC did not significantly lower the interfacial tension at the water/oil interface when 0.5 wt% of HHM-HEC was added to water. Steady flow and oscillatory experimental results show that the rheological behavior of HHM-HEC/water/oil emulsions was similar to that of aqueous solutions of HHM-HEC. In the HHM-HEC/water/oil emulsion system, oil droplets were dispersed and kept stable in the strong gel structure of HHM-HEC. The aqueous solution of HHM-HEC showed salt resistance. It is thought to be due to sulfonic acid groups in HHM-HEC. The stability of the emulsion using HHM-HEC is based on both protective colloidal effects and associative thickening caused by alkyl chains in HHM-HEC.     

Inhibition of Calcium Naphthenate. Experimental Methods to Study the Effect of Commercially Available Naphthenate Inhibitors

In this study, different methods have been developed for studying naphthenate inhibitors. One first method is based on interfacial activity of systems with naphthenic acids, inhibitors, and calcium viewing reaction mechanisms at interfaces of the inhibitors. A second method is based on gravimetrical determination of interfacial layer in a two phase system and gives a thermodynamic approach to naphthenate formation, and a third method utilizes a ultraviolet-active model tetraacid to directly determine the depletion in bulk phase concentration during a two-phase reaction. The results indicate that inhibitors may act through several mechanisms, and depending on the total system different mechanisms may have the highest efficiency also by combining several mechanisms.     

Interfacial and molecular properties of high-pressure-treated beta-lactoglobulin B

Interfacial properties of beta-lactoglobulin B subjected to hydrostatic pressures up to 400 MPa were studied by measuring surface pressure at the air/water interface and the elastic interfacial shear modulus at the oil/water interface. The surface hydrophobicity of pressurized beta-lactoglobulin was determined by an 1-anilino-naphthalene-8-sulfonate assay and exposure of free thiol groups using the Ellman assay. The molar mass of pressure-induced oligomers was measured using a combination of size exclusion chromatography, light scattering, and refractive index measurements. High-pressure treatment of beta-lactoglobulin increased the surface pressure growth rate and its final level at the air/water interface. After high-pressure treatment, the maximum interfacial elasticity at the oil/water interface increased, and the time lag before growth of the interfacial elasticity decreased. Up to 200 MPa, large amounts of monomeric beta-lactoglobulin were formed with increased exposure of thiol groups and increased surface hydrophobicity compared to unpressurized beta-lactoglobulin. At a pressure higher than 200 MPa, surface hydrophobicity continued to increase, while exposure of thiol groups decreased, the latter due to the formation of covalently linked oligomers. We have shown that surface hydrophobicity rather than thiol exposure is important for the pressure-induced increase in growth rate and the final level of surface pressure at the air/water interface and in interfacial elasticity at the oil/water interface.     

Relationship Between the Polymer Structures and Destabilization of Polymer‐Containing Water‐in‐Oil Emulsions

The viscous properties, scanning electronic microscopy (SEM), and water/oil interfacial tension (IFT) of partially hydrolyzed polyacryamide (HPAM) and hydrophobically associating hydrolyzed polyacryamides modified with N‐dodecylacrylamide were studied with the objective of investigating the influence on destabilization of emulsions. As expected, the copolymers exhibit significant viscosity enhancing capacity and three‐dimensional network structures due to intermolecular hydrophobic associations, and also present high interfacial activities as the IFT decrease with increasing polymer concentration. As a result, the existences of copolymers increased both the viscosity of emulsions and the intensity of interfacial film, in which case slow down the diffusion of demulsifier molecules and enhance the stability of emulsions, finally, the separation of water from oil becomes more difficult.     

Direct Observation of Foam Film Rupture by Several Types of Antifoams Using a Scanning Laser Microscope

It is well known that the stability of a pseudoemulsion film, a thin liquid film formed between an antifoam particle and air, can be important during defoaming action. We have compared the bursting behavior of a two-dimensional thin liquid film from an aqueous surfactant solution on a glass plate, in which six types of antifoam particles have been dispersed, using laser microscopic techniques. The used antifoams were a silicone oil, a mixed-type antifoam (mixture of silicone oil and hydrophobic solid particles), a hydrophobic silica, and a silicone-based solid antifoam (prepared by interfacial polymerization with oil and water). The antifoaming performance of these six types of antifoams, measured by the glass cylinder shaking test, was in the order: the mixed-type antifoam >== the silicone-based solid antifoam > the hydrophobic silica >== the silicone oil. Pseudoemulsion film rupture was observed at the film thickness less than 0.1 μm for both the silocone oil and the hydrophobic silica. In the case of particles with rough edges (the silicone-based antifoam), pseudoemulsion film on the top of the particles can be easily ruptured at a convex part of the solid surface. Furthermore, solid particles existing on the surface of an oil droplet in the mixed-type antifoams form marked projections and these projections give rise to distortion of the thinning film. As soon as the distortion of the thinning film took place on the top of the antifoam droplet, the pseudoemulsion film can be instantaneously ruptured. Referring to the antifoaming mechanisms for mixed-type antifoams, both steps from the pseudoemulsion film formation to the lens formation and from the counter pseudoemulsion film formation to the bridge formation would be very fast and cause a very high antifoaming efficiency. Copyright 1999 Academic Press.     

Monitoring of calcium stearate formation by thermogravimetry

Naphthenates are produced when naphthenic acids present in crude oil are mixed with brine. They deposit at oil/water interface and are insoluble in either of the phases causing a large problem to the oil industry. Generally, naphthenates precipitate jointly with others compounds such as sulfates and carbonates. This fact makes difficult their characterization. In this study, calcium stearate formation from stearic acid was investigated, under different conditions, as a previous model to understanding of calcium naphthenate precipitation. Medium reactions distinct were studied and the results indicated that the ethanol medium was the most efficient for the formation of solids because in this only case, the stearic acid was completely converted into stearate. Monitoring of the conversion was performed by thermogravimetry in spite of this technique not be typical in salts characterization. Nevertheless, the thermogravimetric analysis showed that is possible to identify differences between an organic acid, a salt of this acid and an inorganic salt, in the same sample. Infrared spectra was used in order to confirm the results obtained by thermogravimetry. However, this technique showed less efficiency and sensibility.     

Effect of substituent position in coumarin derivatives on the interfacial assembly: reversible photodimerization and supramolecular chirality

The Langmuir and Langmuir-Schaefer (LS) films of two coumarin derivatives, 4-octadecyloxylcoumarin (4-CUMC18) and 7-octadecyloxylcoumarin (7-CUMC18), were newly synthesized, and their interfacial assemblies were investigated. Owing to the different substituent position of the long octadecyloxy chain in the coumarin parent, the two compounds showed completely different behaviors in the interfacial assemblies. When they were spread at the air/water interface, 7-CUMC18 formed a monolayer while 4-CUMC18 formed a multilayer film on the water surface. The spreading films on the water surface were transferred onto solid substrates by a Langmuir-Schaefer method, and the transferred films were characterized by UV-vis, Fourier transfer infrared, X-ray diffraction, circular dichroism, and atomic force microscopy spectra. Different packing of the molecules in the multilayer films was observed. While coumarin groups stacked in a face-to-face way in 7-CUMC18 film, they stacked in a head-to-tail manner in 4-CUMC18 film. Furthermore, distinct properties of the multilayer films were observed. It is revealed that a reversible [2+2] photodimerization and photocleavage could be induced in the LS film of 7-CUMC18 under photoirradiation with UV light of 365 and 254 nm, respectively. No photodimerization occurred in the 4-CUMC18 film. However, the film of 4-CUMC18 showed a supramolecular chirality although the compound itself is achiral.