Formation and rupture mechanisms of visco-elastic interfacial films in polymer-stabilized emulsions

Study on the structure-activity relationship of cationic polyacrylates for the treatment of oilfield produced water

Cationic polyacrylates exhibit both reverse demulsification and flotation performance, which can avoid incompatibility between the reverse demulsifier and flotation agent during treatment of produced water from offshore oilfields. In our previous work, the effect of the structure of the cationic unit on the reverse demulsification and flotation performance of cationic polyacrylates was studied. However, the structure-activity relationship of cationic polyacrylates has not been systematically studied. In this study, the relationships between the structure (acrylate type, tertiary amine type, mass ratio of acrylate to tertiary amine, and degree of cationicity), interfacial properties (surface tension, interfacial tension, zeta potential, interfacial elastic modulus, interaction force between oil droplets, and film drainage time of an oil-covered bubble), and reverse demulsification and flotation performance of cationic polyacrylates were investigated. A reduction in the elastic modulus of the oil-water interface was the key factor for good reverse demulsification performance, whereas a decrease in the film drainage time of an oil-covered bubble was the key factor for good flotation performance. Ethyl acrylate (EA) was superior to methyl acrylate (MA), and dimethylaminopropyl methacrylamide (DPM) was superior to dimethylaminoethyl methacrylate (DEM). Increases in the mass ratio of ethyl acrylate to dimethylaminopropyl methacrylamide and the degree of cationicity were beneficial for reducing the elastic modulus of the oil-water interface and the film drainage time of an oil-covered bubble. This is the first time that the structure-property-performance relationship of cationic polyacrylates has been systematically studied. A cationic polyacrylate that exhibited both good reverse demulsification performance and good flotation performance is recommended.

Polyvinyl acetate-based soil stabilization for rock slope ecological restoration

External-soil spray seeding (ESSS) is a method often used for the ecological restoration of bare rock slopes. However, the direct use of ESSS is normally less satisfactory due to the erosion of sprayed soil and low survival rate of the plants on rock slopes. This study proposes a novel approach to addressing this issue through the combined use of ESSS with polyvinyl acetate (PVA) based soil stabilization. The PVA solutions are added to the soil to stabilize soil and improve soil strength while possessing high water and nutrient retention favorable for plant growth. A series of experimental tests on the mechanical properties, water stability, erosion resistance, water retention, and plant growth of the PVA-stabilized soil were conducted to assess the efficacy of the proposed method. The results showed that the proposed method could be promising for rock slope ecological restoration. A proper curing time (e.g., >3 days) was required to achieve beneficial effects of PVA on the soil properties. A shorter curing time would otherwise result in the decrease in the strength with the increased PVA content. It was found that the optimum PVA content was 3% for achieving the maximum water stability, erosion resistance, water retention, and plant growth. The cohesion increased by up to 50% and the internal friction angle increased by 3.5° compared to the natural soil. The disintegration rate of the stabilized soil was generally < 3e-3%/min. The maximum reduction in erosion was up to 83% when the PVA content ≥3%. The mechanisms behind the findings are also discussed.

Zein-Bonded Graphene and Biosurfactants Enable the Electrokinetic Clean-Up of Hydrocarbons

Nonaqueous phase liquids (NAPL, e.g., hydrocarbons and chlorinated compounds) are common groundwater pollutants. Electrokinetic remediation of NAPLs uses electric fields to draw them toward electrodes and remove them from groundwater. The treatment requires NAPL mobility. Emulsification increases mobility, but at a risk for downstream receptors. We propose using alkaline aqueous solutions of zein and graphene nanoparticles (GNP) to form conductive materials, which could also act as barriers to control NAPL migration. Alkaline zein-GNP solutions can be injected in the polluted soil and solidified by neutralizing the pH (e.g., with glacial acetic acid, GAA). Shear rheology experiments showed that zein-GNP composites were cohesive, and voltammetry showed that GNP increased electrical conductivity of zein-based materials by 3.5 times. Gas chromatography-mass spectroscopy (GC-MS) demonstrated that the electrokinetic treatment of model sandy aquifers yielded >60% and ∼47% removal of emulsified toluene in freshwater and in salt solutions, respectively (with 30 min treatment using a 10 V differential voltage between a zein-GNP and an aluminum electrode. NaCl was used as model salt contaminant. The conductivity of surfactant solutions was lower in saline water than in freshwater, explaining differences in toluene removal. Toluene-water emulsions were stabilized using the natural surfactants lecithin and saponin. These surfactants acted synergistically in stabilizing emulsions in either freshwater or salt solutions. Lecithin and saponin likely interacted at toluene-water interfaces, as indicated by the morphology, interfacial tension and compressional rigidity of toluene-water interfaces with both components (relative to interfaces of either lecithin or saponin alone). The compressional behavior of interfacial films was well-described by the Marczak model. Electrokinetic treatment of saturated model sandy aquifers also decreased the turbidity of emulsions of water and either tricholoroethylene (TCE, by ∼41%) or diesel (by ∼75%), in the presence of a bacterial biosurfactant. This decrease was used as semiquantitative indicator of NAPL removal from water.

Interfacial and emulsifying properties of whey protein concentrate by ultrafiltration

The aim of this study was to concentrate whey protein by ultrafiltration process, evaluating the pressure at 1–3 bar and temperature of 10–20℃. In the conditions that show the more protein concentration were evaluated the interfacial and emulsifying properties at pH 5.7 and 7.0. The whey concentrate at 10℃ and 1.5 bar showed the higher protein value 36% (w/w), with soluble protein of 33.82% (solubility of 93.94%) for pH 5.7 and 34% (solubility of 94.4%) for pH 7.0, respectively. The whey concentrate powder present particle size distribution between 0.4-110 um. The whey at pH 5.7 and 7.0 was not observed significant differences in the resistance parameters of the oil/water layer interface. The interfacial film formed by the proteins presented an essentially elastic behavior in both pH, and in pH 5.7 the emulsion was more stable with lower diameter droplets. The concentrate whey showed techno-functional properties (emulsification and solubility), which allow the use as ingredients in products of industrial interest in food products such as mayonnaise, ice cream, sauces, and others.

Interception Characteristics and Pollution Mechanism of the Filter Medium in Polymer-Flooding Produced Water Filtration Process

Polymer flooding enhances oil recovery, but during the application of this technology, it also creates a large amount of polymer-contained produced water that poses a threat to the environment. The current processing is mainly focused on being able to meet the re-injection requirements. However, many processes face the challenges of purifying effect, facilities pollution, and economical justification in the field practice. In the present work, to fully understand the structure and principle of the oil field filter tank, and based on geometric similarity and similar flow, a set of self-designed filtration simulation devices is used to study the treatment of polymer-contained produced water in order to facilitate the satisfaction of the water injection requirements for medium- and low-permeability reservoirs. The results show that, due to the existence of polymers in oil field produced water, a stable colloidal system is formed on the surface of the filter medium, which reduces the adsorption of oil droplets and suspended solids by the filter medium. The existence of the polymers also increases the viscosity of water, promotes the emulsification of oil pollution, and increases the difficulty of filtration and separation. As filtration progresses, the adsorption of the polymers by the filter medium bed reaches saturation, and the polymers and oil pollution contents in the filtered water increase gradually. The concentration and particle size of the suspended solids eventually exceed the permissible standards for filtered water quality; this is mainly due to the unreasonable size of the particle in relation to the filter medium gradation and the competitive adsorption between the polymers and the suspended solids on the surface of the filter medium. The oil concentration of the filtered water also exceeds the allowable standards and results from the polymers replace the oil droplets in the pores and on the surfaces of the filter medium. Moreover, the suspended particles of the biomass, composed of dead bacteria, hyphae, and spores, have strong attachment and carrying ability with respect to oil droplets, which cause the suspended solids in the filtered water to exceed the permissible standards and oil droplets to be retained in the filtered effluent at the same time.

Role of Shearing Dispersion and Stripping in Wax Deposition in Crude Oil Pipelines

Wax deposition during crude oil transmission can cause a series of negative effects and lead to problems associated with pipeline safety. A considerable number of previous works have investigated the wax deposition mechanism, inhibition technology, and remediation methods. However, studies on the shearing mechanism of wax deposition have focused largely on the characterization of this phenomena. The role of the shearing mechanism on wax deposition has not been completely clarified. This mechanism can be divided into the shearing dispersion effect caused by radial migration of wax particles and the shearing stripping effect caused by hydrodynamic scouring. From the perspective of energy analysis, a novel wax deposition model was proposed that considered the flow parameters of waxy crude oil in pipelines instead of its rheological parameters. Considering the two effects of shearing dispersion and shearing stripping coexist, with either one of them being the dominant mechanism, a shearing dispersion flux model and a shearing stripping model were established. Furthermore, a quantitative method to distinguish between the roles of shearing dispersion and shearing stripping in wax deposition was developed. The results indicated that the shearing mechanism can contribute an average of approximately 10% and a maximum of nearly 30% to the wax deposition process. With an increase in the oil flow rate, the effect of the shearing mechanism on wax deposition is enhanced, and its contribution was demonstrated to be negative; shear stripping was observed to be the dominant mechanism. A critical flow rate was observed when the dominant effect changes. When the oil flow rate is lower than the critical flow rate, the shearing dispersion effect is the dominant effect; its contribution rate increases with an increase in the oil flow temperature. When the oil flow rate is higher than the critical flow rate, the shearing stripping effect is the dominant effect; its contribution rate increases with an increase in the oil flow temperature. This understanding can be used to design operational parameters of the actual crude oil pipelines and address the potential flow assurance problems. The results of this study are of great significance for understanding the wax deposition theory of crude oil and accelerating the development of petroleum industry pipelines.