Developments in CO2 research

CO2 can be a good solvent for many compounds when used in its compressed liq- uid or supercritical fluid state. Above its critical temperature and critical pressure (Tc = 31 °C, Pc = 73.8 bar), CO2 has liquid-like densities and gas-like viscosities, which allows for safe commercial and laboratory operating conditions. Many small molecules are readily soluble in CO2, whereas most macromolecules are not. This has prompted development of several classes of small molecule and polymeric surfactants that enable emulsion and dispersion polymerizations as well as other technological processes

Demulsification mechanism of asphaltene-stabilized water-in-oil emulsions by a polymeric ethylene oxide-propylene oxide demulsifier

The demulsification mechanism of asphaltene-stabilized water-in-toluene emulsions by an ethylene-oxide-propylene oxide (EO-PO) based polymeric demulsifier was studied. Demulsification efficiency was determined by bottle tests and correlated to the physicochemical properties of asphaltene interfacial films after demulsifier addition. From bottle tests and droplet coalescence experiments, the demulsifier showed an optimal performance at 2.3 ppm (mass basis) in toluene. At high concentrations, the demulsification performance deteriorated due to the intrinsic stabilizing capacity of the demulsifier, which was attributed to steric repulsion between water droplets. Addition of demulsifier was shown to soften the asphaltene film (i.e., reduce the viscoelastic moduli of asphaltene films) under both shear and compressional interfacial deformations. Study of the macrostructures and the chemical composition of asphaltene film at the toluene-water interface after demulsifier addition demonstrated gradual penetration of the demulsifier into the asphaltene film. Demulsifier penetration in the asphaltene film changed the asphaltene interfacial mobility and morphology, as probed with Brewster angle and atomic force microscopy

Performance Evaluation of a Newly Developed Demulsifier on Dilbit Dehydration, Demineralization and Hydrocarbon Losses to Tailings

Abstract Chemical demulsification is a cost-effective, convenient, quick, and efficient method for breaking water-in-diluted bitumen emulsions in oil sands processing. The industry is always seeking demulsifiers that act as effective dehydrators and demineralizers, minimize rag layer formation by controlling oil/water interface, and reduce the diluent/bitumen losses to tailings. In this paper, the performance of a newly developed demulsifier “Z” was investigated for its performance on dilbit dehydration, demineralization, and hydrocarbon losses to tailings and compared against the first and second generation demulsifiers “X” and “Y”, respectively. The dehydration and demineralization efficiencies of demulsifier “Z” are 2.0 and 7.6%, respectively, higher than demulsifier “Y” and 6.4 and 10.7%, respectively, higher than demulsifier “X” at 50 ppm dosage after 15 minutes of residence time. Demulsifier “Z” also works better on the diluent and bitumen losses to the underflow as compared to demulsifier “X” and “Y”. To find the reason why demulsifier “Z” performs superior to “X” and “Y”, the solids were collected from the original froth and the top, interface, and bottom fractions of the diluted froth for characterization by X-ray diffraction analysis (XRD), X-ray energy dispersive spectrometry (EDS), scanning electron microscopy (SEM), and particle size distribution (PSD). XRD data shows that demulsifier “Z” reduced the amount of clays, iron, and zirconium oxide minerals from the top and interface dilbit fractions as compared to the control sample. PSD data shows that demulsifier “Z” reduced most of the particles of size less than 0.50 µm from the interface. Thus, demulsifier “Z” helps to resolve the interfacial material by separating the minerals that tend to form rag, especially siderite, pyrite, magnetite, rutile and anatase, from the oil/water interface and sends them to the underflow.</jats:p

Development of Structure-Property Relationships for Oilfield Water Clarifiers

Abstract The production chemical industry currently lacks a comprehensive fundamental understanding of how polymeric oilfield water clarifiers work at the molecular level and which polymer components are most important for increasing field performance. The existing method for choosing a water clarifier involves a brute force approach, bottle testing as many products as possible, and includes a significant amount of trial and error. The study herein describes an approach in which a statistical library of acrylic polymers was used to develop a predictive model of performance for clarifiers in an Alkaline Surfactant Polymer (ASP) flooded reservoir in order to develop a customized polymer. A library of 50 acrylic polymers was synthesized and characterized with Asymmetric Flow Field Flow Fractionation (A4F). The polymers were evaluated for performance in three wells in an ASP flooded field by measuring the oil and grease remaining in the produced water after treatment. A three-step approach was taken to extract structure-property relationships. Principle Component Analysis was employed to reduce the dimensionality of the characterization properties. The principle components were then modeled using the polymer recipes in JMP/SAS. Finally, a model was developed to understand the field performance results in terms of the principle components. In the ASP Flood, the performance model indicated that the molecular weight of the acrylic polymers was the most important parameter for water clarifier performance in the three wells tested. The three evaluated wells showed significant variation in sensitivity to molecular weight, which emphasizes the importance of testing polymers in a representative sample of the wells within a reservoir when choosing a product. Importantly, our method of measuring residual oil and grease levels after treatment to evaluate performance was found to have a strong correlation with the ranking system employed by the field bottle testers. This study is one of the first examples of the determination of quantitative structure-property relationships for polymeric oilfield water clarifiers. By using this approach, one can identify the most important parameters for performance in a given field. Using the resulting predictive model, a customized water clarifier can be built for the field to give optimal performance.</jats:p

Self-Assembly of Phosphate Fluorosurfactants in Carbon Dioxide

Anionic phosphodiester surfactants, possessing either two fluorinated chains (F/F) or one hydrocarbon chain and one fluorinated chain (H/F), were synthesized and evaluated for solubility and self-assembly in liquid and supercritical carbon dioxide. Several surfactants, of both F/F and H/F types and having varied counterions, were found to be capable of solubilizing water-in-CO2 (W/C), via the formation of microemulsions, expanding upon the family of phosphate fluorosurfactants already found to stabilize W/C microemulsions. Small-angle neutron scattering was used to directly characterize the microemulsion particles at varied temperatures, pressures, and water loadings, revealing behavior consistent with previous results on W/C microemulsions

Interfacial Properties of Fluorocarbon and Hydrocarbon Phosphate Surfactants at the Water−CO₂ Interface

With high-pressure pendant-drop tensiometry, the interfacial tension (γ) and surface excess (Γ∞) for a family of ionic surfactants with identical phosphate headgroups and varying fluorocarbon and hydrocarbon tail structures were examined at the water−CO2 interface. To compensate for the unusually weak CO2−surfactant tail interactions, we designed hydrocarbon tails with weak tail−tail interactions to achieve a more favorable hydrophilic−CO2-philic balance. Branching of hydrocarbon surfactant tails is shown to lead to more favorable adsorption at the interface, closer to that of fluorocarbon surfactants. γ for a double-tail hydrocarbon phosphate surfactant with a relatively high degree of tail branching was lowered from the water−CO2 binary interface value of about 20 mN/m at 25 °C and 340 bar to 3.7 mN/m. This reduction in γ is attributed to both a decrease in the free volume between tails at the interface and reduced tail−tail interactions. In addition to tail structure, the effects of surfactant counterion, salt concentration, temperature, and CO2 density on γ and Γ∞ were investigated. The hydrophilic−CO2-philic balances of these surfactants are mapped by investigating changes in interfacial tension with these formulation variables. Low-molecular-weight branched hydrocarbon ionic surfactants are shown to stabilize concentrated CO2-in-water emulsions for greater than 1 h