Determination of Volumetric Properties Using Refractive Index Measurements for Nonpolar Hydrocarbons and Crude Oils

A novel method to evaluate volumetric properties, namely the thermal expansivity (α_<i>P</i>) and the isothermal compressibility (κ_<i>T</i>) for nonpolar hydrocarbon systems using refractive index measurements, is presented in this work. New expressions for α_<i>P</i> and κ_<i>T</i> are derived from the Lorentz–Lorenz equation and the One-Third rule, respectively. A further simplified expression for α_<i>P</i> is proposed requiring only refractive index data and molecular weight for calculation. Densities and refractive indices of 12 pure nonpolar hydrocarbons, 6 hydrocarbon mixtures, and 3 crude oils are measured at temperatures from 283.15 K up to 343.15 K and at 0.1 MPa. The measured refractive indices are used to calculate α_<i>P</i> for a wide range of temperatures using the proposed method, and the measured densities are used to calculate α_<i>P</i> for comparison. Reported densities and refractive indices of benzene at 298.15 K and at pressures up to 90 MPa are used for κ_<i>T</i> evaluations with the proposed method. Values of α_<i>P</i> and κ_<i>T</i> calculated from refractive index measurements are in good agreement with experimental data and those determined from densities. This work aims to establish the foundation for experimental methods to determine volumetric properties of nonpolar hydrocarbon systems based on refractive index measurements. A high temperature and high pressure refractometer is expected to have multiple advantages over conventional techniques for density measurements, which include but are not limited to smaller amounts of sample needed, simpler calibration, faster measurement, and cells that are corrosion-resistant (i.e., sapphire glass)

Functionalized Carbon Nanotubes with Ni(II) Bipyridine Complexes as Efficient Catalysts for the Alkaline Oxygen Evolution Reaction

Among current technologies for hydrogen production as an environmentally friendly fuel, water splitting has attracted increasing attention. However, the efficiency of water electrolysis is severely limited by the large anodic overpotential and sluggish reaction rate of the oxygen evolution reaction (OER). To overcome this issue, the development of efficient electrocatalyst materials for the OER has drawn much attention. Here, we show that organometallic Ni­(II) complexes immobilized on the sidewalls of multiwalled carbon nanotubes (MWNTs) serve as highly active and stable OER electrocatalysts. This class of electrocatalyst materials is synthesized by covalent functionalization of the MWNTs with organometallic Ni bipyridine (bipy) complexes. The Ni-bipy-MWNT catalyst generates a current density of 10 mA cm^–2 at overpotentials of 310 and 290 mV in 0.1 and 1 M NaOH, respectively, with a low Tafel slope of ∼35 mV dec^–1, placing the material among the most active OER electrocatalysts reported so far. Different simple analysis techniques have been developed in this study to characterize such a class of electrocatalyst materials. Furthermore, density functional theory calculations have been performed to predict the stable coordination complexes of Ni before and after OER measurements

Indirect Method: A Novel Technique for Experimental Determination of Asphaltene Precipitation

Asphaltenes represent one of the major potential flow assurance problems in the upstream oil industry. Asphaltene precipitation determination is a key step in studying the asphaltene deposition problems because precipitation is a necessary condition for the asphaltenes to deposit. In this work, a novel experimental technique called the “indirect method” is used for studying asphaltene precipitation on both model oil and real crude oil systems. This method, which is a combination of gravimetric and spectroscopic techniques, is proposed for the detection and quantification of asphaltene precipitation in dead oil samples. The term “indirect” refers to an indirect detection of the precipitation of asphaltenes, by measuring the absorbance of the supernatant fluid after centrifugation of oil/<i>n</i>-alkane mixtures. The results obtained in this study show that the indirect method has three main advantages over direct methods. First, it can be applied to detect asphaltene precipitation and also to quantify the amount precipitated. Also, it can be used for crude oils ranging from very low to high asphaltene content; model oils studied in this work contained 0.1–5 wt % asphaltenes. Finally, the minimum particle size that can be detected with the indirect method is smaller than with the direct methods, and therefore, we can conclude that the indirect method is more sensitive than the direct methods. Different aging times, from 1 h to 1 month, were used in this study, and the results demonstrate that no single concentration of precipitant can be identified as the asphaltene precipitation onset. Detection of asphaltene precipitation depends upon the aging time of the samples, and this time dependency is related to the minimum particle size separated by the centrifugation process. A detailed study on the relation of the aging time and the centrifugation speed is necessary as a future work

Effect of Emulsified Water on Asphaltene Instability in Crude Oils

Understanding asphaltene precipitation and subsequent deposition during oil production is of great importance for the oil industry nowadays because of the potential risk associated with this heavy fraction in plugging wellbores and production equipment. Although water is commonly present in the produced fluids, because of instrument limitations and inadequate techniques, it is usually separated from the oil prior to any experimental analysis. Therefore, the effect of water on asphaltene stability and deposition tendency is not completely understood, and the information available in the literature is scarce. In this work, the effect of emulsified water on asphaltene instability in crude oil systems is investigated. Three crude oils and one bitumen sample were used in this study. The crude oils had American Petroleum Institute (API) gravities ranging from 26° to 40° and asphaltene content between 1.2 and 13 wt %. Model oils were also prepared with asphaltenes extracted from these crude oils. A total of nine systems were investigated with and without the presence of emulsified water. It was found that, for the crude oils from the Middle East and Canada and their corresponding model oils, the addition of water did not have a significant effect on either the detection of asphaltene precipitation or the amount of precipitated asphaltenes. However, the stability of asphaltenes in the crude oil from the Gulf of Mexico and the model oils from the Athabasca bitumen (containing <i>n</i>-C₅ and <i>n</i>-C₇ asphaltenes) was significantly affected by the presence of water. The experimental evidence suggests that some asphaltenes are more prone to interact with water at the oil–water interface. This work provides a simple technique to screen whether water has an effect on asphaltene stability for a given crude oil at ambient pressure and different temperatures. With this study, we aim to contribute to a better understanding of the interaction of water and asphaltenes in crude oil systems, which will eventually lead to the development of cost-effective strategies for the mitigation of this flow assurance problem