Kyeongseok Oh

Yield Stress of Wax Gel using Vane Method

Abstract Wax gel formation occurs in pipelines under quiescent conditions during a scheduled or emergency shutdown of flow. Paraffinic wax precipitates from the bulk oil when oil temperature decreases below the characteristic wax precipitation temperature, while the gelling begins as the temperature decreases below the pour point. Further temperature reductions below the pour point result in the development of a stronger gel. In this study, the gel strength was measured by determining the yield stress using the vane method. The method consisted of identifying the maximum torque exerted on the sample at various temperatures. Model oils were prepared by mixing low vacuum gas oil wax, mineral oil, and kerosene. Linear increase in gel strength with decreasing temperature was observed in the measured temperature range. As the wax content increased, so did the yield strength of the gel below the solution pour point. The slope of the yield-stress versus temperature line was also steeper for the model oil containing higher amount of wax. Recovery of gel strength was also examined by aging at the same temperature and by decreasing temperatures after breaking the gel at certain temperature.

Near Infrared Spectroscopy to Study Asphaltene Aggregation in Solvents

Petroleum asphaltenes are extremely complex and are difficult to characterize. Asphaltenes are a solubility class, defined as that portion of the oil (or organic material) that is soluble in toluene and insoluble in normal heptane. (Sometimes, other alkane solvents are used to define this solubility class, the most common other solvent being, normal pentane.) Asphaltenes present numerous problems during production, transportation, and processing of crude oils because they are on the higher polarity and molecular weight end of the crude oil compositional spectrum. As a result, this solubility class has been widely studied. There are over a thousand papers on various aspects of asphaltenes, including their chemistry, molecular weight, solubility, phase behavior, reactivity, etc.1−4 Crude oils are mixtures of thousands of polar and nonpolar compounds. Asphaltenes are the most polar of crude oil compounds, and are often compared to large amphiphilic molecules. Self-aggregation properties of amphiphilic molecules are well established. In that context, one question has often been posed—do asphaltene molecules self-aggregate? If they do, at what concentrations do they exhibit this behavior? What are sizes and other properties of these aggregates? Based on surface tension measurements, Sheu and coworkers5 answered the first question in the affirmative. They observed distinct break points in surface tensions of asphaltene–solvent mixtures as function of concentration. They were working at concentration ranges of the order of 0.1–10 g/L. Since then, it is generally believed that asphaltenes aggregate; however, different terms have been used to describe the aggregates and the aggregation process. In keeping with the amphiphilic molecule comparison, the term “micelle” has been commonly used to describe an asphaltene aggregate. The term micelle has been used to describe both the socalled asphaltene–resin complexes and the self-associated asphaltene molecules. Because of the polydispersed nature of asphaltenes, several researchers6−8 have argued that micelle is not an appropriate term for these aggregates. Some research

Catalytic activity and characterization of V2O5/γ-Al2O3 for ammoxidation of m-xylene system

An ammoxidation of m-xylene was evaluated in a fixed-bed reactor using V2O5 on various oxides. Catalysts were prepared by wet impregnation method. At first, the loading of V2O5 was varied from 5 wt% to 20 wt% on γ-Al2O3 support to estimate the most effective amount of V2O5. Second, the effect of catalyst supports was examined at 10 wt% loading of V2O5. V2O5/TiO2 and V2O5/SiO2 catalysts were employed to compare the ammoxidation reaction with V2O5/γ-Al2O3. Most catalytic activity was observed when γ-Al2O3 was used as a support. Careful characterization was followed by physicochemical techniques, such as BET measurement, X-ray diffraction (XRD), Raman spectroscopy and temperature-programmed reduction (TPR). The results provided the clue that monolayer V2O5 was favorably dispersed on the surface of γ-Al2O3 up to 10 wt%, which led to the highest yield of isophthalonitrile (IPN).

Method Development to Evaluate Melting Behavior of Glass Fiber-Reinforced Syndiotactic Polystyrene Composites in the Presence of Pressure Loading

Criteria of cycle time include metering, closing a mold, packing, holding, cooling, opening a mold and ejecting. Interestingly, metering time was found relatively lengthy in the composite of glass fiber (GF)-reinforced syndiotactic polystyrene (sPS) during injection molding. It was motivated by the ideas that analyzing dynamic thermal property may provide the correlation with metering time because differential scanning calorimeter does not fully provide dynamic thermal property. We created new measuring system to examine thermal behavior in the presence of pressure loading. The method was very effective to determine the melting rate of thermoplastics in the presence of pressure loadings.

Synthesisand Electrochemical Behaviors of Hybrid Carbon (ACF/Graphene) as Supports by Microwaves-irradiation Method for Polymer Exchange Membrane Fuel Cells (PEMFC)

Carbon materials are mainly used as catalyst supports for polymer exchange membrane fuel cell (PEMFC). Catalyst supports are required specific characteristics of the carbon materials, such as large surface area and high electrical conductivity. Attempted were to improve electrical conductivity and to maintain high surface area of carbon materials using a microwave treatment. Microwave treatment, as a relatively new technique, takes short reaction time and reduce the consumption of the gases used for carbon treatment compared to a traditional heat treatment. Hybrid carbon (ACF/Graphene) as catalyst supports by microwave-irradiation method for PEMFC increase the cell performance because of increased electrical conductivity resulting in triple-phase contact and reduced the interfacial resistance. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-Ray Diffraction (XRD) were employed to analyze carbon materials. The performance of microwave-treated carbon materials was evaluated by measuring current-voltage (I-V) characteristics and electrode impedance.