Browsing by Author "Liu, Ya"

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    A New Assay Method for Scale Inhibitor Detection at Low Concentrations
    (2014-04-23) Liu, Ya; Tomson, Mason B.; Bedient, Philip B.; Li, Qilin
    Accurate detection of scale inhibitors has always been crucial to scale control in industry. However, analyzing scale inhibitors at low concentrations, especially with polymeric scale inhibitors, remains an ongoing challenge. This paper presents an assay method designed to detect all types of scale inhibitors, especially at low concentrations, and an expert program developed to guide the method. The program guides the preparation of a field brine barite solution at a fixed barite super-saturation. Scale inhibitor concentration is then measured via the method of standard additions, assuming a linear relationship between the scale inhibitor concentration and the logarithm of barite induction time. Seven different scale inhibitors, including phosphonates, carboxylates and sulfonates, were detected in two typical synthetic brines at low concentrations. In addition, this assay method has also been applied to scale inhibitor detection in actual field brines. In general, this easily-implemented method can directly detect the residual level of any scale inhibitors in field brine about 0.1 mg/L active. Emphasis in this paper is on low concentrations. Measurement of low concentration scale inhibitors not only helps to monitor scaling tendency but also effectively prevents overuse of scale inhibitors and thereby protects the environment and saves money. This is one of the few methods that can detect most scale inhibitors at such low concentrations. Field applications, strengths, and interferences are discussed using laboratory and field examples.
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    Iron Sulfide Precipitation Kinetics, Solubility, Phase Transformation, and Corrosion versus Temperature and Ionic Strength
    (2017-04-13) Liu, Ya; Tomson, Mason B.
    A reliable anoxic plug flow reactor has been developed to study iron sulfide (FeS) precipitation kinetics, solubility, phase transformation, and corrosion simultaneously. The effects of temperature (23 – 125 °C), ionic strength (0.00886 – 5.03 mol/kg), and ferrous iron (Fe(II)) to sulfide (S(-II)) concentration ratio (1:20 to 1:5) were studied. The kinetics of FeS precipitation was found to be a pseudo first order reaction with respect to Fe(II) concentration, when Fe(II) concentration is significantly lower than S(-II) concentration. FeS precipitation kinetics can be accelerated by high temperature and high ionic strength, but not be affected by Fe(II) to S(-II) concentration ratio at the tested ratio range. A model for predicting FeS solubility and precipitation was developed by using FeS solubility data measured in this study and data from literature. At temperature ≤ 100 °C, freshly precipitated FeS was found to be mackinawite. Mackinawite can transform to troilite at temperature ≥ 50 °C, and low ionic strength favors the phase transformation. Also, mackinawite formed from steel corrosion seems to be easier to transform to troilite than the mackinawite formed from precipitation. H2S corrosion and FeS scale retention on carbon steel can be significantly accelerated by high temperature and impeded by extra high ionic strength (IS ≥ 4 mol/kg). This study presented a new approach for iron sulfide study and contributed valuable FeS thermodynamics and kinetics data for FeS prediction and control in industry.