Wax deposition poses severe risks to crude oil production systems. In order to remediate wax deposition, pigging operation is performed routinely to scrape wax deposits from the pipe wall. Proper determination of the pigging frequency is crucial to estimating the operating costs associated with the pigging operations as well as the risks of pipeline blockage by wax deposit. In order to predict the wax deposition rate and the deposit thickness to be pigged, existing wax deposition models simulate the hydrodynamics, heat and mass transfer of oil pipe flows based on Newtonian fluid mechanics. However, when temperature of the oil drops below the wax appearance temperature (WAT), wax molecules precipitate to form a suspension of wax crystals in oil, resulting in non-Newtonian fluid characteristics. In order to generate more reliable wax deposition predictions, the methodology to model the hydrodynamics, heat and mass transfer as well as deposit growth considering the non-Newtonian fluid characteristics needs to be developed. In this study, we present an improvement of the existing university-developed wax prediction model1 by incorporating the non-Newtonian fluid characteristics of waxy crude oil described by the suspension of fractal aggregates (SoFA) model. This enhancement is first presented for laminar flow regime. This improved model is then applied to provide insights on 1) the impacts of non-Newtonian characteristics on the heat and mass transfer aspects of wax deposition, 2) the effect of shear on wax deposition and 3) the role of wax inhibitors on wax deposition.

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During the enzymatic oxidation of black tea, flavan-3-ols undergo a complicated chemical transformation and generate theaflavins and thearubigins. So far, the oxidation mechanism of flavan-3-ols has not been clarified. Liquid chromatography–tandem mass spectrometry-based metabolomics combined with o-quinone intermediates captured by o-phenylenediamine was developed and successfully applied in the liquid incubation of fresh tea homogenates. During the oxidation, the contents of catechins continuously decreased, while theaflavins increased first but decreased subsequently at the end of incubation. Meanwhile, the content of thearubigins greatly increased at the late stage of incubation. Dehydrotheasinensins were accumulated at the end of oxidation along with the decrease of theasinensins. Through o-phenylenediamine derivation, several adducts of (−)-epigallocatechin gallate, (−)-epigallocatechin, theasinensins A, B, C, and D, and corresponding dehydrotheasinensins were identified, which were considered as the substrates of thearubigins. These results suggested that theaflavins and these oxidation products contributed to the formation of thearubigins.

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