In this study, the memory device of iron oxide (IO) nanoparticles (NPs) embedded in polyvinyl alcohol (PVA) demonstrates the bipolar resistive switching characteristics under an external electric ...field. The phase and magnetic properties of iron oxide nanoparticles change corresponding to its resistive states. At the high resistance state (HRS) of device, iron oxide nanoparticles are primarily in Fe
2
O
3
phase and the ferromagnetism behavior is observed. In contrast, the iron oxide nanoparticles clustered by the bridging oxygen vacancies lead to mainly Fe
3
O
4
phase and no hysteresis magnetic curve is observed at the low resistance state (LRS) of device. The results reveal that oxygen vacancies/ions in nanoparticles notably influence the resistance and magnetic behavior of nanocomposite thin films. Our study indicated that the magnetic NPs is high potential of multi-dimensional storage fields.
Bipolar resistive switching behavior of iron oxide nanoparticles embedded into polyvinyl alcohol matrix.
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•Asphaltenes were easily converted to coke with low catalyst concentration.•Optimum catalyst dose facilitated the conversion of asphaltenes to light products.•Coke induction period ...increased with increasing the catalyst concentration.•Catalyst reduced overall cracking rate during the hydrocracking reaction.
Slurry phase hydrocracking of vacuum residue at various catalyst concentrations was performed in a semi-batch reactor to investigate the effect of catalyst concentration on the reaction performance. The secondary cracking reaction was dominant at high-residue conversion (>60 wt%) without the catalyst but it was suppressed by the catalyst. Moreover, the conversion of asphaltenes at high-residue conversions was found to be dependent on the catalyst concentration. At low catalyst concentrations (0–100 ppm), asphaltenes were converted to light products at low-residue conversions and to coke at high-residue conversions. At high catalyst concentrations (100–500 ppm), asphaltenes were mainly converted to light products even at high conversions. Based on the experimental results, equations for the onset of coke formation with respect to the catalyst concentration were proposed. The higher the catalyst concentration, the longer was the coke induction period. A kinetic model was also proposed, and the experimental data could be predicted well using the same. The transformation of residue to coke was dominant in the non-catalytic hydrocracking and the coke formation rate significantly decreased as the catalyst concentration increased.
A gas phase three-dimensional (3D) computational fluid dynamics (CFD) model was developed to investigate the hydrodynamics of gas distributors used in an amine absorber with a diameter of 3.2 m. A ...standard gas inlet, tubular injectors with short, medium and long lengths, and a Schoepentoeter were considered as feed systems of the gas distributors. The pressure drop, dead-area ratio and coefficient of distribution at the packing entry were used as the performance indexes of the gas distributors. The down-pipe as a liquid collector exhibited a lower dead-area ratio when compared with that of the down-comer. The tubular gas injector with a short length reduced the dead-area ratio and the gas maldistribution. The Schoepentoeter was associated with the lowest pressure drop, dead-area ratio, and coefficient of distribution among the gas distributors. The uniformity of gas distribution was enhanced by 25% in the Schoepentoeter when compared to that of the tubular gas injector.
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The physical properties (density, kinematic viscosity, surface tension, and hydrogen solubility) and their correlations for a slurry-phase hydrocracking reaction were investigated ...with a vacuum residue (VR, as a feedstock) and hydrocracked products from VR conversion of 32.3%, 73.9% at different temperature and pressure conditions. As a result, the density, kinematic viscosity, and surface tension of the product decreased with converting VR, while the solubility of hydrogen increased. And the dependence of product properties on temperature showed to be similar to feedstock. Based on the measured data, the empirical correlations that can predict from VR to products were obtained with R-square of 0.9930 by modifying the existing correlations. From these properties change, it was confirmed that the hydrocracking temperature and the degree of the hydrocracking conversion of VR is the most dominant parameters to govern the change of physical properties. Finally, it was found that the mass transfer rate of hydrogen into oil is important because the hydrogen solubility (0.8mol H2/kg feed or 0.16wt.% on the feed weight at 160bar, 410℃) on the liquid phase is much smaller than the chemical consumption of hydrogen (about 2–3wt.% on the feed weight) for near full conversion of VR.
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•Hydrocracking of vacuum residue (VR) was performed in a slurry bubble column reactor.•Physical properties estimated during hydrocracking were experimentally compared.•A CFD model ...with a new drag coefficient was developed for the bubble column.•Gas holdup at 425 °C and 160 bar (6.2%) was in agreement with empirical value (6.6%).•Axial and radial hydrodynamics of the bubble column were examined via the CFD model.
Vacuum residue (VR) was subjected to catalytic hydrocracking with H2 in a pilot-scale slurry bubble column reactor (SBCR) with 0.05 m diameter and 2 m height at 425 °C and 160 bar in the homogeneous regime. The gas holdup (αG) and composition of the product classified into five pseudo-components were measured in the SBCR. The physical properties such as density, viscosity, and surface tension of VR (feed) were analyzed prior to a three-dimensional Eulerian computational fluid dynamics (CFD) simulation to predict axial and radial hydrodynamics in the SBCR. Rather than considering the hydrocracking reactions in the CFD model, a reaction-mixture model was used to predict the variation of the axial physical properties as the reaction progresses. A customized drag coefficient based on experimental data was applied to the CFD model. The value of αG predicted by the CFD model at a superficial gas velocity of 6.4 mm/s was 6.2% which is comparable to the experimental value (6.6%). The Sauter mean diameter and specific surface area were estimated to be 1.2 mm and 304 m2/m3, respectively. The proposed CFD model, which was integrated with the axial physical properties but decoupled from chemical reaction, successfully predicted the hydrodynamics of the H2-VR SBCR.
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A three-dimensional computational fluid dynamics (CFD) model with new permeability and off-gas emission equations was developed in a four-zone low-temperature furnace (LTF) for carbon ...fiber carbonization. Four performance criteria (residence time, dead-volume ratio, tow temperature standard deviation, and tar formation area) were proposed to identify the optimal ratio between the two N2 flow rates introduced into the front and rear of LTF. A higher N2 flow rate at the front rather than at the rear was preferred to reduce tar formation. The tar formation area calculated from carbon activity provides useful guideline for determining optimal LTF design and operating conditions.
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•The axial dispersion model well predicted reaction performance in the bench-scale SBCR.•Bench-scale SBCR exhibited low back mixing with behavior closer to plug flow.•An asphaltene ...stability index was used to evaluate the operating conditions.•The optimum conditions for recycle mode operation (ROM) were found.
A modeling and simulation were conducted to study the slurry phase hydrocracking of vacuum residue in a bench-scale slurry bubble column reactor (SBCR). The reactor model was based on axial dispersion, and the intrinsic kinetic information was reported in continuous stir tank reactor (CSTR) using the same feedstock in our previous study. The model was validated over a wide range of operating conditions using experimental data from the bench scale unit. The reactor model predicted product yields, sulfur and asphaltenes content with an average error of less than 10%. The bench-scale SBCR demonstrated better hydrocracking (HCK) and hydrotreating (HDT) performance compared to CSTR, mainly due to the mixing behavior in the SBCR. A stability index of asphaltene was proposed from the data reported in our previous study to evaluate the operating conditions. Based on the simulation results, the optimal operating conditions for recycle operating mode were suggested using the simultaneous optimization variables technique.
•Gas hold up and flow regimes is investigated under hydrocracking condition for the design of a slurry phase hydrocracking reactor for heavy oil.•VR conversion considerably affect the gas hold up and ...the flow regime transition.•In the heterogeneous regime, the performance of the hydrocracking reaction is reduced due to backmixing effect.•A flow regime map is proposed to facilitate the reactor design for the slurry-phase hydrocracking reactor.
This study investigated gas hold up and flow regimes according to operating conditions (temperature, pressure, superficial gas velocity) for the design of a slurry phase hydrocracking reactor for heavy oil. Heating medium oil, vacuum residue (VR) and hydrocracking products were used in a bubble column reactor which had a diameter of 0.05 m and a height of 2.3 m. The results confirmed that the gas hold up increased and the flow regime transition point was delayed as VR was converted to a hydrocracking product (change in physical properties), and pressure also affected the flow regime transition. Using the dynamic gas disengagement method, the flow regime transition was observed in the actual hydrocracking reaction, and at the same time, it was confirmed that the hydrocracking reaction performance decreased. A VR slurry phase hydrocracking flow regime map is proposed by modifying the existing correlations, and a guide for reactor design and operation is suggested.
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•Kinetic model for thermal and catalytic hydrocracking of asphaltene was developed.•A linear relationship between coke yields and liquid yields was found.•A critical gas mass fraction ...was proposed as a coke formation determining criterion.•The kinetic model can predict well the moment when coke begins to form.
In this study, a five-lump model was proposed for kinetic modeling of asphaltene placed in a batch reactor with a commercial slurry-phase catalyst (Mo-octoate). Asphaltene was separated from vacuum residue using normal pentane. The kinetic experiments were carried out at 380∼430℃ for 1∼20 h together with a 1000 ppm concentration of Molybdenum in thermal and catalytic hydrocracking reaction modes. The results showed that the coke induction period and maximum maltene yield are changed with reaction temperature and time at thermal and catalytic hydrocracking. In addition, a linear relationship between coke and liquid (maltene + asphaltene remains) yields was shown so that the critical gas amount could be found as a criterion for determining the end of the coke induction period. Significantly, the kinetic model fit the experimental data well and, moreover, was found to be able to predict the moment when coke begins to form as well as maximum maltene yields.
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•Unconverted residue in ROM was found to become more refractory.•A slurry-phase HCK kinetic model was modified to incorporate the recycling effects.•A dynamic Simulink model ...accurately predicted the process performance in ROM.•An operational stability index was proposed to ensure stable ROM operation.•Optimal operating conditions were determined to address multiple process objectives.
The effect of the recycle stream on slurry-phase hydrocracking (HCK) of vacuum residue was examined using a continuous bench-scale unit with the aim of attaining process optimization. This was achieved through a model-based approach that links experimental investigations, kinetic modeling, and model-based optimization. The experiments were conducted at various reaction temperatures, liquid hourly space velocity of fresh feed (LHSVFF) and recycle ratios at a pressure of 160 bar, with the fresh feed containing 1000 wt. ppm of molybdenum. The HCK kinetic model was modified to incorporate the recycling effects and accurately predict the experimental data. The adapted model confirmed that the unconverted residue in recycle operating mode (ROM) became more refractory. By implementing the modified kinetic model in a dynamic Simulink model, the prediction accuracy of RES conversions and product yields can be improved by up to 25.1 wt.% in the case of the lowest conversion. A sensitivity analysis using the dynamic model showed that the temperature exerted a greater impact on the RES conversion and recycle ratio in ROM. An operational stability index was also proposed to prevent operation failure in ROM. Finally, an optimal operating condition from the parametric study was found to meet several process goals simultaneously.
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