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•Carbon nanotube synthesis via catalytic decomposition of methane (CDM) was studied.•The behavior of CeO2-supported Co, Fe, and Ni catalysts in the CDM was examined.•The effects of ...CeO2 on the active metal activity in the CDM reaction were examined.•Ni/CeO2 exhibited high catalytic activity and carbon yield at 600 °C.•The supported catalysts yielded highly crystallized impurity-free carbon nanotubes.
Because of its unique properties, CeO2 is a widely used support material in steam reforming and dry reforming reactions conducted using CH4 as a reactant. However, it has been rarely used in the catalytic decomposition of methane (CDM). In a pre-test, a Co/CeO2 catalyst showed higher activity than Ni/Al2O3, Co/Al2O3, and Mo-Ni/MgO catalysts in the CDM conducted via catalytic chemical vapor deposition (CCVD). Therefore, in this study, the CDM for carbon nanotube (CNT) synthesis over CeO2-supported Co, Fe, and Ni catalysts was investigated, while focusing on the effects of CeO2 on the activities of the active metals in the CDM. Among the investigated catalysts, Ni/CeO2 showed a decent catalytic performance at 600 °C, which is a considerably lower temperature than those previously reported. X-ray diffraction, Brunauer–Emmett–Teller surface area, temperature-programmed reduction/desorption (TPR/TPD), and X-ray photoelectron spectroscopy (XPS) analyses were performed to characterize the catalysts. Through these experiments, it was found that Ni/CeO2 had many adsorption sites for CH4 molecules which could react with mobile oxygen existing in CeO2. Furthermore, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and thermogravimetric (TG) analyses were performed to examine the morphologies and properties of the carbon material grown on the catalysts.
During the coronavirus disease 2019 (COVID-19) pandemic, there was a shortage of medical resources and the need for proper treatment guidelines for brain tumor patients became more pressing. Thus, ...the Korean Society for Neuro-Oncology (KSNO), a multidisciplinary academic society, has undertaken efforts to develop a guideline that is tailored to the domestic situation and that can be used in similar crisis situations in the future. As part II of the guideline, this consensus survey is to suggest management options in specific clinical scenarios during the crisis period.
The KSNO Guideline Working Group consisted of 22 multidisciplinary experts on neuro-oncology in Korea. In order to confirm a consensus reached by the experts, opinions on 5 specific clinical scenarios about the management of brain tumor patients during the crisis period were devised and asked. To build-up the consensus process, Delphi method was employed.
The summary of the final consensus from each scenario are as follows. For patients with newly diagnosed astrocytoma with isocitrate dehydrogenase (
)-mutant and oligodendroglioma with
-mutant/1p19q codeleted, observation was preferred for patients with low-risk, World Health Organization (WHO) grade 2, and Karnofsky Performance Scale (KPS) ≥60, while adjuvant radiotherapy alone was preferred for patients with high-risk, WHO grade 2, and KPS ≥60. For newly diagnosed patients with glioblastoma, the most preferred adjuvant treatment strategy after surgery was radiotherapy plus temozolomide except for patients aged ≥70 years with KPS of 60 and unmethylated
promoters. In patients with symptomatic brain metastasis, the preferred treatment differed according to the number of brain metastasis and performance status. For patients with newly diagnosed atypical meningioma, adjuvant radiation was deferred in patients with older age, poor performance status, complete resection, or low mitotic count.
It is imperative that proper medical care for brain tumor patients be sustained and provided, even during the crisis period. The findings of this consensus survey will be a useful reference in determining appropriate treatment options for brain tumor patients in the specific clinical scenarios covered by the survey during the future crisis.
During the coronavirus disease 2019 (COVID-19) pandemic, the need for appropriate treatment guidelines for patients with brain tumors was indispensable due to the lack and limitations of medical ...resources. Thus, the Korean Society for Neuro-Oncology (KSNO), a multidisciplinary academic society, has undertaken efforts to develop a guideline that is tailored to the domestic situation and that can be used in similar crisis situations in the future.
The KSNO Guideline Working Group was composed of 22 multidisciplinary experts on neuro-oncology in Korea. In order to reach consensus among the experts, the Delphi method was used to build up the final recommendations.
All participating experts completed the series of surveys, and the results of final survey were used to draft the current consensus recommendations. Priority levels of surgery and radiotherapy during crises were proposed using appropriate time window-based criteria for management outcome. The highest priority for surgery is assigned to patients who are life-threatening or have a risk of significant impact on a patient's prognosis unless immediate intervention is given within 24-48 hours. As for the radiotherapy, patients who are at risk of compromising their overall survival or neurological status within 4-6 weeks are assigned to the highest priority. Curative-intent chemotherapy has the highest priority, followed by neoadjuvant/adjuvant and palliative chemotherapy during a crisis period. Telemedicine should be actively considered as a management tool for brain tumor patients during the mass infection crises such as the COVID-19 pandemic.
It is crucial that adequate medical care for patients with brain tumors is maintained and provided, even during times of crisis. This guideline will serve as a valuable resource, assisting in the delivery of treatment to brain tumor patients in the event of any future crisis.
The reaction characteristics of two-step oxychlorination to produce 1,2-dichloroethane as a feedstock of PVC production were determined in a fluidized bed reactor. The effects of superficial gas ...velocity and gas composition on the reactivity and fluidization stability have been determined to find the optimum operating conditions in the continuous fluidized bed reactor system. It has been found that the average ethylene conversion is 94% with ethylene dichloride (EDC) selectivity of 97–98%, the average HCl conversion is 97.4%, the solid reactant conversion is 54% and a solid inventory ratio for the optimum reaction conversion is 3.3 in the process.
•Asphaltene dispersion stability in a slurry phase hydrocracking reaction was studied.•The solubility parameters, the structure of the asphaltene, and sediment content in the liquid product were ...analyzed.•The asphaltene dispersion was deteriorated and the sediment content increased rapidly at about 50% of VR conversion.•Microscopic observation directly confirmed asphaltene flocculation.•Asphaltene dispersion stability was improved with the promotion of hydrogenation reaction.
Asphaltene precipitation is known as a challenging issue to fully upgrade heavy oils. In this study, asphaltene dispersion stability and sediment formation for a slurry phase hydrocracking reaction of vacuum residue was investigated with changes of temperatures (405–435 °C), LHSV (0.20–0.45 hr-1), pressures (80–180 bar) and superficial gas velocities (0.4–2.2 cm/s) in a bench-scale continuous system. The characteristics of dispersion stability were examined with the solubility parameters at the flocculation point (UV titration), the structure of the asphaltenes (H-NMR), and sediment content in the liquid product (Hot filtration). As results, it was found that the dispersion stability of asphaltene was mainly dependent on the VR conversion. In particular, at about 50% of the VR transition, the solubility was found to be unstable and the amount of deposition increased dramatically. At the same time, microscopic observation directly confirmed asphaltene flocculation. However, when H2 partial pressure was increased, the hydrogenation reaction of asphaltene was promoted so that it could reduce sediment formation and improve both the asphaltene solubility and structure for the stable dispersion. On the other hand, increasing the superficial gas velocity did not give an effect on the asphaltene dispersion stability.
Ce-promoted Ni/Al2O3 catalysts with Ce contents of 0, 5, 10, 15, and 20 wt% were investigated for CO2 methanation. Ni/15Ce/Al2O3 showed good selectivity and catalytic performance in CO2 methanation ...and remained stable at 350 °C for 80 h with minor fluctuations. Interactions between Ni and the Ce/Al2O3 support was characterized using X-ray diffraction, temperature-programmed reduction of H2, temperature-programmed desorption of CO2, X-ray photoelectron spectroscopy, Raman spectroscopy, and thermogravimetric analysis. Addition of Ce did not increase the catalytic surface area, which can significantly enhance the heterogeneous catalytic activity. However, XPS analysis showed that the Ce on the Ni/Al2O3 catalyst changed the surface electron states of Ni, Ce, and O. Additionally, CO2 adsorption/desorption was confirmed to be related to the amount of Ce present on Ni/Al2O3 by TGA and CO2-TPD. The Ce addition thus played an important role in determining the CO2 adsorption, desorption, and conversion.
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•Effect of CeO2 addition to Ni/γ-Al2O3 catalysts on CO2 methanation is investigated.•Ni/15Ce/Al2O3 showed good selectivity toward CO2 methanation at low temperatures.•Physical properties of the catalyst have little influence on CO2 methanation.•Oxidation state and chemical properties significantly affect CO2 methanation.•CO2 methanation efficiency is independent on the amount of Ce3+.
A volume of fluid computational fluid dynamics (VOF-CFD) model was used to investigate hydrodynamics of air-water bubble columns in the gas distributor region under bubbling, transient, and jetting ...flow regimes. The Reynolds-averaged Navier-Stokes (RANS) and large eddy simulation (LES) turbulence equations were coupled with the VOF-CFisms@2015D model. A novel bubble detection algorithm was developed to calculate the bubble size, where a gas fraction of 0.5 was adopted to detect bubbles in the gas-liquid mixture. The CFD results for all three flow regimes were compared to the experimental data in terms of the bubble size distribution (BSD) and mean bubble size. In the framework of VOF, the LES turbulence model captured bubble behaviors in the three flow regimes more accurately than the RANS approach by taking computational time 20% more. Increasing the surface tension from 0.025 to 0.0719 N/m resulted in the increment of the Sauter mean diameter from 4.0 to 5.4 mm. The VOF-CFD model coupled with LES yielded the initial BSD near the gas distributor, which is necessary for Eulerian CFD often applied to an entire column.
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•A VOF-CFD model was used to predict the initial bubble size in bubble columns.•A bubble detecting algorithm was proposed to identify the bubble size distribution.•The VOF-CFD model with large eddy simulation (LES) well captured bubble behaviors.•The VOF-CFD with LES providing the initial bubble size is beneficial to Eulerian CFD.
Figure. Bubble dispersion mechanism in the orifice.
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•Pressure drop fluctuation in micro-bubble generation conditions was analyzed.•Micro-bubble flow regime was analyzed with pressure ...drop fluctuation.•With increasing We/Reg−8 in kerosene, bubble size shows decreasing tendency.
The objective of this study was to quantitatively analyze bubble/micro-bubble regime transition point in a bubble column. A test was carried out with a cylindrical stainless-steel column having an inner diameter of 0.097 m and a height of 1.8 m. An air was injected as a gas medium. Kerosene with a density of 800 kg/m3, viscosity of 1.64 × 10−3 Pa•s, and surface tension of 23 × 10−3 N/m at 20 ± 2 °C was used as a liquid. The experiment was conducted on a single nozzle plate with different hole sizes (0.7, 1.5, 2.0, and 3.46 mm). To analyze the standard deviation of the differential pressure signal by air bubbles separated from the jet, 12,000 differential pressure data from 0.05 m to 0.15 m of height were measured at 200 Hz under each condition. As gas velocity at the orifice increased, sizes of bubbles falling apart from the nozzle increased. Standard deviation of differential pressure also increased. Bubbles grew until they fell from the tip of the jet. At higher orifice gas velocity, the standard deviation of the differential pressure was reduced due to the occurrence of micro-bubbles. Since the standard deviation of the differential pressure showed a high peak at We/Reg−8 = 1.2 × 1045 for all cases, this value was selected as a demarcation of bubble/heterogeneous micro-bubble regime transition. The standard deviation of pressure drop fluctuation was the lowest at We/Reg−8 = 6.0 × 1048. This point was determined as the homogeneous micro-bubble regime point.
•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.
