A gas–liquid Eulerian computational fluid dynamics (CFD) model coupled with a population balance equation (PBE) was presented to investigate hydrodynamics of an air–water bubble column (1.8 m in ...height and 0.1 m in inner diameter) under elevated pressure in terms of pressure drop, gas holdup, mean bubble size, and bubble surface area. The CFD‐PBE model was modified with three pressure correction factors to predict both the total gas holdup and the mean bubble size in the homogeneous bubbly flow regime. The three correction factors were optimized compared to experimental data. Increasing the pressure led to increasing the density, reducing the bubble size, and increasing the gas holdup. The bubble size distribution moved toward a smaller bubble size, as the pressure increased. The modified CFD‐PBE model validated with experimental data and empirical models represented well hydrodynamics of the bubble column at P = 0.1, 1.5, and 3.5 MPa.
•A conceptual process model of a bromine-mediated propane oxidative dehydrogenation (Br-PDH) process.•The optimal conditions (Br2/C3H8 ratio, split sequence of columns, heat integration network) were ...found.•Br-PDH increases propylene yield and decreases energy consumption compared to conventional PDH.•Techno-economic analysis identified the competitiveness and barriers of Br-PDH.
The production of propylene from propane is becoming increasingly important. Catalytic propane dehydrogenation (PDH) is the major on-purpose propylene production process today. The conventional PDH process has a relatively high energy consumption (6.1–9.4 kWh/kg C3H6) which results in high direct CO2 emissions and modest propylene yield (0.8–0.9 kg C3H6/kg C3H8). A bromine-mediated propane oxidative dehydrogenation process (Br-ODH) is evaluated in this techno-economic study which can potentially improve both the process energy efficiency and product yield. To investigate the Br-ODH process feasibility, a heat integrated process model was designed using Aspen Plus® V12 for a 450 kta propylene facility using reaction data from the literature. The partial oxidation of propane under bromine limited conditions selectively produces a propylbromide intermediate which can be readily separated from propane. Propylbromide undergoes dehydrobromination under relatively mild conditions to produce the propylene product in a second step. Bromine is regenerated by conversion of the hydrogen bromide byproduct either thermochemically or electrochemically. Due to the current interest in use of renewable electricity in chemical processes, the electrochemical regeneration process was evaluated in this study. Based on the model, the Br-ODH process can achieve approximately 10% higher propylene yield with 37% lower utilities than conventional PDH. However, the use of high-cost electrolyzers resulted in the capital investment increasing by approximately 11%. Capital cost was also increased due to the requirements of high alloy materials of construction for the potentially corrosive halogen containing equipment. The sensitivity analysis showed that the production cost was most sensitive to the propane price. For the electrolyzer-based regeneration process the capital cost was found to be key parameter that might limit competition with conventional PDH; however, the development of a commercial thermochemical HBr oxidation process analogous to the Deacon process for chlorine would likely bring significant cost savings.
The effect of reaction temperature and time on the products and the asphaltene dispersion according to the residue conversion was investigated in a slurry-phase hydrocracking reaction. The ...experiments were carried out with two different approaches to control the hydrocracking reaction, which the reaction time was changed from 4 h to 20 h (at 410 °C) and the reaction temperature from 430 °C to 453 °C (for 1 h) at 100 bar (at 80 °C) of initial hydrogen pressure and 500 wt.ppm of molybdenum concentration. As a result, it was found that the control of the reaction time and reaction temperature may give different effect to the stability of the asphaltene in the liquid phase in spite of the same VR conversion. In order to understand this, the dipole moments of the liquid product and structural change of the asphaltene was compared. And it was found that enhancing hydrogenation reaction by increasing reaction time at low temperature delayed the time of decreasing point for dipole moments of the liquid phase and increased the length of alkyl chain of remaining asphaltene. Therefore, it is considered that the dispersibility of asphaltene with high polarity is increased. Additionally, it was found that enhancing hydrogenation can also improve the catalyst dispersion in the liquid phase below 80% of residue conversion.
•Sediment formation started to form at near 70wt.% VR conversion.•Higher concentration of catalyst delayed sediment formation.•Change of resin content in the maltene was found to be significant to ...form sediment.•ξ-potential showed the colloidal instability of asphaltene during SHC reaction.
This study investigated the characteristics of slurry-phase hydrocracking of vacuum residue (VR >524°C) at a high conversion (40–95wt.%) with a change of reaction temperatures and concentrations of the dispersed molybdenum (Mo Conc. 100–2000wt.ppm) catalyst. Experiments were carried out with an initial hydrogen pressure of 80bar (at 80°C) at a reaction temperature from 385 to 440°C for four hours in a batch reactor. As results, it was found that the sediment formation is mainly dependent on the VR conversion by the reaction temperature and started over 70wt.% of VR conversion. Up to 70–80wt.% of VR conversion, the higher catalysts showed the higher asphaltene conversion and prevented the sediment formation at the boundary of its formation, but it didn’t show any effect over 80wt.% of VR conversion anymore. Based on the analysis of the structural change and ξ-potential of asphaltene from the liquid and sediment, and SARA compositional change in the liquid, the reason for sediment formation was explained.
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•Fixed- and fluidized-beds for CO2 methanation were optimized by parametric study.•A heterogeneous catalytic reaction model was proposed for the fixed-beds (FxBs).•A two-phase ...reaction model was developed for the bubbling fluidized-bed (BFB).•Flow behaviors and reaction kinetics of the optimized FxBs and BFB were evaluated.•Catalyst mass of BFB was 18% and 85% those of the single and two FxBs, respectively.
The performances of three catalytic reactors for CO2 methanation, i.e., single fixed-bed (1FxB), two-stage fixed-bed (2FxB), and bubbling fluidized-bed (BFB), were evaluated at a feed flow rate of 166.5 Nm3/h. A heterogeneous catalytic reaction model (HCRM) combining the one-dimensional plug-flow model on the reactor scale and the reaction–diffusion model on the particle scale was used for 1FxB and 2FxB. A two-phase reaction model (TPRM), including the mass transfer between the bubble and emulsion phases and axial dispersion, was proposed for the BFB. The results from HCRM and TPRM were in good agreement with experimental and modeling data. The 1FxB, 2FxB, and BFB were optimized via the parametric study considering the hot spot temperature, operating temperature and pressure, space velocity, flue gas recirculation ratio, and operational stability. The catalyst weights of 1FxB, 2FxB, and BFB required for a 90% CO2 conversion were 191, 40, and 34 kg, respectively. The proposed models were able to identify the flow behaviors, mass transfer, and reaction kinetics of the fixed- and fluidized-beds, which are useful for the optimal design of CO2 methanation reactors.
This study evaluated the relationship between guideline adherence for heart failure (HF) with reduced ejection fraction (HFrEF) at discharge and relevant clinical outcomes in patients with acute HF ...with preserved ejection fraction (HFpEF) with or without atrial fibrillation (AF).
We analyzed Korean Acute Heart Failure Registry data for 707 patients with HFpEF with documented AF and 687 without AF. Guideline adherence was defined as good or poor according to the prescription of angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, β-blockers, and mineralocorticoid receptor antagonists. Anticoagulation adherence was also incorporated for the AF group.
Among patients with normal sinus rhythm, those with poor guideline adherence had a reduced prevalence of comorbidities and favorable clinical characteristics when compared with those with good guideline adherence. Using inverse probability of treatment weighting (IPTW) to address the bias of nonrandom treatment assignment, good adherence was associated with a poor 60-day composite endpoint in the multivariable Cox model (weighted hazard ratio wHR, 1.74; 95% confidence interval CI, 1.01-3.00;
= 0.045). For patients with AF, baseline clinical characteristics were similar according to the degree of adherence. The IPTW-adjusted analysis indicated that good adherence was significantly associated with the 60-day composite endpoint (wHR, 0.47; 95% CI, 0.27-0.79;
= 0.005). In the analysis excluding warfarin, good adherence was associated with 60-day re-hospitalization (wHR, 0.60; 95% CI, 0.37-0.98;
= 0.040), 1-year re-hospitalization (wHR, 0.67; 95% CI, 0.48-0.93;
= 0.018), and the composite endpoint (wHR, 0.77; 95% CI, 0.59-0.99;
= 0.041).
Our findings indicate that good adherence to guidelines for HFrEF is associated with a better 60-day composite endpoint in patients with HFpEF with AF.
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•The effects of gas density, surface tension, and viscosity on gas holdup and flow regime transition were studied.•The dual effect of viscosity was observed and analyzed.•Transition ...gas holdup was correlated as a function of the gas density, surface tension, and liquid viscosity.
The homogeneous-to-heterogeneous flow regime transition point dependence on gas and liquid properties was investigated in a semi-cylindrical bubble column of 1.8m height and 0.21m inner diameter operating as a semi-batch system. He, air, and CO2 gases were injected at superficial gas velocities of up to 239mm/s. The batch liquids included water, aqueous ethanol solutions, and aqueous glycerol solutions, all with a gas-free liquid height settled at 1m. When the gas density increased, the gas holdup increased at all superficial gas velocities, delaying the flow regime transition. The gas holdups in the liquid mixtures were higher than those for tap water. The transition gas holdup for the ethanol solutions increased to a sharp maximum and then decreased as the surface tension increased. Also, the glycerol solutions showed similar behavior with respect to increasing liquid viscosity, but with a shallower maximum. The transition gas holdup was empirically correlated as a function of the gas density, surface tension, and liquid viscosity, employing dimensional constants. The measured transition gas holdups for liquid mixtures, as well as some data from the literature, were fitted by the correlation.
Clinical practice guidelines have been slowly and inconsistently applied in clinical practice, and certain evidence-based, guideline-driven therapies for heart failure (HF) have been significantly ...underused. The purpose of this study was to survey guideline compliance and its effect on clinical outcomes in the treatment of systolic HF in Korea.
The SUrvey of Guideline Adherence for Treatment of Systolic Heart Failure in Real World (SUGAR) trial was a multi-center, retrospective, observational study on subjects with systolic HF (ejection fraction <45%) admitted to 23 university hospitals. The guideline adherence indicator (GAI) was defined as a performance measure on the basis of 3 pharmacological classes: angiotensin-converting enzyme inhibitor (ACEI) or angiotensin receptor II blocker (ARB), beta-blocker (BB), and aldosterone antagonist (AA). Based on the overall adherence percentage, subjects were divided into 2 groups: those with good guideline adherence (GAI ≥50%) and poor guideline adherence (GAI <50%). We included 1319 regional participants as representatives of the standard population from the Korean national census in 2008. Adherence to drugs at discharge was as follows: ACEI or ARB, 89.7%; BB, 69.2%; and AA, 65.9%. Overall, 82.7% of the patients had good guideline adherence. Overall mortality and re-hospitalization rates at 1 year were 6.2% and 37.4%, respectively. Survival analysis by log-rank test showed a significant difference in event-free survival rate of mortality (94.7% vs. 89.8%, p = 0.003) and re-hospitalization (62.3% vs. 56.4%, p = 0.041) between the good and poor guideline-adherence groups.
Among patients with systolic HF in Korea, adherence to pharmacologic treatment guidelines as determined by performance measures, including prescription of ACEI/ARB and BB at discharge, was associated with improved clinical outcomes.
Partial oxidation of methane and water splitting for hydrogen production were carried out. The reaction kinetics of reduction and oxidation (redox) of Mn and Zn iron oxides were determined using a ...thermogravimetric analyzer. The reduction conversion of the metal oxides increases with temperature above 1073
K and all the experimental data are well represented by the diffusion-limited mechanism except ZnFe
2O
4 due to the solid state diffusion of iron and the reaction with solid carbon. The oxidation reaction was also controlled by the product-layer diffusion mechanism. Substitution of Mn and Zn cations with iron oxides can lower the reaction temperature and increase the reaction rate. The reaction rate and the activation energy (57–110
kJ/mol) for decomposition of water by oxidation of the metal oxides were also determined.
A contact resistance (<inline-formula> <tex-math notation="LaTeX">{R}_{c} </tex-math></inline-formula>) becomes a major parasitic resistance in highly scaled modern semiconductor devices. A ...wrap-around contact (WAC) has been suggested as a promising solution to reduce the <inline-formula> <tex-math notation="LaTeX">{R}_{c} </tex-math></inline-formula>, because its contact area is larger than that for the conventional top contact (TC) structure. Therefore, in this article, the electrical and thermal characteristics are widely investigated in vertically stacked gate-all-around (GAA) MOSFET with a WAC by using a 3-D technology computer-aided design (TCAD) simulation. First, compared with the TC, the WAC shows 1.74 times higher ON-state current. It is attributed in part to the low <inline-formula> <tex-math notation="LaTeX">{R}_{c} </tex-math></inline-formula> and in part to the low source-drain resistance (<inline-formula> <tex-math notation="LaTeX">{R}_{\text {SD}} </tex-math></inline-formula>). Furthermore, thermal resistance (<inline-formula> <tex-math notation="LaTeX">{R}_{\text {th}} </tex-math></inline-formula>) is also reduced by 9.73% in WAC, which improves self-heating effects (SHEs). Considering the results, it is expected that the WAC structure could be an attractive candidate to simultaneously improve device performance and reliability.
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