In South Korea, where there are no resources such as natural gas or crude oil, research on alternative fuels has been actively conducted since the 1990s. The research on synthetic oil is subdivided ...into Coal to Liquid (CTL), Gas to Liquid (GTL), Biomass to Liquid (BTL), etc., and was developed with the focus on catalysts, their preparation, reactor types, and operation technologies according to the product to be obtained. In Fischer–Tropsch synthesis for synthetic oil from syngas, stability, CO conversion rate, and product selectivity of catalysts depends on the design of their components, such as their active material, promoter, and support. Most of the developed catalysts were Fe- and Co-based catalysts and were developed in spherical and cylindrical shapes according to the reactor type. Recently, hybrid catalysts in combination with cracking catalysts were developed to control the distribution of the product. In this review, we survey recent studies related to the design of catalysts for production of light hydrocarbons and middle distillates, including hybrid catalysts, encapsulated core–shell catalysts, catalysts with active materials with well-organized sizes and shapes, and catalysts with shape- and size-controlled supports. Finally, we introduce recent research and development (R&D) trends in the production of light hydrocarbons and middle distillates and in the catalytic processes being applied to the development of catalysts in Korea.
Integrated process models were developed to produce dimethyl ether (DME) from the byproduct gas of the steelmaking process. Two different separation trains (the use of flash drums to separate light ...gases followed by two columns to separate CO
2
and DME vs. the application of an absorber to separate light gas and CO
2
under mild temperatures), and two different recycling strategies (recycling with and without further separation of hydrogen by a membrane) were considered. Detailed kinetic reactions for methanol (MeOH) synthesis from syngas and the dehydration of MeOH to DME were used in the reactor model, which helped predict the compositions of the reactor effluent under various conditions and determine the operating conditions of the separation trains. Both separation trains with recycled stream increased the DME production rate and overall CO
2
conversion, while the sizes of the reactor and separators, and the utility costs of refrigeration, absorbent recovery, recycled stream compression, etc. were significantly increased. The tradeoffs between different cases were quantitatively analyzed by techno-economic and sensitivity analyses. The results showed that the use of the absorber with the recycling of hydrogen is the most feasible process for the economic production of DME with high CO
2
reduction.
The first-principle modeling of heterogeneous catalysts is a revolutionarily approach, as the electronic structure of a catalyst is closely related to its reactivity on the surface with reactant ...molecules. In the past, detailed reaction mechanisms could not be understood, however, computational chemistry has made it possible to analyze a specific elementary reaction of a reaction system. Microkinetic modeling is a powerful tool for investigating elementary reactions and reaction mechanisms for kinetics. Using a microkinetic model, the dominant pathways and rate-determining steps can be elucidated among the competitive reactions, and the effects of operating conditions on the reaction mechanisms can be determined. Therefore, the combination of computational chemistry and microkinetic modeling can significantly improve computational catalysis research. In this study, we reviewed the trends and outlook of this combination technique as applied to the catalytic synthesis of methanol (MeOH) and dimethyl ether (DME), whose detailed mechanisms are still controversial. Although the scope is limited to the catalytic synthesis of limited species, this study is expected to provide a foundation for future works in the field of catalysis research based on computational catalysis.
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•Steam reforming of propane (SRP) was studied over the Ni-supported on Co-modified MgAl2O4@SiC (NCMAS).•Adjusted interactions of Ni nanoparticles largely altered the activity and ...stability.•Cobalt promoter showed the suppressed Ni aggregation with intimate interactions with CMAS support.•Kinetic parameters using LHHW model were properly derived for SRP reaction.
Steam reforming of propane (SRP) for the stable production of hydrogen-rich reformates was investigated using the Ni-supported on the cobalt-modified SiC-embedded MgAl2O4 support (denoted as NCMAS). The adjusted interactions of the Ni nanoparticles with the cobalt-modified SiC-embedded MgAl2O4 (MgAl2O4-SiC) and its crystallite size distributions largely altered the catalytic activity and stability of NCMAS. The introductions of SiC on the NCMAS, where SiC has a higher thermal conductivity, also increased the dispersion of smaller MgAl2O4 grains with the less formations of inactive NiAl2O4 species, which resulted in the higher catalytic activity with smaller formations of unreformed light hydrocarbons. The positive roles of cobalt promoter on the MgAl2O4-SiC matrices were mainly attributed to the suppressed aggregation of nickel nanoparticles by their strong and intimate interactions with the cobalt-modified MgAl2O4. The effects of cobalt promoter at an optimal 5wt%Co in the MgAl2O4-SiC (NCMAS(5)) enhanced the oxidation-resistance of the nickel nanoparticles with less formations of inactive metal aluminates by being reversibly re-reduced under the SRP reaction conditions. These phenomena further lessen coke depositions by intimately interacting with highly dispersed oxophilic cobalt or cobalt aluminate species. The optimal NCMAS(5) was applied to derive kinetic parameters using Langmuir-Hinshelwood-Hougen-Watson (LHHW) mechanisms, and the reasonable activation energy of 73 kJ/mol and optimal operating parameters to maximize hydrogen production by SRP reaction was estimated in terms of the reaction conditions such as space velocity, feed ratio and reaction temperature.
This work addresses the modeling and multi-objective optimization of methanol synthesis to efficiently utilize CO
2
from the CO
2
emissions and economics perspectives. Kinetic reactors for reforming ...and methanol synthesis reactions were used in the process simulator for modeling the entire process, and multi-objective optimization was conducted using the developed process model to maximize CO
2
reduction and the economic profit. The feed composition, operating temperature and pressure of the reformer, and utility temperature of the methanol synthesis reactor were considered as arguments in the non-dominated sorting genetic algorithm (NSGA II) method with the net change of CO
2
and economic profit as the objective elements, and the Pareto front showed a trade-off between CO
2
reduction and economic profit. When the amount of CH
4
in the feed was fixed at 500 kmol/h, CO
2
reduction was 11,588 kg/h, whereas the profit was −5.79 million dollars per year. Meanwhile, a maximum profit of 20 million dollars per year resulted in CO
2
emissions of 7,201 kg/h. The feed composition had the most significant influence on both objective elements (net change of CO
2
and economics); as CO
2
in the feed increased, CO
2
reduction increased and profit decreased, while the increase of H
2
O in the feed increased CO
2
emissions and profit.
A superior catalyst activity and stability for dimethyl ether (DME) conversion to gasoline-range hydrocarbons (DTG) on a novel hierarchically-structured hybridized FER@ZSM-5 were verified in terms of ...the strong interactions of ZSM-5 on the plate-like FER nanostructures, which were prepared by alcohol additive with two organic structure-directing agent (OSDA). The highly active nanostructured FER@ZSM-5 with a propanol additive showed the closely interconnected and highly dispersed ZSM-5 aggregates on the larger plate-like FER surfaces, which were mainly responsible for the suppressed heavy coke depositions with the help of the closely interconnected ZSM-5 and FER interfaces with abundant acidic sites on 8-membered ring (8-MR) channels. The well-dispersed ZSM-5 nanoparticles on Brønsted acid sites of FER surfaces showed coke-resistant natures for DTG reaction due to the synergy effects of the strong acidic sites of the smaller ZSM-5 particles and larger Brønsted acid sites on the plate-like FER structures.
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•Superior activity and stability for DTG on the hybrid FER@ZSM-5 composite were verified.•FER@ZSM-5(Propanol) with closely interconnected nanostructures showed higher stability.•Less coke deposition was observed due to closely interconnected ZSM-5 and FER interfaces.
To evaluate the effects of transfusions in patients with severe sepsis and septic shock on mortality.
Propensity-matched analysis of a prospective observational database (April 2005 to February ...2009).
Twenty-two medical and surgical intensive care units in 12 teaching hospitals in Korea.
One thousand fifty-four patients with community-acquired severe sepsis and septic shock.
None.
Of the 1,054 patients, 407 (38.6%) received a blood transfusion. The mean pretransfusion hemoglobin level was 7.7 ± 1.2 g/dL. Transfused patients had higher 28-day and in-hospital mortality rates (32.7% vs. 17.3%; p < .001, 41.3% vs. 20.3%; p < .001, respectively) and a longer duration of hospital stay (21 interquartile range, 10-35 vs. 13 interquartile range, 8-24 days; p < .001), but were more severely ill at admission (lower systolic blood pressure, higher Acute Physiology and Chronic Health Evaluation II score, and Sequential Organ Failure Assessment score at admission). In 152 pairs matched according to the propensity score depending on patient transfusion status, transfused patients had a lower risk of 7-day (9.2% vs. 27.0%; p < .001), 28-day (24.3% vs. 38.8%; p = .007), and in-hospital mortality rates (31.6% vs. 42.8%; p = .044). After adjusting for blood transfusion as a time-dependent variable in multivariable analysis, blood transfusion was independently associated with lower risk of 7-day (hazard ratio 0.42, 95% confidence interval 0.19-0.50, p = .026), 28-day (hazard ratio 0.43, 95% confidence interval 0.29-0.62, p < .001), and in-hospital mortality (hazard ratio 0.51, 95% confidence interval 0.39-0.69, p < .001).
In this observational study of patients with community-acquired severe sepsis and septic shock, red blood cell transfusions were associated with lower risk of mortality.
Only a few observational studies investigated the association between hypochloremia and mortality in critically ill patients, and these studies included small number of septic patients. Also, no ...study has evaluated the effect of an increase in chloride (Cl
) concentration in hypochloremia on the mortality. A total of 843 Korean septic patients were divided into three groups based on their baseline Cl
level, and Cox analyses were performed to evaluate the 28-day mortality. Moreover, the change in Cl
level (ΔCl) from baseline to 24, 48, or 72 hour was determined, and Cox analyses were also conducted to evaluate the relationship of ΔCl with mortality. 301 (35.7%) patients were hypochloremic (Cl
< 97 mEq/L), and 38 (4.5%) patients were hyperchloremic (Cl
> 110 mEq/L). During the follow-up period, 119 (14.1%) patients died. Hypochloremia was significantly associated with an increased mortality after adjusting for several variables, but an 1 mEq/L increase of ΔCl within 24 hour in patients with hypochloremia was significantly related to a decreased mortality. Caution might be required in severe septic patients with hypochloremia considering their increased mortality rate. However, an increased Cl
concentration might decrease the mortality rate of such patients.
Unfortunately, the options for treating multidrug-resistant (MDR) Acinetobacter baumannii (A. baumannii) infections are extremely limited. Recently, fosfomycin and minocycline were newly introduced ...as a treatment option for MDR A. baumannii infection. Therefore, we investigated the efficacy of the combination of colistin with fosfomycin and minocycline, respectively, as therapeutic options in MDR A. baumannii pneumonia. We examined a carbapenem-resistant A. baumannii isolated from clinical specimens at Severance Hospital, Seoul, Korea. The effect of colistin with fosfomycin, and colistin with minocycline on the bacterial counts in lung tissue was investigated in a mouse model of pneumonia caused by MDR A. baumannii. In vivo, colistin with fosfomycin or minocycline significantly (p < 0.05) reduced the bacterial load in the lungs compared with the controls at 24 and 48 h. In the combination groups, the bacterial loads differed significantly (p < 0.05) from that with the more active antimicrobial alone. Moreover, the combination regimens of colistin with fosfomycin and colistin with minocycline showed bactericidal and synergistic effects compared with the more active antimicrobial alone at 24 and 48 h. This study demonstrated the synergistic effects of combination regimens of colistin with fosfomycin and minocycline, respectively, as therapeutic options in pneumonia caused by MDR A. baumannii.
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•HDC of TCM to DCM was studied on the mesoporous 2wt%Pt-0.05wt%Pd/KIT-6.•At an optimal calcination T=400°C, a maximum DCM yield was obtained.•Close interactions of smaller Pt-Pd ...nanoparticles with higher oxidation states are beneficial for a higher DCM yield.•The kinetic model based on LHHW was well fitted with experimental results.•Higher DCM productivity was achievable at the highest SV and lowest H2/TCM ratio.
Selective hydrodechlorination (HDC) of trichloromethane (TCM, CHCl3) to dichloromethane (DCM, CH2Cl2) was studied on the mesoporous bimetallic Pt-Pd/KIT-6 to verify the roles of the active bimetals to catalytic activity and product distribution. The optimal bimetal ratio of 2wt%Pt-0.05wt%Pd on the highly ordered mesoporous KIT-6 calcined at 400°C showed a maximum TCM conversion with DCM yield, and the optimal calcination temperature of Pt-Pd/KIT-6 was mainly responsible for the formation of homogeneously and closely distributed smaller Pt-Pd nanoparticles with higher oxidation states of Pt crystallites supported by XPS and EXAFS analysis. Based on the proposed kinetic models on the optimal Pt-Pd/KIT-6, the competitive reaction mechanisms of the formations of CH4 and monochloromethane (MCM, CH3Cl) from DCM intermediate can well explain the product distributions. Using the seven different kinetic models, the best model on the basis of the Akaike’s Information Criteria showed the activation energies of the HDC of TCM to be in the range of 18–60kJ/mol. The kinetic model also revealed the inverse relationship between the conversion of TCM and selectivity to DCM. Either an increase of space velocity or decrease of H2/TCM ratio increased the DCM yield, while there existed the optimal operating conditions. The DCM productivity of 1.5mol-DCM/(gcat·h) was achievable at the highest space velocity and lowest H2/TCM ratio under a specific reaction condition of 190°C and 0.1MPa.
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