The higher catalytic activity and stability for a gas-phase carbonylation of dimethyl ether (DME) to methyl acetate (MA) on the seed-derived ferrierite (FER) were attributed to its higher ...crystallinity with small amounts of defect sites by recrystallization methods without using any organic structure directing agent. The recrystallized FER (FER-S1) with its smaller amount of Lewis acidic extraframework Al sites (EFAl) possessed proper number of Brønsted acidic sites in the eight-membered-ring (8-MR) channels in comparison to the pristine FER, which was responsible for an enhanced CO insertion rate to methoxy intermediates formed by dissociated DME molecules by referentially forming acetyl intermediates or to the highly active Brønsted acidic sites. The most active tetrahedral T2 sites with two adjacent Al atoms in the 8-MR channels having next-nearest Al–O–Si–O–Al configurations on the FER-S1 revealed the stronger adsorption of the stably adsorbed DME molecules as confirmed by DFT calculations. FER-S1 containing the proper amounts of Al atoms in the 8-MR with appropriate locations with optimal acidic properties was responsible for its higher activity and stability for the gas-phase carbonylation of DME, where the Al distributions were confirmed by Rietveld refinement XRD analysis, FT-IR, and DFT calculations. In addition, the acidic sites on the outer surfaces and larger cavity including 10-MR channels were responsible for an accelerated formation of aromatic coke precursors.
Sepsis, including severe sepsis and septic shock, is a major cause of morbidity and mortality. Albumin and C-reactive protein (CRP) are considered as good diagnostic markers for sepsis. Thus, initial ...CRP and albumin levels were combined to ascertain their value as an independent predictor of 180-day mortality in patients with severe sepsis and septic shock.
We conducted a retrospective cohort study involving 670 patients (>18 years old) who were admitted to the emergency department and who had received a standardized resuscitation algorithm (early goal-directed therapy) for severe sepsis and septic shock, from November 2007 to February 2013, at a tertiary hospital in Seoul, Korea. The outcome measured was 180-day all-cause mortality. A multivariate Cox proportional hazard model was used to identify the independent risk factors for mortality. A receiver operating characteristic (ROC) curve analysis was conducted to compare the predictive accuracy of the CRP/albumin ratio at admission.
The 180-day mortality was 28.35% (190/670). Based on the multivariate Cox proportional hazard analysis, age, the CRP/albumin ratio at admission (adjusted HR 1.06, 95% CI 1.03-1.10, p<0.001), lactate level at admission (adjusted HR 1.10, 95% CI 1.05-1.14, p<0.001), and the Sequential Organ Failure Assessment (SOFA) score at admission (adjusted HR 1.12, 95% CI 1.07-1.18, p<0.001) were independent predictors of 180-day mortality. The area under the curve of CRP alone and the CRP/albumin ratio at admission for 180-day mortality were 0.5620 (P<0.001) and 0.6211 (P<0.001), respectively.
The CRP/albumin ratio was an independent predictor of mortality in patients with severe sepsis or septic shock.
In this study, the development of kinetic rate equations for catalytic methane chlorination over pellet-type catalysts was addressed. Experimental data at various temperatures, feed compositions, ...space velocities, and pressures were used to estimate the kinetic parameters. The average errors for methane conversion and methyl chloride (MCM) selectivity were 15.9 and 4.4%, respectively, validating the effectiveness of the developed kinetics. A process model was developed by considering a commercial-scale methane chlorination reactor and separation train. HCl, which was responsible for half of the chlorine gas in the feed, might reduce the economics of the process. The MeOH hydrochlorination reaction was combined with methane chlorination, and three variations of the combined process were suggested, depending on the configuration of the separation sequence. The MeOH hydrochlorination reduced the energy requirement by more than 80% compared to methane chlorination. Techno-economic analysis showed that the feeding of pure HCl had the lowest purchase and annual production costs, resulting in the lowest minimum selling price (MSP) of 0.90 $/kg-MCM. The sensitivity analysis of the MSP concerning the MeOH and HCl price showed that the proposed process is the most economical up to 1.8 $/kg-MeOH and 160 $/ton-HCl, respectively.
This paper proposes a kinetic model of the chlorination of methane in the presence of a catalyst. As the reaction involves both gas-phase and catalytic chlorination, the reaction mechanisms with and ...without the catalyst were considered in this study. Experiments were conducted for the case of the gas phase and with catalysts separately, and kinetic parameters for each phase were estimated independently by fitting the experimental data. The proposed model accurately describes the experimental data (means of absolute relative residual values for the conversions of CH4 and Cl2 and the selectivities of methyl chloride, dichloromethane, and trichloromethane were 9.60, 12.91, 7.79, 19.18, and 16.14%, respectively), in which the presence of the catalyst increased the conversion of methane, while it decreased the selectivity of methyl chloride, which is the desired product in this work. Further analysis showed that a high temperature increased the conversion and reduced the size of the reactor. The production rate of methyl chloride was strongly influenced by the methane fraction in the feed. An optimal fraction exists (70% methane) because an excess amount of methane decreased the conversion. Under optimal conditions, toxic chlorine was completely consumed. It was concluded that the developed model can be used to design an effective reactor for catalytic methane chlorination and determine the optimal operating conditions.
The location and distribution of aluminum in zeolites is considered important in determining various properties, such as acidity and reactivity. Controlling the placement of aluminum substitution has ...therefore been of significant interest, and a number of studies have been conducted, including synthesis methods using either different organic structure-directing agents (OSDAs) or cationic species, and the application of dealumination as post-processing. In addition to experimental developments, computational methods have emerged as a useful tool for analyzing the effects of different types of aluminum siting on catalytic properties, especially by incorporating statistical methods. A review of recent developments and findings related to aluminum siting and its effects is presented in this work. Analysis of the thermodynamic distribution of aluminum, as well as synthetically altered distribution in different zeolite frameworks, has been discussed. Computational studies have revealed that catalytic properties are sensitive to adsorbate-dependent properties such as the size of rings and voids for the residence of aluminum, the relative distribution of acid sites, and the adsorption properties of molecules in different framework motifs. Along with the atomic scale evaluation of synthetic treatments in positioning the aluminum, cases of instrumental analysis methods and their verification with simulations is discussed, demonstrating how theories have complemented and, sometimes modified, experimental perspectives. Lastly, recent progress in incorporating machine learning techiques, its application to zeolites, and directions for future work are introduced.
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•A kinetic model was developed for the methane dehydroaromatization over a Mo2C/H-ZSM5 catalyst.•The initial activity of the Mo2C site is low in the early stage of the catalyst bed ...probably due to the carbonization.•The initial activity of the H-ZSM5 site is low in the later stage of the bed due to the encapsulation of coupled aromatics.•The deactivation model indicates a higher temperature dependency of the Mo2C site compared with the H-ZSM5 site.•The developed model explains the deactivation behaviors and can be used to determine the optimal operating conditions.
A kinetic model was developed for the methane dehydroaromatization over a Mo2C/H-ZSM5 catalyst. Because the experimental observations show that the reaction and deactivation simultaneously take place in the catalyst activation (carburization) stage, the initial simulation time was specified as the time at which the activation was completed and the initial activities under each operating condition were estimated. The estimated values show that the initial activity of the Mo2C site is low in the early stage of the catalyst bed, which is probably due to the carbonization, while that of the H-ZSM5 site is very low in the later stage of the bed due to the encapsulation of coupled aromatics caused by the low confinement of Mo2C in the zeolite. Kinetic models were developed for the reaction and deactivation and the kinetic parameters were estimated by fitting the experimental data that were obtained after the activation was completed. The simulated results are in good agreement with the experimental data. The deactivation model indicates a higher temperature dependency of the Mo2C site compared with the H-ZSM5 site. In addition, the benzene and toluene yields abruptly decrease at very high temperature, indicating that a too high temperature should be avoided, although high temperatures are favored because of the endothermic characteristics of the production rate.
This work addresses the development of a DME synthesis process from a mixture of coke oven gas (COG) and FINEX tail gas (FTG) from a steel-making plant. Two different syngas-to-DME processes were ...considered: one using two separate reactors for the methanol synthesis over Cu–ZnO–Al2O3 (CZA) and the methanol dehydration over ferrierite (FER) zeolite catalysts, and the other using a single reactor by physically mixing the two catalysts. Kinetic models were developed for each catalyst and the kinetic parameters were estimated by fitting the experimental data at various conditions of temperatures, pressures, space velocities, and feed compositions. The process modeling results showed that the single reactor achieved a CO conversion of 88.1% and a DME production rate of 450 kg/h, while the corresponding values for the method employing two separate reactors were 38.6% and 240 kg/h, respectively. This difference is attributable to the spontaneous conversion of the produced MeOH to DME, by the coexistence of the two catalysts, which shifted the equilibrium of MeOH production forward. The comparison between the open-loop and recycled cases showed that the carbon efficiency could be more than doubled for both reactor configurations when the unreacted gas was recycled. Finally, the single-reactor configuration employing the recycled stream produced DME at a rate of 825.9 kg/h with the complete consumption of CO and a CO2 conversion of 76%. This indicated that such a process would maximize the use of by-product gas and increase the economic feasibility of steel-making plants.
•The kinetic models for MeOH and DME syntheses were developed.•The syngas was assumed to be a mixture of by-product gas in a steel-making plant.•The physical mixing of CZA and FER catalysts was considered.•The process model was developed using the kinetics with the estimated parameters.•The superiority of the single-step process to the case of two reactors was shown.
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•The industrial LDPE autoclave was comprehensively modeled.•CFD multicompartment model and probability generating function transformation were integrated.•The model performed as ...accurately as the original CFD and MWD model at a low numerical cost.•The model showed good coincidence with the experimental data on the industrial equipment.•The circulation flow pattern increased the accumulation of dead polymers, resulting in a broad MWD with bimodality.
A commercial Low-density polyethylene (LDPE) reactor was modeled to investigate the effects of highly nonlinear hydrodynamics in an industrial-scale autoclave reactor on the polymer Molecular weight distribution (MWD). To reduce the extremely high computational burden of Computational fluid dynamics (CFD) runs and detailed MWD calculations, a combination of the CFD multicompartment model and probability generating function transformation is proposed. The validity of the proposed model was verified by a comparison with experimental data on industrial equipment. The computation time was shown to be only 37% of the actual operation time. The proposed model showed that strong downflow and weak reverse-flow coexisted to form circulation flow between the disks in the autoclave. Polymerization mainly occurred in the strong downflow region of the tubular regime. The circulation flow increased the accumulation of dead polymers to enhance the chain transfer to polymer, which produces long-branched living polymer chains and termination by recombination for a broad MWD with bimodality. Further analysis based on the simulation without the circulation flow showed a narrow MWD and no bimodality. These results indicate that the flow pattern must be properly controlled to produce polymers with desired properties in large-scale polymerization reactors.
Non-volatile liquid organic semiconducting materials have received much attention as emerging functional materials for organic electronic and optoelectronic devices due to their remarkable ...advantages. However, charge injection and transport processes are significantly impeded at interfaces between electrodes and liquid organic semiconductors, resulting in overall lower performance compared to conventional solid-state electronic devices. Here we successfully demonstrate efficient charge injection into solvent-free liquid organic semiconductors via cracked metal structures with a large number of edges leading to local electric field enhancement. For this work, thin metal films on deformable polymer substrates were mechanically stretched to generate cracks on the metal surfaces in a controlled manner, and charge injection properties into a typical non-volatile liquid organic semiconducting material, (9-2-ethylhexyl)carbazole (EHCz), were investigated in low bias region (i.e., ohmic current region). It was found that the cracked structures significantly increased the current density at a fixed external bias voltage via the local electric field enhancement, which was strongly supported by field intensity calculation using COMSOL Multiphysics software. We anticipate that these results will significantly contribute to the development and further refinement of various organic electronic and optoelectronic devices based on non-volatile liquid organic semiconducting materials.
We investigated the conversion of CO
2
in the exhaust gas of an engine plant into methanol. The process consists of CO
2
purification by an acid gas removal unit (AGRU), mixed reforming, and methanol ...synthesis. The AGRU removes a large amount of inert gas, yielding CO2 of 98% purity at a recovery rate of 90% for use as feed to the reformer. The reformer temperature of 900 °C led to the almost total consumption of CH4. In the methanol synthesis reaction, the utility temperature had a greater influence on the conversion and methanol production rate than the inlet temperature. The optimal temperature was determined as 180 °C. Because the amount of hydrogen in the reformer effluent produced by dry reforming was insufficient, the steam available in the engine plant was used for mixed (dry and steam) reforming. The steam increased the hydrogen and methanol production rate; however, the compression cost was too high, and there exists an optimal amount of steam in the feed. The techno-economic analysis of the optimal conditions showed that utilization of CO
2
in the exhaust gas along with freely available steam is economically feasible and reduces CO
2
emissions by over 85%.
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