196746 research outputs found
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High Pressure Ammonia/Methanol Oxidation up to 100 atm
No full textHigh pressure ammonia/methanol oxidation and NOx formations were investigated using a recently developed supercritical pressure jet-stirred reactor (SP-JSR) at 20 and 100 atm with temperatures between 550 and 950 K and equivalence ratios of 0.138 and 1.15. The experimental results show that NH3 oxidation at high pressure is significantly accelerated by the active OH radicals produced from CH3OH oxidation. Furthermore, the kinetic interactions between NH3 and CH3OH are governed mainly by the reactions CH3OH + NH2 = CH2OH + NH3, CH3OH + NH2 = CH3O + NH3, and CH2O + NH2 = HCO + NH3. A HP-Mech model for high-pressure NH3/CH3OH oxidation was developed in this study. It consists of the most recent NH3 and CH3OH models including some new reactions and updated rate constants from the literature as well as NH3-CH3OH interactions where rate constants of CH3OH + NH2 = CH2OH + NH3, CH3OH + NH2 = CH3O + NH3, NH2 + CH2O = NH3 + HCO, and NH2 + CH2O = NH2CHO + H were theoretically calculated in this study. Our model with these updates improves the prediction for the measured N2O/NOx temperature dependence at 100 atm. In addition, the reaction pathway and sensitivity analysis show that N2O/NOx/HONO interactions with HO2 are very important, especially for a fuel-lean mixture at 100 atm. The HONO mole fraction for the fuel-lean mixture at 100 atm was then measured by off-axis integrated cavity output spectroscopy (ICOS) at wavenumber of 6638.26 cm−1. The experimental data show a significant HONO formation at intermediate temperature that is strongly underpredicted by numerical simulation at 100 atm. Therefore, the HONO related reactions with notable uncertainty at high pressure such as NO + OH (+M) = HONO (+M) and H2NO + NO2 = HONO + HNO need deeper exploration in the future
How relevant are sterols in the mode of action of prymnesins?
No full textPrymnesins, produced by the haptophyte Prymnesium parvum, are considered responsible for fish kills when this species blooms. Although their toxic mechanism is not fully understood, membrane disruptive properties have been ascribed to A-type prymnesins. Currently it is suggested that pore-formation is the underlying cause of cell disruption. Here the hypothesis that A-, B-, and C-type prymnesins interact with sterols in order to create pores was tested. Prymnesin mixtures containing various analogs of the same type were applied in hemolysis and cytotoxicity assays using Atlantic salmon Salmo salar erythrocytes or rainbow trout RTgill-W1 cells. The hemolytic potency of the prymnesin types reflected their cytotoxic potential, with approximate concentrations reaching 50 % hemolysis (HC50) of 4 nM (A-type), 54 nM (C-type), and 600 nM (B-type). Variabilities in prymnesin profiles were shown to influence potency. Prymnesin-A (3 Cl) + 2 pentose + hexose was likely responsible for the strong toxicity of A-type samples. Co-incubation with cholesterol and epi-cholesterol pre-hemolysis reduced the potential by about 50 % irrespective of sterol concentration, suggesting interactions with sterols. However, this effect was not observed in RTgill-W1 toxicity. Treatment of RTgill-W1 cells with 10 µM lovastatin or 10 µM methyl-β-cyclodextrin-cholesterol modified cholesterol levels by 20-30 %. Regardless, prymnesin cytotoxicity remained unaltered in the modified cells. SPR data showed that B-type prymnesins likely bound with a single exponential decay while A-types seemed to have a more complex binding. Overall, interaction with cholesterol appeared to play only a partial role in the cytotoxic mechanism of pore-formation. It is suggested that prymnesins initially interact with cholesterol and stabilize pores through a subsequent, still unknown mechanism possibly including other membrane lipids or proteins
Recent progress in mechanistic insights into cation effects on electrochemical CO<sub>2</sub> reduction reaction
No full textThe impact of cations in the local reaction environment has garnered attention as a crucial factor in tailoring the selectivity of CO2 reduction, although the mechanism remains under debate. Understanding these cation effects through first-principles computations can facilitate the design of efficient reaction networks and gas diffusion layers in electrolyzers. In this minireview, the latest insights into cation effects on CO2 reduction reactions are presented, covering aspects such as tuning the interfacial electric field, coordinating reaction intermediates, altering the interfacial water structure, and modulating local CO2 concentration and pH. Future research directions in this area are also discussed
Assessing uncertain technological progress in the decarbonization pathway of China's hydrogen energy system
No full textHydrogen energy is regarded as a promising solution for decarbonizing hard-to-abate sectors, while its role in the energy transition remains debatable. One of the key reasons is that uncertainty in technological progress has significant impacts on investment decision-making. To assess these effects, this study employs the MESSAGEix framework to develop a hydrogen energy system optimization model in China's context and integrates it with a stochastic scenario-tree generation method to assess the effects of uncertain technological progress on decarbonizing China's hydrogen energy system. The modeled system covers a full range of hydrogen production and consumption associated with different technical options for decarbonization, i.e., renewable energy-based water electrolysis (green hydrogen) and fossil-derived hydrogen coupled with carbon capture and storage. The model simulates a wide range of stochastic crucial cost metrics under the carbon-neutral constraint and compares it to a baseline without an emission constraint. Results show that disruptive technological breakthroughs in renewable electricity generation are essential to decarbonizing the hydrogen production system. The proposed hybrid modeling approach proves that computing is effective and could be applied to many other stochastic programming problems in long-term energy system planning
High pressure microreactor for minute amounts of catalyst on planar supports:A case study of CO<sub>2</sub> hydrogenation over Pd<sub>0.25</sub>Zn<sub>0.75</sub>O<sub>x</sub> nanoclusters
No full textHigh-pressure studies of well-defined catalysts, deposited on planar supports in ultra-high vacuum using physical methods, may bridge the gap between surface science and applied catalysis approaches in order to develop better catalysts for crucial reactions such as CO2 hydrogenation. However, the chemical reactors necessary for such investigations, typically involving catalyst quantities down to a few hundred nanograms, are lacking. We present the novel design and evaluation of a 50 µL rectangular microchannel reactor capable of testing small quantities of catalyst at pressures up to 40 bar and temperatures up to 240 °C. To evaluate the microreactor performance, Pd0.25Zn0.75Ox nanoclusters soft-landed on SiO2-coated mica sheets using the cluster beam deposition technique, were tested for CO2 hydrogenation via the reverse water–gas shift reaction through a series of kinetic experiments. Experimental results, combined with computational fluid dynamics and mass transport analysis, demonstrate that the proposed microreactor setup allows for testing minute quantities of catalysts with very high sensitivity at industrially relevant temperatures and pressures. Although not restricted to a particular catalyst preparation method, the setup is an excellent platform for conducting catalytic tests on composition-controlled, mass-selected, gas-phase nanoparticles deposited on planar substrates, facilitating the determination of reliable structure–activity relationships and enabling a more rational design of catalysts.</p
Modelling dynamic feeding in cyclic separation
No full textModelling of cyclic separations is extended to account for a non-instantaneous liquid feeding period succeeding the liquid flow period in established models. The inclusion of variable holdup infers inter-tray variations and time-variant behaviour. For a linear case of ammonia stripping, we employ solution methods involving state-transition matrices derived using a Peano–Baker series expansion to retain linear solution methods for determining the pseudo-steady-states. The expanded model is then utilised to evaluate the impact of prolonged feeding relative to prolonged liquid flow periods on separation performance for established simultaneous and sequential draining strategies. Accounting for the non-instantaneous behaviour showed improved agreement with experimental results and illuminated that prolonged feeding can significantly reduce the overall column separation performance
Snow crab (<i>Chionoecetes opilio</i>) in the Barents Sea — A passive or problematic invader?
No full textThe invasion and continued expansion of snow crab in the Barents Sea have provided the area with a new and valuable resource. On the negative side, this invasion may lead to changes in the ecosystem, including structural changes and shifts in energy pathways, as we generally view invaders as a problem. We investigated potential effects of snow crab invasion by applying an end-to-end ecosystem model under different scenarios of fishing and food availability. Overall, the model indicated a low negative impact of snow crab on the ecosystem in the region, also in a potential future with a much higher snow crab biomass. Although snow crab may be found to have local negative effects on specific benthic species, in general it appears that they have found a vacant ecological niche in the Barents Sea ecosystem. In addition, network analysis show that the food web of the Barents Sea becomes slightly more complex when including the snow crab, adding predator–prey interactions. By introducing more parallel foodpaths to the food web, this results in a more resilient ecosystem. Model simulations where the availability of prey to snow crab, and lack of fishing pressure maximizes snow crab abundance result in a somewhat increased impact on the food web. Nevertheless, the effects are still minor and there is no indications that the existing commercial fisheries for other species will be significantly affected. Hence, their role as a passive invader should be considered when structuring management responses
Arbitrage equilibria in active matter systems
No full textThe motility-induced phase separation (MIPS) phenomenon in active matter has been of great interest for the past decade or so. A central conceptual puzzle is that this behavior, which is generally characterized as a nonequilibrium phenomenon, can yet be explained using simple equilibrium models of thermodynamics. Here, we address this problem using a new theory, statistical teleodynamics, which is a conceptual synthesis of game theory and statistical mechanics. In this framework, active agents compete in their pursuit of maximum effective utility, and this self-organizing dynamics results in an arbitrage equilibrium in which all agents have the same effective utility. We show that MIPS is an example of arbitrage equilibrium and that it is mathematically equivalent to other phase-separation phenomena in entirely different domains, such as sociology and economics. As examples, we present the behavior of Janus particles in a potential trap and the effect of chemotaxis on MIPS
Recyclability of take-back glass fiber-reinforced blends of polyphenylene oxide with high-impact polystyrene for high-performance engineering applications
No full textIncreased recycling of plastics is an essential step toward a more sustainable use of materials, where some of the most challenging fractions are engineering materials and composites. Used pump houses prepared from glass fiber (GF)-reinforced blends of polyphenylene oxide (PPO) and high-impact polystyrene (HIPS) obtained through a take-back scheme (take-back, TB) were characterized and shredded for use in the preparation of new composites by injection molding. Initial degradation was observed on the surface of the TB parts; however, the core of the material was unaffected. Mechanical reprocessing of regrind and virgin material showed a reduction of tensile strength already at 10% regrind, which was attributed to fiber length reduction during reprocessing. At the same time, Young's modulus and extension at break were largely unaffected, confirming that 25% of TB could be included without any additional loss of properties. As a worst-case scenario, tests with extensively degraded material showed that Young's modulus and tensile strength would ultimately be reduced with an increasing amount of heavily degraded material and that a balance would have to be found between loss of properties and recycled content for heavily degraded material
Numerical analysis of the combined influence of fin shape and location on constrained melting of phase change materials in a spherical capsule with double fins
No full textThis study presents a novel approach to investigating the combined influence of fin position and shape on the constrained melting behavior of phase change material (PCM) within a spherical capsule (S.C.) through numerical analysis. Unlike previous research, which predominantly focused on single fin shapes or positions, this work uniquely explores the impact of double, simple, and easily manufacturable fin shapes. A two-dimensional computational model employing the enthalpy–porosity method assesses melting behavior, temperature distribution, and PCM flow. Numerous fin shapes, namely rectangular, trapezoidal converging, trapezoidal diverging stepped, inverse stepped, and triangular, are considered in the analysis. The study reports the influence of the location of two identically shaped fins on the thermal performance. The fins' cross-sectional area and base thickness are kept equal in all cases. The thermal performance of an S.C.-integrated fin system is evaluated by analyzing various attributes such as total saving in the duration of melting, enhancement ratio, and Nusselt number. The results indicate that the position of the fins has a more significant impact on melting performance than the fin shape. The best performance is achieved when fins are placed in the lower half of the capsule, followed by the center and upper halves, regardless of fin shape. For rectangular fins, shifting the position of the fin from the bottom half to the center increases the melting time by 24.7% and the top half by 68.3%. The shortest melting time of 93 min is observed for lower-half rectangular fins, followed by center-placed triangular fins (94 min). This study offers a theoretical foundation for optimizing the performance of different technologies using latent heat thermal energy storage systems such as packed-bed, cascaded thermal energy storage systems.</p