Interfacial Behaviors and Oil Detachment Mechanisms by Modified Silica Nanoparticles: Insights from Molecular Simulations.

Surfactant flooding has been considered as a promising approach for chemically enhanced oil recovery (EOR). However, this technique encounters several limitations, such as high costs, environmental concerns, and reduced efficiency under high-temperature and high-salinity reservoir conditions. Recently, nanoparticles have also been proposed as an alternative for EOR due to their superior properties compared with surfactants. This research employs molecular dynamics simulations to explore the impact of modified SiO2 nanoparticles on oil-water interfacial behaviors and the detachment of oil droplets from an oil-wet surface. The simulation results reveal that modified nanoparticles, featuring hydrophilic and hydrophobic functional groups, have slight impacts on interfacial tension reduction of the oil-water interface. Nanoparticles with varying degrees of modification exhibit distinct positions within the interface, consequently influencing the thickness of the interfacial layer. Notably, the interactions among the nanoparticles, oil molecules, and surface facilitate the formation of a water channel, thereby enhancing the process of oil detachment. Comparative analysis indicates that in terms of oil displacement efficiency, the thickness of the interfacial layer has a more significant impact than interfacial tension reduction. Furthermore, to elucidate the mechanisms of modified nanoparticles enhancing the oil recovery rate, the interaction energies among the oil droplet, nanoparticles, water, and surface are analyzed. The molecular-level insights derived from this investigation could provide valuable guidance for the design of modified nanoparticles tailored to EOR applications.

Multiscale modeling of gas flow behaviors in nanoporous shale matrix considering multiple transport mechanisms.

This study proposes a multiscale model combining molecular simulation and the lattice Boltzmann method (LBM) to explore gas flow behaviors with multiple transport mechanisms in nanoporous media of shale matrix. The gas adsorption characteristics in shale nanopores are first investigated by molecular simulations, which are then integrated and upscaled into the LBM model through a local adsorption density parameter. In order to adapt to high Knudsen number and nanoporous shale matrix, a multiple-relaxation-time pore-scale LBM model with a regularization procedure is developed. The combination of bounce-back and full diffusive boundary condition is adopted to take account of gas slippage and surface diffusion induced by gas adsorption. Molecular simulation results at the atomic scale show that gas adsorption behaviors are greatly affected by the pressure and pore size of the shale organic nanopore. At the pore scale, the gas transport behaviors with multiple transport mechanisms in nanoporous shale matrix are explored by the developed multiscale model. Simulation results indicate that pressure exhibits more significant influences on the transport behaviors of shale gas than temperature does. Compared with porosity, the average pore size of nanoporous shale matrix plays a more significant role in determining the apparent permeability of gas transport. The roles of the gas adsorption layer and surface diffusion in shale gas transport are discussed. It is observed that under low pressure, the gas adsorption layer has a positive influence on gas transport in shale matrix due to the strong surface diffusion effect. The nanoporous structure with the anisotropy characteristic parallel to the flow direction can enhance gas transport in shale matrix. The obtained results may provide underlying and comprehensive understanding of gas flow behaviors considering multiple transport mechanisms in shale matrix. Also, the proposed multiscale model can be considered as a powerful tool to invesigate the multiscale and multiphysical flow behaviors in porous media.

Effects of indole derivatives from Purpureocillium lilacinum in controlling tobacco mosaic virus.

There are various types of compounds studied and applied for plant disease management, and some of them are environment friendly and suitable in organic production. An example is indole-3-carboxaldehyde (A1) and indole-3-carboxylic acid (A2) derived from Purpureocillium lilacinum H1463, which have shown a strong activity in the control of tobacco mosaic virus (TMV). In this study, the effects of these compounds were studied on suppressing TMV and corresponding mechanism. Both A1 and A2 exhibited strong anti-TMV activities in vitro and in vivo. They fractured TMV virions and forced the fractured particles agglomerated. A1 and A2 also induced immune responses or resistance of tobacco to TMV infection, including expressing hypersensitive reaction (HR), increasing defense-related enzymes and overexpressing pathogenesis-related (PR) proteins. The upregulation of salicylic acid (SA) biosynthesis genes PAL, ICS, and PBS3 confirmed that SA served as a defense-related signal molecule. Therefore, indole derivatives have a potential for activating defense of tobacco against TMV and other pathogens and can be used for disease control.

Research on electrostatic shielding characteristics of electrostatic precipitator.

Air pollution control is a worldwide problem of common concern to all mankind. Electrostatic precipitator (ESP) plays an important role in the purification of flue gas and dust. At present, in a multi-electrode ESP, the middle discharge electrode is often inhibited by the outer discharge electrode, commonly known as electrostatic shielding, which seriously affects the electric field distribution and dust removal effect of ESP. In order to explore this characteristic, this research established a mathematical model of ESP and simulated the electrostatic shielding phenomenon of wire-plate ESP, which quantified the influence of various factors on the degree of electrostatic shielding and analyzed the potential impact of electrostatic shielding on particle charging and dust removal efficiency. The results of the study show that the wire-to-plate distance has the greatest impact on electrostatic shielding, followed by the discharge electrode radius, voltage, and the wire-to-wire distance. When the degree of electrostatic shielding increases, the dust removal efficiency of ESP decreases. In addition, increasing the number of discharge electrodes to increase the dust removal efficiency of ESP is only feasible within a certain range. When the number of discharge electrodes exceeds a certain threshold, the dust removal efficiency of ESP decreases due to the effect of electrostatic shielding. The results of the research provide guidance for the determination of the geometric parameters of ESP and can make theoretical predictions for the occurrence of electrostatic shielding, thereby effectively avoiding the occurrence of electrostatic shielding.Implications: Electrostatic precipitator plays an important role in the purification of flue gas and dust. Electrostatic shielding seriously affects the electric field distribution and dust removal effect of ESP. The research quantified the influence of various factors on the degree of electrostatic shielding and analyzed the potential impact of electrostatic shielding on particle charging and dust removal efficiency. It is expected that through the research, some guidance will be provided for the determination of the geometric parameters of ESP and can make theoretical predictions for the occurrence of electrostatic shielding, thereby effectively avoiding the occurrence of electrostatic shielding.

Computational Insights into LixOy Formation, Nucleation, and Adsorption on Carbon Nanotube Electrodes in Nonaqueous Li-O2 Batteries.

Recent theoretical and experimental studies have shown that the formation of Li2O2, the main discharge product of nonaqueous Li-O2 batteries, is a complex multistep reaction process. The formation, nucleation, and adsorption of LixOy (x and y = 0, 1, and 2) and (Li2O2)n clusters with n = 1-4 on the surface of carbon nanotubes (CNTs) were investigated by periodic density functional theory calculation. The results showed that both Li2O2 and Li2O on CNT electrodes are preferentially generated by lithiation reaction rather than disproportionation reaction. The free energy profiles demonstrate that the discharge potentials of 2.54 and 1.29 V are the threshold values of spontaneous nucleation of (Li2O2)2 and (Li2O)2 on a CNT surface, respectively. The electronic structure indicates that Li2O2 is a p-type semiconductor, while Li2O exhibits the properties of an insulator. Interestingly, once Li2O2 molecules condense into large clusters, they will be repelled away from the CNT surface and continue to grow into large-sized Li2O2. Our results provide insights into the full understanding of the electrochemical reaction mechanism and product formation processes of lithium oxides in the cathodes of Li-O2 batteries.

Molecular Investigation of CO2/CH4 Competitive Adsorption and Confinement in Realistic Shale Kerogen.

The adsorption behavior and the mechanism of a CO2/CH4 mixture in shale organic matter play significant roles to predict the carbon dioxide sequestration with enhanced gas recovery (CS-EGR) in shale reservoirs. In the present work, the adsorption performance and the mechanism of a CO2/CH4 binary mixture in realistic shale kerogen were explored by employing grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations. Specifically, the effects of shale organic type and maturity, temperature, pressure, and moisture content on pure CH4 and the competitive adsorption performance of a CO2/CH4 mixture were investigated. It was found that pressure and temperature have a significant influence on both the adsorption capacity and the selectivity of CO2/CH4. The simulated results also show that the adsorption capacities of CO2/CH4 increase with the maturity level of kerogen. Type II-D kerogen exhibits an obvious superiority in the adsorption capacity of CH4 and CO2 compared with other type II kerogen. In addition, the adsorption capacities of CO2 and CH4 are significantly suppressed in moist kerogen due to the strong adsorption strength of H2O molecules on the kerogen surface. Furthermore, to characterize realistic kerogen pore structure, a slit-like kerogen nanopore was constructed. It was observed that the kerogen nanopore plays an important role in determining the potential of CO2 subsurface sequestration in shale reservoirs. With the increase in nanopore size, a transition of the dominated gas adsorption mechanism from micropore filling to monolayer adsorption on the surface due to confinement effects was found. The results obtained in this study could be helpful to estimate original gas-in-place and evaluate carbon dioxide sequestration capacity in a shale matrix.

Molecular simulation of CO2/CH4/H2O competitive adsorption and diffusion in brown coal.

Carbon dioxide enhanced coalbed methane recovery (CO2-ECBM) has been proposed as a promising technology for the natural gas recovery enhancement as well as mitigation of CO2 emissions into the atmosphere. Adsorption and diffusion of CO2/CH4 mixture play key roles in predicting the performance of CO2-ECBM project, i.e., the production of coalbed methane as well as the geological sequestration potential of carbon dioxide. In the present work, the mechanism of competitive adsorption and diffusion of CO2/CH4/H2O mixture in brown coal were investigated by employing grand canonical Monte Carlo and molecular dynamics simulation. The effects of temperature and pressure on competitive adsorption and diffusion behaviours were explored. It is found that CO2 has much stronger adsorption ability on brown coal than CH4. The adsorption amounts of CO2/CH4 increase with pressure but have a decreasing trend with temperature. High adsorption selectivity of CO2/CH4 is observed with pressure lower than 0.1 MPa. In addition, the effects of moisture content in brown coal on the adsorption characteristics have been examined. Simulation results show that the adsorption capacities of CO2/CH4 are significantly suppressed in moist brown coal. The competitive adsorption of CO2/CH4/H2O follows the trend of H2O ≫ CO2 > CH4. Moreover, the results reveal that moisture content has great effects on the self-coefficients of CO2/CH4. Compared with dry coal, the self-diffusion coefficients of CO2 and CH4 reduce by 78.7% and 75.4% in brown coal with moisture content of 7.59 wt%, respectively. The microscopic insights provided in this study will be helpful to understand the competitive adsorption and diffusion mechanism of CO2/CH4/H2O in brown coal and offer some fundamental data for CO2-ECBM project.

Molecular insights into competitive adsorption of CO2/CH4 mixture in shale nanopores.

In the present study, competitive adsorption behaviour of supercritical carbon dioxide and methane binary mixture in shale organic nanopores was investigated by using grand canonical Monte Carlo (GCMC) simulations. The model was firstly validated by comparing with experimental data and a satisfactory agreement was obtained. Then the effects of temperature (298-388 K), pressure (up to 60 MPa), pore size (1-4 nm) and moisture content (0-2.4 wt%) on competitive adsorption behaviour of the binary mixture were examined and discussed in depth. It is found that the adsorption capacity of carbon dioxide in shale organic nanopores is much higher than that of methane under various conditions. The mechanism of competitive adsorption was discussed in detail. In addition, the results show that a lower temperature is favorable to both the adsorption amount and selectivity of CO2/CH4 binary mixture in shale organic nanopores. However, an appropriate CO2 injection pressure should be considered to take into account the CO2 sequestration amount and the exploitation efficiency of shale gas. As for moisture content, different influences on CO2/CH4 adsorption selectivity have been observed at low and high moisture conditions. Therefore, different simulation technologies for shale gas production and CO2 sequestration should be applied depending on the actual moisture conditions of the shale reservoirs. It is expected that the findings in this work could be helpful to estimate and enhance shale gas resource recovery and also evaluate CO2 sequestration efficiency in shale reservoirs.

Experimental study of dust deposition in dynamic granular filters.

The aim of the present study is to investigate the process of dust deposition and its effects on the filtration performance of dynamic granular filters. We proposed a new theoretical explanation about the model for dust cake formation and growth, especially for the compression model at higher filtration superficial velocities in dynamic granular filters. The thickness and porosity of dust cakes can be estimated by formulas. Then, the effects of cake formation and growth on filtration performance were examined. It is found that there is an optimum thickness of the cake at which the dynamic granular filter achieves excellent collection efficiency with low system resistance. Moreover, an increasing pattern of pressure drop with cake thickness under different filtration superficial velocities was observed. Experimental results show that the pressure drops across the filter system and dust cake increase exponentially with increasing filtration superficial velocity. An appropriate filtration superficial velocity should be considered to achieve optimum filtration performance in dynamic granular filters. It is expected that the results of this study could provide useful information on designing dynamic granular filters for removal of dust particulates in Integrated Gasification Combined-Cycle (IGCC) and Pressurized Fluidized-Bed Combustion (PFBC).