Study of the Adsorption Behavior of Surfactants on Carbonate Surface by Experiment and Molecular Dynamics Simulation

Molecular Dynamics Simulation of the Effects of Anionic-Nonionic Surfactants on Interfacial Properties of the Oil-Water Interface

Surfactant oil drive is a crucially enhanced oil recovery method that improves oil recovery rates. The aggregation behavior of surfactant molecules at the oil-water interface significantly influences oil repulsion. In this study, a molecular dynamics simulation is used to investigate this repellent behavior of single and binary surfactants of alkanolamides (6501) and fatty alcohol polyoxyethylene ether sodium sulfate (AES). The oil-water interface is characterized by density distribution, interfacial thickness, radial distribution function, interfacial tension, and interfacial generation energy. The results reveal that the dodecanolamide surfactant (126501) and AES effectively reduce interfacial tension. In the binary 126501/AES system, the interfacial film thickness increases to 18.08 Å, and the diffusion coefficient increases to 0.186 Å2/ps. The radial distribution function shows that oil molecules are located 4.2 Å from the anionic head of AES, which weakens the intermolecular forces within the oil layer. In the 126501/AES system, the interfacial energy of -96.12 kJ/mol indicates a stable interface. Moreover, both the 126501/AES and tetradecanolamide surfactant (146501)/AES systems exhibit excellent resistance to metal ions. The molecular-level mechanism provides useful guidance for designing the surfactant systems for enhanced oil recovery.

Advancements and challenges in the use of surfactants and nanoparticles for enhanced oil recovery: mechanisms, synergies, and field applications

This review highlights the recent advancements and challenges in the use of surfactants and nanoparticles for enhanced oil recovery (EOR). Novel surfactant formulations, including biosurfactants and hybrid systems, have shown improved recovery efficiency and environmental sustainability. Surfactant-polymer mixtures offer synergistic effects that enhance performance across various reservoir conditions. Concurrently, advancements in nanoparticle technology, such as green nanotechnology and improved formulations, have enhanced the stability, dispersion, and functionality of nanoparticles in EOR processes. Critical factors such as nanoparticle size, concentration, and surface modifications play pivotal roles in optimizing oil recovery efficiency. However, significant challenges persist, particularly surfactant adsorption onto rock surfaces and nanoparticle agglomeration, which reduce the overall effectiveness of these techniques. Addressing these limitations requires strategies such as surface modification and advanced delivery mechanisms. Additionally, economic and environmental concerns remain key barriers to large-scale implementation, underscoring the importance of sustainable and cost-effective solutions. A critical gap in the research is the lack of large-scale field studies and long-term monitoring, which are essential for validating laboratory findings and optimizing these technologies for real-world applications. With increasing focus on sustainability, future research is expected to prioritize eco-friendly materials and methods. Integrating surfactant and nanoparticle-based EOR with other recovery techniques, such as thermal and gas injection, holds potential for maximizing oil recovery. Continued research and development are crucial to overcoming current challenges and advancing the sustainability and efficiency of EOR technologies, contributing to a cleaner and more efficient future for oil recovery.

The adsorption behavior at the air/water interface of saturated cardanol nonionic surfactants through molecular dynamic simulations

CONTEXT

Cardanol surfactants exhibit significant development potential owing to their advantages of abundant availability, low cost, and environmental sustainability. In this study, a series of saturated cardanol nonionic surfactants were designed. The structure-activity relationships of these surfactants with varying lengths and positions of PO and EO chains were investigated from three perspectives: surface activity, adsorption morphology, and molecular bonding forces. The results indicated that the chain length ratio and position of PO and EO significantly influenced the performance of cardanol nonionic surfactants at the air/water interface. The PO chains can significantly mitigate the solvation effect at the terminus of surfactants, thereby enhancing their aggregation at the air/water interface. Additionally, the ratio of PO to EO chains influences both the radius of gyration and tilt angle of hydrophilic and hydrophobic segments within surfactant molecules. Notably, when both PO and EO chain lengths are set to 8, optimal adsorption of surfactant molecules occurs at the interface. This phenomenon is primarily attributed to hydrogen bonding interactions that lead water molecules to exhibit varying degrees of aggregation around PO or EO chains; these effects, in conjunction with adsorption morphology, ultimately influence the interfacial properties of surfactants. This study provides a theoretical foundation and reference for the structural design, synthesis, and interfacial properties of cardanol surfactants.

METHOD

In this study, Packmol was employed for model construction, Gromacs for molecular dynamics simulations, and all simulations were conducted using the GAFF force field. The simulation process primarily involved the steepest descent method, followed by NPT ensemble simulations for 1 ns and 10 ns, respectively. The Berendsen and Parrinello-Rahman methods are employed to maintain system pressure. The LINCS algorithm and Lennard-Jones potential are utilized to effectively constrain molecular bond lengths and cutoff radius. The long-range electrostatic interactions are treated using the Particle-Mesh Ewald (PME) summation method.

Wetting Characteristics and Microscopic Synergistic Mechanism of Composite Surfactants on Coal Samples with Different Degrees of Metamorphosis

This study investigates the effects of composite surfactants on the wettability of different coal types using a combination of macroscopic experiments, mesoscopic experiments, and microscopic molecular dynamics simulations, with coal samples of varying degrees of metamorphism as research subjects. First, contact angle and surface tension experiments were performed at the macroscopic level to determine the optimal concentration and ratio of the composite surfactants. The results showed that the composite solution formed by mixing SLES and AEO-9 in a 3:2 ratio significantly reduced both the surface tension of the solution and the contact angle of the coal samples at a mass concentration of 0.5 wt %. Second, the effects of the composite surfactants on the wetting properties of coal samples were analyzed at the mesoscopic level using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and ζ-potential measurements. The results revealed that the total content of hydrophobic groups (-CH3, -CH3&-CH2, C=C) in the coal molecules was significantly reduced after treatment with the composite solution, weakening the hydrophobicity of the coal samples. Additionally, the absolute value of the surface potential of the coal samples was significantly decreased, enhancing the aggregation tendency between coal particles. This facilitated the formation of larger agglomerated coal particles, which contributed to the settling of coal dust. Simultaneously, the cracks between coal particles promoted the penetration of aqueous solutions, aiding in the wetting of the coal seam. Finally, molecular dynamics simulations were conducted to analyze the synergistic wetting mechanism of the composite surfactants at the microscopic level. The results showed that the composite surfactant molecules were effectively adsorbed onto the surface of coal molecules, facilitating the movement of water molecules to the coal surface, increasing the diffusion coefficient of water molecules, and enhancing the interaction energy within the coal/composite surfactant/water system. These findings provide valuable insights for the development of new composite surfactants with wetting effects, offering significant potential for applications in mine dust control.

Recent advances in CO2 capture and mineralization using layered double hydroxide-based materials: A review

The continuous release of substantial amounts of carbon dioxide (CO2) to the atmosphere has resulted in numerous severe adverse effects. Several materials have been synthesized and utilized for CO2 capture. One class of such materials is layered double hydroxides (LDHs), which have emerged as promising materials for CO2 capture due to their tunable properties, high surface area, and excellent CO2 adsorption capabilities. Although there are some review articles on CO2 capture and conversion using various materials, there is still a notable lack of thorough reviews focusing on the utilization of LDH-based materials for CO2 capture. Additionally, the field of CO2 capture and mineralization using LDH-based materials is rapidly evolving, necessitating up-to-date comprehensive reviews to analyze, evaluate, and condense the dispersed information found in recently published research articles. Accordingly, this review article provides a comprehensive overview of recent advancements in CO2 capture using LDH-based materials. After briefly introducing the topic, different synthesis protocols of LDH-based materials are briefly reviewed. Then, CO2 capture using LDHs, calcined LDHs, impregnated LDHs, composites containing LDHs, amine functionalized LDHs, and during steam methane reforming, are thoroughly analyzed and discussed. Additionally, the effects of synthesis method and post treatment of LDH-based materials on CO2 capture, effect of modification and functionalization on LDHs, and the effects of various process conditions including temperature, pressure, water vapor, and gas composition on the performance of CO2 capture by LDH-based materials are reviewed. Limitations, challenges, obstacles, and remaining knowledge gaps are highlighted, and future research works to address them are proposed.

Molecular Dynamics Simulations of the Short-Chain Fluorocarbon Surfactant PFHXA and the Anionic Surfactant SDS at the Air/Water Interface

The research and development of alternatives to long-chain fluorocarbon surfactants are desperately needed because they are extremely toxic, difficult to break down, seriously harm the environment, and limit the use of conventional aqueous film-forming foam fire extinguishing agents. In this study, mixed surfactant systems containing the short-chain fluorocarbon surfactant perfluorohexanoic acid (PFHXA) and the hydrocarbon surfactant sodium dodecyl sulfate (SDS) were investigated by molecular dynamics simulation to investigate the microscopic properties at the air/water interface at different molar ratios. Some representative parameters, such as surface tension, degree of order, density distribution, radial distribution function, number of hydrogen bonds, and solvent-accessible surface area, were calculated. Molecular dynamics simulations show that compared with a single type of surfactant, mixtures of surfactants provide superior performance in improving the interfacial properties of the gas-liquid interface. A dense monolayer film is formed by the strong synergistic impact of the two surfactants. Compared to the pure SDS system, the addition of PFHXA caused SDS to be more vertically oriented at the air/water interface with a reduced tilt angle, and a more ordered structure of the mixed surfactants was observed. Hydrogen bonding between SDS headgroups and water molecules is enhanced with the increasing PFHXA. The surface activity is arranged in the following order: PFHXA/SDS = 1:1 > PFHXA/SDS = 3:1 > PFHXA/SDS = 1:3. These results indicate that a degree of synergistic relationship exists between PFHXA and SDS at the air/water interface.

Mechanism of Low Chemical Agent Adsorption by High Pressure for Hydraulic Fracturing-Assisted Oil Displacement Technology: A Study of Molecular Dynamics Combined with Laboratory Experiments

This study investigates the influence of physical parameters such as porosity, permeability, pore-throat radius, and specific surface area/volume on the adsorption capacity of surfactants in the pore surface of reservoirs. In the meantime, the hydraulic fracturing-assisted oil displacement (HFAD) technique can effectively improve the permeability and porosity of pores in the reservoir, which may affect the adsorption capacity of surfactants in low-permeability reservoirs. This may help to reduce the adsorption loss of surfactants in low-permeability reservoirs. Based on physical simulation methods, dynamic adsorption experiments were conducted to clarify the dynamic saturation adsorption capacity effect of high-pressure and low-pressure displacement agents by the HFAD technique. In addition, the molecular dynamics simulation method was used to study the effect of high-pressure conditions of HFAD on the adsorption capacity of surfactants on weakly lipophilic silica walls. Under the condition of high injection pressure by the HFAD technique, the fluid flow velocity and the initial kinetic energy of molecules increase, while the absolute value of the electrostatic potential energy in the system decreases. In addition, the van der Waals potential energy increases. In other words, the smaller the gravitational attraction experienced by the surfactant molecules during adsorption, the greater the repulsive force. Under the dual action of electrostatic force and van der Waals forces, the absolute values of the adsorption energy and the free energy decrease. The adsorption capacity of the surfactant molecules is weakened. Moreover, the decrease in adsorption capacity has little effect on the improvement of wettability, indicating that the adsorption of the surfactant reduced by HFAD technology is mostly ineffective adsorption.

Study of the Micromechanism of the Effect of Fatty Alcohol Poly(oxyethylene) Ether-9 on the Wettability of Jincheng Anthracite

The influence mechanism of the adsorption of fatty alcohol poly(oxyethylene) ether (AEO₉) on the wettability of anthracite coal was studied by means of experiments and simulations. First, the contact angle and surface tension were measured. When the AEO₉ concentration was 0.5 wt %, the contact angle and surface tension were the smallest, which were 10.28° and 25.39 mN m^-1, respectively. X-ray photoelectron spectroscopy (XPS) indicated that the content of C-O functional groups on the anthracite surface increased by 20.76% after adsorption of AEO₉. The molecular orbital energy and electrostatic potential of AEO₉ and anthracite were calculated by density functional theory (DFT). There are two modes of electron transfer between the two orbitals: highest occupied molecular orbital (HOMO) transfer of AEO₉ to lowest unoccupied molecular orbital (LUMO) transfer of anthracite and HOMO transfer of anthracite to LUMO transfer of AEO₉. The dynamics simulation results show that the addition of AEO₉ increases the migration rate of water molecules, promotes the movement of a large number of water molecules toward the surface of anthracite, and enhances the thickness of the water molecular layer on the surface of anthracite. The analysis of the relative concentration shows that AEO₉ is distributed at the anthracite/water interface. AEO₉ molecules are intertwined and connected by hydrophobic chains to form a network structure, which covers the anthracite surface horizontally, thus promoting the strength of the anthracite/water interaction.