Coarse grained force field for the molecular simulation of natural gases and condensates

AbstractThe atomistically-detailed molecular modelling of petroleum fluids is challenging, amongst other aspects, due to the very diverse multicomponent and asymmetric nature of the mixtures in question. Complicating matters further, the time scales for many important processes can be much larger than the current and foreseeable capacity of modern computers running fully-atomistic models. To overcome these limitations, a coarse grained (CG) model is proposed where some of the less-important degrees of freedom are safely integrated out, leaving as key parameters the average energy levels, the molecular conformations and the range of the Mie intermolecular potentials employed as the basis of the model. The parametrization is performed by using an analytical equation of state of the statistical associating fluid theory (SAFT) family to link the potential parameters to macroscopically observed thermophysical properties. The parameters found through this top-down approach are used directly in molecular dynamics simulations of multi-component multi-phase systems. The procedure is exemplified by calculating the phase envelope of the methane–decane binary and of two synthetic light condensate mixtures. A methodology based on the discrete expansion of a mixture is used to determine the bubble points of these latter mixtures, with an excellent agreement to experimental data. The model presented is entirely predictive and an abridged table of parameters for some fluids of interest is provided

Towards sustainable micro-pollutants’ removal from wastewaters: caffeine solubility, self-diffusion and adsorption studies from aqueous solutions into hydrochars

Hydrochars obtained via hydrothermal carbonisation of pistachio shells are both a sustainable and an efficient alternative to commercial activated carbons for the removal of micro-pollutants from wastewaters that are difficult to handle by conventional treatments. Here a combined experimental and molecular simulation approach is adopted for the study of the caffeine/hydrochars aqueous systems. This case study serves to tune a general framework for the rational customisation of surface functional groups on hydrochars for the selective adsorption of micro-pollutants from wastewaters. Caffeine’s solubility, self-diffusion and adsorption results from aqueous solutions at relevant conditions are presented. Insights about the role of surface functional groups over the caffeine adsorption mechanism into hydrochars are gained and discussed

Predicting the adsorption of n-perfluorohexane in BAM P109 standard activated carbon by molecular simulation using SAFT-gamma Mie coarse-grained force fields

This work is framed within the Eighth Industrial Fluid Properties Simulation Challenge, with the aim of assessing the capability of molecular simulation methods and force fields to accurately predict adsorption in porous media for systems of relevant practical interest. The current challenge focuses on predicting adsorption isotherms of n -perfluorohexane in the certified reference material BAM-P109 standard activated carbon. A temperature of T = 273  K and pressures of p / p 0 = 0 . 1 , 0.3, and 0.6 relative to the bulk saturation pressure p 0 (as predicted by the model) are the conditions selected in this challenge. In our methodology we use coarse-grained intermolecular models and a top-down technique where an accurate equation of state is used to link the experimental macroscopic properties of a fluid to the force-field parameters. The state-of-the-art version of the statistical associating fluid theory (SAFT) for potentials of variable range as reformulated in the Mie group contribution incarnation (SAFT- γ Mie) is employed here. The parameters of the SAFT- γ Mie force field are estimated directly from the vapour pressure and saturated liquid density data of the pure fluids using the equation of state, and further validated by molecular dynamic simulations. The coarse-grained intermolecular potential models are then used to obtain the adsorption isotherm kernels for argon, carbon dioxide, and n -perfluorohexane in graphite slit pores of various widths using Grand Canonical Monte Carlo simulations. A unique and fluid-independent pore size distribution curve with total micropore volume of 0.5802 cm 3 /g is proposed for the BAM-P109. The pore size distribution is obtained by applying a non-linear regression procedure over the adsorption integral equation to minimise the quadratic error between the available experimental adsorption isotherms for argon and carbon dioxide and purpose-built Grand Canonical Monte Carlo kernels. The predicted adsorption levels of n -perfluorohexane at 273 K in BAM-P109 are 72.75 ± 0.01, 73.82 ± 0.01, and 75.44 ± 0.05 cm 3 /g at Standard Temperature and Pressure (STP) conditions for p / p 0 = 0 . 1 , 0.3, and 0.6, respectively

Unusual flexibility of mesophase pitch-derived carbon materials:an approach to the synthesis of graphene

Structural flexibility in a petroleum pitch-derived carbon material has been indirectly evaluated using X-ray diffraction (XRD), immersion calorimetry and inelastic neutron scattering (INS) measurements. Exposure of the carbon material to an organic solvent (e.g., n-nonane) gives rise to a large internal rearrangement, associated with a drastic re-ordering of the graphitic microdomains. These structural changes are also associated with a high flexibility of the internal porous network, as observed by inelastic neutron scattering measurements. The internal rearrangement and the structural flexibility could be responsible for the excellent performance of this kind of activated carbons in a wide variety of adsorption processes. Last but not least, the structural characteristics of these carbon materials composed of graphitic microdomains has been used to synthesize graphene “egg-like” flakes following a simple procedure based on exfoliation with organic solvents

Approaches to the Rational Design of Molecularly Imprinted Polymers Developed for the Selective Extraction or Detection of Antibiotics in Environmental and Food Samples

The World Health Organisation (WHO) reported antimicrobial resistance (AMR) as a global threat comparable to terrorism and climate change. The use of antibiotics in veterinary or clinical practice exerts a selective pressure, which accelerates the emergence of antimicrobial resistance. Therefore, there is a clear need to detect antibiotic residues in complex matrices, such as water, food, and environmental samples, in a fast, selective, cost-effective, and quantitative manner. Once problematic areas are identified, can extraction of the antibiotics then be carried out to reduce AMR development. Molecularly imprinted polymer (MIPs) are synthetic recognition elements produced through the biomarker of interest being used as a template in order to manufacture tailor-made ligand selective polymeric recognition sites. They are emerging steadily as a viable alternative to antibiotics, especially given their low-cost, superior thermal and chemical stability that facilitates on-site detection, simplified manufacturing process, and avoiding the use of animals in the production process. In this paper, the authors critically review literature from primarily 2010–2020 on rational design approaches used to develop MIPs for sensing and extraction of antibiotics, providing an outlook on crucial issues that need to be tackled to bring MIPs for antibiotic sensing to the market

Unusual flexibility of mesophase pitch-derived carbon materials:an approach to the synthesis of graphene

Structural flexibility in a petroleum pitch-derived carbon material has been indirectly evaluated using X-ray diffraction (XRD), immersion calorimetry and inelastic neutron scattering (INS) measurements. Exposure of the carbon material to an organic solvent (e.g., n-nonane) gives rise to a large internal rearrangement, associated with a drastic re-ordering of the graphitic microdomains. These structural changes are also associated with a high flexibility of the internal porous network, as observed by inelastic neutron scattering measurements. The internal rearrangement and the structural flexibility could be responsible for the excellent performance of this kind of activated carbons in a wide variety of adsorption processes. Last but not least, the structural characteristics of these carbon materials composed of graphitic microdomains has been used to synthesize graphene “egg-like” flakes following a simple procedure based on exfoliation with organic solvents

Superspreading: Mechanisms and Molecular Design

The intriguing ability of certain surfactant molecules to drive the superspreading of liquids to complete wetting on hydrophobic substrates is central to numerous applications that range from coating flow technology to enhanced oil recovery. Despite significant experimental efforts, the precise mechanisms underlying superspreading remain unknown to date. Here, we isolate these mechanisms by analyzing coarse-grained molecular dynamics simulations of surfactant molecules of varying molecular architecture and substrate affinity. We observe that for superspreading to occur, two key conditions must be simultaneously satisfied: the adsorption of surfactants from the liquid–vapor surface onto the three-phase contact line augmented by local bilayer formation. Crucially, this must be coordinated with the rapid replenishment of liquid–vapor and solid–liquid interfaces with surfactants from the interior of the droplet. This article also highlights and explores the differences between superspreading and conventional surfactants, paving the way for the design of molecular architectures tailored specifically for applications that rely on the control of wetting

Towards sustainable micro-pollutants’ removal from wastewaters: caffeine solubility, self-diffusion and adsorption studies from aqueous solutions into hydrochars

Hydrochars obtained via hydrothermal carbonisation of pistachio shells are both a sustainable and an efficient alternative to commercial activated carbons for the removal of micro-pollutants from wastewaters that are difficult to handle by conventional treatments. Here a combined experimental and molecular simulation approach is adopted for the study of the caffeine/hydrochars aqueous systems. This case study serves to tune a general framework for the rational customisation of surface functional groups on hydrochars for the selective adsorption of micro-pollutants from wastewaters. Caffeine’s solubility, self-diffusion and adsorption results from aqueous solutions at relevant conditions are presented. Insights about the role of surface functional groups over the caffeine adsorption mechanism into hydrochars are gained and discussed

Prediction of the water/oil interfacial tension from molecular simulations using the coarse-grained SAFT-γ Mie force field

This work reports the award-winning entry for the Ninth Industrial Fluid Properties Simulation Challenge. This worldwide competition was set with the aim of assessing the capability of molecular simulation methods and force fields to accurately predict the interfacial tension of oil + water mixtures at high temperatures and pressures. The challenge focused on predicting the liquid-liquid interfacial tension of binary mixtures of dodecane + water, toluene + water and a 50:50 (wt%) mixture of dodecane:toluene + water at 1.825 MPa (250 psig) and temperatures from 110 to 170 °C. In our entry for the challenge, we employed coarse-grained intermolecular models parametrized via a top-down technique in which an accurate equation of state is used to link experimentally observed macroscopic properties of fluids with the force-field parameters. The state-of-the-art version of the statistical associating fluid theory (SAFT) for potentials of variable range as reformulated in terms of the Mie potential is employed here. Interfacial tensions are calculated through a direct method, where an elongated simulation cell is sampled through molecular dynamics in the isobaric-isothermal constant area ensemble (NPzzAT). The coarse-grained nature of the force field allows for the accelerated calculation of relatively large systems. The binary interaction parameters that describe the cross-interactions have been obtained in previous works by fitting to interfacial tensions of the constituent binaries at lower pressures and temperatures; these are taken as constant for all conditions and mixtures studied. After disclosure of the challenge results, we observe that the interfacial properties of the mixtures are described with an error of less than 5 mN/m over the whole range of conditions, demonstrating the accuracy and transferability of the top-down SAFT-γ Mie force field approach