Multi‐Scale Models for the Prediction of Microscopic Structure and Physical Properties of Chemical Systems Related to Natural Gas Technology

Papavasileiou, Konstantinos D.; Vasileiadis, Manolis; Michalis, Vasileios K.; Peristeras, Loukas D.; Economou, Ioannis G.

doi:10.1002/9781119269618.ch18

Cited by 3 publications

(7 citation statements)

References 173 publications

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“…These techniques cover a wide spectrum of these steps, both in size and time scales. 33 Among them, MD simulation is a reliable tool, because of its ability to access scales and buried interfaces that are experimentally challenging to characterize, 34 especially under reaction conditions. In our previous atomistic (AA) MD simulation study, we showed that inside TiO 2 and SiC mesopores and under reaction conditions the wax (we used n-octacosane (n-C 28 ) as a representative paraffin) and water at high mole fractions (i.e., x H 2 O = 0.9655) segregate into two phases.…”

Section: Introductionmentioning

confidence: 99%

“…44,45 unfortunately, however, the lack of force fields has not yet permitted the capture of all the essential process components, particularly the metal-based catalysts and supports. 33 In the present work, we aimed to explore by means of molecular modeling the phase behavior of the n-C 28 −H 2 O mixture at 473.15 K and 3.4 MPa, conditions typically encountered in low-temperature FTS, 11 inside G and GO catalyst support mesopores using the MARTINI model, one of the most widely used and established force fields for performing CG simulations. 45 In sections 2.1 and 2.2, a detailed description of the simulation details and protocols followed are presented.…”

Section: Introductionmentioning

confidence: 99%

“…Molecular modeling techniques can be used to obtain the microscopic information that aids in understanding the fundamental mechanisms controlling individual steps of the FTS process, which may otherwise be unattainable by current experimental methods. These techniques cover a wide spectrum of these steps, both in size and time scales . Among them, MD simulation is a reliable tool, because of its ability to access scales and buried interfaces that are experimentally challenging to characterize, especially under reaction conditions.…”

Section: Introductionmentioning

confidence: 99%

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Molecular Dynamics Simulation of the n-Octacosane–Water Mixture Confined in Graphene Mesopores: Comparison of Atomistic and Coarse-Grained Calculations and the Effect of Catalyst Nanoparticle

et al. 2021

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Fischer−Tropsch synthesis (FTS) is used extensively in the gas-to-liquids (GTL) process to produce clean, highquality low emission transportation fuels from synthesis gas. In order to gain a better understanding of the phase behavior of the produced wax−water mixtures at reaction conditions by accounting for confinement effects of either hydrophilic or hydrophobic characteristics and catalyst nanoparticles (NPs), one needs to closely examine the validity of incorporating coarse grained approaches in the context of FTS. The present study focuses on simulating by means of atomistic (AA) and coarse-grained (CG) molecular dynamics (MD; CGMD) simulations the n-octacosane (n-C 28 )−water mixture inside graphene (G) and graphene oxide (GO) mesopores under low-temperature FTS conditions (473.15 K) with the inclusion of a Co NP. Graphene derivatives were selected as they are emerging catalyst support materials in the FTS reaction and allow for direct comparisons between the AA and CG methodologies. We also evaluated the presence of long-chain alcohols such as dodecan-1-ol at 7 wt % on the n-C 28 −H 2 O mixture phase behavior. The AA simulations involved the use of the united atom TraPPE (TraPPE-UA) force field for n-C 28 and the alcohols and the TIP4P/2005 force field for water, while the MARTINI force field was used for the CG description. With regard to the mixtures inside the G pore, both AA and CG simulation methods capture the phase separation of the mixture, with water molecules occupying the center of the pore and n-C 28 forming layers at the pore walls; inside GO, both methodologies show that water separates near the surface and the model wax lies at the pore center. Both AA and CG simulations accurately capture the n-C 28 and H 2 O diffusivity as a function of the distance from the G and GO pore centers, respectively, being lower closer to the pore surface. Dodecan-1-ol is mostly located at the n-C 28 −H 2 O interface showing a higher preference toward the wax as a consequence of increased van der Waals intermolecular interactions, slightly reducing the mobility of water. The agreement between AA and CG MD simulations paved the way for novel CGMD simulations with DFT-derived parameters for Co, to study the n-C 28 −H 2 O behavior in its presence. Our results show that the Co NP does not affect phase separation of the n-C 28 −H 2 O mixture inside the pores; however, water at such high concentrations covers the Co NP surface extensively. Given the experimental difficulties in exploring the relevant mechanisms at this scale, our results showcase that CGMD using the MARTINI force field can be employed to study FTS-related processes at this level and are expected to open new pathways in the investigation of confined mixtures relevant to the FTS reaction in the presence of supported catalyst NPs.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Molecular Dynamics Simulation of the n-Octacosane–Water Mixture Confined in Graphene Mesopores: Comparison of Atomistic and Coarse-Grained Calculations and the Effect of Catalyst Nanoparticle

et al. 2021

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“…Molecular simulation has proven highly valuable towards this direction for the oil and gas industry. [17][18][19] With the boost of SG production in the USA, there is a rapidly growing interest in modelling several complex chemical systems, such as clays and kerogen. The majority of work related to clays focuses on different types of fluids in slit type mineral micro and meso pores.…”

Section: Introductionmentioning

confidence: 99%

“…Although this broad variety of experimental techniques enables the identification of the most promising shale fields for commercial exploitation and allows the design of the production processes, it does not provide insight into the underlying molecular and macroscopic phenomena crucial for production that are related to length and time scales inaccessible to experiment. Molecular simulation has proven highly valuable toward this direction for the oil and gas industry. − With the boost of SG production in the United States, there is a rapidly growing interest in modeling several complex chemical systems, such as clays and kerogen. The majority of work related to clays focuses on the behavior of different types of fluids in slit-type mineral micro- and mesopores. − On the other hand, the research effort on kerogens focuses in the creation of realistic models, where the adsorption of fluids of interest to SG technology and their transportation properties can be studied.…”

Section: Introductionmentioning

confidence: 99%

Transport Properties of Shale Gas in Relation to Kerogen Porosity

et al. 2018

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Kerogen is a micro-porous amorphous solid, which consist the major component of the organic matter scattered in the potentially lucrative shale formations hosting shale gas. Deeper understanding of the way kerogen porosity characteristics affect the transport properties of hosted gas is important for the optimal design of the extraction process. In this work, we employ molecular simulation techniques in order to investigate the role of porosity on the adsorption and transport behavior of shale gas in overmature type II kerogen found at many currently productive shales. To account for the wide range of porosity characteristics present in the real system, a large set of 60 kerogen structures that exhibit a diverse set of void space attributes was used. Grand Canonical Monte Carlo (GCMC) simulations were performed for the study of the adsorption of CH4, C2H6, n-C4H10 and CO2 at 298.15 K and 398.15 K and a variety of 2 pressures. The amount adsorbed is found to correlate linearly with the porosity of the kerogen. Furthermore, the adsorption of a quaternary mixture of CH4, C2H6, CO2 and N2 was investigated in the same conditions, indicating that the composition resembling that of the shale gas is achieved under higher temperature and pressure values, i.e. conditions closer to these prevailing in the hosting shale field. The diffusion of CH4, C2H6 and CO2, both as pure components and as components of the quaternary mixture, was investigated using equilibrium Molecular Dynamics (MD) simulations at temperatures of 298.15 and 398.15 K and pressures of 1 and 250 atm. In addition to the effect of temperature and pressure, the importance of limiting pore diameter (LPD), maximum pore diameter (MPD), accessible volume (Vacc) and accessible surface (Sacc) on the observed adsorbed amount and diffusion coefficient was revealed by qualitative relationships. The diffusion across the models was found to be anisotropic and the maximum component of the diffusion coefficient to correlate linearly with LPD, indicating that the controlling step of the transport process is the crossing of the limiting pore region. Finally, the transport behavior of the pure compounds was compared with their transport properties when in mixture and it was found that the diffusion coefficient of each compound in the mixture is similar to the corresponding one in pure. This observation agrees with earlier studies in different kerogen models comprising wider pores that have revealed negligible cross-correlation Onsager coefficients.

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Coarse-Grained Molecular Dynamics Simulation of Cobalt Nanoparticle in the n-Octacosane–Water Mixture: The Effect of Water Concentration and Nanoparticle Size

et al. 2022

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The Fischer–Tropsch synthesis (FTS) is central in the Gas-to-Liquids (GTL) process, which is commercially used in the production of environmentally benign transportation fuels from synthesis gas. However, several factors can impede the performance of FTS reactors and thereby increase the overall GTL cost, among which is water in excess concentrations. Water is a byproduct of the FTS process and is present in varying amounts. In order to gain a better understanding of the behavior of catalyst nanoparticles (NPs) inside the produced wax–water mixtures at reaction conditions and realistic scales and sizes, one needs to incorporate coarse-grained approaches in the context of FTS. The present study focuses on coarse-grained (CG) Molecular Dynamics (MD; CGMD) simulations of n-octacosane (n-C28)–water mixture at low-temperature FTS conditions (473.15 K) and considers various water mole fractions with the inclusion of different-sized Co NPs using the MARTINI force field. The Co NPs are suspended inside these bulk mixtures thereby resembling a slurry phase type of reactor. Water mole fractions below and above the solubility of water in n-C28 as predicted by MARTINI were used so as to better capture the phase behavior of the produced wax–water mixtures. Our results show that, for the NP sizes examined, water in small concentrations does not aggregate on the Co NP surface. For water concentrations above the calculated solubility in n-C28, water forms a cluster that fully encapsulates the NP, and for excess water, the NPs are completely immersed in the aqueous phase. This behavior bears implications in the mobility of the NPs examined, which appears to increase as a function of water concentration. Calculations of Co NPs self-diffusion coefficient show that the smaller nanoparticle moves faster, and that mobility drops as nanoparticle size increases. For high water mole fractions, that is, well-exceeding water solubility in bulk n-C28, an increasing effect in the mobility of the examined Co NPs was observed. The computational approach using the MARTINI force field and the results presented showcase that CGMD simulations can be employed to study the hydrodynamic effects on the NP mobility in FTS-related processes.

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Multi‐Scale Models for the Prediction of Microscopic Structure and Physical Properties of Chemical Systems Related to Natural Gas Technology

Cited by 3 publications

References 173 publications

Molecular Dynamics Simulation of the n-Octacosane–Water Mixture Confined in Graphene Mesopores: Comparison of Atomistic and Coarse-Grained Calculations and the Effect of Catalyst Nanoparticle

Molecular Dynamics Simulation of the n-Octacosane–Water Mixture Confined in Graphene Mesopores: Comparison of Atomistic and Coarse-Grained Calculations and the Effect of Catalyst Nanoparticle

Transport Properties of Shale Gas in Relation to Kerogen Porosity

Coarse-Grained Molecular Dynamics Simulation of Cobalt Nanoparticle in the n-Octacosane–Water Mixture: The Effect of Water Concentration and Nanoparticle Size

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