Title: Molecular Modeling and Adsorption Characterization of Micro-Mesoporous Kerogen Nanostructures
The aim of this work is to enhance the understanding of the pore structure and adsorption properties of kerogens as applied to organic-rich shales and mudstone rocks. Conventional methods of adsorption characterization from low temperature N2 isotherms rely on the use of the so-called standard isotherms on nonporous substrates (typically silica or amorphous carbons), which may not be accurate for the surfaces of kerogens. In this work, we present a new methodology for pore size characterization of kerogens that relies on a realistic molecular model of kerogen surfaces. Taking advantage of recent advances in modeling the molecular structure of kerogens, we create atomistic three-dimensional (3D) models of amorphous bulk kerogens, rough kerogen surfaces, and mesopores imbedded in the amorphous kerogen matrix. Using grand canonical Monte Carlo (GCMC) simulations, we calculate the reference N2 adsorption isotherms in the micropores of the bulk kerogen matrix, on the kerogen surface, as well as in a series of mesopores confined by rough kerogen walls. Next, we parameterized the quenched solid density functional theory (QSDFT) to reproduce the kerogen surface heterogeneity and GCMC-simulated N2 adsorption isotherms. Furthermore, we approximated the isotherm on the reference kerogen surface by a macroscopic disjoining pressure isotherm, which allows us to use the Derjaguin−Broekhoff−de Boer (DBdB) model to predict adsorption and capillary condensation in meso/macropores. The reference GCMC, QSDFT, and DBdB isotherms are combined into the kernel for calculating the micropore volume, meso- and macropore surfaces, and mesopore size distribution from the experimental adsorption isotherms. The proposed methodology is demonstrated on a typical example of a kerogen II-A sample with a wide mesopore size distribution. The methodology can be extended to other kerogen structures of different maturities to provide a comprehensive characterization of organic porosity in kerogen fractions. more »« less
Dantas, Silvio; Cychosz, Katie; Thommes, Matthias; Neimark, Alexander V.
(, Carbon)
null
(Ed.)
An original methodology is suggested for evaluating the pore size distribution in carbons in the wide range of micro- and mesopores from 0.385 to 10 nm from a single isotherm of high-pressure adsorption of CO2 at 273 K. The proposed method is based on the reference theoretical isotherms calculated by Monte Carlo simulations in model pores of slit and cylindrical geometry. The relationship between the pore size and the pore filling pressure is established. Special attention is given to predicting of the capillary condensation transitions in mesopores by using the meso-canonical ensemble (gauge cell) Monte Carlo simulations. The proposed technique is demonstrated and verified against the conventional N2 and Ar low temperature adsorption methods drawing on the example of micro-mesoporous carbons of the CMK family. Advantages and limitations of CO2 adsorption characterization of nanoporous materials are discussed and further improvements are proposed.
Gomaa, Ibrahim; Guerrero, Javier; Heidari, Zoya; Espinoza, D. Nicolas
(, 2022 SPE Annual Technical Conference and Exhibition)
Abstract Geological storage of carbon dioxide (CO2) in depleted gas reservoirs represents a cost-effective solution to mitigate global carbon emissions. The surface chemistry of the reservoir rock, pressure, temperature, and moisture content are critical factors that determine the CO2 adsorption capacity and storage mechanisms. Shale-gas reservoirs are good candidates for this application. However, the interactions of CO2 and organic content still need further investigation. The objectives of this paper are to (i) experimentally investigate the effect of pressure and temperature on the CO2 adsorption capacity of activated carbon, (ii) quantify the nanoscale interfacial interactions between CO2 and the activated carbon surface using Monte Carlo molecular modeling, and (iii) quantify the correlation between the adsorption isotherms of activated carbon-CO2 system and the actual carbon dioxide adsorption on shale-gas rock at different temperatures and geochemical conditions. Activated carbon is used as a proxy for kerogen. The objectives aim at obtaining a better understanding of the behavior of CO2 injection and storage into shale-gas formations. We performed experimental measurements and Grand Canonical Monte Carlo (GCMC) simulations of CO2 adsorption onto activated carbon. The experimental work involved measurements of the high-pressure adsorption capacity of activated carbon using pure CO2 gas. Subsequently, we performed a series of GCMC simulations to calculate CO2 adsorption capacity on activated carbon to validate the experimental results. The simulated activated carbon structure consists of graphite sheets with a distance between the sheets equal to the average actual pore size of the activated carbon sample. Adsorption isotherms were calculated and modeled for each temperature value at various pressures. The adsorption of CO2 on activated carbon is favorable from the energy and kinetic point of view. This is due to the presence of a wide micro to meso pore sizes that can accommodate a large amount of CO2 particles. The results of the experimental work show that excess adsorption results for gas mixtures lie in between the results for pure components. The simulation results agree with the experimental measurements. The strength of CO2 adsorption depends on both surface chemistry and pore size of activated carbon. Once strong adsorption sites within nanoscale network are established, gas adsorption even at very low pressure is governed by pore width rather than chemical composition. The outcomes of this paper provides new insights about the parameters affecting CO2 adsorption and storage in shale-gas reservoirs, which is critical for developing standalone representative models for CO2 adsorption on pure organic carbon.
Yanagimachi, Akimaro; Kono, Takayuki; Ota, Kota; Torita, Takeshi; Bonilla, Daja R; Autrey, Daniel E; Badr, Hussein O; Barsoum, Michel W
(, Langmuir)
The novel material, one-dimensional lepidocrocite (1DL) titanate, is attracting industrial and scientific interest because of its applicability to a wide range of practical applications and its ease of synthesis and scale up of production. In this study, we investigated the CO2 adsorption capability and pore structures of 1DL freeze-dried and lithium chloride washed air-dried powders. The synthesized 1DL was characterized by X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. Using the constant-volume method, CO2 gas adsorption revealed that the 1DL exhibits type IV adsorption–desorption isotherms. The heats of adsorption obtained from the adsorption branches are lower than those obtained from the desorption branches. Brunauer–Emmett–Teller (BET) analysis, using N2 gas adsorption isotherms at 77 K showed that 1DL possesses 80.2 m2/g of BET specific surface area. Nonlocal density functional theory analysis indicated that two types of pores, meso-pores and ultramicro pores, exist in the 1DL freeze-dried powders. This work provides deep insights into the pore structures and CO2 adsorption mechanisms of 1DL powders.
Zhai, Chunhao; Koh, Yung P.; Vogt, Bryan D.; Simon, Sindee L.
(, Journal of Polymer Science)
Abstract The effect of nanoconfinement on the kinetics of benzyl methacrylate radical polymerization is investigated using differential scanning calorimetry. Controlled pore glass (CPG), ordered mesoporous carbons, and mesoporous silica are used as confinement media with pore sizes from 2 to 8 nm. The initial polymerization rate in CPG and mesoporous silica increases relative to the bulk and increases linearly with reciprocal pore size; whereas, the rate in the carbon mesopores decreases linearly with reciprocal pore size; the changes are consistent with the rate being related to the ratio of the pore surface area to pore volume. Induction times are longer for nanoconfined polymerizations, and in the case of CPG and carbon mesopores, autoacceleration occurs earlier, presumably due to the limited diffusivity and lower termination rates for the confined polymer chains. The molecular weight of the polymer synthesized in the nanopores is generally higher than that obtained in the bulk except at the lowest temperatures investigated. The equilibrium conversion under nanoconfinement decreases with decreasing temperature and with confinement size, exhibiting what appears to be a floor temperature at low temperatures.
Abstract Mechanisms of uptake in metal–organic materials are complex and are dependent on the chemistry of the pore space and material interface. In the current study, the importance of the material surface is evaluated on the water uptake of a metal–organic nanotube (UMONT) crystalline solid. This material has previously demonstrated selective water uptake and reported isotherms suggested a two‐step adsorption process that involved initial surface adsorption followed by pore filling. The proposed mechanism and importance of surface chemistry for water adsorption are tested by altering the surface of the UMONT with more hydrophobic surface coatings. Crystals of UMONT are coated with ammonium trifluoroacetate (ATFA), polyvinylidene fluoride (PVDF), and polyacrylonitrile (PAN), and the water adsorption behavior is analyzed through batch and flow‐through experiments. Uptake experiments reveal that ATFA significantly decreased the water uptake compared to observed in pristine UMONT while polymer coatings do not impact the adsorption behavior as significantly. In addition, ATFA disrupts the water selectivity of the UMONT material, allowing both ethanol and methanol to be detected in the system. These results indicate that changing the surface layer from a hydrophilic to hydrophobic with a chemisorbed monolayer will disturb the two‐step mechanism and the water uptake properties of the material.
Parashar, Shivam, Ravikovitch, Peter I., and Neimark, Alexander V. Molecular Modeling and Adsorption Characterization of Micro-Mesoporous Kerogen Nanostructures. Retrieved from https://par.nsf.gov/biblio/10481334. Energy & Fuels 36.21 Web. doi:10.1021/acs.energyfuels.2c02876.
Parashar, Shivam, Ravikovitch, Peter I., & Neimark, Alexander V. Molecular Modeling and Adsorption Characterization of Micro-Mesoporous Kerogen Nanostructures. Energy & Fuels, 36 (21). Retrieved from https://par.nsf.gov/biblio/10481334. https://doi.org/10.1021/acs.energyfuels.2c02876
@article{osti_10481334,
place = {Country unknown/Code not available},
title = {Molecular Modeling and Adsorption Characterization of Micro-Mesoporous Kerogen Nanostructures},
url = {https://par.nsf.gov/biblio/10481334},
DOI = {10.1021/acs.energyfuels.2c02876},
abstractNote = {The aim of this work is to enhance the understanding of the pore structure and adsorption properties of kerogens as applied to organic-rich shales and mudstone rocks. Conventional methods of adsorption characterization from low temperature N2 isotherms rely on the use of the so-called standard isotherms on nonporous substrates (typically silica or amorphous carbons), which may not be accurate for the surfaces of kerogens. In this work, we present a new methodology for pore size characterization of kerogens that relies on a realistic molecular model of kerogen surfaces. Taking advantage of recent advances in modeling the molecular structure of kerogens, we create atomistic three-dimensional (3D) models of amorphous bulk kerogens, rough kerogen surfaces, and mesopores imbedded in the amorphous kerogen matrix. Using grand canonical Monte Carlo (GCMC) simulations, we calculate the reference N2 adsorption isotherms in the micropores of the bulk kerogen matrix, on the kerogen surface, as well as in a series of mesopores confined by rough kerogen walls. Next, we parameterized the quenched solid density functional theory (QSDFT) to reproduce the kerogen surface heterogeneity and GCMC-simulated N2 adsorption isotherms. Furthermore, we approximated the isotherm on the reference kerogen surface by a macroscopic disjoining pressure isotherm, which allows us to use the Derjaguin−Broekhoff−de Boer (DBdB) model to predict adsorption and capillary condensation in meso/macropores. The reference GCMC, QSDFT, and DBdB isotherms are combined into the kernel for calculating the micropore volume, meso- and macropore surfaces, and mesopore size distribution from the experimental adsorption isotherms. The proposed methodology is demonstrated on a typical example of a kerogen II-A sample with a wide mesopore size distribution. The methodology can be extended to other kerogen structures of different maturities to provide a comprehensive characterization of organic porosity in kerogen fractions.},
journal = {Energy & Fuels},
volume = {36},
number = {21},
publisher = {ACS},
author = {Parashar, Shivam and Ravikovitch, Peter I. and Neimark, Alexander V.},
}
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