Molecular Modeling and Adsorption Characterization of Micro-Mesoporous Kerogen Nanostructures
Molecular Modeling and Adsorption Characterization of Micro-Mesoporous Kerogen Nanostructures
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DOI：
10.1021/acs.energyfuels.2c02876
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发表时间：
2022-10
期刊：
影响因子：
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通讯作者：
Shivam Parashar;P. Ravikovitch;A. Neimark
中科院分区：
文献类型：
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作者：
Shivam Parashar;P. Ravikovitch;A. Neimark
这项工作的目的是加强对应用于富含有机质的页岩和泥岩的干酪根的孔结构和吸附特性的了解。根据低温氮气等温线进行吸附表征的传统方法依赖于在非多孔基质(通常是二氧化硅或无定形碳)上使用所谓的标准等温线，这对于干酪根的表面可能不准确。在这项工作中，我们提出了一种新的方法来表征干酪根的孔隙大小，该方法依赖于干酪根表面的真实分子模型。利用最近在模拟干酪根分子结构方面的进展，我们创建了无定形整体干酪根、粗糙的干酪根表面和嵌入无定形干酪根基质中的中孔的原子三维(3D)模型。利用巨正则蒙特卡罗(GCMC)模拟方法，计算了干酪根基质微孔内、干酪根表面以及由粗糙干酪根壁围成的一系列中孔中N2的吸附等温线。接下来，我们用淬火固体密度泛函理论(QSDFT)对干酪根表面的非均质性和GCMC模拟的N2吸附等温线进行了参数化模拟。此外，我们还用宏观分离压力等温线来逼近参考干酪根表面的等温线，这使得我们可以使用Derjaguin-Broekhoff-de Boer(DBDB)模型来预测中/大孔隙中的吸附和毛细凝聚。将参考的GCMC、QSDFT和DBDB等温线组合到核中，从实验的吸附等温线计算微孔体积、中孔和大孔表面以及中孔尺寸分布。该方法在一个典型的干酪根II-A样品上进行了验证，该样品具有较宽的中孔尺寸分布。该方法可以推广到其他不同成熟度的干酪根结构，以提供干酪根馏分中有机孔隙度的综合表征。
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 N2isotherms 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 N2adsorption 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 N2adsorption 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.