VGU RESEARCH REPOSITORY
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Title: | Molecular dynamics simulation study on separation of diamondsdoids in oils using nanoporous materials | Authors: | Nguyen Minh Trung | Keywords: | Molecular dynamics;Diamondoids;Nanoporous materials | Issue Date: | 2023 | Abstract: | Diamondoids are cage-like structures having from one to a few unit cells of the diamond structure and so-called nanodiamond-sized molecules. Hence, the diamondoids have rigidity and excellent thermal stability resembling the bulk diamond. Diamondoids have been found in traceable amounts in extractable organic matter (EOM) from source rocks and moderate maturity oils and high concentrations in condensates as well as highly matured crude oils due to their higher thermal stability than the non-diamondoids. Despite the abiogenic origin of the diamondoids, stable carbon isotope ratios (13C/12C) of diamondoids have been shown as a proxy tool to evaluate oil-oil and oil-source correlations, especially for highly matured oils and condensates in which biomarkers such as hopanes and steranes are mostly absent due to thermal degradation over geological time. Nevertheless, the measurement of stable carbon isotope ratios of diamondoids by gas chromatography isotope ratio mass spectrometer (GCIRMS) essentially requires the gas chromatographic separation of these compounds from oils and EOM. Furthermore, despite the diamond-like structure, diamondoids have distinct optoelectronic properties including negative electron affinity (NEA) for flat panel field-emission displays, and the tunability of the direct band gap energy in ultraviolet (UV) wavelength. These interesting optoelectronic properties result from the hydrogen-terminated surface and size of diamondoids. Despite the numerous methods developed to synthesize diamondoids, they are generally not efficient and the underlying mechanism to form diamondoids is not well understood. Therefore, the separation of diamondoids from petroleum is highly regarded. In our previous work, adamantane and its derivatives are successfully separated from oils by the heat-treated version of commercial β-zeolite. However, the underlying separation mechanism by adsorption has not been elucidated. As a result, in this thesis, the mechanism of the separation of the diamondoids from oil by adsorption at the nanoscale is investigated using molecular dynamics (MD) simulation. Accordingly, we have found that there is molecular sieving to exclude diamondoids by the virgin β-zeolite model, revealing the heat treatment of the β-zeolite leads to the lateral pore opening that enhances the adsorption of larger cyclic alkanes while still excluding diamondoids. This is in good agreement with the previous experimental observation. Furthermore, the adsorption dynamics studies of adamantane, benzene, and 2,2-dimethyl hexane in activated carbon ACF-15 and graphitic slit-like pore models show that there is the molecular sieving to exclude adamantane from the graphitic pore of 5.5 Å while the predominant adsorption of adamantane over benzene and 2,2-dimethyl hexane has been observed for the graphitic pore of 12 Å due to the stability of molecular self-assembly of the adsorbed adamantane phase in this pore. At the same time, only slightly preferential adsorption of adamantane over benzene and 2,2-dimethyl hexane has been observed in the disordered porous carbon-like activated carbon fiber ACF-15 |
URI(1): | https://epub.vgu.edu.vn/handle/dlibvgu/1826 | Rights: | Attribution-NonCommercial 4.0 International |
Appears in Collections: | Mechanical Engineering (MEN) |
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