| Abstract |
Αdsorption and separation of gases are two very important procedures, not only in the industrial but also in the environmental applications. Especially for the second ones, due to the imprudent pollution of the atmosphere, which causes terrible consequences on the greenhouse effect and on the urban life, it is necessary – more than never before – to find solutions in order to reduce at a great extent the dangerous gases released in the environment. In the applications above mentioned, porous materials play an important role as they cover a big part of procedures such as storage, adsorption and separation of gases. The production of more efficient and beneficial – in a financial way – porous materials, used for storage, filtration and cleanup of gases, which are produced either as intermediate industrial products or as engine pollutants, constitute an important technological and scientific challenge. Following this direction, there is a research taking place during the last decades with gases and mixtures of gases consisted of Η2, CO2, CO, CH4, O2, N2, H2S, NOx, SOx etc. As far as the discovery of new porous materials is concerned, nature has been the guideline, providing structures such as the natural zeolites. These are porous materials having an extensive network of pores of low weight with arrangement and diameter that varies. This gives them the opportunity to selectively store and separate small molecules. According to the philosophy of the zeolites, artificial zeolites have been designed and produced for various operations, such as the water purification and catalysis. However, new materials are possible to be produced, which are more capable to store and selectively separate, having properties such as low weight. The theoretical researcher-designer will be oriented towards stable microporous structures, having an extended network of pores and flexibility when choosing their dimensions and arrangements in space. Such structures began to be designed, composed and studied during the last decades and have been characterized as carbon-based nanoporous materials, belonging to the category of nanomaterials. Structures such as pillard grapheme, crossed nanotubes, graphenes and nanotubes with polymeric chains, covalent organic frameworks (COFs) and hybrid metal–organic frameworks (MOFs) are some of which are in the centre of scientific interest during the last years with encouraging properties of storage and separation of gases. In this dissertation, the adsorption of equimolar mixtures of CH4/CO2 (important parts of natural gas) and N2/CO2 (main parts of the combustion of focil fuels) will be studied using six different nanostructures:
i. Porous Network Nanotubes (PNN).
ii. The smaller member of the IRMOFs family (subcategory of MOFs), the ΙRMOF-1. iii. The second smaller member of the IRMOFs family, the IRMOF-8, whose organic bridge has additionally been modified appropriately with three different functional groups, aiming to improve its absorptive features.
All the simulations are carried out using molecular dynamics methods and they are separated into two major categories:
a) Simulations which aim to achieve conditions in equilibrium, where the nanostructures are supplied by tanks which contain mixtures of the molecules.
b) Simulations in non equilibrium conditions, where the nanostructures are also supplied by tanks which contain mixtures of the molecules, aiming to pass through them.
The calculations include the calculation of the adsorption and permeation selectivity of the nanostructures for the molecules CH4, CO2 and Ν2, as well as useful dynamic properties for the movement of the above mentioned molecules in the nanostructures, analyzing the orbits which result from the simulations. The results from the calculations show that the behavior of the molecules is a function of the power of their interaction with the atoms of the nanostructures, as well as of their geometrical characteristics.
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Μελέτη προσρόφησης, διάχυσης και διαχωρισμού μορίων με μεθόδους μοριακής δυναμικής
