Molecular Simulation Of Adsorption And Separation Of Gases In Porous Nanomaterials

The rapid development of industrialization is leading to a series of energy and environmental issues. Due to the combustion of fossil fuels such as coal and oil, a large amount of acid gases such as sulfur dioxide (SO2), carbon dioxide (CO2) were emitted into the air, which will form acid rain and bring severe damage to human and ecological environment. Meanwhile, the excess emission of CO2 will also leads to the greenhouse effect. Thus, it is an important topic to capture the SO2 and CO2. The shortage of fossil fuels and the pollution to the environment inspiresour interests in clean sources of energy.Hydrogenand methane are the widely studied clean energy, but how to use simple method to get pure hydrogen and methane is also an important topic. With the increase demand for energy, shale oilas an unconventional resource has received much attention. Understanding the diffusion of shale oil is very important for exploiting shale oil. In this thesis, we used the molecular simulation to study the adsorption and separation of gases in various porous nano-materials, aiming at providing the microscopic mechanism and reference for practical applications.The main contents and noveltyareconcluded as follows:1. We have systematically investigated adsorption and separation of the sulfur gas H2S and SO2 in covalent-organic materials (COMs) by using molecular simulation. Results indicate that among these materials studied,PAF-302 shows the highest excess uptake of H2S (51.94 mmol/g) and SO2 (50.69 mmol/g) due to its large pore volume and high BET surface area. Both maximum excess uptakes of H2S and SO2follow the order of PAF-302>COF-102> COF-10> COF-5> COF-8> COF-6, which is entirelyconsistent with the orders of the pore volumes. For gas mixtures, the selectivity of these two-dimensional (2D) COM materials is obviously better than the three-dimensional (3D) COM materials, especially for COF-6 with smaller pore size. In short, PAF-302 is an excellent candidate for H2S and SO2 adsorption, while COF-6 is an excellent material for sulfur gas separation.2. We used GCMC simulations to investigate adsorption and separation of metal-organic frameworks and covalent-organic materials for the noble gas Xe. Results indicate that PAF-302 among these materials studied shows not only the highest gravimetric excess uptake of 4009 mg/g, but also largest volumetric uptake of 216 V(STP)/V, so PAF-302 is an excellent candidate for Xe storage at intermediate pressure The gravimetrical excess uptake of Xe atintermediate pressure follows the order of PAF-302>UMCM-1>IRMOF-1> Cu-BTC>COP-4> ZIF-8, which is entirelyconsistent with accessible surface areas.Moreover, the maximum gravimetric excess uptakes of Xe in different materials exhibit an entirely linear correlation with the accessible surface area. For the binary mixtures, the selectivities of Xe/N2 follow the order of Cu-BTC> ZIF-8> COP-4> IRMOF-1> UMCM-1> PAF-302, which is exactly the same with the order of difference of isosteric heats (DIH). In particular, the selectivity of Cu-BTC for Xe over N2 reaches 80, which is an excellent candidate for Xe separation.3. We usedmolecular dynamicssimulations to systematically investigate the membrane-based separation performance of four diamond-like frameworks for CO2/H2, CO2/N2, CO2/CH4 and CH/H2 mixtures. Diamondyne shows high membrane selectivity for gas mixtures of CO2/H2, CO2/N2, CO2/CH4 and CH4/H2, compared toMOFand COF membranes. Comprehensively considering the permeation selectivity and permeability, we find that diamondyne and TND-2 are promising candidates for CO2/H2 and CO2/N2separation. Moreover, diamondyne and TND-2 exceed the Robeson’s upper line for CO2/N2 mixtures. What is more, TND-2 isalso a promising candidate for separating CH4/H2. The separation performance of diamondyne for CO2/CH4 mixtures also exceeds the Robeson’s upper limitation, indicating that diamondyne is also a promising candidate for separation of the CO2/CH4 mixtures.4. We developed a new S(DIH) equation based on the difference of isosteric heats (DIH) to calculate the selectivity for CO2 over CH4 in nano-porous materials. Using the S(DIH) equation to predict the selectivity only needs adsorption isotherms of pure components and the DIH of the two components. By comprehensive comparison with the GCMC data in different types of porous materials including MOFs and COMs, it is found that the new S(DIH) equation can excellently predict the selectivity of different types of porous materials for CO2 over CH4 at the low pressure of p=0-1 bar. Therefore, the new S(DIH) can serve as an efficient tool for the selectivity predictions of porous materials for CO2 over CH4 at p=0-1 bar, especially for the cases that experiment can measure adsorption isotherms and adsorption heats of pure components (say, CO2, CH4, N2 etc), because the new S(DIH) only needs adsorption isotherms and adsorption heats of pure components as input. In short, the new S(DIH) equation can be considered as a valuable screening tool for obtaining an estimate concerning the selectivity of a porous material for a certain component of the gas mixture.5. Molecular dynamics simulations were performed to investigate the diffusion of shale oil in the clay-rich shale. Montmorillonite model was used to represent the clay-rich shale, and octane was used as a shale oil model. Results show that the diffusion coefficient of shale oils is extremely small in the basal spacing of 2.8 nm, and with the increase of basal spacing, the diffusion coefficient increases by several order of magnitudes. This observation indicates that once the shale oils flow from microscopic pores into the mesoscopic pores, it would accompany with the decrease of oil density and extreme increase of diffusion coefficient, which is very beneficial for exploitation of shale oils. However, it is still difficult to exploit the oil molecules adsorbed in the microscopic pore. Besides, by exploring the effect of chain length of oil molecule on the diffusion, we found that the shorter chain oils are beneficial for exploitation. It is expected that these simulation results provide useful reference and important fundamentality for the investigation of shale oil.