| Huge amounts of greenhouse gases have been emitted because of human activities. Greenhouse effect is aggravated by the rapid increase concentration of greenhouse gases in atmosphere, which will lead to the acceleration of global warming followed by severe climate disasters. Therefore, strong measures have to be carried out immediately to reduce the emission of greenhouse gases in order to restrain the influences of global warming on the natural environment. Carbon dioxide is the main greenhouse gas and billions tons of CO2 are emitted due to the combustion of fossil fuel (e.g. coal, petroleum, natural gas) by human activities. Currently, carbon capture and sequestration (CCS) is considered to be the most cost-effective and technically feasible method to reduce the emission of CO2. There are several ways to capture CO2, such as absorption, membrane separation, adsorption, cryogenic distillation. Adopting computer simulation method, we have studied the adsorption and separation of CO2 by porous materials and made a proposal of capturing CO2 by using surfactant micelle.Three adsorbents models, mesoporous MCM-41, microporous MFI and micro/mesoporous MFI/MCM-41, were constructed and studied for CO2 adsorption and separation. The simulated adsorption isotherms and isosteric heats of CO2 in MCM-41, CO2, N2 and CH4 in MFI are consistent well with literature values. Interaction between CO2 and silicate adsorbents is stronger than CH4 and N2, which leads to higher adsorption loading and isosteric heat for CO2 adsorption. The adsorption density of CO2 on active sites is much greater than that on the other area of adsorbent while N2 tends to distributes homogeneously on the adsorbent surface. At low pressure, the loading of CO2 in the three adsorbents is in the following sequence:MFI>MFI/MCM-41>MCM-41. With the increase of pressure, saturated adsorption of MFI gradually approaches while MCM-41 and MFI/MCM-41 are able to accommodate additional adsorbate molecules due to their bigger mesopores. Hence, the sequence of CO2 loading at high pressure changes into MFI/MCM-41>MCM-41>MFI. The adsorption behavior of CH4 in the three adsorbents is similar to CO2. However, throughout the pressure range in our research, the loadings of N2 in the three adsorbents are almost the same. For the adsorption in MFI/MCM-41, adsorbate molecules first locate in micropores and subsequently adsorb in the mesopores.The loading and isosteric heat of each component in mixture are lower than those of pure gas at the same adsorption conditions. In the adsorption of flue gas, the adsorption selectivity of CO2 over N2 is in the sequence of MFI>MFI/MCM-41>MCM-41. At room temperature, the selectivities of MFI and MFI/MCM-41 increase with the rise of pressure while selectivity of MCM-41 decreases. With the increase of temperature, both the gas loading and selectivity decrease rapidly. At high temperature, pressure has no discernible influence on the selectivity. Temperature is the dominant factor for the gas adsorption and selectivity. For the adsorption and separation of natural gas at 300K, with the increase of pressure, the selectivity of CO2 over N2 in MFI increases first and drops later while selectivity in MFI/MCM-41 is a monotonically increasing function of pressure and exceeds the selectivity in MFI at high pressure.Self diffusivity of CH4 is greater than CO2 due to the weaker interaction between CO2 and adsorbent. With the increase of loading, both the self diffusivity of CH4 and CO2 decrease and approach to zero near saturated adsorption. However, the self diffusivities of CH4 and CO2 in MFI/MCM-41 first increase and drop subsequently, experiencing the maximum at the loading about 4mmol/g and 2mmol/g, respectively. Gas diffusion in MFI/MCM-41 is much higher than that in MFI due to the presence of mesopores.For silicate adsorbents, in general, micropore is more adsorptive and selective than mesopore at low and medium pressure. Mesopore is bigger in size than micropore, which leads to higher adsorption capacity at high pressure and low mass transportation resistance for mesopore. By introducing mesopores into microporous adsorbents, it is found to be a good way to solve the problem of low mass transportation rate in microporous materials. This micro/mesoporous composite is able to simultaneously enhance the adsorption capacity, selectivity and mass transportation rate. Micro/mesoporous material is one of the best candidates of high performance adsorbents.The adsorption behavior of CO2 in Na-ZSM-5 zeolites with various Si/Al ratio was also investigated. Strong adsorption sites are introduced with the presence of Na+. Both of the adsorption density and isosteric heat at these sites are greater than the common sites. At low pressure, almost all the adsobate molecules are adsorbed at the strong sites while the contribution of these site decreases with the increase of pressure.We also proposed an idea of capturing the CO2 by surfactant micelle. In order to verify the feasibility of this proposal, molecular dynamics simulation was adopted to investigate the distribution of CO2 in aqueous solution of surfactant AOT. The simulation results were compared with experimental work of Prof. Han Buxing's group. CO2 molecules first adsorb around the ester group of AOT bilayer. With the increase numbers of CO2 added into the system, CO2 accumulate in the center of bilayer, which leads to the expansion of AOT bilayer. Driven by the surface tension, lamellar bilayer changes to spherical micelle. Both of the simulation result and experimental work demonstrate that CO2 molecules are able to aggregate in micelle phase, which validates our proposal indirectly. However, AOT doesn't have good affinity to CO2. Several CO2-active surfactants are promoted to capture CO2. The key point of the idea of capturing CO2 with surfactant micelle is to find out or design a suitable surfactant that is able to form micelle with high CO2 capacity. This proposal is expected to be an innovated high efficient method for capturing CO2 but further investigations are still required.Molecular dynamics simulation was also adopted to unravel the negative thermal expansion of Langmuir monolayer formed by gemini surfactant (17PyOx) at air/water interface. Density distribution function along normal direction of water surface validates the formation of monolayer.17PyOx tends to aggregate rather than distribute homogeneously even at loose monolayer. Hydrocarbon tails of 17PyOx become more orderly at the normal direction of monolayer as closer packing. For a loose Langmuir monolayer, surface pressure is around zero and increased linearly and slowly with the decrease of specific area. The monolayer expands positively with rising temperature. As to a compact Langmuir monolayer, however, surface pressure increases rapidly with the decline of specific area and negative thermal expansion occurs. Surface pressure is in decline with the increase of temperature from 278 to 293 K. Negative thermal expansion at this temperature range is due to the increase of hydrogen bond between surfactant-surfactant with the rise of temperature. It is observed by experiment that 17PyOx can not spread well on air/water interface as temperature greater than 298 K. This phenomenon is well predicted by our simulation that hydrophilic head group of 17PyOx becomes hydrophobic at high temperature.
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