Two main topics are treated in this doctoral thesis from a theoretical and computational point of view: the gas capture and separation from post-combustion flue gases, and the enhanced oil recovery from oil reservoirs. The first topic evaluates the separation of CO2 using three different materials. First, several zeolites from the Faujasite family are studied with a combination of Density Functional Theory (DFT) and Monte Carlo methods. The former is employed to understand the driving mechanisms of adsorption, whereas the latter served to assess the separation of CO2 from a flue gas formed by a ternary mixture of CO2, N2 and O2. Second, the adsorption of CO2, N2 and SO2 into Mg-MOF-74 obtained through DFT calculations is presented to determine the most fundamental gas/MOF interactions. The results are then coupled to a Langmuir isotherm model to derive the macroscopic adsorption isotherms of the three gases in Mg-MOF-74. Finally, the absorption of CO2 and SO2 into three different phosphonium-based Ionic Liquids (ILs) is addressed by using the soft-SAFT equation of state and the COSMO-RS model. From the calculated adsorption/absorption isotherms several properties are obtained, such as the purity in the recovered gas, the working capacity of the materials and their selectivity to capture CO2 in the presence of other contaminant species. The main results obtained from this part of the thesis reveal that the cations of microporous materials are very strong sites of absorption for polar gases (i.e., the Na+ cations in Faujasites or the Mg2+ cations in Mg-MOF-74). This feature makes them very good candidates for CO2 capture, but they can be easily poisoned by other polar gases such as SO2. For this reason, it is highly recommended to desulphurize the flue gas before using any of these adsorbents. Similarly, ILs have higher affinity for SO2 than for CO2. However, the gas/IL interactions are significantly weaker, so they do not become poisoned by SO2. This fact implies that SO2 can be captured and separated from the flue gas by using a phosphonium-based IL.
The second topic describes via Molecular Dynamics simulations the interactions of several model oils with different rocks and brines. The obtained insight can be applied in better understanding the interactions of the species present at oil reservoirs, with direct application in enhanced oil recovery processes. To that end, two wettability indicators are monitored to determine the potential recovery of the model oils. First, the oil/water interfacial tension (IFT) under different conditions of temperature, pressure and salinity (i.e., from pure water to 2.0 mol/kg of NaCl or CaCl2). And second, the oil/water/rock contact angle (CA) on calcite (10-14) and kaolinite (001) also as a function of salinity (i.e., from pure water to 2.0 mol/kg of NaCl or CaCl2). The different model oils are built with molecules of different chemical nature representing the Saturate/Aromatic/Resin/Asphaltene (SARA) fractionation model. In a final stage of the doctoral thesis the effect of non-ionic surfactants at the oil/brine IFT is also included. The main results obtained show that the most polar components of oil migrate to the oil/water interface and reduce the IFT. However, the same compounds feel attracted to the rock, who increase the CA and hamper the oil recovery. Some of these interactions are affected by the presence of salt. Specifically, if a water layer is formed between the oil and the rock in a reservoir, electrolytes can diffuse into it and attract the polar components of oil, ultimately increasing the CA. Finally, cations can be attracted to the oil/water interface due to salt/surfactant interactions. Both species interact synergistically to modify their orientation/distribution at the interface and reduce the oil/water IFT.
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