Adsorptive storage and separation of hydrocarbons in microporous adsorbents

The primary goal of this thesis is to use molecular simulations to identify the structural properties of an adsorbent which control its performance in industrial applications. Molecular models describing the pore size, surface area, and polarity of an adsorbent were developed and analyzed using Monte Carlo simulations. These simulations provided valuable information on the relationship between the adsorbent microstructure and the behavior of the adsorbed phase. This work examines the application of adsorption to produce alternative transportation fuels. Molecular models are used to identify the structural properties of adsorbents which will optimize the production and quality of the alternative fuels. The particular fuels examined are adsorbed natural gas (ANG), where the gas is stored at relatively low pressures in an activated carbon adsorbent, and reformulated gasoline, in which carcinogenic benzene molecules have been removed by adsorptive separation. ANG was examined to determine if it is competitive as an alternative transportation fuel. The strategy was to calculate the maximum storage capacity of carbon for natural gas. The system was modeled as pure methane intercalated between parallel planes of graphite. Adsorption isotherms and isosteric heats of adsorption for methane on activated carbon were calculated using grand canonical Monte Carlo simulations. Comparison of the molecular simulations with experimental data show that the slit model provides an upper bound for the equilibrium capacity. The simulations indicate that ANG is capable of storing methane in quantities comparable to compressed natural gas, but at much lower pressure. However for ANG to be competitive with other transportation fuels, new adsorbents with higher affinity for natural gas must be found. An important result of this work was the determination of an optimum carbon structure for adsorption of natural gas. Assuming isothermal filling at 300 K, the optimum structure is parallel planes of graphite with a slit width of 11.4 A. Based on our recommendations, Osaka Gas Company has developed a carbon adsorbent with a narrow pore distribution around 11.4 A which gives significantly better storage of methane than other commercial adsorbents. Adsorption of aromatic hydrocarbons in synthetic faujasites was examined to determine if adsorptive separation is a viable option for the selective removal of benzene from gasoline. Isotherms and isosteric heats of single-component and binary mixture adsorption were simulated and compared to experimental data. The simulations predict that NaY would be a better adsorbent than NaX for removal of benzene from toluene. However, the selectivity is not large enough to make adsorptive separation techniques economical when compared to distillation. A volumetric apparatus was designed and constructed for low pressure vapor adsorption. Adsorption isotherms, Henry\u27s constants, and isosteric heats were calculated for pure-vapor adsorption of benzene and toluene in NaY at 313 and 333 K. The experimental results confirm that NaY has a stronger affinity for toluene than for benzene. Adsorptive recovery of benzene from other aromatics in gasoline requires a high selectivity for benzene. The experiments showed that the selectivity of the adsorbent increases with temperature. (Abstract shortened by UMI.