Studies On Gas Storage In Porous Media

To develop a clean and renewable energy source is an urgent task for the world. Natural gas and hydrogen are thought to be appropriate alternative fuels. Gas storage on board of vehicle is one of the most important technologies in utilizing these alternative fuels. Many works on hydrogen storage using carbon nanotubes as the carrier have been reported. However, the results reported for the hydrogen storage capacity are quite divergent. In this dissertation, adsorption isotherms of hydrogen on multiwalled carbon nanotubes (MWNT) were measured for a wide range of temperature with a volumetric method, which was compared with the results collected on activated carbon AX-21. It is concluded that the amount of hydrogen absorbed on MWNT is very low, only 0.2wt% at room temperature and 10MPa. Although the storage capacity increases at 77K, it is much lower compared to the DOE criterior. In order to enhance the hydrogen uptake, many experiments, such as the modification of activated carbons using acid and alkali, Pd-loading on SBA-15 and so on were tested. These tests indicate that the physical adsorption above the critical temperature follows a monolayer surface coverage mechanism. Specific surface area and temperature are the decisive factors for the amount adsorbed. Other properties of the porous media only have minor effect on hydrogen storage capacity.Aiming to enhance the storage capacity of methane, methane sorption in porous media in the presence of water was studied. It is shown that 63% more methane was stored pre unit mass of activated carbon BY-1 compared to that of dry sample. The charging/discharging process of methane into/from the wet carbon indicate that the thermal effect is much more less than that with dry carbon. Effects of temperature, water ratio, package density and pore size distribution on the sorption amount of methane are studied. It was proven that the enhanced sorption of methane is due to the formation of methane hydrates in the pore spaces of carbon.Limitations on the equipment dimension of oxygen supplier promoted the study on oxygen storage in high surface activated carbon. Adsorption isotherms of oxygen on activated carbon AX-21 were collected for a range of 118-313K and 0-10 MPa. The isosteric heat of adsorption were evaluated basing of the isotherms. A model is presented for the experimental isotherms basing on the Gibbs definition of adsorption and the determination of absolute adsorption quantity. The model fits the isotherms very well for the whole range tested. Based of the measurements, the enhancement effect of adsorption for the storage of oxygen is proven.Carbon dioxide is an important greenhouse gas, however, it can be sequestrated as hydrates deep in the sea. The sorption isotherms of CO₂ in porous media were measured in the presence of water. All effects affecting the sorption amount of CO₂ in wet materials were discussed. The mechanism of enhanced storage capacity of CO₂ is proved to be the formation of hydrates in the pore spaces. The sorption isotherms of a mixture of CO₂ and CH4 in wet activated carbon were collected and the proportions of components in the adsorbed phase were calculated. These data might be useful for CO₂ sequestration and CH4 exploitation.