Study of a hydrate-based process for the purification of biogas constituents

Abstract : Biogas is a potential source of energy that can be considered as an alternative pathway to the fossil fuels due to its content in methane. However, high energetic efficiency requires a separation of CH4 from the other gases, especially from CO2 and H2S. Separation by gas hydrate formation (SGHF) is a new technique that can be used to upgrade biogas. In order to estimate the possibility of using gas hydrate in order to upgrade biogas, phase envelope diagrams in isothermal process were built. These graphics made it possible to assess the selectivity of the couple methane – carbon dioxide in the hydrate phase in different low concentrations of H2S. Results showed that the presence of H2S decreases the pressure required for the formation of the hydrate phase, indicating that this gas has a major preference in this phase. On the other hand, CO2 showed a slight preference for the hydrate phase compared to methane. These results showed that an efficient separation of biogas using gas hydrates will require a multi-stage process. A simulated biogas upgrading using gas hydrate formation was presented in terms of mass balance. This simulation pointed the difficulty to separate the couple CH4/CO2 in presence of H2S via gas hydrate formation.