Abstract: According to the present invention, in separating carbon dioxide by a membrane separation with a separation membrane system using an inorganic separation membrane from a mixed gas containing methane and carbon dioxide, and then by an acid gas removal process using an absorbent, by specifying the suitable range of the carbon dioxide mole fraction at the outlet on the carbon dioxide non-permeation side XCO2 in the membrane separation, which corresponds to an ideal separation factor of the inorganic separation membrane, the proper distribution conditions become feasible. As a result, a method for separating carbon dioxide in which the decrease of the production amount by methane permeation in the membrane separation and the energy loss accompanying the decrease are suppressed, and further the energy consumption in an acid gas removal process using an absorbent, which is a post-process, can be suppressed, is provided.

Abstract: According to the present invention, in separating carbon dioxide by a membrane separation with a separation membrane system using an inorganic separation membrane from a mixed gas containing methane and carbon dioxide, and then by an acid gas removal process using an absorbent, by specifying the suitable range of the carbon dioxide mole fraction at the outlet on the carbon dioxide non-permeation side XCO2 in the membrane separation, which corresponds to an ideal separation factor of the inorganic separation membrane, the proper distribution conditions become feasible. As a result, a method for separating carbon dioxide in which the decrease of the production amount by methane permeation in the membrane separation and the energy loss accompanying the decrease are suppressed, and further the energy consumption in an acid gas removal process using an absorbent, which is a post-process, can be suppressed, is provided.

Abstract: The present invention is a method for separating carbon dioxide in which the membrane separation is performed such that a carbon dioxide partial pressure difference ?P at the final outlet on the carbon dioxide non-permeation side is ? or more of the carbon dioxide partial pressure on the carbon dioxide non-permeation side (PX·XCO2), in a separation membrane system provided with an inorganic separation membrane that is permeated by carbon dioxide preferentially from a mixed gas containing methane and the carbon dioxide, therefore, the driving force that is a partial pressure difference of carbon dioxide between on the carbon dioxide non-permeation side and on the carbon dioxide permeation side is maintained, and further the membrane area of the inorganic separation membrane to be used can be suppressed smaller, the carbon dioxide can be efficiently separated, and the cost is low.