The impurities in carbon dioxide are mainly methane and nitrogen, and even if their content is low, it will affect the vapor pressure and other properties of CO2. Other common impurities include H2S, N2, and H2O. These impurities will affect the characteristics of CO2, but due to their much lower content than nitrogen and methane, their impact on the various properties of supercritical carbon dioxide is relatively small. During operation, the purity of carbon dioxide should be increased as much as possible. The following mainly considers the impact of methane and nitrogen on the properties of CO2.