Abstract: A recycle process for the separation of landfill gas containing a wide variety of impurities into a carbon dioxide product stream and a fuel-grade-pressurized methane product stream, the process providing for the removal of both the impurities and the carbon dioxide in a cryogenic column as a bottom stream, the separation of the methane from the overhead product stream by a membrane process, and, optionally, the removal of impurities from the carbon dioxide bottom stream in a separate purification column, to recover a high-quality, liquid, carbon dioxide stream.

Abstract: Distillative separations of hydrocarbon feed mixtures containing at least methane and carbon dioxide, as well as other components, such as ethane, higher hydrocarbons, and hydrogen sulfide are disclosed. In the separations described, methane is preferably separated from an acid gas under conditions of composition, temperature and pressure which would normally produce acid gas solids. Acid gas solids are prevented by adding a liquid solids-preventing agent into this distillation column. A second distillation column is subsequently employed to further separate the feed gas mixture. The second distillation column is operated under conditions which an azeotrope would normally form between the light hydrocarbon and carbon dioxide, which azeotrope would limit the carbon dioxide overhead composition. The azeotrope is prevented by introducing an agent for preventing azeotrope formation. Alternatively, the second distillation column may be operated to separate carbon dioxide from hydrogen sulfide.

Abstract: A distillative separation of carbon dioxide and hydrogen sulfide is improved by adding a C.sub.3 -C.sub.6 alkane, a mixture of C.sub.3 -C.sub.6 alkanes, SO.sub.2 or SO.sub.3 to a distillation column to increase the relative volatility of carbon dioxide to hydrogen sulfide. Increasing the relative volatility facilitates the separation.

Abstract: An improved distillative separation of carbon dioxide and light hydrocarbons is disclosed in which the formation of an azeotrope between these components is prevented by addition of an agent to said distillation column and in which prevention of the azeotrope allows a more complete separation to be achieved.

Abstract: A method of eliminating solids formation in a cryogenic distillative separation of acid gases from methane is disclosed. This method comprises adding a solids-preventing agent to the solids potential zone of the distillation column. Typical solids-preventing agents are one or more C.sub.2 -C.sub.5 alkanes, or other nonpolar liquids which are miscible with methane at the column conditions. The elimination of solids formation permits a more complete separation to be achieved.

Abstract: A distillative separation of carbon dioxide and hydrogen sulfide is improved by adding a C.sub.3 -C.sub.6 alkane, a mixture of C.sub.3 -C.sub.6 alkanes, SO.sub.2 or SO.sub.3 to a distillation column to increase the relative volatility of carbon dioxide to hydrogen sulfide. Increasing the relative volatility facilitates the separation.