Abstract: The cryogenic treatment of landfill gas removes troublesome compounds that cause severe corrosion of combustion engines in which the gas is used as fuel. It involves compressing the gas to an elevated pressure and isenthalpically expanding the gas to chill the gas to a temperature below -20 .degree. F. The compressed gas is first cooled to eliminate moisture as condensate. Methanol is injected into the gas so that it can be deeply chilled without forming ice with residual moisture in the gas. An aqueous methanol condensate containing troublesome compounds forms in, and is removed from, the deeply chilled gas before it is expanded to provide refrigeration for chilling the gas. By adding water to the aqueous methanol, the troublesome compounds lose solubility in diluted methanol and form a supernatant layer that can be separated for disposal. The diluted methanol can be recycled.

Abstract: Conventional liquified natural gas (LNG) plants are designed to eliminate moisture and up to 1.0% by volume of carbon dioxide (CO.sub.2) present in gas delivered by pipelines. Pipelines can no longer be expected to supply gas with such a low CO.sub.2 content. The invention pretreates gas with as much as 1.5% to 3.5% by volume of CO.sub.2 so that it becomes acceptable to LNG plants. The pretreatment involves scrubbing natural gas with cold methanol at a temperature below -30.degree. F. and flashing absorbed CO.sub.2 from methanol withdrawn from the scrubber by passing it through a pressure-reducing valve, followed by two successive warming flashings of CO.sub.2. Then, the methanol can be recycled to the scrubber. Required refrigeration is supplied to the methanol entering or leaving the scrubber.

Abstract: Land-fill and other gases containing principally methane and carbon dioxide have been separated into high BTU fuel gas and discard carbon dioxide containing appreciable methane. Such discard gas can now be simply fractionated into high-purity liquid carbon dioxide with recoveries in excess of 80% while using a single refrigerant at a single low temperature to satisfy all refrigeration requirements of fractionation. This novel fractionation is ideally combined with the process of separating land-fill gas into high BTU fuel gas because then the methane and carbon dioxide are recovered completely as two valuable products, high BTU fuel gas and pure liquid carbon dioxide.

Abstract: Refrigeration is produced while delivering transmission pipeline gas of elevated pressure to a branch pipeline of lower pressure by expanding the gas in a turbo-expander to a pressure below the branch pipeline pressure and recovering refrigeration from the expanded gas which is then compressed by a centrifugal compressor directly driven by the turbo-expander to the pressure required for delivery into the branch pipeline. Preferably, the gas is dehydrated by adding methanol and separating aqueous methanol condensate from the expanded gas, and the condensate is distilled with compression heat to recover methanol for reuse.

Abstract: Methane-containing gases with an appreciable content of carbon dioxide are scrubbed with cold methanol to remove the bulk of the carbon dioxide in a simple system comprising a single gas-liquid contact column and featuring regeneration of the methanol containing carbon dioxide solely by multiple-stage flashing. Land-fill gases containing methane and carbon dioxide as the principal components can be economically processed in such a system to yield methane-rich fuel gases.