Membrane-aided distillation for carbon dioxide and hydrocarbon separation

Claim 1

A process for the low temperature distillation separation of a carbonaceous off-gas into a heavy hydrocarbon stream, a high purity fuel gas product and a high purity carbon dioxide-sulfur stream product wherein the fuel gas product is enriched in fuel gas components and the carbon dioxide-sulfur stream product is enriched in carbon dioxide by further separation in a semi-permeable membrane, comprising providing a high purity fuel gas and a carbon dioxide-sulfur stream at high recoveries while minimizing capital investment and energy utilization by: (a) compressing and aftercooling an off-gas containing acid gases, light fuel gases and heavy hydrocarbons; (b) drying the off-gas to remove moisture and subcooling the off-gas against an external refrigeration source and by heat exchange with product streams; (c) initially separating the off-gas at low temperature in a distillation column to recover an initial fuel gas stream as an overhead fraction, a carbon dioxide-sulfur stream as a sidestream fraction and an heavy hydrocarbon-containing stream as a bottom fraction; (d) expanding the carbon dioxide-sulfur stream and potentially the heavy hydrocarbon stream to a lower pressure to provide refrigeration to cool and partially liquefy the initial fuel gas stream by heat exchange; (e) phase separating the initial fuel gas stream into a crude fuel gas product and a carbon dioxide-rich liquid stream which is recycled to the distillation column as reflux; and (f) upgrading the purity of the crude fuel gas product and the carbon dioxide-sulfur stream by passing the relatively higher pressure crude fuel gas stream over a semi-permeable membrane selective to carbon dioxide gas to separate a carbon dioxide permeate from the crude fuel gas stream and combining the carbon dioxide gas permeate with the lower pressure carbon dioxide-sulfur stream to provide a final high purity fuel gas product and a high purity carbon dioxide-sulfur stream product.