Absorption medium and method for removing carbon dioxide from gas streams

#This application is a National Phase filing under 35 U.S.C. §371 of PCT/EP2006/067586 filed Oct. 19, 2006, which claims priority to Patent Application No. 102005050385.3, filed in Germany on Oct. 20, 2005. The entire contents of each of the above-applications are incorporated herein by reference.

#The present invention relates to an absorption medium for removing carbon dioxide from gas streams and to a method using the absorption medium.

#In numerous processes in the chemical industry, fluid streams occur which comprise acid gases such as, for example, CO2, H2S, SO2, CS2, HCN, COS, NOx, disulfides or mercaptans as impurities. These fluid streams can be, for example, gas streams, such as natural gas, synthesis gas, refinery gas, or reaction gases which are produced in the oxidation of organic materials, such as, for example, organic wastes, coal, natural gas or mineral oil, or in the composting of waste materials comprising organic substances.

#The invention will be described in more detail with reference to the accompanying drawings and the examples hereinafter.

#FIG. 1 is a diagrammatic representation of a plant suitable for carrying out the inventive method.

#According to FIG. 1, a suitably pretreated carbon dioxide-containing combustion gas, in an absorber 2, is brought, via a feed line 1, into contact in countercurrent flow with the regenerated absorption medium which is fed via the absorption medium line 3. The absorption medium removes carbon dioxide by absorption from the combustion gas; via an exhaust gas line 7 a pure gas low in carbon dioxide is produced. The absorber 2 can have, above the absorption medium inlet, backwash trays or backwash sections which are preferably equipped with ordered packings (not shown), where, using water or condensate, entrained absorption medium is separated off from the CO2-depleted gas. The liquid on the backwash tray is recycled in a suitable manner via an external cooler.

#Via an absorption medium line 5, a pump 12, a solvent-solvent heat exchanger 11 in which the acid gas-loaded absorption medium is heated by the heat from the regenerated absorption medium coming from the bottom of the desorption column 7, and a throttle valve 6, the carbon dioxide-loaded absorption medium is passed to a desorption column 7. In the lower part of the desorption column 7 the loaded absorption medium is heated by means of a heater (not shown) and regenerated. The carbon dioxide liberated leaves the desorption column 7 via the exhaust gas line 8. The desorption column 7 can, above the absorption medium inlet, have backwash trays or backwash sections which are preferably equipped with ordered packings (not shown), where entrained absorption medium is separated off from the liberated CO2 using water or condensate. In the line 8, a heat exchanger having a top distributor or condenser can be provided. The regenerated absorption medium is subsequently fed by means of a pump 9 via the solvent-solvent heat exchanger 11, in which the regenerated absorption medium heats up the acid gas-loaded absorption medium and is itself cooled, and back to the heat exchanger 10 of the absorption column 2. To prevent the accumulation of absorbed substances which are not expelled or are only incompletely expelled in the regeneration, or of decomposition products in the absorption medium, a substream of the absorption medium taken off from the desorption column 7 can be fed to an evaporator in which low-volatility byproducts and decomposition products are produced as residue and the pure absorption medium is taken off as vapors. The condensed vapors are fed back to the absorption medium circuit. Expediently, a base, such as potassium hydroxide, can be added to the substream which, e.g. together with sulfate ions or chloride ions, forms low-volatility salts which are taken off from the system together with the evaporator residue.

#The resistance of various amines to the action of oxygen was determined as follows: