A METHOD FOR CAPTURING CARBON DIOXIDE

Abstract

A process for capture of carbon dioxide comprising the steps of contacting the carbon dioxide with at least one metal carbonate in an aqueous organic solvent at a predetermined temperature.

Claims

1. A process for capturing carbon dioxide, comprising the steps of: contacting the carbon dioxide with at least one metal carbonate in an aqueous organic solvent at a predetermined temperature.

2. The process as claimed in claim 1, wherein a ratio of CO.sub.2 to metal carbonate is in a range of 1-2:1 molar equivalents.

3. The process as claimed in claim 1, wherein the predetermined temperature is in a range of −50° C. to 100° C.

4. The process as claimed in claim 1, wherein the organic solvents are selected from the group consisting of alcohols, ketones, aldehydes, ethers, aliphatic and aromatic nitriles, aliphatic hydrocarbons, aromatic hydrocarbons and combinations thereof.

5. The process as claimed in claim 1, wherein the at least one metal carbonate is selected from the group consisting of carbonates of alkali metals, alkaline earth metals and combinations thereof.

6. The process as claimed in claim 5, wherein the alkali metal carbonates and alkaline earth metal carbonates are selected from the group consisting of Na.sub.2CO.sub.3, K.sub.2CO.sub.3, Rb.sub.2CO.sub.3, CS.sub.2CO.sub.3, MgCO.sub.3, CaCO.sub.3, SrCO.sub.3, BaCO.sub.3 and combinations thereof.

7. The process as claimed in claim 1, further comprising the step of conducting a simple filtration to remove any metal bicarbonate by-products and unreacted metal carbonates that have been formed as a result of the initial step.

8. The process as claimed in claim 7, wherein the organic solvent is recycled to capture fresh carbon dioxide.

9. The process as claimed in claim 4, wherein the aliphatic hydrocarbons are hexanes.

10. The process as claimed in claim 4, wherein the aromatic hydrocarbons are selected from the group consisting of benzene, toluene and combinations thereof.

Description

DESCRIPTION OF THE INVENTION

[0012] The present invention provides a process for capture of carbon dioxide from air/atmosphere and/or from gas streams. The process is relatively fast and involves the use of inexpensive, non-toxic and readily available raw materials.

[0013] The present invention relates to a process for capture of carbon dioxide comprising the steps of contacting the carbon dioxide with at least one metal carbonate in an aqueous-organic solvent at a predetermined temperature.

[0014] In an embodiment of the invention, the ratio of CO.sub.2 to metal carbonate is in the range of 1-2:1 molar equivalents. The CO.sub.2 gas (1-2 moles) is passed through the aqueous organic solvent (1000 ml) containing water in the molar ratio range of 1-2.

[0015] The predetermined temperature is in the range of −50° C. to 100° C. is preferred.

[0016] The metal carbonate and the reaction temperature are chosen such that metal bicarbonate(s) formed is/are stable at the reaction temperature chosen: [0017] (i) like carbonates of alkali metals (M.sub.2CO.sub.3, where M is an alkali metal cation). The metal carbonate chosen is selected from, but not limited to, Na.sub.2CO.sub.3, K.sub.2CO.sub.3, Rb.sub.2CO.sub.3 and/or Cs.sub.2CO.sub.3. [0018] (ii) like carbonates of alkaline earth metals (MCO.sub.3, where M is an alkaline earth metal cation). The metal carbonate chosen is selected from, but not limited to, MgCO.sub.3, CaCO.sub.3, SrCO.sub.3 and/or BaCO.sub.3. The solid bicarbonates (M(HCO.sub.3).sub.2) of above alkaline earth metals are unstable at ordinary temperatures and hence in such cases a low reaction temperature selected from the range −50° C. to 10° C. is preferred.
In the case of alkali metal salts, the CO.sub.2 combines with water and M.sub.2CO.sub.3 to form solid MHCO.sub.3, according to the following reaction.

M.sub.2CO.sub.3+H.sub.2O+CO.sub.2.fwdarw.2MHCO.sub.3

In the case of alkaline metal salts, the CO.sub.2 combines with water and MCO.sub.3 to form solid M(HCO.sub.3).sub.2, according to the following reaction.

MCO.sub.3+H.sub.2O+CO.sub.2.fwdarw.M(HCO.sub.3).sub.2

When the desired amount of carbon dioxide has been removed as MHCO.sub.3/M(HCO.sub.3).sub.2, the unreacted M.sub.2CO.sub.3/MCO.sub.3, if any, and the MHCO.sub.3/M(HCO.sub.3).sub.2 formed in the reaction are removed by simple filtration. The solubility of MHCO.sub.3/M(HCO.sub.3).sub.2 and M.sub.2CO.sub.3/MCO.sub.3 in the organic solvent should be preferably very low so as to retrieve it by simple filtration. The organic solvent is recycled to capture fresh carbon dioxide. Thus, the present invention provides “green” method for the capture of carbon dioxide from air/atmosphere and/or gas streams.

[0019] The organic solvent is selected from, but not limited to, alcohols, ketones, aldehydes, ethers, aliphatic and aromatic nitriles, aliphatic hydrocarbons like hexane, aromatic hydrocarbons like benzene, toluene. Since the solubilities of both M.sub.2CO.sub.3 and MHCO.sub.3 or MCO.sub.3 and M(HCO.sub.3).sub.2 in most organic solvents are very low, these can be easily filtered from such organic solvents and the organic solvent can be reused or recycled.

[0020] In a preferred process of this invention, an organic solvent is taken in a vessel fitted with an outlet tube and inlet tube. Required amount of M.sub.2CO.sub.3 and H.sub.2O is then added to the organic solvent in the vessel and CO.sub.2 containing gas stream/air is passed through the inlet tube to the suspension of M.sub.2CO.sub.3 in organic solvent containing water under constant stirring. The outlet tube is kept under oil to prevent the entry of moisture to the reaction vessel. The temperature is generally below 50° C., preferably ambient temperature. When most of M.sub.2CO.sub.3 has been converted to MHCO.sub.3 the reaction was stopped. The unreacted M.sub.2CO.sub.3, if any, and MHCO.sub.3 formed in the reaction were collected by simple filtration. The organic solvent can be reused to capture fresh CO.sub.2.

[0021] The method of this invention can be done with any organic solvent which is not acidic enough to react with the M.sub.2CO.sub.3 or the MHCO.sub.3. The M.sub.2CO.sub.3 and CO.sub.2 gas can be regenerated by the thermal decomposition of MHCO.sub.3. The water formed during the thermal decomposition of MHCO.sub.3 can be removed by a cold trap to get a concentrated stream of dry CO.sub.2 gas.

2NaHCO.sub.3Na.sub.2CO.sub.3+H.sub.2O+CO.sub.2

[0022] Alkali metal carbonates like sodium carbonate or potassium carbonate are cheap and environmentally friendly. Thus, the present invention provides ‘green’ and economically viable method for capturing CO.sub.2 from gas streams. The CO.sub.2 capturing method of the present invention can be used with an alkaline fuel cell (AFC) to remove the CO.sub.2 gas present in the air stream supplied at the cathode

Examples

[0023] The following experimental examples are illustrative of the invention but not limitative of the scope thereof:

Example

[0024] About 60 ml of ethanol containing 2 g of water was taken in a flask fitted with an inlet tube and outlet tube. Then about 15 g anhydrous Na.sub.2CO.sub.3 was added to the flask and the gas stream/air containing CO.sub.2 gas was passed through the suspension under constant stirring. The whole reaction was conducted at room temperature. The outlet tube was kept under oil to prevent entry of moisture to the reaction vessel. When most of the Na.sub.2CO.sub.3 was converted to NaHCO.sub.3 the reaction was stopped by stopping the gas flow. The Na.sub.2CO.sub.3 left unreacted and NaHCO.sub.3 formed in the reaction were separated from the organic solvent by simple filtration under dry atmosphere.

[0025] The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. Since the modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to the person skilled in the art, the invention should be construed to include everything within the scope of the disclosure.