PROCESS FOR CAPTURING CO2 AND PROCESS FOR CONTINUOUSLY REGENERATING SOLVENT

Abstract

The present invention describes a process for capturing CO.sub.2 using an optimized mixture of water and alcohols with alkali hydroxides, such as KOH and NaOH, for absorption of CO.sub.2 from gaseous mixtures. The process shows high efficiency and low volatility and corrosivity rate of the solvent, in addition to allowing cost reduction for installation and maintenance of reactors and reducing solvent loss. The present invention also describes a process for regenerating solvent or its reuse, carried out by chemical precipitation, continuously and not in batch, through the reaction with alkaline earth oxides, such as CaO and MgO, and/or alkaline earth hydroxides, such as Ca(OH).sub.2 and Mg(OH).sub.2, for the formation of carbonates, such as CaCO.sub.3 and MgCO.sub.3, which can be discarded in nature without any environmental issue or can be used commercially in industry or agriculture.

Claims

1. PROCESS FOR CAPTURING CO.sub.2, characterized by using alkaline chemical solvent, water and alcohols, comprising the following steps: a) Preparing a hydroalcoholic solution with alcohol at a concentration of 5% v/v and 75% v/v; b) Preparing a mixture of the solution obtained in step “a” with alkali hydroxides, whose concentration should be between 0.5 mol/L to 2 mol/L, c) Placing the aqueous mixture obtained in step “b” in direct contact with the gas mixture containing CO.sub.2, thus promoting the separation of CO.sub.2 from the gas mixture.

2. PROCESS FOR CAPTURING CO.sub.2, according to claim 1,step “a” , characterized in that the alcohol is selected from the group comprising methanol, ethanol, isopropanol, tert-butanol, glycerol and ethylene glycol.

3. PROCESS FOR CAPTURING CO.sub.2, according to claim 1, step “b”, characterized in that alkali hydroxides are selected from the group comprising sodium hydroxide, potassium hydroxide and lithium hydroxide.

4. PROCESS FOR CAPTURING CO.sub.2 , according to claim 1, characterized in that the hydroalcoholic solution is composed of alcohol in a concentration of 10% v/v.

5. PROCESS FOR CAPTURING CO.sub.2, according to claim 1, characterized in that the concentration of alkali hydroxides is 1 mol/L.

6. PROCESS FOR CAPTURING CO.sub.2, according to claim 1, step “c”, characterized in that the temperature of the chemical absorption reaction is between 10° C. and 85° C., preferably between 20° C. to 40° C.

7. PROCESS FOR CAPTURING CO.sub.2, according to claim 1, characterized in that it is carried out in a chemical absorption reactor under pressure between 1 atm to 10 atm, preferably 1 atm.

8. PROCESS FOR CONTINUOUS REGENERATION OF SOLVENT, characterized by being carried out through chemical precipitation, comprising the following steps: a) Placing particles of alkaline earth oxides and/or hydroxides at a concentration of 90% m/m to 100% m/m purity, in a bed; b) Placing the solvent containing CO.sub.2 in contact with the bed of alkaline earth oxides and/or hydroxides particles inserted in step “a”; c) Recirculating the solvent containing CO.sub.2 in a bed of alkaline earth oxides and/or hydroxides particles, for 10 to 300 minutes.

9. PROCESS FOR CONTINUOUS REGENERATION OF SOLVENT, according to claim 8, characterized in that the bed of particles is a fixed bed.

10. PROCESS FOR CONTINUOUS REGENERATION OF SOLVENT, according to claim 8, step “a” characterized in that the concentration of alkaline earth oxides and/or hydroxides particles is preferably 100% m/m.

11. PROCESS FOR CONTINUOUS REGENERATION OF SOLVENT, according to claim 8, step “c”, characterized in that the recirculation time is preferably 10 minutes.

12. PROCESS FOR CONTINUOUS REGENERATION OF SOLVENT, according to claim 8, step “a”, characterized in that the alkaline earth oxide particles are selected from the group comprising calcium oxide, magnesium oxide, strontium oxide and barium oxide, and/or alkaline earth hydroxides such as calcium hydroxide, magnesium hydroxide, strontium hydroxide and barium hydroxide.

13. PROCESS FOR CONTINUOUS REGENERATION OF SOLVENT, according to claim 8, step “a”, characterized in that the particles of alkaline earth oxides and/or hydroxides are in the form of spheres, semi-spheres, pellets or other formats that allow the continuous flow of the solvent chemical through the bed, without clogging of the regenerator.

14. PROCESS FOR CONTINUOUS REGENERATION OF SOLVENT, according to claim 8, step “a”, characterized in that it occurs at a temperature range between 20° C. and 85° C., preferably between 20° C. and 60° C.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0022] FIG. 1 is a graphic demonstration of the efficiency of the chemical absorption process of CO.sub.2 as a function of time using the following aqueous solutions: monoethanolamine (black), ammonia (red), potassium hydroxide (green) and potassium hydroxide containing ethanol (95% water and 5% ethanol—blue). All solutions were used at a concentration of 1 mol/L.

DETAILED DESCRIPTION OF THE TECHNOLOGY

[0023] The present invention describes a process for capturing CO.sub.2 using an optimized mixture of water and alcohols with alkali hydroxides, such as KOH and NaOH, for absorption of CO.sub.2 from gaseous mixtures. The process shows high efficiency and with low volatility and corrosivity rate of the solvent, in addition to allowing cost reduction for installation and maintenance of reactors and reducing solvent loss. The present invention also describes a process for regenerating solvent or its reuse, carried out by chemical precipitation, continuously and not in batch, through the reaction with alkaline earth oxides, such as CaO and MgO, and/or alkaline earth hydroxides, such as Ca(OH).sub.2 e Mg(OH).sub.2, for the formation of carbonates, such as CaCO.sub.3 e MgCO.sub.3, which can be discarded in nature without any environmental issue or can be used commercially in industry or agriculture.

[0024] The process for capturing CO.sub.2 comprises the following steps: [0025] a. Preparing a hydroalcoholic solution with alcohol at a concentration of 2.5% v/v and 75% v/v, preferably 10% v/v, [0026] b. Preparing a mixture of the solution obtained in step “a” with alkali hydroxides, whose concentration should be between 0.5 mol/L to 2 mol/L, preferably 1 mol/L; [0027] c. Placing the aqueous mixture obtained in step “b” in direct contact with the gas mixture containing CO.sub.2, thus promoting the separation of CO.sub.2 from the gas mixture.

[0028] The alcohol used in step “a” of the process for capturing CO.sub.2 can be selected from the group comprising methanol, ethanol, isopropanol, tert-butanol, glycerol and ethylene glycol. Furthermore, alkali hydroxides can be selected from the group comprising sodium hydroxide, potassium hydroxide and lithium hydroxide. In step “c” of the process for capturing CO.sub.2, the temperature of the chemical absorption reaction can be between 10° C. and 85° C., preferably between 20° C. and 40° C. The process for capturing CO.sub.2 can be carried out in a chemical absorption reactor under pressure between 1 atm to 10 atm, preferably 1 atm.

[0029] The process for continuous solvent regeneration is carried out by chemical precipitation and comprises the following steps: [0030] a. Placing particles of alkaline earth oxides and/or hydroxides at a concentration of 90% m/m to 100% m/m purity, preferably 100% m/m, in a bed; [0031] b. Placing the solvent containing CO.sub.2 in contact with the bed of alkaline earth oxides and/or hydroxides particles inserted in step “a”; [0032] c. Recirculating the solvent containing CO.sub.2 in a bed of alkaline earth oxides and/or hydroxides particles, for 10 to 300 minutes, preferably 10 minutes.

[0033] The bed of particles of the continuous solvent regeneration process is preferably a fixed bed. The continuous regeneration of solvent by chemical precipitation can be accomplished circulating the solvent in a bed of alkaline earth oxide particles selected from the group: calcium oxide, magnesium oxide, strontium oxide and barium oxide, and/or alkaline earth hydroxides such as calcium hydroxide, magnesium hydroxide, strontium hydroxide and barium hydroxide.

[0034] The particles of alkaline earth oxides and/or hydroxides can be in the form of spheres, semi-spheres, pellets and other shapes, which allow the continuous flow of the chemical solvent through the bed without clogging the regenerator.

[0035] The circulation of chemical solvent in the regenerator of the continuous solvent regeneration process can be carried out at a temperature between 20° C. and 85° C., preferably between 20° C. and 60° C.

[0036] The present invention can be better understood by the following, non-limiting example.

EXAMPLE 1—CHEMICAL ABSORPTION OF CO.SUB.2 .IN MIXTURES OF CO.SUB.2 .WITH ATMOSPHERIC AIR BY CHEMICAL SOLVENT COMPOSED OF A MIXTURE OF 95% V/V WATER, 5% V/V ETHANOL AND 1 MOL/L POTASSIUM HYDROXIDE AND REGENERATION PROCESS BY CHEMICAL PRECIPITATION

[0037] The chemical absorption of CO.sub.2 was carried out bubbling through a Dreschel type flask, at a flow rate of 8 L/min, a mixture of 5% v/v of CO.sub.2 and 95% v/v of compressed air in 250 mL of chemical solvent containing 95% v/v water, 5% v/v ethanol and 1 mol/L potassium hydroxide. The gas mixture was analyzed instantly by an infrared detector to quantify the chemical absorption of CO.sub.2 by the chemical solvent. Chemical absorption was carried out at room temperature (25° C.). The same procedure was performed for other solvents in order to compare the chemical absorption efficiency of CO.sub.2. FIG. 1 shows the chemical absorption of CO.sub.2 by different solvents. It can be seen in FIG. 1 that the aqueous ammonia solution with a concentration of 1 mol/L has the lowest CO.sub.2 absorption efficiency of all tested solvents. The aqueous monoethanolamine solution has an initial CO.sub.2 absorption efficiency similar to the aqueous potassium hydroxide solution, where approximately 70% of the CO.sub.2 of the gas mixture is solubilized when in contact with the solvent. However, the rate of change of the CO.sub.2 absorption efficiency is different for the two solvents. The aqueous solution of monoethanolamine shows a loss of efficiency since the beginning of the experiment, and at a rate of decay of the efficiency of absorption of CO.sub.2 less variable than that of the aqueous solution of potassium hydroxide. The solvent that shows potassium hydroxide at a concentration of 1 mol/L in 95% water and 5% ethanol is the most efficient in absorbing CO.sub.2 from gas mixtures. The efficiency is greater than 90% at room temperature and extends over a long period until the solvent saturates with CO.sub.2 and reduces its absorption efficiency sharply. The chemical reactions that occur in chemical absorption are described in Equations 1 to 8.

CH.sub.3CH.sub.2OH(aq)+KOH(aq).fwdarw.CH.sub.3CH.sub.2O.sup.−K+(aq)+H.sub.2O(I)   Eq. 1

CO.sub.2(g)+H.sub.2O(I).fwdarw.H.sub.2CO.sub.3(aq)   Eq. 2

H.sub.2CO.sub.3(aq)+H.sub.2)(I).fwdarw.HCO.sub.3.sup.−(aq)+H.sub.3O.sub.+(aq)   Eq. 3

H.sub.2CO.sub.3(aq)+OH.sup.−(aq).fwdarw.HCO.sub.3.sup.−(aq)+H.sub.2O(I)   Eq. 4

H.sub.2CO.sub.3(aq)+CH.sub.3CH.sub.2O.sup.−(aq).fwdarw.HCO.sub.3.sup.−(aq)+CH.sub.3CH.sub.2OH(aq)   Eq. 5

HCO.sub.3.sup.−(aq)+H20(1).fwdarw.CO.sub.3.sup.2−(aq)+H.sub.3O.sub.+(aq)   Eq. 6

HCO.sub.3.sup.−(aq)+OH.sup.−(aq).fwdarw.CO.sub.3.sup.2−(aq)+H.sub.2O(I)   Eq. 7

HCO.sub.3.sup.−(aq)+CH.sub.3CH.sub.2O.sup.−(aq).fwdarw.CO.sub.3.sup.2−(aq)+CH.sub.3CH.sub.2OH(aq)   Eq. 8

[0038] The presence of the ethoxide ion in synergy with the hydroxyl ion in the aqueous solution promotes a significant increase in the efficiency of CO.sub.2 absorption, when compared to the aqueous solution of monoethanolamine at the same concentration of the reagent.

[0039] The regeneration by chemical precipitation was carried out by percolating through a metering pump the saturated solvent at a flow rate of 15 L/h over a fixed bed of 10 cm height of calcium hydroxide semispheres of 8 mm in diameter. The regeneration efficiency is followed by acid titration of the solvent and fixed bed material, to quantify the carbonate soluble in the solvent and insoluble in the fixed bed. Regeneration by chemical precipitation was carried out at room temperature (25° C.). It was observed that the regeneration is not immediate, but that it occurs significantly to promote the reuse of the solvent in chemical absorption after 15 min of percolation of the saturated solvent on the fixed bed containing calcium hydroxide semispheres.

[0040] The chemical regeneration of the solvent takes place through the following reactions (Equations 9 and 10):

Ca(OH).sub.2 (aq)+CO.sub.3.sup.2−(aq).fwdarw.CaCO.sub.3 (s)+2 OH.sup.−(aq)   Eq. 9

Ca(OH).sub.2(aq)+HCO.sub.3.sup.−(aq).fwdarw.CaCO.sub.hd 3(s)+OH.sup.−(aq)+H.sub.2O(I)   Eq. 10