METHOD OF CAPTURING CARBON DIOXIDE

Abstract

The present invention relates to a method of extracting carbon dioxide (CO.sub.2) gas from an aqueous solution comprising dissolved CO.sub.2, the method comprising: (a) contacting the aqueous solution with dissolved CO.sub.2 with an organic phase; (b) heating the aqueous solution and the organic phase to a temperature of at least 50 C., whereby the CO.sub.2 migrates from the aqueous solution to the organic phase; and (c) separating the CO.sub.2 from the organic phase, wherein the aqueous solution comprises at least 50% water by weight at a temperature of 10 C. to and a base; the organic phase has a higher CO.sub.2 solubility relative to water solubility; and the aqueous solution and the organic phase are in direct contact with each other and are maintained as two separate phases.

Claims

1. A method of extracting carbon dioxide (CO.sub.2) gas from an aqueous solution comprising dissolved CO.sub.2, the method comprising: (a) contacting the aqueous solution with dissolved CO.sub.2 with an organic phase; (b) heating the aqueous solution and the organic phase to a temperature of at least 50 C., whereby the CO.sub.2 migrates from the aqueous solution to the organic phase; and (c) separating the CO.sub.2 from the organic phase, wherein the aqueous solution comprises at least 50% water by weight at a temperature of C to 40 C. and a base; the organic phase has a higher CO.sub.2 solubility relative to water solubility; and the aqueous solution and the organic phase are in direct contact with each other and are maintained as two separate phases.

2. The method of claim 1, wherein the base is selected from the group consisting of an amine, a hydroxide or a mixture thereof.

3. The method of claim 1, wherein the organic phase comprises a liquid carbon-based organic solvent that comprises at least one alkyl group.

4. The method of claim 1, wherein the organic phase is at least one alkane.

5. The method of claim 1, wherein the CO.sub.2 in the aqueous solution is first captured from a gas mixture and the flow of the gas mixture is directed through the aqueous solution to obtain the aqueous solution comprising dissolved CO.sub.2.

6. The method of claim 1, further comprising separating the aqueous solution from the organic phase after step (b) at the same temperature as in step (b).

7. The method of claim 6, further comprising cooling the aqueous solution separated from the organic phase and recycling the cooled aqueous solution.

8. The method of claim 6, wherein the CO.sub.2 is separated from the organic phase in step (c) under cooling the organic phase comprising CO.sub.2 and releasing the pressure from the organic phase.

9. The method of claim 8, further comprising recycling the organic phase to step (a).

10. The method of claim 1 wherein the organic phase comprises a solid organic polymer.

11. The method of claim 1, wherein in step (b), the aqueous solution and the organic phase are heated to a temperature between 50 C. and 200 C.

12. The method of claim 1, wherein the CO.sub.2 is separated from the organic phase in step (c) by contacting the organic phase with a aqueous production medium comprising at least one acetogenic cell and wherein the aqueous production medium is contacted with hydrogen (H.sub.2) to produce at least one organic acid and/or alcohol from the CO.sub.2 separated from the organic phase in step (c).

13. The method of claim 12, further comprising the step of contacting the organic acid and/or alcohol with a second organism capable of converting the organic acid and/or alcohol to at least one fatty acid.

14. The method of claim 12, further comprising separating the organic phase from the aqueous production medium and recovering the organic acid and/or alcohol is by contacting the aqueous production medium comprising the produced organic acid and/or alcohol with at least one liquid extractant wherein the liquid extractant is an alkyl-phosphine oxide or at least one trialkylamine.

15. An apparatus for carrying out the method according to claim 1, the apparatus comprising a first chamber (1), wherein the aqueous phase dissolving the CO.sub.2 is contacted with the organic phase, and comprising a heating device (2) for heating the aqueous phase and the organic phase, an inlet stream (3) for directing the aqueous phase dissolving the CO.sub.2 into the first chamber (1), a second chamber (4), an organic phase stream (5) for directing the organic phase from the second chamber (4) to the first chamber (1), an aqueous stream (6) directing the aqueous phase after heating and separation from the organic phase comprising CO.sub.2 to step (a) and comprising a cooling device (7) for cooling down the aqueous phase before recycling to step (a), a third chamber (10) for separating residual water (11) from the organic phase, an organic phase outlet stream (8) comprising a cooling device (9) for cooling down the organic phase before being fed to the third chamber (10), an organic phase CO.sub.2 feeding stream (12) feeding the organic phase dissolving CO.sub.2 to the second chamber (4), wherein the pressure is released, and wherein a pure CO.sub.2 gas stream (13) from the organic phase is released and from where the organic phase is returned to the first chamber (1) through the organic phase stream (5).

Description

BRIEF DESCRIPTION OF THE FIGURES

[0096] FIG. 1 is a schematic drawing of an apparatus according to the present invention.

[0097] FIG. 2 is a schematic picture of a device for carrying out the method according to the present invention wherein the organic phase is a solid organic polymer.

[0098] FIG. 3 is the set-up used for Example 7.

[0099] FIG. 4 is a schematic picture of a device for carrying out the method according to the present invention wherein the organic phase is an organic solution/liquid organic phase.

EXAMPLES

Example 1

[0100] An aqueous phase containing 9.9 wt. % CO.sub.2, 63.1 wt. % H.sub.2O and 27.1 wt. % MEA (Monoethanolamine) was mixed with hexadecane as a organic phase in a wt. ratio of 1:1 in a chamber at 30 C.

[0101] The chamber was closed and heated up to 100 C. The organic phase was analyzed by GC. It contained 0.17 wt. % CO.sub.2 and no MEA.

[0102] The chamber was deloaded by separating half of the organic phase from the residue. The organic phase contained 0.17 wt. % CO.sub.2.

[0103] The residue was cooled down to 30 C., mixed again with pure solvent to achieve a phase ratio of 1:1 again.

[0104] The chamber was heated up to 100 C. again. The organic phase was analyzed by GC. It contained wt. % CO.sub.2 and no MEA.

[0105] The chamber was deloaded by separating half of the organic phase from the residue.

[0106] The solvent phase contained 0.16 wt. % CO.sub.2.

[0107] The residue was cooled down to 30 C., mixed again with pure organic phase to achieve a phase ratio of 1:1 again.

[0108] The chamber was heated up to 100 C. again. The organic phase was analysed by GC. It contained 0.14 wt. % CO.sub.2 and no MEA.

[0109] The chamber was deloaded by separating half of the organic phase from the residue.

[0110] The solvent phase contained 0.14 wt. % CO.sub.2.

[0111] The residue was cooled down to 30 C., mixed again with pure organic phase to achieve a phase ratio of 1:1 again.

[0112] The chamber was heated up to 100 C. again. The organic phase was analysed by GC. It contained wt. % CO.sub.2 and no MEA.

[0113] The chamber was deloaded by separating half of the organic phase from the residue.

[0114] The solvent phase contained 0.13 wt. % CO.sub.2.

[0115] This example shows that CO.sub.2 can be transferred from a scrubbing solution into an alkyl containing organic phase avoiding water losses and because of avoiding water evaporation also energy losses as described in the art.

Example 2

[0116] Two parts of aqueous phase and one part of an organic phase consisting of 100% TAPO were kept under 1 bar 100% CO.sub.2 atmosphere at pH=5.8 at two different temperatures of 23 C. and 50 C.

[0117] The pH was set by a mixture of ammonia and hexanoic acid. The aqueous phase thus contained ammonia and hexanoic acid. The CO.sub.2 concentrations of both phases were measured using gas chromatography (GC). The CO.sub.2 concentration in the aqueous phase dropped from 1.5 mg/g at 23 C. to 0.65 mg/g at 50 C. or 57%. The CO.sub.2 concentration in the organic phase dropped from 2.5 mg/g to 1.7 mg/g or 32%. The water concentration of the organic phase dropped from 13.5 to 9.6 mg/g as the temperature increased.

[0118] This showed that the limited water absorbing alkyl containing organic solvent (TAPO) lost relatively less CO.sub.2 solubility with rising temperatures than water. That meant that increasing the temperature transferred CO.sub.2 from the aqueous to the organic phase. In contrast, water was transferred from the organic phase to the aqueous phase rising the temperature, because the water solubility in the organic phase dropped with rising temperatures. Therefore, no water was lost from the aqueous phase.

Example 3

[0119] Two parts of aqueous phase and one part of an organic phase consisting of 50% TAPO and 50% hexadecane were kept under 1 bar 100% CO.sub.2 atmosphere at pH=5.8 at two different temperatures of 23 C. and 50 C. The pH was set and maintained using a mixture of ammonia and hexanoic acid. The CO.sub.2 concentrations of both phases were measured by GC. The CO.sub.2 concentration of the aqueous phase dropped from 1.7 mg/g at 23 C. to 0.73 mg/g at 50 C. or 57%. The CO.sub.2 concentration of the organic phase dropped from 3.1 mg/g to 2.1 mg/g or 32%. The water concentration of the organic phase was dropped from 5.1 to 4.4 mg/g as the temperature increased.

[0120] This showed that the limited water absorbing alkyl containing organic solvent (TAPO) with hexadecane has a higher CO.sub.2 solubility than water at higher temperatures and a lower CO.sub.2 solubility than water at lower temperatures.

[0121] This showed that the limited water absorbing alkyl containing organic phase (TAPO) lost relatively less CO.sub.2 solubility with rising temperatures than water. That meant that increasing the temperature transferred CO.sub.2 from the aqueous to the organic phase. In contrast, water was transferred from the organic phase to the aqueous phase rising the temperature, because the water solubility in the organic phase dropped with rising temperatures. Therefore, no water was lost from the aqueous solvent.

Example 4

[0122] Two parts of aqueous phase and one part of an organic phase consisting of 6 wt. % TOPO and 94 wt. % hexadecane were kept under 1 bar 100% CO.sub.2 atmosphere at a pH between 5.8 and 6.2 at a temperature of 37 C. The pH was set by a mixture of ammonia and hexanoic acid. The CO.sub.2 concentrations of both phases were measured by GC. The CO.sub.2 concentration of the aqueous phase dropped only very slightly at pH=6.2 from 1.2 mg/g to 1.1 mg/g. The CO.sub.2 concentration of the organic phase dropped also only very slightly from 2.3 mg/g to 2.1 mg/g. The water concentration of the organic phase was 0.3 mg/g.

Example 5

[0123] Two parts of aqueous phase and one part of an organic phase consisting of 6 wt. % TAPO and 94 wt. % hexadecane were kept under 1 bar 100% CO.sub.2 atmosphere at a pH between 5.8 and 6.2 at a temperature of 37 C. The pH was set by a mixture of ammonia and hexanoic acid. The CO.sub.2 concentrations of both phases were measured by GC. The CO.sub.2 concentration of the aqueous phase dropped only very slightly at pH=6.2 from 1.3 mg/g to 1.1 mg/g. The CO.sub.2 concentration of the organic phase was rose also only slightly from 2.5 mg/g to 2.6 mg/g. The water concentration of the organic phase was between 0.1 and 0.2 mg/g.

[0124] In Examples 3 to 5, the temperature was not varied but the pH was raised from 5.8 to 6.2. These examples show that the CO.sub.2 solubilities in different organic solvents were very similar and are not affected by changes in pH. Again, in all cases no water was lost from the aqueous phase.

Example 6

[0125] Two parts of aqueous phase and one part of an organic phase consisting of 100 wt. % TAPO were kept under 1 bar 100% CO.sub.2 atmosphere at a pH between 5.8 and 6.2 at a temperature of 37 C. The pH was set by a mixture of ammonia and hexanoic acid. The CO.sub.2 concentrations of both phases were measured by GC. The CO.sub.2 concentration of the aqueous phase rose only very slightly at pH=6.2 from 1.0 mg/g to 1.1 mg/g. The CO.sub.2 concentration of the organic phase dropped also only very slightly from 2.5 mg/g to 2.4 mg/g. The water concentration of the organic phase was between 8.3 and 8.5 mg/g. In this example 6, the pH was raised from 5.8 to 6.2 and the solvent was varied. Again, it was shown that the CO.sub.2 solubilities in different organic solvents were very similar and were not affected by changes in pH and no water was lost. This confirmed that the organic solvent or solid of the organic phase itself does not have a significant influence on the effectiveness of the method of the present invention provided the organic phase has a higher CO.sub.2 solubility relative to water solubility. In example 6, pure TAPO, which has a higher water than CO.sub.2 solubility, is not effective to be used as an organic phase according to any aspect of the present invention. In contrast, hexadecane and mixtures of hexadecane with TAPO are suitable.

Example 7

[0126] Desorption of CO.sub.2 Relative to Water (Diffusion) in the Mixture of CO.sub.2+Water+Monoethanolamine+Hexadecane

[0127] Materials and Methods

[0128] Table 1 shows the materials that were used in this example. The substances used were obtained commercially and used for the measurements without further purification. The aqueous monoethanolamine mixture was prepared gravimetrically. The mixture and hexadecane were degassed by repeated evacuation of the vapour phase in cooled storage vessels.

TABLE-US-00001 TABLE 1 Materials used in Example 7, Components DDB-Nummer Source Purity*/% Hexadecane 516 Aldrich 99 Monoethanolamine (MEA) 546 Aldrich >99 Carbon dioxide (CO.sub.2) 1050 Air Liquide 99.995 Water 174 *Manufacturer information

[0129] The method was carried out in a cylinder in a set-up as shown in FIG. 3 where organic solution refers to hexadecane, aqueous solution refers to MEA and CO.sub.2 solution and gas refers to helium, CO.sub.2 and water. The cylinder was partially filled with hexadecane heated up to 100 C. and pressurized with Helium to 20 bar. An aqueous solution mixed with 30 wt % Monoethanolamine (MEA) and 0.415 mol CO.sub.2/mol MEA was added slowly below the hexadecane phase, avoiding mixing and gas bubbles until an equilibrium is reached. The volume ratio of the hexadecane and the aqueous phase was 5:1. In the gas phase the mol ratio of CO.sub.2 and water was measured. After one minute the ratio was 0.905:0.095. After four minutes the ratio was 0.865:0.135. After 121 min the equilibrium was reached and the ratio 0.382:0.618. This shows that CO.sub.2 can be extracted from an aqueous solution very effectively with only very little water loss if an organic liquid or solid layer is present through which CO.sub.2 and water have to migrate, meaning have to be absorbed and desorbed.