Compounds for the capture of carbon dioxide from gaseous mixtures and subsequent release, related process and plant

Abstract

The present invention relates to novel molecules suitable to the use in the separation/removal of carbon dioxide from gaseous mixtures as liquid-phase carbon dioxide absorbers and suitable to allow the subsequent release of the absorbed carbon dioxide in form of different ionic liquids, preferentially a glycine salt with choline hexanoate, ester between glycine and hexanoic alcohol (hexyl glycinate) and glycerol ester with glycine and hexanoic acid. The present invention also relates to a method and a plant for the capture of carbon dioxide from gaseous mixtures by using an absorber for carbon dioxide in liquid phase with a heating jacket.

Claims

1. A compound for the absorption of carbon dioxide in the form of ionic liquids having the following general formula (I) or (II): ##STR00009## wherein R3, R4, R5 are each independently H, a C1-C6 alkyl group or an aromatic group, R2 is a C1-C6 alkyl group, R1 is a C5-C19 alkyl group, and X.sup. is a carboxylate anion of a natural or artificial amino acid, or in the form of glycerol esters having the general formula (III): ##STR00010## wherein the groups R6, R7 and R8 are selected from H, an acyl group of formula R.sup.9C(OR) where R9 is a C5-C19 alkyl group, an amino-acyl group deriving from a natural or artificial amino acid or an acyl residue of ectoin of formula (IV), ##STR00011## and wherein at least one of the groups R6, R7, R8 is an acyl group of formula R.sup.9C(OR) and at least one of the groups R6, R7, R8 is an amino-acyl group deriving from a natural or artificial amino acid or an acyl residue of ectoin of formula (IV), or in the form of esters, having the general formula (V)
R.sup.10ORR.sup.11(V) wherein R10 is a C5-C19 alkyl group and R11 is an amino-acyl group deriving from a natural or artificial amino acid or an acyl residue of ectoin of formula (IV).

2. The compound for the absorption of carbon dioxide according to claim 1, which is selected from the group consisting of a glycine salt with choline hexanoate, an ester between glycine and hexanoic alcohol (hexyl glycinate) and a glycerol ester with glycine and hexanoic acid having the following formula: ##STR00012##

3. A process for the separation of carbon dioxide from a gaseous mixture, the process comprising the step of contacting said gaseous mixture containing carbon dioxide with at least one absorbent liquid comprising a compound, wherein said compound is an ionic liquid of the following general formula (I) or (II): ##STR00013## wherein R3, R4, R5 are each independently H, a C1-C6 alkyl group or an aromatic group, R2 is a C1-C6 alkyl group, R1 is a C5-C19 alkyl group, and X.sup.31 0 is a carboxylate anion of a natural or artificial amino acid, and/or at least one glycerol ester having the general formula (III): ##STR00014## wherein the groups R6, R7 and R8 are selected from H, an acyl group of formula R.sup.9C(OR) where R9 is a C5-C19 alkyl group, an amino-acyl group deriving from a natural or artificial amino acid or an acyl residue of ectoin of formula (IV), ##STR00015## and wherein at least one of the groups R6, R7, R8 is an acyl group of formula R.sup.9C(OR) and at least one of the groups R6, R7, R8 is an amino-acyl group deriving from a natural or artificial amino acid or an acyl residue of ectoin of formula (IV), or in the form of an ester, having the general formula (V):
R.sup.10ORR.sup.11(V) wherein R10 is a C5-C19 alkyl group and R11 is an amino-acyl group deriving from a natural or artificial amino acid or an acyl residue of ectoin of formula (IV) under conditions such as to absorb CO.sub.2 in said absorbent liquid.

4. The process according to claim 3, wherein the absorbent liquid is composed of said compound or a mixture comprising said compound.

5. The process according to claim 4, wherein said absorbent liquid is composed of: a mixture between at least one ionic liquid according to the formula (I) or (II), and/or at least one ester according to the formula (III) or (V), and a polar solvent.

6. The process according to claim 4, wherein said absorbent liquid is composed of: a mixture between at least one ionic liquid according to the formula (I) or (II), and/or at least one ester according to the formula (III) or (V), and two immiscible solvents, wherein the immiscible solvents are an aprotic polar solvent and an apolar solvent.

7. The process according to claim 5, wherein said aprotic polar solvent has a boiling point above 200 C.

8. The process according to claim 6, wherein said aprotic polar solvent has a boiling point above 200 C.

9. The process according to claim 8, wherein said apolar solvent has a boiling point above 200 C.

10. The process according to claim 5, further comprising a releasing step of CO.sub.2 in which the absorbent liquid containing CO.sub.2 is treated under conditions to allow the desorption of CO.sub.2, thereby obtaining a gaseous phase containing CO.sub.2 and a regenerated absorbent liquid.

11. A plant for the separation of CO.sub.2 from a gaseous mixture and subsequent release of CO.sub.2, comprising a column having: an absorption section (2) comprising means (5) for feeding a gaseous stream containing CO.sub.2, means (6) for feeding a stream of absorbent liquid, and means (8) for the exit of a gaseous stream deprived of CO.sub.2, a desorption (release of CO.sub.2) and regeneration section (3) in fluid communication with said absorption section (2), said desorption and regeneration section comprising output means (11) for a gaseous stream containing CO.sub.2 and output means (10) for a liquid stream of regenerated absorbent liquid, wherein said absorption section (2) and said desorption and regeneration section (3) each comprise a sequence of first areas (51) of liquid/gas exchange, alternated with a sequence of second areas (52) for the collection of absorbent liquid and a plurality of interspaces (55) arranged externally and adjacent to corresponding first liquid/gas exchange areas (51), each of said interspaces (55) putting in fluid communication a second collection area (52) with a successive first exchange area (51) so as to transfer said absorbent liquid from a second collection area (52) to a first exchange area (51) subsequent thereto, a jacket (56) outside said absorption section (2) and a jacket (56) outside said desorption and regeneration section (3), each run through by a thermal exchange fluid to carry out a thermal exchange between the absorbent liquid running through said interspaces (55) and said thermal exchange fluid, wherein each interspace (55) has an outer length (55a) with a descending path, followed by an inner length (55b) with an ascending path.

12. A process for the absorption of CO.sub.2 and subsequent release by means of the plant according to claim 11, the process comprising the steps of: feeding a gaseous stream containing CO.sub.2 and a stream of absorbent liquid contacting said gaseous stream containing CO.sub.2 and said stream of absorbent liquid in said absorption section (2), obtaining a gaseous stream substantially deprived of CO.sub.2 and a stream of absorbent liquid containing CO.sub.2, feeding said stream of absorbent liquid containing CO.sub.2 in said desorption and regeneration section (3), obtaining a gaseous stream containing CO.sub.2 and a flow of regenerated absorbent liquid.

13. The process according to claim 5, wherein the polar solvent is an aprotic polar solvent.

14. The process according to claim 7, wherein the aprotic polar solvent is selected from the group consisting of cyclic carbonates, propylene glycol, fatty alcohols with a number of carbon atoms higher than 8 and polyethylene glycol.

15. The process according to claim 8, wherein the aprotic polar solvent is selected from the group consisting of cyclic carbonates, propylene glycol, fatty alcohols with a number of carbon atoms higher than 8 and polyethylene glycol.

16. The process according to claim 9, wherein the apolar solvent is selected from the group consisting of vegetal oils, carvone and linear hydrocarbons with a number of carbon atoms above 12.

17. The plant according to claim 11, wherein the stream of absorbent liquid is in countercurrent with respect to said gaseous stream containing CO.sub.2 in said absorption section (2).

18. The plant according to claim 11, wherein the first areas (51) of liquid/gas exchange are filled with a bed of inert material.

19. The process according to claim 12, wherein the stream of absorbent liquid is in countercurrent in said absorption section (2).

Description

(1) Further characteristics and advantages of the present invention will be apparent from the following description of a preferred embodiment, given by way of illustrative, non-limiting example, with reference to the appended drawings, in which:

(2) FIG. 1 schematically shows a plant for the separation (absorption) of carbon dioxide from a gaseous mixture and subsequent release according to an embodiment of the method of the invention;

(3) FIGS. 2 and 3 show a part and a detail, respectively, of the plant of FIG. 1.

(4) FIG. 4 shows a graph illustrating the CO.sub.2 concentration change in the absorbent liquid in an implementation example of the process according to the invention, compared to the CO.sub.2 change of a compound not according to the invention;

(5) FIG. 5 shows a graph illustrating the CO.sub.2 concentration change in the absorbent liquid in another implementation example of the process according to the invention, compared to the CO.sub.2 change of a compound not according to the invention;

(6) FIG. 6 shows a graph illustrating the CO.sub.2 concentration change in the absorbent liquid in a further implementation example of the process according to the invention, compared to the CO.sub.2 change of a compound not according to the invention;

(7) With reference to the FIGS. 1-3, a plant for the separation (absorption) of carbon dioxide from a gaseous mixture and subsequent release according to a first embodiment of the method of the invention is generally indicated with the reference 1.

(8) The plant 1 comprises a first column 2 for the absorption of CO.sub.2, and a second column 3 for the release of CO.sub.2 and regeneration of the absorbent liquid, the above-mentioned columns being in a mutual fluid communication.

(9) The absorption column 2 has a first opening 5 for the inlet of the gaseous mixture containing carbon dioxide to be separated, located at or in the proximity of the bottom, a second opening 6 for the inlet of the liquid-phase absorber for carbon dioxide located at or in the proximity of the top of the first column 2, a first outlet opening 7, located at or in the proximity of the bottom of the first column 2, for the passage of the absorbent liquid containing CO.sub.2 in the second column 3, and a second outlet opening 8 located in the proximity of the top of the first column 2 for the exit of gases not absorbed by the absorbent liquid.

(10) The gaseous mixture containing CO2 is fed to the first opening 5 of the absorption column 2 through the flow line 46 which can suitably contain an insulation ball valve 47, a filter 48, and an electrovalve 49.

(11) The second column 3 for the release of CO2 and the regeneration of the solvent comprises an inlet opening 9 of the absorbent liquid containing CO2 coming from the first absorption column 2, the inlet opening 9 being arranged in the proximity of or at the top of the second column 3, a first outlet opening 10 for the regenerated absorbent liquid located in the proximity of or at the bottom of the second column 10, and a second opening 11 of a gaseous stream containing CO2 separated from the above-mentioned gaseous mixture.

(12) More particularly, as illustrated in the FIGS. 2-3, the first column 2 is a sequence of first liquid/gas exchange areas 51 filled with a bed of inert material alternated with a sequence of second absorbent liquid collection areas 52 exiting the first thermal exchange areas 51. Each second collection area 52 has an absorbent liquid collection chamber 53 descending from the first upper thermal exchange area 51 immediately antecedent thereto, such absorbent liquid being inserted from said first area 51 into the chamber 53 of the second area 52 through a corresponding opening 8.

(13) In each chamber 53 of a second collection area 52, the absorbent liquid is kept separated from the ascending gaseous stream containing CO2 running through the absorption column 2 in countercurrent with respect to the stream of absorbent liquid (arrow A). This is achieved by a plurality of tubes 54 connecting consecutive first exchange areas 51, each tube 54 passing through a second area 52 located between two consecutive first areas 51. Vice versa, in each first area 51, the ascending gaseous stream containing CO2 is in contact with the descending stream of absorbent liquid, thus carrying out a liquid/gas exchange which involves the absorption of CO2 in the absorbent liquid.

(14) The absorption column 2 further comprises a plurality of interspaces 55 arranged externally and adjacent to corresponding first liquid/gas exchange areas 51. Each of such interspaces 55 put a second collection area 52, and precisely a collection chamber 53 of such second area 52 in fluid communication with the inlet of the successive first exchange area 51, so as to transfer said absorbent liquid from a second collection area to a first exchange area successive thereto.

(15) In particular, each interspace 55 has an outer length 55a with a descending path followed by an inner length 55a with an ascending path, so as to make the absorbent liquid run a coil-shaped path before it is introduced in a successive first liquid/gas exchange area 51 (arrows B).

(16) Advantageously, the first column 2 is also provided with an jacket 56 external to the first absorption areas 51, the second collection areas 52, and the interspaces 55 of the absorption section 2 intended to be run through by a cooling fluid, so as to carry out a thermal exchange with the absorbent liquid running through said interspaces 55. In the present embodiment, the outer jacket is arranged vertically substantially along the entire length of the absorption column 2, and it can be divided into sections 56a in fluid communication with one another.

(17) With such solution, the absorbent liquid is inserted in each first liquid/gas exchange area 51 of the absorption column 2 under the optimal temperature conditions, of while minimizing thermal excursions between the central part of said first areas 51, farther from the outer jacket 56 run through by the cooling fluid, and the peripheral part of said first areas 51, nearer to the outer jacket 56 run through by the cooling fluid.

(18) The same solution can be advantageously adopted also in the desorption column 3, which can therefore have a plurality of regeneration areas 51, alternated with absorbent liquid collection areas 52, an interspace path 55 for the absorbent liquid to be transferred from a regeneration area 51 to a successive regeneration area 51, and an outer jacket to the areas 51,52 and the interspaces 55 to carry out an indirect thermal exchange, with an outer jacket which this time is run through by a heated fluid.

(19) The possibility to limit the thermal excursion in the columns 2 and 3 associated to the absorption and release processes, respectively, allows keeping in the two columns the absorbent liquid at a temperature preferably in a range between 70-80 C. for the regeneration column 3 and between 20-30 C. for the absorption column 2.

(20) The plant 1 further comprises a heat pump 12 in fluid communication with the upper sections 56a and the lower section 56a of the jacket 56 of the absorption column 2 through the flow lines (tubing) 13 and 14, respectively, and in fluid communication with the upper sections 56a and the lower section 56a of the jacket 56 of the regeneration column 3 through the flow lines (tubing) 15 and 16, respectively.

(21) The heat pump 12 advantageously allows subtracting heat from the thermal exchange fluid exiting the lower section 56a of the absorption column 2which reaches the pump 12 through the flow line 14 with the aid of a pump 17 in such line 14and transferring the heat extracted from the thermal exchange fluid exiting the lower section 56a of the regeneration column 3which reaches the pump 12 via the flow line 16 with the aid of a pump 18 in such line 16. The thermal exchange fluid heated by the heat pump 12 can then be inserted back in the upper section 56 of the outer jacket 56 of the regeneration column 3 through the flow line 15, while the thermal exchange fluid cooled by the heat pump 12 can then be inserted back in the upper section 56a of the outer jacket 56 of the absorption column 2 via the flow line 13, along which it can be subjected to a further cooling by a heat exchanged 19 arranged in-line.

(22) In this manner, the energy input from the outside is reduced.

(23) The plant 1 further comprises a further heat exchanger 20 in fluid communication with the columns 2,3, which receives in separated flows, through corresponding flow lines 21 and 22, the absorbent liquid containing absorbed CO2 exiting the outlet opening 7 of the absorption column 2 and the regenerated absorbent liquid exiting the outlet opening 10 of the regeneration column 3. In the heat exchanger 20, such separated flows are subjected to a suitable indirect thermal exchange, then they are sent to the columns 2,3, in particular, the regenerated absorbent liquid to the inlet opening 6 of the absorption column 2 through the flow line 23, for a successive absorption cycle, and the absorbent liquid containing absorbed CO2 to the inlet opening 9 of the regeneration column 2 through the flow line 24 for a successive subsequent cycle of CO2 release and regeneration of the absorbent liquid.

(24) Suitable means for the adjustment and control of the flows can be arranged along the flow lines 21,22,23 and 24, which, in particular, a maximum pressure valve 25, an insulation ball valve 26 in the flow line 22, check valves 33 in the flow lines 23 and 24, and electrovalves 27 in the flow lines 21, 23 and 24. Furthermore, a pressurizing pump 28 and a filter 29 can be provided in the flow line 22.

(25) The plant 1 further comprises a first cyclone 30 in fluid communication with the outlet opening 8 of the gaseous stream deprived of CO2 from the absorption column 2 through the flow line 31, and a second cyclone 34 in fluid communication with the outlet opening 11 of the gaseous stream containing CO2 separated from the release and regeneration column 3 through the flow line 32.

(26) The first cyclone 30 allows separating possible liquid dragged by the gaseous stream deprived of CO2 exiting the absorption column 2. The liquid separated in the first cyclone 30 is recycled to the absorption column 2 through the flow line 35, while the gaseous stream deprived of the liquid exiting the first cyclone 30 is recovered through the flow line 36.

(27) Advantageously, a suitable insulation ball valve 37 and a suitable check valve 38 can be inserted in the flow line 36.

(28) The second cyclone 30 allows separating the possible liquid carried by the gaseous stream containing CO2 separated from the releasing and regeneration column 3. The liquid separated in the second cyclone 34 is suitably recovered in the reservoir 40 through the flow line 39, while the gaseous stream deprived of the liquid exiting the second cyclone 34 is recovered via the flow line 41.

(29) Advantageously, a suitable check valve 38, a vacuum pump 42, and a heat exchanger 43 (gas cooler) can be inserted in the flow line 32, while a suitable filter 44 can be inserted in the flow line 41.

(30) Further characteristics and advantages of the present invention will be apparent from the following examples, of given by way of illustrative, non-limiting example.

EXAMPLE 1

(31) 0.2 moles of glycine salified with choline hexyl-ester (a compound according to the invention) is dissolved in 100 ml of a solution of propylene carbonate containing 10% in volume vegetal oil. The solution is stirred for 20 minutes and sonicated during 5 minutes until a stable emulsion is obtained.

(32) A comparison emulsion containing the same mixture of solvents and glycine salified with choline (a compound not according to the invention) is then similarly prepared.

(33) Next, the emulsion according to the invention is put in an absorption column filled with Raschig rings to increase the gas-liquid contact surface. Next, a gas composed of 10% CO.sub.2 in nitrogen with a flow of 45 L/h is made to flow. During this step, the temperature measured with the aid of a thermocouple passes from the initial 20 C. to 32 C. The absorption is stopped when the CO.sub.2 detector arranged at the column outlet opening measures, inside the exiting gaseous mixture, a mass % amount of CO.sub.2 above 5%. The absorption step takes 30 minutes on average (Such step is highlighted in the graph of FIG. 6 by a double arrow). The releasing step is monitored during a temperature scan of the column, starting from 30 C. up to 130 C., with a scanning rate of 2 C./min, and it is subsequently kept at 130 C. during 50 minutes.

(34) The same type of procedure is carried out in order to test a comparison emulsion containing glycine salified with choline. The results of the comparison test were compared to the one previously carried out on the emulsion containing glycine salified with choline, a compound according to the invention.

(35) With reference to FIG. 4, the release temperature of a comparison emulsion is sensibly higher compared to that of the emulsion containing glycine salt with choline hexanoate. Again, the curve slope, in the decreasing phase, indicates a higher difficulty of the Gly-Ch molecule in releasing CO.sub.2 compared to the ester.

EXAMPLE 2

(36) The procedure of the example 1 was repeated replacing the ionic liquid of such example with the following glycerol ester with glycine and hexanoic acid.

(37) ##STR00008##

(38) Results completely comparable to those obtained in example 1 were obtained by the use of the glycine salt with choline esterified with hexanoic acid. In particular, the ester tested in this example showed reactivity to CO.sub.2 essentially identical to that of the ionic liquid of the example 1, having in fact amino acids (in particular, glycine) with the same amine group.

EXAMPLE 3

(39) The procedure of the example 1 was repeated in order to obtain and test two different 3M propylene carbonate solutions of hexyl glycinate (a compound according to the invention) and potassium glycinate (a compound non according to the invention), respectively.

(40) With reference to FIG. 5, results completely comparable to those obtained in example 1 were obtained. In particular, the absorption shows about the same trend: from the graph, it is possible to indicate a flat portion during the first 30 minutes, which precisely correspond to the absorption step, where the column temperature is kept at a value of 20 C. Furthermore, the carbon dioxide release occurs for the ester at a considerably lower temperature compared to that for the potassium salt: the release starts at 55 C., and at approximately 80 C. the amount of released CO.sub.2 is more than 80%. Instead, for the salt the release occurs at a temperature above 120 C.

EXAMPLE 4

(41) The procedure of the example 1 was repeated in order to obtain a 3M propylene carbonate solution of hexyl glycinate.

(42) Such solution is arranged in an absorption column filled with Raschig rings to increase the gas-liquid contact surface. Next, a gas composed of 10% CO.sub.2 in nitrogen with a flow of 45 L/h is made to flow. During this step, the temperature measured with the aid of a thermocouple passes from the initial 20 C. to final 32 C. The absorption is stopped when the CO.sub.2 detector arranged at the column outlet opening measures, inside the exiting gaseous mixture, a mass % amount of CO.sub.2 above 5%. The absorption step takes 30 minutes on average. The successive releasing step is carried out while keeping the column at a constant temperature of 70 C. during 60 minutes. The comparison solution is an aqueous solution of 30% (5M) ethanolamine (MEA).

(43) With reference to FIG. 6, while having the same efficiency in the absorption step, when the solutions are subjected to a temperature of 70 C. in a nitrogen flow, the releasing rate is definitely in favor of the ester, which releases more than 65% CO.sub.2 in the first 20 minutes; instead, the control solution containing MEA has a release quantitatively much lower and constant throughout the duration of the experiment (with a considerable loss of vapor).