Method and device for separating acid gases from a gas mixture

Information

  • Patent Grant
  • 9221007
  • Patent Number
    9,221,007
  • Date Filed
    Tuesday, November 13, 2012
    11 years ago
  • Date Issued
    Tuesday, December 29, 2015
    8 years ago
Abstract
The invention is directed to a method for separating acid gases from a gas mixture in which the gas mixture is contacted with an absorption medium which comprises water and at least one amine and has a phase-separation temperature in the range from 0 to 130° C. In addition, the invention is directed to a device which can be used for carrying out this method.
Description
FIELD OF THE INVENTION

The invention relates to a method and a device for separating an acid gas, in particular CO2, from a gas mixture.


BACKGROUND OF THE INVENTION

In many industrial and chemical operations there are gas streams which contain an unwanted amount of acid gases, more particularly CO2, the amount of which must be reduced for further processing, for transportation or for the prevention of CO2 emissions.


On the industrial scale, CO2 is typically absorbed from a gas mixture by using aqueous solutions of alkanolamines as an absorption medium. The loaded absorption medium is regenerated by heating, depressurization to a lower pressure or stripping, and the carbon dioxide is desorbed. After the regeneration process, the absorption medium can be used again. These methods are described for example in Rolker, J.; Arlt, W.; “Abtrennung von Kohlendioxid aus Rauchgasen mittels Absorption” [Removal of carbon dioxide from flue gases by absorption] in Chemie Ingenieur Technik 2006, 78, pages 416 to 424, and also in Kohl, A. L.; Nielsen, R. B., “Gas Purification”, 5th edition, Gulf Publishing, Houston 1997.


A disadvantage of these methods, however, is that the removal of CO2 by absorption and subsequent desorption requires a relatively large amount of energy and that, on desorption, only a part of the absorbed CO2 is desorbed again, with the consequence that, in a cycle of absorption and desorption, the capacity of the absorption medium is not sufficient. In addition, during a desorption by heating, a thermal and oxidative breakdown of the amine occurs on the hot heat-exchange surfaces.


WO 2008/015217 proposes to use an absorption medium, showing a phase separation into two liquid phases upon heating, for a method for separating CO2 from gas mixtures in order to decrease the energy requirement for the desorption of CO2. In this method the CO2 is desorbed at a high CO2 partial pressure and so only an insufficient capacity of the absorption medium is achieved in a cycle of absorption and desorption.


US 2009/199709 and US 2010/104490 describe methods using such an absorption medium, where the absorption medium loaded with an acid gas is heated to form two liquid phases, these phases are separated and only the acid-gas-rich liquid phase is fed to a desorption column, while the liquid phase that is low in acid gas is returned directly to the absorption. In these methods, however, some of the gas that is bound in the loaded absorption medium is already liberated in the apparatus in which the phase separation proceeds. In practice, this leads to problems, since the acid gas is generally liberated from the heavier phase and ascending gas bubbles counteract the phase separation. In addition, the method of US 2009/199709 and US 2010/104490 may not be operated stably with the devices used in US 2009/199709 and US 2010/104490, if two liquid phases are also formed in the desorption column.


U.S. Pat. No. 4,251,494 describes a method using an absorption medium which comprises water, a sterically hindered amine and an alkali metal carbonate. In this method, the composition of the absorption medium is selected in such a manner, that after the desorption the absorption medium forms two liquid phases in the evaporator of the desorption column due to evaporation of water and the temperature rise, which are separated in the evaporator and are returned to the absorber at different points. The method requires an absorption medium having a high content of alkali metal carbonate, which has an undesirably high corrosivity. In addition, just as with the use of a single-phase absorption medium, a thermal and oxidative breakdown of the amine occurs on the hot heat-exchange surfaces of the evaporator.


There is therefore still a need for a method and a device for separating acid gases from a gas mixture, in which the energy requirement is reduced by forming two liquid phases during the desorption, and which does not have the disadvantages of the methods and devices known from the prior art.


SUMMARY OF THE INVENTION

The invention therefore relates to a method for separating acid gases from a gas mixture, comprising absorption of acid gases by contacting the gas mixture in an absorber with an absorption medium that comprises water and at least one amine, obtaining a loaded absorption medium, and desorption of acid gases from the loaded absorption medium by stripping with steam in a desorption column, wherein the absorption medium used shows phase separation into two liquid phases upon heating above a phase-separation temperature in the range from 0 to 130° C. In the method according to the invention, the desorption is carried out at a temperature at which a phase separation into a water-rich liquid phase and a water-poor liquid phase proceeds in the desorption column, the resultant water-rich liquid phase and water-poor liquid phase are separated from one another, water-rich liquid phase is fed to an evaporator in which steam is generated with which acid gases are stripped in the desorption column, and water-poor liquid phase and water-rich liquid phase are returned to the absorber as absorption medium.


The invention also relates to a device for separating acid gases from a gas mixture, comprising an absorber (1), a desorption column (2) having a mass-transfer zone (3), an evaporator (5) and a phase-separation device (6) for separating two liquid phases having a feed point (7) and separate withdrawal points (8, 9) for the liquid phases. The evaporator (5) is arranged separately from the phase-separation device (6). The phase-separation device (6) comprises withdrawal points (8, 9) for a water-poor liquid phase and a water-rich liquid phase. The mass-transfer zone (3) comprises a liquid outlet (4) which is connected to the feed point (7) of the phase-separation device. The device according to the invention further comprises connecting conduits (10, 11) from the withdrawal point (8) for water-rich liquid phase to the evaporator (5) and from the withdrawal point (9) for water-poor liquid phase to the absorber (1).





BRIEF DESCRIPTION OF THE DRAWINGS


FIG. 1 shows as a flow diagram an embodiment of a device according to the invention in which the phase-separation device (6) is arranged separately from the desorption column (2).



FIG. 2 shows as a flow diagram a preferred embodiment of a device according to the invention in which the phase-separation device (6) is arranged within the desorption column (2) below the mass-transfer zone (3).





DETAILED DESCRIPTION OF THE INVENTION

In the method according to the invention for separating acid gases from a gas mixture, the gas mixture may be a natural gas, a methane-containing biogas from a fermentation, composting or sewage treatment plant, a combustion off-gas, an off-gas from a calcination reaction, such as the burning of lime or the production of cement, a residual gas from a blast-furnace operation for iron production or a gas mixture resulting from a chemical reaction, such as, for example, a synthesis gas comprising carbon monoxide and hydrogen, or a reaction gas from a steam-reforming hydrogen production process. The gas mixture is preferably a combustion off-gas, a natural gas or a biogas, particularly preferably a combustion off-gas, for example from a power plant.


The gas mixture contains at least one acid gas, preferably one or more acid gases from the group CO2, COS, H2S, CH3SH and SO2, particularly preferably CO2. A combustion off-gas is preferably desulphurized beforehand, i.e. SO2 is removed from the gas mixture using a desulphurizing method known from the prior art, preferably by gas scrubbing with milk of lime, before the method according to the invention is carried out.


Prior to contacting with the absorption medium the gas mixture preferably has a CO2 content in the range from 0.1 to 50% by volume, particularly preferably in the range from 1 to 20% by volume, most preferably in the range from 10 to 20% by volume.


The gas mixture may further contain oxygen in addition to acid gases, preferably at a fraction of 0.1 to 25% by volume, and particularly preferably at a fraction of 0.1 to 10% by volume.


In the method according to the invention, the gas mixture is contacted in an absorber with an absorption medium which comprises water and at least one amine and which on heating to above a phase-separation temperature, which is in the range from 0 to 130° C., shows a phase separation into two liquid phases. The phase separation temperature relates in this case to the non-loaded absorption medium without acid gases. Amines, for which mixtures with water have a phase-separation temperature in the range from 0 to 130° C., are known to those skilled in the art from the prior art, for example from WO 2008/015217, US 2009/199709 and US 2010/104490. Preferably, amines are used which, at 100° C., have a solubility of less than 100 g of amine in 1 l of water, particularly preferably less than 60 g of amine in 1 l of water, and most preferably less than 10 g of amine in 1 l of water.


The content of alkali metal salts in the absorption medium is preferably less than 10% by weight, particularly preferably less than 5% by weight, and in particular less than 2% by weight.


In a preferred embodiment, the absorption medium comprises at least one amine of formula (I)




embedded image


wherein the radicals R1 and R2 independently of one another are hydrogen or aliphatic radicals having 1 to 10 carbon atoms that can be substituted with amino groups or alkyl amino groups.


In a further preferred embodiment, the absorption medium comprises at least one amine of formula (I) for which the radicals R1 and R2 independently of one another are hydrogen or alkyl radicals having 1 to 6 carbon atoms, wherein, particularly preferably, R1 is hydrogen and R2 is an alkyl radical having 1 to 6 carbon atoms. Most preference is given to the compounds 4-(n-propylamino)-2,2,6,6-tetramethylpiperidine and 4-(n-butylamino)-2,2,6,6-tetramethylpiperidine, for which R1 is hydrogen and R2 is n-propyl or n-butyl.


In a particularly preferred embodiment, the absorption medium comprises a first amine of formula (I), for which the radicals R1 and R2 independently of one another are hydrogen or alkyl radicals having 1 to 6 carbon atoms, and a second amine of formula (I), for which R1 is hydrogen and R2 is a radical (CH2)nNR3R4 where n=2 to 4, R3=hydrogen or alkyl radical having 1 to 4 carbon atoms, and R4=alkyl radical having 1 to 4 carbon atoms. For the first amine of formula (I), R1 is preferably hydrogen and R2 an alkyl radical having 1 to 6 carbon atoms, wherein R2 particularly preferably is n-propyl or n-butyl. The second amine of formula (I) is preferably 4-(3-dimethylaminopropylamino)-2,2,6,6-tetramethylpiperidine, for which n=3 and R3, R4=methyl, or 4-(2-ethylaminoethylamino)-2,2,6,6-tetramethylpiperidine, for which n=2, R3=methyl and R4=hydrogen. The weight ratio of first amine of formula (I) to second amine of formula (I) is then preferably in the range from 10:1 to 1:10, particularly preferably in the range from 3:1 to 1:5, and in particular in the range from 1:1 to 1:3.


Preferably, the absorption medium comprises 25 to 85% by weight water and 15 to 75% by weight amines of formula (I), in each case based on non-loaded absorption medium without acid gases.


By using an absorption medium which contains amines of the formula (I), a high capacity for the absorption of CO2 may be achieved, even in the case of low CO2 partial pressure. Furthermore, such absorption media are of low corrosivity, show a good stability towards oxidative and thermal breakdown and do not show foam formation in the method according to the invention.


In addition to water and amines of formula (I), the absorption medium may further contain at least one sterically unhindered primary or secondary amine as activator. A sterically unhindered primary amine in the context of the invention is a primary amine in which the amino group is bound to a carbon atom to which at least one hydrogen atom is bound. A sterically unhindered secondary amine in the context of the invention is a secondary amine in which the amino group is bound to carbon atoms to which in each case at least two hydrogen atoms are bound. The content of sterically unhindered primary or secondary amines is preferably 0.1 to 10% by weight, particularly preferably 0.5 to 8% by weight. Activators known from the prior art, such as, for example, ethanolamine, piperazine and 3-(methylamino)propylamine, are suitable as activators. 4-Amino-2,2,6,6-tetramethylpiperidine is also suitable. The addition of an activator leads to an acceleration of the absorption of CO2 from the gas mixture without losing absorption capacity.


In addition to water and amines, the absorption medium may further contain one or more physical solvents. The fraction of physical solvents can be up to 50% by weight. Suitable physical solvents are sulfolane, aliphatic acid amides, such as N-formylmorpholine, N-acetylmorpholine, N-alkyl-pyrrolidones, in particular N-methyl-2-pyrrolidone, or N-alkylpiperidones, and also diethylene glycol, triethylene glycol and polyethylene glycols and alkyl ethers thereof, in particular diethylene glycol monobutyl ether. Preferably, however, the absorption medium does not contain a physical solvent.


The absorption medium may additionally comprise further additives, such as corrosion inhibitors, wetting-promoting additives and defoamers.


All compounds known to the skilled person as suitable corrosion inhibitors for the absorption of CO2 using alkanolamines can be used as corrosion inhibitors in the absorption medium of the invention, in particular the corrosion inhibitors described in U.S. Pat. No. 4,714,597. When amines of formula (I) are used, a significantly lower amount of corrosion inhibitors can be chosen than in the case of a customary absorption medium comprising ethanolamine, since absorption media containing amines of formula (I) are significantly less corrosive towards metallic materials than the customarily used absorption media that contain ethanolamine


The nonionic surfactants, zwitterionic surfactants and cationic surfactants known from WO 2010/089257, page 11, line 18 to page 13, line 7 are preferably used as wetting-promoting additive.


All compounds known to the skilled person as suitable defoamers for the absorption of CO2 using alkanolamines can be used as defoamers in the absorption medium.


The gas mixture is preferably contacted with the absorption medium in an absorption column, wherein the absorption column is preferably operated in countercurrent flow, in order to achieve a low residual content of acid gases in the gas mixture after the absorption.


The absorption is preferably carried out at a temperature in the range from 0° C. to 70° C., particularly preferably 20° C. to 50° C., wherein the temperature of the absorption medium on entry into the absorber is below the phase-separation temperature. Within the absorber, the temperature may also increase above the phase-separation temperature if, owing to the absorption of acid gas into the absorption medium, salts are formed from the amine which have a higher water solubility than the amine. When an absorption column operated in countercurrent flow is used, the temperature of the absorption medium is preferably 30 to 60° C. on entry into the column and 35 to 70° C. on exit from the column.


The absorption is preferably carried out at a pressure of the gas mixture in the range from 0.8 to 50 bar, particularly preferably 0.9 to 30 bar. During separation of CO2, the initial partial pressure of CO2 in the gas mixture is preferably 0.01 to 4 bar, particularly preferably 0.05 to 3 bar. In a particularly preferred embodiment, the absorption is carried out at a total pressure of the gas mixture in the range from 0.8 to 1.5 bar, in particular 0.9 to 1.1 bar. This particularly preferred embodiment is recommendable for the absorption of CO2 from the combustion exhaust gas of a power plant without compression of the combustion exhaust gas.


In the method according to the invention, the loaded absorption medium obtained in the absorber is fed to a desorption column in which acid gases are desorbed from the loaded absorption medium by stripping with steam. The desorption is carried out at a temperature at which a phase separation into a water-rich liquid phase and a water-poor liquid phase occurs in the desorption column. The temperature in the desorption is preferably in the range from 50° C. to 200° C., particularly preferably in the range from 80° C. to 150° C. The desorption is preferably carried out at a pressure in the range from 10 mbar to 10 bar, particularly preferably in the range from 100 mbar to 5 bar.


The water-rich liquid phase and the water-poor liquid phase resulting in the desorption are separated from one another. Part of the water-rich liquid phase is fed to an evaporator in which steam is generated which is fed into the desorption column and by which acid gases are stripped in the desorption column. The water-poor liquid phase and the remaining part of the water-rich liquid phase are returned to the absorber as absorption medium. In doing so, the water-poor liquid phase and the remaining part of the water-rich liquid phase are preferably mixed with one another at a temperature below the phase-separation temperature before they are returned to the absorber. The fraction of water-rich liquid phase that is not vaporized in the evaporator can alternatively be fed to the desorption column or to the absorber.


With the method according to the invention, a high capacity of the absorption medium can be achieved in a cycle of absorption and desorption, since in the method the desorption can be carried out to a low residual content of acid gases and absorption media having a high weight fraction of amines can be used, with which a high loading on absorption is achieved. The thermal and oxidative breakdown of the amines used for the absorption is low in the method according to the invention, since only a small fraction of the amines passes into the evaporator and is exposed there to the high temperatures on the heat-exchange surfaces. The energy requirement of the method according to the invention is markedly lower compared with methods which use a single-phase absorption medium. The method according to the invention does not require any auxiliaries in addition to water and amine and can be carried out in simple and cost-effective apparatuses.



FIGS. 1 and 2 illustrate devices according to the invention. The device according to the invention for separating acid gases from a gas mixture comprises an absorber (1) in which the gas mixture (20) containing the acid gases is contacted with a liquid absorption medium. All apparatus known from the prior art for absorbing a gas from a gas mixture into a liquid can be used as absorber. Preferably, a scrubbing column is used as absorber, which scrubbing column preferably comprises internals for enlarging the phase boundary between the gas mixture and the liquid absorption medium. Suitable internals are, for example, packing elements, e.g. Raschig rings or Pall rings, structured column packings, e.g. metal sheet packings, and also column trays, e.g. sieve trays. Alternatively, a membrane contacter, a radial flow scrubber, a jet scrubber, a Venturi scrubber or a rotary spray scrubber can be used as absorber. Particularly preferably, a scrubbing column for counter-current flow operation is used as absorber, in which the gas mixture containing the acid gases is fed to a lower region of the scrubbing column and the liquid absorption medium is fed to an upper region of the scrubbing column.


The device according to the invention comprises a desorption column (2) having a mass-transfer zone (3) which is arranged within the desorption column. Absorption medium which is loaded with the acid gas is fed to the desorption column from the absorber. Preferably, the absorption medium loaded with the acid gas is fed to the desorption column above the mass-transfer zone. All columns known from the prior art for desorption of a gas from a liquid can be used as desorption column. The mass-transfer zone (3) is preferably designed in the form of internals which effect an enlargement of the surface area. Preferably column trays, random packings or structured packings are used as internals. Suitable column trays are, for example, bubble-cap trays, sieve trays, tunnel trays, valve trays, slotted trays, slotted sieve trays, bubble-cap sieve trays, nozzle trays or centrifugal trays. Suitable random packings are, for example, Raschig rings, Lessing rings, Pall rings, Berl saddles or Intalox saddles. Suitable structured packings are, for example, the Mellapak column packings from Sulzer, the Rombopak type from Kuhni or the Montz-Pak type from Montz. In the mass-transfer zone, sections having column trays, random packings and structured packings may be combined as desired. The mass-transfer zone (3) comprises a liquid outlet (4) at which liquid is collected which exits from the lower end of the mass-transfer zone.


The device according to the invention comprises an evaporator (5) in which steam is generated which is fed to the desorption column (2) in order to supply heat for the desorption of acid gas from the loaded absorption medium and to separate off acid gases from the liquid absorption medium with the steam stream. All evaporators known from the prior art can be used as evaporators, for example natural circulation evaporators, forced-circulation evaporators, falling-film evaporators or thin-film evaporators.


The device according to the invention comprises a phase-separation device (6) for separating two liquid phases having a feed point (7) and separate withdrawal points (8, 9) for the liquid phases, a withdrawal point (8) for water-rich liquid phase and a withdrawal point (9) for water-poor liquid phase. The evaporator (5) and the phase-separation device (6) are arranged separately from one another. The liquid outlet (4) of the mass-transfer zone (3) is connected to the feed point (7) of the phase-separation device in order to feed liquid leaving the mass-transfer zone to the phase-separation device. All apparatuses known from the prior art for separating mixtures of two liquid phases can be used as phase-separation device. Suitable apparatuses are, for example, settlers in which the phases separate due to gravity. Alternatively, separators can be used in which the phases separate by centrifugal forces. In a preferred embodiment, the phase-separation device (6) is arranged within the desorption column (2) below the mass-transfer zone (3).


The device according to the invention comprises a connecting conduit (10) from the withdrawal point (8) for water-rich liquid phase to the evaporator (5), feeding water-rich liquid phase to the evaporator in order to generate steam therefrom. The device according to the invention additionally comprises a connecting conduit (11) from the withdrawal point (9) for water-poor liquid phase to the absorber (1), returning water-poor liquid phase to the absorber. Preferably, the device according to the invention additionally comprises a connecting conduit (16) from the withdrawal point (8) for water-rich liquid phase to the absorber (1), returning water-rich liquid phase to the absorber.


In a preferred embodiment, the device according to the invention additionally comprises a connecting conduit (16) between the withdrawal point (8) for water-rich liquid phase and the absorber (1), wherein a control valve (17) or a controllable pump is arranged in the connecting conduit. In this embodiment, the phase-separation device (6) comprises a level controller (18) for a liquid-liquid phase boundary in the phase-separation device (6), which controls the control valve (17) or the controllable pump. Alternatively, the connecting conduit (16) can also be connected to an additional withdrawal point for water-rich liquid phase in the phase-separation device (6) which is separate from the withdrawal point (8) which is connected to the evaporator (5). The amount of water-rich liquid phase which is returned to the absorber may be controlled with such a level controller in such a manner that no water has to be fed additionally to the absorber for steady-state operation of the device.


In a further preferred embodiment, the device according to the invention additionally comprises a mixing device (19) which is arranged in the connecting conduit (11) from the withdrawal point (9) for water-poor liquid phase to the absorber (1) and which is connected to the withdrawal point (8) for water-rich liquid phase and mixes liquid from the withdrawal point (9) for water-poor liquid phase with liquid from the withdrawal point (8) for water-rich liquid phase. All devices known to those skilled in the art for mixing two liquids can be used as mixing device. Suitable mixing devices are, for example, stirred tanks, tanks having a liquid recirculation via an external circuit, or static mixers. Preference is given to vessels having a liquid recirculation via an external circuit and a feed of water-poor liquid phase and water-rich liquid phase into the external circuit. Preferably, heat exchangers (21, 22) are arranged in the conduits via which water-poor liquid phase and water-rich liquid phase is fed to the mixing device (19), with which heat exchangers the two phases may be cooled to a temperature below the phase-separation temperature of the absorption medium used in the absorber. Particularly preferably, the heat exchangers (21, 22) are arranged in such a manner that they effect a heat exchange between the loaded absorption medium which is fed from the absorber (1) to the desorption column (2) and the liquid phases which are fed to the mixing device (19). Use of the mixing device ensures a uniform composition of the absorption medium in the absorber when operating the device and safeguards that variations in the control of the device do not affect the efficacy of the absorption.


The device according to the invention preferably additionally comprises a condenser (23) which is connected to the top of the desorption column (2) and by which water leaving the desorption column in the vapour state together with the desorbed acid gas is condensed and returned to the desorption column.



FIG. 1 shows an embodiment of the device according to the invention in which the phase-separation device (6) is arranged separately from the desorption column (2) and is designed as a settler having an overflow weir. In this embodiment, the bottom outlet of the desorption column is used as liquid outlet (4) of the mass-transfer zone (3). Coalescence-promoting internals, such as coalescence filters, can be arranged in the connecting conduit between the liquid outlet (4) and the feed point (7) of the phase-separation device in order to achieve a more complete phase separation in the phase-separation device.



FIG. 2 shows a preferred embodiment of the device according to the invention in which the phase-separation device (6) is arranged within the desorption column (2) below the mass-transfer zone (3). The phase-separation device (6) in this case is formed by an overflow weir (13) in the column bottom (12) which separates the column bottom into a first zone (14) and a second zone (15), and also by a feed point (7) to the first zone (14), wherein the feed point is connected to the liquid outlet (4) of the mass-transfer zone (3). The liquid outlet (4) in this case is preferably constructed as a collecting tray for liquid having a liquid outlet above the first zone. The feed point for the first zone (14) can be arranged above the first zone (14), as shown in FIG. 2, or be arranged within the first zone (14) below the upper edge of the overflow weir (13). As shown in FIG. 2, for use with absorption media in which the water-poor phase is lighter than the water-rich phase a withdrawal point (8) is arranged in the first zone (14), which withdrawal point is connected to the evaporator (5) via a connecting conduit (10) and a withdrawal point (9) is arranged in the second zone (15), which withdrawal point (9) is connected to the absorber (1) via a connecting conduit (11). For use with absorption media in which the water-poor phase is heavier than the water-rich phase, the withdrawal points (8) and (9) are exchanged compared with FIG. 2.


The device according to the invention may comprise additional pumps, measuring devices, control fittings, shutoff fittings and buffer tanks which are not shown in FIGS. 1 and 2 and which those skilled in the art can add to the abovedescribed operation of the device in accordance with their general knowledge.


The device according to the invention is of a simple structure and can be constructed using commercially available apparatuses. It makes possible stable operation without fluctuations in the separation performance for acid gases even when absorption media are used which exhibit phase-separation in the desorption column into two liquid phases of which one phase is water-poor, such that no steam can be generated in the evaporator from this phase. When such absorption media are used in the devices known from US 2009/199709, US 2010/104490 and U.S. Pat. No. 4,251,494, in contrast, severe fluctuations occur in steam generation in the evaporator, which lead to unstable operation. Since in the device according to the invention only the water-rich liquid phase, which contains a low fraction of amines, comes into contact with the hot heat-exchange surfaces of the evaporator, only a low thermal and oxidative breakdown of the amines used in the absorption medium occurs during operation.


The examples below illustrate the invention, without, however, restricting the subject matter of the invention.


EXAMPLES

Table 1 shows compositions of absorption media suitable for the method according to the invention and the phase-separation temperatures of these absorption media (loaded with CO2 and without loading).


For determining the phase-separation temperature of CO2-loaded absorption medium, the absorption medium was placed in a pressure-rated glass vessel and saturated with CO2 by adding dry ice at 20° C. and atmospheric pressure. The glass vessel was then sealed and the CO2-loaded absorption medium was slowly heated in an oil bath until separation into two liquid phases occurred, which was recognizable as turbidity of the previously clear mixture.


Abbreviations in Table 1:




  • Propyl-TAD: 4-(n-Propylamino)-2,2,6,6-tetramethylpiperidine

  • Butyl-TAD: 4-(n-Butylamino)-2,2,6,6-tetramethylpiperidine

  • DM-TAD: 4-(Dimethylamino)-2,2,6,6-tetramethylpiperidine

  • TAT: 4-(3-Dimethylaminopropylamino)-2,2,6,6-tetramethylpiperidine, or triacetonetriamine

  • EAE-TAD: 4-(2-Ethylaminoethylamino)-2,2,6,6-tetramethylpiperidine

  • MEA: Ethanolamine

  • DEA: Diethanolamine

  • MDEA: Methyldiethanolamine

  • AMP: 2-Amino-2-methyl-1-propanol

  • n.d.: not determined












TABLE 1









Example















Component in % by weight
1
2
3
4
5
6
7
8





Water
70
70
70
70
70
70
70
70


Propyl-TAD
30
20
10
10
10
10
0
0


Butyl-TAD
0
10
0
0
0
0
30
10


DM-TAD
0
0
0
0
0
0
0
0


TAT
0
0
20
0
0
0
0
20


DEA
0
0
0
20
0
0
0
0


MDEA
0
0
0
0
20
0
0
0


AMP
0
0
0
0
0
20
0
0


Phase-separation temperature
 70° C.
45° C.
 95° C.
 105° C.
 100° C.
 100° C.
45° C.
 70° C.


non-loaded


Phase-separation temperature
110° C.
98° C.
115° C.
>120° C.
>110° C.
>110° C.
90° C.
107° C.


loaded with CO2












Example















Component in % by weight
9
10
11
12
13
14
15
16





Water
70
70
70
70
70
70
70
85


Butyl-TAD
10
10
10
10
0
0
0
15


DM-TAD
0
0
0
0
30
0
0
0


TAT
0
0
0
0
0
30
0
0


EAE-TAD
0
0
0
0
0
0
30
0


MEA
20
0
0
0
0
0
0
0


DEA
0
20
0
0
0
0
0
0


MDEA
0
0
20
0
0
0
0
0


AMP
0
0
0
20
0
0
0
0


Phase-separation temperature
 82° C.
 85° C.
 75° C.
 95° C.
90° C.
 110° C.
 115° C.
n.d.


non-loaded


Phase-separation temperature
>125° C.
>125° C.
>125° C.
112° C.
90° C.
>130° C.
>120° C.
116° C.


loaded with CO2












Example














Component in % by weight
17
18
19
20
21
22
23





Water
55
40
10
85
55
40
25


Butyl-TAD
45
60
90
5
15
20
25


TAT
0
0
0
10
30
40
50


Phase-separation temperature
n.d.
n.d.
n.d.
n.d.
n.d
n.d.
n.d.


non-loaded


Phase-separation temperature
107° C.
105° C.
115° C.
125° C.
110° C.
105° C.
110° C.


loaded with CO2









For a mixture of water and 4-(n-butylamino)-2,2,6,6-tetramethylpiperidine (butyl-TAD), the composition of the two liquid phases in the two-phase region was determined in dependence on the temperature. The results given in Table 2 show that the water-rich liquid phase, which is fed to the evaporator in the method according to the invention, contains only low fractions of amine.











TABLE 2






Water fraction
Water fraction



upper phase in %
lower phase in %


Temperature in ° C.
by weight
by weight

















60
17.5
98.3


67
12.5
98.9


75
9.3
99.2


82
6.8
99.3


93
4.5
99.4








Claims
  • 1. A method for separating acid gases from a gas mixture, said method comprising: a) absorbing acid gases by contacting the gas mixture with an absorption medium comprising water and at least one amine to obtain a loaded absorption medium, wherein absorption takes place in an absorber and the absorption medium: i) shows phase separation into two liquid phases upon heating above a phase-separation temperature in the range of 0 to 130° C.;ii) comprises at least one amine of formula (I):
  • 2. The method of claim 1, wherein the absorption medium comprises an amine that, at 100° C., has a solubility of less than 100 g of amine in 1 l of water.
  • 3. The method of claim 1, wherein R2 the absorption medium comprises 25 to 85% by weight water and 15 to 75% by weight amines of formula (I).
  • 4. The method of claim 1, wherein the absorption medium comprises: a) a first amine of formula (I), wherein R1 is hydrogen and R2 is an alkyl radical having 1 to 6 carbon atoms; andb) a second amine of formula (I), for which R1 is hydrogen and R2 is a radical (CH2)nNR3R4, where n=2 to 4, R3=hydrogen or alkyl radical having 1 to 4 carbon atoms, and R4=alkyl radical having 1 to 4 carbon atoms.
  • 5. The method of claim 1, wherein the absorption medium comprises 25 to 85% by weight water and 15 to 75% by weight amines of formula (I).
  • 6. The method of claim 4, wherein the absorption medium comprises 25 to 85% by weight water and 15 to 75% by weight amines of formula (I).
  • 7. The method of claim 6, wherein, in said second amine of formula (I), R1 is hydrogen and R2 is a radical (CH2)nNR3R4, where n=2 to 4, R3=hydrogen, and R4=alkyl radical having 1 to 4 carbon atoms.
  • 8. The method of claim 6, wherein in said second amine of formula (I), R1 is hydrogen and R2 is a radical (CH2)nNR3R4 where n=2 to 4, R3=alkyl radical having 1 to 4 carbon atoms, and R4=alkyl radical having 1 to 4 carbon atoms.
  • 9. The method of claim 1, wherein absorption is carried out at a temperature in the range of 0° C. to 70° C., and the temperature of the absorption medium on entry into the absorber is below the phase-separation temperature.
  • 10. The method of claim 9, wherein desorption is carried out at a temperature in the range of 50° C. to 200° C.
  • 11. The method of claim 9, wherein desorption is carried out at a temperature in the range of 80° C. to 150° C.
  • 12. The method of claim 1, wherein absorption is carried out at a temperature in the range of 20° C. to 50° C., and the temperature of the absorption medium on entry into the absorber is below the phase-separation temperature.
  • 13. The method of claim 12, wherein desorption is carried out at a temperature in the range of 50° C. to 200° C.
  • 14. The method of claim 12, wherein desorption is carried out at a temperature in the range of 80° C. to 150° C.
Priority Claims (1)
Number Date Country Kind
10 2011 086 252 Nov 2011 DE national
CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. provisional application 61/560,281, filed on Nov. 15, 2011 and priority to German Application DE 10 2011 086 252.8 filed on Nov. 14, 2011.

US Referenced Citations (102)
Number Name Date Kind
1882258 Randel Oct 1932 A
2516625 Haury Jul 1950 A
2601673 McMillan et al. Jun 1952 A
2802344 Witherell Aug 1957 A
3276217 Bourne et al. Oct 1966 A
3580759 Albertson et al. May 1971 A
3609087 Chi et al. Sep 1971 A
4094957 Sartori et al. Jun 1978 A
4106904 Oude Alink et al. Aug 1978 A
4152900 Chopra et al. May 1979 A
4152901 Munters May 1979 A
4201721 Hallgren May 1980 A
4251494 Say Feb 1981 A
4360363 Ferrin et al. Nov 1982 A
4405579 Sartori et al. Sep 1983 A
4405586 Sartori et al. Sep 1983 A
4466915 Lai Aug 1984 A
4524587 Kantor Jun 1985 A
4643000 Rheinfelder Feb 1987 A
4701530 Swearingen et al. Oct 1987 A
4714597 Trevino Dec 1987 A
5016445 Wehr May 1991 A
5126189 Tanny et al. Jun 1992 A
5186009 Rockenfeller Feb 1993 A
5186010 Wehr Feb 1993 A
5255534 Ryan Oct 1993 A
5303565 Pravda Apr 1994 A
5390509 Rockenfeller et al. Feb 1995 A
5873260 Linhardt et al. Feb 1999 A
6117963 Boinowitz et al. Sep 2000 A
6128917 Riesch et al. Oct 2000 A
6130347 Julius et al. Oct 2000 A
6155057 Angell et al. Dec 2000 A
6184433 Harada et al. Feb 2001 B1
6672099 Yoshimi et al. Jan 2004 B1
6680047 Klaveness et al. Jan 2004 B2
6727015 Putter et al. Apr 2004 B1
7419646 Cadours et al. Sep 2008 B2
7435318 Arlt et al. Oct 2008 B2
7827820 Weimer et al. Nov 2010 B2
8069687 Jork et al. Dec 2011 B2
8277615 Ruffert et al. Oct 2012 B2
8318117 Lichtfers et al. Nov 2012 B2
8357344 Bouillon et al. Jan 2013 B2
8362095 Schwab et al. Jan 2013 B2
8470079 Agar et al. Jun 2013 B2
8500867 Seiler et al. Aug 2013 B2
8500892 Seiler et al. Aug 2013 B2
8506839 Shiflett et al. Aug 2013 B2
8523978 Rojey et al. Sep 2013 B2
8623123 Seiler et al. Jan 2014 B2
8696928 Seiler et al. Apr 2014 B2
8715521 Shiflett et al. May 2014 B2
8784537 Seiler et al. Jul 2014 B2
8932478 Seiler et al. Jan 2015 B2
20040133058 Arlt et al. Jul 2004 A1
20050070717 Wasserscheid et al. Mar 2005 A1
20050129598 Chinn Jun 2005 A1
20050202967 Hoefer et al. Sep 2005 A1
20050245769 Kohler et al. Nov 2005 A1
20060104877 Cadours et al. May 2006 A1
20060150665 Weimer et al. Jul 2006 A1
20060197053 Shiflett et al. Sep 2006 A1
20060251961 Olbert et al. Nov 2006 A1
20070144186 Shiflett et al. Jun 2007 A1
20070264180 Carrette et al. Nov 2007 A1
20070286783 Carrette et al. Dec 2007 A1
20080028777 Boesmann et al. Feb 2008 A1
20080283383 Ruffert et al. Nov 2008 A1
20090029121 Hammermann et al. Jan 2009 A1
20090199709 Rojey et al. Aug 2009 A1
20100011958 Cadours et al. Jan 2010 A1
20100029519 Schwab et al. Feb 2010 A1
20100084597 Schwab et al. Apr 2010 A1
20100095703 Jork et al. Apr 2010 A1
20100104490 Bouillon et al. Apr 2010 A1
20100132551 Bouillon et al. Jun 2010 A1
20100288126 Agar et al. Nov 2010 A1
20100326126 Seiler et al. Dec 2010 A1
20110000236 Seiler et al. Jan 2011 A1
20110081287 Bouillon et al. Apr 2011 A1
20110185901 Jacquin et al. Aug 2011 A1
20110256043 Blair et al. Oct 2011 A1
20110309295 Joh et al. Dec 2011 A1
20120011886 Shiflett et al. Jan 2012 A1
20120017762 Seiler et al. Jan 2012 A1
20120080644 Seiler et al. Apr 2012 A1
20120247144 Seiler et al. Oct 2012 A1
20120308458 Seiler et al. Dec 2012 A1
20130011314 Porcheron et al. Jan 2013 A1
20130023712 Porcheron et al. Jan 2013 A1
20130031930 Seiler et al. Feb 2013 A1
20130031931 Seiler et al. Feb 2013 A1
20130219949 Seiler et al. Aug 2013 A1
20130247758 Seiler et al. Sep 2013 A1
20130327084 Shiflett et al. Dec 2013 A1
20140090558 Rolker et al. Apr 2014 A1
20140105801 Rolker et al. Apr 2014 A1
20140120016 Rolker et al. May 2014 A1
20140356268 Schraven et al. Dec 2014 A1
20140360369 Schraven et al. Dec 2014 A1
20150125373 Willy et al. May 2015 A1
Foreign Referenced Citations (49)
Number Date Country
400 488 Aug 1924 DE
633 146 Jul 1936 DE
36 23 680 Jan 1988 DE
266 799 Apr 1989 DE
195 11 709 Oct 1996 DE
103 33 546 Feb 2005 DE
10 2004 053 167 May 2006 DE
10 2009 000 543 Aug 2010 DE
0 033 529 Jan 1981 EP
0 079 767 May 1983 EP
0 187 130 Jul 1986 EP
0 302 020 Feb 1989 EP
2 087 930 Aug 2009 EP
2 093 278 Aug 2009 EP
2 900 841 Nov 2007 FR
1 306 853 Feb 1973 GB
61-129019 Jun 1986 JP
62-73055 Apr 1987 JP
1-134180 May 1989 JP
2-298767 Dec 1990 JP
4-268176 Sep 1992 JP
6-307730 Nov 1994 JP
7-167521 Jul 1995 JP
2001-219164 Aug 2001 JP
2002-047258 Feb 2002 JP
2004-44945 Feb 2004 JP
2006-239516 Sep 2006 JP
WO 9313367 Jul 1993 WO
WO 0061698 Oct 2000 WO
WO 02074718 Sep 2002 WO
WO 03074494 Sep 2003 WO
WO 2004082809 Sep 2004 WO
WO 2004104496 Dec 2004 WO
WO 2005113702 Dec 2005 WO
WO 2006084262 Aug 2006 WO
WO 2006134015 Dec 2006 WO
WO 2007070607 Jun 2007 WO
WO 2008015217 Feb 2008 WO
WO 2009097930 Aug 2009 WO
WO 2009098155 Aug 2009 WO
WO 2009156271 Dec 2009 WO
WO 2010089257 Aug 2010 WO
WO 2012062656 May 2012 WO
WO 2012062830 May 2012 WO
WO 2012168067 Dec 2012 WO
WO 2012168094 Dec 2012 WO
WO 2012168095 Dec 2012 WO
WO 2013050230 Apr 2013 WO
WO 2013050242 Apr 2013 WO
Non-Patent Literature Citations (78)
Entry
“Mutual Solubility of Water and Pyridine Derivatives” by Richard M. Stephenson , J. Chem. Eng. Data, 38, p. 428-431, 1993.
“Review of Organic Functional Groups: Introduction to Medicinal Organic Chemistry” by Thomas L. Lemke, Lippincott Williams & Wilkins, p. 40, 2003.
“Review of Organic Functional Groups: Introduction to Medicinal Organic Chemistry” by Thomas L. Lemke, Lippincott Williams & Wilkins, p. 39, 2003.
Partial English language translation for JP 62-73055 listed as document B2 above and published on Apr. 3, 1987.
English language translation of JP 7-167521 published on Jul. 4, 1995. (Foreign language document submitted with English language abstract in an IDS filed on Feb. 5, 2013).
Office Action mailed Dec. 24, 2013 for co-pending U.S. Appl. No. 13/884,840.
U.S. Appl. No. 14/124,347, filed Dec. 6, 2013, Rolker.
U.S. Appl. No. 14/124,385, filed Dec. 6, 2013, Rolker.
U.S. Appl. No. 14/124,472, filed Dec. 6, 2013, Rolker.
English language abstract for EP 2 093 278 A1.
English language abstract for EP 2 087 930 A1.
English language abstract for WO 2012/062656.
Domanska, et al., Solubility of 1-Alkyl-3-ethylimidazolium-Based Ionic Liquids in Water and 1-Octanol, J. Chem. Eng. Data 53:1126-1132 (Apr. 2008).
Liu, et al., The physical properties of aqueous solution of room-temperature ionic liquids based on imidazolium:Database and Evaluation, J. Mol. Liquids 140:68-72 (Jan. 2008).
Zhou, The Vapor Surfactant Theory of Absorption and Condensation Enhancement, Proc. Int. Sorption Heat Pump Conference, Sep. 24-27, 2002.
English language abstract for WO 2013/050230 published on Apr. 11, 2013.
English language abstract for WO 2013/050242 published on Apr. 11, 2013.
Wasserscheid, et al., “Ionische Flüssigkeiten-neue,,Lösungen für die Übergangsmetallkatalyse,” Angewandte Chemie 112(21):3926-3945 (2000).
Wassersciieid, et al., “Ionic Liquids—New “Solutions” for Transition Metal Catalysis,” Angew. Chem. Int. Ed. 39:3772-3789 (2000).
Ziegler, et al., “Recent developments and future prospects of sorption heat pump systems,” Int. J. Therm. Sci. 38:191-208 (1999).
English language translation of the International Search Report for PCT/EP2012/070380 filed Oct. 15, 2012.
U.S. Appl. No. 13/883,573, filed May 5, 2013, Seiler.
U.S. Appl. No. 13/884,840, filed May 31, 2013, Seiler.
U.S. Appl. No. 13/910,014, filed Jun. 4, 2013, Seiler.
English language abstract for JP 1-134180 published on May 26, 1989.
English language abstract for JP 6-307730 published on Nov. 1, 1994.
English language abstract for JP 2001-219164 published on Aug. 14, 2001.
English language abstract for JP 2004-44945 published on Feb. 12, 2004.
English language abstract for JP 2006-239516 published on Sep. 14, 2006.
Perez-Blanco, “A Model of an Ammonia-Water Falling Film Absorber,” ASHRAE Transactions vol. 94, pp. 467-483, 1988; (Presented at the winter meeting in Dallas Texas of the American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc(1988)).
English language translation of Office Action for Chinese application 201280028524.0 (counterpart of copending U.S. Appl. No. 14/124,472) filed in China on May 25, 2012.
U.S. Appl. No. 14/399,139, filed Nov. 5, 2014, Willy.
English language abstract for DD 266 799 A1.
English language text for DE 400 488.
English language text for DE 633 146.
English language abstract for DE 36 23 680.
English language abstract for DE 195 11 709.
English language abstract for DE 103 33 546.
English language abstract for DE 10 2004 053 167.
English language abstract for EP 0 033 529 A1.
English language abstract for FR 2 900 841.
English language abstract for JP 61-129019.
English language abstract for JP 2-298767.
English language abstract for JP 4-268176.
English language abstract for JP 7-167521.
English language abstract for WO 93/13367.
English language abstract for WO 2008/015217.
English language abstract for WO 2009/098155.
English language abstract for WO 2012/062830.
Brennecke, et al., “Ionic Liquids: Innovative Fluids for Chemical Processing,” AIChE Journal 47(11):2384-2389 (2001).
Chua, et al., “Improved Thermodynamic Property Fields of LiBr—H2O Solution,” International Journal of Refrigeration 23:412-429 (2000).
De Lucas, et al., “Vapor Pressures, Densities, and Viscosities of the (Water + Lithium Bromide + Lithium Formate) System and (Water + Lithium Bromide + Potassium Formate) System,” Journal of Chemical and Engineering Data, American Chemical Society, US 48(1):18-22 (2003).
De Lucas, et al., “Absorption of Water Vapor into Working Fluids for Absorption Refrigeration Systems,” Industrial & Engineering Chemistry Research, American Chemical Society, US 46(1):345-350 (2007).
Galán, et al., “Solvent Properties of Functionalized Ionic Liquids for CO2 Absorption,” IChemE 85(A1):31-39 (2007).
Glebov, et al., “Experimental Study of Heat Transfer Additive Influence on the Absorption Chiller Performance,” International Journal of Refrigeration 25:538-545 (2002).
Kim, et al., “Surface tension and viscosity of 1-butyl-3-methylimidazolium iodide and 1-butyl-3-methylimidazolium tetrafluoroborate, and solubility of lithium bromide+1-butyl-3-methylimidazolium bromide in water,” Korean J. Chem. Eng. 23(1):113-116 (2006).
Kim, et al., “Performance Evaluation of Absorption Chiller Using LiBr + II2N(CII2)2OII + II2O, LiBr + HO(CH2)3OH + H2O, and LiBr + (HOCH2CH2NH + H2O as Working Fluids,” Applied Thermal Engineering 19:217-225 (1999).
Kim, et al., “Refractive Index and Heat Capacity of 1-Butyl-3-Methylimidazolium Bromide and 1-Butyl-3-Methylimidazolium Tetrafluoroborate, and Vapor Pressure of Binary Systems for 1-Butyl-3-Methylimidazolium Tetrafluoroborate-Trifluoroethanol,” Fluid Phase Equilibria 218:215-220 (2004).
Li, et al., “Correlation and Prediction of the Solubility of CO2 and H2S in an Aqueous Solution of 2-Piperidineethanol and Sulfolane,” Ind. Eng. Chem. Res. 37:3098-3104 (1998).
Mitsubishi Heavy Industries, Ltd., “Flue Gas CO2 Recovery Technology and Its Application to EOR: an Effective Strategy for Addressing the Issues of Global Warming and Peaking Oil Supply,” Technical Review:44:20-23 (2007).
English counterpart of Mitsubishi Heavy Industries, Ltd., “Flue Gas CO2 Recovery Technology and Its Application to EOR: an Effective Strategy for Addressing the Issues of Global Warming and Peaking Oil Supply,” Technical Review:44:20-23 (2007).
Rolker, et al., “Abtrennung von Kohlendioxid aus Rauchgasen mittels Absorption,” Chemie Ingenieur Technik 78:416-424 (2006).
Wu, et al., “Novel Ionic Liquid Thermal Storage for Solar Thermal Electric Power Systems,” Proceeding of Solar Forum. Solar Energy: The Power to Choose Apr. 21-25, 2001.
Yoon, et al., “Cycle Analysis of Air-Cooled Absorption Chiller Using a New Working Solution,” Energy 24:795-809 (1999).
Zhang, et al., “Screening of ionic Liquids to Capture CO2 by COSMO-RS and Experiments,” AIChE Journal 54(10):2171-2728 (Oct. 2008).
Ziegler, et al., “Heat-Transfer Enhancement by Additives,” International Journal of Refrigeration 19:301-309 (1996).
Ziegler, et al., “Multi-effect absorption chillers,” Rev. Int. Froid 16(5):301-311 (1993).
English language translation of abstract for Rolker document.
U.S. Appl. No. 13/641,591, filed Oct. 16, 2012, Seiler.
U.S. Appl. No. 13/641,692, filed Oct. 16, 2012, Seiler.
English language abstract for DE 10 2009 000 543.
English language abstract for WO 2012/168067.
English language abstract for WO 2012/168094.
English language abstract for WO 2012/168095.
International Search Report and Written Opinion for PCT/EP2012/070380 filed Oct. 15, 2012.
Notice of Allowance for copending U.S. Appl. No. 13/884,840 mailed Mar. 13, 2014.
U.S. Appl. No. 14/372,287, filed Jul. 15, 2014, Schraven.
U.S. Appl. No. 14/373,350, filed Jul. 19, 2014, Schraven.
Related Publications (1)
Number Date Country
20130118350 A1 May 2013 US
Provisional Applications (1)
Number Date Country
61560281 Nov 2011 US