Patent Application
20250161906
The present invention relates to a method for removing at least one gas from a fluid stream.
The removal of gases from fluid streams has become very important in recent decades. In particular, the removal of carbon dioxide (CO2) from flue gas and offgases is desirable for various reasons. In this context, the reduction of carbon dioxide emissions is of the utmost importance, since these are considered to be the principal cause of the greenhouse effect.
Prior art technology includes the removal of CO2 from fluid streams with amines. CO2-containing gas/offgas streams can for example be contacted with solutions of amines. In its reaction with CO2, the amine used forms different products: carbamates with primary or secondary amines and carbonates with tertiary amines. These products precipitate or go into solution, thereby removing the CO2 from the gases. In order to release the bound CO2 again, the precipitated or dissolved carbamates or carbonates are heated at a suitable point in the process. The resulting CO2 is either stored or undergoes direct chemical reaction.
WO 2010/149599 A1 discloses a method for removing gases from a fluid stream that uses an absorption fluid comprising an amine, a stripping aid and water. The gases to be removed are preferably CO2, H2S, COS, mercaptans, SO3, SO2, CS2 and HCN. Very particularly preferably, the amine is monoethanolamine, piperazine, methylaminopropylamine, diethanolamine or 1-hydroxyethylpiperazine.
WO 2016/068698 A1 and WO 2016/068699 A1 disclose CO2 absorption methods in which primary, secondary or tertiary amines can be used in aqueous solution. Preference is given to using monoamines as the amine. The amines may in addition be substituted with a functional group, preferably a hydroxy group. The amines may also be cyclic amines. Very particularly preferably, the amine is N,N-dimethylcyclohexylamine (DMCA), N-methylcyclohexylamine (MCA) or a mixture thereof.
WO 2014/140108 A1 discloses a method for absorbing CO2 from a CO2-containing gas stream that uses a CO2 absorbent comprising a thermoresponsive copolymer comprising amine monomers. The amine monomers may be any polymerizable monomer having at least one primary, secondary or tertiary amino functional group. Preferred amine monomers may be selected from the group consisting of amine-functionalized acrylamides, amine-functionalized methacrylamides, amine-functionalized acrylates, amine-functionalized methacrylates and cyclic amine monomers. However, a disadvantage of the described method is that the copolymer needs to be laboriously synthesized. The disclosed CO2 absorbent may in addition include an amine component dissolved in water. The compounds mentioned in this regard include inter alia 3,3,5-trimethylcyclohexylamine, N-methylcyclohexylamine, N,N-dimethylcyclohexylamine, N-methyldiethanolamine, piperazine and 2-aminoethanol.
WO 2015/053619 A1 discloses a method for absorbing CO2 from a CO2-containing gas stream that uses a CO2 absorbent comprising an amine-containing component, an inorganic salt and water. The amine-containing component has a boiling point of at least 100° C. The amine-containing component may be an organic compound having 2-20 carbon atoms. The compounds mentioned include inter alia 3,3,5-trimethylcyclohexylamine, N-methylcyclohexylamine, N,N-dimethylcyclohexylamine, N-methyldiethanolamine, piperazine and 2-aminoethanol.
U.S. Pat. No. 4,112,050 A discloses inter alia the suitability for the absorption of CO2 of various cycloaliphatic amines, for example N1-cyclohexylpropane-1,2-diamine, 1-amino-1-(2-aminoisopropyl) cyclohexane, 1-methylamino-1-aminomethylcyclopentane, 1-amino-1-aminomethylcycloheptane, N-isopropyl-1,2-diaminocyclohexane, N2-cyclohexylbutane-1,2-diamine, N2-cyclohexylpropane-1,2-diamine, N-cycloheptylethylene-1,2-diamine, N1-cyclohexyl-2-methylpropane-1,2-diamine, 1-(2-aminoisopropyl)-2-amino-3-methylcyclopentane, N-isopropyl-1,4-diaminocyclohexane, N1-cyclohexyl-N2-methylethylenediamine, N-cyclohexylethylenediamine, N1-cyclohexyl-N2-ethylethylenediamine, N1-cyclohexyl-N2-methylpropane-1,2-diamine, N-cyclohexylpropane-1,3-diamine, p-menthane-1,8-diamine, 1-amino-1-aminomethylcyclohexane, 1,3-diamino-1-methylcyclohexane and N2-cyclohexyl-2-methylpropane-1,2-diamine. The described method uses aqueous solutions of the amines mentioned.
WO 2013/075697 A1 discloses a method for removing CO2 from a fluid mixture and/or stream in which a cyclic amine is used. The disclosed cyclic amines include 1,2-diaminocyclohexane, 1,3-diaminocyclohexane, 1,4-diaminocyclohexane, 1,2,3-triaminocyclohexane, 1,2,4-triaminocyclohexane, 1,3,5-triaminocyclohexane, 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5-diazabicyclo[4.3.0]non-5-ene, N-methylcyclohexanediamine, N1, N2-1,2-dimethylcyclohexanediamine, N1, N1, N2-trimethylcyclohexane-1,2-diamine, N-methyl-1,3-cyclohexanediamine, N1, N1-dimethyl-1,3-cyclohexanediamine, N1, N3-dimethyl-1,3-cyclohexanediamine, N-methylcyclohexane-1,4-diamine, N1, N1-dimethylcyclohexane-1,4-diamine, N1, N4-dimethylcyclohexane-1,4-diamine, N1, N4, N4-trimethylcyclohexane-1,4-diamine, indole and isophoronediamine. Very particular preference is given to isophoronediamine. Preferred amines, more particularly isophoronediamine, form carbamates with CO2 that are at least partially insoluble in the solvent used and can be removed as a solid or liquid phase. This permits an easier and less energy-intensive recovery of the bound CO2.
WO 2022/085789 A1 also discloses a method for storing CO2 that uses amines in which the hydrocarbon framework is cyclic in form. Examples of compounds mentioned and used in the experiments include isophoronediamine, cyclohexylamine, cyclohexane-1,2-diamine, cyclohexane-1,4-diamine and 4,4′-methylenebis (2-methylcyclohexylamine).
ACS Environ. Au 2022, 2, 354-362 discloses a study in which the absorption capacities of different amines are compared. Primary amines show higher storage efficiency than secondary and tertiary amines, possibly on account of steric hindrance. However, primary aromatic amines such as aniline absorb virtually no CO2.
Diamines with an aminocyclohexyl group have a higher storage capacity than monoamines and, unlike the latter, have the advantage of resulting in insoluble precipitates. In addition, a particularly high CO2 storage capacity in conjunction with a particularly advantageous long efficiency period (T90) is surprisingly disclosed for isophoronediamine. In combination with the lower desorption temperature that is also observed, isophoronediamine is found to be particularly preferable compared with monoethanolamine.
However, it would be desirable to provide methods in which the amines employed are equally suitable for storing CO2, but the energy required for the removal of CO2 from the carbamates of the amines employed can be reduced further.
Surprisingly, it has now been found that aminoalkylated isophoronediamine achieves the object of absorbing CO2 particularly well and desorbing it again at particularly low temperatures.
The present invention thus provides a method for removing at least one gas from a fluid stream, in which an absorbent is contacted with the fluid stream, the absorbent comprising at least one amino-containing compound that is an aminoalkylated isophoronediamine.
The fluid stream from which at least one gas is to be removed may be the stream of a fluid selected from gases and liquids. If the fluid is a gas, the fluid is preferably selected from the group of gases consisting of natural gas, syngas, coke oven gas, cleavage gas, coal gasification gas, recycle gas, landfill gas and combustion gas. If the fluid is a liquid, the liquid is preferably selected from liquefied petroleum gas (LPG, autogas) and liquid natural gas (LNG) or one of the preferred gases mentioned above in liquefied form.
The method according to the invention is particularly suitable for removing gases from likewise gaseous fluid streams.
Under the method conditions and further preferably under SATP conditions (298.15 K, 1.013 bar) too, the gas to be removed is present in the form of gaseous compounds. Preferably, the gas is a gas selected from CO2, H2S, COS, the group of gaseous thiols, SO3, SO2, CS2 and HCN. Advantageously, the method according to the invention is particularly well suited for the removal of CO2.
In the method according to the invention, the fluid stream is contacted with an 5 absorbent comprising at least one amino-containing compound. This means that the fluid stream may be contacted with an absorbent comprising one, two, three or more than three amino-containing compounds. Particularly preferably, the fluid stream is contacted with an absorbent comprising only one amino-containing compound. In order to achieve advantageous properties, it may alternatively be advantageous to contact the fluid stream with an absorbent comprising two amino-containing compounds.
An absorbent is to be understood as meaning a liquid or gaseous composition capable of absorbing the gas present in the fluid stream. Further preferably, the absorbent is liquid under the method conditions and more preferably under SATP conditions too.
At least one of the amino-containing compounds in the absorbent is an alkylated isophoronediamine. If the absorbent comprises only one amino-containing compound, the amino-containing compound is thus an aminoalkylated isophoronediamine. If the absorbent comprises more than one amino-containing compound, the amino-containing compounds may all be aminoalkylated isophoronediamines that are differently alkylated. Alternatively, the absorbent may also comprise a plurality of differently aminoalkylated isophoronediamines and other amino-containing compounds.
Aminoalkylated isophoronediamines that are alkylated exclusively at the amino group attached to the ring in the 1-position are preferred. These are able to absorb and re-release CO2 particularly well. Corresponding aminoalkylated isophoronediamines have the formula (I) shown below,
in which R is
Very particularly preferably, it is methylated or ethylated isophoronediamine, i.e. compounds of the formula (I) in which R=—CH3 or —C2H5.
When at least one aminoalkylated isophoronediamine is used together with at least one other amino-containing compound, any amino-containing compound may in principle be used as the latter. Preference is given to primary, secondary, tertiary, optionally hydroxy-substituted and optionally aminoalkylated amines. Very particularly preferred other amino-containing compounds may be selected from the group consisting of isophoronediamine, 4,4′-diaminodicyclohexylmethane (PACM), aminoalkylated 4,4′-diaminodicyclohexylmethanes (aminoalkylated PACMs), N,N-dimethylcyclohexylamine, N-methyldiethanolamine, piperazine and 2-aminoethanol.
Preferably, the proportion by weight of aminoalkylated isophoronediamine based on the total mass of amino-containing compounds present in the absorbent is 50-100% by weight, further preferably 70-100% by weight, even further preferably 90-100% by weight, since this allows the gas to be absorbed particularly well and desorbed again at particularly low temperatures. As already mentioned, very particular preference is given to a method in which only aminoalkylated isophoronediamine is used. The mass fraction of aminoalkylated isophoronediamine based on the total mass of amino-containing compounds present in the absorbent is in that case accordingly 100% by weight.
In principle, a solvent may be present in the absorbent. Solvents used with preference are water and organic solvents having a boiling temperature at 1.013 bar lower than that of water (appropriate alcohols and ethers in particular). Very particularly preferably, a solvent selected from the group consisting of water, methanol, ethanol, n-propanol, isopropanol, tetrahydrofuran, diethyl ether, diisopropyl ether, methyl t-butyl ether and toluene is used.
Preferably, the mass fraction of solvent in the absorbent, based on the mass of the other components present, is 0-50% by weight, preferably 0-30% by weight, very particularly preferably 0-10% by weight.
However, the method is even further preferably executed without solvent. Thus, very particularly preferably, the mass fraction of solvent in the absorbent, based on the mass of the other components present, is no added solvent, i.e. 0% by weight. Surprisingly, it was found that the products formed from aminoalkylated isophoronediamine and the gas to be removed, more particularly the carbamates formed from aminoalkylated isophoronediamine and CO2, precipitate not only from the typical solvents, but also from the liquid aminoalkylated isophoronediamine present and serving as solvent. Thus, the solvent-free method variant surprisingly permits the method to be executed as a particularly preferred two-stage method with reduced energy consumption, since the solvent does not need to be laboriously removed, purified or heated with the product obtained. Furthermore, the use of solvents is generally disadvantageous, given the desired reduction in the VOC content. A particularly preferred method is thus a method for removing at least one gas, preferably CO2, from a fluid stream in which an absorbent is contacted with a fluid stream, wherein
Preferably, the absorbent is contacted with the fluid stream in such a way that the fluid stream is passed through the absorbent. For better distribution, the fluid stream may be passed through a percolator or through another appropriate measure that makes the interface between the liquid absorbent and the gas larger. Further preferably, this is done by spraying the absorbent in the fluid stream.
Preferred reaction times are between 5 minutes and 48 h, preferably 10 minutes and 12 h. Preferred reaction temperatures are between ambient temperature (i.e. no heating) and 80° C. The reaction temperatures are preferably between room temperature and 50° C.
The precipitation of the product from aminoalkylated isophoronediamine and the gas to be removed can be aided by adding substances that promote precipitation. Particularly suitable solvents that promote precipitation can be selected from the group of alcohols and ethers.
Preference is given to removing the product that has formed by filtration or centrifugation.
The release of the absorbed gas may be effected by standard means known to those skilled in the art. The released gas may either be stored in a manner known to those skilled the art or may undergo direct chemical reaction. If the absorbent is recovered in the same form when the gas is released, it is preferably returned to the method of the invention.
More particularly, where the gas to be removed is CO2, the release of the CO2 can be effected by heating the carbamates formed. The amino-containing compounds initially employed that are then likewise released, more particularly the recovered aminoalkylated isophoronediamine, may be returned to the absorbent for the method. In principle, a basic or acidic catalyst may be supplied for the elimination of CO2. Preference is however given to executing the method without a catalyst. It is in addition possible to adjust the pH by electrolytic methods in order to lower the elimination temperature still further. In addition, it may be helpful to introduce an inert gas, more particularly nitrogen, for the elimination of CO2.
Air is blown through isophoronediamine for 24 hours until crystals have formed. According to NMR spectroscopy, these crystals consist of the carbamate of IPD and CO2. The crystals are stable in air. DSC shows a decomposition (elimination of CO2) at 144-149° C. (848 J/g). When these crystals are heated in air (30 min, 150° C.), pure IPD is recovered (NMR).
CO2 is blown through N-methylcyclohexylamine for 24 hours until crystals have formed. The crystals obtained are unstable and rapidly liquefy in air. DSC shows a decomposition (elimination of CO2) at 54-87° C. (650 J/g) and at 148-149°° C. (220 J/g). The first peak explains the lack of stability at room temperature, while the second one documents an increased input of energy compared with inventive example c).
Air is blown through N-methyl-IPD for 24 hours until crystals have formed. According to NMR spectroscopy, these crystals consist of the carbamate of N-methyl-IPD and CO2. The crystals are stable in air. DSC shows a decomposition (elimination of CO2) at 123-126° C. (742 J/g). When these crystals are heated in air (30 min, 130° C.), pure N-methyl-IPD is recovered (NMR).
Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.
In the foregoing and in the examples, all temperatures are set forth uncorrected in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated.
The entire disclosures of all applications, patents and publications, cited herein and of corresponding European application No. 23210903, filed Nov. 20, 2023, are incorporated by reference herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 23210903 | Nov 2023 | EP | regional |
