Method and system for removing co2 gas from a gas stream

Abstract

This invention relates to a method comprising contacting a gas stream comprising a first amount of CO2 with a CO2-lean solvent stream that comprises a compound according to Formula (I) to form a treated gas stream comprising a second amount of CO2 that is less than the first amount, and a CO2-rich solvent stream, and heating the CO2-rich solvent stream to form a CO2 stream and a CO2-lean solvent stream, wherein R1 and R2 are independently selected from linear or branched C1-C4 alkyl, and n is selected from 2 to 4.

Description

[0001] Method and system for removing CO2 gas from a gas stream

[0002] Description

[0003] This invention concerns a method and system for removing CC gas from a gas stream, using an aqueous solution of polyol-tertiary amine compounds derived from naturally occurring sugars.

[0004] For the past century and a half, fossil fuels such as gas, oil and coal have been used in energy production, such as electricity generation. Carbon dioxide, and other acidic gases that are a result of the combustion process, have been identified to be responsible for adverse environmental effects, and have been emitted to the atmosphere on the gigaton scale globally. For example, according to the U.S. Department of Energy, a single subcritical coal-fired power plant of 550 MW size may produce over 6 million pounds of gas per hour, of which 1 million or more may be CO2. The United States Department of Energy, in its efforts to maintain cost-effective energy production and reduce the environmental impact of fossil fuels, has set a target for next-generation CO2 capture technology to have a total cost of $40 / metric ton CO2.

[0005] Various strategies have been developed for capturing acid gases, including carbon dioxide, from a gas stream using binding organic liquid (BOLs). However, these binding organic liquids have several issues that prevent them from achieving the DOE goal. These issues include 1 ) susceptibility to disproportionation and hydrolysis, therefore posing a huge challenge in terms of its recyclability and increased solvent replenishment costs; 2) significantly high viscosity of the CO2 rich solvents requiring high recirculation rate leading to increased capital and operating expenses; and 3) the need for co-solvents leading to increased costs. The compounds disclosed herein are readily synthesized, typically via only one or two reaction steps, and often from commercially available and inexpensive, starting materials. The compounds not only remain liquid when CO2-rich, at typical operating temperatures, such as 40° C or more, but they have a CO2-lean viscosity sufficiently low that a co-solvent is not needed to facilitate efficient recirculation. Furthermore, the compounds are stable under conditions typically used for releasing the captured CC and recycling liquid, such as heating to 100°C or more, thereby reducing losses due to decomposition and extending the operating lifetime of the solvent.

[0006] Additionally, when exposed to a gas stream, such as during CO2 capture as described herein, gaseous solvent molecules are lost with the treated gas stream. For amine-based solvents having low vapor pressures, i.e. water determines the vapor pressure of the aqueous amine mixture, water can be condensed and feed back into the circulation flow of the solvent or evaporated water can be replenished easily. However, volatile amine components are on the one hand hazardous to humans and the environment, on the other hand are rather difficult and expensive to replace.

[0007] Off-gas cleaning is one of the key technologies to achieve our climate goals and reduce CO2 emission from emissive processes. Amine based gas cleaning is among these technologies (chemical absorption). Other technologies, like Genosorb™, can be based on physisorption of CO2 and other contaminants and do not require amine-based compounds. An overview on different CO2 capture technologies is available from the US department of energy (DOE) and the National Energy Technology Laboratory (NETL), in the “CARBON DIOXIDE CAPTURE HANDBOOK”.

[0008] US 4336233 describes an aqueous solution containing from 0.81 to 1 .3 moles of piperazine per liter is used as a washing agent for removing impurities such as H2S, CO2 and COS from gases. Piperazine can also be used, in amounts of up to 0.8 mole per liter, together with physical or chemical solvents, to accelerate the absorption of H2S, CO2 and COS. The washing process is used for natural gases, coke-oven gases, gases from the gasification of coal and synthesis gases, of any origin. Urvashi K Saraode et al (Canadian Journal of Chemical Engineering Vol 101 , no. 10, 2023, p 5956-5966) teaches that CO2 separation with harmful chemicals will damage the environment. It is essential to explore greener solvents that are producible from renewable resources such as biomass. The suitability of N-methyl- D-glucamine (MG), also known as meglumine, for capturing CO2, was explored in this work. This nontoxic amino sugar, which is derived from sorbitol, represents a renewable bio-solvent. It was found that MG is especially reactive with CO2. Trials were performed in a stirred cell reactor with a flat gas-liquid interface between 303 and 313 K. The values of the pseudo-first-order reaction rate constant, reaction orders, and activation energy were found. The loading capacity (a) of 0.5 M MG solution was measured at T = 308 K. For a typical value of a = 0.524 mol CO2 / mol MG, the corresponding equilibrium partial pressure of CO2 was 22 kPa. Finally, it was found that the catalyst AI2O3 aided in the desorption of CO2-loaded MG solutions. Desorption efficiency using AI2O3 was higher (74%) than that achieved without this catalyst (45%). It is thus clear that MG represents a potential solvent for improved CO2 separation from gases.

[0009] CA3211717 relates to a process for absorbing carbon dioxide from an air stream, wherein the air stream is contacted with a carbon dioxide absorbent, the carbon dioxide absorbent comprising at least: a) water; b) polyethylene glycols or polyols having a molecular weight of less than or equal to 1000 g / mol; and c) carbon dioxide absorbing agents, the carbon dioxide absorbing agent being selected from the group of inorganic carbonates, amines, polyethylene glycolamines, diaminopolyethylene glycols, carboxylic acid derivatives of the polyethylene glycolamines, polyethylene imines, amine-containing sugar derivatives, amino acids, or mixtures of at least two of these components. The present invention further relates to a carbon dioxide absorbent for absorbing carbon dioxide from an air stream.

[0010] US4814104A describes the absorption of carbon dioxide from gas mixtures with aqueous absorbent solutions of tertiary alkanolamines is improved by incorporating at least one alkyleneamine in the solution. The presence of the alkyleneamine promotes the rate of carbon dioxide absorption and the carbon dioxide capacity of the aqueous tertiary alkanolamine solution. As a result, absorption can be carried out in shorter absorber columns, and process energy requirements can be lowered by reducing the rate at which the absorbent solution is circulated.

[0011] US 8221712 describes an absorption medium for the removal of acid gases from a fluid stream comprising of an aqueous solution a) of at least one amine and b) at least one phosphonic acid, wherein the molar ratio of b) to a) is in the range from 0.0005 to 1.0. The phosphonic acid is, e.g., 1-hydroxyethane-1 ,1-diphosphonic acid. The absorption medium exhibits a reduced regeneration energy requirement compared with absorption media based on amines or amine / promoter combinations, without significantly decreasing the absorption capacity of the solution for acid gases.

[0012] US8388738 discloses a process for removing carbon dioxide from a fluid flow, wherein a) the fluid flow is brought into contact with an absorption agent which contains a solution of ammonia and at least one amino carboxylic acid and / or amino sulfonic acid, a charged absorption agent being obtained, and b) the charged absorption agent is regenerated while releasing carbon dioxide. The additional use of the amino carboxylic acid and / or amino sulfonic acid increases the circulation absorption capacity of the absorption agent.

[0013] US6290754B1 discloses a regenerative process for deacidification of a gas containing CO2 and liquid hydrocarbons including contacting the gas to be treated, in an absorption zone, with an absorbent liquid including methyldiethanolamine (MDEA) and an accelerator of absorption of CO2 by the amine, thereby producing a treated gas with reduced CO2 content and an absorbent liquid loaded with CO2, subjecting the loaded absorbent liquid to a regeneration treatment to release CO2 which it has bound, to produce 1 ) at least one acid gas fraction rich in CO2 and 2) at least one regenerated absorbent liquid; and recycling into the absorption zone the at least one regenerated absorbent liquid, wherein the overall liquid hydrocarbon content in the gas to be deacidified containing CO2 is greater than 14 liters of liquid hydrocarbons per million standard cubic meters of gas, and the activator combined with methyldiethanolamine in the absorbent liquid brought into contact with the gas containing CO2 and liquid hydrocarbons consists of at least one compound of formula H2N — CnH2n — NH — CH2 — CH2OH in which n represents an integer ranging from 1 to 4.

[0014] EP4072703 describes a non-aqueous solvent system configured to remove acidic gas from a gas stream comprises a solution formed of a chemical absorption component and a physical absorption component. The chemical absorption component includes a nitrogenous base, wherein the nitrogenous base has a structure such that it reacts with a portion of the acidic gas. The physical absorption component includes an organic diluent that is non-reactive with the acidic gas and that has a structure such that it absorbs a portion of the acidic gas at a pressure above atmospheric pressure. The solvent system has a solubility with water of less than about 10 g of solvent per 100 mL of water

[0015] There is a difference in the reaction mechanism of secondary and tertiary amines with CO2. Secondary and primary amines can reversibly form carbamate anions and the addition proton is bound by a second molecule of amine. Therefore, two equivalents of amine are required to capture one equivalent of CO2. In contrast, tertiary amines, like the amine compounds described in this invention, can bind CO2 in an equimolar ratio in aqueous solutions, due to the formation of carbonic acid salts. The reactions are shown below:

[0016] There is a strong demand for improved amines for amines-based gas cleaning processes since amines are associated with challenges in their production and use phase. Especially the emission of potentially hazardous components to the environment, i.e. loss of amine due to high volatility, or the requirements for intense post treatment procedures are to be mentioned.

[0017] Shorter chain / simple amines usually have the advantage of low viscosity, reducing the operations costs for amine-solvent circulation and assuring high mass transfer rates in the absorption process. However, these amines are typically volatile, i.e. show rather high vapor pressure, which leads to constant losses in the desorption step at elevated temperature, or they require sophisticated recovering methods.

[0018] Amines with higher boiling point / reduced vapor pressure are typically toxic and show a higher viscosity. At the same time, higher molecular weight usually reduced the loading capacity of the amines-based solvent system, due to the stoichiometry.

[0019] Due to the difference in reaction mechanism, secondary amines suffer from lowered CO2 loading and from carbamate formation, which can lead to severe corrosion issues in the gas treatment plants.

[0020] Urvashi K. Sarode et al., Ind. Eng. Chem. Res. 2023, 62, 1492-1498 teaches that Amino sugars, i.e. sugars wherein the amine group substitutes the hydroxyl group, are renewable and ecofriendly CO2 separation solvents. The kinetics of CO2 absorption in the amino sugar glucosamine (GA), A / -acetyl-D-glucosamine (NAG) and / V-methyl-D-glucamine (NMG) were studied.

[0021] US11266947 teaches a method comprising contacting a gas stream comprising a first amount of CO2 with a CO2-lean solvent stream comprising a compound according to Formula I to form a treated gas stream comprising a second amount of CO2 that is less than the first amount, and a CO2-rich solvent stream, and heating the CO2-rich solvent stream to form a CO2 stream and regenerate the CO2-lean solvent, wherein the compound has the structure:

[0022] R<1 >(R<2>)N-L<1 >-NH-R<3 > (I) wherein each of R<1 >and R<2 independently is aliphatic, cycloaliphatic, or R<1 >and R<2 >together with the nitrogen to which they are attached, form a heterocyclic ring, L<1 >is aliphatic, cycloaliphatic, or L<1 >and R<1 >together with the nitrogen to which they are attached form a heterocyclic ring, and R<3 >is aliphatic, cycloaliphatic, cycloalkylalkyl, or alkoxyalkyl.

[0023] The ideal amine-based solution should comprise tertiary amines with low vapor pressure and low viscosity. At the same time, the material needs to be compatible with the environment, ideally non-toxic and based on renewable resources.

[0024] To be useful in the absorption and desorption process, suitable amine shall exhibit an excellent stability towards thermal and oxidative degradation, they shall be low foaming, especially during the gas intake step at low temp and at the desorption step, low corrosion, especially at elevated temperature during desorption, high cyclic loading and unloading and show a low level of nitrosam ines as oxidative side products.

[0025] In the instant invention it was found that an aqueous solvent system, comprising of polyol tertiary amines according to Formula (I), originated from highly abundant, naturally occurring sugar compounds is suitable as an absorption liquid for CO2 absorption and shows the above mentioned properties. Disclosed herein is a method and system for removing CC from a gas stream using a solvent comprising, consisting essentially of, or consisting of, polyol tertiary amines according to Formula (I) and water as a co-solvent.

[0026] Object of the invention is a method comprising contacting a gas stream comprising a first amount of CO2with a C02-lean solvent stream that comprises a compound according to Formula I to form a treated gas stream comprising a second amount of CC that is less than the first amount, and a CO2-rich solvent stream, and heating the CO2-rich solvent stream to form a CO2 stream and a C02-lean solvent stream, wherein R1and R2are independently selected from linear or branched C1-C4 alkyl, and n is selected from 2 to 4.

[0027] Another object of the invention is the use of a compound according to Formula I wherein

[0028] R1and R2are independently selected from linear or branched C1-C4 alkyl, and n is selected from 2 to 4, as an absorbent for CO2.

[0029] Preferably, the CO2-rich solvent stream and the C02-lean solvent stream comprise a compound according to Formula (I) and water.

[0030] In a preferred embodiment of the invention, n in Formula (I) is 3 or 4, more preferably 4.

[0031] In a preferred embodiment of the invention, n in Formula (I) is 3 or 4, more preferably 4.

[0032] In a preferred embodiment of the invention, R1and R2are independently selected from methyl and ethyl, and more preferably are methyl. Particularly, R1and R2are methyl and n is 4. Particularly preferred, the compound according to Formula I is / V, / V-Dimethyl-D-glucamine (DMG). The solvent that forms the solvent stream comprises at least one compound according to Formula I. The solvent may comprise mixtures of compounds according to Formula (I) or single compounds according to Formula (I).

[0033] Besides one or more compounds according to Formula I, the solvent may comprise other compounds. In this case, the solvent is a solvent system comprising at least one compound according to Formula (I) and one or more additional solvent system components. Suitable amines to be combined with the compound according to Formula (I), selected from Monoethanolamine (MEA), Diethanolamine, Methyldiethanolamine (MDEA), Diglycolamine (DGA) / 2-(2- aminoethoxy)ethanol, Diisopropanolamine (DIPA), Triethanolamine (TEA), 2- Amino-2-methyl-1 -propanol (AMP), Piperazine (PZ), Aminoethylethanolamine (AEEA) I N-(2-aminoethyl)ethanolamine, Aminoethylpiperazine (AEP), Hydroxyethylpiperazine (HEP), Ethylenediamine (EDA), Diethylenetriamine (DETA), Triethylenetetramine (TETA), Tetraethylenepentamine (TEPA), N,N- Dimethylethanolamine (DMMEA), 3-Amino-1 -methylaminopropane (MAPA), N,N- Diethylethanolamine (DEEA), 1 ,6-Hexamethylenediamine (HMDA), Polyethyleneimines (PEI), 2-Aminoethanol (Ethanolamine), Monomethylethanolamine (MMEA), 2,4,6-Trimethylaniline, 2,6-Diisopropylaniline, 2,4,6-Tri-tert-butylaniline, Methylamine, Ethylamine, Propylamine, Butylamine, Dimethylamine, Diethylamine, Dipropylamine, Dibutylamine, Trimethylamine, Triethylamine, Tripropylamine, Tributylamine, Pyrrolidine, Piperidine, Azepane, Azocane, Pyrrole, Aniline, o-Toluidine, m-Toluidine, p-Toluidine, Xylidines, 1 - Naphthylamine, 2-Naphthylamine, o-Phenylenediamine, m-Phenylenediamine, p- Phenylenediamine, Imidazole, Benzimidazole, Pyridine, Quinoline, 1 ,4- diazabicyclo-undec-7-ene (DBU), 1 ,4-diazabicyclo-2,2,2-octane, Triethylamine (TEA), 1 ,1 ,3,3-tetramethyl guanidine (TMG), 1 ,8-diazabicycloundec-7-ene, Diethylamine (DEA), 1 ,3-diamino propane, 1 ,4-diaminobutane, Hexamethylenediamine, 1 ,7-diaminoheptane, Diisopropylamine (DIPA), 4- aminopyridine, Pentylamine, Hexylamine, Heptylamine, Octylamine, Nonylamine, Decylamine, tert-Octylamine, Dioctylamine, Dihexylamine, 2-ethyl-1 -hexylamine, 2 -fluorophenethylamine, 3-fluorophenethyl amine, 3,5-difluorobenzylamine, N- methylbenzylamine, 3-fluoro-N-methylbenzylamine, 4-fluoro-N- methylbenzylamine, N-methyl imidazole, 1 -trifluoroacetylimidazole, 1 ,2,3-triazole, 1 ,2,4-triazole, sugar based amines with 3 to 6 carbon atoms and mixtures thereof.

[0034] In a preferred embodiment of the invention, the solvent is a solvent system that comprises at least one compound according to Formula (I) and water.

[0035] When water is used as an additional solvent system component, the solvent system comprises 25 wt.-%-70 wt.-% water.

[0036] In a preferred embodiment, the solvent system comprises 10 to 50 wt.-% of a compound according to Formula I, more preferably 20 to 45 wt.-%.

[0037] This invention concerns a method for removing CC gas from a gas stream. The CO2-rich solvent stream has a higher CO2 content than the CO2-lean solvent stream. It is preferred that the CO2 capture occurs under a first set of conditions and the CO2 release and solvent regeneration occurs under a second set of conditions.

[0038] Contacting the gas stream with the CO2-lean solvent stream preferably occurs at a first temperature of 20°C to 65°C.

[0039] Heating the CO2-rich solvent stream is a desorption step. It causes desorption of CO2 and serves the purpose of recycling the absorption liquid and to form a regenerated CO2-lean solvent stream. Heating the CO2-rich solvent stream preferably occurs at a second temperature of from 65°C to 100°C. Heating the CO2-rich solvent stream may be performed at a pressure of from 1 bar to 6 bar, such as from greater than 1 bar to 3 bar, or from 1 bar to 2 bar.

[0040] In a preferred embodiment, the method further comprises cooling the regenerated CO2-lean solvent stream to a temperature of - 20° C to 65° C. In a preferred embodiment, the method and the use occur at a CO2 partial pressure of the CO2 rich gas stream below 300 mbar, preferably 250 mbar or lower, most preferably 200 mbar or lower.

[0041] Due to their polyol structure, the compounds according to Formula (I) have a vapor pressure of less than 0.1 Pa at 20 °C and can be classified as non-volatile organic components, i.e. the compounds according to Formula (I) one are non-volatile during the absorption and desorption process. As a result, an aqueous solvent comprising one or more compounds according to formula (I) has a similar vapor pressure like water.

[0042] Since the compounds according to Formula (I) have a low vapor pressure, loss of such compounds during absorption, and regeneration is minimized.

[0043] Water can be condensed and recycled during the desorption step.

[0044] The advantage of using the non-volatile compound according to Formula (I) is that loss of material is reduced during the desorption process. This has a positive impact on A) the avoidance of operational costs caused by handling and refilling a volatile organic amine and B) the avoidance of emission of potentially hazardous components to the environment.

[0045] Thitakamol et al. / Energy Procedia 1 (2009) 1381 -1386 states, that foaming impacts integrity of plant operation, causing excessive loss of absorption solvents, premature flooding, reduction in plant throughput, off-specification of products, and high absorption solvent carryover to downstream plants.

[0046] Furthermore, literature known amine-polyols (e.g. NMG) show certain advantages but they suffer from intense foaming. It was surprisingly found that DMG (Formula (I) shows significant less foam, as is shown in the examples. According to the state of the art, e.g., MDEA, MEA and DEA are used as absorbents for CO2 capture. MDEA exhibits superior low vapor pressure compared to primary and secondary amines, e.g., mono ethanol amine (MEA) or di ethanol amine (DEA), and reduced hazardous risks, but is limited in CO2 absorption performance. The performance gap requires the application of performance boosters, as indicated in the cited prior art, especially at low partial pressure of CO2. In addition, MDEA is derived from fossil feedstock and is not hazardous label-free. Furthermore, the compounds according to Formula (I) show a low toxicity to humans and the environment. Due to the nature of the chemical structure, compounds according to Formula (I) show reduced hazardous potential, e.g. N,N- dimethyl-D-glucamine is classified as non-hazardous substance (see table below). At the same time, the compounds according to Formula (I) show high biodegradability and are classified as readily biodegradable according to OECD Test 301 F.

[0047] The following table compares basic substance and hazardous material data of a selected compound according to Formula I and amines for CO2 capture from the prior art. The following abbreviations are used: DMG = N,N-dimethyl-D-glucamine, MEA = mono ethanol amine, MDEA = Methyldiethanolamine, DEA = diethanolamine, DGA = diglycol amine (1-Amino-2-(2-hydroxyethoxy)ethane) , HEP = 1-(2-Hydroxyethyl)piperazine

[0048] Table 1 : Properties of amines for CO2 capture

[0049] It has been found that aqueous mixtures of the compounds according to Formula (I) show high potency in CO2 absorption. Despite their comparable high molecular weight, they exhibit surprisingly high performance at low CO2 partial pressure and efficient release of CO2 in the desorption step.

[0050] “Vapor pressure” refers to the equilibrium pressure of a vapor above its liquid resulting from evaporation of the liquid at a particular temperature. As used herein, vapor pressure is reported at 20° C unless otherwise specified. Typically, vapor pressure is measured in a closed container.

[0051] General process of amine-based CO2 capture

[0052] A CO2 containing gas streams enters an absorber column and flows against a CO2-lean, amine-based solvent. The CO2 is absorbed by the solvents, reacts with the amines to form water-soluble compounds like carbamates or carbonate salts. The treated, CO2 depleted gas stream leaves the absorber column and the CO2- rich amine solution is pumped to a stripper column for regeneration. In the stripper column, the CO2-rich solution is heated in order to regenerate the amine by reversing the reaction. Consequently, CO2 is released, producing a CO2-rich gas stream which exits the stripper. The CO2 rich gas stream can be further processed and used for CO2 storage or utilization. From the stripper column, the CO2- depleated (lean) amine solution is cooled and returned to the absorber for reuse.

[0053] In general, any acidic gas components, like H2S, COS, can react with an amine and can be treated by such a process.

[0054] Compounds:

[0055] Sugar-based amine derivatives are known in literature, e.g. their synthesis is described in EP3601211. Sugar based amines according to EP3601211 can be made from any aldose (sugar with terminal aldehyde group) with any given stereo configuration.

[0056] Methods according to the state of the art for improvement of CO2 absorption and desorption performance by addition of phosphonic acids or primary / secondary amines to the absorbent, e.g. MDEA, can also be applied for compounds according to formula (I).

[0057] In a preferred embodiment, the method according to the invention includes the additional presence of primary and secondary amines. The secondary amine may preferably be a secondary sugar-based amines, e.g. N-Methyl-D-Glucamine, according to Urvashi K. Sarode et al., Ind. Eng. Chem. Res. 2023, 62, 1492-1498). The additional presence of primary and secondary amines may result in an improved CO2 absorption compared to the presence of compounds according to formula 1 alone.

[0058] The solvent system according to the invention may further comprise one or more additives selected from substance classes of defoamers, stabilizers, antioxidants, corrosion inhibitors, lubricity improvers, anti-cavitation agents and cycle capacity improvers such as amino acids and amidosulfonic acids.

[0059] Examples

[0060] DMG was synthesized according to patent EP3601211 from naturally occurring D- Glucose. The material was used as aqueous solution at different weight-% concentrations.

[0061] Experimental setup for CO2 capture testing

[0062] In the test setup, a gas stream, with adjustable volume proportions of CO2 and N2, is bubbled through the test solution in a column, which is placed in a thermally controlled bath filled with thermal oil. The required volume flows (in = L / h) of the components of the raw gas flow can be precisely controlled by mass flow controllers. According to the ideal gas equation, the volume flow ratio corresponds to the mass flow ratio. The adjusted gas flow can either be directed into the bubble column via a frit near the bottom of the column or to the CO2 analyzer (Infralyt 80 from SAXON Junkalor GmbH) device to check the volume flow ratio. The gas stream escaping from the bubble column, represents the “clean gas stream”, is passed via a reflux condenser, to the CO2 analyzer. Entrained water is removed by the condenser and fed back to the solvent in the column.

[0063] The absorption process is carried out at temperatures of 25 °C or 40 °C. Solvent loading with CO2 can be assessed by differential gas composition of the feed and the analyzed gas mixture. Upon saturation of the solution, the gas composition exiting the column shows the set composition of the mass flow meters, what is used to determine the end point of absorption.

[0064] The gas composition is adjusted via mass flow meters by mixing defined flow rates of Nitrogen (N2) and CO2 at a total pressure of 1 bar.

[0065] 1 ) CO2 solubility and absorption C02 solubility / uptake was measured at 40 °C, comparing DMG 50 wt.-% (aq.) with MDEA 50 wt.-% aq., by variation of CO2 partial pressure via a mass flow controller and a total pressure of 1 bar, adjusted with nitrogen. The CO2 solubility is derived from the difference in CO2 partial pressure of the feed gas stream and the exhaust gas stream.

[0066] Table 2

[0067] The data clearly show that, especially at low partial pressure of CO2, DMG takes up more CO2 compared to MDEA. At a partial pressure of around 300 mbar, the C02 absorption capacity is identical. Considering the molecular weight of the different amine compounds and the stoichiometry of the absorption reaction in tertiary amines, a significantly higher molar loading with CO2 can be observed with the inventive examples.

[0068] 2) Desorption and differential loading To assess the differential load of different amine compounds, CO2 absorption was carried out at 25 °C. The solvent is then heated to 95 °C to simulate the desorption process at elevated temperature. CO2 loading was assessed after absorption and desorption respectively. DMG shows low residual loading, comparable value of comparative example MDEA. Almost identical differential loading (delta), while the difference in molecular weight is almost factor 2. Measurements were taken at 0.1 bar CO2 partial pressure.

[0069] Table 3 Even if desorption rate or residual loading does not outperform the comparative example, the superior CO2 capacity in absorption at low CO2 partial pressures and the overall low residual loading prove the inventive polyol tertiary amines in aqueous solution as useful in CO2 capture and release applications.

[0070] 3) Thermal stability testing and data Thermal stability was assessed by storage of the aqueous mixture of DMG 50% aq. at 120 °C for 28 days in air-tight, pressure stable containers. Samples were analyzed by gas chromatography and NMR and referenced on the results of a fresh solution. Via NMR analysis, virtually no degradation could be observed. The analysis by gas chromatography revealed at maximum a 1 .5% loss of DMG purity, suggesting a sufficient thermal stability for routine applications which are usually at lowered temperature, e.g. 70 to 100 °C.

[0071] Table 4

[0072] 4) Foaming

[0073] Foam height of NMG is 1 ,5 times higher than DMG (Formula I), additionally the foam decay time of DMG (Formula I) is found to be 3,6 times faster than of NMG.

[0074] Table 5

Claims

AMENDED CLAIMS received by the International Bureau on 10 March 2025 (10.03.2025)1 . A method, comprising contacting a gas stream comprising a first amount ofCO2with a CO2-lean solvent stream that comprises a compound according to Formula Ito form a treated gas stream comprising a second amount of CC that is less than the first amount, and a CO2-rich solvent stream, and heating the CO2-rich solvent stream to form a CO2 stream and a CO2-lean solvent stream, wherein R1and R2are independently selected from linear or branched C1-C4 alkyl, and n is selected from 2 to 4.

2. The method of claim 1 , wherein the CO2-rich solvent stream and the CO2- lean solvent stream comprise a compound according to Formula (I) and water.

3. The method of claim 1 and / or 2, wherein n is 3 or 4, preferably 4.

4. The method of one or more of claims 1 -3, wherein R1and R2are independently selected from methyl and ethyl, and preferably are methyl.

5. The method of one or more of claims 1 -4, wherein R1and R2are methyl and n is 4.

6. The method of claim 1 , wherein the compound according to Formula I is / V, / V-Dimethyl-D-glucamine.

7. The method of one or more of claims 1 -6, wherein the compound according to Formula I is present in the C02-lean solvent stream in a concentration of 10 to 50 wt.-%.

8. The method of one or more of claims 2-7, wherein water is present in the CO2-lean solvent stream in a concentration of 25 to 70 wt.-%.

9. The method of one or more of claims 1 -8, wherein and the CO2 partial pressure of the CO2 rich gas stream is below 300 mbar, preferably below 250 mbar.

10. Use of a compound according to Formula IwhereinR1and R2are independently selected from linear or branched C1-C4 alkyl, and n is selected from 2 to 4, as an absorbent for CO2.11 . The use of claim 10, wherein n is 3 or 4, preferably 4.

12. The use of claim 10 and / or 11 , wherein R1and R2are independently selected from methyl and ethyl, and preferably are methyl.

13. The use of one or more of claims 10-12, wherein R1and R2are methyl and n is 4.

14. The use of claim 10, wherein the compound according to Formula I is / V, / V-Dimethyl-D-glucamine.

15. The use of one or more of claims 10-14, occurring at a CO2 partial pressure of below 300 mbar, preferably below 250 mbar.

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