Thermally stable amino acids for co2 capture

Abstract

Systems and methods are provided for sorption of CO2 from a CO2-containing stream, along with corresponding desorption of the CO2 to regenerate the sorbent. The sorption is performed using an aqueous amine sorbent where at least a portion of the amine sorbent corresponds to an amino acid, where the amine nitrogen of the amino acid is part of a six-member organic ring structure. Examples of this type of amino acid include various types of amino acid derivatives of piperazine and piperidine

Description

THERMALLY STABLE AMINO ACIDS FOR CQ2 CAPTUREFIELD OF THE INVENTION

[0001] Methods are provided for sorption of acid gases using thermally stable amino acids.BACKGROUND OF THE INVENTION

[0002] Solvent phase capture of a CO2 is a commonly used method for separating CO2 from gas phase streams. The properties of a solvent phase capture system, such as an amine wash, are primarily driven by the nature of the sorbent used for adsorbing CO2. Generally, it is beneficial to use a sorbent that has one or more of the following properties: high cyclic CO2 capacity, low regeneration energy requirements, oxidative stability, thermal stability, and low volatility.

[0003] One of the benefits of a sorbent that has increased thermal stability is that CO2 desorption can be performed at higher temperature while reducing or minimizing degradation of the sorbent during a soiption / desorption cycle. For example, conventionally, desorption of CO2 involves increasing the temperature of the solvent, which includes the sorbent, to a desorption temperature. If a sorbent does not have sufficient thermal stability at the desorption temperature, the sorbent will degrade over the course of a limited number of cycles. Such a sorbent that degrades after only a few cycles has little value commercially. Due to this difficulty, the desorption temperature for a given sorbent is limited to temperatures where the sorbent is sufficiently stable.

[0004] Amines are a commonly used type of sorbent for sorption and desorption of CO2. While a variety of amines have been used as sorbents, it would be desirable to have improved amine sorbents and / or sorbent systems that can provide combinations of thermal stability, oxidative stability, volatility, and CO2 capacity that are not readily achieved by conventional amine sorbent systems.

[0005] U.S. Patent 5,744,110 describes removal of CO2 from combustion exhaust gas using an aqueous mixture of piperazine and an amino acid salt of an amino acid that includes lower alkyl groups.

[0006] U.S. Patent 10,583,388 describes capturing CO2 using aqueous solutions of amino acids, where the amino acids are alkyl substituted variations of twenty amino acids commonly encountered in biological processes.

[0007] U.S. Patent Application Publication 2015 / 0196895 describes using ionic liquids supported on porous carrier materials for CO2 sorption. The ionic liquids are derived from amino acids.

[0008] A dissertation by Yang Du (University of Texas at Austin, May 2016) describes amine solvent development for carbon capture. Mixtures of piperazine and proline were studied for thermal degradation. A maximum stripper temperature was determined for a number of different amines for potential use in a mixture with piperazine. The maximum stripper temperature represents a maximum temperature during CO2 desorption. A maximum stripper temperature of proline was reported as being less than 110°C.

[0009] The operating manual for the Dionex AAA-Direct Amino Acid Analysis system (available from Thermo Scientific) describes a test method for characterizing amino acids in a solution.SUMMARY OF THE INVENTION

[0010] In an aspect, a method for sorbing CO2 from a gas stream is provided. The method includes exposing a gas stream containing CO2 to an aqueous amine sorbent containing an amino acid and a base to form a CO2-rich sorbent under sorption conditions including a temperature of -10°C to 100°C. An amine group of the amino acid can be part of a six-membered ring structure in the amino acid, the carboxylic acid group being connected to the ring via an atom that is different from a carbon that is alpha to the amine of the amino acid. A molar ratio of the base to the amino acid can be 0.5 to 2.0. Additionally, the method includes desorbing CO2 from the CCh-rich sorbent under desorption conditions including a temperature of 100°C to 180°C to regenerate the aqueous amine sorbent and form a product stream that contains CO2.BRIEF DESCRIPTION OF THE DRAWING

[0011] FIG. 1 shows examples of amino acids where the nitrogen atom of the amine is part of a six-membered ring.

[0012] FIG. 2 shows an example of a system for performing sorption and desorption using an aqueous amine sorbent.DETAILED DESCRIPTION OF THE INVENTION

[0013] All numerical values within the detailed description and the claims herein are modified by “about" or “approximately" the indicated value, and take into account experimental error and variations that would be expected by a person having ordinary skill in the art.Overview

[0014] In various aspects, systems and methods are provided for sorption of CO2 from a CO2-containing stream, along with corresponding desorption of the CO2 to regenerate the sorbent. The sorption is performed using an aqueous amine sorbent where at least a portion of the amine sorbent corresponds to an amino acid, where the amine nitrogen of the amino acid is part of a six-member organic ring structure. Examples of this type of amino acid include various types of amino acid derivatives of piperazine and piperidine.

[0015] Amino acids are potential sorbents that have low volatility and that are oxidatively stable. These characteristics are valuable for managing emissions caused by the sorbent, such as emissions due to evaporation of sorbent from the absorber column to the atmosphere. However, amino acids typically do not have favorable thermal stability, which limits their regeneration pressure and / or temperature. In particular, this limits the desorption temperature that can be used during a sorption I desorption cycle. When desorbing CO2 from an aqueous amine solution, at any temperature greater than 100°C, the amount of H2O in the vapor phase above the aqueous amine solution will be similar. However, as the temperature is increased, the partial pressure of CO2 that can be achieved above the aqueous amine solution is increased. In other words, the ratio of CO2 to H2O that can be achieved during desorption is increased as the desorption temperature increases. This is beneficial for various reasons, such as reducing the separation costs per CO2 that is captured by a sorption I desorption cycle. Thus, it is beneficial to have sorbents that remain thermally stable at higher desorption temperatures.

[0016] In contrast to conventional amino acids, it has been determined that specific types of amino acids can have improved thermal stability. This allows for wider temperature and / or pressure swings between sorption and desorption, thus allowing for greater working capacity. These amino acids correspond to amino acids where the nitrogen atom of the amine in the amino acid is part of a six membered aliphatic ring. The nitrogen atoms in piperidine and piperazine are examples of nitrogen atoms that are part of a six membered aliphatic ring. Additionally, for the amino acids with improved thermal stability, the carboxylic acid of the amino acid is not connected to the ring via a carbon atom that is alpha to a nitrogen in the ring. Instead, the carboxylic acid isconnected to the ring via a nitrogen, or connected via a carbon that is beta to a nitrogen, or connected to the ring via a carbon that is gamma to a nitrogen. In this discussion, being “connected to the ring via an atom” means that the carboxylic acid is either directly bonded to an atom, or the carboxylic atom is separated from the ring by an i nlervening alkyl chain, and the intervening alkyl chain is bonded to the atom. 2-(piperazin-l-yl) acetic acid is an example of an amino acid where the carboxylic acid is bonded to an alkyl chain (a Ci chain, or methylene group) that is bonded to a ring nitrogen. Amino acids that include a) an amine nitrogen that is part of a six membered aliphatic ring, and b) a carboxylic acid connected to the ring at a location different from an alpha carbon relative to a ring nitrogen, are believed to have improved thermal stability. These amino acids with improved thermal stability can be used as part of an aqueous amine sorbent for sorption and desorption of CO2.

[0017] One of the advantages of using an amino acid with improved thermal stability in an aqueous amine system is that temperatures substantially above 100°C can be used during the desorption step. This can substantially increase the partial pressure of CO2 in a desorption effluent relative to the partial pressure of H2O. In various aspects, an amino acid that includes an amine nitrogen as part of a six-membered ring can be sufficiently stable to allow for use in desorption steps at temperature of 125°C to 180°C, or 125°C to 165°C, or 125°C to 150°C, or 140°C to 180°C, or 140°C to 165°C, or 150°C to 180°C.

[0018] FIG. 1 shows four examples of amino acids that include the amine nitrogen for the amino acid as part of a six-membered organic ring structure. The amino acids in FIG. 1 correspond to 2-(piperazin-l-yl) acetic acid (PZAA), piperazine-2-carboxylic acid (PZCA), 4-piperidine carboxylic acid (common name isonipecotic acid, INPA), and 3-piperidine carboxylic acid (common name nipecotic acid, NPA). The amino acids in FIG. 1 each have either one amine nitrogen in the six-membered ring structure (the piperidine derivatives), or two amine nitrogens in the six-membered ring structure (the piperazine derivatives).

[0019] It is noted that the location where the carboxylic acid functionality is connected to the six-membered ring structure is also relevant. 2-(piperazin-l-yl) acetic acid (PZAA) corresponds to an amino acid where the side chain containing the carboxylic acid is connected to the ring via an amine nitrogen in the ring structure. By contrast, piperazine-2-carboxylic acid (PZCA) has a carboxylic acid bonded at a carbon on the ring structure. This type of structure is believed to have reduced thermal stability, as opposed to the improved thermal stability of a structure such as PZAA. It is noted that in a ring structure that is a piperazine derivative, all carbons in the ring structure are alpha to a ring nitrogen. By contrast, for a piperadine derivative, carbons are presentin the ring that are beta to the ring nitrogen (such as NPA) or gamma to the ring nitrogen (such as INPA).

[0020] It is further noted that in 2-(piperazin- 1 -yl) acetic acid, the carboxylic acid functionality is separated from the ring structure by a methylene group. In some aspects, the carboxylic acid functionality can be bonded directly to a nitrogen atom or carbon atom that is part of the sixmembered ring structure. Examples of this are piperazine-2-carboxylic acid, 4-piperidine carboxylic acid, and 3-piperidine carboxylic acid. In other aspects, the carboxylic acid functionality can be separated from the six-membered ring structure by an alkylene group. In this discussion, this is defined as a carboxylic acid that is bonded to an aliphatic side chain, with the aliphatic side chain being bonded to the six-membered ring structure. For example, in 2-(piperazin-1-yl) acetic acid, the carboxylic acid functionality is bonded to a methylene group, and the methylene group is bonded to the six-membered ring structure. Thus, in 2-(piperazin-l-yl), the methylene group corresponds to an aliphatic side chain that contains one carbon atom. More generally, when a carboxylic acid group is bonded to an aliphatic side chain, the aliphatic side chain can correspond to a Ci - Ce aliphatic side chain (a side chain that includes 1 to 6 carbon atoms). When a carboxylic acid is bonded to an aliphatic side chain, the atom in the ring that is bonded to the aliphatic side chain is the atom that the carboxylic acid is “connected” to.

[0021] It is noted that while amino acids arc effective for CO2 sorption and dcsoiption, other components of a gas phase stream may also be sorbed and desorbed by an aqueous amine sorbent that contains an amino acid as described herein. Other gas phase components that can be sorbed include, but are not limited to, H2S, carbonyl sulfide, mercaptans, and dimethylsulfide.

[0022] In this discussion, unless otherwise specified, the term amine is defined broadly to include any compound that contains an amine nitrogen, whether other functional groups are present in the compound or not. For example, an amino acid includes an amine nitrogen.Aqueous Amine Sorbents Including Amino Acids with Improved Thermal Stability

[0023] In various aspects, an aqueous amine sorbent can be used for sorption of CO2 from a CO2 containing stream, followed by desorption of the CO2 to regenerate the aqueous amine sorbent. An aqueous amine sorbent can contain at least water, an amino acid with improved thermal stability, and a sufficient amount of a base to activate the amino acid. Optionally, the aqueous amine sorbent can further include other components to assist with and / or facilitate CO2 sorption. Such additional components can include, for example, alkali or alkaline earth carbonates. Other additional components can correspond to additional amines that are hindered and / or tertiary amines. More generally, it is noted that other organic components can also be present in theaqueous amine sorbent, so long as the other organic components are present in sufficiently small amounts relative to the amount of water. Examples of other organic components can include organic co-solvents.

[0024] The primary solvent for the aqueous amine sorbent is water. Several types of descriptions can be used for providing the relative amounts of amino acids, bases, and other components in an aqueous amine sorbent. One option is to describe the amount of an amino acid, base, or other component in terms of molality, which is the number of moles of a component per 1 kilogram of water in the aqueous amine sorbent. The amount of amino acid with improved thermal stability in the aqueous amine sorbent can range from 0.1 moles amino acid / kg water to 10 moles amino acid I kg waler. This corresponds to a molality of 0.1 to 10. More generally, the amount of amino acid with improved thermal stability in the aqueous amine sorbent can correspond to a molality of 0.1 to 10, or 0.1 to 7.0, or 0.1 to 5.0, or 0.1 to 3.0, or 0.5 to 10, or 0.5 to 7.0, or 0.5 to 5.0, or 0.5 to 3.0, or 1.0 to 10, or 1.0 to 7.0, or 1.0 to 5.0, or 2.5 to 10, or 2.5 to 7.0, or 2.5 to 5.0, or 4.0 to 10, or 4.0 to 7.0. It is noted that the molality of the amino acid can be selected so that after sorption of CO2 during a sorption step, the amino acid remains substantially dissolved in water.

[0025] Another type of description is to describe the weight percentage of components dissolved in the water. In this type of description, the weight of water in the solution is not considered. Instead, the weights of the components dissolved in the water are described. As an example, a full description of an aqueous amine sorbent can be provided by specifying the molality of amino acid in the water, and then providing weight percentages for the amino acid and other components dissolved in the water.

[0026] Still another type of description can be to specify relative molar quantities for two components. Yet another type of description can be to specify a weight percentage of a component relative to the weight of water.

[0027] In various aspects, an aqueous amine sorbent can contain 1.0 wt% to 60 wt% of one or more amino acids with improved thermal stability, relative to the weight of components dissolved in water, or 1.0 wt% to 45 wt%, or 1.0 wt% to 30 wt%, or 1.0 wt% to 20 wt%, or 5.0 wt% to 60 wt%, or 5.0 wt% to 45 wt%, or 5.0 wt% to 30 wt%, or 5.0 wt% to 20 wt%, or 10 wt% to 60 wt%, or 10 wt% to 45 wt%, or 10 wt% to 30 wt%, or 20 wt% to 60 wt%, or 20 wt% to 45 wt%, or 30 wt% to 60 wt%, or 40 wt% to 60 wt%.

[0028] Another component in the aqueous amine sorbent is a base. Generally, the aqueous amine sorbent can contain a sufficient amount of base so that neither the carboxylic acid nor theamine(s) in the amino acid are substantially protonated. This can be achieved by adding an amount of base that is roughly equimolar to the amount of the molar amount of the amino acid. Preferably, the base is a strong base that undergoes substantially complete dissociation in aqueous solution, such as an alkali metal hydroxide (examples are KOH, NaOH). In various aspects, a molar ratio of the amount of base to the amount of amino acid can be from 0.5 to 2.0, or 0.5 to 1.5, or 0.5 to 1.1, or 0.9 to 2.0, or 0.9 to 1.5, or0.9 to 1.1. Additionally or alternately, the amount of base can be specified as a weight percentage relative to the weight of the components in solution. In various aspects, the amount of base can be 1.0 wt% to 50 wt%, relative to the weight of the components in solution, or 1.0 wt% to 35 wt%, or 1.0 wt% to 20 wt%, or 1.0 wt% to 10 wt%, or 3.0 wt% to 50 wt%, or 3.0 wt% to 35 wl%, or 3.0 wt% to 20 wt%, or 3.0 wt% to 10 wt%, or 5.0 wt% to 50 wt%, or 5.0 wt% to 35 wt%, or 5.0 wt% to 20 wt%, or 10 wt% to 50 wt%, or 10 wt% to 35 wt%, or 10 wt% to 20 wt% or 20 wt.% to 50 wt%, or 20 wt% to 35 wt%.

[0029] Other components that can be included in the aqueous amine sorbent are additional components that facilitate CO2 sorption and / or desoiption. Such components can include, for example, components that facilitate formation of carbamates when CO2 is sorbed.

[0030] Some types of additional components are carbonates, such as alkali metal carbonates and / or alkaline earth carbonates. Examples of carbonates are Na2CC>3, K2CO3, and CaCCT In various aspects, the weight percent of carbonate relative to the components dissolved in solution can be 1.0 wt% to 60 wt%, or 1.0 wt% to 25 wt%, or 1.0 wt% to 15 wt%, or 1.0 wt% to 5.0 wt%, or 5.0 wt% to 60 wt%, or 5.0 wt% to 25 wt%, or 5.0 wt% to 15 wt%, or 10 wt% to 60 wt%, or 10 wt% to 25 wt%.

[0031] Other additional components can correspond to primary amines, secondary amines, tertiary amines, and / or hindered amines. While it is possible that such primary / secondary / tertiary I hindered amines could include amino acids that do not have a 6-membered ring structure, optionally but preferably, such other additional components can correspond to primary / secondary I tertiary / hindered amines that are different from amino acids. Due to the ring structures, piperazine and piperidine are examples of hindered amines. In some aspects where both an amino acid and a separate hindered and / or tertiary amine are included in the aqueous amine solution, the amino acid can be present in a higher concentration and / or weight percentage, with the amino acid serving as the primary sorbent for CO2. In other aspects, the separate hindered and / or tertiary amine can correspond to the primary sorbent, with the amino acid being present in a lower amount. The molar ratio of amino acid to combined hindered and / or tertiary amines in an aqueous amine sorbent can be 0.1 to 10, or 0.1 to 5.0, or 0.1 to 2.0, or 0.1 to 1.0, or 0.5 to 10, or 0.5 to 5.0, or 0.5 to 2.0,or 0.5 to 1.0, or 1.0 to 10, or 1.0 to 5.0, or 1.0 to 2.0, or 2.0 to 10, or 2.0 to 5.0, or 5.0 to 10. Additionally or alternately, the weight percent of tertiary and / or hindered amine in the aqueous amine solution can be 1.0 wt% to 50 wt% relative to the weight of components dissolved in the solution, or 1.0 wt% to 35 wt%, or 1.0 wt% to 20 wt%, or 5.0 wt% to 50 wt%, or 5.0 wt% to 35 wt%, or 5.0 wt% to 20 wt%, or 10 wt% to 50 wt%, or 10 wt% to 35 wt%, or 20 wt% to 50 wt%, or 20 wt% to 35 wt%.

[0032] Still other organic components can also be present. For example, small amounts of cosolvents, such as di -ethylene glycol, tri-ethylene glycol, and / or other polyglycols can be present in the aqueous amine sorbent. The amount of such co-solvents can be expressed relative to the weight of water. In various aspects, if other organic components are present, such as organic co-solvents, the weight of the other organic components, can be 0.01 wt% to 10 wt% relative to the weight of water in the aqueous amine sorbent, or 0.01 wt% to 5.0 wt.%, or 0.01 wt.% to 2.0 wt%, or 0.01 wt% to 0.2 wt%, or 0.1 wt% to 10 wt%, or 0.1 wt% to 5.0 wt%, or 0.1 wt% to 2.0 wt%.

[0033] Yet another way to characterize the contents of an aqueous amine sorbent can be based on a molar ratio of combined primary and secondary amines of any type (including amines in amino acids) to combined hindered and tertiary amines of any type (including amines in amino acids). In various aspects, the molar ratio of combined primary and secondary amines to combined hindered and tertiary amines can be 0.1 to 10, or 0.2 to 10, or 1.0 to 10, or 0.1 to 1.0, or 0.2 to 1.0.Additionally, or alternately, the molar ratio of combined primary and secondary amino acids to combined hindered and tertiary amines can be 0.1 to 10, or 0.2 to 10, or 1.0 to 10, or 0.1 to 1.0, or 0.2 to 1.0.CO2 Capture Configuration and Applications

[0034] CO2 capture can be used for a variety of applications. One type of CO2 capture process is direct air capture. Other types of CO2 capture applications can correspond to separation of CO2 from various types of flue gases, such as flue gases generated by natural gas power plants or coal-fired power plants. More generally, CO2 capture can be performed on any convenient type of CO2-containing stream so long as the CO2-containing stream has a suitably low content of components that could interfere with the CO2 sorption / desorption process.

[0035] In a typical CO2 capture process that uses an aqueous amine sorbent, a CCb-containing gas enters into the bottom of an absorption column. Optionally but preferably, the CO2-containing gas can be substantially free from particulate matter, SO2, SO3, NO, and NO2. In direct air capture applications, fans or blowers can help carry the air directly to the absorption column. In post-combustion capture applications, the flue gas is first quenched to roughly 40°C to 100°C andoptionally treated with caustic or other chemicals (e.g. thiosulphate) to scrub residual SO2, SO3, NO, and / or NO2 in a quenching column or in a trim removal column downstream of the quenching column. A fan or blower can be used to push the flue gas through the quencher, trim removal column, and / or the absorber column if the flue gas pressure needs to be boosted.

[0036] Gas sources can include but are not limited to, ambient air, natural gas combined cycle power plants, simple cycle natural gas or liquid-fuelled turbines, natural gas I oil / diesel boilers for heat or power generation, coal boilers for power generation, steel mills, cement kilns, and biomass boilers and power plants. The CO2 from these flue gas sources can vary from as little as about 3 volume percent to up to as much as about 30 volume percent with inlet absorber pressure from the gas varying anywhere from 1-3 bar atmospheric (-100 kPa-a to -300 kPa-a). It is noted that for direct air capture, the concentration of CO2 can be substantially lower. Air typically has a CO2 concentration near 400 vppm. For example, for direct air capture, the CO2 concentration in the CO2-containing gas can be 300 vppm to 600 vppm.

[0037] The absorption column is packed with equipment to increase mass transfer contact area and can include, but is not limited to, structured packing, random packing, or trays. An aqueous amine sorbent that can capture the CO2 from the feed is introduced at or near the top of the column. In various aspects, an aqueous amine sorbent can include an amino acid with improved thermal stability. The aqueous amine sorbent captures the CO2 as it is contacted with the air or flue gas, generally flowing countercurrently with respect to the air or flue gas. The absorption process is exothermic.

[0038] The aqueous amine sorbent flowing out of the absorber, now complexed with an increased amount of CO2 (and referred to as a rich sorbent), is heated (optionally in a crossexchanger) and fed to a flash stripper or a stripping column. Heat is introduced to the stripping column and CO2 is liberated from the sorbent. The CO2 is cooled to condense any stripped water and then is compressed and dried prior to being sequestered.

[0039] The stripping process regenerates the sorbent (called lean sorbent as it has a lower amount complexed with CO2). It is then cooled in the cross exchanger (which also heats the rich solvent) and is further cooled in a trim cooler before being fed to the top of the absorber column. A small amount of sorbent is purged either batchwise or continuously to manage quality.

[0040] FIG. 2 shows an example general configuration for using an aqueous amine sorbent to separate CO2 from a gas stream. In the example configuration shown in FIG. 2, a CCF-containing stream 205 is introduced into an absorption column 210 or other contactor where the CO2-containing stream 205 is contacted with an optionally cooled lean-amine stream 236 under CO2sorption conditions. Optionally, the temperature and / or pressure of the lean-amine stream 236 can be adjusted prior to entering absorption column 210. An example of such temperature adjustment is by passing the lean amine-stream 255 through heat exchanger 235 to form the optionally cooled lean amine stream 236, but other heat exchangers and / or coolers and / or compressors and / or other pressure adjustment devices can also be used. More generally, any of the streams shown in FIG. 2 can undergo additional temperature and / or pressure adjustment to be more suitable for processing.

[0041] Contacting CCF-containing stream 205 with lean-amine stream 236 results in formation of a CO2-depleted gas stream 212. The CCh-depleted gas stream 212 is then passed into a wash stage 220 to remove any excess amine that might be entrained with the CCh-depleted gas stream 212. The resulting washed CCh-depleted stream can then be exhausted to the atmosphere, or sent to another process for any convenient type of further processing.

[0042] Contacting CCh-containing stream 205 with lean-amine stream 236 also results in formation of a rich-amine stream 215. The rich-amine stream 215 is referred to as “rich” due to the increased amount of CO2 present in the stream. The rich-amine stream 215 can optionally be heat exchanged 235 with the lean-amine stream 255 to form an optionally heated rich-amine stream 234. The optionally heated rich-amine stream 234 is then passed into a stripper 240. Stripper 240 heats the rich-amine stream to desorb CO2. Heat for the stripper is provided by reboiler 250. The vapor from reboiler 250 is returned 252 to the stripper. The regenerated lean-amine stream 255 is then ready for use again for sorption of additional CO2. The CO2 that is desorbed in stripper 240 exits as CO2 product 242. The CO2 product 242 can be further processed in any convenient manner, such as undergoing compression prior to sequester.Sorption and Desorption Conditions

[0043] In various aspects, sorption of CO2 using an aqueous amine sorbent can be performed at temperatures of -10°C to 100°C, or 10°C to 100°C, or 40°C to 100°C. The pressure during sorption can be 90 kPa-a to 350 kPa- a, or 90 kPa-a to 250 kPa-a, or 90 kPa-a to 200 kPa-a, or 90 kPa-a to 150 kPa-a, or 105 kPa-a to 350 kPa-a, or 105 kPa-a to 250 kPa-a, or 105 kPa-a to 200 kPa-a, or 105 kPa-a to 150 kPa-a, or 130 kPa-a to 350 kPa-a, or 130 kPa-a to 250 kPa-a, or 130 kPa-a to 200 kPa-a, or 170 kPa-a to 350 kPa-a, or 170 kPa-a to 250 kPa-a, or 200 kPa-a to 350 kPa-a.

[0044] In various aspects, desorption of CO2 from an aqueous amine sorbent can be performed at temperatures of 100°C to 180°C, or 120°C to 180°C, or 140°C to 180°C, or 100°C to 165°C, or 120°C to 165°C, or 140°C to 165°C, or 100°C to 150°C, or 120°C to 150°C, or 100°C to 135°C. This can correspond to a temperature difference between sorption and desorption of 20°C or more,or 30°C or more, or 40°C or more, or 50°C or more, or 60°C or more, or 70°C or more, or 80°C or more, such as up to 120°C or possibly still more. Additionally or alternately, the pressure during desorption can be 90 kPa-a to 1000 kPa-a, or 90 kPa-a to 800 kPa-a, or 90 kPa-a to 650 kPa-a, or 90 kPa-a to 500 kPa-a, or 90 kPa-a to 300 kPa-a, or 90 kPa-a to 150 kPa-a, or 200 kPa-a to 1000 kPa-a, or 200 kPa-a to 800 kPa-a, or 200 kPa-a to 650 kPa-a, or 200 kPa-a to 500 kPa-a, or 350 kPa-a to 1000 kPa-a, or 350 kPa-a to 800 kPa-a, or 350 kPa-a to 650 kPa-a, or 350 kPa-a to 500 kPa-a, or 450 kPa-a to 1000 kPa-a, or 450 kPa-a to 800 kPa-a, or 450 kPa-a to 650 kPa-a, or 550 kPa-a to 1000 kPa-a, or 550 kPa-a to 800 kPa-a, or 700 kPa-a to 1000 kPa-a.

[0045] In aspects where direct air capture is performed, the CCh-containing gas can contain 300 vppm to 600 vppm of CO2. In other aspects, the CCh-containing gas can contain 2.0 vol% to 40 vol% of CO2, or 2.0 vol% to 30 vol%, or 2.0 vol% to 20 vol%, or 2.0 vol% to 15 vol%, or 2.0 vol% to 10 vol%, or 2.0 vol% to 6.0 vol%, or 3.5 vol% to 40 vol%, or 3.5 vol% to 30 vol%, or 3.5 vol% to 20 vol%, or 3.5 vol% to 15 vol%, or 3.0 vol% to 10 vol%, or 3.0 vol% to 6.0 vol%, or 6.0 vol% to 40 vol%, or 6.0 vol% to 30 vol%, or 6.0 vol% to 20 vol%, or 6.0 vol% to 15 vol%, or 10 vol% to 40 vol%, or 10 vol% to 30 vol%, or 10 vol% to 20 vol%.

[0046] In some aspects, sorption of other components from a gas stream can also occur. For example, some types of CCF-containing gas flows can also contain low levels of H2S and / or other reduced sulfur species, such as carbonyl sulfide, mercaptans, dimethyl sulfide. For example, low levels of H2S can correspond to the original level of H2S in a flue gas, or can represent a level of H2S that is present after a removal process. In such aspects, the CCh-coniaining gas can contain 1.0 vppm to 200 vppm of H2S, or 1.0 vppm to 100 vppm, or 1.0 vppm to 50 vppm, or 10 vppm to 200 vppm, or 10 vppm to 100 vppm, or 10 vppm to 50 vppm, or 50 vppm to 200 vppm, or 50 vppm or 100 vppm. Additionally or alternately, the CCF-containing gas can contain 1.0 vppm to 200 vppm of reduced sulfur species, or 1.0 vppm to 100 vppm, or 1.0 vppm to 50 vppm, or 10 vppm to 200 vppm, or 10 vppm to 100 vppm, or 10 vppm to 50 vppm, or 50 vppm to 200 vppm, or 50 vppm or 100 vppm.

[0047] During operation, the working capacity of the aqueous amine sorbent corresponds to the difference between the loading of the rich sorbent after the sorption step and the loading of the lean sorbent after the desorption or stripping step. The loading can be expressed as moles of CO2 that are currently sorbed by the sorbent versus the total moles of amine in the sorbent. The total moles of amine includes any amine nitrogens in the sorbent. Thus, for an amine such as piperazine, each mole of piperazine includes two moles of amines. Additionally, the moles of amine includes any amines that are present in compounds different from amino acids, such as amines present in ahindered and / or tertiary amine. In various aspects, the working capacity of the aqueous amine sorbent is 0.05 moles CO2 / mole amine or more, or 0.10 moles CO21 mole amine or more, or 0.15 moles CO2 / mole amine or more, or 0.20 moles CO2 / mole amine or more, or 0.25 moles CO21 mole amine or more, or 0.40 moles CO2 / mole amine or more, such as up to 0.50 moles CO2 / mole amine, or up to 1.0 moles CO2 / mole amine, or possibly still higher. It is noted that for aqueous amine sorbents where a substantial portion of amines are primary amines or secondary amine, any upper end of the range for the working capacity can typically be closer to 0.50 moles CO2 / mole amine. For aqueous amine sorbents where a substantial portion of the amines are hindered amines and / or tertiary amines, working capacities closer to 1.0 moles CO2 / mole amine can be achieved. For the rich sorbent, this can correspond to a rich sorbent loading of 0.10 moles CO2 / mole amine or more, or 0.15 moles CO2 / mole amine or more, or 0.20 moles CO2 / mole amine or more, or 0.25 moles CO21 mole amine or more, or 0.30 moles CO21 mole amine or more, or 0.35 moles CO2 I mole amine or more, or 0.40 moles CO2 / mole amine or more, or 0.5 moles CO2 / mole amine or more, or 0.6 moles CO21 mole amine or more, or 0.7 moles CO2 / mole amine or more, such as up to 1.0 moles CO2 / mole amine, or up to 1.2 moles CO2 / mole amine or possibly still higher. For the lean sorbent, this can correspond to a lean sorbent loading of 0.05 moles CO21 mole amine to 0.35 moles CO2 / mole amine, or 0.05 moles CO2 / mole amine to 0.25 moles CO2 I mole amine, or 0.05 moles CO2 I mole amine to 0.20 moles CO2 / mole amine, or 0.05 moles CO2 / mole amine to 0.15 moles CO2 / mole amine, or 0.15 moles CO2 / mole amine to 0.35 moles CO2 / mole amine, or 0.15 moles CO2 / mole amine to 0.25 moles CO21 mole amine, or 0.15 moles CO2 I mole amine to 0.20 moles CO2 I mole amine.

[0048] For aqueous amine sorbents where the majority of amines in the sorbent are part of an amino acid, the working capacity of the aqueous amine sorbent can be 0.05 moles CO2 I mole amino acid or more, or 0.10 moles CO2 / mole amino acid or more, or 0.15 moles CO2 / mole amino acid or more, or 0.20 moles CO2 I mole amino acid or more, or 0.25 moles CO2 I mole amino acid or more, or 0.40 moles CO2 / mole amino acid or more, such as up to 0.50 moles CO2 I mole amino acid, or up to 1.0 moles CO2 I mole amino acid, or possibly still higher. For the rich sorbent, this can correspond to a rich sorbent loading of 0.10 moles CO2 I mole amino acid or more, or 0.15 moles CO2 / mole amino acid or more, or 0.20 moles CO2 / mole amino acid or more, or 0.25 moles CO2 / mole amino acid or more, or 0.30 moles CO2 / mole amino acid or more, or 0.35 moles CO2 / mole amino acid or more, or 0.40 moles CO2 / mole amino acid or more, or 0.5 moles CO2 I mole amino acid or more, or 0.6 moles CO2 / mole amino acid or more, or 0.7 moles CO2 / mole amino acid or more, such as up to 1.0 moles CO2 / mole amino acid, or up to 1.2 molesC02 / mole amino acid or possibly still higher. For the lean sorbent, this can correspond to a lean sorbent loading of 0.05 moles CO2 / mole amino acid to 0.35 moles CO2 1 mole amino acid, or 0.05 moles CO2 / mole amino acid to 0.25 moles CO2 / mole amino acid, or 0.05 moles CO21 mole amino acid to 0.20 moles CO2 / mole amino acid, or 0.05 moles CO2 / mole amino acid to 0.15 moles CO2 I mole amino acid, or 0.15 moles CO2 / mole amino acid to 0.35 moles CO2 I mole amino acid, or 0.15 moles CO2 / mole amino acid to 0.25 moles CO2 / mole amino acid, or 0.15 moles CO21 mole amino acid to 0.20 moles CO2 / mole amino acid.Examples

[0049] A scries of amino acids were tested to characterize the degradation over time. The characterization tests also allowed for measurement of how the amino acids impacted corrosion within the reaction system. Table 1 shows the amino acids that were tested. It is noted that glycine, sarcosine, and lysine were tested due to prior use of such amino acids in the literature.Table 1 - Amino Acids TestedName Structure Active NGlycine (Gly) 1Sarcosine (Sar)H II 1H3C ^ OHL-Lysine (Lys) 02NH22-(Piperazin-l-yl) OH^ ^0 1Acetic Acid (PZAA)Piperazine-2 H 2Carboxylic Acid(PZCA) r "isVh0Nipecotic Acid (NPA) O 1J '°HHIsonipecotic Acid .OH 1(INPA)0NH

[0050] Solvents were prepared gravimetrically (4 molal amino acid / kg water) and were then activated with KOH (1 mole KOH : mole amino acid) to enable the amino functions to capture CO2. The amino acid-KOH solution was sparged with CO2 in a gas washing bottle to achieve the target loading. The amount of CO2 added was measured gravimetrically. The target loading was set to 0.25 mol CO21 mol active N in the amino acid.

[0051] The CO2-loaded, KOH-activated amino acid solvents were loaded in 316L stainless steel cylindrical batch reactors. The cylinders were not passivated prior to use. Each reactor had a diameter of about 0.95 cm and a length of about 10 cm. The reactors were sealed and placed in convection ovens at 120°C, 135"C, 150°C, and 165°C. The reactors were removed after a predetermined time and their contents decanted in vials. The vial contents were analyzed using HPAE-PAD (high performance anion-exchange chromatography with pulsed amperometric detection). This method can determine the concentration of the amino acid over time. The samples were also analyzed using ICP-OES (Inductively Coupled Plasma - Optical Emission Spectroscopy) to determine the concentration of leached metals (Iron, Chromium, and Nickel) from the cylinder to the amino acid. This was used to estimate the corrosivity of the amino acids. It is noted that leached metals can catalyze the oxidation of amino acids, so reducing or minimizing corrosivity is another mechanism for improving the lifetime of amino acids during service for CO2 sorption and desorption.

[0052] The samples were then degraded at 120°C and 150°C over several hundred hours. Tables 2 - 4 list the percentage of amino acids which did not degrade over a given time period. The degradation results for PZAA, NPA, INPA, and PZCA at 120°C are shown in Table 2.Table 2 - Percent Remaining Amino Acids with Ring Structures at 120°CAmino Acid T=360 hr T=2000 hrPZAA 99 wt % 96 wt %PZCA 64 wt % 6 wt %NPA 90 wt % 81 wt %INPA 82 wt % 80 wt %

[0053] It is noted that PZCA has a carboxylic acid at the alpha position relative to a ring nitrogen. This resulted in a substantial increase in degradation for PZCA. The results for glycine and sarcosine are shown in Table 3.Table 3 - Percent Remaining Comparative Amino Acids at 120°CAmino Acid T=370 hr T=1700 hrGly 83 wt % 78 wt %Sar 81 wt % 67 wt%

[0054] As shown in Table 2 and Table 3, it was unexpectedly discovered that PZAA, NPA, and INPA had improved degradation performance relative to glycine and sarcosine when exposed to degradation for extended periods. By contrast, PZCA had substantially worse degradation performance, due to the presence of a carboxylic acid bonded at the alpha position relative to a ring nitrogen. The improved degradation performance of PZAA, NPA, and INPA is more pronounced at the higher temperature of 150°C, as shown in Table 4 and Table 5.Table 4 - Percent Remaining Amino Acids with Ring Structures at 150°CAmino Acid T=50 hr T=700 hrPZAA 96 wt % 96 wt %PZCA 25 wt % 1 wt %NPA 96 wt % 96 wt %INPA 87 wt % 90 wt %

[0055] As shown in Table 4, PZAA, NPA, and INPA all provided at least comparable degradation performance at 150°C as compared with the 120°C data in Table 2. By contrast, PZCA had even lower degradation performance at 150°C.Table 5 - Percent Remaining Comparative Amino Acids at 150°CAmino Acid T=50 hr T=380 hrGly 72 wt % 56 wt %Sar 44 wt % 19 wt %Lys 53 wt % 36 wt %

[0056] As shown in Table 5, the comparative amino acids had substantially lower degradation performance at the higher temperature of 150°C. The ability of PZAA, NPA, and INPA to maintain good degradation performance as the temperature is increased is another unexpected benefit of using those amines for CO2 sorption and desorption, as the improved degradation performance of PZAA, NPA, and INPA can enable higher temperature operation of a sorption / desorption process.

[0057] In addition to degradation performance, the corrosion performance of PZAA, glycine, and sarcosine was also characterized. Corrosion performance was characterized based on the amount of trace metals from the stainless steel that were found in the decanted reaction products. The results from processing at 120°C are shown in Table 6.Table 6 - Corrosion Results at 120°CAmino Acid Cr Mn Fe Ni Mommol / kg mmol / kg mmol / kg mmol / kg mmol / kg Gly (2200 2 4 148 23 1hours)Sar (2200 2 < 1 34 7 < 1hours)PZAA (2000 < 1 2 4 1 < 1 hours)

[0058] It is noted that the measurement time for the PZAA was slightly shorter than for the other two amines. However, the times were comparable, and the corrosion benefit for PZAA is substantial. The primary components that would be expected to leach from stainless steel are Fe and Ni. As shown in Table 6, substantial amounts of Fe were present in the decanted reaction products for both glycine and sarcosine. By contrast, only a minimal amount of Fe was detected in the reaction products for PZAA. This is yet another unexpected benefit of using PZAA, as corrosion within the reaction system is reduced or minimized. The unexpected corrosion benefits of PZAA are even more pronounced at 150°C, as shown in Table 7.Table 7 - Corrosion Results at 150°CAmino Acid Cr Mn Fe Ni Mommol / kg mmol / kg mmol / kg mmol / kg mmol / kg Gly (290 8 3 130 19 1hours)Sar (290 5 1 100 17 2hours)PZAA (700 < 1 2 6 1 < 1hours)

[0059] In Table 7, the run length for sampling the PZAA decanted products (700 hours) was more than twice the run length (290 hours) for the other amines. In spite of this, the PZAA decanted products contained only minimal amounts of Fe and Ni, while substantial amounts of Fe and Ni were present in the decanted products for both glycine and sarcosine.Additional Embodiments

[0060] Embodiment 1. A method for sorbing CO2 from a gas stream, comprising: exposing a gas stream comprising CO2 to an aqueous amine sorbent comprising an amino acid and a base to form a CCh-rich sorbent under sorption conditions comprising a temperature of -10°C to 100°C, an amine group of the amino acid being part of a six-membered ring structure in the amino acid, the carboxylic acid group being connected to the ring via an atom that is different from a carbon that is alpha to the amine of the amino acid, a molar ratio of the base to the amino acid being 0.5 to 2.0; and desorbing CO2 from the CCE-rich sorbent under desorption conditions comprising atemperature of 100°C to 180°C to regenerate the aqueous amine sorbent and form a product stream that comprises CO2.

[0061] Embodiment 2. The method of Embodiment 1, wherein the aqueous amine sorbent comprises 10 wt% to 60 wt% of amino acid, relative to a weight of components dissolved in the aqueous amine sorbent; or wherein the CCh-rich sorbent comprises 10 wt% to 60 wt% of amino acid, relative to a weight of components dissolved in the aqueous amine sorbent; or a combination thereof.

[0062] Embodiment s. The method of any of the above embodiments, wherein the desorption conditions comprise a temperature of 150°C to 180°C, or wherein the desorption conditions comprise a temperature of 125 °C to 150°C.

[0063] Embodiment 4. The method of any of the above embodiments, a) wherein the sorption conditions comprise a pressure of 90 kPa-a to 350 kPa-a, b) wherein the desorption conditions comprise a pressure of 90 kPa-a to 1000 kPa-a, c) wherein a difference between the temperature of the sorption conditions and the temperature of the desorption conditions is 50°C or more, or d) a combination of two or more of a), b), and c).

[0064] Embodiment 5. The method of any of the above embodiments, wherein under the sorption conditions and desorption conditions, i) the aqueous amine sorbent provides a working capacity of 0.05 moles CO2 1 mole amine to 1.0 moles CO2 1 mole amine, or 0.05 moles CO2 / mole amine to 0.5 moles CO2 / mole amine; or ii) wherein the aqueous amine sorbent provides a working capacity of 0.05 moles CO2 / mole amino acid to 1.0 moles CO2 / mole amino acid, or 0.05 moles CO2 / mole amino acid to 0.5 moles CO2 / mole amino acid; or iii) a combination of i) and ii).

[0065] Embodiment 6. The method of any of the embodiments, wherein the amino acid is an a-amino acid, or wherein the carboxylic acid of the amino acid is bonded to a carbon atom of the six-membered ring, or a combination thereof, the carboxylic acid of the amino acid optionally being bonded to a carbon atom that is beta or gamma to the amine of the amino acid.

[0066] Embodiment 7. The method of any of embodiments 1 to 6, wherein the carboxylic acid is bonded to an aliphatic side chain that is bonded to the ring structure, the aliphatic side chain comprising 1 to 6 carbon atoms, the aliphatic side chain optionally being bonded to an amine group of the amino acid.

[0067] Embodiment 8. The method of any of the above embodiments, wherein the ring structure comprises a plurality of nitrogen atoms that are part of the ring structure.

[0068] Eiiibodiment 9. The method of any of the above embodiments, wherein the amino acid is isonipecotic acid, nipecotic acid, piperazine-2-carboxylic acid, 2-(piperazin-l-yl) acetic acid, or a combination thereof.

[0069] Embodiment 10. The method of any of the above embodiments, wherein the amino acid is a derivative of piperidine, or wherein the amino acid is a derivative of piperazine, or a combination thereof.

[0070] Embodiment 11. The method of any of the above embodiments, wherein the aqueous amine sorbent further comprises an alkali metal carbonate, an alkaline earth metal carbonate, or a combination thereof, the aqueous amine sorbent optionally comprising 1.0 wt% to 60 wt% of the alkali metal carbonate, alkaline earth metal carbonate, or the combination thereof, relative to a weight of components dissolved in the aqueous amine sorbent.

[0071] Embodiment 12. The method of any of the above embodiments, wherein the aqueous amine sorbent further comprises an additional primary amine, an additional secondary amine, an additional hindered amine, an additional tertiary amine, or a combination thereof, a molar ratio of amino acid to the additional primary amine, the additional secondary amine, the additional hindered amine, the additional tertiary amine, or the combination thereof optionally being 1.0 or more.

[0072] Embodiment 13. The method of any of the above embodiments, wherein the gas stream comprises 300 vppm to 600 vppm of CO2, or wherein the gas stream comprises 2.0 vol% to 40 vol% of CO2.

[0073] Embodiment 14. The method of any of the above embodiments, wherein the CO2-containing stream further comprises H2S, wherein the CCh-rich sorbent further comprises adsorbed H2S, and wherein the desorption conditions form a product stream that comprises CO2 and H2S.

[0074] Embodiment 15. The method of any of the above embodiments, wherein the aqueous amine sorbent further comprises 0.01 wt% to 10 wt% of a co-solvent, relative to a weight of water in the aqueous amine sorbent.

[0075] Additional Embodiment A. The method of any of the above embodiments, wherein the liquid sorbent has a pH of 8.0 or higher.

[0076] Certain features have been described using a set of numerical upper limits and a set of numerical lower limits. It should be appreciated that ranges from any lower limit to any upper limit are contemplated unless otherwise indicated. Certain lower limits, upper limits and ranges appear in one or more claims below. All numerical values take into account experimental error and variations that would be expected by a person having ordinary skill in the art.

[0077] The foregoing description of the disclosure illustrates and describes the present methodologies. Additionally, the disclosure shows and describes exemplary methods, but it is to be understood that various other combinations, modifications, and environments may be employed and the present methods are capable of changes or modifications within the scope of the concept as expressed herein, commensurate with the above teachings and / or the skill or knowledge of the relevant art.

Claims

CLAIMSWe claim:

1. A method for sorbing CO2 from a gas stream, comprising: exposing a gas stream comprising CO2 to an aqueous amine sorbent comprising an amino acid and a base to form a CO2-rich sorbent under sorption conditions comprising a temperature of 10°C to 100°C, an amine group of the amino acid being part of a six-membered ring structure in the amino acid, the carboxylic acid group being connected to the ring via an atom that is different from a carbon that is alpha to the amine of the amino acid, a molar ratio of the base to the amino acid being 0.5 to 2.0; and desorbing CO2 from the CO2-rich sorbent under desorption conditions comprising a temperature of 100°C to 180°C to regenerate the aqueous amine sorbent and form a product stream that comprises CO2.

2. The method of claim 1, wherein the aqueous amine sorbent comprises 10 wt% to 60 wt% of amino acid, relative to a weight of components dissolved in the aqueous amine sorbent; or wherein the CO2-rich sorbent comprises 10 wt% to 60 wt% of amino acid, relative to a weight of components dissolved in the aqueous amine sorbent; or a combination thereof.

3. The method of any of the above claims, wherein the desorption conditions comprise a temperature of 150°C to 180°C, or wherein the desorption conditions comprise a temperature of 125°C to 150°C.

4. The method of any of the above claims, a) wherein the sorption conditions comprise a pressure of 90 kPa-a to 350 kPa-a, b) wherein the desorption conditions comprise a pressure of 90 kPa-a to 1000 kPa-a, c) wherein a difference between the temperature of the sorption conditions and the temperature of the desorption conditions is 50°C or more, or d) a combination of two or more of a), b), and c).

5. The method of any of the above claims, wherein under the sorption conditions and desorption conditions, i) the aqueous amine sorbent provides a working capacity of 0.05 moles CO2 / mole amine to 1.0 moles CO2 I mole amine, or 0.05 moles CO2 I mole amine to 0.5 moles CO2 / mole amine; or ii) wherein the aqueous amine sorbent provides a working capacity of 0.05 moles CO2 / mole amino acid to 1.0 moles CO2 I mole amino acid, or 0.05 moles CO2 / mole amino acid to 0.5 moles CO2 / mole amino acid; or iii) a combination of i) and ii).- l -6. The method of any of the claims, wherein the amino acid is an a-amino acid, or wherein the carboxylic acid of the amino acid is bonded to a carbon atom of the sixmembered ring, the carboxylic acid of the amino acid optionally being bonded to a carbon atom that is beta or gamma to the amine of the amino acid.

7. The method of any of claims 1 to 6, wherein the carboxylic acid is bonded to an aliphatic side chain that is bonded to the ring slruclure, the aliphatic side chain comprising 1 to 6 carbon atoms, the aliphatic side chain optionally being bonded to an amine group of the amino acid.

8. The method of any of the above claims, wherein the ring structure comprises a plurality of nitrogen atoms that are part of the ring structure.

9. The method of any of the above claims, wherein the amino acid is isonipecotic acid, nipecotic acid, piperazine-2-carboxylic acid, 2-(piperazin-l-yl) acetic acid, or a combination thereof.

10. The method of any of the above claims, wherein the amino acid is a derivative of piperidine, or wherein the amino acid is a derivative of piperazine, or a combination thereof.

11. The method of any of the above claims, wherein the aqueous amine sorbent further comprises an alkali metal carbonate, an alkaline earth metal carbonate, or a combination thereof, the aqueous amine sorbent optionally comprising 1.0 wt% to 60 wt% of the alkali metal carbonate, alkaline earth metal carbonate, or the combination thereof, relative to a weight of components dissolved in the aqueous amine sorbent.

12. The method of any of the above claims, wherein the aqueous amine sorbent further comprises an additional primary amine, an additional secondary amine, an additional hindered amine, an additional tertiary amine, or a combination thereof, a molar ratio of amino acid to the additional primary amine, the additional secondary amine, the additional hindered amine, the additional tertiary amine, or the combination thereof optionally being 1.0 or more.

13. The method of any of the above claims, wherein the gas stream comprises 300 vppm to 600 vppm of CO2, or wherein the gas stream comprises 2.0 vol% to 40 vol% of CO2.

14. The method of any of the above claims, wherein the CO2-containing stream further comprises H2S, wherein the CO2-rich sorbent further comprises adsorbed H2S, and wherein the desorption conditions form a product stream that comprises CO2 and H2S.

15. The method of any of the above claims, wherein the aqueous amine sorbent further comprises 0.01 wt% to 10 wt% of a co-solvent, relative to a weight of water in the aqueous amine sorbent.

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