Solvents and methods for gas separation from gas streams

Abstract

A method of removing acid gases from a gaseous stream is provided. The acid gases may include carbon dioxide, hydrogen sulfide and/or sulfur dioxide, by example. Embodiments of the method include mixing an amine-terminated branched polymer solvent with the gaseous stream, resulting in the substantial absorption of at least some of the acid gases. The solvent is an amine-terminated branched PEG, such as by example amine-terminated glycerol ethoxylate, amine-terminated trimethylolpropane ethoxylate, and/or amine-terminated pentaerithritol ethoxylate. Embodiments of the present inventive methods further include regenerating the solvent using electrolysis.

Claims

1. A method of removing acid gases from a gaseous stream, the method comprising mixing an amine-terminated branched PEG polymer solvent with the gaseous stream.

2. The method of claim 1, wherein the solvent comprises amine-terminated glycerol ethoxylate.

3. The method of claim 1, wherein the solvent comprises amine-terminated trimethylolpropane ethoxylate.

4. The method of claim 1, wherein the solvent comprises amine-terminated pentaerithritol ethoxylate.

5. The method of claim 1, further comprising regenerating the solvent using electrolysis.

6. The method of claim 1, wherein the acid gas comprises carbon dioxide.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The aforementioned objects and advantages of the present invention, as well as additional objects and advantages thereof, will be more fully understood hereinafter as a result of a detailed description of a preferred embodiment when taken in conjunction with the following drawings in which:

(2) FIG. 1 shows a schematic process of testing absorption of CO.sub.2 employed herein for assessing CO.sub.2 absorption of solvent compounds;

(3) FIG. 2 shows examples of linear and branched PEGs;

(4) FIG. 3 shows an amine-terminated glycerol ethoxylate compound;

(5) FIG. 4 shows an amine-terminated pentaerithritol ethoxylate compound;

(6) FIG. 5 shows an amine-terminated trimethylolpropane ethoxylate compound.

(7) FIG. 6 is a schematic process flow diagram for one embodiment of a gas absorption and solvent regeneration system as described herein.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

(8) Embodiments of the present invention comprise systems and methods for both chemical and physical absorption of CO.sub.2 from gases, at both high and ambient pressures and for a wide range of acid gas concentration in the incoming raw gas flow. In one embodiment of the present invention, amines are employed to chemically react with incoming raw gas (with CO.sub.2 and other undesirable acid gases) to form ionic carbonates and bicarbonates. For example, monoethanolamine (MEA) absorbs CO.sub.2 by reacting with it in the presence of water to form MEAH.sup.+.HCO.sub.3.sup.−. Similar reactions can occur with diethanolamine (DEA), N-methyl diethanolamine (MDEA) and diglycolamine (DGA). Instead of using conventional thermal processes (typically heating to 120° C.) to desorb the CO.sub.2 and regenerate the amines, however, certain embodiments of the present invention use electrolysis for doing so at ambient conditions, and with low energy. In one application, the electrolysis process comprises the following reactions:
Cathode: [MEAH.sup.++e.sup.−.fwdarw.MDEA+1/2H.sub.2]×2
Anode: 2HCO.sub.3.sup.−.fwdarw.2CO.sub.2+2OH.sup.−
2OH.sup.−.fwdarw.H.sub.2O+1/2O.sub.2+2e.sup.−
2HCO.sub.3.sup.−.fwdarw.2CO.sub.2↑+H.sub.2O+1/2O.sub.2↑+2e.sup.−
Overall reaction: 2MEAH.sup.++2HCO.sub.3.sup.−.fwdarw.2MEA+2CO.sub.2↑+H.sub.2↑+H.sub.2O+1/2O.sub.2↑

(9) Only electrical energy is consumed in the regeneration process, and is dependent on the amount of CO.sub.2 absorbed by the amine, as predicted by Faraday's Laws. The presence of water can be helpful for the electrolytic regeneration reaction, maintaining ionic conductivity in the solution. In one specific application, the expected voltage for each cell is expected to be around 1.5 VDC, due to the low polarization losses in the cell. At a 90% coulombic efficiency, 45 watt-hours can desorb 22.4 liters of CO.sub.2 at standard conditions, or 1 kWh can desorb 497.78 liters of CO.sub.2. Conversely, only around 2 kWh of energy will be consumed for desorbing 1 cubic meter (1,000 liters) of CO.sub.2 under standard conditions. Even assuming the price of electricity at $0.08/kWh, it would cost only $0.16 to desorb a cubic meter of CO.sub.2 from the amine-based solution by using electrochemical pathways. The cell architecture would be fairly simple, without any need of expensive membranes or electrodes, like Nafion™ or titanium anodes/cathodes that are commonly used in brine electrolysis.

(10) In another example of acid gas removal contemplated by the present invention, hydrogen sulfide (H.sub.2S) can also be absorbed by amine-based scrubbing agents, with a similar reaction forming amine sulfides. Thus, for example, MEA combines with hydrogen sulfide, H.sub.2S, to form MEAH+.HS— salts. The amine can be regenerated by a similar electrochemical route.
Cathode: MEAH.sup.+e.sup.−.fwdarw.MEA+1/2H.sub.2↑
Anode: HS.sup.−.fwdarw.1/2H.sub.2↑+S↑+2e.sup.−
Overall reaction: MEAH.sup.++HS.sup.−.fwdarw.MEA+H.sub.2↑+S↓

(11) Embodiments of the present invention are advantageous over thermal regeneration of amines because the H.sub.2S has to be sequestered or converted into other chemicals by various chemical processes, and because, during thermal desorption, breakdown of the amines by various side reactions is a major issue, and thus, after regeneration, it is common to absorb the unwanted products by absorption in activated charcoal.

(12) Some embodiments of the present invention comprise the physical absorption of CO.sub.2 using branched polymers. In one specific application, the solvent comprises a branched polyethylene glycol (PEG). The ethylene oxide (EO) monomer in a polyethylene glycol facilitates hydrogen bonding with water molecules. Although CO.sub.2 is a non-polar molecule, it can act as a Lewis acid or a Lewis base and can participate in hydrogen bonding. Thus, the acid-base reactions of the acidic carbon dioxide with the electron-rich ether oxygen in the PEG molecule enables high solubility of CO.sub.2 in PEGs. The terminal [—OH] groups in the PEGs also have an affinity for carbon dioxide molecules, resulting in improved electron interaction with the bonds in the carbon dioxide molecule. If both the above interactions, namely the electron-rich ether oxygen in the PEG molecule, and the terminal [—OH] groups at the end of the PEG molecules, result in higher carbon dioxide solubility, PEGs would show higher absorption capacity than the physical solvents like polyethylene glycol dimethyl ethers (which are end-capped with methyl groups, instead of the —OH group in PEGs) used by industry. Also, the greater the number of EO monomers in the PEGs, the greater would be the CO.sub.2 absorption. Thus, higher chain-length PEGs should show higher CO.sub.2 absorption than smaller chain-length PEGs.

(13) One issue with longer chain-length PEGs is the higher viscosity and higher melting points, as the chain length increases. PEG 200 (EO=4), PEG 300 (EO=6-7) and PEG 400 (EO=9) are all liquid at room temperatures, whereas PEG 600 (EO=12-13) is a waxy solid at room temperature, as are the higher molecular weight PEGs. In addition, the higher the viscosity of the solvent, the lesser the gas-liquid interaction during the absorption processes, and the greater the energy expended during desorption. Thus, a practical limit in the PEG chain length prevents use of longer chain-length PEGs for CO.sub.2 absorption. Nonetheless, if liquid polymers can be synthesized, containing higher chain-length PEGs, it would be possible to increase CO.sub.2 absorption by increasing the number of EO monomers in the solvent.

(14) While the commonly used PEGs are linear in structure, and increase in melting point and viscosity as the chain-length increases, there are other forms of PEGs available, with different geometries, which are termed branched or multi-armed PEGs. Branched PEGs have 3-10 PEG chains emanating from a central core group. Star PEGS have 10 to 100 PEG chains emanating from a central core group, while comb PEGs have multiple PEG chains grafted onto a polymer backbone. Such branched PEGs allow more EO groups in the polymer, while still having lower melting points and viscosity than comparable linear PEGs with the same number of EO monomers. Thus, the use of such PEG geometries can enable higher CO.sub.2 absorption, while retaining the practicality of using higher number of EO monomers for CO.sub.2 interaction and absorption.

(15) Branched PEGs can be synthesized from glycerol (3 arms), trimethylolpropane (4 arms, though one of the arms has a methyl group), pentaerythriol (4 arms) and other organic compounds. Some simple branched PEGs commercially available are glycerol ethoxylates (GE), trimethylolpropane ethoxylates (TMPE) and pentaerythriol ethoxylates (PEE). Glycerol ethoxylate, with a molecular weight of 1000, has approximately 20 EO groups, but is a liquid at room temperature, and less viscous than PEG 300 (EO=6). Trimethylolpropane ethoxylate, with a MW of 1014, also has 20 EO groups, is liquid at room temperatures, and also less viscous than PEG 300. Other liquid branched ethoxylates include pentaerythriol ethoxylate, MW 270 (EO=3) and pentaerythriol ethoxylate, MW 797 (EO=15). All of these ethoxylates have terminal [—OH] groups, except for the TMP ethoxylates, which have one terminal methyl group replacing one [—OH] group, out of the four available. Branched PEGs also have advantageous properties of steric hindrance, enabling better absorption of gases.

(16) CO.sub.2 absorption experiments were performed with several PEG polymers, including both linear and branched polymers, block co-polymers of ethoxylates and propoxylates, as well as polyethylene glycol dimethyl ether (Selexol or PGDME, also referred to as DEPG), to compare CO.sub.2 absorption capacity, and ease of desorption. Butyl diglyme (diethylene glycol dibutyl ether) and glycerol were also tested, to assess the effect of —OH groups against terminal methyl or butyl groups, for CO.sub.2 absorption tendencies. Table 1 shows the CO.sub.2 absorption capacity for the various solvents tested.

(17) Laboratory-scale tests were performed with all these solvents to determine CO.sub.2 absorption capacity at ambient conditions. A test apparatus was fabricated that consisted of a CO.sub.2 supply (gas cylinder, 99.5% purity CO.sub.2), 0-2 SCFH rotameter, clear PVC bubbler and tubing with a porous-metal gas diffuser assembly and magnetic stirrer, as shown in FIG. 1. The experimental procedure consisted of the following steps: Initially, the test solvent (50-ml) was heated up to 100° C. in a separate glass flask to remove any moisture or absorbed gases. The solvent was then placed in a dehumidifier chamber and allowed to cool down. Once at room temperature, the solvent was poured into the gas bubbler and a weight was taken of the empty bubbler, using a Mettler Toledo PG503-S weigh station (accuracy=1 mg), as well as after filling with the test solvent. CO.sub.2 was then bubbled from the gas cylinder into the solvent and the sample was weighed after each 30-minute interval, up to three hours, at a flow rate of 0.2 SCFH of CO.sub.2, until a constant weight was obtained, indicating attainment of a maximum solubility in the solvent. In most of the tests, it was observed that the maximum CO.sub.2 uptake was attained in the first 30 minutes, after which no appreciable weight gains were obtained. The only exception was PEG-PPG 2500 (BASF Pluronic 10R5), where the maximum weight was recorded after two hours. However, to maintain consistency, all tests were continued for the full three hours.

(18) In addition to CO.sub.2 absorption testing, CO.sub.2 desorption was also tested. The desorption procedure consisted of stirring the CO.sub.2-solvent mixture with a magnetic stirrer (FIG. 1), without any heating, for increments of 5 minutes to expel desorbed CO.sub.2 and re-weighing the solvent each time. Desorption times ranged from about 5 to 20 minutes for all the solvents tested (as observed by cessation of bubbling from the solvent). Desorption time is important to assess the practicality of the CO.sub.2 absorption-desorption system. Comparison of the chemical structures of these newly discovered CO.sub.2-philic physical solvents, as compared to conventional PEGs, is shown in FIG. 2.

(19) TABLE-US-00001 TABLE 1 Comparison of CO.sub.2 absorption capacity by physical solvents mgCO.sub.2/g mgCO.sub.2/ S. Solvents tested (CO.sub.2 Solvent ml Desorption No. stabilized to 1 atm) Density Absorption Solvent Tendency 1 Glycerol 1.250 1.816 2.270 Very slow desorption 2 Butyl Diglyme 0.874 4.904 4.286 Slow (Gensorb 1843) desorption Diethylene glycol >10 min dibutyl ether 3 Tetraglyme (Selexol, 1.030 7.319 7.539 Slow Gensorb 1753) desorption tetraethylene glycol >10 min dimethyl ether 4 Pluronic 1.300 8.279 10.763 Slow 10R5PEG-PPG 2500 desorption, equimolar EO-PO >20 min 5 PEG 200 (EO = 4) 1.127 11.550 13.017 Slow desorption >10 min 6 PEG 400 (EO = 8) 1.250 11.538 14.423 Very slow desorption >20 min 7 Glycerol ethoxylate 1.138 12.829 14.599 Fast 1000 (EO = 20) desorption <5 min 8 Trimethylolpropane Fast ethoxylate desorption 1014 (EO = 20) 1.100 13.143 14.457 <5 min

(20) From the above experiments, the tendency to absorb more CO.sub.2, based on the PEG chain length, as shown by PEG 200 and PEG 400, can be observed, as compared to tetraglyme (EO=4) or butyl diglyme (EO=2). GE-1000 and TMPE-1014 (EO=20) showed the highest CO.sub.2 solubility, while PEG 200 (EO=4) and PEG 400 (EO=8) also indicated appreciable CO.sub.2 solubility, well in excess of the capacities of tetraglyme and butyl diglyme, due to their [—OH] end-caps. The desorption experiments also showed faster CO.sub.2 desorption for the lower viscosity three-armed ethoxylates (GE-1000 and TMPE-1014), as compared to the much higher viscosity linear PEGs. The extra [—OH] terminal groups in GE-1000 and TMPE-1014 also seem to aid in CO.sub.2 absorption tendency, as compared to the glymes and linear PEGs.

(21) Based on these experiments, it is possible to use the above branched PEG solvents by themselves or as mixtures, to maximize CO.sub.2 absorption and desorption with minimal energy expenditure. Assuming that the inlet raw gas is at 100 psig (6.8 bar), and the CO.sub.2 composition of the raw gas is at 45%, if we use GE-1000 as the CO.sub.2-philic solvent, we have an absorption capacity of 39.255 mg CO.sub.2/g of solvent, comparable to the ethanolamines in absorption capacity (43.8 mg CO.sub.2/g for MEA, as reported in literature), but much easier to desorb, without the associated energy penalties for amines. For TMPE-1014, the absorption numbers are 40.216 mg CO.sub.2/g of solvent. Similar, but much higher, characteristics of absorption are also expected for H.sub.2S, due to its more acidic nature than CO.sub.2, and its increased hydrogen bonding to the EO monomers in these polymerized glycols. Another branched ethoxylate, pentaerierythriol ethoxylate, with four arms, is also suitable for high physical absorption capacity for carbon dioxide and other acid gases.

(22) Given the propensity for CO.sub.2 absorption of the EO monomers in the physical solvents described above, as well as the superior absorption characteristics of amine-based solvents for CO.sub.2 and H.sub.2S, a new class of solvents, based on aminated branched polyethylene glycols, is postulated herein. Such a solvent consists of a branched polyethylene glycol, the ends of which have amine molecules attached, instead of [—OH] molecules. The EO monomers are capable of physically absorbing acid gases like CO.sub.2 or H.sub.2S, the branched nature of the polymer keeps the solvent liquid and with low viscosity, while maximizing the number of EO monomers for acid gas molecular absorption, and the end-capping with amine molecules also enables chemical absorption of the acid gas molecules in a mole-to-mole ratio. The entire structure of the branched polyethylene glycol amine molecule is rendered water-soluble, due to both the large number of EO monomers and the amine ends. The amine terminations at the branched ends of the polymer render the polymer to behave like a primary amine, with increased absorption capacity of acid gases over conventional primary, secondary and tertiary amines.

(23) For a higher absorption capacity for acid gases like CO.sub.2 and H.sub.2S, it is proposed to use an amine-terminated branched polyethylene glycol, having amine molecules at its ends, for acid gas absorption. The amine ends act as a chemical absorbent, and with branched molecules, more acid gases per mole of solvent can be absorbed chemically by the increased number of amine molecules terminating the branches of the solvent molecule. Thus, a 3-armed molecule, with three amine molecules, can chemically absorb three acid gas molecules, compared to a single amine in conventional alkanolamines, which can absorb a single acid gas molecule per mole. If the 3-armed molecule is, in addition to its amine-terminated ends, a 3-armed PEG, like an amine-terminated glycerol ethoxylate, an amine-terminated trimethylolpropane ethoxylate, and/or a 4-armed molecule like an amine-terminated pentaerythriol ethoxylate, every EO monomer in the PEG also can absorb its equivalent proportion of acid gas molecules by physical absorption. Other branched PEGs with amine terminated ends can also be used for acid gas absorption, with higher capacities, compared to traditional physical solvents or conventional amine-based chemical solvents. Such a combination of chemical and physical absorption can maximize the absorption capacity of the solvent for acid gases. Regeneration of the solvent is easily facilitated by a combination of electrochemical processes (for CO.sub.2 removal from the amine ends) as described earlier, or thermal processes, and physical processes (like pressure swings, inert gas purging or vacuum processes for CO.sub.2 removal and regeneration of the physical component of the solvent).

(24) An amine-terminated, branched polyethylene glycol would thus have maximized absorption capacity for acid gases like CO.sub.2 and H.sub.2S, while minimizing the energy expended in regeneration of the solvent. FIG. 3 shows the example of a glycerol ethoxylate with amine-terminated ends, where ‘n’ denotes the number of EO monomers. Similar solvents can be made with pentaerythriol ethoxylates and trimethylolpropane ethoxylates, each with amine-terminated ends, as shown in FIGS. 4 and 5, respectively, for example.

(25) The synthesis of such amine-terminated branched ethoxylates may be as follows: glycerol ethoxylate is reacted with diethylene triamine (DETA) in the presence of acid catalyst at 95-100 Deg C in an inert atmosphere. The DETA quantity can be varied depending on requirements, with the maximum amount being 3.3 moles to 1 mole of Glycerol Ethoxylate. Other amines can be used, instead of DETA. DETA is preferred as this gives greater stability to the amine functionality. Amine-terminated glycerol ethoxylate and pentaerithritol ethoxylates were synthesized in the above manner and tested for CO.sub.2 absorption capacities.

(26) The absorption capacity of such a molecule would be at least around 3-10 times the capacity of commonly used amines (MEA, DEA and MDEA), and around 200-300 mg CO.sub.2/g solvent, if not higher. The solvent can be easily regenerated by a mix of pressure swing desorption and electrochemical processes for continued use for acid gas removal from raw gas sources. In addition, such a hybrid solvent can function in both low-pressure and high-pressure environments, and at low or high concentrations of CO.sub.2 and other acid gases, since it is a hybrid of both chemical and physical solvents, based on its molecular structure.

(27) The absorption capacity for CO.sub.2 were tested in the apparatus shown in FIG. 1, for both the synthesized molecules, glycerol ethoxylate (amine-terminated), having a MW of 1,000 for the precursor molecule of glycerol ethoxylate, and pentaerithritol ethoxylate (amine-terminated), having a MW of 797 for the precursor molecule of pentaerythritol ethoxylate. Various other molecular weights of the precursor molecules can also be used for synthesis of these amine-terminated branched polymers, as well as other branched ethoxylates. The results were as follows: the amine-terminated glycerol ethoxylate (MW 1000) exhibited an absorption capacity for CO.sub.2, of 196.560 mg CO.sub.2/g of solvent. The amine-terminated pentaerythritol ethoxylate (MW 797) showed an even better absorption capacity for CO.sub.2, of 250.067 mg CO.sub.2/g of solvent. Both solvents were used as a 50% solution in water during testing.

(28) In comparison, monoethanolamine (MEA), a commercially available solvent for CO.sub.2 absorption, used in industrial practice as a 20% solution in water, exhibits only 43.8 mg CO.sub.2/g of solvent, as reported in literature (R. Notz, N. Asprion, I. Clausen and H. Hasse, Chem. Eng. Res. Des., 2007, 85(A4), 510-515 and A. B. Rao and E. S. Rubin, Environ. Sci. Technol., 2002, 36, 4467-4475). This is equivalent to absorption of 0.2 moles CO.sub.2 per mole of solvent. Even if the theoretical capacity of 1 mole of CO.sub.2 per mole of solvent is absorbed, under ideal conditions, the maximum capacity computes to 219 mg CO.sub.2/g of solvent (MEA). Other studies have shown that MEA has a higher CO.sub.2 absorption capacity over DEA, which in turn is higher than the absorption capacity of MDEA for CO.sub.2.

(29) Thus, the synthesized amine-terminated branched polymers exhibit higher capacities for acid gas absorption over the traditional amines used in industry, resulting in absorption of multiple gas moles per mole of solvent. Traditional amines can at the maximum absorb only 1 mole of gas per mole of solvent. The use of higher absorption capacity solvents, especially if they can also be used at higher concentrations in water, enables more cost-effective acid gas scrubbing, lower column heights and faster kinetics of absorption, as well as lower thermal energy consumption during the desorption process. An additional physical phenomenon was discovered during the absorption of CO.sub.2 by aqueous solutions of these amine-terminated branched polymers. Before the absorption of carbon dioxide gas was performed, these polymers were completely soluble in water. However, after absorption of CO.sub.2, the aqueous polymer solution formed a two-phase mixture, clearly separated from each other—an amine-rich phase and a water-rich phase, in roughly the same proportions used for the original water-polymer mixtures before acid gas absorption. Both the amine-terminated glycerol ethoxylate and the amine-terminated pentaerythritol ethoxylate exhibited the same phenomena for complete water solubility before CO.sub.2 absorption and insolubility after CO.sub.2 absorption.

(30) The above phenomena of phase separation after gas absorption has important implications for practical use of these chemicals, and major advantages in energy consumption for regeneration of these solvents, in comparison to traditional amines like MEA, DEA and MDEA used for acid gas absorption. MEA is used as a 20-25% solution in water, while DEA is used as a 30-35% solution in water, and MDEA is used as a 50% solution in water. During regeneration of these chemical solvents, typically done at 120-135° C., even the water is vaporized while desorbing the absorbed gas, and at 540 kcal/liter, is a substantial energy penalty for regeneration of the solvent, while also increasing the complexity of the processing and heat exchangers involved.

(31) However, if the amine-terminated branched polymers are used for gas absorption, and phase separate from water after gas absorption, the water-rich portion can be removed and only the polymer-rich portion needs to be heated up to desorb the absorbed acid gas. In comparison to conventional amines, after the water has been separated out by decantation or filtration techniques, desorption of the absorbed gas from these amine-terminated amines, occurs at much lower temperatures of around 60-75° C. After the desorption is complete, the water-rich phase and the rich polymer can be remixed and recycled back to the gas absorption process. Such a system would be much more energy-efficient, saving on operating costs, and also save on capital costs for the system. The high boiling points and very low vapor pressures of these amine-terminated ethoxylates, and their comparative chemical stability also results in less solvent degradation and losses from volatilization.

(32) FIG. 6 shows a simplified process flow diagram for the acid gas removal system, using these amine-terminated branched polymers. Referring to FIG. 6, the acid gas laden stream is directed into a liquid scrubber system, wherein the acid gases are absorbed by the physico-chemical solvent described herein, and clean gas vented out of the scrubber. The solvent, now enriched with the absorbed acid gas, is directed to a flash chamber, wherein any physically absorbed gas species is desorbed by low-pressure swing or vacuum processes. The solvent-water mixture is therein directed to a liquid phase separator system, wherein the two liquid phases are separated by density differentials, using commercially available systems like liquid-liquid coalescers or other suitable apparatus. The solvent-rich stream is therein directed into a heated gas desorption system, wherein the absorbed acid gas is thermally desorbed for sequestration or other uses, and a stream of fresh polymer obtained. The polymer stream is now mixed with the water-rich portion from the liquid-liquid separator, and re-introduced into the scrubber system for more acid gas absorption.

(33) Dependent on the conditions of operation, the new solvents can be used either without dilution in water, or as a solution in water. For low-pressure, low CO.sub.2-concentration mixed gas streams, an aqueous solution of the amine-terminated branched ethoxylate, can be used as a chemical solvent, preferably at higher concentrations than commonly used for MEA, DEA or MDEA, and will still exhibit greater than 3 times the CO.sub.2 absorption capacity of MEA, DEA and MDEA. For high-pressure, high CO.sub.2-concentration mixed gas streams, a pure solution of the amine-terminated branched ethoxylate can be used as a physical solvent, and will still exhibit greater than 3 times the CO.sub.2 absorption capacity of Selexol™ (also known as PGDME or DEPG). The proposed solvent can further be tuned to specific applications by varying the number ‘n’ of the ethoxylate monomers in the amine-terminated branched ethoxylate. Thus, when needed to be used predominantly as a chemical solvent, the number ‘n’ may be kept small with fewer EO monomers in the molecule, just enough to ensure solubility in water. Conversely, when used predominantly as a physical solvent, the number ‘n’ may be increased to accommodate larger numbers of EO monomers to optimize CO.sub.2 absorption capacity, while maintaining liquid fluidity and low viscosity.

(34) Persons of ordinary skill in the art may appreciate that numerous design configurations may be possible to enjoy the functional benefits of the inventive systems. Thus, given the wide variety of configurations and arrangements of embodiments of the present invention the scope of the invention is reflected by the breadth of the claims below rather than narrowed by the embodiments described above.