Air collector with functionalized ion exchange membrane for capturing ambient CO2

Abstract

Disclosed is a process for forming a CO2 capture element comprises providing a mixture of a monomer or monomer blend or a polymer binder, a miscible liquid carrier for the binder and a CO2 sorbent or getter in particle form, forming the mixture into a wet film or membrane, evaporating the liquid carrier to form a film or membrane, and treating the wet film or membrane to form pores in the body of the film or membrane. Also disclosed is a process of forming a CO2 capture element which comprises the steps of applying a mixture including a sorbent material and a polymer to an underlying material; polymerizing the mixture in place on the material; and aminating the polymer-coated material.

Description

FIELD OF THE INVENTION

The embodiments of the present invention in one aspect relates to removal of selected gases from air. The embodiments of the invention have particular utility for the extraction of carbon dioxide (CO₂) from air and will be described in connection with such utilities, although other utilities are contemplated, including the sequestration of other gases including NO_x and SO₂.

BACKGROUND OF THE INVENTION

There is compelling evidence to suggest that there is a strong correlation between the sharply increasing levels of atmospheric CO₂ with a commensurate increase in global surface temperatures. This effect is commonly known as Global Warming. Of the various sources of the CO₂ emissions, there are a vast number of small, widely distributed emitters that are impractical to mitigate at the source. Additionally, large scale emitters such as hydrocarbon-fueled power plants are not fully protected from exhausting CO₂ into the atmosphere. Combined, these major sources, as well as others, have lead to the creation of a sharply increasing rate of atmospheric CO₂ concentration. Until all emitters are corrected at their source, other technologies are required to capture the increasing, albeit relatively low, background levels of atmospheric CO₂. Efforts are underway to augment existing emissions reducing technologies as well as the development of new and novel techniques for the direct capture of ambient CO₂. These efforts require methodologies to manage the resulting concentrated waste streams of CO₂ in such a manner as to prevent its reintroduction to the atmosphere.

The production of CO₂ occurs in a variety of industrial applications such as the generation of electricity power plants from coal and in the use of hydrocarbons that are typically the main components of fuels that are combusted in combustion devices, such as engines. Exhaust gas discharged from such combustion devices contains CO₂ gas, which at present is simply released to the atmosphere. However, as greenhouse gas concerns mount, CO₂ emissions from all sources will have to be curtailed. For mobile sources the best option is likely to be the collection of CO₂ directly from the air rather than from the mobile combustion device in a car or an airplane. The advantage of removing CO₂ from air is that it eliminates the need for storing CO₂ on the mobile device.

Extracting carbon dioxide (CO₂) from ambient air would make it possible to use carbon-based fuels and deal with the associated greenhouse gas emissions after the fact. Since CO₂ is neither poisonous nor harmful in parts per million quantities, but creates environmental problems simply by accumulating in the atmosphere, it is possible to remove CO₂ from air in order to compensate for equally sized emissions elsewhere and at different times.

Various methods and apparatus have been developed for removing CO₂ from air. In one prior art method, air is washed with a sorbent such as an alkaline solution in tanks filled with what are referred to as Raschig rings that maximize the mixing of the gas and liquid. The CO₂ interacts with and is captured by the sorbent. For the elimination of small amounts of CO₂, gel absorbers also have been used. Although these methods are effective in removing CO₂, they have a serious disadvantage in that for them to efficiently remove carbon dioxide from the air; the air must be driven past the sorbent at fairly high pressures.

The most daunting challenge for any technology to scrub significant amounts of low concentration CO₂ from the air involves processing vast amounts of air and concentrating the CO₂ with an energy consumption less than that that originally generated the CO₂. Relatively high pressure losses occur during the scrubbing process resulting in a large expense of energy necessary to compress the air. This additional energy used in compressing the air can have an unfavorable effect with regard to the overall carbon dioxide balance of the process, as the energy required for increasing the air pressure may produce its own CO₂ that may exceed the amount captured negating the value of the process.

Prior art methods result in the inefficient capture of CO₂ from air because these prior art methods heat or cool the air, or change the pressure of the air by substantial amounts. As a result, the net reduction in CO₂ is negligible as the capture process may introduce CO₂ into the atmosphere as a byproduct of the generation of electricity used to power the process.

In co-pending U.S. application Ser. No. 11/683,824, filed Mar. 8, 2007, U.S. Publication No. U.S.-2007-0217982-A1, assigned to a common assignee, there is described an air capture device that utilizes a solid functionalized anion exchange material that is formed to provide a relatively large surface area which allows for air flow. The solid anion exchange material may be formed from membranes of anion exchange material such as functionalized polystyrene or the like, or comprise membranes of inert substrate material coated with anion exchange material. In a preferred embodiment of our prior invention, the anion exchange material comprises “noodle-like” 1 mm thick by 1 mm wide strands formed by slitting commercially available anion exchange membrane material available from Snowpure, LLC, San Clemente, Calif. The manufacturer describes this membrane material as comprising crushed anionic exchange resin mixed in a polypropylene matrix and extruded as a membrane according to the teachings of U.S. Pat. Nos. 6,503,957 and 6,716,888. The solid anion exchange polymer also maybe formed into cells or the like.

SUMMARY OF THE INVENTION

The present invention explores alternative solid ion exchange materials for currently utilized ion exchange materials as above described as solid sorbent materials for CO₂ air-capture. More particularly, there is provided a process for forming solid sorbent materials for CO₂ air capture by immobilizing solid CO₂ sorbent materials in or on a support. In a preferred embodiment of the invention the solid CO₂ sorbent materials comprise solid particulate sorbent materials held together in a porous matrix. Alternatively, the solid CO₂ sorbent materials may comprise solid particulate sorbent materials supported on a surface of a support matrix. The support matrix may take a form of a membrane, which may be cut or slit into elongate elements, fiber strands which may be ordered or unordered, various geometric shapes such as tubes or bundles of tubes, honeycombs, discs or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present invention will be seen from the following detailed description taken in conjunction with the accompanying drawings, wherein like numerals depict like parts, and wherein:

FIG. 1 is a three-dimensional depiction of a polymer matrix of the prior art Snowpure membrane showing resin beads interspersed throughout the matrix.

FIG. 2 is a schematic depiction of the CO₂/H₂O vapor measurement device apparatus used in this investigation.

FIG. 3 shows the PSU-resin membrane before gelling.

FIG. 4 shows the PSU-resin membrane after the final membrane formation.

FIG. 5 is a graph showing the CO₂ adsorption capacity or desorption kinetics of a 0.78 gram sample of a PSU-resin composite membrane. Adsorption capacity of a sample in the chamber can be estimated from the area between the horizontal dashed line representing the atmospheric concentration of CO₂ (˜400 ppm), and the adsorption curve, which shows the amount of CO₂ being adsorbed by the membranes as the 400 ppm CO₂ air goes through the chamber.

FIG. 6 is another graph of CO₂ versus time showing a CO₂ adsorption of the reference membrane Snowpure, 1.13 g.

FIG. 7 is a graph of CO₂ versus time showing the CO₂ adsorption capacity of two membranes, the Snowpure 1.13 g reference membrane, and a PSU PVP 1.03 g membrane.

FIG. 8 is a graph of CO₂ versus time showing the CO₂ adsorption capacity of two membranes, the same Snowpure reference membrane plotted with a PVDF-HFP 0.88 g membrane.

FIG. 9 is a graph of CO₂ versus time showing the CO₂ desorption pattern that occurs when air saturated with water vapor is purged through the chamber.

FIG. 10 is a graph of CO₂ versus time showing the VBC/styrene ratio equal to one as air is purged through it to dry the membrane.

FIG. 11 is a graph of CO₂ versus time for the membrane and VBC\styrene equal to one with a water vapor purge through the chamber.

FIG. 12 is a graph of CO₂ versus time for the VBC/styrene ratio equal to one air purge of the membrane in the chamber.

FIG. 13 is a graph of CO₂ versus time showing the behavior of the sample VBC/styrene ratio equal to two when air is purged through the chamber containing the sample membrane.

FIG. 14 is a graph of CO₂ versus time for the VBC/styrene ratio equal to two sample membrane with a high humidity air purge.

FIG. 15 is a graph of CO₂ versus time for her the membranes and VBC only, 2.7 g, and the snow pure 2.9 Graeme membrane.

FIG. 16 is a graph of CO₂ concentration versus time for the sample polyester/cotton thread VBC only, 2.0 g, with a dry air purge.

DETAILED DESCRIPTION OF THE INVENTION

In order to develop alternative methods for forming solid CO₂ sorbent materials we first needed to better understand the structure of the currently utilized commercially available materials and the reasons why such materials are capable of absorbing CO₂. As best understood from the aforesaid U.S. Pat. Nos. 6,503,957 and 6,716,888, the Snowpure materials are made by a thermal extrusion method using polypropylene as the support matrix and ground anion exchange resin powder as an active filler. The polypropylene polymer is hydrophobic so it can afford physical support and not be soluble in aqueous solutions. The polypropylene polymer matrix has a narrow molecular weight distribution and low melting point (125˜130° C., although usually polypropylene melts at around 160° C.). The low melting temperature helps avoid thermal decomposition of the resin powders during the extrusion process. Also the polypropylene matrix is stable under chemical conditions such as high basicity or acidity.

According to the aforesaid U.S. patents of Snowpure, in the manufacturing process described by Snowpure, the polypropylene is melted in an extruder, and the resin powders are added into the melted polymer together with glycerin. The resin particles are hydrophilic and have exchangeable ions when wet. Glycerin is believed to help disperse the resin particles in the polymer matrix and form a barrier layer between resin and polymer. After extrusion, the membrane is soaked in an 80° C. water bath to remove the glycerin and to fully expand the resin. The structure is called a “composite” membrane because it consists of two phases, the polypropylene polymer matrix and the agglomeration of resin powders which it is believed forms continuous channels in the polymer. FIG. 1 is a simplified representation of the basic structure of the material obtained from Snowpure, except that the volume fill of the resin is much larger than depicted below.

The continuous channel shown by the continuous resin beads is believed to be important for membrane function in the Snowpure material. If the resin agglomerations are discontinuous or separated from each other and surrounded by polymer, the final membrane would be hydrophobic and would not be able to conduct ions in water or adsorb CO₂ at all.

The following examples describe alternative methods for forming solid sorbent materials for CO₂ air capture:

A first method of fabrication is based on solvent casting techniques.

This process starts with a polymerizable monomer or polymer in a liquid carrier having dispersed therein particles of a solid CO₂ sorbent material. There are two major properties for the polymerizable monomers used in this method. First, the polymerizable monomer or monomer blend or polymer should be soluble in the liquid carrier; second, the polymerizable monomer or monomer blend or polymer should be able to form a polymer sheet or film. Amongst preferred polymers are mentioned polybisphenol-A-carbonate, poly(ethylene terephthalate), polystyrene, poly(methyl methacrylate), poly(vinyl acetate), poly(vinyl chloride), polytetrafluoroethylene, polysulfone, poly(vinylidene fluoride), styrene/butyl acrylate/methacrylic acid terpolymer, and poly(vinylidene fluoride-co-hexafluoropropylene).

The solid CO₂ sorbent materials are materials capable of absorbing and releasing gaseous CO₂ under controlled conditions. The solid CO₂ sorbent materials may comprise solid ion exchange resins such as described in U.S. Pat. Nos. 6,503,957 and 6,716,888, as well as solid CO₂ sorbents or “getters” such as strong base Type 1 and Type 2 functionality ion exchange materials as are available commercially from a variety of vendors including Dow, Dupont and Rohm and Haas.

A mixture of the polymerizable monomer or monomer blend or polymer and the solid CO₂ sorbent material is mixed with the solid sorbent materials and liquid carrier, and applied in a solvent casting method. The monomer or monomer blend or polymer is dissolved and the solid CO₂ sorbent materials particles are homogeneously dispersed in the liquid carrier. When the mixture is poured on a flat surface, e.g., a stainless steel block on a hot plate, and the liquid carrier evaporated, a sheet or film having the particles dispersed throughout is left on the surface. However in this method the structure of the sheet is determined by the interactions among the liquid carrier, the monomer or monomer blend and the particles.

In one experiment we made a sheet by mixing poly(vinylidene fluoride) and resin particles in dimethylformamid (DMF). The ion-exchange resin is ground or chopped to particle size of 100 to 1000 microns, preferably 200 to 500 microns. The resin particles should comprise 10 to 90 volume percent of the cast film, preferably 20 to 80 volume percent. The finished sheet preferably has a thickness of 0.1 to 2.0 mm, preferably 0.2 to 1.0 mm. Experiments showed that without glycerin addition the sheet with even 50% resin content is still hydrophobic, which indicates the particle agglomerations are separated by polymer. When glycerin or phenolphthalene is added into the monomer, filler and liquid carrier mixture, the sheets formed are hydrophilic and ion-conductive. FIG. 2 is an CO₂ absorption curve of both membranes under similar conditions.

A second method of fabrication of polymer membranes is the phase inversion/immersion precipitation method. Phase inversion methods are described generally in U.S. Pat. Nos. 3,876,738, 4,340,480, 4,770,777, and 5,215,662, all of which are incorporated herein by reference. Generally, the process is to immerse a polymer solution made by a polymer dissolved in a solvent or mixture of solvents into a miscible non-solvent such as water (i.e., a liquid in which the polymer is not soluble, but the non-solvent is miscible with the solvent). In a non-solvent such as a water bath, the polymer starts to solidify because of the penetration of water molecules whereas the solvent component diffuses into the water, leaving spaces throughout the polymer where the solvent formerly was. Thus the formed membrane is asymmetric. The surface of the membrane has a relatively dense gel surface, while the bulk interior of the membrane is relatively porous. Spaces formed by this method are interconnecting, however. The phase inversion technique has been established for about twenty years. Reverse osmosis and nanofiltration membranes are also made using this technique. It is also applied in hollow fiber membranes for pervaporation separation of ethanol/water solutions or gas separations. In our application the porous structure enables the easy access of air to the resins embedded in the polymer matrix.

A third method of fabrication of polymer membranes is the sorption method in which a mixture of liquid monomers and initiators are absorbed in a woven or non-woven fiber matrix of polypropylene, PVC, polyester, cellulose etc. The monomers polymerize under thermal or radiation conditions forming a thin layer on the matrix surface. Mizutani, Y., Journal of Membrane Science, 1990, 49, 121-144 reported the preparation of an ion exchange membrane using the paste method, in which the paste, consisting of monomers and finely powdered PVC was coated onto PVC cloth and the cloth was exposed to heat. Later Choi et. al. published papers describing the making of ion exchange membranes by the sorption method, in which monomers were absorbed in non-porous reinforcing materials such as polypropylene, or PVC films. Choi, Y., et al., Desalination, 2002, 146, 287-291; Choi, Y. et al., Journal of Membrane Science, 2003, 221, 219-231; Choi, Y., et al., Journal of Membrane Science, 2003, 223, 201-215. The non-porous reinforcing material was swollen while monomers were absorbed in non-porous reinforcing materials. The swollen reinforcing material permitted enlarged free volume for the adsorbed monomers. The membrane was treated with UV radiation for monomer polymerization (anion exchange membranes). In our experiments solutions of monomers such as vinylbenzyl chloride, styrene, divinylbenzene and the initiator benzoyl peroxide were absorbed into non porous or porous fabrics such as filter paper, polyester/cellulose paper, cloth etc, or porous film such as porous alumina, polycarbonate etc. through capillary action. The solution-saturated fabrics were then exposed to heat or radiation to polymerize the monomers. The resulting membranes in carbonate form showed moisture swing effects in absorbing CO₂ from the atmosphere.

Materials and Methods.

The following protocols or material preparation processes recur throughout the Examples, and so they are presented here for purposes of streamlining the disclosure of the various embodiments.

1) Amination protocol. Synthetic membranes were soaked in a 40% aqueous solution of trimethylamine for 10 hours at 50° C. They were then rinsed with tap water, and placed twice in 100 ml 0.1M HCl solution to neutralize any residual unbound trimethylamine. At this point the counterion on the membrane is chloride, and the chloride was exchanged with carbonate via the carbonation process (see below).

Carbonation protocol. Samples in the chloride form are exchanged with carbonate counterion by immersing them in 0.5 M Na₂CO₃ with stirring for 30 minutes twice at room temperature, and then rinsing with DI water until neutral.

Polymer loading capacity. A supporting matrix should be chemically and mechanically stable through all polymerization and derivatization processes and should be loaded with the highest amount of coated polymers. We define “loading capacity of a matrix” as (weight of net polymers coated on matrix)/(weight of net matrix).

Ion exchange capacity measurement process. Sample membranes made hereunder had their Ion Exchange Capacity (“IEC”) measured to test their efficiency of CO₂ adsorption. IEC is defined as the total amount of ion groups per unit mass of dry material (mmol/g). The higher the IEC number the higher the corresponding CO₂ absorption capacity. Generally, samples were heated in an oven at about 60° C. until dry (no more weight loss). About 1.0 g of dried sample was weighed and soaked in 20 ml 0.5M NaNO₃ solution for 30 minutes with stirring. The sample was filtered and soaked in another fresh 20 ml 0.5M NaNO₃ solution for another 30 min. with stirring. All filtered solutions were collected and were titrated to pH 7 with 0.1M standard HCl solution. The total ionic numbers could be deduced from the titration results and IEC could be calculated as a ratio: total ionic number (mmols)/dried sample weight (grams).

CO₂/H₂O measurement process. FIG. 2 is a schematic of the CO₂/H₂O vapor measurement device used in this investigation. In order to compare samples created hereunder against the Snowpure® standard material accurately in terms of their CO₂ adsorption ability, the same or similar weight of samples or Snowpure® were sealed in a container (glass jar, 0.25 liter) with two vents. In order to dry or hydrate the membranes, air (absolute humidity ˜5 ppt) or air saturated with moisture vapor (absolute humidity ˜30 ppt) was pumped into and through the container at a fixed flow rate (usually 0.1 L/min) at 75° F. and was passed through the glass jar containing the sample material. The exiting air is then directed through an IRGA (IR Gas Analyzer, Model LI-840, LI-COR, Inc.), which detects CO₂ and H₂O vapor content at selected intervals, usually every 10 seconds. The air is then vented to atmosphere.

Phase inversion method. Materials: DMF (dimethyl formamide) solvent (95%); PSU (polysulfone) pellets (Aldrich, P/N 428302, Mw˜35,000); PVDF powder (poly(vinylidene fluoride), Aldrich, P/N 182702, Mw˜534,000); PVP (Polyvinylpyrrolidone, Sigma-Aldrich, Mw˜10,000); PVDF-HFP (poly(vinylidene fluoride-co-hexafluoropropylene) and Dowex® Marathon A anion exchange resin C1 form (SigmaAldrich, P/N 433942). Resin beads were ball milled to 40˜100 microns at room temperature before use. Polymer matrix materials that may be used herein include but are not limited to polybisphenol-A-carbonate, poly(ethylene terephthalate), polystyrene, poly(methyl methacrylate), poly(vinyl acetate), poly(vinyl chloride), polytetrafluoroethylene, polysulfone, polyether sulfone, poly(vinylidene fluoride), styrene/butyl acrylate/methacrylic acid terpolymer, and poly(vinylidene fluoride-co-hexafluoropropylene). Preferred organic solvents for the polymers may be selected from dimethylformamide or tetrahydrofuran, or N-methylpyrrolidone (NMP). Glycerin, polyvinyl pyrolidone (PVP), dibutylphthalate (DBP), phenolphthalene or other plasticizers may be added to the mixture. For the phase inversion procedure, the aqueous-based solution may be water or methanol, ethanol, isopropanol or mixtures thereof. The resin particles used in the composite membranes may vary in diameter from 10˜100 micrometer and the resin content may vary from 20˜80% of polymer matrix by weight, preferably 30˜60%. The final heterogeneous membrane thickness may vary from 0.1˜1.0 mm, preferably 0.5 mm.

Example I

Phase Immersion of PSU-Resin Membrane

PSU-resin membrane: 0.5 g of PSU pellets were weighed in a 20 ml vial, 2.5 ml of DMF was added into the vial and the mixture was stirred until the polymer dissolved in the DMF. In another vial 0.5 g of ground ion-exchange resin powders were weighed and 2.0 ml of DMF was added. The mixture was stirred until homogeneous. The two vial contents were combined and stirred for another half hour. The mixture was cast on a rectangular 6×4 inch stainless steel block surface on a hot plate maintained at 50° C. In about 10 minutes the membrane completely gelled (the membrane looked transparent at this time and there was no liquid solvent on the surface). The block was removed from the hot plate, allowed to cool to room temperature and then soaked in a deionized water bath (2 liters). After several minutes, the membrane was peeled from the block. The membrane was left in the water bath with stirring for two days (the water in the bath was changed after one day) and boiled in hot water for 1 hour to get rid of any residual solvent inside the membrane. The membranes are then carbonated by the general carbonation protocol.

FIGS. 3 and 4 show the PSU-resin membrane before gelling and after the final membrane formation, respectively. The IRGA measures the air that has contacted the membrane, and thus reflects the membrane's CO₂ adsorption capacity in real time. Snowpure® membranes are used as the standard CO₂ absorbent material against which the inventive membranes described herein are compared against.

Results:

With respect to FIG. 5 and FIG. 6, the CO₂ adsorption capacity of a given membrane in the chamber can be estimated from the area between the horizontal dashed line representing the atmospheric concentration of CO₂ (˜400 ppm), and the adsorption curves, which show the amount of CO₂ being adsorbed by the membranes as the 400 ppm CO₂ air goes through the chamber. Simply, we can cut the areas and measure paper weight. The ratio of paper weights between the membranes being compared is directly proportional to CO₂ capacity if the sample weights are similar. This is also known as the integral of the area under the 400 ppm curve and above the CO₂ adsorption curve.

From FIGS. 5 and 6, the CO2 capacity of the PSU membrane is smaller than that of the Snowpure sample (absorption area per unit weight of PSU is smaller than that of Snowpure). Theoretically with the same amount of resin the membranes should absorb the same quantity of CO₂. One possible reason for the lower CO₂ absorption by the PVDF- and the PSU-resin-CO₃ membranes compared to the Snowpure® membranes is that the resin particles are more tightly surrounded by polypropylene polymer. One way to resolve this is to make the membranes more porous. In the following experiment we added PVP (polyvinylpyrrolidone) into the mixture before casting. PVP is soluble in both polar aprotic solvent and water. After the membrane is cast and later soaked in water, the PVP mixed with the water and left pores inside the membrane.

Example II

Phase Inversion Aided by PVP

Membrane (PSUPVP) preparation: 0.5 g of PSU was weighed in a 20 ml vial and 2.5 ml DMF was added and the mixture stirred until all polymers were dissolved. 0.5 g of resin and 0.2 g of PVP was weighed in another vial and 2.5 ml DMF was added. The mixture was stirred until homogeneous. The two vial contents were combined and stirred for another 0.5 hour at room temperature. The mixture was cast on the same rectangular stainless steel block surface, 6×4 inches on a hot plate at 50° C. After about 10 minutes, the membrane completely gelled (the whole membrane appears transparent at this time and there was no flowing solvent on the surface). The block was removed from the hot plate, allowed to cool to room temperature, and then soaked in a deionized water bath. After several minutes, the membrane was peeled from the block. The membrane then was left in the water bath with stirring for two days (the water in bath was changed after one day) and boiled in hot water for 1 hour to eliminate the solvent and any PVP inside the membrane. The membrane was then carbonated according to the standard protocol.

Results:

From FIG. 7 the CO2 adsorption capacity of PSUPVP membrane is much bigger than that of the PSU membrane in Experiment I, which indicates that the addition of PVP increases membrane porosity. The IEC value is 1.90 mmol/g. A comparison was made of the CO₂ adsorption for this PSUPVP membrane to the membrane material from Snowpure® (FIG. 7) which also has an IEC value of 1.9. Numerical estimates of the CO₂ uptake for the Snowpure material and PSUPVP membrane based on the integral of the CO₂ deficit in the exhaust stream suggest that the total uptake capacities are quite similar. We conclude that the PSUPVP membrane has comparable CO₂ absorption capacity to the Snowpure®.

Except for PSU polymer, other thermal plastic polymers could also be used as matrix via phase immersion process.

Example III

Phase Immersion of PVDF-HFP Membrane

Membrane (PVDF-HFP) preparation: 0.5 g of PVDF-HFP were weighed in a 20 ml vial and 3.0 ml DMF was added and the mixture stirred until all polymers were dissolved. 0.5 g of resin was weighed in another vial and 2.0 ml DMF was added. The mixture was stirred until homogeneous. The two vial contents were combined and stirred for another 0.5 hour at room temperature. The mixture was cast on the same rectangular stainless steel block surface, 6×4 inches, on a hot plate at 50° C. After about 10 minutes, the membrane completely gelled (the whole membrane appears transparent at this time and there was no flowing solvent on the surface). The block was removed from the hot plate, allowed to cool to room temperature, and then soaked in a deionized water bath. After several minutes, the membrane was peeled from the block. The membrane then was left in the water bath with stirring for two days (the water in bath was changed after one day) and boiled in hot water for 1 hour to eliminate the solvent and any remaining PVP inside the membrane. The membrane was then carbonated according to the standard protocol.

Results: PVDF-HFP membrane shows comparable CO2 absorption ability of Snowpure in FIG. 8 with no addition of PVP. This membrane has a IEC of 1.85.

B. Sorption Method

In the following embodiments solutions of monomers such as vinylbenzyl chloride, styrene, divinylbenzene and the polymerization initiator benzoyl peroxide were absorbed into non-porous fabrics such as filter paper, polyester/cellulose paper, cloth, etc, or porous film such as porous alumina, polycarbonate film, etc. through capillary action. The solution-saturated fabrics were then exposed to heat or radiation to polymerize the monomers. The resulting membranes in carbonated form showed moisture swing effects in absorbing and de-sorbing CO₂ from the atmosphere.

Reagents:

Vinyl benzyl chloride (VBC, Aldrich, 97%), Styrene (Sigma-Aldrich, 99%), Divinyl benzene (Aldrich, 80%) and Benzoic acid (Fltika, 99%) were all dried by passing them through an Al₂O₃ column and stored at 0° C. and purified by recrystalization. Benzoyl peroxide (powder) in a beaker was dissolved in a minimum amount of chloroform. The solution was transferred into a separation funnel. The solution was separated into two layers. The water layer was on top and bottom layer was BP-chloroform solution. The bottom layer was collected in a clean beaker and methanol was added until no more precipitation occurred. The solvent was decanted and white precipitate was purged under N₂ and stored in a desiccator.

Example IV

Membranes Synthesized from Polyester/Cellulose Matrixes

1.5 ml VBC, 1.5 ml styrene, 0.3 ml divinylbenzene and 0.02 g BP were added into a 20 ml vial and were stirred until all BP was dissolved at room temperature. The mixed solution was poured onto Durx® 670 polyester/cellulose papers and was spread on the paper under capillary effect. The wet papers were put in a closed glass container and were purged with N₂ to eliminate residual O₂ in the container. The container was placed in an oil bath and heated to about 68˜70° C. for 10 hours. After reaction completion, the container was cooled to room temperature and was left open for 2˜3 hours to evaporate excess reagents. The membranes were soaked in 40% trimethylamine aqueous solution for 3 hours at 30° C. to aminate them and then were rinsed with tap water. The aminated membranes were soaked in 2×100 ml 0.1M HCl solution to wash off any excess trimethylamine, and then rinsed with tap water. Finally the membrane was carbonated by soaking in 0.5 M Na₂CO₃ 2×100 ml. The final product was rinsed with water until neutral before use.

VBC was the reagent utilized to enable the subsequent addition of functional amine groups via amination to the final product. Para- or ortho-VBC, or mixtures of both, function adequately. Styrene was the non-functional matrix polymer that increased hydrophobicity of the membrane. Divinyl benzene was the cross-linking reagent, and BP was the initiator for the polymerization reaction. The VBC and styrene ratio could be changed from 100% VBC to 10% VBC, according to product requirements. The cross-linking percentage could be changed from 2% to 20% of total VBC and styrene weight. Reaction vessels can be made from glass, stainless steel or ceramic.

Membrane CO₂ Binding Performance:

For membrane measurements of CO₂ adsorption capacity, samples were sealed in the 250 ml glass jar mentioned previously and were purged with air at 0.1 L/min flow rate. The measurement protocol was described previously. FIGS. 9-12 are measured from a single sample weighing 3.5 g having an IEC of 0.55 mmol/g.

In FIGS. 9-12, the 3.4 g sample was purged by dry air (FIG. 9) followed by moisture saturated air (FIG. 10). The process was repeated once (FIGS. 11-12). With atmospheric CO₂ levels at about the 390 ppm level, the sample showed a repeatable “moisture swing” CO2 adsorption/desorption effect: when the membrane sample was purged by relatively dry air (absolute humidity ˜5 ppt), the membrane adsorbed CO₂; when the sample was purged with moisturized air (absolute humidity 30 ppt), it gave off or desorbed CO₂.

In FIGS. 9-12, during sample preparation the VBC to styrene ratio was 1. Under the same reaction conditions but varying the VBC to styrene ratio, it is expected to help increase the membrane's CO₂ absorption capacity, as shown by the following example.

Example V

Membranes Synthesized from Polyester/Cellulose Matrixes-Effect of Increase in VBC Content

In this experiment samples were made under the same conditions as in experiment IV except that VBC and styrene were present at a 2:1 ratio respectively. The sample weights in FIGS. 13-14 are 4.1 g. IEC is 1.35 mmol/g, which is significantly higher than the 1:1 ratio's 0.55 mmol/g.

In experiment V the samples were made with a higher VBC to styrene ratio (VBC/styrene=2) compared with samples made in experiment IV (VBC/styrene=1). FIGS. 13 and 14 demonstrate that the increased amount of VBC may have provided more ionic sites on the membrane thereby increasing the membrane's CO2 adsorption capacity. The resulting membranes show retention of the moisture swing effect.

When the amount of VBC was increased to 100%, the resulting samples did not show enhanced performance. IEC titration of the sample with VBC only and the sample with VBC/styrene=1 both resulted in an IEC of 1.0 mmol/g of dry sample, much lower than the IEC of Snowpure® (1.9 mmol/g). The following method is to conduct amination at elevated temperature (from 30° C. to 50° C.) and extended reaction time (from 3 hrs to 10 hrs).

Example VI

Membranes Synthesized From Polyester/Cellulose Matrixes-Improved Amination Condition

3.0 ml ml VBC, 0.45 ml divinylbenzene and 0.02 g BP were added into a 20 ml vial and were stirred until all BP was dissolved at room temperature. The mixed solution was poured onto Durx® 670 polyester/cellulose papers and was distributed through the paper by the capillary effect. The wet papers were put in a closed glass container and were purged with N₂ to eliminate residual O₂ in the container. The container was placed in an oil bath and heated to about 68˜70° C. for 10 hours. After reaction completion, the container was cooled to room temperature and was left open for 2˜3 hours to evaporate excess reagents. Instead of aminating at 30° C. for 3 hours, the membranes were soaked in 40% trimethylamine aqueous solution for 10 hours at 50° C. and then were rinsed with tap water. The aminated membranes were soaked 2× in 100 ml 0.1M HCl solution to wash off any excess trimethylamine, and then rinsed with tap water. Finally the membrane was carbonated by soaking in 0.5 M Na₂CO₃ 2×100 ml. The final product was rinsed with water until neutral before use.

Sample membranes or Snowpure® membranes were sealed in a container (glass jar, 0.25 liter) with two vents. Dry air (atmospheric air passed through dry silica column, absolute humidity ˜0 ppt) was pumped into the container at a fixed flow rate (0.1 L/min) at 75° F. and was purged through the sample. The exiting air is then directed through an IRGA (IR Gas Analyzer, Model LI-840, LI-COR, Inc.), which detects CO₂ and H₂O vapor content at every 10 seconds. The air is then vented to atmosphere.

FIG. 15 showed that samples made under improved amination conditions had similar CO2 absorption capacity compared with Snowpure®. IEC titration of samples was 2.2 mmol/g, a bit higher than that of Snowpure® (1.9 mmol/g).

In the above coating method, the matrix we used was polyester/cellulose fabric. This coating method could also be applied to fibers such as polyester thread, nylon thread, polyester/cotton thread etc.

Example VII

Polyester/Cotton Thread Synthesized by Sorption Method

3.0 ml VBC, 0.45 ml divinylbenzene and 0.02 g BP were added into a 20 ml vial and were stirred until all BP was dissolved at room temperature. The mixed solution was dropped onto polyester/cotton thread (sewing thread, 37% cotton, 63% polyester) and was spread along thread under capillary effect. The wet threads were put in a closed glass container and were purged with N₂ to eliminate residual O₂ in the container. The container was placed in an oil bath and heated to about 68˜70° C. for 10 hours. After reaction completion, the container was cooled to room temperature and was left open for 2˜3 hours to evaporate excess reagents. The threads were soaked in 40% trimethylamine aqueous solution for 10 hours at 50° C. to aminate them and then were rinsed with tap water. The aminated threads were soaked in 2×100 ml 0.1M HCl solution to wash off any excess trimethylamine, and then rinsed with tap water. Finally the threads were carbonated by soaking in 0.5 M Na₂CO₃ 2×100 ml. The final product was rinsed with water until neutral before use.

The IEC of the coated polyester/cotton thread shown in FIG. 16 is 1.5 meq/g, which is a relatively lower IEC compared with that of Snowpure® (1.9 meq/g) and is from the thread having a lower polymer loading capacity defined in Protocol 3.

The loading capacity of sample matrixes were measured according to Protocol 3 and used the following matrices: braided nylon thread: 0.5; polyester/cotton thread: 0.85; polyester thread: 0.89 polyester/cellulose fabric: 2.0. The fabrics or fibers such as polyester/cellulose paper, polyester thread, polyester/cotton thread etc. proved to be good matrices. Light weight and high absorption material is optimal.

The methods described above, and other conceivable methods, may be used to form various superstructures having active resins embedded therein. For example, it is possible using the solid sorbents and polymers or other matrices discussed above to form films that can be arranged in the configurations described in co-pending application PCT Application Serial No. PCT/US08/60672, which describes several geometries that may be used to form a collapsible collector to optimize the porosity of the collector for alternating liquid and gas streams. The films may be formed in flat membranes, concentric cylinders or tubes, or wound up spirals. Some configurations may require the use of spacers, which may be formed of a polymer material, to form the structure.

Other examples of superstructures that are possible using the present invention include the formation of flat membranes, tubes, hexagons, or monolithic structures, using porous materials. Porous structures will naturally increase the amount of surface area for CO₂ uptake. Alternatively, the solid sorbent material may be produced in a foam that can be manipulated into complex shapes for a specific application or for optimal performance. In another alternative formation, the material could be spun into thin threads or woven into textile or felt-like materials.

The sorbent materials of the present disclosure may also be applied as surface coating to an underlying structure formed of a durable and inexpensive material. For example, monoliths made out of inexpensive materials could be soaked in the polymer/resin combination and then harden into a useful filter system. These monoliths may be constructed of paper materials, ceramic materials, textiles, or other appropriate materials. The coatings may be applied similar to a paint, such as by spraying, rolling, dipping, or the like.

In another aspect of the present invention, the superstructure may be formed as the sorbent materials are polymerized around a fibrous structure, similar to a carbon composite matrix structure.

The present invention may also be used to create a sorbent superstructure with very rough surfaces, which would then increase the uptake rate of the CO₂ capture process. In particular, solvents may be used to form a dendritic structure. A rough surface could also be accomplished by a method involving a step of etching the solid material to create more surface area.

In embodiments where a high concentration of uptake sites are present, it may be possible to use turbulent flows through the filter, as this would decrease the air side transport limitations of the system.

Various changes may be made without departing from the spirit and cope of the invention. For example, CO₂ capture elements may be formed using solid amines as the CO₂ sorbent or getter. The solid amine getters preferably are the amines as described in our co-pending U.S. Provisional Application Ser. No. 60/989,405, filed Nov. 20, 2007. The solid amines may be formed on porous solid supports, membranes or films, e.g. from liquid amines which are dried in place on a support. Also, the membranes and films may be formed by roll casting, or doctor blade casting from a solution containing the monomer or monomer blend or polymer dissolved or a solvent containing the particulate CO₂ sorbent or getter. Also, films, membranes or fibers may be formed by spin coating.

Claims

1. A method for the capture of CO2 from air, comprising capturing CO2 from atmospheric air with a solid capture material, and treating said solid capture material to release captured CO2; wherein said solid capture material (i) comprises a CO2 sorbent material comprising a polymer immobilized in or on a porous support material; and (ii) has a CO2 adsorption capacity higher than 1.9 mmol/g.

2. The method of claim 1, wherein said solid capture material comprises a polymer selected from the group consisting of: polybisphenol-A-carbonate, poly(ethylene terephthalate), polystyrene, poly(methyl methacrylate), poly(vinyl acetate), poly(vinyl chloride), polytetrafluoroethylene, polysulfone, polyether sulfone, poly(vinylidene fluoride), styrene/butyl acrylate/methacrylic acid terpolymer, and poly(vinylidene fluoride-cohexafluoropropylene).

3. The method of claim 1, wherein said solid capture material is formed using a CO2 sorbent comprising particles having a diameter between 10-1000 micrometers.

4. The method of claim 1, wherein the CO2 sorbent material content of said solid capture material is 20% to 80% by weight.

5. The method of claim 1, further comprising releasing CO2 captured by said solid capture material by hydrating said solid capture material.

6. The method of claim 1, wherein said solid capture material releases CO2 when hydrated.

7. The method of claim 1, wherein said CO2 sorbent material comprises an ion exchange resin.

8. The method of claim 7, wherein said ion exchange resin comprises a Type I or Type II functionality ion exchange resin.

9. The method of claim 1, wherein said CO2 sorbent material comprises polysulfone, poly(vinylidene fluoride-co-hexafluoropropylene), or vinyl benzyl chloride.