Renewable rotor and preparation method thereof

Abstract

A method for forming a gas adsorption media includes providing a media substrate with a defunctionalized moisture absorption layer, coating at least a portion of the media substrate with a solution of an amine and a solvent, and removing excess solution from the media substrate by evaporation to leave an amine coating on the substrate.

Description

Technical Field

[0001] The present invention relates to an adsorbent technology for removing gases such as carbon dioxide (CO2) from an air stream. Specifically, the present invention relates to an amine-coated medium for gas adsorption, such as a high specific surface area rotor, and methods for its preparation and use. Particularly suitable uses of the gas adsorption medium are, for example, continuously providing low CO2 (ppm) air for a habitable environment and continuously providing desorbed CO2 ppm air for a horticultural enclosed environment. Background Art

[0002] Solid and liquid adsorbents have been used to remove or eliminate CO2 from combustion process exhaust gases and from the air in enclosed areas such as the ambient atmosphere and residential and agricultural enclosures. For example, as described in International Publication WO 2021 / 150722. In recent years, improving indoor air quality has received increasing attention due to more air purification technologies entering the market and the cost of conditioning outdoor air. Many processes are performance-based and apply a mass balance to calculate the required outdoor air flow rate for a particular area based on the relevant pollutants. These processes consider the effectiveness of air purification equipment when calculating the required ventilation flow rate and generally aim to apply less outdoor air while maintaining a high indoor air quality, thereby reducing the peak capacity and overall energy consumption of heating and cooling equipment. While some air cleaning technologies are more effective than others at cleaning specific pollutants, most technologies have no effect on the CO2 continuously generated by the occupants inside a building. CO2 concentration is typically controlled by diluting the indoor air with outdoor air having a lower CO2 concentration.

[0003] There is increasing concern about the effects of high CO2 concentrations on human cognitive function. ASHRAE Standards 62.1 and 62.2 (incorporated herein by reference) set the minimum ventilation requirements for buildings to ensure optimal indoor air quality and to minimize negative impacts on the health of the occupants. Appendix D of Standard 62.1 states that an indoor CO2 concentration not exceeding 700 ppm above the outdoor CO2 concentration will meet the requirements of the vast majority (about 80%) of the occupants. Adsorbents for removing CO2 can be formed into various shapes, such as individual particles in a fixed bed or a single monomer shape for a specific use. Certain CO2 adsorption materials include at least one organic amine, at least one high surface area particle, and water, which are mixed and dried to form particles or a surface coating of the desired shape. For example, as described in European Patent Publication No. EP 2 054 151 B1 and U.S. Patent No. 9 919 287.

[0004] Current methods utilize an adsorbent packed bed with an amine adsorbent on a solid support to remove CO2 or other gases from indoor air. The adsorbent includes at least one support particle and at least one organic amine, where the organic amine and the support particle aggregate to form larger spheres, clusters, or shaped forms for use as a fixed bed for flow-through adsorption. The amines include, but are not limited to, polyethyleneimine (PEI), aziridine, ethanolamine, diethanolamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, or mixtures thereof. The support particles are composed of carbon, silica alumina, or combinations thereof. Typically, the support particles are calcined, pyrolyzed, or precipitated. The solid adsorbent for removing CO2 also includes a chemical activator such as polyethylene glycol (PEG).

[0005] A particular class of solid adsorbents for removing CO2 is solid-supported amines (compositions made from organic amine materials and high-surface-area particles). However, these solid adsorbents have some problems when removing CO2 in an atmospheric environment, as described below.

[0006] A. In current temperature swing adsorption / absorption technologies, energy loss is significant as the adsorption medium has to be heated to 60 °C or higher to initiate the desorption cycle.

[0007] B. Moisture present in the air stream requires a moisture-resistant adsorbent. The packed bed may form a moisture-filled volume, which reduces its ability to adsorb CO2.

[0008] C. A solid adsorption bed does not allow for a continuous adsorption process as the adsorption bed needs to undergo intermediate regeneration cycles (temperature or pressure swing).

[0009] D. Friction is generated between the particles due to the movement of the adsorption bed particles by the air flow. This friction reduces the particle adsorption efficiency and results in the phenomenon of carrying dust particles.

[0010] E. A solid adsorption bed system has a high bed pressure drop, which requires the system to apply high-pressure air treatment equipment that is prone to air leakage.

[0011] F. Particle adsorbents are typically made using expensive solvents or water-soluble alcohols (such as ethanol or methanol). These solvents make the methods for manufacturing solid adsorbents either too expensive for large-scale industrial development or too dangerous as some solvents are flammable.

[0012] G. Generally, solid adsorbents include very small functionalized particles that may be carried away by the moving gas or are difficult to handle due to their size and shape limitations.

[0013] Currently available CO2 habitable atmosphere adsorption technologies (mainly packed beds that require temperature swing adsorption / desorption) are energy-intensive. To achieve low energy consumption, it is necessary to improve CO2 capture technologies.

[0014] Known adsorbent rotors are used to adsorb or remove other components in an air stream, such as moisture, volatile organic compounds (VOCs), and CO2. Many of these rotors have a limited service life and are typically discarded in landfills when their life expires. Appropriately reusing used adsorbent rotors would be both economically and ecologically beneficial. Summary of the Invention

[0015] In one aspect, the present invention relates to a method for forming a gas adsorption medium, the method comprising: providing a media substrate with a defunctionalized moisture-absorbing layer, coating at least a portion of the media substrate with a solution of an amine and a solvent, and removing excess solution from the media substrate by evaporation to leave an amine coating on the substrate.

[0016] In another aspect, the present invention relates to a method for converting a medium designed to adsorb a first gas into a medium designed to adsorb a second gas, where the second gas is different from the first gas. The method comprises providing a media substrate having a substrate capable of adsorbing the first gas, coating at least a portion of the media substrate with a solution of an amine and a solvent, the amine being capable of adsorbing the second gas, and removing excess solution from the media substrate by evaporation to leave an amine coating on the substrate.

[0017] In yet another aspect, the present invention relates to a gas adsorption medium comprising a media substrate initially provided with a defunctionalized moisture-absorbing layer, and a coating of an amine and a solvent provided on at least a portion of the defunctionalized moisture-absorbing layer.

[0018] These and other aspects, objects, features, and advantages of the present invention will become more apparent from the following detailed description of its exemplary embodiments, which are to be read in conjunction with the accompanying drawings. Brief Description of the Drawings

[0019] Figure 1 is a schematic flow chart depicting a preferred embodiment of the rotary adsorption system of the present invention.

[0020] Figure 2 is a schematic diagram of the regions of an adsorbent rotor in a preferred embodiment of the rotary adsorption system of the present invention.

[0021] Figure 3 The flow chart of depicts the steps for manufacturing the adsorbent rotor of the present invention.

[0022] Figure 4 is a schematic flow chart depicting another preferred embodiment of the rotary adsorption system of the present invention.

[0023] Figure 5 is a schematic diagram of the regions of an adsorbent rotor in another preferred embodiment of the rotary adsorption system of the present invention. Detailed Description

[0024] As described above, currently available CO2 habitable atmosphere adsorption technologies (mainly packed beds that require temperature swing adsorption / absorption) are energy-intensive. Therefore, it is necessary to improve CO2 capture technologies to achieve low energy consumption and overcome other known defects of packed bed systems. Adsorbent rotors are known to adsorb or remove other components in an air stream, such as moisture and volatile organic compounds (VOCs). For example, the rotor systems (RS) and integrated ZeolSystem systems (IZS) produced by Munters Corporation. In contrast, based on the cross-sectional area of the air passing through, the adsorbent bed with a monolithic size of 0.1 - 10 mm has a smaller impregnated surface area compared to a titanium silica gel rotor (the porous hygroscopic coating of an exemplary rotor is about 10 - 20 μm on each side of the foil). The frictional loss of an exemplary rotor is also smaller, that is, the packed bed particles are vulnerable to particulate friction under air movement, and its adsorption capacity will decrease over time. The exemplary rotor requires a shorter regeneration time when the temperature changes, that is, compared to a continuous regeneration process, the packed bed requires an intermediate temperature change for regeneration. Additionally, the packed bed is sensitive to alternating steam pressures. The large particles in the compact adsorbent bed are vulnerable to moisture accumulation, resulting in a reduction in the available functionalized pore surface area. On the other hand, rotors with a hydrophobic surface treatment can better control this phenomenon. The fine pores and capillaries of the rotor with hydrophobic characteristics are difficult to clog, and moisture tends to condense in them, thereby reducing the adsorption capacity. In summary, the rotating adsorption system is superior to the packed bed adsorption system. The present inventors have designed a method for forming a rotating adsorption system that can effectively remove certain gases, especially carbon dioxide, from an air stream.

[0025] Figure 1 and Figure 2 A preferred embodiment of the rotating adsorption system 10 of the present invention is described. The system includes a rotating disk-shaped porous rotor 11 containing or coated with a renewable adsorbent material, which sequentially passes through at least two zones, namely the first zone 1 and the second zone 2, during an operating cycle. The adsorbent rotor 11 rotates about its axis in the direction shown by arrow A through a known rotor mechanism (not shown). These two zones can be identified as the treatment zone 1 and the regeneration zone 2, and process air flows through the treatment zone 1, and heated regeneration air flows through the regeneration zone 2. The present invention is not limited to two zones, and more than two zones can be provided. As a non-limiting example, by adding a purge zone, three zones can be applied, and as Figure 4 and Figure 5 shown, by adding two recycle zones and / or a purge zone, four zones can be applied.

[0026] Referring to Figure 1 and Figure 2In the first embodiment shown, a process fluid stream 12 (such as air) carrying an adsorbate (such as carbon dioxide (CO2)) flows through an adsorbent rotor 11 in a first zone 1, where the adsorbate is adsorbed (i.e., loaded) onto the adsorbent rotor 11. The concentration of the adsorbate in the process fluid stream leaving the adsorbent body is reduced compared to the process fluid stream entering the adsorbent body. A fan, blower, or other fluid moving device 13 can be applied to drive the process fluid stream through a piping system (not shown). In this example, the adsorbate is CO2 and the system 10 functions as a CO2 scrubber.

[0027] A regeneration fluid stream 14 flows through the adsorbent rotor 11 in a second zone 2, preferably in a direction opposite to the flow direction of the process fluid stream 12. The adsorbate (in this case CO2) collected from the process fluid stream in the adsorbent body 11 is released into the regeneration fluid stream. A heater 15 can be provided to supply heat to the regeneration fluid stream 14 before it flows through the adsorbent body 11. Similar to the process fluid stream, a fan, blower, or other fluid moving device 16 can be applied to drive the flow of the regeneration fluid.

[0028] Most of the energy required for the adsorption process is used to heat the regeneration air stream. In the first embodiment, since the treatment zone 1 is adjacent to the regeneration zone 2, most of the heat in the regeneration zone will enter the process air stream. To minimize this effect, referring to Figure 4 and Figure 5 In the second embodiment shown, the system includes a rotating disk-shaped porous rotor 11T, in which a renewable adsorbent material sequentially flows through four zones, namely a first zone 1, a second zone 2, a third zone 3, and a fourth zone 4. With a slight adjustment to the description of the first embodiment, where the first and second zones have been re-numbered and can be identified as a treatment zone 1 and a regeneration zone 3. The second zone 2 and the fourth zone 4 are located between the treatment zone 1 and the regeneration zone 3, i.e., at the leading and trailing edges of each treatment zone 1 and regeneration zone 3. A purge fluid stream 17 flows through the adsorbent rotor 11' in a fourth cooling purge zone 4 after the third regeneration zone 3, and then is led back as a purge fluid circuit through a second warm purge zone 2. The purge fluid circuit recovers waste heat from the hottest part of the rotor 11T and uses it for auxiliary regeneration, and can also reduce the discharge temperature of the process air, thereby reducing the energy cost of post-cooling. Similar to the process stream and the regeneration fluid stream, a fan, blower, or other fluid moving device 18 can be applied to drive the purge fluid through a piping system (not shown). As previously mentioned, the present invention is not limited to the above two-zone and four-zone rotors, and can also include rotors with different numbers of zones.

[0029] As described above, adsorbent rotors for removing moisture and certain volatile organic compounds (VOCs) are known. In order to effectively remove or scavenge CO2 from process stream 12, the adsorbent rotor 11 must be provided with an adsorbent material capable of adsorbing CO2. Organic amines are known to adsorb CO2 and include, but are not limited to, polyethyleneimine (PEI), aziridine, ethanolamine, diethanolamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, or mixtures thereof. The present inventors have found that branched polyethyleneimine (BPEI) is particularly effective in CO2 scavenging and is also effective in a rotary scavenging system.

[0030] While the present disclosure contemplates the preparation of a dedicated hydrophobic CO2 scavenger rotor from basic components, the present disclosure also includes methods for converting an existing moisture-absorbing rotary wheel into a hydrophobic CO2 scavenger rotor, thereby enabling continuous scavenging while accommodating flow rates suitable for applications such as indoor ventilation or continuous adsorption and desorption of atmospheric CO2. The present inventors have further discovered how to incorporate organic amines, particularly BPEI, into known adsorbent rotors to obtain a CO2 scavenging adsorbent rotor with unexpected properties. The resulting rotor CO2 adsorbent will effect air exchange, thereby reducing the formation of water pockets, reducing the pressure drop therebetween, and minimizing energy losses during the adsorption / absorption process. To date, no rotor has the function of continuously adsorbing CO2 in a habitable environment, where the rotor is manufactured using a wet impregnation method after corrugating a sheet and forming it into a rotor shape.

[0031] Rotors currently designed to adsorb moisture and / or VOCs require multiple processes to provide the rotor with the desired performance. The material of the sheet forming the adsorption matrix is impregnated with several substances to achieve the required mechanical strength, especially in the wet condition. Rotors currently designed to adsorb moisture and / or VOCs can have their moisture-absorbing coatings concentrated by repeated immersion in an aluminate solution in a first treatment step. Additionally, at some stage during the immersion process, crushed or pulverized solid adsorption medium is introduced into the aluminate solution. After the rotor has been treated with aluminate, it is immersed in water glass and then exposed to carbon dioxide. This results in an additional layer of chemically precipitated silica (or silica) coating while increasing the porosity. All of these inherent prior art characteristics of the rotor are critical for the CO2 adsorption of the BPEI and PEG wet impregnation treatments described below.

[0032] The preparation steps of the aforementioned rotor designed to adsorb moisture and / or VOCs may include, as a first step, preparing a dedicated hydrophobic CO2 scavenger rotor from basic components. The following steps are to functionalize or transform an existing unused or recycled rotor to capture CO2 in the presence of water at ambient temperature. That is, the following steps are subsequent steps of the preparation process of preparing a dedicated hydrophobic CO2 scavenger rotor from basic components, or complete steps in the transformation preparation process. The following steps are described according to Figure 3 the flowchart of, and applying a liquid impregnation technique to treat the adsorbent matrix to capture CO2 in the presence of water at ambient temperature and be regenerable at temperatures below 50 °C. This technique applies a solvent containing an organic amine (such as branched polyethyleneimine (BPEI)) for wet impregnation of the high-surface-area rotor. Although BPEI is preferred, the present invention is not limited to BPEI, and other amines can also be applied. What is important is that the amine material can be impregnated / functionalized on the microporous / nanoporous structure of the rotor matrix. The amine is deposited into the matrix, increasing the CO2 affinity sites between the adsorbent and CO2, which correspondingly improves the CO2 adsorption selectivity and capacity. For example, many CO2-trapping amino groups are carried on the branches of BPEI. Since BPEI is a low-level branched amine and has a lower heat of adsorption (exothermic process), it is more preferred compared to primary amines (with lower adsorption energy). The amines mentioned will be mixed with a water solvent and a water-soluble polymer (such as polypropylene glycol (PEG)) on the support material. PEG on the amine sites will increase the CO2 adsorption rate, increase the formation of weakly adsorbed CO2, and can reduce the requirement for high-temperature peaks during the desorption process. Then, the excess solvent is removed by evaporating the dilute solution. Wet impregnation allows for a high amine capacity. The rotor formed of mesoporous silica will be amine-functionalized, that is, the amine groups will be covalently linked to the surface of the rotor silica.

[0033] Refer to Figure 3, which describes a preferred embodiment of the method for preparing the rotor of the present invention. In step S10, a rotor substrate is provided. This step requires providing an existing rotor designed to remove other gas components, whether used or unused, or preparing such a rotor from basic components. Existing rotors, especially those from Munters Corporation designed to adsorb moisture and / or VOCs, have excellent moisture absorption properties, while the manufacturing process is simple and the cost of the substrate material is low. However, when removing CO2, a hydrophobic material is preferred because, as described above, the accumulated moisture will have an adverse effect on the CO2 removal efficiency and will affect the underlying structure of the rotor substrate. Therefore, the selected underlying rotor preferably has the lowest moisture absorption. The selected rotor preferably includes multiple layers of corrugated foils forming a plurality of continuous air flow channels, and the surface of the foils has a porous titanium dioxide silica gel moisture absorption coating. Examples of suitable rotors include HPS (High Performance Silicagel), HCR, HPX, Quantum TM and TiGel rotors produced by Munters Corporation. In step S20, the selected rotor substrate is pretreated. This may require preparing the rotor surface for wet impregnation by drying at 20 mTorr and 100 °C for 12 - 16 hours, but these conditions are not restrictive.

[0034] The preferred preparation method utilizes the inherently porous moisture absorption structure of the selected rotor and, as part of the wet impregnation process in step S30, deposits a BPEI solvent solution into the porous structure. In this process, the organic amine is mixed with water and PEG and deposited into the grooves formed by the rotor foils. The rotor foils are treated with an aqueous solution, and the weight ratio of BPEI to the water and PEG mixture in the aqueous solution ranges from 1:7 to 1:4, but this range is not restrictive. Preferably, treating with the solution includes immersing the entire rotor in a water bath of the BPEI / PEG aqueous solution or applying the solution to the rotor in a sufficient amount to achieve treatment, such as pouring the solution onto the rotor. When implemented in a bath, the bath should be at room temperature or lower, and the treatment time is relatively short, such as 10 - 30 minutes. In this way, at least part of the channels of the rotor are filled with the solution, thereby impregnating the surface of the foils and forming a surface deposition of BPEI / PEG on the existing coating.

[0035] In step S40, excess solution is removed from the rotor substrate. If a solution bath is used, the rotor substrate is removed from the bath or the bath is emptied. If the solution is poured onto the rotor substrate, pouring is stopped. After removing the rotor from the immersion bath, emptying the bath or stopping the solution supply, substantially all of the solution will leave the channels, except for the solution film or skin that remains on the rotor surface. Rotating the rotor immediately after emptying the solution so that the rotor axis is in a horizontal position can make it easier to retain this film.

[0036] After removing the excess solution from the rotor, in step S50, the rotor is dried until it reaches the weight of the rotor and the BPEI / PEG layer in the dry state. This can be determined by weighing the rotor after pretreatment in step S20 and then weighing the rotor again after complete drying in step S50, and calculating the weight difference as the deposited dry weight. The amount of organic amine deposited on the rotor is preferably 10 - 40 wt%, but this is not restrictive, and the target range can be determined according to the desired characteristics of the rotor, which will depend on the intended use and environmental conditions of the rotor. If this range is not achieved ( "No" in step S60), the rotor is re - immersed in the BPEI / PEG aqueous solution, and then the process is repeated starting from step S30 until the BPEI is completely deposited and the solvent is removed. If the desired coating property range is obtained ( "Yes" in step S60), the process ends. The drying step S50 can include heat drying, air drying or vacuum treatment.

[0037] This BPEI / PEG coating is formed as described below during the above - mentioned process. By generating heat and significantly heating the rotor foil, the BPEI / PEG deposited on the surface adheres to the de - functionalized moisture - absorbing coating of the rotor mainly composed of hydrogel, converting the BPEI / PEG liquid in the rotor channels. This process induces the covalent bonding of BPEI / PEG to the hydrogel layer through amine bonds and completes the dual - polymer functionalization of silica, but depending on the substrate material and the chemicals used, other processes or reactions may also occur. This subsequent reaction step (drying of the rotor: heat drying, air drying or vacuum treatment) preferably lasts longer than the impregnation step, preferably as long as the liquid retention time in the channels. When the reaction stops, the rotor will maintain its dry - state weight and have the dual - polymer deposited. During the reaction stage, in a low - CO2 environment, the coating can be further strengthened by aging the rotor foil over time.

[0038] The resulting rotor substrate with a functionalized BPEI layer allows for the regeneration of large - area pores and can be used at any time for continuous dry scrubbing. This product can be used to remove CO2 from non - industrial, residential, biological and atmospheric emissions. For wet impregnation, a rotor with low hygroscopicity is preferred. This will promote the formation of a hydrophobic surface, thereby retaining the amine groups and incorporating them within the hydrophobic surface.

[0039] The resulting core rotor can be used as a small CO2 removal device or can be installed in a dual-stream, single heat source air handling unit for institutional, commercial, residential, retail or healthcare facilities. The core rotor can provide continuous CO2 removal technology for the living / livestock / horticultural environment while maintaining low operating costs. The CO2 adsorption treatment side can bring it into compliance with indoor air quality regulations for specific environments, particularly ASHRAE Standard 62.1. The regeneration side can improve horticultural productivity.

[0040] Although the invention has been described in certain specific exemplary embodiments, many additional modifications and changes will be apparent to those skilled in the art upon the inspiration of the present disclosure. Therefore, it should be understood that the invention can be practiced in ways other than as specifically described. Accordingly, the exemplary embodiments of the invention should be considered in all respects to be illustrative rather than restrictive, and the scope of the invention should be determined by all the claims supported by this application and its equivalents, rather than by the above description.

Claims

1. A method for forming a gas adsorption medium, the method comprising: providing a media substrate with a defunctionalized moisture-absorbing layer; coating at least a portion of the media substrate with a solution of an amine and a solvent; and removing excess solution from the media substrate by evaporation to leave an amine coating on the substrate.

2. The method of claim 1, wherein the amine comprises branched polyethyleneimine (BPEI).

3. The method of claim 1, wherein the solvent comprises water and polypropylene glycol (PEG).

4. The method of claim 1, wherein the media substrate is in the form of a rotor.

5. The method of claim 1, wherein the step of removing excess solution comprises separating the media substrate from the solution and drying the wet media substrate.

6. The method of claim 1, wherein the step of coating the media substrate with the solution comprises immersing the media substrate in the solution.

7. The method of claim 1, wherein a titanium dioxide silica coating is provided for the substrate prior to the coating step.

8. The method of claim 7, further comprising drying the media substrate prior to the coating step.

9. A gas adsorption medium formed by the method of claim 1.

10. A method for converting a medium designed to adsorb a first gas into a medium designed to adsorb a second gas, wherein the second gas is different from the first gas, the method comprising: providing a media substrate having a substrate capable of adsorbing the first gas; coating at least a portion of the media substrate with a solution of an amine and a solvent, wherein the amine is capable of adsorbing the second gas; and removing excess solution from the media substrate by evaporation to leave an amine coating on the substrate.

11. The method of claim 10, wherein the amine comprises branched polyethyleneimine (BPEI).

12. The method of claim 10, wherein the solvent comprises water and polypropylene glycol (PEG).

13. The method of claim 10, wherein the media substrate is in the form of a rotor.

14. The method of claim 10, wherein the step of removing excess solution comprises separating the media substrate from the solution and drying the wet media substrate.

15. The method of claim 10, wherein the step of coating the media substrate with the solution comprises immersing the media substrate in the solution.

16. The method of claim 10, wherein the substrate capable of adsorbing the first gas comprises a titanium dioxide silica coating.

17. The method of claim 16, further comprising drying the media substrate prior to the coating step.

18. A gas adsorption medium formed by the method of claim 10.

19. A gas adsorption medium, comprising: a media substrate initially provided with a defunctionalized moisture-absorbing layer; and a coating of an amine and a solvent provided on at least a portion of the defunctionalized moisture-absorbing layer.

20. The gas adsorption medium of claim 19, wherein the amine comprises branched polyethyleneimine (BPEI).

21. The gas adsorption medium of claim 19, wherein the solvent comprises water and polypropylene glycol (PEG).

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