Recyclable rotor and method for manufacturing the same

Abstract

A method of forming a media for gas adsorption includes providing a defunctionalized hygroscopic layer on a media substrate, covering 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 a coating of the amine on the substrate.

Description

[Technical Field]

[0001] The present invention relates to sorbent technology for scrubbing gases, such as carbon dioxide (CO2), from air streams. The present invention particularly relates to amine-coated media for gas adsorption, such as high surface area rotors, methods for their manufacture, and their use. Particularly suitable applications for media for gas adsorption include, for example, continuous low CO2 parts per million (ppm) air supply to habitable environments and continuous desorbed CO2 ppm air supply to enclosed horticultural environments. [Background technology]

[0002] Solid and liquid sorbents have been used to scrub, or remove, CO2 from gases emitted by combustion processes and the ambient air, as well as from the air in enclosed spaces such as homes and agricultural enclosures. See, for example, U.S. Patent No. 6,277,994. In recent years, as more air purification technologies have become available on the market, the cost of conditioning outdoor air has led to increased emphasis on improving indoor air quality. Many procedures are performance-based, using mass balance equations to calculate the outdoor air intake rate required for a specific zone based on the pollutants of concern. These procedures take into account the effectiveness of air purification devices in calculating the required ventilation rate, often with the goal of using less outdoor air to reduce peak heating and cooling capacity and overall energy consumption while maintaining high indoor air quality. While some air purification technologies purify certain pollutants more effectively than others, most are ineffective against CO2, which is constantly generated by building occupants. CO2 concentrations are typically controlled by diluting indoor air with low-CO2 outdoor air.

[0003] There has been growing concern about the effects of high CO2 concentrations on people's cognitive function. ASHRAE Standards 62.1 and 62.2 (incorporated herein by reference) set minimum ventilation requirements for buildings to ensure optimal indoor air quality and minimize adverse health effects on occupants. Appendix D of Standard 62.1 states that indoor CO2 concentrations should not exceed outdoor CO2 concentrations by 700 ppm to satisfy the majority of occupants (approximately 80%). Sorbents for CO2 removal can be formed into various shapes, including freestanding particles in fixed beds and special-purpose single-monomer shapes. Some CO2 adsorbents contain at least one organic amine, at least one high-surface-area particle, and water, which are combined and dried to form a particle surface coating or the required shape. See, for example, U.S. Patent Nos. 5,929,949 and 5,929,949.

[0004] Current methodologies utilize packed beds of solid-supported amine sorbents to scrub CO2 and other gases from indoor air. The sorbent includes at least one type of support particle and at least one type of organic amine, which aggregate to form larger pellets, clusters, or shaped articles used as fixed beds 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 have a composition of carbon, silica alumina, or a combination thereof. Typically, the support particles are fumed, pyrolyzed, or precipitated. Solid sorbents for scrubbing CO2 further include a chemical activator, such as polyethylene glycol (PEG).

[0005] One particular class of solid sorbents for scrubbing CO2 is solid-supported amines (compositions made of organic amine materials and high surface area granules). However, these solid sorbents have the following problems when used to scrub CO2 in the atmospheric environment:

[0006] A. Current temperature swing adsorption / sorption technologies involve heating the sorption media to above 60°C to induce the desorption swing, resulting in high energy losses.

[0007] B. The moisture present in the air stream requires a moisture-tolerant adsorbent. Packed beds can form moisture-filled volumes that can reduce their ability to adsorb CO2.

[0008] C. Solid sorption beds do not allow for a continuous sorption process because the sorption bed must undergo intermediate regeneration cycles (temperature or pressure swings).

[0009] D. Due to the movement of particles in the sorption bed, air flow causes friction between particles, which reduces the sorption efficiency of the granules and causes the carryover phenomenon of dusty granules.

[0010] E. Solid sorption bed systems require the use of high-pressure air handling equipment that is prone to air leaks due to the high pressure drop across the bed.

[0011] F. Granular sorbents are often manufactured using either expensive solvents or water-soluble alcohols such as ethanol or methanol. These solvents make the manufacturing process for solid sorbents either too expensive for large-scale commercial development or too dangerous due to the flammability of some solvents.

[0012] G. Typically, solid sorbents comprise very small functionalized particles that are either carried away by the moving gas or are difficult to handle due to their restricted size and shape. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] International Publication No. 2021 / 150722 [Patent Document 2] European Patent No. 2054151B1 [Patent Document 3] U.S. Patent No. 9,919,287 Summary of the Invention [Problem to be solved by the invention]

[0014] Currently available CO2 habitable atmosphere sorption technologies (mainly packed beds requiring temperature swing adsorption / desorption) are energy intensive. Improved technologies for CO2 capture are needed to lower energy costs.

[0015] Sorbent rotors are known to adsorb or scrub other components in airstreams, such as moisture, volatile organic compounds (VOCs), and CO2. Many of these rotors have a limited useful life and are often disposed of in landfills at the end of their useful life. Suitable repurposing of used sorbent rotors would be economically and ecologically beneficial. [Means for solving the problem]

[0016] In one embodiment, the present invention relates to a method of forming a media for gas adsorption, the method comprising the steps of providing a media substrate with a defunctionalized hygroscopic layer, covering 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 a coating of the amine on the substrate.

[0017] In another aspect, the invention relates to a method for converting a media designed for the adsorption of a first gas into a media designed for the adsorption of a second gas different from the first gas, the method comprising the steps of providing a media substrate having a material capable of adsorbing the first gas, covering 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 a coating of the amine on the substrate.

[0018] In yet another aspect, the present invention relates to a media for gas adsorption comprising a media substrate initially provided with a defunctionalized hygroscopic layer, and a coating of an amine and a solvent provided on at least a portion of the defunctionalized hygroscopic layer.

[0019] These and other aspects, objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments, which is to be read in connection with the accompanying drawings. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a schematic flow chart illustrating a preferred embodiment of a rotating sorption system according to the present invention. [Figure 2] Schematic diagram of the zones of the sorbent rotor in a preferred embodiment of the rotary sorption system according to the present invention. [Figure 3] 1 is a flow diagram illustrating a process for manufacturing a sorbent rotor according to the present invention. [Figure 4] 1 is a schematic flow chart illustrating another preferred embodiment of a rotating sorption system according to the present invention. [Figure 5] Schematic diagram of the zones of the sorbent rotor in another preferred embodiment of the rotary sorption system according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] As previously mentioned, currently available CO2 habitable atmosphere sorption technologies (primarily packed beds requiring temperature swing adsorption / sorption) are energy intensive; therefore, improved CO2 capture technologies are needed to achieve low energy losses and overcome other known drawbacks of packed bed systems. Sorbent rotors are known for adsorbing or scrubbing other components in airstreams, such as moisture and volatile organic compounds (VOCs). For example, note the Rotor System (RS) and Integrated Zeol System (IZS) manufactured by Munters Corporation. By comparison, adsorbent beds containing monoliths ranging in size from 0.1 mm to 10 mm have a smaller impregnated surface area than titanium silica gel rotors based on the cross-sectional area through which air passes (the porous hygroscopic coating of the exemplary rotor is approximately 10 to 20 μm on both sides of the foil). The exemplary rotors also have lower friction losses; that is, the packed bed particles are more susceptible to granular agglomeration friction under airflow, which degrades their sorption capacity over time. The exemplary rotors take less time to regenerate during temperature swings; i.e., packed beds have intermediate temperature swing requirements for regeneration purposes compared to continuous regeneration processes. Furthermore, packed beds are sensitive to alternating vapor pressures. Large particles in compact sorption beds are susceptible to moisture accumulation and a reduction in available functionalized pore surface area. On the other hand, rotors with hydrophobic surface treatments may better manage this phenomenon. Hydrophobic rotors are prone to clogging of fine pores and capillaries, where moisture tends to condense, reducing sorption capacity. In short, rotating sorption systems may be preferable to packed bed sorption systems. The present inventors have devised a method for forming a rotating sorption system that is effective for scrubbing specific gases, particularly carbon dioxide, from air streams.

[0022] 1 and 2 illustrate a preferred embodiment of a rotating sorption system 10 according to the present invention. The system comprises a rotating, disk-shaped, porous rotor 11 containing or coated with a regenerable sorbent that passes successively through at least two zones during an operating cycle: a first zone 1 and a second zone 2. The sorbent rotor 11 is rotated about its axis in the direction indicated by arrow A by a known rotor mechanism (not shown). The two zones can be identified as a treatment zone 1, through which treatment air flows, and a regeneration zone 2, through which heated regeneration air flows. The present invention is not limited to two zones; three or more zones can be provided. As non-limiting examples, three zones can be used by adding a purge zone, and four zones can be used by adding two recycle and / or purge zones, as shown in FIGS. 4 and 5.

[0023] Referring to the first embodiment shown in Figures 1 and 2, a process fluid stream 12 (e.g., air) carrying a sorbate (e.g., carbon dioxide (CO2)) is passed through a sorbent rotor 11 in a first zone 1, where the sorbate is sorbed (i.e., entrained) onto the sorbent rotor 11. The process fluid stream exiting the sorbent mass has a reduced sorbate concentration compared to the process fluid stream entering the sorbent mass. A fan, blower, or other fluid mover 13 can be used to force the process fluid stream through piping (not shown). In this example, the sorbate is CO2, and the system 10 functions as a CO2 scrubber.

[0024] A regeneration fluid stream 14 is passed through a sorbent rotor 11 in the second zone 2, preferably in a direction opposite to the flow of the treatment fluid stream 12. Sorbent (in this example, CO2) from the treatment fluid stream collected in the sorbent rotor 11 is released into the regeneration fluid stream. A heater 15 can be provided to heat the regeneration fluid stream 14 before passing through the sorbent mass 11. As with the treatment fluid stream, a fan, blower, or other fluid moving device 16 can be used to propel the regeneration fluid stream.

[0025] Most of the energy required for the sorption process is used to heat the reactivation air stream, and in the first embodiment, much of the heat from the reactivation zone flows into the treatment air stream because treatment zone 1 is directly adjacent to regeneration zone 2. To minimize this effect, referring to the second embodiment shown in Figures 4 and 5, the system includes a rotating, disk-shaped porous rotor 11' in which the regenerable sorbent passes sequentially through four zones: first zone 1, second zone 2, third zone 3, and fourth zone 4. With minor modifications to the description of the first embodiment, the first and second zones have been renumbered and can be identified as treatment zone 1 and regeneration zone 3. The second and fourth zones 2 and 4 are sandwiched between treatment zone 1 and regeneration zone 3, i.e., located at the leading and trailing edges of treatment zone 1 and regeneration zone 3, respectively. A purge fluid stream 17 is passed through the sorbent rotor 11' in the fourth cooling purge zone 4 after the third regeneration zone 3 and then returned through the second warming purge zone 2 as a purge fluid loop. The purge fluid loop recovers waste heat from the hottest section of the rotor 11' and uses it to aid in reactivation and to lower the discharge temperature of the process air, reducing post-cooling energy costs. Like the process and regeneration fluid streams, a fan, blower, or other fluid mover 18 can be used to force the purge fluid stream through piping (not shown). As previously mentioned, the present invention is not limited to the two- and four-zone rotors described above, but can be directed to rotors having various numbers of zones.

[0026] As previously mentioned, sorbent rotors are known for removing moisture and certain volatile organic compounds (VOCs). To effectively remove or scrub CO from the process stream 12, the sorbent rotor 11 must be provided with a sorbent material capable of adsorbing CO. Organic amines are known to adsorb CO, including, but not limited to, polyethyleneimine (PEI), aziridine, ethanolamine, diethanolamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, or mixtures thereof. The present inventors have discovered that branched polyethyleneimine (BPEI) can be particularly effective for CO scrubbing and would be effective in rotary scrubbing systems.

[0027] While this disclosure discusses fabricating a dedicated hydrophobic CO2 scrubber rotor from basic components, it also includes a method for converting existing hygroscopic rotor wheels into hydrophobic CO2 scrubber rotors to enable continuous scrubbing while adjusting flow rates for applications such as room ventilation or continuous atmospheric CO2 adsorption and desorption. The present inventors have further discovered how to incorporate organic amines, specifically BPEI, into known sorbent rotors to yield CO2 scrubbing sorbent rotors with unexpected attributes. The resulting rotor CO2 sorbent minimizes the formation of moisture pockets, has a low pressure drop across it, and undergoes air exchange with minimal energy loss during the adsorption / sorption process. To date, no known rotors capable of continuous CO2 sorption for habitable environments are available that are fabricated using wet impregnation after the sheet is corrugated and formed into the rotor shape.

[0028] Current rotors designed for moisture and / or VOC sorption undergo numerous operations necessary to impart the rotor with desired properties. To achieve the required mechanical strength, especially when wet, several substances are impregnated into the material forming the sheet that forms the sorption substrate. Current rotors designed for moisture and / or VOC sorption can have a concentrated hygroscopic coating by repeatedly immersing them in an aluminate solution in a first treatment step. Additionally, at some stage in the immersion process, a crushed or finely divided solid sorption medium is introduced into the aluminate solution. Once treated with aluminate, the rotor is immersed in water glass and then exposed to carbon dioxide. This imparts an additional coating of chemically precipitated silicon dioxide (or silica), thereby increasing porosity. All of these inherent current state-of-the-art rotor properties are important for the BPEI and PEG wet impregnation process for CO2 sorption, described below.

[0029] The previous manufacturing process for rotors designed for moisture and / or VOC sorption can be included as the first step in the manufacturing process for dedicated hydrophobic CO2 scrubber rotors from basic components. The following steps functionalize or convert existing rotors, either unused or to be reused, to enable CO2 capture in the presence of water at ambient temperature. That is, the following steps can be either subsequent steps in the manufacturing process for dedicated hydrophobic CO2 scrubber rotors from basic components or the completion of the conversion manufacturing process. The following steps are described with reference to the flow diagram in Figure 3 and involve treating a sorbent substrate using a liquid impregnation technique that can capture CO2 in the presence of water at ambient temperature and can be regenerated at temperatures below 50°C. This technique utilizes a sorbent material with an organic amine, such as branched polyethyleneimine (BPEI), to wet-impregnate a high-surface-area rotor. While BPEI is preferred, the invention is not limited to BPEI; other amines can be used. What is important is the ability to impregnate / functionalize the amine material on the micro / nanoporous structure of the rotor substrate. Deposition of amines on the substrate increases the CO2 affinity sites between the adsorbent and CO2, which in turn increases CO2 adsorption selectivity and capacity. BPEI, for example, has branched chains with many CO2-trapping amino groups. BPEI is preferred because it has fewer branched amines and a lower heat of adsorption (an exothermic process) compared to primary amines (which require less energy to adsorb). The proposed amines are mixed with a solvent of water and a water-soluble polymer, such as polypropylene glycol (PEG), on the support material. The PEG at the amine sites increases the proportion of adsorbed CO2, increasing the formation of weakly adsorbed CO2 and reducing the requirement for a high-temperature peak during the desorption process. Evaporation of the dilute solution then removes excess solvent. This wet impregnation allows for high amine capacity. Rotor-shaped geometries with mesoporous silica are then amine-functionalized; that is, amine groups are covalently bonded to the silica surface of the rotor.

[0030] Referring to FIG. 3, a preferred embodiment of the rotor manufacturing method of the present invention is described. In step S10, a rotor substrate is provided. This step involves providing a used or unused existing rotor designed to scrub other gas components, or fabricating such a rotor from basic components. Existing rotors, particularly rotors from Munters Corporation designed for moisture and / or VOC sorption, have excellent hygroscopic properties while being manufactured using a simple manufacturing process from low-cost substrate materials. However, since accumulated moisture, as previously described, can adversely affect CO2 scrubbing efficiency and affect the basic structure of the rotor substrate, hydrophobic materials are preferred when scrubbing CO2. Therefore, the selected basic rotor is preferably one with minimal hygroscopicity. The selected rotor preferably includes a layer of foil corrugated to form multiple continuous passages for the gas flow, with the surface of the foil bearing a porous hygroscopic coating of titanium silica gel. Examples of suitable rotors include HPS (High Performance Silicagel), HCR, HPX, Quantum™, and TiGel rotors manufactured by Munters Corporation. In step S20, the selected rotor substrate is pretreated. This involves preparing the rotor surface for wet impregnation by drying it at 20 millitorr (about 2.6 Pa) at 100°C for 12-16 hours, although these conditions are not limiting.

[0031] A preferred manufacturing process utilizes the inherent porous, hygroscopic structure of the selected rotor and deposits a BPEI-solvent solution into the porous structure as part of a wet impregnation process in step S30. In this process, an organic amine is mixed with water and PEG and deposited into the grooves formed in the rotor foil. The rotor foil is treated with an aqueous solution, e.g., a BPEI-to-water-to-PEG ratio of between 1:7 and 1:4 by mass, although this range is not limiting. Treatment with this solution preferably involves either immersing the completed rotor in a bath of the aqueous BPEI / PEG solution or applying the solution to the rotor in a volume large enough to effect the treatment, e.g., by pouring the solution onto the rotor. If performed in a bath, the bath is suitably at room temperature or slightly below, and the treatment time is relatively short, e.g., 10 to 30 minutes. In this way, the surface of the foil is impregnated, and the rotor passages are at least partially filled with the solution, so that the existing coating forms a surface deposit of BPEI / PEG.

[0032] 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 solution is drained from the bath. If solution is poured onto the rotor substrate, the pouring process is then stopped. After the rotor is lifted from the impregnation bath, the solution is drained from the bath, or the solution supply is stopped, substantially all of the solution exits the passages except for a film or skin of solution remaining on the rotor surface. This film is more easily maintained by rotating the rotor immediately after the solution is drained so that the rotor axis is in a horizontal position.

[0033] After excess solution is removed from the rotor, the rotor is subjected to a drying process in step S50 until a dry rotor mass and BPEI / PEG layer are obtained. This can be determined by weighing the rotor after pretreatment in step S20 and then after complete drying in step S50, and calculating the mass difference as the deposited dry mass. The amount of organic amine deposited on the rotor is preferably within the range of 10% to 40% by weight, but this is not limiting. The target range can be determined based on the desired characteristics of the rotor, which will depend on the intended use and environmental conditions. If this range is not achieved (No in step S60), the rotor is immersed again in the BPEI / PEG aqueous solution, and the process is repeated from step S30 until BPEI is completely deposited and the solvent is removed. Once the desired range of coating characteristics is achieved (Yes in step S60), the process ends. The drying step S50 can include heat drying, air drying, or vacuum treatment.

[0034] This BPEI / PEG coating is produced by the following process: The BPEI / PEG liquid in the rotor passages is converted by applying heat and exposing the rotor foil to a substantial temperature increase, so that the BPEI / PEG deposited on the surface adheres to the rotor's defunctionalized, hygroscopic coating, which is primarily composed of hydrogel. This process induces covalent bonding of the BPEI / PEG to the hydrogel layer via amine bonds, resulting in the formation of a dual-polymer-functionalized silica; however, other processes or reactions may occur depending on the underlying substrate material and the chemicals used. This subsequent reaction step (wheel drying; heat drying, air drying, or vacuum treatment) preferably continues longer than the immersion step, preferably as long as the liquid remains in the passages. After the reaction is stopped, the rotor retains its dry mass and deposited dual-polymer. The coating may be further strengthened by allowing the rotor foil time to age during the reaction step in a low CO2 environment.

[0035] The resulting rotor substrate with a functionalized BPEI layer can regenerate a large surface area with pore channels, easily enabling continuous dry scrubbing. This product would be useful for scrubbing CO2 from non-industrial, habitable, biological, and airborne emissions. For wet impregnation, a rotor with low hygroscopicity is preferred. This improves the formation of a hydrophobic surface, allowing for the retention and inclusion of amine groups.

[0036] The resulting Core Rotor can be used as a compact CO2 scrubbing unit or housed within a dual-airflow, single-heat-source air handling unit for corporate, commercial, residential, retail, or healthcare facilities. The Core Rotor enables continuous CO2 scrubbing technology for residential, livestock, and horticultural environments while keeping operating costs low. The CO2 adsorption treatment side enables compliance with indoor air quality regulations, particularly the ASHRAE 62.1 standard, for dedicated environments. The regeneration side enables increased horticultural productivity.

[0037] While the present invention has been described in terms of specific exemplary embodiments, many additional modifications and variations will be apparent to those skilled in the art in light of this disclosure. It is therefore to be understood that the invention can be practiced otherwise than as specifically described. The present exemplary embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being determined not by the foregoing description but by any claims supportable by this application and their equivalents. [Explanation of symbols]

[0038] 1 Zone 1 2 Zone 2 3 Third Zone 4. Zone 4 10 Rotating Sorption System 11, 11' porous rotor, sorbent mass 12 Treatment flow 13, 16, 18 Fluid transfer devices 14 Regeneration fluid flow 15 Heater 17 Purge Fluid Flow

Claims

1. 1. A method of forming a medium for gas adsorption, comprising: providing a defunctionalized moisture-absorbing layer on a media substrate; 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 a coating of the amine on the substrate; A method comprising:

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 polyethylene 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 the excess solution comprises separating the media substrate and the solution and drying the wet media substrate.

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

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

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

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

10. 1. A method for converting a medium designed for the adsorption of a first gas into a medium designed for the adsorption of a second gas different from the first gas, comprising: providing a media substrate having a material capable of adsorbing the first gas; covering 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 a coating of the amine on the substrate; A method comprising:

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

12. 11. The method of claim 10, wherein the solvent comprises water and polyethylene 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 removing the excess solution comprises separating the media substrate and the solution and drying the wet media substrate.

15. The method of claim 10 , wherein covering the media substrate with a 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 coating of titanium silica.

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

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

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

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

21. 20. The gas adsorption medium of claim 19, wherein the solvent comprises polyethylene glycol (PEG).

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