Adsorbent for gas flow separation

Abstract

The present invention relates to a zeolite adsorbent for separating oxygen from a gas stream. The adsorbent is a mixture of lithium-exchanged zeolite 13X, lithium-exchanged low-silica X zeolite, and halloysite clay. A method for producing the zeolite adsorbent is also disclosed. Furthermore, a method for producing oxygen from a gas stream using this zeolite adsorbent is provided.

Description

Background Art

[0001] [Technical Field to which the Invention Belongs]

[0002] The present invention relates to a zeolite adsorbent that is particularly useful for the separation of gas streams. This adsorbent has surprising physical properties such as high tapped bulk density and crush strength, and preferably exhibits a high volume, fast kinetics, excellent porosity, and a significantly improved pore structure compared to the prior art.

[0003] One embodiment is suitable for the separation and concentration of oxygen by adsorption from a mixed gas stream, for example, a gas stream mainly composed of nitrogen and oxygen.

[0004] The present invention also includes gas separation methods that utilize this adsorbent. These gas separation methods include, but are not limited to, pressure swing adsorption (PSA), vacuum pressure swing adsorption (VPSA), and temperature swing adsorption (TSA). These methods are particularly useful for the separation and recovery of gases such as oxygen, nitrogen, carbon dioxide, hydrogen, and other gaseous substances. Among these gases, oxygen is important for medical applications. Oxygen production by the PSA / VPSA method involves selectively adsorbing nitrogen gas in the air onto the adsorbent, extracting the remaining concentrated oxygen, and recovering it as the final product.

[0005] The present invention is also a process for the production and manufacture of a zeolite adsorbent useful for gas separation, particularly the separation of oxygen from a gas stream. Background of the Invention

[0006] The adsorbent of the present invention is particularly useful for the adsorption and separation of gases. In one embodiment, the adsorbent composition is used in a process for separating O2 from a mixture containing N2, O2, and other gases by contacting the mixture with the adsorbent composition. The adsorbent composition selectively adsorbs N2, and components with not-so-strong adsorption forces are recovered as products.

[0007] Of particular interest is the use of these adsorbents in non-cryogenic gas separation processes for O2 production. For example, the separation of nitrogen from a gas mixture forms the basis of several industrial adsorption processes, including the production of oxygen from air. When producing oxygen cyclically from air, the air passes through an adsorbent bed that selectively adsorbs nitrogen molecules, leaving oxygen and argon (a component with weak adsorption force). The adsorbed nitrogen is then desorbed through a purge process, and the adsorbent is usually regenerated through a change in pressure, including vacuum, and / or a change in temperature, and the cycle is repeated. Such processes include pressure swing adsorption (PSA), temperature swing adsorption (TSA), vacuum swing adsorption (VSA), and vacuum pressure swing adsorption (VPSA) processes. Such processes are commonly used not only in commercial air separation operations but also in other industrial and medical processes.

[0008] The adsorbents used in these processes are important elements in achieving an efficient, effective, and competitive process. The performance of the adsorbent depends on several factors, such as the adsorption volume of N2, the selectivity between gases that affects production yield, and the adsorption rate that can optimize the adsorption cycle time to improve the productivity of the process. The bulk density / crush strength / wear rate of agglomerated particles is also very important, especially in achieving a sufficient adsorption life in adsorption processes and systems. Improvement of the pore structure, represented by the median pore diameter, the proportion of small pores, and the connectivity characteristics of the pores, is also important in the performance of the adsorbent. A particularly important parameter in evaluating the pore structure is hysteresis, which is a useful factor in evaluating the connectivity of the pores. Another important parameter useful for evaluating the adsorption rate of the adsorbent is the pore diffusivity of nitrogen (D p ) which is a measure of the adsorption rate. These factors generally depend on the pore structure of the particles and the overall pore structure, and the definitions of each factor are well-known to those skilled in the art.

[0009] Conventional agglomerated adsorbents used in such adsorption processes are composed of zeolite powder (microcrystalline particles) containing ion-exchange zeolite powder, depending on the process and binder. The binder is generally intended to ensure the agglomeration of agglomerated particles in the form of beads, pellets, and extrudates. The binder generally has no adsorptivity, and its only function is to give the agglomerated particles sufficient mechanical strength to withstand the severity of placement in a packed-bed adsorption system and the vibrations and stresses received during the adsorption process such as pressurization and depressurization. The selected binder and its concentration also affect the final pore structure of the agglomerated particles and the properties of the adsorbent. It is known that the concentration of the binder needs to be as low as possible in order to reduce the mass transfer resistance that may be adversely affected by the presence of excessive binder in the pores. Lowering the binder concentration can also increase the overall adsorption volume of the adsorbent. Specific binders, temporary binders, and other processing aids may also fill or partially block the pores of the particles, while other binders may adversely affect the final pore structure depending on the carrier solvent of the binder.

[0010] One common method utilized to obtain agglomerated adsorbent particles with a low binder concentration, improved pore structure, and further low mass transfer resistance is to use the caustic digestion method to prepare what is known as a "binderless adsorbent". These binderless adsorbents represent one approach to obtaining a low binder content, preferably less than about 5% by weight, but at the expense of additional manufacturing steps and higher costs. The conventional approach to caustic digestion is to use a clay binder that can be converted to an active adsorbent zeolite material by the caustic digestion treatment. Some conventional disclosures have demonstrated various levels of improvement in adsorption rate characteristics from the use of these binderless adsorbents, which have the claimed novel pore structure.

[0011] Therefore, it is desirable to provide a binderless adsorbent, a method for manufacturing an adsorbent, and a method for separating oxygen from a mixed air environment by processes such as pressure swing adsorption, temperature swing adsorption, vacuum swing adsorption, and vacuum pressure swing adsorption. The desirable features and characteristics of the present invention will become apparent from the following detailed description of the invention, the appended claims, and the accompanying examples and background of the invention.

Summary of the Invention

[0012] The present invention includes an adsorbent for separating a gas stream, and this adsorbent includes a mixture of lithium-exchanged zeolite 13X ("Li13X"), lithium-exchanged low-silica X zeolite ("LiLSX"), and residual halloysite clay. The amount of Li13X is from about 5% to about 20% of the adsorbent by weight. The amount of LiLSX is from about 80% to about 90% of the adsorbent by weight. The amount of halloysite clay is preferably from about 0.1% to about 5.0% of the adsorbent by weight. Preferably, the adsorbent comprises at least 98%, particularly 99%, of the mixture of the aforementioned Li13X, LiLSX, and residual halloysite clay. For the purposes of the present disclosure, all ratios and percentages are by weight.

[0013] This binderless adsorbent preferably exhibits a high crushing strength while preferably showing a high gas absorption volume, fast kinetics measured in kinetic tests, and good pore structure characteristics. The binderless adsorbent also shows a high bulk density of about 640 g / L or more, measured in accordance with DIN / ISO 787.

[0014] The adsorbent also preferably exhibits a high hysteresis coefficient representing a pore connectivity of at least about 0.6, as measured by standard mercury intrusion (porosimetry) data, as described, for example, in U.S. Patent No. 9,486,732 B2. The hysteresis coefficient "R" is defined from standard mercury intrusion (porosimetry) data as shown in Equation (1). Here, I(60,000 psia) is the cumulative intrusion volume at 60,000 psia from the intrusion curve (pressure increasing curve), I(50 psia) is the cumulative intrusion volume at 50 psia from the intrusion curve (pressure increasing curve), and E(50 psia) is the cumulative intrusion volume at 50 psia from the extrusion curve (pressure decreasing curve).

[0015]

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[0016]

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[0017] The adsorbent also preferably has an improved pore structure with a median pore diameter of at least about 5 microns and a proportion of pores of 0.1 micron or less of less than about 6.0%.

[0018] The present invention further provides a method for manufacturing an adsorbent for separating a gas stream using the following steps: providing a low-silica X zeolite, mixing the low-silica X zeolite with halloysite clay to form a mixture, The halloysite clay contains from about 5% to about 20% of the mixture by weight, a step of forming a molded article from the mixture, a step of firing the molded article, a step of caustically digesting the molded article to convert at least about 70% of the halloysite clay by weight to zeolite 13X, and a step of producing an adsorbent by exchanging the zeolite component in the molded article with lithium, the adsorbent has a bulk density of at least about 640 g / L as measured in accordance with DIN / ISO 787, for example, as described in U.S. Patent No. 9,486,732 B2, the hysteresis coefficient measured by mercury intrusion porosimetry is preferably 0.6 or more, and a high pore diffusivity (Dp) for nitrogen is preferably 5.0×10 -6 m 2 / s or more, a manufacturing method.

[0019] The present invention also includes a method (process) of using an adsorbent for separating gaseous substances, particularly oxygen, from a gas stream. A brief summary of embodiments of the present invention

[0020] In particular, adsorbents useful for separation by pressure swing adsorption (PSA), vacuum pressure swing adsorption (VPSA), or temperature swing adsorption (TSA) of a gas stream, particularly for the separation of O2 from air, are disclosed.

[0021] One adsorbent particularly useful in this process consists of X or Y zeolite crystals, particularly X zeolite. Preferred are one or more zeolite X incorporating cations such as Li, Ca, K, Na, Ag, and mixtures thereof, particularly zeolite X incorporating Li, where one embodiment is zeolite X containing Li cations. The SiO2 / Al2O3 ratio is preferably less than 15, in one embodiment less than 5, and in another embodiment 2.5 or less. Particularly alternative embodiments have a SiO2 / Al2O3 ratio of from about 1.9 to about 2.3. (For the purposes of this disclosure, zeolite X with a silica to alumina ratio of 2.3 or less is referred to as "low silica X zeolite LSX zeolite" or "LSX". Zeolite X with a ratio of silica to alumina greater than 2.3 and up to 2.6 is referred to as "13X zeolite", "zeolite 13X" or "13X". For the purposes of this disclosure, lithium-exchanged zeolite 13X is referred to as "lithium-exchanged zeolite 13X", "Li13X", or "Li13X zeolite", and lithium-exchanged low silica zeolite X is referred to as "lithium-exchanged low silica X zeolite", "LiLSX", "LiX" or "zeolite LiX".)

[0022] A limitation in the use of zeolite crystals is that their particle size is very fine. Aggregates of these naturally formed crystals break easily. Since the pressure drop through these zeolite crystal beds is very high, they generally cannot be used alone in fixed beds in many applications.

[0023]

[0024] Various clay materials such as kaolin or attapulgite clay have generally been used as binder materials for these zeolite crystals. Also, binders derived from silicone have been utilized, for example, as disclosed in U.S. Patent No. 9,486,732 B2 and U.S. Patent No. 9,050,582 B2.

[0025] Despite the usefulness of such binder materials, it has been found that the binders used in these agglomerated materials reduce the overall effectiveness of the zeolite product for the adsorption process.

[0026] To overcome this problem, so-called "binderless adsorbent" materials have been produced in which the clay binder material is at least substantially converted to zeolite.

[0027] To produce this binderless material, it is necessary to convert at least substantially all of the binder into a useful zeolite mixed material. Since kaolin clay can be converted to a low-silica LiX zeolite material using a caustic digestion process, prior art binderless LiX adsorbents have generally utilized kaolin clay as a binder for forming the binderless adsorbent.

[0028] Surprisingly, it has been found that when halloysite clay is utilized as a binder material for low-silica LiX zeolite, improved properties can be produced in the adsorbent. In a preferred embodiment, the halloysite clay has a tubular shape having a length of about 0.5 - 2.0 microns and a diameter of about 50 - 100 nm.

[0029] In one embodiment, a method for producing an agglomerated binderless adsorbent composition is as follows. a. Prepare a mixture containing one or more active zeolite materials and a halloysite clay binder, b. Mix the zeolite material and the halloysite clay material with water to form agglomerated adsorbent particles, c. Dry the agglomerated adsorbent particles, d. Bake the dried agglomerated adsorbent particles to form baked adsorbent particles, e. Treat the baked adsorbent particles caustically to convert at least a portion of the halloysite clay binder agent to 13X zeolite, f. Treat the fired adsorbent particles with a metal salt solution to ion-exchange at least a portion of the cations present in the ion-exchange aggregated adsorbent particles, and g. By heating the ion-exchanged aggregated particles, the ion-exchanged particles are dried and activated to form an aggregated adsorbent composition.

[0030] In one process for the manufacture of a binderless adsorbent, LSX zeolite is provided, which comprises from about 80 to about 95 weight percent of the total material mixture. The LSX zeolite is mixed with halloysite clay in an amount of from about 5 to about 20 weight percent of the total mixture, and the mixed components are kneaded together to form a homogeneous mixed product. Water is preferably utilized during the formation of the mixture. The amount of water added and other characteristics of the mixing step depend on the amounts of materials utilized therein.

[0031] The mixed product is kneaded, granulated, and formed into a product of a preferred shape. This can be formed into beads, extrudates, and / or spray-dried microspheres, and in one embodiment, can be formed into beads.

[0032] The resulting product is then dried at a temperature of from about 100 °C to 400 °C. After drying, it is fired at a temperature of from about 500 to about 700 °C to produce a formed LSX / halloysite clay blend.

[0033] Next, the mixed product of LSX / halloysite clay is treated with a caustic solution to convert an important portion of the halloysite clay into zeolite 13X. In one embodiment, from about 60 to about 95% or more of the halloysite clay on a weight basis is converted to zeolite 13X. The process of caustically digesting the halloysite clay material is carried out at a temperature of about 80° C. using a caustic solution. In one embodiment, the caustic solution mainly contains sodium hydroxide and potassium hydroxide. In a further embodiment, the caustic solution is substantially sodium hydroxide. Utilizing a large amount of sodium hydroxide for the caustic treatment results in substantially more zeolite 13X being produced from the halloysite clay. Other combinations of hydroxides and other materials can be utilized to modify the final composition of the adsorbent.

[0034] The exact manner of contacting the mixed product with the caustic solution is not limited. In one method, the mixed product is filled into a fixed bed column and the caustic solution is circulated throughout.

[0035] Following this conversion process, the product is lithium exchanged at at least about 90%, in one embodiment at least about 95%, and in another embodiment at least about 98% to produce the final adsorbent. The final adsorbent contains from about 80% to about 90% LiLSX on a weight basis and from about 5% to about 20% Li13X on a weight basis, with the remaining amount being about 0.1% to about 5% by weight of residual halloysite clay. Also, the final composition of the adsorbent after conversion includes oxides of any of the elements Al, Si, Ba, Li, Na, K, Mg, Ca, Fe, Ti, Y, Zr, either alone or in combination, along with other residual components.

[0036] In the prior art, it is preferable that the preferred adsorbent, when converted to zeolite, uses kaolin clay having the same composition as the primary zeolite used in the desired adsorption process as a binder. For example, caustic digestion of kaolin clay generally produces low-silica LiX zeolite. The applicant has discovered that it is possible to produce a surprisingly useful adsorbent containing both LiLSX zeolite and Li13X zeolite and a certain amount of residual halloysite clay.

[0037] The adsorbent produced by this process has improved physical properties compared to prior art adsorbents.

[0038] In one embodiment, the adsorbent exhibits a tapped bulk density of at least about 640 g / L and a crush strength of at least about 8 N / mm, as measured by DIN / ISO 787.

[0039] Despite these physical properties, the adsorbent surprisingly also exhibits a rather favorable pore structure, as measured by median pore diameter, low proportion of pores below 0.1 micron, and high hysteresis coefficient representing pore connectivity. The median pore diameter in one embodiment is preferably 5 microns or more, the proportion of pores below 0.1 micron is preferably less than about 10%, and in one embodiment, less than about 6%. Also, the adsorbent surprisingly exhibits a hysteresis coefficient of preferably about 0.6 or more when measured by standard mercury intrusion porosimetry data, as described, for example, in U.S. Patent No. 9,486,732B2.

[0040] Typically, materials with high density and high crush strength have low porosity and tend to have a slow nitrogen uptake rate. Surprisingly, the disclosed adsorbent composition has high strength and high crush strength similar to low porosity and a surprisingly fast nitrogen uptake rate that may be attributed to the characteristics of the pore structure.

[0041] As a result of these characteristics of the disclosed adsorbent composition, the pore diffusion rate (D) for nitrogenp ) The high adsorption rate measured by is preferably shown to exceed 5.0×10 -6 m 2 / s. The higher the value of the pore diffusivity (D p ) for nitrogen, the faster the diffusion of the substance within the particles. A high pore diffusivity (D p ) for nitrogen is particularly surprising considering the physical properties of the adsorbent particles. The disclosure of this pore diffusivity (D p ) is determined based on the nitrogen pore diffusivity measured at 1.5 bar and 300 K, as described, for example, in U.S. Patent No. 6,500,234 B2, U.S. Patent No. 6,790,260 B2, and U.S. Patent No. 9,486,732 B2. Embodiments of the Invention

[0042] <Example 1> Low silica zeolite X (silica / alumina ratio of 2.0) is mixed with halloysite clay at a ratio of about 85 / 15 by weight of zeolite to clay. Next, this mixture is formed into spheres and fired. Next, these fired particles are placed in a hot (~90 °C) sodium hydroxide solution for several hours to convert the clay to 13X zeolite. Next, the particles are washed with water to remove excess caustic alkali, and then the particles are subjected to lithium ion exchange until at least about 95%. The amount of lithium-exchanged low silica zeolite X is 85%, the amount of lithium-exchanged zeolite 13X is 12%, and the amount of residual halloysite clay is 3%.

[0043] <Comparative Sample 1 (C-l)> As described in columns 3 to 8 of U.S. Patent No. 7,300,899, it is a shaped adsorbent containing lithium-exchanged low silica X zeolite with an attapulgite binder.

[0044] <Comparative Sample 2 (C-2)> As described in columns 8 and 9 of U.S. Patent No. 6,425,940 B1, it is an adsorbent without a binder.

[0045] As described in Example 2 of U.S. Patent No. 9,486,732 B2, it is a molded adsorbent containing a lithium-exchanged low-silica X zeolite containing a silica-based binder.

[0046] <Comparative Sample 4 (C-4)> It is a binderless molded adsorbent obtained from Tosoh containing LiLSX, which is sold under the trade name NSA-700.

[0047] <Comparative Sample 5 (C-5)> It is a binderless adsorbent obtained from Hanchang containing LiLSX.

[0048] In Table 1 below, the properties of Example 1 of the present invention are compared with the adsorbents of Comparative Samples C-1, C-2, C-3, C-4, and C-5.

[0049]

Table 1

[0050] From the data in Table 1, it is clear that the adsorbent composition of the present invention containing a combination of LiX and Li13X with residual halloysite clay has the best combination of both physical properties and pore structure, including median pore diameter, pore fraction less than 0.1 μm, improved hysteresis coefficient, and high pore diffusivity for nitrogen. Despite these improved properties, the composition of the present invention also had a higher tapped bulk density and greater crush strength than the comparative examples.

[0051] Conventional compositions having high density and crush strength have conventionally meant compositions with reduced mass transfer or pore diffusivity (D p ). Surprisingly, however, the compositions of the present invention exhibited a higher pore diffusivity (D p ) for nitrogen than the comparative compositions. The compositions of the present invention also showed that the intra-particle diffusion rate was surprisingly fast despite the compositions having high density and crush strength. The nitrogen absorption rate of the compositions of the present invention was also surprisingly fast compared to other compositions.

[0052] The binderless adsorbent of the present invention is particularly useful for gas stream separation, such as selectively adsorbing nitrogen in air to recover enriched oxygen gas. When oxygen in air is concentrated using the PSA, VPSA or TSA method, the operation includes a series of steps including an adsorption step of contacting a packed bed of the binderless zeolite material with air for selective adsorption of nitrogen. Then, the enriched oxygen is collected from the outlet of the packed bed. Further treatment of the gas material is as conventional.

[0053] The adsorbent of the present invention is particularly effective for air separation by the PSA / VPSA / TSA method. When air is separated by the PSA / VPSA / TSA method, the amount and yield of the enriched oxygen gas are high, and the adsorbent exhibits good physical properties during a long life.

[0054] The above detailed description is provided for understanding and is not intended to limit the scope of the claims. It will be apparent to those skilled in the art that the present invention can be modified without departing from the scope of the claims upon consideration of the disclosure.

Claims

1. An adsorbent for separating gas streams, comprising a mixture of lithium-exchanged zeolite 13X (Li13X), lithium-exchanged low-silica X zeolite (LiLSX), and halloysite clay, wherein Li13X comprises from about 5 to about 20% of the adsorbent by weight, LiLSX comprises from 80 to about 90% of the adsorbent by weight, halloysite clay comprises from about 0.1% to 5.0% of the adsorbent by weight, and the adsorbent has a bulk density of at least about 640 g / L as measured according to DIN / ISO 787.

2. The adsorbent has a pore diffusion rate (D ｐ ) for nitrogen as described in U.S. Patent No. 6,500,234 B2 and U.S. Patent No. 6,790,260 B2, which is greater than 5.0×10 －６ m ２ / s. The adsorbent according to claim 1.

3. The adsorbent according to claim 1 or 2, wherein the median pore diameter of the adsorbent is 5 microns or more, and the proportion of pores less than 0.1 micron is less than 6.0 percent.

4. The adsorbent according to any one of claims 1 to 3, wherein the adsorbent exhibits a crushing strength greater than 8 N / mm.

5. The adsorbent according to any one of claims 1 to 4, wherein the adsorbent exhibits a hysteresis coefficient of at least about 0.6 as measured by the mercury intrusion method described in U.S. Patent No. 9,486,732 B2.

6. A method for manufacturing an adsorbent for separating gas streams, comprising: providing a low-silica X zeolite; mixing the zeolite with halloysite clay to form a mixture, wherein the halloysite clay comprises from about 5% to about 20% of the mixture by weight; forming a shaped article from the mixture; firing the shaped article; caustically treating the fired shaped article to convert at least a portion of the halloysite clay to 13X zeolite; and lithium-exchanging the LSX and 13X zeolites of the shaped article to produce an adsorbent, wherein the adsorbent comprises from about 0.1 to about 5% halloysite clay by weight, and wherein the adsorbent has a bulk density of at least about 640 g / L as measured in accordance with DIN / ISO 787.

7. The method according to claim 6, wherein the halloysite clay has a tubular shape with a length of about 0.5 to 2.0 microns and a diameter of about 50 to 100 nm.

8. The method according to claim 6 or 7, wherein a hydroxide substantially comprising sodium hydroxide is used to caustically treat the shaped article.

9. The adsorbent has a pore diffusion rate (D ｐ ) for nitrogen of 5.0×10 ー６ m ２ / s or more, and is the production method according to any one of claims 6 to 8, characterized in that.

10. The adsorbent has a median pore diameter of 5 microns or more and a proportion of pores less than 0.1 micron is less than 6.0 percent. The production method according to any one of claims 6 to 9.

11. The adsorbent exhibits a crushing strength greater than 8 N / mm. The production method according to any one of claims 6 to 10.

12. The adsorbent has a hysteresis coefficient of at least about 0.6 as measured by mercury intrusion porosimetry as described in U.S. Patent No. 9,486,732 B2. The production method according to any one of claims 6 to 11.

13. A method for producing enriched oxygen from a gas stream using the adsorbent of claim 1.

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