Li l s x molecular sieve adsorbent and method of making same
By introducing a non-framework cross-linked structure during the preparation of LiLSX molecular sieves, the problems of insufficient mechanical and adsorption properties were solved, and LiLSX molecular sieve adsorbents that meet industrial standards were prepared and applied to pressure swing adsorption air separation.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-10-20
- Publication Date
- 2026-05-15
AI Technical Summary
Existing LiLSX molecular sieve adsorbents have insufficient mechanical properties and poor adsorption performance during lithium-ion exchange, making it difficult to meet industrial standards simultaneously.
LiLSX molecular sieve adsorbents were prepared by mixing kaolin and NaLSX molecular sieve powders, molding them, drying and calcining them, and then contacting them with alkali and silicon or aluminum sources in the presence of water to form non-framework crosslinks and combine them with lithium ion exchange.
The mechanical strength and adsorption performance of LiLSX molecular sieve adsorbents have been significantly improved, meeting the requirements of industrial applications, especially demonstrating excellent nitrogen adsorption capacity and selectivity in pressure swing adsorption air separation.
Smart Images
Figure CN117917377B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of adsorbents, specifically to a LiLSX molecular sieve adsorbent and its preparation method. Background Technology
[0002] Pressure swing adsorption (PSA) air separation technology has been widely used in many fields such as home healthcare, metallurgy, steelmaking, carbon black production, fertilizer gasification, chemical oxidation, glass processing, pulp bleaching, aquaculture, wastewater treatment, and military applications, and has enormous market potential.
[0003] Currently, the most effective commercial air separation oxygen generation adsorbent is lithium-modified LSX molecular sieve (LiLSX molecular sieve). This molecular sieve has a large nitrogen adsorption capacity and a high nitrogen-oxygen separation coefficient, making it a core component of the pressure swing adsorption oxygen generation process.
[0004] However, currently synthesized LSX molecular sieves have relatively small particle sizes (1-10 μm) and cannot be directly applied industrially. Therefore, binders are usually used to shape the molecular sieves into certain shapes (e.g., spherical or strip-shaped). Commonly used binders are mainly kaolin and attapulgite. However, since the adsorption performance of binders is lower than that of molecular sieves and they can clog the pores of molecular sieves, they can severely affect the adsorption activity of the product.
[0005] To address this issue, most current methods employ alkali treatment to process the binder-formed molecular sieves. This cleans the structure of the active molecular sieve and promotes the formation of ordered channels in the binder, thereby improving the adsorption performance of the formed molecular sieve. However, alkali treatment reduces the binder content in the product and weakens the interaction between molecular sieve particles, often resulting in insufficient strength. This is especially true when further modified with lithium-ion exchange, as the modification itself significantly reduces the mechanical properties of the molecular sieve, leading to significant breakage or peeling. Consequently, the mechanical properties of the final LiLSX molecular sieve adsorbent fail to meet industry standards (HG / T 5337-2018).
[0006] Extensive research has been conducted in this field. For example, CN103170317A provides a method for improving the strength of molecular sieves. In this method, zeolite and binder are mixed in a disc kneader, then water is added and kneading continues for 30-60 minutes. Finally, the mixture is pulverized and molded. This method fully utilizes and leverages the hydration effect of the binder, and the clay tubular structure is effectively opened, increasing particle bonding. However, it cannot compensate for the loss of activity caused by the introduction of inactive binder and the blockage of pores.
[0007] Currently, there is no suitable method that can simultaneously solve the problems of insufficient mechanical properties and poor adsorption performance of LSX molecular sieves for lithium exchange. Therefore, there is an urgent need to provide a method for preparing LiLSX molecular sieve adsorbents that have both high adsorption performance and high mechanical strength. Summary of the Invention
[0008] The purpose of this invention is to overcome the problem that existing LiLSX molecular sieve adsorbents cannot simultaneously achieve both adsorption performance and mechanical strength, and to provide a LiLSX molecular sieve adsorbent, its preparation method, and its application. This method is simple and easy to implement, and enables the prepared LiLSX molecular sieve adsorbent to possess both excellent adsorption performance and mechanical strength.
[0009] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a LiLSX molecular sieve adsorbent, the method comprising the following steps:
[0010] 1) The mixture of kaolin and NaLSX molecular sieve powder was subjected to molding, first drying and first calcination in sequence to obtain the first calcined product;
[0011] 2) The first calcined product is pre-wetted to obtain a pre-wetted product;
[0012] 3) In the presence of water, the pre-wetted product is contacted with an alkali and a silicon source, or the pre-wetted product is contacted with an alkali and an aluminum source to obtain a contacted product;
[0013] 4) The contact product is subjected to a second drying and a second calcination to obtain a second calcined product;
[0014] 5) The second calcined product is subjected to lithium-ion exchange with a lithium-ion-containing exchange solution.
[0015] The amount of NaLSX molecular sieve powder used is 85% by weight or more, based on the total weight of the mixture.
[0016] The second aspect of the present invention provides a LiLSX molecular sieve adsorbent prepared by the method described in the first aspect of the present invention.
[0017] The third aspect of the present invention provides an application of the LiLSX molecular sieve adsorbent described in the second aspect of the present invention in pressure swing adsorption air separation.
[0018] By using the above technical solution, non-framework crosslinks can be formed between molecular sieve crystal clusters by contacting the pre-wetted product with alkali and silicon or aluminum sources. This crosslinked structure can exist stably in a lithium-ion exchange environment, thereby significantly improving the mechanical properties of the prepared adsorbent.
[0019] Furthermore, in this invention, a high proportion of NaLSX molecular sieve powder (more than 85% by weight) can be mixed with kaolin, which can not only significantly improve the adsorption performance of the obtained adsorbent, but also ensure the mechanical strength of the obtained adsorbent through the method described in this invention.
[0020] On the other hand, the calcination conditions described in this invention can promote the conversion of kaolin to metakaolin, and the concentration of the alkali solution can further convert metakaolin into X and A type molecular sieves with adsorption activity, inhibiting the formation of inactive sodalite impurities, thereby ensuring that the obtained molecular sieve adsorbent has excellent nitrogen adsorption capacity and significantly reducing the decrease in adsorption performance caused by the introduction of kaolin. Attached Figure Description
[0021] Figure 1 This is a scanning electron microscope image of the LiLSX molecular sieve adsorbent prepared in Example 1;
[0022] Figure 2 This is a scanning electron microscope image of the LiLSX molecular sieve adsorbent prepared in Comparative Example 1. Detailed Implementation
[0023] The endpoints and any values of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of the various ranges, the endpoint values of the various ranges and individual point values, and individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.
[0024] The first aspect of this invention provides a method for preparing a LiLSX molecular sieve adsorbent, the method comprising the following steps:
[0025] 1) The mixture of kaolin and NaLSX molecular sieve powder was subjected to molding, first drying and first calcination in sequence to obtain the first calcined product;
[0026] 2) The first calcined product is pre-wetted to obtain a pre-wetted product;
[0027] 3) In the presence of water, the pre-wetted product is contacted with an alkali and a silicon source, or the pre-wetted product is contacted with an alkali and an aluminum source to obtain a contacted product;
[0028] 4) The contact product is subjected to a second drying and a second calcination to obtain a second calcined product;
[0029] 5) The second calcined product is subjected to lithium-ion exchange with a lithium-ion-containing exchange solution.
[0030] The amount of NaLSX molecular sieve powder used is 85% by weight or more, based on the total weight of the mixture.
[0031] The preparation method of the LiLSX molecular sieve adsorbent described in the first aspect of the present invention will be described in detail below.
[0032] First, in step 1), kaolin and NaLSX molecular sieve powder are mixed to obtain a mixture.
[0033] In this invention, there is no particular limitation on the NaLSX molecular sieve powder. It can be any NaLSX molecular sieve powder that is conventional in the art and can be obtained commercially or prepared using conventional methods in the art.
[0034] Furthermore, the particle size of the NaLSX molecular sieve powder can be 1-10 μm.
[0035] The silicon-to-aluminum ratio of the NaLSX molecular sieve powder can be, for example, 2-2.1:1.
[0036] In this invention, unless otherwise specified, the silicon-to-aluminum ratio refers to the molar ratio of SiO2 to Al2O3.
[0037] In addition, the content of molecular sieve in the NaLSX molecular sieve powder can be, for example, 70-100% by weight, preferably 80-90% by weight.
[0038] The Na2O content in the NaLSX molecular sieve powder can be 14-22% by weight, preferably 16-20% by weight.
[0039] Furthermore, the kaolin used in this invention is not particularly limited and can be any type of kaolin commonly used in the art, and can be obtained through commercial purchase or other conventional means.
[0040] In this invention, preferably, the kaolin has a silicon-aluminum oxide content of 90% or more.
[0041] Furthermore, preferably, the silica-alumina ratio of the kaolin is 1.7-2.2:1, more preferably 1.9-2:1.
[0042] According to the present invention, since the method of the present invention can introduce non-framework crosslinking between molecular sieve clusters, thereby significantly improving the mechanical strength of LiLSX molecular sieve adsorbent, in the mixture obtained by mixing kaolin and NaLSX molecular sieve powder, the amount of NaLSX molecular sieve powder can be as high as 85% by weight or more based on the total weight of the mixture, thereby significantly improving the adsorption performance of the prepared LiLSX molecular sieve adsorbent.
[0043] Furthermore, preferably, the amount of NaLSX molecular sieve powder used is 90% by weight or more, more preferably 90-95% by weight, based on the total weight of the mixture. By increasing the amount of NaLSX molecular sieve powder to the above level, the adsorption performance of the adsorbent can be significantly improved, and even if the amount of NaLSX molecular sieve powder is increased to the above level, the mechanical properties of the prepared adsorbent can still be guaranteed by using the method of the present invention.
[0044] In addition, to make the mixing more uniform, the mixing in step 1) can be carried out under mechanical stirring, which is a conventional method in the art and will not be described in detail here.
[0045] Next, the mixture is molded to obtain a molded product.
[0046] In this invention, kaolin and NaLSX molecular sieve powders are prepared into the desired shape through molding process to meet the needs of industrial use.
[0047] Here, the molding process can be carried out using various conventional methods for molding molecular sieve powders in the art. For example, spherical molding can be used to obtain spherical molded products, or strip molding can be used to obtain strip molded products. The molding process is a conventional operation in the art and will not be described in detail here.
[0048] In addition, there are no particular limitations on the size of the molded article obtained by the molding process, as long as it meets the usage requirements.
[0049] When the molded product is spherical, the particle size of the spherical molded product can be, for example, 0.4-2.5 mm; when the molded product is strip-shaped, the length of the strip-shaped molded product can be, for example, 0.3-1.5 cm, and the width can be, for example, 1-5 mm.
[0050] Then, the molded article obtained by the molding process is subjected to a first drying and a first calcination to obtain a first calcined product.
[0051] In this invention, since the strength of the resulting molded article is insufficient, it is necessary to increase its strength and achieve shaping through a first drying and a first firing.
[0052] In addition, during the first calcination process, the kaolin can be activated into metakaolin, thereby improving the adsorption performance of the obtained LiLSX molecular sieve adsorbent in conjunction with subsequent treatments.
[0053] In this invention, the conditions for the first drying are not particularly limited. For example, the conditions for the first drying may include: a temperature of 40-120°C and a time of 10-20 hours; preferably, the conditions for the first drying include: a temperature of 80-100°C and a time of 10-12 hours.
[0054] Furthermore, in this invention, the first calcination can be carried out using conventional methods and conditions in the art. However, the inventors of this invention have discovered through extensive research that the strength and adsorption performance of the prepared LiLSX molecular sieve adsorbent can be significantly improved by performing the first calcination treatment under the following conditions.
[0055] That is, the conditions for the first calcination treatment include: heating to 80-150°C at a rate of 2-8°C / min and holding at that temperature for 20-60 min; then heating to 200-300°C at a rate of 2-8°C / min and holding at that temperature for 30-90 min; then heating to 400-550°C at a rate of 2-8°C / min and holding at that temperature for 20-60 min; and then heating to 600-850°C at a rate of 2-8°C / min and holding at that temperature for 100-150 min.
[0056] Next, in step 2), the first roasted product is pre-humidified to obtain a pre-humidified product.
[0057] In this invention, because the product after the first roasting treatment has an extremely low moisture content, it has a very strong absorption capacity when directly contacted with alkalis or the like, resulting in a large amount of exothermic reaction. This not only affects product quality but can also cause problems such as cracking of the formed first roasted product. Therefore, in this invention, the first roasted product undergoes a pre-wetting treatment after the first roasting.
[0058] In this invention, there are no particular limitations on the method of pre-humidification. For example, it can be pre-humidified by exposing it to air containing water vapor, or it can be placed directly in water.
[0059] In this invention, in order to improve the pre-wetting treatment rate, it is preferable to pre-wet the first roasted product by contacting it with water.
[0060] Therefore, according to the present invention, the pre-wetting treatment method may include: contacting the first roasted product with water for more than 5 minutes, wherein the amount of water used is more than 2g relative to 1g of the first roasted product; preferably, the pre-wetting treatment method includes: contacting the first roasted product with water for 10-30 minutes, wherein the amount of water used is 2-5g relative to 1g of the first roasted product.
[0061] Next, in step 3), the pre-wetted product is contacted with an alkali and a silicon source in the presence of water, or the pre-wetted product is contacted with an alkali and an aluminum source to obtain a contacted product.
[0062] Through in-depth research, the inventors of this invention have discovered that by contacting the pre-wetted product with an alkali and a silicon source in the presence of water, or by contacting the pre-wetted product with an alkali and an aluminum source in the presence of water, amorphous impurities in the molecular sieve can be effectively removed, and metakaolin can be transformed into a material with ordered channels. This unblocks the channels of the molecular sieve. Furthermore, by introducing a silicon or aluminum source in this step, non-skeleton crosslinks can be formed between the molecular sieve crystal clusters. These crosslinks can remain stable for a long time, thereby significantly improving the strength of the LiLSX molecular sieve adsorbent.
[0063] In this invention, the non-skeleton crosslinking refers to crosslinking that occurs at the edge of the molecular sieve cluster and is not embedded inside the molecular sieve cluster. The non-skeleton crosslinking allows the crosslinked molecular sieve cluster to retain its original skeleton structure.
[0064] Furthermore, according to the present invention, preferably, the pre-wetted product is contacted with a mixture containing an alkali and a silicon source, or the pre-wetted product is contacted with a mixture containing an alkali and an aluminum source to obtain a contacted product.
[0065] According to a preferred embodiment of the present invention, in step 3), the alkali and silicon source are first mixed with water to obtain a mixture containing alkali and silicon source, and then the pre-wetted product is contacted with the mixture; or, the alkali and aluminum source are mixed with water to obtain a mixture containing alkali and aluminum source, and then the pre-wetted product is contacted with the mixture to obtain a contact product.
[0066] Furthermore, the inventors of this invention have discovered that in step 3), when using an aluminum source, the mechanical strength of the obtained LiLSX molecular sieve adsorbent is more stable and its performance is better compared to the method using a silicon source. The inventors speculate that this may be because lithium ions have a certain corrosiveness to the non-framework structure formed using a silicon source, while the non-framework cross-linked structure formed using an aluminum source is very stable in the presence of lithium ions.
[0067] Therefore, in this invention, preferably, in step 3), the pre-wetted product is contacted with an alkali and an aluminum source in the presence of water to obtain a contact product.
[0068] Furthermore, in this invention, the alkali is not particularly limited and can be sodium hydroxide, potassium hydroxide, etc., with sodium hydroxide being more preferred.
[0069] Furthermore, the concentration of the alkali in the mixture can vary within a wide range. For example, the concentration of the alkali in the mixture can be 20-165 g / L, preferably 30-100 g / L, and more preferably 40-55 g / L. The inventors of this invention have discovered that by limiting the concentration of the alkali in the mixture within the above-mentioned preferred range, the adsorption performance and mechanical properties of the prepared LiLSX molecular sieve adsorbent can be significantly improved, while suppressing the formation of inactive sodalite crystals.
[0070] Furthermore, in this invention, when the method of contacting the alkali and the silicon source is selected, the silicon source is not particularly limited and can be any silicon source commonly used in the art. For example, the silicon source can be selected from one or more of sodium silicate, silica sol, water glass, potassium silicate, silica gel and silicon dioxide, preferably sodium silicate and / or silica sol.
[0071] Furthermore, the concentration of the silicon source in the mixture can vary within a wide range. For example, the concentration of the silicon source, calculated as silicon dioxide, in the mixture can be 2-12 g / L, preferably 6-10 g / L. The inventors of this invention have discovered that by limiting the concentration of the silicon source in the mixture within the above-mentioned preferred range, the adsorption performance and mechanical properties of the prepared LiLSX molecular sieve adsorbent can be significantly improved.
[0072] Furthermore, in this invention, when the method of contacting the alkali and the aluminum source is selected, there is no particular limitation on the aluminum source. It can be any aluminum source commonly used in the art. For example, the aluminum source can be selected from one or more of sodium aluminate, aluminum nitrate, aluminum sulfate, aluminum sol and boehmite, preferably sodium aluminate and / or boehmite.
[0073] Furthermore, the concentration of the aluminum source in the mixture can vary within a wide range. For example, the concentration of the aluminum source, calculated as aluminum oxide, in the mixture can be 2-12 g / L, preferably 6-10 g / L. The inventors of this invention have discovered that by limiting the concentration of the aluminum source in the mixture within the above-mentioned preferred range, the adsorption performance and mechanical properties of the prepared LiLSX molecular sieve adsorbent can be significantly improved.
[0074] According to the present invention, the amount of the mixture can be determined according to the amount of the pre-wetted product, and there is no particular limitation. For example, the amount of the mixture can be 1-10 mL, preferably 1-4 mL, relative to 1 g of the pre-wetted product.
[0075] Furthermore, the contact conditions are not particularly limited. Preferably, the contact conditions include a temperature of 80-100℃ and a time of 1-5h, which can further improve the preparation efficiency and the performance of the prepared LiLSX molecular sieve adsorbent.
[0076] In this invention, after the contact is completed, the contact product can be further washed to remove the mixture on the product surface.
[0077] The washing can be performed using washing methods conventional in the art, without any particular limitation. For example, the washing can be performed using deionized water, and preferably, the contact product is washed until the pH of the filtrate is 8-9.
[0078] Subsequently, in step 4), the contact product is subjected to a second drying and a second calcination to further improve the strength of the prepared LiLSX molecular sieve adsorbent.
[0079] According to the present invention, there is no particular limitation on the second drying, and conventional methods in the art can be used. For example, the conditions for the second drying may include: a temperature of 70-150°C and a time of 10-20 hours; preferably, the conditions for the second drying include: a temperature of 100-120°C and a time of 10-12 hours.
[0080] Furthermore, in this invention, the second calcination can be carried out using conventional methods and conditions in the art. However, the inventors of this invention have discovered through extensive research that the strength of the prepared LiLSX molecular sieve adsorbent can be significantly improved by performing the second calcination treatment under the following conditions: the conditions for the second calcination include: heating to 80-150°C at a rate of 2-8°C / min and holding at that temperature for 20-60 min; then heating to 200-300°C at a rate of 2-8°C / min and holding at that temperature for 30-90 min; then heating to 400-550°C at a rate of 2-8°C / min and holding at that temperature for 20-60 min; and then heating to 600-850°C at a rate of 2-8°C / min and holding at that temperature for 100-150 min.
[0081] Next, step 5) is performed, which involves exchanging the second calcined product with a lithium-ion-containing exchange solution for lithium ions.
[0082] According to the present invention, the concentration of lithium ions in the lithium ion exchange solution is not particularly limited, for example, it can be 1-5 mol / L, preferably 2-3 mol / L.
[0083] Furthermore, in existing technologies, lithium-ion exchange is typically performed at a pH of around 9 to maximize the protection of LSX molecular sieves. However, the inventors of this invention have discovered that, unlike existing technologies, when preparing LiLSX molecular sieve adsorbents using the method described in this invention, by controlling the pH of the lithium-ion-containing exchange solution to 6-8, more preferably 6.5-7.5, the destruction of non-framework crosslinks between crystal clusters can be minimized, thereby enabling the preparation of LiLSX molecular sieve adsorbents with significantly superior mechanical strength.
[0084] In addition, the amount of the exchange liquid can be determined according to the amount of the second calcination product. For example, relative to 1g of the second calcination product, the amount of the lithium-ion-containing exchange liquid can be 5-30mL, preferably 10-20mL.
[0085] Furthermore, the specific method for lithium-ion exchange is not particularly limited in this invention, and various methods conventional in the art can be used. For example, in a preferred embodiment of this invention, a tank exchange method is used for lithium-ion exchange.
[0086] Furthermore, the conditions for lithium-ion exchange can be conventionally chosen in the art. For example, the conditions for lithium-ion exchange may include a temperature of 60-120°C and a time of 1-5 hours; preferably, the conditions for lithium-ion exchange include a temperature of 80-100°C and a time of 1-3 hours. By performing lithium-ion exchange under the above conditions, the degree of lithium-ion exchange can be further improved.
[0087] Furthermore, in order to improve the lithium ion exchange rate, preferably, the lithium ion exchange can be repeated multiple times, for example, 3-7 times.
[0088] When performing the repeated exchange, the molecular sieve obtained from the previous lithium-ion exchange is used for the next lithium-ion exchange. The composition of the exchange liquid and the exchange conditions can be the same as described above. This is a conventional method in the field and will not be elaborated here.
[0089] In this invention, the degree of lithium ion exchange refers to the ratio of the number of moles of lithium ions to the sum of the number of moles of lithium ions and sodium ions in the LiLSX molecular sieve after exchange, that is, the degree of lithium ion exchange = (number of moles of lithium ions) / (number of moles of lithium ions + number of moles of sodium ions).
[0090] Furthermore, in this invention, preferably, the lithium ion exchange results in an exchange rate of 95% or higher, more preferably 97.5% or higher.
[0091] According to the present invention, after the lithium-ion exchange is performed, in order to activate the obtained exchange product, the method may further include an activation step. The activation method is not particularly limited and can be carried out by conventional methods in the art. For example, the lithium-ion exchange product can be placed in a degassing station and activated at 3-7 Pa and 300-400 °C for 4-6 h to obtain LiLSX molecular sieve adsorbent.
[0092] Using the method described in this invention, through specific preparation steps and methods, non-skeleton crosslinks can be formed between molecular sieve clusters. Thus, with only a small amount of kaolin (less than 15% by weight), the adsorption performance can be maximized, and LiLSX molecular sieve adsorbents that meet mechanical properties can also be prepared.
[0093] According to a particularly preferred embodiment of the present invention, the preparation method of the LiLSX molecular sieve adsorbent includes the following steps:
[0094] 1) Kaolin and NaLSX molecular sieve powder are mixed to obtain a mixture, wherein the amount of NaLSX molecular sieve powder is 90-95% by weight, based on the total weight of the mixture.
[0095] 2) The mixture is subjected to ball rolling molding to obtain a molded product;
[0096] 3) The molded article is subjected to a first drying and a first calcination to obtain a first calcined product. The conditions for the first drying include: a temperature of 80-100℃ and a time of 10-12h; the conditions for the first calcination include: heating to 90-110℃ at a rate of 4-6℃ / min and holding the temperature for 20-40min; then heating to 240-260℃ at a rate of 4-6℃ / min and holding the temperature for 50-70min; then heating to 540-560℃ at a rate of 4-6℃ / min and holding the temperature for 20-40min; and then heating to 690-710℃ at a rate of 4-6℃ / min and holding the temperature for 110-130min.
[0097] 4) Contact the first roasted product with water for 10-30 minutes to obtain a pre-wetted product, wherein the amount of water used is 2-5g relative to 1g of the first roasted product;
[0098] 5) Sodium hydroxide and sodium aluminate are mixed with water to obtain a mixture. The pre-wetted product is then contacted with the mixture at 80-100°C for 1-5 hours to obtain a contacted product. The amount of the mixture is 1-4 mL relative to 1 g of the pre-wetted product. The concentration of sodium hydroxide in the mixture is 40-55 g / L, and the concentration of sodium aluminate is 6-10 g / L (calculated as aluminum oxide). The resulting contacted product is then washed with deionized water until the pH of the filtrate is 8-9.
[0099] 6) The washed product is subjected to a second drying and a second calcination. The conditions for the second drying include: a temperature of 100-120℃ and a time of 10-12h. The conditions for the second calcination include: heating to 90-110℃ at a rate of 4-6℃ / min and holding at that temperature for 20-40min; then heating to 240-260℃ at a rate of 4-6℃ / min and holding at that temperature for 50-70min; then heating to 540-560℃ at a rate of 4-6℃ / min and holding at that temperature for 20-40min; and then heating to 690-710℃ at a rate of 4-6℃ / min and holding at that temperature for 110-130min to obtain the second calcined product.
[0100] 7) The second calcined product is subjected to lithium-ion exchange with a lithium-ion-containing exchange solution at 80-100℃ for 1-3 hours, and the exchange is repeated 3-7 times. The lithium-ion concentration in the lithium-ion-containing exchange solution is 2-3 mol / L, the pH of the lithium-ion-containing exchange solution is 6.5-7.5, and the amount of lithium-ion-containing exchange solution used is 10-20 mL relative to 1 g of the second calcined product, to obtain the exchange product.
[0101] 8) Activate the exchange products. Specifically, activate the exchange products at 340-360℃ and 3-6Pa for 3-6 hours.
[0102] The above method can be used to prepare LiLSX molecular sieve adsorbents with excellent adsorption performance and mechanical strength.
[0103] The second aspect of the present invention provides a LiLSX molecular sieve adsorbent prepared by the method described in the first aspect of the present invention.
[0104] The crushing resistance of the LiLSX molecular sieve adsorbent described in this invention can reach more than 13 N / particle (particle size is 1.3-1.7 mm).
[0105] The third aspect of this invention provides the application of the LiLSX molecular sieve adsorbent described in the second aspect of this invention in pressure swing adsorption air separation.
[0106] The LiLSX molecular sieve adsorbent described in this invention has excellent nitrogen adsorption performance, while its oxygen adsorption capacity is extremely low. It has excellent selectivity and nitrogen-oxygen separation capability. When used for pressure swing adsorption air separation, it can effectively remove nitrogen from the air, thereby improving the purity and yield of oxygen.
[0107] The present invention will be described in detail below through embodiments.
[0108] Unless otherwise specified, the raw materials and reagents used in the following examples and comparative examples are all commercially available products or can be prepared by conventional methods.
[0109] The crushing force parameter was measured using the method specified in the industry standard (HG / T 2783-1996);
[0110] Kaolin is a commercially available product, containing 96% by weight of silicon and aluminum oxides, with a silicon-to-aluminum ratio of 2:1.
[0111] The NaLSX molecular sieve powder has an average particle size of 4.3 μm, a silica-to-alumina ratio of 2:1, and a molecular sieve content of 83% by weight.
[0112] Example 1
[0113] 1) Kaolin and NaLSX molecular sieve powder are mixed to obtain a mixture, wherein the amount of NaLSX molecular sieve powder is 95% by weight, based on the total weight of the mixture.
[0114] 2) The mixture is subjected to balling molding using a sugar coating pan, and sieving is performed to obtain spherical particles with a diameter of 1.3-1.7 mm;
[0115] 3) After drying the spherical particles at 80°C for 12 hours, a first calcination is performed. The conditions for the first calcination include: heating to 100°C at a rate of 5°C / min and holding the temperature for 30 minutes; then heating to 250°C at a rate of 5°C / min and holding the temperature for 60 minutes; then heating to 550°C at a rate of 5°C / min and holding the temperature for 30 minutes; and then heating to 700°C at a rate of 5°C / min and holding the temperature for 120 minutes to obtain the first calcined product.
[0116] 4) Contact the first roasted product with water for 10 minutes to obtain a pre-wetted product, wherein the amount of water used is 5g relative to 1g of the first roasted product;
[0117] 5) Sodium hydroxide and sodium aluminate are added to water to obtain a mixture. Then, the pre-wetted product is mixed with the mixture and placed at 98°C for 1 hour to obtain a contact product. The amount of the mixture is 2 mL relative to 1 g of the pre-wetted product. The concentration of sodium hydroxide in the mixture is 50 g / L. The concentration of sodium aluminate is 8 g / L based on aluminum oxide.
[0118] The resulting product was then washed with deionized water until the pH of the filtrate was 8.
[0119] 6) After drying the washed product at 120℃ for 12 hours, a second calcination was carried out. The conditions for the second calcination were the same as those for the first calcination, and the second calcined product was obtained.
[0120] 7) Lithium chloride monohydrate was mixed with water and stirred thoroughly to prepare an exchange solution with a lithium ion concentration of 2.5 mol / L. Then, the pH of the exchange solution was adjusted to 7 with lithium hydroxide solution (concentration of 0.1 wt%). The second calcined product was then mixed with the exchange solution. The amount of lithium ion-containing exchange solution used was 10 mL relative to 1 g of the second calcined product. The exchange was then carried out at 90 °C using a tank exchange method for 2 h. This process was repeated 5 times to obtain the exchange product.
[0121] 8) The exchange product was activated in the degassing station at 5 Pa and 350 °C for 5 h to obtain LiLSX molecular sieve adsorbent, denoted as A1.
[0122] A1 has a lithium-ion exchange rate of 99% and a crushing resistance of 19 N / particle.
[0123] The scanning electron microscope image of A1 is shown below. Figure 1 As shown.
[0124] Depend on Figure 1 It can be seen that there is a clear non-framework cross-linked structure between the molecular sieve clusters. Furthermore, XRD analysis shows that the binder between the molecular sieve clusters is effectively transformed into type X and type A molecular sieves.
[0125] Example 2
[0126] 1) Kaolin and NaLSX molecular sieve powder are mixed to obtain a mixture, wherein the amount of NaLSX molecular sieve powder is 93% by weight, based on the total weight of the mixture.
[0127] 2) The mixture is subjected to balling molding using a sugar coating pan, and sieving is performed to obtain spherical particles with a diameter of 1.3-1.7 mm;
[0128] 3) After drying the spherical particles at 90°C for 10 hours, a first calcination is performed. The conditions for the first calcination include: heating to 90°C at a rate of 6°C / min and holding the temperature for 40 minutes; then heating to 240°C at a rate of 6°C / min and holding the temperature for 70 minutes; then heating to 540°C at a rate of 6°C / min and holding the temperature for 40 minutes; and then heating to 690°C at a rate of 6°C / min and holding the temperature for 130 minutes to obtain the first calcined product.
[0129] 4) Contact the first roasted product with water for 20 minutes to obtain a pre-wetted product, wherein the amount of water used is 3g relative to 1g of the first roasted product;
[0130] 5) Sodium hydroxide and sodium aluminate are added to water to obtain a mixture. Then, the pre-wetted product is mixed with the mixture and placed at 90°C for 3 hours. The amount of the mixture is 3 mL relative to 1 g of the pre-wetted product. The concentration of sodium hydroxide in the mixture is 40 g / L. The concentration of sodium aluminate is 10 g / L based on aluminum oxide.
[0131] The resulting product was then washed with deionized water until the pH of the filtrate was 9.
[0132] 6) After drying the washed product at 110℃ for 10h, a second calcination was carried out. The conditions for the second calcination were the same as those for the first calcination, and the second calcined product was obtained.
[0133] 7) Lithium chloride monohydrate was mixed with water and stirred thoroughly to prepare an exchange solution with a lithium ion concentration of 2 mol / L. The pH of the exchange solution was then adjusted to 7.5 with lithium hydroxide. The second calcined product was then mixed with the exchange solution. The amount of lithium ion-containing exchange solution used was 15 mL relative to 1 g of the second calcined product. The exchange was then carried out at 100 °C using a tank exchange method for 1 h. This process was repeated 5 times to obtain the exchange product.
[0134] 8) The exchange product was activated in the degassing station at 5 Pa and 350 °C for 5 h to obtain LiLSX molecular sieve adsorbent, denoted as A2.
[0135] A2 has a lithium-ion exchange rate of 98% and a crushing resistance of 18 N / particle.
[0136] A2 scanning electron microscope image and Figure 1 Similarly, scanning electron microscopy (SEM) images of A2 show obvious non-framework cross-linked structures between the molecular sieve clusters. Furthermore, XRD analysis reveals that the binder between the molecular sieve clusters is effectively transformed into type X and type A molecular sieves.
[0137] Example 3
[0138] 1) Kaolin and NaLSX molecular sieve powder are mixed to obtain a mixture, wherein the amount of NaLSX molecular sieve powder is 90% by weight, based on the total weight of the mixture.
[0139] 2) The mixture is subjected to balling molding using a sugar coating pan, and sieving is performed to obtain spherical particles with a diameter of 1.3-1.7 mm;
[0140] 3) After drying the spherical particles at 90°C for 10 hours, a first calcination is performed. The conditions for the first calcination include: heating to 110°C at a rate of 4°C / min and holding the temperature for 20 minutes; then heating to 260°C at a rate of 4°C / min and holding the temperature for 50 minutes; then heating to 560°C at a rate of 4°C / min and holding the temperature for 20 minutes; and then heating to 710°C at a rate of 4°C / min and holding the temperature for 110 minutes to obtain the first calcined product.
[0141] 4) Contact the first roasted product with water for 30 minutes to obtain a pre-wetted product, wherein the amount of water used is 2g relative to 1g of the first roasted product;
[0142] 5) Sodium hydroxide and sodium aluminate are added to water to obtain a mixture. Then, the pre-wetted product is mixed with the mixture and placed at 80°C for 5 hours. The amount of the mixture is 4 mL relative to 1 g of the pre-wetted product. The concentration of sodium hydroxide in the mixture is 55 g / L. The concentration of sodium aluminate is 6 g / L based on aluminum oxide.
[0143] The product after contact was then washed with deionized water until the pH of the filtrate was 9.
[0144] 6) After drying the washed product at 110℃ for 10h, a second calcination was carried out. The conditions for the second calcination were the same as those for the first calcination, and the second calcined product was obtained.
[0145] 7) Lithium chloride monohydrate was mixed with water and stirred thoroughly to prepare an exchange solution with a lithium ion concentration of 3 mol / L. The pH of the exchange solution was then adjusted to 6.5 with lithium hydroxide. The second calcined product was then mixed with the exchange solution. The amount of lithium ion-containing exchange solution used was 10 mL relative to 1 g of the second calcined product. The exchange was then carried out at 80 °C using a tank exchange method for 3 h. This process was repeated 5 times to obtain the exchange product.
[0146] 8) The exchange product was activated in the degassing station at 5 Pa and 350 °C for 5 h to obtain LiLSX molecular sieve adsorbent, denoted as A3.
[0147] A3 has a lithium-ion exchange capacity of 97.6% and a crushing resistance of 17 N / particle.
[0148] A3 scanning electron microscope image and Figure 1 Similarly, scanning electron microscopy (SEM) images of A3 show obvious non-framework cross-linked structures between the molecular sieve clusters. Furthermore, XRD analysis reveals that the binder between the molecular sieve clusters is effectively transformed into type X and type A molecular sieves.
[0149] Example 4
[0150] The procedure is carried out according to the method of Example 1, except that...
[0151] In step 5), sodium aluminate is replaced with sodium silicate, and the concentration of sodium silicate in the mixture is 8 g / L, calculated as silicon dioxide.
[0152] The LiLSX molecular sieve adsorbent was prepared and denoted as A4.
[0153] A4 has a lithium-ion exchange rate of 99% and a crushing resistance of 15 N / particle.
[0154] A4 scanning electron microscope image and Figure 1 Similar, but the number of non-skeleton cross-linked structures is somewhat reduced in the scanning electron microscope image of A4 compared to that of A1.
[0155] Example 5
[0156] The procedure is carried out according to the method of Example 1, except that...
[0157] In step 5), the concentration of sodium hydroxide in the mixture is 110 g / L.
[0158] The LiLSX molecular sieve adsorbent was obtained and denoted as A5.
[0159] A5 has a lithium-ion exchange rate of 99% and a crushing resistance of 13 N / particle.
[0160] A5 scanning electron microscope image and Figure 1 Similarly, scanning electron microscopy (SEM) images on A5 show obvious non-framework cross-linked structures between the molecular sieve clusters. Furthermore, XRD analysis reveals that the binder between the molecular sieve clusters is effectively transformed into type X and type A molecular sieves.
[0161] Example 6
[0162] The procedure is carried out according to the method of Example 1, except that...
[0163] In step 5), the concentration of sodium aluminate in the mixture is 4 g / L, calculated as aluminum oxide.
[0164] The LiLSX molecular sieve adsorbent was obtained and denoted as A6.
[0165] The lithium-ion exchange capacity of A6 is 98.6%, and its crushing resistance is 14 N / particle.
[0166] Scanning electron microscope image of A6 and Figure 1 Similarly, scanning electron microscopy (SEM) images on A6 show obvious non-framework cross-linked structures between the molecular sieve clusters. Furthermore, XRD analysis reveals that the binder between the molecular sieve clusters is effectively transformed into type X and type A molecular sieves.
[0167] Example 7
[0168] The procedure is carried out according to the method described in Example 1, except that...
[0169] In step 1), the amount of NaLSX molecular sieve powder used is 90% by weight, based on the total weight of the mixture.
[0170] The LiLSX molecular sieve adsorbent was obtained and denoted as A7.
[0171] The A7 has a lithium-ion exchange capacity of 96.8% and a crushing resistance of 16 N / particle.
[0172] Scanning electron microscope image of A7 and Figure 1 Similarly, scanning electron microscopy (SEM) images on A7 show obvious non-framework cross-linked structures between the molecular sieve clusters. Furthermore, XRD analysis reveals that the binder between the molecular sieve clusters is effectively transformed into type X and type A molecular sieves.
[0173] Example 8
[0174] The procedure is carried out according to the method described in Example 1, except that...
[0175] In step 1), the amount of NaLSX molecular sieve powder used is 85% by weight, based on the total weight of the mixture.
[0176] The LiLSX molecular sieve adsorbent was obtained and denoted as A8.
[0177] A8 has a lithium-ion exchange rate of 96% and a crushing resistance of 17 N / particle.
[0178] A8 scanning electron microscope image and Figure 1 Similarly, scanning electron microscopy (SEM) images on A8 show obvious non-framework cross-linked structures between the molecular sieve clusters. Furthermore, XRD analysis reveals that the binder between the molecular sieve clusters is effectively transformed into type X and type A molecular sieves.
[0179] Example 9
[0180] The procedure is carried out according to the method described in Example 1, except that...
[0181] The conditions for both the first and second calcinations were: heating to 700°C at a rate of 5°C / min and holding at that temperature for 240 min.
[0182] The LiLSX molecular sieve adsorbent was obtained and denoted as A9.
[0183] The A9 has a lithium-ion exchange capacity of 96.5% and a crushing resistance of 16 N / particle.
[0184] Scanning electron microscope image of A9 and Figure 1 Similarly, scanning electron microscopy (SEM) images from A9 show obvious non-framework cross-linked structures between the molecular sieve clusters. Furthermore, XRD analysis reveals that the binder between the molecular sieve clusters is effectively transformed into type X and type A molecular sieves.
[0185] Example 10
[0186] The procedure is carried out according to the method described in Example 1, except that...
[0187] In step 7), the pH of the exchange solution is adjusted to 9 using lithium hydroxide solution.
[0188] The LiLSX molecular sieve adsorbent was obtained and denoted as A10.
[0189] A10 has a lithium-ion exchange rate of 99% and a crushing resistance of 10 N / particle.
[0190] As can be seen from the scanning electron microscope image of A10, there is no obvious non-skeleton cross-linking structure between the molecular sieve clusters.
[0191] Comparative Example 1
[0192] The procedure is carried out according to the method described in Example 1, except that...
[0193] Step 5 is skipped, and the pre-wetted product is directly subjected to the second drying and second calcination.
[0194] The LiLSX molecular sieve adsorbent was obtained and denoted as D1.
[0195] D1 has a lithium-ion exchange rate of 97% and a crushing resistance of 15 N / particle.
[0196] The scanning electron microscope image of D1 is as follows: Figure 2 As shown. By Figure 2 It can be seen that there is no obvious non-skeleton cross-linking structure between the molecular sieve clusters, and XRD analysis shows that the binder on the surface of the molecular sieve clusters has not been converted into X or A type molecular sieves.
[0197] Comparative Example 2
[0198] The procedure is carried out according to the method described in Example 1, except that...
[0199] In step 5), sodium aluminate is not used; that is, sodium hydroxide and water are mixed to obtain a mixture, and the concentration of sodium hydroxide in the mixture is 50 g / L.
[0200] The LiLSX molecular sieve adsorbent was obtained and denoted as D2.
[0201] D2 has a lithium-ion exchange rate of 99% and a crushing resistance of 8 N / particle.
[0202] As can be seen from the scanning electron microscope image of D2, there is no obvious non-skeleton cross-linking structure between the molecular sieve crystal clusters.
[0203] Comparative Example 3
[0204] The procedure is carried out according to the method described in Example 1, except that...
[0205] In step 1), the amount of NaLSX molecular sieve powder used is 80% by weight, based on the total weight of the mixture.
[0206] The LiLSX molecular sieve adsorbent was obtained and denoted as D3.
[0207] D3 has a lithium-ion exchange capacity of 95.5% and a crushing resistance of 17 N / particle.
[0208] The scanning electron microscope image of D3 and Figure 1 resemblance.
[0209] Test Example 1 - Nitrogen Adsorption Performance Test
[0210] The test shall be conducted according to the methods specified in the national standard (GB-T 35109-2017).
[0211] The nitrogen adsorption performance test results of LiLSX molecular sieve adsorbents A1-A10 and D1-D3 are shown in Table 1.
[0212] Table 1
[0213]
[0214] Test Example 2 - Nitrogen-Oxygen Separation Coefficient Test
[0215] The test shall be conducted according to the methods specified in the national standard (GB-T 35109-2017).
[0216] The nitrogen-oxygen separation coefficient test results of LiLSX molecular sieve adsorbents A1-A10 and D1-D3 are shown in Table 2.
[0217] Table 2
[0218] serial number A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 D1 D2 D3 Nitrogen-oxygen separation coefficient 6.42 6.38 6.39 6.28 6.24 6.27 6.28 6.23 6.22 6.15 5.91 6.02 5.99
[0219] As can be seen from Table 2, the LiLSX molecular sieve adsorbent prepared by the method described in this invention has excellent nitrogen and oxygen separation capabilities and high selectivity for nitrogen, making it very suitable for pressure swing adsorption air separation to produce oxygen.
[0220] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.
Claims
1. A method for preparing a LiLSX molecular sieve adsorbent, characterized in that, The method includes the following steps: 1) The mixture of kaolin and NaLSX molecular sieve powder was subjected to molding, first drying and first calcination in sequence to obtain the first calcined product; 2) The first calcined product is pre-wetted to obtain a pre-wetted product; 3) In the presence of water, the pre-wetted product is contacted with an alkali and an aluminum source to obtain a contact product; 4) The contact product is subjected to a second drying and a second calcination to obtain a second calcined product; 5) The second calcined product is subjected to lithium-ion exchange with a lithium-ion-containing exchange solution. Based on the total weight of the mixture, the amount of NaLSX molecular sieve powder used is 85% by weight or more.
2. The preparation method according to claim 1, wherein, In step 1), the content of silicon and aluminum oxides in the kaolin is 90% by weight or more; The silica-alumina ratio of the kaolin is 1.9-2:
1.
3. The preparation method according to claim 1, wherein, The silicon-to-aluminum ratio of the NaLSX molecular sieve powder is 2-2.1:
1.
4. The preparation method according to claim 1, wherein, Based on the total weight of the mixture, the amount of NaLSX molecular sieve powder used is 90% by weight or more.
5. The preparation method according to claim 4, wherein, Based on the total weight of the mixture, the amount of NaLSX molecular sieve powder used is 90-95% by weight.
6. The preparation method according to any one of claims 1-5, wherein, In step 1), the conditions for the first drying include: a temperature of 40-120℃ and a time of 10-20h.
7. The preparation method according to any one of claims 1-5, wherein, In step 1), the conditions for the first calcination include: heating to 80-150°C at a rate of 2-8°C / min and holding the temperature for 20-60 min; then heating to 200-300°C at a rate of 2-8°C / min and holding the temperature for 30-90 min; then heating to 400-550°C at a rate of 2-8°C / min and holding the temperature for 20-60 min; and then heating to 600-850°C at a rate of 2-8°C / min and holding the temperature for 100-150 min.
8. The preparation method according to any one of claims 1-5, wherein, In step 2), the pre-wetting treatment method includes: contacting the first roasted product with water for more than 5 minutes, wherein the amount of water used is more than 2g relative to 1g of the first roasted product.
9. The preparation method according to claim 8, wherein, The pre-wetting treatment method includes: contacting the first roasted product with water for 10-30 minutes, wherein the amount of water used is 2-5g relative to 1g of the first roasted product.
10. The preparation method according to any one of claims 1-5, wherein, In step 3), the pre-wetted product is contacted with a mixture containing alkali and an aluminum source to obtain the contact product.
11. The preparation method according to claim 10, wherein, In step 3), the alkali is sodium hydroxide and / or potassium hydroxide; In the mixture, the concentration of the alkali is 20-165 g / L.
12. The preparation method according to claim 11, wherein, In step 3), the alkali is sodium hydroxide; In the mixture, the concentration of the alkali is 40-55 g / L.
13. The preparation method according to claim 10, wherein, In step 3), the aluminum source is selected from one or more of sodium aluminate, aluminum nitrate, aluminum sulfate, aluminum sol, and boehmite; In the mixture, the concentration of the aluminum source, calculated as aluminum oxide, is 2-12 g / L.
14. The preparation method according to claim 13, wherein, In step 3), the aluminum source is selected from sodium aluminate and / or boehmite; In the mixture, the concentration of the aluminum source, calculated as aluminum oxide, is 6-10 g / L.
15. The preparation method according to claim 10, wherein, In step 3), the amount of the mixture used is 1-4 mL relative to 1 g of the pre-wetted product; The contact conditions include a temperature of 80-100℃ and a time of 1-5 hours.
16. The preparation method according to any one of claims 1-5, wherein, The method further includes the step of washing the contact product; washing the contact product until the pH of the filtrate is 8-9.
17. The preparation method according to any one of claims 1-5, wherein, In step 4), the conditions for the second drying include: a temperature of 70-150℃ and a time of 10-20h.
18. The preparation method according to any one of claims 1-5, wherein, In step 4), the conditions for the second calcination include: heating to 80-150°C at a rate of 2-8°C / min and holding the temperature for 20-60 min; then heating to 200-300°C at a rate of 2-8°C / min and holding the temperature for 30-90 min; then heating to 400-550°C at a rate of 2-8°C / min and holding the temperature for 20-60 min; and then heating to 600-850°C at a rate of 2-8°C / min and holding the temperature for 100-150 min.
19. The preparation method according to any one of claims 1-5, wherein, In step 5), the concentration of lithium ions in the lithium-ion-containing exchange solution is 1-5 mol / L; The pH of the lithium-ion-containing exchange solution is 6-8; The amount of lithium-ion-containing exchange solution used is 5-30 mL relative to 1 g of the second calcined product; The conditions for lithium-ion exchange include: a temperature of 60-120℃ and a time of 1-5h; The lithium-ion exchange achieves an exchange rate of over 95%.
20. The preparation method according to claim 19, wherein, In step 5), the concentration of lithium ions in the lithium-ion-containing exchange solution is 2-3 mol / L; The pH of the lithium-ion-containing exchange solution is 6.5-7.5; The amount of lithium-ion-containing exchange solution used is 10-20 mL relative to 1 g of the second calcined product; The conditions for lithium-ion exchange include: a temperature of 80-100℃ and a time of 1-3 hours; The lithium-ion exchange achieves an exchange rate of over 97.5%.
21. The LiLSX molecular sieve adsorbent prepared by the method according to any one of claims 1-20.
22. The application of the LiLSX molecular sieve adsorbent according to claim 21 in pressure swing adsorption air separation.