CN115779854A - Adsorption separation application of Ca-CHA containing calcium molecular sieve - Google Patents

Abstract

The invention discloses a calcium-chabazite-containing molecular sieve adsorbent Ca-CHA capable of efficiently separating krypton-xenon mixtures and nitrogen-oxygen mixtures. The commercial Na-Y molecular sieves are used as raw materials and synthesized through steps such as ion exchange and crystal transformation. The prepared Ca-CHA molecular sieve has a strong local electric field and has a strong adsorption effect on xenon and nitrogen. Ca-CHA can selectively adsorb xenon from krypton-xenon mixture to realize the separation of krypton and xenon; and can selectively adsorb nitrogen from nitrogen-oxygen mixture, which can be used as nitrogen selective adsorbent in adsorption oxygen production process. In the present invention, the method for separating the krypton-xenon mixture and the nitrogen-oxygen mixture by using the chabazite-containing Ca-CHA is simple and convenient, the cost of the adsorbent is low, and it has strong industrial promotion prospects.

Description

Adsorption and separation application of a calcium-containing molecular sieve Ca-CHA

technical field

The invention belongs to the field of adsorption and separation of zeolite molecular sieves, and mainly relates to the preparation of a calchabazite molecular sieve which has a strong adsorption effect on nitrogen and xenon and its application in the preparation of pure oxygen by the separation of nitrogen and oxygen and the separation and enrichment of xenon by krypton and xenon .

Background technique

Inert gases, namely helium, neon, argon, krypton, and xenon, are usually obtained through the process of low-temperature rectification of air, and the natural abundance of inert gases decreases in the order of Ar>Ne>He>Kr>Xe>Rn, And the market price rises suddenly with this sequence. Xenon in the noble gas is widely used in lighting, medical imaging anesthesia, laser and other fields, so the market demand for high-purity xenon is increasing. In the by-products of air separation, we can obtain a mixture of xenon and krypton (20/80, v/v), and high-purity xenon can be obtained through separation. In addition, part of krypton and xenon are also contained in nuclear industry waste ( The concentration of krypton is about 40ppm, and the concentration of xenon is about 400ppm), from which efficient capture of xenon is expected to reduce the price of xenon, so the separation of xenon/krypton and the enrichment of xenon are of great significance. Compared with the low-temperature distillation method commonly used in industry, adsorption separation is more economical and environmentally friendly. At present, the research on xenon/krypton adsorption and separation of molecular sieves is still in its infancy. Most of them use theoretical simulation methods to predict the separation performance of molecular sieves. Studies have shown that molecular sieves loaded with silver and other precious metals may be beneficial to the adsorption and separation of xenon/krypton. However, the introduction of precious metals such as silver will cause a substantial increase in the cost of the adsorbent.

Oxygen is not only the source of life, high-purity oxygen also has very important applications in many fields such as industry, medical treatment, military affairs, aerospace and scientific research. In addition, oxyfuel combustion is considered to be an effective way to improve energy utilization efficiency. Based on the broad application prospects of high-purity oxygen, it is of great significance to efficiently remove nitrogen from oxygen. The current common low-temperature distillation method has the disadvantages of high energy consumption and complicated equipment. It is an energy-saving and environmentally-friendly technology to use the selective adsorption of porous materials to achieve separation at room temperature. Zeolite molecular sieves have a certain ability to selectively adsorb nitrogen from oxygen. This is because nitrogen molecules contain lone pairs of electrons and have a larger quadrupole moment than oxygen molecules, so the force ratio between nitrogen molecules and the cation electric field in molecular sieves Oxygen is stronger and has a higher adsorption capacity. It is of great significance to develop molecular sieve materials with higher nitrogen/oxygen separation performance.

Chabazite is a natural zeolite, which can be synthesized by commercial molecular sieve Na-Y through ion exchange, crystal transformation and other methods, and the synthesis cost is low. The purpose of the invention is to utilize calcium-containing chabazite Ca-CHA to realize the adsorption separation of highly selective krypton-xenon mixture and nitrogen-oxygen mixture.

Contents of the invention

The present invention uses Na-Y molecular sieves as raw materials, and prepares Ca-CHA molecular sieves through steps such as ion exchange and crystal transformation. The preparation cost is low and industrial production is easy, and the internal local electric field is strong, so it has a relatively high separation coefficient.

The technical solution of the present invention is to provide a method for selectively adsorbing xenon by using calcium chabazite Ca-CHA to enrich xenon. The agent can selectively adsorb xenon, and when the separation column reaches the adsorption equilibrium, the separation column is purged with helium to realize the regeneration of the adsorbent and the recovery of the enriched xenon, wherein the chabazite is SiO ₂ with 4-6 /Al ₂ O ₃ ratio of pure phase chabazite, the topological structure is CHA structure; where:

The chabazite molecular sieve with a calcium ion exchange degree of more than 90% meets the following conditions at room temperature:

Under the corresponding partial pressure of the gas, the static separation factor K of the xenon/krypton mixture, the dynamic separation factor S and the xenon adsorption heat Q _Xe and krypton adsorption heat Q _Kr satisfy the following relationship:

S/K>Q _Xe /Q _Kr +1.

Among them: K is the ratio of the static adsorption capacity of the two gases under the corresponding gas partial pressure;

S is the ratio of the dynamic adsorption amounts of the two gases in the dynamic breakthrough experiment.

Further, the content of krypton gas in the krypton-xenon mixture is 40ppm-80%, and the content of xenon gas is 40ppm-20%.

Further, the operating temperature of the separation process is 0°C-30°C, and the pressure is 1 bar.

Further, the Ca-CHA molecular sieve contains only one type of cation, and the exchange degree of Ca ²⁺ is 90%-100%.

The present invention also provides a method for producing oxygen by selectively adsorbing nitrogen from a nitrogen-oxygen mixture by using the calcium-containing chabazite Ca-CHA. The nitrogen-oxygen mixture is passed into the calcium-containing chabazite Ca-CHA, and the adsorbent selectivity Adsorbed nitrogen can collect high-purity oxygen directly at the outlet. Wherein the chabazite is a pure-phase chabazite with a ratio of SiO ₂ /Al ₂ O ₃ of 4-6, and its topological structure is a CHA structure; it is characterized in that:

A chabazite molecular sieve with a calcium ion exchange degree of more than 90%. Under the corresponding partial pressure of the gas, the molecular sieve has a static separation factor K for a nitrogen/oxygen mixture, a dynamic separation factor S, and the difference between the nitrogen adsorption heat Q _N2 and the oxygen adsorption heat Q _O2 satisfy the following relationship:

S/K>Q _N2 /Q _O2 +1;

Among them: K is the ratio of the static adsorption capacity of the two gases under the corresponding gas partial pressure;

S is the ratio of the dynamic adsorption amounts of the two gases in the dynamic breakthrough experiment.

Further, in the mixed gas of nitrogen and oxygen, wherein the nitrogen concentration is 1%-80%, the corresponding oxygen concentration is 99%-20%.

Further, the operating temperature of the separation process is 0°C-30°C, and the pressure is 1 bar.

Compared with the prior art, the specific advantages and beneficial effects of the present invention are:

1. The present invention realizes efficient separation of krypton and xenon mixtures by molecular sieve materials, and the used adsorbent Ca-CHA molecular sieve has simple synthesis steps, no precious metal and transition metal raw materials are used in the preparation process, and the cost is low.

2. The silicon-aluminum ratio of the Ca-CHA molecular sieve prepared in the present invention is higher than that of the LSX molecular sieve with low silicon-aluminum ratio commonly used in PSA oxygen production, so Ca-CHA has higher stability.

3. The Ca-CHA molecular sieve of the present invention shows a high nitrogen adsorption capacity in the nitrogen/oxygen dynamic breakthrough experiment, and the pure oxygen production has been greatly improved.

Description of drawings

The accompanying drawings are used to provide a further understanding of the present invention, and constitute a part of the description, together with the following specific embodiments, are used to explain the present invention, but do not constitute a limitation to the present invention. In the attached picture:

Fig. 1 is the XRD pattern of Ca-CHA molecular sieve.

Fig. 2 is the SEM photo of Ca-CHA molecular sieve.

Fig. 3 is the adsorption isotherm of xenon gas and krypton gas of Ca-CHA molecular sieve at 25°C.

Figure 4 is the nitrogen and oxygen adsorption isotherms of Ca-CHA molecular sieve at 25°C.

Fig. 5 is a dynamic breakthrough curve of Ca-CHA separating a mixture of krypton and xenon (80% krypton and 20% xenon) under the condition of 25°C and 1 bar.

Fig. 6 is the dynamic breakthrough curve of Ca-CHA separating nitrogen and oxygen mixture (20% nitrogen and 80% oxygen) under the condition of 25°C and 1 bar.

Fig. 7 is the dynamic breakthrough curve of Ca-CHA separating krypton and xenon mixture (krypton 40ppm, xenon 400ppm, balance gas helium) under the condition of 25°C and 1bar.

Detailed ways

Below in conjunction with accompanying drawing and embodiment this patent is done further explanation. It should be understood that the specific embodiments described here are only used to illustrate and explain the present invention, and are not intended to limit the present invention.

The synthetic method of Ca-CHA molecular sieve of the present invention, concrete steps are:

Step 1: Preparation of K-Y molecular sieve

A solution containing K ⁺ is used to perform multiple ion exchanges with Na-Y molecular sieves, and all Na ⁺ in Na-Y molecular sieves are exchanged for K ⁺ . The exchange temperature is 80 ° C. The molecular sieves after suction filtration and washing are dried and roasted to obtain the exchange. KY molecular sieve with a degree greater than 95%.

Preferably, the solution containing K ⁺ is KNO ₃ solution, the concentration of the solution is 0.5-1mol/L, the number of exchanges is 2 times, and the time for each exchange is 10 hours.

Step 2: Preparation of K-CHA molecular sieve

Add potassium hydroxide to deionized water, dissolve and add K-Y sample, continue stirring for 1 hour, then transfer to a hydrothermal synthesis kettle for crystallization in a high-temperature oven to obtain a K-CHA sample.

Preferably, the molar ratio of raw materials is: 1.0SiO ₂ : (0.8-1) KOH: (120-130) H ₂ O, the crystallization temperature is 100-200°C, and the time is 20-60 hours. Under the preferred conditions, the crystallization temperature It is 120-160 ℃, and the time is 30-50 hours.

Step 3: Preparation of Ca-CHA

The solution containing Ca ²⁺ is used to carry out ion exchange with K-CHA molecular sieve for many times, all K ⁺ is exchanged into Ca ²⁺ , the exchange temperature is 80°C, and the molecular sieve after suction filtration and washing is dried and roasted to obtain an exchange degree greater than 95%. Ca-CHA molecular sieves.

Preferably, Ca(NO ₃ ) ₂ solution is used as the solution containing Ca ²⁺ , the concentration of the solution is 0.5-1 mol/L, the number of exchanges is 3 times, and the time for each exchange is 10 hours.

In another embodiment, a method for separating krypton and xenon and enriching xenon by Ca-CHA is also provided, which specifically includes the following steps:

(1) Weigh a certain amount of Ca-CHA molecular sieve and add it to the separation column, and pretreat it with helium at 100-400° C. (preferably 250° C.) for 0.5-1 hour.

(2) After the sample is lowered to room temperature, a mixed gas containing krypton and xenon is introduced, and the total space velocity of the gas is 100-5000/hour (preferably 300-1000/hour).

(3) Keep the temperature of the separation column at room temperature, and Ca-CHA can selectively adsorb xenon. The gas composition change at the outlet of the separation column was detected online by a directly connected mass spectrometer, and the dynamic adsorption of krypton and xenon by Ca-CHA was calculated. When the separation column filled with Ca-CHA molecular sieve reaches the adsorption equilibrium, the separation column is purged with helium to realize the regeneration of the adsorbent and the recovery of the enriched xenon gas.

Ca-CHA is under the corresponding partial pressure of the gas, that is, when it is consistent with the partial pressure in the mixed gas, the static separation factor K (the ratio of the static adsorption capacity of the two gases) of the xenon/krypton mixture, and the dynamic separation factor S (dynamic The ratio of the dynamic adsorption capacity of the two gases in the breakthrough experiment), and the xenon gas adsorption heat Q _Xe and the krypton gas adsorption heat Q _Kr satisfy the following relationship:

S/K>Q _Xe /Q _Kr +1.

The method for Ca-CHA adsorption separation nitrogen and oxygen provided by the invention comprises the following steps:

(1) Weigh a certain amount of Ca-CHA molecular sieve and add it to a column separation device, and pretreat it with helium at 100-400° C. (preferably 250° C.) for 0.5-1 hour.

(2) After the sample is cooled to room temperature, a mixed gas of nitrogen and oxygen is introduced, and the total space velocity of the gas is 100-5000/hour (preferably 200-1500/hour).

(3) The temperature of the separation column is maintained at room temperature, and the pure oxygen flow is directly collected at the outlet. The directly connected mass spectrometer was used to detect the change of the gas composition at the outlet of the separation column online, and the dynamic adsorption capacity of Ca-CHA for nitrogen and oxygen was calculated. When the nitrogen adsorption reached equilibrium, the adsorption column was purged with helium to realize the regeneration of the adsorbent.

Ca-CHA is characterized in that, under the corresponding partial pressure of the gas (consistent with the partial pressure in the mixed gas), the static separation factor K of the nitrogen/oxygen mixture (the ratio of the static adsorption capacity of the two gases under the corresponding gas partial pressure), the dynamic The separation factor S (the ratio of the dynamic adsorption capacity of the two gases in the dynamic breakthrough experiment), and the nitrogen adsorption heat Q _N2 and oxygen adsorption heat Q _O2 satisfy the following relationship:

S/K>Q _N2 /Q _O2 +1.

Example 1

1. Exchange Na-Y molecular sieves for K-Y molecular sieves

A three-necked flask was used for ion exchange, the exchange time was 10 hours, and the exchange temperature was 80°C. The specific operation is as follows: add 3g of Na-Y raw powder (Si/Al=2.6) to 100mL of 1mmol/ _{L KNO3} solution, stir with a magnetic stirrer for 10 hours, then carry out suction filtration and washing, and filter cake in a drum at 80°C Dry in an air drying oven, and the obtained solid continues to be ion-exchanged, and KY molecular sieves are obtained after repeating 2 times.

2. Convert K-Y molecular sieve to K-CHA molecular sieve

Add 2.5g of potassium hydroxide to 150mL of deionized water, dissolve and add 5g of K-Y sample, continue to stir for 1 hour, then transfer to a hydrothermal synthesis kettle for crystallization in an oven at 150°C for 48 hours, then filter and wash the obtained solid Get the K-CHA sample.

3. Exchange K-CHA molecular sieves for Ca-CHA molecular sieves

A three-necked flask was used for ion exchange, the exchange time was 10 hours, and the exchange temperature was 80°C. The specific operation is: add 3g K-CHA molecular sieve to 100mL solution with a concentration of 1mmol/LCa(NO ₃ ) ₂ , use a magnetic stirrer to stir for 10 hours, then carry out suction filtration and washing, and filter cake in a blast drying oven at 80°C After drying, the obtained solid was further subjected to ion exchange, and Ca-CHA molecular sieves were obtained after repeated three times. The XRD pattern of the obtained sample is shown in FIG. 1 , and the scanning electron microscope image is shown in FIG. 2 .

Example 2 The adsorption isotherms of xenon, krypton, nitrogen and oxygen were measured by a Quantachrome iQ physical adsorption instrument, and the results are shown in Fig. 3 and Fig. 4 . According to the adsorption isotherm data, the adsorption heats of Ca-CHA on xenon, krypton, nitrogen and oxygen were calculated by Van't Hoff equation, and the results are shown in Table 1. The static separation factor (K) of Ca-CHA to xenon and krypton at the corresponding partial pressure (0.2/0.8bar) is 1.12, and the static separation factor (K) of nitrogen and oxygen at the corresponding partial pressure (0.2/0.8bar) is 2.78.

Example 3

The Ca-CHA molecular sieve synthesized by the above steps was applied to the xenon/krypton breakthrough experiment by using a self-made column separation device. The specific operation is: put a certain amount of Ca-CHA sample into the sample cell of the self-made separation column, pretreat the sample with helium gas purging at a temperature of 250 °C for 1 hour, and after the pretreatment is completed and cool down to room temperature, The balance gas containing krypton and xenon (80% krypton and 20% xenon) is passed into the sample, the gas space velocity is 300/hour, the gas outlet of the separation column is connected to a mass spectrometer, and the composition of the outlet gas is monitored in real time online Components, and the test results are shown in Figure 5. The detection time of krypton is 1.6 minutes, the dynamic adsorption capacity of Ca-CHA to krypton is 0.32mmol/g, the detection time of xenon is 25.2 minutes, the dynamic adsorption capacity of Ca-CHA to xenon is 1.31mmol/g, The dynamic separation factor S of xenon/krypton is 4.09, satisfying S/K>Q _Xe /Q _Kr +1.

Example 4

The Ca-CHA molecular sieve synthesized by the above steps was applied to the nitrogen/oxygen breakthrough experiment using a self-made column separation device. The specific operation is: put a certain amount of Ca-CHA sample into the sample cell of the self-made separation column, pretreat the sample with helium gas purging at a temperature of 250°C for 1 hour, and after the pretreatment is completed and cool down to room temperature, Pass nitrogen/oxygen mixed gas (gas concentration: 80%/20%) into the sample, the gas space velocity is 600/hour, the gas outlet of the separation column is connected to a mass spectrometer, and the composition of the outlet gas is monitored in real time online, and the test results As shown in Figure 6. The detection time of oxygen is 0.2 minutes, the dynamic adsorption capacity of Ca-CHA to oxygen is 0.09mmol/g, the measurement time of nitrogen gas is 7.3 minutes, the adsorption capacity of Ca-CHA to nitrogen gas is 0.67mmol/g, and the pure oxygen output is 2.32mmol/g, Ca-CHA nitrogen/oxygen dynamic separation factor S is 7.44. The dynamic adsorption ratio (α) of nitrogen and oxygen is 7.44, satisfying S/K>Q _N2 /Q _O2 +1.

Table 1 Gas adsorption capacity and heat of adsorption of Ca-CHA

Example 5

The Ca-CHA molecular sieve synthesized by the above steps was applied to the low-concentration xenon/krypton breakthrough experiment using a self-made column separation device. The specific operation is: put a certain amount of Ca-CHA sample into the sample cell of the self-made separation column, pretreat the sample with helium gas purging at a temperature of 250 °C for 1 hour, and after the pretreatment is completed and cool down to room temperature, The balance gas containing krypton and xenon (the concentration of krypton gas is 40ppm, the concentration of xenon gas is 400ppm, and the balance gas is helium) is passed into the sample, the gas space velocity is 600/hour, and the gas outlet of the separation column is connected to the mass spectrometer, and the online real-time The composition of the outlet gas was monitored, and the test results are shown in Figure 7. The detection time of krypton gas was 1.2 minutes, the detection time of xenon gas was 66.1 minutes, and the xenon/krypton separation selectivity was 12.6.

Claims (7)

1. A method for enriching xenon by utilizing calcite Ca-CHA to selectively adsorb xenon, the method comprising passing krypton/xenon mixture into a separation column filled with Ca-CHA, and the adsorbent can selectively adsorb xenon , when the separation column reaches the adsorption equilibrium, the separation column is purged with helium to realize the regeneration of the adsorbent and the recovery of the enriched xenon gas, wherein the chabazite has a SiO ₂ /Al ₂ O ₃ ratio of 4-6 The pure phase chabazite, the topological structure is CHA structure; where: The chabazite molecular sieve with a calcium ion exchange degree of more than 90% meets the following conditions at room temperature: Under the corresponding partial pressure of the gas, the static separation factor K of the xenon/krypton mixture, the dynamic separation factor S and the xenon adsorption heat Q _Xe and krypton adsorption heat Q _Kr satisfy the following relationship: S/K>Q _Xe /Q _Kr +1. Among them: K is the ratio of the static adsorption capacity of the two gases under the corresponding gas partial pressure; S is the ratio of the dynamic adsorption amounts of the two gases in the dynamic breakthrough experiment. 2. the method for enriching xenon by utilizing the calcium-containing chabazite Ca-CHA selective adsorption of xenon according to claim 1 is characterized in that: the content of krypton in the mixture of krypton and xenon is 40ppm-80%, and the content of xenon is 40ppm-20%. 3. The method for selectively adsorbing xenon by using calcium chabazite Ca-CHA to enrich xenon according to claim 2, characterized in that: the operating temperature of the separation process is 0°C-30°C, and the pressure is 1 bar. 4. the method for enriching xenon by using calchabazite Ca-CHA to selectively adsorb xenon according to claim 2 is characterized in that: Ca-CHA molecular sieve only contains a kind of cation type, and the exchange degree of Ca ²⁺ 90%-100%. 5. A kind of method that utilizes chabazite Ca-CHA to selectively adsorb nitrogen from the nitrogen-oxygen mixture to produce oxygen, the nitrogen-oxygen mixture is passed into the calcium-containing chabazite Ca-CHA, and the adsorbent selectively adsorbs nitrogen. High-purity oxygen is collected directly at the outlet. Wherein the chabazite is a pure-phase chabazite with a ratio of SiO ₂ /Al ₂ O ₃ of 4-6, and its topological structure is a CHA structure; it is characterized in that: A chabazite molecular sieve with a calcium ion exchange degree of more than 90%. Under the corresponding partial pressure of the gas, the molecular sieve has a static separation factor K for a nitrogen/oxygen mixture, a dynamic separation factor S, and the difference between the nitrogen adsorption heat Q _N2 and the oxygen adsorption heat Q _O2 satisfy the following relationship: S/K>Q _N2 /Q _O2 +1; Among them: K is the ratio of the static adsorption capacity of the two gases under the corresponding gas partial pressure; S is the ratio of the dynamic adsorption amounts of the two gases in the dynamic breakthrough experiment. 6. The method for producing oxygen by selectively adsorbing nitrogen from the nitrogen-oxygen mixture by using calcium-containing chabazite Ca-CHA according to claim 5, characterized in that: the nitrogen concentration in the nitrogen and oxygen mixture is 1%-80 %, the corresponding oxygen concentration is 99%-20%. 7. The method for producing oxygen by selectively adsorbing nitrogen from a nitrogen-oxygen mixture by using calcium chabazite Ca-CHA according to claim 5, characterized in that: the operating temperature of the separation process is 0°C-30°C, the pressure for 1bar.

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