Self-forming MOR molecular sieve adsorbent, preparation and application of self-forming MOR molecular sieve adsorbent in efficient trapping of low-concentration CO2

Abstract

The invention relates to a self-forming MOR molecular sieve adsorbent, preparation and application of the self-forming MOR molecular sieve adsorbent in efficient trapping of low-concentration CO2, and belongs to the technical field of adsorption separation. The self-forming MOR molecular sieve adsorbent with excellent low-concentration CO2 adsorption performance is synthesized by regulating and controlling the raw material proportion in hydrothermal method synthesis and adding the electron sacrificial agent rare earth metal ions. The MOR molecular sieve adsorbent synthesized by the method provided by the invention has a self-forming structure, and does not need a tedious powder forming technology; compared with an unmodified MOR molecular sieve, the low-concentration CO2 adsorption capacity is remarkably improved, and the modified MOR molecular sieve can be applied to low-concentration trapping scenes such as CO2 purification in closed spaces such as a room and direct air trapping of CO2.

Description

Technical Field

[0001] The present invention belongs to the field of adsorption separation technology, and more specifically, relates to a self-forming MOR molecular sieve adsorbent, its preparation and application for efficiently capturing low-concentration CO2. Background Art

[0002] Since the Industrial Revolution, excessive CO2 emissions have led to a rapid increase in the CO2 content in the air. Excessive CO2 emissions have caused the global surface temperature to continue to rise, triggering a series of environmental problems, such as melting glaciers, rising sea levels, floods, droughts, etc. In addition, excessive CO2 in the closed environment where humans work and live also has a very serious harmful effect, which can cause direct damage to the human body, thus attracting more and more attention. For multi-person office spaces that are not convenient for ventilation in bad weather or for closed places such as space stations and submarines, CO2 in the environment will gradually accumulate as people breathe. When the CO2 concentration exceeds 3000ppm, it will cause dizziness in the brain, which is not conducive to the normal life and work, and more seriously lead to coma, which is harmful to human health. Although some alkaline solutions, alkaline earth metal oxides, and solid amines commonly used in industry have been recognized to have excellent adsorption effects on CO2, however, the high regeneration temperature, volatilization of harmful substances and poor stability limit their long-term use in relatively closed spaces. Therefore, in order to balance the CO2 concentration in a closed environment and accelerate the process of green and sustainable development, it is necessary to develop efficient and stable low-concentration CO2 adsorbents.

[0003] Molecular sieves are considered to be an efficient physical adsorption material for CO2 capture in closed spaces because of their rich pore structure, excellent stability, and no volatilization of harmful substances. However, conventional powdered molecular sieves require cumbersome molding technology before actual application. It is usually necessary to add a binder to the molecular sieve powder and form it into a certain shape by extrusion. This process will inevitably cause pore blockage and lead to a decrease in adsorption capacity. In addition, molecular sieves extruded with a binder are prone to pulverization during use, which affects the stability of the downstream adsorption device for long-term operation.

[0004] In order to simplify the application process of the adsorbent and avoid the reduction of adsorption capacity, we designed a method to directly synthesize self-forming MOR molecular sieve adsorbents by precisely controlling the raw material ratio in the hydrothermal synthesis process. This method does not require the addition of binders and the use of cumbersome molding processes. However, the number and accessibility of adsorption sites of self-forming MOR molecular sieves are significantly reduced compared to powders, resulting in a significant reduction in the performance of self-forming MOR molecular sieves under low CO2 concentration conditions. Therefore, MOR molecular sieve adsorbents face the trade-off between self-forming properties and low-concentration CO2 adsorption performance. In addition, molecular sieve physical adsorbents themselves also face the problem of weak adsorption strength for low-concentration CO2. In order to take into account both the self-forming characteristics of MOR molecular sieve adsorbents and the efficient low-concentration CO2 capture performance, it is necessary to develop a method to improve the low-concentration adsorption performance based on self-forming. At present, many methods have been used to improve the adsorption of CO2 by molecular sieves, including changing the molecular sieve structure, adding metal ions and basic functional groups, etc. These strategies aim to increase the number and strength of CO2 adsorption sites and improve the selectivity of CO2 for other gases. The most widely used strategy is to add metal ions to molecular sieves through ion exchange. The type of metal ions is a key factor affecting the adsorption performance. For example, the potential of alkali metals, alkaline earth metals and transition metals to enhance CO2 adsorption through various mechanisms such as electrostatic interactions, polarization effects and chemical bonds has been widely studied. Although the introduction of ions through ion exchange can effectively improve the adsorption performance, it requires additional and complex post-processing processes, which limits its large-scale application in industry. In addition, the introduction of alkaline earth metals and transition metals may lead to excessively strong ion-gas interactions, requiring higher regeneration temperatures and increasing regeneration energy consumption. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a method for preparing a self-forming MOR molecular sieve adsorbent for efficiently capturing low-concentration CO2. By adjusting the ratio between the synthetic components of the MOR molecular sieve and introducing rare earth metals, a MOR molecular sieve with both self-forming and excellent low-concentration CO2 adsorption performance is obtained. The method is simple in process, easy to repeat and has good consistency. The prepared MOR molecular sieve has excellent CO2 adsorption capacity, moderate adsorption heat and fast adsorption rate, and can be applied to low-concentration CO2 capture and CO2 direct air capture in enclosed spaces such as indoors or space stations.

[0006] According to a first aspect of the present invention, there is provided a method for preparing a self-forming MOR molecular sieve adsorbent, comprising the following steps:

[0007] (1) adding an inorganic base into water, and after fully dissolving, adding a silicon source, an aluminum source and a template agent, and stirring and mixing them thoroughly to form an aluminosilicate gel;

[0008] The molar ratio of the silicon atoms in the silicon source to the aluminum atoms in the aluminum source is (5-10):1; the silicon atoms in the silicon source and the OH in the inorganic base are - The molar ratio of the template to the silicon atom is (2-5):1; the molar ratio of the template to the silicon atom is (0.1-0.6):1;

[0009] (2) adding rare earth metal to the aluminosilicate gel obtained in (1) above, and stirring thoroughly to obtain an aluminosilicate gel mixture containing rare earth metal; the amount of the rare earth metal atomic substance accounts for 0.1 to 0.5% of the amount of the silicon atomic substance in the silicon source;

[0010] (3) adding seed crystals MOR to the aluminosilicate gel mixture obtained in step (2) to obtain an initial gel;

[0011] (4) The initial gel obtained in step (3) is crystallized by a hydrothermal reaction, and then calcined to remove the template, thereby obtaining a block-shaped self-forming MOR molecular sieve adsorbent.

[0012] Preferably, the rare earth metal is Ce, Sm or La.

[0013] Preferably, the temperature of the hydrothermal reaction is 160-190° C., and the time is at least 48 hours.

[0014] Preferably, the calcination temperature is 500-700° C. and the calcination time is 4-12 hours.

[0015] Preferably, the template agent is 4-methylpiperidine, hexamethyleneimine, pyrrole or tetraethylammonium hydroxide.

[0016] According to another aspect of the present invention, a self-forming MOR molecular sieve adsorbent prepared by the method is provided.

[0017] According to another aspect of the present invention, there is provided an application of the self-forming MOR molecular sieve adsorbent for CO2 purification in a closed space or for a CO2 direct air capture adsorbent in a closed space.

[0018] According to another aspect of the present invention, there is provided an application of the self-forming MOR molecular sieve adsorbent for CO2 purification under low CO2 concentration conditions or for direct air capture of CO2 under low CO2 concentration conditions, characterized in that the CO2 concentration under the low CO2 concentration conditions is 300-5000ppm.

[0019] According to another aspect of the present invention, a mobile source and / or fixed source low-concentration CO2 treatment system is provided, comprising the self-forming MOR molecular sieve adsorbent, wherein the CO2 concentration treated by the low-concentration CO2 treatment system is 300-5000ppm.

[0020] In general, the above technical solution conceived by the present invention has the following technical advantages compared with the prior art:

[0021] (1) The present invention synthesizes a self-forming MOR molecular sieve adsorbent with excellent low-concentration CO2 adsorption performance by regulating the raw material ratio in the hydrothermal synthesis and adding electron sacrificial agent rare earth metal ions. The preparation method is simple, easy to repeat, and has good consistency. The present invention synthesizes a self-forming structure with high compressive strength through process regulation. Compared with traditional molecular sieve powders, the molecular sieve does not need to undergo a cumbersome molding process, which simplifies the process and avoids damage to the adsorbent performance.

[0022] (2) The introduction of rare earth metals (preferably Ce) into the molecular sieve framework of the present invention can significantly improve the adsorption performance of the MOR molecular sieve. At 0.0004 bar (the concentration of direct air capture scenario), the adsorption capacity is increased from 0.22 mmol / g to 0.73 mmol / g. At 0.003 bar (application scenarios in closed spaces such as indoors), the adsorption capacity is increased from 1.30 mmol / g to 1.71 mmol / g. At 1 bar, the adsorption capacity is increased from 2.65 mmol / g to 3.50 mmol / g. The adsorption capacity of the obtained MOR molecular sieve remains almost unchanged in ten cycles of the penetration experiment, indicating excellent cyclic stability.

[0023] (3) The rare earth metal of the present invention has a strong spin-orbit coupling effect and a suitable 4f orbital position relative to the Fermi level (Ef). The 4f valence orbital of the rare earth metal has a narrowband characteristic, which can effectively induce the localized electrons to shift to the surrounding atomic chains, thereby regulating the local electronic structure. The present invention improves the adsorption performance of the self-forming MOR molecular sieve for low-concentration CO2 by using rare earth metal ions.

[0024] (4) In the present invention, the rare earth metal introduced is Ce. The orbital coupling between the 4f orbital of Ce and the coordinated O atom causes electrons to be transferred from the Ce atom to the O atom, thereby forming an electronic configuration that is convenient for capturing CO2 and enhancing the adsorption of CO2. The Ce atom and the electron-rich O atom are respectively δ+ ···O δ- (CO2) and O δ- (framework)···C δ+ The interaction between (CO2) forms a synergistic effect, giving the optimal adsorption configuration when capturing low-concentration CO2. This study not only introduces a practical and efficient low-concentration CO2 adsorbent, but also proposes a new angle to improve the adsorption characteristics by regulating the local electron distribution of the adsorption site through orbital coupling. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 X-ray diffraction (XRD) patterns of Ce(n)-MOR molecular sieves (n=0.1, 0.2, 0.5) prepared in Examples 1 to 3, Ce(0)-MOR in Comparative Example 1, and Ce(1.0)-MOR in Comparative Example 2.

[0026] Figure 2 The overall molding diagram of Ce(n)-MOR molecular sieves (n=0.1, 0.2, 0.5) prepared in Examples 1 to 3 and Ce(0)-MOR in Comparative Example 1 and Ce(1.0)-MOR in Comparative Example 2.

[0027] Figure 3 These are the adsorption isotherms of the Ce(n)-MOR molecular sieves (n=0.1, 0.2, 0.5) prepared in Examples 1 to 3, the Ce(0)-MOR in Comparative Example 1, and the Ce(1.0)-MOR in Comparative Example 2. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0029] In a first aspect, the present invention provides a method for preparing a MOR molecular sieve having self-forming and excellent low-concentration CO2 adsorption performance by regulating the ratio of synthetic components and introducing rare earth metals, comprising the following steps:

[0030] (1) adding an inorganic base into water, and after fully dissolving, adding a silicon source, an aluminum source and a template agent, and stirring and mixing them thoroughly to form an aluminosilicate gel;

[0031] (2) adding rare earth metal to the precursor obtained in (1) above, and stirring thoroughly to obtain a rare earth metal-containing aluminosilicate gel mixture;

[0032] (3) adding seed crystals MOR to the aluminosilicate gel mixture obtained in step (2) to obtain an initial gel;

[0033] (4) The synthetic gel obtained in step (3) is placed in a stainless steel crystallization kettle lined with polytetrafluoroethylene for crystallization, and the obtained product is then cooled, filtered, washed, dried and calcined to remove the structure directing agent, thereby obtaining the MOR molecular sieve having self-forming and excellent low-concentration CO2 adsorption performance.

[0034] The molar ratio of the raw materials is: SiO2:Al2O3:Na2O:OSDA:H2O=1.0:0.05-0.125:0.2-0.5:0.1-0.6:10-33; wherein: OSDA is a structure directing agent.

[0035] In some embodiments, the crystallization temperature in step (4) is 160-190° C., and the crystallization time is greater than 48 hours.

[0036] In some embodiments, the calcination temperature in step (4) is 500-700° C., and the calcination time is 4-12 hours.

[0037] In a second aspect, the present invention provides a highly efficient self-forming MOR molecular sieve CO2 adsorbent, wherein rare earth metals regulate the electronic structure of the adsorption site in MOR, forming a synergistic adsorption effect of rare earth metal atoms and their adjacent O atoms on CO2; the use of rare earth metals can regulate the electronic structure of the adsorption site. Preferably, the rare earth metal is Ce. Preferably, the rare earth metal content is rare earth metal to silicon atoms.

[0038] In some embodiments, the amount of rare earth atoms is 0.1-0.5% of silicon atoms, more preferably 0.2%.

[0039] The third aspect of the present invention provides an indoor or other closed space air purification device and a direct air capture device comprising the above-mentioned rare earth metal modified self-forming MOR molecular sieve adsorbent.

[0040] In a fourth aspect, the present invention provides a mobile source and fixed source CO2 treatment system comprising the above-mentioned enclosed space air purification device and direct air capture device.

[0041] The following are specific embodiments

[0042] Example 1

[0043] A method for preparing Ce(0.2)-MOR molecular sieve comprises the following steps:

[0044] 0.91 g NaOH was dissolved in 16 g deionized water, and 1.13 g NaAlO2 was added after stirring evenly, and stirring was continued for 0.5 h. Then 16 g silica sol and 1.8 g 4-methylpiperidine were added to the mixture and stirred for 1 h. 0.069 g Ce(NO3)3·6H2O was added and stirred for 1 h until a uniform aluminosilicate gel mixture was formed. The molar composition of the aluminosilicate gel mixture in this embodiment is: 1.0 SiO2: 0.174 NaAlO2: 0.23 OSDA: 0.285 NaOH: 11 H2O: 0.2% Ce.

[0045] Then, about 5 wt.% (based on SiO2) of MOR seed crystals were added and stirred for 1 hour to obtain the initial synthesis gel. The initial synthesis gel was transferred to a stainless steel reactor with a polytetrafluoroethylene liner and crystallized at 180°C for 4 days. After the crystallization was completed, a block was obtained by filtration, washing and drying. The dried block was calcined at 550°C for 6 hours to finally obtain the MOR molecular sieve adsorbent.

[0046] XRD characterization analysis (see attached Figure 1 ) shows that the obtained product is MOR molecular sieve. It presents a self-forming block structure (see Appendix Figure 2 ). Adsorption isotherm test (see attached Figure 3 ) obtained its static adsorption capacity, which was 1.71 mmol / g at 3000 ppm and 0.73 mmol / g at 400 ppm.

[0047] Comparative Example 1

[0048] A method for preparing Ce(0)-MOR molecular sieve. The steps and raw materials of this comparative example are the same as those of Example 1, except that rare earth metal Ce is not added. XRD characterization analysis (see attached Figure 1 ) shows that the obtained product is MOR molecular sieve. It presents a self-forming block structure (see Appendix Figure 2 ). Adsorption isotherm test (see attached Figure 3 ) obtained its static adsorption capacity, which was 1.30 mmol / g at 3000 ppm and 0.22 mmol / g at 400 ppm.

[0049] Compared with the static adsorption capacity of Example 1, the results show that adding 0.2% rare earth metal Ce can significantly improve the adsorption capacity of low-concentration CO2 of MOR.

[0050] Example 2

[0051] A method for preparing Ce(0.1)-MOR molecular sieve. The steps and raw materials of this embodiment are the same as those of embodiment 1, except that 0.035 g Ce(NO3)3·6H2O is added. XRD characterization analysis (see attached Figure 1 ) shows that the obtained product is MOR molecular sieve. It presents a self-forming block structure (see Appendix Figure 2 ). Adsorption isotherm test (see attached Figure 3 ) obtained its static adsorption capacity, which was 1.48 mmol / g at 3000 ppm and 0.52 mmol / g at 400 ppm.

[0052] Compared with the static adsorption capacity of Comparative Example 1, the results show that the addition of 0.1% Ce can improve the adsorption capacity of low-concentration CO2 of MOR.

[0053] Example 3

[0054] A method for preparing Ce(0.5)-MOR molecular sieve. The steps and raw materials of this embodiment are the same as those of Example 1, except that 0.174 g Ce(NO3)3·6H2O is added. XRD characterization analysis (see attached Figure 1 ) shows that the obtained product is MOR molecular sieve. It presents a self-forming block structure (see Appendix Figure 2 ). Adsorption isotherm test (see attached Figure 3 ) obtained its static adsorption capacity, which was 1.38 mmol / g at 3000 ppm and 0.66 mmol / g at 400 ppm.

[0055] Compared with the static adsorption capacity of comparative example 1, the results show that adding 0.5% can improve the adsorption capacity of low-concentration CO2 of MOR. Compared with the static adsorption capacity of example 1, the results show that adding too much rare earth metal Ce content will lead to a decrease in adsorption capacity.

[0056] Comparative Example 2

[0057] A method for preparing Ce(1.0)-MOR molecular sieve. The steps and raw materials of this comparative example are the same as those of Example 1, except that 0.349 g Ce(NO3)3·6H2O is added. XRD characterization analysis (see attached Figure 1 ) shows that the obtained product is MOR molecular sieve. It presents an integrated block structure (see Appendix Figure 2 ). Adsorption isotherm test (see attached Figure 3 ) obtained its static adsorption capacity, which was 1.28 mmol / g at 3000 ppm and 0.62 mmol / g at 400 ppm.

[0058] Compared with Examples 1 to 3 and Comparative Example 1, the static adsorption capacity of this comparative example is reduced at 3000 ppm. The results show that adding too much rare earth metal Ce will reduce the static adsorption capacity of the MOR adsorbent.

[0059] Comparative Example 3

[0060] The steps and raw materials of this comparative example are the same as those of Example 1, except that the molar composition of the aluminosilicate gel mixture is changed to: 1.0SiO2: 0.174NaAlO2: 0.23OSDA: 0.295NaOH: 11H2O: 0.2% Ce, and the content of NaOH is increased.

[0061] Although this comparative example presents a self-formed bulk structure, its crystal structure has problems of low crystallinity and the presence of impurity crystals, indicating that too high a NaOH content cannot synthesize a complete MOR structure.

[0062] Comparative Example 4

[0063] The steps and raw materials of this comparative example are the same as those of Example 1, except that the molar composition of the aluminosilicate gel mixture is changed to: 1.0SiO2: 0.174NaAlO2: 0.23OSDA: 0.265NaOH: 11H2O: 0.2% Ce.

[0064] Compared with Example 1, this comparative example does not have a self-forming bulk structure, indicating that too low a NaOH content cannot synthesize a self-forming bulk structure.

[0065] Comparative Example 5

[0066] The steps and raw materials of this comparative example are the same as those of Example 1, except that the molar composition of the aluminosilicate gel mixture is changed to: 1.0SiO2:0.183NaAlO2:0.23OSDA:0.265NaOH:11H2O:0.2% Ce.

[0067] Compared with Example 1, this comparative example does not have a self-forming bulk structure, indicating that too high a NaAlO2 content cannot synthesize a self-forming bulk structure.

[0068] Comparative Example 6

[0069] The steps and raw materials of this comparative example are the same as those of Example 1, except that the molar composition of the aluminosilicate gel mixture is changed to: 1.0SiO2: 0.167NaAlO2: 0.23OSDA: 0.285NaOH: 11H2O: 0.2% Ce.

[0070] Compared with Example 1, the adsorption performance of this comparative example is significantly reduced, which is due to the fact that the too low NaAlO2 content leads to a decrease in the number of adsorption sites. The results show that too low NaAlO2 content leads to a decrease in adsorption performance.

[0071] Embodiment 4-5

[0072] The steps and raw materials of this embodiment are the same as those of Embodiment 1, except that Ce metal is replaced by La and Sm respectively.

[0073] The adsorption capacity of this embodiment is 1.48mmol / g and 1.55mmol / g respectively. Compared with Example 1 and Comparative Example 1, the adsorption capacity of this embodiment is lower than that of Example 1, but higher than that of Comparative Example 1. The results show that the addition of La and Sm rare earth metals can increase the adsorption capacity, but the most preferred is the addition of Ce rare earth metal.

[0074] The self-forming MOR of the present invention does not require subsequent cumbersome forming processes and avoids structural damage and performance loss. At the same time, the incorporation of Ce with a unique 4f valence electron structure optimizes the local electronic environment of the binding site and improves the adsorption performance of low-concentration CO2. The synthesized Ce-MOR exhibits an adsorption capacity of up to 1.71 mmol / g at 3000 ppm.

[0075] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a self-forming MOR molecular sieve adsorbent, characterized in that: The following steps are involved: (1) adding an inorganic base into water, and after fully dissolving, adding a silicon source, an aluminum source and a template agent, and stirring and mixing them thoroughly to form an aluminosilicate gel; The molar ratio of the silicon atoms in the silicon source to the aluminum atoms in the aluminum source is (5-10):1; the silicon atoms in the silicon source and the OH in the inorganic base are - The molar ratio of the template to the silicon atom is (2-5):1; the molar ratio of the template to the silicon atom is (0.1-0.6):1; (2) adding rare earth metal to the aluminosilicate gel obtained in (1) above, and stirring thoroughly to obtain an aluminosilicate gel mixture containing rare earth metal; the amount of the rare earth metal atomic substance accounts for 0.1 to 0.5% of the amount of the silicon atomic substance in the silicon source; (3) adding seed crystals MOR to the aluminosilicate gel mixture obtained in step (2) to obtain an initial gel; (4) The initial gel obtained in step (3) is crystallized by a hydrothermal reaction, and then calcined to remove the template, thereby obtaining a block-shaped self-forming MOR molecular sieve adsorbent.

2. The method for preparing the self-forming MOR molecular sieve adsorbent according to claim 1, characterized in that: The rare earth metal is Ce, Sm or La.

3. The method for preparing the self-forming MOR molecular sieve adsorbent according to claim 1, characterized in that: The temperature of the hydrothermal reaction is 160-190° C. and the time is at least 48 hours.

4. The method for preparing the self-forming MOR molecular sieve adsorbent according to claim 1, characterized in that: The calcination temperature is 500-700° C. and the calcination time is 4-12 hours.

5. The method for preparing the self-forming MOR molecular sieve adsorbent according to claim 1, characterized in that: The template agent is 4-methylpiperidine, hexamethyleneimine, pyrrole or tetraethylammonium hydroxide.

6. The self-forming MOR molecular sieve adsorbent prepared by the method according to any one of claims 1 to 5.

7. Use of the self-forming MOR molecular sieve adsorbent as claimed in claim 6 for CO2 purification in a closed space or for direct air capture of CO2 in a closed space.

8. The use of the self-forming MOR molecular sieve adsorbent as claimed in claim 6 for CO2 purification under low CO2 concentration conditions or for direct air capture of CO2 under low CO2 concentration conditions, characterized in that: The CO2 concentration of the low-concentration CO2 condition is 300-5000ppm.

9. A mobile source and / or fixed source low concentration CO2 treatment system, characterized in that: Comprising the self-forming MOR molecular sieve adsorbent as described in claim 6, the CO2 concentration treated by the low-concentration CO2 treatment system is 300-5000ppm.

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