A self-forming MOR molecular sieve adsorbent, its preparation and application in the efficient capture of low-concentration CO2.

Abstract

The present application relates to a kind of self-forming MOR molecular sieve adsorbent, preparation and the application of high-efficiency trapping low concentration CO2, belong to adsorption separation technical field.The present application is synthesized by regulating and controlling the proportion of raw materials in hydrothermal synthesis and adding rare earth metal ions as electronic sacrificial agent, and the self-forming MOR molecular sieve adsorbent with excellent low concentration CO2 adsorption performance is synthesized.The MOR molecular sieve adsorbent synthesized by the method of the present application has a self-forming structure, and does not need complicated powder forming technology;Compared with unmodified MOR molecular sieve, the low concentration CO2 adsorption capacity is significantly improved, and can be applied to CO2 purification and CO2 direct air trapping in indoor closed space and other low concentration trapping scenarios.

Description

Technical Field

[0001] This invention belongs to the field of adsorption and separation technology, and more specifically, relates to a self-forming MOR molecular sieve adsorbent, its preparation, and its application in the efficient capture of low-concentration CO2. Background Technology

[0002] Since the Industrial Revolution, excessive CO2 emissions have led to a rapid increase in atmospheric CO2 levels. Excessive CO2 emissions have caused a sustained rise in global surface temperatures, triggering a series of environmental problems such as glacial melting, sea-level rise, floods, and droughts. Furthermore, excessive CO2 in enclosed environments where humans work and live also poses serious health risks, directly harming human health and drawing increasing attention. In multi-person offices with poor ventilation during inclement weather, or in enclosed spaces like space stations and submarines, CO2 gradually accumulates through respiration. When CO2 concentrations exceed 3000 ppm, it can cause dizziness, hindering normal work and life, and in severe cases, leading to coma and harming human health. Although some industrially used alkaline solutions, alkaline earth metal oxides, and solid amines are recognized as having excellent CO2 adsorption properties, their high regeneration temperatures, the volatilization of harmful substances, and poor stability limit their long-term use in relatively enclosed spaces. Therefore, in order to balance the CO2 concentration in enclosed environments and accelerate the process of achieving green and sustainable development, it is necessary to develop efficient and stable low-concentration CO2 adsorbents.

[0003] Molecular sieves are considered highly efficient physical adsorption materials for CO2 capture in enclosed spaces due to their abundant pore structure, excellent stability, and lack of harmful volatile substances. However, conventional powdered molecular sieves require cumbersome molding techniques before practical application. Typically, binders are added to the molecular sieve powder and extruded to form a specific shape, a process that inevitably leads to pore blockage and a decrease in adsorption capacity. Furthermore, molecular sieves formed using binders are prone to pulverization during use, affecting the long-term operational stability of downstream adsorption devices.

[0004] To simplify the application process of adsorbents and avoid reducing 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 eliminates the need for binders and cumbersome molding processes. However, the number and accessibility of adsorption sites in self-forming MOR molecular sieves are significantly reduced compared to powder adsorbents, leading to a significant decrease in the performance of self-forming MOR molecular sieves under low CO2 concentration conditions. Therefore, MOR molecular sieve adsorbents face a trade-off between self-forming characteristics and low-concentration CO2 adsorption performance. Furthermore, molecular sieve physical adsorbents themselves also suffer from weak adsorption strength for low-concentration CO2. To simultaneously achieve both the self-forming characteristics of MOR molecular sieve adsorbents and efficient low-concentration CO2 capture performance, a method to improve low-concentration adsorption performance based on self-forming needs to be developed. Currently, many methods have been used to improve the adsorption of CO2 by molecular sieves, including modifying the molecular sieve structure, adding metal ions and basic functional groups. 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 introduce metal ions into molecular sieves via ion exchange. The type of metal ion is a key factor affecting 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 extensively studied. Although introducing ions via ion exchange can effectively improve adsorption performance, it requires additional and complex post-processing, limiting its large-scale industrial application. Furthermore, the introduction of alkaline earth metals and transition metals may lead to excessively strong ion-gas interactions, thus requiring higher regeneration temperatures and increasing regeneration energy consumption. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing a self-forming MOR molecular sieve adsorbent for efficiently capturing low-concentration CO2. By controlling the ratio between the synthetic components of the MOR molecular sieve and introducing rare earth metals, a MOR molecular sieve exhibiting both self-forming properties and excellent low-concentration CO2 adsorption performance is obtained. This method is simple, easily reproducible, and exhibits good consistency. The prepared MOR molecular sieve possesses excellent CO2 adsorption capacity, moderate heat of adsorption, and rapid adsorption rate, making it suitable for low-concentration CO2 capture in enclosed spaces such as indoor spaces or space stations, as well as direct air CO2 capture.

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

[0007] (1) Add inorganic base to water, dissolve it completely, then add silicon source, aluminum source and template agent, stir and mix thoroughly to form aluminosilicate gel;

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

[0009] (2) Add rare earth metals to the aluminosilicate gel obtained in (1) above, and stir thoroughly to obtain a mixture of aluminosilicate gels containing rare earth metals; the amount of rare earth metal atoms accounts for 0.1 to 0.5% of the amount of silicon atoms in the silicon source.

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

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

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

[0013] Preferably, the hydrothermal reaction is carried out at a temperature of 160–190°C for at least 48 hours.

[0014] Preferably, the calcination temperature is 500–700°C and the 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, the self-forming MOR molecular sieve adsorbent is provided for use in CO2 purification in enclosed spaces or as a direct air capture adsorbent for CO2 in enclosed spaces.

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

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

[0020] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages:

[0021] (1) This invention synthesizes a self-forming MOR molecular sieve adsorbent with excellent low-concentration CO2 adsorption performance by controlling the proportion of raw materials in the hydrothermal synthesis and adding rare earth metal ions as electron sacrificial agents. The preparation method is simple, easy to repeat, and has good consistency. This invention synthesizes a self-forming structure with high compressive strength through process control. Compared with traditional molecular sieve powders, it does not require a cumbersome forming process for the molecular sieve, simplifying the process and avoiding damage to the adsorbent performance.

[0022] (2) The introduction of rare earth metals (preferably Ce) into the molecular sieve framework of this invention can significantly improve the adsorption performance of MOR molecular sieves. At 0.0004 bar (concentration in a direct air capture scenario), the adsorption capacity increased from 0.22 mmol / g to 0.73 mmol / g. At 0.003 bar (application scenarios in enclosed spaces such as indoors), the adsorption capacity increased from 1.30 mmol / g to 1.71 mmol / g. At 1 bar, the adsorption capacity increased from 2.65 mmol / g to 3.50 mmol / g. The adsorption capacity of the resulting MOR molecular sieve remained almost unchanged after ten cycles of breakthrough experiments, indicating excellent cycling stability.

[0023] (3) The rare earth metals of this invention possess strong spin-orbit coupling effects and suitable 4f orbital positions relative to the Fermi level (Ef). The 4f valence orbitals of rare earth metals exhibit narrow-band characteristics, effectively inducing local electrons to shift to surrounding atomic chains, thereby regulating the local electronic structure. This invention improves the adsorption performance of self-forming MOR molecular sieves for low-concentration CO2 by using rare earth metal ions.

[0024] (4) Preferably, the rare earth metal introduced in this invention is Ce. The orbital coupling between the 4f orbital of Ce and the coordinated O atom causes electrons to transfer from the Ce atom to the O atom, thereby forming an electronic configuration that facilitates CO2 capture and enhances CO2 adsorption. The Ce atom and the electron-rich O atom respectively pass through Ce... δ+ ···O δ- (CO2) and O δ- (framework)···C δ+ The interaction between CO2 and other CO2 molecules creates a synergistic effect, yielding the optimal adsorption configuration for capturing low concentrations of CO2. This study not only introduces a practical and efficient low-concentration CO2 adsorbent but also proposes a novel approach to improving adsorption properties by modulating the local electron distribution of adsorption sites through orbital coupling. Attached Figure Description

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

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

[0027] Figure 3 Adsorption isotherms of Ce(n)-MOR molecular sieves (n = 0.1, 0.2, 0.5) prepared in Examples 1-3 and Comparative Example 1 Ce(0)-MOR and Comparative Example 2 Ce(1.0)-MOR. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

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

[0030] (1) Add inorganic base to water, dissolve it completely, then add silicon source, aluminum source and template agent, stir and mix thoroughly to form aluminosilicate gel;

[0031] (2) Add rare earth metals to the precursor obtained in (1) above, and stir thoroughly to obtain a silicate aluminate gel mixture containing rare earth metals.

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

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

[0034] The molar ratio of each raw material is as follows: 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 h.

[0037] In a second aspect, this invention provides a highly efficient self-forming MOR molecular sieve CO2 adsorbent. Rare earth metals regulate the electronic structure of the adsorption sites in the MOR, forming a synergistic adsorption effect of rare earth metal atoms and their adjacent O atoms on CO2. The use of rare earth metals allows for the regulation of the electronic structure of the adsorption sites. Preferably, the rare earth metal is Ce. Preferably, the rare earth metal content is a certain percentage of silicon atoms.

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

[0039] In a third aspect, the present invention provides an indoor or other enclosed 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 a stationary source CO2 treatment system comprising the above-described 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 sieves includes the following steps:

[0044] Dissolve 0.91 g NaOH in 16 g deionized water, stir until homogeneous, then add 1.13 g NaAlO2 and continue stirring for 0.5 h. Next, add 16 g silica sol and 1.8 g 4-methylpiperidine to the mixture and stir for 1 h. Then add 0.069 g Ce(NO3)3·6H2O and stir for 1 h until a homogeneous aluminosilicate gel mixture is 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, approximately 5 wt.% (based on SiO2) of MOR seed crystals were added and stirring continued for 1 hour to obtain the initial synthesized gel. The initial synthesized gel was transferred to a stainless steel reactor with a polytetrafluoroethylene liner and crystallized at 180°C for 4 days. After crystallization, the gel was obtained by filtration, washing, and drying to obtain a bulk material. The dried bulk material was calcined at 550°C for 6 hours to finally obtain the MOR molecular sieve adsorbent.

[0046] XRD characterization analysis (see appendix) Figure 1 This indicates that the obtained product is a MOR molecular sieve. It exhibits a self-forming bulk structure (see attached diagram). Figure 2 Adsorption isotherm test (see appendix) Figure 3 The static adsorption capacity was obtained as 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 sieves. The steps and raw materials in this comparative example are the same as in Example 1, except that rare earth metal Ce is not added. XRD characterization analysis (see appendix). Figure 1 This indicates that the obtained product is a MOR molecular sieve. It exhibits a self-forming bulk structure (see attached diagram). Figure 2 Adsorption isotherm test (see appendix) Figure 3 The static adsorption capacity was obtained as 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 the addition of 0.2% rare earth metal Ce can significantly improve the adsorption capacity of low concentration CO2 in MOR.

[0050] Example 2

[0051] A method for preparing Ce(0.1)-MOR molecular sieves. The steps and raw materials in this example are the same as in Example 1, except that 0.035 g of Ce(NO3)3·6H2O is added. XRD characterization analysis (see attached). Figure 1 This indicates that the obtained product is a MOR molecular sieve. It exhibits a self-forming bulk structure (see attached diagram). Figure 2 Adsorption isotherm test (see appendix) Figure 3 The static adsorption capacity was obtained as 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 MOR for low concentrations of CO2.

[0053] Example 3

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

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

[0056] Comparative Example 2

[0057] A method for preparing Ce(1.0)-MOR molecular sieves. The steps and raw materials in this comparative example are the same as in Example 1, except that 0.349 g of Ce(NO3)3·6H2O is added. XRD characterization analysis (see attached). Figure 1 This indicates that the obtained product is a MOR molecular sieve. It exhibits a monolithic bulk structure (see attached diagram). Figure 2 Adsorption isotherm test (see appendix) Figure 3 The static adsorption capacity was obtained as 1.28 mmol / g at 3000 ppm and 0.62 mmol / g at 400 ppm.

[0058] Compared with Examples 1-3 and Comparative Example 1, the static adsorption capacity of this comparative example was reduced at 3000 ppm, indicating 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 in 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, which increases the NaOH content.

[0061] Although this comparative example exhibits a self-forming bulk structure, its crystal structure suffers from low crystallinity and the presence of impurities, indicating that excessively high 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 in 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 in 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 in 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 to Example 1, the adsorption performance of this comparative example was significantly reduced, which was due to the reduced number of adsorption sites caused by the excessively low NaAlO2 content. The results indicate that too low a NaAlO2 content leads to decreased adsorption performance.

[0071] Examples 4-5

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

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

[0074] This invention provides a self-forming Ce-MOR that eliminates the need for cumbersome subsequent molding processes, avoiding structural damage and performance loss. Simultaneously, the incorporation of Ce, with its unique 4f valence electron structure, optimizes the local electronic environment at the binding site, improving adsorption performance for low concentrations of CO2. The synthesized Ce-MOR exhibits an adsorption capacity as high as 1.71 mmol / g at 3000 ppm.

[0075] Those skilled in the art will readily understand that the above description is merely 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 within the scope of protection of the present invention.

Claims

1. A self-forming block-shaped MOR molecular sieve adsorbent for CO2 purification under low-concentration CO2 conditions or for direct air capture adsorbent application under low-concentration CO2 conditions, characterized in that, The CO2 concentration under the low-concentration CO2 conditions is 300-5000 ppm; The self-forming block-shaped MOR molecular sieve adsorbent is prepared through the following steps: (1) Add the inorganic base to water, dissolve it completely, then add the silicon source, aluminum source and template agent, and stir and mix thoroughly to form an aluminosilicate gel; The molar ratio of silicon atoms in the silicon source to aluminum atoms in the aluminum source is (5~10):1; the molar ratio of silicon atoms in the silicon source to OH groups in the inorganic base is... - The molar ratio of the template agent to silicon atoms is (2~5):1; the molar ratio of the template agent to silicon atoms is (0.1~0.6):

1. (2) Add rare earth metals to the aluminosilicate gel obtained in (1) above, and stir thoroughly to obtain an aluminosilicate gel mixture containing rare earth metals; the amount of rare earth metal atoms accounts for 0.1~0.2% of the amount of silicon atoms in the silicon source; (3) Add seed crystal MOR to the aluminosilicate gel mixture obtained in step (2) to obtain the initial gel; (4) The initial gel obtained in step (3) is crystallized by hydrothermal reaction and then calcined to remove the template agent, thus obtaining a blocky self-forming MOR molecular sieve adsorbent.

2. The application as described in claim 1, characterized in that, The rare earth metal is Ce, Sm, or La.

3. The application as described in claim 1, characterized in that, The hydrothermal reaction is carried out at a temperature of 160~190 ℃ for a time of at least 48 h.

4. The application as described in claim 1, characterized in that, The calcination temperature is 500~700 ℃, and the time is 4~12 h.

5. The application as described in claim 1, characterized in that, The template agent is 4-methylpiperidine, hexamethyleneimine, pyrrole, or tetraethylammonium hydroxide.

Images