Preparation of transition metal doped mor zeolite molecular sieve adsorbents and their use in separating nitrogen / methane

Abstract

The present application relates to the technical field of separation materials, and relates to in-situ preparation of a transition metal doped MOR zeolite molecular sieve adsorbent and application of the adsorbent in separation of nitrogen / methane, wherein sodium hydroxide and sodium metaaluminate are added into water, stirred to completely dissolve, and a solution A is obtained; anhydrous oxalic acid and a cobalt salt, a nickel salt, a copper salt or a zinc salt are added into water, stirred to obtain a solution B; the solution B is added into the solution A, stirred to obtain a mixed solution; then, silicon sol is added dropwise under stirring at room temperature, and after stirring for a certain time at room temperature, the mixed solution is transferred to a reaction kettle, and a crystallization reaction is carried out in a homogeneous phase reactor; after a certain time, the reaction kettle is taken out, cooled to room temperature, centrifuged, washed and dried, and then high-temperature calcination is carried out, so as to obtain the transition metal doped MOR zeolite molecular sieve adsorbent. The metal components introduced in the present application precisely control the pore of the adsorbent, and solve the problem that the adsorption capacity and selectivity of the zeolite molecular sieve are difficult to be considered simultaneously.

Description

Technical Field

[0001] This invention relates to the field of separation materials technology, specifically to the preparation of a transition metal-doped MOR zeolite molecular sieve adsorbent and its application in the separation of nitrogen / methane. Background Technology

[0002] Separating methane (CH4) and nitrogen (N2) is a significant challenge in natural gas purification, especially for removing trace amounts of N2. Currently, cryogenic distillation at approximately 100 K is commercially available for N2 removal, but this method is extremely energy-intensive. Pressure swing adsorption (PSA) technology, with its low energy consumption and simple process, is the most suitable technology for widespread CH4 purification from natural gas. Its core lies in developing highly efficient physical adsorbent materials. Zeolite molecular sieves possess high thermal / hydrothermal stability and low cost, leading to large-scale industrial applications in adsorption separation and offering unparalleled industrial advantages compared to other materials. Since the main component of natural gas reservoirs is CH4, comprising 80-90% of the gas, with only a small amount of nitrogen (<5%), constructing N2-selective adsorbents that preferentially adsorb N2 and directly purify CH4 can improve CH4 utilization and reduce compression energy consumption during subsequent liquefaction processes by utilizing residual adsorption pressure. However, compared to CH4, N2 has lower polarizability. For most zeolite molecular sieves, the equilibrium adsorption capacity of CH4 is greater than that of N2, making it a CH4-selective adsorbent. To date, only a few zeolite molecular sieve materials have been reported for the selective separation of N2 / CH4. Since the kinetic diameters of N2 (3.64 Å) and CH4 (3.80 Å) differ by 0.2 Å, in principle, N2 / CH4 separation can be achieved through kinetic separation or size sieving effects. However, achieving such sub-angstrom pore size tuning is extremely difficult in practice. Currently, zeolites that selectively adsorb N2 include clinoptilolite (Na, Ca, and Ag types), K-CHA, K-ZSM-25, Sr-ETS-4, and Ba-ETS-4. Studies by Kouvelos et al. have shown that parent clinoptilolite and sodium-type clinoptilolite (obtained via ion exchange) are CH4-selective adsorbents at 298 K; at 273 K, they transform into N2-selective adsorbents, but the selectivity of both is less than 3.5. The adsorption and separation capacity of K-ZSM-25 for N2 and CH4 varies relatively greatly with temperature. At a lower temperature of 253 K, it exhibits a high N2 / CH4 separation ratio (34), with an N2 adsorption capacity of 0.41 mmol / g. As the adsorption temperature increases, the N2 adsorption capacity and N2 / CH4 selectivity decrease significantly, reaching 0.15 mmol / g and 3.9 mmol / g, respectively, at room temperature. The above findings indicate that, in the process of natural gas enrichment and purification, the adsorption capacity and selectivity of these zeolite materials are still insufficient to meet the requirements for efficient separation of N2 from CH4. Summary of the Invention

[0003] This invention addresses the challenge of current zeolite materials' limited adsorption capacity and selectivity for efficient N2 separation from CH4. It provides a method for preparing a transition metal-doped MOR zeolite molecular sieve (mordenite) adsorbent and its application in nitrogen / methane separation. Based on the significant molecular shape / morphology difference between N2 and CH4 (N2 is linear, while CH4 is tetrahedral), this invention utilizes the smaller radius of transition metal ions. By introducing transition metals in situ, the pore size of the adsorbent is precisely controlled, allowing only smaller nitrogen molecules to enter the pores while blocking larger methane molecules, thus achieving ultra-high separation selectivity. To also ensure high adsorption capacity, a large-pore-volume 12-membered ring MOR zeolite molecular sieve is chosen as the research object. This invention aims to provide a method for in-situ synthesis of transition metal-doped MOR zeolite molecular sieve adsorbents with excellent performance in nitrogen / methane separation.

[0004] This invention is achieved through the following technical solution: a method for preparing a transition metal-doped MOR zeolite molecular sieve adsorbent, comprising the following steps: S1: Add sodium hydroxide and sodium aluminate to water and stir until completely dissolved to obtain solution A; S2: Add anhydrous oxalic acid and cobalt, nickel, copper or zinc salts to water and stir to obtain solution B; S3: Add solution B to solution A and stir to obtain a mixture; then add silica sol dropwise under stirring at room temperature, stir at room temperature for a certain time, transfer to a reaction vessel, carry out crystallization reaction in a homogeneous reactor, take it out after a certain time, cool to room temperature, centrifuge, wash, dry, and then calcine at high temperature to obtain transition metal-doped MOR zeolite molecular sieve adsorbent.

[0005] As a further improvement to the preparation method of the present invention, the molar ratio of SiO2, Al2O3, Na2O, MeO, oxalic acid, and H2O in solution A, solution B, and silica sol is 10:1:2:0.5:0.25:220; and the MeO is CoO, NiO, CuO, or ZnO.

[0006] As a further improvement to the preparation method of the present invention, in step S3, the stirring time at room temperature is 10-12 h.

[0007] As a further improvement to the preparation method of the present invention, the crystallization reaction takes 24-72 hours and the temperature is 150-200℃.

[0008] As a further improvement to the preparation method of the present invention, the high-temperature calcination time is 4-8 hours and the temperature is not lower than 550℃.

[0009] As a further improvement to the preparation method of the present invention, the rotation speed of the homogeneous reactor is 60 rpm.

[0010] The present invention further provides a method for preparing a transition metal-doped MOR zeolite molecular sieve adsorbent, and the application of the obtained transition metal-doped MOR zeolite molecular sieve adsorbent as a nitrogen selective adsorbent.

[0011] The present invention further provides a method for preparing a transition metal-doped MOR zeolite molecular sieve adsorbent and the application of the obtained transition metal-doped MOR zeolite molecular sieve adsorbent in the adsorption and separation of N2 / CH4.

[0012] As a further improvement to the application technology of the present invention, the transition metal-doped MOR zeolite molecular sieve adsorbent preferentially adsorbs N2 in a mixture of N2 and CH4.

[0013] The technical solution provided by this invention has the following advantages compared with the prior art: The in-situ synthesis method of this invention produces transition metal-doped MOR zeolite adsorbents that achieve N2 / CH4 adsorption reversal. The introduced transition metal component precisely controls the pore structure of the adsorbent, with the best adsorbent exhibiting the highest N2 adsorption capacity (among all reported zeolite materials) and the highest N2 / CH4 adsorption selectivity (among all reported materials), solving the common problem of balancing adsorption capacity and selectivity in zeolite molecular sieves. The adsorbents of this invention can be applied to nitrogen / methane separation operations in fixed-bed and simulated moving-bed environments. Attached Figure Description

[0014] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0016] Figure 1The figures show the X-ray diffraction patterns obtained from the synthesis of the MOR zeolite molecular sieves in Examples 1 to 4 of this invention. As can be seen from the figures, the positions and relative intensities of the diffraction peaks of the transition metal-doped MOR zeolite molecular sieves synthesized in Examples 1 to 4 are consistent with those in existing literature, proving that the MOR zeolite molecular sieves prepared in these examples are indeed MOR zeolite molecular sieves.

[0017] Figure 2 The figures show the X-ray diffraction patterns of the MOR zeolite molecular sieves synthesized in Comparative Examples 1 to 3 of this invention. As can be seen from the figures, the positions and relative intensities of the diffraction peaks of the MOR zeolite molecular sieves synthesized in Comparative Examples 1 to 3 are consistent with those in existing literature, proving that the comparative examples prepared are indeed MOR zeolite molecular sieves.

[0018] Figure 3 The figure shows the adsorption isotherms of CH4 and N2 of the MOR-Na zeolite molecular sieve synthesized in Comparative Example 1 of this invention at 25 °C. From the figure, we can see that the MOR-Na material adsorbs more CH4 than N2, preferentially adsorbing methane, making it a selective adsorbent for methane.

[0019] Figure 4 The figure shows the adsorption isotherms of CH4 and N2 of the MOR-Cu-Ex zeolite molecular sieve synthesized in Comparative Example 2 of this invention at 25 °C. From the figure, we can see that the CH4 adsorption capacity of the MOR-Cu-Ex material is also higher than that of N2, preferentially adsorbing methane, making it a methane-selective adsorbent.

[0020] Figure 5 The figure shows the adsorption isotherms of CH4 and N2 of the MOR-Cu-Im zeolite molecular sieve obtained by the comparative synthesis of the present invention at 25 °C. From the figure, we can see that the CH4 adsorption capacity of the MOR-Cu-Im material is slightly higher than that of N2, preferentially adsorbing methane, making it a methane-selective adsorbent.

[0021] Figure 6 The figures show the adsorption isotherms of CH4 and N2 of the transition metal-doped MOR zeolite molecular sieves synthesized in Examples 1 to 4 of this invention at 25 °C. As can be seen from the figures, the CH4 adsorption capacity of all transition metal-doped MOR zeolite molecular sieves is lower than that of N2, indicating preferential adsorption of nitrogen gas, making them nitrogen-selective adsorbents. Compared to the three samples in the comparative examples, the gas adsorption performance of the transition metal-doped MOR zeolite molecular sieves synthesized in Examples 1 to 4 exhibits a reversal; among them, the nitrogen adsorption capacity of MOR-Ni is as high as 17.6 cm⁻¹. 3 / g, this value exceeds that of all nitrogen-selective zeolite adsorbents reported to date. The nitrogen adsorption capacities of the three samples, MOR-Co, MOR-Cu, and MOR-Zn, are also around 15 cm⁻¹. 3 Approximately / g.

[0022] Figure 7 The bar chart shows the N2 / CH4 or CH4 / N2 adsorption ratio of the adsorbents synthesized in all embodiments and comparative examples of the present invention at 25 °C (adsorption ratio: defined as the ratio of the adsorbed amounts of N2 and CH4 in a single-component adsorption isotherm at 25 °C and 1 bar). From the figure, we can see that the MOR-Cu adsorbent has the highest N2 / CH4 adsorption ratio of 62.1. Detailed Implementation

[0023] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0024] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0025] This invention provides a specific embodiment of a method for preparing a transition metal-doped MOR zeolite molecular sieve adsorbent, comprising the following steps: S1: Add sodium hydroxide and sodium aluminate to water and stir until completely dissolved to obtain solution A; S2: Add anhydrous oxalic acid and cobalt, nickel, copper or zinc salts to water and stir to obtain solution B; S3: Add solution B to solution A and stir to obtain a mixture; then add silica sol dropwise under stirring at room temperature, stir at room temperature for a certain time, transfer to a reaction vessel, carry out crystallization reaction in a homogeneous reactor, take it out after a certain time, cool to room temperature, centrifuge, wash, dry, and then calcine at high temperature to obtain transition metal-doped MOR zeolite molecular sieve adsorbent.

[0026] In one embodiment of the present invention, the molar ratio of SiO2, Al2O3, Na2O, MeO, oxalic acid, and H2O in solution A, solution B, and silica sol is 10:1:2:0.5:0.25:220; and the MeO is CoO, NiO, CuO, or ZnO.

[0027] In another embodiment of the present invention, in step S3, the stirring time at room temperature is 10-12 hours. Furthermore, in the present invention, the stirring time after solution B is added to solution A is preferably at least 30 minutes.

[0028] In one embodiment of the present invention, the crystallization reaction takes 24-72 hours and is carried out at a temperature of 150-200°C. Preferably, the homogeneous reactor rotates at a speed of 60 rpm.

[0029] In another embodiment of the present invention, the high-temperature calcination time is 4-8 hours, and the temperature is not lower than 550°C. Furthermore, the high-temperature calcination in the present invention is carried out in an air atmosphere.

[0030] The present invention further provides the application of the transition metal-doped MOR zeolite molecular sieve adsorbent prepared by the above-mentioned method as a nitrogen selective adsorbent.

[0031] Specifically, the present invention also provides the application of the transition metal-doped MOR zeolite molecular sieve adsorbent prepared by the above-mentioned method for preparing the transition metal-doped MOR zeolite molecular sieve adsorbent in the adsorption and separation of N2 / CH4.

[0032] Furthermore, the transition metal-doped MOR zeolite molecular sieve adsorbent preferentially adsorbs N2 in a mixture of N2 and CH4.

[0033] The specific embodiments of the present invention will be described in detail below. Example 1

[0034] A method for preparing a cobalt-doped MOR zeolite molecular sieve adsorbent for efficient separation of nitrogen / methane, comprising the following steps: (1) According to the molar ratio of 10 SiO2: 1 Al2O3: 2 Na2O: 0.5 CoO: 0.25 oxalic acid: 220 H2O, 7 ml of distilled water was added to a beaker, followed by 0.253 g of sodium hydroxide and 0.497 g of sodium aluminate. The mixture was stirred for 10 minutes to completely dissolve the solution, thus obtaining solution A. (2) Transfer 5 ml of distilled water into a beaker, then add 0.069 g of anhydrous oxalic acid and 0.364 g of cobalt chloride hexahydrate, stir for 30 minutes to obtain solution B; (3) Add solution B obtained in step (2) dropwise to solution A in step (1) and stir for 30 minutes; (4) Under vigorous stirring, 3.5 ml of silica sol was added dropwise to the mixture obtained in step (3), stirred at room temperature for 12 hours, then transferred to a polytetrafluoroethylene liner, loaded into a stainless steel reactor, and crystallized in a homogeneous reactor at 190 °C for 24 hours at 60 rpm. After cooling to room temperature, the product was washed 5 times by centrifugation with deionized water, dried overnight in an oven at 80 °C, and then calcined at 550 °C for 6 hours to obtain the target product (MOR-Co). Example 2

[0035] A method for preparing a nickel-doped MOR zeolite molecular sieve adsorbent for efficient separation of nitrogen / methane, comprising the following steps: (1) According to the molar ratio of 10 SiO2: 1 Al2O3: 2 Na2O: 0.5 NiO: 0.25 oxalic acid: 220 H2O, 7 ml of distilled water was added to a beaker, followed by 0.253 g of sodium hydroxide and 0.497 g of sodium aluminate. The mixture was stirred for 10 minutes to completely dissolve the solution, thus obtaining solution A. (2) Transfer 5 ml of distilled water into a beaker, then add 0.069 g of anhydrous oxalic acid and 0.364 g of nickel chloride hexahydrate, stir for 30 minutes to obtain solution B; (3) Add solution B obtained in step (2) dropwise to solution A in step (1) and stir for 30 minutes; (4) Under vigorous stirring, 3.5 ml of silica sol was added dropwise to the mixture obtained in step (3), stirred at room temperature for 12 hours, then transferred to a polytetrafluoroethylene liner, loaded into a stainless steel reactor, and crystallized in a homogeneous reactor at 190 °C for 24 hours at 60 rpm. After cooling to room temperature, the mixture was washed 5 times by centrifugation with deionized water, dried overnight in an oven at 80 °C, and then calcined at 550 °C for 6 hours to obtain the target product (MOR-Ni). Example 3

[0036] A method for preparing a copper-doped MOR zeolite molecular sieve adsorbent for efficient separation of nitrogen / methane, comprising the following steps: (1) According to the molar ratio of 10 SiO2: 1 Al2O3: 2 Na2O: 0.5 CuO: 0.25 oxalic acid: 220 H2O, 7 ml of distilled water was added to a beaker, followed by 0.253 g of sodium hydroxide and 0.497 g of sodium aluminate. The mixture was stirred for 10 minutes to completely dissolve the solution, thus obtaining solution A. (2) Transfer 5 ml of distilled water into a beaker, then add 0.069 g of anhydrous oxalic acid and 0.261 g of copper chloride dihydrate, stir for 30 minutes to obtain emulsion B; (3) Add the emulsion B obtained in step (2) dropwise to the solution A in step (1) and stir for 30 minutes; (4) Under vigorous stirring, 3.5 ml of silica sol was added dropwise to the mixture obtained in step (3), stirred at room temperature for 12 hours, then transferred to a polytetrafluoroethylene liner, loaded into a stainless steel reactor, and crystallized in a homogeneous reactor at 190 °C for 24 hours at 60 rpm. After cooling to room temperature, the mixture was washed 5 times by centrifugation with deionized water, dried overnight in an oven at 80 °C, and then calcined at 550 °C for 6 hours to obtain the target product (MOR-Cu). Example 4

[0037] A method for preparing a zinc-doped MOR zeolite molecular sieve adsorbent for efficient separation of nitrogen / methane, comprising the following steps: (1) According to the molar ratio of 10 SiO2: 1 Al2O3: 2 Na2O: 0.5 ZnO: 0.25 oxalic acid: 220 H2O, 7 ml of distilled water was added to a beaker, followed by 0.253 g of sodium hydroxide and 0.497 g of sodium aluminate. The mixture was stirred for 10 minutes to completely dissolve the solution, thus obtaining solution A. (2) Transfer 5 ml of distilled water into a beaker, then add 0.069 g of anhydrous oxalic acid and 0.209 g of anhydrous zinc chloride, stir for 30 minutes to obtain solution B; (3) Add solution B obtained in step (2) dropwise to solution A in step (1) and stir for 30 minutes; (4) Under vigorous stirring, 3.5 ml of silica sol was added dropwise to the mixture obtained in step (3), stirred at room temperature for 12 hours, then transferred to a polytetrafluoroethylene liner, loaded into a stainless steel reactor, and crystallized in a homogeneous reactor at 190 °C for 24 hours at 60 rpm. After cooling to room temperature, the mixture was washed 5 times by centrifugation with deionized water, dried overnight in an oven at 80 °C, and then calcined at 550 °C for 6 hours to obtain the target product (MOR-Zn). Comparative Example 1

[0038] References (Hyun June Choi and Suk Bong Hong, Chem. Eng. J. The method used to synthesize conventional sodium-based MOR zeolites with a balanced cation (2022, 433,133800.) is as follows: (1) According to the molar ratio of 10 SiO2: 1 Al2O3: 2 Na2O: 220 H2O, transfer 12 ml of distilled water into a beaker, then add 0.253 g of sodium hydroxide and 0.497 g of sodium aluminate, stir for 10 minutes to dissolve completely; (2) Under vigorous stirring, 3.5 ml of silica sol was added dropwise to the mixture obtained in step (1), stirred at room temperature for 12 hours, then transferred to a polytetrafluoroethylene liner, loaded into a stainless steel reactor, and crystallized in a homogeneous reactor at 150 °C for 72 hours at 60 rpm. After cooling to room temperature, the product was washed 5 times by centrifugation with deionized water and dried overnight in an oven at 80 °C to obtain the target product (MOR-Na). Comparative Example 2

[0039] The steps for synthesizing Cu-MOR zeolite by copper ion exchange are as follows: 1.5 g of the MOR-Na synthesized in Comparative Example 1 was subjected to ion exchange with an aqueous solution of copper chloride dihydrate (0.3 mol / L, 40 ml) at 70 °C and stirred for 3 hours. The solid was recovered by centrifugation, washed three times with deionized water, and dried overnight in an oven at 80 °C to obtain the target product (MOR-Cu-Ex). Comparative Example 3

[0040] The steps for wet impregnation synthesis of Cu-MOR zeolite are as follows: 1.5 g of the MOR-Na synthesized in Comparative Example 1 was mixed with an aqueous solution of copper chloride dihydrate (0.3 mol / L, 40 ml) and stirred at room temperature for 10 hours. The solid was recovered by centrifugation, washed three times with deionized water, and dried overnight in an oven at 80 °C to obtain the target product (MOR-Cu-Im).

[0041] Test case

[0042] Single-component gas adsorption test The CH4 and N2 adsorption isotherms at 25 °C for all samples from the above examples and comparative examples were measured using a Micromeritics ASAP 2460 instrument. 120 mg of adsorbent was loaded into each sample tube, and each sample was degassed under vacuum at 250 °C for 5–10 h prior to testing. The purities of CH4 and N2 used were 99.99% and 99.999%, respectively. The obtained adsorption isotherm data are attached. Figure 3-6 As shown in the image.

[0043] Based on the appendix Figure 3-6 Based on the adsorption isotherm data, we calculated the adsorption ratio of each adsorbent for N2 / CH4 or CH4 / N2 at 25℃, as shown in the attached bar chart. Figure 7 As shown.

[0044] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the present invention. Although detailed descriptions have been provided with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments, and all should be covered by the protection scope of the claims.

Claims

1. The application of a transition metal-doped MOR zeolite molecular sieve adsorbent as a nitrogen selective adsorbent, wherein the preparation method of the adsorbent includes the following steps: S1: Add sodium hydroxide and sodium aluminate to water and stir until completely dissolved to obtain solution A; S2: Add anhydrous oxalic acid and cobalt, nickel, copper or zinc salts to water and stir to obtain solution B; S3: Add solution B to solution A and stir to obtain a mixture; then add silica sol dropwise under stirring at room temperature, stir at room temperature for a certain time and then transfer to a reaction vessel to carry out crystallization reaction in a homogeneous reactor. After a certain time, take it out and cool it to room temperature, centrifuge, wash and dry it, and then calcine it at high temperature to obtain metal-doped MOR zeolite molecular sieve adsorbent. The molar ratio of SiO2, Al2O3, Na2O, MeO, oxalic acid, and H2O in solutions A, B, and the silica sol is 10:1:2:0.5:0.25:220; the MeO is CoO, NiO, CuO, or ZnO.

2. The application as described in claim 1, characterized in that, In step S3, the stirring time at room temperature is 10-12 hours.

3. The application as described in claim 1, characterized in that, The crystallization reaction takes 24-72 hours and is carried out at a temperature of 150-200℃.

4. The application as described in claim 1, characterized in that, The high-temperature roasting time is 4-8 hours, and the temperature is not lower than 550℃.

5. The application as described in claim 1, characterized in that, The homogeneous reactor rotates at a speed of 60 revolutions per minute.

6. The application as described in claim 1, characterized in that, The metal-doped MOR zeolite molecular sieve adsorbent is used in the adsorption and separation of N2 / CH4.

7. The application as described in claim 6, characterized in that, The transition metal-doped MOR zeolite molecular sieve adsorbent preferentially adsorbs N2 in a mixture of N2 and CH4.

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