A bimetallic zif-8 adsorbent, its preparation method and application thereof

Abstract

The application provides a bimetallic ZIF-8 adsorbent, a preparation method and application thereof, and the preparation method of the bimetallic ZIF-8 adsorbent is that a zinc metal precursor, a cobalt metal precursor and 2-methyl imidazole are fully ball-milled and uniformly mixed in a molar ratio of 1:(0.1-0.9):(2-10), then the uniformly mixed material is put into a reaction kettle, and is reacted at 120-200 DEG C, and then the product after reaction is calcined under air isolation conditions, so that the bimetallic ZIF-8 product is obtained. The preparation method of the bimetallic ZIF-8 adsorbent is simple in process, free of pollution and friendly to the environment. The bimetallic ZIF-8 adsorbent has a large specific surface area and pore volume, is used for separating single branched-chain and double branched-chain (multi branched-chain) alkanes from a C6-C10 isomeric alkane mixture, has a large adsorption amount of single branched-chain alkanes, and can efficiently separate single branched-chain / double branched-chain (multi branched-chain) alkanes.

Description

Technical Field

[0001] This invention belongs to the field of porous adsorption materials, specifically relating to a bimetallic ZIF-8 adsorbent, its preparation method and its application. Background Technology

[0002] To produce high-octane gasoline, current industrial plants use catalytic isomerization to convert straight-chain alkanes in an alkane mixture into branched-chain alkanes. However, the thermodynamic equilibrium of the isomerization reaction limits the conversion rate, resulting in the presence of unreacted straight-chain alkanes and low-octane monobranched alkanes in the products. Industrially, 5A molecular sieves can separate normal and isoalkanes, but cannot separate monobranched alkanes from isoalkanes to obtain higher-octane dibranched and multibranched alkanes. Therefore, to further improve the octane number of gasoline and achieve refined separation of monobranched / dibranched (multibranched) alkanes, novel adsorption separation materials need to be developed.

[0003] Metal-organic frameworks (MOFs), as porous materials formed by the coordination of metals and organic ligands, have become the most actively researched and fruitful adsorbent materials in the field of alkane purification due to their rich variety, tunable pore structure, and modifiable pore surface, showing promising development prospects. Herm et al. [Herm ZR, Wiers BM, Mason JA, et al. Separation of hexane isomers in a metal-organic framework with triangular channels[J]. Science, 2013, 340(6135): 960-964.] synthesized a MOF material (Fe2(BDP)3) with one-dimensional triangular channels by solvent method. Fe2(BDP)3 effectively separated single-branched and double-branched alkanes based on thermodynamic mechanisms. However, the adsorption affinity between single-branched and double-branched alkanes was not significantly different, resulting in low separation selectivity. CN111450804A proposes the preparation of an aluminum-based metal-organic framework material with a pore size of 0.56 nm in N,N-dimethylformamide solvent, which can achieve the adsorption and separation of 3-methylpentane and 2,2-dimethylbutane. However, due to diffusion control limitations, the dynamic adsorption capacity of 3-methylpentane is only 30% of the static adsorption capacity. Therefore, it is evident that currently, all MOF adsorbents suitable for the adsorption and separation of single-branched / double-branched (multi-branched) alkanes require solvent synthesis, resulting in large solvent consumption, which is inconsistent with the concept of green and environmentally friendly development. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a bimetallic ZIF-8 adsorbent, its preparation method, and its applications.

[0005] The technical solution of this invention is as follows: A method for preparing a bimetallic ZIF-8 adsorbent involves thoroughly ball-milling a zinc metal precursor, a cobalt metal precursor, and 2-methylimidazole in a molar ratio of 1:(0.1-0.9):(2-10). The homogeneous mixture is then placed in a reaction vessel and reacted at 120-200°C. The resulting product is then calcined under air-free conditions to obtain the bimetallic ZIF-8 product. This method provides a solvent-free preparation of bimetallic ZIF-8 material, is simple, pollution-free, and environmentally friendly.

[0006] As a further improvement to the technical solution, the zinc metal precursor is one or a mixture of two of zinc oxide, zinc hydroxide, basic zinc carbonate, and zinc acetate.

[0007] As a further improvement to the technical solution, the cobalt metal precursor is one or a mixture of two of cobalt oxide, cobalt hydroxide, cobalt carbonate, and cobalt oxalate.

[0008] As a further improvement to the technical solution, in order to ensure uniform ball milling, the ball milling speed is 500-1000 rpm and the ball milling time is 5-60 min.

[0009] As a further improvement to the technical solution, in order to ensure a full reaction and take into account reaction efficiency, the reaction time is 4-72 hours.

[0010] As a further improvement to the technical solution, in order to remove 2-methylimidazole without damaging the crystal structure of the adsorbent, the calcination temperature is 250-350℃.

[0011] The present invention also discloses a bimetallic ZIF-8 adsorbent prepared by the above preparation method, which has uniform crystal image, high thermal stability, and large specific surface area and pore volume.

[0012] As a further improvement to the technical solution, the specific surface area of ​​the bimetallic ZIF-8 adsorbent is 1800–2200 m². 2 / g, pore volume 0.60~0.75 cm³ 3 / g.

[0013] This invention also discloses an application of the bimetallic ZIF-8 adsorbent, in which a mixture of C5-C10 isoalkanes containing monobranched alkanes is vaporized and then adsorbed by the bimetallic ZIF-8 adsorbent at an adsorption temperature of 100–200°C and an adsorption pressure of 0–0.5 MPa. The principle of separating isoalkanes mixtures is that the adsorbent has a greater adsorption capacity or stronger adsorption force for monobranched alkanes in the mixture. During the adsorption separation process, monobranched alkanes are preferentially adsorbed. The bimetallic organic framework material has a large specific surface area and pore volume, resulting in a large adsorption capacity for monobranched alkanes, enabling efficient separation of monobranched / dibranched (multibranched) alkanes.

[0014] As a further improvement to the technical solution, the single-branched alkane is one or more selected from 2-methylbutane, 3-methylpentane, 3-methylhexane, 2-methylheptane, 2-methyloctane, and 2-methylnonane.

[0015] As a further improvement to the technical solution, the mass percentage of monobranched alkanes in the mixture is 20%-80%.

[0016] This invention represents a significant advancement over existing technologies, possessing substantial advantages. Specifically, the method employed in this invention utilizes a solid-state synthesis approach to synthesize bimetallic MOF materials. The synthesized bimetallic ZIF-8 material exhibits uniform crystal structure and high thermal stability. Furthermore, the solid-state synthesis of bimetallic ZIF-8 materials under solvent-free conditions is simple, pollution-free, and environmentally friendly. Moreover, the adsorbent of this invention possesses a large specific surface area and pore volume, exhibiting strong adsorption capacity for single-branched alkanes and significantly improving adsorption and separation performance. Attached Figure Description

[0017] Figure 1 The XRD patterns of bimetallic ZIF-8 in Examples 1-4 are shown.

[0018] Figure 2 The image shows the TG-DTA curve of bimetallic ZIF-8 in Example 1.

[0019] Figure 3 This is a graph showing the relationship between the relative content of single and double branched isoalkanes at the outlet of the adsorption tower in Example 1 and the change over time. Detailed Implementation

[0020] The technical solution of the present invention will be further described in detail below through specific embodiments.

[0021] Example 1 Zinc oxide, cobalt oxide, and 2-methylimidazole were mixed in a molar ratio of 1:0.2:2 and ball-milled at 500 rpm for 10 minutes. The ball-milled product was loaded into a reaction vessel and reacted at 140°C for 12 hours to obtain a white solid. The white reaction product was then calcined in a tube furnace under a nitrogen atmosphere for 2 hours at 250°C to obtain the bimetallic ZIF-8 adsorbent. The specific surface area of ​​the bimetallic ZIF-8 was determined to be 1856 m² using a nitrogen adsorption analyzer. 2 / g, pore volume 0.63 cm³ 3 / g.

[0022] The TG-DTA curve of bimetallic ZIF-8 was determined using a WCT-1 thermal analyzer, as shown below. Figure 2 As shown. By Figure 2 It is known that ZIF-8 can remain stable up to 350℃.

[0023] 100g of bimetallic ZIF-8 adsorbent was loaded into an adsorption tower with a height-to-diameter ratio of 5. The raw material consisted of a C5-C10 isoalkanes mixture with 80wt% 3-methylpentane content, and the remaining components were branched isoalkanes. After vaporization at 150℃, the mixture entered from the bottom of the adsorption tower. The adsorption temperature was 120℃, and the adsorption pressure was 0.1MPa. Figure 3 As shown, the content of single and double branched isoalkanes at the outlet of the adsorption tower was determined by gas chromatography. In this embodiment, C6-C10 double branched alkanes at the outlet of the adsorption tower broke through in 2 minutes, while 3-methylpentane broke through after 50 minutes. A mixture of isoalkanes with high octane number can be obtained between 2 and 50 minutes of adsorption time.

[0024] Example 2 The difference between this embodiment and Example 1 is as follows: 1. Zinc oxide, basic zinc carbonate, cobalt oxide, and 2-methylimidazole are mixed in a molar ratio of 0.5:0.5:0.9:10 to prepare the bimetallic ZIF-8 adsorbent. The specific surface area of ​​the bimetallic ZIF-8 was determined to be 1970 m² using a nitrogen adsorption analyzer. 2 / g, pore volume 0.67cm 3 / g.

[0025] 2. The bimetallic ZIF-8 adsorbent was applied to the separation of a mixture of isoalkanes containing 60 wt% 2-methyloctane.

[0026] At the outlet of the adsorption tower, C5-C10 bibranched alkanes penetrated in 1.5 minutes, while 2-methyloctane penetrated after 55 minutes. A mixture of isoparaffins with high octane numbers can be obtained within an adsorption time of 1.5 to 55 minutes.

[0027] Example 3 The difference between this embodiment and Example 1 is that: 1. The bimetallic ZIF-8 adsorbent was prepared at a reaction temperature of 200℃ and a reaction time of 4 hours. The specific surface area of ​​the bimetallic ZIF-8 was determined to be 2056 m² using a nitrogen adsorption analyzer. 2 / g, pore volume 0.69cm 3 / g.

[0028] 2. The bimetallic ZIF-8 adsorbent was applied to the separation of isoalkanes containing 40 wt% 2-methylhexane.

[0029] At the outlet of the adsorption tower, C5-C10 bibranched alkanes penetrate in 1 minute, while 2-methylhexane penetrates after 65 minutes. A mixture of isoparaffins with high octane number can be obtained between 1 and 65 minutes of adsorption time.

[0030] Example 4 The difference between this embodiment and Example 1 is as follows: 1. Zinc oxide, cobalt oxide, and 2-methylimidazole were mixed in a molar ratio of 1:0.4:4 and reacted at 160°C to prepare the bimetallic ZIF-8 adsorbent. The specific surface area of ​​the bimetallic ZIF-8 was determined to be 2078 m² using a nitrogen adsorption analyzer. 2 / g, pore volume 0.70 cm³ 3 / g.

[0031] 2. The bimetallic ZIF-8 adsorbent was applied to the separation of isoalkanes containing 20 wt% 2-methylnonane.

[0032] C5-C10 bibranched alkanes penetrate at the adsorption tower outlet in 1 minute, while 2-methylnonane penetrates after 70 minutes. A mixture of isoparaffins with high octane number can be obtained between 1 and 70 minutes of adsorption time.

[0033] The XRD patterns of the bimetallic ZIF-8 adsorbents prepared in Examples 1-4 were determined using a D8 DVANCE X-ray powder polycrystalline diffractometer. Figure 1 As shown. By Figure 1 It can be seen that the adsorbents prepared in Examples 1-4 have peaks at diffraction angles of 7.3°, 12.8°, 16.4° and 18.1°, which are consistent with the characteristic peaks of ZIF-8.

[0034] The TG-DTA curve of the bimetallic ZIF-8 prepared in Example 1 was determined using a WCT-1 thermal analyzer as follows: Figure 2 As shown. By Figure 2 It is known that ZIF-8 can remain stable up to 350℃.

[0035] Comparative Example 1 The difference between this embodiment and Example 1 is that the raw materials were reacted in a molar ratio of zinc oxide:cobalt oxide:2-methylimidazolium of 1:0.05:8. A white powder was synthesized, and X-ray powder diffraction using a D8 DVANCE type X-ray powder diffractometer revealed no ZIF-8 characteristic peaks. Acid hydrolysis of the white powder and ICP analysis of its elemental content revealed that the structure mainly consisted of zinc, with no cobalt present.

[0036] Comparative Example 2 The difference between this embodiment and Example 1 is that the raw materials were reacted with zinc oxide:cobalt oxide:2-methylimidazole in a molar ratio of 1:0.2:15. A white powder was synthesized, and X-ray powder diffraction using a D8 DVANCE type X-ray powder diffractometer revealed that the peak position of the product was consistent with that of 2-methylimidazole, indicating that ZIF-8 adsorbent was not synthesized.

[0037] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A method for preparing a bimetallic ZIF-8 adsorbent, characterized in that, Zinc metal precursor, cobalt metal precursor and 2-methylimidazole with a molar ratio of 1:(0.1~0.9):(2~10) are thoroughly ball-milled and mixed evenly. Then the evenly mixed material is put into a reaction vessel and reacted at 120~200℃. The product after reaction is then calcined under air-isolated conditions to obtain the bimetallic ZIF-8 product. The ball milling speed is 500-1000 rpm, and the ball milling time is 5-60 min; The reaction time is 4–72 h; The roasting temperature is 250–350°C.

2. The preparation method according to claim 1, characterized in that, The zinc metal precursor is one or more of zinc oxide, zinc hydroxide, basic zinc carbonate, and zinc acetate.

3. The preparation method according to claim 1, characterized in that, The cobalt metal precursor is one or a mixture of two of cobalt oxide, cobalt hydroxide, cobalt carbonate, and cobalt oxalate.

4. A bimetallic ZIF-8 adsorbent, characterized in that, It is prepared by the method shown in any one of claims 1 to 3.

5. The bimetallic ZIF-8 adsorbent according to claim 4, characterized in that, The bimetallic ZIF-8 adsorbent has a specific surface area of ​​1800-2200 m2 / g and a pore volume of 0.60-0.75 cm3 / g.

6. An application of the bimetallic ZIF-8 adsorbent according to claim 4, characterized in that, A mixture of C5-C10 isoalkanes containing monobranched alkanes is vaporized and then adsorbed by the bimetallic ZIF-8 at an adsorption temperature of 100-200℃ and an adsorption pressure of 0-0.5MPa.

7. The application of the bimetallic ZIF-8 adsorbent according to claim 6, characterized in that, The single-branched alkane is one or more selected from 2-methylbutane, 3-methylpentane, 3-methylhexane, 2-methylheptane, 2-methyloctane, and 2-methylnonane.

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