Molecular sieve with point screening structure, and preparation method therefor and use thereof in adsorption and separation of propylene and propane

Abstract

Disclosed in the present invention are a molecular sieve with a point screening structure, and a preparation method therefor and the use thereof in adsorption and separation of propylene and propane. The molecular sieve of the present invention is formed by bonding 1,2-ethane disulfonate anions, 4,4'-dipyridyl sulfide and Cu2+ via coordinate bond, and has a chemical formula of [MSL2]∞, wherein M represents Cu2+, S represents 1,2-ethane disulfonate anions, L represents 4,4'-dipyridyl sulfide, and ∞ denotes that the molecular sieve is formed by spatially expanding several structural units composed of MSL2; and the molecular sieve in the present invention has local point-like pore channel shrinkage. The preparation method comprises: mixing a Cu2+ source, 1,2-ethane disulfonate and 4,4'-dipyridyl sulfide in a reaction solvent for reaction to obtain the molecular sieve with a point screening structure. The present invention has the outstanding advantages of good material stability, high adsorption selectivity, high adsorption capacity, high adsorption rate, easy regeneration, etc., and has a good industrial application prospect.

Description

Molecular sieve with point screening structure, preparation method thereof and application in adsorption separation of propylene and propane Technical Field

[0001] The present invention relates to the technical field of molecular sieves and chemical separation, and in particular to a molecular sieve with a point screening structure, a preparation method thereof, and application thereof in the adsorption separation of propylene and propane. Background Art

[0002] Propylene, a cornerstone of the petrochemical industry, is one of the world's most produced chemicals. Its downstream products, including polypropylene, propylene oxide, and acrylonitrile, are widely used in various sectors of the national economy, including plastics, pharmaceuticals, textiles, and coatings. Currently, industrial propylene production primarily involves separating and preparing a mixture of low-carbon hydrocarbons from naphtha cracking. The key and technical difficulty in separating these low-carbon hydrocarbons lies in the similar molecular size and physical properties of ethylene / ethane and propylene / propane. However, the structural properties of propylene and propane are highly similar, differing only slightly in the degree of unsaturation, making propylene / propane separation difficult and energy-intensive. Currently, propylene and propane separation technologies primarily include cryogenic distillation, solvent absorption, membrane separation, and adsorption separation. Cryogenic distillation is the most mature and widely used in industry. However, due to the similar boiling points and low relative volatility of propylene and propane, separation requires relatively high pressure (~22 bar), extremely low temperatures (~160°C), and a high reflux ratio. The number of stages typically exceeds 150, resulting in high energy consumption and significant equipment investment. The solvent absorption method not only has the problem of large organic solvent pollution, but also has low selectivity; the membrane separation method is limited in industrial application due to the low selectivity of existing membranes, complex membrane manufacturing process and high cost.

[0003] As a low-energy, environmentally friendly separation technology, adsorption separation technology is suitable for the separation of structurally similar substances, such as the separation and purification of low-carbon hydrocarbon gases. However, existing adsorption materials, such as zeolite molecular sieves, activated carbon, polymers, metal organic framework materials, etc., often find it difficult to accurately identify the slight differences between propylene and propane molecules. They have the disadvantages of low separation selectivity, small adsorption capacity, poor stability, and slow adsorption rate, which restrict the feasibility of propylene / propane adsorption separation technology. For example, although 4A molecular sieve can achieve molecular sieving of propylene and propane, it has a propylene diffusion coefficient (10 -11 cm -2 s -1) is too slow, so the separation of propylene and propane can only be achieved by enhancing the diffusion of propylene at a high temperature of 150°C (Separation Science and Technology, 2010, 45: 1252-1259). As an emerging porous adsorption material, metal-organic framework materials have outstanding advantages such as large specific surface area, high pore volume, easy chemical modification of pores and precise adjustment of pore size. However, the separation performance of the π-complexation framework materials currently widely studied for mixed gas still needs to be improved. For example, Fe-MOF-74 (Science, 2012, 335 (6076): 1606-1610) has a high density of unsaturated metal sites, which can generate electrostatic effects with the π electrons of the double bond of propylene, but due to the large pore size The selectivity for propylene / propane mixtures is low. By utilizing the molecular size difference between propylene and propane, designing propylene-propane molecular sieve materials with suitable pore sizes can significantly improve the separation selectivity of propylene / propane. For example, KAUST-7 (Science, 2016, 353: 137-140) and Y-abtc (Advanced Materials, 2018, 30: 1805088) have suitable pore sizes and can adsorb smaller propylene molecules while rejecting larger propane molecules. However, current propylene-propane sieving materials face defects such as low working capacity, slow adsorption rate, and difficulty in regeneration. Therefore, the design and preparation of new porous materials that can achieve propylene-propane molecular sieving, have high propylene adsorption capacity, high propylene adsorption rate, and easy desorption and regeneration of propylene are crucial for the development of propylene and propane adsorption separation technology. Summary of the Invention

[0004] In order to solve the above technical problems and the shortcomings in the art, the present invention provides a molecular sieve with a point screening structure (which can be recorded as ZU-609), which is composed of 1,2-ethanedisulfonate anion with rigid long strip characteristics, 4,4'-dipyridyl sulfide (CAS No. 37968-97-1) with flexible and tortuous characteristics, and metal cation Cu 2+ The molecular sieve is formed by coordination bonds. A mixture containing propylene and propane is contacted with the molecular sieve, which preferentially adsorbs propylene from the mixture, thereby purifying the propylene and obtaining high-purity propylene. The present invention constructs a molecular sieve porous material ZU-609 with a point-screening structure by precisely controlling the pore size and pore shape of the molecular sieve. This allows propylene to be adsorbed in the pores with high selectivity and capacity while excluding propane from entering the pores, thereby achieving the production of high-purity propylene. The present invention has outstanding advantages such as good material stability, high adsorption selectivity, high adsorption capacity, high adsorption rate, and easy regeneration, and has good prospects for industrial application.

[0005] A molecular sieve with a point screening structure, composed of 1,2-ethanedisulfonic acid anion (organic anion), 4,4'-dipyridyl sulfide (organic ligand) and Cu 2+ (Metal cations) are connected by coordination bonds, chemical formula [MSL2] ∞ , where M represents Cu 2+ , S represents 1,2-ethanedisulfonate anion, L represents 4,4'-dipyridyl sulfide, and ∞ represents that the molecular sieve is formed by spatial expansion of several structural units consisting of MSL2;

[0006] The molecular sieve having a point screening structure has local point-shaped pore contraction (see FIG. 1 ).

[0007] In the molecular sieve structure with a point sieving structure, organic ligands are coordinated with metal cations through nitrogen atoms, and all organic ligands are di-coordinated; 1,2-ethanedisulfonate anions are coordinated with metal cations through oxygen atoms, and each 1,2-ethanedisulfonate anion is connected to two metal cations; each metal cation is connected to four different organic ligands and coordinated with two oxygen atoms at the same time.

[0008] The present invention prepares a novel molecular sieve material with a point-sieving structure by combining metal cations, organic ligands, and organic anions, enabling precise control of the pore size of the molecular sieve porous material. When propylene and propane molecules come into contact with the molecular sieve porous material ZU-609 with a point-sieving structure, because propylene has a smaller molecular size than propane, the precisely adjusted pore size allows propylene to enter the molecular sieve porous material while simultaneously preventing propane from entering the pores, thereby exhibiting excellent size-sieving properties. Furthermore, due to the structural characteristics of the molecular sieve of the present invention, the high diffusion barrier path formed by the diffusion of propylene molecules in the pores is relatively short (see Figure 3).

[0009] The 1,2-ethanedisulfonate anion of the present invention can be represented as follows:

[0010] The molecular sieve with a point screening structure of the present invention has a screening hole window cross-sectional size of Propane size exclusion can be achieved.

[0011] The flexible, bendable 4,4'-dipyridyl sulfide ligand and the rigid, elongated 1,2-ethanedisulfonate anion contribute to the construction of the molecular sieve's macroporous cavity (see Figure 2). The rigid pyridine ring on the ligand molecule creates conditions for the construction of the sieving window.

[0012] The molecular sieve of the present invention also has The large pores provide sufficient space to achieve extremely high diffusion coefficient and adsorption capacity of propylene.

[0013] Propylene can enter the pores of the molecular sieve of the present invention due to its smaller kinetic size, while propane cannot enter the pores of the molecular sieve of the present invention due to its larger kinetic size. Therefore, the molecular sieve of the present invention can achieve efficient adsorption separation of propylene / propane mixed gases.

[0014] The present invention also provides a method for preparing the molecular sieve having a point screening structure, Cu 2+ The source, 1,2-ethanedisulfonate and 4,4'-dipyridyl sulfide are mixed and reacted in a reaction solvent to obtain the molecular sieve with a point sieving structure.

[0015] The reaction solvent may be water and / or an organic solvent. The organic solvent may include methanol, etc. If the reaction solvent is water and an organic solvent, the volume ratio of water to organic solvent may be 1:1 to 5.

[0016] The Cu 2+ The source may include at least one of a chloride, a nitric acid compound, and the like.

[0017] The 1,2-ethanedisulfonate salt may include sodium 1,2-ethanedisulfonate, and the like.

[0018] In the preparation method, Cu 2+ The molar ratio of Cu 2+, 1,2-ethanedisulfonate and 4,4'-dipyridyl sulfide can be 2+ :1,2-ethanedisulfonic acid anion:4,4'-dipyridyl sulfide is 1:0.5~3:1~5.

[0019] Cu 2+ The usage ratio of the source to the reaction solvent can be 1 mol:35-45L.

[0020] In one embodiment, after the mixing reaction is completed, the solid and liquid are separated, and the solid is taken to remove the solvent molecules in the pores to obtain the molecular sieve having a point sieving structure. Furthermore, the solvent molecules in the pores can be removed by drying using vacuum desorption and / or flowing gas (N2 and / or rare gases such as He, Ar, etc.) purging.

[0021] In the method for preparing the molecular sieve with a point sieving structure, the reaction can be a solvent thermal reaction, an interface diffusion reaction during a dropwise addition process, or a direct room temperature mixing reaction.

[0022] The present invention also provides the use of the molecular sieve with the point screening structure in adsorbing propylene.

[0023] The propylene adsorption performance of ZU-609 has the following characteristics: the propylene adsorption isotherm shows a linear adsorption isotherm, which is conducive to pressure swing adsorption; the diffusion coefficient of propylene in ZU-609 at room temperature is 10.02×10 -10 cm -2 s -1 The adsorption capacity difference of ZU-609 between 0.1 bar and 1 bar is 2.0 mmol g -1 ; The propylene / propane adsorption ratio at 1 bar reaches 22.

[0024] The adsorption rate of propylene in the pores of the molecular sieve of the present invention is fast, and the molecular sieve can be operated at a high gas velocity of the propylene-propane mixture in a dynamic separation experiment.

[0025] As a general inventive concept, the present invention also provides a method for separating propylene and propane by adsorptive separation, wherein the molecular sieve having a point screening structure is used as an adsorbent and is brought into contact with a mixture containing propylene and propane. The adsorbent selectively adsorbs propylene while excluding propane, thereby achieving separation of propylene and propane.

[0026] The invention can realize efficient separation of propylene and propane under mild operating conditions, and can separate propylene gas with a purity of 97.0% to 99.99% from a mixture containing propylene and propane.

[0027] The contacting mode of the adsorbent and the mixture containing propylene and propane can be any one or more combinations of fixed bed adsorption, moving bed adsorption, and multi-tower pressure swing adsorption.

[0028] For example, the multi-tower pressure swing adsorption is described as follows:

[0029] 1) A mixed gas containing propylene and propane is pressurized by a compressor and fed into a first adsorption tower at a constant pressure for adsorption. The adsorption pressure in the first adsorption tower is controlled at 1 to 10 bar and the adsorption temperature is controlled at 25 to 40°C. Propane is directly enriched at the outlet of the first adsorption tower, and its purity is greater than 99.9%.

[0030] 2) The second adsorption tower is replaced and vacuumed, and the remaining 3, ..., n (n ≥ 3) adsorption towers are subjected to pressure equalization operation; when the adsorption of the first adsorption tower is completed, the vacuuming of the second adsorption tower is stopped, and the first adsorption tower starts to perform pressure equalization operation on the second adsorption tower;

[0031] 3) Using part of the high-purity propylene collected in the previous cycle to perform a reflux replacement operation on the first adsorption tower, the nth adsorption tower is rapidly pressurized with product gas and enters the adsorption stage;

[0032] 4) Desorbing the first adsorption tower by vacuum pumping, controlling the desorption pressure at 0-0.1 bar, and obtaining high-purity propylene at the outlet, with a purity of up to 99.5%; most of the propylene at the outlet is used as the product, and a small amount of propylene is used to complete the reflux replacement of the next cycle;

[0033] 5) Prepare to boost the pressure again for the next cycle.

[0034] For example, the fixed bed adsorption is described as follows:

[0035] a) A mixed gas containing propylene and propane enters a fixed bed adsorption column at a set flow rate under a certain adsorption temperature and pressure and contacts with a molecular sieve having a point screening structure. The adsorption temperature is -30 to 100°C, preferably 25 to 40°C, and the adsorption pressure is 0 to 10 bar, preferably 1 to 5 bar. The propane component has a slow adsorption rate and a lower adsorption amount than the propylene component. The propane component preferentially penetrates the fixed bed adsorption column, and propane gas can be directly obtained at the outlet of the adsorption column.

[0036] b) After the propane component breaks through, the feed gas is continued to be introduced for adsorption. Adsorption is continued for a certain period of time until the propylene adsorption front is no less than 2 / 3 of the bed layer, or until the propylene component breaks through. Then, the introduction of the mixed gas is stopped and desorption is carried out by one of the following methods: heating, reducing pressure, etc., or a combination of these methods. The desorption temperature is 0-40°C, preferably 30-40°C, and the desorption pressure is 0.01-1 bar, preferably 0.01-0.1 bar. The propylene is further concentrated by purging and displacement with high-purity propylene or product gas to obtain propylene gas.

[0037] The contact adsorption process between the adsorbent and the mixture containing propylene and propane may be temperature swing adsorption and / or pressure swing adsorption.

[0038] The mixture containing propylene and propane may contain 99.8 vol% to 0.2 vol% propylene, 0.2 vol% to 99.8 vol% propane, and 0 to 10 vol% other substances. For example, the volume ratio of propylene:propane:other substances in the mixture containing propylene and propane is 50:40:10. Other substances have little effect on the adsorption and separation performance of the molecular sieve with a point-sieving structure for propylene / propane.

[0039] The other substances may include at least one of methane, oxygen, nitrogen, hydrogen, ethane, and ethylene.

[0040] After the adsorbent has adsorbed propylene, the adsorbent can be desorbed by at least one of reducing pressure, increasing temperature, and purging with an inert gas to obtain propylene and simultaneously regenerate the adsorbent. The purity of the propylene obtained by desorption can be greater than 99.95%.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] 1. The molecular sieve ZU-609 with a point screening structure used in the present invention has a linear propylene adsorption isotherm and a high pressure swing adsorption capacity (the propylene working capacity from 0.1 bar to 1 bar is as high as 2 mmol g -1 , see Figure 4), the desorption efficiency is high, and complete regeneration can be achieved under normal temperature inert gas purge or vacuum decompression conditions.

[0043] 2. High selectivity for propylene and propane, achieving molecular sieving of propylene and propane at room temperature. The adsorption capacity ratio of propylene and propane at 1 bar is as high as 22 (see Figure 5).

[0044] 3. Compared with other propylene propane molecular sieve materials, the molecular sieve ZU-609 with a point sieve structure of the present invention has a higher propylene diffusion coefficient (see Figure 6) and can be adsorbed and desorbed at high gas flow rates.

[0045] 4. The molecular sieve porous material with a point screening structure of the present invention is made of raw materials with a wide range of sources and low prices. The synthesis conditions are mild, the method is simple, the repeatability is good, and it has the advantages of good water and thermal stability and long service life. At the same time, the separation performance is less affected by moisture, sulfide, etc.

[0046] 5. The separation method provided by the present invention can obtain propylene gas with a purity of more than 99.95%. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] FIG1 is a schematic diagram of the point screening pores of the molecular sieve ZU-609 of the present invention and the traditional screening pores.

[0048] FIG2 is a schematic structural diagram of the molecular sieve ZU-609 of the present invention.

[0049] FIG3 is a diffusion energy barrier path diagram of propylene molecules diffusing in the pores of the molecular sieve ZU-609 of the present invention.

[0050] FIG4 is a graph showing the pressure swing adsorption capacity of the molecular sieve ZU-609 of the present invention and some materials disclosed in the prior art.

[0051] FIG5 is an adsorption isotherm diagram of propylene and propane at 298K for the molecular sieve ZU-609 of the present invention.

[0052] FIG6 is a graph showing the diffusion coefficients of the molecular sieve ZU-609 of the present invention and some materials disclosed in the prior art for propylene.

[0053] FIG7 is a penetration curve diagram of Example 2. DETAILED DESCRIPTION

[0054] The present invention will be further described below with reference to the accompanying drawings and specific examples. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0055] Example 1

[0056] 1 mol of copper nitrate, 1 mol of sodium 1,2-ethanedisulfonate, and 1 mol of 4,4'-dipyridyl sulfide were added to 40 L of methanol and stirred at room temperature for 1 hour. After the reaction, the resulting solid product was collected by vacuum filtration at 25°C. The sample was then activated under vacuum at 100°C to remove the guest solvent molecules in the pores, yielding the molecular sieve porous material ZU-609 with a point-sieving structure.

[0057] The adsorption isotherms of ZU-609 material for propylene and propane at 298K are shown in Figure 5.

[0058] Example 2

[0059] A 10 cm long fixed-bed adsorption column was filled with a porous molecular sieve material, ZU-609, featuring a point-screening structure. A propylene / propane mixture (50:50 by volume) was introduced into the bed at a flow rate of 3.0 mL / min at 25°C and 1 bar for fixed-bed adsorption. High-purity propane (greater than 99.999%) was obtained in the effluent gas. Adsorption ceased when propylene broke through. At room temperature, the column was purged with nitrogen at 3.0 mL / min, resulting in desorption of propylene with a purity greater than 99.5%, completing column regeneration. The breakthrough curve is shown in Figure 7.

[0060] Example 3

[0061] A 5cm fixed-bed adsorption column was filled with a porous molecular sieve material, ZU-609, featuring a point-sieving structure. A propylene / propane mixture (40:60 by volume) was introduced into the column at a flow rate of 0.5 mL / min at 40°C and 5 bar for fixed-bed adsorption. After the propylene component penetrated the column, the adsorption was stopped. The propylene component accumulated in the fixed bed was desorbed by reducing the pressure to 1 bar at 25°C, yielding propylene gas with a purity of 99.5%.

[0062] Example 4

[0063] The porous molecular sieve material ZU-609 with a point screening structure is made into particles and loaded into a fixed bed adsorption column. A propylene / propane / ethylene / ethane mixture (volume ratio of 45:45:5:5) is introduced into the bed at 20 mL / min at 100°C and 10 bar for fixed bed adsorption, allowing full contact with the adsorbent particles. After adsorption for a certain period of time and after the propylene component penetrates, the introduction of the mixed gas is stopped, and the gas enriched in the adsorbent particles is desorbed by heating to 30°C and reducing the pressure to 0.1 bar for desorption. The desorbed gas is then circulated into the fixed bed for adsorption, and desorption is performed after the propylene adsorption is saturated, obtaining propylene gas with a purity greater than 98%.

[0064] Example 5

[0065] The porous molecular sieve material ZU-609 with a point screening structure was filled in a 50 cm long fixed-bed adsorption column. A propylene / propane mixture containing a small amount of methane (volume ratio of propylene:propane:methane = 80:15:5) was introduced at 5°C and 4 bar at a flow rate of 100 mL / min for fixed-bed adsorption. Propylene was preferentially adsorbed. When the propylene adsorption front reached about 2 / 3 of the bed, the introduction of the mixed gas was stopped, the adsorption column was depressurized until propylene just penetrated, and an appropriate amount of high-purity propylene was introduced for reverse displacement. The gas in the adsorption column was desorbed by heating to 40°C and then reducing the pressure to 0.5 bar to obtain propylene gas with a purity of 99.99%, completing the regeneration of the adsorption material.

[0066] Example 6

[0067] Two 100 mL fixed-bed adsorption columns were filled with ZU-609, a porous molecular sieve material with a point-sieving structure. A propylene / propane mixture (99.8:0.2 by volume) containing a small amount of methane was introduced into column 1 at a flow rate of 100 mL / min at 15°C and 6 bar. Propylene was preferentially adsorbed, and the gas flow was stopped when the propylene adsorption front reached approximately two-thirds of the bed. After removing unabsorbed impurities from column 1, column 1 was evacuated to 0.05 bar to obtain a preliminary product gas, completing the regeneration of column 1. The preliminary product gas was introduced into column 2 for adsorption. When the propylene adsorption front reached approximately two-thirds of the bed, the gas flow was stopped. After removing unabsorbed impurities from column 2, column 2 was evacuated to 0.05 bar to obtain a product gas, completing the regeneration of column 2. These two adsorption and desorption processes yielded propylene gas with a purity of 99.999%.

[0068] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. A molecular sieve having a point screening structure, characterized in that: Composed of 1,2-ethanedisulfonate anion, 4,4'-dipyridyl sulfide and Cu 2+ Formed by coordination bonds, chemical formula [MSL2] ∞ , where M represents Cu 2+ , S represents 1,2-ethanedisulfonate anion, L represents 4,4'-dipyridyl sulfide, and ∞ represents that the molecular sieve is formed by spatial expansion of a plurality of structural units constituting MSL2; The molecular sieve with the point screening structure has local point-shaped pore contraction.

2. The molecular sieve with a point screening structure according to claim 1, characterized in that: The cross-sectional size of the sieve pore window of the molecular sieve is The molecular sieve has The large pore cavity.

3. The method for preparing a molecular sieve having a point screening structure according to claim 1 or 2, characterized in that: Cu 2+ The source, 1,2-ethanedisulfonate and 4,4'-bipyridine sulfide are mixed and reacted in a reaction solvent to obtain the molecular sieve with a point sieving structure.

4. The preparation method according to claim 3, characterized in that: The reaction solvent is water and / or an organic solvent; the organic solvent includes methanol; The Cu 2+ The source includes at least one of a chloride and a nitric acid compound; The 1,2-ethanedisulfonate includes sodium 1,2-ethanedisulfonate; Cu 2+ The molar ratio of Cu 2+, 1,2-ethanedisulfonate and 4,4'-bipyridyl sulfide was calculated. 2+ : 1,2-ethanedisulfonate anion: 4,4'-dipyridyl sulfide is calculated as 1:0.5~3:1~5; Cu 2+ The ratio of the source to the reaction solvent is 1 mol:35-45 L; After the mixing reaction is completed, the solid and liquid are separated, and the solid is taken to remove the solvent molecules in the pores to obtain the molecular sieve with the point screening structure.

5. Use of the molecular sieve with a point sieving structure according to claim 1 or 2 in adsorbing propylene.

6. A method for separating propylene and propane by adsorption, characterized in that: The molecular sieve with a point sieving structure as claimed in claim 1 or 2 is used as an adsorbent and is contacted with a mixture containing propylene and propane. The adsorbent selectively adsorbs propylene and excludes propane, thereby achieving separation of propylene and propane.

7. The method according to claim 6, characterized in that The contacting mode of the adsorbent and the mixture containing propylene and propane is any one or more combinations of fixed bed adsorption, moving bed adsorption and multi-tower pressure swing adsorption.

8. The method according to claim 6, characterized in that The contact adsorption process between the adsorbent and the mixture containing propylene and propane is temperature swing adsorption and / or pressure swing adsorption.

9. The method according to claim 6, characterized in that The mixture containing propylene and propane contains 99.8 vol% to 0.2 vol% of propylene, 0.2 vol% to 99.8 vol% of propane and 0 to 10 vol% of other substances; The other substances include at least one of methane, oxygen, nitrogen, hydrogen, ethane and ethylene.

10. The method according to claim 6, characterized in that After the adsorbent has completed the adsorption of propylene, the adsorbent is desorbed from the adsorbent by at least one of reducing pressure, increasing temperature, and purging with an inert gas to obtain propylene, and the adsorbent is regenerated at the same time.

Images