Molecular sieve with point sieving structure, its preparation method and application in adsorptive separation of propylene and propane

Abstract

The present invention discloses a molecular sieve with a point screening structure, a preparation method thereof, and an application thereof in the adsorption separation of propylene and propane. The molecular sieve of the present invention is 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 several structural units composed of MSL2 and expanded in space; the molecular sieve of the present invention has local point-like pore contraction. Preparation method: Cu 2+ A molecular sieve having a point-sieving structure is prepared by mixing a source, 1,2-ethanedisulfonate, and 4,4'-dipyridyl sulfide in a reaction solvent. 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 industrial application prospects.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of molecular sieve and chemical separation technology, and particularly relates to a molecular sieve with point sieve structure, a preparation method thereof and application of the molecular sieve in adsorption separation of propylene and propane. BACKGROUND

[0002] Propylene is a cornerstone of petrochemical industry and is one of the largest chemical products in the world. Its downstream products mainly include polypropylene, propylene oxide, acrylonitrile, etc., and are widely used in various national economic industries such as plastics, pharmaceuticals, textiles, coatings, etc. At present, propylene is mainly prepared by separation from a low-carbon hydrocarbon mixture obtained by cracking of naphtha, and the key and technical difficulty of low-carbon hydrocarbon separation lies in the separation of ethylene / ethane and propylene / propane with similar molecular sizes and physical properties. However, propylene and propane have highly similar structural properties and only a slight difference in unsaturation, which makes the separation of propylene / propane difficult and energy-consuming. At present, the separation technologies of propylene / propane mainly include low-temperature rectification, solvent absorption, membrane separation and adsorption separation, etc. Among them, the low-temperature rectification technology is the most mature and is widely used in industry, but due to the close boiling points of propylene and propane and the small relative volatility, the separation can only be realized at a high pressure (~22 bar), a very low temperature (~160℃) and a large reflux ratio, and the number of trays is usually more than 150, which has the disadvantages of high energy consumption and large device 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, the complex membrane manufacturing process and high cost.

[0003] As a low-energy and environmentally friendly separation technology, the adsorption separation technology is suitable for the separation of substances with similar structures, such as the separation and purification of low-carbon hydrocarbon gases. However, the existing adsorption materials, such as zeolite molecular sieve, activated carbon, polymer and metal organic framework material, often have difficulty in accurately identifying the slight difference between propylene and propane molecules, and 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, 4A molecular sieve can realize molecular sieve separation of propylene and propane, but has the problems of low propylene diffusion coefficient (10 - 11 cm -2 s -1)overly slow, so that the separation of propylene and propane can only be achieved at high temperature of 150℃ (Separation Science and Technology, 2010, 45: 1252-1259). As a new type of porous adsorption material, metal-organic framework material has the advantages of large specific surface area, high pore volume, and easy chemical modification of pore channel and accurate adjustment of pore size. However, the separation performance of the widely studied π-complex type framework material 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 and can form electrostatic interaction with the π electrons of the double bond of propylene, but due to the relatively large pore size The selectivity for propylene / propane mixed gas is low. By taking advantage of the difference in molecular size between propylene and propane, the design of a propylene / propane molecular sieve material with a suitable pore size can greatly improve the separation selectivity of propylene / propane, such as KAUST-7 (Science, 2016, 353: 137-140) and Y-abtc (Advanced Materials, 2018, 30: 1805088), which have a suitable pore size and can adsorb small-sized propylene molecules while excluding large-sized propane molecules. However, the current propylene / propane sieving material has the defects of low working capacity, slow adsorption rate, and difficult regeneration. Therefore, the design and preparation of a new type of porous material that can realize propylene / propane molecular sieving, with high propylene adsorption capacity, high propylene adsorption rate, and easy desorption and regeneration of propylene, is of great importance to the development of propylene / propane adsorption and separation technology. SUMMARY

[0004] In view of the above technical problems and the deficiencies in the field, the present application provides a molecular sieve with point sieving structure (which can be referred to as ZU-609), which is composed of 1,2-ethane disulfonate anion with rigid strip-shaped characteristics, 4,4'-dipyridyl sulfide (CAS No. 37968-97-1) with flexible and foldable characteristics, and metal cation Cu 2+ The mixture containing propylene and propane is contacted with the molecular sieve, and the molecular sieve can preferentially adsorb propylene in the mixture to achieve purification of propylene and obtain high-purity propylene. The present application precisely controls the pore size and channel shape of the molecular sieve to construct a molecular sieve porous material ZU-609 with point sieving structure, so that propylene is adsorbed in the channel with high selectivity and high capacity, while propane is excluded from the channel, thereby realizing the production of high-purity propylene. The present application has the outstanding advantages of good material stability, high adsorption selectivity, high adsorption capacity, high adsorption rate, easy regeneration, and good industrial application prospect.

[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 with a point screening structure has local point-like pore contraction (see Figure 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 screening structure by combining metal cations, organic ligands, and organic anions, thereby achieving precise control of the pore size of the molecular sieve porous material with a point screening structure. When propylene and propane molecules come into contact with the molecular sieve porous material ZU-609 with a point screening structure, since propylene has a smaller molecular size than propane, the precisely adjusted pore size of the material allows propylene to enter the molecular sieve porous material with a point screening structure while excluding propane from entering the pores, thereby exhibiting good size screening properties. At the same time, due to the structural characteristics of the molecular sieve of the present invention, the high diffusion energy 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]

[0011] 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.

[0012] The flexible and tortuous 4,4'-dipyridyl sulfide ligand and the rigid and elongated 1,2-ethanedisulfonate anion contribute to the construction of the macroporous cavity of the molecular sieve (see Figure 2 ). The rigid pyridine ring on the ligand molecule creates conditions for the construction of the screening window.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] The Cu 2+ The source may include at least one of a chloride, a nitric acid compound, and the like.

[0018] The 1,2-ethanedisulfonate salt may include sodium 1,2-ethanedisulfonate, and the like.

[0019] 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.

[0020] Cu 2+ The usage ratio of the source to the reaction solvent can be 1 mol:35-45L.

[0021] 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.

[0022] 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.

[0023] The present invention also provides the use of the molecular sieve with the point screening structure in adsorbing propylene.

[0024] ZU-609 has the following characteristics of propylene adsorption performance: the propylene adsorption isotherm shows a linear adsorption isotherm, which is beneficial to pressure swing adsorption; the diffusion coefficient of propylene in ZU-609 at normal temperature reaches 10.02*10 -10 cm -2 s -1 ; the adsorption capacity difference of ZU-609 between 0.1 bar and 1 bar reaches 2.0 mmol g -1 ; the propylene / propane adsorption capacity ratio at 1 bar reaches 22.

[0025] The adsorption rate of propylene in the pore channel of the molecular sieve is fast, and the molecular sieve can be operated at a high propylene / propane mixed gas velocity in a dynamic separation experiment.

[0026] As a general inventive concept, the application further provides a method for adsorptive separation of propylene / propane, which comprises contacting a mixture containing propylene and propane with the molecular sieve with point sieve structure as an adsorbent, and selectively adsorbing propylene while rejecting propane to realize separation of propylene and propane.

[0027] The application can realize efficient separation of propylene / 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.

[0028] The contact mode of the adsorbent and the mixture containing propylene and propane can be any one or a combination of fixed bed adsorption, moving bed adsorption, and multi-tower pressure swing adsorption.

[0029] For example, the multi-tower pressure swing adsorption is introduced as follows:

[0030] 1) The mixed gas containing propylene and propane is pressurized by a compressor and sent into a first adsorption tower for adsorption under constant pressure, the adsorption pressure in the first adsorption tower is controlled to be 1 to 10 bar, the adsorption temperature is 25 to 40°C, and the outlet of the first adsorption tower directly enriches propane with a purity of more than 99.9%.

[0031] 2) The second adsorption tower is subjected to displacement and vacuumization operation, and the remaining third, …, n (n≥3) adsorption towers are subjected to equalization operation; when the first adsorption tower is adsorbed, the second adsorption tower stops vacuumization, and the first adsorption tower starts equalization operation on the second adsorption tower;

[0032] 3) The first adsorption tower is subjected to backflow displacement operation using part of the high-purity propylene collected in the last cycle, and at this time, the n-th adsorption tower is subjected to product gas rapid pressurization and enters the adsorption stage.

[0033] 4) The first adsorption column is desorbed by vacuum pumping, the desorption pressure is controlled at 0-0.1 bar, and high-purity propylene is obtained at the outlet, with a purity of 99.5%; most of the propylene at the outlet is used as a product, and a small amount of propylene is used to complete the reflux displacement of the next cycle;

[0034] 5) The pressure is prepared to be increased again for the next cycle.

[0035] For example, the fixed bed adsorption is introduced as follows:

[0036] a) The mixed gas containing propylene and propane is introduced into the fixed bed adsorption column at a set flow rate to contact the molecular sieve with a point sieve structure at a certain adsorption temperature and pressure, the adsorption temperature is -30-100°C, preferably 25-40°C, the adsorption pressure is 0-10 bar, preferably 1-5 bar, the adsorption rate of the propane component is slow, and the adsorption capacity is lower than that of the propylene component, the propane component penetrates the fixed bed adsorption column first, and propane gas can be directly obtained at the outlet of the adsorption column;

[0037] b) After the propane component penetrates, the raw material gas is continuously introduced for adsorption, and the adsorption is performed for a certain time, so that the propylene adsorption front is not less than 2 / 3 of the bed layer, or when the propylene component penetrates, the mixed gas is stopped, and one or a combination of methods such as temperature increase and pressure reduction is used for desorption, the desorption temperature is 0-40°C, preferably 30-40°C, the desorption pressure is 0.01-1 bar, preferably 0.01-0.1 bar. High-purity propylene or product gas is used for further concentration of propylene by sweeping displacement, and propylene gas is obtained.

[0038] The contact adsorption process of the adsorbent and the mixed gas containing propylene and propane can be temperature swing adsorption and / or pressure swing adsorption.

[0039] The mixed gas containing propylene and propane can contain 99.8vol%-0.2vol% propylene, 0.2vol%-99.8vol% propane, and 0-10vol% other substances. For example, the volume ratio of propylene:propane:other substances in the mixed gas containing propylene and propane is 50:40:10. The other substances have little effect on the adsorption separation performance of the molecular sieve with a point sieve structure for propylene / propane.

[0040] The other substances can include at least one of methane, oxygen, nitrogen, hydrogen, ethane, and ethylene.

[0041] After the adsorbent completes the adsorption of propylene, at least one of pressure reduction, temperature increase, and inert gas sweeping can be used to desorb the propylene from the adsorbent, obtain propylene, and regenerate the adsorbent. The purity of the desorbed propylene can be greater than 99.95%.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] 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 it can be completely regenerated under the conditions of inert gas purge or vacuum decompression at room temperature.

[0044] 2. High selectivity for propylene and propane, achieving molecular sieving of propylene and propane at room temperature, with an adsorption capacity ratio of propylene and propane as high as 22 at 1 bar (see Figure 5 ).

[0045] 3. The molecular sieve ZU-609 with a point screening structure of the present invention has a higher propylene diffusion coefficient than other propylene propane molecular sieve materials (see Figure 6 ), which can be adsorbed and desorbed at high gas flow rates.

[0046] 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.

[0047] 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

[0048] Figure 1 Schematic diagram of the point screening pores of the molecular sieve ZU-609 of the present invention and the traditional screening pores.

[0049] Figure 2 Schematic diagram of the structure of the molecular sieve ZU-609 of the present invention.

[0050] Figure 3 This is a diffusion energy barrier path diagram formed by the diffusion of propylene molecules in the pores of the molecular sieve ZU-609 of the present invention.

[0051] Figure 4 This is a pressure swing adsorption capacity diagram of the molecular sieve ZU-609 of the present invention and some materials disclosed in the prior art.

[0052] Figure 5 This is the adsorption isotherm diagram of the molecular sieve ZU-609 of the present invention for propylene and propane at 298K.

[0053] Figure 6 This is a graph showing the diffusion coefficient of propylene for the molecular sieve ZU-609 of the present invention and some materials disclosed in the prior art.

[0054] Figure 7 The breakthrough curve of Example 2. DETAILED DESCRIPTION

[0055] The application will be further described below in conjunction with the accompanying drawings and specific examples. It should be understood that these examples are only used to illustrate the application and not to limit the scope of the application.

[0056] Example 1

[0057] 1 mol of copper nitrate, 1 mol of sodium 1,2-ethane disulfonate and 1 mol of 4,4'-dipyridyl sulfide were added into 40 L of methanol, and stirred at room temperature for 1 h. After the reaction was completed, the obtained solid product was collected by vacuum filtration at 25 °C, and then the sample was activated at 100 °C under vacuum to remove the guest solvent molecules in the pores, thereby obtaining a porous molecular sieve material ZU-609 with point sieving structure.

[0058] The adsorption isotherms of ZU-609 material at 298 K for propylene and propane are shown in Figure 5 .

[0059] Example 2

[0060] The porous molecular sieve material ZU-609 with point sieving structure was packed in a 10 cm long fixed bed adsorption column, and a propylene / propane mixed gas (volume ratio 50:50) was passed into the bed at a flow rate of 3.0 mL / min at 25 °C and 1 bar for fixed bed adsorption, and high purity propane (more than 99.999%) gas could be obtained in the effluent gas. When the propylene breakthrough occurred, the adsorption was stopped. At room temperature, the adsorption column was purged with 3.0 mL / min of nitrogen gas to desorb and obtain propylene gas with a purity of more than 99.5%, and the regeneration of the adsorption column was completed. The breakthrough curve is shown in Figure 7 .

[0061] Example 3

[0062] The porous molecular sieve material ZU-609 product with point sieving structure was packed in a 5 cm fixed bed adsorption column, and a propylene / propane mixed gas (volume ratio 40:60) was passed into the bed at a flow rate of 0.5 mL / min at 40 °C and 5 bar for fixed bed adsorption. After a certain period of time, the mixed gas was stopped when the propylene component breakthrough occurred. The propylene gas component enriched in the fixed bed was desorbed by depressurization to 1 bar at 25 °C, and propylene gas with a purity of 99.5% was obtained.

[0063] Example 4

[0064] The molecular sieve porous material ZU-609 with point sieving structure is made into particles and filled in a fixed bed adsorption column. A mixed gas of propylene / propane / ethylene / ethane (volume ratio 45:45:5:5) is passed into the bed at 100°C and 10 bar at a flow rate of 20 mL / min to perform fixed bed adsorption, so that the mixed gas is in full contact with the adsorbent particles for a certain time. After the propylene component penetrates, the passing of the mixed gas is stopped. The gas enriched in the adsorbent particles is desorbed by heating to 30°C and reducing the pressure to 0.1 bar. Then the desorbed gas is recycled into the fixed bed to perform adsorption, and after the adsorption of propylene is saturated, the desorption is performed to obtain propylene gas with a purity of more than 98%.

[0065] Example 5

[0066] The molecular sieve porous material ZU-609 with point sieving structure is filled in a fixed bed adsorption column with a length of 50 cm. A mixed gas of propylene / propane containing a small amount of methane (volume ratio propylene:propane:methane = 80:15:5) is passed into the bed at 5°C and 4 bar at a flow rate of 100 mL / min to perform fixed bed adsorption, so that propylene is preferentially adsorbed. When the front of the adsorption of propylene reaches about 2 / 3 of the bed, the passing of the mixed gas is stopped. The adsorption column is reduced to the pressure at which propylene just penetrates, and an appropriate amount of high-purity propylene is passed in to perform reverse displacement. The gas in the adsorption column is desorbed by heating to 40°C and reducing the pressure to 0.5 bar to obtain propylene gas with a purity of 99.99%, and the regeneration of the adsorption material is completed.

[0067] Example 6

[0068] The molecular sieve porous material ZU-609 with point sieving structure is filled in two fixed bed adsorption columns with a volume of 100 mL. A mixed gas of propylene / propane containing a small amount of methane (volume ratio propylene:propane = 99.8:0.2) is passed into column 1 at 15°C and 6 bar at a flow rate of 100 mL / min to perform fixed bed adsorption, so that propylene is preferentially adsorbed. When the front of the adsorption of propylene reaches about 2 / 3 of the bed, the passing of the mixed gas is stopped. After the unadsorbed impurity gas in column 1 is discharged, column 1 is vacuumed to 0.05 bar by a vacuum pump to obtain the primary product gas and complete the regeneration of column 1. The primary product gas is passed into column 2 to perform adsorption. When the front of the adsorption of propylene reaches about 2 / 3 of the bed, the passing of the mixed gas is stopped. After the unadsorbed impurity gas in column 2 is discharged, column 2 is vacuumed to 0.05 bar by a vacuum pump to obtain the product gas and complete the regeneration of column 2. Propylene gas with a purity of 99.999% is obtained through the two adsorption and desorption processes.

[0069] In addition, it should be understood that, after reading the above description of the present application, those skilled in the art can make various modifications or changes to the present application, and these equivalent forms also fall within the scope defined by the claims attached hereto.

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 several structural units consisting of MSL2; The molecular sieve with a 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 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'-dipyridyl 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(Ⅱ) 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 screening 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 sieve structure according to claim 1 or 2 is used as an adsorbent and is contacted with a mixture containing propylene and propane. The adsorbent selectively adsorbs propylene while excluding propane, thereby achieving separation of propylene and propane.

7. The method according to claim 6, characterized in that The contact 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 completes the adsorption of propylene, the adsorbent is desorbed 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.

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