Zeolite molecular sieve for adsorption separation of propylene and propane and preparation method thereof

Abstract

The present invention belongs to the technical field of propylene separation and purification, and specifically discloses a zeolite molecular sieve for adsorptive separation of propylene and propane and a preparation method thereof. It is used to solve the problem that currently 5A zeolite molecular sieve cannot be used as an adsorption material to effectively separate propylene and propane. The steps are as follows: first, adding alkylphosphonic acid solid powder to tetrahydrofuran solvent to prepare an alkylphosphonic acid solution; then, calcining and cooling the 5A zeolite molecular sieve to room temperature, adding the alkylphosphonic acid solution, stirring, centrifuging, and removing the supernatant; then, cooling to room temperature after heat treatment, washing with tetrahydrofuran solvent; and finally, vacuum drying to obtain a 5A zeolite molecular sieve modified with an alkylphosphonic acid monolayer. The present invention effectively improves the selectivity of propylene / propane adsorption separation based on a kinetic separation mechanism by regulating the relative resistance of propylene and propane to passing through the alkylphosphonic acid monolayer.

Description

Technical Field

[0001] The present invention belongs to the technical field of propylene separation and purification, and in particular relates to a zeolite molecular sieve for adsorption separation of propylene and propane and a preparation method thereof. Background Art

[0002] Industrial production methods for propylene include naphtha steam cracking, heavy oil fluidized catalytic cracking, propane dehydrogenation, and coal-to-methanol olefins. The crude propylene produced is mixed with propane, which can be separated and purified to produce polymerization-grade propylene (≥99.5%). Because the molecular structures of propylene and propane are similar, their boiling points are similar and both below room temperature. Industrial separation of propylene and propane generally uses cryogenic distillation. However, this method requires a large number of distillation stages (150 to 200), low operating temperatures (-90 to -40°C), high pressures (16 to 20 atmospheres), and a high reflux ratio, resulting in high capital equipment investment and high production energy consumption. Absorption, membrane separation, and adsorption are potential alternatives to energy-intensive distillation, with adsorption promising significant reductions in energy consumption.

[0003] Adsorption can replace the energy-intensive distillation method. Adsorption can be categorized by separation mechanism into equilibrium, kinetic, and steric separation. Materials that can separate propylene and propane by kinetic adsorption include zeolites (DD3R, SiCHA, ITQ-55, ZSM-58, etc.), carbon molecular sieves (CMS, CNP, etc.), and metal-organic frameworks (ELM12, ZIF-8, Zn-ATA, etc.).

[0004] 5A zeolite molecular sieve is a zeolite molecular sieve with simple synthesis method, low raw material cost and environmental friendliness. It has high thermal stability and high hydrothermal stability and is a very promising adsorption material. The kinetic diameters of propylene and propane molecules are similar (respectively and ), both of which can pass through the octahedral pores of the 5A zeolite molecular sieve and enter the interior of the zeolite. The kinetic diameter of a propylene molecule is slightly smaller than that of a propane molecule, and its adsorption rate is slightly greater than that of propane. However, the adsorption kinetic selectivity is very low, with its ideal adsorption solution theory (IAST) kinetic selectivity (the ratio of the adsorption amounts of two gases at the same adsorption time and temperature, when subjected to single-gas adsorption tests at the same initial pressure) being only approximately 1.2 at room temperature and pressure, making it ineffective for separating propylene and propane.

[0005] Therefore, it is urgent to adjust the pore structure of 5A zeolite molecular sieve to expand the difference in adsorption rates of propylene and propane and improve the kinetic selectivity of adsorption separation. Summary of the Invention

[0006] One object of the present invention is to provide a method for preparing a zeolite molecular sieve for separation of propylene and propane by adsorptive separation, thereby effectively solving the problem that 5A zeolite molecular sieve cannot be used as an adsorption material to achieve effective separation of propylene and propane.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0008] A method for preparing a zeolite molecular sieve for adsorption separation of propylene and propane comprises the following steps: S1, adding alkylphosphonic acid solid powder into tetrahydrofuran solvent to prepare an alkylphosphonic acid solution.

[0009] S2. After high-energy ball milling, 5A zeolite molecular sieve is calcined at 400-500° C. for 5-7 h and cooled to room temperature.

[0010] S3. Add the 5A zeolite molecular sieve calcined in step S2 to the alkylphosphonic acid solution, stir for 10 to 20 hours, centrifuge at a speed of 10,000 to 16,000 r / min for 5 to 15 minutes, remove the supernatant, and obtain a solid product.

[0011] The usage ratio of the alkylphosphonic acid solid powder to the 5A zeolite molecular sieve is 0.66-1.97 mmol:1 g, and the usage ratio of the tetrahydrofuran solvent to the 5A zeolite molecular sieve is 150-250 mL:1 g.

[0012] S4. Heat-treating the solid product at 110-130° C. for 2-6 h, then cooling to room temperature, and washing with tetrahydrofuran solvent 3-5 times, with the amount of tetrahydrofuran solvent used in each washing being 100-200 mL.

[0013] S5. The solid product washed in step S4 is vacuum dried to obtain a 5A zeolite molecular sieve modified with an alkylphosphonic acid monolayer, which is used for adsorptive separation of propylene and propane.

[0014] Furthermore, in step S1, the alkylphosphonic acid is any one or more of methylphosphonic acid (MPA), tert-butylphosphonic acid (TBPA), n-butylphosphonic acid (BPA) and octadecylphosphonic acid (ODPA).

[0015] Furthermore, in step S2, the calcination temperature is 450°C and the calcination time is 6 hours.

[0016] Furthermore, the usage ratio of the alkylphosphonic acid solid powder to the 5A zeolite molecular sieve is 0.66 mmol:1 g, and the usage ratio of the tetrahydrofuran solvent to the 5A zeolite molecular sieve is 200 mL:1 g.

[0017] Furthermore, in step S3, the stirring time is 15 hours, the centrifuge speed is 12000 r / min, and the centrifugation time is 10 minutes.

[0018] Furthermore, in step S4, the heat treatment temperature is 120° C., and the heat treatment time is 4 hours.

[0019] Furthermore, in step S4, the mixture is washed with tetrahydrofuran solvent 4 times, and the amount of tetrahydrofuran solvent used in each washing is 150 mL.

[0020] Another object of the present invention is to provide a zeolite molecular sieve for the adsorptive separation of propylene and propane, which is prepared using the preparation method described in the above embodiment.

[0021] Compared with the prior art, the beneficial technical effects of the present invention are:

[0022] The present invention increases the resistance of gas molecules to diffuse into the interior of the zeolite molecular sieve by adding a layer of alkylphosphonic acid monolayer on the outer surface of the 5A zeolite molecular sieve. The organic monolayer has a greater resistance to larger propane molecules than to smaller propylene molecules, making the propane adsorption rate much lower than the propylene adsorption rate, thereby effectively improving the propylene / propane adsorption kinetic selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the infrared spectrum of 5A zeolite molecular sieve modified with TBPA, BPA, ODPA and MPA monolayers.

[0024] Figure 2 This is a temperature-programmed desorption-mass spectrometry (mass-to-charge ratio m / z is 15) analysis chart of 5A zeolite molecular sieve modified with TBPA, BPA, ODPA and MPA monolayers.

[0025] Figure 3 It is the X-ray diffraction pattern of 5A zeolite molecular sieve modified with TBPA, BPA, ODPA and MPA monolayer.

[0026] Figure 4 Graph showing the change in propylene adsorption over time at 25° C. for the TBPA, BPA, ODPA and MPA monolayer-modified and unmodified 5A zeolite molecular sieves of Examples 1 to 4.

[0027] Figure 5 Graph showing the change in propane adsorption capacity over time at 25° C. for TBPA, BPA, ODPA and MPA monolayer-modified and unmodified 5A zeolite molecular sieves of Examples 1 to 4.

[0028] Figure 6 Graph showing the change in adsorption selectivity of propylene / propane over time at 25° C. for TBPA, BPA, ODPA and MPA monolayer-modified and unmodified 5A zeolite molecular sieves of Examples 1 to 4.

[0029] Figure 7 Graph showing the change in adsorption selectivity of propylene / propane over time for the 5A zeolite molecular sieve modified with ODPA monolayer in Examples 5 to 8 at different temperatures. The dotted line in the graph represents the standard deviation of three sample preparations and adsorption tests.

[0030] Figure 8 This is a graph showing the change in adsorption selectivity of propylene / propane over time for the mixed alkylphosphonic acid-modified 5A zeolite molecular sieves of Examples 9 to 12 at 25°C. DETAILED DESCRIPTION

[0031] Embodiment 1: A method for preparing a zeolite molecular sieve for adsorption separation of propylene and propane, comprising the following steps:

[0032] (1) Adding alkylphosphonic acid solid powder into tetrahydrofuran solvent to prepare an alkylphosphonic acid solution. The alkylphosphonic acid is any one or more of methylphosphonic acid (MPA), tert-butylphosphonic acid (TBPA), n-butylphosphonic acid (BPA) and octadecylphosphonic acid (ODPA).

[0033] (2) After high-energy ball milling, 5A zeolite molecular sieve was calcined at 400-500°C for 5-7h and cooled to room temperature.

[0034] (3) adding the 5A zeolite molecular sieve calcined in step (2) to the alkylphosphonic acid solution, stirring for 10 to 20 hours, centrifuging in a centrifuge at a speed of 10,000 to 16,000 r / min for 5 to 15 minutes, removing the supernatant, and obtaining a solid product.

[0035] The usage ratio of the alkylphosphonic acid solid powder to the 5A zeolite molecular sieve is 0.66-1.97 mmol:1 g, and the usage ratio of the tetrahydrofuran solvent to the 5A zeolite molecular sieve is 150-250 mL:1 g.

[0036] (4) The solid product is heat-treated at 110-130° C. for 2-6 h, then cooled to room temperature, and washed 3-5 times with tetrahydrofuran solvent, with the amount of tetrahydrofuran solvent used in each washing being 100-200 mL.

[0037] (5) The solid product washed in step (4) is vacuum dried to obtain a 5A zeolite molecular sieve modified with an alkylphosphonic acid monolayer, which is used for the adsorptive separation of propylene and propane.

[0038] like Figure 1As shown, the infrared spectrum of 5A zeolite molecular sieve modified with a monolayer of alkylphosphonic acid (TBPA, BPA, ODPA and MPA) (tested using a Thermo Fisher Scientific iS10 infrared spectrometer) shows that after the outer surface of the 5A zeolite molecular sieve is modified with alkylphosphonic acid, the infrared spectrum shows methyl (-CH3) and methylene (-CH2-) absorption peaks in the solid material, indicating that the alkylphosphonic acid has been modified to the surface of the 5A zeolite molecular sieve.

[0039] Alkylphosphonic acid reacts with aluminum hydroxyl group / silanol group on the surface of zeolite molecular sieve to form covalent bonds, which makes the alkylphosphonic acid monolayer have high thermal stability (it will not volatilize or decompose below 300℃). Figure 2 The programmed temperature desorption-mass spectra of 5A zeolite molecular sieve modified with a monolayer of alkylphosphonic acids (TBPA, BPA, ODPA, and MPA) (tested using a Bruker MALDI-TOF mass spectrometer) show that no thermal decomposition occurs at 300°C to produce methyl groups (mass-to-charge ratio (m / z) of 15).

[0040] The alkylphosphonic acid monolayer is modified on the outer surface of 5A zeolite molecular sieve without changing the internal crystal structure of 5A zeolite molecular sieve, such as Figure 3 As shown in the X-ray diffraction (XRD) pattern of 5A zeolite molecular sieve modified with a monolayer of alkylphosphonic acid (TBPA, BPA, ODPA and MPA) (tested by Japan Rigaku Smartlab X-ray diffractometer, Cu target Kα ray, scanning step size 0.01°, scanning speed 2° / min), the crystal diffraction peak of 5A zeolite molecular sieve does not change.

[0041] The principle of the present invention is to use self-assembled monolayer (SAM) technology to add an alkylphosphonic acid monolayer to the outer surface of 5A zeolite molecular sieve. This adds a resistance layer to the adsorption of propylene and propane within the 5A zeolite molecular sieve, amplifying the difference in adsorption rates between propylene and propane, thereby improving the kinetic selectivity of adsorption separation. The chain length and spatial structure of the alkylphosphonic acid molecules used affect the structure of the alkylphosphonic acid monolayer, thereby affecting the diffusion resistance of gas molecules through the alkylphosphonic acid monolayer during the adsorption process. The alkylphosphonic acid molecules used can be changed as needed to achieve regulation of the kinetic selectivity of gas adsorption. Before modification with the alkylphosphonic acid, the 5A zeolite molecular sieve is subjected to high-energy ball milling to reduce the particle size and increase the surface area of the 5A zeolite, facilitating modification with the alkylphosphonic acid.

[0042] The adsorption test method of this embodiment is as follows: for a 5A zeolite molecular sieve modified with an alkylphosphonic acid monolayer, a high-pressure gas adsorption instrument (PCT-Pro model, Setteram, France) is used to measure the pressure drop during the adsorption of single gases of propylene and propane at a certain temperature and initial pressure (15 kPa) in a closed system, thereby obtaining the change in gas adsorption amount over time, and then calculating the adsorption kinetic selectivity of propylene / propane (based on the ideal adsorption solution theory model IAST).

[0043] The present invention is further described in detail below with reference to specific embodiments.

[0044] Example 1: (1) 0.091 g of tert-butylphosphonic acid (TBPA, CAS No. 4923-84-6, (HO)2POC(CH3)3, purity 99%, the same below) solid powder was added to 200 mL of tetrahydrofuran solvent (THF, CAS No. 109-99-9, purity 99%, the same below) to prepare a tert-butylphosphonic acid solution.

[0045] (2) 5A zeolite molecular sieve (<10 μm, Sigma-Aldrich 233676, the same below) was subjected to high-energy ball milling (ND8-1L ball mill, Nanjing Nanda Tianzun Electronics Co., Ltd., zirconium dioxide grinding balls, the ratio of grinding balls to material mass was 45:1, the ball milling speed was 600 r / min, and the ball milling time was 30 min). After ball milling, the external specific surface area was reduced from 30 m 2 / g increased to 33m 2 / g (the nitrogen adsorption isotherm at liquid nitrogen temperature was measured using an ASAP 2460 adsorption instrument from Micromeritics Instruments, USA, and the surface area was calculated using the t-Plot method), and then the 5A zeolite molecular sieve was calcined in air at 450°C for 6h and then cooled to room temperature.

[0046] (3) 1 g of the 5A zeolite molecular sieve calcined in step (2) was added to the tert-butylphosphonic acid solution, stirred for 15 h, and then centrifuged at 12,000 r / min for 10 min in a centrifuge to remove the supernatant.

[0047] (4) After heat treatment at 120°C for 4 h, the mixture was cooled to room temperature and washed with tetrahydrofuran solvent 4 times, with the amount of tetrahydrofuran solvent used for each washing being 150 mL.

[0048] (5) Finally, the product was dried in a vacuum oven under vacuum (1 Pa) for 10 h to obtain tert-butylphosphonic acid monolayer-modified 5A zeolite molecular sieve (5A-TBPA).

[0049] 0.3 g of the 5A zeolite molecular sieve modified with a monolayer of tert-butylphosphonic acid prepared in this example was taken and measured at 25° C. using a high-pressure gas adsorption instrument to measure the changes in the adsorption amount of propylene and propane at an initial pressure of 15 kPa as a function of adsorption time. Figure 4 and Figure 5 The 5A-TBPA curve is shown in the figure; the adsorption selectivity of propylene / propane changes with time as shown in the figure Figure 6 As shown in the 5A-TBPA curve, the maximum kinetic selectivity is 4.8, which is higher than that of the unmodified 5A zeolite molecular sieve (such as Figure 6 As shown by the 5A curve, it is about 1.2).

[0050] Example 2: The difference between this example and Example 1 is that 0.091 g of n-butylphosphonic acid (BPA, CAS No. 3321-64-0, (HO)2PO(CH2)3CH3, purity 99%, the same below) is used instead of the tert-butylphosphonic acid in Example 1 to prepare a 5A zeolite molecular sieve modified with a monolayer of n-butylphosphonic acid (5A-BPA).

[0051] 0.3 g of the 5A zeolite molecular sieve modified with a monolayer of n-butylphosphonic acid prepared in this example was taken and measured at 25° C. using a high-pressure gas adsorption instrument to measure the changes in the adsorption amount of propylene and propane at an initial pressure of 15 kPa as a function of adsorption time. Figure 4 and Figure 5 The 5A-BPA curve is shown in FIG. 5A-BPA; the adsorption selectivity of propylene / propane changes with time as shown in FIG. Figure 6 As shown in the 5A-BPA curve, the maximum kinetic selectivity is 5.0.

[0052] Example 3: This example differs from Example 1 in that 0.220 g of octadecylphosphonic acid (ODPA, CAS No. 4724-47-4, (HO)2PO(CH2) 17 CH3, purity 99%, the same below) was used to replace the tert-butylphosphonic acid in Example 1 to prepare 5A zeolite molecular sieve modified with octadecylphosphonic acid monolayer (5A-ODPA).

[0053] 0.3 g of the 5A zeolite molecular sieve modified with octadecylphosphonic acid monolayer prepared in this example was taken and measured at 25° C. using a high-pressure gas adsorption instrument to measure the changes in the adsorption amount of propylene and propane at an initial pressure of 15 kPa as a function of adsorption time. Figure 4 and Figure 5 The 5A-ODPA curve is shown in the figure; the adsorption selectivity of propylene / propane changes with time as shown in the figure Figure 6 As shown in the 5A-ODPA curve, the maximum kinetic selectivity is 8.8.

[0054] Example 4: The difference between this example and Example 1 is that 0.063 g of methylphosphonic acid (MPA, CAS No. 993-13-5, (HO)2POCH3, purity 99%, the same below) is used instead of tert-butylphosphonic acid in Example 1 to prepare a methylphosphonic acid monolayer modified 5A zeolite molecular sieve (5A-MPA).

[0055] 0.3 g of the 5A zeolite molecular sieve modified with a monolayer of methylphosphonic acid prepared in this example was taken and measured at 25° C. using a high-pressure gas adsorption instrument to measure the changes in the adsorption amount of propylene and propane at an initial pressure of 15 kPa as a function of adsorption time. Figure 4 and Figure 5 The 5A-MPA curve is shown in FIG5; the adsorption selectivity of propylene / propane changes with time as shown in FIG5. Figure 6 As shown in the 5A-MPA curve, the maximum kinetic selectivity is 7.8.

[0056] Example 5: 0.220 g of octadecylphosphonic acid solid powder was added to 150 mL of tetrahydrofuran solvent to prepare an octadecylphosphonic acid solution; 5A zeolite molecular sieve was then subjected to high-energy ball milling (the ball milling process was the same as in Example 1) and calcined in air at 400° C. for 7 h, then cooled to room temperature. 1 g of the calcined 5A zeolite molecular sieve was added to the octadecylphosphonic acid solution and stirred for 10 h; the mixture was then centrifuged at 10,000 r / min for 15 min, and the supernatant was removed; the mixture was heat treated at 110° C. for 6 h, cooled to room temperature, and washed three times with tetrahydrofuran solvent, using 200 mL of tetrahydrofuran solvent for each wash; finally, the mixture was dried in a vacuum drying oven under vacuum (1 Pa) for 10 h to obtain a 5A zeolite molecular sieve modified with an octadecylphosphonic acid monolayer.

[0057] 0.3 g of the 5A zeolite molecular sieve modified with octadecylphosphonic acid monolayer prepared in this example was taken and the adsorption selectivity of propylene / propane at an initial pressure of 15 kPa was measured with a high pressure gas adsorption instrument at 50°C. The sample was repeated three times and the adsorption test results were as follows: Figure 7 As shown in the 50℃ curve, the average maximum kinetic selectivity is 8.6.

[0058] Example 6: 0.220 g of octadecylphosphonic acid solid powder was added to 250 mL of tetrahydrofuran solvent to prepare an octadecylphosphonic acid solution; 5A zeolite molecular sieve was then subjected to high-energy ball milling (the ball milling process was the same as in Example 1) and calcined in air at 500° C. for 5 h, then cooled to room temperature. 1 g of the calcined 5A zeolite molecular sieve was added to the octadecylphosphonic acid solution and stirred for 20 h; the mixture was then centrifuged at 16,000 r / min for 5 min, and the supernatant was removed; the mixture was heat treated at 160° C. for 2 h, cooled to room temperature, and washed 5 times with tetrahydrofuran solvent, with 100 mL of tetrahydrofuran solvent used for each wash; finally, the mixture was dried in a vacuum drying oven under vacuum (1 Pa) for 10 h to obtain a 5A zeolite molecular sieve modified with an octadecylphosphonic acid monolayer.

[0059] 0.3 g of the 5A zeolite molecular sieve modified with octadecylphosphonic acid monolayer prepared in this example was taken and the adsorption selectivity of propylene / propane at an initial pressure of 15 kPa was measured using a high pressure gas adsorption instrument at 100°C. The sample was repeated three times and the adsorption test results were as follows: Figure 7 As shown in the 100°C curve, the average maximum kinetic selectivity is 9.0.

[0060] Example 7: This example differs from Example 1 in that 0.440 g of octadecylphosphonic acid is used instead of tert-butylphosphonic acid in Example 1 to prepare 5A zeolite molecular sieve modified with octadecylphosphonic acid monolayer.

[0061] 0.3 g of the 5A zeolite molecular sieve modified with octadecylphosphonic acid monolayer prepared in this example was taken and the adsorption selectivity of propylene / propane at an initial pressure of 15 kPa was measured using a high pressure gas adsorption instrument at 150°C. The sample was repeated three times and the adsorption test results were as follows: Figure 7 As shown in the 150℃ curve, the average maximum kinetic selectivity is 9.2.

[0062] Example 8: This example differs from Example 1 in that 0.660 g of octadecylphosphonic acid is used instead of tert-butylphosphonic acid in Example 1 to prepare 5A zeolite molecular sieve modified with octadecylphosphonic acid monolayer.

[0063] 0.3 g of the 5A zeolite molecular sieve modified with octadecylphosphonic acid monolayer prepared in this example was taken and the adsorption selectivity of propylene / propane at an initial pressure of 15 kPa was measured with a high pressure gas adsorption instrument at 25°C. The sample was repeated three times and the adsorption test results were as follows: Figure 7 As shown in the 25℃ curve, the average maximum kinetic selectivity is 9.2.

[0064] Example 9: The difference between this example and Example 1 is that a mixture of 0.032 g of methylphosphonic acid and 0.046 g of tert-butylphosphonic acid (the molar numbers of the two are equal) is used instead of the tert-butylphosphonic acid in Example 1 to prepare a 5A zeolite molecular sieve modified with a methylphosphonic acid-n-butylphosphonic acid mixed monolayer.

[0065] 0.3 g of the 5A zeolite molecular sieve modified with a mixed monolayer of methylphosphonic acid and tert-butylphosphonic acid prepared in this example was taken and the change in the adsorption selectivity of propylene / propane over time at an initial pressure of 15 kPa was measured using a high-pressure gas adsorption instrument at 25°C. Figure 8 As shown in the 5A-MPA-TBPA curve, the maximum kinetic selectivity is 13.6.

[0066] Example 10: The difference between this example and Example 1 is that a mixture of 0.032 g of methylphosphonic acid and 0.046 g of n-butylphosphonic acid (the molar numbers of the two are equal) is used instead of the tert-butylphosphonic acid in Example 1 to prepare a 5A zeolite molecular sieve modified with a methylphosphonic acid-n-butylphosphonic acid mixed monolayer.

[0067] 0.3 g of the 5A zeolite molecular sieve modified with a mixed monolayer of methylphosphonic acid and n-butylphosphonic acid prepared in this example was taken and measured at 25° C. using a high-pressure gas adsorption instrument to measure the change in the adsorption selectivity of propylene / propane with time at an initial pressure of 15 kPa. Figure 8 As shown in the 5A-MPA-BPA curve, the maximum kinetic selectivity is 16.2.

[0068] Example 11: The difference between this example and Example 1 is that a mixture of 0.021 g of methylphosphonic acid, 0.030 g of tert-butylphosphonic acid and 0.073 g of octadecylphosphonic acid (the molar numbers of the three are equal) is used instead of the tert-butylphosphonic acid in Example 1 to prepare a 5A zeolite molecular sieve modified with a mixed monolayer of methylphosphonic acid-tert-butylphosphonic acid-octadecylphosphonic acid.

[0069] 0.3 g of the 5A zeolite molecular sieve modified with a mixed monolayer of methylphosphonic acid, tert-butylphosphonic acid, and octadecylphosphonic acid prepared in this example was taken and measured at 25° C. using a high-pressure gas adsorption instrument to measure the change in the adsorption selectivity of propylene / propane with time at an initial pressure of 15 kPa. Figure 8 As shown in the 5A-MPA-TBPA-ODPA curve, the maximum kinetic selectivity is 21.1.

[0070] Example 12: The difference between this example and Example 1 is that a mixture of 0.021 g of methylphosphonic acid, 0.030 g of n-butylphosphonic acid and 0.073 g of octadecylphosphonic acid (the molar numbers of the three are equal) is used to replace the tert-butylphosphonic acid in Example 1 to prepare a 5A zeolite molecular sieve modified with a mixed monolayer of methylphosphonic acid-n-butylphosphonic acid-octadecylphosphonic acid.

[0071] 0.3 g of the 5A zeolite molecular sieve modified with a mixed monolayer of methylphosphonic acid, n-butylphosphonic acid, and octadecylphosphonic acid prepared in this example was taken and the change in the adsorption selectivity of propylene / propane over time at an initial pressure of 15 kPa was measured using a high-pressure gas adsorption instrument at 25°C. Figure 8 As shown in the 5A-MPA-BPA-ODPA curve, the maximum kinetic selectivity is 23.1.

[0072] It can be seen from Examples 1 to 12 that by modifying the surface of 5A zeolite molecular sieve with any one or more alkylphosphonic acids among methylphosphonic acid, tert-butylphosphonic acid, n-butylphosphonic acid and octadecylphosphonic acid, and adjusting the amount of organic phosphonic acid and the material preparation process conditions, the adsorption kinetic selectivity of propylene / propane of the modified 5A zeolite molecular sieve can be controlled.

[0073] The preferred process conditions for preparing alkylphosphonic acid-modified 5A zeolite molecular sieve with high C3H6 / C3H8 adsorption kinetic selectivity are as follows: calcination temperature of 450°C, calcination time of 6 h, the alkylphosphonic acid used is a mixture of methylphosphonic acid, n-butylphosphonic acid and octadecylphosphonic acid in equal moles, the ratio of alkylphosphonic acid to 5A zeolite molecular sieve is 0.66 mmol:1 g, the ratio of tetrahydrofuran solvent to 5A zeolite molecular sieve is 200 mL:1 g, stirring time is 15 h, centrifugal separation speed is 12000 r / min, centrifugal separation time is 10 min, heat treatment temperature is 120°C, heat treatment time is 4 h, and washing is done 4 times with tetrahydrofuran solvent, with 150 mL of solvent used for each wash.

[0074] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. The present invention can also adopt other zeolite molecular sieves and ball milling process conditions. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the scope of protection of the present invention.

Claims

1. A method for preparing a zeolite molecular sieve for adsorption separation of propylene and propane, characterized in that: The following steps are involved: S1, adding alkylphosphonic acid solid powder into tetrahydrofuran solvent to prepare alkylphosphonic acid solution; S2. After high-energy ball milling, 5A zeolite molecular sieve was calcined at 400-500°C for 5-7h and cooled to room temperature; S3, adding the 5A zeolite molecular sieve calcined in step S2 to the alkylphosphonic acid solution, stirring for 15 hours, centrifuging at 12000 r / min for 10 minutes in a centrifuge, removing the supernatant, and obtaining a solid product; The alkylphosphonic acid used was a mixture of methylphosphonic acid, n-butylphosphonic acid, and octadecylphosphonic acid in equal moles. The ratio of alkylphosphonic acid to 5A zeolite molecular sieve was 0.66 mmol:1 g, and the ratio of tetrahydrofuran solvent to 5A zeolite molecular sieve was 200 mL:1 g. S4, heat-treating the solid product at 120° C. for 4 h, then cooling to room temperature, and washing with tetrahydrofuran solvent 4 times, with the amount of tetrahydrofuran solvent used for each washing being 150 mL; S5. The solid product washed in step S4 is vacuum dried to obtain a 5A zeolite molecular sieve modified with an alkylphosphonic acid monolayer, which is used for the adsorptive separation of propylene and propane.

2. A zeolite molecular sieve for adsorption separation of propylene and propane, characterized in that: The preparation method according to claim 1 is used for preparation.

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