Zeolite molecular sieve for adsorbing and separating propylene and propane and preparation method thereof

Abstract

The invention belongs to the technical field of propylene separation and purification, and particularly discloses a zeolite molecular sieve for adsorbing and separating propylene and propane and a preparation method of the zeolite molecular sieve. The method is used for solving the problem that effective separation of propylene and propane cannot be realized when a 5A zeolite molecular sieve is used as an adsorption material at present. The method comprises the following steps: firstly, adding alkyl phosphonic acid solid powder into a tetrahydrofuran solvent to prepare an alkyl phosphonic acid solution, then roasting a 5A zeolite molecular sieve, cooling to room temperature, then adding the 5A zeolite molecular sieve into the alkyl phosphonic acid solution, stirring, carrying out centrifugal separation, and removing supernate; carrying out heat treatment, cooling to room temperature, and washing with a tetrahydrofuran solvent; and finally, carrying out vacuum drying to obtain the 5A zeolite molecular sieve modified by the alkyl phosphonic acid monomolecular layer. The propylene / propane adsorption separation selectivity based on a dynamic separation mechanism is effectively improved by regulating and controlling the relative resistance of propylene and propane penetrating through an alkyl phosphonic acid monomolecular layer.

Description

Technical Field

[0001] The 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] The industrial production methods of propylene include naphtha steam cracking, heavy oil fluidized catalytic cracking, propane dehydrogenation to produce propylene, coal methanol to olefins, etc. The crude propylene produced is mixed with propane. After separation and purification, polymerization grade purity propylene (purity ≥ 99.5%) can be obtained. Since the molecular structures of propylene and propane are not much different, their boiling points are similar and both are below room temperature. The separation method of propylene and propane in industry generally adopts low-temperature distillation, but the number of distillation plates is large (150 to 200 levels), the operating temperature is low (-90 to -40°C), the pressure is high (16 to 20 atmospheres), and the reflux ratio is large, so the fixed equipment investment is large and the production energy consumption is large. Absorption method, membrane separation method and adsorption method can replace the high energy consumption distillation method, among which adsorption method is expected to greatly reduce energy consumption.

[0003] Adsorption can replace the high-energy distillation method. Adsorption can be divided into equilibrium separation, kinetic separation and steric separation according to the separation mechanism. The materials that can be separated by adsorption from propylene and propane based on the kinetic separation mechanism mainly include: zeolite molecular sieves (DD3R, SiCHA, ITQ-55, ZSM-58, etc.), carbon molecular sieves (CMS, CNP, etc.) and metal organic framework materials (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 potential adsorption material. The kinetic diameters of propylene and propane molecules are similar (respectively and ), both of which can pass through the octahedral pores of 5A zeolite molecular sieve and enter the interior of zeolite molecular sieve. The kinetic diameter of propylene molecule is slightly smaller than that of propane molecule, and its adsorption rate is slightly greater than that of propane, but the adsorption kinetic selectivity is very small. Its ideal adsorption solution theory (IAST) kinetic selectivity (the ratio of the adsorption amount of two gases at the same adsorption time when two gases are subjected to single gas adsorption tests at the same temperature and initial pressure, hereinafter referred to as kinetic selectivity) is only about 1.2 at room temperature and pressure, which cannot achieve effective separation of propylene and propane.

[0005] Therefore, it is urgent to expand the difference in adsorption rates of propylene and propane by adjusting the pore structure of 5A zeolite molecular sieve 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 adsorption separation of propylene and propane, which effectively solves the problem that the current 5A zeolite molecular sieve as an adsorption material cannot 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 alkylphosphonic acid solution.

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

[0010] S3, adding the 5A zeolite molecular sieve calcined in step S2 to the alkylphosphonic acid solution, stirring for 10 to 20 hours, centrifuging in a centrifuge at a speed of 10000 to 16000 r / min for 5 to 15 minutes, removing the supernatant, and obtaining 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. The solid product is heat-treated at 110-130° C. for 2-6 hours, then cooled to room temperature, and washed with tetrahydrofuran solvent for 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 the adsorption 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] Further, in step S3, the stirring time is 15 hours, the centrifuge speed is 12000 r / min, and the centrifugation time is 10 minutes.

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

[0019] Further, in step S4, washing is performed 4 times with tetrahydrofuran solvent, 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 adsorption separation of propylene and propane, which is prepared by 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 diffusing 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 resistance of the organic monolayer to larger propane molecules is greater than that to smaller propylene molecules, so that the propane adsorption rate is much lower than the propylene adsorption rate, thereby effectively improving the adsorption kinetic selectivity of propylene / propane. 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 monolayer.

[0024] Figure 2 This is a temperature-programmed desorption-mass spectrometry (mass-to-charge ratio m / z is 15) analysis diagram 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 It is a graph showing the change in the amount of 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 It is a graph showing the change of propane adsorption amount 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 It is a graph showing the change of the adsorption selectivity of propylene / propane 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.

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

[0030] Figure 8 It is a graph showing the change of the adsorption selectivity of propylene / propane over time at 25° C. for the 5A zeolite molecular sieve modified with mixed alkylphosphonic acid of Examples 9 to 12. 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 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 is 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 with tetrahydrofuran solvent for 3-5 times, 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 adsorption 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 the 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 / silanol groups 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°C). Figure 2 The programmed temperature desorption-mass spectrum of 5A zeolite molecular sieve modified with monolayer of alkylphosphonic acid (TBPA, BPA, ODPA and MPA) (tested by MALDI-TOF mass spectrometer of Bruker) shows that it will not thermally decompose to produce methyl groups (mass-to-charge ratio (m / z) is 15) at 300°C.

[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: using the self-assembled monolayer (SAM) technology to add a layer of alkylphosphonic acid monolayer on the outer surface of 5A zeolite molecular sieve, adding a resistance layer to the adsorption of propylene and propane in the 5A zeolite molecular sieve, expanding the difference in the adsorption rate of propylene and propane, thereby improving the kinetic selectivity of adsorption separation. The chain length and spatial structure of the alkylphosphonic acid molecules used will affect the structure of the alkylphosphonic acid monolayer, thereby affecting the diffusion resistance of gas molecules passing through the alkylphosphonic acid monolayer during the adsorption process. The alkylphosphonic acid molecules used can be changed as needed to achieve the regulation of gas adsorption kinetic selectivity. Before the 5A zeolite molecular sieve is modified with alkylphosphonic acid, high-energy ball milling is first performed to reduce the particles of the 5A zeolite molecular sieve and increase the surface area, so as to facilitate modification with alkylphosphonic acid.

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

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

[0044] Example 1: (1) Take 0.091 g of tert-butylphosphonic acid (TBPA, CAS No. 4923-84-6, (HO)2POC(CH3)3, purity 99%, the same below) solid powder and add it 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 then subjected to high-energy ball milling (ND8-1L ball mill, Nanjing Nanda Tianzun Electronics Co., Ltd., zirconium dioxide grinding balls, the mass ratio of grinding balls to materials 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 increased from 30 m 2 / g increased to 33m 2 / g (the nitrogen adsorption isotherm at liquid nitrogen temperature was measured by ASAP 2460 adsorption instrument of Micromeritics Instrument Company, USA, and the surface area was calculated by t-Plot method), and then the 5A zeolite molecular sieve was calcined at 450°C in air for 6h and then cooled to room temperature.

[0046] (3) 1 g of the calcined 5A zeolite molecular sieve 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 for 4 times, with the amount of tetrahydrofuran solvent used for each washing being 150 mL.

[0048] (5) Finally, the 5A zeolite molecular sieve modified with tert-butylphosphonic acid monolayer (5A-TBPA) was obtained by drying the 5A zeolite molecular sieve in a vacuum oven at 1 Pa for 10 h.

[0049] 0.3 g of the 5A zeolite molecular sieve modified with tert-butylphosphonic 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 amounts 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 in 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 to replace 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 amounts 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 the figure; the adsorption selectivity of propylene / propane changes with time as shown in the figure Figure 6 As shown in the 5A-BPA curve, the maximum kinetic selectivity is 5.0.

[0052] Example 3: This example is different 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 amounts 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 5A zeolite molecular sieve modified with methylphosphonic acid monolayer (5A-MPA).

[0055] 0.3 g of the 5A zeolite molecular sieve modified with methylphosphonic 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 amounts 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 the figure; the adsorption selectivity of propylene / propane changes with time as shown in the figure 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 subjected to high-energy ball milling (the ball milling process was the same as in Example 1), and calcined at 400° C. in air for 7 h and 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; then centrifuged at a speed of 10000 r / min in a centrifuge for 15 min, and the supernatant was removed; then heat treated at 110° C. for 6 h and then cooled to room temperature, and washed 3 times with tetrahydrofuran solvent, with 200 mL of tetrahydrofuran solvent used for each washing; finally, 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 are shown in FIG. Figure 7 As shown in the 50°C 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 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 and 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; then centrifuged at a speed of 16000 r / min in a centrifuge for 5 min, and the supernatant was removed; then heat treated at 160° C. for 2 h and then cooled to room temperature, and washed 5 times with tetrahydrofuran solvent, with the amount of tetrahydrofuran solvent used for each washing being 100 mL; finally, 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 with 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 maximum kinetic selectivity is 9.0 on average.

[0060] Example 7: The difference between this example and Example 1 is 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 with a high pressure gas adsorption instrument at 150°C. The sample was repeated three times and the adsorption test results are shown in FIG. Figure 7 As shown in the 150℃ curve, the average maximum kinetic selectivity is 9.2.

[0062] Example 8: The difference between this example and Example 1 is 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 are shown in FIG. Figure 7 As shown in the 25°C 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 to replace 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 measured at 25° C. using a high pressure gas adsorption instrument to determine 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 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 to replace 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 the change of the adsorption selectivity of propylene / propane with time at an initial pressure of 15 kPa was measured by a high pressure gas adsorption instrument at 25°C. 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 to replace 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-octadecylphosphonic acid prepared in this example was taken and the change of the adsorption selectivity of propylene / propane with time at an initial pressure of 15 kPa was measured by a high-pressure gas adsorption instrument at 25° C., as shown in FIG. 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-octadecylphosphonic acid prepared in this example was taken and the change of the adsorption selectivity of propylene / propane with time at an initial pressure of 15 kPa was measured by a high-pressure gas adsorption instrument at 25° C., as shown in FIG. 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 of 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 5A zeolite molecular sieve modified with alkylphosphonic acid with high C3H6 / C3H8 adsorption kinetic selectivity are as follows: calcination temperature of 450°C, calcination time of 6 hours, 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 hours, centrifugal separation speed is 12000 r / min, centrifugal separation time is 10 minutes, heat treatment temperature is 120°C, heat treatment time is 4 hours, and washing is performed 4 times with tetrahydrofuran solvent, with 150 mL of solvent used for each washing.

[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, calcining 5A zeolite molecular sieve at 400-500°C for 5-7h after high-energy ball milling, and cooling to room temperature; S3, adding the 5A zeolite molecular sieve calcined in step S2 to the alkylphosphonic acid solution, stirring for 10 to 20 hours, centrifuging in a centrifuge at a speed of 10000 to 16000 r / min for 5 to 15 minutes, removing the supernatant, and obtaining a solid product; 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; S4, heat-treating the solid product at 110-130° C. for 2-6 h, then cooling to room temperature, and washing with tetrahydrofuran solvent for 3-5 times, with the amount of tetrahydrofuran solvent used for each washing being 100-200 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 adsorption separation of propylene and propane.

2. The method for preparing the zeolite molecular sieve for adsorption separation of propylene and propane according to claim 1, characterized in that: In step S1, the alkylphosphonic acid is any one or more of methylphosphonic acid, tert-butylphosphonic acid, n-butylphosphonic acid and octadecylphosphonic acid.

3. The method for preparing the zeolite molecular sieve for adsorption separation of propylene and propane according to claim 2, characterized in that: In step S2, the calcination temperature is 450°C and the calcination time is 6 hours.

4. The method for preparing the zeolite molecular sieve for adsorption separation of propylene and propane according to claim 3, characterized in that: 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.

5. The method for preparing the zeolite molecular sieve for adsorption separation of propylene and propane according to claim 4, characterized in that: In step S3, the stirring time is 15 hours, the centrifuge speed is 12000 r / min, and the centrifugation time is 10 minutes.

6. The method for preparing the zeolite molecular sieve for adsorption separation of propylene and propane according to claim 5, characterized in that: In step S4, the heat treatment temperature is 120° C. and the heat treatment time is 4 hours.

7. The method for preparing the zeolite molecular sieve for adsorption separation of propylene and propane according to claim 6, characterized in that: In step S4, the mixture is washed with tetrahydrofuran solvent for 4 times, and the amount of tetrahydrofuran solvent used in each washing is 150 mL.

8. A zeolite molecular sieve for adsorption separation of propylene and propane, characterized in that: The method is prepared by the preparation method described in any one of claims 1 to 7.

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