A lithium- and manganese-modified SAPO molecular sieve, its preparation method and application

Abstract

The present invention relates to a lithium and manganese modified SAPO molecular sieve, its preparation method and application, belonging to the technical field of adsorbents. The technical problem solved by the present invention is to provide a preparation method of a lithium and manganese modified SAPO molecular sieve. The method comprises the following steps: after impregnating the SAPO molecular sieve with a salt solution, performing solid-liquid separation, drying the solid and then calcining it to obtain the lithium and manganese modified SAPO molecular sieve. The present invention uses specific lithium salt and manganese salt solutions to impregnate and modify the SAPO molecular sieve, and successfully prepares the lithium and manganese modified SAPO molecular sieve. Its preparation method is simple and controllable, with low energy consumption and low cost. Moreover, the obtained modified molecular sieve can separate a nitrogen and methane mixed system, with an extremely low adsorption amount of methane, a large separation ratio of nitrogen to methane, and can also be applied to purify methane in coalbed methane, oilfield gas or landfill gas.

Description

Technical Field

[0001] The present invention belongs to the technical field of adsorption, and relates to a lithium- and manganese-modified SAPO molecular sieve, a preparation method thereof, and an application thereof. Background Art

[0002] As a high-quality and clean fuel and an important chemical raw material, natural gas has attracted more and more attention in its application. Accelerating the development of the natural gas industry has become a trend in the world today. However, a large amount of nitrogen is contained in natural gas produced from many oil and gas-bearing basins at home and abroad. This kind of natural gas with too high nitrogen content not only has a low calorific value and high energy consumption in the gathering and transportation process, but also cannot be directly used as fuel for natural gas vehicles (NGV) and certain chemical raw materials. Therefore, natural gas denitrification is an important condition for the rational and full utilization of natural gas. Currently, the commonly used natural gas denitrification processes mainly include cryogenic denitrification process, solvent absorption process, and pressure swing adsorption process.

[0003] The pressure swing adsorption (PSA) process has a simple process, strong adaptability, and low energy consumption, and has been successfully applied in air separation, hydrogen purification, etc. However, when used for natural gas denitrification, it has disadvantages such as low adsorption selectivity, limited adsorption capacity, and low methane recovery rate. The core of PSA lies in the adsorbent therein, and the performance of the adsorbent determines whether the separation of the mixed gas can be achieved and the separation effect. Theoretically, the main components of coalbed methane, natural gas, oilfield gas, etc. are CO2, CH4, and N2, etc. The physical properties of CO2 and CH4 molecules are quite different and are easy to separate; however, the critical temperatures of N2 and CH4 are both very low, their physical properties are similar, and their kinetic diameters are similar, making them difficult to separate. Therefore, the core technology for CH4 gas separation lies in the effective separation of CH4 and N2, that is, the use of an adsorbent with very high selectivity. There are many types of molecular sieves as high-quality adsorbents. Silicoaluminophosphate molecular sieve (SAPO) is a microporous crystal composed of three tetrahedral units of SiO2, AlO2 - and PO2 + It is a new molecular sieve material with excellent selectivity and thermal stability, whose physicochemical properties are not only similar to those of silica-aluminum zeolite, but also have some characteristics of aluminum phosphate molecular sieves.

[0004] Chinese Patent Application CN 108383100 A discloses a carbon molecular sieve for methane enrichment and its preparation method. First, the mesoporous molecular sieve is impregnated in a mixed solution of an acid catalyst and an organic solvent to obtain a filter cake, then it is placed in an aqueous solution of an organic polymer and continuously irradiated in ultrasonic waves, followed by processes such as preliminary carbonization and hydrofluoric acid soaking to obtain a precursor, and further loading a cracking catalytic material on the surface of the precursor. After reduction treatment, preliminary pore adjustment and precise pore adjustment, the final carbon molecular sieve product capable of enriching methane is obtained. The molecular sieve product prepared by this process has obvious CH4 / N2 separation performance and preferentially adsorbs N2, enabling the product gas to be directly enriched and recovered at the top of the tower, which can significantly reduce the operating cost of pressure swing adsorption. However, the method for adjusting the internal pore size of this molecular sieve has a complex process flow, requires precise time and temperature control, and involves chemisorption and high-temperature cracking of alkanes and methane during the process. The effect of regulating the pore size of the molecular sieve still needs to be further verified.

[0005] Chinese Patent Application CN 105439170 A discloses a SAPO-35 molecular sieve, whose anhydrous chemical composition is: mMDEA·(Si x Al y P z )O2, where MDEA is N-methyldiethanolamine, distributed in the molecular sieve cages and pores; m is the number of moles of N-methyldiethanolamine per mole of (Si x Al y P z )O2, m = 0.05 - 0.25; x, y, z respectively represent the molar fractions of Si, Al, P, and their ranges are x = 0.01 - 0.25, y = 0.35 - 0.50, z = 0.25 - 0.50, and x + y + z = 1. The synthesized SAPO-35 molecular sieve in this application can be used as a catalyst for acid-catalyzed reactions, such as methanol to olefins reaction. This application also relates to the application of this SAPO-35 molecular sieve in the adsorption separation of methane, carbon dioxide, and nitrogen. However, when the SAPO molecular sieve is used in PSA, its adsorption effect is not good, and the separation ratio of CH4 and N2 is not high.

[0006] Therefore, it is necessary to explore a preparation method of SAPO molecular sieve with simple method, low cost and high CH4 and N2 separation ratio. Summary of the Invention

[0007] In view of the problems existing in the prior art, the present invention uses lithium salts and manganese salts for modification to modify the pore channels and change the acid-base properties of the adsorbent at the same time. The purpose is to modify the SAPO molecular sieve so that the modified adsorbent has better adsorption selectivity for nitrogen, thereby reducing its adsorption amount of methane and effectively separating nitrogen and methane.

[0008] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0009] First, a preparation method of lithium and manganese modified SAPO molecular sieve is provided, which includes the following steps:

[0010] (1) Dissolve lithium salt and manganese salt in a solvent to obtain a salt solution;

[0011] (2) Grind the SAPO molecular sieve, mix it evenly with the salt solution obtained in step (1), filter, dry the obtained filter residue, and finally calcine it to obtain the lithium and manganese modified SAPO molecular sieve.

[0012] The weight ratio of the total amount of the lithium salt and the manganese salt to the weight of the SAPO molecular sieve is 1.5 - 2.5 g: 19 - 21 mL.

[0013] Furthermore, in step (1), the lithium salt is one or more of lithium nitrate, lithium sulfate, and lithium chloride, preferably lithium nitrate; the manganese salt is one or more of manganese nitrate, manganese sulfate, and manganese chloride, preferably manganese nitrate.

[0014] Furthermore, in step (1), the concentration of lithium ions in the salt solution is 0.01 - 8 wt%, and the concentration of manganese ions is 0.1 - 10 wt%.

[0015] Preferably, in step (1), the concentration of lithium ions in the salt solution is 0.5 - 8 wt%, and the concentration of manganese ions is 1 - 10 wt%.

[0016] Furthermore, after the SAPO molecular sieve in step (2) is ground, the particle size distribution is 40 - 60 mesh.

[0017] Furthermore, the SAPO molecular sieve in step (2) includes one or more of SAPO - 20, SAPO - 25, SAPO - 28, and SAPO - 35, preferably SAPO - 35.

[0018] In some specific embodiments, the SAPO molecular sieve is SAPO - 35. SAPO - 35 is an intergrowth chabazite - type (LEV) molecular sieve with mutually intersecting eight - membered ring channels and a pore size of a small - pore molecular sieve. The framework of SAPO - 35 is composed of LEV cages connected by single six - membered rings and double six - membered rings. There are two different T - atom positions in the framework, one in the double six - membered ring and the other in the single six - membered ring, and the distribution ratio of these two positions is 2:1. By using SAPO - 35 and modifying and blocking the pores with lithium salt and manganese salt, the separation ratio of nitrogen and methane can be improved.

[0019] Furthermore, the drying temperature in step (2) is set to 60 - 200 °C.

[0020] Further, the calcination in step (2) is a gradient temperature increase, and the gradient temperature increase program is set as follows: The temperature is increased from 100°C to 300°C at a heating rate of 5°C / min and held at a constant temperature for 2 h; then the temperature is increased from 300°C to 450°C at a heating rate of 3°C / min and held at a constant temperature for 4 h; finally, the temperature is increased from 450°C to 600°C at a heating rate of 2°C / min and held at a constant temperature for 3 h.

[0021] Further, the mixing method in step (2) is impregnation, and the impregnation is equal-volume impregnation or excess impregnation.

[0022] Further, the lithium- and manganese-modified SAPO molecular sieve obtained by the above-mentioned preparation method.

[0023] Further, the application of the lithium- and manganese-modified SAPO molecular sieve obtained by the preparation method or the lithium- and manganese-modified SAPO molecular sieve in purifying methane from coalbed methane, oilfield gas or landfill gas.

[0024] In some specific embodiments, a preparation method of a lithium- and manganese-modified SAPO molecular sieve includes the following steps:

[0025] (1) At room temperature, a certain amount of lithium nitrate and manganese nitrate are mixed with deionized water, and then stirred to completely dissolve lithium nitrate and manganese nitrate in water to obtain a salt solution. In this salt solution, the concentration of lithium ions is 0.5-8 wt%, and the concentration of manganese ions is 1-10 wt%.

[0026] (2) Take 2 g of ground SAPO-35 molecular sieve, mix it with 20 mL of the salt solution, stir well, then place it in an ultrasonic bath for oscillating mixing, then perform suction filtration separation, dry the filter residue overnight at 80°C, place the dried sample in a tube furnace, and calcine it under a nitrogen atmosphere. The temperature is increased from 100°C to 300°C at a heating rate of 5°C / min and held at a constant temperature for 2 h; then the temperature is increased from 300°C to 450°C at a heating rate of 3°C / min and held at a constant temperature for 4 h; finally, the temperature is increased from 450°C to 600°C at a heating rate of 2°C / min and held at a constant temperature for 3 h.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The present invention uses specific dosage ratios of lithium salt, manganese salt, and SAPO molecular sieve, and bakes them under a gradient temperature increase program to successfully prepare a lithium- and manganese-modified SAPO molecular sieve;

[0029] (2) The preparation method of the present invention is simple and controllable, has low energy consumption, and low cost;

[0030] (3) The lithium- and manganese-modified SAPO molecular sieve prepared by the present invention is used for separating a nitrogen and methane mixed system. The adsorption amount of methane is extremely low, and the separation ratio of nitrogen to methane is large. Detailed implementation manners

[0031] It should be noted that the raw materials used in the present invention are all ordinary commercially available products, and no specific limitation is imposed on their sources.

[0032] The following raw material sources are for exemplary illustration:

[0033] SAPO molecular sieve: purchased from Shanghai Kelaman Reagent Co., Ltd., product number 101759.

[0034] Example 1

[0035] The lithium- and manganese-modified SAPO molecular sieve was prepared by the following method:

[0036] (1) Prepare a salt solution: At room temperature, a certain amount of lithium nitrate and manganese nitrate are mixed with deionized water, and then stirred to completely dissolve lithium nitrate and manganese nitrate in water to obtain a salt solution. In this salt solution, the concentration of lithium ions is 0.5 wt%, and the concentration of manganese ions is 1 wt%.

[0037] (2) Take 2 g of the ground SAPO-35 molecular sieve, mix it with 20 mL of the salt solution, stir well, then place it in an ultrasonic bath for oscillating mixing, and then perform suction filtration separation. The filter residue is dried overnight at 80 °C. The dried sample is placed in a tubular furnace and calcined under a nitrogen atmosphere. It is heated from 100 °C to 300 °C at a heating rate of 5 °C / min and kept at a constant temperature for 2 h; then it is heated from 300 °C to 450 °C at a heating rate of 3 °C / min and kept at a constant temperature for 4 h; finally, it is heated from 450 °C to 600 °C at a heating rate of 2 °C / min and kept at a constant temperature for 3 h.

[0038] The static adsorption method was used to measure the adsorption amounts of nitrogen and methane of the above modified samples. The static adsorption method was carried out according to the method disclosed in Patent Application No. 201911089480.2 for sample determination. The measurement results are shown in Table 1.

[0039] Table 1

[0040]

[0041]

[0042] Example 2

[0043] The lithium- and manganese-modified SAPO molecular sieve was prepared by the following method:

[0044] (1) Prepare the salt solution: At room temperature, mix a certain amount of lithium nitrate and manganese nitrate with deionized water, and then stir it to completely dissolve lithium nitrate and manganese nitrate in water to obtain a salt solution. In this salt solution, the concentration of lithium ions is 4 wt%, and the concentration of manganese ions is 5 wt%.

[0045] (2) Take 2 g of ground SAPO-35 molecular sieve, mix it with 20 mL of the salt solution, stir well, then place it in an ultrasonic bath for oscillating mixing, and then perform suction filtration separation. Dry the filter residue overnight at 80 °C. Place the dried sample in a tube furnace and calcine it under a nitrogen atmosphere. Heat it from 100 °C to 300 °C at a heating rate of 5 °C / min and hold for 2 h; then heat it from 300 °C to 450 °C at a heating rate of 3 °C / min and hold for 4 h; finally, heat it from 450 °C to 600 °C at a heating rate of 2 °C / min and hold for 3 h.

[0046] Use the static adsorption method in Example 1 to measure the adsorption amounts of nitrogen and methane by the modified sample, and the results are shown in Table 2.

[0047] Table 2

[0048]

[0049]

[0050] Example 3

[0051] The lithium- and manganese-modified SAPO molecular sieve was prepared by the following method:

[0052] (1) Prepare the salt solution: At room temperature, mix a certain amount of lithium nitrate and manganese nitrate with deionized water, and then stir it to completely dissolve lithium nitrate and manganese nitrate in water to obtain a salt solution. In this salt solution, the concentration of lithium ions is 8 wt%, and the concentration of manganese ions is 3 wt%.

[0053] Take 2 g of ground SAPO-35 molecular sieve, mix it with 20 mL of the salt solution, stir well, then place it in an ultrasonic bath for oscillating mixing, and then perform suction filtration separation. Dry the filter residue overnight at 80 °C. Place the dried sample in a tube furnace and calcine it under a nitrogen atmosphere. Heat it from 100 °C to 300 °C at a heating rate of 5 °C / min and hold for 2 h; then heat it from 300 °C to 450 °C at a heating rate of 3 °C / min and hold for 4 h; finally, heat it from 450 °C to 600 °C at a heating rate of 2 °C / min and hold for 3 h.

[0054] Use the static adsorption method in Example 1 to measure the adsorption amounts of nitrogen and methane by the modified sample, and the results are shown in Table 3.

[0055] Table 3

[0056]

[0057]

[0058] Example 4

[0059] The lithium- and manganese-modified SAPO molecular sieve was prepared by the following method:

[0060] (1) Prepare a salt solution: At room temperature, a certain amount of lithium nitrate and manganese nitrate were mixed with deionized water, and then stirred to completely dissolve lithium nitrate and manganese nitrate in water to obtain a salt solution. In this salt solution, the concentration of lithium ions was 2 wt%, and the concentration of manganese ions was 10 wt%.

[0061] (2) Take 2 g of the ground SAPO-35 molecular sieve, mix it with 20 mL of the salt solution, stir well, then place it in an ultrasonic bath for oscillating mixing, and then perform suction filtration separation. The filter cake was dried overnight at 80 °C. The dried sample was placed in a tubular furnace and calcined under a nitrogen atmosphere. It was heated from 100 °C to 300 °C at a heating rate of 5 °C / min and held at a constant temperature for 2 h; then it was heated from 300 °C to 450 °C at a heating rate of 3 °C / min and held at a constant temperature for 4 h; finally, it was heated from 450 °C to 600 °C at a heating rate of 2 °C / min and held at a constant temperature for 3 h.

[0062] The static adsorption method in Example 1 was used to measure the adsorption amounts of nitrogen and methane on the modified sample, and the results are shown in Table 4.

[0063] Table 4

[0064]

[0065]

[0066] Comparative Example 1

[0067] The lithium- and manganese-modified SAPO molecular sieve was prepared by the following method:

[0068] (1) Prepare a salt solution: At room temperature, a certain amount of lithium nitrate and manganese nitrate were mixed with deionized water, and then stirred to completely dissolve lithium nitrate and manganese nitrate in water to obtain a salt solution. In this salt solution, the concentration of lithium ions was 8.5 wt%, and the concentration of manganese ions was 11 wt%.

[0069] (2) Take 2 g of the ground SAPO-35 molecular sieve, mix it with 20 mL of the salt solution, stir well, then place it in an ultrasonic bath for oscillating mixing, followed by suction filtration separation. The filter residue is dried overnight at 80 °C. The dried sample is placed in a tubular furnace and calcined under a nitrogen atmosphere. It is heated from 100 °C to 300 °C at a heating rate of 5 °C / min and held at a constant temperature for 2 h; then it is heated from 300 °C to 450 °C at a heating rate of 3 °C / min and held at a constant temperature for 4 h; finally, it is heated from 450 °C to 600 °C at a heating rate of 2 °C / min and held at a constant temperature for 3 h.

[0070] Use the static adsorption method in Example 1 to measure the adsorption amounts of nitrogen and methane by the modified sample, and the results are shown in Table 5.

[0071] Table 5

[0072]

[0073] Comparative Example 2

[0074] The lithium- and manganese-modified SAPO molecular sieve was prepared by the following method:

[0075] (1) Prepare the salt solution: At room temperature, mix a certain amount of lithium nitrate and manganese nitrate with deionized water, then stir it to completely dissolve lithium nitrate and manganese nitrate in water to obtain the salt solution. In this salt solution, the concentration of lithium ions is 4 wt% and the concentration of manganese ions is 5 wt%.

[0076] (2) Take 5 g of the ground SAPO-35 molecular sieve, mix it with 20 mL of the salt solution, stir well, then place it in an ultrasonic bath for oscillating mixing, followed by suction filtration separation. The filter residue is dried overnight at 80 °C. The dried sample is placed in a tubular furnace and calcined under a nitrogen atmosphere. It is heated from 100 °C to 300 °C at a heating rate of 5 °C / min and held at a constant temperature for 2 h; then it is heated from 300 °C to 450 °C at a heating rate of 3 °C / min and held at a constant temperature for 4 h; finally, it is heated from 450 °C to 600 °C at a heating rate of 2 °C / min and held at a constant temperature for 3 h.

[0077] Use the static adsorption method in Example 1 to measure the adsorption amounts of nitrogen and methane by the modified sample, and the results are shown in Table 6.

[0078] Table 6

[0079]

[0080] Comparative Example 3

[0081] The lithium- and manganese-modified SAPO molecular sieve was prepared by the following method:

[0082] (1) preparing a salt solution: at room temperature, mixing a certain amount of lithium nitrate and manganese nitrate with deionized water, and then stirring the mixture to completely dissolve the lithium nitrate and manganese nitrate in the water to obtain a salt solution, wherein the concentration of lithium ions is 4 wt % and the concentration of manganese ions is 5 wt %;

[0083] (2) 2 g of ground SAPO-35 molecular sieve was mixed with 20 mL of salt solution and stirred thoroughly. The mixture was then placed in an ultrasonic oven for oscillation mixing and then separated by filtration. The residue was dried overnight at 80 °C. The dried sample was placed in a tubular furnace and calcined in a nitrogen atmosphere at a heating rate of 4 °C / min from 100 °C to 450 °C for 6 h.

[0084] The static adsorption method in Example 1 was used to measure the adsorption amount of nitrogen and methane by the modified sample. The results are shown in Table 7.

[0085] Table 7

[0086]

[0087] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A preparation method of lithium and manganese modified SAPO molecular sieve, characterized in that, It includes the following steps: (1) Dissolve lithium salt and manganese salt in a solvent to obtain a salt solution; (2) Grind the SAPO molecular sieve, mix it evenly with the salt solution obtained in step (1), filter, dry the obtained filter residue, and finally calcine it to obtain a lithium and manganese modified SAPO molecular sieve; In the salt solution described in step (1), the concentration of lithium ions is 0.01 - 8 wt%, and the concentration of manganese ions is 0.1 - 10 wt%; In step (2), the dosage ratio of the SAPO molecular sieve to the salt solution is 1.5 - 2.5 g : 19 - 21 mL; The calcination in step (2) is gradient heating, and the gradient heating program is set as follows: heat from 100°C to 300°C at a heating rate of 5°C / min and keep the temperature constant for 2 h; then heat from 300°C to 450°C at a heating rate of 3°C / min and keep the temperature constant for 4 h; finally heat from 450°C to 600°C at a heating rate of 2°C / min and keep the temperature constant for 3 h.

2. The preparation method according to claim 1, characterized in that, The lithium salt described in step (1) is one or more of lithium nitrate, lithium sulfate, and lithium chloride, and the manganese salt is one or more of manganese nitrate, manganese sulfate, and manganese chloride.

3. The preparation method according to claim 1, wherein In the salt solution described in step (1), the concentration of lithium ions is 0.5 - 8 wt%, and the concentration of manganese ions is 1 - 10 wt%.

4. The preparation method according to claim 1, characterized in that, After the SAPO molecular sieve described in step (2) is ground, the particle size distribution is 40 - 60 mesh.

5. The preparation method according to claim 1, characterized in that, The SAPO molecular sieve described in step (2) includes one or more of SAPO - 20, SAPO - 25, SAPO - 28, and SAPO - 35.

6. The preparation method according to claim 1, characterized in that, The drying temperature described in step (2) is set at 60 - 200°C.

7. The lithium and manganese modified SAPO molecular sieve obtained by the preparation method according to any one of claims 1 - 6.

8. The application of the lithium and manganese modified SAPO molecular sieve obtained by the preparation method according to any one of claims 1 - 6 or the lithium and manganese modified SAPO molecular sieve according to claim 7 in purifying methane in coalbed methane, oilfield gas, or landfill gas.

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