Method for preparing ultra-pure helium and co-producing ultra-pure hydrogen from ammonia purge gas

Abstract

The invention discloses a method for preparing ultra-pure helium and co-producing ultra-pure hydrogen from ammonia purge gas, and relates to the technical field of gas separation. The method comprises the following steps: adsorbing and removing ammonia and other impurities by using an isobaric recovery tower and a pressure swing adsorption tower to obtain a material gas mainly containing helium, hydrogen and neon, separating by using a palladium tube to obtain high-purity hydrogen, and adsorbing and refining tail gas of the palladium tube by using a low-temperature adsorption tower and a special low-temperature adsorbent to obtain high-purity helium. The process method is simple in flow, and can effectively realize co-production of ultra-pure helium and ultra-pure hydrogen taking synthetic ammonia purge gas as a raw material, so that waste of hydrogen and helium resources is effectively avoided, meanwhile, the process omits tedious steps of multiple times of catalytic combustion dehydrogenation, deoxidation and drying, the process cost is effectively reduced, and the process economic benefit is improved.

Description

Technical Field

[0001] The present application relates to the field of gas separation technology, and in particular to a method for preparing ultra-pure helium from ammonia purge gas and co-producing ultra-pure hydrogen. Background Art

[0002] Helium is a precious resource and plays a pivotal role in the national economy and national security. Helium and natural gas are associated but the content is extremely low. The efficiency of directly purifying helium from natural gas is low and the energy consumption is high. In the process of synthesizing ammonia with helium-containing natural gas as raw material, the inert gas helium is concentrated because it does not participate in the reaction. The helium content in the purge gas has increased by nearly 10 times, but the content is only 0.3-0.9%. Hydrogen, helium and most of the argon can be removed by pressure swing adsorption or membrane separation, but hydrogen, helium and trace amounts of argon are difficult to remove. Hydrogen is usually removed by oxidative combustion, methanation or cryogenic liquefaction. But all three have shortcomings. The direct combustion method requires the direct combustion of hydrogen, which is about 100 times the amount of helium, and the waste of hydrogen resources is serious. Methanation requires the introduction of carbon monoxide, which is toxic and needs to be further removed later. The process is complicated, and the purge gas volume is usually small, there is no scale effect, and the economy is not ideal. The cryogenic liquefaction process is simple, but the investment and energy consumption are huge, and the cost of producing helium is high. In addition, the inert trace argon gas in the traditional process is difficult to completely remove, and the product purity can generally only reach 99.999%, not 99.9999%. Summary of the invention

[0003] The purpose of the present application is to provide a method for preparing ultra-pure helium and co-producing ultra-pure hydrogen from ammonia purge gas, which can effectively purify and remove most of the impurities in the purge gas, separate and obtain ultra-pure hydrogen with a purity of 99.9999%, and can also obtain ultra-pure helium at the same time; the process flow is simple, the cost is relatively low, and the economic benefits are good.

[0004] The technical solution of this application is as follows:

[0005] The present invention provides a method for preparing ultra-pure helium and co-producing ultra-pure hydrogen from ammonia purge gas, which comprises the following steps:

[0006] The synthetic ammonia purge gas is sent to an isobaric recovery tower to absorb ammonia in the purge gas until the ammonia content is less than 20 mg / L, and then the material gas produced by the isobaric recovery tower is sent to a pressure swing adsorption tower equipped with an adsorbent for adsorption treatment to reduce the ammonia content in the material gas to less than 5 mg / L, and at the same time, water, carbon dioxide, methane and part of argon impurities are adsorbed and removed. At this time, the material gas mainly contains helium, hydrogen and neon;

[0007] The material gas is then sent to the palladium tube, where the hydrogen in the material gas is ionized into protons under the action of palladium, which pass through the palladium tube and then combine with electrons to re-form hydrogen to obtain high-purity hydrogen and tail gas discharged after hydrogen separation;

[0008] The tail gas discharged from the palladium tube is sent to a low-temperature adsorption tower equipped with a special low-temperature adsorbent for low-temperature adsorption refining, denemonization and dehydrogenation to obtain high-purity helium.

[0009] Furthermore, in some embodiments of the present application, the adsorbent in the pressure swing adsorption tower is any one or more of activated carbon, silica gel, alumina and molecular sieve.

[0010] Furthermore, in some embodiments of the present application, when the pressure swing adsorption tower performs adsorption treatment, the adsorption pressure is 0.3-3 MPa and the adsorption temperature is 10-50°C.

[0011] Furthermore, in some embodiments of the present application, the pressure of the material gas entering the palladium tube is 0.3-3 MPa, the temperature is 200-500° C., and the hydrogen flux is 0.04-3 mol / m 2 ·s.

[0012] Furthermore, in some embodiments of the present application, when the low-temperature adsorption tower performs low-temperature adsorption, the low-temperature adsorption pressure is 0.5 to 4 MPa and the temperature is -110°C to -200°C.

[0013] Further, in some embodiments of the present application, the isobaric recovery tower comprises a bubbling layer and a cooling layer from bottom to top, and an isobaric composite absorption tower tray is arranged in the cooling layer;

[0014] The synthetic ammonia purge gas first enters the bubbling layer, washes ammonia under the heat exchange conditions of the 18-23 groups of water tanks, and then passes through the isobaric composite absorption tower tray of the cooling layer, mixes with the dilute ammonia water or soft water from the high-pressure ammonia purification tower, and absorbs ammonia in the purge gas until the ammonia content is less than 20 mg / L;

[0015] When the pressure swing adsorption tower performs adsorption treatment on the material gas, the steps are: adsorption-average reduction-reversal-flushing-evacuation-average increase-final increase-adsorption, so as to reduce the ammonia content in the material gas to less than 5 mg / L.

[0016] Furthermore, in some embodiments of the present application, the special low-temperature adsorbent is a molecular sieve-carbon composite adsorbent with a core-shell structure, which is prepared from raw materials including the following components: molecular sieve, phenol, aldehyde, amine, surfactant and water.

[0017] Furthermore, in some embodiments of the present application, the special low-temperature adsorbent is prepared by the following method:

[0018] dissolving phenol in water, adding a surfactant thereto and stirring to obtain a soaking solution;

[0019] Add molecular sieve beads to the soaking solution and soak for 2 to 4 hours, then add the mixed solution of amine and aldehyde and stir, then age at 40 to 95° C. for 5 to 20 hours, filter to obtain a solid phase material, and dry the solid phase material at 60° C. for 8 to 12 hours to obtain a benzoxazine resin with a molecular sieve as a core;

[0020] In a nitrogen atmosphere, the temperature is increased to 400°C at a rate of 1-4°C / min, and the prepared benzoxazine resin with the molecular sieve as the core is dried at a constant temperature for 2-3 hours. Then, the temperature is increased from 400°C to the carbonization final temperature of 550-900°C at a rate of 1-4°C / min, and the temperature is kept constant for 1-5 hours to obtain a molecular sieve-carbon composite adsorbent with a core-shell structure as a special low-temperature adsorbent.

[0021] Furthermore, in some embodiments of the present application, during the preparation of the special low-temperature adsorbent:

[0022] The molar ratio of phenol to aldehyde is 1:(0.6-4), the molar ratio of phenol to amine is 1:(0.1-1.5), the mass ratio of phenol to water is 1:(50-1000), the molar ratio of phenol to surfactant is 100:(1-10), and the volume ratio of molecular sieve to soaking liquid is 1:(5-200).

[0023] Further, in some embodiments of the present application, the phenol is any one or more of hydroquinone, resorcinol and phenol;

[0024] The aldehyde is any one or more of formaldehyde, trioxymethylene, polyformaldehyde, and adipaldehyde;

[0025] The amine is any one or more of ethylenediamine, 1,4-butanediamine, and 1,6-hexanediamine;

[0026] The surfactant is any one or more of polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer F127, polyvinyl pyrrolidone, polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer P123, sodium dodecylbenzene sulfonate, and hexadecyltrimethylammonium bromide;

[0027] The molecular sieve is any one or more of A-type, X-type, and Y-type molecular sieves.

[0028] Compared with the prior art, the embodiments of the present application have at least the following advantages or beneficial effects:

[0029] In view of the above aspects, an embodiment of the present application provides a method for preparing ultra-pure helium and co-producing ultra-pure hydrogen from ammonia purge gas. The process first feeds the synthetic ammonia purge gas into an isobaric recovery tower, and uses the isobaric recovery tower to absorb ammonia in the purge gas, and simultaneously adsorbs and removes excess water, carbon dioxide, methane, argon and other impurities to obtain a hydrogen-helium-neon mixed gas, which is further separated and purified using a palladium tube to obtain ultra-pure hydrogen; at the same time, the tail gas discharged from the palladium tube is subjected to low-temperature adsorption, and the neon in the tail gas and the remaining part of the hydrogen are adsorbed and removed using a low-temperature adsorption tower and a special low-temperature adsorbent, thereby simultaneously obtaining ultra-pure helium, thereby realizing the co-production of ultra-pure hydrogen and ultra-pure helium using synthetic ammonia purge gas as raw material.

[0030] The process method is simple in flow and can effectively realize the co-production of ultra-pure helium and ultra-pure hydrogen using synthetic ammonia purge gas as raw materials, thereby effectively avoiding the waste of hydrogen and helium resources. At the same time, the process eliminates the tedious steps of multiple catalytic combustion dehydrogenation followed by deoxygenation and drying, effectively reducing process costs and improving process economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 A schematic diagram of the process flow of a method for preparing ultra-pure helium and co-producing ultra-pure hydrogen from ammonia purge gas provided in an embodiment of the present application. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0034] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application may be combined with each other.

[0035] The features and performance of the present application are further described in detail below in conjunction with the embodiments.

[0036] Example 1

[0037] The present application provides a special low-temperature adsorbent, which is prepared by the following method:

[0038] Weigh 16 g of hydroquinone into a round-bottom flask, add 3.2 L of deionized water and stir at room temperature, add 2.8 g of surfactant F127 after dissolution to obtain a soaking solution;

[0039] Take 2.7 g of 1,4-butanediamine and 15 ml of 37% formaldehyde and mix them to obtain a mixed solution;

[0040] Weigh 100 g of 5A molecular sieve, add it to the soaking solution and soak for 2 h, then add the mixed solution dropwise and continue stirring, heat to 65 ° C in a water bath and age for 12 h, then filter and wash three times with 100 ml of water, place the obtained solid phase material in an oven, and dry it at 65 ° C for 8 h to obtain molecular sieve-benzoxazine resin;

[0041] The dried molecular sieve-benzoxazine resin is placed in a carbonization furnace for carbonization. The carbonization conditions are as follows: in a nitrogen atmosphere, the temperature is increased from room temperature to 400°C at a rate of 2°C / min, maintained at a constant temperature for 2 hours, and then increased from 400°C to a carbonization final temperature of 790°C at a rate of 3°C / min, maintained at a constant temperature for 1 hour to obtain a molecular sieve-carbon composite adsorbent with a core-shell structure, which is used as a special low-temperature adsorbent.

[0042] Example 2

[0043] The present application provides a special low-temperature adsorbent, which is prepared by the following method:

[0044] Weigh 13 g of resorcinol into a round-bottom flask, add 3.8 L of deionized water and stir at room temperature, add 3.1 g of surfactant F123 after dissolution to obtain a soaking solution;

[0045] Take 3.2 g of 1,6-hexanediamine and 7 ml of 37% glutaraldehyde and mix them to obtain a mixed solution;

[0046] Weigh 100 g of 13X molecular sieve, add it to the soaking solution and soak for 2 hours, then add the mixed solution dropwise and continue stirring, heat the water bath to 70°C for aging for 15 hours, then filter and wash three times with 120 ml of water, place the obtained solid phase material in an oven, and dry it at 60°C for 10 hours to obtain molecular sieve-benzoxazine resin;

[0047] The dried molecular sieve-benzoxazine resin is placed in a carbonization furnace for carbonization. The carbonization conditions are as follows: in a nitrogen atmosphere, the temperature is increased from room temperature to 400°C at a rate of 2°C / min, maintained at a constant temperature for 2 hours, and then increased from 400°C to a carbonization final temperature of 820°C at a rate of 3°C / min, maintained at a constant temperature for 1 hour to obtain a molecular sieve-carbon composite adsorbent with a core-shell structure, which is used as a special low-temperature adsorbent.

[0048] Example 3

[0049] This embodiment provides a method for preparing ultrapure helium and co-producing ultrapure hydrogen from ammonia purge gas, wherein the parameters of the synthetic ammonia purge gas are: 0.3-0.9% helium, 13-15% ammonia, 2.5 MPa pressure, and 30°C temperature;

[0050] The process is roughly as follows Figure 1 As shown, the method steps are as follows:

[0051] The synthetic ammonia purge gas is sent to the bubbling layer of the lower section of the isobaric recovery tower to wash ammonia under the heat exchange conditions of 21 groups of water tanks. After leaving the bubbling layer, the unabsorbed ammonia passes through the isobaric composite absorption tower tray of the cooling layer from bottom to top, and is successively mixed with the dilute ammonia water or soft water from the high-pressure ammonia purification tower to further absorb the ammonia in the purge gas to reduce the ammonia content to 18 mg / L.

[0052] The material gas produced by the isobaric recovery tower is then sent to a pressure swing adsorption tower, which is filled with activated carbon and 5A molecular sieve adsorbent. Under the conditions of an adsorption pressure of 1.5 MPa and an adsorption temperature of 25°C, the adsorption treatment is carried out through the steps of adsorption-average reduction-reversal-flushing-evacuation-average increase-final increase-adsorption. The two towers are operated alternately to reduce the ammonia content in the material gas to 4 mg / L, and at the same time, water, carbon dioxide, methane and some argon impurities are removed by adsorption. The material gas produced mainly contains helium, hydrogen and neon.

[0053] The material gas produced by the isobaric recovery tower is then passed into the palladium tube. The pressure of the material gas entering the palladium tube is 0.8Mpa, the temperature is 410℃, and the hydrogen flux is 0.8mol / m 2 ·s; Under the action of palladium, hydrogen is ionized into protons that pass through the palladium tube, and then combines with electrons to re-form hydrogen molecules, obtaining ultra-pure hydrogen with a purity greater than 99.9999%, as well as tail gas discharged after hydrogen separation;

[0054] The tail gas discharged from the palladium tube is introduced into a low-temperature adsorption tower, which is filled with the special low-temperature adsorbent provided in Example 1, and low-temperature adsorption refining is carried out under the conditions of 2.5 MPa and -190°C to obtain ultra-pure helium with a purity of 99.9999%; the special low-temperature adsorbent is used for the next production after vacuum regeneration.

[0055] Example 4

[0056] This embodiment provides a method for preparing ultrapure helium and co-producing ultrapure hydrogen from ammonia purge gas, wherein the parameters of the synthetic ammonia purge gas are: 0.3-0.9% helium, 13-15% ammonia, 2.5 MPa pressure, and 30°C temperature;

[0057] The process is roughly as follows Figure 1 As shown, the method steps are as follows:

[0058] The synthetic ammonia purge gas is sent to the bubbling layer of the lower section of the isobaric recovery tower to wash ammonia under the heat exchange conditions of 20 groups of water tanks. After leaving the bubbling layer, the unabsorbed ammonia passes through the isobaric composite absorption tower tray of the cooling layer from bottom to top, and is successively mixed with the dilute ammonia water or soft water from the high-pressure ammonia purification tower to further absorb the ammonia in the purge gas, so that the ammonia content is reduced to 19mg / L;

[0059] The material gas produced by the isobaric recovery tower is then sent to a pressure swing adsorption tower, which is filled with silica gel and alumina adsorbents. Under the conditions of an adsorption pressure of 0.9 MPa and an adsorption temperature of 150°C, the adsorption treatment is carried out through the steps of adsorption-average reduction-reversal-flushing-evacuation-average increase-final increase-adsorption. The two towers are operated alternately to reduce the ammonia content in the material gas to 4 mg / L, and at the same time, water, carbon dioxide, methane and some argon impurities are removed by adsorption. The material gas produced mainly contains helium, hydrogen and neon.

[0060] The material gas produced by the isobaric recovery tower is then passed into the palladium tube. The pressure of the material gas entering the palladium tube is 1.2Mpa, the temperature is 380℃, and the hydrogen flux is 0.6mol / m 2 ·s; Under the action of palladium, hydrogen is ionized into protons that pass through the palladium tube, and then combines with electrons to re-form hydrogen molecules, obtaining ultra-pure hydrogen with a purity greater than 99.9999%, as well as tail gas discharged after hydrogen separation;

[0061] The tail gas discharged from the palladium tube is introduced into a low-temperature adsorption tower, which is filled with the special low-temperature adsorbent provided in Example 2, and low-temperature adsorption refining is carried out under the conditions of 1.8 MPa and -180°C to obtain ultra-pure helium with a purity of 99.9999%; the special low-temperature adsorbent is used for the next production after vacuum regeneration.

[0062] Comparative Example

[0063] This comparative example is based on Example 4, and the difference from Example 4 is that the low-temperature adsorption tower is filled with conventional 5A molecular sieve adsorbent instead of the special low-temperature adsorbent provided in Example 2;

[0064] The details are as follows:

[0065] The parameters of synthetic ammonia purge gas are: helium 0.3-0.9%, ammonia 13-15%, pressure 2.5MPa, temperature 30℃;

[0066] The process is roughly as follows Figure 1 As shown, the method steps are as follows:

[0067] The synthetic ammonia purge gas is sent to the bubbling layer of the lower section of the isobaric recovery tower to wash ammonia under the heat exchange conditions of 20 groups of water tanks. After leaving the bubbling layer, the unabsorbed ammonia passes through the isobaric composite absorption tower tray of the cooling layer from bottom to top, and is successively mixed with the dilute ammonia water or soft water from the high-pressure ammonia purification tower to further absorb the ammonia in the purge gas, so that the ammonia content is reduced to 19mg / L;

[0068] The material gas produced by the isobaric recovery tower is then sent to a pressure swing adsorption tower, which is filled with silica gel and alumina adsorbents. Under the conditions of an adsorption pressure of 0.9 MPa and an adsorption temperature of 150°C, the adsorption treatment is carried out through the steps of adsorption-average reduction-reversal-flushing-evacuation-average increase-final increase-adsorption. The two towers are operated alternately to reduce the ammonia content in the material gas to 4 mg / L, and at the same time, water, carbon dioxide, methane and some argon impurities are removed by adsorption. The material gas produced mainly contains helium, hydrogen and neon.

[0069] The material gas produced by the isobaric recovery tower is then passed into the palladium tube. The pressure of the material gas entering the palladium tube is 1.2Mpa, the temperature is 380℃, and the hydrogen flux is 0.6mol / m 2 ·s; Under the action of palladium, hydrogen is ionized into protons that pass through the palladium tube, and then combines with electrons to re-form hydrogen molecules, obtaining ultra-pure hydrogen with a purity greater than 99.9999%, as well as tail gas discharged after hydrogen separation;

[0070] The tail gas discharged from the palladium tube is introduced into a low-temperature adsorption tower, which is filled with a commonly used 5A molecular sieve adsorbent, and is subjected to low-temperature adsorption refining at 1.8MPa and -180°C to obtain product helium;

[0071] The purity of its product helium was tested and found to be 99.9991%, that is, the comparative solution could not obtain ultra-pure helium with a purity of 99.9999%.

[0072] In summary, the embodiments of the present application provide a method for preparing ultra-pure helium and co-producing ultra-pure hydrogen from ammonia purge gas. The process method has a simple flow and can effectively realize the co-production of ultra-pure helium and ultra-pure hydrogen using synthetic ammonia purge gas as raw materials, thereby effectively avoiding the waste of hydrogen and helium resources. At the same time, the process eliminates the tedious steps of multiple catalytic combustion dehydrogenation and then deoxygenation and drying, effectively reducing the process cost and improving the process economic benefits.

[0073] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents the selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

Claims

1. A method for preparing ultrapure helium and co-producing ultrapure hydrogen from ammonia purge gas, characterized in that: It includes the following steps: The synthetic ammonia purge gas is sent to an isobaric recovery tower to absorb ammonia in the purge gas until the ammonia content is less than 20 mg / L, and then the material gas produced by the isobaric recovery tower is sent to a pressure swing adsorption tower equipped with an adsorbent for adsorption treatment to reduce the ammonia content in the material gas to less than 5 mg / L, and at the same time, water, carbon dioxide, methane and part of argon impurities are adsorbed and removed. At this time, the material gas mainly contains helium, hydrogen and neon; The material gas is then sent to the palladium tube, where the hydrogen in the material gas is ionized into protons under the action of palladium, which pass through the palladium tube and then combine with electrons to re-form hydrogen to obtain high-purity hydrogen and tail gas discharged after hydrogen separation; The tail gas discharged from the palladium tube is sent to a low-temperature adsorption tower equipped with a special low-temperature adsorbent for low-temperature adsorption refining, denemonization and dehydrogenation to obtain high-purity helium.

2. The method for preparing ultrapure helium and co-producing ultrapure hydrogen from ammonia purge gas according to claim 1, characterized in that: The adsorbent in the pressure swing adsorption tower is any one or more of activated carbon, silica gel, alumina and molecular sieve.

3. The method for preparing ultrapure helium and co-producing ultrapure hydrogen from ammonia purge gas according to claim 1, characterized in that: When the pressure swing adsorption tower performs adsorption treatment, the adsorption pressure is 0.3-3 MPa and the adsorption temperature is 10-50°C.

4. The method for preparing ultrapure helium and co-producing ultrapure hydrogen from ammonia purge gas according to claim 1, characterized in that: The pressure of the material gas entering the palladium tube is 0.3-3 MPa, the temperature is 200-500°C, and the hydrogen flux is 0.04-3 mol / m 2 ·s.

5. The method for preparing ultrapure helium and co-producing ultrapure hydrogen from ammonia purge gas according to claim 1, characterized in that: When the low-temperature adsorption tower performs low-temperature adsorption, the low-temperature adsorption pressure is 0.5 to 4 MPa and the temperature is -110°C to -200°C.

6. The method for preparing ultrapure helium and co-producing ultrapure hydrogen from ammonia purge gas according to claim 1, characterized in that: The isobaric recovery tower comprises a bubbling layer and a cooling layer from bottom to top, and an isobaric composite absorption tower tray is arranged in the cooling layer; The synthetic ammonia purge gas first enters the bubbling layer, washes ammonia under the heat exchange conditions of the 18-23 groups of water tanks, and then passes through the isobaric composite absorption tower tray of the cooling layer, mixes with the dilute ammonia water or soft water from the high-pressure ammonia purification tower, and absorbs ammonia in the purge gas until the ammonia content is less than 20 mg / L; When the pressure swing adsorption tower performs adsorption treatment on the material gas, the steps are: adsorption-average reduction-reversal-flushing-evacuation-average increase-final increase-adsorption, so as to reduce the ammonia content in the material gas to less than 5 mg / L.

7. The method for preparing ultrapure helium and co-producing ultrapure hydrogen from ammonia purge gas according to claim 1, characterized in that: The special low-temperature adsorbent is a molecular sieve-carbon composite adsorbent with a core-shell structure, which is prepared from raw materials including the following components: molecular sieve, phenol, aldehyde, amine, surfactant and water.

8. The method for preparing ultrapure helium and co-producing ultrapure hydrogen from ammonia purge gas according to claim 7, characterized in that: The special low-temperature adsorbent is prepared by the following method: dissolving phenol in water, adding a surfactant thereto and stirring to obtain a soaking solution; Add molecular sieve beads to the soaking solution and soak for 2 to 4 hours, then add the mixed solution of amine and aldehyde and stir, then age at 40 to 95° C. for 5 to 20 hours, filter to obtain a solid phase material, and dry the solid phase material at 60° C. for 8 to 12 hours to obtain a benzoxazine resin with a molecular sieve as a core; In a nitrogen atmosphere, the temperature is increased to 400°C at a rate of 1-4°C / min, and the prepared benzoxazine resin with the molecular sieve as the core is dried at a constant temperature for 2-3 hours. Then, the temperature is increased from 400°C to the carbonization final temperature of 550-900°C at a rate of 1-4°C / min, and the temperature is kept constant for 1-5 hours to obtain a molecular sieve-carbon composite adsorbent with a core-shell structure as a special low-temperature adsorbent.

9. The method for preparing ultrapure helium and co-producing ultrapure hydrogen from ammonia purge gas according to claim 8, characterized in that: During the preparation of the special low-temperature adsorbent: The molar ratio of phenol to aldehyde is 1:(0.6-4), the molar ratio of phenol to amine is 1:(0.1-1.5), the mass ratio of phenol to water is 1:(50-1000), the molar ratio of phenol to surfactant is 100:(1-10), and the volume ratio of molecular sieve to soaking liquid is 1:(5-200).

10. The method for preparing ultrapure helium and co-producing ultrapure hydrogen from ammonia purge gas according to claim 7, characterized in that: The phenol is any one or more of hydroquinone, resorcinol and phenol; The aldehyde is any one or more of formaldehyde, trioxymethylene, polyformaldehyde, and adipaldehyde; The amine is any one or more of ethylenediamine, 1,4-butanediamine, and 1,6-hexanediamine; The surfactant is any one or more of polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer F127, polyvinyl pyrrolidone, polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer P123, sodium dodecylbenzene sulfonate, and hexadecyltrimethylammonium bromide; The molecular sieve is any one or more of A-type, X-type, and Y-type molecular sieves.

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