A high-purity ammonia production system

Abstract

The present invention discloses a high-purity ammonia production system, including: a dilute ammonia dehydration unit, which includes a feed buffer tank, a filter, a first heat exchanger, a dehydration tower, a second heat exchanger, a dehydration buffer tank, an ammonia concentration tower, a fourth heat exchanger, a liquid ammonia buffer tank, a third heat exchanger, a fifth heat exchanger, and a sixth heat exchanger; a high-purity ammonia purification unit, which includes a seventh heat exchanger, a primary adsorber, a secondary adsorber, a light removal tower, a heavy removal tower, a ninth heat exchanger, a product temporary storage tank, a high-purity ammonia product tank, an eighth heat exchanger, a tenth heat exchanger, and an eleventh heat exchanger; and a tail gas absorption unit, which includes a waste buffer tank, a tail gas absorption tower, and a twelfth heat exchanger. The present invention first conducts secondary ammonia evaporation on the raw material ammonia water before entering the high-purity ammonia purification unit, thereby ensuring the quality stability of subsequent products; then, the deep dehydration of ammonia can be achieved by using the secondary adsorption treatment; finally, the deep impurity removal can be achieved by using the secondary distillation, and finally a 7N grade high-purity ammonia product can be obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of high-purity ammonia preparation, and in particular to a high-purity ammonia production system. Background Art

[0002] Ultra-pure ammonia used in the semiconductor field has extremely high purity requirements, especially the oxygen, water and other impurities that affect the growth of semiconductor materials must reach the ppm-ppb level. The main impurities in ammonia include H 2 O、N 2 , CH 4 , H 2 , CO and CO 2 The traditional purification process mainly uses distillation process to obtain 5N-6N electronic grade ammonia, but it is usually difficult to reach 7N level, so it cannot meet the stringent requirements of ammonia purity in some semiconductor fields. Therefore, it is necessary to improve the existing process to provide a more reliable solution. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a high-purity ammonia production system in view of the deficiencies in the above-mentioned prior art.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: a high-purity ammonia production system, comprising:

[0005] A dilute ammonia dehydration unit, comprising a feed buffer tank, a filter, a first heat exchanger, a dehydration tower, a second heat exchanger, a dehydration buffer tank, an ammonia concentration tower, a fourth heat exchanger, a liquid ammonia buffer tank, and a third heat exchanger connected to the dehydration tower, a fifth heat exchanger connected to the upper part of the ammonia concentration tower, and a sixth heat exchanger connected to the lower part of the ammonia concentration tower.

[0006] A high-purity ammonia purification unit, comprising a seventh heat exchanger connected in sequence to the liquid ammonia buffer tank, a primary adsorber, a secondary adsorber, a lightness removal tower, a heavyness removal tower, a ninth heat exchanger, a product temporary storage tank, a high-purity ammonia product tank, an eighth heat exchanger connected to the upper part of the lightness removal tower, a tenth heat exchanger connected to the lower part of the lightness removal tower, and an eleventh heat exchanger connected to the lower part of the heavyness removal tower;

[0007] and a tail gas absorption unit, which comprises a waste buffer tank, a tail gas absorption tower and a twelfth heat exchanger which are sequentially connected to the deweighting tower.

[0008] Preferably, the raw ammonia water first enters the feed buffer tank for buffering, the ammonia water discharged from the feed buffer tank is filtered by the filter and then heated and gasified by the first heat exchanger, and then enters the dehydration tower from the middle, the ammonia gas obtained by dehydration is discharged from the top of the tower, and then condensed into liquid ammonia by the second heat exchanger and enters the dehydration buffer tank, a part of the liquid ammonia discharged from the dehydration buffer tank returns from the upper part to enter the dehydration tower, forming a downward-flowing dehydrated liquid ammonia spray liquid in the dehydration tower, and the other part of the liquid ammonia enters the ammonia water concentration tower in the next step;

[0009] A portion of the dehydrated mixture obtained at the bottom of the dehydration tower is heated and vaporized by the third heat exchanger and then returned to the dehydration tower to form an ascending ammonia gas flow, and the other portion is discharged from the system as wastewater after heat recovery by the first heat exchanger.

[0010] Preferably, part of the liquid ammonia discharged from the dehydration buffer tank enters the ammonia water concentration tower from the middle, part of the ammonia gas obtained at the top of the tower is condensed by the fourth heat exchanger to obtain the initial liquid ammonia product and then enters the liquid ammonia buffer tank for storage, and the other part of the ammonia gas is condensed into liquid ammonia by the fifth heat exchanger and then returns to the top of the ammonia water concentration tower, forming a concentrated liquid ammonia spray liquid flowing downward in the ammonia water concentration tower;

[0011] A portion of the concentrated mixture obtained at the bottom of the ammonia concentration tower is heated and vaporized by the sixth heat exchanger and then re-enters the ammonia concentration tower to form an ascending ammonia gas flow, and the other portion is returned to the dehydration tower.

[0012] Preferably, the liquid ammonia initial product in the liquid ammonia buffer tank is heated and gasified by the seventh heat exchanger, and then sequentially processed by the primary adsorber and the secondary adsorber before entering the light removal tower from the middle;

[0013] The ammonia gas obtained at the top of the light-removal tower is condensed into liquid ammonia by the eighth heat exchanger to obtain liquid ammonia containing light component impurities, a part of the liquid ammonia containing light component impurities enters the tail material buffer tank in the tail gas absorption unit, and the other part returns from the upper part to enter the light-removal tower to form a liquid ammonia spray liquid flowing downward;

[0014] A portion of the pure liquid ammonia obtained at the bottom of the light-removal tower after light component impurities are removed is heated and vaporized by the tenth heat exchanger and then returned to the light-removal tower to form an ascending ammonia gas flow, and the other portion enters the heavy-removal tower in the next step.

[0015] Preferably, part of the pure liquid ammonia obtained in the light removal tower enters the heavy removal tower from the middle, and the ammonia gas obtained at the top of the tower is condensed into liquid ammonia by the ninth heater to obtain high-purity liquid ammonia after the heavy component impurities are removed, and part of the high-purity liquid ammonia enters the product temporary storage tank, and enters the high-purity ammonia product tank for storage after the product is analyzed and qualified, and another part of the high-purity liquid ammonia returns from the upper part to enter the heavy removal tower to form a liquid ammonia spray liquid flowing downward;

[0016] A portion of the liquid ammonia containing heavy impurities obtained at the bottom of the de-weighting tower is heated and vaporized by the eleventh heat exchanger and then returned to the de-weighting tower to form an ascending ammonia gas flow, and the other portion enters the tailing buffer tank in the tail gas absorption unit.

[0017] Preferably, the tailings in the tailings buffer tank enter the tail gas absorption tower from the bottom, supplementary process water enters the top of the tower and is sprayed downward to absorb ammonia, the tail gas obtained by the tail gas absorption tower is discharged from the top of the tower, a part of the tailings mixture obtained at the bottom of the tail gas absorption tower is discharged from the system as dilute ammonia water, and the other part is heated and vaporized by the twelfth heat exchanger and then returned to the tail gas absorption tower to form an upward airflow.

[0018] Preferably, the primary adsorber and the secondary adsorber have the same structure, both comprising an adsorber body and a first adsorbent and a second adsorbent filled in the adsorber body, and the gas entering the adsorber body passes through the first adsorbent and the second adsorbent and then is discharged;

[0019] The adsorber body comprises an adsorber shell, a desiccant chamber, a first adsorption chamber and a second adsorption chamber sequentially formed in the adsorber shell from bottom to top, a first filter cartridge in an annular shape arranged in the first adsorption chamber, a second filter cartridge arranged in the first adsorption chamber and in a cavity in the middle of the first filter cartridge, a third filter cartridge in an inverted cone shape arranged in the second adsorption chamber, a partition arranged between the second filter cartridge and the third filter cartridge, an air intake guide cavity formed between the partition and the upper part of the second filter cartridge, a transition guide cavity formed between the lower part of the first filter cartridge, the second filter cartridge and the first adsorption chamber, an air intake pipe communicated with the air intake guide cavity, an air collecting hood arranged on the upper part of the third filter cartridge, an air outlet pipe communicated with the air collecting hood, and a reflux component connected between the air outlet pipe and the second adsorption chamber;

[0020] The top of the desiccant chamber is communicated with the transition guide cavity;

[0021] The partition plate is provided with a connecting hole connecting the second filter cartridge and the third filter cartridge.

[0022] Preferably, a conical reflux cavity is formed between the outer wall of the third filter cartridge and the inner wall of the second adsorption chamber, and the reflux assembly comprises a reflux main pipe connected to the outlet pipe, a reflux valve arranged on the reflux main pipe, and a plurality of reflux branches connected to the output end of the reflux main pipe, wherein the plurality of reflux branches are arranged at intervals in the vertical direction and are all connected to the reflux cavity;

[0023] The adsorber shell is cylindrical, and the reflux branch pipe is connected to the adsorber shell along a circumferential tangent direction;

[0024] The first filter cartridge and the second filter cartridge each have filter holes densely formed only on the upper and lower end surfaces, and the outer wall and the upper and lower end surfaces of the third filter cartridge each have filter holes densely formed;

[0025] The first filter cartridge is filled with the first adsorbent, the second filter cartridge and the third filter cartridge are both filled with the second adsorbent, and the desiccant chamber is filled with desiccant.

[0026] Preferably, the first adsorbent is 5A molecular sieve or MCM-41 molecular sieve, and the second adsorbent is a modified enhanced molecular sieve, and the modified enhanced molecular sieve is prepared by the following method:

[0027] 1) Preparation of carbon dots:

[0028] 1-1) Dissolve folic acid, citric acid and ethylenediamine in an ethanol aqueous solution, perform ultrasonic treatment for 5-30 minutes, transfer the obtained mixed solution to a reaction kettle, and react at 180-250°C for 4-12 hours;

[0029] 1-2) After the reaction is completed, cool the mixture, filter the product with a filter membrane, and dialyze the filtrate in water for 12-24 hours using a dialysis bag with a molecular weight cutoff of 500-1200D. After dialysis, take the inner liquid and freeze-dry it to obtain carbon dots;

[0030] 2) Molecular sieve pretreatment:

[0031] 2-1) Heat the molecular sieve at 250-350℃ for 1-4h, then add it into ethanol and soak it for 0.5-3h;

[0032] 2-2) Filtering, adding the obtained molecular sieve to an ethanol solution of lanthanum nitrate, ultrasonicating for 0.5-3h, and filtering again to obtain the pretreated molecular sieve;

[0033] The molecular sieve is 5A molecular sieve or MCM-41 molecular sieve, and the mass ratio of the added lanthanum to the molecular sieve is 0.5:100-5:100;

[0034] 3) Grafting carbon dots onto molecular sieves:

[0035] 3-1) adding the carbon dots prepared in step 1) into ethanol and ultrasonicating for 20-60 min to prepare a carbon dots dispersion;

[0036] 3-2) adding the pretreated molecular sieve prepared in step 2) to the carbon dot dispersion obtained in step 3-1), shaking on a shaker at 40-55° C. for 2-6 hours, filtering, and vacuum drying at 40-60° C. for 2-6 hours to obtain a carbon dot grafted molecular sieve;

[0037] The mass ratio of the added carbon dots to the pretreated molecular sieve is 1:4-1:10;

[0038] 4) Modification of molecular sieve with metal salt:

[0039] 4-1) dissolving a metal salt in an ethanol aqueous solution to obtain a metal salt solution;

[0040] Wherein, the metal salt is a mixture of at least one of strontium nitrate, zirconium nitrate, barium nitrate, magnesium nitrate, nickel nitrate and manganese nitrate, ferrous nitrate, and ferric nitrate;

[0041] 4-2) Add the carbon dot grafted molecular sieve obtained in step 3) to the metal salt solution obtained in step 4-1), ultrasonicate for 10-60 min, transfer the obtained mixture to a reactor, react at 140-200° C. for 6-24 h, filter and wash the product after the reaction, and calcine the solid product at 300-480° C. for 4-12 h to obtain a modified enhanced adsorbent.

[0042] Wherein, the mass ratio of the added metal salt to the carbon dot grafted molecular sieve is 5:1-1:1.

[0043] Preferably, the modified enhanced molecular sieve is prepared by the following method:

[0044] 1) Preparation of carbon dots:

[0045] 1-1) Dissolve 1.5 g of folic acid, 2.8 g of citric acid, and 3 mL of ethylenediamine in 500 mL of ethanol-water solution, and ultrasonicate for 15 min. Transfer the resulting mixture to a reactor and react at 220°C for 6 hours. The volume ratio of ethanol to water in the ethanol-water solution is 1:1.

[0046] 1-2) After the reaction is completed, the mixture is cooled and the product is filtered with a 0.22 μm filter membrane. The filtrate is dialyzed in water for 18 hours using a dialysis bag with a molecular weight cutoff of 800 D. After dialysis, the inner liquid is collected and freeze-dried to obtain carbon dots;

[0047] 2) Molecular sieve pretreatment:

[0048] 2-1) Heat 10 g of molecular sieve at 280 °C for 1.5 h, then add it to 400 mL of ethanol and soak for 1 h;

[0049] 2-2) Filtering, adding the obtained molecular sieve into an ethanol solution of lanthanum nitrate with a concentration of 0.05 mol / L, ultrasonicating for 1 hour, and filtering again to obtain the pretreated molecular sieve;

[0050] The molecular sieve is 5A molecular sieve, and the mass ratio of the added lanthanum to the molecular sieve is 2:100;

[0051] 3) Grafting carbon dots onto molecular sieves:

[0052] 3-1) adding the carbon dots prepared in step 1) into ethanol and ultrasonicating for 0.5 h to prepare a carbon dots dispersion with a concentration of 0.5 mol / L;

[0053] 3-2) adding the pretreated molecular sieve prepared in step 2) to the carbon dot dispersion obtained in step 3-1), shaking on a shaker at 45°C for 3 hours, filtering, and vacuum drying at 50°C for 3 hours to obtain a carbon dot grafted molecular sieve;

[0054] Among them, the mass ratio of added carbon dots to pretreated molecular sieve is 1:6;

[0055] 4) Modification of molecular sieve with metal salt:

[0056] 4-1) Add 1.4 g strontium nitrate, 1.2 g zirconium nitrate, 0.5 g barium nitrate, 8.6 g manganese nitrate, 0.9 g ferrous nitrate, and 1.8 g ferric nitrate to 300 mL of an ethanol aqueous solution having a volume ratio of deionized water to ethanol of 3:7, and stir to dissolve to obtain a metal salt solution;

[0057] 4-2) Add 7.2 g of the carbon-dot grafted molecular sieve obtained in step 3) to the metal salt solution obtained in step 4-1), ultrasonicate for 0.5 h, transfer the obtained mixture to a reactor, react at 160° C. for 12 h, filter the product after the reaction, wash with ethanol, and calcine the solid product at 350° C. for 8 h to obtain a modified enhanced adsorbent.

[0058] The beneficial effects of the present invention are:

[0059] In the high-purity ammonia production system provided by the present invention, the raw material ammonia water is first subjected to secondary ammonia distillation (dehydration tower, ammonia water concentration tower) and then enters the high-purity ammonia purification unit, thereby ensuring the quality stability of subsequent products; the present invention adopts secondary adsorption treatment in the high-purity ammonia purification unit, while basically removing impurities such as oil and organic matter, it can achieve deep dehydration of ammonia gas, further ensuring the quality of subsequent products; the present invention adopts secondary distillation (light removal tower, heavy removal tower) after the secondary adsorption treatment to achieve deep impurity removal, and the light removal tower removes the component N lighter than ammonia water. 2 , CH 4 , H 2 Then remove CO and CO in the deweighting tower.2 Equally heavy component impurities can finally obtain 7N grade high purity ammonia product;

[0060] In the present invention, spray water adsorption is used in the tail gas absorption unit to recover ammonia, which can reduce the tail waste discharged from the system;

[0061] In some embodiments of the present invention, an improved adsorber structure is used to improve the filtration and purification effect of the adsorber and increase the purity of the product;

[0062] In some embodiments of the present invention, a modified enhanced molecular sieve is used as an adsorbent. By modifying the molecular sieve with a metal salt and introducing a hygroscopic or water-reactive metal oxide as an enhanced desiccant, the deep dehydration effect of the adsorbent can be greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 It is a structural schematic diagram of the high-purity ammonia production system of the present invention;

[0064] Figure 2 It is a structural schematic diagram of the dilute ammonia water dehydration unit of the present invention;

[0065] Figure 3 It is a structural schematic diagram of the high-purity ammonia purification unit of the present invention;

[0066] Figure 4 It is a structural schematic diagram of the tail gas absorption unit of the present invention;

[0067] Figure 5 It is a schematic diagram of the internal structure of the primary adsorber or the secondary adsorber of the present invention;

[0068] Figure 6 A schematic diagram of the top view of the connection between the reflux branch pipe and the adsorber shell of the present invention;

[0069] Figure 7 This is the infrared spectra of the 5A molecular sieve and the modified enhanced molecular sieve in Example 1 of the present invention.

[0070] Description of reference numerals:

[0071] 100—dilute ammonia dehydration unit; 101—feed buffer tank; 102—filter; 103—first heat exchanger; 104—dehydration tower; 105—second heat exchanger; 106—dehydration buffer tank; 107—ammonia concentration tower; 108—fourth heat exchanger; 109—liquid ammonia buffer tank; 110—third heat exchanger; 111—fifth heat exchanger; 112—sixth heat exchanger;

[0072] 200—high-purity ammonia purification unit; 201—seventh heat exchanger; 202—primary adsorber; 203—secondary adsorber; 204—lightness removal tower; 205—heavyness removal tower; 206—ninth heat exchanger; 207—high-purity ammonia product tank; 208—eighth heat exchanger; 209—tenth heat exchanger; 210—eleventh heat exchanger;

[0073] 300—tail gas absorption unit; 301—waste buffer tank; 302—tail gas absorption tower; 303—twelfth heat exchanger;

[0074] 400—adsorber body; 401—adsorber shell; 402—desiccant chamber; 403—first adsorption chamber; 404—second adsorption chamber; 405—first filter cartridge; 406—second filter cartridge; 407—third filter cartridge; 408—partition plate; 409—connecting hole; 410—intake guide chamber; 411—transition guide chamber; 412—intake pipe; 413—air collecting cover; 414—exhaust pipe; 415—reflux chamber; 416—reflux assembly; 4160—reflux main pipe; 4161—reflux valve; 4162—reflux branch pipe;

[0075] 500—first adsorbent;

[0076] 600—Second adsorbent. DETAILED DESCRIPTION

[0077] The present invention is further described in detail below in conjunction with embodiments so that those skilled in the art can implement the invention with reference to the description.

[0078] It should be understood that the terms such as “having”, “including” and “comprising” used herein do not exclude the existence or addition of one or more other elements or combinations thereof.

[0079] The test methods used in the following examples are conventional methods unless otherwise specified. The materials and reagents used in the following examples are all commercially available unless otherwise specified. In the following examples, if no specific conditions are specified, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used, if the manufacturer is not specified, are all conventional products that can be purchased commercially.

[0080] The present invention provides a high-purity ammonia production system, comprising:

[0081] The dilute ammonia dehydration unit 100 includes a feed buffer tank 101, a filter 102, a first heat exchanger 103, a dehydration tower 104, a second heat exchanger 105, a dehydration buffer tank 106, an ammonia concentration tower 107, a fourth heat exchanger 108, a liquid ammonia buffer tank 109, and a third heat exchanger 110 connected to the dehydration tower 104, a fifth heat exchanger 111 connected to the upper part of the ammonia concentration tower 107, and a sixth heat exchanger 112 connected to the lower part of the ammonia concentration tower 107.

[0082] The high-purity ammonia purification unit 200 includes a seventh heat exchanger 201 connected to the liquid ammonia buffer tank 109 in sequence, a primary adsorber 202, a secondary adsorber 203, a lightness removal column 204, a heavyness removal column 205, a ninth heat exchanger 206, a product temporary storage tank (not shown in the figure), a high-purity ammonia product tank 207, an eighth heat exchanger 208 connected to the upper part of the lightness removal column 204, a tenth heat exchanger 209 connected to the lower part of the lightness removal column 204, and an eleventh heat exchanger 210 connected to the lower part of the heavyness removal column 205;

[0083] And a tail gas absorption unit 300, which includes a waste buffer tank 301, a tail gas absorption tower 302 and a twelfth heat exchanger 303 connected to the deweighting tower 205 in sequence.

[0084] The main process of the present invention is described in detail below to facilitate the understanding of the present invention.

[0085] First stage dilute ammonia dehydration unit 100

[0086] 1. Initial dehydration in dehydration tower 104:

[0087] The raw ammonia water (mass concentration 20%) first enters the feed buffer tank 101 for buffering. The ammonia water discharged from the feed buffer tank 101 is filtered out of solid impurities by the filter 102, and then heated and gasified by the first heat exchanger 103, and then enters the dehydration tower 104 from the middle for preliminary dehydration; the ammonia gas obtained by dehydration is discharged from the top of the tower, and then condensed into liquid ammonia by the second heat exchanger 105 and enters the dehydration buffer tank 106. A part of the liquid ammonia discharged from the dehydration buffer tank 106 returns from the upper part to the dehydration tower 104, forming a downward-flowing dehydrated liquid ammonia spray liquid in the dehydration tower 104, and the other part of the liquid ammonia enters the ammonia concentration tower 107 in the next step;

[0088] A portion of the dehydrated mixture (ammonia water, ammonia gas) obtained at the bottom of the dehydration tower 104 is heated and gasified by the third heat exchanger 110 and then returned to the dehydration tower 104 to form an ascending ammonia gas flow, and the other portion is discharged from the system as waste water after heat recovery by the first heat exchanger 103 (the waste water can be used as supplementary process water in the subsequent tail gas absorption unit 300);

[0089] The dehydration tower 104 mainly carries out the process of ammonia evaporation and water removal. Specifically, the relatively dilute ammonia vapor rising in the tower and the relatively concentrated ammonia liquid (dehydrated liquid ammonia spray liquid) sprayed from the top of the tower carry out countercurrent mass transfer and heat transfer. The concentrated ammonia liquid is partially vaporized to be concentrated and rises to the top of the tower, while the relatively dilute ammonia vapor is partially liquefied to reduce the ammonia concentration and descend to the bottom of the tower. A large amount of water and oil in the ammonia gas obtained at the top of the tower are basically removed.

[0090] 2. Ammonia concentration tower 107 further dehydrates and purifies:

[0091] The ammonia water (ammonia mass concentration>98%) obtained in the dehydration tower 104 after preliminary dehydration enters the dehydration buffer tank 106 for gas-liquid separation, and the liquid part enters the ammonia water concentration tower 107 from the middle. A part of the ammonia gas obtained at the top of the tower is condensed by the fourth heat exchanger 108 to obtain the initial liquid ammonia product (mass concentration>99.5%) and then enters the liquid ammonia buffer tank 109 for storage, and the other part of the ammonia gas is condensed into liquid ammonia by the fifth heat exchanger 111 and then returned to the top of the ammonia water concentration tower 107, forming a concentrated liquid ammonia spray liquid flowing downward in the ammonia water concentration tower 107;

[0092] A portion of the concentrated mixture (ammonia water, ammonia gas) obtained at the bottom of the ammonia water concentration tower 107 is heated and gasified by the sixth heat exchanger 112 and then re-enters the ammonia water concentration tower 107 to form an ascending ammonia gas flow, and the other portion is returned to the dehydration tower 104. The ammonia water concentration tower 107 is also mainly a process of evaporating ammonia and removing water, which is similar to the principle of the dehydration tower 104 and will not be described in detail.

[0093] Second stage high purity ammonia purification unit 200

[0094] 1. Adsorber purification

[0095] The liquid ammonia primary product in the liquid ammonia buffer tank 109 is heated and gasified by the seventh heat exchanger 201, and then is processed by the primary adsorber 202 and the secondary adsorber 203 in sequence, and then enters the light removal tower 204 from the middle;

[0096] The primary adsorber 202 can remove most of the H 2 O and almost all oil, organic matter and other complex impurities, and the secondary adsorber 203 performs deep water removal to further reduce the water content.

[0097] In one embodiment, the primary adsorber 202 and the secondary adsorber 203 each include two adsorbers arranged in parallel.

[0098] 2. Light component impurities are removed in the light removal tower 204

[0099] The ammonia gas obtained at the top of the light-removal tower 204 is condensed into liquid ammonia by the eighth heat exchanger 208 to obtain liquid ammonia containing light component impurities. A portion of the liquid ammonia containing light component impurities enters the tailings buffer tank in the tail gas absorption unit 300, and the other portion returns from the upper part to enter the light-removal tower 204 to form a liquid ammonia spray liquid flowing downward.

[0100] A portion of the pure liquid ammonia obtained at the bottom of the light-removal tower 204 after light component impurities are removed is heated and vaporized by the tenth heat exchanger 209 and then returned to the light-removal tower 204 to form an ascending ammonia gas flow, and the other portion enters the next heavy-removal tower 205.

[0101] 3. De-weighting tower 205 removes heavy impurities

[0102] Part of the pure liquid ammonia obtained in the light removal tower 204 enters the de-weighting tower 205 from the middle, and the ammonia gas obtained at the top of the tower is condensed into liquid ammonia by the ninth heater to obtain high-purity liquid ammonia after the heavy component impurities are removed. Part of the high-purity liquid ammonia enters the product temporary storage tank, and enters the high-purity ammonia product tank 207 for storage after the product is analyzed and qualified. Another part of the high-purity liquid ammonia returns from the upper part to enter the de-weighting tower 205 to form a liquid ammonia spray liquid flowing downward;

[0103] A portion of the liquid ammonia containing heavy impurities obtained at the bottom of the de-weighting tower 205 is heated and vaporized by the eleventh heat exchanger 210 and then returned to the de-weighting tower 205 to form an ascending ammonia gas flow, and the other portion enters the tailing buffer tank in the tail gas absorption unit 300.

[0104] After deoiling and dehydration, ammonia still contains a large amount of light impurities that are not easily adsorbed (N 2 , CH 4 , H 2 etc.) and heavy impurities (CO, CO 2 In the light-removal tower 204, the light impurities are discharged together with the ammonia gas at the top of the tower along with the rising air flow, and liquid ammonia after the light impurities are removed is obtained at the bottom of the tower; in the heavy-removal tower 205, the heavy impurities are mixed into the liquid ammonia downward and enter the bottom of the tower, and the solid particle impurities and metal ion impurities will not enter the gas phase, so that ammonia gas after the heavy impurities are removed is obtained at the top of the tower, and a 7N grade high-purity liquid ammonia product can be obtained after condensation, which is temporarily stored in the product temporary storage tank, and then transferred to the high-purity ammonia product tank 207 for storage after the purity analysis is qualified.

[0105] The third stage tail gas absorption unit 300

[0106] The tailings in the tailings buffer tank enter the tail gas absorption tower 302 from the bottom, and the supplementary process water enters the top of the tower and is sprayed downward to absorb ammonia. The tail gas obtained by the tail gas absorption tower 302 is discharged from the top of the tower. A part of the tailings mixture obtained at the bottom of the tail gas absorption tower 302 is discharged from the system as dilute ammonia water, which can be used for ammonia recovery, and the other part is heated and vaporized by the twelfth heat exchanger 303 and then returned to the tail gas absorption tower 302 to form an upward airflow.

[0107] In the process provided by the present invention, the raw material ammonia water is first subjected to secondary ammonia distillation (dehydration tower 104, ammonia water concentration tower 107) and then enters the high-purity ammonia purification unit 200, thereby ensuring the quality stability of subsequent products; the present invention adopts secondary adsorption treatment in the high-purity ammonia purification unit 200, while basically removing impurities such as oil and organic matter, it can achieve deep dehydration of ammonia, thereby further ensuring the quality of subsequent products; the present invention adopts secondary distillation (light removal tower 204, heavy removal tower 205) after the secondary adsorption treatment to achieve deep impurity removal, and the light removal tower 204 removes the component N lighter than ammonia water. 2 , CH 4 , H 2 Then, CO and CO are removed in the deweighting tower 205. 2 Equal weight component impurities; in the present invention, spray water adsorption is used in the tail gas absorption unit 300 to recover ammonia, which can reduce the tail waste discharged from the system.

[0108] In a preferred embodiment, the main process parameters of the high purity ammonia production system are:

[0109] The temperature T in the dehydration tower 104 is 10-100°C, the reflux ratio R is 0.5-1, and the pressure P is 0.5-0.6Mpa;

[0110] The temperature T in the ammonia concentration tower 107 is 10-100°C, the reflux ratio R is 0.5-1, and the pressure P is 0.5-0.6 MPa;

[0111] The temperature T in the light removal tower 204 is 4-20°C, the reflux ratio R is 5-8, and the pressure P is 0.3-0.5Mpa;

[0112] The temperature T in the deweighting tower 205 is 4-20°C, the reflux ratio R is 4-6, and the pressure P is 0.3-0.5 MPa;

[0113] The tail gas absorption tower 302 operates at normal temperature and pressure, with a reflux ratio R of 0.5-3.

[0114] The primary adsorber 202 and the secondary adsorber 203 are mainly used to remove impurities such as oil, organic matter, and solid particles in the ammonia gas to ensure that a qualified and stable product can be obtained after subsequent further purification. The secondary adsorber 203 is particularly important for deeply removing moisture from the ammonia gas. The reason is that the secondary distillation treatment in the subsequent high-purity ammonia purification unit 200 can remove light component impurities (N 2 , CH 4 , H 2 etc.) and heavy impurities (CO, CO 2 , solid particles and metal ions and other impurities) can be removed well, but the effect of removing water is limited, mainly because H2O and ammonia have similar chemical properties and hydrogen bonds with each other, and the two have high affinity, so it is the most difficult to remove. Therefore, in the present invention, the deep dehydration of ammonia is mainly achieved by connecting the first-stage adsorber 202 and the second-stage adsorber 203 in series.

[0115] In order to improve the dehydration and impurity removal effects of the secondary adsorption treatment, the present invention also provides an improved adsorber structure, which is specifically as follows.

[0116] In the present invention, the primary adsorber 202 and the secondary adsorber 203 have the same structure, both comprising an adsorber body 400 and a first adsorbent 500 and a second adsorbent 600 filled in the adsorber body 400. The gas entering the adsorber body 400 passes through the first adsorbent 500 and the second adsorbent 600 in sequence and then is discharged.

[0117] The adsorber body 400 includes an adsorber housing 401, a desiccant chamber 402, a first adsorption chamber 403, a second adsorption chamber 404, a first filter cartridge 405 in an annular shape disposed in the first adsorption chamber 403, a second filter cartridge 406 disposed in the first adsorption chamber 403 and in a cavity in the middle of the first filter cartridge 405, a third filter cartridge 407 in an inverted cone shape disposed in the second adsorption chamber 404, and a filter cartridge 408 disposed in the second filter cartridge 406 and the third filter cartridge 408. 07, an air inlet guide cavity 410 formed between the air inlet guide cavity 410 and the upper part of the second filter cartridge 406, a transition guide cavity 411 formed between the first filter cartridge 405, the lower part of the second filter cartridge 406 and the first adsorption chamber 403, an air inlet pipe 412 communicated with the air inlet guide cavity 410, an air collecting hood 413 arranged on the upper part of the third filter cartridge 407, an air outlet pipe 414 communicated with the air collecting hood 413, and a reflux component 416 connected between the air outlet pipe 414 and the second adsorption chamber 404;

[0118] The top of the desiccant chamber 402 is connected to the transition guide cavity 411;

[0119] The partition plate 408 is provided with a connecting hole 409 connecting the second filter cartridge 406 and the third filter cartridge 407 .

[0120] A conical reflux chamber 415 is formed between the outer wall of the third filter cartridge 407 and the inner wall of the second adsorption chamber 404. The reflux assembly 416 includes a reflux main pipe 4160 connected to the gas outlet pipe 414, a reflux valve 4161 disposed on the reflux main pipe 4160, and a plurality of reflux branch pipes 4162 connected to the output end of the reflux main pipe 4160. The plurality of reflux branch pipes 4162 are arranged at intervals in the vertical direction and are all connected to the reflux chamber 415.

[0121] The adsorber housing 401 is cylindrical, and the reflux branch pipe 4162 is connected to the adsorber housing 401 along the circumferential tangent direction. Figure 6 , when viewed from the top, the return branch pipe 4162 is tangent to the outer periphery of the adsorber shell 401, and the airflow entering the return branch pipe 4162 can form a swirl in the adsorber shell 401, and all the return branch pipes 4162 are connected to the adsorber shell 401 in the same manner, thereby forming a swirl in the same direction (for example, all in the clockwise direction as shown in the figure);

[0122] The first filter cartridge 405 and the second filter cartridge 406 have filter holes densely formed only on the upper and lower end surfaces, and the third filter cartridge 407 has filter holes densely formed on the outer wall and the upper and lower end surfaces;

[0123] The first filter cartridge 405 is filled with the first adsorbent 500, the second filter cartridge 406 and the third filter cartridge 407 are filled with the second adsorbent 600, and the desiccant chamber 402 is filled with desiccant. In a preferred embodiment, absorbent cotton is further provided between the desiccant chamber 402 and the transition guide cavity 411, and the desiccant is calcium sulfate.

[0124] Reference Figure 5 The gas enters the middle air intake guide chamber 410 from the air intake pipe 412. The air intake guide chamber 410 is annular and is located above the annular first filter cartridge 405. Then the gas passes downward through the first adsorbent 500 in the first filter cartridge 405 for preliminary filtration, and a large amount of impurities are filtered out.

[0125] After that, the gas enters the transition guide chamber 411, and then moves upward into the second filter cartridge 406, and is filtered again by the second adsorbent 600 in the second filter cartridge 406; in the transition guide chamber 411, the gas flow direction changes from downward to upward, and the particulate impurities mixed in the gas are easy to move downward and separate from the gas; the first adsorbent 500 in the first filter cartridge 405 filters the ammonia gas with a high impurity content, so the impurity content therein will be relatively large. By providing the first filter cartridge 405 with a ring-shaped structure and the second filter cartridge 406 matched therewith, on the one hand, the first adsorbent 500 in the first filter cartridge 405 can be separated from the ammonia gas with a high impurity content. The second adsorbent 600 in the second filter cartridge 406 is isolated to prevent the high-content impurities, especially water, in the first adsorbent 500 from penetrating into the second adsorbent 600, thereby affecting the re-filtration effect of the second filter cartridge 406. On the other hand, the space in the adsorber housing 401 can be fully utilized, and some tiny particle impurities can be easily separated from the airflow during the process of changing the airflow direction; at the same time, the transition guide cavity 411 is connected to the desiccant chamber 402 below, and the desiccant in the desiccant chamber 402 can reduce the moisture content in the air in the transition guide cavity 411, which is conducive to further improving the dehydration effect of the adsorber;

[0126] The gas passing through the second filter cartridge 406 continues to flow upward, flows through the connecting hole 409, and enters the third filter cartridge 407 from bottom to top, undergoes deep dehydration filtration through the second adsorbent 600 in the third filter cartridge 407, and then passes through the gas collecting hood 413 and is discharged from the gas outlet pipe 414. A portion of the discharged dry ammonia gas flows back into the conical reflux chamber 415 through the reflux component 416. Specifically, part of the dry ammonia gas enters the reflux main pipe 4160, and the flow rate is adjusted by the reflux valve 4161, and then enters the reflux chamber 415 tangentially through a plurality of reflux branch pipes 4162, and then enters from the side outer wall of the third filter cartridge 407, and undergoes deep dehydration filtration again through the second adsorbent 600 inside;

[0127] On the one hand, by allowing part of the dried ammonia to reflux into the third filter cartridge 407 for deep dehydration and filtration again, the impurity content in the ammonia discharged from the adsorber can be adjusted within a certain range by adjusting the proportion of the refluxed ammonia, thereby ensuring the filtration effect of the adsorber and improving the adaptability to the upstream liquid ammonia primary product (for example, when the impurities, especially the water content, in the upstream liquid ammonia primary product increase, the ammonia reflux can be increased to ensure the purity of the product, and when it decreases, the ammonia reflux can be reduced to improve the efficiency);

[0128] On the other hand, the airflow input along the reflux branch pipe 4162 will form a swirl in the horizontal plane in the reflux chamber 415. In addition, the design of the rising airflow and the conical reflux chamber 415 can form a spiral rising flow in the reflux chamber 415. The gas of the spiral rising flow enters the third filter cartridge 407 and is superimposed with the above-mentioned airflow inside, so that the airflow in the third filter cartridge 407 also passes through the second adsorbent 600 therein in a spiral rising manner, and finally makes the contact surface between the gas and the second adsorbent 600 larger, the contact collision intensity greater, and the contact adsorption more sufficient, so that the second adsorbent 600 can be more fully utilized and the filtering effect is improved. When there is only a vertical rising airflow, the airflow flows vertically through the adsorbent, and is more inclined to form a large number of fine airflow channels in the vertical direction in the adsorbent, and mainly contacts with the adsorbent particles in the vertical direction, while the side areas of the adsorbent particles are relatively less in contact with the gas, and the utilization rate is low, resulting in uneven contact between the adsorbent and the gas, and poor utilization of some areas. When there is a spiral upward airflow, in addition to the fine airflow channels in the vertical direction, the airflow will also collide and contact with the adsorbent in the horizontal direction, and at the same time form a large number of fine airflow channels in the horizontal direction, so that each area of ​​the adsorbent particles can be more fully in contact with the gas, thereby improving the utilization effect of the adsorbent particles and enhancing the filtration performance.

[0129] In the present invention, the first adsorbent 500 is 5A molecular sieve or MCM-41 molecular sieve. Of course, other adsorbents with better dehydration performance may also be selected.

[0130] In the present invention, in order to further improve the deep dehydration effect of the secondary adsorber 203, a self-made modified enhanced molecular sieve is used as the adsorption medium of the secondary adsorber 203, and combined with the above specific adsorber structure, the moisture content of the high-purity ammonia product finally obtained can be reduced to ppb level.

[0131] In the present invention, the modified enhanced molecular sieve is prepared by the following method:

[0132] 1) Preparation of carbon dots:

[0133] 1-1) Dissolve folic acid, citric acid and ethylenediamine in an ethanol aqueous solution, perform ultrasonic treatment for 5-30 minutes, transfer the obtained mixed solution to a reaction kettle, and react at 180-250°C for 4-12 hours;

[0134] 1-2) After the reaction is completed, the mixture is cooled and the product is filtered with a filter membrane. The filtrate is dialyzed in water for 12-24 hours using a dialysis bag with a molecular weight cutoff of 500-1200D. After dialysis, the inner liquid is collected and freeze-dried to obtain carbon dots;

[0135] 2) Molecular sieve pretreatment:

[0136] 2-1) Heat the molecular sieve at 250-350℃ for 1-4h, then add it into ethanol and soak it for 0.5-3h;

[0137] 2-2) Filtering, adding the obtained molecular sieve to an ethanol solution of lanthanum nitrate, ultrasonicating for 0.5-3h, and filtering again to obtain the pretreated molecular sieve;

[0138] The molecular sieve is 5A molecular sieve or MCM-41 molecular sieve, and the mass ratio of the added lanthanum to the molecular sieve is 0.5:100-5:100;

[0139] 3) Grafting carbon dots onto molecular sieves:

[0140] 3-1) adding the carbon dots prepared in step 1) into ethanol and ultrasonicating for 20-60 min to prepare a carbon dots dispersion;

[0141] 3-2) adding the pretreated molecular sieve prepared in step 2) to the carbon dot dispersion obtained in step 3-1), shaking on a shaker at 40-55° C. for 2-6 hours, filtering, and vacuum drying at 40-60° C. for 2-6 hours to obtain a carbon dot grafted molecular sieve;

[0142] The mass ratio of the added carbon dots to the pretreated molecular sieve is 1:4-1:10;

[0143] 4) Modification of molecular sieve with metal salt:

[0144] 4-1) dissolving a metal salt in an ethanol aqueous solution to obtain a metal salt solution;

[0145] Wherein, the metal salt is a mixture of at least one of strontium nitrate, zirconium nitrate, barium nitrate, magnesium nitrate, nickel nitrate and manganese nitrate, ferrous nitrate, and ferric nitrate;

[0146] 4-2) Add the carbon dot grafted molecular sieve obtained in step 3) to the metal salt solution obtained in step 4-1), ultrasonicate for 10-60 min, transfer the obtained mixture to a reactor, react at 140-200° C. for 6-24 h, filter and wash the product after the reaction, and calcine the solid product at 300-480° C. for 4-12 h to obtain a modified enhanced adsorbent.

[0147] Wherein, the mass ratio of the added metal salt to the carbon dot grafted molecular sieve is 5:1-1:1.

[0148] In the present invention, molecular sieve is used as the basic adsorbent, and metal salt modification is performed on it, and metal oxides with hygroscopicity or capable of reacting with water are introduced as enhanced desiccants, which can greatly improve the deep dehydration effect of the adsorbent.

[0149] The introduced metal salt is a mixture of at least one of strontium nitrate, zirconium nitrate, barium nitrate, magnesium nitrate, and nickel nitrate with manganese nitrate, ferrous nitrate, and ferric nitrate. These metal salts can generate mixed oxides with deep dehydration performance after roasting, such as magnesium oxide, iron oxide, barium oxide, zirconium oxide, etc. The metal oxides have a strong attraction and / or chemical activity for water molecules, thereby achieving water removal. At the same time, these metal oxides also have a certain adsorption and removal effect on gases such as oxygen and carbon dioxide.

[0150] In the traditional scheme, a simple impregnation method is usually used to introduce metal salts into the molecular sieve, such as a metal salt modified molecular sieve type deep dehydration adsorbent and preparation method disclosed in patent CN103949206B, and a method for removing water from ammonia disclosed in patent US2005120581A1. This method mainly realizes modification through the adsorption between metal ions and molecular sieves, and has defects such as low modification efficiency and weak connection of metal ions on molecular sieves. Another type of scheme is to first graft organic matter on the molecular sieve, such as silane coupling agent, and then graft metal ions through organic matter. When this type of scheme is used to functionalize the molecular sieve with organic matter, the organic matter is more easily modified to the surface of the molecular sieve, and it is difficult to enter its pores, and the organic matter component also has the disadvantage of poor stability.

[0151] On the other hand, in the traditional scheme, when modifying metal oxides on molecular sieves, the metal oxides are obtained by directly decomposing and depositing metal salts on the molecular sieves at high temperatures, which makes it difficult to control the morphology of the metal oxides.

[0152] In the present invention, unlike the traditional scheme, rare earth ions and carbon dots are used as intermediate bridges to introduce metal salts onto the surface of the molecular sieve, which can improve the grafting strength of the metal oxide on the molecular sieve on the one hand, and control the morphology of the metal oxide on the other hand, as follows:

[0153] The present invention firstly prepares a carbon dot with a surface rich in functional groups such as carboxyl and hydroxyl groups by a hydrothermal method, and then uses rare earth lanthanum ions to impregnate the molecular sieve. The lanthanum ions have a strong coordination effect with the silanol groups on the molecular sieve, so that they can be evenly and firmly connected to the surface and mesopores of the molecular sieve.

[0154] Then, the molecular sieve connected with lanthanum ions is mixed with carbon dots whose surfaces are rich in functional groups such as carboxyl and hydroxyl groups for reaction. Since lanthanum ions have large and numerous coordination bonds and can coordinate with carboxyl groups, carbon dots can be connected to the surface and mesopores of the molecular sieve in large quantities and uniformly with the help of the bridging effect of lanthanum ions, and have high connection strength, thus obtaining a carbon dot-grafted molecular sieve.

[0155] Finally, the carbon dot-grafted molecular sieve is reacted with a metal salt under heating. The abundant carboxyl and hydroxyl groups on the surface of the carbon dots can adsorb metal cations through electrostatic action. As the temperature rises, the reaction proceeds further, and the metal cations on the surface of the carbon dots are converted into metal oxide nuclei, thereby generating a large number of oxide nuclei on the surface of the carbon dots, which are finally deposited to form a mixed metal oxide layer of a certain thickness. The carbon dots, as nucleation centers, can promote the isotropic growth of crystals, facilitate the deposition to form a stable metal oxide layer, and regulate the growth of metal oxides. At the same time, at high temperatures, the lanthanum between the carbon dots and the molecular sieve forms an oxide, thereby enabling the bridging between the carbon dots and the molecular sieve to be achieved through strong chemical bonds.

[0156] Usually, when metal salts are deposited on the surface of molecular sieves and converted into metal oxides, they are easy to fall off due to the low interface connection strength, resulting in low efficiency of metal oxide formation. Also, the morphology of metal oxides on molecular sieves is usually difficult to control, and they may form layered, solid spherical and other morphologies. As metal oxides that are active ingredients for removing moisture, their irregular morphologies easily lead to their functions not being fully exerted. For example, the inner layer of layered and solid spherical metal oxides cannot be utilized because they are difficult to contact with gas.

[0157] In the present invention, the carbon dots are nano-sized spherical structures, and the metal oxides are coated on the surface of the carbon dots to form a core-shell structure. The outer layer is the metal oxide, which can fully contact with the gas to maximize its function of removing moisture; the inner layer is the carbon dots with stable mechanical properties, which not only play a role in morphology regulation and nucleation induction, but also can improve the mechanical strength of the core-shell structure, reduce the pulverization of the metal oxide, thereby extending its service life and facilitating regeneration. At the same time, the carbon dots and metal oxides are connected to the surface of the molecular sieve in a core-shell structure, which can also increase the specific surface area of ​​the molecular sieve and increase the number of active adsorption sites.

[0158] The above is the general concept of the present invention. Detailed embodiments and comparative examples are provided below to further illustrate the present invention.

[0159] Example 1

[0160] In this embodiment, the main process parameters of the high-purity ammonia production system are:

[0161] The temperature T in the dehydration tower 104 is 20-35°C, the reflux ratio R is 0.6, and the pressure P is 0.5-0.6 MPa;

[0162] The temperature T in the ammonia concentration tower 107 is 25-32°C, the reflux ratio R is 0.8, and the pressure P is 0.5-0.6 MPa;

[0163] The temperature T in the light removal tower 204 is 6-15°C, the reflux ratio R is 7, and the pressure P is 0.3-0.5 MPa;

[0164] The temperature T in the deweighting tower 205 is 6-15°C, the reflux ratio R is 5, and the pressure P is 0.3-0.5 MPa;

[0165] The tail gas absorption tower 302 operates at normal temperature and pressure, with a reflux ratio R of 0.8.

[0166] In this embodiment, there is no gas reflux in the primary adsorber 202 and the secondary adsorber 203 (ie, the reflux valve 4161 is closed).

[0167] In this embodiment, the first adsorbent 500 is 5A molecular sieve, Alfa Aesar (China) Chemical Co., Ltd., particle size 3-5mm, SiO 2 / Al 2 O 3 The molar ratio is 2.

[0168] In this embodiment, the modified enhanced molecular sieve is prepared by the following method:

[0169] 1) Preparation of carbon dots:

[0170] 1-1) Dissolve 1.5 g of folic acid, 2.8 g of citric acid, and 3 mL of ethylenediamine in 500 mL of ethanol-water solution, and ultrasonicate for 15 min. Transfer the resulting mixture to a reactor and react at 220°C for 6 hours. The volume ratio of ethanol to water in the ethanol-water solution is 1:1.

[0171] 1-2) After the reaction is completed, the mixture is cooled and the product is filtered with a 0.22 μm filter membrane. The filtrate is dialyzed in water for 18 hours using a dialysis bag with a molecular weight cutoff of 800 D. After dialysis, the inner liquid is collected and freeze-dried to obtain carbon dots;

[0172] 2) Molecular sieve pretreatment:

[0173] 2-1) Heat 10 g of molecular sieve at 280 °C for 1.5 h, then add it to 400 mL of ethanol and soak for 1 h;

[0174] Among them, the molecular sieve is 5A molecular sieve, Alfa Aesar (China) Chemical Co., Ltd., particle size 3-5mm, SiO 2 / Al 2 O 3 The molar ratio is 2;

[0175] 2-2) Filtering, adding the obtained molecular sieve into an ethanol solution of lanthanum nitrate with a concentration of 0.05 mol / L, ultrasonicating for 1 hour, and filtering again to obtain the pretreated molecular sieve;

[0176] The mass ratio of the added lanthanum to the molecular sieve is 2:100;

[0177] 3) Grafting carbon dots onto molecular sieves:

[0178] 3-1) adding the carbon dots prepared in step 1) into ethanol and ultrasonicating for 0.5 h to prepare a carbon dots dispersion with a concentration of 0.5 mol / L;

[0179] 3-2) adding the pretreated molecular sieve prepared in step 2) to the carbon dot dispersion obtained in step 3-1), shaking on a shaker at 45°C for 3 hours, filtering, and vacuum drying at 50°C for 3 hours to obtain a carbon dot grafted molecular sieve;

[0180] Among them, the mass ratio of added carbon dots to pretreated molecular sieve is 1:6;

[0181] 4) Modification of molecular sieve with metal salt:

[0182] 4-1) Add 1.4 g strontium nitrate, 1.2 g zirconium nitrate, 0.5 g barium nitrate, 8.6 g manganese nitrate, 0.9 g ferrous nitrate, and 1.8 g ferric nitrate to 300 mL of an ethanol aqueous solution having a volume ratio of deionized water to ethanol of 3:7, and stir to dissolve to obtain a metal salt solution;

[0183] 4-2) Add 7.2 g of the carbon-dot grafted molecular sieve obtained in step 3) to the metal salt solution obtained in step 4-1), ultrasonicate for 0.5 h, transfer the obtained mixture to a reactor, react at 160° C. for 12 h, filter the product after the reaction, wash with ethanol, and calcine the solid product at 350° C. for 8 h to obtain a modified enhanced adsorbent.

[0184] Example 2

[0185] In this embodiment, the main process parameters of the high-purity ammonia production system are:

[0186] The temperature T in the dehydration tower 104 is 25-35°C, the reflux ratio R is 0.6, and the pressure P is 0.5-0.6 MPa;

[0187] The temperature T in the ammonia concentration tower 107 is 28-40°C, the reflux ratio R is 0.8, and the pressure P is 0.5-0.6 MPa;

[0188] The temperature T in the light removal tower 204 is 8-16°C, the reflux ratio R is 7, and the pressure P is 0.3-0.5 MPa;

[0189] The temperature T in the deweighting tower 205 is 6-15°C, the reflux ratio R is 5, and the pressure P is 0.3-0.5 MPa;

[0190] The tail gas absorption tower 302 operates at normal temperature and pressure, with a reflux ratio R of 0.8.

[0191] In this embodiment, the gas reflux ratios in the primary adsorber 202 and the secondary adsorber 203 are 0.22 and 0.4%, respectively.

[0192] In this embodiment, the first adsorbent 500 is 5A molecular sieve, Alfa Aesar (China) Chemical Co., Ltd., particle size 3-5mm, SiO 2 / Al 2 O 3 The molar ratio is 2.

[0193] In this embodiment, the modified enhanced molecular sieve is prepared by the following method:

[0194] 1) Preparation of carbon dots:

[0195] 1-1) Dissolve 1.5 g of folic acid, 2.8 g of citric acid, and 3 mL of ethylenediamine in 500 mL of ethanol-water solution, and ultrasonicate for 15 min. Transfer the resulting mixture to a reactor and react at 220°C for 6 hours. The volume ratio of ethanol to water in the ethanol-water solution is 1:1.

[0196] 1-2) After the reaction is completed, the mixture is cooled and the product is filtered with a 0.22 μm filter membrane. The filtrate is dialyzed in water for 18 hours using a dialysis bag with a molecular weight cutoff of 800 D. After dialysis, the inner liquid is collected and freeze-dried to obtain carbon dots;

[0197] 2) Molecular sieve pretreatment:

[0198] 2-1) Heat 10 g of molecular sieve at 280 °C for 1.5 h, then add it to 400 mL of ethanol and soak for 1 h;

[0199] Among them, the molecular sieve is 5A molecular sieve, Alfa Aesar (China) Chemical Co., Ltd., particle size 3-5mm, SiO 2 / Al 2 O 3 The molar ratio is 2;

[0200] 2-2) Filtering, adding the obtained molecular sieve into an ethanol solution of lanthanum nitrate with a concentration of 0.05 mol / L, ultrasonicating for 1 hour, and filtering again to obtain the pretreated molecular sieve;

[0201] The mass ratio of the added lanthanum to the molecular sieve is 2:100;

[0202] 3) Grafting carbon dots onto molecular sieves:

[0203] 3-1) adding the carbon dots prepared in step 1) into ethanol and ultrasonicating for 0.5 h to prepare a carbon dots dispersion with a concentration of 0.5 mol / L;

[0204] 3-2) adding the pretreated molecular sieve prepared in step 2) to the carbon dot dispersion obtained in step 3-1), shaking on a shaker at 45°C for 3 hours, filtering, and vacuum drying at 50°C for 3 hours to obtain a carbon dot grafted molecular sieve;

[0205] Among them, the mass ratio of added carbon dots to pretreated molecular sieve is 1:6;

[0206] 4) Modification of molecular sieve with metal salt:

[0207] 4-1) Add 1.4 g strontium nitrate, 1.2 g zirconium nitrate, 0.5 g barium nitrate, 8.6 g manganese nitrate, 0.9 g ferrous nitrate, and 1.8 g ferric nitrate to 300 mL of an ethanol aqueous solution having a volume ratio of deionized water to ethanol of 3:7, and stir to dissolve to obtain a metal salt solution;

[0208] 4-2) Add 7.2 g of the carbon-dot grafted molecular sieve obtained in step 3) to the metal salt solution obtained in step 4-1), ultrasonicate for 0.5 h, transfer the obtained mixture to a reactor, react at 160° C. for 12 h, filter the product after the reaction, wash with ethanol, and calcine the solid product at 350° C. for 8 h to obtain a modified enhanced adsorbent.

[0209] Example 3

[0210] In this embodiment, the main process parameters of the high-purity ammonia production system are:

[0211] The temperature T in the dehydration tower 104 is 28-38°C, the reflux ratio R is 0.6, and the pressure P is 0.5-0.6 MPa;

[0212] The temperature T in the ammonia concentration tower 107 is 28-35°C, the reflux ratio R is 0.8, and the pressure P is 0.5-0.6 MPa;

[0213] The temperature T in the light removal tower 204 is 6-15°C, the reflux ratio R is 7, and the pressure P is 0.3-0.5 MPa;

[0214] The temperature T in the deweighting tower 205 is 8-17°C, the reflux ratio R is 5, and the pressure P is 0.3-0.5 MPa;

[0215] The tail gas absorption tower 302 operates at normal temperature and pressure, with a reflux ratio R of 0.8.

[0216] In this embodiment, the gas reflux ratios in the primary adsorber 202 and the secondary adsorber 203 are 0.28 and 0.5 respectively.

[0217] In this embodiment, the first adsorbent 500 is 5A molecular sieve, Alfa Aesar (China) Chemical Co., Ltd., particle size 3-5mm, SiO 2 / Al 2 O 3 The molar ratio is 2.

[0218] In this embodiment, the modified enhanced molecular sieve is prepared by the following method:

[0219] 1) Preparation of carbon dots:

[0220] 1-1) Dissolve 1.5 g of folic acid, 2.8 g of citric acid, and 3 mL of ethylenediamine in 500 mL of ethanol-water solution, and ultrasonicate for 15 min. Transfer the resulting mixture to a reactor and react at 220°C for 6 hours. The volume ratio of ethanol to water in the ethanol-water solution is 1:1.

[0221] 1-2) After the reaction is completed, the mixture is cooled and the product is filtered with a 0.22 μm filter membrane. The filtrate is dialyzed in water for 18 hours using a dialysis bag with a molecular weight cutoff of 800 D. After dialysis, the inner liquid is collected and freeze-dried to obtain carbon dots;

[0222] 2) Molecular sieve pretreatment:

[0223] 2-1) Heat 10 g of molecular sieve at 280 °C for 1.5 h, then add it to 400 mL of ethanol and soak for 1 h;

[0224] Among them, the molecular sieve is 5A molecular sieve, Alfa Aesar (China) Chemical Co., Ltd., particle size 3-5mm, SiO 2 / Al 2 O 3 The molar ratio is 2;

[0225] 2-2) Filtering, adding the obtained molecular sieve into an ethanol solution of lanthanum nitrate with a concentration of 0.05 mol / L, ultrasonicating for 1 hour, and filtering again to obtain the pretreated molecular sieve;

[0226] The mass ratio of the added lanthanum to the molecular sieve is 2:100;

[0227] 3) Grafting carbon dots onto molecular sieves:

[0228] 3-1) adding the carbon dots prepared in step 1) into ethanol and ultrasonicating for 0.5 h to prepare a carbon dots dispersion with a concentration of 0.5 mol / L;

[0229] 3-2) adding the pretreated molecular sieve prepared in step 2) to the carbon dot dispersion obtained in step 3-1), shaking on a shaker at 45°C for 3 hours, filtering, and vacuum drying at 50°C for 3 hours to obtain a carbon dot grafted molecular sieve;

[0230] Among them, the mass ratio of added carbon dots to pretreated molecular sieve is 1:6;

[0231] 4) Modification of molecular sieve with metal salt:

[0232] 4-1) Add 1.4 g strontium nitrate, 1.2 g zirconium nitrate, 0.5 g barium nitrate, 8.6 g manganese nitrate, 0.9 g ferrous nitrate, and 1.8 g ferric nitrate to 300 mL of an ethanol aqueous solution having a volume ratio of deionized water to ethanol of 3:7, and stir to dissolve to obtain a metal salt solution;

[0233] 4-2) Add 7.2 g of the carbon-dot grafted molecular sieve obtained in step 3) to the metal salt solution obtained in step 4-1), ultrasonicate for 0.5 h, transfer the obtained mixture to a reactor, react at 160° C. for 12 h, filter the product after the reaction, wash with ethanol, and calcine the solid product at 350° C. for 8 h to obtain a modified enhanced adsorbent.

[0234] Example 4

[0235] In this embodiment, the main process parameters of the high-purity ammonia production system are:

[0236] The temperature T in the dehydration tower 104 is 20-35°C, the reflux ratio R is 0.6, and the pressure P is 0.5-0.6 MPa;

[0237] The temperature T in the ammonia concentration tower 107 is 25-32°C, the reflux ratio R is 0.8, and the pressure P is 0.5-0.6 MPa;

[0238] The temperature T in the light removal tower 204 is 6-15°C, the reflux ratio R is 7, and the pressure P is 0.3-0.5 MPa;

[0239] The temperature T in the deweighting tower 205 is 6-15°C, the reflux ratio R is 5, and the pressure P is 0.3-0.5 MPa;

[0240] The tail gas absorption tower 302 operates at normal temperature and pressure, with a reflux ratio R of 0.8.

[0241] In this embodiment, the gas reflux ratios in the primary adsorber 202 and the secondary adsorber 203 are 0.28 and 0.5 respectively.

[0242] In this embodiment, the first adsorbent 500 is 5A molecular sieve, Alfa Aesar (China) Chemical Co., Ltd., particle size 3-5mm, SiO 2 / Al 2 O 3 The molar ratio is 2.

[0243] In this embodiment, the modified enhanced molecular sieve is prepared by the following method:

[0244] 1) Preparation of carbon dots:

[0245] 1-1) Dissolve 1.5 g of folic acid, 2.8 g of citric acid, and 3 mL of ethylenediamine in 500 mL of ethanol-water solution, and ultrasonicate for 15 min. Transfer the resulting mixture to a reactor and react at 220°C for 6 hours. The volume ratio of ethanol to water in the ethanol-water solution is 1:1.

[0246] 1-2) After the reaction is completed, the mixture is cooled and the product is filtered with a 0.22 μm filter membrane. The filtrate is dialyzed in water for 18 hours using a dialysis bag with a molecular weight cutoff of 800 D. After dialysis, the inner liquid is collected and freeze-dried to obtain carbon dots;

[0247] 2) Molecular sieve pretreatment:

[0248] 2-1) Heat 10 g of molecular sieve at 280 °C for 1.5 h, then add it to 400 mL of ethanol and soak for 1 h;

[0249] Among them, the molecular sieve is 5A molecular sieve, Alfa Aesar (China) Chemical Co., Ltd., particle size 3-5mm, SiO 2 / Al 2 O 3 The molar ratio is 2;

[0250] 2-2) Filtering, adding the obtained molecular sieve into an ethanol solution of lanthanum nitrate with a concentration of 0.05 mol / L, ultrasonicating for 1 hour, and filtering again to obtain the pretreated molecular sieve;

[0251] The mass ratio of the added lanthanum to the molecular sieve is 4:100;

[0252] 3) Grafting carbon dots onto molecular sieves:

[0253] 3-1) adding the carbon dots prepared in step 1) into ethanol and ultrasonicating for 0.5 h to prepare a carbon dots dispersion with a concentration of 0.5 mol / L;

[0254] 3-2) adding the pretreated molecular sieve prepared in step 2) to the carbon dot dispersion obtained in step 3-1), shaking on a shaker at 45°C for 3 hours, filtering, and vacuum drying at 50°C for 3 hours to obtain a carbon dot grafted molecular sieve;

[0255] Among them, the mass ratio of added carbon dots to pretreated molecular sieve is 1:6;

[0256] 4) Modification of molecular sieve with metal salt:

[0257] 4-1) Add 1.4 g strontium nitrate, 1.2 g zirconium nitrate, 0.5 g barium nitrate, 8.6 g manganese nitrate, 0.9 g ferrous nitrate, and 1.8 g ferric nitrate to 300 mL of an ethanol aqueous solution having a volume ratio of deionized water to ethanol of 3:7, and stir to dissolve to obtain a metal salt solution;

[0258] 4-2) Add 7.2 g of the carbon-dot grafted molecular sieve obtained in step 3) to the metal salt solution obtained in step 4-1), ultrasonicate for 0.5 h, transfer the obtained mixture to a reactor, react at 160° C. for 12 h, filter the product after the reaction, wash with ethanol, and calcine the solid product at 350° C. for 8 h to obtain a modified enhanced adsorbent.

[0259] Example 5

[0260] In this embodiment, the main process parameters of the high-purity ammonia production system are:

[0261] The temperature T in the dehydration tower 104 is 20-35°C, the reflux ratio R is 0.6, and the pressure P is 0.5-0.6 MPa;

[0262] The temperature T in the ammonia concentration tower 107 is 25-32°C, the reflux ratio R is 0.8, and the pressure P is 0.5-0.6 MPa;

[0263] The temperature T in the light removal tower 204 is 6-15°C, the reflux ratio R is 7, and the pressure P is 0.3-0.5 MPa;

[0264] The temperature T in the deweighting tower 205 is 6-15°C, the reflux ratio R is 5, and the pressure P is 0.3-0.5 MPa;

[0265] The tail gas absorption tower 302 operates at normal temperature and pressure, with a reflux ratio R of 0.8.

[0266] In this embodiment, the gas reflux ratios in the primary adsorber 202 and the secondary adsorber 203 are 0.28 and 0.5 respectively.

[0267] In this embodiment, the first adsorbent 500 is 5A molecular sieve, Alfa Aesar (China) Chemical Co., Ltd., particle size 3-5mm, SiO 2 / Al 2 O 3 The molar ratio is 2.

[0268] In this embodiment, the modified enhanced molecular sieve is prepared by the following method:

[0269] 1) Preparation of carbon dots:

[0270] 1-1) Dissolve 1.5 g of folic acid, 2.8 g of citric acid, and 3 mL of ethylenediamine in 500 mL of ethanol-water solution, and ultrasonicate for 15 min. Transfer the resulting mixture to a reactor and react at 220°C for 6 hours. The volume ratio of ethanol to water in the ethanol-water solution is 1:1.

[0271] 1-2) After the reaction is completed, the mixture is cooled and the product is filtered with a 0.22 μm filter membrane. The filtrate is dialyzed in water for 18 hours using a dialysis bag with a molecular weight cutoff of 800 D. After dialysis, the inner liquid is collected and freeze-dried to obtain carbon dots;

[0272] 2) Molecular sieve pretreatment:

[0273] 2-1) Heat 10 g of molecular sieve at 280 °C for 1.5 h, then add it to 400 mL of ethanol and soak for 1 h;

[0274] Among them, the molecular sieve is 5A molecular sieve, Alfa Aesar (China) Chemical Co., Ltd., particle size 3-5mm, SiO 2 / Al 2 O 3 The molar ratio is 2;

[0275] 2-2) Filtering, adding the obtained molecular sieve into an ethanol solution of lanthanum nitrate with a concentration of 0.05 mol / L, ultrasonicating for 1 hour, and filtering again to obtain the pretreated molecular sieve;

[0276] The mass ratio of the added lanthanum to the molecular sieve is 4:100;

[0277] 3) Grafting carbon dots onto molecular sieves:

[0278] 3-1) adding the carbon dots prepared in step 1) into ethanol and ultrasonicating for 0.5 h to prepare a carbon dots dispersion with a concentration of 0.5 mol / L;

[0279] 3-2) adding the pretreated molecular sieve prepared in step 2) to the carbon dot dispersion obtained in step 3-1), shaking on a shaker at 45°C for 3 hours, filtering, and vacuum drying at 50°C for 3 hours to obtain a carbon dot grafted molecular sieve;

[0280] Among them, the mass ratio of added carbon dots to pretreated molecular sieve is 1:6;

[0281] 4) Modification of molecular sieve with metal salt:

[0282] 4-1) Add 1.4 g strontium nitrate, 1.2 g zirconium nitrate, 0.5 g barium nitrate, 8.6 g manganese nitrate, 0.9 g ferrous nitrate, and 1.8 g ferric nitrate to 300 mL of an ethanol aqueous solution having a volume ratio of deionized water to ethanol of 3:7, and stir to dissolve to obtain a metal salt solution;

[0283] 4-2) Add 4.8 g of the carbon-dot grafted molecular sieve obtained in step 3) to the metal salt solution obtained in step 4-1), ultrasonicate for 0.5 h, transfer the obtained mixture to a reactor, react at 160° C. for 12 h, filter the product after the reaction, wash with ethanol, and calcine the solid product at 350° C. for 8 h to obtain a modified enhanced adsorbent.

[0284] Comparative Example 1

[0285] This example is basically the same as Example 5, except that the second adsorbent 600 in this example: the modified enhanced molecular sieve is replaced with the 5A molecular sieve that is the same as the first adsorbent 500.

[0286] In the above embodiments and comparative examples, the first adsorbent 500 and the second adsorbent 600 were both vacuum dried at 280° C. for 12 h for activation before use.

[0287] Reference Figure 7 , are infrared spectra of the 5A molecular sieve (5A) used to prepare the modified and enhanced molecular sieve in Example 1 and the prepared modified and enhanced molecular sieve (Me-CD-5A); characteristic peaks in 5A and Me-CD-5A: 1032cm -1 、774cm -1 The asymmetric stretching vibration and symmetric stretching vibration of Si-O-Si bond are respectively assigned to 651cm -1 It is attributed to the Al-O bond. Among the several absorption peaks added by Me-CD-5A, 3211cm -1 、1674cm -1 The vibration peaks corresponding to amino and carboxyl groups are 2913 cm -1 The corresponding stretching vibration peak of alkanes indicates that carbon dots were successfully grafted onto Me-CD-5A.

[0288] Referring to Table 1 below, the BET specific surface area measurement results of the 5A molecular sieve used in Examples 3-5 and the prepared modified enhanced molecular sieve are shown:

[0289] Table 1

[0290] 5A molecular sieve Example 3 Example 4 Example 5 <![CDATA[Specific surface area m 2 / g]]> 454.7 511.4 528.1 514.7

[0291] Refer to Table 2 below, which shows the purity analysis results of the high-purity ammonia products obtained in Examples 1-5 and Comparative Example 1:

[0292] Table 2

[0293]

[0294] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to specific details.

Claims

1. A high-purity ammonia production system, characterized in that: include: A dilute ammonia dehydration unit, comprising a feed buffer tank, a filter, a first heat exchanger, a dehydration tower, a second heat exchanger, a dehydration buffer tank, an ammonia concentration tower, a fourth heat exchanger, a liquid ammonia buffer tank, and a third heat exchanger connected to the dehydration tower, a fifth heat exchanger connected to the upper part of the ammonia concentration tower, and a sixth heat exchanger connected to the lower part of the ammonia concentration tower. A high-purity ammonia purification unit, comprising a seventh heat exchanger connected in sequence to the liquid ammonia buffer tank, a primary adsorber, a secondary adsorber, a lightness removal tower, a heavyness removal tower, a ninth heat exchanger, a product temporary storage tank, a high-purity ammonia product tank, an eighth heat exchanger connected to the upper part of the lightness removal tower, a tenth heat exchanger connected to the lower part of the lightness removal tower, and an eleventh heat exchanger connected to the lower part of the heavyness removal tower; and a tail gas absorption unit, which includes a waste buffer tank, a tail gas absorption tower and a twelfth heat exchanger connected in sequence to the deweighting tower; The primary adsorber and the secondary adsorber have the same structure, both comprising an adsorber body and a first adsorbent and a second adsorbent filled in the adsorber body, and the gas entering the adsorber body passes through the first adsorbent and the second adsorbent and then is discharged; The adsorber body comprises an adsorber shell, a desiccant chamber, a first adsorption chamber and a second adsorption chamber sequentially formed in the adsorber shell from bottom to top, a first filter cartridge in an annular shape arranged in the first adsorption chamber, a second filter cartridge arranged in the first adsorption chamber and in a cavity in the middle of the first filter cartridge, a third filter cartridge in an inverted cone shape arranged in the second adsorption chamber, a partition arranged between the second filter cartridge and the third filter cartridge, an air intake guide cavity formed between the partition and the upper part of the second filter cartridge, a transition guide cavity formed between the lower part of the first filter cartridge, the second filter cartridge and the first adsorption chamber, an air intake pipe communicated with the air intake guide cavity, an air collecting hood arranged on the upper part of the third filter cartridge, an air outlet pipe communicated with the air collecting hood, and a reflux component connected between the air outlet pipe and the second adsorption chamber; The top of the desiccant chamber is communicated with the transition guide cavity; The partition plate is provided with a connecting hole connecting the second filter cartridge and the third filter cartridge.

2. The high-purity ammonia production system according to claim 1, characterized in that: The raw ammonia water first enters the feed buffer tank for buffering, the ammonia water discharged from the feed buffer tank is filtered by the filter and then heated and gasified by the first heat exchanger, and then enters the dehydration tower from the middle, the ammonia gas obtained by dehydration is discharged from the top of the tower, and then condensed into liquid ammonia by the second heat exchanger and enters the dehydration buffer tank, a part of the liquid ammonia discharged from the dehydration buffer tank returns from the upper part to enter the dehydration tower, forming a dehydrated liquid ammonia spray liquid flowing downward in the dehydration tower, and the other part of the liquid ammonia enters the ammonia water concentration tower in the next step; A portion of the dehydrated mixture obtained at the bottom of the dehydration tower is heated and vaporized by the third heat exchanger and then returned to the dehydration tower to form an ascending ammonia gas flow, and the other portion is discharged from the system as wastewater after heat recovery by the first heat exchanger.

3. The high-purity ammonia production system according to claim 2, characterized in that: Part of the liquid ammonia discharged from the dehydration buffer tank enters the ammonia water concentration tower from the middle, and part of the ammonia gas obtained at the top of the tower is condensed by the fourth heat exchanger to obtain the initial liquid ammonia product and then enters the liquid ammonia buffer tank for storage, and the other part of the ammonia gas is condensed into liquid ammonia by the fifth heat exchanger and then returns to the top of the ammonia water concentration tower, forming a concentrated liquid ammonia spray liquid flowing downward in the ammonia water concentration tower; A portion of the concentrated mixture obtained at the bottom of the ammonia concentration tower is heated and vaporized by the sixth heat exchanger and then re-enters the ammonia concentration tower to form an ascending ammonia gas flow, and the other portion is returned to the dehydration tower.

4. The high-purity ammonia production system according to claim 3, characterized in that: The liquid ammonia initial product in the liquid ammonia buffer tank is heated and gasified by the seventh heat exchanger, and then sequentially processed by the first-stage adsorber and the second-stage adsorber, and then enters the light removal tower from the middle; The ammonia gas obtained at the top of the light-removal tower is condensed into liquid ammonia by the eighth heat exchanger to obtain liquid ammonia containing light component impurities, a part of the liquid ammonia containing light component impurities enters the waste buffer tank in the tail gas absorption unit, and the other part returns from the upper part to enter the light-removal tower to form a liquid ammonia spray liquid flowing downward; A portion of the pure liquid ammonia obtained at the bottom of the light-removal tower after light component impurities are removed is heated and vaporized by the tenth heat exchanger and then returned to the light-removal tower to form an ascending ammonia gas flow, and the other portion enters the heavy-removal tower in the next step.

5. The high-purity ammonia production system according to claim 4, characterized in that: Part of the pure liquid ammonia obtained in the light removal tower enters the de-weighting tower from the middle, and the ammonia gas obtained at the top of the tower is condensed into liquid ammonia by the ninth heat exchanger to obtain high-purity liquid ammonia after the heavy component impurities are removed. Part of the high-purity liquid ammonia enters the product temporary storage tank, and enters the high-purity ammonia product tank for storage after the product is analyzed to be qualified. Another part of the high-purity liquid ammonia returns from the upper part to enter the de-weighting tower to form a liquid ammonia spray liquid flowing downward; A portion of the liquid ammonia containing heavy impurities obtained at the bottom of the de-weighting tower is heated and vaporized by the eleventh heat exchanger and then returned to the de-weighting tower to form an ascending ammonia gas flow, and the other portion enters the waste buffer tank in the tail gas absorption unit.

6. The high-purity ammonia production system according to claim 5, characterized in that: The tailings in the waste buffer tank enter the tail gas absorption tower from the bottom, and the supplementary process water enters the top of the tower and is sprayed downward to absorb ammonia. The tail gas obtained by the tail gas absorption tower is discharged from the top of the tower. A part of the tailings mixture obtained at the bottom of the tail gas absorption tower is discharged from the system as dilute ammonia water, and the other part is heated and vaporized by the twelfth heat exchanger and then returned to the tail gas absorption tower to form an upward airflow.

7. The high-purity ammonia production system according to claim 1, characterized in that: A conical reflux cavity is formed between the outer wall of the third filter cartridge and the inner wall of the second adsorption chamber, and the reflux assembly includes a reflux main pipe connected to the outlet pipe, a reflux valve arranged on the reflux main pipe, and a plurality of reflux branches connected to the output end of the reflux main pipe, wherein the plurality of reflux branches are arranged at intervals in the vertical direction and are all connected to the reflux cavity; The adsorber shell is cylindrical, and the reflux branch pipe is connected to the adsorber shell along a circumferential tangent direction; The first filter cartridge and the second filter cartridge each have filter holes densely formed only on the upper and lower end surfaces, and the outer wall and the upper and lower end surfaces of the third filter cartridge each have filter holes densely formed; The first filter cartridge is filled with the first adsorbent, the second filter cartridge and the third filter cartridge are both filled with the second adsorbent, and the desiccant chamber is filled with desiccant.

8. The high-purity ammonia production system according to claim 1, characterized in that: The first adsorbent is 5A molecular sieve or MCM-41 molecular sieve, and the second adsorbent is a modified enhanced molecular sieve, which is prepared by the following method: 1) Preparation of carbon dots: 1-1) dissolving folic acid, citric acid and ethylenediamine in an ethanol aqueous solution, ultrasonicating for 5-30 min, transferring the obtained mixed solution to a reaction kettle, and reacting at 180-250° C. for 4-12 hours; 1-2) After the reaction is completed, the product is cooled and filtered with a filter membrane. The filtrate is dialyzed in water for 12-24 hours using a dialysis bag with a molecular weight cutoff of 500-1200D. After dialysis, the inner liquid is taken and freeze-dried to obtain carbon dots; 2) Molecular sieve pretreatment: 2-1) Activate the molecular sieve by heating at 250-350°C for 1-4h, then add it into ethanol and soak it for 0.5-3h; 2-2) filtering, adding the obtained molecular sieve to an ethanol solution of lanthanum nitrate, ultrasonicating for 0.5-3h, and filtering again to obtain the pretreated molecular sieve; The molecular sieve is 5A molecular sieve or MCM-41 molecular sieve, and the mass ratio of the added lanthanum to the molecular sieve is 0.5:100-5:100; 3) Grafting carbon dots onto molecular sieves: 3-1) adding the carbon dots prepared in step 1) into ethanol and ultrasonicating for 20-60 min to prepare a carbon dot dispersion; 3-2) adding the pretreated molecular sieve prepared in step 2) to the carbon dot dispersion obtained in step 3-1), shaking on a shaker at 40-55° C. for 2-6 h, filtering, and vacuum drying at 40-60° C. for 2-6 h to obtain a carbon dot grafted molecular sieve; The mass ratio of the added carbon dots to the pretreated molecular sieve is 1:4-1:10; 4) Modification of molecular sieve with metal salt: 4-1) dissolving a metal salt in an ethanol aqueous solution to obtain a metal salt solution; Wherein, the metal salt is a mixture of at least one of strontium nitrate, zirconium nitrate, barium nitrate, magnesium nitrate, nickel nitrate and manganese nitrate, ferrous nitrate, and ferric nitrate; 4-2) adding the carbon dot grafted molecular sieve obtained in step 3) to the metal salt solution obtained in step 4-1), ultrasonicating for 10-60 min, transferring the obtained mixture to a reactor, reacting at 140-200° C. for 6-24 h, filtering and washing the product after the reaction, and calcining the solid product at 300-480° C. for 4-12 h to obtain a modified enhanced adsorbent; Wherein, the mass ratio of the added metal salt to the carbon dot grafted molecular sieve is 5:1-1:

1.

9. The high-purity ammonia production system according to claim 8, characterized in that: The modified enhanced molecular sieve is prepared by the following method: 1) Preparation of carbon dots: 1-1) 1.5 g of folic acid, 2.8 g of citric acid, and 3 mL of ethylenediamine were dissolved in 500 mL of ethanol aqueous solution, and ultrasonicated for 15 min. The obtained mixed solution was transferred to a reactor and reacted at 220° C. for 6 hours; the volume ratio of ethanol to water in the ethanol aqueous solution was 1:1; 1-2) After the reaction is completed, the mixture is cooled and the product is filtered with a 0.22 μm filter membrane. The filtrate is dialyzed in water for 18 hours with a dialysis bag with a molecular weight cutoff of 800D. After dialysis, the inner liquid is collected and freeze-dried to obtain carbon dots; 2) Molecular sieve pretreatment: 2-1) 10 g of molecular sieve was heated at 280°C for 1.5 h for activation, then added into 400 mL of ethanol and soaked for 1 h; 2-2) filtering, adding the obtained molecular sieve to an ethanol solution of lanthanum nitrate with a concentration of 0.05 mol / L, ultrasonicating for 1 h, and filtering again to obtain the pretreated molecular sieve; The molecular sieve is 5A molecular sieve, and the mass ratio of the added lanthanum to the molecular sieve is 2:100; 3) Grafting carbon dots onto molecular sieves: 3-1) adding the carbon dots prepared in step 1) into ethanol and ultrasonicating for 0.5 h to prepare a carbon dot dispersion with a concentration of 0.5 mol / L; 3-2) adding the pretreated molecular sieve prepared in step 2) to the carbon dot dispersion obtained in step 3-1), shaking on a shaker at 45° C. for 3 h, filtering, and vacuum drying at 50° C. for 3 h to obtain a carbon dot-grafted molecular sieve; Among them, the mass ratio of added carbon dots to pretreated molecular sieve is 1:6; 4) Modification of molecular sieve with metal salt: 4-1) 1.4 g of strontium nitrate, 1.2 g of zirconium nitrate, 0.5 g of barium nitrate, 8.6 g of manganese nitrate, 0.9 g of ferrous nitrate, and 1.8 g of ferric nitrate were added to 300 mL of an ethanol aqueous solution having a volume ratio of deionized water to ethanol of 3:7, and stirred to dissolve to obtain a metal salt solution; 4-2) Add 7.2 g of the carbon-dot grafted molecular sieve obtained in step 3) to the metal salt solution obtained in step 4-1), ultrasonicate for 0.5 h, transfer the obtained mixture to a reactor, react at 160° C. for 12 h, filter the product after the reaction, wash with ethanol, and calcine the solid product at 350° C. for 8 h to obtain a modified enhanced adsorbent.

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