A process for producing synthetic ammonia using hydrogen-containing tail gas

Abstract

The present application relates to a process for producing synthetic ammonia by using hydrogen-containing tail gas, comprising the following steps: S1: sodium cyanide tail gas is pressurized, then heated and water-cooled. S2: the impurity-removed tail gas is desulfurized. S3: the desulfurized tail gas is mixed with chlor-alkali tail gas, the mixed gas is heated and deoxidized. S4: the deoxidized tail gas is pressurized and enters a PSA (pressure swing adsorption) device for pressure swing adsorption treatment, obtaining high-purity hydrogen. In the PSA device, dehydrating, carbon dioxide, methane, carbon monoxide and nitrogen adsorbents are sequentially arranged. The carbon dioxide adsorbent is activated carbon modified by carbonate and strong alkali, and the nitrogen adsorbent is 13X zeolite molecular sieve modified by Na + and Ba 2+ and Ca 2+ ion exchange. S5: nitrogen reacts with the high-purity hydrogen obtained in step S4 to generate ammonia. The present application can improve the adsorption capacity of the adsorbent for impurity gas, thereby reducing the replacement frequency of the adsorbent, prolonging the service period and service life of the adsorbent, and improving the production efficiency.

Description

Technical Field

[0001] This invention belongs to the field of tail gas utilization technology, specifically relating to a process for producing synthetic ammonia using hydrogen-containing tail gas. Background Technology

[0002] In modern chemical industry, ammonia is a major raw material for fertilizer production and basic organic chemicals. It is a primary raw material for producing chemical fertilizers such as urea, ammonium phosphate, and ammonium nitrate. Liquid ammonia can also be used as a raw material for amination synthesis in organic chemicals, such as the synthesis of acrylonitrile. Furthermore, ammonia is widely used as an important refrigerant in the refrigeration industry. Current technologies for ammonia synthesis primarily use natural gas, crude oil, coal, and coke as initial raw materials; however, existing processes for producing ammonia from these raw materials are complex and costly.

[0003] The main components of sodium cyanide tail gas produced during sodium cyanide production and chlor-alkali tail gas produced during chlor-alkali production are hydrogen, referred to as hydrogen-containing tail gas. Currently, these two types of tail gas are mostly sent to boiler rooms for combustion to heat steam for production and domestic use. This treatment method only utilizes their thermal energy, which will cause serious waste of resources.

[0004] Patent application number 200710010222.1 discloses a method for producing synthetic ammonia by purifying hydrogen from sodium cyanide tail gas and chlor-alkali tail gas. The method involves removing impurities from the sodium cyanide and chlor-alkali tail gas, followed by pressurization and high-purity hydrogen production via pressure swing adsorption (PSA). This high-purity hydrogen and high-purity nitrogen are then used as raw materials to produce synthetic ammonia. While this method utilizes a hydrogen purification adsorbent to adsorb impurities from the tail gas, the adsorbent used in this PSA purification method requires frequent replacement, directly impacting production efficiency.

[0005] Therefore, in the process of purifying hydrogen from hydrogen-containing tail gas to produce synthetic ammonia, it is necessary to reduce the frequency of adsorbent replacement and improve production efficiency. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] To address the problem of reduced production efficiency caused by frequent adsorbent replacements during the pressure swing adsorption (PSA) process for purifying hydrogen, this invention provides a process for producing synthetic ammonia using hydrogen-containing tail gas.

[0008] (II) Technical Solution

[0009] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0010] A process for producing synthetic ammonia using hydrogen-containing tail gas, wherein the hydrogen-containing tail gas includes chlor-alkali tail gas and sodium cyanide tail gas, comprising the following steps:

[0011] S1: The sodium cyanide tail gas is pressurized, then heated and cooled with water to obtain impurity-free tail gas;

[0012] S2: Desulfurize the impurity removal tail gas to obtain desulfurized tail gas;

[0013] S3: Mix the desulfurization tail gas with the chlor-alkali tail gas, heat the mixed gas and then perform deoxygenation treatment to obtain deoxygenated tail gas.

[0014] S4: After being pressurized, the deoxygenated tail gas enters the PSA pressure swing adsorption unit for pressure swing adsorption treatment to obtain high-purity hydrogen. According to the airflow direction, the PSA pressure swing adsorption unit is sequentially equipped with dehydration adsorbent, carbon dioxide adsorbent, methane adsorbent, carbon monoxide adsorbent and nitrogen adsorbent.

[0015] The carbon dioxide adsorbent is activated carbon modified with carbonate and strong alkali, and the nitrogen adsorbent is activated carbon modified with Na+. + with Ba 2+ and Ca 2+ Ion-exchange modified 13X zeolite molecular sieve;

[0016] S5: Nitrogen reacts with the high-purity hydrogen obtained in step S4 to produce ammonia.

[0017] In the process of producing synthetic ammonia using hydrogen-containing tail gas as described above, preferably, in step S1, the sodium cyanide tail gas is pressurized to a pressure of 0.085 MPa, then heated to 55-60°C, and then cooled to below 30°C with water to obtain purified tail gas. In step S1, the sodium cyanide tail gas exits directly through the buffer in the production system. Because the sodium cyanide production system is under negative pressure, the temperature of the tail gas exiting the buffer is 65-70°C and the pressure is -0.034 MPa, so pressurization is necessary. After the temperature of the sodium cyanide tail gas rises to 55-60°C, it is then cooled to below 30°C with water to wash away ammonia and trace amounts of hydrogen cyanide and other impurities.

[0018] In the process of producing synthetic ammonia using hydrogen-containing tail gas as described above, preferably, in step S2, the impurity-removed tail gas enters a desulfurization unit for desulfurization treatment. The packing material in the desulfurization unit is a mixture of activated carbon desulfurizing agent and zinc oxide refined desulfurizing agent. The mixture of activated carbon desulfurizing agent and zinc oxide refined desulfurizing agent can remove sulfide impurities in the tail gas and control the sulfide content to 0.1 PPM or below. Using a mixture of activated carbon desulfurizing agent and zinc oxide refined desulfurizing agent as the desulfurizing agent in this step has the following advantages: 1. Broadening the desulfurization range: Activated carbon desulfurizing agent mainly removes organic sulfur and a small amount of hydrogen sulfide through physical adsorption, while zinc oxide refined desulfurizing agent effectively removes inorganic sulfur through chemical reaction. The combination of the two can more comprehensively remove different types of sulfides, improving desulfurization efficiency and depth. 2. Improved selectivity and efficiency: Zinc oxide desulfurizer exhibits high chemical reactivity selectivity for certain sulfides, while activated carbon desulfurizer's high specific surface area helps adsorb a wider range of sulfides. The combined use of both can improve the removal selectivity for target sulfides and the overall desulfurization efficiency. 3. Extended service life: Zinc oxide desulfurizer can handle most of the chemical reaction load, reducing the loss of activated carbon desulfurizer due to chemical reactions and protecting its physical structure, thereby extending the service life of the entire mixed desulfurizer.

[0019] In the process of producing synthetic ammonia using hydrogen-containing tail gas as described above, preferably, in step S3, the flow ratio of sodium cyanide tail gas to chlor-alkali tail gas in the mixed gas is 3.5-4:1, the pressure of the chlor-alkali tail gas is 0.01 MPa, and the temperature is room temperature. The mixed gas is heated to 120°C and then enters a deoxygenation unit for deoxygenation treatment. The packing material in the deoxygenation unit is SPH hydrogen deoxygenation catalyst. After deoxygenation treatment, the oxygen content in the deoxygenated tail gas is less than 10 ppm.

[0020] In the process of producing synthetic ammonia using hydrogen-containing tail gas as described above, preferably, in step S4, the deoxygenated tail gas is cooled to about 40°C by a cooler, and then the mixed gas is sent into a gas storage tank. The pressure of the gas storage tank is 400 mm water column and the temperature is room temperature. The mixed gas is then pressurized to 0.85-1 MPa by a hydrogen compressor and the temperature is between 20-30°C. Then it enters a PSA pressure swing adsorption device for pressure swing adsorption treatment. The dehydration adsorbent is activated alumina or silica gel, preferably activated alumina.

[0021] In the process of producing synthetic ammonia using hydrogen-containing tail gas as described above, preferably, the preparation method of the carbon dioxide adsorbent in step S4 includes the following steps:

[0022] A1: Add acid to activated carbon for acid washing, then filter, followed by washing with deionized water. After filtration and drying, pretreated activated carbon is obtained. Activated carbon usually contains a certain amount of ash. To avoid problems in later molding and use, this step involves acid washing the activated carbon with an acid solution, such as hydrochloric acid. Specifically, the activated carbon can be added to an acid solution with a concentration of 0.05-0.1M and then heated to boiling for 1-2 hours. After acid washing, the activated carbon is washed several times with deionized water to remove excess acid.

[0023] A2: A mixture of carbonate and strong alkali is added to the pretreated activated carbon. Then, under anaerobic conditions, such as a nitrogen atmosphere, the mixture is heated to 700-750℃, preferably 720℃, and held at this temperature for 1-1.5 hours, preferably 1.5 hours, to obtain modified activated carbon. The mass ratio of carbonate to strong alkali is 1:1-1:3, preferably 1:2, and the mixture of carbonate and strong alkali accounts for 15-20% of the mass of the pretreated activated carbon, preferably 18%. In this step, under the combined effects of high temperature, carbonate, and strong alkali, the pore structure inside the activated carbon is significantly increased, especially the number of micropores and ultramicropores. The specific surface area increases, the degree of graphitization improves, and a mature and robust pore structure is formed. Furthermore, the content of hydroxyl and carboxyl groups in the activated carbon decreases during the modification process, reducing acidity and making it easier to adsorb carbon dioxide. In this step, when the temperature is below 700℃, the adsorption capacity of the activated carbon for carbon dioxide and other impurity gases cannot be significantly improved. In addition, the mass ratio of carbonate to strong alkali is also a key factor determining the gas adsorption capacity of modified activated carbon. Excessive proportions of carbonate and strong alkali, or excessively high temperatures, can cause the collapse of the pore structure within the activated carbon, thus hindering its carbon dioxide adsorption capacity.

[0024] A3: Modified activated carbon is subjected to high-pressure extrusion molding to obtain a carbon dioxide adsorbent. The carbon dioxide adsorbent prepared by this invention has an adsorption capacity that is approximately 30% higher than that of Grade 1 activated carbon specified in the standard for pressure swing adsorption (PSA) hydrogen purification. Furthermore, in addition to improving the adsorption capacity for carbon dioxide, the carbon dioxide adsorbent of this invention can further enhance the adsorption capacity for carbon monoxide, methane, and nitrogen, increasing them by approximately 8%, 13%, and 9%, respectively, compared to Grade 1 activated carbon specified in the standard for PSA hydrogen purification.

[0025] In the process of producing synthetic ammonia using hydrogen-containing tail gas as described above, preferably, in step A1, the activated carbon used is coconut shell activated carbon, bamboo activated carbon, or wood activated carbon.

[0026] In step A2, the carbonate is sodium carbonate or potassium carbonate, and the strong base is sodium hydroxide or potassium hydroxide.

[0027] In the process of producing synthetic ammonia using hydrogen-containing tail gas as described above, preferably, in step S4, the methane adsorbent is 5A zeolite molecular sieve, and the carbon monoxide adsorbent is Na-LSX molecular sieve.

[0028] In the process for producing synthetic ammonia using hydrogen-containing tail gas as described above, preferably, the preparation method of the nitrogen adsorbent in step S4 includes the following steps:

[0029] B1: The 13X zeolite molecular sieve is sequentially cleaned and modified with deionized water and sodium hydroxide solution. The concentration of the sodium hydroxide solution is 0.5-1M, the modification temperature is 70-80℃, and the modification time is 1-2 hours. The 13X zeolite molecular sieve mainly contains sodium ions. In this step, the 13X zeolite molecular sieve is cleaned with deionized water to remove impurities and substances that may clog the pores, thus activating it. The 13X zeolite molecular sieve is modified with sodium hydroxide solution to adjust its pore structure, allowing for the subsequent removal of sodium ions from the zeolite molecular sieve. + With Ca 2+ and Ba 2+ Ion exchange is performed.

[0030] B2: Place the modified 13X zeolite molecular sieve into a container containing Ca. 2+ and Ba 2+ The solution is soaked for 12-24 hours, preferably 18 hours, and the process is subjected to shaking to allow the Na to... + With Ca 2+ and Ba 2+ Ion exchange is performed to allow Ca to... 2+ and Ba 2+ Replace Na + Original location; contains Ca 2+ and Ba 2+ In the solution, Ca 2+ with Ba 2+ The total concentration is 0.2-0.3M, preferably 0.25M, of which Ca 2+ and Ba 2+ The molar ratio is 1:2-2:1, preferably 1:1;

[0031] B3: Repeat step B2 2-3 times to complete Na. + With Ca 2+ and Ba 2+ Ion exchange;

[0032] B4: After ion exchange, the 13X zeolite molecular sieve is washed with deionized water and calcined. The preferred calcination temperature is 500-550℃ to restore its adsorption performance and obtain a nitrogen adsorbent. Compared to Na... +The ion-exchange modified 13X zeolite molecular sieve prepared in this invention has an adsorption capacity for nitrogen that is increased by approximately 47%.

[0033] In the process of producing synthetic ammonia using hydrogen-containing tail gas as described above, preferably, in step S5, air is used as raw material, and high-purity nitrogen gas with a purity of not less than 99.999% can be prepared by high-pressure adsorption. Then, the high-purity nitrogen gas and the high-purity hydrogen gas prepared in step S4 are mixed at a molar ratio of 1:3 and fed into a compressor and pressurized to 18 MPa. Then, it is fed into an ammonia synthesis tower, where it reacts to produce ammonia under the action of an iron catalyst. The reaction temperature can be 460-480℃.

[0034] (III) Beneficial Effects

[0035] The beneficial effects of this invention are:

[0036] This invention pressurizes, heats, and cools sodium cyanide tail gas with water to remove ammonia and hydrogen cyanide. Then, it undergoes desulfurization to remove sulfur. The sodium cyanide tail gas is then mixed with chlor-alkali tail gas, deoxygenated, and then fed into a PSA (Pressure Swing Adsorption) unit for further treatment. Various adsorbents are used to remove moisture, carbon dioxide, methane, carbon monoxide, and nitrogen. The resulting hydrogen has a purity of at least 99.99%, a sulfur content of less than 0.1 ppm, an oxygen content of less than 10 ppm, and a total concentration of carbon dioxide, methane, carbon monoxide, nitrogen, and water ≤ 5 ppm.

[0037] This invention uses activated carbon modified with carbonates and strong bases as a carbon dioxide adsorbent. Compared to the adsorption capacity of Grade I activated carbon specified in the standard for pressure swing adsorption (PSA) for hydrogen purification, the activated carbon modified with carbonates and strong bases in this invention has an adsorption capacity for carbon dioxide that is increased by approximately 30%. This invention uses activated carbon modified with Na... + with Ba 2+ and Ca 2+ Ion-exchange modified 13X zeolite molecular sieve, as a nitrogen adsorbent, compared to Na... + The nitrogen adsorbent of the present invention, based on the 13X zeolite molecular sieve, has an adsorption capacity for nitrogen that is increased by approximately 47%.

[0038] In addition, compared with existing grade A activated carbon, the carbon dioxide adsorbent of the present invention can not only improve the adsorption capacity for carbon dioxide, but also further enhance the adsorption capacity for carbon monoxide, methane and nitrogen.

[0039] Therefore, this invention can improve the adsorption capacity of the adsorbent for carbon dioxide, methane, carbon monoxide, and nitrogen, thus reducing the frequency of adsorbent replacement, extending the adsorbent's service life, and improving production efficiency. Furthermore, while improving the adsorbent's adsorption capacity for carbon dioxide, methane, carbon monoxide, and nitrogen, this invention can also reduce the amount of adsorbent used, thereby reducing the volume of the PSA pressure swing adsorption unit. Detailed Implementation

[0040] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below through specific embodiments.

[0041] Example 1

[0042] This embodiment provides a process for producing synthetic ammonia using hydrogen-containing tail gas, including the following steps:

[0043] S1: The sodium cyanide tail gas is pressurized to 0.085 MPa, then heated to 55°C, and then cooled to 25°C by water to obtain the purified tail gas.

[0044] S2: The impurity-removed tail gas enters the desulfurization unit for desulfurization treatment. The packing material in the desulfurization unit is a mixture of activated carbon desulfurizing agent and zinc oxide refined desulfurizing agent, resulting in desulfurized tail gas with a sulfide content of less than 0.1 PPM.

[0045] S3: Sodium cyanide tail gas and chlor-alkali tail gas are mixed at a flow ratio of 3.5:1. The mixed gas is then heated to 120°C and then enters the deoxygenation unit for deoxygenation treatment. The packing material in the deoxygenation unit is SPH hydrogen deoxygenation catalyst, resulting in deoxygenated tail gas with an oxygen content of less than 10ppm.

[0046] S4: The deoxygenated tail gas is cooled to 40℃ by a cooler, and then sent to a gas storage tank at a pressure of 400 mm water column and a room temperature. The mixed gas is then pressurized to 0.85 MPa and 25℃ by a hydrogen compressor, and then enters the PSA (Pressure Swing Adsorption) unit for PSA treatment. The resulting hydrogen has a purity of 99.99%, and the total concentration of carbon dioxide, methane, carbon monoxide, nitrogen, and water is ≤5 ppm. Following the airflow direction, the PSA unit sequentially contains a dehydration adsorbent, a carbon dioxide adsorbent, a methane adsorbent, a carbon monoxide adsorbent, and a nitrogen adsorbent. The dehydration adsorbent is activated alumina, the carbon dioxide adsorbent is activated carbon modified with carbonates and strong alkalis, the methane adsorbent is 5A zeolite molecular sieve, the carbon monoxide adsorbent is Na-LSX molecular sieve, and the nitrogen adsorbent is Na... + with Ba 2+ and Ca 2+ Ion-exchange modified 13X zeolite molecular sieve.

[0047] S5: Using air as raw material, high-purity nitrogen gas with a purity of 99.999% is prepared by high-pressure adsorption. Then, the high-purity nitrogen gas and the high-purity hydrogen gas prepared in step S4 are mixed in a molar ratio of 1:3 and fed into a compressor and pressurized to 18MPa. Then, it is fed into an ammonia synthesis tower and reacted to produce ammonia under the action of an iron catalyst at a reaction temperature of 460℃.

[0048] In step S4 above, the preparation method of the carbon dioxide adsorbent includes the following steps:

[0049] A1: Add coconut shell activated carbon to a 0.05M hydrochloric acid solution, then heat and boil for 2 hours, then filter, then wash with deionized water, filter and dry to obtain pretreated activated carbon.

[0050] A2: A mixture of potassium carbonate and potassium hydroxide is added to the pretreated activated carbon. The mixture is then heated to 720℃ under a nitrogen atmosphere and held at that temperature for 1.5 hours to perform modification treatment, resulting in modified activated carbon. The mass ratio of potassium carbonate to potassium hydroxide is 1.2, and the mixture of potassium carbonate and potassium hydroxide accounts for 18% of the mass of the pretreated activated carbon.

[0051] A3: Modified activated carbon is subjected to high-pressure extrusion molding to obtain a carbon dioxide adsorbent.

[0052] In step S4 above, the preparation method of the nitrogen adsorbent includes the following steps:

[0053] B1: Clean the 13X zeolite molecular sieve with deionized water, then place the 13X zeolite molecular sieve into a 0.8M sodium hydroxide solution, heat to 75℃, and treat for 1.5h.

[0054] B2: Place the modified 13X zeolite molecular sieve into a container containing Ca. 2+ and Ba 2+ The sample was immersed in a solution containing Ca for 18 hours, with continuous shaking during the immersion process. 2+ and Ba 2+ In the solution, Ca 2+ with Ba 2+ The total concentration was 0.25 M, of which Ca 2+ and Ba 2+ The molar ratio is 1:1.

[0055] B3: Repeat step B2 3 times to complete Na. + With Ca 2+ and Ba 2+ Ion exchange.

[0056] B4: The 13X zeolite molecular sieve was cleaned with deionized water and then calcined at 500℃ to obtain a nitrogen adsorbent.

[0057] After testing, the carbon dioxide adsorbent prepared in this embodiment has an adsorption capacity of 54.18 mL / g for carbon dioxide, which is 29% higher than the first-grade activated carbon index (42 mL / g) specified in the standard LY / T 1971-2011 for activated carbon used in pressure swing adsorption (PSA) hydrogen purification. The adsorption capacities for carbon monoxide, methane, and nitrogen are 7.6%, 12.3%, and 8.7% higher than those specified in the standard for activated carbon used in PSA hydrogen purification, respectively.

[0058] Compared to Na + The ion-exchange modified 13X zeolite molecular sieve prepared in this embodiment has a 46.6% higher adsorption capacity for nitrogen.

[0059] Example 2

[0060] This embodiment provides a process for producing synthetic ammonia using hydrogen-containing tail gas, including the following steps:

[0061] S1: The sodium cyanide tail gas is pressurized to 0.085 MPa, then heated to 60°C, and then cooled to 20°C by water to obtain the purified tail gas.

[0062] S2: The impurity-removed tail gas enters the desulfurization unit for desulfurization treatment. The packing material in the desulfurization unit is a mixture of activated carbon desulfurizing agent and zinc oxide refined desulfurizing agent, resulting in desulfurized tail gas with a sulfide content of less than 0.1 PPM.

[0063] S3: Sodium cyanide tail gas and chlor-alkali tail gas are mixed at a flow ratio of 4:1. The mixed gas is then heated to 120°C and then enters the deoxygenation unit for deoxygenation treatment. The packing material in the deoxygenation unit is SPH hydrogen deoxygenation catalyst, resulting in deoxygenated tail gas with an oxygen content of less than 10 ppm.

[0064] S4: The deoxygenated tail gas is cooled to 40℃ by a cooler, and then sent to a gas storage tank at a pressure of 400 mm water column and a room temperature. The mixed gas is then pressurized to 0.85 MPa and 25℃ by a hydrogen compressor, and then enters the PSA (Pressure Swing Adsorption) unit for PSA treatment. The resulting hydrogen has a purity of 99.99%, and the total concentration of carbon dioxide, methane, carbon monoxide, nitrogen, and water is ≤5 ppm. Following the airflow direction, the PSA unit sequentially contains a dehydration adsorbent, a carbon dioxide adsorbent, a methane adsorbent, a carbon monoxide adsorbent, and a nitrogen adsorbent. The dehydration adsorbent is silica gel, the carbon dioxide adsorbent is activated carbon modified with carbonates and strong alkalis, the methane adsorbent is 5A zeolite molecular sieve, the carbon monoxide adsorbent is Na-LSX molecular sieve, and the nitrogen adsorbent is Na... + with Ba 2+ and Ca 2+ Ion-exchange modified 13X zeolite molecular sieve.

[0065] S5: Using air as raw material, high-purity nitrogen gas with a purity of 99.999% is prepared by high-pressure adsorption. Then, the high-purity nitrogen gas and the high-purity hydrogen gas prepared in step S4 are mixed at a molar ratio of 1:3 and fed into a compressor and pressurized to 18MPa. Then, it is fed into an ammonia synthesis tower and reacted to produce ammonia under the action of an iron catalyst at a reaction temperature of 480℃.

[0066] In step S4 above, the preparation method of the carbon dioxide adsorbent includes the following steps:

[0067] A1: Add bamboo activated carbon to a 0.1M hydrochloric acid solution, then heat and boil for 1 hour, then filter, then wash with deionized water, filter and dry to obtain pretreated activated carbon.

[0068] A2: A mixture of potassium carbonate and potassium hydroxide is added to the pretreated activated carbon. The mixture is then heated to 700℃ under a nitrogen atmosphere and held for 1 hour to perform modification treatment, resulting in modified activated carbon. The mass ratio of potassium carbonate to potassium hydroxide is 1:1, and the mixture of potassium carbonate and potassium hydroxide accounts for 15% of the mass of the pretreated activated carbon.

[0069] A3: Modified activated carbon is subjected to high-pressure extrusion molding to obtain a carbon dioxide adsorbent.

[0070] In step S4 above, the preparation method of the nitrogen adsorbent includes the following steps:

[0071] B1: Clean the 13X zeolite molecular sieve with deionized water, then put the 13X zeolite molecular sieve into a 0.5M sodium hydroxide solution, heat it to 70℃, and treat it for 1 hour.

[0072] B2: Place the modified 13X zeolite molecular sieve into a container containing Ca. 2+ and Ba 2+ The sample was immersed in a solution containing Ca for 12 hours, with continuous shaking during the immersion process. 2+ and Ba 2+ In the solution, Ca 2+ with Ba 2+ The total concentration was 0.2 M, of which Ca 2+ and Ba 2+ The molar ratio is 1:2.

[0073] B3: Repeat step B2 twice to complete Na. + With Ca 2+ and Ba 2+ Ion exchange.

[0074] B4: The 13X zeolite molecular sieve was cleaned with deionized water and then calcined at 550℃ to obtain a nitrogen adsorbent.

[0075] After testing, the carbon dioxide adsorbent prepared in this embodiment has an adsorption capacity of 53.21 mL / g for carbon dioxide, which is 26.7% higher than the first-grade activated carbon index (42 mL / g) specified in the standard LY / T 1971-2011 for activated carbon used in pressure swing adsorption (PSA) hydrogen purification. The adsorption capacities for carbon monoxide, methane, and nitrogen are 7.2%, 12%, and 8.1% higher, respectively, than those specified in the standard for activated carbon used in PSA hydrogen purification.

[0076] Compared to Na + The ion-exchange modified 13X zeolite molecular sieve prepared in this embodiment has a 43.1% higher adsorption capacity for nitrogen.

[0077] Example 3

[0078] This embodiment provides a process for producing synthetic ammonia using hydrogen-containing tail gas, including the following steps:

[0079] S1: The sodium cyanide tail gas is pressurized to 0.085 MPa, then heated to 57°C, and then cooled to 25°C by water to obtain the impurity-removed tail gas.

[0080] S2: The impurity-removed tail gas enters the desulfurization unit for desulfurization treatment. The packing material in the desulfurization unit is a mixture of activated carbon desulfurizing agent and zinc oxide refined desulfurizing agent, resulting in desulfurized tail gas with a sulfide content of less than 0.1 PPM.

[0081] S3: Sodium cyanide tail gas and chlor-alkali tail gas are mixed at a flow ratio of 3.8:1. The mixed gas is then heated to 120°C and then enters the deoxygenation unit for deoxygenation treatment. The packing material in the deoxygenation unit is SPH hydrogen deoxygenation catalyst, resulting in deoxygenated tail gas with an oxygen content of less than 10ppm.

[0082] S4: The deoxygenated tail gas is cooled to 40℃ by a cooler, and then sent to a gas storage tank at a pressure of 400 mm water column and a room temperature. The mixed gas is then pressurized to 0.85 MPa and 25℃ by a hydrogen compressor, and then enters the PSA (Pressure Swing Adsorption) unit for PSA treatment. The resulting hydrogen has a purity of 99.99%, and the total concentration of carbon dioxide, methane, carbon monoxide, nitrogen, and water is ≤5 ppm. Following the airflow direction, the PSA unit sequentially contains a dehydration adsorbent, a carbon dioxide adsorbent, a methane adsorbent, a carbon monoxide adsorbent, and a nitrogen adsorbent. The dehydration adsorbent is activated alumina, the carbon dioxide adsorbent is activated carbon modified with carbonates and strong alkalis, the methane adsorbent is 5A zeolite molecular sieve, the carbon monoxide adsorbent is Na-LSX molecular sieve, and the nitrogen adsorbent is Na... + with Ba 2+ and Ca 2+ Ion-exchange modified 13X zeolite molecular sieve.

[0083] S5: Using air as raw material, high-purity nitrogen gas with a purity of 99.999% is prepared by high-pressure adsorption. Then, the high-purity nitrogen gas and the high-purity hydrogen gas prepared in step S4 are mixed in a molar ratio of 1:3 and fed into a compressor and pressurized to 18MPa. Then, it is fed into an ammonia synthesis tower and reacted to produce ammonia under the action of an iron catalyst at a reaction temperature of 470℃.

[0084] In step S4 above, the preparation method of the carbon dioxide adsorbent includes the following steps:

[0085] A1: Add wood-based activated carbon to a 0.08M hydrochloric acid solution, then heat and boil for 1.5 hours, then filter, wash with deionized water, filter and dry to obtain pretreated activated carbon.

[0086] A2: A mixture of potassium carbonate and potassium hydroxide is added to the pretreated activated carbon. The mixture is then heated to 750℃ under a nitrogen atmosphere and held for 1.2 hours to perform modification treatment, resulting in modified activated carbon. The mass ratio of potassium carbonate to potassium hydroxide is 1:3, and the mixture of potassium carbonate and potassium hydroxide accounts for 20% of the mass of the pretreated activated carbon.

[0087] A3: Modified activated carbon is subjected to high-pressure extrusion molding to obtain a carbon dioxide adsorbent.

[0088] In step S4 above, the preparation method of the nitrogen adsorbent includes the following steps:

[0089] B1: Clean the 13X zeolite molecular sieve with deionized water, then place the 13X zeolite molecular sieve into a 1M sodium hydroxide solution, heat to 80℃, and treat for 2 hours.

[0090] B2: Place the modified 13X zeolite molecular sieve into a container containing Ca. 2+ and Ba 2+ The sample was immersed in a solution containing Ca for 24 hours, with continuous shaking during the immersion process. 2+ and Ba 2+ In the solution, Ca 2+ with Ba 2+ The total concentration was 0.3 M, of which Ca 2+ and Ba 2+ The molar ratio is 2:1.

[0091] B3: Repeat step B2 3 times to complete Na. + With Ca 2+ and Ba 2+ Ion exchange.

[0092] B4: The 13X zeolite molecular sieve was cleaned with deionized water and then calcined at 520℃ to obtain a nitrogen adsorbent.

[0093] After testing, the carbon dioxide adsorbent prepared in this embodiment has an adsorption capacity of 54.05 mL / g for carbon dioxide, which is 28.7% higher than the first-grade activated carbon index (42 mL / g) specified in the standard LY / T 1971-2011 for activated carbon used in pressure swing adsorption (PSA) hydrogen purification. The adsorption capacities for carbon monoxide, methane, and nitrogen are 6.8%, 12.5%, and 8.3% higher than those specified in the standard for activated carbon used in PSA hydrogen purification, respectively.

[0094] Compared to Na + The ion-exchange modified 13X zeolite molecular sieve prepared in this embodiment has a 41.6% higher adsorption capacity for nitrogen.

[0095] Example 4

[0096] This embodiment provides a process for producing synthetic ammonia using hydrogen-containing tail gas. The difference from Embodiment 1 is that in step A2, the mass ratio of potassium carbonate to strong alkali is 1:2.5, and potassium carbonate and strong alkali account for 16% of the mass of pretreated activated carbon. The mixed system is heated to 710°C under a nitrogen atmosphere and kept at that temperature for 1.3 hours.

[0097] Step B2 contains Ca 2+ and Ba2+ In the solution, Ca 2+ with Ba 2+ The total concentration was 0.27 M, of which Ca 2+ and Ba 2+ The molar ratio is 1.5:1.

[0098] After testing, the carbon dioxide adsorbent prepared in this embodiment has an adsorption capacity of 51.3 mL / g for carbon dioxide. Its adsorption capacity for carbon monoxide, methane, and nitrogen is 6.9%, 12%, and 8.2% higher, respectively, than that of Grade I activated carbon specified in the standard for activated carbon used in pressure swing adsorption for hydrogen purification.

[0099] Compared to Na + The ion-exchange modified 13X zeolite molecular sieve prepared in this embodiment has a 45.7% higher adsorption capacity for nitrogen.

[0100] Example 5

[0101] This embodiment provides a process for producing synthetic ammonia using hydrogen-containing tail gas. The difference from Embodiment 1 is that in step A2, the mass ratio of potassium carbonate to strong alkali is 1:1.5, and potassium carbonate and strong alkali account for 19% of the mass of pretreated activated carbon. The mixed system is heated to 725°C under a nitrogen atmosphere and kept at that temperature for 1.1 hours.

[0102] Step B2 contains Ca 2+ and Ba 2+ In the solution, Ca 2+ with Ba 2+ The total concentration was 0.22 M, of which Ca 2+ and Ba 2+ The molar ratio is 1.7:1.

[0103] After testing, the carbon dioxide adsorbent prepared in this embodiment has an adsorption capacity of 50.9 mL / g for carbon dioxide. Its adsorption capacity for carbon monoxide, methane, and nitrogen is 6.8%, 12.5%, and 8.6% higher, respectively, than that of Grade I activated carbon specified in the standard for activated carbon used in pressure swing adsorption for hydrogen purification.

[0104] Compared to Na + The ion-exchange modified 13X zeolite molecular sieve prepared in this embodiment has a 44.7% higher adsorption capacity for nitrogen.

[0105] Comparative Example 1

[0106] This comparative example provides a process for producing synthetic ammonia using hydrogen-containing tail gas. The difference from Example 1 is that in step A2, the mixed system is heated to 650°C under a nitrogen atmosphere and held at that temperature for 0.5 hours.

[0107] Step B2 contains Ca 2+ and Ba 2+ In the solution, Ca 2+ with Ba 2+ The total concentration was 0.05 M, of which Ca 2+ and Ba 2+ The molar ratio is 5:1.

[0108] The carbon dioxide adsorbent prepared in this comparative example has an adsorption capacity of 37.8 mL / g for carbon dioxide, which is lower than the first-grade activated carbon index (42 mL / g) specified in the standard LY / T 1971-2011 for activated carbon used in pressure swing adsorption for hydrogen purification. The adsorption capacity for carbon monoxide, methane, and nitrogen is also lower than that of the first-grade activated carbon specified in the standard for activated carbon used in pressure swing adsorption for hydrogen purification.

[0109] Compared with Na, the nitrogen adsorbent prepared in this comparative example... + The adsorption capacity of the 13X zeolite molecular sieve for nitrogen was increased by 15.7%.

[0110] Comparative Example 2

[0111] This comparative example provides a process for producing synthetic ammonia using hydrogen-containing tail gas. The difference from Example 1 is that in step A2, the mixed system is heated to 800°C under a nitrogen atmosphere and held at that temperature for 2.5 hours.

[0112] The carbon dioxide adsorbent prepared in this comparative example has collapsed and cannot be used.

[0113] Comparative Example 3

[0114] This comparative example provides a process for producing synthetic ammonia using hydrogen-containing tail gas. The difference from Example 1 is that in step A2, the amount of potassium carbonate added is 0, and potassium hydroxide accounts for 15% of the mass of the pretreated activated carbon.

[0115] Step B2 contains Ca 2+ and Ba 2+ In the solution, Ca 2+ with Ba 2+ The total concentration was 0.05 M, of which Ca 2+ and Ba 2+ The molar ratio is 1:5.

[0116] The carbon dioxide adsorbent prepared in this comparative example had an adsorption capacity of 37.8 mL / g for carbon dioxide, but its adsorption capacity for carbon monoxide, methane, and nitrogen was not significantly improved.

[0117] Compared with Na, the nitrogen adsorbent prepared in this comparative example... +The adsorption capacity of the 13X zeolite molecular sieve for nitrogen was increased by 10.3%.

[0118] Comparative Example 4

[0119] This comparative example provides a process for producing synthetic ammonia using hydrogen-containing tail gas. The difference from Example 1 is that in step A2, the amount of potassium hydroxide added is 0, and potassium carbonate accounts for 15% of the mass of the pretreated activated carbon.

[0120] The carbon dioxide adsorbent prepared in this comparative example had an adsorption capacity of 35.1 mL / g for carbon dioxide, but its adsorption capacity for carbon monoxide, methane, and nitrogen was not significantly improved.

[0121] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make modifications, alterations, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A process for producing synthetic ammonia using hydrogen-containing tail gas, wherein the hydrogen-containing tail gas includes chlor-alkali tail gas and sodium cyanide tail gas, characterized in that, Includes the following steps: S1: The sodium cyanide tail gas is pressurized to a pressure of 0.085 MPa, then heated to 55-60℃, and then cooled to below 30℃ by water to obtain the impurity-removed tail gas. S2: Desulfurize the impurity removal tail gas to obtain desulfurized tail gas; S3: Mix the desulfurization tail gas with chlor-alkali tail gas at a flow ratio of 3.5-4:1, heat the mixed gas to 120°C and then enter the deoxygenation unit for deoxygenation treatment to obtain deoxygenated tail gas. The packing material in the deoxygenation unit is SPH hydrogen deoxygenation catalyst. S4: After being pressurized, the deoxygenated tail gas enters the PSA pressure swing adsorption unit for pressure swing adsorption treatment to obtain high-purity hydrogen. According to the airflow direction, the PSA pressure swing adsorption unit is sequentially equipped with dehydration adsorbent, carbon dioxide adsorbent, methane adsorbent, carbon monoxide adsorbent and nitrogen adsorbent. The carbon dioxide adsorbent is activated carbon modified with carbonate and strong alkali, and the nitrogen adsorbent is activated carbon modified with Na+. + with Ba 2+ and Ca 2+ Ion-exchange modified 13X zeolite molecular sieve; S5: Nitrogen reacts with the high-purity hydrogen obtained in step S4 to produce ammonia; In step S4, the preparation method of the carbon dioxide adsorbent includes the following steps: A1: Add acid to activated carbon, perform acid washing, then filter, then wash with deionized water, filter and dry to obtain pretreated activated carbon; A2: Add a mixture of carbonate and strong alkali to the pretreated activated carbon, then heat the mixture to 700-750℃ under anaerobic conditions and keep it at that temperature for 1-1.5h to carry out the modification treatment and obtain modified activated carbon. The mass ratio of carbonate to strong alkali is 1:1 to 1:3, and the mixture of carbonate and strong alkali accounts for 15-20% of the mass of the pretreated activated carbon. A3: Modified activated carbon is subjected to high-pressure extrusion molding to obtain a carbon dioxide adsorbent; The preparation method of nitrogen adsorbent includes the following steps: B1: The 13X zeolite molecular sieve was cleaned and modified sequentially with deionized water and sodium hydroxide solution; the concentration of sodium hydroxide solution was 0.5-1M, the temperature of modification treatment was 70-80℃, and the duration of modification treatment was 1-2h. B2: Place the modified 13X zeolite molecular sieve into a container containing Ca. 2+ and Ba 2+ Soak in the solution for 12-24 hours, and shake during the soaking process to allow Na to... + With Ca 2+ and Ba 2+ Ion exchange is performed. Contains Ca 2+ and Ba 2+ In the solution, Ca 2+ with Ba 2+ The total concentration is 0.2-0.3 M, of which Ca 2+ and Ba 2+ The molar ratio is 1:2-2:1; B3: Repeat step B2 2-3 times to complete the ion exchange; B4: After ion exchange, the 13X zeolite molecular sieve is washed with deionized water and calcined to obtain nitrogen adsorbent.

2. The process for producing synthetic ammonia from hydrogen-containing tail gas according to claim 1, characterized in that, In step S2, the exhaust gas is introduced into the desulfurization unit for desulfurization treatment. The packing material in the desulfurization unit is a mixture of activated carbon desulfurizing agent and zinc oxide desulfurizing agent.

3. The process for producing synthetic ammonia from hydrogen-containing tail gas according to claim 1, characterized in that, In step S4, the deoxygenated tail gas is pressurized to 0.85-1 MPa and then enters the PSA pressure swing adsorption device for pressure swing adsorption treatment. The dehydration adsorbent is activated alumina or silica gel.

4. The process for producing synthetic ammonia from hydrogen-containing tail gas according to claim 1, characterized in that, In step A1, the activated carbon used is coconut shell activated carbon, bamboo activated carbon, or wood activated carbon; In step A2, the carbonate is sodium carbonate or potassium carbonate, and the strong base is sodium hydroxide or potassium hydroxide.

5. The process for producing synthetic ammonia from hydrogen-containing tail gas according to claim 1, characterized in that, In step S4, the methane adsorbent is 5A zeolite molecular sieve, and the carbon monoxide adsorbent is Na-LSX molecular sieve.

6. The process for producing synthetic ammonia from hydrogen-containing tail gas according to claim 1, characterized in that, In step S5, high-purity nitrogen is prepared by high-pressure adsorption using air as raw material. Then, the high-purity nitrogen is mixed with the high-purity hydrogen prepared in step S4 at a molar ratio of 1:3 and fed into the ammonia synthesis tower, where it reacts to produce ammonia under the action of an iron catalyst.