A process for recovering ammonia from acidic wastewater to produce hydrogen

Abstract

The present invention relates to a process for recovering ammonia from acidic wastewater to produce hydrogen, and belongs to the technical field of wastewater treatment. The process of the present invention first uses the volatility of ammonia to separate ammonia from impurities such as carbon dioxide and hydrogen sulfide in wastewater through a deammonification tower, and at the same time uses a three-stage condensation technology to improve the recovery rate of ammonia; uses an ammonia crystallization tower and an ammonia refining unit to remove impurities in ammonia and improve the purity of ammonia; then, ammonia is decomposed into hydrogen and nitrogen under the action of a modified catalyst, wherein the nickel-iron layered double hydroxide prepared by a simple coprecipitation method is intercalated with citric acid to adjust the interlayer spacing, and a highly cross-linked and uniformly distributed mixed oxide is obtained after high-temperature roasting treatment, and on this basis, the precious metal ruthenium is introduced as a catalytic active center, which produces a synergistic effect with nickel, significantly improving the catalytic performance of the ammonia decomposition reaction, realizing efficient and low-cost ammonia decomposition catalyst preparation, and providing a new solution for wastewater treatment and hydrogen production.

Description

Technical Field

[0001] The invention belongs to the technical field of hydrogen production and relates to a process for recovering ammonia from acidic wastewater to produce hydrogen. Background Art

[0002] As a clean renewable energy source, hydrogen can be widely used in chemical synthesis, metal smelting, glass production, refrigeration, fuel cells, semiconductor production and other fields. Traditional hydrogen production from fossil fuels will produce a large amount of pollutants such as carbon dioxide, sulfur dioxide, and nitrogen oxides. Hydrogen production from renewable energy has the advantage of low emissions, but is constrained by cost. Ammonia molecules have a high hydrogen content and are easy to liquefy and transport. Compared with other carbon-containing raw materials, ammonia can be directly decomposed into hydrogen and nitrogen under certain conditions without carbon oxide emissions. Therefore, ammonia is expected to be a promising hydrogen carrier, providing an efficient, highly safe and eco-friendly option for large-scale hydrogen storage and utilization.

[0003] The hydrocracking, atmospheric and vacuum, catalytic cracking, coking and other processes in the oil refining industry and the coal gasification and conversion processes in the coal chemical industry will produce acidic wastewater. The main harmful components of these acidic waters are hydrogen sulfide and ammonia. Most of the sulfur, ammonia and other impurities need to be removed by steam stripping before they can be sent to the wastewater treatment unit. For acidic water with low ammonia content, single-tower low-pressure steam stripping is generally used, and the Claus sulfur recovery process is used to convert the hydrogen sulfide in the top acid gas into sulfur. There is also a process of burning acid gas to generate sulfur dioxide from hydrogen sulfide, and finally converting it into sulfur trioxide to produce sulfuric acid. In the above two methods, the ammonia in the acid gas is burned at high temperature to generate nitrogen, water and a small amount of nitrogen oxides. This process of decomposing ammonia by combustion causes a waste of ammonia resources and may also lead to excessive emissions of nitrogen oxides in the final tail gas. For acidic water with high ammonia content, a single-tower or double-tower pressurized stripping process is used to configure the extracted ammonia gas into liquid ammonia or ammonia water, which is reused for ammonia injection in upstream devices or sold as a product. However, on the one hand, the demand for ammonia injection in upstream devices is limited; on the other hand, the price of this type of ammonia water is low and the economic benefits are poor. In addition, there are reports on the co-production of ammonium bicarbonate with ammonia-containing gas, but ammonium bicarbonate is generally used as a fertilizer, and its price and market are greatly affected by the season, which affects the operating load of the device and has poor economic benefits. Therefore, it is urgent to develop a new acidic wastewater treatment process with high economic benefits, low energy consumption, energy saving and environmental protection. Summary of the invention

[0004] The object of the present invention is to provide a process for recovering ammonia from acidic wastewater to produce hydrogen, which has the characteristics of good economic benefits, low energy consumption and low hydrogen production cost.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] A process for recovering ammonia from acidic wastewater to produce hydrogen, the process is specifically as follows:

[0007] S1-1: The acid wastewater discharged from the oil refining or coal chemical plant is sent to the oil removal tank, and the floating oil is removed by using the density difference between water and oil to obtain deoiled wastewater;

[0008] S1-2: a portion of the deoiled wastewater is heat exchanged with the circulating water and then sent to the top of the deamination tower, and the remaining deoiled wastewater is heat exchanged with the deamination tower bottom liquid and then fed from the middle of the deamination tower, and the deamination tower bottom liquid is heated by a reboiler to generate rising steam, which is countercurrently contacted with the wastewater to remove carbon dioxide and hydrogen sulfide in the wastewater, and the waste gas is discharged from the top of the tower and sent to the waste gas treatment unit, and the wastewater discharged from the deamination tower bottom is sent to the wastewater treatment unit after heat exchange;

[0009] S1-3: The crude ammonia produced by the side line of the deammonification tower is condensed in three stages, and the condensate is refluxed to the deoiling tank through a reflux pump, while the uncondensed rich ammonia gas enters the ammonia crystallization tower and the ammonia refining unit in turn, and is adsorbed by the adsorbent to remove water, hydrogen sulfide and carbonyl sulfide impurities to obtain refined ammonia;

[0010] S1-4: feeding the refined ammonia into an ammonia decomposition reactor, decomposing the ammonia under the action of a modified ammonia decomposition catalyst to obtain crude hydrogen;

[0011] S1-5: The crude hydrogen is sent to the hydrogen refining unit to remove hydrogen sulfide, hydrogen cyanide and ammonia impurities through PSA pressure swing adsorption, and finally the product hydrogen is obtained.

[0012] Furthermore, the amount of wastewater coming out of the oil removal tank and entering the top of the deamination tower in S1-2 accounts for 14.5-15.5% of the total volume of the oil removal wastewater.

[0013] Furthermore, the operating pressure at the bottom of the deamination tower in S1-2 is 0.4-0.6 MPa, the top temperature is 15-40°C, and the bottom temperature is 150-165°C.

[0014] Furthermore, the crude ammonia in S1-3 is produced from the side line of the deamination tower, the ammonia concentration is controlled to be 15-35%, and the temperature of the side line production tray is controlled to be 138-144°C.

[0015] Furthermore, the conditions for the three-stage condensation in S1-3 are set as follows: the operating temperature of the first-stage condenser is 125~130°C, and the operating pressure is 0.3~0.35 MPa; the operating temperature of the second-stage condenser is 80~110°C, and the operating pressure is 0.15~0.25MPa; the operating temperature of the third-stage condenser is 15~40°C, and the operating pressure is 0.12~0.15 MPa.

[0016] Furthermore, the operating temperature of the ammonia crystallization tower in S1-3 is -5~10°C.

[0017] Furthermore, the adsorbent filled in the ammonia refining unit in S1-3 is one of activated carbon and activated alumina.

[0018] Furthermore, the operating temperature of the ammonia decomposition reactor in S1-4 is 400-450°C, and the operating pressure is normal pressure.

[0019] Furthermore, the preparation method of the modified ammonia decomposition catalyst in S1-4 is as follows:

[0020] S9-1: Nickel nitrate and ferric nitrate were mixed in a molar ratio of 3:1 and added to deionized water. The mixture was ultrasonically stirred at room temperature for 30 min to obtain solution A, in which the solid-liquid mass ratio was 1:50. A 1M NaOH solution was added dropwise to solution A at a stirring speed of 750-850 r / min until the pH value was 9-10. The mixture was stirred at room temperature for 6 h. A precipitate was obtained after rotary evaporation. The precipitate was washed with deionized water and dried in a freeze dryer for 12 h to obtain powder B.

[0021] S9-2: Powder B was added to a 2 M citric acid solution, ultrasonicated at 60 °C for 2-3 h, washed with deionized water until the pH of the eluent was 7, and dried in a vacuum oven at 60 °C for 6 h to obtain powder C;

[0022] S9-3: Powder C was placed in a muffle furnace and calcined under the protection of high-purity helium. The calcination time was 20-30 min and the calcination temperature was 400-500 °C. After calcination, the powder was ball-milled at a speed of 450 r / min and a time of 1 h to obtain powder D.

[0023] S9-4: Powder D and 3 M ruthenium trichloride aqueous solution were mixed in a mass ratio of 1: (3~4), ultrasonically stirred for 30 min, 1 wt% sodium borohydride solution was added, and stirring was continued for 1 h. After washing with deionized water, the mixture was placed in a vacuum drying oven at 100 °C for 12 h to obtain the modified ammonia decomposition catalyst.

[0024] Furthermore, the operating pressure of the hydrogen refining unit in S1-5 is 1.5~1.7 MPa.

[0025] First, the oil removal tank is used to remove oil, and the grease in the wastewater is removed by gravity sedimentation and density difference, so as to prevent the grease from clogging and polluting the subsequent equipment and improve the wastewater treatment efficiency. The deamination tower is used to remove ammonia, and the ammonia in the wastewater forms a gas-liquid equilibrium with the rising steam, and the volatility of ammonia is used for separation, and carbon dioxide and hydrogen sulfide waste gas are effectively removed. The three-stage condensation uses the phase change principle of substances at different temperatures to effectively improve the recovery rate of ammonia and reduce the loss of ammonia. The ammonia crystallization tower and the ammonia refining unit use the solubility and adsorption of different substances under specific conditions to separate, remove water, hydrogen sulfide and carbonyl sulfide impurities in ammonia, improve the purity of ammonia, and provide high-quality raw materials for subsequent ammonia decomposition. At a suitable temperature, ammonia is decomposed into hydrogen and nitrogen under the action of a catalyst, providing raw materials for subsequent hydrogen refining. The hydrogen refining unit uses the difference in the physical properties of impurities and absorbents to separate, improve the purity of hydrogen, and meet the requirements of subsequent use. In addition, through processes such as heat exchange and condensation, energy utilization efficiency is improved and production costs are reduced.

[0026] Ruthenium-based catalysts are recognized as the most efficient catalysts in ammonia decomposition reactions due to their excellent catalytic performance. However, the scarcity and high cost of ruthenium on Earth limit its widespread application, and it is urgent to prepare new ammonia decomposition catalysts to reduce the amount of ruthenium and improve its low-temperature activity. The present invention adopts a simple coprecipitation method to prepare nickel-iron layered double hydroxide (NiFe LDH) with an ordered layered structure. On this basis, by introducing citric acid and utilizing its intercalation effect, the interlayer spacing of NiFe LDH is adjusted, the types of interlayer anions are enriched, and chelates are formed with metal ions, thereby significantly improving the dispersibility of metal ions. Subsequently, high-temperature calcination treatment is used to effectively remove the interlayer anions of NiFe LDH, and a mixed oxide with high cross-linking and uniform distribution between the components is obtained. In this process, not only more oxygen vacancies and alkaline sites are generated, but also favorable conditions are provided for the introduction of active sites, which promotes nitrogen desorption and hydrogen evolution at low temperatures. In order to further improve the catalytic performance of the ammonia decomposition reaction, ruthenium is introduced as a catalytic active center in the above structure. The addition of ruthenium not only enhances the catalytic activity, but also produces a certain synergistic effect with nickel. Nickel can effectively promote the adsorption and activation of ammonia molecules, while ruthenium is mainly responsible for the catalytic decomposition process and promotes the release of hydrogen. This synergistic effect significantly improves the overall catalytic efficiency and provides a new idea for the efficient and low-cost application of ammonia decomposition catalysts.

[0027] Beneficial effects of the present invention:

[0028] (1) The process flow of the present invention can enrich and purify ammonia in acidic wastewater and then use it for hydrogen preparation, which solves the problem of poor economic benefits of ammonia recovery and utilization in acidic wastewater in existing processes. The ammonia decomposition reaction temperature carried out by the process flow and catalyst is low and the ammonia conversion efficiency is high, providing an efficient and eco-friendly option for clean hydrogen production and safe hydrogen storage. The obtained hydrogen can be directly used for hydrogen in various hydrogenation units, and can also be used as a hydrogen source for adjusting the hydrogen-to-carbon ratio of synthesis gas raw materials of methanol, ammonia and methane. The process flow has the characteristics of good economic benefits, low energy consumption and low hydrogen production cost, and provides a new way for the recovery and utilization of acidic wastewater.

[0029] (2) The present invention adopts a co-precipitation method to prepare ordered layered NiFe LDH, and adjusts the interlayer spacing and anion types through citric acid intercalation to improve the dispersion of metal ions; after high-temperature calcination, a highly cross-distributed mixed oxide is obtained, which produces more oxygen vacancies and alkaline sites; ruthenium is further introduced as a catalytic active center, and synergistically acts with nickel to significantly improve the overall catalytic efficiency. At the same time, the cost is effectively reduced compared with traditional ruthenium-based ammonia decomposition catalysts. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to facilitate understanding by those skilled in the art, the present invention is further described below with reference to the accompanying drawings.

[0031] Figure 1 The present invention is a process flow chart for recovering ammonia from acidic wastewater to produce hydrogen.

[0032] Among them, 1-oil removal tank; 2-circulating water heat exchanger; 3-deammonia tower; 4-deammonia tower bottom liquid heat exchanger; 5-three-stage condensing device; 6-ammonia crystallization tower; 7-ammonia refining unit; 8-ammonia decomposition reactor; 9-hydrogen refining unit. DETAILED DESCRIPTION

[0033] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation methods, structures, features and effects of the present invention are described in detail below in conjunction with the accompanying drawings and preferred embodiments.

[0034] Example 1

[0035] A process for recovering ammonia from acidic wastewater to produce hydrogen, the process is specifically as follows:

[0036] S1-1: The acid wastewater discharged from the oil refining or coal chemical plant is sent to the oil removal tank, and the floating oil is removed by using the density difference between water and oil to obtain deoiled wastewater;

[0037] S1-2: 15% of the deoiled wastewater by volume is heat exchanged with circulating water and sent to the top of the deamination tower. The remaining deoiled wastewater is heat exchanged with the deamination tower bottom liquid and fed from the middle of the deamination tower. The deamination tower bottom liquid is heated by a reboiler to generate rising steam, which is countercurrently contacted with the wastewater to remove carbon dioxide and hydrogen sulfide in the wastewater and then discharged from the top of the tower and sent to the waste gas treatment unit. The wastewater discharged from the deamination tower bottom is sent to the wastewater treatment unit after heat exchange. The operating pressure of the deamination tower bottom is 0.5 MPa, the tower top temperature is 25°C, and the tower bottom temperature is 160°C;

[0038] S1-3: The side line of the deamination tower produces crude ammonia gas, and the ammonia concentration is controlled to be 30%. The temperature of the side line extraction tower plate is controlled to be 141°C. The crude ammonia gas enters the condenser for three-stage condensation. The conditions of the three-stage condensation are set as follows: the operating temperature of the first condenser is 127°C, the operating pressure is 0.33 MPa, the operating temperature of the second condenser is 95°C, the operating pressure is 0.2 MPa, and the operating temperature of the third condenser is 25°C, and the operating pressure is 0.13 MPa. The condensate is refluxed to the deoiling tank through a reflux pump, and the uncondensed ammonia-rich gas enters the ammonia crystallization tower, where the operating temperature of the ammonia crystallization tower is -5°C, and then enters the ammonia refining unit to remove water, hydrogen sulfide and carbonyl sulfide impurities through activated carbon adsorption to obtain refined ammonia gas;

[0039] S1-4: feeding the refined ammonia into an ammonia decomposition reactor, decomposing the ammonia under the action of a modified ammonia decomposition catalyst, the operating temperature of the ammonia decomposition reactor is 420°C, the operating pressure is normal pressure, and obtaining crude hydrogen;

[0040] S1-5: The crude hydrogen is sent to the hydrogen refining unit for removal of hydrogen sulfide, hydrogen cyanide and ammonia impurities through PSA pressure swing adsorption. The operating pressure is 1.6 MPa, and finally the product hydrogen is obtained.

[0041] Wherein, the preparation method of the modified ammonia decomposition catalyst in S1-4 is as follows:

[0042] S9-1: Nickel nitrate and ferric nitrate were mixed in a molar ratio of 3:1 and added to deionized water. The mixture was ultrasonically stirred at room temperature for 30 min to obtain solution A. The solid-liquid mass ratio in solution A was 1:50. 1 M NaOH solution was added dropwise to solution A at a stirring speed of 800 r / min until the pH value reached 9. The mixture was stirred at room temperature for 6 h. A precipitate was obtained after rotary evaporation. The precipitate was washed with deionized water and dried in a freeze dryer for 12 h to obtain powder B.

[0043] S9-2: Powder B was added to a 2 M citric acid solution, ultrasonicated at 60 °C for 2.5 h, washed with deionized water until the pH of the eluate was 7, and dried in a vacuum oven at 60 °C for 6 h to obtain powder C;

[0044] S9-3: Powder C was placed in a muffle furnace and calcined under the protection of high-purity helium. The calcination time was 25 min and the calcination temperature was 450 °C. After calcination, the powder was ball-milled at a speed of 450 r / min and a time of 1 h to obtain powder D.

[0045] S9-4: Powder D and 3 M ruthenium trichloride aqueous solution were mixed in a mass ratio of 1:3, ultrasonically stirred for 30 min, 1 wt% sodium borohydride solution was added, stirring was continued for 1 h, and the mixture was washed with deionized water and dried in a vacuum drying oven at 100 °C for 12 h to obtain the modified ammonia decomposition catalyst.

[0046] In this embodiment, the ammonia conversion rate is 71.3%.

[0047] Comparative Example 1

[0048] A process for recovering ammonia from acidic wastewater to produce hydrogen, the process is specifically as follows:

[0049] S1-1: The acid wastewater discharged from the oil refining or coal chemical plant is sent to the oil removal tank, and the floating oil is removed by using the density difference between water and oil to obtain deoiled wastewater;

[0050] S1-2: The deoiling wastewater accounting for 14.5% by volume is heat exchanged with the circulating water and sent to the top of the deamination tower. The remaining deoiling wastewater is heat exchanged with the deamination tower bottom liquid and fed from the middle of the deamination tower. The deamination tower bottom liquid is heated by a reboiler to generate rising steam, which is countercurrently contacted with the wastewater to remove carbon dioxide and hydrogen sulfide in the wastewater and then discharged from the top of the tower and sent to the waste gas treatment unit. The wastewater discharged from the deamination tower bottom is sent to the wastewater treatment unit after heat exchange. The operating pressure of the deamination tower bottom is 0.4 MPa, the tower top temperature is 15°C, and the tower bottom temperature is 150°C;

[0051] S1-3: The side line of the deamination tower produces crude ammonia gas, and the ammonia concentration is controlled to be 15%. The temperature of the side line extraction tower plate is controlled to be 138°C. The crude ammonia gas enters the condenser for three-stage condensation. The conditions of the three-stage condensation are set as follows: the operating temperature of the first condenser is 125°C, the operating pressure is 0.35 MPa, the operating temperature of the second condenser is 80°C, the operating pressure is 0.15 MPa, and the operating temperature of the third condenser is 15°C, and the operating pressure is 0.12 MPa. The condensate is refluxed to the deoiling tank through a reflux pump, and the uncondensed ammonia-rich gas enters the ammonia crystallization tower, where the operating temperature of the ammonia crystallization tower is -5°C, and then enters the ammonia refining unit to remove water, hydrogen sulfide and carbonyl sulfide impurities through activated carbon adsorption to obtain refined ammonia gas;

[0052] S1-4: feeding the refined ammonia into an ammonia decomposition reactor, decomposing the ammonia under the action of a modified ammonia decomposition catalyst, the operating temperature of the ammonia decomposition reactor is 400°C, the operating pressure is normal pressure, and obtaining crude hydrogen;

[0053] S1-5: The crude hydrogen is sent to the hydrogen refining unit for removal of hydrogen sulfide, hydrogen cyanide and ammonia impurities through PSA pressure swing adsorption. The operating pressure is 1.5 MPa, and finally the product hydrogen is obtained.

[0054] Wherein, the preparation method of the modified ammonia decomposition catalyst in S1-4 is as follows:

[0055] S9-1: Nickel nitrate and ferric nitrate were mixed in a molar ratio of 3:1 and added to deionized water. The mixture was ultrasonically stirred at room temperature for 30 min to obtain solution A, in which the solid-liquid mass ratio was 1:50. 1 M NaOH solution was added dropwise to solution A at a stirring speed of 750 r / min until the pH value reached 9. The mixture was stirred at room temperature for 6 h. A precipitate was obtained after rotary evaporation. The precipitate was washed with deionized water and dried in a freeze dryer for 12 h to obtain powder B.

[0056] S9-2: Powder B was placed in a muffle furnace and calcined under the protection of high-purity helium. The calcination time was 20-30 min and the calcination temperature was 450 °C. After calcination, the powder was ball-milled at a speed of 450 r / min and a time of 1 h to obtain powder C.

[0057] S9-3: Powder C and 3 M ruthenium trichloride aqueous solution were mixed in a mass ratio of 1:3, ultrasonically stirred for 30 min, 1 wt% sodium borohydride solution was added, stirring was continued for 1 h, and the mixture was washed with deionized water and dried in a vacuum drying oven at 100 °C for 12 h to obtain the modified ammonia decomposition catalyst.

[0058] The ammonia conversion rate in this comparative example was 64.5%.

[0059] Comparative Example 2

[0060] A process for recovering ammonia from acidic wastewater to produce hydrogen, the process is specifically as follows:

[0061] S1-1: The acid wastewater discharged from the oil refining or coal chemical plant is sent to the oil removal tank, and the floating oil is removed by using the density difference between water and oil to obtain deoiled wastewater;

[0062] S1-2: 15.5% of the deoiled wastewater by volume is heat exchanged with circulating water and sent to the top of the deamination tower. The remaining deoiled wastewater is heat exchanged with the deamination tower bottom liquid and fed from the middle of the deamination tower. The deamination tower bottom liquid is heated by a reboiler to generate rising steam, which is countercurrently contacted with the wastewater to remove carbon dioxide and hydrogen sulfide in the wastewater and then discharged from the top of the tower and sent to the waste gas treatment unit. The wastewater discharged from the deamination tower bottom is sent to the wastewater treatment unit after heat exchange. The operating pressure of the deamination tower bottom is 0.6 MPa, the tower top temperature is 40°C, and the tower bottom temperature is 165°C.

[0063] S1-3: The side line of the deamination tower produces crude ammonia gas, and the ammonia concentration is controlled to be 30%. The temperature of the side line extraction tower plate is controlled to be 140 ℃. The crude ammonia gas enters the condenser for three-stage condensation. The conditions of the three-stage condensation are set as follows: the operating temperature of the first condenser is 130 ℃, the operating pressure is 0.35 MPa, the operating temperature of the second condenser is 110 ℃, the operating pressure is 0.25 MPa, and the operating temperature of the third condenser is 40 ℃, and the operating pressure is 0.15 MPa. The condensate is refluxed to the deoiling tank through the reflux pump, and the uncondensed ammonia-rich gas enters the ammonia crystallization tower, where the operating temperature of the ammonia crystallization tower is 10 ℃, and then enters the ammonia refining unit to remove water, hydrogen sulfide and carbonyl sulfide impurities through activated carbon adsorption to obtain refined ammonia gas;

[0064] S1-4: feeding the refined ammonia into an ammonia decomposition reactor, decomposing the ammonia under the action of a modified ammonia decomposition catalyst, the operating temperature of the ammonia decomposition reactor is 450°C, the operating pressure is normal pressure, and obtaining crude hydrogen;

[0065] S1-5: The crude hydrogen is sent to the hydrogen refining unit for removal of hydrogen sulfide, hydrogen cyanide and ammonia impurities through PSA pressure swing adsorption. The operating pressure is 1.7 MPa, and finally the product hydrogen is obtained.

[0066] Wherein, the preparation method of the modified ammonia decomposition catalyst in S1-4 is as follows:

[0067] S9-1: Nickel nitrate and iron nitrate were mixed in a molar ratio of 3:1 and added to deionized water. The mixture was ultrasonically stirred at room temperature for 30 min to obtain solution A. The solid-liquid mass ratio in solution A was 1:50. 1 M NaOH solution was added dropwise to solution A at a stirring speed of 850 r / min until the pH value reached 10. The mixture was stirred at room temperature for 6 h. A precipitate was obtained after rotary evaporation. The precipitate was washed with deionized water and dried in a freeze dryer for 12 h to obtain powder B.

[0068] S9-2: Powder B was added to a 2 M citric acid solution, ultrasonicated at 60 °C for 3 h, washed with deionized water until the pH of the eluate was 7, and dried in a vacuum oven at 60 °C for 6 h to obtain powder C;

[0069] S9-3: Powder C and 3 M ruthenium trichloride aqueous solution were mixed in a mass ratio of 1:4, ultrasonically stirred for 30 min, 1 wt% sodium borohydride solution was added, and stirring was continued for 1 h. After washing with deionized water, the mixture was placed in a vacuum drying oven at 100 °C for 12 h to obtain the modified ammonia decomposition catalyst.

[0070] The ammonia conversion rate in this comparative example was 66.3%.

[0071] Comparative Example 3

[0072] A process for recovering ammonia from acidic wastewater to produce hydrogen, the process is specifically as follows:

[0073] S1-1: The acid wastewater discharged from the oil refining or coal chemical plant is sent to the oil removal tank, and the floating oil is removed by using the density difference between water and oil to obtain deoiled wastewater;

[0074] S1-2: 14.5% of the deoiled wastewater by volume is heat exchanged with circulating water and sent to the top of the deamination tower. The remaining deoiled wastewater is heat exchanged with the deamination tower bottom liquid and fed from the middle of the deamination tower. The deamination tower bottom liquid is heated by a reboiler to generate rising steam, which is countercurrently contacted with the wastewater to remove carbon dioxide and hydrogen sulfide in the wastewater and then discharged from the top of the tower and sent to the waste gas treatment unit. The wastewater discharged from the deamination tower bottom is sent to the wastewater treatment unit after heat exchange. The operating pressure of the deamination tower bottom is 0.5 MPa, the tower top temperature is 25°C, and the tower bottom temperature is 160°C;

[0075] S1-3: The side line of the deamination tower produces crude ammonia gas, and the ammonia concentration is controlled to be 35%. The temperature of the side line extraction tower plate is controlled to be 144 ℃. The crude ammonia gas enters the condenser for three-stage condensation. The conditions of the three-stage condensation are set as follows: the operating temperature of the first condenser is 127 ℃, the operating pressure is 0.32 MPa, the operating temperature of the second condenser is 90 ℃, the operating pressure is 0.2 MPa, and the operating temperature of the third condenser is 20 ℃, and the operating pressure is 0.15 MPa. The condensate is refluxed to the deoiling tank through the reflux pump, and the uncondensed ammonia-rich gas enters the ammonia crystallization tower, where the operating temperature of the ammonia crystallization tower is -5 ℃, and then enters the ammonia refining unit to remove water, hydrogen sulfide and carbonyl sulfide impurities through activated carbon adsorption to obtain refined ammonia gas;

[0076] S1-4: feeding the refined ammonia into an ammonia decomposition reactor, decomposing the ammonia under the action of a modified ammonia decomposition catalyst, the operating temperature of the ammonia decomposition reactor is 450°C, the operating pressure is normal pressure, and obtaining crude hydrogen;

[0077] S1-5: The crude hydrogen is sent to the hydrogen refining unit for removal of hydrogen sulfide, hydrogen cyanide and ammonia impurities through PSA pressure swing adsorption. The operating pressure is 1.6 MPa, and finally the product hydrogen is obtained.

[0078] Wherein, the preparation method of the modified ammonia decomposition catalyst in S1-4 is as follows:

[0079] S9-1: Nickel nitrate and ferric nitrate were mixed in a molar ratio of 3:1 and added to deionized water. The mixture was ultrasonically stirred at room temperature for 30 min to obtain solution A, in which the solid-liquid mass ratio was 1:50. 1 M NaOH solution was added dropwise to solution A at a stirring speed of 750 r / min until the pH value reached 9. The mixture was stirred at room temperature for 6 h. A precipitate was obtained after rotary evaporation. The precipitate was washed with deionized water and dried in a freeze dryer for 12 h to obtain powder B.

[0080] S9-2: Powder B was added to a 2 M citric acid solution, ultrasonicated at 60 °C for 2.5 h, washed with deionized water until the pH of the eluate was 7, and dried in a vacuum oven at 60 °C for 6 h to obtain powder C;

[0081] S9-3: Powder C is placed in a muffle furnace and calcined under the protection of high-purity helium. The calcination time is 25 minutes and the calcination temperature is 450°C. After calcination, the powder is ball-milled at a speed of 450 r / min and a time of 1 hour to obtain the modified ammonia decomposition catalyst.

[0082] The ammonia conversion rate in this comparative example was 29.1%.

[0083] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A process for recovering ammonia from acidic wastewater to produce hydrogen, characterized in that: The process flow is as follows: S1-1: The acid wastewater discharged from the oil refining or coal chemical plant is sent to the oil removal tank, and the floating oil is removed by using the density difference between water and oil to obtain deoiled wastewater; S1-2: a portion of the deoiled wastewater is heat exchanged with the circulating water and then sent to the top of the deamination tower, and the remaining deoiled wastewater is heat exchanged with the deamination tower bottom liquid and then fed from the middle of the deamination tower, and the deamination tower bottom liquid is heated by a reboiler to generate rising steam, which is countercurrently contacted with the wastewater to remove carbon dioxide and hydrogen sulfide in the wastewater, and the waste gas is discharged from the top of the tower and sent to the waste gas treatment unit, and the wastewater discharged from the deamination tower bottom is sent to the wastewater treatment unit after heat exchange; S1-3: The crude ammonia produced by the side line of the deammonification tower is condensed in three stages, and the condensate is refluxed to the deoiling tank through a reflux pump, while the uncondensed rich ammonia gas enters the ammonia crystallization tower and the ammonia refining unit in turn, and is adsorbed by the adsorbent to remove water, hydrogen sulfide and carbonyl sulfide impurities to obtain refined ammonia; S1-4: feeding the refined ammonia into an ammonia decomposition reactor, decomposing the ammonia under the action of a modified ammonia decomposition catalyst to obtain crude hydrogen; Wherein, the preparation method of the modified ammonia decomposition catalyst is as follows: S9-1: Nickel nitrate and ferric nitrate were mixed in a molar ratio of 3:1 and added to deionized water. The mixture was ultrasonically stirred at room temperature for 30 min to obtain solution A. The solid-liquid mass ratio in solution A was 1:

50. 1 M NaOH solution was added dropwise to solution A at a stirring speed of 750-850 r / min until the pH value was 9-10. The mixture was stirred at room temperature for 6 h. A precipitate was obtained after rotary evaporation. The precipitate was washed with deionized water and dried in a freeze dryer for 12 h to obtain powder B. S9-2: Powder B was added to a 2 M citric acid solution, ultrasonicated at 60 °C for 2-3 h, washed with deionized water until the pH of the eluent was 7, and dried in a vacuum oven at 60 °C for 6 h to obtain powder C; S9-3: Powder C was placed in a muffle furnace and calcined under the protection of high-purity helium. The calcination time was 20-30 min and the calcination temperature was 400-500 °C. After calcination, the powder was ball-milled at a speed of 450 r / min and a time of 1 h to obtain powder D. S9-4: Powder D and 3 M ruthenium trichloride aqueous solution were mixed in a mass ratio of 1: (3-4), ultrasonically stirred for 30 min, 1 wt% sodium borohydride solution was added, stirring was continued for 1 h, and the mixture was washed with deionized water and dried in a vacuum drying oven at 100 °C for 12 h to obtain the modified ammonia decomposition catalyst; S1-5: The crude hydrogen is sent to the hydrogen refining unit to remove hydrogen sulfide, hydrogen cyanide and ammonia impurities through PSA pressure swing adsorption, and finally the product hydrogen is obtained.

2. The process for recovering ammonia from acidic wastewater to produce hydrogen according to claim 1, characterized in that: The amount of wastewater coming out of the oil removal tank and entering the top of the deamination tower in S1-2 accounts for 14.5-15.5% of the total volume of the oil removal wastewater.

3. The process for recovering ammonia from acidic wastewater to produce hydrogen according to claim 1, characterized in that: The operating pressure at the bottom of the deamination tower in S1-2 is 0.4-0.6 MPa, the top temperature is 15-40°C, and the bottom temperature is 150-165°C.

4. The process for recovering ammonia from acidic wastewater to produce hydrogen according to claim 1, characterized in that: The crude ammonia in S1-3 is produced from the side line of the deamination tower, the ammonia concentration is controlled to be 15-35%, and the temperature of the side line production tower tray is controlled to be 138-144°C.

5. The process for recovering ammonia from acidic wastewater to produce hydrogen according to claim 1, characterized in that: The conditions for the three-stage condensation in S1-3 are set as follows: the operating temperature of the first-stage condenser is 125-130°C and the operating pressure is 0.3-0.35MPa; The operating temperature of the secondary condenser is 80~110 ℃, and the operating pressure is 0.15~0.25 MPa; the operating temperature of the tertiary condenser is 15~40℃, and the operating pressure is 0.12~0.15 MPa.

6. The process for recovering ammonia from acidic wastewater to produce hydrogen according to claim 1, characterized in that: The operating temperature of the ammonia crystallization tower in S1-3 is -5~10°C.

7. The process for recovering ammonia from acidic wastewater to produce hydrogen according to claim 1, characterized in that: The adsorbent filled in the ammonia refining unit in S1-3 is one of activated carbon and activated alumina.

8. The process for recovering ammonia from acidic wastewater to produce hydrogen according to claim 1, characterized in that: The operating temperature of the ammonia decomposition reactor in S1-4 is 400-450°C, and the operating pressure is normal pressure.

9. The process for recovering ammonia from acidic wastewater to produce hydrogen according to claim 1, characterized in that: The operating pressure of the hydrogen refining unit in S1-5 is 1.5~1.7 MPa.

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