CN106964247B

CN106964247B - Process for treating ammonia-containing gas stream in acrylonitrile plant

Info

Publication number: CN106964247B
Application number: CN201710273130.6A
Authority: CN
Inventors: 郭宗英; 吴粮华; 陈航宁; 郑育元; 姜家乐
Original assignee: China Petroleum and Chemical Corp; Sinopec Shanghai Research Institute of Petrochemical Technology
Current assignee: China Petroleum and Chemical Corp; Sinopec Shanghai Research Institute of Petrochemical Technology
Priority date: 2017-04-24
Filing date: 2017-04-24
Publication date: 2020-10-30
Anticipated expiration: 2037-04-24
Also published as: CN106964247A

Abstract

A process for treating ammonia-containing gas flow in an acrylonitrile device comprises the steps of enabling high-ammonia product gas flow coming out of an ammonia oxidation reactor to be in contact with low-COD ammonium-poor absorption liquid in a quenching tower to absorb unreacted ammonia in the high-ammonia product gas flow to obtain ammonium-rich absorption liquid and low-ammonia product gas flow; stripping the ammonium-rich absorption liquid in a stripping tower by stripping tower stripping gas to remove volatile organic components, separating and removing light components floating on the upper layer and heavy components sinking on the lower layer in a separating device, heating in an analytical tower and stripping the stripping gas in the analytical tower to obtain crude ammonia gas flow and high-COD lean ammonium absorption liquid, and carrying out wet oxidation reaction on the high-COD lean ammonium absorption liquid and a first oxidant in a wet oxidation reactor to obtain low-COD lean ammonium absorption liquid which is returned to a quenching tower for absorbing unreacted ammonia; the crude ammonia gas flow and the oxidant are rectified to obtain anhydrous ammonia material flow after organic matters are removed in the catalytic wet oxidation reactor.

Description

Process for treating ammonia-containing gas stream in acrylonitrile plant

Technical Field

The invention relates to a process for treating ammonia-containing gas flow in an acrylonitrile device.

Background

About 10% of the unreacted ammonia needs to be absorbed and separated from the reaction stream in the acrylonitrile production process. Although the technology can reduce the content of ammonia at the outlet of the reactor, a large amount of unreacted ammonia still exists. The prior production process mainly absorbs unreacted ammonia by sulfuric acid washing, ammonium sulfate wastewater is directly injected into a deep well for treatment, or ammonium sulfate is recovered by an ammonium sulfate recovery working section to crystallize ammonium sulfate, or ammonium sulfate is burned to prepare SO₃Then the sulfuric acid is prepared by absorption and is recycled by the system. Also in part by phosphoric acid, monoammonium phosphate or diThe mixture is neutralized to recover the unreacted ammonia.

Patent CN1204620A discloses a process for recovering unreacted ammonia from the reactor effluent obtained from a reaction zone for the production of an alkenenitrile or methacrylonitrile by quenching the reactor effluent with an aqueous solution of ammonium phosphate and heating the quench liquid to an elevated temperature to produce an ammonia-containing vapor stream which is recycled to the fluidized reactor. Wherein the ratio of ammonium ions to phosphate ions in the solution is from about 0.7 to 1.3, preferably from 1.0 to 1.2. In order to remove the waste organic substances in the absorption liquid, a wet oxidation unit is added in the method, and the wet oxidation reaction is carried out at the temperature of about 200-650 ℃ and the pressure of 600-3000 psi.

Patent CN101027252A discloses an improved process for recovering and recycling ammonia from a steam stream, which process comprises quenching the reactor effluent with an aqueous solution of ammonium phosphate in at least two stages, thereby capturing the ammonia component of the effluent. The ammonia captured annually can be recovered by heating the aqueous ammonium phosphate solution, which is then recycled. The contaminants contained in the aqueous ammonium phosphate solution can be reduced by wet oxidation before recycling.

In the process of recycling and recycling ammonia, a part of organic matters are inevitably mixed in the steam flow of the ammonia, so that the subsequent recycling and utilization of the ammonia are adversely affected, and the problem can be effectively solved.

Disclosure of Invention

The invention aims to solve the technical problem that organic matters in ammonia-containing steam flow in a process of recovering unreacted ammonia by an ammonium sulfate-free process in an acrylonitrile reaction device in the prior art are unfavorable for the recovery and utilization of subsequent ammonia, and provides a process for treating the ammonia-containing steam flow in the acrylonitrile device. The wet oxidation catalyst in the method is used for treating organic matters contained in ammonia-containing gas flow in the acrylonitrile device by heterogeneous catalytic wet oxidation reaction, and has the advantage of high COD removal efficiency.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows:

a process for treating an ammonia-containing gas stream in an acrylonitrile plant comprising:

enabling a high-ammonia product gas flow (6) from the ammonia oxidation reactor to contact with a low-COD lean ammonium absorption liquid (17) in a quenching tower (1) to absorb unreacted ammonia in the high-ammonia product gas flow to obtain an ammonium-rich absorption liquid (8) and a low-ammonia product gas flow (7); stripping the ammonium-rich absorption liquid (8) in a stripping tower (2) by stripping tower stripping gas (9) to remove volatile organic components (10), separating and removing light components (11) floating on the upper layer and heavy components (12) sinking on the lower layer in a separation device (3), then heating and stripping in a stripping tower (4) by stripping tower stripping gas (13) to obtain a crude ammonia gas stream (15) and a high-COD lean ammonium absorption liquid (14), carrying out wet oxidation reaction on the high-COD lean ammonium absorption liquid (14) and a first oxidant (16) in a wet oxidation reactor (5) to obtain a low-COD lean ammonium absorption liquid (17), and returning the low-COD lean ammonium absorption liquid (17) to a quenching tower (1) for absorbing unreacted ammonia; the crude ammonia stream (15) and a second oxidant (19) are rectified to obtain an anhydrous ammonia stream after organic matters are removed in a catalytic wet oxidation reactor (18).

In the above technical solution, the high COD lean ammonium absorption liquid and/or the low COD lean ammonium absorption liquid contains at least one absorbent preferably selected from phosphoric acid or ammonium dihydrogen phosphate.

In the above technical solution, the first oxidant (16) and the second oxidant (19) are preferably gases containing oxygen molecules independently.

In the technical scheme, the first oxidant (16) and the second oxidant (19) are independently and preferably pure oxygen, air or oxygen-enriched air.

In the technical scheme, the reaction temperature in the catalytic wet oxidation reactor (18) is preferably 180-300 ℃.

In the technical scheme, the reaction pressure in the catalytic wet oxidation reactor (18) is preferably 3.0-12.0 MPa.

In the technical scheme, the volume ratio of the second oxidant (19) to the crude ammonia gas flow (15) after condensation is preferably 50-400.

In the technical scheme, the residence time of the crude ammonia gas flow (15) in the wet oxidation reactor (18) is preferably 10-90 minutes.

In the above technical solution, the COD of the crude ammonia gas stream (15) after condensation is not particularly limited, for example, but not limited to, 500 to 100000 mg/L.

In the above solutions, the stripping column stripping gas (9) and/or the stripper stripping gas (13) are those gases which are inert towards the stripping material, as is known to the person skilled in the art.

In the above technical solution, the gas inert to the stripping material is, for example, but not limited to, at least one of water vapor, air and nitrogen.

In the above technical solutions, those skilled in the art know that the high COD lean ammonium absorption liquid (14) and the low COD lean ammonium absorption liquid (17) use water as solvent.

In the above technical scheme, the temperature of the desorption tower is preferably 150-.

In the above embodiment, the heavy component (12) is preferably a high polymer and/or an ammoxidation catalyst powder.

In the above technical solution, the wet oxidation catalyst used in the catalytic wet oxidation reactor (18) comprises the following components: (1) 90-99.5 parts of a catalyst carrier; (2)0.1 to 5 parts of at least one noble metal selected from platinum group.

In the technical scheme, the catalyst preferably further comprises (3) 0.1-5 parts of indium, and the noble metal and the indium have a synergistic effect in removing COD in the wastewater.

One of the technical keys of the present invention is the wet oxidation catalyst used in the catalytic wet oxidation reactor (18), and the wet oxidation catalyst may not be used in the wet oxidation reactor (5), or those commonly used in the art may be used, and those skilled in the art can reasonably select and reasonably determine the process conditions.

In the above technical solution, the wet oxidation catalyst used in the catalytic wet oxidation reactor (18) may be used in the wet oxidation reactor (5), and the process conditions of the catalytic wet oxidation reactor (18) may be selected.

In the above technical solution, the wet oxidation heterogeneous catalyst carrier is selected from TiO₂、ZrO₂、SiO₂And Al₂O₃One kind of (1).

The inventors have found that when TiO is used₂Supported catalystsWith Al₂O₃When the supported catalysts are mixed to obtain the mixed catalyst, the two catalysts have synergistic effect on reducing COD of wastewater in the mixed catalyst.

In the above technical solution, the noble metal is selected from at least one of Ru, Pd, Pt, Ir, and Rh.

To solve the second technical problem, the technical solution of the present invention is as follows:

the method for preparing the catalyst according to any one of the above technical problems, comprising:

1) mixing a compound solution containing a noble metal element with a carrier;

2) reducing the combined-state noble metal introduced in the step 1) into a simple substance.

In the above technical solution, when the catalyst contains indium, the preparation method further may include:

(1) mixing a mixed aqueous solution containing a noble metal and a compound and an indium-containing compound with a carrier;

(2) reducing the noble metal and the indium in the combined state into simple substances.

In the above technical solution, the most preferred preparation method comprises:

(i) mixing an aqueous solution containing a noble metal and a compound with a carrier;

(ii) reducing the combined noble metal introduced in the step (I) into a simple substance to obtain a catalyst precursor I;

(iii) mixing a mixed aqueous solution of an indium-containing compound with a catalyst precursor I;

(iv) (iv) reducing the combined indium introduced in step (iii) to elemental indium.

When the catalyst is prepared by a procedure of impregnating noble metal and reducing the noble metal, and then impregnating indium and reducing the noble metal, the catalyst has a surprisingly good technical effect on removing COD.

In the above technical scheme, the specific method of reduction is not particularly limited as long as the active component in a combined state can be reduced to a simple substance. For example, the precursor may be reduced in the gas phase with a gaseous reducing agent, or may be reduced in the liquid phase with a solution of a reducing agent or a liquid phase reducing agent. Gaseous reducing agents commonly used may include hydrogen gas, such as hydrogen gas, hydrogen-nitrogen mixtures, and the like. The reducing agent for liquid phase reduction may be hydrazine hydrate, formic acid or sodium formate, etc.

In the above technical scheme, the compound of the active component is not particularly limited, such as but not limited to ruthenium trichloride, palladium chloride, chloropalladic acid, chloroplatinic acid, rhodium chloride, indium nitrate, and the like.

In the above technical scheme, when the gas containing hydrogen is used for gas phase reduction by using the gas containing hydrogen as the gaseous reducing agent, the catalyst precursor is preferably dried first, or may further comprise roasting, the roasting temperature is preferably 400-600 ℃, and the roasting time is preferably 2-4.5 hours.

It is known to those skilled in the art that when hydrogen is used as the reducing agent for reduction, a hydrogen-nitrogen mixture having a hydrogen content of 5% by volume or less is preferred for safety.

In the technical scheme, when hydrogen is used for reduction, the reduction temperature is preferably 300-700 ℃, and is further preferably 350-600 ℃; the reduction time is preferably 1 to 5 hours, and more preferably 2.5 to 4.5 hours.

It is known to those skilled in the art that wet oxidation catalysts are particularly effective on certain process-specific wastewaters, and have very high specificity. In the technical scheme, the wet oxidation catalyst is particularly suitable for being applied to wet oxidation treatment of ammonia-containing organic wastewater in an acrylonitrile production process.

In the presence of the catalyst in any one of the technical schemes, the wastewater and the oxidant containing oxygen react in a reactor to remove reducing substances in the wastewater. The reactor is preferably a fixed bed reactor.

By adopting the technical scheme, the result shows that the A-04 catalyst containing platinum and indium prepared by the method can effectively reduce the organic matter content of high-concentration organic wastewater under the conditions of reaction temperature of 250 ℃, pressure of 6.5MPa and retention time of 20 minutes, and the COD value of the ammonia-containing organic wastewater is reduced to 23mg/L from 63,500mg/L of raw water after wet oxidation treatment, so that better technical effect is achieved.

The invention is further illustrated by the following description of the figures and examples, which however do not in any way limit the scope of the invention.

Drawings

FIG. 1 is a process flow diagram of the application of the wet oxidation catalyst of the present invention in the wet oxidation treatment of ammonia-containing organic wastewater in the production process of acrylonitrile.

1 is a quench tower; 2 is a stripping tower; 3 is a separation device; 4 is a resolving tower; 5 is a wet oxidation reactor; 6 is high ammonia product gas flow; 7 is a low ammonia product gas stream; 8 is rich ammonium absorption liquid; 9 is stripping gas of a stripping tower; 10 is a volatile organic component; 11 is a light component; 12 is a heavy component; 13 is stripping gas of the desorption tower; 14 is high COD lean ammonium absorption liquid; 15 is a crude ammonia stream; 16 is a first oxidant; 17 low COD lean ammonium absorption liquid; 18 is a catalytic wet oxidation reactor; 19 is a second oxidizing agent.

The wet oxidation catalyst absorbs unreacted ammonia in the high ammonia product gas flow by contacting the high ammonia product gas flow 6 from the ammonia oxidation reactor with high COD lean ammonium absorption liquid 14 in a quenching tower 1 to obtain ammonium-rich absorption liquid 8 and low ammonia product gas flow 7; stripping the ammonium-rich absorption liquid 8 in a stripping tower 2 by stripping tower stripping gas 9 to remove volatile organic components 10, separating and removing light components 11 floating on the upper layer and heavy components 12 sinking on the lower layer in a separation device 3, then heating and stripping the stripping gas 13 in a desorption tower 4 to obtain a crude ammonia gas stream 15 and an ammonium-poor absorption liquid 14, and carrying out wet oxidation reaction on the ammonium-poor absorption liquid 14 and an oxygen-containing gas 16 in a wet oxidation reactor 5 filled with a wet oxidation catalyst to obtain a low-COD ammonium-poor absorption liquid 17 which is returned to a quenching tower 1 for absorbing unreacted ammonia; the crude ammonia stream 15 and the second oxidant 19 are rectified to obtain an anhydrous ammonia stream after organic matter is removed in the catalytic wet oxidation reactor 18.

The anhydrous ammonia stream may be returned to the acrylonitrile synthesis reactor (not shown).

Detailed Description

[ example 1 ]

1. Catalyst preparation

In weight ratio, ZrO₂Ru and In is 97:2:1 to prepare the catalyst A-01.

97 parts of ZrO₂The catalyst support was impregnated with RuCl equivalent to 2 parts Ru at room temperature₃And 1 part In (NO)₃)₃The solution is kept overnight in water, dried at 80 ℃ and reduced for 4 hours at 300 ℃ in a hydrogen atmosphere (hydrogen-nitrogen mixed gas with 4 percent of hydrogen content), thus obtaining the catalyst A-01. The catalyst formulation is shown in table 1.

2. Catalyst evaluation

The condensate of ammonia-containing material flow of an acrylonitrile device is used as a raw material, and the COD value of the waste water is 54,500 mg/L. The wastewater was mixed with oxygen and passed through a 125mL fixed bed reactor packed with 120g A-01 catalyst. The reaction temperature in the reactor was 250 ℃, the pressure 6.5MPa, and the residence time 20 minutes. The reaction results are shown in Table 2.

[ example 2 ]

1. Catalyst preparation

In weight ratio, ZrO₂Pd and In is 97:2:1 to prepare the catalyst A-02.

97 parts of ZrO₂The catalyst support was impregnated with PdCl equivalent to 2 parts of Pd at room temperature₂And 1 part In (NO)₃)₃The catalyst A-02 was obtained by allowing the reaction mixture to stand overnight in an aqueous solution, drying the reaction mixture at 80 ℃ and then reducing the reaction mixture for 4 hours in a hydrogen atmosphere (hydrogen-nitrogen mixed gas having a hydrogen content of 4%) at 300 ℃. The catalyst formulation is shown in table 1.

2. Catalyst evaluation

The condensate of ammonia-containing material flow of an acrylonitrile device is used as a raw material, and the COD value of the waste water is 54,500 mg/L. The wastewater was mixed with oxygen and passed through a 125mL fixed bed reactor packed with 120g A-02 catalyst. The reaction temperature in the reactor was 250 ℃, the pressure 6.5MPa, and the residence time 20 minutes. The reaction results are shown in Table 2.

[ example 3 ]

1. Catalyst preparation

In weight ratio, ZrO₂Pt and In is 97:2:1, and catalyst A-03 is prepared.

97 parts of ZrO₂The catalyst carrier was impregnated with H equivalent to 2 parts of Pt at room temperature₂PtCl₆And 1 part In (NO)₃)₃The catalyst A-03 is obtained by reducing the catalyst A-03 in a hydrogen atmosphere (hydrogen-nitrogen mixed gas with 4% hydrogen content) at 300 ℃ for 4 hours after the catalyst A is dried at 80 ℃. The catalyst formulation is shown in table 1.

2. Catalyst evaluation

The condensate of ammonia-containing material flow of an acrylonitrile device is used as a raw material, and the COD value of the waste water is 54,500 mg/L. The wastewater was mixed with oxygen and passed through a 125mL fixed bed reactor packed with 120g A-03 catalyst. The reaction temperature in the reactor was 250 ℃, the pressure 6.5MPa, and the residence time 20 minutes. The reaction results are shown in Table 2.

[ example 4 ]

1. Catalyst preparation

In weight ratio, ZrO₂Pt and In is 97:2:1, and catalyst A-04 is prepared.

97 parts of ZrO₂The catalyst carrier was impregnated with H equivalent to 2 parts of Pt at room temperature₂PtCl₆The solution is kept overnight in the water solution, dried at 80 ℃ and reduced for 4 hours in a hydrogen atmosphere (hydrogen and nitrogen mixed gas with 4 percent of hydrogen content) at 300 ℃ to obtain a catalyst precursor B-04. B-04 was immersed In an amount of In (NO) corresponding to 1 part of In₃)₃The solution is kept overnight in water, dried at 80 ℃ and reduced for 4 hours at 300 ℃ in a hydrogen atmosphere (hydrogen-nitrogen mixed gas with 4 percent of hydrogen content), thus obtaining the catalyst A-04. The catalyst formulation is shown in table 1.

2. Catalyst evaluation

The condensate of ammonia-containing material flow of an acrylonitrile device is used as a raw material, and the COD value of the waste water is 54,500 mg/L. The wastewater was mixed with oxygen and passed through a 125mL fixed bed reactor packed with 120g A-04 catalyst. The reaction temperature in the reactor was 250 ℃, the pressure 6.5MPa, and the residence time 20 minutes. The reaction results are shown in Table 2.

As can be seen from the comparison between example 3 and example 4, the noble metal and the indium are respectively impregnated and reduced in sequence, and the obtained catalyst has a surprisingly good effect on removing COD.

[ example 5 ]

1. Catalyst preparation

In weight ratio, ZrO₂Pt and In is 97:2:1, and catalyst A-05 is prepared.

97 parts of ZrO₂The catalyst carrier was impregnated with In (NO) equivalent to 1 part of In at room temperature₃)₃The solution is kept overnight in the water solution, dried at 80 ℃ and reduced for 4 hours in a hydrogen atmosphere (hydrogen and nitrogen mixed gas with 4 percent of hydrogen content) at 300 ℃ to obtain a catalyst precursor B-05. B-04 was immersed in H corresponding to 2 parts of Pt₂PtCl₆The solution is kept overnight in water, dried at 80 ℃ and reduced for 4 hours at 300 ℃ in a hydrogen atmosphere (hydrogen-nitrogen mixed gas with 4 percent of hydrogen content), thus obtaining the catalyst A-05. The catalyst formulation is shown in table 1.

2. Catalyst evaluation

The condensate of ammonia-containing material flow of an acrylonitrile device is used as a raw material, and the COD value of the waste water is 54,500 mg/L. The wastewater was mixed with oxygen and passed through a 125mL fixed bed reactor packed with 120g A-05 catalyst. The reaction temperature in the reactor was 250 ℃, the pressure 6.5MPa, and the residence time 20 minutes. The reaction results are shown in Table 2.

[ example 6 ]

1. Catalyst preparation

In weight ratio, TiO₂Pt and In is 97:2:1, and catalyst A-06 is prepared.

97 parts of TiO₂The catalyst carrier was impregnated with H equivalent to 2 parts of Pt at room temperature₂PtCl₆The solution is kept overnight in water, dried at 80 ℃ and reduced for 4 hours in a hydrogen atmosphere (hydrogen and nitrogen mixed gas with 4 percent of hydrogen content) at 300 ℃ to obtain a catalyst precursor B-06. B-06 was impregnated with In (NO) In an amount corresponding to 1 part of In₃)₃The catalyst A-06 is obtained by reducing the catalyst in a hydrogen atmosphere (hydrogen and nitrogen mixed gas with 4 percent of hydrogen) at 300 ℃ for 4 hours after the catalyst is dried in water solution overnight and at 80 ℃. The catalyst formulation is shown in table 1.

2. Catalyst evaluation

The condensate of ammonia-containing material flow of an acrylonitrile device is used as a raw material, and the COD value of the waste water is 54,500 mg/L. The wastewater was mixed with oxygen and passed through a 125mL fixed bed reactor packed with 120g A-06 catalyst. The reaction temperature in the reactor was 250 ℃, the pressure 6.5MPa, and the residence time 20 minutes. The reaction results are shown in Table 2.

[ example 7 ]

Calculated by weight ratio, Al₂O₃Pt and In is 97:2:1, and catalyst A-07 is prepared.

97 parts of Al₂O₃The catalyst carrier was impregnated with H equivalent to 2 parts of Pt at room temperature₂PtCl₆The solution is kept overnight in water, dried at 80 ℃ and reduced for 4 hours in a hydrogen atmosphere (hydrogen and nitrogen mixed gas with 4 percent of hydrogen content) at 300 ℃ to obtain a catalyst precursor B-07. B-07 was immersed In an amount of In (NO) corresponding to 1 part of In₃)₃The solution was left overnight in the aqueous solution, dried at 80 ℃ and then reduced at 300 ℃ for 4 hours in a hydrogen atmosphere (hydrogen-nitrogen mixed gas having a hydrogen content of 4%) to obtain catalyst A-07. The catalyst formulation is shown in table 1.

2. Catalyst evaluation

The condensate of ammonia-containing material flow of an acrylonitrile device is used as a raw material, and the COD value of the waste water is 54,500 mg/L. The wastewater was mixed with oxygen and passed through a 125mL fixed bed reactor packed with 120g A-07 catalyst. The reaction temperature in the reactor was 250 ℃, the pressure 6.5MPa, and the residence time 20 minutes. The reaction results are shown in Table 2.

[ example 8 ]

In terms of weight ratio, SiO₂Pt and In is 97:2:1, and catalyst A-08 is prepared.

97 parts of SiO₂The catalyst carrier was impregnated with H equivalent to 2 parts of Pt at room temperature₂PtCl₆The solution is kept overnight in water, dried at 80 ℃ and reduced for 4 hours in a hydrogen atmosphere (hydrogen and nitrogen mixed gas with 4 percent of hydrogen content) at 300 ℃ to obtain a catalyst precursor B-08. B-08 was impregnated with In (NO) corresponding to 1 part of In₃)₃The solution is kept overnight in water, dried at 80 ℃ and reduced for 4 hours at 300 ℃ in a hydrogen atmosphere (hydrogen-nitrogen mixed gas with 4 percent of hydrogen content), thus obtaining the catalyst A-08. The catalyst formulation is shown in table 1.

2. Catalyst evaluation

The condensate of ammonia-containing material flow of an acrylonitrile device is used as a raw material, and the COD value of the waste water is 54,500 mg/L. The wastewater was mixed with oxygen and passed through a 125mL fixed bed reactor packed with 120g A-08 catalyst. The reaction temperature in the reactor was 250 ℃, the pressure 6.5MPa, and the residence time 20 minutes. The reaction results are shown in Table 2.

[ example 9 ]

The catalyst prepared in example 6 and the catalyst prepared in example 7 were mixed in a weight ratio of 1:1 to obtain catalyst A09. The catalyst formulation is shown in table 1.

2. Catalyst evaluation

The condensate of ammonia-containing material flow of an acrylonitrile device is used as a raw material, and the COD value of the waste water is 54,500 mg/L. The wastewater was mixed with oxygen and passed through a 125mL fixed bed reactor packed with 120g A-09 catalyst. The reaction temperature in the reactor was 250 ℃, the pressure 6.5MPa, and the residence time 20 minutes. The reaction results are shown in Table 2.

As can be seen from the comparison of example 9 with examples 6 and 7, TiO is used₂Supported catalyst and Al₂O₃The mode of mixing the supported catalyst to obtain the mixed catalyst obtains better technical effect than that of a single catalyst, and the two catalysts have synergistic effect on the aspect of reducing COD of wastewater after being mixed.

[ COMPARATIVE EXAMPLE 1 ]

1. Catalyst preparation

In weight ratio, ZrO₂Pt is 97:3 to prepare the catalyst D-01.

97 parts of ZrO₂The catalyst carrier was impregnated with H equivalent to 3 parts of Pt at room temperature₂PtCl₆The solution is kept overnight in water, dried at 80 ℃ and reduced for 4 hours at 300 ℃ in a hydrogen atmosphere (hydrogen-nitrogen mixed gas with 4 percent of hydrogen content), thus obtaining the catalyst D-01. The catalyst formulation is shown in table 1.

2. Catalyst evaluation

The condensate of ammonia-containing material flow of an acrylonitrile device is used as a raw material, and the COD value of the waste water is 54,500 mg/L. The wastewater was mixed with oxygen and passed through a 125mL fixed bed reactor packed with 120g D-01 catalyst. The reaction temperature in the reactor was 250 ℃, the pressure 6.5MPa, and the residence time 20 minutes. The reaction results are shown in Table 2.

[ COMPARATIVE EXAMPLE 2 ]

1. Catalyst preparation

In weight ratio, ZrO₂In is 97:3, and catalyst D-02 is prepared.

97 parts of ZrO₂The catalyst carrier was impregnated with In (NO) corresponding to 3 parts of In at room temperature₃)₃The solution is kept overnight in water, dried at 80 ℃ and reduced for 4 hours at 300 ℃ in a hydrogen atmosphere (hydrogen-nitrogen mixed gas with 4 percent of hydrogen content), and the catalyst D-02 is obtained. The catalyst formulation is shown in table 1.

2. Catalyst evaluation

The condensate of ammonia-containing material flow of an acrylonitrile device is used as a raw material, and the COD value of the waste water is 54,500 mg/L. The wastewater was mixed with oxygen and passed through a 125mL fixed bed reactor packed with 120g D-02 catalyst. The reaction temperature in the reactor was 250 ℃, the pressure 6.5MPa, and the residence time 20 minutes. The reaction results are shown in Table 2.

TABLE 1 formulation of the catalyst

Examples	Catalyst and process for preparing same	Catalyst formulation	The mass ratio of each component
				Example 1	A-01	ZrO₂:Ru:In	97:2:1
Example 2	A-02	ZrO₂:Pd:In	97:2:1
				Example 3	A-03	ZrO₂:Pt:In	97:2:1
Example 4	A-04	ZrO₂:Pt:In	97:2:1
				Example 5	A-05	ZrO₂:Pt:In	97:2:1
Example 6	A-06	TiO₂:Pt:In	97:2:1
				Example 7	A-07	Al₂O₃:Pt:In	97:2:1
Example 8	A-08	SiO₂:Pt:In	97:2:1
				Example 9	A-09	TiO₂:Pt:In/Al₂O₃:Pt:In	97:2:1
Comparative example 1	D-01	ZrO₂:Pt	97:3
				Comparative example 2	D-02	ZrO₂:In	97:3

TABLE 2 reaction results

Claims

1. A process for treating an ammonia-containing gas stream in an acrylonitrile plant comprising:

enabling a high-ammonia product gas flow (6) from the ammonia oxidation reactor to contact with a low-COD lean ammonium absorption liquid (17) in a quenching tower (1) to absorb unreacted ammonia in the high-ammonia product gas flow to obtain an ammonium-rich absorption liquid (8) and a low-ammonia product gas flow (7); stripping the ammonium-rich absorption liquid (8) in a stripping tower (2) by stripping tower stripping gas (9) to remove volatile organic components (10), separating and removing light components (11) floating on the upper layer and heavy components (12) sinking on the lower layer in a separation device (3), then heating and stripping in a stripping tower (4) by stripping tower stripping gas (13) to obtain a crude ammonia gas stream (15) and a high-COD lean ammonium absorption liquid (14), carrying out wet oxidation reaction on the high-COD lean ammonium absorption liquid (14) and a first oxidant (16) in a wet oxidation reactor (5) to obtain a low-COD lean ammonium absorption liquid (17), and returning the low-COD lean ammonium absorption liquid (17) to a quenching tower (1) for absorbing unreacted ammonia; condensing the crude ammonia gas flow (15), removing organic matters from the crude ammonia gas flow and a second oxidant (19) in a catalytic wet oxidation reactor (18), and rectifying to obtain an anhydrous ammonia material flow; the wet oxidation catalyst used in the catalytic wet oxidation reactor (18) comprises the following components: (1) 90-99.5 parts of catalyst carrierA body; (2) 0.1-5 parts of at least one noble metal selected from platinum group; (3) 0.1-5 parts of indium; the catalyst carrier is TiO₂And Al₂O₃。

2. The method according to claim 1, wherein the high COD ammonium-poor absorbent solution and/or the low COD ammonium-poor absorbent solution contains at least one absorbent selected from phosphoric acid and ammonium dihydrogen phosphate.

3. A process for the treatment of an ammonia-containing gas stream in an acrylonitrile plant according to claim 1, characterized in that the first oxidant (16) and the second oxidant (19) are independently selected from molecular oxygen-containing gases.

4. A process for the treatment of an ammonia-containing gas stream in an acrylonitrile plant as claimed in claim 3, characterized in that the first oxidant (16) and the second oxidant (19) are independently selected from pure oxygen, air or oxygen-enriched air.

5. The method for treating an ammonia-containing gas stream in an acrylonitrile plant as claimed in claim 1, wherein the reaction temperature in the catalytic wet oxidation reactor (18) is 180 to 300 ℃.

6. The method for treating an ammonia-containing gas stream in an acrylonitrile plant according to claim 1, wherein the reaction pressure in the catalytic wet oxidation reactor (18) is 3.0 to 12.0 MPa.

7. A process according to claim 3, wherein the volume ratio of the second oxidant to the crude ammonia stream (15) after condensation is 50 to 400.

8. The method according to claim 1, wherein the crude ammonia gas stream has a residence time of 10 to 90 minutes in the wet oxidation reactor (18).

9. A process for the treatment of an ammonia-containing gas stream in an acrylonitrile plant as claimed in claim 1, characterized in that the heavy component (12) is a polymer and/or an ammoxidation catalyst powder.