JPH09253497A - Method of regenerating catalyst for treating ammonia-containing waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simply remove catalyst poisons from a metal catalyst which has been poisoned by metals such as copper, and regenerate the catalyst by bringing the catalyst suffering from deterioration of activity into contact with an ammonia-containing waste water to which an oxidizing agent has not been added. SOLUTION: Ammonia-containing waste water received in a crude water tank 1 is transferred to an adjustment tank 3 by means of a pump 2, and a pH controlling agent is added as necessary, and a sodium nitrile aqueous solution is injected from an oxidizing agent tank 5 in the above process and then temperature is adjusted before ammonia nitrogen is decomposed in a catalyst packed tower 9. When activity of the metal catalyst in the catalyst packed tower 9 is deteriorated, a pump 6 is stopped and injection of the oxidizing agent is stopped, and a valve 11 is closed, and a valve 12 is opened, and the ammonia containing waste water, into which the oxidizing agent has not been added, is introduced into the catalyst packed tower 9. The metal catalyst is regenerated and copper contained in the ammonia containing waste water used for regeneration of the metal catalyst is simultaneously removed before the waste water is returned to the crude water tank 1. As described above, the metal catalyst is regenerated in the process of treating the ammonia containing waste water in a short period of time and treatment can be restarted.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for regenerating a catalyst for treating wastewater containing ammonia. For more information,
The present invention adds an oxidizing agent to ammonia-containing wastewater, decomposes ammonia to remove it as nitrogen, and easily removes a metal catalyst having a reduced activity due to a metal adhering to an active site without using an acid. The present invention relates to a method for regenerating a catalyst for treating wastewater containing ammonia that can be regenerated.

[0002]

BACKGROUND ART Wastewater from thermal power plants, wastewater from semiconductor factories, wastewater from dyestuff factories and wastewater from fertilizer factories often contain a considerable amount of ammoniacal nitrogen. Ammoniacal nitrogen is a source of eutrophication in closed waters and must be removed by wastewater treatment. Conventionally, a treatment method has been known in which an oxidizing agent is added to wastewater containing ammoniacal nitrogen, and ammoniacal nitrogen is decomposed into harmless nitrogen gas in the presence of a catalyst (JP-A-6-99180).
JP-A-7-8974). For example, when nitrite is used as the oxidizing agent, ammoniacal nitrogen is decomposed according to the following equation. NH ₄ ⁺ + NO ₂ ⁻ → N ₂ + 2H ₂ O When the treatment of catalytically decomposing ammonia nitrogen in wastewater by reaction with an oxidant is continued, the activity of the catalyst gradually decreases. This is often because the metal such as copper contained in the waste water is adsorbed on the active sites of the catalyst. Conventionally, as a method of removing the metal such as copper adsorbed from the catalyst poisoned in this way, a method of contacting the catalyst with an acid solution to dissolve the metal such as copper and removing it is known (Japanese Patent Laid-Open No. 2003-242242). Sho 5
8-114731, JP-A-58-114732, JP-A-58-114734, etc.). However, in these conventional techniques, if an acid solution is passed through a packed tower to remove metals such as copper adhering to the catalyst, the packed tower and piping materials must be made of corrosion-resistant materials, There was a problem that equipment costs increased. Further, there is a problem that the strength of the catalyst carrier and the performance of the supported metal are impaired by the load of acid.

[0003]

DISCLOSURE OF THE INVENTION It is an object of the present invention to provide a method for easily removing a catalyst poison from a catalyst poisoned by a metal such as copper in the oxidation treatment of ammonia-containing wastewater to regenerate the catalyst. It was done for the purpose.

[0004]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that in the oxidative decomposition treatment of ammonia-containing wastewater in the presence of a catalyst, a metal catalyst with reduced activity is added, It was found that the catalytic activity was easily recovered by contacting the ammonia-containing wastewater to which the oxidizing agent was not added, and the present invention was completed based on this finding. That is, the present invention, after adding an oxidizing agent to the ammonia-containing wastewater, in the decomposition treatment of ammonia to be brought into contact with the metal catalyst under heating, contact the ammonia-containing wastewater without addition of the oxidizing agent to the metal catalyst of reduced activity. The present invention provides a method for regenerating a catalyst for treating wastewater containing ammonia, which is characterized in that it is regenerated.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION
Decomposition of ammonia by adding an oxidizing agent to wastewater containing copper and other metals that are catalyst poisons along with ammoniacal nitrogen, such as semiconductor factory wastewater, dye factory wastewater, and fertilizer factory wastewater. It can be applied to processing. In the method of the present invention, the pH of the wastewater is adjusted to 4 to 7 prior to the addition of the oxidizing agent to the wastewater containing ammoniacal nitrogen.
It is preferable to adjust the pH to 5 and more preferable to adjust the pH to 5 to 6. The pH is preferably adjusted by adding an inorganic acid or an inorganic base. As the inorganic acid, for example, hydrochloric acid, sulfuric acid or the like can be used, and as the inorganic base, for example, sodium hydroxide or potassium hydroxide. ,
Calcium hydroxide or the like can be used. The oxidizing agent used in the method of the present invention is not particularly limited, and for example, hydrogen peroxide, nitrite, persulfate, ozone, high-purity oxygen gas, air and the like can be used. These oxidizing agents may be used alone or in combination of two or more. Among these oxidizers, nitrite can be added in an equivalent amount to ammonia,
Since it becomes completely harmless nitrogen gas and water as shown in the following formula, it can be used particularly preferably. _{^{NH 4 + + NO 2 - →}} N 2 + 2H 2 O

There is no particular limitation on the metal catalyst used in the method of the present invention. For example, a noble metal catalyst such as platinum, iridium, palladium, ruthenium, rhodium or gold, or a base metal catalyst such as cobalt or nickel can be used. it can. These catalysts may be used alone or in combination of two or more. The catalyst can be used in the form of powder, but from the viewpoint of operation, it is preferable to support the catalyst on a carrier and use it as a granular, plate-shaped or other shaped body. The loading amount of the catalyst is 0.
It is preferably from 05 to 10% by weight, more preferably from 0.1 to 1% by weight. There is no particular limitation on the carrier supporting the catalyst, for example, titania, α-alumina,
γ-alumina, silica, zeolite, activated carbon, polytetrafluoroethylene, etc. can be used, but a porous carrier is preferable. As the porous carrier, titania particles having a specific surface area of 10 to 100 m ² / g can be particularly preferably used. In the method of the present invention, the method of contact-treating wastewater containing ammoniacal nitrogen in the presence of an oxidant is not particularly limited, but it is preferable to use a packed tower packed with a catalyst such as granular shaped bodies. After adding an oxidizer to wastewater containing ammoniacal nitrogen, the ammoniacal nitrogen can be decomposed into nitrogen gas by passing water through a packed column filled with a metal catalyst in an upward flow or a downward flow. .

In the method of the present invention, the heating conditions for reacting the ammoniacal nitrogen and the oxidizing agent are 100 to 250.
C. is preferable, and 120 to 180.degree. C. is more preferable. If the heating condition is less than 100 ° C., the decomposition rate of ammoniacal nitrogen may decrease, and the equipment may be large. When the heating condition exceeds 250 ° C., the reaction rate increases, but the handling is dangerous, and the equipment is expensive because it is necessary to increase the pressure resistance of the equipment. In the method of the present invention, when waste water containing ammoniacal nitrogen added with an oxidizer is passed through the metal catalyst packed bed, S
V (superficial velocity) is preferably set to 0.5~20hr ^-1, and more preferably a 1~5hr ^-1. The required reaction time is influenced by the water quality of the wastewater containing ammoniacal nitrogen and the reaction temperature, and therefore the SV can be appropriately selected in consideration of these conditions. In the method of the present invention, when an oxidizing agent is added to the wastewater containing ammoniacal nitrogen, the decomposition treatment of the ammoniacal nitrogen is continued by contacting with the metal catalyst under heating, and the removal rate of the ammoniacal nitrogen decreases. The metal catalyst is regenerated by stopping the addition of the oxidizer to the waste water and bringing the ammonia-containing waste water containing no oxidizer into contact with the metal catalyst. The timing for starting the regeneration of the metal catalyst is not particularly limited, and can be appropriately selected depending on the desired water quality of the treated water.

[0008] In the method of the present invention, the temperature at which the ammonia-containing wastewater containing no oxidizing agent is brought into contact with the metal catalyst having reduced activity is preferably 100 to 250 ° C, more preferably 120 to 180 ° C. preferable. If the contact temperature is less than 100 ° C, it may take a long time to regenerate the metal catalyst. When the heating condition exceeds 250 ° C., the rate of regeneration becomes faster, but there is a danger in handling, and the equipment becomes expensive because it is necessary to increase the pressure resistance of the equipment. Usually, the temperature for regenerating the metal catalyst is preferably the same as the decomposition temperature for ammoniacal nitrogen. By keeping the decomposition treatment temperature of ammoniacal nitrogen and the temperature of regeneration of the metal catalyst at the same temperature, the addition of oxidizer to the ammonia-containing wastewater can be simply stopped without significantly changing the operating conditions of the equipment. It is possible to switch the process from the decomposition treatment of (1) to the regeneration of the metal catalyst. In the method of the present invention, when the metal catalyst is packed in a packed column, the SV at the time when the ammonia-containing wastewater without addition of an oxidizing agent is brought into contact with the metal catalyst whose activity has decreased
(Superficial velocity) is preferably set to 0.5~20hr ^-1, and more preferably a 1~5hr ^-1. SV when decomposing ammoniacal nitrogen and S when regenerating the metal catalyst
By making V the same, the process can be switched from the decomposition process of ammonia nitrogen to the regeneration of the metal catalyst by simply stopping the addition of the oxidant to the ammonia-containing wastewater, but the SV can be easily changed. Therefore, it can be appropriately selected according to the regeneration conditions of the metal catalyst. The flow rate of the ammonia-containing wastewater without addition of an oxidizing agent for the regeneration of the metal catalyst can be appropriately selected according to the state of the metal catalyst, but it is necessary for the metal attached to the catalyst surface to form a complex with ammonia. It is desirable to determine the water flow rate so that it will be equal to or more than this amount. If the ammonia content is too low, it may be added externally. Usually 1 catalyst volume
The metal catalyst is regenerated by passing water in an amount of ˜5 times, and in many cases, the metal catalyst is regenerated by passing water in an amount of 1 to 3 times the catalyst volume. In the method of the present invention, the mechanism of regeneration by contacting ammonia-containing wastewater without addition of an oxidizer to the metal catalyst with reduced activity is not clear, but a metal that becomes a catalyst poison such as copper adsorbed at the active site of the metal catalyst. However, it is considered that the complex is desorbed by forming a complex with ammonium ion and is removed from the active site.

FIG. 1 is a process system diagram of one embodiment of an ammonia-containing wastewater treatment for carrying out the method of the present invention. The ammonia-containing wastewater received in the raw water tank 1 is sent to the adjusting tank 3 by the pump A2, and a pH adjusting agent is added (not shown) as needed to adjust the pH. The water to be treated whose pH has been adjusted is sent out by the pump B4, and an oxidizer such as an aqueous sodium nitrite solution is injected by the pump C6 from the oxidizer tank 5 in the middle of the piping. The water to be treated to which the oxidizing agent has been added is the heat exchanger 7
The residual heat is recovered by, and the temperature is further raised to a predetermined temperature by the heater 8 and sent to the catalyst packed tower 9 to decompose the ammonia nitrogen. The treated water from which ammonia nitrogen has been decomposed and removed is sent to the next step via the heat exchanger, the pressure adjusting valve 10 and the valve A11. When the activity of the metal catalyst in the catalyst packed tower is lowered, the pump C6 is stopped to stop the injection of the oxidant, the valve A11 is closed, the valve B12 is opened, and the oxidant not added to the catalyst packed tower is ammonia. After passing the contained wastewater to regenerate the metal catalyst and remove the copper contained in the ammonia-containing wastewater used for regenerating the metal catalyst, it is returned to the raw water tank 1. The wastewater treatment method for removing copper is not particularly limited, but it is usually performed by the coagulation sedimentation method by providing the coagulation sedimentation tank 13 and the filter 14. According to the method of the present invention, unlike the conventional method of regenerating a metal catalyst by acid treatment, it is not necessary to take out the metal catalyst from the catalyst packed column and separately perform acid treatment, so that the wastewater treatment can be interrupted,
It is not necessary to provide two catalyst packed towers. Further, since the acid solution is not passed through the catalyst packed tower, it is not necessary to make the catalyst tower or the pipe with a corrosion resistant material. According to the method of the present invention, the addition of the oxidizer is simply stopped during the treatment of the ammonia-containing wastewater, and the valve is simply switched to treat the ammonia-containing wastewater without changing the temperature or the water flow rate of the catalyst packed tower. Under the same conditions, the metal catalyst can be easily regenerated in a short time.

[0010]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention. Example 1 Treatment of cation exchange resin regeneration wastewater of a condensate demineralizer of a power plant and regeneration of a catalyst whose activity has decreased due to the treatment were performed. The water quality of the raw water was 4,000 mg / liter of ammonia nitrogen, 3.3 mg / liter of copper, and pH 5.8. Sodium nitrite was added to this raw water in an amount equivalent to that of ammoniacal nitrogen, and 0.5 wt% platinum-supported titania catalyst was added.
14 liters were filled and water was passed through the catalyst packed column whose temperature was kept at 160 ° C. at SV = 2 hr ⁻¹ . Immediately after the passage of water, the removal rate of ammonia nitrogen was 99%,
When water was passed through a liter / liter catalyst, the removal rate of ammonia nitrogen decreased to 85%. Then, the addition of sodium nitrite was stopped, and raw water of pH 5.8 containing 4000 mg / l of ammonia nitrogen was passed under the condition of 2 liter / liter catalyst SV = 2 hr ⁻¹ . When 0.14 liters of raw water is directly passed through the washing water,
It contained 1,040 mg / l Cu ²⁺ . After adding sodium sulfide to this waste water and adjusting the pH to 7.5 to cause coagulation and precipitation, the residual amount of Cu ²⁺ was 3 mg / liter or less, and this was returned to the raw water tank. After that, when the equivalent amount of sodium nitrite was added to the raw water again, the removal ratio of ammonia nitrogen was recovered to 98%.

[0011]

EFFECTS OF THE INVENTION According to the method of the present invention, in the treatment of wastewater containing ammonia, the metal catalyst having a reduced activity can be regenerated by simply passing the wastewater containing ammonia containing no oxidizing agent. The metal catalyst can be regenerated and the treatment can be restarted in a short time in the ammonia-containing wastewater treatment process without requiring a take-out operation or a device made of a corrosion resistant material.

[Brief description of drawings]

FIG. 1 is a process system diagram of one embodiment of an ammonia-containing wastewater treatment for carrying out the method of the present invention.

[Explanation of symbols]

 1 Raw Water Tank 2 Pump A 3 Adjustment Tank 4 Pump B 5 Oxidizer Tank 6 Pump C 7 Heat Exchanger 8 Heater 9 Catalyst Packing Tower 10 Pressure Adjustment Valve 11 Valve A 12 Valve B 13 Coagulation Sedimentation Tank 14 Filter

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display location C02F 1/72 CDJ C02F 1/72 CDJZ

Claims (1)

[Claims] 1. A method of decomposing ammonia by adding an oxidizing agent to ammonia-containing wastewater and then contacting it with a metal catalyst under heating, by contacting ammonia-containing wastewater to which the oxidizing agent is not added to the metal catalyst whose activity has decreased. A method for regenerating a catalyst for treating wastewater containing ammonia, which comprises regenerating.