JPH11156379A - Method for supercritical hydroxylation-decomposition of nitrogen-containing organic compound - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove N2 O in exhaust gas efficiently by a method in which a nitrogen- containing organic compound is subjected to supercritical hydroxylation decomposition under conditions in which ammonia can be oxidized/decomposed, and treated fluid, after being cooled below the critical temperature of water is gas-liquid-separated, and the separated gas is treated with a nitrogen dioxide decomposing catalyst. SOLUTION: A nitrogen-containing organic compound in a tank 1 and water in a water storage tank 3 are pressurized by high pressure pumps 2, 4 respectively, air is pressurized by a high pressure compressor 5, the organic compound is mixed with water, and the mixture is introduced into a reactor 7. A supercritical hydroxylation decomposition reaction is advanced in a mixed fluid brought into a supercritical state in the reactor 7, the carbon atom skeleton of the nitrogen-containing organic compound is decomposed into carbon dioxide, and the nitrogen atom skeleton is decomposed into nitrogen gas through ammonia. The treated fluid subjected to supercritical hydroxylation decomposition is cooled by a cooler 8 and gas-liquid-separated by a gas-liquid separator 9. The separated gas is passed through a catalyst column 11 through a gas discharge line 10 to remove N2 O in the gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for supercritical hydroxylic decomposition of nitrogen-containing organic compounds such as alkaline wastewater discharged from an electronics factory and organic sludge generated from a biological treatment apparatus for organic wastewater, and its treatment. It concerns the device.

[0002]

2. Description of the Related Art There are many types of nitrogen-containing organic compounds. Among them, those containing a large amount of nitrogen-containing organic compounds to be decomposed include, for example, alkaline wastewater discharged from an electronics factory and biological treatment of organic wastewater. There is organic sludge generated from the apparatus.

[0003] Among them, most of the alkaline waste liquid discharged from the electronics factory is concentrated and incinerated. Most of organic sludge is also incinerated after concentration and dehydration.

However, when nitrogen-containing organic compounds are incinerated,
It is a well-known fact that NOx is generated, and an exhaust gas treatment facility for removing NOx from exhaust gas is required, causing an increase in size and cost of an incinerator.

On the other hand, in recent years, the supercritical condition of water (374
(22 ° C. or higher), a so-called supercritical hydroxylation decomposition method has been proposed. As is clear from the flow chart of the conventional supercritical hydroxylation decomposition treatment apparatus shown in FIG. 4, the nitrogen-containing organic compound in the tank 1 and the water in the water storage tank 3 are supercritically pressurized by the high-pressure pumps 2 and 4. Pressure, and air as an oxidant is supplied to a high-pressure compressor 5
And becomes a mixed fluid. The pressurized mixed fluid is heated to a supercritical temperature by the preheater 6, and a supercritical hydroxylation decomposition reaction occurs in the tubular reactor 7. The processing fluid decomposed by supercritical hydroxylation is cooled by a cooler 8 and a pressure reducing valve 8
The gas is separated into gas and liquid by the gas-liquid separation device 9 via the gas outlet, and is discharged out of the system as exhaust gas and treated water.

The supercritical hydroxylation decomposition method is capable of completely decomposing a nitrogen-containing organic compound, and the carbon skeleton and nitrogen skeleton constituting the nitrogen-containing organic compound are harmless gases such as carbon dioxide and nitrogen gas, respectively. NOx removal treatment equipment is not required because the gas is decomposed and discharged.

However, in the conventional supercritical hydroxylation decomposition method, the nitrogen skeleton in the nitrogen-containing organic compound may not be decomposed to nitrogen gas but may remain in the treated water as ammonia depending on the reaction conditions. Further, even under the condition that ammonia does not remain in the treated water, nitrous oxide (N ₂ O) is generated in the exhaust gas, and a longer time may be required for complete decomposition.

Ammonia in treated water is subject to total nitrogen, so its emission must be regulated and reduced. On the other hand, there is no emission standard for N ₂ O in exhaust gas at present, but since it has a warming effect 100 times that of carbon dioxide, it is desirable to reduce the emission as much as possible.

[0009]

In the supercritical water splitting method, it is necessary to prevent ammonia from remaining in the treated water and to prevent N ₂ O from remaining in the exhaust gas. This can be achieved by limiting the reaction conditions.

For example, in order to prevent ammonia from remaining in the treated water, the reaction temperature is 650 ° C. and the reaction pressure is 25 MPa, depending on the initial concentration of nitrogen in the object to be treated.
Under the conditions described above, it is possible in about 60 to 90 seconds. However, in order to prevent N ₂ O from remaining in the exhaust gas, it may be necessary for a longer time under the same conditions,
The reactor for supercritical hydroxylation decomposition becomes larger.

An object of the present invention is to provide a method for supercritically hydrolyzing a nitrogen-containing organic compound by removing N ₂ O from exhaust gas without containing ammonia in treated water.
It is another object of the present invention to provide a method and apparatus for supercritical hydroxylation decomposition that can be performed with a small reactor.

[0012]

Means for Solving the Problems As a result of intensive studies conducted by the present inventors, in the supercritical hydroxylation decomposition method of a nitrogen-containing organic compound, the processing fluid subjected to the supercritical hydroxylation decomposition is subjected to gas-liquid separation.
The inventors have found that the above problem can be solved by catalytically treating the separated exhaust gas, and have completed the present invention.

That is, the present invention according to claim 1 is a method for supercritically hydrolyzing a nitrogen-containing organic compound, wherein the nitrogen-containing organic compound is oxidized and decomposed in a process capable of oxidatively decomposing ammonia. By supercritically hydrolyzing an organic compound and cooling the processing fluid after supercritically hydrolyzing to below the critical temperature of water, gas-liquid separation is performed, and the separated gas is treated with an N ₂ O decomposition catalyst. The present invention relates to a method for supercritically decomposing a nitrogen-containing organic compound by removing N ₂ O.

[0014] The present invention according to claim 2, after cooling the supercritical water oxidation decomposed process fluid to below the critical temperature of 300 ° C. or more water, and gas-liquid separation, the separated gas N ₂ O decomposition 2. The method for supercritically hydrolyzing a nitrogen-containing organic compound according to claim 1, wherein the method is performed with a catalyst.

The present invention according to claim 3 is characterized in that the separated gas is treated with an N ₂ O decomposition catalyst before depressurizing the separated gas. The present invention relates to a supercritical water splitting decomposition method.

According to a fourth aspect of the present invention, there is provided an apparatus for supercritically hydrolyzing a nitrogen-containing organic compound, comprising a reactor for oxidatively decomposing a processed product in the supercritical state of water in the presence of an oxidizing agent. Cooling means for cooling the fluid to a temperature lower than supercritical conditions, gas-liquid separation means for gas-liquid separation of the cooled processing fluid, and an N ₂ O catalyst layer through which the separated gas passes;
A supercritical nitrogen-containing organic compound, comprising: a decompression means for decompressing a gas that has passed through the catalyst layer; a cooling means for cooling the gas-liquid separated liquid; and a decompression means for decompressing the cooled liquid. The present invention relates to a hydroxylation decomposition apparatus.

According to a fifth aspect of the present invention, there is provided the apparatus for supercritically hydrolyzing and decomposing a nitrogen-containing organic compound according to the fourth aspect, wherein the cooling means is a heat exchanger.

[0018]

DETAILED DESCRIPTION OF THE INVENTION The invention according to claim 1 is a method for supercritically hydrolyzing a nitrogen-containing organic compound, wherein the supercritically hydrolyzed decomposition is carried out under conditions capable of removing ammonia from treated water, Is cooled to a temperature lower than the critical temperature of water, gas-liquid separation is performed, and the separated gas is treated with an N ₂ O decomposition catalyst to remove N ₂ O in the exhaust gas. The nitrogen-containing organic compound to be treated in the present invention includes a compound containing a nitrogen atom in the molecular skeleton of the organic compound such as a nitrogen-containing heterocyclic compound and a nitrogen atom in a substituent such as an amine compound and an amide compound. It may contain, for example, alkaline waste liquid discharged from an electronics factory, sludge of organic waste water, and the like. In addition, an aqueous ammonia solution containing no organic substance can be subjected to the supercritical hydroxylation decomposition treatment.

When supercritically hydrolyzing a nitrogen-containing organic compound according to the present invention, it is necessary to decompose ammonia generated in the process of supercritically hydrolyzing the nitrogen-containing organic compound. 25-22MPa
It is preferable to carry out the supercritical hydroxylation decomposition under the following conditions.
The reaction time depends on the nitrogen concentration in the processed product, but is generally about 60 to 90 seconds even at a high concentration. When the reaction time is at this level, it is not necessary to use a large reactor.

However, under the above reaction conditions, N ₂ O is generated in the processed product (exhaust gas) subjected to supercritical hydroxylation decomposition. In order to decompose N ₂ O in the exhaust gas, the reaction time must be further extended under the above reaction conditions, which requires a large-sized reactor, which is not preferable because the cost increases.

According to the present invention, in order to remove N ₂ O in exhaust gas and not to increase the size of the reactor, the processing fluid after supercritical hydroxylation is separated into gas and liquid, and the separated gas is subjected to N ₂ O decomposition. It is characterized by treating with a catalyst.

The N ₂ O decomposition catalyst used in the present invention is not particularly limited as long as it can decompose N ₂ O.
Group A compounds consisting of rhodium sesquioxide, cobalt sesquioxide or mixtures thereof, Group B compounds consisting of cerium compounds, manganese compounds or tin compounds, alkali metals, alkaline earth metals or C consisting of mixtures thereof
A multi-component catalyst containing at least one of each of the group compounds as an active ingredient, or at least one selected from the group consisting of uthenium, rhodium, rhenium, osmium, iridium, palladium and platinum on a hydrophobic carrier;
Use a catalyst that supports more than one kind of noble metal, a catalyst that supports rhodium oxide on a zinc oxide carrier or a porous zinc oxide carrier, or a zeolite whose exchangeable cation is hydrogen inside and on the surface of pores. Can be.

In general, in the presence of SOx or water, the N ₂ O decomposition catalyst has a problem that its substance becomes a catalyst poison, deteriorating the performance or failing to exhibit a predetermined ability. SOx is contained in exhaust gas after critical hydroxylation decomposition.
And water is removed by gas-liquid separation, so that the above-described problem does not occur. The N ₂ O decomposition catalyst may be filled in a catalyst tower as a fixed bed, and the gas-liquid separated exhaust gas may be passed through.

The decomposition of N ₂ O is preferably performed at a relatively high temperature even in the presence of a catalyst. As described above, the supercritical hydroxylation decomposition reaction is performed at a reaction temperature of 600 ° C. or higher, and thus this heat can be used. However, in the critical state of water, the processing fluid is not separated into gas and liquid, and passing this processing fluid directly through the catalyst layer causes a large amount of water to come into contact with the catalyst, so that the catalyst is in a predetermined state. No effect.

Therefore, gas-liquid separation is required. For that purpose, it is necessary to cool water to a temperature lower than the critical temperature (347 ° C.).

The treatment temperature of the N ₂ O decomposition catalyst after gas-liquid separation is preferably 300 ° C. or higher and lower than the critical temperature of water, ie, 300 to 350 ° C. In order to cool the temperature of the processing fluid, the processing fluid may be cooled by a cooling device.However, a heat exchanger is used to cool the processing fluid with the fluid containing the nitrogen-containing organic compound before being introduced into the reactor. It is preferable to perform heat exchange and cool.

[0027] Incidentally, the gas-liquid separated exhaust gas, in order to increase the removal rate of N ₂ O, depending on the catalyst used, N ₂
It is preferable to reheat to 300 to 400 ° C. before ventilating the O decomposition catalyst layer. In order to reheat the exhaust gas, a heater usually used for starting a supercritical water oxidation apparatus may be used. The heater is used to heat water at the time of activation of the supercritical water oxidation apparatus to make it supercritical water, but when the supercritical water oxidation reaction proceeds steadily in the reactor, it is not used. It is. If the processing gas is reheated by using the heater used at the time of starting, the heater for reheating the processing gas becomes unnecessary, and the apparatus does not increase in size.

According to the second aspect of the present invention, since the exhaust gas is treated at a relatively high temperature, the amount of exhaust gas passing through the N ₂ O decomposition catalyst layer can be made relatively large, and the exhaust gas treatment apparatus can be downsized. .

[0029] According to a third aspect of the invention are those with N ₂ O decomposition catalyst process for removing N ₂ O in the exhaust gas before decompressing the exhaust gas.

According to the third aspect of the present invention, since there is no volume expansion due to reduced pressure and no temperature decrease due to evaporation of the liquid, N ₂
The temperature of the exhaust gas passing through the O decomposition catalyst layer can be maintained at a high temperature. Further, by passing the exhaust gas at a high pressure, the density of the exhaust gas increases, and the amount of the exhaust gas passing through the N ₂ O decomposition catalyst layer can be increased, so that the exhaust gas treatment device can be downsized.

In the supercritical hydroxylation decomposition of the present invention, examples of the oxidizing agent include air, pure oxygen, hydrogen peroxide, and liquid oxygen, and these oxidizing agents have a stoichiometric amount or more. It may be used.

The reactor for performing the supercritical hydroxylation decomposition may be either a pipe (tubular) type or a vessel type, but the structure can be simplified since only one pipe is required from the heating section to the reactor and the cooling section. In the case of treating an object having no possibility of salt formation, a tubular reactor is preferred.

An embodiment of the apparatus for supercritically hydrolyzing and decomposing a nitrogen-containing organic compound according to the present invention will be described with reference to FIGS.

FIG. 1 is a flow chart showing one embodiment of a supercritical hydroxylation decomposition treatment apparatus in which the apparatus of the present invention according to claim 4 is applied to a tubular reactor.

In the tank 1 storing the nitrogen-containing organic compound to be treated, the nitrogen-containing organic compound is stored in the form of an aqueous solution or slurry. The nitrogen-containing organic compound and the water in the water storage tank 3 are pressurized by the high-pressure pumps 2 and 4, respectively, and the air as the oxidant is pressurized by the high-pressure compressor 5 and merged with the nitrogen-containing organic compound and water to form a tube. It is introduced into the mold reactor 7. Before the tubular reactor 7, the mixed fluid is heated by the heater 6 to the supercritical temperature. In the mixed fluid in a supercritical state in the tubular reactor 7, the supercritical hydroxylation decomposition reaction proceeds in a short time, and the carbon atom skeleton of the nitrogen-containing organic compound becomes carbon dioxide.
The nitrogen atom skeleton is decomposed into nitrogen gas via ammonia. The supercritical temperature is maintained by the calorific value of the oxidation reaction of the nitrogen-containing organic compound to be treated, and the supercritical hydroxylation decomposition reaction is maintained. The processing fluid subjected to the supercritical hydroxylation decomposition is cooled to 300 to 350 ° C. by the cooler 8, and separated by the gas-liquid separation device 9. The separated gas through the gas discharge line 10, passed through the catalyst tower 11 N ₂ O decomposition catalyst is filled, N ₂ O contained in a gas is removed. The gas from which N ₂ O has been removed is depressurized by the pressure reducing valve 12, released to the atmospheric pressure, and discharged as exhaust gas. On the other hand, the liquid separated into gas and liquid passes through a liquid discharge line 13 and is cooled to a normal temperature by a cooler 14 and then the pressure reducing valve 1
The pressure is reduced by 5 and discharged out of the system as treated water. The supercritical hydroxylation decomposition treatment apparatus for nitrogen-containing organic compounds in FIG.
Ammonia is not contained in the treated water and N _{2 in the} exhaust gas
O can be removed, and the reactor and the catalyst layer can be miniaturized.

FIG. 2 is a view showing one embodiment of the supercritical hydroxylation decomposition apparatus according to the present invention according to claim 5. The supercritical hydroxylation decomposition treatment apparatus according to claim 5 has the same main parts as the apparatus described in claim 4, and common parts have the same reference numerals. The supercritical hydroxylation decomposition apparatus according to claim 5 is different from the supercritical hydroxylation decomposition treatment apparatus according to claim 4 in that preheating and cooling of the mixed fluid are realized using a heat exchanger.

That is, the mixed fluid of the nitrogen-containing organic compound, water and the oxidizing agent which has been pressurized to a predetermined pressure is supplied to the heat exchanger 1
6, and is subjected to supercritical hydrolytic decomposition in a tubular reactor 7. The processing fluid decomposed by supercritical hydroxylation is cooled to 300 to 350 ° C. by heat exchange in the heat exchanger 16.

The cooled processing fluid is subjected to gas-liquid separation by a gas-liquid separation device 9 in the same manner as in the supercritical hydroxylation decomposition treatment device shown in FIG. 1, and the separated gas passes through a gas discharge line 10. After passing through the catalyst tower 11 filled with the N ₂ O decomposition catalyst,
N ₂ O contained in the gas is removed. The gas from which N ₂ O has been removed is reduced in pressure by the pressure reducing valve 12 and discharged as exhaust gas. On the other hand, the liquid separated into gas and liquid passes through the liquid discharge line 13, is cooled by the cooler 14, is depressurized by the pressure reducing valve 15, and is discharged out of the system as treated water.

FIG. 3 is a flow chart of a processing apparatus for reheating gas-liquid separated exhaust gas before passing it through the catalyst layer.
The main part of the supercritical hydroxylation decomposition treatment apparatus shown in FIG. 3 is the same as that of the apparatus shown in FIG. 1, and the common parts are denoted by the same reference numerals.

The supercritical hydroxylation decomposition treatment apparatus shown in FIG.
The difference from the above is that the exhaust gas separated from gas and liquid is reheated by using a heater used at the time of starting the supercritical hydroxylation decomposition apparatus, and then N ₂ O is decomposed by a catalyst.

First, at the time of starting, the valves v2, v
By closing the valve 5 and opening the valves v1, v3, v4, the water used at the time of starting can be heated, and the supercritical hydroxylation reaction can be started. When the supercritical water oxidation progresses and reaches a steady state, the valves v1, v3, and v4 are closed,
By opening the valves v2 and v5, the processing fluid subjected to the supercritical hydroxylation decomposition in the reactor 7 is cooled in the cooler 8, and then the exhaust gas separated in the gas-liquid separator 9 is guided to the heater 6 for reheating. Then, N ₂ O can be decomposed by ventilating the catalyst tower 11.

[0042]

EXAMPLES Example 1 Alkaline waste liquid discharged from an electronics factory (main components: ammonium hydroxide, tetramethylammonium hydroxide, TC: 100000 ppm,
(TN: 50000 ppm) was subjected to supercritical hydroxyl decomposition at a reaction temperature of 650 ° C. and a reaction pressure of 25 MPa. The processing fluid subjected to the supercritical hydroxyl decomposition was subjected to gas-liquid separation, and the separated gas was compared with a case where the separated gas was passed through an N ₂ O decomposition catalyst layer and a case where the separated gas was not passed. An experiment was performed using a supercritical hydroxylation decomposition apparatus as shown in FIG. The catalyst used was one in which 1.5% Rh (rhodium) was supported on aluminum oxide, and the gas separated by gas-liquid separation at a space velocity of 5000 Hr ^-1 of the catalyst layer was passed.
After the supercritical water splitting, the ammonia concentration in the treated water and the N ₂ O concentration in the exhaust gas were measured. Table 1 shows the measurement results.

[0043]

[Table 1]

As is clear from the results shown in Table 1, the treatment fluid after the nitrogen-containing organic compound was subjected to supercritical hydroxylation and decomposition was subjected to gas-liquid separation, and the separated gas was subjected to N ₂ O catalyst treatment. Even if the reaction time is short, N ₂
It was possible to reduce O to 50 ppm or less.

[0045]

According to the method and apparatus of the present invention, N ₂ O in the exhaust gas obtained by subjecting a nitrogen-containing organic compound to supercritical hydroxylation decomposition treatment is used.
Can be effectively reduced.

Since the N ₂ O in the exhaust gas can be reduced even in a short-time reaction, the size of the reactor used for the supercritical water splitting can be reduced to 1/3 or less.

[0047] Since the waste heat by supercritical water oxidation decomposition can be used to N ₂ O removal, it is possible to reduce the running cost for the N ₂ O removal.

In the case of the third aspect, since the exhaust gas treatment is performed at a high density without a decrease in the temperature due to the reduced pressure, N ₂ O is applied at normal pressure.
The amount of catalyst used can be reduced as compared with the case where removal is performed.

[Brief description of the drawings]

FIG. 1 is a flow chart showing an embodiment of the apparatus for supercritically hydrolyzing and decomposing a nitrogen-containing organic compound of the present invention according to claim 4.

FIG. 2 is a flow chart showing an embodiment of the apparatus for supercritically hydrolyzing and decomposing a nitrogen-containing organic compound of the present invention according to claim 5;

FIG. 3 is a flow chart showing one embodiment of a supercritical hydroxylation decomposition treatment apparatus for reheating an exhaust gas subjected to gas-liquid separation and performing N ₂ O decomposition treatment using a catalyst.

FIG. 4 is a flow chart of a conventional apparatus for supercritically hydrolyzing and decomposing nitrogen-containing organic compounds.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 nitrogen-containing organic compound storage tank 2 high-pressure pump 3 water storage tank 4 high-pressure pump 5 high-pressure compressor 6 heater 7 tubular reactor 8 cooler 9 gas-liquid separator 10 gas discharge line 11 catalyst tower 12 pressure reducing valve 13 liquid discharge line 14 cooler 15 pressure reducing valve 16 heat exchanger

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C02F 1/72 ZAB B01D 53/36 101Z

Claims (5)

[Claims] 1. A method for supercritically hydrolyzing a nitrogen-containing organic compound, wherein the nitrogen-containing organic compound is supercritically hydrolyzed under conditions capable of oxidatively decomposing ammonia generated in the process of oxidatively decomposing the nitrogen-containing organic compound. After cooling the processing fluid after supercritical water splitting to below the critical temperature of water, gas-liquid separation is performed, and the separated gas is treated with a N ₂ O decomposition catalyst to remove N ₂ O. Supercritical water oxidation decomposition method of nitrogen-containing organic compound. 2. The processing fluid decomposed by supercritical hydroxylation is treated with 30
2. The supercritical nitrogen-containing organic compound according to claim 1, wherein after cooling the water to a temperature not lower than the critical temperature of 0 ° C. or more, gas-liquid separation is performed, and the separated gas is treated with an N ₂ O decomposition catalyst. Hydrolysis decomposition method. 3. Prior to depressurizing the separated gas, N ₂ O
3. The method for supercritically hydrolyzing and decomposing a nitrogen-containing organic compound according to claim 1 or 2, wherein the treatment is carried out with a decomposition catalyst. 4. An apparatus for supercritically hydrolyzing a nitrogen-containing organic compound, comprising a reactor for oxidatively decomposing a processed product in the supercritical state of water in the presence of an oxidizing agent. Cooling means for cooling to a temperature, gas-liquid separation means for gas-liquid separation of the cooled processing fluid, N ₂ O catalyst layer through which the separated gas passes, and decompression means for depressurizing the gas passing through the catalyst layer. An apparatus for supercritically decomposing a nitrogen-containing organic compound, comprising: a cooling means for cooling the liquid separated from the gas and liquid; and a pressure reducing means for reducing the pressure of the cooled liquid. 5. The apparatus for supercritically hydrolyzing and decomposing a nitrogen-containing organic compound according to claim 4, wherein the cooling means is a heat exchanger.