JP2005087927A - In situ catalyst for supercritical water oxidation and supercritical water oxidation method and device using the catalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device capable of suppressing or controlling the undesired deposition of a salt caused during supercritical water oxidation and efficiently performing a supercritical water oxidation reaction, and to produce an in situ catalyst for the supercritical water oxidation used in the method and the device. <P>SOLUTION: The method for subjecting liquid to be treated containing organic materials to the supercritical water oxidation comprises a process of introducing a catalyst precursor into a reactor, a process of letting the liquid to be treated to the supercritical water state and introducing the liquid to be treated into the reactor so as to allow an alkali metal or an alkali earth metal to exist in the liquid to be treated, an oxidation decomposition process of oxidizing and decomposing the liquid to be treated under the presence of an oxidant and the alkali metal or the alkali earth metal in the supercritical state, and a catalyst formation process of forming the in situ catalyst which is hydrothermally synthesized under the presence of the oxidant and the alkali metal or the alkali earth metal in the supercritical state and comprises a metal acid salt. Therein, the catalyst formation process and the oxidation decomposition process are cooperatively performed, and the oxidation decomposition process is facilitated by the in situ catalyst. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an in situ catalyst for supercritical water oxidation treatment, a supercritical water oxidation method and apparatus using the catalyst.

  In recent years, supercritical water oxidation has attracted attention as a harmless treatment method for hazardous waste liquids in place of the incineration method. The supercritical water oxidation method is an organic substance oxidation / decomposition method utilizing the characteristics of water in a supercritical state, that is, water having a pressure of 22.1 MPa or more and a temperature of 374 ° C. or more. Supercritical water becomes a uniform reaction field between oxygen and organic matter and has high diffusivity, so that the organic matter can be completely decomposed into water and carbon dioxide in a very short time.

  However, since supercritical water is sparingly soluble in salts such as inorganic salts, salts contained in the waste liquid or salts generated during supercritical water oxidation treatment are likely to precipitate, and the treatment route such as reaction is caused by the precipitated salt. The first problem is that clogging occurs in the vessel and piping. Further, since the reaction and operation are performed in a supercritical state, that is, in a high temperature and high pressure state, there is a second problem that the apparatus is easily corroded.

  With respect to the first problem, a method in which a temperature difference is provided in the reactor to divide into a subcritical phase and a supercritical phase, and a salt is dissolved in the subcritical phase has been studied (for example, see Patent Document 1). . However, providing a temperature difference in the reactor is likely to cause corrosion and deterioration of the reactor material, and requires a specially shaped reactor, which causes further problems economically and technically. .

Regarding the second problem, it is conceivable to improve the material of the reactor, and a method for suppressing the progress of corrosion by operating at a relatively low temperature and low pressure even in a supercritical state has been proposed (for example, (See Patent Document 2 and Non-Patent Documents 1 to 4). However, the improvement of the material of the reactor causes further economic and technical problems. In addition, the operation at a relatively low temperature and low pressure will cause incomplete decomposition of the organic matter and lose the advantages of the supercritical water oxidation treatment method. As a technique for performing a reaction at a relatively low temperature and low pressure without causing incomplete decomposition of organic substances, it has been proposed to perform the reaction in the presence of a catalyst. However, when a catalyst is used, salt deposition, which is the first problem, occurs on the surface of the catalyst, which causes a new problem of catalyst poisoning.
For example, [0004] to [0005]. International publication number WO00 / 25913. Environmental Science & Technology, 29 (11), p.2748-2753 (Nov 1995). Industrial & Engineering Chemistry Research, 35 (10), p.3257-3279 (Oct 1996). Industrial & Engineering Chemistry Research, 36 (9), p.3439-3445 (Sep 1997). . Industrial & Engineering Chemistry Research, 38 (10), p.3793-3801 (Oct 1996).

Therefore, an object of the present invention is to solve the problems in the prior art.
Specifically, the object of the present invention is to convert the originally undesired salt precipitation that occurs during supercritical water oxidation into an in situ catalyst for supercritical water oxidation, thereby depositing unwanted salts. It is an object to provide a supercritical water oxidation treatment method and apparatus for efficiently controlling a supercritical water oxidation reaction, and an in situ catalyst for supercritical water oxidation treatment.

  Another object of the present invention is to provide a method for regenerating a catalyst precursor by regenerating the converted in situ catalyst for supercritical water oxidation treatment into a catalyst precursor again, whereby the salt generated in the reactor is removed. It can be discharged out of the reactor.

The present inventors have found that the above-described problems can be solved by the following invention.
<1> A method of supercritical water oxidation treatment of a liquid to be treated containing an organic substance, the method comprising introducing a catalyst precursor into a reactor; bringing the liquid to be treated into a supercritical water state and treating Introducing into the reactor such that the alkali liquid or alkaline earth metal is present in the liquid; the reactor should be treated in the presence of an oxidizing agent and an alkali metal or alkaline earth metal and in a supercritical water state An oxidative decomposition step in which the liquid is oxidized and decomposed; the catalyst precursor is hydrothermally synthesized in a supercritical water state in the presence of an oxidizing agent and an alkali metal or alkaline earth metal in a reactor, A catalyst forming step in which an in situ catalyst for supercritical water oxidation treatment is formed, and the catalyst forming step and the oxidative decomposition step are performed in concert, and formed by the catalyst forming step. Said catalyst Reduction decomposition step is accelerated, the method described above.

  <2> In the above <1>, the catalyst precursor includes a titanium group element (eg, Ti, Zr, etc.), a group VIII element (eg, Fe, Co, Ni, etc.), a group VIIA element (eg, Mn, etc.), and It may be selected from the group consisting of Group IIIB elements (eg, Al, etc.). In particular, the catalyst precursor is preferably Ti, Fe, Al, Zr, or Mn, and more preferably Ti or Fe.

  <3> In the above <1> or <2>, the metal acid salt is at least one alkali metal or alkaline earth selected from the group consisting of Na, K, Rb, Cs, Mg, Ca, Sr, Ba and Ra. From group metals, titanium group elements (eg, Ti, Zr, etc.), group VIII elements (eg, Fe, Co, Ni, etc.), group VIIA elements (eg, Mn, etc.), and group IIIB elements (eg, Al, etc.) It is good to have at least one metal species selected from the group consisting of: The at least one metal species is preferably Ti, Fe, Al, Zr, or Mn, and more preferably Ti or Fe.

<4> In any one of the above items <1> to <3>, the metal acid salt may be a titanate or an iron salt, such as sodium titanate, potassium titanate, sodium ferrate, and potassium ferrate. Preferably selected from the group consisting of
<5> In any one of the above items <1> to <4>, the step of regenerating the catalyst precursor by dissolving and washing the in situ catalyst for supercritical water oxidation treatment formed in the reactor with subcritical water It is good to have.

  <6> Step of regenerating the catalyst precursor by dissolving and washing the in situ catalyst for supercritical water oxidation treatment in the reactor formed by any one of the above methods <1> to <4> with subcritical water A catalyst precursor regeneration method comprising:

  <7> A supercritical water oxidation treatment apparatus having a reactor for supercritical water oxidation treatment, comprising a catalyst precursor in the reactor, wherein an oxidizing agent and an alkali metal or alkaline earth metal are contained in the reactor. The liquid to be treated in the presence and in the supercritical water state is oxidized and decomposed, and in the reactor, the catalyst precursor is in the presence of an oxidizing agent and an alkali metal or an alkaline earth metal, and in the supercritical water state. A supercritical water oxidation treatment apparatus characterized in that an in situ catalyst for supercritical water oxidation treatment that is hydrothermally synthesized with a metal salt is formed, and the oxidation and decomposition are promoted by the catalyst.

  <8> In the above <7>, the catalyst precursor includes a titanium group element (eg, Ti, Zr, etc.), a group VIII element (eg, Fe, Co, Ni, etc.), a group VIIA element (eg, Mn, etc.), and It may be selected from the group consisting of Group IIIB elements (eg, Al, etc.). In particular, the catalyst precursor is preferably Ti, Fe, Al, Zr, or Mn, and more preferably Ti or Fe.

  <9> In the above <7> or <8>, the metal acid salt is at least one alkali metal or alkaline earth selected from the group consisting of Na, K, Rb, Cs, Mg, Ca, Sr, Ba and Ra. From group metals, titanium group elements (eg, Ti, Zr, etc.), group VIII elements (eg, Fe, Co, Ni, etc.), group VIIA elements (eg, Mn, etc.), and group IIIB elements (eg, Al, etc.) It is good to have at least one metal species selected from the group consisting of: The at least one metal species is preferably Ti, Fe, Al, Zr, or Mn, and more preferably Ti or Fe.

<10> In any one of the above items <7> to <9>, the metal acid salt may be a titanate or an iron salt, such as sodium titanate, potassium titanate, sodium ferrate, and potassium ferrate. Preferably selected from the group consisting of
<11> In any one of the above items <7> to <10>, further comprising means for regenerating the catalyst precursor by dissolving and washing the in situ catalyst for supercritical water oxidation treatment formed in the reactor with subcritical water It is good to have.

  <12> An in situ catalyst for supercritical water oxidation treatment comprising a metal acid salt hydrothermally synthesized in a supercritical water state in the presence of an alkali metal or an alkaline earth metal.

  <13> In the above item <12>, the metal acid salt is at least one alkali metal or alkali selected from the group consisting of Na, K, Rb, Cs, Mg, Ca, Sr, Ba, and Ra. Earth metals, titanium group elements (eg, Ti, Zr, etc.), group VIII elements (eg, Fe, Co, Ni, etc.), group VIIA elements (eg, Mn, etc.), and group IIIB elements (eg, Al, etc.) And at least one metal species selected from the group consisting of: The at least one metal species is preferably Ti, Fe, Al, Zr, or Mn, and more preferably Ti or Fe.

<14> In the above item <12> or <13>, the metal acid salt may be a titanate or an iron salt, for example, a group consisting of sodium titanate, potassium titanate, sodium ferrate and potassium ferrate. It is good to be chosen from.
<15> In any one of the above items <12> to <14>, the in situ catalyst for supercritical water oxidation treatment is preferably dissolved and washed with subcritical water to be regenerated into a catalyst precursor.

  According to the present invention, originally undesired salt precipitation that occurs during supercritical water oxidation treatment is converted into an in situ catalyst for supercritical water oxidation treatment, thereby suppressing or controlling the precipitation of unwanted salt, and It is possible to provide a supercritical water treatment method and apparatus for efficiently performing supercritical water oxidation, and an in situ catalyst for supercritical water treatment.

  In addition, according to the present invention, it is possible to provide a method for regenerating a catalyst precursor by regenerating the converted in situ catalyst for supercritical water oxidation treatment into a catalyst precursor again, thereby reacting the salt generated in the reactor. It can be discharged outside the vessel.

Hereinafter, the present invention will be described in detail.
First, a method for supercritical water oxidation treatment of a liquid to be treated containing an organic substance according to the present invention will be described.
The method of the present invention comprises a step of introducing a catalyst precursor into a reactor; the liquid to be treated is introduced into the reactor so that the liquid to be treated is in a supercritical water state and the alkali metal or alkaline earth metal is present in the liquid to be treated. A process; an oxidative decomposition process in which a liquid to be treated in the presence of an oxidant and an alkali metal or an alkaline earth metal and in a supercritical water state is oxidized and decomposed in a reactor; the catalyst precursor is an oxidant, And a catalyst forming step in which an in situ catalyst for supercritical water oxidation treatment is formed by hydrothermal synthesis in the presence of an alkali metal or alkaline earth metal and in the supercritical water state to have a metal acid salt. .

  Here, the catalyst formation step and the oxidative decomposition step are performed in concert, and the oxidative decomposition step is further promoted by the catalyst formed by the catalyst formation step. Further, in the catalyst formation step, an in situ catalyst for supercritical water oxidation treatment containing a component that forms the salt is formed instead of the formation and precipitation of the salt that was originally undesirable. Thus, the present invention allows unwanted salts to be converted into useful catalysts.

The method of the present invention is first subjected to a step of introducing a catalyst precursor into the reactor.
The catalyst precursor is not particularly limited as long as it is a substance that can be hydrothermally synthesized into a metal acid salt in the presence of an oxidizing agent and an alkali metal or alkaline earth metal and in a supercritical water state. However, the substance should have a catalytic action that promotes supercritical water oxidation.
These catalyst precursors include titanium group elements (eg, Ti, Zr, etc.), group VIII elements (eg, Fe, Co, Ni, etc.), group VIIA elements (eg, Mn, etc.), and group IIIB elements (eg, Al). Etc.), as well as these compounds. In particular, the catalyst precursor is preferably Ti, Fe, Al, Zr, or Mn, and more preferably Ti or Fe.

Next, the method of the present invention is subjected to a step of introducing the liquid to be treated into a supercritical water state into the reactor.
The liquid to be treated is a liquid containing an organic substance that is decomposed by the supercritical water oxidation treatment, and may contain an inorganic substance if desired.
The supercritical water state refers to a state where the temperature is 374 ° C. or higher and the pressure is 22.1 MPa or higher. In the present invention, the preferred temperature and pressure depend on the liquid to be treated. For example, the temperature can be 374-700 ° C. In the present invention, by using the in situ catalyst for supercritical water oxidation treatment, the working temperature can be relatively lowered as compared with the conventional method or apparatus. For example, what was conventionally processed at 600 degreeC can be processed at about 500 degreeC in this invention. As described above, the present invention can be operated at a lower temperature than the conventional one, and thus can exhibit the merit in cost, the merit of suppressing the energy loss when shifting to the subcritical state described later, and the like. .

  The pressure may be 22.1 to 40 MPa, preferably 25 to 30 MPa. The latter value is a pressure that exhibits a stable supercritical state, and is a pressure that does not cause an excessive load on the compressor used in a part of the apparatus of the present invention.

  The liquid to be treated should be introduced into the reactor so that alkali metal or alkaline earth metal is present in the liquid. That is, if the liquid to be treated does not contain an alkali metal or alkaline earth metal, a step of incorporating the alkali metal or alkaline earth metal into the liquid before introducing the liquid to be treated into the reactor; Alternatively, an aqueous solution of an alkali metal or alkaline earth metal compound is introduced into the reactor so that the liquid to be treated is introduced into the reactor and the alkali metal or alkaline earth metal is contained in the liquid to be treated in the reactor. It is preferable to provide a process for introducing the above. In addition, when the liquid to be processed originally contains an alkali metal or an alkaline earth metal, the above process may or may not be provided.

  The alkali metal or alkaline earth metal may be sodium, potassium, rubidium, cesium, magnesium, calcium, strontium, barium and / or radium, preferably sodium, potassium, magnesium and / or calcium. More preferably sodium and / or potassium.

  The liquid to be treated containing an alkali metal or alkaline earth metal is preferably in a state of basicity at 25 ° C. and 1 atm. Therefore, when providing a step of introducing an aqueous solution of an alkali metal or alkaline earth metal compound into the reactor, carbonates such as sodium carbonate, potassium carbonate, and magnesium carbonate; acetates such as sodium acetate, potassium acetate, and magnesium acetate A formic acid salt such as sodium formate, potassium formate and magnesium formate; an aqueous solution of a basic compound such as a hydroxide salt such as sodium hydroxide, potassium hydroxide and magnesium hydroxide is preferred.

Furthermore, the method of the present invention is subjected to an oxidative decomposition step in which the liquid to be treated is oxidized and decomposed.
In this step, the organic matter contained in the liquid to be treated reacts with oxygen, which is an oxidant, in the supercritical water state, and is oxidized and decomposed into carbon dioxide. Here, the supercritical water state is the same state as described above.
As the oxidizing agent, in addition to oxygen, air containing oxygen, oxygen-enriched air, oxygen-containing gas, hydrogen peroxide water, or the like can be used.

  In the method of the present invention, the catalyst formation step occurs in concert with the oxidative decomposition step. That is, the catalyst precursor provided in the reactor is hydrothermally synthesized in the presence of an oxidant and in a supercritical water state, and further in the presence of an alkali metal or alkaline earth metal to have a metal acid salt. Thus, an in situ catalyst for supercritical water oxidation treatment is formed.

The catalyst formed during the critical hydroxylation process further accelerates the critical hydroxylation process. This catalyst is also formed in place of the undesired precipitated salt in conventional methods. That is, in the present invention, undesired salt precipitation is not observed, or even if observed, it does not cause “clogging”.
The metal acid salt formed in the catalyst forming step is preferably a titanate or a ferrate, and examples thereof include sodium titanate, potassium titanate, sodium ferrate and potassium ferrate.

  The method of the present invention can include a step of regenerating the in situ catalyst for supercritical water oxidation treatment into a catalyst precursor separately from the above-described series of operations for oxidizing and decomposing the liquid to be treated. This step is a step of dissolving and washing the in situ catalyst for supercritical water oxidation treatment having a metal acid salt formed in the reactor with subcritical water.

Subcritical water can be obtained by bringing the subcritical state by shifting temperature and pressure from the critical state. The shift from the critical state to the subcritical state is generally caused by shifting the temperature. Theoretically, it is possible to shift to the subcritical state by shifting the pressure, but it is general to use a temperature shift from the viewpoint of difficulty in pressure control and cost.
The temperature shift is not particularly limited as long as the metal salt can be dissolved, but from the viewpoint of energy efficiency and the temperature at which the ionic product of water increases, for example, 200 ° C. or more and 374 ° C. or less, preferably around 300 ° C. There should be.

Unlike supercritical water, subcritical water has the property of dissolving inorganic salts. Therefore, the formed metal acid salt can be dissolved and the in situ catalyst for supercritical water oxidation treatment can be regenerated into a catalyst precursor.
In addition, each component contained in the metal acid salt can be recovered from the waste liquid obtained in this step by a desired treatment. In addition, each recovered component, particularly alkali metal or alkaline earth metal, or a compound thereof can be recycled for use in the method of the present invention.

The present invention also provides a supercritical water oxidation treatment apparatus.
The supercritical water oxidation treatment apparatus of the present invention is an apparatus that can achieve the above method. That is, the apparatus of the present invention has a reactor for supercritical water oxidation treatment, the reactor is provided with a catalyst precursor, and in the reactor, in the presence of an oxidizing agent and an alkali metal or an alkaline earth metal, And the liquid to be treated in the supercritical water state is oxidized and decomposed, and in the reactor, the catalyst precursor is hydrothermally present in the presence of an oxidizing agent and an alkali metal or alkaline earth metal and in the supercritical water state. An in situ catalyst for supercritical water oxidation treatment which is synthesized and has a metal acid salt is formed, and the oxidation and decomposition are promoted by the catalyst.

  In the present invention, the shape and characteristics of the reactor are not particularly limited. Specifically, it is not necessary that the reactor has a subcritical water area and a supercritical water area as compared with the above-mentioned Patent Document 1 (Japanese Patent Laid-Open No. 2002-361669). For this reason, a reactor can be manufactured cheaply compared with the past.

  Also, the apparatus of the present invention is a catalyst precursor that regenerates an in situ catalyst for supercritical water oxidation treatment into a catalyst precursor separately from a series of operations for oxidizing and decomposing a liquid to be treated, as in the above-described method. It can have a reproducing means. Specifically, the catalyst precursor regeneration means includes means for bringing water into a subcritical water state, means for introducing water, particularly subcritical water, into the reactor, and reacting subcritical water with an in situ catalyst for supercritical water oxidation treatment. It is preferable to have a means for discharging the waste liquid obtained in this way out of the reactor. The apparatus of the present invention requires the above-mentioned various means, and these various means can be manufactured at a low cost and can be easily operated as compared with the prior art (for example, Patent Document 1 (Japanese Patent Laid-Open No. 2002-361669)). It can be carried out.

FIG. 1 shows one embodiment of the device of the present invention. In FIG. 1, an apparatus 1 of the present invention includes a tank 3 for storing a liquid to be treated, an inlet 5 for an oxidant such as air and oxygen, an introduction pipe 8a for introducing the liquid to be treated into a reactor 7, and an oxidation. An introduction pipe 8b for introducing the agent to the reactor 7, compressors 9a and 9b for bringing the liquid to be processed and the oxidizing agent to the reactor 7 at a desired pressure, and the liquid and oxidizing agent to be processed at a desired temperature It has heating means 11a and 11b. The apparatus of the present invention is disposed downstream of the discharge pipe 13 for discharging discharges such as reactants from the reactor 7, the temperature controller 15 for temperature control (mainly cooling) the discharges, and A valve 17 for controlling the pressure (mainly reducing the pressure to atmospheric pressure) and a post-treatment tank 19 disposed downstream of the valve 17 are provided. Further, the apparatus 1 has a discharge destination changing means 21 between the valve 17 and the post-treatment tank 19, and guides the discharged material to the post-treatment tank 19 or the post-treatment tank 23.
When supercritical water oxidation treatment is performed, the liquid to be treated and the oxidizing agent are pressurized to a pressure that brings about a supercritical water state by the compressors 9a and 9b, and a temperature that brings about a supercritical water state by the heating means 11a and 11b. To the reactor 7. The reactor 7 in FIG. 1 has a coil type. The shape and characteristics of the reactor are not particularly limited as described above. However, the reactor is of a coil type in order to increase temperature efficiency and reaction efficiency and save space. The reactor 7 has an in situ catalyst for supercritical water oxidation treatment, and the supercritical water oxidation treatment is promoted.
CO ₂ , water, and the like discharged through the discharge pipe 13 by the supercritical water oxidation treatment are lowered in temperature by the temperature controller 15, and the pressure is reduced to the atmospheric pressure or the vicinity thereof by the valve 17, to the post-treatment tank 19. It is guided. In the post-treatment tank 19, gas-liquid separation or the like is performed, and the water separated in the post-treatment tank 19 is guided to the introduction pipe 8a via the introduction pipe 25 and the introduction pipe 25a as needed, and reused. The air or oxygen separated in the processing tank 19 is led to the introduction pipe 8b through the introduction pipe 25 and the introduction pipe 25b and reused. Treated substances such as CO ₂ , water, etc. are discharged from the apparatus 1 via the means 22.
On the other hand, when regenerating the in situ catalyst for supercritical water oxidation treatment as a catalyst precursor, the following operation is performed. That is, the liquid to be treated is pressurized to a pressure that brings about a subcritical water state by the compressor 9 a, heated to a temperature that brings about the subcritical water state by the heating means 11 a, and guided to the reactor 7. In the reactor 7, since the liquid to be treated is in a subcritical water state, the metal acid salt as an in situ catalyst for supercritical water oxidation treatment is dissolved and regenerated into a catalyst precursor. After dissolving the metal acid salt, the liquid in the subcritical water state is cooled by the temperature controller 15 through the discharge pipe 13, and the pressure is reduced to the atmospheric pressure or the vicinity thereof by the valve 17. In this case, the liquid in the subcritical water state is guided to the post-treatment tank 23 after the metal salt is dissolved by the discharge destination changing means 21. In the post-treatment tank 23, separation treatment is appropriately performed, and the liquid containing the organic matter to be treated is led to the tank 3 through the introduction pipe 27, and the treated substance is discharged from the apparatus 1 through the means 29. .

  Furthermore, the present invention provides an in situ catalyst for supercritical water oxidation treatment. As described above, the catalyst is a catalyst generated in situ when the supercritical water oxidation treatment is performed. Further, in the prior art, it is composed of a component that generates an undesired precipitated salt, and in the method or apparatus of the present invention, a catalyst that occurs in situ is generated, and an undesired precipitated salt is not generated or even generated. However, “clogging” does not occur.

The in situ catalyst for supercritical water oxidation treatment of the present invention is an apparatus having the same conditions as the present invention, that is, a catalyst precursor is placed in the reactor, and the presence of an oxidizing agent and an alkali metal or alkaline earth metal is present. If the catalyst precursor is placed in an apparatus having a condition for hydrothermal reaction of the catalyst precursor in a supercritical water state, the same effect, that is, generation of undesired precipitated salts can be achieved in various supercritical water oxidation treatment apparatuses. The effect of preventing and promoting supercritical water oxidation treatment can be achieved.
EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited to a present Example.

(Supercritical water oxidation equipment)
A supercritical water oxidation treatment experiment was conducted using an experimental apparatus having a continuous reactor. The experimental apparatus used is shown in FIG. In the apparatus 201 of FIG. 2, the reactor 203 is a pipe made of SUS-316 having an inner diameter of 7.05 mm and a length of 7 cm. In order to bring the inside of the reactor 203 to a desired temperature, a molten salt bath 205 and an electric furnace 207 is provided. A treatment liquid introduction pipe 209 for introducing a liquid to be treated into the reactor 203 and an oxidant introduction pipe 211 for introducing an oxidant are provided. A liquid container 213 to be processed and a pump 215 for bringing the liquid to a desired pressure to the reactor are provided upstream of the processing liquid introduction pipe 209. Further, a container 217 for the oxidizing agent and a pump 219 for introducing the oxidizing agent to a desired pressure are provided upstream of the oxidizing agent introduction pipe 211. The treatment liquid introduction pipe 209 and the oxidant introduction pipe 211 were arranged so as to be heated to a desired temperature through the molten salt bath 205 and led to the reactor 203.
The reactor 203 has a discharge port for discharging a gas (such as carbon dioxide) generated by the supercritical water oxidation treatment. The discharge port is provided with a cooling pipe 221 and cooled to room temperature in the cooling pipe. The pressure was reduced to atmospheric pressure through 223. A gas-liquid separator 225 and a gas bag 227 are disposed downstream of the back pressure valve 223.

  An aqueous solution of sodium acetate: 1.75 mmol / l (at room temperature and normal pressure) was placed in the container 213 of the above apparatus to prepare a liquid to be treated. In addition, supercritical water oxidation was carried out for both the case where the titanium titanium particles (φ2.0 to 3.35 mm, 2.313 g) were placed in the reactor (Example 1) and the case where the sponge titanium particles were not placed (Reference Example 1). A treatment experiment was conducted. The conditions for the supercritical water treatment were: pressure 25 MPa; temperature 450 ° C .; initial concentration of sodium acetate: 1.75 mmol / l; initial concentration of oxygen: 20 times that of acetate; residence time: 10 seconds.

About what arrange | positioned sponge titanium particle ((phi) 2.0-3.35mm, 2.313g) (Example 1) and what does not arrange | position (reference example 1), the ratio from which sodium was removed from sodium acetate aqueous solution was observed. . The observation results are shown in FIG. In FIG. 3, the horizontal axis is the elapsed time from the start of the experiment, and the vertical axis is the Na removal rate. In FIG. 3, ◆ indicates the results of Example 1, and ■ indicates the results of Reference Example 1. The removal rate of Na was calculated by the following formula. In the formula, C _t represents the Na concentration in the supercritical state of the solution in the reactor after the processing time t has elapsed, and C _i represents the Na concentration (supercritical state) at the reactor inlet.
(Na removal rate) = 1- (C _t / C _i )

  FIG. 3 shows that in Example 1, the removal rate of Na is high by disposing the sponge titanium particles in the reactor. This suggests that most of Na is bonded or adsorbed to the sponge titanium particles, and that no Na salt is deposited in the reactor or other piping. On the other hand, Reference Example 1 in which no sponge titanium particles are arranged has a low Na removal rate. The low removal rate of Na in Reference Example 1 suggests that Na salt may be precipitated in the reactor or other piping.

  A supercritical water oxidation treatment experiment was conducted for 5 hours in the same manner as in Example 1 except that a 6.0 mm × 10.0 mm titanium piece was used in place of the sponge titanium particles of Example 1. The surface of the titanium piece before and after Example 2 was observed with SEM. The results are shown in FIGS. 4 is an image before the experiment of Example 2, and FIG. 5 is an image after the experiment of Example 2. It can be seen from FIG. 5 that acicular crystals are precipitated on the titanium surface. Elemental analysis of this crystal with SEM-EPMA confirmed that it was sodium titanate. That is, it is presumed that sodium titanate was hydrothermally synthesized from titanium in the supercritical water state in the presence of sodium acetate.

Supercritical water oxidation treatment was performed using the same apparatus as in Example 1. However, the reactor of Example 3 was the same as that of Example 1 that was subjected to supercritical water oxidation treatment. That is, in the reactor, sponge titanium particles (φ2.0 to 3.35 mm, 2.313 g) were placed on a SUS-316 pipe having an inner diameter of 7.05 mm and a length of 7 cm, and sodium titanium was placed on the surface of the sponge titanium particles. In which precipitation (precipitation amount: 0.177 mmol) was confirmed was used.
Further, as Reference Example 2 to be compared with Example 3, a reactor in which sponge titanium particles (φ2.0 to 3.35 mm, 2.313 g) are arranged on a SUS-316 pipe having an inner diameter of 7.05 mm and a length of 7 cm ( That is, the surface of the sponge titanium particles was subjected to supercritical water oxidation using no sodium).
In Example 3 and Reference Example 2, the liquid to be treated was acetic acid: 1.75 mmol / l (normal temperature and normal pressure).

For Example 3 and Reference Example 2, the decomposition rate of acetic acid by supercritical water oxidation was measured. The result is shown in FIG. In FIG. 6, the vertical axis represents the acetic acid decomposition rate, and the horizontal axis (W / F) represents (W: catalyst amount) / (F: flow rate of liquid to be treated) (unit: g (catalyst amount) / ( L / min)). In this specification, “decomposition rate of acetic acid” was calculated by the following formula. In the formula, Ca represents the acetic acid concentration (supercritical state) in the liquid in the reactor when treated with a certain W / F, and Ci represents the acetic acid concentration (supercritical state) at the reactor inlet.
(Decomposition rate) = 1− (C _a / C _i )

  FIG. 6 shows that when sodium is present on the surface of the sponge titanium particles (Example 3), the decomposition rate of acetic acid increases. That is, it can be seen that the conditions in the presence of sodium and titanium accelerate the supercritical water oxidation treatment.

Supercritical water oxidation treatment was performed using the same apparatus as in Example 1. However, as the reactor of Example 4, a SUS-316 pipe having an inner diameter of 2.18 mm and a length of 5 m was used, and one in which precipitation of sodium was confirmed on the inner surface of the pipe was used. In addition, the reactor of Example 4 was produced as follows. That is, in place of the reactor of Example 1, an SUS-316 pipe having an inner diameter of 2.18 mm and a length of 5 m was used, and the same apparatus as in Example 1 was used, except that sponge titanium was not used. Was subjected to supercritical water oxidation treatment to obtain a pipe made of SUS-316 in which the presence of sodium was confirmed on the inner surface.
Further, as Reference Example 3 to be compared with Example 4, supercritical water oxidation treatment was performed using a SUS-316 pipe having an inner diameter of 2.18 mm and a length of 5 m (that is, no presence of sodium on the inner surface) as a reactor. Went.
In Example 4 and Reference Example 3, the liquid to be treated was acetic acid: 1.75 mmol / l (normal temperature and normal pressure).

Regarding Example 4 and Reference Example 3, the decomposition rate of acetic acid by supercritical water oxidation treatment was measured in the same manner as Example 3 and Reference Example 2. The result is shown in FIG. In FIG. 7, the vertical axis represents the decomposition rate of acetic acid, and the horizontal axis represents the residence time (seconds).
FIG. 7 shows that the decomposition rate of acetic acid increases due to the presence of sodium on the inner surface of the SUS reactor (Example 4). From this, it can be seen that SUS, that is, the conditions in which Fe and sodium coexist promote the supercritical water oxidation treatment. Moreover, when Example 3 and Example 4 are compared, it turns out that SUS, ie, Fe acts as a catalyst precursor instead of sponge titanium.

Supercritical water oxidation treatment was performed using the same apparatus as in Example 1. However, the reactor of Example 5 was a titanium pipe having an inner diameter of 1.775 mm and a length of 2 m, and the one in which precipitation of potassium (deposition amount: 0.529 mmol) was confirmed on the inner surface of the pipe was used. . In addition, the reactor of Example 5 was produced as follows. That is, in place of the reactor of Example 1, a titanium pipe having an inner diameter of 1.775 mm and a length of 2 m was used, and a sponge titanium was not used. Titanium pipe in which the presence of potassium was confirmed on the inner surface was obtained by performing critical hydroxylation treatment.
Further, as Reference Example 4 compared with Example 5, supercritical water oxidation treatment was performed using a titanium pipe having an inner diameter of 1.775 mm and a length of 2 m (that is, no presence of potassium on the inner surface) as a reactor. It was.
In Example 5 and Reference Example 4, the liquid to be treated was acetic acid: 1.75 mmol / l (normal temperature and normal pressure).

Regarding Example 5 and Reference Example 4, the decomposition rate of acetic acid by supercritical water oxidation treatment was measured in the same manner as Example 4 and Reference Example 3. The result is shown in FIG.
FIG. 8 shows that the decomposition rate of acetic acid increases due to the presence of potassium on the inner surface of the titanium reactor (Example 5). From this, it can be seen that the conditions in which titanium and potassium coexist promote the supercritical water oxidation treatment. Moreover, when Example 3 and Example 5 are compared, it turns out that supercritical water oxidation treatment is similarly promoted when potassium is used instead of sodium.

Supercritical water oxidation treatment was performed using the same apparatus as in Example 1.
However, as the reactor of Example 6, a reactor in which sponge titanium particles (φ2.0 to 3.35 mm, 3.262 g) were arranged in a SUS-316 pipe having an inner diameter of 7.05 mm and a length of 7 cm was used.

Supercritical water oxidation treatment was performed using the same apparatus as in Example 1.
However, in the reactor of Example 7, sponge titanium particles (φ2.0 to 3.35 mm, 3.262 g) were placed in a SUS-316 pipe having an inner diameter of 7.05 mm and a length of 7 cm, and the sponge titanium. What confirmed the precipitation of sodium (precipitation amount: 0.023 mmol) on the surface of particle | grains was used. In addition, the reactor obtained in the same method as the reactor of Example 3 was used for the reactor of Example 7.

Supercritical water oxidation treatment was performed using the same apparatus as in Example 1.
However, in the reactor of Example 8, the titanium sponge particles in which precipitation of sodium contained in the reactor of Example 7 was confirmed were immersed in subcritical water at a pressure of 25 MPa and a temperature of 350 ° C. What was dissolved and removed was used. That is, the reactor of Example 8 has a structure in which sponge titanium particles (φ2.0 to 3.35 mm, 3.262 g) are arranged in a SUS-316 pipe having an inner diameter of 7.05 mm and a length of 7 cm (dissolution of sodium). Used).

Supercritical water oxidation treatment was performed using the same apparatus as in Example 1.
However, the reactor obtained in Example 9 was obtained by performing the same supercritical water oxidation treatment as in Example 1 on the reactor in Example 8 again. That is, in the reactor of Example 9, sponge titanium particles (φ2.0 to 3.35 mm, 3.262 g) were placed in a SUS-316 pipe having an inner diameter of 7.05 mm and a length of 7 cm, and the sponge titanium. What confirmed the precipitation of sodium on the surface of particle | grains (after sodium dissolution process, Na reprecipitation) was used.

  In addition, it was confirmed that 95% of the precipitated sodium salt can be dissolved by dissolution with subcritical water in Example 8. Moreover, it was confirmed by the reactor of Example 8 and Example 9 that sodium reprecipitates on the surface of the sponge titanium particles. From this, it can be seen that the sodium salt can be dissolved by subcritical water to make the sponge titanium particles free from sodium precipitation, and sodium can be re-precipitated on the sponge titanium particles by further supercritical water oxidation treatment.

In Examples 6, 7, and 9, the liquid to be treated was acetic acid: 1.75 mmol / l (normal temperature and normal pressure).
FIG. 9 shows the decomposition rate of acetic acid by supercritical water oxidation treatment in Example 6, Example 7, and Example 9. In FIG. 9, ◆ represents Example 6, ■ represents Example 7, and □ represents Example 9.
From FIG. 9, it can be seen that Examples 7 and 9 show almost the same acetic acid decomposition rate and a high value. From this, it can be seen that even the regenerated reactor has almost the same catalytic activity as before the regeneration. In addition, when Examples 7 and 9 and Example 6 of FIG. 9 are compared, the reactor (Examples 7 and 9) in which precipitation of sodium is confirmed before the supercritical water oxidation treatment is more supercritical water oxidation. It can be seen that the catalyst activity is higher than that of the reactor (Example 6) in which no precipitation of sodium was confirmed before the treatment.

FIG. 10 shows the sodium removal rate of supercritical water oxidation using the reactor shown in Examples 6 and 8. However, the solution to be treated in FIG. 10 was sodium acetate: 1.75 mmol / l (normal temperature / normal pressure state), and the removal rate of sodium from the solution to be treated was measured.
In FIG. 10, ◯ shows the result when the reactor shown in Example 6 is used, and ◆ shows the result when the reactor shown in Example 8 is used.
From FIG. 10, even when the reactor having the regenerated sponge titanium particles (reactor shown in Example 8) is used, the reactor having the fresh sponge titanium particles (reactor shown in Example 6). It can be seen that a similar sodium removal rate is exhibited even in the case of using a).
From this, it can be seen that recycling is possible by removing the sodium salt with subcritical water in Example 8.

It is a conceptual diagram which shows the one aspect | mode of the supercritical water oxidation processing apparatus of this invention. It is a conceptual diagram of the supercritical water oxidation apparatus used for the Example and the reference example. It is a graph which shows the Na removal rate in the supercritical water oxidation treatment experiment of Example 1 and Reference Example 1. 4 is a diagram showing an SEM image of the surface of a titanium piece before a supercritical water oxidation treatment experiment in Example 2. FIG. 4 is a diagram showing an SEM image of the surface of a titanium piece after a supercritical water oxidation treatment experiment in Example 2. FIG. It is a graph which shows the decomposition rate of the acetic acid in the supercritical water oxidation treatment experiment of Example 3 and Reference Example 2. It is a graph which shows the decomposition rate of the acetic acid in the supercritical water oxidation treatment experiment of Example 4 and Reference Example 3. 6 is a graph showing the decomposition rate of acetic acid in the supercritical water oxidation treatment experiment of Example 5 and Reference Example 4. 6 is a graph showing the decomposition rate of acetic acid in supercritical water oxidation treatment experiments of Example 6, Example 7, and Example 9. It is a graph which shows the Na removal rate in the supercritical water oxidation treatment experiment of Example 6 and Example 8.

Claims (14)

A method of supercritical water oxidation treatment of a liquid to be treated containing an organic substance, the method comprising introducing a catalyst precursor into a reactor; bringing the liquid to be treated into a supercritical water state and converting it to a liquid to be treated. Introducing into the reactor such that alkali metal or alkaline earth metal is present; in the reactor, the liquid to be treated in the presence of an oxidizing agent and alkali metal or alkaline earth metal and in a supercritical water state is oxidized; The catalyst precursor is hydrothermally synthesized in a supercritical water state in the presence of an oxidant and an alkali metal or alkaline earth metal in a reactor, and has a metal acid salt. A catalyst formation step in which an in situ catalyst for supercritical water oxidation treatment is formed, wherein the catalyst formation step and the oxidative decomposition step are performed in concert, and the catalyst formed by the catalyst formation step Oxidative decomposition The above method, wherein the process is facilitated. The method of claim 1, wherein the catalyst precursor is selected from the group consisting of titanium group elements, group VIII elements, group VIIA elements, and group IIIB elements. The metal acid salt includes at least one alkali metal or alkaline earth metal selected from the group consisting of Na, K, Rb, Cs, Mg, Ca, Sr, Ba and Ra, a titanium group element, and a group VIII element. And at least one metal species selected from the group consisting of Group VIIA elements and Group IIIB elements. The method according to claim 1, wherein the metal acid salt is a titanate or a ferrate. The method according to any one of claims 1 to 4, further comprising a step of regenerating the catalyst precursor by dissolving and washing the in situ catalyst for supercritical water oxidation treatment formed in the reactor with subcritical water. Catalyst precursor regeneration comprising a step of regenerating a catalyst precursor by dissolving and washing the in situ catalyst for supercritical water oxidation treatment in the reactor formed by the method according to any one of claims 1 to 4 with subcritical water Method. A supercritical water oxidation treatment apparatus having a reactor for supercritical water oxidation treatment, comprising a catalyst precursor in the reaction vessel, and in the presence of an oxidizing agent and an alkali metal or an alkaline earth metal in the reactor, And the liquid to be treated in the supercritical water state is oxidized and decomposed, and in the reactor, the catalyst precursor is hydrothermally present in the presence of an oxidizing agent and an alkali metal or alkaline earth metal and in the supercritical water state. A supercritical water treatment apparatus characterized in that a supercritical water treatment in situ catalyst for synthesis comprising a metal acid salt is formed, and the oxidation and decomposition are promoted by the catalyst. 8. The apparatus of claim 7, wherein the catalyst precursor is selected from the group consisting of a titanium group element, a group VIII element, a group VIIA element, and a group IIIB element. The metal acid salt includes at least one alkali metal or alkaline earth metal selected from the group consisting of Na, K, Rb, Cs, Mg, Ca, Sr, Ba and Ra, a titanium group element, and a group VIII element. The device according to claim 7 or 8, comprising at least one metal species selected from the group consisting of: a group VIIA element; and a group IIIB element. The device according to claim 7, wherein the metal acid salt is a titanate or a ferrate. The apparatus according to any one of claims 7 to 11, further comprising means for regenerating the catalyst precursor by dissolving and washing the in situ catalyst for supercritical water oxidation treatment formed in the reactor with subcritical water. An in situ catalyst for supercritical water oxidation treatment comprising a metal acid salt hydrothermally synthesized in a supercritical water state in the presence of an alkali metal or an alkaline earth metal. The metal acid salt includes at least one alkali metal or alkaline earth metal selected from the group consisting of Na, K, Rb, Cs, Mg, Ca, Sr, Ba and Ra, a titanium group element, and a group VIII element. The catalyst according to claim 12, comprising at least one metal species selected from the group consisting of: a group VIIA element; and a group IIIB element. The catalyst according to claim 12 or 13, wherein the metal acid salt is a titanate or a ferrate.