JP5349930B2 - Method for oxidizing toluene - Google Patents

Description

  The present invention relates to a method for oxidizing toluene. That is, the present invention relates to an oxidation treatment method in which toluene is oxidized to benzaldehyde using a microreactor with a photocatalyst.

《Technical background》
For example, toluene (C ₆ H ₅ —CH ₃ ) is obtained by fractional distillation of coal tar, reforming of petroleum, distillation of coal gas light oil, etc., and is used as a raw material or solvent for various organic industrial substances. Yes.
Benzaldehyde (C ₆ H ₅ —CHO) is typically obtained by oxidizing toluene, and is used as a raw material for the synthesis of soap, other fragrances, pharmaceuticals, dyes and the like.

<Conventional technology>
The following methods are known as methods for obtaining benzaldehyde as a product by using toluene as a starting material and oxidizing it.
For example, a method of hydrolyzing benzal chloride obtained by chlorinating toluene, a method of directly oxidizing air with toluene using a molybdenum oxide catalyst, a method of oxidizing toluene with manganese dioxide in the presence of sulfuric acid, etc. are known. Yes.
However, industrially, it has been pointed out that any of the methods is complicated and the process is a multi-stage batch type, and the operation is complicated, the work is troublesome, and the cost is high.

Therefore, in order to cope with these problems, a method and an apparatus for oxidizing toluene to benzaldehyde simply and easily by using a microreactor have been proposed.
That is, it has also been proposed to use a microreactor with a photocatalyst and oxidize the supplied toluene to benzaldehyde based on the ultraviolet irradiation of the photocatalyst in the microchannel.
In addition, as a technique for supplying the target liquid to the microchannel of the microreactor with a photocatalyst and performing a reaction process such as oxidation as described above, for example, the technique disclosed in Patent Document 1 is disclosed.

《Information on prior art documents》
JP 2005-279595 A

By the way, as described above, a method and apparatus for obtaining a product by reacting a starting material by oxidation or the like using a microreactor has been as follows.
In other words, in this type of microreactor, the basic concept is to press-fit and supply a target liquid with high affinity to the photocatalyst titanium oxide.
Therefore, in the case of a starting material having a low affinity for titanium oxide, it is dissolved in an organic solvent such as a high affinity alcohol as a solute, and as a whole, a target solution having an affinity is added to the microchannel. The starting material was reacted to the product by press-fitting. This is exactly the case when the starting material is toluene with poor affinity.
However, since a large amount of organic solvent is used for the target solution in this way, the amount of toluene is reduced by that amount, and the problem of poor reaction efficiency has been pointed out.
That is, at the interface between the photocatalyst titanium oxide and the target solution, the concentration and ratio of toluene oxidized to benzaldehyde are reduced, and the oxidation reaction efficiency to benzaldehyde is poor. The poor production efficiency of the product relative to the starting material has been a problem.

In view of such a situation, the method for oxidizing toluene of the present invention has been made in order to solve the problems of the conventional examples.
A first object of the present invention is to propose a method for oxidizing toluene, which is excellent in reaction efficiency and secondly, which can be easily and easily realized.

The technical means described in the claims of the present invention for solving such a problem is as follows. First, claim 1 is as follows.
The method for oxidizing toluene according to claim 1 uses a microreactor with a photocatalyst to oxidize toluene to benzaldehyde. The photocatalyst is attached and coated on the flow path forming surface other than the ultraviolet irradiation surface of the micro flow path.
And in this microchannel, it becomes as follows.

In the microchannel, the toluenes are first press-fitted to form a laminar toluene layer, and a single laminar flow is formed from the entrance to the middle.
In the oxidation reaction step, at the interface between the toluene layer and the photocatalyst, the toluene is oxidized into benzyl cations by molecular diffusion based on the ultraviolet irradiation of the photocatalyst by the ultraviolet irradiation means, and the toluene is oxidized from the interface. Diffuses in the toluene layer.

The microchannel is formed by laminating water from the middle to form a laminar water layer, in contact with the poorly hydrophilic toluene layer, and from the middle toward the outlet. It becomes a two-layer flow with the toluene layer.
In the reaction step with water, at the interface between the toluene layer and the aqueous layer, the benzyl cations migrate from the toluene layer to the aqueous layer due to their hydrophilicity by molecular diffusion, and are reactive. It reacts with water in the aqueous layer based on being a cation rich in water to form benzyl alcohol, and diffuses from the interface into the aqueous layer.
Then, in the oxidation reaction step again, at the interface between the water layer and the photocatalyst, the benzyl alcohol is oxidized to the benzaldehyde by molecular diffusion based on the ultraviolet irradiation of the photocatalyst by the ultraviolet irradiation means. And diffusing from the interface into the aqueous layer.

Claims 2 and 3 are as follows.
The method for oxidizing toluene according to claim 2 is the method for oxidizing toluene according to claim 1, wherein the photocatalyst is atomized by ultraviolet irradiation at the interface between the toluene layer and the photocatalyst and at the interface between the aqueous layer and the photocatalyst. Electrons in the outer shell orbit of the structure are excited to form holes that are electron deficient vacancies, and thus the holes exhibit a strong oxidizing power.
The method for oxidizing toluene according to claim 3 is the method according to claim 2, wherein water is further oxidized at the interface between the water layer and the photocatalyst to generate OH radicals. Thus, the OH radical exhibits a strong oxidizing power.

<About the action>
Since the present invention comprises such means, the following is achieved.
(1) First, toluene is press-fitted into the micro flow path of the microreactor, and water is press-fitted and supplied from the middle.
(2) Then, ultraviolet rays are irradiated from the ultraviolet irradiation means, and holes are formed in the outer shell orbit of the photocatalyst adhered and coated on the microchannel.
(3) Therefore, at the interface between the toluene layer of the microchannel and the photocatalyst, toluene is oxidized into benzyl cations by molecular diffusion based on the oxidizing power of holes.
(4) The benzyl cations migrate from the toluene layer to the aqueous layer via the interface by molecular diffusion based on hydrophilicity. Since it is a highly reactive cation, it reacts with water in the aqueous layer by molecular diffusion at the interface, and is converted into benzyl alcohol.
(5) The benzyl alcohols are oxidized into benzaldehydes by molecular diffusion based on the oxidizing power of holes at the interface between the aqueous layer and the photocatalyst.
(6) At the interface between the water layer and the photocatalyst, the water in the water layer is oxidized by the holes of the photocatalyst to generate OH radicals. Therefore, also from this aspect, benzyl alcohols are oxidized to benzaldehydes by molecular diffusion based on the oxidizing power.
(7) In this oxidation treatment method, the above-described series of reaction treatment processes from toluenes proceed sequentially in the microchannel. This is due to the single-layer flow system of the toluenes layer and water from the middle. This is achieved for the first time by adopting a combination of the two laminar flow system that lays the layers.
(8) The oxidation reaction and the reaction with water in the reaction treatment process are performed quickly and reliably within a short time by molecular diffusion at the interface and over a wide contact area. Benzaldehydes can be efficiently obtained from the products.
(9) Now, the method for oxidizing toluene of the present invention exhibits the following effects.

<< First effect >>
First, it is excellent in reaction efficiency. In other words, in the toluene oxidation treatment method of the present invention, a single laminar flow method of a toluene layer and a two-layer flow method in which an aqueous layer runs along the way are used in combination for the micro flow path of the microreactor. Become.
As a result, a series of sequential reaction processes such as toluene → benzyl cation → benzyl alcohol → benzaldehyde proceed, but each reaction process is performed at the interface of laminar contact with a wide contact area. Done by molecular diffusion.
Thus, in the present invention, the product benzaldehyde can be efficiently obtained from the starting material toluene.
Compared to the case where toluene is used as a solute and dissolved in an organic solvent having a high affinity as in the conventional example of this kind using a microreactor, the present invention provides an oxidation reaction efficiency of toluene and Excellent production efficiency of benzaldehydes.

<< Second effect >>
Secondly, this is easily and easily realized. That is, in the toluene oxidation treatment method of the present invention, by adopting a single laminar flow method and a two-layer flow method from the middle for the microchannel of the microreactor with a photocatalyst, the oxidation reaction step, A sequential reaction treatment process proceeds, followed by a reaction step with water and then an oxidation reaction step again.
With such a simple configuration, the above-described effect of excellent first reaction efficiency can be easily realized. Like the above-mentioned conventional example, which follows a complicated and multi-stage batch process, the operation is not complicated and the work is not troublesome. In addition, benzaldehydes can be obtained from toluene.
As described above, the effects exerted by the present invention are remarkably large, such as all the problems existing in this type of conventional example are solved.

《About drawing》
Hereinafter, the method for oxidizing toluene of the present invention will be described in detail based on the best mode for carrying out the invention shown in the drawings.
1 to 3 are used to explain the best mode for carrying out the present invention. 1 is a side sectional view of an enlarged main part, and FIG. 1 (2) is a plan view. FIG. 2 is an exploded perspective view. FIG. 3 is an enlarged plan cross-sectional view of the main part.

<About Microreactor 1>
In the method for oxidizing toluene according to the present invention, the microreactor 1 is used to oxidize toluene to benzaldehyde. First, the microreactor 1 will be described.
The microreactor 1 of the oxidation treatment apparatus 2 includes a microchannel 3, a photocatalyst 4, and an ultraviolet irradiation means 5. To the micro flow path 3, toluene is press-fitted and water is press-fitted and supplied from the middle. The photocatalyst 4 is irradiated by the ultraviolet irradiation means 5 and exhibits oxidizing power.

Such a microreactor 1 will be further described in detail. The microreactor 1 includes a reactor including a micro flow path 3 having a micro-order fine structure. The micro flow path 3 has, for example, a flow path width of about 100 μm to 500 μm and a flow path depth of 25 μm to 100 μm. It consists of a degree.
The illustrated microreactor 1 is made of, for example, a three-layered (quartz) glass plate plate having a thickness of about 2 mm (in addition, a resin plate or a metal plate can be used if it is an inert material). The holder plates 7 and 8 have a sandwich structure in which they are densely stacked, covered and fixed.
In the main body plate 6, the micro flow path 3 is formed. In the illustrated example, the upper holder plate 7 is essentially transparent and light-transmitting because of the relationship with ultraviolet irradiation. The lower holder plate 8 may not be transparent.
The micro flow path 3 has a channel shape. In the illustrated example, the micro flow path 3 is linearly formed in the longitudinal direction of the main body plate 6 and reciprocated repeatedly in the short direction, and is continuously engraved and formed in a substantially zigzag shape and a meandering shape. Each bend is curved in a curved shape.

Then, toluene is press-fitted and supplied from the supply tank 9 through the pump and the fine tube 11 to the inlet of the microchannel 3. At the same time, to the micro flow path 3, water is press-fitted and supplied from the supply tank 12 through the pump 13 and the fine tube 11 through the inlet in the middle of the flow path.
The micro flow path 3 formed in the main body plate 6 has a semicircular cross section or a rectangular cross section with an upper surface, both side surfaces, a bottom surface and the like so as to form a flow path therein. In the illustrated example, the upper surface is an ultraviolet irradiation surface for transmitting ultraviolet rays, but the upper ultraviolet irradiation surface is opened and hermetically sealed with a higher holder plate 7. Except for such an ultraviolet irradiation surface, the micro flow path 3 formed in the main body plate 6 has the photo catalyst 4 attached to the flow path forming surfaces on both side surfaces and the bottom surface.
As the photocatalyst 4, titanium dioxide (titania) is typically used, and the particles are fixed and supported in a film shape by coating and sintering on the flow path forming surface together with metal fine particles and an adsorbent. . Metal oxides other than titanium dioxide and others can be used as the photocatalyst 4 as long as they can be photoexcited to exhibit a catalytic action and are chemically stable.
And the ultraviolet irradiation means 5 is opposingly arranged with respect to such a microchannel 3. FIG. The ultraviolet irradiation means 5 is disposed opposite to the micro flow path 3 of the main body plate 6 via a transparent upper holder plate 7.
As the ultraviolet irradiation means 5 that is a light source, a mercury lamp, black light, LED, or the like can be used. Therefore, ultraviolet rays (UV) having a wavelength for photoexcitation (photochemical reaction) of the photocatalyst 8 are irradiated. Specifically, medium wavelength ultraviolet rays of 240 nm to 280 nm are irradiated, but those that irradiate short wavelength ultraviolet rays or long wavelength ultraviolet rays are also used. Is possible.
The microreactor 1 is as described above.

<Toluenes and benzaldehydes>
The oxidation treatment method of the present invention uses such a microreactor 1 to oxidize starting materials and starting materials, toluene, into target materials and product, benzaldehydes. Then, next, these toluenes and benzaldehydes will be described.
Toluene (C ₆ H ₅ —CH ₃ ), which is a representative example of toluenes, is an aromatic hydrocarbon in which one hydrogen atom of benzene is substituted with a methyl group (CH ₃ ). From a colorless liquid hardly soluble in water It is known as a raw material and solvent for various organic industrial substances.
Benzaldehyde (benzaldehyde) (C ₆ H ₅ -CHO), which is a representative example of benzaldehydes (benzaldehydes), is the simplest aromatic aldehyde in which one hydrogen atom of benzene is substituted with an aldehyde group (CHO). It is a colorless liquid and is known as a synthetic raw material for fragrances, pharmaceuticals, agricultural chemicals, dyes, pigments and the like.

The present invention applies such toluene and other toluenes as starting materials and raw materials, and also applies benzaldehyde and other benzaldehydes as target substances and products.
A typical example of a combination of such a toluene as a starting material and a benzaldehyde as a product is as follows.
・ Toluene → Benzaldehyde ・ Parachlorotoluene → Parachlorobenzaldehyde ・ Orthochlorotoluene → Orthochlorobenzaldehyde ・ Orthofluorotoluene → Orthofluorobenzaldehyde ・ Orthocyanotoluene → Orthocyanobenzaldehyde ・ Metachlorotoluene → Metachlorobenzaldehyde・ Metafluorotoluene → Metafluorobenzoaldehyde ・ Metacyanotoluene → Metacyanobenzaldehyde ・ Parachlorotoluene → Parachlorobenzoaldehyde ・ Parafluorotoluene → Parafluorotoluenealdehyde ・ Paracyanotoluene → Paracyanobenzaldehyde ・ Fluorotoluene → Para Fluorobenzaldehyde ・ Cyanotoluene → Cyanobenzaldehyde

Further, in the present specification, toluene includes xylene (C ₆ H) in which one hydrogen atom of benzene is substituted with one methyl group (CH ₃ ) and two hydrogen atoms of benzene are each substituted with a methyl group. ₄ - even _{(CH 3) 2)} compound, including. At the same time, benzaldehydes include aldehydes in which two hydrogen atoms of benzene are substituted with aldehyde groups (CHO).
Typical examples of combinations of such starting materials and product materials are as follows.
-Para-xylene → terephthalaldehyde / ortho-xylene → phthalaldehyde The starting toluenes and the product benzaldehydes are like this.

<About laminar flow and oxidizing power>
In the oxidation method using the microreactor 1 of the present invention, a laminar flow is formed in the microchannel 3 and the toluenes are oxidized. Next, the laminar flow and the oxidizing power will be described.
First, in the micro flow path 3 of the microreactor 1, toluene is press-fitted to form a laminar flow toluene layer 14, and water is press-fed from the middle to form a laminar flow water layer 15. Thus, it is aligned with the toluene layer 14 and contacts at the interface 16. The toluenes in the toluene layer 14 have poor hydrophilicity and do not intersect with the water layer 15, and both layers form an interface 16.
That is, toluene or other toluene that is press-fitted and supplied from the supply tank 9 to the microchannel 3 flows in the microchannel 3 from its inlet to its outlet, forming a laminar toluene layer 14. Further, the water that is press-fitted and supplied from the supply tank 12 to the micro flow path 3 flows through the micro flow path 3 from the middle toward the outlet, forming a laminar water layer 15. And this toluenes layer 14 and the water layer 15 along this contact | abut at the interface 16 (refer FIG. 3).
Regarding laminar flow, it is as follows. The microchannel 3 has a very small channel width and is supplied with toluene and water supplied by the pumps 10 and 13, so that the Reynolds number (the dimensionless number that is the ratio of the inertial force to the frictional force due to viscosity). ) Is small and a laminar flow is formed. The viscosity of the toluene layer 14 and the water layer 15 flowing through the micro flow path 3 is dominant, and the laminar flow is slid without slipping into the turbulent flow.
In a state where the contact area per unit volume (specific surface area) is extremely wide, the toluene layer 14 and the water layer 15 are in contact with each other at the interface 16 and are in contact with the photocatalyst 4 at the interfaces 17 and 18. However, it flows as a laminar flow (see FIG. 3).

In addition, ultraviolet rays are irradiated from the ultraviolet irradiation means 5 to the toluene layers 14 and the water layer 15 flowing through the micro flow path 3 and the photocatalyst 4 coated on the flow path forming surface of the micro flow path 3 in this way. The
Then, at the interface 17 between the toluene layer 14 and the photocatalyst 4 and at the interface 18 between the water layer 15 and the photocatalyst 4, the photocatalyst 4 is excited by ultraviolet irradiation to excite electrons in the outer shell orbit of the atomic structure. Holes that are electron-deficient vacancies are formed. Holes exert a strong oxidizing power.
In addition to this, at the interface 18 between the water layer 15 and the photocatalyst 4, water is further oxidized by the holes of the photocatalyst 4, thereby generating OH radicals. OH radicals exhibit extremely strong oxidizing power.
Such an oxidizing power, that is, a photo-oxidation effect is further promoted by using a promoter such as platinum (Pt).
The laminar flow and oxidizing power are as described above.

<Oxidation treatment of toluenes>
Next, the oxidation treatment of toluene will be described. In the oxidation treatment apparatus 2 and the oxidation treatment method, the oxidation treatment and reaction treatment process of toluene sequentially proceed in the micro flow path 3 of the microreactor 1.
That is, the oxidation treatment and reaction treatment process such as toluenes → benzyl cations → benzyl alcohols → benzaldehydes, etc. proceed sequentially and sequentially in the microchannel 3 in time.
By the way, toluene has poor affinity for titanium oxide of the photocatalyst 4. Therefore, it is preferable that the microchannels 3 on which the photocatalyst 4 is attached and coated in advance are lightly wetted with an alcohol such as ethanol so that the toluene can be easily adapted to the microchannels 3 and flow easily.

The reaction treatment process will be further described in detail. In the microchannel 3, first, at the interface 17 between the toluene layer 14 and the photocatalyst 4, based on the oxidizing power of holes generated based on the irradiation of the photocatalyst 4 with ultraviolet rays, molecular diffusion causes the toluene layer 14 to Toluenes are oxidized to benzyl cations. Benzyl cations diffuse from the interface 17 into the toluene layer 14.
Then, at the interface 16 between the toluene layer 14 and the aqueous layer 15 introduced from the middle, due to molecular diffusion, the benzyl cations in the toluene layer 14 are changed from the toluene layer 14 to the aqueous layer based on their hydrophilicity. Move to 15. Along with the migration, the benzyl cations react with the water in the aqueous layer 15 to form benzyl alcohol based on the fact that they are highly reactive cations. The benzyl alcohol diffuses from the interface 16 into the aqueous layer 15.
Then, at the interface 18 between the water layer 15 and the photocatalyst 4, the benzyl alcohol in the water layer 15 is formed by molecular diffusion based on the holes generated based on the ultraviolet irradiation of the photocatalyst 4 and further on the oxidizing power of OH radicals. Are oxidized to benzaldehyde or other benzaldehydes. Benzaldehyde diffuses from the interface 18 into the water layer 15.

The series of oxidation treatment and reaction treatment processes described above are performed by molecular diffusion at the interfaces 16, 17 and 18, respectively.
That is, in the oxidation treatment apparatus 2 and the oxidation treatment method, the oxidation treatment is performed by laminating the interface 17 between the toluene layers 14 and the photocatalyst 4 that have been press-fitted and laminar, and the laminar flow that has been press-fitted and fed. This is performed by molecular diffusion at the interface 18 between the water layer 15 and the photocatalyst 4. Further, the transition to water and the reaction treatment with water are performed by molecular diffusion at the interface 16 between the toluene layer 14 and the water layer 15.
The hydrodynamics between the toluene layer 14 and the aqueous layer 15 flowing in a laminar flow through the microchannel 3 and at the interfaces 16, 17 and 18 between these and the photocatalyst 4, as in the case of turbulence, There is almost no mass transfer in the channel width direction due to a strong force, and there is no energy loss for that. Mass transfer in the channel width direction is mainly molecular diffusion, and mass transfer due to hydrodynamic force works only in the flow direction. Both the oxidation treatment and the reaction treatment process are performed by molecular diffusion between substances and in a wide contact area. Through the interfaces 16, 17, and 18, the molecules of the reaction target chemical species interact and react with each other, thereby maximizing the reaction efficiency.
In the figure, reference numeral 19 denotes a recovery tank. In the recovery tank 19, unprocessed starting materials, raw material toluenes, water introduced in the middle, and target substances are passed from the microchannel 3 through the microtube 11. , The product benzaldehydes and the like are discharged and recovered in a multi-layered manner. In addition, 20 in FIG. 3 shows the flow direction of a laminar flow.
The oxidation treatment of toluene is performed in this way.

<< Reaction in microchannel 3: Part 1 >>
Next, the oxidation treatment and reaction treatment process in the micro flow path 3 of the microreactor 1 will be described more specifically and in detail based on the reaction formula and the like (mainly refer to FIG. 3). Here, the oxidation process to benzaldehyde is demonstrated about toluene which is a typical example of toluene.
In the microchannel 3, first, outer electrons in the outer shell orbit (steady orbit) on the titanium dioxide (TiO ₂ ) surface of the photocatalyst 4 by irradiation with ultraviolet rays (obtained as photon hν, hereinafter the same) from the ultraviolet irradiation means 5. (E ⁻ ) is excited and moved from the outer shell orbit to the excitation orbit. As a result, holes (hole ⁺ ), which are electron vacancies that are lost due to escape of electrons, are formed on the outer shell orbit of the surface of the photocatalyst 4. See the reaction formula of the following chemical formula 1.
The holes thus formed have a property of drawing out electrons from other substances and filling the electron vacancies, that is, a strong oxidizing power (electron capturing power). When the ultraviolet irradiation is eliminated, the promoted electrons return from the excitation orbit to the outer orbit. The reaction formula of the following chemical formula 1 is considered to be a two-photon (2hν) reaction, and two holes (2hole ⁺ ) are formed.
Now, the holes (hole ⁺ ) of the photocatalyst 4 generated in this way extract electrons (e ⁻ ) from the toluene in the toluene layer 14 in contact with the interface 17. Therefore, the starting material, the starting material toluene (C ₆ H ₅ —CH ₃ ) is first oxidized to the benzyl cation (C ₆ H ₅ —CH ₂ ⁺ ) by the oxidation reaction of the following chemical formula _2. .
This oxidation reaction is performed based on molecular diffusion at the interface 17, and the generated benzyl cation is diffused from the interface 17 to the toluene layer 14.

<< Reaction in the microchannel 3: Part 2 >>
The benzyl cation in the toluene layer 14 thus produced is hydrophilic. Therefore, the toluene layer 14 shifts to the water layer 15 based on molecular diffusion at the interface 16.
At the same time, the benzyl cation (C ₆ H ₅ —CH ₂ ⁺ ) is a highly reactive cation and reacts with water (H ₂ O) in the aqueous layer 15 based on molecular diffusion at the interface 16 to react with the benzyl cation. It is an alcohol _{(C 6 H 5 -CH 2 -OH} ) of. See the reaction formula of the following chemical formula 3.
The benzyl alcohol generated at the interface 16 is diffused from the interface 17 to the aqueous layer 15.

<< Reaction in microchannel 3: Part 3 >>
The benzyl alcohol in the aqueous layer 15 thus generated is oxidized by the holes generated based on the irradiation of the photocatalyst 4 with ultraviolet rays, as described above.
That is, the holes (hole ⁺ ) of the photocatalyst 4 generated by the reaction formula of the following chemical formula 4 extract electrons from the benzyl alcohol of the water layer 15 that is in contact with the interface 18. Accordingly, benzyl alcohol (C ₆ H ₅ —CH ₂ —OH) is oxidized to a benzaldehyde (C ₆ H ₅ —CHO), which is a benzaldehyde, by a photo-oxidation reaction of the following reaction formula 5:
This oxidation reaction is performed based on molecular diffusion at the interface 18, and the generated target substance and the generated substance benzaldehyde are diffused from the interface 18 into the aqueous layer 15, and finally into the recovery tank 19. Collected.

<< Reaction in the microchannel 3: Part 4 >>
Now, when the above reaction formulas are summarized, a general reaction formula of the following chemical formula 6 is obtained. That is, when the reaction formulas of the chemical formula 1, the chemical formula 2, the chemical formula 3, the chemical formula 4, the chemical formula 5, etc. are added together, the reaction formula of the following chemical formula 6 is obtained.
Then, protons (H ⁺ ) in the reaction formula of the following chemical formula 6 are converted into hydrogen molecules (H ₂ ) by the subsequent discharge of the electrons (4e ⁻ ) from which the holes of the photocatalyst 4 are extracted. . See the reaction formula of the following chemical formula 7.
Therefore, when the overall reaction formula of Chemical Formula 6 is further added and summarized, the following general reaction formula of Chemical Formula 8 is obtained.

<< Reaction in the microchannel 3: Part 5 >>
By the way, at the interface 18 between the water layer 15 and the photocatalyst 4, the water in the water layer 15 is oxidized by the holes of the photocatalyst 4 to generate OH radicals.
That is, for example, holes (hole ⁺ ) generated as in the reaction formula of Chemical Formula 4 on the one hand oxidize benzyl alcohol in the aqueous layer 15 in contact with the interface 18 to benzaldehyde on the other hand. Then, electrons (e ⁻ ) are extracted from the water (H ₂ O) of the water layer 15 and oxidized, thereby radical splitting into protons (H ⁺ ) and OH radicals (.OH). See the reaction formula of the following chemical formula 9.
As is well known, the OH radical, that is, the hydroxy radical generated in this manner has a strong oxidizing power (electron-trapping power).
Therefore, the OH radicals extract electrons from the benzyl alcohol in the water layer 15 in contact with the interface 18. Accordingly, in addition to the reaction formula of Chemical Formula 5, benzyl alcohol (C ₆ H ₅ —CH ₂ —OH) is oxidized to benzaldehyde (C ₆ H ₅ —CHO) based on the oxidation reaction from this aspect. . See the reaction formula of the following chemical formula 10.
Then, when the reaction formula of this chemical formula 9 and the reaction formula of chemical formula 10 are added together, a general reaction formula of the following chemical formula 11 is obtained. That is, if the OH radical production reaction is made latent, the following reaction formula 11 is obtained.

Then, with respect to the general reaction formula of the chemical formula 11, the generation of holes (2hole ⁺ ) in the chemical formula of the chemical formula 9 and the hydrogenation of proton (2H ⁺ ) in the chemical formula of the chemical formula 11 are considered. Then, the general reaction formula of the following chemical formula 12 is obtained.
That is, protons are converted into hydrogen molecules by the reaction of generating 2hν → 2hole ⁺ holes (see, for example, the reaction formula of Chemical Formula 4) and the post-discharge of the electrons (2e ⁻ ) extracted by the holes of the photocatalyst 4. When the above reaction (for example, refer to the reaction formula of the chemical formula 7) is added to the chemical formula of the chemical formula 11, the general reaction formula of the following chemical formula 12 is obtained.
Regarding toluene, which is a representative example of toluene, the details of the reaction treatment process in the micro flow path 3 of the microreactor 1 are as described above.

《Action etc.》
The method for oxidizing toluene of the present invention is configured as described above. Therefore, it becomes as follows.
(1) First, toluene or other toluenes are injected and supplied to the micro flow path 3 of the microreactor 1 and water is injected and supplied from the middle.

(2) Then, the ultraviolet ray (hν) is irradiated from the ultraviolet irradiation means 5 to the microchannel 3. Therefore, the photocatalyst 4 attached to the microchannel 3 is irradiated with ultraviolet rays, and the electrons (e ⁻ ) in the outer shell orbit of the atomic structure are excited, and holes (hole ⁺ ) that are electron deficient vacancies are generated. (See the reaction formulas of Chemical Formula 1 and Chemical Formula 4).

(3) Therefore, at the interface 17 between the toluene layer 14 and the photocatalyst 4 of the microchannel 3, toluene (C ₆ H ₅ —CH ₃ ) or other toluenes are converted to benzyl cations (C ₆ H ₅ —CH _2). ⁺ ), Or other benzyl cations are oxidized by molecular diffusion based on the oxidizing power of holes (see the reaction formula of Chemical Formula 2).

(4) Then, the benzyl cation or other benzyl cations generated in this manner in the toluene layer 14 is converted from the toluene layer 14 to the water layer via the interface 16 by molecular diffusion based on its hydrophilicity. Move to 15.
Since the benzyl cation or other benzyl cations are highly reactive cations, they react with the water (H ₂ O) in the aqueous layer 15 by molecular diffusion at the interface 16 to cause benzyl alcohol (C ₆ H ₅ —CH ₂ —OH), or other benzyl alcohols (see the reaction formula of Chemical Formula 3).

(5) Then, the benzyl alcohol or other benzyl alcohols in the aqueous layer 15 thus generated are subjected to molecular diffusion based on the oxidizing power of holes at the interface 18 between the aqueous layer 15 and the photocatalyst 4. It is oxidized to benzaldehyde (C ₆ H ₅ —CHO) or other benzaldehydes (see the reaction formula of Chemical Formula 5 above).
In this way, toluene or other toluenes are oxidized to benzaldehyde or other benzaldehydes (see the general reaction formulas of Chemical Formula 6 and Chemical Formula 8).

(6) In addition, at the interface 18 between the water layer 15 and the photocatalyst 4, the water in the water layer 15 is oxidized by the holes of the photocatalyst 4 to generate OH radicals (.OH) (described above) (See reaction formula 9).
Therefore, in addition to the place described in (5) above, benzyl alcohol or other benzyl alcohols are converted into benzaldehyde or other benzaldehydes by molecular diffusion based on the oxidizing power of this OH radical. Oxidized (see reaction formula of chemical formula 10 above, and general reaction formulas of chemical formulas 11 and 12).

(7) In the oxidation treatment method of the present invention, in the micro flow path 3 of the microreactor 1, the series of oxidation treatments and reaction treatment processes from toluene described above progresses sequentially, and benzaldehydes are produced. The
And these are realized by the following. That is, with respect to the micro flow path 3, the above-described reaction treatment process is achieved by adopting a combination of a single laminar flow method of the toluene layer 14 and a two-layer flow method in which the water layer 15 is placed along the toluene layer 14 from the middle. Has been realized for the first time.
In particular, the benzyl cations, which are intermediate products of the reaction treatment process in the toluene layer 14, are moved from the toluene layer 14 to the water layer 15 side along the toluene layer 14 from the middle. After that, it can be realized for the first time by proceeding with the reaction treatment process toward benzaldehydes.

(8) The oxidation reaction and the reaction with water in this reaction treatment process are carried out by the interface 17 between the toluene layer 14 and the photocatalyst 4, the interface 18 between the aqueous layer 15 and the photocatalyst 4, and the toluene layer 14 respectively. This is performed by molecular diffusion at the interface 16 with the water layer 15 or the like.
That is, in this toluene oxidation treatment method, each reaction treatment process is performed quickly and reliably in an extremely short time based on the molecular diffusion action between the molecules via the interfaces 16, 17, and 18. . Moreover, at the interfaces 16, 17, and 18, the contact area per unit volume is performed in a very wide state.
This oxidation treatment method is based on such molecular diffusion and a wide contact area, so that the target substance and the product benzaldehyde can be obtained efficiently and efficiently from the starting materials and raw materials of toluene. become.
The OH radical described above (see the reaction formula of Chemical Formula 9) has an extremely short existence time and an instantaneous and ultra-short lifetime, but based on the rapid molecular diffusion and the large contact area described above, The oxidation reaction (see the above reaction formula 10) is reliably performed as expected. Further, there is no possibility that the OH radical reacts to generate other secondary by-products. Therefore, also from this aspect, the reaction yield and reaction efficiency are excellent.
The operation of the present invention is as described above.

The method for oxidizing toluene according to the present invention will be described for the best mode for carrying out the invention. And (1) figure is a sectional side view of the principal part which expanded, (2) figure is a top view. It is an exploded perspective view for explaining the best mode for carrying out the invention. It is a plane sectional view of an enlarged principal part for explanation of the best mode for carrying out the invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Microreactor 2 Oxidation processing device 3 Micro flow path 4 Photocatalyst 5 Ultraviolet irradiation means 6 Main body plate 7 Holder plate 8 Holder plate 9 Supply tank 10 Pump 11 Fine tube 12 Supply tank 13 Pump 14 Toluene layers 15 Water layer 16 Interface 17 Interface 18 Interface 19 Recovery tank 20 Flow direction

Claims (3)

A method of oxidizing toluene to benzaldehyde using a microreactor with a photocatalyst, wherein the photocatalyst is adhered and coated on a flow path forming surface other than the ultraviolet irradiation surface of the micro flow path. And
In the microchannel, first, the toluenes are press-fitted to form a laminar toluene layer, and a single laminar flow is formed from the entrance to the middle.
In the oxidation reaction step, at the interface between the toluene layer and the photocatalyst, the toluene is oxidized into benzyl cations by molecular diffusion based on the ultraviolet irradiation of the photocatalyst by the ultraviolet irradiation means, and the toluene is oxidized from the interface. Diffuses into the toluene layer,
The microchannel is formed by laminating water from the middle to form a laminar water layer, in contact with the poorly hydrophilic toluene layer, and from the middle toward the outlet. A two-layer flow with the toluene layer,
In the reaction step with water, at the interface between the toluene layer and the aqueous layer, the benzyl cations migrate from the toluene layer to the aqueous layer due to their hydrophilicity by molecular diffusion, and are reactive. Reacting with water in the aqueous layer based on being a cation rich in benzyl alcohol, and diffusing from the interface into the aqueous layer,
Then, in the oxidation reaction step again, at the interface between the water layer and the photocatalyst, the benzyl alcohol is oxidized to the benzaldehyde by molecular diffusion based on the ultraviolet irradiation of the photocatalyst by the ultraviolet irradiation means. And diffusing into the aqueous layer from the interface. The method for oxidizing toluene according to claim 1, wherein the interface between the toluene layer and the photocatalyst and the interface between the aqueous layer and the photocatalyst are as follows:
The photocatalyst is characterized in that electrons in the outer orbital of the atomic structure are excited by ultraviolet irradiation to form holes that are electron-deficient vacancies, and the holes exhibit a strong oxidizing power. And a method for oxidizing toluene. The method for oxidizing toluene according to claim 2, further comprising: at the interface between the aqueous layer and the photocatalyst;
A method for oxidizing toluene, characterized in that water is oxidized by holes of the photocatalyst to generate OH radicals, and the OH radicals exhibit a strong oxidizing power.

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