JP2021069996A - Catalyst for voc treatment, voc treatment apparatus and voc treatment method - Google Patents

Abstract

To provide a catalyst for VOC treatment that has acid resistance and can be used for a long time even in the treatment of a halogen VOC.SOLUTION: There is provided a catalyst for VOC treatment, said catalyst being obtained by having the surface of a carrier, which is mainly composed of silicon carbide (SiC), support a composite oxide of cobalt (Co) and cerium (Ce).SELECTED DRAWING: Figure 1

Description

The present invention relates to a VOC treatment catalyst having acid resistance, a VOC treatment apparatus having the catalyst, and a VOC treatment method.

Exhaust gas containing organic substances emitted from factories, etc. has a bad influence on the living environment and causes health hazards and foul odor complaints. For example, volatile organic compounds (Volatile Organic Compounds: hereinafter referred to as "VOC") emitted from painting factories, printing factories, chemical manufacturing processes, etc., ammonia compounds emitted from leather factories, urine processing factories, etc., and coatings. Some tars are discharged from factories and restaurants. Many of these compounds are harmful to the human body and the natural environment.

Various VOC treatment methods such as direct combustion method, catalytic combustion method, physicochemical adsorption method, biological treatment method, and plasma method have been proposed. Among these, the catalytic combustion method is used for equipment and maintenance. Is widely used because it is easy to use.

In the catalyst combustion method, precious metals such as platinum and palladium have been conventionally used as catalysts, but it is difficult to keep costs down because precious metals are expensive, and the development of alternative materials has been promoted.

So far, the applicants have proposed a metal oxide catalyst containing cerium (Ce) and cobalt (Co) as main components supported on a cordierite substrate (Patent Documents 1 and 2).

Patent No. 5423320 Patent No. 5717491 Re-table 2014/157721 Japanese Unexamined Patent Publication No. 2018-126738

When VOCs are treated by the catalytic combustion method, in the decomposition of organic compounds composed only of carbon (C), oxygen (O), hydrogen (H) such as toluene, xylene, butanol, ethyl acetate, after complete combustion, Since only carbon dioxide (CO ₂ ) and water (H ₂ O) are produced, it is unlikely to adversely affect the catalyst. However, when a halogen-based organic compound containing chlorine, for example, dichloromethane (methylene chloride), chloroethylene, or the like is to be treated, hydrogen chloride (changes to hydrochloric acid) is generated by combustion.

Therefore, in the conventional catalyst using metallic platinum using an alumina carrier as a catalyst component, there is a problem that platinum chloride appears and the catalytic activity is lowered. Furthermore, the carrier alumina also lost its strength due to erosion by hydrochloric acid and had a phenomenon of shape collapse, and could not be used as an effective catalyst. Further, the catalysts of Patent Documents 1 and 2 also have a problem that the catalyst is deteriorated due to the elution of the carrier due to the strong acidity and the aggregation and peeling of the catalyst components accompanying the elution.

The present invention has been made in view of the above circumstances, and is a VOC treatment catalyst which has acid resistance and can be used for a long period of time even in the treatment of halogen-based VOCs, and a VOC treatment apparatus having the catalyst. , A subject is to provide a VOC processing method.

In order to solve the above problems, in the VOC treatment catalyst of the present invention, a composite oxide of cobalt (Co) and cerium (Ce) is supported on the surface of a carrier containing silicon carbide (SiC) as a main component. It is characterized by that.

The VOC processing apparatus of the present invention is characterized by having the VOC processing catalyst and an energizing device for the VOC processing catalyst.

The VOC processing method of the present invention is a VOC processing method using the VOC processing device, and is characterized by including a step of energizing and heating the carrier of the VOC processing catalyst by the energizing device.

Since the catalyst for VOC treatment of the present invention has acid resistance, deterioration of the catalyst due to halogen-based VOC can be suppressed. Therefore, in factories and the like where halogen-based VOCs are generated, which is difficult to deal with with existing platinum catalysts and the like, it becomes possible to perform treatment by a catalyst combustion method.

According to the VOC processing device and the VOC processing method of the present invention, the VOC can be decomposed by utilizing the self-heating ability of the SiC carrier by directly energizing and heating the SiC carrier from the energizing device. Therefore, the external heating device can be omitted, and the device can be downsized and the processing cost can be reduced.

It is an electron micrograph of a Co, Ce oxide supported on a SiC carrier. It is a figure which showed the outline of the catalyst acceleration deterioration apparatus. It is a figure which showed the experimental result in the catalyst acceleration deterioration test apparatus. It is a schematic diagram which showed the deterioration suppression mechanism of a catalyst on a carrier surface. It is a figure which showed the decomposition experiment result (SV 22000h-1, each VOC concentration 1000ppm) of various chlorine-based VOCs using a Co, Ce oxide / SiC catalyst. It is a figure which showed the decomposition experiment result (SV 10000h-1, each VOC concentration 2000ppm) of various chlorine-based VOCs using a Co, Ce oxide / SiC catalyst, and a platinum-supported alumina catalyst. It is a photograph which showed the state of the catalyst (platinum-supported alumina catalyst, Co, Ce oxide / cordierite catalyst, Co, Ce oxide / SiC catalyst after exposure to hydrochloric acid.

The present inventors easily use silicon carbide (SiC) as a main component in the composite oxide (cobalt-cerium-based composite oxide) of cobalt (Co) and cerium (Ce) proposed in Patent Documents 1 and 2, etc. The present invention has been completed by obtaining a novel finding that it adheres to a base material. SiC is a material having poor wettability and high temperature resistance, and is known to have a substance that is difficult to adhere to (has a repellent property). Therefore, it was unpredictable that the cobalt-cerium-based composite oxide would adhere to the SiC base material.

Hereinafter, an embodiment of the VOC treatment catalyst, the VOC treatment apparatus, and the VOC treatment method of the present invention will be described.

Examples of the VOC to be the target of the VOC treatment catalyst of the present invention include one or more of toluene, acetaldehyde, formaldehyde, benzene, xylene, ethyl acetate, dichloromethane (methylene chloride), chloroethylene and the like. can do.

In the catalyst for VOC treatment of the present invention, a composite oxide of cobalt (Co) and cerium (Ce) (cobalt-cerium-based composite oxide) is supported on the surface of a carrier containing silicon carbide (SiC) as a main component. There is.

The cobalt-cerium-based composite oxide is not particularly limited, but Patent Documents 3 and 4 can be referred to.

As an example, the catalyst for VOC treatment is
(A) Cobalt oxide particles having an average particle diameter of 0.8 to 2.0 μm are mixed with a salt or compound capable of producing cobalt ions, a salt or compound capable of producing cerium ions, and water to prepare a catalyst immersion liquid. Process,
It can be produced by a method including (B) a step of immersing a carrier containing silicon carbide (SiC) as a main component in the obtained catalyst immersion liquid, and (C) a step of calcining the carrier after the immersion treatment. As a result, catalyst particles (cobalt-cerium-based composite oxide) are supported on the SiC carrier. The catalyst particles are covered with cobalt oxide having a cobalt ion as a precursor and cerium oxide having a cerium ion as a precursor around cobalt oxide particles having an average particle diameter of 0.8 to 2.0 μm. Here, the average particle size means the particle size (d0.5) at an integrated value of 50% in the particle size distribution obtained by the laser diffraction method. Further, "the circumference of the cobalt oxide particles is covered with the cobalt oxide and the cerium oxide" means that the cobalt oxide and the cerium oxide are formed on the surface of the cobalt oxide particles. Therefore, the catalyst particles include cobalt oxide particles having an average particle diameter of 0.8 to 2.0 μm, cobalt oxide having cobalt ion as a precursor, and cerium oxide having cerium ion as a precursor. ing.

The catalyst particles may be covered with a copper oxide having a copper ion as a precursor, in addition to the cobalt oxide and the cerium oxide, around the cobalt oxide particles. That is, the catalyst particles are further composed of a copper oxide having a copper ion as a precursor, and the cobalt oxide, the cerium oxide, and the copper oxide are formed on the surface of the cobalt oxide particles. You may be. The supported catalyst may have a clay mineral mainly composed of a composite silicate in order to improve the dispersibility of the catalyst particles, or may have a structure in which the catalyst particles are dispersed.

Cobalt oxide particles include various cobalt compounds such as inorganic acid salts such as carbonates, nitrates, sulfates and chlorides, organic compounds such as alcoholates, carboxylates and complex salts, calcined products such as organic salts, and dry products. May be. Of these, a compound prepared by calcining a compound using a carbonate as a precursor at a low temperature of 250 to 400 ° C. in the air is preferable. Further, it is also preferable that the cobalt oxide particles are pulverized within the range of an average particle diameter of 0.8 to 2.0 μm. The pulverization treatment may be a dry pulverization treatment or a wet pulverization treatment, and the treatment method is not limited. For example, the pulverization treatment may be performed using a dry jet mill, or the pulverization treatment may be performed by a dry bead mill method, a wet rotary ball mill method, or the like. When the average particle size of the cobalt oxide particles is less than 0.8 μm, the cobalt oxide particles tend to agglomerate with each other, which causes a decrease in the specific surface area under heating and a decrease in activity, which is not preferable. On the other hand, if it exceeds 2.0 μm, the adhesion area with the carrier is small and the peeling is easy, which is not preferable. From this point of view, in order to obtain a supported catalyst that does not easily decrease in activity, has good durability, and has good peelability, and has a good balance between durability and peelability, the average particle size of the cobalt oxide particles should be set. The range of 0.8 to 2.0 μm is preferable.

Then, the cobalt ion and cerium ion in the present invention are formed as cobalt and cerium being water-soluble as a salt or a compound. For example, nitrates, sulfates and the like. Copper ions may coexist with such cobalt ions and cerium ions. In the supported catalyst produced in the coexistence of copper ions, the cobalt oxide particles are covered with a copper oxide having a copper ion as a precursor in addition to the cobalt oxide and the cerium oxide. It is more preferable that the copper ion coexists with the cobalt ion and the cerium ion so that the oxide mass ratio of the catalyst particles is in the range of 0.1 to 30% by mass. Thereby, a supported catalyst having better catalytic performance can be obtained.

The carrier used in the present invention has various shapes containing silicon carbide (SiC) as a main component. Specifically, a ball-shaped or honeycomb-shaped shape can be exemplified. Further, as the carrier, a porous structure having pores having a diameter of about 5 μm to 50 μm on the surface can also be adopted.

As a more specific method for producing a catalyst for VOC treatment, for example, cobalt oxide particles having an average particle diameter of 0.8 to 2.0 μm are used as a salt or compound capable of producing cobalt ions, or a salt or compound capable of producing cerium ions. , And mix with water to prepare a catalytic immersion solution. If necessary, a catalyst dipping solution may be prepared by mixing salts and compounds capable of producing copper ions and clay minerals mainly composed of complex silicates such as kaolin and activated clay. Next, this is immersed in a SiC carrier, dehydrated and then fired. By this firing, cobalt ions and cerium ions are each converted into oxides. When the catalyst immersion liquid contains copper ions, the copper ions are also converted into oxides by this firing.

In the VOC treatment catalyst of the present invention, (i) cobalt oxide particles having an average particle diameter of 0.8 to 2.0 μm, (ii) cobalt oxide having cobalt ions as a precursor, and (iii) cerium ions as precursors. The mass ratio of the cerium oxide to be used is not particularly limited, but (i): 20 to 50% by mass, (ii): 6 to 12% by mass, and (iii): 39 to 66% by mass are taken into consideration. The firing temperature is not particularly limited, but 200 to 500 ° C. is considered. The amount carried on the SiC carrier can also be appropriately determined in consideration of the type of VOC to be used for the catalyst, treatment conditions, etc., but in general, the mass ratio is 10 with respect to the SiC carrier. A range of ~ 30% by weight is preferably considered.

When the VOC treatment catalyst of the present invention is used to decompose the VOC contained in the gas phase, the gas containing the VOC is mixed with the VOC treatment catalyst of the present invention at 150 ° C. to 350 ° C., preferably 200 ° C. to 300 ° C. You just have to make contact.

In the VOC treatment catalyst of the present invention, the carrier is composed of silicon carbide (SiC), and the catalyst has acid resistance due to the synergistic effect of the SiC and the Co and Ce catalysts. Therefore, the catalyst for VOC treatment of the present invention can be used for a long period of time because the deterioration of the catalyst performance due to hydrogen chloride, sulfur oxides, etc. generated by the decomposition of the halogen-based VOC is suppressed. The generated hydrogen chloride and sulfur oxides can be removed by performing a separate water treatment or the like.

According to the VOC treatment catalyst of the present invention, the catalyst combustion type can be applied at a VOC treatment site such as a factory where halogen-based VOCs are generated, which was difficult to deal with with the existing platinum catalyst. This is expected to contribute to revitalizing the market for environmental catalysts and exhaust gas treatment equipment, improving the working environment, and improving the living environment.

Further, the VOC processing apparatus of the present invention includes the above-mentioned VOC processing catalyst of the present invention and an energizing device for the VOC processing catalyst. The VOC treatment method of the present invention includes a step of bringing the gas containing VOC into contact with the VOC treatment catalyst, and a step of energizing and heating the carrier of the VOC treatment catalyst by an energizing device.

By directly energizing and heating the SiC carrier of the VOC treatment catalyst from the energizing device, the VOC can be decomposed by immediately raising the temperature to a predetermined temperature by utilizing the self-heating ability of the SiC carrier. Therefore, the external heating device can be omitted, and the device can be downsized and the processing cost can be reduced.

The VOC treatment catalyst, VOC treatment apparatus, and VOC treatment method of the present invention are not limited to the above embodiments.

Hereinafter, the present invention will be described together with Examples, but the present invention is not limited to the following Examples.

<Example 1> Preparation of catalyst As the method for producing the catalyst, the method devised by the present inventors (Patent Document 2) was referred to. Specifically, cobalt carbonate was calcined in air at a constant temperature in the range of 300 ° C. to 500 ° C. for 5 hours, and then pulverized by a jet mill method. Distilled water, cobalt nitrate, cerium nitrate and the like were added to the pulverized cobalt oxide and mixed well with stirring to prepare a cobalt-cerium-based precursor solution. A carrier catalyst carrying a cobalt-cerium-based composite oxide was immersed in a storage container for this precursor solution for 1 minute, then air-blown and calcined in air at 500 ° C. for 1 hour. (Hereinafter referred to as "Co, Ce oxide / SiC catalyst") was obtained.

Similarly, a honeycomb-type cordierite ceramic carrier is immersed in a storage container for a precursor solution for 1 minute, air-blown, and then the ceramic carrier is calcined in air at 500 ° C. for 1 hour to support a catalyst (hereinafter, “” Co, Ce oxide / corderite catalyst ”) was obtained.

<Example 2> Evaluation of peelability In order to evaluate the peelability of the catalyst obtained in Example 1, the sample was immersed in distilled water and used in water using an ultrasonic cleaner (USK-1R manufactured by AS ONE Co., Ltd.). After sonication for seconds, the sample was dried. After drying, the adhesion state of the catalyst was visually observed.

For comparison, a supported catalyst using alumina sludge as a precursor instead of a cobalt-cerium-based precursor solution was also prepared, and the same peelability evaluation was performed. Specifically, an alumina slurry was prepared with reference to a publicly known document (International Publication No .: WO2010103669 A1), and the SiC carrier and the cordierite carrier were coated.

The results are shown in Table 1. Further, FIG. 1 shows a scanning electron micrograph of a catalyst in which a cobalt-cerium-based composite oxide is supported on the surface of a SiC carrier.

As shown in Table 1, no exfoliation was confirmed in the cobalt-cerium-based precursor solution when either the SiC carrier or the cordierite carrier was used. On the other hand, it was confirmed that the alumina particles coated on the SiC carrier were peeled off by ultrasonic waves in water, and that the alumina was difficult to peel off on the cordierite carrier.

<Example 3> Accelerated deterioration test The performance of the Co, Ce oxide / SiC catalyst and the Co, Ce oxide / cordierite catalyst obtained in Example 1 was evaluated.

FIG. 2 is a diagram showing an outline of the catalyst accelerated deterioration apparatus. The catalyst accelerated aging apparatus includes a catalyst part for installing a catalyst and a volatile part for volatilizing a solvent, and each of the catalyst part and the volatile part can be heated to about 400 ° C. It is a mechanism in which the organic component volatilized in the heated volatile part is sprayed at a high concentration on the heated catalyst while the gas is released in one direction by a fan. The temperature of the catalyst part and the volatile part is monitored, and when the organic matter is decomposed by the catalyst, the temperature of the catalyst part rises due to the heat of reaction, so it is easy to check whether the catalyst is active or not. evaluated. The experimental conditions were the temperature setting of the catalyst part and the volatile part: 400 ° C., the solvent inflow rate: 500 μl / min, the installed catalyst amount: 0.5 g, and the poisoning precursor (dichloromethane) concentration: 5 vol% / toluene.

The results are shown in FIG. 3 (a) and 3 (b) are the results of using only toluene as a solvent, and FIGS. 3 (c) and 3 (d) are the results of using a solvent in which toluene is mixed with dichloromethane. Further, FIGS. 3 (a) and 3 (c) show results using a Co, Ce oxide / carbide catalyst, and FIGS. 3 (b) and 3 (d) show results using a Co, Ce oxide / SiC catalyst.

It was confirmed that the activity of the Co and Ce oxide / cordierite catalysts deteriorated due to the mixing of Cl-based substances. On the other hand, it was confirmed that the deterioration of the Co and Ce oxide / SiC catalysts stopped in the middle and the activity was maintained. It has been shown that the use of a SiC carrier as a base imparts acid resistance to chlorine-based VOCs and suppresses deterioration of the catalyst.

FIG. 4 is a schematic view showing a mechanism for suppressing deterioration of the catalyst on the surface of the carrier. As shown in FIG. 4, it was considered that one of the factors was that HCl gas was difficult to permeate into SiC and the influence of damaging the catalyst in the portion other than the active site of the reaction was small.

<Example 4> Catalytic activity test A decomposition experiment (catalytic activity test) of various chlorine-based VOCs was carried out on the Co, Ce oxide / SiC catalyst obtained in Example 1.

For the catalyst activity test, an apparatus was used in which the air supplied from the compressor whose flow rate was set so as to have a predetermined space velocity (SV) was constantly sent so as to be in contact with the catalyst. The target VOC was mixed with heated air in the form of gas by injecting it into an injection tube heated to 200 ° C. with a liquid feed pump. The catalyst was heated to any temperature up to 450 ° C. with an external heater. While adjusting the heater temperature and changing the reaction temperature, the gas before entering the reaction tank and the gas that passed through the reaction tank are analyzed by GC-MS (gas chromatograph with mass spectrometer), and the concentration of each gas is determined. It was determined (the concentration of gas before entering the reaction layer is C1, and the concentration of gas that has passed through the reaction layer is C2). The decomposition rate c (%) was calculated from the formula c = C2 / C1 × 100.

The results are shown in FIGS. 5 to 7. The air volume was adjusted so that the space velocity (SV) was 22000 h-1 in FIG. 5 and 10000 h-1 in FIG.

As shown in FIG. 5 (each VOC concentration 1000 ppm), it was confirmed that the Co, Ce oxide / SiC catalyst can decompose all three components by 90% or more at a decomposition temperature of 500 ° C. or higher. In particular, methylene chloride and 1,2-dichloroethane showed a decomposition rate of 95% or more at 400 to 450 ° C. Further, as shown in FIG. 6 (each VOC concentration 2000 ppm), it was confirmed that the Co, Ce-based / SiC catalyst can be substantially decomposed at about 500 ° C. even when various chlorine-based VOCs have a high concentration. It was shown that the decomposition rate was higher than that of the platinum-supported alumina catalyst of.

<Example 5> Hydroxide exposure test In order to test the durability of the catalyst in the presence of acid gas, the conventional platinum-supported alumina catalyst, Co, Ce oxide / cordierite catalyst, and Co, Ce oxide / SiC catalyst hydrochloric acid The deterioration conditions under the exposed atmosphere were compared. As a method, a bottle containing 40 mL of concentrated hydrochloric acid was placed in a desiccator to adjust the hydrochloric acid exposure atmosphere. Further, the above three kinds of catalysts were placed in a desiccator and allowed to stand at room temperature for 2 weeks.

As shown in FIG. 7, the conventional platinum-supported alumina catalyst discolored yellow, the Co, Ce oxide / cordierite catalyst discolored and the surface became shabby, but the Co, Ce oxide / SiC catalyst deteriorated. Was not confirmed.

Claims (5)

A catalyst for VOC treatment, characterized in that a composite oxide of cobalt (Co) and cerium (Ce) is supported on the surface of a carrier containing silicon carbide (SiC) as a main component. The catalyst for VOC treatment according to claim 1, wherein the VOC is a halogen-based organic compound. A VOC processing apparatus according to claim 1, further comprising a VOC processing catalyst and an energizing device for the VOC processing catalyst. A VOC processing method using the VOC processing apparatus according to claim 3.
The step of bringing the gas containing VOC into contact with the VOC treatment catalyst, and
A step of energizing and heating the carrier of the VOC treatment catalyst by the energizing device.
A VOC processing method comprising. The method for treating VOC according to claim 4, wherein the VOC is a halogen-based organic compound.

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