JP4602165B2 - Decomposition and removal method of volatile organic compounds and catalyst for decomposition and removal - Google Patents

Description

  The present invention relates to a method for decomposing and removing volatile organic compounds and a catalyst for decomposing and removing. More specifically, the present invention relates to an improvement in measures against environmental pollution caused by volatile organic compounds such as aliphatic hydrocarbons such as hexane, aromatic hydrocarbons such as benzene, and polycyclic aromatic hydrocarbons such as naphthalene.

  Volatile organic compounds (VOC) are also aliphatic hydrocarbons such as hexane, aromatic hydrocarbons such as benzene, and polycyclic aromatic hydrocarbons (PAH) such as naphthalene. : Polycyclic Aromatic Hydrocarbons). Aromatic hydrocarbons, particularly benzene and toluene, which are typical components of VOCs, are used in a wide range of applications such as organic solvents and paints, many of which have the potential to cause air pollution. Among them, benzene is known as a carcinogen, and environmental standards are set as shown in Table 1. In addition, the VOC component itself is not only carcinogenic and harmful, but when released into the atmosphere, it synthesizes photochemical oxidants such as ozone and is a major cause of photochemical air pollution along with nitrogen oxides (NOx). It becomes a causative substance. These secondary photochemical oxidants and suspended particulate matter (SPM) have an environmental standard because they affect the human body (see Table 1). In short, the VOC mentioned here is one of the harmful pollutants that are likely to affect the environment and the human body, like nitrogen oxides (NOx) and sulfur oxides (SOx) that are already regulated as air pollutants. It is. For this reason, in recent years, VOC emissions into the atmosphere have been regarded as a problem, and not only various combustion exhaust gas such as diesel engine exhaust gas, but also the amount of VOC generated in fixed sources such as various factories and waste treatment in the future. Processing techniques for suppression may be required.

VOC processing technology has been developed with the strengthening of laws and regulations, mainly in Europe and the United States, and there has been a history of the introduction of various devices. On the other hand, in Japan, odor countermeasures are the main, and it has been introduced as an exhaust gas deodorizer, and as a result, VOC has been treated. Such VOC exhaust gas treatment technologies are broadly divided into combustion oxidation methods (direct combustion, catalytic combustion), adsorption methods, and activated sludge methods (biological treatment methods), and which method is determined according to the exhaust gas treatment amount, VOC concentration, etc. Is done. Recently, new treatment methods such as plasma decomposition have been developed. Among various treatment technologies, there are various problems. Decomposition by photocatalytic action such as titanium oxide (TiO ₂ ), and catalytic combustion (catalytic oxidation) by noble metal supported catalyst, etc., ultimately result in carbon dioxide (CO ₂ ) and water. Since VOC is decomposed to (H ₂ O), it is mentioned as an effective processing means.

  Here, with regard to the VOC processing technology using the latter noble metal supported catalyst, 1) low reaction temperature, saving fuel costs, 2) almost no thermal NOx generation, 3) simple system and miniaturization ( The installation space is small). Specific examples of the VOC treatment technology using such a noble metal-supported catalyst include a metal oxide support in which a noble metal such as platinum (Pt) or palladium (Pd) is supported as an active component, and a combination of several types of metal oxides. There are those using complex oxides (see, for example, Patent Document 1 and Patent Document 2).

JP 2001-38207 A JP-A-11-57470

  However, these noble metal-supported catalysts have a problem that the cost is high because a noble metal such as Pt is supported on a high surface area support such as alumina. This is a serious problem when VOC treatment is performed on a huge amount of VOC-containing exhaust gas discharged from various factories or combustion exhaust gas from a diesel engine. Therefore, there is a demand for a low-cost catalyst that can replace the current noble metal-supported catalyst while ensuring sufficient resolution of VOC.

In addition, the VOC treatment technique using the noble metal-supported catalyst as described above has the following problems. That is, when a noble metal-supported catalyst is used, a very high decomposition rate is achieved under dry gas conditions, but there is a problem that the decomposition rate is greatly reduced under conditions where water vapor is mixed. For example, when PdPt / Al ₂ O ₃ is used as a noble metal supported catalyst, dry gas conditions (CO ₂ : 15%, O ₂ : 5%, N ₂ : balance gas, space velocity SV (supply gas amount / catalyst filling amount) ): 12000h ^-1 , temperature: 150 ° C), the decomposition rate was 98.2%, including water vapor (CO ₂ : 15%, O ₂ : 5%, H ₂ O: 9%, N ₂ : balance) Under gas, it drops to 25% (see Table 4). However, since the exhaust gas discharged from various factories contains 2-3% of water vapor and the combustion exhaust gas contains about 8% of water vapor, the noble metal-supported catalyst cannot be used as it is as a VOC decomposition catalyst. For this reason, it has been necessary to use or mix another catalyst component under conditions where water vapor can be mixed into the VOC, such as exhaust from a factory.

  Therefore, in the present invention, there is provided a method for decomposing and removing a volatile organic compound that can exhibit a high VOC (volatile organic compound) decomposition rate even under the presence of water vapor, and can achieve a lower cost than a noble metal supported catalyst. An object is to provide a catalyst for decomposition and removal.

In order to achieve this object, the present inventor conducted various experiments and studies. Specifically, seven types of noble metal supported catalysts supporting palladium (Pd), platinum (Pt), etc. used in deodorizers such as toluene, and titanium oxide (as oxide catalysts cheaper than these noble metal supported catalysts). As a result of conducting a decomposition reaction test of benzene, which is a typical VOC, using nine types such as TiO ₂ ), ceria (CeO ₂ ), and zirconia ceria (ZrO ₂ CeO ₂ ), it is less expensive than noble metal supported catalysts. However, under dry gas, the VOC decomposition rate is extremely low, and ceria that is used as a support for precious metal supported catalysts but not as a catalyst can exhibit a high decomposition rate under steam conditions. I got the knowledge.

Furthermore, when various conditions for applying CeO ₂ to decompose and remove benzene and toluene were studied, it was possible to decompose VOCs in exhaust gas without water vapor, and the reaction temperature and space velocity SV were constant. It was found that the VOC decomposition performance equivalent to the precious metal supported catalyst can be obtained by controlling the conditions.

  It was also found that VOC decomposition performance equivalent to that of noble metal-supported catalysts can be obtained under certain conditions even when removing VOCs from exhaust gas containing water vapor.

The present invention is based on such findings, the invention described in claim 1, in exploded removal method by catalytic gas of volatile organic compounds in the exhaust gas, ceria (CeO ₂₎ said use alone as a catalyst Thus, the gas of the volatile organic compound is decomposed and removed .

In the VOC (volatile organic compound) decomposition reaction, the reaction temperature and space velocity SV (feed gas amount / catalyst charge amount) are important parameters that affect the decomposition performance. If CeO ₂ is used as a catalyst under conditions where water vapor is present in the gas , VOC decomposition equivalent to Pt / Al ₂ O ₃ , PdPt / ZrO ₂ CeO ₂ , and noble metal supported catalysts It is possible to demonstrate the rate. Further, the cost can be reduced as compared with the noble metal supported catalyst.

Here, as in the invention described in claim 2 , the exhaust gas is preferably combustion exhaust gas .

Next, the catalyst for decomposing and removing volatile organic compound gas according to claim 3 is used for decomposing volatile organic compound gas in the exhaust gas in which water vapor is present , and is composed of ceria (CeO ₂ ). It is characterized by this.

Ceria (CeO ₂ ) catalysts are less expensive than noble metal-supported catalysts, and even if water vapor is present in the exhaust gas, there is a feature that there is no significant decrease in the decomposition rate unlike noble metal-supported catalysts. Yes. Therefore, by using a ceria (CeO ₂ ) catalyst as a catalyst for decomposing and removing volatile organic compound gas, even if water vapor is present in the exhaust gas, decomposition of the volatile organic compound gas when it is not present In addition to maintaining the performance, under certain conditions, it has the same VOC decomposition performance as a noble metal supported catalyst .

Here, as in the invention described in claim 4 , the exhaust gas is preferably combustion exhaust gas .

Thus, according to the decomposition and removal method of the present invention , it is possible to decompose VOC at the same decomposition rate as when using a noble metal-supported catalyst while using a catalyst (CeO ₂ ) that is lower in cost than the noble metal-supported catalyst. It becomes. Therefore, it is possible to realize cost reduction while ensuring a predetermined disassembly / removability.

Moreover, in the case of using ceria (CeO ₂₎ to the catalyst, to exhibit a high decomposition rate even in the presence of water vapor, such as that the decomposition ratio steam as the noble metal loaded catalyst is mixed decreases, instantly There is nothing. Therefore, for example, there is an advantage that it is not necessary to use or mix another catalyst component under conditions where water vapor can be mixed into the VOC such as exhaust from a factory.

In addition, according to the present invention, since the oxide (CeO ₂ ) is used as a single catalyst without using a support as in the noble metal-supported catalyst, there is an effect that the catalyst production and handling are easy. Further, there is an advantage that it can be incorporated into a gas line (or a system including the same) as it is without using a carrier.

Next, according to the gas decomposition / removal catalyst of the volatile organic compound of the present invention , while realizing a catalyst that is lower in cost than the noble metal-supported catalyst, the VOC is reduced at the same decomposition rate as when the noble metal-supported catalyst is used. It becomes possible to disassemble. Therefore, it is possible to realize cost reduction while ensuring a predetermined disassembly / removability.

  Moreover, since the catalyst according to the present invention exhibits a high decomposition rate in the presence of water vapor when it is decomposed and removed, when water vapor is mixed in like a noble metal-supported catalyst, the decomposition rate is gradually reduced. Absent. Therefore, for example, there is an advantage that it is not necessary to use or mix another catalyst component under conditions where water vapor can be mixed into the VOC such as exhaust from a factory.

In addition, according to this catalyst, the oxide (CeO ₂ ) is used as a single catalyst without using a support as in the noble metal-supported catalyst. Further, there is an advantage that it can be incorporated into a gas line (or a system including the same) as it is without using a carrier.

Hereinafter, the configuration of the present invention will be described in detail based on the best mode shown in the drawings.

The method for decomposing and removing volatile organic compounds from exhaust gas according to the present invention is characterized by using ceria (CeO ₂ ) as a catalyst.

  The VOC (volatile organic compound) to be used in the present invention refers to substances such as aliphatic hydrocarbons such as hexane, aromatic hydrocarbons such as benzene and toluene, and polycyclic aromatic hydrocarbons such as naphthalene. However, it is not limited to these. Among them, benzene, toluene and the like are volatile organic compounds used for a wide range of applications such as organic solvents and paints.

  Further, as described above, in the VOC (volatile organic compound) decomposition reaction, the reaction temperature and the space velocity SV (feed gas amount / catalyst filling amount) are important parameters that influence the VOC decomposition performance. To increase the VOC decomposition performance of the catalyst, increase the reaction temperature and decrease SV, that is, increase the amount of catalyst filling or decrease the amount of gas supply. It is preferable to keep the reaction temperature as low as possible, reduce the catalyst filling amount, and increase the amount of supply gas. Accordingly, the reaction temperature, space velocity SV, and water vapor concentration suitable for removing benzene and toluene in the exhaust gas will be described in detail below.

  When ceria is used for decomposition and removal of benzene in exhaust gas not containing water vapor, as shown in FIG. 10, with respect to the reaction temperature, the decomposition rate increases from 150 ° C. to 200 ° C., and the decomposition rate at 200 ° C. to 300 ° C. Gradually decreases. Then, the decomposition rate starts to rise again from 300 ° C.

  Such temperature dependence of the decomposition rate is explained as follows. That is, benzene is gradually adsorbed on the catalyst surface at 150 ° C. to 200 ° C. and decomposition reaction occurs, but in this temperature range, the adsorption reaction is more likely to occur than the decomposition reaction. It will be covered with. Next, at 200 ° C. to 300 ° C., benzene that is not adsorbed on the catalyst surface passes as it is, and the decomposition rate decreases. Then, the catalytic activity on the catalyst surface increases at 300 ° C. or higher, and the decomposition rate is improved again, so that the decomposition reaction is more likely to occur than the adsorption reaction. From this viewpoint, the reaction temperature is preferably 300 ° C. or higher, more preferably 350 ° C. or higher, and most preferably 400 ° C. or higher.

  When the reaction temperature is 150 ° C. to 300 ° C., the adsorption of VOC to the catalyst surface is more likely to occur than the decomposition reaction. Therefore, when only aiming at adsorption | suction of VOC, what is necessary is just to make reaction temperature 150 to 300 degreeC.

  Furthermore, the reaction temperature is set to 150 ° C. to 300 ° C., and the catalyst surface is treated until it is covered with adsorbed benzene until it is no longer adsorbed. Thereafter, the temperature is raised to about 400 ° C. and held for a certain time. You may make it repeat. By doing so, benzene adsorbed at 150 ° C. to 300 ° C. can be decomposed at 400 ° C., and the running cost can be significantly reduced as compared with the case where the reaction temperature is always maintained at 400 ° C.

  Next, as shown in FIG. 10, the influence of the space velocity SV is greatest at 300 ° C., and the influence gradually decreases as the temperature becomes lower than 300 ° C. and as the temperature becomes higher.

That is, when the reaction temperature is around 300 ° C., a higher decomposition rate can be obtained by reducing SV. However, as the reaction temperature becomes higher than 300 ° C., the SV dependency of the decomposition rate decreases, and 400 ° C. In this case, even if SV is 12000 h ⁻¹ , a sufficiently high decomposition rate can be obtained. If the temperature is 350 ° C. or higher, a decomposition efficiency of 90% or higher can be obtained even if SV is 12000 h ⁻¹ .

  Next, when ceria is used for decomposition and removal of toluene in the exhaust gas not containing water vapor, decomposition starts at a reaction temperature of 150 ° C. as shown in FIG. 12, and is 95% or higher near 180 ° C., and 97% at 200 ° C. or higher. Degradation rate is shown. That is, the reaction temperature is preferably 150 ° C. or higher, more preferably 180 ° C. or higher, and most preferably 200 ° C. or higher.

As described above, the VOC decomposition performance may vary depending on SV. When SV is 5600 h ⁻¹ , a decomposition rate of 95% or more is obtained at 180 ° C., but it is considered that the decomposition rate at 180 ° C. decreases as SV increases. Therefore, when SV becomes larger than 5600 h ⁻¹ , the reaction temperature may be increased so as to obtain a desired decomposition rate. Conversely, when SV is less than 5600 h ⁻¹ , the reaction temperature may be less than 180 ° C.

After all, in order to improve the VOC decomposition performance in exhaust gas, the balance between reaction temperature and space velocity SV is important. If the reaction temperature is set high, the space velocity SV has sufficient decomposition performance even if it increases to some extent. On the other hand, when the reaction temperature is low, a sufficient decomposition performance can be obtained by reducing the space velocity SV.

  Next, a method for decomposing and removing volatile organic compounds in exhaust gas containing water vapor will be described.

In this case, an important parameter that affects the VOC decomposition rate is the water vapor concentration in addition to the reaction temperature and the space velocity SV. In order to improve the decomposition performance of the catalyst, as described above, the reaction temperature is increased and the SV is decreased, that is, the catalyst filling amount is increased or the supply gas amount is decreased, but when the water vapor concentration is increased, VOC decomposition performance may be affected. Therefore, the reaction temperature, space velocity SV, and water vapor concentration suitable for removing benzene and toluene in the exhaust gas in which water vapor is present will be described in detail below.

  When ceria is applied to the removal of benzene in exhaust gas containing water vapor, as shown in FIG. 11, the reaction temperature starts to increase from 300 ° C., and shows a very high decomposition rate around 400 ° C. That is, the reaction temperature is preferably 300 ° C. or higher, more preferably 350 ° C. or higher, and most preferably 400 ° C. or higher.

  Also, the temperature dependence of the decomposition rate is different between the case where the water vapor concentration is 2.07 to 7.34% and the case where it is 8.84 to 10.83%, and the case where it is 8.84 to 10.83% is different. Decomposition rate is slightly lower. That is, it can be considered that the decomposition rate slightly decreases as the water vapor concentration increases. Therefore, when the water vapor concentration is high, a desired decomposition rate may be obtained by increasing the reaction temperature and reducing SV.

A suitable example in the case of applying ceria to the removal of benzene in exhaust gas containing water vapor is as follows. That is, when SV is 5600 h ⁻¹ , the reaction temperature is 400 ° C. or more, and the water vapor concentration in the exhaust gas is 11% or less, the decomposition rate is 90% or more, the water vapor concentration in the exhaust gas is 7% or less, and When the reaction temperature is 400 ° C. or higher, the decomposition rate is as high as 95% or higher, which is comparable to that of the noble metal supported catalyst.

  Next, the handling of the other two parameters when one of the reaction temperature, space velocity SV, and water vapor concentration is fixed will be discussed.

First, the case where the reaction temperature is fixed will be described. When the reaction temperature is 400 ° C. or more, the VOC decomposition performance is 90% or more when the water vapor concentration is 11% or less and the SV is 5600 h ⁻¹ or less. Regarding SV, considering that there is almost no influence of SV at 400 ° C. in dry gas, it is considered that the decomposition performance is 90% or more even when SV is 12000 h ⁻¹ .

Next, the case where the water vapor concentration is fixed will be described. When the water vapor concentration is 11% or less, the decomposition temperature is 90% or more when the reaction temperature is 400 ° C. or more and the SV is 5600 h ⁻¹ or less. Regarding SV, considering that there is almost no influence of SV at 400 ° C. in dry gas, it is considered that the decomposition performance is 90% or more even when SV is 12000 h ⁻¹ .

  Next, when ceria is applied to remove toluene in exhaust gas containing water vapor, as shown in FIGS. 14 and 15, the decomposition rate starts to increase from 150 ° C. and rapidly decomposes to around 180 ° C. The rate increases, and when the temperature is 200 ° C. or higher, a substantially constant decomposition rate is exhibited. However, when the water vapor concentration is 3% or less, the decomposition rate gradually increases from 200 ° C. That is, the reaction temperature is preferably higher than 150 ° C, more preferably 180 ° C or higher, and most preferably 200 ° C or higher. Furthermore, when the water vapor concentration is 3% or less, the temperature is most preferably 350 ° C. or more.

  Regarding the water vapor concentration, as shown in FIG. 15, the decomposition rate slightly decreases as the water vapor concentration increases. Therefore, it is conceivable that the decomposition performance decreases as the water vapor concentration increases. In this case, the desired decomposition rate may be obtained by increasing the reaction temperature and decreasing SV. .

For the SV, but not so much difference in the 5600h ^-1 ~7500h ^-1 in decomposition rate, as shown in FIG. 14, the decomposition rate 10000h ^-1 is slightly lower. However, even at 10000 h ⁻¹ , sufficiently high decomposition performance can be obtained at 350 ° C. That is, when SV is larger than 10,000 h ⁻¹ , a desired decomposition rate may be obtained by raising the reaction temperature.

A suitable example in the case of applying ceria to the removal of toluene in exhaust gas containing water vapor is as follows. That is, when SV is 5600 h ⁻¹ , the water vapor concentration in the exhaust gas is 7% or less, and the reaction temperature is 180 ° C. or higher, the decomposition rate is as high as 90% or more, which is comparable to that of the noble metal supported catalyst. Can decompose toluene.

Further, if the water vapor concentration in the exhaust gas is 3% or less, the reaction temperature is 180 ° C. or higher within the SV range of 5600 h ^{−1 to} 10000 h ⁻¹ , which is as high as 90% or higher, comparable to the case of the noble metal supported catalyst. Toluene can be decomposed at a decomposition rate. When SV is 7000 h ⁻¹ , the decomposition performance is about 75% even at 165 ° C. That is, when SV is 7000 h ⁻¹ or less, it is considered that the decomposition performance is 75% or more even at 165 ° C., and the decomposition performance at 165 ° C. decreases gradually as it becomes larger than 7000 h ^−1. Can be considered.

  Next, the handling of the other two parameters when one of the reaction temperature, space velocity SV, and water vapor concentration is fixed will be discussed.

First, the case where the reaction temperature is fixed will be described. When the reaction temperature is 300 ° C. or higher, the VOC decomposition performance is 90% or higher when SV is 10,000 h ⁻¹ or lower and the water vapor concentration is 10% or lower. Further, when the reaction temperature is 180 ° C. or more and the water vapor is 3% or less, the SV is 10,000 h ⁻¹ or less and the decomposition performance is 90% or more, and when the SV is 5600 h ⁻¹ or less, If the water vapor concentration is 7% or less, the decomposition performance is 90% or more.

Next, a case where the space velocity SV is fixed will be described. When SV is 5600 h ⁻¹ , if the reaction temperature is 180 ° C. or higher and the water vapor concentration is 7% or lower, the VOC decomposition performance is 90% or higher. If the SV is 10,000 h ⁻¹ or less, the VOC decomposition performance is 90% or more when the water vapor concentration is 3% or less and the reaction temperature is 180 ° C. or more.

Further, a case where the water vapor concentration is fixed will be described. When the water vapor concentration is 3% or less, the decomposition performance is 90% or more when the reaction temperature is 180 ° C. and the SV is 10000 h ⁻¹ or less. Further, when the water vapor concentration is 10%, the decomposition temperature is 90% or more when the reaction temperature is 200 ° C. or more and the SV is 5600 h ⁻¹ or less.

  After all, the balance of reaction temperature, space velocity SV, and water vapor concentration is important in order to enhance the VOC decomposition performance in the exhaust gas in which water vapor exists. If the reaction temperature is increased, sufficient decomposition performance is obtained even if the space velocity SV and the water vapor concentration are increased to some extent, and if the space velocity SV is further decreased, it is sufficient even if the water vapor concentration is further increased. It has a decomposition performance, and if the water vapor concentration is reduced, the decomposition performance is sufficient even if the space velocity SV is further increased. On the other hand, when the reaction temperature is low, sufficient decomposition performance can be obtained by reducing the space velocity SV and lowering the water vapor concentration.

Next, the catalyst for decomposing and removing volatile organic compounds composed of ceria (CeO ₂ ) will be described in detail.

The ceria (CeO ₂ ) catalyst is lower in cost than the noble metal supported catalyst, and the oxide (CeO ₂ ) is used as a single catalyst without using a support as in the noble metal supported catalyst. Easy to manufacture and handle the catalyst. Further, there is an advantage that it can be incorporated into a gas line or a system including the same without using a carrier.

As a form when using the ceria (CeO ₂ ) catalyst, it may be used in a powder form or a pellet form, but it may be used after being formed into a desired shape. In this case, it may be formed by a press forming method, an extrusion forming method, a mold forming method, a granulating method or the like, but is not limited to these as long as a desired shape can be obtained.

  By using this catalyst under the conditions as described above, it becomes possible to obtain higher decomposition performance, and further, under certain conditions, it has VOC decomposition performance equivalent to that of the noble metal-supported catalyst.

Ceria (CeO ₂ ) catalyst can be applied to VOC decomposition and removal from exhaust gas from printing factories, paint factories and organic solvent factories, and exhaust gas from various combustion equipment such as automobile engines, oil fan heaters, gas stoves, etc. However, it is not limited to these.

The above-described embodiment is an example of a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the scope of the present invention. For example, two or more ceria (CeO ₂ ) catalysts are arranged in the VOC flow path, the reaction temperature where the VOC decomposition rate is very high only at the part where VOC finally passes, and the catalyst filling amount is also reduced. And make the heat source small. If the conditions are such that the gas can be decomposed and removed to some extent in the previous stage, it is possible to reduce the running cost while maintaining a high VOC decomposition rate.

[Example 1]
A VOC decomposition catalyst applicable to combustion exhaust gas and the like was screened from the viewpoint of finding a catalyst having excellent low-temperature activity and low cost. Hereinafter, the contents of this experiment will be described in detail as Example 1 with reference to the drawings. As will be described in the following examples, ceria (CeO ₂ ) is the most suitable catalyst from this viewpoint.

1. VOC decomposition catalysts Various researches have been conducted on VOC decomposition catalysts using TiO ₂ and their composite oxides for photolysis, and catalysts supporting Pt and other precious metals with Al ₂ O ₃ as the support mainly for catalytic oxidation. Yes. On the other hand, the present inventor conducted a study of actually decomposing benzene by selecting ceria (CeO ₂ ; first rare element chemical industry, HS) as an example. In addition, as reference examples, TiO ₂ , iron oxide (Fe ₂ O ₃ ) and TiO ₂ (Kanto Chemical Co., Anatase), copper oxide (CuO; Kanto Chemical Co., Ltd.), Al ₂ O ₃ (Sumitomo Chemical Co., Ltd., TA-1301), Zirconia (ZrO ₂ ; 1st rare element chemical industry, RC-100) , ZrO ₂ CeO ₂ (1st rare element chemical industry, ACZ-58) , TiO ₂ ZrO ₂ (Daiichi Rare Element Chemical Industry) selected eight types of oxide catalysts and conducted research to actually decompose benzene. Furthermore, as reference examples, PdPt-supported catalysts (PdPt / Al ₂ O ₃ ) and PdPt / Al ₂ O ₃ that have been studied for the low-temperature oxidation of methane at the Central Research Institute of Electric Power, the applicant of the present invention, are co-catalysts. Catalysts with added ZrO ₂ , CeO ₂ etc. (PdPt / ZrO ₂ , PdPt / ZrO ₂ CeO ₂ etc.), Pd supported catalysts (Pd / Al ₂ O ₃ ), Pt supported catalysts (Pt / Al ₂ O ₃ ) The performance as a VOC decomposition catalyst was examined for 6 types of noble metal-supported catalysts . Table 2 shows the specifications of each noble metal supported catalyst. The various catalysts were sized to 9 to 16 mesh after press molding (for example, the openings were 2 mm (8.6 mesh) and 1 mm (16 mesh)) and used for the physical property analysis and reaction test of the catalyst.

2. Physical properties analysis The specific surface area, which is an important factor in comparing and evaluating catalyst performance, and the amount of CO adsorbed on the metal component as the active component on the surface of the noble metal-supported catalyst were measured. The specific surface area was measured using an automatic specific surface area measuring device (Micromeritics, GEMINI 2360) based on the BET method. The amount of chemical adsorption by CO was measured using a fully automatic catalytic gas adsorption amount measuring device (Okura Riken, MODEL R6015). This equipment utilizes the property that active components on the surface of the catalyst, etc., chemisorb active gases such as CO and H _2, and the active gas is introduced into the catalyst in pulses to measure the total amount of adsorption. . Note that this device complies with the measurement method of the Catalysis Society of Japan. As a pretreatment, the temperature was raised from room temperature to 400 ° C at 10 ° C / min in a helium stream as a pretreatment, hydrogen reduced at 400 ° C for 15 minutes, then degassed for 15 minutes, and then cooled at 10 ° C / min. Held at 0C. Next, while measuring the CO concentration at the sample outlet with a thermal conductivity detector (TCD), 49.7% of CO 2 was supplied to the sample in a helium stream and the amount of CO 2 adsorbed up to the saturation point was measured. It was measured.

3. VOC Decomposition Reaction Test An experimental apparatus used for the VOC decomposition reaction test is shown in FIG. A quartz reaction tube 2 was filled with 2 ml of catalyst 1, and the front and back of catalyst 1 were fixed with quartz wool (not shown). The reaction tube 2 filled with the catalyst 1 was installed in a tubular electric furnace 3, and after raising the temperature to a predetermined temperature, a reaction test was started under the experimental conditions shown in Table 3. Benzene (special reagent grade:> 99.5%, manufactured by Kanto Chemical Co., Inc.) was injected into the glass diffusion tube 4 and then maintained at a constant temperature, and diluted gas was generated by flowing nitrogen at a constant flow rate. Moreover, water vapor | steam was introduce | transduced by bubbling water in the water vapor generation part 5 at a fixed temperature. The gas flow path containing benzene and water vapor was kept at 120 ° C. or higher by a ribbon heater (the portion heated by the ribbon heater is indicated by hatching in the figure). The VOC concentration in the exhaust gas from various fixed sources is several ppm to several hundred ppm in chemical factories, and several ppm to 20 ppm in waste treatment. Controlled. The benzene concentration was measured using a gas detector tube (manufactured by Gastec). The remaining gas that was not sampled was exhausted after passing through a water trap 6 and activated carbon 7.

4). Experimental Results 4-1 Benzene Decomposition Reaction Test Results with Various Catalysts FIG. 4 shows the benzene decomposition reaction test results of main oxide catalysts and noble metal supported catalysts. Assuming combustion exhaust gas composition as experimental conditions, first, a reaction test was performed at CO ₂ : 15%, O ₂ : 5%, gas flow rate 400 ml / min (space velocity SV: 12000 h ⁻¹ ), and reaction temperature 150 ° C. Such as _{TiO 2, Al 2 O 3,} CeO 2, ZrO 2 CeO 2, 9 kinds of oxides of showing the decomposition performance in the catalyst CeO _2, ZrO ₂ CeO ₂ alone, other seven oxide catalyst Showed no decomposition performance. CeO ₂ showed a decomposition rate of 45% as an initial activity, but then decreased to 20% or less and was stabilized as it was. ZrO ₂ CeO ₂ showed a decomposition rate equivalent to that of CeO ₂ until 30 minutes after the start of the reaction, but showed no decomposition performance after 60 minutes. On the other hand, 6 types such as Pd / Al ₂ O ₃ , Pt / Al ₂ O ₃ , PdPt / Al ₂ O ₃ , and PdPt / ZrO ₂ show high decomposition rates from the start of the reaction, and each is over 98%. The decomposition rate was obtained.
In addition, about 30 minutes after the start of the reaction, the oxide catalysts CeO ₂ and ZrO ₂ CeO ₂ were only able to obtain a decomposition rate of about 10 to 15% under dry gas conditions, respectively, whereas noble metal supported catalysts Six of them showed a decomposition rate of 98% or more under dry gas conditions (see (i) in Table 4).

For CeO ₂ which showed the only decomposition performance among oxide catalysts, Pd / CeO ₂ carrying Pd (Pd carrying amount: 1 wt%) was prepared by the impregnation method, and a reaction test was attempted. As shown in FIG. 4, the decomposition rate greatly increased from 15% to 55% by loading Pd, but it was about half of Pd / Al ₂ O ₃ and PdPt / Al ₂ O ₃ . Table 5 shows the initial physical properties of CeO ₂ and ZrO ₂ CeO ₂ , which showed decomposition performance among seven kinds of noble metal-supported catalysts and oxide catalysts. CeO ₂ has about 150 meters ² / g and high specific surface area, after Pd on was also nearly twice about 112m ² / g of other noble metal supported catalysts. However, the amount of CO 2 adsorption was less than half of PdPt / Al ₂ O ₃ and Pd / Al ₂ O ₃ , and it was speculated that this difference appeared in the catalyst performance.

The combustion exhaust gas contains water vapor together with VOC. Therefore, the test was conducted at a CO ₂ containing 9% of water vapor: 15%, O ₂ : 5%, a gas flow rate of 400 ml / min (SV: 12000 h ⁻¹ ), and a reaction temperature of 150 ° C. Catalysts include 7 kinds of noble metal supported catalysts such as PdPt / Al ₂ O ₃ and PdPt / ZrO ₂ CeO ₂ which showed high decomposition rate under dry gas conditions, and CeO ₂ and ZrO ₂ which showed decomposition performance among oxide catalysts. CeO ₂ was selected. FIG. 5 shows the experimental results of various catalysts. In Pd / Al ₂ O ₃ , PdPt / Al ₂ O ₃ , PdPt / ZrO _2, etc., the decomposition rate was greatly reduced by the presence of water vapor, and Pd / Al ₂ O ₃ was reduced to 20% or less. Four types of PdPt-supported catalysts in which Pt was added to Pd / Al ₂ O ₃ showed a higher decomposition rate than Pd / Al ₂ O ₃ , and the effect of combining active components was revealed. In comparison with the carrier component differences, Al ₂ O ₃ alone is PdPt / Al ₂ O ₃ is most decomposition rate is low, then the order of _{PdPt / ZrO 2, PdPt / CeO} 2, PdPt / ZrO 2 CeO 2 became. In contrast, Pt / Al ₂ O ₃ maintained a decomposition rate of 70% or more, and it was revealed that the influence of water vapor was less than that of Pd / Al ₂ O ₃ and PdPt supported catalysts. On the other hand, regarding CeO ₂ , it was found that the decomposition rate was rather improved by the presence of water vapor (see (i) and (ii) in Table 4).

4-2 Effect of space velocity (SV) Exhaust gas from chemical factories, petrochemical plants, and various combustion processes contains water vapor along with VOC components, making water vapor one of the causes of catalyst deterioration and shortening catalyst life. To do. Therefore, the catalyst performance is improved by improving the catalyst such as addition of a promoter. Besides the gas composition such as water vapor, the residence time of the catalyst and the reaction temperature are important factors that determine the catalyst performance. Therefore, in this example, first, the change in the decomposition rate was examined by lowering the SV. The experimental conditions were a reaction temperature of 300 ° C. and SV: 6000 h ⁻¹ under the same conditions as the water vapor introduction test in FIG. Three types of catalysts, Pt / Al ₂ O ₃ , PdPt / ZrO ₂ CeO ₂ , and PdPt / CeO ₂ were selected. As shown in the reaction test results in FIG. 6, an increase in the decomposition rate was confirmed by lowering SV in each catalyst. The decomposition rates of PdPt / ZrO ₂ CeO ₂ and PdPt / CeO ₂ increased to about 65%, but were below the decomposition rate of Pt / Al ₂ O ₃ at SV12000h ⁻¹ . In contrast, Pt / Al ₂ O ₃ was found to have a decomposition rate almost equal to that of the dry gas condition. In addition, as a result of examining the oxide catalyst CeO _{2 in the} same manner, it became clear that a decomposition rate of 98% or more equivalent to Pt / Al ₂ O ₃ was obtained (see Table 4 (iii), FIG. 1). ).

4-3 Effect of reaction temperature By lowering SV, Pt / Al ₂ O ₃ showed the same decomposition performance as that under dry gas conditions, but PdPt / ZrO ₂ CeO ₂ and PdPt / CeO ₂ The decomposition rate of Al ₂ O ₃ was less than or equal to SV: 12000 h ⁻¹ . Then, the change when reaction temperature was raised about PdPt / ZrO ₂ CeO ₂ was examined. FIG. 7 shows the results of increasing the reaction temperature with the same gas composition and SV: 6000 h ⁻¹ as in the water vapor introduction test. It was confirmed that the decomposition rate greatly increased with the increase of the reaction temperature, and that a decomposition rate equivalent to Pt / Al ₂ O ₃ was obtained at 180 ° C. Therefore, the catalyst was further narrowed down to Pt / Al ₂ O ₃ and PdPt / ZrO ₂ CeO _2, and the change when the reaction temperature was increased in the steam introduction test at SV: 12000 h ⁻¹ was examined. As shown in FIG. 7, it was revealed that a decomposition rate equivalent to dry gas conditions can be obtained at 180 ° C. for Pt / Al ₂ O _{3 and} 200 ° C. for PdPt / ZrO ₂ CeO ₂ . Regarding CeO ₂ , it became clear that a decomposition rate of 98% or more equivalent to Pt / Al ₂ O ₃ and PdPt / ZrO ₂ CeO ₂ was obtained at SV: 6000 h ⁻¹ and 300 ° C. (FIG. 2). reference)

From the above results, in the case of ZrO ₂ CeO ₂ and CeO ₂ which are the same oxide catalysts, a certain degree of increase in the decomposition rate was observed by increasing the reaction temperature. The change in rate was not recognized, and it was far from the target decomposition rate. For CeO ₂ , the decomposition rate was over 98% by reducing the SV to 6000 h ⁻¹ and the reaction temperature to 300 ° C., so CeO ₂ is a low-cost VOC decomposition catalyst that can replace the precious metal supported catalyst. (See Figure 2, Table 4 (v)).

From these results, Pt / Al ₂ O ₃ and PdPt / ZrO ₂ CeO ₂ can be applied as VOC decomposition catalysts by setting SV to 6000h ^-1 or a reaction temperature of 180 ° C or higher even in a gas composition containing water vapor. I found out.

4-4 Reaction characteristics of CeO ₂ It was confirmed that the influence of water vapor was great in various catalysts. However, although CeO ₂ has a low decomposition rate as shown in FIG. 8, there is almost no influence of water vapor. In addition, a noble metal-supported catalyst such as Pt has high catalytic performance, but on the other hand, since it is expensive, a cheaper oxide catalyst such as CeO ₂ is desirable from the viewpoint of cost. Therefore, in order to improve the decomposition rate with CeO ₂ , the reaction test was attempted with SV reduced to 6000 h ⁻¹ . In the precious metal supported catalyst, the effect of SV was confirmed, but in CeO _{2 the} decomposition rate was only slightly higher at the initial stage of the reaction, and both SV: 12000h ^-1 and 6000h ^-1 had a decomposition rate of 20% or less. It was not confirmed. Therefore, as with the noble metal-supported catalyst, an attempt was made to increase the reaction temperature. As shown in FIG. 9, the decomposition rate did not change significantly up to the reaction temperature of 220 ° C., but gradually increased from 250 ° C. to 300 ° C. It became clear that the decomposition rate was equivalent to Pt / Al ₂ O ₃ and PdPt / ZrO ₂ CeO ₂ . However, since the reaction gas was measured with a gas detector tube (manufactured by Gastec) having a low detection capability, there was a concern that an accurate reaction gas amount at a reaction temperature of 250 ° C. or higher could not be measured. Therefore, in Example 2, as a result of detecting the reaction gas by the gas chromatograph, as will be described in detail later, a decomposition rate of 95% is obtained at a reaction temperature of 400 ° C., SV = 5600 h ⁻¹ , a water vapor concentration of about 9%, and 300 ° C. In the vicinity, the decomposition rate was about 30%.

  As described above, as a result of screening with an oxide catalyst and a noble metal-supported catalyst as a VOC decomposition catalyst in the simulated combustion exhaust gas, the following results were obtained.

(1) CO ₂ : 15%, O ₂ : 5%, gas flow rate 400ml / min (space velocity SV: 12000h ^-1 ), benzene decomposition reaction test at 150 ° C, Pd / Al ₂ O ₃ , Pt It was found that noble metal supported catalysts such as / Al ₂ O ₃ and PdPt / ZrO ₂ CeO ₂ show high catalytic performance.

(2) In reaction tests with various catalysts, it was found that the decomposition rate was greatly reduced by the presence of water vapor. However, the decrease in SV (12000h ^-1 → 6000h ^-1 ), Pt / Al ₂ O ₃ , PdPt / ZrO ₂ CeO ₂ with a reaction temperature of 180 ° C or higher can provide catalytic performance equivalent to that under dry gas conditions. I found it.

(3) Among various catalysts, CeO ₂ is hardly affected by water vapor, and in the presence of water vapor, SV: 6000 h ⁻¹ , reaction temperature of 300 ° C., Pt / Al ₂ O ₃ , PdPt / ZrO ₂ It has been found that the catalyst performance is equivalent to that of CeO ₂ and is promising as a VOC decomposition catalyst that is cheaper than an expensive noble metal catalyst. However, as described above, the reaction gas was detected by gas chromatograph in Example 2, and as a result, the reaction temperature was 400 ° C., SV = 5600 h ⁻¹ , the water vapor concentration was about 9%, and the decomposition rate was 95%. Then, the decomposition rate was about 30%.

[Example 2]
Next, an experiment was conducted on ceria (CeO ₂ ) as a catalyst for decomposing VOC contained in factory exhaust gas and the like, and suitable reaction conditions at that time. In the experiment, the effects of SV, reaction temperature, and water vapor concentration in the VOC decomposition reaction were examined when VOC was benzene or toluene.

1. Benzene or Toluene Decomposition Test For the benzene or toluene decomposition reaction test, the same experimental apparatus as in FIG. 3 was used. The reaction tube 2 made of quartz was filled with 2 to 2.7 ml of ceria (CeO ₂ ; 1st rare element chemical industry, HS) as the catalyst 1, and the front and back of the catalyst 1 were fixed with quartz wool (not shown). The reaction tube 2 filled with the catalyst 1 was installed in a tubular electric furnace 3, and after raising the temperature to a predetermined temperature, a reaction test was started. Benzene (special reagent grade:> 99.5%, manufactured by Kanto Chemical Co., Inc.) or toluene (special reagent grade:> 99.5%, manufactured by Kanto Chemical Co., Ltd.) is injected into the glass diffusion tube 4, then kept at a constant temperature, and nitrogen is flowed at a constant flow rate. To generate a diluted gas. Moreover, water vapor | steam was introduce | transduced by bubbling water in the water vapor generation part 5 at a fixed temperature. The flow path of the gas containing benzene and water vapor or toluene and water vapor was kept at 130 ° C. or higher by a ribbon heater (the portion heated by the ribbon heater is indicated by diagonal lines in the figure). Assuming the combustion exhaust gas composition, the reaction conditions are such that the total gas flow rate of 15% CO ₂ , 5% O ₂ and N ₂ balance gas is 250 to 400 ml / min (space velocity SV = 5600 to 12000 h ⁻¹ ), and the reaction temperature. The reaction test was conducted at 150 ° C. The VOC concentration in the exhaust gas from various fixed sources varies from several ppm to several hundred ppm at chemical factories and several ppm to 20 ppm in waste treatment, but this time, the range that can be stably supplied from the VOC generator Benzene (about 30-40 ppm) or toluene (80, 220, 230-250 ppm) was introduced. The reaction gas is not the gas detector tube (manufactured by Gastec) used in Example 1, but a gas chromatograph (Shimadzu: C-R14A CHROMATAPAC, detector: FID) for the purpose of increasing the measurement accuracy. Measured.

2. Product analysis after toluene decomposition reaction After the decomposition reaction of toluene, the reaction gas was detected by gas chromatography. As a result, toluene and a trace amount of benzene were detected, but other components were not confirmed. Therefore, the gas after the reaction was qualitatively analyzed by GC-MS (Yokogawa Analytical System Co., Ltd .: 5973A-N series GC / MSD system), and the gas composition after the toluene decomposition reaction was examined.

3. Experimental results 3-1. The effect of reaction temperature and SV under dry gas conditions of benzene FIG. 10 shows the results of detailed examination of the effect of reaction temperature and SV under dry gas conditions of benzene. In 0.99 ° C., SV is from 30 to 33% at 6000h ^-1 or less, although the 6900H ^-1 or higher showed 20% or less and a low decomposition performance, raising the reaction temperature to 180 ° C., decomposition ratio of each SV is It was greatly improved. When the SV was 6000 h ⁻¹ or less, a decomposition rate of 95% or more was obtained. When the temperature was further increased, the decomposition rate gradually decreased, but showed a tendency to increase again from 300 ° C. When the SV was 8000h ^-1 or less, the decomposition rate was 95% or more at 350 ° C and 99% or more at 400 ° C. Obtained. Moreover, 99% or more was exhibited at 400 ° C. even at 12000 h ⁻¹ . Since no difference in decomposition rate due to the SV value was observed at 400 ° C., the reaction temperature at 400 ° C. or higher seems not to be affected by the SV value. Therefore, when the exhaust gas containing VOC discharged from a factory or the like is at a low temperature, it is preferable to raise the temperature using waste heat using a heat exchanger or the like. From these results, it was found that it is preferable to set SV to 5600 h ⁻¹ in order to obtain the target performance at a lower temperature. Therefore, in the following, experiments were performed with SV set to 5600 h ⁻¹ .
In addition, in each SV, the temperature dependence which the decomposition rate fell from 200 degreeC or more and the decomposition rate rose again above 300 degreeC was confirmed. In this reaction test, the decomposition rate is calculated from the difference in benzene concentration at the catalyst inlet and outlet. This phenomenon is that from the start of the reaction to 200 ° C, benzene is gradually adsorbed on the catalyst surface and a decomposition reaction occurs and the decomposition rate increases, but when it exceeds 200 ° C, benzene not adsorbed on the catalyst surface passes as it is. Therefore, at 200 ° C. or higher, the outlet concentration increases and the decomposition rate decreases. Furthermore, it was speculated that the decomposition rate increased again due to the activity of the catalyst surface increasing at 300 ° C. or higher.

3-2. Effect of water vapor concentration on benzene decomposition reaction The effect of water vapor was examined when SV was 5600 h- ¹ . The water vapor concentration assumed in the exhaust gas ranges from about 8% of the combustion gas level to 2 to 3% which is the exhaust gas level in various factory facilities other than the combustion process. Therefore, the water vapor concentration was controlled so that the exhaust gas level in various factories was about 2% to about 10% above the combustion exhaust gas level. FIG. 11 shows the results of the water vapor introduction test. Compared to FIG. 10, the degradation rate was confirmed to be lower due to the presence of water vapor, but the degradation rate increased from 300 ° C. or higher at water vapor concentrations of 2.07%, 6.05%, and 7.34%. It was confirmed that a decomposition rate of 95% or more was obtained at 400 ° C. It was also confirmed that the decomposition rate increased from 300 ° C. or higher even at a water vapor concentration of 8.84% and 10.83%, and a decomposition rate of 90% or higher was obtained at 400 ° C.

  From the above results, although the decomposition rate decreases somewhat due to the mixing of water vapor, when the water vapor concentration is 11% or less, the decomposition rate is improved from 300 ° C. or higher, and sufficient decomposition performance can be obtained by increasing to 400 ° C. It was confirmed to show. In other words, if the reaction temperature is 300 ° C. or higher with respect to the water vapor concentration (2 to 3%) contained in the exhaust gas from the factory or the like, as well as the water vapor concentration (8%) at the combustion exhaust gas level, It was confirmed that the present invention is sufficiently applicable to the benzene decomposition reaction.

3-3. Effect of reaction temperature on decomposition reaction of toluene From the results of benzene decomposition reaction tests, it was confirmed that the decomposition rate was 90% or higher at 400 ° C. or higher under the same conditions. The same decomposition was applied to VOC components other than benzene. Performance is desired. Therefore, the decomposition performance of toluene, which is used for various applications among the VOC components and has a high emission ratio among the VOC emissions, was examined. In various factories that generate toluene, especially in printing and painting facilities, the need for VOC countermeasures is increasing, and its emission concentration varies from tens of ppm to several hundred ppm depending on the source, depending on the type of industry. First, decomposition performance at 100 ppm or less was examined. The reaction conditions were a toluene concentration of 80 ppm, a reaction gas of 15% CO ₂ , 5% O ₂ and N ₂ balance gas with a total gas flow rate of 250 ml / min (SV: 5600 h ⁻¹ ) and a reaction temperature of 150 ° C. to 300 ° C. The reaction test was conducted. The result of the toluene reaction test under dry gas conditions is indicated by symbol Δ in FIG. Although the decomposition rate was about 35% at 150 ° C, the decomposition rate suddenly increased when the temperature was raised to 180 ° C. A decomposition performance of 99% or higher was obtained at 200 ° C, and a higher decomposition rate was obtained at a lower temperature than benzene. It became clear that

Next, the effect of water vapor was examined. The result of the toluene reaction test in the presence of water vapor is indicated by symbol ◯ in FIG. The water vapor concentration is controlled to 3% or less, which is the water vapor level in exhaust gas from various factory facilities that are the source of toluene, and is a total gas of 15% CO ₂ , 5% O ₂ and N ₂ balance gas including water vapor. The test was conducted at a flow rate of 250 ml / min (SV: 5600 h ⁻¹ ) and at a reaction temperature of 150 to 300 ° C. At 150 ° C, the decomposition rate is as low as about 8%. However, as with dry gas conditions, the decomposition rate increases greatly at 180 ° C, with 95% or more at 180 ° C, 97% or more at 200 ° C, and about 300% at 300 ° C. It was revealed that 99% decomposition performance was obtained. Therefore, when the water vapor concentration was 3% or less and the toluene concentration was 80 ppm or less, it was confirmed that the ceria catalyst can be sufficiently applied to the toluene decomposition reaction if the reaction temperature is 180 ° C. or higher. If the reaction temperature is 400 ° C. or higher, both benzene and toluene can be decomposed by 99% or more.

As described above, toluene is used for various purposes, and the VOC concentration in the exhaust gas varies from several tens ppm to 100 ppm or more depending on the generation source. Therefore, in order to examine the influence of the inlet concentration, a reaction test with increasing toluene concentration was conducted. The toluene concentration was controlled at a concentration range in which toluene could be stably supplied from the VOC generation part of the present reactor, and was about 220 ppm. FIG. 13 shows the reaction test results. Similar to the result of 80 ppm, the decomposition rate rapidly increased from 180 ° C., showed a decomposition performance of 98% or more at 200 ° C., and it was confirmed that there was no influence of the inlet concentration.
Next, the influence of the SV and water vapor concentration when the inlet concentration was further increased (230 to 250 ppm) was examined. FIG. 14 shows the results of a reaction test in which SV is 5600 to 10,000 h ^{−1 at} a water vapor concentration of about 3%. The decomposition performance under each condition increased as the reaction temperature increased, and a decomposition rate of 90% or more was obtained at 180 ° C., and a decomposition rate of 95% or more was obtained at 300 ° C.
Next, FIG. 15 shows the results of a reaction test in which the water vapor concentration at 5600 h ⁻¹ is about 2% to 10%. Increasing the reaction temperature from 150 ° C. to 180 ° C. increases the decomposition rate, and the decomposition performance slightly decreases as the water vapor concentration increases. However, when the water vapor concentration is 7% or less, the decomposition rate is 90% or higher. When the concentration was 10%, it was revealed that the decomposition rate was about 80%.
Therefore, it was confirmed that when the water vapor concentration is 10% or less, the ceria catalyst can be sufficiently applied to the toluene decomposition reaction if the reaction temperature is 180 ° C. or higher.

3-4. Product Analysis after Toluene Decomposition Reaction FIG. 16 shows the result of qualitative analysis of the gas after toluene decomposition reaction by GC-MS. From this result, only the unreacted toluene was detected as the VOC component, and it was confirmed that no other VOC component was produced. The reason why benzene was not detected is considered to be due to adhesion to the collected pack or the change with time. Therefore, it was confirmed that no new VOCs other than toluene and benzene were generated by the decomposition reaction of toluene.

As described above, the effects of SV, temperature, and water vapor concentration in the VOC decomposition reaction when ceria (CeO ₂ ) was used as the VOC decomposition catalyst were examined in the case where VOC was benzene and toluene, and the following knowledge was obtained.

(1) Benzene decomposition reaction test Under a dry gas condition, a decomposition performance of 99% or more is obtained at 400 ° C., and it is clear that SV = 5600h ⁻¹ shows a high decomposition rate of 97% or more even at a lower temperature. became.
Further, as a result of the steam introduction test at SV = 5600 h ⁻¹ , a decomposition rate of 90% or higher at 400 ° C. was obtained at a water vapor concentration of about 11%, and 97% or higher at about 2%. Performance was confirmed.

(2) Toluene decomposition reaction test With a dry gas, the decomposition performance is 98% or more at 180 ° C or higher. In the water vapor introduction test (water vapor concentration 3%, SV = 5600h ^-1 ), the decomposition performance is 95% or higher at 180 ° C or higher. Indicated. It was also confirmed that there was no effect on the decomposition performance even when the inlet concentration (80 ppm, 220 ppm) was changed. Furthermore, when SV is 10,000 h ⁻¹ or less (water vapor concentration 3% or less), the decomposition temperature is 90% or more at a reaction temperature of 180 ° C., and when the water vapor concentration is 10% or less (SV: 5600 h ⁻¹ ), the reaction temperature is It was revealed that the decomposition performance was 80% or more at 180 ° C. Therefore, it was confirmed that the ceria catalyst is sufficiently applicable as the VOC decomposition catalyst.
Further, as a result of GC-MS analysis of the reaction product gas, only unreacted toluene was detected, and it was confirmed that no other VOC component was produced. That is, it was confirmed that no new VOCs other than toluene and benzene were generated by the decomposition reaction of toluene.

  The above results were obtained under the condition that the concentration of water vapor in the gas was 11% or less in the case of benzene and 10% or less in the case of toluene. The conditions to which the present invention can be applied are not limited to these examples, and the present invention can be applied even in a range where the water vapor concentration is different or in dry gas.

  In addition, in the present specification, “the condition that water vapor exists in the gas” refers to, for example, when water vapor is originally contained in the exhaust gas such as fossil fuel combustion exhaust gas, and water vapor is artificially introduced. This is also included. Therefore, for example, the present invention can also be applied to a gas in which water vapor is artificially injected into a dry gas as in a VOC process using a conventional noble metal-supported catalyst to form a water vapor mixture state.

It is a graph which shows the result (effect of SV) of the benzene decomposition reaction test in the Example of this invention. It is a graph which shows the result (effect of reaction temperature) of the benzene decomposition reaction test in a present Example. It is a block diagram of the VOC decomposition reaction test apparatus in a present Example. It is a graph which shows the result of the benzene decomposition reaction test in a present Example. It is a graph which shows the result of the water vapor | steam introduction test in a present Example. It is a graph which shows the result (effect of SV) of the benzene decomposition reaction test in a present Example. It is a graph which shows the result (effect of reaction temperature) of the benzene decomposition reaction test in a present Example. It is a graph showing the effect of water vapor on the CeO ₂ in the present embodiment. Is a graph showing the effect of reaction in CeO ₂ in the present embodiment. It is a graph which shows the result (influence of SV with dry gas) of the benzene decomposition reaction test in a present Example. It is a graph which shows the result (influence of water vapor | steam) of the benzene decomposition reaction test in a present Example. It is a graph which shows the result (effect of water vapor | steam) of the toluene decomposition reaction test in a present Example. It is a graph which shows the result (effect of inlet_port | entrance concentration) of the toluene decomposition reaction test in a present Example. It is a graph which shows the result (effect of SV) of the toluene decomposition reaction test in a present Example. It is a graph which shows the result (effect of water vapor | steam) of the toluene decomposition reaction test in a present Example. It is a figure which shows the result of having analyzed the gas after the decomposition reaction of toluene in a present Example by GC-MS.

Explanation of symbols

1 Catalyst

Claims (4)

In the method of catalytic decomposition of volatile organic compound gas in exhaust gas, the exhaust gas contains water vapor, and ceria (CeO ₂ ) is used alone as the catalyst to decompose and remove the volatile organic compound gas. A method for decomposing and removing volatile organic compounds.   The method for decomposing and removing a volatile organic compound according to claim 1, wherein the exhaust gas is a combustion exhaust gas. A catalyst for decomposing and removing volatile organic compounds, characterized by comprising ceria (CeO ₂ ), which is used for decomposing volatile organic compound gases in exhaust gas containing water vapor. The catalyst for decomposing and removing volatile organic compounds according to claim 3 , wherein the exhaust gas is combustion exhaust gas.