JP5448465B2 - Method for treating exhaust gas containing aliphatic halogenated hydrocarbons - Google Patents

Description

  The present invention relates to a novel method for treating exhaust gas containing aliphatic halogenated hydrocarbons such as 1,2-dichloroethane and vinyl chloride monomer. Specifically, the present invention relates to an exhaust gas treatment method in which an aliphatic halogenated hydrocarbon-containing exhaust gas is brought into contact with a cracking catalyst to decompose and detoxify the contained aliphatic halogenated hydrocarbon.

  In exhaust gas discharged from organochlorine compound production facilities and various industrial processes, 1,2-dichloroethane (EDC), vinyl chloride monomer (VCM), methylene chloride, chloroform, carbon tetrachloride, methyl chloride, trichloroethylene, tetrachloroethylene, Organic chlorine compounds such as dichloroethylene and vinylidene chloride are included. These are produced as various useful intermediate materials and products, but are often harmful, and various environmental regulations are required to reduce or prevent the release of these substances into the atmosphere. .

  As a typical treatment method for exhaust gas containing these, organic substances are recovered using a direct combustion method using a fuel such as propane or butane at a high temperature of 800 ° C. or higher, and an adsorbent such as activated carbon or silica gel. There are an adsorption method that causes the catalyst to oxidize and decomposes at a relatively low temperature using a catalyst.

  Responding to places where waste liquids and exhaust gases with a high concentration of harmful pollutants are regularly discharged, which are relatively easy to deal with, against the backdrop of recent stricter regulations on harmful air pollutants and increased environmental awareness Is progressing. However, in order to further reduce emission in the future, it is necessary to efficiently treat exhaust gas having a lower concentration and a larger air volume.

  In such an exhaust gas treatment, the direct combustion method, which has been adopted relatively frequently so far, requires a large amount of fuel to raise the gas flow to a predetermined temperature of 800 ° C. or higher, and the equipment cost and proportional cost Both are expensive processing methods. On the other hand, with respect to the adsorption method, it is difficult to recover depending on the adsorbed material, and eventually some incineration equipment may be required, and the concentration of the object to be treated in the exhaust gas after treatment cannot be extremely reduced. is there.

  As a method for processing a large amount of low concentration organic substance-containing gas among the prior arts, a catalytic oxidation method that can reduce the concentration of the processed material in the exhaust gas after processing at a relatively low cost is considered advantageous. Many catalysts have been proposed for this purpose.

  In general, since a halogen-containing compound is difficult to decompose, such a catalyst usually has a high oxidizing power by supporting a metal or metal chloride on a support made of an oxide. However, such a catalyst supporting a metal or metal chloride, due to its strong oxidizing power, generates chlorine as a decomposition product when, for example, a chlorine-containing compound is decomposed. Chlorine has low solubility in neutral water, so it is necessary to absorb chlorine contained in the exhaust gas in a basic aqueous solution such as an aqueous solution of caustic soda. Further, hypochlorous acid generated by absorption is further added to sodium bisulfite, etc. It was necessary to decompose by. In addition, there was a problem of equipment corrosion due to the generated hypochlorous acid.

  On the other hand, it is possible to use a catalyst having a relatively low oxidizability of the catalyst so as not to generate chlorine, or to adjust the conditions such as temperature. However, in this case, the oxidation of organic substances becomes insufficient, Another problem arises that carbon oxide is generated.

  That is, when an organic halogen compound is decomposed, it is very difficult to generate neither chlorine nor carbon monoxide after decomposition even if a single decomposition catalyst is used. In particular, aliphatic halogenated hydrocarbons require much more treatment than aromatic halogenated hydrocarbons such as dioxins, and a large amount of chlorine (halogen) and carbon monoxide is generated. Therefore, the solution to this problem is urgent.

  In order to solve such problems, the catalyst has a two-stage configuration, and a catalyst having an oxidizing power that does not generate chlorine is used in the first stage, and the carbon monoxide generated here is in the second stage. A method of decomposing with a catalyst has been proposed (for example, Patent Document 1).

  In the catalyst system specifically disclosed in Patent Document 1, it is necessary to support a metal such as Cr or Ru in order to avoid halogen poisoning of the first stage catalyst and to improve the catalyst life. There is.

JP-A-6-63357

  However, when the metal as described above is supported on the catalyst, the oxidizing power becomes relatively high, so that it is necessary to add a large amount of water vapor (water) in order not to generate chlorine. The water vapor thus added has a problem of promoting corrosion of the apparatus. On the other hand, a catalyst that does not carry a metal has a problem in the catalyst life.

  Furthermore, in the absence of water vapor, the second stage catalyst for oxidizing carbon monoxide may further decompose the hydrogen halide, eventually producing halogen.

  Accordingly, the present invention has an object to provide an aliphatic halogenated hydrocarbon decomposition catalyst system that solves the above-described problems, does not generate halogen without adding water vapor, and completely oxidizes carbon monoxide. And

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that, by adopting a specific support in the first stage catalyst, a sufficient life can be expressed without supporting a metal. As a second stage catalyst, it has been found that a combination of a specific carrier and a specific supported metal does not generate halogen and completely oxidizes carbon monoxide, so that it is contained in the exhaust gas. The inventors have found that a high degree of decomposition treatment of an organic halogen compound can be achieved, and have completed the present invention.

That is, the present invention is an exhaust gas treatment method for treating exhaust gas containing an aliphatic chlorinated hydrocarbon using a catalyst without adding water vapor, and the exhaust gas is treated with (A) titanium oxide and tungsten oxide. In contact with a first catalyst that does not carry a metal in a non-oxide state, and then (B) a second catalyst made of titanium oxide supporting metal Pd. The exhaust gas treatment method is characterized.

  According to the method of the present invention, the aliphatic halogenated hydrocarbon is decomposed with the first catalyst capable of generating carbon monoxide but generating no halogen, and then generating the generated carbon monoxide. Is a second catalyst that can oxidize without generating halogen, and it is a highly aliphatic system while suppressing the generation of both carbon monoxide and halogen by using two types of catalysts with different effects. The halogenated hydrocarbon-containing gas can be treated, the catalyst life is good, and further, halogen is hardly generated without adding water vapor, so that the problem of equipment corrosion hardly occurs.

  Therefore, by using the decomposition method of the present invention, it becomes possible to generate no harmful gas such as carbon monoxide and chlorine, and in the equipment such as a detoxification tower provided in the subsequent stage, caustic soda It is possible to fully decompose and detoxify aliphatic halogenated hydrocarbons in exhaust gas without the need for expensive reducing agents such as alkali and bisulfite, and industrially sufficient A long lifespan.

The figure which shows the result of the experiment which evaluated the lifetime of the catalyst which consists of various metal oxides in EDC decomposition | disassembly. Shows the results of experiments assaying the _TiO 2 _-WO 3 _-V 2 _{O 5} or lifetime of a catalyst consisting of TiO ₂ in the EDC degradation. Shows the results of experiments assaying the life of a catalyst consisting of _TiO 2 _-WO 3 _-V 2 _{O 5} or _TiO 2 -WO ₃ in EDC degradation.

  The exhaust gas targeted for the decomposition method of the present invention is a gas containing an aliphatic halogenated hydrocarbon. Such an aliphatic halogenated hydrocarbon is a linear or cyclic compound having at least one element selected from the group consisting of chlorine, fluorine, bromine and iodine which are halogen elements in the aliphatic hydrocarbon molecular structure. It is. Among these aliphatic halogenated hydrocarbons, aliphatic chlorinated hydrocarbons having at least one chlorine atom in the molecule can be efficiently decomposed. Specific examples thereof include aliphatic halogenated hydrocarbons such as dichloroethane, vinyl chloride monomer, methylene chloride, chloroform, methyl chloride, carbon tetrachloride, dichloroethylene, trichloroethylene, tetrachloroethylene, chlorotoluene, and propylene dichloride.

The necessity of treating a large amount of exhaust gas containing an organic halogen compound as described above is high when treating exhaust gas generated when an organic halogen compound or its derivative is produced. For example, a vinyl chloride monomer (VCM: CH ₂ CHCl) is often produced by reacting ethylene and chlorine to obtain 1,2-dichloroethane (EDC), and further decomposing this EDC. EDC and VCM are contained in exhaust gas, and as by-products, methylene chloride, chloroform, carbon tetrachloride, 1,1-dichloroethane, chloroethane, vinylidene chloride, allyl chloride, chloroprene, 1,1,1-trichloroethane Monochlorobenzene, trichloroethylene, 1,2-dichloropropane, etc. may also be present in the exhaust gas.

  The treatment method of the present invention is applicable to the treatment of exhaust gas in which a plurality of types of organic halogen compounds are mixed, and may further contain an organic substance (raw material or by-product) that does not contain a halogen atom. .

  Examples of organic compounds other than such organic halogen compounds include saturated hydrocarbons such as ethane, propane, and butane, unsaturated hydrocarbons such as ethylene, propylene, and butene, alcohols such as methanol and ethanol, methyl ether, and ethyl. And ethers such as ether and dimethyl ether. For example, in the production of the vinyl chloride monomer, the exhaust gas may contain components derived from raw materials such as ethylene and ethane, ethylene, acetylene, etc. generated by side reactions.

  In the present invention, the exhaust gas containing the organic halogen compound as described above and optionally other organic compounds is decomposed in contact with the catalyst in at least two stages. As described above, the catalyst in the first stage (first catalyst) contains (A) a titanium oxide and a tungsten oxide as main components and does not bear a non-oxide metal. The second stage catalyst (second catalyst) for contacting the gas generated by contacting with this catalyst is a catalyst made of (B) titanium oxide supporting metal Pd.

  It is extremely important that the first catalyst is a catalyst that does not bear a non-oxide metal. When a metal in a non-oxide state such as a metal or a metal in a chloride state is supported, the oxidizing power is too strong, and halogens such as chlorine are generated under the condition that the organic halogen compound is sufficiently decomposed. This causes various problems. Even if a metal is supported, a large amount of halogen is often generated unless water vapor is present, as described in Comparative Examples of JP-A No. 51-11065.

  However, many of the catalysts that do not carry a metal in a non-oxide state are poisoned by halogens as described in Patent Document 1 (paragraph 0015 of JP-A-6-63357). Therefore, the catalyst life is shortened, or sufficient decomposition performance of the organic halogen compound cannot be obtained. In the present invention, it is necessary to use a catalyst mainly composed of titanium oxide and tungsten oxide in order to solve these problems and obtain sufficient decomposition performance and lifetime of the organic halogen compound. When both of these titanium oxides and tungsten oxides are not included, the catalyst life is shortened as described above, or sufficient decomposition performance of the organic halogen compound cannot be obtained.

  As this first catalyst, the total of titanium oxide and tungsten oxide is 100% by mass, titanium oxide is preferably 97 to 70% by mass, and tungsten oxide is preferably 3 to 30% by mass. . In particular, when the content of tungsten oxide is within the above range, high decomposition activity can be obtained.

  These titanium oxide and tungsten oxide may exist as a mixture of independent oxides, or may exist in the form of a composite oxide.

  The first stage catalyst in the present invention may contain a metal other than titanium and tungsten as long as it is in an oxide state. Examples of oxides of metals other than titanium and tungsten include silica, alumina, zirconia, niobium oxide, molybdenum oxide, vanadium oxide, and the like.

  Among these, it is preferable that vanadium oxide is contained in that the decomposition activity of the organic halogen compound is improved. Since the heat resistance tends to decrease as the vanadium oxide content increases, the vanadium oxide content in the first catalyst may be 30% by mass or less based on 100% by mass of the entire first catalyst. preferable. More preferably, it is 0.1-15 mass%.

  The content of oxides other than titanium oxide, tungsten oxide and vanadium oxide is preferably 15% by mass or less, more preferably 10% by mass or less, based on 100% by mass of the entire first catalyst. It is preferably 5% by mass or less.

  There is no restriction | limiting in particular about the shape of said 1st catalyst, It shape | molds and uses for desired shapes, such as honeycomb shape, corrugated plate shape, net shape, columnar shape, cylindrical shape, spherical shape, pellet shape. More preferably, a honeycomb shape or the like is desirable in order to reduce the pressure loss when the gas passes.

The BET specific surface area of the first catalyst is not particularly limited, is preferably 10 to 150 m ² / g, more preferably from 30 to 100 m ² / g.

The amount of catalyst used depends on the shape of the catalyst used and the aliphatic halogenated hydrocarbons and other organic substances in the exhaust gas to be treated. However, if the total amount of all organic compounds in the exhaust gas is usually about 3000 ppm, It is preferable that the space velocity is 1500 to 10000 hr ⁻¹ .

  In the present invention, the exhaust gas is first brought into contact with the catalyst as described above, whereby the aliphatic halogenated hydrocarbon contained in the exhaust gas is decomposed to generate carbon dioxide, carbon monoxide and hydrogen chloride. The higher the contact temperature, the higher the decomposition efficiency of the aliphatic halogenated hydrocarbons. However, if the contact temperature is higher than necessary, deterioration of the catalyst tends to proceed, and in some cases, halogens may still be generated even when the above catalysts are used. There is also.

  Therefore, at the time of the contact, the catalyst inlet gas temperature is preferably adjusted to 200 to 500 ° C, and particularly preferably adjusted to a range of 200 to 450 ° C. The temperature is adjusted by using a heater such as a burner or an electric heater in the front stage of the catalyst reactor, changing the amount of fuel such as LPG or propane, or the amount of electric power so that the temperature becomes an arbitrary temperature, A method for adjusting the heating temperature or the like can be appropriately employed.

  In the present invention, the gas generated by contacting the first catalyst as described above is brought into contact with the second catalyst, and carbon monoxide in the gas is oxidized and converted to carbon dioxide.

  In the present invention, it is necessary to use a catalyst made of titanium oxide supporting metal Pd as the second catalyst. A catalyst that does not carry any metal cannot sufficiently oxidize carbon monoxide. Further, even when the supported metal is the same platinum group element, although carbon monoxide is sufficiently oxidized, halogen is also generated at the same time, which makes it meaningless to have a two-stage catalyst. In addition, when other carriers such as silica and alumina are used, carbon monoxide is not sufficiently oxidized. Furthermore, a gas containing hydrogen halide is inevitably treated, but a basic carrier such as alumina has poor acid resistance and thus has a problem in life.

  In the second catalyst composed of the titanium oxide supporting the metal Pd used in the present invention, the titanium oxide serving as the carrier may be a rutile type, anatase type, or amorphous one, preferably Is anatase type.

  The carrier of the second catalyst needs to be substantially made of titanium oxide. Here, “substantially” refers to 85% by mass or more of titanium oxide with 100% by mass as a whole excluding the supported metal component. It is preferably 90% by mass or more, and more preferably 95% by mass or more.

  There is no restriction | limiting in particular also about the shape of the said 2nd catalyst of this invention, It can shape | mold and use in desired shapes, such as spherical shape, pellet shape, column shape, cylindrical shape, honeycomb shape, corrugated plate shape, net shape. More preferably, a spherical shape or the like is desirable. In the spherical catalyst, the pressure loss is increased as compared with the honeycomb-shaped catalyst, but the contact efficiency between the gas and the active point on the catalyst is increased, so that the reactivity is increased, and as a result, the amount of metal used can be reduced. Therefore, in the second catalyst using Pd, the influence of the economic effect is great.

The value of the BET specific surface area of the carrier is not particularly limited, but is preferably 10 to 200 m ² / g, and more preferably 30 to 150 m ² / g.

  The metal Pd supported on such a carrier is 0.01 to 5% by mass, preferably 0.01 to 3% by mass, more preferably 0.05 to 2% by mass with respect to 100% by mass of the titanium oxide. It is. When the amount is increased to a certain extent, the oxidation performance is better. However, if the amount is larger than the above range, the oxidation ability cannot be improved so much, which is economically disadvantageous.

  The distribution in the depth direction of the metal Pd supported on the support made of titanium oxide is not particularly limited in any manner of uniform support, outer layer support, inner layer support, and center support, It is during the outer layer. Since this reaction has a particularly high reaction rate on the surface of the catalyst, the oxidation performance can be maximized with a small amount by supporting the metal Pd on the outer layer of titanium oxide.

  The method for supporting the metal Pd on the titanium oxide in the present invention is not particularly limited, and a known method can be adopted. For example, a generally used method such as an impregnation method can be used, and a nitrate such as a palladium nitrate solution, a chloride such as a palladium chloride solution, and other ammonium salt solutions are used to impregnate a desired amount with respect to the titania carrier weight. By firing, and then reducing palladium chloride with various reducing agents, metal Pd can be obtained. Examples of the reducing agent include alcohols such as ethanol and glycol, hydrogen, hydrazine, formamide, ethanolamine, citric acid and the like.

The amount of the second catalyst used depends on the shape of the catalyst used, etc., but if the total amount of all organic compounds in the exhaust gas before contacting with the first catalyst is usually about 3000 ppm, It is preferable to set the space velocity to 3000 to 20000 hr ⁻¹ .

  In the exhaust gas treatment method of the present invention, it is necessary to sequentially contact the exhaust gas containing the aliphatic halogenated hydrocarbon with the two kinds of catalysts described above. The apparatus for performing the contact is not particularly limited, and a known exhaust gas treatment apparatus may be applied. In this case, for example, one in which the first catalyst and the second catalyst are sequentially charged in the first and second order in the gas flow direction in the same catalyst reactor may be used. It is also possible to use a catalyst reactor filled with the above and connected in series.

  The concentration of the aliphatic halogenated hydrocarbon contained in the exhaust gas in the exhaust gas treatment method of the present invention is not particularly limited, but catalytic oxidation as compared with other treatment methods such as adsorption method, plasma method, direct combustion method and the like. In view of sufficiently obtaining the merit of the method, it is preferable to apply it to the treatment of exhaust gas having an aliphatic halogenated hydrocarbon concentration of 1 ppm or more, and more preferably to treat the exhaust gas of 10 ppm or more. For the same reason, it is preferably applied to the treatment of exhaust gas having a concentration of 10% or less, and more preferably applied to the treatment of exhaust gas having a concentration of 5% or less. Of course, if necessary, for example, when the concentration of the aliphatic halogenated hydrocarbon contained in the exhaust gas is low, it may be treated after concentration using an adsorption device or the like. You may process after diluting with other gas, such as air. In the present specification, the concentration of each component in the gas is a volume concentration.

  In the exhaust gas treatment method of the present invention, the temperature when the exhaust gas is brought into contact with the catalyst is preferably 200 to 500 ° C. at the inlet temperature of the catalyst reactor filled with the first catalyst, and is in the range of 200 to 450 ° C. It is more preferable to adjust to. The higher the temperature, the higher the efficiency of the reaction (decomposition), but the cost for preheating to increase the temperature also increases, and the durability (pot life) of the catalyst tends to decrease. If it is extremely high, chlorine gas may be produced even if the first catalyst of the present invention is employed. The inlet temperature is adjusted by using a heater such as a burner or an electric heater in the previous stage of the catalyst reactor, and changing the amount of fuel such as LPG or propane or the amount of electric power so as to reach a desired temperature, reactor A method for adjusting the heating temperature can be appropriately employed.

  Most of the reactions for decomposing aliphatic halogenated hydrocarbons are exothermic reactions, and the more organic components in the exhaust gas, the higher the actual temperature in the catalyst layer. That is, the actual temperature in the catalyst layer is higher than the catalyst inlet temperature.

  Some of the conventionally known catalysts do not generate chlorine gas even when aliphatic halogenated hydrocarbons are decomposed at low temperatures, but the decomposition efficiency is relatively low at low temperatures, so that aliphatics that decompose A large amount of catalyst is required with respect to the amount of halogenated hydrocarbon, and eventually it was difficult for the aliphatic halogenated hydrocarbon to efficiently decompose high-concentration exhaust gas.

  In the present invention, the use of the specific catalyst prevents chlorine gas from being substantially generated even at a high temperature such that the catalyst temperature reaches 500 ° C. Can be processed efficiently.

  In the method for treating exhaust gas containing an aliphatic halogenated hydrocarbon of the present invention, in terms of energy efficiency, the gas to be treated after being brought into contact with the second catalyst is brought into contact with a heat exchanger to perform heat recovery, It is also preferable to preheat the exhaust gas before being introduced into the catalytic reactor with this recovered heat. As the heat exchanger, a commonly used heat exchanger such as a plate type or a shell and tube type can be used. Usually, since sufficient preheating cannot be performed only with the recovered heat, it is preferable to use preheating with a burner or an electric heater as described above.

In addition, the exhaust gas treated using the exhaust gas treatment method of the present invention contains dioxins, chlorophenol, PCB and other harmful substances, such as exhaust gas discharged from an incineration facility that treats industrial waste, etc. In this case, it is preferable that the gas to be treated after being brought into contact with the second stage catalyst is further subjected to a dioxins decomposition step. This is because the permissible concentration of dioxins is significantly lower than the aliphatic halogenated hydrocarbons treated by the treatment method of the present invention (the strictest standard value for each treatment capacity of the incinerator is 0.1 ng-TEQ / m ³ or less), even if the aliphatic halogenated hydrocarbon concentration is sufficiently reduced by the treatment method of the present invention, dioxins may have to be treated to a lower concentration.

  As a method for decomposing dioxins, a known method can be adopted without particular limitation, and examples thereof include a method for decomposing with a catalyst. When using a catalyst to detoxify dioxins, the catalyst decomposition step may be performed immediately after contacting the second stage catalyst, or the exhaust gas is cooled to some extent by the heat exchanger described above. It doesn't matter even after. Desirably, in order to reduce the synthesis of dioxins on the catalyst and the load on the catalyst, it is better to provide a step of detoxifying the dioxins after the gas temperature is lowered to some extent.

  According to the exhaust gas treatment method of the present invention, both the concentration of halogen gas (chlorine gas, etc.) and the concentration of carbon monoxide in the gas to be treated can be made lower than the level that causes a problem. However, in this state, the gas still contains hydrogen halide such as hydrogen chloride generated by the decomposition of the aliphatic halogenated hydrocarbon. Therefore, after passing through a detoxification facility for removing the hydrogen halide. It is necessary to release to the atmosphere. As a method for removing hydrogen halide, a known method may be adopted as appropriate. For example, a method of contacting and absorbing the gas to be treated with an alkaline aqueous solution such as sodium hydroxide or calcium hydroxide may be mentioned. In view of energy efficiency, the contact with the aqueous alkali solution is preferably performed after the heat exchange described above. Furthermore, when providing the decomposition process of said dioxins, it is preferable to provide the contact with this alkaline aqueous solution after this decomposition process.

  The gas to be treated in which the aliphatic halogenated hydrocarbon is decomposed by the exhaust gas treatment method of the present invention and the above (decomposition of dioxins and hydrogen halide is removed) is usually a substantially harmful substance. Can be released into the atmosphere as it is. However, if other substances that need to be removed are included, a detoxification method suitable for the substance should be applied before or after applying the exhaust gas treatment method of the present invention, and then released into the atmosphere. .

  EXAMPLES Hereinafter, examples will be shown to describe the present invention more specifically, but the present invention is not limited to these examples.

  In each experimental example, the concentration of 1,2-dichloroethane (hereinafter abbreviated as EDC) in the gas was analyzed with a gas chromatograph GC2014 (FID detector) manufactured by Shimadzu Corporation. The analysis of the carbon monoxide concentration was performed using a Shimadzu gas chromatograph GC8A (TCD detector). As for the chlorine concentration, the gas detector No. 8La and No. 8H, no. 8HH was appropriately selected, and the gas to be analyzed was sucked and measured.

  The lower limit of the analytical concentration of carbon monoxide was 10 ppm, and that of chlorine was 0.5 ppm. When it was below the lower limit of detection, it was indicated as “N.D.”.

1. Life comparison of first stage catalyst Reference Comparative Example 1
The EDC decomposition rate was measured using commercially available catalysts composed of various metal oxides shown in Table 1. The experimental conditions are as shown in Table 2 below. The results are shown in FIG.

Reference Comparative Example 2, Reference Example 1
The catalyst used and the conditions were changed as shown in Tables 3 and 4 to measure the EDC decomposition rate. In this experimental example, since the EDC concentration in the gas is high, the conditions are more severe than those in Reference Comparative Example 1. The results are shown in FIG.

Reference Example 2
The catalyst used and the conditions were changed as shown in Tables 5 and 6 to measure the EDC decomposition rate. The results are shown in FIG.

  As understood from each of the above reference comparative examples and reference examples, the catalyst mainly composed of titanium oxide and tungsten oxide used in the present invention has a very good life compared to the catalyst composed of other metal oxides. It is understood that

  In addition, although the catalyst which does not carry | support vanadium oxide is not evaluating the lifetime on the same conditions as the catalyst which consists of another metal oxide, from Reference Example 2, even if it does not carry vanadium oxide, Obviously, it has a lifespan equivalent to that carried.

2. Examination of EDC decomposition rate and by-products of first stage catalyst Reference Examples 3-6
TiO ₂ —WO ₃ (WO ₃ content: 15.5%) having a diameter of 50 mm and a honeycomb shape (pitch: 3.3 mm) was used as a catalyst, and the EDC decomposition rate and chlorine generation amount were measured under the conditions described in Tables 7 and 8 below. evaluated. The results are shown in Table 8. The conditions listed in Table 7 are common to Reference Examples 3-6.

Reference Comparative Example 3
Evaluation was performed in the same manner as in Reference Examples 3 to 6, using a catalyst in which RuCl ₃ corresponding to 0.5% by mass was further supported on TiO ₂ —WO ₃ (WO ₃ content 15.5%). It was. The results are shown in Table 8.

3. Examination of catalyst in the second stage A gas containing 7,000 ppm of CO and 8,000 ppm of HCl was prepared by thermally decomposing EDC, and the CO decomposition rate and Cl ₂ generation concentration were evaluated under the conditions shown in Tables 9 and 10. did. In all experiments, the metal loading was 0.5% by mass. The results are shown in Table 10 together.

  Hereinafter, an experimental result in which the gas containing EDC is allowed to pass through both the first catalyst and the second catalyst to evaluate the final hazardous substance decomposition performance is shown. In each evaluation, an air balance gas containing 2500 ppm of EDC was subjected to the test as a simulated exhaust gas.

Example 1
As the first catalyst, a TiO ₂ —WO ₃ catalyst having a honeycomb shape with a pitch of 3.3 mm and a length of 50 mm × width of 50 mm × height of 1000 mm is used, and the second catalyst has a spherical diameter of ₂ to 4 mm and 0.5 A TiO ₂ catalyst loaded with mass% metal Pd as an outer layer and filled with 1 kg in a catalyst layer portion of 70 mm length × 70 mm width was used.

Note first catalyst, TiO ₂ 80.8% by weight, WO ₃ was 14.8 wt% (WO ₃ 15.5 wt% per 100 wt% of TiO ₂ and WO ₃₎ . Molybdenden oxide was not included.

The simulated exhaust gas was supplied to the catalyst reactor 1 filled with the first catalyst so that the inlet temperature was 360 ° C., the linear velocity was 1.1 Nm / s, and the space velocity was 4000 Nm ³ / h.

The gas discharged from the catalyst reactor was introduced as it was into the catalyst reactor 2 filled with the second catalyst (inlet temperature 420 ° C., linear velocity 0.57 Nm / s, space velocity 10000 Nm ³ / h).

  Table 11 summarizes the results of analyzing the EDC concentration, carbon monoxide concentration, and chlorine gas concentration of the gas discharged from the catalytic reactor 2.

  When the gas discharged from the catalyst reactor 1 filled with the first catalyst was sampled and analyzed for each gas concentration, the EDC decomposition rate was 99.9% or more, the carbon monoxide concentration was about 4000 ppm, and chlorine was detected. It was below the limit.

Examples 2-5, Comparative Examples 1-6
Evaluation was performed in the same manner as in Example 1 except that the inlet temperature in the catalyst reactor 1 and the type (composition) of the second catalyst were changed as shown in Table 11. The results are also shown in Table 11.

Example 6
As a first catalyst, 0.4% by mass of V ₂ O ₅ is contained, TiO ₂ is 86.8% by mass, WO ₃ is 8.1% by mass (based on 100% by mass of TiO ₂ and WO ₃ in total) Evaluation was conducted in the same manner as in Example 1 except that a catalyst having a composition of WO ₃ of 8.5% by mass was used. The results are also shown in Table 11.

Example 7
The same procedure as in Example 1 was used, except that a catalyst having a spherical diameter of ₂ to 4 mm, a TiO ₂ content of 97% by mass and a metal Pd corresponding to 0.5% by weight of the total weight was used as an inner layer. And evaluated. The results are also shown in Table 11.

Claims (2)

An exhaust gas treatment method for treating an exhaust gas containing an aliphatic chlorinated hydrocarbon using a catalyst without adding water vapor, the exhaust gas comprising (A) titanium oxide and tungsten oxide as main components, and The non-oxide state metal is brought into contact with a non-supported first catalyst, and then (B) a second catalyst made of titanium oxide supporting metal Pd is brought into contact with the exhaust gas. Method.
  The exhaust gas treatment method according to claim 1, wherein the first catalyst is a catalyst further containing vanadium oxide.

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