JP2008207102A - Wastewater treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique related to a treatment method for performing the wet oxidation of wastewater to especially prevent a drift flow of a gas and a liquid in a reactor wherein wastewater and a treatment gas forms a counter flow in a vertical direction. <P>SOLUTION: In the treatment method of wastewater for treating an oxidizable substance using a catalyst, wastewater is passed through a dispersion bed, a dilution bed and a catalyst bed successively. The volume of the dispersion bed is preferably 0.06-0.6 and the volume of the dilution bed is 0.2-0.5 with respect to the volume 1 of the catalyst bed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technique relating to a treatment method for wet oxidation of waste water.

  Conventionally, biological treatment methods, combustion treatment methods, wet oxidation treatment methods and the like are widely used as methods for treating waste water. In the biological treatment method, surplus sludge and other by-products are generated, so that the treatment often becomes a problem, and there are also problems such as the presence of a lot of wastewater that is difficult to treat. In the combustion treatment method, fossil fuel is often used as a fuel, so that resources are wasted and often a problem as an emission source of exhaust gas such as carbon dioxide.

On the other hand, the wet oxidation method that purifies wastewater by heat treatment in the liquid phase is excellent without the above-mentioned problems. There are various types of wet oxidation treatment methods, and there are a method of treating in a reaction tower by gas-liquid upward cocurrent flow, a method of gas-liquid downward cocurrent flow, a method of gas-liquid countercurrent treatment, and the like. In order to obtain high processing performance in the non-catalytic wet oxidation method, it is necessary to use high-temperature and high-pressure harsh processing conditions and increase the reaction time, which increases the equipment size and operating costs. It is often high. In particular, in the gas-liquid downward co-current type non-catalytic wet oxidation treatment, the residence time of the liquid in the reaction tower is short, and it is often difficult to obtain sufficient treatment performance.
Therefore, a catalytic wet oxidation method has been proposed in which the treatment performance is improved by using a solid catalyst. When the gas-liquid downward co-current method is used in the catalyst wet oxidation method, it is possible to suppress the catalyst from rising and wearing. Particularly in recent years, the composition and shape of solid catalysts have been improved, and the durability and processing capacity of solid catalysts have been improved. However, the wet oxidation treatment conditions from the viewpoint of maximizing the capacity of the solid catalyst have not been sufficiently studied, and treatment conditions that can improve the wastewater treatment capacity by increasing the activity of the catalyst have been demanded. .

JP 61-275238 A JP 61-259754 JP-A-11-179378

  Conventionally, when wet oxidization of wastewater, when the amount of oxidizable substances in the wastewater is large, or when the wastewater contains a lot of components that precipitate during wastewater treatment, the treatment capacity of the catalyst is lowered for a long time. There is a need for technology that will not let you.

  The present invention has solved the above problems by providing a dispersion layer and a dilution layer on the front side of the catalyst with respect to the flow of the waste water when the waste water is subjected to wet oxidation treatment.

  The present invention provides a treatment capacity of a catalyst for a long time when the wastewater is subjected to wet oxidation treatment when the amount of oxidizable substances in the wastewater is large or when the wastewater contains a large amount of components that precipitate during wastewater treatment. Can be maintained.

  Examples of the wastewater to be treated in the present invention include chemical plants, electronic component manufacturing equipment, food processing equipment, printing plate making equipment, power generation equipment, photo processing equipment, metal processing equipment, metal plating equipment, metal refining equipment, and paper pulp. Examples of such wastewater include wastewater discharged from various industrial plants such as manufacturing facilities, domestic wastewater such as manure and sewage, waste incinerator wastewater such as wet smoke washing wastewater, and landfill leachate. Moreover, in order to process the soil containing a toxic substance, the extract which extracted the toxic substance in this soil in the liquid can also be handled as the wastewater to be treated of the present invention. Among these, in particular, wastewater is discharged from aliphatic carboxylic acids such as acrylic acid, acrylic acid esters, methacrylic acid, and methacrylic acid esters, aliphatic carboxylic acid ester production facilities, or aromatic carboxylic acids such as terephthalic acid and terephthalic acid esters, aromatic Particularly effective for wastewater containing organic matter discharged from carboxylic acid ester manufacturing equipment, EOG manufacturing equipment, alcohol manufacturing equipment such as methanol, ethanol, and higher alcohol, or food additives, pharmaceuticals, industrial chemical manufacturing equipment, etc. Is. It is also effective when the wastewater is ammonia-containing wastewater discharged from power generation equipment, electronic component manufacturing equipment, or the like.

  The “oxidizable substance” in the present invention is a substance that can be purified by oxidation / decomposition treatment, preferably organic and / or inorganic compounds, and various organic compounds, sulfur compounds, nitrogen compounds, and organic compounds. It refers to a halogen compound, an organic phosphorus compound, and the like. Specifically, for example, organic compounds such as methanol, ethanol, acetaldehyde, formic acid, acetone, acetic acid, propionic acid, THF, phenol; nitrogen compounds such as ammonia, hydrazine, nitrite, DMF, monoethanolamine, pyridine, urea; Sulfur compounds such as thiosulfate, sodium sulfide, dimethyl sulfoxide, and alkylbenzene sulfonate; hydrogen peroxide and the like can be mentioned, but not limited thereto. These substances may be dissolved in water or may be present as suspended substances. The oxidation / decomposition treatment referred to here is, for example, an oxidation treatment using ethanol as acetic acid, an oxidative decomposition treatment using acetic acid as carbon dioxide and water, a decarboxylation treatment using acetic acid as carbon dioxide and methane, and reducing various organic substances. Decomposition treatment for molecular weight, hydrolysis treatment for urea and ammonia to carbon dioxide, oxidative decomposition treatment for ammonia and hydrazine to nitrogen gas and water, decomposition treatment to convert nitrate ion or nitrite ion to nitrogen gas, organic halogen compound Including dechlorination treatment, it means that hazardous substances in waste water are converted into substantially harmless ones.

  It is preferable that the density | concentration of an oxidizable substance is 5000-50000 mg / liter with respect to a waste_water | drain, More preferably, it is 10000-40000 mg / liter. If it is less than 5000 mg / liter, the reaction heat obtained by the catalytic wet oxidation reaction is small, so even if heat recovery is performed using a heat exchange device, it becomes difficult to operate the device independently by this heat, and a separate heat supply device is required. It becomes disadvantageous in terms of energy. On the other hand, when it exceeds 50000 mg / liter, the reaction heat obtained by the catalytic wet oxidation reaction becomes very large, so that it becomes difficult to control the apparatus.

  The inflow rate of the waste water in the present invention is preferably in the range of 0.1 to 10 / hr, more preferably in the range of 0.3 to 7 / hr in terms of space velocity (LHSV) with respect to the catalyst volume. . Here, the catalyst volume refers to the sum of the value obtained by multiplying the volume of the diluent filled in the dilution layer by the ratio of the concentration of the catalytic active component and the volume of the catalyst filled in the catalyst layer. When LHSV is less than 0.1 / hr, the catalyst amount increases and the catalyst cost increases, but it is not preferable because it is difficult to obtain an improvement in the treatment efficiency corresponding to the catalyst cost. Further, when LHSV exceeds 10 / hr, the processing performance is often insufficient.

  The temperature which concerns on this invention is 50-170 degreeC in a catalyst layer, Preferably it is 100-165 degreeC. If it is less than 50 degreeC, it will become difficult to perform the oxidation and decomposition process of an organic substance and / or an inorganic oxidizable substance efficiently. On the other hand, when the temperature exceeds 170 ° C., the durability of the catalyst is often lowered and impractical.

  The dilution layer of the present invention is provided in order to prevent a reaction from abruptly occurring at the inlet of the catalyst layer and making it difficult to control the temperature or lowering the catalyst performance. The temperature of the dilution layer is usually set to be lower than the temperature of the catalyst layer in consideration of the temperature rise caused by the reaction heat, but is preferably 5 to 30 ° C lower than the temperature of the catalyst layer inlet portion. More preferably, it is lower by -25 ° C. If the difference from the temperature of the catalyst layer inlet portion is less than 5 ° C., the effect of alleviating the rapid reaction at the catalyst layer inlet portion is often not sufficiently obtained. In addition, when the difference from the temperature of the catalyst layer inlet portion exceeds 25 ° C., the size of the reaction tower becomes unnecessarily large, and the amount of heat released from the outer wall of the reaction tower becomes larger than the amount of heat obtained by the reaction. Often it is difficult to control to the desired reaction temperature.

    The pressure according to the present invention may be any pressure as long as the waste water maintains a liquid phase in the catalyst layer, and is appropriately selected depending on the correlation with the temperature in the catalyst layer.

  The oxygen-containing gas according to the present invention may be any gas as long as it can oxidize oxidizable substances in the waste water, preferably pure oxygen gas, oxygen-enriched gas, air, more preferably Air. The amount of oxygen-containing gas introduced is [the amount of oxygen in the supplied oxygen-containing gas] / [the amount of oxygen consumed by the wastewater when the treatment efficiency of the wastewater is maximized] (hereinafter, the value of this ratio is referred to as the “D value”) May be within a range of 0.8 to 1.3 times, preferably 0.9 to 1.1 times. When the D value is less than 0.8, the oxygen supply amount becomes smaller than the oxygen amount required for the oxidation / decomposition treatment of the oxidizable substance, and the treatment performance is lowered, which is not practical. On the other hand, when it exceeds 1.3, the catalyst may be exposed to excess oxygen, and the activity and durability of the catalyst may decrease.

  In the present invention, the method for supplying the oxygen-containing gas is not particularly limited, and for example, all the oxygen-containing gas may be supplied from the front of the catalyst layer, or the oxygen-containing gas may be supplied separately. Also good.

  The flow of the waste water and the processing gas may be any flow as long as the effects of the present invention can be achieved. For example, the flow may be either parallel flow or alternating current, and is preferably parallel flow. The liquid phase and gas phase flows may be either a downward flow or an upward flow, but are preferably a downward flow.

  The treatment apparatus used in the present invention may be a single tube type, a multi-tube type, or a heat exchange type, but is preferably a single tube type.

  The dispersion layer according to the present invention is preferably as follows. The component of the dispersion layer is inert to the oxidizable substance contained in the wastewater (hereinafter referred to as “inert substance”). “Inert” means that the oxidizable substance is not oxidized, or even if it is oxidized, the oxidizable substance in the waste water is oxidized by 5% or less, preferably 2% or less in the entire decomposition layer. The inert material is not particularly limited in terms of material, type, size, and the like as long as it can improve the gas-liquid stirring and contact efficiency and reduce the gas-liquid drift. An active can be used. Examples of the inert material include, for example, metals such as stainless steel, hastelloy, inconel, and titanium; oxides including at least one selected from the group consisting of iron, titanium, silicon, aluminum, and zirconium, or one or more. Metal oxides such as multi-component oxides (including complex oxides) containing; or ceramics; glass; resins and the like. Examples of the type of filler include, for example, pellets, spheres, granules, rings (such as Raschig rings, Lessing rings, and ball rings), honeycombs, nets, and nets or plates formed into a woven structure. It is done. The size of the filler is not particularly limited, but in the case of a pellet-like, spherical, granular, or ring-like filler, those having a size of 3 mm to 50 mm are preferable.

The specific surface area of the inert material is 1 to 200 m ² / g, preferably 20 to 100 m ² / g. If it is less than 1 m < ² > / g, the dispersibility of waste_water | drain will worsen and a dilution effect will not fully be acquired. Moreover, when it exceeds 200 m < ² > / g, it becomes easy to adsorb | suck the oxidizable substance in waste_water | drain, and the contact efficiency of a catalyst and an oxidizable substance will fall.

  As the solid catalyst according to the present invention, a solid catalyst generally used in catalytic wet oxidation treatment can be used. Specifically, any catalyst that has both activity and durability under the conditions of liquid phase oxidation can be used. For example, at least one elemental metal selected from titanium, silicon, aluminum, zirconium, manganese, iron, cobalt, nickel, cerium, tungsten, copper, silver, gold, platinum, palladium, rhodium, ruthenium and iridium and / or Mention may be made of catalysts containing compounds and / or activated carbon. The activated carbon here includes activated carbon fibers in addition to normal activated carbon. In particular, a solid catalyst containing the following catalyst A component and catalyst B component is preferably used. Here, the catalyst A component is an oxide of at least one element selected from iron, titanium, silicon, aluminum and zirconium, or activated carbon, and the catalyst B component is manganese, cobalt, nickel, cerium, tungsten. A metal and / or a compound of at least one element selected from copper, silver, gold, platinum, palladium, rhodium, ruthenium and iridium.

  Specific examples of the catalyst A component include metal oxides such as titanium oxide, iron oxide and zirconium oxide, and binary or multi-component oxides such as titanium oxide-zirconium oxide and titanium oxide-iron oxide. In addition to (including complex oxides), activated carbon or a mixture of metal oxide and activated carbon can be used. The proportion of the catalyst A component in the solid catalyst is preferably in the range of 30 to 99.95% by weight, and the durability of the solid catalyst is improved by using the catalyst A component in a proportion of 30% by weight or more.

  Specific examples of the catalyst B component include metals, oxides, and composite oxides of the above elements. The ratio of the catalyst B component in the solid catalyst is preferably 0.05 to 70% by weight, and by setting the ratio to 0.05% by weight, the oxidizable substance in the waste water can be sufficiently oxidized and / or It becomes possible to disassemble. In the case of silver, gold, platinum, palladium, rhodium, ruthenium and iridium (hereinafter referred to as “component B-1”) among the above elements, the ratio (total amount) of the metal and / or compound is solid. The amount is preferably 0.05 to 10% by weight of the catalyst. Even if it is used in a proportion exceeding 10% by weight, no corresponding improvement in processing performance is recognized, but it is an expensive raw material, which is economically disadvantageous because of the increased cost of the solid catalyst. In the case of other manganese, cobalt, nickel, cerium, tungsten and copper (hereinafter referred to as “B-2 component”), the ratio (total amount) of the metal and / or compound is 0.05 to 70% by weight is preferred. Of course, when the total amount is in the range of 0.05 to 70% by weight, the B-1 component and the B-2 component are used in combination in the range of 0.05 to 10% by weight and 0.05 to 70% by weight, respectively. You can also.

  When the solid catalyst contains the B-1 component as the catalyst B component, the catalyst activity is particularly high and effective. In particular, among the B-1 components, when a metal and / or a compound of at least one element selected from platinum, palladium, rhodium, ruthenium and iridium is contained, the catalytic activity is high and preferable. Among the components B-2, manganese, cobalt, nickel and copper are preferably used.

  The shape of the catalyst is not particularly limited, and may be any of a granular shape, a spherical shape, a pellet shape, a saddle shape, a honeycomb shape, and a ring shape, for example. In the case of a pellet shape, an arbitrary shape such as an elliptical shape, a polygonal shape, a trilobal shape, and a quadrilateral shape can be used in addition to a circular cross section. The shape length is 0.5 to 15 mm, preferably 1.0 to 10 mm in terms of equivalent diameter.

The specific surface area (BET surface area) of the catalyst is 10 to 2000 m ² / g, preferably 30 to 1500 m ² / g. If it is less than 10 m < ² > / g, since an oxidizable substance becomes difficult to adsorb | suck with respect to a catalyst, processing performance will become low. Moreover, when it exceeds 2000 m < ² > / g, the problem which the mechanical strength of a catalyst falls arises.

  The average particle diameter of the catalyst particles is 1 to 10 mm, preferably 2 to 7 mm. If it is less than 1 mm, the pressure loss of the catalyst layer increases, and when the suspended matter is contained in the waste water, the catalyst layer may be clogged.

  The dilution layer according to the present invention may be any one as long as it has the effects of the present invention (in addition, it may be referred to as a dilution as a generic term for what is filled in the dilution layer). The catalyst component used in the dilution layer can be arbitrarily selected from the combination of the catalyst components according to the present invention, and the catalyst component in the catalyst layer and the catalyst component in the dilution layer may be the same or different.

  Further, “dilution” means that the concentration of the catalyst component in the diluted layer is lower or the activity of the catalyst component is lower than the concentration of the catalyst component in the catalyst layer. When the concentration of the catalyst component is low, the catalyst component concentration in the dilution layer is 10 to 80%, preferably 30 to 60%, compared to the catalyst component concentration in the catalyst layer. The dilution layer of the present invention is provided in order to prevent the reaction from abruptly occurring at the inlet of the catalyst layer, thereby making it difficult to control the temperature or lowering the catalyst performance. If it is less than%, the effect is often not sufficiently obtained. On the other hand, when it exceeds 80%, the reaction in the diluted layer hardly proceeds, so that the effect is often not obtained sufficiently. The low activity of the catalyst component means that the catalytic activity of the diluted layer is 10 to 80%, preferably 30 to 60%, compared to the catalytic activity of the catalyst layer with respect to the oxidizable substance in the waste water.

  As the dilution method, there can be used a method of mixing the catalyst and an inert substance, or a method of supporting and coating a catalyst component on an inert substance.

The specific surface area of the dilution is 1 to 200 m ² / g, preferably 20 to 100 m ² / g. If it is less than 1 m < ² > / g, the dispersibility of waste_water | drain will worsen and a dilution effect will not fully be acquired. Moreover, when it exceeds 200 m < ² > / g, it becomes easy to adsorb | suck the oxidizable substance in waste_water | drain, and the contact efficiency of a catalyst and an oxidizable substance will fall.

  The volume of the dispersion layer, the dilution layer, and the catalyst layer is 0.06 to 0.6, and the volume of the dilution layer is 0.2 to 0.5, with respect to the volume 1 of the catalyst layer. Preferably, the volume of the dispersion layer is 0.1 to 0.5, and the volume of the dilution layer is 0.25 to 0.4. When the volume of the dispersion layer is less than 0.06, the diffusion of the liquid in the cross-sectional direction of the reaction tower in the dispersion layer becomes insufficient, and when it exceeds 0.6, only the dispersion material that is not effectively used increases. Moreover, if the volume of the dilution layer is less than 0.2, the effect of alleviating a rapid reaction at the catalyst layer inlet is insufficient, and if it exceeds 0.5, the size of the reaction tower is merely unnecessarily large. Become.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, if there exists an effect of this invention, it will not be limited to a present Example.

(Example 1)
Using the apparatus shown in FIG. 1, processing was performed under the following conditions. The reaction tower 1 has a cylindrical shape with a diameter of 400 mmφ and a length of 5000 mm, and a dispersion layer, a dilution layer, and a catalyst layer are provided in that order in the order from 600 mm, 700 mm, and 2100 mm, respectively. The dispersion layer is filled with titania pellets having a diameter of 5 mm as an inert material, and the catalyst layer is mainly composed of activated carbon, platinum, and ruthenium, and contains 0.15% by mass of platinum and 0.1% by mass of ruthenium. The pellet catalyst was filled. The diluted layer was filled with a mixture of the inert material and the catalyst in a volume ratio of 1: 1. The wastewater used for the treatment was wastewater discharged from a chemical plant, contained compounds such as carboxylic acid and aldehyde, and had a COD (Cr) concentration of 20000 mg / liter. The waste water contained 7.3% by mass of sodium sulfate.

The wastewater was pressure-fed by a wastewater supply pump 5 at a flow rate of 300 liters / hr, heated to 120 ° C. by a heater 3, and supplied from the upper part of the reaction tower 1 in a downward flow manner. In addition, air was introduced from the oxygen-containing gas supply line 8, the pressure was increased by the compressor 7, and then mixed with the waste water at the upstream side of the heater 3 at a flow rate of 20 m ³ N / hr. The D value at this time was equivalent to 1.0.

  In the reaction tower 1, the temperature was kept at 120 ° C. using the electric heater 2 and the catalyst wet oxidation treatment was performed. The processing liquid was cooled to 30 ° C. by the cooler 4, then discharged from the pressure control valve 12, and gas-liquid separated by the gas-liquid separator 11. At this time, the pressure control valve 12 detected the pressure with the pressure controller PC, and controlled so that the inside of the reaction tower 1 kept the pressure of 0.5 MPa (Gauge).

  As a result of measuring the COD (Cr) concentration of the treated water after 100 hours and calculating the COD (Cr) treatment efficiency, it was 95%. Thereafter, the processing was continued until 3000 hours passed from the start, but after 3000 hours, the processing performance was not particularly deteriorated, and the COD (Cr) processing efficiency was 95%.

(Comparative Example 1)
Only the catalyst layer 2450 mm was provided inside the reaction tower 1, and no dispersion layer or dilution layer was provided. Except this, the same processing as in Example 1 was performed.

  As a result of measuring the COD (Cr) concentration of the treated water after 100 hours and calculating the COD (Cr) treatment efficiency, it was 91%. Thereafter, the treatment was continued, but after about 700 hours, a pressure increase was observed with the pressure gauge PI on the gas-liquid inlet side to the reaction tower 1. At this time, outflow of catalyst powder was confirmed in the treated water. For this reason, when the treatment was interrupted and the reaction tower 1 was opened, it was confirmed that a part of the upper part of the catalyst layer (inlet side) was dried and a solid containing sodium sulfate as a main component was deposited on the surface. It was confirmed that there was a portion where the catalyst shape collapsed and the amount of catalyst decreased.

(Comparative Example 2)
In the reaction tower 1, a dispersion layer and a catalyst layer were provided in order of 600 mm and 2450 mm, respectively, from the top, and no dilution layer was provided. Except this, the same processing as in Example 1 was performed.

  As a result of measuring the COD (Cr) concentration of the treated water after 100 hours and calculating the COD (Cr) treatment efficiency, it was 93%. Thereafter, the treatment was continued, but after about 1800 hours, a pressure increase was observed with the pressure gauge PI on the gas-liquid inlet side to the reaction tower 1. At this time, outflow of catalyst powder was confirmed in the treated water. For this reason, when the treatment was interrupted and the reaction tower 1 was opened, it was confirmed that the catalyst shape collapsed on the upper side (inlet side) of the catalyst layer and the amount of catalyst was reduced.

(Comparative Example 3)
Inside the reaction tower 1, a dilution layer and a catalyst layer were provided in order of 700 mm and 2100 mm, respectively, from the top, and no dispersion layer was provided. Except this, the same processing as in Example 1 was performed.

  As a result of measuring the COD (Cr) concentration of the treated water after 100 hours and calculating the COD (Cr) treatment efficiency, it was 92%. Thereafter, the treatment was continued, but after about 1100 hours, an increase in pressure was observed with the pressure gauge PI on the gas-liquid inlet side to the reaction tower 1. At this time, outflow of catalyst powder was confirmed in the treated water. For this reason, when the process was interrupted and the reaction tower 1 was opened and confirmed, a part of the upper part of the dilution layer (inlet side) was dried, and solids mainly composed of sodium sulfate were deposited on the surface. It was confirmed that there was a portion where the catalyst shape collapsed and the amount of catalyst decreased.

  The present invention can be used for wastewater treatment. Especially in a reactor in which wastewater and processing gas are placed vertically and countercurrent, gas and liquid can be prevented from drifting, enabling efficient wastewater treatment and long-term wastewater treatment. Is.

It is an apparatus figure used for an Example and a comparative example.

Explanation of symbols

1. Reaction tower 2. 2. Electric heater Heater 4. 4. Cooler Waste water supply pump 6. 6. Waste water supply line Compressor8. 8. Oxygen-containing gas supply line 9. Oxygen-containing gas flow control valve 10. Treatment liquid line Gas-liquid separator 12. Pressure control valve 13. Gas discharge line 14. Treatment liquid discharge pump 15. Process liquid discharge line 16. Oxygen concentration meter 21. Dispersion layer 22. Dilution layer 23. Catalyst layer

Claims (7)

  A wastewater treatment method for treating an oxidizable substance using a catalyst, wherein the wastewater is passed in the order of a dispersion layer, a dilution layer, and a catalyst layer.   The processing method according to claim 1, wherein the dispersion layer is inert to an oxidizable substance contained in the waste water.   The catalyst of the catalyst layer is at least one element selected from titanium, silicon, aluminum, zirconium, manganese, iron, cobalt, nickel, cerium, tungsten, copper, silver, gold, platinum, palladium, rhodium, ruthenium and iridium The processing method according to claim 1, comprising a metal and / or a compound and / or activated carbon.   The processing method according to claim 1, wherein the amount of the catalyst component in the dilution layer is diluted to 10 to 80% by mass with respect to the amount of the catalyst component in the catalyst layer.   The processing method according to claim 1, wherein the waste water is processed using an oxygen-containing gas.   The processing method according to claim 1, wherein the waste water and the oxygen-containing gas are circulated by a gas-liquid downward flow system.   The processing method according to claim 1, wherein the volume of the dispersion layer is 0.06 to 0.6 and the volume of the dilution layer is 0.2 to 0.5 with respect to the volume 1 of the catalyst layer.

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