JP2016064358A - Marine exhaust gas treatment catalyst, and exhaust treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a marine exhaust gas treatment catalyst which is used for treating the exhaust gas to be generated from a marine diesel engine, allows NOx to be treated stably over a long time even when the exhaust gas has a low temperature range, and allows NOx to be treated stably over a long time even when sulfur oxide is contained in the exhaust gas in particular.SOLUTION: The marine exhaust gas treatment catalyst contains: a compound oxide and/or a mixed oxide, which are obtained from three kinds of compounds of titanium, silicon and tungsten by a coprecipitation method, as an A component; a compound of at least one element selected from vanadium, niobium and tantalum as a B component; and another compound of at least one element selected from zinc, manganese, iron and cobalt.SELECTED DRAWING: None

Description

  The present invention relates to a catalyst for treating exhaust gas generated from marine diesel engines, and to treatment of exhaust gas using the catalyst. In particular, it relates to treatment of exhaust gas containing sulfur oxides.

  In general, a diesel engine is an oxygen-excess type internal combustion engine, and its exhaust gas contains a relatively large amount of nitrogen oxide (hereinafter also referred to as NOx). Since this NOx can cause pollution and environmental destruction, a method for removing NOx from exhaust gas is indispensable for diesel engines. As the method, a selective catalytic reduction method (SCR method) in which nitrogen oxide in exhaust gas is catalytically reduced on a catalyst using a reducing agent such as ammonia or urea and decomposed into nitrogen and water is generally used. Yes.

  As an exhaust gas treatment catalyst used in the SCR method, for example, a catalyst containing titanium oxide, vanadium oxide and tungsten oxide (Patent Document 1), or a catalyst containing titanium oxide, vanadium oxide and molybdenum oxide (Patent Document 2) and the like have been proposed.

  On the other hand, in ships and the like, there are many examples of mounting an SCR internal combustion engine on a ship equipped with a medium-speed diesel engine, and studies are being made on mounting an SCR internal combustion engine in a low-speed diesel engine. The catalyst used to purify exhaust gas from marine diesel engines is selected from zeolite with a high silica / alumina ratio, vanadium, tungsten, molybdenum, niobium, or titanium as a catalyst component with excellent sulfur poisoning resistance. The use of one or more oxides is disclosed (Patent Document 3).

The most notable problem in mounting SCR on ships is poisoning of the catalyst by sulfur contained in fuel oil. Ammonia used as a reducing agent reacts with sulfur oxides (hereinafter also referred to as SOx) in exhaust gas to produce acidic ammonium sulfate (ammonium hydrogen sulfide: NH ₄ HSO ₄ ), which adheres to the catalyst surface, thereby In particular, this problem is considered to be remarkable in an atmosphere having an exhaust gas temperature of about 300 ° C. or lower. In medium speed diesel engines, this problem is mitigated because the exhaust gas temperature in most engines is above 300 ° C.

On the other hand, in most low speed diesel engines, the exhaust gas temperature is 300 ° C. or lower in most engines, and in particular, the latest models with excellent engine performance are below 250 ° C. In a low-speed diesel engine, a low exhaust gas temperature means that the amount of heat to be discarded is small, and it is also a testament to high efficiency, low fuel consumption, and low CO ₂ emissions. On the other hand, since the exhaust gas treatment temperature is 300 ° C. or less, poisoning such as SOx becomes remarkable, and there is a problem in terms of durability of the catalyst. Therefore, even if the catalyst is superior in sulfur poisoning resistance described in Patent Document 3 above, NOx is efficiently removed while maintaining high efficiency, low fuel consumption, and low CO ₂ emission performance, and further, SOx, etc. There was room for improvement in maintaining durability against poisoning.

Japanese Patent No. 3337634 Japanese Patent No. 3749078 JP 2011-32953 A

  An object of the present invention is a marine diesel capable of removing nitrogen oxides in exhaust gas over a longer period of time even in a low temperature range of exhaust gas, with less performance degradation due to sulfur oxide or the like than conventional catalysts. An object of the present invention is to provide a catalyst for treating exhaust gas from an engine and a method for treating exhaust gas generated from a marine diesel engine using the catalyst.

  As a result of intensive studies in order to solve the above problems, the present inventor has found that a catalyst having the following composition is effective.

  That is, the first invention of the present invention is a catalyst for treating exhaust gas generated from marine diesel engines, which is a composite obtained by coprecipitation from three compounds of titanium, silicon and tungsten as a catalyst A component. Oxides and / or mixed oxides, catalyst B component contains at least one elemental compound of vanadium, niobium and tantalum, and catalyst C component contains at least one compound of zinc, manganese, iron and cobalt It is characterized by this.

  A second invention of the present invention is a method for treating exhaust gas from a marine diesel engine characterized by using the catalyst of the first invention.

  By using the present invention, it becomes possible to suppress the performance deterioration due to sulfur oxide even in the low temperature range, particularly in the temperature range of 300 ° C. or less, and the NOx contained in the exhaust gas can be stabilized for a long time. Can be processed automatically.

  The exhaust gas treatment catalyst of the present invention is a composite oxide and / or mixed oxide obtained by coprecipitation from three compounds of titanium, silicon and tungsten as the catalyst A component, and vanadium, niobium and tantalum as the catalyst B component. And at least one compound of zinc, manganese, iron and cobalt as the component of the at least one element and the catalyst C component.

  The composition of the catalyst A component greatly affects the NOx removal performance and durability. Specifically, the catalyst A component essentially contains elements of titanium, silicon, and tungsten, and a composite oxidation obtained from a compound of these elements by a coprecipitation method. And / or mixed oxides. The content of titanium in the catalyst A component is 70 to 98% by mass in terms of oxide, preferably 75 to 96% by mass, and more preferably 80 to 94% by mass. If the titanium content in the catalyst A component exceeds 98% by mass in terms of oxides, sufficient durability cannot be obtained, and if it is less than 70% by mass, the NOx removal performance decreases. Further, the content of silicon in the catalyst A component is preferably 1 to 20% by mass in terms of oxide, preferably 1.5 to 15% by mass, and more preferably 2 to 10% by mass. . If the content of silicon in the catalyst A component exceeds 20% by mass in terms of oxide, the NOx removal performance decreases, and if it is less than 1% by mass, sufficient durability cannot be obtained. Content of tungsten should just be 1-20 mass, Preferably it is 1.5-15 mass%, More preferably, it is 2-12 mass%. This is because if the amount exceeds 20% by mass, the initial performance is remarkably lowered, and if it is less than 1% by mass, sufficient durability cannot be obtained. The content of the catalyst A component in the catalyst is preferably 90 to 99.8% by mass in terms of oxide with respect to the total of the catalyst A component and the catalyst B component, and more preferably 91 to 99.7. It is good that it is mass%, More preferably, it is 91.5-99.6 mass%. When the content of the catalyst A component is less than 90% by mass or exceeds 99.8% by mass, the NOx removal performance or durability is lowered.

  In addition, as starting materials for preparing the catalyst A component, oxides, hydroxides, inorganic salts, organic salts and the like of each element are used. For example, titanyl sulfate, titanium tetrachloride, tetraisopropyl titanate, etc. are used as the titanium source, silica sol, water glass, silicon tetrachloride, etc. are used as the silicon source, and ammonium metatungstate as the tungsten source. , Ammonium paratungstate and the like can be used.

  Furthermore, the catalyst A component in the present invention is prepared by a coprecipitation method. Specifically, the catalyst A component is added by adding an acidic solution of a titanium source to a basic solution of a mixture of a silicon source and a tungsten source. It is good to obtain the precursor of a component. By preparing in this way, each component of titanium, silicon, or tungsten is in a highly dispersed state, and a catalyst having high NOx removal performance and durability can be obtained. In this case, the pH after the coprecipitation reaction is preferably controlled to 4 to 10, more preferably 6 to 8 in the case of a ternary oxide of titanium, silicon and tungsten. By controlling in this way, a catalyst excellent in performance and durability can be obtained. Furthermore, the temperature of the liquid or slurry during the coprecipitation reaction is preferably controlled between 5 and 60 ° C, more preferably between 10 and 50 ° C, and even more preferably between 15 and 45 ° C. . This is because if the temperature of the liquid or slurry during the coprecipitation reaction exceeds the range of 5 to 60 ° C., the NOx removal performance or durability of the catalyst is lowered.

  Even if it is a complex oxide containing titanium, silicon and tungsten, the effect of the invention cannot be obtained even if a complex oxide prepared without using the coprecipitation method is used instead of the component A of the present invention.

  The catalyst B component of the present invention is a compound of at least one element of vanadium, niobium and tantalum selected from Group 5 elements, but is contained in the catalyst in the form of an oxide from the viewpoint of removal performance preferable. In particular, a vanadium oxide is preferably contained, and a catalyst excellent in NOx removal performance and durability can be obtained.

The content of the catalyst B component also greatly affects the removal performance and durability. In the present invention, it is 0.2 to 10% by mass in terms of oxide with respect to the total of the catalyst A component and the catalyst B component, but more preferably Is 0.3 to 9% by mass, more preferably 0.4 to 8.5% by mass. If the content of the catalyst B component is less than 0.2% by mass, sufficient removal performance cannot be obtained, and if it exceeds 10% by mass, the performance may be deteriorated due to sintering of metal species. This is because the oxidation of SO ₂ to SO ₃ is promoted to increase the accumulation of acidic ammonium sulfate, which may adversely affect the catalyst life. In addition, when using the compound of a some element from vanadium, niobium, and a tantalum as a catalyst B component, it is good that the total amount in conversion of the oxide of each compound exists in the said range. Further, as starting materials for preparing the catalyst B component, oxides, hydroxides, inorganic salts, organic salts, and the like of each element are used. For example, ammonium metavanadate is preferably used as the vanadium source. As a source, niobium oxalate or its ammonium salt can be used.

  The method for adding the catalyst B component is not particularly limited, and there are a method for adding the catalyst A component after it is obtained by the coprecipitation method and a method for obtaining the catalyst B component by mixing the raw materials of the catalyst A component and the catalyst B component.

  In the catalyst of the present invention, the catalyst C component is an important component for improving durability against poisoning such as SOx. The catalyst component C is a compound of at least one element of zinc, manganese, iron and cobalt, but is preferably contained in the catalyst in the form of a sulfate. When the sulfate of at least one element of zinc, manganese, iron and cobalt is used as the catalyst C component, the content thereof is 0.5 to 10 mass with respect to the total of the catalyst A component, the catalyst B component and the catalyst C component. %, Preferably 1 to 8% by mass, and more preferably 2 to 6% by mass. This is because if the content is less than 0.5% by mass, sufficient durability against poisoning of SOx cannot be obtained, and if it exceeds 10% by mass, the NOx removal performance may deteriorate. In addition, when using the sulfate of the some element of zinc, manganese, iron, and cobalt as a catalyst C component, it is good that the total amount of each compound exists in the said range.

  In addition, another compound can also be added as long as the performance of the catalyst according to the present invention is not impaired.

  The pore volume of the denitration catalyst used in the present invention is such that the total pore volume is in the range of 0.20 to 0.70 mL / g, more preferably 0.25 to 0.60 mL / g, Preferably it is in the range of 0.28 to 0.50 mL / g. If the pore volume of the catalyst is too small, sufficient catalyst performance will not be obtained, and if it is too large, the catalyst performance will not be improved so much, but the mechanical strength of the catalyst will be reduced, causing trouble in handling and wear resistance. This is not preferable because there is a risk that it may be lowered.

  As the catalyst preparation method according to the present invention, (1) after obtaining the composite oxide and / or mixed oxide precursor related to the catalyst A component by the above procedure, an aqueous solution of the catalyst B component and the catalyst C component is added. A method of thoroughly mixing with a kneader, etc., forming a predetermined shape, drying and firing, (2) mixing raw materials of the catalyst A component and the catalyst B component, adding an aqueous solution of the catalyst C component to this and mixing well with a kneader (3) Mixing raw materials of catalyst A component and catalyst C component, adding aqueous solution of catalyst B component to this, mixing well with a kneader, etc., shaping to a predetermined shape, drying and firing (4) Add the aqueous solution of the catalyst B component to the catalyst A component, mix well with a kneader, etc., shape and dry and calcinate to a predetermined shape to obtain a formed body. Impregnation, drying, firing method, 5) Add aqueous solution of catalyst C component to catalyst A component, mix well with a kneader, etc., shape to a predetermined shape, dry and calcinate to obtain a formed body, impregnate this formed body with aqueous solution of catalyst B component, dry (6) A method in which the raw materials of the catalyst A component, the catalyst B component and the catalyst C component are mixed once, dried and fired, and further formed into a slurry after adding an aqueous medium to form a slurry, (7 ) After mixing the raw materials of the catalyst A component, the catalyst B component and the catalyst C component at a time, and adjusting the pH in some cases to obtain a precipitate (precursor), the precipitate is dried, calcined, and further aqueous. A method of forming a slurry after adding a medium to the slurry, or the slurry obtained in (8), (6), or (7) can be coated on a carrier usually used as a catalyst carrier. In addition, when shape | molding by (9) (1)-(7), it can also shape | mold into a honeycomb, a pellet, and a granule, can also be dried and baked, and can also be set as a catalyst.

  In the catalyst preparation method described above, the drying conditions are not particularly limited, and the temperature is 50 to 100 ° C., preferably 60 to 80 ° C. in hydrogen, nitrogen, air or a mixed gas thereof, preferably 20 to 500 minutes, preferably It can be performed for 30 to 100 minutes. Also, the firing conditions are not particularly limited, and hydrogen, nitrogen, air, or a mixed gas thereof is 300 to 600 ° C, preferably 400 to 550 ° C, and 2 to 50 hours, preferably 3 to 10 hours. It can be carried out.

  The catalyst according to the present invention can be formed into a saddle, pellet, sphere, or honeycomb by extrusion molding, tableting, rolling granulation, or the like. Further, a saddle-shaped, pellet, sphere, or honeycomb-shaped carrier can be used by coating the components of the denitration catalyst. A honeycomb shape is preferable for reducing the pressure loss of the exhaust gas treatment apparatus. Further, in the preparation, general adjustment methods using various metal compounds can be used. For example, a method of impregnating a molded product of the catalyst A component with a solution of the catalyst B component, or a powder of the catalyst A component Although the method of kneading after mixing the solution or powder of the catalyst B component is mentioned, the kneading method is suitably used from the viewpoint of controlling the pore volume.

  The exhaust gas treatment method of the present invention is an exhaust gas treatment method for removing NOx in exhaust gas using the catalyst of the present invention. At this time, the exhaust gas treatment temperature is 180 to 330 ° C, preferably 200 to 300 ° C, More preferably, it is in the range of 220 to 290 ° C, more preferably 230 to 270 ° C. When the exhaust gas treatment temperature is less than 180 ° C, sufficient NOx removal efficiency cannot be obtained, and the accumulation of acidic ammonium sulfate increases, resulting in a large decrease in catalyst performance. This is because it may cause a decrease. Regarding the deterioration of the catalyst performance due to SOx poisoning, the treatment method using the catalyst of the present invention is superior in the durability against poisoning of SOx and the like in the temperature range of the exhaust gas treatment as compared with the treatment method using the conventional catalyst. Show the effect.

  The exhaust gas to be treated by the catalyst according to the present invention contains nitrogen oxides (NOx), and the NOx concentration in the exhaust gas is preferably 5 to 1000 ppm (volume basis), more preferably 10 to 500 ppm, More preferably, it is in the range of 20 to 300 ppm. If the NOx concentration in the exhaust gas is less than 5 ppm, sufficient NOx removal performance will not be exhibited. On the other hand, if it exceeds 1000 ppm, if sulfur oxide is contained in the exhaust gas, the amount of acidic ammonium sulfate will increase and the performance will deteriorate. This is because it is not preferable because it becomes large.

  Although the exhaust gas may contain an organic compound, the concentration of the organic compound is preferably 3000 ppm or less (volume basis), more preferably 1000 ppm or less, and even more preferably 500 ppm or less. This is because if the concentration of the organic compound in the exhaust gas exceeds 3000 ppm, heat generated by the reaction increases and the catalyst may be thermally damaged.

  In the method for treating exhaust gas of the present invention, a form in which ammonia or urea (also referred to as ammonia or the like) is added to the exhaust gas is preferably used. The addition amount of ammonia or the like is 0.2 to 2.0 mol, preferably 0.5 to 1. mol in terms of ammonia (1/2 mol in the case of urea) with respect to 1 mol of nitrogen oxide (in terms of NOx). 0 mole.

  In addition, when an organic halogen compound is contained in the exhaust gas, it is not necessary to add ammonia or the like, but even if ammonia or the like is added to the exhaust gas, the effect of the catalyst according to the present invention is not impaired.

Furthermore, oxygen, water, SOx, etc. are contained in the exhaust gas. For example, it is preferably used under conditions where oxygen is present in the exhaust gas. In this case, the oxygen concentration is preferably in the range of 0.1 to 50% by volume, more preferably 0.3 to 20% by volume. More preferably, it is in the range of 0.5 to 16% by volume. If the oxygen concentration is less than 0.1% by volume, the removal efficiency decreases, and if it exceeds 50% by volume, SO ₂ oxidation as a side reaction is promoted, which is not preferable. When the exhaust gas contains moisture, the concentration is preferably 50% by volume or less. More preferably, it is 40 volume% or less, More preferably, it is 30 volume% or less. This is because when the moisture concentration in the exhaust gas exceeds 50% by volume, the removal efficiency is lowered and, in some cases, the performance is greatly lowered.

  The exhaust gas treatment method of the present invention can be suitably used when sulfur oxide (SOx) is contained in the exhaust gas. The SOx concentration in the exhaust gas at that time should be in the range of 5 to 5000 ppm (volume basis), preferably 10 to 2000 ppm, more preferably 50 to 1000 ppm, and still more preferably 100 to 500 ppm. The effect of the present invention is exhibited in the treatment of exhaust gas having a SOx concentration of 0.1 ppm or more. On the other hand, if the SOx concentration in the exhaust gas exceeds 2000 ppm, performance degradation due to SOx becomes large, which is not preferable. Further, among SOx, SO3 greatly contributes to performance degradation, but its concentration is in the range of 0.1 to 200 ppm, preferably 0.5 to 100 ppm, more preferably 1 to 50 ppm, and still more preferably 2 to 30 ppm. It is good. If the SO3 concentration in the exhaust gas exceeds 200 ppm, performance degradation due to SOx becomes large, which is not preferable.

Also, space velocity during the exhaust gas treatment of the present invention, 100~100,000h ^-1 (STP), preferably not 200~50,000h ^-1 (STP), more preferably 500~30,000h ^-1 ( STP) is preferable. If the space velocity exceeds 100,000 h ⁻¹ (STP), sufficient removal efficiency of NOx and organic halides cannot be obtained. If the space velocity is less than 100 h ⁻¹ (STP), the removal efficiency does not change greatly, but the pressure loss of the exhaust gas treatment device. This is because the height of the apparatus becomes large and the apparatus itself becomes large, which hinders mounting on a ship. Furthermore, the linear velocity of the gas passing through the catalyst layer in the exhaust gas treatment of the present invention is 0.1 to 10 m / s (Normal), preferably 0.5 to 7 m / s (Normal), more preferably 0.7. It should be in the range of ˜4 m / s (Normal). If the linear velocity is less than 0.1 m / s (Normal), sufficient removal efficiency cannot be obtained, and if it exceeds 10 m / s (Normal), the removal efficiency does not change greatly, but the pressure loss of the exhaust gas treatment device increases. is there.

  The present invention will be described in detail below with reference to examples. However, the present invention is not limited to the following examples as long as the effects of the present invention are achieved.

Example 1
<Preparation of Ti-Si-W ternary oxide>
In 90 L of water, 14.4 kg of ammonium paratungstate and 6.2 kg of monoethanolamine were heated to 65 ° C. and mixed to obtain a uniform solution. 105 kg of silica sol (Snowtex-30 (product name), manufactured by Nissan Chemical Industries, containing 30% by mass in terms of SiO ₂ ), 801 kg of industrial ammonia water (containing 20% by mass NH 3), 2950 L of water, and a tungsten-containing solution To the mixed solution, 8500 L of titanyl sulfate (manufactured by Teika, 70 g / L as TiO _{2 and} 280 g / L as H ₂ SO ₄ ) was gradually added dropwise with stirring to form a precipitate, and then an appropriate amount of aqueous ammonia Was added to adjust the pH to 7. The coprecipitated slurry was allowed to stand for about 40 hours, sufficiently washed with water, filtered, and dried at 100 ° C. for 1 hour. Further, it was fired at 500 ° C. in an air atmosphere for 5 hours, further pulverized using a hammer mill, and classified by a classifier to obtain a Ti—Si—W ternary oxide powder. The composition of the Ti—Si—W ternary oxide powder thus prepared was TiO ₂ : SiO ₂ : WO ₃ = 93: 5: 2 (mass ratio).

<Addition of vanadium oxide and loading of zinc>
In 5 L of water, 1.9 kg of ammonium metavanadate, 2.6 kg of oxalic acid, and 0.9 kg of monoethanolamine were mixed and dissolved to prepare a uniform solution. After adding 18.4 kg of the Ti-Si-W ternary oxide powder prepared earlier to a kneader, a vanadium-containing solution was added together with a molding aid such as an organic binder and stirred well. Further, after mixing well with a blender while adding an appropriate amount of water, the mixture was sufficiently kneaded with a continuous kneader and extruded into a honeycomb shape having an outer diameter of 80 mm square, a length of 144 mm, an aperture of 2.8 mm, and a wall thickness of 0.5 mm. The obtained molded product was dried at 60 ° C. for 50 minutes while ventilating air, and then fired at 500 ° C. for 5 hours in an air atmosphere to obtain a molded product a. Next, this molded body a was impregnated with an aqueous zinc sulfate solution, dried at 80 ° C. for 20 minutes while ventilating air, and calcined at 450 ° C. for 2 hours in an air atmosphere to obtain Catalyst A. The composition of the catalyst A is TiO ₂ : SiO ₂ : WO ₃ : V ₂ O ₅ : ZnSO ₄ = 83.7: 4.5: 1.8: 7.0: 3.0 (mass ratio), The total pore volume was 0.47 mL / g.

(Comparative Example 1)
The molded object a which does not perform the process after the impregnation to the zinc nitrate aqueous solution in Example 1 was obtained. The composition of the molded body a is TiO ₂ : SiO ₂ : WO ₃ : V ₂ O ₅ = 86.2: 4.7: 1.9: 7.2 (mass ratio), and the total pore volume is 0.8. It was 50 mL / g.

(NOx removal test)
Using the catalyst A and molded body a obtained in Example 1 and Comparative Example 1, the initial NOx removal performance was evaluated under the following performance evaluation conditions.

[NOx removal performance evaluation conditions]
NOx: 300 ppm, NH ₃ : 300 ppm, O ₂ : 12 vol%, H ₂ O: 10 vol%, N2: balance, gas temperature: 250 ° C., space velocity: 23,000 h ⁻¹ (STP), gas linear velocity: 1.0m / s (Normal)
(SO ₂ exposure durability test)
Next, after exposure for 100 hours under the following conditions, the NOx removal performance was evaluated again.

[Exposure conditions]
_{NOx: 1,000ppm, NH 3: 1,000ppm} , SOx: 600ppm, SO 3: 10ppm, O 2: 12 _volume%, H 2 O: 10 _volume%, N 2: balance, gas temperature: 250 ° C., a space velocity : 12,500 h ^-1 (STP), gas linear velocity: 0.5 m / s (Normal)
In the NOx removal performance evaluation, the NOx concentration at the catalyst inlet and the catalyst outlet was measured, and the NOx removal rate was calculated according to the following equation (Formula 1). The results are shown in Table 1. It can be seen that the molded product a has the same initial performance as the catalyst A, but is inferior in durability.

  The present invention stably treats NOx over a long time even when the temperature of the exhaust gas is low, in the treatment of exhaust gas containing sulfur oxides and nitrogen oxides (NOx) in the exhaust gas generated from marine diesel engines. In particular, even when sulfur oxide is contained in the exhaust gas, NOx contained in the exhaust gas can be treated stably over a long period of time.

Claims (2)

A catalyst for treating exhaust gas from a marine diesel engine, a composite oxide and / or mixed oxide obtained by a coprecipitation method from three compounds of titanium, silicon and tungsten as a catalyst A component, a catalyst Vessel diesel containing at least one elemental compound of vanadium, niobium and tantalum as component B, and at least one elemental compound of zinc, manganese, iron and cobalt as catalyst C component Catalyst for treating exhaust gas from engines. A method for treating exhaust gas from a marine diesel engine, comprising using the catalyst according to claim 1.