JPH07213916A - Production of honeycomb catalyst - Google Patents

Abstract

PURPOSE:To produce a honeycomb catalyst excellent in catalytic activity not generating a crack or blackening even when a honeycomb molded object of a thin-walled narrow pitch is baked. CONSTITUTION:A catalyst raw material compsn., a cellulosic thickener and water are kneaded to be molded into a honeycomb molded object by an extrusion molding method and the molded object is dried and baked to produce a honeycomb catalyst. In this method, the baking of the honeycomb object is finally performed at 500 deg.C or higher while baking temp. is controlled so that temp. rising speed in a low temp. region of 300 deg.C or lower is set to 50 deg.C/hr less and temp. is gradually raised so as to finally reach 500 deg.C or higher (1). The honeycomb molded object is baked in an air non-passing state with respect to a hot air direction (2). When the honeycomb molded objects are baked in a stacked state, a gap of 50mm or more is provided between lower and upper stage honeycomb molded objects (3).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a honeycomb catalyst, and more specifically, to contact nitrogen oxides in exhaust gas containing nitrogen oxides discharged from a thermal power plant, various factories, etc. in the presence of ammonia. The present invention relates to a method for manufacturing a honeycomb catalyst suitable for reduction and removal.

[0002]

2. Description of the Related Art As a so-called denitration device for removing nitrogen oxides discharged from a boiler for thermal power generation and various factories, a method of reducing nitrogen oxides with ammonia is generally adopted. A titania-based denitration catalyst that accelerates the reaction is used in this reduction method, and granular, plate-shaped, and honeycomb-shaped catalysts are used depending on the properties of the gas. In particular, the honeycomb shape has the advantage that a narrow pitch shape can be used because there is no risk of clogging when targeting clean gas such as gas-fired, and the catalyst volume becomes compact, so the narrow pitch thin wall Honeycomb development is being actively pursued.

For example, in JP-A-49-74705, a ceramic body containing an organic binder is heated in a non-oxidizing atmosphere at 600 ° C. or lower at the beginning of heating and then 60
A method of firing in an oxidizing atmosphere at 0 ° C. or higher, JP-B-53-
No. 35877, after kneading and molding TiO ₂ and an organic binder, a non-oxidizing atmosphere (380 to 830 ° C./3 to 5) is used.
h), followed by firing in an oxidizing atmosphere,
JP-A-57-119843 discloses a method in which a kneaded molded body of a carrier, a binder and a catalyst component is heated and heated stepwise, and is fired while ventilating an atmosphere gas, JP-A-2-830.
Japanese Patent Laid-Open No. 63-210593 discloses a method of firing a catalyst raw material containing an organic binder at an inlet gas temperature of not lower than the binder combustion start temperature and at an outlet gas temperature of not higher than the melting point of the catalyst raw material. Ventilates a gas having the same temperature as the ambient temperature through the through holes (flow velocity: 1.0 to 5.
0 m / s) is shown.

However, when the honeycomb-shaped narrow-pitch thin-walling is advanced, distortion tends to occur at the time of molding, and the use of an organic thickener at the time of molding causes a problem of cracking at the time of firing, which is a great manufacturing problem. It has become a challenge. Honeycomb catalyst is usually extruded into a honeycomb shape by an extruder equipped with a die at the tip, after adding a catalyst raw material containing titania as a main component, an organic thickener and water, mixing and kneading to form a clay. After that, it is manufactured through a drying step of removing water in the molded body and a calcination step of thermally decomposing the organic thickener contained in the molded body and activating the catalyst.

FIG. 6 shows a perspective view of a narrow-pitch thinned honeycomb catalyst obtained by a conventional manufacturing method. Two types of cracks are seen in this honeycomb catalyst during firing. One is vertical cracks (Type I: vertical cracks parallel to the extrusion direction of the molded body) caused by a temperature difference between the inside and the outer surface of the honeycomb that occurs when the temperature rises, and the vertical cracks occur in almost all cases. The other is that a flow velocity difference occurs depending on the extrusion position during molding and remains as internal strain in the molded body, which becomes cracks during the drying process and lateral cracks that develop during firing (Type II: the direction perpendicular to the molded body extrusion direction). Cracks). The honeycomb catalyst having these firing cracks has a problem that the catalytic activity is lowered and the denitration performance is poor. Further, in the conventional method, there is a problem that unburned carbon of the organic thickener remains in the central portion of the honeycomb to cause blackening and the catalytic activity decreases.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and not to cause cracking or blackening even when firing a thin-walled, narrow-pitch honeycomb-shaped molded article, which is excellent in catalytic activity. It is to provide a method for producing a catalyst.

[0007]

Means for Solving the Problems The inventors of the present invention have found that firing cracking of a honeycomb catalyst is caused by combustion of an organic thickener contained in the honeycomb molded body and temperature inside and outside the honeycomb molded body caused by heat generation. In view of the difference caused by the difference, as a result of diligent study on a firing method that enables high temperature firing while suppressing combustion (oxidation) and heat generation of the organic thickener, as a result, in the low temperature range, the temperature rises at a certain rate or less. The inventors have found that the above problems can be solved by heating and then heating the temperature to 500 ° C. or higher to complete the present invention.

That is, the invention claimed in the present application is as follows. (1) In a method for producing a honeycomb catalyst, which comprises extruding a kneaded material of a catalyst raw material composition, a cellulosic organic thickener and water into a honeycomb-shaped molded body, and drying and firing the honeycomb-shaped molded body, Firing is performed at a temperature rising rate of 50 ° C./hour or less in a low temperature region of 300 ° C. or less,
A method for manufacturing a honeycomb catalyst, characterized in that the temperature is gradually raised and finally carried out at a temperature of 500 ° C. or higher. (2) The method for producing a honeycomb catalyst according to (1), wherein the honeycomb formed body is fired in a non-ventilated state in the hot air gas direction. (3) The method for producing a honeycomb catalyst according to (1), wherein a gap of 50 mm or more is provided between the lower and upper honeycomb-shaped compacts when stacking and firing the honeycomb-shaped compacts.

[0009]

In the extrusion of the honeycomb, a cellulosic organic thickener having a heat-gelling property is usually used as a molding aid, and when the catalyst containing the organic thickener is burned, the result shown in FIG. As shown in the example, when the heating rate is fast (continuous furnace, heating rate 360 ° C./h), the atmosphere temperature (dotted line) in the furnace is 100 ° C. in the central part of the honeycomb (solid line).
Around the time when the temperature reaches the vicinity, the heat is rapidly generated and an exothermic peak reaching 600 ° C. appears.

FIG. 8 shows a temperature rising rate of 250 ° C./h, 125
The temperature changes (A, B, C) on the honeycomb surface and the central portion at ° C / h and 62.5 ° C / h and the cross-sectional views (a, b, c) of the honeycomb catalyst obtained under each condition are shown. From FIG. 8, the higher the heating rate, the larger the temperature difference (δT) between the honeycomb surface and the central part of the honeycomb, the higher the rate of vertical cracking, and the unburned carbon remaining part () due to the decomposition of the organic thickener ( It is shown that the (black discoloration) largely spreads around the center of the plane. This is a reducing atmosphere in the central portion of the long honeycomb, and unburned carbon remains due to the decomposition of the organic thickener, resulting in a blackened portion. The blackened portion is an unfavorable phenomenon because it lowers the activity (denitration rate) of the catalyst.

FIG. 9 shows the relationship between the temperature difference in the honeycomb (the temperature difference δT between the in-plane central portion and the outer peripheral portion) and the temperature rising rate, which is linearly increased up to a peak temperature of 550 ° C. using an electric furnace and a continuous furnace. It is the figure which heated and calculated | required. As is clear from this result, the slower the heating rate is, the smaller the temperature difference δT is, and the heating rate is 9%.
It can be seen that no cracks occur at 0 ° C./h or less.

As a result of various examinations under various firing conditions,
It has been found that the prevention of firing cracking can be solved by suppressing the combustion (oxidation) and heat generation of the organic thickener, that is, by suppressing the temperature rising rate to reduce the temperature difference inside and outside the honeycomb. As another measure against the deterioration of performance (low activity) due to the occurrence of a black discoloration part due to the decomposition of the organic thickener, the temperature rising rate in the low temperature range of 300 ° C or lower is 50 ° C / h.
Or less, preferably 40 ° C / h or less, further 300 ° C
It has become clear that the problem can be solved by setting the heating time until the temperature is raised to 10 hours or longer and finally firing at a peak temperature of 500 ° C. or higher, preferably 550 ° C. or higher. In the present invention, as shown in FIG.
With a step firing pattern of 0 ° C, 300 ° C, and 500 ° C or higher, and a heating rate of 5 at a low temperature side of 300 ° C or lower.
It is preferably 0 ° C./h or less.

[0013]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited thereto. In addition, the part in an example means a weight part. Examples 1 to 4 and Comparative Examples 1 to 15 15 parts of inorganic fiber and 100 parts of catalyst raw material consisting of oxides of Ti, W, and V, organic thickener (trade name of Shin-Etsu Chemical Co., Ltd.,
65SH4000) 3 parts and 39 parts of water are added and mixed and kneaded in a kneader, and then the external dimensions are 150 mm by an extruder.
A honeycomb having a square shape, a pitch of 3.5 mm, and a rib thickness of 0.6 mm is extruded, cut to a length of 550 mm, and dried under predetermined conditions. The step firing pattern shown in FIG.
The rate of temperature rise up to 20 ° C is 20 ° C / h, 30 ° C / h,
40 ° C / h, 50 ° C / h (Examples 1 to 4), 70 ° C / h
h, 90 ° C./h, 110 ° C./h (Comparative Examples 1 to 3),
A honeycomb catalyst was manufactured by carrying out firing at a holding time (y) at 300 ° C. for 2 hours and a holding time (z) at 500 ° C. for 2 hours. The honeycomb was fired in a non-aerated state with respect to hot air gas.

When the presence or absence of cracking and blackening of each of the obtained honeycomb catalysts was examined, in Comparative Example 3, there was a temperature difference between the inside of the honeycomb and the outer surface, and vertical cracking (type I) occurred. Further, in Comparative Examples 1 to 3, a blackened portion having a diameter of about 20 to 50 mm was observed at the center of the honeycomb surface. On the other hand, in Examples 1 to 4, neither cracks nor blackened portions were found. From these results, it was found that firing cracks occurred when the temperature rising rate exceeded 90 ° C./h, and blackening occurred when the temperature rising rate exceeded 50 ° C./h. In addition, heating rate 50 ℃ /
The heating time (x) required to raise the temperature to 300 ° C. in h was 10 hours.

Next, the denitration rate of the obtained honeycomb catalyst was investigated, and the relationship between the denitration rate and the temperature rising rate from room temperature to 300 ° C. is shown in FIG. From FIG. 2, the denitrification rate is 75 in Examples 1 to 4.
%, But the denitration rate in Comparative Examples 1 to 3 was inferior at 70% or less.

Example 5 In Example 1, the firing temperature of 500 ° C. was changed to 530 ° C., 5
Example 1 except that 50 ° C., 570 ° C. and 600 ° C.
Honeycomb catalysts were manufactured in the same manner as above, and the denitration rate of each of the obtained honeycomb catalysts was examined. The results are shown in FIG.
From FIG. 3, it has been found that a sufficient denitration rate can be obtained by firing at a temperature of 500 ° C. or higher.

In summary of the above results, in the present invention, it is preferable to keep the temperature at a low temperature in order to prevent the combustion and heat generation of the organic thickener, but from the viewpoint of control of the apparatus or work efficiency, 250 ° C. It is preferable to bake in a step heating pattern of 300 ° C. and 550 ° C., and 30
The heating rate up to 0 ° C is 50 ° C / h or less, preferably 40
C./h or less, heating time (x) to 300 ° C. is 10 hours or more, holding time (y) at 300 ° C. is 2 hours or more, and firing time (z) at 500 ° C. or more is 2 hours or more. Is preferred.

Example 6 As shown in FIG. 4, a honeycomb molded body was non-ventilated on a mesh belt passing through a furnace in which hot air gas flows from the lower side to the upper side at a speed of 22 mm / min. The state of occurrence of vertical cracking and blackening of the honeycomb catalyst was examined in the case where the honeycomb catalyst was placed horizontally (A) and in the state where it was ventilated (B). In the case of firing in an aerated state (B), the temperature rising rate was 250 ° C./h or more, vertical cracks occurred, and unburned carbon remained,
In the case of firing in a non-aerated state (A), there was no increase in the temperature rising rate, and neither vertical cracking nor blackening was observed.

Example 7 As shown in FIGS. 5A and 5B, when honeycomb formed bodies were stacked in two and three stages and fired, a gap of 50 mm was provided between the lower and upper stages. The flow of hot air gas was sufficient, and the fired bodies obtained in the first to third stages were comparable to each other and a uniform honeycomb catalyst was obtained. By stacking and firing the honeycomb-shaped compacts in this manner, the productivity of the honeycomb catalyst is improved.

[0020]

According to the manufacturing method of the present invention, it is possible to fire a thin-walled narrow-pitch honeycomb-shaped molded product without causing cracks and blackening, and it is possible to obtain a honeycomb catalyst excellent in catalytic activity. .

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a firing pattern in a method for manufacturing a honeycomb catalyst of the present invention.

FIG. 2 is a diagram showing the relationship between the temperature rising rate up to 300 ° C. and the denitration rate.

FIG. 3 is a diagram showing the relationship between the firing temperature and the denitration rate.

FIG. 4 is a view showing a mounted state of a honeycomb-shaped molded body on hot air gas.

FIG. 5 is a view showing a mounting state when the honeycomb formed bodies are stacked and fired.

FIG. 6 is a perspective view of a narrow-pitch thinned honeycomb catalyst obtained by a conventional firing method.

FIG. 7 is a view showing a temperature change inside the honeycomb-shaped molded body at a temperature rising rate of 360 ° C./h.

FIG. 8 is a cross-sectional view of a temperature change inside and outside the honeycomb-shaped molded body when the temperature rising rate is changed and a honeycomb catalyst obtained thereby.

FIG. 9 is a view showing the relationship between the temperature difference (δT) in the honeycomb formed body and the temperature rising rate.

Claims (3)

[Claims] 1. A method of producing a honeycomb catalyst by extruding a kneaded material of a catalyst raw material composition, a cellulosic organic thickener and water into a honeycomb molded article, which is dried and fired to produce a honeycomb catalyst. Firing the molded body,
A method for manufacturing a honeycomb catalyst, characterized in that the temperature rising rate in a low temperature range of 0 ° C. or lower is 50 ° C./h or lower, the temperature is gradually raised, and finally performed at a temperature of 500 ° C. or higher. 2. The method for manufacturing a honeycomb catalyst according to claim 1, wherein the honeycomb formed body is fired in a non-ventilated state in the hot air gas direction. 3. The method for producing a honeycomb catalyst according to claim 1, wherein a gap of 50 mm or more is provided between the lower and upper honeycomb-shaped compacts when stacking and firing the honeycomb-shaped compacts.