JPH09122483A - Absorbent for nitrogen oxide and sulfur oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an acidic gas absorbent to be reproduced several times to scores of times by impregnating a honeycomb-shaped material formed by active carbon, calcium hydroxide and gypsum with calcium hydroxide solution. SOLUTION: A bonding force is decreased by the variation of structure caused by the reaction of gypsum as an aggregate with potassium carbonate in an acidic gas absorbing material heretofore available. Also, for instance, calcium hydroxide is turned into calcium nitrite through the reaction with nitrogen dioxide and becomes water-soluble and its shape is broken. To avoid the above trouble, potassium carbonate is removed and the required shape is formed, and then impregnation with potassium hydroxide water solution is carried out to control the change of gypsum, and an acidic gas absorption material to be reproduced several times can be manufactured without lowering the absorption performance. Also the number of the reproductions can be improved up to scores of times by adding an inorganic bonding material producing no chemical change.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used as an absorbent for sulfur oxides and nitrogen oxides in the atmosphere, and the sulfur contained in the gas in a tunnel filled with exhaust gas from a domestic air cleaner or an automobile. It is used in equipment for removing oxides and nitrogen oxides.

[0002]

2. Description of the Related Art Conventionally, as disclosed in JP-A-1-176449 and JP-A-1-176450, there have been proposed activated carbon and an acidic gas absorbent mainly containing calcium hydroxide, but gypsum is used. It was used as a binder and was necessary because potassium carbonate and potassium hydroxide mixed in the absorbent have high absorbency.

Further, Japanese Patent Publication No. 58-5699 discloses that
A nitrogen oxide removing agent using a hardening material such as hydraulic cement material or bentonite has been devised, but it contains a carbonate.

[0004]

SUMMARY OF THE INVENTION In the above-described absorbents of the prior art, once the acidic gas is absorbed to the end, the water-soluble components are mainly contained in the absorbents. In particular, when potassium carbonate or potassium hydroxide is contained in the absorbent, the gypsum to be used as the bone agent is changed to potassium sulfate, which further increases the water-soluble component. Therefore, when it was soaked in water to remove the absorbed NO ₂ gas and SO ₂ gas components, its shape collapsed and it could not be reused.

[0005]

In order to solve the above-mentioned drawbacks, instead of mixing conventional potassium carbonate in a state where potassium carbonate is removed or an inorganic binder having a binding force at a relatively low temperature is used, By impregnating the aqueous potassium hydroxide solution after forming the honeycomb body, it is possible to obtain an acidic gas absorbent that can be regenerated several times to ten times or more. Here, since calcium hydroxide begins to lose structural water at 100 ° C. or higher and completely changes to calcium oxide at 580 ° C. or higher, it is preferable to manufacture or use it at a relatively low temperature.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In the conventional acid gas absorbent, gypsum as an aggregate reacts with potassium carbonate to form potassium sulfate and calcium carbonate, and the binding force becomes small due to the change in structure. In addition, for example, upon absorption by reaction with nitrogen dioxide, calcium hydroxide, which is the main material, also changes to calcium nitrite and becomes water-soluble, so that the shape collapses when immersed in water after absorption and use.

[0007] Therefore, after the potassium carbonate is formed into a required shape and then impregnated with an aqueous solution of potassium hydroxide, the change of gypsum (calcium sulfate) is suppressed and the acid gas absorbent which can be regenerated several times is deteriorated in absorption performance. Can be made without After the regeneration of several times, the shape collapse occurs before the acid gas absorption performance deteriorates.

From the above, it has become possible to increase the number of times of regeneration to a dozen or more by adding an inorganic binder which does not cause a chemical change.

[0009]

Embodiments of the present invention will be described below.

(Example 1) 20 wt% of activated carbon, 40 wt% of calcium hydroxide and 40 wt% of gypsum were mixed with a molding aid, and a 1.5 mm square hole was extruded into a honeycomb shape in which the pitch was 2.0 mm and the holes were arranged vertically and horizontally. After that, heat treatment was performed in a dry / inert atmosphere to obtain a honeycomb body. This honeycomb body was immersed in a 15 wt% potassium hydroxide aqueous solution for 1 minute to obtain a honeycomb body of the present invention.

The shape of this honeycomb body is shown in FIG. Honeycomb bodies shown in (Table 1) were manufactured in the same manner, and data regarding the purification performance and the usable number of recycles were obtained for each. The results are shown in (Table 2).

Regarding the evaluation, all of the nitrogen oxides N
O ₂ was used. Regarding sulfur oxides, NO ₂ is used because it is easy to remove more than NO ₂ actually from the viewpoint of chemical reactivity, so NO ₂ which is likely to affect the purification rate was used.

[0013]

[Table 1]

The comparative product contains 1% potassium carbonate when the raw materials are mixed.
It is a conventional product with a mixture of 0%.

The usable number of times of reproduction was confirmed by the following method. 1. Absorb 50 ppm of NO ₂ into the sample (about 3 hours until the purification rate becomes 20% or less) Soak the 2.1 sample in water for 1 hour to remove water-soluble components 3.2 Dry the sample to 15% KOH The cycles of 1 to 3 in which the sample was impregnated with the aqueous solution for 1 minute were confirmed for the sample of n = 5, and the number of times until collapse in 2 was averaged.

Table 2 shows the evaluation results of the above samples. The NO ₂ purification performance is obtained by diluting NO ₂ gas with compressor air adjusted to have a humidity of 60% to give a NO ₂ concentration of about 10 ppm, and measuring about 10 mm in length and width and 20 m in length.
It was passed through the sample cut into m and expressed as the purification rate from the difference in concentration before and after. The space velocity of the measurement was 50,000 h ^-1 .

[0017]

[Table 2]

From the above results, when the activated carbon increased (No.
1 to 4) The purification performance is improved, but the number of times of regeneration tends to decrease because other materials decrease relatively. However, in the above range, the number of times of reproduction is greatly increased as compared with the comparative product.
In No. 7, since the gypsum is 10%, the number of times of regeneration is small. Further, if the immersion time in the aqueous potassium hydroxide solution is too long, the purification performance is affected, but the regeneration frequency is not significantly affected.

(Example 2) In the same manner as in Example 1, a honeycomb was experimentally manufactured by adding hydrous magnesium aluminum silicate as a binder as an inorganic binder. This hydrous magnesium aluminum silicate has a silica content of 60 to 80 wt.
%, Alumina content 5 to 20 wt%, magnesia 5 to 2
It is a material composed of 0 wt% and exhibits a binding force at 300 ° C to 400 ° C. Table 3 shows various trial formulations.

[0020]

[Table 3]

Table 4 shows the evaluation results of the above samples. The sample and evaluation gas conditions were the same as in Example 1.

[0022]

[Table 4]

From the above test results, it is clear that the number of times of regeneration is greatly increased by adding the binder. However, if the conventional binder gypsum is reduced, the purification performance will be greatly affected. Therefore, it is desirable to use 5 to 30 wt% of binder.

(Example 3) In the same manner as in Example 2, a honeycomb was prepared by adding lime aluminate as a binder as an inorganic binder. This lime aluminate is a material having an alumina content of 70 wt% or more and silica of 0.5 wt% or less, and is a cement material that exhibits a binding force in a hydration reaction. Table 5 shows various trial formulations.

[0025]

[Table 5]

Table 6 shows the evaluation results of the above samples. The sample and evaluation gas conditions were the same as in Example 1.

[0027]

[Table 6]

Results similar to those of Example 2 were obtained.
As described above, it was effective to use an inorganic binder having a binding force at a relatively low temperature, that is, 400 ° C. or lower.

[0029]

From the above results, according to the present invention, NO ₂
It is possible to obtain a honeycomb-shaped absorbent that can be reused with an alkali without deteriorating the purification performance.

[Brief description of the drawings]

FIG. 1 is a perspective view of a sample used in a test of the present invention.

Claims (3)

[Claims] 1. A nitrogen oxide / sulfur oxide absorbent obtained by impregnating a honeycomb material formed of activated carbon, calcium hydroxide, and gypsum with an aqueous solution of potassium hydroxide. 2. A nitrogen oxide / sulfur oxide absorbent obtained by impregnating a honeycomb-shaped material formed of activated carbon, calcium hydroxide, gypsum and an inorganic binder with an aqueous solution of potassium hydroxide. 3. The nitrogen oxide / sulfur oxide absorbent according to claim 2, wherein the inorganic binder is lime aluminate, hydrous magnesium aluminum silicate, or a mixture thereof.