JPH07265692A - Production of nox adsorbent - Google Patents

Abstract

PURPOSE:To obtain a NOx adsorbent having excellent heat resistance and SOx resistance by adsorbing a prescribed amt. of Ru ions at the acidic points of a porous alumina carrier having the solid acidic points, adsorbing rare earth ions at the residual acidic points after drying and calcining, and further adsorbing the excessive rare earth ions at points exclusive of the acidic points and drying and firing the carrier. CONSTITUTION:The porous silica alumina carrier having the solid acidic points is immersed into an acidic soln. contg. the Ru ions to adsorb the prescribed amt. of the Ru ions at the acidic points and thereafter, the carrier is dried and fired. This carrier is immersed into an acidic soln. contg. the rare earth ions to adsorb the rare earth ions at the remaining acidic points; further, the excessive rare earth ions are adsorbed on the inside surfaces of the fine pores of the carrier exclusive of the acidic points and thereafter, the carrier is dried and fired. Alkaline earth metal ions are added to the acidic soln. contg. the rare earth ions in this process for producing the NOx adsorbent. Consequently, the NOx adsorbent having the excellent heat resistance and SOx resistance is produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is applicable to ventilation gas in various tunnels such as various road tunnels, mountain tunnels, undersea tunnels, underground roads, and roads with shelter (collectively referred to as "road tunnels"). The present invention relates to a method for producing a NOx adsorption / removal agent that efficiently removes contained low-concentration nitrogen oxides (NOx).

[0002]

BACKGROUND OF THE INVENTION In a road tunnel or the like, which is particularly long and has a large amount of automobile traffic, it is necessary to provide a considerable amount of ventilation for the purpose of protecting the health of passersby and improving the visual distance. Even in a relatively short-distance tunnel, carbon monoxide (C
O), as a method of preventing air pollution due to NOx, etc.
There is a method to suck and exhaust (ventilate) the air in the tunnel.

However, if the ventilation gas is diffused to the surroundings as it is, it does not improve the local environment, and in particular, the highly contaminated area is expanded in the urban area where the exhaust gas pollution is spreading in the plane or its suburbs. It could lead to.

NOx in the ventilation gas of a road tunnel or the like generally has a concentration of 10 ppm or less, and most of it is NO and contains a small amount of NO ₂ and N ₂ O. Moisture content of several%, CO _{2 of} 0.1% or less, S of 1 ppm or less
O ₂ and several ppm of hydrocarbons coexist.

The following requirements are required for an adsorbent for adsorbing and removing NOx from such a gas.

The NOx adsorption performance is not impaired.

The adsorbent is CO ₂ , hydrocarbons, SO ₂
It is not poisoned by etc.

Further, although the adsorption is carried out near room temperature, the adsorbent is required to have a high heat resistance in order to maintain a stable performance for a long period of time even after repeated adsorption and thermal regeneration (desorption).

[0009]

2. Description of the Related Art The present inventors have previously proposed, as an adsorbent satisfying the above requirements, an adsorbent obtained by supporting Ru, Ce, etc. on titania (TiO ₂ ) or alumina (Al ₂ O ₃ ). Kaihei 5-200281 and Japanese Patent Application 5-20
9673).

This adsorbent adsorbs NOx almost selectively in spite of the presence of moisture, and poisoning by CO ₂ , hydrocarbons, SO _{2 and the} like is suppressed as much as possible.

[0011]

When titania (TiO ₂ ) or alumina (Al ₂ O ₃ ) is used as a carrier, the thermal stability of Ru carried at 300 ° C. or higher becomes a problem. That is, in the case of supporting Ce after supporting and baking Ru, and in the case of supporting Ru and Ce at the same time, although it is desired that Ce is baked at a relatively high temperature (around 400 ° C.), The temperature is limited to around 300 ° C. Further, when Ce is supported and calcined first, and then Ru is supported, high temperature calcination is possible. However, the NOx adsorbent obtained by this method is a method of supporting Ce after supporting Ru and a method of supporting Ru and Ce. It is inferior in terms of heat resistance and SOx resistance compared to an adsorbent produced by the simultaneous loading method.

[0012] In view of the above points, an object of the present invention is to provide a NOx adsorbent having excellent heat resistance and SOx resistance.

[0013]

The present inventors have adopted silica-alumina, which has a large amount of solid acid point, which is stronger than that of titania, as a carrier, and Ru until the acid point is almost saturated.
A method for producing a NOx adsorbent has been developed in which Ce is supported and then Ce is supported at a relatively low temperature and then baked at a high temperature.

That is, in the method for producing a NOx adsorbent according to the present invention, a porous silica-alumina carrier having solid acidic points is immersed in an acidic solution containing Ru ions to adsorb a predetermined amount of Ru ions. After drying and calcination, the carrier is immersed in an acidic solution containing rare earth ions to adsorb the rare earth ions at the remaining acidic points, and to allow excess rare earth ions to be adsorbed on the inner surface of the carrier pores other than the acidic points. It is characterized by being dried and fired.

As the carrier, a commercially available silica-alumina colloid sol (solid content: about 20% by weight) impregnated in a preform made of heat resistant fibers may be used.
As the preform body, glass, ceramics, metal,
Examples include cloths, papers, mats, and the like made of heat resistant fibers such as heat resistant polymers. The preform may be plate-shaped, honeycomb-shaped, or bent.

When the colloidal sol is dried and calcined, if the calcination temperature is high, it takes a long time to elute the alkali metal, and if the calcination temperature is too low, the carrier is likely to collapse during the main treatment.
The colloidal sol impregnated in the preform body is dried at 200 ° C or lower, preferably 150 ° C or lower.

The silica-alumina particles retained in the inter-fiber voids of the preform also have a function as a strong binder for binding fibers by drying and firing, and have a strong plate-like or honeycomb-like shape without adding a binder separately. The silica-alumina carrier can be obtained.

When the adsorbent obtained by the present invention is applied to a system that handles a large amount of gas such as a road tunnel ventilation gas purification, the adsorbent is used for the purpose of eliminating clogging trouble due to dust and reducing gas flow resistance. It is preferable to form a plate shape and a honeycomb shape.

Commercially available silica alumina carriers or colloidal sols generally contain alkali metals such as Na.
This is because it is adsorbed at the acidic point and interferes with the Ru adsorption function, or is eluted into the Ru ion solution to raise the pH of the solution,
This causes the phenomenon that Ru in the solution precipitates as a hydroxide. In order to prevent this, the carrier after firing is immersed in warm water in which an equivalent amount of ammonium chloride, which is more than twice that of the alkali metal in the carrier, is dissolved for several hours or more to replace the alkali metal with ammonia, and then wash with water. It is preferable to perform drying and firing, and finally perform a treatment that does not leave an alkali content on the acidic point.

The ammonium salt is preferably ammonium chloride, ammonium nitrate or the like, which is easily decomposed and volatilized.

Treatment with an aqueous ammonium salt solution is carried out at 50 ° C.
As described above, it is preferably performed at 70 to 90 ° C. for 1 hour or more, preferably 2 to 5 hours, and firing is performed at 250 ° C. or more in the air flow, preferably at 350 to 500 ° C. for 0.5 hour or more, preferably 1
Do ~ 3 hours.

A typical example of the acidic solution containing Ru ions is an aqueous solution containing an oxide, hydroxide or halide of ruthenium (Ru).

In order to adsorb as much Ru as possible at the acidic point of the carrier and prevent excess Ru from existing in the pores,
The following operations are preferably performed.

The Ru solution concentration is adjusted according to the silica-alumina retention amount, the liquid retention amount, etc. so that the Ru ions in the liquid amount (liquid retention amount) that permeates the plate-shaped carrier are comparable to the Ru saturated adsorption amount of silica alumina. .

The pH of the Ru solution is 1.5 or less,
The immersion time should be limited to the minimum time required for the solution to soak in, as the alumina content elutes from the support and contaminates the Ru solution.

Ru provided by the impregnating solution
To reach the acidic point of the carrier and ensure the adsorption, the carrier is immersed in an acidic solution containing Ru ions and pulled up, and then left in a wet state for 1 hour or longer, preferably 3 to 5 hours, and aged. I do.

After supporting and adsorbing Ru, drying and calcination are carried out. This is carried out in the subsequent step of supporting rare earth to reduce the re-elution of Ru, and there is sufficient heat resistance when rare earth is not supported. Since it does not develop, it is preferable to carry out firing at the lowest temperature at which re-elution can be prevented. 1 firing after supporting Ru
0.5 at 80 to 300 ° C, preferably 200 to 250 ° C
~ 3 hours, preferably 1-2 hours.

Typical examples of acidic solutions containing rare earth ions are:
It is an aqueous solution containing at least one oxide, hydroxide or halide of a rare earth such as lanthanum (La) or cerium (Ce). It is also preferable to add alkaline earth metal ions such as calcium and magnesium to the acidic solution containing rare earth ions. As a result, the rare earth ions can be easily adsorbed and supported on the acidic points where it is difficult to adsorb.

Considering the purpose of adding the rare earth, it is desirable to support the rare earth in a large amount as long as it does not hinder the diffusion of NOx in the pores of the adsorbent. Taking into consideration the economical point of view,
It is considered sufficient if the final product carries 25 to 35% by weight of rare earths.

Since the adsorbent already has high heat resistance, it is desirable to carry out the firing after supporting the rare earth at a relatively high temperature in order to form a complete oxide in a short time.

Firing after carrying rare earth and preferably alkaline earth is 350 ° C to 500 ° C, preferably 400 to 45.
It is performed at 0 ° C. for 2 hours or more, preferably 3 to 4 hours.

[0032]

According to the production method of the present invention, the heat resistance of Ru is dramatically improved by the action of the solid acid point and rare earth,
The performance does not deteriorate at all when heated to around ℃. As a result, calcination at a temperature of 380 ° C. or higher, which is desired to completely decompose rare earth compounds such as cerium chloride and to develop appropriate alkalinity, is possible.

Rare earths showing moderate alkalinity are NO ₂
The adsorption capacity of the adsorbent is increased by providing an adsorption site for NO ₂ oxidized and produced on the Ru surface. At the same time, the rare earth has a trapping effect on SOx that deteriorates the characteristics of Ru, and contributes to stabilization of the adsorption performance.

If there is an acidic point which does not adsorb Ru or a rare earth on the surface of the carrier, moisture is adsorbed to this when the adsorbent is used, which increases the heating regeneration energy and reversibly but NOx adsorption. It causes a decrease in capacity. Therefore,
By adding an alkaline earth ion that is easily adsorbed to the acidic point to reduce the free acidic point, the influence of moisture coexisting with NOx is reduced, and an adsorbent having more preferable characteristics can be obtained.

[0035]

Embodiments of the present invention will be described below.

Example 1 (1) Production Method of Plate-shaped Carrier Commercially available ceramics paper (paper thickness: 0.25 mm) was dipped in commercially available silica-alumina colloid sol (solid content: about 20% by weight), and the sol was made into ceramics paper. Sufficiently soak the paper, pull up the paper, cut the liquid sag, put the paper on a stainless steel plate and dry it.
Calcination was performed for 1 hour. Thus, a plate-shaped silica-alumina carrier was obtained.

The silica-alumina retention of the obtained plate-like carrier was 110 g / m ² (basis weight), and the tensile strength was 1.
It was 6 kgf / mm ² .

(2) Salt Ammonium Treatment 10 g of the plate-like carrier was immersed in a 1 mol / liter ammonium chloride aqueous solution at a temperature of 90 ° C. for 120 minutes to perform ammonium salt treatment.

(3) Support of Ru and Ce This salt-ammonium-treated carrier was dipped in an aqueous solution of ruthenium chloride (RuCl ₃ ) adjusted to Ru of 15.2 g / liter for 3 minutes, cut to a wet state. It was aged at room temperature for 1 hour while maintaining the temperature at room temperature. Then, this was baked at 250 degreeC for 2 hours.

Then, the carrier carrying Ru was changed to Ce 2
It was immersed in an aqueous solution of cerium chloride (CeCl ₃ ) adjusted to 45 g / liter for 0.5 hour, pulled up, and fired at 400 ° C. for 4 hours. A final adsorbent product was thus obtained.

(4) Performance test The aging time and the initial NOx adsorption performance of the final product were examined. The result is shown in FIG.

The NOx adsorption performance is determined by the saturated adsorption amount (cm ³ / g) = room temperature irreversible NO adsorption amount (c
m ³ ) / weight of silica-alumina in the adsorbent (g).

Further, the final product is subjected to forced heat deterioration treatment at 450 ° C. for 24 hours, and this heat deterioration-treated product also has NOx.
The adsorption performance was investigated. The results are also shown in Table 1.

As is clear from FIG. 1, this adsorbent has excellent heat resistance.

Example 2 In the same manner as in Example 1, after aging for 4 hours, the amount of supported Ce (C
The adsorbent was prepared by changing e weight (g) / silica alumina weight (g) × 100). The Ce loading and the initial NOx adsorption performance of the final products were examined. The result is shown in FIG.

The NOx adsorption performance was expressed by the saturated adsorption amount (cm ³ / g) as in Example 1.

Further, the final product was 24 hours forced thermal aging treatment at 450 ° C. for an additional 50PpmSO 12 h SO ₂ accelerated aging processed (SO ₂ to 1.5 l / m ² adsorbed) at 250 ° C. at ₂ containing gas . The NOx adsorption performance of this SO ₂ forced deterioration treated product was also examined. The results are also shown in FIG.

As is clear from FIG. 2, this adsorbent has excellent SO ₂ resistance.

Reference Example 1 10 g of a silica-alumina powder obtained by evaporating and drying a commercially available silica-alumina colloid sol at 60 ° C. was immersed in a 0.2 mol / liter ammonium chloride aqueous solution to obtain a temperature of 80-9.
Ammonium salt treatment was performed at 0 ° C. for 3 hours. 5 salt-treated powder
Firing was performed at 00 ° C. for 1 hour under air circulation.

The ammonium salt-treated powder was fired at different firing temperatures.

Each sample thus obtained was analyzed for Na before and after treatment with ammonium chloride to determine the elution rate. The result is shown in FIG.

As is apparent from FIG. 3, the firing temperature is 80 ° C.
Below, the mechanical strength of the sample is very weak. Therefore, it is considered that the firing temperature is practically required to be 100 ° C. or higher.

[0053]

According to the manufacturing method of the present invention, heat resistance and S resistance
It is possible to provide a NOx adsorbent having excellent Ox properties.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between aging time and saturated adsorption amount.

FIG. 2 is a graph showing the relationship between the amount of Ce carried and the amount of saturated adsorption.

FIG. 3 is a graph showing the relationship between firing temperature and Na elution rate.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location B01D 53/81 B01J 20/08 ZAB C (72) Inventor Atsushi Fukuju Nishikujo 5-chome, Konohana-ku, Osaka City No. 28 in Hitachi Shipbuilding Co., Ltd.

Claims (9)

[Claims] 1. A porous silica-alumina carrier having solid acidic points is immersed in an acidic solution containing Ru ions to adsorb a predetermined amount of Ru ions to the acidic points, and after drying and firing,
Immersing the carrier in an acidic solution containing rare earth ions to adsorb the rare earth ions to the remaining acidic points, and to adsorb excess rare earth ions on the inner surface of the carrier pores other than the acidic points for drying and firing. A method for producing an NOx adsorbent, comprising: 2. The method for producing a NOx adsorbent according to claim 1, wherein alkaline earth metal ions are added to an acidic solution containing rare earth ions. 3. The NOx adsorbent according to claim 1 or 2, wherein a carrier obtained by impregnating a colloid sol of silica-alumina into a preform made of heat-resistant fiber is used as the carrier. Manufacturing method. 4. The method for producing a NOx adsorbent according to claim 3, wherein the colloid sol impregnated in the preform body is dried at a temperature of 200 ° C. or lower. 5. The method for producing a NOx adsorbent according to claim 1, wherein the carrier is previously treated with an aqueous ammonium salt solution and calcined. 6. The method according to claim 4, wherein the treatment with the ammonium salt aqueous solution is performed at 50 ° C. or higher for 1 hour or more, and the calcination is performed at 250 ° C. or higher for 0.5 hour or more under flowing air. Method for manufacturing NOx adsorbent. 7. The method for producing a NOx adsorbent according to claim 1, wherein firing after Ru adsorption is performed at 180 to 300 ° C. for 0.5 to 3 hours. 8. The method for producing an NOx adsorbent according to claim 1, wherein the firing after the rare earth adsorption is performed at 350 ° C. to 500 ° C. for 2 hours or more. 9. The method according to claim 1, wherein the carrier is immersed in an acidic solution containing Ru ions, pulled up, and then left in a wet state for 1 hour or more.
A method for producing an Ox adsorbent.