JP3137497B2 - Adsorbent and adsorption removal method for hydrocarbon - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adsorbent for purifying hydrocarbons (hereinafter abbreviated as HC) discharged from an internal combustion engine or the like and a method for adsorbing and removing HC.

[0002]

2. Description of the Related Art In recent years, with the development of catalytic converters, exhaust gas from gasoline vehicles has been increasingly purified. However, the temperature at which the catalyst acts is as high as 200 ° C. or more, and there is still a problem that unburned HC and the like generated from the internal combustion engine are directly discharged into the atmosphere at a low temperature such as at the time of starting.

[0003]

In view of the above-mentioned situation, attempts to adsorb and remove HC and the like generated at low temperatures by using an adsorbent have been carried out by many research institutions. For example, when activated carbon is used as an adsorbent, a large amount of unburned HC is adsorbed in a low temperature region, but the activated carbon itself has no oxidizing effect in a high temperature region, so the adsorbed HC is desorbed and released into the atmosphere. There is a problem. Furthermore, since activated carbon is an organic adsorbent, there is a danger that the activated carbon itself will burn and ignite at high temperatures. On the other hand, examples of the inorganic adsorbent include alumina and silica, but there is a problem that a large amount of adsorbent is required due to a small capacity of adsorbing HC. Therefore, application of an adsorbent capable of adsorbing a large amount of HC at a low temperature and burning and removing the HC adsorbed at a high temperature to self-regenerate has been desired.

The present invention has been made in view of the above-mentioned state of the art,
Provided is an adsorbent capable of adsorbing a large amount of C and burning and removing the adsorbed HC at a high temperature to be able to self-regenerate, and a method capable of adsorbing and removing HC generated from an internal combustion engine or the like using the adsorbent. What you want to do.

[0005]

The present inventors have studied the development of an adsorbent suitable for the above-mentioned purpose. As a result, a crystalline silicate having a special molecular sieve structure carrying silver is preferred. The present invention has been found to be an agent.

That is, the present invention relates to (1) a crystalline silicate having a molecular sieve structure carrying silver, and the crystalline silicate having a molecular sieve structure is expressed by a molar ratio of an oxide in a dehydrated state; 1 ± 0.6) R ₂ O. [aM ₂ O ₃ .bAl ₂ O _3.
cMeO] · ySiO ₂ (wherein R is an alkali metal ion and / or hydrogen ion, M is one selected from the group consisting of group VIII metals, rare earth metals, titanium, vanadium, chromium, niobium, antimony and gallium. The above metals and Me are alkaline earth metals, a ≧ 0, b ≧ 0, c ≧ 0, a + b = 1, y / c> 1
2,2>y> 12) and a crystalline silicate having an X-ray diffraction pattern shown in Table A described in detail below. A crystalline silicate having a crystalline silicate previously synthesized is used as a mother crystal, and a crystalline silicate composed of Si and O having the same crystal structure as the mother crystal is grown on the outer surface of the mother crystal. A. The hydrocarbon adsorbent according to the above (1), which is a layered composite crystalline silicate having an X-ray pattern shown in A. (3) The crystalline silicate having a molecular sieve structure is a Y-type zeolite, mordenite, A hydrocarbon adsorbent according to the above (1), which is an L-type zeolite, a clinoptilolite, an A-type zeolite, a ferrierite, or a ZSM-5-type zeolite; A crystalline silicate having the above (1) to (3) molecular sieve structure formed by carrying one of silver, further cobalt, nickel, chromium, iron, manganese, iridium,
A hydrocarbon adsorbent, which carries one or more metals selected from the group consisting of gold, platinum, palladium, ruthenium, rhodium and vanadium; (5) exhaust gas when starting an internal combustion engine or the like When removing hydrocarbons in the wastewater, the exhaust gas at low temperature is used for the above (1) to
(4) Contacting any of the hydrocarbon adsorbents to adsorb and remove the hydrocarbons in the exhaust gas, and then burning the adsorbed hydrocarbons under the high temperature condition of the adsorbent and regenerating the adsorbent. (6) cutting out the inside of the hydrocarbon adsorbent, installing a switching valve at the cut-out point, and adsorbing the hydrocarbons in the exhaust gas at low temperature to the adsorbent. Close the switching valve and contact the exhaust gas with the adsorbent to allow the adsorbent to adsorb hydrocarbons,
(5) The method for adsorbing and removing hydrocarbons according to the above (5), wherein, when the adsorbed hydrocarbons are burned and removed, the switching valve is opened and the high-temperature exhaust gas is purged through a cut-out portion to bring the adsorbent to a high temperature condition. .

[0007]

[Table 1] W: Weak M: Intermediate S: Strong VS: Very strong (Irradiation is copper Kα ray) (I ₀ is the strongest peak intensity and I / I ₀ is the relative intensity)

[0008]

The crystalline silicate having a molecular sieve structure according to the present invention has an X-ray diffraction pattern as shown in Table A above, and is expressed as a molar ratio of oxide (1 ± 0.6) R _{2 in} a dehydrated state. O. [aM ₂ O ₃ .bAl ₂ O _3.
cMeO] .ySiO ₂ (wherein R is an alkali metal ion and / or hydrogen ion, M is at least one selected from the group consisting of group VIII elements, rare earth elements, titanium, vanadium, chromium, niobium, antimony and gallium. More than one kind of metal, Me is an alkaline earth metal of magnesium, calcium, strontium, barium, a ≧ 0, b ≧ 0, c ≧ 0, a + b =
1, y / c> 12, y> 12).

Further, a layered structure in which a crystalline silicate previously synthesized from a crystalline silicate is used as a mother crystal and a crystalline silicate made of Si and O having the same crystal structure as the mother crystal is grown on the outer surface of the mother crystal. It is a composite crystalline silicate, and may be a crystalline silicate having improved heat resistance and steam resistance. Further, the crystalline silicate may be Y-type zeolite, mordenite, L-type zeolite, clinoptilolite, A-type zeolite, ferrierite, ZSM. Even a -5 type zeolite is sufficiently effective as an adsorbent.

Further, the metal supported on the crystalline silicate is silver alone or a metal selected from the group consisting of silver and cobalt, nickel, chromium, iron, manganese, iridium, gold, platinum, palladium, ruthenium, rhodium and vanadium. HC adsorbing power and oxidizing power can be controlled by using an adsorbent in which at least one kind of metal is supported and coexisted.

As a method of incorporating silver into a crystalline silicate having a molecular sieve structure, a method of supporting silver by using an aqueous solution such as silver nitrate by an ion exchange method or an impregnation method is preferable.

In addition, silver and cobalt, nickel, chromium,
As a method of supporting iron, manganese, iridium, gold, platinum, palladium, ruthenium, rhodium, and vanadium on crystalline silicate, a method of performing coion exchange or co-impregnation using an aqueous solution such as nitrate of each metal is used. can give.

The HC adsorbent of the present invention is downstream of a three-way catalyst for a gasoline engine (usually a catalyst containing a Pt, Rh-based noble metal and capable of simultaneously removing NOx, CO, and HC near the stoichiometric air-fuel ratio). When installed, the temperature of the exhaust gas at the time of startup is usually from room temperature to about 100 ° C., and a large amount of HC can be adsorbed in this temperature range. The temperature at which the three-way catalyst operates is about 200 ° C. or more, and the exhaust gas temperature is 250 ° C.
In the above, HC can be removed by the three-way catalyst. Therefore, the HC adsorbent of the present invention is installed downstream of the three-way catalyst to adsorb HC at a temperature of 200 ° C. or lower where the three-way catalyst does not act, thereby preventing HC from being discharged out of the system. As the warm air progresses, the temperature of the adsorbent becomes about 15
When the temperature rises to 0 ° C. or higher, the adsorbed HC is burned and H ₂ O, C
It becomes O ₂ , is desorbed and the HC adsorbent is regenerated, and again adsorbs unburned HC in a low temperature range.

Further, the HC adsorbent of the present invention is used to
When considering a system that adsorbs and removes gas, it is necessary to take into account the pressure loss due to the magnitude of the gas amount. Normally, when starting at low temperature, the amount of gas is small, so that the entire amount of exhaust gas containing HC may be circulated to the HC adsorbent. However, at high temperatures, the amount of gas increases, so that the entire amount of gas is flowed through the adsorbent and adsorbed. H
Regeneration of the HC adsorbent by burning and removing C may affect pressure loss and adsorbent life. In this case, HC
Cut out the inside of the adsorbent, install a valve at this cutout location, close the valve when adsorbing HC at low temperature, flow HC-containing gas to the HC adsorbent to adsorb HC, while at high temperature because when the amount of gas is large to reduce the pressure loss, taking a method of directly purging exhaust gas opened valve, in this case, adsorbed HC but is burned off by the oxidation action of the HC adsorbent, the resulting CO _2, It is preferable to adopt a method in which H ₂ O is purged by self-diffusion and discharged out of the system to regenerate the HC adsorbent.

[0015]

【Example】

(Example 1) Water glass No. 1 (SiO ₂ : 30%): 56
16 g was dissolved in 5429 g of water, and this solution was designated as solution A. On the other hand, water: 4175 g and aluminum sulfate: 71
8.9 g, ferric chloride: 110 g, calcium acetate: 4
7.2 g, sodium chloride: 262 g, concentrated hydrochloric acid: 202
0 g is dissolved, and this solution is referred to as solution B. The solution A and the solution B are supplied at a constant ratio to form a precipitate, and the mixture is sufficiently stirred to obtain a slurry having a pH of 8.0. This slurry was charged into a 20-liter autoclave, and 500 g of tetrapropylammonium bromide was further added. Hydrothermal synthesis was performed at 160 ° C. for 72 hours. After the synthesis, the resultant was washed with water and dried. Obtain silicate 1. This crystalline silicate is represented by the following composition formula in terms of the molar ratio of the oxide (omitting the crystallization water), and the crystal structure is represented by X-ray diffraction in Table A above. 0.5Na ₂ O.0.5H ₂ O. [0.8Al ₂ O _3.
0.2Fe ₂ O ₃ .0.25CaO] .25SiO ₂

Using the above crystalline silicate 1, 0.0
It was immersed in a 4M silver nitrate aqueous solution and stirred for 24 hours to carry out Ag ion exchange. After washing and drying, powder adsorbent 1 was obtained.

Next, 3 parts of alumina sol as a binder and 200 parts of water were added to 55 parts of silica sol (SiO ₂ : 20%) with respect to 100 parts of the powder adsorbent 1 and sufficiently stirred to obtain a slurry for wash coating. . Next, a cordierite monolith substrate (400-cell grid) is immersed in the slurry, taken out, and then sprayed with excess slurry.
Dried at 00 ° C. The coated amount is 200 g per liter of the base material.

Example 2 In the synthesis of the crystalline silicate of Example 1, cobalt chloride was used instead of ferric chloride.
Crystallinity except that ruthenium chloride, rhodium chloride, lanthanum chloride, cerium chloride, titanium chloride, vanadium chloride, chromium chloride, antimony chloride, gallium chloride and niobium chloride are each added in the same mole number as Fe ₂ O _{3 in} terms of oxide. The same operation as in silicate 1 was repeated to prepare crystalline silicates 2 to 12. The crystal structures of these crystalline silicates are shown in Table A above by X-ray diffraction, and their compositions are represented by the molar ratio of oxides (dehydrated form) of 0.5Na ₂ O · 0.5H ₂ O ・ [0.2M ₂ O
₃ · 0.8Al ₂ O ₃ · 0.25CaO] · 25SiO
₂ Where M is Co, Ru, Rh, La, Ce,
It is a crystalline silicate of Ti, V, Cr, Sb, Ga, Nb.

The same operation as that of the crystalline silicate 1 was carried out except that magnesium acetate, strontium acetate and barium acetate were added in the same manner as in the case of CaO in terms of oxide in place of calcium acetate in the method for synthesizing the crystalline silicate 1. Was repeated to prepare crystalline silicates 13 to 15. The crystal structures of these mother crystals are shown in Table A by X-ray diffraction, and the composition is represented by a molar ratio of oxide (dehydrated form) of 0.5Na ₂ O.O.
5H ₂ O · _{[0.2Fe 2 O 3 · 0.8Al 2 O} 3 ·
0.25MeO] is a · 25SiO _2. Here, Me is Mg, Sr, and Ba.

The above crystalline silicates 2 to 15 were used in Example 1.
Ag ion exchange was performed in the same manner as in Example 1 to obtain powder adsorbents 2 to 15, and the powder adsorbent was formed into a honeycomb in the same manner as in Example 1 to obtain honeycomb adsorbents 2 to 15.

(Example 3) 1000 g of the crystalline silicate 1 obtained in Example 1 was used as a mother crystal, and this was mixed with water: 2160
g of colloidal silica (SiO ₂ : 20)
%): 4590 g was added and sufficiently stirred, and this solution was designated as solution a. On the other hand, 105.8 g of sodium hydroxide is dissolved in 2008 g of water to obtain a solution b. While stirring the solution a, the solution b is gradually added dropwise to form a precipitate to obtain a slurry. The slurry was placed in an autoclave, and 568 g of tetrapropylammonium bromide was added to water:
The solution dissolved in 2106 g is added to the autoclave. Hydrothermal synthesis is performed in this autoclave at 160 ° C. for 72 hours (stirring at 200 rpm), and after stirring, washing and drying, baking is performed at 500 ° C. for 3 hours to obtain a layered composite crystalline silicate 1. This surface layered silicate is called silicalite.

The layered composite crystalline silicate 1 was subjected to Ag ion exchange and honeycomb formation in the same manner as in Example 1 to obtain a powder adsorbent 16 and a honeycomb adsorbent 16.

Example 4 Na-type Y-type zeolite (S
iO ₂ / Al ₂ O ₃ ratio: 5), mordenite (SiO ₂
/ Al ₂ O ₃ ratio: 15), L-type zeolite (SiO ₂ /
Al ₂ O ₃ ratio: 6), clinoptilolite (SiO ₂ /
Al ₂ O ₃ ratio: 5), A-type zeolite (SiO ₂ / Al)
₂ O ₃ ratio: 1), ferrierite (SiO ₂ / Al ₂ O)
₃ ratio: 5), ZSM-5 type zeolite (SiO ₂ / Al
₂ O ₃ ratio: 30) zeolite was likewise Ag ion exchange and honeycomb of the crystalline silicate 1 in Example 1 to obtain a powder sorbent 17 through 23 and the honeycomb adsorbent 17 to 23.

Example 5 The crystalline silicate 1 obtained in Example 1 was treated with an aqueous solution of (0.04 M silver nitrate + 0.04 M cobalt nitrate), an aqueous solution of (0.04 M silver nitrate + 0.04 M nickel nitrate), and (0.04 M silver nitrate). +0.04 M ferric nitrate) aqueous solution, (0.04 M silver nitrate + 0.04 M manganese nitrate) aqueous solution, and (0.04 M silver nitrate + 0.01 M ammonium vanadate) aqueous solution and agitated. Similarly, the powder adsorbents 24-2
8 and honeycomb adsorbents 24-28.

The powder adsorbent 1 obtained in Example 1 was impregnated with an aqueous solution of iridium chloride, chloroauric acid, chloroplatinic acid, palladium chloride, ruthenium chloride, and rhodium chloride. Au, Pt, Pd, R
About 1% of u and Rh were supported and evaporated to dryness to obtain powder adsorbents 29 to 34. Further, these powder adsorbents were wash-coated to obtain honeycomb adsorbents 29 to 34.

Example 6 The layered composite crystalline silicate 1 obtained in Example 3 was prepared in the same manner as in Example 5 (0.04M
Aqueous solution of silver nitrate + 0.04M cobalt nitrate), (0.04
M silver nitrate + 0.04 M nickel nitrate) aqueous solution, (0.0
4M silver nitrate + 0.04M ferric nitrate aqueous solution, (0.0
4M silver nitrate + 0.04M manganese nitrate) aqueous solution, (0.
04M silver nitrate + 0.01M ammonium vanadate) aqueous solution and stirred, and powder adsorbent 3
5 to 39, and further, honeycomb adsorbents 35 to 39 were obtained.

The powder adsorbent 17 obtained in Example 4 (Ag
/ Y-type zeolite) is impregnated with an aqueous solution of iridium chloride, chloroauric acid, chloroplatinic acid, palladium chloride, ruthenium chloride, or rhodium chloride to obtain I per powder adsorbent.
0.6 wt% of r, Au, Pt, Pd, Ru, and Rh were supported, and after evaporating to dryness, powder adsorbents 40 to 45 were obtained, and further, honeycombs 40 to 45 were obtained.

(Comparative Example 1) Powdered activated carbon and silver-supported γ-Al ₂ O ₃ (Ag ₂ O: 10 wt%) were coated on a honeycomb substrate by a wash coat method, and the same method as in Example 1 was applied. Comparative honeycomb adsorbents 46 and 47 were obtained.

The honeycomb adsorbents 1 to 47 described in Examples 1 to 6 and Comparative Example 1 are summarized in Table B below.

[0030]

[Table 2]

[0031]

[Table 3]

[0032]

[Table 4]

(Experimental Example 1) One liter of honeycomb adsorbents 1 to 47 were set in an adsorption tower, and a hydrocarbon adsorption test was carried out. The test conditions are as follows. ○ Gas composition C ₂ H ₄ : 2000 ppm C ₃ H ₆ : 2000 ppm (THC = 10,000 ppm) O ₂ : 5% CO ₂ : 10% H ₂ O: 10% NO: 50 ppm N ₂ : balance ○ GHSV: 30, 000h ^-1 ○ Adsorption temperature: 50 ℃ ○ Desorption temperature: 150 ℃

FIG. 1 shows the test apparatus, and FIG. 2 shows the temperature patterns of the exhaust gas and the adsorbent. The adsorbed HC is detected by the FID meter. When the desorption temperature is set to 150 ° C., HC
Other gases, except for, were supplied as they were. Table C below shows the amounts of HC adsorbed and desorbed when the equilibrium is reached while alternately repeating the adsorption temperature and the desorption temperature with the above gas composition.

[0035]

[Table 5]

[0036]

[Table 6]

[0037]

[Table 7]

From these results, it can be seen that the honeycomb adsorbent 1 of the present invention was used.
By using ~ 45, a considerable amount of H
It was found that C was adsorbed and the adsorbed HC was burned and removed at 150 ° C., so that HC was not exhausted. On the other hand, activated carbon (honeycomb adsorbent 46) adsorbs at 50 ° C.
At 50 ° C., the adsorbed HC is desorbed as it is and Ag
Γ-Al ₂ O ₃ (honeycomb adsorbent 47) carrying
Almost no hydrocarbon is adsorbed even at 0 ° C. I understand.

(Experimental Example 2) As a test similar to Experimental Example 1, the honeycomb adsorbent 1 was installed as shown in FIG. 3, an intermediate portion was cut out, and a switching valve was provided behind the cutout portion. The gas composition was the same as in Experimental Example 1, except that the adsorption temperature of 50 ° C.
HSV: 30,000h ^-1 , desorption temperature 150 ° C is GHS
V: carried out at 100,000 h ^-1 . In the test apparatus method of FIG. 1 described above, there is a disadvantage that the pressure loss becomes large under the desorption condition of GHSV: 100,000 h ⁻¹ ,
By passing the intermediate part as it is as shown in FIG.
No pressure loss is applied under the desorption condition. Under the desorption conditions, almost no gas flows into the honeycomb adsorbent 1, but the adsorbed HC is sufficiently burned off at 150 ° C., and the generated H ₂ O and CO ₂ are purged by self-diffusion. Therefore, it was found that the reproduction was stable.

[0040]

According to the present invention, there is provided an adsorbent for HC in which HC is adsorbed and removed in a low temperature range, and the adsorbed HC is quickly burned and removed in a high temperature range. HC can be effectively removed, and the effect is industrially remarkable.

[Brief description of the drawings]

FIG. 1 is an explanatory view of an adsorption test device for a hydrocarbon adsorbent of the present invention.

FIG. 2 is a diagram showing a temperature change pattern in a test of the hydrocarbon adsorbent of the present invention.

FIG. 3 is an explanatory diagram of one mode of use of the hydrocarbon adsorbent of the present invention.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-126165 (JP, A) JP-A-6-63394 (JP, A) JP-A-5-317701 (JP, A) JP-A-5-317701 293369 (JP, A) JP-A-5-285378 (JP, A) JP-A-5-31359 (JP, A) JP-A-64-34440 (JP, A) JP-B-46-10064 (JP, B1) (58) Field surveyed (Int. Cl. ⁷ , DB name) B01J 20/00-20/34

Claims (6)

(57) [Claims] 1. A crystalline silicate having a molecular sieve structure carrying silver, wherein the crystalline silicate having a molecular sieve structure is dehydrated and expressed as a molar ratio of oxides: (1 ± 0.6 ) R ₂ O · _{[aM 2 O 3 · bAl 2 O} 3 ·
cMeO] · ySiO ₂ (wherein R is an alkali metal ion and / or hydrogen ion, M is one selected from the group consisting of group VIII metals, rare earth metals, titanium, vanadium, chromium, niobium, antimony and gallium. The above metals and Me are alkaline earth metals, a ≧ 0, b ≧ 0, c ≧ 0, a + b = 1, y / c> 1
2, y> 12) and a crystalline silicate having an X-ray diffraction pattern shown in Table A described in detail in the text. 2. A crystalline silicate having a molecular sieving structure and a crystalline silicate synthesized in advance is used as a mother crystal, and a crystalline silicate made of Si and O having the same crystal structure as the mother crystal is grown on an outer surface thereof. The hydrocarbon adsorbent according to claim 1, which is a layered composite crystalline silicate having an X-ray pattern shown in Table A described in detail in the text. 3. The crystalline silicate having a molecular sieve structure is Y
Zeolite, mordenite, zeolite L, clinoptilolite, zeolite A, ferrierite, ZS
The hydrocarbon adsorbent according to claim 1, wherein the adsorbent is an M-5 type zeolite. 4. A crystalline silicate having a molecular sieve structure carrying any one of claims 1 to 3, further comprising cobalt, nickel, chromium, iron, manganese, iridium,
A hydrocarbon adsorbent comprising one or more metals selected from the group consisting of gold, platinum, palladium, ruthenium, rhodium and vanadium. 5. When removing hydrocarbons in exhaust gas at the time of starting an internal combustion engine or the like, the exhaust gas at a low temperature is brought into contact with a hydrocarbon adsorbent according to any one of claims 1 to 4, and the hydrocarbons in the exhaust gas are removed. And removing the adsorbent by burning the adsorbent under high-temperature conditions and regenerating the adsorbent. 6. A method for cutting out the interior of a hydrocarbon adsorbent, installing a switching valve at the cut-out point, and closing the switching valve when adsorbing hydrocarbons in exhaust gas at a low temperature to the exhaust gas and the adsorbent. Contacting the adsorbent to adsorb the hydrocarbons, and burning and removing the adsorbed hydrocarbons, the switching valve is opened and the high-temperature exhaust gas is purged through a cut-out portion to bring the adsorbent to high-temperature conditions. 5. The method for adsorbing and removing hydrocarbons according to 5.