JP2838097B2 - A water-resistant carbon dioxide-friendly material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon dioxide affinity substance which can be used for a carbon dioxide separation membrane or the like used in a high-temperature and water vapor atmosphere. With a basic oxide layer provided on the surface of the carrier, for example, in a process of separating an acidic gas from a high-temperature combustion exhaust gas, etc., to provide a water vapor resistance that enables carbon dioxide adsorption in a high temperature and water vapor atmosphere. The present invention relates to a carbon dioxide affinity substance having the same.

[0002]

2. Description of the Related Art At present, global warming is a major environmental problem. Controlling the emission of carbon dioxide, the main causative substance, is an important issue. As a method of suppressing carbon dioxide emission, a method of separating carbon dioxide from combustion exhaust gas at a high temperature in a large-scale fixed generation source such as a power plant and fixing it by a catalytic reaction is considered.

In general, a polymer membrane is generally used for gas separation using a membrane. However, in consideration of the above-described separation at a high temperature, the polymer membrane is used because of insufficient heat resistance. Can not do. Therefore, the use of a ceramic membrane having excellent heat resistance is essential for the separation of high-temperature combustion exhaust gas of several hundred degrees Celsius, and several studies on high-temperature gas separation using a ceramic separation membrane have already been conducted.

[0004] By the way, the gas separation method using a ceramic membrane includes a method in which fine pores of the same size as the gas molecules to be separated are formed, the gas is separated by a molecular sieve effect based on the pore diameter, and a pore in which chemical affinity is imparted. There are several separation methods such as a method in which gas molecules to be separated are chemically adsorbed on the surface and separation is performed by utilizing surface diffusion of adsorbed species, and a method in which Knudsen diffusion is performed by utilizing a difference in gas molecular weight. Of these separation methods, the object of the present invention is a separation method utilizing the above-mentioned chemical affinity.

[0005] Among the above separation methods, a method utilizing Knudsen diffusion has been considerably studied. In addition, research on a method utilizing the molecular sieve effect has recently been advanced. However, the objects to be separated by these methods are limited to gases having a small molecular weight and relatively easy to separate, such as hydrogen.

[0006] On the other hand, the method utilizing chemisorption has been theoretically studied, and at present, there are not many concrete research examples. Therefore, there are few studies on the affinity of ceramics for carbon dioxide at high temperatures on the premise of membrane separation. In such a situation, the inventors of the present invention have proposed “carbon dioxide-friendly substance” (Japanese Patent Application No.
68243) found that the affinity for carbon dioxide was maintained even at a high temperature of 500 ° C. or higher by introducing a very thin basic oxide onto the surface of the membrane material and modifying the surface.

In the gas separation process, when a high-temperature combustion exhaust gas is mainly used as a gas to be separated, the components of the combustion exhaust gas are mainly nitrogen, but each contains about 10% of carbon dioxide and water. In the above-mentioned carbon dioxide affinity substance, the basic oxide surface has a high affinity for water, and when water coexists, the surface is covered with a hydroxyl group. Therefore, it is expected that the affinity for carbon dioxide is impaired.
However, there has been almost no example of studying the affinity of carbon dioxide for carbon dioxide in the presence of water vapor as described above.

[0008]

Therefore, in view of the above prior art, the present inventors focused on a technique relating to affinity for carbon dioxide in a high-temperature and steam atmosphere, and even when steam coexisted as described above, the present inventors As a result of intensive research aimed at developing a new carbon dioxide-affinitive substance that maintains carbon affinity, the basic oxide layer was introduced by introducing a basic oxide on the surface of the porous ceramic separation membrane material. It has been found that the intended purpose can be achieved by forming the same, and the present invention has been completed. That is, an object of the present invention is to provide a carbon dioxide affinity substance that can separate an acidic gas such as carbon dioxide at a high temperature from a high-temperature combustion exhaust gas or the like by using a chemical adsorption action as described above. Things. In addition, the present invention provides a method for imparting carbon dioxide carbon affinity to a surface of a porous ceramics carrier at a high temperature and in a steam atmosphere in order to separate carbon dioxide at a high temperature by utilizing chemisorption from a high temperature combustion exhaust gas or the like. It is intended to provide.

[0009]

The present invention for solving the above-mentioned problems comprises a porous ceramic carrier and a basic oxide layer provided on the surface of the carrier. The present invention relates to a carbon dioxide-affinitive substance capable of adsorbing carbon, and the present invention further provides the ceramic carrier, wherein the ceramic carrier is a metal oxide film. The amount of metal ions forming the basic oxide layer is 2 to 8 μmo.
1 / m ² , wherein the carbon dioxide affinity material and the ceramics carrier are mainly composed of γ-alumina, and the basic oxide layer is formed of sodium, potassium, rubidium, cesium, magnesium, calcium, strontium. In a preferred embodiment, the above-mentioned carbon dioxide-friendly substance is formed of at least one of barium, lanthanum, praseodymium, and neodymium. Hereinafter, the present invention will be described in more detail. In solving the above technical problems, the present inventors have found that carbon dioxide is an acidic gas and is easily bonded to a basic compound by an acid-base reaction. As a result, the surface of the membrane material is made strongly basic. We focused on the increase in carbon dioxide affinity. As a result of intensive studies, they have found that the affinity for carbon dioxide can be maintained even at a high temperature exceeding 400 ° C. by introducing a very thin basic oxide onto the surface of the carrier material and modifying the surface. Further, as a result of further research, it was found that the affinity for carbon dioxide in a water vapor atmosphere has a correlation with the ion radius of metal ions introduced to the surface of the membrane material. That is, when the membrane material is modified with a large ion radius and electrically positive metal ions,
It has been revealed that it has the ability to retain carbon dioxide at high temperatures even in a steam atmosphere.

The method for imparting carbon dioxide affinity to the surface of a porous ceramic carrier in a high-temperature and steam atmosphere according to the present invention will be described in detail below.

In the present invention, silica, alumina, titania, and the like are preferably used as the porous ceramics carrier imparting carbon dioxide affinity, for example. Several nm
Any ceramic carrier capable of forming a small number of pores can be used in the same manner, and the ceramic carrier is not limited to the above-described one. In particular, when the ceramic carrier is a metal oxide, a metal component adheres to the surface,
Heating is preferred because a metal oxide (basic oxide) layer can be easily formed on the surface of the carrier. Further, γ-alumina is more preferable because it is easy to form a porous thin film having pores of several nm and is superior to silica in heat resistance. Further, as a form of such a ceramic carrier, an appropriate form such as a sphere, a plate, a thin film or the like can be adopted as required. Above all, a film-like body is preferable. This is because the film can efficiently contact a large amount of combustion exhaust gas and the like.

Specific examples of the component imparting carbon dioxide affinity to the surface of the ceramic carrier include alkali metals such as sodium, potassium, rubidium and cesium, alkaline earth metals such as magnesium, calcium, strontium and barium, and lanthanum. , Praseodymium, neodymium and other rare earth metals are used, and other electrically positive elements such as zinc can be used.In a high-temperature, steam atmosphere, potassium, rubidium, cesium, calcium, strontium, It is preferable to use a basic metal ion having a large ionic radius, such as barium, lanthanum, praseodymium, or neodymium. FIG. 11 shows the heat of adsorption of alumina when the basic oxide layer was formed with various metal ions. As shown in this figure, in the basic oxide applied to the surface of the ceramic carrier, the smaller the electronegativity of the metal ion, the more the negative partial charge of the surface oxygen and the higher the heat of adsorption. The basicity of surface oxygen increases as the coordination number of a metal atom increases, and conversely, increases as the coordination number of an oxygen atom decreases.

In order to apply these metals to the ceramic carrier, an impregnation method, a CVD method or the like can be used. For example, in the case of the impregnation method, nitrates of these metals,
The ceramic carrier is impregnated with an aqueous solution of acetate or carbonate to introduce a basic component to the surface.

After impregnation with the above metal salt, the mixture is heated at a high temperature to decompose the salt to an oxide state. The heating temperature must be equal to or higher than the decomposition temperature of the salt.
C. for 1-3 hours.

The amount of metal ions introduced is preferably 2 to 8 μm.
ol / m ² . If the amount is small, the affinity for carbon dioxide is insufficient. If the amount is too large, the pores of the ceramic carrier may be blocked by the introduced components. The amount of metal ions introduced is more preferably 3 to 5 μmol / m.
²

[0016]

The reason why the introduction of the basic oxide layer maintains the affinity for carbon dioxide even at a high temperature is considered as follows. For example,
In carbon dioxide, since the electron distribution is biased toward O ₂ atoms, the carbon atoms are electrophilic. For this reason, carbon dioxide is an acid gas. On the other hand, basic oxides have a high electron density on oxygen, which is the reason for showing basicity. Therefore, it is considered that carbon atoms and the like of carbon dioxide are chemically adsorbed to oxygen of the basic oxide. Furthermore, the reason that the affinity for carbon dioxide is maintained even at high temperatures is that, in the case of chemisorption, the adsorption energy is large, showing a large value such as the interatomic bond energy within the molecule, and the bond must be broken at a very high temperature. Is not possible.

It is considered that the affinity for carbon dioxide is maintained when the membrane surface is modified with a cation having a large ionic radius in a steam atmosphere. Carbon dioxide is a Lewis acid and adsorbs to oxygen ions, which are basic points on the oxide surface. There are two types of adsorption. Monodentate in which carbon atoms of carbon dioxide adsorb to oxygen ions
There are adsorbed species and, in addition, bididentate adsorbed species in which the oxygen atoms of carbon dioxide also interact with the metal ions of the oxide. The latter adsorbed species has a higher binding order and is strongly adsorbed.

Since the hydroxyl group also has basicity, it can adsorb carbon dioxide, but is less basic than oxygen ions. In addition, since the oxide surface is covered with a hydroxyl group, metal ions are not exposed, and it is difficult to perform bidetate type adsorption.

When the ionic radius of the metal ion is large, even if a hydroxyl group is present on the metal ion, the metal ion is larger than the size of the hydroxyl group, and the surface coverage with the hydroxyl group is not complete.

Therefore, even if a hydroxyl group is present, it is expected that oxygen atoms of carbon dioxide can interact to some extent with metal ions on the oxide surface. It can be interpreted that the carbon dioxide affinity is maintained by adsorbing the bidentate type even in a water vapor atmosphere.

[0021]

Next, the present invention will be specifically described based on examples, but the present invention is not limited to the examples. Example 1 Using γ-alumina (20/30 mesh granular material) as a ceramics carrier, the surface of alumina was changed to an alkali metal (sodium, potassium, rubidium, cesium), an alkaline earth metal (magnesium, calcium, strontium, barium), Modified with basic oxides of rare earth metals (lanthanum, cerium, praseodymium, neodymium). In this example, each nitrate solution was used,
γ-alumina is impregnated with these nitrate solutions, and 4 μmol / m ^{2 is} introduced as a metal ion concentration, respectively.
The mixture was heated at 1 ° C. for 1 hour to decompose the salt to an oxide state.

In order to evaluate the affinity of carbon dioxide for such γ-alumina, as shown in FIG. 1, a surface-modified alumina was filled in a quartz tube (column length: 10 cm) and subjected to high-temperature chromatography (separation temperature 400 ° C.). ~ 800
C), a nitrogen / carbon dioxide mixed gas was injected, and the retention time of each gas was measured.

FIG. 2 shows γ surface-modified with an alkaline earth metal.
The relation between the separation temperature and the retention time in alumina is shown. Alumina which has not been subjected to surface modification also shows weak basicity, and thus exhibits a certain degree of affinity for carbon dioxide at 400 ° C. or lower (see the unfilled solid line in FIG. 2). However, when the temperature exceeds 400 ° C., the retention times of nitrogen and carbon dioxide become the same, and the affinity for carbon dioxide becomes insufficient. In contrast, in the surface-modified alumina, the retention time of nitrogen is about 0.4 minutes even at 600 ° C., whereas the retention time of carbon dioxide is 1 to
It is a long time of 1.5 minutes. As a result of such surface modification, it was found that the material had affinity for carbon dioxide despite the high separation temperature of 500 ° C. or higher.

In particular, in the case of strontium, as shown in FIG. 3, when the heat of adsorption when the basic oxide layer is provided with strontium is calculated, a high value of about 160 kJ / mol near 4 μmol / m ² is obtained. As shown, it was confirmed that the affinity for carbon dioxide was significantly improved as compared with 50 kJ / mol of γ-alumina to which strontium was not introduced.

The heat of adsorption (Q) was calculated by the method of Experimental Chemistry Course (continued) 9 (1965, Maruzen Co., Ltd.). That is, the retention time of carbon dioxide (t ₁ ) and nitrogen (t ₀ ) was measured by gas chromatography, and 1n (μ / T) and 1 / (1) were calculated by the following formulas (1), (2), and (3).
Q / R was calculated from the slope of the plot of T to obtain Q. μ = (t ₁ −t ₀ ) / t ₀ ─── (1) μ / T = c · exp (−Q / RT) ─── (2) 1n (μ / T) = 1 nc−Q / RT ─ ── (3) where c: constant T: separation temperature (K) R: gas constant

Further, as shown in FIG.
(300-700 ° C), change the strontium concentration
When the retention time of carbon dioxide was measured,
l / m ^TwoAffinity effect begins to appear at a concentration of 2 μmol /
m^TwoTo 6 μmol / m^TwoAs it goes up,
The nature has also improved. This result is opposite to the calculation result of heat of adsorption.
It responds.

FIG. 5 shows the results of measuring the retention time of carbon dioxide when the surface is modified with an alkali metal. As is clear from these results, in any of the alkali metals, γ-alumina having no surface modification (see the solid line in FIG. 5).
And exhibited a carbon dioxide affinity similar to alkaline earth metals.

FIG. 6 shows the results of measuring the retention time of carbon dioxide when the surface is modified with a rare earth metal (lanthanum, cerium, neodymium, praseodymium). Since these metals have high electronegativity, their ability to chemically adsorb carbon of carbon dioxide is lower than that of alkaline earth metals or alkali metals. However, as compared with γ-alumina having no surface modification (see the solid line in FIG. 6), it was confirmed that it had affinity for carbon dioxide at high temperature.

Example 2 γ-alumina was used as a film material for a ceramic carrier.
Alkaline metal, alkaline earth metal,
Modified with basic oxide of rare earth metal. That is, in the present example, the γ-alumina compact particles having a size of 20/30 mesh were impregnated with an aqueous nitrate solution of the above-mentioned metal, and a component having an affinity for carbon dioxide was introduced to the alumina surface at a surface concentration of 4 μmol / m ² . . After the impregnation, heat treatment was performed at 800 ° C. for 1 hour.

An apparatus as shown in FIG. 7 was used to evaluate the affinity of the surface-modified alumina thus synthesized for carbon dioxide in a steam atmosphere. When the surface-modified alumina is filled in a quartz tube and kept at a high temperature, and a mixed gas of nitrogen and carbon dioxide is added to the carrier gas at the inlet of the packed bed, nitrogen and carbon dioxide are separated in the packed bed by the principle of gas chromatography. The retention times of both were measured to evaluate the affinity for carbon dioxide.

Helium as a carrier gas contained water vapor at 0.1 atm. Sample filling amount is 1 g, column inner diameter is 4
mm, column length is 10 cm.

FIGS. 8 to 10 show the relationship between the retention time of carbon dioxide and the separation temperature measured by the above-described method.
The nitrogen retention time was 0.4 minutes without changing with temperature. Alumina modified with barium, strontium, calcium, cesium, rubidium, potassium, lanthanum, neodymium, and praseodymium having a large ionic radius has a longer carbon dioxide retention time even at 300 ° C than a nitrogen retention time even at 300 ° C. It turns out that it has. Magnesium with a small ionic radius,
When modified with sodium, cerium or the like, a sufficient carbon dioxide retention time is not exhibited unless the temperature is 150 ° C. or lower.

FIG. 11 shows the affinity of carbon dioxide based on the heat of adsorption. When the surface was modified with barium, lanthanum, and cesium, the heat of adsorption was about 70 to 80 kJ / mol.

The approximate transmission coefficient of carbon dioxide by surface diffusion was estimated. When the heat of carbon dioxide adsorption is 80 kJ / mol in a membrane having pores with a pore radius of 1 nm, 2
A transmission coefficient of carbon dioxide of about × 10 ⁻¹¹ mol · m / · m ² · Pa · s is expected. This value is the calculated value of the permeability coefficient of nitrogen by Knudsen diffusion (2.6 × 10 ⁻¹² mo)
1 · m / · m ² · Pa · s), and selective permeation of carbon dioxide is expected. The appropriate value of the heat of adsorption differs depending on the temperature used. If the heat of adsorption is larger than necessary, surface diffusion is hindered.

[0035]

As described in detail above, the present invention comprises a porous ceramic carrier and a basic oxide layer provided on the surface of the carrier, and is capable of adsorbing carbon dioxide in a high-temperature and steam atmosphere. According to the present invention, it is possible to provide a carbon dioxide affinity substance that can bind carbon dioxide to a basic oxide layer by chemisorption at a high temperature. it can. Further, according to the present invention, it is possible to provide a carbon dioxide-affinitive substance having steam resistance, which enables selective adsorption of carbon dioxide in a high-temperature and steam atmosphere. Utilizing the carbon dioxide-affinitive substance, carbon dioxide can be separated at a higher temperature than the high-temperature combustion exhaust gas.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an outline of measurement of a carbon dioxide retention time in Example 1 of the present invention.

FIG. 2 is a graph showing the retention time of carbon dioxide when γ-alumina is surface-modified with an alkaline earth metal (γ
Alumina is indicated by an unfilled solid line).

FIG. 3 is a graph showing the relationship between the strontium introduction concentration and the heat of adsorption when γ-alumina is surface-modified with strontium.

FIG. 4 is a graph showing the relationship between the concentration of strontium introduced and the retention time for each separation temperature when γ-alumina is surface-modified with strontium.

FIG. 5 is a graph showing the retention time of carbon dioxide when γ-alumina is surface-modified with an alkali metal (γ-alumina is shown by a solid line without a mark).

FIG. 6 is a graph showing the retention time of carbon dioxide when γ-alumina is surface-modified with a rare earth metal (γ-alumina is indicated by a solid line without a mark).

FIG. 7 is a schematic diagram of an apparatus for evaluating affinity for carbon dioxide in a high-temperature and water-vapor atmosphere according to a second embodiment of the present invention.

FIG. 8 is an explanatory diagram showing the relationship between the retention time of carbon dioxide and the separation temperature.

FIG. 9 is an explanatory diagram showing a relationship between a retention time of carbon dioxide and a separation temperature.

FIG. 10 is an explanatory diagram showing the relationship between the retention time of carbon dioxide and the separation temperature.

FIG. 11 is an explanatory diagram showing the heat of adsorption of carbon dioxide of a surface-modified material.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tatsuro Horiuchi 2-4-1 Rokuno, Atsuta-ku, Nagoya, Aichi Prefecture Inside the Fine Ceramics Center (72) Takehisa Fukui, Rokuno, Atsuta-ku, Nagoya-shi, Aichi 2-4-1, Japan Fine Ceramics Center (72) Inventor Hiroaki Hidaka 2-4-1, Rokuno, Atsuta-ku, Nagoya-shi, Aichi Examiner in Fine Ceramics Center Satoshi Hattori (56) References JP-A-62-110744 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B01D 53/62 B01D 53/34

Claims (4)

(57) [Claims] 1. A carbon dioxide affinity substance comprising a porous ceramic carrier and a basic oxide layer provided on the surface of the carrier, and capable of adsorbing carbon dioxide in a high-temperature and steam atmosphere. 2. The carbon dioxide-friendly material according to claim 1, wherein the ceramics carrier is a metal oxide film. 3. The carbon dioxide affinity substance according to claim 1, wherein an amount of the metal ions forming the basic oxide layer is ² to 8 μmol / m ² . 4. The ceramic carrier is mainly composed of γ-alumina, and the basic oxide layer is formed of sodium, potassium,
Rubidium, cesium, magnesium, calcium, strontium, barium, lanthanum, praseodymium,
The carbon dioxide-affinitive substance according to claim 1, wherein the substance is formed of at least one of neodymium and neodymium.