JPH06102150B2 - Acid gas adsorption separation - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for adsorbing and separating an acidic gas contained therein from an acidic gas-containing gas and an acidic gas adsorption / separating agent used therefor.

[Prior art]

Synthetic gas that is a chemical raw material (gas mainly composed of CO and H ₂ )
Contains carbon dioxide (CO ₂ ) at various concentrations depending on its raw material, manufacturing method and the like. When a catalytic reaction is carried out using such a synthesis gas, carbon dioxide gas present in the synthesis gas may not only dilute the reaction system as an inert component but also become a catalyst poisoning substance, Removal is required.

Conventionally, the following method is known as such a method for separating carbon dioxide gas.

(I) Hot potassium carbonate method This method is a method of removing carbon dioxide gas in a gas by using a concentrated solution of potassium carbonate at a high temperature.

(Ii) Pressurized water washing method This method is a method of absorbing carbon dioxide gas in cold water under pressure and releasing carbon dioxide gas under normal pressure.

(Iii) Garbottle method (Gardler method) This method is a method of absorbing and removing an acidic gas using a fatty acid amine, amino alcohol, or the like.

However, each of the above-mentioned methods has various drawbacks and is not satisfactory. For example, the method (i) includes a high working temperature of 115 ° C. and a relatively large amount of residual carbon dioxide in the purified gas, and the method (ii) uses a large amount of water, The method (iii) includes the drawback that the power cost is high, and the amine is entrained in the purified gas.

Further, during the chemical reaction step, gas containing an acidic gas such as hydrogen sulfide or hydrogen halide such as hydrogen chloride or hydrogen fluoride may be generated, and the acidic gas contained in the gas may be separated from these gases. It is also required to do. Although these acidic gases can be separated by the above-mentioned methods,
However, this case also has the same drawbacks as described above.

〔Purpose〕

The present invention provides a solid acid gas adsorption / separation agent which overcomes the drawbacks found in the prior art, and a method for adsorbing and separating the acid gas contained therein from a gaseous substance using the adsorption / separation agent. The purpose is to provide.

〔Constitution〕

According to the present invention, as a first invention, the acidic gas-containing gas comprises at least one selected from a basic alkali metal compound and a basic alkaline earth metal compound and a non-zeolitic porous oxide. After adsorbing the acidic gas by contacting it with the complex, the complex gas is desorbed to maintain the complex gas under a pressure lower or a temperature condition higher than that during the adsorption. A second aspect of the present invention provides a method for adsorptive separation of acidic gas, which comprises separating at least one selected from a basic alkali metal compound and a basic alkaline earth metal compound and a non-zeolitic porous material. An acidic gas adsorption separating agent comprising a complex with a porous oxide is provided.

The acidic gas adsorption separating agent of the present invention (hereinafter, also simply referred to as a separating agent) is at least one selected from a basic alkali metal compound and a basic alkaline earth metal compound and a non-zeolitic porous oxide. Composed of a complex. In this case, the non-zeolitic porous oxide has substantially no micropores of about several angstroms, and therefore means an oxide having no molecular sieving ability, and specific examples thereof include alumina, silica and silica. Alumina, titania, magnesia, etc. may be mentioned. Further, as the alumina, γ-alumina obtained by dehydrating and firing a pseudo-boehmite structure obtained from a hydrosol of aluminum is preferable, and one fired in air at a high temperature of 1100 ° C or higher or steam treated at 800 ° C or higher. However, activated alumina obtained from aluminum hydroxide having a high degree of crystallinity is also not preferred. Similarly, with respect to silica, silica-alumina, titania, magnesia, etc., those prepared from those having a small primary particle diameter are preferable to those prepared from those in which the colloidal particles of the sol are grown large. Those that have Zeolitec pores such as zeolite, those that have micropores such as activated carbon, and those that have molecular sieve capacity are
Since it is difficult for the solution of the alkali metal compound or the alkaline earth metal compound to enter the inner surface of the pores, it is not possible to sufficiently exhibit high selective absorption of the acidic gas. On the other hand, the non-zeolitic porous oxide having no micropores used in the present invention and therefore having no molecular sieving ability is
Pore size is large, the above solution is easy to enter, and not only can it fully support an alkali metal compound or alkaline earth metal that exhibits high selective adsorption of acid gas, but also the coordination state around this oxide and the metal. Shows interactions that do not change. As a result, a stable complex of the supported alkali metal compound or alkaline earth metal compound and the oxide is formed.

In the above non-zeolitic porous oxide used in the present invention, it is also important to control the pore volume,
If the pore volume is too small, the contact efficiency between the metal inside the pores and the raw material gas decreases, and the adsorption capacity decreases. Further, as the pore volume increases, the amount of unabsorbed raw material gas (low-concentration acidic gas) remaining in the pores increases, and if it is too large, it causes the purity of the recovered product gas to decrease. Therefore, the non-zeolitic porous oxide used in the present invention has a preferable range as a pore volume, and in the case of the present separating agent,
Pore volume is 0.2cc / g-1.5cc / g, preferably 0.3cc / g-1.0
It is cc / g. Further, there is a preferable range for the pore size as well as the pore volume, and when the pore size is too small, the molecular sieving ability is expressed, and O ₂ , H ₂ O and the like are easily adsorbed, and in addition, alkali The pores are crushed when composited with a metal or alkaline earth metal. Therefore, it is necessary to use an oxide having an average pore size of 20 Å or more before preparation. Further, if the pore volume is the same, the surface area decreases as the pore diameter increases, but in order to uniformly disperse and support the alcal metal or alkaline earth metal, the surface area is preferably high. For the above reasons, the average pore diameter (diameter) of the porous oxide is preferably 20 Å or more and 200 Å or less, more preferably 50 Å or more and 150 Å or less.

The term "alkali metal" as used in the specification means an element belonging to group IA of the periodic table, and includes Li, Na, K, Rb and the like. The alkaline earth metal is an element belonging to Group II-A of the periodic table, and includes Be, Mg, Ca, Sr and the like. Further, these basic compounds mean salts with weak acids such as hydroxides, carbonates and acetates of the above elements, and do not include chlorides, sulfates, nitrates and the like. For example, in the case of Na, sodium hydroxide (Na
OH), sodium acetate (CH ₃ COONa), sodium aluminate (NaAlO ₂ ), sodium amide (NaNH ₂ ), sodium ammonium hydrogen phosphate (NaNH ₄ HPO ₄ ), sodium sulfite (NaAsO ₂ ), sodium bismuthate (NaBi)
O ₃ ), sodium carbonate (NaCO ₃ ), sodium hydrogen carbonate (NaHCO ₃ ), sodium formate (HCOONa), sodium chromate (Na ₂ CrO ₄ ), and the like, but sodium hydroxide and sodium carbonate are preferably used. To be

As a method for compositing the basic compound and the non-zeolitic porous oxide, a usual method can be used.
That is, it can be prepared by a method of dissolving the basic compound in water, adding a non-zeolitic porous oxide to the solution, sufficiently immersing the solution, and then heating or / and reducing the pressure to remove the water. Is. At that time, there is an optimum value for the amount of the carrier to uniformly and uniformly carry the basic compound.
This optimum value varies depending on the surface area of the porous oxide, but in the case of a sodium compound, the weight ratio of Na to the porous oxide is in the range of 0.01 to 0.1.

According to the study by the present inventors, as the non-zeolitic porous oxide, a) a step of obtaining an alumina hydrogel from an alumina hydrogel-forming substance, b) the pH of the alumina hydrogel is set to an alumina hydrogel dissolution region and a boehmite gel precipitation region. Alternating with the above, and at the time of changing the pH to at least one of the alumina hydrogel dissolution region and the boehmite gel precipitation region, adding an alumina hydrogel-forming substance to obtain a crystal-grown alumina hydrogel, and / or alumina. While maintaining the hydrogel in the boehmite gel precipitation region, a step of adding an alumina hydrogel-forming substance in a continuous flow or an intermittent flow to obtain a crystal-grown alumina gel, c) a combination of washing and drying or firing of the crystal-grown alumina hydrogel No alumina xerogel It has been found that the use of alumina formed by the combination of: This alumina has substantially no micropores having a diameter of several angstroms, and therefore has no molecular sieving ability and has either a Bressted acid point that is stable at low temperature or a Lewis acid point that is easily generated at high temperature. Since it has an acid point, a large pore size, and a high surface area, it has the ability to uniformly and uniformly support the basic compound.

Furthermore, this alumina has the property of retaining the basic compound without significantly changing the coordination state around the alkali metal compound. As a result, the basic compound carried and dispersed is kept stable. Then, the alumina composite containing the stable basic compound exhibits its high selectivity as it is without reducing the chemical absorption capacity of the basic compound.

According to the combination of the specific steps as described above, the pore volume is 0.3
~ 1.2 cc / g, especially 0.5.-0.9 cc / g and average pore size (diameter) 50-150 angstroms, especially alumina having physical properties of 100-130 angstroms can be easily prepared. Is advantageously used as the non-zeolitic porous oxide in the separating agent of the present invention. This alumina is usually used as a molded body. The shape of the molding can be any shape such as a cylindrical shape or a spherical shape. Therefore, it can be appropriately selected according to the usage conditions. Generally, a cylindrical molded body having a diameter of 1/16 inch or 1/32 inch is used.

Further, when the alumina is used as a raw material for the separating agent in the present invention, its chemical properties are also important characteristics. This chemical property generally differs depending on the difference in the preparation method. For example, even when the same raw material is used, different production methods such as precipitation method, aging method, and sintering method are used. When it is produced by using it, the obtained alumina has different acidic carbon, acid strength distribution and the like. This property has a great influence on the preparation of the separating agent of the present invention, and when a basic compound is carried, a difference occurs in its carrying ability and dispersibility, so it is necessary to control it appropriately. Conventionally, a method for producing a porous alumina molded body, to produce an alumina hydrogel as a seed from an alumina hydrogel forming substance which is a precursor to produce an alumina hydrogel, to grow the crystal particles,
It is common to produce a desired porous alumina molded body by a process such as washing, dehydration molding, drying, and firing after making these into a sol or gel-like substance. In this manufacturing operation, an important step for controlling the chemical properties is a step of obtaining a sol-like gel-like substance. Conventionally, an alumina hydrogel that is a seed is produced from an alumina hydrogel-forming substance that is a precursor that produces a porous alumina molded body, and this alumina hydrogel is grown,
The method for producing the alumina hydrogel which becomes the seed in the gelation step for obtaining these gelled substances includes a precipitation method, a uniform precipitation method and a hydrolysis method. In the precipitation method, a compound containing aluminum is neutralized with an acid or an alkali to produce an alumina hydrogel which becomes seeds. Further, the homogeneous precipitation method is broadly included in the precipitation method, and overcomes the drawback of the precipitation method, that is, the point that the alumina hydrogel that becomes the seed is non-uniform because the neutralization operation is difficult to control. It is characterized in that an organic compound such as urea or hexamethylenetetramine is used as a solvating agent and the neutralization operation becomes slow. The hydrolysis method is a method of producing an alumina hydrogel by hydrolyzing an aluminum compound without using a neutralizing agent. Any of these methods can be used in the step a) of obtaining the alumina hydrogel from the alumina hydrogel-forming substance in the above-mentioned alumina production step, but an unnecessarily complicated method is used in combination with the following step b). Since it is not preferable to use it, it is sufficient to use the precipitation method by a simple neutralization operation. However, when the method of adding the alumina hydrogel-forming substance in a continuous flow or an intermittent flow while maintaining the alumina hydrogel in the alumina hydrogel precipitation region in step b) is used, in step a), the seed alumina hydrogel is When the precipitation method is used, it is necessary to adopt a method for producing it uniformly. Because in this way,
Since the effect of making the alumina hydrogel of non-uniform particles uniform is insufficient, the desired alumina cannot be obtained. Conventionally, the alumina hydrogel obtained from the step a) is supplied as it is or after being aged as a sol or a gel-like substance to the steps such as dehydration and drying. However, this method gives an alumina excellent in adsorption separation performance. Absent. In order to adjust alumina to the above properties,
Although it is necessary to adjust the basic particles, regarding the method of controlling the pore structure such as the pore size, pore volume and pore size distribution of the alumina, the present applicant has already disclosed in JP-A-56-1205.
It is disclosed in Japanese Patent Publication No. 08. That is, in a method for producing a porous inorganic oxide from a hydrogel-forming substance as a raw material, (1) a step of obtaining the seed hydrogel from the hydrogel-forming substance, and (2) a step of producing the hydrogel.
The pH is alternately changed between the hydrogel dissolution region and the hydrogel precipitation region, and when the pH is changed to at least one of the hydrogel dissolution region and the hydrogel precipitation region, a hydrogel forming substance is added to finally obtain a target size. A method for obtaining a hydrogel in which crystals have grown in a form suitable for By this method, it is possible to obtain a gel in which the basic particles are relatively aligned in the target size. Further, the present applicant discloses an alumina hydrogel having fibrous basic particles in JP-A-55-27830, and further, an alumina hydrogel composed of boehmite particles which are very uniform fibrous basic particles. The sol is disclosed in JP-A-58-213632. Further, the inventors of the present invention relate to a method for obtaining a crystal-grown alumina hydrogel by adding an alumina hydrogel-forming substance in a continuous flow or an intermittent flow while maintaining the alumina hydrogel in a boehmite gel precipitation region. No. 190823,
The technology is disclosed in Japanese Patent Application Laid-Open No. 59-97526 and Japanese Patent Application No. 60-54917. The inventors of the present invention have studied the preparation of porous alumina having properties suitable for the purpose of the present invention using such a technique, and found that the pH of the alumina hydrogel alternates between the alumina hydrogel dissolution region and the boehmite gel precipitation region. PH to at least one of the alumina hydrogel dissolution area and the boehmite gel precipitation area.
When changing, add an alumina hydrogel-forming substance,
A step of obtaining a crystal-grown alumina hydrogel and / or an alumina hydrogel-forming substance is added in a continuous flow or an intermittent flow while maintaining the alumina hydrogel in the boehmite gel precipitation region, and the crystal growth is performed to a size in which a desired specific property is obtained. It was found that the purpose can be achieved by including the step of obtaining the above-mentioned alumina hydrogel in the separating agent manufacturing step. That is, the pore volume of alumina obtained by such a process is 0.3 to 1.2 cc / g, especially 0.5 to 0.9 cc.
/ g range, average pore size 50-150 Å,
Especially when adjusted to the range of 100 to 130 angstroms, the surface area of the alumina becomes very large, and by supporting the basic compound on the alumina, an acidic gas adsorption separator having a very high capacity can be obtained. I found that. It is considered that this is because not only the pore structure of the alumina but also the chemical properties of the surface of the alumina play an important role in combination with the basic compound. In order to support the basic compound on the alumina, the solution containing the basic compound is sufficiently contacted with the alumina, and then the solvent is removed.

Next, the manufacturing process of the alumina will be described in detail.

[Alumina hydrogel-forming substance]

The alumina hydrogel-forming substance used in the production of this alumina is a compound containing aluminum as an element. For example, metallic aluminum (Al), aluminum chloride _{(AlCl 3, AlCl 3 · 6H} 2 O), aluminum nitrate [Al
_{(NO 3) 3 · 9H 2} O ], aluminum sulfate [Al ₂ (S
_{O 4) 3, Al 2 (} SO 4) 3 · 18H 2 O ], poly aluminum chloride {[Al ₂ (OH) nCl _6- n] m (1 <n <5, m <10)}, ammonium alum [ _{(NH 4) 2 SO 4 ·} Al (SO 4) 3 · 24
H ₂ O], sodium aluminate (NaAlO ₂ ), potassium aluminate (KAlO ₂ ), aluminum isopropoxide {Al [OCH
(CH ₃ ) ₂ ] ₃ }, aluminum ethoxide [Al (OC
₂ H _{5) 3],} aluminum · t-butoxide {Al [OC (C
H _{3) 3] 3},} and the like of aluminum hydroxide [Al _{(OH) 3].} Preferably, an aluminum salt, e.g., aluminum chloride _{(AlCl 3, AlCl 3 · 6H} 2 O), aluminum nitrate _{[Al (NO 3) 3 · 9H} 2 O ], aluminum sulfate [Al ₂ (S
O ₄ ) ₃ , Al ₂ (SO ₄ ) ₃ · 18H ₂ O], aluminates such as sodium aluminate (NaAlO ₂ ), and aluminum hydroxide [Al (OH) ₃ ].

[Production of Seed Alumina Hydrogel] [Step a)] The seed alumina hydrogel is formed using the above-mentioned alumina hydrogel-forming substance. The particles contained in the seed alumina hydrogel (alumina hydrogel particles) are used as seeds for adding the alumina hydrogel-forming substance to produce crystal-grown alumina hydrogel in the subsequent step [step b)] of obtaining crystal-grown alumina hydrogel. Therefore, in the alumina hydrogel,
Present in the form of hydroxide. This seed alumina hydrogel is generally manufactured according to a conventionally known method. That is, a common method such as a precipitation method, a uniform precipitation method, an ion exchange method, a hydrolysis method and a metal dissolution method can be adopted. In this case, the precipitation method is a method of neutralizing the alumina hydrogel-forming substance with an acidic or alkaline solution. For example, ammonia, sodium hydroxide or the like as a neutralizing agent is added as a solution to a solution of aluminum nitrate or aluminum sulfate, or hydrochloric acid, sulfuric acid or nitric acid is added as a neutralizing agent to a solution of an alkali metal salt or an ammonium salt. Neutralize and convert to aluminum hydroxide. Specifically, it includes a method by a neutralization reaction using a combination of a solution of aluminum nitrate and sodium aluminate and a solution of aluminum sulfate and sodium aluminate. The homogeneous precipitation method is the same as the above-mentioned precipitation method in principle, but is different in that the neutralizing agent concentration during neutralization is kept uniform and the precipitation is carried out uniformly. For example, when performing uniform precipitation from a solution containing an alumina hydrogel-forming substance in the form of an acid salt, an ammonia-releasing substance such as urea or hexamethylenetetramine is used as a neutralizing agent. Specifically, the required amount of urea is dissolved in a solution containing aluminum nitrate or aluminum sulfate, the mixed solution is gradually heated with stirring, the neutralizing agent is gradually decomposed to release ammonia, and this release is performed. The method includes gradually neutralizing an aluminum salt with ammonia to convert it into an alumina hydrogel. The ion exchange method is a method in which cations or anions coexisting in a solution of an alumina hydrogel-forming substance are ion-exchanged by using an ion exchange resin to form a gel on a colloid. What is called commercially available colloidal alumina is usually manufactured by these methods. The hydrolysis method is a method in which a hydrolyzable alumina hydrogel-forming substance is added to water to cause a hydrolysis reaction to generate an alumina hydrogel. Specifically, the reaction of an alcohol solution of aluminum isopropoxide is included. As a metal dissolution method, there is a method in which basic aluminum hydroxide is generated by adding aluminum metal powder to boiling aluminum nitrate or an aluminum nitrate solution.

As described above, the alumina hydrogel to be the seed can be obtained by various methods familiar to those skilled in the art.
That is, step a) is well known to those skilled in the art, and is not limited by the above-mentioned matters. The kind of hydrogel-forming substance used as a starting material, etc. should be considered in consideration of factors such as economic efficiency. It can be selected appropriately. In some cases, a commercially available alumina hydrogel can be used as it is, or can be prepared by combining the alumina hydrogel-forming substance used in obtaining the crystal-grown alumina hydrogel in step b) with a pH fluctuation or regulator. is there. In this case, there is an advantage that step a) and step b) can be performed in a continuous operation without a complicated operation such as a separation operation in the middle. That is, step a) and step b) can be performed using the same reagent under the same conditions. The concentration of the seed alumina hydrogel is not limited, but may be within a range that allows stirring as a whole and does not hinder the execution of step b), and is usually 10% by weight or less, particularly 0.1 to 5% by weight. %.

[Step of Obtaining Crystal-Grown Alumina Hydrogel] [Step b)] In this step, the seed alumina alumina hydrogel obtained in the step a) is subjected to pH fluctuation and / or control,
The step of adding an alumina hydrogel-forming substance and growing crystals of the alumina hydrogel is included. In this step, the alumina hydrogel basic particles can be grown very uniformly and controlled to a target size. In this step, the pH of the seed alumina hydrogel obtained in the step a) is alternately changed between the alumina hydrogel dissolution region and the boehmite gel precipitation region, and at least one of the alumina hydrogel dissolution region and the boehmite precipitation region. When the pH changes to the region of, the alumina hydrogel-forming substance is added to obtain a crystal-grown alumina hydrogel, and / or the alumina hydrogel-forming substance is kept in the boehmite gel precipitation region to form a continuous flow or an intermittent flow. Added
Obtaining a crystal-grown alumina hydrogel is performed. In the case of operation under pH fluctuation, as one of preferred methods of implementation, only when changing to the boehmite gel precipitation region, the above-mentioned alumina hydrogel-forming substance or pH adjusting agent is added alone or in the form of a mixture, and boehmite gel is added. Get a precipitate. In this case, the alumina hydrogel means not only boehmite but also general alumina hydrogel such as bayerite and amorphous alumina hydrogel. Further, boehmite gel is composed of fine boehmite crystallites having a fibrous shape among alumina hydrogels, and when the crystallites aggregate, they form remarkably aggregates as compared with other alumina hydrogels. Therefore, the alumina obtained by drying and calcining this has a remarkably high surface area and a metal species supporting ability. In the case of operation while maintaining the pH, one of the preferred methods is to obtain a boehmite gel precipitate by using one in which at least one of the alumina hydrogel-forming substance and the pH adjusting agent substantially contains a sulfate group. is there. As used herein, the alumina hydrogel dissolution region refers to a pH of 5 or less or 11 or more, and the boehmite gel precipitation region refers to a pH of 6 to 11. That is, the alumina hydrogel dissolution region is a pH region where the alumina hydrogel fine particles can be solubilized, and the boehmite gel precipitation region is a pH region under the condition where the growth of boehmite microcrystallites can be caused. Therefore, the crystal growth operation of alumina hydrogel under pH fluctuation and the crystal growth operation of alumina hydrogel under pH maintenance are completely different in principle, and conceptually, there is a completely opposite part. That is,
When the pH is changed, in order to change the pH more effectively, the presence of polyvalent ions and a high concentration of dissolved salt are likely to act as an inhibitor. However, it is believed that the presence of dissolved salts has a buffering effect and the presence of multiply charged ions has a positive effect on catalyzing crystal growth in order to maintain the pH within a certain range.

Under pH fluctuation, in the boehmite gel precipitation region, the fine alumina hydrogel particles dissolved in the alumina hydrogel dissolution region and the alumina hydrogel-forming substance added at the time of pH fluctuation are rapidly occluded in large hydrogel particles, that is, boehmite microcrystallites. , The crystals grow to a larger alumina hydrogel, while the mixed fine alumina hydrogel particles are dissolved in the alumina hydrogel dissolution region, and the remaining particles of the alumina hydrogel are homogenized. On the other hand, under the condition that the pH is maintained, the uniform seed alumina hydrogel is subjected to the conditions controlled in the boehmite gel precipitation region, that is, the alumina hydrogel is uniformly occluded in the hydrogel particles. The homogenization of the particles of the crystal-grown alumina hydrogel produced by adding the forming substance is realized. That is, in step b), the pH of the hydrogel with respect to the seed alumina hydrogel.
By carrying out the addition or the adjustment of the alumina hydrogel-forming substance while maintaining the pH, a precipitation of the alumina hydrogel particles having a uniform particle size is obtained. In short, when the particles of alumina hydrogel are non-uniform, it is possible to repeatedly and alternately fluctuate the reaction system between dissolution conditions and growth conditions by utilizing the property that the particles are more likely to be dissolved and grow easily. , Or when the alumina hydrogel particles are uniform, it is difficult to generate secondary nuclei, and the conditions under which the particle growth is uniform, that is, the alumina hydrogel-forming substance is maintained while maintaining the pH at a preferable addition rate. By introducing into the system, a uniformly grown alumina hydrogel of seed alumina hydrogel is obtained. The change to the dissolution area of the alumina hydrogel or the precipitation area of the boehmite gel, or the retention thereof is performed using a pH adjusting agent. As the pH adjuster, an alumina hydrogel-forming substance itself or a non-alumina hydrogel-forming substance may be used. However, in the case of fluctuation or retention in at least one region, the pH adjusting agent used is preferably the alumina hydrogel-forming substance itself. More preferably,
Under the pH fluctuation, the alumina hydrogel-forming substance is used as the pH adjusting agent only when the pH changes to the boehmite gel precipitation region, and in the operation while maintaining the pH, at least one of the alumina hydrogel forming substance and the pH adjusting agent is substantially It is to contain sulfate. That is, since most of the alumina hydrogel-forming substances show acidity or alkalinity in a state of being dissolved in water, they can be used as a pH adjusting agent. For example, those exhibiting acidity include aluminum chloride, aluminum nitrate, aluminum sulfate, etc., those exhibiting alkalinity include sodium aluminate, etc., and those containing sulfate include aluminum sulfate, Is also one of those exhibiting acidity. Examples of the pH adjusting agent composed of a non-alumina hydrogel-forming substance include acids such as hydrochloric acid, nitric acid and sulfuric acid, alkalis such as sodium hydroxide and aqueous ammonia, and sulfuric acid containing a sulfate group.

[Conversion of Alumina Hydrogel to Alumina] [Step c)] The crystal-grown alumina hydrogel is made into an alumina xerogel by a combined operation of washing and drying, followed by firing.
A porous alumina molded body having a desired shape and characteristics is obtained. To remove coexisting unwanted ions or impurities,
A washing operation is performed according to the state of the alumina hydrogel and / or the state of the alumina xerogel. Conversion from alumina hydrogel to alumina xerogel can be carried out by drying, and this drying method is generally carried out at a temperature of room temperature or higher and 200 ° C. or lower under conditions such that water in the alumina hydrogel is sufficiently evaporated. Firing is generally 300-1
200 ℃, preferably 400 ~ 800 ℃ γ-alumina is formed
Performed at the temperature of. In this step, the alumina molded body is molded in the state of alumina hydrogel or xerogel, or rarely in the state of a fired product.
The method may be a gel molding method by adjusting the humidity of alumina hydrogel or a molding method using alumina xerogel powder and a binder. Further, the step is a step of converting alumina hydrogel into alumina, and a conventionally known method can be adopted. The porous alumina molded body thus obtained is advantageously used as a raw material for the separating agent of the present invention, and particularly by adopting the step b), an alumina molded body having desired physical properties and chemical characteristics. Can be formed.

The separating agent of the present invention can be obtained by supporting and complexing a basic compound of an alkali metal or an alkaline earth metal on the alumina molded body obtained as described above.

The separating agent of the present invention has the property of adsorbing acidic gases such as carbon dioxide, hydrogen sulfide, hydrogen chloride, etc. with good selectivity,
Further, it has a property of desorbing the adsorbed acidic gas by heating or holding the separating agent adsorbing the acidic gas under reduced pressure. Therefore, by applying the separating agent of the present invention to a gas containing an acidic gas, for example, a synthesis gas,
The carbon dioxide gas contained in it can be selectively separated and recovered.

When the acidic gas contained in the gaseous substance is separated and recovered using the separating agent of the present invention, any of the temperature fluctuation method and the pressure fluctuation method can be adopted. When used in the temperature fluctuation method, it is preferable that the acid-containing gas and the separating agent of the present invention are contacted at a temperature as low as possible.
In order to desorb the adsorbed acidic gas from the separating agent, the temperature is higher than the adsorption treatment temperature. The larger the temperature difference, the larger the desorption amount of the adsorbed gas. Therefore, the temperature difference may be selected according to the desired recovery amount. adsorption·
The desorption treatment temperature can also be appropriately selected. Generally, adsorption treatment is performed at a temperature of 5 to 100 ° C, and desorption treatment is performed at a temperature of 90 to 150 ° C.

Further, in the pressure fluctuation method, adsorption and desorption are performed by treating an acidic gas-containing gas with the adsorbent of the present invention with a pressure difference. Adsorption is performed on the high pressure side of pressure fluctuation, and desorption is performed on the low pressure side. After pressurizing and adsorbing, desorption may be performed by returning to normal pressure, or desorption may be performed after adsorbing at normal pressure and depressurizing. In this case, the pressure difference is selected according to the amount of acid gas recovered. The recovery amount increases as the pressure difference increases. Further, the temperature fluctuation method and the pressure fluctuation method can be combined.

〔effect〕

The separating agent of the present invention exhibits a high selective adsorption property to an acidic gas, and can be applied to a method for separating an acidic gas from a mixed gas and a separation recovery. For example, by applying a separating agent of the present invention, only the CO ₂ efficiently separated and recovered from the mixed gas, it is possible to produce high-purity CO ₂ gas and CO ₂ from a gas containing CO ₂ as an impurity Can be separated and removed to obtain a high-purity gas from which CO ₂ has been removed.

Further, the separating agent of the present invention is in a solid state, and when regenerating the separating agent having adsorbed the acidic gas, not only the heating method but also the method of varying the pressure can be adopted. Therefore, when the separating agent of the present invention is used, the acidic gas can be separated and collected and separated and removed with a simple operation and at a power cost.

〔Example〕

 Next, the present invention will be described in more detail with reference to Examples.

The pore size distribution shown below was determined by the so-called mercury porosimetry method using Mercury, Pressure, and Porosimeter Model 70 (manufactured by Carlo Erba Co., Milan, Italy). The surface tension of mercury is 474 dyn at 25 ℃.
e / cm, contact angle 140 °, absolute mercury pressure 1-200
The measurement was performed while changing the pressure to 0 kg / cm ² .

Example 1 1.27 g of sodium carbonate (manufactured by Wako Pure Chemical Industries, Ltd., special grade reagent)
Was placed in a 200 cc 2-neck eggplant flask and dissolved in 20 cc of water at room temperature. An alumina A carrier (manufactured by Catalysts and Chemicals Co., Ltd., average pore size 110
Å, BET surface area 230m ² / g) 10g was added and left for 30 minutes.
Then, it was completely dried in a dry bath at 120 ° C to obtain a white adsorbing and separating agent.

A mixed gas (CO ₂ , N ₂ , binary system) at 1 atm was repeatedly aerated through this adsorption / separation agent, and the CO ₂ adsorption amount was measured. The adsorption amount was measured by the low pressure volume method. The adsorption conditions are room temperature,
The pressure is 1 atm and the flow rate is 3.4 for approximately 11 g of adsorbent separating agent.
/ min, the adsorption time was 5 minutes.

After completion of the adsorption, the flask was put into an oil bath, heated to 90 ° C. and blown with nitrogen to desorb the adsorbed gas.
Then, it cooled to room temperature, sprayed the mixed gas again, and measured the adsorption amount. The above operation was repeated until the adsorption amount became constant.

The above operation was repeated several times considering the CO ₂ / N ₂ ratio of the mixed gas (composition was analyzed by gas chromatography). The adsorption values at which the partial pressure of CO ₂ became steady are shown in the following table.

Furthermore, a mixed gas having a composition of 46% CO _{2 and} 54% N ₂ was passed through the adsorption / separation agent at room temperature for 5 minutes at a flow rate of 3.4 / min to sufficiently adsorb it. Next, the inside of the system was pulled to 100 torr with a vacuum pump, and left in this state for 5 minutes. After returning the system to normal pressure at room temperature, the mixed gas was ventilated again. The adsorption amount was 38 ml. After this, the system was kept at 100 torr again, the exhaust gas of the vacuum pump was collected in its entirety, and analyzed by gas chromatography. It was found that 40 ml of CO ₂ had been desorbed. As described above, in the case of the adsorption separating agent of the present invention, the
It was confirmed that CO ₂ could be separated by adsorption.

Example 2 A CO mixed gas of 1 atm (CO partial pressure: 0.8 atm, N ₂ partial pressure: 0.2 atm) was repeatedly bubbled through the adsorption separation agent prepared in Example 1,
The amount of adsorption was measured by the same method as in Example 1. Adsorption amount is 4cc
It was confirmed that this adsorbent / separator hardly adsorbs CO.

Example 3 A mixture of 70 wt% of magnesia powder and 30 wt% of silica was extruded to obtain a molded body. This molded body was calcined at 550 ° C. for 3 hours to obtain an adsorption separator (BET surface area 223 m ² / g). Using this adsorption / separation agent, the CO ₂ adsorption amount was measured in the same manner as in Example 1 as follows.

10 g of the above-described adsorption separator was placed in a 200 ml two-necked eggplant flask and incorporated into a constant pressure volumetric adsorption measuring apparatus. Next, when 1 atmosphere of CO ₂ mixed gas (CO ₂ / N ₂ volume ratio = 30/70) was sufficiently contacted at room temperature, 46 ml of CO ₂ was adsorbed. Next, when the adsorption / separation agent was heated to 90 ° C., N ₂ was blown to remove CO _2, and then the above-mentioned mixed gas was ventilated again, the CO ₂ adsorption amount was 4
It did not change to 4 ml.

Example 4 A 11.6 wt% sulfuric acid aqueous solution 0.15 and deionized water 10 were placed in a enamel jar and heated to 90 ° C., then with vigorous stirring, an Al ₂ O ₃ concentration 69 g / sodium aluminate aqueous solution 0.39 was added.
When was charged instantly, a slurry-like aluminum hydroxide aqueous solution having a pH of 10 was obtained. Using this as seed aluminum hydroxide, stirring was continued, and after 10 minutes, 0.15 of the sulfuric acid aqueous solution was added as the first step operation, and the pH was 3.
5 was shown. Keep stirring this solution at 90 ℃ and continue stirring.
After the addition of 0.3 of the aqueous sodium aluminate solution after the minute, a pH of 10 was exhibited. This operation of alternately adding sulfuric acid and sodium aluminate after a fixed period of time was repeated 8 steps. After that, the slurry was filtered, redispersed in deionized water 10 and filtered and washed three times to obtain a cake. This cake was taken out and molded into 1.6 mmφ by extrusion molding, and the extruded product was dried at 120 ° C. for 6 hours and then calcined at 500 ° C. for 3 hours to obtain alumina B. The properties of this alumina are shown in Table 2.

Table-2 Average pore diameter [Å]: 119 Pore volume [cm ³ / g]: 0.713 Surface area [m ² / g]: 240 Next, in a 200 ml 2-neck eggplant flask, a commercially available sodium hydroxide special grade reagent (Wako Pure Chemical Industries, Ltd. 0.96 g (24 mmol) manufactured by Kogyo Co., Ltd. was added, and 20 ml of water was added and dissolved. To this solution, 10 g of the alumina carrier A dried at 120 ° C. for 2 hours was added, and immersed at room temperature for 30 minutes. Then, the eggplant flask was depressurized with an aspirator and simultaneously heated to 70 ° C., and water was sufficiently exhausted to obtain a white adsorption separation agent.

Next, a gas mixture (composition CO ₂ 5
0%, N ₂ 50%) was repeatedly aerated at room temperature, and the adsorption amount was measured by the constant pressure volume method. The CO ₂ adsorption amount was 4.5 mmol. After completion of the adsorption, the eggplant flask was put in an oil bath and heated to 90 ° C., and nitrogen gas was blown to desorb the adsorbed gas. Then, the mixture was cooled, and the mixed gas was repeatedly contacted again. The amount of CO ₂ adsorbed was 4.5 mol and remained unchanged. After completion of adsorption, the system was pulled to 100 torr with a vacuum pump and kept for 10 minutes. Then, the inside of the system was returned to 1 atm with nitrogen gas, and the above mixed gas was ventilated again. And CO ₂ adsorption of 1.9 mmol, was confirmed to be capable of adsorption separation of CO ₂ by the pressure fluctuation method. Also, after heating this adsorption / separation agent to 90 ° C and degassing CO ₂ by blowing nitrogen gas, a separately prepared mixed gas (composition CO 80%, N ₂ 20%) was aerated at room temperature. ,
Almost no gas adsorption was observed.
Was confirmed not to be adsorbed.

Example 5 Al ₂ O ₃ concentration of 80 g / aluminum sulfate aqueous solution 0.05 and deionized water 10 were placed in a enamel jar and heated to 90 ° C., and while vigorous stirring 350 ml of Al ₂ O ₃ concentration of 69 g / sodium aluminate aqueous solution. When was charged instantly, it became cloudy and a slurry-like aluminum hydroxide aqueous solution having a pH of 10 was obtained. This was used as seed aluminum hydroxide, to which was added an aluminum sulfate aqueous solution with an Al ₂ O ₃ concentration of 8 g / 0.2.
r, Al ₂ O ₃ concentration 69 g / sodium aluminate aqueous solution 0.20
It was added using a constant rate injector at a rate of / hr. The temperature was 90 ° C. and the pH was 9 to 10 for 6 hours after the addition operation was continued.
Also, 3 hours after the start of injection, 0.3 sample liquid was collected, filtered, redispersed in deionized water 2, and washing by the operation of filtering was repeated 3 times to obtain a cake. This cake showed pseudo-boehmite on X-ray diffraction. The cake solid content concentration was about 25%, and the mixture was molded into a column shape by an extrusion molding machine having a die having a hole of 1.6 mmφ and dried at a temperature of 120 ° C. for 6 hours. Then put it in the electric path and blow air,
It was baked at 500 ° C. for 3 hours. The properties of the obtained alumina C are shown in Table 3.

Table-3 Average pore diameter [Å]: 108 Pore volume [cm ³ / g]: 0.722 Surface area [m ² / g]: 266m ² / g Then, a sodium hydroxide aqueous solution was added in the same manner as in Example 4. 10 g of the above alumina carrier B prepared and dried at 120 ° C. for 2 hours was added thereto. After soaking at room temperature for 30 minutes, 70 ℃
The mixture was heated to 0 ° C., decompressed in an eggplant-shaped flask with an aspirator and evacuated for 8 hours to sufficiently remove water to obtain a white adsorptive separating agent.

The CO ₂ adsorption capacity of this adsorption / separation agent was measured by the constant pressure volume method as in Example 4. That is, mixed gas of 1 atm (composition CO ₂ 50
%, N ₂ 50%) was repeatedly sprayed on the adsorption / separation agent at room temperature to adsorb 4.6 mmol of CO ₂ . After completion of the adsorption, the eggplant flask was placed in an oil bath, heated to 90 ° C. and blown with nitrogen gas to desorb adsorbed CO ₂ . After cooling to room temperature and ventilating the mixed gas again, CO ₂
The adsorption amount was 4.7 mol.

Example 6 2.28 Normal hydrochloric acid solution 0.13 and deionized water 10 were placed in a enamel jar and heated to 90 ° C., and then vigorously stirred with an Al ₂ O ₃ concentration of 69 g / sodium aluminate aqueous solution 0.28
Was added instantaneously and, after stirring for 15 minutes, this was used as an aqueous solution of seed aluminum hydroxide, and 0.13 of the above-mentioned hydrochloric acid solution was added as a first step operation. When the temperature was kept at 90 ° C. and stirring was continued, 5 minutes later, 0.35 of the aqueous sodium aluminate solution was added, and the pH became 9. The operation of alternately adding hydrochloric acid and sodium aluminate at a fixed time was continued in the second and subsequent steps, and after the 10th step was completed, the mixture was held for 15 minutes to obtain alumina D in the same manner as in Example 4. It was The properties of this alumina D are shown in Table 4.

Table-4 Average pore diameter [Å]: 114 Pore volume [cm ³ / g]: 0.650 Surface area [m ² / g]: 228 Next, an adsorption separation agent was obtained by the same operation as in Example 4,
When the CO ₂ adsorption capacity was examined, the adsorption amount was 4.5 mmol.
The adsorptive separating agent playing at 90 ° C. cooled to room temperature, CO ₂
When the adsorption amount was measured again, the adsorption amount was 4.5 mol, which was unchanged.

Example 7 0.244 Al ₂ O ₃ aqueous solution of aluminum sulfate and 10 of deionized water were placed in a enamel jar and heated to 90 ° C., and then vigorously stirred and aqueous solution of sodium aluminate with Al ₂ O ₃ concentration of 69 g / 69 g. 1.55 was charged instantaneously to obtain a slurry white liquid having a pH of 10. This was kept at 90 ° C for 6 hours. At that point the solution had a pH of 10. The liquor was filtered and washed with deionized water to remove most of the Na ⁺ and SO ₄ ²⁻ ions. The obtained filter cake is extruded using a molding machine 1.
Molded into 6mmφ and dried at 120 ° C for 6 hours, then at 500 ° C for 3 hours
Alumina compact E was obtained by firing for a time. The physical properties of this molded product E were as follows.

Table-5 Surface area [m ² / g]: 159 Pore volume [cc / g]: 0.31 Average pore size [Å]: 78 Using this alumina molded product E10g, the adsorption separator was prepared by the method of Example 4. Prepared. When the amount of CO ₂ adsorbed from the mixed gas (CO ₂ 50%, N ₂ 50%) was measured by the same operation as in Example 14, it was 3.0 mmol at room temperature. The adsorptive capacity of the adsorptive separating agent in this case was smaller than that of Example 4, but this is considered to be due to the difference in the production of the alumina used.

Example 8 A mixed gas of 1 atm (HCl 10 v was added to the adsorbent obtained in Example 1).
ol%, N ₂ 90 vol%) was repeatedly aerated, and the adsorption amount of hydrogen chloride was measured. The adsorption amount was measured by the constant pressure capacity method.
The adsorption conditions are room temperature and atmospheric pressure, and the gas flow rate is about 11 for the adsorbent and separation agent.
The adsorption time was 5 minutes at 3.4 / min against g. The adsorption amount was 96 cc (0.38 mmol / g). After completion of the adsorption, the flask was placed in an oil bath, heated to 90 ° C., and nitrogen was blown to desorb the adsorbed gas. Then, the mixture was cooled to room temperature, the mixed gas was blown again, and the amount of adsorption was measured.
This operation was repeated until the adsorption amount became constant. The adsorption amount became stable at 85 cc (0.34 mmol / g).

Next, after thoroughly admixing the mixed gas with this adsorbent, the system was drawn to 100 torr with a vacuum pump and left in this state for 5 minutes. After returning to normal pressure with nitrogen at room temperature, the above mixed gas was ventilated again. The adsorption amount was 57 cc (0.23 mmol / g).
Again pull the system to 1000 torr with a vacuum pump, and in this state 5
After holding for 1 minute and returning to normal pressure with nitrogen, the above mixed gas was aerated. The adsorption amount was 55 cc (0.22 mmol / g), and it was confirmed that hydrogen chloride was adsorbed and desorbed by the pressure fluctuation method.

Claims (3)

[Claims] 1. A gas containing an acidic gas is brought into contact with a complex of at least one selected from a basic alkali metal compound and a basic alkaline earth metal compound and a non-zeolitic porous oxide, After adsorbing the acidic gas, the complex is retained under a pressure lower or at a temperature higher than that during the adsorption to desorb the acidic gas adsorbed to the complex. Acid gas adsorption separation method. 2. An acidic gas adsorption separator comprising a complex of at least one selected from a basic alkali metal compound and a basic alkaline earth metal compound and a non-zeolitic porous oxide. 3. The non-zeolitic oxide comprises: a) a step of obtaining an alumina hydrogel from an alumina hydrogel-forming substance; b) alternating pH of the alumina hydrogel between an alumina hydrogel dissolution region and a boehmite gel precipitation region. A step of adding an alumina hydrogel-forming substance to obtain a crystal-grown alumina hydrogel when the pH changes to at least one of the alumina hydrogel dissolution area and the boehmite gel precipitation area, and / or holding the alumina hydrogel in the boehmite gel precipitation area While adding an alumina hydrogel-forming substance in a continuous flow or an intermittent flow to obtain a crystal-grown alumina hydrogel, c) a step of obtaining the alumina gel or alumina by a combined operation of washing and drying or firing the crystal-grown alumina hydrogel , of Acid gas adsorption separation agent range of the second term of the claims is alumina formed by mating.