JP2006263612A - Absorbent material of carbonic acid gas and method for treating gas containing carbonic acid gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a absorbent material of a carbonic acid gas showing high absorption performance of carbonic acid gas even after repeating absorption of carbonic acid gas and regeneration after a reduction in adsorption capability of a carbonic acid gas for a long period of time. <P>SOLUTION: The carbonic acid gas absorbent material comprises a porous particulate material having a through-hole and containing lithium silicate as a main component, wherein a wall thickness between an inner surface of the through-hole and an exterior surface is not larger than 3 mm in a cross section vertically crossing the through-hole. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention separates and recovers carbon dioxide in a gas (treated gas) generated from an energy plant, chemical plant, automobile, etc. that uses a fuel whose main component is hydrocarbon, or separates and recovers carbon dioxide in a fuel supply unit. The present invention relates to a carbon dioxide absorber and a method for treating a gas to be treated containing carbon dioxide.

  In an apparatus such as an engine that burns fuel mainly composed of hydrocarbons, the temperature of an exhaust gas discharge portion, which is a place suitable for the recovery of carbon dioxide gas, often reaches a high temperature of 300 ° C. or higher. Conventionally known methods for separating carbon dioxide include a method using cellulose acetate, a chemical absorption method using an alkanolamine solvent, and the like. However, any of these separation methods needs to suppress the introduced gas temperature to 200 ° C. or lower. Therefore, in order to separate the carbon dioxide in the exhaust gas that is required to be recycled at a high temperature, it is necessary to cool the exhaust gas to 200 ° C. or less once with a heat exchanger or the like. There was a problem that the amount of energy consumption increased.

  In Patent Document 1 and Patent Document 2, a carbon dioxide gas separation method using a lithium composite oxide that reacts with carbon dioxide therein without undergoing a cooling step from a high temperature gas containing carbon dioxide in a temperature range exceeding 500 ° C. It is disclosed. These lithium composite oxides react with carbon dioxide gas and decompose into oxides and lithium carbonate, thereby absorbing carbon dioxide. In addition, the oxide and lithium carbonate generated by the reaction between the lithium composite oxide and carbon dioxide gas can be regenerated as a lithium composite oxide because a reverse reaction occurs at a higher temperature. Patent Document 2 discloses that lithium silicate using silicon dioxide as an oxide can be synthesized in a lighter weight than other lithium composite oxides and has an advantage of high absorption rate. Carbon dioxide of lithium silicate is disclosed. The use as an absorbent material has attracted attention.

On the other hand, Patent Document 3 discloses a columnar and honeycomb-shaped carbon dioxide absorbent, and Patent Document 4 discloses an assembled block-shaped carbon dioxide absorbent. Among these carbon dioxide gas absorbents, cylindrical ones are desired from the viewpoint of handling. However, if cylindrical lithium silicate is used as a carbon dioxide absorbent, and the carbon dioxide absorption and release reactions (regeneration reactions) are repeated over a long period of time, the carbon dioxide absorption performance will gradually decrease and the high carbon dioxide absorption performance There was a problem that it was difficult to maintain.
JP-A-9-99214 JP 2000-262890 A JP 11-262632 A JP 2001-232148 A

As described above, in the conventional carbon dioxide absorbent, if the carbon dioxide absorption and release reactions are repeated over a long period of time, the amount of carbon dioxide absorbed gradually decreases, making it difficult to maintain high carbon dioxide absorption performance. There was a problem.
An object of the present invention is to provide a carbon dioxide absorbing material that can obtain high carbon dioxide absorbing performance even when carbon dioxide absorption and regeneration after a decrease in absorption capacity are repeated over a long period of time.

  In the present invention, when carbon dioxide in the gas to be treated is repeatedly removed by carbon dioxide absorption by the carbon dioxide absorbent and regeneration of the carbon dioxide absorbent, the regeneration of the carbon dioxide absorbent is repeated for a long period of time. Another object of the present invention is to provide a method for treating a gas to be treated containing carbon dioxide that can efficiently absorb carbon dioxide.

  According to the present invention, a granular porous body having lithium silicate as a main component and having a through hole, the thickness between the through hole and the outer surface in a cross section perpendicularly crossing the through hole is 3 mm or less. A carbon dioxide absorbent characterized by the above is provided.

  Further, according to the present invention, there is provided a carbon dioxide gas absorbent characterized by being a rectangular flat plate-shaped porous body mainly composed of lithium silicate and having a thickness of 3 mm or less.

Further, according to the present invention, the porous porous body is mainly composed of lithium silicate and has a through hole, and the thickness between the through hole and the outer surface is 3 mm or less in a cross section perpendicularly crossing the through hole. A step of contacting a gas to be treated containing carbon dioxide with a carbon dioxide absorbent to absorb the carbon dioxide;
Treating the treated gas containing carbon dioxide, comprising: heating the carbon dioxide absorbent after absorbing the carbon dioxide, releasing the absorbed carbon dioxide, and regenerating the carbon dioxide absorbent A method is provided.

  ADVANTAGE OF THE INVENTION According to this invention, even if it repeats carbon dioxide absorption and reproduction | regeneration over a long period of time, the carbon dioxide absorption material which can suppress absorption performance fall and can maintain high carbon dioxide absorption performance can be provided. .

  Further, according to the present invention, when carbon dioxide in the gas to be treated is repeatedly removed by carbon dioxide absorption by the carbon dioxide absorbent and regeneration of the carbon dioxide absorbent, the regeneration of the carbon dioxide absorbent is repeated over a long period of time. In addition, it is possible to provide a method for treating a gas to be treated containing carbon dioxide that can efficiently absorb carbon dioxide even after.

  Hereinafter, the processing method of the to-be-processed gas containing the carbon dioxide absorber and carbon dioxide which concerns on this invention is demonstrated in detail.

(First embodiment)
The carbon dioxide absorbent according to the first embodiment is a granular porous body mainly composed of lithium silicate and having a through hole, and the gap between the through hole and the outer surface is perpendicular to the through hole. The wall thickness is 3 mm or less.

Here, the “through hole” means one that substantially passes through the center of the granular porous body. However, the through-hole is allowed to pass slightly off from the center of the granular porous body.
The “cross section perpendicularly crossing the through hole of the porous body” means a cross section having the largest area among the cross sections. In other words, in a form in which the granular porous body is a cylinder or a prism and has a through hole in the axial direction, the cross section perpendicularly crossing the through hole has the same area at any location. On the other hand, in a form in which the porous body is a sphere or an ellipsoid and has a through-hole passing through the center point, the cross-section perpendicularly crossing the through-hole at the center point has the largest area, and the through-hole separated from the center point As the cross section crosses perpendicularly, the area becomes smaller. That is, the area of the cross section perpendicularly crossing the through hole varies depending on the position of the through hole, and the thickness between the through hole and the outer surface also varies. In such spheres and ellipsoids, the thickness is determined by the cross section perpendicular to the through-hole and having the largest area (the cross section where the thickness is the largest).
The “thickness between the through hole and the outer surface in the cross section” is defined as the thickest portion in the cross section between the through hole (outer peripheral surface) and the outer surface (distance). That is, for example, in the form in which the through hole is formed in the axial direction in a porous body such as a cylindrical body, when the through hole and the outer surface (distance) are different due to some uneven distribution of the through hole, the shape of the through hole, etc. The point of the largest distance is defined as the wall thickness.
The lithium silicate is preferably lithium orthosilicate (Li ₄ SiO ₄ ). The reaction in which lithium orthosilicate absorbs carbon dioxide is shown in the following formula (1), and the regenerating reaction is shown in the following formula (2).

Absorption: Li ₄ SiO ₄ + CO ₂ → Li ₂ SiO ₃ + Li ₂ CO ₃ (1)
Regeneration: Li ₂ SiO ₃ + Li ₂ CO ₃ → Li ₄ SiO ₄ + CO ₂ (2)
That is, when lithium orthosilicate comes into contact with carbon dioxide in a temperature range (first temperature range) of, for example, room temperature to about 700 ° C., it reacts according to the above formula (1), absorbs the carbon dioxide and absorbs lithium metasilicate (Li ₂ SiO _{2 3} ) and lithium carbonate (Li ₂ CO ₃ ). When the carbon dioxide absorbing material that has absorbed carbon dioxide is heated to a temperature range (second temperature range) of 720 ° C. or higher that exceeds the first temperature range, the carbon dioxide absorbent reacts according to the formula (2), Released and regenerated to the original lithium orthosilicate. Such carbon dioxide absorption of the carbon dioxide absorbent and regeneration reaction to the carbon dioxide absorbent can be repeated. The absorption temperature range of carbon dioxide gas varies depending on the carbon dioxide concentration in the reaction atmosphere, and the upper limit temperature of the absorption temperature region increases as the carbon dioxide concentration increases. Since the melting point of lithium carbonate produced by the carbon dioxide absorption reaction is around 720 ° C., when the carbon dioxide absorbent is heated at a temperature of 720 ° C. or higher to release carbon dioxide, the lithium carbonate is in a molten state. .

  In the carbon dioxide absorbent comprising a granular porous body containing lithium silicate as a main component, the carbon dioxide absorption performance is gradually lowered when the carbon dioxide absorption and release reactions are repeated many times. As a result of intensive studies on the decrease in carbon dioxide absorption performance of the carbon dioxide absorbent by the present inventors, lithium carbonate is accumulated in the central portion of the absorbent where the absorption performance has been reduced. It became clear that. The accumulation of lithium carbonate inside the absorbent is thought to be due to the following reasons. In the carbon dioxide absorbent, grain growth occurs every time carbon dioxide is absorbed and released, and the pores of the carbon dioxide absorbent comprising a granular porous body gradually decrease. When the pores are reduced, the probability of filling the pores with molten lithium carbonate generated when carbon dioxide is absorbed increases, and the gas path is reduced. Since the regeneration reaction (carbon dioxide gas release reaction) occurs sequentially from the outer surface of the absorbent toward the center, the regenerative reaction is less likely to occur as the distance from the outer surface is reduced due to the reduction of the gas path. It is thought that lithium carbonate accumulates. In fact, it was confirmed that lithium carbonate was accumulated in the interior of more than 3 mm from the outer surface in the carbon dioxide absorbing material having reduced absorption performance.

  Accumulation of lithium carbonate in the carbon dioxide absorbing material means that the regeneration reaction represented by the above-described formula (2) is not completed. For this reason, the amount of lithium orthosilicate that reacts with carbon dioxide decreases, and as a result, the amount of carbon dioxide absorbed decreases. Further, in the state where molten lithium carbonate is present, the reaction between the lithium orthosilicate represented by the above-described formula (1) and the carbon dioxide gas is inhibited, so that the carbon dioxide absorption reaction is further difficult to occur. Therefore, by preventing lithium carbonate from remaining and accumulating inside the carbon dioxide absorber during the regeneration reaction, stable and high carbon dioxide absorption performance even if carbon dioxide absorption / regeneration is repeated over a long period of time. We found the knowledge that can be obtained.

Based on such knowledge, as described above, there is a through hole, and in the cross section perpendicularly crossing the through hole, a granular material mainly composed of lithium silicate having a thickness between the through hole and the outer surface of 3 mm or less is used. By constituting the carbon dioxide absorbent from the porous body, almost all the absorbent is released as shown in the above formula (2) without the lithium carbonate remaining and accumulated in the absorbent during the regeneration. Can be converted to lithium silicate. As a result, even if carbon dioxide absorption / regeneration is repeated over a long period of time, stable and high carbon dioxide absorption performance can be achieved.
When the wall thickness between the through hole and the outer surface exceeds 3 mm in a cross section perpendicularly crossing the through hole of the porous body, after absorbing and releasing (regenerating) carbon dioxide gas, the above-described formula (1) is formed inside the absorbent material. It becomes difficult to maintain high carbon dioxide gas absorption performance when the lithium carbonate shown accumulates and is repeatedly absorbed and regenerated over a long period of time.
The size of the through hole is not particularly limited, but the diameter is preferably 0.5 mm or more. When the diameter of the through hole is less than 0.5 mm, the through hole is blocked by molten lithium carbonate generated when carbon dioxide is absorbed, making it difficult to efficiently perform the carbon dioxide gas release reaction during regeneration.
The granular porous body having the through-hole is, for example, a cylinder having a polygonal through-hole such as a circle or a quadrangle, a polygonal cylinder such as a quadrangular cylinder or a hexagonal cylinder, or a sphere or an ellipsoid. Can be mentioned. This through-hole is formed so as to pass along the center point of the column body along the axial direction, and is formed through the center point of a sphere or ellipsoid.
As a specific form, a cylindrical porous body 2 in which the cylindrical through-hole 1 shown in FIG. 1A is formed so that the center point is along the axial direction, that is, a cylindrical porous body is given. It is done. The cylindrical porous body 2 having the circular through-hole 1 has a diameter L of the cylindrical porous body 2 and a diameter of the through-hole 1 in a cross section perpendicular to the through-hole 1 (FIG. 1B). Is L1, and the thickness between the through hole 1 and the outer peripheral surface is L2 and L3, L2 and L3 (both are equal) are 3 mm or less. The particularly preferable thickness is not less than L / 4 mm and not more than 3 mm.

The outer diameter of the cylindrical porous body 2 shown in FIG. 1 is preferably 3 to 10 mm in diameter L and 3 to 10 mm in height H. If the diameter of the porous body 2 is less than 3 mm, when the gas to be treated containing carbon dioxide gas is circulated through the filling portion of the absorbent material, the pressure loss increases and the energy efficiency may be reduced. On the other hand, when the diameter of the porous body 2 exceeds 10 mm, the absorbent material portion that reacts with carbon dioxide gas is limited, and there are portions that do not react with carbon dioxide gas, making it difficult to effectively absorb carbon dioxide gas with the absorbent material. . The through hole 1 of the porous body 2 preferably has a diameter L1 of 0.5 mm or more.
Another specific form is a spherical porous body 3 in which the cylindrical through-hole 1 shown in FIG. 2A is formed through the center point. The spherical porous body 3 having the circular through-hole 1 has a diameter L of the spherical porous body 3 in the cross section perpendicular to the center point of the through-hole 1 (FIG. 2B) and the through-hole 1. When the diameter is L1, and the thickness between the through hole 1 and the outer peripheral surface is L2 and L3, L2 and L3 (both are equal) are 3 mm or less. The particularly preferable thickness is not less than L / 4 mm and not more than 3 mm. The outer diameter of the spherical porous body 3 is preferably 3 to 10 mm in diameter L for the same reason in the case of the cylindrical shape described above. Further, the size of the through-hole 1 of the spherical porous body 3 is not particularly limited, but the diameter L1 is preferably 0.5 mm or more.
The granular porous body desirably has a porosity of 30% or more, more preferably 35% or more, and most preferably 40 to 60%. This porosity does not include through holes. If the porosity of the porous body is less than 30%, there is a risk that the space for allowing the lithium carbonate produced by the absorption of carbon dioxide to exist is insufficient and the carbon dioxide absorption performance is lowered.
The granular porous body is allowed to further contain an alkali carbonate such as potassium carbonate or sodium carbonate in order to improve the absorption rate of carbon dioxide gas. Lithium carbonate produced by the absorption of carbon dioxide by the lithium silicate reacts with such an alkali carbonate to form a eutectic salt, and the melting point of the material is lowered to a molten state. As a result, lithium easily moves and the absorption rate of carbon dioxide gas is promoted.

  Next, the manufacturing method of the carbon dioxide absorbent according to the first embodiment will be described in detail.

Lithium carbonate and silicon dioxide are mixed so that the molar ratio of Li ₂ CO ₃ : SiO ₂ is 2: 1 to prepare a lithium orthosilicate raw material powder. When this raw material powder is heated to 600 to 1200 ° C. in an electric furnace, for example, the reaction represented by the above-described formula (2) occurs to synthesize lithium silicate (for example, lithium orthosilicate). At this time, in order to accelerate the absorption rate of carbon dioxide, it is allowed to add an alkali carbonate such as potassium carbonate or sodium carbonate after the raw material powder or after the synthesis of lithium silicate. The amount of alkali carbonate added is preferably 40 mol% or less with respect to lithium silicate. If the amount added exceeds 40 mol%, the carbon dioxide absorption reaction is accelerated, and the proportion of lithium silicate involved in the carbon dioxide absorption reaction with respect to the total amount of the absorbent is reduced. May decrease.

Next, the lithium silicate powder and, if necessary, a powder to which an alkali carbonate is added are formed into a porous body having a cylindrical shape, a spherical shape, a prismatic shape having through-holes by, for example, extrusion molding, and a carbon dioxide absorbent is used. To manufacture.
In the production of the carbon dioxide absorbent, the material powder is not necessarily fired and fired in this order, and may be fired after the raw material powder is formed.

  In the molding step, a binder for binding powder can be used. As the binder, both inorganic and organic materials can be used. Examples of the inorganic material include clay, mineral, and lime milk. Examples of the organic material include starch, methyl cellulose, polyvinyl alcohol, and paraffin. The addition amount of the binder is preferably 0.1 to 20% by weight with respect to the lithium silicate powder. The binder can be added in a state dispersed or dissolved in an appropriate solvent. As the solvent, water or an organic solvent can also be used.

Next, the processing method of the to-be-processed gas containing the carbon dioxide gas by the carbon dioxide absorber mentioned above is demonstrated.
A carbonaceous gas absorbent comprising a lithium silicate as a main component and having a through-hole, and having a wall thickness of 3 mm or less between the through-hole and an outer surface in a cross section perpendicular to the through-hole. By contacting the gas to be treated containing carbon dioxide at a temperature that enables the carbon dioxide to be absorbed, the absorbent reacts with the carbon dioxide in the gas to be treated according to the above-described formula (1), and the carbon dioxide is absorbed. (Removed).

Examples of the gas to be treated include exhaust gas discharged from energy plants and chemical plants that use fuels mainly composed of hydrocarbons, and exhaust gas generated from automobiles.
The temperature that enables absorption of the carbon dioxide gas is, for example, 500 to 700 ° C.

  Next, when the carbon dioxide absorbent reacts with the carbon dioxide in the gas to be treated and its absorption capacity is reduced, the carbon dioxide is heated to a temperature higher than the temperature that allows the carbon dioxide to be absorbed. The absorbed absorbent material reacts and is regenerated according to the above-described equation (2).

  The temperature during the regeneration is, for example, 720 ° C. or higher.

An inert gas such as nitrogen gas may be circulated through the absorbent material that has absorbed carbon dioxide gas during the regeneration.
Thus, by regenerating the absorbent after absorption of carbon dioxide, it becomes possible to repeatedly use the absorbent for absorption / removal of carbon dioxide in the gas to be treated.

For example, the reactor shown in FIG. 3 is used for the treatment of the gas to be treated containing carbon dioxide. The reactor 11 includes a cylindrical main body 13 having flanges 12a and 12b at both ends, an upper disk-shaped lid 15 having a gas introduction pipe 14 in contact with a flange 12a at one end (upper end) of the main body 13. And a lower disc-shaped lid 17 having a gas discharge pipe 16 in contact with the flange 12b at the other end (lower end) of the main body 13. A plurality of bolt insertion holes (not shown) are opened in the flanges 12a and 12b of the cylindrical main body 13, and the disc-like lid bodies 15 and 17 also have bolt insertion holes (corresponding to these insertion holes). (Not shown) is opened, and the bolt 12 insertion hole of the upper end of the cylindrical body 13 and the upper disk-shaped lid 15 is matched, and the lower end of the cylindrical body 13 is aligned with the lower disk-shaped lid 17 of the flange 12b. The disc-shaped lids 15 and 17 are fixed to the cylindrical body 13 by inserting bolts into the bolt insertion holes and tightening them with nuts. Meshes 18 and 19 are respectively attached to the opening of the gas introduction pipe 14 in the upper disk-shaped lid 15 and the opening of the gas discharge pipe 16 in the lower disk-shaped lid 17.
In such a reactor 11 shown in FIG. 3, the upper disk-shaped lid body 15 is removed from the cylindrical main body 13, and lithium silicate is mainly contained in the cylindrical main body 13 having the lower disk-shaped lid body 17. For example, in a cylindrical porous body having a columnar through hole, the carbon dioxide absorbent lithium 20 having a thickness of 3 mm or less between the through hole and the outer surface in a cross section perpendicular to the through hole is filled, and then again. The upper disk-shaped lid 15 is attached to the cylindrical main body 13. Subsequently, the carbon dioxide absorbing material 20 filled in the cylindrical main body 13 is passed through and brought into contact with the gas to be treated containing carbon dioxide through the gas introduction pipe 14 of the upper disk-shaped lid 15. At this time, by using the gas to be treated heated to 500 to 700 ° C., or by heating the absorbent 20 in the reactor 11 to 500 to 700 ° C. with a heater (not shown) arranged on the outer periphery of the reactor 11, for example. The absorbent 20 reacts with the carbon dioxide in the gas to be treated according to the above-described formula (1), and the carbon dioxide is absorbed (removed). The gas to be treated after reacting with the absorbent 20 is discharged through the gas discharge pipe 16 of the lower disk-shaped lid 17.
On the other hand, when the carbon dioxide absorbent 20 reacts with the carbon dioxide in the gas to be treated and the absorption capacity thereof is reduced, the supply of the gas to be treated is stopped and, for example, a heater (not shown) disposed on the outer periphery of the reactor 11 By heating the absorbent that has absorbed the carbon dioxide gas in the reactor 11 to, for example, 720 ° C. or higher, the absorbent that has absorbed the carbon dioxide reacts and is regenerated according to the above-described equation (2). The carbon dioxide gas generated in the reactor 11 by this regeneration process is discharged and collected through the gas discharge pipe 16.
(Second Embodiment)
The carbon dioxide absorbing material according to the second embodiment is a rectangular flat plate-shaped porous body mainly composed of lithium silicate and having a thickness of 3 mm or less.

The lithium silicate is preferably lithium orthosilicate (Li ₄ SiO ₄ ). This lithium orthosilicate reacts with carbon dioxide according to the above formula (1) and absorbs, reacts according to the following formula (2), and is regenerated.

When the thickness of the porous body exceeds 3 mm, after the carbon dioxide absorption / release (regeneration), the lithium carbonate represented by the above formula (1) accumulates in the absorbent material and absorbs over a long period of time. -It becomes difficult to maintain a high carbon dioxide absorption performance during repeated regeneration.
The porous body has, for example, a triangular flat plate shape, a rectangular flat plate shape, a hexagonal flat plate shape, or the like.
As a specific form, a rectangular flat plate-like porous body 21 having a thickness (T) shown in FIG. The rectangular flat porous body 21 preferably has a width (W) and a length (L) of 3 to 10 mm, respectively.
It is desirable that the porous body has a porosity of 30% or more, more preferably 35% or more, and most preferably 40 to 60%. If the porosity of the porous body is less than 30%, there is a risk that the space for allowing the lithium carbonate produced by the absorption of carbon dioxide to exist is insufficient and the carbon dioxide absorption performance is lowered.
The porous body may further contain an alkali carbonate such as potassium carbonate or sodium carbonate in order to improve the absorption rate of carbon dioxide gas. Lithium carbonate produced by the absorption of carbon dioxide by the lithium silicate reacts with such an alkali carbonate to form a eutectic salt, and the melting point of the material is lowered to a molten state. As a result, lithium easily moves and the absorption rate of carbon dioxide gas is promoted.

  Next, the manufacturing method of the carbon dioxide absorbent according to the second embodiment will be described in detail.

Lithium silicate (for example, lithium orthosilicate) is synthesized by the same method as in the first embodiment described above, and this lithium silicate powder and a powder to which an alkali carbonate is added as required are, for example, extruded to form a rectangular flat plate-like porous material. A carbon dioxide gas absorbent is manufactured as a material.
In the production of the carbon dioxide absorbent, the material powder is not necessarily fired and fired in this order, and may be fired after the raw material powder is formed.

In the molding step, as described in the first embodiment, it is allowed to use a binder for binding powder.
Next, the processing method of the to-be-processed gas containing the carbon dioxide gas by the carbon dioxide absorber mentioned above is demonstrated.
A temperature (for example, 500 to 700 ° C.) that makes it possible to absorb a gas to be treated containing carbon dioxide in a carbon dioxide absorbent that is a rectangular flat porous body having a thickness of 3 mm or less, the main component of which is lithium silicate. ), The absorbent reacts with the carbon dioxide in the gas to be treated in accordance with the above-described formula (1) to absorb (remove) the carbon dioxide.

Examples of the gas to be treated include exhaust gas discharged from energy plants and chemical plants that use fuels mainly composed of hydrocarbons, and exhaust gas generated from automobiles.
Next, when the carbon dioxide absorbing material reacts with the carbon dioxide in the gas to be treated and the absorption capacity thereof decreases, the carbon dioxide absorbent is heated to a temperature higher than the temperature at which the carbon dioxide can be absorbed (for example, 720 ° C. or higher). Thus, the absorbent that has absorbed the carbon dioxide gas reacts and is regenerated in accordance with the above-described equation (2).

An inert gas such as nitrogen gas may be circulated through the absorbent material that has absorbed carbon dioxide gas during the regeneration.
The above-described treatment of the gas to be treated containing carbon dioxide gas can be performed using, for example, the reactor shown in FIG. 3 as in the first embodiment.

  Thus, by regenerating the absorbent after absorption of carbon dioxide, it becomes possible to repeatedly use the absorbent for absorption / removal of carbon dioxide in the gas to be treated.

As described above, according to the second embodiment, the carbon dioxide gas absorbent is composed of a rectangular flat plate-shaped porous body mainly composed of lithium silicate and having a thickness of 3 mm or less, so that lithium carbonate remains in the absorbent during regeneration. Without accumulating, almost all of the absorbent can be converted to lithium silicate by releasing carbon dioxide as shown in Equation (2) above. As a result, even if carbon dioxide absorption / regeneration is repeated over a long period of time, stable and high carbon dioxide absorption performance can be achieved.
Hereinafter, embodiments of the present invention will be described in detail.

Example 1
Silicon dioxide powder having an average particle diameter of 10 μm and lithium carbonate powder having an average particle diameter of 1 μm were mixed so that the molar ratio of silicon dioxide: lithium carbonate was 1: 2. The obtained mixed raw material powder was fired at 1000 ° C. for 8 hours in the air in a box-type electric furnace to obtain a lithium orthosilicate powder. This lithium orthosilicate powder was put into an extruder, and a carbon dioxide absorbing material comprising a hollow cylindrical porous body was produced by an extrusion method. This hollow cylindrical porous body has an outer diameter of 8 mm, a height of 8 mm, and a 3 mm diameter cylindrical through hole formed so that its center point is along the axial direction. The hollow cylindrical porous body had a porosity of 40% by mercury adsorption method (excluding the through hole), and the thickness between the through hole and the outer surface was 2.5 mm in a cross section perpendicular to the through hole. .

(Example 2)
The same lithium orthosilicate powder as in Example 1 was put into an extruder, and a carbon dioxide gas absorbent comprising a hollow cylindrical porous body was produced by an extrusion method. This hollow cylindrical porous body has an outer diameter of 8 mm, a height of 8 mm, and a 2 mm diameter cylindrical through hole formed so that its center point is along the axial direction. The hollow cylindrical porous body has a porosity (excluding through holes) of 40% by the mercury adsorption method, and the thickness between the through hole and the outer surface in a cross section perpendicular to the through hole. Was 3 mm.

(Comparative Example 1)
The same lithium orthosilicate powder as in Example 1 was put into an extruder, and a carbon dioxide gas absorbent comprising a hollow cylindrical porous body was produced by an extrusion method. This hollow cylindrical porous body has an outer diameter of 8 mm, a height of 8 mm, and a 1 mm diameter cylindrical through hole formed so that its center point is along the axial direction. The hollow cylindrical porous body has a porosity (excluding through holes) of 40% by the mercury adsorption method, and the thickness between the through hole and the outer surface in a cross section perpendicular to the through hole. Was 3.5 mm.

(Comparative Example 2)
The same lithium orthosilicate powder as in Example 1 was put into an extruder, and a carbon dioxide gas absorbent composed of a cylindrical porous body having an outer diameter of 8 mm and a height of 8 mm by an extrusion method and a porosity of 40% by a mercury adsorption method was used. Manufactured.

  With respect to the carbon dioxide gas absorbents of Examples 1 and 2 and Comparative Examples 1 and 2 thus obtained, the carbon dioxide absorption and release repetition performance was evaluated. That is, 50 g of the carbon dioxide absorbent was placed in an alumina mortar, and this mortar was installed in an electric furnace. While flowing a mixed gas of carbon dioxide and air (carbon dioxide: air in a volume ratio of 20:80) into the mortar, the carbon dioxide is absorbed in the carbon dioxide absorbent by holding at 600 ° C. for 1 hour by heating in an electric furnace. After absorption, the weight of the carbon dioxide absorbent was measured. Next, the temperature of the electric furnace was raised to 850 ° C. and maintained at that temperature for 1 hour to release carbon dioxide from the carbon dioxide absorbent, and the weight of the carbon dioxide absorbent after release was measured. The first absorption performance was calculated from the weight change rate (wt%) after absorption.

  Under the same conditions, absorption and release of carbon dioxide gas were repeated 100 times, and the absorption performance at the 100th time was obtained by the same method as in the first time. Absorption / release of carbon dioxide gas was repeated 200 times under the same conditions, and the absorption performance at the 200th time was determined by the same method as in the first time.

The obtained absorption performance at the 100th time and the 200th time was substituted into the following formulas (3) and (4) to obtain the absorption performance maintenance ratio of each number.
(Absorption performance after 100 times / Absorption performance after 1 time) × 100 (%) (3)
(Absorption performance after 200 times / Absorption performance after 1 time) × 100 (%) (4)
The results are shown in Table 1 below.

As apparent from Table 1, the carbon dioxide absorbents of Examples 1 and 2 comprising a hollow cylindrical porous body having a thickness of 3 mm or less are comparative examples comprising a hollow cylindrical porous body having a thickness exceeding 3 mm. Compared with the carbon dioxide gas absorbent material of Comparative Example 2 consisting of a carbon dioxide gas absorbent material of 1 and a cylindrical porous body having a wall thickness exceeding 3 mm, the absorption performance maintenance rate after repeating 100 times of absorption and release of carbon dioxide gas is only high. Furthermore, the absorption performance maintenance rate after repeating absorption / release of carbon dioxide 200 times is also high, and it is possible to maintain excellent carbon dioxide absorption performance even in repeated absorption / release of carbon dioxide for a long time. I understand that.
Note that a silicon dioxide powder having an average particle diameter of 10 μm, a lithium carbonate powder having an average particle diameter of 1 μm, and a potassium carbonate powder having an average particle diameter of 1 μm have a molar ratio of silicon dioxide: lithium carbonate: potassium carbonate of 1: 2: 0.1. The mixed raw material powder was calcined in a box-type electric furnace at 1000 ° C. for 8 hours in the air to prepare lithium orthosilicate powder containing potassium carbonate. This lithium orthosilicate powder was the same as in Examples 1 and 2. The carbon dioxide absorbing material comprising a hollow cylindrical porous body manufactured by a simple method was able to maintain the same excellent carbon dioxide absorbing performance in evaluating the repeated performance of carbon dioxide absorption and release described above.

(Example 3)
Silicon dioxide powder having an average particle diameter of 10 μm and lithium carbonate powder having an average particle diameter of 1 μm were mixed so that the molar ratio of silicon dioxide: lithium carbonate was 1: 2. The obtained mixed raw material powder was fired at 1000 ° C. for 8 hours in the air in a box-type electric furnace to obtain a lithium orthosilicate powder. This lithium orthosilicate powder was put into an extruder, and a carbon dioxide absorbing material made of a rectangular flat porous body having a thickness of 2 mm, a width of 4 mm, and a length of 4 mm was produced by an extrusion method. This rectangular flat porous body had a porosity of 40% by the mercury adsorption method.

Example 4
The same lithium orthosilicate powder as in Example 3 was put into an extruder, and a carbon dioxide gas absorbing material composed of a rectangular flat porous body having a thickness of 3 mm, a width of 4 mm, and a length of 4 mm was produced by an extrusion method. This rectangular flat porous body had a porosity of 40% by the mercury adsorption method.

(Comparative Example 3)
The same lithium orthosilicate powder as in Example 3 was put into an extruder, and a carbon dioxide absorbent comprising a rectangular flat porous body having a thickness of 3.5 mm, a width of 4 mm, and a length of 4 mm was produced by an extrusion method. This rectangular flat porous body had a porosity of 40% by the mercury adsorption method.

With respect to the obtained carbon dioxide absorbents of Examples 3 and 4 and Comparative Example 3, the carbon dioxide absorption and release repeatability, that is, the absorption performance maintenance rate at the 100th and 200th evaluations was evaluated in the same manner as described above. . The results are shown in Table 2 below.

  As apparent from Table 2, the carbon dioxide absorbents of Examples 3 and 4 comprising a rectangular flat porous body having a thickness of 3 mm or less are comparative examples comprising a rectangular flat porous body having a thickness exceeding 3 mm. Compared to the carbon dioxide absorbent material 3, the absorption performance maintenance rate after 100 times of carbon dioxide absorption / release is high, and the absorption performance maintenance rate after 200 times of carbon dioxide absorption / release is also high. It can be seen that excellent carbon dioxide absorption performance can be maintained even during repeated absorption and release of carbon dioxide for a long period of time.

The figure which shows the cylindrical porous body (carbon dioxide gas absorber) which concerns on 1st Embodiment. The figure which shows the spherical porous body (carbon dioxide gas absorber) which concerns on 1st Embodiment. Sectional drawing which shows the reactor used for the processing method of the to-be-processed gas containing the carbon dioxide gas which concerns on 1st Embodiment. The perspective view which shows the rectangular flat plate-shaped porous body (carbon dioxide gas absorber) which concerns on 2nd Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Cylindrical through-hole, 2 ... Cylindrical porous body (carbon dioxide absorbing material), 3 ... Spherical porous body (carbon dioxide absorbing material), 11 ... Reactor, 13 ... Cylindrical main body, 14 ... Gas introduction pipe , 16 ... gas exhaust pipe, 20 ... carbon dioxide absorbent, 21 ... rectangular flat plate porous body (carbon dioxide absorbent).

Claims (5)

  A granular porous body mainly composed of lithium silicate and having a through hole, wherein a thickness between the through hole and the outer surface is 3 mm or less in a cross section perpendicularly crossing the through hole. Carbon dioxide absorber.   2. The carbon dioxide absorbent according to claim 1, wherein the granular porous body has a cylindrical shape with a diameter of 3 to 10 mm and a length of 3 to 10 mm.   2. The carbon dioxide absorbent according to claim 1, wherein the granular porous body is spherical with a diameter of 3 to 10 mm.   A carbon dioxide gas absorbent, characterized by being a rectangular flat plate-shaped porous body containing lithium silicate as a main component and having a thickness of 3 mm or less. A carbonaceous gas absorbent comprising a lithium silicate as a main component and having a through-hole, and having a wall thickness of 3 mm or less between the through-hole and an outer surface in a cross section perpendicular to the through-hole. A step of contacting a gas to be treated containing carbon dioxide gas to absorb the carbon dioxide gas;
Treating the treated gas containing carbon dioxide, comprising: heating the carbon dioxide absorbent after absorbing the carbon dioxide, releasing the absorbed carbon dioxide, and regenerating the carbon dioxide absorbent Method.

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