JP2535764B2 - Method for separating nitrogen and carbon dioxide using ceramics as a separating material - Google Patents

Description

Detailed Description of the Invention

[0001]

[Industrial application] Global warming is becoming a major social problem today, and one of the main causative agents is carbon dioxide emitted from factories as a result of production activities. There is. In order to solve global warming, it is necessary and urgent to develop technologies such as collecting and fixing carbon dioxide that has already been discharged, and separating and collecting high-concentration and high-temperature carbon dioxide at an exhaust gas source. Organic separation materials cannot be used for separation / recovery of high-temperature carbon dioxide because of problems with heat resistance. Therefore, thermally stable ceramics are listed as a strong candidate for the separation material. However, the present invention provides a method for separating nitrogen and carbon dioxide by the clay mineral sepiolite, and is considered to greatly contribute to global environmental protection.

[0002]

2. Description of the Related Art Heretofore, no ceramic separating material has been found for separating and recovering high-temperature carbon dioxide in exhaust gas from factories and the like.

[0003]

In order to separate nitrogen and carbon dioxide in a high-temperature state discharged from a fixed source such as a factory, it is necessary and urgent to develop a thermally stable ceramic separating material. Therefore, the present invention is to provide a ceramic capable of separating nitrogen and carbon dioxide in a high temperature state.

[0004]

DISCLOSURE OF THE INVENTION The present invention is to provide a ceramic capable of separating nitrogen and carbon dioxide in exhaust gas at high temperature. Since the molecular diameters of nitrogen and carbon dioxide are almost the same, it is very difficult to separate them by the molecular sieving effect. Therefore, separation by a method other than molecular sieve is required. Comparing the chemical properties of nitrogen and carbon dioxide, it is known that nitrogen does not adsorb at either the acid site or the base site, but carbon dioxide adsorbs at the base site with an acidic gas. The method of separating nitrogen and carbon dioxide from this may be carried out by utilizing the adsorption phenomenon of each gas to the ceramics.

The ceramics separating material of the present invention is obtained by subjecting sepiolite, which is a kind of clay mineral, to ion exchange with zinc ions and then heating at a temperature of 800 ° C. or lower. Here, sepiolite will be described. FIG. 1 is an ab plane projection view of a crystal structure model of sepiolite (Brauner,
K. and Preisinger, A .; , Mine
r. Petro. Mitt. , Vol. 6, pp. 12
0-140 (1956)). Since sepiolite takes a fibrous form extending in the direction perpendicular to the ab plane shown in FIG. 1, that is, in the c-axis direction, FIG. 1 shows a cross section of the sepiolite fiber. This structure is formed by talc-like 2: 1 type layers inverting the apex direction of their Si-O tetrahedral sheets at a period of about 13.4 Å. A characteristic of the crystal structure of sepiolite is the presence of channels, which are micropores with a cross-sectional area of about 13.4 x 6.7 due to staggered chains of 2: 1 type layers. In this channel, there are zeolitic water, exchangeable cations, and water molecules that coordinate to Mg in the octahedron layer of the 2: 1 type layer (Ryohei Otsuka, Ryushi Shimoda, Yasuya Shimosaka, Hiroshi Nagata, Shinohara). Yasushi, Masahiro Shimizu, Naofumi Sakamoto, Clay Science, Volume 32, No. 3, pp. 1
54-172 (1992)).

[0006] Sepiolite exhibits a dehydration behavior upon heating, and then undergoes a structural change with dehydration. Examination of the thermogravimetric curve of sepiolite shows that the temperature is 100 ° C. or less (step 1), 200-350 ° C. (step 2), 400-60
0 ° C. (Step 3), 750-820 ° C. (Step 4)
Weight loss due to 4 stages of dehydration is observed. In addition, the differential thermal analysis curve shows an endothermic peak corresponding to these weight loss, and 8
A sharp exothermic peak around 30 ° C is observed. Step 1
The reduction of water content is carried out by dehydration of adsorbed water and boiling water, steps 2 and 3
Corresponds to the dehydration of 結合 of the bound water, and the reduction of Step 4 corresponds to the dehydration of the structural water. In addition,
The exothermic peak at around 830 ° C. is due to the transition to pyroxene. The dehydration behavior of each step is again shown by a composition formula as follows.

Embedded image

When sepiolite is heated at a temperature of about 400 ° C. or more in a dry state, a phenomenon called “folding” occurs, and the 2: 1 type layer turns into a bent structure. The temperature at which the folding occurs depends on the place of production of sepiolite and the like, and may occur even at 200 ° C.

The surface of sepiolite has three kinds of surfaces as shown in FIG. One is an oxygen surface of a silica tetrahedral sheet which is the same as the surface of a normal phyllosilicate.
It has little activity and acts only as a physisorption surface. Next is -Si-OH only on the outer surface where the bond is broken
Which is similar to the surface of silica gel. The other is the surface of the channel surface where Mg or water molecules bound to it exist. This is the philosophy
The surface is in the same state as it would be at the crystal edge of the crystal, but in sepiolite it is innumerable along the channel. The fact that these active sites are innumerable is a feature of sepiolite that is not found in other minerals (Yoshiaki Fukushima, Yoshie Kitayama,
Kazuo Tobe, Clay Science, Vol. 32, No. 3, pp. 177
-183 (1992)).

Next, a method for preparing the zinc ion-exchanged sepiolite of the present invention will be described. 5.0 g of sepiolite was added to 20 ml of a 0.5 M zinc nitrate aqueous solution, stirred well and allowed to stand at room temperature for 24 hours. The concentration and liquid amount of the zinc nitrate aqueous solution are selected so that the total amount of exchangeable cations of sepiolite is preferably ion-exchanged.
After the ion exchange, the sepiolite is collected by centrifugation or filtration, washed with water, dried, and then heated at a temperature of 800 ° C. or lower for 2 hours. Washing and drying may be omitted. The heating conditions for sepiolite, which are determined by the heating temperature and the heating time, may be selected within the range in which sepiolite does not transfer to pyroxene.

A method for evaluating the ability of ceramics to separate nitrogen from carbon dioxide will be described. When nitrogen or carbon dioxide is brought into contact with ceramics, they are adsorbed on the surface of the ceramics and desorbed after a while. When the temperature of the ceramic is low, both physical adsorption and chemical adsorption occur, but when the temperature rises, only chemical adsorption occurs. In other words, physical adsorption is weak adsorption and chemical adsorption is strong adsorption. When the retention time is defined as the time from when the gas is adsorbed on the surface of the ceramics to when it is desorbed, the retention time is strongly affected by the adsorption and desorption ability of the gas to the ceramics.
That is, it is suggested that when the retention time is long, the gas is strongly adsorbed on the ceramic surface and is not easily desorbed. On the other hand, when the retention time is short, the interaction between the gas and the ceramic surface is weak,
It is suggested that the gas easily desorbs from the ceramic surface. Therefore, the retention times of nitrogen and carbon dioxide with respect to the ceramics are measured, the difference between them is determined, and the larger the difference, the better the separability of nitrogen and carbon dioxide. The retention time may be measured by any method as long as it can measure the time from gas injection to desorption, but it is easy to carry out by gas chromatography with TCD using helium as a carrier gas.

FIG. 2 shows a schematic view of a measuring device used for evaluating the nitrogen / carbon dioxide separation ability of the zinc ion-exchanged sepiolite of the present invention. The measuring device consists of a sample packed column (1), a heating furnace (2), a temperature controller (3), a gas chromatography (4), a pen recorder (5), and a nitrogen / carbon dioxide inlet (6). In the measurement method, first, 5.0 g of zinc ion-exchange sepiolite is packed in a sample packed column made of a stainless steel pipe having an inner diameter of 3 mmφ and a length of about 1 m. Next, it is calcined at 300 ° C. for 1 to 2 hours while flowing helium as a carrier gas at a flow rate of 20 ml / min. After that, the sample is brought to the measurement temperature and the mixed gas of nitrogen and carbon dioxide is 2 m.
1 is injected from the nitrogen / carbon dioxide inlet with a microsyringe, and recording is started at the same time. The retention times of nitrogen and carbon dioxide were measured, and it can be concluded that the larger the difference, the higher the nitrogen / carbon dioxide separation ability.

When the nitrogen / carbon dioxide separation ability of zinc ion-exchanged sepiolite subjected to various heat treatments was examined, it was found that nitrogen and carbon dioxide can be separated by zinc ion-exchanged sepiolite in a high temperature state, and the heat treatment was performed. It was found that the higher the temperature, the better the resolution. Hereinafter, the details will be described in Examples and Comparative Examples.

[0013]

【Example】

Example 1 5.0 g of zinc ion-exchanged sepiolite heated at 300 ° C. for 2 hours in an electric furnace in an air atmosphere was packed in a sample packed column, and 300 ° C. with helium flowing at 20 ml / min.
It was calcined for 2 hours. After calcination, set the sample temperature (separation temperature) to 12
The temperature was set to 0 ° C., and 2 ml of a nitrogen / carbon dioxide mixed gas was injected. The retention times of nitrogen and carbon dioxide were 26 seconds for the former and 343 seconds for the latter, and the difference was 317 seconds.

Example 2 Only separation temperature was set to 200 ° C., and other conditions were set to Example 1.
When the retention times of nitrogen and carbon dioxide were measured under the same sample and measurement conditions as above, the former was 23 seconds, the latter was 61 seconds, and the difference was 38 seconds.

Example 3 Only the separation temperature was 220 ° C., and other conditions were the same as in Example 1.
When the retention times of nitrogen and carbon dioxide were measured under the same sample and measurement conditions as above, the former was 22 seconds, the latter was 49 seconds, and the difference was 27 seconds.

Example 4 A sample packed column was packed with 5.0 g of zinc ion-exchanged sepiolite heated at 500 ° C. for 2 hours in an electric furnace in an air atmosphere, and 350 ° C. while flowing helium at 20 ml / min.
It was calcined for 2 hours. After the calcination, the separation temperature was set to 240 ° C. and 2 ml of nitrogen / carbon dioxide mixed gas was injected. The retention times of nitrogen and carbon dioxide were 22 seconds for the former and 208 seconds for the latter, and the difference was 186 seconds.

Example 5 The separation temperature was set to 300 ° C., and other conditions were set to Example 4.
When the retention times of nitrogen and carbon dioxide were measured under the same sample and measurement conditions as in the above, the former was 21 seconds, the latter was 70 seconds, and the difference was 49 seconds.

Example 6 Only the separation temperature was set to 320 ° C., and the other conditions were set to Example 4.
When the retention times of nitrogen and carbon dioxide were measured under the same sample and measurement conditions as above, the former was 20 seconds, the latter was 55 seconds, and the difference was 35 seconds.

Example 7 A sample packed column was packed with 5.0 g of zinc ion-exchanged sepiolite heated at 600 ° C. for 2 hours in an electric furnace in an air atmosphere, and 400 ° C. while flowing helium at 20 ml / min.
It was calcined for 2 hours. After calcination, the separation temperature was set to 280 ° C. and 2 ml of a nitrogen / carbon dioxide mixed gas was injected. The retention times of nitrogen and carbon dioxide were 20 seconds for the former and 155 seconds for the latter, and the difference was 135 seconds.

Example 8 The separation temperature was set to 300 ° C., and the other conditions were set to Example 7.
When the retention times of nitrogen and carbon dioxide were measured under the same sample and measurement conditions as in the above, the former was 20 seconds, the latter was 109 seconds, and the difference was 89 seconds.

Example 9 Only the separation temperature was set to 360 ° C., and other conditions were set in Example 7.
When the retention times of nitrogen and carbon dioxide were measured under the same sample and measurement conditions as above, the former was 20 seconds, the latter was 48 seconds, and the difference was 28 seconds.

Comparative Example 1 5.0 g of silica gel was packed in a sample packed column and calcined at 300 ° C. for 2 hours while flowing helium at 20 ml / min. After the calcination, the separation temperature was set to 120 ° C., and 2 ml of a nitrogen / carbon dioxide mixed gas was injected. The retention times of nitrogen and carbon dioxide were 32 seconds for the former and 63 seconds for the latter, and the difference was 31 seconds.

Comparative Example 2 The separation temperature was set to 160 ° C., and other conditions were set to Comparative Example 1.
When the retention times of nitrogen and carbon dioxide were measured under the same sample and under the same measurement conditions, the former was 31 seconds, the latter was 47 seconds, and the difference was 16 seconds.

[0025]

INDUSTRIAL APPLICABILITY The present invention provides a method for separating nitrogen and carbon dioxide by a zinc ion exchange sepiolite of clay mineral, and is considered to greatly contribute to global-scale environmental protection.

[Brief description of drawings]

FIG. 1 shows the crystal structure of sepiolite.

FIG. 2 is a schematic diagram of an apparatus for evaluating and measuring nitrogen / carbon dioxide separation ability.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sample packed column 2 Heating furnace 3 Temperature controller 4 Gas chromatography 5 Pen recorder 6 Nitrogen / carbon dioxide inlet

Continuation of front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location C04B 35/16 C04B 35/16 Z (72) Inventor Shinji Watamura 1-70, Heiwagaoka, Meito-ku, Aichi prefecture Inoishi House 3-103 (56) Reference JP-A-5-138021 (JP, A)

Claims (1)

(57) [Claims] 1. A ceramic separating material and nitrogen and carbon dioxide separation methods, and nitrogen, wherein said ceramic is a sepiolite was heated at 800 ° C. below the temperature was ion-exchanged with zinc How to separate carbon dioxide.