CO.SUB.2 .desorption catalyst

Abstract

This invention provides a CO.sub.2 desorption catalyst that has an excellent CO.sub.2 desorption activity and that can be used to replace metal filler. This invention provides a CO.sub.2 desorption catalyst comprising an inorganic powder or inorganic powder compact, the inorganic powder or inorganic powder compact having a BET specific surface area of 7 m.sup.2/g or more.

Claims

1. A CO.sub.2 desorption device including: a CO.sub.2 absorption tower for absorbing and removing CO.sub.2 from exhaust gas by using an absorbing solution; and a regeneration tower for regenerating the absorbing solution containing absorbed CO.sub.2, wherein the regeneration tower contains a CO.sub.2 desorption catalyst comprising an inorganic powder or inorganic powder compact, wherein the inorganic powder or inorganic powder compact has a BET specific surface area of 7 m.sup.2/g or more, wherein the inorganic powder or inorganic powder compact is at least one member selected from the group consisting of Al.sub.2O.sub.3 and zeolites, and wherein at least one metal selected from the group consisting of Pd, Fe, Co, Ag, Ni, and Pt is supported on the catalyst.

2. The CO.sub.2 desorption device according to claim 1, wherein the inorganic powder or inorganic powder compact further comprises BN.

3. A method for desorbing CO.sub.2, the method comprising the step of regenerating an absorbing solution containing absorbed CO.sub.2, wherein the regeneration step brings the absorbing solution containing absorbed CO.sub.2 into contact with a CO.sub.2 desorption catalyst comprising an inorganic powder or inorganic powder compact, wherein the inorganic powder or inorganic powder compact has a BET specific surface area of 7 m.sup.2/g or more, wherein the inorganic powder or inorganic powder compact is at least one member selected from the group consisting of Al.sub.2O.sub.3 and zeolites, and wherein at least one metal selected from the group consisting of Pd, Fe, Co, Ag, Ni, and Pt is supported on the catalyst.

4. The method for desorbing CO.sub.2 according to claim 3, wherein the inorganic powder or inorganic powder compact further comprises BN.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic diagram roughly illustrating a CO.sub.2 desorption device according to one embodiment of the invention. The arrow A in FIG. 1 indicates a movement of exhaust gas free from CO.sub.2 towards a flue. The arrow B in FIG. 1 indicates that CO.sub.2 is separated from the absorbing solution. The arrow C in FIG. 1 indicates that CO.sub.2 is collected.

(2) FIG. 2 is a schematic diagram roughly illustrating the inside of the regeneration tower of FIG. 1. The arrow D in FIG. 2 indicates that a CO.sub.2-containing absorbing solution is transferred from the absorption tower. The arrow E in FIG. 2 indicates that the CO.sub.2-containing absorbing solution transferred from the absorption tower moves down through the surface of the CO.sub.2 desorption catalyst of the invention while allowing desorption of CO.sub.2 under the heat of high-temperature water vapor. The arrows F in FIG. 2 indicate upward movement of the high-temperature water vapor and CO.sub.2, and downward movement of the not evaporated absorbing solution. The arrow G in FIG. 2 indicates that the absorbing solution is partially extracted to be heated by the heater (high-temperature water vapor is generated when the absorbing solution is heated by the heater).

DESCRIPTION OF EMBODIMENTS

(3) The invention is described in further detail below with reference to Examples. However, the scope of the invention is not limited to these Examples.

Example 1

(4) 15 mg of a BN powder (produced by Sigma-Aldrich) was pressed into a disk shape having a diameter of about 5 mm to produce the inorganic powder compact (catalyst) (metals unsupported) of Example 1. Based on the size of this compact, the external surface area was calculated to be 0.55 cm.sup.2. Hereinafter, this simple external surface area of the external surface of the compact is referred to as the apparent surface area.

Example 2

(5) An aqueous solution was prepared by dissolving gallium nitrate n-hydrate (Ga=18.9%) (Mitsuwa Chemistry Co., Ltd.) and aluminum nitrate nonahydrate (Nacalai Tesque, Inc.) in 100 mL of water, in such a manner that Ga/(Ga+Al)=0.5. Next, ammonium carbonate (5-fold equivalent) (the equivalent as used herein is based on the total molar numbers of Ga ions and Al ions) was added at once to the aqueous solution above, and stirred for 1 hour with a stirrer. The produced precipitate was washed several times with water and collected, followed by calcination at 700 C. in air to obtain Ga.sub.2O.sub.3Al.sub.2O.sub.3. Subsequently, 15 mg of the BN powder used in Example 1 and 15 mg of this Ga.sub.2O.sub.3Al.sub.2O.sub.3 were thoroughly mixed and pressed into a disk shape as in Example 1 to thereby produce the inorganic powder compact of Example 2.

Examples 3 to 14

(6) Each metal salt powder was dissolved in water to produce each metal salt aqueous solution. Each metal salt aqueous solution was impregnated onto an Al.sub.2O.sub.3 powder (Sumitomo Chemical Co., Ltd., product name: AKP-G05) or onto an SiO.sub.2 powder (Fuji Silysia Chemical Ltd., product name: CARiACT G-10), in such a manner that the weight of each metal after reduction treatment was 2 wt %, followed by drying in air at 100 C. for 6 hours and then calcination in air at 400 C. for 30 minutes to thereby obtain various inorganic powders (produced by an impregnation method). Each metal salt powder used herein is shown below.

(7) Metal Salt Powders

(8) Pd salt: a palladium nitrate n-hydrate (Pd(NO.sub.3).sub.2.nH.sub.2O) powder, produced by Kishida Chemical Co., Ltd.) Fe salt: an iron nitrate nonahydrate (Fe(NO.sub.3).sub.3.9H.sub.2O) powder, produced by Sigma-Aldrich Co salt: a cobalt nitrate hexahydrate (Co(NO.sub.3).sub.2.6H.sub.2O) powder, produced by Sigma-Aldrich Ag salt: a silver nitrate (AgNO.sub.3) powder, produced by Sigma-Aldrich Ni salt: a nickel nitrate hexahydrate (Ni(NO.sub.3).sub.2.6H.sub.2O) powder, produced by Kanto Chemical Co., Inc. Pt salt: a diammine dinitro platinum (Pt(NH.sub.3).sub.2(NO.sub.2).sub.2) powder, produced by Kojima Chemicals Co., Ltd.

(9) 15 mg of the BN powder used in Example 1 and 15 mg of each of these various inorganic powders obtained by the impregnation method above were thoroughly mixed, and pressed into a disk shape as in Example 1. A heat treatment was further performed at 300 to 400 C. in 1% H.sub.2N.sub.2 gas for 2 hours to thereby produce the inorganic powder compacts of Examples 3 to 14.

Example 15

(10) 2.5 mol of sodium carbonate was dissolved in 2 L of water and kept warm at 60 C. This aqueous alkaline solution was used as Solution A. 0.15 mol of zinc nitrate, 0.015 mol of aluminum nitrate, 0.012 mol of gallium nitrate, and 0.003 mol of magnesium nitrate were dissolved in 600 mL of water, and kept warm at 60 C. This acidic solution was used as Solution B. 0.3 mol of copper nitrate was dissolved in 300 mL of water and kept warm at 60 C. This acidic solution was used as Solution C. First, Solution B was uniformly added to Solution A dropwise over 30 minutes while being stirred to obtain a suspension. Next, Solution C was added to this suspension dropwise over 30 minutes at a constant rate to obtain a precipitate. After completion of the dropwise addition, aging was performed for 2 hours. Next, the precipitate was filtered and washed to the extent that neither sodium ions nor nitrate ions were detected. Further, the resulting product was dried at 100 C. for 24 hours and then calcined at 300 C. for 3 hours to produce a cylindrical compact of a composite oxide (CuOZnOAl.sub.2O.sub.3Ga.sub.2O.sub.3MgO; metal molar ratio: Cu:Zn:Al:Ga:Mg=100:50:5:4:1). A portion of this cylindrical compact was chipped off to give 15 mg of a spherical compact, which was subjected to heat treatment at 300 to 400 C. in 1% H.sub.2N.sub.2 gas for 2 hours to produce the inorganic powder compact of Example 15.

Example 16

(11) A portion of Cr-based catalyst (Sud-Chemie Catalyst Co., Ltd., product name: ActiSorb 410RS) was chipped off to give 15 mg of a spherical inorganic powder, which was subjected to heat treatment at 300 to 400 C. in 1% H.sub.2N.sub.2 gas for 2 hours to produce the inorganic powder compact of Example 16.

Example 17

(12) 660 mg of Zeolite (produced by Tosoh Corporation, product name: HSZ-640 HOD1A; BET specific surface area catalog value: 400 m.sup.2/g; diameter: about 1.5 mm; length: about 6 mm; extruded shape) was prepared.

Example 18

(13) 660 mg of spherical Al.sub.2O.sub.3 (produced by Sumitomo Chemical Co., Ltd., product name: KHA-46; BET specific surface area catalog value: 150 m.sup.2/g) was prepared. Specifically, six spherical Al.sub.2O.sub.3 articles (110 mg each) each having a diameter of about 5 mm were prepared.

Comparative Example 1

(14) Conventionally used metal filler (100 mg) was prepared. Specifically, one metal filler (100 mg) was prepared by wadding a stainless steel mesh with a width of 6 mm and a length of 30 mm into a ball having a diameter of 6 mm.

Comparative Example 2

(15) Conventionally used metal filler (660 mg) was prepared. Specifically, seven fillers in total were prepared: six metal fillers (100 mg each) used in Comparative Example 1; and one metal filler (60 mg) obtained by wadding a stainless steel mesh with a width of 6 mm and a length of 18 mm into a ball having a diameter of 6 mm.

Test Example 1: Surface Area Measurement

(16) The apparent surface area of each catalyst obtained in Examples 1 to 16 and Comparative Examples 1 to 2 (inorganic powder compacts, fillers, etc.) was calculated, and the BET specific surface area was measured.

(17) The apparent surface area was calculated based on the size and shape of each catalyst. The apparent surface area of each metal filler of Comparative Examples 1 and 2 was calculated based on the diameter, length, and number of stainless steel wires used to form the mesh. The BET specific surface area was obtained using the NOVA-4200e produced by Quantachrome. Tables 1 and 2 below show the measurement results.

Test Example 2: Measurement of CO.SUB.2 .Amount Present in Test Liquid and Calculation of Desorption Amount Per Apparent Surface Area

(18) 30 wt % of aqueous monoethanolamine (MEA) solution (50 mL) containing absorbed CO.sub.2 (123.4 or 127.1 g-CO.sub.2/L) was placed into a volumetric flask, to which one of each of the catalysts obtained in Examples 1 to 16 and Comparative Example 1 was added. The aqueous MEA solution was then heated. The heating was performed using a silicone oil bath. The temperature was increased at a rate of 1.4 C./min. After the temperature of the aqueous MEA solution reached 104 C. and was maintained at 104 C. for 30 minutes, a small amount of the aqueous MEA solution was sampled to measure the amount of residual CO.sub.2. Based on the measured amount of residual CO.sub.2, the CO.sub.2 desorption amount per apparent surface area was calculated. The CO.sub.2 desorption amount per apparent surface area was obtained by subtracting the amount of residual CO.sub.2 after the temperature reached 104 C. and was maintained at this temperature for 30 minutes from the CO.sub.2 amount before the test, and dividing the result by the apparent surface area. Table 1 shows the test results.

Test Example 3: Calculation of Desorption Rate of CO.SUB.2 .Present in Test Liquid and Desorption Rate of CO.SUB.2 .Per Apparent Surface Area

(19) An aqueous amine solution (150 mL) containing absorbed CO.sub.2 (151.6 g-CO.sub.2/L) was placed into a flask, to which one of each of the catalysts obtained in Examples 17 and 18 and Comparative Example 2 was added. This absorbing solution was heated to 75 C. The heating was performed by immersing the flask in a silicone oil bath heated to 120 C. The flow rate of desorbed CO.sub.2 when the absorbing solution had a temperature of 75 C. was measured using a mass flow meter (Azbil Corporation, MQV0002). Table 2 shows the test results.

(20) Consideration 1:

(21) Referring to the results obtained in Test Example 2 in terms of the CO.sub.2 desorption amount per apparent surface area obtained 30 minutes after the solution temperature reached 104 C., the use of the catalysts of Examples 1 to 16 resulted in much greater values, compared to the results of Comparative Example 1. This indicates that the CO.sub.2 desorption activity of each catalyst (inorganic powder compact) of Examples 1 to 16 is far more excellent than that of metal filler. The use of a catalyst free from BN, such as the catalysts obtained in Examples 15 and 16, also resulted in a high CO.sub.2 desorption amount per apparent surface area. Therefore, BN is not an essential component in the catalyst of the invention.

(22) Consideration 2:

(23) Referring to the results obtained in Test Example 3 in terms of the CO.sub.2 desorption rate when the absorbing solution had a temperature of 75 C., the use of the catalysts of Examples 17 and 18 showed much higher values, compared to the results obtained with the use of the metal filler of Comparative Example 2. This indicates that the CO.sub.2 desorption activity of each catalyst of Examples 17 and 18 is far more excellent than that of metal filler.

(24) When each inorganic powder compact of Examples 1 to 18 is observed at the micro level, the surface thereof is not flat due to the presence of microscopic unevenness, pores, and the like, unlike metal filler. The presence of the microscopic unevenness, pores, and the like is assumed to be one of the reasons for the high CO.sub.2 desorption activity. Considering this, high CO.sub.2 desorption activity is achieved not only by the catalysts of Examples 1 to 16, but also by those having microscopic unevenness and pores to some extent. Among the catalysts of Examples 1 to 16, the compact of the BN powder used in Example 1 has the smallest BET surface area of 7 m.sup.2/g. A catalyst having a BET specific surface area equal to or higher than this value is therefore expected to achieve an effect similar to the above.

(25) TABLE-US-00001 TABLE 1 CO.sub.2 amount Weight and surface area of in test liquid Desorption test catalyst (g-CO.sub.2/L) amount per BET 30 min apparent surface Catalyst Apparent specific after the area 30 min other surface surface temp. after the temp. than BN BN area area Before reached reached 104 C. (mg) (mg) (cm.sup.2) (m.sup.2/g) test 104 C. (g-CO.sub.2/cm.sup.2) Ex. 1 BN 0 15 0.55 7 127.1 31.3 174 Ex. 2 BN + Ga.sub.2O.sub.3Al.sub.2O.sub.3-based 15 15 0.46 78 123.4 29.9 203 catalyst Ex. 3 BN + Pd/Al.sub.2O.sub.3 catalyst 15 15 0.48 80 123.4 31.7 191 Ex. 4 BN + Fe/Al.sub.2O.sub.3 catalyst 15 15 0.49 73 123.4 32.9 185 Ex. 5 BN + Pd/SiO.sub.2 catalyst 15 15 0.51 113 123.4 34.6 174 Ex. 6 BN + Co/SiO.sub.2 catalyst 15 15 0.50 77 123.4 35.5 176 Ex. 7 BN + Fe/SiO.sub.2 catalyst 15 15 0.50 96 123.4 36.1 175 Ex. 8 BN + Co/Al.sub.2O.sub.3 catalyst 15 15 0.49 74 123.4 36.2 178 Ex. 9 BN + Ag/Al.sub.2O.sub.3 catalyst 15 15 0.48 68 123.4 36.8 180 Ex. 10 BN + Ag/SiO.sub.2 catalyst 15 15 0.51 89 123.4 37.1 169 Ex. 11 BN + Ni/Al.sub.2O.sub.3 catalyst 15 15 0.49 77 123.4 37.3 176 Ex. 12 BN + Pt/SiO.sub.2 catalyst 15 15 0.51 112 123.4 37.8 168 Ex. 13 BN + Pt/Al.sub.2O.sub.3 catalyst 15 15 0.49 71 123.4 40.2 170 Ex. 14 BN + Ni/SiO.sub.2 catalyst 15 15 0.50 70 123.4 40.4 166 Ex. 15 CuOZnO-based catalyst 15 0 0.24 63 123.4 34.6 370 Ex. 16 Cr-based catalyst 15 0 0.43 245 123.4 37.5 200 Comp. Metal filler 100 0 3.4 <3 (less 123.4 40.2 24 Ex. 1 than 3)

(26) TABLE-US-00002 TABLE 2 CO.sub.2 desorption rate when absorbing solution is at 75 C. CO.sub.2 Weight and surface area of desorption test catalyst rate per BET apparent Apparent specific CO.sub.2 surface surface surface desorption area Weight area area rate (mL/ (mg) (cm.sup.2) (m.sup.2/g) (mL/min) (min .Math. cm.sup.2) Ex. 17 Zeolite 660 21 400 473 23 catalyst Ex. 18 Al.sub.2O.sub.3 660 4.7 150 419 89 catalyst Comp. Metal 660 22 <3 (less 144 7 Ex. 2 filler than 3)

EXPLANATION OF REFERENCE NUMERALS

(27) 1. Exhaust Gas 2. Exhaust Gas Cooling Tower 3. Exhaust Gas Cooler 4. Exhaust Gas Blower 5. Absorption Tower 6. Filler 7. Extraction Pump 8. CO.sub.2-containing Absorbing Solution 9. Heat Exchanger 10. Regeneration Tower 11. Filler 12. Heater 13. Heated Vapor (High-temperature Water Vapor) 14. Cooler 15. CO.sub.2 Separator 16. Cooler 17. CO.sub.2-containing Absorbing Solution 18. CO.sub.2 Desorption Catalyst of the Invention 19. Heated Water Vapor (High-temperature Water Vapor) 20. Mixture of High-temperature Absorbing Solution, Water Vapor, and CO.sub.2 21. Unabsorbed Solution after CO.sub.2 has been desorbed therefrom 22. Mixture of CO.sub.2 Gas and Water Vapor