CARBON AEROGELS, PROCESS FOR THEIR PREPARATION AND THEIR USE

Abstract

The invention relates to carbon aerogels with particle sizes less than 1 μm. The carbon aerogels are prepared by (A)reacting a mono- and/or polyhydroxybenzene, an aldehyde and a catalyst in a reactor at a reaction temperature T in the range from 75-200° C. at a pressure of 80-2400 kPa, (B) then spraying the reaction mixture from process step (A) into an acid, (C) drying the resulting product from process step (B) and (D) carbonizing it. The carbon aerogels according to the invention can be used as filler, reinforcing filler, UV stabilizer, electrode material, sound absorbents, thermal insulating material, catalyst, catalyst support, conductivity additive, absorbent for gas and/or liquid preparation or pigment.

Claims

1. A process for producing a carbon aerogel having particles with a mean particle size of less than 1 μm, said method comprising: a) reacting a mono- and/or polyhydroxybenzene and an aldehyde in the presence of a catalyst, wherein the reaction is carried out at a temperature in the range of 75-200° C. and at a pressure of 80-2400 kPa; b) spraying the reaction mixture produced in step a) into an acid; c) drying the product produced in step (b); and d) carbonizing the dried product produced in step c).

2. The process of claim 1, wherein said mono- and/or polyhydroxybenzene is selected from the group consisting of: phenol, catechol, resorcinol, phloroglucinol, hydroquinone and mixtures thereof.

3. The process of claim 2, wherein said aldehyde is selected from the group consisting of: formaldehyde, glyoxal, glutaraldehyde, furfural and mixtures thereof.

4. The process of claim 1, wherein said catalyst is an alkali metal hydroxide or alkaline earth metal hydroxide.

5. The process of claim 1, wherein said catalyst is selected from the group consisting of: NaOH, KOH, Na.sub.2CO.sub.3, Li.sub.2CO.sub.3, K.sub.2CO.sub.3, and NH.sub.3.

6. The process of claim 5, wherein the concentration of mono- and/or polyhydroxybenzene and aldehyde in the reaction mixture is 10-60% by weight, and a) said mono- and/or polyhydroxybenzene is selected from the group consisting of: phenol, catechol, resorcinol, phloroglucinol, hydroquinone and mixtures thereof; and b) said aldehyde is selected from the group consisting of: formaldehyde, glyoxal, glutaraldehyde, furfural and mixtures thereof.

7. The process of claim 6, wherein the concentration of mono- and/or polyhydroxybenzene and aldehyde in the reaction mixture is 20-40% by weight.

8. The process of claim 6, wherein the molar ratio of mono- and/or polyhydroxybenzene to aldehyde is 1:1 to 1:4.

9. The process of claim 6, wherein said acid is selected from the group consisting of hydrochloric acid, nitric acid, phosphoric acid, sulphuric acid, acetic acid, formic acid and oxalic acid.

10. The process of claim 9, wherein the reaction of step a) is performed in the presence of a pore former selected from the group consisting of: ethylene glycol, polyethylene glycol, butylene glycol, diethylene glycol, triethylene glycol, gamma-butyrolactone, propylene carbonate, dimethyl-formamide, monoethanolamine, N-methyl-2-pyrrolidinone, and mixtures of thereof.

11. The process of claim 1, wherein said carbon aerogel comprises a mean particle size of between 0.05 and fpm as determined by means of laser diffraction according to ISO 13320-1 and comprises a carbon content of 95-100% by weight.

12. The process of claim 11, wherein the concentration of mono- and/or polyhydroxybenzene and aldehyde in the reaction mixture is 10-60% by weight.

13. The process of claim 12, wherein said mono- and/or polyhydroxybenzene is selected from the group consisting of: phenol, catechol, resorcinol, phloroglucinol, hydroquinone and mixtures thereof.

14. The process of claim 13, wherein said aldehyde is selected from the group consisting of: formaldehyde, glyoxal, glutaraldehyde, furfural and mixtures thereof.

15. The process of claim 14, wherein said catalyst is an alkali metal hydroxide or alkaline earth metal hydroxide.

16. The process of claim 15, wherein said catalyst is selected from the group consisting of: NaOH, KOH, Na.sub.2CO.sub.3, Li.sub.2CO.sub.3, K.sub.2CO.sub.3, and NH.sub.3.

17. The process of claim 16, wherein the concentration of mono- and/or polyhydroxybenzene and aldehyde in the reaction mixture is 20-40% by weight and the molar ratio of mono- and/or polyhydroxybenzene to aldehyde is 1:1 to 1:4.

18. The process of claim 17, wherein the reaction of step a) is performed in the presence of a pore former selected from the group consisting of: ethylene glycol, polyethylene glycol, butylene glycol, diethylene glycol, triethylene glycol, gamma-butyrolactone, propylene carbonate, dimethylformamide, monoethanolamine, N-methyl-2-pyrrolidinone, and mixtures of thereof.

19. The process of claim 18, wherein said carbon aerogel has a micropore volume of 0.1-0.35 cm.sup.3/g and wherein the density of said carbon aerogel is 0.15-1.5 g/cm.sup.3.

20. The process of claim 18, wherein said carbon aerogel comprises a mean particle size of between 0.5 and 0.95 μm as determined by means of laser diffraction according to ISO 13320-1 and has a carbon content of 99-100% by weight.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0120] FIG. 1: FIG. 1 shows the mesopore distribution of the carbon aerogel produced as described in Example 4.

[0121] FIG. 2: FIG. 2 shows the mesopore distribution of the carbon aerogel produced as described in Example 5.

[0122] FIG. 3: FIG. 3 shows the mesopore distribution of the carbon aerogel produced as described in Example 6.

[0123] FIG. 4: FIG. 4 shows the mesopore distribution of the carbon aerogel produced as described in Example 7.

EXAMPLES

[0124] Example 1 (comparative example, Barral, Journal of Non-Crystalline Solids, Vol. 225, p. 47 (double step process), 1998)

[0125] 0.68 g of phloroglucinol is dissolved in 101.6 g of water at room temperature. 0.32 g of 37% formaldehyde solution is added to the solution. Subsequently, 0.02 g of calcium hydroxide is added. A closed glass vessel containing the solution is heated without stirring in a silicone oil bath at 90° C. After a 5-minute residence time in the silicone oil bath, the still liquid solution is cooled to room temperature. Subsequently, 0.128 g of 37% HCl solution is added. The resulting solution is kept at a temperature of 92° C. for 72 h. The resulting organic gel is dried at room temperature and then carbonized in a muffle furnace at 800° C. under nitrogen for 1.5 hours. The resulting carbon system has a particle size distribution with x.sub.50=1.07 μm (mean particle size) and x.sub.95=3.09 μm. The carbon aerogel has a specific surface area of 233.5 m.sup.2/g and a mesopore volume of 0.008 cm.sup.3/g.

[0126] Example 2 (comparative example, WO 02/12380 A2, examples 1-2)

[0127] Examples 1-2 mentioned in the patent WO 02/12380 A2 are reworked according to the description.

[0128] The resulting carbon system has a particle size distribution which cannot be characterized fully by means of the analysis method specified (x.sub.95>3.0 mm). The carbon aerogel has a specific surface area of 535.2 m.sup.2/g and a mesopore volume of 0.459 cm.sup.3/g. The M.sub.y value of this carbon aerogel is 226.9.

Example 3

[0129] 4.5 g of phenol are dissolved in 19.5 g of water at room temperature. 11.77 g of 37% formaldehyde solution are added to the solution. Subsequently, the solution is adjusted to the pH of 9.1 with 0.73 g of 25% sodium hydroxide solution. A closed glass vessel containing the solution is heated without stirring in a silicone oil bath at 90° C. After an eight-hour residence time in the silicone oil bath, the still liquid solution is sprayed by means of a Schlick model 121 V, type 8 hollow-cone nozzle (bore 0.8 mm) at a pressure of 2.5 bar into ten times the volume of the HCl solution at pH=1.0. After 20 hours of residence time at room temperature, the acid solution containing the organic fine particulate sediment is dried at 160° C. in a spray dryer. The dry gel is carbonized in a muffle furnace at 800° C. under nitrogen for 1.5 hours. The resulting fine particulate carbon system has a particle size distribution with x.sub.50=316 nm (mean particle size) and x.sub.95<512 nm. The carbon aerogel has a specific surface area of 613.3 m.sup.2/g and a mesopore volume of 0.044 cm.sup.3/g. The M.sub.y value of this carbon aerogel is 239.0. The M.sub.y value is higher than in example 2 (comparative example) and thus indicates better dispersibility.

Example 4

[0130] 1.9 g of phenol (P) are dissolved in 11.52 g of water at room temperature. 4.97 g of 37% formaldehyde (F) solution are added to the solution. Subsequently, the solution is adjusted to the pH of 9.1 with 0.31 g of 25% sodium hydroxide solution. A closed vessel containing the solution is heated without stirring in a silicone oil bath at 85° C. After a ten-hour residence time in the silicone oil bath, the still liquid solution is sprayed by means of a Schlick model 121 V, type 8 hollow-cone nozzle (bore 0.8 mm) at a pressure of 2.5 bar into ten times the volume of the oxalic acid solution with pH=0.95 at a temperature of 85° C. The acid solution containing the organic fine particulate sediment formed is stored in a likewise closed vessel at 85° C. After 90 hours, the acid solution containing the fine particulate sediment is dried in a spray dryer at 160° C. The dried gel is carbonized in a muffle furnace at 800° C. under nitrogen for 1.5 hours. The resulting fine particulate carbon system has a particle size distribution with x.sub.50=495 nm (mean particle size) and x.sub.95=917 nm. The carbon aerogel has a specific surface area of 734.8 m.sup.2/g and a mesopore volume of 1.07 cm.sup.3/g. The mesopore distribution is shown in FIG. 1. The M.sub.y value of this carbon aerogel is 285.7. The M.sub.y value is higher than in example 2 (comparative example) and thus indicates better dispersibility.

Example 5

[0131] 1.9 g of phenol are dissolved in 11.52 g of water at room temperature. 4.97 g of 37% formaldehyde solution are added to the solution. Subsequently, the solution is adjusted to the pH of 9.1 with 0.31 g of 25% sodium hydroxide solution. A closed vessel containing the solution is heated without stirring in a silicone oil bath at 85° C. After a ten-hour residence time in the silicone oil bath, the still liquid solution is sprayed by means of a Schlick model 121 V, type 8 hollow-cone nozzle (bore 0.8 mm) at a pressure of 2.5 bar into ten times the volume of the oxalic acid solution with pH=0.95 at a temperature of 85° C. The acid solution containing the organic fine particulate sediment formed is stored in a likewise closed vessel at 85° C. After 90 hours, the acid solution containing the fine particulate sediment is dried in a spray dryer at 160° C. The dried gel is carbonized in a muffle furnace at 800° C. under nitrogen for 1.5 hours. The resulting fine particulate carbon system has a particle size distribution with x.sub.50=770 nm (mean particle size) and x.sub.95=1916 nm. The carbon aerogel has a specific surface area of 699.9 m.sup.2/g and a mesopore volume of 0.85 cm.sup.3/g. The mesopore distribution is shown in FIG. 2. The M.sub.y value of this carbon aerogel is 272.7. The M.sub.y value is higher than in example 2 (comparative example) and thus indicates better dispersibility.

Example 6

[0132] 1.9 g of phenol are dissolved in 11.52 g of water at room temperature. 4.97 g of 37% formaldehyde solution are added to the solution. Subsequently, the solution is adjusted to the pH of 9.1 with 0.31 g of 25% sodium hydroxide solution. A closed vessel containing the solution is heated without stirring in a silicone oil bath at 125° C. The interior of the vessel is pressurized with a pressure of 4.5 bar (absolute). After an 18-minute residence time in the silicone oil bath, the still liquid solution is sprayed by means of a Schlick model 121 V, type 8 hollow-cone nozzle (bore 0.8 mm) at a pressure of 2.5 bar into ten times the volume of HCl with pH=0.95 at a temperature of 25° C. The acid solution containing the organic fine particulate sediment formed is stored in a likewise closed vessel at 25° C. After 24 hours, the acid solution containing the fine particulate sediment is dried in a spray dryer at 200° C. The dried gel is carbonized in a muffle furnace at 800° C. under nitrogen for 1.5 hours. The resulting fine particulate carbon system has a particle size distribution with x.sub.50=810 nm (mean particle size) and x.sub.95=1956 nm. The carbon aerogel has a specific surface area of 700.0 m.sup.2/g and a mesopore volume of 1.03 cm.sup.3/g. The mesopore distribution is shown in FIG. 3. The M.sub.y value of this carbon aerogel is 276.3. The M.sub.y value is higher than in example 2 (comparative example) and thus indicates better dispersibility.

Example 7

[0133] 3.8 g of phenol are dissolved in 23.00 g of water at room temperature. 9.84 g of 37% formaldehyde solution are added to the solution. Subsequently, the solution is adjusted to the pH of 9.1 with 0.62 g of 25% sodium hydroxide solution. A closed vessel containing the solution is heated without stirring in a silicone oil bath at 125° C. The interior of the vessel is pressurized with a pressure of 4.5 bar (absolute). After a 19-minute residence time in the silicone oil bath, the still liquid solution is sprayed by means of a Schlick model 121 V, type 8 hollow-cone nozzle (bore 0.8 mm) at a pressure of 2.5 bar into ten times the volume of HCl with pH=1.01 at a temperature of 25° C. The acid solution containing the organic fine particulate sediment formed is stored in a likewise closed vessel at 25° C. After 24 hours, the acid solution containing the fine particulate sediment is dried in a spray dryer at 220° C. The dried gel is carbonized in a muffle furnace at 800° C. under nitrogen for 1.5 hours. The resulting fine particulate carbon system has a particle size distribution with x.sub.50=830 nm (mean particle size) and x.sub.95=1990 nm. The carbon aerogel has a specific surface area of 689.9 m.sup.2/g and a mesopore volume of 0.91 cm.sup.3/g. The mesopore distribution is shown in FIG. 4. The M.sub.y value of this carbon aerogel is 274.2. The M.sub.y value is higher than in example 2 (comparative example) and thus indicates better dispersibility