Economically viable process for producing organically modified lyo- or aerogels

Abstract

It is an object of the invention to provide a rapid and economically viable process which is notable for efficient use of material, especially of the silylating agent, and by means of which organically modified lyo- or aerogels are obtained in a rapid and simple manner. This object is achieved by virtue of the invention providing a process for producing organically modified gels selected from lyo- and aerosols by (i) emulsifying a basic polar phase comprising water and starting materials for silicatic gels in a nonpolar phase containing a water-immiscible precursor for an active silylating agent, (ii) starting formation of gel and ageing by lowering the pH, and then (iii) starting the silylation and the exchange of solvent by lowering the pH. If the gels are aerogels, the gels provided can be used for thermal and/or acoustic insulation.

Claims

1. A process for producing lyogels or aerogels, said process comprising the following steps i) emulsifying a basic, polar phase comprising water and starting materials for silicatic gels in an apolar phase consisting of a water-immiscible precursor of an active silylating agent, ii) commencing gel formation and aging by lowering a pH, and then iii) lowering the pH to commence silylation and solvent exchange.

2. A process for producing lyogels or aerogels, said process comprising the following steps i) emulsifying a basic, polar phase comprising water and starting materials for silicatic gels in an apolar phase comprising a water-immiscible precursor of an active silylating agent, ii) commencing gel formation and aging by lowering a pH with a chlorosilane, and then iii) lowering the pH to commence silylation and solvent exchange.

3. A process for producing lyogels or aerogels, said process comprising the following steps i) emulsifying a basic, polar phase comprising water and starting materials for silicatic gels in an apolar phase consisting of a water-immiscible precursor of an active silylating agent, ii) commencing gel formation and aging by lowering a pH, and then iii) lowering the pH to commence silylation and solvent exchange, and iv) recovering the water-immiscible precursor of the active silylating agent which remains unreacted in the apolar phase, wherein (a) disiloxanes or mixtures thereof are used as the water-immiscible precursor of an active silylating agent, (b) the basic, polar phase is produced by mixing individual components in the apolar phase, and (c) there is a phase mediator in the basic, polar phase.

4. The process as claimed in claim 3, wherein the basic, polar phase comprises a mixture of the starting materials for [SiO.sub.4/2] and [R.sub.xSiO.sub.(4-x/2)] units where x=1 or 2 or mixtures thereof and R is identical or different and is hydrogen or an organic, substituted or unsubstituted radical.

5. The process as claimed in claim 3, wherein hexamethyldisiloxane is used as the water-immiscible precursor of an active silylating agent.

6. The process as claimed in claim 3, wherein a mineral acid is used in step ii) for lowering the pH.

7. The process as claimed in claim 6, wherein the mineral acid used for lowering the pH in step ii) is also used in step iii) to lower the pH.

8. The process as claimed in claim 3, further comprising drying to provide aerogels.

9. The process as claimed in claim 3, wherein a chlorosilane is used in step ii) for lowering the pH.

Description

WORKING EXAMPLES

(1) The invention is described in more detail below using working examples without being restricted as a result.

(2) Provenances

(3) Alkali metal silicate (examples 1-5: Sigma-Aldrich: SiO.sub.2 content: 26.5 wt %, Na.sub.2O content: 10.6 wt %; example 7: Wllner: sodium silicate 38/40, solids content: 36 wt %, SiO.sub.2/Na.sub.2O=3.3)

(4) Potassium methylsiliconate (SILRES BS 16 from Wacker Chemie AG: aqueous solution with 34 wt % active substance fraction and 20 wt % K.sub.2O)

(5) SiO.sub.2 nanosol (Bindzil 17/750 from Akzo Nobel: SiO.sub.2 content: 15 wt %, average particle diameter according to manufacturer: 4 nm, pH 10.5)

(6) Hexamethyldisiloxane (AK 0.65 from Wacker Chemie AG)

(7) Unless mentioned specifically, all other laboratory chemicals were obtained from Sigma-Aldrich.

Example 1

(8) In a glass vessel, 10 g of alkali metal silicate and 5 g of potassium methylsiliconate were mixed and diluted with 40 g of water and 8 g of ethanol. 50 g of the resulting solution were emulsified in 200 ml of hexamethyldisiloxane by stirring with a KPG stirrer at 400 rpm in a 500 ml round-bottom flask, and the emulsion obtained was heated to 40 C. 20 ml of HNO.sub.3 solution (10 wt %) were added to this emulsion in order to commence gel formation. In this operation, the pH fell to about 9. After stirring for 1.5 hours at 40 C., 20 ml of HCl solution (32 wt %) were added to start the silylation and the solvent exchange, with a pH of 1 becoming established. After 45 minutes, displacement of water was complete. The aqueous phase (86 ml) was separated off and the organic phase containing the lyogel was reagitated twice more with 50 ml of water each time at room temperature (400 rpm), and the aqueous phase was again separated off. The resulting organic phase was filtered and the lyogel obtained was dried to constant weight in a drying cabinet at 120 C.

(9) Analytical Data

(10) Bulk density: 0.095 g/cm.sup.3

(11) BET: 630 m.sup.2/g

(12) BJH pore volume: 3.9 cm.sup.3/g

(13) Average pore diameter: 20 nm

(14) Yield: 3.6 g

(15) C content: 13.7%

(16) Na content: <0.1%

(17) K content: <0.1%

(18) Thermal conductivity (bed): 17.5 mW/K*m

Example 2

(19) In a glass vessel, 10 g of alkali metal silicate and 5 g of potassium methylsiliconate were mixed and diluted with 40 g of water and 8 g of ethanol. 50 g of the resulting solution were emulsified in 200 ml of hexamethyldisiloxane by stirring with a KPG stirrer at 400 rpm in a 500 ml round-bottom flask, and the emulsion obtained was heated to 40 C. 20 ml of HCl solution (6 wt %) were added to this emulsion in order to commence gel formation. In this operation, the pH fell to about 9. After stirring for 1.5 hours at 40 C., 20 ml of HCl solution (32 wt %) were added to start the silylation and the solvent exchange, with a pH of 1 becoming established. After 30 minutes, displacement of water was complete. The aqueous phase (85 ml) was separated off and the organic phase containing the lyogel was reagitated twice more with 50 ml of water each time at room temperature intensely for 5 minutes (400 rpm), and the aqueous phase was again separated off. The resulting organic phase was filtered and the lyogel obtained was dried to constant weight in a drying cabinet at 120 C.

(20) Analytical Data

(21) Bulk density: 0.12 g/cm.sup.3

(22) BET: 640 m.sup.2/g

(23) BJH pore volume: 3.2 cm.sup.3/g

(24) Average pore diameter: 14 nm

(25) Yield: 3.7 g

(26) C content: 13.5%

(27) Na content: <0.1%

(28) K content: <0.1%

(29) Thermal conductivity (bed): 18.5 mW/K*m

Example 3

(30) In a glass vessel, 11.25 g of alkali metal silicate and 3.75 g of potassium methylsiliconate were mixed and diluted with 40 ml of water and 10 ml of ethanol. 50 ml of the resulting solution were emulsified in 100 ml of hexamethyldisiloxane by stirring with a KPG stirrer at 400 rpm in a 500 ml round-bottom flask. The resulting emulsion was heated to 40 C. 20 ml of HCl solution (6 wt %) were added to this emulsion in order to commence gel formation. In this operation, the pH fell to about 10. After stirring for 1.5 hours at 40 C., 20 ml of HCl solution (32 wt %) were added to start the silylation and the solvent exchange, with a pH of 1 becoming established. After 45 minutes, displacement of water was complete. The aqueous phase (81 ml) was separated off and the organic phase containing the lyogel was reagitated twice more with 50 ml of water each time at room temperature (400 rpm), and the aqueous phase was again separated off. The resulting organic phase was filtered and the lyogel obtained was dried to constant weight in a drying cabinet at 120 C.

(31) Analytical Data

(32) Bulk density: 0.11 g/cm.sup.3

(33) BET: 630 m.sup.2/g

(34) BJH pore volume: 3.0 cm.sup.3/g

(35) Average pore diameter: 14 nm

(36) Yield: 3.5 g

(37) C content: 12.2%

(38) Na content: 0.14%

(39) K content: 0.10%

(40) Thermal conductivity: 19.1 mW/K*m

Example 4

(41) In a glass vessel, 11.25 g of alkali metal silicate and 3.75 g of potassium methylsiliconate were mixed and diluted with 40 ml of water and 10 ml of ethanol. 50 ml of the resulting solution were emulsified in 100 ml of hexamethyldisiloxane by stirring with a KPG stirrer at 400 rpm in a 500 ml round-bottom flask. The resulting emulsion was heated to 40 C. 20 ml of HCl solution (6 wt %) were added to this emulsion in order to commence gel formation. In this operation, the pH fell to about 10. After stirring for 30 minutes at 40 C., 20 ml of HCl solution (32 wt %) were added to start the silylation and the solvent exchange, with a pH of 1 becoming established. After 45 minutes, displacement of water was complete. The aqueous phase (83 ml) was separated off and the organic phase containing the lyogel was reagitated twice more with 50 ml of water each time at room temperature (400 rpm), and the aqueous phase was again separated off. The resulting organic phase was filtered and the lyogel obtained was dried to constant weight in a drying cabinet at 120 C.

(42) Analytical Data

(43) Bulk density: 0.11 g/cm.sup.3

(44) BET: 690 m.sup.2/g

(45) BJH pore volume: 3.1 cm.sup.3/g

(46) Average pore diameter: 15 nm

(47) Yield: 3.5 g

(48) C content: 13.1%

(49) Na content: 0.35%

(50) K content: 0.27%

(51) Thermal conductivity: 20.9 mW/K*m

Example 5

(52) In a glass vessel, 15 g of alkali metal silicate were diluted with 50 ml of water. 50 ml of the resulting solution were emulsified in 100 ml of hexamethyldisiloxane by stirring with a KPG stirrer at 400 rpm in a 500 ml round-bottom flask. The resulting emulsion was heated to 40 C. 20 ml of HCl solution (6 wt %) were added to this emulsion in order to commence gel formation. In this operation, the pH fell to about 8. After stirring for 1.5 hours at 40 C., 20 ml of ethanol and 20 ml of HCl solution (32 wt %) were added to start the silylation and the solvent exchange, with a pH of 1 becoming established. After 75 minutes, displacement of water was complete. The aqueous phase (100 ml) was separated off and the organic phase containing the lyogel was reagitated twice more with 50 ml of water each time at room temperature (400 rpm), and the aqueous phase was again separated off. The resulting organic phase was filtered and the lyogel obtained was dried to constant weight in a drying cabinet at 120 C.

(53) Analytical Data

(54) Bulk density: 0.06 g/cm.sup.3

(55) BET: 580 m2/g

(56) BJH pore volume: 4.9 cm.sup.3/g

(57) Average pore diameter: 24 nm

(58) Yield: 3.1 g

(59) C content: 6.9%

(60) Na content: 0.32%

(61) Thermal conductivity: 18.5 mW/K*m

Example 6

(62) In a glass vessel, 15 g of Bindzil 15/750 and 3.1 g of SILRES BS16 were diluted with 35 g of water. The resulting solution was emulsified in 100 ml of hexamethyldisiloxane by stirring with a KPG stirrer at 400 rpm in a 500 ml round-bottom flask. The resulting emulsion was heated to 40 C. 5.7 g of HCl solution (10 wt %) were added to this emulsion in order to commence gel formation. In this operation, the pH fell to about 8. After stirring for 1.5 hours at 40 C., 20 ml of ethanol and 20 ml of HCl solution (32 wt %) were added to start the silylation and the solvent exchange and the mixture was heated to 80 C., with a pH of 1 becoming established. After 45 minutes, displacement of water was complete. The aqueous phase (81 ml) was separated off and the organic phase containing the lyogel was reagitated twice more with 50 ml of water each time at room temperature (400 rpm), and the aqueous phase was again separated off. The resulting organic phase was filtered and the lyogel obtained was dried to constant weight in a drying cabinet at 120 C.

(63) Analytical Data

(64) Bulk density: 0.12 g/cm.sup.3

(65) BET: 470 m.sup.2/g

(66) BJH pore volume: 2.9 cm.sup.3/g

(67) Average pore diameter: 18 nm

(68) Yield: 2.7 g

(69) C content: 8.5%

(70) Na content: <0.1%

(71) Thermal conductivity: 18.7 mW/K*m

Example 7

(72) In a glass flask (500 ml) equipped with a KPG stirrer (400 rpm), 200 ml of hexamethyldisiloxane were introduced and 84.36 g of water and 21.74 g of alkali metal silicate (Wollner) were added successively. The emulsion obtained was heated to 40 C. This was followed by addition of 2.5 g of methyltrichlorosilane in order to commence gel formation. In this operation, the pH fell to about 8. After stirring for 1.5 hours at 40 C., 20 ml of ethanol and 20 ml of HCl solution (32 wt %) were added to start the silylation and the solvent exchange with a pH of 1 becoming established, and the mixture was heated to 80 C. After 30 minutes, displacement of water was complete. The aqueous phase (115 ml) was separated off and the organic phase containing the lyogel was reagitated twice more with 50 ml of water each time at room temperature (400 rpm), and the aqueous phase was again separated off. The resulting organic phase was filtered and the lyogel obtained was dried to constant weight in a drying cabinet at 120 C.

(73) Analytical Data

(74) Bulk density: 0.13 g/cm.sup.3

(75) BET: 680 m.sup.2/g

(76) BJH pore volume: 2.9 cm.sup.3/g

(77) Average pore diameter: 11 nm

(78) Yield: 6.4 g

(79) C content: 10.0%

(80) Na content: 0.68%

(81) Thermal conductivity: 19.3 mW/K*m