Process for the hydrophobization of porous silica

Abstract

A process for the hydrophobization of a porous silica based compound involves the steps of providing a composition (I) containing a porous silica based compound, treating the composition (I) with a composition (II) containing hexamethyldisiloxane or its hydrolyzed form, and removing the treated silica based compound. The porous silica based compound obtained by the process is useful. A porous silica based compound obtained or obtainable by the process can be used for medical and pharmaceutical applications, as adsorbents, for cosmetic applications, as an additive for food, as a catalyst support, for the preparation of sensors, or for thermal insulation.

Claims

1. A process for the hydrophobization of a porous silica-based compound, the process comprising: (i) providing a composition (I) comprising a porous silica-based compound, (ii) treating the composition (I) in a treatment vessel with a composition (II) comprising hexamethyldisiloxane or its hydrolyzed form, to obtain a treated porous silica-based compound, and (iii) removing the treated porous silica-based compound from the treatment vessel, wherein the treatment according to (ii) is carried out at a temperature in the range of from 60 to 90? C. and at a pH value in the range of from 0.5 to 3, and wherein the porous silica-based compound is a silica-based aerogel.

2. The process according to claim 1, wherein the porous silica-based compound is selected from the group consisting of a silicate, an alumino-silicate, a calcium silicate, precipitated silica, and fumed silica.

3. The process according to claim 1, wherein the silica-based compound is obtained from a sodium silicate precursor, a silica hydrogel, a fumed silica, or a precipitated silica.

4. The process according to claim 1, wherein the composition (II) comprises hexamethyldisiloxane and an alcohol.

5. The process according to claim 1, wherein the composition (II) comprises hexamethyldisiloxane, ethanol, and optionally, water.

6. The process according to claim 1, wherein the composition (II) comprises hexamethyldisiloxane, ethanol, and optionally, dilute acid.

7. The process of claim 1, wherein the porous silica-based compound is an aerogel, and wherein providing the composition (I) comprising the porous silica-based compound comprises providing a gel and drying the gel under supercritical conditions.

8. The process of claim 1, wherein the porous silica-based compound is an aerogel, and wherein providing the composition (I) comprising the porous silica-based compound comprises providing a gel, acidifying the gel, and drying the gel under supercritical conditions.

9. The process of claim 1, wherein the treated porous silica-based compound has a contact angle of from 138.8? to 149.5?.

10. The process of claim 1, wherein, before (ii) treating the composition (I) in a treatment vessel, the porous silica-based compound is a hydrophilic compound having a contact angle of from 0? to 72?.

Description

EXAMPLES

(1) The preparation methodology for above possibilities is given below.

1. Preparation Examples

(2) 1.1 Hydrophobic Silica (Aerogel) from Sodium Silicate Precursor (Formsil)

(3) Solution 1: 250 g Formsil (Sodium metasilicate nonahydrate; CAS Number 13517-24-3; Mwt: 284) powder was mixed with 250 g deionized water and stirred for 2 h at 50? C. until a clear solution was obtained. Solution 2: 200 g (32 wt %) HCl was added to 1800 g water and stirred at room temperature. 1.1.1 497.5 g of solution 1 was added to solution 2000 g of solution 2. The solution solidified into a soft gel in less than 30 seconds. The pH was measured to be 6.8. The total mass of the soft gel was 2497.5 g. (Silica aerogel density adjustments can be made by adjusting the water amount) The soft gel was mechanically crushed and filtered through a 125 ?m sieve. The residual mass of the gel (>125 ?m) was determined to be 1659 g. The gel mass was solvent exchanged with recycled ethanol (93%) and pH was measured to be between 6.65-9.06 (4 separate experiments). The last solvent exchange was performed with 100% fresh ethanol (final solvent concentration 94-98%) HCl (32%) was added to the alcogel (solution+gel) system until a pH of 0.96 (glass electrode) was reached. This translated to 0.7 wt % HCl (32%) in ethanol or 0.22 wt % HCl (absolute) in ethanol. This methodology should also work for TEOS based silica alcogels. Acidify the TEOS (CAS number: 78-10-4) gel with HCl to pH 1.0 before supercritical drying The acidified alcogel was dried at 60? C., 120 bar, 1 h to get an acidified hydrophilic aerogel. Surface area: 986 m.sup.2/g Pore volume: 5.42 cm.sup.3/g Bulk density: 0.058 g/cm.sup.3 Contact angle: 0? 1.1.2 2 g acidified hydrophilic aerogel was packed in a filter and place in a closed vessel at 80? C. 5 g HMDSO was added to the vessel. After 30 min the aerogel was removed and observed to be hydrophobic (floats on water). Surface area: 690 m.sup.2/g Pore volume: 4.36 cm.sup.3/g Bulk density: 0.063 g/cm.sup.3 Contact angle: 149.5?
1.2 Hydrophobic Silica (Aerogel) from Commercial Hydrogels (Example Wet KC-Trockenperlen Beads) KC Trockenperlen Hydrogel (CAS Number 1327-36-2) (BASF) with a pH of 4 was solvent exchanged with ethanol (final solvent concentration 94-98%).
1.2.1 Step A The alcogel was dried at 60? C., 120 bar, 1 h to get a hydrophilic aerogel. Surface area: 862 m.sup.2/g Pore volume: 4.92 cm.sup.3/g Bulk density (crushed): 0.113 g/cm.sup.3 Contact angle: 72?
1.2.2 Step B 5.2 g of above hydrophilic aerogel was packed in a filter and place in a closed vessel (250 ml) at 80? C. 13.4 g HMDSO+2.3 g ethanol+0.3 g water mixture was added to the vessel. After 30 min the aerogel was removed and observed to be hydrophobic. Surface area: 647 m.sup.2/g Pore volume: 4.0 cm.sup.3/g Bulk density: 0.123 g/cm.sup.3 Contact angle: 141.5?
1.2.3 Hydrophobization Variations: Step B1: 4.3 g of aerogel from example 1.2 Step A was evacuated and afterwards packed in a filter and place in a closed vessel (250 ml) at 80? C. 11.07 g HMDSO added to the vessel. After 90 min the aerogel was removed and observed to be hydrophobic. Surface area: 592 m.sup.2/g Pore volume: 2.56 cm.sup.3/g Contact angle: 138.8? Step B2: 4.61 g of aerogel from example 1.2 Step A was evacuated and afterwards packed in a filter and place in a closed vessel (250 ml) at 80? C. 22.9 g of recycled HMDSO/ethanol/water mixture was added to the vessel. After 90 min the aerogel was removed and observed to be hydrophobic. Contact angle: 148.7?
1.3 Hydrophobizing Commercial Precipitated and Fumed Silica (Example Sipemat 2200) 1.3.1 The surface area of commercial silica (Sipemat 2200, CAS number 112926-00-8 or CAS number 7631-86-9) was measured as follows Surface area: 168 m.sup.2/g Pore volume: 1.6 cm.sup.3/g Bulk density: 0.211 g/cm.sup.3 Contact angle: 5? 1.3.2 This Sipernat 2200 precipitated silica was dispersed in 100% ethanol and HCl (32%) was added (alcogel solution pH<0.1). The acidified alcogel was dried at 60? C., 120 bar, 1 h to get an acidified hydrophilic aerogel Surface area: 214 m.sup.2/g Pore volume: 1.3 cm.sup.3/g Bulk density: 0.311 g/cm.sup.3 Contact angle: 5? 1.3.3 2 g acidified hydrophilic aerogel was packed in a filter and place in a closed vessel at 80? C. 5 g HMDSO was added to the vessel. After 30 min the aerogel was removed and observed to be hydrophobic (floats on water). Surface area: 181 m.sup.2/g Pore volume: 1.39 cm.sup.3/g Bulk density: 0.262 g/cm.sup.3 Contact angle: 144? Fumed silica (Aerosil, CAS number 112945-52-5) could also be hydrophobized
1.4 Hydrophobic Silica (Aerogel) from Sodium Silicate Precursor (Formsil) Solution 1: 300 g Formsil (Sodium metasilicate nonahydrate; CAS Number 13517-24-3; Mwt 284) powder was mixed with 750 g deionized water and stirred for 2 h at 50? C. until a clear solution was obtained. The solution was sprayed into supercritical CO2 at 60? C. and 80 bar. After spraying the solution, the autoclave system was depressurized and silica hydrogel was obtained. The pH of the system was between 7.0-9.5. Silica aerogel density adjustments can be made by adjusting the water amount. The gel mass was solvent exchanged with recycled ethanol (93%) and pH was measured to be between 6.9-8.5. The last solvent exchange was performed with 100% fresh ethanol (final solvent concentration 94-98%) The alcogel was dried at 60? C., 120 bar, 1 h to get an hydrophilic aerogel Surface area: 719 m.sup.2/g Pore volume: 6.16 cm.sup.3/g Bulk density: 0.040 g/cm.sup.3 Contact angle: 0? 2 g hydrophilic aerogel was packed in a filter and place in a closed vessel at 80? C. 5 g hydrolyzed HMDSO or trimethylsilanol (TMS) was added to the vessel. After 30 min, the aerogel was removed and observed to be hydrophobic (floats on water). Surface area: 624 m.sup.2/g Pore volume: 4.98 cm.sup.3/g Bulk density: 0.058 g/cm.sup.3 Contact angle: 142?

LITERATURE CITED

(4) WO 2012/041823 A1 WO 00/24799 A1