A novel 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

1-12. (canceled)

13: 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) 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, 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.

14: The process according to claim 13, 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.

15: The process according to claim 13, wherein the porous silica based compound is a silica based aerogel.

16: The process according to claim 15, wherein the silica based aerogel is obtained from a sodium silicate precursor, a silica hydrogel, a fumed silica, or a precipitated silica.

17: The process according to claim 13, wherein the composition (II) comprises hexamethyldisiloxane and an alcohol.

18: The process according to claim 13, wherein the composition (II) comprises hexamethyldisiloxane, ethanol, and optionally, water.

19: The process according to claim 13, wherein the composition (II) comprises hexamethyldisiloxane, ethanol, and optionally, dilute acid.

20: A treated porous silica based compound obtained or obtainable by the process according to claim 13.

21: The treated porous silica based compound according to claim 20, wherein the porous silica based compound is a silica based aerogel.

22: An article, comprising the treated porous silica based compound according to claim 20, wherein the article is an adsorbent, an additive for food, a catalyst support, or a thermal insulation.

23: A method, comprising: preparing the treated porous silica based compound according to claim 20 for a medical application, a pharmaceutical application, a cosmetic application, or for a sensor.

Description

EXAMPLES

[0105] The preparation methodology for above possibilities is given below.

1. Preparation Examples

[0106] 1.1 Hydrophobic Silica (Aerogel) from Sodium Silicate Precursor (Formsil) [0107] 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. [0108] Solution 2: 200 g (32 wt %) HCl was added to 1800 g water and stirred at room temperature. [0109] 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. [0110] (Silica aerogel density adjustments can be made by adjusting the water amount) [0111] The soft gel was mechanically crushed and filtered through a 125 μm sieve. The residual mass of the gel (>125 μm) was determined to be 1659 g. [0112] The gel mass was solvent exchanged with recycled ethanol (93%) and pH was measured to be between 6.65-9.06 (4 separate experiments). [0113] The last solvent exchange was performed with 100% fresh ethanol (final solvent concentration 94-98%) [0114] 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. [0115] 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 [0116] The acidified alcogel was dried at 60° C., 120 bar, 1 h to get an acidified hydrophilic aerogel. [0117] Surface area: 986 m.sup.2/g [0118] Pore volume: 5.42 cm.sup.3/g [0119] Bulk density: 0.058 g/cm.sup.3 [0120] Contact angle: 0° [0121] 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). [0122] Surface area: 690 m.sup.2/g [0123] Pore volume: 4.36 cm.sup.3/g [0124] Bulk density: 0.063 g/cm.sup.3 [0125] Contact angle: 149.5°
1.2 Hydrophobic Silica (Aerogel) from Commercial Hydrogels (Example Wet KC-Trockenperlen Beads) [0126] 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

[0127] The alcogel was dried at 60° C., 120 bar, 1 h to get a hydrophilic aerogel. [0128] Surface area: 862 m.sup.2/g [0129] Pore volume: 4.92 cm.sup.3/g [0130] Bulk density (crushed): 0.113 g/cm.sup.3 [0131] Contact angle: 72°

1.2.2 Step B

[0132] 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. [0133] Surface area: 647 m.sup.2/g [0134] Pore volume: 4.0 cm.sup.3/g [0135] Bulk density: 0.123 g/cm.sup.3 [0136] Contact angle: 141.5°

1.2.3 Hydrophobization Variations:

[0137] 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. [0138] Surface area: 592 m.sup.2/g [0139] Pore volume: 2.56 cm.sup.3/g [0140] Contact angle: 138.8° [0141] 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. [0142] Contact angle: 148.7° [0143] 1.3 Hydrophobizing commercial precipitated and fumed silica (Example Sipemat 2200) [0144] 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 [0145] Surface area: 168 m.sup.2/g [0146] Pore volume: 1.6 cm.sup.3/g [0147] Bulk density: 0.211 g/cm.sup.3 [0148] Contact angle: 5° [0149] 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 [0150] Surface area: 214 m.sup.2/g [0151] Pore volume: 1.3 cm.sup.3/g [0152] Bulk density: 0.311 g/cm.sup.3 [0153] Contact angle: 5° [0154] 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). [0155] Surface area: 181 m.sup.2/g [0156] Pore volume: 1.39 cm.sup.3/g [0157] Bulk density: 0.262 g/cm.sup.3 [0158] Contact angle: 144° [0159] Fumed silica (Aerosil, CAS number 112945-52-5) could also be hydrophobized
1.4 Hydrophobic Silica (Aerogel) from Sodium Silicate Precursor (Formsil) [0160] 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. [0161] 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. [0162] Silica aerogel density adjustments can be made by adjusting the water amount. [0163] The gel mass was solvent exchanged with recycled ethanol (93%) and pH was measured to be between 6.9-8.5. [0164] The last solvent exchange was performed with 100% fresh ethanol (final solvent concentration 94-98%) [0165] The alcogel was dried at 60° C., 120 bar, 1 h to get an hydrophilic aerogel [0166] Surface area: 719 m.sup.2/g [0167] Pore volume: 6.16 cm.sup.3/g [0168] Bulk density: 0.040 g/cm.sup.3 [0169] Contact angle: 0° [0170] 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). [0171] Surface area: 624 m.sup.2/g [0172] Pore volume: 4.98 cm.sup.3/g [0173] Bulk density: 0.058 g/cm.sup.3 [0174] Contact angle: 142°

LITERATURE CITED

[0175] WO 2012/041823 A1 [0176] WO 00/24799 A1