GLYCOXY SILANES AS A SOURCE OF SILICA AND SILICATE PRECIPITATES

Abstract

The present invention discloses glycoxy silanes as a source of silica and silica precipitated by advantageous chemical reactions preferably beginning with biogenic silica. Alkoxy COS.sub.1 are hydrolyzed in a controlled fashion to nucleate formation of nanoparticles of silica. The growth rate of the particles is controlled by various parameters such that particles of known sizes, size distributions, specific surface areas and pore sizes and size distributions are recovered.

Claims

1. A method to precipitate silica comprising: neutralizing an amount of base in a solution comprising a silicon alkoxide containing 10-40 wt % dissolved silica, wherein alkoxy groups are selected from the group consisting of 1,2; 1,3; 1,4 diols; and triols; and polyols and mixtures thereof; hydrolyzing alkoxy COSi bonds; recovering precipitated silica by filtration; and recycling recovered filtrate into a dissolution process, wherein silica is dissolved in a base to produce water soluble alkoxysilanes.

2. The method of claim 1, wherein water is added to reduce pH.

3. The method of claim 1, further comprising the step of controlling the pH of the solution to control a parameter selected from the group consisting of surface area, pore size, size distribution, and pore volume and combinations thereof.

4. The method of claim 1, wherein the neutralizing step comprises adding water and a sufficient amount of acid or CO.sub.2 gas to lower the pH below about 8 to control a parameter selected from the group consisting of surface area, pore size, size distribution, and pore volume and combinations thereof.

5. The method of claim 1, wherein the neutralizing step comprises adding a sufficient amount of acid to lower the pH below 5 and adding a second base to control a parameter selected from the group consisting of surface area, pore size, size distribution, and pore volume and combinations thereof.

6. The method of claim 5, wherein the second base is ammonium hydroxide or an ammonium salt and the precipitated silica is a crystalline solid structure.

7. The method of claim 1, wherein the neutralizing step comprises adding a sufficient amount of acid to lower the pH below 8 and adding a long chain alkyl ammonium salt and the precipitated silica is a crystalline solid structure.

8. The method of claim 1, wherein neutralizing the step of lowering the pH comprises adding a sufficient amount of acid to lower the pH below 5 and adding a second base comprising a short chain alkyl ammonium salt selected from the group consisting of (HOCH.sub.2CH.sub.2)N(CH.sub.3).sub.3Cl; N(CH.sub.3).sub.4Cl; (HOCH.sub.2CH.sub.2)N(CH.sub.3).sub.3OH; N(CH.sub.3).sub.4OH; and combinations thereof to yield (R.sub.4N)(OSiO.sub.1.5).sub.8

9. The method of claim 1, wherein the 1, 2 diol is ethylene glycol, and the 1,3 diol is propylene glycol or glycerol and combinations thereof

10. The method of claim 1, wherein the silicon alkoxide contains approximately 20-35 wt % dissolved silica.

11. The method of claim 1, wherein the recovering step is preformed at temperatures of 20 to 180 o C.

12. The method of claim 1, further comprising the steps of acid washing and drying the precipitated silica to produce silica with specific surface areas in excess of 400 m.sup.2/g and pore volumes of 0.5 to 1.5 cc/g.

13. The method of claim 1, wherein the precipitated silica is acid washed and dried to produce silica with purities ranging from 99% to 99.9999%.

14. The method of claim 1 wherein the precipitated silica is acid washed and dried to produce silica with water contents of 0.1-10 wt %.

15. The method of claim 1 further comprising the step of recycling a filtrate to recover the diols, triols or polyols.

Description

A BRIEF DESCRIPTION OF FIGURES

[0016] FIG. 1 is a flow chart of a prior art Precipitated silica production flowchart.

[0017] FIG. 2 is an FTIR spectrum of silica precipitated per the process described in Example 1.

[0018] FIG. 3 is a TGA/DTA of silica precipitated in acid water from Example 1.

[0019] FIG. 4 is an FTIR spectrum of silica precipitated per the process described in Example 2.

[0020] FIG. 5 is a TGA/DTA of silica precipitated in hot water from Example 2.

[0021] FIG. 6 is an FTIR spectrum of silica precipitated in hot water per the process described in Example 3.

[0022] FIG. 7 is a TGA/DTA of silica precipitated in accordance with Example 3.

[0023] FIG. 8 is an FTIR spectrum at silica precipitated per the process described in Example 4.

[0024] FIG. 9 is a TGA/DTA of silica precipitated in accordance with Example 4.

[0025] FIG. 10 is an FTIR spectrum of precipitated silica made by H.sub.2SO.sub.4 addition.

[0026] FIG. 11 is an FTIR of silica precipitated by acetic acid addition.

[0027] FIG. 12 is a TGA/DTA of silica precipitated by reverse acid addition when the acid is acetic acid.

[0028] FIG. 13 is an FTIR of silica precipitated by acetic acid addition.

[0029] FIG. 14 is a TGA/DTA of silica precipitated by reverse acid addition where the acid is acetic acid.

[0030] FIG. 15 is a TGA/DTA of silica made by reverse acid addition where the acid is acetic acid.

DETAILED DESCRIPTION OF INVENTION

[0031] It is well known that the rate of precipitation of silica can be controlled by pH, temperature and also solution viscosity, R. K. Iler, The chemistry of silica; John Wiley & Sons: New York, 1979, C. J. Brinker, G. Scherer Sol-Gel science: The Physics and Chemistry of Sol-Gel Processing, Academic Press, Boston, 1990, Sol-Gel Science and Technology; E. J. A. Pope, S. Sakka, L. C. Klein, Eds.; Amer. Cer. Soc., Ohio, 1997) which in turn controls the physical properties of the resulting precipitated silica. Control of viscosity in silica precipitation is not a traditionally used to control particle properties.

[0032] The reactions below enable the creation of precipitated silicas from glycoxysilanes.

##STR00004##

[0033] Thus, for example, the resulting mixture of glycoxysilane and silicon glycolate from reaction (9) can be treated with anhydrous acid to neutralize the base leaving pure Si(EGH).sub.4 as in reaction (10). Alternately, the as-formed reaction solution can be treated with excess water with or without added acid or CO.sub.2 to perform the reverse of reaction (9) and precipitate silica as seen in reaction (11). It is also possible to remove the salt impurities by ion exchange before or after precipitation to make high purity silicon glycolates and/or precipitated silica. The degree of purity will be defined by the care in which the impurities are removed and/or the purity of the reactants and vessels in which reaction is effected.

##STR00005##

[0034] The following examples illustrate several methods of precipitating silica.

EXAMPLE 1

Typical Silica Precipitation Using Aqueous Acid Precipitation (Silicon Glycolate Obtained from KOH Catalyzed RHA Extraction)

[0035] To a dry 12-L-reactor, equipped with a mechanical stirrer, was added 1600 g of silicon glycolate solution (20 wt % silica). Thereafter 2.6 L of aqueous acid pH<4 was added with vigorous stirring. After addition, the reaction mixture was stirred for an additional 30 min and the resulting precipitated silica filtered off. This recovered silica was stirred in methanol (15 h), then washed with a 10% HCl solution, filtered and washed with cold water. It was then dried at 65 C. for 3 days. The yields minus mechanical losses are 80% with typical specific surface areas (SSA=700 m.sup.2/g). The FTIR and TGA analyses are shown in FIGS. 2 and 3.

EXAMPLE 2

Silica Precipitation Using Hot Water Precipitation (Silicon Glycolate Solution Obtained from KOH Catalyzed RHA Extraction)

[0036] To a dry 12-L-reactor, equipped with a mechanical stirrer, was added 3265 g of concentrated silicon glycolate solution, CY (Clean Yield)21 wt %, with vigorous stirring to 4 L of water pre-heated to 80 C. The solution was stirred for 1 h, cooled down and filtered. The obtained silica was then stirred in 3 L of hot HCl (10%) for 2 h, filtered and washed with cold water giving an 85% yield of white powder after drying at 65 C. The SSA was found to be 225 m.sup.2/g. The FTIR and TGA analyses are shown in FIGS. 4 and 5. In this example, the particle surfaces are highly hydrated but this surface water can be removed by heating at 200 C. as suggested by the TGA data.

EXAMPLE 3

Silica Precipitation Using Hot Water Precipitation (Reduced Water) (Silicon Glycolate Solution Obtained from KOH Catalyzed RHA Extraction)

[0037] To a dry 12-L-reactor, equipped with a mechanical stirrer and a heating mantle, was added 1440 g of concentrated silicon glycolate solution, CY15 wt % with vigorous stirring to 2.5 L of water pre-heated to 80 C. The solution was stirred for 1 h, cooled down and filtered. The recovered filtrate can be recycled directly to dissolve biogenic silica per reaction (9). The obtained silica was then stirred in 2 L of hot HCl (10%) for 2 h and filtered and washed with cold water giving an 83% yield of white powder after drying at 65 C. overnight. The SSA was found to be 470 m.sup.2/g. The FTIR and TGA analyses are shown in FIGS. 6 and 7. In this example, the particle surfaces are highly hydrated but this surface water can be removed by heating at 200 C. as suggested by the TGA data.

EXAMPLE 4

Silica Precipitation with Hot Aqueous Acid (Silicon Glycolate Solution Obtained from NaOH Catalyzed RHA Extraction)

[0038] Water (700 ml) was added to a beaker and subjected to rapid stirring. This water was heated to 70 C. and then 236 g of silicon glycolate solution (CY=15 wt %) was added. The water/silicon glycolate mixture was heated to 80 with continuous agitation C for 1-2 h. Hydrochloric acid (10% solution) was added until the pH was adjusted to 5 and then the temperature was raised to 85-90 C. The mixture was stirred for another 75 min and then filtered. The isolated silica was washed with cold water until the pH was 7. The precipitated silica was then washed with methanol, filtered and dried at 60 C. for 24 h resulting in an 86 wt % yield of a white powder with SSAs of 180-250 m.sup.2/g. The FTIR and TGA analyses are shown in FIGS. 8 and 9.

EXAMPLE 5

Silica Precipitation Using Acid Addition (Silicon Glycolate Solution Obtained from NaOH Catalyzed RHA Extraction)

[0039] Distilled water (4.5 L) was introduced to a 12-L-reactor, equipped with a mechanical stirrer and heating mantle, and pre-heated to 80. Then, silicon glycolate solution (3570 g, CY8 wt %) was added with vigorous stirring. Sufficient sulfuric acid (10%) was added to bring the pH to 5. The mixture was then left stirring vigorously at 80 C. 1 h.

[0040] In an aging step, a basic agent (ammonium hydroxide) was added until the pH was adjusted to 8. Vigorous stirring was continued for 1 h more. Finally the mixture was cooled and filtered. The obtained white silica was then washed in hot methanol and then filtered. The white silica powder was oven dried at 70 C. for 2-5 days and then milled with zirconia media for 3 h. The FTIR and TGA analyses are shown in FIGS. 10 and 11.

EXAMPLE 6

Silica Precipitation Using Acetic Acid Addition Followed by Aging

[0041] Silicon glycolate (60 g, CY=15 wt. %) was added drop-wise to 160 mL of water pre-heated to 80 C. Acetic acid was added to decrease the pH to 5 and the suspension was left to stir for 1 h at 80 C. Ammonium hydroxide was then added to increase the pH to 8 and the suspension was left to stir for 1 h. Finally the suspension was cooled and filtered. The obtained white silica was then washed in hot methanol and then filtered. The silica powder was oven dried at 70 C. overnight and then dried at 250 C. for 35 min. The silica was obtained in 90% yield (8.1 g obtained, theoretical yield 9 g). The FTIR and TGA analyses are shown in FIGS. 11 and 12.

[0042] The precipitated silica may also be obtained as a zeolite. Zeolites are crystalline solids structures made of silicon, aluminum and oxygen that form a framework with cavities and internal channels where cations, water and/or small molecules may reside. Zeolites exhibit an open 3D framework made of SiO.sub.4 and AlO.sub.4 tetrahedra linked to each other by sharing all the oxygen atoms to form regular intra-crystalline cavities and channels of molecular dimensions. A defining feature of zeolites is that their frameworks are made up of 4-coordinated atoms forming tetrahedra. The framework structure may contain linked cages, cavities or channels, which are big enough to allow small molecules to enter. The system of large voids explains the consistent low specific density of these compounds. In zeolites used for various applications, the voids are interconnected and form long wide channels of various sizes depending on the compound. These channels allow the easy drift of the resident ions and molecules into and out of the structure. The aluminosilicate framework is negatively charged and attracts the positive cations that reside in cages to compensate for the negative charge of the framework.

EXAMPLE 7

Silica Precipitation Using Acetic Acid Addition (Silicon Glycolate Solution Obtained from NaOH Catalyzed RHA Extraction)

[0043] Distilled water (150 mL) was introduced to a 1-L-reactor, equipped with a magnetic stirrer and a heating mantle, and pre-heated to 80. Then, silicon glycolate solution (55 g, CY17 wt %) was added with vigorous stirring. Then, 15 mL of acetic acid (10%) was added drop-wise. The mixture was left stirring vigorously at 80 C. for 30 min. The mixture was cooled down and filtered. The obtained white silica was then washed in hot methanol and filtered. The silica powder was oven dried at 70 C. overnight, and at 250 C. for 30 min. The FTIR and TGA analyses are shown in FIGS. 13 and 14.

[0044] The following references disclose general principles of sol-gel processing of silica containing materials and are specifically incorporated by reference. [0045] 1. R. K. Iler, The chemistry of silica; John Wiley & Sons: New York, 1979. [0046] 2. C. J. Brinker, G. Scherer Sol-Gel science: The Physics and Chemistry of Sol-Gel Processing, Academic Press, Boston, 1990. [0047] 3. Sol-Gel Science and Technology; E. J. A. Pope, S. Sakka, L. C. Klein, Eds.; Amer. Cer. Soc., Ohio, 1997.

[0048] 4. Organic/Inorganic Hybrid Materials, MRS Symp. Ser. Vol. 519, R. M. Laine, C. Sanchez, C. J. Brinker, E. Giannelis eds. December 1998

[0049] 5. Organic/Inorganic Hybrid Materials 2000, MRS Symp. Ser. Vol. 628, R. M. Laine, C. Sanchez, and C. J. Brinker, eds. Mater. Res. Soc., 2001

[0050] 6. Organic/Inorganic Hybrid Materials 2002, MRS Symp. Ser. Vol. 726, C. Sanchez, R. M. Laine, S. Yang and C. J. Brinker, eds. Mater. Res. Soc., December 2002.

[0051] 7. D. W. Schaeffer, Science 243 (1989) 1023-1027.