Process for the synthesis of hybrid allophane

Abstract

A process for preparing hollow particles of aluminosilicates having a spherical shape of allophane type which are hybrid at the core, comprising: (a) having, at ambient temperature, an aqueous medium containing at least one aluminum precursor and one silicon alkoxide in an Al/Si molar ratio varying from 1 to 3, (b) carrying out, with stirring, the alkaline hydrolysis of said medium with gradual addition of at least one base in a base/Al molar ratio of 2.3 to 3, (c) maintaining, on conclusion of the addition of all of said base, stirring at ambient temperature until said medium is obtained in the clear state, and (d) heating the solution obtained at a temperature varying from 50 to 150 C. for 2 to 8 days, the combined stages (a) to (d) are carried out within a reactor consisting of a material which is chemically inert with respect to the reactants and expected aluminosilicate.

Claims

1. Process for preparing hollow particles of aluminosilicates having a spherical shape of allophane type which are hybrid at the core, the process comprising: (a) having available, at ambient temperature, an aqueous medium containing at least one aluminum precursor and one silicon alkoxide in an Al/Si molar ratio ranging from 1 to 3, (b) carrying out, with stirring, the alkaline hydrolysis of said medium with gradual addition of at least one base in a base/Al molar ratio of 2.3 to 3, (c) maintaining, on conclusion of the addition of all of said base, the stirring at ambient temperature until a clear solution is obtained, and (d) heating the clear solution obtained at a temperature ranging from 50 to 150 C. for 2 to 8 days, wherein the combined stages (b) to (d) are carried out within one rector comprising a material which is chemically inert with respect to reactants used in the process and the particles of aluminosilicate, said hollow particles of aluminosilicates having at least 90% by number of the silicon atoms present on an internal face of a cavity functionalized by a hydrocarbon radical.

2. Process according to claim 1, in which the combined stages (a) to (d) are carried out consecutively within the same reactor.

3. Process according to claim 1, in which the material constituting the reactor is devoid of a silanol group and of a free fluorine atom.

4. Process according to claim 1, in which the material constituting the reactor is chosen from stainless steel, polypropylene and inert porcelains.

5. Process according to claim 1, in which the silicon alkoxide is of formula RSi(OR).sub.3 in which R is a C.sub.1 to C.sub.2 alkyl group and R is a saturated or unsaturated C.sub.1 to C.sub.2 hydrocarbon group.

6. Process according to claim 1, in which the silicon alkoxide is methyltrimethoxysilane (OCH.sub.3).sub.3SiCH.sub.3 and/or vinyltrimethoxysilane (OCH.sub.3).sub.3Si(CHCH.sub.2).

7. Process according to claim 1, in which the aluminum precursor is chosen from aluminum perchlorate Al(ClO.sub.4).sub.3, aluminum nitrate Al(NO.sub.3).sub.3 or aluminum chloride AlCl.sub.3.

8. Process according to claim 1, in which the Al/Si molar ratio of stage (a) is between 1.5 and 2.5.

9. Process according to claim 1, in which the base added during stage (b) is chosen from sodium hydroxide, potassium hydroxide or lithium hydroxide.

10. Process according to claim 1, in which the addition of the base during stage (b) is carried out at a flow rate of between 50 and 300 ml.Math.h.sup.1.

11. Process according to claim 1, in which the heating stage (d) is carried out at a temperature of between 70 and 150 C.

12. Process according to claim 1, wherein it comprises, following stage (d), a stage (e) of ultrafiltration of a solution obtained from stage (d).

Description

EXAMPLE 1

(1) Synthesis of (OH).sub.3Al.sub.2O.sub.3SiMe

(2) 32.46 g of Al(ClO.sub.4).sub.3.Math.9H.sub.2O are added to 700 ml of DI water in a vessel made of polypropylene or of stainless steel. The medium is left stirring for hour. 4.53 g of MeSi(OMe).sub.3 are subsequently added. The homogeneous reaction mixture is kept stirred at ambient temperature.

(3) A fresh sodium hydroxide solution (5.33 g of NaOH in 1333 ml of DI water) is subsequently added to a dropping funnel. The addition is carried out at the rate of 250 ml per minute. The reaction medium is clear after hour. The reaction medium is stirred at ambient temperature for 12 hours before being heated at 90 C. for 5 days in a vessel made of polypropylene or of stainless steel. After cooling at ambient temperature, the reaction medium is washed (diafiltered) and concentrated by ultrafiltration through a 10 kD membrane.

(4) The (OH).sub.3Al.sub.2O.sub.3SiMe yield with respect to the aluminum introduced is 76% (mean measurement over three batches: two in polypropylene bottles and one in a stainless steel vessel).

(5) At 10% by weight of (OH).sub.3Al.sub.2O.sub.3SiMe, the aqueous colloidal sol is completely transparent and clear. The surface potential, measured by zetametry, is +40 mV, which is comparable to a conventional allophane. The SAXS also reveals that hollow spheres are concerned.

EXAMPLE 2

(6) Synthesis of (OH).sub.3Al.sub.2O.sub.3Sivinyl

(7) The procedure selected is that of example 1, except that 50 ml of EtOH were added to the aqueous medium in order to bring about therein the solubility/dispersion of (OMe).sub.3Sivinyl.

(8) The (OH).sub.3Al.sub.2O.sub.3Sivinyl yield with respect to the aluminum introduced is 67% (obtained over three batches: 2 in a stainless steel vessel and 1 in a polypropylene vessel). The zeta potential is +37 mV.