GB2103196A

GB2103196A - Producing highly-stable hydrophobic silicates

Info

Publication number: GB2103196A
Application number: GB08122418A
Authority: GB
Inventors: Efraim Mendelovici
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-07-21
Filing date: 1981-07-21
Publication date: 1983-02-16

Abstract

A process for the preparation of a hydrophobic (alumino) silicate or refractory oxide comprises contacting a hydrophilic hydrous (alumino) silicate or refractory oxide with at least one hydrolysable organisilicon compound present in the vapour phase.

Description

SPECIFICATION A simple method for producing highly-stable hydrophobic silicates This invention relates to (alumino) silicates and refractory oxides; more particularly, this invention relates to a process for rendering hydrophilic (alumino) silicates and refractory oxides hydrophobic.

Procedures for rendering hydrophilic (alumino) silicates hydrophobic are known which are variations of the technique pioneered by Lentz, originally as an analytical tool. In this technique, the (alumino) silicate is at least partly digested in an aqueous/isopropanol solution of hydrogen chloride. The resulting material, comprising at least a surface layer of at least one silicic acid, is then reacted with an organosilicon compound, typically trimethylsilyl chloride, resulting in a hydrophobic material.

Such procedures are expensive in their use of substantial amounts of solvent and in the consequent materials separation and handling problems.

This invention seeks to provide a process where these difficulties are mitigated or obviated.

According, therefore, to the present invention there is provided a process for the preparation of a hydrophobic (alumino) silicate or refractory oxide which process comprises contacting a hydrophilic hydrous (alumino) silicate or refractory oxide with at least one hydrolysable organosilicon compound present in the vapour phase.

Preferably, the hydrophilic hydrous (alumino) silicate or refractory oxide is finely-divided.

Suitably, the hydrolysable organosilicon compound comprises a hydrocarbyl halosilane of the formula: R1R2R3R4Si Wherein: R1,R2,R3 and4, which may be the same or different, each represent an unsubstituted or substituted hydrocarbyl group or a halogen atom with the proviso that not all of the R1,R2,R3 and R4, may represent a halogen atom. Preferably, the or at least one hydrocarbyl group is a substituted or unsubstituted, especially unsubstituted alkyl group. Particuiarly preferred such hydrocarbyl groups include unsubstituted C, to C4 alkyl groups, especially methyl.Suitably, the or at least one halogen atom is a chlorine or bromine atom, preferably a chlorine atom; where 2 or 3 of the R; represent halogen atoms both chlorine and bromine may be present. Dimethyldichlorosilane and methyltrichlorosilane are particularly preferred such compounds.

In accordance with a preferred feature of the invention a mixture of hydrolysable organosilicon compounds is used, for example a mixture of a dihalo and a trihalo compound such as dimethyldichlorosilane with methyltrichlorosilane. Good results have been obtained with such mixtures wherein the weight ratio of the components is from 5:1 to 1:5, preferably from 3:1 to 1:1, especially about 2:1 (herein referred to as "OCS" mixture).

Preferably the hydrophilic hydrous (alumino) silicate or refractory oxide is agitated during contact with the hydrolysable organosilicon compound.

By "(alumino) silicate" we mean herein a natural or synthetic silicate or aluminosilicate.

By "hydrous" we mean that the (alumino) silicate or refractory oxide comprises water, whether chemically bound or "lattice wate".

Examples of suitable hydrous (alumino) silicates include asbestos minerals which include both amphibole forms such as tremalite, amosite, crocidolite and the serpentine form crysotile; clays such as kaolinite and metakealinite; talc including steatite; and diatomaceous earth.

Examples of suitable refractory oxides include alumina, silica and titania.

By "finely-divided" we mean that the hydrous material is either particulate or, where fibrous, comminuted so that a felt of material is farmed.

Preferably, the surface area of the hydrous material is greater than 10 m2/g, preferably greater than 1 5 m2/g.

Where the hydrous material has a low water content or surface area it may be necessary, to achieve the desired degree of hydrophobicity, to make several treatments with the hydrolysable organosilicon compound.

The amount of OCS needed is partly related to the water (H20) contained by the hydrous material. About 1 g of H20 is necessary for the hydrolysis of 3 g OCS, but an excess of OCS shouid be present to ensure that the process is effective. The contact may be effected at any temperature at which the OCS is present as vapour and substantially undecomposed. Ambient temperature is very suitable.

As a result of this contact, a thin layer of organopolysiloxane is thought to coat the surface of the original hydrous material. The existence of the coating layer is inferred from the decrease of the specific surface area (So) of the treated solid.

Thus, i.e. the surface areas (BET) of crysotile before and after the OCS exposure treatment, are 16.73 and 4.63 m2/g respectively.

The characteristic and size of the polymers which are formed on the surface of the original hydrous material depend on the functionality of the starting silane monomers as well as on the nature of the material's surfaces (H20, So, porosity and catalytic capacity for example).

In our simple, fast and economic procedure, the hydrophobic materials which are obtained maintain a very tenacious and stable film of organopolysiloxanes even at high temperature and in the presence of water, acid or organic solvents.

The following Examples illustrate the invention.

Example 1 (a) Five grams of fine powdered Venetian talc were conditioned at 75% Relative Humidity with a saturated KCI solution. The talc was spread out on a watch glass and put in a vacuum desiccator. The desiccator was then evacuated to a tension of 1 50 mm Hg. Maintaining this vacuum, the desiccator was disconnected from the pump and then connected through a glass stopcock to a flask or ampoule containing OCS. The stopcock was then carfully opened so that OCS evaporated and penetrated the talc. After at least ten minutes contact, the desiccator was disconnected and air admitted until the HCI vapours were driven out (a strip of pH test-paper should indicate 7). The resulting product is mostly hydrophobic and organophilic.The organophilic test is positive when i.e. in a water-n butanol system, the solid concentrates in the alcohol layer.

(b) The same treatment of the talc was etfected on a bigger scale by substituting the glass desiccator for a rialgene cylinder of 25 litres capacity, covered by a lid fitted with a stopcock for evacuation or admission of gas.

Thus, about 2 Kg of talc conditioned at high Relative Humidity, (RH) were placed into the cylinder; then upon evacuation, 10 g of gaseous OCS were driven in. The stopcock was then closed and the cylinder was horizontally laid on a Eberbach type shaker, and shaken for at least 10 minutes at a vigorous speed. After the admission of air into the cylinder the lid was removed and the substrate shaken in a hood until the HCI vapours were driven out (pH test-paper).

The resulting talc is unctuous, mostly hydrophobic, and organophilic. If this talc is to be used for cosmetic purposes, it may be sterilized by exposure to an ultra-violet lamp. This treatment, adequately carried out, has proved to remove bacteria and fungi which may contaminate the unsterilized powder, with no deteriment to its hydrophobic properties.

The hydrophilic talc varieties used in this invention were obtained from Merck (DAB) and Hopkin Williams (UK). When hydrophilic talc is shaken with water in a test tube, the bulk of the solid sinks to the bottom of the tube. The opposite occurs with hydrophobic talc.

Example 2 Chromosorb W, 60/80 mesh (Johns Manville) was treated in similar experimental conditions as those described in Example 1(a).

The resulting solid is 100% hydrophobic and organophilic, keeping these properties if heated in air until 425 cm. or if refluxed with benzene in a Soxhlet apparatus for 24 hours.

Example 3 Kaolinite purchased from Wards (NSE) and which passes a 100 mesh sieve, having an initial H20 content of 1.8% and So about 20.5 m2/g, was treated under experimental conditions similar to those described in Examples 1 (a) and (2). The resulting solid is 100% hydrophobic and organophilic and keeps these properties if heated in air at no more than 4500C. or if refluxed with benzene in a Soxhlet apparatus for 24 hours. The hydrophobic clay contains 2.56% of carbon whereas the hydrophilic kaolinite 0.63% carbon.

Infrared absorption spectra (KBr pellets) of the modified clay, show in addition to the absorption bands due to kaolinite, frequencies at 1,260 and 800 cm~1 attributed to Si-C vibrations. The So of the mineral decreases about 50% with the OCS coating treatment.

Example 4 Fine powdered metakaolinite from Georgia (USA) was treated as described in Examples 1 (a) and 3, but left in contact with the OCS vapors preferably over 24 hours in a closed vessel. The resulting product is organophilic and mostly hydrophobic, being stable until 3000C temperature.

Example 5 107 grams of crysotile-asbestos fibers (Canadian variety) > 2 mm, were conditioned to 75% RH, then placed in the nalgene cylinder of 25 litres, covered by a lid fitted with a stopcock for evacuation or admission of gas. The cylinder was evacuated by a mechanical pump reaching about 200 mm vacuum. Maintaining this vacuum the cylinder was disconnected from the pump and then connected through a stopcock to the ampoule which contained OCS. The stopcock was carefully opened and the gaseous OCS were driven into the cylinder. After closing the stopcock, the cylinder was horizontally shaken for 10 minutes. Then, air was let into the cylinder and the lid removed. The mineral was then ventilated in the hood in order to eliminate the HCI vapours (pH indicator test-paper). The resulting fibers are organophilic and 100% hydrophobic.Carbon micro-analysis shows an increase in the carbon content, i.e. 1.22% for the hydrophobic product versus 0.77% (probably impurities) in the unmodified crysotile.

Example 6 300 g of "woolly" long fiber crysotile-asbestos (purchased from Hopkins Williams reagents, Britain) were placed into the nalgene cylinder.

Upon evacuation, 1.2 g of OCS were driven in.

Then, the cylinder was shaken vigorously for about 10 minutes. After the admission of air into the cylinder through the stopcock, the lid was removed and the substrate ventilated in the hood, by shaking the solid in the cylinder until the pH test-paper indicated 7.

The same method can be used for processing bigger amounts of material.

The resulting 100% hydrophobic product contains 1.35% carbon (0.35% in the starting material). The infrared spectrum of the hydrophobic crysotile exhibits again the absorptions at 1,260 and 800 cm-l,in addition to the absorptions of the untreated material.

A careful magnesium analysis of the hydrophobic fibers gave the same value as the starting material. This means that no brucite is removed from the octahedral layer by the OCS treatment, as in the procedure employed in liquid phases, in order to render crysatile hydrophobic.

The low carbon (hydrophobic) asbestos described in this invention are about 2 and 2.5 times more stable to acid attack than the HMD derivatives (quoted in page 1) and unmodified crysotile-asbestos respectively. This may be deduced from the weight loss results, when the corresponding products were shaken for several hours with N HCl. On the other hand, chemical analysis of the magnesia extracted by the HCI attack from the different fibers aforementioned, indicates a similar trend.

The low carbon asbestos we describe in this invention retain their hydrophobic properties after being heated in a furnace (in air) until 5200C, whereas the high carbon asbestos obtained by other methods (aforementioned in page 1) lose their hydrophobic properties at about 4000C.

These products obtained by my one-step procedure are quite hydrophobic and very stable; it means that the solids have not at all tendency to be wetted by water and seem to preserve this property permanently. Thus, the crysotileasbestos, for instance, are still hydrophobic after ten years of preparation. As well, the hydrophobic fibers are not wet when kept in contact with sea water at about 50C and < 50C. In an oil-water system the hydrophobic fibers are not at all wetted by water but wetted by the organic liquid.

As well, in an oil-sea water system, all the hydrophobic silicates obtained by my procedure disperse in the oily phase. The unmodified hydrophilic silicates do not show the same behaviour.

Claims

1. A process for the preparation of a hydrophobic (alumino) silicate or refractory oxide which process comprises contacting a hydrophilic hydrous (alumino) silicate or refractory oxide with at least one hydrolysable organosilicon compound present in the vapour phase.

2. A process according to Claim 1 wherein the hydrophilic hydrous (alumino) silicate or refractory oxide is finely-divided.

3. A process according to Claim 1 or 2 wherein the hydrolysable organosilicon compound comprises a hydrocarbyl halosilane of the formula: R1R2R3R4Si wherein R1, R2, R3 and4, which may be the same or different, each represent an unsubstituted or substituted hydrocarbyl group or a halogen atom with the proviso that not all of R1, R2, R3 and R4 may represent a halogen atom.

4. A process according to Claim 3 wherein the or at least one hydrocarbyl group is an unsubstituted C, to C4 alkyl group.

5. A process according to Claim 3 or 4 wherein the or at least one halogen atom is a chlorine atom.

6. A process according to Claim 3, 4 or 5 wherein a mixture of hydrolysable organosilicon compounds is used.

7. A process according to Claim 6 wherein the mixture comprises a dihalo and a trihalo compound.

8. A process according to Claim 7 wherein the weight ratio of the components is from 5:1 to 1 :5.

9. A process according to Claim 8 wherein the mixture comprises dimethyldichlorosilane and methyltrichlorosilane in a weight ratio from 3:1 to 1:1.

1 0. A process according to any preceding claim wherein the hydrophilic hydrous (alumina), silicate or refractory oxide is agitated during contact with the hydrolysable organosilicon compound.

11. A process according to any preceding claim wherein the hydrophilic hydrous (alumino) silicate comprises asbestos, clay, talc or diatomaceous earth.

1 2. A process according to any preceding claim wherein the hydrophilic hydrous refractory oxide comprises alumina, silica or titania.