Process for recovering organoalkoxysilane from polyorganosiloxan

Details Process for recovering organoalkoxysilane from polyorganosiloxan Process for recovering organoalkoxysilane from polyorganosiloxan

1996-06-27

1998-07-21

Dean, Ralph H.

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Process of treating scrap or waste product containing solid...

528 20, 528 12, C08G 7701

Patent

active

057836094

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

This invention relates to a process for recovering a useful silicon-containing compound such as an organoalkoxysilane and/or a polyorganosiloxane low molecular weight compound, etc. by using a high molecular weight polyorganosiloxane or a composition containing the same as a starting material. In particular, it relates to a process for recovering an industrially useful silicon-containing compound from the above starting material which is a waste.
By significant spread of silicone rubbers, the amount of a silicone rubber waste which is vulcanized (hereinafter used as a general term of a crosslinking reaction for forming a rubbery elastic material) has been increased significantly. Also, when a silicone rubber is molded, for example, when flashes are removed, a residue of a vulcanized silicone rubber containing relatively less impurities other than a filler is generated. Silicone rubbers have been used frequently for making a model or for reproduction, and wastes thereof have been increased. Particularly, among silicone rubbers, in a moisture curing type liquid silicone rubber which has been used as a sealing material for construction, an adhesive or sealing material for industrial use, etc., there are materials which are cured after opening a package without use, or cured on a masking tape and discharged. On the other hand, there have been generated wastes of a silicone oil which is deteriorated by being used as a heating medium or an insulating oil, a used silicone grease for preventing salt damage and air pollution by dust, a semi-cured product or a cured product of a silicone resin for coating or for electric insulation, etc. in addition to silicone rubbers.
All of these contain a high molecular weight polyorganosiloxane, and the silicone rubbers and silicone grease further contain a filler such as a silica, etc. Heretofore, most of them have been disposed of as industrial wastes.
In U.K. Patent No. 716,024, there has been disclosed a process for regenerating a vulcanized silicone rubber waste by partially hydrolyzing a vulcanized silicone rubber using superheated steam. However, in this process, a filler existing in said silicone rubber cannot be separated so that the process has a utility value at most for reusing it as a silicone rubber by mixing it with an unvulcanized silicone rubber.
In U.S. Pat. No. 2,673,843, there has been disclosed a process for partially depolymerizing a silicone rubber by carrying out treatment with acid anhydride at about room temperature. By this process, a mixture of volatile polysiloxane low molecular weight compounds (oligomers) can be obtained. However, before reusing it, complicated steps for removing an acid and, depending on the case, a filler are required.
In West German Patent No. 875,046, there has been disclosed a process for preparing a cyclic polydialkylsiloxane by heating a hydrolyzed mixture comprising a dialkylsiloxane unit and a monoalkylsiloxane unit in the absence of oxygen. However, there have been not described utilization of a vulcanized silicone rubber nor separation of a filler from a product in that case.
Voronkov has reported that a methylalkoxysilane and a methylalkoxysiloxane are produced by adding an alcohol and a tetraalkoxysilane to a polydimethylsiloxane such as octamethylcyclotetrasiloxane and heating the mixture by using potassium hydroxide as a catalyst (J. Gen. Chem. Vol. 28, p. 2,128 (1958), etc.). However, it has been not described to obtain an organoalkoxysilane from a composition prepared by formulating a filler into a high molecular weight polyorganosiloxane and from a cured product thereof. Also, it has been not described to recover a cyclic polyorganosiloxane low molecular weight compound, in addition to the organoalkoxysilane.
In Japanese Provisional Patent Publication No. 132590/1989, it has been disclosed that by reacting a polyorganosiloxane with an alkoxysilane in the presence of a titanium compound such as tetrabutyl titanate, an organoalkoxysilane which is different from the alkoxysilane used can

REFERENCES:
patent: 2392713 (1946-01-01), Wright et al.
patent: 3099671 (1963-07-01), George et al.
Database WPI Derwent Publications Ltd., London, GB; AN AN83-704016 & SU 952 895 (Shalaev B. I.), Aug. 23, 1982 * abstract * & SU 952 895 A (Shalaev B.I.) Aug. 23, 1982.
Patent Abstracts of Japan vol. 013, No. 384 (C-629), Aug. 24, 1989 & JP 01 132590 A (Toshiba Silicone Co Ltd) May 25, 1989 * abstract *.

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