JPS6332357B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing polysiloxane hydrolysis products and anhydrous hydrogen chloride by hydrolyzing chlorosilanes, including organochlorosilanes, in a stoichiometric amount of water. . More particularly, the present invention relates to a process for hydrolyzing dimethyldichlorosilanes to produce a resulting dimethylpolysiloxane hydrolysis product, anhydrous hydrogen chloride, and a saturated aqueous hydrogen chloride solution that can be recycled.

Prior to the present invention, dimethyldichlorosilane was hydrolyzed in the presence of excess amounts of water to produce dimethylcyclopolysiloxane whose basic composition was predominant and linear in nature, with the ends of the molecule A dimethylpolysiloxane hydrolysis product consisting of silanol-terminated dimethylpolysiloxane was prepared. An aqueous solution of hydrogen chloride is also produced, but
This contains significant amounts of recoverable hydrogen chloride. This hydrogen chloride is used to convert methanol to methyl chloride to make dimethyldichlorosilane in a direct process.

One way to recover hydrogen chloride from an aqueous solution of hydrochloric acid is to distill the mixture into HCl−H ₂ O, which has a constant boiling point.
The azeotrope was to be prepared together with anhydrous hydrogen chloride. Distillation to recover usable amounts of hydrogen chloride from the hydrolysis of dimethyldichlorosilane requires significant energy. An Introduction to The Chemistry of Silicones
Chemistry of The Silicones) 2nd edition (1951
), John Wiley & Sons, Inc.
Wiley & Sons Inc.), New York, E.
EGRochow states that if you supply an insufficient amount of water without using a common solvent, some of the dimethyldichlorosilane will completely hydrolyze to dimethylpolysiloxane, and some of it will dry out. This indicates that either the reaction does not occur or the end result is a linear polysiloxane that ends with a halogen atom. In addition, if the hydrolysis is carried out in the presence of excessive amounts of water, significant amounts of heat are generated in the exothermic reaction, which can lead to processing problems in individual situations.

The discovery underlying the present invention is that when dimethyldichlorosilane is hydrolyzed using substantially stoichiometric amounts of water, the anhydrous hydrogen chloride, together with a saturated solution of hydrogen chloride and water, is It lies in direct generation. Additionally, it has been found that additional benefits can be achieved if the saturated aqueous hydrogen chloride solution is recycled to the hydrolysis reactor. In addition, the dimethylpolysiloxane produced was found to be substantially identical to dimethylpolysiloxane hydrolysis products produced by prior art processes that utilized excess water. Furthermore, the anhydrous hydrogen chloride provided by the process of the invention separates from the hydrolysis mixture as it is formed during the reaction. Essentially, the reactor is used as a theoretical distillation plate and chlorosilane hydrolysis reactor.

The present invention comprises hydrolyzing chlorosilane in a stoichiometric excess of water to produce a polysiloxane hydrolysis product and an aqueous hydrogen chloride solution, heating the resulting aqueous hydrogen chloride solution resulting from the hydrolysis,
In the hydrolysis process of chlorosilanes, which consists of recirculating hydrogen chloride and consuming most of the input energy through the process of producing an HCl-water azeotrope with a constant boiling point and anhydrous hydrogen chloride, it is essentially a chemical process. Hydrolysis of chlorosilanes using stoichiometric equivalents of water yields virtually identical polysiloxane hydrolysis products and anhydrous and saturated aqueous hydrogen chloride solutions, thereby requiring the greatest amount of input energy. The present invention relates to an improved method for hydrolyzing chlorosilanes which avoids

To enable those skilled in the art to better understand embodiments of the invention, reference will now be made to the drawings. The hydrolysis reactor is shown at 10, which flows into a phase separator at 20 and a storage tank at 30. This tank can be equipped to recirculate the concentrated aqueous hydrogen chloride solution to the water supply. Although not shown, multiple storage tanks can also be used.

More specifically, the water is added to 12 of the hydrolysis reactor and the chlorosilane is added to 1 of the hydrolysis reactor.
1 and the rate is sufficient to maintain approximately stoichiometric equivalence between each feeder. For example, if the molar ratio in the feed mixture is D/
Can be maintained within the range of H ₂ O1/2.
Here, D is dimethyldichlorosilane. The chlorosilane that can be used in the practice of the invention can be represented by the following structural formula.

(R) _a (H) _b SiX _4-(a+b) Here, R is a C _{(1 to 6)} hydrocarbon group selected from an alkyl group or an aryl group, and a is from 1 to 3. b is an integer from 0 to 2, and a+b is from 1 to 3. Groups included within the range of R include, for example, a methyl group, an ethyl group, a propyl group, a phenyl group, etc., and when a is 2 or more, it may be the same as or different from R.

When chlorosilane and water come into contact, a reaction occurs immediately. However, temperatures ranging from about 25°C to 65°C can be used, while residence times with stirring, such as by a stirrer, can vary from about 0.1 to about 20 minutes. Reaction times can be longer or shorter if desired. Polysiloxane hydrolysis product is recovered from 21 and saturated aqueous hydrogen chloride solution is separated from 22 and stored in storage tank 3.
0. When the saturated aqueous hydrogen chloride solution is recycled, it is supplied from 31 to the water supply device and then to the hydrolysis reactor. Anhydrous HCl can be removed from 14 and also from 23 and 32 for further processing.

In order to enable those skilled in the art to better carry out the invention, the following examples are given by way of illustration, but without limiting the invention.

Example 1 Dimethyldichlorosilane (ie, D) and water were fed to a continuous hydrolysis reactor maintained at about 25°C. With an average residence time of about 5 minutes and a constant feed molar ratio of D to water of 1:2, the composition of the steady-state hydrolysis product is about 51.1% octamethyltetracyclosiloxane ( _D4 ),
About 66.4% was the total amount of cyclic polysiloxane. During the same operation, about the total amount of chlorine in D
66.2% came out as anhydrous HCl and 27.6% came out as aqueous HCl. The aqueous HCl solution could be recovered by recycling the aqueous stream back to the hydrolysis reactor.

Example 2 The operation is similar to Example 1, but if the temperature is maintained at approximately 60°C and the average residence time of the liquid is approximately 15 minutes, approximately 87% of the total amount of chlorine in D will be generated as anhydrous HCl. , about 12.5% came out as an aqueous HCl solution. The steady-state hydrolysis product composition is approximately ₄₀ % D4
Approximately 50% was the total amount of cyclic polysiloxane.

Example 3 In this run, dimethyldichlorosilane and
A stream of 37% by weight HCl was fed to a continuous hydrolysis reactor maintained at approximately 60°C. The average residence time of the liquid is approximately 12
When the molar ratio of D to water in the injection feeder was kept at 1:4, a hydrolysis product consisting of 52% D ₄ and 73% total cyclics was obtained. At the same time, almost 66% of the total amount of D chlorine supplied
was generated as anhydrous HCl.

Although the above examples are directed to only a few of the many variations of the process of the invention, the present invention covers a wide range of chlorosilanes as shown in the description preceding such examples. It should be understood that the present invention is directed to the hydrolysis of various species, and the conditions used in the hydrolysis mixture.

[Brief explanation of the drawing]

The drawings are process diagrams of the chlorosilane hydrolysis method of the present invention. 10 is a hydrolysis reactor, 20 is a phase separator, 30
is a storage tank for an aqueous hydrogen chloride solution.

Claims (1)

[Claims] 1. Hydrolyzing chlorosilane in a stoichiometric excess of water to produce a polysiloxane hydrolysis product and an aqueous hydrogen chloride solution, and heating the aqueous hydrogen chloride solution obtained from the hydrolysis. and the boiling point is constant
In a process for the hydrolysis of chlorosilanes, which involves recirculation of hydrogen chloride at the expense of most of the input energy, the process of forming an HCl-water azeotrope and anhydrous hydrogen chloride is essentially stoichiometric. Hydrolysis of chlorosilane in an equivalent amount of water yields a polysiloxane hydrolysis product that is substantially the same as that obtained using excess water, as well as anhydrous hydrogen chloride and a saturated aqueous solution of hydrogen chloride, thereby producing The improved method for hydrolyzing chlorosilanes described above in which the need for most input energy is avoided. 2. The method according to claim 1, wherein the saturated aqueous hydrogen chloride solution is recycled back to the hydrolysis reactor. 3. The method of claim 1 for recovering anhydrous hydrogen chloride from a hydrolysis mixture. 4. The method according to claim 1, wherein the chlorosilane is dimethyldichlorosilane.