SU1735317A1 - Method of obtaining low-molecular dimethyl syloxane rubber - Google Patents

Abstract

Use: manufacture of rubber products operating in the air in the range from (-50) to (+250) ° C. SUMMARY OF THE INVENTION: hydrolysis of dimethyldichlorosilane, neutralization of the hydrolyzate, its depolymerization, heating of the de-polymerisate to 80-85 °, drying it under vacuum at least 0.08 MPa, spraying the depolymerisate onto the surface heated to 90-95 ° ; C, and holding on this surface for 2-4 seconds, polymerizing the depolymerizate, stabilizing the obtained polymer, removing the volatile and filtering. Table 2, 15, etc.

Description

The invention relates to the production of siloxane rubbers used for the manufacture of rubber products operating in air at temperatures ranging from -50 to + 250 ° C and having high dielectric properties.

A known method for producing organocyclosiloxanes by hydrolyzing organochlorosilanes in the presence of oxides of metals of groups I and II of the periodic system: CuO, PbO, HdO, MgO, BeO when the initial reagents are heated at boiling point in anhydrous conditions with or without a solvent. According to this method, it is necessary to carry out the process with long boiling. The group II metal emitted in this case is an energetic catalyst for the rearrangement of siloxane bonds. This, under the conditions of the method, results in a decrease in the yields of cyclosiloxanes, especially cyclotrisiloxanes, having a stressed ring, and makes it unsuitable for

preparation of cyclosiloxanes containing functional groups.

Closest to the present invention is a method for producing low molecular weight dimethylsiloxane rubber, including hydrolysis of dimethyldichlorosilane, neutralizing the hydrolyzate, depolymerizing it, drying the depolymerisate under vacuum with at least 0.08 MPa in a fixed-bed reactor while simultaneously heating to 130 ° C with deaf vapor. depolymerizate, stabilization of the polymer obtained, removal of volatile therefrom and filtration.

A significant disadvantage of this method is its long duration due to the low productivity of the depolymerisate drying stage. According to the existing technology, the depolymerisate is dried with a fixed thick layer. Moisture is evaporated only from the open surface of the layer, therefore, the evaporation rate is determined by heat supply to

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last. Heat transfer coefficients at low-intensity random circulation of the dried depolymerization due to the difference in densities of more heated and less heated particles are low. Accordingly, the intensity of drying will also be small. The layer of depolymerisate, in addition, has significant internal resistance to heat and mass transfer (low diffusion and thermal diffusivity).

The aim of the invention is to intensify the process of obtaining rubber.

This goal is achieved by the fact that, according to the method for producing low molecular weight dimethylsiloxane rubber, including hydrolysis of dimethyl dichlorosilane, neutralizing the hydrolyzate, a sample, depolymerization, drying the depolymerisate under vacuum at least 0.08 MPa with simultaneous heating, polymerization of depolymerization, a mixture of hydrogen. removing volatiles from it and filtering, the depolymerisate is heated to 80-85 ° C before drying and the drying is carried out by spraying the depolymerisate onto the surface heated to 90-95 ° C, and you erzhkoy on the surface 2-4.

The method is carried out as follows.

Getting low molecular weight rubber SKTN-A.

The hydrolysis of dimethyldichlorosilane (DDS) is carried out with filtered water at a ratio by volume of water and DDS (1.3-1.9): the resulting hydroxyl derivatives (silanols) are condensed. In the process of hydrolysis, heat is generated due to the dissolution of the hydrochloric acid formed. Increasing the temperature above 60 ° C promotes the formation of a product with a high content of high molecular weight cyclosiloxanes. Such a hydrolyzate has an increased viscosity, which makes it difficult to separate it from the acid and subsequent neutralization, and also leads to the formation of emulsions upon neutralization. Therefore, the operation of hydrolysis is carried out with continuous stirring and cooling with brine of the reaction mass.

The products of hydrolysis are: a hydrolyzate, which is a mixture of 50% cyclic and 50% linear siloxanes, and hydrochloric acid. Separation of products is carried out in a settling tank (Florentine vessel) due to the difference in the density of d of the hydrolyzate 960 kg / m3, d of the acid 1120 kg / m

After separation of the products, the acidity of the hydrolyzate is determined and carried out

neutralizing solid soda ash. The amount of loaded soda exceeds the calculated value by 2 times. At the end of the neutralization in the reaction mass serves water. Water provides the dissolution of salts formed during neutralization. The amount of water is 10 times the amount of soda. The process is carried out with stirring and heating to 80 ° C.

Neutral hydrolyzate and washings are poured into the sump. After settling, the bottom layer — an aqueous solution of salts — is drained to the sewage system, and the remaining hydrolyzate is analyzed for neutrality. Upon completion of the analysis, the hydrolyzate is fed for depolymerization,

The essence of the depolymerization process is as follows. Under the action of alkali, when heated to a temperature of not more than 130 ° C and under vacuum of at least 730 mm Hg, non-volatile linear siloxanes are rearranged into low-molecular volatile siloxanes discharged from the reaction zone. In these conditions, hrifunctional, monofunctional, silicon hydride impurities polymerize and remain in a cube, which allows for additional purification of cyclosiloxanes from impurities.

The amount of loaded caustic potash in the first load is 1% of the loaded hydrolyzate. In subsequent downloads of the hydrolyzate KOH serves in an amount of not more than 0.2% by weight of the hydrolyzate. The depolymerization takes place under vacuum and with continuous stirring. Upon reaching a vacuum of 730 mm Hg. heating is turned on.

The depolymerized vapors formed during the reaction flow into a surface condenser where they condense. Condensed depolymerisate is collected in a collection.

In the process of condensation, as well as during transportation and storage of the depolymerizate, water enters it. The water content usually ranges from 4-5%. To ensure high quality rubber produced on the basis of depolymerizat, the moisture content in the latter should not exceed 0.01%,

Moisture removal is carried out in a vacuum spray dryer. The pre-depolymerisate is heated in a pipe-type heat exchanger in a pipe to 80-85 ° C. From the heat exchanger, the depolymerisate is fed into the spray chamber through mechanical centrifugal nozzles. When the depolymerisate is injected into the chamber, its pressure drops. In this case, the heated solution is sprayed, and the moisture is partially evaporated and removed from the chamber as vapor. The resulting product with low humidity falls on a heat transfer surface having a temperature of 90-95 ° C, and, by means of a stack, is finally dried. The contact time of the product particles with the heat supply surface is limited to 2-4 s. During the spraying process, a vacuum of at least 0.08 MPa is maintained in the chamber. The water vapor formed during the drying process is trapped in the condenser. The total drying time is 1.6-1.75 hours, while in the known method it is 20-24 hours.

The dried depolymerizate is analyzed for moisture, and if it is normal, the depolymerizate is sent for polymerization. The depolymerizate is the starting product for the synthesis of CTPA-A. The polymerization process is carried out by heating the reaction mass. Upon reaching the specified temperature, a catalyst — potassium hydroxide in the form of a 4N solution — is introduced into the mass.

The molecular weight of the polymer is viscous and is controlled by the flow of water into the reaction mixture. The amount of water in the reaction mixture should be 0.05% -0.35%. Water, due to the termination of the reaction in the early stages or the destruction of an already formed polymer, promotes the formation of a lower molecular weight rubber. The polymerization process after the introduction of the catalyst takes at least another 15 minutes.

In the resulting polymer, the process of viscosity change continues under the action of the remaining catalyst and high temperature. To stop this process, the polymer is stabilized. The passivation of the catalyst is carried out with a concentrated mixture of stabilizer and polymer. The stabilizer is white soot U-333 or aerosil. The process is carried out with cooling and stirring of the reaction mass. Duration 30 min. Then a sample is taken for determination of viscosity and volatile content.

The conversion of cyclosiloxanes during alkali polymerization is 82-88%. In order to improve the performance properties of the vulcanizates based on SKTN, the content of unconverted cyclosiloxanes in the polymer should be reduced by removing volatile.

Removal of volatiles is carried out by vacuum distillation when the polymer is heated to a temperature of not more than 160 ° C. To speed up the process of distilling volatiles from a polymer after distilling out the main amount of volatiles in

the reactor supplies water in the amount of 20 l / s, but not more than 40 l in one operation.

The volatiles removed from the polymer and water are condensed in water condensers. Trapped volatiles can be used.

to obtain low and high molecular weight rubbers without re-depolymerization.

The non-volatile polymer is sent for filtration to remove mechanical impurities.

The specific properties of SKTN-A elastomers make it possible to use them as thermal, moisture and electrically insulating casts for all kinds of

miniature and large-sized working units of machines, mechanisms, as well as for thermo-, electro- and vibration-proof sealing of various devices. On the basis of low molecular weight elastomers, various rubber compositions, in particular sealants and compounds, are infused from Goth.

Examples 1-15. Low molecular weight dimethylsiloxane rubber is prepared as described above. The modes of the process are given in table. 1, and the properties of the obtained rubbers - in table. 2

Claims (1)

Thus, in carrying out the process by reducing the drying time of the depolymerisate, the intensity of the process increases by more than 13 times without deteriorating the quality of the rubber produced. The method of obtaining low molecular weight dimethylsiloxane rubber, including hydrolysis of dimethyldichlorosilane, neutralizing the hydrolyzate, its depolymerization, drying the depolymerisate under vacuum at least 0.08 MPa with simultaneous heating, polymerization of the depolymerisate, stabilization of the resulting polymer, a template the fact that, in order to intensify the process, the depolymerization is heated to 80-85 ° С before drying, and the drying is carried out by spraying the depolymerized on the surface l, heated to 90-95 ° C, and exposure on this surface for 2-4 s. More than 85 92.5 4 82.5 Less than 90 5 82.5 More than S5 6 82.5 92.5 Less than 2 0.02-0.04 Less than 3.2 82.5 92.5 More than 4 0.007-0.009 More than 10 80 90 , 007-0,009 Over 8 , 025-0.03 Less than 3.2, 006-0.008 More than 9.5 , 02-0.04 Less than 3.2 , 007-0,009 More than 10 , 09-0.095 3.42 norm, its further use is unacceptable; viscosity is normal Humidity is normal; viscosity exceeds the norm, further use of the product is unacceptable Humidity exceeds the norm, the further use of the product is unacceptable; viscosity is normal Humidity is normal; viscosity exceeds the norm, its further use is unacceptable Humidity sates norm, further use of the product is unacceptable; viscosity is normal Humidity is normal; viscosity exceeds the norm, further use of the product is unacceptable Moisture and viscosity in nor .-. table 2