NL8301315A - PROCESS FOR PREPARING METHYL CHLORO SILANES. - Google Patents

Description

P&C, A

S 2348-1235 Ned / LE / WVR

Short designation: Process for preparing methylchlorosilanes.

The invention relates to a process for preparing methylchlorosilanes by reacting particulate silicon and methyl chloride in the presence of a copper and silicon-containing catalyst. More particularly, the invention relates to the use of particulate silicon which has been contacted with a mixture of partially oxidized copper and copper formate in the preparation of methylchlorosilanes.

In the past, methyl chlorosilanes have been prepared by direct conversion of particulate silicon and methyl chloride in the presence of metallic copper or silver as. catalyst, while copper chloride or alloys of the above metallic catalysts are also frequently used, see Rochow, Chemistry of the Silicones, 2nd Edition (1951), pp. 36-46, John Wiley & Sons, New York. In addition to dimethyldichlorosilane, a variety of other silanes can be formed, for example, tetramethylsilane, trimethylchlorosilane, methyltrichlorosilane, silicon tetrachloride, trichlorosilane, methyldichlorosilane and dimethylchlorosilane.

In addition to dimethyldichlorosilane, which is the preferred methylchlorosilane of the invention, "crude" is formed in the formation of the crude methylchlorosilane. The term "residue" as used herein refers to products in the crude methylchlorosilane which have a boiling point above 70 ° C at atmospheric pressure.

The residue consists of materials such as disilanes, for example symmetrical 1,1,2,2-tetrachlorodimethyl-30 disilane, 1,1,2-trichlorotrimethyldisilane, disiloxanes, disilraethylenes and other high boiling compounds, for example trisilanes, trisiloxanes, trisilethylene, etc.

It has been found that certain components in the residue defined above, in particular 1,1,2,2-tetrachlorodimethyl-35-disilane and 1,1,2-trichlorotrimethyldisilane, can be "cleaved" according to U.S. Patent 2,709,176, French Patent 1,447,304 or 8301315

• 'V

- 2 - A <

Japanese Patent 1,783,419, to form useful methyl chlorosilane monomers. The term "cleavability" as used herein means the weight percent of the above-mentioned disilanes in the residue. The "cleavage" of the above-mentioned disilanes can be accomplished by continuously stirring the residue in a reactor vessel using a tertiary amine, for example tributylamine, continuously feeding anhydrous hydrogen chloride.

Except in preparing methyl chlorosilanes by direct conversion between particulate silicon and methyl chloride in the presence of a copper-containing catalyst to form crude methyl chlorosilanes with a reduced weight percent residue, based on the total weight of the crude methyl chlorosilane, and the splittability of this residue (as defined above), is also interested in the T / D ratio of the crude methylchlorosilane. The T / D ratio is the ratio between methyltrichlorosilane and dimethyldichlorosilane in the crude methylchlorosilane obtained as reaction product. Therefore, an increase in the T / D ratio means that the formation of the preferred dimethyldichlorosilane decreases.

As described in U.S. Patent Application No. 25,288,175, improved results can be obtained in the reaction between particulate silicon and methyl chloride, source of the catalyst using partially oxidized copper as copper. As disclosed in U.S. Patent Application No. 288,175, the use of partially oxidized or cemented copper with a particular particle size distribution and minimal surface area (determined by the BET method) as a catalyst provides an improvement in selectivity in terms of T / D ratio in the reaction between particulate silicon and methyl chloride.

The partially oxidized copper used in U.S. Patent Application 288,175 can be prepared by passing a copper compound solution over scrap iron resulting in the deposition of 8301315 V * 4-3 of metallic copper in the form of a fine precipitate. The precipitate is then subjected to a pyrometallic process, which results in partial oxidation of the cemented copper. In the -5 partially oxidized copper, a total of 77-87 wt% copper may be present in bonded or unbound form, and preferably 83 wt%. The total reducing. power of the partially oxidized copper is preferably 75-80, but a range of 70-90 can be used. The total reducing power "TRP", the percentage of cuprous oxide, can be determined by titration with a standard iron sulfate solution using Ferroin as an indicator.

The metallic copper content of the -15 partially oxidized copper can be 10-20% by weight of the partially oxidized copper? this content is preferably 15-20% by weight. The partially oxidized copper may contain 30-50 wt% cuprous oxide, while 39-50 wt% cuprous oxide is preferred. The partially oxidized copper may contain 30-50 wt.% Cuprous oxide, while 35-43 wt.% Cuprous oxide is preferred.

The partially oxidized copper used according to the invention can further be characterized as partially oxidized copper particles with a specific surface area of at least 3.5 m / gram, determined according to the nitrogen> adsorption method of Brunauer, Emmett and Teller,

You. Am. Chem. Soc., Vol 60, 309 (1938). Furthermore, the partially oxidized copper used as a catalyst has the following particle size distribution; the diameter of the particles is less than 35 microns and more than 0.7 microns, while 50% of the particles are 4-7 microns in diameter and the average diameter of the particles is from 3.0 to 5.5 microns.

In general, the chloride content of the partially oxidized copper ·. egg. 0-0.2 wt%; this content is preferably 0-0.1% by weight. The sulfate content is 0-1.5 wt.% And preferably 0-0.8 wt.%. The iron content of copper 8301315 4-4 copper can range from 0-1.5 wt%, and is preferably 0-1 wt%. The partially oxidized copper can contain a variety of impurities, e.g. up to about 0.2 wt% lead and up to about 0.42 wt% tin, while the water content may range from 0 to 0.75 wt%. Other desirable properties of the partially oxidized copper are an apparent density of 1.2-1.4 grams per cm and a Fisher number determined by the Fisher Scientific Company's "Sub Seive Sizer" of 1.8-2 .4 µm 10 (µm), a measure of the powder's permeability to air.

As described in U.S. patent application 288,175, the preparation of methyl chlorosilanes by the Rochow direct method using the above-mentioned partially oxidized copper provides methylchlorosilane mixtures with a satisfactory T / D ratio. However, the Applicant has found that the weight percent residue of the methylchlorosilane mixtures obtained using the partially oxidized copper often exceeds acceptable limits.

Further research has been conducted to improve the performance of copper for the direct reaction between particulate silicon and organic chloride, as described in 25 "Chemistry and Practical Uses of Organosilicon Compounds", VI, Leningrad (1958), by PS Rostsishevskii, "A Study of the Direct Synthesis of Methylchlorosilanes ", Institute of Artificial Resins, Warsaw, pp. 42-59. Rostsishevskii used, in combination with methyl chloride, 30 contact masses obtained by heating mixtures of particulate silicon and copper formate.

It has been found that by using copper formate in place of the catalysed partially oxidized copper in the Rochow direct method, a significant reduction in the weight percent residue obtained in the crude methylchlorosilane mixture is obtained. Furthermore, it was found, however, that the splittability of this residue is significantly reduced compared to the splittability of the residue provided by the partially oxidized copper.

The invention is based on the discovery that a mixture of the partially oxidized copper and copper formate can provide crude methylchlorosilane with a significant reduction in the weight percent residue, compared to the use of only partially oxidized copper. Furthermore, the splittability of the residue, which is obtained by using the mixture of partially oxidized copper and copper formate, is practically equal to the splittability of the residue, which is obtained by using the partly oxidized copper. Thus, according to the invention, a significant increase in the formation of dimethyl dichlorosilane and useful methyl chlorosilane monomer is provided by a combination of partially oxidized copper and copper formate. Further improvements,.

such as the weight percentage / utilization of the silicon charge and the maximum rate of formation, as well as in most cases a significant improvement in the T / D ratio have also been observed.

The invention provides a process for preparing crude methylchlorosilane with at least 70 wt% dimethyldichlorosilane by reacting methyl chloride with particulate silicon in the presence of an effective amount of a copper and silicon-containing catalyst using partially oxidized copper. formation of a substantial amount of cleavable disilane-containing residue in the crude methylchlorosilane, which residue has a boiling point above 70 ° C under atmospheric conditions, thereby obtaining an overall reduction in the recoverable weight percent of Sorsilane from the crude methylchlorosilane. is becoming; the improvement provided by the invention is that copper formate is used in combination with the partially oxidized copper to yield 8301315 * 6-6 crude methyl chlorosilane with a significantly reduced weight percentage of this residue, based on the total weight of the new methyl chlorosilane is formed, while the weight percentage of cleavable disilane in this residue is substantially the same as that provided by the partially oxidized copper used as the catalyst.

Although methyl chloride is preferably used according to the invention, other alkyl chlorides, for example ethyl chloride, propyl chloride, etc., can also be used.

Methyl chloride or an inert gas such as argon can be used to fluidize the bed of silicon particles and the catalyst particles in the column. The fluidized bed consists of silicon and catalyst particles. The silicon-15 particles are present in the form of particles with a size of less than 700 microns and an average size of more than 20 microns and less than 300 microns. The average diameter of the silicon particles is preferably 100-150 microns.

Silicon is usually obtained with a purity of at least 98% by weight and is then comminuted into silicon particles of a size in the above range; the silicon is then fed into a suitable reactor. Although a fluidized bed is preferred, the process of the invention can be carried out in other types of reactors, for example with a fixed bed and a stirred bed. Preferably, a fluidized bed reactor is used, since the maximum selectivity and the maximum amount of dimethyldichlorosilane is then obtained. The process of the invention is carried out at a temperature in the range of 250-350 ° C and preferably in the range of 280-330 ° C. The reaction can be run continuously or discontinuously.

It is also recommended to carry out the process under pressure, as this increases the yield and conversion of methyl chloride to methyl chlorosilanes. It is generally desirable to carry out the process under a pressure of 1 - 10 atmospheres, and preferably under an atmospheric pressure of 1 - 5 atmospheres. Under these conditions, the desired amount of particulate silicon as well as the desired amount of "copper-containing mixture", that is, a mixture of 0.25-4 parts of copper formate per part of partially oxidized copper, are fed into the reactor. If desired, the partially oxidized copper and the copper formate can be fed separately into the reactor. About 0.5-10 parts of copper-containing catalyst per 100 parts of silicon powder can be used.

Methyl chloride gas is continuously fed through the reactor to fluidize the reaction mass; gaseous methyl chlorosilanes and unreacted methyl chloride are fed from the reactor. The gaseous reaction product 15 and entrained particulate matter are passed from the fluidized bed reactor and then through one or more cyclones to separate the relatively large particles from the product gas stream. These particles can be returned to the reactor to be used further in the process to maximize the yield of dimethyldichlorosilane from the silicon. Smaller particles are discharged with the product stream, after which the stream is subjected to condensation.

Purified methyl chloride is heated and recycled through the fluidized bed reactor 25 to further form methylchlorosilane. The crude methyl chlorosilanes stream is fed to a distillation column to distill off various chlorosilane fractions formed in the process in substantially pure form. It is necessary to distill and purify the dimethyl dichlorosilane and the other chlorosilanes so that they can be used to prepare siloxane materials.

The copper formate used according to the invention can be further characterized as a practically anhydrous granular material obtained from cupric formate dihydrate (CuiCHC ^) 2 * 2 ^ 0) or cupric formate tetrahydrate (CuiCHC ^ ^ · 4H_0) of technical quality. , and which has a BET specific Δ 2 surface area of 0.5-20 m / gram according to the nitrogen adsorption 830 1 3 1 5 - 8 method.

The copper-containing mixture may be a dry-mixing mixture of partially oxidized copper and copper formate, or the partially oxidized copper and the copper formate may be mixed together in the presence of an inert organic solvent, such as hexane, to improve mixing. Preferably, 1.5r2.5 parts of copper formate per part of partially oxidized copper is used to prepare the copper-containing mixture.

In addition to the copper-containing mixture, it is also possible to use 0.005-2 parts of powdered zinc metal per 100 parts of powdered silicon as promoter.

It is noted that in the above-described process for preparing methylchlorosilanes, the amount of copper-containing mixture per 100 parts of powdered silicon can vary widely within the above range.

The dimethyldichlorosilane prepared according to the invention can be hydrolysed by the Rochow method to provide a wide variety of useful products such as polydimethylsiloxanes with silanol-terminated fluids, gums and greases.

The following non-limiting examples further illustrate the invention. All parts listed are parts by weight.

Example I

Experimental fluidized bed reactors, which had an internal diameter of about 3.8 cm, and a stirred bed reactor, which had an internal diameter of about 2.5 cm, were used to determine the activity of copper formate and a mixture of copper formate and partially oxidized copper to prepare crude methylchlorosilane by conversion of silicon powder and methyl chloride.

The copper formate was from ICN Company (Plainview, New York); this copper formate was obtained by dehydration of cupric formate dihydrate by heating at 90 ° C for 24 hours. The partially oxidized copper was from Glidden Company (Cleveland, Ohio), and this 8301315-9 material had the analysis below (herein "TRP" means total reducing power, "BET" refers to the method of Brunauer, Eiranet, and Counter, and. Is the "Fisher number" as defined above): 8301315 - 10 - Η <c Ρ α>

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Eh G Λ co • nP g r * ιο 'S · co co

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Eh r- I c * »r- r- 8301315 - ^ - 11 -

The silicon powder used in the examination of the catalyst had an average specific surface area of 0.5 m / gram and a maximum particle size of 70 microns.

The activity of the catalyst was determined by determining the maximum normalized rate of crude methyl chlorosilane formation (grams of raw material / grams of silicon in the reactor / hour), the "percent utilization of the silicon", the T / D value, the "residue" and "splittability".

The fluidized bed reactor consisted of 3 concentric glass tubes of about 50.8 cm with internal diameters of about 7.0 cm, 5.1 cm and 3.8 cm. The reactor tube with an internal diameter of 3.8 cm had a distribution plate in the middle and was located in the tin oxide-coated oven-tube with an internal diameter of 5.1 cm, which was again inside the insulating tube with an internal diameter of about 7.0 cm.

20 grams of the above-defined silicon powder, 0.1 grams of zinc powder, 0.62 grams of partially oxidized copper with a total of about 84 wt% bonded and unbound copper and 1.21 grams of anhydrous cupric formate were mixed dry by stirring with a spatula and shake vigorously in a closed vessel. The resulting mixture was poured into the fluidized bed reactor, which was at a temperature of 300 ° C and through which argon gas flowed. Similar dry mixing blends were prepared for the stirred bed reactor. The decomposition of the copper formate was completed in about 5 minutes, as evidenced by the deposition of metallic copper on the interior walls of the clearly visible interior of the fluidized bed reactor.

Then methyl chloride was introduced into the fluidized bed reactor at a rate of 1.5 m per second and the argon flow was terminated. After a period of 89 minutes, the first drop of crude methylchlorosilane was collected by condensation at -20 ° C. The reaction was allowed to proceed for 28 hours. 59.8 grams of crude chlorosilanes consisting of dimethyldichlorosilane, methyltrichlorosilane 8301315-12 and the following monomers were obtained: Me ^ Si, HSiCl ^ N ^ HSiCl,

MeHSiC ^, Me ^ SiCl and SiCl ^. This corresponds to a utilization of the silicone of 68% by weight.

The maximum normalized rate of crude chlorosilane formation in the fluidized bed test was 0.255 grams of crude chlorosilane / gram of silicon in the reactor per hour, which maximum rate occurred at 61% utilization of the silicon. To compare the rates of formation of crude chlorosilane, a reaction rate constant defined by the empirical kinetic rate equation for the reaction between powdered silicon and organic chloride reported by R. Voorhoeve, "Organohalosilanes: Precursors to Silicones", was used. Elsevier, (1967), Using the above empirical kinetic rate equation, a normalized rate constant of 39.5 grams of raw material / grams of silicon / hour was obtained.

The crude chlorosilane mixtures were analyzed by gas chromatography using a Hewlett-Packard-20 and a Perkin-Elmer gas chromatograph equipped with filled columns and thermal conductivity detectors. The fluidized bed crude methylchlorosilane gave a T / D value of 0.072 and a residue of 3.05 wt%. The above residue was found to have a potential cleavability of 86%, ie 86% by weight symmetrical tetrachlorodimethyl disilane and trichlorotrimethyl disilane.

The stirred reactor bed consisted of a stainless steel tube with a length of about 45.7 cm and an internal diameter of 2.54 cm. The reactor was equipped with 2 electrical zone heaters to provide a reaction zone of about 2.5 cm x about 15.2 cm. The reactor was also equipped with a helical stainless steel stirrer.

The stirred bed reactor was preheated to 300 ° C with nitrogen purging until stabilization had occurred. A pre-prepared mixture of 50 grams of powdered silicon, 0.25 grams of zinc, 1.55 grams of partially oxidized copper and 3.02 grams of anhydrous cupric formate was then introduced into the reactor.

After the temperature of the reaction zone had stabilized at 300 ° C for 15-30 minutes, methyl chloride was introduced into the stirred bath at a rate of 12.5 grams per hour. 165 grams of crude methylchlorosilane were obtained using a cooler kept at -20 ° C.

According to the method of the above-mentioned U.S. Patent Application 288,175, a mixture of 20 grams of silicon powder, 0.1 grams of powdered zinc and 1.26 grams of partially oxidized copper was introduced into the fluidized bed reactor. The first drop of crude methylchlorosilane appeared after 66 minutes. The maximum normalized rate constant was found to be 29 grams of crude methylchlorosilane / gram of silicon / hour and the utilization of the silicon was 55%. The T / D ratio was found to be 0.141, the residue 5.9% by weight and the splittability 85%.

Further experiments were conducted with a fluidized bed and stirred bed reactor. The results of the tests with the fluidized bed reactor (1 and 3) and with the stirred bed reactor (2) are shown in the table below, in which the "maximum speed" is a rate constant K, expressed in grams of crude methylchlorosilane /

P

25 grams Si / hr, "POC" means partially oxidized copper, and "T / D", "residue" and "splittability" are as defined above: 8301315 t 1 - 14 - 0)

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From the above results it appears that the mixture of partially oxidized copper and copper formate significantly improves the total maximum formation rate of methylchlorosilane, the final utilization of the silicon / 5, the final utilization of silicon and the T / D ratio. Furthermore, with the combination of copper formate and partially oxidized copper achieves the benefits of the copper formate in terms of the percent residue, while retaining the splittability benefits provided by the partially oxidized copper.

Example IX

The following example illustrates the invention when run under continuous conditions in a fluidized bed reactor:

In a fluidized bed reactor at a pressure of about 207 kPa (gauge pressure) and a temperature of 300 ° C, a mixture of 100 parts by weight of powdered silicon, 2.4 parts by weight of anhydrous copper formate, 1.2 parts by weight was introduced. parts of partially oxidized copper and 0.2 parts by weight of powdered zinc per hour. 600 parts by weight of methyl chloride per hour were also introduced at the bottom of the reactor. On top of the reactor, 240 parts / hour of unreacted methyl chloride was obtained, which material was recycled, and about 460 parts by weight of crude methyl chlorosilanes / hour.

The above reactants provided a total amount of copper of 2%, based on the equivalent weight of the copper from the copper formate and partially oxidized copper used in the reaction, and 0.2% by weight of zinc. The recovered crude methylchlorosilane was found to contain 3 wt.% Residue with a splittability of 90 wt.%, Based on the total weight of the residue, while the remainder of the methylchlorosilane from the crude mixture had a T / D ratio of 0.06 owned.

The above examples relate to only some of the very many variables according to the invention; the invention is directed to the use of a wider variety of alkyl chlorides, partially oxidized copper and amounts of partially oxidized copper and copper formate.

8301315

Claims (10)

1. Process for the preparation of methyl chlorosilanes, in which methyl chloride and powdered silicon are reacted with one another in the presence of a copper and silicon-containing catalyst, characterized in that the catalyst is prepared by adding oxidized copper and copper formate. 2. Process according to claim 1, characterized in that crude methyl chlorosilane with at least 70% by weight of dimethyl dichlorosilane is prepared. 3. Process according to claim 1 or 2, characterized in that 0.25-4 parts by weight of copper formate per part by weight of partly oxidized copper in the mixture of particulate silicon, partly oxidized copper and copper formate is used. 4. Process according to claims 1-3, characterized in that an effective amount of zinc is also included as a promoter in the catalyst mixture. 5. Process according to claims 1-4, characterized in that partially oxidized copper with a specific surface area 2 of at least 3.5 m per gram is used. 6. Process according to claims 1-5, characterized in that sufficient copper formate and partly oxidized copper are used to provide 0.5-10 parts by weight of copper per 100 parts by weight of particulate silicon. 7. Process according to claims 1-6, characterized in that the process is carried out continuously. Process according to claims 1-7, characterized in that the process is carried out in a fluidized bed reactor. 9. Process according to claims 1-7, characterized in that the process is carried out in a stirred bed reactor. 10. Process according to claims 1-9, characterized in that crude methylchlorosilane is prepared with a significantly reduced weight percentage of residue, based on the total weight of the crude methylchlorosilane, which residue has a boiling point above 70 ° C under atmospheric conditions, while the weight percentage of cleavable disilane in the residue is practically the same as that provided by the partially oxidized copper. 8301315