DE2005835A1 - Production of alkyl silicates - Google Patents

Description

DR. BERG DIPL.-ING. STAPF

PATENTANWÄLTE 8 MÜNCHEN 2. H1LBLESTRASSE 2O

Dr. Berg Dipl.-Ing. Stopf, 8 Munich 1. HilblestroBe 20 · Your sign Our sign

date

Attorney File 19 $ 30
Yeh / i

Monsanto Chemical Limited London / England

Feb 9, 1970

"Production of alkyl silicates" Addition to P 16 6? 609.8

This invention relates to a process for the preparation of alkyl silicates.

Alkyl silicates are well known chemical compounds with established commercial uses, for example as a binder for the production of fire-resistant

Gases R-598

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(MIi) * 5 16 20 81 Telegrams: PATENTEULE Munich Bank. Bayerische Vereinsbank Munich 453 100 Postsdiecki Mönchen 653 43

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solid forms for metal casting. In the usual specific process for their preparation, alcohols are reacted with silicon tetra chloride, which is itself degraded by the action of chlorine on bilicium; this process suffers from the economic benefits of each multi-stage process and there is a process for the direct conversion of silicon to alkali Issilicates wansctieuswert. The present invention provides a, ± n such verification.

The process is related to the Uritiscnen patent specification 1 1 ^ 6 0'16 (üeutscne patent application 1b 67 bO9.ö), where a process for the production of a bilicasol is operated, for which purpose an electric btrom (JUi ¹ Ch leads a liquid licdiuin, the .vasser and a monovalent alcohol having from 1 to y ^ ivohlen toffatonie in the molecule includes una ochwei'elsiiure or üalzsäure as' irägerelektrolyt ontnillj, v; obei to an anode which contains silicon, in contact aIIb the liquid medium used In the applicant's British patent application;> u4i / b9 it is described that certain metal salts can take over the function of early electrolytes in an electrical electrolyte process of the type described above.

It has now been found that alkyl silicates are also used in this Processes, believed to be the primary products of the anodic reaction, can be formed and it is believed that the colloidal oil dioxide is a guarantee

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nis of the hydrolysis of the alkyl silicates with the aid of the liquid iiedium existing ivassers forms.

concludes from the fact that when ÖIE dium in the liquid Ke first amount of water present suf an i-iinimum is maintained and the .elektrolyse proceeds, it is used to this water, occur the alkyl silicates subsequently formed as such in the liquid medium continuing from which They can be isolated using electrolysis. Under suitable conditions, the ^{alkyl silicates available in diesel 1} represent a larger part of the aiiodosilicon consumed during electrolysis.

The method of the present Jirfindung used accordingly for the production of an alkyl silicate, whose AllQlgruppe has from 1 to $ carbon atoms to which one electrical Ütrom passes through a liquid medium, the holekül a solution in eineiyeinwertigen alcohol atoms of 1 to 3 carbon atoms Iji ¹ O comprises, an acid or a metal ele which is compatible with the monohydric alcohol, and this sufficiently ionized and used in a sufficient amount that it can perform the function of a carrier electrolyte, the hediurn not more than 3? o water , based on the weight of the monohydric alcohol, contains a bilicium-containing anode, which is in contact with the liquid

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Medium is located, used and so long electric current until there is persistence of alkyl silicate in the liquid medium and a time thereafter.

Preferably, the water content of the liquid medium is less than 1 Gew./6, for example, from above to 0.5 wt. #, Preferably the electrolysis is continued until the liquid medium at least 20 wt. 'Yo silicon compounds, expressed as silicon dioxide, and even more preferably until the liquid medium contains from 25 to 10% by weight of silicon compounds, expressed in terms of oil.

To the monohydric alcohols with 1 to 1? Carbon atoms in) Molecule used in the process of the present invention are usable, include the alkanols, methanol, ethanol, l'ropanol and isopropanol and mixtures of these alcohols. Ethanol is the preferred alcohol.

The acids useful in the process include sulfuric and hydrochloric acids, the former being generally preferred because of their lower volatility. The rate is essentially a current carrier and the amount used is usually the minimum required to achieve practical conductivity. This minimum depends of course on a number of actuators, but can typically be about 1 wt. # of the liquid medium. Ks is preferred because the

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tration in the liquid hedium 5% by weight, ο not exceed and that they are not less than 0.1 wt should be.

Suitable metal salts include metal chlorides and metal sulfates, for example zinc chloride, copper (± 1) sulfate, black sulphate, magnesium sulphate, zinc sulphate and iron (III) sulphate, the use of the last-mentioned salt is preferred in the present process. ±) s can hydrated or anhydrous salts can be used, however In many cases the former have a higher solubility in the lower monohydric alcohols and are therefore more suitable in order to obtain liquid media with the desired physical abilities. The metal salt muli sufficient solubility and ionization in the liquid medium to form a solution that has sufficient conductivity, to serve as an electricity carrier. The amount of such a metal salt, which must be dissolved in the liquid medium to form a practical conductivity depends, of course, on on a number of factors. However, there is a practical lower limit to the specific conductivity

-5-1-1 of the liquid at about 2.4 χ 10 ^J ohra cm. If the conductivities are lower, the process is unnecessarily extended. The liquid medium preferably has a specific conductivity of at least 3.0 10 "^, for example a conductivity in the range from 10 to 10 ^ ohm

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cm, such as from $ χ 10 to 5 χ 10 ohm cm

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In the event that the metal salt ferric sulfate is not hydrate is, satisfactory results are obtained if one absolute ethanol solutions with concentrations from 4 to 8 g courtship used per 1.

The liquid medium is preferably free of components other than those specified above, but an inert organic liquid can be present which is miscible with the liquid medium, for example a ketone, an ether or an ester as a liquid diluent, if so desired if, for example, the presence of up to d ^ P acetone, based on the volume of the liquid medium, can be tolerated. Where such a diluent is present, the basis for the water content of the medium, as discussed above, is the combined weight of the monohydric alcohol and the diluent.

The anode used can essentially consist of pure silicon exist and there can be different qualities of ilalüleiter of the material, for example silicon, in which essentially the only impurity is a substance, those in a controlled amount to give conductivity of a certain type and size is admitted to be used successfully. However, it is impractical to use silicon for the anode with a resistance which is significantly higher than 10 ohm-cm in the

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to use the present procedure. Silicon with a Resistance in the range of 0.005 to 1.0 ohm-cm is generally most satisfactory.

For economic reasons, the anode used in the process of the present invention is usually preferred made from a compound or alloy of bilicium than from a HalDleiter quality of the Clement. Ferro

Species of oil have been found to be particularly suitable. The oilicium.f-ehalt of Ferro-Üiliciums example, in the bex'eich from 60 to 99 / ό or ^r / 0 to 77 wt. ^ And in typical cases in the ranges of ^r / 0 to 8O J _7, 90 and 95 / ° or up to 99 üew. / Ύ.

Any inert conductive material can serve as a cathode. Graphite is a useful fodder material that, in view of in comparison to other functionally suitable materials, such as .platinum or oilber, significant Offers advantages.

That used in the method of the present invention electrical current can be a simple direct current or a similarly-routed alternating current with or without smoothing. The current density at the anode can typically be

Q.

ranging from 7 to 200 mA / cm bars, although working at ötromdichten over a wider range than the specified is possible. For economic reasons, the who should

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Voltage exceeding the decay range must be kept as low as possible. In practice, the working voltage by such factors as cell design and electrolyte concentration determined and wide changes are possible.

The electrolysis can be carried out over a wide temperature range. Generally the most suitable mode of operation is to equip the electrolysis cell with a liückfluJikühler and the process at the boiling point of the liquid medium. Often the resistance heating by the btrom is sufficient for the to keep liquid medium at its boiling point. However, the process can also be used at lower temperatures, for example from 10 ° C to the boiling point of the liquid medium, but os is then generally necessary to provide coolant.

It is customary to carry out the electrolysis in the presence of an inert atmosphere, for example nitrogen, however this is not essential.

The exactness of the product of the electrolysis depends on the process conditions, in particular on the water content of the liquid medium, but it is usually a mixture containing alkyl orthosilicates and alkyl polycilicates of varying degrees of condensation. Some

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colloidal silicon dioxide can also be formed, when the initial water content of the liquid medium is relatively high. The components of the mixture can, if desired, by conventional methods such as fractional distillation under reduced pressure, usually after neutralizing any acid present, by column chromatography or gas chromatography separated or partially separated. However, where the product is used as a binder in the manufacture of refractory articles is required, such a separation is not necessary.

The invention is illustrated by the following example.

example

A mixture of concentrated sulfuric acid (5 ml) and absolute ethanol (300 ml) is electrolyzed under a nitrogen atmosphere in a flask, which is equipped with a graphite cathode, a silicon anode and a backflow condenser. A direct current of ^L V A was passed through the cell, although the remaining power was reduced towards the end of the cycle. The initial saving used was 33 to 34 volts, later being increased to 60 to 70 / olfc. During the cycle, 100 amperes were applied to the line Resistance heating

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Heated the oil electrolyte to its boiling point and held him during the rest of the process on the Küc'kfluss.

The electrolyte was made neutral to bromophenol bluu by adding a solution of sodium ethoxide in ethanol. The ethanol was then distilled off, leaving a liquid which was more than half the volume of the initial electrolyte. This liquid was distilled under reduced pressure, whereby two fractions boiling point 110 to 122 ° C / 9 Torr and boiling point 160 to 250 ° C / 8 Torr and a residue which could not be distilled even at 300 ° C / 8 Torr were obtained . The first and second fractions had a silicon compound content of 2β, 9 and 47% by weight, respectively, in relation to silicon dioxide. The nuclear magnetic resonance spectrum of these fractions showed the presence of very little tetraethyl orthosilicate, but mainly straight-chain and branched-chain polysilicates. The specific gravity of the first and second fractions showed ratios of silicon atoms to ethoxy groups of 2.4 and 1.9, respectively, if the ^{method described in J. Inorg Nuclear Uhem., 1967, 29, r} / ö is used, which is closely related to agree with the ratios derived from the nuclear magnetic iiesotiaiu-, spectra of the fractions.

The üleiiLroLytisch) process delivered a product with a

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Gesaintgeiiult üiliciumv gen erbindun in terms of silica of 27, ο Gew.P and therefore expressed as silica ötroinausbeute of u, 49 S oiliciunidioxid Px ¹ OA hour. The product of the process consisted of elektrolytiscaen ^ 5 Gew./.i ethanol, 25 wt., J i-iotei'ial i'orr with a oiedepunkt between 11ü ^o o / 9 and 250 ° G / 8 i'orr and 4 ( J w / j non-distilled material.

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Claims (1)

2Ü05835 - 12 patent claims: 1. A process for the preparation of an alk, ylsilicate, wherein the alkyl group has from 1 to 5 carbon atoms, thereby characterized in that one carries an electric current through a Liquid medium that is a solution in a monohydric alcohol containing from 1 to 3 carbon atoms per molecule comprises, an acid or a metal salt which is compatible with the monohydric alcohol, and the medium ionizes to a sufficient extent and it functions as a carrier electrolyte in a sufficient amount used, the medium being based on no more than 3 # water On the weight of the monohydric alcohol, one contains an oilicium-containing anode, which is connected to the liquid Medium is in contact, used and the electric current passed through until alkyl silicate in the liquid Medium occurs persistently and remains for a time afterwards » 2. The method according to claim 1, characterized in that the liquid medium used is a solution which has a specific conductivity of at least 2.0 x 10 ^v ohm cm at work temperature. 5. The method according to claim 2, characterized in that a liquid medium is used which has a specific conductivity in the range of 10 to 10 ~ ohm "cm. -13- 009845/1919 4. The method according to any one of claims 1 to 3, characterized in that a liquid medium is used which contains less than Λ '-, Ό water, based on the weight of the monohydric alcohol. 5. The method according to any one of the preceding claims thereby marked that ethanol is a monohydric alcohol is used. 6. The method according to any one of claims 1 to 5, characterized in that that sulfuric acid or hydrochloric acid is used as the carrier electrolyte. 7. The method according to claim 1 or either claim 4 or 5 as a function of claim 1, characterized in that the carrier electrolyte is sulfuric acid or hydrochloric acid and using a liquid medium containing from 0.1 to 5 wt% acid. 8. The method according to any one of claims 1 to 5, characterized in that that the carrier electrolyte is a metal chloride or sulfate is used. 9 »Method according to claim 8, characterized in that the carrier electrolyte Eiaen- (II-E) -oulfat is-Jb. 009845/1919 BAO ORIGINAL 1Q. Method according to one of the preceding claims thereby characterized in that the electric otrom is passed through the liquid medium until this at least 20 (iew./£> oil compounds, expressed as silicon dioxide, contains « 11. The method according to claim 10, characterized in that the liquid medium contains from 25 to $ Q wt. ^> Silicon compounds, expressed as silicon dioxide. 12. The method according to one of the preceding claims thereby characterized in that a Perro-üilicium with as anode a content of 60 to 99 wt. # silicon is used. 13. The method according to any one of the preceding claims, characterized in that a liquid medium is used that is from 0 to 0.5 ^ water by weight of monohydric alcohol. 14. The method according to claim β, characterized in that zinc chloride is used as the carrier electrolyte. 1b · Process for the preparation of an alkali silicate according to Claim 1 essentially described in the example. It). AlIi ₁ ) Li) LiLIvCiL, if e ^ by uinem procedure g U 0 9845/1919 BATH ORIGINAL - 15 one of claims 1 to 12 and 15 is made. 17. AlkjlsiliKat, provided it is made according to a procedure in accordance with one of claims 15 and 14- is made. 009845/1919