DEP0007042MA - - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

Registration date: February 1, 1952. Advertised on: September 8, 1955

GERMAN PATENT OFFICE

The invention relates to a high temperature heat transfer medium.

Due to their relatively high boiling points, tetraphenyl- and tetrakresyl orthosilicates have been suggested. Also mixtures, the tetrakresylorthosilicates and Containing tetraphenylorthosilicates have been recommended and used for this purpose.

Pure tetrakresylorthosilicate or its mixtures with tetraphenylorthosilicate do not have a satisfactory resistance at high temperatures. If they are exposed to temperatures on the order of about 371 ° C for a normal long period of operation, even in a closed system that is free from liquid and vapor and into which neither air, moisture nor contaminants can enter, then considerable amounts of Decomposition products formed. These contain free phenol, free cresol, polymerized silicates, benzene, toluene xylenes, low-boiling aliphatic hydrocarbons, crystalline anthracene-like hydrocarbons and solid resin polymers. Pure tetraphenylorthosilicate does not show such a pronounced tendency to decompose at elevated temperatures. Its use is limited, however, by its high melting point (50 ^° C.), at which temperature it becomes a crystalline, solid body, and by its relatively low boiling point, which is 408 ^° C. Such a low boiling point does not ensure a sufficiently safe limit range for use at temperatures above approximately 315 ^° C., and such a high one

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Melting point is especially in a liquid syslein, which is often reduced to room temperature, undesirable.

Uni to raise the boiling point and the melting point It has already been proposed to add tetracresyl silicate to the tetraphenyl silicate. In the literature a mixture containing 20% tetracresyl silicate is given, but the practical ones Experience has shown that such an addition

ίο does not lower the melting point sufficiently and daü all known commercial mixtures approximately · | <) "/ ο tetracresyl silicate (keep up. These (generally have a sufficiently low melting point, however, the presence of tetracresyl silicate, as noted, raises the issue of decomposition on. Mixtures containing tetracresyl silicate in the above The specified amounts are due to their decomposition at elevated temperatures, in particular in the range from 315 to 370 "C, not satisfactory.

ICs, therefore, has a need for a heat transfer medium that that is a liquid of suitable viscosity at low temperatures and that furthermore without danger at temperatures of about 370 "G a decomposition can be used. It is the purpose of the present invention to address this need to meet.

The I hole temperature heat transfer medium ingenious.! of the invention now consists essentially of a mixture of fhenyl orthosilicate and diphenyl orthosilicate and mixed Phenyldiphenylorthosilicalcn with such proportions within the Hreiches from o ,. | to 3.0 diphenyl radicals and 3.6 to 0.4 lienyl radicals on each silicate radical. Such Mixtures are exceptionally stable and have boiling points up to about 510 C and at least . ·). ■] () "C as well as very low freezing points and sufficient Viscosity at low and high temperatures.

In the case of the heat transfer medium according to the invention, (! -Diphenyl can preferably be used as the diphenyl radical.

These mixtures contain, as main ingredients, a mixture of diphenyl, phenyl and mixed ones

• 15 Dipliciiyl-I'lienylortliosilicaten of the following general, empirical formula:

(C ₁₂ II ₀ O) _x (C ₁₁ H ₀ O) ₁ , Si,

in the .v a number between o ,. | up to about 3.6. When .v is significantly less than about 0.4, the material partially crystallizes at room temperature. the upper limit of 3.0 is dictated by practical considerations as a by means of known procedures Material with a higher proportion of diphenyl radical cannot be produced quickly.

If a mixture, the diphenyl and phenyl orthosilicale within the limits given above, for a few hours at elevated temperatures within the range of 205 to 260 ° C or in the presence of a catalyst at a lower one If the temperature is heated, an equilibrium is established between the five possible orthosilicates out:

i. Tetra (diphenyl) orthosilicate C ₁₂ H ₉ O. .OC ₁₂ H ₀

Si,
C ₁₂ H ₉ O ^ OC ₁₂ H ₀

2. Tri (diphenyl) monophenylorthosilicate C ₁₂ H ₀ O, OC ₀ H ₅

Si
C ₁₂ H ₀ O OC ₁₂ H ₀

3. Di (diphenyl) diphenylorthosilicate C ₁₂ H ₀ O .OC ₀ H ₅ -

Si

OC ₀ H ₅

4. Mono (diphenyl) triphenylorthosilicate C ₁₈ H ₉ O OC ₀ H ₅

Si
C ₀ H ₅ O ^{y X} OC ₀ H ₅

5. Tctraphenylorthosilicat C ₀ H O ₅ / OC H _{0 0}

Si '
C ₆ H ₆ O ^/ OC ₀ H ₅

The equilibrium mixture that is obtained thereby contains, depending on the ratio of diphenyl to Phenyl radicals in the starting mixture varying proportions within the limits given above of the above components. Equilibrium mixtures of any desired proportion of ingredients can therefore due to the ratio of the two original reactants to one another getting produced.

This equilibrium becomes independent of the process and the starting materials for production of the mixture reached. For example, if the mixture according to the invention is made from Tetradiphenylorthosilicate and Tetraphenylorthosilicate, the equilibrium is established by disproportionation set. The mixture can, however, also by reacting silicon tetrachloride with phenol and Phenylphenol are produced. In this case, the equilibrium becomes by itself in the course of the Synthesis achieved. Equilibrium is also reached when tetraphenylorthosilicate with a calculated amount of phenylphenol is reacted to replace an equimolecular amount of phenol or vice versa.

The term equilibrium mixture is used here to describe the mixture of the five components, that is obtained in each of the processes given above and in a certain ratio

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Contains diphenyl and phenyl radicals within the specified limits.

In general, the higher the boiling point and the viscosity at lower temperatures the proportion of diphenyl radicals is higher. Therefore, the ratio of the total number of diphenyl radicals becomes (in grams of radical weight) to the total number of phenyl radicals (in grams of radical weight) when mixing the orthosilicates of the mixture

ίο within the previously specified range like this chosen that the mixture has the desired boiling point and low viscosity depending on has special requirements. Due to the usual requirements, a mixture is preferred in which on on a molecular basis, the amount of diphenyl radical is not greater than that of phenyl radical.

The following proportions of total diphenyl and total phenyl radicals in a mixture of the orthosilicates fall within the requirements of the invention and it has been found that such Mixtures of the desired melting points, viscosities and boiling points as well as the desired resistance at elevated temperatures have:

₂ . Ratio of radicals per silicate group

(given in grams of radical weight)

No. Diphenyl Phenyl Molecular weight (I) o, 4 3.6 449.2 . (2) I. : 3 476.6 (3) i, 8 2.2 536.0 (4) 2. 2 552.7 (5) .2.85 1.15 620.1 (6) 3 I. 628.8 (7) 3.6 0.4 673.5 -,

The boiling points, flash points, focal points and viscosities of the typical mixtures given above are given in the following tables in which these mixtures with the known tetraphenylsilicate to be compared:

No. Beginner
Boiling point ° C Flash point
⁰ C Focus
⁰ C (760 mm) Tetraphenyl orthosilicate 408 245 282 (i) 465 263 304 (2) 492 277 321 (3) 515 296 346 (4) 512 ■■ 302 327 (5) 527 327 388 (6) 530 333 393 (7) 531 354 421

Tetraphenylorthosilicate is a pure compound and therefore has a sharp freezing point of 50 ° C and no cloud point to indicate the onset of crystallization, as is the case with a number of others Silicate is the case.

Mixtures 1 to 7 become in increasingly viscous, however, neither turbidity nor freezing was observed, which is a Crystallization would indicate above the temperature range that these substances normally would get abandoned.

- 6.6 ° C 0 ⁰ C Viscosity in centistokes *) 25 ° c 38 ° C 54.5 ° C 7i ° C 85 ⁰ C No. 6 997 ι 667 10 ⁰ C 93.5 42.9 19.9 11.28 7.76 (i) - - • 314.3 220 75 33 16.9. 11.1 (2) - - ι 300 933 240.5 72.0 3i, 4 18.7 (3) - - 9 925 1580 330 89 37.5 21.9 (4) - - - 19 900 1948 294.7 88.5 43.2 (5) - - ■ - 30,000 - 400 100 Si (6) - - - - - ι 887 313.7 "5.7 (7) -

*) "If no value is given, no measurement was carried out, or the viscosity was too high to be compatible with the usual methods to be measured.

. 55 The tables show that mixtures with different boiling points, flash points, Focuses and viscosities by adjusting the ratio of diphenyl and phenyl radicals can be produced within the stated general range.

In order to determine the relative heat resistance, a according to the method of the invention Tested mixture produced in addition to a commercially available mixture according to the state of the art. This latter mixture contained the equilibrium mixture of 60% tetraphenylorthosilicate and 40% Tetrakresyl orthosilicate. This mixture was refluxed for 100 days at a temperature of heated to about 370 ° C. Decomposition occurred immediately and continued to increase. After heating for 100 Days the mixture was analyzed and it was found that it contained 20% volatiles, the

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under 370 "('boiled, were included. Among these Components were phenol, cresols and flammable hydrocarbons such as benzene, toluene and xylene, found. The heated (iemiscli also contained 40% of a solid polymer which is soluble in the liquid silicate. The (in place of the solid polymer was determined by distilling off the tetraarylsilicate from the non-desillable polymer and also by observing the observed increase in the viscosity of the material after distillation of the volatile constituents compared to the viscosity of the starting material. The material had one viscous, syrupy consistency and was almost black in color.

For comparison, a mixture was prepared according to the method according to the invention, which contained a light weight mixture of one molecular part of telradiphynyl orthosilicate and three molecular parts of tetraphynyl orthosilicate (Example 2 in the tables above). This mixture was subjected to the same test, ie for 100 days heated under reflux at about 370 ⁰ C. the mixture zeigle only 3 · '/ "volatiles below 370" boiled C, and a large part of these components was due to the presence of impurities due to the technical degree of purity of at Prod RECOVERY The decomposition took place early in the heating period, indicating that any tendency to decompose as soon as the impurities decomposed, and no polymer was formed, as evidenced by the fact that there was no increase in viscosity as well as no other change in phy sicatic properties took place and the liquid was brightly colored before and after the experiment.

In order to determine the heat resistance of a mixture of) "/" Telrapheiiylorthosilat and 20 ° / _(l tetrakresylorthosilicate (the gel niche given in the literature) with a mixture of iSo "/" tetraphenylorlhosilicate and 2o "/ _o tetradiphenylorthosilicate (all proportions in percent by weight) compare, these mixtures were heated in the same way to about 370 "C. for 2 weeks. The experiment was no longer set in foil because the end result could be predicted from the results obtained during this time first liquid decomposed, whereby benzene, toluene and xylene had been set free.

Within a day the liquid had started simmering quite briskly. The boiling went on all the time. The second mixture, the had been prepared according to the invention did not boil during the entire test period; also were no low-boiling tunnels formed. A loss of material was not noticed. Other mixtures that had been made according to the invention, showed the same advantages in terms of heat

ßo Besländigkrit,

In the mixtures tested above, the dipheuyl radical was the ortho isomer that was more readily available and that is to illustrate the best mode for carrying out the method according to the invention was chosen. The other isomers can also be used alone or in mixtures.

The above results demonstrate the superior properties of the blends made according to the invention have been produced, both in terms of their physical properties and their heat resistance. When compared with tetraphenylsilicate, which is replaced by other alkylated arylsilicates, Alkyl silicates, naphthyl silicates and the like Comparison with tetraphenylorthosilicate modified with tetrakresylorthosilicate.

A number of methods can be used to prepare the mixtures of the invention. There are three satisfactory experiences:

1. The direct synthesis from the corresponding phenylphenol, phenol and silicon trachloride.

2. Phenolvse by replacing phenolic resp. Diphenyl radicals in tetraphenyl orthosilicates or tetradiphenyl orthosilicates by phenylphenol or Phenol.

3. Transesterification of tetraphenylorthosilicate and tetradiphenylorthosilicate.

In the first method, the phenylphenol and the phenol with silicon tetrachloride in the desired ratio implemented, preferably an excess of phenols is used. The silicon tetrachloride is quickly added to the phenol mixture with stirring, with such a mixture Rate that hydrogen chloride gas is evolved at great rate, but not unreacted silicon tetrachloride is entrained. After all the silicon tetrachloride has been added the reaction mixture is used to terminate the reaction, to drive off residual hydrogen chloride and heated to about 226-265 ° C to remove excess unreacted phenol.

If the reaction mixture is up to 2 moles of o-phenylphenol contains, the phenol mixture has a relatively low melting point, and the silicon tetrachloride can therefore combine with the melt. For reaction mixtures that are more than 2 mol Contain phenylphenol, it may be necessary to use a solvent such as toluene, benzene or xylene, zn to facilitate the implementation of the silicon tetrachloride. If a solvent is used it is necessary to remove it before the reaction is complete in order to keep the reaction mixture can be heated to the necessary temperature.

The reactants can be pure; however, technical grade materials can also be used. The phenol can contain up to 2 ¹ Z ₂ ⁰ /!) Water. In this case, silicate polymers can be formed; however, their presence does not seem to bother, since they do not significantly affect the stability of the reaction mixture and, moreover, tend to lower its freezing point.

The following general procedure can be used to prepare Examples 1-7. the Apparatus consists of a mechanically stirred reaction vessel that can be heated, a

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adequate condenser or condenser system capable of both refluxing and refluxing can also be used for distillation, an acid absorption column, an alcohol column for Absorption and conversion of the entrained silicon tetrachloride, a drying tower system for prevention the entry of moisture into the reaction chamber and a device for adding of silicon tetrachloride.

ίο The reaction vessel is filled with phenylphenol and Phenol filled and the mixture to ensure complete mixing of the phenols touched. The condenser is then refluxed with the acid absorption column via the alcohol

column connected to a io ° / ₀ contains sodium excess relative to the combined weights of phenol. The drying towers are arranged so that no moisture can enter the system from the alcohol column to the silicon tetrachloride addition tank. The silicon tetrachloride is then added quickly.

When all the silicon tetrachloride is added

has been, the reaction mixture will slowly rise

- Heated about 226 to 232 ⁰ C to drive off all hydrochloric acid. The reaction mixture is then refluxed at about 260 to 266 ° C. for at least 10 hours, but preferably longer, until the reaction is complete.

The condenser is then set up for distillation, whereupon the unreacted phenolic Substances are removed first at atmospheric pressure and then at reduced pressure. The reaction mixture is then quenched with inert gas, e.g. B. with nitrogen, blown to remove all traces of hydrochloric acid to remove. The reaction vessel is then allowed to cool and the desired one is removed Product.

The phenylphenol appears to react more slowly than the phenol, especially when the phenylphenol is reacted with the last chlorine to be replaced in the original silicon tetrachloride. The phenylphenol is therefore preferably first reacted with the silicon tetrachloride. In the case of a mixture of about 1 mole of phenylphenol and about 3 moles of phenol, the procedure described above was used, with the difference that all of the phenylphenol was ^{reacted with a stoichiometric excess of, for example, about x} / ₂ mol of silicon tetrachloride, whereupon the phenol was added and initially reacted and then the amount of silicon tetrachloride corresponding to the equilibrium was added and the reaction mixture was completed according to the procedure outlined above.

Synthesis by phenolysis relies on the fact that when a tetraphenylorthosilicate is heated in the presence of a phenylphenol, or vice versa, the phenylphenol replaces an equivalent amount of phenyl radicals from the silicate. In this method, tetraphenyl be or -diphenylorthosilicat and mixed phenylphenol or phenol and heated together under reflux at temperatures heated to 10 to 15 hours at 243 ⁰ C. The released phenol is then distilled. During this distillation, the temperature is slowly increased to about 273-315 ⁰ C. When the phenol distillation is completed at atmospheric pressure, it is continued under reduced pressure to completion.

When the mixture is prepared by transesterification according to the invention, so tetraphenyl orthosilicate and Tetradiphenylorthosilicat are mixed and heated at a temperature in the range between 227 ° and 315 ⁰ C. The time required for the reaction to complete, ie the time required to establish equilibrium between the possible phenyl diphenyl silicates, depends on the temperature. At 227 to 232 ^° C., equilibrium is reached in about 24 hours or less.

The transesterification can be accelerated by adding a catalyst. Satisfactory catalysts are for example compounds which contain chlorine in direct bond with silicon and which rapidly decompose in the presence of water, such as B. monochlorosilicates of isopropyl alcohol, Isobutyl alcohol or phenol, corresponding di- and tri-chlorosilicates or silicon oxychlorides, such as Hexachlorodisiloxane. After the reaction has ended, the catalyst can be removed by distillation will.

It should be noted that the one of the above-mentioned processes produced by go The heat transfer fluid is sufficiently pure and does not need to be distilled.

The new transfer fluids can take advantage of indirect heat transfer contact be used for substances that are to be heated. For example, they can be in any suitable Way to be heated, to be conveyed to the liquid of the substances to be heated, with these exchange their heat and then be returned to a storage container for rewarming.

All parts and percentages in the description and in the claims are given by weight, if it is not specifically stated that the figures are molar.

Claims (2)

PATENT CLAIMS: ι. High temperature heat transfer medium, consisting essentially of a mixture of phenyl orthosilicate, diphenyl orthosilicate and mixed ones Phenyldiphenylorthosilicates with such proportions within the range of 0.4 up to 3.6 diphenyl groups and 3.6 to 0.4 phenyl groups for each silicate radical. 2. Heat transfer medium according to claim 1, characterized in that the diphenyl radical o-Diphenyl is used.