RU2537302C1 - Method of tetraethoxysilane purification - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to methods of purification of alkoxysilanes and deals with obtaining highly pure tetraethoxysilane. Claimed is a method of tetraethoxysilane purification, including the initial processing of a product to be purified with a 0.3-1.5% water ammonia solution, added with intensive mixing to tetraethoxysilane which must be purified in a volume ratio (4-6):1, further rectification of the preliminarily purified product and its purification by distillation without boiling at a rate of evaporation from the surface of 0.5-1.5 ml/cm²·hour. The technical result consists in the following: the method makes it possible to obtain a highly pure product with the content of limited metal admixtures at the level of 10^-6 wt %, chlorine less than 10^-3 wt % and suspended particles with the diameter of 0.3 mcm about 200 particles/cm³.

EFFECT: indices of the obtained tetraethoxysilane quality satisfy the requirements for initial products for highly technological materials.

3 cl, 1 tbl, 4 ex

Description

The present invention relates to methods for the purification of alkoxysilanes and relates to the production of high-purity tetraethoxysilane, which can be used in many technical fields, in particular, for the manufacture of materials used in the aerospace industry, microelectronics, optical glass melting.

It is known that industrially produced tetraethoxysilane usually contains impurities of halogen-containing compounds, for example, triethoxychlor, as well as other chlorosilanes and metals. For the purification of tetraethoxysilane from these impurities, the following are used: distillation, for example, conventional distillation (EP 879821, C07F 7 / 04,2006), azeotropic distillation (KR 20050099835, C07F 7/02, 2005), a gas chromatographic method used, for example, to purify TEOS from impurities of metals (US 5840953, C07F 7/04, 1997), chemical treatment. Distillation and chemical treatment are the most applicable methods for the purification of tetraethoxysilane. So for the purification of alkoxysilanes from halide impurities, a wide group of chemical compounds is used: C ₁ -C ₄ alkyl alcohols and / or orthoformates (EP 974596, C07F 7/18, 2000), alkali metal compounds, alkali metal alkoxides or amines (US 5247117, C07F 7/20, 1992), metallic zinc or organozinc compounds (EP 4357175, C07F 7/20, 1990), activated carbon (US 2009270646, C07F 7/04, 2009)

The closest in technical essence to the present invention are known methods for the purification of alkoxysilanes from chlorine, considered by the example of purification of tetraethoxysilane. So, to obtain alkoxysilanes with a minimum chlorine content, gaseous ammonia is added to the reaction mixture obtained by the interaction of tetrachlorosilane with anhydrous alkanol (to neutralize chlorine ions) , and the resulting alkoxysilane is subjected to distillation to obtain a product with a chlorine content of less than 10 ppm (US 6150551, C07F 7/18, 2000), or 0.1-2 ve .% transition metal (magnesium, calcium, titanium, strontium, zinc, barium, lead, cadmium, tin) followed by distillation, which provides tetraalkoxysilane with a chlorine content of 0.5 ppm (KR 20030030477, C07F 7/12, 2003 )

One of the requirements for products for microelectronics, for materials used in aerospace engineering and microelectronics, is the minimum content of metal impurities in them. For the purification of tetraalkoxysilanes, including tetraethoxysilane, the most effective is the treatment of the purified products with complexing agents (EP 0879821, C07F 7/02, 1998; JP 04082893, C07F 7/02, 1990). For example, to remove cations of calcium, potassium, sodium, and copper, chelating aminocarboxylic acids are used that are effective in removing cations of calcium, potassium, sodium, and copper, but are not very effective in removing others, including heavy metals (JP 04082893). After treatment of alkoxysilanes with complexing agents, in some cases, additional distillation purification is carried out (EP 0879821).

From the achieved level of technology it is seen that distillation methods, including simple distillation and rectification, are widely used for the purification of tetraalkoxysilanes. They are usually used as additional purification steps. (US 6150551, KR 20030030477).

However, both simple distillation and azeotropic distillation and distillation in combination with various chemical treatments do not provide deep purification of lower tetraalkoxysilanes, including tetraethoxysilane, from impurities of submicron heterogeneous particles carried away in the vapor phase upon boiling in a bubble mode. To eliminate this disadvantage of the known methods for the purification of tetraalkoxysilanes, but with reference only to tetramethoxysilane, it was possible in another invention (RU 2463305, C07F 7/04, 2012). In this known method for the purification of tetramethoxysilane, the treated product is first treated with ammonia gas until a pH of 7.5-8.5 is reached, then rectification is carried out (preferably on a packed quartz column with an efficiency of 30 theoretical separation stages), and then a distillation step is carried out with evaporation from the surface without boiling at a certain speed, selected for only tetramethoxysilane (with a speed of 0.1-0.5 g / cm ² per hour). The evaporation distillation step can be carried out according to the invention even before the chemical treatment step. However, the above purification conditions, unchanged, are not suitable for tetraethoxysilane and do not allow to obtain tetraethoxysilane of the required high degree of purity, according to the content of metal impurities at the level of 10 ^-5 -10 ^-6 mass%.

Since the present invention relates to a method for purifying only tetraethoxysilane, and not other tetraalkoxysilanes, the known method for purifying organosilanes, which is considered by the example of purifying only tetraethoxysilane (EP 0879821), is selected as a prototype. Purification of tetraethoxysilane in the known prototype method includes the initial stage of processing the starting product with a chemical compound selected from the group: thiols, alkanols, carboxylic acids, organic amines and mixtures thereof having a pKa of 3-19.7, introduced in an amount of 10% a different or more stoichiometric excess of the number of output elements. After the chemical treatment step, a distillation purification step is carried out. This method during chemical processing, for example, trimethylphenol, provides the purification of tetraethoxysilane from chlorine, as well as boron and phosphorus to obtain a final product of 99.9999% degree of purity. However, the known method does not provide cleaning from suspended particles, and also, as shown by additional experimental studies, it is not effective enough to clean from impurities of other metals, in particular aluminum.

In addition, the introduced complex organic compounds can themselves serve as a source of additional impurities that are unacceptable when using the obtained tetraethoxysilane in the above areas of modern technology.

To obtain high-purity tetraethoxysilane containing minimal impurities of chlorine, metals and suspended particles, satisfying the requirements for the initial products for the manufacture of materials for the aerospace and electronic industries, as well as in fiber optic glass melting, a new method for the purification of tetraethoxysilane is proposed, including initial processing of the product to be purified 0.3-1.5% aqueous ammonia solution added with stirring to the purified tetraethoxysilane in a volume ratio and 4-6: 1, and the subsequent rectification of tetraethoxysilane without additional purification distillation at the boiling evaporation rate from the surface of 0.5-1.5 ml / cm ² per hour. In this case, the rectification stage is carried out at atmospheric or reduced pressure. The treatment of the initial tetraethoxysilane with an aqueous solution of ammonia is carried out with vigorous stirring of the mixture at a speed of 120-300 rpm

The proposed method has the main significant differences from the prototype - this is the presence of an additional stage of purification — distillation without boiling, carried out with a surface evaporation rate specially selected for tetraethoxysilane equal to 0.5-1.5 ml / cm ² hour. This cleaning step maximizes the removal of suspended particles. The value of the selected range of evaporation rate allows, on the one hand, to optimize the efficiency of the cleaning process, and on the other hand, to ensure a high yield of the final product.

Another significant difference between the new purification method and the prototype method is the use of exactly 0.3-1.5% aqueous ammonia solution used as a chemical agent in the volume ratio of tetraethoxysilane equal to 4-6: 1. Such values, selected experimentally specifically for tetraethoxysilane, can effectively ensure the removal of chlorine-containing impurities from the product even at a high concentration in the starting product (more than 0.1 wt.%).

The effectiveness of the process is also affected by the presence of an intermediate rectification stage, which is preferably carried out on a quartz packed column.

It is such a deep complex purification of tetraethoxysilane, performed within the claimed parameters, that allows to obtain a high-purity product with the content of limited metal impurities at the level of 10 ^-6 wt.%, Chlorine less than 10 ^-3 wt.% And suspended particles of about 200 pcs / cm ³ diameter less than 0.3 microns. Such quality indicators of the obtained tetraethoxysilane satisfy the requirements for products for the manufacture of materials used in the aviation and space industries, as well as in microelectronics and fiber optic glassmaking.

Below the invention is illustrated by examples 1-4 and table 1, which contains indications of the quality of the resulting product.

Example 1

First, the original technical tetraethoxysilane (1 kg) is pretreated. To do this, with vigorous stirring at a speed of 120 rpm, tetraethoxysilane is treated with a 0.5% aqueous solution of osch ammonia in a volume ratio of 4: 1 (to remove chlorosilane impurities). Then the product is subjected to distillation at atmospheric pressure on a packed quartz column with an efficiency of 30 theoretical separation stages to separate the volatile fraction in an amount of 20 g (4%) from the charge. The target fraction in an amount of 920 g (92%) from the charge is distilled in a distillation apparatus without boiling with an evaporation rate of 1.5 ml / cm ² hour. 890 g of the final product are taken. The quality of the resulting product is shown below in the Table.

Example 2

The purification is carried out analogously to example 1, changing only the fact that 1.5% aqueous ammonia in a volume ratio of 6: 1 is used for purification.

Example 3

The purification is carried out analogously to example 1 with the exception of the rectification stage, which is carried out under reduced pressure of 500 mm Hg.

Example 4

The purification is carried out analogously to example 1, changing only the rate of evaporation from the surface at the stage of distillation without boiling by 0.5 ml / cm ² hour.

All samples obtained (examples 1-4) have the same quality indicators of the purified tetraethoxysilane product, given below.

Table 1 No. p / p Name of indicator one Mass fraction of the main substance,% mass., Not less 99.9 2 Mass fraction of iron (Fe),% mass., No more 1 · 10 ^-5 3 Mass fraction of manganese (Mn),% mass., No more 1 · 10 ^-6 four Mass fraction of copper (Cu),% mass., No more 1 · 10 ^-6 5 Mass fraction of nickel (Ni),% mass., Not more than 1 · 10 ^-6 6 Mass fraction of chromium (Cr),% mass., No more 1 · 10 ^-5 7 Mass fraction of calcium (Ca),% wt., No more 1 · 10 ^-5 8 Mass fraction of vanadium (V),% mass., Not more than 1 · 10 ^-6 9 Mass fraction of cobalt (Co),% mass., No more 1 · 10 ^-6 10 Mass fraction of magnesium (Mg),% wt., No more 2 · 10 ^-6 eleven Mass fraction of aluminum (Al),% wt., No more 5 · 10 ^-6 12 Mass fraction of tin (Sn),% mass., No more 1 · 10 ^-6 13 Mass fraction of lead (Pb),% mass., No more 1 · 10 ^-6 fourteen Mass fraction of silver (Ag),% mass., No more 1 · 10 ^-6 fifteen Mass fraction of titanium (Ti),% wt., No more 5 · 10 ^-6 16 Mass fraction of chlorine,% wt., No more 10 ^-3 17 The particle content, microns, pcs./cm About 450 pcs / cm ^{3 with a} diameter of 0.3 microns.

Claims (3)

1. The method of purification of tetraethoxysilane, comprising treating the product to be purified with a chemical reagent and subsequent rectification, characterized in that it further includes a distillation step without boiling with a evaporation rate from the surface of 0.5-1.5 ml / cm ² · hour, and As a chemical reagent, a 0.3-1.5% aqueous ammonia solution is used, which is added to the tetraethoxysilane to be purified with stirring in a volume ratio of (4-6): 1. 2. The method according to claim 1, characterized in that the distillation is carried out at atmospheric or reduced pressure. 3. The method according to claim 1, characterized in that the treatment of the initial tetraethoxysilane with an aqueous solution of ammonia is carried out with stirring at a speed of 120-300 rpm