RU2463305C1 - Method of purifying tetramethoxysilane - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to methods of purifying lower tetramethoxysilanes, particularly tetramethoxysilane which can be used in microelectronics and in mixtures for fibre-optic glassmaking. The disclosed method of purifying tetramethoxysilane consists of three steps: chemical treatment of the product to be purified with ammonia gas until achieving pH 7.5-8.5, rectification after chemical treatment and distillation with evaporation from the surface without boiling, carried out at rate of 0.1-0.5 g/cm² h, either before chemical treatment or after rectification. Optimally, the rectification step is carried out on a packed quartz column with efficiency of 30 theoretical separation steps.

EFFECT: obtaining highly pure tetramethoxysilane containing limiting impurities of metals, chlorine and suspended particles with diameter 0,3 mcm.

2 cl, 3 tbl, 3 ex

Description

The invention relates to methods for the purification of tetraalkoxysilanes, in particular tetramethoxysilane, which can be used as a starting product in the technology of manufacturing microelectronic components and for producing blends for fiber optic glass melting.

One of the requirements for products used in the electronic industry and in optical glassmaking is their high degree of purity, which implies a minimum content of impurities of metals, metalloids and solid microparticles. In the case of using tetraalkoxysilanes in electronics, in particular lower tetraalkoxysilanes (tetramethoxysilane, tetraethoxysilane), the minimum content of chlorine impurities in them becomes an additional requirement. The overestimated content of chlorine impurities in lower tetraalkoxysilanes is explained by the use of chlorine and chlorine-containing compounds in their synthesis. To reduce the chlorine content, either special conditions for the synthesis of tetraalkoxysilanes or additional purification of the synthesized products are proposed. So, for example, in the known method for reducing the chlorine content in the final product, it is proposed to obtain lower tetraalkoxysilanes by the interaction of metallic silicon with monoalcohols in the presence of catalysts, which are used as organometallic compounds or polyalkoxides (EP 0934945, C07F 7/04, 2001).

One of the known methods used to purify tetraalkoxysilanes from chlorine impurities is chemical treatment. As the reagents used in this method, it is known to use calcium hypochlorite (SU 2793413, C07F 7/04, 1979), aqueous solutions of alkali metal hydroxides (US 2972626, 260-448, 1961), water-alcohol solutions of a mixture of sodium hypochlorite and hydroxide sodium (SU 958424, C07F 7/04, 1982), zinc metal (US 5104999, 1987). However, the use of the known listed reagents does not provide high efficiency for the purification of tetraalkoxysilanes, including tetramethoxysilane, from chlorine impurities. In addition, the use of alkali metals for the treatment of hydroxides leads to contamination of the product to be purified with alkali metal cations.

An additional requirement for products for microelectronics and fiber optics is the minimum content of metal impurities. For the purification of tetraalkoxysilanes from this type of impurities in the known methods for purifying these compounds, treatment of the products to be purified with complexing agents, as well as an ion-exchange purification method and rectification are used. For example, for the purification of tetraalkoxysilanes, including tetramethoxysilane, ion-exchange resins containing chelating aminocarboxylic groups are used (JP 04082893, C07F 7/02, 1990). However, such resins are effective only for the removal of Ca, K, Na, Cu cations, but are ineffective for the removal of other cations. Also, for the purification of tetraalkoxysilanes from metal impurities, treatment of the products to be purified with complexing agents can be applied. Thus, in the known method for the purification of tetraalkoxysilanes from impurities of boron, aluminum, gallium, indium, thallium, phosphorus, arsenic, antimony and bismuth, complexing agents having a pK at the level of 3-19.7 are used (EP 0879821, C07F 7/02, 1998) . However, as stated in the description of the cited patent, this method is preferably used only for the purification of tetraethoxysilane and only for impurities of boron and phosphorus. For the purification of tetraalkoxysilanes, the distillation purification method is widely used and, as an option, distillation. Distillation is used as an additional step in ion exchange purification (JP 04082893), in the treatment of purified alkoxysilanes with complexing agents (EP 0879821). It is known to use distillation in the presence of alkoxides of alkali and alkaline earth metals for the purification of tetraalkoxysilanes from chlorine and water impurities (Chem. Abstr., Vol. 119, no. 21 (1993)). Tetraalkoxysilanes, including tetramethoxysilane, of 99.0-99.99% purity are obtained after the azeotropic distillation step using n-hexane as an azeotropically (US 7507850, C07F 7/18, 2008). However, simple distillation, like azeotropic distillation, makes it impossible to purify tetramethoxysilane from impurities of submicron heterogeneous particles carried away into the vapor phase upon boiling in the bubble mode.

The closest in technical essence and the result to the proposed method is the well-known, already cited above, method of purification of organosilanes from impurities of elements of the IIIA and YA groups, extending to a wide class of organosilanes, including tetraalkoxysilanes, including tetramethoxysilane (EP 0879821). This purification method includes the initial step of treating the purified tetramethoxysilane with a chemical compound and subsequent distillation. As a chemical compound in the prototype method, complexing agents selected from the group of the following compounds are used: thiols, alkanols, carboxylic acids, organic amines or mixtures thereof having a pKa of 3-19.7, which are introduced in an amount of at least 10% stoichiometric excess of the number of output elements. In this way, high purity products are obtained that meet the requirements for the content of elements of IIIA, YA groups in products for electronics. However, specifically in the examples, this method is considered only for the purification of tetraethoxysilane and only from impurities of boron and phosphorus. So, for example, by purifying tetraethoxysilane containing 3000 ppb boron, treating with 2,4,6-trimethylphenol, and then rectifying at atmospheric pressure, 99.9999% purity tetraethoxysilane containing boron and phosphorus impurities at the level of 1-5 ppb is obtained . Specific information on the effectiveness of the purification of other organosilanes, including tetramethoxysilane, is not given in the description of this patent. As can be seen from the above description, the main purpose of the method under consideration is purification from boron and phosphorus, and not deep purification as from impurities of metals, metalloids, and also suspended particles, which can be considered as a disadvantage of the prototype method. Additional experimental studies have shown that the introduction of complexing compounds does not purify tetramethoxysilane from chlorine impurities and is ineffective for purification from aluminum impurities. In addition, complex organic compounds introduced, such as these complexing agents, can serve as a source of additional impurities that are undesirable when using purified tetramethoxysilane in microelectronics technology.

To obtain high-purity tetramethoxysilane, in all respects satisfying the requirements for products for microelectronics and fiber optic glass melting, a method for purifying tetramethoxysilane is proposed, which includes treating the product to be purified with a chemical reagent - gaseous ammonia, which is carried out until pH 7.5-8.5 is reached, and the subsequent distillation, as well as an additional stage of distillation with evaporation from a surface without boiling, which is carried out either before the stage of processing with ammonia, or after rectification and carried out at a rate of 0.1-0.5 g / cm ² · hour.

Rectification is preferably carried out on a packed quartz column with an efficiency of 30 theoretical separation steps.

The proposed method, as well as the prototype method, is aimed at obtaining high-purity tetramethoxysilane, however, it differs significantly in technical features. These differences primarily lie in the presence of an additional purification step (distillation with evaporation from the surface without boiling), as well as in the use of another chemical reagent (gaseous ammonia) at the stage of chemical treatment of the purified tetramethoxysilane.

The use of gaseous ammonia is aimed at purifying tetramethoxysilane from chlorine impurities present in the synthesized product. The efficiency of using precisely gaseous ammonia is expressed in the possibility of purifying a product with a high content of total chlorine (more than 0.1 wt.%). Ammonia treatment is carried out until the pH of 7.5-8.5 of the product being purified is achieved, at which effective removal of chlorine is achieved. Experimental studies have shown that an increase in pH of more than 8.5 no longer affects the purification efficiency of tetramethoxysilane, and a pH of less than 7.5 indicates the presence of chlorine impurities in the product.

Another significant difference of the proposed method is the presence of a stage of distillation with evaporation from a surface without boiling, which provides purification from submicron heterogeneous particles. This stage is carried out at a certain distillation rate (0.1-0.5 g / cm ² · hour), which is optimal for the extraction of submicron impurities. A decrease in speed below the minimum of the proposed indicator adversely affects the efficiency of cleaning from suspended particles, and an increase above the maximum value can lead to undesirable entrainment of the product being cleaned.

Distillation with evaporation from the surface without boiling can be carried out both before the stage of processing with gaseous ammonia, and after the stage of rectification, as can be seen from tables 1-3. The purification process also includes a rectification stage, which, preferably, is carried out on a quartz packed column with an efficiency of 30 theoretical stages of separation. Such conditions are the optimal relative load during rectification. With an increase in the relative load during rectification, an increase in the number of particles in the product is observed, which is associated with the abrasion of the material of the distillation column and packing during intensification of the liquid and vapor flows, as well as the breakthrough of ammonium chloride particles through the packing.

Below the invention is illustrated by examples 1-3 and the attached tables.

Example 1

Through the original technical tetramethoxysilane in an amount of 1 kg, having a pH of 5.5 and containing impurities (Table 1), dried ammonia gas is passed through until a pH of 7.5 is reached. After that, the product is subjected to rectification on a packed quartz column with an efficiency of 30 theoretical separation stages. A volatile fraction was separated in an amount of 30 g (3%) from the charge. The target fraction in an amount of 920 g (92%) from the charge is distilled in the apparatus without boiling. Selected 910 g of the final product. The yield of the process is 91%.

The following is a table. 1, which presents the results of experiments on the purification of tetramethoxysilane from impurities at a distillation rate without boiling of 0.1 g / cm ² · hour.

Table 1 No. op. pH Tetramethoxysilane Quality Indicators The content of impurities,% wt. × 10 ⁶ Content% wt. × 10 The particle content of 0.3 μm, pcs / cm ³ Al Fe Ni Cr Ca Mg Cl AND TO AND TO AND TO AND TO AND TO AND TO AND TO AND TO one 6 fifty one 80 one 2 one 2 one 80 one 12 one 0.5 0.08 > 1000 80 2 6.5 fifty one 80 one 2 one 2 one 80 one 12 one 0.5 0.05 > 1000 60 3 7 fifty one 80 one 2 one 2 one 80 one 12 one 0.5 0.04 > 1000 fifty four 7.5 fifty one 80 one 2 one 2 one 80 one 12 one 0.5 0.003 > 1000 40 5 8 fifty one 80 one 2 one 2 one 80 one 12 one 0.5 <0.001 > 1000 40 6 8 fifty one 80 one 2 one 2 one 80 one 12 one 0.5 <0.001 > 1000 40 7 8.5 fifty one 80 one 2 one 2 one 80 one 12 one 0.5 <0.001 > 1000 40 8 9 fifty one 80 one 2 one 2 one 80 one 12 one 0.5 <0.001 > 1000 40 where And - the initial product, K - the final product

Example 2. An example is carried out analogously to example 1, but at different rates of distillation without boiling and at a pH of 8.1 after treatment with gaseous ammonia.

table 2 No. op. Coming soon driving. g / cm ² · hour Tetramethoxysilane Quality Indicators The content of impurities,% mass. × 10 ⁶ Content% wt. × 10 The particle content of 0.3 μm, pcs / cm ³ Al Fe Ni Cr Ca Mg Cl AND TO AND TO AND TO AND TO AND TO AND TO AND TO AND TO one 0.2 fifty one 80 one 2 <1 2 one 80 one 12 one 0.5 <0.001 > 1000 80 2 0.5 fifty one 80 one 2 <1 2 one 80 one 12 one 0.5 > 0.001 > 1000 60 3 0.6 fifty one 80 one 2 <1 2 one 80 one 12 one 0.5 0.001 > 1000 one hundred four 0.8 fifty one 80 one 2 <1 2 one 80 one 12 one 0.5 0.002 > 1000 150 5 1,0 fifty one 80 one 2 <1 2 one 80 2 12 one 0.5 0.005 > 1000 240 6 2.0 fifty one 80 2 2 <1 2 one 80 2 12 one 0.5 0.01 > 1000 300 7 3.0 fifty one 80 2 2 <1 2 one 80 2 12 one 0.5 0.02 > 1000 > 450

Example 3

The process was carried out analogously to example 1, table 1, op.6 with the difference that distillation with evaporation without boiling was carried out before processing with ammonia and distillation (L and L * - working and ultimate load on the column during distillation, respectively, kg / m ² · Hour), and the treatment with ammonia was carried out until a pH of 8.5 was established.

Table 3 No. op. Relation load. L / L * Tetramethoxysilane Quality Indicators The content of impurities,% mass. × 10 ⁶ Content% wt. × 10 The particle content of 0.3 μm, pcs / cm ³ Al Fe Ni Cr Ca Mg Cl AND TO AND TO AND TO AND TO AND TO AND TO AND TO AND TO one 0.5 fifty one 80 one 2 one 2 one 80 one 12 one 0.5 <0.001 > 1000 > 450 2 0.6 fifty one 80 one 2 one 2 one 80 one 12 one 0.5 <0.001 > 1000 > 450 3 0.7 fifty one 80 one 2 one 2 one 80 one 12 one 0.5 0.002 > 1000 > 450 four 0.8 fifty one 80 one 2 one 2 one 80 one 12 one 0.5 0.004 > 1000 > 450 5 0.9 fifty one 80 one 2 one 2 one 80 2 12 one 0.5 0.005 > 1000 > 100

Thus, the tables show that, as a result of the proposed method, under all conditions of its implementation, tetramethoxysilane of high purity is obtained by impurities that determine its quality when used in the production of microelectronic components and blends for fiber optic glassmaking.

Claims (2)

1. The method of purification of tetramethoxysilane, comprising treating the product to be purified with a chemical reagent and subsequent rectification, characterized in that it further includes a step of distillation with evaporation from a non-boiling surface, carried out either after rectification or before treatment with a chemical reagent, and distillation with evaporation from a surface without boiling carried out at a speed of 0.1-0.5 g / cm ² · h, and for chemical treatment, gaseous ammonia is used, which is passed through the product to be purified until a pH of 7.5-8.5 is reached. 2. The method according to claim 1, characterized in that the distillation is preferably carried out on a packed quartz column with an efficiency of 30 theoretical separation stages.