JPH06643B2 - How to recover alcohol - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for recovering alcohol, and more specifically, a gel is prepared by hydrolysis of alkoxysilane, and the gel is heated and dehydrated and then fired to produce high-purity synthetic quartz. At this time, the present invention relates to a method for recovering alcohol, in which alcohol contained in the gel can be easily removed and recovered so that black foreign matter is not generated in the obtained synthetic quartz.

[0002]

BACKGROUND OF THE INVENTION Conventionally, quartz powder has been produced by crushing high-quality natural quartz (quartz) with a ball mill or the like. However, in recent years, natural quartz is a quartz powder used as a filler for a resin composition for electronic parts, particularly for semiconductor VLSIs, in addition to resource restrictions that the production areas are unevenly distributed and tends to be depleted. In addition, as a quartz for producing a semiconductor single crystal pulling crucible, there is a problem that its purity is low.

That is, naturally occurring quartz powder contains various heavy metal impurities, and it is known that these impurities deteriorate the characteristics of electronic parts, and particularly LS.
As the sealant filler of I, it has been recognized that α rays emitted from a trace amount of uranium or thorium contained in the filler causes an operation error of the device. Therefore, high-purity quartz powder with a low content of uranium or thorium is demanded, and particularly, a high-purity product having a concentration of uranium as an impurity of 1 ppb or less is required as a filling material for a sealing agent for VLSI. There is.

Under these circumstances, attempts have been made to chemically synthesize quartz powder, not to produce it from naturally occurring quartz. For example, a method of oxidizing a silicon compound such as SiCl ₄ by an oxyhydrogen flame and then sintering the obtained silica, or hydrolyzing an alkoxysilane Si (OR) ₄ in the presence of an acid or base catalyst to obtain a gel There have been proposed methods such as firing the.

Of these methods, the method of producing synthetic quartz by hydrolyzing an alkoxysilane into a gel and firing the gel can lower the firing temperature and distill the alkoxysilane as a starting material. Since it has the advantage that it can increase its purity, research has been actively conducted.

By the way, in the production of synthetic quartz using alkoxysilane as a starting material, specifically, first, water and an acid as a catalyst are added to tetraalkoxysilane for hydrolysis and condensation polymerization to prepare a gel. Generally, it has been carried out by drying the obtained gel and then firing it at a temperature of around 1200 ° C. At this time, the gel obtained by hydrolysis / condensation polymerization of the alkoxysilane contains a large amount of alcohol produced by hydrolysis, but if this alcohol is baked without being completely removed from the gel, the carbon of the alcohol The atoms are carbonized, and black foreign matter may be generated in the resulting synthetic quartz.

In order to prevent the generation of such a black foreign substance, the gel is not heated rapidly and fired, but is gradually heated in stages and fired, and carbon-containing carbon such as alcohol is burned during firing. A method of gradually evaporating atomic compounds has been proposed. However, in this method, there are restrictions on the selection of the firing furnace and the firing time becomes long.

A method of thoroughly washing the gel with water before firing has also been proposed. However, in this method, the alcohol concentration in the wash water obtained by washing the gel is low, so that the alcohol is recovered from the wash water. There was a problem that it was difficult.

[0009]

SUMMARY OF THE INVENTION The present invention is intended to solve the problems associated with the prior art as described above, and facilitates the removal of alcohol from the gel obtained by the hydrolysis / condensation polymerization of alkoxysilane. It is an object of the present invention to provide a method for recovering alcohol that can be recovered.

[0010]

SUMMARY OF THE INVENTION The alcohol recovery method according to the present invention comprises:
When a synthetic quartz is produced by contacting a gel obtained by hydrolyzing and condensation-polymerizing a tetraalkoxysilane with superheated steam at 150 ° C. or higher, and then drying and firing, separation of alcohol contained in the gel is almost eliminated. Cools the superheated steam that was in contact with the gel until the end.
It is characterized in that it is condensed into a concentrate containing alcohol in a high concentration, and alcohol is recovered from this concentrate.

In the present invention, a gel obtained by hydrolysis and condensation polymerization of tetraalkoxysilane is treated at 150 ° C.
Since it is in contact with the above superheated steam, the alcohol contained in the gel is transferred to the superheated steam and completely removed from the gel. Therefore, superheated steam after contact with the gel,
That is, since the concentrated liquid containing a high concentration of alcohol can be obtained by cooling the superheated steam containing alcohol, the alcohol can be easily recovered from this concentrated liquid. Further, no black foreign matter is generated in the obtained synthetic quartz.

[0012]

DETAILED DESCRIPTION OF THE INVENTION The method for recovering alcohol according to the present invention will be specifically described below. First, a general method for producing synthetic quartz from tetraalkoxysilane will be described. By adding water and an acid or base as a catalyst to tetraalkoxysilane as a starting material, the tetraalkoxysilane is hydrolyzed and condensation-polymerized. Prepare the gel.

As the starting material tetraalkoxysilane, tetramethyl orthosilicate, tetraethyl orthosilicate and the like are used. The mixing ratio of tetraalkoxysilane and water is usually 0.2 to 2 parts by weight with respect to 1 part by weight of tetraalkoxysilane.

As a catalyst for the hydrolysis and condensation polymerization of tetraalkoxysilane, an acid such as formic acid or acetic acid or a base such as ammonia is used. The gel thus prepared is usually dried after the alcohol contained in the gel is removed and then fired to obtain synthetic quartz. The gel is generally baked at 1000 to 1200 ° C.
For 2 to 4 hours. A synthetic quartz powder can be obtained by crushing after firing.

In the present invention, the gel obtained by the hydrolysis and condensation polymerization of tetraalkoxysilane in the above-mentioned general method for producing tetraalkoxysilane is heated to 150 ° C. or higher, preferably 200 ° C. or higher. Upon contacting with the gel, the superheated steam is cooled and condensed until the separation of the alcohol contained in the gel is almost completed to obtain a concentrate containing a high concentration of alcohol, and the alcohol is recovered from the concentrate. I am trying.

The contact between the gel and the superheated steam is carried out, for example, by placing the gel in a cylinder such as a drum and continuously supplying the superheated steam from the lower part of the cylinder under normal pressure or under pressure. You can

When the above gel is contacted with superheated steam at 150 ° C. or higher, the alcohol contained in the gel is mainly separated first, and then the water taken in the gel is mainly separated. . That is, when the gel is contacted with superheated steam at 250 ° C., for example, the temperature of the gel rises and alcohol is separated as shown in FIG. 1, but the alcohol is almost separated at the point indicated by A in the figure. finish. Continuing to keep the gel in contact with superheated steam,
The water taken into the gel separates, but the separation of the water taken into the gel is almost completed at the point indicated by B in the figure. Thus, by detecting the temperature of the superheated steam after being brought into contact with the gel, the end point of dealcoholization and the end point of dehydration can be easily determined.

In order to efficiently recover the alcohol separated from the gel, by cooling and condensing the superheated steam in contact with the gel up to the end point of dealcoholization as shown in FIG. Water in the superheated steam is condensed and separated to obtain a concentrated liquid containing alcohol at a high concentration of 5 to 30% by weight. Alcohol can be easily recovered from this concentrated solution by a conventional method such as distillation.

The gel thus treated with superheated steam is then brought into contact with an inert gas such as nitrogen gas and dried, and then calcined as described above.
If necessary, it is crushed to obtain synthetic quartz powder.

By the way, the gel treated with superheated steam according to the present invention does not generate black foreign matter due to alcohol in the obtained synthetic quartz powder, even if it is fired under any conditions.

[0021]

INDUSTRIAL APPLICABILITY In the present invention, a gel obtained by hydrolysis and condensation polymerization of tetraalkoxysilane is
The alcohol contained in the gel is transferred to the superheated steam and is completely removed from the gel because it is contacted with the superheated steam at a temperature of not less than ° C. Therefore, a concentrated solution containing a high concentration of alcohol can be obtained by cooling the superheated steam after contact with the gel, that is, the superheated steam containing alcohol. Therefore, the concentrated solution can be easily distilled by a known method such as distillation. Can be recovered.

The present invention will be described below with reference to examples.
The present invention is not limited to these examples.

[0023]

Example 1 Tetramethyl orthosilicate and 1% acetic acid aqueous solution were mixed (weight ratio 2/1), and 400 kg of the gel obtained by hydrolysis and polycondensation was put in a drum with an internal volume of 1 m ^3. Superheated steam at 250 ° C. was supplied and ventilated from below the drum at 1.3 tons / hour. Cool the outlet steam until the steam temperature of superheated steam at the outlet reaches 95 ° C.
It was condensed and collected. The methanol of the obtained condensate was 8.
The concentration was 9% by weight. From this condensate, methanol could be easily separated and recovered by ordinary distillation. The superheated steam is supplied at a temperature of 180 ° C at the outlet.
Was continued for 2 hours and then purged with nitrogen gas for several minutes.

When the obtained dried gel was calcined in an electric furnace at 1100 ° C., no black matter adhered due to carbonization was found on the obtained synthetic quartz.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a contact time and a temperature of superheated steam after contact when a gel and superheated steam are brought into contact with each other.

Claims (1)

[Claims] 1. A gel obtained by hydrolyzing and condensation-polymerizing tetraalkoxysilane is brought into contact with superheated steam at 150 ° C. or higher, and then dried and fired to produce synthetic quartz, which is contained in the gel. By cooling and condensing the superheated steam that was in contact with the gel until the alcohol separation is almost completed,
A method for recovering alcohol, comprising preparing a concentrate containing alcohol at a high concentration and recovering alcohol from the concentrate.