JPH01249617A - Burned chaff ash composition and its production - Google Patents

Abstract

PURPOSE:To obtain the subject compsn. consisting of prescribed amts. of SiO2 and C, having superior reactivity and enabling efficient production of Si3N4, SiCl4, etc., by burning chaff under specified conditions. CONSTITUTION:Chaff is burned at 600-800 deg.C in an inert atmosphere contg. O2 controlled to 2-5vol.% concn. to obtain the title compsn. contg. 60-80wt.% SiO2 and 20-40wt.% carbon.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention is characterized in that silicon dioxide contains 60 to 80 weight percent, carbon 2
The present invention relates to a rice husk combustion ash composition, which is a raw material for producing silicon and/or silicon compounds, and a method for producing the same, which has a content of 0 to 40%.

[Conventional techniques and problems to be solved by the invention] Conventionally, a mixture of silicon dioxide such as silica stone and carbon such as coke has been used as a raw material for producing silicon carbide, silicon nitride, silicon, and silicon tetrachloride. In this case, in order to improve the efficiency of the raw materials and the reaction, it was necessary to crush silica, etc. and coke, and it was also necessary to thoroughly mix them.

For example, silicon tetrachloride is used as a raw material for synthesizing various organic silicon compounds, as well as fine silica, high-purity synthetic quartz, silicon nitride, silicon carbide, and the like. There are six existing methods for producing silicon tetrachloride:

(1) A method of producing silicon tetrachloride as a by-product in the process of producing trichlorosilane by chlorinating a metal science compound with hydrogen chloride. (2) A method of reacting ferrosilicon, silicon carbide, etc. with chlorine. (3) A method in which a mixture of a siliceous raw material such as silica stone and carbon is reacted with chlorine.

In method (1), since silicon tetrachloride is used as a by-product in the trichlorosilane production process, the amount of silicon tetrachloride depends on the amount of trichlorosilane demanded. Furthermore, in order to manufacture metal silicon, which is a raw material, a large amount of electric power is required, and the cost of the raw material becomes high. The method (2) requires a large amount of electricity to produce ferrosilicon and silicon carbide, resulting in high raw material costs. Although the cost of raw materials is low in method (3), the reactivity of the mixture of silica stone and carbon with chlorine is low, so it is necessary to pelletize the raw materials or add expensive reaction accelerators, which increases the cost. becomes higher.

As described above, each of the conventional techniques has drawbacks and is not satisfactory.

As a method for solving these difficulties, JP-A-58-55330 proposes reacting carbide of silicon-integrated biomass with chlorine at a temperature of 4[]D to 1100°C. This method has problems such as the accumulation of reaction residues during long-term continuous operation, the need for a large amount of energy to produce carbide from rice husks, and the need to dispose of tar generated during carbonization. It's not a completely satisfactory method.

The present inventors have made various efforts for the purpose of providing a composition that is suitable as a raw material for the production of silicon carbide, silicon nitride, silicon, and silicon tetrachloride and does not require complicated operations such as pulverization and mixing, and a method for producing the same. conducted research.

Among the conventional techniques for producing silicon tetrachloride, the present inventors have developed a method in which a mixture of a siliceous raw material such as silica stone and carbon is reacted with chlorine, which is inexpensive in raw material price, and in more detail, A raw material composition for producing silicon tetrachloride and a method for producing the same, which uses carbide of silicon-integrated biomass, has little reaction residue, does not require a large amount of energy when producing the raw material composition, and does not require tar treatment. Various studies were carried out with the aim of developing this technology.

[Means to solve the problem]

As a result, the ash obtained after burning rice husks in a combustion furnace, etc., contained 60 to 80 percent by weight of silicon dioxide and 20 to 40 percent by weight of carbon under combustion conditions, and the silicon dioxide and carbon were segregated. The present invention was completed by discovering that the mixture is mixed without any mixing. Furthermore, according to the present invention, volatile matter such as tar generated during carbonization is combusted, and the combustion temperature can be maintained with that energy.
No or little external heating energy is required.

That is, the present invention contains 60 to 80 percent silicon dioxide,
A rice husk combustion ash composition having 20 to 4 o*i percent carbon and the rice husk are burned at a temperature of 600 to 80 ml °C under an inert atmosphere with a controlled oxygen concentration of 2 to 5 volume percent. , a method for producing a rice husk combustion ash composition containing 60 to 80 percent by weight of silicon dioxide and 20 to 40 percent by weight of carbon.

There are no particular restrictions on the origin of the rice husks used in the present invention.

The content of silicon dioxide is always 15 to 2 in all products.
By selecting the combustion conditions, it is possible to produce rice husk combustion ash containing 60-80% silicon dioxide and 20-40% carbon.

The silicon compound referred to in the present invention refers to silicon carbide, silicon nitride, silicon tetrachloride, and the like.

Preferably, the carbon content of the composition is between 20 and 40 percent by weight. If the carbon content exceeds 40 I% and it is reacted with chlorine, a large amount of carbon will be produced as a reaction residue, causing problems in the continuous production of silicon tetrachloride.

On the other hand, if the carbon content is less than 20% by weight, a large amount of silicon dioxide will be produced as an unreacted residue, causing problems in the continuous production of silicon tetrachloride.

The composition is obtained by burning rice husks at a temperature of 600 to 800°C in an inert atmosphere with a controlled oxygen concentration of 2 to 5 percent. Combustion ash with a desired composition can be obtained by appropriately selecting the oxygen concentration and temperature. If the temperature is lower than 60 °C, combustion will not be complete, hydrocarbons will remain, and when reacting with chlorine, chlorine becomes hydrogen chloride and is lost. Also, if it is higher than 800'0, the carbon itself will burn, making it difficult to control the carbon content, and the carbon content will be 20! The amount will be less than 1%. If the oxygen concentration is less than 2 percent, the combustion time will be long and impractical; if it is more than 5 percent, the combustion rate will be high, making it difficult to control the reaction, and the carbon content will be less than 20 percent by weight.

The combustion furnace may be either a fluidized bed or a fixed bed, but a fixed bed electric heating furnace is suitable for small-scale combustion, and a fluidized bed combustion furnace is suitable for large-scale combustion. In either case, it is necessary to use a gas with an oxygen concentration controlled at 2 to 5 percent instead of air. A gas with a controlled concentration of 1 to 5 percent can be produced, for example, by recycling combustion waste gas.

When continuously producing combustion ash using a fluidized bed combustion furnace, it is necessary to supply heating gas immediately after combustion begins, but once combustion has begun, there is no need to preheat the supplied gas.

The rice husk combustion ash composition obtained according to the present invention is used as a raw material for producing silicon carbide, silicon nitride, silicon and silicon tetrachloride according to the following reaction formula.

5io2+3a-+sia+2c.

5i02 +2C+2/6N2 →i/3Si3N4
+ 200Si02 +20→Si + 2CO E102 + 20 + 2oz 2 →S 1ciA
! As is clear from the equation 4 + 200°C, in order to complete the above reaction, the molar ratio of silicon dioxide and carbon must be between 2 and 6.
It is necessary to be in the vicinity of . Generally, it is preferable to have a slight excess of carbon than the theoretical molar ratio of silicon dioxide and carbon calculated from the target product.

If the carbon content in the composition according to the present invention is less than 20 imaginary percent, there will be a lack of carbon in the above reaction, resulting in a poor yield of silicon dioxide.

In addition, if the amount exceeds 40 imaginary percent, there will be a large excess of carbon, and it will take time and effort to separate the carbon remaining after the reaction. Explain.

Example 1 Rice husks 2~ were filled into an electric heating furnace, heated to 700°C, and 2 m3 of nitrogen gas added with 6% oxygen was supplied per minute to burn for 1 hour. 560 y of combustion ash was obtained, and chemical fractionation of this resulted in silicon dioxide content of 67.5%, carbon content of 61.7%, and ash content of 0.8%. 265 g of the obtained combustion ash was mixed with water iooy and made into a disk pellet with a diameter of 1 crr and a length of about 1 cIr.
It was molded into a L shape and dried at 700°C for 1 hour under a nitrogen atmosphere. The obtained dried pellet was 75 F% k product 60
Fill a 0M graphite reactor and add chlorine from the bottom at 16 min.
The reaction was carried out at 160 °C while supplying 0M. The reaction products were analyzed using a gas chromatograph every 15 minutes, and when unreacted chlorine was detected at 1% by volume or more, the introduction of chlorine was stopped and the reaction was terminated. The reaction product gas is -60”C
was introduced into a condenser to collect the generated silicon tetrachloride.

The chlorine introduction time was 210 minutes, and the amount of silicon tetrachloride collected in the condenser was 118.9 #.

In addition, the residue remaining in the reactor after the reaction is completed is as described in 16.1. ?
Met.

Comparative Example 1 vJ, shell under nitrogen atmosphere, 2 at 8[][]'O
Carbonized for hours. The carbon content +T content of the obtained rice husk carbide is 5
The electric power was 6% and the bulk specific gravity U was 06. Volume 30
An ON graphite reactor was filled with 16.9 g of the obtained rice husk carbide, and the reaction temperature was 1050'C! A chlorination reaction was carried out in the same manner as in Example 1.

When the reaction gas was analyzed 20 minutes after the start of chlorine introduction, unreacted chlorine exceeded 1% by volume, and the reaction was terminated.

Comparative Example 2 The vJ shell carbide obtained in Comparative Example 1 was pulverized to a bulk specific gravity of 0.
25 carbonized rice husks were obtained. 75% of the obtained rice husk carbide powder
The mixture was filled into a graphite reactor having a volume of 300 + 1 t, and a chlorination reaction was carried out in the same manner as in Example 1 at a reaction temperature of 1050'0.

The chlorine introduction time was 105 minutes, and the amount of silicon tetrachloride collected in the condenser was 57.5.

Further, the residue remaining in the reactor after the reaction was completed was 45.2I.

Comparative Example 6 100 parts of Sababa silica with an average particle size of 60 μm and an average particle size of 5
A mixture of 0μm Niges 40 and 75,! 9. Filled in a graphite reactor with a volume of 30 [3 mi] and a reaction temperature of 1
The chlorination reaction was carried out in the same manner as in Example 1 at 300'O.

When the reaction gas was analyzed 20 minutes after the start of the chlorine test, unreacted chlorine exceeded 1% by volume, and the reaction was completed.

It was released into the atmosphere via an Alka 1 scrubber. Unreacted chlorine was detected 2 hours and 10 minutes after the start of the reaction, so the reaction was terminated. 510 cc of silicon tetrachloride was obtained in the trap.

Example 2 50g of combustion ash obtained by the method of Example 1 was placed in a 600M graphite reactor, and heated at a rate of 1000°C/hour to 1400°C while flowing nitrogen gas from the bottom to the top of the reactor at ID0Dcc/min. When the temperature reached 1400"O, the nitrogen gas flow rate was set to 50OCC/min and held for 4 hours, and then the nitrogen gas flow rate was increased to 500CCZ/min and the temperature was increased to 1000"G.
The temperature was lowered to 0, after which the gas supply was stopped and the mixture was cooled. The fired product in the reactor was placed in a mixture of kerosene and water (3 = 7), stirred for 60 minutes, and then cooled.
After firing for an hour, an off-white powder 21.9.9 was obtained. The water-side separated product was dehydrated and dried to obtain 27.5 F whiskers. It was confirmed by xg diffraction that both the powder and the whiskers were α-silicon nitride.

[Effects of the Invention] As described above, by using the composition, the steps of crushing and mixing silica stone and carbon can be omitted, and furthermore, the composition can be used as a raw material for producing silicon nitride and silicon tetrachloride with high reaction activity. It has the effect of saying.

In particular, the conventional method for producing silicon tetrachloride using carbide from silicon-integrated biomass has the problem of accumulation of reaction residues during long-term continuous operation, and requires a large amount of energy during the carbonization process and requires treatment of generated tar etc. However, since the method of the present invention burns rice husks, treatment of tar etc. is not necessary, and by using the rice husk combustion ash composition of the present invention, there is almost no accumulation of reaction residue.
Silicon tetrachloride can be produced efficiently.

Patent applicant Denki Kagaku Kogyo Co., Ltd. % Kanade J Applicant Sumikin Bussan Co., Ltd.

Claims (2)

[Claims] (1) 60-80% by weight silicon dioxide, 20% carbon
Rice husk combustion ash composition containing ~40 weight percent (2) Rice husk combustion containing 60 to 80 weight percent silicon dioxide and 20 to 40 weight percent carbon by burning rice husk at a temperature of 600 to 800°C in an inert atmosphere with an oxygen concentration controlled to 2 to 5 volume percent. Method for producing ash composition