JP4589779B2 - Generation method of hydrogen gas - Google Patents

Description

  The present invention relates to a method for generating hydrogen gas, and more particularly to a method for generating hydrogen gas from silicon powder containing copper powder. The present invention further relates to a method for recovering silica fine powder and / or alkali metal silicate or an aqueous solution thereof.

  Hydrogen gas is widely used for synthesis of ammonia, methanol, etc., hydrogenation of fats and oils, oxyhydrogen flame welding, and the like, and has attracted attention as a fuel for pollution-free fuel cells. Hydrogen is industrially produced by methods such as electrolysis of water and brine, and steam reforming of petroleum and natural gas. However, the former is expensive in energy cost, and the latter is low in purity, so further purification is required, and a simple and inexpensive generation method is required.

It is known that silicon reacts with water to generate hydrogen gas. In Patent Document 1,
High-purity hydrogen is produced by reacting silicon scrap generated in large quantities in the semiconductor wafer manufacturing process with an aqueous sodium carbonate solution or an alkaline aqueous solution such as an alkaline waste liquid generated in the semiconductor device manufacturing process at a temperature of 50 ° C. or higher. Generating is disclosed. In order to prevent the formation of a gel by silicate ions during the above reaction and hindering the generation of hydrogen, Patent Document 2 proposes using silicon powder in a slurry form with water. Patent Document 3 discloses storing generated hydrogen as a hydrogen storage alloy. However, silicon used in these methods is of high purity for semiconductors, and although it is scrap, its cost is high.

  Patent Document 4 prepares a refractory solution by adding an alkaline aqueous solution obtained by reacting potassium hydroxide, sodium carbonate, silicon and water to a solution obtained by mixing water, borax, phosphoric acid and boric acid. However, it is disclosed that the coating material is processed into various substrates. Regarding silicon as a raw material, there is no description other than that described as metal silicon, and in the examples, commercially available silicon lumps are used, but most of the charged silicon lumps remain without being dissolved.

  On the other hand, organochlorosilanes such as methylchlorosilane have been synthesized as intermediate raw materials for silicone and organosilicon compounds. Taking methylchlorosilane as an example, a contact body obtained by mixing silicon powder with copper and / or copper compound powder (hereinafter referred to as copper catalyst) as a catalyst is charged into a reactor and reacted with silicon through methyl chloride. The crude methylchlorosilane is synthesized and various methylchlorosilanes are obtained by rectification. The reaction is continued by supplying methyl chloride continuously while replenishing the silicon powder consumed by the reaction. When the copper catalyst is deteriorated, the reaction is stopped and the contact body is taken out from the reactor. In addition, it is also possible to collect fine silicon powder and a contact body, which are carried along with the methyl chloride flow during the reaction, with a cyclone.

  Similarly, the synthesis reaction of a silane compound using a copper catalyst is a reaction of synthesizing trichlorosilane useful as an intermediate for obtaining high-purity silicon for semiconductors from silicon and hydrogen chloride; synthesizing methoxysilanes from silicon and methanol. There are examples used in the reaction as well, resulting in waste contacts containing silicon and copper.

  The waste contact body by-produced in this way still has an activity that ignites in the air. For this reason, manufacturers of silane compounds stabilize it by a method such as heat treatment and then dispose of it. In Patent Document 5, as a method for reusing silicon and copper catalysts contained in waste contact bodies, the waste contact bodies are dispersed in dilute hydrochloric acid, and contacted with chlorine at 20 to 100 ° C. to convert copper into copper (II) chloride. It is disclosed that it is changed and separated, reduced and reused as a catalyst, and silicon particles are recovered as a precipitate. Patent Document 6 discloses that a waste contact body is brought into contact with hydrogen chloride or chlorine at 500 to 1,200 ° C. and recovered as silicon chloride and metal chloride.

  However, these methods are cumbersome and costly when considering making the apparatus corrosion resistant. In particular, silicon tetrachloride obtained in Patent Document 6 has a lower utility value than other silane compounds. Therefore, these methods cannot be said to be effective utilization methods of the waste contact body.

  In Patent Document 7, in the presence of a polyalkylene ether surfactant, the waste contactor is brought into contact with water in an acidic region at a temperature of 20 to 100 ° C. to generate hydrogen, and then a binder is added. It is disclosed that the waste contact body is made inactive by dehydration.

  When the above-described method is applied to silicon powder having copper and / or copper compound powder and having an activity like a waste contact body, the hydrogen generation reaction by contact with water is an exothermic reaction. In addition, it is difficult to generate hydrogen violently by the activity remaining in the waste contact body and to generate hydrogen safely and stably.

JP 2000-191303 A Japanese Patent Laid-Open No. 2001-213609 JP-A-2004-213609 JP 2002-121424 A US Pat. No. 2,803,521 Japanese Patent Laid-Open No. 9-110411 Japanese Patent Laid-Open No. 7-145176

  An object of the present invention is to provide a method of generating hydrogen safely and stably from silicon powder containing copper and / or copper compound powder. Another object of the present invention is to provide a method for effectively utilizing the residue remaining after the generation of hydrogen as silica fine powder and / or alkali metal silicate or an aqueous solution thereof. .

  As a result of repeated studies to solve the above problems, the present inventor has found that the object can be achieved by allowing the hydrogen generation reaction to proceed while cooling to less than 20 ° C., thereby completing the present invention. It came to.

  That is, the present invention is a method of generating hydrogen by reacting silicon powder containing copper catalyst powder and having an average particle size of 500 μm or less with water, and performing the reaction at a temperature of less than 20 ° C. The present invention relates to a characteristic method, and further relates to a method for recovering silica fine powder and / or alkali metal silicate or an aqueous solution thereof together with the hydrogen.

  According to the present invention, hydrogen can be generated safely and stably from silicon powder containing copper catalyst powder. In addition, it can be used as a silicon resource as a silica fine powder and / or an alkali metal silicate salt or a binder containing the same as a main component.

  The silicon powder used in the present invention includes a copper catalyst powder. The silicon powder may be for industrial use with a purity of 95 to 99% by weight before blending the catalyst, and the purity is not particularly limited. Silicon powder containing such copper catalyst powder is used for the synthesis of organochlorosilanes by direct method of silicon and halogenated hydrocarbons, such as the synthesis of methylchlorosilanes from silicon and methyl chloride; silicon and hydrogen chloride. When a silane compound is synthesized, such as a reaction for synthesizing trichlorosilane from silicon; a reaction for synthesizing methoxysilanes from silicon and methanol.

  The copper catalyst is copper and / or a copper compound as described above. Examples of the copper catalyst include copper, and copper compounds such as cuprous oxide, copper oxide, and copper (I) chloride. Moreover, you may use metals other than copper, for example, zinc, tin, iron, nickel, silver etc., together with copper as a promoter. These may be used as mixed powder with a copper catalyst or in the form of alloy powder with copper. Furthermore, these catalysts such as copper may at least partially form an intermetallic compound with silicon by pretreatment before the reaction or during the reaction. In the present invention, the copper catalyst includes all these forms of catalyst.

  The copper catalyst smoothly advances the silane synthesis reaction and, in the case of methylchlorosilanes, in order to synthesize dimethyldichlorosilane with a high selectivity, usually 0 in terms of copper atoms relative to silicon powder. It is inserted into the reactor so as to be in the range of 5 to 10% by weight, preferably 1 to 6% by weight, but since silicon is consumed as the reaction proceeds, the copper catalyst in the removed waste catalyst The amount can reach 5-60% by weight. The cocatalyst may not be added. In the case of zinc, the amount is usually 0.01 to 0.5 parts by weight with respect to 1 part by weight of copper.

  The silicon powder is supplied with an average particle size of 500 μm or less, preferably 1 to 200 μm, more preferably 20 to 100 μm, in order to smoothly advance the flow reaction for synthesizing the silane compound, but silicon is consumed as the reaction proceeds. Thus, the average particle size of the silicon powder recovered as a waste contact body is generally 0.5 to 200 μm although it depends on the reaction time. In particular, what is carried out from the reactor with the gas and recovered by the cyclone may have an average particle diameter of about 0.1 to 5 μm. In the synthesis of organochlorosilanes, the recovered waste contact body includes high boiling point organosilicon compounds such as disilane compounds and silmethylene compounds generated by side reactions, and / or silicon powder and copper by thermal decomposition during the reaction. May contain carbon deposited on the surface of the catalyst. The activity remaining in the waste contact body depends on the final stage of silane compound synthesis, the copper content in the waste contact body, the average particle size and particle size distribution of the silicon powder, the storage state and storage period after removal, etc. Is also different.

  In the present invention, the water used for reacting with the silicon powder is usually a stoichiometric amount because the following hydrogen generation reaction is an exothermic reaction and also serves as a coolant for maintaining the required reaction temperature. It is much more excessive and is usually 3 to 200 times, preferably 5 to 100 times the weight of silicon powder. As for the amount of water, 5 to 50 times the amount is sufficient when the target product is fine silica, but in the case of sodium silicate or the like, the amount is more preferably 20 to 100 times in order to allow the reaction to proceed more slowly. .

Si + 2H ₂ O → SiO ₂ + 2H ₂

  The water may be pure water or city water, and may be brine water containing a freezing point depressant such as sodium chloride, magnesium chloride or calcium chloride, for example, when the reaction is conducted at less than 0 ° C. In order to neutralize hydrogen chloride produced by hydrolysis from an organosilicon compound having a chlorine atom bonded to a silicon atom present in the system and / or to convert the produced silicon dioxide to sodium silicate, An aqueous solution containing a basic sodium compound such as sodium hydroxide, sodium carbonate, sodium hydrogen carbonate; and / or a basic potassium compound or a basic lithium compound corresponding to them may be used. A basic alkali metal compound may also serve as a freezing point depressant, and a basic alkali metal compound may be used in combination with another freezing point depressant. When solubility of the resulting silicate in water is required, a basic sodium compound such as sodium hydroxide is preferred. In order to omit the step of purifying the obtained alkali metal silicate, the same water-soluble silicate as the target silicate may be used as a part of the freezing point depressant.

  A silicon compound containing a copper catalyst, such as a waste catalyst, has activity, and its activity cannot be easily measured. Since silicon is in a fine powder state, in order to suppress the explosive progress of the reaction, The reaction is carried out by keeping the temperature below 20 ° C., preferably below 0 ° C., by controlling the introduction rate. In practice, the lower limit of the preferred reaction temperature is about -15 ° C. In order to keep the system at a low temperature, the reaction solution is preferably water containing a freezing point depressant as described above. Further, it is preferable to cool the outer periphery of the reactor with the same refrigerant or use other cooling means such as latent heat. In addition, after performing reaction at said temperature, in order to complete reaction, you may raise temperature to about room temperature.

  In order to easily control the progress of the reaction, the reaction may be performed in a neutral region of pH 6 to 8, and may be performed in an alkaline region where the pH exceeds 8 when the activity of the waste contactor is low. In order to make the system alkaline, a basic alkali metal compound such as the above basic sodium compound and / or basic potassium compound, or a corresponding basic lithium compound may be used in some cases.

  The generated hydrogen can be collected in a hydrogen storage device such as a pressurized container, or adsorbed on a hydrogen storage alloy.

  By performing the hydrogen generation reaction in a neutral region, precipitation of fine silica powder occurs. Silica fine powder contains components that are not involved in the reaction in the waste contact body, such as copper, metals used as promoters, iron, carbon, and organic compounds mixed from the reactor for synthesizing silane compounds. . By removing these impurities by a method such as acid treatment, purified fine powder silica can be obtained.

  Alternatively, a hydrogen generation reaction may be performed in the presence of a basic alkali metal compound such as a basic sodium compound to obtain an aqueous solution containing an alkali metal silicate salt such as sodium silicate such as sodium metasilicate. The amount of the basic alkali metal compound used may be a theoretical amount or an excess amount, for example, an excess amount of up to 10%, may be used to complete the reaction. However, the concentration of the basic alkali metal compound in the aqueous solution is preferably less than 1N so as not to cause a rapid reaction, and more preferably 0.5N or less. In that case, use another freezing point depressant if necessary. The compound may be present in its entirety when starting the reaction, or may be added sequentially as an aqueous solution to control the reaction rate. Since sodium silicate is obtained as an aqueous solution, impurities derived from the waste contact body as described above can be removed by filtration. Sodium silicate may be used as it is for various applications as it is, or may be used after being concentrated by a method such as heating under reduced pressure.

  When the activity of the waste contactor is high or possibly, the silica fine powder is formed without a basic alkali metal compound or with a minimum amount thereof, and then, for example, sodium hydroxide. An alkali metal silicate salt such as sodium silicate may be formed by reaction with a basic alkali metal compound. Conversely, precipitated silica or silica hydrogel can be obtained by adding an inorganic acid such as hydrochloric acid to an aqueous solution containing sodium silicate obtained in the presence of a basic alkali metal compound.

  Hereinafter, the present invention will be described in more detail by way of examples. The present invention is not limited by these examples. In the following examples and comparative examples, unless otherwise specified, parts represent parts by weight, and% of concentration represents weight%.

  The waste contact materials used in Examples and Comparative Examples were taken out of the reactor after being used for the synthesis of methylchlorosilanes. According to X-ray fluorescence analysis, 82% silicon, 12% copper and carbon It contains 1.5%, has an average particle size of 10 μm, and still has considerable activity.

Example 1
Stirring device, solid insertion device, hydrogen discharge hole and pressure-resistant storage tank connected to it, and thermometer, and charged with 352 parts of sodium chloride 15% aqueous solution in nitrogen atmosphere in pressure-resistant and corrosion-resistant reaction vessel surrounded by brine bath It is. Chilled brine containing 18% calcium chloride is circulated in the brine bath to maintain the liquid temperature in the container at -5 ° C., and 68.3 parts of waste contactor is added to the stirring sodium chloride aqueous solution. In order not to exceed 5 ° C., it was added in small portions over 80 minutes and brought into contact with water, and hydrogen generated by the reaction was introduced into the storage tank. As the reaction progressed, fine silica powder precipitated in the reaction vessel. After completion of the addition, stirring was continued for 1 hour, the brine bath was changed to a water bath, the temperature of the liquid in the container was raised to 15 ° C. over 20 minutes, and stirring was further continued for 30 minutes at the liquid temperature of 15 ° C. Was completed. The reaction proceeded slowly and stably, and hydrogen corresponding to 91% of the theoretical amount (8 parts) was obtained. The solid deposited in the container was collected by filtration and classified to recover 105.6 parts of silica fine powder.

Example 2
As a reactant, 1,200 parts of an aqueous solution containing 2% sodium hydroxide and 5% sodium metasilicate was used. The liquid temperature in the container was set to −2 ° C. at the start of the reaction, and the liquid temperature during the reaction was controlled to below 0 ° C. Then, except that the liquid temperature at the final stage was set to 10 ° C., 20.5 parts of the waste contact body was added and reacted in the same manner as in Example 1. The reaction proceeded slowly and stably, and hydrogen corresponding to 87% of the theoretical amount was obtained. An aqueous solution containing sodium metasilicate in a total amount of sodium hydroxide involved in the reaction and charged as a freezing point depressant of the reactant and the amount obtained by the reaction was obtained. The powdered solid was filtered off from the product solution, and the solution was concentrated by heating under reduced pressure to obtain 778 parts of an aqueous solution containing 20% sodium metasilicate.

Comparative Example 1
The reaction was conducted in the same manner as in Example 1 except that a water bath was used instead of the brine bath and the reaction start temperature was 30 ° C. As the temperature rose, the reaction proceeded violently and it was difficult to control the reaction.

Comparative Example 2
The reaction was performed in the same manner as in Example 2 except that a water bath was used instead of the brine bath and the reaction start temperature was 30 ° C. The temperature rose rapidly and the reaction proceeded explosively, making it difficult to control the reaction.

  According to the present invention, hydrogen gas and, if necessary, fine silica powder and / or sodium silicate are obtained from silicon powder containing a copper catalyst, which is by-produced during the synthesis of silanes and is costly discarded. Obtainable. Hydrogen gas is useful for small-scale applications of hydrogen gas, such as oxyhydrogen flame welding and fuel cell fuel. Silica fine powder has uses such as fillers and extender pigments. Sodium silicate or an aqueous solution thereof is used as a water glass for binders, adhesives, and the like, and is also used as a raw material for fireproof cement, synthetic silicate, paint, and the like. Furthermore, it is useful in the silicone industry as a raw material for tetrafunctional siloxane units of branched or reticulated polyorganosiloxane.

Claims (7)

A method of generating hydrogen by reacting silicon powder, which is a waste contact body for synthesizing a silane compound, containing copper and / or copper compound powder and having an average particle diameter of 500 μm or less with water. A method characterized in that it is carried out at a temperature of less than ° C. The process according to claim 1, wherein the reaction is carried out at a temperature below 0 ° C. The process according to claim 1 or 2 , wherein the reaction is carried out at pH 6-8. The method as described in any one of Claims 1-3 which collect | recovers a silica fine powder. The method according to claim 1 or 2 , wherein the reaction is carried out in an aqueous solution containing a basic alkali metal compound, and an alkali metal silicate salt or an aqueous solution thereof is recovered. The method according to claim 5 , wherein the concentration of the basic alkali metal compound in the aqueous solution is 0.5 N or less. The method according to claim 5 or 6 , wherein the alkali metal silicate is sodium silicate.