JPS6228120B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of thermally decomposing hydrocarbon gas to obtain high-quality whiskers directly from the gas phase with high efficiency. More specifically, in an oxidizing atmosphere, a catalyst in a substantially finely dispersed state and a saturated hydrocarbon gas are
The present invention relates to a method for producing carbonaceous whiskers, which comprises contacting at 900°C to 1400°C. Conventionally, various researchers have attempted to thermally decompose hydrocarbon gas in the presence of a catalyst to generate short carbon fibers and whiskers using a gas phase method. For example, JP-A-52-
103528, JP 53-7538, JP 54-6891,
The method is presented. According to these conventional techniques, the whisker production reaction is carried out in the presence of hydrogen gas, which is a byproduct of thermal decomposition, or an inert gas or hydrogen gas used as a carrier gas, and the atmosphere is non-oxidizing or reducing. be. Under such conditions, the activity of the catalyst present in the tip region of the whisker, which is the growth point, is likely to be lost during the whisker growth process, so the number of whiskers generated on a unit substrate is small, and the aspect ratio ( There was a problem in that it was difficult to efficiently obtain whiskers with a large ratio (length to diameter). Whisker generation by the gas phase method uses a reaction system that has an inlet for feedstock hydrocarbon gas at one end of a reaction tube kept at high temperature and an exhaust gas outlet at the other end, and is placed at the temperature center of the reaction tube. A method is used in which a hydrocarbon gas is brought into contact with a substrate containing a catalyst to generate whiskers. Improvement in whisker generation efficiency or yield can be measured by increasing the number of whiskers generated on a unit substrate or increasing the length of generated whiskers, assuming the diameter of generated whiskers is constant. is possible. The latter method requires an extension of the reaction time and an increase in the number of reactors, and has the aspect that it is difficult to improve essential efficiency. The present inventors have conducted intensive research into a method for efficiently generating whiskers by increasing the number of whiskers generated by developing a new catalyst system. We have found that whiskers can be generated with extremely high efficiency by performing the following steps. Surprisingly, according to the method of the present invention, not only is whisker nucleation effectively carried out, but also the activity is sustained during growth, so that the substantial The number of whiskers generated has increased dramatically, and the whiskers obtained are of high quality and have an aspect ratio of over 100 for practical use. The actual number of generated whiskers here refers to the number of generated whiskers per unit base material area after peeling the generated whiskers from the base material, based on the generated base material area, total weight, average length, and average diameter specific gravity. Refers to the converted value. The present invention will be explained in more detail below. As the gas for creating an oxidizing atmosphere that can be used in carrying out the present invention, carbon dioxide gas or an oxygen-containing gas such as carbon monoxide or water vapor that substantially generates carbon dioxide gas in the reaction system can be used. . In particular, carbon dioxide gas is preferred because of its ease of operation. In general, carbon dioxide gas is a non-oxidizing gas at low temperatures, but it has been confirmed that it acts as an oxidizing gas in high-temperature reactions such as whisker-forming reactions. Whiskers are generated extremely efficiently in a new catalyst system consisting of an atmosphere and a catalyst, and the actual number of whiskers generated is 10 to 100 times higher than in conventional methods. The degree of the oxidizing atmosphere is determined by the mixing ratio of the oxidizing gas and the raw material hydrocarbon gas. The composition ratio preferably used is 0.05 to 5 volumes of carbon dioxide per volume of raw material gas, and more preferably
It has a volume of 0.1 to 3. In carrying out the present invention, the catalyst composition includes iron,
Known catalysts such as simple substances such as cobalt, nickel, transition metals, etc., or compounds thereof can be used. Particularly preferable catalysts are single group metals such as iron or compounds thereof, and more preferably catalyst compositions prepared from thiocyanic acid compounds such as iron rhodan, cyanides such as red blood salts and yellow blood salts. It will be done. Other preferred catalyst compositions include:
A catalyst composition consisting of a group metal and a group B metal and a compound thereof, in particular _a group metal and a compound thereof, in terms of a single metal, a group metal or an atomic equivalent of a group _B metal. but
Catalyst compositions with a ratio of 0.05 to 0.2 are preferred. These catalyst compositions made of metals or metal compounds may be placed on the substrate in a state in which they exist in substantially particulate form during whisker generation; It may be formed on the base material by coating it in the form of a thin film, or by adhering it to the base material in the form of a thin film using a method such as vapor deposition. Raw material hydrocarbon gases include methane, ethane,
A saturated hydrocarbon gas such as propane or butane is used. These raw material hydrocarbon gases are introduced into the catalyst layer alone or using a carrier gas such as argon, nitrogen, or hydrogen as necessary. The feeding speed of the hydrocarbon gas to be supplied is not particularly limited, but it is determined by the ratio of the feed rate (cm ³ /min) of the raw material hydrocarbon gas converted to standard conditions to the cross-sectional area (cm ² ) of the reaction vessel in the whisker generation section. The flow velocity expressed in (cm/min) (hereinafter simply referred to as flow velocity) is approximately 0.1
It is desirable that the rate is within the range of 20 cm/min, and in order to obtain higher quality whiskers, the rate is 0.5 to 5 cm/min.
A speed of about cm/min is particularly desirable. According to the present invention, when saturated hydrocarbon gas is subjected to gas phase pyrolysis to produce carbonaceous whiskers,
The furnace core tube can be made of heat-resistant materials with low air permeability such as alumina, mullite, and quartz, and the whisker-generating base material placed inside the furnace core tube can be made of alumina, mullite, etc. A plate, circular tube, or boat-shaped material made of porcelain material, quartz, graphite, etc. can be used. Any reaction system can be used, such as a fixed bed or a moving bed. The heating temperature can be arbitrarily selected within the range of 900°C to 1400°C, but a temperature range of 1000°C to 1200°C is particularly desirable, and the pressure may be increased, normal pressure, or reduced pressure; for example, 10 mmHg. Good results can be obtained even when the pressure is reduced to about 2 to 3 kg/cm ² . Industrially, normal pressure is most preferred. The reaction time is usually about 0.5 to 8 hours, preferably about 1 to 3 hours. According to the present invention, whiskers that are uniform, highly flexible, have excellent gloss, and have a large aspect ratio can be efficiently produced, and these whiskers are extremely useful as materials for composite materials. EXAMPLES Hereinafter, the present invention will be explained in more detail using Examples, but it goes without saying that the present invention is not limited to these Examples. Example 1 A resistance heating furnace with a length of 30 cm has an inner diameter with a raw material hydrocarbon gas inlet at one end and a gas outlet at the other end.
A 30 mm mullite furnace core tube was inserted and maintained at 1100°C. A mullite tube with an inner diameter of 26 mm and a length of 10 cm was installed in the center of the furnace, and its inner wall was used as the whisker generation base material surface. On the base material surface, ferric oxide powder and sodium tungsten citrate were mixed in an atomic equivalent ratio of 1:0.1 in terms of iron and tungsten, and the mixture was made into a paste with a small amount of water. On the other hand, 3×10 ⁻⁵ mol/cm ² of iron metal was uniformly applied and adhered. Do this in an air stream
It was calcined at 600°C for 30 minutes and used as a catalyst. Using this device and catalyst, propane gas is fed into the reaction tube at a flow rate of 1 cm/min, 0.05 to 5 volumes of carbon dioxide gas is added, and the reaction is carried out for 90 minutes in an oxidizing atmosphere. Ivy. After the reaction, the residual gas was replaced with argon, the furnace temperature was lowered, and the whiskers were taken out together with the base material. After determining the whisker production area, scrape off the product and measure its total weight, average length, average diameter, and specific gravity: 2.1 g/cm ³
The actual number of occurrences was calculated from this. As comparative examples, Table 1 also shows the results in a system without carbon dioxide gas and in a non-oxidizing atmosphere with hydrogen gas added.

[Table] Example 2 Using the same apparatus as in Example 1, 0.2 volume of carbon dioxide gas was added to 1 volume of propane, a catalyst was added, and an experiment was conducted. Divide the inner cannula in half and apply the deposited film to the inner surface of each half.
It was deposited to a thickness of 300 Å. A water-soluble salt such as Rodan's iron was applied to the inner wall of the internal tube in an amount of 3×10 ^-5 mol/cm ² in terms of iron, and then calcined in air at 600° C. for 2 hours before being used in the reaction. As a comparative example, an example in which hydrogen gas was added instead of carbon dioxide gas, and a 2 cm width as a catalyst,
Table 2 also shows examples using 10 cm long metal iron pieces or nickel plates.

[Table] Example 3 Similar to Example 2, experiments were conducted using catalyst systems made of various catalyst compositions. The catalyst composition is made by mixing tungsten, molybdenum, and chromium compounds in various ratios to ferric oxide, and then applying the mixture to the inner wall of the base material with a small amount of water at a concentration of 3×10 ^-5 mol/cm ² in terms of iron. After being uniformly deposited, the material was calcined at 600°C for 2 hours. The reaction was carried out using an oxidizing catalyst system in which 0.2 volume of CO ₂ was added to 1 volume of propane gas. As a comparative example, Table 3 shows an example of a non-oxidizing catalyst system using hydrogen gas instead of carbon dioxide gas.

【table】

[Table] Example 4 Butane was used as the raw material hydrocarbon gas. The catalyst reaction temperature and gas flow rate were the same as in Example 1. An experiment was conducted in an oxidation system by adding 0.1 volume of carbon dioxide gas to 1 volume of raw material hydrocarbon gas. As a comparative example, a non-oxidizing experiment was conducted using hydrogen instead of carbon dioxide gas. After reacting for 2 hours, the number of generated whiskers was 6.5×10 ⁴ , about 200 times that of the latter, and the diameter of the whiskers was 8μ and the length was 5.
mm, aspect ratio of 625, and had excellent uniformity with rich photo-selectivity. Comparative Experimental Example Propane gas was applied at 1 cm/min to the same equipment as in Example 1, except that no catalyst was applied to the substrate surface.
Carbon dioxide gas was introduced into the reaction tube at a flow rate of 0.1 cm/min, and the reaction was carried out for 90 minutes. The number of whiskers generated was 10/cm ² .

Claims (1)

[Scope of Claims] 1 A catalyst in a substantially finely dispersed state and a saturated hydrocarbon gas are mixed with 0.05 to 5 volumes of carbon dioxide, carbon monoxide, or water vapor in terms of carbon dioxide gas per volume of saturated hydrocarbon gas. A method for producing carbonaceous whiskers, comprising contacting at 900°C to 1400°C in the presence of carbonaceous whiskers. 2. The method according to claim 1, wherein the catalyst is an elemental group metal or a compound thereof. 3 The catalyst is a group metal or its compound and _B
2. The method according to claim 1, which is a composition comprising an elemental group metal or a compound thereof.