JPS6154352B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing pitch containing mesophasic pitch as a raw material for high-strength, high-modulus carbon fibers, and is capable of producing high-strength, high-modulus carbon fibers suitable as raw materials for composite materials at low cost and in a short time. The purpose is to provide a method to do so. The present invention provides heat treatment when heat treating petroleum-based pitch and coal-based tar, which are residual carbon substances produced by thermal catalytic cracking (FCC) of vacuum gas oil or thermal cracking of naphtha, at a temperature of 360°C to 420°C. In order to shorten the reaction time and make the reaction smooth, a non-oxidizing carrier gas is used to remove from the reaction system volatile fractions already mixed in the raw material pitch and volatile heavy substances that are by-products during heat treatment that interfere with mesophase formation. Mesophase fraction (easily measured with polarized light microscopy) is generated in the heated pitch by expelling it using gas.
The method is to produce a heat-generated pitch containing mesophasic pitch by heat-treating it under a non-oxidizing air flow at normal pressure or under pressure for 30 minutes to 20 hours so that the mesophase pitch contains 20% to 60% of mesophasic pitch. As a result of the rapid growth of the aircraft, automobile, and other transportation manufacturing industries in recent years, the materials required for them are made up of special combinations of substances, some of which have extremely superior physical properties and exhibit unique properties. There has been an increasing demand for materials that have high strength and elasticity, and there is a strong demand for materials that are lightweight and inexpensive at the same time. However, with the current technology, it is still not possible to stably supply materials that meet these demands in large quantities, and therefore research is being actively conducted on the production of composite materials (reinforced resins) to meet this demand. One of the most promising materials for use in reinforced resins is high-strength, high-modulus carbon fiber. This material appeared at the beginning of the rapid growth of the aforementioned industry, and when used in combination with resins, the carbon fibers produced reinforced resins with properties that were completely unparalleled. You can. Unfortunately, however, the demand for high-strength, high-elastic carbon fibers for use in reinforced resins as described above has not been fully exploited, even though they exhibit extremely remarkable properties. The main reason for this is the high manufacturing cost, as described below. It is known that the raw material for currently available high-strength, high-elastic carbon fibers is mainly polyacronitrile fibers produced using special manufacturing and spinning methods. In addition to being expensive as a carbon fiber, the yield of carbon fiber from this precursor is extremely poor at less than 45%, which complicates the processing steps to produce superior carbon fiber and hinders the production of the final carbon fiber. This is leading to increased costs. As a method for producing high-strength, high-modulus carbon fibers at low cost, a method for producing them from pitch containing 40% to 90% mesophase is described in U.S. Patent No. 4005183. It is known that it is an excellent raw material. It is also a known fact that mesophase-containing pitches can be produced using nitrogen, argon xenon, helmium, steam, etc. as inert gases, as described in JP-A-53-86717. . However, all of the known methods for producing high-strength, high-modulus carbon fibers are expensive to produce. Manufacturing takes time. As a result of research, the inventor of the present application has found that when producing heat-generated pitch containing 20% to 60% mesophase using extremely cheap petroleum-based or tar-based pitch as a raw material, the raw material must be heated to 360°C to 420°C. In order to remove the volatile fraction already mixed in the raw material pitch and the volatile by-products that interfere with mesophase production from the reaction system in a particularly efficient and rapid manner, a non-oxidizing gas is used as a carrier gas to remove the volatile substances mentioned above. The present invention was completed based on the discovery that the heat treatment reaction could proceed smoothly under a non-oxidizing gas flow by expelling the heat treatment, and at the same time, the heat treatment time could be shortened. Generally, petroleum-based and tar-based pitches are heated to 380°C or more.
Heat treatment at 440° C. typically requires 2 to 60 hours to produce a heat-produced pitch containing the preferred amount of mesophase. In order to shorten this time, we adopted a heat treatment temperature as high as possible, 420℃ to 440℃, and the treatment time was also reduced to 2.
If the heating time is increased to 20 hours, the average molecular weight of the produced mesophase becomes large and the anti-threading properties become poor. Therefore, the preferred heating temperature for producing mesophase-containing pitches with good thread blocking properties is 390°C.
℃ to 410℃, the heating time is 6 at this temperature condition.
It takes between 40 hours and 40 hours. However, under these temperature conditions, heat treatment using 2 to 10/Kg of non-oxidizing gas selects volatile fractions already mixed in the raw material and volatile by-product fractions that interfere with mesophase production. If it is efficiently removed from the reaction system, the heating time can be extremely shortened to about 2 to 6 hours, and at the same time the reaction can proceed smoothly. Non-oxidizing gases that can be used are those that can demonstrate their performance as carrier gas under the above heat treatment conditions, but hydrocarbons with a small number of carbon atoms, such as methane, ethane, propane, and butane, and heavy gases with low boiling points, The most economically advantageous gas is dry gas (mainly a mixture of hydrocarbons with a small number of carbon atoms) produced as a by-product by heat-treating raw materials.
Moreover, compared to the inert gas used in JP-A-53-86717, non-oxidizing gas requires less gas, although the reason for this is not well understood (probably due to its compatibility with the raw material pitch). It was found that the processing time was shortened. The content of mesophase was measured using quinoline insoluble content (Q1), and quinoline soluble content (QS) was measured using quinoline (80°C). Example 1 Residual carbon material with a BP of 380°C to 384°C or higher produced by thermal catalytic cracking (FCC) of vacuum gas oil was heat-treated at 400°C for 2 hours under a non-oxidizing air flow to produce a precursor pitch. Furthermore, this precursor was treated under the following heat treatment conditions. The yield of precursor was 54%. Next, the obtained precursor was treated under the following heat treatment conditions. In the production of the precursor, a dry gas produced as a by-product in the heat treatment reaction was circulated and used as a non-oxidizing gas stream used in the heat treatment of the precursor.

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[Table] Example 2 BP200℃ produced by thermal decomposition of naphtha
The above residual carbon material was treated under the following conditions. still,
Propane gas was used as the non-oxidizing gas stream.

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[Table] × minutes

Claims (1)

[Claims] 1. In a method for producing pitch containing mesophase as a raw material for high-strength, high-elastic carbon fibers by passing a carrier gas through petroleum-based or tar-based pitch to drive out volatile fractions mixed in the pitch, the above-mentioned carrier gas is used. Propane, butane, or a mixture thereof, or a naphtha distillation with a low boiling point that does not become heavy, or a dry gas that is a mixture of hydrocarbons with a low carbon number, which are by-produced by heating the raw material, is used to add it to the raw material pitch. A method for producing pitucci containing mesophase, characterized by expelling volatile fractions already mixed therein and volatile fractions produced as by-products during heat treatment.