JPH01210494A - Method of purifying mesophase pitch - Google Patents

Abstract

PURPOSE:To efficiently remove gel materials and obtain a mesophase pitch suited for use in the production of a carbon fiber, by filtering a mesophase pitch heated to a predetermined temp. through a filter. CONSTITUTION:A mesophase pitch from an oil or a coal, which has a mesophase content of 70-100%, a glass transition tamp. (Tg) of 200-280 deg.C and a pour point (Ts) of 270-350 deg.C, is heated to a temp. in the range of from Tg to Ts, and filtered through a filter having a bore diameter being up to 1/3 of the diameter of a carbon fiber, and having a void ratio of at least 30% (e.g., sintered metallic filter). Then, a mesophase pitch heated to a temp. of Ts or higher is passed through the filter to clean it. This sequence of operations is repeated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for purifying mesophase pitch, and more particularly to an efficient method for purifying mesophase pitch suitable for producing carbon materials, particularly carbon fibers.

[Prior Art and Problems to be Solved by the Invention] In recent years, methods using pitch-based raw materials have been widely used as methods for obtaining carbon materials. Among carbon materials, carbon fibers in particular are usually obtained by heat-treating decant oil from fluid catalytic cracking of heavy oil or coal tar to obtain optical anisotropy (
A method of manufacturing mesophase is carried out by spinning pitch and then firing it.

A filter is provided to remove foreign matter or solid matter such as residual catalyst in the raw material during spinning.

However, even if it is not a completely solid substance, if a gel-like substance that is difficult to deform at that temperature exists in the raw mesophase pitch,
This may cause thread breakage during spinning or blockage of the spinning machine filter or nozzle, making it difficult to thread smoothly. For this reason, it is necessary to remove such gel-like substances in addition to solid foreign matter before spinning.

The mesophase pitch for carbon fiber has a number average molecular weight of 1.00.
A value of about 0 is suitable. In order to suppress the formation of high molecular weight substances at this time, a method has been proposed in which high molecular weight substances are removed by solvent fractionation or the like at a stage before mesophase pitch formation. However, this method requires a complicated process because it uses a solvent, and furthermore, since it has not yet been converted to the meso phase,
It is impossible to completely suppress or eliminate the formation of gel-like substances that adversely affect spinning.

On the other hand, a filtration method has been proposed as a pitch purification method (
(Japanese Unexamined Patent Publication No. 62-64889), this method aims to remove the optically isotropic pitch from the pitch where the optically isotropic phase and the optically anisotropic phase coexist. The reality is that a method for removing gel-like substances from anisotropic (mesophase) pitch has not yet been established.

[Means to solve the problem]

Therefore, the inventors of the present invention conducted intensive research on a method for efficiently removing the above-mentioned gel-like substances, and as a result, they discovered that this gel-like substance could be removed by performing filtration in a specific temperature range, and hereby completed the invention. I ended up doing it.

That is, the present invention provides a method for purifying mesophase pitch, which is characterized by filtering mesophase pitch through a filter at a temperature ranging from the glass transition temperature to the pour point of the pitch; An operation of filtering the pitch through a filter at a temperature ranging from the glass transition temperature to the pour point of the pitch; The present invention provides a method for purifying mesophase pitch, which is characterized by sequentially repeating the steps of passing the phase pitch through and washing a filter.

70 to 100%, particularly preferably substantially 10
0%. As such mesophase pitch,
The glass transition temperature (Tg) is 200 to 280°C,
Also, the pour point (Ts) is 270~.

A temperature of 350°C is preferred. Here, the glass transition temperature and pour point were measured using a flow tester or a thermomechanical analyzer (TMA).

In the present invention, the mesophase pitch as described above is used.

The pitch is filtered through a filter at a temperature ranging from the glass transition temperature to the pour point (filtration operation).

This filtration operation may be carried out in the above temperature range, but preferably at a temperature 5° C. or more below the pour point.

At the pour point, the viscosity is about 1,000 poise, and on the other hand, below the glass transition temperature, it does not flow as a complete solid, so it is filtered at an appropriate temperature between this point so that the viscosity is about 10,000 poise or less. It is efficient to do this.

By performing the filtration operation in such a specific temperature range, it is possible to improve spinnability by removing gel-like substances in the mesophase pitch and to prevent deterioration of the mesophase pitch during filtration.

The filter used for this filtration operation is preferably a sintered metal filter, a metal fiber filter, a sand-filled filter, or the like, which has a smaller bore diameter and a higher porosity than one using a wire mesh. At this time, the bore diameter is preferably 1/3 or less of the diameter of the carbon fiber obtained by spinning, and the porosity is 30.
% or more, more preferably the bore diameter is 11% of the thread diameter.
5 or less, and the porosity is 60 to 90%.

In addition, when the spinning machine is equipped with another filter in addition to the filter equipped with the above-mentioned filter, the filter of this spinning machine is preferably of the same size as the mesh of the filter of the filter.

The purpose of the spinning machine filter is to remove foreign matter or gel-like substances that are generated in the spinning machine, mixed in from the outside, or passed through the filter. If a filter that is extremely finer than the filter is used, it will clog and the spinning will be delayed for a long time. This is not desirable as it interferes with Therefore, it is desirable to remove most of the foreign substances and gel-like substances using a filter before spinning.

Further, the residence time in the filter is preferably as short as possible in order to prevent pitch deterioration, but it is preferably 1 hour or less.

In the present invention, only a filtration operation such as on a ridge may be used, but this filtration operation is also used as the first step, and as a second step, the filter used in the first step is heated to a temperature higher than its pour point. The first step and the second step may be repeated in sequence by combining the operation of washing the filter through the heated mesophase pitch. By performing this washing operation, gel-like substances clogging the filter can be removed, the life of the filter can be extended, and mesophase pitch can be spun for a long time.

This washing operation is carried out by passing the mesophase pitch heated to a temperature above the pour point through the filter filled with the gel-like substance in the first step (filtration operation) and extruding the gel-like substance. It will be done.

The mesophase pitch used herein preferably has a mesophase content of 70 to 100%, more preferably substantially 100% mesophase. Although there are no particular limitations, the same one used in the first step (filtration operation) is desirable.

This is because there is no need to purge after cleaning and removing the gel material, and continuous operation is possible. In order to wash and remove gel-like substances, it is desirable that the flow rate of mesophase pitch be at least three times the capacity of the filter.

This cleaning operation can be carried out by heating the mesophase pitch to a temperature above the pour point and passing it through a filter filled with a gel-like substance, but a high temperature is preferable and 5° below the pour point.
It is preferable to carry out the process at a temperature higher than C (usually 275 to 380 C, although it varies depending on the type of mesophase pitch used). However, temperatures above 380°C should be avoided because the reaction proceeds and may even cause the formation of gel-like substances. The extrusion direction of the gel-like substance may be the filtration direction or the opposite direction.

The gel-like substance extruded by this washing operation may be removed by appropriate means. The guideline for performing the cleaning operation is determined by the differential pressure. Differential pressure varies depending on pinch properties, filter shape, bore diameter, filter design strength, etc., but is 30~
300 kg/c4G is suitable for operation.

The method of the present invention, such as the one on the ridge, can also be incorporated into the manufacturing process of the carbon material, thereby allowing spinning to be carried out continuously over a long period of time and at low cost.

The mesophase pitch purified in this way can be melt-spun, further infusible treated, and fired (carbonized) to form carbon fibers by a conventional method.

〔Example〕

Next, the present invention will be explained in detail with reference to Examples.

Example I Decant oil from FCC (fluid catalytic cracker) to 400
After heat treatment at ~500°C, Ql (quinoline solubility) 18
．． 3%, a pitch with a mesophase content of 100% was obtained. Glass transition temperature (Tg) of this mesophase pitch.

When the pour point (Ts) was measured using TMA, Tg=2
66°C, Ts=318°C. This pitch is set to 30 mm using a metal fiber filter with a nominal 3μ bore diameter.
Filtered at 0°C.

1c1 until the filter differential pressure reaches 50kg/Cll1
It was possible to filter 65 g of pitch per sample 11 (the pitch obtained at this time is referred to as ■).

The filter differential pressure increased to 50 kg/afl and the filter became clogged, so the temperature of the filter equipped with the filter was raised to 345"C, and the The filter was passed through a mesophase pitch to wash and remove gel-like substances clogging the filter.

After that, when the temperature of the filter was lowered to 300'C,
The filter differential pressure was 12 kg/afl, and it was clearly recognized that the gel-like substance clogging the filter could be removed. When the filtration operation was performed again, the filter differential pressure increased again to 50 kg/afl when 38 g per led was filtered (the pitch obtained at this time is assumed to be ■). Therefore, it is clear that the filter is becoming clogged with gel-like substances and that the gel-like substances are being filtered out.

The resulting two pitches were each spun at 341°C using a spinning die having 250 holes.

The number of thread breakages was 0.2 times/hour in both cases, and no particular problem occurred even after continuous spinning for two days. These pitch fibers were heated to 360°C in a conventional manner to make them infusible, and then heated to 15°C.
It was carbonized by raising the temperature to 00°C.

The physical properties of the obtained carbon fiber are shown below.

Comparative Example When filtering was performed at 340°C using the same pitch as in Example 1, the differential pressure across the filter was 12 kg/cIIl even when 65g of pitch per IC11I was filtered. Therefore, it was confirmed that the filter was not clogged with gel material. When this pitch was spun under the same conditions as in Example 1, the average number of yarn breakages was 1.5 times/hour. The fibers obtained by infusible and fired in the same manner as in Example 1 had a thread diameter of 10.2 μ, a tensile strength of 22.0 kg/mm, and a tensile modulus of 25 t/mm.

〔Effect of the invention〕

According to the present invention, gel-like substances in mesophase pitch can be efficiently filtered and removed. Therefore, problems such as thread breakage during spinning due to the presence of gel-like substances do not occur, and the spinnability can be improved, and when made into carbon fibers, it is possible to obtain carbon fibers with excellent strength.

Further, in the present invention, since the gel-like substance is not removed at a very high temperature, there is no fear that the mesophase pitch will be altered during filtration.

Furthermore, according to the present invention, it is possible to efficiently clean the filter, and as a result, the life of the filter can be extended, making it possible to perform spinning for a long time and reducing the cost during carbon material production. can be done.

Claims (2)

[Claims] (1) A method for purifying mesophase pitch, which comprises filtering the mesophase pitch through a filter at a temperature ranging from the glass transition temperature to the pour point of the pitch. (2) (a) An operation of filtering the mesophase pitch through a filter at a temperature ranging from the glass transition temperature to the pour point of the pitch; 1. A method for purifying mesophase pitch, which comprises sequentially repeating an operation of passing the mesophase pitch at a raised temperature and washing a filter.