JPS59106519A - Porduction of carbon fiber - Google Patents

Abstract

PURPOSE:To improve operation environment and safety, by providing a heating furnace for converting thermally stabilized fiber into carbon fiber with an exhaust gas line for discharging an inert gas in the furnace, attaching a filter box to it. CONSTITUTION:The heating furnace 1 wherein precursor yarn is heated in an oxidizing atmosphere to give the thermally stabilized yarn 8, which is heated in an inert atmosphere to a high temperature, and it is converted into carbon yarn, is equipped with an exhaust gas line, and this exhaust gas line is provided with the filter box 1. Preferably the exhaust gas separator boxes 3 and 3' having the trap parts 4 and 4' are set in the downstream side of the filter box 2. The filter 9 packed into the filter box 2 is preferably exchangeable.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing carbon fibers and graphite fibers obtained via carbon IIi fibers. This invention relates to a method for producing carbon fibers or graphite fibers (hereinafter collectively referred to as carbon fibers) which eliminates problems caused by minute fiber waste generated from fluff (hereinafter referred to as I! fiber mist) and which has excellent operational stability.

Conventionally, carbon fibers are produced by heating precursors such as acrylic fibers and pitch fibers (hereinafter referred to as precursors) in an oxidizing atmosphere to thermally stabilize them, and then heating them at higher temperatures in an inert atmosphere. FA is produced industrially using a method of converting carbon fiber into carbon fiber.

In the manufacturing process of carbon fibers, the process of continuously carbonizing or graphitizing thermally stabilized fibers in a high-temperature inert atmosphere produces rigid, brittle, thin particles with a diameter of about 2 to 20 μm. Carbon fibers or graphite fibers, which are made of fibers, can generate fuzz or breakage of single filaments due to slight fluctuations in external stress such as from a tension saw, and these fuzz or single filament ends can be cut off and released into an inert atmosphere. The fiber mist is mixed into the inert atmosphere as the fiber mist, but this fiber mist is usually passed through the inert atmosphere outlet in the furnace used for carbonization or graphitization, the atmosphere discharge from the furnace, and the circulation line. Attach,
There is a problem in that it not only fluctuates the pressure inside the furnace, but also blocks the inert atmosphere discharge and circulation lines, significantly increasing the pressure drop inside the furnace and putting the operation in a dangerous state.

In addition, according to the studies of the present inventors, when heating heat-stabilized fibers in such a high-temperature inert atmosphere, reactants that are difficult to condense at room temperature are removed due to the carbonization reaction of the fibers. is generated. Moreover, carbon fibers carbonized at 600 to 1000°C have remarkable hygroscopic properties, so when they come out of the high-temperature furnace, they absorb moisture in the outside air, and when they are introduced into the high-temperature heating furnace, they absorb moisture. The easily condensable gas in the atmosphere and the moisture adsorbed on the carbon fibers condense in the exhaust gas line outside the furnace, and when this condensed moisture accumulates, it causes a problem in the smooth gas flow in the exhaust gas line, similar to the fiber mist mentioned above. In particular, the liquid that condenses in the exhaust gas line absorbs and dissolves impurities such as thermal decomposition products in the exhaust gas, gradually increasing its viscosity, and there is a great danger of blocking the exhaust gas line. It turned out to be a big problem.

An object of the present invention is to provide a method for producing carbon fibers that eliminates such problems, has excellent operational stability, and ensures safety.

Hereinafter, the present invention will be explained specifically and in detail based on the drawings.

FIG. 1 is a flowchart showing one embodiment of the exhaust gas treatment line for the carbonization process used in the present invention. In the figure, (1) is a vertical carbonization furnace, (2) is a filter box installed in the exhaust gas treatment line of the furnace (1), (3), (3'
) is also a separator box, (4), (4') are trap parts, (5) is an orifice (referred to as flow rate orifice) that measures and controls the flow rate of inert gas flowing through the exhaust gas treatment line, (6), (6') (7) and (7'
) indicates the switching valve, (8) indicates the fiber running in the old furnace, and the arrow indicates the flow direction of the inert gas.

As shown in the figure, the inert gas flows through the furnace (1) and the fibers (8)
The gas flows in the opposite direction to the traveling direction of the gas, and is discharged outside the furnace through the exhaust gas treatment line.

The lower part of the furnace (1) is sealed with water, and the upper part of the furnace (1) is sealed with inert gas, and the inert gas introduced into the furnace is discharged outside the furnace via the exhaust gas treatment line. but,
In some cases, part or all of it may be reused as seal gas or the like.

The high-temperature exhaust gas in the furnace (1) is discharged outside the furnace through an exhaust gas treatment line (pipe, etc.) installed in the furnace. 3'), flow rate orifices (5) are provided in sequence, and the exhaust gas that has passed through the flow rate orifices (5) is usually treated with a catalyst that oxidizes and renders the thermally decomposed products of the thermally stabilized fibers contained in the exhaust gas harmless. After passing through a treatment layer, it is either released into the outside air or mixed with oxidizing gas (air) and subjected to combustion treatment (neither is shown).

The feature of the present invention is that a filter box (2) is provided in the exhaust gas treatment line of the furnace (1), and the
The exhaust gas containing 1i fibers 1~ is treated with this filter box (2)'r-, and the ll contained in the inert atmosphere is
Ill Smith collection, at the point of removal.

Figure 2 shows the filter box (2) of the exhaust gas treatment line.
) is a perspective view showing one specific aspect of the invention.

In the figure, (2) indicates the filter box (9), (10) indicates the exhaust gas outlet to the filter box (2), (1) indicates the furnace, and the arrows indicate the flow of the exhaust gas.

Exhaust gas discharged from the upper part of the furnace (1) is guided into the filter box (2) through the exhaust gas outlet (10) provided at the upper part of the furnace (1), and is passed through the filter (9) in the filter box (2). ), and an exhaust device such as an exhaust blower installed at the final stage of the exhaust gas treatment line (not shown)
is forcibly sucked in and exhausted. The filter (9) to be filled in the filter box (2) is not particularly limited as long as it does not chemically react with the thermal decomposition products contained in the exhaust gas or melt due to high temperature gas. , usually stainless steel wire is used. However, in order to effectively remove m-fiber mist in the exhaust gas and reduce pressure loss, it is preferable that the filter has 2 to 20 meshes. If it is smaller than 2 meshes, the filter will clog quickly and it is not industrially viable for continuous operation, and if it is larger than 20 meshes, the filter efficiency will be insufficient.

In addition, the filter box (
2) should be installed close to the furnace (1), particularly immediately after the exhaust gas outlet, in order to prevent clogging of the exhaust gas treatment line and flowmeter due to the m-fiber mist.

Next, the exhaust gas that has been filtered through the filter box (2) is preferably provided in the exhaust gas treatment line, and water and the like contained in the exhaust gas are separated and removed by a separator section having a wrap section.

FIG. 3 is a sectional view showing one embodiment of a separator box having such a trap portion.

In the figure, (3) and (3') are separator boxes, (11) and (11') are wire mesh provided inside the separator,
(6), (6') are separator box inlet switching valves, (7), (7') are separator box outlet switching valves, (4), (4') are trap parts, (12), (12)
') indicates the extraction valve of the trap section, and the arrow indicates the flow of exhaust gas.

As shown in the figure, the exhaust gas from the filter box enters the separator box (3) along the arrow (solid line),
Easily condensable components contained in the exhaust gas are condensed in this separator box (3) and stored in a trap (4) at the bottom of the separator section. When the liquid accumulated in this trap (4) reaches a certain amount, the extraction valve (12) is opened and removed from the system. A wire mesh (11) is provided inside the separator box (3) to remove fiber mist remaining in the exhaust gas.

In Fig. 3, two separator boxes are provided, and after processing the exhaust gas for a predetermined time in the exhaust gas flow path indicated by the solid arrow, the switching valves (6) and (7) are closed and the switching valve (6' ), (7') and switching to the exhaust gas flow path indicated by the dotted arrow allows continuous processing.

In order to carry out the exhaust gas treatment of the present invention continuously over a long period of time, two or more separator boxes (3) are installed in parallel, as shown in Fig. 1, at the entrance of the separator box. It is preferable to switch the separator as appropriate using a partial switching valve.

Note that the flow rate orifice 5 for measuring the flow rate of the exhaust gas passing through the exhaust gas treatment line is preferably provided in a process after the gas passes through the separator 4, so that the measured value of the flow rate orifice due to the Il fiber mist and liquid can be reduced. Fluctuations can be prevented and failures can be reduced.

In this way, the exhaust gas that has passed through the exhaust gas treatment line of the present invention is either directly sent to the combustion furnace for treatment, or it is subjected to catalytic treatment and then released, but even in this case, fiber mist is produced. The deterioration in performance of the catalyst treatment device or the direct combustion treatment device caused by the mist or condensate that does not contain any condensate can be greatly suppressed.

In addition, as another effect, it becomes possible to reduce the energy required for heating and heat-insulating the exhaust gas line for the purpose of avoiding condensation of condensate in the exhaust gas, and it is extremely advantageous from the viewpoint of continuous operation.

Hereinafter, one specific example of the results of the present invention will be shown with reference to Examples and Comparative Examples.

Example 1 A single yarn fineness of 1.0 was produced from an acrylic copolymer consisting of 99.5 mol% acrylonitrile and 0.5 mol% acrylic acid.
A bundle of 3,000 single-denier acrylic filaments is heated and oxidized in air at an average temperature of 240°C! 1 fiber bundle was created.

This oxidized 11 fiber bundle was continuously introduced into a vertical carbonization furnace equipped with an exhaust gas treatment line shown in FIGS. 1 to 3 and carbonized. The atmospheric temperature inside the carbonization furnace is 1300°C, the feeding rate of fiber bundles to the furnace is 0.8 kg/min, and the inert gas feeding rate is 1/3.
N ra”/min.

After continuous operation for about 20 days, about 10 e of condensed water was collected from the trap section shown in Fig. 3, and about 12,009 g of fiber mist was collected from the filter box.

During this operation period, the pressure in the carbonization furnace was kept stable, and no 4iI mist was observed in the exhaust gas treatment line.

Moreover, the quality and grade of the obtained carbon lli residue were constant, and no tar or the like was observed at all.

On the other hand, when carbonization was performed in the same manner without installing the exhaust gas treatment line shown in Figures 1 to 3 above, pressure fluctuations in the furnace due to clogging of the flow rate orifice were detected for about two days, and tar etc. were attached to the resulting carbon fibers. It was recognized that

[Brief explanation of the drawing]

FIG. 1 is a flowchart 1 of exhaust gas treatment in a vertical carbonization furnace showing one embodiment of the present invention, FIG. 2 is a perspective view showing a filter box installed in the exhaust gas treatment line, and FIG. FIG. 2 is a cross-sectional view showing an example of a separator box having a trap section provided in a processing line. 1: Vertical carbonization furnace 2: Filter part box 3.3': Separator box 4.4' Nidrap section 5: Flow rate orifice 6.6', 7.7': Switching valve 8: Fiber 9 running in the furnace ; Filter 10: Exhaust gas outlet 11.11': Wire mesh 12.12': I-wrap extraction valve Patent applicant
Toshi Co., Ltd.

Claims (1)

[Claims] (1) Heating the precursor fiber in an oxidizing atmosphere
3. When heating the heat-stabilized fibers obtained in step 3 at high temperatures in an inert atmosphere to convert the heat-stabilized fibers into carbon fibers, a heating furnace for converting the heat-stabilized fibers into carbon fibers is used. A method for producing carbon fibers, comprising: providing an exhaust gas line for taking out an inert atmosphere in a furnace as exhaust gas; and providing this exhaust gas line with at least one filter box having a filter function. (2. In claim 1, the method for producing carbon fibers is characterized in that the filter box is equipped with a replaceable filter. (3) In claims 1 to 2, the method for producing carbon fiber A method for manufacturing carbon fiber, characterized in that an exhaust gas separator box having a trap portion is provided in the exhaust gas line after the box. A method for manufacturing carbon fiber characterized by the following.