EP0326587A1

EP0326587A1 - Process and device for manufacturing anisotropic carbon fibres

Info

Publication number: EP0326587A1
Application number: EP19880901236
Authority: EP
Inventors: Rudolf Geier; Rolf Joest; Wilhelm WÜLLSCHEIDT
Original assignee: Deutsche Voest Alpine Industrieanlagenbau GmbH; Didier Engineering GmbH
Current assignee: Deutsche Voest Alpine Industrieanlagenbau GmbH
Priority date: 1987-07-21
Filing date: 1988-01-06
Publication date: 1989-08-09
Also published as: DE3724102C1; AU1240488A; CN1030799A; WO1989000618A2; GR880100059A; ES2006118A6; WO1989000618A3; IN168633B; DD280982A5

Abstract

Es handelt sich um ein Verfahren zum Herstellen von anisotropen Kohlenstoffasern aus Kohlenteerpech, wonach das Kohlenteerpech vor dem Verspinnen filtriert und das Pechfiltrat in einem Dünnschichtverdampfer destilliert bzw. zu einer mesophasenbildenden Pechfraktion aufkonzentriert wird. Das erhaltene Pechkonzentrat wird im Wege einer thermi schen Behandlung zu einem Mesophasenpech umgewandelt, so daß sich die schwierige und kostenintensive Verfahrensstu fe im Zuge der Faserherstellung, nämlich der thermischen Nachbehandlung der ersponnenen Pechfasern besonders schnell und einfach durchführen läßt. Das hochviskose Pech wird wirtschaftlich in einer Zentrifugalspinnmaschine ver sponnen, wobei vor der Verspinnung eine Einbringung oder vor der Oxidation eine Aufbringung pulverförmiger Ab standshalter erfolgt. Die thermische Nachbehandlung findet in einer zyklisch arbeitenden Behandlungsanlage statt, und zwar laufen dort die Prozesse Oxidation, Evakuierung, Carbonisation, Evakuierung, Graphitierung und Kühlung ab. It is a process for producing anisotropic carbon fibers from coal tar pitch, according to which the coal tar pitch is filtered before spinning and the pitch filtrate is distilled in a thin-film evaporator a mesophase-forming pitch fraction is concentrated. The pitch concentrate obtained is thermi treatment converted to a mesophase pitch, so that the difficult and costly procedural step fe in the course of fiber production, namely the thermal aftertreatment of the spun pitch fibers can be carried out quickly and easily. The highly viscous pitch is economically processed in a centrifugal spinning machine spinning, an introduction before the spinning or an application before the oxidation of a powdered Ab stand holder takes place. The thermal aftertreatment takes place in a cyclically operating treatment plant, and the processes of oxidation, evacuation, carbonization, evacuation, graphitization and cooling take place there.

Abstract

Process for manufacturing anisotropic carbon fibres from coaltar pitch, in which said pitch is filtered prior to spin ning and the pitch filtrate is distilled in a thin-layer evaporator or concentrated to a mesophase-forming pitch fraction. The pitch concentrate obtained is converted to a mesophase pitch by a heat treatment so that the difficult and costly stage of the process is carried out very rapidly and easily during the fibre manufacturing, namely during the subsequent heat treat ment of the spun pitch fibers. The highly viscous pitch is spun economically in a centrifugal spinning frame. Powdered spacers are introduced before spinning or sprinkled before oxidation. The subsequent heat treatment is carried out in a cyclically operating treatment installation and it is there that the oxidation, evacuation, carbonization, evacuation, graphi tization, and cooling processes take place. Process for manufacturing anisotropic carbon fibers from coaltar pitch, in which said pitch is filtered prior to spin ning and the pitch filtrate is distilled in a thin-layer evaporator or concentrated to a mesophase-forming pitch fraction. The pitch concentrate obtained is converted to a mesophase pitch by a heat treatment so that the difficult and costly stage of the process is carried out very rapidly and easily during the fiber manufacturing, namely during the subsequent heat treat ment of the spun pitch fibers. The highly viscous pitch is spun economically in a centrifugal spinning frame. Powdered spacers are introduced before spinning or sprinkled before oxidation. The subsequent heat treatment is carried out in a cyclically operating treatment installation and it is there that the oxidation, evacuation, carbonization, evacuation, graphi tization, and cooling processes take place.

Description

Method and device for producing anisotropic carbon fibers

The invention relates to a process for producing anisotropic carbon fibers from coal tar pitch, in particular hard coal tar pitch, according to which the coal tar pitch is freed of infusible components by filtration prior to spinning, then the pitch filtrate is distilled in a thin-film evaporator to remove volatile components, then those obtained Pitch fibers spun pitch melt are oxidized at a predetermined oxidation temperature and carbonized at a predetermined carbonization temperature. In the same way, the invention comprises the production of anisotropic carbon filaments.

A method for producing isotropic carbon fibers from coal tar pitch is known, according to which the

Coal tar pitch is spun from the melt and the pitch fibers obtained are subjected to oxidation, then carbonization and optionally graphitization. The coal tar pitch has a softening point of at most 190 ° C (KS or Krämer-Sarnow) and is heated to a temperature up to 100 ° C above the softening point before spinning. At this temperature, the pitch melt obtained is essentially freed from the solid constituents by filtration under elevated pressure. The solid or infusible components are identical to components insoluble in quinoline. To remove volatile or low molecular weight constituents, the filtered pitch melt is either distilled to Subjected to 350 ° C or after cooling to small pitch, which are brought into contact with an aliphatic solvent with a boiling point of up to 70 ° C. The solvent with the pitch constituents dissolved therein is separated from the insoluble pitch constituents. Before the carbonization, the carbon fibers spun from the pitch melt are dusted with finely ground activated carbon, which is impregnated with liquid oxidizing agents, and heated to 400 ° C. in an oxidizing atmosphere. The subsequent carbonization of the oxidized carbon fibers takes place at a temperature of approximately 1000 ° C. (cf. DE-PS 24 19 659). - According to this known method, one wants to produce isotropic carbon aers from coal tar pitch, which can be oxidized and carbonized in a very short time. However, it has been found that the specified distillation possibilities lead to the regression of disruptive quinolim soluble or infusible components and are limited in their efficiency. In fact, the thermal aftertreatment - oxidation and carbonization of the spun pitch fibers - can be carried out more easily and quickly, the fewer volatile pitch components are present. For this reason, according to an older proposal according to patent application P 37 03 825.7-43, the pitch filtrate is increased its softening point is distilled in a thin-film evaporator to values above 200 ° C (KS - Krämer-Sarnow). - This is where the invention begins.

The invention is based on the object of specifying a process for producing anisotropic carbon fibers from coal tar pitch, in particular coal tar pitch, of the type described at the outset, according to which short treatment or residence times during the thermal conversion and aftertreatment as well as high throughputs and low energy and inert gas consumption can be achieved, so that the anisotropic carbon fibers can be produced efficiently and economically.

The invention achieves this object in a generic method in that the pitch filtrate or its toluene-soluble portion is concentrated in the thin-film evaporator to form a mesophase-forming pitch filtration, and the pitch concentrate obtained is converted to a mesophase pitch in the course of a thermal treatment, and in that the mesophase pitch is spun by means of a spinning centrifuge, if necessary under increased initial pressure, and that the carbon fibers are further graphitized after carbonization. According to the teaching of the invention, the use of a thin-film evaporator first of all substantially simplifies the process by removing the volatile pitch constituents on the one hand and the concentration of the mesophase-forming pitch fraction on the other. In the former case, the degassing of the mesophase deposits is simplified and the thermal treatment times are shortened. In addition, a higher carbon fiber yield is achieved because the spun pitch fibers have a high C content. Atmospheric oxygen is sufficient as the oxidizing agent for the oxidation process. Furthermore, no fiber bonds occur during the thermal aftertreatment. In the latter case, the thermal conversion into mesophase pitch is simplified, a mesophase with anisotropy running over a large area being achieved. Furthermore, a higher yield, less exhaust gas development and shorter residence times during the thermal conversion are guaranteed. - The use of a spinning centrifuge enables the take-off speeds which are 10 to 30 times higher than conventional fiber spinning devices due to the centrifugal forces which occur and, if appropriate, an additional, increased admission pressure, without their problems such as fiber sticking or operational interruptions occurring due to the overgrowth of nozzle holes .

Usually, the compounds present in coal tar pitch are soluble in various organic solvents, e.g. B. hexane, toluene and quinoline classified. The quinoline-insoluble compounds represent the high molecular weight fraction, the toluene-insoluble compounds the medium molecular weight fraction. The part which is insoluble in toluene has proven to be particularly suitable for producing a mesophase. The quinoline-insoluble substances present in the raw pitch can be removed quantitatively by known filtration processes. It is difficult to separate off the toluene-soluble fraction since, in the known processes, undesired substances with higher molecular weights are formed due to the residence times and temperatures used. According to the invention, the concentration of the toluene-insoluble fraction takes place in a thin-film evaporator without the re-formation of quinoline-insoluble substances, preferably at dwell times of less than one minute, temperatures above 200 ° C. and vacuum to 1 mbar. By varying the pressure and temperature, practically any content of volatile and toluene-insoluble substances can be achieved. Examples:

Rohpech- Konzen¬ Concentrate filtrate entered I entered II

Dest.Temp. (° C) 330 360 Dest. Pressure (mbar) 1 0.8

Softening point (KS) (° C) 72 210 255

Quinoline insoluble (%) <0.3 <0.3 <0.3

Toluene insoluble (%) 21 58 70

Volatile order (%) 52 19 14

Coke (Alcan) (%) 48 82 86

(Provisions according to the applicable DIN standards)

The concentrate obtained is an excellent mesophase former and can be converted, for example, after thermal treatment at temperatures from 400 ° C. to 500 ° C., preferably 450 ° C. Compared to known processes, however, this conversion can be achieved in significantly shorter dwell times. In addition, the conversion takes place almost quantitatively with corresponding dwell times. At a treatment temperature of 450 ° C, starting from concentrate II, a light-optically determined mesophase content of 60% can be achieved after only 30 minutes, which increases to over 75% after a further 30 minutes. A centrifugal spinning machine is particularly suitable for spinning and orienting the mesophase pitch, the high viscosity of the spinning melt being taken into account, if appropriate, by the combination of centrifugal forces and increased form. The process according to the invention enables the anisotropic carbon fibers to be produced economically by means of the shortest residence times, which is synonymous with high throughputs and low investment costs. In order to make full use of the method according to the invention in terms of its efficiency, ie to be able to implement the short residence times, a device for storage and thermal treatment is used which uses the retort technique and, in addition to short residence times and consequently reduced investment costs, low energy - and inert gas consumption guaranteed. In detail, it is a device with at least

- A lower rotating stage with an oxidation furnace, a first vacuum retort, a carbonization furnace and one

Cooling retort, all treatment facilities in open construction,

an upper revolving stage which can be rotated independently of the lower revolving stage and has a traversing device for treatment retorts for temporarily receiving the fiber deposit with the pitch fibers to be treated,

- A loading level above the upper rotating platform with at least one loading opening and at least one

Retort lid holder for retort lid with connection for air and inert gas supply, vacuum and exhaust air,

wherein the traversing device for the treatment retorts for connection to the respective retort lid is transferred from the upper rotating platform under the relevant retort lid and vice versa, and wherein the lower rotating platform has at least one lifting device for each of the oxidation oven which has the vacuum retort, the carbonization oven and the cooling retort and these treatment devices for accommodating the treatment retorts can be moved and raised under the retort lid receptacle or the relevant retort lid and vice versa. This device, which is now used more for the production of anisotropic carbon fibers, is characterized in that the lower revolving stage is equipped with a second vacuum retort and a graphitization furnace as a further treatment device in an open design. In the device according to the invention, one of the six processes of oxidation, evacuation, carbonization, evacuation, graphitization and cooling can take place under each retort lid.

In the following, the invention will be explained in more detail with reference to a drawing showing only one exemplary embodiment. Show it

1 shows a schematic process flow diagram for the production of anisotropic carbon fibers,

2 shows the device for thermal aftertreatment in a schematic top view below the loading level and

3 to 23 a treatment cycle with the object of FIG. 2 in a schematic side view.

In the course of the production of anisotropic carbon fibers 1 from coal tar pitch and in particular coal tar pitch, the coal tar pitch is freed of infusible or quinoline-insoluble constituents by filtration prior to spinning. Then the pitch filtrate subjected to a distillation to remove volatile or low molecular weight constituents. Then, the pitch fibers 2 spun from the pitch melt obtained, using powdered substances introduced or applied, at a predetermined oxidation temperature

Making infusible oxidized. Furthermore, the oxidized pitch fibers 2 are carbonized using an inert gas at a predetermined carbonization temperature. The pitch filtrate is continuously introduced into a thin-film evaporator in the course of the distillation and is evenly distributed over the inner circumference by means of a rotating distributor ring. The rotor wiper blades moving along the evaporator zone capture the pitch filtrate and spread a thin film over the heating wall. The volatile product portion evaporates under the influence of an applied vacuum and is deposited on a condenser. The non-evaporated product portion, namely a mesophase-forming pitch fraction, leaves the thin-film evaporator and is converted to a mesophase pitch by means of a thermal treatment. The mesophase pitch is granulated. None of this is shown.

The mesophase pitch granules are melted in an extruder 3. The pitch melt runs through a filter 4 and is fed to a centrifugal spinning head 6 by means of a metering pump 5. The spinning centrifuge, which is provided with nozzle holes on its lower part, presses the pitch melt due to centrifugal forces and an additional pressure support through the nozzle holes. Endless filaments are created, which are placed on a slowly rotating catch ring. The catch ring is provided with a cutting device which cuts the continuous filaments to the desired fiber length. Since you want to have a fuse for the subsequent thermal aftertreatment, you will need a fuse Number of individual fibers, which result in the desired sliver cross-section, are placed one above the other on the catch ring. The sliver deposit takes place in a coiler 7. The fiber sliver is deposited over deflection rollers 8 in free-hanging loops on an extended scissor gate 9. After the storage has ended, the scissors gate 9 is pushed together in order to ensure a high space utilization of the oxidation furnace 10 or carbonization furnace 11 and is placed in a treatment retort 12. During the subsequent oxidation process, a first vacuum retort 13 is located in the basement and the oxidation furnace 10 is moved over the treatment retort from below

12 driven. The treatment retort 12 is heated up according to a graduated temperature program. During this oxidation process to make the pitch fibers 2 infusible, hot oxidation air flows through the treatment retort 12 from bottom to top. The subsequent carbonization process must be carried out under inert gas in order to avoid burning the pitch fibers 2. In order to remove the oxygen as quantitatively as possible from the fiber sliver, the treatment retort 12 is first evacuated. Since the treatment retort 12 is made of non-vacuum-proof thin sheet for the purpose of good heat transfer, the carbonization furnace 11 is moved down and heated to 1000 ° C. while the vacuum retort

13 is lifted from the basement under the treatment retort 12. A vacuum unit is then put into operation. After a few minutes, the vacuum retort 13 or treatment retort 12 can be expanded to normal pressure with nitrogen. For safety reasons, it is flushed again with nitrogen. Then the vacuum retort 13 is lowered back into the basement and against the car heated up to 1000 ° C Rating furnace 11 replaced. The carbonization requires a ten minute residence time, volatile compounds being transported through preheated nitrogen via the treatment retort 12 for condensation or exhaust air combustion. After the carbonization has ended, the carbonization furnace 11 is moved down and a further vacuum retort 13a is lifted from below over the treatment retort 12. For safety reasons, the treatment retort 12 is flushed with argon while relieving pressure. After the vacuum retort 13a has been lowered, a graphitization furnace 14 heated to 2800 ° C. is moved over the treatment retort 12. During the graphitization process that follows, preheated argon is passed through the treatment retort 12 and transports the volatile compounds to the exhaust system. Finally, the carbon fibers 1 are cooled to temperatures below 600 ° C. by supplying cold argon or nitrogen. Further cooling can take place in a cooling retort 15 with cold air.

In particular, the device for the thermal aftertreatment of the pitch fibers 2 has a lower rotating stage 16 with the oxidation furnace 10, the vacuum retorts 13, 13a, the carbonization furnace 11, the graphitization furnace 14 and the cooling retort 15. All treatment devices 10 to 15 are designed in an open container construction for receiving treatment retorts 12. Furthermore, an upper rotary stage 17 which can be rotated independently of the lower rotary stage 16 and has a traversing device for treatment retorts 12 for the temporary reception of the

Fiber trays 9 provided with the pitch fibers 2 to be treated. Above the upper rotating platform 17 there is a loading level 18 with at least one loading opening 19 and at least one retort lid holder 20 for Cake lid 21 with connection for air and inert gas supply, vacuum and exhaust air. The traversing device guides the treatment retorts 12 for connection to the respective retort cover 21 from the upper rotating platform 17 under the relevant retort cover 21 and vice versa. The lower rotating stage 16 has at least one lifting device 22 for each of the oxidation furnace 10, the vacuum retorts 13, 13a, the carbonization furnace 11, the graphization furnace 14 and the cooling retort 15. These treatment devices 10 to 15 can be moved and raised to receive the treatment retorts 12 under the retort lid receptacles 20 or the relevant retort lid 21 or vice versa. The treatment devices 10 to 15 can be displaced by 60 ° to one another on the lower rotating platform 16 and are arranged on a rotating circle which, in vertical projection, exceeds the outer circumference of the upper rotating platform 17 for passing the treatment devices 10 to 15 to be raised and for Connection of the raised treatment devices 10 to 15 to the respective retort lid 21 extends below the retort lid receptacles 20, which are offset by 60 ° in relation to one another. Each treatment device 10 to 15 is assigned its own lifting device 22, so that one of the six processes of oxidation, evacuation, carbonization, evacuation, graphitization and cooling can take place simultaneously under each retort lid 21. The fiber tray is designed as a collapsible scissors gate 9 for fiber loops hanging freely on horizontal bars and, when pushed together, can be inserted into a treatment retort 12 in each case. - 12 -

In detail, the device operates as follows if one of the six processes of oxidation, evacuation, carbonization, evacuation, graphitization and cooling takes place simultaneously under each retort lid 21:

2: On the upper revolving stage 17, an empty treatment retort 12 is filled from above with a contracted scissors gate 9.

Fig. 4: The upper revolving stage 17 rotates through 180 °. While a scissors gate 9 with finished anisotropic carbon fibers 1 is removed from the other treatment retort 12, the lower rotating stage rotates by 60 °, so that the cooling retort 15 is exchanged for the oxidation furnace 10.

Flg. 5: The treatment retort 12 with the untreated pitch fibers 2 is transported through the traversing device under the assigned retort cover 21.

6: The lifting device 22 moves the oxidation furnace 10 - a low-temperature furnace - from below over the treatment retort 12. During the now following oxidation process, hot oxidation air is passed through the treatment retort 12 and the oxidation furnace 10 is heated up in accordance with the optimized temperature profile. The hot process gases are fed to the exhaust air cleaning system.

Fig. 7: After oxidation has ended, the oxidation furnace 10 is moved down to the lower rotating platform 16.

Fig. 8: The lower rotating stage 16 rotates by 60 °, so that the first vacuum retort 13 comes under the treatment retort 12 _Z. 9: The vacuum retort 13 is lifted from below over the treatment retort 12 by means of the hydraulic lifting device 22. The vacuum applied evacuates the furnace.

Fig. 10: For safety, the treatment retort 12 is still flushed with nitrogen while relieving pressure. The vacuum retort 13 is moved down to the lower rotating platform.

Fig. 11: The lower rotating stage rotates by 60 °, so that the now 1000 ° C hot carbonization furnace 11 - a high temperature furnace - is under the treatment retort 12.

Fig. 12: The carbonization furnace 11 is moved from below over the treatment retort 12 by means of the hydraulic lifting device. During the subsequent carbonation process, preheated nitrogen is passed through the treatment retort 12 and transports the volatile compounds to the exhaust system.

Fig. 13: The carbonization furnace 11 is moved down to the lower rotating platform 16.

14: The lower rotating stage 16 rotates by 60 °, so that the further vacuum retort 13a comes to rest under the treatment retort 12.

Fig. 15: The vacuum retort 13a is via the hydraulic

Lifting device lifted from below over the treatment retort 12. The vacuum applied evacuates the furnace. Fig. 16: For safety, the treatment retort 12 is flushed with argon while relieving pressure. The vacuum retort 13a is moved down to the lower rotating stage 16.

Fig. 17: The lower rotating stage 16 rotates by 60 °, so that the 2800 ° C hot graphitization furnace 14 is under the treatment retort 12.

18: The graphitization furnace 14 is moved from below over the treatment retort 12 via the hydraulic lifting device 22. During the subsequent graphitization process, preheated argon is passed through the treatment retort 12 and transports the volatile compounds to the exhaust system.

Fig. 19: The graphitization furnace 14 is brought down to the lower rotating stage 16.

Fig. 20: The lower rotating stage 16 rotates by 60 °, so that the cooling retort 15 comes to rest under the treatment retort 12. The carbon fibers 1 are cooled to temperatures below 600 ° C. by supplying cold argon or nitrogen.

Fig. 21: Further cooling can take place in the cooling retort 15 with cold air.

Fig. 22: The cooling retort 15 is moved down to the lower rotating platform 16.

23: The retort 12 is transported to the upper rotary stage 17 by the traversing device. A new cycle begins.

Claims

1. A process for producing anisotropic carbon fibers from coal tar pitch, in particular hard coal tar pitch, after which the coal tar pitch is freed of infusible components by filtration before filtration, then the pitch filtrate is distilled in a thin-film evaporator to remove volatile components, then from the pitch fibers spun out of the pitch melt obtained are oxidized and carbonized, characterized by the fact that the pitch filtrate is concentrated in the thin-film evaporator to form a mesophase-forming pitch fraction and the pitch concentrate obtained is converted to a mesophase pitch by means of thermal treatment becomes.

2. The method according to claim 1, characterized in that the pitch concentrate is thermally treated at temperatures from 400 ° C to 500 ° C, preferably 450 ° C.

3. The method according to claim 1 or 2, characterized in that the thermally treated pitch concentrate is spun by means of a spinning centrifuge.

4. The method according to claim 3, characterized in that the spinning centrifuge is operated with an increased form.

5. The method according to any one of claims 1 to 4, characterized in that the spun carbon fibers from the oxidation to the spacing with powdery substances such as. B. SiO ", TiO_, A1" 0_. etc. are pollinated. - 16 -

6. The method according to any one of claims 1 to 5, characterized in that the additives are introduced into the spinning melt before spinning.

7. The method according to any one of claims 1 to 6 _r characterized in that the carbon fibers graphitized after carbonizing and before graphitizing in a vacuum with inert gas, for. B. argon.

8. Device for performing the method according to one of claims 1 to 7 in the course of the thermal aftertreatment of the pitch fibers, with at least

- a lower revolving stage with an oxidation furnace, a first vacuum retort, a carbonization furnace and a cooling retort, all treatment facilities in an open container design,

an upper revolving stage which can be rotated independently of the lower revolving stage and has a traversing device for treatment retorts for temporarily receiving the fiber deposits with the pitch fibers to be treated,

wherein the traversing device transfers the treatment retorts for connection to the respective retort lid from the upper revolving stage under the relevant retort lid and vice versa, and wherein the lower revolving stage has at least one lifting device for each of the oxidation oven, the vacuum retort, the carbonization oven and the Has cooling retort and these treatment devices for accommodating the treatment retort under the retort cover receptacle or the relevant retort cover can be moved and raised, and vice versa, since ¬ characterized in that the lower rotating stage (18) with a second vacuum retort (13a) and one Graphitization furnace (14) is fitted as a further treatment device in an open container construction.