EP0302084A1

EP0302084A1 - Apparatus for thermal aftertreatment of carbon fibres from coaltar pitch, in particular from glance- (hard)- coaltar pitch.

Info

Publication number: EP0302084A1
Application number: EP88900817A
Authority: EP
Inventors: Rudolf Geier; Rolf Joest; Wilhelm Wullscheidt; Horst Mathejka; Heinrich Patalon
Original assignee: Didier Engineering GmbH
Current assignee: Deutsche Voest Alpine Industrieanlagenbau GmbH
Priority date: 1987-02-07
Filing date: 1988-01-05
Publication date: 1989-02-08
Anticipated expiration: 2008-01-05
Also published as: WO1988005805A1; GR880100060A; EP0302084B1; DE3703825C2; DE3867365D1; GR1000124B; DE3703825A1; CN88100656A; DD279907A5; ATE71132T1; AU1103888A; IN168504B; ES2006553A6

Abstract

In a process for producing carbon fibres from coal tar pitch, the coal tar pitch is filtered before being spun and the pitch filtrate is distilled in a thin-film evaporator in order to increase its softening point over 260 C. A pure and homogeneous hard pitch is thus obtained, without the re-formation of infusable, chinolin-insoluble components. The most difficult and cost intensive step of the fibre production process, namely the thermal aftertreatment of the spun pitch fibres, can thus be easily and quickly carried out. The subsequent thermal treatment is carried out in a cyclic treatment installation.

Description

Process for producing coal tar pitch.

The invention relates to a process for producing carbon fibers from coal tar pitch, in particular hard coal tar pitch, according to which the coal tar pitch is freed of infusible constituents prior to spinning by filtration, then the pitch filtrate is removed from a distillation to remove volatile constituents, then from the The pitch melt obtained and the spun pitch fibers are oxidized at a given oxidation temperature and carbonized at a given carbonization temperature. - The invention comprises in the same way the production of carbon threads. Graphite fibers or threads can also be produced in a known manner from the carbon fibers or threads produced.

A process for the production of carbon or graphite fibers or filaments from coal tar pitch is known, after 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 maximum 190 ° C (KS or Krämer-Sarnow) and is heated to a temperature up to 100 ° C above the softening point before spinning. The pitch melt obtained is essentially freed from the solid constituents at this temperature by filtration under elevated pressure. The solid or infusible components are identical to quinoline-insoluble components. To remove volatile or low molecular weight components, the filtered pitch melt is either a distillate subjected to up to 350 ° C or, after cooling, ground into small pitch parts which are brought into contact with an aliphatic solvent with a boiling point of up to 70 ° C. The solvent with the pitch components dissolved therein is separated from the insoluble pitch components. The carbon fibers or threads spun from the pitch melt are dusted before carbonization with finely ground activated carbon, which is impregnated with liquid oxidation aids, and heated to 400 ° C. in an oxidizing atmosphere. The subsequent carbonization of the oxidized carbon filaments takes place at a temperature of approx. 1000 ° C (cf. DE-PS 24 19 659). - According to this known process, carbon fibers or threads are to be produced from coal tar pitch, which can be oxidized and carbonized in the shortest possible time. However, it has been found that the specified distillation possibilities lead to the regression of disruptive quinoline-insoluble 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 more quickly, the fewer volatile pitch components are present.

For the rest, it is known for the production of carbon fibers or graphite fibers from petroleum-derived pitch to use a thin-film evaporator for distillation; however, this causes problems regarding the production of carbon fibers or threads from carbon. stocky pitch was not significantly influenced, rather their production is rejected in this way (cf. EP-OS 00 84 237).

The invention has for its object to provide a method for producing carbon fibers from coal tarpec, in particular hard coal tar pitch, of the type described above, according to which the thermal aftertreatment can be carried out extremely simply and quickly, so that the production of the carbon fibers or . -Overall becomes particularly efficient and economical.

This object is achieved by the invention in a generic method in that the pitch filtrate is distilled into a thin-film evaporator to increase its softening point to values above 200 ° (KS = Kramer-Sarnow). According to a preferred embodiment, the pitch filtrate is treated in the thin-film evaporator at temperatures above 200 ° C. and under vacuum to 1 mbar to increase its softening point above 260 ° C. (KS). The invention is based on the knowledge that the softening point for coal-derived pitch or coal tar pitch can surprisingly be increased to over 260 ° C. if the distillation is carried out in a thin-film evaporator. Coal tar pitch with a high softening point is advantageous in that an increased crosslinking or mechanical strength is achieved in the course of the thermal aftertreatment. A significant reduction in volatile pitch components is also achieved. Due to the very short dwell times in the thin Layer evaporators do not re-form disturbing, ie infusible, quinoline-insoluble solids, so that a homogeneous and high-purity pitch melt is formed which is particularly suitable as a starting material for the production of carbon fibers and surprisingly spins even at a softening point> 200 ° C leaves.

In addition, very short residence times and extremely low inert gas and energy consumption are also achieved in the course of the thermal aftertreatment of the pitch fibers to carbon fibers. In fact, the thermal aftertreatment time and in particular the oxidation time can be shortened considerably. The further measures of the invention also contribute to this, according to which the carbon fibers after carbonization by supplying cold inert gas, eg. B. nitrogen, are cooled to temperatures below 600 ° C and then a further cooling with cold air is carried out. In economic terms, this results in rationally produced carbon fibers or threads of high quality and in particular tensile strength.

The invention also relates to a device for carrying out the claimed method, which is particularly suitable for the thermal aftertreatment of the pitch fibers and has at least one fiber deposit, an oxidation furnace and a carbonization furnace. This device is characterized by a lower revolving stage with the oxidation furnace, a vacuum retort, the carbonization furnace and a cooling retort, all treatment facilities in an open container construction,

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

- A loading level above the upper revolving platform with at least one loading opening and at least one retort lid run for retort lid with connection for air and inert gas supply, vacuum and exhaust air

wherein the traversing device transfers the treatment retorts to the respective retort lid from the upper revolving platform under the relevant retort lid and vice versa, and wherein the lower revolving platform has at least one lifting device for each of the oxidation oven, the vacuum retort, the carbonization oven and the cooling retort and these treatment devices for Inclusion of the treatment retorts under the retort lid receptacle or the relevant retort lid can be moved and raised and vice versa. - So that one of the four processes of oxidation, evacuation, carbonization and cooling can run simultaneously under each retort lid, the invention further provides that the treatment facilities on the lower The rotating stage is offset by 90 ° to one another and arranged on a rotating circle which, in a vertical projection, exceeds the outer circumference of the upper rotating platform for the lateral passage of the treatment devices to be raised and for connecting the raised treatment devices to the respective retort cover below the in in the same way, retort lid receptacles offset by 90 ° to one another, each treatment device being assigned its own lifting device. At least two treatment retorts offset by 180 ° to one another can be placed simultaneously on the upper revolving stage, so that a treatment retort with pitch fibers to be treated can alternately be fed to the treatment system and a treatment retort with finished carbon fibers can be removed. According to a preferred embodiment of the invention it is provided that the fiber tray is designed as a collapsible scissor gate for fiber loops hanging freely on horizontal bars and can be inserted in a retracted treatment position when pushed together. Such a thing

Scissors creel enables the storage of a strand consisting of a large number of individual pitch fibers or pitch threads, in such a way that no fiber or thread sticking occurs during the thermal aftertreatment and free shrinkage is made possible. By pushing the scissor gate together, a high

3 density _> 0.03 g / cm reached.

The invention is explained in more detail below with reference to a drawing which represents only one exemplary embodiment. Show it 1 shows a schematic process flow diagram for the production of carbon fibers,

Fig. 2 shows the device for thermal aftertreatment in a schematic plan view below the level and

3 to 17 a treatment cycle with the article according to FIG. 2 in side view.

In the course of the production of carbon fibers 1 from coal tar pitch and in particular coal tar pitch, the coal tar pitch is freed from infusible or quinoline-insoluble constituents by filtration before spinning. Then the pitch filtrate becomes one

Distillation to remove volatile or low molecular weight constituents. Then the pitch fibers 2 spun from the pitch melt or hard pitch melt are oxidized using an oxidation aid such as activated carbon at a given oxidation temperature to make them infusible. Finally, the oxidized pitch fibers 2 are carbonized using an inert gas at a predetermined carbonization temperature to drive off volatile by-products. Pitch filtrate is continuously fed into a thin-film evaporator during the distillation and evenly distributed on the inner circumference by means of a rotating distributor ring. The rotor wiper blades moving along the evaporator zone capture the pitch filtrate and a thin film over the heating wall. there the volatile product portion evaporates under the influence of an applied vacuum and is deposited on a condenser. The non-evaporated part of the product, namely hard pitch, leaves the thin film evaporator. A vacuum pump conveys the hard pitch for granulation. None of this is shown.

The 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 bores on its lower part, presses the pitch melt through the nozzle bores. Endless filaments are created, which are placed on a slowly rotating catch ring. The catch ring is with one

Provide cutting device that cuts the continuous filaments to the desired fiber length. Since one wants to have a fuse for the subsequent thermal aftertreatment, a corresponding number of individual fibers, which result in the desired fuse cross section, are placed one above the other on the catching ring. The sliver is deposited in a coiler 7. The fiber sliver is deposited over deflection rollers 8 in free-hanging loops on an extended scissor gate 9. After storage has been completed, 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 placed in a treatment retort 12. During the subsequent oxidation process, there is a vacuum retort 13 in the basement and the oxidation furnace 10 is from below drove over the treatment retort 12. According to a graduated temperature program, the treatment retort 12 is heated to 350 ° C. During this oxidation process to make the pitch fibers 2 infusible, air is passed through a filter 14 through a pump 14 via an electrical heat exchanger 15 and flows through the treatment retort 12 as hot oxidation air from bottom to top. Since volatile pitch components escape during the oxidation process, the exhaust air is first fed to a heat exchanger 16. Non-condensable pollutants are then burned in an externally flame-protected exhaust air combustion system. - 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 metal for the purpose of good heat transfer mass arm, 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 17 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, nitrogen is purged again. The vacuum retort 13 is then lowered back into the basement and exchanged for the carbonization furnace 11, which has meanwhile been heated to 1000 ° C. Carbonization takes ten minutes for a while, during which volatile compounds are transported through preheated nitrogen via the treatment retort 12 for condensation or combustion of exhaust air. After completion of the carbonization of Carbonisationsofe is descended 11 _r of the heat exchanger 15 ge inoperative taken and the interior of the treatment retort 12 with cold nitrogen to temperatures below 600 ° C cooled Now, the scissors gate 9 taken, subjected auseinanderge¬ and transported to the cooling state where the From cooling the carbon fibers 1 to room temperature.

In particular, the device for the thermal aftertreatment of the pitch fibers 2 has a lower rotating stage 18 with the oxidation furnace 10, the vacuum retort 13, the carbonation furnace 11 and a cooling retort 19. All treatment devices 10, 11, 13, 19 are designed in an open container construction for receiving treatment retorts 12. Furthermore, an upper rotating platform 20, which can be rotated independently of the lower rotating platform 18, is provided with a traversing device for treatment retorts 12 for temporarily receiving the fiber trays 9 with the pitch fibers 2 to be treated. Above the upper rotating platform 20 there is a loading level 21 with at least one loading opening 22 and at least one retort lid receptacle 23 for retort lid 24 with connection for air and inert gas supply, vacuum and air. The traversing device transfers the treatment retorts 12 for connection to the respective retort cover 24 from the upper turntable 20 below the hitting retort lid 24 and vice versa. The lower turntable 18 has at least one lifting device 25 for the oxidation furnace 10, the vacuum retort 13, the carbonization furnace 11 and the cooling retort 19. These treatment devices can be moved to accommodate the treatment retorts 12 under the retort lid receptacles 23 or the relevant retort lid 24 and raised or vice versa. The treatment devices 10, 11, 13, 19 are displaceable on the lower turntable 18 by 90 ° to one another and arranged on a rotating circle which, in vertical projection, the outer periphery of the upper turntable 20 for passing the upper turntable 20 to be raised to the side for lateral pass ¬ the treatment devices 10, 11, 13, 19 to be raised and for connecting the raised treatment devices to the respective retort cover 24 extends below the retort cover receptacles 23, which are offset by 90 ° to one another. Each treatment device 10, 11, 13, 19 is assigned an egg-like lifting device 25, so that one of the four processes oxidation, evacuation, carbonization and cooling can take place at the same time under each retort lid 24. At least two treatment retorts 12 offset from one another by 180 ° C. can be placed simultaneously on the upper rotating stage 20. 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. In detail, the device works as follows if one of the four processes of oxidation, evacuation, carbonization and cooling takes place simultaneously under each retort lid 24:

3) On the upper rotating platform 20, an empty treatment retort 12 is filled from above with a contracted scissor gate 9.

Fig. 4) The upper rotating stage 20 rotates by 180 ° C. While a scissor gate 9 with finished carbon fibers 1 is removed from the other treatment retort 12, the lower rotating stage 18 rotates by 90 °, so that the cooling retort 19 against the Oxidation furnace 10 is replaced.

5) The treatment retort 12 with the untreated pitch fibers 2 is transported through the traversing device under the assigned retort cover 24.

Fig. 6) by the lifting device 25, the oxidation furnace 10 - a low temperature furnace - is moved from below over the treatment retort 12. During the now following oxidation process it gets hot

Oxidation air is passed through the treatment retort 12 and the oxidation furnace 10 is heated in accordance with the optimized temperature profile. The hot process gases are led to the exhaust air purification. 7) After the oxidation has ended, the oxidation furnace 10 is moved down to the lower rotating stage 18.

Fig. 8) The lower rotating stage 18 rotates by 90 °, so that the vacuum retort 13 comes under the treatment retort 12.

Fig. 9) The vacuum retort 13 is via the lifting device 25 from below via the treatment retort

12 raised. The vacuum applied evacuates the oxidation furnace 10.

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 18.

Fig. 11) The lower turntable 18 rotates by 90 °, so that the now 1000 ° hot carbonization furnace

11 - a high-temperature furnace - under the treatment retort 12 is.

12) The carbonization furnace 11 is moved from below over the treatment retort 12 by means of the lifting device 25. During the subsequent carbonization process, preheated embroidery 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 stage 18.

Fig. 14) The lower rotating stage 18 rotates 90 °, so that the cooling retort 19 under the treatment retort

12 comes to a standstill. The pitch fibers 2 are cooled by supplying cold nitrogen to temperatures below 600 ° C.

Fig. 15) The further cooling can take place in the cooling station 19 with cold air.

16) The cooling station 19 is moved down to the lower rotating stage 18.

17) The treatment retort 12 is transported to the upper rotating stage 20 by the traversing device. A new cycle begins.

Example of the oxidation process

The characteristic data of a coal tar pitch distilled in a thin film evaporator are listed below: quinoline unl. <0.1%

quinoline solution toluene. 56.0

toluene solvent - n-hexane 36.6 -≤

n-hexane solvent 7.4%

EP (KS) 228 ° C

ash

Fl. Best, wf 31.5

Coke 68.5%

10 elementary analysis (%)

C 93.4

H 4.05

N 1.32

15 0 0.8

S 0.38

C / H 1.92 This high-melting coal tar pitch (EP (KS): 228 ° C) obtained by thin-layer evaporation was spun into pitch fibers 2. The pitch fibers obtained were heated in an oxidation oven 10 in 16 minutes to an oxidation temperature of 340 ° C. A critical oxidation range (softening point ± 25 ° C) was run through with a maximum heating rate of 20 ° C / m. The air flow rate was 2000 to 3000 1 / h. The pitch fibers 2 did not fuse during the oxidation, nor did they show any external damage. The infusibility achieved allowed a subsequent rapid carbonization according to the usual method. For the rest, activated carbon (without H-.SO.) Was used as an oxidation aid.

Claims

1. A process for producing carbon fibers from coal tar pitch, in particular coal tar pitch, the coal tar pitch being freed of infusible components by filtration prior to spinning, then the pitch filtrate is subjected to a distillation to remove volatile components, then d from the obtained The pitch melt spun pitch fiber is oxidized at a given oxidation temperature and carbonized at a given carbonization temperature, characterized in that the pitch filtrate is distilled in a thin-film evaporator to increase its softening point to values above 200 ° C (KS).

2. The method according to claim 1, characterized in that the pitch filtrate is in the thin film evaporator at temperatures above 200 ° C and under vacuum to 1 mbar z increase its softening point above 260 ° C (KS) be.

3. The method according to claim 1 or 2, characterized gekennzeic net that the carbon fibers after .dem carbonization by supplying cold inert gas, for. B. nitrogen, are cooled to temperatures below 600 ° C.

4. The method according to any one of claims 1 to 3, characterized in that the further cooling is carried out with cold air.

5. Device for carrying out the method according to one of claims 1 to 4, in the course of the thermal aftertreatment of the pitch fibers, with at least one fiber layer, an oxidation oven and a carbonization oven, characterized by

a lower revolving stage (18) with the oxidation furnace (10), a vacuum retort (13), the carbonization furnace (11) and a cooling retort (19), all treatment devices in an open container construction,

an upper rotating platform (20) which can be rotated independently of the lower rotating platform (18) and has a traversing device for treatment retorts (12) for temporarily receiving the fiber deposit (9) with the pitch fibers (2) to be treated,

- a loading level (21) above the upper rotating platform (20) with at least one loading opening (22) and at least one retort lid opening (23) for retort lid (24) with connection for air and inert gas supply, vacuum and exhaust air,

wherein the traversing device transfers the treatment retorts (12) for connection to the respective retort lid (24) from the upper revolving platform (20) under the relevant retort lid (24) and vice versa, and wherein the lower revolving platform (18) has at least one lifting device (25 ) for each of the oxidation furnace (10), the vacuum retort (13), the carbonization furnace (11) and the cooling retort (19) and these treatment devices (10, 11, 13, 19) for receiving the treatment retorts (12) under the retort lid receptacles (23) or the relevant retort lid (24) can be moved and raised and vice versa.

6. The device according to claim 5, characterized in that the treatment devices (10, 11, 13, 19) on the lower rotating stage (18) offset by 90 ° to each other and arranged on a rotating circle which in vertical projection the outer circumference of the the upper turntable (20) for laterally passing the treatment devices (10, 11, 13, 19) to be raised and for connecting the raised treatment devices to the respective retort cover (24) below the retorts¬ offset in the same way by 90 ° Cover receptacles (23), each treatment device (10, 11, 13, 19) being assigned its own lifting device (25).

7. The device according to claim 5 or 6, characterized gekenn¬ characterized in that on the upper turntable (20) at least two 180 ° offset treatment retorts (12) can be placed simultaneously.

8. Device according to one of claims 5 to 7, dadurc characterized in that the fiber tray is designed as a scissors gate (9) that can be freely assembled for fiber loops hanging freely on horizontal bars and that can be inserted into a treatment retort (12) when pushed together.