JPS5810494B2 - Method for producing adsorbent carbon fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Various heat treatment residues, such as pitch, are widely available, inexpensive, and have attractive chemical properties, making them suitable for use in binders and coating materials. It has wide applications as a starting material for manufacturing.

Pitches are used as part of component mixtures in the manufacture of various carbon products and in the formulation of carbon fibers.

One of the applications for carbon fibers arises from treating the fibers by appropriate means to increase the surface area and adsorptive properties of the fibers.

Activated fibers of this type are useful in applications involving fluid purification.

Currently, fibers of this type are derived by carbonization and activation of relatively expensive organic resins.

Although pitch is cheap, it can only be formed into stable fibers by a difficult and lengthy oxidation process.

An activation treatment for making such fibers adsorbent is not yet known.

It is therefore an object of the present invention to provide pitch fibers modified by the addition of small amounts of resin and a process for their production, which can effectively produce highly adsorptive activated carbon fibers.

The present invention relates to flexible adsorptive carbon fibers made from a mixture of pitch and phenol-formaldehyde novolak and having a surface area ranging from about 300 to about 2500 m2/P.

The pitch-novolak mixture can contain from about 5 to about 40% novolak in carbon fibers having diameters ranging from about 0.1 to about 300 microns.

This fiber is produced by converting a molten mixture of pitch and novolac heated and mixed at a temperature of up to about 190°C into fibers at a temperature of 120 to 150°C, and hardening the fiber to make it infusible.
Adsorbent carbon fibers are produced by heating the fibers in air to a temperature in the range of about 250°C to about 450°C and then heating the fibers under an inert atmosphere to a temperature in the range of about 700°C to about 900°C. Manufactured by forcing.

The surface area of the fibers is about 800°C to about 900°C in steam.
Further increases can be achieved by heating at temperatures in the range of .degree.

Starting heat treatment residues that can be used in the method of the present invention include, for example, coal tar pitch, pitch obtained by distillation of oils, petroleum pitch, pyrolyzed asphalt,
and various pinch-like substances, such as distillation residues, which are produced as by-products of various industrial processes.

Preferably, the starting heat-treated residue has a softening point of from about 80°C to about 200°C, more preferably from about 100°C to about 150°C.

The heat treatment residue is about 18 to about 25 percent by weight.
Preferably, the carbon to hydrogen ratio is .

The content of aromatic and unsaturated components varies depending on the source of the raw heat treatment residue.

The heat treatment residues or pitches used as starting materials have a beta resin content of greater than about 5%, preferably 10%.
It is preferred to have a beta resin content of more than 10%.

The beta resin is obtained by subtracting the quinoline dissolved content from the benzene insoluble part in the heat treatment residue.

To quantify it, for example, use toluene instead of benzene, pyridine instead of quinoline, etc.
Other solvents can also be used.

The beta resin moieties in the heat treated residue appear to improve the bonding and adhesion properties of the heat treated residue.

Appropriate amounts of beta resin are believed to render meltable fibers infusible through a short curing process.

The upper limit for the percentage of beta resin in the starting heat treatment residue is not critical, but is generally limited by the type of pitch used and the processing conditions.

Commercially available pitches have beta resin contents of less than about 30%, but pitches having beta resin contents of greater than 45% can be used in the present invention.

Generally, industrially available coal tar pitch is about 2
It has 0 to about 50% pentene insoluble and about 10 to about 20% quinoline soluble, so the beta resin content ranges from about 10 to 30%.

These pitches can be processed without further modification.
Suitable for use as starting material in the process of the invention.

Petroleum pitch and pyrolytic asphalts often have a beta resin content of less than about 5%.

This is generally due to the low content of benzene insolubles, which is usually less than about 10%.

In such cases, the soluble fibers consisting of heat treatment residue and novolak can be made infusible by reacting with formaldehyde, but the curing process is relatively slow.

It is also possible to increase the quality of the pitch by increasing the beta resin content.

Such upgrading is achieved by reacting the pitch or asphalt// with the aldehyde and phenolic compound in the presence of an acidic catalyst at a temperature high enough to effect condensation between the pitch or asphalt, the aldehyde and the phenolic compound. , can be done.

Such methods are described in British Patent No. 1,080,866 and United States Patent No. 3,301,803;
These patents may be referred to in the present invention.

The amounts of aldehyde and phenolic compounds used can vary widely depending on the degree of upgrading required.

This reaction is carried out by heating at a temperature of about 150°F to about 600°F for a suitable period of time.

The amount of quinolinine melt in the starting heat treatment residue should be less than about 20%, preferably less than about 10%.

As the percentage of quinoline melt in the starting heat treatment residue decreases, the ease of fiberization of the melt increases and the uniformity of the fibers improves.

Most preferred starting heat treatment residues are those containing very low percentages of cello or quinoline dissolved matter.

Quinoline melt represents a material that does not dissolve and forms an undesirable second phase in the heat treatment residue at spinning temperatures.

Removal of the quinoline solution can be accomplished by dissolving the pitch in a suitable solvent and removing undissolved material by filtering or centrifuging.

Such a method is described in U.S. Patent No. 359,594.
It is written in No. 6.

A wide range of novolac resins can be used as starting materials in the process of the invention.

The term “novolak’ refers to the condensation product of a phenolic compound and formaldehyde;
It is carried out in the presence of a catalyst to form a novolac resin.

In novolaks there are almost no methylol groups present, such as those present in resols, and in which the molecules of the phenolic compound are interconnected by methylene groups.

The phenolic compound can be phenol or phenols in which one or more of the non-hydroxyl hydrogens is substituted by various substituents attached to the benzene ring, to give some examples of the latter. and cresol, phenylphenol, 3,5-dialkylphenol, chlorophenol, resorcinol, hydroquinone,
Examples include chloroglycytool.

Additionally, the phenolic compound can be a hydroxyl derivative of naphthyl or hydroxyphenanthrene, or other compounds with fused ring systems.

For the purposes of the present invention, meltable novolacs which can be further polymerized with suitable aldehydes can be used for the production of the fibers.

In other words, the novolak molecule must have two or more than two locations available for further polymerization.

Apart from these limitations, modified novolacs, i.e.
For example diphenyl oxide or bis-phenol A
Any novolak may be used, including novolaks that also contain non-phenolic compounds in the molecule, such as modified phenol-formaldehyde novolaks.

Mixtures of novolaks may be used, or novolaks containing more than one phenolic compound may be used.

Novolacs generally have an average molecular weight in the range of about 500 to about 1200, although there are exceptions, such as those as low as 300 or as high as 2000 or more.

Unmodified phenol-formaltehythobolanc typically has a number average molecular weight in the range of about 500 to about 900, with the majority of commercially available materials falling within this range.

Novolacs having a molecular weight of about 500 to about 1200 are preferably used in the method of the invention.

The temperature at which low molecular weight novolaks soften and become sticky is
generally relatively low.

Therefore, it is necessary to cure the fiberized novolac at very low temperatures to avoid fiber adhesion and/or deformation.

It is usually not preferred to use such low curing temperatures because the curing rate increases very rapidly with increasing temperature and low curing temperatures result in a practical disadvantage of a lengthy curing process.

In general, it is preferred to use a novolak with a suitably high molecular weight so that curing can be achieved in a reasonable amount of time without fear of sticking and/or deformation, but to minimize problems due to gelation during fiberization. Therefore, it is preferable to avoid the highest molecular weight limit.

The mixture of heat treated residue or pitch and novolak can be formed by any convenient method such as dry mixing or melt mixing by heating the heat treated residue and novolak together to form a homogeneous mixture.

Mixtures containing from about 5 to about 40% novolak can be used for preparing the fibers of the present invention.

Since the heat treatment residue is the most economically available component in the mixture, it is preferred to use less than about 35% novolak.

In order to improve the spinnability of the fibers and to sufficiently reduce the setting time, the novolak content in the mixture is preferably at least about 10%, and more preferably low (at least about 25%).

Preferably, the mixture consists essentially of heat treatment residue and novolac.

Fiberization can be accomplished by any convenient method, such as by drawing continuous fibers downward through an orifice in the bottom of a container containing a pinch and a molten mixture of novolak.

The Lyramen is wound onto a rotating take-up spool stepped under the orifice.

The take-up spool also serves to thin the filament as it is drawn from the orifice before it contacts the atmosphere between the orifice and the spooler to cool and solidify.

The melt can be short-cut by conventional methods such as blowing it through a fiberizing nozzle and collecting the cooled fibers, or blowing a trickle of the melt into the path of a hot gas stream. It can also be a stable fiber.

These methods provide a stable consisting of a large number of meltable, uncured pitch-novolac fibers of different lengths and diameters.

The diameter of such fibers ranges from 0.1 micron to about 300 microns.
It can be varied in the micron range.

When melt spinning produces continuous filaments of uniform diameter, the fibers preferably have a diameter of about 10 to about 30 microns.

The filament diameter mainly depends on two factors:
It is related to the withdrawal speed and the flow rate of the melt in the orifice.

The fiber diameter decreases as the withdrawal speed increases and increases as the melt flow rate increases.

The melt flow rate is primarily related to the diameter and length of the orifice and the viscosity of the melt, increasing as the orifice diameter increases, decreasing as the orifice length increases, and decreasing as the melt viscosity increases. It rises as it falls.

Increased flow rate can also be achieved, if desired, by applying pressure to the melt and forcing it out of the orifice.

As a further alternative, the modified pitch material fibers are
A mixture of pitch and novolak can be produced by injecting it into a container connected to a nozzle.

Meanwhile, the nozzle is also connected to a source of air pressure for forcing the mixture into the nozzle.

In this way short staples or blown fibers of suitable diameter can be collected.

Fibers produced by either drawing or blowing are meltable and can be further processed to harden or crosslink them, at least to the point that they become infusible.

Curing is generally in the presence of a methylene radical source, such as formaldehyde, and preferably further comprises:
It is produced by heating the fibers in the presence of a suitable catalyst, such as an acid.

Blowing provides staples consisting of fibers with different lengths and diameters.

Diameters as small as about 0.1 microns or more can be obtained, or fibers can be obtained much thicker.

By using melt spinning, fibers can be produced as continuous filaments with diameters ranging from as small as about 4 microns to as large as about 300 microns or more, if desired.

After curing, the fibers can be processed by a variety of methods to provide rovings and threads, paper, felt, woven or knitted fabrics, and a variety of other fiber forms.

Infusible, hardened phenol-formaldehyde
A particularly preferred method of producing novolac fibers is described in detail in U.S. Pat. Can be done.

According to the present invention, infusible modified pitch fibers are heated in air from room temperature (about 25°C) to about 250°C to about 450°C.
Approximately 50 °C per hour up to intermediate temperatures in the range of °C.
℃ to about 200℃ at a rate that can be varied from
Carbonization is achieved by heating while continuously increasing the temperature.

Heating is then continued from the intermediate temperature to a final temperature in the range of about 700°C to about 900°C in a non-oxidizing atmosphere, such as nitrogen or a similar inert gas.

In this case, the temperature ranges from about 50°C to about 200°C west for 1 hour.
Continuously rise at a speed of .

Although the exact nature of the reaction that occurs is not yet clear, heating in air leads to increased crosslinking, partial pyrolysis and carbonization of the starting fibers, and during heating in a non-oxidizing atmosphere It is believed that the fibers undergo further carbonization.

This process results in the production of carbon fibers that are generally low in carbon (both having a surface area of between 300 m2/g and about 800 m1/?).

Additionally, if the starting cured modified pitch fiber is swollen by soaking in a highly polar solvent before carbonizing it by the method described above, the resulting carbon fiber will generally be at least about 400 r"/ ?, was found to have some increased surface area, typically in the range of about 400 m2/g to about 1000 m2/?.

A particularly desirable feature of the above method is that it provides about 3
In addition to having carbon surface areas ranging from 00 m2/g to about 1000 m2/g, relatively strong and extremely flexible carbon fibers can be produced.

Another interesting feature of the present invention is that the modified pitch fibers are
1 after curing in the presence of formaldehyde, before rapidly heating to a relatively high temperature at a rate of 50 to 100 hr.
When heated in air from 0°C to 250°C at a rate of 50°C/hour, the resulting fibers, in addition to being adsorbent and active, also have improved flexibility. be.

Another particularly important feature of the method of the invention is that the carbon surface area of the carbon fibers produced by this method can be
by heating the fibers in steam at a temperature in the range of about 800°C to about 900°C.
This means that the initial surface area of 0r2/g can be successively increased to about 2500 m2/g.

This is extremely important because carbon adsorption capacity and fiber flexibility generally increase with increasing surface area.

It is noteworthy that infusible fibers with pinch contents approaching 95% can be produced by the method of the invention and that fibers with a significantly increased surface area can be provided by heat treatment.

This behavior is completely unexpected considering the behavior of fibers consisting entirely of heat treatment residues or pitch.

Since this latter fiber is thermoplastic, it passes through a fluid state when heated to a carbonization temperature of 800°C.

If such fibers are subjected to an activation treatment as described for the activation of modified pitch fibers, 1
Only products with surface areas smaller than ~5 m2/g are obtained.

Considering this behavior, the significant changes caused by the addition of as little as 5% resin to the modified fibers are completely unexpected.

Although the exact reason is not clear, it appears that crosslinking of the modified pitch material during the curing and activation process may be one of the factors that provides the superior fibers of the present invention.

The present invention will be further explained in part according to the following examples, but these examples are only illustrative of the invention and are not intended to limit the scope of the invention.

Example 1 Starting coal tar pinch (Allied Chemical Company) had a softening point of 125°C, a beta resin content of 22%,
and had a quinoline soluble content of 13.6%.

This pitch was mixed with a novolac resin (Barcum) having a molecular weight of about 800 to 10,000 to give a ratio of 70% pitch to 30% resin in the final mixture.

The novolak and pitch were heated together to 190°C to form a homogeneous mixture and the resulting mixture was placed in a fiberizing vessel.

The container was a cylinder with an orifice at the bottom and a plunger at the top to force the liquid into the orifice.

This container was mounted on a fiberizing device.

This device included a spool attached to the shaft of a variable speed electric motor mounted below the container to collect the fibers.

A controlled amount of heat was applied to the container and its contents by surrounding the container with an electric heating coil connected to an adjustable power source.

The fibers were spun through an orifice having a length of approximately 1.5 mm and an internal diameter of approximately 0.3 mm.

The vessel containing the resin mixture was kept at a temperature of about 120°C, while the bottom with the orifice was kept at about 150°C.

A mixture of pinch and novolac was extruded through the orifice by a ram at a pressure of about 110 psi.

The resulting mixed pinch-novolac filament is
It had an average diameter of approximately 15-25 microns and was wound onto a cylindrical cone of graphite at a speed of 500 revolutions/minute.

The fiber bundle thus obtained was cured by suspending the fiber-containing graphite cone on a graphite support and immersing it in a curing solution.

This solution was prepared by mixing equal parts of an aqueous solution containing hydrochloric acid at a concentration of approximately 18% and paraformaldehyde at the same concentration.

The curing solution in which the graphite cone carrying the fibers is immersed is heated from room temperature to 100°C by increasing the temperature from 25°C to 50°C over 1 hour and from 50°C to 100°C over 1/2 hour. And it was held at a temperature of 100°C for 4 hours.

Total residence time was approximately 5.5 to 6 hours.

After taking out the hardened fibers and washing them with water, they are left in the air for about 60 minutes.
Dry at °C.

The cured fibers were infusible and did not soften when heated in an oven or in a flame.

Example 2 A mixture of pitch and novolac resin prepared according to the method of Example 1 was poured into a fiberizing vessel equipped with a nozzle.

The nozzle was connected to a source of air pressure in order to force the pitch-novolak mixture through the nozzle in air.

In this way, short stable fibers or blown fibers were accumulated after cooling by falling through the air.

The nozzle was heated to approximately 250°C and the air pressure used was approximately 20°C.
It was psi.

The fibers thus assembled were placed in a graphite container to form a mat and cured as in Example 1 by heating in a curing solution.

The average diameter of the cured fibers was approximately 2 microns.

These fibers were infusible as in Example 1.

Example 3 A tow of infusible modified pitch filaments consisting of coal tar pitch and phenol-formaltehyde novolak was prepared substantially according to the method of Example 1.

The filament had a diameter of approximately 12-18 microns.

The tow was cut into 15 cm (approximately 6 inch) pieces and 5 g of the cut fibers were placed in a tube furnace.

The fibers are heated at a temperature increase rate of 200°C per hour from room temperature to an intermediate temperature of 400°C, while passing a slow air stream through a tube furnace to remove the volatile substances released by the fibers (and to remove the air Maintained the atmosphere.

When the temperature reached 400°C, change the air flow to a slow nitrogen flow,
After continuing heating in this nitrogen atmosphere at a temperature increase rate of 200°C per hour until reaching a final temperature of 900°C,
The resulting carbon fibers were allowed to cool to room temperature.

To prevent oxidation of the carbon during this cooling step, nitrogen was used to provide a non-oxidizing atmosphere.

A yield of flexible carbon fiber of 31 was obtained, but this carbon
It had an average surface area of 0r2/g.

Example 4 Fibers were heated gradually in air to an intermediate temperature of 10-250°C, then more rapidly at a rate of 100°C/hour to 450°C, and then heated in nitrogen at a rate of 100°C/hour. Example 3 was repeated except that heating was continued to a final temperature of 700°C.

The resulting fibers were found to be extremely flexible.

Although the exact mechanism is not clear, slow heating of formaldehyde cured fibers to 250°C is believed to cause the fibers to crosslink more completely, which appears to improve mechanical properties.

These fibers have an average surface area of 705r2/g;
And the individual fibers are about 1000r2/? It had a carbon surface area of up to .

Example 5 The surface area of carbon fibers made in accordance with the present invention, as illustrated in Examples 3-4, is determined by adding the carbon fibers in steam at a temperature in the range of about 800°C to about 900°C, if desired. It can be increased by

Thereby, it is possible to increase the surface area from about 300 to 1000 m/g to as much as about 2500 m2/g.

During this heating, the carbon fibers gradually increase in porosity and surface area and lose weight as the carbon burns off, so that if the heating is too long it will dissipate completely.

Therefore, heating must be of sufficient duration to cause an increase in surface area, but not unduly long; a suitable time is generally one that provides the desired surface area with minimal weight loss. be.

The higher the temperature within the above range, the shorter the time required for a given increase in surface area.

For example, at 800°C, it takes about 90 minutes to increase the surface area to 2000 m2/g;
At 900° C., the latter temperature is preferred as it takes about 20 minutes.

To obtain a surface area of approximately 2500 m2/g, slightly more time is required.

Example 6 The carbon fibers prepared in Example 4 were placed in a tube furnace at 800°C under a slow stream of steam, and under these conditions 2
After a period of time, the fibers were cooled to room temperature in a non-oxidizing (nitrogen) atmosphere.

The resulting carbon fibers had an average carbon surface area of 2400 m2/' and exhibited good flexibility and mechanical properties.

The method of the present invention can be carried out with fibers in almost any desired form, including, for example, tow, rovings and yarns, staples and battings, felts, papers, woven and knitted fabrics, etc. are possible, and the choice of form primarily depends on the intended use of the carbon fiber.

Similarly, the fibers may be of any desired diameter, the choice being primarily related to the intended use for the resulting carbon fibers.

Although surface area does not appear to be related to diameter: a carbon fiber's tensile strength tends to increase with increasing diameter and its flexibility tends to decrease with decreasing diameter.

Although the embodiments illustrate the invention in a batch manner, it would be easy to devise suitable equipment for carrying out each step in a continuous manner.

The carbon in the fibers produced according to the invention is amorphous (glass-like) and of the type known as hard carbon, ie, highly crosslinked carbon that is extremely difficult to graphitize.

High surface area carbon fibers have many uses in a variety of forms.

For example, they are particularly useful as adsorbents in gas masks and absorbent protective clothing and permeable media.

Percentages expressed herein are by weight, unless otherwise indicated or the context clearly indicates otherwise.

The surface areas stated herein are determined using the BET method and Brunner (
Brunauer) Emmett and Teller [Journal of the American Chemical Society, 60; 309-316 (1
938)], the automatic surface area analyzer 220
Surface area measured using Model 0 (Micrometrics Instrumental Corporation, Norcross, Georgia).

This method is based on measuring the amount of gas, such as nitrogen, required to form an adsorbed monolayer on the surface of the sample.

Although the present invention has been described herein with respect to several embodiments and preferred embodiments, those skilled in the art will appreciate that various changes and modifications can be made thereto without departing from the scope of the invention. It should be understood that the scope of the invention should be determined by reference to the following embodiments.

The embodiments of the present invention are as follows.

■ A fiber made from a mixture consisting of pitch and phenol-formaldehyde novolac, the fiber having a content of at least about 300 v2/? A flexible adsorptive carbon fiber characterized by having a surface area of .

2.Surface area is approximately 300m2/g to approximately 2500m2/β
The carbon fiber according to 1 above, which is within the range of .

3. The carbon fiber according to 2 above, having a range of about 300 r2/g to about 1000 m2/g.

4. The range is about 300m2/? The carbon fiber according to 3 above, which is from about 800 m2/g.

5. The carbon fiber according to 1 above, wherein the mixture contains about 5 to about 40% novolac.

6. The carbon fiber according to 5 above, wherein the mixture contains about 10 to about 25% novolac.

7. The carbon fiber according to 1 above, wherein the fiber diameter ranges from about 0.1 to about 300 microns.

8. The carbon fiber according to 7 above, wherein the fiber diameter ranges from about 10 to about 30 microns.

9. (a) Fiberizing the molten mixture of pitch and novolak; (b) rendering the fiber infusible by curing it with formaldehyde under acid; (c) heating the fiber in air; then (d) A method for producing flexible adsorptive carbon fibers, comprising: heating the fibers in an inert atmosphere to produce adsorptive carbon fibers.

10, a mixture of pinch and novolak from about 5 to about 4
9. Process according to 9 above, having a novolak content of 0%.

11. The method according to 10 above, wherein the mixture has a novolak content ranging from about 10 to about 25%.

12. The method according to 9 above, wherein the diameter of the fibers ranges from about 0.1 to about 300 microns.

13. The method according to 12 above, wherein the fiber diameter ranges from about 10 to about 30 microns.

14. Cured fibers are heated from room temperature to about 250℃ in air.
9. The method according to 9 above, comprising heating to an intermediate temperature in the range of from about 450°C.

15. The fibers are heated under an inert atmosphere from intermediate temperature to about 70°C.
15. The method according to claim 14, wherein the method is heated to a final temperature in the range of 0°C to about 900°C.

16. In addition, the carbon fiber is heated to about 800°C to about 900°C.
10. A method according to claim 9, comprising a subsequent step consisting of heating the carbon fibers in steam at a temperature in the range of 10 to 10 for a time sufficient to increase the surface area of the carbon fibers.

Claims (1)

[Claims] 1. (a) a mixture of pitch and novolac of about 190%
(b) the melt of the pinch and novolac mixture is fiberized at a temperature of about 120-150°C; (e) the fibers are cured with formaldehyde under acid to make them infusible; (d) heating the fibers in air to a temperature of about 250 to 450°C at a temperature increase rate of about 50 to 200°C per hour; and (e) heating the fibers under an inert atmosphere to a temperature of about 700 to 900°C. A method for producing flexible adsorptive carbon fibers, comprising the steps of heating to a temperature to generate adsorptive carbon fibers.