Patent Application
20240360596
A process for preparing a carbon fiber precursor is hereby disclosed. The precursor is in the form of a PAN fiber. It is heated in a first step, called the densification step or the oxidation step, for a time of about three to four hours in length. This is because the internal temperature of the PAN fiber rises too quickly unless the heating is controlled by a series of increases and reductions over an extended period of time.
The PAN fiber does not begin to form cross-links until the “fusion point” of the fiber is almost reached. Once the “fusion point” is reached, the internal temperature of the fiber quickly shoots up to a temperature of about 400 degrees C. and even higher, thus destroying the fiber (burnout).
U.S. Pat. No. 4,336,022 (Lynch and Wilkinson), herein included as by reference, avoids this situation by allowing the PAN fiber to begin forming both internal (within a particular polymer segment) and external (between two or more polymer segments) cross-links soon after the densification step begins. The cross-links exhibit the structure of an amidine moiety. This structure is formed when ammonium nitrogen or quaternary ammonium nitrogen attacks a pendant cyano group on the PAN polymer.
With the presence of ammonium or quaternary ammonium groups in the PAN polymer, cross-linking activity begins rather quickly as the heating reaches about 180 degrees C. Cross-linking starts well before the “fusion point” of the fiber is reached. The density of the fiber goes from about 1.14 grams/cc. to about 1.4 grams/cc at the conclusion of the first heating step. Any possibility of “burn out” is avoided.
The '022 patent discloses the addition of the ammonium salt of 2-acrylamido-2-methyl propane sulfonic acid monomer to the acrylonitrile monomer before polymerization. After polymerization is complete, a spin dope of the PAN material is prepared and the spin dope is conducted to a wet spinning zone for preparation of filaments.
The presence of ammonium nitrogen or quaternary ammonium nitrogen in the solid PAN fiber is essential for the ability of the fiber to be densified quickly. This densification takes place during the initial heating step of the process. The PAN fiber, which contains the ammonium salt of 2-acrylamido-2-methyl propane sulfonic acid, can be employed as a carbon fiber precursor.
In an embodiment, the present disclosure relates to a carbon fiber precursor prepared from a unique process. In another embodiment, the present disclosure relates to a process for choosing the best carbon fiber precursor from a series of fibers. In yet another embodiment, the present disclosure relates to an apparatus for making carbon fiber. In still another embodiment, the present disclosure relates to a carbon fiber prepared according to the presently disclosed process. In another embodiment, the present disclosure relates to a mixture of two monomers useful in the preparation of carbon fiber, the two monomers being acrylonitrile and the ammonium salt of 2-acrylamido-2-methyl propane sulfonic acid.
The ammonium salt of 2-acrylamido-2-methyl propane sulfonic acid can be prepared by contacting the sulfonic acid with a base selected from the group consisting of ammonia, an inorganic ammonium base, a low molecular weight primary amine and a low molecular weight secondary amine. Preferably the ammonium base is ammonium hydroxide. Both the primary amine and the secondary amine contain aliphatic hydrocarbon groups of from one to six carbon atoms.
A PAN (polyacrylonitrile) polymer is then prepared from acrylonitrile monomer and the ammonium salt (or quaternary ammonium salt) of 2-acrylamido-2-methyl propane sulfonic acid monomer.
Following purification of the polymer, a spin dope of the polymer is prepared. The spin dope is spun through a die plate to obtain gelled filaments of PAN fiber. The filaments are solidified, gathered and bundled into a PAN fiber, which is then washed and stretched to obtain a carbon fiber precursor. The PAN fiber can contain from about one thousand filaments up to about fifty thousand filaments.
The PAN fiber is analyzed for physical properties such as: number of surface defects (the lower number of defects the better), interior homogeneity (the more homogeneous the better), degree of orientation (the higher degree of orientation the better), tenacity (the higher tenacity the better), number and size of micro voids (the smaller number and the smaller size of micro voids the better), arrangement of crystallites on the surface (homogeneous arrangement is better) and compactness of structure (the more compact the better).
In an embodiment, other PAN fibers are prepared from acrylonitrile monomer and the ammonium salt of 2-acrylamido-2-methyl propane sulfonic acid in various other ratios of monomers. These other PAN fibers are then analyzed for physical properties in the same manner as recited above.
After analysis of all the PAN fibers is complete, the fibers are ranked based on best combination of all the qualities. The highest ranked PAN fiber is then retained for densification and carbonization to obtain a carbon fiber.
In an embodiment, the densification step, unlike prior art processes, can be conducted in the absence of oxygen. An inert gas such as nitrogen or argon can be employed. As is practiced in the art, an inert gas atmosphere is provided for the carbonization step.
In the present disclosure, an ammonium salt of 2-acrylamido-2-methyl propane sulfonic acid monomer is added to a polymerization unit along with acrylonitrile monomer. In an embodiment, the amount of ammonium salt of 2-acrylamido-2-methyl propane sulfonic acid monomer is about 0.5 mole % to about 8 mole %. The acrylonitrile monomer is present in an amount of about 92 mole % to about 99.5 mole %.
A restriction imposed on the present process is that a vinyl sulfonic acid monomer, allyl sulfonic acid monomer, metal salts thereof, and the like cannot be included in the feedstock composition. It has been observed that the presence of sulfonic acid groups in the final acrylonitrile copolymer causes retention of metal ions. Metal ions are deleterious to formation of the final carbon fiber product.
The feedstock for use in the present process must be substantially free of sulfonic acid groups. By substantially free of sulfonic acid groups is meant not more than 0.2 mole % sulfonic acid groups are present in the polymer composition.
Another restriction imposed on the present process is that a vinyl carboxylic acid, allyl carboxylic acid, or metal salts thereof and the like cannot be included in the feedstock composition.
In an embodiment, the ammonium salt of 2-acrylamido-2-methyl propane sulfonic acid monomer can be substantially replaced with a quaternary ammonium salt of 2-acrylamido-2-methyl propane sulfonic acid. The quaternary ammonium salt can be prepared from a C1-C6 primary amine or a C1-C6 secondary amine. It is within the scope of the present process to employ a mixture of an ammonium salt of 2-acrylamido-2-methyl propane sulfonic acid and a quaternary ammonium salt of 2-acrylamido-2-methyl propane sulfonic acid.
In an embodiment, an ester of a vinyl carboxylic acid can be employed as a co-monomer to yield a terpolymer. Examples are methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate and the like. Esters can be employed in the monomer mixture in an amount of about 0.5 mole % to about 2 mole %.
In an embodiment, the polymerization unit is a precipitation polymerization unit as disclosed in U.S. Pat. No. 5,364,581 (Wilkinson). The '581 patent is incorporated herein by reference. By precipitation polymerization is meant a polymerization process wherein the growing polymer comes out of solution at a certain stage, usually when about ten monomer units have been polymerized to form a polymer chain. Once out of solution, the polymer is unaffected by initiators and the like which tend to chain-stop the polymer. Monomer is able to penetrate the polymer and allows for the rapid continued growth of the polymer chain to a high molecular weight. Since the polymer growth is rapid, precipitation polymerization can be conducted in a continuous manner.
In an alternative embodiment, the polymerization reaction can be conducted in a batch reactor.
The solvent system used in the precipitation polymerization process can be a mixture of water and an organic solvent. The organic solvent must be capable of dissolving polyacrylonitrile co-polymer of a number average molecular weight of about 40,000 to about 100,000. In a preferred embodiment, the organic solvent is a member selected from the group consisting of dimethyl formamide, dimethyl acetamide, dimethyl sulfoxide, tetramethylene cyclic sulfone and butyrolactone. The organic solvent or mixtures of solvents can be present in the aqueous solvent system in an amount of from about 30% by volume to about 90% by volume.
It has been found that the polymerization rate of the co-monomers is dramatically increased when the water plus the solvent does not completely dissolve the co-polymer. In a preferred embodiment, a solvent system comprising dimethyl formamide (DMF) and water or dimethyl acetamide (DMAC) and water is employed.
Catalysts useful for the precipitation polymerization of acrylonitrile monomer and the ammonium salt of 2-acrylamido 2-methyl propane sulfonic acid monomer are hydrogen peroxide or an organic peroxide or a low molecular weight volatile organic mercaptan. The organic mercaptan should have low volatility. The initiator system cannot contain any metal or metal ion containing compounds greater than about 10 ppm. The peroxide is hydrogen peroxide, t-butyl hydroperoxide, t-butyl per oxide and lauroyl peroxide or mixtures thereof. The mercaptan is a member selected from the group consisting of 1-thioglycerol, mercaptoethanol and butylmercaptan isomers. By butyl mercaptan isomers is meant normal butyl mercaptan, sec-butyl mercaptan and iso-butyl mercaptan. By low molecular weight organic mercaptan is meant a C1-C6 organic mercaptan.
A catalytic amount (about 10 ppm) of an iron compound is added to the mixture of solvent, initiator and monomer systems. Examples of iron catalysts are ferric (or ferrous) nitrate, ferric (or ferrous) chloride, and ferric (or ferrous) ammonium sulfate. The compounds can have water of hydration associated therewith.
A polyacrylonitrile can be prepared from a mixture of at least two monomers. The monomers can be acrylonitrile and the ammonium salt of 2-acrylamido-2-methyl propane sulfonic acid. Catalysts are employed under suitable conditions of temperature and pressure. In a preferred embodiment, the reaction is conducted at a temperature of about 50 C. to about 70° C.; and at a pressure of about 1.0 to about 1.2 atmospheres.
As the polymerization continues, feedstock, solvent and initiator can be added either in a continuous fashion or at regular intervals to maintain correct amounts of reactants and the like in accordance with parameters well-known to those skilled in the art. Preferably the polymerization is continued until the solids content reaches about 20% to about 40%. The precipitation polymerization provides for a rapid rate of conversion and a high molecular weight product.
The present process is best conducted in a continuous precipitation polymerization manner, which allows good dissipation of the heat of polymerization and allows reaction times as short as 30-60 minutes.
Once the polymerization is complete, the water and unreacted acrylonitrile, unreacted ammonium salt of 2-acrylamido-2-methyl propane sulfonic acid and unreacted acrylate ester (if present) are removed as by stripping; and the polyacrylonitrile polymer dissolves in the organic solvent. Additional organic solvent is added to adjust solids to the proper viscosity.
In an alternative embodiment, acrylonitrile monomer and the ammonium salt of 2-acrylamido-2-methyl propane sulfonic acid monomer are co-polymerized in dimethyl sulfoxide (DMSO). A free radical solution polymerization is conducted in the presence of a radical initiator such as azobisisobutyronitrile (AIBN). A polyacrylonitrile (PAN) material is obtained.
The polyacrylonitrile material is then purified as by washing, drying and forming a powder. The powder is then slurried with organic solvent to produce a spin dope. In an embodiment, the organic solvent can be DMF or DMAC. The spin dope is extruded through a die plate to obtain fine filaments having a dernier of about 1 to about 8. In an embodiment, the die plate contains about 2100 holes, which provides for 2100 filaments.
Wet spinning of the material allows formation of filaments having a substantially circular cross-section. After wet spinning, the filaments are bundled into fibers and passed to a wash zone. Fibers are then washed to remove solvent and drawn over tensioning rollers.
In an embodiment, the fibers are optionally passed into a relaxation unit where they are relaxed to about 10%.
Carbon fibers are then prepared by removing the PAN fiber to a densification zone (oxidizing zone) and then to a carbonizing zone. The densification zone can be a single heating oven or a series of three heating rolls, each roll increasing in temperature in a step-wise fashion.
In an embodiment, the heating oven includes a cylindrical oven containing programmed heating coils which adjust in temperature in accordance with a predetermined heating cycle of increasing temperature. The cylindrical oven can be sealed to prevent addition of oxygen or air. An inert atmosphere of nitrogen or argon or the like can be maintained in the heating oven.
In an alternative embodiment, the series of three heating rolls includes a first heating roll maintained at a temperature of about 235 degrees C. to about 245 degrees C., a second heating roll maintained at a temperature of about 245 degrees C. to about 255 degrees C., and a third heating roll maintained at a temperature of about 255 degrees C. to about 265 degrees C. Densification of the polyacrylonitrile fiber begins on the first heating roll and continues until the end of the heating process. The fiber is removed from the third heating roll and passed to an uptake roll. The density of the fiber has increased from about 1.14 grams per cc to about 1.4 grams per cc. This densification is achieved in a short period of time, preferably about fifteen minutes to about thirty minutes.
The densified polyacrylonitrile fiber is then passed to a carbonization zone, which is maintained at a temperature of about 1000 degrees C. to about 2500 degrees C. In a matter of a few seconds or less the fiber is stripped of all atoms except carbon. The carbon fiber removed from the carbonization zone has excellent homogeneity and tensile strength. Very little, if any, “waste” carbon fiber is produced.
In an embodiment, a process for preparing a carbon fiber precursor is hereby disclosed. The process includes the steps of: obtaining an acrylonitrile monomer; obtaining an ammonium salt of 2-acrylamido-2-methyl propane sulfonic acid monomer; polymerizing the acrylonitrile monomer with the ammonium salt of 2-acrylamido-2-methyl propane sulfonic acid monomer in a polymerization reactor; and withdrawing the PAN carbon fiber precursor. The acrylonitrile monomer is present in an amount of about 92 mole % to about 99.5 mole %. The ammonium salt of 2-acrylamido-2-methyl propane sulfonic acid monomer is present in an amount of about 0.5 mole % to about 8 mole %.
The 2-acrylamido-2-methyl propane sulfonic acid is neutralized with a base selected from the group consisting of ammonia, ammonium hydroxide, a low molecular weight primary amine and a low molecular weight secondary amine. Preferably, the base is ammonium hydroxide.
The polymerization reactor is a precipitation polymerization reactor. A batch reactor can also be employed, but it is not as desirable.
In a further embodiment, PAN fiber is heated in two steps to obtain a carbon fiber. The heating includes a densification (oxidation) step and a carbonization step. In the densification step, the temperatures can range from about 250 degrees C. to about 400 degrees C.
In prior art processes for preparing carbon fiber, oxygen (or air) is employed to initiate the necessary cross-linking of the PAN fiber. Cross-linking with oxygen results in non-homogeneous crosslinks, which ultimately damages the tensile strength of the fiber. In a preferred embodiment, densification of the carbon fiber precursor is performed in an inert atmosphere such as nitrogen or argon. In this atmosphere, all of the cross-linking occurs due to the presence of the ammonium salt.
In an embodiment, a densified PAN fiber, also called a PANOX (oxidized polyacrylonitrile) fiber, having a density of about 1.4 grams per cubic centimeter, can be carbonized in a carbonization zone in a few seconds or less to obtain a carbon fiber having superior homogeneity and tensile strength.
Referring to
The spin dope is transferred through a sixth transfer means 9 to a spinning zone 10. In an embodiment, the spinning zone 10 is a wet spinning zone. Wet spinning allows formation of filaments having substantially circular cross-sections. Dry spinning causes the filaments to have dog-bone shaped cross sections, which shape is not desirable for preparing PANOX fiber.
PAN filaments are removed from the spinning zone 10 and added to a bundling zone 12 via a seventh transfer means 11. Filaments are bundled together and a PAN fiber 13 is withdrawn from the bundling zone 12 and removed to a second solvent removal zone 15 by employing an eighth transfer means 14. The solvent removal zone 15 also contains a drawing apparatus (not shown) for stretching the PAN fiber 13.
While immersed in the second solvent removal zone 15, the PAN fiber 13 is drawn at least about 7× to set the physical properties of the fiber. Also, solvent is removed from the fiber. The drawn PAN fiber can then optionally be added to a relaxation zone (not shown), which can comprise a set of steamed rollers (not shown) in order to relax the drawn PAN fiber. The drawn fiber is relaxed at least about 8% to about 12%. Preferably, the PAN fiber is relaxed about 10% in the relaxation zone.
Prior to densification, the drawn and relaxed PAN fiber is removed to an analysis zone (not shown), where the fiber is measured for various physical properties. The PAN fiber is analyzed for physical properties such as: number of surface defects (the lower number of defects the better), interior homogeneity (the more homogeneous the better), degree of orientation (the higher degree of orientation the better), tenacity (the higher tenacity the better), number and size of microvoids (the smaller number and the smaller size of microvoids the better), arrangement of crystallites on the surface (homogeneous arrangement is better) and compactness of structure (the more compact the better). It is within the scope of the present invention to perform certain other physical measurements of the PAN fiber in the analysis zone.
Once a series of PAN fibers are prepared and analyzed, they can then be removed to a ranking zone and ranked based on the physical measurements employed. When ranking is complete, the PAN fiber obtaining the highest ranking across the categories of physical measurements is allowed to proceed to the densification step.
In an embodiment, the most highly ranked PAN fiber can be transferred to rolls and stored as a carbon fiber precursor which is ready to be shipped to customers for later densification and carbonization.
PAN fiber is then removed to a densification zone 17 via a ninth transfer means 16. Within the densification zone 17, the density of the fiber increases from about 1.14 grams per cc. to about 1.41 grams per cc. The time of the densification reaction is about thirty minutes or less.
This PANOX (oxidized polyacrylonitrile) fiber, although not the same as pristine carbon fiber, can be employed in many areas of technology.
If pristine carbon fiber is desired, PANOX fiber is removed as by a tenth transfer means 18 to a carbonization zone 19 which contains an inert atmosphere such as argon gas or the like. The conversion temperature in the carbonization zone 19 is in the range of about 1000 degrees C. to about 2500 degrees C. or higher. The PANOX fiber is converted into pristine carbon fiber. The pristine carbon fiber 21 is withdrawn from the carbonization zone 19 via an eleventh transfer means 20.
In an embodiment, the densification step takes place over a set of three rollers of sequentially higher temperatures. In an alternative embodiment, the densification step is conducted in a sealed cylindrical oven containing programmable heating coils. In another embodiment, the densification step can be conducted in the presence of an inert atmosphere. The inert gas can be nitrogen or argon or the like.
In an embodiment, the present disclosure relates to a carbon fiber having high tensile strength, wherein the carbon fiber is prepared according to the process disclosed herein below. The process includes the steps of: obtaining a series of PAN fibers, wherein each PAN fiber in the series includes an amount of ammonium salt of 2-acrylamido-2-methyl propane sulfonic acid in the range of about 0.5 mole % to about 8 mole %. The 2-acrylamido-2-methyl propane sulfonic acid is neutralized with a base selected from the group consisting of ammonia, ammonium hydroxide, a low molecular weight primary amine and a low molecular weight secondary amine.
An analysis of each PAN fiber in the series is performed in an analysis zone. The analysis zone includes instruments for determining: number of surface defects (a lower number of surface defects ranks higher), interior homogeneity (a more homogeneous situation ranks higher), degree of orientation (a higher degree of orientation ranks higher), tenacity (a greater tenacity ranks higher), number and size of micro voids (a smaller number and smaller size ranks higher), compactness of structure (a more compact structure ranks higher) and arrangement of crystallites on the surface (a more homogeneous arrangement ranks higher). The PAN fibers are then passed to a ranking zone where all the fibers are ranked based on their physical properties. The ranking is based on combined qualities of each fiber.
It is within the scope of the present invention to provide a weighted ranking of the various physical characteristics. For example, substantial lack of micro voids in the fiber may be seen as being of more significance than some other physical property of the fiber.
The process further includes: obtaining the most highly ranked PAN fiber, removing the most highly ranked fiber to a densification zone and withdrawing from the densification zone a PANOX (oxidized polyacrylonitrile) fiber. The process then includes: removing the PANOX fiber to a carbonization zone and withdrawing the carbon fiber having high tensile strength.
The low molecular weight primary amine useful in neutralizing the 2-acrylamido-2-methyl propane sulfonic acid includes a C1 to C6 alkyl group, and the low molecular weight secondary amine includes two C1 to C6 alkyl groups. In an embodiment, the two alkyl groups on the secondary amine can be the same or different.
In an embodiment, the present disclosure relates to an apparatus for the preparation of carbon fiber. The apparatus includes: a neutralization reactor (if needed) for preparing a completely neutralized 2-acrylamido-2-methyl propane sulfonic acid monomer; a polymerization zone; a first solvent extraction zone; a spin dope preparation zone; and a spinning zone. The apparatus further includes: a bundling zone; a second solvent extraction zone; a drawing zone; a relaxation zone; a densification zone; and a carbonization zone.
The apparatus also includes a first transfer means for transferring the 2-acrylamido-2-methyl propane sulfonic acid to the neutralization zone; a second transfer means for addition of base to the neutralization zone; a third transfer means for addition of completely neutralized sulfonic acid monomer to the polymerization zone; and a fourth transfer means for addition of acrylonitrile monomer to the polymerization zone.
The apparatus also contains a fifth transfer means for removing a polyacrylonitrile from the polymerization zone and adding the polymer to the first solvent extraction zone; a sixth transfer means for removing a purified polyacrylonitrile from the first solvent extraction zone and adding the purified polymer to the spin dope preparation zone; a seventh transfer means for adding a chemical which is a member selected from the group consisting of DMF and DMAC to the spin dope preparation zone; and an eighth transfer means for removing a spin dope from the spin dope preparation zone and adding said spin dope to the spinning zone. Furthermore, the apparatus includes a ninth transfer means for removing spun filaments from the spinning zone and adding said filaments to the bundling zone; a tenth transfer means for removing a PAN fiber from the bundling zone and transferring the fiber to the second solvent extraction zone; an eleventh transfer means for removing a purified PAN fiber from the second solvent extraction zone and transferring said purified fiber to the densification zone; a twelfth transfer means for removing a PANOX fiber from the densification zone and transferring to the carbonization zone; and a thirteenth transfer means for removing a carbon fiber from the carbonization zone.
The polymerization zone is preferably a precipitation polymerization zone. The spinning zone includes a die plate.
In an embodiment, the densification zone comprises a set of three rollers of sequentially higher temperatures. In an alternative embodiment, the densification zone comprises a sealed cylindrical oven containing programmable heating coils.
In an embodiment, the present disclosure relates to a precursor fiber useful for the preparation of carbon fiber of high tensile strength. The precursor fiber is obtained by a process including: preparing a series of monomer mixtures, wherein each of the monomer mixtures includes acrylonitrile and an ammonium salt of 2-acrylamido-2-methyl propane sulfonic acid. The amount of completely neutralized acid monomer found in the series ranges from about 0.5 mole % to about 8 mole %.
The base for neutralizing the sulfonic acid can be ammonia, ammonium hydroxide, a low molecular weight primary amine, a low molecular weight secondary amine or mixtures thereof.
In a preferred embodiment, the number of monomer mixtures in the series can be four. The four monomer mixtures can be as follows: 0.5 mole % ammonium salt of 2-acrylamido-2-methyl propane sulfonic acid (99.5 mole % acrylonitrile), 2 mole % ammonium salt of 2-acrylamido-2-methyl propane sulfonic acid (98 mole % acrylonitrile), 6 mole % 2-acrylamido-2-methyl propane sulfonic acid (94 mole % acrylonitrile), and 8 mole % 2-acrylamido-2-methyl propane sulfonic acid (92 mole % acrylonitrile).
Each of the separate monomer mixtures is then polymerized in a polymerization unit to obtain a PAN material. In an embodiment, the PAN material is in the form of flakes or powder.
Each of the separate PAN materials is mixed with a suitable organic solvent to obtain a spin dope. Preferably, the solvents are dimethyl formamide (DMF), dimethyl acetamide (DMAC) or mixtures thereof.
Each of the spin dopes is removed to a spinning unit to obtain filaments in the gel state. The filaments are removed to a first solvent extraction zone and a tensioning zone. Solid filaments are then combined in a bundling zone to obtain a PAN fiber. This fiber can be further treated in a second solvent extraction zone, a stretching zone and a relaxation zone. In the present disclosure, this PAN fiber is called the “carbon fiber precursor”.
Each of the carbon fiber precursors is then removed to an analysis zone. The analysis zone includes analytic devices for measuring physical properties of the carbon fiber precursors.
Each of the carbon fiber precursors (PAN fibers) is then categorized and ranked based on comparison of the various physical properties. For example, a fiber having better aligned crystallites in the skin of the fiber ranks higher than a fiber that has less aligned crystallites. Also, a fiber that has a more homogeneous internal structure is ranked more highly than one which has a more heterogeneous internal structure.
The most highly ranked carbon fiber precursor (PAN fiber) is then conducted to a densification unit, where it is densified to obtain an oxidized PAN (PANOX) fiber. The PANOX fiber is then removed to a carbonization unit. A carbon fiber having a high tensile strength is then removed from the carbonization unit.
It is within the scope of the present disclosure to employ more than four monomer mixtures. It is possible to employ monomer mixtures that differ in only one unit of mole %, or even less. Thus a series of monomer mixtures can be those containing 1 mole %, 2 mole %, 3 mole %, and so on up to 8 mole % of an ammonium salt of 2-acrylamido-2-methyl propane sulfonic acid monomer. Such a series allows for a more fine tuned approach for discovering a leading candidate for later densification and carbonization.
In an embodiment, the present disclosure relates to a monomer mixture useful in preparing the most highly ranked carbon fiber precursor (PAN fiber). A mixture of monomers useful in preparing a carbon fiber precursor is hereby disclosed. The mixture is selected from a series of monomer mixtures comprising acrylonitrile in an amount of about 92 mole % to about 99.5 mole % and an ammonium salt of 2-acrylamido-2-methyl propane sulfonic acid in an amount of about 0.5 mole % to about 8 mole %.
A series of solid PAN fibers is prepared from the series of monomer mixtures. The series of solid PAN fibers is analyzed for one or more physical properties. The physical properties include: number of surface defects, interior homogeneity, degree of orientation, tenacity, number and size of micro voids, arrangement of crystallites on the surface, compactness of structure, or combinations thereof to obtain a set of analysis results for each solid PAN fiber. The solid PAN fibers are then ranked based on the analysis results.
In an embodiment, the present disclosure relates to a PAN polymer composition useful in preparing the most highly ranked carbon fiber precursor (PAN fiber).
In an embodiment, the present disclosure relates to a PAN fiber (carbon fiber precursor) which is the most highly ranked.
In an embodiment, the present disclosure relates to a PANOX fiber obtained from the most highly ranked carbon fiber precursor (PAN fiber).
In an embodiment, the present disclosure relates to a carbon fiber prepared from a PANOX fiber obtained from the most highly ranked carbon fiber precursor (solid PAN fiber).
In an embodiment, the present disclosure relates to an apparatus for preparing carbon fiber according to the process disclosed above.
In an embodiment, a process for preparing a carbon fiber precursor is hereby disclosed. The process includes the steps of: obtaining a series of monomer mixtures, individually polymerizing the series of monomer mixtures in a polymerization unit, individually withdrawing from the polymerization unit a series of polymers. The process further includes: individually forming spin dopes from the series of polymers, individually removing the spin dopes to a spinning unit and spinning each spin dope in the series. Further, the process includes: individually withdrawing from the spinning unit a series of gelled filaments, individually removing the series of gelled filaments to a first solvent extraction zone, and individually withdrawing from the first solvent extraction zone a series of filaments. The process further includes the steps of:
The series of monomer mixtures includes a mixture of acrylonitrile monomer and an ammonium salt of 2-acrylamido-2-methyl propane sulfonic acid monomer. In an embodiment, the acrylonitrile monomer is present in an amount of about 92 mole % to about 99.5 mole %, and the ammonium salt of 2-acrylamido-2-methyl propane sulfonic acid monomer is present in an amount of about 0.5 mole % to about 8 mole %.
In an embodiment, a carbon fiber is prepared from a mixture of monomers. The specific mixture of monomers is obtained from a ranking of a series of solid PAN fibers. The solid PAN fibers are obtained from a series of monomer mixtures, wherein the series of monomer mixtures includes acrylonitrile in an amount of about 92 mole % to about 99.5 mole %; and the ammonium salt of 2-acrylamido-2-methyl propane sulfonic acid monomer in an amount of about 0.5 mole % to about 8 mole %.
The series of monomers are the starting materials for preparing the series of solid PAN fibers employed in the ranking step. Ranking is based on physical properties selected from: number of surface defects, interior homogeneity, degree of orientation, tenacity, number and size of micro voids, arrangement of crystallites on the surface, and compactness of structure. Preferably, all of the physical properties listed above are employed in ranking the series of solid PAN fibers.
In an embodiment, the present disclosure relates to an apparatus for preparing a carbon fiber precursor. The apparatus includes: a neutralization zone for obtaining a completely neutralized 2-acrylamido-2-methyl propane sulfonic acid. The neutralizing agent can be ammonia, ammonium hydroxide, a C1-C6 alkyl primary amine and a C1-C6 dialkyl secondary amine. The apparatus further includes: a polymerization zone for obtaining a solid PAN polymer. The polymerization zone includes a polymerization reactor charged with acrylonitrile monomer and an ammonium salt of 2-acrylamido-2-methyl propane sulfonic acid monomer. A first transfer means is provided for removing the ammonium salt of the sulfonic acid to the polymerization zone. The apparatus further includes: a spin dope preparation zone for addition of an organic solvent to the PAN polymer to obtain a spin dope; a second transfer means for removing the PAN polymer to the spin dope preparation zone; a spinning zone for obtaining a gelled PAN filament; and a third transfer means for removing the spin dope to the spinning zone.
The apparatus includes: a solvent removal zone for solidifying the gelled PAN filament to obtain a solid PAN filament; a fourth transfer means for removing the gelled PAN filament to the solvent removal zone; a stretching zone for obtaining an elongated solid PAN filament; and a fifth transfer means for removing the solid PAN filament to the stretching zone. The apparatus further includes: a relaxation zone for obtaining a relaxed elongated solid PAN filament; a sixth transfer means for removing the elongated solid PAN filament to the relaxation zone; a bundling zone for obtaining a solid PAN fiber from a collection of relaxed elongated solid PAN filaments; and a seventh transfer means for removing the relaxed elongated solid PAN filament to the bundling zone.
In an embodiment, the apparatus further includes: an analysis zone for obtaining an analyzed solid PAN fiber. The analysis zone includes measurement devices for obtaining a physical property of the solid PAN fiber. The physical properties include: number of surface defects, interior homogeneity, degree of orientation, tenacity, number and size of micro-voids, arrangement of crystallites on the surface of the fiber, compactness of structure and combinations thereof. The apparatus includes: an eighth transfer means for removing the solid PAN fiber to the analysis zone; a ranking zone for obtaining a ranked solid PAN fiber; and a ninth transfer means for removing the analyzed solid PAN fiber to the ranking zone.
In an embodiment, a mixture of monomers useful in preparing a carbon fiber precursor is disclosed. The mixture is selected from a series of monomer mixtures comprising acrylonitrile in an amount of about 92 mole % to about 99.5 mole %; and an ammonium salt of 2-acrylamido-2-methyl propane sulfonic acid in an amount of about 0.5 mole % to about 8 mole %. The sulfonic acid is neutralized with a base selected from the group consisting of ammonia, ammonium hydroxide, a low molecular weight primary amine, a low molecular weight secondary amine and mixtures thereof. A series of solid PAN fibers is prepared from the series of monomer mixtures.
The series of solid PAN fibers is then analyzed for at least one physical property. The physical property can be: number of surface defects, interior homogeneity, degree of orientation, tenacity, number and size of micro voids, arrangement of crystallites on the surface, and compactness of structure. Combinations of physical properties are preferred. In a most preferred embodiment, analysis of all of the physical properties listed above is conducted on each solid PAN fiber in the series.
A set of analysis results is obtained, and the solid PAN fibers are ranked based on the set of analysis results. The mixture of monomers yielding the most highly ranked solid PAN fiber is employed for use on an industrial scale.
In an embodiment, the number of monomer mixtures in the series can be two monomer mixtures, three monomer mixtures, four monomer mixtures, five monomer mixtures, six monomer mixtures, seven monomer mixtures and eight monomer mixtures. It is within the scope of the invention to employ more than eight monomer mixtures.
A jacketed aluminum reactor is charged with a solvent mixture of dimethyl formamide (DMF) and water in a ratio of about 80:20 by volume and in an amount of 0.6 liters. An acrylonitrile monomer and an ammonium salt of 2-acrylamido-2-methyl propane sulfonic acid monomer are added to the reactor in a mole ratio of 95:5 and in an amount of 400 grams.
Hydrogen peroxide catalyst in an amount of about 0.5% based on total monomer weight is then added to the reactor. 1-Thioglycerol is added to the reactor in an amount of about 0.3% based on total monomer weight. Ferrous Ammonium Sulfate Hydrate is added to the reactor in an amount of about 10 ppm based on total reagents.
The precipitation polymerization is conducted in the aluminum reactor at a temperature of about 30 degrees C. to about 50 C. and a pressure of about 1.0 atmospheres. Polymerization is continued until the solids content reaches about 25% to 30% solids (about 1 hour). After polymerization is complete, a vacuum stripping system is employed to remove water and unreacted monomers. The stripping operation yields a direct spin dope without isolation of polymer. To reduce the solids to 30%, add 220 grams of DMF.
While the invention has been described as by a specific example and various embodiments, there is no intent to limit the inventive concept except as set forth in the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| PCT/US23/19578 | Apr 2023 | WO | international |
This application is a Continuation-In-Part of U.S. patent application Ser. No. 18/038,625, filed on May 24, 2024, which claims the benefits of the International Application Serial Number PCT/US23/19578, filed on Apr. 24, 2023, and the subject matter of which is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 18038625 | Jan 0001 | US |
| Child | 18761880 | US |
