Claims:We claim:
1. A process (100) of producing an isotropic pitch precursor for carbon fiber, wherein the process (100) comprises:
treating coal tar pitch with oxygen donating compound to obtain oxygen rich pitch;
washing the oxygen rich pitch with water and filtering the aqueous mixture to obtain filtered residue;
drying the filtered residue to obtain dried oxygen rich pitch;
crushing the dried oxygen rich pitch to powdered pitch of predetermined size; and
heating the powdered pitch to obtain isotropic pitch.
2. The process (100) of producing an isotropic pitch precursor for carbon fiber as claimed in the claim 1, wherein the coal tar pitch used exhibits a softening point in the range of 70°C to 120 °C, and atomic ratio of carbon to hydrogen is less than two.
3. The process (100) of producing an isotropic pitch precursor for carbon fiber as claimed in the claim 2, wherein the coal tar pitch used exhibits a softening point in the range of 80°C to 95 °C, and atomic ratio of carbon to hydrogen is in between 1.9 to 2.
4. The process (100) of producing an isotropic pitch precursor for carbon fiber as claimed in the claim 1, wherein the quinoline insoluble (QI) content of the used coal tar pitch is in between 0.5 to 4.0 % by weight, toluene insoluble (TI) content is in between 25 to 45 % by weight, and n-methyl 2- pyrrolidone insoluble (NMPI) content is in the range of 5 to 25 % by weight.
5. The process (100) of producing an isotropic pitch precursor for carbon fiber as claimed in the claim 1, wherein the said coal tar pitch is heated in a glass reactor at a specific temperature range of 50°C - 250oC and temperature of reactor is maintained throughout the process.
6. The process (100) of producing an isotropic pitch precursor for carbon fiber as claimed in the claim 1, wherein quantity of oxygen donating compound added to treat the coal tar pitch is 0.1 – 5 wt.% of the quantity of coal tar pitch.
7. The process (100) of producing an isotropic pitch precursor for carbon fiber as claimed in the claim 5, wherein the coal tar pitch is treated with oxygen donating compound at temperature in the range of 50°C to 250°C for 10 to 60 mins.
8. The process (100) of producing an isotropic pitch precursor for carbon fiber as claimed in the claims 1 to 7, wherein the oxygen donating compound is perchloric acid.
9. The process (100) of producing an isotropic pitch precursor for carbon fiber as claimed in the claims 1 to 7, wherein the oxygen donating compound is calcium chlorohypochlorite.
10. The process (100) of producing an isotropic pitch precursor for carbon fiber as claimed in the claim 1, wherein the aqueous mixture is filtered using a vacuum filtration setup to obtain the filtered residue.
11. The process (100) of producing an isotropic pitch precursor for carbon fiber as claimed in the claims 1 to 7, wherein the filtered residue is dried at 60-120°C for 1-10 hours in a hot air oven.
12. The process (100) of producing an isotropic pitch precursor for carbon fiber as claimed in the claim 1, wherein the dried oxygen rich pitch exhibits a softening point in the range of 100 -200 °C with a yield in the range of 85-92% by weight of the used coal tar pitch.
13. The process (100) of producing an isotropic pitch precursor for carbon fiber as claimed in the claim 1, wherein the dried oxygen rich pitch is crushed to powered pitch of less than 75-micron size.
14. The process (100) of producing an isotropic pitch precursor for carbon fiber as claimed in the claim 1, wherein the powdered pitch is heated at a temperature in the range of 200-350°C for 1-6 hours in a tube furnace.
15. The process (100) of producing an isotropic pitch precursor for carbon fiber as claimed in the claim 14, wherein the powdered pitch is heated in an inert atmosphere.
16. The process (100) of producing an isotropic pitch precursor for carbon fiber as claimed in the claim 14, wherein the powdered pitch is heated in an oxidizing atmosphere.
17. The process (100) of producing an isotropic pitch precursor for carbon fiber as claimed in the claim 1, wherein the obtained isotropic pitch precursor has a softening point in the range of 150 to 250°C, a toluene insoluble (TI) content in the range of 25-75% by weight, and a n-methyl 2 pyrrolidone insoluble (NMPI) content in the range of 1-55% by weight.
18. The process (100) of producing an isotropic pitch precursor for carbon fiber as claimed in the claim 1, wherein the obtained isotropic pitch precursor have yield approximately in the range of 40 to 75 % by weight.
19. The process (100) of producing an isotropic pitch precursor for carbon fiber as claimed in the claim 13, wherein a stainless-steel wire mesh filter of 75-micron nominal diameter of Tyler standard is used.
, Description:FIELD OF INVENTION
[0001] The present invention relates to a process for producing pitch precursor suitable for preparation of carbon fiber.
BACKGROUND
[0002] Carbon fibers possesses a unique combination of properties like low bulk density and high tensile strength and tensile modulus. These properties made carbon fiber, a new age material for the application in many industries like automotive, aerospace, sporting goods, wind turbine. Preparation of carbon fiber from carbonaceous precursor had been started almost half a decade ago. Earlier, coal had been used as raw material used for carbonaceous precursor preparation. For example, in US3959448A, a process is disclosed where coal is extracted with a solvent, essentially having boiling point over 200 °C. The said extract was then concentrated to a mixture, having 40-60 % solvent by weight. The said mixture is then spun, stabilized, and carbonized to prepare carbon fibers. However, extraction of coal was a cost increasing process. Gradually, focus shifted from to a cheaper source of carbonaceous material.
[0003] Coal tar became a topic of interest as it was an inevitable byproduct of steel plant. It was cheap and was available in abundance. In patent NL7102137A, a process was disclosed, where tarry material was mixed with a polymer called caprolactum and then spun to produce carbon fibers. Polymer was chosen with the criteria that it must have a very low melt flow index at spinning or extrusion temperature as compared to the tarry material.
[0004] Carbon fiber production from coal tar pitch has been a very challenging research domain for the past few decades. In another example, BE790878A, a process is disclosed, where coal tar pitch was mixed with Novolak resin, which is essentially a polyester material. The mixture was heat treated at 407°C until formation of anisotropic pitch. Thus, the said isotropic pitch produced was spun to produce the green fibers. Adding of any foreign substances with the pitch helped in increases the spinnability, but the resultant fiber had non homogeneity due to presence of external polymers. This resulted in low mechanical properties. To increase mechanical properties, precursor must be homogeneous and essentially free from any foreign substances. However, increasing the softening point of precursor was very crucial for the stabilization process.
[0005] To increase the softening point of precursors, different methods came out. For example, in patent DE2221707A1, a process is disclosed, where liquid aromatic distillate, essentially coal tar was contacted with air to increase its softening point. Process was conducted in the temperature range of 200 to 420 °C. The resultant product was spun in at a temperature range of 200 to 280 °C to produce green fibers.
[0006] Investigation has also been done to find an alternate route to produce spinnable isotropic pitch apart from heat treatment method. For example, in patent KR101543534B1, a method is disclosed, where coal tar pitch is mixed with aromatic compounds comprising of hydroxyl (-OH) group. For example, phenol, cresol, xylenol etc. The said mixture was then heat treated at 300-350 °C to produce high softening point isotropic pitch. However, use of too many chemicals decreased its cost effectiveness. Moreover, focus on the raw material quality also gained attention. Both thermal and chemical treatment route was found to be promising. Chemical method had advantage of low temperature processes.
[0007] All the prior arts described herein, relates to a process of thermal treatment of coal tar pitch in the temperature range of 400 °C. Said process becomes very energy intensive when it is related to a large amount of pitch. Also, uniform heating at such temperature is also difficult to achieve for pitch-based materials. For the chemical route of pitch treatment, in most of the cases, required chemical quantity is huge which adds to the cost of the process, which is undesirable.
OBJECTIVE OF INVENTION
[0008] It is an object of the invention to solve the aforementioned problems of the prior art and to provide a process of producing an isotropic pitch precursor for the production of carbon fibers having improved yield of the precursor from the raw feedstock, heat stability, spinnability and infusibility.
[0009] It is further object of this invention is to develop the process to produce a purely isotropic pitch, with tunable softening point and insoluble content.
[0010] It is further an object of the present invention is to develop a process to produce spinnable isotropic precursor from coal tar pitch.
SUMMARY OF INVENTION
[0011] This summary is provided to introduce concepts related to a process for producing an isotropic pitch precursor. The concepts are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
[0012] In one aspect of the present invention, a process of producing an isotropic pitch precursor for carbon fiber is provided. The process comprises treating coal tar pitch with oxygen donating compound to obtain oxygen rich pitch. The process also comprises washing the oxygen rich pitch with water and filtering the aqueous mixture to obtain filtered residue. The process further comprises drying the filtered residue to obtain dried oxygen rich pitch. The process comprises crushing the dried oxygen rich pitch to powdered pitch of predetermined size. The process further comprises heating the powdered pitch to produce isotropic pitch.
[0013] In an embodiment, the coal tar pitch used exhibits a softening point in the range of 70°C to 120 °C, and atomic ratio of carbon to hydrogen is less than two.
[0014] In an embodiment, the coal tar pitch used exhibits a softening point in the range of 80°C to 95°C, and atomic ratio of carbon to hydrogen is in between 1.9 to 2.
[0015] In an embodiment, the quinoline insoluble (QI) content of the used coal tar pitch is in between 0.5 to 4.0 % by weight, toluene insoluble (TI) content is in between 25 to 45 % by weight, and n-methyl 2- pyrrolidone insoluble (NMPI) content is in the range of 5 to 25 % by weight.
[0016] In an embodiment, the said coal tar pitch is heated in a glass reactor at a specific temperature range of 50°C - 250oC and temperature of reactor is maintained throughout the process.
[0017] In an embodiment, quantity of oxygen donating compound added to treat the coal tar pitch is 0.1 – 5 wt.% of the quantity of coal tar pitch.
[0018] In an embodiment, the coal tar pitch is treated with oxygen donating compound at temperature in the range of 50°C to 250°C for 10 to 60 mins.
[0019] In an embodiment, the oxygen donating compound is perchloric acid.
[0020] In an embodiment, the oxygen donating compound is calcium chlorohypochlorite.
[0021] In an embodiment, the aqueous mixture is filtered using a vacuum filtration setup to obtain the filtered residue.
[0022] In an embodiment, the filtered residue is dried at 60-120°C for 1-10 hours in a hot air oven.
[0023] In an embodiment, the dried oxygen rich pitch exhibits a softening point in the range of 100 -200°C with a yield in the range of 85-92% by weight of the used coal tar pitch.
[0024] In an embodiment, the dried oxygen rich pitch is crushed to powered pitch of less than 75-micron size.
[0025] In an embodiment, the powdered pitch is heated at a temperature in the range of 200-350°C for 1-6 hours in a tube furnace.
[0026] In an embodiment, the powdered pitch is heated in an inert atmosphere.
[0027] In an embodiment, the powdered pitch is heated in an oxidizing atmosphere.
[0028] In an embodiment, the obtained isotropic pitch precursor has a softening point in the range of 150 to 250°C, a toluene insoluble (TI) content in the range of 25-75% by weight, and a n-methyl 2 pyrrolidone insoluble (NMPI) content in the range of 1-55% by weight.
[0029] In an embodiment, the obtained isotropic pitch precursor have yield approximately in the range of 40 to 75 % by weight.
[0030] In an embodiment, a stainless-steel wire mesh filter of 75-micron nominal diameter of Tyler standard is used.
[0031] Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] Figure 1 is a process flow diagram of process of producing isotropic precursor, according to an embodiment of the present invention;
[0033] Figure 2 is a flowchart which illustrates a process of preparing isotropic pitch precursor, according to an embodiment of the present invention;
[0034] Figure 3 illustrates an optical image of obtained product in example 1, according to an embodiment of the present invention; and
[0035] Figure 4 illustrates an optical image of the obtained product of example 2, according to an embodiment of the present invention.
[0036] The drawings referred to in this description are not to be understood as being drawn to scale except if specifically noted, and such drawings are only exemplary in nature.

DETAILED DESCRIPTION
[0037] The detailed description of various exemplary embodiments of the disclosure is described herein with reference to the accompanying drawings. It should be noted that the embodiments are described herein in such details as to clearly communicate the disclosure. However, the amount of details provided herein is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0038] It is also to be understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects, and embodiments of the present disclosure, as well as specific examples, are intended to encompass equivalents thereof.
[0039] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “includes” and/or “including,” when used herein, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof.
[0040] It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may, in fact, be executed concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved.
[0041] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
[0042] Figures 1 and 2 illustrate an exemplary process (100) for producing isotropic pitch precursor useful as a raw material for carbon fibers. Each step shown in figure 2 represents one or more process, method or subroutine steps carried out in the method. Furthermore, the order of blocks is illustrative only and the blocks can change in accordance with the present disclosure. Additional blocks can be added, or fewer blocks can be utilized, without departing from this disclosure. The process (100) for producing isotropic pitch precursor from coal tar pitch begins at step (102).
[0043] At step (102), coal tar pitch is treated with an oxygen donating compound to obtain an oxygen rich pitch. The said coal tar pitch is obtained as the bottom product of coal tar distillation under vacuum. The coal tar pitch used has a softening point in between 70 to 120 °C, preferably between 80 to 95 °C. Atomic ratio of carbon to hydrogen must be less than two, preferably in between 1.9 to 2. The quinoline insoluble (QI) content of the used coal tar pitch is in between 0.5 to 4.0 % by weight, toluene insoluble (TI) content is in between 25 to 45 % by weight, and n-methyl 2- pyrrolidone insoluble (NMPI) content is in the range of 5 to 25 % by weight.
[0044] In the preferred embodiment, the quantity of oxygen donating compound added to treat the coal tar pitch is 0.1 – 5 wt.% of the quantity of coal tar pitch. In the preferred embodiment, the oxygen donating compound is perchloric acid. An optimum perchloric acid concentration and reaction temperature is required to obtain desired precursor properties. Excessive oxidation of coal tar pitch takes place in presence of high concentration of perchloric acid and thus produce non-spinnable precursor. Hence, very less quantity of perchloric acid is used to chemically modify coal tar pitch.
[0045] In another embodiment, the oxygen donating compound is calcium chlorohypochlorite.
[0046] The said coal tar pitch is heated in a glass reactor at a specific temperature range of 50-250oC and temperature of reactor is maintained throughout the process. When the pitch powder is completely liquefied, specific quantity of perchloric acid (0.1-5 wt% of coal tar pitch) is added and the reaction mixture is continuously stirred. Oxygen donating process (in this case acid treatment process) is completed within 10-60 minutes. In lab scale, the perchloric acid is added dropwise using a micro pipette. In industrial scale, the perchloric acid is added using atomizer spray.
[0047] Acid treatment temperature has significant influence on the insoluble content (TI, QI, NMPI) of the precursor. At high reaction temperature, in presence of perchloric acid, large polycyclic aromatic compounds (generally, secondary QI and NMPI) get dissociated to produce relatively small molecule by the process of depolymerization and thus QI and NMPI content is reduced. Degree of depolymerization increases with increasing reaction temperature. This interesting temperature effect on degree of depolymerization can be utilized to control insoluble content. Thus, insoluble content of the precursor can be tuned by selecting suitable acid treatment temperature. By this process of acid treatment, softening point of the treated pitch is slightly elevated by the process of polymerization of relatively small molecule.
[0048] At step (104), the oxygen rich pitch obtained in step (102) is finely powdered and is washed with water. Aqueous mixture is then filtered using a vacuum filtration setup to obtain filtered residue. In an embodiment, a 60-mesh sieve is used.
[0049] At step (106), the filtered residue is dried to obtain dried oxygen rich pitch. In preferred embodiment, the filtered residue is dried at 60-120°C for 1-10 hours in a hot air oven. The dried oxygen rich pitch exhibits a softening point in the range of 100 -200 °C with a yield in the range of 85-92% by weight of the used coal tar pitch.
[0050] At step (108), the dried oxygen rich pitch is crushed to powdered pitch of predetermined size. In the preferred embodiment, the dried oxygen rich pitch is crushed to powered pitch of less than 75-micron size. In an example, a stainless-steel wire mesh filter of 75-micron nominal diameter of Tyler standard is used to obtain the powered pitch of less than 75-micron size.
[0051] At step (110), the powdered pitch having predetermined size is heated to obtain isotropic pitch. In the preferred embodiment, the powdered pitch is heated at a temperature in the range of 200-350°C for 1-6 hours in a tube furnace. In one example, the powdered pitch is heated in an inert atmosphere. In another example, the powdered pitch is heated in an oxidizing atmosphere.
[0052] With increasing heat treatment temperature and soaking time, softening point and insoluble contents are gradually increased. Softening point and insoluble contents also varies depending upon heat treatment atmosphere, inert or in presence of oxygen. Hence, heat treatment conditions are optimized to get optimized precursor properties.
[0053] Quality of the resultant products are checked through analysis of different insoluble contents. These insoluble contents help to determine the beta resin content of the product. Beta resin content signifies a certain cut of the pitch, which is reactive and produces spinnable precursor of good quality. Softening point of the products are also determined to estimate the spinnability of the materials. Optical images of the samples (Figures 3 and 4) have been studied to confirm the isotropic morphology of the products.
[0054] The obtained isotropic pitch precursor has a softening point in the range of 150 to 250°C, a toluene insoluble (TI) content in the range of 25-75% by weight, and a n-methyl 2 pyrrolidone insoluble (NMPI) content in the range of 1-55% by weight. The obtained isotropic pitch precursor have yield approximately in the range of 40 to 75 % by weight.
[0055] Following examples further illustrates the details of the present invention. However, the present invention is comprised of but not limited to these illustrations.
EXAMPLE 1
[0056] A coal tar pitch with quinoline insoluble (QI) content of 2 percent by weight is taken for the said thermal oxidation process. The said coal tar pitch has a softening point of 88 °C, as per ASTM D-3104 standard. The said pitch has an N-methyl 2 pyrrolidone insoluble (NMPI) content of 13 % by weight and toluene insoluble content (TI) of 30 % by weight. The pitch has a volatile matter content of 54% by weight and has a C/H ratio of 1.91, calculated on dry mineral matter free basis. The said coal tar pitch was treated with 1 wt. % perchloric acid at 100 °C for 15 mins to obtain acid treated pitch. 1 % by weight perchloric acid was used for chemical treatment of raw pitch. The said acid treated pitch was then heat treated at tube furnace at 320 °C with heating rate: 3 °C/min, soaking time of 1 hour and nitrogen flow rate of 3 liters per minute. By the said process, isotropic pitch having softening point 208 °C is obtained. Insoluble contents (TI and NMPI) of the two isotropic precursors are 62% and 12% by weight respectively. Resultant product is a clear isotropic pitch. Yield of 73 % by weight is obtained by this method.
COMPARATIVE EXAMPLE 1
[0057] Acid treated pitch mentioned in example 1 is subjected to heat treatment in tube furnace with the same condition as mentioned in example 1. Soaking time was increased from 1 hour to 2 hours. By the said process, isotropic pitch having softening point 229 °C was obtained. Insoluble contents (TI and NMPI) of the isotropic precursor are 66 % and 5 % by weight respectively. Increase in softening point and TI content indicates that higher heat treatment temperature is favoring the macromolecule formation by oxygen cross linking of smaller aromatic compounds. Yield of 69 % by weight is obtained by this method.

COMPARATIVE EXAMPLE 2
[0058] Acid treated pitch mentioned in example 1 is treated in the same way as mentioned in comparative example 1. Instead of nitrogen, air is used to maintain an oxidizing atmosphere to see the effect of polymerization in different media. Resultant product obtained exhibited softening point of 231 °C. TI and NMPI content of the product is 70 % and 41 % by weight respectively. A major change in NMPI content is observed by changing the heat treatment media. This is because of presence of oxygen in the external atmosphere. Beside internal cross linking of the compounds by the nascent oxygens, external oxygen cross linking has also been done. This over oxidation led to rise in NMPI content. Optical image of the precursor also shows some regions of different phase formations. Yield of 75 % by weight is obtained by this method. Yield is comparatively higher than that of the product mentioned in comparative example 1. This clearly indicates further insertion of oxygen in the compound.
EXAMPLE 2
[0059] Coal tar pitch mentioned in example 1 is at first extracted using n-methyl 2 pyrrolidone (NMP) as a solvent. Pitch and solvent are mixed in a ratio of 1:10 and the said mixture is extracted at 180 °C. The extracted pitch is separated from the solvent-by-solvent evaporation method. The said coal tar pitch was treated with perchloric acid at 100 °C for 15 mins to obtain acid treated pitch. 1 % by weight perchloric acid was used for chemical treatment of raw pitch. The said acid treated pitch was then heat treated at tube furnace at 300 °C with heating rate: 3 °C/min, soaking time of 1 hour and nitrogen flow rate of 3 liters per minute. By the said process, isotropic pitch having softening point 200 °C is obtained. Insoluble contents (TI and NMPI) of the two isotropic precursors are 61% and 1% by weight respectively. Resultant product is a clear isotropic pitch. Yield of 46 % by weight is obtained by this method. Lower yield is due to the extraction of the coal tar pitch with certain organic solvents.
Pitch Softening point
(°C) Yield from raw coal tar pitch NMPI
(% by weight) TI
(% by weight)
Raw pitch 88 -- 13 30
Product in example 1 208 73 12 62
Product in comparative example 1 229 69 5 66
Product in comparative example 2 231 75 41 70
Product in example 2 200 46 1 61
TABLE 1: Properties of raw pitch and resultant products
[0060] The pitch precursor produced using the above process is suitable for preparation of carbon fibers which are used for manufacturing any component relating to any industry, without departing from the scope of the present invention. The process improves yield of the precursor from the raw feedstock, and improves heat stability, spinnability and infusibility of the resultant product.
[0061] The present invention relates to a process (100) for producing isotropic pitch precursor for the production of carbon fibers having improved yield of the precursor from the raw feedstock, heat stability, spinnability and infusibility. The process (100) produces a purely isotropic pitch, with tunable softening point and insoluble content. Further, the disclosed process is a chemical route of modifying coal tar pitch to isotropic pitch. As the prime focus of recent investigations are on thermal treatments, this investigation results in development of a chemical process to produce an isotropic pitch with very low chemical consumption of 1 wt. % maximum, combined with low temperature process in the temperature range of 250 to 350 °C.
[0062] Furthermore, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims.
[0063] The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.
[0064] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.