JPS6257722B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing carbon fiber from mesophasic pitch. Mesophasic pitches are used in the production of carbon products, especially carbon fibers with excellent mechanical properties. Carbon fibers made from mesophasic pitch are well known to be lightweight, strong, stiff, electrically conductive, and chemically and thermally inert. Mesophacepitch carbon fibers are highly effective in composites and are used in the aerospace industry and high-end sporting goods. As used herein, "methophace" is understood as used in the art,
Generally synonymous with liquid crystal. Liquid crystals are in a state of matter intermediate between crystalline solids and ordinary liquids. Normally, mesophase-like materials have anisotropy and liquid properties. As used herein, "mesophase pitch" refers to a pitch that contains more than about 40% by weight of mesophase and is capable of forming an anisotropic continuous phase when dispersed by stirring or the like according to conventional techniques. Generally, decant oil is converted to pitch by distillation. Sometimes a heat treatment step is performed before distillation. The product obtained from the distillation is an isotropic pitch which must be further processed to convert it into a mesophatic pitch. Conventional methods for producing mesophase pitch from isotropic pitch raw materials include heat treating the raw materials at about 350-450°C to effect thermal polymerization. A typical conventional method is to maintain the reactor at about 400° C. for about 20 hours. The properties of the mesophase pitch produced can be controlled by the reaction temperature, heat treatment time and volatilization rate. Because of the high molecular weight portion due to polymerization, the softening point of mesophace pitch is at least 300 at a mesophace content of about 80% by weight.
It becomes ℃. As the mesophase content increases, the softening point increases. Typically, to spin the mesophase pitch, the temperature is about 30 to about 50 degrees Celsius above the softening point of the mesophase pitch. It is desirable to be able to spin at relatively low temperatures. This is to avoid excess polymerization that could clog the narrow orifices used for spinning, and to minimize energy consumption. The mesophace content in pituti is determined by the paper,
(“Quantitative Determination of Mesophase
Content in pitch”S.Chwastiak, RT Lewis,
Co-authored by JDRuggiero, Fifteenth Biennial
Conference on Carbon, June 1981, pp. 148, 149
It can be measured by the method described in p. Generally, the terms "softening point" and "melting point" are used interchangeably in the art to broadly characterize pitches in terms of molecular weight composition and to estimate the required spinning temperature. There are several methods of measuring softening temperature, and the temperatures measured by these different methods differ somewhat from each other. The Mettler softening point measurement method is widely used as a standard for pitch evaluation. This method can be applied to mesophasic pitch. The softening temperature of mesophasic pitch can also be determined by hot stage microscopy. In this method, a mesophasic pitch is heated under polarized light on a hot stage of a microscope in an inert atmosphere. The temperature of the mesophase pitch is increased while controlling the rate of increase in temperature, and when the mesophase pitch begins to deform, the temperature at that time is recorded as the softening temperature. "Softening point" or "softening temperature" are used interchangeably herein to refer to the temperature determined by the Mettler measurement method for both the precursor and the mesophase pitch. Herein, the empirical formula of the decant oil before and after hydrogen treatment was obtained from the molecular weight and elemental analysis data by conventional methods. Decanted oil is widely used in the production of isotropic pitch-like raw materials to be converted into mesophase pitch. Methods for producing pitch precursors from decant oil are well known and typically involve distilling the decant oil under reduced pressure while applying heat to the decant oil. Since decant oil is highly aromatic and the industry teaches that high aromaticity is necessary in the raw materials to produce good mesophase pitch, decant oil is suitable for use in mesophase pitch. Particularly desirable for producing pitch precursors. Edited by PL Walker, “Chemistry and physics
of Carbon”, vol. 4, pages 261, 262 (1960),
“Carbon”, 12 , p. 332 (1974) and U.S. Pat.
See specification No. 4005183. The decant oil used in the industry to make mesophace pitch raw materials has a sulfur content of about 1 to about
Low at 2.5% by weight. Mesophasic pitches made from this material can form anisotropic domains larger than about 200 microns under static heating. Being able to form such large areas is important. Because it shows that mesophasic pitch is suitable for producing carbon fibers with good mechanical properties as well as good spinnability. Mesophase pitches that can form large anisotropic regions are known to have high deformability. When commercially spun, the mesophace content of the mesophace pitch should be at least 70% by weight, preferably about 80% by weight to produce good carbon fibers.
It is. This is the goal of the present invention. The sulfur content of the decant oil is important for commercial carbon fiber manufacturing. Problems may arise with carbon fibers that require processing temperatures above about 2500°C. This is because at such high temperatures, sulfur is driven out, resulting in lower tensile strength and lower density of the resulting carbon fibers. According to the prior art, high sulfur decant oils have been deemed unsuitable for the production of mesophasic pitches for high quality carbon fibers. It is desirable to subject the high sulfur decant oil to hydrodesulfurization by known methods as taught in US Pat. No. 4,075,084 or US Pat. No. 4,166,026. in general,
Through hydrodesulfurization, hydrocarbon oil is contacted with hydrogen in the presence of a catalyst. However, it is well known that hydrotreating reduces the aromaticity of hydrocarbon oils, and therefore hydrotreated decant oils yield mesophase pitches with relatively poor spinnability; It is expected in the art that carbon fibers made from pitch will have poor mechanical properties.
Edited by PHEmmett, “Catalysis”, vol.V,
Rheinhold Publishing Corp., New York,
1957, published and edited by C.L.Thomas, “Catalytic
Processes and Proven Catalysts”，Academic
Press (1970) points out that hydrogen treatment reduces aromaticity. As used herein, "hydroprocessing" is any method of contacting decanted oil with hydrogen in the presence of a catalyst according to techniques in the art. Contrary to the teachings of the art, the hydrotreated decant oil of the present invention produces mesophasic pitch with improved properties compared to mesophasic pitch made from non-hydrotreated decant oil. It has been newly discovered that it can be processed to Additionally, the improved mesophasic pitch can be processed into carbon fibers with improved properties by known methods. A general explanation of these surprising results is as follows. However, this explanation is only a guideline that can be considered when applying the present invention, and is not intended to be limiting. A thermal polymerization process for converting pitch precursor material into mesophase pitch is described. Typically, pitch precursors have a relatively broad molecular weight distribution. Pits contain both low and high reactivity molecules. Rapid polymerization by highly reactive molecules is not preferred. This is because very large molecular weight components are generated in the mesophase pitch produced. These high molecular weight components result in a relatively high viscosity of the mesophasic pitch and a corresponding reduction in the size of the mesophasic pitch area. This phenomenon is discussed in US Pat. No. 3,976,729. Hydrogenation of decant oil according to the invention provides
It slows down the reaction rate of highly reactive molecules, allowing them to undergo desired structural rearrangements before and during the polymerization reaction. As a result, the viscosity of the mesophase pitch is relatively low and the size of the anisotropic region is relatively large. The pitch precursor raw material produced according to the present invention is described in JEZimmer, “Mesophase Transformation”.
in a Solvent-Extracted Pitch”, Fifteenth
Biennial Conference on Carbon, June, 1981,
It can also be converted to mesophasic pitch by solvent extraction as described on page 146, page 147 and in the literature cited herein. Surprisingly, the mesophasic pitches produced are characterized by excellent area size and softening point. The mesophase yield from hydrogenated decant oil is lower compared to untreated decant oil. However, this lower yield and increased cost associated with the hydrotreating step is compensated for by a surprising improvement in the quality of the mesophasic pitch. In its broadest embodiment, the invention comprises the steps of hydrotreating a decant oil until the average number of hydrogen atoms per molecule of the decant oil is increased by about 2 to about 3, and distilling the hydrotreated decant oil to produce pitch. The present invention relates to a method for producing carbon fiber, comprising the steps of forming the pitch, converting the pitch into mesophase, and producing carbon fiber from the mesophase pitch. Another embodiment of the present invention relates to an improvement in which the hydrotreated decant oil is subjected to heat-pressure treatment to create a tar residue and the tar residue is distilled to form pitch. Compared to the process of the invention without heat treatment, the overall yield of raw material for decanted oil is increased by heat-pressure treatment. Generally, heat-pressure treatment is described in U.S. Patent Application No. 087186
Specification (U.S. Pat. No. 4,317,809) (October 22, 1979)
This is done by the method described in the patent application filed in 1999 and assigned to the applicant. This patent application has been granted and is incorporated herein by reference. The outline of this application is as follows. The stringency of heating under pressure can be assessed by soaking volume factor, a technical term widely used in the petroleum industry. A soaking volume factor of 1.0 corresponds to heating at a pressure of about 750 ^psig and a temperature of about 427° C. for 4.28 hours. The effect of temperature on the rate of polymerization or decomposition of hydrocarbons is known in the art. For example, the decomposition rate at 450°C is 3.68 of the decomposition rate at 427°C.
It's double. Most of the examples presented herein were conducted at approximately 450°C, so the stringency of the heat treatments were calculated on an equivalent basis for that temperature. In the case of batch heat-pressure treatment, the preferred temperature,
The pressure and soaking volume factor ranges depend on the precursor. For decant oil, the temperature range is about 400 to about 475℃, and the pressure range is about 14 to about 105Kgcm ^-2・G (about 200 to about
1500 psig) and the soaking volume factor is about 0.4 to about 8.6. The soaking volume factor corresponds to about 0.5 to about 10 hours at about 450°C. The batch heat-pressure treatment is stopped when the Conradson carbon content is in the range of at least about 20%, preferably greater than about 30% and greater than about 65%. the mesophace content is less than about 60% by weight;
If infusible solids are present, high temperature filtration is preferred. If the product is filtrated, the temperature can be raised to liquefy the product and the infusible solids can then be separated by filtration. During the heat-pressure treatment, stirring is preferably performed to maintain homogeneous distribution. The present invention is more economical in that continuous heat-pressure treatment is used instead of batch treatment. In the case of continuous heat-pressure treatment, the temperature range is approximately 420 to approximately 550°C, and the pressure range is approximately 14 to approximately 105 Kgcm ^-2・G (approximately 200 to approximately
1500 psig) and the soaking volume factor is about 0.4 to about 2.6. The soaking volume factor corresponds to about 0.5 to about 3 hours at about 450°C. The continuous heat-pressure treatment is stopped when the Conradson carbon content of the treated material is at least about 5%, preferably greater than about 10% and less than about 65%. The mesophace content is less than about 60% by weight. If infusible solids are present, elevated temperatures are preferred. Accordingly, the invention encompasses the steps and their relationship to each other, all of which are detailed in the following description, and the scope of the invention as pointed out in the claims. For a further understanding of the nature and objects of the invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings. Illustrative, non-limiting examples of the invention are described below. Many other examples may easily be derived in light of the guiding principles and teachings contained in the text.
The examples described herein are merely illustrative of the invention and are not intended to limit the manner in which the invention may be practiced. Unless otherwise specified herein, parts and percentages are by weight. In FIG. 1, the decant oil is hydrogen treated as follows. Reactor 1 has a stainless steel tube with an internal diameter of 32 mm and is heated in a resistance furnace (not shown). Reactor 1
In this case, decant oil is introduced from the top from the decant oil supply source 2 to create a trickle bed system.
mode). The reactor hydrotreating catalyst is of the type commonly used for hydrodesulfurization of petroleum feedstocks. 100 ml of catalyst pellets are mixed with 200 ml of quartz chips (12/16 mesh) and charged into a stainless steel tube. The length of the catalyst bed obtained is 370 mm. The fresh catalyst bed is activated with hydrogen and hydrogen sulfide fed from lines 3 and 4 and controlled by valves 6 and 7. Nitrogen, supplied via line 9 and controlled by valve 8, is used to remove dissolved hydrogen sulfide from the catalyst. Gas from reactor 1 is removed via line 11 to separator 12 and recovered hydrogen is removed via valve 14 via line 13. The hydrotreated decant oil is sent from reactor 1 via line 16 to storage 17 . The continuous heat-pressure treatment shown in FIG. 2 is as follows. Hydrogenated decant oil is supplied to supply tank 1.
It can be placed in 8. If desired, a heater can be provided in the supply tank 18 to heat the decant oil to reduce its viscosity and improve its flowability. Supply tank 18 is connected to pump 21 by path 19.
The pump conveys the decant oil through line 22 and is monitored by a pressure gauge 23. The decant oil passes through a furnace coil in a fluidized sand bath 24. If a long treatment is desired, several fluidized sand baths can be used in tandem. The treated decant oil passes through line 26 to valve 27 controlled by pressure regulator 29 and is collected via line 31 into product collection tank 32 for use in subsequent steps of the invention. Example 1 Decanted oil was subjected to hydrogen treatment until analysis showed that the average number of hydrogen atoms per molecule of the decanted oil increased by about 3. Hydrogen treatment was carried out in a conventional manner. The hydrogenated decant oil was distilled and converted to pitch under a vacuum of about 2 mm Hg and a final pot temperature of about 260°C. In order to evaluate the properties of the pitch precursor as a raw material for mesophase pitch, a portion of the pitch precursor was heat-treated at about 400°C for about 24 hours to convert it into mesophase pitch. The area size of the mesophasic pitch produced by the heat treatment was measured and was approximately 500 microns. Mesophasic pitches made in the same manner from unprocessed decant oil typically had a size in the area of about 250 microns. The larger area size of the mesophasic pitch produced according to the present invention indicates that the quality of the mesophasic pitch is good. And, because of this, it can be expected that it is well suited for commercial spinning. Furthermore, the relatively large area size also indicates that: The mesophasic pitch produced according to the present invention has high deformability, and when spun into fibers, it can be expected that the molecules will align relatively easily. This results in favorable low orientation parameters and excellent mechanical properties for carbon fibers. The yield of pitch precursor obtained reached 21% by weight with respect to the decant oil. Reacting pitch
Approximately 0.14 standard m ³ /h (approx.
The pitch precursor was converted to mesophasic pitch by conventional heat treatment at about 390° C. for about 29 hours with argon sparging and stirring at a rate of 5 scfh). The resulting mesophace pitch is approximately 100% by weight.
of mesophase pitch, with a yield of 14% with respect to the pitch precursor. The Mettler softening point of Mesophace pitch was approximately 289°C. This softening point is surprisingly low for a thermally generated mesophase with 100% mesophase content. Furthermore, this mesophasic pitch can be spun at a temperature about 30 to about 40° C. lower than that of conventional 100% mesophasic pitch. The overall yield of mesophasic pitch relative to the decant oil was approximately 3% by weight. Example 2 Hydrogenated decant oil from Example 1 was heated in a stirred autoclave at approximately 28 to 35 cm ^-2・G (approximately 400 to
Batch heat-pressure treatment was carried out at a temperature of about 430° C. for about 4 hours under nitrogen at a pressure of about 500 psig. A tar residue amounting to approximately 90% by weight was obtained. The residue was then distilled to yield pitch precursors reaching a yield of about 37% by weight on the hydrotreated decant oil. The pitch precursor was then heat treated at about 390° C. for about 30 hours to convert it into mesophase pitch. The resulting mesophace pitch contained about 100% mesophace and had a Mettler softening point of about 317°C. The mesophase pitch yield is approximately
34% by weight, and the overall yield of mesophasic pitch was about 11.3% by weight on the hydrotreated decant oil. This overall yield is significantly greater than that obtained in Example 1 and demonstrates the value of subjecting the hydrotreated decant oil to heat-pressure treatment. The resulting mesophasic pitch was spun into a monofilament, thermosetted, and then carbonized at about 1700° C. in a conventional manner. The diameter of the filament was approximately 8 microns. Typically, the mechanical properties of the filaments were excellent. The average Young's modulus is approximately
^{The average tensile strength was about 39400 Kgcm -2 (} about ⁵⁶⁰⁰⁰⁰ psi) ^. The ratio of these values shows that the strain to failure is approximately 2%, which is approximately twice that for prior art mesophasic carbon fibers. High strain-to-failure values are considered advantageous for many commercial products. Example 3 A second decant oil was hydrotreated until the average number of decant oil molecules increased by about 2 hydrogen atoms. To evaluate the hydrotreated decant oil, a portion was heat treated at approximately 400°C for 24 hours to produce mesophasic pitch. The area size of the mesophasic pitch was about 300 microns. In contrast, untreated decant oil produced mesophasic pitches with an area size of about 200 microns in the same test. The hydrotreated decant oil was subjected to batch heat-pressure treatment in an agitated pressure autoclave at a pressure of about 23 Kgcm ^-2 ·G (about 330 psig) and a temperature of about 440° C. for about 4 hours. The resulting tar residue reached a yield of about 79% by weight with respect to the decant oil. The tar residue was vacuum distilled at 2 mm pressure to a pot temperature of about 262°C. The raw material obtained is 58% in terms of tar residues.
After reaching a weight percent yield, this residue was heated in a reactor at about 390° C. for about 24 hours while sparging with argon at a rate of about 0.14 standard m ³ /h (about 5 scfh) per pound of pitch. It was converted into mesophasic pitch by conventional thermal polymerization. The resulting mesophacetic pitch reached a yield of about 58% by weight with respect to the raw material and had a softening point of about 332°C. The mesophace content was approximately 100% by weight. The mesophasic pitch was spun into a monofilament, and the monofilament was heat cured by heating at about 375° C. in air. The thermoset filament was carbonized at approximately 1700°C using conventional techniques. The carbon fiber diameter was approximately 18 microns. The average Young's modulus of carbon fiber is approximately 1.55×10 ⁶ Kgcm ^-2
(approximately 22 × 10 ⁶ psi), and the average tensile strength is approximately 14.1
×10 ³ Kgcm ^-2 (approximately 200 × 10 ³ psi). As a comparison, the average Young's modulus of carbon fibers obtained from mesophase pitch from untreated decanted oil is approximately 1.55.
×10 ⁶ Kgcm ^-2 (approximately 22 × 10 ⁶ psi), and the average tensile strength was approximately 11.6 × 10 ³ Kgcm ^-2 (approximately 165 × 10 ³ psi). Example 4 Another decant oil was hydrotreated until the average number of decant oil molecules was approximately 2 more hydrogen atoms per molecule. A portion of the hydrotreated decant oil was converted to mesophasic pitch as in the previous example.
The area size of the mesophasic pitch was approximately 260 microns. In contrast, the area size of mesophasic pitches made from unhydrogenated decant oil was approximately 179 microns. Example 5 The decant oil of Example 1 was hydrotreated until the average number of hydrogen atoms per molecule of the decant oil increased by about 3. About 123Kgcm of hydrogen treated decant oil
It was subjected to continuous heat-pressure treatment at a pressure of ^-2 ·G (about 1750 psig) and a temperature of about 525° C. for about 9 minutes. A tar residue was obtained with a yield of approximately 97% by weight relative to the decant oil. Distillation of tar residue to softening point 104℃
The raw material for pituti was obtained. The yield was about 27% by weight with respect to tar residue. Approximately 0.028 kg/0.454 kg (1 pound) of this raw material is mixed in a stirred reactor.
Heat treatment was carried out at about 400° C. for about 18.5 hours while sparging steam at a standard m ³ /h (about 1 scfh) rate. The yield of mesophacetic pitch obtained was approximately 52% with respect to the raw material.
% by weight, and the softening point was about 318°C. The mesophace content was approximately 95% by weight. The mesophasic pitch is spun into a multifilament, and this multifilament is spun in the air at approximately 375 mm.
It was thermoset by heating to 0.degree. C. and then carbonized by conventional techniques at about 2500.degree. C. in an inert atmosphere. The average property of carbon fiber is Young's modulus of approximately 7.0×10 ⁶ Kgcm ^-2 (approximately 100
×10 ⁶ psi) and tensile strength approximately 27.4 × 10 ³ Kgcm ^-2 (approximately
390×10 ³ psi). As a comparison, mesophasic pitch was produced by processing decant oil that had not been hydrotreated. Decant oil to about 70.3Kgcm ^-2・G (about 1000psig)
Patch-type heating at a pressure of about 470℃ for about 8 minutes.
It was converted to a tar residue by pressure treatment. The yield of the tar residue obtained is with respect to the decant oil
It was 98.5% by weight. This residue was distilled to form a pitch precursor with a softening point of about 116°C. The yield was about 34% by weight with respect to tar residue.
This pitch was heated at about 400°C for about 16.5 hours to convert it into mesophasic pitch. The yield of this mesophase pitch is approximately 56% by weight with respect to the pitch precursor.
The softening point was approximately 318°C. The mesophace content was approximately 90% by weight. This mesophase pitch was processed into carbon filaments in the same manner as the mesophase pitch from hydrotreated decant oil. The average Young's modulus of the obtained carbon fibers was approximately 4.4×10 ⁶ Kgcm ^-2 (approximately 63×
10 ⁶ psi) and tensile strength is 19.7×10 ³ Kgcm ^-2 (approx.
280×10 ³ psi). Carbon fibers made with feedstock obtained from hydrotreated decant oil had superior mechanical properties compared to carbon fibers obtained from untreated decant oil. Example 6 The pitch raw material obtained from the hydrotreated decant oil of Example 5 was subjected to solvent extraction to obtain mesophase pitch. Solvent extraction was performed by stirring the solid raw material with toluene for 1 hour at room temperature. The raw material to toluene ratio was 1 g:10 ml. The inert portion obtained with a yield of 8.3% by weight was mesophace pitch containing approximately 85% by weight mesophace. This mesophase pitch had a Mettler softening point of 272°C and an anisotropic region size of about 500 microns. Summary of Examples A summary of the data of Nos. 1 to 6 is shown. The hydrotreated decant oil is desulfurized as shown in the data. Aromatic hydrogen content was determined by conventional magnetic resonance (NMR).

Table The invention is not to be limited to the precise description shown and described. This is because obvious modifications will occur to those skilled in the art.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing hydrogen treatment of decant oil, and FIG. 2 is a diagram showing continuous heat-pressure treatment. 1... Reactor, 2... Decant oil supply source, 3...
Route, 4... Route, 6... Valve, 7... Valve, 8... Valve, 9...
route, 11... route, 12... separator, 13... route,
14... Valve, 16... Route, 17... Storage device, 18... Supply tank, 19... Route, 21... Pump, 22... Route, 23... Pressure gauge, 24... Fluidized sand bath, 26... Route, 27... Valve, 29 ...pressure control valve, 31...pathway,
32...Product collection tank.

Claims (1)

[Scope of Claims] 1. A method for producing carbon fiber, which comprises the following steps. (b) A process of hydrogen-treating the decant oil until the average number of hydrogen atoms per molecule of the decant oil increases by 2 to 3. (b) A process of distilling the hydrogen-treated decant oil to form pitch. (c) This process Step (d) of converting pitch into mesophace pitch (provided that it has a mesophace content of at least 70% by weight); Step 2 of producing carbon fiber from this mesophace pitch; characterized by comprising the following steps: , Carbon fiber manufacturing method. (a) A process of hydrogen-treating the decant oil until the average number of hydrogen atoms per molecule of the decant oil increases by 2 to 3. (b) A process of subjecting the hydrogen-treated decant oil to heat-pressure treatment to create a tar residue. Step (c) A step of distilling this tar residue to form pitch. (d) A step of converting this pitch into mesophace pitch (provided that it has a mesophace content of at least 70% by weight). The process of producing carbon fiber from mesophasic pitch