JPH0433889B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to a method for producing carbon fibers from lignin, in which wood-based resources are solubilized by high-temperature treatment with high-temperature, high-pressure saturated steam or an organic solvent such as alcohol. [Background of the invention] Currently, lignin, which is the main component of wood-based resources,
Research is being actively conducted to develop new processes for efficiently separating hemicellulose and cellulose and converting them into food, feed, raw materials for the chemical industry, pulp, etc. As a method for efficiently separating these main components, there is a treatment at high temperature with high temperature and high pressure saturated steam or an organic solvent such as alcohol.
In order for these processes to become economical,
A comprehensive utilization system must be developed that effectively utilizes each separated component. [Object of the Invention] The present invention has been made based on the above viewpoint, and its purpose is to improve lignin, which is one of the main components separated from the woody resources and for which no effective utilization method has yet been established. The purpose of the present invention is to provide a method for manufacturing carbon fiber with high added value. [Summary of the Invention] The method for producing the lignin carbon fiber according to the present invention, which has been made for the above purpose, is characterized by: Alternatively, lignin that has been directly solubilized in an organic solvent at high temperatures is used as the target raw material, and this lignin is hydrogenated and decomposed.
Next, heat treatment is performed in an inert gas atmosphere, and after that, the material is spun and carbonized by a melting method. When wood resources are treated at high temperatures with saturated steam at 180°C or higher or organic solvents such as alcohol, a significant amount of lignin can be obtained that is soluble in organic solvents, although this varies depending on the processing conditions and the type of wood resources used as raw materials. (Kazumasa Shimizu et al.: Journal of the Japan Society of Wood Science, Vol. 24, p. 632)
-637, 1978, vol. 29, p.428-437, 1983). Unlike existing industrial lignins (lignins in pulp wastewater, such as lignin sulfonic acid and kraft lignins), these lignins are less likely to be modified by polycondensation, etc., and do not contain sulfur or halogens in their molecules. It has characteristics such as being soluble in organic solvents and having a weight average molecular weight of approximately 2000 (Kenichi Sudo et al.: Holzforschung, vol. 39, p. 281-
288, 1985). However, the molecular weight distribution of these lignins ranges over a wide range from around 150 to several thousand.
The low molecular weight part undergoes thermal fluidization as it is heated, but
Contains a polymeric part that does not flow thermally. The present inventor once reduced the molecular weight of this polymer part by hydrogenolysis, and then heat-treated it under a nitrogen stream to re-condense the hydrogenolysis product,
The present invention was completed by obtaining the knowledge that it can be modified into a thermofluid polymer. The present inventor has revealed that the main components of wood-based raw materials can be efficiently separated by the method shown below. One is to process chips or powder of wood-based raw materials (wood, bamboo, bamboo grass, etc.) with high-pressure steam [10 kg/
cm ² (gauge pressure) or higher], hemicellulose and lignin are reduced in molecular weight, and the former can be obtained by hot water extraction, the latter by organic solvent or dilute alkali extraction, and cellulose is obtained as a residue. It is. The other is 110 in acetic acid.
℃ (Nimz, HHISWPC Proceedings,
Technical Papers p.265-266, 1985, Vancouver Canada) or organic solvents such as hydroalcohols (Kleinert, TN: Tappi, vol. 57, p.99-102,
1974, Kazumasa Shimizu et al.: Journal of the Japan Society of Wood Science, vol. 24, p.632−
637, 1978), hemicellulose and lignin separate from cellulose and dissolve, and the organic solvent is distilled off from these reaction solutions, leaving the latter as a precipitate and the former as a water-soluble substance. This is a method to separate the waste. The present inventor used lignin obtained by these methods as a raw material. Although these lignins melt and flow when heated, it has been impossible to make them into fibers because they contain polymeric parts that do not inherently flow when heated. Therefore, we attempted to modify these lignins by hydrogenolysis. 0.5-5 as a solvent
% of sodium hydroxide was depolymerized under hydrogen pressure using Raney nickel as a catalyst. This treatment cleaves some of the ether bonds and carbon-carbon bonds within the lignin molecule, making the rigid lignin molecule flexible, and also softening the lignin molecule by removing hydroxymethyl groups and reducing hydroxyl groups. The amount of oxygen can be reduced. After the reaction, lignin was fractionated using the following two methods. In the first method, the hydrogenolysis reaction solution is acidified with hydrochloric acid, extracted with chloroform, concentrated and dried, and the low molecular weight portion is extracted with carbon disulfide.
By removing the lignin, a chloroform-soluble/carbon disulfide-insoluble modified lignin was prepared. Most of the aromatic monomers and dimers produced by hydrogenolysis of lignin can be removed by carbon disulfide extraction. In the second method, the modified lignin precipitated by acidifying the reaction solution with dilute hydrochloric acid is obtained by centrifugation. In this case, the precipitate does not contain aromatic monomers or dimer fractions. The modified lignin thus obtained had a low thermal softening point and started thermal flow at 70°C, making it possible to form continuous fibers through 0.3 mm pinholes. However, due to the low thermal flow initiation temperature, it was not possible to harden the fibers by air oxidation, which is necessary before carbonizing the fibers. This suggests that the fibers remelt or fuse during carbonization at high temperatures. Therefore,
Before fiberization, the modified lignin is re-condensed and heat treated for 30 minutes at a temperature of 300 to 340°C under a nitrogen stream to increase the thermal softening point and flow start temperature of the modified lignin. Summer. The lignin material prepared in this way has extremely good spinnability using the hot melt method, and approximately 100 m of lignin material is produced every day.
It was possible to spin at a speed of . At this time,
The width of the spun fibers was 10 to 40 μm, but
The majority was ~30 μm. This fiber is
It was easily thermally stabilized by heating in air at a heating rate of 1.0-5.0°C/min. When heated in air at a constant temperature increase rate, the fibers softened and sagged slightly, but when the temperature was further increased, they hardened and re-tensioned, becoming insoluble and infusible fibers. This thermal stabilization treatment is completed at 210°C or lower, which is extremely simple compared to the thermal stabilization treatment method for Piti carbon fibers, and can be said to be a characteristic of the lignin carbon fiber manufacturing method using this method. This thermally stabilized fiber can be carbonized, for example, by raising the temperature in a tube furnace at a rate of 5° C./min to a temperature of 1000° C. or higher under a nitrogen stream and holding the temperature at a predetermined temperature for 20 minutes. [Examples of the Invention] Here, examples and results of the production of carbon fiber using lignin, which is soluble in organic solvents, as the only raw material, by treating wood resources with high temperature and high pressure saturated steam according to the present invention. Explain. Example 1 (1) Wood-based resource: birch wood chips (2) Steaming treatment conditions: The birch wood chips were steamed as they were in saturated steam at 15 kg/cm ² (gauge pressure) (200°C) for 15 minutes, then double descliffed. Defibrate with Einar. (3) Fractionation of lignin: The steamed birch wood sample was extracted with hot water (70°C, 2 hours) to remove hemicellulose, then extracted with methanol using a Soxhlet extractor, and the extract was concentrated and dried. Obtained lignin. The amount of lignin in the methanol extract was about 82%. In this case, the yield of lignin was about 60% based on the lignin in the wood. (4) Selection of solvent for hydrogenolysis of lignin: The hydrogenolysis of lignin obtained by the method (3) above is carried out in the presence of a Raney-nickel catalyst.
5% sodium hydroxide aqueous solution or alkaline
In 90% dioxane solution (liquid ratio: per sample weight)
The test was carried out by holding the temperature at 250° C. for 60 minutes under a hydrogen pressure of 50 kg/cm ² (10 times the volume). The lignin modified by hydrogenolysis is recovered by removing the catalyst in the reaction solution by filtration, and then by solvent fractionation as described above as the chloroform-soluble carbon monodisulfide insoluble part. The sample was obtained by centrifuging the precipitate produced when the reaction solution from which the catalyst had been removed was acidified with 2N-HCl.

[Table] *: Yield of precipitate produced when the reaction solution is made acidic with dilute hydrochloric acid As shown in Table 1, the lower the alkali concentration, the higher the yield of modified lignin. However, when the sodium hydroxide concentration was 2% or less, a significant amount of lignin precipitate was observed in the reaction solution after hydrogenolysis. Therefore, when recovering the modified lignin, it is essential to use an organic solvent such as dioxane to dissolve the precipitate, making the operation complicated.
Further, even when dioxane was used as a solvent for hydrogenolysis, no increase in the yield of modified lignin was observed. On the other hand, when a 5% aqueous sodium hydroxide solution is used as a solvent, although the yield decreases, the lignin is completely dissolved in the reaction solution after the reaction, and the subsequent fractionation operation of the modified lignin is simplified.
Therefore, a 5% aqueous sodium hydroxide solution is recommended as the solvent. (5) Thermal properties and spinnability of modified lignin To describe this section in detail, fiberization by the hot melt method in this example will be explained. In other words, fiberization by thermal melting means that raw materials are placed in a melting tank with a 0.5 mm diameter pinhole at the bottom and heated and melted under a nitrogen stream. Therefore, it flows out from the pinhole in the form of fibers, so it is turned into fibers by continuously winding it onto a bobbin that has been rotated in advance. Note that the sample may be continuously extruded into fibers by mechanically applying a larger load to the heated and molten sample. Therefore, in order to fiberize lignin by this method, it is important that the lignin be thermally melted and thermally fluid. Therefore, the suitability of the raw material for fiberization was determined by measuring and observing the thermal fluidity of the raw material using a flow tester. As shown in Table 2, lignin obtained by methanol extraction softened at 69.1°C under flow tester measurement conditions (heating rate: 2°C/min, load: 10 kg, pinhole diameter: 0.3 mm). do
Flow started at 101.0°C. The fluidity is determined by whether or not the sample flows out from a pinhole at the bottom of the melting tank, and the temperature at which the sample starts flowing out is defined as the starting temperature. Although the methanol extract flowed out at 101.0°C, the fibers were extremely thick and brittle for a sample that had passed through a 0.3 mm pinhole, and were determined to be unsuitable as a raw material for fiber production. Therefore, we attempted to modify lignin by hydrogenolysis as described above. The modified lignin had an extremely low thermal softening point and started thermal flow at low temperatures. As an example, the chloroform-soluble carbon monodisulfide-insoluble portion of the product hydrogenolyzed under the conditions of Experiment No. 3 in Table 1 started thermal flow at 70°C (Table 2). At this time, the sample flowed out continuously through the 0.3 mm pinhole and could be spun. However, the flow initiation temperature was low, making it difficult to achieve thermal stabilization by air oxidation, which is necessary before carbonization. Therefore, the modified lignin is heat treated under a nitrogen stream,
The thermal softening point and flow initiation temperature of the modified lignin were increased by recondensation. Heat treatment temperature 300~350
°C, and the treatment time was fixed at 30 min.

[Table] As shown in Table 2, the heat treatment increased the thermal softening point and flow initiation temperature, and the sample flowed out continuously in the form of fibers through a 0.3 mm pinhole. Table 3 shows the difficulty of spinnability and thermal stabilization of the heat-treated modified lignin. heat at each temperature

〔Effect of the invention〕

As mentioned above, the only raw material is lignin, which is separated by treating wood-based resources with high-pressure saturated steam or organic solvents such as alcohol at high temperatures, which is then hydrogenolyzed and then heat-treated under a nitrogen stream. When modified, it became possible to spin fibers using a hot melt method, and by thermally stabilizing the fibers with air oxidation and carbonizing them, it became possible to produce carbon fibers.

[Brief explanation of drawings]

The drawing shows the relationship between the width and tensile strength of the carbon fibers obtained in Example 1.

Claims (1)

[Claims] 1 After treating wood-based resources with high-pressure saturated steam, lignin that can be extracted with an organic solvent or dilute alkali, and lignin that can be solubilized by treating with an organic solvent such as alcohol at high temperature, are subjected to hydrogenolysis. A method for producing lignin carbon fibers, which comprises: then heat-treating the fibers under a stream of an inert gas such as nitrogen, and then spinning and carbonizing the fibers by a thermal melting method.