Lignin precursor and process for producing a lignin precursor for the production of carbon fibers

Abstract

A method for producing a precursor (11) from lignin for the production of carbon fibers by melt spinning, characterized in that during melt spinning or extrusion lignin is pressed through at least one nozzle and coated with a polymeric sheath layer and the precursor (11) consisting of the lignin and the polymer is plied several times to obtain a desired number of filaments before it is passed through a washing bath to separate the polymer from the lignin and wherein the lignin precursor is stabilized by a temperature-controlled heating process and wherein the precursor is dried before stabilization and wherein after stabilization of the precursor the number of multifilaments for industrial application can be further increased by plying.

Description

[0001] The invention relates to a process for producing a lignin precursor according to the preamble of claim 1. Furthermore, the invention relates to a lignin precursor according to claim 10.

[0002] The lignin used here is a bio-based raw material for the production of carbon fibers. Lignin serves as a precursor material for the carbon fibers. Its molecular structure is similar to the widely used precursor material polyacrylonitrile (PAN). One of lignin's outstanding properties is its melt-spinnability. Because it is a byproduct of paper production, it is also available in large quantities.

[0003] However, melt spinning of lignin has proven problematic, firstly, due to its low melt elongation and, secondly, due to the strong dependence of melt viscosity on the process temperature. Furthermore, lignin is very brittle. Therefore, lignin is very difficult to handle as a precursor for further conversion to carbon fibers.

[0004] Little is known about the melt spinning of lignin. Previous attempts to process lignin using the melt spinning process have only resulted in single carbon filaments on a laboratory scale. To further increase the number of filaments, the lignin had to be modified and blended (mixed) with a thermoplastic. Known processes for melt spinning lignin are described, for example, in US 2014 / 0087618 A1 and DE 102018 120 626 A1.

[0005] Previously, lignin spinning on a laboratory scale required mixing the lignin with a pyrolyzed heavy fuel oil, where the island-in-the-sea structure changes due to interactions between the two materials. As a result, the filament structure cannot be controlled or defined when using these materials. The possibility of using island-in-the-sea technology in a defined manner in the production of a carbon fiber precursor is known for PAN in the solvent / gel spinning process, although only single filaments could be produced for the studies. To date, no processes are known for producing lignin into carbon fibers with a variety of filaments for industrial application.

[0006] The invention is based on the object of creating a precursor from lignin and a process by which carbon fibers can be produced from lignin.

[0007] A method for achieving this object comprises the measures of claim 1. Accordingly, it is provided that in an extruder-based spinning process, lignin is pressed through at least one nozzle and coated with a polymeric sheath layer, in particular a thermoplastic sheath layer, and the precursor, consisting of the lignin and the polymer, is plied several times to obtain a desired number of filaments before it is passed through a washing bath to separate the polymer from the lignin. The lignin precursor is stabilized by a temperature-controlled heating process, the precursor is dried before stabilization, and after stabilization of the precursor, the number of multifilaments can be further increased for industrial application by plying. This makes it possible to produce a lignin precursor yarn with greater than or equal to 1000 filaments and to process these further.The protective polymer coating allows the yarn to be plied multiple times to achieve the desired filament count. Subsequent modified conversion enables the production of continuous, lignin-based carbon fibers or carbon fiber rovings with a sufficient filament count for industrial applications.

[0008] In particular, the invention provides that the polymeric coating layer of the lignin is dissolved either in a solvent or in water, wherein the coating layer is preferably formed from a water-soluble polymer.

[0009] Furthermore, according to the invention, the type of solvent for dissolving the coating layer can be selected depending on the polymer used.

[0010] Depending on the type of polymer, it is conceivable to choose the solvent accordingly in order to achieve a particularly preferential detachment of the coating layer from the lignin.

[0011] It is also envisaged that, in particular, pure lignin is melted and pressed through at least one nozzle, so that the precursor preferably consists of at least nearly 100% lignin. A spin-carrier system with the water-soluble spin carrier in the island-in-the-sea spinning process is preferably used. A core-sheath spinning process can also be used as a technical alternative. Subsequent conversion and deposition make it possible to create a continuous, lignin-based carbon fiber roving with a sufficient number of filaments for industrial application.

[0012] It is envisaged that the lignin and the polymer are pressed through the at least one nozzle at a temperature of 130°C to 250°C, in particular from 160°C to 220°C, preferably from 170°C to 190°C. This choice of material temperature allows the lignin to be processed together with the polymer particularly advantageously. Preferred viscosities of the lignin and / or the polymer are from 10 Pas to 2000 Pas, preferably 100 Pas to 2000 Pas, in particular 100 Pas to 500 Pas. A particularly preferred viscosity ratio between the lignin and the polymer is from 0.5 to 2.0. This viscosity ratio allows the polymer sheath material to be bonded particularly well around the lignin filaments in the aforementioned process.

[0013] By combining the two-component system in the island-in-the-sea spinning process, a multifilament yarn can be spun. Depending on the geometry of the nozzle, it is possible, for example, to spin 24 sea fibers, each with 14 islands, into a yarn with 336 lignin filaments. By further plying the yarn, a carbon fiber with a multiple of the aforementioned number of filaments can be produced.

[0014] After the yarn or precursor consisting of lignin and polymer is combined or plied, it is passed through a washing bath or water bath to separate the polymer from the lignin. This spinning process of the lignin with the polymer coating layer and the subsequent washing bath results in a lignin precursor with a purity of up to 100%. The carrier also significantly simplifies the unwinding of the feed yarn spools in the feeder for stabilization, as the carrier or coating minimizes capillary breakage of the yarn during unwinding.

[0015] The temperature-controlled heating process allows the at least nearly pure lignin precursor to be stabilized. The precursor is preferably dried prior to stabilization. After stabilization of the precursor, the number of multifilaments can be further increased for industrial applications by plying.

[0016] Furthermore, according to the invention, a stabilized continuous lignin yarn can be either wound onto tubes, preferably bobbins, or deposited in cans or transported to a subsequent carbonization process. After winding the lignin yarn onto a tube, it is possible to further ply several stabilized lignin yarn strands.

[0017] A precursor for achieving this object has the features of claim 10. Accordingly, it is provided that the lignin precursor consists of lignin and can be plied together to form a yarn consisting of a plurality of continuous filaments, wherein the lignin is at least temporarily coated by a polymeric coating layer. The precursor can be produced by a method according to any one of claims 1 to 9.

[0018] A preferred embodiment of the invention is explained in more detail below with reference to the drawing.

[0019] The single figure in the drawing illustrates an apparatus 10 for the method according to the invention for producing a precursor 11 from lignin. It should be expressly noted that this apparatus 10 is only one of many possible embodiments for producing the precursor 11 from lignin for carbon fibers. In addition to the apparatus illustrated in the figure, it is conceivable that this apparatus may have additional or fewer components with which the lignin precursor 11 is processed.

[0020] After the lignin has been melt-spun with the polymer under the conditions described above to form the lignin precursor yarn 11, it is placed onto a spool 12, preferably onto several spools 12, of a creel 13. Starting from this creel 13, several precursor yarns 11, each wound on different spools 12 of the creel 13, are brought together for plying. The multiply plied lignin precursor yarns 11 are then passed through a washing bath 14. In this washing bath 14, the polymeric sheath layer, which is preferably a thermoplastic, is separated from the lignin by a solvent, particularly water.

[0021] After the washing bath 14, the plied yarn or multifilament is passed through a drying oven 15 to remove residual solvent or water from the filaments.

[0022] After the multifilaments have left the drying oven 15, they can be passed over at least one preparation roller 16. This preparation roller 16 serves to prepare or modify the multifilaments accordingly before entering the stabilization or oxidation oven 17. This preparation roller 16, in particular, protects the surface of the multifilaments or the yarn, so that it can be easily transported during the post-treatment steps.

[0023] An elevated temperature prevails in the stabilization or oxidation furnace 17. The required temperature is adjusted by an air heater 18 in the furnace 17 depending on the material used. The multifilaments are guided and converted in the furnace 17 along several godets 19. These godets 19 can be driven in such a way that they pull the filaments through the furnace. By slightly varying the rotational speeds of the godets 19 or by different rotational speeds of the godets 19, the multifilaments are at least slightly stretched. Stabilization is carried out by applying heat under oxygen in the furnace 17. After the stabilized filaments have left the furnace 17, they can either be deposited in a can or—as shown in the figure—wound up by a winder 20.The yarn wound in this way can be transported further for a subsequent carbonization process or can be plied again to further increase the number of filaments in the yarn.

[0024] By this process of melt spinning the lignin together with the polymer, separating the lignin from the shell layer and then stabilizing the precursor in the furnace 17 with subsequent carbonization, it is possible to produce a carbon fiber yarn (roving) with a variety of filaments for industrial application. List of reference symbols: 10 Furnishings 11 Precursor Yarn 12 coil 13 creels 14 Wash bath 15 drying oven 16 Preparation roller 17 Stabilization / Oxidation Furnace 18 air heaters 19 Galette 20 winders

Claims

[1] Process for producing a precursor (11) from lignin for the production of carbon fibers by melt spinning, characterized by that during melt spinning or extrusion lignin is pressed through at least one nozzle and coated by a polymeric sheath layer and the precursor (11) consisting of the lignin and the polymer is plied several times to obtain a desired number of filaments before it is passed through a washing bath to separate the polymer from the lignin and wherein the lignin precursor is stabilized by a temperature-controlled heating process and wherein the precursor is dried before stabilization and wherein after stabilization of the precursor the number of multifilaments for industrial application can be further increased by plying. [2] Method according to claim 1, characterized bythat the coating layer of the lignin is dissolved either in a solvent or in water, wherein the coating layer is preferably formed from a water-soluble polymer. [3] Method according to claim 1 or 2, characterized by that the type of solvent for dissolving the coating layer is selected depending on the polymer used. [4] Method according to one of the preceding claims, characterized by that the lignin and the polymer are pressed through the at least one nozzle at a temperature of 130°C to 250°C, in particular from 160°C to 220°C, preferably from 170°C to 190°C. [5] Method according to one of the preceding claims, characterized by that the viscosity of the lignin and / or the polymer is 10 Pas to 2000 Pas, preferably 100 Pas to 2000 Pas, in particular 100 Pas to 500 Pas. [6] Method according to claim 5, characterized bythat the viscosity of the lignin and the viscosity of the polymer are in a ratio of 0.5 to 2.

0. [7] Method according to one of the preceding claims, characterized by that the polymer and lignin are spun using the sheath-core spinning process or the island-in-the-sea spinning process. [8] Method according to one of the preceding claims, characterized by that a stabilized endless lignin yarn is either wound onto tubes, preferably bobbins, or is deposited in cans or is transported further to a subsequent carbonization process or that after winding onto a tube several stabilized lignin yarn strands are further plied. [9] Method according to claim 1, characterized by that the polymeric coating layer is a thermoplastic coating layer. [10] Precursor (11) from lignin for the production of carbon fibers, characterized byin that the lignin precursor consists of lignin and is plied together to form a yarn consisting of a plurality of continuous multifilaments, wherein the lignin is at least temporarily covered by a polymeric sheath layer and wherein the precursor (11) is produced by a method according to one of claims 1 to 9.

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