CS261540B1 - A method of preparing a fiberizable resin for making carbon fibers - Google Patents

Abstract

Method for preparing a spinnable resin for the production of carbon fibers with a reduced content of solid impurities. The method consists in that the pyrolysis resin, after the first stage of heat treatment and subsequent removal of solid impurities by filtration or centrifugation of its solutions in solvents, with a predominant content of aromatics, is subjected to a second stage of heat treatment at a temperature of up to 410 °C. The temperature in the second stage of heat treatment is 5 °C to 20 °C higher than in the first stage of treatment

Description

3 261540

It is an object of the present invention to provide a process for the preparation of spinning resins for carbon fiber fabrics with reduced solids content, achieved by the novel post-heat treatment of processed heavy pyrolysis materials. Heavy pyrolysis products such as heavy ipyrolysis oils, pitch resins are by-products of pyrolysis of crude oil, respectively. its fractions, or the final products of the black tar tars, are obtained and the distillation residues are obtained after separation of the more valuable pyrolysis products.

The predominant proportion of their production is extensively exploited as flame-retardant, protective-coatings, admixtures or asphalt substitutes, coking substrates, and the like. In recent years, they have been used more efficiently to prepare carbon fibers, needle coke, and so on. however, it does not impose high demands on the properties that untreated pyrolysis resins and pitch resins do not achieve. This is mainly due to the fact that heavy pyrolysis oils, resins and pitch are the ultimate residualization separation of pyrolysis products. Their composition is preceded by impurities from the starting materials, the non-volatile complexes of the pyrolysis products and the secondary products produced by the distillation separation of the pyrolysis product components. As a result, the pyrolysis resins are a very complex mixture of heterogeneous liquids with different chemical and physical properties. In order to process the resins, the components need to be removed from them. which prevent or substantially deteriorate their processing processes. The properties of other substances in the mixture need to be adjusted by thermal condensation processes.

Particularly serious negative effects on the properties of resins have solid, non-volatile and insoluble impurities present predominantly in the form of very fine particles. These originate from the initial starting materials of the pyrolysis process of their processing or are formed secondary to the heat reactivity of the resins by condensing the reactants. Solid admixtures impart aliens as foreign non-volatile substances that deteriorate its deformability and flow properties. In contrast to the effects of solid particles on the properties of conventional polymers, the situation is complicated. The pyrolysis resins, depending on the heat treatment conditions, take on a more or less the character of the two-component melt - the mixed system of the isotropic and anisotropic phase, which increases during the heat treatment.

The solid particles in such a system are densified at the phase boundary to form a discontinuous surface that translates into the drawn processability of the resin and the deteriorated properties of the products. This effect is increasingly seen with increasing solids content as well as increasing the anisotropic content of the so-called mesophase.

Pyrolysis resins intended for processed demanding products are generally undergoing finishing operations. These usually involve the separation of undesirable components, especially solid and insoluble impurities, volatiles and heat condensation treatment of the resins. In doing so, the thermal condensation treatment and the distillation of the volatile components are combined in a single operation.

Filtration, sedimentation procedures and extraction are used to remove insoluble components. In order to facilitate the handling and separation processes and to increase their performance, sometimes it is preferred to work with the solution of the resins before processing their melts. The technical purification is due to the high viscosity of the resins, the small particle sizes and the small differences in particle density and intrinsic properties, and their effect is limited. Furthermore, in many pyrolysis products, the solids content is relatively high. The mentioned properties of the resins prevent in many cases the removal of insoluble components in one operation.

The application of separation processes for a particular case of reducing the solids content of pyrolysis products prior to their further processing has been described. Taking into account the specific properties of the resins and satisfying the requirements of their demanding, they have introduced to the reduction of undesirable impurities, the problem is that, in addition to the complexity of the technical application, the procedures proposed hitherto do not take into account the fact that the secondary formation of insoluble substances during the heat treatment.

The removal of impurities prior to the heat treatment process has a negligible effect on the secondary formation of solids. This necessitates additional operations in the resin treatment process which also remove these secondary contaminants. For this purpose, the filtration of the resin has been proposed after the end of the treatment process.

This method encounters the problem of high viscosity melt-treated resin. It can be applied only to resins with low final content of solids. In addition, the process, i.e., the application of separation post-treatment operation, cannot be facilitated by diluting and reducing the viscosity of the product with solvents. Since this requires the inclusion of additional operations, but mainly because the resin in this stage usually contains a high proportion of insoluble components, but suitable prior reduction, and these would be removed from the solution.

In order to generalize and simplify the method of removing solid impurities in the preparation of pyrolysis resins and carbon fibers, it has been found necessary to develop these 2B14040s manageable processes which allow the removal of primary and secondary non-fusible impurities or processes that reduce secondary impurities.

It has been found experimentally that a low solids pyrolysis resin suitable for the preparation of C-fibers can be prepared by a previously unsuccessful combination of separation processes with the modification of the heat treatment process.

It has been found that the spinning pyrolysis resin for producing carbon fibers with reduced solids content can be prepared by a process in which the pyrolysis resin is subjected to a first stage of heat treatment and then the solids are removed therefrom by filtration or removal of the solution. the heat treated resin in solvents with predominant aromatic content, after which the solvent is removed by distillation of the solvent and the resulting resin is subjected to a second heat treatment step at a temperature of up to 410 ° C and the solids are separated.

The second stage of the heat treatment is carried out at a temperature of from 5 ° C to 20 ° C higher than that of the first stage of treatment and at least 60% of the heat treatment time during the entire treatment step. As the aromatic solvent, benzene, toluene, xylene, tetralin or technical mixtures such as light oil, hydrogenated oil, or general liquid mixtures with a predominance of aromatic solvents can be used. In the first stage, partial condensation of the resin takes place, with the preferential reaction of the reactive constituents of the insoluble and partially non-volatile components.

These are treated with the other solid impurities by the filtration and sedimentation methods after dissolution of the main part of the resin. As a rule, the solvent is removed from the resin solution which has been decomposed at this stage of the undesirable admixture, and the distillation residue is subjected to a second stage of thinning. The resulting treated resin has a low residual solid impurity content and good processability.

The proposed process has several advantages over the prior art. In particular, it allows the pyrolysis resin to be freed from solid impurities introduced by the raw materials and formed during the heat treatment prior to a high increase in its viscosity in one operation, but converted to insoluble substances at the stage where the majority of reactive substances prevail. j. separable from the solution. The possibility of using other additional separation operations, for example prior to heat treatment, which can be of great importance for high-flooded raw materials, does not exclude this. Removal of the used solvents with the proposed procedure is ensured in one operation with the 2nd stage treatment.

The process utilizes the co-agglomeration effects of the resulting insoluble particles to coalesce the fine particles of solid impurities and thereby improve their separation. Furthermore, the process allows for the preparation of resins with an elevated melting point without increasing the content of solids, i.e.. applicable rework to demanding product types.

Finally, the proposed process makes it possible to process C-fiber as well as resins with a high proportion of reactive substances, from which a high proportion of solid impurities has been formed and unprocessable at the present treatment. Example 1

Heavy pyrolysis oil containing 2.7% solid impurities was subjected to a first step treatment by heating to 380 ° C for one hour maintaining this temperature. It was then dissolved in a two-fold amount of tetralin and filtered at 80 ° C at a pressure of up to 0.5 MPa. The solvent was distilled off from the filtrate and the residue was heated to 390 ° C without interruption and kept at this temperature under low vacuum. in the past hours. The treated resin contained 0.85% non-volatile impurities in a yield of 40% for the starting pyrolysis oil. Example 2 20 kg of heavy pyrolysis oil were treated similarly to Example 1, except that solid impurities from the resin solution were treated with 1% by weight. the degree of treatment was removed by centrifugation. 8 kg of treated pigments containing 0.95% solids were obtained. The tube was spun at 260 ° C. The fibers satermoset by gradual heating to 290 ° C in air and carbonized in an inert atmosphere by heating to 1000 ° C. Example 3

The heavy pyrolysis oil containing 2.7% solid impurities was subjected to a single treatment without removing impurities. that the sample was heated to 390 ° C for 3 hours at this temperature. The resin contained more than 9% solids and was practically unprocessable for fibers. Example 4

The procedure was as in Example 3, with the exception that a heavy pyrolysis oil with a residual content of 0.9% solid impurities was used for the heat treatment. The main part of the soil impurities was modified in advance. Modified pyrolysis resin

Claims (2)

SUBJECT 1. A process for the preparation of a fiberizable carbon fiber resin, wherein the pyrolysis resin is subjected to a first stage of heat treatment and thereafter removed solids by filtering or centrifuging solutions of the thermally treated resin in a predominantly aromatic-containing solvent and removing the resulting solutions by distilling the solvents. characterized in that the resulting resin is subjected to a second step it tepelVYNÁLEZU treatment at the 410 ^Q C and the obtained product was separated solids. 2. The method of claim 1, wherein the second heat treatment stage is carried out at a temperature of 5 ° C to 20 ° C above the treatment temperature in the first stage and the heating time in the second treatment stage is at least 60% of the cooking time during throughout the edit.