Method for preparing high-quality special mesophase pitch material

Abstract

The invention provides a preparation method of mesophase pitch, which comprises the following steps: by taking an ethylene tar narrow fraction extract as a raw material, carrying out polycyclic aromatic hydrocarbon aggregation-sedimentation at room temperature under the action of a dissolving agent and a precipitating agent. The preparation method comprises the following steps: carrying out pre-aggregation treatment, and carrying out catalytic thermal condensation reaction in an autoclave under the protection of inert gas and the action of a Lewis acid catalyst to synthesize the high-quality mesophase asphalt material.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of high-quality special mesophase asphalt materials, in particular to the technical field of preparation of high-quality special mesophase asphalt materials by utilizing ethylene tar. Background Art

[0002] Mesophase pitch is a special asphalt material with liquid crystal properties and is the core precursor for the preparation of high-performance carbon materials. This type of material forms a disc-shaped molecular structure (mesophase) with directional arrangement during heat treatment. This unique microstructure makes it an ideal choice for the manufacture of high-end carbon materials. As an important carbon material precursor, mesophase pitch is mainly derived from heavy aromatic hydrocarbon raw materials such as coal tar and petroleum asphalt. In terms of preparation methods, the traditional process mainly uses thermal polycondensation, which promotes the transformation of isotropic asphalt to anisotropic by precisely controlling the heat treatment temperature (350-450°C) and time; modern preparation technology introduces new methods such as catalytic polymerization and solvent extraction, which significantly improves the mesophase content and purity. With its unique molecular orientation characteristics, this material has demonstrated irreplaceable application value in high-tech fields such as aerospace (missile nose cones, rocket nozzles), new energy (lithium battery negative electrodes, fuel cell bipolar plates), and electronic packaging (chip heat dissipation substrates).

[0003] The current development of high-quality special mesophase asphalt material preparation technology still faces three major bottlenecks: first, it is difficult to control the purity of raw materials, and the quinoline insoluble content is difficult to be stably lower than 0.1%; second, the molecular orientation control accuracy is insufficient, resulting in large fluctuations in product performance; finally, production costs remain high.

[0004] Ethylene tar, a byproduct of ethylene production, is a low-value-added hydrocarbon resource rich in condensed-ring aromatics. Its high carbon content (>90%) and unique molecular structure make it an ideal raw material for preparing mesophase pitch. Compared with traditional coal tar pitch, ethylene tar-based mesophase pitch has inherent advantages such as a narrow molecular weight distribution and low impurity content, making it easier to manipulate to produce highly oriented, high-purity specialty asphalt materials. Currently, the predominant process used internationally is a combined thermal polycondensation-solvent refining process. By precisely controlling the reaction temperature (380-420°C) and pressure (0.1-1MPa), the aromatic molecules in ethylene tar are oriented and polycondensed to form an anisotropic mesophase.

[0005] However, this technology still faces key challenges: on the one hand, the composition of ethylene tar is complex, and the unsaturated components are prone to excessive cross-linking, resulting in a low conversion rate of the intermediate phase (usually <60%); on the other hand, the content of quinoline insoluble matter (QI) in the product fluctuates greatly (0.5-3%), which seriously affects the performance of subsequent carbon materials. In addition, the existing process has problems such as high energy consumption and low solvent recovery rate, which restricts large-scale production. In recent years, the introduction of new technologies such as catalytic polymerization and molecular distillation has provided the possibility of breaking through these bottlenecks, but how to achieve low-cost, high-yield (>85%) and stable preparation is still a key problem for industrialization. The development of high-value utilization technology for ethylene tar can not only solve the problem of petrochemical by-product disposal, but also provide high-performance carbon material precursors for aerospace, nuclear industry and other fields, which has significant economic and strategic value. Summary of the Invention

[0006] The present invention provides a method for preparing mesophase pitch. The process uses a specific distillation range extract of ethylene tar as raw material. After pre-aggregation, a catalytic condensation reaction occurs in an autoclave under inert gas protection and the action of a Lewis acid catalyst to synthesize a high-quality mesophase pitch material. First, the ethylene tar is cut by vacuum distillation, and the fraction with a normal pressure boiling point of 300-450°C is collected. This narrow ethylene tar fraction is then dissolved in solvent A and ultrasonically treated to fully dissolve it, obtaining solution A. Next, under continuous stirring, a precipitant B is slowly added to solution A. Precipitant B promotes the aggregation of condensed aromatic hydrocarbons to form a large number of aggregates. The aggregates and solvent are separated using a centrifuge, and the light components in the solution are then subjected to vacuum distillation to remove the remaining solvent and light components, thereby obtaining precursor T. The precursor T is transferred to an autoclave, an acid catalyst is added, and it is purged and replaced with nitrogen. Then, a condensation reaction is carried out at 350-450°C and 0.5 MPa for 4-10 hours. After cooling, an intermediate phase asphalt material with good properties and 50-100% optical anisotropy is obtained.

[0007] The preparation process is as follows:

[0008] In the first step, the ethylene tar is subjected to vacuum distillation and cutting to collect the fraction in the range of 350 to 480°C, which mainly contains condensed-ring aromatic raw materials with 3 to 5 rings.

[0009] In the second step, the narrow fraction of ethylene tar obtained in the first step is added to solvent A, and ultrasonic treatment is used to fully disperse and dissolve the narrow fraction of ethylene tar, thereby obtaining a solution A containing the narrow fraction of ethylene tar.

[0010] The third step is to gradually add the precipitant B to the A solution under continuous stirring to promote the formation of aggregates of polycyclic aromatic hydrocarbons, and then let it stand for 10 to 20 hours to promote the aggregates to fully attract each other and form larger aggregates.

[0011] In the fourth step, the solution is treated with a high-speed centrifuge to centrifugally separate the aggregates and the solvent, and the remaining light components in the solution are distilled under reduced pressure to remove the solvent and light components to obtain the precursor T.

[0012] In the fifth step, the precursor T is transferred to an autoclave, a catalyst is added, and the autoclave is purged with nitrogen to displace the air. A condensation reaction is then carried out at 350-450°C and 0.5 MPa for 4-10 hours. After cooling, a mesophase pitch material with good properties and optical anisotropy is obtained.

[0013] The solvent A is a mixture of one or more of toluene, xylene, quinoline, and dichloromethane. The precipitant B is a mixture of one or more of n-heptane, n-hexane, ethanol, methanol, and butanol. The catalyst is anhydrous AlCl3 or anhydrous FeCl3, added in an amount of 0.05% to 0.1%.

[0014] The mesophase pitch prepared by the above method has a softening point of 260-300° C., an H / C ratio of 0.4-0.6, a residual carbon value of 75-85%, and an anisotropic mesophase pitch content of 50-100%.

[0015] The specific innovations of this technology include:

[0016] (1) In order to solve the problem that the raw material sources and properties of the traditional direct thermal polycondensation method for preparing mesophase asphalt are unstable and changeable, resulting in unstable performance and low yield of the prepared special asphalt materials, this technology pre-treats the raw materials and finely cuts the distillation range of the polycyclic aromatic hydrocarbons to obtain polycyclic aromatic hydrocarbons with 3 to 5 rings.

[0017] (2) In order to solve the problem that polycyclic aromatic hydrocarbons are irregularly stacked during high-temperature indentation, which leads to low yield of intermediate phase asphalt materials due to rapid indentation, this technology uses solvent-dissolved-aggregated raw materials to slowly aggregate polycyclic aromatic hydrocarbons at room temperature, and then allows them to stand to obtain a large number of aggregates. Then, catalytic polymerization is carried out under high temperature conditions, and the intermediate phase asphalt obtained has the advantages of high yield and high performance.

[0018] (3) Due to the use of pre-aggregation technology, the raw materials can be in close contact with the catalyst, which improves the catalytic effect, significantly reduces the amount of catalyst used, reduces post-processing costs and improves the quality of asphalt materials. Example

[0019] The technical content and effects of the present invention are further illustrated below with reference to the embodiments, but the scope of the present invention is not limited thereby.

[0020] Example 1:

[0021] The preparation process is as follows:

[0022] In the first step, the ethylene tar is subjected to vacuum distillation and cutting to collect fractions within the range of 350 to 480°C, which mainly contain condensed-ring aromatic raw materials with 3 to 5 rings.

[0023] In the second step, the ethylene tar fraction obtained in the first step is added to solvent A, and ultrasonic treatment is used to fully disperse and dissolve the narrow fraction of ethylene tar to obtain a solution A of the narrow fraction of ethylene tar.

[0024] In the third step, under continuous stirring, the precipitant B was gradually added to the A solution to promote the formation of aggregates of polycyclic aromatic hydrocarbons, and then the solution was allowed to stand for 20 hours.

[0025] In the fourth step, a high-speed centrifuge is then used to centrifugally separate the aggregates and the solvent, and the remaining light components in the solution are then subjected to reduced pressure distillation to remove the solvent and light components to obtain precursor T.

[0026] The fifth step is to transfer the precursor T into the autoclave, add the catalyst, purge and replace the autoclave with nitrogen, and then carry out the condensation reaction at 430°C and 0.5 MPa for 10 hours. After cooling, an intermediate phase asphalt material with good optical anisotropy is obtained.

[0027] The solvent A is a mixture of xylene and quinoline at a mixing ratio of 1:5, the precipitant B is a mixture of n-heptane and ethanol at a mixing ratio of 3:1, and the catalyst is anhydrous AlCl3 at an addition amount of 0.05%.

[0028] The mesophase pitch prepared by the above method has a softening point of 280° C., an H / C ratio of 0.5, a residual carbon value of 82%, and an anisotropic mesophase pitch content of 85%.

[0029] Example 2:

[0030] The preparation process is as follows:

[0031] In the first step, the ethylene tar is subjected to vacuum distillation to collect the fraction within the range of 350 to 480°C, which mainly contains condensed-ring aromatic hydrocarbon raw materials with 3 to 5 rings.

[0032] In the second step, the ethylene tar narrow fraction from the first step is gradually added to the solution A with sedimentation agent B under continuous stirring, stirred thoroughly, and then allowed to stand for 15 hours.

[0033] In the third step, a high-speed centrifuge is then used to centrifugally separate the aggregates and the solvent, and the remaining light components in the solution are then subjected to reduced pressure distillation to remove the solvent and light components to obtain precursor T.

[0034] The fourth step is to transfer the precursor T into the autoclave, add the catalyst, purge and replace the autoclave with nitrogen, and then carry out the condensation reaction at 420°C and 0.5 MPa for 6 hours. After cooling, an intermediate phase asphalt material with good properties and optical anisotropy is obtained.

[0035] The precipitant B is a mixture of one or more of n-heptane, n-hexane, ethanol, methanol, and butanol. The catalyst is anhydrous AlCl3 and anhydrous FeCl3, and the addition amount is 0.06%.

[0036] The mesophase pitch prepared by the above method has a softening point of 275° C., an H / C ratio of 0.6, a carbon residue value of 82%, and an anisotropic mesophase pitch content of 88%.

[0037] Comparative Example 1:

[0038] The preparation process is as follows:

[0039] In the first step, the ethylene tar is subjected to vacuum distillation and cutting to collect fractions within the range of 350 to 480°C, which mainly contain condensed-ring aromatic raw materials with 3 to 5 rings.

[0040] In the second step, the narrow fraction is transferred to an autoclave, a catalyst is added, and the autoclave is purged and replaced with nitrogen. Then, a condensation reaction is carried out at 430°C and 0.5 MPa for 10 hours. After cooling, an intermediate phase asphalt material with good optical anisotropy is obtained.

[0041] The solvent A is a mixture of xylene and quinoline at a ratio of 1:5. The precipitant B is a mixture of n-heptane and ethanol at a ratio of 3:1. The catalyst is anhydrous AlCl3, added in an amount of 0.05%.

[0042] The mesophase pitch prepared by the above method has a softening point of 250° C., an H / C ratio of 0.4, a carbon residue value of 80%, and an anisotropic mesophase pitch content of 40%.

[0043] Comparative Example 2:

[0044] The preparation process is as follows:

[0045] In the first step, the ethylene tar is subjected to vacuum distillation and cutting to collect fractions within the range of 350 to 480°C, which mainly contain condensed-ring aromatic raw materials with 3 to 5 rings.

[0046] In the second step, each narrow fraction of ethylene tar obtained in the first step is added to solvent A, and ultrasonic treatment is used to fully disperse and dissolve the narrow fraction of ethylene tar to obtain a solution A of the narrow fraction of ethylene tar.

[0047] In the third step, solution A is distilled, and then the remaining light components are distilled under reduced pressure to remove the solvent and light components to obtain precursor T.

[0048] The fifth step is to transfer the precursor T into the autoclave, add the catalyst, purge and replace the autoclave with nitrogen, and then carry out the condensation reaction at 430°C and 0.5 MPa for 10 hours. After cooling, an intermediate phase asphalt material with good optical anisotropy is obtained.

[0049] The sedimentation agent B is a mixture of n-heptane and ethanol with a mixing ratio of 3:1, and the catalyst is anhydrous AlCl3 with an addition amount of 0.05%.

[0050] The mesophase pitch prepared by the above method has a softening point of 300° C., an H / C ratio of 0.7, a carbon residue value of 85%, and an anisotropic mesophase pitch content of 30%.

[0051] Performance evaluation of examples and comparative examples

[0052] Compared with directly preparing mesophase asphalt using the 350-480°C fraction of ethylene tar, the mesophase asphalt obtained by the pre-aggregate method of the present invention has a lower softening point, is more conducive to the preparation of lithium battery negative electrode coating materials, and has a higher optical mesophase ratio and higher product quality.

[0053] The mesophase asphalt preparation technology based on the narrow fraction of ethylene tar of the present invention adopts solvent dissolution-aggregation raw materials, performs moderate aggregation of condensed ring aromatic hydrocarbons at room temperature to obtain aggregates, and then performs catalytic polymerization under high temperature conditions, which can significantly reduce the amount of catalyst used. The obtained mesophase asphalt has a significantly high yield and performance advantages.

Claims

1. A method for preparing high-quality special mesophase pitch material: In the first step, ethylene tar is subjected to vacuum distillation and cutting to collect the fraction in the range of 350-480°C, which mainly contains condensed aromatic hydrocarbons with 3-5 rings; In the second step, the narrow fraction of ethylene tar obtained in the first step is added to solvent A, and the narrow fraction of ethylene tar is fully dispersed and dissolved by ultrasonic treatment to obtain a solution A containing the narrow fraction of ethylene tar; The third step is to gradually add the sedimentation agent B to the A solution under continuous stirring to promote the formation of polycyclic aromatic hydrocarbons aggregates, and then let it stand for 10 to 20 hours to promote the aggregates to fully attract each other and form larger aggregates; In the fourth step, the solution is treated with a high-speed centrifuge to separate the aggregates and the solvent, and the remaining light components in the solution are distilled under reduced pressure to remove the solvent and light components to obtain the precursor T. The fifth step is to transfer the precursor T to an autoclave, add a catalyst, purge the autoclave with nitrogen, and then carry out a condensation reaction at 350-450°C and 0.5 MPa for 4-10 hours. After cooling, a mesophase pitch material with good properties and optical anisotropy is obtained. The solvent A is a mixture of one or more of toluene, xylene, quinoline, and dichloromethane; the precipitant B is a mixture of one or more of n-heptane, n-hexane, ethanol, methanol, and butanol; the catalyst is anhydrous AlCl3 or anhydrous FeCl3, and the catalyst addition amount is 0.05wt% to 0.1wt%.