Method for preparing aromatic hydrocarbon oligomer

Abstract

The present application provides a method for preparing an aromatic hydrocarbon oligomer. The preparation method comprises: under the catalysis of a chloroaluminate ionic liquid, enabling an aromatic hydrocarbon compound to undergo an oligomerization reaction to obtain the aromatic hydrocarbon oligomer, wherein the oligomerization reaction is carried out in a solvent system, the solvent is selected from chlorinated hydrocarbon solvents, and the aromatic hydrocarbon compound is selected from condensed ring aromatic hydrocarbons having a ring number of 2-4. According to the preparation method of the present application, an aromatic hydrocarbon oligomer with a simple composition and narrow molecular weight distribution can be efficiently prepared under mild conditions, providing a high-quality precursor for the preparation of high-quality mesophase pitch.

Description

A method for preparing aromatic hydrocarbon oligomers

[0001] This application claims priority to the Chinese patent application filed with the Patent Office of China on December 18, 2023, with application number 202311744989.2 and application name “A method for preparing aromatic hydrocarbon polymers”, and the Chinese patent application filed with the Patent Office of China on January 17, 2024, with application number 202410070565.0 and application name “A method for preparing aromatic hydrocarbon polymers”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application belongs to the technical field of polymer preparation and relates to a method for preparing aromatic hydrocarbon oligomers. Background Art

[0003] Mesophase pitch is a typical carbonaceous mesophase raw material and an important precursor for obtaining pitch-based carbon fibers. Its quality directly determines the mechanical properties of the final carbon fiber product. Currently, the raw materials for preparing mesophase pitch mainly include petroleum pitch, coal pitch, and pure aromatic compounds. Among them, pure aromatic compounds are considered to be ideal raw materials for preparing high-quality mesophase pitch due to their simple molecular structure, containing only carbon and hydrogen elements, no ash, and high aromaticity. When preparing mesophase pitch, pure aromatic compounds, such as naphthalene, must first be polymerized under the catalysis of an acidic catalyst to obtain naphthalene polymers, and then the mesophase pitch is obtained through a high-temperature thermal polycondensation reaction. The molecular weight and molecular weight distribution of the naphthalene polymers have a significant impact on the performance of the mesophase pitch. Generally speaking, the more concentrated the molecular weight distribution of the naphthalene polymers, the more concentrated the molecular weight distribution of the mesophase pitch will be, the better its homogeneity will be, and the smaller the viscosity fluctuation during the subsequent spinning process will be, which can achieve stable and long-lasting spinning operation and produce high-performance pitch-based carbon fibers. Therefore, how to prepare aromatic oligomers with controllable molecular weight and concentrated molecular weight distribution is of great significance for obtaining mesophase pitch with excellent spinning performance.

[0004] At present, there are many reports on the preparation of mesophase pitch using pure aromatic compounds as raw materials. For example, patent CN102899061A discloses a method for preparing high-purity mesophase pitch, which uses refined naphthalene as raw material and anhydrous aluminum oxide as catalyst to catalyze the polymerization of naphthalene in an oil bath at 100-220°C to prepare naphthalene pitch, and then further heat-condenses at 350-480°C to obtain mesophase pitch; patent CN1208065A discloses a method for preparing mesophase pitch using solid super acid, which uses pure aromatics or petroleum residue and petroleum asphalt with a softening point less than 200°C as raw materials, ZrO2 / SO4 2- or TiO2 / SO4 2-Using 2-nitrogen as catalyst, the reaction is carried out at a constant temperature of 90-300°C to obtain aromatic oligomers, which are then pyrolyzed at 400-500°C under normal pressure to obtain the corresponding mesophase asphalt.

[0005] However, these preparation methods lack control over the molecular weight and molecular weight distribution of the aromatic oligomers. The resulting naphthalene oligomers are complex in composition, resulting in poor homogenization of the mesophase pitch prepared using them. This leads to significant viscosity fluctuations during the spinning process, making stable and continuous spinning difficult, and ultimately preventing the production of high-quality pitch-based carbon fiber products. Therefore, the development of aromatic oligomers with a simpler, more regular composition and a more concentrated molecular weight distribution, providing a superior precursor for the preparation of high-quality mesophase pitch, remains a significant challenge for those skilled in the art.

[0006] Summary of the Invention

[0007] In response to the defects existing in the prior art, the present application provides a method for preparing aromatic polymers, which can efficiently prepare aromatic polymers with simple composition and narrow molecular weight distribution under mild conditions, thereby providing high-quality precursors for the preparation of high-quality mesophase asphalt.

[0008] The present application provides a method for preparing an aromatic hydrocarbon oligomer, the method comprising: causing an aromatic hydrocarbon compound to undergo an oligomerization reaction under the catalysis of a chloroaluminate ionic liquid to obtain the aromatic hydrocarbon oligomer;

[0009] The oligomerization reaction is carried out in a solvent system, and the solvent is selected from chlorinated hydrocarbon solvents;

[0010] The aromatic hydrocarbon compound is selected from condensed-ring aromatic hydrocarbons having 2 to 4 rings.

[0011] In the preparation method as described above, the chlorinated hydrocarbon solvent is selected from one or more of dichloromethane, chloroform, and dichloroethane.

[0012] In the preparation method as described above, the aromatic hydrocarbon compound is selected from one or more of naphthalene, methylnaphthalene, anthracene, phenanthrene, and pyrene.

[0013] As described above, the preparation method, wherein the molecular formula of the chloroaluminate ionic liquid is Et3NHCl-xAlCl3, wherein 1<x≤2.

[0014] In the preparation method as described above, the amount of the chloroaluminate ionic liquid used is 5 mol% to 25 mol% of the amount of the aromatic compound used.

[0015] In the preparation method as described above, the temperature of the oligomerization reaction is 30-180°C.

[0016] The preparation method as described above, wherein the time of the oligomerization reaction is 1 to 11 hours.

[0017] In the preparation method as described above, the temperature of the oligomerization reaction is 30 to 90° C., and the time of the oligomerization reaction is 1 to 3 hours.

[0018] In the preparation method as described above, the volume ratio of the solvent to the chloroaluminate ionic liquid is (50-500):1.

[0019] The preparation method as described above, wherein, after the polymerization reaction is completed, further includes a process of post-treating the reaction system, wherein the post-treatment includes: adding alkaline solution to the reaction solution after the polymerization reaction is completed, causing it to react with the ionic liquid in the reaction solution, then allowing it to stand and separate into layers, collecting the organic phase, and washing, concentrating, and drying the organic phase to obtain the aromatic hydrocarbon oligomer.

[0020] The preparation method as described above, wherein

[0021] The implementation of this application has at least the following beneficial effects:

[0022] The method for preparing an aromatic oligomer provided by the present application, under the catalysis of a chloroaluminate ionic liquid, causes an aromatic compound to undergo an oligomerization reaction in a chlorinated hydrocarbon solvent system, wherein the chlorinated hydrocarbon solvent has good solubility for the chloroaluminate ionic liquid and the aromatic compound, and the chlorine atom in the solvent forms a weak coordination with the aluminum in the chloroaluminate ionic liquid, thereby reducing the acidity of the chloroaluminate ionic liquid, suppressing the occurrence of side reactions such as ring opening and cracking, and improving the selectivity of the oligomerization reaction, thereby making the obtained naphthalene oligomer have the advantages of simple and regular composition and narrow molecular weight distribution. The mesophase pitch prepared using the naphthalene oligomer of the present application as raw material has a high mesophase content and a narrow molecular weight distribution, and thus its homogeneity and quality are higher, which is conducive to obtaining high-quality carbon fiber products by continuous and stable spinning. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG1 is a comparison diagram of matrix-assisted laser desorption / time-of-flight mass spectra of naphthalene oligomers of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3;

[0024] FIG2 is a comparison of matrix-assisted laser desorption / ionization time-of-flight mass spectra of naphthalene oligomers catalyzed by different types of chloroaluminate ionic liquids;

[0025] FIG3 is a comparison diagram of matrix-assisted laser desorption / emission time-of-flight mass spectra of naphthalene oligomers obtained under different catalyst dosages;

[0026] FIG4 is a comparison diagram of matrix-assisted laser desorption / emission time-of-flight mass spectra of naphthalene oligomers obtained at different polymerization temperatures;

[0027] FIG5 is a comparison diagram of matrix-assisted laser desorption / emission time-of-flight mass spectra of naphthalene oligomers obtained at different polymerization times;

[0028] FIG6 is a matrix-assisted laser desorption / ionization time-of-flight mass spectrometer of naphthalene oligomers obtained using chloroform as solvent;

[0029] FIG7 is a matrix-assisted laser desorption / ionization time-of-flight mass spectrometry of naphthalene oligomers obtained using dichloroethane as solvent;

[0030] FIG8 is a matrix-assisted laser desorption / ionization time-of-flight mass spectrum of the pyrene oligomer prepared in Example 9;

[0031] FIG9 is a matrix-assisted laser desorption / ionization time-of-flight mass spectrum of anthracene oligomer prepared in Example 10;

[0032] FIG10 is a time-of-flight mass spectrum of the mesophase pitch prepared using the naphthalene oligomer of Example 1 as a raw material;

[0033] FIG11 is a time-of-flight mass spectrum of the mesophase pitch prepared using the naphthalene oligomer of Comparative Example 1 as a raw material;

[0034] FIG12 is a time-of-flight mass spectrum of the mesophase pitch prepared using the naphthalene oligomer of Comparative Example 2 as a raw material;

[0035] FIG13 is a time-of-flight mass spectrum of the mesophase pitch prepared using the naphthalene oligomer of Comparative Example 3 as a raw material;

[0036] FIG14 is a polarized micrograph of the mesophase pitch prepared using the naphthalene oligomer of Example 1 as a raw material;

[0037] FIG15 is a polarized micrograph of the mesophase pitch prepared using the naphthalene oligomer of Comparative Example 1 as a raw material;

[0038] FIG16 is a polarized micrograph of the mesophase pitch prepared using the naphthalene oligomer of Comparative Example 2 as a raw material;

[0039] FIG17 is a polarized micrograph of the mesophase pitch prepared using the naphthalene oligomer of Comparative Example 3 as a raw material. DETAILED DESCRIPTION

[0040] To make the purpose, technical solutions, and advantages of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0041] Pure aromatic compounds have the characteristics of simple molecular structure, only containing carbon and hydrogen elements, no ash, and high aromaticity. They are ideal raw materials for preparing high-quality mesophase asphalt. Pure aromatic compounds are obtained by polymerization to obtain oligomers, and then thermally condensed to obtain mesophase asphalt. Among them, the molecular weight distribution of the oligomers has an important influence on the processing properties of the mesophase asphalt. Catalysts such as aluminum trichloride, hydrofluoric acid, and solid superacids are conventional catalysts for catalyzing pure aromatic compounds. However, these catalysts have the defects of low catalytic activity, high corrosiveness, and difficulty in separating from the product. As a new type of catalyst, chloroaluminate ionic liquid has both the high reactivity of liquid acid and the non-volatility of solid acid. Its structure and acidity are adjustable. It shows high catalytic activity in the polymerization reaction of aromatic compounds, can significantly improve the preparation efficiency of aromatic oligomers, and compared with the aforementioned conventional catalysts, it also has the advantages of being environmentally friendly, less corrosive, and reusable. However, although chloroaluminate ionic liquid can significantly improve the preparation efficiency of aromatic polymers, the obtained aromatic polymers still have disadvantages such as complex composition, many by-products of ring opening and cracking, and wide molecular weight distribution, which is not conducive to obtaining high-quality intermediate phase asphalt.

[0042] Based on this, the present application provides a method for preparing an aromatic hydrocarbon oligomer, comprising: causing an aromatic hydrocarbon compound to undergo an oligomerization reaction under the catalysis of a chloroaluminate ionic liquid to obtain an aromatic hydrocarbon oligomer;

[0043] The oligomerization reaction is carried out in a solvent system, the solvent is selected from chlorinated hydrocarbon solvents; and the aromatic compound is selected from condensed-ring aromatic hydrocarbons with 2 to 4 rings.

[0044] The inventors have discovered that when a chlorinated hydrocarbon solvent is used as the reaction solvent for the oligomerization reaction, aromatic oligomers with a narrow molecular weight distribution, simple composition, and few byproducts can be obtained in high yield, facilitating the preparation of high-quality mesophase pitch. This may be due to the following: Firstly, the chlorine atoms in the chlorinated hydrocarbon solvent form a weak coordination with the aluminum in the chloroaluminate ionic liquid, reducing its acidity and inhibiting side reactions such as ring-opening, cracking, and hydrogen transfer reactions, thereby improving the selectivity of the oligomerization reaction and facilitating the production of aromatic oligomers with a narrow molecular weight distribution and simple, regular composition; secondly, the chlorinated hydrocarbon solvent has good solubility for both the chloroaluminate ionic liquid and the aromatic compound, enabling the reaction system to proceed under homogeneous conditions. Homogeneous conditions not only promote efficient reaction performance but also regulate the viscosity of the reaction system and the concentrations of the catalyst and substrate, thereby improving the selectivity of the oligomerization reaction.

[0045] During the research process, the inventors also tried commonly used organic solvents such as toluene, xylene, trimethylbenzene, DMSO, DMF, ethanol, n-hexane, petroleum ether, isobutane, and cyclohexane. Among them, solvents such as DMSO, DMF, and ethanol react with chloroaluminate ionic liquids, making it difficult for the chloroaluminate ionic liquids to exert their catalytic effect. Alkane solvents such as n-hexane, petroleum ether, isobutane, and cyclohexane cannot act as solvents because they are poorly soluble in chloroaluminate ionic liquids and oligomers. Solvents such as toluene, xylene, and trimethylbenzene have poor solubility in chloroaluminate ionic liquids, making it difficult to carry out the reaction in a homogeneous system, resulting in low preparation efficiency of aromatic oligomers. In addition, the prepared aromatic oligomers have a complex composition and a wide molecular weight distribution.

[0046] The composition information and molecular weight distribution of the above-mentioned aromatic hydrocarbon oligomers can be obtained by utilizing matrix-assisted laser desorption / emission time-of-flight mass spectrometer analysis. Fig. 1 is the matrix-assisted laser desorption / emission time-of-flight mass spectrogram of the naphthalene oligomers of embodiment 1, comparative example 1, comparative example 2, and comparative example 3. Taking Fig. 1 as an example, the composition information and molecular weight distribution of the naphthalene oligomers are analyzed as follows: 10 peak clusters can be seen on the mass spectrum of embodiment 1, representing 2 to 9 polymers of naphthalene respectively, wherein, the peak cluster of m / z in the range of 254 to 350 is the dimer of naphthalene, the peak cluster of m / z in the range of 350 to 490 is the trimer of naphthalene, the peak cluster of m / z in the range of 490 to 620 is the tetramer of naphthalene, and the peak cluster of m / z in the range of 620 to 850 is the tetramer of naphthalene. The peak cluster in the range of 0 to 740 is a pentamer of naphthalene, the peak cluster in the range of m / z 740 to 870 is a hexamer of naphthalene, the peak cluster in the range of m / z 870 to 1020 is a heptamer of naphthalene, and the three peak clusters in the range of m / z 1020 to 1400 are, from left to right, an octamer, a nonamer, and a decamer of naphthalene. As can be seen from Figure 1, peak intensity weakens successively from left to right, and especially 8 to 10-mer peak intensity of naphthalene is obviously very weak, indicating that its content in naphthalene oligomers is very low. Therefore, the naphthalene oligomer composition of Example 1 is mainly 2 to 7. Although the molecular weight range of the naphthalene oligomers of Comparative Examples 1 to 3 is basically the same as that of Example 1, the boundaries between the peak clusters in the mass spectrum of Example 1 are clear, while the molecular weight distribution of Comparative Examples 1 to 3 is dispersed, and the peak clusters of each polymer of naphthalene cannot be clearly seen. This shows that the naphthalene oligomers of Comparative Examples 1 to 3 are more complex in composition than those of Example 1, and may contain many undesirable substances that should be produced as by-products such as ring opening and cracking.

[0047] The present application does not impose any particular limitation on the chlorinated hydrocarbon solvent, which may be selected from the low-carbon chlorinated hydrocarbon solvents conventionally used in the art, including but not limited to one or more of dichloromethane, chloroform, and dichloroethane.

[0048] The inventors have found that the amount of solvent used has no significant effect on the yield and selectivity of the reaction. Therefore, the present application does not impose any particular limitation on the amount of solvent used. In a preferred embodiment, the volume ratio of solvent to chloroaluminate ionic liquid is (50-500):1. When the amount of solvent used meets the above ratio range, the reaction is carried out under homogeneous conditions while also achieving an appropriate catalytic concentration of the chloroaluminate ionic liquid, further ensuring high catalytic activity and reaction selectivity in the oligomerization reaction.

[0049] The aromatic compounds used in this application are condensed-ring aromatic hydrocarbons with two to four rings, including but not limited to one or more of naphthalene, methylnaphthalene, anthracene, phenanthrene, and pyrene, with naphthalene being preferred. The oligomers prepared from these aromatic compounds have the advantages of simple, regular composition and narrow molecular weight distribution, making them excellent raw materials for the preparation of high-quality mesophase pitch.

[0050] Chloroaluminate ionic liquid is a Lewis acid catalyst, the acidity of which comes from [Al x Cl 3x+1 ] - , for example [AlCl4] - and [Al2Cl7] - , whose cations can be derived from ammonium salts.

[0051] In a specific embodiment, the molecular formula of the chloroaluminate ionic liquid used in this application is Et3NHCl-xAlCl3, where 1<x≤2. Here, x can be selected from 1.1, 1.2, 1.4, 1.6, 1.8, 2.0, or a range consisting of any two thereof. Chloroaluminate ionic liquids having the above compositions can efficiently catalyze the oligomerization of aromatic compounds, and the resulting aromatic oligomers have the advantages of simple, regular composition and narrow molecular weight distribution.

[0052] The chloroaluminate ionic liquid having the above composition can be obtained by reacting anhydrous aluminum chloride with triethylammonium chloride. Specifically, the value of x can be controlled by controlling the reaction molar ratio of anhydrous aluminum chloride to triethylammonium chloride. For example, the reaction molar ratio of anhydrous aluminum chloride to triethylammonium chloride can be controlled to 1:1.2 to produce an ionic liquid with the molecular formula Et3NHCl-1.2AlCl3.

[0053] In a specific embodiment, the amount of chloroaluminate ionic liquid used is 5 mol% to 25 mol% of the amount of the aromatic compound used, specifically 5 mol%, 10 mol%, 15 mol%, 20 mol%, 25 mol% or any two thereof.

[0054] The highly conjugated structure of condensed aromatic hydrocarbons makes them very stable, and obtaining oligomers through polycondensation requires relatively high temperatures. The introduction of a catalyst can reduce the energy required for the oligomerization reaction, thereby reducing the severity and energy consumption of the reaction and allowing the reaction to proceed at a lower temperature. However, in previously reported reactions using chloroaluminate ionic liquids to catalyze the oligomerization of aromatic compounds, the reaction temperature is generally still not lower than 100°C. The present application, by introducing a chlorinated hydrocarbon solvent into the reaction system, can enable the reaction to proceed efficiently at temperatures below 100°C, and even at 30°C, aromatic oligomers with a simple composition and a narrow molecular weight distribution can be efficiently obtained with a high yield, greatly reducing the severity and energy consumption of the reaction. Specifically, the oligomerization reaction of the present application can proceed smoothly within a temperature range of 30 to 180°C.

[0055] In a specific embodiment, the oligomerization reaction time of the present application is 1 to 11 hours, for example, 1 hour, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 9 hours, 11 hours or the range consisting of any two thereof.

[0056] Furthermore, the oligomerization reaction of the present application can produce aromatic oligomers with high yield and high selectivity under the conditions of a temperature of 30-90°C and a time of 1-3 hours. The reaction under the above conditions can further reduce the energy consumption of the reaction and improve the efficiency of the preparation.

[0057] The oligomerization reaction pressure is not particularly limited in this application; the reaction can be carried out under normal pressure, and the reaction process can be completed in a reactor. To minimize interference from other impurities, the oligomerization reaction can be carried out under an inert gas atmosphere.

[0058] After the polymerization reaction is completed, the reaction system is subjected to a post-treatment process. In a specific embodiment, the post-treatment includes: adding alkaline solution to the reaction solution after the polymerization reaction is completed, so that it reacts with the ionic liquid in the reaction solution, then allowing it to stand and separate into layers, collecting the organic phase, and washing, concentrating, and drying the organic phase to obtain aromatic hydrocarbon polymers.

[0059] Furthermore, the alkali solution can be selected from a sodium hydroxide solution or a potassium hydroxide solution with a concentration of 0.5 to 2 mol / L.

[0060] After the alkali solution is added to the reaction solution, it will react with the AlCl3 in the ionic liquid structure, first converting it into solid precipitated aluminum hydroxide, and then continuing to react, converting it into aluminate and dissolving it in the inorganic phase. After standing and stratification, the organic phase including the aromatic hydrocarbon polymers is collected, and then the organic phase is washed with water to neutrality, concentrated to remove the reaction solvent, and then dried to remove residual water to obtain the aromatic hydrocarbon polymers.

[0061] In summary, the preparation method of aromatic oligomers provided in the present application is to obtain aromatic oligomers with narrow molecular weight distribution and simple and regular composition in a high yield by allowing aromatic compounds to undergo polymerization reaction in a chlorinated hydrocarbon solvent system under the catalysis of chloroaluminate ionic liquid. The aromatic oligomers can be prepared into mesophase asphalt through a simple thermal polycondensation reaction. The prepared mesophase asphalt has the advantages of high mesophase content, narrow molecular weight distribution and good homogeneity, which is conducive to stable and long-lasting spinning operations, and thus prepare carbon fiber products with excellent performance.

[0062] The preparation method of the aromatic hydrocarbon oligomer provided in this application will be described in detail below with reference to specific examples.

[0063] In the following examples, unless otherwise specified, all raw materials can be purchased commercially or prepared by conventional methods. Experimental methods without specific conditions are carried out according to conventional methods and conditions in the art or according to the product specifications.

[0064] Example 1

[0065] This embodiment provides a method for preparing a naphthalene oligomer, comprising the following steps:

[0066] 1) Under nitrogen protection at normal pressure, 10 g of naphthalene (1 eq.) and 1.58 g (1 mL) of Et3NHCl-2.0AlCl3 (25 mol%) were added to a polytetrafluoroethylene-lined autoclave, and 50 mL of dichloromethane was added as a reaction solvent, and a catalytic polymerization reaction was carried out at 160°C;

[0067] 2) after reaction finishes, reaction mixture is transferred in the glass beaker, slowly to the NaOH aqueous solution of wherein dripping 2mol / L, there is solid precipitation to separate out, constantly stir with glass rod during this period, after solid precipitation disappears completely, stop to add the NaOH aqueous solution, collect organic phase after stratification, use deionized water that organic phase is washed to it and be neutral, finally remove dichloromethane solvent and moisture in the organic phase by revolving steam and vacuum-drying, obtain naphthalene oligomers, its yield is 48%.Sampling adopts matrix-assisted laser desorption / emission time-of-flight mass spectrometer that the composition of naphthalene oligomers is analyzed, Fig. 1 is the matrix-assisted laser desorption / emission time-of-flight mass spectrum comparison diagram of the naphthalene oligomers of embodiment 1, comparative example 1, comparative example 2, comparative example 3, as can be seen from Figure 1, the composition of the naphthalene oligomers of present embodiment mainly is 2~7 aggressiveness of naphthalene, and peak cluster is clear between each aggressiveness.

[0068] It should be noted that the composition of the naphthalene oligomers listed in this embodiment and the following embodiments is its main composition, rather than the absolute composition. Taking this embodiment as an example, the composition of the naphthalene oligomers is mainly 2-7 polymers of naphthalene, but it does not exclude that it also contains a low content of oligomers with a higher degree of polymerization.

[0069] Example 2: Screening of catalyst types

[0070] The naphthalene oligomer was prepared by referring to the preparation method of Example 1 and the catalyst type was screened. The specific reaction conditions are listed in Table 1.

[0071] The yield of naphthalene oligomers was calculated, and samples were taken for analysis of their composition using matrix-assisted laser desorption / ionization time-of-flight mass spectrometry. Figure 2 shows a comparison of matrix-assisted laser desorption / ionization time-of-flight mass spectra of naphthalene oligomers catalyzed by different types of chloroaluminate ionic liquids. As shown in Figure 2, naphthalene oligomers catalyzed by chloroaluminate ionic liquids with x in the range of 1.2 to 2.0 exhibit simple, regular compositions, with distinct peak clusters between the oligomers. The yield and composition of naphthalene oligomers are listed in Table 1.

[0072] Table 1

[0073] It can be seen from Table 1 that with the increase of x, the yield of naphthalene oligomers is getting higher and higher.

[0074] Example 3: Screening of catalyst dosage

[0075] The naphthalene oligomer was prepared by referring to the preparation method of Example 1 and the amount of catalyst was screened. The specific reaction conditions are listed in Table 2.

[0076] Calculate the yield of naphthalene oligomers and sample and adopt matrix-assisted laser desorption / emission time-of-flight mass spectrometer to analyze the composition of naphthalene oligomers. Fig. 3 is the matrix-assisted laser desorption / emission time-of-flight mass spectrometer comparison diagram of the naphthalene oligomers obtained under different catalyst dosages. As can be seen from Fig. 3, the naphthalene oligomers obtained in the scope of 1 mol% to 25 mol% of catalyst dosage have simple and regular compositions, and peak clusters are clear between each polymer. The yield of naphthalene oligomers and composition are listed in Table 2.

[0077] Table 2

[0078] It can be seen from Table 2 that with the increase of the amount of catalyst, the yield of naphthalene oligomers also gradually increases.

[0079] Example 4: Screening of polymerization temperature

[0080] The naphthalene oligomer was prepared by referring to the preparation method of Example 1 and the polymerization temperature was screened. The specific reaction conditions are listed in Table 3.

[0081] Calculate the yield of naphthalene oligomer and sample and adopt matrix-assisted laser desorption / emission time-of-flight mass spectrometer to analyze the composition of naphthalene oligomer, Fig. 4 is the matrix-assisted laser desorption / emission time-of-flight mass spectrometer comparison diagram of the naphthalene oligomer obtained under different polymerization temperatures, on the basis of Fig. 4, in conjunction with Fig. 2 and Fig. 3, can find out that the naphthalene oligomer composition obtained in the scope of 30~180 ℃ is simple and regular, peak cluster is distinct between each polymer, and along with the rising of reaction temperature, the polymerization degree of naphthalene also increases thereupon, the content of hexameric and heptamer of naphthalene is more and more higher, and the 2~5 polymer content of naphthalene does not obviously reduce, illustrate that along with the rising of temperature, the molecular weight distribution of naphthalene oligomer can broaden.The yield of naphthalene oligomer and composition are listed in table 3.

[0082] Table 3

[0083] As can be seen from Table 3, with the increase of reaction temperature, the yield of naphthalene oligomers is getting higher and higher.

[0084] Example 5: Screening of polymerization time

[0085] The naphthalene oligomer was prepared by referring to the preparation method of Example 1 and the polymerization time was screened. The specific reaction conditions are listed in Table 4.

[0086] The yield of naphthalene oligomers was calculated, and samples were taken for analysis of their composition using matrix-assisted laser desorption / ionization time-of-flight mass spectrometry. Figure 5 shows a comparison of matrix-assisted laser desorption / ionization time-of-flight mass spectra of naphthalene oligomers obtained at different polymerization times. As shown in Figure 5, within a reaction time of 1 to 11 hours, naphthalene oligomers with a degree of polymerization of 2 to 5 were consistently obtained. The peaks of the oligomers were distinct, and the composition was simple and regular. The yield and composition of the naphthalene oligomers are listed in Table 4.

[0087] Table 4

[0088] As can be seen from Table 4, as the polymerization time increases, the yield of naphthalene oligomers increases.

[0089] Example 6: Screening of reaction solvent dosage

[0090] The naphthalene oligomer was prepared by referring to the preparation method of Example 1, and the amount of the reaction solvent was screened. The specific reaction conditions and the yield of the naphthalene oligomer are listed in Table 5.

[0091] Table 5

[0092] As can be seen from Table 5, the amount of solvent used has no significant effect on the reaction yield.

[0093] Example 7

[0094] This embodiment provides a method for preparing naphthalene oligomers. The preparation method is basically the same as the preparation steps in Example 1, except that the reaction solvent is replaced by chloroform instead of dichloromethane, and naphthalene is catalyzed and polymerized under the same reaction conditions to obtain naphthalene oligomers.

[0095] The yield of the naphthalene oligomers in this embodiment was 47%. The naphthalene oligomers of this embodiment were sampled and analyzed using a matrix-assisted laser desorption / ionization time-of-flight mass spectrometer. FIG6 is a matrix-assisted laser desorption / ionization time-of-flight mass spectrometer of the naphthalene oligomers prepared in Example 7. As can be seen from FIG6 , the polymers of the naphthalene oligomers are clearly distributed, and are mainly 2-6 polymers of naphthalene.

[0096] Example 8

[0097] This embodiment provides a method for preparing naphthalene oligomers. The preparation method is basically the same as the preparation steps in Example 1, except that the reaction solvent is replaced by dichloroethane instead of dichloromethane, and naphthalene is catalyzed and polymerized under the same reaction conditions to obtain naphthalene oligomers.

[0098] The yield of the naphthalene oligomers in this embodiment was 46%. The naphthalene oligomers of this embodiment were sampled and analyzed using a matrix-assisted laser desorption / ionization time-of-flight mass spectrometer. FIG7 is a matrix-assisted laser desorption / ionization time-of-flight mass spectrometer of the naphthalene oligomers prepared in Example 8. As can be seen from FIG7 , the polymers of the naphthalene oligomers are clearly distributed, and are mainly 2-6 polymers of naphthalene.

[0099] Example 9

[0100] This embodiment provides a method for preparing pyrene oligomers. The preparation method is basically the same as the preparation steps in Example 1, except that naphthalene is replaced as the polymerization raw material with pyrene, and pyrene is catalyzed and polymerized under the same reaction conditions to obtain pyrene oligomers.

[0101] The yield of pyrene oligomers in this example was 70%. The pyrene oligomers in this example were sampled and analyzed using matrix-assisted laser desorption / ionization time-of-flight mass spectrometry. Figure 8 shows the matrix-assisted laser desorption / ionization time-of-flight mass spectrum of the pyrene oligomers prepared in Example 9. As can be seen from Figure 8, the pyrene oligomers are 2-4-mers of pyrene, and the individual oligomers are clearly distributed.

[0102] Example 10

[0103] This embodiment provides a method for preparing anthracene oligomers. The preparation method is basically the same as the preparation steps in Example 1, except that the polymerization raw material is replaced by anthracene instead of naphthalene, and pyrene is catalyzed and polymerized under the same reaction conditions to obtain anthracene oligomers.

[0104] The yield of anthracene oligomers in this example was 57%. Samples of the anthracene oligomers in this example were analyzed using matrix-assisted laser desorption / ionization time-of-flight mass spectrometry. FIG9 is a matrix-assisted laser desorption / ionization time-of-flight mass spectrometry of the anthracene oligomers prepared in Example 10. FIG9 shows that the anthracene oligomers are 2-4-mers of anthracene, and the oligomers are clearly distributed.

[0105] Comparative Example 1

[0106] This comparative example provides a method for preparing a naphthalene oligomer, which is substantially the same as the preparation steps in Example 1, except that the naphthalene oligomer in this comparative example is prepared in the absence of a solvent, and the other conditions are the same as in Example 1. The yield of the naphthalene oligomer in this comparative example is 36%.

[0107] Comparative Example 2

[0108] This comparative example provides a method for preparing a naphthalene oligomer. The preparation steps of the method are basically the same as those of Example 1, except that the reaction solvent is replaced by toluene instead of dichloromethane, and naphthalene is catalyzed and polymerized under the same reaction conditions to obtain the naphthalene oligomer. The yield of the naphthalene oligomer in this comparative example is 35%.

[0109] Comparative Example 3

[0110] This comparative example provides a method for preparing a naphthalene oligomer. The preparation steps of the method are basically the same as those of Example 1, except that the reaction solvent is replaced by xylene instead of dichloromethane, and naphthalene is catalyzed and polymerized under the same reaction conditions to obtain the naphthalene oligomer. The yield of the naphthalene oligomer in this comparative example is 38%.

[0111] The naphthalene oligomers of Comparative Examples 1, 2, and 3 were sampled and analyzed by matrix-assisted laser desorption / emission time-of-flight mass spectrometry. Fig. 1 is a matrix-assisted laser desorption / emission time-of-flight mass spectrometer comparison diagram of the naphthalene oligomers of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3. As can be seen from Fig. 1, compared to taking dichloromethane as solvent, the molecular weight distribution of the naphthalene oligomers obtained when solvent-free, taking toluene as solvent, and taking dimethylbenzene as solvent is comparatively dispersed, and the peak clusters of each polymer of naphthalene are not clear, and the composition of naphthalene oligomers is complicated.

[0112] Test Case

[0113] Mesophase pitch was prepared using the naphthalene polymers prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 as raw materials. The preparation method was as follows: 120 g of naphthalene polymer was added to a reactor, the air in the reactor was removed by purging with nitrogen, and then the reactor was sealed. A thermal polycondensation reaction was carried out at a temperature of 400° C. for 4 h to prepare the mesophase pitch. The preparation yield is shown in Table 6.

[0114] Table 6

[0115] It can be seen from Table 6 that the yield of mesophase pitch obtained by Example 1 is significantly higher than that of Comparative Examples 1-3.

[0116] The prepared mesophase pitch was sampled and analyzed for molecular weight and distribution using a time-of-flight mass spectrometer. FIG10 is a time-of-flight mass spectrum of the mesophase pitch prepared using the naphthalene oligomer of Example 1 as a raw material, FIG11 is a time-of-flight mass spectrum of the mesophase pitch prepared using the naphthalene oligomer of Comparative Example 1 as a raw material, FIG12 is a time-of-flight mass spectrum of the mesophase pitch prepared using the naphthalene oligomer of Comparative Example 2 as a raw material, and FIG13 is a time-of-flight mass spectrum of the mesophase pitch prepared using the naphthalene oligomer of Comparative Example 3 as a raw material. As can be seen from FIG10 to FIG13, the molecular weight distribution of the mesophase pitch prepared using the naphthalene oligomer of Example 1 as a raw material is 500-6000, mainly concentrated in the range of 1500-4000, and the molecular weight distribution of the mesophase pitch prepared using the naphthalene oligomer of Comparative Examples 1-3 as a raw material is 300-6000, mainly concentrated in the range of 400-4000. The molecular weight distribution is obviously narrower than that of comparative examples 1 to 3, and the mesophase pitch with a more concentrated molecular weight distribution has better spinning stability, which shows the advantages of the mesophase pitch of Example 1.

[0117] The type and mesophase content of the prepared mesophase pitch were analyzed using a polarizing microscope. Figure 14 is a polarized micrograph of the mesophase pitch prepared using the naphthalene oligomer of Example 1 as raw material, Figure 15 is a polarized micrograph of the mesophase pitch prepared using the naphthalene oligomer of Comparative Example 1 as raw material, Figure 16 is a polarized micrograph of the mesophase pitch prepared using the naphthalene oligomer of Comparative Example 2 as raw material, and Figure 17 is a polarized micrograph of the mesophase pitch prepared using the naphthalene oligomer of Comparative Example 3 as raw material. It can be seen from Figures 14 to 17 that the mesophase pitch prepared using the naphthalene oligomer of Example 1 as raw material is a wide-area type, wherein the mesophase content is close to 100%, while the mesophase pitches prepared using the naphthalene oligomers of Comparative Examples 1 to 3 as raw materials are streamlined, wherein the mesophase content is all about 97%.

[0118] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing an aromatic hydrocarbon oligomer, wherein: The preparation method comprises: under the catalysis of chloroaluminate ionic liquid, causing an aromatic compound to undergo an oligomerization reaction to obtain the aromatic oligomer; The oligomerization reaction is carried out in a solvent system, and the solvent is selected from chlorinated hydrocarbon solvents; The aromatic hydrocarbon compound is selected from condensed ring aromatic hydrocarbons having 2 to 4 rings.

2. The preparation method according to claim 1, wherein The chlorinated hydrocarbon solvent is selected from one or more of dichloromethane, chloroform and dichloroethane.

3. The preparation method according to claim 1, wherein The aromatic hydrocarbon compound is selected from one or more of naphthalene, methylnaphthalene, anthracene, phenanthrene and pyrene.

4. The preparation method according to claim 1, wherein The molecular formula of the chloroaluminate ionic liquid is Et3NHCl-xAlCl3, wherein 1<x≤2.

5. The preparation method according to any one of claims 1 to 4, wherein: The amount of the chloroaluminate ionic liquid used is 5 mol% to 25 mol% of the amount of the aromatic compound used.

6. The preparation method according to claim 1, wherein The temperature of the oligomerization reaction is 30-180°C.

7. The preparation method according to claim 1 or 6, wherein: The polymerization reaction time is 1 to 11 hours.

8. The preparation method according to claim 6 or 7, wherein: The temperature of the polymerization reaction is 30 to 90° C., and the time of the polymerization reaction is 1 to 3 hours.

9. The preparation method according to claim 1 or 2, wherein: The volume ratio of the solvent to the chloroaluminate ionic liquid is (50-500):

1.

10. The preparation method according to claim 1, wherein: After the polymerization reaction is completed, the process of post-treating the reaction system is also included, and the post-treatment includes: adding alkali solution to the reaction solution after the polymerization reaction is completed, so that it reacts with the ionic liquid in the reaction solution, and then collecting the organic phase after standing and stratifying, and washing, concentrating and drying the organic phase to obtain the aromatic hydrocarbon polymer.

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