General-purpose pitch based on ethylene cracking tar, mesophase pitch and method for producing the same

Abstract

The present application belongs to the technical field of asphalt production, and relates to a general grade asphalt, mesophase pitch and a preparation method based on ethylene cracking tar. The preparation method comprises the following steps: mixing ethylene cracking tar with hydrogen, and performing hydrogenation reaction in the presence of a hydrogenation catalyst; separating the product after the hydrogenation reaction to obtain gas, naphtha, diesel, high-aromatics distillate oil and an external tail oil; the general grade asphalt is prepared by one-step thermal polymerization of the high-aromatics distillate oil, has an anisotropy content of less than or equal to 10%, a softening point of 100-260 DEG C, and the characteristics of low ash content and low impurity; the mesophase pitch is prepared by two-step reactions of pre-polymerization and thermal polymerization of the high-aromatics distillate oil, has an anisotropy content of greater than or equal to 90%, a softening point of 270-310 DEG C, and an ash content of less than 50 ppm. The present application can stably prepare high-purity, structure-controllable and high-quality general grade asphalt and mesophase pitch.

Description

Technical Field

[0001] This invention belongs to the field of asphalt production technology, and relates to a general-purpose asphalt, mesophase asphalt and preparation method based on ethylene cracking tar. Background Technology

[0002] Mesophase pitch, as a high-performance carbon material precursor, has its raw material selection and pretreatment process directly affecting the performance and preparation efficiency of the final product. Currently, the raw materials for generating mesophase pitch mainly include heavy aromatic hydrocarbons, such as coal tar pitch, petroleum pitch, and pure aromatic hydrocarbons, as well as their blends. Coal tar pitch, as a heavy component of coal tar, has a complex chemical composition, mainly composed of polycyclic aromatic hydrocarbons and containing small amounts of small molecules; it is typically prepared using medium-temperature coal tar pitch. Petroleum pitch is a residue obtained from natural crude oil through fractional distillation; its chemical composition is also complex, containing numerous alkyl substituents and some hydrogenated aromatics, thus its aromaticity is relatively lower than that of coal tar pitch. Pure aromatic hydrocarbons, on the other hand, possess the characteristics of high purity of polycyclic aromatic hydrocarbons (PAHs) and the absence of ash and other residues; common pure aromatic compounds include naphthalene, phenene, tetrabenzophenone, and phenanthrene. When selecting raw materials, it is necessary to comprehensively consider whether the raw materials contain aromatic molecules or substances that can generate aromatic molecules, and at the same time ensure that they contain an appropriate amount of aliphatic chains or cycloalkanes to increase the fluidity of the system.

[0003] However, existing raw material systems and corresponding processes still have many limitations. For example, ethylene tar, as a potential resource, is currently mainly used to produce low-tech, low-value-added products such as pitch, carbon black, and fuels, failing to fully realize and utilize its intrinsic value. Therefore, developing a method to convert ethylene cracking tar into high-aromatic distillate oil through hydrogenation technology, thereby achieving high-value utilization of downstream products from the hydrogenation and decomposition of ethylene cracking tar, is of great significance. Furthermore, different pretreatment methods are required depending on the basic raw materials used to prepare mesophase pitch, but these methods generally suffer from complex processes and low yields. When using petroleum bitumen as raw material, its complex composition necessitates pretreatment processes such as solvent extraction and supercritical fluid extraction, resulting in high costs and low yields. When using catalytic slurry as raw material, multi-stage fractionation and purification are generally required to obtain mesophase bitumen, with product yields typically less than 3%. Using ethylene cracking tar directly as raw material is problematic due to its high reactivity and tendency to coke, requiring a complex process of distillation, polymerization, air oxidation, and redistillation to obtain mesophase bitumen, with yields below 10%. Similarly, coal tar bitumen requires solvent extraction and purification before polymerization to prepare mesophase bitumen. While all these processes can produce mesophase bitumen with anisotropic components ≥90%, they generally suffer from cumbersome processes and low yields, hindering the efficient preparation and large-scale application of mesophase bitumen. Summary of the Invention

[0004] To address the problems in the prior art, this invention provides a general-purpose grade asphalt and mesophase asphalt based on ethylene cracking tar, and a preparation method thereof, which can stably produce high-purity, high-quality general-purpose grade asphalt and mesophase asphalt with controllable structure.

[0005] To achieve the above objectives, the present invention employs the following technical solution: In a first aspect, the present invention provides a method for preparing general-purpose pitch based on ethylene cracked tar, comprising the following steps: S1. Mix ethylene cracked tar with hydrogen and carry out a hydrogenation reaction in the presence of a hydrogenation catalyst; S2. Separate the products after hydrogenation reaction to obtain gas, naphtha, diesel, high aromatic distillate oil and tail oil. S3. The high aromatic fraction oil is subjected to a thermal polymerization reaction under an inert atmosphere to obtain the general-purpose asphalt.

[0006] Preferably, the ethylene cracked tar has a distillation range of 200-700°C, a total content of gums and asphaltenes of <40wt%, and a density of ≤1.1 g / cm³ at 20°C. 3 The high aromatics distillate oil has a distillation range of 350~550℃, an aromatics content of >80wt%, a sulfur content of ≤100ppm, a nitrogen content of ≤100ppm, and an ash content of ≤100ppm.

[0007] Preferably, the conditions for the hydrogenation reaction are: reaction temperature 200~430℃, reaction pressure 2~20 MPa, and volume hourly space velocity 0.1~10 h⁻¹. -1 The hydrogen-to-oil volume ratio is 100-2000; the conditions for the thermal polymerization reaction are: reaction temperature 350-480℃, reaction pressure 0.1-3.0 MPa, reaction time 1-24 h, and stirring rate 10-500 r / min.

[0008] Preferably, the diesel fuel obtained from the separation in S2 is recycled back to S1, mixed with ethylene cracked tar and hydrogen, and subjected to another hydrogenation reaction.

[0009] Secondly, the present invention provides a general-purpose asphalt based on ethylene cracked tar, wherein the anisotropic composition content of the general-purpose asphalt is ≤10% and the softening point is 100~260℃.

[0010] Thirdly, the present invention provides a method for preparing mesophase pitch based on ethylene cracked tar, comprising the following steps: S1. Mix ethylene cracking tar with hydrogen and carry out a hydrogenation reaction in the presence of a hydrogenation catalyst; S2. Separate the products after hydrogenation reaction to obtain gas, naphtha, diesel, high aromatic distillate oil and tail oil. S3. The high aromatic fraction oil is subjected to a prepolymerization reaction under an inert atmosphere to obtain an intermediate phase prepolymer; the intermediate phase prepolymer is subjected to a thermal polymerization reaction under an inert atmosphere to obtain the intermediate phase asphalt.

[0011] Preferably, the ethylene cracked tar has a distillation range of 200-700°C, a total content of gums and asphaltenes of <40wt%, and a density of ≤1.1 g / cm³ at 20°C. 3 The high aromatics distillate oil has a distillation range of 350~550℃, an aromatics content of >80wt%, a sulfur content of ≤100ppm, a nitrogen content of ≤100ppm, and an ash content of ≤100ppm.

[0012] Preferably, the conditions for the hydrogenation reaction are: reaction temperature 200~430℃, reaction pressure 2~20 MPa, and volume hourly space velocity 0.1~10 h⁻¹. -1 The hydrogen-to-oil volume ratio is 100-2000; the conditions for the prepolymerization reaction are: reaction temperature 380-500℃, reaction pressure 0.1-3.0 MPa, reaction time 1-18h, and stirring rate 10-500 r / min, to obtain an intermediate phase prepolymer; the conditions for the thermal polymerization reaction are: reaction temperature 400-520℃, reaction pressure 0.1-3.0 MPa, reaction time 1-18h, and stirring rate 10-500 r / min.

[0013] Preferably, the diesel fuel obtained from the separation in S2 is recycled back to S1, mixed with ethylene cracked tar and hydrogen, and subjected to another hydrogenation reaction.

[0014] Fourthly, the present invention provides an mesophase pitch based on ethylene cracking tar, wherein the mesophase pitch has an anisotropic component content of ≥90%, a softening point of 270~310℃, and an ash content of less than 50ppm.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The two asphalt preparation methods provided by this invention effectively remove sulfur, nitrogen, and other heteroatoms and metallic impurities from ethylene cracking tar through a shared raw material hydrogenation pretreatment step, significantly reducing ash content and obtaining high-aromatic distillate oil with high aromatic content (≥80%), stable composition, and excellent purity. This lays a common high-quality raw material foundation for the subsequent preparation of high-performance asphalt products. For the preparation of general-purpose asphalt, a one-step thermal polymerization process achieves appropriate molecular condensation, ensuring that the product has low anisotropy content (≤10%) and a suitable softening point (100~260℃), exhibiting good homogeneity and processability. For the preparation of mesophase asphalt, a two-step polymerization process is used. Prepolymerization forms a mesophase prepolymer, followed by thermal polymerization to promote further aromatization and ordered stacking of molecules, thereby efficiently preparing high-quality mesophase asphalt with high anisotropy content (≥90%), a moderate softening point (270~310℃), and extremely low ash content (<50ppm), exhibiting an ideal wide-area or streamlined optical texture. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a polarized light microscope image of the mesophase pitch obtained in Example 1 of the present invention; Figure 2 This is a polarizing microscope image of general-purpose asphalt obtained in Example 7 of the present invention. Detailed Implementation

[0018] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0019] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0020] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0021] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0022] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0023] The present invention will now be described in further detail with reference to the accompanying drawings: The first objective of this invention is to provide a method for preparing general-purpose pitch based on ethylene cracked tar, comprising the following steps: S1. Mix ethylene cracking tar with hydrogen and carry out a hydrogenation reaction in the presence of a hydrogenation catalyst; S2. Separate the products after hydrogenation reaction to obtain gas, naphtha, diesel, high aromatic distillate oil and tail oil. S3. The high aromatic fraction oil is subjected to a thermal polymerization reaction under an inert atmosphere to obtain the general-purpose asphalt.

[0024] This method uses ethylene cracked tar as raw material. First, it is mixed with hydrogen and hydrogenated under the action of a suitable hydrogenation catalyst. This process can effectively remove impurities such as sulfur and nitrogen from the raw material, while significantly reducing the content of gum, asphaltenes and metallic ash, thereby obtaining a high aromatic fraction oil with rich aromatics and stable composition. Subsequently, the hydrogenation reaction products are separated and purified to accurately extract the high aromatic fraction oil component with a suitable distillation range. Finally, under the protection of an inert atmosphere, the high aromatic fraction oil undergoes a controlled condensation and aromatization reaction through thermal polymerization, ultimately producing a general-purpose asphalt product with low anisotropy content, suitable softening point and excellent purification characteristics.

[0025] For example, the ethylene cracking tar used in this invention is a heavy fraction with a distillation range of 200-700℃, wherein the total content of gums and asphaltenes is controlled below 40wt%, and the density at 20℃ is not higher than 1.1 g / cm³. 3The characteristics of this raw material ensure good reactivity and suitable fluidity during hydrogenation, avoiding rapid catalyst deactivation or system coking problems caused by excessive gum and asphaltenes content. The product after hydrogenation is separated into gaseous and liquid phases by a high- and low-pressure separator. The liquid phase is frequently separated under reduced pressure to obtain a high-aromatic distillate oil. The high-aromatic distillate oil obtained under atmospheric and reduced pressure exhibits good component homogeneity, low S and N content, and low ash content. Its boiling range is 350–550℃. Thin-layer chromatography analysis shows that its aromatic content is increased to over 80 wt%, while sulfur and nitrogen impurities are reduced to below 100 ppm, and ash content does not exceed 100 ppm. This combination of high aromatics, low impurities, and low ash makes this distillate oil an ideal precursor for preparing high-quality asphalt. This combination of indicators not only ensures that subsequent polymerization reactions can proceed with high selectivity and high yield, but also effectively suppresses the residue of heteroatoms and ash in the final product, thereby significantly improving the purity and homogeneity of the obtained general-purpose asphalt.

[0026] The high-aromatic distillate oil prepared by ethylene cracking tar in this invention has the characteristics of fewer heteroatoms, lower ash content, and higher aromatic content compared with other mesophase pitch, general-purpose pitch, and needle coke feedstocks, as shown in Table 1: Table 1. Comparison of key indicators of the high-aromatic distillate oil of this invention with common asphalt feedstocks.

[0027] Meanwhile, compared with ethylene cracking tar feedstock, the high-aromatic distillate oil has significantly reduced sulfur content and asphaltenes content by more than 90%, as shown in Table 2: Table 2 Comparison of property changes between ethylene cracking tar and high-aromatic distillate oil

[0028] For example, the conditions for the hydrogenation reaction are: reaction temperature 200~430℃, preferably 350~410℃; reaction pressure 2~20 MPa, preferably 6~18 MPa; volume hourly space velocity 0.1~10 h⁻¹. -1 Preferably 0.2~3h -1The hydrogen-to-oil volume ratio (volume ratio of hydrogen to ethylene cracked tar) is 100-2000, preferably 500-1800. This condition effectively achieves purification goals such as olefin saturation, partial hydrogenation of aromatics, and desulfurization, denitrification, and demetallization, while maximizing the preservation of the aromatic ring structure in the raw material and inhibiting excessive cracking. This provides an ideal intermediate feedstock with both high aromatic content and low impurity levels for subsequent polymerization steps. The conditions for the thermal polymerization reaction are: reaction temperature 350-480℃, preferably 380-440℃; reaction pressure 0.1-3.0 MPa, preferably 0.5-2.0 MPa; reaction time 1-24 h, preferably 6-18 h; stirring speed 10-500 r / min, preferably 50-300 r / min. This parameter ensures that the molecules of high aromatic distillate oil can undergo orderly and controllable condensation and aromatization reactions, promoting the growth of appropriate molecular weight and the formation of planar aromatic ring structures. At the same time, stirring ensures the uniformity of heat and material transfer in the reaction system, effectively avoiding excessive coking or uneven reaction caused by local overheating.

[0029] For example, the hydrogenation catalyst can be a commercially available catalyst conventional in the art or prepared by existing mature methods. Its active component is preferably an oxide of Group VIB (such as molybdenum, tungsten) and / or Group VIII (such as cobalt, nickel) metals. These components can exist in single or combined forms and are usually supported on heat-resistant carriers such as alumina and silica to provide highly dispersed active centers. The hydrogenation catalyst can also be a soluble salt of metal or an organometallic compound.

[0030] The second objective of this invention is to provide a general-purpose pitch based on ethylene cracking tar. This general-purpose pitch, prepared by the aforementioned method, has an anisotropic content ≤10%, a softening point controlled within the range of 100~260℃, and features low ash content and low sulfur and nitrogen impurity content. The general-purpose pitch exhibits excellent isotropic characteristics, displaying a uniform optical morphology under a polarizing microscope. Its chemical composition is dominated by polycyclic aromatic hydrocarbons, with a relatively concentrated molecular weight distribution, and it possesses suitable rheological properties and thermal stability. This comprehensive performance makes it particularly suitable as a high-performance binder pitch, impregnating pitch, or precursor for preparing isotropic carbon materials. Its low softening point range ensures good processability and wettability, facilitating molding or compounding under mild conditions, while the extremely low anisotropic content guarantees uniform shrinkage and low internal stress during carbonization, thereby enabling the production of carbon products with dense structure and uniform properties.

[0031] A third objective of this invention is to provide a method for preparing mesophase pitch based on ethylene cracked tar, comprising the following steps: S1. Mix ethylene cracking tar with hydrogen and carry out a hydrogenation reaction in the presence of a hydrogenation catalyst; S2. Separate the products after hydrogenation reaction to obtain gas, naphtha, diesel, high aromatic distillate oil and tail oil. S3. The high aromatic fraction oil is subjected to a prepolymerization reaction under an inert atmosphere to obtain an intermediate phase prepolymer; the intermediate phase prepolymer is subjected to a thermal polymerization reaction under an inert atmosphere to obtain the intermediate phase asphalt.

[0032] This method uses ethylene cracked tar as raw material. First, it is mixed with hydrogen and hydrogenated under the action of a suitable hydrogenation catalyst. This process can effectively remove impurity atoms such as sulfur and nitrogen from the raw material, while significantly reducing the content of gum, asphaltenes and metal ash, thereby obtaining a high aromatic fraction oil with rich aromatics and stable composition. The high aromatic fraction oil obtained after separation is subjected to a prepolymerization reaction under an inert atmosphere, causing the molecules to undergo preliminary condensation and orientation, forming an intermediate phase prepolymer with liquid crystal precursor characteristics. Subsequently, the intermediate phase prepolymer undergoes thermal polymerization, which promotes further aromatization, planarization and orderly stacking of molecules, and finally grows into a wide-area or streamlined mesophase structure, thereby producing an intermediate phase asphalt product with high anisotropy content, excellent optical structure and extremely low impurity content.

[0033] For example, the distillation range of the ethylene cracking tar is controlled between 200 and 700°C, the total content of resins and asphaltenes is less than 40 wt%, and the density at 20°C does not exceed 1.1 g / cm³. 3 The above indicators ensure that the feedstock has a suitable aromatic potential content while avoiding the risk of excessive pressure drop in the catalyst bed or coking in the reactor during hydrogenation due to excessively heavy components, thus providing a foundation for subsequent efficient and stable hydrorefining. The products after the hydrogenation reaction are separated into gas phase and liquid phase components by high and low pressure separators. The liquid phase components are often separated by depressurization to obtain high aromatic fraction oil. The high-aromatic distillate oil obtained by atmospheric and vacuum distillation has the characteristics of good component homogeneity, low S and N content, and low ash content. Its distillation range is 350~550℃. Thin-layer chromatography analysis shows that its aromatic content is significantly increased to over 80wt%, while the sulfur and nitrogen impurities are effectively controlled within 100ppm, and the ash content does not exceed 100ppm. This distillate oil not only has a highly enriched aromatic molecular structure, providing abundant structural units for the formation of the mesophase, but its extremely low heteroatom and ash content also greatly eliminates interference with the orderly molecular stacking in the subsequent polymerization reaction. This ensures that the mesophase liquid crystal can grow and develop in a high-purity and high-orientation manner, thus laying the foundation for finally obtaining high-quality mesophase pitch with excellent optical structure and stable performance.

[0034] For example, the conditions for the hydrogenation reaction are: reaction temperature 200~430℃, preferably 350~410℃; reaction pressure 2~20 MPa, preferably 6~18 MPa; volume hourly space velocity 0.1~10 h⁻¹.-1 Preferably 0.2~3h -1 The hydrogen-to-oil volume ratio is 100-2000, preferably 500-1800. This combination of conditions can achieve efficient desulfurization, denitrification and demetallization while selectively saturating unstable components and moderately retaining the aromatic ring structure, thereby obtaining intermediate feedstock with both high aromatic content and excellent stability.

[0035] The conditions for the prepolymerization reaction are as follows: reaction temperature is 380~500℃, preferably 400~460℃; reaction pressure is 0.1~3.0 MPa, preferably 0.2~2.0 MPa; reaction time is 1~18h, preferably 3~14h; stirring rate is 10~500 r / min, preferably 50~300 r / min, to obtain an intermediate phase prepolymer. This stage aims to promote the initial condensation and planarization of aromatic molecules to form an intermediate phase prepolymer with liquid crystal growth potential, and to ensure uniform heat and mass transfer through stirring to prevent premature coking caused by local overheating.

[0036] The conditions for the thermal polymerization reaction are as follows: reaction temperature of 400~520℃, preferably 420~470℃; reaction pressure of 0.1~3.0 MPa, preferably 0.2~2.0 MPa; reaction time of 1~18h, preferably 3~14h; and stirring rate of 10~500 r / min, preferably 100~350 r / min. This stage further drives the prepolymer molecules to undergo deep aromatization, directional alignment, and growth into well-developed mesophase domains, thereby obtaining mesophase asphalt with high anisotropy content and excellent optical texture.

[0037] In this invention, the diesel obtained from the separation of S2 is recycled back to S1, mixed with ethylene cracking tar and hydrogen, and then subjected to another hydrogenation reaction. The effect of this step is the same as described above, and the selection of the hydrogenation catalyst is also the same as described above. Therefore, this invention will not elaborate further here.

[0038] The hydrogenation reaction processes involved in the above two preparation methods are carried out in a batch reactor equipped with a mechanical stirring system. The stirring forms that can be selected include, but are not limited to, one or more combinations of paddle, frame, anchor or ribbon stirring. At the same time, the inert protective gas (such as nitrogen) required for the reaction can be introduced through the gas inlet at the top or bottom of the reactor.

[0039] In addition, to ensure the smoothness and stability of the hydrogenation reaction step in the two preparation methods mentioned above, the following measures can be taken: Before feeding, the ethylene cracking tar can be preheated separately in the feed tank to 120~150℃ to reduce its viscosity and ensure fluidity. Alternatively, to more effectively suppress its tendency to coke during subsequent high-temperature hydrogenation reactions, alleviate catalyst deactivation rates, and control reactor pressure drop, it is preferable to pre-mix it with diesel fractions before preheating. Regarding catalyst use, homogeneous catalysts can be directly mixed with the feed, while heterogeneous catalysts need to be loaded into the reactor according to regulations. In specific operation, the feed tank is maintained at a slightly positive pressure and the material is appropriately stirred to make it uniform. Then, it is pumped to the reactor, which has been raised to the specified temperature and pressure, through a feed pump. Meanwhile, in both preparation methods, the obtained high aromatic fraction oil can be preheated to 50~80℃ and then accurately delivered to the polymerization reaction unit through a metering pump; at the same time, inert gas is introduced into the unit to maintain a slightly positive pressure inert atmosphere, and the system is controlled to gradually rise to the preset target reaction temperature at a heating rate of 0.5~10℃ / min.

[0040] The fourth objective of this invention is to provide a mesophase pitch based on ethylene cracking tar, wherein the mesophase pitch has an anisotropic component content of ≥90%, a softening point of 270~310℃, and an ash content of less than 50ppm. Under a polarizing microscope, the mesophase pitch exhibits a well-developed wide-area or streamlined optical texture, indicating that its internal aromatic molecular sheets are highly oriented and orderly arranged, possessing excellent liquid crystal properties and potential spinnability. Its moderate softening point range ensures that the material has both good flowability and thermal stability during subsequent melt spinning or molding processes, facilitating process control. The extremely low ash content significantly reduces the formation of defects caused by impurities during high-temperature carbonization or graphitization, which is beneficial for obtaining high-modulus carbon fibers or high-thermal-conductivity, high-purity graphite products with complete structure and uniform performance.

[0041] The performance of general-purpose asphalt and mesophase asphalt prepared by the method of this invention is closely related to the ash, sulfur, and nitrogen content in the raw materials. The lower the content of these impurities, the higher the purity and the better the performance of the final asphalt-based carbon material. Taking asphalt-based carbon fiber spinning, which is technically challenging, as an example: For mesophase asphalt, it is generally required to have a high mesophase content (≥90%) and exhibit a well-developed wide-area or streamlined optical texture under a polarizing microscope. This structure gives the asphalt suitable fluidity and orientation, which is beneficial for subsequent melt spinning. Its softening point is generally controlled between 270 and 310°C to meet the requirements of the spinning process for melt viscosity and thermal stability. For general-purpose asphalt, it is required to have a low anisotropic component content (≤10%) and exhibit a uniform isotropic morphology under a polarizing microscope with almost no extinction phenomenon. This structural uniformity helps to obtain spinning raw materials with stable components and consistent rheological behavior. Its softening point is generally controlled within the range of 100 to 260°C to adapt to different impregnation, bonding, or molding processes. The two bitumen products prepared by this invention have significant advantages in terms of structural control and performance optimization due to their high raw material purity and extremely low impurity content, and are especially suitable as precursors for high-performance carbon fibers and other high-end carbon materials.

[0042] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0043] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0044] Example 1 The preparation of mesophase pitch from ethylene cracked tar includes: The hydrogenation reaction is carried out first: ethylene cracking tar and diesel oil are mixed at a mass ratio of 1:0.4 and then fed into a fixed-bed hydrogenation reactor. The mixture reacts with the hydrogenation catalyst in a hydrogen atmosphere. Specific reaction conditions are: temperature 380℃, pressure 12 MPa, feed flow rate 10 L / h, and volumetric hourly space velocity (VHSV) 0.3 h⁻¹. -1 The hydrogen-to-oil volume ratio is 1000. The hydrogenation catalyst used is a composite catalyst containing active components of nickel, cobalt, and molybdenum.

[0045] The hydrogenation reaction products are frequently fractionated by vacuum distillation to obtain a high-aromatic fraction of the target distillate. This fraction has a boiling range of 375–420 °C, a yield of 21.6%, an ash content of less than 100 ppm, and an aromatic content of more than 80% (determined by thin-layer chromatography).

[0046] Subsequently, prepolymerization and thermal polymerization reactions were carried out sequentially: the above-mentioned high-aromatic distillate oil was preheated to 50-80℃ and then fed into the polymerization reactor through a metering pump. Under the condition of continuously introducing inert gas to maintain a slight positive pressure, the temperature was increased to the reaction temperature at a rate of 3℃ / min for prepolymerization. The prepolymerization reaction conditions were: temperature 410℃, pressure 0.5 MPa, time 3 h, inert gas flow rate 4 L / min, and stirring speed 300 r / min, to obtain an intermediate phase prepolymer. Then, thermal polymerization was carried out in the same reaction system with adjusted reaction conditions: temperature 430℃, pressure 0.6 MPa, time 2 h, inert gas flow rate 6 L / min, and stirring speed 200 r / min.

[0047] The mesophase bitumen product finally obtained in this embodiment has an anisotropy content greater than 96.17%, a softening point of 271~275℃, and an ash content of less than 50 ppm.

[0048] like Figure 1 As shown in the polarizing microscope image of the mesophase pitch obtained in this embodiment, its optical texture exhibits a typical wide-area morphology, and the anisotropy content is significantly higher than 90%, which meets the basic requirements of high-quality mesophase pitch for liquid crystal structure in spinning.

[0049] Example 2 The preparation of mesophase pitch from ethylene cracked tar includes: The hydrogenation reaction is carried out first: Ethylene cracking tar is preheated and fed into a suspended bed hydrogenation reactor, where it reacts with the hydrogenation catalyst in the presence of hydrogen. Specific reaction conditions are: temperature 410℃, pressure 17 MPa, feed flow rate 20 L / h, and volumetric hourly space velocity 0.5 h⁻¹. -1 The hydrogen-to-oil volume ratio is 1100. The hydrogenation catalyst used is a molybdenum-containing compound.

[0050] The hydrogenation reaction products are frequently fractionated by vacuum distillation to obtain a high-aromatic fraction of the target distillate. This fraction has a boiling range of 380–435 °C, a yield of 32.5%, an ash content of less than 100 ppm, and an aromatic content of more than 80% (determined by thin-layer chromatography).

[0051] Subsequently, prepolymerization and thermal polymerization reactions were carried out sequentially: the above-mentioned high-aromatic distillate oil was preheated to 50-80℃ and then fed into the polymerization reactor through a metering pump. Under the condition of continuously introducing inert gas to maintain a slight positive pressure, the temperature was increased to the reaction temperature at a rate of 3℃ / min for prepolymerization. The prepolymerization reaction conditions were: temperature 410℃, pressure 0.5 MPa, time 3 h, inert gas flow rate 4 L / min, and stirring speed 200 r / min, to obtain an intermediate phase prepolymer. Then, thermal polymerization was carried out in the same reaction system with adjusted reaction conditions: temperature 420℃, pressure 0.5 MPa, time 4 h, inert gas flow rate 8 L / min, and stirring speed 200 r / min.

[0052] The mesophase bitumen product finally obtained in this embodiment has an anisotropy content of greater than 99.43%, a softening point of 285~290℃, and an ash content of less than 50 ppm.

[0053] Example 3 The difference between this embodiment and Example 2 is that the hydrogenation reaction conditions are: temperature 350℃, pressure 18 MPa, feed flow rate 80 L / h, and volumetric hourly space velocity 0.2 h⁻¹. -1 The hydrogen-to-oil volume ratio is 1800.

[0054] The prepolymerization reaction conditions were: temperature 400℃, pressure 0.2MPa, time 14 h, inert gas flow rate 4 L / min, and stirring rate 500 r / min.

[0055] The thermal polymerization reaction conditions were: temperature 470℃, pressure 3.0 MPa, time 3 h, inert gas flow rate 8 L / min, and stirring rate 100 r / min.

[0056] Example 4 The difference between this embodiment and Example 2 is that the hydrogenation reaction conditions are: temperature 200℃, pressure 6 MPa, feed flow rate 120 L / h, and volumetric hourly space velocity 3 h⁻¹. -1 The hydrogen-to-oil volume ratio is 500.

[0057] The prepolymerization reaction conditions were: temperature 460℃, pressure 3.0MPa, time 14 h, inert gas flow rate 4 L / min, and stirring rate 300 r / min.

[0058] The thermal polymerization reaction conditions were: temperature 420℃, pressure 0.1 MPa, time 14 h, inert gas flow rate 8 L / min, and stirring rate 350 r / min.

[0059] Example 5 The difference between this embodiment and Example 2 is that the hydrogenation reaction conditions are: temperature 430℃, pressure 2 MPa, feed flow rate 20 L / h, and volumetric hourly space velocity 0.1 h⁻¹. -1 The hydrogen-to-oil volume ratio is 100.

[0060] The prepolymerization reaction conditions were: temperature 380℃, pressure 0.1MPa, time 18 h, inert gas flow rate 4 L / min, and stirring rate 10 r / min.

[0061] The thermal polymerization reaction conditions were: temperature 400℃, pressure 2.0 MPa, time 1 h, inert gas flow rate 8 L / min, and stirring rate 10 r / min.

[0062] Example 6 The difference between this embodiment and Example 2 is that the hydrogenation reaction conditions are: temperature 430℃, pressure 20 MPa, feed flow rate 20 L / h, and volumetric hourly space velocity 20 h⁻¹. -1 The hydrogen-to-oil volume ratio is 2000.

[0063] The prepolymerization reaction conditions were: temperature 500℃, pressure 2MPa, time 1 h, inert gas flow rate 4 L / min, and stirring rate 50 r / min.

[0064] The thermal polymerization reaction conditions were: temperature 520℃, pressure 0.2 MPa, time 18 h, inert gas flow rate 8 L / min, and stirring rate 500 r / min.

[0065] Example 7 Preparation of general-purpose bitumen from ethylene cracking tar, including: The hydrogenation reaction is carried out first: ethylene cracking tar and diesel oil are mixed at a mass ratio of 1:0.4 and then fed into a fixed-bed hydrogenation reactor. The mixture reacts with the hydrogenation catalyst in the presence of hydrogen. Specific reaction conditions are: temperature 380℃, pressure 12 MPa, feed flow rate 10 L / h, and volumetric hourly space velocity (VHSV) 0.3 h⁻¹. -1 The hydrogen-to-oil volume ratio is 1000. The hydrogenation catalyst used is a composite catalyst containing active components of nickel, cobalt, and molybdenum.

[0066] The hydrogenation reaction products are frequently fractionated by vacuum distillation to obtain a high-aromatic fraction of the target distillate. This fraction has a boiling range of 375–420 °C, a yield of 21.6%, an ash content of less than 100 ppm, and an aromatic content of more than 80% (determined by thin-layer chromatography).

[0067] The polymerization reaction then proceeds: the high-aromatic distillate oil is preheated to 50-80°C and then fed into the polymerization reactor via a metering pump. Under the condition of continuously introducing inert gas to maintain a slight positive pressure, the temperature is increased to the reaction temperature at a rate of 5°C / min for thermal polymerization. The specific reaction conditions are: temperature 400°C, pressure 1.5 MPa, time 6 h, inert gas flow rate 5 L / min, and stirring speed 500 r / min.

[0068] The general-purpose asphalt product finally obtained in this embodiment has an anisotropic content of 3.16% and a softening point of 107~110℃.

[0069] like Figure 2 As shown in the polarized light microscope image, the obtained general-purpose asphalt clearly shows that its optical texture exhibits uniform isotropic characteristics, and the anisotropic content is close to and less than 10%, which meets the basic requirements of high-quality general-purpose asphalt for structural uniformity.

[0070] Example 8 Preparation of general-purpose bitumen from ethylene cracking tar, including: The hydrogenation reaction is carried out first: Ethylene cracking tar is preheated and fed into a suspended bed hydrogenation reactor, where it reacts with the hydrogenation catalyst in the presence of hydrogen. Specific reaction conditions are: temperature 410℃, pressure 17 MPa, feed flow rate 20 L / h, and volumetric hourly space velocity 0.5 h⁻¹. -1 The hydrogen-to-oil volume ratio is 1100. The hydrogenation catalyst used is a molybdenum-containing compound.

[0071] The hydrogenation reaction products are frequently fractionated by vacuum distillation to obtain a high-aromatic fraction of the target distillate. This fraction has a boiling range of 380–435 °C, a yield of 32.5%, an ash content of less than 100 ppm, and an aromatic content of more than 80% (determined by thin-layer chromatography).

[0072] The polymerization reaction then proceeds: the high-aromatic distillate oil is preheated to 50-80°C and then fed into the polymerization reactor via a metering pump. Under the condition of continuously introducing inert gas to maintain a slight positive pressure, the temperature is increased to the reaction temperature at a rate of 5°C / min for thermal polymerization. The specific reaction conditions are: temperature 410°C, pressure 1.2 MPa, time 7 h, inert gas flow rate 8 L / min, and stirring speed 500 r / min.

[0073] The general-purpose asphalt product finally obtained in this embodiment has an anisotropic content of 6.88% and a softening point of 125~130℃.

[0074] Example 9 The difference between this embodiment and Example 9 is that the hydrogenation reaction conditions are: temperature 200°C, pressure 2 MPa, feed flow rate 20 L / h, and volumetric hourly space velocity 0.1 h⁻¹.-1 The hydrogen-to-oil volume ratio is 100.

[0075] The thermal polymerization reaction conditions were: temperature 350℃, pressure 0.1 MPa, time 1 h, inert gas flow rate 8 L / min, and stirring rate 500 r / min.

[0076] Example 10 The difference between this embodiment and Example 9 is that the hydrogenation reaction conditions are: temperature 430℃, pressure 20 MPa, feed flow rate 20 L / h, and volumetric hourly space velocity 10 h⁻¹. -1 The hydrogen-to-oil volume ratio is 2000.

[0077] The thermal polymerization reaction conditions were: temperature 480℃, pressure 3.0 MPa, time 24 h, inert gas flow rate 8 L / min, and stirring rate 10 r / min.

[0078] Example 11 The difference between this embodiment and Example 9 is that the hydrogenation reaction conditions are: temperature 350℃, pressure 6 MPa, feed flow rate 20 L / h, and volumetric hourly space velocity 0.2 h⁻¹. -1 The hydrogen-to-oil volume ratio is 500.

[0079] The thermal polymerization reaction conditions were: temperature 380℃, pressure 0.5 MPa, time 6 h, inert gas flow rate 8 L / min, and stirring rate 50 r / min.

[0080] Example 12 The difference between this embodiment and Example 9 is that the hydrogenation reaction conditions are: temperature 410°C, pressure 18 MPa, feed flow rate 20 L / h, and volumetric hourly space velocity 3 h⁻¹. -1 The hydrogen-to-oil volume ratio is 1800.

[0081] The thermal polymerization reaction conditions were: temperature 440℃, pressure 2.0 MPa, time 18 h, inert gas flow rate 8 L / min, and stirring rate 300 r / min.

[0082] In summary, the method of this invention has significant advantages over existing technologies: Existing technologies generally suffer from unstable raw material quality; the raw materials used to prepare mesophase pitch are usually of heterogeneous molecular composition and contain a large number of heteroatoms and metallic ash, thus requiring complex purification and pretreatment processes. In contrast, this invention, through selective hydrogenation of ethylene cracking tar, obtains a high-aromatic fraction oil with an aromatic content ≥80%, uniform molecular structure, few light components, and extremely low heteroatom and ash content (ash ≤100 ppm), significantly improving raw material stability and resulting in higher yield and superior performance of the final product. Furthermore, compared to existing fixed-bed hydrogenation processes that directly utilize ethylene tar (such as Chinese patent publication number "CN101724423A"), existing technologies typically require deep cracking or isomerization of aromatics, resulting in complex processes and lower efficiency. The hydrogenation process used in this invention, under reasonable control conditions, can achieve highly efficient enrichment (content ≥80%) of aromatics in the 350~550℃ fraction, making the process simpler and more efficient. To address the issue of low added value from the direct utilization of ethylene cracking tar, this invention provides a complete process route for converting its high value into high-quality asphalt materials, thereby expanding its industrial chain and added value potential.

[0083] Secondly, compared with the process of preparing asphalt using other raw materials, the pretreatment method of this invention also shows significant advantages: when using petroleum asphalt as raw material, due to its complex composition, it is necessary to adopt cumbersome purification methods such as solvent extraction and supercritical extraction, resulting in high costs and low product yield. For relevant technical background, please refer to the literature (Chen QX, Li TH, Zhuang Q, et al. Research progress of mesophase pitch-based carbon foams[J]. CarbonTechniques, 2010, 29(1): 28-32); When using catalytic oil slurry as raw material, it usually requires pretreatment steps such as multi-stage fractionation and deep purification to obtain qualified intermediates, and the final yield is often less than 3% (such as Chinese patent with publication number "CN112552946"); If ethylene cracking tar is used directly as raw material, it needs to go through multiple complex processes such as distillation, polymerization, air oxidation and secondary distillation, and the overall yield is still less than 10% (such as Chinese patent with publication number "CN111925818A"); Even if coal tar pitch is used as raw material, it also needs to rely on purification processes such as solvent extraction for pretreatment, and the process is also relatively complicated. The relevant methods are recorded in the literature (Qian SA, Zhang PZ, Li BL. Structural characterization of pitch feedstocks for coke making: Use of 13C coupled 1Hn.mr spectroscopy[J]. Fuel, 1985, 64(8): 1085-1091). In contrast, this invention can obtain a suitable fraction with high purity and high aromatic content from ethylene cracking tar through a one-step hydrogenation process, significantly shortening the process flow and significantly improving the utilization rate of raw materials and the product yield, demonstrating better technical and economic efficiency and application prospects.

[0084] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing general-purpose pitch based on ethylene cracking tar, characterized in that, Includes the following steps: S1. Mix ethylene cracking tar with hydrogen and carry out a hydrogenation reaction in the presence of a hydrogenation catalyst; S2. Separate the products after hydrogenation reaction to obtain gas, naphtha, diesel, high aromatic distillate oil and tail oil. S3. The high aromatic fraction oil is subjected to a thermal polymerization reaction under an inert atmosphere to obtain the general-purpose asphalt.

2. The method for preparing general-purpose pitch based on ethylene cracking tar according to claim 1, characterized in that, The ethylene cracked tar has a distillation range of 200–700°C, a total content of resins and asphaltenes of <40 wt%, and a density of ≤1.1 g / cm³ at 20°C. 3 The high aromatics distillate oil has a distillation range of 350~550℃, an aromatics content of >80wt%, a sulfur content of ≤100ppm, a nitrogen content of ≤100ppm, and an ash content of ≤100ppm.

3. The method for preparing general-purpose pitch based on ethylene cracking tar according to claim 1, characterized in that, The conditions for the hydrogenation reaction are: reaction temperature 200~430℃, reaction pressure 2~20 MPa, and volume hourly space velocity 0.1~10 h⁻¹. -1 The hydrogen-to-oil volume ratio is 100-2000; the conditions for the thermal polymerization reaction are: reaction temperature 350-480℃, reaction pressure 0.1-3.0MPa, reaction time 1-24 h, and stirring rate 10-500 r / min.

4. The method for preparing general-purpose pitch based on ethylene cracking tar according to claim 1, characterized in that, The diesel fuel obtained from the separation in S2 is recycled back to S1, where it is mixed with ethylene cracking tar and hydrogen for another hydrogenation reaction.

5. A general-purpose pitch based on ethylene cracked tar, characterized in that, The general-purpose asphalt is prepared by the preparation method according to any one of claims 1 to 4, wherein the anisotropic composition content is ≤10% and the softening point is 100~260℃.

6. A method for preparing mesophase pitch based on ethylene cracked tar, characterized in that, Includes the following steps: S1. Mix ethylene cracking tar with hydrogen and carry out a hydrogenation reaction in the presence of a hydrogenation catalyst; S2. Separate the products after hydrogenation reaction to obtain gas, naphtha, diesel, high aromatic distillate oil and tail oil. S3. The high aromatic fraction oil is subjected to a prepolymerization reaction under an inert atmosphere to obtain an intermediate phase prepolymer; the intermediate phase prepolymer is subjected to a thermal polymerization reaction under an inert atmosphere to obtain the intermediate phase asphalt.

7. The method for preparing mesophase pitch based on ethylene cracked tar according to claim 6, characterized in that, The ethylene cracked tar has a distillation range of 200–700°C, a total content of resins and asphaltenes of <40 wt%, and a density of ≤1.1 g / cm³ at 20°C. 3 The high aromatics distillate oil has a distillation range of 350~550℃, an aromatics content of >80wt%, a sulfur content of ≤100ppm, a nitrogen content of ≤100ppm, and an ash content of ≤100ppm.

8. The method for preparing mesophase pitch based on ethylene cracked tar according to claim 6, characterized in that, The conditions for the hydrogenation reaction are: reaction temperature 200~430℃, reaction pressure 2~20 MPa, and volume hourly space velocity 0.1~10 h⁻¹. -1 The hydrogen-to-oil volume ratio is 100-2000; the conditions for the prepolymerization reaction are: reaction temperature 380-500℃, reaction pressure 0.1-3.0 MPa, reaction time 1-18h, and stirring rate 10-500 r / min, to obtain an intermediate phase prepolymer; the conditions for the thermal polymerization reaction are: reaction temperature 400-520℃, reaction pressure 0.1-3.0 MPa, reaction time 1-18h, and stirring rate 10-500 r / min.

9. The method for preparing general-purpose pitch based on ethylene cracking tar according to claim 6, characterized in that, The diesel fuel obtained from the separation in S2 is recycled back to S1, where it is mixed with ethylene cracking tar and hydrogen for another hydrogenation reaction.

10. A mesophase pitch based on ethylene cracked tar, characterized in that, The mesophase asphalt is prepared by any one of claims 6 to 9, wherein the anisotropic component content is ≥90%, the softening point is 270~310℃, and the ash content is less than 50ppm.

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