Method for preparing mesophase pitch from coal liquefaction pitch

Abstract

The invention discloses a method for preparing mesophase pitch from coal liquefaction pitch, which comprises the following steps: (1) carrying out pyrolysis pretreatment on the coal liquefaction pitch to obtain a pre-pyrolysis product; (2) extracting soluble components in the pre-pyrolysis product obtained in the step (1) by using a first aromatic solvent, and carrying out distillation separation on the obtained extract phase to remove the aromatic solvent so as to obtain refined asphalt; (3) uniformly mixing the refined asphalt obtained in the step (2) with a hydrogen donor solvent, and then putting the mixture into a reaction kettle for thermal polycondensation treatment to obtain thermal polycondensation asphalt; (4) crushing the thermal polycondensation asphalt obtained in the step (3), uniformly mixing the crushed thermal polycondensation asphalt with a second aromatic solvent for extraction, and then separating out insoluble components; and (5) drying the insoluble component obtained in the step (4), and carrying out heat treatment in a protective atmosphere to obtain the mesophase pitch. The problem that the quality of the prepared mesophase pitch is poor due to the fact that pitch macromolecules are coked in the thermal polycondensation process is solved, and the high-quality mesophase pitch is obtained.

Description

Technical Field

[0001] The present invention belongs to the technical fields of new carbon materials, fuel chemical industry and coal chemical industry, and particularly relates to a method for preparing mesophase asphalt from coal liquefaction asphalt. Background Art

[0002] With the continuous advancement of science and technology, mesophase asphalt-based carbon fibers have gradually become an important product for national strategic development. Because of its high thermal conductivity, electrical conductivity, high modulus, low density and other characteristics, it has a wide range of applications in military materials, aerospace, life energy storage and other fields. Therefore, the preparation of high-performance spinnable mesophase asphalt is particularly critical. High-quality spinnable mesophase asphalt requires a high mesophase content while maintaining a low softening point and having a good optical texture. During the thermal polycondensation process, the macromolecular components will rapidly polycondense during the thermal reaction, and it is easy to generate isotropic coke adsorbed on the surface of the mesophase spheres, which hinders the fusion of the mesophase spheres, increases the viscosity of the system, and makes it difficult to form a wide-area streamlined optical texture. Therefore, it is particularly important to optimize the components of the raw materials.

[0003] CN103205271A discloses a method for producing mesophase asphalt by hydrogenating high-temperature coal tar pitch, wherein the method comprises catalytic refining of high-temperature coal tar and blending oil to obtain hydrogenated refined oil, and then preparing mesophase asphalt by thermal polycondensation. However, the method requires consumption of a large amount of hydrogen supply solvent, which increases the reaction cost.

[0004] CN114395411A discloses a method for preparing mesophase pitch by hydrogenating coal tar, wherein the method comprises adding a nano catalyst to coal tar to carry out a hydrogenation reaction in a slurry bed reactor, and then preparing the mesophase pitch by thermal polycondensation. However, the removal and regeneration of the nano-catalyst in this method is relatively difficult, and the industrial production operation is complicated.

[0005] CN116694347A discloses a method for preparing mesophase asphalt by catalytic hydrogenation of coal tar pitch at low temperature and low pressure, wherein the coal tar pitch is mixed with an acidic catalyst and then co-carbonized with a hydrogen-donating solvent such as tetralin to prepare the mesophase asphalt. However, the catalyst removal in this method is difficult, and the hydrogen-donating solvent such as tetralin is expensive, which increases the reaction cost.

[0006] CN118291165A discloses a method for preparing mesophase asphalt by pretreating coal liquefaction asphalt. In this method, the raw material is subjected to a pre-pyrolysis reaction to promote thermal condensation of highly reactive components, and then the soluble components of the pre-pyrolysis product are extracted by solvent as refined asphalt. Thereafter, the refined asphalt is subjected to a two-step thermal condensation method to prepare spinnable mesophase asphalt. However, the thermal condensation process is not ideal and affects the preparation of the mesophase asphalt.

[0007] The traditional method of preparing mesophase pitch by hydrogenation is often too costly and requires a large amount of hydrogen-donating solvent. In addition, the molecular weight of the traditional hydrogen-donating solvent is quite different from that of coal liquefaction pitch, and the compatibility is poor. The large and expensive consumption of hydrogen-donating solvent does not meet the industrial requirements of high-quality spinnable mesophase pitch. Therefore, a low-cost and easy-to-operate method is needed to solve the problem of high molecular weight and high reaction activity of the raw material, so as to improve the quality of the spinnable mesophase. Summary of the invention

[0008] The purpose of the present invention is to provide a method for preparing mesophase asphalt from coal liquefaction asphalt, so as to solve the problem of poor quality of prepared mesophase asphalt caused by coking of asphalt macromolecules during thermal polycondensation, thereby preparing high-quality spinnable mesophase asphalt.

[0009] In order to achieve the above-mentioned invention object, the present invention adopts the following technical solutions:

[0010] A method for preparing mesophase pitch from coal liquefaction pitch comprises the following steps:

[0011] (1) pre-treating coal liquefaction pitch by pyrolysis to obtain a pre-pyrolysis product;

[0012] (2) extracting the soluble components in the pre-pyrolysis product obtained in step (1) with a first aromatic solvent, and separating the obtained extract by distillation to remove the aromatic solvent to obtain refined asphalt;

[0013] (3) uniformly mixing the refined asphalt obtained in step (2) with the hydrogen supply solvent and placing the mixture in a reactor for thermal polycondensation treatment to obtain thermal polycondensed asphalt;

[0014] (4) crushing the heat-condensed asphalt obtained in step (3) and mixing it evenly with a second aromatic solvent for extraction, and then separating the insoluble components;

[0015] (5) After drying the insoluble component obtained in step (4), heat treatment is performed under a protective atmosphere to obtain a mesophase pitch.

[0016] In step (1) of the present invention, the coal liquefaction pitch is subjected to a pyrolysis pretreatment to obtain a pre-pyrolysis product; the pre-pyrolysis treatment allows the macromolecular components and components with higher thermal reaction activity in the coal liquefaction pitch to be further thermally condensed, and these highly reactive components can be removed by solvent extraction. The pyrolysis pretreatment is also beneficial for achieving the cleavage of long alkyl side chains and the removal of heteroatoms.

[0017] In a preferred embodiment, in step (1), the pyrolysis pretreatment is carried out in a protective atmosphere such as a nitrogen atmosphere or an inert gas atmosphere; the pyrolysis pretreatment temperature is 380-420°C, such as 390, 400 or 410°C, and the pyrolysis pretreatment time is 15-180 min, such as 20, 50, 80, 100, 120 or 150 min.

[0018] In step (2) of the present invention, the soluble components in the pre-pyrolysis product obtained in step (1) are extracted with a first aromatic solvent; in a preferred embodiment, the first aromatic solvent is selected from one or more of benzene, toluene, and xylene; the specific extraction process is well known in the art, for example, the pre-pyrolysis product can also be crushed before extraction to facilitate the sufficient extraction of the soluble components. Preferably, in step (2), the mass ratio of the pre-pyrolysis product to the first aromatic solvent is 1:1-10, such as 1:2, 1:5 or 1:8, the extraction temperature is 20-120°C, such as 40, 60, 80 or 100°C, and the extraction time is 30-240min, such as 50, 80, 100, 150 or 200min.

[0019] In step (2) of the present invention, the obtained extract phase is distilled and separated to remove the first aromatic solvent to obtain refined asphalt; preferably, the obtained extract phase after extraction is distilled under reduced pressure at 80-150°C, such as 100 or 120°C, to remove the aromatic solvent to obtain refined asphalt.

[0020] In step (3) of the present invention, the refined asphalt obtained in step (2) is uniformly mixed with a hydrogen-donating solvent and then placed in a reactor for thermal polycondensation treatment to obtain thermal polycondensation asphalt; in the present invention, the introduction of a hydrogen-donating solvent provides more methyl side chains and cycloalkane structures, which work together to effectively reduce the viscosity of the system, promote the orderly progress of the hydrogen transfer reaction, and provide suitable free radicals and active centers for the thermal polycondensation process, which is beneficial to the orderliness of the arrangement of planar condensed-ring aromatic hydrocarbon molecules and the compactness of carbon layer stacking, thereby promoting the orientation and movement of intermediate phase liquid mesocrystals.

[0021] In a preferred embodiment, in step (3), the thermal polycondensation temperature is 380-450°C, such as 400 or 420°C, the time is 120-1800 min, such as 150, 200, 500, 1000 or 1500 min, and the pressure is 0.5-3 MPa, such as 0.8, 1, 1.5, 2 or 2.5 MPa.

[0022] In a preferred embodiment, in step (3), the hydrogen supply solvent is a partially saturated product of hydrogenated condensed aromatic hydrocarbons, which is controlled to be a refined asphalt hydrogen supply and thermal polycondensation effect is better; preferably, the hydrogen supply solvent contains 10-30% pentacyclic aromatic hydrocarbons, such as 15%, 20% or 25%, 10%-30% tetracyclic aromatic hydrocarbons, such as 15%, 20% or 25%, and 50-80% tricyclic and lower aromatic hydrocarbons, such as 55%, 60%, 65%, 70% or 75%, so as to ensure the hydrogen supply effect when a good reaction system is formed, wherein the surface three The hydrogen supply capacity of the aromatic hydrocarbons with rings and below is relatively weak, and they are mainly used to adjust the viscosity of the system, while the hydrogen supply capacity of the pentacyclic aromatic hydrocarbons is relatively strong, and they play the main role of hydrogen supply; more preferably, in the hydrogen supply solvent, the content of monocyclic aromatic hydrocarbons is not more than 5%, such as 0 or 2%, the content of dicyclic aromatic hydrocarbons is 5%-35%, such as 20%, 25% or 30%, preferably 10-20%, the content of tricyclic aromatic hydrocarbons is 40%-60%, such as 45%, 50% or 55%, preferably 45-55%, the content of tetracyclic aromatic hydrocarbons is 10%-30%, preferably 15-25%, and the content of pentacyclic aromatic hydrocarbons is 5-30%, preferably 10-20%. Specifically, when the condensed-ring aromatic hydrocarbons are partially saturated by hydrogenation, the condensed-ring aromatic hydrocarbons with the corresponding number of rings having the corresponding content can be configured, and then the hydrogenation is partially saturated. The specific hydrogenation process is well known in the art and will not be repeated here.

[0023] In a preferred embodiment, in step (3), in order to better ensure the hydrogen supply effect, in the obtained hydrogen supply solvent, cycloalkanes account for 30%-60% of the total number of rings of the condensed aromatic hydrocarbons, such as 40% or 50%; it is understood in the art that, for example, when a condensed aromatic hydrocarbon with five rings is partially saturated by hydrogenation, some of the rings, such as 1-4 rings, will be hydrogenated to form saturated rings, namely cycloalkanes, and the same is true for condensed aromatic hydrocarbons with other numbers of rings. Therefore, the proportion of cycloalkanes in the total number of rings of condensed aromatic hydrocarbons refers to the proportion of this part of saturated rings in the total number of rings of condensed aromatic hydrocarbons, that is, the proportion of saturated rings.

[0024] In a preferred embodiment, in step (3), the amount of the hydrogen-donating solvent used is 10%-50%, such as 20%, 30% or 40%, which is more conducive to the subsequent thermal polycondensation reaction.

[0025] In step (4) of the present invention, the heat-condensed asphalt obtained in step (3) is crushed and uniformly mixed with a second aromatic solvent for extraction, so as to remove soluble components from the heat-condensed asphalt, thereby obtaining insoluble components after solid-liquid separation.

[0026] In a preferred embodiment, in step (4), the second aromatic solvent is selected from benzene, toluene and xylene.

[0027] In a preferred embodiment, in step (4), the heat-condensed asphalt is crushed to a particle size less than 60 mesh (Tyler standard sieve), such as crushed to pass through 60 mesh, 100 mesh or 200 mesh, so as to be fully extracted, as is well known in the art; preferably, during extraction, it is mixed with a second aromatic solvent at a mass ratio of 1:1 to 10, such as 1:2, 1:5 or 1:8 at 20 to 120°C, such as 40, 60, 80 or 100°C.

[0028] In step (5) of the present invention, the insoluble component obtained in step (4) is dried and then heat-treated under a protective atmosphere to obtain mesophase pitch. In a preferred embodiment, in step (5), when the insoluble component is heat-treated, it is heated to 360-390°C, such as 370 or 380°C, for 20-60 minutes, such as 30, 40 or 50 minutes.

[0029] In the present invention, unless otherwise specified, all percentages or percentage contents involved are mass percentages or mass percentage contents.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] (a) The pre-pyrolysis process of the present invention is simple and easy to scale up. The high-reactivity components can be polycondensed in advance by preheating the raw materials, and then the large molecular insoluble components are removed by solvent extraction, thereby solving the problem of wide molecular weight of coal liquefaction pitch;

[0032] (b) The present invention introduces a hydrogen-donating solvent to increase the cycloalkane structure and alkyl side chains, which is conducive to the polycondensation reaction between aromatic sheets, the stacking of carbon layers and the densification of interlayer spacing, thereby reducing the viscosity of the system and improving the optical texture;

[0033] (c) The present invention achieves separation of different components of coal liquefaction pitch by solvent extraction, thereby achieving the purpose of component optimization. The method is simple and the solvent can be recycled, thereby reducing costs.

[0034] In summary, the present invention optimizes the molecular structure by pretreating the raw materials, effectively controlling the aromatic ring cross-linking polymerization reaction, dehydrogenation aromatization reaction and cracking reaction. Through pre-pyrolysis treatment, the macromolecular components and components with high thermal reaction activity in the coal liquefaction pitch are further thermally condensed, and then these highly reactive components are removed by solvent extraction, and the long alkyl side chain is broken and the heteroatom is removed by thermal pretreatment.

[0035] In addition, the present invention uses a pre-pyrolysis method to remove large component molecules in a simple one-step manner, and effectively aggregates small molecules into potential intermediate phase components with suitable molecular weights; at the same time, more methyl side chains and cycloalkane structures are provided by the introduction of a hydrogen supply solvent, and the two work together to effectively reduce the viscosity of the system, promote the orderly progress of the hydrogen transfer reaction, and provide suitable free radicals and active centers for the thermal polycondensation process, which is beneficial to the orderliness of the arrangement of planar condensed ring aromatic hydrocarbon molecules and the compactness of carbon layer stacking, thereby promoting the orientation and movement of intermediate phase liquid mesocrystals.

[0036] In addition, in addition to coal liquefaction pitch, the raw materials of the present invention may also include coal tar pitch, petroleum pitch, ethylene tar and the like to prepare spinnable mesophase pitch. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a polarizing microscope photograph of the mesophase pitch prepared in Example 1 of the present invention;

[0038] Figure 2 is an infrared spectrum of the mesophase asphalt prepared in Example 1 of the present invention;

[0039] Figure 3 This is the XRD diagram of the mesophase asphalt prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0040] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiment of the present invention will be further described below in conjunction with the embodiment of the present invention. Obviously, the described embodiment is only a part of the embodiment of the present invention, not all of the embodiments. Based on the embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0041] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values, such as values ​​of ±10% of the endpoint values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article. In the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other.

[0042] It should be noted that the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products or apparatus.

[0043] Example 1

[0044] Step 1: Grind the dried coal liquefaction pitch through a 30-mesh sieve. Step 2: Take 100 g of the coal liquefaction pitch in step 1 and add it to a reactor. Purge the air in the reactor with N2 for 10 minutes, heat it to 400°C, and react for 60 minutes to obtain a pre-pyrolysis product. Step 3: Grind the pre-pyrolysis product through a 30-mesh sieve, extract it with xylene, the extraction ratio is 1:10, the extraction temperature is 50°C, the extraction time is 180 minutes, filter to obtain the extraction phase, and distill the extraction phase under reduced pressure at 120°C for 45 minutes to obtain refined asphalt. Step 4: Grind and sieve the refined asphalt in step 3, and take 30g and mix it with a hydrogen supply solvent with a mass ratio of 30wt.% (the saturated ring accounts for about 45%, and its composition: about 15% of pentacyclic aromatic hydrocarbons, about 20% of tetracyclic aromatic hydrocarbons, about 50% of tricyclic aromatic hydrocarbons, and about 15% of dicyclic aromatic hydrocarbons) and add it to a high-temperature and high-pressure reactor. After N2 is purged for 10 minutes, it is heated to 430°C and the reaction time is controlled to 420min. The pressure in the reactor is 0.1Mpa and the stirring rate is 30rpm to obtain hydrogenated asphalt. Step 5: Grind the hydrogenated asphalt obtained in step 4 through a 30-mesh sieve and extract it with xylene. The extraction ratio is 1:10, the extraction temperature is 75°C, and the extraction time is 180min. Filter to obtain the raffinate phase, and vacuum dry the raffinate phase at 150°C for 120min. Step 6: Add the raffinate phase obtained in step 5 to a high-temperature and high-pressure autoclave, purge it with N2 for 10 minutes, heat it to 380°C, and react for 30min to obtain the intermediate phase asphalt.

[0045] The mesophase asphalt obtained has a mesophase content of 94%, and the optical texture is an obvious wide-area streamlined structure of 80%, and the elemental analysis results show that the C / H atomic ratio is 2.03. The polarizing microscope photo, infrared spectrum and XRD diagram of the prepared mesophase asphalt are shown in Figure 1-3 .

[0046] Comparative Example 1

[0047] Step 1, grind the dried coal liquefaction pitch through a 30-mesh sieve. Step 2, take 100g and extract it with xylene, the extraction ratio is 1:10, the extraction temperature is 50°C, the extraction time is 180min, filter to obtain the extraction phase, and distill the extraction phase at 120°C under reduced pressure for 45min to obtain refined asphalt. Step 3, grind and sieve the refined asphalt in step 2, and take 30g and mix it with a hydrogen supply solvent (same as Example 1) with a mass ratio of 30wt.% and add it to a high-temperature and high-pressure reactor. After N2 purging for 10 minutes, heat to 430°C and control the reaction time to 420min. The pressure in the reactor is 0.1Mpa, and the stirring rate is 30rpm to obtain hydrogenated asphalt. Step 4, grind the hydrogenated asphalt obtained in step 3 through a 30-mesh sieve and extract it with xylene, the extraction ratio is 1:10, the extraction temperature is 75°C, the extraction time is 180min, filter to obtain the residual phase, and dry the residual phase at 150°C in vacuum for 120min. Step 5: Add the raffinate phase obtained in step 4 into a high-temperature autoclave and purge it with N2 for 10 minutes, then heat it to 380°C and react for 30 minutes to obtain the mesophase asphalt.

[0048] The obtained mesophase asphalt has an mesophase content of 80%, and the optical texture is a coarse fiber structure of 60%, and the rest presents a relatively disordered mosaic structure accounting for 27%. The elemental analysis results show that the C / H atom of the sample after hydrogenation is 2.32.

[0049] Comparative Example 2

[0050] Step 1, grind the dried coal liquefaction pitch through a 30-mesh sieve. Step 2, take 100g and extract it through xylene, the extraction ratio is 1:10, the extraction temperature is 50°C, the extraction time is 180min, filter to obtain the extraction phase, and distill the extraction phase at 120°C for 45min to obtain a soluble component. Step 3, grind and sieve the soluble component in step 2, take 30g and add it to a high-temperature and high-pressure reactor, heat to 430°C after N2 purging for 10 minutes, control the reaction time to 420min, the pressure in the reactor is 0.1Mpa, and the stirring rate is 30rpm to obtain refined asphalt. Step 4, grind the refined asphalt obtained in step 3 through a 30-mesh sieve and extract it through xylene, the extraction ratio is 1:10, the extraction temperature is 75°C, the extraction time is 180min, filter to obtain the residual phase, and vacuum dry the residual phase at 150°C for 120min. Step 5: Add the raffinate phase obtained in step 4 into a high-temperature autoclave and purge it with N2 for 10 minutes, then heat it to 380°C and react for 30 minutes to obtain the mesophase asphalt.

[0051] The obtained mesophase asphalt has an mesophase content of 95%, and the optical texture is a coarse fiber structure and a mosaic structure, accounting for 36% and 55% respectively, and the elemental analysis results show that the C / H atom of the sample is 2.53.

[0052] Compared with Comparative Example 1, the pre-pyrolysis treatment in Example 1 effectively removes the macromolecular components and high-reactivity components in the coal liquefaction asphalt, and is accompanied by the cleavage of long alkyl side chains and the occurrence of ring-opening reactions, which helps to reduce the high reactivity of the coal liquefaction asphalt, maintain appropriate aromaticity and viscosity in the system, and optimize the optical texture of the intermediate phase asphalt.

[0053] Compared with Example 2, the introduction of hydrogen-donating solvent in Example 1 provides more methyl structures and cycloalkane structures. The two work together to effectively reduce the viscosity of the system, promote the orderly progress of hydrogen transfer reaction, and provide suitable free radicals and active centers for the thermal polycondensation process, which is beneficial to the orderliness of the arrangement of planar condensed-ring aromatic hydrocarbon molecules and the compactness of carbon layer stacking, thereby promoting the orientation and movement of mesophase asphalt molecules.

[0054] Example 2

[0055] Step 1: Grind the dried coal liquefaction asphalt through a 30-mesh sieve. Step 2: Take 100g of the coal liquefaction asphalt in step 1 and add it to the reactor. Purge the air in the reactor with N2 for 10 minutes, heat it to 380°C, and react for 60 minutes to obtain a pre-pyrolysis product. Step 3: Grind the pre-pyrolysis product through a 30-mesh sieve, extract it with xylene, the extraction ratio is 1:10, the extraction temperature is 50°C, the extraction time is 180 minutes, filter to obtain the extraction phase, and distill the extraction phase at 120°C under reduced pressure for 45 minutes to obtain refined asphalt. Step 4: Grind and sieve the refined asphalt in step 3, and take 30g and mix it with a hydrogen supply solvent with a mass ratio of 30wt.% (the saturated ring accounts for about 45%, and its composition: about 5% pentacyclic aromatic hydrocarbons, about 25% tetracyclic aromatic hydrocarbons, about 55% tricyclic aromatic hydrocarbons, and about 15% dicyclic aromatic hydrocarbons) and add it to a high-temperature and high-pressure reactor. After N2 is purged for 10 minutes, it is heated to 430°C and the reaction time is controlled to 420min. The pressure in the reactor is 0.1Mpa and the stirring rate is 30rpm to obtain hydrogenated asphalt. Step 5: Grind the hydrogenated asphalt obtained in step 4 through a 30-mesh sieve and extract it with xylene. The extraction ratio is 1:10, the extraction temperature is 75°C, and the extraction time is 180min. Filter to obtain the raffinate phase, and vacuum dry the raffinate phase at 150°C for 120min. Step 6: Add the raffinate phase obtained in step 5 to a high-temperature and high-pressure reactor, purge it with N2 for 10 minutes, heat it to 380°C, and react for 30min to obtain the intermediate phase asphalt.

[0056] The mesophase asphalt obtained by changing the pyrolysis conditions has an mesophase content of 87%, and the optical texture presents a coarse fiber structure and a streamlined structure, which account for 71% and 23% respectively. The results of elemental analysis show that the C / H atomic ratio is 2.12.

[0057] Example 3

[0058] Step 1: Grind the dried coal liquefaction pitch through a 30-mesh sieve. Step 2: Take 100 g of the coal liquefaction pitch in step 1 and add it to a reactor. Purge the air in the reactor with N2 for 10 minutes, heat it to 420°C, and react for 60 minutes to obtain a pre-pyrolysis product. Step 3: Grind the pre-pyrolysis product through a 30-mesh sieve, extract it with xylene, the extraction ratio is 1:10, the extraction temperature is 50°C, the extraction time is 180 minutes, filter to obtain the extraction phase, and distill the extraction phase at 120°C under reduced pressure for 45 minutes to obtain refined asphalt. Step 4: Grind and sieve the refined asphalt in step 3, and take 30g and mix it with a hydrogen supply solvent with a mass ratio of 30wt.% (the saturated ring accounts for about 45%, and its composition: about 30% of pentacyclic aromatic hydrocarbons, about 10% of tetracyclic aromatic hydrocarbons, about 45% of tricyclic aromatic hydrocarbons, and about 15% of dicyclic aromatic hydrocarbons) and add it to a high-temperature and high-pressure reactor. After N2 is purged for 10 minutes, it is heated to 430°C and the reaction time is controlled to 420min. The pressure in the reactor is 0.1Mpa and the stirring rate is 30rpm to obtain hydrogenated asphalt. Step 5: Grind the hydrogenated asphalt obtained in step 4 through a 30-mesh sieve and extract it with xylene. The extraction ratio is 1:10, the extraction temperature is 75°C, and the extraction time is 180min. Filter to obtain the raffinate phase, and vacuum dry the raffinate phase at 150°C for 120min. Step 6: Add the raffinate phase obtained in step 5 to a high-temperature and high-pressure reactor, purge it with N2 for 10 minutes, heat it to 380°C, and react for 30min to obtain the intermediate phase asphalt.

[0059] The mesophase asphalt obtained by changing the pyrolysis conditions has an mesophase content of 81%, and the optical texture presents a coarse fiber structure and a streamlined structure, which account for 36% and 33% respectively. The results of elemental analysis show that the C / H atomic ratio is 2.13.

[0060] Example 4

[0061] Step 1: Grind the dried coal liquefaction pitch through a 30-mesh sieve. Step 2: Take 100 g of the coal liquefaction pitch in step 1 and add it to a reactor. Purge the air in the reactor with N2 for 10 minutes, heat it to 400°C, and react for 120 minutes to obtain a pre-pyrolysis product. Step 3: Grind the pre-pyrolysis product through a 30-mesh sieve, extract it with xylene, the extraction ratio is 1:10, the extraction temperature is 50°C, the extraction time is 180 minutes, filter to obtain the extraction phase, and distill the extraction phase under reduced pressure at 120°C for 45 minutes to obtain refined asphalt. Step 4: Grind and sieve the refined asphalt in step 3, and take 30g and mix it with a hydrogen supply solvent with a mass ratio of 30wt.% (the saturated ring accounts for about 40%, and its composition: about 20% of pentacyclic aromatic hydrocarbons, about 15% of tetracyclic aromatic hydrocarbons, about 50% of tricyclic aromatic hydrocarbons, and about 15% of dicyclic aromatic hydrocarbons) and add it to a high-temperature and high-pressure reactor. After N2 is purged for 10 minutes, it is heated to 430°C and the reaction time is controlled to 420min. The pressure in the reactor is 0.1Mpa and the stirring rate is 30rpm to obtain hydrogenated asphalt. Step 5: Grind the hydrogenated asphalt obtained in step 4 through a 30-mesh sieve and extract it with xylene. The extraction ratio is 1:10, the extraction temperature is 75°C, and the extraction time is 180min. Filter to obtain the raffinate phase, and vacuum dry the raffinate phase at 150°C for 120min. Step 6: Add the raffinate phase obtained in step 5 to a high-temperature and high-pressure reactor, purge it with N2 for 10 minutes, heat it to 380°C, and react for 30min to obtain the intermediate phase asphalt.

[0062] The mesophase asphalt obtained by changing the pyrolysis conditions has an mesophase content of 69%, and the optical texture shows that the coarse fiber structure and fine fiber structure account for 43% and 48% respectively. The results of elemental analysis show that the C / H atomic ratio is 2.18.

[0063] Example 5

[0064] Step 1: Grind the dried coal liquefaction pitch through a 30-mesh sieve. Step 2: Take 100 g of the coal liquefaction pitch in step 1 and add it to a reactor. Purge the air in the reactor with N2 for 10 minutes, heat it to 400°C, and react for 60 minutes to obtain a pre-pyrolysis product. Step 3: Grind the pre-pyrolysis product through a 30-mesh sieve, extract it with xylene, the extraction ratio is 1:10, the extraction temperature is 50°C, the extraction time is 180 minutes, filter to obtain the extraction phase, and distill the extraction phase under reduced pressure at 120°C for 45 minutes to obtain refined asphalt. Step 4: Grind and sieve the refined asphalt in step 3, and take 30g and mix it with a hydrogen supply solvent with a mass ratio of 30wt.% (the saturated ring accounts for about 50%, and its composition: about 12% of pentacyclic aromatic hydrocarbons, about 23% of tetracyclic aromatic hydrocarbons, about 50% of tricyclic aromatic hydrocarbons, and about 15% of dicyclic aromatic hydrocarbons) and add it to a high-temperature and high-pressure reactor. After N2 is purged for 10 minutes, it is heated to 430°C and the reaction time is controlled to 420min. The pressure in the reactor is 0.1Mpa and the stirring rate is 30rpm to obtain hydrogenated asphalt. Step 5: Grind the hydrogenated asphalt obtained in step 4 through a 30-mesh sieve and extract it with xylene. The extraction ratio is 1:10, the extraction temperature is 75°C, and the extraction time is 180min. Filter to obtain the raffinate phase, and vacuum dry the raffinate phase at 150°C for 120min. Step 6: Add the raffinate phase obtained in step 5 to a high-temperature and high-pressure reactor, purge it with N2 for 10 minutes, heat it to 380°C, and react for 30min to obtain the intermediate phase asphalt.

[0065] The obtained mesophase asphalt has a mesophase content of 86%, and the optical texture is an obvious wide-area streamlined structure of 73%, and the element analysis results show that the C / H atomic ratio is 2.14.

[0066] Example 6

[0067] Step 1: Grind the dried coal liquefaction pitch through a 30-mesh sieve. Step 2: Take 100 g of the coal liquefaction pitch in step 1 and add it to a reactor. Purge the air in the reactor with N2 for 10 minutes, heat it to 400°C, and react for 60 minutes to obtain a pre-pyrolysis product. Step 3: Grind the pre-pyrolysis product through a 30-mesh sieve, extract it with xylene, the extraction ratio is 1:10, the extraction temperature is 50°C, the extraction time is 180 minutes, filter to obtain the extraction phase, and distill the extraction phase under reduced pressure at 120°C for 45 minutes to obtain refined asphalt. Step 4: Grind and sieve the refined asphalt in step 3, and take 30g and mix it with a hydrogen supply solvent with a mass ratio of 30wt.% (the saturated ring ratio is about 45%, and its composition is: about 30% of pentacyclic aromatic hydrocarbons, about 15% of tetracyclic aromatic hydrocarbons, about 45% of tricyclic aromatic hydrocarbons, and about 10% of dicyclic aromatic hydrocarbons) and add it to a high-temperature and high-pressure reactor. After N2 purging for 10 minutes, heat it to 430°C and control the reaction time to 420min. The pressure in the reactor is 0.1Mpa and the stirring rate is 30rpm to obtain hydrogenated asphalt. Step 5: Grind the hydrogenated asphalt obtained in step 4 through a 30-mesh sieve and extract it with xylene. The extraction ratio is 1:10, the extraction temperature is 75°C, and the extraction time is 180min. Filter to obtain the raffinate phase, and vacuum dry the raffinate phase at 150°C for 120min. Step 6: Add the raffinate phase obtained in step 5 to a high-temperature and high-pressure reactor, purge it with N2 for 10 minutes, heat it to 380°C, and react for 30min to obtain the intermediate phase asphalt.

[0068] The obtained mesophase asphalt has an mesophase content of 71%, and the optical texture presents a coarse fiber structure and a streamlined structure, which account for 45% and 37% respectively. The results of elemental analysis show that the C / H atomic ratio is 2.07.

[0069] In the above-mentioned Examples 2-6, different pre-pyrolysis temperatures and pre-pyrolysis times, as well as hydrogen-donating solvents with different pentacyclic contents, are further explored. Suitable reaction conditions remove macromolecular components and highly reactive components in the raw material molecules, solve the problem of high reactive activity of the raw materials, and avoid rapid coking during thermal polycondensation. And hydrogenation treatment effectively provides more alkyl side chains and cycloalkane structures, promotes the high frequency of hydrogen transfer reaction and the orderly arrangement of planar condensed aromatic molecules during thermal polycondensation, and thus improves the optical texture of mesophase asphalt. Too high pre-pyrolysis temperature or too long pre-pyrolysis time leads to an increase in the degree of dehydrogenation aromatization of the system, affecting the growth of the carbon layer structure. When the content of pentacyclic and above aromatics in the hydrogen-donating solvent is high, it produces too many alkyl active sites and cannot be completely condensed. The residual alkyl side chains and free radicals are present at the edge of the planar condensed aromatic molecular layer and inserted between the planar sheets, which destroys the compactness of the stacking, causes steric hindrance and structural strain in the planar condensed aromatic molecular layer, thereby affecting the growth of the carbon layer structure, reducing the conjugation effect between the aromatic nuclei, and causing the destruction of the carbon layer structure of the mesophase asphalt.

Claims

1. A method for preparing mesophase pitch from coal liquefaction pitch, comprising the following steps: (1) pre-treating coal liquefaction pitch by pyrolysis to obtain a pre-pyrolysis product; (2) extracting the soluble components in the pre-pyrolysis product obtained in step (1) with a first aromatic solvent, and separating the obtained extract by distillation to remove the aromatic solvent to obtain refined asphalt; (3) uniformly mixing the refined asphalt obtained in step (2) with the hydrogen supply solvent and placing the mixture in a reactor for thermal polycondensation treatment to obtain thermal polycondensed asphalt; (4) crushing the heat-condensed asphalt obtained in step (3) and mixing it evenly with a second aromatic solvent for extraction, and then separating the insoluble components; (5) After drying the insoluble component obtained in step (4), heat treatment is performed under a protective atmosphere to obtain a mesophase pitch.

2. The method according to claim 1, characterized in that In step (1), the pyrolysis pretreatment is carried out in a protective atmosphere, the pyrolysis pretreatment temperature is 380 to 420° C., and the pyrolysis pretreatment time is 15 to 180 minutes.

3. The method according to claim 1 or 2, characterized in that: The first aromatic solvent is selected from one or more of benzene, toluene and xylene.

4. The method according to claim 3, characterized in that In step (2), the mass ratio of the pre-pyrolysis product to the first aromatic solvent is 1:1-10, the extraction temperature is 20-120°C, and the extraction time is 30-240 min; the extract phase obtained after extraction is distilled under reduced pressure at 80-150°C to remove the aromatic solvent to obtain refined asphalt.

5. The method according to any one of claims 1 to 4, characterized in that In step (3), the thermal polycondensation temperature is 380-450° C., the time is 120-1800 min, and the pressure is 0.5-3 MPa.

6. The method according to claim 5, characterized in that In step (3), the hydrogen-donating solvent is a partially saturated product of hydrogenated condensed aromatic hydrocarbons, wherein cycloalkanes account for 30% to 60% of the total number of rings of the condensed aromatic hydrocarbons; Preferably, the amount of the hydrogen-donating solvent used is 10%-50%.

7. The method according to claim 6, characterized in that The hydrogen-donating solvent contains 10-30% pentacyclic aromatic hydrocarbons, 10%-30% tetracyclic aromatic hydrocarbons, and 50-80% tricyclic aromatic hydrocarbons or less; Preferably, in the hydrogen supply solvent, the content of monocyclic aromatic hydrocarbons is no more than 5%, the content of dicyclic aromatic hydrocarbons is 5%-35%, the content of tricyclic aromatic hydrocarbons is 40%-60%, the content of tetracyclic aromatic hydrocarbons is 10%-30%, and the content of pentacyclic aromatic hydrocarbons is 5-30%, preferably 10-20%.

8. The method according to any one of claims 1 to 7, characterized in that In step (4), the second aromatic solvent is selected from one of benzene, toluene and xylene.

9. The method according to claim 1, characterized in that: In step (4), the heat-condensed asphalt is crushed to a particle size smaller than a 60-mesh sieve; and during extraction, it is mixed with a second aromatic solvent at a mass ratio of 1:1 to 10 at 20 to 120° C. for extraction.

10. The method according to claim 1, characterized in that In step (5), when the insoluble component is heat-treated, it is heated to 360-390° C. for 20-60 minutes.

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