Process for the preparation of pure, spinnable mesophase pitch

Abstract

The present application relates to a method for preparing pure spinnable mesophase pitch, comprising: (1) mixing two kinds of heavy oil or residual oil with a distillation fraction above 400 DEG C, and carrying out a preliminary thermal polycondensation and a first co-carbonization treatment to obtain a pre-polycondensation pitch; (2) under a nitrogen atmosphere, the pre-polycondensation pitch is subjected to constant temperature stirring and blowing to remove part of the evaporable components, and then extracted with an organic solvent to separate into light and heavy components; (3) the light and heavy components are mixed in a certain proportion, and a second co-carbonization agent is added to carry out a second thermal polycondensation to obtain a mesophase pitch precursor; (4) the light components in the precursor are removed by extraction with an organic solvent, and the precursor is kept at a constant temperature to obtain a pure spinnable mesophase pitch. The method has the advantages of mild reaction conditions, low equipment requirements, safety and sustainability; the product has high aromaticity, uniform molecular composition, and low content of heteroatoms and ash.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for preparing mesophase pitch, in particular, a method for preparing pure and spinnable mesophase pitch by twice co-carbonization. BACKGROUND

[0002] Mesophase pitch, also known as anisotropic pitch, is a kind of discotic macromolecular condensed ring nematic liquid crystal compound, which has a regular oriented macromolecular lamellar structure inside and is easy to graphitize when treated at high temperature. It is a precursor for preparing mesophase pitch-based carbon fiber, mesophase carbon microbeads, needle coke and mesophase foam carbon, etc. high-performance carbon materials, and has a huge application prospect in aerospace, electronic technology, daily life, etc.

[0003] Compared with other applications, the quality requirement of mesophase pitch for spinning is high, so the requirement of raw material is also high. The raw material for producing mesophase pitch for spinning generally requires a concentrated molecular weight distribution, a high carbon-hydrogen ratio, a certain amount of short alkyl side chains and naphthenic ring structures; at the same time, the raw material requires no solid impurities, no or a small amount of asphaltene, low S, N and other heteroatoms; and has appropriate viscosity, fluidity and thermal stability in the process of melt spinning. However, the raw materials such as coal and petroleum pitch have a wide range of molecular weight distribution, high ash content and heteroatom content, and contain a certain amount of asphaltene and other insoluble components, so the raw materials need to be refined before reaction. However, the existing traditional single treatment process cannot meet the requirements.

[0004] CN107474866 and CN110157476 disclose that the purified asphalt is directionally catalyzed by HF / BF3 and HF respectively, and then polymerized to obtain high-quality mesophase pitch. However, HF is corrosive, and the requirement for equipment material is harsh. Although the reaction system has low temperature, it needs pressurized operation and removal of the catalyst in the later stage, and there is a great safety hazard to personnel. CN106929084 discloses that high softening point asphalt is obtained by preliminary heat treatment and distillation of medium temperature petroleum asphalt as raw material, and then secondary hydrogenation heat treatment is carried out in hydrogen-donor solvent, and then insoluble matter is removed, and hydrogenated pitch is obtained by secondary flash distillation, and mesophase pitch is obtained by three times of heat treatment of the hydrogenated pitch. This method can well remove insoluble impurities and part of heteroatoms, but the process is segmented, the operation is complicated, the energy consumption of multiple flash distillations is large, the hydrogenation agent has low boiling point, which can easily cause excessive reaction pressure, the requirement for equipment is high, and the final yield is low. CN201810322789 discloses that refined coal pitch is used as raw material, a small amount of mesophase pitch is used as additive, and mesophase pitch product is obtained by direct heat polymerization after crushing and uniform mixing. However, the ash content of the purified asphalt is relatively high, and no purification treatment is carried out. After adding mesophase pitch, some heavy components will appear after reaction, resulting in uneven molecular weight distribution, which has certain influence on spinning and graphitization of carbonization. CN110041952 discloses that heavy products with a boiling point of 350-410℃ prepared by brown coal hot-solvent catalytic process are used as raw materials, and heavy components are obtained by hydrogenation heat polycondensation and vacuum distillation. The heavy components are subjected to short-time heat polycondensation and then subjected to secondary vacuum distillation to obtain crude pitch. The crude pitch is subjected to hydrogenation treatment again to obtain hydrogenated pitch. The hydrogenated pitch is subjected to flash distillation and hydrogen heat sensitization treatment to obtain mesophase pitch product. The process flow is complex, the energy consumption is high, the hydrogenation reaction pressure is very high, the requirement for equipment is harsh, there is a certain safety hazard, and the continuous vacuum distillation and hydrogenation reaction make the softening point of the mesophase pitch high, and the chemical structure is very stable, which is not conducive to spinning and later pre-oxidation treatment.

[0005] In view of the above problems, the present application provides a method for preparing pure mesophase pitch with good spinnability. The method uses heavy oil or residual oil with a boiling point of 400℃ or higher in atmospheric distillation, vacuum distillation, catalytic cracking and other process flows in petroleum refining process as raw material, and realizes secondary co-carbonization. The reaction conditions of the method are not harsh, the requirement for equipment is low, and the method is safe and sustainable. The obtained mesophase pitch has high aromaticity, uniform molecular composition, and low content of heteroatoms and ash. SUMMARY

[0006] The present application aims to provide a method for preparing pure and spinnable mesophase pitch, which uses heavy oil or residual oil from 400 DEG C or above distillation in atmospheric distillation, vacuum distillation, catalytic cracking and other processes in coal and petroleum refining as raw material, and performs one co-carbonization treatment through preliminary thermal polycondensation of the raw material oil obtained from two different processes, which can make up for the shortage of raw material and improve the utilization rate of raw material, and then solvent extraction is performed to purify the reaction raw material and obtain the required components, and then a second co-carbon agent is added to perform a second co-carbonization treatment to optimize the molecular structure of the mesophase pitch and control the composition and structure of the mesophase pitch, so as to solve the problems of low content, high ash content and low softening point of the mesophase pitch, complex preparation process and high energy consumption, and prepare pure and spinnable mesophase pitch with good spinnability.

[0007] To achieve the above-mentioned purpose, the present application adopts the following technical scheme:

[0008] A method for preparing pure and spinnable mesophase pitch comprises the following steps:

[0009] (1) two kinds of heavy oil or residual oil from 400 DEG C or above distillation in different processes in coal and petroleum refining are mixed uniformly in a stirred tank, and preliminary thermal polycondensation is performed to realize one co-carbonization treatment, and pre-polycondensation pitch is obtained;

[0010] (2) the pre-polycondensation pitch obtained in step (1) is stirred at constant temperature under nitrogen atmosphere, and part of the evaporable components are removed by blowing, and then extraction is performed by using an organic solvent to perform extraction layering, and the pre-polycondensation pitch is divided into light and heavy components;

[0011] (3) the light and heavy components obtained in step (2) are mixed in a certain proportion, a certain amount of a second co-carbon agent is added, and second thermal polycondensation is performed to realize second co-carbonization treatment, and mesophase pitch precursor is obtained;

[0012] (4) extraction is performed by using an organic solvent to remove the light components in the mesophase pitch precursor obtained in step (3), and then the temperature is kept for a period of time, and wide-range flow-line mesophase pitch with good spinnability is obtained.

[0013] In step (1), the reaction raw material is a distillate oil with a temperature greater than 400℃, a heavy oil or residual oil from coal, atmospheric distillation, vacuum distillation, catalytic cracking, etc. The two raw materials differ in the process of their origin, such as atmospheric tower bottom oil, vacuum residual oil, hydrocracking tail oil, catalytic cracking oil slurry, coal tar, etc., which makes their molecular weight distribution and molecular structure different. For example, compared with atmospheric tower bottom oil, vacuum residual oil has a larger molecular weight, a larger carbon-hydrogen ratio, and a higher softening point of the oil product; hydrocracking tail oil has fewer impurities and a high material reactivity; catalytic cracking oil slurry has a very high aromatic fraction, but contains catalyst particles; coal tar has a disc-shaped molecule with fewer branched chains and side chains, and a stronger molecular rigidity. The ratio of the two raw materials is 10:1 to 10.

[0014] The two raw materials are heated in a stirred tank under nitrogen protection at a heating rate of 3 to 10℃ / min to a temperature of 100 to 200℃ under a pressure of 0 to 2MPa, and then stirred at a constant temperature for 30 to 60 minutes at a stirring rate of 100 to 500rpm.

[0015] The preliminary thermal polycondensation reaction conditions are as follows: the reaction is carried out under a hydrogen atmosphere at a heating rate of 3 to 10℃ / min, a reaction temperature of 380 to 500℃, a pressure of 0 to 6MPa, a stirring speed of 300 to 800rpm, and a holding time of 1 to 5 hours. The preliminary thermal polycondensation reaction is completed to obtain a pre-polycondensation pitch.

[0016] In step (2), the stirring and purging time is 30 to 120 minutes, the temperature is 150 to 250℃, the stirring rate is 400 to 800rpm, and the purging gas flow rate is 60 to 120mL / (h·g); the organic solvent is a mixed solvent of n-heptane, toluene, and quinoline in any proportion. The light component is mainly a component dissolved in the mixed solvent of n-heptane and toluene in any proportion; the heavy component is a component not dissolved in the light component solvent but dissolved in the mixed solvent of toluene and quinoline in any proportion.

[0017] In step (3), the light and heavy components and the carbonization agent of step (2) are stirred at a constant temperature for 30 to 60 minutes under a nitrogen atmosphere at a heating rate of 3 to 10℃ / min to a temperature of 100 to 250℃ under a pressure of 0 to 2MPa at a stirring rate of 100 to 500rpm.

[0018] The secondary pre-polycondensation reaction is carried out under a nitrogen atmosphere at a heating rate of 3 to 10℃ / min, a reaction temperature of 450 to 580℃, a pressure of 5 to 10MPa, a stirring speed of 50 to 600rpm, and a holding time of 4 to 8 hours. The secondary pre-polycondensation reaction is completed to obtain a precursor of mesophase pitch;

[0019] The secondary co-carbon agent is a polycyclic aromatic compound containing side chains, such as methyl naphthalene, 2-methyl pyrene, etc., or a condensing agent, such as polyvinyl alcohol, polybutadiene diol, polyacrylic acid, etc. The mass ratio of the secondary co-carbon agent to the mixture of light and heavy components obtained by extraction in step (2) is 1-30:100, and the mass ratio of the mixture of light and heavy components obtained by extraction in step (2) is 1-3:7-9.

[0020] In step (4), the organic solvent used is a mixed solvent of n-heptane and toluene in any proportion. The heat preservation is carried out under a hydrogen or nitrogen atmosphere, at a temperature of 450-580°C, a pressure of -0.1 MPa to 2 MPa, a stirring rate of 0-600 rpm, and a heat preservation time of 2-5 hours, thereby obtaining a spinnable high-quality pitch with low content of heteroatoms and low ash content.

[0021] The present application has the following advantages:

[0022] 1. No strong acid or strong base is involved, no catalyst or other impurities are introduced, the requirement for equipment is low, and the safety and reliability are high. The intermediate phase pitch obtained has a low softening point, a high content of intermediate phase, low ash content, and good rheological property.

[0023] 2. The requirement for the properties of raw materials is not strict, and the raw materials are widely available. The co-carbon agent is co-carbonized with the raw materials for a short time, which makes up for the deficiency of the raw materials, rapidly increases the molecular weight of the pitch, and the hydrogen atmosphere is beneficial to the removal of impurity elements. Then, the part with too large molecular weight in the raw materials is removed by solvent extraction, and the reaction raw materials are purified for the second time.

[0024] 3. The product of the preliminary thermal polycondensation is added to pure compounds for secondary co-carbonization, which makes the pitch molecules further grow, improves the composition and structure of the planar macromolecules of the pitch, and the hydrogen donor can prevent the viscosity of the system from increasing too fast during the reaction, and reduces the softening point of the intermediate phase pitch.

[0025] 4. Finally, the obtained product is removed of light components and subjected to heat preservation, which promotes the fusion of the intermediate phase small balls, is beneficial to the improvement of the optical structure of the intermediate phase pitch, and obtains a high-quality intermediate phase pitch product with a wide range of flow lines and a relatively low softening point. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is the operation step flow chart of the preparation method of the present application.

[0027] Figure 2 is the softening point and intermediate phase content of the intermediate phase pitch obtained in Examples 1-14 of the present application. DETAILED DESCRIPTION

[0028] The application will be further described below in connection with specific embodiments, which are only a part of the embodiments of the application, and the application is not limited by any of these embodiments. Those skilled in the art can make various modifications within the technical concept of the application. All other embodiments obtained by those skilled in the art without creative labor based on the embodiments in the application fall within the scope of protection of the application.

[0029] Embodiment 1

[0030] (1) The hydrogen cracking tail oil of the fraction at about 400℃ was mixed with the vacuum residue at a ratio of 1:1 in a high-pressure reaction kettle, N2 was introduced, and constant temperature stirring was carried out at a temperature of 150℃, a temperature increasing rate of 3℃ / min, a pressure of 0MPa, and a stirring rate of 500r / min for 30min to obtain a mixed raw material; (2) the mixed raw material was heated to 400℃ at a temperature increasing rate of 3℃ / min under a hydrogen atmosphere, and reacted for 2h under the conditions of an initial pressure of 2MPa and a stirring speed of 300r / min to obtain a pre-polycondensation pitch; (3) part of the evaporable components were removed by stirring and purging at a temperature of 150℃, a stirring rate of 500r / min, a nitrogen atmosphere, and a gas flow rate of 100mL / (h.g) for 60min; (4) then the pre-polycondensation pitch was extracted with a mixed solvent of n-heptane:toluene=3:1 and a mixed solvent of toluene:quinoline=1:3, respectively, and was divided into light and heavy components; (5) the light component:heavy component:methyl naphthalene=1:9:1 were mixed according to the mass ratio, and a secondary mixed raw material was obtained by constant temperature stirring at a nitrogen atmosphere, a temperature of 180℃, a temperature increasing rate of 3℃ / min, a pressure of 0MPa, and a stirring rate of 500r / min for 30min; (6) the secondary mixed raw material was heated to 500℃ at a temperature increasing rate of 3℃ / min under a nitrogen atmosphere, and reacted for 6h under the conditions of an initial pressure of 2MPa and a stirring speed of 300r / min to obtain a mesophase pitch precursor; (7) the mesophase pitch precursor was extracted with a mixed solvent of n-heptane:toluene=1:3 to remove light components; then, high-quality mesophase pitch was obtained by constant temperature for 2h at a temperature of 550℃ and a pressure of 1MPa under a nitrogen atmosphere.

[0031] The structure and content of the mesophase pitch were measured by polarized light microscopy, the softening point was measured by the needle penetration method, and the contents of C, H, S and other elements were measured by an elemental analyzer. The test results show that the mesophase pitch obtained in this embodiment is a wide-range flow-line mesophase pitch, the mesophase content is 90%, the softening point is 260℃, the aromaticity is 0.82, the carbon-hydrogen ratio is 1.63, the ash content is less than 50ppm, and the non-carbon element is less than 1%.

[0032] Embodiment 2

[0033] The first co-carbon thermal polycondensation in Example 1 was changed from hydrogen atmosphere to nitrogen atmosphere, and other conditions were the same as in Example 1. The obtained mesophase pitch was wide-range flow-line mesophase pitch, the mesophase content was 92%, the softening point was 268°C, the aromaticity was 0.88, the carbon-hydrogen ratio was 1.68, the ash content was less than 50 ppm, and the non-carbon elements were less than 1%.

[0034] Example 3:

[0035] The first co-carbon thermal polycondensation in Example 1 was changed from 400°C to 450°C, and other conditions were the same as in Example 1. The obtained mesophase pitch was wide-range flow-line mesophase pitch, the mesophase content was 96%, the softening point was 275°C, the aromaticity was 0.9, the carbon-hydrogen ratio was 1.72, the ash content was less than 50 ppm, and the non-carbon elements were less than 1%.

[0036] Example 4:

[0037] The second co-carbon thermal polycondensation in Example 1 was changed from 500°C to 460°C, and other conditions were the same as in Example 1. The obtained mesophase pitch was wide-range flow-line mesophase pitch, the mesophase content was 93%, the softening point was 267°C, the aromaticity was 0.87, the carbon-hydrogen ratio was 1.70, the ash content was less than 50 ppm, and the non-carbon elements were less than 1%.

[0038] Example 5:

[0039] The first co-carbon thermal polycondensation in Example 1 was changed from 2 MPa to 4 MPa, and other conditions were the same as in Example 1. The obtained mesophase pitch was wide-range flow-line mesophase pitch, the mesophase content was 91%, the softening point was 263°C, the aromaticity was 0.79, the carbon-hydrogen ratio was 1.66, the ash content was less than 50 ppm, and the non-carbon elements were less than 1%.

[0040] Example 6:

[0041] The first co-carbon thermal polycondensation in Example 1 was changed from 1 MPa to 0 MPa, and other conditions were the same as in Example 1. The obtained mesophase pitch was wide-range flow-line mesophase pitch, the mesophase content was 94%, the softening point was 285°C, the aromaticity was 0.86, the carbon-hydrogen ratio was 1.77, the ash content was less than 50 ppm, and the non-carbon elements were less than 1%.

[0042] Example 7:

[0043] The third holding pressure in Example 1 was changed from 1 MPa to 0.5 MPa, and other conditions were the same as in Example 1. The obtained mesophase pitch was wide-range flow-line mesophase pitch, the mesophase content was 93%, the softening point was 281°C, the aromaticity was 0.90, the carbon-hydrogen ratio was 1.83, the ash content was less than 50 ppm, and the non-carbon elements were less than 1%.

[0044] Example 8:

[0045] The time of the first co-carbon thermal polycondensation in Example 1 was extended from 2 hours to 3 hours, and other conditions were the same as in Example 1. The obtained mesophase pitch was a wide-range flow-line mesophase pitch, the mesophase content was 96%, the softening point was 290°C, the aromaticity was 0.93, the carbon-hydrogen ratio was 1.92, the ash content was less than 50 ppm, and the non-carbon elements were less than 1%.

[0046] Example 9:

[0047] The time of the second co-carbon thermal polycondensation in Example 1 was reduced from 6 hours to 4 hours, and other conditions were the same as in Example 1. The obtained mesophase pitch was a wide-range flow-line mesophase pitch, the mesophase content was 92%, the softening point was 266°C, the aromaticity was 0.84, the carbon-hydrogen ratio was 1.85, the ash content was less than 50 ppm, and the non-carbon elements were less than 1%.

[0048] Example 10:

[0049] The time of the third holding in Example 1 was extended from 2 hours to 3 hours, and other conditions were the same as in Example 1. The obtained mesophase pitch was a wide-range flow-line mesophase pitch, the mesophase content was 97%, the softening point was 292°C, the aromaticity was 0.93, the carbon-hydrogen ratio was 1.92, the ash content was less than 50 ppm, and the non-carbon elements were less than 1%.

[0050] Example 11:

[0051] The ratio of the second mixed raw materials in Example 1 was changed from light component: heavy component: methyl naphthalene = 1:9:1 to light component: heavy component: methyl naphthalene = 3:9:1, and other conditions were the same as in Example 1. The obtained mesophase pitch was a wide-range flow-line mesophase pitch, the mesophase content was 93%, the softening point was 260°C, the aromaticity was 0.72, the carbon-hydrogen ratio was 1.80, the ash content was less than 50 ppm, and the non-carbon elements were less than 1%.

[0052] Example 12:

[0053] The ratio of the second mixed raw materials in Example 1 was changed from light component: heavy component: methyl naphthalene = 1:9:1 to light component: heavy component: methyl naphthalene = 1:9:3, and other conditions were the same as in Example 1. The obtained mesophase pitch was a wide-range flow-line mesophase pitch, the mesophase content was 92%, the softening point was 262°C, the aromaticity was 0.70, the carbon-hydrogen ratio was 1.78, the ash content was less than 50 ppm, and the non-carbon elements were less than 1%.

[0054] Example 13:

[0055] The methyl naphthalene in the secondary mixing raw material in Example 1 was replaced by polyacrylic acid, and other conditions were the same as in Example 1. The obtained mesophase pitch was a wide-range flow-line mesophase pitch, the mesophase content was 96%, the softening point was 302°C, the aromaticity was 0.84, the carbon-hydrogen ratio was 1.88, the ash content was less than 50 ppm, and the non-carbon element was less than 1%.

[0056] Example 14:

[0057] The extraction solvent mixture of the pre-polymerization pitch in Example 1, n-heptane:toluene=3:1, and the mixture of toluene and quinoline=1:3, was changed to n-heptane:toluene=3:2 and toluene:quinoline=1:5, and other conditions were the same as in Example 1. The obtained mesophase pitch was a wide-range flow-line mesophase pitch, the mesophase content was 95%, the softening point was 285°C, the aromaticity was 0.92, the carbon-hydrogen ratio was 1.94, the ash content was less than 50 ppm, and the non-carbon element was less than 1%.

Claims

1. A method for preparing pure spinnable mesophase pitch, comprising the following steps: (1) adding two kinds of heavy oil or residual oil with a distillation temperature above 400 ℃ from different processes of coal or petroleum refining into a stirred tank to mix uniformly, and then performing a preliminary thermal polycondensation to realize a first co-carbonization treatment, thereby obtaining a pre-polycondensation pitch; (2) under a nitrogen atmosphere, performing a constant-temperature stirring and blowing to remove part of the evaporable components of the pre-polycondensation pitch obtained in step (1), and then performing an extraction with an organic solvent, thereby separating the pre-polycondensation pitch into a light component and a heavy component, wherein the light component is soluble in a solvent formed by mixing n-heptane and toluene in any proportion, and the heavy component is insoluble in the light component solvent but soluble in a solvent formed by mixing toluene and quinoline in any proportion; (3) mixing the light component and the heavy component obtained in step (2) in a certain proportion, adding a certain amount of a second co-carbon agent, and then performing a second thermal polycondensation to realize a second co-carbonization treatment, thereby obtaining a mesophase pitch precursor; (4) performing an extraction with an organic solvent to remove the light components in the mesophase pitch precursor obtained in step (3), and then performing a heat preservation for a period of time, thereby obtaining a wide-range flow-line mesophase pitch with good spinning performance. 2.The method according to claim 1, wherein in step (1), the use amount ratio of the two kinds of raw materials is 10:1-10. 3.The method according to claim 1, wherein in step (1), the preliminary thermal polycondensation is performed under a hydrogen atmosphere, the heating rate is 3-10 ℃ / min, the reaction temperature is 380-500 ℃, the pressure is 0-6 MPa, the stirring speed is 300-800 rpm, and the heat preservation time is 1-5 hours. 4.The method according to claim 1, wherein in step (2), the stirring and blowing time is 30-120 min, the temperature is 150-250 ℃, the stirring speed is 400-800 rpm, and the blowing gas flow rate is 60-120 mL / (h·g). 5.The method according to claim 1, wherein in step (3), the second thermal polycondensation is performed under a nitrogen atmosphere, the heating rate is 3-10 ℃ / min, the reaction temperature is 450-580 ℃, the pressure is 5-10 MPa, the stirring speed is 50-600 rpm, and the heat preservation time is 4-8 hours. 6.The method according to claim 1, wherein in step (3), the second co-carbon agent is a polycyclic aromatic hydrocarbon compound containing a side chain or a condensing agent. 7.The method according to claim 6, wherein the polycyclic aromatic hydrocarbon compound containing a side chain is methyl naphthalene or 2-methyl pyrene, and the condensing agent is polyvinyl alcohol, polybutadiene diol or polyacrylic acid. 8.The method according to claim 1, wherein in step (3), the mixing mass ratio of the light component and the heavy component obtained in step (2) is 1-3:7-9, and the mass ratio of the second co-carbon agent to the light component and the heavy component mixture of step (2) is 1-30:

100. ​ ​ ​ ​ 9. The method according to claim 1, wherein in step (4), the organic solvent is a mixed solvent of n-heptane and toluene in any ratio.

10. The method according to claim 1, wherein in step (4), the heat preservation is performed under a hydrogen or nitrogen atmosphere at a temperature of 450-580°C, a pressure of -0.1 MPa to 2 MPa, a stirring rate of 0-600 rpm, and a heat preservation time of 2-5 hours.

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