Device and method for preparing isotropic spinnable pitch

Abstract

The present invention discloses a device and method for preparing isotropic spinnable pitch, which relates to the technical field of asphalt-based carbon fiber production. The purpose is to effectively solve the problems of uneven heating of materials and poor batch stability in the preparation of isotropic spinnable pitch. The main technical solution of the present invention is as follows: the device for preparing isotropic spinnable pitch comprises: a reactor and a twin-screw reactor; the upper end of the reactor is connected to a feed pipe and an exhaust pipe, the interior of the reactor is provided with an air jet pipe, the tube wall of the air jet pipe is uniformly distributed with multiple air jet holes, and the air jet pipe is respectively connected to an air pipe and a nitrogen pipe; the front end of the twin-screw reactor is provided with a feed port and an air injection port, the middle section of the twin-screw reactor is provided with a first exhaust port, and the tail end of the twin-screw reactor is provided with a second exhaust port; one end of the feed pipe is connected to the lower end of the reactor, and the other end is connected to the feed port; one end of the circulation pipe is connected to the upper end of the reactor, and the other end is connected to the discharge pipe of the twin-screw reactor.

Description

Technical Field

[0001] The present invention relates to the technical field of asphalt-based carbon fiber production, and in particular to a device and method for preparing isotropic spinnable asphalt. Background Art

[0002] Industrially produced general-grade pitch carbon fiber is inexpensive and has the typical properties of carbon materials, such as light weight, conductivity, heat resistance, wear resistance and good chemical stability. It is suitable for furnace insulation materials, fuel cell electrodes and cement reinforcements. It can also be used in automotive brake pads, sealing materials, audio materials and gas masks.

[0003] General-grade pitch carbon fiber is produced from isotropic spinnable pitch, a byproduct of petroleum and coal chemical industries. This raw material is abundant and inexpensive. It should have a high softening point, a concentrated molecular weight distribution, good non-thixotropic viscosity-temperature characteristics within the spinning temperature range, uniform plastic flow behavior, and the ability to be spun stably and continuously.

[0004] Chinese patent CN103184062A discloses a method for preparing a high-softening-point spinning pitch. First, the coal tar pitch from which quinoline insolubles have been removed is subjected to scraping evaporation under appropriate conditions to remove some light components to obtain refined pitch. The refined pitch is then thermally polycondensed in a reactor and then subjected to a second scraping evaporation to remove the light components to obtain a spinning pitch with a high softening point of 260-275°C.

[0005] Chinese patent CN102776014A discloses a method for preparing a petroleum-based spinning pitch with a high softening point, wherein light components are removed from ethylene tar by scraping film evaporation, followed by further constant temperature thermal polycondensation, and then scraping film evaporation to remove light components to obtain a spinning pitch with a high softening point of 270-285°C.

[0006] Chinese patent 201210541249.4 discloses a method for preparing a general-grade coal-based asphalt carbon fiber. The method involves oxidizing high-purity impregnating agent asphalt in a continuous reactor to obtain high-softening point asphalt. In order to improve the quality of carbon fiber, an additive composition is added during the preparation of the high-softening point asphalt.

[0007] Chinese patent CN200710163857.5 discloses a method for preparing general-grade pitch carbon fiber, in which ethylene tar with a residual carbon content of 7-10% and an ash content of 0.01-0.04% is placed in a reactor and air oxidation is used to prepare spinnable pitch.

[0008] Chinese patent CN105885907A discloses "A method for preparing general-grade pitch carbon fiber spinning pitch". This method uses a combination of liquid-phase oxidant oxidation and thermal polycondensation to prepare spinning pitch. Compared with the previous air oxidation method or thermal polycondensation method, the use of liquid-phase oxidant makes the reaction temperature milder and the time is greatly shortened.

[0009] Chinese patent CN202011055631.5 discloses "A method for preparing general-grade asphalt-based carbon fibers", which involves heat-treating the raw coal tar or ethylene tar to melt the raw materials. In an inert atmosphere, the melted raw materials are heated to the reaction temperature, and chlorine gas is introduced to carry out a chlorination reaction to prepare an asphalt precursor.

[0010] In the above scheme, when the temperature rises, dehydrogenation, cross-linking, condensation and other reactions occur, releasing H2, H2O, H2S and small molecular weight compounds, and obtaining better spinnable asphalt, but no solution is given to local material overheating and uneven heating during the preparation process. Summary of the Invention

[0011] In view of this, the present invention provides a device and method for preparing isotropic spinnable pitch, the main purpose of which is to effectively solve the problems of uneven heating of materials and poor batch stability in the preparation of isotropic spinnable pitch.

[0012] To achieve the above objectives, the present invention mainly provides the following technical solutions:

[0013] In one aspect, the present invention provides a device for preparing isotropic spinnable pitch, the device comprising: a reaction kettle and a twin-screw reactor;

[0014] The upper end of the reactor is connected to the feed pipe and the exhaust pipe. The interior of the reactor is provided with an air jet pipe, the wall of which is uniformly distributed with a plurality of air jet holes. The air jet pipe is respectively connected to the air pipe and the nitrogen pipe.

[0015] The front end of the twin-screw reactor is provided with a feed port and a gas injection port, the middle section of the twin-screw reactor is provided with a first exhaust port, and the tail end of the twin-screw reactor is provided with a second exhaust port;

[0016] Among them, it also includes a feed pipe and a circulation pipe, one end of the feed pipe is connected to the lower end of the reactor, and the other end is connected to the feed port, one end of the circulation pipe is connected to the upper end of the reactor, and the other end is connected to the discharge pipe of the twin-screw reactor.

[0017] On the other hand, the present invention provides a method for preparing isotropic spinnable pitch, the method comprising the following steps:

[0018] (1) First, the material is added to the reactor through the feed pipe, the material is stirred, and the temperature of the reactor is increased. At the same time, air is introduced into the reactor through the air pipe, and the material undergoes an oxidation reaction. The tail gas generated by the reaction is discharged from the exhaust pipe. After the twin-screw reactor is started, the material in the reactor enters the twin-screw reactor through the feed pipe and then flows back to the reactor through the circulation pipe. At the same time, the air injection port is opened and air is injected. The pressure of the first exhaust port and the pressure of the second exhaust port are respectively adjusted to a slightly negative pressure;

[0019] (2) After the oxidation reaction is completed, the reaction temperature of the material is maintained, the air pipe valve and the air injection port are closed, and at the same time, the nitrogen pipe valve is opened to introduce nitrogen into the reactor, and the mixture of volatile components in the material and nitrogen is discharged through the exhaust pipe, the first exhaust port, and the second exhaust port respectively;

[0020] (3) the nitrogen pipe valve is closed, the gas injection port is opened, the circulation pipe valve is closed, and the material in the reactor continues to enter the twin-screw reactor, and a thermal polycondensation reaction occurs in the medium flow channel of the twin-screw reactor, or an oxidation reaction occurs in the medium flow channel of the twin-screw reactor between the gas injection port and the first exhaust port, and a thermal polycondensation reaction occurs in the medium flow channel of the twin-screw reactor between the first exhaust port and the second exhaust port;

[0021] (4) The finished product produced after the material that has completed the thermal polycondensation reaction is devolatilized through the second exhaust port is discharged through the discharge pipe.

[0022] The purpose of the present invention and the solution to its technical problems can be further achieved by adopting the following technical measures.

[0023] Optionally, in step (1), the material is petroleum asphalt or coal asphalt.

[0024] Optionally, in step (1), during the oxidation reaction, the reaction temperature is 300-320° C., and the residence time of the material in the twin-screw reactor is 20-50 min.

[0025] Optionally, in step (2), the residence time of the material in the twin-screw reactor is 19-21 minutes.

[0026] Optionally, in step (3), the residence time of the material in the twin-screw reactor is 30-50 min, and the vacuum degree of the first exhaust port and the vacuum degree of the second exhaust port are both 50-70 Pa.

[0027] Optionally, in step (3), the oxidation reaction temperature is 300-310°C, and the thermal polycondensation reaction temperature is 345-360°C.

[0028] Optionally, in step (4), the extrusion pressure of the twin-screw reactor is greater than 4 MPa, the vacuum degree of the second exhaust port is 50-70 Pa, and the target softening point of the finished material is 223-307°C.

[0029] Optionally, the target softening point of the finished material is 273-276°C.

[0030] Optionally, in step (1) and step (2), the reaction temperature is ≤ the heating temperature of the reactor ≤ the reaction temperature + 5°C, and the reaction temperature is ≤ the heating temperature of the twin-screw reactor ≤ the reaction temperature + 3°C; in step (3) and step (4), the reaction temperature is ≤ the heating temperature of the twin-screw reactor ≤ the reaction temperature + 3°C.

[0031] By means of the above technical solution, the present invention has at least the following advantages:

[0032] The reactor and the twin-screw reactor form a linked circulating reaction system. During the reaction and devolatilization of the material in the reactor, the twin-screw reactor and the reactor are linked to obtain the material from the bottom of the reactor. The material processed by the twin-screw reactor (extrusion, extrusion pressure ≥ 2MPa) is returned to the reactor and plays the role of circulating material.

[0033] Subsequently, the material properties are only regulated by the twin-screw reactor, and finally the spinnable asphalt is extruded by the twin-screw reactor. The entire preparation process strictly controls the heating temperature ≤ 5°C from the reaction temperature, and the material is heated evenly without overheating. This allows the preparation of isotropic spinnable asphalt with a target softening point of ±3°C, good batch-to-batch stability, and excellent spinnability. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A schematic structural diagram of a device for preparing isotropic spinnable pitch provided in an embodiment of the present invention.

[0035] The reference numerals in the drawings of the specification include: reactor 1, twin-screw reactor 2, feed pipe 3, exhaust pipe 4, injection pipe 5, air pipe 6, nitrogen pipe 7, gas injection port 8, first exhaust port 9, second exhaust port 10, feed pipe 11, and circulation pipe 12. DETAILED DESCRIPTION

[0036] To further illustrate the technical means and effects employed by the present invention to achieve its intended objectives, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention is provided in conjunction with the accompanying drawings and preferred embodiments. In the following description, different references to "one embodiment" or "embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics of one or more embodiments may be combined in any suitable manner.

[0037] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0038] like Figure 1 As shown, on the one hand, an embodiment of the present invention provides a device for preparing isotropic spinnable pitch, which includes: a reactor 1 and a twin-screw reactor 2;

[0039] The upper end of the reactor 1 is connected to the feed pipe 3 and the exhaust pipe 4. The reactor 1 is provided with an air injection pipe 5. The wall of the air injection pipe 5 is uniformly distributed with multiple air injection holes. The air injection pipe 5 is respectively connected to the air pipe 6 and the nitrogen pipe 7.

[0040] The front end of the twin-screw reactor 2 is provided with a feed port and a gas injection port 8, the middle section of the twin-screw reactor 2 is provided with a first exhaust port 9, and the tail end of the twin-screw reactor 2 is provided with a second exhaust port 10;

[0041] It also includes a feed pipe 11 and a circulation pipe 12, one end of the feed pipe 11 is connected to the lower end of the reactor 1, and the other end is connected to the feed port, one end of the circulation pipe 12 is connected to the upper end of the reactor 1, and the other end is connected to the discharge pipe of the twin-screw reactor 2.

[0042] Specifically, the reactor 1 is a batch reactor.

[0043] Specifically, the twin-screw reactor 2 is a twin-screw extruder with reaction, devolatilization and extrusion functions. The twin-screw reactor 2 is provided with vacuum exhaust ports at the outlet section and the middle section (the exhaust ports have the function of preventing material backflow) for removing volatiles; an air injection port 8 is added between the front section of the inlet section and the middle exhaust port; the extrusion pressure is ≥2MPa; the residence time of the flowing material in the twin-screw reactor 2 is controlled at 20-50min.

[0044] Specifically, a stirrer is provided in the reactor 1 , an air injection pipe 5 is provided in an annular shape at the lower end of the stirrer, and a heat transfer oil jacket is provided on the side wall of the reactor 1 .

[0045] Specifically, a heating wire is provided on the outer surface of the medium flow channel shell of the twin-screw reactor 2 .

[0046] Specifically, when the device is running, when the materials in the reactor are purged with air or nitrogen, the tail gas in the reactor can be discharged through the exhaust pipe.

[0047] On the other hand, an embodiment of the present invention provides a method for preparing isotropic spinnable pitch, and the specific embodiments are as follows:

[0048] Example 1

[0049] (1) Low-temperature coal tar with an ash content of less than 1 ppm and a softening point of 38°C is added to the reactor through a feed pipe, the asphalt material is stirred, and heat transfer oil is passed through the jacket to increase the temperature of the reactor. At the same time, air is introduced into the reactor through an air pipe to cause an oxidation reaction of the material. The heating temperature of the reactor (temperature of the heat transfer oil in the reactor jacket) is controlled to be ≤325°C, the reaction temperature of the material is 320°C, the reaction pressure is slightly positive (gauge pressure, ≤100 Pa), and the reaction time is 4 hours.

[0050] During the air-purging oxidation reaction of the material in the reactor, the tail gas generated by the reaction is discharged from the exhaust pipe, the material in the reactor enters the twin-screw reactor through the feed pipe, and air is injected from the air injection port of the twin-screw reactor. The material and air undergo an oxidation reaction in the twin-screw reactor. The heating temperature of the twin-screw reactor electric heating wire, the material reaction temperature of 320°C, and the pressure of the first exhaust port and the second exhaust port are both slightly negative (gauge pressure, ≥-100Pa); the material after treatment in the twin-screw reactor (extrusion, extrusion pressure 2MPa) is refluxed to the reactor through the circulation pipe, and the material stays in the twin-screw reactor for 50min.

[0051] (2) The reaction temperature was then maintained at 320°C, and a slight positive pressure nitrogen purge was performed for 0.5 hours to remove the volatile components. During the nitrogen purge of the materials in the reactor, the gas injection port of the twin-screw reactor was closed, and the materials in the twin-screw reactor no longer underwent oxidation reaction. The temperature was kept constant at 320°C, and devolatilization continued (the pressures at the first and second exhaust ports were both slightly negative). The materials continued to circulate between the reactor and the twin-screw reactor, and the materials stayed in the twin-screw reactor for 21 minutes.

[0052] (3) Stop nitrogen purging in the reactor, close the valve of the circulation pipe, and allow the material in the reactor to continue to enter the twin-screw reactor through the feed pipe. The flowing material stays in the twin-screw reactor for 30 minutes to undergo thermal polycondensation and devolatilization. The heating temperature of the twin-screw reactor's heating wire is controlled to be ≤363°C, the thermal polycondensation reaction temperature to be 360°C, the devolatilization operating temperature to be 360°C, and the vacuum degree of the first exhaust port and the second exhaust port to be 70Pa.

[0053] (4) The material treated in the twin-screw reactor is extruded into isotropic spinnable asphalt with a softening point of 279°C under an extrusion pressure of 4 MPa.

[0054] Example 2

[0055] (1) Medium-temperature coal tar pitch with an ash content of less than 1 ppm and a softening point of 86°C is added to the reactor through a feed pipe, the asphalt material is stirred, and the temperature of the reactor is increased by passing heat transfer oil through the jacket. At the same time, air is introduced into the reactor through an air pipe to cause an oxidation reaction of the material. The heating temperature of the reactor (temperature of the heat transfer oil in the reactor jacket) is controlled to be ≤305°C, the reaction temperature is 300°C, the reaction pressure is slightly positive (gauge pressure, ≤100 Pa), and the reaction time is 6 hours.

[0056] During the air-purging oxidation reaction of the material in the reactor, the tail gas generated by the reaction is discharged from the exhaust pipe, the material in the reactor enters the twin-screw reactor through the feed pipe, and air is injected from the air injection port of the twin-screw reactor. The material and air undergo an oxidation reaction in the twin-screw reactor. The heating temperature of the twin-screw reactor electric heating wire is controlled to be ≤303°C, the material reaction temperature is 300°C, and the pressures of the first exhaust port and the second exhaust port are both slightly negative (gauge pressure, ≥-100Pa); the material after treatment in the twin-screw reactor (extrusion, extrusion pressure 2.5MPa) is refluxed to the reactor through the circulation pipe, and the material resides in the twin-screw reactor for 20min.

[0057] (2) The reaction temperature was then maintained at 300°C, and a slight positive pressure nitrogen purge was performed for 0.5 hours to remove the volatile components. During the nitrogen purge of the materials in the reactor, the gas injection port of the twin-screw reactor was closed, and the materials in the twin-screw reactor no longer underwent oxidation reaction. The temperature was kept constant at 300°C, and the devolatilization was continued (the pressures at the first and second exhaust ports were both slightly negative). The materials continued to circulate between the reactor and the twin-screw reactor, and the materials stayed in the twin-screw reactor for 19 minutes.

[0058] (3) Stop nitrogen purging in the reactor, close the valve of the circulation pipe, and the material in the reactor continues to enter the twin-screw reactor through the feed pipe. The flowing material stays in the twin-screw reactor for 50 minutes to undergo oxidation reaction, thermal polycondensation reaction and devolatilization; ① Oxidation reaction: air is injected from the air injection port of the twin-screw reactor, and the material and air undergo oxidation reaction in the medium flow channel of the twin-screw reactor between the air injection port and the first exhaust port of the twin-screw reactor, and the heating temperature of the electric heating wire of the twin-screw reactor is controlled to be ≤303℃ and the reaction temperature of the material is 300℃; ② Thermal polycondensation reaction: the material after the oxidation reaction undergoes thermal polycondensation reaction in the medium flow channel of the twin-screw reactor between the first exhaust port and the second exhaust port, and the heating temperature of the electric heating wire of the twin-screw reactor is controlled to be ≤353℃ and the reaction temperature of the material is 350℃; ③ Devolatilization: the temperature of the first exhaust port is 300℃, the temperature of the second exhaust port is 350℃, and the vacuum degree of the first exhaust port and the second exhaust port is 50Pa.

[0059] (4) The material treated in the twin-screw reactor is extruded into isotropic spinnable asphalt with a softening point of 270°C under an extrusion pressure of 5 MPa.

[0060] Example 3

[0061] (1) Ethylene tar pitch with an ash content of less than 1 ppm and a viscous oily liquid at room temperature is added to the reactor through a feed pipe, the asphalt material is stirred, and the jacket is passed through heat transfer oil to increase the temperature of the reactor. At the same time, air is passed into the reactor through an air pipe to cause an oxidation reaction of the material. The heating temperature of the reactor (heat transfer oil temperature of the reactor jacket) is controlled to be ≤313°C, the reaction temperature is 308°C, the reaction pressure is slightly positive (gauge pressure, ≤100 Pa), and the reaction time is 5 hours.

[0062] During the air-purging oxidation reaction of the material in the reactor, the tail gas generated by the reaction is discharged from the exhaust pipe, and the material in the reactor enters the twin-screw reactor through the feed pipe, and air is injected from the air injection port of the twin-screw reactor. The material and air undergo oxidation reaction in the twin-screw reactor, and the heating temperature of the twin-screw reactor electric heating wire, the material reaction temperature, and the pressure of the first exhaust port and the second exhaust port are controlled to be slightly negative pressure (gauge pressure, ≥-100Pa). The material after treatment in the twin-screw reactor (extrusion, extrusion pressure 3MPa) is refluxed to the reactor through the circulation pipe, and the material resides in the twin-screw reactor for 20min.

[0063] (2) The reaction temperature was then maintained at 308°C, and a slight positive pressure nitrogen purge was performed for 0.5 hours to remove the volatile components. During the nitrogen purge of the reactor, the gas injection port of the twin-screw reactor was closed, and the twin-screw reactor no longer underwent oxidation reaction. The temperature was kept constant at 308°C, and the devolatilization continued (the pressures at the first and second exhaust ports were both slightly negative). The material continued to circulate between the reactor and the twin-screw reactor, and the material stayed in the twin-screw reactor for 20 minutes.

[0064] (3) Stop nitrogen purging in the reactor, close the valve of the circulation pipe, and the material in the reactor continues to enter the twin-screw reactor through the feed pipe. The flowing material then stays in the twin-screw reactor for 45 minutes to undergo oxidation reaction, thermal polycondensation reaction and devolatilization; ① Oxidation reaction: air is injected from the air injection port of the twin-screw reactor, and the material and air undergo oxidation reaction in the medium flow channel of the twin-screw reactor between the air injection port and the first exhaust port of the twin-screw reactor, and the heating temperature of the electric heating wire of the twin-screw reactor is controlled to be ≤303℃ and the reaction temperature of the material is 300℃; ② Thermal polycondensation reaction: the material after the oxidation reaction undergoes thermal polycondensation reaction in the medium flow channel of the twin-screw reactor between the first exhaust port and the second exhaust port, and the heating temperature of the electric heating wire of the twin-screw reactor is controlled to be ≤348℃ and the reaction temperature of the material is 345℃; ③ Devolatilization: the temperature of the first exhaust port is 300℃, the temperature of the second exhaust port is 345℃, and the vacuum degree of the first exhaust port and the second exhaust port is 60Pa.

[0065] (4) The material treated in the twin-screw reactor is extruded into isotropic spinnable asphalt with a softening point of 273°C under an extrusion pressure of 4.5 MPa.

[0066] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing isotropic spinnable pitch, characterized in that: The spinnable pitch is prepared using an isotropic spinnable pitch preparation device; The device for preparing the isotropic spinnable pitch comprises: A reactor, the upper end of which is connected to a feed pipe and an exhaust pipe, an air jet pipe is provided inside the reactor, a wall of which is uniformly distributed with a plurality of air jet holes, and the air jet pipe is respectively connected to an air pipe and a nitrogen pipe; A twin-screw reactor, wherein the front end of the twin-screw reactor is provided with a feed port and a gas injection port, the middle section of the twin-screw reactor is provided with a first exhaust port, and the tail end of the twin-screw reactor is provided with a second exhaust port; Among them, it also includes a feed pipe and a circulation pipe, one end of the feed pipe is connected to the lower end of the reactor, and the other end is connected to the feed port, one end of the circulation pipe is connected to the upper end of the reactor, and the other end is connected to the discharge pipe of the twin-screw reactor; The method comprises the following steps: (1) First, the material is added to the reactor through the feed pipe, the material is stirred, and the temperature of the reactor is increased. At the same time, air is introduced into the reactor through the air pipe, and the material undergoes an oxidation reaction. The tail gas generated by the reaction is discharged from the exhaust pipe. After the twin-screw reactor is started, the material in the reactor enters the twin-screw reactor through the feed pipe and then flows back to the reactor through the circulation pipe. At the same time, the air injection port is opened and air is injected. The pressure of the first exhaust port and the pressure of the second exhaust port are respectively adjusted to a slightly negative pressure; (2) After the oxidation reaction is completed, the reaction temperature of the material is maintained, the air pipe valve and the air injection port are closed, and at the same time, the nitrogen pipe valve is opened to introduce nitrogen into the reactor, and the mixture of volatile components in the material and nitrogen is discharged through the exhaust pipe, the first exhaust port, and the second exhaust port respectively; (3) the nitrogen pipe valve is closed, the gas injection port is opened, the circulation pipe valve is closed, and the material in the reactor continues to enter the twin-screw reactor, and a thermal polycondensation reaction occurs in the medium flow channel of the twin-screw reactor, or an oxidation reaction occurs in the medium flow channel of the twin-screw reactor between the gas injection port and the first exhaust port, and a thermal polycondensation reaction occurs in the medium flow channel of the twin-screw reactor between the first exhaust port and the second exhaust port; (4) The finished product produced after the material that has completed the thermal polycondensation reaction is devolatilized through the second exhaust port is discharged through the discharge pipe under the extrusion pressure of the twin-screw reactor.

2. The method for preparing isotropic spinnable pitch according to claim 1, characterized in that: In step (1), the material is petroleum asphalt or coal asphalt.

3. The method for preparing isotropic spinnable pitch according to claim 1, characterized in that: In the step (1), during the oxidation reaction, the reaction temperature is 300-320° C., and the residence time of the material in the twin-screw reactor is 20-50 minutes.

4. The method for preparing isotropic spinnable pitch according to claim 1, characterized in that: In the step (3), the residence time of the material in the twin-screw reactor is 30-50 min, and the vacuum degree of the first exhaust port and the vacuum degree of the second exhaust port are both 50-70 Pa.

5. The method for preparing isotropic spinnable pitch according to claim 1, characterized in that: In the step (3), the oxidation reaction temperature is 300-310°C, and the thermal polycondensation reaction temperature is 345-360°C.

6. The method for preparing isotropic spinnable pitch according to claim 1, characterized in that: In the step (4), the extrusion pressure of the twin-screw reactor is greater than 4 MPa, the vacuum degree of the second exhaust port is 50-70 Pa, and the target softening point of the finished material is 223-307°C.

7. The method for preparing isotropic spinnable pitch according to claim 6, characterized in that: The target softening point of the finished material is 273-276°C.

8. The method for preparing isotropic spinnable pitch according to claim 1, characterized in that: In the step (1), the reaction temperature is ≤ the heating temperature of the reactor ≤ the reaction temperature + 5°C, and the reaction temperature is ≤ the heating temperature of the twin-screw reactor ≤ the reaction temperature + 3°C; in the step (3), the reaction temperature is ≤ the heating temperature of the twin-screw reactor ≤ the reaction temperature + 3°C.

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