CN111548813B - A method for preparing mesophase pitch for high thermal conductivity carbon fiber - Google Patents

Abstract

The present invention provides a method for preparing mesophase pitch for high thermal conductivity carbon fiber, comprising the following steps: (1) thermally filtering petroleum residue at 100° C. to obtain refined residue with particle diameter ≤ 0.2 μm. (2) Atomize the refined residue oil, and continuously inject it into the reactor to carry out the reaction at 460-480 ° C. When the pressure in the reactor exceeds the set pressure of the valve at the top of the reactor, the low-boiling point product is discharged as a by-product ; When the liquid level of the high-boiling product settled at the bottom reaches a certain height, the high-boiling product is discharged. The method of the invention has the advantages of high product yield, low requirements for equipment control precision, and large-scale continuous industrial production. Compared with the existing method, the cost of producing mesophase pitch of the same quality is more than 50%.

Description

A method for preparing mesophase pitch for high thermal conductivity carbon fiber

technical field

The invention belongs to the field of carbon fibers, and relates to a method for preparing mesophase pitch for high thermal conductivity carbon fibers.

technical background

The high specific strength, specific modulus, high temperature resistance, ablation resistance and other characteristics of high thermal conductivity mesophase pitch-based carbon fiber composites play an irreplaceable role in the lightweight structure and ablation heat-proof components of aerospace and other weapons and equipment. effect.

Mesophase pitch is the only raw material of high thermal conductivity carbon fiber, and its performance stability is related to the final performance of the produced carbon fiber. In the existing preparation method of mesophase pitch, it is necessary to clean up the reaction kettle in time during the preparation process. If the reaction kettle is not cleaned up, the remaining mesophase pitch will continue to react to form petroleum coke that is not easily softened in the next production process. Particles, these particles do not melt at the spinning temperature and will block the spinneret holes. Even if the spinneret holes are not blocked during spinning, in the process of preparing the mesophase pitch fibers into carbon fibers, it is easy to cause the carbon fibers to break, and extremely The fine petroleum coke particles will cause defects to form inside the carbon fiber and affect the performance of the carbon fiber. Therefore, it is necessary to completely clean up the participating mesophase pitch in the reaction kettle before proceeding to the production of the next kettle. This leads to the general defect that the production of mesophase pitch cannot be continuously produced, resulting in different performance indicators of each batch of mesophase. Affects the stability of mesophase pitch.

Chinese patent document CN108264915A (201810233342.6) discloses a preparation method of spinnable mesophase pitch, which mainly includes the following steps: using catalytic cracking oil slurry as raw material, using catalytically synthesized naphthalene oligomeric pitch as co-carbonizing agent and hydrogen-donating agent, Under the temperature condition of 380～450℃, under the pressure of 0.5～6MPa, carry out co-carbonization and pressure polymerization reaction for 3～12h, and then discharge to normal pressure to obtain co-carbonized polymer pitch; Under the temperature condition of ℃, nitrogen bubbling and purging is carried out at a gas volume of 3-10 L/(min·Kg) for 1-20 h, and the high-quality spinnable mesophase pitch can be obtained after the reaction is completed and lowered to room temperature. Chinese patent document CN108795466A (201810594195.5) discloses a method for preparing mesophase pitch by induced polycondensation of FCC clarified oil. Under 2MPa, the reaction is carried out for 2-10h to obtain a low softening point mesophase pitch. The mesophase pitch was settled for 1 h at a temperature of 180-300 °C, and the lower anisotropic phase was cut out as an inducer. The raw materials and a certain proportion of the inducer are mixed evenly, and the reaction is carried out for 2 to 12 hours at a temperature of 380 to 450 ° C and a pressure of 2 MPa to obtain a high-quality mesophase pitch.

It can be seen that the existing methods for producing mesophase pitch all adopt the batch method, that is, the two-step method of pressurization and decompression, and the steps are cumbersome. Due to the high reaction temperature, the temperature must be raised slowly to the predetermined temperature and the temperature should not be too high. During this process, the heating rate may be as low as 0.5 °C/min. The whole heating process may be as long as 10 hours, and the reaction time is as long as 20 hours. The production cycle of mesophase pitch reached more than 30 hours in the time of cleaning the reactor. Since the production of mesophase pitch is sensitive to temperature, the production equipment must adopt the indirect heating method of molten salt heating, and the hysteresis of molten salt heating is large, so this heating method cannot achieve the technology that can not only increase the temperature rapidly but also ensure that the temperature does not exceed the temperature. , all adopt the method of slow heating to produce mesophase pitch, which leads to extremely low production efficiency of mesophase pitch. In addition, in the process of batch production of mesophase pitch, the reaction gas needs to be discharged frequently due to the increase of the system pressure due to the production of more small molecular compounds during the polymerization process, and a large amount of raw materials are also discharged during the exhaust process. The rate is relatively low, generally below 50%.

Chinese patent document CN110041952A (201910269933.3) discloses a mesophase pitch and a preparation method thereof, and finally obtains a high-quality intermediate having a mesophase pitch content of not less than 61.2%, a softening point of 274-282° C. and a yield of not less than 99.3% Phase pitch products. However, since this method requires heat-sensing and pressure and heat preservation for a period of time, the real continuous production is: continuously adding raw materials and continuously producing products, this process should not be interrupted. Therefore, this method is not a real continuous production. Moreover, the production has undergone two distillations, and also requires hydrotreating (the pressure resistance requirement of the equipment reaches 11MPa), and after flash evaporation, the mesophase pitch can be obtained by thermal treatment, which is a cumbersome production process.

SUMMARY OF THE INVENTION

The present invention provides a method for producing mesophase pitch in order to solve the problem in the prior art that the production of mesophase pitch cannot be continuously produced, resulting in low product yield.

In order to achieve the above object, the present invention adopts the following technical solutions:

A method for preparing mesophase pitch for high thermal conductivity carbon fiber, comprising the following steps:

(1) The petroleum residue is thermally filtered at 100° C. to obtain a refined residue with a particle diameter of ≤0.2 μm.

(2) atomize the refined residue oil, and continuously inject it into the reactor to carry out the reaction at 460-480 ° C, when the pressure in the reactor exceeds the set pressure of the valve at the top of the reactor, the low-boiling point product is discharged as a by-product ; When the liquid level of the high-boiling product settled at the bottom reaches a certain height, the high-boiling product is discharged.

The high boiling point product is the mesophase pitch with excellent performance. The boiling point is above 400°C.

Preferably, in step (1), the petroleum residue is thermally filtered by a filter, and the filter element can be a stainless steel sintered filter element, and the filter element has a pore size of ≤0.2 μm.

Preferably, the atomized particle size of the refined residue oil after atomization in step (2) is 1-10 μm.

Preferably, the set pressure of the top valve in step (2) is 0.1-2.0 MPa.

Preferably, the height of the liquid level in step (2) is 5-10% of the height of the reactor.

Preferably, the viscosity of the refined residue oil is 1-100 Pa·S. The primary condition for the formation of mesophase is temperature, that is, at a certain temperature, mesophase can be formed. If the viscosity is too low, there are many small molecules with low boiling point in the residual oil. When it is injected into the reactor, the gasification is violent, and the pressure resistance of the reactor is high. Although reducing the injection amount of the residual oil can reduce the pressure, the yield is also Very low; if the viscosity is too high, the residual oil will not be easily atomized when sprayed into the reactor, and it will fall directly into the bottom of the reactor, which is also unfavorable for the reaction.

In order to realize the above method, the present invention also provides a preferred device for producing mesophase pitch, but the realization of the present invention is not limited to the device provided by the present invention, as long as the device that can meet the requirements of the above preparation method is The invention can be implemented. Including atomizer 3 and reactor 4, the upper part of the reactor 4 is provided with a top one-way valve 5, and the lower part is provided with a bottom automatic drain valve 6, the atomizer 3 is arranged on the top of the reactor 4, and the atomization The outlet of the vessel 3 is facing the reactor 4.

The residual oil enters the atomizer 3 through the high pressure pump 2 . The pressure of the high-pressure pump 2 is 5 to 15 MPa.

Preferably, the maximum design temperature of the reactor 4 is 550°C, and the design pressure is 5Mpa. The pressure resistance of atomizer 3 is greater than or equal to 20MPa, and the particle size is less than or equal to 2.5μm.

Reactor 4 is heated by a built-in heating tube, that is, the heating tube is inside the reactor.

The atomizer 3 is a single-channel nozzle, and the front end of the nozzle has a layer of mesh structure. When the residual oil is sprayed from the nozzle, it is in an atomized state, and the droplets become smaller when heated, which makes the atomization effect better.

The atomized refined residual oil reacts in the reactor to form two types of products, one is the light component with low density (low boiling point product), which is in the gaseous state at high temperature and concentrated at the top of the reactor; the other is the light component with low density (low boiling point product) It is the heavy component with high density (high boiling point product), which settles at the bottom of the reactor. As the reaction progresses, the pressure in the reactor gradually increases. After the set pressure is exceeded, the top valve is passively opened to discharge the low-boiling product out of the reactor as a by-product for collection; when the liquid level of the high-boiling product settles at the bottom When a certain height is reached, the bottom automatic drain valve opens automatically and is pressed into the collector by means of the pressure in the reactor. These high-boiling products are mesophase pitches with excellent performance.

The method of the invention adopts a continuous method to produce mesophase pitch, the raw materials are sprayed into the reactor, and the reaction is carried out in the form of mist droplets. Due to the different boiling points of the reaction products, the low-boiling point products are concentrated at the top of the reactor in gaseous form, and the high-boiling point products are in liquid form. deposited at the bottom of the reactor. After the reaction has progressed to a certain extent, due to the increase of the internal pressure of the reactor, the gaseous products are discharged from the top, and the liquid products are discharged from the bottom drain valve and cooled to form the mesophase pitch. The above process continues with the injection of new feedstock. During this process, no petroleum coke is produced because the liquid product deposited at the bottom of the reactor has decreased in temperature and is continuously discharged from the reactor.

The present invention is characterized by instant product separation. About the formation of mesophase pitch: Temperature is the key factor that determines whether the mesophase can be formed. As long as the temperature is reached, the residual oil will form mesophase pitch and small molecular products. By removing these small molecular products by distillation, we can get Mesophase pitch with high mesophase content. The invention adopts a one-step method to produce mesophase pitch. When the residual oil is injected into the reactor, various polymerization reactions occur between the residual oil molecules due to the effect of temperature. Therefore, it is deposited at the bottom in a liquid state. After being deposited to the bottom, the ambient temperature of the high-boiling point product is low and will not continue to react, so there will be no production of high-melting point petroleum coke, which ensures the quality of the mesophase pitch; and The continuous discharge of the reactor from the raw material to the product is not interrupted, so it is a continuous reaction.

Chinese patent document CN109777463A (201711117545.0) adopts the atomization method to produce modified asphalt, but it atomizes the asphalt to improve its dispersibility, thereby better oxidizing the asphalt, not for the production of mesophase asphalt. Chinese patent document CN 202912702U (201220624878.9) is sprayed into lye by the spray method developed for improving the quality of iron phosphate product, the lye is injected into the pre-set iron salt and phosphate mixed liquid in the reactor by atomization, To achieve the purpose of adding the lye to the mixed solution uniformly. In addition, double pipes are used in the nozzle, that is, one pipe is lye, and the other is gas, which is atomized by the flow of gas. It is for the purpose of mixing uniformly to achieve stable reaction.

However, in the present invention, the residual oil is atomized and then reacted to produce mesophase pitch, which is different from the atomization method, principle and purpose in the prior art. The present invention adopts a single-channel nozzle to spray the residual oil with pressure. change. The collision between molecules in the reaction system at high temperature is relatively mild, and the reaction is relatively stable, so similar effects can be produced in a wide temperature and pressure range.

Beneficial effects of the present invention:

The method of the invention has the advantages of high product yield, low requirements for equipment control precision, and large-scale continuous industrial production. Compared with the existing method, the cost of producing mesophase pitch of the same quality is more than 50%. The mesophase pitch prepared by this method has a moderate softening point (products with different softening points of 260-280°C can be produced as required), low ash content, low quinoline insoluble matter, and regular molecular arrangement (polycyclic aromatic hydrocarbons are mostly small during polymerization. bit condensation).

Description of drawings

Fig. 1 is a device for continuous production of mesophase pitch;

Fig. 2 is the carbon fiber prepared with the mesophase pitch produced by Example 2;

Fig. 3 uses the carbon fiber prepared by the mesophase pitch produced in Example 9;

Figure 4 shows carbon fibers produced with mesophase pitches produced in Comparative Examples 4-3.

Reference number:

1-container; 2-high pressure pump; 3-atomizer; 4-reactor; 5-top check valve; 6-bottom automatic drain valve.

Detailed ways

Example 1

A method for preparing mesophase pitch for carbon fiber with high thermal conductivity is prepared by the following steps: firstly, using a stainless steel sintered filter element (filter element aperture≤0.2μm), and filtering petroleum residue into a container 1 at 100°C. The pressure of the high-pressure pump 2 was set to 5.00 MPa, the temperature of the reactor 4 was set to 460° C., and the pressure of the check valve 5 was set to 0.10 MPa. After the temperature of the reactor 4 reaches the set value, the high-pressure pump 2 is turned on to pump the refined residual oil into the atomizer 3, and the refined residual oil is atomized into tiny droplets and continuously enters the reactor 4. Under the action of the temperature, the refined residual oil is added. The components of the reactor undergo cracking, condensation, polycondensation and polyaddition reactions to generate mesophase macromolecules, low molecular hydrocarbons, water and other small molecular compounds, which are distributed in the top and bottom of the reactor 4 in gaseous and liquid forms respectively. With the gradual increase of the reaction product, the pressure in the reactor 4 also increases. After reaching the set pressure of the one-way valve 5 , the small molecule products (low boiling point products) escape through the one-way valve 5 . At the same time, the volume of the liquid macromolecular products at the bottom of the reactor also increases continuously. After reaching a predetermined height (10% of the inner height of the reactor), the automatic drain valve opens to discharge the macromolecular products. The macromolecular product (high boiling point product) discharged from the bottom is the high-quality mesophase pitch.

Example 2

In a method for preparing mesophase pitch for high thermal conductivity carbon fiber, the temperature in the reactor 4 is set to 480°C, and other conditions are the same as those shown in Example 1.

Example 3

A method for preparing mesophase pitch for high thermal conductivity carbon fiber, the pressure of the one-way valve 5 is set to 0.50MPa, and other conditions are the same as those shown in Example 1.

Example 4

In a method for preparing mesophase pitch for high thermal conductivity carbon fiber, the pressure of the one-way valve 5 is set to 1.00 MPa, and other conditions are the same as those shown in Example 1.

Example 5

In a method for preparing mesophase pitch for high thermal conductivity carbon fiber, the pressure of the one-way valve 5 is set to 1.50MPa, and other conditions are the same as those shown in Example 1.

Example 6

A method for preparing mesophase pitch for high thermal conductivity carbon fiber, the pressure of the one-way valve 5 is set to 2.00MPa, and other conditions are the same as those shown in Example 1.

Example 7

In a method for preparing mesophase pitch for high thermal conductivity carbon fiber, the pressure of the one-way valve 5 is set to 2.00 MPa, the ejection pressure of the high-pressure pump 2 is 7.50 MPa, and other conditions are the same as in Example 1.

Example 8

In a method for preparing mesophase pitch for high thermal conductivity carbon fiber, the pressure of the one-way valve 5 is set to 2.00 MPa, the pressure of the high-pressure pump 2 is set to 10.00 MPa, and other conditions are the same as in Example 1.

Example 9

In a method for preparing mesophase pitch for high thermal conductivity carbon fiber, the pressure of the one-way valve 5 is set to 2.00 MPa, the pressure of the high-pressure pump 2 is changed to 15.00 MPa, and other conditions are the same as in Example 1.

Comparative Examples 1 to 3

In a method for mesophase pitch, the temperature in the reactor 4 is set to 440°C, 460°C, and 500°C respectively, and other conditions are the same as those shown in Example 1.

When the ejection pressure of the high-pressure pump 2 is greater than 15.00Mpa, the present invention can also be realized, but the performance of the obtained mesophase pitch is not significantly improved, and the excessive pressure increases the requirements for the safety performance of the equipment. If the pressure is too low, it will affect the output.

The properties of the mesophase pitch obtained under different experimental conditions are shown in Table 1 below.

Table 1

As can be seen from the above table, the performance indicators of the mesophase pitches prepared in Examples 1 to 9 can meet the requirements for manufacturing high thermal conductivity carbon fibers (softening point 260-280°C, mesophase content ≥98%, quinoline insoluble matter 20～40%, ash content≤40PPm.). The preparation of mesophase pitch by this method is carried out in a gas phase system, the collision between molecules in the system is relatively mild, and the reaction is relatively stable, so similar effects can be produced in a wide temperature and pressure range (for example, Example 1 The softening point and mesophase content of the mesophase pitches obtained at different temperatures and pressures have little difference, and all have good spinnability.), which shows that the method of the present invention has low requirements on equipment control accuracy and can meet the requirements of large-scale continuous requirements for industrial production.

Comparative Example 4:

The preparation method of the mesophase pitch in the prior art: the raw material residue is put into the kettle, the molten salt is heated to 200 degrees, the reaction kettle is immersed in the molten salt kettle, and the temperature is raised to 420 degrees at a rate of 1 degree/min and kept at a constant temperature for 10 hours, during which the pressure is maintained. 2.0MPa (pressurized section). The temperature was lowered to 400 degrees at a constant temperature of 400 degrees for 8 hours at a rate of 2 degrees/min, during which the pressure was maintained at 1000Pa (decompression section), and nitrogen protection was introduced. Then it is lowered to room temperature, the reaction kettle is opened to take out the product, and the reaction kettle is cleaned and then loaded with raw materials to produce the next kettle of mesophase pitch.

Using the above preparation method, four batches of mesophase pitches were produced in parallel under the same conditions, and the properties of the obtained different batches of mesophase pitches are shown in Table 2.

Table 2

The existing production method adopts the two-stage method of pressurization and decompression, and each production needs to go through the process of heating-constant temperature-cooling. Due to the characteristics of the equipment, this heating-cooling process is not linear, and the temperature control of each reaction process has some differences. , due to the temperature sensitivity during the reaction of mesophase pitch, which leads to a large difference in the properties of pitches produced from different batches (for the production of mesophase pitch, a difference of 5°C in softening point between batches is unacceptable. In addition, the mesophase content of different batches of mesophase pitches varies greatly. In fact, pitches with a mesophase content of more than 95% are called mesophase pitches, and those with mesophase content below 95% are called mesophase pitches. Mesophase pitch.), in addition, due to the frequent opening and closing of the gas outlet valve during the pressurized reaction process, it leads to low yield, high softening point, poor spinnability, quinoline insoluble matter and high ash content. In addition, since the production is not continuous, the reactor needs to be manually opened and cleaned after the reaction of each kettle, which greatly reduces the degree of automation in the production process.

It can be seen from theory and practice that the thermal conductivity of carbon fibers with radial cross-sections is significantly higher than that of carbon fibers with concentric circular cross-sections. It can be seen from Fig. 2 and Fig. 3 that the cross-section is radial, while the interior of Fig. 4 is an obvious concentric circle, except that some areas in the outer layer of the fiber are radial. This shows that the mesophase pitch for the high thermal conductivity carbon fiber produced by the present invention is more suitable for producing the high thermal conductivity carbon fiber than the mesophase pitch produced by the conventional method.

Claims (6)

1. A method for preparing mesophase pitch for high-thermal-conductivity carbon fibers is characterized by comprising the following steps:

(1) carrying out hot filtration on petroleum residual oil at 100 ℃ to obtain refined residual oil with the particle diameter of less than or equal to 0.2 mu m, wherein the viscosity of the refined residual oil is 1-100 Pa.S;

(2) atomizing the refined residual oil, wherein the atomized particle size is 1-10 mu m; continuously injecting the mixture into a reactor for reaction at 460-480 ℃, and discharging a low-boiling-point product as a byproduct when the pressure in the reactor exceeds the set pressure of a valve at the top of the reactor; when the liquid level of the high boiling point product settled at the bottom reaches a certain height, discharging the high boiling point product; the set pressure of the top valve is 0.1-2.0 MPa; the performance indexes of the obtained mesophase pitch are as follows: the softening point is 260-280 ℃, the content of a mesophase is more than or equal to 98%, the content of quinoline insoluble substances is 20-40%, and the ash content is less than or equal to 40 PPm.

2. The method as claimed in claim 1, wherein the pore size of the filter element used for the hot filtration of the petroleum residue in the step (1) is less than or equal to 0.2 μm.

3. The process according to any one of claims 1 to 2, wherein the liquid level in step (2) is 5 to 10% of the height of the reactor.

4. The method of claim 1, wherein the reactor is provided with a top check valve at the upper part and a bottom automatic drain valve at the lower part, the atomizer is arranged at the top of the reactor, and the outlet of the atomizer is opposite to the reactor.

5. The method of claim 4, wherein the residuum enters the atomizer through a high pressure pump; the pressure of the high-pressure pump is 5-15 MPa.

6. The process according to claim 5, wherein the maximum design temperature of the reactor is 550 ℃ and the design pressure is 5 MPa.

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