A method for accurately predicting the thermal decomposition process of mesophase asphalt

Abstract

The present invention belongs to the technical field of high-performance carbon material preparation. The present invention discloses a method for accurately predicting the thermal decomposition process of mesophase asphalt. First, a mesophase asphalt powder sample is loaded into a thermal analyzer and three groups of tests are performed at different temperatures by changing the constant temperature time. The data of the weight loss Δw of the mesophase asphalt thermal decomposition and the constant temperature time t are obtained, and the power function Δw=Ct is obtained by fitting the data. b , and the reaction rate constant k=bC is derived; then according to the Arrhenius equation k=Aexp(‑Ea / (RT)), the activation energy Ea and pre-exponential factor A of the thermal decomposition reaction of the mesophase asphalt are obtained, and finally the decomposition reaction kinetic equation of the mesophase asphalt Δw=exp(ln(A / b)‑8.314Ea / T+blnt) is obtained. The present invention can accurately predict the thermal decomposition process of the corresponding mesophase asphalt, and provide theoretical guidance for the preparation of mesophase asphalt-based foamed carbon, mesophase asphalt-based carbon fiber and needle coke.

Description

Technical Field

[0001] The present invention relates to the technical field of high-performance carbon material preparation, and in particular to a method for accurately predicting the thermal decomposition process of mesophase asphalt. Background Art

[0002] Mesophase pitch is an excellent precursor for manufacturing high-performance carbon materials (such as mesophase pitch-based foamed carbon, mesophase pitch-based carbon fibers, needle coke, mesophase carbon microbeads and ultra-high specific surface area activated carbon, etc.), and is widely used in aerospace, defense industry, cutting-edge technology, daily life and many other aspects.

[0003] Mesophase pitch is a macromolecular condensed ring compound obtained by thermal polycondensation or catalytic polymerization of coal tar pitch, petroleum pitch and aromatic compounds, and its relative molecular mass is usually distributed between 370 and 2000. In the preparation process of mesophase pitch-based foamed carbon, mesophase pitch-based carbon fiber and needle coke, it is usually necessary to perform a high-temperature and long-term heat treatment of the mesophase pitch at a temperature above 300°C under the protection of an inert gas, at which time volatiles generated by the thermal decomposition of small or large molecules in the mesophase pitch system will continuously escape. For example, the Chinese invention patent (CN105197912A) obtains a raw material of carbon nanotube / foamed carbon composite material by self-foaming of volatiles generated by thermal decomposition of mesophase pitch; the Chinese invention patent (CN100374367C) uses petroleum-based mesophase pitch as a raw material for self-reaction foaming to prepare a foamed carbon material.

[0004] However, the existing methods of using mesophase pitch to synthesize foamed carbon materials and other materials such as composite materials do not monitor the thermal decomposition process of mesophase pitch. If the heat treatment constant temperature time is too long, it will lead to high production costs. If the heat treatment constant temperature time is too short, the light components and pyrolysis components volatilized during the heat treatment of the mesophase pitch will form less foam, which is not conducive to the preparation of mesophase pitch-based foamed carbon; and if the heat treatment constant temperature time is too short, the light components are not completely removed, which is not conducive to the melt spinning of mesophase pitch fibers and the preparation of needle coke. Therefore, it is necessary to develop a method that can accurately predict the thermal decomposition process of mesophase pitch and accurately predict the heat treatment constant temperature time. Summary of the invention

[0005] In view of this, the present invention provides a method for accurately predicting the thermal decomposition process of mesophase asphalt. The present invention uses a thermal analyzer to monitor the thermal decomposition process of mesophase asphalt, and then combines the Aleunius equation to obtain the thermal decomposition kinetic equation of the mesophase asphalt to accurately predict the thermal decomposition process of the mesophase asphalt.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] The present invention provides a method for accurately predicting the thermal decomposition process of mesophase asphalt, comprising the following steps:

[0008] (1) crushing the mesophase asphalt to obtain a mesophase asphalt powder sample;

[0009] (2) Turn on the protective gas of the thermal analyzer, set the flow rate to 100±1mL / min, and perform the peeling operation;

[0010] (3) loading the mesophase pitch powder sample obtained in step (1) into a thermal analyzer, first heating it, and then maintaining the temperature at a constant level for a period of time;

[0011] (4) Select three temperature points for testing, adjust different constant temperature time to obtain three sets of comparison data of the weight loss of mesophase asphalt thermal decomposition Δw and constant temperature time t at different temperatures, and fit the three sets of data to obtain the power function Δw=Ct b , b is the exponential factor of the constant temperature duration, C is the corresponding t of the three sets of data Δw b The slope of

[0012] (5) Substitute the power function Δw = Ct b The reaction rate constant k=bC is obtained by taking the derivative of the constant temperature time t on both sides at the same time; according to the Arrhenius equation k=Aexp(-Ea / (RT)), the logarithm of both sides is obtained by taking the logarithm of lnk=lnA-Ea / (RT), and the lnk value of the thermal decomposition of the mesophase asphalt at three different temperatures is used as the ordinate, and the 1 / T value is used as the abscissa to draw a graph, the slope is the value of -Ea / R, the intercept is the value of lnA, and R is the molar gas constant, thereby the activation energy Ea and the pre-exponential factor A of the thermal decomposition reaction of the mesophase asphalt can be obtained;

[0013] (6) Finally, the decomposition reaction kinetic equation of the intermediate phase asphalt is obtained. Δw=exp(ln(A / b)-8.314Ea / T+blnt).

[0014] Preferably, the mesophase asphalt in step (1) is one of naphthalene-based mesophase asphalt, oil-based mesophase asphalt and coal-based mesophase asphalt; the mesophase content of the mesophase asphalt is greater than 95% and the softening point is greater than 200°C.

[0015] Preferably, the particle size of the mesophase asphalt powder sample in step (1) is greater than 180 mesh.

[0016] Preferably, the amount of the mesophase asphalt powder sample added in step (3) is 25 to 30 mg; the heating rate of the heating treatment is 1 to 3°C / min, the temperature is 300 to 500°C; and the constant temperature time is 4 to 900 min.

[0017] Preferably, the three temperature points selected in step (4) are 320°C, 330°C and 340°C.

[0018] Preferably, in step (5), the molar gas constant R is 8.314 J / (mol·K).

[0019] It can be seen from the above technical solution that compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] The method for accurately predicting the thermal decomposition process of mesophase asphalt described in the present invention can accurately predict the thermal decomposition process of mesophase asphalt, better optimize the preparation process of mesophase asphalt-based foamed carbon, mesophase asphalt-based carbon fiber and needle coke, accurately determine the constant temperature duration of heat treatment, and its prediction steps are simple, which is suitable for promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0022] Figure 1 The power function Δw=Ct obtained by thermally decomposing the mesophase pitch at 320°C, 330°C, and 340°C in step (4) of Example 1 of the present invention b The image shows that the C values ​​at 320℃, 330℃, and 340℃ are 0.2435, 0.3253, and 0.4147, respectively.

[0023] Figure 2 This is a functional relationship graph of lnk=lnA-Ea / (RT) obtained by thermal decomposition of the intermediate phase asphalt at 320°C, 330°C, and 340°C in step (5) of Example 1 of the present invention. DETAILED DESCRIPTION

[0024] The present invention provides a method for accurately predicting the thermal decomposition process of mesophase asphalt, comprising the following steps:

[0025] (1) crushing the mesophase asphalt to obtain a mesophase asphalt powder sample;

[0026] (2) Turn on the protective gas of the thermal analyzer, set the flow rate to 100±1mL / min, and perform the peeling operation;

[0027] (3) loading the mesophase pitch powder sample obtained in step (1) into a thermal analyzer, first heating it, and then maintaining the temperature at a constant level for a period of time;

[0028] (4) Select three temperature points for testing, adjust different constant temperature time to obtain three sets of comparison data of the weight loss of mesophase asphalt thermal decomposition Δw and constant temperature time t at different temperatures, and fit the three sets of data to obtain the power function Δw=Ct b , b is the exponential factor of the constant temperature duration, C is the corresponding t of the three sets of data Δw b The slope of

[0029] (5) Substitute the power function Δw = Ct b The reaction rate constant k=bC is obtained by taking the derivative of the constant temperature time t on both sides at the same time; according to the Arrhenius equation k=Aexp(-Ea / (RT)), the logarithm of both sides is obtained by taking the logarithm of lnk=lnA-Ea / (RT), and the lnk value of the thermal decomposition of the mesophase asphalt at three different temperatures is used as the ordinate, and the 1 / T value is used as the abscissa to draw a graph, the slope is the value of -Ea / R, the intercept is the value of lnA, and R is the molar gas constant, thereby the activation energy Ea and the pre-exponential factor A of the thermal decomposition reaction of the mesophase asphalt can be obtained;

[0030] (6) Finally, the decomposition reaction kinetic equation of the intermediate phase asphalt is obtained. Δw=exp(ln(A / b)-8.314Ea / T+blnt).

[0031] In the present invention, the mesophase asphalt in the step (1) is preferably one of naphthalene-based mesophase asphalt, oil-based mesophase asphalt, and coal-based mesophase asphalt, and is further preferably oil-based mesophase asphalt; the mesophase content of the mesophase asphalt is preferably >95%, and is further preferably >97%, and the softening point is preferably >200°C, and is further preferably >250°C.

[0032] In the present invention, the particle size of the mesophase asphalt powder sample in step (1) is preferably >180 mesh, and more preferably >200 mesh;

[0033] Specifically, the mesophase asphalt powder sample is preferably obtained by grinding it into powder using a mortar and then passing it through a 180-mesh sieve; more preferably, it is obtained by grinding it into powder using a mortar and then passing it through a 200-mesh sieve.

[0034] Furthermore, the specific process of the peeling operation in step (2) is: take two clean 90 μL alumina crucibles and respectively load them into the reference end and sample end of the thermal analyzer to perform the peeling operation.

[0035] In the present invention, the amount of the mesophase asphalt powder sample added in step (3) is preferably 25 to 30 mg, and more preferably 28 mg.

[0036] Specifically, the mesophase pitch powder sample is added to the sample end of the thermal analyzer.

[0037] In the present invention, the heating rate of the heating treatment in step (3) is preferably 1-3°C / min, more preferably 2°C / min, the temperature is preferably 300-500°C, more preferably 320-340°C. The constant temperature time is preferably 4-900min, more preferably 5-850min.

[0038] In the present invention, the three temperature points selected in step (4) are preferably 320°C, 330°C, and 340°C.

[0039] Furthermore, the molar gas constant R in the Arrhenius equation k=Aexp(-Ea / (RT)) is 8.314 J / (mol·K), and the thermodynamic temperature scale T=(thermal decomposition temperature of mesophase asphalt-273°C)K.

[0040] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be understood as limiting the protection scope of the present invention.

[0041] Example 1

[0042] This embodiment is a specific implementation of the present invention, which specifically includes the following steps:

[0043] (1) Grinding the oil-based mesophase asphalt into powder, and passing it through a 200-mesh sieve to obtain a mesophase asphalt powder sample;

[0044] (2) Turn on the protective gas of the thermal analyzer, set the nitrogen flow rate to 100 mL / min, take two clean 90 μL alumina crucibles and place them into the reference end and sample end of the synchronous thermal analyzer respectively, and perform the peeling operation;

[0045] (3) Place 28 mg of sieved mesophase asphalt powder sample into the crucible at the sample end, heat the temperature to 320°C at a rate of 2°C / min, and then keep the temperature constant for different periods of time for testing;

[0046] (4) Two temperature points, 330°C and 340°C, were selected and tested at different constant temperatures for different time periods to obtain the comparison data of the weight loss Δw of the mesophase asphalt at three different temperatures and the constant temperature time t. The three sets of data were fitted to obtain the power function Δw = Ct 0.42 , the C corresponding to 320℃, 330℃, and 340℃ are 0.2435, 0.3253, and 0.4147, respectively;

[0047] (5) Substitute the power function Δw = Ct 0.42The reaction rate constant k = 0.42C was obtained by taking the derivative of the constant temperature time t on both sides at the same time; according to the Arrhenius equation k = Aexp(-Ea / (RT)), the logarithm of both sides was taken to obtain lnk = lnA-Ea / (RT), and the lnk value of the thermal decomposition of the mesophase asphalt at three different temperatures was used as the ordinate and the 1 / T value was used as the abscissa to plot, the slope was the value of -Ea / R, and the intercept was the value of lnA, thus the activation energy of the thermal decomposition reaction of the mesophase asphalt was obtained to be Ea = 80.49 kJ / mol, and the pre-exponential factor A = 1266794;

[0048] (6) Substitute k = Aexp(-Ea / (RT)) through k = 0.42C into the power function Δw = Ct 0.42 After a series of simplifications, the known parameters are substituted into the decomposition reaction kinetic equation of the mesophase asphalt to obtain Δw=exp(14.92-9681 / T+0.42lnt).

[0049] It can be seen from Example 1 that the present invention provides a method for accurately predicting the thermal decomposition process of mesophase asphalt. The use of this technology can accurately predict the thermal decomposition process of mesophase asphalt, better optimize the preparation process of mesophase asphalt-based foamed carbon, mesophase asphalt-based carbon fiber and needle coke, and accurately determine the constant temperature duration of heat treatment. The technical testing method has a simple process flow and is easy to realize large-scale production.

[0050] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for accurately predicting the thermal decomposition process of mesophase pitch, characterized in that: The steps include: (1) crushing the mesophase asphalt to obtain a mesophase asphalt powder sample; (2) Turn on the protective gas of the thermal analyzer, set the flow rate to 100±1mL / min, and perform the peeling operation; (3) loading the mesophase pitch powder sample obtained in step (1) into a thermal analyzer, first heating it, and then maintaining the temperature at a constant level for a period of time; (4) Select three temperature points for testing, adjust different constant temperature time to obtain three sets of comparison data of the weight loss of mesophase asphalt thermal decomposition Δw and constant temperature time t at different temperatures, and fit the three sets of data to obtain the power function Δw=Ct b , b is the exponential factor of the constant temperature duration, C is the corresponding t of the three sets of data Δw b The slope of (5) Substitute the power function Δw = Ct b The reaction rate constant k=bC is obtained by taking the derivative of the constant temperature time t on both sides at the same time; according to the Arrhenius equation k=Aexp(-Ea / (RT)), the logarithm of both sides is obtained by taking the logarithm of lnk=lnA-Ea / (RT), and the lnk value of the thermal decomposition of the mesophase asphalt at three different temperatures is used as the ordinate, and the 1 / T value is used as the abscissa to draw a graph, the slope is the value of -Ea / R, the intercept is the value of lnA, and R is the molar gas constant, thereby the activation energy Ea and the pre-exponential factor A of the thermal decomposition reaction of the mesophase asphalt can be obtained; (6) Finally, the decomposition reaction kinetic equation of the mesophase asphalt was obtained. Δw = exp(ln(A / b)-8.314Ea / T+blnt); The particle size of the mesophase asphalt powder sample in step (1) is greater than 180 mesh; The heating rate of the heating treatment is 2-3°C / min, and the temperature is 300-500°C; The three temperature points selected in step (4) are 320°C, 330°C and 340°C.

2. The method for accurately predicting the thermal decomposition process of mesophase pitch according to claim 1, characterized in that: The mesophase pitch in the step (1) is one of naphthalene-based mesophase pitch, oil-based mesophase pitch and coal-based mesophase pitch.

3. The method for accurately predicting the thermal decomposition process of mesophase pitch according to claim 2, characterized in that: The mesophase content of the mesophase asphalt is greater than 95%, and the softening point is greater than 200°C.

4. The method for accurately predicting the thermal decomposition process of mesophase pitch according to claim 1, characterized in that: The amount of mesophase asphalt powder sample added in step (3) is 25 to 30 mg.

5. The method for accurately predicting the thermal decomposition process of mesophase pitch according to claim 4, characterized in that: The constant temperature time is 4 to 900 minutes.

6. The method for accurately predicting the thermal decomposition process of mesophase pitch according to claim 1, characterized in that: The molar gas constant R in step (5) is 8.314 J / (mol·K).

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