Modified pitch production process based on medium and low temperature coal tar heavy components

Abstract

The invention discloses a modified pitch production process based on medium and low temperature coal tar heavy components, and relates to the technical field of modified pitch, the modified pitch production process comprises the following steps: raw material pretreatment: filtering and centrifuging medium and low temperature coal tar; hydrotreating: mixing the primary tar and a hydrogen-donor solvent according to the mass ratio of 1: (0.3-0.5), and adding a catalyst for hydrocracking reaction to obtain a hydrogenated product; thermal polycondensation reaction: separating heavy components in the hydrogenation product by adopting reduced pressure distillation, and feeding the heavy components into a two-stage thermal polycondensation reactor to generate a modified pitch intermediate; and gas-liquid separation: enabling the modified pitch intermediate to sequentially pass through a high-temperature cyclone separator, a condensation system and a supercritical extraction tower, and separating out light oil gas, a medium fraction and a modified pitch product. When the production process provided by the invention is adopted to treat the medium and low temperature coal tar, a cross-linking agent does not need to be added, so that the content of quinoline insoluble substances is reduced to 5-12%, and the softening point reaches 240-280 DEG C.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of modified pitch, in particular to a modified pitch production process based on heavy components of medium-low temperature coal tar. BACKGROUND

[0002] In recent years, with the rapid development of coal chemical technology, efficient utilization of heavy components of medium-low temperature coal tar has become an important direction to improve the added value of the coal chemical industry chain. Modified pitch, as a precursor of high-value-added carbon materials, has increasing demand in the fields of aerospace, lithium battery negative materials, and high-thermal-conductivity carbon fibers. The patent application with the publication number CN107603671A discloses a system and method for preparing mesophase pitch and oil products based on medium-low temperature coal tar hydrogenation. The patent prepares mesophase pitch by coal tar pretreatment, hydrogenation deasphalting, and thermal polycondensation of heavy components, and prepares oil products by hydrogenation refining of light components, realizing high-value-added utilization of medium-low temperature coal tar. However, it still has the following problems: first, thermal polycondensation of heavy components needs to rely on external crosslinking agents (such as polycyclic aromatic hydrocarbons or aldehyde compounds) to promote molecular crosslinking, which not only increases raw material cost but also leads to increased complexity of the reaction system and uncontrollable byproduct generation; second, the single temperature control mode used in the thermal polycondensation process results in high quinoline insoluble (QI) content of mesophase pitch; third, the removal efficiency of ash (metal impurities) is low (usually > 300 ppm) in the raw material pretreatment stage, which leads to accelerated coking rate of the subsequent thermal polycondensation reactor and shortened catalyst life; and fourth, the existing process only performs conventional hydrogenation refining on light components, failing to deeply couple heavy component modification and light component aromatization, which limits the overall economy. Therefore, it is urgent to develop a modified pitch production process without external crosslinking agents, with efficient ash removal, mild reaction conditions, and low production cost. SUMMARY

[0003] The present application aims to overcome the deficiencies of the prior art and provide a modified pitch production process based on heavy components of medium-low temperature coal tar, which does not need external crosslinking agents, has efficient ash removal, and is low in production cost.

[0004] To achieve the above-mentioned purpose, the technical solution adopted by the present application is as follows:

[0005] A modified pitch production process based on heavy components of medium-low temperature coal tar, comprising the following steps:

[0006] S1, raw material pretreatment: filtering and centrifuging medium-low temperature coal tar to remove solid particles with a particle size > 5 μm, obtaining primary tar with an ash content < 100 ppm;

[0007] S2, hydrotreatment: the primary tar is mixed with hydrogen-donor solvent at a mass ratio of 1:0.3-0.5, and a catalyst is added for hydrotreatment reaction, the reaction temperature is 320-380℃, the pressure is 8-12 MPa, the reaction time is 60-120 min, and a hydrotreated product is obtained;

[0008] S3, thermal polycondensation reaction: heavy components in the hydrotreated product are separated by vacuum distillation, and the heavy components are sent to a two-stage thermal polycondensation reactor, the first stage is reacted at 420-450℃ for 1-2 h, the second stage is heated to 460-480℃ and nitrogen is introduced, the reaction is performed for 0.5-1 h, the flow rate of the introduced nitrogen is 0.5-1.5 L / min, and a modified pitch intermediate is generated;

[0009] S4, gas-liquid separation: the modified pitch intermediate is sequentially passed through a high-temperature cyclone separator, a condensation system and a supercritical extraction tower, and light oil gas, medium fraction and modified pitch product are separated, wherein the quinoline insoluble content of the modified pitch is 5-12%, and the softening point is 240-280℃.

[0010] Further, in step S1, a metal sintered filter and a ceramic membrane filter are combined for gradient filtration, the pore size of the metal sintered filter is 10-15 μm, and the pore size of the ceramic membrane filter is 1-5 μm; the centrifugal speed is 8000-12000 rpm, and the centrifugal time is 20-40 min.

[0011] Further, in step S2, the hydrogen-donor solvent is a hydrogen-rich aromatic hydrocarbon mixture generated by aromatization of light oil gas, the hydrogen-carbon molar ratio is 1.5-2.5:1, and the aromatic hydrocarbon content is ≥60 wt%.

[0012] Further, in step S2, the catalyst is a supported Ni-Mo / Al2O3 or Co-Mo / Al2O3 catalyst, the active metal loading in the catalyst is 12-18 wt%, and the mass ratio of the catalyst to the primary tar is 1:50-100.

[0013] Further, in step S3, the operating pressure during vacuum distillation is 5-20 kPa, the top temperature is 150-200℃, the bottom temperature is 280-320℃, and the heavy components are discharged from the bottom; the reaction pressure in the second stage of the two-stage thermal polycondensation reactor is 0.1-0.5 MPa, and 2-5% hydrogen by volume is mixed into the nitrogen.

[0014] Further, in step S4, the supercritical extraction tower uses carbon dioxide as the solvent, the pressure is 10-15 MPa, the temperature is 50-80℃, and the extraction time is 30-60 min.

[0015] Further, the production process in the present application further comprises recycling the light oil gas obtained in step S4 to step S2 as the hydrogen-donating solvent after being treated by an aromatization reactor.

[0016] Further, the aromatization reactor in step S5 adopts a ZSM-5 molecular sieve catalyst, the reaction temperature is 350-400℃, the space velocity is 1-3h -1 , and the molar ratio of hydrogen to light oil gas is 3-5:1.

[0017] Further, the catalyst in step S2 is subjected to regeneration treatment after reaction, and the regeneration conditions are as follows: the temperature is increased to 500-600℃ at a temperature increasing rate of 2-5℃ / min in a nitrogen atmosphere with an oxygen volume fraction of 5-10%, and then the temperature is kept for 2-4 hours, followed by reduction with hydrogen.

[0018] Compared with the prior art, the present application has the following beneficial effects:

[0019] (1) The present application can completely remove the solid particles with a particle size of >5μm in the medium and low temperature coal tar by combining the gradient filter (metal sintered filter element + ceramic membrane filter) with high-speed centrifugal treatment, so that the ash content is reduced to <100ppm. The low-ash primary tar can greatly reduce the coking problem of the subsequent thermal polycondensation reactor, and the activity of the catalyst can still be maintained at 86%-95% after 10 times of circulation, thereby significantly prolonging the service life of the catalyst and reducing the production cost.

[0020] (2) The present application can realize precise control of the molecular crosslinking degree by using a two-stage thermal polycondensation reactor (the first stage is 420-450℃, and the second stage is 460-480℃) combined with the process design of hydrogen-doped nitrogen, so that the quinoline insoluble (QI) content of the modified asphalt is reduced to 5-12%, and the softening point is up to 240-280℃.

[0021] (3) The present application generates a hydrogen-rich aromatic hydrocarbon mixture by aromatizing the light oil gas, and the hydrogen-rich aromatic hydrocarbon mixture is recycled as a hydrogen-donating solvent for the hydrogenolysis reaction, which not only replaces the external hydrogen-donating solvent and reduces the raw material cost, but also realizes high-value utilization of the light components. DETAILED DESCRIPTION

[0022] The present application will be further described below in conjunction with examples, and the modes of the present application include but are not limited to the following examples.

[0023] Example 1

[0024] The present example provides a modified asphalt production process based on the heavy components of medium and low temperature coal tar, which comprises the following steps:

[0025] S1, raw material pretreatment

[0026] The low and medium temperature coal tar is filtered by a metal sintered filter and a ceramic membrane filter in sequence. The pore size of the metal sintered filter is 10 μm, and the pore size of the ceramic membrane filter is 1 μm. After the filtering treatment, the primary tar is subjected to centrifugal treatment at a speed of 8000 rpm for 40 min. The double treatment of filtering and centrifugal treatment can remove solid particles with a particle size of >5 μm, and the ash content of the primary tar is 85 ppm.

[0027] S2, hydrotreatment

[0028] The primary tar is mixed with a hydrogen-donating solvent at a mass ratio of 1:0.3, and a catalyst is added for hydrcloclization reaction. The reaction temperature is 320 °C, the pressure is 8 MPa, and the reaction time is 60 min, to obtain a hydrogenation product. In this step, the hydrogen-donating solvent is a hydrogen-rich aromatic mixture generated by aromatization of light oil gas, the hydrogen-carbon molar ratio of which is 1.5:1, and the aromatic content is ≥60 wt%. The supported Ni-Mo / Al2O3 catalyst, in which the active metal loading is 12 wt%, is used at a mass ratio of 1:50 to the primary tar. The catalyst is regenerated after the reaction. The regeneration conditions are as follows: the temperature is increased to 500 °C at a rate of 2 °C / min in a nitrogen atmosphere with an oxygen volume fraction of 5%, and then the temperature is maintained for 2 h, followed by reduction with hydrogen.

[0029] S3, thermal polycondensation reaction

[0030] The heavy components in the hydrogenation product are separated by vacuum distillation. The operating pressure during the vacuum distillation is 5 kPa, the overhead temperature is 150 °C, and the bottom temperature is 280 °C. The heavy components are directly sent to a two-stage thermal polycondensation reactor after being discharged from the bottom of the distillation column. In the first stage, the temperature is 420 °C, and the reaction time is 2 h. In the second stage, the temperature is increased to 460 °C, nitrogen gas (with 2% hydrogen by volume) is introduced, and the reaction is carried out at a pressure of 0.1 MPa for 1 h. The flow rate of the nitrogen gas is 0.5 L / min, to generate a modified pitch intermediate.

[0031] S4, gas-liquid separation

[0032] The modified pitch intermediate is sequentially passed through a high-temperature cyclone separator, a condensation system, and a supercritical extraction column, to separate light oil gas, medium fraction, and modified pitch products. The supercritical extraction column uses carbon dioxide as the solvent, the pressure is 10 MPa, the temperature is 50 °C, and the extraction time is 30 min. After testing, the quinoline insoluble content of the modified pitch obtained in this embodiment is 8%, and the softening point is 240 °C.

[0033] S5, light oil gas reuse treatment

[0034] The light oil gas obtained in step S4 is treated by an aromatization reactor and then recycled to step S2 as a hydrogen-donating solvent. The aromatization reactor uses a ZSM-5 molecular sieve catalyst, the reaction temperature is 350°C, the space velocity is 1 h -1 , and the molar ratio of hydrogen to light oil gas is 3:1.

[0035] Example 2

[0036] This example provides a production process of modified pitch based on medium-low temperature coal tar heavy components, which comprises the following steps:

[0037] S1, raw material pretreatment

[0038] The medium-low temperature coal tar is sequentially filtered by a metal sintered filter element and a ceramic membrane filter. The pore size of the metal sintered filter element is 10 μm, and the filter hole size of the ceramic membrane filter is 5 μm. After the filtering treatment, centrifugal treatment is performed at a speed of 10,000 rpm for 30 min. After the double treatment of filtering and centrifugation, solid particles with a particle size of >5 μm are removed, and a primary tar with an ash content of 75 ppm is obtained.

[0039] S2, hydrotreatment

[0040] The primary tar is mixed with a hydrogen-donating solvent at a mass ratio of 1:0.4, and a catalyst is added for hydrocracking reaction. The reaction temperature is 360°C, the pressure is 10 MPa, and the reaction time is 80 min to obtain a hydrogenation product. In this step, the hydrogen-donating solvent is a hydrogen-rich aromatic hydrocarbon mixture generated by aromatization of light oil gas, the hydrogen-carbon molar ratio of which is 2:1, and the aromatic hydrocarbon content is ≥60 wt%. The supported Co-Mo / Al2O3 catalyst, in which the active metal loading is 16 wt%, is used at a mass ratio of 1:80 to the primary tar. The catalyst is regenerated after the reaction. The regeneration conditions are as follows: in a nitrogen atmosphere with an oxygen volume fraction of 8%, the temperature is increased to 550°C at a rate of 4°C / min, and then maintained for 3 hours, followed by reduction with hydrogen.

[0041] S3, thermal polycondensation reaction

[0042] The heavy components in the hydrogenation product are separated by vacuum distillation. The operating pressure during vacuum distillation is 10 kPa, the overhead temperature is 180°C, and the bottom temperature is 300°C. The heavy components are directly sent to a two-stage thermal polycondensation reactor after being discharged from the bottom of the distillation column. The first stage is reacted at 430°C for 1.5 h, and the second stage is reacted at 470°C under a pressure of 0.3 MPa for 0.8 h by introducing nitrogen gas (with a hydrogen volume fraction of 3%) at a flow rate of 1.0 L / min. The modified pitch intermediate is generated.

[0043] S4, gas-liquid separation

[0044] The modified pitch intermediate is sequentially passed through a high-temperature cyclone separator, a condensation system and a supercritical extraction tower to separate light oil gas, medium fraction and modified pitch product. The supercritical extraction tower uses carbon dioxide as solvent, the pressure is 12 MPa, the temperature is 65°C, and the extraction time is 45 min. After testing, the quinoline insoluble content of the modified pitch obtained in this embodiment is 12%, and the softening point is 270°C.

[0045] S5, light oil gas reuse treatment

[0046] The light oil gas obtained in step S4 is treated by an aromatization reactor and then recycled to step S2 as a hydrogen-donor solvent. The aromatization reactor uses a ZSM-5 molecular sieve catalyst, the reaction temperature is 380°C, the space velocity is 2h -1 , and the molar ratio of hydrogen to light oil gas is 4:1.

[0047] Example 3

[0048] This embodiment provides a modified pitch production process based on medium-low temperature coal tar heavy components, which includes the following steps:

[0049] S1, raw material pretreatment

[0050] The medium-low temperature coal tar is sequentially filtered by a metal sintered filter element and a ceramic membrane filter. The pore size of the metal sintered filter element is 15 μm, and the pore size of the ceramic membrane filter is 5 μm. After the filtration treatment, centrifugal treatment is performed at a speed of 12000 rpm for 40 min. After the double treatment of filtration + centrifugation, solid particles with a particle size of >5 μm are removed, and a primary tar with an ash content of 95 ppm is obtained.

[0051] S2, hydrotreatment

[0052] The primary tar is mixed with a hydrogen-donor solvent at a mass ratio of 1:0.5, and a catalyst is added for hydrocracking reaction. The reaction temperature is 380°C, the pressure is 12 MPa, and the reaction time is 120 min to obtain a hydrogenation product. In this step, the hydrogen-donor solvent is a hydrogen-rich aromatic mixture generated by aromatization of light oil gas, and the hydrogen-carbon molar ratio is 2.5:1, and the aromatic content is ≥60 wt%; the supported Co-Mo / Al2O3 catalyst, the active metal loading in the catalyst is 18 wt%, and the mass ratio of catalyst to primary tar is 1:100. The catalyst is regenerated after reaction. The regeneration conditions are as follows: in a nitrogen atmosphere with an oxygen volume fraction of 10%, the temperature is increased to 600°C at a rate of 5°C / min, and then reduced with hydrogen.

[0053] S3, thermal polycondensation reaction

[0054] The heavy components in the hydrogenated product were separated by vacuum distillation, the operating pressure in vacuum distillation was 20 kPa, the overhead temperature was 200°C, and the bottom temperature was 320°C. In this example, the fraction with boiling point > 350°C was defined as heavy component, which was discharged from the bottom of the distillation column and directly sent to the two-stage thermal polycondensation reactor. In the first stage, the temperature was 450°C and the reaction time was 1 h. In the second stage, the temperature was increased to 480°C and nitrogen gas (mixed with 5% hydrogen gas by volume) was introduced, and the reaction was carried out at 0.5 MPa for 0.5 h. The flow rate of nitrogen gas was 1.5 L / min, and the modified pitch intermediate was produced.

[0055] S4, gas-liquid separation

[0056] The modified pitch intermediate was sequentially passed through a high-temperature cyclone separator, a condensation system, and a supercritical extraction column, and light oil gas, medium fraction, and modified pitch product were separated. The supercritical extraction column used carbon dioxide as the solvent, the pressure was 15 MPa, the temperature was 80°C, and the extraction time was 60 min. After testing, the quinoline insoluble content of the modified pitch obtained in this example was 5%, and the softening point was 280°C.

[0057] S5, light oil gas reuse treatment

[0058] The light oil gas obtained in step S4 was treated by an aromatization reactor and then recycled to step S2 as a hydrogen-donor solvent. The aromatization reactor used a ZSM-5 molecular sieve catalyst, the reaction temperature was 400°C, the space velocity was 3 h -1 , and the molar ratio of hydrogen to light oil gas was 5:1.

[0059] Comparative Example

[0060] Pretreatment of raw material: only a metal filter (pore size 20 μm) was used, the centrifugal speed was 5000 rpm, and the time was 10 min. After testing, the ash content was 320 ppm.

[0061] Hydroprocessing: no hydrogen-donor solvent was used, and direct hydrocracking was carried out (the catalyst was the same as in Example 1, and the reaction temperature, pressure, and time were the same as in Example 1);

[0062] Thermal polycondensation reaction: single temperature control mode (450°C for 2 h), without nitrogen or hydrogen gas being introduced;

[0063] Gas-liquid separation: conventional distillation separation, without supercritical extraction;

[0064] The quinoline insoluble content and softening point of the modified pitch in this comparative example were tested, and the quinoline insoluble content was 22% and the softening point was 180°C. The properties of the modified pitch products obtained in Examples 1, 2, 3, and the comparative example were compared, as shown in the following table. In addition, the activity of the catalyst after being recycled for 10 times in the examples and the comparative example was tested, and the test data were supplemented to the table.

[0065] Index Example 1 Example 2 Example 3 Comparative Example 1 Ash content (ppm) 85 75 95 320 Quinoline insolubles content (%) 8 12 5 22 Softening point (°C) 240 270 280 180 Catalyst life (10 cycles) 90％ 86％ 95％ 50％

[0066] The low-temperature coal tar is treated by the production process provided by the application, the ash content is less than 100 ppm by the double action of filtration and centrifugation during pretreatment, which is significantly lower than that of the comparative example 1, the ash content of the primary tar is reduced, the catalyst life can be effectively prolonged, the activity of the catalyst in the example 1, 2 and 3 is still greater than 86% after 10 times of recycling, the ash content of the primary tar in the comparative example is higher (320 ppm), so the activity of the catalyst is greatly reduced after 10 times of recycling. In addition, the content of quinoline insoluble is reduced to 5-12% and the softening point reaches 240-280 DEG C by adjusting the heat polycondensation temperature and nitrogen flow and other parameters.

[0067] The above examples are only one of the preferred embodiments of the application, should not be used to limit the protection scope of the application, but any modification or polishing without substantial meaning made in the main design idea and spirit of the application, the technical problems solved are still consistent with the application, should be included in the protection scope of the application.

Claims

1. A process for producing modified asphalt based on medium and low temperature coal tar heavy components, characterized in that: The following steps are involved: S1, raw material pretreatment: medium and low temperature coal tar is filtered and centrifuged to remove solid particles with a particle size greater than 5 μm to obtain primary tar with an ash content less than 100 ppm; S2, hydrogenation treatment: the primary tar and the hydrogen-donating solvent are mixed in a mass ratio of 1:0.3-0.5, and a catalyst is added to carry out a hydrocracking reaction at a reaction temperature of 320-380°C and a pressure of 8-12 MPa for 60-120 min to obtain a hydrogenated product; S3, thermal polycondensation reaction: The heavy components in the hydrogenation product are separated by vacuum distillation and fed into a two-stage thermal polycondensation reactor. The first stage is reacted at 420-450°C for 1-2 hours. The second stage is heated to 460-480°C and nitrogen is introduced for 0.5-1 hour at a nitrogen flow rate of 0.5-1.5 L / min to produce a modified asphalt intermediate. S4, gas-liquid separation: The modified asphalt intermediate is passed through a high-temperature cyclone separator, a condensation system and a supercritical extraction tower in sequence to separate light oil and gas, a medium fraction and a modified asphalt product, wherein the quinoline insoluble content of the modified asphalt is 5-12% and the softening point is 240-280°C.

2. The process for producing modified asphalt based on medium and low temperature coal tar heavy components according to claim 1, characterized in that: In step S1, a metal sintered filter element and a ceramic membrane filter are used for combined gradient filtration. The pore size of the metal sintered filter element is 10-15 μm, and the pore size of the ceramic membrane filter is 1-5 μm. The rotation speed during centrifugation is 8000-12000 rpm, and the centrifugation time is 20-40 min.

3. A modified asphalt production process based on medium and low temperature coal tar heavy components according to claim 2, characterized in that: In step S2, the hydrogen-donating solvent is a hydrogen-rich aromatic hydrocarbon mixture generated by aromatization of light oil and gas, with a hydrogen-to-carbon molar ratio of 1.5 to 2.5:1 and an aromatic hydrocarbon content of ≥60 wt%.

4. The process for producing modified asphalt based on medium- and low-temperature coal tar heavy components according to claim 3, characterized in that: The catalyst in step S2 is a supported Ni-Mo / Al2O3 or Co-Mo / Al2O3 catalyst, the active metal loading in the catalyst is 12-18 wt%, and the mass ratio of the catalyst to the primary tar is 1:50-100.

5. The process for producing modified asphalt based on medium and low temperature coal tar heavy components according to claim 4, characterized in that: In step S3, the operating pressure during the reduced pressure distillation is 5-20 kPa, the tower top temperature is 150-200°C, the tower bottom temperature is 280-320°C, and the heavy components are discharged from the bottom of the tower; the second stage reaction pressure of the two-stage thermal polycondensation reactor is 0.1-0.5 MPa, and hydrogen is added to the nitrogen with a volume fraction of 2-5%.

6. The process for producing modified asphalt based on medium- and low-temperature coal tar heavy components according to claim 5, characterized in that: In step S4, the supercritical extraction tower uses carbon dioxide as solvent, has a pressure of 10-15 MPa, a temperature of 50-80° C., and extracts for 30-60 minutes.

7. The process for producing modified asphalt based on medium- and low-temperature coal tar heavy components according to claim 6, characterized in that: The method further includes processing the light oil gas obtained in step S4 through an aromatization reactor and recycling the processed oil gas to step S2 as a hydrogen supply solvent.

8. The process for producing modified asphalt based on medium- and low-temperature coal tar heavy components according to claim 7, characterized in that: In step S5, the aromatization reactor uses ZSM-5 molecular sieve catalyst, the reaction temperature is 350-400°C, and the space velocity is 1-3h -1 The molar ratio of hydrogen to light oil and gas is 3 to 5:

1.

9. The process for producing modified asphalt based on medium- and low-temperature coal tar heavy components according to claim 8, characterized in that: In step S2, the catalyst is regenerated after the reaction. The regeneration conditions are: in a nitrogen atmosphere with an oxygen volume fraction of 5 to 10%, the temperature is raised to 500 to 600° C. at a heating rate of 2 to 5° C. / min, maintained for 2 to 4 hours, and then reduced with hydrogen.