Method for preparing hard asphalt by solvent extraction of coal tar

Abstract

The invention relates to the field of coal chemical industry, and discloses a method for preparing hard asphalt by solvent extraction of coal tar. The method comprises the following steps: mixing a first solvent with coal tar, heating and stirring, standing for a period of time, separating a first extract liquor on the upper layer, adding the first solvent into the raffinate again, heating, stirring, standing and circularly extracting to obtain a first raffinate, wherein the first solvent is selected from methanol or ethanol; and mixing a second solvent with the first raffinate, heating, stirring, standing, and separating an upper-layer second extract, the raffinate being the hard asphalt component, and the second solvent being selected from toluene or xylene. According to the method, high-quality hard asphalt is obtained by extracting coal tar step by step through two solvents, the softening point of the high-quality hard asphalt is high, and the content of toluene insoluble substances and quinoline insoluble substances is relatively high; the selected solvent is low in toxicity, low in boiling point and good in extraction effect, the extraction process is simple, the extraction temperature is low, and the solvent can be recycled; the method has the advantages of low energy consumption, less investment, stable quality of the hard asphalt product and less discharge of three wastes.

Description

Technical Field

[0001] This invention relates to the field of coal chemical industry, and specifically to a method for preparing hard pitch by solvent extraction of coal tar. Background Technology

[0002] Hard pitch (usually referring to special pitch with a softening point above 120℃) is a key carbon material precursor with extremely high added value. Due to its excellent physicochemical properties, such as high residual carbon value, high coking value, good graphitizability, low impurity content, and superior bonding properties, hard pitch plays an irreplaceable role in many high-end fields such as electrode materials, high-performance carbon fibers, and special carbon materials.

[0003] Currently, the main industrial methods for producing hard pitch from coal tar include vacuum distillation and air oxidation. Vacuum distillation removes as much of the light and medium fractions from the coal tar as possible through deep vacuum distillation, with the residue being hard pitch. However, this method is extremely energy-intensive, requiring high temperatures (>350℃) and high vacuum, resulting in huge equipment investment and operating costs. Furthermore, relying solely on distillation makes it difficult to consistently obtain hard pitch with extremely high softening points (e.g., >150℃), and further increasing the softening point leads to severe coking of the pitch, clogging equipment. Air oxidation involves introducing air (sometimes with a catalyst) into soft pitch with a low softening point, causing an oxidative polymerization reaction at high temperatures to increase its molecular weight and thus raise the softening point. However, the oxidation process generates large amounts of toxic and harmful waste gases such as sulfur and nitrogen oxides and phenols. The acidic substances produced by the reaction severely corrode equipment, and the vigorous oxidation reaction destroys the aromatic structure of the pitch molecules, introducing a large number of oxygen-containing functional groups (such as carbonyl and hydroxyl groups), leading to a decline in pitch performance and making it difficult to meet the stringent requirements of high-end carbon materials for raw materials.

[0004] Solvent extraction can be carried out at room temperature or low temperatures (usually below 100°C), resulting in very low energy consumption. Simultaneously, the low-temperature environment reduces the decomposition or polymerization of asphalt components caused by high temperatures, ensuring the stability and consistency of product performance. Solvent extraction can rapidly separate the light and heavy components of coal tar, and the solvents used in extraction generally have low boiling points, allowing for recovery and recycling through simple distillation. Solvent selection is crucial, determining solvent separation efficiency and asphalt product quality. Inappropriate solvent selection may fail to separate light and heavy components, resulting in a large amount of effective asphalt components entrained in the extract phase, while excessive oil phase remains in the extract residue. Residual oil will degrade the softening point and coking value of the asphalt, reducing the quality of the asphalt product. Therefore, in-depth research into the solvent extraction process is necessary to produce high-quality hard asphalt. Summary of the Invention

[0005] In view of the above-mentioned problems in the existing technology, the main objective of the present invention is to provide a method for preparing hard pitch by solvent extraction of coal tar.

[0006] According to one aspect of the present invention, a method for preparing hard pitch by solvent extraction of coal tar is provided, the method comprising the following steps: The first solvent is mixed with coal tar, heated and stirred, and then allowed to stand for a period of time. The upper first extract is separated, and the first solvent is added to the raffinate again, heated and stirred, and allowed to stand. The extraction is repeated to obtain the first raffinate. The first solvent is selected from methanol or ethanol. The second solvent is mixed with the first extract, heated and stirred, and then allowed to stand for a period of time. The upper second extract is separated, and the extract is the hard asphalt component. The second solvent is selected from toluene or xylene.

[0007] According to one embodiment of the present invention, the mass ratio of the first solvent to the coal tar is 1:1.

[0008] According to one embodiment of the present invention, the heating is carried out by water bath heating, and the heating temperature is 50~70℃.

[0009] According to one embodiment of the present invention, the stirring rate is 100~150 r / min and the stirring time is 10~20 min.

[0010] According to one embodiment of the present invention, the first solvent is used for cyclic extraction 2 to 6 times.

[0011] According to one embodiment of the present invention, the mass ratio of the second solvent to the coal tar is 1:1.

[0012] According to one embodiment of the present invention, the second solvent is used for cyclic extraction 1 to 4 times.

[0013] According to one embodiment of the present invention, the method further includes: The first extract from multiple extraction cycles is collected, heated to 65-85°C, and distilled off to remove the first solvent, which is then recycled; and / or The second extract produced by multiple cycles of extraction is collected together, heated to 110~145℃ to distill off the second solvent, and the distilled second solvent is recycled.

[0014] According to one embodiment of the present invention, the coal tar is low-temperature coal tar.

[0015] According to one embodiment of the present invention, the softening point of the prepared hard asphalt is 138.5~146.3℃, the toluene insoluble content is 59%~69%, and the quinoline insoluble content is 30%~36%.

[0016] The method for preparing hard pitch by solvent extraction of coal tar according to the present invention has at least one of the following advantages compared with the prior art: (1) The present invention obtains high-quality hard pitch by stepwise extraction of coal tar with two solvents. It has a high softening point and high content of toluene-insoluble and quinoline-insoluble substances. (2) The selected solvent has low toxicity, low boiling point and good extraction effect. The extraction process is simple, the extraction temperature is low and the solvent can be recycled. (3) Compared with traditional vacuum distillation and oxidative polymerization methods, the method of the present invention has the advantages of low energy consumption, low investment, stable quality of hard asphalt products and low emissions of three wastes. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A flowchart of a method for preparing hard pitch by solvent extraction of coal tar according to an embodiment of the present invention is shown; Figure 2 A process flow diagram for preparing hard pitch by solvent extraction of coal tar according to an embodiment of the present invention is shown. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0020] Furthermore, the reference to "embodiment" herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0021] It should be understood that the embodiments of the invention shown in the exemplary embodiments are merely illustrative. Although only a few embodiments have been described in detail in this invention, those skilled in the art will readily recognize that various modifications are possible without substantially departing from the teachings of the invention. Accordingly, all such modifications should be included within the scope of the invention. Other substitutions, modifications, variations, and deletions can be made to the design, operating conditions, and parameters of the following exemplary embodiments without departing from the spirit of the invention.

[0022] According to one aspect of the present invention, a method for preparing hard pitch by solvent extraction of coal tar is provided. For example... Figure 1 As shown, the method mainly includes the following steps: Step S1: Mix the first solvent with coal tar, heat and stir, let stand for a period of time, separate the upper first extract, add the first solvent to the raffinate again, heat and stir, let stand, and circulate to extract to obtain the first raffinate. The first solvent is selected from methanol or ethanol. Step S2: Mix the second solvent with the first extract, heat and stir, let stand for a period of time, separate the upper second extract, and the extract is the hard asphalt component. The second solvent is selected from toluene or xylene.

[0023] For example, in one embodiment of the invention, such as Figure 2 As shown, solvent 1 and coal tar are placed in a container at a certain mass ratio, a reflux condenser is installed, and mechanical stirring is used for heating and stirring. After standing for a period of time, the upper yellow-green first extract is separated, while the black viscous substance remains in the container. Solvent 1 is methanol or ethanol, preferably ethanol.

[0024] Add solvent 1 to the container again, repeat the extraction operation in the above steps, continue the cyclic extraction, and then collect the upper first extract.

[0025] Solvent 2 is added to the container, and the extraction process of heating, stirring, and settling is repeated for a predetermined number of cycles. The upper second extract is then collected, and the residue is the hard asphalt component. Solvent 2 is toluene or xylene, preferably xylene.

[0026] In the above process, methanol or ethanol is used to separate phenols and some neutral components (such as benzene, toluene, and xylene) from coal tar. Using methanol or ethanol first has the advantages of good solubility, low toxicity, and easy recovery. After separating the phenols and some neutral components from the coal tar with methanol or ethanol, toluene or xylene is then used to separate aromatic hydrocarbons, such as naphthalene and anthracene, which are high-boiling-point components. Using toluene or xylene has the advantages of high selectivity, moderate boiling point, convenient recovery, and wide applicability.

[0027] In some embodiments of the present invention, the mass ratio of the first solvent to coal tar is 1:1. Controlling the mass ratio of the first solvent to coal tar at this ratio can improve the extraction rate. At a 1:1 mass ratio, the interaction between the solvent and coal tar reaches equilibrium, significantly improving the extraction efficiency of target components (such as phenols or heterocyclic compounds) and reducing residues. It also reduces solvent loss: avoiding the use of excessive solvent saves costs and reduces energy consumption for subsequent solvent recovery, conforming to green chemistry principles. Furthermore, it simplifies the operation process; a stable mass ratio reduces process fluctuations, facilitates automated control, and improves production consistency and reliability. Finally, it enhances environmental friendliness by reducing solvent use and wastewater generation, lowering the environmental burden while improving resource utilization efficiency.

[0028] In some embodiments of the present invention, heating in each extraction step is performed using a water bath at a temperature of 50-70°C. Temperature control within this range ensures safety and stability. Water bath heating, through indirect temperature control, avoids direct contact between organic solvents and open flames, significantly reducing the risk of flammability and explosion, and ensuring safe and reliable operation. Uniform and controllable temperature: Water, as a heat transfer medium, achieves uniform heating, preventing container rupture or sample degradation due to localized overheating, making it particularly suitable for the stable extraction of temperature-sensitive active ingredients. Optimized extraction efficiency: Within this temperature range, the solubility of the target compound is significantly increased, while solvent viscosity decreases, accelerating molecular diffusion, thereby improving the extraction rate and product yield. Reduced component loss: Compared to higher temperatures, 50-70°C effectively inhibits the decomposition or volatilization of heat-sensitive substances, ensuring the integrity and quality of the extract. Simple and environmentally friendly operation: Water bath equipment is easy to control and maintain, and water as a medium is low-cost and pollution-free, meeting the environmental protection requirements of routine laboratory operations.

[0029] In some embodiments of the present invention, the stirring rate in each extraction step is 100-150 r / min, and the stirring time is 10-20 min. Controlling the stirring rate and time within this range optimizes mass transfer efficiency. This stirring rate range effectively promotes thorough mixing of the two phases, increases the contact area, and thus accelerates the transfer of the target substance from one phase to another, significantly improving extraction efficiency. Simultaneously, the 10-20 min stirring time ensures sufficient contact, avoiding incomplete extraction due to insufficient time. Balancing operational stability, controlling the stirring rate at 100-150 r / min reduces emulsification caused by vigorous stirring, lowers the difficulty of phase separation, and improves subsequent stratification efficiency. Limiting the time to within 20 min prevents increased energy consumption or equipment wear due to excessive stirring. Ensuring reliable results, this parameter combination reduces human error, ensures consistency in parallel experiments, avoids the need for repeated experiments due to uneven stirring or time deviations, thereby improving data accuracy and experimental repeatability.

[0030] In some embodiments of the present invention, the first solvent is used for cyclic extraction 2 to 6 times, preferably 2 to 3 times. Too few extractions will result in some components remaining in the raffinate phase, affecting the extraction effect of step S2. Too many extractions will reduce extraction efficiency and increase costs.

[0031] In some embodiments of the present invention, the mass ratio of the second solvent to coal tar is 1:1. Maintaining this 1:1 mass ratio ensures that the interaction between the solvent and coal tar reaches equilibrium, significantly improving the extraction efficiency of target components (such as phenols or heterocyclic compounds) and reducing residues. This also reduces solvent loss by avoiding excessive solvent use, saving costs, and reducing energy consumption for subsequent solvent recovery, aligning with green chemistry principles. Furthermore, it simplifies the operation process, and the stable mass ratio reduces process fluctuations, facilitating automated control and improving production consistency and reliability. Finally, it enhances environmental friendliness by reducing solvent use and wastewater generation, lowering the environmental burden while improving resource utilization efficiency.

[0032] In some embodiments of the present invention, the second solvent is used for cyclic extraction 1 to 4 times, preferably 1 to 2 times.

[0033] In some embodiments of the present invention, the method further includes: collecting the first extract produced by multiple cycles of extraction, heating it to 65~85°C to distill off the first solvent, and returning the distilled first solvent to step S1 for recycling.

[0034] In some embodiments of the present invention, the method further includes: collecting the second extract produced by multiple cycles of extraction, heating it to 110~145°C to distill off the second solvent, and returning the distilled second solvent to step S2 for recycling.

[0035] In some embodiments of the present invention, the coal tar is a low-temperature tar.

[0036] In some embodiments of the present invention, the softening point of the prepared hard asphalt is 138.5~146.3℃, the toluene insoluble content is 59%~69%, and the quinoline insoluble content is 30%~36%.

[0037] This invention yields high-quality hard pitch through stepwise extraction of coal tar using two solvents. This hard pitch has a high softening point and high content of toluene- and quinoline-insoluble matter. The selected solvents are low in toxicity, have low boiling points, and provide good extraction efficiency. The extraction process is simple, the extraction temperature is low, and the solvents can be recycled. Compared to traditional vacuum distillation and oxidative polymerization methods, this invention offers advantages such as low energy consumption, low investment, stable hard pitch product quality, and low emissions. The method of this invention is simple, low-cost, and can obtain high-softening-point hard pitch, which can be used as a precursor for high-performance carbon materials.

[0038] The method of the present invention will be further described and illustrated below with reference to embodiments.

[0039] Example 1 Weigh 60g of coal tar into a three-necked flask, then add 60g of ethanol and mix. Attach a reflux condenser and mechanically stir at 125 rpm. Heat to 60°C in a water bath and maintain stirring for 15 minutes. Allow to stand and separate the layers, keeping the black, viscous substance in the container. Continue adding 60g of ethanol to the container and repeat the extraction under the same conditions once more, collecting the upper ethanol extract.

[0040] Next, 60g of xylene was added to the container, and reflux and mechanical stirring were used at a speed of 125 rpm. The mixture was heated to 60°C in a water bath and stirred for 15 minutes. The mixture was then allowed to stand and separate into layers, with the upper extract separated and the residue remaining in the container. Another 60g of xylene was added to the container, and the extraction was repeated twice more under the same conditions. The upper extracts were then collected. The residue was dried in an oven at 105°C for 2 hours to obtain hard asphalt.

[0041] The separated ethanol extract was heated to 85°C and the solvent was distilled off. The separated xylene extract was heated to 145°C and the solvent was distilled off. The distilled ethanol and xylene were recycled.

[0042] The softening point, toluene insoluble content, and quinoline insoluble content of the obtained hard asphalt were tested, and the test results are shown in Table 1.

[0043] Table 1 Test results of the obtained hard asphalt

[0044] Example 2 Weigh 60g of coal tar into a three-necked flask, then add 60g of ethanol and mix. Attach a reflux condenser and mechanically stir at 100 rpm. Heat to 70°C in a water bath and maintain stirring for 10 minutes. Allow to stand and separate the layers, keeping the black, viscous substance in the container. Continue adding 60g of ethanol to the container and repeat the extraction twice more under the same conditions, collecting the upper ethanol extracts.

[0045] Next, 60g of xylene was added to the container, and reflux and mechanical stirring were used at a speed of 100 rpm. The mixture was heated to 70°C in a water bath and stirred for 10 minutes. The mixture was then allowed to stand and separate into layers, with the upper extract separated and the residue remaining in the container. Another 60g of xylene was added to the container, and the extraction was repeated once more under the same conditions. The upper extracts were then collected. The residue was dried in an oven at 105°C for 2 hours to obtain hard asphalt.

[0046] The separated ethanol extract was heated to 65°C and the solvent was distilled off. The separated xylene extract was heated to 110°C and the solvent was distilled off. The distilled ethanol and xylene were recycled.

[0047] The softening point, toluene insoluble content, and quinoline insoluble content of the obtained hard asphalt were tested, and the test results are shown in Table 2.

[0048] Table 2 Test results of the obtained hard asphalt

[0049] Example 3 Weigh 60g of coal tar into a three-necked flask, then add 60g of methanol to mix with the coal tar. Attach a reflux condenser and mechanically stir at 150 rpm. Heat to 50°C in a water bath and maintain stirring for 20 minutes. Allow to stand and separate the layers, keeping the black, viscous substance in the container. Continue adding 60g of methanol to the container and repeat the extraction once more under the same conditions. Collect the upper methanol extract.

[0050] Next, 60g of toluene was added to the container, and the mixture was refluxed and mechanically stirred at a rate of 150 rpm. The mixture was heated to 50°C in a water bath and stirred for 20 minutes. Then, the mixture was allowed to stand and separate into layers. The upper extract was separated, and the residue was left in the container. The residue was dried in an oven at 105°C for 2 hours to obtain hard asphalt.

[0051] The separated methanol extract was heated to 70°C and the solvent was distilled off. The separated toluene extract was heated to 120°C and the solvent was distilled off. The distilled methanol and toluene were recycled.

[0052] The softening point, toluene insoluble content, and quinoline insoluble content of the obtained hard asphalt were tested, and the test results are shown in Table 3.

[0053] Table 3 Test results of the obtained hard asphalt

[0054] Comparative Example 1 Using only ethanol as solvent: Weigh 60g of coal tar into a three-necked flask, add 60g of ethanol and mix. Attach a reflux condenser and mechanically stir at 100 rpm. Heat to 60°C in a water bath and maintain stirring for 10 minutes. Allow to stand and separate the layers, keeping the black viscous substance in the container. Continue adding 60g of ethanol to the container and repeat the extraction twice more under the same conditions. Collect the upper ethanol extracts. Dry the residue in an oven at 105°C for 2 hours to obtain asphalt.

[0055] The softening point, toluene insoluble content, and quinoline insoluble content of the obtained asphalt were tested, and the test results are shown in Table 4.

[0056] Table 4 Test results of the obtained hard asphalt

[0057] Comparative Example 2 Using only xylene solvent: Weigh 60g of coal tar into a three-necked flask, then add 60g of xylene and mix with the coal tar. Attach a reflux condenser, use mechanical stirring at a speed of 100r / min, heat to 60℃ in a water bath, keep stirring for 10min, and then let stand. No obvious stratification phenomenon was observed, making separation difficult.

[0058] The test results of Examples 1-3 and Comparative Examples 1-2 show that: (1) Ethanol / methanol can effectively extract light components (such as resins) from coal tar, while xylene further extracts heavy components (such as asphaltenes). The combined use can improve the heat resistance and structural stability of hard asphalt; (2) The use of a combined solvent can effectively retain the high molecular weight components in coal tar, forming hard asphalt with a high softening point. However, the content of toluene-insoluble and quinoline-insoluble matter in Comparative Example 1 is low (36.7% and 10.4%), indicating that using ethanol alone will lead to a decrease in the performance of hard asphalt; (3) The comparison between Examples 1 and 2 shows that increasing the number of extractions (2 times vs. 3 times) slightly increases the softening point of hard asphalt (138.5°C vs. 138.7°C), but reduces the content of toluene-insoluble matter (67.6%). (vs. 59.0%), indicating that the adjustment of the number of ethanol extractions needs to balance extraction efficiency and product quality. Excessive extraction may reduce the retention of heavy components; (4) Xylene has a stronger ability to dissolve heavy components (such as asphaltene), but its use alone (Comparative Example 2) makes the process infeasible due to the difficulty of layering. The combined use of ethanol / methanol and xylene can overcome this defect and achieve efficient layering and product separation.

[0059] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the disclosed embodiments of the present invention is limited to these examples; within the framework of the embodiments of the present invention, the technical features of the above embodiments or different embodiments can also be combined, and there are many other variations of different aspects of the embodiments of the present invention as described above, which are not provided in detail for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the embodiments of the present invention should be included within the protection scope of the embodiments of the present invention.

Claims

1. A method of preparing hard pitch from coal tar by solvent extraction, characterized by, The method comprises the following steps: mixing a first solvent with the coal tar, heating and stirring, and then standing for a period of time, separating the first extraction liquid, adding the first solvent to the residue again, heating and stirring, standing, and then repeating the extraction to obtain a first residue, wherein the first solvent is selected from methanol or ethanol; mixing a second solvent with the first residue, heating and stirring, and then standing for a period of time, separating the second extraction liquid, and then obtaining the pitch component, wherein the second solvent is selected from toluene or xylene.

2. The method of claim 1, wherein the solvent-extracted coal tar is prepared into hard pitch. The mass ratio of the first solvent to the coal tar is 1:

1.

3. The method of claim 1, wherein the solvent-extracted coal tar is prepared into hard pitch. The heating is performed by using a water bath, and the heating temperature is 50-70℃.

4. The method of claim 1, wherein the solvent-extracted coal tar is prepared into hard pitch. The stirring rate is 100-150r / min, and the stirring time is 10-20min.

5. The method of claim 1, wherein the solvent-extracted coal tar is prepared into hard pitch. The number of times of repeating the extraction with the first solvent is 2-6 times.

6. The method of claim 1, wherein the solvent-extracted coal tar is prepared into hard pitch. The mass ratio of the second solvent to the coal tar is 1:

1.

7. The method of claim 1, wherein the solvent-extracted coal tar is prepared into hard pitch. The number of times of repeating the extraction with the second solvent is 1-4 times.

8. The method of claim 1, wherein the solvent-extracted coal tar is prepared into hard pitch. The method further comprises: concentrating the first extraction liquids obtained by repeating the extraction, heating to 65-85℃ to distill the first solvent, and recycling the distilled first solvent; and / or concentrating the second extraction liquids obtained by repeating the extraction, heating to 110-145℃ to distill the second solvent, and recycling the distilled second solvent.

9. The method of claim 1, wherein the solvent-extracted coal tar is prepared into hard pitch. The coal tar is a low-temperature coal tar.

10. The method of claim 1, wherein the solvent-extracted coal tar is prepared into hard pitch. The prepared pitch has a softening point of 138.5-146.3℃, a toluene insoluble content of 59%-69%, and a quinoline insoluble content of 30%-36%.

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