Production method and production system of low-sulfur low-nitrogen coal tar pitch based on air oxidation

Abstract

The invention belongs to the technical field of coal chemical industry, and particularly relates to a production method and a production system of low-sulfur low-nitrogen coal tar pitch based on air oxidation. The method comprises the following steps: mixing coal tar pitch with a solvent to obtain mixed oil, heating the mixed oil to 80-120 DEG C, adding a supported iron-based metal oxide catalyst, carrying out an air reaction, extracting, and evaporating to obtain the low-sulfur low-nitrogen coal tar pitch. The low-sulfur and low-nitrogen coal tar pitch prepared by the method is low in sulfur and nitrogen content and remarkable in effect progress, the reaction can be realized by using air, the air is easy to obtain, and the production cost can be reduced. The low-sulfur low-nitrogen coal tar pitch production system disclosed by the invention comprises the dissolution reaction kettle, the oxidation tower, the extraction tower group and the evaporation tower, and by adopting the system, the desulfurization reaction is more sufficient, so that the desulfurization and denitrification efficiency is improved, meanwhile, a solvent is recycled, raw materials are saved, and the cost is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of coal chemical industry, and in particular relates to a production method and a production system of low-sulfur and low-nitrogen coal tar pitch based on air oxidation. Background Art

[0002] Coal tar pitch is mainly produced by removing the light fraction from coal tar (separating anthracene oil and dianthracene oil) and then undergoing high-temperature distillation to produce soft pitch. Coal tar pitch has a strong ability to bind to carbonaceous aggregates, and the sources of coal tar pitch are extremely wide. In traditional industrial production, coal tar pitch is often used to manufacture fuels, adhesives, impregnants, epoxy coal coatings and other purposes. It is also used as a raw material for producing high-value-added carbon materials such as needle coke, carbon fiber and lithium battery negative electrodes. However, heteroatoms such as sulfur and nitrogen in coal tar pitch affect the processing of the pitch and the quality of downstream products. The sulfur and nitrogen in the pitch will remain in the downstream products such as needle coke, carbon fiber and other high-grade carbon materials, seriously affecting the performance of the carbon material products. Due to the quality of the coal tar feed, the sulfur content of the soft pitch currently produced is about 0.60% and the nitrogen content is about 0.90%, which is difficult to meet the use requirements of soft pitch in specific occasions. Therefore, it is necessary to further reduce the sulfur and nitrogen content of the soft pitch.

[0003] Because nitrogen in asphalt primarily exists in the form of pyridine and pyrrole, which are stable within asphaltene molecules at high concentrations, removing nitrogen from asphalt is more difficult than removing sulfur, given the high thermal stability of the pyridine and pyrrole ring structures. Prior art invention patent application number 202310363129.8 discloses an asphalt desulfurization method, which includes: mixing asphalt with a solvent to produce a mixed oil; heating the mixed oil (150-400°C); flashing the heated mixed oil in an oxidation tower, where a gaseous oxidant is introduced for reaction; after the reaction, the solvent and unreacted gaseous oxidant enter the light phase and escape from the top of the tower; the asphalt enters the heavy phase and is discharged from the bottom of the tower; the asphalt enters a wash tank, where a desulfurization solution is introduced for mixing and stirring; the sulfur-rich desulfurization solution is discharged from the top of the wash tank, and the desulfurized asphalt is discharged from the bottom of the wash tank. The gaseous oxidant includes at least one of ozone, oxygen, or air. However, in actual production, using air as the gaseous oxidant has a low desulfurization rate and unsatisfactory desulfurization results. Summary of the Invention

[0004] Based on this, the present application provides a production method and production system for low-sulfur and low-nitrogen coal tar pitch based on air oxidation to solve the technical problems in the prior art that air as a gas oxidant has a low desulfurization rate and an unsatisfactory desulfurization effect.

[0005] The technical solutions of this application to solve the above technical problems are as follows:

[0006] A method for producing low-sulfur and low-nitrogen coal tar pitch based on air oxidation, characterized by comprising the following steps:

[0007] S10. Adding a solvent to the coal tar pitch, heating to a first preset temperature and mixing uniformly to obtain a mixed oil;

[0008] S20. The mixed oil is heated to 140°C to 220°C, and in the presence of a catalyst, air is introduced into the reaction to obtain a mixed oil; the catalyst comprises a supported iron-based metal oxide catalyst;

[0009] S30. Extracting and evaporating the primary mixed oil to obtain low-sulfur and low-nitrogen coal tar pitch.

[0010] A low-sulfur and low-nitrogen coal tar pitch production system based on air oxidation, comprising:

[0011] A dissolution reactor, wherein the inlet of the dissolution reactor is connected to a coal tar pitch tank and a solvent tank, and the bottom outlet of the dissolution reactor is provided with a mixed oil discharge pipe;

[0012] An oxidation tower is provided with a spray layer, a fixed bed, and a gas distributor from top to bottom in the height direction. A primary discharge pipe is provided at the bottom outlet of the oxidation tower. The other end of the mixed oil discharge pipe is connected to the primary discharge pipe. The primary discharge pipe is also connected to a circulation pipe. The circulation pipe is provided with a first heater. The other end of the circulation pipe is connected to the spray layer. The fixed bed is used to load the catalyst. The gas distributor is connected to an air compressor via an air feed pipe.

[0013] The other end of the primary discharge pipe is connected to the light liquid inlet of the extraction tower group;

[0014] The light liquid outlet of the extraction tower group is connected to the inlet of the evaporation tower, the bottom outlet of the evaporation tower is connected to the finished product extraction pipe; the top outlet of the evaporation tower is connected to the inlet of the solvent tank.

[0015] Compared with the prior art, this application has at least the following advantages:

[0016] The present application discloses a method for producing low-sulfur and low-nitrogen coal tar pitch based on air oxidation, in which coal tar pitch is mixed with a solvent to obtain a mixed oil, and the mixed oil is heated to 140°C to 220°C and air is introduced into the mixed oil in the presence of a supported iron-based metal oxide catalyst for reaction, followed by extraction and evaporation to obtain low-sulfur and low-nitrogen coal tar pitch. The combined action of air and the supported iron-based metal oxide catalyst promotes the occurrence of the oxidation reaction, thereby enhancing the desulfurization and denitrification effects. Experiments have shown that the low-sulfur and low-nitrogen coal tar pitch prepared by the present application has a desulfurization rate of 61.7% and a denitrification rate of 44.8%, with excellent desulfurization and denitrification effects. Moreover, the reaction process can be realized by using air during the reaction process, and air is easy to obtain, which can reduce production costs.

[0017] The low-sulfur and low-nitrogen coal tar pitch production system based on air oxidation disclosed in this application includes a dissolution reactor, an oxidation tower, an extraction tower group and an evaporation tower. Coal tar pitch and a solvent are mixed and heated in the dissolution reactor to obtain a mixed oil; the mixed oil enters the oxidation tower after heating and is sprayed downward from the spray layer at the top of the oxidation tower. Air is evenly distributed in the oxidation tower through a gas distributor. The fixed bed is filled with a catalyst. The mixed oil undergoes a full oxidation reaction in the oxidation tower, effectively separating the sulfur and nitrogen in the coal tar pitch. The reacted mixed oil is extracted in the extraction tower group to remove the sulfur, nitrogen, organic matter, salt, etc. The light phase after extraction, that is, the mixture of coal tar pitch and solvent, is evaporated in the evaporation tower to obtain a low-sulfur and low-nitrogen coal tar pitch finished product. The evaporated solvent is transported to the solvent tank for recycling. The use of this system makes the desulfurization reaction more complete, thereby improving the desulfurization and denitrification efficiency, while recycling the solvent, saving raw materials and reducing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a system diagram of a low-sulfur and low-nitrogen coal tar pitch production system based on air oxidation according to an embodiment of the present application.

[0019] In the figure: dissolution reactor 100, coal tar pitch tank 110, solvent tank 120, mixed oil discharge pipe 130, second heater 131, oxidation tower 200, spray layer 210, fixed bed 220, gas distributor 230, primary discharge pipe 240, circulation pipe 250, first heater 251, air feed pipe 260, gas discharge pipe 270, air compressor 280, first extraction tower 300, waste liquid pipe 310, second extraction tower 400, heavy liquid feed pipe 410, evaporation tower 500, finished product extraction pipe 510, asphalt circulation pipe 520, third heater 530. DETAILED DESCRIPTION

[0020] To facilitate understanding of the present application, a more comprehensive description of the present application will be provided below with reference to the accompanying drawings. The accompanying drawings illustrate preferred embodiments of the present application. However, the present application may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the disclosure of the present application.

[0021] It should be noted that when an element is referred to as being "disposed on" another element, it may be directly on the other element or there may be an intermediate element. When an element is referred to as being "connected to" another element, it may be directly connected to the other element or there may be an intermediate element. The terms "vertical," "horizontal," "left," "right," "top," "bottom," "bottom end," "top end," and similar expressions used herein are for illustrative purposes only and do not represent the only implementation methods.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains. The terms used in the specification herein are for the purpose of describing specific embodiments only and are not intended to limit this application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0023] In one embodiment of the present application, a method for producing low-sulfur and low-nitrogen coal tar pitch based on air oxidation is characterized by comprising the following steps:

[0024] S10. Adding a solvent to the coal tar pitch, heating to a first preset temperature and mixing uniformly to obtain a mixed oil;

[0025] Coal tar pitch is one of the main products of coal tar processing. It is the residue left after coal tar distillation and extraction. It is a brown or black viscous liquid. During desulfurization, a solvent is added to dissolve it. Furthermore, the solvent includes at least one of wash oil or anthracene oil. The first preset temperature is 50°C to 110°C. To ensure sufficient dissolution and facilitate subsequent production processes, the mass ratio of coal tar pitch to solvent is 1:(1 to 5).

[0026] S20. The mixed oil is heated to 140°C to 220°C, and in the presence of a catalyst, air is introduced into the reaction to obtain a mixed oil; the catalyst comprises a supported iron-based metal oxide catalyst;

[0027] The oxygen O2 in the air provides an oxidizing environment for the reaction. It should be noted that the air in this application can also be replaced by a mixed gas containing O2, such as a mixed gas of nitrogen, carbon dioxide fire extinguisher and oxygen. Since air is easier to obtain, air is preferred in this application.

[0028] In a preferred embodiment, the mass ratio of the mixed oil to the air is 1:(1.4 to 4).

[0029] The catalyst includes a supported iron-based metal oxide catalyst, which is reusable and easy to separate. Furthermore, the substrate of the supported iron-based metal oxide catalyst includes any one of diatomaceous earth and alumina, and the iron-based metal includes any two of titanium, vanadium, chromium, manganese, iron, cobalt and nickel. For example, alumina-supported iron-manganese catalyst, diatomaceous earth cobalt-nickel catalyst, etc. This type of catalyst provides a valence change of metal ions (such as V 5+ / V 4+ 、Co 3+ / Co 2+ 、Fe 3+ / Fe 2+ In a preferred embodiment, the amount of the catalyst added is 0.5 wt% to 3 wt% of the coal tar pitch.

[0030] The preparation method of the catalyst is as follows: (1) pre-treating the substrate material. The pre-treatment method depends on the specific substrate material. For example, when the substrate material is diatomaceous earth, the diatomaceous earth is repeatedly washed with deionized water to remove surface impurities, and then dried at a certain temperature (such as 100°C to 120°C) for several hours to remove moisture. The dried diatomaceous earth is then calcined in a muffle furnace. The calcination temperature is usually between 400°C and 600°C, and the calcination time is 2 to 4 hours to increase the specific surface area and pore structure of the diatomaceous earth and enhance its loading capacity. When the substrate material is alumina, a suitable alumina carrier is selected, such as γ-alumina. First, the alumina is soaked in dilute acid (such as dilute nitric acid, dilute hydrochloric acid, etc.) for a period of time to remove surface impurities and some amorphous alumina, thereby improving the purity and activity of the carrier. The soaking time is generally 1 to 2 hours, and the acid concentration is 0.1 to 1 mol / L. Then wash with deionized water until neutral, dry at 100°C to 120°C for several hours, and then calcine in a muffle furnace at 500°C to 700°C for 3 to 5 hours to obtain a stable crystalline structure and a large specific surface area. (2) Preparation of precursor solution: weigh a certain amount of iron-based metal salt (such as titanium nitrate, ammonium metavanadate, chromium nitrate, manganese sulfate, iron nitrate, cobalt nitrate, nickel nitrate, etc.). In this application, two iron-based metals are loaded, so two iron-based metal salts are weighed and dissolved in an appropriate amount of deionized water to prepare a solution. (3) Add the pretreated substrate material to deionized water to prepare a suspension. Under stirring, slowly add the precursor solution to the substrate material suspension, and at the same time add a precipitant (such as potassium hydroxide, potassium carbonate, etc.) to uniformly precipitate the metal ions on the alumina / diatomaceous earth. (4) After precipitation is completed, perform aging treatment, and let the suspension stand at a certain temperature (such as room temperature to 60°C) for a period of time, usually 1 to 24 hours. After aging, the alumina / diatomaceous earth loaded with iron-based metal precipitates is separated by filtration and washed several times with deionized water until the washing liquid is free of impurity ions. (5) Drying and calcination: The washed sample is dried at 80°C to 100°C for 6 to 10 hours and then calcined in a muffle furnace. The calcination temperature is generally between 400°C and 700°C, and the calcination time is 3 to 5 hours. This converts the metal precipitates into an active phase and firmly supports them on the alumina / diatomaceous earth, resulting in a supported iron-based metal oxide catalyst.

[0031] S30. Extracting and evaporating the primary mixed oil to obtain low-sulfur and low-nitrogen coal tar pitch.

[0032] It is worth noting that the process temperature and process time involved in the above-mentioned embodiments are the temperature or time adopted in the experimental process. Those skilled in the art can make reasonable adjustments within the error range based on the process temperature and process time provided by the present invention, which should be included in the protection scope of the present invention.

[0033] The following is a detailed description of the technical solutions and effects of the present invention through specific experimental examples.

[0034] 1. Experimental Materials and Methods

[0035] 1.1 Experimental Materials

[0036] Coal tar pitch was obtained from Ningxia Xitai Coal Chemical Co., Ltd.; other raw materials and reagents were commercially available and used without further purification. The sulfur and nitrogen content of coal tar pitch was determined in accordance with relevant Chinese standards (GB / T 38395-2019, Determination of Sulfur and Nitrogen Content of Coal Tar). Coal tar pitch sample parameters and sulfur and nitrogen contents are shown in Table 1.

[0037] Table 1 Coal tar pitch sample parameters

[0038]

[0039] 1.2 Determination and calculation of sulfur content

[0040] The total sulfur content of coal tar pitch was measured using a KZDL-500 micro automatic sulfur analyzer (Hebi Huadian Analytical Instrument Co., Ltd.).

[0041] Desulfurization rate calculation: The desulfurization rate refers to the percentage of sulfide removed from coal tar pitch, that is, the ratio of sulfide removed from coal tar pitch after treatment to the sulfur content in the original coal tar pitch, expressed as DRS, as shown in the following calculation formula:

[0042]

[0043] Where: DR S —Desulfurization rate, %;

[0044] S t1 —Total sulfur content in asphalt before desulfurization;

[0045] S t2 —Sulfur content in treated asphalt samples.

[0046] 1.3 Determination and calculation of nitrogen content

[0047] The total ammonia content in coal tar was determined using the HD-CN500 automatic nitrogen analyzer, which meets the national standard requirements for ammonia content in coal tar.

[0048] Calculation of denitrification rate: The denitrification rate refers to the percentage of nitrogen compounds removed from coal tar pitch, that is, the ratio of nitrogen compounds removed from coal tar pitch after treatment to the nitrogen content in the original coal tar pitch, expressed as DR, as shown in the following calculation formula:

[0049]

[0050] Where: DRN —Denitrification rate, %;

[0051] N t1 —Total sulfur content in asphalt before denitrification;

[0052] N t2 —Nitrogen content in asphalt samples after treatment.

[0053] 2. Example 1

[0054] Preparation of Catalyst 1:

[0055] (1) 2 kg of diatomaceous earth was repeatedly washed with deionized water to remove surface impurities, and then dried at 100°C to remove moisture. The dried diatomaceous earth was then calcined in a muffle furnace at 500°C for 3 hours.

[0056] (2) Preparation of precursor solution: 1.94 kg of cobalt nitrate was weighed and dissolved in 1.94 kg of deionized water (the mass ratio of cobalt nitrate to deionized water was 1:1) to prepare a precursor solution;

[0057] (3) The pretreated diatomaceous earth was added to 4 kg of deionized water to form a suspension. The precursor solution was slowly added dropwise to the diatomaceous earth suspension while stirring. At the same time, sodium hydroxide as a precipitant was added dropwise to adjust the solution pH to 8.

[0058] (4) After precipitation is complete, an aging treatment is performed, and the suspension is allowed to stand and age for 12 hours at 30°C (e.g., room temperature to 60°C). After aging, the diatomaceous earth loaded with the cobalt nitrate precipitate is separated by filtration and washed several times with deionized water until the washing liquid is free of impurity ions. (5) The washed sample is dried at 90°C for 8 hours and then calcined in a muffle furnace at 600°C for 4 hours to obtain a supported iron-based metal oxide catalyst, i.e., a diatomaceous earth-loaded cobalt catalyst.

[0059] Preparation of Catalyst 2:

[0060] (1) 2 kg of diatomaceous earth was repeatedly washed with deionized water to remove surface impurities, and then dried at 100°C to remove moisture. The dried diatomaceous earth was then calcined in a muffle furnace at 500°C for 3 hours.

[0061] (2) Preparation of precursor solution: 974 g of cobalt nitrate and 974 g of nickel nitrate were weighed and dissolved in 1.94 kg of deionized water (the mass ratio of cobalt nitrate to deionized water was 1:1) to prepare a precursor solution;

[0062] (3) The pretreated diatomaceous earth was added to 4 kg of deionized water to form a suspension. The precursor solution was slowly added dropwise to the diatomaceous earth suspension while stirring. At the same time, sodium hydroxide as a precipitant was added dropwise to adjust the solution pH to 8.

[0063] (4) After precipitation is complete, an aging treatment is performed, and the suspension is allowed to stand and age for 12 hours at 30°C (e.g., room temperature to 60°C). After aging, the diatomaceous earth loaded with the cobalt nitrate precipitate is separated by filtration and washed several times with deionized water until the washing liquid is free of impurity ions. (5) The washed sample is dried at 90°C for 8 hours and then calcined in a muffle furnace at 600°C for 4 hours to obtain a supported composite iron-based metal oxide catalyst, that is, a diatomaceous earth-loaded cobalt-nickel catalyst.

[0064] 3. Example 2

[0065] 200 kg of coal tar pitch was added to a dissolution reactor, and 400 kg of washing oil was added thereto. The temperature in the reactor was 70°C and the mixture was fully mixed for 1 hour to obtain a mixed oil.

[0066] The mixed oil was heated to 140°C, contacted with 2 kg of catalyst 1, and introduced with 1500 kg of air (with a mass ratio of 1:2.5) to produce a primary mixed oil. The primary mixed oil was then washed with water and evaporated to obtain a low-sulfur, low-nitrogen coal tar pitch, designated Sample 1.

[0067] 4. Example 3

[0068] The method is the same as that of Example 2, except that the mixed oil is heated to 160° C. The resulting low-sulfur and low-nitrogen coal tar pitch is labeled as Sample 2.

[0069] 5. Example 4

[0070] The method is the same as that of Example 2, except that the mixed oil is heated to 280° C. The obtained low-sulfur and low-nitrogen coal tar pitch is marked as Sample 3.

[0071] 6. Example 5

[0072] The method is the same as that of Example 2, except that the mixed oil is heated to 200° C. The obtained low-sulfur and low-nitrogen coal tar pitch is marked as Sample 4.

[0073] 7. Example 6

[0074] The method is the same as that of Example 2, except that the mixed oil is heated to 220° C. The obtained low-sulfur and low-nitrogen coal tar pitch is marked as Sample 5.

[0075] 8. Example 7

[0076] The method is the same as that of Example 2, except that the mixed oil is heated to 250° C. The obtained low-sulfur and low-nitrogen coal tar pitch is marked as Sample 6.

[0077] 9. Example 8

[0078] The method is the same as that of Example 2, except that the mixed oil is heated to 110° C. The obtained low-sulfur and low-nitrogen coal tar pitch is marked as Sample 7.

[0079] 10. Example 9

[0080] The method is the same as that of Example 4, except that Catalyst 1 is replaced with Catalyst 2. The resulting low-sulfur and low-nitrogen coal tar pitch is marked as Sample 8.

[0081] 11. Comparative Example

[0082] The method is the same as that of Example 4, except that there is no catalyst. The resulting coal tar pitch is labeled as Sample 9.

[0083] The sulfur content and nitrogen content of the above examples and comparative examples were tested. The sulfur content and nitrogen content of each sample are shown in the following table:

[0084] Table 2 Sulfur content and nitrogen content of each sample

[0085]

[0086]

[0087] As shown in Table 2, the average sulfur content of Samples 1 to 5 was approximately 0.3%, a decrease of approximately 0.3% compared to the raw coal tar pitch, with an average desulfurization rate of 50%. The average nitrogen content was approximately 0.61%, a decrease of approximately 0.26% compared to the raw coal tar pitch, with an average denitrification rate of 30%. Sample 8 had the lowest sulfur and nitrogen contents, with a sulfur content of 0.23%, a decrease of 0.37% compared to the raw coal tar pitch, and a desulfurization rate of 61.7%. The nitrogen content of Sample 8 was 0.48%, a decrease of 0.39% compared to the raw coal tar pitch, and a denitrification rate of 44.8%, demonstrating excellent denitrification performance. This demonstrates that, when other reaction conditions are the same, Catalyst 2, a supported composite iron-based metal catalyst (diatomaceous earth-supported cobalt-nickel catalyst), achieves better desulfurization and denitrification performance than Catalyst 1 (diatomaceous earth-supported cobalt catalyst), resulting in samples with lower sulfur and nitrogen contents. Furthermore, easier access to air can reduce production costs.

[0088] The reduction in sulfur and nitrogen content in Samples 6 and 7 was not very significant, which may be due to reasons such as the reaction temperature being too low (Sample 6) or too high (Sample 7).

[0089] The sulfur and nitrogen content of sample 9 was almost not reduced, indicating that under the experimental conditions of this application, only introducing air without adding a catalyst could not significantly reduce the sulfur and nitrogen content in coal tar pitch.

[0090] In another specific embodiment of the present application, a low-sulfur and low-nitrogen coal tar pitch production system based on air oxidation comprises:

[0091] The dissolution reactor 100 has a coal tar pitch tank 110 and a solvent tank 120 connected to its inlet, and a mixed oil discharge pipe 130 provided at its bottom outlet; the oxidation tower 200 has a spray layer 210, a fixed bed 220, and a gas distributor 230 provided from top to bottom in the oxidation tower 200 in the height direction, and a primary discharge pipe 240 provided at its bottom outlet, and the other end of the mixed oil discharge pipe 130 is connected to the primary discharge pipe 240, and the primary discharge pipe 240 is further connected to a circulation pipe 250, which is provided with a first Heater 251, the other end of the circulation pipe 250 is connected to the spray layer 210, the fixed bed 220 is used to fill the catalyst, the gas distributor 230 is connected to the gas distributor 230 through the air feed pipe 260, and the air compressor 280 is connected; extraction tower group, the other end of the primary discharge pipe 240 is connected to the light liquid inlet of the extraction tower group; evaporation tower 500, the light liquid outlet of the extraction tower group is connected to the inlet of the evaporation tower 500, and the bottom outlet of the evaporation tower 500 is connected to the finished product extraction pipe 510; the top outlet of the evaporation tower 500 is connected to the inlet of the solvent tank 120.

[0092] Specifically, it should be noted that the spray layer 210 primarily sprays the mixed oil onto the fixed bed 220, ensuring uniform contact with the catalyst within the fixed bed 220. The spray layer 210 should be oriented downward, allowing the sprayed mixed oil to contact the incoming air and the catalyst within the fixed bed 220, thereby initiating an oxidation reaction. Simultaneously, the mixed oil is ejected through the spray layer 210 to form small droplets or a liquid film, which fully contact the air and catalyst, accelerating the oxidation reaction. The fixed bed 220, also known as a fixed bed reactor, is filled with a catalyst. The gas distributor 230 evenly distributes the air across the entire cross-section of the oxidation tower 200, accelerating the reaction. The dissolution reactor 100 has a heating function, which can be jacketed, allowing the coal tar pitch and solvent to mix and heat within the dissolution reactor 100. There are two ways to connect the mixed oil discharge pipe 130 to the oxidation tower 200: the first is to connect the mixed oil discharge pipe 130 directly to the spray layer 210 of the oxidation tower 200; the second is to connect the mixed oil discharge pipe 130 to the primary discharge pipe 240, and then to the spray layer 210 via the circulation pipe 250 connected to the primary discharge pipe 240. In this application, the second method is preferred. In this process, the unreacted mixed oil discharged from the oxidation tower 200 and the mixed oil from the mixed oil discharge pipe 130 are heated by the first heater 251 on the circulation pipe 250 and then sent to the spray layer 210 for reaction in the oxidation tower 200.

[0093] The production process is as follows: coal tar pitch and solvent are mixed and heated in a dissolution reactor 100 to obtain a mixed oil, thereby achieving step S10; the mixed oil enters the primary discharge pipe 240 through the mixed oil discharge pipe 130, and flows through the circulation pipe 250 connected to the primary discharge pipe 240. After being heated by the primary heater on the circulation pipe 250, it enters the spray layer 210 of the oxidation tower 200 and is ejected from the spray layer 210. At the same time, the air is compressed by the air compressor 280 and sent into the gas distributor 230 through the air feed pipe 260. After being evenly distributed through the gas distributor 230, the air contacts the mixed oil in the fixed bed 220, and an oxidation reaction occurs under the action of the catalyst in the fixed bed 220. The reaction generates a primary mixed oil, completing step S20. The reacted primary mixed oil is transported via primary discharge pipe 240 to the light liquid inlet of the extraction tower group. There, it undergoes extraction to remove sulfur, nitrogen, organic matter, salt, and other components. The extracted light phase, a mixture of low-sulfur and low-nitrogen coal tar pitch and solvent, is discharged from the light liquid outlet of the extraction tower and transported to evaporation tower 500. Evaporation in evaporation tower 500 produces a finished low-sulfur and low-nitrogen coal tar pitch product, which is extracted from finished product extraction pipe 510 at the bottom of evaporation tower 500. The evaporated solvent is discharged from the top outlet of evaporation tower 500 and transported to solvent tank 120 for recycling, completing step S30. This system ensures a more complete desulfurization reaction, thereby improving desulfurization efficiency. The solvent is also recycled, saving raw materials and reducing costs.

[0094] In a preferred embodiment, a gas discharge pipe 270 is further provided on the top of the oxidation tower 200 to extract the waste gas generated by the reaction in the tower. Usually, the gas discharge pipe 270 is also connected to a post-processing device for processing the waste gas.

[0095] To achieve more complete extraction of the primary mixed oil and more efficiently remove sulfur, nitrogen, organic matter, and salts therefrom, in a preferred embodiment, the extraction tower group includes a first extraction tower 300 and a second extraction tower 400 arranged in series. The other end of the primary discharge pipe 240 is connected to the light liquid inlet of the first extraction tower 300, the light liquid outlet of the first extraction tower 300 is connected to the light liquid inlet of the second extraction tower 400, and the light liquid outlet of the second extraction tower 400 is connected to the inlet of the evaporation tower 500. The second extraction tower 400 is provided with a heavy liquid feed pipe 410, the heavy liquid outlet of the second extraction tower 400 is connected to the heavy liquid inlet of the first extraction tower 300, and the heavy liquid outlet of the first extraction tower 300 is connected to a waste liquid pipe 310. In the prior art, extraction towers are generally provided with a light liquid inlet, a light liquid outlet, a heavy liquid inlet, and a heavy liquid outlet. In this application, the light liquid fed into the first extraction tower 300 is the primary mixed oil, and the heavy liquid fed into the second extraction tower 400 is water. On the one hand, the primary mixed oil after the oxidation reaction is transported to the light liquid inlet of the first extraction tower 300 through the primary discharge pipe 240. After extraction in the first extraction tower 300, it is output from the light liquid outlet of the first extraction tower 300 and sent to the second extraction tower 400 through the light liquid inlet of the second extraction tower 400 for further extraction. The light liquid after extraction in the second extraction tower 400 is a mixture of low-sulfur and low-nitrogen coal tar asphalt and solvent, which is discharged from the light liquid outlet of the second extraction tower 400. On the other hand, water is fed into the second extraction tower 400 through the heavy liquid inlet of the second extraction tower 400 to extract the light liquid in the second extraction tower 400 (that is, the primary mixed oil after extraction in the first extraction tower 300), and then fed into the heavy liquid inlet of the first extraction tower 300 through the heavy liquid outlet of the second extraction tower 400. In the first extraction tower 300, the light liquid in the first extraction tower 300 (that is, the primary mixed oil) is extracted. The heavy liquid generated after the extraction, that is, the waste liquid containing sulfur, nitrogen, organic matter and salt, is discharged from the heavy liquid outlet of the first extraction tower 300 through the waste liquid pipe 310.

[0096] As mentioned above, the reaction between the mixed oil and air in the oxidation tower 200 needs to be carried out under heating conditions, which in this application is 80°C to 120°C. A second heater 131 is provided on the mixed oil discharge pipe 130, which can preheat the mixed oil so that it enters the primary discharge pipe 240 and the circulation pipe 250 at a certain temperature, saving the heating time in the first heater 251 and ensuring continuous production.

[0097] Furthermore, an asphalt circulation pipe 520 is installed at the bottom outlet of the evaporation tower 500. A third heater 530 is installed on this asphalt circulation pipe 520. The other end of this asphalt circulation pipe 520 is connected to the circulation inlet at the top of the evaporation tower 500. This asphalt circulation pipe 520 is also connected to the finished product extraction pipe 510. The heavy components evaporated by the evaporation tower 500 enter the asphalt circulation pipe 520 from the bottom outlet, are heated by the third heater 530, and then recirculate into the evaporation tower 500 through the circulation inlet at the top of the evaporation tower 500. At the same time, qualified heavy components, namely low-sulfur and low-nitrogen coal tar pitch, can be extracted from the finished product extraction pipe 510.

[0098] The above embodiments merely illustrate several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A method for producing low-sulfur and low-nitrogen coal tar pitch based on air oxidation, characterized in that: The following steps are involved: S10. Adding a solvent to the coal tar pitch, heating to a first preset temperature and mixing uniformly to obtain a mixed oil; S20. The mixed oil is heated to 140°C to 220°C, and in the presence of a catalyst, air is introduced into the reaction to obtain a mixed oil; the catalyst comprises a supported iron-based metal oxide catalyst; S30. Extracting and evaporating the primary mixed oil to obtain low-sulfur and low-nitrogen coal tar pitch.

2. The method for producing low-sulfur and low-nitrogen coal tar pitch based on air oxidation according to claim 1, characterized in that: In step S10, the solvent includes at least one of wash oil or anthracene oil.

3. The method for producing low-sulfur and low-nitrogen coal tar pitch based on air oxidation according to claim 1, characterized in that: In step S10, the first preset temperature is 50°C to 110°C.

4. The method for producing low-sulfur and low-nitrogen coal tar pitch based on air oxidation according to claim 1, characterized in that: In step S20, the mass ratio of the mixed oil to the air is 1:(1.4 to 4).

5. The method for producing low-sulfur and low-nitrogen coal tar pitch based on air oxidation according to claim 1, characterized in that: In step S20, the substrate of the supported iron-based metal oxide catalyst includes any one of diatomaceous earth and alumina, and the iron-based metal includes any two of titanium, vanadium, chromium, manganese, iron, cobalt and nickel.

6. The method for producing low-sulfur and low-nitrogen coal tar pitch based on air oxidation according to claim 1, characterized in that: In step S20, the amount of the catalyst added is 0.5 wt% to 3 wt% of the coal tar pitch.

7. A low-sulfur and low-nitrogen coal tar pitch production system based on air oxidation, characterized in that: The method for producing low-sulfur and low-nitrogen coal tar pitch based on air oxidation according to any one of claims 1 to 6 comprises: A dissolution reactor, wherein the inlet of the dissolution reactor is connected to a coal tar pitch tank and a solvent tank, and the bottom outlet of the dissolution reactor is provided with a mixed oil discharge pipe; An oxidation tower is provided with a spray layer, a fixed bed, and a gas distributor from top to bottom in the height direction. A primary discharge pipe is provided at the bottom outlet of the oxidation tower. The other end of the mixed oil discharge pipe is connected to the primary discharge pipe. The primary discharge pipe is also connected to a circulation pipe. The circulation pipe is provided with a first heater. The other end of the circulation pipe is connected to the spray layer. The fixed bed is used to load the catalyst. The gas distributor is connected to an air compressor via an air feed pipe. The other end of the primary discharge pipe is connected to the light liquid inlet of the extraction tower group; The light liquid outlet of the extraction tower group is connected to the inlet of the evaporation tower, the bottom outlet of the evaporation tower is connected to the finished product extraction pipe; the top outlet of the evaporation tower is connected to the inlet of the solvent tank.

8. The low-sulfur and low-nitrogen coal tar pitch production system based on air oxidation according to claim 7, characterized in that: The extraction tower group includes a first extraction tower and a second extraction tower arranged in series, the other end of the primary discharge pipe is connected to the light liquid inlet of the first extraction tower, the light liquid outlet of the first extraction tower is connected to the light liquid inlet of the second extraction tower, and the light liquid outlet of the second extraction tower is connected to the inlet of the evaporation tower; the second extraction tower is provided with a heavy liquid feed pipe, the heavy liquid outlet of the second extraction tower is connected to the heavy liquid inlet of the first extraction tower, and the heavy liquid outlet of the first extraction tower is connected to a waste liquid pipe.

9. The low-sulfur and low-nitrogen coal tar pitch production system based on air oxidation according to claim 7, characterized in that: A second heater is provided on the mixed oil discharge pipe.

10. The low-sulfur and low-nitrogen coal tar pitch production system based on air oxidation according to claim 7, characterized in that: The bottom outlet of the evaporation tower is provided with an asphalt circulation pipe, a third heater is provided on the asphalt circulation pipe, the other end of the asphalt circulation pipe is connected to the circulation inlet at the top of the evaporation tower, and the asphalt circulation pipe is connected to the finished product extraction pipe.

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