Desulfurization modification method of high-sulfur petroleum coke and method for preparing prebaked anode from high-sulfur petroleum coke

Abstract

The invention provides a desulfurization modification method of high-sulfur petroleum coke and a method for preparing a prebaked anode from the high-sulfur petroleum coke, and belongs to the technical field of prebaked anode production. The desulfurization modification method comprises the following steps: crushing high-sulfur petroleum coke, grading and screening, and then carrying out alkali treatment and acid treatment; then carrying out oxidative desulfurization treatment by using choline chloride-urea, a TiO2 / WO3 heterojunction catalyst, ozone and hydrogen peroxide; and finally carrying out carbonization treatment to obtain the desulfurized modified petroleum coke suitable for preparing the prebaked anode. The method for preparing the prebaked anode comprises the following steps: taking coal pitch and medium-temperature pitch as binders, doping anthracene oil, and carrying out air oxidation to obtain pretreated pitch; the pre-baked anode is obtained by kneading the pre-treated asphalt with the desulfurized modified petroleum coke and roasting at a controlled temperature. According to the method, the sulfur content of the high-sulfur petroleum coke can be reduced to 1.5% or below, and a product of which the ash content, the mechanical strength, the conductivity and other key indexes meet the prebaked anode performance standard is prepared.

Description

Technical Field

[0001] The invention relates to the technical field of production of prebaked anodes, and in particular to a method for desulfurization modification of high-sulfur petroleum coke and preparation of the prebaked anodes. Background Art

[0002] Prebaked anodes are one of the primary raw materials for aluminum electrolysis production, playing a crucial role in the process and contributing significantly to the production cost. Petroleum coke is the primary raw material for aluminum prebaked anodes, generally accounting for 70% of the total raw material weight. Its varying properties significantly impact the physical and chemical performance of the prebaked anodes. With the annual increase in high-sulfur crude oil production, the sulfur content of crude oil processed by refineries has also increased. Sulfides in crude oil migrate during the refining process and ultimately accumulate in petroleum coke, leading to an annual increase in the production of high-sulfur petroleum coke. At the same time, with the rapid development of the domestic electrolytic aluminum industry, low-sulfur petroleum coke is in short supply, leading to rising prices. The prebaked anode industry is facing the prospect of shifting to high-sulfur petroleum coke for prebaked anode production. my country has industrial sulfur emission standards. According to GB9078-19965, the Light Metal Industry Pollutant Emission Standard (relevant to industrial furnaces), SO2 emissions are subject to strict limits on both concentration and emission rate. The increased sulfur content of high-sulfur coke will lead to excessive sulfur emissions from carbon plants and aluminum electrolysis plants, and will also cause a decline or deterioration in the quality of prebaked anodes. Therefore, the use of high-sulfur petroleum coke in prebaked anode production requires breakthroughs in high-sulfur petroleum coke desulfurization technology. Common petroleum coke desulfurization methods include solvent extraction, high-temperature calcination, oxidation, alkali metal compound treatment, hydrogenation, and biological methods. When using desulfurized high-sulfur petroleum coke in the production of prebaked anodes, it is important to ensure that key indicators such as ash content, mechanical strength, and conductivity meet the requirements for prebaked anodes.

[0003] The Chinese invention patent with publication number CN112843979A discloses a process for ultra-low emission of pre-baked anode flue gas, in which high-sulfur coke is directly used in the production of pre-baked anodes without desulfurization. The production process involves calcination, kneading and roasting, and the acidic SO2 emitted by roasting is purified by a flue gas desulfurization system. The calcination stage of this method is a key link in the generation of high pollution, especially when high-sulfur petroleum coke is used as raw material. If no treatment measures are configured for the calcination flue gas, a large amount of pollutants will be emitted, which will directly affect the realization of ultra-low emission goals. Flue gas absorbent (1500-3000 mg / Nm 3 High dosages of solvents (500-2000 mg / L) and co-solvents significantly increase raw material costs, and wastewater treatment costs may further increase. Chemical residues from co-solvents or absorbents may form new pollutants in the desulfurization slurry, requiring additional treatment to avoid secondary contamination.

[0004] The Chinese invention patent application with publication number CN110527550A discloses a method for achieving oxidative desulfurization of high-sulfur petroleum coke under mild conditions. In the desulfurization process, quaternary ammonium salt is first used as an auxiliary agent to swell the high-sulfur petroleum coke, and then polyoxometalate ionic liquid is used to activate H2O2 to achieve catalytic oxidative desulfurization of the high-sulfur petroleum coke. However, the market price of [Bmim]BF4 used in this invention is relatively high. According to the addition ratio of the scheme, the cost of a single ton of petroleum coke solvent is as high as tens of thousands of yuan. The synthesis of polyoxometalate (POM) ionic liquid catalysts is complex (multi-step coordination reactions are required), the catalyst preparation cost accounts for more than 40% of the total investment, and the active center (such as Keggin structure) is prone to collapse and deactivation after multiple cycles, and reagent recovery is difficult. BF4 - Hydrolysis generates HF (concentration > 50 mg / L), which requires additional lime addition for neutralization (generating fluoride-containing sludge, a hazardous waste), increasing treatment costs by 800 yuan per ton of wastewater. Industrialized implementation faces three bottlenecks: uncontrolled costs, amplified pollution, and diminished efficiency.

[0005] There are still many problems that need to be overcome in using desulfurized high-sulfur petroleum coke to prepare prebaked anodes. Summary of the Invention

[0006] The object of the present invention is to address the above-mentioned problems and provide a method for desulfurization modification of high-sulfur petroleum coke and preparation of prebaked anodes. The present invention can reduce the sulfur content of high-sulfur petroleum coke to below 1.5%, and prepare a product whose key indicators such as ash content, mechanical strength, and conductivity meet the prebaked anode performance standards.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] The present invention provides a desulfurization and modification method for high-sulfur petroleum coke, comprising the following steps:

[0009] S1. Crushing and classifying high-sulfur petroleum coke to obtain crushed high-sulfur petroleum coke, wherein the content of 4-2 mm particles is 38-42%, the content of 2-0.5 mm particles is 33-40%, and the content of powder below 0.5 mm is 22-25%, and the crushed high-sulfur petroleum coke is divided into medium particles of 2 mm or more and fine particles of less than 2 mm. The medium particles and fine particles are respectively mixed with a NaOH solution with a mass concentration of 5-10% and continuously stirred, and alkali-treated at 1-2 MPa and 80° C., applying 20 kHz ultrasonic waves during the alkali treatment; then washing with a hydrochloric acid solution with a pH of 2.8-3.3, and then washing with a citric acid solution with a pH of 4.8-5.2, and finally washing with water until neutral, to obtain pretreated medium particles and pretreated fine particles;

[0010] S2. Add choline chloride-urea, TiO2 / WO3 heterojunction catalyst and the pretreated fine particles into the photoreactor in a mass ratio of 10-15:1.2-1.8:100. After sufficient infiltration, continuously add ozone and hydrogen peroxide into the photoreactor under stirring. Perform the first stage of oxidation treatment at a temperature of 55-65°C and under ultraviolet irradiation for 3-5 hours. In the second stage, add H2O2 as an oxidant and oxidize at 70-75°C for 2-3 hours. The exhaust gas in the oxidation process is neutralized by a NaOH spray tower. Filter with a plate and frame filter press, wash the filter cake with ethanol and deionized water twice in turn, filter, and dry to obtain fine particle desulfurized coke.

[0011] S3, repeating step S2 to desulfurize the pretreated medium granular material, adding choline chloride-urea, TiO2 / WO3 heterojunction and the pretreated medium granular material into the photoreactor at a mass ratio of 10-15:1.2-1.8:100, the first stage of oxidation treatment takes 6-8 hours, and the second stage of oxidation treatment takes 4-6 hours to obtain medium granular desulfurized coke;

[0012] S4. Carbonization treatment: Carbonize the fine-particle desulfurized coke and the medium-particle desulfurized coke under N2 protection, control the heating rate to be ≤5℃ / min, the first stage: 480-520℃ treatment for 50-70min; the second stage: 720-760℃ treatment for 50-70min; the third stage: 880-900℃ treatment for 40-50min, to obtain desulfurized modified petroleum coke.

[0013] In the present invention, preferably, in step S1, the liquid-to-solid ratio of the NaOH solution to the high-sulfur petroleum coke crushed material to be treated is 2-3.5 L:1 kg.

[0014] In the present invention, preferably, in step S1, the alkali treatment time is 2.5 to 4.5 hours, the frequency of the ultrasonic wave is 20 kHz, and the ultrasonic wave is performed in the first 0.5 hours of the alkali treatment.

[0015] In the present invention, preferably, in step S2, the ozone concentration is 50-100 ppm, the H2O2 concentration is 10-15%, the liquid-solid ratio of H2O2 to petroleum coke is 8-12 L:1 kg; and the stirring rate is 200-300 rpm.

[0016] In the present invention, preferably, the TiO2 / WO3 heterojunction catalyst used in step S2 is prepared by the following method: (1) preparing TiO2 sol: dissolving tetrabutyl titanate in anhydrous ethanol; adding nitric acid dropwise and stirring continuously until a transparent sol is formed; standing at room temperature for a period of time to form a gel, and drying to obtain a TiO2 precursor; (2) WO3 loading and compounding: preparing a Na2WO4 solution, adding the TiO2 precursor and ultrasonically dispersing it; adjusting the pH to 9-10, precipitating WO3·H2O to encapsulate TiO2; magnetic stirring for more than 3 hours, then centrifuging, and washing with deionized water until neutral; heating to 400-450°C at 5°C / min in an air atmosphere and calcining for 3-4 hours to obtain a TiO2 / WO3 heterojunction catalyst.

[0017] In the present invention, preferably, the ultraviolet light source adopts a 365nm LED light source and a 280nm LED light source.

[0018] In the present invention, preferably, the addition of O3 as an oxidant is carried out in a phased manner, with an initial stage of 0.1 Nm 3 / min / ton of coke, quickly start the oxidation reaction; main reaction stage: 0.25~0.3Nm 3 / min / ton of coke, maintaining a high active oxygen concentration; in the last 30 minutes: drop to 0.05Nm 3 / min / ton of coke.

[0019] The present invention also provides a method for preparing a prebaked anode using desulfurized modified petroleum coke. The desulfurized modified petroleum coke prepared by the above method comprises the following steps:

[0020] (1) Coal tar pitch and medium-temperature asphalt with a softening point of 95-105°C are prepared in a weight ratio of 85:15, and anthracene oil is added. The amount of anthracene oil added is 5-8% of the total weight of the coal tar pitch and the medium-temperature asphalt, so that the softening point of the asphalt is reduced to 100-105°C and the viscosity is reduced to 2000-2200 mPa·s; the asphalt is heated to 190-210°C and air-oxidized for 100-150 minutes to obtain pretreated asphalt;

[0021] (2) mixing desulfurized modified petroleum coke, conductive carbon black, and magnesium aluminum spinel, dispersing them uniformly, and then kneading them with pretreated asphalt at a kneading temperature of 165-170° C., stirring time of 80-90 min, and vacuum degassing to obtain a mixture; the mass ratio of the desulfurized modified petroleum coke, pretreated asphalt, conductive carbon black, and magnesium aluminum spinel is 100:24-28:4-5:1.5-2.0; and compression molding the mixture to obtain an anode green body;

[0022] (3) Preheating and calcining the anode green body to obtain a prebaked anode.

[0023] In the present invention, preferably, the specific method of forming and roasting is: first preheating, heating the roasting furnace to 250-400°C at 5-10°C / h, and keeping warm for 5-6h; then heating to 1000-1100°C at 15-20°C / h, and keeping warm for 6-10h; the anode cooling rate is ≤5°C / min.

[0024] In the present invention, preferably, the β resin content of the pretreated asphalt obtained after air oxidation is 40-45%, while maintaining QI≤8% and a coking value of 58-62wt%.

[0025] The present invention first graded and crushed the high-sulfur petroleum coke, which can increase the reaction contact surface area and match the aggregate requirements for the subsequent preparation of pre-baked anodes. The role of alkali treatment is to perform preliminary removal and surface modification on part of the sulfur and minerals in the high-sulfur petroleum coke. The acidic sulfides (such as mercaptans) in the petroleum coke can react with NaOH to generate water-soluble sodium thiolate (RSNa) and water, which are removed by subsequent washing. Alkali solution promotes partial hydrolysis or oxidation of the CS bond of organic sulfur (such as thiophene and sulfide) to generate intermediates (such as mercaptans and sulfoxides) that are more susceptible to subsequent photocatalytic oxidation. NaOH solution can also corrode the surface of petroleum coke, expand the pore size, and improve the penetration efficiency of subsequent oxidants. Alkali treatment under pressurized conditions is more conducive to destroying the chemical bond between sulfur and carbon. Applying 20kHz ultrasonic waves during alkali treatment promotes the penetration of reagents into the interior of the particles and improves the desulfurization rate. After the alkaline treatment, the remaining alkali is neutralized with hydrochloric acid at pH 3 to dissolve the metal sulfides. The remaining sulfur is then complexed with citric acid at pH 5. Finally, the product is washed with water to dissolve the soluble sulfur compounds. Step S1 can initially remove 30-40% of the sulfur (primarily inorganic sulfur), reducing the subsequent ozone / H2O2 oxidation pressure and reducing the oxidant dosage by over 20%.

[0026] Secondly, the present invention uses the synergistic effect of ozone (gas phase) and hydrogen peroxide (liquid phase). Ozone (gas phase) penetrates the sulfur on the outer surface, and H2O2 (liquid phase) penetrates deep into the pores. The two compositely cover the entire scale of sulfur, converting the refractory organic sulfur into water-soluble sulfate (SO4 2- ) to achieve complete sulfur removal; the initial high O3 concentration can quickly remove the surface sulfur, and later switch to H2O2 low concentration continuous oxidation, achieving rapid oxidation in the early stage and deep desulfurization in the final stage, reducing the total oxidant cost. Under UV irradiation, the TiO2 / WO3 heterojunction catalyst generates electron-hole pairs, which react with O3 / H2O2 to generate highly active oxygen species (·OH, ·O2 -etc.), strengthens the oxidative decomposition of organic sulfur and enhances oxidation capacity. Compared with TiO2, it has higher photosensitivity and stability, and can significantly improve the desulfurization efficiency of petroleum coke. The present invention also oxidizes medium particles with larger particle sizes for a longer time (8 to 10 hours), and solves the problem of low mass transfer rate of coarse particles by extending the reaction time to penetrate the pores. The present invention performs carbonization treatment after desulfurization, mainly to make up for the problems of excessive porosity and insufficient strength of desulfurized petroleum coke. Slowly increase the temperature in the early stage of carbonization to avoid stress cracking of the carbon layer and make the microcrystals grow uniformly. The first stage of staged heating accelerates the volatilization of middle molecules, removes residual aromatic hydrocarbons and small molecules, eliminates the source of gas expansion between carbon layers, improves compressive strength, and decomposes residual inorganic sulfur compounds, releases SO2 (carried to the tail gas treatment system via nitrogen), and further reduces the sulfur content by 0.2-0.3%, reducing residual sulfur; the second stage repairs the microcrystalline structure and promotes the ordering of microcrystalline; the third stage promotes the transformation of petroleum coke from amorphous carbon to graphite-like carbon structure, significantly reduces resistivity, and meets the conductivity requirements of prebaked anodes; at high temperatures, micropores (<2nm) collapse and mesopores (2-50nm) shrink, thereby enhancing the densification and strength improvement of the material. After being treated with the desulfurization method of the present invention, it becomes possible to apply high-sulfur petroleum coke to the production of prebaked anodes.

[0027] When preparing prebaked anodes, coal tar pitch is selected to enhance the chemical compatibility between the asphalt and desulfurized coke. The polycyclic aromatic hydrocarbons in the aromatic asphalt are used to generate π-dipole interactions with polar groups such as hydroxyl (-OH) and carboxyl (-COOH) groups remaining on the surface of the desulfurized coke, thereby improving bonding strength. A medium-temperature asphalt is also compounded and anthracene oil is added to optimize the asphalt's fluidity and pore penetration capacity, ensuring that the desulfurized coke (especially the micropores caused by the increased porosity after oxidation) can be fully filled during the mixing and molding stages, while meeting both chemical polarity and fluidity requirements. Air oxidation of the asphalt increases the β-resin content to 40%, increasing the mesophase content, enhancing the asphalt's adhesion and structural strength after high-temperature coking. At the same time, the QI is maintained at ≤8% to avoid brittle fracture caused by excessive insoluble matter and maintain flexibility. The pretreated asphalt exhibits both suitable fluidity and bonding properties, with a moderate amount of coke residue, providing an ideal bonding phase for anode molding. Adding conductive carbon black during the molding process can enhance conductivity and compensate for the increase in resistance caused by sulfur removal. Magnesium aluminum spinel can improve the anode's resistance to electrolyte corrosion and oxidation.

[0028] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0029] 1. In the desulfurization and modification process of high-sulfur petroleum coke, the present invention achieves inorganic sulfur removal and surface activation through alkali treatment and acid treatment, significantly reducing the load of the downstream oxidation section and improving the overall desulfurization efficiency. The desulfurization and modification of high-sulfur petroleum coke adopts a photocatalytic oxidation method. Through the synergistic effect of ozone (O3) and hydrogen peroxide (H2O2), combined with photocatalytic reaction, high-stability organic sulfur (such as thiophene, benzothiophene, etc.) in the petroleum coke is deeply removed; low-temperature step-by-step carbonization achieves the optimization of carbon structure and the ultimate removal of sulfur; the method of the present invention can reduce the sulfur content of high-sulfur petroleum coke from 4%-6% to 1.0-1.5%, and the desulfurization process makes it possible to use high-sulfur petroleum coke in the production of prebaked anodes.

[0030] 2. The present invention also successfully prepares products that meet the pre-baked anode performance standards (YS / T 285-2022) through staged asphalt modification, precise mixing and temperature-controlled roasting. DETAILED DESCRIPTION

[0031] In order to express the present invention more clearly, the present invention will be further described below by specific examples. Below in conjunction with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. Unless otherwise specified, the various raw materials, reagents, instruments and equipment etc. used in this application, if not otherwise specified, can be purchased from the market or can be prepared by existing methods.

[0032] The TiO2 / WO3 heterojunction catalyst used in the embodiment of the present invention is homemade, and the specific method is as follows: (1) Preparation of TiO2 sol: Tetrabutyl titanate and anhydrous ethanol are mixed in a volume ratio of 1:5, and dilute nitric acid is added simultaneously to a pH of about 3, and stirring is continued at 70°C until a transparent TiO2 sol is formed; (2) WO3 loading and compounding: The TiO2 sol is pumped into a reactor and mixed with 1250L 0.1M Na2WO4 solution with a TiO2:WO3 molar ratio of 1:1 to 1:3, and hydrochloric acid is added to adjust the pH to 1.5. WO3·H2O is uniformly nucleated on the TiO2 surface by a high-speed shear emulsifier (5000-8000rpm); then centrifuged and washed with deionized water until neutral; heated to 420°C at 5°C / min in an air atmosphere and calcined for 3.5h, and the particle size was regulated by air flow milling and vibrating screen (200-400 mesh) to obtain a TiO2 / WO3 heterojunction catalyst.

[0033] Choline chloride-urea is prepared according to the existing technology: choline chloride and urea powder are weighed in a molar ratio of 1:2, placed in a dry reaction vessel, stirred until initially mixed uniformly, and heated at 80-85°C until the mixture gradually melts into a transparent liquid.

[0034] Example 1

[0035] The desulfurization and modification method of high-sulfur petroleum coke comprises the following steps:

[0036] S1. Crushing and classifying high-sulfur petroleum coke to obtain high-sulfur petroleum coke crushed material, wherein the content of 4-2mm is 38%, the content of 2-0.5mm is 40%, and the content of powder below 0.5mm is 22%. The crushed material is divided into medium particles larger than 2mm and fine particles smaller than 2mm. The medium particles and fine particles are respectively mixed with a NaOH solution with a mass concentration of 5% and continuously stirred. The liquid-solid ratio of the NaOH solution to the high-sulfur petroleum coke crushed material to be treated is 3.5L:1kg. The crushed material is subjected to alkali treatment under conditions of 1MPa and 80°C for 4.5h. Ultrasonic waves with a frequency of 20kHz are applied for the first 0.5h of the alkali treatment. After the alkali treatment, the material is washed with a hydrochloric acid solution with a pH of 2.8 to dissolve metal sulfides, and then washed with a citric acid solution with a pH of 5.2 to complex residual sulfur. Finally, the material is washed with water until neutral to obtain pretreated medium particles and pretreated fine particles.

[0037] S2. Add choline chloride-urea, TiO2 / WO3 heterojunction catalyst and pretreated fine particles into the photoreactor in a mass ratio of 10:1.2:100. After fully soaking for 3 hours, ozone and hydrogen peroxide are continuously added into the photoreactor under stirring. The stirring rate is 200 rpm, the ozone concentration is 100 ppm, the H2O2 mass concentration is 10%, the liquid-solid ratio of H2O2 to petroleum coke is 12L:1kg, and the addition of O3 as an oxidant is carried out in a staged manner. In the initial stage of the first 30 minutes: 0.1Nm 3 / min / ton coke, quickly start the oxidation reaction; main reaction stage: 0.25Nm 3 / min / ton of coke, maintaining a high active oxygen concentration; in the last 30 minutes: drop to 0.05Nm 3 / min / ton of coke; the first stage of oxidation treatment is carried out at a temperature of 55°C and under ultraviolet light irradiation conditions, with a total treatment time of 5 hours, and the ultraviolet light light sources adopt 365nm LED light sources and 280nm LED light sources; in the second stage, H2O2 is added dropwise as an oxidant, and the H2O2 mass concentration is 10%. In this stage, the liquid-solid ratio of H2O2 to petroleum coke is 4L:1kg, and oxidation is carried out at 70°C for 3 hours; the exhaust gas in the oxidation process is neutralized by a NaOH spray tower; the filter is filtered by a plate and frame filter press, and the filter cake is washed twice with ethanol and deionized water respectively, and then filtered and dried to obtain fine-grained desulfurized coke.

[0038] S3. Repeat step S2 to desulfurize the pretreated granular material, add choline chloride-urea, TiO2 / WO3 heterojunction catalyst and pretreated granular material into the photoreactor at a mass ratio of 10:1.2:100; after sufficient infiltration for 3 hours, continuously add ozone and hydrogen peroxide into the photoreactor under stirring, with a stirring rate of 200 rpm, an ozone concentration of 100 ppm, a H2O2 mass concentration of 10%, a liquid-solid ratio of H2O2 to petroleum coke of 12L:1kg, and the addition of O3 as an oxidant is carried out in a staged supply manner, with an initial stage of 0.1Nm 3 / min / ton coke, quickly start the oxidation reaction; main reaction stage: 0.25Nm 3 / min / ton of coke, maintaining a high active oxygen concentration; in the last 30 minutes: drop to 0.05Nm 3 / min / ton of coke; the first stage of oxidation treatment was carried out at a temperature of 55°C and under ultraviolet light irradiation conditions for a treatment time of 6 hours, and the ultraviolet light light source used was a 365nm LED light source and a 280nm LED light source; in the second stage, H2O2 was added dropwise as an oxidant, with an H2O2 mass concentration of 10%. In this stage, the liquid-solid ratio of H2O2 to petroleum coke was 4L:1kg, and oxidation was carried out at 70°C for 6 hours; the exhaust gas from the oxidation process was neutralized in a NaOH spray tower; the filter cake was filtered through a plate and frame filter press, and the filter cake was washed twice with ethanol and deionized water respectively, and then filtered and dried to obtain medium-particle desulfurized coke;

[0039] S4. Carbonization treatment: The fine-particle desulfurized coke and the medium-particle desulfurized coke are carbonized under N2 protection, and the heating rate is controlled to be ≤5℃ / min. The first stage is 480℃ treatment for 70min; the second stage is 720℃ treatment for 70min; the third stage is 880℃ treatment for 50min to obtain desulfurized modified petroleum coke.

[0040] A method for preparing a prebaked anode using desulfurized modified petroleum coke, wherein the desulfurized modified petroleum coke prepared by the above method comprises the following steps:

[0041] (1) Coal tar pitch and medium-temperature asphalt with a softening point of 95-105°C were prepared in a weight ratio of 85:15, and anthracene oil was added, with the amount of anthracene oil added being 5% of the total weight of the coal tar pitch and the medium-temperature asphalt, so that the softening point of the asphalt was reduced to 105°C and the viscosity was reduced to 2200 mPa·s; the asphalt was heated to 190°C and air-oxidized for 150 minutes to obtain pretreated asphalt; the pretreated asphalt obtained after air oxidation had a β resin content of 40%, while maintaining a QI of ≤8% and a coking value of 58 wt%;

[0042] (2) mixing desulfurized modified petroleum coke, conductive carbon black, and magnesium aluminum spinel, dispersing them uniformly, and then kneading them with pretreated asphalt at a kneading temperature of 165-170° C. for 80 min, and vacuum degassing to obtain a mixture; the mass ratio of desulfurized modified petroleum coke, pretreated asphalt, conductive carbon black, and magnesium aluminum spinel is 100:24:4:1.5; and compression molding the mixture to obtain an anode green body;

[0043] (3) Preheat the anode green body by heating the baking furnace to 250°C at a rate of 5°C / h and keeping it at that temperature for 6 hours; then heat it to 1000°C at a rate of 15°C / h and keep it at that temperature for 10 hours; the anode cooling rate is ≤5°C / min; and a prebaked anode is obtained.

[0044] Example 2

[0045] The desulfurization and modification method of high-sulfur petroleum coke comprises the following steps:

[0046] S1. Crushing and classifying high-sulfur petroleum coke to obtain high-sulfur petroleum coke crushed material, wherein the content of 4-2mm particles is 40%, the content of 2-0.5mm particles is 35%, and the content of powder below 0.5mm is 25%, and the crushed material is divided into medium particles larger than 2mm and fine particles smaller than 2mm. The medium particles and fine particles are respectively mixed with a NaOH solution with a mass concentration of 8% and continuously stirred. The liquid-solid ratio of the NaOH solution to the high-sulfur petroleum coke crushed material to be treated is 3L:1kg. The crushed material is subjected to alkali treatment under conditions of 1.5MPa and 80°C for 3h. Ultrasonic waves with a frequency of 20kHz are applied for the first 0.5h of the alkali treatment. After the alkali treatment, the material is washed with a hydrochloric acid solution with a pH of 3.0 to dissolve metal sulfides, and then washed with a citric acid solution with a pH of 5.0 to complex residual sulfur. Finally, the material is washed with water until neutral to obtain pretreated medium particles and pretreated fine particles.

[0047] S2. Add choline chloride-urea, TiO2 / WO3 heterojunction catalyst and pretreated fine particles into the photoreactor in a mass ratio of 12:1.5:100. After fully soaking for 3 hours, ozone and hydrogen peroxide are continuously added into the photoreactor under stirring. The stirring rate is 300 rpm, the ozone concentration is 80 ppm, the H2O2 mass concentration is 12%, the liquid-solid ratio of H2O2 to petroleum coke is 10 L:1 kg, and the addition of O3 as an oxidant is carried out in a staged manner. In the initial stage of the first 30 minutes: 0.1 Nm 3 / min / ton coke, quickly start the oxidation reaction; main reaction stage: 0.28Nm 3 / min / ton of coke, maintaining a high active oxygen concentration; in the last 30 minutes: drop to 0.05Nm 3 / min / ton of coke; the first stage of oxidation treatment is carried out at a temperature of 60°C and under ultraviolet light irradiation conditions, with a total treatment time of 4 hours, and the ultraviolet light light sources adopt 365nm LED light sources and 280nm LED light sources; in the second stage, H2O2 is added dropwise as an oxidant, and the H2O2 mass concentration is 12%. In this stage, the liquid-solid ratio of H2O2 to petroleum coke is 3L:1kg, and oxidation is carried out at 72°C for 2.5 hours; the exhaust gas in the oxidation process is neutralized by a NaOH spray tower; the filter is filtered by a plate and frame filter press, and the filter cake is washed twice with ethanol and deionized water respectively, and then filtered and dried to obtain fine-grained desulfurized coke.

[0048] S3. Repeat step S2 to desulfurize the pretreated granular material, add choline chloride-urea, TiO2 / WO3 heterojunction catalyst and pretreated granular material into the photoreactor at a mass ratio of 12:1.5:100; after sufficient infiltration for 3 hours, continuously add ozone and hydrogen peroxide into the photoreactor under stirring, with a stirring rate of 300 rpm, an ozone concentration of 80 ppm, a H2O2 mass concentration of 12%, a liquid-solid ratio of H2O2 to petroleum coke of 10 L:1 kg, and add O3 as an oxidant in a staged supply manner, with an initial stage of 0.1 Nm 3 / min / ton coke, quickly start the oxidation reaction; main reaction stage: 0.28Nm 3 / min / ton of coke, maintaining a high active oxygen concentration; in the last 30 minutes: drop to 0.05Nm 3 / min / ton of coke; the first stage of oxidation treatment was carried out at a temperature of 60°C and under ultraviolet light irradiation conditions for 7 hours, with 365nm LED light sources and 280nm LED light sources being used as the ultraviolet light sources; in the second stage, H2O2 was added dropwise as an oxidant with an H2O2 mass concentration of 12%. The liquid-to-solid ratio of H2O2 to petroleum coke in this stage was 3L:1kg, and oxidation was carried out at 72°C for 5 hours; the exhaust gas from the oxidation process was neutralized in a NaOH spray tower; the filter cake was filtered through a plate and frame filter press, and the filter cake was washed twice with ethanol and deionized water respectively, and then filtered and dried to obtain medium-particle desulfurized coke;

[0049] S4. Carbonization treatment: Carbonize the fine-particle desulfurized coke and the medium-particle desulfurized coke under N2 protection, control the heating rate to ≤5℃ / min, the first stage: 500℃ treatment for 60min; the second stage: 750℃ treatment for 60min; the third stage: 890℃ treatment for 45min, to obtain desulfurized modified petroleum coke.

[0050] A method for preparing a prebaked anode using desulfurized modified petroleum coke, wherein the desulfurized modified petroleum coke prepared by the above method comprises the following steps:

[0051] (1) Coal tar pitch and medium-temperature asphalt with a softening point of about 100°C were prepared in a weight ratio of 85:15, and anthracene oil was added, with the anthracene oil added in an amount of 6% of the total weight of the coal tar pitch and the medium-temperature asphalt, so that the asphalt softening point was reduced to 102°C and the viscosity was reduced to 2088 mPa·s; the asphalt was heated to 200°C and air-oxidized for 120 minutes to obtain pretreated asphalt; the pretreated asphalt obtained after air oxidation had a β resin content of 42%, while maintaining a QI of ≤8% and a coking value of 60 wt%;

[0052] (2) mixing desulfurized modified petroleum coke, conductive carbon black, and magnesium aluminum spinel, dispersing them uniformly, and then kneading them with pretreated asphalt at a kneading temperature of 165-170° C., stirring time of 85 min, and vacuum degassing to obtain a mixture; the mass ratio of desulfurized modified petroleum coke, pretreated asphalt, conductive carbon black, and magnesium aluminum spinel is 100:26:4.5:1.8; and compression molding the mixture to obtain an anode green body;

[0053] (3) Preheat the anode green body by heating the baking furnace to 320°C at a rate of 8°C / h and keeping the temperature for 5.5h; then heat the furnace to 1050°C at a rate of 18°C / h and keep the temperature for 8h; the anode cooling rate is ≤5°C / min; and a prebaked anode is obtained.

[0054] Example 3

[0055] The desulfurization and modification method of high-sulfur petroleum coke comprises the following steps:

[0056] S1. Crushing and classifying high-sulfur petroleum coke to obtain high-sulfur petroleum coke crushed material, wherein the content of 4-2mm particles is 42%, the content of 2-0.5mm particles is 33%, and the content of powder below 0.5mm is 25%. The crushed material is divided into medium particles larger than 2mm and fine particles smaller than 2mm. The medium particles and fine particles are respectively mixed with a NaOH solution with a mass concentration of 10% and continuously stirred. The liquid-solid ratio of the NaOH solution to the high-sulfur petroleum coke crushed material to be treated is 2L:1kg. The crushed material is subjected to alkali treatment at 2MPa and 80℃ for 2.5h. Ultrasonic waves with a frequency of 20kHz are applied for the first 0.5h of the alkali treatment. After the alkali treatment, the material is washed with a hydrochloric acid solution with a pH of 3.3 to dissolve metal sulfides, and then washed with a citric acid solution with a pH of 4.8 to complex residual sulfur. Finally, the material is washed with water until neutral to obtain pretreated medium particles and pretreated fine particles.

[0057] S2. Add choline chloride-urea, TiO2 / WO3 heterojunction catalyst and pretreated fine particles into the photoreactor in a mass ratio of 15:1.8:100. After fully soaking for 3 hours, ozone and hydrogen peroxide are continuously added into the photoreactor under stirring. The stirring rate is 300 rpm, the ozone concentration is 50 ppm, the H2O2 mass concentration is 15%, the liquid-solid ratio of H2O2 to petroleum coke is 8L:1kg, and the addition of O3 as an oxidant is carried out in a staged manner. In the initial stage of the first 30 minutes: 0.1Nm 3 / min / ton coke, quickly start the oxidation reaction; main reaction stage: 0.3Nm 3 / min / ton of coke, maintaining a high active oxygen concentration; in the last 30 minutes: drop to 0.05Nm 3 / min / ton of coke; the first stage of oxidation treatment is carried out at a temperature of 65°C and ultraviolet light irradiation conditions, with a total treatment time of 3 hours, and the ultraviolet light light sources adopt 365nm LED light sources and 280nm LED light sources; in the second stage, H2O2 is added dropwise as an oxidant, and the H2O2 mass concentration is 15%. In this stage, the liquid-solid ratio of H2O2 to petroleum coke is 2L:1kg, and oxidation is carried out at 75°C for 2 hours; the exhaust gas in the oxidation process is neutralized by a NaOH spray tower; the filter is filtered by a plate and frame filter press, and the filter cake is washed twice with ethanol and deionized water respectively, and then filtered and dried to obtain fine-grained desulfurized coke.

[0058] S3. Repeat step S2 to desulfurize the pretreated pellets, add choline chloride-urea, TiO2 / WO3 heterojunction catalyst and pretreated pellets to the photoreactor at a mass ratio of 15:1.8:100; after sufficient infiltration for 3 hours, continuously add ozone and hydrogen peroxide to the photoreactor under stirring, with a stirring rate of 300 rpm, an ozone concentration of 50 ppm, a H2O2 mass concentration of 15%, a liquid-solid ratio of H2O2 to petroleum coke of 8 L:1 kg, and add O3 as an oxidant in a staged supply manner, with an initial stage of 0.1 Nm 3 / min / ton coke, quickly start the oxidation reaction; main reaction stage: 0.3Nm 3 / min / ton of coke, maintaining a high active oxygen concentration; in the last 30 minutes: drop to 0.05Nm 3 / min / ton of coke; the first stage of oxidation treatment was carried out at a temperature of 65°C and under ultraviolet light irradiation conditions for 6 hours, with a 365nm LED light source and a 280nm LED light source being used as the ultraviolet light source; in the second stage, H2O2 was added dropwise as an oxidant with an H2O2 mass concentration of 15%. The liquid-solid ratio of H2O2 to petroleum coke in this stage was 2L:1kg, and oxidation was carried out at 75°C for 4 hours; the exhaust gas from the oxidation process was neutralized in a NaOH spray tower; the filter cake was filtered through a plate and frame filter press, and the filter cake was washed twice with ethanol and deionized water respectively, and then filtered and dried to obtain medium-particle desulfurized coke;

[0059] S4. Carbonization treatment: Carbonize the fine-particle desulfurized coke and the medium-particle desulfurized coke under N2 protection, control the heating rate to ≤5℃ / min, the first stage: 520℃ treatment for 50min; the second stage: 760℃ treatment for 50min; the third stage: 900℃ treatment for 40min, to obtain desulfurized modified petroleum coke.

[0060] A method for preparing a prebaked anode using desulfurized modified petroleum coke, wherein the desulfurized modified petroleum coke prepared by the above method comprises the following steps:

[0061] (1) Coal tar pitch and medium-temperature asphalt with a softening point of 95-105°C were prepared in a weight ratio of 85:15, and anthracene oil was added. The amount of anthracene oil added was 8% of the total weight of the coal tar pitch and the medium-temperature asphalt, so that the asphalt softening point was reduced to 100°C and the viscosity was reduced to 2000 mPa·s; the asphalt was heated to 210°C and air-oxidized for 100 minutes to obtain pretreated asphalt; the pretreated asphalt obtained after air oxidation had a β resin content of 45%, while maintaining a QI of ≤8% and a coking value of 62 wt%;

[0062] (2) mixing desulfurized modified petroleum coke, conductive carbon black, and magnesium aluminum spinel, dispersing them uniformly, and then kneading them with pretreated asphalt at a kneading temperature of 165-170° C. for 90 min, and vacuum degassing to obtain a mixture; the mass ratio of the desulfurized modified petroleum coke, pretreated asphalt, conductive carbon black, and magnesium aluminum spinel is 100:28:5:2.0; and compression molding the mixture to obtain an anode green body;

[0063] (3) Preheat the anode green body by heating the baking furnace to 400°C at a rate of 10°C / h and keeping it warm for 5 hours; then heat it to 1100°C at a rate of 20°C / h and keep it warm for 6 hours; the anode cooling rate is ≤5°C / min to obtain a prebaked anode.

[0064] Comparative Example 1

[0065] The difference between this comparative example and Example 2 is that step S1 does not include the steps of washing with hydrochloric acid and washing with citric acid.

[0066] Comparative Example 2

[0067] The difference between this comparative example and Example 2 is that the oxidant is only hydrogen peroxide, without ozone.

[0068] Comparative Example 3

[0069] The difference between this comparative example and Example 2 is that there is no carbonization process in step S4.

[0070] Comparative Example 4

[0071] The difference between this comparative example and Example 2 is that the material used in step (1) of preparing the prebaked anode is entirely coal tar.

[0072] The sulfur content of the desulfurized and modified petroleum cokes of Examples 1-3 and Comparative Examples 1-3 was measured using a ZDL-9 automatic sulfur analyzer. Five replicate samples of carbonized fine-grained desulfurized coke and medium-grained desulfurized coke were taken at a mass ratio of 1:1. The average value was calculated for each sample. The initial sulfur content of the high-sulfur petroleum coke was 5.89%. The performance parameters of the prebaked anodes obtained from Examples 1-3 and Comparative Examples were tested according to industry standard YS / T63. All performance parameters of the prebaked anodes of the examples were within acceptable limits. The key performance test results are shown in Table 1 below.

[0073] Table 1

[0074] project Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Sulfur content (wt%) 1.2 2.8 2.0 1.8 1.4 Compressive strength (MPa) 42 28 33 33 31 <![CDATA[True density (g / cm 3 )]]> 2.05 1.58 1.63 1.64 1.60 Resistivity (μΩ·m) 50 68 55 61 54 <![CDATA[CO2 reaction residue rate (%)]]> 85 65 72 78 73 Ash content (%) 0.4 0.7 0.5 0.6 0.45

[0075] The test data of the embodiments and comparative examples reversely verify the necessity of the core process steps, indicating that the comprehensive performance cannot be achieved by optimizing only one link.

[0076] The above description is a detailed description of the preferred embodiments of the present invention, but the embodiments are not intended to limit the scope of the patent application of the present invention. Any equivalent changes or modifications completed under the technical spirit suggested by the present invention should fall within the patent scope covered by the present invention.

Claims

1. A desulfurization and modification method for high-sulfur petroleum coke, characterized in that it comprises the following steps: S1. Crushing and classifying high-sulfur petroleum coke to obtain crushed high-sulfur petroleum coke, wherein the content of 4-2 mm particles is 38-42%, the content of 2-0.5 mm particles is 33-40%, and the content of powder below 0.5 mm is 22-25%, and the crushed high-sulfur petroleum coke is divided into medium particles of 2 mm or more and fine particles of less than 2 mm. The medium particles and fine particles are respectively mixed with a NaOH solution with a mass concentration of 5-10% and continuously stirred, and alkali-treated at 1-2 MPa and 80° C., applying 20 kHz ultrasonic waves during the alkali treatment; then washing with a hydrochloric acid solution with a pH of 2.8-3.3, and then washing with a citric acid solution with a pH of 4.8-5.2, and finally washing with water until neutral, to obtain pretreated medium particles and pretreated fine particles; S2, according to the mass ratio of 10 to 15: 1.2-1.8:100, choline chloride-urea, TiO2 / WO2 heterojunction catalyst and the pretreated fine particles are added to the photoreactor, and after sufficient infiltration, ozone and hydrogen peroxide are continuously added to the photoreactor under stirring, and the first stage of oxidation treatment is carried out at a temperature of 55-65° C. and under ultraviolet irradiation conditions, and the treatment time is 3-5 hours; in the second stage, H2O2 is added dropwise as an oxidant, and oxidation is carried out at a temperature of 70-75° C. for 2-3 hours; the waste gas in the oxidation process is neutralized by a NaOH spray tower; the filter cake is filtered with a plate and frame filter press, and the filter cake is washed twice with ethanol and deionized water respectively, and then filtered and dried to obtain fine particle desulfurized coke; S3, repeating step S2 to desulfurize the pretreated medium granular material, adding choline chloride-urea, TiO2 / WO3 heterojunction and the pretreated medium granular material into the photoreactor at a mass ratio of 10-15:1.2-1.8:100, the first stage of oxidation treatment takes 6-8 hours, and the second stage of oxidation treatment takes 4-6 hours to obtain medium granular desulfurized coke; S4. Carbonization treatment: Carbonize the fine-particle desulfurized coke and the medium-particle desulfurized coke under N2 protection, control the heating rate to be ≤5℃ / min, the first stage: 480-520℃ treatment for 50-70min; the second stage: 720-760℃ treatment for 50-70min; the third stage: 880-900℃ treatment for 40-50min, to obtain desulfurized modified petroleum coke.

2. The desulfurization and modification method of high-sulfur petroleum coke according to claim 1, characterized in that: In step S1, the liquid-to-solid ratio of the NaOH solution to the high-sulfur petroleum coke crushed material to be treated is 2-3.5 L:1 kg.

3. The desulfurization and modification method of high-sulfur petroleum coke according to claim 1, characterized in that: In step S1, the alkali treatment time is 2.5 to 4.5 hours, the frequency of the ultrasonic wave is 20 kHz, and the ultrasonic wave is performed in the first 0.5 hours of the alkali treatment.

4. The desulfurization and modification method of high-sulfur petroleum coke according to claim 1, characterized in that: In step S2, the ozone concentration is 50-100 ppm, the H2O2 concentration is 10-15%, the liquid-solid ratio of H2O2 to petroleum coke is 8-12 L:1 kg; and the stirring rate is 200-300 rpm.

5. The desulfurization and modification method of high-sulfur petroleum coke according to claim 1, characterized in that: The TiO2 / WO3 heterojunction catalyst used in step S2 is prepared by the following method: (1) preparing TiO2 sol: mixing tetrabutyl titanate and anhydrous ethanol in a volume ratio of 1:5; simultaneously adding nitric acid dropwise and stirring continuously until a transparent sol is formed; (2) WO3 loading and compounding: pumping the TiO2 sol into a reactor and mixing it with a Na2WO4 solution, adding hydrochloric acid to adjust the pH to 1.5, using a high-speed shear emulsifier to uniformly nucleate WO3·H2O on the TiO2 surface, then centrifuging, and washing with deionized water until neutral; in an air atmosphere, heating to 400-450°C at 5°C / min and calcining for 3-4h, and regulating the particle size to obtain a TiO2 / WO3 heterojunction catalyst.

6. The desulfurization and modification method of high-sulfur petroleum coke according to claim 1, characterized in that: The light source of the ultraviolet light adopts a 365nm LED light source and a 280nm LED.

7. The desulfurization and modification method of high-sulfur petroleum coke according to claim 1, characterized in that: The ozone is added in stages. The initial stage of the first 30 minutes is 0.1 Nm 3 / min / ton of coke, quickly start the oxidation reaction; main reaction stage: 0.25~0.3Nm 3 / min / ton of coke, maintaining a high active oxygen concentration; in the last 30 minutes: drop to 0.05Nm 3 / min / ton of coke.

8. A method for preparing a prebaked anode using desulfurized modified petroleum coke, characterized in that: The desulfurized modified petroleum coke prepared by the method according to any one of claims 1 to 7 comprises the following steps: (1) Coal tar pitch and medium-temperature asphalt with a softening point of 95-105°C are prepared in a weight ratio of 85:15, and anthracene oil is added. The amount of anthracene oil added is 5-8% of the total weight of the coal tar pitch and the medium-temperature asphalt, so that the softening point of the asphalt is reduced to 100-105°C and the viscosity is reduced to 2000-2200 mPa·s; the asphalt is heated to 190-210°C and air-oxidized for 100-150 minutes to obtain pretreated asphalt; (2) mixing desulfurized modified petroleum coke, conductive carbon black, and magnesium aluminum spinel, dispersing them uniformly, and then kneading them with pretreated asphalt at a kneading temperature of 165-170° C., stirring time of 80-90 min, and vacuum degassing to obtain a mixture; the mass ratio of the desulfurized modified petroleum coke, pretreated asphalt, conductive carbon black, and magnesium aluminum spinel is 100:24-28:4-5:1.5-2.0; and compression molding the mixture to obtain an anode green body; (3) Preheating and calcining the anode green body to obtain a prebaked anode.

9. The method for preparing a prebaked anode according to claim 8, wherein: The specific method of forming and roasting is: preheating first, heating the roasting furnace to 250-400°C at 5-10°C / h and keeping it warm for 5-6h; then heating to 1000-1100°C at 15-20°C / h and keeping it warm for 6-10h; the anode cooling rate is ≤5°C / min.

10. The method for preparing a prebaked anode according to claim 8, wherein: The β resin content of the pretreated asphalt obtained after air oxidation is 40-45%, while maintaining QI≤8% and a coking value of 58-62wt%.