A method for preparing ultra-pure coal based on pre-carbonization-flotation combination

Abstract

This invention discloses a method for preparing ultrapure coal based on a combined pre-carbonization-flotation process, belonging to the field of deep coal processing and high-value utilization. The steps are as follows: Raw coal is crushed and ground, then subjected to low-temperature pre-carbonization in an inert atmosphere. The pre-carbonized coal sample is then slurried and a collector and frother are added sequentially, followed by flotation to obtain clean coal. The clean coal undergoes two further cleaning processes, followed by filtration and drying to obtain ultrapure coal. This invention effectively removes hydrophilic oxygen-containing functional groups from the coal surface through low-temperature pre-carbonization, enhancing surface hydrophobicity, reducing surface charge density, optimizing surface morphology, and significantly improving the floatability of coal, resulting in ultrapure coal with an ash content of less than 1.0%. This method is simple and efficient, placing the low-temperature pre-carbonization process, used to regulate the structure of coal-based carbon materials, before flotation deashing. The resulting ultrapure coal has a complete organic structure and can serve as a high-quality precursor for high-value-added coal-based carbon materials such as hard carbon, porous carbon, and graphite.

Description

Technical Field

[0001] This invention relates to the fields of deep coal processing and high-value utilization, specifically to a method for preparing ultrapure coal based on a pre-carbonization-flotation combined process. Background Technology

[0002] Coal, as an important fossil energy source, plays a vital role in optimizing energy structure and preparing high-end carbon materials. In recent years, increasing research has focused on converting coal into high-value-added carbon materials (such as hard carbon, porous carbon, and graphite) to reduce the environmental impact of direct combustion and improve resource utilization efficiency. The key to the high-value utilization of coal lies in the preparation of ultra-pure coal. Ash elements in coal can catalyze side reactions and inhibit pore structure closure during high-temperature carbonization, affecting the structural integrity and electrochemical performance of carbon materials. Therefore, developing efficient methods for preparing ultra-pure coal is crucial for improving the performance of coal-based carbon materials.

[0003] Currently, ultrapure coal is mainly obtained through chemical and physical methods for ash removal. Chemical methods for preparing ultrapure coal suffer from severe pollution and damage to the coal's macromolecular structure. In contrast, physical methods, such as flotation, are the preferred method for deep deashing of fine-grained coal because they do not alter the coal's organic structure and are environmentally friendly. Flotation utilizes the difference in surface hydrophobicity between coal and ash to achieve separation, preserving the coal's organic structure and providing ideal raw materials for the preparation of high-performance coal-based carbon materials. However, the complex surface properties of coal hinder the effective adhesion of bubbles and particles, reducing flotation efficiency. Therefore, there is an urgent need to develop a new process that can control the physicochemical properties of the coal surface, without damaging the coal's macromolecular framework, and improve flotation efficiency for the preparation of raw materials for high-end coal-based carbon materials. Summary of the Invention

[0004] One objective of this invention is to provide a method for preparing ultrapure coal based on pre-carbonization-flotation. This method places the low-temperature pre-carbonization process, which is used to regulate the structure of coal-based carbon materials, before flotation deashing. By controlling the temperature and holding time of pre-carbonization, the functional groups, roughness, wettability, and charge properties of the coal surface are regulated, thereby optimizing hydrophobicity, dispersibility, and floatability while preserving its organic macromolecular framework structure. This improves the flotation efficiency of fine-grained coal and yields ultrapure coal with low ash content and high yield.

[0005] The second objective of this invention is to provide ultrapure coal prepared by the above-mentioned method, which has an ash content of less than 1% and an intact organic structure, and can be used as a precursor for high-value-added coal-based carbon materials.

[0006] To achieve the above objectives, this invention provides a method for preparing ultrapure coal based on pre-carbonization-flotation, the specific steps of which are as follows: (1) The raw coal is crushed and ground to fully dissociate the coal from the minerals; (2) The coal particles obtained in step (1) are placed in an inert atmosphere for low-temperature pre-carbonization treatment and naturally cooled to room temperature to obtain a pre-carbonized coal sample; (3) Add water to the pre-carbonized coal sample obtained in step (2) for slurry treatment, add collector and frother in sequence, stir and aerate for flotation to obtain clean coal 1 and tailings 1; (4) Add water to the clean coal 1 obtained in step (3) to make slurry, and then sort it to obtain clean coal 2 and tailings 2; (5) Add water to the clean coal 2 obtained in step (4) to make slurry, and then sort it to obtain clean coal 3 and tailings 3; (6) The clean coal 3 obtained in step (5) is filtered and dried to obtain ultrapure coal with ash content of less than 1.0%.

[0007] Preferably, the raw coal in step (1) is selected from one or more of anthracite, lean coal, semi-coking coal, coking coal, fat coal, gas coal, weakly caking coal, non-caking coal, and long-flame coal.

[0008] Preferably, the crushing and grinding method in step (1) is as follows: first, the raw coal is put into a double roll crusher for coarse crushing, and then it is put into a rod mill for fine grinding.

[0009] Preferably, the inert atmosphere in step (2) includes one of nitrogen, helium, argon, neon and xenon, and the gas flow rate is 80~120mL / min.

[0010] Preferably, the low-temperature pre-carbonization treatment in step (2) is performed at a temperature of 250~350℃, a heating rate of 2~10℃ / min, and a holding time of 1~3h.

[0011] Preferably, in step (3), the concentration of the slurry after the slurry conditioning treatment is 50~70g / L.

[0012] Preferably, the collector in step (3) is kerosene or diesel oil with a concentration of 1000~2000 g / t; the foaming agent is 2-octanol with a concentration of 100~200 g / t.

[0013] Preferably, the stirring rate of the flotation process in steps (3) to (5) is 1900 to 2100 r / min and the aeration rate is 100 to 200 L / h.

[0014] Preferably, in step (6), the drying temperature is 80°C and the drying time is 12 hours.

[0015] Secondly, it provides ultrapure coal prepared by the above method, with an ash content of less than 1%, which can be used as a precursor for high-value-added coal-based carbon materials.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention places low-temperature pre-carbonization, a method for regulating the structure of coal-based carbon materials, before flotation deashing. Through low-temperature pre-carbonization, hydrophilic oxygen-containing functional groups on the coal surface are effectively removed, enhancing surface hydrophobicity while preserving the organic macromolecular framework structure of the coal, providing an ideal raw material basis for subsequent flotation. The low-temperature pre-carbonization process effectively removes oxygen-containing functional groups through chemical reactions, transforming the molecular structure into a low-oxygen aromatic carbon framework. Changes in chemical structure affect surface morphology, specific surface area, and surface charge properties. These changes in chemical structure and physical structure evolution jointly regulate the wettability of the coal surface, thereby optimizing hydrophobicity, dispersibility, and floatability. The use of a "double-roll crusher + rod mill crushing" process yields coal powder with uniform particle size, providing a superior raw material basis for subsequent pre-carbonization and flotation. The combination of low-temperature pre-carbonization and multi-stage flotation results in a simple process, high preparation efficiency, and ultra-pure coal with an ash content of less than 1%, providing reliable support for the efficient purification and high-value utilization of coal. Attached Figure Description

[0017] Figure 1 This is a technical roadmap for the present invention.

[0018] Figure 2 The images show the X-ray photoelectron spectroscopy (XPS) spectra of coal samples from Examples 1-3 and Comparative Examples 1 and 3.

[0019] Figure 3 The images shown are scanning electron microscope (SEM) images of coal samples from Examples 1-3 and Comparative Examples 1 and 3; wherein: Figure 3 (a) is a SEM image of Example 1; Figure 3 (b) is a SEM image of Example 2; Figure 3 (c) is a SEM image of Example 3; Figure 3 (d) is the SEM image of Comparative Example 1; Figure 3 (e) is the SEM image of Comparative Example 3.

[0020] Figure 4 The contact angle and zeta potential diagrams are for the pre-carbonized coal samples of Examples 1-3 and the coal samples of Comparative Examples 1 and 3. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The technical roadmap of the present invention is shown below. Figure 1 As shown.

[0022] Example 1 This embodiment provides a method for preparing ultrapure coal based on pre-carbonization-flotation, including the following steps: (1) First, put the raw coal into a double roll crusher for coarse crushing, then put it into a rod mill for fine grinding, and then pass it through a 200-mesh (0.074mm) sieve to collect the undersize material.

[0023] (2) Place the sample obtained in step (1) into a tube furnace, raise the temperature to 250°C at a flow rate of 100 mL / min and a heating rate of 5°C / min under an argon atmosphere, hold for 120 min, and cool to room temperature to obtain a pre-carbonized coal sample.

[0024] (3) Add water to the pre-carbonized coal sample obtained in step (2) to adjust the slurry, pour the slurry into the flotation cell, replenish the liquid level to the standard scale line, and obtain a slurry with a concentration of 60 g / L. The impeller speed of the flotation machine is 2100 r / min. After adjusting the slurry for 3 min, add kerosene with a concentration of 2000 g / t collector. After adjusting the slurry for another 2 min, add octanol with a concentration of 100 g / t frother. After adjusting the slurry for 30 s, start aeration and separation. The aeration rate is 150 L / h, and the frothing time is 3 min, to obtain clean coal 1 and tailings 1.

[0025] (4) Pour the clean coal 1 obtained in step (3) into the flotation cell, replenish the liquid level to the standard scale line, and obtain a slurry with a concentration of 60 g / L. The impeller speed of the flotation machine is 2100 r / min. After adjusting the slurry for 30 seconds, start aeration and separation. The aeration volume is 150 L / h, and the skimming time is 3 min, to obtain clean coal 2 and tailings 2.

[0026] (5) Pour the clean coal 2 obtained in step (4) into the flotation cell, replenish the liquid level to the standard scale line, and obtain a slurry with a concentration of 60 g / L. The impeller speed of the flotation machine is 2100 r / min. After adjusting the slurry for 30 seconds, start aeration and separation. The aeration volume is 150 L / h, and the foaming time is 3 min, to obtain clean coal 3 and tailings 3.

[0027] (6) The obtained clean coal is filtered and dried at 80°C for 12 hours to obtain ultrapure coal.

[0028] Example 2 The difference between this embodiment and embodiment 1 is that the pre-carbonization temperature in step (2) is 300°C, while the other steps and parameters are the same as in embodiment 1.

[0029] Example 3 The difference between this embodiment and embodiment 1 is that the pre-carbonization temperature in step (2) is 350°C; the other steps and parameters are the same as in embodiment 1.

[0030] Example 4 The difference between this embodiment and embodiment 1 is that in step (1), the raw coal is placed in a 325-mesh (0.045 mm) sieve to collect the undersize material; the other steps and parameters are the same as in embodiment 1.

[0031] Comparative Example 1 The difference between this comparative example and Example 1 is that the pre-carbonization treatment in step (2) is not performed, and the undersize obtained in step (1) is directly floated; the other steps and parameters are the same as in Example 1.

[0032] Comparative Example 2 The difference between this comparative example and Example 1 is that: in step (1), a universal crusher is used for crushing, and the material is screened through a 200-mesh (0.074mm) sieve; the other steps and parameters are the same as in Example 1.

[0033] Comparative Example 3 The difference between this comparative example and Example 1 is that the pre-carbonization temperature in step (2) is 400°C; the other steps and parameters are the same as in Example 1.

[0034] The ash content and yield of the clean coal obtained from the above examples and comparative examples were determined, and the flotation results are shown in Table 1.

[0035] Table 1. Flotation results of different embodiments and comparative examples Figure 2 The images show the X-ray photoelectron spectroscopy (XPS) spectra of coal samples from Examples 1-3 (pre-carbonization temperatures of 250°C, 300°C, and 350°C), Comparative Example 1 (without pre-carbonization), and Comparative Example 3 (pre-carbonization temperature of 400°C). Figure 2 As can be seen, Comparative Example 1, which was not pre-carbonized, had the highest total content of oxygen-containing functional groups on its surface, resulting in poor floatability. In Examples 1-3, the content of oxygen-containing functional groups decreased with increasing pre-carbonization temperature. The content of ether bonds decreased with increasing pre-carbonization temperature, indicating poor thermal stability. Example 1 (250℃) had the highest carbonyl content at 2.63% and the lowest strongly hydrophilic carboxyl content at 1.37%. These changes were caused by the combined effects of dehydration, decarboxylation, and decarbonylation reactions, leading to asynchronous rates of functional group formation and consumption. Example 1 (250℃) showed significantly improved floatability due to sufficient carboxyl group removal, consistent with the results in Table 1 showing the lowest ash content and highest yield. In Comparative Example 3 (400℃), the oxygen-containing functional groups continued to decompose, but excessive pyrolysis led to changes in the surface structure, which was detrimental to flotation.

[0036] Figure 3 Scanning electron microscope (SEM) images of coal samples from Examples 1-3 (pre-carbonization temperatures of 250℃, 300℃, and 350℃) and Comparative Example 1 (without pre-carbonization) and Comparative Example 3 (pre-carbonization temperature of 400℃). Figure 3 (a) is a SEM image of Example 1; Figure 3 (b) is a SEM image of Example 2; Figure 3 (c) is a SEM image of Example 3; Figure 3 (d) is the SEM image of Comparative Example 1; Figure 3 (e) is the SEM image of Comparative Example 3. From Figure 3 It can be seen that the surface of Comparative Example 1 (without pre-carbonization) is relatively smooth; after pre-carbonization at 250℃ (Example 1), slight wrinkles and cracks appear on the surface, which is conducive to the adhesion of bubbles and particles; as the pre-carbonization temperature increases, the wrinkles and cracks on the surface of the coal samples in Examples 2, 3 and Comparative Example 3 increase, and the roughness increases. A moderately rough surface is conducive to the adhesion of bubbles and particles, but excessive roughness (Comparative Example 3) will destroy the stability of the bubble-particle interface, leading to a decrease in flotation efficiency. In summary, Example 1 has the best flotation effect.

[0037] Figure 4 The diagram shows the contact angle and Zeta potential of coal samples from Examples 1-3 and Comparative Examples 1 and 3. See also... Figure 4 As the pre-carbonization temperature increased, the contact angle of the coal samples increased, and the hydrophobicity improved. The contact angle of Comparative Example 1 (uncarbonized) was 113.75°, indicating that the raw coal had a certain degree of hydrophobicity. The contact angle of Example 1 (250°C) increased to 123.50°; with increasing pre-carbonization temperature, the contact angles of the coal samples in Examples 2, 3, and Comparative Example 3 increased to 128.38°, 131.13°, and 131.29°, respectively, indicating that pre-carbonization treatment improved the hydrophobicity of the coal samples. The absolute value of the Zeta potential decreased with increasing pre-carbonization temperature. The reduction of surface negative charge weakened the electrostatic repulsion between coal particles and bubbles, promoting the adhesion of bubbles to particles.

[0038] Table 1 shows that Example 1 (pre-carbonization temperature of 250℃) yielded the lowest ash content (0.81%) and the highest yield (40.36%) of clean coal, indicating that 250℃ is the optimal pre-carbonization temperature. Example 2 (pre-carbonization temperature of 300℃) yielded 0.92% ash content and a yield of 37.32% of clean coal; Example 3 (pre-carbonization temperature of 350℃) yielded 0.96% ash content and a yield of 38.41% of clean coal. As temperature increases, the clean coal yield decreases and the ash content increases, due to excessive coarseness and agglomeration leading to ash entrainment.

[0039] Compared with Comparative Example 1 (without pre-carbonization), the yield of Example 1 increased from 7.19% to 40.36%, and the ash content decreased from 1.06% to 0.81%, demonstrating that pre-carbonization treatment can remove hydrophilic oxygen-containing functional groups from the surface of coal, enhance hydrophobicity, and improve flotation performance.

[0040] Compared to Comparative Example 2 (crushing with a universal crusher), the yield of Example 1 increased from 3.43% to 40.36%, demonstrating that the "roll mill + rod mill" crushing process used in this invention can obtain fine coal with uniform particle size and few surface defects, providing a better raw material for subsequent pre-carbonization and flotation. The universal crusher mainly crushes materials through impact, easily generating a large amount of fine powder, and the crushed particles have many surface cracks and irregular shapes, which is not conducive to subsequent flotation separation.

[0041] Compared with Comparative Example 3 (pre-carbonization temperature of 400°C), the ash content of Example 1 decreased from 1.09% to 0.81%, demonstrating that excessively high pre-carbonization temperatures are not conducive to flotation deashing. This is because greater surface roughness will disrupt the stability of the bubble-particle interface, and the absolute value of the Zeta potential will decrease, promoting agglomeration between particles and leading to ash entrainment.

[0042] Example 4 used a 325-mesh (0.045 mm) sieve, resulting in finer coal powder particles with a larger specific surface area, increasing the probability of collision between the collector and bubbles, thus increasing the clean coal yield to 64.98%. Simultaneously, the smaller particle size facilitates the dissociation of coal and ash; however, excessively fine particles may also lead to the entrainment of some high-ash fine mud, slightly increasing the clean coal ash content (0.97%). In actual production, the sieve particle size can be rationally selected based on the characteristics of the raw materials and product requirements.

[0043] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing ultrapure coal based on pre-carbonization-flotation combined process, characterized in that, Includes the following steps: (1) The raw coal is crushed and ground to fully dissociate the coal from the minerals; (2) The coal particles obtained in step (1) are placed in an inert atmosphere for low-temperature pre-carbonization treatment, and then naturally cooled to room temperature to obtain a pre-carbonized coal sample. (3) Add water to the pre-carbonized coal sample obtained in step (2) for slurry treatment, add collector and frother in sequence, stir and aerate for flotation to obtain clean coal 1 and tailings 1; (4) Add water to the clean coal 1 obtained in step (3) to make slurry, and then sort it to obtain clean coal 2 and tailings 2; (5) Add water to the clean coal 2 obtained in step (4) to make slurry, and then sort it to obtain clean coal 3 and tailings 3; (6) The clean coal 3 obtained in step (5) is filtered and dried to obtain ultrapure coal with ash content of less than 1.0%.

2. The method for preparing ultrapure coal based on pre-carbonization-flotation combined according to claim 1, characterized in that, The raw coal mentioned in step (1) is selected from one or more of anthracite, lean coal, semi-coking coal, coking coal, fat coal, gas coal, weakly caking coal, non-caking coal, and long-flame coal.

3. The method for preparing ultrapure coal based on pre-carbonization-flotation combined according to claim 1, characterized in that, The crushing and grinding method in step (1) is as follows: first, put the raw coal into a double roll crusher for coarse crushing, and then put it into a rod mill for fine grinding.

4. The method for preparing ultrapure coal based on pre-carbonization-flotation combined according to claim 1, characterized in that, The inert atmosphere mentioned in step (2) includes one of nitrogen, helium, argon, neon and xenon, with a gas flow rate of 80~120mL / min.

5. The method for preparing ultrapure coal based on pre-carbonization-flotation combined according to claim 1, characterized in that, The low-temperature pre-carbonization treatment in step (2) is carried out at a temperature of 250~350℃, a heating rate of 2~10℃ / min, and a holding time of 1~3h.

6. The method for preparing ultrapure coal based on pre-carbonization-flotation combined according to claim 1, characterized in that, In step (3), the concentration of the slurry after the slurry conditioning treatment is 50~70g / L.

7. The method for preparing ultrapure coal based on pre-carbonization-flotation combined according to claim 1, characterized in that, The collector in step (3) is kerosene with a concentration of 1000~2000g / t; the foaming agent is 2-octanol with a concentration of 100~200g / t.

8. The method for preparing ultrapure coal based on pre-carbonization-flotation combined according to claim 1, characterized in that, In step (3), the stirring rate of the flotation process is 1900~2100 r / min and the aeration rate is 100~200 L / h.

9. The method for preparing ultrapure coal based on pre-carbonization-flotation combined according to claim 1, characterized in that, In step (6), the drying temperature is 80°C and the drying time is 12 hours.

10. The ultrapure coal prepared by the preparation method according to any one of claims 1 to 9, characterized in that, Ash content is less than 1.0%.

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