A method for modifying coal by a solvothermal method and modified coal

Abstract

This invention belongs to the field of efficient coal conversion and utilization technology, specifically a method for modifying coal using a solvothermal method and the modified coal. Coal is mixed with an organic solvent in a sealed container for heat treatment, followed by vacuum distillation to remove the solvent. After cooling, modified coal is obtained. During the heat treatment, solvent molecules penetrate and act on the macromolecular network of the coal, selectively breaking weak chemical bonds such as aliphatic side chains and ether bonds. This moderately dissociates and activates the inherent three- to five-ring aromatic clusters in the coal, forming a colloidal precursor rich in active small molecules. Then, direct vacuum distillation occurs, resulting in mild structural rearrangement and physical cross-linking, ultimately forming a uniform, dense, and highly adhesive solid modified coal product.

Description

Technical Field

[0001] This invention belongs to the field of efficient coal conversion and utilization technology, specifically relating to a method for modifying coal using a solvothermal method and modified coal. Background Technology

[0002] my country has abundant coal resources, but high-caking coking coal is relatively scarce, while reserves of low-quality coal (such as lignite and long-flame coal), weakly caking coal, and some non-caking coal are enormous. These types of coal, due to their poor or non-caking properties, are difficult to use directly for producing high-quality coke or as caking components in briquettes; they are typically only used for power generation and have low value. How to efficiently and cleanly increase the added value of these low-quality coals is an urgent problem to be solved in the coal processing industry.

[0003] Thermal extraction is a method for treating coal using organic solvents under mild conditions. Existing technologies primarily focus on extracting soluble components from coal as precursors for carbon materials or liquid fuels. However, these traditional applications treat coal as an object to be "separated," with the core objective of obtaining different product components, without fully considering and utilizing the profound impact of the thermal extraction process itself on the coal's bulk structure. In particular, existing technologies have not recognized or systematically reported that, through careful design of solvent systems and thermodynamic conditions, the thermal extraction process can be guided away from complete component separation and towards selective deconstruction and in-situ reforming of the coal's macromolecular structure. This allows for the direct transformation of low-quality coal into a homogeneous product with high binding properties without relying on physical mixing. This directional modification technology, capable of "upgrading and reshaping" the bulk properties of coal, remains a gap in current understanding.

[0004] Therefore, developing a technology that can bypass complex separation and compounding steps and transform non-caking or weakly caking coal into highly caking coal through one-step solvothermal modification has significant scientific importance, industrial application value, and market prospects. Summary of the Invention

[0005] The purpose of this invention is to provide a method for modifying coal using a solvothermal method and the modified coal. Through solvothermal modification technology, the molecular structure of low-caking coal is directionally controlled under mild conditions, thereby converting it into high-caking coal.

[0006] To achieve the above objectives, the present invention provides a method for modifying coal using a solvothermal method, comprising: mixing coal with an organic solvent in a closed container for heat treatment, then performing vacuum distillation to remove the solvent, and cooling to obtain modified coal.

[0007] Furthermore, the organic solvent includes one or more of substituted or unsubstituted aromatic hydrocarbons; the aromatic hydrocarbons include one or more of naphthalene, biphenyl, pyridine, quinoline, and phenol. The substitution group is selected from one or more of methyl, ethyl, and halogen.

[0008] Furthermore, the organic solvent includes one or more of 1-methylnaphthalene, 2-methylnaphthalene, naphthalene, biphenyl, pyridine, quinoline, and cresol.

[0009] Furthermore, the mass ratio of the coal to the organic solvent is 1:(4-10).

[0010] Furthermore, the heat treatment temperature is 300-400℃ and the time is 0.1-150min.

[0011] Furthermore, the temperature of the vacuum distillation is 160-220℃, and the vacuum degree is -0.08 to -0.1 MPa.

[0012] Furthermore, the coal is coal with a caking index (G) value of less than 60, preferably coal with a G value of less than 20.

[0013] Furthermore, the coal is in powder form, with a particle size preferably of 10-100 mesh, and more preferably 18-30 mesh.

[0014] The present invention also provides a modified coal, obtained by the method described above for modifying coal using a solvothermal method.

[0015] Furthermore, the modified coal has a caking index G value greater than 80.

[0016] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages: 1. Fundamental Innovation in Process Principles: From "Physical Compounding" to "Chemical Reconstruction" Unlike existing technologies that employ a physical compounding approach of "extraction and separation followed by mechanical mixing," this invention proposes and implements a novel technical path of "one-step solvothermal modification-overall chemical reconstruction." This method bypasses separation, instead utilizing a solvent to directly chemically modify the coal matrix under mild conditions. Through "in-situ deconstruction-reforming," inferior coal undergoes structural upgrading at the molecular level, thereby transforming it into highly caking coal in a homogeneous and overall manner. This eliminates the cumbersome separation, transportation, and mixing processes, representing a fundamental revolution in process principles.

[0017] 2. Strong adaptability to raw materials, uniform and adjustable product performance. This invention is applicable to a variety of low-quality coal raw materials, including low-rank coal, non-caking coal, and weakly caking coal, overcoming the resource limitations of high-quality caking coal. Furthermore, by adjusting parameters such as solvent type, modification temperature, and time, the modification process can be optimized and controlled, thereby customizing the caking index (G value) of the final product within a certain range. This results in stable, uniform, and highly caking coal products that meet the diverse needs of downstream applications.

[0018] 3. Extreme simplification of process flow and cost advantage By eliminating all intermediate steps such as separation, purification, and remixing of the extract, the process flow of this invention is simplified like never before. The core steps are only "one modification reaction" and "one solvent recovery," resulting in a significant reduction in equipment investment and operating costs, and a substantial decrease in energy consumption. This extremely simple one-step process makes its industrial implementation feasibility and economic efficiency far superior to any existing technology that requires multiple separation and reprocessing steps. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0020] This invention provides a method for modifying coal using a solvothermal method, comprising: mixing coal with an organic solvent in a closed container for heat treatment, then performing vacuum distillation to remove the solvent, and cooling to obtain modified coal.

[0021] In this invention, during the heat treatment process, solvent molecules penetrate and act on the macromolecular network of coal, selectively breaking weak chemical bonds such as aliphatic side chains and ether bonds, causing the inherent three to five ring aromatic clusters in the coal to be moderately dissociated and activated, forming a colloidal precursor rich in active small molecules (aromatic molecules); then, during the solvent removal and system cooling process, the aforementioned activated aromatic molecules undergo mild structural reorganization and physical cross-linking under the action of van der Waals forces, π-π stacking, etc., ultimately forming a uniform, dense and highly adhesive solid modified coal product.

[0022] The organic solvent includes one or more substituted or unsubstituted aromatic hydrocarbon compounds; the aromatic hydrocarbon compounds include one or more of naphthalene, biphenyl, pyridine, quinoline, and phenol; the substituted group is selected from one or more of methyl, ethyl, and halogen.

[0023] Preferably, the organic solvent includes one or more of 1-methylnaphthalene, 2-methylnaphthalene, naphthalene, biphenyl, pyridine, quinoline, and cresol; in some embodiments, the organic solvent is obtained by compounding two or more.

[0024] The mass ratio of coal to organic solvent is 1:(4-10), preferably 1:(5-9).

[0025] Furthermore, the heat treatment temperature is 300-400℃, and the time is 0.1-150 min, preferably 10-120 min. Preferably, the heat treatment is carried out under an inert atmosphere. The vacuum distillation temperature is 160-220℃, and the vacuum degree is -0.08 to -0.1 MPa.

[0026] The coal is a coal with a caking index (G) value of less than 60, preferably a coal with a G value of less than 20. In some embodiments, the coal is one or more of low-quality coals such as lignite, long-flame coal, non-caking coal, or weakly caking coal.

[0027] Furthermore, the coal is in powder form, with a particle size preferably of 10-100 mesh, more preferably 18-30 mesh. Specifically, the raw coal is crushed and screened to obtain coal particles of the desired particle size.

[0028] The testing method for the adhesion index in the following examples is as follows: Test method for caking index G value: In this invention, the determination of the G value of the blended coal is carried out in accordance with the national standard GB / T 55447-2014 "Determination Method of Caking Index of Bituminous Coal". Specifically, 1.00g of test coal sample is mixed with 5.00g of special anthracite standard sample, stirred and briquetteed under standard conditions, and rapidly coked at 850℃ for 15 minutes. The resulting coke lumps are subjected to two drum strength tests at 250 revolutions each, and then sieved and weighed. Finally, the caking index G value is calculated using a specific formula based on the abrasion resistance of the coke lumps (i.e., the mass of the material remaining on the sieve after the drum test).

[0029] Example 1 Xinjiang Jiankou mine lignite (G value 0) was pulverized to a particle size of 18-30 mesh. 50g of coal powder and 400g of a compound solvent of methylnaphthalene and quinoline in equal proportions were added to a reaction vessel. Stirring was started, and the mixture was kept at 350℃ under sealed conditions for 60 min. After the reaction, the liquid mixture was directly subjected to vacuum distillation at -0.1MPa and 200℃ to recover the solvent. After cooling, a solid product was obtained. The product was pulverized and its caking index (G value) was tested according to national standards.

[0030] The solid product obtained by the method described in Example 1 has an adhesion index of 90, and the mass loss rate of the obtained solid product compared with the raw coal powder is 4.2%.

[0031] Example 2 Xinjiang Jiankou mine lignite (G value 0) was pulverized to a particle size of 18-30 mesh. 50g of coal powder and 450g of a compound solvent of methylnaphthalene and quinoline in equal proportions were added to a reaction vessel. Stirring was started, and the mixture was kept at 300℃ under sealed conditions for 60 min. After the reaction was completed, the liquid mixture was subjected to vacuum distillation at -0.1MPa and 200℃ to recover the solvent. After cooling, a solid product was obtained. The product was pulverized and its caking index (G value) was tested according to national standards.

[0032] The solid product obtained based on the method described in Example 2 has an adhesion index of 80. The mass loss rate of the obtained solid product compared to the raw coal powder is 3.8%.

[0033] Example 3 Xinjiang Jiankou mine lignite (G value 0) was pulverized to a particle size of 18-30 mesh. 50g of coal powder and 500g of a compound solvent of dimethylnaphthalene and biphenyl in equal proportions were added to a reaction vessel. Stirring was started, and the mixture was kept at 350℃ under sealed conditions for 120 min. After the reaction was completed, the liquid mixture was subjected to vacuum distillation at -0.1MPa and 200℃ to recover the solvent. After cooling, a solid product was obtained. The product was pulverized and its viscous index (G value) was tested according to national standards.

[0034] The solid product obtained by the method described in Example 3 has an adhesion index of 83, and the mass loss rate of the obtained solid product compared with the raw coal powder is 4.4%.

[0035] Example 4 Lignite (G value 0) from Xigou Mine in Xinjiang was pulverized to a particle size of 18-30 mesh. 50g of pulverized coal and 400g of a compound solvent of dimethylnaphthalene and biphenyl in equal proportions were added to a reaction vessel. Stirring was started, and the mixture was kept at 350℃ under sealed conditions for 60 min. After the reaction was completed, the liquid mixture was subjected to vacuum distillation at -0.1MPa and 200℃ to recover the solvent. After cooling, a solid product was obtained. The product was pulverized and its caking index (G value) was tested according to national standards.

[0036] The solid product obtained by the method described in Example 4 has an adhesion index of 85, and the mass loss rate of the obtained solid product compared with the raw coal powder is 3.9%.

[0037] Example 5 Xinjiang Xigou mine lignite (G value 0) was pulverized to a particle size of 18-30 mesh. 50g of pulverized coal and 450g of a compound solvent of biphenyl and quinoline in equal proportions were added to a reaction vessel. Stirring was started, and the mixture was kept at 400℃ under sealed conditions for 60 min. After the reaction was completed, the liquid mixture was subjected to vacuum distillation at -0.1MPa and 200℃ to recover the solvent. After cooling, a solid product was obtained. The product was pulverized and its caking index (G value) was tested according to national standards.

[0038] The solid product obtained by the method described in Example 5 has an adhesion index of 86, and the mass loss rate of the obtained solid product compared with the raw coal powder is 4.8%.

[0039] Example 6 Lignite (G value 0) from Xigou Mine in Xinjiang was pulverized to a particle size of 18-30 mesh. 50g of pulverized coal and 500g of a compound solvent of biphenyl and quinoline in equal proportions were added to a reaction vessel. Stirring was started, and the mixture was kept at 350℃ under sealed conditions for 120 min. After the reaction was completed, the liquid mixture was subjected to vacuum distillation at -0.1MPa and 200℃ to recover the solvent. After cooling, a solid product was obtained. The product was pulverized and its caking index (G value) was tested according to national standards.

[0040] The solid product obtained by the method described in Example 6 has an adhesion index of 85, and the mass loss rate of the obtained solid product compared with the raw coal powder is 4.6%.

[0041] Table 1. Test results of G-value in the example

[0042] In summary, this invention utilizes solvothermal treatment and in-situ vacuum distillation on low-caking coal. Under mild thermal conditions, the organic solvent selectively breaks down the weak bonds in the macromolecular structure of inferior coal without excessively cleaving its aromatic core. This process "releases" the inherent aromatic molecules of suitable size (e.g., three to five rings) within the coal, bringing them to a highly active colloidal state within the system. When the solvent is removed, these activated molecules, deprived of the solvent's dispersing effect, spontaneously reorganize and assemble through intermolecular forces, forming a novel, tightly bound condensed structure. This structure macroscopically manifests as excellent caking properties. Therefore, this method does not simply "extract" a component from the coal, but rather achieves structural upgrading and performance leaps in the coal itself through "deconstruction-reorganization." In the examples, while ensuring a mass loss of less than 5%, the caking properties of the coal are significantly improved, thereby enhancing its industrial application value and indicating a broad market prospect.

[0043] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for modifying coal using a solvothermal method, characterized in that, include: Coal is mixed with an organic solvent in a sealed container and subjected to heat treatment, followed by vacuum distillation to remove the solvent, and then cooled to obtain modified coal.

2. The method for modifying coal using a solvothermal method according to claim 1, characterized in that, The organic solvent includes one or more of substituted or unsubstituted aromatic hydrocarbons; the aromatic hydrocarbons include one or more of naphthalene, biphenyl, pyridine, quinoline, and phenol. The substitution group is selected from one or more of methyl, ethyl, and halogen.

3. The method for modifying coal using a solvothermal method according to claim 2, characterized in that, The organic solvent includes one or more of 1-methylnaphthalene, 2-methylnaphthalene, naphthalene, biphenyl, pyridine, quinoline, and cresol.

4. The method for modifying coal using a solvothermal method according to claim 1, characterized in that, The mass ratio of coal to organic solvent is 1:(4-10).

5. The method for modifying coal using a solvothermal method according to claim 1, characterized in that, The heat treatment temperature is 300-400℃ and the time is 0.1-150min.

6. The method for modifying coal using a solvothermal method according to claim 1, characterized in that, The vacuum distillation temperature is 160-220℃, and the vacuum degree is -0.08 to -0.1 MPa.

7. The method for modifying coal using a solvothermal method according to claim 1, characterized in that, The coal is coal with a caking index (G) value of less than 60, preferably coal with a G value of less than 20.

8. The method for modifying coal using a solvothermal method according to claim 1, characterized in that, The coal is in powder form, with a particle size preferably 10-100 mesh, and more preferably 18-30 mesh.

9. A modified coal, characterized in that, It is obtained by the method of modifying coal using a solvothermal method as described in any one of claims 1-8.

10. The modified coal according to claim 9, characterized in that, The modified coal has a caking index (G) value greater than 80.

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