Low-rank coal mild modification tackifying method based on reducing gas and organic solvent

Abstract

The invention relates to the technical field of clean and efficient utilization of coal, and discloses a low-rank coal mild modification tackifying method based on a reducing gas and an organic solvent, which comprises the following steps: pre-activating the organic solvent and a catalyst in a reducing gas atmosphere; cooling, adding low-rank coal powder with the water content of 3.0-35.0 wt%, and mixing with the pre-activation system; carrying out hydrogenation reaction on the prepared mixture, namely introducing reducing gas into the system to the initial pressure in the initial heating stage, and then continuously heating to the final reaction temperature of 330-390 DEG C to carry out constant-temperature reaction; and finally cooling, separating and drying the product to obtain the modified coal product. According to the present invention, with the gas phase and liquid phase synergistic hydrogenation strategy, the accurate control of the coal depolymerization and the hydrogenation stability is achieved, the excellent caking property is given to the low-rank coal under the mild condition, the reaction condition is mild, the energy consumption is low, the high water content coal can be directly utilized, and the economy is improved.

Description

Technical Field

[0001] This invention relates to the field of clean and efficient utilization of coal technology, specifically a method for mild modification and thickening of low-rank coal based on reducing gas and organic solvent. Background Technology

[0002] Coking coal is an indispensable basic raw material for my country's steel industry, and its resource shortage has long existed, severely restricting the stable development of related industrial chains. Meanwhile, my country's abundant reserves of low-rank coal, due to its inherent characteristics of high volatile matter and low caking properties, are difficult to use directly for coking, resulting in low overall utilization value. Therefore, developing modification technologies that can economically and efficiently transform low-rank coal into a coking supplementary resource with excellent caking properties is of great significance for ensuring energy security and enhancing the value of low-rank coal.

[0003] To improve the caking properties of low-rank coal, various modification pathways have been explored in existing technologies. However, these technologies still face challenges in achieving industrial application. For example, while hydrothermal modification technology can effectively increase viscosity, it is usually carried out in subcritical / supercritical water systems, where the reaction pressure easily exceeds 15-20 MPa, affecting the safety, reliability, and investment costs of the reaction equipment. Some hydromodification processes also have similar problems; their process design requires maintaining a high-pressure environment from the initial stage of the reaction, resulting in high overall energy consumption and increased operational complexity and safety risks.

[0004] Furthermore, existing hydrogenation technologies are highly dependent on raw materials and fail to fully utilize the inherent characteristics of low-rank coal. On the one hand, some processes rely on expensive pure hydrogen, high-purity carbon monoxide, or fully hydrogenated hydrogen-donating solvents as hydrogen sources, increasing production costs. On the other hand, the high natural moisture content of low-rank coal is often considered a disadvantage, requiring costly deep drying before the reaction. This not only adds extra steps and energy consumption but also fails to explore the potential of moisture to be converted into usable resources in specific reaction systems. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a mild modification and thickening method for low-rank coal based on reducing gas and organic solvents. This method solves the problems of harsh reaction conditions, high energy consumption and raw material costs, poor adaptability to high-moisture coal, and limited thickening effect due to inaccurate process control in existing technologies.

[0006] To achieve the above objectives, this invention provides a method for mild modification and thickening of low-rank coal based on reducing gas and organic solvent, employing the following technical solution: A mild modification and thickening method for low-rank coal based on reducing gas and organic solvent includes the following steps: Step S1: Mix the organic solvent and the catalyst, and perform pre-activation treatment under a reducing gas atmosphere to obtain a pre-activated system, wherein the mass ratio of the organic solvent to the catalyst is (28-700):1; Step S2: After cooling the obtained pre-activated system, add low-rank coal powder with a water content of 3.0-35.0 wt% and mix evenly to prepare a mixed system, wherein the mass ratio of organic solvent to low-rank coal powder in the pre-activated system is 0.8-1.5:1; Step S3: The prepared mixed system is subjected to a hydrogenation reaction under the reducing gas atmosphere to obtain a liquid-solid mixture; Step S4: Cool the liquid-solid mixture, separate and dry it to obtain the modified coal product.

[0007] This invention, through ingenious process design, achieves ordered and efficient modification of the macromolecular structure of low-rank coal under relatively mild operating conditions. The specific reaction mechanism and innovative effects can be described in stages as follows: Stage 1: Synergistic pre-activation of catalyst and solvent (corresponding to step S1) Before adding the coal sample, the catalyst and organic solvent are pretreated under a reducing atmosphere and at a specific temperature (200-250℃). This step is not a simple physical mixing, but a crucial process for initial activation of the catalyst and preliminary activation of the solvent. During this stage, the surface of the metal-based catalyst undergoes preliminary reduction, forming highly catalytically active sites; simultaneously, some hydrogen-donating solvent molecules are activated under catalysis, making them more likely to provide active hydrogen radicals in subsequent reactions. This process prepares a highly active liquid-phase reaction environment for the subsequent efficient conversion of coal.

[0008] Second stage: pressurization and heating, simultaneous depolymerization and in-situ hydrogen production (corresponding to heating processes S2 and S3). After the low-rank coal powder with high moisture content is introduced into the pre-activation system for mixing in step S2, in step S3, reducing gas at an initial pressure (4.0-6.0 MPa) is first introduced into the reaction system at the initial temperature. Subsequently, under this pressure condition, the reaction system is directly heated to the final reaction temperature (330-390℃).

[0009] During this heating process, the coal conversion occurs simultaneously: Physical swelling and thermal depolymerization: The thermal effect of the liquid solvent causes the macromolecular network structure of low-rank coal to swell, the intermolecular forces weaken, and some chemically unstable bridging bonds (such as ether bonds) begin to break, realizing the initial depolymerization of coal and generating a large number of active free radical fragments.

[0010] In-situ resource utilization of moisture: Since the reducing gas (containing carbon monoxide) is introduced before the heating process begins, the high moisture content inherent in the coal can undergo in-situ water-gas shift reaction (WGSR) with carbon monoxide under the action of the catalyst, generating highly reactive nascent hydrogen in situ, providing an important endogenous hydrogen supplement for the reaction.

[0011] Third stage: Isothermal hydrogenation stabilization and curing of binder components (corresponding to isothermal step S3 and step S4) Once the reaction system reaches the final reaction temperature, it enters the isothermal reaction stage (30-90 minutes). During this stage, multiple hydrogen sources in the system—namely, the externally injected reducing gas (gas-phase hydrogen source), the active hydrogen generated in situ by WGSR, and the liquid-phase hydrogen source provided by the solvent—work together to rapidly and fully capture and hydrogenate and stabilize the large number of active free radical fragments generated during the depolymerization stage.

[0012] This efficient stabilization process effectively inhibits the re-condensation reaction between active fragments (generating non-binding semi-coke), maximizing their conversion into flowable and thermoplastic binding components (colloids). The subsequent step S4 (cooling, separation, and drying) solidifies these newly generated binding components in the modified coal product, thereby achieving a deep reconstruction of the chemical structure of low-rank coal and endowing it with excellent binding properties.

[0013] Preferably, in step S1, the pre-activation treatment includes: heating the product of the mixture of the organic solvent and the catalyst to 200-250°C and reacting at a constant temperature for 15-30 minutes to obtain the pre-activated system. This parameter setting ensures that the catalyst is fully activated while avoiding deep cracking of the organic solvent.

[0014] Preferably, in step S3, the heating and hydrogenation reaction includes: introducing the reducing gas into the reaction system at an initial temperature until the initial pressure reaches 4.0-6.0 MPa; then continuing to heat to the final reaction temperature of 330-390°C and maintaining the temperature for 30-90 minutes to obtain the liquid-solid mixture. By adopting the above technical solution, the application of temperature and pressure is precisely controlled, enabling efficient coupling of the coal depolymerization process and the hydrogenation stabilization process, achieving optimal synergistic effects.

[0015] Preferably, the organic solvent is any one or more of Shenhua coal liquefaction crude oil, 1-methylnaphthalene, tetrahydronaphthalene, and naphthalene to form a solvent.

[0016] Preferably, when the organic solvent is a mixed solvent formed from two solvents, the mixed solvent is prepared by mixing the tetrahydronaphthalene and the 1-methylnaphthalene in a mass ratio of (0.9-1.1):1, or the mixed solvent is prepared by mixing the Shenhua coal liquefaction crude oil and the naphthalene in a mass ratio of (3.8-4.2):1. Using a specific compound solvent can optimize the solvent's hydrogen supply capacity, solubility, and cost, achieving better technical and economic results.

[0017] Preferably, the catalyst is any one of copper oxide, ferric oxide, ferric oxide, or red mud.

[0018] The catalysts selected in this invention are mainly based on the following two types of mechanisms of action: one type is transition metal catalysts represented by iron-based and copper-based oxides, which are well known in the art and can efficiently catalyze water-gas shift reaction (WGSR) and hydrogenation reaction.

[0019] Red mud, as an industrial solid waste, has ferric oxide as its main chemical component. Therefore, it can be used as a cheap substitute for iron-based catalysts in this invention, and its catalytic principle is similar to that of pure ferric oxide.

[0020] Therefore, those skilled in the art can expect that the above-mentioned catalysts can all achieve the technical objectives of the present invention.

[0021] Preferably, when the catalyst is ferric oxide, the pre-activation treatment step further includes adding sulfur as an additive, and the atomic ratio of iron atoms in the ferric oxide to sulfur atoms in the sulfur is (0.9-1.1):1. The sulfur additive can promote the conversion of ferric oxide into highly active iron sulfide species during pre-activation and the reaction process, significantly improving catalytic efficiency.

[0022] Preferably, the reducing gas is any one of carbon monoxide, hydrogen, or a synthesis gas of carbon monoxide and hydrogen; wherein, when the reducing gas is the synthesis gas, the volume ratio of hydrogen to carbon monoxide is (0.2-4):1. This allows the method to adapt to a variety of commonly used industrial reducing gases, has good industrial versatility, and the hydrogen used does not require the use of expensive pure hydrogen.

[0023] Preferably, the low-rank coal powder includes any one of long-flame coal powder, lignite coal powder, non-caking coal powder, and gas-flame coal powder, and the particle size of the low-rank coal powder is 80-200 mesh. This particle size range ensures that the coal powder has a sufficiently large specific surface area, which is beneficial to mass and heat transfer and reaction.

[0024] Preferably, the amount of catalyst used is 0.2-6 wt% of the dry, ash-free mass of the low-rank coal powder. This dosage range ensures catalytic activity while also taking into account the economy of the reaction.

[0025] This invention provides a method for the mild modification and thickening of low-rank coal based on reducing gas and organic solvent. It has the following beneficial effects: 1. This invention pre-activates the catalyst and solvent system and utilizes the synergistic effect of reducing gas and a specific organic solvent. Under mild reaction conditions (final reaction temperature 330-390℃, initial pressure 4.0-6.0MPa), low-rank coal with extremely low caking index (G value) can be efficiently converted into high-caking coal with excellent caking properties. This achieves the upgrading and transformation of low-rank coal, improves its caking properties, and has a good upgrading and transformation effect.

[0026] 2. This invention uses inexpensive industrial gases such as carbon monoxide, hydrogen, or their syngas as hydrogen sources instead of expensive pure hydrogen. It can also use industrial by-product solvents such as crude oil from Shenhua coal liquefaction that are not or partially hydrogenated to replace expensive high-efficiency hydrogen-supplying solvents such as tetrahydronaphthalene. The raw material cost is low, and the economic advantage is obvious. It reduces the cost of raw materials and hydrogen consumption, and provides an effective way to solve the problem of high cost of low-rank coal modification.

[0027] 3. This invention controls the reaction pressure below 10MPa, resulting in mild reaction conditions, which reduces investment in high-pressure equipment and safety requirements. At the same time, this method can directly process low-rank coal with high moisture content without the need for pre-drying. It also utilizes the inherent moisture in the coal to react with carbon monoxide in the reducing gas to generate supplementary endogenous active hydrogen, thereby improving raw material adaptability and atom economy. Detailed Implementation

[0028] The technical solutions in the preparation examples and embodiments of the present invention will be clearly and completely described below with reference to comparative examples and test examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Preparation Examples 1-2: Preparation Example 1: Preparation of Mixed Solvent M1 At room temperature (25°C), add 500g of organic solvent B (tetrahydronaphthalene) and 500g of organic solvent C (1-methylnaphthalene) to a 1000mL beaker equipped with a magnetic stir bar, in a mass ratio of 1:1. Turn on the magnetic stir bar and stir continuously at a medium speed (approximately 300 rpm) for 30 minutes to ensure that the two liquids are completely miscible and thoroughly mixed. Seal and store the resulting mixture, and denote it as mixed solvent M1.

[0030] Preparation Example 2: Preparation of Mixed Solvent M2 Add 800g of organic solvent A (Shenhua coal liquefaction crude oil) and 200g of organic solvent D (naphthalene) to a 1000mL beaker equipped with a magnetic stirrer and a heating mantle, in a mass ratio of 4:1. Turn on the stirrer and the heating mantle, and slowly heat the mixture to 100℃ (ensuring it is above the melting point of naphthalene, 80.26℃), stirring continuously at this temperature for 30 minutes until the solid naphthalene is completely dissolved and the system forms a homogeneous liquid phase. Stop heating and allow the mixture to cool naturally to room temperature with stirring. Seal and store the resulting mixture, denoted as mixed solvent M2.

[0031] Examples 1-3: Example 1: This embodiment provides a method for mild modification and thickening of low-rank coal based on reducing gas and organic solvent, specifically including the following steps: 118g of the mixed solvent M2 prepared in Preparation Example 2 and 0.17g of catalyst B (Fe3O4) were added to a 1L high-pressure reactor.

[0032] The sealed reactor was purged three times using reducing gas B (H2 / CO volume ratio of 0.2:1). Under sealed conditions, mechanical stirring (500 rpm) was started to heat the material inside the reactor to 200°C, and pre-activation was performed at this temperature for 15 minutes.

[0033] After pre-activation, the reactor is cooled to room temperature. Using a high-pressure feed tank (or lock hopper system) connected to the reactor, 147g of long-flame coal powder with a moisture content of 35.0wt%, sieved through a 200-mesh sieve, is added while maintaining a reducing atmosphere inside the reactor. At this point, the mass ratio of solvent to water-containing coal powder is 0.8:1.

[0034] The air inside the reactor was replaced three times again using reducing gas B.

[0035] When the reactor reaches its initial temperature, reducing gas B is rapidly introduced into the reactor through the inlet valve, bringing the initial pressure inside the reactor to 4.0 MPa. Subsequently, the temperature is further increased to the final reaction temperature of 330°C.

[0036] The reaction was carried out at a constant temperature of 330℃ for 60 minutes, during which the pressure inside the reactor was recorded to ensure that the peak pressure was below 10MPa.

[0037] After the reaction is complete, the reactor is cooled to room temperature. The gaseous products are slowly released from the reactor, and the liquid-solid mixture is removed. The mixture is washed and filtered multiple times with sufficient n-hexane until the filtrate is clear. The solid material is collected and dried in a vacuum drying oven at 80°C to constant weight to obtain the modified coal product.

[0038] Example 2: This embodiment provides a method for mild modification and thickening of low-rank coal based on reducing gas and organic solvent, specifically including the following steps: 115g of the mixed solvent M1 prepared in Preparation Example 1, 2.6g of catalyst A (ferric oxide) and 1.5g of auxiliary agent A (sulfur) were added to a 1L high-pressure reactor.

[0039] The sealed reactor was purged three times using reducing gas A (H2 / COH2 / CO volume ratio of 1.5:1). Under sealed conditions, mechanical stirring (600 rpm) was started to heat the material inside the reactor to 225°C, and pre-activation was performed at this temperature for 22 minutes.

[0040] After pre-activation, the reactor is cooled to room temperature. Using a high-pressure feed tank (or lock hopper system) connected to the reactor, 100g of long-flame coal powder with a water content of 15.0wt%, sieved through a 100-mesh sieve, is added (and an appropriate amount of deionized water is added to adjust the total water content), while maintaining a reducing atmosphere inside the reactor. At this point, the mass ratio of solvent to water-containing coal powder is 1.15:1.

[0041] The air inside the reactor was replaced three times again using reducing gas A.

[0042] When the reactor reaches its initial temperature, reducing gas A is rapidly introduced into the reactor through the inlet valve, bringing the initial pressure inside the reactor to 5.0 MPa. Subsequently, the temperature is further increased to the final reaction temperature of 350°C.

[0043] The reaction was carried out at a constant temperature of 350℃ for 60 minutes, during which the pressure inside the reactor was recorded to ensure that the peak pressure was below 10MPa.

[0044] After the reaction was complete, the reactor was cooled to room temperature. The product separation procedure was the same as in Example 1, yielding the modified coal product.

[0045] Example 3: This embodiment provides a method for mild modification and thickening of low-rank coal based on reducing gas and organic solvent, specifically including the following steps: Add 150g of organic solvent B (tetrahydronaphthalene) and 5.2g of catalyst C (copper oxide) to a 1L high-pressure reactor.

[0046] The sealed reactor was purged three times with reducing gas C (H2 / CO volume ratio of 4:1). Under sealed conditions, mechanical stirring (800 rpm) was started to heat the material inside the reactor to 250°C, and pre-activation treatment was carried out at this temperature for 30 minutes.

[0047] After pre-activation, the reactor is cooled to room temperature. Using a high-pressure feed tank (or lock hopper system) connected to the reactor, 100g of long-flame coal powder with a moisture content of 3.0wt%, sieved through an 80-mesh sieve, is added while maintaining a reducing atmosphere inside the reactor. At this point, the mass ratio of solvent to water-containing coal powder is 1.5:1.

[0048] The air inside the reactor was replaced three times with reducing gas C.

[0049] When the reactor reaches its initial temperature, reducing gas C is rapidly introduced into the reactor through the inlet valve, bringing the initial pressure inside the reactor to 6.0 MPa. Subsequently, the temperature is further increased to the final reaction temperature of 390℃.

[0050] The reaction was carried out at a constant temperature of 370℃ for 60 minutes, during which the pressure inside the reactor was recorded to ensure that the peak pressure was below 10MPa.

[0051] After the reaction was complete, the reactor was cooled to room temperature. The product separation procedure was the same as in Example 1, yielding the modified coal product.

[0052] Comparative Examples 1-5: Comparative Example 1: Compared to Example 2, the difference is that the mixed solvent M1, catalyst A, auxiliary agent A, and long-flame coal powder are all added to the reactor at once in step 1, without separate pre-activation treatment of the catalyst and solvent, and directly proceed to the heating operation in step 4. All other operations are the same.

[0053] Comparative Example 2: Compared to Example 2, the difference lies in the following: a conventional one-step process is used, in which all materials (mixed solvent M1, catalyst A, auxiliary agent A, and pulverized coal) are added to the reactor at once, and reducing gas A is introduced at room temperature to an initial pressure of 5.0 MPa before directly heating to 350°C for reaction. This comparative example omits the pre-activation and dynamic gas injection steps. All other operations are the same.

[0054] Comparative Example 3: Compared to Example 2, the difference is that in all gas replacement and pressure filling steps, inert gas E (high-purity nitrogen) is used instead of reducing gas A (synthesis gas), and the initial pressure remains 5.0 MPa. All other operations are the same.

[0055] Comparative Example 4: This comparative example simulates a high-cost existing hydrogenation technology. The differences from Example 2 are: the reaction solvent is replaced with 250g of organic solvent B (tetrahydronaphthalene); the reducing gas is replaced with reducing gas D (high-purity hydrogen); and the pre-activation and dynamic gas injection steps are omitted, with a one-time feeding, room temperature pressurization, and direct heating to 350°C.

[0056] Comparative Example 5: This comparative example simulates a high-pressure hydrothermal modification technology. The difference from Example 2 is that: instead of an organic solvent, 200g of deionized water is used instead of the mixed solvent M1 in the reaction medium; and a one-time feeding method is employed, followed by pressurization at room temperature and direct heating to 350°C. During the reaction, the peak pressure must be carefully recorded.

[0057] Test Examples 1-4: Test Example 1: Experimental description: This test case aims to verify whether the modified coal products prepared by Examples 1, 2 and 3 have binding properties and to determine their solid product yield.

[0058] Adhesion index (G-value) test: Approximately 1.0 g each of untreated long-flame coal and the dried modified coal products obtained in Examples 1, 2, and 3 were taken. The samples were tested according to the national standard GB / T5447-2014, "Determination of Caking Index of Bituminous Coal". The samples were placed in a metallurgical crucible and heated to a final temperature of 600°C under a specified temperature program. After the crucible cooled to room temperature, the coke residue was removed, and its appearance was compared with a standard spectrum to determine the caking index (G value) of the sample.

[0059] Calculation of modified coal yield: Modified coal yield is defined as the percentage of the final mass of dried modified coal product to the mass of the initial coal sample on a dry ash-free (daf) basis. The calculation formula is as follows: Yield (%) % in: To ensure the quality of the modified coal products after drying; The total mass of the water-bearing coal sample input; The moisture content of the coal sample received; The ash content is the received basis of the coal sample.

[0060] Experimental data: Table 1. Results of caking index and yield tests of modified coal products from the examples. Note: '-' in the table indicates that it is not applicable.

[0061] in conclusion: Test results show that long-flame coal, initially lacking any caking properties (G=0), achieved caking indices of 68, 86, and 79 respectively after treatment using the methods described in Examples 1, 2, and 3 of this invention, all demonstrating excellent caking performance. This directly proves the feasibility of this technical solution.

[0062] The core mechanism of this scheme lies in constructing a reaction system under mild pressure conditions, where active hydrogen generated in situ from a liquid-phase hydrogen-supplying solvent and a gas-phase active hydrogen interacts synergistically. The pre-activation step of the catalyst and solvent prepares a highly active catalytic center for the subsequent water-gas shift reaction (WGSR). When the reaction enters the critical temperature range where coal pyrolysis generates a large number of free radicals, the dynamically injected reducing gas (CO) undergoes WGSR under the combined action of the catalyst and water in the coal, producing a high concentration of active hydrogen. This in-situ generated active hydrogen, together with the hydrogen provided by the solvent, rapidly and efficiently capsulates and stabilizes the free radical fragments generated by coal pyrolysis, inhibiting the irreversible reaction that leads to their condensation and formation of large molecular coke, thereby promoting the generation and retention of the mesophase component (asphaltite) with flow and binding capabilities.

[0063] The data in Table 1 further confirm that this method can stably achieve viscosity enhancement and modification of low-rank coal. The differences in the viscosity index and yield among the various examples reflect the influence of different combinations of parameters such as reaction temperature, pressure, solvent type, and catalyst on the balance between coal depolymerization, hydrogenation stabilization, and secondary cracking, indicating that the process has the ability to be controlled within a specific parameter range.

[0064] Test Example 2: Experimental description: This test example aims to evaluate the contributions of the catalyst and solvent pre-activation steps and the gas injection step to the modification effect of low-rank coal through comparative experiments. The test subjects are the products prepared in Example 2, and the products prepared in Comparative Examples 1, 2, and 3, which omitted one or two of the above key steps. The bonding index (G value) test method follows the GB / T5447-2014 standard, and the modified coal yield is calculated using the same method as in Test Example 1.

[0065] Experimental data: Table 2. Comparative test results of the impact of key technical steps on the modification effect Note: '-' in the table indicates that it is not applicable.

[0066] in conclusion: The data from this set of comparative experiments clearly demonstrate the necessity of each key step in this invention.

[0067] Comparing the results of Example 2 (G=86) and Comparative Example 1 (G=35), it can be seen that the caking index of the modified coal decreased significantly after the catalyst and solvent pre-activation step was omitted. The mechanism is that the pre-activation step provides the necessary environment for the catalyst precursor (Fe2O3) to be converted into a highly active phase (such as ferrous sulfide) in situ under mild conditions. Without this step, the catalyst activity is insufficient in the main reaction stage, resulting in low efficiency of the water-gas shift reaction (WGSR) and an inability to generate a sufficient concentration of active hydrogen to stabilize coal pyrolysis free radicals, thus hindering the formation of caking components.

[0068] Comparative Example 2 (G=15) omitted both the pre-activation and dynamic gas injection steps, and its adhesion index was the lowest among all comparisons, approaching the unmodified state. This demonstrates a synergistic effect between the two core technical steps of this invention, which together constitute the integrity and advancement of the technical solution of this invention and are necessary conditions for achieving efficient adhesion enhancement of low-rank coal.

[0069] Test Example 3: Experimental description: This test example aims to verify the necessity of the gas-liquid dual hydrogen source synergistic system in this invention. The test compares and analyzes the difference in adhesion of the products obtained under a complete reaction system (Example 2) and a system with only liquid phase hydrogen supply (Comparative Example 3). The adhesion index (G value) test method follows the GB / T5447-2014 standard, and the modified coal yield is calculated using the same method as in Test Example 1.

[0070] Experimental data: Table 3. Comparative test results of the influence of hydrogen source system on modification effect Note: '-' in the table indicates that it is not applicable.

[0071] in conclusion: The experimental data confirm the necessity of the synergistic effect of gas and liquid dual hydrogen sources.

[0072] Example 2, under the combined effect of a liquid-phase hydrogen-supplying solvent and a gas-phase reducing atmosphere, achieved a adhesion index as high as 86. In contrast, Comparative Example 3, under conditions of only a liquid-phase hydrogen-supplying solvent and no gas-phase active hydrogen source (using inert gas N2 instead), produced an adhesion index of only 41, far lower than the result of Example 2.

[0073] The mechanism of this phenomenon lies in the fact that hydrogen is supplied through two pathways in the reaction system constructed in this invention. The liquid-phase hydrogen-supplying solvent, as the basic hydrogen source, can provide a portion of active hydrogen. However, relying solely on solvent-supplyed hydrogen has limited capacity and activity, insufficient to saturate and stabilize the large number of free radicals generated during the intense coal pyrolysis phase. The core of this invention is to dynamically inject reducing gas (CO) in stages, utilizing the inherent moisture in the coal to undergo an in-situ water-gas shift reaction under the action of a catalyst, generating high-concentration, highly active gaseous hydrogen. This portion of active hydrogen synergistically with the solvent-supplyed hydrogen, efficiently capturing and capping free radicals from coal pyrolysis, thereby maximally inhibiting their agglomeration into coke and promoting the formation and retention of binding components such as asphaltene.

[0074] The results of Comparative Example 3 show that while solvent-based hydrogen supply can achieve a certain degree of viscosity enhancement, the effect is limited. Only when gas and liquid hydrogen sources work synergistically can a fundamental improvement in the caking properties of low-rank coal be achieved under mild conditions. Therefore, the introduction of a gas-phase reducing atmosphere is the key to achieving excellent modification results in this technical solution.

[0075] Test Example 4: Experimental description: This test example aims to compare the technical effects and process conditions of the present invention with two representative prior art technologies (high-cost hydrogenation technology and high-pressure hydrothermal technology). The test subjects are the product prepared in Example 2, and the products prepared in Comparative Examples 4 and 5, which simulate prior art technologies. Evaluation indicators include the adhesion index, modified coal yield, and peak pressure during the reaction process. The adhesion index was tested according to GB / T5447-2014 standard, the modified coal yield was calculated using the same method as in Test Example 1, and the peak reaction pressure was recorded by a pressure sensor equipped in the reactor during the isothermal reaction stage.

[0076] Experimental data: Table 4. Comparison of the modification effects and process conditions between the present invention and existing technologies. Note: '-' in the table indicates that it is not applicable.

[0077] in conclusion: Based on the data in Table 4, this invention demonstrates significant advantages in terms of process conditions and economic efficiency compared to the two existing technical routes for achieving viscosity enhancement and modification of low-rank coal.

[0078] Comparing Example 2 and Comparative Example 4 (simulating high-cost hydrogenation technology), both achieved excellent adhesion indices (G values ​​of 86 and 90, respectively), demonstrating that the modification effect of this invention is comparable to high-specification hydrogenation technology. However, the advantage of this invention lies in the economy and mildness of its process. Example 2 uses inexpensive syngas (H2 / CO) as the gaseous hydrogen source, while Comparative Example 4 uses high-cost, high-purity hydrogen; at the same time, the reaction pressure of Example 2 (8.8 MPa) is significantly lower than that of Comparative Example 4 (12.5 MPa).

[0079] Compared with Example 2 and Comparative Example 5 (simulated high-pressure hydrothermal technology), the advantages of this invention are more prominent. The adhesion index (G=86) of the product of Example 2 is much higher than that of the product of Comparative Example 5 (G=5), indicating that in a pure hydrothermal system lacking an organic hydrogen-donating solvent, the pyrolysis radicals of coal cannot be effectively stabilized, but instead undergo violent secondary condensation, thus losing their adhesion. More importantly, the process conditions are different. The peak reaction pressure of Example 2 is maintained below 10 MPa (8.8 MPa), while the peak pressure of Comparative Example 5, due to the supercritical behavior of water, reaches as high as 23.7 MPa. Such high pressure places extremely stringent requirements on the reaction equipment, leading to a sharp increase in investment costs and operational risks.

[0080] Therefore, this invention, by constructing a gas-liquid dual-hydrogen source synergistic system and combining key steps such as catalyst pre-activation and staged dynamic gas injection, successfully solves the problem of balancing cost and effect (as in Comparative Example 4) or pressure and effect (as in Comparative Example 5) in existing technologies. This solution can achieve highly efficient improvement in the caking properties of low-rank coal while significantly reducing operating pressure and raw material costs, providing a technically feasible and economically reasonable approach for the resource utilization of low-rank coal.

Claims

1. A method for mild modification and thickening of low-rank coal based on reducing gas and organic solvent, characterized in that, Includes the following steps: S1. Mix the organic solvent with the catalyst and perform pre-activation treatment under a reducing gas atmosphere to obtain a pre-activated system, wherein the mass ratio of the organic solvent to the catalyst is 28-700:

1. S2. After cooling the obtained pre-activated system, add low-rank coal powder with a water content of 3.0-35.0 wt% and mix evenly to prepare a mixed system, wherein the mass ratio of organic solvent to low-rank coal powder in the pre-activated system is 0.8-1.5:1; S3. The prepared mixed system is subjected to a hydrogenation reaction under the reducing gas atmosphere to obtain a liquid-solid mixture; S4. The liquid-solid mixture is cooled, separated, and dried to obtain the modified coal product.

2. The method for mild modification and thickening of low-rank coal based on reducing gas and organic solvent according to claim 1, characterized in that, In step S1, the pre-activation treatment includes: The product of the mixture of the organic solvent and the catalyst is heated to 200-250°C and reacted at a constant temperature for 15-30 minutes to obtain the pre-activated system.

3. The method for mild modification and thickening of low-rank coal based on reducing gas and organic solvent according to claim 1, characterized in that, In step S3, the heating and hydrogenation reaction includes: The reducing gas is introduced into the reaction system at the initial temperature until the initial pressure reaches 4.0-6.0 MPa; then the temperature is raised to the final reaction temperature of 330-390℃ and kept at the temperature for 30-90 minutes to obtain the liquid-solid mixture.

4. The method for mild modification and thickening of low-rank coal based on reducing gas and organic solvent according to claim 1, characterized in that, The organic solvent is any one or more of Shenhua coal liquefaction crude oil, 1-methylnaphthalene, tetrahydronaphthalene, and naphthalene that are mixed together to form a solvent.

5. The method for mild modification and thickening of low-rank coal based on reducing gas and organic solvent according to claim 4, characterized in that, When the organic solvent is a mixed solvent formed by two solvents, the mixed solvent is prepared by mixing the tetrahydronaphthalene and the 1-methylnaphthalene at a mass ratio of 0.9-1.1:1, or the mixed solvent is prepared by mixing the Shenhua coal liquefaction crude oil and the naphthalene at a mass ratio of 3.8-4.2:

1.

6. The method for mild modification and thickening of low-rank coal based on reducing gas and organic solvent according to claim 1, characterized in that, The catalyst is any one of copper oxide, ferric oxide, ferric oxide, or red mud.

7. The method for mild modification and thickening of low-rank coal based on reducing gas and organic solvent according to claim 6, characterized in that, When the catalyst is ferric oxide, the pre-activation treatment step further includes adding sulfur as an auxiliary agent, and the atomic ratio of iron atoms in ferric oxide to sulfur atoms in sulfur is 0.9-1.1:

1.

8. The method for mild modification and thickening of low-rank coal based on reducing gas and organic solvent according to claim 1, characterized in that, The reducing gas is any one of carbon monoxide, hydrogen, the synthesis gas of carbon monoxide and hydrogen, coke oven gas, or gasified coal gas. When the reducing gas is the synthesis gas, the volume ratio of hydrogen to carbon monoxide is 0.2-4:

1.

9. The method for mild modification and thickening of low-rank coal based on reducing gas and organic solvent according to claim 1, characterized in that, The low-rank coal powder is any one of long-flame coal powder, lignite coal powder, non-caking coal powder, and gas-flame coal powder, and the particle size of the low-rank coal powder is 80-200 mesh.

10. The method for mild modification and thickening of low-rank coal based on reducing gas and organic solvent according to claim 1, characterized in that, The amount of catalyst used is 0.2-6 wt% of the dry, ash-free mass of the low-rank coal powder.

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