Method for low-temperature pyrolysis and oxidation pretreatment to strengthen lignite fractional depolymerization

Abstract

This invention relates to a method for enhancing the graded depolymerization of lignite through low-temperature pyrolysis and oxidative pretreatment, comprising the following steps: weighing lignite and placing it in a low-temperature pyrolysis system, introducing inert gas, and pretreating it to the low-temperature pyrolysis temperature; after pyrolysis is completed, allowing it to cool naturally to room temperature, and collecting the semi-coke in the system; adding the semi-coke, oxidant, oxidizing agent, additive, and solvent to the system, and performing oxidative pretreatment at room temperature and in an air atmosphere, filtering to obtain residue; adding the residue and solvent to the system, and introducing inert gas to carry out a thermal dissolution polymerization reaction; after the reaction is completed, cooling the system to room temperature, collecting the gas in the system, and filtering to separate the solid residue and soluble matter. This method regulates the physicochemical structure of lignite through a low-temperature pyrolysis pretreatment process and weakens strong ether bonds using a mild oxidative pretreatment method, thereby increasing the yield of lignite depolymerization products and enhancing the process of obtaining chemicals through graded depolymerization of lignite.

Description

Technical Field

[0001] This invention relates to the field of comprehensive utilization technology of lignite, specifically to a method for enhancing the graded deagglomeration of lignite through low-temperature pyrolysis and oxidation pretreatment. Background Technology

[0002] Coal, as the world's most abundant fossil fuel, is receiving increasing attention for its efficient and clean utilization. Lignite, as the least coalified type of coal, accounts for approximately 40% of the world's proven geological reserves. In my country, lignite reserves account for about 13% of the country's total coal reserves, giving it a significant resource advantage. However, as a low-rank coal, lignite's high moisture content, high ash content, and complex molecular structure result in low efficiency and environmental pollution from direct combustion. In recent years, with the advancement of the "dual carbon" target (carbon reduction and emission reduction), exploring the clean and efficient utilization of lignite has become an important research direction in the energy and chemical industry. Therefore, developing a lignite graded deagglomeration method based on its composition and structural characteristics can further optimize the lignite graded deagglomeration process, explore high-value utilization pathways for deagglomeration products, and simultaneously achieve process optimization and product value enhancement, providing a new path for the clean conversion of lignite.

[0003] According to the subject-guest model, lignite organic matter is composed of a three-dimensional network of covalently cross-linked aromatic rings and guest small molecules embedded by non-covalent forces. This complex structure leads to fundamental limitations in traditional utilization technologies. While traditional processes such as drying and upgrading, and direct liquefaction can optimize combustion efficiency or conversion effects to some extent, they still suffer from common problems that are difficult to overcome, severely restricting the efficient utilization of lignite resources. In practical applications, the products produced by these traditional technologies generally have low added value, failing to fully exploit the economic value of lignite. Therefore, based on the differences in the breaking energy of different chemical bonds in the lignite molecular structure, a multi-stage, gradient, and mild reaction condition is used to gradually decompose the large molecules of lignite into smaller molecule compounds. This approach maximizes the preservation of high-value components in lignite while avoiding product degradation caused by over-reaction in traditional processes, opening a new path for the conversion of lignite into clean fuels and high-value-added chemicals. To achieve this objective, this invention selects low-rank lignite as the research object. Starting from the composition and structural characteristics of lignite, it first employs low-temperature pyrolysis with simultaneous dehydration and pore structure regulation to inhibit condensation reactions and promote organic matter dissolution. Then, it uses oxidative pretreatment to target and break stubborn aromatic ether bonds in the pyrolyzed residue, enhancing subsequent catalytic hydrocracking. This synergistic process avoids product degradation, maximizes the retention of light oils and phenolic chemicals, and overcomes the technical limitations of lignite staged depolymerization conversion rate and selectivity. Summary of the Invention

[0004] To address the aforementioned technical shortcomings, this invention provides a method for enhancing the graded depolymerization of lignite through low-temperature pyrolysis and oxidative pretreatment. This method addresses the issues of easy condensation during the dissolution of soluble organic matter in lignite and the difficulty in breaking oxygen-containing bonds. It regulates the physicochemical structure of lignite through a low-temperature pyrolysis pretreatment process and weakens strong ether bonds using a mild oxidative pretreatment method, thereby increasing the yield of lignite depolymerization products and enhancing the process of obtaining chemicals through graded depolymerization of lignite.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] The present invention provides a method for enhancing the graded deagglomeration of lignite through low-temperature pyrolysis and oxidative pretreatment, comprising the following steps:

[0007] (1) Low-temperature pyrolysis: Weigh lignite and place it in the low-temperature pyrolysis reaction system. Connect the tar and gas collection devices, purge with inert gas, set the heating program and holding time of the reaction system, heat to the low-temperature pyrolysis temperature for pyrolysis pretreatment, and allow it to cool naturally to room temperature after pyrolysis is terminated. Collect the semi-coke in the reaction system and record it as Char- T ;

[0008] (2) Oxidation pretreatment: The semi-coke Char- obtained in step (1) is subjected to oxidation pretreatment. T The oxidant, oxidizing agent, additive, and reaction solvent are added to the oxidation reaction system, and oxidation pretreatment is carried out at room temperature and in air atmosphere. The oxidation pretreatment residue is obtained by filtration and separation, and is denoted as Char-oxid.

[0009] (3) Thermal dissolution polymerization: Add the Char-oxid and thermal dissolution reaction solvent from step (2) into the thermal dissolution reaction system, introduce inert gas, and set the heating rate and reaction time of the reaction system to carry out the thermal dissolution polymerization reaction;

[0010] (4) Post-processing: After the reaction in step (3) is completed, the reaction system is cooled to room temperature, the gas in the reaction system is collected, and the solid residue and soluble matter are separated by filtration.

[0011] Further, in step (1), the lignite is one of Zhaotong lignite, Inner Mongolia East lignite, Shengli lignite and Xilingol lignite; the reaction system is a ceramic boat placed in a tube furnace, and the reaction system is connected to a tar and gas collection device; the inert gas is nitrogen, the gas purging time is 10~30 min, the gas flow rate is 50-100 mL / min, the tube furnace heating rate is 1~20 ℃ / min, and the holding time is 10~120 min.

[0012] Further, in step (1), after the low-temperature pyrolysis reaction is completed, the pyrolysis gas is detected by gas chromatography, the collected tar is dried with anhydrous magnesium sulfate to remove the solvent and the tar mass is calculated, and the yield of pyrolysis products is calculated by the difference method, wherein the mass ratio of the added anhydrous magnesium sulfate to the tar mass is 1:1 to 20:1.

[0013] Further, in step (1), the low-temperature pyrolysis temperature is 200-320 ℃.

[0014] Further, in step (2), the reaction solvent is at least one of dichloromethane, dichloroethane, or trichloromethane; the oxidant is at least one of Fe(NO3)3·9H2O, Fe(NO3)3·6H2O, Co(NO3)3·6H2O, Mn(NO3)2·4H2O, or Cu(NO3)3·3H2O; the oxidizing aid is one of tetramethylpiperidine oxide or N-hydroxyphthalimide; and the additive is one of KCl, NaCl, FeCl3, or KBr.

[0015] Further, in step (2), the semi-focal Char- T The mass-to-volume ratio of the oxidant to the reaction solvent is 1:5 to 1:50 g / mL; the mass-to-volume ratio of the oxidant to the reaction solvent is 1:30 to 1:100 g / mL; the mass-to-volume ratio of the oxidizing agent to the reaction solvent is 1:200 to 1:600 ​​g / mL; the mass-to-volume ratio of the additive to the reaction solvent is 1:500 to 1:1100 g / mL; the stirring speed is set to 200 to 500 rpm / min; the reaction conditions are room temperature; and the reaction time is 4 to 8 h.

[0016] Further, in step (3), the mass ratio of the reactant Char-oxid to the reaction solvent is 1:50~1:100; the temperature of the reaction vessel is 200~450 ℃, the heating rate is 2~10 ℃ / min, and the holding time is 1~4 h.

[0017] Further, in step (3), the inert gas is nitrogen, which replaces the air in the reaction system, and then 0.5~1.0 MPa of nitrogen is introduced.

[0018] Furthermore, in step (3), the thermal reaction solvent is toluene and methanol, and the volume ratio of the two is 1:1.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] (1) Based on the composition and structural characteristics of lignite, this invention regulates the physicochemical structure of lignite during drying and dehydration through low-temperature pyrolysis pretreatment, improves the connectivity and porosity of pores in lignite, reduces the association between hydroxyl groups in lignite, thereby promoting the dissolution of soluble organic matter in lignite and reducing the condensation of heat-soluble substances.

[0021] (2) Based on low-temperature pyrolysis, this invention uses the typical model compound 2-phenoxy-1-phenylethanol in lignite to screen out the optimal oxidation reaction conditions, and performs oxidative pretreatment on lignite or lignite pyrolysis semi-coke under the optimal oxidation conditions, thereby realizing the morphological transfer or breakage of strong aromatic ether bonds in lignite or lignite pyrolysis semi-coke, and thus strengthening the thermal dissolution and upgrading process of lignite macromolecular structure.

[0022] (3) Based on low-temperature and oxidative pyrolysis pretreatment, this invention enhances the graded depolymerization of lignite through low-temperature pyrolysis and oxidative pretreatment, and performs thermal dissolution polymerization on the residue after lignite pyrolysis-oxidative pretreatment. Compared with the results of direct thermal dissolution of raw coal, the yield of soluble matter in the graded thermal dissolution product is increased to 45.09%, light oil to 19.72%, and heavy component yield to 25.37%. Attached Figure Description

[0023] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a distribution diagram of the oxidation products of 2-phenoxy-1-phenylethanol under different oxidation pretreatment times in Example 1 of the present invention;

[0025] Figure 2 This is a distribution diagram of the products of the oxidation reaction of 2-phenoxy-1-phenylethanol using dichloromethane as the oxidation reaction solvent in Example 2 of the present invention;

[0026] Figure 3 This is a distribution diagram of the oxidation reaction products of 2-phenoxy-1-phenylethanol when NaCl is used as the additive in Example 3 of the present invention;

[0027] Figure 4 This is a distribution diagram of the oxidation reaction products of 2-phenoxy-1-phenylethanol when FeCl3 is used as the additive in Example 3 of the present invention;

[0028] Figure 5 The distribution diagrams of low-temperature pyrolysis products of Zhaotong lignite at different low-temperature pyrolysis temperatures in Examples 4-10 of this invention are shown.

[0029] Figure 6 The diagram shows the distribution of group components in the low-temperature pyrolysis tar of Zhaotong lignite in Examples 4 and 9-10 of this invention.

[0030] Figure 7 Char, the semi-coke product obtained from the low-temperature pyrolysis of Zhaotong lignite at 280 ℃ in Example 4 of this invention. -280 ℃ SEM image;

[0031] Figure 8 Char is the semi-coke product obtained by low-temperature pyrolysis of different lignites at 280 °C in Examples 11-13 of this invention. -280 ℃ Distribution;

[0032] Figure 9 This is a distribution diagram of depolymerization products of Zhaotong lignite under different thermal dissolution pretreatment conditions in Examples 4 and Comparative Examples 14-15 of the present invention. Detailed Implementation

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The following examples are provided to better understand the present invention and are not intended to limit the preferred embodiments. They do not constitute a limitation on the content and scope of protection of the present invention. Any product identical or similar to the present invention derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art falls within the protection scope of the present invention.

[0034] For experiments not specifically described in the examples, conventional experimental procedures or conditions as described in the literature in this field can be followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0035] Example 1: Oxidation of 2-phenoxy-1-phenylethanol at different reaction times

[0036] 100 mg of 2-phenoxy-1-phenylethanol (PPE-ol), a typical model compound of lignite, 20 mg of oxidant Fe(NO3)3·9H2O, 70 mg of oxidizing agent tetramethylpiperidine oxide, 4 mg of additive KCl, and 4 mL of chloroform, an oxidation reaction solvent, were added to a three-necked flask equipped with a stirrer. The reaction was carried out under air atmosphere at room temperature for 2 h, 4 h, 5 h, and 6 h, respectively. During the reaction, samples were taken for analysis at intervals of 0.5–2 h.

[0037] Figure 1The conversion rate and product yield of PPE-ol under the above oxidation reaction conditions at different reaction times are shown. With the extension of oxidation pretreatment time, the content of PPE-ol decreased significantly, while the content of 2-phenoxy-1-acetophenone (POP) increased significantly, indicating that C... α -OH is gradually oxidized to C. α =O. Furthermore, the results in the figure show that the selectivity of POP remained at 100%, indicating that the oxidant can selectively oxidize C in PPE-ol. α -OH.

[0038] Example 2: Oxidation of 2-phenoxy-1-phenylethanol under different oxidation reaction solvent conditions

[0039] The difference from Example 1 is that the "oxidation reaction solvent chloroform" in the reaction process is replaced with "oxidation reaction solvent dichloromethane" to explore the effect of oxidative pretreatment of 2-phenoxy-1-phenylethanol in different oxidation reaction solvents.

[0040] Figure 2 The distribution of oxidation products of PPE-ol in dichloromethane at different reaction times is shown. The results indicate that, under the same reaction conditions, using dichloromethane as the solvent, although the selectivity for product POP reaches 100%, the conversion rate of PPE-ol is low, with a yield of only 69.13% after 10 h of reaction. In contrast, PPE-ol can be completely converted in trichloromethane under the same conditions.

[0041] Example 3: Oxidation of 2-phenoxy-1-phenylethanol under different additive conditions

[0042] The difference from Example 1 is that the "additive KCl" in the reaction process was replaced with "additive NaCl" and "additive FeCl3" to explore the effect of oxidative pretreatment of 2-phenoxy-1-phenylethanol under additive conditions.

[0043] Figure 3 When NaCl was used as an additive, the conversion rate of PPE-ol was low in the first 4 hours. After the reaction time was extended to 10 hours, PPE-ol was completely converted into POP. Figure 4 When FeCl3 was used as an additive, the conversion of PPE-ol was improved in the first 4 hours, but the conversion rate stabilized after 6 hours, and after 10 hours, PPE-ol could not be completely converted. + The ionic radius is greater than that of Na +Its weaker Lewis acidity avoids the inhibition of reactivity by excessive coordination, while the concentration of Cl⁻ is moderate, participating in the oxidation cycle without hindering the formation of reactive oxygen species. In summary, NaCl requires a longer conversion time due to its slower reaction kinetics, while FeCl₃ contains Fe 3+ The strong coordination of Cl can easily deactivate the intermediate, and excessive Cl can also cause this. - This may cause the reaction to terminate prematurely, thus halting the conversion. In contrast, KCl oxidation pretreatment is the most effective additive.

[0044] Example 4: Low-temperature pyrolysis and oxidation pretreatment to enhance the graded deagglomeration process of lignite

[0045] (1) Weigh 5000 mg of Zhaotong lignite and place it in a porcelain boat. Place the porcelain boat containing the lignite in a tubular furnace and connect it to a tar and gas collection device.

[0046] (2) Purge with inert gas for 30 min, stabilize the carrier gas flow rate at 80 mL / min, raise the temperature of the tube furnace to 280 ℃ at a heating rate of 10 ℃ / min, and hold for 30 min.

[0047] (3) After the low-temperature pyrolysis is terminated, the mixture is allowed to cool naturally to room temperature, and the semi-coke collected in the tubular furnace is recorded as Char. -280 ℃ The yield was calculated; the gaseous products were collected directly through an aluminum foil composite gas bag, while the liquid products were absorbed and captured by hexane solvent in a -15 ℃ low-temperature cold trap.

[0048] (4) Based on the optimal oxidation pretreatment reaction conditions obtained from the typical model compounds of lignite in Examples 1-3 above, 500 mg of pyrolysis semi-coke Char was added. -280 101 mg of oxidant Fe(NO3)3·9H2O, 39 mg of oxidizing agent tetramethylpiperidine oxide, 18 mg of additive KCl and 10 mL of oxidation reaction solvent chloroform were added to a three-necked flask and subjected to oxidation pretreatment for 6 h at room temperature and air atmosphere. The low-temperature pyrolysis-oxidation pretreatment residue was obtained by filtration and separation and was denoted as Char-oxid.

[0049] (5) Add 500 mg of Char-oxid and 20 mL of hot-dissolving reaction solvent to a high-pressure reactor. Replace the air in the reactor with nitrogen. Repeat the replacement three times. Then fill with 0.5~1.0 MPa of nitrogen. Set the reactor heating rate to 5 ℃ / min, the hot dissolving polymerization reaction temperature to 320 ℃, and the reaction time to 2 h.

[0050] (6) After the reaction is complete, cool the reactor to room temperature, collect the gas inside the reactor, filter to separate the solid residue and soluble matter (SP), extract the soluble matter with n-hexane to obtain oil and heavy components (AS+PAS), and calculate the yield of each component according to the following formula:

[0051] Y sp = W sp / (1-A d ) / M

[0052] Y oil = W oil / (1-A d ) / M

[0053] Y AS+PAS = W AS+PAS / (1-A d ) / M

[0054] In the formula A d The ash content is ZT dry basis, M is the mass of raw coal, and W is... SP For the mass of soluble matter, W oil For the quality of the oil, W AS+PAS This represents the mass of the heavier component in the soluble substance.

[0055] Example 5: Low-temperature pyrolysis pretreatment of Zhaotong lignite at 200 °C

[0056] The difference from Example 4 is that in step (2), "raising the temperature of the tubular furnace to 280 ℃" is replaced with "raising the temperature of the tubular furnace to 200 ℃ respectively", and the semi-coke collected in the tubular furnace is recorded as Char. -200 ℃ .

[0057] Example 6: Low-temperature pyrolysis pretreatment of Zhaotong lignite at 220 °C

[0058] The difference from Example 4 is that in step (2), "raising the temperature of the tubular furnace to 280 ℃" is replaced with "raising the temperature of the tubular furnace to 220 ℃ respectively", and the semi-coke collected in the tubular furnace is recorded as Char. -220 ℃ .

[0059] Example 7: Low-temperature pyrolysis pretreatment of Zhaotong lignite at 240 °C

[0060] The difference from Example 4 is that in step (2), "raising the temperature of the tubular furnace to 280 ℃" is replaced with "raising the temperature of the tubular furnace to 240 ℃ respectively", and the semi-coke collected in the tubular furnace is recorded as Char. -240 ℃ .

[0061] Example 8: Low-temperature pyrolysis pretreatment of Zhaotong lignite at 260 °C

[0062] The difference from Example 4 is that in step (2), "raising the temperature of the tubular furnace to 280 ℃" is replaced with "raising the temperature of the tubular furnace to 260 ℃ respectively", and the semi-coke collected in the tubular furnace is recorded as Char. -260 ℃ .

[0063] Example 9: Low-temperature pyrolysis pretreatment of Zhaotong lignite at 300 ℃

[0064] The difference from Example 4 is that in step (2), "raising the temperature of the tubular furnace to 280 ℃" is replaced with "raising the temperature of the tubular furnace to 300 ℃ respectively", and the semi-coke collected in the tubular furnace is recorded as Char. -300 ℃ .

[0065] Example 10: Low-temperature pyrolysis pretreatment of Zhaotong lignite at 320 °C

[0066] The difference from Example 4 is that in step (2), "raising the temperature of the tubular furnace to 280 ℃" is replaced with "raising the temperature of the tubular furnace to 320 ℃ respectively", and the semi-coke collected in the tubular furnace is recorded as Char. -320 ℃ .

[0067] Figure 5 Char- products of Zhaotong lignite at different low-temperature pyrolysis temperatures T Distribution map. Within the temperature range of 280–320 °C, the pyrolysis behavior of Zhaotong lignite exhibits a significant temperature dependence. Within this temperature range, the reaction can better preserve the integrity of the coal's structure while improving its reactivity, increasing product yield during thermal dissolution, and regulating the conversion process of thermally dissolved products. When the low-temperature pyrolysis temperature is below 280 °C, the provided heat is insufficient to destroy the cross-linked and associated structures formed by non-covalent bonds such as hydrogen bonds in the coal molecules, preventing the effective release of small-molecule volatile components; therefore, tar and gases are almost undetectable. When the low-temperature pyrolysis temperature is increased to 280 °C, the tar yield is only 0.18%; after increasing to 320 °C, the tar yield significantly increases to 6.61%, indicating that the degree of cracking in lignite deepens under high-temperature conditions, organic matter is released, and the coal's structure is destroyed.

[0068] Figure 6 This is a distribution map of the group components in the low-temperature pyrolysis tar of Zhaotong lignite. The changes in tar composition show that at a pyrolysis temperature of 280 ℃, the relative contents of cycloalkanes and alkanes are relatively high, indicating that the aliphatic structures in the lignite preferentially crack at this temperature, mainly generating saturated hydrocarbons. When the pyrolysis temperature increases to 320 ℃, the relative contents of phenolic compounds and aromatic compounds significantly increase, while the relative contents of cycloalkanes and straight-chain alkanes decrease accordingly. This indicates that increasing the pyrolysis temperature leads to the cracking of aromatic structures in the lignite, generating more phenolic and aromatic compounds; simultaneously, saturated hydrocarbons may further crack or transform into other types of compounds at high temperatures.

[0069] Figure 7 Char is a semi-coke product obtained from the low-temperature pyrolysis of Zhaotong lignite at 280 ℃. -280 ℃ SEM image. From Figure 7 As can be seen, the microstructure of the semi-coke undergoes significant loosening, with a well-developed, interconnected porous network of varying pore sizes forming on the surface. This structure facilitates more effective solvent penetration into the coal matrix, improving the leaching efficiency of soluble substances.

[0070] Example 11: Low-temperature pyrolysis pretreatment of lignite from eastern Inner Mongolia

[0071] The method is the same as in Example 4, except that the pyrolysis coal sample is lignite from eastern Inner Mongolia.

[0072] Example 12: Low-temperature pyrolysis pretreatment of Shengli lignite

[0073] The method is the same as in Example 4, except that the pyrolysis coal sample is Shengli lignite.

[0074] Example 13: Low-temperature pyrolysis pretreatment of Xilingol lignite

[0075] The method is the same as in Example 4, except that the pyrolysis coal sample is Xilingol lignite.

[0076] Table 1 presents the industrial analysis results of lignite from eastern Inner Mongolia, Shengli, and Xilingol. Figure 8 Char, a semi-coke product obtained from the low-temperature pyrolysis of different lignites at 280 °C -280 ℃ The distribution of lignite products is as follows: Since the H / C ratio and volatile matter content of lignite from Inner Mongolia East, Shengli and Xilingol are lower than those of lignite, the tar yield during pyrolysis is lower. However, the semi-coke yield of the three types of lignite shows a trend that is basically consistent with that of Zhaotong lignite, indicating that the effect of pyrolysis pretreatment temperature on the distribution of lignite pyrolysis products is universal.

[0077] Table 1. Industrial and elemental analysis of lignite.

[0078]

[0079] Comparative Example 1: Direct Depolymerization of Low-Temperature Pyrolysis Semi-Coke

[0080] Similar to the method in Example 4, the difference is that in step (6), the pre-treated semi-coke from low-temperature pyrolysis is weighed and added to a reaction vessel along with 20 mL of methanol and 20 mL of toluene for reaction at a temperature of 320 °C and a reaction time of 2 h.

[0081] Comparative Example 2: Direct Depolymerization of Zhaotong Lignite

[0082] Similar to the method in Example 4, the difference is that in step (6), Zhaotong lignite, 20 mL of methanol and 20 mL of toluene are weighed and added to the reaction vessel for reaction, with a reaction temperature of 320 °C and a reaction time of 2 h.

[0083] Figure 9 The distribution of deagglomeration products in Zhaotong lignite under different thermal pretreatment conditions is shown. Figure 9 The results show that the total yield of soluble matter in the thermally dissolved polymerized products of semi-coke is similar to that of direct thermal dissolution of raw coal, but the oil yield is increased. The total yield of soluble matter in the thermally dissolved polymerized products of semi-coke pretreated by low-temperature pyrolysis-oxidation synergistic pretreatment is significantly improved, which confirms that the two-step pretreatment synergistically enhances the efficient depolymerization of lignite by destroying the cross-linked structure in coal and enhancing solvent permeability.

[0084] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for enhancing the graded deagglomeration of lignite through low-temperature pyrolysis and oxidation pretreatment, characterized in that: Includes the following steps: (1) Low-temperature pyrolysis: Weigh lignite and place it in the low-temperature pyrolysis reaction system. Connect the tar and gas collection devices, purge with nitrogen, and set the heating rate and holding time of the low-temperature pyrolysis reaction system. Heat to the low-temperature pyrolysis temperature for pyrolysis pretreatment. After pyrolysis is terminated, allow it to cool naturally to room temperature. Collect the semi-coke in the reaction system and record it as Char- T The low-temperature pyrolysis temperature is 200~320℃; (2) Oxidation pretreatment: The semi-coke Char- obtained in step (1) is subjected to oxidation pretreatment. T An oxidizing agent, an oxidizing agent, an additive, and a reaction solvent are added to an oxidation reaction system. Oxidation pretreatment is performed at room temperature and in an air atmosphere. The pretreated residue is obtained by filtration and is denoted as Char-oxid. The reaction solvent is at least one of dichloromethane, dichloroethane, or trichloromethane. The oxidizing agent is at least one of Fe(NO3)3·9H2O, Fe(NO3)3·6H2O, Co(NO3)3·6H2O, Mn(NO3)2·4H2O, or Cu(NO3)2·3H2O. The oxidizing agent is one of tetramethylpiperidine oxide or N-hydroxyphthalimide. The additive is one of KCl, NaCl, FeCl3, or KBr. (3) Thermal dissolution polymerization: Add the Char-oxid and thermal dissolution reaction solvent from step (2) into the thermal dissolution reaction system, introduce nitrogen gas, and set the heating rate and reaction time of the reaction system to carry out the thermal dissolution polymerization reaction; (4) Post-processing: After the reaction in step (3) is completed, cool the reaction system to room temperature, collect the gas in the reaction system, and filter to separate the solid residue and soluble matter.

2. The method for enhancing the graded deagglomeration of lignite through low-temperature pyrolysis and oxidation pretreatment according to claim 1, characterized in that, In step (1), the lignite is one of Zhaotong lignite, Inner Mongolia lignite, Shengli lignite and Xilingol lignite; the low-temperature pyrolysis reaction system is a ceramic boat placed in a tubular furnace, and the reaction system is connected to a tar and gas collection device; the nitrogen purging time is 10~30 min, and the nitrogen flow rate is 50-100 mL / min.

3. The method for enhancing the graded deagglomeration of lignite through low-temperature pyrolysis and oxidation pretreatment according to claim 1, characterized in that: In step (1), after the low-temperature pyrolysis reaction is completed, the pyrolysis gas is detected by gas chromatography. The collected tar is dried with anhydrous magnesium sulfate to remove the solvent and the tar mass is calculated. The yield of the pyrolysis product is calculated by the difference method. The mass ratio of the added anhydrous magnesium sulfate to the tar mass is 1:1 to 20:

1.

4. The method for enhancing the graded deagglomeration of lignite through low-temperature pyrolysis and oxidation pretreatment according to claim 2, characterized in that: In step (1), the heating rate of the tubular furnace is 1~20 ℃ / min, and the holding time is 10~120 min.

5. The method for enhancing the graded deagglomeration of lignite through low-temperature pyrolysis and oxidation pretreatment according to claim 1, characterized in that: In step (2), the semi-focal Char- T The mass-to-volume ratio of the oxidant to the reaction solvent is 1:5 to 1:50 g / mL; the mass-to-volume ratio of the oxidant to the reaction solvent is 1:30 to 1:100 g / mL; the mass-to-volume ratio of the oxidizing agent to the reaction solvent is 1:200 to 1:600 ​​g / mL; the mass-to-volume ratio of the additive to the reaction solvent is 1:500 to 1:1100 g / mL; the oxidation pretreatment reaction conditions are room temperature and the reaction time is 4 to 8 h.

6. The method for enhancing the graded deagglomeration of lignite through low-temperature pyrolysis and oxidation pretreatment according to claim 1, characterized in that: In step (3), the mass ratio of Char-oxid to the hot-dissolving reaction solvent is 1:50~1:100 g / mL; the hot-dissolving polymerization temperature is 200~450 ℃, the heating rate is 2~10 ℃ / min, and the holding time is 1~4 h.

7. The method for enhancing the graded deagglomeration of lignite through low-temperature pyrolysis and oxidation pretreatment according to claim 1, characterized in that: In step (3), the air in the reaction system is replaced with nitrogen, and then 0.5~1.0 MPa of nitrogen is introduced.

8. The method for enhancing the graded deagglomeration of lignite through low-temperature pyrolysis and oxidation pretreatment according to claim 1, characterized in that: In step (3), the thermal reaction solvent is toluene and methanol, and the volume ratio of the two is 1:1.

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