Method for recovering residual heavy oil and asphalt components from coal liquefaction residues

Abstract

The invention provides a method for recovering residual heavy oil and asphalt components from coal liquefaction residues, and belongs to the technical field of coal liquefaction residue treatment. The method comprises the following steps: S1, mixing the coal liquefaction residues, a hot-melting solvent and a viscosity reducer, performing hot melting, and performing solid-liquid separation to obtain a hot-melting mixture and hot-melting residues; s2, condensing the hot-melt mixture to obtain a hot-melt substance and a recycled hot-melt solvent; s3, mixing the hot-melt residues, the hot-melt solvent and the viscosity reducer, repeating the operation processes of the step S1 and the step S2, and repeating the steps for a plurality of times; and S4, the hot melt residues finally obtained in the step S3 are dried and subjected to rapid pyrolysis, and residual heavy oil and asphalt components are recycled. According to the method, the pyrolysis strong cohesiveness of the liquefied residues is reduced through step-by-step hot melting treatment of the hot melting solvent and the viscosity reducer, part of heavy oil and asphalt substances are recycled, meanwhile, energy consumption in the solvent recycling process is reduced through the fractional condensation technology, and finally the recycling rate of the heavy oil and the asphalt substances is further increased through rapid pyrolysis of the hot melting residues.

Description

Technical Field

[0001] The invention belongs to the technical field of coal liquefaction residue treatment, and in particular relates to a method for recovering residual heavy oil and asphalt components from coal liquefaction residue. Background Art

[0002] Direct coal liquefaction is an important coal-to-liquids technology, crucial for promoting the clean and efficient use of coal and safeguarding my country's energy security. The direct coal liquefaction process produces a liquefaction residue comprising approximately 20-30% by weight of the raw coal, consisting of 50% liquefied heavy oil and asphalt-like substances, with the remainder consisting of unconverted coal, inorganic minerals, and liquefaction catalysts. The heavy oil and asphalt in the liquefaction residue are important raw materials for preparing high-end carbon materials and replenishing liquefied circulating oil. Extracting the heavy oil and asphalt from the liquefaction residue is crucial for improving the economic viability of direct coal liquefaction.

[0003] Pyrolysis is an important method for large-scale recovery of oil-containing components from liquefied residue. The strong adhesiveness of the liquefied residue during the pyrolysis process will affect the feed of raw materials in the continuous pyrolysis process, the flow of materials in the reactor, and the uniformity of heating. It is easy to coke in the reactor, affecting the stable operation of the production equipment, and at the same time reducing the recovery rate of the oil-containing components in the liquefied residue. Hot-melt extraction is another method for separating heavy oil and asphalt from liquefied residue. Currently, most of the refined asphalt and extractant are separated by flash evaporation, and the process energy consumption is relatively high. These factors have affected the large-scale clean and efficient conversion of liquefied residue. Therefore, reducing the thermal viscosity of the liquefied residue during the pyrolysis process, improving the recovery rate of heavy oil, and reducing the energy consumption of the extractant separation process are still technical problems that need to be solved urgently.

[0004] CN201713483U discloses a continuous coking device for coal liquefaction residue, which puts the coking furnace in a vacuum state so that the coal liquefaction residue is heated and coked under vacuum. A differential double-screw conveying device is provided in the coking furnace to facilitate the discharge of pyrolysis gas and semi-coke. However, the liquefied residue has a strong adhesiveness when in a molten state, which affects the uniformity of material heating, resulting in an increase in the polycondensation reaction of the residue and a decrease in the yield of oil-containing components. CN109385286A discloses a continuous pyrolysis device and method suitable for direct coal liquefaction residue, which is provided with a freely movable metal rod in a reaction chamber so that the semi-coke produced by the pyrolysis of the direct coal liquefaction residue can be crushed online under the impact of the freely moving metal rod, which is beneficial to the continuous pyrolysis of the direct coal liquefaction residue. This method still does not solve the adhesiveness of the liquefied residue under a heated state. The volatile matter generated by the liquefied residue forms a liquid-solid mixed state with the semi-coke, which will cause an increase in the polycondensation reaction of the residue and the material cannot be smoothly discharged from the pyrolysis furnace. The above method also faces the problem of low pyrolysis oil yield, and does not fully utilize the heavy oil and asphalt-like substances in the direct coal liquefaction residue. CN116376593A discloses a coal liquefaction residue solvent extraction deashing and refining system and method, which includes a slurry preparation tank, a pre-coating liquid preparation tank, a candle filter, a dryer, a filtrate storage tank and a flash tower. The candle filtration technology and the pre-coating technology are used to improve the extraction efficiency of the liquefied residue and reduce the viscosity of the extraction system. This method separates the refined asphalt and the extractant by flash evaporation, which increases the energy consumption of the process. CN101962560A and CN101962561A disclose a method for extracting heavy liquefied oil and asphalt-like substances from coal liquefaction residue using two-stage extraction. This method uses two different fractions of oil products produced by direct coal liquefaction itself to perform two-stage sequential extraction on the liquefied residue to obtain heavy liquefied oil and asphalt-like substances. This method recovers the extractant by distillation and evaporation, and separates the heavy liquefied oil and mesophase asphalt-like substances by heating and dry distilling the liquefied residue extract. This process has high energy consumption and is not conducive to improving the technical and economic performance of the liquefied residue extraction process. CN119614229A discloses a method for treating direct coal liquefaction residue extract. This method processes the direct coal liquefaction residue in sections by extraction and pyrolysis, distilling the extract filtrate to obtain asphalt, and pyrolysis the residue to obtain pyrolysis oil. This method recovers the extractant by distillation and evaporation, which increases the energy consumption of the process. At the same time, it does not involve improving the cohesiveness of the hot-melt residue, which is not conducive to solving the feeding and material flow problems in the thermal conversion process of the liquefied residue extract.

[0005] In view of this, this application is hereby filed. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for recovering residual heavy oil and asphalt components from coal liquefaction residue. The method reduces the strong adhesiveness of the liquefied residue during pyrolysis by using a hot-melt solvent and a viscosity reducer in a step-by-step hot-melt treatment, recovers part of the heavy oil and asphalt substances, and simultaneously utilizes a graded condensation process to reduce the energy consumption of the solvent recovery process. Finally, the recovery rate of heavy oil and asphalt substances is further improved by rapid pyrolysis of the hot-melt residue.

[0007] To achieve the above objectives, the present invention adopts the following specific technical solutions:

[0008] A method for recovering residual heavy oil and asphalt components from coal liquefaction residue comprises the following steps:

[0009] S1: Mixing coal liquefaction residue, hot-melt solvent and viscosity reducer, and then hot-melting, followed by solid-liquid separation to obtain hot-melt mixture and hot-melt residue;

[0010] S2: condensing the hot melt mixture to obtain a hot melt and recovering the hot melt solvent, obtaining hot melts with different molecular weights and structural components, and recycling the hot melt solvent;

[0011] S3: mixing the hot-melt residue, hot-melt solvent and viscosity reducing agent and repeating the operation process of step S1 and step S2 for several times;

[0012] S4: drying and rapidly pyrolyzing the hot-melt residue (viscosity-reducing residue) finally obtained in step S3 to recover the remaining heavy oil and asphalt components.

[0013] Optionally, in steps S1 and S3, the hot solvent comprises oil from direct coal liquefaction and / or oil from coal pyrolysis. The recovery of residual heavy oil and asphalt components from coal liquefaction residues in the present invention, along with coal pyrolysis and liquefaction, is part of the coal chemical industry. Oil from direct coal liquefaction and / or coal pyrolysis is generated in the coal chemical industry, and their application in the recovery of residual heavy oil and asphalt reduces the need for externally purchased hot solvents, saving costs.

[0014] Optionally, the oil obtained by direct liquefaction of coal includes one of liquefied light oil, medium oil or heavy oil; the oil obtained by pyrolysis of coal includes one of pyrolysis light oil, phenol oil, wash oil, naphthalene oil or anthracene oil.

[0015] Furthermore, when the hot-soluble solvent includes oil obtained from direct coal liquefaction and oil obtained from coal pyrolysis, the mass ratio of the oil obtained from direct coal liquefaction to the oil obtained from coal pyrolysis is 1:1-10.

[0016] Preferably, the hot-soluble solvent in step S1 includes liquefied light oil and / or pyrolysis light oil;

[0017] Preferably, the hot-melt solvent described in step S3 is replaced with an oil component with a larger molecular weight as the number of cycles increases. For example, during the second cycle (i.e., the second-stage hot melt), the hot-melt solvent may be liquefied medium oil, wash oil, naphthalene oil, or two composite solvents; during the third cycle (i.e., the third-stage hot melt), the hot-melt solvent may be liquefied heavy oil and / or anthracene oil.

[0018] Optionally, in steps S1 and S3, the viscosity reducing agent includes an alkane-rich component; the alkane-rich component includes one or more of gasoline, diesel, petroleum-based residual oil or Fischer-Tropsch wax.

[0019] Preferably, the viscosity reducing agent further comprises one or more C5-C8 normal alkanes.

[0020] Furthermore, in steps S1 and S3, the mass ratio of the alkane-rich component to normal alkanes is 15-20:1.

[0021] Furthermore, the mass ratio of the coal liquefaction residue in step S1 or the hot-melt residue in step S3 to the hot-melt solvent is 1:1-10;

[0022] Furthermore, in steps S1 and S3, the amount of the viscosity reducing agent added is 1‰-1% of the mass of the hot-melt solvent;

[0023] Furthermore, in step S1, the temperature of the thermal dissolution is 25-100° C. and the pressure is 0.1-2 MPa.

[0024] Furthermore, in step S3, the temperature of the hot melt is 100-300°C, the pressure is 2-6 MPa, and the hot melt time is 0.5-6 h, and the temperature and pressure of the hot melt increase with the number of cycles. For example, during the second cycle operation (i.e., the second stage hot melt), the hot melt temperature is 100-200°C, the hot melt time is 0.5-6 h, and the pressure is 2-4 MPa. During the third cycle operation (i.e., the third stage hot melt), the hot melt temperature is 200-300°C, the hot melt time is 0.5-6 h, and the pressure is 4-6 MPa.

[0025] Optionally, in step S1, the solid-liquid separation is performed by in-situ filtration, and the obtained hot-melt residue adhesion index is 0-100.

[0026] Furthermore, in step S2, the condensation temperature is 25-99°C.

[0027] Furthermore, in step S3, the temperature of the condensation in step S2 is repeated at a temperature of 25-299° C., and the condensation temperature increases with the number of cycles. For example, during the second cycle (i.e., the second stage of condensation), the condensation temperature of the secondary thermosol mixture is 25-199° C.; during the third cycle (i.e., the third stage of condensation), the condensation temperature of the tertiary thermosol mixture is 25-299° C.

[0028] Optionally, in step S4, the drying is carried out at normal pressure or under vacuum (vacuum degree is 0-0.1 MPa); further, the drying temperature is 50-200°C.

[0029] Furthermore, the pyrolysis temperature is 400-800°C, the pyrolysis atmosphere can be one of N2, CO, H2, and CH4, and the pyrolysis time is 0-60 minutes. Preferably, the pyrolysis is carried out using a down-flow pyrolysis device.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] (1) The strong adhesiveness of the liquefied residue after pyrolysis is reduced by using step-by-step hot dissolution. It is proposed to use a combined viscosity reducer and a hot dissolving solvent to synergistically improve the viscosity reduction effect. The heavy oil and asphalt substances in the liquefied residue are hot-dissolved step by step to obtain a hot-dissolving residue with a lower adhesive index.

[0032] (2) Based on the differences in fluidity and solubility between hot-melt solvents and heavy oils and asphalt-like substances, the hot-melt mixture is cooled and graded to condense and recover the hot-melt solvent, which greatly reduces the energy consumption of the solvent recovery process and can also finely separate hot-melt substances with different molecular weights and structural components.

[0033] (3) The recovery rate of heavy oil and asphalt-like substances is improved through the hot dissolution of liquefied residue and the pyrolysis of hot-dissolved residue. The fast and uniform heat and mass transfer and the short residence time of the down-flow bed pyrolysis can reduce coking in the reactor and improve the selectivity of oil and gas products. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the background technology and technical solutions of the embodiments of the present invention, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings may only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0035] Figure 1 This is a process flow chart of a method for recovering residual heavy oil and asphalt components from coal liquefaction residue according to the present invention;

[0036] Figure 2This is a photo of the pyrolyzed semi-coke sample obtained in Example 6 of the present invention;

[0037] Figure 3 This is a photo of the semi-coke sample after pyrolysis obtained in Comparative Example 1. DETAILED DESCRIPTION

[0038] The following describes embodiments of the present invention in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended only to explain the present invention and are not to be construed as limiting the present invention.

[0039] In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "multiple" and "several" mean two or more, unless otherwise clearly and specifically defined. The coal liquefaction residue in the embodiments and comparative examples of the present invention was produced by the Shenhua Ordos direct coal liquefaction project.

[0040] In the embodiments of the present invention, the test standard for the adhesion index refers to the "Determination Method of Adhesion Index of Bituminous Coal" (Xing Xiuyun; Li Hongtu; Chen Baohua; Chen Peng, General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China; China National Standardization Administration, Standard No.: GB / T 5447-2014).

[0041] Example 1

[0042] A method for recovering residual heavy oil and asphalt components from coal liquefaction residue, such as Figure 1 As shown, the following steps are included:

[0043] (1) Coal direct liquefaction residue, first-level hot-melt solvent liquefied light oil and first-level viscosity reducer diesel are mixed and then hot-melted at 100°C and a pressure of 2 MPa for 4 hours. The mass ratio of coal direct liquefaction residue and first-level hot-melt solvent liquefied light oil (Shenhua Ordos coal direct liquefaction project, IBP-220°C) is 1:3, and the mass of the first-level viscosity reducer added is 1‰ of the first-level hot-melt solvent. Subsequently, the solid-liquid separation is carried out by in-situ filtration to obtain a first-level hot-melt mixture and a first-level hot-melt residue. The first-level hot-melt mixture is condensed at 20°C to obtain a first-level hot-melt and a recovered hot-melt solvent, and the hot-melt solvent is recycled.

[0044] (2) The first-stage hot melt residue, the second-stage hot melt solvent wash oil and the second-stage viscosity reducing agent petroleum-based residual oil are mixed and then hot melted at 200°C and a pressure of 4 MPa for 4 hours, wherein the mass ratio of the first-stage hot melt residue to the second-stage hot melt solvent wash oil is 1:3, and the mass of the second-stage viscosity reducing agent added is 1‰ of the second-stage hot melt solvent. Subsequently, the solid-liquid separation is performed by in-situ filtration to obtain a second-stage hot melt mixture and a second-stage hot melt residue. The second-stage hot melt mixture is condensed at 40°C to obtain a second-stage hot melt and a recovered hot melt solvent, and the hot melt solvent is recycled.

[0045] (3) The secondary hot melt residue, the tertiary hot melt solvent liquefied heavy oil and the tertiary viscosity reducing agent Fischer-Tropsch wax are mixed and hot melted at 300°C and a pressure of 6 MPa for 4 hours, wherein the mass ratio of the secondary hot melt residue to the tertiary hot melt solvent is 1:3, and the mass of the tertiary viscosity reducing agent added is 1‰ of the tertiary hot melt solvent. Subsequently, the solid-liquid separation is performed by in-situ filtration to obtain a tertiary hot melt mixture and a tertiary hot melt residue. The tertiary hot melt mixture is condensed at 60°C to obtain a tertiary hot melt and a recovered hot melt solvent, and the hot melt solvent is recycled.

[0046] (4) The final tertiary hot melt residue was dried at 150°C and a vacuum degree of 0.1 MPa, and then placed in a down-flow bed reactor and subjected to rapid pyrolysis at 550°C in a nitrogen atmosphere for 60 minutes to recover the remaining heavy oil and asphalt components.

[0047] The measurement results showed that the yield of the hot solution liquid was 40 wt%, the cohesive index of the third-stage hot solution residue was 13, the pyrolysis liquid yield was 8 wt%, and the total liquid yield of hot solution and pyrolysis was 48 wt%.

[0048] Example 2

[0049] The difference from Example 1 is that the first-stage viscosity reducer, the second-stage viscosity reducer, and the third-stage viscosity reducer are all petroleum-based residual oil.

[0050] The measurement results showed that the yield of the hot solution liquid was 36 wt%, the cohesive index of the third-stage hot solution residue was 17, the pyrolysis liquid yield was 8 wt%, and the total liquid yield of hot solution and pyrolysis was 44 wt%.

[0051] Example 3

[0052] The difference from Example 1 is that the dosage of the first-level viscosity reducer, the second-level viscosity reducer and the third-level viscosity reducer is 2‰ of the corresponding first-level hot-melt solvent, the second-level hot-melt solvent and the third-level hot-melt solvent respectively.

[0053] The measurement results showed that the yield of the hot solution liquid was 42 wt%, the cohesive index of the third-stage hot solution residue was 9, the pyrolysis liquid yield was 7 wt%, and the total liquid yield of hot solution and pyrolysis was 49 wt%.

[0054] Example 4

[0055] The difference from Example 1 is that the condensation in step (1), step (2) and step (3) is not performed, and is replaced by flash evaporation separation and recovery of the solvent.

[0056] The measurement results showed that the yield of the hot solution liquid was 32 wt%, the cohesive index of the third-stage hot solution residue was 13, the pyrolysis liquid yield was 8 wt%, and the total liquid yield of the hot solution and pyrolysis was 40 wt%.

[0057] Example 5

[0058] The difference from Example 1 is that the first-level viscosity reducer is a mixture of gasoline and n-pentane in a mass ratio of 15:1.

[0059] The measurement results showed that the yield of the hot solution liquid was 46 wt%, the cohesive index of the third-stage hot solution residue was 7, the pyrolysis liquid yield was 5 wt%, and the total liquid yield of hot solution and pyrolysis was 51 wt%.

[0060] Example 6

[0061] The difference from Example 1 is that the first-stage viscosity reducer is a mixture of gasoline and n-pentane in a mass ratio of 15:1; the second-stage viscosity reducer is a mixture of petroleum-based residual oil and n-pentane in a mass ratio of 15:1; and the third-stage viscosity reducer is a mixture of Fischer-Tropsch wax and n-pentane in a mass ratio of 15:1.

[0062] The measurement results show that the yield of the hot solution liquid is 52wt%, and the cohesive index of the third-level hot solution residue is 5. The pyrolysis liquid yield is 3wt%, and the total liquid yield of hot solution and pyrolysis is 55wt%. The final morphology of the semi-coke after pyrolysis is as follows Figure 2 shown.

[0063] Example 7

[0064] The difference from Example 1 is that the primary hot-melt solvent is a composite solvent of liquefied light oil and pyrolysis light oil in a mass ratio of 1:1.

[0065] The measurement results showed that the yield of the hot solution liquid was 43 wt%, the cohesive index of the third-stage hot solution residue was 12, the pyrolysis liquid yield was 6 wt%, and the total liquid yield of hot solution and pyrolysis was 49 wt%.

[0066] Example 8

[0067] The difference from Example 1 is that: the hot dissolution temperature of step (1) is 50°C and the pressure is 1 MPa; the hot dissolution temperature of step (2) is 150°C and the pressure is 2 MPa; the hot dissolution temperature of step (3) is 250°C and the pressure is 4 MPa.

[0068] The measurement results showed that the yield of the hot solution liquid was 37 wt%, the cohesive index of the third-stage hot solution residue was 16, the pyrolysis liquid yield was 8 wt%, and the total liquid yield of hot solution and pyrolysis was 45 wt%.

[0069] Comparative Example 1

[0070] The difference from Example 1 is that the coal direct liquefaction residue in step (1) is directly pyrolyzed, and the pyrolysis conditions are the same as those in Example 1.

[0071] The measurement results show that the cohesive index of the liquefied residue is 98 and the pyrolysis liquid yield is 25 wt%. The final morphology of the semi-coke after pyrolysis is as follows: Figure 3 shown.

[0072] Comparative Example 2

[0073] The difference from Example 1 is that the corresponding first-level viscosity reducer, second-level viscosity reducer, and third-level viscosity reducer are not added during the hot melt process in step (1), step (2), and step (3).

[0074] The measurement results showed that the yield of the hot solution liquid was 30 wt%, the cohesive index of the third-stage hot solution residue was 45, the yield of the pyrolysis liquid was 5 wt%, and the total liquid yield of the hot solution and pyrolysis was 35 wt%.

[0075] By comparing Comparative Examples 1 and 2 with the embodiment, it can be seen that the addition of a viscosity reducing agent and a hot-melt solvent reduces the strong adhesiveness of the coal liquefaction residue during pyrolysis, while graded hot dissolution can amplify the viscosity reducing effect.

[0076] It can be seen from Example 2 that different grades use different viscosity reducing agents according to the structure of their hot-melt residues, which can correspondingly reduce the adhesion index and improve the yield of the hot-melt liquid.

[0077] It can be seen from Example 3 that increasing the dosage of viscosity reducing agent at each level can correspondingly reduce the bonding index and increase the yield of the hot solution liquid, but reduce the yield of the pyrolysis liquid.

[0078] It can be seen from Example 4 that if flash separation is used instead of graded condensation recovery, the yield of the hot solution liquid is reduced.

[0079] It can be seen from Example 5 that the first-stage viscosity reducer uses a combination of gasoline and n-pentane. Although the pyrolysis liquid yield is reduced, the viscosity index is greatly reduced and the total liquid yield is improved.

[0080] It can be seen from Example 6 that the viscosity reducing agent at each level is the combination of the viscosity reducing agent of Example 1 and n-pentane, which has the best viscosity reducing effect and the best total liquid yield.

[0081] It can be seen from Example 7 that when a composite solvent is used as the hot-dissolving solvent, the yield of the hot-dissolving liquid is increased, but the yield of the pyrolysis liquid is reduced.

[0082] It can be seen from Example 8 that when the temperature and pressure of each level of hot dissolution are reduced, the yield of the hot dissolution liquid decreases, the adhesion index also increases, and the overall effect is not good.

[0083] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for recovering residual heavy oil and asphalt components from coal liquefaction residue, characterized in that: The steps include: S1: Mixing coal liquefaction residue, hot-melt solvent and viscosity reducer, and then hot-melting, followed by solid-liquid separation to obtain hot-melt mixture and hot-melt residue; S2: condensing the hot molten mixture to obtain a hot molten product and a recovered hot molten solvent; S3: mixing the hot-melt residue, hot-melt solvent and viscosity reducing agent and repeating the operation process of step S1 and step S2 for several times; S4: drying and rapidly pyrolyzing the hot-melt residue obtained in step S3 to recover the remaining heavy oil and asphalt components.

2. The method according to claim 1, characterized in that In steps S1 and S3, the hot solvent includes oil obtained by direct liquefaction of coal and / or oil obtained by pyrolysis of coal; Preferably, the oil obtained by direct coal liquefaction includes one of liquefied light oil, medium oil or heavy oil; the oil obtained by coal pyrolysis includes one of pyrolysis light oil, phenol oil, wash oil, naphthalene oil or anthracene oil; Preferably, when the hot-melt solvent includes both oil obtained from direct coal liquefaction and oil obtained from coal pyrolysis, the mass ratio of the oil obtained from direct coal liquefaction to the oil obtained from coal pyrolysis is 1:1-10.

3. The method according to claim 2, characterized in that The hot soluble solvent in step S1 includes liquefied light oil and / or pyrolysis light oil; And / or, the hot-melt solvent in step S3 is replaced with oils with larger molecular weight as the number of cycles increases.

4. The method according to claim 1, wherein In steps S1 and S3, the viscosity reducing agent includes an alkane-rich component; Preferably, the alkane-rich component comprises one or more of gasoline, diesel, petroleum-based residual oil or Fischer-Tropsch wax; Preferably, the viscosity reducing agent further comprises one or more C5-C8 normal alkanes.

5. The method according to claim 4, characterized in that The mass ratio of the coal liquefaction residue in step S1 or the hot-melt residue in step S3 to the hot-melt solvent is 1:1-10; and / or, in steps S1 and S3, the amount of the viscosity reducing agent added is 1‰-1% of the mass of the hot-melt solvent; And / or, in steps S1 and S3, the mass ratio of the alkane-rich component to normal alkanes is 15-20:

1.

6. The method according to claim 1, wherein In step S1, the temperature of the hot melt is 25-100°C and the pressure is 0.1-2 MPa; And / or, in step S3, the temperature of the hot melt is 100-300° C., and the pressure is 2-6 MPa, and the temperature and pressure of the hot melt increase with increasing number of cycles.

7. The method according to claim 1, characterized in that In step S1, the solid-liquid separation is performed by in-situ filtration.

8. The method according to claim 1, characterized in that In step S2, the condensation temperature is 25-99°C; And / or, in step S3, the temperature of the condensation in the repeated step S2 is 25-299° C., and the condensation temperature increases with increasing number of cycles.

9. The method according to claim 1, characterized in that In step S4, the drying is performed under normal pressure or vacuum; And / or, the drying temperature is 50-200°C.

10. The method according to claim 1, characterized in that The pyrolysis temperature is 400-800°C.

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