Method for separating and purifying monocyclic aromatic hydrocarbons from direct coal liquefaction oil

Abstract

The present invention relates to the technical field of separation of direct coal liquefaction oil, and provides a method for separating and purifying monocyclic aromatic hydrocarbons from direct coal liquefaction oil. The method comprises: (1) performing fractional distillation and composition analysis on direct coal liquefaction oil to determine a fraction having the highest content of monocyclic aromatic hydrocarbons; (2) removing low-carbon alkanes and cycloalkanes from a selected fraction by means of column chromatography; (3) separating toluene, a monocyclic aromatic hydrocarbon mixture, and high-carbon alkanes by means of an atmospheric and vacuum distillation column; (4) purifying ethylbenzene from the monocyclic aromatic hydrocarbon mixture by means of an extractive distillation column; and (5) purifying p-xylene by means of a solvent recovery column. The separation method provided by the present invention can make full use of the composition characteristics of direct coal liquefaction oil to obtain two or three high-purity monocyclic aromatic hydrocarbon monomers at a time without introducing additional chemical reaction steps, showing significant economic and environmental benefits.

Description

Method for separating and purifying monocyclic aromatic hydrocarbons from coal direct liquefaction oil TECHNICAL FIELD

[0001] The present application relates to the technical field of coal direct liquefaction oil separation, and particularly relates to a method for separating and purifying monocyclic aromatic hydrocarbons from coal direct liquefaction oil. BACKGROUND

[0002] Toluene, ethylbenzene and p-xylene all belong to basic chemical raw materials. In recent years, the demand for toluene, ethylbenzene and p-xylene in China is increasing year by year, and the raw material for producing p-xylene is usually petroleum-based naphtha, such as straight-run naphtha and secondary processing naphtha. However, with the obvious trend of heavy and poor quality of crude oil exploitation, the supply of petroleum-based naphtha for producing toluene, ethylbenzene and p-xylene is tight, which is not enough to match the increasing demand for toluene, ethylbenzene and p-xylene, so there is an urgent need for raw materials suitable for producing toluene, ethylbenzene and p-xylene.

[0003] The separation of hydrocarbons in coal-based crude oil and the separation of xylene isomers have important significance. Coal direct liquefaction technology is one of the methods of coal-to-oil, which is a process of converting coal into liquid fuel. In the coal liquefaction oil obtained from this process, the naphtha fraction accounts for about 15-30wt%, and the fraction has a very high aromatic content, which can further obtain coal-based mixed aromatic hydrocarbons with an aromatic content of more than 80wt%, which is very suitable for producing toluene, ethylbenzene and p-xylene.

[0004] At present, the process for separating and purifying p-xylene from coal-based crude oil mainly uses catalytic conversion combined with separation. Catalytic conversion is to convert p-xylene into other compounds through catalytic reaction, so as to separate from other isomers. CN 103436288 A discloses a method for preparing aromatic hydrocarbons from coal tar naphtha, which pretreats the coal tar, performs atmospheric and vacuum distillation and coking, cracking or hydroprocessing to obtain a naphtha fraction, then performs pre-fractionation, pre-hydrogenation and reforming on the naphtha fraction to obtain a light aromatic hydrocarbon mixture, and finally separates and further isomerizes the light aromatic hydrocarbon to obtain benzene and p-xylene. CN 106187671 A discloses a method for separating p-xylene from coal direct liquefaction naphtha, which performs hydrogenation treatment, reforming and aromatic extraction on the coal direct liquefaction naphtha to obtain coal-based mixed aromatic hydrocarbons, then performs fractionation, alkylation reaction, disproportionation and transalkylation reaction, and adsorption separation on the coal-based mixed aromatic hydrocarbons to obtain p-xylene with a purity of 99.5wt%.

[0005] Currently, the catalytic conversion method for producing p-xylene from coal-based crude oil needs to pass through reaction conversion auxiliary separation, control variable is complicated, and additional chemical reaction steps may be introduced, and economic benefits and environmental impact need to be considered comprehensively. Therefore, a more simple process is needed to separate p-xylene in coal-based oil, so as to fully utilize coal direct liquefaction oil as a raw material for producing p-xylene, to do well in deep processing and high value utilization of coal direct liquefaction products, and to meet the increasing demand of the market for p-xylene products. SUMMARY

[0006] The purpose of the present application is to provide a method for separating and purifying monocyclic aromatic hydrocarbons in coal direct liquefaction oil, which solves the technical problem that the separation process of p-xylene in existing coal-based oil is complicated and economic benefits and environmental benefits need to be considered comprehensively.

[0007] In order to achieve the above-mentioned purpose of the application, the present application provides the following technical solutions:

[0008] The present application provides a method for separating and purifying monocyclic aromatic hydrocarbons from coal direct liquefaction oil, comprising the following steps:

[0009] 1) Fine fractionation of coal direct liquefaction oil, and component analysis of the obtained fraction segments;

[0010] 2) Selecting the fraction segment with the highest content of monocyclic aromatic hydrocarbons, and sequentially performing column chromatography, atmospheric and vacuum distillation and extractive distillation on the fractions in the fraction segment to obtain a distillation product;

[0011] 3) Solvent recovery of the distillation product to obtain monocyclic aromatic hydrocarbons;

[0012] The monocyclic aromatic hydrocarbons include one or more of toluene, ethylbenzene and p-xylene.

[0013] Further, in step 1), the reflux ratio of the fine fractionation is ≥3, the temperature range is ≤180℃, and the number of fraction segments is 8-15 segments.

[0014] Further, in step 2), the stationary phase of the column chromatography is chromatographic silica gel and / or neutral alumina;

[0015] When the stationary phase is chromatographic silica gel and neutral alumina, the mass ratio of chromatographic silica gel to neutral alumina is 3-4:2-3.

[0016] Further, in step 2), the mobile phase comprises eluent 1 and eluent 2, and the volume ratio of eluent 1 to eluent 2 is 10:3-5;

[0017] Wherein, eluent 1 and eluent 2 are independently one or more of n-pentane, isopentane, petroleum ether, n-hexane, n-heptane, dichloromethane, ethyl acetate and chloroform.

[0018] Further, in step 2), after the column chromatography, the obtained column chromatography product is a mixture from which low-carbon alkanes and cycloalkanes are removed.

[0019] Further, in step 2), the number of times of the atmospheric-vacuum distillation is not less than 1, and the atmospheric-vacuum distillation product is a mixture from which high-carbon alkanes are removed.

[0020] Further, the atmospheric-vacuum distillation has a top temperature of 100-140 DEG C, a bottom temperature of 150-220 DEG C, a plate number of 20-40, a reflux ratio of 2-5, a top pressure of 0.10-0.15 MPa, and a bottom pressure of 0.15-0.17 MPa.

[0021] Further, in step 2), the extractant for the extractive distillation is one or more of polychlorobenzenes, acid anhydrides, esters, ketones, alcohols and pyridines.

[0022] Further, in step 3), the extractive distillation has a top temperature of 130-200 DEG C, a bottom temperature of 130-200 DEG C, a plate number of 130-220, a reflux ratio of 35-45, a top pressure of 0.1-0.15 MPa, and a bottom pressure of 0.2-0.25 MPa.

[0023] Further, in step 3), the solvent recovery has a top temperature of 130-140 DEG C, a bottom temperature of 195-215 DEG C, a plate number of 24-30, a reflux ratio of 2-3, a top pressure of 0.1-0.15 MPa, and a bottom pressure of 0.17-0.2 MPa.

[0024] The present application has the following beneficial effects:

[0025] By using the method for producing monocyclic aromatic hydrocarbons provided by the present application, high-purity toluene, ethylbenzene and p-xylene can be produced by fully utilizing coal direct liquefaction oil resources. In particular, high-purity p-xylene can be produced by utilizing the composition characteristics of coal conversion resources. The method for producing p-xylene provided by the present application avoids additional chemical reaction steps introduced by catalytic conversion and the environmental problems caused thereby, and has a simple process flow and high economic efficiency. The present application fully utilizes coal direct liquefaction oil resources to alleviate the problem of insufficient supply of petroleum-based naphtha in China, and provides a new idea for fully utilizing energy. BRIEF DESCRIPTION OF DRAWINGS

[0026] Fig. 1 is a process flow diagram of the present application for separating and purifying monocyclic aromatic hydrocarbons from coal direct liquefaction oil. DETAILED DESCRIPTION

[0027] The present application provides a method for separating and purifying monocyclic aromatic hydrocarbons from coal direct liquefaction oil, comprising the following steps:

[0028] 1) fine fraction of direct coal liquefaction oil is carried out, and component analysis is carried out on the obtained fraction segment;

[0029] 2) the fraction segment with the highest single ring aromatic hydrocarbon content is selected, and column chromatography, atmospheric and vacuum distillation and extractive distillation are carried out on the fractions in sequence, so as to obtain a distillation product;

[0030] 3) the distillation product is subjected to solvent recovery, so as to obtain a single ring aromatic hydrocarbon;

[0031] The single ring aromatic hydrocarbon comprises one or more of toluene, ethylbenzene and p-xylene.

[0032] In the present application, the single ring aromatic hydrocarbon is preferably toluene, ethylbenzene and p-xylene, and is further preferably ethylbenzene and p-xylene.

[0033] In the present application, in step 1), the reflux ratio of the fine fraction is ≥ 3, preferably ≥ 5, and further preferably ≥ 7; the temperature range is preferably ≤ 180℃, the number of fraction segments is 8-15 segments, preferably 9-12 segments, and further preferably < 80℃, 80-100℃, 100-110℃, 110-120℃, 120-130℃, 130-140℃, 140-150℃, 150-160℃, 160-170℃ and 170-180℃ 10 fraction segments.

[0034] In the present application, in step 2), the stationary phase of the column chromatography is chromatographic silica gel and / or neutral alumina, and is preferably chromatographic silica gel and neutral alumina;

[0035] When the stationary phase is chromatographic silica gel and neutral alumina, the mass ratio of chromatographic silica gel to neutral alumina is 3-4:2-3, preferably 3.2-3.8:2.2-2.8, further preferably 3.4-3.6:2.4-2.6, and more preferably 3.5:2.5.

[0036] In the present application, in step 2), the mobile phase comprises eluent 1 and eluent 2, and the volume ratio of eluent 1 to eluent 2 is 10:3-5, preferably 10:3.5-4.5, and further preferably 10:4;

[0037] wherein eluent 1 and eluent 2 are independently one or more of n-pentane, isopentane, petroleum ether, n-hexane, n-heptane, dichloromethane, ethyl acetate and chloroform, preferably one or more of n-hexane, n-heptane, dichloromethane, ethyl acetate and chloroform, and further preferably n-hexane and dichloromethane.

[0038] In the present application, in step 2), after the column chromatography, the obtained column chromatography product is a mixture of removing low carbon alkanes and naphthenes, preferably a component rich in monocyclic aromatic hydrocarbons and removing low carbon alkanes and naphthenes, further preferably a component rich in carbon eight aromatic hydrocarbons and removing low carbon alkanes and naphthenes.

[0039] In the present application, in step 2), the number of times of the atmospheric and vacuum distillation is not less than 1, preferably not less than 2, further preferably not less than 3, and the atmospheric and vacuum distillation product is a mixture of removing high carbon alkanes, preferably a mixture after removing carbon seven aromatic hydrocarbons and high carbon alkanes, further preferably a mixture of ethylbenzene and p-xylene.

[0040] In the present application, the overhead temperature of the atmospheric and vacuum distillation is independently 100-140℃, preferably 110-130℃, further preferably 120℃, the bottom temperature is independently 150-220℃, preferably 170-200℃, further preferably 190℃, the plate number is independently 20-40, preferably 25-35, further preferably 30, the reflux ratio is independently 2-5, preferably 2.5-4.5, further preferably 3, the overhead pressure is independently 0.10-0.15MPa, preferably 0.12-0.14MPa, further preferably 0.13MPa, and the bottom pressure is independently 0.15-0.17MPa, preferably 0.16MPa.

[0041] In the present application, in step 2), the extractant of the extractive distillation is one or several of polychlorobenzenes, acid anhydrides, esters, ketones, alcohols and pyridines, preferably one or several of polychlorobenzenes, acid anhydrides and esters, further preferably polychlorobenzenes or acid anhydrides, more preferably 1,2,4-trichlorobenzene.

[0042] In the present application, in step 3), the overhead temperature of the extractive distillation is 130-200℃, preferably 150-180℃, further preferably 160℃, the bottom temperature is 130-200℃, preferably 150-180℃, further preferably 160℃; the plate number is 130-220, preferably 150-200, further preferably 170-190, more preferably 180; the reflux ratio is 35-45, preferably 38-42, further preferably 40; the overhead pressure is 0.1-0.15MPa, preferably 0.12-0.14MPa, further preferably 0.13MPa; and the bottom pressure is 0.2-0.25MPa, preferably 0.22-0.24MPa, further preferably 0.23MPa.

[0043] In the present application, in step 3), the tower top temperature of the solvent recovery is 130-140℃, preferably 132-138℃, further preferably 135℃, the tower bottom temperature is 195-215℃, preferably 200-210℃, further preferably 205℃, the plate number is 24-30, preferably 25-28, further preferably 27, the reflux ratio is 2-3, preferably 2.3-2.8, further preferably 2.5, the tower top pressure is 0.1-0.15MPa, preferably 0.12-0.14MPa, further preferably 0.13MPa, and the tower bottom pressure is 0.17-0.2MPa, preferably 0.18MPa.

[0044] The technical solutions provided by the present application are described in detail below in combination with examples, but they should not be understood as limiting the scope of protection of the present application.

[0045] Example 1

[0046] The reflux ratio of the rectification column is set to 5, and the Xinjiang coal direct liquefaction oil is cut into 10 fraction sections of <80℃, 80-100℃, 100-110℃, 110-120℃, 120-130℃, 130-140℃, 140-150℃, 150-160℃, 160-170℃ and 170-180℃ at a temperature interval of 10℃, and the composition of each fraction section is analyzed, and the fraction section with the highest content of single-ring aromatic hydrocarbons is selected as 120-130℃;

[0047] The fraction in the 120-130℃ fraction section is subjected to column chromatography (the lower layer of the stationary phase is 3.28g of chromatographic silica gel, and the upper layer is 2.82g of neutral alumina, and the chromatographic column specification is 15*300mm), first, 30mL of n-hexane, i.e. eluent 1, is used to completely elute and remove paraffin and naphthene, and then 9mL of a mixed solution of dichloromethane and n-hexane (volume ratio of 2:1), i.e. eluent 2, is used to elute to obtain a component with a single-ring aromatic hydrocarbon content of 5.12wt% (toluene accounts for 24wt% of the single-ring aromatic hydrocarbons, ethylbenzene accounts for 26wt%, and p-xylene accounts for 50wt%);

[0048] The column chromatography product is subjected to first atmospheric and vacuum distillation to obtain toluene and first tower bottom distillate; the first tower bottom distillate is subjected to second atmospheric and vacuum distillation to obtain mixed aromatic hydrocarbons and second tower bottom distillate; the second tower bottom distillate is subjected to extractive distillation using 1,2,4-trichlorobenzene to obtain ethylbenzene, and then solvent recovery is performed through a solvent recovery tower to obtain p-xylene.

[0049] Table 1 is the process conditions in Example 1, and Table 2 is the product composition of the tower top in Example 1.

[0050] Table 1 is the process conditions in Example 1. Table 1 is the process conditions in Example 1.

[0051] Table 2 Product composition at the top of the column in Example 1

[0052] Example 2

[0053] In this example, the stationary phase of the column chromatography consists of 3.71 g of lower layer chromatographic silica gel and 2.64 g of upper layer neutral alumina; the amount of eluent 2 is 12 mL, and the content of single ring aromatic hydrocarbons in the component obtained after elution is 7.57 wt% (toluene accounts for 12 wt% of the single ring aromatic hydrocarbons, ethylbenzene accounts for 36 wt%, and p-xylene accounts for 52 wt%).

[0054] One atmospheric and vacuum distillation of the column chromatography product separates toluene from ethylbenzene, p-xylene and high carbon alkanes, and toluene with a purity of 99.57 wt% is obtained.

[0055] The bottom distillate is subjected to another atmospheric and vacuum distillation to separate ethylbenzene and p-xylene from high carbon alkanes.

[0056] The ethylbenzene and p-xylene mixture enriched by extraction distillation using 1,2,4-trichlorobenzene obtains ethylbenzene with a purity of 98.55 wt%.

[0057] The mixture of p-xylene and 1,2,4-trichlorobenzene is subjected to solvent recovery by a solvent recovery column to obtain p-xylene with a purity of 99.17 wt%.

[0058] Table 3 is the process conditions in Example 2, and Table 4 is the product composition at the top of the column in Example 2.

[0059] Table 3 Process conditions in Example 2

[0060] Table 4 Product composition at the top of the column in Example 2

[0061] Example 3

[0062] In this example, the stationary phase of the column chromatography consists of 3.61 g of lower layer chromatographic silica gel and 2.54 g of upper layer neutral alumina; 30 mL of eluent 1 and 9 mL of eluent 2 are used in turn for elution, and the low carbon alkanes and naphthenes are completely removed, and then 3 mL of eluent 2 is used for elution to obtain a component with a single ring aromatic hydrocarbon content of 14.94 wt% (ethylbenzene accounts for 47 wt% of the single ring aromatic hydrocarbons, and p-xylene accounts for 53 wt%); the number of atmospheric and vacuum distillations of the column chromatography product is 1.

[0063] One atmospheric and vacuum distillation of the column chromatography product separates ethylbenzene and p-xylene from high carbon alkanes.

[0064] The mixture of ethylbenzene and p-xylene was subjected to extractive distillation using 1,2,4-trichlorobenzene to obtain ethylbenzene with a purity of 96.03 wt%.

[0065] The mixture of p-xylene and 1,2,4-trichlorobenzene was subjected to solvent recovery through a solvent recovery column to obtain p-xylene with a purity of 96.69 wt%.

[0066] Table 5 is the process conditions in Example 3, and Table 6 is the product composition at the top of the column in Example 3.

[0067] Table 5 is the process conditions in Example 3

[0068] Table 6 is the product composition at the top of the column in Example 3

[0069] Example 4

[0070] Different from Example 1, in this example, the stationary phase of column chromatography is composed of 3.76 g of lower-layer chromatographic silica gel and 2.88 g of upper-layer neutral alumina; during elution, 30 mL of eluent 1 and 6 mL of eluent 2 are used to elute successively, completely removing low-carbon alkanes and cycloalkanes, and then 3 mL of eluent 2 is used to elute to obtain a component with a monocyclic aromatic hydrocarbon content of 15.35 wt% (toluene accounts for 24 wt% of the monocyclic aromatic hydrocarbons, ethylbenzene accounts for 26 wt%, and p-xylene accounts for 50 wt%).

[0071] The column chromatography product is subjected to once normal pressure and reduced pressure distillation to separate toluene from ethylbenzene, p-xylene and high-carbon alkanes, to obtain toluene with a purity of 99.83 wt%.

[0072] The bottom distillate is subjected to once normal pressure and reduced pressure distillation to separate ethylbenzene and p-xylene from high-carbon alkanes.

[0073] The mixture of enriched ethylbenzene and p-xylene is subjected to extractive distillation using 1,2,4-trichlorobenzene to obtain ethylbenzene with a purity of 97.99 wt%.

[0074] The mixture of p-xylene and 1,2,4-trichlorobenzene is subjected to solvent recovery through a solvent recovery column to obtain p-xylene with a purity of 99.42 wt%.

[0075] Table 7 is the process conditions in Example 4, and Table 8 is the product composition at the top of the column in Example 4.

[0076] Table 7 is the process conditions in Example 4

[0077] Table 8 is the product composition at the top of the column in Example 4

[0078] Example 5

[0079] Different from example 1, in this example, the stationary phase of column chromatography is composed of 3.61 g of lower layer chromatographic silica gel and 2.54 g of upper layer neutral alumina; when eluting, first elute sequentially with 30 mL of eluent 1 and 9 mL of eluent 2 to completely remove low carbon alkanes and naphthenes, and then elute with 3 mL of eluent 2 to obtain a component with a monocyclic aromatic content of 14.94 wt% (in monocyclic aromatics, ethylbenzene accounts for 47 wt%, and p-xylene accounts for 53 wt%); the number of times of atmospheric and vacuum distillation of the column chromatography product is 1.

[0080] The ethylbenzene and p-xylene are separated from high carbon alkanes by once atmospheric and vacuum distillation of the column chromatography product.

[0081] The mixture of enriched ethylbenzene and p-xylene is subjected to extractive distillation using 1,2,4-trichlorobenzene to obtain ethylbenzene with a purity of 99.09 wt%.

[0082] The mixture of p-xylene and 1,2,4-trichlorobenzene is subjected to solvent recovery through a solvent recovery column to obtain p-xylene with a purity of 99.10 wt%.

[0083] Table 9 is the process condition in example 5, and table 10 is the product composition of the overhead in example 5.

[0084] Table 9 is the process condition in example 5.

[0085] Table 10 is the product composition of the overhead in example 5.

[0086] From the above examples, it can be seen that the present application provides a method for separating and purifying monocyclic aromatics from coal direct liquefaction oil. After fine fractionation and composition analysis of the coal direct liquefaction oil, the present application selects a fraction rich in monocyclic aromatics, and then removes low carbon alkanes and naphthenes from the selected fraction by column chromatography. Atmospheric and vacuum distillation of the component from which the low carbon alkanes are removed can obtain toluene with a purity of > 99 wt% and plays a role in enriching ethylbenzene and p-xylene. The use of extractive distillation method separates ethylbenzene and p-xylene to obtain ethylbenzene with a purity of > 96%, and finally solvent recovery obtains p-xylene with a purity of > 99 wt%. The present application fully utilizes the composition advantage of coal direct liquefaction oil, and can obtain 2-3 kinds of high-purity monocyclic aromatic monomers at one time. The present application does not need to introduce additional chemical reaction steps, and has obvious economic and environmental benefits compared with catalytic conversion method, and provides a new idea for fully utilizing coal-based energy.

[0087] The above merely describes the preferred embodiments of the present application, and it should be pointed out that, for those skilled in the art, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered as falling within the protection scope of the present application.

Claims

1. A method for separating and purifying monocyclic aromatic hydrocarbons from coal direct liquefaction oil, characterized by, The method comprises the following steps: 1) performing fine fractionation on direct coal liquefaction oil, and performing component analysis on the obtained fraction segments; 2) selecting a fraction segment with the highest content of single-ring aromatic hydrocarbons, and sequentially performing column chromatography, atmospheric and vacuum distillation, and extractive distillation on the fractions in the fraction segment to obtain distillation products; 3) recovering solvents from the distillation products to obtain single-ring aromatic hydrocarbons. The single-ring aromatic hydrocarbons include one or more of toluene, ethylbenzene, and p-xylene.

2. The method of claim 1, wherein the method is characterized by, In step 1), the reflux ratio of the fine fractionation is greater than or equal to 3, the temperature range is less than or equal to 180 DEG C, and the number of fraction segments is 8 to 15.

3. The method of purifying monocyclic aromatic hydrocarbons from direct coal liquefaction oil according to claim 1 or 2, characterized by, In step 2), the stationary phase of the column chromatography is chromatographic silica gel and / or neutral alumina. When the stationary phase is chromatographic silica gel and neutral alumina, the mass ratio of chromatographic silica gel to neutral alumina is 3 to 4:2 to 3.

4. The method of purifying monocyclic aromatic hydrocarbons from direct coal liquefaction oil according to claim 3, characterized by, In step 2), the mobile phase comprises eluent 1 and eluent 2, and the volume ratio of eluent 1 to eluent 2 is 10:3 to 5. The eluent 1 and the eluent 2 are independently one or more of n-pentane, isopentane, petroleum ether, n-hexane, n-heptane, dichloromethane, ethyl acetate, and chloroform.

5. The method of purifying monocyclic aromatic hydrocarbons from direct coal liquefaction oil according to claim 1 or 2 or 4, characterized by, In step 2), after the column chromatography, the obtained column chromatography product is a mixture from which low-carbon alkanes and naphthenes are removed.

6. The method of purifying monocyclic aromatic hydrocarbons from direct coal liquefaction oil according to claim 5, wherein In step 2), the atmospheric and vacuum distillation is performed for no less than one time, and the atmospheric and vacuum distillation product is a mixture from which high-carbon alkanes are removed.

7. The method of purifying monocyclic aromatic hydrocarbons from direct coal liquefaction oil according to claim 6, wherein The atmospheric and vacuum distillation has a top temperature independently of 100 to 140 DEG C, a bottom temperature independently of 150 to 220 DEG C, a plate number independently of 20 to 40, a reflux ratio independently of 2 to 5, a top pressure independently of 0.10 to 0.15 MPa, and a bottom pressure independently of 0.15 to 0.17 MPa.

8. The method of claim 1, wherein the coal direct liquefaction oil is separated and purified into the monocyclic aromatic hydrocarbons. In step 2), the extractive distillation uses one or more of polychlorobenzenes, acid anhydrides, esters, ketones, alcohols, and pyridines as extractants.

9. The method of claim 1, wherein the coal direct liquefaction oil is separated and purified into the monocyclic aromatic hydrocarbons. In step 3), the extractive distillation has a top temperature of 130 to 200 DEG C, a bottom temperature of 130 to 200 DEG C, a plate number of 130 to 220, a reflux ratio of 35 to 45, a top pressure of 0.1 to 0.15 MPa, and a bottom pressure of 0.2 to 0.25 MPa.

10. The method of claim 1, wherein the coal direct liquefaction oil is separated and purified into monocyclic aromatic hydrocarbons. In step 3), the solvent recovery has a top temperature of 130 to 140 DEG C, a bottom temperature of 195 to 215 DEG C, a plate number of 24 to 30, a reflux ratio of 2 to 3, a top pressure of 0.1 to 0.15 MPa, and a bottom pressure of 0.17 to 0.2 MPa.

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