A method and system for separating mixed dimethylnaphthalenes from mineral oil

Abstract

The application relates to a method and system for separating mixed dimethylnaphthalene from mineral oil, which comprises: an extraction step, including extracting the mineral oil by using an extraction solvent to obtain an alkane-rich raffinate oil stream and an aromatic hydrocarbon and extraction solvent-rich extract phase stream; wherein the extraction solvent is an ionic liquid; a distillation step, including: performing first distillation on the aromatic hydrocarbon and extraction solvent-rich extract phase stream in a first distillation column to obtain a first distillation column overhead stream and a first distillation column bottom stream; performing second distillation on the first distillation column bottom stream in a second distillation column to obtain a product mixed dimethylnaphthalene. By using the method, the mixed dimethylnaphthalene component contained in the mineral oil fraction can be enriched to more than 95%, thereby providing a high-purity raw material for further high-value utilization of the mixed dimethylnaphthalene.

Description

Technical Field

[0001] This invention relates to the field of mineral oil separation, and more specifically, to a method for separating mixed dimethylnaphthalene from mineral oil. Background Technology

[0002] Dimethylnaphthalene (DMN) has 10 isomers, all of which are basic raw materials for the preparation of various high-end chemicals. DMN is also a precursor for the oxidation preparation of naphthalenedicarboxylic acid (NDA), which is a monomer known to be used to prepare various high-end polymers. For example, 1,4-dimethylnaphthalene (1,4-DMN) is a high-value-added fine chemical product, mainly used in the fields of plant growth regulators and fluorescent whitening agents. In addition, 1,4-naphthalenedicarboxylic acid (1,4-NDA), obtained by oxidizing 1,4-DMN, is an important intermediate in the fields of pigments, resins, fuels, and pharmaceuticals, and can be used as a mixed material additive in the fields of clothing materials, high-strength container materials, etc. 2,6-dimethylnaphthalene (2,6-DMN) is an important raw material for synthesizing polymer materials with excellent performance. 2,6-naphthalenedicarboxylic acid (2,6-NDA), which is produced by oxidizing 2,6-dimethylnaphthalene, is condensed with ethylene glycol to obtain ethylene glycol 2,6-naphthalenedicarboxylic acid (PEN). Due to its excellent mechanical properties, gas barrier properties, water resistance, UV resistance, heat resistance, chemical resistance, and radiation resistance, it has broad application prospects in the fields of films, packaging containers, and fibers. It is also a major raw material for preparing novel liquid crystal polyesters (LCPs).

[0003] Currently, the high market price of naphthalene-based high-end polymer monomers, especially NDA, is a major factor restricting their large-scale market entry. The production of DMN, the NDA synthesis monomer, is one of the main reasons for the persistently high price of NDA, making the development of low-cost DMN production technology a current research hotspot.

[0004] The boiling points of the 10 isomers of DMN are relatively similar, making it very difficult to obtain high-purity DMN monomer using only distillation. Furthermore, although the melting points of these ten isomers differ significantly, the yield of DMN monomer is also very low when using crystallization separation because eutectic crystallization occurs between the different isomers. Therefore, the overall economic efficiency of conventional physical separation methods is poor.

[0005] Currently, the main industrial production route for DMN is chemical synthesis, including the naphthylmethylation route and the cyclization route between aromatics and dienes. Most of these synthetic routes involve expensive raw materials, highly toxic and risky catalytic systems, demanding reaction conditions, low overall product yields, and high industrialization costs. Furthermore, because chemical synthesis routes rarely achieve 100% DMN monomer selectivity, isomer separation is also a problem. Summary of the Invention

[0006] The purpose of this invention is to provide a method and system for separating mixed dimethylnaphthalene from mineral oil. This method can effectively enrich high-value-added components in mineral oil fractions to obtain mixed dimethylnaphthalene with a content of more than 95%.

[0007] This application provides a method for separating mixed dimethylnaphthalenes from mineral oil, comprising:

[0008] The extraction step includes extracting the mineral oil using an extraction solvent to obtain a raffinate stream rich in alkane and an extractant stream rich in aromatics and the extraction solvent; wherein the extraction solvent is an ionic liquid.

[0009] The distillation process includes:

[0010] The extract phase stream rich in aromatics and extraction solvent is subjected to a first distillation in a first distillation column to obtain the top stream and bottom stream of the first distillation column.

[0011] The bottom stream from the first distillation column is subjected to a second distillation in the second distillation column to obtain the product mixed dimethylnaphthalene.

[0012] In one embodiment, the extraction unit includes an extraction tower, into which mineral oil is fed from the bottom and an extraction solvent is fed from the top for liquid-phase extraction. The resulting alkane-rich raffinate stream is discharged from the top of the extraction tower, and the resulting aromatic-rich and solvent-rich extract phase stream is discharged from the bottom of the extraction tower.

[0013] In one embodiment, the ionic liquid is selected from imidazole or pyridine cations with alkyl substituted cations, and hexafluorophosphate (PF6) anion. - ), tetrafluoroborate (BF4) - ) or bis(trifluoromethanesulfonyl)imide (NTF2) - ) ionic liquids,

[0014] Preferably, the alkyl-substituted imidazole cation has the structure of formula (I), and the alkyl-substituted pyridine cation has the structure of formula (II):

[0015]

[0016] Among them, R1, R2, R3, and R4 are each independently a C1 to C8 alkyl group.

[0017] In one embodiment, the mass ratio of the extraction solvent to the mineral oil is (0.5-50):1, preferably (1-10):1.

[0018] In one embodiment, the extraction tower has an extraction temperature of 15–120°C and an extraction pressure of 0.1–0.5 MPa.

[0019] In one embodiment, the first distillation column adopts a vacuum distillation process, with a bottom temperature of 50–180°C, a top pressure of 1–20 kPa, a reflux ratio of 0.1–1.0, and 1–10 trays; the second distillation column adopts a vacuum flash distillation process, with an operating temperature of 80–200°C and a top pressure of 0.1–10 kPa.

[0020] In one embodiment, the method further includes recycling at least a portion of the bottom stream from the second distillation column back to the extraction column.

[0021] In one embodiment, before at least a portion of the bottom stream from the second distillation column is recycled back to the extraction column, it is also subjected to heat exchange with the bottom stream from the first distillation column and / or the extract phase stream rich in aromatics and extraction solvent.

[0022] In one embodiment, the method further includes a purification step, which includes removing a portion of the heavy components in the bottom stream of the second distillation column using a back-extraction agent.

[0023] In one embodiment, the purification step includes:

[0024] A portion of the bottom stream from the second distillation column is fed into the upper part of the stripping column, while the stripping agent is fed into the stripping column from the lower part for back-extraction. The resulting lean solvent is discharged from the bottom of the stripping column and recycled back to the extraction column. The resulting stripped phase is discharged from the top of the stripping column. The stripped phase is fed into the stripping agent recovery column to recover the stripping agent. The resulting stripping agent is discharged from the top of the stripping agent recovery column and recycled back to the lower part of the stripping column. The resulting aromatic-rich extractable oil is discharged from the bottom of the stripping agent recovery column.

[0025] In one embodiment, the stripping agent is selected from C4 to C10 alkanes or cycloalkanes; the mass ratio of the stripping agent to the bottom stream of the second distillation column entering the stripping column is (0.2 to 7): 1; the operating temperature of the stripping column is 15 to 50°C, and the operating pressure of the stripping column is 0.1 to 0.5 MPa.

[0026] In one embodiment, the mineral oil is a 250-280°C fraction, preferably obtained by distillation fractionation of at least one of straight-run diesel, catalytic cracking light cycle oil, coking diesel, diesel fraction obtained from direct coal liquefaction, and diesel fraction obtained from coal tar.

[0027] This application provides a system for separating mixed dimethylnaphthalene from mineral oil, comprising:

[0028] An extraction unit is provided with one or more extraction unit stream inlets for inputting mineral oil and extraction solvent, such that the extraction solvent extracts and separates the mineral oil within the extraction unit; the extraction unit also includes a raffinate outlet and an extractable phase outlet, such that an alkane-rich raffinate stream is discharged from the raffinate outlet, and an aromatic hydrocarbon- and extraction solvent-rich extractable phase stream is discharged from the extractable phase outlet.

[0029] A distillation separation unit, comprising a first distillation column and a second distillation column;

[0030] The first distillation column is provided with a first distillation column inlet, a first distillation column top stream outlet, and a first distillation column bottom stream outlet; wherein, the first distillation column inlet is connected to the extract phase outlet of the extraction unit, so that the extract phase stream rich in aromatics and extraction solvent from the extraction unit enters the first distillation column, the first distillation column top stream is discharged from the first distillation column top stream outlet, and the first distillation column bottom stream is discharged from the first distillation column bottom stream outlet;

[0031] The second distillation column is provided with a second distillation column inlet, a second distillation column top outlet, and a second distillation column bottom outlet. The second distillation column inlet is connected to the first distillation column bottom outlet, so that the first distillation column bottom stream from the first distillation column enters the second distillation column. The second distillation column top outlet is used to discharge the product mixture dimethylnaphthalene.

[0032] In one embodiment, the bottom stream outlet of the second distillation column is also connected to the stream inlet of the extraction unit, so that at least a portion of the bottom stream of the second distillation column is recycled back to the extraction unit.

[0033] In one embodiment, a first heat exchanger and / or a second heat exchanger are further included, such that at least a portion of the bottom stream of the second distillation column is circulated back to the extraction unit before exchanging heat with the bottom stream of the first distillation column and / or the extract phase stream rich in aromatics and extraction solvent through the first heat exchanger and / or the second heat exchanger.

[0034] In one embodiment, the system further includes a solvent purification unit, the solvent purification unit comprising:

[0035] The back-extraction column is provided with a back-extraction column inlet, a back-extraction column top stream outlet, and a back-extraction column bottom stream outlet. The back-extraction column inlet is connected to the bottom stream outlet of the second distillation column, so that a portion of the bottom stream of the second distillation column is fed into the back-extraction column. The back-extraction column bottom stream outlet is connected to the extraction unit stream inlet, so that the back-extraction column bottom stream from the back-extraction column is recycled back to the extraction unit.

[0036] A back-extraction agent recovery tower is provided with a back-extraction agent recovery tower material inlet, a back-extraction agent recovery tower top material outlet, and a back-extraction agent recovery tower bottom material outlet. The back-extraction agent recovery tower material inlet is connected to the back-extraction tower top material outlet, so that the back-extraction tower top material from the back-extraction tower enters the back-extraction agent recovery tower; the back-extraction agent recovery tower material inlet is also connected to the back-extraction agent recovery tower top material outlet, so that the back-extraction agent recovery tower top material from the back-extraction agent recovery tower is recycled back to the back-extraction tower.

[0037] This application uses ionic liquid as an extractant. Through extraction, distillation, and optional purification steps, the mixed dimethylnaphthalene components contained in mineral oil fractions can be enriched to more than 95%, providing high-purity raw materials for further high-value-added utilization of mixed dimethylnaphthalene. Attached Figure Description

[0038] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings:

[0039] Figure 1 This is a schematic diagram of the method and system for separating mixed dimethylnaphthalene from mineral oil according to the present invention. Detailed Implementation

[0040] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. Through these descriptions, the features and advantages of the present application will become clearer and more apparent.

[0041] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments. Although various aspects of embodiments are shown in the accompanying drawings, the drawings are not necessarily drawn to scale unless specifically indicated otherwise.

[0042] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0043] This application provides a method for separating mixed dimethylnaphthalene from mineral oil fractions, comprising:

[0044] The extraction step includes extracting the mineral oil using an extraction solvent to obtain a raffinate stream rich in alkane and an extractant stream rich in aromatics and the extraction solvent; wherein the extraction solvent is an ionic liquid.

[0045] The distillation process includes:

[0046] The extract phase stream rich in aromatics and extraction solvent is subjected to a first distillation in a first distillation column to obtain the top stream and bottom stream of the first distillation column.

[0047] The bottom stream from the first distillation column is subjected to a second distillation in the second distillation column to obtain the product mixed dimethylnaphthalene.

[0048] In one embodiment, the extraction unit includes an extraction tower, into which mineral oil is fed from the bottom and an extraction solvent is fed from the top for liquid-phase extraction. The resulting alkane-rich raffinate stream is discharged from the top of the extraction tower, and the resulting aromatic-rich and solvent-rich extract phase stream is discharged from the bottom of the extraction tower.

[0049] In this invention, the extraction unit uses a highly selective ionic liquid solvent system, which can effectively separate mixed dimethylnaphthalene from alkanes, cycloalkanes, and some monocyclic aromatic hydrocarbons. In one embodiment, the ionic liquid is selected from imidazole or pyridine cations with alkyl-substituted cations; preferably, the alkyl-substituted imidazole cation has the structure of formula (I), and the alkyl-substituted pyridine cation has the structure of formula (II).

[0050]

[0051] Among them, R1, R2, R3, and R4 are each independently a C1 to C8 alkyl group.

[0052] In one embodiment, the anion of the ionic liquid can be hexafluorophosphate (PF6). - ), tetrafluoroborate (BF4) - ) or bis(trifluoromethanesulfonyl)imide (NTF2) - ).

[0053] The extraction solvent used in this invention can be a single ionic liquid or a composite extraction solvent formed by two or more ionic liquids.

[0054] In one embodiment, the mass ratio of the extraction solvent to the mineral oil can be (0.5–50):1, preferably (1–10):1. In one embodiment, the extraction temperature in the extraction tower is 15–120°C, and the extraction pressure is 0.1–0.5 MPa.

[0055] In this invention, the distillation separation unit comprises two columns. The first distillation column is used to separate monocyclic aromatic hydrocarbons, further increasing the content of mixed dimethylnaphthalene in the extract phase. The second distillation column is used to separate the ionic liquid solvent and the mixed dimethylnaphthalene. In one embodiment, the first distillation column employs a vacuum distillation process, with a bottom temperature of 50–180°C, a top pressure of 1–20 kPa, a reflux ratio of 0.1–1.0, and 1–10 trays.

[0056] In one embodiment, the second distillation column employs a reduced-pressure flash distillation process, with an operating temperature of 80–200°C and a top pressure of 0.1–10 kPa. The product mixture, dimethylnaphthalene, can be discharged from the top of the second distillation column.

[0057] To improve the recovery rate, the method of the present invention further includes recycling at least a portion of the bottom stream from the second distillation column back to the extraction column. In one embodiment, before recycling at least a portion of the bottom stream from the second distillation column back to the extraction column, it undergoes heat exchange with the bottom stream from the first distillation column and / or the extractant stream rich in aromatics and extraction solvent, thereby achieving thermal coupling and saving energy. In another embodiment, before recycling at least a portion of the bottom stream from the second distillation column back to the extraction column, it undergoes heat exchange sequentially with the bottom stream from the first distillation column and the extractant stream rich in aromatics and extraction solvent, thereby correspondingly controlling the temperature at which the bottom stream from the first distillation column enters the first distillation column and the temperature at which the extractant stream rich in aromatics and extraction solvent enters the second distillation column. The distillation separation step employs vacuum distillation and / or vacuum flash evaporation processes, which can separate ionic liquid solvents, mixed dimethylnaphthalene, and monocyclic aromatics.

[0058] The method of the present invention can also include a purification step based on the composition of the raw materials. This step can use back-extraction to remove trace amounts of heavy components remaining in the solvent. When the content of heavy components with boiling points >270℃ in the raw materials is high, setting up a solvent purification unit can effectively ensure the long-term stable use of the extraction solvent system. In one embodiment, the present invention further includes a purification step, which includes removing a portion of the heavy components in the bottom stream of the second distillation column using a back-extraction agent.

[0059] In one embodiment, the purification step includes:

[0060] A portion of the bottom stream from the second distillation column is fed into the upper part of the stripping column, while the stripping agent is fed into the stripping column from the lower part for back-extraction. The resulting lean solvent is discharged from the bottom of the stripping column and recycled back to the extraction column. The resulting stripped phase is discharged from the top of the stripping column. The stripped phase is fed into the stripping agent recovery column to recover the stripping agent. The resulting stripping agent is discharged from the top of the stripping agent recovery column and recycled back to the lower part of the stripping column. The resulting aromatic-rich extractable oil is discharged from the bottom of the stripping agent recovery column.

[0061] In one embodiment, the stripping agent is selected from C4 to C10 alkanes or cycloalkanes; the mass ratio of the stripping agent to the bottom stream of the second distillation column entering the stripping column is (0.2 to 7): 1; the operating temperature of the stripping column is 15 to 50°C, and the operating pressure of the stripping column is 0.1 to 0.5 MPa.

[0062] Mineral oils produced by industries such as petrochemicals and coal chemicals contain a large amount of naphthalene-based aromatics. Due to the complex composition of these aromatics, their utilization as clean fuels is difficult, and they are generally used as low-value products such as inferior diesel or fuel oil, resulting in poor resource utilization and serious environmental pollution. The method of this application can separate mixed DMN fractions from these low-value mineral oils for the production of DMN monomers, which not only greatly improves the resource utilization rate of these mineral oils but also provides a new way to obtain DMN monomers at low cost. In one embodiment, the mineral oil used in this invention is a 250-280°C fraction, preferably selected from at least one of straight-run diesel, catalytic cracking light cycle oil, coking diesel, diesel fraction obtained from direct coal liquefaction, and diesel fraction obtained from coal tar, obtained through rectification and fractionation.

[0063] like Figure 1 As shown, this application provides a system for separating mixed dimethylnaphthalene from mineral oil, comprising:

[0064] Extraction unit 1, the extraction unit is provided with one or more extraction unit stream inlets for inputting mineral oil and extraction solvent, so that the extraction solvent extracts and separates the mineral oil within the extraction unit; the extraction unit also includes a raffinate outlet and an extract phase outlet, so that the raffinate stream rich in alkane is discharged from the raffinate outlet, and the extract phase stream rich in aromatics and extraction solvent is discharged from the extract phase outlet.

[0065] A distillation separation unit, comprising a first distillation column 2 and a second distillation column 3;

[0066] The first distillation column 2 is provided with a first distillation column inlet, a first distillation column top stream outlet, and a first distillation column bottom stream outlet; wherein, the first distillation column inlet is connected to the extract phase outlet of the extraction unit, so that the extract phase stream rich in aromatics and extraction solvent from the extraction unit enters the first distillation column, the first distillation column top stream is discharged from the first distillation column top stream outlet, and the first distillation column bottom stream is discharged from the first distillation column bottom stream outlet;

[0067] The second distillation column 3 is provided with a second distillation column inlet, a second distillation column top outlet, and a second distillation column bottom outlet. The second distillation column inlet is connected to the first distillation column bottom outlet, so that the first distillation column bottom stream from the first distillation column enters the second distillation column. The second distillation column top outlet is used to discharge the product mixture dimethylnaphthalene.

[0068] In one embodiment, the bottom stream outlet of the second distillation column is also connected to the stream inlet of the extraction unit, so that at least a portion of the bottom stream of the second distillation column is recycled back to the extraction unit 1.

[0069] In one embodiment, the system further includes a first heat exchanger E1 and / or a second heat exchanger E2, such that before at least a portion of the bottom stream of the second distillation column is recycled back to the extraction unit, it exchanges heat with the bottom stream of the first distillation column and / or the extractant stream rich in aromatics and extraction solvent through the first heat exchanger E1 and / or the second heat exchanger E2. In another embodiment, the system further includes a first heat exchanger E1 and a second heat exchanger E2, such that before at least a portion of the bottom stream of the second distillation column is recycled back to the extraction unit, it exchanges heat with the bottom stream of the first distillation column and / or the extractant stream rich in aromatics and extraction solvent through the first heat exchanger E1 and the second heat exchanger E2.

[0070] In one embodiment, the system of the present invention further includes a solvent purification unit, the solvent purification unit comprising:

[0071] The back-extraction column 4 is provided with a back-extraction column inlet, a back-extraction column top stream outlet, and a back-extraction column bottom stream outlet. The back-extraction column inlet is connected to the bottom stream outlet of the second distillation column, so that a portion of the bottom stream of the second distillation column is fed into the back-extraction column 4. The back-extraction column bottom stream outlet is connected to the extraction unit stream inlet, so that the back-extraction column bottom stream from the back-extraction column 4 is recycled back to the extraction unit 1.

[0072] The back-extraction agent recovery tower 5 is provided with a back-extraction agent recovery tower material inlet, a back-extraction agent recovery tower top material outlet, and a back-extraction agent recovery tower bottom material outlet. The back-extraction agent recovery tower material inlet and the back-extraction tower top material outlet are connected, so that the back-extraction tower top material from the back-extraction tower 4 enters the back-extraction agent recovery tower. The back-extraction agent recovery tower material inlet and the back-extraction agent recovery tower top material outlet are also connected, so that the back-extraction agent recovery tower top material from the back-extraction agent recovery tower 5 is recycled back to the back-extraction tower 4.

[0073] like Figure 1As shown, the ionic liquid is fed into the extraction tower (extraction unit) 1 from the top via pipeline 6, and the mineral oil fraction at 250-280℃ is fed into the extraction tower (extraction unit) 1 from the bottom via pipeline 7 for countercurrent extraction. The top pipeline 9 yields the raffinate oil rich in saturated hydrocarbons and monocyclic aromatics, and the bottom pipeline 8 yields the extract phase rich in mixed dimethylnaphthalene and ionic liquid. The extract phase is fed into the first distillation tower 2 from the middle, and a small amount of monocyclic aromatics is distilled off from the top pipeline 10 by vacuum distillation. The bottom fraction is fed into the second distillation tower 3 from the middle via pipeline 11, and mixed dimethylnaphthalene is distilled off from the top pipeline 12 by vacuum distillation. The lean solvent stream from the bottom of the tower is fed into the extraction tower (exchanges heat twice via heat exchanger E1 with the bottom fraction from the first distillation tower 2, and via heat exchanger E2 with the extract phase from the extraction tower 1) for recycling after two heat exchanges via pipeline 13. Depending on the composition of the raw materials, a portion of the lean solvent stream from the bottom of the tower will be sent to the back-extraction tower 4 for purification via pipeline 14. The back-extraction agent will be sent from the bottom of the back-extraction tower 4 via pipeline 15 to perform countercurrent extraction with the ionic liquid to be purified. The purified ionic liquid will be returned to the extraction tower 1 for recycling from the bottom of the back-extraction tower via pipeline 16. The back-extraction oil will be sent to the back-extraction agent recovery tower 5 via pipeline 17. After vacuum distillation, the back-extraction agent will be returned to the back-extraction tower 4 for recycling via pipeline 18. The aromatic heavy components obtained at the bottom of the tower will be discharged via pipeline 19.

[0074] Heat exchangers E3, E4, and E5 can be installed at the bottom of the first distillation column 2, the bottom of the second distillation column 3, and the bottom of the stripping agent recovery column 5, respectively, to heat the bottom streams of each column and circulate them back to the respective columns, thereby improving processing efficiency.

[0075] In this invention, except for the mixed dimethylnaphthalene produced by pipeline 12, the raffinate obtained from pipeline 9 has a low content of bicyclic aromatics and can be further processed as a diesel blending component; the monocyclic aromatics obtained from pipeline 10 can be used for hydrogenation saturation to produce naphthenic solvent oil, or for hydrocracking to produce high-octane gasoline, light aromatics—benzene, toluene and xylene.

[0076] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the term "...connected" means that two interconnected entities can be directly connected by a pipeline, or that the pipeline connecting the two entities may contain equipment such as storage tanks, heat exchangers, pressure control devices, detection devices, or other equipment. It should also be noted that, even if not explicitly stated, in the system of this application, one or more of the following can be installed as needed between the inlet and outlet of each unit device or equipment, or between any identical devices or equipment, to maintain or regulate the stability and continuity of the production process, as well as to regulate the temperature and pressure of subsequent processes and monitor process parameters. The use of these devices or equipment does not change the flow direction of materials in the production system; therefore, the system including these devices or equipment still falls within the protection scope of this application.

[0077] The present invention will be described in detail below through embodiments. In the present invention, all pressures shown are absolute pressures.

[0078] The composition and properties of the mineral oil feedstock used in the following examples and comparative examples are shown in Table 1.

[0079] Raw material A is selected from petrochemical products, specifically catalytic cracking light cycle oil (LCO, also known as catalytic diesel) with a high content of bicyclic aromatics; raw material B is selected from coal tar wash oil fraction from coal chemical industry. A 250–280°C fraction is extracted from both (due to insufficient precision in the number of trays in the distillation column, the raw material distillation range is not strictly between 250–280°C, which better demonstrates the superiority of this invention).

[0080] Petrochemical raw materials have a relatively high content of alkanes and cycloalkanes, while coal chemical raw materials contain virtually no alkanes or cycloalkanes.

[0081] Table 1

[0082] Raw material diesel A (Catalytic diesel fraction) B (coal tar wash oil fraction) Composition, wt% Alkanes 11.6 0.3 Cycloalkanes 14.7 0.2 Total aromatics 73.7 99.5 Monocyclic aromatic hydrocarbons 19.6 21.0 Bicyclic aromatic hydrocarbons 54.1 78.5 Distillation range, °C IBP 221.9 212.4 5v％ 238.1 225.3 10v％ 246.5 228.5 30v％ 254.4 249.0 50v％ 260.9 254.9 70v％ 270.7 259.2 90v％ 277.8 269.0 95v％ 281.0 271.8 FBP 288.6 279.8

[0083] Example 1

[0084] according to Figure 1 The process uses ionic liquid 1-n-butyl-3-methylimidazolium hexafluorophosphate (hereinafter abbreviated as IL1) as the extraction solvent to process mineral oil A. The operating conditions of the extraction unit (extraction tower), distillation separation unit (first distillation tower, second distillation tower), and solvent purification unit (back-extraction tower, back-extraction agent recovery tower) are shown in Table 2. The composition of the raffinate oil obtained from the top of the extraction tower is shown in Table 3. The composition of the product obtained from the top of the first distillation tower is shown in Table 4. The composition of the mixed dimethylnaphthalene product obtained from the top of the second distillation tower is shown in Table 5.

[0085] Example 2

[0086] according to Figure 1 The process uses ionic liquid 1-n-heptyl-3-methylimidazolium tetrafluoroborate (hereinafter abbreviated as IL2) as the extraction solvent to process mineral oil A. The operating conditions of the extraction unit, distillation separation unit, and solvent purification unit are shown in Table 2. The composition of the raffinate obtained from the top of the extraction column is shown in Table 3. The composition of the product obtained from the top of the first distillation column is shown in Table 4. The composition of the mixed dimethylnaphthalene product obtained from the top of the second distillation column is shown in Table 5.

[0087] Example 3

[0088] according to Figure 1 The process uses the ionic liquid N-n-heptyl-4-methylpyridine bis(trifluoromethanesulfonyl)imide salt (hereinafter abbreviated as IL3) as the extraction solvent to process mineral oil A. The operating conditions of the extraction unit (extraction tower), distillation separation unit (first distillation tower, second distillation tower), and solvent purification unit (back-extraction tower, back-extraction agent recovery tower) are shown in Table 2. The composition of the raffinate oil obtained at the top of the extraction tower is shown in Table 3. The composition of the product obtained at the top of the first distillation tower is shown in Table 4. The composition of the mixed dimethylnaphthalene product obtained at the top of the second distillation tower is shown in Table 5.

[0089] Example 4

[0090] Mineral oil B was treated using ionic liquid IL3 as the extraction solvent. Since mineral oil B contains virtually no alkanes or cycloalkanes, an extraction column was not required; the mixture of IL3 and mineral oil B was directly fed into the distillation separation unit. Furthermore, because the final boiling point of mineral oil B is <280℃, the second distillation column could completely distill off the mixed dimethylnaphthalene, therefore a solvent purification unit was not required. The operating conditions of the distillation separation unit are shown in Table 2, the product composition results at the top of the first distillation column are shown in Table 4, and the mixed dimethylnaphthalene product composition results at the top of the second distillation column are shown in Table 5.

[0091] Example 5

[0092] Mineral oil B was processed using the ionic liquid N-n-heptyl-4-methylpyridine hexafluorophosphate (IL4) as the extraction solvent, following the operating steps of Example 4. The operating conditions of the distillation separation unit are shown in Table 2, the product composition results at the top of the first distillation column are shown in Table 4, and the mixed dimethylnaphthalene product composition results obtained at the top of the second distillation column are shown in Table 5.

[0093] Example 6

[0094] Mineral oil B was processed using the ionic liquid N-n-butyl-4-methylpyridine hexafluorophosphate (IL4) as the extraction solvent, following the operating steps of Example 4. The operating conditions of the distillation separation unit are shown in Table 2. The product composition results at the top of the first distillation column are shown in Table 4. The mixed dimethylnaphthalene product composition results obtained at the top of the second distillation column are shown in Table 5.

[0095] Comparative Example 1

[0096] Raw material A was processed according to the method in Example 2, except that sulfolane was used instead of IL2. The operating conditions of the extraction unit are shown in Table 2, and the composition of the raffinate obtained from the top of the extraction column is shown in Table 3. Since the boiling point of sulfolane is within the boiling range of raw material A, flash evaporation separation is not possible, and the calculated composition of the extracted aromatics is shown in Table 6.

[0097] Comparative Example 2

[0098] Raw material A was treated according to the method in Example 2, except that N,N-dimethylformamide (DMF) was used instead of IL2. The operating conditions of the extraction unit are shown in Table 2. The results showed that DMF was miscible with the raw material. Since the boiling point of DMF is lower than that of raw material A, flash evaporation separation was not effective in increasing the content of mixed dimethylnaphthalene.

[0099] Comparative Example 3

[0100] Raw material A was processed according to the method of Example 2, except that 1-n-heptyl-3-methylimidazolium p-toluenesulfonate (IL6) was used instead of IL2. The operating conditions of the extraction unit (extraction tower), distillation separation unit (first distillation tower, second distillation tower), and solvent purification unit (back-extraction tower, back-extraction agent recovery tower) are shown in Table 2. The composition of the raffinate oil obtained at the top of the extraction tower is shown in Table 3, and the composition of the mixed dimethylnaphthalene product obtained at the top of the second distillation tower is shown in Table 6.

[0101] Comparative Example 4

[0102] Raw material A was processed according to the method in Example 2, except that only one vacuum flash distillation tower was installed in the distillation separation unit. The operating conditions of the extraction unit (extraction tower), the distillation separation unit (first distillation tower, second distillation tower), and the solvent purification unit (back-extraction tower, back-extraction agent recovery tower) are shown in Table 2. The composition of the raffinate oil obtained at the top of the extraction tower is shown in Table 3, and the composition of the mixed dimethylnaphthalene product obtained at the top of the second distillation tower is shown in Table 6.

[0103] As can be seen from the above embodiments, comparative examples, and tabular data, the method for separating mixed dimethylnaphthalene from mineral oil provided by the present invention utilizes an ionic liquid extraction solvent with high selectivity, low raw material cost, and yields a product with a mixed dimethylnaphthalene content of over 95%, resulting in higher utilization value. Simultaneously, the raffinate oil has a low content of bicyclic aromatic hydrocarbons, and the material obtained from the top of the first distillation column, mainly composed of monocyclic aromatic hydrocarbons, can be utilized separately, increasing added value.

[0104] The present application has been described above with reference to preferred embodiments; however, these embodiments are merely exemplary and illustrative. Various substitutions and modifications can be made to the present application based on these embodiments, all of which fall within the protection scope of the present application.

[0105]

[0106] Table 3

[0107]

[0108] Table 4

[0109] Example 1 2 3 4 5 6 Composition, wt% Alkanes 3.6 3.0 2.0 1.2 1.4 1.1 Cycloalkanes 6.1 3.9 4.7 1.4 1.3 1.3 Total aromatics 90.3 93.1 93.3 97.4 97.3 97.6 Monocyclic aromatic hydrocarbons 81.4 88.3 89.7 89.5 88.8 88.7 Bicyclic aromatic hydrocarbons 8.9 4.8 3.6 7.9 8.5 8.9

[0110] Table 5

[0111] Example 1 2 3 4 5 6 Composition, wt% Alkanes 0 0 0 0 0 0 Cycloalkanes 0 0 0 0 0 0 Total aromatics 100 100 100 100 100 100 Monocyclic aromatic hydrocarbons 4.7 4.3 4.1 2.2 2.9 3.0 Bicyclic aromatic hydrocarbons 95.3 95.7 95.9 97.8 97.1 97.0

[0112] Table 6

[0113]

Claims

1. A method for separating mixed dimethylnaphthalenes from mineral oil, comprising: The extraction step includes extracting the mineral oil using an extraction solvent to obtain a raffinate stream rich in alkane and an extractant stream rich in aromatics and the extraction solvent; wherein the extraction solvent is an ionic liquid. The distillation process includes: The extract phase stream rich in aromatics and extraction solvent is subjected to a first distillation in a first distillation column to obtain the top stream and bottom stream of the first distillation column. The bottom stream from the first distillation column is subjected to a second distillation in the second distillation column to obtain the product mixed dimethylnaphthalene; The method also includes recycling at least a portion of the bottom stream from the second distillation column back to the extraction column; Before at least a portion of the bottom stream from the second distillation column is recycled back to the extraction column, it also undergoes heat exchange with the bottom stream from the first distillation column and / or the extract phase stream rich in aromatics and extraction solvent.

2. The method according to claim 1, wherein, The extraction unit includes an extraction tower, into which mineral oil is fed from the bottom and extraction solvent is fed from the top for liquid-phase extraction. The resulting alkane-rich raffinate stream is discharged from the top of the extraction tower, and the resulting aromatic-rich and solvent-rich extract phase stream is discharged from the bottom of the extraction tower.

3. The method according to claim 1, wherein, The ionic liquid is selected from imidazole or pyridine cations with alkyl substituted cations, and hexafluorophosphate (PF6) anion. - ), tetrafluoroborate (BF4) - ) or bis(trifluoromethanesulfonyl)imide (NTF2) - ) is an ionic liquid.

4. The method according to claim 1, wherein, The mass ratio of the extraction solvent to the mineral oil is (0.5-50):

1.

5. The method according to claim 2, wherein, In the extraction tower, the extraction temperature is 15–120℃ and the extraction pressure is 0.1–0.5 MPa.

6. The method according to claim 1, wherein, The first distillation column uses a vacuum distillation process, with a bottom temperature of 50–180℃, a top pressure of 1–20 kPa, a reflux ratio of 0.1–1.0, and 1–10 trays. The second distillation column uses a vacuum flash distillation process, with an operating temperature of 80–200℃ and a top pressure of 0.1–10 kPa.

7. The method according to claim 3, wherein, The alkyl-substituted imidazole cation has the structure of formula (I), and the alkyl-substituted pyridine cation has the structure of formula (II): Formula (I), Equation (II), Among them, R1, R2, R3, and R4 are each independently a C1 to C8 alkyl group.

8. The method according to claim 4, wherein, The mass ratio of the extraction solvent to the mineral oil is (1-10):

1.

9. The method according to claim 2, wherein, The method further includes a purification step, which involves removing a portion of the heavy components in the bottom stream of the second distillation column using a back-extraction agent.

10. The method according to claim 9, wherein, The purification steps include: A portion of the bottom stream from the second distillation column is fed into the upper part of the stripping column, while the stripping agent is fed into the stripping column from the lower part for back-extraction. The resulting lean solvent is discharged from the bottom of the stripping column and recycled back to the extraction column. The resulting stripped phase is discharged from the top of the stripping column. The stripped phase is fed into the stripping agent recovery column to recover the stripping agent. The resulting stripping agent is discharged from the top of the stripping agent recovery column and recycled back to the lower part of the stripping column. The resulting aromatic-rich extractable oil is discharged from the bottom of the stripping agent recovery column.

11. The method according to claim 9 or 10, wherein, The stripping agent is selected from C4 to C10 alkanes or cycloalkanes; the mass ratio of the stripping agent to the bottom stream of the second distillation column entering the stripping column is (0.2 to 7): 1; the operating temperature of the stripping column is 15 to 50°C, and the operating pressure of the stripping column is 0.1 to 0.5 MPa.

12. The method according to claim 1, wherein, The mineral oil is a 250-280℃ fraction, obtained by distillation from at least one of straight-run diesel, catalytic cracking light cycle oil, coking diesel, diesel fraction obtained from direct coal liquefaction, and diesel fraction obtained from coal tar.

13. A system for separating mixed dimethylnaphthalenes from mineral oil, comprising: An extraction unit is provided with one or more extraction unit stream inlets for inputting mineral oil and extraction solvent, such that the extraction solvent extracts and separates the mineral oil within the extraction unit; the extraction unit also includes a raffinate outlet and an extractable phase outlet, such that an alkane-rich raffinate stream is discharged from the raffinate outlet, and an aromatic hydrocarbon- and extraction solvent-rich extractable phase stream is discharged from the extractable phase outlet. A distillation separation unit, comprising a first distillation column and a second distillation column; The first distillation column is provided with a first distillation column inlet, a first distillation column top stream outlet, and a first distillation column bottom stream outlet; wherein, the first distillation column inlet is connected to the extract phase outlet of the extraction unit, so that the extract phase stream rich in aromatics and extraction solvent from the extraction unit enters the first distillation column, the first distillation column top stream is discharged from the first distillation column top stream outlet, and the first distillation column bottom stream is discharged from the first distillation column bottom stream outlet; The second distillation column is provided with a second distillation column inlet, a second distillation column top outlet, and a second distillation column bottom outlet. The second distillation column inlet is connected to the first distillation column bottom outlet, allowing the first distillation column bottom stream from the first distillation column to enter the second distillation column. The second distillation column top outlet is used to discharge the product mixture dimethylnaphthalene. The bottom stream outlet of the second distillation column is also connected to the stream inlet of the extraction unit, allowing at least a portion of the bottom stream from the second distillation column to be recycled back to the extraction unit; and The system further includes a first heat exchanger and / or a second heat exchanger, such that at least a portion of the bottom stream of the second distillation column is recycled back to the extraction unit before exchanging heat with the bottom stream of the first distillation column and / or the extract phase stream rich in aromatics and extraction solvent through the first heat exchanger and / or the second heat exchanger.

14. The system according to claim 13, wherein, The system further includes a solvent purification unit, which comprises: The back-extraction column is provided with a back-extraction column inlet, a back-extraction column top stream outlet, and a back-extraction column bottom stream outlet. The back-extraction column inlet is connected to the bottom stream outlet of the second distillation column, so that a portion of the bottom stream of the second distillation column is fed into the back-extraction column. The back-extraction column bottom stream outlet is connected to the extraction unit stream inlet, so that the back-extraction column bottom stream from the back-extraction column is recycled back to the extraction unit. A back-extraction agent recovery tower is provided with a back-extraction agent recovery tower material inlet, a back-extraction agent recovery tower top material outlet, and a back-extraction agent recovery tower bottom material outlet. The back-extraction agent recovery tower material inlet is connected to the back-extraction tower top material outlet, so that the back-extraction tower top material from the back-extraction tower enters the back-extraction agent recovery tower; the back-extraction agent recovery tower material inlet is also connected to the back-extraction agent recovery tower top material outlet, so that the back-extraction agent recovery tower top material from the back-extraction agent recovery tower is recycled back to the back-extraction tower.

Images