Method for separating polycyclic aromatic hydrocarbon in aromatic hydrocarbon-rich oil and processing device

Abstract

The invention relates to a method for separating polycyclic aromatic hydrocarbon in aromatic hydrocarbon-rich oil and a processing device, the method comprises the following steps: the aromatic hydrocarbon-rich oil and a main solvent enter an extraction tower from the upper part, an anti-solvent enters the extraction tower from the lower part, and under the extraction separation condition, the aromatic hydrocarbon-rich oil, the main solvent and the anti-solvent are in countercurrent contact for extraction separation; raffinate flows out of the top of the extraction tower, and raffinate oil is obtained after solvent recovery; the extraction liquid flows out of the bottom of the extraction tower, and the obtained extraction oil is polycyclic aromatic hydrocarbon oil after solvent recovery; the solubility of the main solvent to aromatic hydrocarbon is greater than the solubility of the main solvent to alkane, and the anti-solvent is C3-C5 alkane. According to the method provided by the invention, C3-C5 is used as an anti-solvent, the selectivity is strong, the light aromatic hydrocarbon in the extraction liquid can be effectively subjected to back extraction, the yield of the raffinate oil is improved, and meanwhile, the content of polycyclic aromatic hydrocarbon in the raffinate oil is not increased. The obtained raffinate oil can be used as environment-friendly aromatic rubber oil, and the extract oil can be used as polycyclic aromatic oil for blending asphalt products or low-sulfur ship fuel.

Description

Technical Field

[0001] This invention belongs to the field of petroleum processing, and specifically relates to a method and separation apparatus for extracting and separating polycyclic aromatic hydrocarbons from aromatic oil. Background Technology

[0002] The European Union's environmental regulation 2005 / 69 / EC stipulates that the mass fraction of polycyclic aromatic hydrocarbons (PCA) in rubber oils sold and used on the market must be less than 3%. The mass fraction of PCA can characterize the carcinogenic potential of oils. They are generally pure hydrocarbons with 3 to 5 rings. Among them, PCA with a mass fraction greater than 3% is considered carcinogenic, while less than 3% is considered safe.

[0003] Treated Distrillate Aromatic Extract (TDAE) uses high-aromatic oils as raw materials for solvent refining to remove carcinogenic and teratogenic polycyclic aromatic hydrocarbons (PAHs). A drawback of TDAE is that while meeting environmental standards, the yield of environmentally friendly rubber oil is relatively low, meaning the solvent has low selectivity for carcinogenic PAH components. Improving solvent efficiency to efficiently separate PAHs from non-PAH components and increase the yield of raffinate oil remains a challenging problem.

[0004] Adding a weak solubilizing agent for antisolvent extraction is a good approach. US4381234A discloses a solvent extraction process for preparing lubricating oil products, using surfactants to improve the yield of raffinate. Experimental results show that the yield of raffinate increased by 2% to 4.5% after adding trace amounts of sodium dodecylbenzenesulfonate. However, the surfactant is difficult to separate during the subsequent solvent recovery, making it unsuitable for industrial application.

[0005] The paper "Orthogonal Experimental Study on the Production of Environmentally Friendly Rubber Filler Oil by Furfural and Additives" (Liu Jie, Fu Cancan, Wu Kunpeng, et al., Applied Chemical Industry, 2015, Vol. 44, pp. 314-317) discloses an experiment on the extraction of Karamay reduced-temperature oil using furfural and petroleum ether. The results show that with the increase of the agent-to-oil ratio and extraction temperature, the polycyclic aromatic hydrocarbon content, refractive index, and yield of the refined oil all decrease. The addition of additives can increase the yield of refined oil by up to 14 percentage points, but the polycyclic aromatic hydrocarbon content is prone to exceed the standard.

[0006] CN103589453A discloses a method for preparing aromatic rubber oil, using C6-C12 light alkanes as the antisolvent and furfural as the main solvent to extract aromatic oil. This method can effectively improve the yield of raffinate oil. However, C6-C12 light alkanes have high density and boiling point, which is not much different from the boiling point of the main solvent, making it difficult to completely separate them. They can only be recovered by mixing them with the main solvent. Under long-term operating conditions, it is difficult to maintain the ratio of main solvent to antisolvent, resulting in a decrease in solvent extraction efficiency. At the same time, C6-C12 light alkanes have strong solubility, and some polycyclic aromatic hydrocarbons will dissolve into the raffinate oil during back-extraction, causing the amount of polycyclic aromatic hydrocarbons to exceed the standard. Summary of the Invention

[0007] The technical problems to be solved by this invention are: in the prior art, the yield of raffinate is too low when solvent extraction and separation of polycyclic aromatic hydrocarbons (PAHs) from aromatic oils; and when C6-C12 light alkanes are used as antisolvents, the content of PAHs easily exceeds the standard, and it is difficult to separate and recover the antisolvent. This invention provides a method and processing apparatus for solvent extraction and separation of PAHs from aromatic oils.

[0008] In a first aspect, the present invention provides a method for separating polycyclic aromatic hydrocarbons from aromatic oil, comprising:

[0009] Aromatic oil and main solvent enter the extraction tower from the top, while antisolvent enters from the bottom. Under extraction separation conditions, the aromatic oil, main solvent, and antisolvent are in countercurrent contact for extraction separation. Raffinate flows out from the top of the extraction tower and is recovered by solvent to obtain raffinate oil. Extract flows out from the bottom of the extraction tower and is recovered by solvent to obtain extracted oil, which is polycyclic aromatic hydrocarbon oil. The main solvent has a higher solubility for aromatics than for alkanes, and the antisolvent is a C3-C5 alkane.

[0010] The raffinate oil is used as an environmentally friendly rubber oil, and the polycyclic aromatic hydrocarbon oil can be used as a blending component for asphalt products or low-sulfur marine fuel.

[0011] The aromatic oil has a distillation range of 290-580℃ and its physical properties meet the following requirements: aromatic content >45wt%, polycyclic aromatic hydrocarbon content >8wt%.

[0012] The primary solvent is selected from one or more of furfural, N-methylpyrrolidone (NMP), dimethyl sulfoxide, sulfolane, and phenol. The antisolvent is a C3-C5 light hydrocarbon.

[0013] In a second aspect, the present invention provides a processing apparatus for separating polycyclic aromatic hydrocarbons from aromatic oil, and a method for separating polycyclic aromatic hydrocarbons from aromatic oil, comprising:

[0014] An extraction tower is used for the countercurrent contact extraction and separation of aromatic oil, main solvent and antisolvent. The extraction tower is provided with an upper inlet, a lower inlet, a top outlet and a bottom outlet.

[0015] The raffinate solvent recovery unit includes a first antisolvent recovery tower and a first main solvent recovery tower connected in sequence. The first antisolvent recovery tower has an antisolvent outlet at the top and is connected to the first main solvent recovery tower at the bottom. The first main solvent recovery tower has a raffinate oil outlet at the bottom and a main solvent outlet at the top. The top outlet of the extraction tower is connected to the raffinate solvent recovery unit.

[0016] The extract solvent recovery unit includes a second antisolvent recovery tower and a second main solvent recovery tower connected in sequence. The second antisolvent recovery tower has an antisolvent outlet at the top and is connected to the second main solvent recovery tower at the bottom. The second main solvent recovery tower has an extract oil outlet at the bottom and a main solvent outlet at the top. The bottom outlet of the extraction tower is connected to the extract solvent recovery unit.

[0017] The beneficial effects of the method and apparatus for separating polycyclic aromatic hydrocarbons from aromatic oils provided by this invention are as follows:

[0018] (1) The method provided by the present invention uses solvent extraction to separate polycyclic aromatic hydrocarbons in aromatic oil. C3 to C5 light hydrocarbons are used as antisolvents. It has high selectivity for ideal components such as saturated hydrocarbons and mono- and dicyclic aromatic hydrocarbons, and can effectively back-extract saturated hydrocarbons and light aromatic hydrocarbons in the extract phase. However, it has extremely low solubility for non-ideal polycyclic aromatic hydrocarbon components. It can not only improve the yield of raffinate oil under the premise that the content of polycyclic aromatic hydrocarbons meets the standard, but also facilitate the separation and recovery of antisolvents, effectively ensuring the long-term stable operation of the process.

[0019] (2) This invention uses C3-C5 light hydrocarbons as the antisolvent, which have low density and boiling point. In the extractor, most of these hydrocarbons concentrate in the upper raffinate phase, avoiding backmixing and contamination. Furthermore, this invention employs a two-stage solvent recovery process: first, C3-C5 light hydrocarbons are recovered under supercritical conditions, facilitating separation from the main solvent; then, the main solvent is recovered. This two-stage solvent recovery ensures the purity of both the main solvent and the antisolvent, making it easier to control the ratio of main solvent to antisolvent and maintaining the solvent extraction and separation effect during long-term operation. Attached Figure Description

[0020] Figure 1 This is a schematic flowchart of one embodiment of the method for separating polycyclic aromatic hydrocarbons from aromatic oil provided by the present invention.

[0021] Explanation of reference numerals in the attached figures:

[0022] 1-Frequency oil tank; 2-Main solvent tank; 3-Antisolvent tank

[0023] 4-Mixing unit; 5-Extraction tower; 6-First antisolvent recovery tower

[0024] 7-First main solvent recovery tower; 8-Raw oil tank; 9-Second antisolvent recovery tower

[0025] 10-Second main solvent recovery tower; 11-Extraction oil tank

[0026] I-Aromatic Oil II-Main Solvent III-Antisolvent

[0027] IV - Raffinate; V - Extract; VI - First Recovered Antisolvent

[0028] VII - Raffinate containing main solvent; VIII - First recovered main solvent; IX - Raffinate oil

[0029] X - Second recovered antisolvent; XI - Extract containing main solvent; XII - Second recovered main solvent

[0030] XIII-Extracted Oil

[0031] Figure 2 This is a schematic flowchart of the method for separating polycyclic aromatic hydrocarbons from aromatic oil in Comparative Example 1.

[0032] Explanation of reference numerals in the attached figures:

[0033] 1-Feed oil tank; 2-Main solvent tank; 5-Extraction tower

[0034] 7-Solvent recovery tower for raffinate; 8-Raffinate oil tank; 10-Solvent recovery tower for extract. 11-Extraction Tank

[0035] I - Aromatic oil; II, XII, VIII - Extraction solvent; IV - Raffinate V-Extract IX-Residual Oil XIII-Extract Oil Detailed Implementation

[0036] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0037] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0038] In this invention, unless otherwise specified, the top of the container refers to the position of 0-10% of the container from top to bottom; the upper part of the container refers to the position of 10-40% of the container from top to bottom; the lower part of the container refers to the position of 60-90% of the container from top to bottom; and the bottom of the container refers to the position of 90-100% of the container from top to bottom.

[0039] In a first aspect, the present invention provides a method for separating polycyclic aromatic hydrocarbons (PAHs) from aromatic-rich oil, comprising: the aromatic-rich oil and a main solvent entering an extraction tower from the top, and an antisolvent entering the extraction tower from the bottom; under extraction separation conditions, the aromatic-rich oil, the main solvent, and the antisolvent are subjected to countercurrent contact for extraction separation; the raffinate flows out from the top of the extraction tower, and the raffinate oil obtained after solvent recovery is used as an environmentally friendly rubber oil; the extract flows out from the bottom of the extraction tower, and the extract oil obtained after solvent recovery is a PAH oil; wherein the main solvent has a greater solubility for aromatic hydrocarbons than for alkanes, and the antisolvent is a C3-C5 alkanes.

[0040] In this invention, the aromatic oil has a distillation range of 290-580℃, an aromatic content of >45wt%, and a polycyclic aromatic hydrocarbon content of >8%; the type of aromatic oil has a wide range of selection, as long as the physical properties of the aromatic oil meet the above-mentioned limitations.

[0041] Preferably, the aromatic oil is selected from one or more of the following: reduced-pressure second-line distillate oil (distillation range 290-520℃), reduced-pressure third-line distillate oil (distillation range 330-540℃), reduced-pressure fourth-line distillate oil (distillation range 350-580℃), furfural extract oil (distillation range 300-620℃), and catalytic slurry oil (distillation range 340-580℃).

[0042] In this invention, the main solvent has a greater solubility for aromatics than for alkanes, and is selected from one or more of furfural, N-methylpyrrolidone, dimethyl sulfoxide, sulfolane, and phenol, preferably furfural or N-methylpyrrolidone. The antisolvent is selected from C3-C5 alkanes, preferably n-butane and / or isobutane.

[0043] Preferably, the mass ratio of the aromatic oil to the extraction solvent is 1:1-5, more preferably 1:1.5-3. An excessively high mass ratio of extraction solvent to aromatic oil will lead to excessive energy consumption in the subsequent solvent separation process, while an excessively low ratio will result in the inability to separate the miscible phases. The extraction solvent consists of a main solvent and a reverse solvent. The mass ratio of the main solvent to the reverse solvent is 1:0.05-0.50, more preferably 1:0.1-0.3. An excessively high mass ratio of the main solvent to the reverse solvent will not achieve the effect of back-extraction, while an excessively low mass ratio will affect the extraction effect of the main solvent on the polycyclic aromatic hydrocarbon components, leading to an increase in the polycyclic aromatic hydrocarbon content in the raffinate and a decrease in yield.

[0044] In this invention, the extraction and separation conditions of the extraction tower are as follows: pressure is 1-8 MPa, preferably 1.5-5 MPa; top temperature is 50-200℃, preferably 80-150℃; bottom temperature is 40-190℃, preferably 70-140℃.

[0045] Preferably, the raffinate enters the raffinate solvent recovery unit, which includes: the raffinate enters the first anti-solvent recovery tower, where the anti-solvent is recovered at a temperature of 150-250°C and a pressure of 2-5 MPa, and then enters the first main solvent recovery tower, where the main solvent is recovered at a temperature of 150-230°C and a pressure of -0.1-1.0 MPa, to obtain raffinate oil;

[0046] Preferably, the operating conditions of the first anti-solvent recovery tower are: temperature 180-220℃ and pressure 3.5-4.3MPa; the operating conditions of the first main solvent recovery tower are: temperature 175-200℃ and pressure -0.05-0.1MPa.

[0047] Preferably, the extract enters the extract solvent recovery unit, which includes: the extract entering a second antisolvent recovery tower, where the antisolvent is recovered at a temperature of 150-250°C and a pressure of 2-5 MPa; then entering a second main solvent recovery tower, where the main solvent is recovered at a temperature of 150-230°C and a pressure of -0.1-1.0 MPa, to obtain the extracted oil. Only by employing these preferred extraction conditions can the polycyclic aromatic hydrocarbons in the aromatic-rich oil be effectively separated and removed.

[0048] Preferably, the operating conditions of the second anti-solvent recovery tower are: temperature 180-220℃ and pressure 3.5-4.3MPa; the operating conditions of the second main solvent recovery tower are: temperature 175-200℃ and pressure -0.05-0.1MPa.

[0049] Preferably, the main solvent and antisolvent obtained from the solvent recovery tower are each independently returned as circulating extraction solvents.

[0050] Preferably, the aromatic oil and the main solvent are mixed first and then enter the extraction tower from the top, where they are countercurrently contacted with the antisolvent entering from the bottom for extraction and separation.

[0051] In this invention, a mixture of aromatic oil and main solvent is countercurrently contacted with an antisolvent for extraction and separation. Raffinate flows out from the top of the extraction tower. The raffinate contains aromatic oil from which polycyclic aromatic hydrocarbons have been removed, a large amount of antisolvent, and a small amount of main solvent. Preferably, based on the raffinate, the antisolvent content is 12-25 wt%, and the main solvent content is 40-55 wt%. The raffinate oil obtained after solvent recovery is used as an environmentally friendly rubber oil. This invention does not limit the method for solvent recovery from the raffinate. Preferably, a two-stage solvent separation method is used, first recovering the antisolvent, and then recovering the main solvent. Preferably, supercritical recovery of the antisolvent is performed first, with the operating conditions being: temperature 150-250℃, preferably 180-220℃, and pressure 2-5 MPa, preferably 3.5-4.3 MPa. Then, the main solvent is recovered. The recovery of the main solvent can employ conventional recovery methods in the art, such as supercritical solvent recovery, stripping recovery, flash evaporation, and multi-effect evaporation. This invention does not limit this method. In a preferred embodiment, a solvent recovery tower is used to recover the main solvent. The operating conditions of the solvent recovery tower are: temperature of 150-230℃, preferably 175-200℃, and pressure of -0.1-1.0MPa, preferably -0.05-0.1MPa.

[0052] In this invention, the extract flows out from the bottom of the extraction tower. The extract contains polycyclic aromatic hydrocarbons (PAHs), a small amount of antisolvent, and a large amount of main solvent. Preferably, based on the extract, the antisolvent content is 3-10 wt%, and the main solvent content is 70-85 wt%. The extracted oil obtained after solvent recovery is a PAH oil, which is used as a blending component for asphalt products or low-sulfur marine fuel. The solvent recovery method can employ conventional solvent recovery methods in the art; this invention does not limit the solvent recovery method for the raffinate. Preferably, a two-stage solvent separation method is used: first, supercritical recovery of the antisolvent is performed under the following operating conditions: temperature 150-250℃, preferably 180-220℃, and pressure 2-5 MPa, preferably 3.5-4.3 MPa; then, the main solvent is recovered using conventional recovery methods in the art. In a preferred embodiment, a solvent recovery tower is used to recover the main solvent. The operating conditions of the solvent recovery tower are: temperature of 150-230℃, preferably 175-200℃, and pressure of -0.1-1.0MPa, preferably -0.05-0.1MPa.

[0053] In this invention, supercritical recovery of antisolvents has two advantages: first, under supercritical conditions, the solubility of C3-C5 light hydrocarbons changes greatly with temperature and pressure, making them easy to completely separate from oil and main solvent; second, under supercritical conditions, C3-C5 hydrocarbons do not vaporize and can enter the heat exchange network in a supercritical phase to exchange heat with other streams, which helps to reduce the energy consumption of the device.

[0054] In this invention, a two-stage solvent recovery process is used to separate and recycle the main solvent and the antisolvent, ensuring the purity of the main solvent and the antisolvent, making it easier to control the ratio of the main solvent to the antisolvent, and helping to maintain the solvent extraction and separation effect during long-term operation.

[0055] In this invention, the physical properties of the raffinate oil satisfy the following: mass yield ≥35%, preferably ≥45%; polycyclic aromatic hydrocarbon content <3%.

[0056] In this invention, unless otherwise specified, the extraction tower can be a well-known rotating disc tower, sieve plate tower, or packed tower, or it can be an empty tower; the form is not limited.

[0057] Secondly, the present invention provides a processing apparatus for separating polycyclic aromatic hydrocarbons from aromatic oil, used in the above-mentioned method for separating polycyclic aromatic hydrocarbons from aromatic oil, the processing apparatus comprising:

[0058] An extraction tower is used for the countercurrent contact extraction and separation of aromatic oil, main solvent and antisolvent. The extraction tower is provided with an upper inlet, a bottom inlet, a top outlet and a bottom outlet.

[0059] The raffinate solvent recovery unit includes a first antisolvent recovery tower and a first main solvent recovery tower connected in sequence. The first antisolvent recovery tower has an antisolvent outlet at the top and is connected to the first main solvent recovery tower at the bottom. The first main solvent recovery tower has a raffinate oil outlet at the bottom and a main solvent outlet at the top. The top outlet of the extraction tower is connected to the raffinate solvent recovery unit.

[0060] The extract solvent recovery unit includes a second antisolvent recovery tower and a second main solvent recovery tower connected in sequence. The second antisolvent recovery tower has an antisolvent outlet at the top and is connected to the second main solvent recovery tower at the bottom. The second main solvent recovery tower has an extract oil outlet at the bottom and a main solvent outlet at the top. The bottom outlet of the extraction tower is connected to the extract solvent recovery unit.

[0061] Preferably, the processing apparatus provided by the present invention further includes:

[0062] A mixing unit is used to premix aromatic oil with the main solvent, and the mixing unit is connected to the upper inlet of the extraction tower.

[0063] Preferably, the processing apparatus provided by the present invention further includes:

[0064] The raw material oil tank, connected to the mixing unit, is used to store aromatic oil.

[0065] The main solvent tank, connected to the mixing unit, is used to store the main solvent;

[0066] The antisolvent tank, connected to the bottom inlet of the extraction tower, is used to store the antisolvent.

[0067] Preferably, the top outlets of the first antisolvent recovery tower and the second antisolvent recovery tower are respectively connected to the antisolvent tank, and the top outlets of the first main solvent recovery tower and the second main solvent recovery tower are respectively connected to the main solvent tank, for recycling the separated main solvent and antisolvent.

[0068] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention, but the drawings and embodiments do not constitute a limitation of the present invention.

[0069] Appendix Figure 1 A schematic flowchart of one embodiment of a method for separating polycyclic aromatic hydrocarbons from aromatic oils is attached. Figure 1 As shown, aromatic oil I from feedstock tank 1 and main solvent II from main solvent tank 2 enter mixing unit 4 for mixing, and then enter the upper part of extraction tower 5; antisolvent III from antisolvent tank 3 enters the lower part of extraction tower 5 and undergoes countercurrent extraction with the aforementioned streams. Raffinate IV flowing out from the top of extraction tower 5 enters first antisolvent recovery tower 6. First recovered antisolvent VI flows out from the top of first antisolvent recovery tower 6, and raffinate VII containing main solvent flows out from the bottom of first antisolvent recovery tower 6 enters first main solvent recovery tower 7. First recovered main solvent VIII flows out from the top of first main solvent recovery tower 7, and raffinate IX flows out from the bottom of first main solvent recovery tower 7 enters raffinate oil tank 8. On the other hand, extract V flowing out from the bottom of extraction tower 5 enters second antisolvent recovery tower 9. Second recovered antisolvent X flows out from the top of second antisolvent recovery tower 9, and extract XI containing main solvent flows out from the bottom of second antisolvent recovery tower 9 enters second main solvent recovery tower 10. Second recovered main solvent XII flows out from the top of second main solvent recovery tower 10, and extract XIII flows out from the bottom of second main solvent recovery tower 10 enters extract oil tank 11. The first recovered antisolvent VI and the second recovered antisolvent X are combined and recycled back to antisolvent tank 3, and the first recovered main solvent VIII and the second recovered main solvent XII are combined and recycled back to main solvent tank 2.

[0070] The raffinate IX can be used as an environmentally friendly aromatic rubber oil; the extract XIII can be used as a blending component for asphalt products or low-sulfur marine fuel.

[0071] The processing apparatus for separating polycyclic aromatic hydrocarbons (PAHs) from aromatic-rich oils provided by this invention includes: an extraction tower 5, which has an upper inlet, a lower inlet, a top outlet, and a bottom outlet; a raffinate solvent recovery unit connected to the top outlet of the extraction tower, comprising a first antisolvent recovery tower 6 and a first main solvent recovery tower 7 connected in sequence, the first antisolvent recovery tower 6 having an antisolvent outlet at its top and being connected to the first main solvent recovery tower 7 at its bottom, the first main solvent recovery tower 7 having a raffinate oil outlet at its bottom and a main solvent outlet at its top; and an extract solvent recovery unit connected to the bottom outlet of the extraction tower 5, comprising a second antisolvent recovery tower 9 and a second main solvent recovery tower 10 connected in sequence, the second antisolvent recovery tower 9 having an antisolvent outlet at its top and being connected to the second main solvent recovery tower 10 at its bottom, the second main solvent recovery tower 10 having an extract oil outlet at its bottom and a main solvent outlet at its top. The feed oil tank 1 and the main solvent tank 2 are connected to the upper inlet of the extraction tower 5 via a mixing unit 4. The antisolvent tank 3 is connected to the lower inlet of the extraction tower 5.

[0072] The present invention will be described in detail below through embodiments.

[0073] Example 1

[0074] As shown in the attached document Figure 1 The process flow shown is for separating polycyclic aromatic hydrocarbons from aromatic oil. The raw material aromatic oil is high-grade anti-dewaxing extract oil (properties are shown in Table 1), the main solvent is furfural, and the anti-solvent is n-butane.

[0075] Includes the following steps:

[0076] (1) The Takahashi reduced 4 dewaxing extract oil is mixed with the main solvent furfural and injected into the upper part of the extraction tower. The antisolvent n-butane enters the extraction tower from the bottom and comes into countercurrent contact with the aforementioned stream for extraction and separation.

[0077] The mass ratio of feedstock oil to extraction solvent (furfural + n-butane) is 1:2.5, and the mass ratio of furfural to n-butane is 1:0.15. The extraction and separation conditions are: pressure 4 MPa, top temperature 120℃, and bottom temperature 110℃.

[0078] (2) The raffinate flows out from the top of the extraction tower and is recycled after two stages of solvent recovery to obtain raffinate oil, a large amount of antisolvent and a small amount of main solvent. The solvent can be recycled.

[0079] The conditions for the recovery of the first anti-solvent are: pressure 4.2 MPa and temperature 210℃; the conditions for the recovery of the first main solvent are: temperature 170℃ and pressure 0.1 MPa.

[0080] (3) The extract flows out from the bottom of the extraction tower and is recycled after two stages of solvent recovery to obtain the extract oil. A large amount of main solvent and a small amount of anti-solvent are recycled.

[0081] The conditions for the recovery of the second antisolvent are: pressure 4.2 MPa and temperature 220℃; the conditions for the recovery of the first main solvent are: temperature 180℃ and pressure 0.2 MPa.

[0082] The physical properties of raffinate oil R1 and raffinate oil E1 are listed in Table 2.

[0083] Example 2

[0084] The aromatic oil feedstock, process flow, and processing equipment are the same as in Example 1;

[0085] The difference is that in step (2), the main solvent is N-methylpyrrolidone and the antisolvent is n-pentane; the mass ratio of the feed oil to the extraction solvent (NMP + n-pentane) is 1:3, and the mass ratio of NMP to n-pentane is 1:0.10.

[0086] The extraction and separation conditions were: pressure 4.3 MPa, top temperature 130°C, and bottom temperature 120°C.

[0087] Under the same conditions, the physical properties of the obtained raffinate oil R2 and raffinate oil E2 are listed in Table 2.

[0088] Comparative Example 1

[0089] The aromatic oil feedstock is the same as in Example 1, except that a reverse solvent was not used in step (2); instead, an auxiliary solvent was used. Figure 2 The process separates polycyclic aromatic hydrocarbons from aromatic oil. Specifically, aromatic feedstock I enters extraction tower 5 through the lower inlet, and extraction solvent II enters extraction tower 5 through the upper inlet to perform countercurrent extraction with the aforementioned feedstock. The raffinate IV flowing out from the top of the extraction tower enters the raffinate solvent recovery tower 7, where the extraction solvent VIII recovered at the top is recycled, and raffinate oil IX is obtained from the bottom. The extract V flowing out from the bottom of extraction tower 5 enters the extract solvent recovery tower 10, where the extraction solvent XII recovered at the top is recycled, and extract oil XIII is discharged from the bottom.

[0090] The extraction and separation conditions were: pressure 4 MPa, top temperature 120°C, and bottom temperature 110°C.

[0091] The operating conditions for the solvent recovery tower of the extract were 170℃ and 0.1MPa; the operating conditions for the solvent recovery tower of the raffinate were 180℃ and 0.2MPa; the physical properties of the obtained raffinate oil R3 and raffinate oil E3 are listed in Table 3.

[0092] Comparative Example 2

[0093] The aromatic raw materials, process flow and processing equipment are the same as in Example 1, except that in step (2), the antisolvent is petroleum ether;

[0094] The mass ratio of feedstock oil to extraction solvent (furfural + petroleum ether) is 1:2.7, and the mass ratio of furfural to petroleum ether is 1:0.10.

[0095] The extraction and separation conditions were: pressure 4.2 MPa, top temperature 160°C, and bottom temperature 150°C.

[0096] Under the same conditions, the physical properties of the obtained raffinate oil R4 and raffinate oil E4 are listed in Table 3.

[0097] Comparative Example 3

[0098] The aromatic hydrocarbon feedstock, process flow, and processing equipment are the same as in Example 1. The difference is that in step (2), the antisolvent is cyclohexane; the mass ratio of feedstock oil to extraction solvent (furfural + cyclohexane) is 1:3.0, and the mass ratio of furfural to cyclohexane is 1:0.10; the extraction and separation conditions are a pressure of 0.5 MPa, a top temperature of 90°C, and a bottom temperature of 80°C; the other conditions are the same, and the physical properties of the obtained raffinate oil R5 and raffinate oil E5 are listed in Table 4.

[0099] Comparative Example 4

[0100] The aromatic hydrocarbon raw materials, process flow, and processing equipment are the same as in Example 1. The difference is that in step (2), the antisolvent is cyclohexane + water;

[0101] The mass ratio of feedstock oil to extraction solvent (furfural + cyclohexane) was 1:3.0, and the mass ratio of furfural:cyclohexane:water was 1:0.95:0.05.

[0102] The extraction and separation conditions were: pressure 0.5 MPa, top temperature 90°C, and bottom temperature 80°C; all other conditions were the same. The physical properties of the obtained raffinate oil R6 and raffinate oil E6 are listed in Table 4.

[0103] Table 1 Properties of Takahashi Decaluminate IV Dewaxing Extract Oil

[0104] <![CDATA[Density (15 °C) / (kg / m 3 )]]> 1004.5 <![CDATA[Density (20 °C) / (kg / m 3 )]]> 1001.1 <![CDATA[Kinematic viscosity / (mm 2 / s)]]> 80℃ 170.1 100℃ 54.70 Pour point / ℃ 12 Total acid value (mgKOH / g) 0.86 Carbon residue value / % 3.91 w(aromatic fraction) / % 64.7 Flash point / °C 265 w(C7 insoluble matter) / (mg / kg) 60 w(PCA) / % 20.0 carbon / % 88.14 hydrogen / % 10.39 w(sulfur) / % 0.659 w(nitrogen) / % 0.49

[0105] Table 2

[0106]

[0107] Table 3

[0108]

[0109] Table 4

[0110]

[0111] As shown in Table 2, Examples 1-2, employing the method of this invention and using C3-C5 light hydrocarbons as the anti-solvent, exhibit high back-extraction selectivity and can effectively back-extract saturated hydrocarbons and light aromatics from the extract phase. The resulting raffinate yield is ≥45wt%, and the polycyclic aromatic hydrocarbon content is <3%, making it suitable as an environmentally friendly aromatic rubber oil.

[0112] Compared to Example 1, Comparative Example 1 did not use a reverse solvent, thus failing to achieve the effect of back-extracting beneficial components such as saturated hydrocarbons and light aromatics from the extract phase. As can be seen from the data in Table 3, the raffinate yield decreased by 9 percentage points.

[0113] Compared to Example 1, Comparative Example 2 used petroleum ether as the antisolvent. As shown in Table 3, although the raffinate oil yield was significantly improved, the high density and solubility of petroleum ether caused some polycyclic aromatic hydrocarbons (PAHs) to be back-extracted into the raffinate phase, resulting in a severely excessive PAH content in the raffinate oil. Furthermore, the high boiling point of petroleum ether makes it difficult to separate from the main solvent during solvent recovery, gradually leading to solvent contamination.

[0114] Compared to Example 1, Comparative Example 3 used cyclohexane as the antisolvent. As can be seen from the data in Table 4, using alkanes with a larger number of carbon atoms as the antisolvent did indeed slightly improve the raffinate yield. However, cyclohexane has relatively poor selectivity, which causes some polycyclic aromatic hydrocarbons to be back-extracted into the raffinate phase, resulting in a slightly excessive content of polycyclic aromatic hydrocarbons in the raffinate.

[0115] Comparative Example 4 used cyclohexane + water as the antisolvent. The addition of water can increase the polarity of furfural solvent and enhance its selectivity for dissolving polycyclic aromatic hydrocarbons. Therefore, while the raffinate yield was slightly higher than that of Example 1, the polycyclic aromatic hydrocarbon content also met the standard (<3%). However, due to the addition of more additives, it was difficult to completely separate the solvents during solvent recovery, which not only increased the cost and energy consumption of the equipment, but also gradually caused solvent contamination during long-term operation.

Claims

1. A method for separating polycyclic aromatic hydrocarbons from aromatic oil, characterized in that, The method includes: aromatic oil and main solvent entering the extraction tower from the top, and antisolvent entering the extraction tower from the bottom; under extraction separation conditions, the aromatic oil, main solvent and antisolvent are contacted countercurrently for extraction separation; raffinate flows out from the top of the extraction tower, and after solvent recovery, raffinate oil is obtained; extract flows out from the bottom of the extraction tower, and after solvent recovery, the extracted oil is a polycyclic aromatic hydrocarbon oil; the main solvent has a greater solubility for aromatics than for alkanes, and the antisolvent is a C3-C5 alkane.

2. The method for separating polycyclic aromatic hydrocarbons from aromatic-rich oil according to claim 1, characterized in that, The aromatic oil has a distillation range of 290-580℃, an aromatic content of >45wt%, and a polycyclic aromatic hydrocarbon content of >8%. Preferably, the aromatic oil is selected from one or more of the following: reduced second-line distillate oil, reduced third-line distillate oil, reduced fourth-line distillate oil, furfural extract oil, and catalytic slurry oil.

3. The method for separating polycyclic aromatic hydrocarbons from aromatic-rich oil according to claim 1 or 2, characterized in that, The main solvent is selected from one or more of furfural, N-methylpyrrolidone, dimethyl sulfoxide, sulfolane, and phenol; Preferably, the main solvent is furfural or N-methylpyrrolidone.

4. The method for separating polycyclic aromatic hydrocarbons from aromatic-rich oil according to claim 1 or 2, characterized in that, The mass ratio of the aromatic oil to the extraction solvent is 1:1-5, and the mass ratio of the main solvent to the antisolvent is 1:0.05-0.50, wherein the extraction solvent is the main solvent and the antisolvent. Preferably, the mass ratio of the aromatic oil to the extraction solvent is 1:1.5-3; and the mass ratio of the main solvent to the antisolvent is 1:0.1-0.

3.

5. The method for separating polycyclic aromatic hydrocarbons from aromatic-rich oil according to claim 4, characterized in that, The extraction and separation conditions of the extraction column are: pressure 1-8 MPa, top temperature 50-200℃, and bottom temperature 40-190℃. Preferably, the pressure is 1.5-5 MPa; the top temperature is 80-150℃; and the bottom temperature is 70-140℃.

6. The method for separating polycyclic aromatic hydrocarbons from aromatic-rich oil according to claim 5, characterized in that, The raffinate enters the first anti-solvent recovery tower, where the anti-solvent is recovered at a temperature of 150-250℃ and a pressure of 2-5 MPa. Then it enters the first main solvent recovery tower, where the main solvent is recovered at a temperature of 150-230℃ and a pressure of -0.1-1.0 MPa, to obtain raffinate oil. Preferably, the operating conditions of the first anti-solvent recovery tower are: temperature 180-220℃ and pressure 3.5-4.3MPa; the operating conditions of the first main solvent recovery tower are: temperature 175-200℃ and pressure -0.05-0.1MPa.

7. The method for separating polycyclic aromatic hydrocarbons from aromatic-rich oil according to claim 5, characterized in that, The extract enters the second antisolvent recovery tower, where the antisolvent is recovered at a temperature of 150-250℃ and a pressure of 2-5 MPa. Then it enters the second main solvent recovery tower, where the main solvent is recovered at a temperature of 150-230℃ and a pressure of -0.1-1.0 MPa, to obtain the extract oil. Preferably, the operating conditions of the second anti-solvent recovery tower are: temperature 180-220℃ and pressure 3.5-4.3MPa; the operating conditions of the second main solvent recovery tower are: temperature 175-200℃ and pressure -0.05-0.1MPa.

8. The method for separating polycyclic aromatic hydrocarbons from aromatic-rich oil according to any one of claims 1-7, characterized in that, The main solvent and antisolvent obtained from the solvent recovery are each independently returned as circulating extraction solvents.

9. A processing apparatus for separating polycyclic aromatic hydrocarbons from aromatic oil, used in the method for separating polycyclic aromatic hydrocarbons from aromatic oil according to any one of claims 1-8, characterized in that, include: An extraction tower is used for the countercurrent contact extraction and separation of aromatic oil, main solvent and antisolvent. The extraction tower is provided with an upper inlet, a lower inlet, a top outlet and a bottom outlet. The raffinate solvent recovery unit includes a first antisolvent recovery tower and a first main solvent recovery tower connected in sequence. The first antisolvent recovery tower has an antisolvent outlet at the top and is connected to the first main solvent recovery tower at the bottom. The first main solvent recovery tower has a raffinate oil outlet at the bottom and a main solvent outlet at the top. The top outlet of the extraction tower is connected to the raffinate solvent recovery unit. The extract solvent recovery unit includes a second antisolvent recovery tower and a second main solvent recovery tower connected in sequence. The second antisolvent recovery tower has an antisolvent outlet at the top and is connected to the second main solvent recovery tower at the bottom. The second main solvent recovery tower has an extract oil outlet at the bottom and a main solvent outlet at the top. The bottom outlet of the extraction tower is connected to the extract solvent recovery unit.

10. The processing apparatus for separating polycyclic aromatic hydrocarbons from aromatic oil according to claim 9, characterized in that, Also includes: A mixing unit is used to premix aromatic oil with the main solvent, and the mixing unit is connected to the upper inlet of the extraction tower. Preferably, it further includes: The raw material oil tank, connected to the mixing unit, is used to store aromatic oil. The main solvent tank, connected to the mixing unit, is used to store the main solvent; The antisolvent tank, connected to the bottom inlet of the extraction tower, is used to store the antisolvent. Preferably, the top outlets of the first antisolvent recovery tower and the second antisolvent recovery tower are respectively connected to the antisolvent tank, and the top outlets of the first main solvent recovery tower and the second main solvent recovery tower are respectively connected to the main solvent tank, for recycling the separated main solvent and antisolvent.

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