Separation method and separation device for mixed aromatic hydrocarbons

Abstract

The invention provides a separation method and a separation device for mixed aromatic hydrocarbons, and the separation method comprises the following steps: 1) mixing the mixed aromatic hydrocarbons to be separated with a first solvent to obtain diluent oil; 2) performing first extraction treatment on the diluent oil by using a second solvent to obtain alkane-rich oil and first extraction oil; 3) carrying out second extraction treatment on the first extraction oil by using a second solvent to obtain tricyclic and above heavy aromatics and second extraction oil; 4) performing third extraction treatment on the second extraction oil by using a second solvent to obtain bicyclic aromatic hydrocarbon and third extraction oil; and 5) performing fourth extraction treatment on the third extraction oil by using a second solvent to obtain the monocyclic aromatic hydrocarbon and a mixed solvent. According to the separation method of the mixed aromatic hydrocarbon provided by the invention, the purity of the separated aromatic hydrocarbon with different ring numbers is relatively high.

Description

Technical Field

[0001] This invention belongs to the field of aromatic hydrocarbon processing and refining technology, and particularly relates to a method and apparatus for separating mixed aromatic hydrocarbons. Background Technology

[0002] With the development of my country's petroleum refining industry, the expansion and upgrading of multiple large-scale catalytic cracking (FCC) units have resulted in the production of large quantities of FCC diesel and slurry oil as byproducts. Therefore, the rational utilization of excess heavy distillate oil, especially high-purity aromatic hydrocarbon resources, is an important way to reduce and solidify carbon, and also provides high-quality raw materials for the production of high-end carbon materials. Taking FCC diesel as an example, it is rich in monocyclic and dicyclic aromatic hydrocarbons. Monocyclic aromatic hydrocarbons are chemical raw materials for the preparation of light aromatic hydrocarbons (BTX), while dicyclic aromatic hydrocarbons can be used to prepare high-end carbon materials such as graphite electrodes. Therefore, the stepwise separation of high-purity aromatic hydrocarbon components is an important route for high-value utilization.

[0003] Currently, the purity of aromatic hydrocarbons with different ring numbers obtained by traditional distillation and cutting methods is relatively low. Therefore, developing a method for separating mixed aromatic hydrocarbons with higher purity of different ring numbers is an urgent technical problem to be solved at this stage. Summary of the Invention

[0004] The main objective of this invention is to provide a method for separating mixed aromatic hydrocarbons, which can achieve high purity of aromatic hydrocarbons with different ring numbers obtained by the separation.

[0005] The present invention also provides a separation apparatus for performing the above separation method, which can achieve high purity of aromatic hydrocarbons of different ring numbers obtained by separation.

[0006] In a first aspect, the present invention provides a method for separating mixed aromatic hydrocarbons, comprising the following steps:

[0007] 1) The mixed aromatics to be separated and the first solvent are mixed to obtain diluted oil;

[0008] 2) The diluted oil is subjected to a first extraction treatment using a second solvent to obtain alkyl-rich oil and a first-extracted oil;

[0009] 3) The first extract oil is subjected to a second extraction process using a second solvent to obtain tricyclic or higher heavy aromatics and a second extract oil;

[0010] 4) The second extract oil is subjected to a third extraction process using a second solvent to obtain bicyclic aromatic hydrocarbons and a third extract oil;

[0011] 5) The third extract oil is subjected to a fourth extraction process using a second solvent to obtain monocyclic aromatic hydrocarbons and a mixed solvent;

[0012] Wherein, the second solvent is a mixed solvent comprising at least two or more solvents;

[0013] The absolute value of the difference between the average molecular polarity index of the first solvent and the mixed aromatic hydrocarbons to be separated is <10;

[0014] The second solvent has a larger average molecular polarity index than the first solvent, and the difference between them, S, is: 4 < S < 6.

[0015] In the separation method described above, the second solvent includes at least one third solvent with a molecular polarity index of 18-22, and the volume percentage of the third solvent in the second solvent is 40-100%.

[0016] In the separation method described above, the first solvent includes at least one fourth solvent with a molecular polarity index of 12-18, and the volume percentage of the fourth solvent in the first solvent is not less than 80%.

[0017] In the separation method described above, the average molecular polarity index of the mixed aromatic hydrocarbons to be separated is 5-9.

[0018] In the separation method described above, the volume ratio of the first solvent to the mixed aromatic hydrocarbons to be separated is 0.5-2:1; and / or,

[0019] The volume ratio of the second solvent to the diluent oil is 0.05-0.1:1;

[0020] The volume ratio of the second solvent to the first extraction oil is 0.1-0.2:1;

[0021] The volume ratio of the second solvent to the second extraction oil is 0.1-0.3:1;

[0022] The volume ratio of the second solvent to the third extract oil is 0.1-0.5:1.

[0023] In the separation method described above, in the first extraction process, the diluted oil is contacted counter-currently with the second solvent; and / or,

[0024] In the second extraction process, the first extract oil and the second solvent are in counter-current contact; and / or,

[0025] In the third extraction process, the second extract oil and the second solvent are in counter-current contact; and / or,

[0026] In the fourth extraction process, the third extraction oil and the second solvent are in counter-current contact.

[0027] In the separation method described above, the aromatic hydrocarbon content in the mixed aromatic hydrocarbons to be separated is >90%.

[0028] The separation method described above further includes: distilling the mixed solvent to obtain a first solvent and a second solvent;

[0029] The first solvent and the second solvent are returned to participate in the mixing process and / or the first extraction process and / or the second extraction process and / or the third extraction process and / or the fourth extraction process.

[0030] In a second aspect, the present invention provides a separation apparatus for performing the above-described separation method, comprising a mixing unit, a first extraction unit, a second extraction unit, a third extraction unit, and a fourth extraction unit;

[0031] The mixing unit includes a raw material inlet and a diluent oil outlet; the first extraction unit includes a diluent oil inlet and a first extract oil outlet; the second extraction unit includes a first extract oil inlet and a second extract oil outlet; the third extraction unit includes a second extract oil inlet and a third extract oil outlet; and the fourth extraction unit includes a third extract oil inlet and a mixed solvent outlet.

[0032] The dilution oil outlet of the mixing unit is connected to the dilution oil inlet of the first extraction unit, the first extraction oil outlet of the first extraction unit is connected to the first extraction oil inlet of the second extraction unit, the second extraction oil outlet of the second extraction unit is connected to the second extraction oil inlet of the third extraction unit, and the third extraction oil outlet of the third extraction unit is connected to the third extraction oil inlet of the fourth extraction unit.

[0033] The separation device described above further includes: a solvent recovery unit;

[0034] The mixed solvent inlet of the solvent recovery unit is connected to the mixed solvent outlet of the fourth extraction unit.

[0035] The method for separating mixed aromatics provided by the present invention uses a first solvent to dilute the mixed aromatics to be separated, and uses a mixed solvent including at least two solvents, namely a second solvent, to perform a first extraction treatment, a second extraction treatment, a third extraction treatment, and a fourth extraction treatment on the diluted oil, the first extraction oil, the second extraction oil, and the third extraction oil, respectively. The absolute value of the difference between the average molecular polarity index of the first solvent and the mixed aromatics, and the difference between the average molecular polarity index of the second solvent and the first solvent are limited, which can make the purity of the separated aromatics with different ring numbers relatively high. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the accompanying drawings used in the description of the embodiments of the present invention or related technologies are briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a schematic diagram of a mixed aromatic hydrocarbon separation device provided by the present invention.

[0038] Explanation of reference numerals in the attached figures:

[0039] 1-Mixing unit; 2-First extraction unit; 3-Second extraction unit; 4-Third extraction unit; 5-Fourth extraction unit; 6-Solvent recovery unit; 7-First solvent storage unit; 8-Second solvent storage unit. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0041] In a first aspect, the present invention provides a method for separating mixed aromatic hydrocarbons, comprising the following steps:

[0042] 1) The mixed aromatics to be separated and the first solvent are mixed to obtain diluted oil;

[0043] 2) The diluted oil is subjected to a first extraction treatment using a second solvent to obtain alkyl-rich oil and a first-extracted oil;

[0044] 3) The first extract oil is subjected to a second extraction process using a second solvent to obtain tricyclic or higher heavy aromatics and a second extract oil;

[0045] 4) The second extract oil is subjected to a third extraction process using a second solvent to obtain bicyclic aromatic hydrocarbons and a third extract oil;

[0046] 5) The third extract oil is subjected to a fourth extraction process using a second solvent to obtain monocyclic aromatic hydrocarbons and a mixed solvent;

[0047] Wherein, the second solvent is a mixed solvent comprising at least two or more solvents;

[0048] The absolute value of the difference between the average molecular polarity index of the first solvent and the mixed aromatic hydrocarbons to be separated is <10;

[0049] The second solvent has a larger average molecular polarity index than the first solvent, and the difference between them, S, is: 4 < S < 6.

[0050] The method for separating mixed aromatics provided by the present invention obtains aromatics with different ring numbers through mixing treatment, first extraction treatment, second extraction treatment, third extraction treatment and fourth extraction treatment.

[0051] Specifically, in step 1), the mixed aromatics to be separated are mixed using a first solvent to obtain a diluted oil. The absolute value of the difference between the average molecular polarity index of the first solvent and the mixed aromatics to be separated is <10. The first solvent readily interacts with the mixed aromatics to be separated, which is beneficial for the dissolution of the mixed aromatics in the first solvent. The first solvent is at least one of sulfolane, dimethyl sulfoxide, N-methylpyrrolidone, N-formylmorpholine, N,N-dimethylformamide, N,N-dimethylacetamide, dioxane, furfural, and furfuryl alcohol.

[0052] In step 2), the diluted oil obtained above is subjected to a first extraction treatment using a second solvent to obtain alkane-rich oil and a first extracted oil. The alkane-rich oil has an alkane content greater than 90% and can be used as a high-quality steam cracking feedstock. In this invention, the temperature of the first extraction treatment can be 20-30°C. The second solvent is a mixed solvent comprising at least two solvents, for example, at least two of alcohols, esters, ketones, nitriles, furans, and water. The average molecular polarity index of the second solvent is greater than that of the first solvent, and the difference S between them is 4 < S < 6. Within a suitable range, the second solvent is miscible with the first solvent. Using the second solvent to perform the first extraction treatment on the diluted oil can extract the aromatics. The second solvent containing the dissolved aromatics and the first solvent constitute the first extracted oil. The remaining portion is alkane-rich oil.

[0053] In step 3), the first extract oil is subjected to a second extraction treatment using a second solvent. In this invention, the temperature of the second extraction treatment can be 20-30℃, which can cause the tricyclic and higher-level heavy aromatics in the first extract oil to precipitate out, while the monocyclic and bicyclic aromatics dissolve in the solvent. The solvent containing the monocyclic and bicyclic aromatics is the second extract oil, and finally, tricyclic and higher-level heavy aromatics and the second extract oil are obtained.

[0054] In step 4), the second solvent is used to perform a third extraction treatment on the second extract oil. In this invention, the temperature of the third extraction treatment can be 20-30℃, which can cause the bicyclic aromatic hydrocarbons in the second extract oil to precipitate out, while the monocyclic aromatic hydrocarbons dissolve in the solvent. The solvent containing the monocyclic aromatic hydrocarbons is the third extract oil, and finally, bicyclic aromatic hydrocarbons and the third extract oil are obtained.

[0055] In step 5), the third extract oil is subjected to a fourth extraction process using the second solvent. In this invention, the temperature of the fourth extraction process can be 20-30°C, which can cause the monocyclic aromatic hydrocarbons in the third extract oil to precipitate out. The remaining solvent is a mixture of the first solvent and the second solvent, and finally, monocyclic aromatic hydrocarbons and the mixed solvent are obtained.

[0056] The method for separating mixed aromatics of the present invention achieves a purity greater than 90% for the separated aromatics of different ring numbers, indicating high purity, which can be used as raw materials for the production of light aromatics (BTX) and carbon material precursors. It is speculated that this is because the addition of a second solvent as an antisolvent allows the less polar alkanes to precipitate first, based on their different polarities. Then, the second solvent is gradually added, and based on differences in solubility, heavy aromatics with three or more rings, bicyclic aromatics, and monocyclic aromatics precipitate sequentially, thus achieving the separation of aromatics of different ring numbers from the mixed aromatics.

[0057] The average molecular polarity index for different mixed solvents and mixed aromatics is calculated using the following steps:

[0058] 1) The group composition distribution of mixed aromatic hydrocarbons was determined using gas chromatography-mass spectrometry. As those skilled in the art know, due to the overlap of peaks in the spectra, it is difficult to accurately distinguish isomers with the same number of carbon atoms in complex mixtures using existing instruments. The inventors of this invention discovered that the differences in molecular polarity indices between isomers with the same number of carbon atoms and homologues with different substituents are small. Therefore, representative model compounds can be screened to simplify the components of mixed aromatic hydrocarbons, and the average molecular polarity index of the mixed aromatic hydrocarbons can be calculated accordingly.

[0059] 2) Based on the screened mixed aromatic model compounds and solvent molecular structures, the quantum chemical calculation software Gaussian and the wave function analysis software Multiwfn were used to perform quantitative analysis of the van der Waals surface of different molecules and calculate the molecular polarity index.

[0060] 3) The average molecular polarity indices of the mixed aromatics and mixed solvents are calculated according to the following formulas:

[0061] The average molecular polarity index of a mixed aromatic hydrocarbon = polarity index of molecule 1 × M1 + polarity index of molecule 2 × M2 + ... + polarity index of molecule n × M n , of which M i (i = 1, 2, ..., n) represents the mass fraction of molecules of different representative model compounds in the mixed aromatic hydrocarbons.

[0062] The average molecular polarity index of the mixed solvents = polarity index of solvent 1 × S1 + polarity index of solvent 2 × S2 + ... + polarity index of solvent n × S n , of which S i (i = 1, 2, ..., n) represents the mass fraction of each solvent in the mixed solvent.

[0063] The method for separating mixed aromatics provided by the present invention uses a first solvent to dilute the mixed aromatics to be separated, and uses a mixed solvent including at least two solvents, namely a second solvent, to perform a first extraction treatment, a second extraction treatment, a third extraction treatment, and a fourth extraction treatment on the diluted oil, the first extraction oil, the second extraction oil, and the third extraction oil, respectively. The absolute value of the difference between the average molecular polarity index of the first solvent and the mixed aromatics, and the difference between the average molecular polarity index of the second solvent and the first solvent are limited, which can make the purity of the separated aromatics with different ring numbers relatively high.

[0064] In some embodiments of the present invention, the second solvent includes at least one third solvent with a molecular polarity index of 18-22, and the third solvent accounts for 40-100% by volume in the second solvent.

[0065] The present invention specifies that the second solvent includes at least one third solvent with a molecular polarity index of 18-22, and the volume percentage of the third solvent in the second solvent is 40-100%. This is beneficial to obtain a second solvent with a suitable average molecular polarity index, i.e., suitable polarity. By using the second solvent to sequentially precipitate alkanes and aromatic hydrocarbons with different ring numbers, the purity of the separated aromatic hydrocarbons with different ring numbers can be relatively high.

[0066] In some embodiments of the present invention, the first solvent includes at least one fourth solvent with a molecular polarity index of 12-18, and the volume percentage of the fourth solvent in the first solvent is not less than 80%.

[0067] The present invention specifies that the first solvent includes at least one fourth solvent with a molecular polarity index of 12-18, and the volume percentage of the fourth solvent in the first solvent is not less than 80%. This is beneficial to obtaining a first solvent with a larger molecular polarity index, i.e., a larger polarity, which is beneficial to the dissolution of mixed aromatics by the first solvent and can further improve the purity of the separated aromatics with different ring numbers.

[0068] In some embodiments of the present invention, the average molecular polarity index of the mixed aromatic hydrocarbons to be separated is 5-9.

[0069] In this invention, the average molecular polarity index of the mixed aromatic hydrocarbons to be separated is limited to 5-9, which is a moderate polarity and can interact with the solvent relatively easily, so that aromatic hydrocarbons with different ring numbers can be separated from the mixed aromatic hydrocarbons in sequence, thereby achieving high purity of aromatic hydrocarbons with different ring numbers separated from the mixed aromatic hydrocarbons.

[0070] In some embodiments of the present invention, the volume ratio of the first solvent to the mixed aromatic hydrocarbons to be separated is 0.5-2:1; and / or,

[0071] The volume ratio of the second solvent to the diluent oil is 0.05-0.1:1;

[0072] The volume ratio of the second solvent to the first extraction oil is 0.1-0.2:1;

[0073] The volume ratio of the second solvent to the second extraction oil is 0.1-0.3:1;

[0074] The volume ratio of the second solvent to the third extract oil is 0.1-0.5:1.

[0075] In this invention, the volume ratio of the first solvent to the mixed aromatics to be separated is defined as 0.5-2:1, preferably 0.5-1:1; the volume ratio of the second solvent to the diluent oil is 0.05-0.1:1, preferably 0.05-0.08:1; the volume ratio of the second solvent to the first extraction oil is 0.1-0.2:1, preferably 0.1-0.15:1; the volume ratio of the second solvent to the second extraction oil is 0.1-0.3:1, preferably 0.1-0.2:1; and the volume ratio of the second solvent to the third extraction oil is 0.1-0.5:1, preferably 0.2-0.4:1. A suitable volume ratio facilitates the dissolution of the mixed aromatics by the first solvent and allows for the sequential precipitation of alkanes and aromatics with different ring numbers by adding the second solvent, resulting in higher purity of the separated aromatics with different ring numbers.

[0076] In some embodiments of the present invention, in the first extraction process, the diluent oil is contacted in reverse with the second solvent; and / or,

[0077] In the second extraction process, the first extract oil and the second solvent are in counter-current contact; and / or,

[0078] In the third extraction process, the second extract oil and the second solvent are in counter-current contact; and / or,

[0079] In the fourth extraction process, the third extraction oil and the second solvent are in counter-current contact.

[0080] In this invention, the diluent oil, the first extraction oil, the second extraction oil, and the third extraction oil are in counter-current contact with the second solvent, which helps to increase the contact area and contact time. This further enables the second solvent to sequentially precipitate alkanes and aromatic hydrocarbons with different ring numbers, resulting in higher purity of the separated aromatic hydrocarbons with different ring numbers.

[0081] In some embodiments of the present invention, the aromatic hydrocarbon content in the mixed aromatic hydrocarbons to be separated is >90%.

[0082] In this invention, the aromatic hydrocarbon content in the mixed aromatic hydrocarbons to be separated is >90%, which is beneficial for the subsequent addition of a second solvent to precipitate aromatic hydrocarbons with different ring numbers in sequence, thereby resulting in higher purity of the separated aromatic hydrocarbons with different ring numbers.

[0083] In some embodiments of the present invention, the method further includes: performing distillation on the mixed solvent to obtain a first solvent and a second solvent;

[0084] The first solvent and the second solvent are returned to participate in the mixing process and / or the first extraction process and / or the second extraction process and / or the third extraction process and / or the fourth extraction process.

[0085] It is understood that the mixed solvent includes a first solvent and a second solvent. Distillation of the mixed solvent yields the first and second solvents. The distillation pressure can be 5-10 kPa, and the temperature can be 50-60℃. Recycling and reusing the first and second solvents—for example, returning the first solvent to participate in the mixing process, and returning the second solvent to participate in the first and / or second and / or third and / or fourth extraction processes—can achieve the goals of saving resources and reducing costs.

[0086] In a second aspect, the present invention provides a separation apparatus for performing the above-described separation method, comprising a mixing unit 1, a first extraction unit 2, a second extraction unit 3, a third extraction unit 4, and a fourth extraction unit 5;

[0087] The mixing unit 1 includes a raw material inlet and a diluent oil outlet; the first extraction unit 2 includes a diluent oil inlet and a first extract oil outlet; the second extraction unit 3 includes a first extract oil inlet and a second extract oil outlet; the third extraction unit 4 includes a second extract oil inlet and a third extract oil outlet; and the fourth extraction unit 5 includes a third extract oil inlet and a mixed solvent outlet.

[0088] The dilution oil outlet of the mixing unit 1 is connected to the dilution oil inlet of the first extraction unit 2, the first extraction oil outlet of the first extraction unit 2 is connected to the first extraction oil inlet of the second extraction unit 3, the second extraction oil outlet of the second extraction unit 3 is connected to the second extraction oil inlet of the third extraction unit 4, and the third extraction oil outlet of the third extraction unit 4 is connected to the third extraction oil inlet of the fourth extraction unit 5.

[0089] In one embodiment, the mixed aromatics to be separated and the first solvent are mixed in mixing unit 1 to obtain a diluted oil. The diluted oil is output from the diluted oil outlet of mixing unit 1 and enters the first extraction unit 2 through the diluted oil inlet at the top of the first extraction unit 2. The diluted oil is subjected to a first extraction treatment using a second solvent to obtain alkyl-rich oil and a first extracted oil. The first extracted oil is output from the first extracted oil outlet at the bottom of the first extraction unit 2 and enters the second extraction unit 3 through the first extracted oil inlet at the top of the second extraction unit 3. In the second extraction unit 3, the first extracted oil is subjected to a second extraction treatment using a second solvent to obtain tricyclic or higher heavy aromatics and a second extracted oil. The second extracted oil is output from the second extracted oil outlet at the top of the second extraction unit 3 and enters the third extraction unit 4 through the second extracted oil inlet at the top of the third extraction unit 4. The second extracted oil is subjected to a third extraction treatment using a second solvent to obtain bicyclic aromatics and a third extracted oil. The third extracted oil is output from the third extracted oil outlet at the top of the third extraction unit 4 and enters the fourth extraction unit 5 through the third extracted oil inlet at the top of the fourth extraction unit 5. The third extracted oil is subjected to a fourth extraction treatment using a second solvent to obtain monocyclic aromatics and a mixed solvent.

[0090] The present invention does not limit the specific type of mixing unit 1, as long as it can achieve the mixing of the mixed aromatics to be separated and the first solvent. For example, it can be a dilution oil mixing tank.

[0091] The present invention does not limit the specific types of the first extraction unit 2, the second extraction unit 3, the third extraction unit 4, and the fourth extraction unit 5, as long as they can perform extraction processing on the diluted oil, the first extraction oil, the second extraction oil, and the third extraction oil. For example, it can be a packed extraction tower.

[0092] In this invention, the mixed aromatic hydrocarbons to be separated are first diluted, and then subjected to a first extraction treatment, a second extraction treatment, a third extraction treatment, and a fourth extraction treatment, which can result in higher purity of the aromatic hydrocarbons with different ring numbers obtained by separation.

[0093] In some embodiments of the present invention, a solvent recovery unit 6 is also included;

[0094] The mixed solvent inlet of the solvent recovery unit 6 is connected to the mixed solvent outlet of the fourth extraction unit 5.

[0095] In this invention, the mixed solvent obtained in the fourth extraction unit 5 is output from the mixed solvent outlet at the bottom of the fourth extraction unit 5, and enters the solvent recovery unit 6 through the mixed solvent inlet at the bottom of the solvent recovery unit 6 for distillation to obtain a first solvent and a second solvent. The first solvent is output from the first solvent outlet at the bottom of the solvent recovery unit 6, enters the first solvent storage unit 7 through the solvent inlet of the first solvent storage unit 7 for storage, and can be returned to participate in the mixing process; the second solvent is output from the second solvent outlet at the top of the solvent recovery unit 6, enters the second solvent storage unit 8 through the solvent inlet of the second solvent storage unit 8 for storage, and can be returned to participate in the first extraction process and / or the second extraction process and / or the third extraction process and / or the fourth extraction process.

[0096] The solvent recovery unit 6 in this invention can recover and reuse the first solvent and the second solvent, saving costs and reducing energy consumption.

[0097] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0098] The apparatus in this embodiment of the invention is a separation device for mixed aromatic hydrocarbons, such as... Figure 1 As shown, the separation device includes a mixing unit 1 (diluted oil mixing tank); a first extraction unit 2 (packed extraction tower); a second extraction unit 3 (packed extraction tower); a third extraction unit 4 (packed extraction tower); a fourth extraction unit 5 (packed extraction tower); a solvent recovery unit 6 (solvent recovery tower); a first solvent storage unit 7 (first solvent storage tank); and a second solvent storage unit 8 (second solvent storage tank).

[0099] Mixing unit 1 includes a feed inlet, a solvent inlet, and a dilution oil outlet. The feed inlet receives the mixed aromatics to be separated. The dilution oil inlet at the top of the first extraction unit 2 is connected to the dilution oil outlet of the mixing unit 1. The solvent inlet in the middle of the first extraction unit 2 is connected to the solvent outlet of the second solvent storage unit 8. Alkane-rich oil is collected from the top of the first extraction unit 2. The first extraction oil outlet at the bottom of the first extraction unit 2 is connected to the first extraction oil inlet of the second extraction unit 3. The solvent inlet in the middle of the second extraction unit 3 is connected to the solvent outlet of the second solvent storage unit 8. Tricyclic and higher heavy aromatics are collected from the bottom of the second extraction unit 3. The second extraction oil outlet at the top of the second extraction unit 3 is connected to the second extraction oil inlet at the top of the third extraction unit 4. The solvent inlet in the middle of the third extraction unit 4... The solvent inlet is connected to the solvent outlet of the second solvent storage unit 8. Bicyclic aromatic hydrocarbons are extracted from the bottom of the third extraction unit 4. The third extraction oil outlet at the top of the third extraction unit 4 is connected to the third extraction oil inlet at the top of the fourth extraction unit 5. The solvent inlet in the middle of the fourth extraction unit 5 is connected to the solvent outlet of the second solvent storage unit 8. Monocyclic aromatic hydrocarbons are extracted from the top of the fourth extraction unit 5. The mixed solvent outlet at the bottom of the fourth extraction unit 5 is connected to the mixed solvent inlet at the bottom of the solvent recovery unit 6. The first solvent outlet at the bottom of the solvent recovery unit 6 is connected to the solvent inlet of the first solvent storage unit 7. The second solvent outlet at the top of the solvent recovery unit 6 is connected to the solvent inlet of the second solvent storage unit 8. The solvent outlet of the first solvent storage unit 7 is connected to the solvent inlet of the mixing unit 1.

[0100] The composition and basic properties of the mixed aromatic hydrocarbons used in the embodiments of the present invention are shown in Table 1.

[0101] Table 1. Composition and property parameters of mixed aromatic hydrocarbons

[0102]

[0103] Wherein, A1 represents monocyclic aromatic hydrocarbons; A2 represents bicyclic aromatic hydrocarbons; and A3 represents tricyclic or higher heavy aromatic hydrocarbons.

[0104] Example 1

[0105] The method for separating mixed aromatics in this embodiment includes the following steps:

[0106] Using mixed aromatic hydrocarbons #1 and #2 as the aromatic hydrocarbons to be separated, the second solvent was a mixture of acetone and water, with a volume ratio of acetone to water of 2:3; the first solvent was N,N-dimethylacetamide. The molecular polarity index of acetone is 13.24, that of water is 21.77, and that of N,N-dimethylacetamide is 13.36. Calculations based on the formula yielded an average molecular polarity of 18.36 for the second solvent. The difference between the average molecular polarity indices of the second and first solvents was 5.00.

[0107] use Figure 1The separation device shown allows the mixed aromatics to be separated and the first solvent to be fully mixed in mixing unit 1 to obtain diluted oil. The diluted oil and the second solvent are pumped into the first extraction unit 2 from the diluted oil inlet at the top and the solvent inlet at the middle, respectively, for the first extraction process. The volume ratio of the first solvent to the mixed aromatics is 1.0, and the volume ratio of the second solvent to the diluted oil is 0.06. The second solvent and the diluted oil are in counter-current contact in the first extraction unit 2. The alkyl-rich oil collected from the first extraction unit 2 is output from the alkyl-rich oil outlet at the top of the first extraction unit 2, and the first extracted oil collected from the first extraction unit 2 is output from the first extracted oil outlet at the bottom of the first extraction unit 2, entering the second extraction unit 3 via the first extracted oil inlet at the top. In the second extraction unit 3, a second extraction process is performed with a second solvent, wherein the volume ratio of the second solvent to the first extract oil is 0.12. Tricyclic and higher-order heavy aromatics collected in the second extraction unit 3 are output from the tricyclic and higher-order heavy aromatics outlet at the bottom of the second extraction unit 3. The second extract oil collected in the second extraction unit 3 is output from the second extract oil outlet at the top of the second extraction unit 3 and enters the third extraction unit 4 via the second extract oil inlet at the top of the third extraction unit 4 for a third extraction process with the second solvent, wherein the volume ratio of the second solvent to the second extract oil is 0.2. Bicyclic aromatics collected in the third extraction unit 4 are output from the bicyclic aromatics outlet at the bottom of the third extraction unit 4. The third extract oil collected in the third extraction unit 4 is output from the third extraction unit 4. The third extraction oil from the top of the fourth extraction unit 5 exits and enters the fourth extraction unit 5 through the third extraction oil inlet at the top of the fourth extraction unit 5 to undergo fourth extraction with the second solvent. The volume ratio of the second solvent to the third extraction oil is 0.3. The monocyclic aromatic hydrocarbons collected from the fourth extraction unit 5 exit from the monocyclic aromatic hydrocarbon outlet at the top of the fourth extraction unit 5. The mixed solvent collected from the fourth extraction unit 5 exits from the mixed solvent outlet at the bottom of the fourth extraction unit 5 and enters the solvent recovery unit 6 through the mixed solvent inlet at the bottom of the solvent recovery unit 6 for distillation to obtain the first solvent and the second solvent. The first solvent exits from the first solvent outlet at the bottom of the solvent recovery unit 6 and enters the first solvent storage unit 7 through the solvent inlet of the first solvent storage unit 7. The solvent can be output through the solvent outlet of the first solvent storage unit 7, enter the mixing unit 1 through the solvent inlet of the mixing unit 1 to participate in the mixing process, and the second solvent is output from the second solvent outlet at the top of the solvent recovery unit 6, enter the second solvent storage unit 8 through the solvent inlet of the second solvent storage unit 8, and can be output through the solvent outlet of the second solvent storage unit 8, enter the first extraction unit 2 and / or the second extraction unit 3 and / or the third extraction unit 4 and / or the fourth extraction unit 5 through the solvent inlet in the middle of the first extraction unit 2 and / or the second extraction unit 3 and / or the third extraction unit 4 and / or the fourth extraction unit 5 to participate in the first extraction process and / or the second extraction process and / or the third extraction process and / or the fourth extraction process.The temperature of the first, second, third, and fourth extraction processes was controlled at 25℃, and the pressure of the distillation process was 8 kPa and the temperature was 50℃. The composition and properties of the alkyl-rich oil and various grades of aromatics obtained from the separation of #1 mixed aromatics are shown in Table 2, and the composition and properties of the alkyl-rich oil and various grades of aromatics obtained from the separation of #2 mixed aromatics are shown in Table 3.

[0108] Table 2

[0109]

[0110]

[0111] Table 3

[0112]

[0113] As shown in Tables 2 and 3, the higher the content of aromatics in the mixed aromatics, the higher the purity of the aromatics with different ring numbers obtained, that is, the better the effect of stepwise separation.

[0114] Example 2

[0115] The separation method of mixed aromatics in Example 2 is basically the same as that in Example 1, except that the mixed aromatics to be separated is No. 2 mixed aromatics, the first solvent is N-methylpyrrolidone with a molecular polarity index of 13.64, and the composition and various property parameters of the alkyl-rich oil and aromatics of each grade obtained by separating No. 2 mixed aromatics are shown in Table 4.

[0116] Table 4

[0117]

[0118] As shown in Tables 3 and 4, when the molecular polarity indices of the first solvents are not significantly different, their solubility is also basically similar. It is speculated that the key factors determining their solubility in aromatic hydrocarbons at this time may be molecular weight and molecular structure. For example, the molecular polarity indices of N-methylpyrrolidone and N,N-dimethylacetamide are not significantly different, but because N-methylpyrrolidone has a larger molecular weight and a cyclic structure, it has stronger solubility in mixed aromatic hydrocarbons and relatively lower selectivity for aromatic hydrocarbons with different ring numbers. Therefore, its separation effect is not as good as that of N,N-dimethylacetamide.

[0119] Example 3

[0120] The separation method for mixed aromatics in Example 3 is basically the same as that in Example 1, except that mixed aromatics #2 are used as the mixed aromatics to be separated. The first solvent is a mixture of furfuryl alcohol and N,N-dimethylformamide, with a volume ratio of furfuryl alcohol to N,N-dimethylformamide of 1:4. The volume percentage of N,N-dimethylformamide in the first solvent is 80%. The molecular polarity index of furfuryl alcohol is 10.11, and that of N,N-dimethylformamide is 15.38. According to the formula, the average molecular polarity of the first solvent is 14.33, and the average molecular polarity index of the second solvent is 18.36. The difference between the average molecular polarity index of the second solvent and the first solvent is 4.03. The composition and various property parameters of the alkyl-rich oil and aromatics of various grades obtained from the separation of mixed aromatics #2 are shown in Table 5.

[0121] Table 5

[0122]

[0123] Example 4

[0124] The separation method of mixed aromatics in Example 4 is basically the same as that in Example 1, except that mixed aromatics #2 are used as the mixed aromatics to be separated. The volume ratio of the first solvent to the mixed aromatics is 1.0, the volume ratio of the second solvent to the diluent oil is 0.08, the volume ratio of the second solvent to the first extract oil is 0.15, the volume ratio of the second solvent to the second extract oil is 0.25, and the volume ratio of the second solvent to the third extract oil is 0.4. The composition and various property parameters of the alkyl-rich oil and aromatics of each grade obtained by separating mixed aromatics #2 are shown in Table 6.

[0125] Table 6

[0126]

[0127]

[0128] Example 5

[0129] The separation method of mixed aromatics in Example 5 is basically the same as that in Example 1, except that mixed aromatics #2 are used as the mixed aromatics to be separated, and the second solvent is a mixture of isopropanol, furan, and water, with a volume ratio of 1:1:8, and water accounting for 80% by volume. The molecular polarity index of isopropanol is 9.01, that of furan is 9.13, and that of water is 21.77. Calculations based on the formula show that the average molecular polarity of the second solvent is 19.23, and the molecular polarity index of the first solvent, N,N-dimethylacetamide, is 13.36. The difference between the average molecular polarity indices of the second and first solvents is 5.87. The composition and properties of the alkyl-rich oil and various grades of aromatics obtained from the separation of mixed aromatics #2 are shown in Table 7.

[0130] Table 7

[0131]

[0132] Example 6

[0133] The separation method for mixed aromatics in Example 6 is basically the same as that in Example 1, except that mixed aromatics #2 are used as the mixed aromatics to be separated, and the second solvent is a mixture of propanol, methyl formate, and water, with a volume ratio of 2:3:5. The total volume percentage of methyl formate and water in the second solvent is 80%. The molecular polarity index of propanol is 9.08, that of methyl formate is 19.56, and that of water is 21.77. Calculations based on the formula show that the average molecular polarity of the second solvent is 18.57, and the molecular polarity index of the first solvent, N,N-dimethylacetamide, is 13.36. The difference between the average molecular polarity indices of the second solvent and the first solvent is 5.21. The composition and properties of the alkyl-rich oil and various grades of aromatics obtained from the separation of mixed aromatics #2 are shown in Table 8.

[0134] Table 8

[0135]

[0136] Comparative Example 1

[0137] The separation method for the mixed aromatics in Comparative Example 1 and Example 1 is basically the same, except that 2# mixed aromatics is used as the mixed aromatics to be separated. The first solvent is not used to mix the mixed aromatics to be separated. Instead, the second solvent (acetone and water in a volume ratio of 2:3) is used directly to perform the first, second, third, and fourth extraction processes on the mixed aromatics to be separated. The composition and various property parameters of the alkyl-rich oil and aromatics of each grade obtained from the separation of 2# mixed aromatics are shown in Table 9.

[0138] Table 9

[0139]

[0140] Comparative Example 2

[0141] The separation method for the mixed aromatics in Comparative Example 2 is basically the same as that in Example 1, except that the mixed aromatics to be separated are No. 2 mixed aromatics. A second solvent (acetone and water in a volume ratio of 2:3) is used to mix the mixed aromatics to be separated, and a first solvent (N,N-dimethylacetamide) is used to perform a first extraction, a second extraction, a third extraction, and a fourth extraction on the diluted oil. The composition and various property parameters of the alkyl-rich oil and aromatics of each grade obtained by separating No. 2 mixed aromatics are shown in Table 10.

[0142] Table 10

[0143]

[0144] Comparative Example 3

[0145] The separation method for the mixed aromatics in Comparative Example 3 is basically the same as that in Example 1, except that the mixed aromatics to be separated were 2# mixed aromatics. Instead of mixing the mixed aromatics, the first solvent (N,N-dimethylacetamide) was directly used to perform the first, second, third, and fourth extraction processes on the mixed aromatics to be separated. The composition and properties of the alkyl-rich oil and various grades of aromatics obtained from the separation of 2# mixed aromatics are shown in Table 11.

[0146] Table 11

[0147]

[0148] Comparative Example 4

[0149] The separation method for the mixed aromatics in Comparative Example 4 is basically the same as that in Example 1, except that the mixed aromatics to be separated is No. 2 mixed aromatics, and the first solvent (N,N-dimethylacetamide) is used to perform a second extraction treatment on the first extract oil. The composition and various property parameters of the alkyl-rich oil and aromatics of each grade obtained by separating No. 2 mixed aromatics are shown in Table 12.

[0150] Table 12

[0151]

[0152] Comparative Example 5

[0153] The separation method for the mixed aromatics in Comparative Example 5 is basically the same as that in Example 1, except that the mixed aromatics to be separated is No. 2 mixed aromatics, and the second extract oil is subjected to a third extraction treatment using the first solvent (N,N-dimethylacetamide). The composition and various property parameters of the alkyl-rich oil and aromatics of each grade obtained by separating No. 2 mixed aromatics are shown in Table 13.

[0154] Table 13

[0155]

[0156] Comparative Example 6

[0157] The separation method for the mixed aromatics in Comparative Example 6 is basically the same as that in Example 1, except that the mixed aromatics to be separated is No. 2 mixed aromatics, and the third extract oil is subjected to a fourth extraction treatment using the first solvent (N,N-dimethylacetamide). The composition and various property parameters of the alkyl-rich oil and aromatics of each grade obtained by separating No. 2 mixed aromatics are shown in Table 14.

[0158] Table 14

[0159]

[0160]

[0161] As shown in Tables 1-14, compared with the comparative examples, the method for separating mixed aromatics provided by the present invention uses a first solvent to dilute the mixed aromatics to be separated, and uses a mixed solvent including at least two solvents, namely a second solvent, to perform a first extraction treatment, a second extraction treatment, a third extraction treatment, and a fourth extraction treatment on the diluted oil, the first extraction oil, the second extraction oil, and the third extraction oil, respectively. The absolute value of the difference between the average molecular polarity index of the first solvent and the mixed aromatics, and the difference between the average molecular polarity index of the second solvent and the first solvent are limited, which can result in higher purity of the separated aromatics with different ring numbers.

[0162] As can be seen from the comparison between Example 1 and Comparative Examples 1-6, the method for separating mixed aromatics provided by the present invention can achieve high purity of aromatics with different ring numbers, and the alkane content in the obtained alkane-rich oil is greater than 90%, and the purity of aromatics with different ring numbers is greater than 90%.

[0163] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for separating mixed aromatic hydrocarbons, characterized in that, Includes the following steps: 1) The mixed aromatics to be separated and the first solvent are mixed to obtain diluted oil; 2) The diluted oil is subjected to a first extraction treatment using a second solvent to obtain alkyl-rich oil and a first-extracted oil; 3) The first extract oil is subjected to a second extraction process using a second solvent to obtain tricyclic or higher heavy aromatics and a second extract oil; 4) The second extract oil is subjected to a third extraction process using a second solvent to obtain bicyclic aromatic hydrocarbons and a third extract oil; 5) The third extract oil is subjected to a fourth extraction process using a second solvent to obtain monocyclic aromatic hydrocarbons and a mixed solvent; Wherein, the second solvent is a mixed solvent comprising at least two or more solvents; The absolute value of the difference between the average molecular polarity index of the first solvent and the mixed aromatic hydrocarbons to be separated is <10; The second solvent has a larger average molecular polarity index than the first solvent, and the difference between them, S, is: 4 < S < 6.

2. The separation method according to claim 1, characterized in that, The second solvent includes at least one third solvent with a molecular polarity index of 18-22, and the third solvent accounts for 40-100% by volume in the second solvent.

3. The separation method according to claim 1 or 2, characterized in that, The first solvent includes at least one fourth solvent with a molecular polarity index of 12-18, and the volume percentage of the fourth solvent in the first solvent is not less than 80%.

4. The separation method according to any one of claims 1-3, characterized in that, The average molecular polarity index of the mixed aromatic hydrocarbons to be separated is 5-9.

5. The separation method according to any one of claims 1-4, characterized in that, The volume ratio of the first solvent to the mixed aromatic hydrocarbons to be separated is 0.5-2:1; and / or, The volume ratio of the second solvent to the diluent oil is 0.05-0.1:1; The volume ratio of the second solvent to the first extraction oil is 0.1-0.2:1; The volume ratio of the second solvent to the second extraction oil is 0.1-0.3:1; The volume ratio of the second solvent to the third extract oil is 0.1-0.5:

1.

6. The separation method according to any one of claims 1-5, characterized in that, In the first extraction process, the diluted oil is in counter-current contact with the second solvent; and / or, In the second extraction process, the first extract oil and the second solvent are in counter-current contact; and / or, In the third extraction process, the second extract oil and the second solvent are in counter-current contact; and / or, In the fourth extraction process, the third extraction oil and the second solvent are in counter-current contact.

7. The separation method according to any one of claims 1-6, characterized in that, The aromatic hydrocarbons to be separated contain >90% aromatic hydrocarbons.

8. The separation method according to any one of claims 1-7, characterized in that, Also includes: The mixed solvent is subjected to distillation to obtain a first solvent and a second solvent; The first solvent and the second solvent are returned to participate in the mixing process and / or the first extraction process and / or the second extraction process and / or the third extraction process and / or the fourth extraction process.

9. A separation apparatus for performing the separation method according to any one of claims 1-8, characterized in that, It includes a mixing unit, a first extraction unit, a second extraction unit, a third extraction unit, and a fourth extraction unit; The mixing unit includes a raw material inlet and a diluent oil outlet; the first extraction unit includes a diluent oil inlet and a first extract oil outlet; the second extraction unit includes a first extract oil inlet and a second extract oil outlet; the third extraction unit includes a second extract oil inlet and a third extract oil outlet; and the fourth extraction unit includes a third extract oil inlet and a mixed solvent outlet. The dilution oil outlet of the mixing unit is connected to the dilution oil inlet of the first extraction unit, the first extraction oil outlet of the first extraction unit is connected to the first extraction oil inlet of the second extraction unit, the second extraction oil outlet of the second extraction unit is connected to the second extraction oil inlet of the third extraction unit, and the third extraction oil outlet of the third extraction unit is connected to the third extraction oil inlet of the fourth extraction unit.

10. The separation device according to claim 9, characterized in that, Also includes: Solvent recovery unit; The mixed solvent inlet of the solvent recovery unit is connected to the mixed solvent outlet of the fourth extraction unit.

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