Separation method and separation device for aromatic hydrocarbons and alkanes in straight-run diesel oil

Abstract

The invention provides a separation method and a separation device for aromatic hydrocarbon and alkane in straight-run diesel oil, and the separation method comprises the following steps: 1) mixing straight-run diesel oil to be separated with a first solvent to obtain diluent oil; 2) performing extraction treatment on the diluent oil by using a second solvent to obtain raffinate oil and extracted oil; (3) carrying out back extraction treatment on the extracted oil by utilizing a first solvent to obtain back extraction residual oil and back extraction oil; wherein the second solvent is a mixed solvent comprising at least two or more solvents; the absolute value of the difference value of the average molecular polarity indexes of the first solvent and the straight-run diesel oil to be separated is less than 5; the difference value of the average molecular polarity indexes of the second solvent and the first solvent is greater than 10. The method for separating aromatic hydrocarbons and alkanes in straight-run diesel oil provided by the invention can realize high separation selectivity and high removal rate of aromatic hydrocarbons in straight-run diesel oil.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of diesel oil processing and refining, and particularly relates to a separation method and a separation device for separating aromatic hydrocarbons and alkane hydrocarbons in straight-run diesel oil. BACKGROUND

[0002] The development trend of the petroleum refining field in China gradually turns to "reducing oil and increasing chemical" with the continuous reduction of the consumption ratio of diesel oil to gasoline. The processing and conversion of excess diesel oil is an important way to cope with the change in the product oil consumption structure. The alkane content in straight-run diesel oil is relatively high, which is a relatively high-quality steam cracking raw material. However, the aromatic hydrocarbons in the straight-run diesel oil not only reduce the yield of trienes (ethylene, propylene, and butadiene), but also increase the amount of coking in the furnace tube, thereby shortening the operation cycle of the device. Therefore, it is necessary to select a suitable separation technology to remove the aromatic hydrocarbons in the straight-run diesel oil.

[0003] The liquid-liquid extraction technology can effectively separate the aromatic hydrocarbons and alkane components in diesel oil, and achieve the goal of classified management of each component of diesel oil. However, the existing mature aromatic hydrocarbon extraction and separation process in the industry generally has the following problems: the selectivity for heavy fraction oil with low aromatic hydrocarbon content, especially straight-run diesel oil, is low, and the aromatic hydrocarbon removal rate is low. SUMMARY

[0004] The main purpose of the present application is to provide a separation method for separating aromatic hydrocarbons and alkane hydrocarbons in straight-run diesel oil, which can achieve high separation selectivity of aromatic hydrocarbons in straight-run diesel oil and high aromatic hydrocarbon removal rate.

[0005] The present application also provides a separation device for performing the above separation method, which can achieve high separation selectivity of aromatic hydrocarbons in straight-run diesel oil and high aromatic hydrocarbon removal rate.

[0006] In a first aspect, the present application provides a separation method for separating aromatic hydrocarbons and alkane hydrocarbons in straight-run diesel oil, which comprises the following steps:

[0007] 1) mixing the straight-run diesel oil to be separated and a first solvent to obtain a diluted oil;

[0008] 2) using a second solvent to extract the diluted oil to obtain raffinate oil and extract oil;

[0009] 3) using the first solvent to back-extract the extract oil to obtain back-extracted raffinate oil and back-extracted oil;

[0010] wherein the second solvent is a mixed solvent comprising at least two or more solvents;

[0011] The absolute value of the difference between the average molecular polarity index of the first solvent and the straight-run diesel oil to be separated is less than 5;

[0012] The difference between the average molecular polarity index of the second solvent and the first solvent is greater than 10.

[0013] The separation method as described above, wherein the second solvent comprises at least one third solvent having a molecular polarity index greater than 15, and the third solvent has a volume percentage in the second solvent no less than 40%.

[0014] The separation method as described above, wherein the first solvent is at least one light hydrocarbon having a boiling point of 40-100℃.

[0015] The separation method as described above, wherein the straight-run diesel oil to be separated has an average molecular polarity index of 3-5.

[0016] The separation method as described above, wherein the volume ratio of the first solvent to the straight-run diesel oil to be separated is 0.1-2:1; and / or,

[0017] The volume ratio of the second solvent to the dilution oil is 1-5:1; and / or,

[0018] The volume ratio of the first solvent to the extraction oil is 0.1-1:1.

[0019] The separation method as described above, wherein, in the extraction treatment, the dilution oil is countercurrently contacted with the second solvent; and / or,

[0020] In the back-extraction treatment, the extraction oil is countercurrently contacted with the first solvent.

[0021] The separation method as described above, further comprising: subjecting the raffinate to a first desolventizing treatment to obtain an alkane-rich oil and the first solvent; and / or,

[0022] Subjecting the back- raffinate to a second desolventizing treatment to obtain an aromatic-rich oil and the second solvent; and / or,

[0023] Subjecting the back-extraction oil to a third desolventizing treatment to obtain a cycle oil and the first solvent; and returning the cycle oil to participate in the extraction treatment.

[0024] The separation method as described above, wherein the straight-run diesel oil to be separated has an aromatic content of 10-30wt%; and / or,

[0025] The straight-run diesel oil to be separated has at least one alkane having a carbon atom number of 12-40.

[0026] In a second aspect, the present application provides a separation device for performing the above separation method, comprising a mixing unit, an extraction unit and a back-extraction unit.

[0027] The mixing unit comprises a raw material inlet and a dilution oil outlet, the extraction unit comprises a dilution oil inlet, a raffinate outlet and an extraction oil outlet, and the back-extraction unit comprises an extraction oil inlet, a back-extraction oil outlet and a back- raffinate outlet.

[0028] The dilution oil outlet of the mixing unit is communicated with the dilution oil inlet of the extraction unit; the extraction oil outlet of the extraction unit is communicated with the extraction oil inlet of the reverse extraction unit.

[0029] The separation device as described above further comprises a first solvent recovery unit, a second solvent recovery unit and a third solvent recovery unit.

[0030] The reverse extraction oil inlet of the first solvent recovery unit is communicated with the reverse extraction oil outlet of the reverse extraction unit, the raffinate oil inlet of the second solvent recovery unit is communicated with the raffinate oil outlet of the extraction unit; the reverse raffinate oil inlet of the third solvent recovery unit is communicated with the reverse raffinate oil outlet of the reverse extraction unit.

[0031] The separation method of the aromatic hydrocarbon and the alkane in the straight-run diesel oil provided by the present application utilizes the first solvent to dilute the straight-run diesel oil to be separated, utilizes the mixed solvent including at least two solvents, i.e., the second solvent, to extract the dilution oil, utilizes the first solvent to reverse extract the extraction oil, and limits the absolute value of the difference between the average molecular polarity index of the first solvent and the straight-run diesel oil and the difference between the average molecular polarity index of the second solvent and the first solvent, so that the separation selectivity of the aromatic hydrocarbon in the straight-run diesel oil is high, and the removal rate of the aromatic hydrocarbon is high. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the related art, the drawings needed to be used in the description of the embodiments of the present application or the related art are briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0033] Figure 1 A schematic diagram of a separation device for aromatic hydrocarbon and alkane in straight-run diesel oil provided by the present application.

[0034] Explanation of reference signs:

[0035] 1-mixing unit; 2-extraction unit; 3-reverse extraction unit; 4-first solvent recovery unit; 5-second solvent recovery unit; 6-third solvent recovery unit; 7-first solvent storage unit; 8-second solvent storage unit. DETAILED DESCRIPTION

[0036] In order to make the objects, technical solutions and advantages of the present application clearer, the following will be combined with the embodiments of the present application to make a clear and complete description of the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0037] In a first aspect, the present application provides a method for separating aromatics and alkanes in straight-run diesel oil, comprising the following steps:

[0038] 1) mixing the straight-run diesel oil to be separated with a first solvent to obtain diluted oil;

[0039] 2) using a second solvent to extract the diluted oil to obtain raffinate oil and extract oil;

[0040] 3) using the first solvent to back-extract the extract oil to obtain back-extracted raffinate oil and back-extracted oil;

[0041] wherein the second solvent is a mixed solvent comprising at least two or more solvents;

[0042] the absolute value of the difference between the average molecular polarity index of the first solvent and the straight-run diesel oil to be separated is less than 5;

[0043] the difference between the average molecular polarity index of the second solvent and the first solvent is greater than 10.

[0044] The method for separating aromatics and alkanes in straight-run diesel oil provided by the present application obtains rich-alkane oil and rich-aromatic oil through mixing, extraction and back-extraction.

[0045] Specifically, in step 1), the first solvent is used to mix the straight-run diesel oil to be separated to obtain diluted oil, wherein the absolute value of the difference between the average molecular polarity index of the first solvent and the straight-run diesel oil to be separated is less than 5, i.e. the polarity of the first solvent is similar to that of the straight-run diesel oil to be separated, which is easy to interact and is beneficial to the dissolution of the straight-run diesel oil in the first solvent. The first solvent is at least one of carbon disulfide, petroleum ether, n-alkane with carbon atom number of 5-7, isomeric alkane with carbon atom number of 5-7 and cycloalkane with carbon atom number of 5-7.

[0046] In step 2), the dilute oil obtained above is subjected to extraction treatment using a second solvent to obtain raffinate oil and extract oil. The extraction treatment temperature in the present application can be 20-30°C, wherein the second solvent is a mixed solvent comprising at least two or more solvents, for example, the second solvent can be at least two of alcohol, ester, ketone, nitrile and furan. The difference between the average molecular polarity index of the second solvent and the first solvent is >10, that is, the polarity difference between the second solvent and the first solvent is large. The aromatics in the dilute oil can be extracted by using the second solvent for extraction treatment. Since the straight-run diesel oil contains a large amount of alkanes, part of the alkanes are also extracted by the second solvent. At this time, the second solvent dissolves the aromatics and alkanes, which is the extract oil. The first solvent dissolves the alkanes and a small amount of aromatics, which is the raffinate oil, also known as alkane-rich oil.

[0047] In step 3), the extract oil is subjected to back-extraction treatment using the first solvent to obtain back-extract oil and back-extract oil. The back-extraction treatment temperature in the present application can be 20-30°C. Since the first solvent has a high solubility for alkanes, the alkanes in the extract oil can be dissolved in the first solvent by using the first solvent for back-extraction treatment of the extract oil, and part of the aromatics can also be dissolved. This part is the back-extract oil, also known as the recycle oil. The remaining aromatics are dissolved in the second solvent, which is the back-extract oil, also known as the aromatic-rich oil. The alkanes in the extract oil can be extracted by using the first solvent for back-extraction treatment, which can be understood as a purification treatment process for the aromatics dissolved in the second solvent. Therefore, the method uses a two-phase solvent system to achieve high selectivity in the separation of aromatics in the straight-run diesel oil to be separated, and high removal rate of the aromatics.

[0048] For the average molecular polarity index of different mixed solvents and straight-run diesel oil, the following steps are used to calculate:

[0049] 1) The group composition distribution of straight-run diesel oil is determined by gas chromatography-mass spectrometry. It is known to those skilled in the art that due to the overlap of peaks in the spectrum, it is difficult to accurately distinguish isomers with the same carbon number in complex mixtures by existing instruments. The inventors of the present application found that the molecular polarity index difference between isomers with the same carbon number and homologues with different substituents is small, so representative model compounds can be selected to simplify the components of straight-run diesel oil, and the average molecular polarity index of straight-run diesel oil is calculated accordingly.

[0050] 2) According to the selected model compounds of straight-run diesel oil and the molecular structure formula of the solvent, the van der Waals surface of different molecules is quantitatively analyzed by using quantum chemistry calculation software Gaussian and wave function analysis software Multiwfn to calculate the molecular polarity index.

[0051] 3) The average molecular polarity index of straight-run diesel oil and mixed solvent is calculated according to the following formula respectively:

[0052] The average molecular polarity index of straight-run diesel oil = polarity index of molecule 1 * M1 + polarity index of molecule 2 * M2 + … + polarity index of molecule n * M n Wherein, M i The mass fraction of different representative model compound molecules in straight-run diesel oil (i = 1, 2 … n).

[0053] The average molecular polarity index of mixed solvent = polarity index of solvent 1 * S1 + polarity index of solvent 2 * S2 + … + polarity index of solvent n * S n Wherein, S i The mass fraction of various solvents in the mixed solvent (i = 1, 2 … n).

[0054] The method for separating aromatics and alkanes in straight-run diesel oil provided by the application dilutes the straight-run diesel oil to be separated by using a first solvent, extracts the diluted oil by using a mixed solvent, i.e., a second solvent, which comprises at least two solvents, and back extracts the extracted oil by using the first solvent, and limits the absolute value of the difference between the average molecular polarity index of the first solvent and the straight-run diesel oil and the difference between the average molecular polarity index of the second solvent and the first solvent, so that the separation selectivity of the aromatics in the straight-run diesel oil is high, and the removal rate of the aromatics is high.

[0055] In some embodiments of the application, the second solvent comprises at least one third solvent with a molecular polarity index greater than 15, and the volume percentage of the third solvent in the second solvent is not less than 40%.

[0056] The application limits the second solvent to comprise at least one third solvent with a molecular polarity index greater than 15, and the volume percentage of the third solvent in the second solvent is not less than 40%, which is beneficial to obtaining a second solvent with a larger average molecular polarity index, i.e., a stronger polarity, so as to improve the extraction rate of the aromatics in the diluted oil by the second solvent, i.e., to realize higher separation selectivity of the aromatics in the straight-run diesel oil and higher removal rate of the aromatics.

[0057] In some embodiments of the application, the first solvent is at least one light hydrocarbon with a boiling point of 40-100°C.

[0058] The first solvent in the application can be a single solvent or a mixed solvent, for example, the first solvent is at least one light hydrocarbon with a boiling point of 40-100°C, which can realize better solubility of the straight-run diesel oil to be separated, can fully utilize by-products produced in a refinery, is inexpensive and easy to obtain, has a wide source, is beneficial to saving energy consumption and reducing production cost, and has lower regeneration energy consumption.

[0059] In some embodiments of the application, the average molecular polarity index of the straight-run diesel oil to be separated is 3-5.

[0060] The average molecular polarity index of the straight-run diesel oil to be separated is limited to 3-5 in the present application, which is moderate and can interact with the solvent more easily, so that the aromatic hydrocarbons can be effectively extracted from the straight-run diesel oil, thereby realizing higher separation selectivity and higher removal rate of the aromatic hydrocarbons in the straight-run diesel oil.

[0061] In some embodiments of the present application, the volume ratio of the first solvent to the straight-run diesel oil to be separated is 0.1-2:1; and / or,

[0062] The volume ratio of the second solvent to the dilution oil is 1-5:1; and / or,

[0063] The volume ratio of the first solvent to the extraction oil is 0.1-1:1.

[0064] In the present application, the volume ratio of the first solvent to the straight-run diesel oil to be separated is limited to 0.1-2:1, preferably 0.5-1:1, the volume ratio of the second solvent to the dilution oil is 1-5:1, preferably 1-2:1, and the volume ratio of the first solvent to the extraction oil is 0.1-1:1, preferably 0.1-0.5:1. The volume ratio in the appropriate range is conducive to the sufficient dissolution of the first solvent to the straight-run diesel oil to be separated, the sufficient extraction of the aromatic hydrocarbons in the dilution oil by the second solvent, and the sufficient dissolution of the alkanes in the extraction oil by the first solvent, which can further realize higher separation selectivity and higher removal rate of the aromatic hydrocarbons in the straight-run diesel oil.

[0065] In some embodiments of the present application, in the extraction treatment, the dilution oil is countercurrently contacted with the second solvent; and / or,

[0066] In the back-extraction treatment, the extraction oil is countercurrently contacted with the first solvent.

[0067] In the present application, the dilution oil is countercurrently contacted with the second solvent, and the extraction oil is countercurrently contacted with the first solvent, which helps to increase the contact area and contact time, realizes the sufficient extraction of the aromatic hydrocarbons in the straight-run diesel oil to be separated by the second solvent, and the sufficient dissolution of the alkanes in the extraction oil by the first solvent, and improves the purity of the aromatic hydrocarbons in the back-extracted oil.

[0068] In some embodiments of the present application, further comprising: performing a first desolventization treatment on the raffinate oil to obtain an alkane-rich oil and the first solvent; and / or,

[0069] performing a second desolventization treatment on the back-extracted oil to obtain an aromatic-rich oil and the second solvent; and / or,

[0070] performing a third desolventization treatment on the back-extracted oil to obtain a cycle oil and the first solvent; and the cycle oil is returned to participate in the extraction treatment.

[0071] It can be understood that, since the raffinate oil includes alkanes and the first solvent, the first desolventizing treatment can obtain alkane-rich oil and the first solvent, the first solvent has a boiling point < 100℃ in the present application, the first desolventizing treatment has a pressure of 100kPa and a temperature of 60-120℃; and / or, the first desolventizing treatment has a pressure of 5-10kPa and a temperature of 30-60℃. The first solvent is evaporated and recycled, for example, returned to the dilution oil mixing tank to participate in the mixing treatment again, or returned to the back-extraction tower to participate in the back-extraction treatment again. The alkane content in the alkane-rich oil is greater than 95%, which can be used as a high-quality raw material for steam cracking to produce ethylene.

[0072] Since the back-extracted raffinate oil includes aromatic hydrocarbons and the second solvent, the second desolventizing treatment can obtain aromatic-rich oil and the second solvent, the second solvent has a boiling point < 100℃ in the present application, the second desolventizing treatment has a pressure of 100kPa and a temperature of 60-120℃; and / or, the second desolventizing treatment has a pressure of 5-10kPa and a temperature of 30-60℃. The second solvent is evaporated and recycled, for example, returned to the extraction tower to participate in the extraction treatment again. The aromatic hydrocarbon content in the aromatic-rich oil is greater than 95%, which can be used to prepare special aromatic hydrocarbon oil or further separation.

[0073] Since the back-extracted oil includes alkanes, aromatic hydrocarbons and the first solvent, the third desolventizing treatment can obtain cycle oil and the first solvent, the cycle oil contains alkanes and aromatic hydrocarbons, which can be combined with the dilution oil and subjected to extraction treatment.

[0074] In the present application, the desolventizing treatment is performed on the raffinate oil, the back-extracted raffinate oil and the back-extracted oil respectively, and the first solvent and the second solvent obtained are returned to participate in the extraction treatment and the back-extraction treatment again, and the cycle oil is returned to participate in the extraction treatment, so that the purposes of saving energy consumption and reducing cost can be achieved.

[0075] In some embodiments of the present application, the aromatic hydrocarbon content in the straight-run diesel oil to be separated is 10-30wt%; and / or,

[0076] The alkanes in the straight-run diesel oil to be separated are at least one of carbon atoms 12-40.

[0077] The aromatic hydrocarbon content in the straight-run diesel oil to be separated in the present application is 10-30wt%, and the alkanes are at least one of carbon atoms 12-40, i.e., the aromatic hydrocarbon content in the straight-run diesel oil to be separated is moderate, and the alkanes are of a specific carbon atom number, which is beneficial to the extraction of aromatic hydrocarbons. By controlling the aromatic hydrocarbon content and the carbon atom number of the alkanes in the straight-run diesel oil, the separation selectivity of aromatic hydrocarbons can be further improved, and the removal rate of aromatic hydrocarbons can be higher.

[0078] In a second aspect, the present application provides a separation device for performing the above separation method, such as Figure 1As shown, the separation device comprises a mixing unit 1, an extraction unit 2 and a back-extraction unit 3;

[0079] The mixing unit 1 comprises a raw material inlet and a dilution oil outlet, the extraction unit 2 comprises a dilution oil inlet, a raffinate oil outlet and an extract oil outlet, and the back-extraction unit 3 comprises an extract oil inlet, a back-extraction oil outlet and a back- raffinate oil outlet.

[0080] The dilution oil outlet of the mixing unit 1 is in communication with the dilution oil inlet of the extraction unit 2, and the extract oil outlet of the extraction unit 2 is in communication with the extract oil inlet of the back-extraction unit 3.

[0081] In an embodiment, the straight-run diesel to be separated and the first solvent are mixed in the mixing unit 1 to obtain dilution oil, which is output from the dilution oil outlet of the mixing unit 1 and enters the extraction unit 2 through the dilution oil inlet at the lower part of the extraction unit 2, in the extraction unit 2, the dilution oil is subjected to extraction treatment by the second solvent to obtain raffinate oil and extract oil, which is output from the extract oil outlet at the bottom of the extraction unit 2 and enters the back-extraction unit 3 through the extract oil inlet at the upper part of the back-extraction unit 3, in the back-extraction unit 3, the extract oil is subjected to back-extraction treatment by the first solvent to obtain back- raffinate oil and back-extraction oil.

[0082] The present application does not limit the specific type of the mixing unit 1, as long as it can mix the straight-run diesel to be separated and the first solvent, for example, it can be a dilution oil mixing tank.

[0083] The present application does not limit the specific type of the extraction unit 2, as long as it can perform extraction treatment on the dilution oil, for example, it can be a packed extraction column with 45 theoretical trays.

[0084] The present application does not limit the specific type of the back-extraction unit 3, as long as it can perform back-extraction treatment on the extract oil, for example, it can be a packed extraction column with 5 theoretical trays.

[0085] In the present application, the straight-run diesel to be separated is first diluted, and then subjected to extraction treatment and back-extraction treatment, which can achieve the purpose of high selectivity of aromatic hydrocarbon separation and high removal rate of aromatic hydrocarbon.

[0086] In some embodiments of the present application, it further comprises a first solvent recovery unit 4, a second solvent recovery unit 5 and a third solvent recovery unit 6.

[0087] The back-extraction oil inlet of the first solvent recovery unit 4 is in communication with the back-extraction oil outlet of the back-extraction unit 3, the raffinate oil inlet of the second solvent recovery unit 5 is in communication with the raffinate oil outlet of the extraction unit 2, and the back- raffinate oil inlet of the third solvent recovery unit 6 is in communication with the back- raffinate oil outlet of the back-extraction unit 3.

[0088] In the present application, the stripping oil obtained in the stripping unit 3 is output from the stripping oil outlet at the top of the stripping unit 3, enters the first solvent recovery unit 4 through the stripping oil inlet at the lower part of the first solvent recovery unit 4, solvent recovery is performed, and the circulating oil and the first solvent are obtained. The circulating oil is output from the circulating oil outlet at the bottom of the first solvent recovery unit 4 and can be returned to participate in the extraction process. The first solvent is output from the solvent outlet at the top of the first solvent recovery unit 4, enters the first solvent storage unit 7 through the solvent inlet of the first solvent storage unit 7, is stored in the first solvent storage unit 7, and can be returned to the mixing unit 1 or the stripping unit 3 to be used for dissolving and diluting the straight-run diesel oil to be separated or stripping the extraction oil.

[0089] In the present application, the raffinate oil obtained in the extraction unit 2 is output from the raffinate oil outlet at the top of the extraction unit 2, enters the second solvent recovery unit 5 through the raffinate oil inlet at the lower part of the second solvent recovery unit 5, solvent recovery is performed, and the rich-alkane oil and the first solvent are obtained. The rich-alkane oil is output from the rich-alkane oil outlet at the bottom of the second solvent recovery unit 5 and can be used as a high-quality raw material for steam cracking to produce ethylene. The first solvent is output from the solvent outlet at the top of the second solvent recovery unit 5, enters the first solvent storage unit 7 through the solvent inlet of the first solvent storage unit 7, is stored in the first solvent storage unit 7, and can be returned to the mixing unit 1 or the stripping unit 3 to be used for dissolving and diluting the straight-run diesel oil to be separated or stripping the extraction oil.

[0090] In the present application, the raffinate oil obtained in the stripping unit 3 is output from the raffinate oil outlet at the top of the stripping unit 3, enters the first solvent recovery unit 4 through the raffinate oil inlet at the lower part of the first solvent recovery unit 4, solvent recovery is performed, and the rich-alkane oil and the first solvent are obtained. The rich-alkane oil is output from the rich-alkane oil outlet at the bottom of the second solvent recovery unit 5 and can be used as a high-quality raw material for steam cracking to produce ethylene. The first solvent is output from the solvent outlet at the top of the second solvent recovery unit 5, enters the first solvent storage unit 7 through the solvent inlet of the first solvent storage unit 7, is stored in the first solvent storage unit 7, and can be returned to the mixing unit 1 or the stripping unit 3 to be used for dissolving and diluting the straight-run diesel oil to be separated or stripping the extraction oil.

[0091] The first solvent recovery unit 4, the second solvent recovery unit 5 and the third solvent recovery unit 6 in the present application can recover and reuse the first solvent, the second solvent and the circulating oil, save costs and reduce energy consumption.

[0092] Hereinafter, the technical solutions of the present application will be further described in conjunction with specific embodiments.

[0093] The device of the embodiment of the present application is a device for separating aromatic hydrocarbons and alkane hydrocarbons in straight-run diesel oil, which comprises a mixing unit 1, an extraction unit 2, a stripping unit 3, a first solvent recovery unit 4, a second solvent recovery unit 5, a third solvent recovery unit 6, a first solvent storage unit 7 and a second solvent storage unit 8. Figure 1As shown, the separation device comprises a mixing unit 1 (diluted oil mixing tank), an extraction unit 2 (packed extraction column), a reverse extraction unit 3 (packed extraction column), a first solvent recovery unit 4 (first solvent recovery column), a second solvent recovery unit 5 (second solvent recovery column), a third solvent recovery unit 6 (third solvent recovery column), a first solvent storage unit 7 (first solvent storage tank), and a second solvent storage unit 8 (second solvent storage tank).

[0094] The mixing unit 1 comprises a raw material inlet, a solvent inlet and a diluted oil outlet, the raw material inlet is used for receiving straight-run diesel to be separated, the extraction unit 2 is provided with a solvent inlet at the upper portion and a diluted oil inlet at the lower portion, the solvent inlet is in communication with the solvent outlet of the second solvent storage unit 8, the diluted oil inlet is in communication with the diluted oil outlet of the mixing unit 1, the raffinate oil outlet at the top of the extraction unit 2 is in communication with the raffinate oil inlet at the lower portion of the second solvent recovery unit 5, the extraction oil outlet at the bottom of the extraction unit 2 is in communication with the extraction oil inlet at the upper portion of the reverse extraction unit 3, the solvent inlet at the lower portion of the reverse extraction unit 3 is in communication with the solvent outlet of the first solvent storage unit 7, the reverse extraction oil outlet at the top of the reverse extraction unit 3 is in communication with the reverse extraction oil inlet at the lower portion of the first solvent recovery unit 4, the reverse raffinate oil outlet at the bottom of the reverse extraction unit 3 is in communication with the reverse raffinate oil inlet at the lower portion of the third solvent recovery unit 6, the solvent outlet at the top of the first solvent recovery unit 4 is in communication with the solvent inlet of the second solvent storage unit 8, the circulating oil outlet at the bottom of the first solvent recovery unit 4 is in communication with the diluted oil inlet of the extraction unit 2, the solvent outlet at the top of the second solvent recovery unit 5 is in communication with the solvent inlet of the first solvent storage unit 7, the outlet at the bottom of the second solvent recovery unit 5 outputs rich-alkane oil, the solvent outlet at the top of the third solvent recovery unit 6 is in communication with the solvent inlet of the second solvent storage unit 8, the outlet at the bottom of the third solvent recovery unit 6 outputs rich-aromatic oil, and the solvent outlet of the first solvent storage unit 7 is in communication with the solvent inlet of the mixing unit 1.

[0095] The basic properties of the straight-run diesel adopted in the embodiment of the present application are shown in Table 1, and the basic properties of part of the solvents are shown in Table 2.

[0096] Table 1: Various property parameters of straight-run diesel

[0097]

[0098]

[0099] Table 2: Various performance parameters of traditional de-aromatic solvents and part of the low-boiling-point solvents in the present application

[0100]

[0101] The calculation formula of the aromatic hydrocarbon selectivity S' is as follows:

[0102]

[0103] The calculation formula of the aromatic removal rate R is as follows:

[0104]

[0105] wherein w0 is the mass percentage content of the aromatic hydrocarbon in the straight-run diesel oil, %; w1 is the mass percentage content of the aromatic hydrocarbon in the rich-alkane oil, %; w2 is the mass percentage content of the aromatic hydrocarbon in the rich-aromatic oil, %; w3 is the mass percentage content of the alkane in the rich-alkane oil, %; w4 is the mass percentage content of the alkane in the rich-aromatic oil, %; m0 is the mass of the straight-run diesel oil, g; and m1 is the mass of the rich-alkane oil, g.

[0106] Example 1

[0107] The method for separating the aromatic hydrocarbon and the alkane in the straight-run diesel oil of the present example comprises the following steps:

[0108] The 1#, 2# and 3# straight-run diesel oils are used as the straight-run diesel oil to be separated, the alkane in the 1#, 2# and 3# straight-run diesel oils is at least one of the carbon atoms of 12-40, the second solvent is a mixed solvent of furan, methyl formate and methanol, wherein the volume ratio of the furan, the methyl formate and the methanol is 1:2:2; and the first solvent is 2,2-dimethylbutane. The molecular polarity index of the furan is 9.13, the molecular polarity index of the methyl formate is 19.56, the molecular polarity index of the methanol is 20.67, and the volume percentage content of the methyl formate and the methanol in the second solvent is 80%, according to the calculation formula, the average molecular polarity index of the second solvent is 17.92, and the molecular polarity index of the 2,2-dimethylbutane is 3.07. The difference between the average molecular polarity index of the second solvent and the first solvent is 14.85.

[0109] The 1#, 2# and 3# straight-run diesel oils are used as the straight-run diesel oil to be separated, the alkane in the 1#, 2# and 3# straight-run diesel oils is at least one of the carbon atoms of 12-40, the second solvent is a mixed solvent of furan, methyl formate and methanol, wherein the volume ratio of the furan, the methyl formate and the methanol is 1:2:2; and the first solvent is 2,2-dimethylbutane. The molecular polarity index of the furan is 9.13, the molecular polarity index of the methyl formate is 19.56, the molecular polarity index of the methanol is 20.67, and the volume percentage content of the methyl formate and the methanol in the second solvent is 80%, according to the calculation formula, the average molecular polarity index of the second solvent is 17.92, and the molecular polarity index of the 2,2-dimethylbutane is 3.07. The difference between the average molecular polarity index of the second solvent and the first solvent is 14.85. Figure 1The separation device is shown, the straight-run diesel oil and the first solvent to be separated are fully mixed in the mixing unit 1 to obtain the diluted oil, the second solvent and the diluted oil are pumped into the extraction unit 2 from the upper solvent inlet and the lower diluted oil inlet of the extraction unit 2 respectively for extraction treatment, wherein the volume ratio of the first solvent to the straight-run diesel oil is 1:1, the volume ratio of the second solvent to the diluted oil is 2:1, the second solvent and the diluted oil are countercurrently contacted in the extraction unit 2, the raffinate oil output by the extraction unit 2 is output through the raffinate oil outlet at the top of the extraction unit 2, enters the second solvent recovery unit 5 through the raffinate oil inlet at the lower part of the second solvent recovery unit 5 for first desolventizing treatment, and the rich-alkane oil and the first solvent are obtained; the rich-alkane oil is output from the rich-alkane oil outlet at the bottom of the second solvent recovery unit 5, the first solvent is output from the solvent outlet at the top of the second solvent recovery unit 5, enters the first solvent storage unit 7 through the solvent inlet of the first solvent storage unit 7, and can be output through the solvent outlet of the first solvent storage unit 7, enters the mixing unit 1 through the solvent inlet of the mixing unit 1 to participate in the mixing treatment, or enters the back-extraction unit 3 through the solvent inlet of the back-extraction unit 3 to participate in the back-extraction treatment. The extraction oil output by the extraction unit 2 is output through the extraction oil outlet at the bottom of the extraction unit 2, enters the back-extraction unit 3 through the extraction oil inlet at the upper part of the back-extraction unit 3 to participate in the back-extraction treatment with the first solvent, wherein the volume ratio of the first solvent to the extraction oil is 0.2:1, the back-extraction oil in the back-extraction unit 3 is output from the back-extraction oil outlet at the top of the back-extraction unit 3, enters the first solvent recovery unit 4 through the back-extraction oil inlet at the lower part of the first solvent recovery unit 4 for third desolventizing treatment, and the circulating oil and the first solvent are obtained, the circulating oil is output from the circulating oil outlet at the bottom of the first solvent recovery unit 4, enters the extraction unit 2 through the circulating oil inlet of the extraction unit 2 to participate in the extraction treatment, the first solvent is output from the solvent outlet at the top of the first solvent recovery unit 4, enters the first solvent storage unit 7 through the solvent inlet of the first solvent storage unit 7, and can be output through the solvent outlet of the first solvent storage unit 7, enters the mixing unit 1 through the solvent inlet of the mixing unit 1 to participate in the mixing treatment, or enters the back-extraction unit 3 through the solvent inlet of the back-extraction unit 3 to participate in the back-extraction treatment. The back-extraction raffinate oil in the back-extraction unit 3 is output from the back-extraction raffinate oil outlet at the bottom of the back-extraction unit 3, enters the third solvent recovery unit 6 through the back-extraction raffinate oil inlet at the lower part of the third solvent recovery unit 6 for second desolventizing treatment, and the rich-aromatic oil and the second solvent are obtained, the rich-aromatic oil is output from the rich-aromatic oil outlet at the bottom of the third solvent recovery unit 6, the second solvent is output from the solvent outlet at the top of the third solvent recovery unit 6, enters 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, enters the extraction unit 2 through the solvent inlet at the upper part of the extraction unit 2 to participate in the extraction treatment.During the extraction and back-extraction processes, the temperature of the extraction unit 2 was controlled at 25℃, the temperature of the back-extraction unit 3 was controlled at 25℃, the pressure of the first, second and third solvent removal treatments was 8kPa, and the temperature was 50℃. The properties of the obtained rich-alkane oil and rich-aromatic oil are shown in Table 3.

[0110] Table 3

[0111]

[0112] The yield of the rich-alkane oil is the percentage of the mass of the rich-alkane oil to the total mass of the straight-run diesel oil, the yield of the rich-aromatic oil is the percentage of the mass of the rich-aromatic oil to the total mass of the straight-run diesel oil, and the removal rate of the aromatic hydrocarbon is the percentage of the mass of the aromatic hydrocarbon in the rich-aromatic oil to the mass of the aromatic hydrocarbon in the straight-run diesel oil.

[0113] Example 2

[0114] The separation method of the aromatic hydrocarbon and the alkane in the straight-run diesel oil of Example 2 was basically the same as that of Example 1, except that the first solvent was n-hexane, and the molecular polarity index thereof was 2.83. The properties of the obtained rich-alkane oil and rich-aromatic oil are shown in Table 4.

[0115] Table 4

[0116]

[0117]

[0118] Example 3

[0119] The separation method of the aromatic hydrocarbon and the alkane in the straight-run diesel oil of Example 3 was basically the same as that of Example 1, except that the first solvent was cyclohexane, and the molecular polarity index thereof was 2.45. The properties of the obtained rich-alkane oil and rich-aromatic oil are shown in Table 5.

[0120] Table 5

[0121]

[0122] Example 4

[0123] The separation method of the aromatic hydrocarbon and the alkane in the straight-run diesel oil of Example 4 was basically the same as that of Example 1, except that the volume ratio of the first solvent to the straight-run diesel oil was 0.5:1, the volume ratio of the second solvent to the dilution oil was 2:1, and the volume ratio of the first solvent to the extraction oil was 0.3:1. The properties of the obtained rich-alkane oil and rich-aromatic oil are shown in Table 6.

[0124] Table 6

[0125]

[0126] Example 5

[0127] The separation method of aromatics and alkanes in the straight-run diesel oil of Example 5 is basically the same as that of Example 1, except that the second solvent is a mixed solvent of furan, acetone and methanol, wherein the volume ratio of furan, acetone and methanol is 1:2:2, and the volume percentage content of methyl formate in the second solvent is 40%. The molecular polarity index of furan is 9.13, the molecular polarity index of acetone is 13.24, and the molecular polarity index of methanol is 20.67. The average molecular polarity index of the second solvent is 15.39, which is calculated according to the formula, and the molecular polarity index of 2,2-dimethylbutane is 3.07. The difference between the average molecular polarity index of the second solvent and that of the first solvent is 12.32. The properties of the alkane-rich oil and the aromatic-rich oil obtained by separation are shown in Table 7.

[0128] Table 7

[0129]

[0130] Example 6

[0131] The separation method of aromatics and alkanes in the straight-run diesel oil of Example 6 is basically the same as that of Example 1, except that the second solvent is a mixed solvent of ethyl acetate, ethanol, acetone and methanol, wherein the volume ratio of ethyl acetate, ethanol, acetone and methanol is 1:1:1:2, and the volume percentage content of methanol in the second solvent is 40%. The molecular polarity index of ethyl acetate is 9.96, the molecular polarity index of ethanol is 10.11, the molecular polarity index of acetone is 13.24, and the molecular polarity index of methanol is 20.67. The average molecular polarity index of the second solvent is 14.93, which is calculated according to the formula, and the molecular polarity index of 2,2-dimethylbutane is 3.07. The difference between the average molecular polarity index of the second solvent and that of the first solvent is 11.86. The properties of the alkane-rich oil and the aromatic-rich oil obtained by separation are shown in Table 8.

[0132] Table 8

[0133]

[0134] Comparative Example 1

[0135] The separation method of aromatics and alkanes in the straight-run diesel oil of Comparative Example 1 is basically the same as that of Example 1, except that the first solvent is not used to mix the straight-run diesel oil to be separated, and the second solvent (furan, methyl formate and methanol with a volume ratio of 1:2:2) is directly used to extract the straight-run diesel oil to be separated, and the first solvent 2,2-dimethylbutane is used to back-extract the extracted oil. The properties of the alkane-rich oil and the aromatic-rich oil obtained by separation are shown in Table 9.

[0136] Table 9

[0137]

[0138] Comparative Example 2

[0139] Comparative Example 2 and Example 1 are basically the same in the separation method of the aromatics and alkanes in the straight-run diesel, except that the second solvent (furan, methyl formate and methanol in a volume ratio of 1:2:2) is used to mix the straight-run diesel to be separated, the first solvent (2,2-dimethylbutane) is used to extract the diluted oil, and the second solvent (furan, methyl formate and methanol in a volume ratio of 1:2:2) is used to back-extract the extracted oil. It is found that the second solvent is directly phase-separated from the straight-run diesel, and the mixing cannot be completed.

[0140] Comparative Example 3

[0141] Comparative Example 3 and Example 1 are basically the same in the separation method of the aromatics and alkanes in the straight-run diesel, except that the straight-run diesel to be separated is not mixed, and the first solvent (2,2-dimethylbutane) is directly used to extract the straight-run diesel to be separated, and the second solvent (furan, methyl formate and methanol in a volume ratio of 1:2:2) is used to back-extract the extracted oil. It is found that the first solvent is completely miscible with the straight-run diesel, and the extraction cannot be completed.

[0142] Comparative Example 4

[0143] Comparative Example 4 and Example 1 are basically the same in the separation method of the aromatics and alkanes in the straight-run diesel, except that the straight-run diesel to be separated is not mixed, and the traditional high-boiling solvent dimethyl sulfoxide is directly used to extract the straight-run diesel to be separated, and no back-extraction is performed. The properties of the alkane-rich oil and the aromatic-rich oil obtained by separation are shown in Table 10.

[0144] Table 10

[0145]

[0146] From Tables 1-10, it can be seen that, compared with the comparative examples, the separation method of the aromatics and alkanes in the straight-run diesel provided by the present application can realize high separation selectivity of the aromatics in the straight-run diesel and high removal rate of the aromatics, by using the first solvent to dilute the straight-run diesel to be separated, using the mixed solvent including at least two solvents, i.e., the second solvent, to extract the diluted oil, using the first solvent to back-extract the extracted oil, and limiting the absolute value of the difference between the average molecular polarity index of the first solvent and the straight-run diesel and the difference between the average molecular polarity index of the second solvent and the first solvent.

[0147] From the comparison of Example 1 and Comparative Examples 1-4, it can be seen that the separation method of the aromatics and alkanes in the straight-run diesel provided by the present application can realize high separation selectivity of the aromatics in the straight-run diesel and high removal rate of the aromatics, and the alkane content in the alkane-rich oil obtained is greater than 95%, and the aromatic content in the aromatic-rich oil obtained is greater than 95%.

[0148] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions described in the foregoing embodiments can still be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for separating aromatics and alkanes in straight run diesel, characterized by, The method comprises the following steps: 1) mixing straight-run diesel to be separated and a first solvent to obtain diluted oil; 2) performing extraction treatment on the diluted oil by using a second solvent to obtain raffinate oil and extracted oil; 3) performing reverse extraction treatment on the extracted oil by using the first solvent to obtain reverse raffinate oil and reverse extracted oil; The second solvent is a mixed solvent comprising at least two solvents; The absolute value of the difference between the average molecular polarity index of the first solvent and that of the straight-run diesel to be separated is less than 5; The difference between the average molecular polarity index of the second solvent and that of the first solvent is greater than 10.

2. The separation method of claim 1, wherein, The second solvent comprises at least one third solvent with a molecular polarity index greater than 15, and the volume percentage of the third solvent in the second solvent is not less than 40%.

3. The separation method according to claim 1 or 2, characterized in that, The first solvent is at least one light hydrocarbon with a boiling point of 40-100℃.

4. The separation method according to any one of claims 1 to 3, characterized in that, The average molecular polarity index of the straight-run diesel to be separated is 3-5.

5. The separation method according to any one of claims 1 to 4, characterized in that, The volume ratio of the first solvent to the straight-run diesel to be separated is 0.1-2:1; and / or, The volume ratio of the second solvent to the diluted oil is 1-5:1; and / or, The volume ratio of the first solvent to the extracted oil is 0.1-1:

1.

6. The separation method according to any one of claims 1 to 5, characterized in that, In the extraction treatment, the diluted oil and the second solvent are in counter- contact; and / or, In the reverse extraction treatment, the extracted oil and the first solvent are in counter-contact.

7. The separation method according to any one of claims 1 to 6, characterized in that, Further comprising: performing first desolventization treatment on the raffinate oil to obtain rich-alkane oil and the first solvent; and / or, performing second desolventization treatment on the reverse raffinate oil to obtain rich-aromatic oil and the second solvent; and / or, performing third desolventization treatment on the reverse extracted oil to obtain cycle oil and the first solvent; the cycle oil is returned to participate in the extraction treatment.

8. The separation method according to any one of claims 1 to 7, characterized in that, The content of aromatic hydrocarbon in the straight-run diesel to be separated is 10-30wt%; and / or, The alkane in the straight-run diesel to be separated is at least one with a carbon atom number of 12-40.

9. A separation device for performing the separation method according to any one of claims 1 to 8, characterized in that, The method comprises a mixing unit, an extraction unit and a reverse extraction unit; The mixing unit comprises a raw material inlet and a diluted oil outlet, the extraction unit comprises a diluted oil inlet, a raffinate oil outlet and an extracted oil outlet, and the reverse extraction unit comprises an extracted oil inlet, a reverse extracted oil outlet and a reverse raffinate oil outlet; The diluted oil outlet of the mixing unit is in communication with the diluted oil inlet of the extraction unit, and the extracted oil outlet of the extraction unit is in communication with the extracted oil inlet of the reverse extraction unit.

10. The separation device of claim 9, wherein, Further comprising: a first solvent recovery unit, a second solvent recovery unit and a third solvent recovery unit; The reverse extracted oil inlet of the first solvent recovery unit is in communication with the reverse extracted oil outlet of the reverse extraction unit, the raffinate oil inlet of the second solvent recovery unit is in communication with the raffinate oil outlet of the extraction unit, and the reverse raffinate oil inlet of the third solvent recovery unit is in communication with the reverse raffinate oil outlet of the reverse extraction unit.

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