Separation method and separation device for aromatic hydrocarbons and alkanes in FCC diesel oil

Abstract

The invention provides a separation method and a separation device for aromatic hydrocarbon and alkane in FCC diesel oil, and the separation method comprises the following steps: 1) mixing to-be-separated FCC diesel oil 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; wherein the second solvent is a mixed solvent comprising at least two or more solvents; the absolute value of the difference value between the average molecular polarity index of the first solvent and the average molecular polarity index of the FCC 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. According to the method for separating the aromatic hydrocarbons and the alkanes in the FCC diesel oil, provided by the invention, the separation selectivity of the aromatic hydrocarbons in the FCC diesel oil is high, and the removal rate of the aromatic hydrocarbons is high.

Description

Technical Field

[0001] This invention belongs to the field of diesel refining technology, and particularly relates to a method and apparatus for separating aromatics and alkanes from FCC diesel. Background Technology

[0002] Against the backdrop of "dual carbon" (carbon dioxide, carbon emissions, and carbon sequestration), my country's oil quality upgrade is accelerating, and environmental regulations are becoming increasingly stringent regarding the cetane number and aromatic content of diesel fuel, especially heavy aromatics. Meanwhile, my country's apparent diesel consumption has already peaked, and the problem of overcapacity urgently needs to be addressed, while there remains a certain gap in demand for basic chemical raw materials such as aromatics and olefins. Therefore, the targeted separation and separate conversion of aromatic and alkane components in diesel fuel is an effective measure to achieve high-value utilization of diesel. Catalytic cracking (FCC) diesel is rich in mono- and dicyclic aromatics, serving as both a chemical raw material for the preparation of specialty aromatic oils and a component for producing high-octane gasoline blending, thus possessing significant potential economic value.

[0003] Liquid-liquid extraction technology can effectively separate aromatic and alkane components in diesel fuel, achieving the goal of classifying and managing the various components of diesel fuel. However, most of the aromatic extraction solvents commonly used in industry are high-boiling-point organic solvents (boiling points between 162-285℃), such as dimethyl sulfoxide, sulfolane, and furfural, which have low selectivity for separating aromatics and low aromatic removal rates. Summary of the Invention

[0004] The main objective of this invention is to provide a method for separating aromatics and alkanes in FCC diesel fuel. This method can achieve high selectivity and high aromatic removal rate for separating aromatics in FCC diesel fuel.

[0005] The present invention also provides a separation device for performing the above separation method, which can achieve high selectivity and high aromatic removal rate for separating aromatics in FCC diesel.

[0006] In a first aspect, the present invention provides a method for separating aromatics and alkanes in FCC diesel fuel, comprising the following steps:

[0007] 1) Mix the FCC diesel fuel to be separated with the first solvent to obtain diluted oil;

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

[0009] Wherein, the second solvent is a mixed solvent comprising at least two or more solvents;

[0010] The absolute value of the difference between the average molecular polarity index of the first solvent and the FCC diesel to be separated is <5;

[0011] The difference between the average molecular polarity index of the second solvent and the first solvent is >10.

[0012] In the separation method described above, the second solvent includes 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%.

[0013] In the separation method described above, the first solvent is at least one of light hydrocarbons with a boiling point of 40-100°C.

[0014] In the separation method described above, the average molecular polarity index of the FCC diesel to be separated is 5-8.

[0015] In the separation method described above, the volume ratio of the first solvent to the FCC diesel fuel to be separated is 0.1-2:1; and / or,

[0016] The volume ratio of the second solvent to the diluent oil is 1-5:1.

[0017] In the separation method described above, during the extraction process, the diluted oil and the second solvent are in countercurrent contact.

[0018] The separation method described above further includes: subjecting the raffinate oil to a first desolventizing treatment to obtain alkyl-rich oil and a first solvent; and / or,

[0019] The extracted oil is subjected to a second desolventizing treatment to obtain an aromatic oil and a second solvent.

[0020] In the separation method described above, the aromatic content in the FCC diesel to be separated is 50-90 wt%; and / or,

[0021] The alkane in the FCC diesel to be separated is at least one of 12-40 carbon atoms.

[0022] In a second aspect, the present invention provides a separation apparatus for performing the above-described separation method, comprising a mixing unit and an extraction unit;

[0023] The mixing unit includes a raw material inlet and a dilution oil outlet, and the extraction unit includes a dilution oil inlet, a raffinate oil outlet, and an extract oil outlet;

[0024] The dilution oil outlet of the mixing unit is connected to the dilution oil inlet of the extraction unit.

[0025] The separation device described above further includes: a first solvent recovery unit and a second solvent recovery unit;

[0026] The raffinate inlet of the first solvent recovery unit is connected to the raffinate outlet of the extraction unit; the extract oil inlet of the second solvent recovery unit is connected to the extract oil outlet of the extraction unit.

[0027] The present invention provides a method for separating aromatics and alkanes in FCC diesel fuel. The method involves diluting the FCC diesel fuel to be separated using a first solvent, and extracting the diluted oil using a mixed solvent comprising at least two solvents, namely a second solvent. The method limits the absolute value of the difference between the average molecular polarity index of the first solvent and the FCC diesel fuel, and the difference between the average molecular polarity index of the second solvent and the first solvent. This method can achieve high selectivity and high aromatic removal rate in the separation of aromatics in FCC diesel fuel. Attached Figure Description

[0028] 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.

[0029] Figure 1 This is a schematic diagram of a separation device for aromatics and alkanes in FCC diesel fuel provided by the present invention.

[0030] Explanation of reference numerals in the attached figures:

[0031] 1-Mixing unit; 2-Extraction unit; 3-First solvent recovery unit; 4-Second solvent recovery unit; 5-First solvent storage unit; 6-Second solvent storage unit. Detailed Implementation

[0032] 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.

[0033] In a first aspect, the present invention provides a method for separating aromatics and alkanes in FCC diesel fuel, comprising the following steps:

[0034] 1) Mix the FCC diesel fuel to be separated with the first solvent to obtain diluted oil;

[0035] 2) The diluted oil is extracted using a second solvent to obtain raffinate oil and extract oil;

[0036] Wherein, the second solvent is a mixed solvent comprising at least two or more solvents;

[0037] The absolute value of the difference between the average molecular polarity index of the first solvent and the FCC diesel to be separated is <5;

[0038] The difference between the average molecular polarity index of the second solvent and the first solvent is >10.

[0039] The present invention provides a method for separating aromatics and alkanes in FCC diesel fuel, which obtains alkane-rich oil and aromatic-rich oil through mixing and extraction.

[0040] Specifically, in step 1), the FCC diesel fuel to be separated is mixed with a first solvent to obtain diluted oil. The absolute value of the difference in the average molecular polarity index between the first solvent and the FCC diesel fuel is <5, meaning the polarity of the first solvent and the FCC diesel fuel is similar, making them prone to interaction and facilitating the dissolution of the FCC diesel fuel in the first solvent. The first solvent is at least one of carbon disulfide, petroleum ether, n-alkanes with 5-7 carbon atoms, isoalkanes with 5-7 carbon atoms, and cycloalkanes with 5-7 carbon atoms.

[0041] In step 2), the diluted oil obtained above is extracted using a second solvent to obtain raffinate oil and extract oil. In this invention, the extraction temperature can be 20-30℃. The second solvent is a mixed solvent comprising at least two solvents, for example, at least two of alcohols, esters, ketones, nitrile compounds, and furans. The difference in average molecular polarity index between the second solvent and the first solvent is >10, meaning the polarity difference between the two solvents is significant. Using the second solvent to extract the diluted oil allows for the extraction of aromatics; that is, the aromatics dissolve in the second solvent, and the second solvent containing dissolved aromatics is the extract oil, also known as aromatic-rich oil. Alkanes, due to the presence of the first solvent, dissolve in it, and the first solvent containing dissolved alkanes is the raffinate oil, also known as alkane-rich oil. Therefore, this method uses a two-phase solvent system to achieve high selectivity and a high aromatic removal rate in the FCC diesel oil to be separated.

[0042] The average molecular polarity index for different mixed solvents and FCC diesel fuels is calculated using the following steps:

[0043] The group composition distribution of FCC diesel fuel 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 relatively small. Therefore, representative model compounds can be screened to simplify the composition of FCC diesel fuel, and the average molecular polarity index of FCC diesel fuel can be calculated accordingly.

[0044] Based on the screened FCC diesel model compounds and solvent molecular structures, the van der Waals surfaces of different molecules were quantitatively analyzed using the quantum chemical calculation software Gaussian and the wave function analysis software Multiwfn, and the molecular polarity index was calculated.

[0045] The average molecular polarity of FCC diesel and mixed solvents is calculated using the following formulas:

[0046] The average molecular polarity index of FCC diesel fuel = 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 FCC diesel.

[0047] 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 , among which, S i (i = 1, 2, ..., n) represents the mass fraction of each solvent in the mixed solvent.

[0048] The present invention provides a method for separating aromatics and alkanes in FCC diesel fuel. The method involves diluting the FCC diesel fuel to be separated using a first solvent, and extracting the diluted oil using a mixed solvent comprising at least two solvents, namely a second solvent. The method limits the absolute value of the difference between the average molecular polarity index of the first solvent and the FCC diesel fuel, and the difference between the average molecular polarity index of the second solvent and the first solvent. This method can achieve high selectivity and high aromatic removal rate in the separation of aromatics in FCC diesel fuel.

[0049] In some embodiments of the present invention, the second solvent includes 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%.

[0050] The present invention specifies that the second solvent includes 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%. This is beneficial to obtain a second solvent with a larger average molecular polarity index, i.e., stronger polarity, thereby improving the extraction rate of aromatics in the diluted oil by the second solvent. This can achieve a higher separation selectivity and a higher aromatic removal rate of aromatics in FCC diesel.

[0051] In some embodiments of the present invention, the first solvent is at least one of light hydrocarbons with a boiling point of 40-100°C.

[0052] The first solvent in this invention can be a single solvent or a mixed solvent. For example, the first solvent is at least one of light hydrocarbons with a boiling point of 40-100℃, which can achieve good solubility of the FCC diesel to be separated, and can also make full use of the by-products generated by the refinery. It is inexpensive, readily available, and widely sourced, which is conducive to saving energy consumption, reducing production costs, and having low regeneration energy consumption.

[0053] In some embodiments of the present invention, the average molecular polarity index of the FCC diesel to be separated is 5-8.

[0054] In this invention, the average molecular polarity index of the FCC diesel to be separated is defined as 5-8, which is relatively moderate and can interact with the solvent relatively easily, so that aromatics can be effectively extracted from the FCC diesel. This results in high selectivity and high aromatic removal rate of aromatics in FCC diesel.

[0055] In some embodiments of the present invention, the volume ratio of the first solvent to the FCC diesel fuel to be separated is 0.1-2:1; and / or,

[0056] The volume ratio of the second solvent to the diluent oil is 1-5:1.

[0057] In this invention, the volume ratio of the first solvent to the FCC diesel to be separated is limited to 0.1-2:1, preferably 0.5-1:1, and the volume ratio of the second solvent to the diluent oil is 1-5:1, preferably 1-2:1. The volume ratio is within a suitable range, which is conducive to the full dissolution of the FCC diesel to be separated by the first solvent and the full extraction of aromatics in the diluent oil by the second solvent. This can further achieve a high selectivity for the separation of aromatics in FCC diesel and a high aromatics removal rate.

[0058] In some embodiments of the present invention, during the extraction process, the diluent oil is in countercurrent contact with the second solvent.

[0059] In this invention, the diluent oil and the second solvent come into contact in opposite directions, which helps to increase the contact area and contact time, and enables the second solvent to fully extract the aromatics from the FCC diesel to be separated, thereby improving the extraction rate of aromatics.

[0060] In some embodiments of the present invention, the method further includes: subjecting the raffinate oil to a first desolventizing treatment to obtain an alkyl-rich oil and a first solvent; and / or,

[0061] The extracted oil is subjected to a second desolventizing treatment to obtain an aromatic oil and a second solvent.

[0062] It is understood that since the raffinate oil contains alkanes and a first solvent, a first desolventizing treatment is performed on it to obtain alkane-rich oil and the first solvent. In this invention, the boiling point of the first solvent is <100℃, the pressure of the first desolventizing treatment is 100kPa, and the temperature is 60-120℃; and / or, the pressure of the first desolventizing treatment is 5-10kPa, and the temperature is 30-60℃. The first solvent is evaporated and recycled, for example, returned to the dilution oil mixing tank for further mixing. The alkane-rich oil has an alkane content greater than 80% and can be used as a feedstock for steam cracking to produce ethylene.

[0063] Because the extracted oil contains aromatics and a second solvent, a second desolventizing treatment is performed to obtain a rich aromatic oil and a second solvent. In this invention, the boiling point of the second solvent is <100℃, and the pressure of the second desolventizing treatment is 100 kPa and the temperature is 60-120℃; and / or, the pressure of the second desolventizing treatment is 5-10 kPa and the temperature is 30-60℃. The second solvent is evaporated and recovered for reuse, for example, by returning it to the extraction tower for further extraction. The rich aromatic oil contains more than 95% aromatics and can be used to prepare specialty aromatic oils or for further separation.

[0064] In this invention, by performing desolventizing treatment on the raffinate oil and the extract oil respectively, and returning the first solvent and the second solvent obtained to participate in the extraction treatment again, the purpose of saving energy and reducing costs can be achieved.

[0065] In some embodiments of the present invention, the aromatic hydrocarbon content in the FCC diesel oil to be separated is 50-90 wt%; and / or,

[0066] The alkane in the FCC diesel to be separated is at least one of 12-40 carbon atoms.

[0067] The aromatic hydrocarbon content in the FCC diesel to be separated in this invention is 50-90 wt%, preferably 70-90 wt%, and the alkane is at least one of 12-40 carbon atoms. That is, the aromatic hydrocarbon content in the FCC diesel to be separated is relatively high, and the alkane has a specific number of carbon atoms, which is beneficial to the extraction of aromatic hydrocarbons. By controlling the aromatic hydrocarbon content and the number of carbon atoms of the alkane in the FCC diesel, the separation selectivity of aromatic hydrocarbons can be further improved and the aromatic hydrocarbon removal rate can be increased.

[0068] Secondly, the present invention provides a separation apparatus for performing the above-described separation method, such as... Figure 1 As shown, the separation device includes a mixing unit 1 and an extraction unit 2;

[0069] The mixing unit 1 includes a raw material inlet and a dilution oil outlet, and the extraction unit 2 includes a dilution oil inlet, a raffinate oil outlet, and an extraction oil outlet;

[0070] The dilution oil outlet of the mixing unit 1 is connected to the dilution oil inlet of the extraction unit 2.

[0071] In one embodiment, the FCC diesel oil to be separated and the first solvent are mixed in mixing unit 1 to obtain diluted oil. The diluted oil is output from the diluted oil outlet of mixing unit 1 and enters the extraction unit 2 through the diluted oil inlet at the bottom of extraction unit 2. In extraction unit 2, the diluted oil is extracted using a second solvent to obtain raffinate oil and extract oil.

[0072] The present invention does not limit the specific type of mixing unit 1, as long as it can mix the FCC diesel to be separated and the first solvent. For example, it can be a dilution oil mixing tank.

[0073] The present invention does not limit the specific type of extraction unit 2, as long as it can achieve the extraction treatment of diluted oil. For example, it can be a packed extraction tower with a theoretical number of 30 plates.

[0074] In this invention, the FCC diesel to be separated is first diluted and then extracted, which can achieve a high selectivity for the separation of aromatics and a high aromatics removal rate.

[0075] In some embodiments of the present invention, the present invention further includes: a first solvent recovery unit 3 and a second solvent recovery unit 4;

[0076] The raffinate inlet of the first solvent recovery unit 3 is connected to the raffinate outlet of the extraction unit 2; the extract oil inlet of the second solvent recovery unit 4 is connected to the extract oil outlet of the extraction unit 2.

[0077] In this invention, the raffinate obtained from extraction unit 2 is output from the raffinate outlet at the top of extraction unit 2 and enters the first solvent recovery unit 3 through the raffinate inlet at the bottom of the first solvent recovery unit 3 for solvent recovery, yielding alkyl-rich oil and a first solvent. The alkyl-rich oil is output from the alkyl-rich oil outlet at the bottom of the first solvent recovery unit 3 and can be used as a feedstock for steam cracking to produce ethylene. The first solvent is output from the solvent outlet at the top of the first solvent recovery unit 3 and enters the first solvent storage unit 5 through the solvent inlet of the first solvent storage unit 5 for storage. It can also be returned to the mixing unit 1 for dissolving and diluting the FCC diesel to be separated.

[0078] In this invention, the extracted oil obtained in extraction unit 2 is output from the extracted oil outlet at the bottom of extraction unit 2 and enters the second solvent recovery unit 4 through the extracted oil inlet at the bottom of the second solvent recovery unit 4 for solvent recovery, yielding a rich aromatic oil and a second solvent. The rich aromatic oil is output from the rich aromatic oil outlet at the bottom of the second solvent recovery unit 4 and can be used to prepare special aromatic oils or for further separation. The second solvent is output from the solvent outlet at the top of the second solvent recovery unit 4 and enters the second solvent storage unit 6 through the solvent inlet of the second solvent storage unit 6 for storage, and can be returned to extraction unit 2 to participate in the extraction process.

[0079] The first solvent recovery unit 3 and the second solvent recovery unit 4 in this invention can recover and reuse the first solvent and the second solvent, saving costs and reducing energy consumption.

[0080] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0081] The apparatus in this embodiment of the invention is a separation device for aromatics and alkanes in FCC diesel fuel, such as... Figure 1 As shown, the separation device includes a mixing unit 1 (diluent oil mixing tank); an extraction unit 2 (packed extraction tower); a first solvent recovery unit 3 (first solvent recovery tower); a second solvent recovery unit 4 (second solvent recovery tower); a first solvent storage unit 5 (first solvent storage tank); and a second solvent storage unit 6 (second solvent storage tank).

[0082] The mixing unit 1 includes a raw material inlet, a solvent inlet, and a dilution oil outlet. The raw material inlet is used to receive FCC diesel fuel to be separated. The extraction unit 2 has a solvent inlet at the top and a dilution oil inlet at the bottom. The solvent inlet is connected to the solvent outlet of the second solvent storage unit 6. The dilution oil inlet is connected to the dilution oil outlet of the mixing unit 1. The raffinate oil outlet at the top of the extraction unit 2 is connected to the raffinate oil inlet at the bottom of the first solvent recovery unit 3. The extract oil outlet at the bottom of the extraction unit 2 is connected to the extract oil inlet at the bottom of the second solvent recovery unit 4. The solvent outlet at the top of the first solvent recovery unit 3 is connected to the solvent inlet of the first solvent storage unit 5. The bottom outlet of the first solvent recovery unit 3 outputs alkyl-rich oil. The solvent outlet at the top of the second solvent recovery unit 4 is connected to the solvent inlet of the second solvent storage unit 6. The bottom outlet of the second solvent recovery unit 4 outputs aromatic-rich oil. The solvent outlet of the first solvent storage unit 5 is connected to the solvent inlet of the mixing unit 1.

[0083] The basic properties of the FCC diesel used in the embodiments of this invention are shown in Table 1, and the basic properties of some solvents are shown in Table 2.

[0084] Table 1. Properties of FCC Diesel

[0085]

[0086] Table 2. Performance parameters of traditional dearomatization solvents and some low-boiling-point solvents in this invention.

[0087]

[0088] The formula for calculating the aromatic selectivity S' is as follows:

[0089]

[0090] The formula for calculating the aromatic hydrocarbon removal rate R is as follows:

[0091]

[0092] Wherein, w0 is the mass percentage of aromatics in FCC diesel, %; w1 is the mass percentage of aromatics in alkyl-rich oil, %; w2 is the mass percentage of aromatics in alkyl-rich oil, %; w3 is the mass percentage of alkyl-rich oil, %; w4 is the mass percentage of alkyl-rich oil, %; m0 is the mass of FCC diesel, g; m1 is the mass of alkyl-rich oil, g.

[0093] Example 1

[0094] The method for separating aromatics and alkanes in FCC diesel fuel in this embodiment includes the following steps:

[0095] FCC diesel fuels #1, #2, and #3 were used as the FCC diesel fuels to be separated. All three FCC diesel fuels contained at least one alkane with 12-40 carbon atoms. The second solvent was a mixture of furan, ethyl acetate, and methanol, with a volume ratio of 1:1:3. The first solvent was 2,2-dimethylbutane. The molecular polarity index of furan was 9.13, that of ethyl acetate was 9.96, and that of methanol was 20.67. The volume percentage of methanol in the second solvent was 60%. Based on the formula, the average molecular polarity of the second solvent was calculated to be 16.22, and the molecular polarity index of 2,2-dimethylbutane was 3.07. The difference between the average molecular polarity indices of the second and first solvents was 13.15.

[0096] use Figure 1The separation device shown allows the FCC diesel fuel to be separated and the first solvent to be fully mixed in the mixing unit 1 to obtain 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, respectively, for extraction. The volume ratio of the first solvent to the FCC diesel fuel is 1:1, and the volume ratio of the second solvent to the diluted oil is 5:1. The second solvent and the diluted oil are in counter-current contact in the extraction unit 2. The raffinate output from the extraction unit 2 is output through the raffinate outlet at the top of the extraction unit 2 and enters the first solvent recovery unit 3 through the raffinate inlet at the bottom of the first solvent recovery unit 3 for the first solvent removal treatment to obtain alkyl-rich oil and the first solvent. The alkyl-rich oil is output from the alkyl-rich oil outlet at the bottom of the first solvent recovery unit 3, and the first solvent enters the first solvent storage unit 5 from the solvent outlet at the top of the first solvent recovery unit 3. It can also be output through the solvent outlet of the first solvent storage unit 5 and enter the mixing unit 1 through the solvent inlet of the mixing unit 1 to participate in the mixing treatment. The extract oil output from extraction unit 2 is discharged through the extract oil outlet at the bottom of extraction unit 2 and enters the second solvent recovery unit 4 through the extract oil inlet at the bottom of the second solvent recovery unit 4 for the second solvent removal treatment, obtaining rich aromatic oil and a second solvent. The rich aromatic oil is discharged from the rich aromatic oil outlet at the bottom of the second solvent recovery unit 4, and the second solvent enters the second solvent storage unit 6 through the solvent outlet at the top of the second solvent recovery unit 4. It can also be discharged through the solvent outlet of the second solvent storage unit 6 and enter the extraction unit 2 through the solvent inlet at the top of extraction unit 2 to participate in the extraction treatment. During the extraction process, the temperature of extraction unit 2 is controlled at 25°C, the pressure of the first solvent removal treatment and the second solvent removal treatment is 8 kPa, and the temperature is 50°C. The properties of the separated alkyl rich oil and rich aromatic oil are shown in Table 3.

[0097] Table 3

[0098]

[0099] Table 3 shows the yield of alkyl-rich oil as a percentage of the total mass of FCC diesel, the yield of aromatic-rich oil as a percentage of the total mass of FCC diesel, and the aromatic removal rate as a percentage of the mass of aromatics in the aromatic-rich oil as a percentage of the mass of aromatics in the FCC diesel.

[0100] Example 2

[0101] The separation methods for aromatics and alkanes in FCC diesel oil in Example 2 and Example 1 are basically the same, except that the first solvent is n-hexane, which has a molecular polarity index of 2.83. The properties of the separated alkane-rich oil and aromatic-rich oil are shown in Table 4.

[0102] Table 4

[0103]

[0104] Example 3

[0105] The separation methods for aromatics and alkanes in FCC diesel oil in Example 3 and Example 1 are basically the same, except that the first solvent is cyclohexane, which has a molecular polarity index of 2.45. The properties of the separated alkane-rich oil and aromatic-rich oil are shown in Table 5.

[0106] Table 5

[0107]

[0108] Example 4

[0109] The separation methods for aromatics and alkanes in FCC diesel oil in Example 4 and Example 1 are basically the same, except that the volume ratio of the first solvent to FCC diesel oil is 0.5:1, and the volume ratio of the second solvent to diluent oil is 3:1. The properties of the separated alkane-rich oil and aromatic-rich oil are shown in Table 6.

[0110] Table 6

[0111]

[0112] Example 5

[0113] The separation method for aromatics and alkanes in FCC diesel oil in Example 5 is basically the same as that in Example 1, except that the second solvent is a mixed solvent of furan, methyl formate, and methanol, with a volume ratio of furan, methyl formate, and methanol of 1:2:2, and the total volume percentage of methyl formate and methanol in the second solvent is 80%. The molecular polarity index of furan is 9.13, that of methyl formate is 19.56, and that of methanol is 20.67. Calculations based on the formula show that the average molecular polarity of the second solvent is 17.92, and that of 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. The properties of the separated alkane-rich oil and aromatic-rich oil are shown in Table 7.

[0114] Table 7

[0115]

[0116] Example 6

[0117] The separation method for aromatics and alkanes in FCC diesel oil in Example 6 is basically the same as that in Example 1, except that the second solvent is a mixed solvent of furan, ethyl formate, and methanol, with a volume ratio of furan, ethyl formate, and methanol of 1:2:2, and the volume percentage of ethyl formate and methanol in the second solvent is 80%. The molecular polarity index of furan is 9.13, that of ethyl formate is 17.87, and that of methanol is 20.67. According to the formula, the average molecular polarity of the second solvent is calculated to be 17.24, 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 the first solvent is 14.17. The properties of the separated alkane-rich oil and aromatic-rich oil are shown in Table 8.

[0118] Table 8

[0119]

[0120] Comparative Example 1

[0121] The separation methods for aromatics and alkanes in the FCC diesel fuel of Comparative Example 1 and Example 1 are basically the same, except that the first solvent was not used to mix the FCC diesel fuel to be separated, and the second solvent (furan, ethyl acetate and methanol in a volume ratio of 1:2:2) was used directly for extraction. The properties of the separated alkane-rich oil and aromatic-rich oil are shown in Table 9.

[0122] Table 9

[0123]

[0124] Comparative Example 2

[0125] The separation methods for aromatics and alkanes in the FCC diesel fuel of Comparative Example 2 and Example 1 were basically the same, except that a second solvent (furan, ethyl acetate, and methanol in a volume ratio of 1:2:2) was used to mix the FCC diesel fuel to be separated, and a first solvent (2,2-dimethylbutane) was used to extract the diluted oil. It was found that the second solvent directly separated from the FCC diesel fuel and could not be mixed.

[0126] Comparative Example 3

[0127] The separation methods for aromatics and alkanes in the FCC diesel fuel of Comparative Example 3 and Example 1 were basically the same, except that the FCC diesel fuel to be separated was not mixed, and the first solvent (2,2-dimethylbutane) was directly used for extraction. It was found that the first solvent was completely miscible with the FCC diesel fuel, and extraction could not be completed.

[0128] Comparative Example 4

[0129] The separation methods for aromatics and alkanes in the FCC diesel oil of Comparative Example 4 and Example 1 were basically the same, except that the FCC diesel oil to be separated was not mixed, and the FCC diesel oil to be separated was directly extracted using the conventional high-boiling-point solvent dimethyl sulfoxide. The properties of the separated alkane-rich oil and aromatic-rich oil are shown in Table 10.

[0130] Table 10

[0131]

[0132]

[0133] As shown in Tables 1-10, compared with the comparative examples, the method for separating aromatics and alkanes in FCC diesel provided by the present invention uses a first solvent to dilute the FCC diesel to be separated, and uses a mixed solvent including at least two solvents, i.e., a second solvent, to extract the diluted oil. The method also limits the absolute value of the difference between the average molecular polarity index of the first solvent and the FCC diesel, and the difference between the average molecular polarity index of the second solvent and the first solvent. This method can achieve high selectivity and high aromatic removal rate in the separation of aromatics in FCC diesel.

[0134] As can be seen from the comparison between Example 1 and Comparative Examples 1-4, the method for separating aromatics and alkanes in FCC diesel provided by the present invention can achieve high selectivity for separating aromatics in FCC diesel, high aromatic removal rate, and the alkanes-rich oil obtained has an alkane content of more than 80% and the aromatics-rich oil has an aromatic content of more than 95%.

[0135] 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 process for the separation of aromatics and alkanes in FCC diesel, characterized by, The method comprises the following steps: 1) mixing FCC diesel to be separated and a first solvent to obtain diluted oil; 2) treating the diluted oil with a second solvent to obtain raffinate oil and extract 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 FCC 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 FCC diesel to be separated is 5-8.

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 FCC 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.

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 countercurrently contacted.

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 extract oil to obtain rich-aromatic oil and the second solvent.

8. The separation method according to any one of claims 1 to 7, characterized in that, The content of aromatic hydrocarbon in the FCC diesel to be separated is 50-90wt%; and / or, The alkanes in the FCC diesel to be separated are 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 and an extraction unit; The mixing unit comprises a raw material inlet and a diluted oil outlet, and the extraction unit comprises a diluted oil inlet, a raffinate oil outlet and an extract oil outlet; The diluted oil outlet of the mixing unit is in communication with the diluted oil inlet of the extraction unit.

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

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