A process for the removal of benzene from catalytically cracked raw gasoline

Abstract

A method for removing benzene from catalytic cracking crude gasoline, which comprises introducing C6 fraction of catalytic cracking crude gasoline into an extraction separation equipment to contact with a composite solvent, carrying out liquid phase extraction and static separation, discharging benzene-removed material from the upper part of the equipment to a water washing tower, discharging benzene-removed C6 fraction from the top of the water washing tower, introducing the water after washing into a water stripping tower, discharging water from the top of the water stripping tower to the lower part of a solvent recovery tower, discharging recovered solvent from the bottom of the water stripping tower to the solvent recovery tower, introducing benzene-rich material from the lower part of the extraction separation equipment into the solvent recovery tower, discharging the separated lean solvent from the bottom of the solvent recovery tower, separating water and oil phase from the overhead of the solvent recovery tower, introducing the obtained water into the upper part of the water washing tower, discharging the oil phase as benzene-rich fraction from the device, wherein the composite solvent comprises 80-97% by mass of sulfolane and 3-20% by mass of C2-C4 polyhydric alcohol, and the benzene-removed C6 fraction is mixed with other fractions to obtain benzene-removed gasoline, wherein the benzene content can be reduced to below 0.8% by volume.

Description

Technical Field

[0001] This invention relates to a method for removing benzene from crude gasoline produced by catalytic cracking. Specifically, it is a method for removing benzene from crude gasoline produced by catalytic cracking via liquid-phase extraction. Background Technology

[0002] With increasing environmental awareness, environmental regulations are becoming increasingly stringent regarding vehicle exhaust emissions. Since benzene is a carcinogen, incomplete combustion increases pollutants in exhaust emissions, endangering public health. The China VI emission standard for gasoline stipulates that the volume fraction of benzene in gasoline must be reduced to ≤0.8%. In my country, gasoline produced by conventional catalytic cracking processes contains approximately 0.5%–1.3% benzene by volume, while gasoline produced by selective hydrotreating of light cycle oil with saturated-selective catalytic cracking to produce high-octane gasoline (LTG) or light aromatics (LTA) contains 0.9%–2.5% benzene by mass and 0.8%–2.1% by volume. Therefore, it is necessary to develop benzene removal technologies suitable for gasolines with varying benzene contents produced by different catalytic cracking processes.

[0003] There are two main challenges in removing benzene from catalytic cracking gasoline: (1) the benzene content is low, making conventional physical separation methods such as aromatics extraction, adsorption, and membrane separation uneconomical; (2) olefins have a significant impact, as catalytic cracking gasoline contains a large amount of olefins. If hydrodebenzene is used, these olefins will react with benzene before being removed, resulting in olefin loss and a decrease in the gasoline's octane number. If alkylation is used for benzene removal, olefins have a fatal impact on the solid acid catalyst. Therefore, there is currently no mature process route for benzene removal from catalytic cracking gasoline.

[0004] CN1541988A discloses a method for separating aromatics by extractive distillation. The method involves pre-fractionating a hydrocarbon mixture containing aromatics to obtain C6-C7 and C8 fractions. The C8 fraction is discharged from the system, while the C6-C7 fraction is introduced into an extractive distillation column to contact a selective solvent for extractive distillation. The aromatic-rich solvent discharged from the bottom of the column enters a recovery column, undergoes vacuum distillation, and the lean solvent obtained from the bottom is injected with a certain amount of water and recycled back to the top of the extractive distillation column. The pure aromatic mixture obtained at the top is discharged from the system. Further distillation yields high-purity benzene and toluene products. The non-aromatic hydrocarbons obtained from the extractive distillation column overhead stream are separated and discharged from the system. Water is quantitatively injected into the lean solvent to obtain optimal selectivity and good solubility. The solvent is selected from sulfones, glycols, or morpholine compounds containing 7-8 carbon atoms. The hydrocarbon mixture in this method is selected from catalytic reformed aromatics or thermally cracked hydrogenated gasoline, wherein the aromatic content is at least 30% by weight. Catalytic cracked gasoline has a low aromatic content and is not suitable for this method. In addition, this method requires the extraction of non-aromatic hydrocarbons from the top of the distillation column and the extraction of high-purity aromatic hydrocarbons from the top of the solvent recovery column. This requires the separate evaporation of non-aromatic hydrocarbons and aromatic hydrocarbons from the raw materials, resulting in high energy consumption.

[0005] CN106187771A discloses a method for separating trace amounts of benzene from vinyl acetate. The method uses one or more alkanes with 10-18 carbon atoms as the extractant, and obtains vinyl acetate with a benzene content of less than 1 ppm through extractive distillation. This method requires evaporating more than 90% by mass of vinyl acetate to the top of the extractive distillation column, resulting in high energy consumption, and the solvent used is unsuitable for removing benzene from catalytic cracking gasoline.

[0006] CN106554811A discloses a method for utilizing the benzene-rich fraction (C6 fraction) in depentane-reformed oil. The method involves distilling the depentane-reformed oil from a reforming unit to obtain the benzene-rich fraction from the top of the distillation column. This benzene-rich fraction is then mixed with a light naphtha fraction, and a coking inhibitor is added to initiate a cracking reaction, thereby maximizing the benefits and value of the benzene-rich fraction. However, if this method is used to separate the benzene-rich fraction from crude gasoline feedstock in catalytic cracking, the resulting gasoline product will lose the C6 fraction, and its 50% evaporation temperature and composition will change significantly, thus affecting the properties of the final gasoline product. Summary of the Invention

[0007] The purpose of this invention is to provide a method for removing benzene from crude gasoline produced by catalytic cracking. This method uses a composite solvent to remove benzene from crude gasoline by liquid-phase extraction, which can reduce the benzene content in the gasoline after benzene removal to below 0.8% by volume.

[0008] A method for removing benzene from catalytic cracking crude gasoline includes: pre-fractionating the catalytic cracking crude gasoline to obtain C5-, C6-, and C7+ fractions; introducing the C6 fraction into an extraction and phase separation device for contact with a composite solvent, performing liquid-phase extraction, followed by static phase separation; discharging the benzene-removed material from the upper part of the extraction and phase separation device and discharging the benzene-rich material from the lower part; introducing the benzene-removed material into the lower part of a water washing tower for countercurrent contact with water entering from the upper part, performing water washing; discharging the benzene-removed C6 fraction from the top of the water washing tower, mixing it with the C5- and C7+ fractions to obtain benzene-removed gasoline; and discharging the water from the bottom of the water washing tower and introducing... In the water stripping tower, water vapor is stripped from the top and introduced into the lower part of the solvent recovery tower; the recovered solvent is discharged from the bottom of the water stripping tower and introduced into the middle and lower part of the solvent recovery tower; the benzene-rich material is introduced into the middle of the solvent recovery tower and separated by distillation. The lean solvent is discharged from the bottom of the solvent recovery tower and returned to the extraction phase separation equipment for recycling. The distillate from the top of the solvent recovery tower is introduced into a condenser, where water and oil phases are separated by condensation. The resulting water is introduced into the upper part of the water washing tower, and the resulting oil phase is discharged as the benzene-rich fraction. The composite solvent includes 80-97% by mass of sulfolane and 3-20% by mass of C2-C4 polyols.

[0009] This invention separates the C6 fraction from catalytic cracking crude gasoline, using the composite solvent described in this invention to separate the benzene-rich fraction through a single-stage liquid-phase extraction method, thereby reducing the benzene content in the crude gasoline. The method is simple to operate, requires low equipment investment, operates under mild conditions, and achieves good benzene removal results. Attached Figure Description

[0010] Figure 1 This is a flowchart illustrating the method of the present invention. Detailed Implementation

[0011] The method of this invention first pre-fractionates catalytic cracking crude gasoline to obtain C5-, C6-, and C7+ fractions. The obtained C6 fraction is then contacted with a composite solvent in an extraction phase-separation device. After primary liquid-phase extraction, a benzene-free C6 fraction is obtained. The benzene-free C6 fraction is then combined with the pre-fractionated C5- and C7+ fractions to obtain a benzene-free gasoline product with a benzene content of less than 0.8% by volume. Because this method uses liquid-phase extraction for benzene removal, the composite solvent used has sulfolane as the main solvent and C2-C4 polyols as co-solvents. These co-solvents increase the selectivity of the main solvent while maintaining the solubility of the composite solvent for benzene. The method of this invention is applicable to benzene removal from crude gasoline produced by catalytic cracking with varying benzene contents. The benzene removal rate is adjustable so that the benzene content in the gasoline obtained after benzene removal is just below the required amount. Because extraction is used for benzene removal, there is no loss of olefins in the gasoline. The loss of gasoline octane number caused by benzene removal is small. The total hydrocarbon loss during the benzene removal process, i.e., the loss of alkanes, olefins, cycloalkanes, and C7 and above aromatics, is less than 3% of the mass of the crude gasoline feedstock.

[0012] The composite solvent described in this invention preferably consists of 84-97% by mass sulfolane and 3-16% by mass C2-C4 polyol.

[0013] The composite solvent further contains water, preferably comprising 84-95% by mass of sulfolane, 3-15% by mass of C2-C4 polyol and 0.5-2% by mass of water.

[0014] The C2-C4 polyols described in this invention can be diols or triols, preferably one or more of ethylene glycol, 1,3-propanediol, 1,4-butanediol, and glycerol.

[0015] This invention first pre-fractionates the crude gasoline from catalytic cracking. Preferably, the pre-fractionation is carried out using two distillation towers. More preferably, the pre-fractionation includes introducing the crude gasoline into the middle of a C5 removal tower, and after rectification separation, the C5- fraction is discharged from the top of the C5 removal tower, and the C6+ fraction discharged from the bottom of the C5 removal tower is introduced into the middle of a C6 removal tower, and after rectification separation, the C6 fraction is discharged from the top of the C6 removal tower, and the C7+ fraction is discharged from the bottom of the C6 removal tower.

[0016] The preferred pressure at the top of the C5 removal column is 200–350 kPa, the preferred temperature at the bottom is 120–160 °C, the preferred temperature at the top is 50 °C–70 °C, the preferred reflux ratio is 1–3, and the preferred number of theoretical plates is 20–40. The benzene content in the C5 fraction is preferably not higher than 0.03% by mass, more preferably not higher than 0.02% by mass.

[0017] The preferred top pressure of the C6 removal column is 100–300 kPa, the preferred bottom temperature is 140–180 °C, the preferred top temperature is 70 °C–100 °C, the preferred reflux ratio is 1–3, and the preferred number of theoretical plates is 20–40. The preferred benzene content in the C6 fraction is 3%–30% by mass, and the preferred benzene content in the C7+ fraction is no more than 0.03% by mass, more preferably no more than 0.02% by mass.

[0018] The extraction and phase separation equipment is used to contact the C6 fraction with the composite solvent, perform liquid-phase extraction, and then allow the mixture to stand for phase separation. The liquid-phase extraction is a single-stage extraction and can be carried out by mixing. After extraction, the material is allowed to stand for phase separation. The upper layer is the benzene-free material, and the lower layer is the benzene-rich material. The benzene-free material is discharged from the upper layer, and the benzene-rich material is discharged from the lower layer. The temperature of the extraction and phase separation is preferably 40-70°C, the mass ratio of the composite solvent to the C6 fraction (i.e., the solvent ratio) is preferably 0.5-8:1, more preferably 0.5-6:1, and the pressure is preferably 100-300 kPa.

[0019] The extraction phase separation equipment is preferably a mixing and clarification tank or a device obtained by connecting a mixer and a settling phase separation tank in series.

[0020] The water washing tower of this invention is used to wash the benzene-removed material to remove the solvent. After washing, the benzene-removed C6 fraction is discharged from the top of the tower, and water containing a small amount of complex solvent is discharged from the bottom of the tower. The preferred washing temperature of the water washing tower is 40-80℃, the preferred mass ratio of washing water to benzene-removed material is 0.01-1:1, the preferred top pressure is 80-500 kPa, and the preferred number of theoretical plates is 4-15.

[0021] The aforementioned water stripping tower is used to purify the water after washing, that is, to separate the solvent from the water in the water after washing. After stripping, water vapor is discharged from the top of the tower, and the recovered solvent is discharged from the bottom of the tower. The bottom temperature of the water stripping tower is preferably 100-150℃, more preferably 100-130℃, the top pressure is preferably 100-500kPa, more preferably 100-300kPa, and the theoretical plate number is preferably 2-12.

[0022] The solvent recovery tower is used for distillation separation of the complex solvent in the benzene-rich material. After distillation separation, the benzene-rich fraction is discharged from the top of the tower, and the lean solvent is discharged from the bottom. The top pressure of the solvent recovery tower is preferably 15-80 kPa, more preferably 30-60 kPa; the bottom temperature is preferably 150-180°C; the reflux ratio is preferably 0.25-2.0, more preferably 0.25-1.5; and the theoretical plate number is preferably 10-50, more preferably 20-45.

[0023] The reflux ratio described in this invention is the mass ratio of the material refluxed into the upper part of the column to the material distilled from the top of the column.

[0024] The benzene-free gasoline described in this invention can directly enter the S-zorb unit or be dehydrated first through a coalescer, drying tower, or molecular sieve before entering the S-zorb unit to further remove sulfur from the gasoline, thereby further reducing the sulfur content of the gasoline product to meet the required standards.

[0025] The catalytic cracking crude gasoline described in this invention can be conventional catalytic cracking crude gasoline, or crude gasoline produced by DCC (deep catalytic cracking) or LTA processes, wherein the benzene content is 0.8-10% by volume (0.94-12% by mass).

[0026] The invention will be further described below with reference to the accompanying drawings.

[0027] Figure 1In the process, crude gasoline from catalytic cracking is introduced into the middle of the C5 stripping tower 101 via pipeline 1. After rectification and separation, the C5- fraction is discharged from the top of the C5 stripping tower 101 and discharged into the condenser 107 via pipeline 15. After condensation, part of it flows back into the upper part of the C5 stripping tower via pipeline 16, and the rest is discharged via pipeline 2. The C6+ fraction discharged from the bottom of the C5 stripping tower 101 is introduced into the middle of the C6 stripping tower 102 via pipeline 3. After rectification and separation, the C7+ fraction is discharged from the bottom of the C6 stripping tower 102 via pipeline 5, and the C6 fraction is discharged from the top of the C6 stripping tower 102 and introduced into the condenser 108 via pipeline 17. After condensation, part of it flows back into the upper part of the C6 stripping tower 102 via pipeline 18, and the rest is introduced into the lower part of the mixing and clarification tank 103 via pipeline 4. The composite solvent is introduced into the upper part of the mixing and clarification tank 103 via pipeline 6. After mixing and extraction, the mixture is allowed to stand and separate into phases. The upper layer is the benzene-removed material, and the lower layer is the benzene-rich material. The benzene-removed material is introduced into the lower part of the water washing tower 104 via pipeline 7, where it comes into countercurrent contact with water entering from the upper part via pipeline 8. After washing, the benzene-removed C6 fraction is discharged from the top of the water washing tower 104 via pipeline 9, and mixed with the C5- and C7+ fractions from pipelines 2 and 5 to obtain the benzene-removed gasoline product. The water after washing is discharged from the bottom of the water washing tower 104 and introduced into the middle part of the water stripping tower 106 via pipeline 10. After stripping, the water vapor is distilled off from the top of the water stripping tower 106 and introduced into the lower part of the solvent recovery tower 105 via pipeline 14 as stripping gas. The recovered solvent is discharged from the bottom of the water stripping tower 106 via pipeline 1. 3. The benzene-rich material is introduced into the lower part of the solvent recovery tower 105 via pipeline 11. After distillation separation, the lean solvent is discharged from the bottom of the solvent recovery tower 105 and introduced into the upper part of the mixing and clarifying tank 103 via pipeline 6 for recycling. The distillate from the top of the solvent recovery tower 105 is introduced into the condenser 109 via pipeline 19. After condensation separation, water and oil phases are separated. The resulting water is introduced into the upper part of the water washing tower 104 via pipeline 8 as water washing water. The resulting oil phase is returned to the upper part of the solvent recovery tower 105 via pipeline 20, and the remainder is discharged from the device via pipeline 12. This is a benzene-rich fraction rich in benzene and a small amount of olefins.

[0028] The invention is further illustrated below with examples, but the invention is not limited thereto.

[0029] Example 1

[0030] according to Figure 1The process removes benzene from crude gasoline from catalytic cracking. Operating conditions for each tower and mixing / clarifying tank are shown in Table 1. The composite solvent used contains 93% by mass sulfolane, 6.2% by mass 1,3-propanediol, and 0.8% by mass water. The hydrocarbon composition of the feedstock crude gasoline from catalytic cracking is shown in Table 2. The C5- fraction separated by the C5 removal tower has a benzene content of 0.01% by mass, and the C7+ fraction separated by the C6 removal tower has a benzene content of 0.02% by mass. The hydrocarbon composition of the C6 fraction is shown in Table 3. After extraction and benzene removal and water washing, the hydrocarbon composition of the benzene-free C6 fraction obtained from pipeline 9 is shown in Table 3, with a flow rate of 4.30 t / h. The hydrocarbon composition of the benzene-rich fraction obtained from pipeline 12 is shown in Table 3, with a flow rate of 0.20 t / h. The benzene-free C6 fraction is mixed with the C5- fraction and C7+ fraction to obtain benzene-free gasoline, with a flow rate of 29.80 t / h. The benzene content, RON octane number, benzene removal rate, total hydrocarbon loss, and benzene-free gasoline yield of the benzene-free gasoline are shown in Table 4.

[0031] Total hydrocarbon loss = ((benzene-rich fraction flow rate × hydrocarbon content other than benzene in the benzene-rich fraction) ÷ catalytic cracking crude gasoline flow rate) × 100%

[0032] Table 1

[0033]

[0034]

[0035] Table 2

[0036] project Example 1 Example 2 Example 3 Raw material name Catalytic cracking crude gasoline DCC crude gasoline LTA crude gasoline Saturated hydrocarbons, mass% 37.9 17.8 41.4 Olefins, by mass % 24.5 27.2 10.1 Aromatics (excluding benzene), by mass % 36.6 51.4 46.5 Benzene, mass % 1.0 3.6 2.0 RON Octane Number 88.0 93.4 91.5

[0037] Table 3

[0038]

[0039] Table 4

[0040] project Example 1 Example 2 Example 3 Comparative Example 1 Benzene content (by volume) of benzene-free gasoline 0.60 0.65 0.74 0.65 RON octane number of benzene-free gasoline 87.8 93.2 91.4 93.3 Benzene removal rate, mass % 31 80 58 80 Total hydrocarbon loss, % by mass 0.36 2.25 1.35 4.41 Benzene-free gasoline yield, % by mass 99.3 94.9 97.8 92.7

[0041] Example 2

[0042] according to Figure 1The process for removing benzene from DCC crude gasoline is shown in Table 1. The operating conditions of each tower and the mixing and clarification tank are shown in Table 2. The composite solvent used contains 93% by mass sulfolane and 7% by mass glycerol. The hydrocarbon composition of the raw material DCC crude gasoline is shown in Table 2. The benzene content of the C5- fraction separated by the C5 removal tower is 0.02% by mass, and the benzene content of the C7+ fraction separated by the C6 removal tower is 0.01% by mass. The hydrocarbon composition of the C6 fraction is shown in Table 5. After extraction and water washing, the hydrocarbon composition of the benzene-free C6 fraction obtained from pipeline 9 is shown in Table 5, with a flow rate of 2.46 t / h. The hydrocarbon composition of the benzene-rich fraction obtained from pipeline 12 is shown in Table 5, with a flow rate of 1.54 t / h. The benzene-free C6 fraction is mixed with the C5- and C7+ fractions to obtain benzene-free gasoline with a flow rate of 28.46 t / h. The benzene content, RON octane number, benzene removal rate, total hydrocarbon loss, and benzene-free gasoline yield of the benzene-free gasoline are shown in Table 4.

[0043] Table 5

[0044]

[0045] Example 3

[0046] according to Figure 1 The process for removing benzene from crude LTA gasoline is shown in Table 1. The operating conditions of each tower and the mixing and clarifying tank are shown in Table 2. The composite solvent used contains 95% by mass sulfolane and 5% by mass ethylene glycol. The hydrocarbon composition of the raw material crude LTA gasoline is shown in Table 2. The benzene content of the C5- fraction separated by the C5 removal tower is 0.02% by mass, and the benzene content of the C7+ fraction separated by the C6 removal tower is 0.01% by mass. The hydrocarbon composition of the C6 fraction is shown in Table 3. After extraction and water washing, the hydrocarbon composition of the benzene-free C6 fraction obtained from pipeline 9 is shown in Table 6, with a flow rate of 4.34 t / h. The hydrocarbon composition of the benzene-rich fraction obtained from pipeline 12 is shown in Table 6, with a flow rate of 0.66 t / h. The benzene-free C6 fraction is mixed with the C5- and C7+ fractions to obtain benzene-free gasoline with a flow rate of 29.34 t / h. The benzene content, RON octane number, benzene removal rate, total hydrocarbon loss, and benzene-free gasoline yield of the benzene-free gasoline are shown in Table 4.

[0047] Table 6

[0048]

[0049] Comparative Example 1

[0050] The method in Example 2 was used to remove benzene from crude DCC gasoline, except that sulfolane containing 1% by mass of water was used as the solvent. After extraction, the flow rates of the benzene-removed material and the benzene-rich material discharged from the mixing and clarification tank were 1.85 t / h and 22.15 t / h, respectively. The flow rate of the washing water in the water washing tower was 1.48 t / h. After water washing, the hydrocarbon composition of the benzene-removed C6 fraction obtained from pipeline 9 is shown in Table 7, with a flow rate of 1.81 t / h. The hydrocarbon composition of the benzene-rich fraction obtained from pipeline 12 is shown in Table 7, with a flow rate of 2.19 t / h. The benzene-removed C6 fraction was mixed with C5- and C7+ fractions to obtain benzene-removed gasoline with a flow rate of 27.81 t / h. The benzene content, RON octane number, benzene removal rate, total hydrocarbon loss, and benzene-removed gasoline yield of the benzene-removed gasoline are shown in Table 4.

[0051] As shown in Table 4, under the same benzene removal rate, the composite solvent described in this invention has a higher benzene removal gasoline yield and lower total hydrocarbon loss due to benzene removal compared to Comparative Example 1 which uses conventional solvents.

[0052] Table 7

[0053]

[0054] Example 4

[0055] The selectivity of the composite solvent of the present invention to benzene was determined.

[0056] 52.47% by mass of benzene and 47.53% by mass of cyclohexane were mixed to prepare C6 feedstock oil. The composite solvents 1-10 shown in Table 8 were prepared. The composite solvents and C6 feedstock oil were mixed at a 1:1 mass ratio (i.e., solvent ratio) at 40°C. After static equilibrium, the mass fraction x of benzene in the upper oil phase after extraction equilibrium was measured. 苯 and the mass fraction of cyclohexane x 环己烷 And the mass fraction x′ of benzene in the lower solvent phase. 苯 and the mass fraction x′ of cyclohexane 环己烷 The selectivity S of the solvent to benzene was calculated according to formula (1), and the results are shown in Table 8.

[0057]

[0058] Table 8

[0059]

[0060] Comparative Example 2

[0061] The selectivity of conventional solvents to benzene was determined according to the method in Example 4, except that the solvents used were control solvents 1 to 4. The results are shown in Table 8.

Claims

1. A method for removing benzene from catalytic cracking crude gasoline, comprising: Crude gasoline from catalytic cracking is pre-fractionated to obtain C5-, C6-, and C7+ fractions. The C6 fraction is introduced into an extraction and phase separation device and contacted with a composite solvent for liquid-phase extraction. After settling and phase separation, the benzene-free material is discharged from the upper part of the extraction and phase separation device, and the benzene-rich material is discharged from the lower part. The benzene-free material is introduced into the lower part of a water washing tower (104) and contacted countercurrently with water entering from the upper part. After washing, the benzene-free C6 fraction is discharged from the top of the water washing tower and mixed with the C5- and C7+ fractions to obtain benzene-free gasoline. The water after washing is discharged from the bottom of the water washing tower and introduced into a water stripping tower (106). After stripping, the steam is distilled off from the top of the water stripping tower and introduced into the lower part of a solvent recovery tower (105). The recovered solvent is discharged from the water stripping tower. The residue is discharged from the bottom and introduced into the lower part of the solvent recovery tower; the benzene-rich material is introduced into the middle part of the solvent recovery tower, and separated by distillation. The lean solvent is discharged from the bottom of the solvent recovery tower and returned to the extraction phase separation equipment for recycling. The distillate from the top of the solvent recovery tower is introduced into the condenser (109), and the water and oil phases are separated by condensation. The water obtained is introduced into the upper part of the water washing tower, and the oil obtained is used as the benzene-rich fraction discharge device. The composite solvent includes 80-97% by mass of sulfolane and 3-20% by mass of C2-C4 polyols. In the extraction phase separation equipment, the extraction phase separation temperature is 40-70℃. The C2-C4 polyols are selected from one or more of ethylene glycol, 1,3-propanediol, 1,4-butanediol and glycerol.

2. The method according to claim 1, characterized in that... The composite solvent comprises 84-95% by mass of sulfolane, 3-15% by mass of C2-C4 polyol, and 0.5-2% by mass of water.

3. The method according to claim 1, characterized in that... The pre-fractionation includes introducing crude catalytic cracked gasoline into the middle of the C5 removal tower (101), and after rectification separation, the C5- fraction is discharged from the top of the C5 removal tower, and the C6+ fraction discharged from the bottom of the C5 removal tower is introduced into the middle of the C6 removal tower (102), and after rectification separation, the C7+ fraction is discharged from the bottom of the C6 removal tower, and the C6 fraction is discharged from the top of the C6 removal tower.

4. The method according to claim 3, characterized in that... The C5 removal tower has a top pressure of 200~350 kPa, a bottom temperature of 120~160℃, a top temperature of 50℃~70℃, and a reflux ratio of 1~3.

5. The method according to claim 3, characterized in that... The C6 removal tower has a top pressure of 100~300kPa, a bottom temperature of 140~180℃, a top temperature of 70℃~100℃, and a reflux ratio of 1~3.

6. The method according to claim 1, characterized in that... The benzene content in the C5 fraction is no higher than 0.03% by mass.

7. The method according to claim 1, characterized in that... The benzene content in the C6 fraction is 3% to 30% by mass.

8. The method according to claim 1, characterized in that... The benzene content in the C7+ fraction is no higher than 0.03% by mass.

9. The method according to claim 1, characterized in that... In the extraction and phase separation equipment, the mass ratio of the composite solvent to the C6 fraction is 0.5 to 8:

1.

10. The method according to claim 1, characterized in that... The extraction phase separation equipment is selected from a mixing and clarification tank or a device obtained by connecting a mixer and a settling phase separation tank in series.

11. The method according to claim 1, characterized in that... The water washing temperature of the water washing tower is 40~80℃, and the mass ratio of water used for washing to benzene-removed material is 0.01~1:

1.

12. The method according to claim 1, characterized in that... The bottom temperature of the water stripping tower is 100~150℃ and the pressure is 100~500kPa.

13. The method according to claim 1, characterized in that... The solvent recovery tower has a top pressure of 15~80 kPa, a bottom temperature of 150~180℃, and a reflux ratio of 0.25~2.0.

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