Naphtha Pretreatment Method Based on Aromatic Extraction

Abstract

The present invention discloses a method for pre-treating naphtha based on aromatics extraction. First, straight-run naphtha is preliminarily treated with an ion exchange resin to obtain preliminarily treated naphtha. Then, a desulfurization agent is placed in a desulfurization reactor, and the preliminarily treated naphtha is fed into the desulfurization reactor for desulfurization treatment to obtain desulfurized naphtha. The desulfurized naphtha enters an aromatics extraction column and undergoes aromatics extraction under the action of an extractant to obtain a rich solvent containing dissolved mixed aromatics and pre-treated naphtha. The present invention has good aromatics separation effect and good desulfurization effect, providing a good basis for the subsequent utilization of naphtha.

Description

Technical Field

[0001] The present invention relates to a method for naphtha pretreatment based on aromatics extraction, belonging to the technical field of petrochemical industry. Background Art

[0002] Naphtha, also known as light gasoline and crude gasoline, is a colorless and transparent liquid containing normal paraffins, isoparaffins, naphthenes, aromatics, etc. Naphtha has light fractions, high contents of paraffins and naphthenes, good stability, low heavy metal content, low sulfur content, and low toxicity. Naphtha is the light fraction distilled from crude oil through primary distillation and atmospheric distillation under certain conditions, or the gasoline fraction obtained by hydrofining of secondary processed gasoline. The distillation range is generally from the initial boiling point to 220°C, and can also be adjusted according to the usage occasion. For example, when used as a catalytic reforming feedstock to produce aromatics, the fraction of 60°C - 145°C can be taken (referred to as light naphtha); when used as a catalytic reforming feedstock to produce high-octane gasoline components, the fraction of 60°C - 180°C can be taken (referred to as heavy naphtha); when used as a feedstock for steam cracking to produce ethylene or a feedstock for ammonia synthesis gas production, the fraction from the initial boiling point to 220°C can be taken; when used as a solvent, it is called solvent naphtha, and the aromatic solvent from coal tar is also called heavy naphtha or solvent naphtha.

[0003] When naphtha is used as a feedstock for ethylene cracking, normal paraffins and isoparaffins are good feedstocks for ethylene cracking, while naphthenes and aromatics are non-ideal components. Especially for aromatic components, during the cracking process in the ethylene cracking furnace, part of them "idle" without undergoing the reaction to produce ethylene, and part will form coke adhering to the inner wall of the cracking tubular furnace, thus shortening the service life of the cracking tubular furnace. Therefore, for naphtha used in ethylene cracking, it is required to minimize the aromatic content therein.

[0004] Aromatics are important basic raw materials in the petrochemical industry. Catalytic reforming is one of the main methods for aromatics production, which can convert naphtha with low octane number into high-octane fuel or aromatic products such as benzene, toluene, and xylene. Catalytic reforming is mainly divided into two methods according to the catalyst regeneration method: semi-regeneration (fixed bed) and continuous regeneration (moving bed). In recent years, with the development of catalytic reforming from mainly producing gasoline to mainly producing aromatics and the large-scale of reforming units, the reforming technology using low-pressure continuous regeneration process has occupied the dominant position. However, whether it is the early semi-regeneration reforming process or the continuous reforming process after catalyst and process improvement, both require the feedstock to have a certain aromatic potential content, and the requirements for the feedstock composition actually limit the feedstock resources for aromatics production by catalytic reforming. The cost of the feedstock for steam cracking to produce ethylene accounts for 60 - 80% of the total production cost. More than 50% of the ethylene cracking feedstock is naphtha, and the aromatic component in naphtha accounts for 10%, and its diolefin yield is 0.

[0005] Therefore, removing aromatics from naphtha can not only save cracking raw materials but also avoid the coking problem caused by aromatics in the ethylene cracking process, which has very good promotion value.

[0006] At present, solvent extraction method is usually used to extract aromatics from naphtha. According to different solvents used, it can be divided into Dix method, sulfolane method, N-methylpyrrolidone method, dimethyl sulfoxide method and N-formylmorpholine method. However, the solubility and selectivity of a single solvent often restrict each other, resulting in a high content of non-aromatics in the solvent-rich liquid and a high content of solvent in the de-aromatized naphtha.

[0007] Patent CN105219422B discloses a composite extractant suitable for coal-based naphtha and a method for preparing solvent oil. The coal-based naphtha raw material and the composite extractant are respectively added into the extraction column. The raw material enters from the middle of the extraction column, and the extractant enters from the top of the extraction column. Countercurrent extraction is carried out in the extraction column. The extraction temperature is 60-90 °C, the pressure is 0.7-0.8 MPa, and the volume ratio of the extractant to the raw material coal-based naphtha is 2:1-3:1. De-aromatized naphtha and rich solvent are obtained at the top and bottom of the column respectively; the de-aromatized naphtha obtained at the top of the column is sent to the fractionating column for fractionation to obtain solvent oil. The composite extractant used in this patented technology is a mixture of sulfolane, propylene carbonate, triethylene glycol ether and water, etc., which is more suitable for coal-based naphtha. The highest aromatics removal rate is 87.61%. Obviously, the aromatics separation effect is still not ideal enough.

[0008] In addition, naphtha often contains sulfides such as hydrogen sulfide, elemental sulfur, mercaptan, and thiophene. Among them, hydrogen sulfide, elemental sulfur, and mercaptan are active sulfur, which are corrosive. Moreover, mercaptan is extremely easy to react with unsaturated hydrocarbons in naphtha to form colloidal substances, reducing the stability of naphtha; if the content of hydrogen sulfide is too high, it will cause a large amount of sulfur dioxide to be emitted during the use of the oil product, causing environmental pollution. Therefore, it is very necessary to desulfurize naphtha. In the prior art, processes such as hydrodesulfurization, alkali washing and water washing desulfurization, alkali extraction, acid washing desulfurization, adsorption desulfurization, and alkanolamine desulfurization are usually used to achieve desulfurization, and the desulfurization effects vary greatly. Summary of the Invention

[0009] The purpose of the present invention is to overcome the above-mentioned deficiencies of the prior art and provide a naphtha pretreatment method based on aromatics extraction, which has good aromatics separation effect and good desulfurization effect, providing a good basis for the subsequent utilization of naphtha.

[0010] To achieve the above purpose, the present invention adopts the following technical solutions:

[0011] A naphtha pretreatment method based on aromatics extraction, the specific steps are as follows:

[0012] (1) First, the straight-run naphtha is preliminarily treated with ion exchange resin to obtain preliminarily treated naphtha;

[0013] (2) Then place the desulfurizer in the desulfurization reactor, and feed the preliminarily treated naphtha into the desulfurization reactor for desulfurization treatment to obtain desulfurized naphtha;

[0014] (3) The desulfurized naphtha enters the aromatic extraction column, and aromatic extraction is carried out under the action of the extractant to obtain a rich solvent containing dissolved mixed aromatics and pretreated naphtha;

[0015] Among them, the desulfurizer is first prepared by using copper nitrate hexahydrate, zirconium nitrate hexahydrate, yttrium nitrate hexahydrate, and praseodymium nitrate hexahydrate as raw materials to make a mixed solution, precipitating, calcining, and pulverizing to obtain a mixed powder, and then mixing the mixed powder with a carrier, ball milling, heat treating, and tabletting; the extractant is obtained by mixing 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester, N,N-dimethylformamide, 1-benzyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide salt, and ethyltriphenylphosphonium bis(trifluoromethylsulfonyl)imide salt.

[0016] Preferably, by weight, the carrier is prepared by the following method: first mix 25-28 parts of aluminum chloride, 12-15 parts of tetraethyl orthosilicate, 100-120 parts of absolute ethanol, and 0.1-0.2 parts of cetyltrimethylammonium bromide evenly, then adjust the pH = 3-5 with a nitric acid solution with a mass concentration of 25-30%, react at 120-130 °C for 3-5 hours, filter to obtain the solid, dry, calcine in an oxygen atmosphere at 500-520 °C for 3-4 hours, and grind to 30-40 mesh to obtain.

[0017] Preferably, the desulfurizer is prepared by the following method: first dissolve copper nitrate hexahydrate, zirconium nitrate hexahydrate, yttrium nitrate hexahydrate, and praseodymium nitrate hexahydrate in water respectively to obtain a copper nitrate solution, a zirconium nitrate solution, a yttrium nitrate solution, and a praseodymium nitrate solution with a concentration of 1 mol / L, and then mix them according to a volume ratio of 5-6:3-4:1-2:0.8-1 to make a mixed solution; then heat the mixed solution to 60-70 °C, and under the condition of heat preservation and stirring at 400-500 r / min, dropwise add 1 mol / L sodium carbonate solution, continue to stir for 50-60 minutes after dropping, generate precipitation, naturally cool to room temperature and stand for aging for 18-20 hours, wash with distilled water and absolute ethanol alternately for 2-3 times, dry, calcine at 400-420 °C for 3-4 hours, grind to 30-40 mesh to obtain a mixed powder; finally, mix the mixed powder with the carrier, ball mill, heat treat, and tablet to obtain.

[0018] More preferably, the volume ratio of the mixed solution to the sodium carbonate solution is 1:1.3-1.4; the mass ratio of the mixed powder to the carrier is 1:3-4.

[0019] Further preferably, the process conditions for ball milling are: ball milling at 500 - 600 r / min for 45 - 55 minutes.

[0020] Further preferably, the specific method for heat treatment is: under nitrogen protection, heating to 400 - 450 °C at a rate of 10 - 12 °C / min, holding for 4 - 5 hours, and then naturally cooling to room temperature.

[0021] Preferably, the volume ratio of 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester, N,N-dimethylformamide, 1-benzyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide salt, and ethyltriphenylphosphonium bis(trifluoromethylsulfonyl)imide salt is 8 - 10:4 - 5:2 - 3:1 - 2.

[0022] Preferably, the extractant is prepared by the following method: first, stir and mix 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester and N,N-dimethylformamide evenly, then slowly dropwise add the premixed solution of 1-benzyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide salt and ethyltriphenylphosphonium bis(trifluoromethylsulfonyl)imide salt while stirring. After the dropping is completed, perform ultrasonic oscillation treatment at 300 - 400 W for 30 - 40 minutes.

[0023] Further preferably, the time for slow dropping is 30 - 40 minutes.

[0024] Preferably, in step (1), the distillation range of the straight-run naphtha is 30 - 180 °C.

[0025] Preferably, in step (1), the ion exchange resin is a hydrogen-form styrene-based cation exchange resin, and further preferably a D005-II hydrogen-form macroporous sulfonic acid resin.

[0026] Preferably, in step (1), the process conditions for preliminary treatment are: temperature 45 - 55 °C, pressure 0.7 - 0.9 MPa, and weight hourly space velocity 3 - 4 h -1 .

[0027] Preferably, in step (2), the height-to-diameter ratio of the desulfurization agent bed in the desulfurization reactor is 3.0 - 3.2.

[0028] Preferably, in step (2), the process conditions for desulfurization treatment are: temperature 80 - 100 °C, pressure 5 - 7 MPa, and volume hourly space velocity 2 - 3 h -1 .

[0029] Preferably, in step (3), the desulfurized naphtha enters from the middle of the aromatic extraction column, and the extractant enters from the top of the aromatic extraction column, and countercurrent extraction is carried out in the aromatic extraction column. Pretreated naphtha and a rich solvent dissolving mixed aromatics are obtained at the top and bottom of the aromatic extraction column respectively.

[0030] Preferably, in step (3), the process conditions of the aromatics extraction column are as follows: the volume ratio of the extractant to the desulfurized naphtha is 1.6 - 1.8:1, the extraction temperature is 60 - 70 °C, and the pressure is 0.7 - 0.8 MPa.

[0031] Advantages of the present invention:

[0032] The present invention provides a naphtha pretreatment method based on aromatics extraction. First, straight-run naphtha is preliminarily treated with an ion exchange resin to obtain preliminarily treated naphtha. Then, a desulfurization agent is placed in a desulfurization reactor, and the preliminarily treated naphtha is fed into the desulfurization reactor for desulfurization treatment to obtain desulfurized naphtha. The desulfurized naphtha enters an aromatics extraction column and undergoes aromatics extraction under the action of an extractant to obtain a rich solvent containing dissolved mixed aromatics and pretreated naphtha. The present invention has good aromatics separation effect and desulfurization effect, providing a good basis for the subsequent utilization of naphtha.

[0033] It is very necessary to perform preliminary treatment and desulfurization treatment on straight-run naphtha before aromatics extraction. The presence of basic nitrogen and sulfides will affect the subsequent treatment of naphtha. The presence of basic nitrogen will also compete with sulfides for catalytic sites and affect the desulfurization effect. The present invention uses an ion exchange resin for preliminary treatment to remove components such as basic nitrogen in straight-run naphtha. The desulfurization agent of the present invention is first prepared by using copper nitrate hexahydrate, zirconium nitrate hexahydrate, yttrium nitrate hexahydrate, and praseodymium nitrate hexahydrate as raw materials to form a mixed solution, followed by precipitation, calcination, and pulverization to obtain a mixed powder. Then, the mixed powder is mixed with a carrier, ball-milled, heat-treated, and tableted to obtain the desulfurization agent. Under the loading effect of the carrier, the desulfurization agent realizes the removal of sulfides through the composite metal oxides of copper, zirconium, yttrium, and praseodymium, and has a good desulfurization effect.

[0034] The key to determining the aromatics extraction effect lies in the selection of the extractant. The extractant of the present invention is obtained by mixing 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester, N,N-dimethylformamide, 1-benzyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide, and ethyltriphenylphosphonium bis(trifluoromethylsulfonyl)imide. Through the cooperation of the four components, the extractant regulates the dissolution of aromatics to achieve the full extraction of aromatics in naphtha. The obtained pretreated naphtha can be used as high-quality ethylene cracking raw material. Specific embodiments

[0035] The present invention will be further elaborated below in conjunction with examples. It should be noted that the following description is only for explaining the present invention and does not limit its content. Example 1

[0036] The naphtha pretreatment method based on aromatics extraction comprises the following specific steps:

[0037] (1) First, the straight-run naphtha with a boiling range of 30 - 180 °C is preliminarily treated with D005-II hydrogen-form macroporous sulfonic acid resin to obtain the preliminarily treated naphtha. The process conditions for the preliminary treatment are: temperature 45 °C, pressure 0.7 MPa, and weight hourly space velocity 3 h -1 ;

[0038] (2) Then, the desulfurizer is placed in the desulfurization reactor, and the preliminarily treated naphtha is fed into the desulfurization reactor for desulfurization treatment to obtain desulfurized naphtha. The height-to-diameter ratio of the desulfurizer bed in the desulfurization reactor is 3.0. The process conditions for the desulfurization treatment are: temperature 80 °C, pressure 5 MPa, and volume hourly space velocity 2 h -1 ;

[0039] (3) The desulfurized naphtha enters from the middle of the aromatics extraction column, and the extractant enters from the top of the aromatics extraction column. Countercurrent extraction is carried out in the aromatics extraction column, and pretreated naphtha and a rich solvent containing dissolved mixed aromatics are obtained at the top and bottom of the aromatics extraction column respectively. The process conditions of the aromatics extraction column are: the volume ratio of the extractant to the desulfurized naphtha is 1.6:1, the extraction temperature is 60 °C, and the pressure is 0.7 MPa.

[0040] The desulfurizer is prepared by first using copper nitrate hexahydrate, zirconium nitrate hexahydrate, yttrium nitrate hexahydrate, and praseodymium nitrate hexahydrate as raw materials to make a mixed solution, followed by precipitation, calcination, pulverization to obtain a mixed powder, and then mixing the mixed powder with a carrier, ball milling, heat treatment, and tabletting. The extractant is obtained by mixing 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester, N,N-dimethylformamide, 1-benzyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide, and ethyltriphenylphosphonium bis(trifluoromethylsulfonyl)imide.

[0041] The carrier is prepared by the following method: First, 2.5 kg of aluminum chloride, 1.2 kg of tetraethyl orthosilicate, 10 kg of absolute ethanol, and 0.01 kg of cetyltrimethylammonium bromide are mixed evenly. Then, the pH is adjusted to 3 with a 25% nitric acid solution by mass concentration, and the reaction is carried out at 120 °C for 3 hours. The solid is filtered, dried, calcined in an oxygen atmosphere at 500 °C for 3 hours, and ground to 30 mesh to obtain.

[0042] The desulfurizer is prepared by the following method: First, copper nitrate hexahydrate, zirconium nitrate hexahydrate, yttrium nitrate hexahydrate, and praseodymium nitrate hexahydrate are respectively dissolved in water to obtain copper nitrate solution, zirconium nitrate solution, yttrium nitrate solution, and praseodymium nitrate solution with a concentration of 1 mol / L. Then, they are mixed according to a volume ratio of 5:3:1:0.8 to form a mixed solution. Next, the mixed solution is heated to 60 °C, and under the condition of heat preservation and stirring at 400 r / min, 1 mol / L sodium carbonate solution is added dropwise. After the addition is completed, stirring is continued for 50 minutes to form a precipitate. It is naturally cooled to room temperature and left to age for 18 hours, washed twice alternately with distilled water and absolute ethanol, dried, calcined at 400 °C for 3 hours, and ground to 30 mesh to obtain a mixed powder. Finally, the mixed powder and the carrier are mixed and ball-milled, heat-treated, and tableted to obtain the product. Among them, the volume ratio of the mixed solution to the sodium carbonate solution is 1:1.3; the mass ratio of the mixed powder to the carrier is 1:3. The process conditions for ball milling are: ball milling at 500 r / min for 45 minutes. The specific method for heat treatment is: under nitrogen protection, heating to 400 °C at a rate of 10 °C / min, holding for 4 hours, and naturally cooling to room temperature.

[0043] The volume ratio of 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester, N,N-dimethylformamide, 1-benzyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide salt, and ethyltriphenylphosphonium bis(trifluoromethanesulfonyl)imide salt is 8:4:2:1.

[0044] The extractant is prepared by the following method: First, 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester and N,N-dimethylformamide are stirred and mixed evenly. Then, a premixed solution of 1-benzyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide salt and ethyltriphenylphosphonium bis(trifluoromethanesulfonyl)imide salt is slowly added dropwise while stirring. After the addition is completed, ultrasonic oscillation treatment is carried out at 300 W for 30 minutes. The time for slow addition is 30 minutes. Example 2

[0045] The pre-treatment method of naphtha based on aromatics extraction is as follows:

[0046] (1) First, straight-run naphtha with a boiling range of 30 - 180 °C is preliminarily treated with D005-II hydrogen-type macroporous sulfonic acid resin to obtain preliminarily treated naphtha. The process conditions for preliminary treatment are: temperature 55 °C, pressure 0.9 MPa, and weight hourly space velocity 4 h -1 ;

[0047] (2) Then, the desulfurizer is placed in a desulfurization reactor, and the preliminarily treated naphtha is sent into the desulfurization reactor for desulfurization treatment to obtain desulfurized naphtha. The height-to-diameter ratio of the desulfurizer bed in the desulfurization reactor is 3.2. The process conditions for desulfurization treatment are: temperature 100 °C, pressure 7 MPa, and volume hourly space velocity 3 h -1 ;

[0048] (3) The desulfurized naphtha enters from the middle of the aromatic extraction column, and the extractant enters from the top of the aromatic extraction column. Countercurrent extraction occurs in the aromatic extraction column, and pretreated naphtha and a rich solvent dissolving mixed aromatics are obtained at the top and bottom of the aromatic extraction column respectively. The process conditions of the aromatic extraction column are as follows: the volume ratio of the extractant to the desulfurized naphtha is 1.8:1, the extraction temperature is 70 °C, and the pressure is 0.8 MPa.

[0049] The desulfurizer is first prepared by using copper nitrate hexahydrate, zirconium nitrate hexahydrate, yttrium nitrate hexahydrate, and praseodymium nitrate hexahydrate as raw materials to make a mixed solution, followed by precipitation, calcination, and pulverization to obtain a mixed powder. Then, the mixed powder is mixed with a carrier, ball-milled, heat-treated, and tableted. The extractant is obtained by mixing 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester, N,N-dimethylformamide, 1-benzyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide, and ethyltriphenylphosphonium bis(trifluoromethylsulfonyl)imide.

[0050] The carrier is prepared by the following method: First, 2.8 kg of aluminum chloride, 1.5 kg of tetraethyl orthosilicate, 12 kg of absolute ethanol, and 0.02 kg of cetyltrimethylammonium bromide are mixed evenly. Then, the pH is adjusted to 5 with a 30% nitric acid solution by mass concentration, and the reaction is carried out at 130 °C for 5 hours. The solid is filtered, dried, calcined in an oxygen atmosphere at 520 °C for 4 hours, and ground to 40 mesh to obtain the carrier.

[0051] The desulfurizer is prepared by the following method: First, copper nitrate hexahydrate, zirconium nitrate hexahydrate, yttrium nitrate hexahydrate, and praseodymium nitrate hexahydrate are respectively dissolved in water to obtain copper nitrate solution, zirconium nitrate solution, yttrium nitrate solution, and praseodymium nitrate solution with a concentration of 1 mol / L. Then, they are mixed according to a volume ratio of 6:4:2:1 to make a mixed solution. Then, the mixed solution is heated to 70 °C, and under the condition of heat preservation and stirring at 500 r / min, 1 mol / L sodium carbonate solution is added dropwise. After the addition is complete, stirring is continued for 60 minutes to form a precipitate. It is naturally cooled to room temperature and left to age for 20 hours, washed 3 times alternately with distilled water and absolute ethanol, dried, calcined at 420 °C for 4 hours, and ground to 40 mesh to obtain a mixed powder. Finally, the mixed powder is mixed with the carrier, ball-milled, heat-treated, and tableted to obtain the desulfurizer. Among them, the volume ratio of the mixed solution to the sodium carbonate solution is 1:1.4; the mass ratio of the mixed powder to the carrier is 1:4. The process conditions of ball milling are: ball milling at 600 r / min for 55 minutes. The specific method of heat treatment is: Under nitrogen protection, it is heated to 450 °C at a rate of 12 °C / min, held for 5 hours, and then naturally cooled to room temperature.

[0052] The volume ratio of 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester, N,N-dimethylformamide, 1-benzyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide salt, and ethyltriphenylphosphonium bis(trifluoromethylsulfonyl)imide salt is 10:5:3:2.

[0053] The extractant is prepared by the following method: First, stir and mix 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester and N,N-dimethylformamide evenly, then slowly dropwise add a premixed solution of 1-benzyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide salt and ethyltriphenylphosphonium bis(trifluoromethylsulfonyl)imide salt while stirring. After the dropping is completed, perform ultrasonic oscillation treatment at 400W for 40 minutes. The time for slow dropping is 40 minutes. Example 3

[0054] A naphtha pretreatment method based on aromatics extraction, the specific steps are as follows:

[0055] (1) First, preliminarily treat straight-run naphtha with a boiling range of 30-180°C using D005-II hydrogen-type macroporous sulfonic acid resin to obtain preliminarily treated naphtha; the process conditions for preliminary treatment are: temperature 45°C, pressure 0.9 MPa, weight hourly space velocity 3h -1 ;

[0056] (2) Then place the desulfurizer in the desulfurization reactor, and send the preliminarily treated naphtha into the desulfurization reactor for desulfurization treatment to obtain desulfurized naphtha; the height-to-diameter ratio of the desulfurizer bed in the desulfurization reactor is 3.2; the process conditions for desulfurization treatment are: temperature 80°C, pressure 7 MPa, volume hourly space velocity 2h -1 ;

[0057] (3) The desulfurized naphtha enters from the middle of the aromatics extraction tower, and the extractant enters from the top of the aromatics extraction tower, and countercurrent extraction is carried out in the aromatics extraction tower. Pretreated naphtha and a rich solvent dissolving mixed aromatics are obtained at the top and bottom of the aromatics extraction tower respectively; the process conditions of the aromatics extraction tower are: the volume ratio of the extractant to the desulfurized naphtha is 1.8:1, the extraction temperature is 60°C, and the pressure is 0.8 MPa.

[0058] The desulfurizer is first prepared from copper nitrate hexahydrate, zirconium nitrate hexahydrate, yttrium nitrate hexahydrate, and praseodymium nitrate hexahydrate as raw materials to form a mixed solution, precipitate, calcine, and pulverize to obtain a mixed powder, and then the mixed powder is mixed with a carrier, ball-milled, heat-treated, and tableted; the extractant is obtained by mixing 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester, N,N-dimethylformamide, 1-benzyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide salt, and ethyltriphenylphosphonium bis(trifluoromethylsulfonyl)imide salt.

[0059] The carrier is prepared by the following method: First, 2.5 kg of aluminum chloride, 1.5 kg of tetraethyl orthosilicate, 10 kg of absolute ethanol, and 0.02 kg of cetyltrimethylammonium bromide are mixed evenly. Then, the pH is adjusted to 5 with a 25% nitric acid solution by mass concentration, and the reaction is carried out at 120 °C for 5 hours. The solid is filtered, dried, calcined at 500 °C for 4 hours in an oxygen atmosphere, and ground to 30 mesh to obtain the product.

[0060] The desulfurizer is prepared by the following method: First, copper nitrate hexahydrate, zirconium nitrate hexahydrate, yttrium nitrate hexahydrate, and praseodymium nitrate hexahydrate are dissolved in water respectively to obtain copper nitrate solution, zirconium nitrate solution, yttrium nitrate solution, and praseodymium nitrate solution with a concentration of 1 mol / L. Then, they are mixed according to a volume ratio of 6:3:2:0.8 to form a mixed solution. Then, the mixed solution is heated to 70 °C, and under the condition of heat preservation and stirring at 400 r / min, 1 mol / L sodium carbonate solution is added dropwise. After the addition is completed, stirring is continued for 60 minutes to form a precipitate, which is naturally cooled to room temperature and left to age for 18 hours, washed 3 times alternately with distilled water and absolute ethanol, dried, calcined at 400 °C for 4 hours, and ground to 30 mesh to obtain a mixed powder. Finally, the mixed powder and the carrier are mixed and ball-milled, heat-treated, and tableted to obtain the product. Among them, the volume ratio of the mixed solution to the sodium carbonate solution is 1:1.4; the mass ratio of the mixed powder to the carrier is 1:3. The process conditions of ball milling are: ball milling at 600 r / min for 45 minutes. The specific method of heat treatment is: Under nitrogen protection, it is heated to 400 °C at a rate of 12 °C / min, held for 5 hours, and then naturally cooled to room temperature.

[0061] The volume ratio of 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester, N,N-dimethylformamide, 1-benzyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide salt, and ethyltriphenylphosphonium bis(trifluoromethylsulfonyl)imide salt is 8:5:2:2.

[0062] The extractant is prepared by the following method: First, 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester and N,N-dimethylformamide are stirred and mixed evenly. Then, a premixed solution of 1-benzyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide salt and ethyltriphenylphosphonium bis(trifluoromethylsulfonyl)imide salt is slowly added dropwise while stirring. After the addition is completed, ultrasonic oscillation treatment is carried out at 300 W for 40 minutes. The time for slow addition is 30 minutes. Example 4

[0063] The pre-treatment method of naphtha based on aromatics extraction is as follows:

[0064] (1) First, the straight-run naphtha with a distillation range of 30-180 °C is preliminarily treated with D005-II hydrogen-type macroporous sulfonic acid resin to obtain preliminarily treated naphtha; the process conditions of preliminary treatment are: temperature 50 °C, pressure 0.8 MPa, weight hourly space velocity 3.5 h-1 ;

[0065] (2) Then place the desulfurizer in the desulfurization reactor, and feed the preliminarily treated naphtha into the desulfurization reactor for desulfurization treatment to obtain desulfurized naphtha; the height-diameter ratio of the desulfurizer bed in the desulfurization reactor is 3.1; the process conditions for desulfurization treatment are: temperature 90 °C, pressure 6 MPa, volume space velocity 2.5 h -1 ;

[0066] (3) The desulfurized naphtha enters from the middle of the aromatics extraction column, and the extractant enters from the top of the aromatics extraction column, and countercurrent extraction is carried out in the aromatics extraction column. Pretreated naphtha and a rich solvent containing dissolved mixed aromatics are obtained at the top and bottom of the aromatics extraction column respectively; the process conditions of the aromatics extraction column are: the volume ratio of the extractant to the desulfurized naphtha is 1.7:1, the extraction temperature is 65 °C, and the pressure is 0.7 MPa.

[0067] The desulfurizer is first prepared by using copper nitrate hexahydrate, zirconium nitrate hexahydrate, yttrium nitrate hexahydrate, and praseodymium nitrate hexahydrate as raw materials to form a mixed solution, precipitating, calcining, pulverizing to obtain a mixed powder, and then mixing the mixed powder with a carrier, ball milling, heat treating, and tableting; the extractant is obtained by mixing 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester, N,N-dimethylformamide, 1-benzyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide salt, and ethyltriphenylphosphonium bis(trifluoromethylsulfonyl)imide salt.

[0068] The carrier is prepared by the following method: first mix 2.6 kg of aluminum chloride, 1.4 kg of tetraethyl orthosilicate, 11 kg of absolute ethanol, and 0.02 kg of cetyltrimethylammonium bromide evenly, then adjust the pH = 4 with a 28% nitric acid solution by mass concentration, react at 125 °C for 4 hours, filter to obtain the solid, dry it, calcine it in an oxygen atmosphere at 510 °C for 4 hours, and grind it to 40 mesh to obtain it.

[0069] The desulfurizer is prepared by the following method: First, copper nitrate hexahydrate, zirconium nitrate hexahydrate, yttrium nitrate hexahydrate, and praseodymium nitrate hexahydrate are respectively dissolved in water to obtain a copper nitrate solution, a zirconium nitrate solution, a yttrium nitrate solution, and a praseodymium nitrate solution with a concentration of 1 mol / L. Then, they are mixed in a volume ratio of 5.5:3.5:1.5:0.9 to form a mixed solution. Next, the mixed solution is heated to 65°C, and under the condition of heat preservation and stirring at 500 r / min, a 1 mol / L sodium carbonate solution is gradually added dropwise. After the addition is completed, stirring is continued for 55 minutes to form a precipitate. It is naturally cooled to room temperature and left to stand for aging for 19 hours, washed alternately with distilled water and absolute ethanol 3 times, dried, calcined at 410°C for 4 hours, and ground to 40 mesh to obtain a mixed powder. Finally, the mixed powder and the carrier are mixed and ball-milled, heat-treated, and tableted to obtain the product. Among them, the volume ratio of the mixed solution to the sodium carbonate solution is 1:1.35; the mass ratio of the mixed powder to the carrier is 1:3.5. The process conditions for ball milling are: ball milling at 600 r / min for 50 minutes. The specific method for heat treatment is: under nitrogen protection, heated to 420°C at a rate of 11°C / min, held for 4.5 hours, and naturally cooled to room temperature.

[0070] The volume ratio of 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester, N,N-dimethylformamide, 1-benzyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide salt, and ethyltriphenylphosphonium bis(trifluoromethanesulfonyl)imide salt is 9:4.5:2.5:1.5.

[0071] The extractant is prepared by the following method: First, 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester and N,N-dimethylformamide are stirred and mixed evenly. Then, a premixed solution of 1-benzyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide salt and ethyltriphenylphosphonium bis(trifluoromethanesulfonyl)imide salt is slowly added dropwise while stirring. After the addition is completed, ultrasonic oscillation treatment is carried out at 400 W for 35 minutes. The time for slow addition is 35 minutes.

[0072] Comparative Example 1

[0073] When preparing the desulfurizer, praseodymium nitrate hexahydrate is omitted.

[0074] The rest is the same as in Example 1.

[0075] Comparative Example 2

[0076] When preparing the extractant, 1-benzyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide salt is omitted.

[0077] The rest is the same as in Example 1.

[0078] Test Example

[0079] The pretreated naphtha obtained from Examples 1 to 4 and Comparative Examples 1 and 2 was subjected to compositional analysis. Among them, the sulfur content was detected using an ANTEK-9000 sulfur-nitrogen analyzer, and the content of mixed aromatics in the pretreated naphtha was detected by liquid chromatography. The liquid chromatography conditions (Determination of the content of alkanes and aromatics in naphtha by high performance liquid chromatography, He Zhiqin, Journal of Liaoyang Petrochemical College, 2000, 16(1): 30-33) are as follows:

[0080] Chromatographic column: silica gel column and amino column connected in series front and back

[0081] Column temperature: room temperature

[0082] Mobile phase: n-hexane

[0083] Flow rate: 1.3 mL / min

[0084] Injection volume: 1 μL

[0085] Aromatic standard sample: ethylbenzene.

[0086] The test results are shown in Table 1.

[0087] Table 1. Sulfur content and aromatic content in pretreated naphtha

[0088] Sulfur content (ppm) Aromatic hydrocarbon mass content (%) Example 1 ＜5 0.31 Example 2 ＜5 0.32 Example 3 ＜5 0.29 Example 4 ＜3 0.25 Comparative Example 1 850 0.33 Comparative Example 2 ＜5 1.59

[0089] As can be seen from Table 1, the pretreated naphtha obtained from Examples 1 to 4 has a low sulfur content and a low aromatic content, and can be used as a high-quality ethylene cracking raw material.

[0090] In Comparative Example 1, praseodymium nitrate hexahydrate was omitted during the preparation of the desulfurizer, and the sulfur content of the obtained pretreated naphtha was significantly higher. In Comparative Example 2, 1-benzyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide was omitted during the preparation of the extractant, and the aromatic content was significantly higher. This shows that the desulfurizer of the present invention realizes the removal of sulfides through the synergistic effect of the composite metal oxides of copper, zirconium, yttrium, and praseodymium, and the extractant realizes the full extraction of aromatics in naphtha by the cooperation of four components: 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester, N,N-dimethylformamide, 1-benzyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide, and ethyltriphenylphosphonium bis(trifluoromethanesulfonyl)imide, which jointly regulate the dissolution of aromatics.

[0091] Although the specific implementation manners of the present invention have been described above, they are not limitations on the protection scope of the present invention. Based on the technical solutions of the present invention, various modifications or deformations that can be made by those skilled in the art without creative efforts are still within the protection scope of the present invention.

Claims

1. A naphtha pretreatment method based on aromatics extraction, characterized in that, The specific steps are as follows: (1) First, the straight-run naphtha is preliminarily treated with an ion exchange resin to obtain the preliminarily treated naphtha; (2) Then, the desulfurization agent is placed in a desulfurization reactor, and the preliminarily treated naphtha is fed into the desulfurization reactor for desulfurization treatment to obtain desulfurized naphtha; (3) The desulfurized naphtha enters an aromatics extraction column, and aromatics extraction is carried out under the action of an extractant to obtain a rich solvent containing dissolved mixed aromatics and pretreated naphtha; Among them, the desulfurization agent is first prepared by using copper nitrate hexahydrate, zirconium nitrate hexahydrate, yttrium nitrate hexahydrate, and praseodymium nitrate hexahydrate as raw materials to make a mixed solution, precipitating, calcining, pulverizing to obtain a mixed powder, and then mixing the mixed powder with a carrier, ball milling, heat treating, and tableting; the extractant is obtained by mixing 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester, N,N-dimethylformamide, 1-benzyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide, and ethyltriphenylphosphonium bis(trifluoromethanesulfonyl)imide.

2. The naphtha pretreatment method based on aromatics extraction according to claim 1, characterized in that, By weight, the carrier is prepared by the following method: First, 25-28 parts of aluminum chloride, 12-15 parts of tetraethyl orthosilicate, 100-120 parts of absolute ethanol, and 0.1-0.2 parts of cetyltrimethylammonium bromide are mixed evenly, then the pH is adjusted to 3-5 with a nitric acid solution with a mass concentration of 25-30%, reacted at 120-130 °C for 3-5 hours, filtered to obtain the solid, dried, calcined in an oxygen atmosphere at 500-520 °C for 3-4 hours, and ground to 30-40 mesh to obtain.

3. The naphtha pretreatment method based on aromatics extraction according to claim 1, wherein The desulfurization agent is prepared by the following method: First, copper nitrate hexahydrate, zirconium nitrate hexahydrate, yttrium nitrate hexahydrate, and praseodymium nitrate hexahydrate are respectively dissolved in water to obtain a copper nitrate solution, a zirconium nitrate solution, a yttrium nitrate solution, and a praseodymium nitrate solution with a concentration of 1 mol / L, and then they are mixed in a volume ratio of 5-6:3-4:1-2:0.8-1 to make a mixed solution; then the mixed solution is heated to 60-70 °C, and under the condition of heat preservation and stirring at 400-500 r / min, 1 mol / L sodium carbonate solution is added dropwise, and after the addition is completed, stirring is continued for 50-60 minutes to form a precipitate, naturally cooled to room temperature and left to age for 18-20 hours, washed alternately with distilled water and absolute ethanol 2-3 times, dried, calcined at 400-420 °C for 3-4 hours, ground to 30-40 mesh to obtain a mixed powder; finally, the mixed powder is mixed with a carrier, ball milled, heat treated, and tabletted to obtain.

4. The naphtha pretreatment method based on aromatics extraction according to claim 1, wherein The volume ratio of 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester, N,N-dimethylformamide, 1-benzyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide, and ethyltriphenylphosphonium bis(trifluoromethanesulfonyl)imide is 8-10:4-5:2-3:1-2.

5. The naphtha pretreatment method based on aromatics extraction according to claim 1, wherein The extractant is prepared by the following method: First, 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester and N,N-dimethylformamide are stirred and mixed evenly, and then a premixed solution of 1-benzyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide salt and ethyltriphenylphosphonium bis(trifluoromethylsulfonyl)imide salt is slowly added dropwise while stirring. After the addition is completed, ultrasonic oscillation treatment is carried out at 300-400 W for 30-40 minutes.

6. The naphtha pretreatment method based on aromatics extraction according to claim 1, characterized in that, In step (1), the distillation range of the straight-run naphtha is 30-180 °C.

7. The naphtha pretreatment method based on aromatics extraction according to claim 1, characterized in that, In step (1), the ion exchange resin is a hydrogen-type styrene-based cation exchange resin.

8. The naphtha pretreatment method based on aromatics extraction according to claim 1, characterized in that, In step (1), the process conditions for preliminary treatment are: temperature 45 - 55°C, pressure 0.7 - 0.9 MPa, and weight hourly space velocity 3 - 4 h -1 .

9. The naphtha pretreatment method based on aromatic hydrocarbon extraction according to claim 1, wherein In step (2), the height-to-diameter ratio of the desulfurization agent bed in the desulfurization reactor is 3.0-3.2; The process conditions for desulfurization treatment are: temperature 80 - 100 °C, pressure 5 - 7 MPa, volumetric space velocity 2 - 3 h -1 .

10. The naphtha pretreatment method based on aromatics extraction according to claim 1, characterized in that, In step (3), the desulfurized naphtha enters from the middle of the aromatic extraction column, and the extractant enters from the top of the aromatic extraction column, and countercurrent extraction is carried out in the aromatic extraction column. Pretreated naphtha and a rich solvent dissolving mixed aromatics are obtained at the top and bottom of the aromatic extraction column respectively; The process conditions of the aromatic extraction column are: the volume ratio of the extractant to the desulfurized naphtha is 1.6-1.8:1, the extraction temperature is 60-70 °C, and the pressure is 0.7-0.8 MPa.