Recovery method and recovery system for benzene in catalytically cracked gasoline benzene-rich liquid

Abstract

The invention discloses a method and a device for recovering benzene in catalytically cracked gasoline. The method comprises the following steps: sequentially carrying out desulfurization and debenzolization treatment on the catalytically cracked gasoline; carrying out first separation treatment on the benzene-rich liquid generated by the debenzolization treatment to respectively obtain an aromatic hydrocarbon component and an alkane component; and carrying out second separation treatment on the aromatic hydrocarbon component to respectively obtain benzene and methylbenzene. Compared with the prior art, the method has the advantages that the desulfurization and debenzolization processes are optimized, other components of the catalytic gasoline can be completely blended into gasoline while benzene and toluene products are obtained, the condition that benzene-rich components are sent to an ethylene device is avoided, and the economic benefits of the products are effectively improved.

Description

Technical Field

[0001] The invention relates to a method and a system for recovering benzene in benzene-rich liquid of catalytic cracking gasoline, belonging to the technical field of petrochemical industry. Background Art

[0002] Benzene is one of the most important organic chemical raw materials and is widely used in various chemical production. It is reported that the domestic benzene product market is in a state of supply shortage at present and for a long time in the future. Gasoline, as an important product of petroleum processing, will inevitably contain benzene components. With the continuous enhancement of people's environmental protection and health awareness, the control indicators of benzene content in gasoline products are becoming more and more stringent. The "National VI" gasoline product quality standard implemented in 2019 requires that the volume fraction of benzene in gasoline be reduced to below 0.8%. Catalytic cracking gasoline is an important blending component of finished gasoline, in which the volume fraction of benzene is generally 0.5% to 1.3%, and some are as high as 1.5%, so it must be debenzened. In summary, separating benzene from gasoline and producing pure benzene products has certain social and economic benefits.

[0003] At present, the technologies for reducing the benzene content in gasoline mainly include benzene hydrogenation saturation technology, alkylation benzene reduction technology, isomerization benzene reduction technology, fractionation debenzenization technology, etc. Among them: benzene hydrogenation saturation technology can enrich the benzene in gasoline and then hydrogenate it to produce cyclohexane. This technology has been applied in many refineries, but its gasoline octane number loss is large and hydrogen consumption is large; alkylation benzene reduction technology can convert benzene and olefin components in gasoline into high-octane alkylbenzene compounds, which can significantly reduce the benzene content and increase the octane number, but this process requires a dedicated ZSM-5 catalyst, and the technology is not yet mature; isomerization benzene reduction technology first hydrogenates the benzene in gasoline and then performs ring opening, isomerization and other reactions to produce isopentane and isohexane, which can increase the octane number of gasoline, but the catalyst is easily deactivated during the reaction.

[0004] Fractional debenzenization refers to the process of enriching and separating benzene from gasoline. The gasoline after benzene removal is debenzenized gasoline. After the benzene-rich fraction is separated, it can be used as a hydrogenation raw material or a reforming raw material, or enter the absorption stabilization system of a catalytic cracking unit, a delayed coking unit, a hydrocracking unit, and a constant pressure reduction unit for subsequent treatment. Fractional debenzenization technology is relatively mature, with low investment, greater production and operation flexibility, and better benzene reduction effect. At the same time, benzene is a petrochemical product with high added value. Therefore, fractional debenzenization can not only reduce the benzene content of gasoline, but also produce high value-added products, with significant benefits. The benzene-rich fraction produced by gasoline debenzenization contains about 10% benzene. If it is simply treated and sent to an ethylene unit as a cracking raw material to increase ethylene production, not only will most of the gasoline components be lost, but the benzene resources will not be fully recovered, and the economic efficiency is relatively low. Therefore, it is necessary to deeply process the benzene-rich fraction.

[0005] The Chinese invention patent application publication specification CN 103131465 A discloses a method for reducing the benzene content in gasoline. The material can be introduced into the alkylation debenzenization process through the catalytic gasoline distillation process, and the olefins in the gasoline itself react with benzene to generate alkylated benzene to remove the benzene in the catalytic gasoline. The Chinese invention patent application publication specification CN 1735675A discloses a method for producing low-benzene gasoline. By reacting in a distillation tower reactor, benzene is converted into cyclohexane that can be isomerized to improve octane. Existing patents mainly use catalysts or process optimization to isomerize the benzene component in gasoline or react with olefins to convert it into other substances. High-value benzene products are not obtained, and the economic benefits are not high.

[0006] The fractional distillation debenzenization technology can process catalytic cracking gasoline with high benzene content and achieve better benzene reduction effect. However, the existing processes mostly perform debenzenization first and then desulfurization, and the benzene-rich materials are directly fed into the ethylene unit as cracking raw materials, wasting the high-value benzene component. Therefore, it is necessary to optimize the process to improve economic benefits. Summary of the invention

[0007] The present invention provides a method and system for recovering benzene products by removing benzene from catalytic cracking gasoline. The sulfur content in catalytic gasoline is reduced by a desulfurization device, and then refined gasoline is obtained by fractionation and debenzenation. The byproduct benzene-rich liquid is then extracted and distilled to obtain product benzene and gasoline blending components. After the catalytic gasoline is produced from the catalytic cracking device, it is first sent to the desulfurization device for desulfurization, and then sent to the debenzenization tower for fractionation and debenzenization. The low-sulfur debenzened gasoline produced is directly blended with gasoline, and the benzene-rich liquid extracted from the side line is sent to the extraction device for deep processing. The main purpose is to optimize the desulfurization and fractionation process of catalytic gasoline, improve the economic benefits of oil products and by-products, reduce the sulfur content of catalytic gasoline by desulfurization, and then obtain refined gasoline and benzene-rich liquid with a high benzene content through a fractionation tower. The benzene-rich liquid is sent to the extraction device, and the benzene product and gasoline blending components are obtained by aromatic extraction. This process can increase the production of national standard benzene products, and can greatly improve the economic benefits compared to sending the benzene-rich liquid to the ethylene device.

[0008] On the one hand, the present invention provides a method for recovering benzene in catalytic cracking gasoline, the method comprising the steps of: subjecting the catalytic cracking gasoline to desulfurization and debenzenization treatments in sequence; subjecting the benzene-rich liquid produced by the debenzenization treatment to a first separation treatment to obtain aromatic components and alkane components respectively; and subjecting the aromatic components to a second separation treatment to obtain benzene and toluene respectively.

[0009] Optionally, the desulfurization is an S Zorb adsorption desulfurization technology; preferably, the S Zorb technology uses a fluidized bed device.

[0010] Optionally, the desulfurization conditions include: reaction temperature of 410-420°C, pressure of 3.1 MPa, reaction space velocity of 4 h-1 , the hydrogen-to-oil ratio (mol) is 0.29. The "hydrogen-to-oil ratio" described in the present invention refers to the mass ratio of hydrogen to catalytic cracking gasoline.

[0011] Optionally, the conditions for debenzening include: temperature of 160-175° C. and pressure of 0.03-0.07 MPa.

[0012] Optionally, the first separation is performed by extractive distillation.

[0013] Optionally, the solvent used in the first separation and extraction distillation is sulfolane, and the solvent-to-oil ratio is 4.6. The solvent-to-oil ratio of the present invention refers to a mass ratio of the lean solvent flow rate to the feed amount of 4.6.

[0014] Optionally, the conditions for the first separation include: an extractive distillation temperature of 160-175° C. and a pressure of 0.03-0.08 MPa.

[0015] Preferably, the first separation is carried out by extractive distillation, and the conditions of the first separation refer to the operating mild pressure of the extractive distillation tower.

[0016] Optionally, the second separation conditions include: temperature 160 to 175° C., pressure -0.06 to -0.03 MPa.

[0017] Preferably, the second separation is carried out in the form of extraction recovery, and the conditions of the second separation refer to the operating temperature and pressure of the extraction recovery tower.

[0018] Optionally, the alkane component is used for blending gasoline or for ethylene cracking feedstock.

[0019] Optionally, the catalytic cracking gasoline contains 16wt% to 26wt%, benzene content is 1wt% to 2wt%, and sulfur content does not exceed 260mg / kg.

[0020] On the other hand, the present invention provides a system for recovering benzene in catalytic cracking gasoline, the system comprising a desulfurization tower, a debenzenization tower and an extraction device connected in sequence.

[0021] Optionally, the desulfurization tower is an S Zorb stabilization tower.

[0022] Optionally, the debenzene tower is a plate-type floating valve tower with 35 to 45 plates.

[0023] Optionally, the outlet of the desulfurization tower is connected to the 8th to 10th trays of the debenzenization tower;

[0024] Optionally, the 19th to 21st plates of the debenzene tower are connected to an extraction device.

[0025] The present invention transforms the catalytic gasoline blending process from first debenzening and then desulfurizing to first desulfurizing and then debenzenizing, and the benzene-rich liquid after debenzening is subjected to secondary processing by extraction, thereby reducing the benzene content in gasoline and obtaining a high-value benzene product. The method includes gasoline desulfurization and fractionation debenzening processes, wherein the sulfur content in catalytic gasoline is reduced by desulfurization, and then refined gasoline is obtained by fractionation debenzening, and the byproduct benzene-rich liquid is further subjected to extraction distillation to obtain product benzene and gasoline blending components.

[0026] Compared with the prior art, the present invention optimizes the desulfurization and debenzenization processes, and can blend all the other components of catalytic gasoline with gasoline while obtaining benzene and toluene products, thus avoiding sending the benzene-rich components to the ethylene unit and effectively improving the economic benefits of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the process of the present invention;

[0028] In the figure: 1 is a feed pump; 2 is an S Zorb device; 3 is a desulfurized gasoline pump; 4 is a fractionation debenzenization device; 5 is a benzene-rich liquid pump; and 6 is an aromatics extraction device. DETAILED DESCRIPTION

[0029] To further illustrate the process of the present invention, the process flow of the present invention is described below.

[0030] A method for recovering benzene from benzene-rich liquid in catalytic gasoline is to transform the existing blending process of catalytic gasoline into first desulfurization and then debenzenization. The benzene-rich liquid in the desulfurization unit gasoline obtained by this process directly enters the existing extraction unit for processing, and the national standard benzene product and gasoline components are separated for sale.

[0031] After the catalytic gasoline is produced from the catalytic cracking unit, it is first sent to the desulfurization unit (S Zorb unit) for desulfurization, and its refined gasoline (catalytic gasoline after desulfurization) is sent to the debenzene tower (fractionation debenzene unit). The debenzene gasoline produced is directly blended with gasoline, and the benzene-rich liquid extracted from the side line is sent to the extraction unit for deep processing depending on the working conditions. The benzene-rich liquid entering the extraction unit for processing, its aromatic components enter the distillation separation unit with the mixed aromatic intermediate products in the extraction feed, and benzene and toluene are further separated. The non-aromatic components are blended with gasoline with the raffinate oil product depending on the working conditions or sent to the ethylene unit as ethylene cracking raw materials.

[0032] In the method provided by the present invention, the desulfurization part uses S Zorb adsorption desulfurization technology, which desulfurizes gasoline based on the adsorption principle, and achieves the purpose of desulfurization by selectively adsorbing sulfur atoms in sulfur-containing compounds by the adsorbent. S Zorb technology uses a fluidized bed device, with a reaction temperature of 410-420°C, a pressure of 3.1Mpa, and a reaction space velocity of 4h -1, the hydrogen-to-oil ratio is 0.29, and the sulfur content of catalytic gasoline can be reduced to below 10 mg / kg. The desulfurization technology of catalytic gasoline of the present invention is preferably the proprietary S Zorb technology (US20030723355), and the adsorbent used is the special adsorbent FCAS-R09 (patent CN101433817) produced by Nanjing Branch of Sinopec Catalyst Co., Ltd. In addition, desulfurization technologies such as extractive desulfurization and membrane desulfurization can also be used.

[0033] In the method provided by the present invention, as one embodiment thereof, the fractionation and debenzenization part uses a plate-type floating valve tower with a total of 38 tower plates. The desulfurized catalytic gasoline enters from the 8th tower plate, and the benzene-rich liquid is extracted from the 19th tower plate. The top and bottom components are mixed to obtain debenzenized gasoline, and its sulfur content is less than 0.7%. The operating temperature of the fractionation tower is 67-118°C and the pressure is 0.15Mpa. The extraction solvent of the extraction device of the present invention preferably uses cyclopentane solvent. In addition, solvents such as tetradecyl alcohol ether can also be used for aromatic extraction.

[0034] Example 1 Benzene recovery system for catalytic gasoline

[0035] like Figure 1 As shown, the benzene recovery device for catalytic gasoline includes an S Zorb device 2, a fractionation debenzenization device 4 and an aromatics extraction device 6 which are connected in sequence. Catalytic cracking gasoline is fed into the S Zorb device 2 through a feed pump 1 for adsorption desulfurization, and then the desulfurized gasoline is fed into the fractionation debenzenization device 4 through a desulfurized gasoline pump 3 for fractionation to obtain refined gasoline and benzene-rich liquid. The fractionation debenzenization part uses a plate-type floating valve tower with a total of 38 plates. The desulfurized catalytic gasoline enters from the 8th plate, and the benzene-rich liquid is extracted from the 19th plate. The benzene-rich liquid is fed into the aromatics extraction device 6 through a benzene-rich liquid pump 5, and gasoline components and benzene products are obtained through extraction and distillation.

[0036] Example 2

[0037] like Figure 1 As shown, according to the process flow of Example 1, catalytic gasoline is used as raw material, and the properties are shown in Table 1:

[0038] Table 1 Raw material properties

[0039] raw material Catalytic cracking gasoline Benzene, V% 1.24 Olefins, V% 16 Aromatics, V% 32.4 Sulfur content, mg / kg 150 Distillation range, ℃ 10％ 49.55 50％ 96.75 90％ 176 Final distillation point 201

[0040] The specific operating conditions for desulfurization are: reaction temperature 426℃, reaction pressure 2.35MPa, reaction space velocity 5.3h -1 , hydrogen-to-oil ratio is 0.29.

[0041] The obtained benzene-rich liquid components are shown in Table 2.

[0042] Table 2 Properties of Benzene-Rich Liquid

[0043]

[0044] The specific process operating conditions for debenzening are: the first separation temperature is 175°C, the pressure is 0.065MPa, and the solvent ratio is 0.41; the second separation temperature is 170°C and the pressure is -0.05MPa.

[0045] The final products are refined gasoline and benzene products, and their properties are shown in Table 3.

[0046] Table 3 Product properties

[0047]

[0048] Example 3

[0049] The process is the same as that of Example 2, but the composition of the catalytic gasoline is different. The properties of the raw materials are shown in Table 4:

[0050] Table 4 Raw material properties

[0051] raw material Catalytic cracking gasoline Benzene, V% 1.97 Olefins, V% 18 Aromatics, V% 35.4 Sulfur content, mg / kg 137 Distillation range, ℃ 10％ 47.25 50％ 95.40 90％ 173 Final distillation point 204

[0052] The specific operating conditions for desulfurization are: reaction temperature 426℃, reaction pressure 2.45MPa, reaction space velocity 5.6h -1 , hydrogen-to-oil ratio is 0.27.

[0053] The components of the obtained benzene-rich liquid are shown in Table 5:

[0054] Table 5 Properties of Benzene-rich Liquid

[0055] Benzene-rich liquid Benzene, V% 9.8 Olefins, V% 7.23 Aromatics, V% 11.15 Sulfur content, mg / kg 12.45

[0056] The specific process operating conditions for debenzening are: the first separation temperature is 174°C, the pressure is 0.063MPa, and the solvent ratio is 0.42; the second separation temperature is 171°C and the pressure is -0.05MPa.

[0057] The final products are refined gasoline and benzene products, and their properties are shown in Table 6.

[0058] Table 6 Product properties

[0059]

[0060] The above method can obtain benzene products from catalytic gasoline by distillation. Compared with the existing process of first debenzenizing and then desulfurizing, it avoids directly sending benzene-rich materials as cracking raw materials to the ethylene unit, obtains benzene products with high economic value, and improves economic benefits. At the same time, this process mainly optimizes the original process flow, with low investment in device transformation and good economic benefits.

[0061] The benzene-rich liquid of petrochemical catalytic gasoline of a certain company is currently sent to the ethylene unit as a raw material for ethylene cracking, and its market price is relatively low. In view of this situation, the refined gasoline products of the existing desulfurization unit are analyzed according to the 70℃~90℃ cut fraction (i.e. the benzene-rich liquid of the desulfurization unit gasoline). The total sulfur content of the benzene-rich liquid of the desulfurization unit is reduced to 0.41mg / L, and the sulfur form is mostly distributed in mercaptans and sulfides, without thiophene components, and will not pollute products such as benzene and toluene. It meets the requirements for sulfur content and benzene content in gasoline and can enter the extraction unit for processing. After entering the extraction unit for processing, its annual profitability exceeds 50 million. The calculation process based on recent material prices and fuel prices is as follows:

[0062] The benzene-rich liquid entering the extraction device for processing is composed of 9.75wt% benzene, 0.93wt% toluene, and 85.32wt% non-aromatics, of which non-aromatics are used to blend gasoline 80% of the time and ethylene cracking raw materials 20% of the time according to actual working conditions. The profit of processing each ton of benzene-rich liquid material is: 9.75%*6893 yuan+0.93%*7142 yuan+85.32%*(4704 yuan*0.2+6526*0.8)-4704 yuan=1291.6 yuan.

[0063] The processing cost is calculated based on the assumption that every ton of extracted feed will consume 0.4 tons of medium-pressure steam, and the processing cost of the distillation unit per ton is 18Nm3+0.1 tons of low-pressure steam+0.06 tons of medium-pressure steam. The processing cost per ton of benzene-rich liquid is 0.4 tons*321 yuan / ton+10.48%*18Nm3 / h*2134 yuan / ton*0.6*10-3t / m3+10.48%*0.1 tons*301 yuan / ton+10.48%*0.06 tons*321 yuan / ton=142.6 yuan / ton.

[0064] The profit per ton of processing benzene-rich liquid is 1291.6 yuan / ton-142.6 yuan / ton=1149 yuan / ton. If 6 tons of benzene-rich liquid are processed per hour, the profitability is 6t / h*1149 yuan / t*8000h / year=55.122 million yuan / year.

[0065] Therefore, all improvements and modifications made without departing from the spirit of the present invention are within the scope of protection required by the present invention.

Claims

1. A method for recovering benzene from catalytic cracking gasoline, characterized in that: The method comprises the steps of: Catalytic cracking gasoline is successively treated with desulfurization and debenzenization; The benzene-rich liquid produced by the debenzenization treatment is subjected to a first separation treatment to obtain aromatic components and alkane components respectively; The aromatic components are subjected to a second separation treatment to obtain benzene and toluene respectively.

2. The method according to claim 1, characterized in that The desulfurization adopts S Zorb adsorption desulfurization technology; preferably, the S Zorb technology uses a fluidized bed device; And / or, the desulfurization conditions include: reaction temperature of 410-420°C, pressure of 3.1 MPa, reaction space velocity of 4 h -1 , the hydrogen to oil molar ratio is 0.

29.

3. The method according to claim 1 or 2, characterized in that: The conditions for debenzening include: temperature of 160-175° C. and pressure of 0.03-0.07 MPa.

4. The method according to any one of claims 1 to 3, characterized in that: The first separation adopts extractive distillation; And / or, the solvent used in the first separation is sulfolane, and the solvent-to-oil ratio is 4.6; And / or, the first separation conditions include: temperature 160-175° C., pressure 0.03-0.08 MPa; Preferably, the first separation is carried out by extractive distillation; And / or, the second separation conditions include: temperature 160-175°C, pressure -0.06--0.03Mpa; Preferably, the second separation is carried out by extraction and recovery.

5. The method according to any one of claims 1 to 4, characterized in that: The alkane component is used for blending gasoline or for ethylene cracking raw material.

6. The method according to any one of claims 1 to 5, characterized in that: The catalytic cracking gasoline has an olefin content higher than 16wt% to 26wt%, a benzene content of 1wt% to 2wt%, and a sulfur content not exceeding 260mg / kg.

7. A system for recovering benzene from catalytic cracking gasoline, characterized in that: The system comprises a desulfurization tower, a debenzene tower and an extraction device which are connected in sequence.

8. The recovery system according to claim 7, characterized in that: The desulfurization tower is an S Zorb stabilization tower.

9. The recovery system according to claim 7 or 8, characterized in that: The debenzene tower is a plate-type floating valve tower with 35 to 45 plates.

10. The recovery system according to claim 9, characterized in that: The outlet of the desulfurization tower is connected to the 8th to 10th trays of the debenzenization tower; The 19th to 21st tower plates of the debenzene tower are connected to an extraction device.

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