A combined hydroprocessing and extraction process for diesel

Abstract

The application discloses a combined processing method of hydrogenation and extraction with diesel raw oil as a raw material, high temperature and low pressure are adopted for hydrogenation refining, sulfur and nitrogen impurities are reduced, and only a small amount of aromatic hydrocarbons is saturated, the content of paraffin in raffinate oil is increased, and hydrogen consumption is reduced. Compared with direct extraction of straight-run diesel to produce low-carbon olefin raw material, the method has higher raffinate oil yield, reduces the influence of sulfur and nitrogen impurities on the extraction solvent, reduces the energy consumption and material consumption generated by solvent purification and solvent loss, and is more suitable for producing low-carbon olefin raw material.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of diesel oil processing, and particularly relates to a hydrogenation and extraction combined processing method taking diesel oil as raw material. BACKGROUND

[0002] In recent years, the continuous expansion and modification of ethylene devices have increased the contradiction between supply and demand of raw materials, and how to select appropriate oil products to expand the source of raw materials has attracted much attention. Domestic and foreign research institutions have studied the relationship between the properties of raw materials and the yield of low-carbon olefins in the steam cracking process, and found that the higher the content of n-alkanes in the cracking raw material, the lower the content of aromatics, the more conducive to improving the yield of olefins and reducing the coking of equipment, and the more suitable as a cracking raw material.

[0003] In recent years, the adjustment of industrial structure has led to great changes in the consumption structure of refined oil products, and the most prominent is the significant reduction in the consumption of diesel and gasoline. The diesel-to-gasoline ratio has decreased from 2.18 in 2010 to 1.50 in 2015, and further to 1.37 in 2016. In the future, the growth of diesel consumption will be much slower than that of gasoline, and the demand differentiation trend of refined oil products will be more obvious. The surplus of diesel resources will intensify, and the balance of gasoline will turn to tight. This puts new requirements on the adjustment of product structure and device structure, and the task of reducing the production of diesel and gasoline is arduous. Therefore, how to reduce diesel has become a topic of discussion among major refining enterprises.

[0004] Diesel oil has a high content of paraffin and a large proportion of n-alkanes, which is a potential cracking raw material. However, if part of the aromatics in diesel oil directly enters the ethylene cracking device, it will cause an increase in the amount of coking in the cracking furnace. Because only the side chain of the aromatics in the cracking raw material can be cracked to produce ethylene or propylene, the aromatic ring itself is difficult to open due to the high bond energy of C-C conjugated bond, which is 611 KJ / mol. At 500-900℃, it generates coking precursors. With the catalytic action of the furnace tube material nickel alloy steel, it can dehydrogenate and condense to form asphalt with poor flowability at 300-400℃, which seriously affects production. In addition, the naphthenes in diesel oil are also not ideal ethylene cracking raw materials. Therefore, in order to use diesel oil as an ethylene raw material, it is necessary to remove the aromatics therein and reduce the content of naphthenes while increasing the content of paraffin. Hydrogenation reaction and conventional solvent extraction are common methods for removing aromatics from oil.

[0005] The method for producing low-carbon olefins or aromatics from distillate oil in the prior art has poor raw material properties. If the easily coking components in the raw material are effectively removed, the overall process flow is complex, the energy consumption increases, and the economic benefit is not obvious.

[0006] In the prior art, the raw oil first enters the extraction device, and the raffinate oil obtained by extraction enters the ethylene cracking device. This technology can reduce the amount of feed of the ethylene cracking device prone to coking, but the content of impurities such as sulfur and nitrogen in the raw oil is high. If the raw oil directly enters the extraction device, the content of impurities in the extraction solvent is easy to increase, which affects the extraction effect and the recycling of the extraction solvent, and reduces the economic benefit of the extraction unit. In addition, part of the technology discloses that the raw oil is directly introduced into the ethylene cracking device after hydrogenation. However, since most of the aromatic hydrocarbons are saturated as naphthenes, the hydrogen consumption is increased, and a large amount of naphthenes and even part of polycyclic naphthenes are contained in the hydrogenation product, which is easy to cause coking of the ethylene cracking device and affect the operation cycle of the device.

[0007] If the advantages of the refining and chemical integrated enterprise can be utilized, the raw materials and process structure of the existing device can be optimized through diesel hydrofining, aromatic extraction device and ethylene cracking device, and various types of raw material resources can be fully utilized, which is expected to solve the problem of outlet of diesel and shortage of ethylene material. On the one hand, the hydrogenation technology is used to realize deep desulfurization and denitrification of diesel under the condition of minimizing saturation of aromatic hydrocarbons. On the other hand, the aromatic extraction technology can greatly reduce the content of aromatic hydrocarbons in the ethylene feed and improve the quality of the ethylene material. SUMMARY

[0008] In order to overcome the above technical problems, the present application provides a combined processing method for hydrogenation and extraction of diesel raw oil, which specifically comprises the following steps:

[0009] S1, diesel raw oil is mixed with hydrogen and subjected to hydrofining reaction in a diesel hydrofining reaction system; the operating conditions of hydrofining satisfy T≥2.0345P-29.297P+144.79P+135 and T≥355℃; wherein T is the weighted average reaction temperature of the hydrogenation reactor, and P is the hydrogen partial pressure at the inlet of the hydrogenation reactor; wherein the unit of temperature T is ℃, and the unit of pressure P is MPa; 3 -29.297P 2 +144.79P+135 and T≥355℃; wherein T is the weighted average reaction temperature of the hydrogenation reactor, and P is the hydrogen partial pressure at the inlet of the hydrogenation reactor; wherein the unit of temperature T is ℃, and the unit of pressure P is MPa;

[0010] S2, the hydrofining product obtained in step S1 is introduced into an extraction tower for extraction to obtain raffinate oil rich in alkanes and extract oil rich in aromatic hydrocarbons; the raffinate oil can be used as a raw material for low-carbon olefin cracking;

[0011] S3, the extract oil rich in aromatic hydrocarbons obtained in step S2 is separated by a separation solvent to obtain a diesel fraction rich in aromatic hydrocarbons, which can be directly used as a raw material for hydrocracking or catalytic cracking to produce high-octane gasoline or BTX light components.

[0012] In step S1, diesel is mixed with hydrogen and subjected to hydrofining reaction in a diesel hydrofining reaction system, which aims to remove sulfur and nitrogen, and to realize olefin saturation and partial hydrogenation saturation of aromatic hydrocarbons.

[0013] The formula T≥2.0345P is satisfied 3 -29.297P 2 +144.79P+135 and T≥355℃, the sulfur and nitrogen impurities are reduced while only a small amount of aromatic hydrocarbons are saturated, the content of paraffin in the raffinate oil is increased, and the hydrogen consumption is reduced.

[0014] According to an embodiment of the present application, in the step S1, the hydrofining catalyst is a supported catalyst containing VIB and / or VIII group metals, and the carrier is an alumina and / or silica carrier; or the hydrofining catalyst is a non-supported catalyst containing VIB and / or VIII group active metal components.

[0015] According to an embodiment of the present application, in the step S1, a hydroprotection agent accounting for 5-20% of the total volume of the hydrofining catalyst is loaded at the top of the catalyst bed in the reactor of the hydrogenation reaction system.

[0016] According to an embodiment of the present application, in the step S1, a hydroprotection agent accounting for 5-20% of the total volume of the hydrofining catalyst is loaded at the top of the catalyst bed in the hydrofining reaction to protect the main catalyst and avoid rapid coking of the bed, and to prevent the pressure drop of the catalyst bed from reaching the limit too quickly when the content of olefins or metals in the diesel is high. The hydroprotection agent is composed of 1.0-5.0 wt% nickel oxide, 5.5-10.0 wt% molybdenum oxide, and the balance of alumina carrier with a bimodal pore distribution.

[0017] According to an embodiment of the present application, in the step S1, the reaction conditions for hydrofining are: hydrogen partial pressure 1.2-4.8 MPa, temperature <420℃, liquid hourly space velocity 0.2-8.0 h -1 , hydrogen / oil volume ratio 100-1000:1, and the hydrofining reaction operation mode is production at a relatively low temperature and hydrogen partial pressure, and as the activity of the catalyst decreases, the reaction temperature and hydrogen partial pressure are gradually increased, and the relationship between the temperature and the pressure always satisfies the relationship between the temperature and the pressure in the step 1).

[0018] According to an embodiment of the present application, in the step S1, the saturation rate of aromatic hydrocarbons in the hydrofining product is less than 10%.

[0019] According to an embodiment of the present application, in the step S2, the extraction solvent is an organic solvent with a vaporization temperature not lower than 380℃ at normal pressure, and preferably, the extraction solvent is an ionic liquid.

[0020] According to an embodiment of the present application, the extraction solvent is an ionic liquid: the cation is an alkyl-substituted imidazole or an alkyl-substituted pyridine, and the anion is a tetrafluoroborate or a hexafluorophosphate;

[0021] Preferably, the extraction solvent is one or more of 1-heptyl-4-methylpyridine tetrafluoroborate, 1-heptyl-4-methylpyridine hexafluorophosphate, 1-heptyl-3-methylimidazole tetrafluoroborate, 1-heptyl-3-methylimidazole hexafluoroborate, 1-hexyl-4-methylpyridine tetrafluoroborate, 1-hexyl-4-methylpyridine hexafluorophosphate.

[0022] According to an embodiment of the present application, in the step S2, the mass ratio of the extraction solvent to the hydrofining product is 0.5-5.0:1, the pressure of the extraction tower is 0.1-0.6 MPa, and the extraction temperature is 15-135℃.

[0023] According to an embodiment of the present application, in the step S2, the hydrofining product is introduced from the bottom of the aromatic hydrocarbon extraction tower to be contacted with the extraction solvent in countercurrent in the extraction tower, the raffinate oil with poor aromatic hydrocarbons is obtained from the top of the tower, and the extract oil with rich aromatic hydrocarbons and solvent is obtained from the bottom of the tower; the obtained raffinate oil with poor aromatic hydrocarbons is washed with water or adsorbed to separate a small amount of solvent to obtain high-quality ethylene cracking raw material; the extract oil with rich aromatic hydrocarbons is sent to a rectifying column to recover the solvent, a stream with rich aromatic hydrocarbons is obtained from the top of the rectifying column, a solvent stream with an aromatic hydrocarbon content less than 0.5% by mass is obtained from the bottom of the rectifying column, and is returned to the top of the aromatic hydrocarbon extraction tower in the step S2 for recycling.

[0024] According to an embodiment of the present application, the adsorbent in the process of adsorbing and removing the solvent from the raffinate oil is selected from activated carbon and molecular sieve.

[0025] According to an embodiment of the present application, in the step S2, the sulfur and nitrogen contents in the raffinate oil with rich alkanes are both ≤10 μg / g, the paraffin content is increased by more than 8 wt% compared with the diesel raw oil, and the aromatic hydrocarbon content is less than 15 wt%.

[0026] According to an embodiment of the present application, in the step S3, the solvent in the extract oil is separated by rectification, the diesel fraction with rich aromatic hydrocarbons is obtained from the top of the tower, and the extraction solvent is recycled.

[0027] According to an embodiment of the present application, the diesel raw oil is selected from one or more of straight-run diesel, catalytic cracking diesel, coking diesel, diesel fraction of coal direct liquefaction oil, and diesel fraction of coal tar.

[0028] According to an embodiment of the present application, the diesel raw oil has a distillation range of 150-400℃, a paraffin content ≥40 wt%, and a total aromatic hydrocarbon content ≤30 wt%.

[0029] The “polycyclic aromatic hydrocarbon” in the present application refers to the sum of the mass fractions of the di-cyclic aromatic hydrocarbons and the aromatic hydrocarbons with three or more rings in the mass spectrum composition data obtained by mass spectrometry (analysis method SH / T-0606).

[0030] Compared with the prior art, the method has the advantages that:

[0031] 1、 The method opens up an effective utilization way for diesel oil, and expands the source of low-carbon olefin cracking raw materials.

[0032] 2、 The method adopts high temperature and low pressure (i.e. meets the formula T≥2.0345P 3 -29.297P 2 +144.79P+135 and T≥355℃) for hydrofining, so that the sulfur and nitrogen impurities are reduced, and only a small amount of aromatic hydrocarbons are saturated, the content of paraffin in the raffinate oil is increased, and the hydrogen consumption is reduced. Compared with the production of low-carbon olefin raw materials by directly extracting low-carbon olefin raw materials from straight-run diesel oil, the method has higher raffinate oil yield, reduces the influence of sulfur and nitrogen impurities on the extraction solvent, reduces the energy consumption and material consumption generated by solvent purification and solvent loss; compared with the traditional hydrogenation technology, the raffinate oil has higher paraffin content and is more suitable as a low-carbon olefin raw material. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The flowchart is a preferred embodiment of the method for producing low-carbon olefin raw materials from diesel oil.

[0034] 1 is the raw material oil, 2 is hydrogen, 3 is a hydrofining reaction device, 4 is a hydrofining product, 5 is an extraction column, 6 is raffinate oil rich in alkanes, 7 is extract oil rich in aromatic hydrocarbons, 8 is a solvent recovery column, 9 is an extraction solvent, and 10 is aromatic hydrocarbon extract oil. DETAILED DESCRIPTION

[0035] The method provided by the present application will be further described below in combination with the drawings and examples, but the present application is not limited thereto.

[0036] Figure 1 The flowchart is a preferred embodiment of the method for producing low-carbon olefin raw materials from diesel oil. Figure 1 The flowchart is a preferred embodiment of the method for producing low-carbon olefin raw materials from diesel oil.

[0037] The method provided by the present application will be further described below in combination with the drawings and examples, but the present application is not limited thereto.

[0038] The diesel oil feedstock 1 and hydrogen 2 are mixed through a pipeline and then enter a hydrofining reaction device 3 to perform desulfurization, denitrification, olefin saturation and moderate aromatic saturation reaction. The moderate aromatic saturation is mainly the reaction of polycyclic aromatic hydrocarbons being hydrogenated to form monocyclic aromatic hydrocarbons. The product 4 after hydrofining enters the lower part of an extraction column 5, and the extraction solvent 9 enters the upper part of the extraction column 5 to exchange and extract in countercurrent. Due to the extraction of a large amount of aromatic hydrocarbons, the aromatic hydrocarbon content in the raffinate oil rich in alkanes extracted from the top of the extraction column is low, and the content of alkanes is high. In addition, the raffinate oil rich in alkanes is subjected to adsorption of the solvent by activated carbon or molecular sieve (not shown in the figure), and then the content of heteroatoms such as sulfur and nitrogen is ≤10 μg / g, the content of alkanes is increased by more than 8 mass% compared with the raw material, the content of aromatic hydrocarbons is less than 15 mass%, and the raffinate oil can be used as a high-quality ethylene cracking raw material. The aromatic extraction oil 7 rich in aromatic hydrocarbons extracted from the bottom of the extraction column 5 enters a solvent recovery column 8, and is subjected to heating and vacuum distillation. The extraction solvent 9 separated from the solvent recovery column 8 is discharged from the bottom and returned to the extraction column 5 for recycling. The aromatic extraction oil 10 discharged from the top of the solvent recovery column 8 can be directly used as a raw material for hydrocracking or catalytic cracking to produce high-octane gasoline or BTX light components.

[0039] The hydrofining process conditions are selected to control the total content of sulfur, nitrogen and other heteroatoms in the fractionated oil after hydrofining to be ≤300 μg / g. On the one hand, the influence of sulfur and nitrogen impurities on the extraction solvent is reduced, and the impurity content in the extracted oil and the raffinate oil is reduced. On the other hand, the moderate severity of hydrofining is controlled to avoid excessive hydrogenation saturation of aromatic hydrocarbons to naphthenes, and the content of naphthenes in the raffinate oil is reduced.

[0040] The type of the hydrofining catalyst is not particularly limited in the present application, and those skilled in the art can select various hydrofining catalysts commonly used in the art. In order to make the product quality of the present application more excellent, the method of the present application preferably comprises the following composition of the hydrofining catalyst based on the catalyst: 1-10 wt% of nickel oxide, 10-50 wt% of the sum of the content of molybdenum oxide and tungsten oxide, 0.5-8 wt% of the content of phosphorus oxide, and the balance of the carrier. Preferably, the carrier of the hydrofining catalyst contains silica-alumina. Based on the silica-alumina, the content of silica in the silica-alumina is 2-45 wt%, and the content of alumina is 55-98 wt%.

[0041] The hydrogenation protectors and the hydrorefining catalysts used in the examples can be prepared according to the prior art or obtained commercially. For example, one or more of the hydrogenation protectors with trade marks of RG-30A, RG-30B or RG-1 and the hydrorefining catalysts with trade marks of RS-2000, RS-2100 and RS-2200 from China Petroleum & Chemical Corporation can be used. RS-2200 is exemplarily used as the diesel hydrorefining catalyst in the examples of the present application, which should not be construed as a limitation to the present application.

[0042] A typical diesel is selected as the raw oil in the examples and is denoted as raw oil A. The main properties of the raw oil are shown in Table 1.

[0043] Table 1 Properties of raw oil

[0044] Feed oil A B Density (20°C), g / cm 3 ]] 0.8484 0.8358 Sulfur content, pg / g 12310 12210 Nitrogen content, pg / g 259 121 Hydrocarbon composition, wt% Paraffins 45.7 53.9 Total naphthenes 28.8 25.9 Total monoaromatics 15.8 13.9 Total diaromatics 8.7 6.0 Triaromatics 1.0 0.3 Total aromatics 25.5 20.2

[0045] Example 1

[0046] The A oil is mixed with hydrogen and then fed into the hydrogenation reactor. The reactor is divided into two beds, each of which is loaded with 50 ml of catalyst, and a total of 100 ml of catalyst is loaded. The operating conditions of the reactor are as follows: the average reaction temperature of the first bed is 375°C, the average reaction temperature of the second bed is 385°C, the weighted average reaction temperature of the reactor is 380°C, the hydrogen partial pressure is 3.2 MPa, the volume space velocity of the raw oil is 1.5 h"1, and the volume ratio of hydrogen to oil is 300: 1. The reactor effluent is subjected to gas-liquid separation in a separator, the gas phase is returned to the inlet of the reactor, and the liquid phase with a total sulfur and nitrogen content of <300 μg / g is fed into an extraction column. The mass ratio of the 1-hexyl-4-methylpyridine hexafluorophosphate ionic liquid to the liquid phase stream is 3: 1, solvent extraction is carried out, and the raffinate oil is obtained by adsorbing the solvent on activated carbon and can be used as a high-quality ethylene cracking raw material. The properties of the raffinate oil are shown in Table 3. The extract phase obtained after separating the raffinate phase is subjected to vacuum distillation, and the extract oil can be directly used as a raw material for hydrocracking or catalytic cracking to produce high-octane gasoline or BTX light components.

[0047] The sulfur and nitrogen contents in the ionic liquid after extraction are increased and need to be purified. The energy consumption and solvent loss involved in the ionic liquid extraction are positively correlated with the total sulfur and nitrogen content in the hydrogenation product. The energy consumption is based on the extraction energy consumption in the example. The relationship between the energy consumption and the sulfur and nitrogen content is as follows: y = 0.4167x 3 - 2.5x 2 + 5.0833x - 2; wherein y is the multiple of the reference energy consumption, and x is the total of the sulfur and nitrogen content in the hydrorefined product.

[0048] Example 2

[0049] The A oil is mixed with hydrogen and fed into the hydrogenation reactor. The reactor is divided into two beds, each bed is filled with 50 ml of catalyst, and a total of 100 ml of catalyst is filled. The operating conditions of the reactor are: the average reaction temperature of the first bed is 375°C, the average reaction temperature of the second bed is 385°C, the weighted average reaction temperature is 380°C, the hydrogen partial pressure is 1.6 MPa, the volume space velocity of the raw oil is 1.5 h-1, and the volume ratio of hydrogen to oil is 300:1. The reactor effluent is separated into gas and liquid in the separator, the gas is returned to the reactor inlet, the liquid with a total sulfur and nitrogen content of less than 300 μg / g is fed into the extraction tower, the mass ratio of 1-hexyl-4-methylpyridine hexafluorophosphate ionic liquid to the liquid stream is 3:1 for solvent extraction, and the raffinate is obtained by adsorbing the solvent on activated carbon. The raffinate can be used as a high-quality ethylene cracking raw material, and its properties are shown in Table 3. The extracted phase obtained after separating the raffinate phase is subjected to vacuum distillation to obtain an extracted oil which can be directly used as a raw material for hydrocracking or catalytic cracking to produce high-octane gasoline or BTX light components.

[0050] After the ionic liquid extraction is used, the sulfur and nitrogen contents in the ionic liquid increase and need to be purified. The energy consumption and solvent loss involved in the ionic liquid extraction are positively correlated with the total sulfur and nitrogen contents in the hydrogenation product. The extraction energy consumption of this example is 5 times the reference.

[0051] Example 3

[0052] The B oil is mixed with hydrogen and fed into the hydrogenation reactor. The reactor is divided into two beds, each bed is filled with 50 ml of catalyst, and a total of 100 ml of catalyst is filled. The operating conditions of the reactor are: the average reaction temperature of the first bed is 375°C, the average reaction temperature of the second bed is 385°C, the weighted average reaction temperature of the reactor is 380°C, the hydrogen partial pressure is 3.2 MPa, the volume space velocity of the raw oil is 1.5 h-1, and the volume ratio of hydrogen to oil is 300:1. The reactor effluent is separated into gas and liquid in the separator, the gas is returned to the reactor inlet, the liquid with a total sulfur and nitrogen content of less than 300 μg / g is fed into the extraction tower, the mass ratio of 1-hexyl-4-methylpyridine hexafluorophosphate ionic liquid to the liquid stream is 3:1 for solvent extraction, and the raffinate is obtained by adsorbing the solvent on activated carbon. The raffinate can be used as a high-quality ethylene cracking raw material, and its properties are shown in Table 3. The extracted phase obtained after separating the raffinate phase is subjected to vacuum distillation to obtain an extracted oil which can be directly used as a raw material for hydrocracking or catalytic cracking to produce high-octane gasoline or BTX light components.

[0053] After the ionic liquid extraction is used, the sulfur and nitrogen contents in the ionic liquid increase and need to be purified. The energy consumption and solvent loss involved in the ionic liquid extraction are positively correlated with the total sulfur and nitrogen contents in the hydrogenation product. The extraction energy consumption of this example is 5 times the reference.

[0054] Comparative Example 1

[0055] The A oil is used as the raw oil, and the raw oil is directly used as the ethylene feed after passing through the hydrofining unit. The hydrofining process conditions are as follows: the reaction temperature is 340°C, the hydrogen partial pressure is 6.4 MPa, the raw oil volume space velocity is 1.5 h-1, and the hydrogen / oil volume ratio is 300:1. The reactor effluent is subjected to gas-liquid separation in a separator, the gas phase is returned to the reactor inlet, and the liquid phase with a total sulfur and nitrogen content of <300 μg / g is used as the ethylene feed. The properties are shown in Table 3.

[0056] Comparative Example 2

[0057] The A oil is used as the raw oil, and the raw oil is directly used as the ethylene feed after passing through the hydrofining unit. The hydrofining process conditions are as follows: the reaction temperature is 340°C, the hydrogen partial pressure is 6.4 MPa, the raw oil volume space velocity is 1.5 h-1, and the hydrogen / oil volume ratio is 300:1. The reactor effluent is subjected to gas-liquid separation in a separator, the gas phase is returned to the reactor inlet, and the liquid phase with a total sulfur and nitrogen content of <300 μg / g is used as the ethylene feed. The properties are shown in Table 3.

[0058] The ion liquid extraction is used, and the sulfur and nitrogen contents are increased, and need to be purified. The energy consumption and solvent loss of the ion liquid extraction are positively correlated with the sulfur and nitrogen contents in the hydrogenation product. Since the raw material contains a relatively high content of sulfur and nitrogen, but most of them are sulfur and nitrogen without aromatic rings, the influence of the sulfur and nitrogen compounds without aromatic hydrocarbons on the extraction solvent is relatively low under the same sulfur and nitrogen content. Therefore, the energy consumption of the direct extraction of the raw material is deviated from the above energy consumption formula, and it is expected that the extraction energy consumption of the present comparative example is 50% of the base value.

[0059] Comparative Example 3

[0060] The A oil is used as the raw oil, and the raw oil is directly used as the ethylene feed after passing through the hydrofining unit. The hydrofining process conditions are as follows: the reaction temperature is 340°C, the hydrogen partial pressure is 6.4 MPa, the raw oil volume space velocity is 1.5 h-1, and the hydrogen / oil volume ratio is 300:1. The reactor effluent is subjected to gas-liquid separation in a separator, the gas phase is returned to the reactor inlet, and the liquid phase with a total sulfur and nitrogen content of <300 μg / g is used as the ethylene feed. The properties are shown in Table 3. -1 The reactor effluent is subjected to gas-liquid separation in a separator, the gas phase is returned to the reactor inlet, and the liquid phase with a total sulfur and nitrogen content of <300 μg / g is used as the ethylene feed. The properties are shown in Table 3.

[0061] The ion liquid extract has increased sulfur and nitrogen content after use, and needs purification treatment. The energy consumption and solvent loss of the ion liquid are positively correlated with the sulfur and nitrogen content in the hydrogenated product. The extraction energy consumption of the comparative example is 2.0 times that of the benchmark.

[0062] Comparative Example 4

[0063] The other conditions are the same as in Example 2, but the reaction temperature of the hydrofining unit is 340°C.

[0064] Table 2 Hydrofining process conditions and properties of the product after hydrogenation

[0065] Item Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Feed oil A A B A A A A Reaction temperature, °C 380 380 380 340 / 340 340 Hydrogen partial pressure, MPa 3.2 1.6 3.2 6.4 / 6.4 1.6 volume space velocity, h -1 ]] 1.5 1.5 1.5 1.5 / 1.5 1.5 Hydrogen / oil volume ratio, v / v 300 300 300 300 / 300 300 Density (20°C), g / cm 3 ]] 834.3 837.4 832.1 832.6 832.6 838.0 Sulfur content, pg / g 13 90 14 92 92 523 Nitrogen content, pg / g 18 97 16 12 12 176 Sum of sulfur and nitrogen content, pg / g 31 187 30 104 104 699 Chemical hydrogen consumption, w% 0.48 0.33 0.47 0.58 0.58 0.40 Paraffins, wt% 47.9 46.4 55 46.7 46.7 46.7 Naphthenes, wt% 28.5 27.3 26 32.6 32.6 29.7 Monoaromatics, wt% 17.4 18.0 15 18.3 18.3 17.2 Diaromatics, wt% 5.8 7.8 4 2.2 2.2 6.0 Triaromatics, wt% 0.4 0.5 0 0.2 0.2 0.4 Total aromatics, wt% 23.6 26.3 19 20.7 20.7 23.6 Total aromatics saturation rate, % 7.5 -3.1 5.9 18.8 18.8 7.5

[0066] Table 3 Solvent extraction process conditions and properties of the raffinate oil

[0067]

[0068]

[0069] As can be seen from the results in Tables 2 and 3, the product after simple hydrogenation using a conventional hydrogenation scheme, without extraction (Comparative Example 1), has a paraffin content of only 46.7%, which is not ideal for low-carbon olefin cracking raw material.

[0070] Comparative Example 2 is direct extraction of the diesel raw material without hydrogenation, and the paraffin content of the raffinate oil obtained is 56.6%, which is 10.9 percentage points higher than the paraffin content of the raw material. However, the raffinate oil yield is only 79%, which is 5% lower than the raffinate oil yield of the scheme in Example 1, which has a paraffin content increase of the same value. And because there is no hydrogenation, a large amount of sulfur and nitrogen compounds are extracted into the solvent, and the energy consumption for solvent purification treatment is more than 50 times that of Example 1.

[0071] Comparative Example 3 is a conventional hydrogenation followed by solvent extraction of the product after hydrogenation. Although the raffinate oil yield is high, the paraffin content increase is only 7.5 percentage points, which is 3.3-3.7 percentage points lower than the paraffin content increase of Examples 1 and 2. Moreover, the chemical hydrogen consumption is high, which is 0.10-0.25% higher than that of Examples 1 and 2, and the process economy for producing ethylene cracking raw material is poor.

[0072] Comparative Example 4 uses a hydrogenation process condition with low pressure, but the temperature does not meet the requirements of the formula. Although the method of hydrogenation first and then extraction is used, there are still a large number of sulfur and nitrogen compounds in the reaction process of the hydrofining, which significantly increases the energy consumption of the extraction process. Compared with Example 1, the raffinate oil yields of the two are comparable, but the paraffin content increase is 1.4 percentage points lower.

Claims

1. A combined hydroprocessing and extraction process for a diesel feedstock, characterized by: Specifically comprising the following steps: S1, the diesel feed oil is mixed with hydrogen and then subjected to hydrofining reaction in a diesel hydrofining reaction system, the operating conditions of the hydrofining meet T≥2.0345P 3 -29.297P 2 +144.79P+135, and T≥355℃; wherein T is the weighted average reaction temperature of the hydrogenation reactor, and P is the hydrogen partial pressure at the inlet of the hydrogenation reactor; wherein the unit of temperature T is ℃, and the unit of pressure P is MPa; S2, the hydrofinished product obtained from step S1 is introduced into an extraction column for extraction to obtain raffinate oil rich in alkanes and extract oil rich in aromatics; the raffinate oil is used as raw material for low-carbon olefin cracking; S3, the extract oil rich in aromatics obtained from step S2 is separated by a separation solvent to obtain a diesel fraction rich in aromatics, which is directly used as raw material for hydrocracking or catalytic cracking to produce high-octane gasoline or BTX light components; In the step S1, the reaction conditions of the hydrofining are: hydrogen partial pressure 1.2-3.2 MPa, temperature <420℃, liquid hourly space velocity 0.2~8.0 h -1 , hydrogen / oil volume ratio 100~1000:

1.

2. The method of claim 1, wherein: In the step S1, the hydrofining catalyst is a supported catalyst containing Group VIB and / or Group VIII active metal components, and the support of the supported catalyst is an alumina and / or silica support; or the hydrofining catalyst is a non-supported catalyst containing Group VIB and / or Group VIII active metal components.

3. The method of claim 1, wherein: In the step S1, a hydrogenation protection agent accounting for 5-20% of the total volume of the hydrofining catalyst is loaded at the top of the catalyst bed in the reactor of the hydrogenation reaction system.

4. The method of claim 1, wherein: In the step S1, the saturation rate of aromatics in the hydrofining product is less than 10%.

5. The method of claim 1, wherein: In the step S2, the extraction solvent is an organic solvent with a vaporization temperature of not less than 380℃ under normal pressure.

6. The method of claim 5, wherein: The extraction solvent is an ionic liquid, and the ionic liquid is: the cation is an alkyl-substituted imidazole or an alkyl-substituted pyridine, and the anion is a tetrafluoroborate or a hexafluorophosphate.

7. The method of claim 5, wherein: The extraction solvent is one or more of 1-heptyl-4-methylpyridine tetrafluoroborate, 1-heptyl-4-methylpyridine hexafluorophosphate, 1-heptyl-3-methylimidazole tetrafluoroborate, 1-heptyl-3-methylimidazole hexafluoroborate, 1-hexyl-4-methylpyridine tetrafluoroborate, and 1-hexyl-4-methylpyridine hexafluorophosphate.

8. The method of claim 1, wherein: In the step S2, the mass ratio of the extraction solvent to the hydrofining product is 0.5-5.0:1, the pressure of the extraction column is 0.1-0.6 MPa, and the extraction temperature is 15-135℃.

9. The method of claim 1, wherein: In the step S2, the hydrofining product is introduced from the bottom of the aromatics extraction column to be in countercurrent contact with the extraction solvent from top to bottom in the extraction column, the raffinate oil rich in alkanes is obtained from the top of the column, and the extract oil rich in aromatics is obtained from the bottom of the column; the obtained raffinate oil rich in alkanes is washed with water or adsorbed to separate a small amount of solvent to obtain high-quality ethylene cracking raw material; in the step S3, the extract oil rich in aromatics is sent to a rectifying column to recover the solvent, a diesel fraction rich in aromatics is obtained from the top of the rectifying column, a solvent stream with an aromatic content of less than 0.5% by mass is obtained from the bottom of the rectifying column, and the solvent stream is returned to the top of the aromatics extraction column in step S2 for recycling.

10. The method of claim 9, wherein: The adsorbent used for adsorbing and separating a small amount of solvent from the raffinate oil is selected from activated carbon or molecular sieves.

11. The method of claim 1, wherein: In the step S2, the sulfur and nitrogen contents in the raffinate oil rich in alkanes are both ≤10 μg / g, the paraffin content is increased by more than 8% by weight compared with the diesel raw oil, and the aromatic content is less than 15% by weight.

12. The method of claim 1, wherein: In the step S3, the solvent in the extract oil is separated by rectification, a diesel fraction rich in aromatics is obtained from the top of the column, and the extraction solvent is recycled.

13. The method of claim 1, wherein: The diesel oil raw material is selected from one or more of straight-run diesel oil, catalytic cracking diesel oil, coking diesel oil, diesel oil fraction of coal direct liquefaction oil, and diesel oil fraction of coal tar.

14. The method of claim 1, wherein: The diesel oil raw material has a distillation range of 150-400 DEG C, a paraffin content of ≥40wt%, and a total aromatic content of ≤30wt%.

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