A method for processing diesel feedstock based on a moving bed hydrogenation reaction system

Abstract

This invention discloses a diesel feedstock processing method based on a moving bed hydrogenation reaction system, which solves the problem of rapid deactivation rate of hydrogenation catalysts under low pressure and high temperature, and the serious impact of frequent catalyst replacement on production efficiency. It opens up an effective utilization path for diesel and expands the source of feedstock for low-carbon olefin cracking.

Description

Technical Field

[0001] This invention belongs to the field of diesel processing technology, specifically relating to a diesel feedstock processing method based on a moving bed hydrogenation reaction system. Background Technology

[0002] Domestic and international research institutions have studied the relationship between feedstock properties and low-carbon olefin yield during steam cracking. They have found that higher n-alkane content and lower aromatic content in the cracking feedstock are more conducive to increasing olefin yield and reducing coking in the equipment, making it more suitable as a cracking feedstock.

[0003] In recent years, industrial restructuring has led to significant changes in the consumption structure of refined oil products, most notably in the substantial decrease in the diesel-to-gasoline ratio, which dropped from 2.18 in 2010 to 1.50 in 2015, and further decreased to 1.37 in 2016. Future diesel consumption growth will be significantly slower than gasoline growth, and the divergence in refined oil demand will become more pronounced. It is projected that by 2020, the diesel-to-gasoline ratio will fall sharply to below 1.1, while the production ratio will drop to around 1.18. This will exacerbate the oversupply of diesel resources and lead to a tight balance in gasoline production. This presents new challenges for adjusting the refining product structure and equipment structure, making the task of reducing the production diesel-to-gasoline ratio extremely difficult. Therefore, how to reduce diesel consumption has become a hotly debated topic among major refining and chemical enterprises.

[0004] CN 1176293A discloses a method for preparing ethylene cracking feedstock, characterized by using light wax oil and diesel oil as raw materials, and producing ethylene cracking feedstock through high-pressure hydrogenation refining. This method features a simple production process, reduced operating costs, high total yield and good quality of ethylene, propylene, and butadiene obtained from cracking, low yield of fuel oil from cracking, less coking by the cracking process, and expanded sources of ethylene cracking feedstock.

[0005] CN1022844C discloses a method for producing high-value products using wax oil. The method is characterized by the use of solvent extraction combined with other technologies to process low-value, difficult-to-process inferior wax oil into high-quality, high-value products such as steam cracking feedstock for ethylene production, catalytic cracking feedstock, rubber filler oil, and asphalt modifier. This technology has low production costs, no environmental pollution, and high economic benefits, and represents a brand-new heavy oil processing route.

[0006] The aforementioned prior art discloses a method where the feedstock oil first enters an extraction unit, and the extracted residue oil then enters an ethylene cracking unit. This technology can reduce the feed amount of easily coking components in the ethylene cracking unit. However, the feedstock oil has high levels of impurities such as sulfur and nitrogen. If it directly enters the extraction unit, it can easily lead to an increase in the impurity content in the extraction solvent, affecting the extraction effect and the recycling of the extraction solvent, thus reducing the economic efficiency of the extraction unit. In addition, some technologies disclose the use of feedstock oil that has been hydrogenated before directly entering the ethylene cracking unit. However, since most aromatics are hydrogenated to cycloalkanes, this not only increases hydrogen consumption but also results in the hydrogenated product containing a large amount of cycloalkanes, and even some polycyclic cycloalkanes, which can easily lead to coking in the ethylene cracking unit and affect the unit's operating cycle. Summary of the Invention

[0007] To overcome the above technical problems, the present invention provides a diesel feedstock processing method based on a moving bed hydrogenation reaction system. This method uses diesel as feedstock and combines hydrogenation refining and solvent extraction to obtain high-quality ethylene cracking feedstock, while also producing high-value-added aromatic products or high-octane gasoline blending components as byproducts.

[0008] The processing method provided by this invention uses diesel feedstock as raw material, and sequentially performs hydrorefining and solvent extraction to simultaneously produce low-carbon olefin cracking feedstock and hydrocracking or catalytic cracking feedstock. The hydrorefining employs a moving bed hydrorefining reaction system. This system consists of one or more moving bed reactors, with the flow direction of the hydrorefining catalyst between reactors opposite to the flow direction of the feedstock and hydrogen. The feedstock and hydrogen flow sequentially from the first moving bed reactor to the last, contacting the hydrorefining catalyst in each reactor. The hydrorefining product enters subsequent units for processing. The catalyst flows sequentially from the last moving bed reactor to the first, then through a regeneration reactor, with the regenerated catalyst entering from the last moving bed reactor.

[0009] This invention employs a moving bed reaction system, which solves the problem of rapid deactivation rate of hydrogenation catalysts under low pressure and high temperature, and the serious impact of frequent catalyst replacement on production efficiency.

[0010] According to an embodiment of the present invention, the above processing method specifically includes the following steps:

[0011] S1. Diesel feedstock and hydrogen undergo hydrorefining reaction in a moving bed diesel hydrotreating system to remove sulfur and nitrogen and achieve olefin saturation and partial hydrogenation saturation of aromatics. The hydrorefining operation conditions satisfy T≥2.0345P3-29.297P2+144.79P+135 and T≥355℃; where T is the weighted average reaction temperature of the hydrotreating reactor in °C, and P is the hydrogen partial pressure at the inlet of the hydrotreating reactor in MPa.

[0012] S2. The hydrorefined product obtained in step S1 is fed into an extraction tower for extraction to obtain raffinate oil rich in alkane and extract oil rich in aromatics; the raffinate oil can be used as a feedstock for the cracking of low-carbon olefins.

[0013] S3. The aromatic-rich extracted oil, through separation, yields an aromatic-rich diesel fraction that can be directly used as feedstock for hydrocracking or catalytic cracking to produce high-octane gasoline or BTX light components.

[0014] The formula T≥2.0345P is used. 3 -29.297P 2 Hydrorefining under conditions of +144.79P+135 and T≥355℃ reduces sulfur and nitrogen impurities while saturating only a very small amount of aromatics, thereby increasing the alkane content in the raffinate and reducing hydrogen consumption.

[0015] The selection of diesel hydrorefining process conditions reduces the impact of sulfur and nitrogen impurities on the extraction solvent, thereby reducing the impurity content in the extracted and residual oils. On the other hand, it controls the appropriate degree of harshness in hydrorefining to avoid excessive hydrogenation saturation of aromatics into cycloalkanes, which would increase the difficulty of solvent extraction.

[0016] This invention does not particularly limit the type of hydrorefining catalyst, and those skilled in the art can select from various conventionally used hydrorefining catalysts. To improve the quality of the product described in this invention, the preferred composition of the hydrorefining catalyst, based on the catalyst itself, comprises: 1-10% by weight of nickel oxide, 10-50% by weight of the sum of molybdenum oxide and tungsten oxide, 0.5-8% by weight of phosphorus oxide, and the balance being a support. Preferably, the support of the hydrorefining catalyst contains silica-alumina. Based on the silica-alumina, the silica content in the silica-alumina is 2-45% by weight, and the alumina content is 55-98% by weight.

[0017] According to one embodiment of the present invention, the hydrogenation refining reaction conditions in step S1 are: hydrogen partial pressure 1.2-3.2 MPa, temperature <420°C, liquid hourly space velocity 0.2-8.0 h⁻¹, hydrogen / oil volume ratio 100-1000:1, and the relationship between temperature and pressure always satisfies the temperature and pressure relationship formula in step S1.

[0018] According to one embodiment of the present invention, in step S1, the hydrorefining catalyst is a supported catalyst containing group VIB and / or group VIII metals, and the support is an alumina and / or silica support; or, the hydrorefining catalyst is a non-supported catalyst containing group VIB and / or group VIII active metal components.

[0019] According to one embodiment of the present invention, in step S1, the aromatic saturation rate in the hydrorefined product is less than 10%.

[0020] According to one embodiment of the present invention, the regenerated catalyst does not need to be pre-sulfurized and can be directly added to the reactor.

[0021] According to one embodiment of the present invention, in step S2, the extraction solvent is an organic solvent with a vaporization temperature of not less than 380°C under normal pressure, preferably an ionic liquid.

[0022] According to one embodiment of the present invention, the ionic liquid is: the cation is an alkyl-substituted imidazole or an alkyl-substituted pyridine, and the anion is tetrafluoroborate or hexafluorophosphate; preferably, the ionic liquid is one or more of 1-heptyl-4-methylpyridine tetrafluoroborate, 1-heptyl-4-methylpyridine hexafluorophosphate, 1-heptyl-3-methylimidazolium tetrafluoroborate, 1-heptyl-3-methylimidazolium hexafluoroborate, 1-hexyl-4-methylpyridine tetrafluoroborate, and 1-hexyl-4-methylpyridine hexafluorophosphate.

[0023] According to one embodiment of the present invention, the mass ratio of the extraction solvent to the hydrogenated product is 0.5 to 5.0:1, the pressure of the extraction tower is 0.1 to 0.6 MPa, and the extraction temperature is 15 to 135°C.

[0024] According to one embodiment of the present invention, in step S2, the hydrorefining product is introduced from the bottom of the aromatics extraction tower, and is brought into countercurrent contact with the extraction solvent flowing from top to bottom in the extraction tower. A raffinate oil with low aromatics content is obtained from the top of the tower, and an extract oil rich in aromatics and solvent is obtained from the bottom of the tower. The obtained raffinate oil with low aromatics content is washed with water or adsorbed to separate trace amounts of solvent to obtain high-quality ethylene cracking feedstock. The extract oil rich in aromatics is sent to a distillation tower to recover the solvent. A stream rich in aromatics is obtained from the top of the distillation tower, and a solvent stream with an aromatics content of less than 0.5% by mass is obtained from the bottom of the distillation tower. This stream is returned to the top of the aromatics extraction tower in step S2 for recycling.

[0025] According to one embodiment of the present invention, the adsorbent used in the solvent removal process of the residual oil is selected from activated carbon and molecular sieve.

[0026] According to one embodiment of the present invention, in step S2, the sulfur and nitrogen contents of the alkane-rich raffinate are both ≤10μg / g, the alkane content is increased by more than 8wt% compared with the diesel feedstock, and the aromatic content is less than 15wt%.

[0027] According to one embodiment of the present invention, in step S3, the solvent in the extracted oil is separated by distillation, and a diesel fraction rich in aromatics is obtained at the top of the column, while the extraction solvent is obtained at the bottom of the column and recycled.

[0028] According to one embodiment of the present invention, the diesel feedstock is selected from one or more of straight-run diesel, catalytic cracking diesel, coking diesel, diesel fraction of direct coal liquefaction oil, and diesel fraction of coal tar.

[0029] According to one embodiment of the present invention, the diesel feedstock has a boiling point range of 150–400°C, an alkane content of ≥40% by mass, and a total aromatic content of ≤40% by mass.

[0030] The "polycyclic aromatic hydrocarbons" mentioned in this invention refer to the sum of the mass fractions of bicyclic aromatic hydrocarbons and aromatic hydrocarbons with three or more rings in the mass spectrometry composition data obtained by mass spectrometry (analytical method SH / T-0606).

[0031] The hydrorefining catalyst of the present invention comprises, based on the catalyst, 1-10% by weight of nickel oxide, 10-50% by weight of the sum of molybdenum oxide and tungsten oxide, 0.5-8% by weight of phosphorus oxide, and the balance being a support. Preferably, the support of the hydrorefining catalyst contains silica-alumina. Based on the silica-alumina, the silica content in the silica-alumina is 2-45% by weight, and the alumina content is 55-98% by weight.

[0032] Compared with the prior art, the advantages of the method of the present invention are:

[0033] 1. This invention employs a moving bed reaction system, which solves the problem of rapid deactivation rate of hydrogenation catalysts under low pressure and high temperature, and the serious impact of frequent catalyst replacement on production efficiency.

[0034] 2. This invention opens up an effective way to utilize diesel fuel and expands the sources of feedstock for low-carbon olefin cracking.

[0035] 3. This invention employs high temperature and low pressure (i.e., conforming to the formula T≥2.0345P). 3 -29.297P 2 Hydrorefining (using +144.79P+135 and T≥355℃) reduces sulfur and nitrogen impurities while producing only minimal amounts of aromatics, thus increasing the alkane content in the raffinate. Compared to direct extraction from straight-run diesel, the method of this invention for producing low-carbon olefin feedstock has a higher raffinate yield, while reducing the impact of sulfur and nitrogen impurities on the extraction solvent, and minimizing energy and material consumption and solvent loss during solvent purification. Furthermore, compared to traditional hydrorefining techniques, the raffinate produced using this method has a higher alkane content, making it more suitable as a feedstock for low-carbon olefin production.

[0036] 4. The method of the present invention utilizes diesel fuel to produce high-quality low-carbon olefin cracking feedstock while simultaneously providing feedstock for hydrocracking or catalytic cracking, and also produces high-octane gasoline or BTX light components. Attached Figure Description

[0037] Appendix Figure 1 The diagram shows a diesel hydrogenation reaction system with two moving bed reactors provided by the present invention, but the present invention is not limited to two reactors.

[0038] 1 is moving bed reactor 1, 2 is moving bed reactor 2, 3 is regeneration reactor, 4 is vapor-liquid separator, 5 is extraction tower, 6 is solvent recovery tower, 7 is upper hopper of reactor 1, 8 is lower hopper of reactor 1, 9 is upper hopper of reactor 2, 10 is lower hopper of reactor 2, 11 is upper hopper of regeneration reactor, 12 is lower hopper of regeneration reactor, 13 is reactant, 14 is post-reaction gas, 15 is extraction feedstock, 16 is extraction solvent, 17 is raffinate oil rich in alkane, 18 is extracted oil rich in aromatics, and 19 is diesel fraction rich in aromatics. Detailed Implementation

[0039] The method provided by the present invention will be further described below with reference to the accompanying drawings and embodiments, but this does not limit the present invention.

[0040] Figure 1 This is a schematic flow diagram illustrating one embodiment of a method for producing low-carbon olefin feedstock using a moving bed diesel hydrogenation reaction system according to the present invention. Many pieces of equipment, such as pumps, heat exchangers, compressors, extraction section washing towers, and dehydration towers, are omitted from the diagram, but these are well-known to those skilled in the art. Figure 1 As shown:

[0041] The process of the method provided by this invention is described in detail below:

[0042] Reactant 13 enters moving bed reactor 1 for desulfurization, denitrification, olefin saturation, and moderate aromatic saturation reactions. Moderate aromatic saturation primarily involves the hydrogenation of polycyclic aromatic hydrocarbons (PAHs) to monocyclic aromatic hydrocarbons (MAHs). Reactant exiting the lower part of moving bed reactor 1 enters moving bed reactor 2, and reactant exiting the lower part of moving bed reactor 2 enters gas-liquid separator 4. Post-reaction gas 14 enters the hydrogen recovery system, while the liquid phase stream, as extraction feedstock 15, enters the lower part of extraction tower 5. Extraction solvent 9 enters the upper part of extraction tower 5 for countercurrent exchange extraction. Due to the extraction of a large amount of aromatics, the raffinate oil, rich in alkane, distilled from the top of the extraction tower, has a low aromatic content and a high alkanes content. Furthermore, after the alkane-rich raffinate oil undergoes solvent adsorption via activated carbon or molecular sieves (not shown in the figure), the sulfur and nitrogen heteroatom content is ≤10 μg / g, the alkanes content is increased by more than 8% by mass compared to the feedstock, and the aromatic content is less than 15% by mass, making it a high-quality feedstock for ethylene cracking. The aromatic-rich extracted oil 18 distilled from the bottom of extraction tower 5 enters solvent recovery tower 6. After heating and distillation, the separated extraction solvent 16 is discharged from the bottom of the tower and returned to extraction tower 5 for recycling. The aromatic extracted oil 19 discharged from the top of solvent recovery tower 6 can be directly used as feedstock for hydrocracking or catalytic cracking to produce high-octane gasoline or BTX light components.

[0043] The regenerated catalyst exiting from the lower hopper 12 of the regeneration reactor 3 enters the upper hopper 9 of the moving bed reactor 2, where it contacts the reactants. The reacted catalyst then enters the lower hopper 10 from the bottom of the moving bed reactor 2, and is then conveyed to the upper hopper 7 of the moving bed reactor 1, where it contacts the reactants again. The reacted catalyst then enters the lower hopper 8 from the bottom of the moving bed reactor 1, and is then conveyed to the upper hopper 11 of the regeneration reactor 3, where it is regenerated. The regenerated catalyst then enters the lower hopper 12 from the regeneration reactor 3, thus completing the catalyst circulation process.

[0044] The hydrotreating protectant and hydrorefining catalyst used in the examples can be prepared according to existing technology or obtained commercially. For example, they can be one or more of the commercial hydrorefining catalysts with the brand names RS-2000, RS-2100, and RS-2200 purchased from China Petroleum & Chemical Corporation. In the examples of this invention, RS-2200 is used exemplarily as a diesel hydrorefining catalyst, and this should not be construed as a limitation of the invention by those skilled in the art.

[0045] In this embodiment, two typical diesel fuels were selected as feedstocks and denoted as feedstock A. The main properties of the feedstocks are shown in Table 1.

[0046] Table 1 Properties of Crude Oil

[0047]

[0048]

[0049] Example 1

[0050] Oil A is used as feedstock and mixed with hydrogen before entering a moving bed diesel hydrotreating system. The moving bed diesel hydrotreating system consists of two moving bed reactors. Oil A and hydrogen enter the moving bed reactors under the following operating conditions: reaction temperature 400℃, hydrogen partial pressure 1.6 MPa, feedstock volume hourly space velocity (VHSV) 1.5 h⁻¹, and hydrogen / oil volume ratio 300:1. The reactor effluent undergoes gas-liquid separation in a separator. The gas phase returns to the reactor inlet, while the liquid phase, with total sulfur and nitrogen content <300 μg / g, enters an extraction tower. Solvent extraction is performed using an ionic liquid of 1-hexyl-4-methylpyridine hexafluorophosphate at a mass ratio of 3:1 to the liquid phase stream. The raffinate is then passed through activated carbon to adsorb the solvent, yielding raffinate oil, which can be used as a high-quality feedstock for ethylene cracking. Its properties are shown in Table 3. The extracted phase obtained after separating the raffinate is subjected to vacuum distillation to obtain raffinate oil, which can be directly used as feedstock for hydrocracking or catalytic cracking to produce high-octane gasoline or BTX light components.

[0051] The hydrorefining catalyst is recycled between two moving bed reactors and a regeneration reactor.

[0052] After ionic liquid extraction, the sulfur and nitrogen content increases, requiring purification. The energy and material consumption and solvent loss involved in ionic liquid extraction are positively correlated with the sulfur and nitrogen content in the raw materials. The energy consumption in this embodiment is the baseline.

[0053] Example 2

[0054] Oil A is used as feedstock and mixed with hydrogen before entering a moving bed diesel hydrotreating system. The moving bed diesel hydrotreating system consists of two moving bed reactors. Oil A and hydrogen enter the moving bed reactors under the following operating conditions: reaction temperature 380℃, hydrogen partial pressure 1.6 MPa, feedstock volume hourly space velocity (VHSV) 1.5 h⁻¹, and hydrogen / oil volume ratio 300:1. The reactor effluent undergoes gas-liquid separation in a separator. The gas phase returns to the reactor inlet, while the liquid phase, with sulfur and nitrogen content both <300 μg / g, enters an extraction tower. Solvent extraction is performed using an ionic liquid of 1-hexyl-4-methylpyridine hexafluorophosphate at a mass ratio of 4:1 to the liquid phase stream. The raffinate is then passed through activated carbon to adsorb the solvent, yielding raffinate oil, which can be used as a high-quality feedstock for ethylene cracking. Its properties are shown in Table 3. The extracted phase obtained after separating the raffinate is subjected to vacuum distillation to obtain raffinate oil, which can be directly used as feedstock for hydrocracking or catalytic cracking to produce high-octane gasoline or BTX light components.

[0055] The hydrorefining catalyst is recycled between two moving bed reactors and a regeneration reactor.

[0056] After ionic liquid extraction, the sulfur and nitrogen content increases, requiring purification. The energy and material consumption and solvent loss involved in ionic liquid extraction are positively correlated with the sulfur and nitrogen content in the raw materials. The energy consumption in this embodiment is the baseline.

[0057] Example 3

[0058] Oil A is used as feedstock and mixed with hydrogen before entering a moving bed diesel hydrotreating system. The moving bed diesel hydrotreating system consists of two moving bed reactors. Oil A and hydrogen enter the moving bed reactors under the following operating conditions: reaction temperature 400℃, hydrogen partial pressure 3.2 MPa, feedstock volume hourly space velocity (VHSV) 1.5 h⁻¹, and hydrogen / oil volume ratio 300:1. The reactor effluent undergoes gas-liquid separation in a separator. The gas phase returns to the reactor inlet, while the liquid phase, with total sulfur and nitrogen content <300 μg / g, enters an extraction tower. Solvent extraction is performed using an ionic liquid of 1-hexyl-4-methylpyridine hexafluorophosphate at a mass ratio of 5:1 to the liquid phase stream. The raffinate is then passed through activated carbon to adsorb the solvent, yielding raffinate oil, which can be used as a high-quality feedstock for ethylene cracking. Its properties are shown in Table 3. The extracted phase obtained after separating the raffinate is subjected to vacuum distillation to obtain raffinate oil, which can be directly used as feedstock for hydrocracking or catalytic cracking to produce high-octane gasoline or BTX light components.

[0059] The hydrorefining catalyst is recycled between two moving bed reactors and a regeneration reactor.

[0060] After ionic liquid extraction, the sulfur and nitrogen content increases, requiring purification. The energy and material consumption and solvent loss involved in ionic liquid extraction are positively correlated with the sulfur and nitrogen content in the raw materials. The energy consumption in this embodiment is the baseline * 0.3.

[0061] Comparative Example 1

[0062] Oil A was used as the feedstock, and after passing through a hydrorefining unit, it was directly used as the ethylene feedstock. The hydrorefining process conditions were: reaction temperature 340℃, hydrogen partial pressure 6.4 MPa, feedstock volume hourly space velocity 1.5 h⁻¹, and hydrogen / oil volume ratio 300:1. The reactor effluent underwent gas-liquid separation in a separator. The gas phase was returned to the reactor inlet, while the liquid phase, with a total sulfur and nitrogen content of <300 μg / g, was used as the ethylene feedstock. The properties are shown in Table 3.

[0063] Comparative Example 2

[0064] Using oil A as feedstock, the feedstock bypasses the hydrorefining unit and directly enters the solvent extraction unit. Solvent extraction is performed using an ionic liquid of 1-hexyl-4-methylpyridine hexafluorophosphate at a mass ratio of 3:1 to the liquid phase. The raffinate is then passed through activated carbon to adsorb the solvent, yielding a high-quality feedstock for ethylene cracking, the properties of which are shown in Table 3. The extracted phase obtained after separating the raffinate is subjected to vacuum distillation to obtain an extractable oil that can be directly used as feedstock for hydrocracking or catalytic cracking to produce high-octane gasoline or BTX light components.

[0065] After ionic liquid extraction, the sulfur and nitrogen content increases, requiring purification. The energy and material consumption and solvent loss involved in ionic liquid extraction are positively correlated with the sulfur and nitrogen content in the raw materials. The energy consumption in this comparative example is the baseline * 10.

[0066] Comparative Example 3

[0067] Using oil A as the feedstock, the feedstock is directly used as ethylene feed after passing through a hydrorefining unit. The hydrorefining process conditions are: reaction temperature 340℃, hydrogen partial pressure 6.4 MPa, and feedstock volume hourly space velocity 1.5 h⁻¹. -1 The hydrogen / oil volume ratio is 300:1. The reactor effluent undergoes gas-liquid separation in the separator. The gas phase returns to the reactor inlet, while the liquid phase, with total sulfur and nitrogen content both <300 μg / g, enters the extraction tower. Solvent extraction is performed using an ionic liquid of 1-hexyl-4-methylpyridine hexafluorophosphate at a mass ratio of 3:1 to the liquid phase stream. The raffinate is then purified by solvent adsorption on activated carbon to obtain raffinate oil, which can be used as a high-quality feedstock for ethylene cracking. Its properties are shown in Table 3. The extracted phase obtained after separating the raffinate is subjected to vacuum distillation to obtain extracted oil, which can be directly used as feedstock for hydrocracking or catalytic cracking to produce high-octane gasoline or BTX light components.

[0068] After ionic liquid extraction, the sulfur and nitrogen content increases, requiring purification. The energy and material consumption and solvent loss involved in ionic liquid extraction are positively correlated with the sulfur and nitrogen content in the raw materials. The energy consumption in this comparative example is the baseline * 0.4.

[0069] Comparative Example 4

[0070] Other conditions were the same as in Example 3, except that the reaction temperature of the hydrorefining unit was 340°C.

[0071] Table 2 Hydrorefining Process Conditions and Properties of Products After Hydrorefining

[0072]

[0073]

[0074] Table 3 Solvent extraction process conditions and properties of residual oil

[0075]

[0076] As shown in Tables 2 and 3, when hydrogenation is performed using a conventional hydrogenation scheme, the product after hydrogenation is not extracted (Comparative Example 1), and the alkane content of diesel is only 46.7%, which is not an ideal feedstock for low-carbon olefin cracking.

[0077] Comparative Example 2 involved direct extraction of diesel feedstock without hydrogenation. The resulting raffinate contained 56.6% alkanes, an increase of 10.9 percentage points compared to the feedstock. However, the raffinate yield was only 79%, 2% lower than the equivalent increase in alkanes content achieved in Example 2, and more than 2 percentage points lower than the equivalent increases in raffinate yield achieved in Examples 1 and 3. Furthermore, because Comparative Example 2 did not involve hydrogenation, a large amount of sulfur and nitrogen compounds were extracted into the solvent, resulting in solvent purification energy consumption more than eight times that of Examples 1-3.

[0078] Comparative Example 3 uses conventional fixed-bed hydrogenation followed by solvent extraction of the hydrogenated product. Although the raffinate yield is relatively high, the increase in alkane content is only 7.5 percentage points, which is 3.3 to 5.7 percentage points lower than the increase in alkane content in Examples 1 to 3. It is not an ideal feedstock for low-carbon olefin cracking, and the chemical hydrogen consumption is high, 0.17% to 0.28% higher than in Examples 1 to 3. The process of producing ethylene cracking feedstock using this method is not economically viable.

[0079] Although the hydrogenation process in Comparative Example 4 used low pressure, the temperature did not meet the requirements of the formula. Despite employing a method of hydrogenation followed by extraction, a large amount of sulfur and nitrogen compounds remained during the hydrogenation purification reaction, leading to a significant increase in energy consumption during the extraction process. Compared to Examples 1-3, the increase in alkane content was 1 to 3.4 percentage points lower.

Claims

1. A method for processing diesel feedstock based on a moving bed hydrogenation reaction system, characterized in that, Using diesel feedstock as raw material, hydrorefining and solvent extraction are carried out sequentially to produce low-carbon olefin cracking feedstock and hydrocracking / catalytic cracking feedstock. The hydrorefining process employs a moving bed hydrorefining reaction system. This system comprises one or more moving bed reactors, with the flow direction of the hydrorefining catalyst opposite to that of the feedstock oil and hydrogen. When the moving bed hydrorefining reaction system consists of multiple moving bed reactors, the feedstock oil and hydrogen flow sequentially from the first moving bed reactor to the last, contacting the hydrorefining catalyst in each reactor. The hydrorefining product then enters subsequent processing units. The catalyst flows sequentially from the last moving bed reactor to the first moving bed reactor, and then through a regeneration reactor. The regenerated catalyst then enters from the last moving bed reactor. The processing method specifically includes the following steps: S1. The diesel feedstock and hydrogen undergo a hydrorefining reaction in the moving bed hydrotreating system to remove sulfur and nitrogen, and achieve olefin saturation and partial hydrogenation saturation of aromatics; the hydrorefining operation conditions satisfy T≥2.0345P. 3 -29.297P 2 +144.79P+135 and T≥355℃; where T is the weighted average reaction temperature of the hydrogenation reactor in ℃, and P is the hydrogen partial pressure at the inlet of the hydrogenation reactor in MPa. S2. The hydrorefined product obtained in step S1 is fed into an extraction tower for extraction to obtain raffinate oil rich in alkane and extract oil rich in aromatics; the raffinate oil is used as feedstock for low-carbon olefin cracking. S3. The aromatic-rich extracted oil is separated to obtain an aromatic-rich diesel fraction, which is directly used as feedstock for hydrocracking / catalytic cracking to produce high-octane gasoline or BTX light components. The hydrogenation purification reaction conditions described in step S1 are: hydrogen partial pressure 1.2–3.2 MPa, temperature <420℃, and liquid hourly space velocity 0.2–8.0 h⁻¹. -1 The hydrogen-to-oil volume ratio is 100-1000:1, and the relationship between temperature and pressure always satisfies the temperature-pressure relationship formula in step S1.

2. The method according to claim 1, characterized in that: The hydrorefining catalyst is a supported catalyst containing a Group VIB and / or Group VIII active metal component, and the support is an alumina and / or silica support; or, the hydrorefining catalyst is a non-supported catalyst containing a Group VIB and / or Group VIII active metal component.

3. The method according to claim 1, characterized in that: In step S1, the aromatic saturation rate in the hydrorefined product is less than 10%.

4. The method according to claim 1, characterized in that: The regenerated catalyst is not pre-sulfurized and is directly added to the reactor.

5. The method according to claim 1, characterized in that: In step S2, the extraction solvent is an organic solvent with a vaporization temperature of not less than 380°C under normal pressure.

6. The method according to claim 5, characterized in that: 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 hexafluorophosphate.

7. The method according to claim 5, characterized in that: The extraction solvent is one or more of the following ionic liquids: 1-heptyl-4-methylpyridine tetrafluoroborate, 1-heptyl-4-methylpyridine hexafluorophosphate, 1-heptyl-3-methylimidazolium tetrafluoroborate, 1-heptyl-3-methylimidazolium hexafluoroborate, 1-hexyl-4-methylpyridine tetrafluoroborate, and 1-hexyl-4-methylpyridine hexafluorophosphate.

8. The method according to claim 1, characterized in that: The mass ratio of the extraction solvent to the hydrogenated 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℃.

9. The method according to claim 1, characterized in that: In step S2, the hydrorefining product is introduced from the bottom of the aromatics extraction tower, where it comes into countercurrent contact with the extraction solvent flowing from top to bottom. A raffinate oil low in aromatics is obtained from the top of the tower, while an extract oil rich in aromatics and solvent is obtained from the bottom. The raffinate oil low in aromatics is washed with water or adsorbed to separate trace amounts of solvent, yielding a high-quality ethylene cracking feedstock. The extract oil rich in aromatics is sent to a distillation tower to recover the solvent. A stream rich in aromatics is obtained from the top of the distillation tower, while a solvent stream with an aromatics content of less than 0.5% by mass is obtained from the bottom. This solvent stream is returned to the top of the aromatics extraction tower in step S2 for recycling.

10. The method according to claim 9, characterized in that: The adsorbent used for the adsorption and separation of trace amounts of solvent from the raffinate oil is either activated carbon or molecular sieve.

11. The method according to claim 1, characterized in that: In step S2, the sulfur and nitrogen content in the alkane-rich raffinate is ≤10μg / g, the alkane content is more than 8wt% higher than that of diesel feedstock, and the aromatic content is less than 15wt%.

12. The method according to claim 1, characterized in that: In step S3, the solvent in the extracted oil is separated by distillation. A diesel fraction rich in aromatics is obtained at the top of the column, and the extraction solvent is obtained at the bottom of the column and recycled.

13. The method according to claim 1, characterized in that: The diesel feedstock is selected from one or more of the following: straight-run diesel, catalytic cracking diesel, coking diesel, diesel fraction of direct coal liquefaction oil, and diesel fraction of coal tar.

14. The method according to claim 1, characterized in that: The diesel feedstock has a distillation range of 150-400℃, an alkane content of ≥40% by mass, and a total aromatic content of ≤40% by mass.

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