A method for producing chemical raw materials by hydrocracking diesel oil

Abstract

The present invention discloses a method for producing chemical raw materials by diesel hydrocracking. The method includes: (1) in the presence of hydrogen, a diesel raw material is mixed with hydrogen and enters a first hydrocracking reaction zone for first hydrocracking, and the mass content of C7 + n-alkanes in the first hydrocracking product is controlled to be 1 wt% to 3 wt%; (2) the reaction effluent from step (1) enters a second hydrocracking reaction zone to perform selective ring-opening cracking on polycyclic hydrocarbons to obtain a second hydrocracking product; the hydrogen-rich gas obtained after the gas-liquid separation of the second hydrocracking product through a separator is used as recycle hydrogen, and the liquid phase enters a fractionation system for fractionation to obtain gas, light naphtha, heavy naphtha and tail oil; (3) the tail oil is mixed with hydrogen and enters a third hydrocracking reaction zone to obtain a third hydrocracking product containing monocyclic hydrocarbons, and the third hydrocracking product enters a separation and fractionation system. This method can significantly improve the yield and quality of chemical raw materials.

Description

Technical Field

[0001] The present invention belongs to the field of hydrocarbon oil hydrocracking, and particularly relates to a method for producing chemical raw materials by diesel hydrocracking. Background Art

[0002] Ethylene is the leading product in petrochemical industry. The level of its cost plays a decisive role in the competitiveness of petrochemical enterprises. The selection of ethylene cracking feedstock has a great impact on cost, and the raw material cost accounts for a very high proportion in the production cost of ethylene. Generally, depending on the raw material, it accounts for about 60% - 80% of the total ethylene production cost. Thus, it can be seen that ethylene feedstock is of great significance in the development of ethylene industry, and the optimization of ethylene feedstock plays a crucial role in reducing the cost of petrochemical products.

[0003] CN201580070326.4 discloses a method for preparing LPG and BTX, including: a) subjecting a mixed hydrocarbon stream to a first hydrocracking in the presence of a first hydrocracking catalyst to prepare a first hydrocracking product stream; b) separating the first hydrocracking product stream to provide at least one light hydrocarbon stream containing at least C2 and C3 hydrocarbons, an intermediate hydrocarbon stream composed of C4 and / or C5 hydrocarbons, and a heavy hydrocarbon stream containing at least C6+ hydrocarbons, and c) subjecting the heavy hydrocarbon stream to a second hydrocracking in the presence of a second hydrocracking catalyst to prepare a second hydrocracking product stream containing BTX, wherein the second hydrocracking is more severe than the first hydrocracking, d) wherein, in the presence of a C4 hydrocracking catalyst, at least part of the intermediate hydrocarbon stream is subjected to C4 hydrocracking to prepare a C4 hydrocracking product stream, and the C4 hydrocracking is optimized for converting C4 hydrocarbons into C3 hydrocarbons.

[0004] CN201480037272.7 discloses a method for producing light olefin hydrocarbon compounds from a hydrocarbon raw material, including the following steps: (a) feeding the hydrocarbon raw material to a reaction zone for ring opening; (b) separating the reaction product generated from the reaction zone into an overhead stream and a side stream; (c) feeding the side stream from (b) to a gasoline hydrocracker (GHC) unit; (d) separating the reaction product of the GHC in step (c) into an overhead stream containing hydrogen, methane, ethane and liquefied petroleum gas and a stream containing aromatic hydrocarbon compounds and a small amount of hydrogen and non-aromatic hydrocarbon compounds; (e) feeding the overhead stream from the gasoline hydrocracker (GHC) unit to a steam cracker unit.

[0005] The above methods are mainly used for producing LPG and BTX. At the same time, when producing ethylene feedstock, the content of normal paraffins in the ethylene feedstock is low, which will also result in a relatively low triolefin yield in the steam cracking to ethylene unit. Therefore, it is of great significance to develop a hydrocracking method suitable for producing high-quality chemical raw materials from diesel as the raw material. Summary of the Invention

[0006] In response to the problems of the prior art, the present invention aims to provide a method for producing chemical raw materials by hydrocracking diesel. This method uses diesel as a raw material to produce chemical raw materials by hydrocracking, which can significantly improve the yield and quality of chemical raw materials (i.e., ethylene raw materials and reforming raw materials).

[0007] The present invention provides a method for producing chemical raw materials by hydrocracking diesel, wherein the method uses diesel as a raw material to produce chemical raw materials by hydrocracking, wherein the chemical raw materials are ethylene raw materials and reforming raw materials, wherein the method comprises:

[0008] (1) In the presence of hydrogen, the diesel feedstock is mixed with hydrogen and enters the first hydrocracking reaction zone for the first hydrocracking, and the C7 + The mass content of normal alkanes is 1wt% to 3wt%;

[0009] (2) The reaction effluent from step (1) enters a second hydrocracking reaction zone, where bicyclic or higher cyclic hydrocarbons are subjected to selective ring-opening cracking to obtain a second hydrocracking product; the second hydrocracking product is subjected to gas-liquid separation in a separator to obtain hydrogen-rich gas, which is used as circulating hydrogen, and the liquid phase enters a fractionation system for fractionation to obtain gas, light naphtha, heavy naphtha, and tail oil;

[0010] (3) The tail oil in step (2) is mixed with hydrogen and enters the third hydrocracking reaction zone to obtain a third hydrocracking product containing monocyclic cyclic hydrocarbons. The third hydrocracking product enters the separation and fractionation system to obtain gas, light naphtha, and heavy naphtha.

[0011] Preferably, the reaction pressure of the first hydrocracking reaction zone in step (1) is 0.5 to 5 MPa higher than the reaction pressure of the third hydrocracking reaction zone in step (3).

[0012] According to the present invention, preferably, the reaction pressure of the first hydrocracking reaction zone in step (1) is 0.5 to 3.0 MPa higher than the reaction pressure of the third hydrocracking reaction zone in step (3).

[0013] According to the present invention, the reaction conditions of the first hydrocracking reaction zone in step (1) are as follows: the reaction pressure is 6 to 13 MPa, preferably 8 to 10 MPa.

[0014] According to the present invention, the reaction conditions of the first hydrocracking reaction zone in step (1) are as follows: the average reaction temperature is 250-450°C, preferably 300-400°C; the liquid hourly volume space velocity is 0.1-15.0h -1 , preferably 1.0~5.0h -1 ; The volume ratio of hydrogen to oil is 100:1 to 2500:1, preferably 400:1 to 2000:1.

[0015] According to the present invention, in the diesel raw material described in step (1), the mass content of n-alkanes is 5% to 60%, preferably 10% to 40%.

[0016] According to the present invention, in the diesel raw material described in step (1), the mass content of cyclic hydrocarbons is 30% to 80%, and the cyclic hydrocarbons are the sum of naphthenes and aromatics.

[0017] According to the present invention, in step (1), the diesel can be straight-run diesel, coking diesel and other diesel fractions with a relatively high content of n-alkanes. The content of n-alkanes in the diesel is 10% to 60%, preferably 20% to 50%; the initial boiling point is 180°C to 280°C, preferably 200°C to 260°C; the final boiling point is 300°C to 400°C, preferably 340°C to 380°C.

[0018] According to the present invention, in step (1), the diesel may contain impurities such as sulfur and nitrogen. According to actual needs, a hydrofining catalyst may be provided upstream of the first hydrocracking catalyst to remove impurities such as sulfur and nitrogen. Among them, the nitrogen content in the reaction stream in contact with the first hydrocracking catalyst is preferably below 50 mg / kg, and more preferably below 20 mg / kg.

[0019] According to the present invention, in step (1), the first hydrocracking reaction zone is filled with a first hydrocracking catalyst. The first hydrocracking catalyst can be one or more catalysts.

[0020] According to the present invention, in step (1), a conventional hydrofining catalyst can be used for the hydrofining catalyst provided upstream of the first hydrocracking catalyst, which is mainly used for hydrodesulfurization and removal of impurities such as nitrogen. The hydrofining catalyst includes a carrier and a hydroactive metal. The carrier is an inorganic refractory oxide, generally selected from one or several of alumina, amorphous silica-alumina, silica or titanium oxide, etc.; the hydroactive metal includes Group VIB and / or Group VIII metal components. In the hydrofining catalyst, Group VIB is preferably selected from tungsten and / or molybdenum, and its content in the catalyst based on the mass of the oxide is 5% to 30%, preferably 10% to 20%; Group VIII is preferably selected from nickel and / or cobalt, and its content in the catalyst based on the mass of the oxide is 1% to 6%, preferably 1.5% to 5%. The content of the carrier in the catalyst based on the mass of the oxide is 64% to 94%, preferably 75% to 88.5%.

[0021] According to the present invention, in step (1), the first hydrocracking catalyst comprises an active metal component and a carrier; the carrier comprises a molecular sieve having selective cracking of normal paraffins, preferably selected from one or more of ZSM-5 molecular sieve, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35 and ZSM-38 molecular sieves, preferably ZSM-5 molecular sieve. The carrier may further comprise a binder. Preferably, the binder is alumina. The active metal component comprises at least one of metals of Group VIB and Group VIII, the metal of Group VIB is preferably molybdenum and / or tungsten, and the metal of Group VIII is preferably cobalt and / or nickel.

[0022] According to the present invention, in step (1), preferably, in the first hydrocracking catalyst, based on the weight of the catalyst, the content of the metal of Group VIB (calculated as the oxide) is 5.0% to 15.0%, the content of the metal of Group VIII (calculated as the oxide) is 2.0% to 5.0%, and the content of the carrier is 80.0% to 93.0%.

[0023] According to the present invention, in step (1), preferably, in the carrier of the first hydrocracking catalyst, based on the weight of the carrier, the content of the binder is 8% to 60%, and the content of the molecular sieve is 40% to 92%.

[0024] According to the present invention, in step (1), the specific surface area of the first hydrocracking catalyst is 200 - 400 m 2 / g, and the pore volume is 0.25 - 0.45 mL / g.

[0025] According to the present invention, in step (1), the preparation method of the first hydrocracking catalyst can be prepared according to the conventional methods in the art. The preparation method includes the preparation of the carrier and the loading of the active metal component. The process of preparing the carrier is as follows: the shape-selective cracking molecular sieve and the binder are mechanically mixed, formed, and then dried and calcined to make the catalyst carrier. The drying and calcining of the carrier can adopt conventional conditions. The conditions for drying are: drying at 100°C - 150°C for 1 - 12 hours. The conditions for calcining are: calcining at 450°C - 550°C for 2.5 - 6.0 hours.

[0026] According to the present invention, in step (1), in the preparation method of the first hydrocracking catalyst, the method for loading the active metal component is a conventional method, such as kneading method, impregnation method, etc., preferably impregnation method. The impregnation method can be saturated impregnation method, excess impregnation method or complex impregnation method, that is, the catalyst carrier is impregnated with a solution containing the required active component, and then dried and calcined to obtain the first hydrocracking catalyst. The conditions for drying are: drying at 100°C - 150°C for 1 - 12 hours. The conditions for calcining are: calcining at 450°C - 550°C for 2.5 - 6.0 hours.

[0027] According to the present invention, the content of bicyclic and higher aromatic hydrocarbons in the second hydrocracking product of step (2) is 0.1 wt% to 1 wt%, preferably 0.2 wt% to 0.5 wt%.

[0028] According to the present invention, the separation and fractionation of the second hydrocracking product in step (2) and the third hydrocracking product in step (3) preferably share a set of separation and fractionation systems.

[0029] According to the present invention, in step (2), the reaction conditions in the second hydrocracking reaction zone are as follows: the reaction pressure is 6 to 13 MPa, preferably 8 to 10 MPa.

[0030] According to the present invention, in step (2), the reaction conditions for the second hydrocracking reaction are as follows: the average reaction temperature is 250 to 450 °C, preferably 300 to 400 °C; the liquid hourly space velocity is 0.1 to 15.0 h -1 [[ID=IS13]]-1, preferably 1.0 to 5.0 h -1 ; the hydrogen-oil volume ratio is 100:1 to 2500:1, preferably 400:1 to 2000:1.

[0031] According to the present invention, preferably, the first hydrocracking reaction zone and the second hydrocracking reaction zone adopt the same reaction pressure.

[0032] According to the present invention, in step (2), the second hydrocracking reaction zone is filled with a second hydrocracking catalyst. The second hydrocracking catalyst can be one or more catalysts.

[0033] According to the present invention, in step (3), the third hydrocracking reaction zone is filled with a third hydrocracking catalyst. The third hydrocracking catalyst can be one or more catalysts.

[0034] According to the present invention, the second hydrocracking catalyst in step (2) has the function of ring-opening cracking of polycyclic cyclic hydrocarbons.

[0035] According to the present invention, the third hydrocracking catalyst in step (3) has the function of selectively cracking isoparaffins or the side chains of cyclic hydrocarbons and retaining monocyclic cyclic hydrocarbons.

[0036] According to the present invention, the second hydrocracking catalyst described in step (2) and / or the third hydrocracking catalyst described in step (3) include a cracking component, a hydrogenation component, and a binder. The second hydrocracking catalyst and / or the third hydrocracking catalyst can be commercially available products or prepared according to the prior art. The hydrogenation component is at least one of a metal, a metal oxide, and a metal sulfide of an active metal component; the active metal component includes a Group VIB and / or Group VIII metal; the active metal component is more preferably at least one of iron, chromium, molybdenum, tungsten, cobalt, and nickel. The binder is alumina and / or silica; the cracking component includes an acidic molecular sieve, preferably at least one of Beta zeolite and Y zeolite.

[0037] According to the present invention, further preferably, the cracking component of the second hydrocracking catalyst in step (2) is Y zeolite.

[0038] According to the present invention, further preferably, the cracking component of the third hydrocracking catalyst in step (3) is Beta zeolite.

[0039] According to the present invention, in the second hydrocracking catalyst described in step (2) and / or the third hydrocracking catalyst described in step (3), based on the mass of the catalyst, the content of the hydrogenation component calculated as the oxide is 5 wt% to 40 wt%, preferably 10 wt% to 30 wt%; the content of the cracking component is 10 wt% to 80 wt%, preferably 20 wt% to 60 wt%; the content of the binder is 5 wt% to 85 wt%, preferably 10 wt% to 50 wt%.

[0040] According to the present invention, the preparation method of the second hydrocracking catalyst described in step (2) and / or the third hydrocracking catalyst described in step (3) can be prepared according to the conventional methods in the art. The preparation method includes the preparation of a support and the loading of a hydrogenation component, and the preparation process of the support is as follows: the cracking component and the binder are mechanically mixed, formed, and then dried and calcined to make a catalyst support. The drying and calcination of the support can adopt conventional conditions. The conditions for drying are: drying at 100°C to 150°C for 1 to 12 hours. The conditions for calcination are: calcining at 450°C to 550°C for 2.5 to 6.0 hours.

[0041] According to the present invention, in the preparation method of the second hydrocracking catalyst described in step (2) and / or the third hydrocracking catalyst described in step (3), the method for loading the hydrogenation component is a conventional method, such as kneading method, impregnation method, etc., and the impregnation method is preferred. The impregnation method can be saturated impregnation method, excess impregnation method or complex impregnation method, that is, impregnating the catalyst carrier with a solution containing the required hydrogenation component, and then drying and calcining to obtain a hydrocracking catalyst. The conditions for the drying are: drying at 100°C to 150°C for 1 to 12 hours. The conditions for the calcination are: calcining at 450°C to 550°C for 2.5 to 6.0 hours.

[0042] According to the present invention, in the third hydrocracking product of step (3), the mass ratio of the C6 - C8 monocyclic cyclic hydrocarbons to the total cyclic hydrocarbons in the raw material is 0.20 to 0.40, preferably 0.30 to 0.37.

[0043] According to the present invention, the reaction conditions in the third hydrocracking reaction zone of step (3) are as follows: the reaction pressure is 3 to 10 MPa, preferably 4 to 8 MPa.

[0044] According to the present invention, the reaction conditions in the third hydrocracking reaction zone of step (3) are as follows: the average reaction temperature is 250 to 450°C, preferably 300 to 400°C; the liquid hourly space velocity is 0.1 to 15.0 h -1 , preferably 1.0 to 5.0 h -1 ; the hydrogen-oil volume ratio is 100:1 to 2500:1, preferably 400:1 to 2000:1.

[0045] According to the present invention, the chemical raw materials mainly include ethane, propane, butane, light naphtha, and heavy naphtha. Among them, heavy naphtha is used as a reforming raw material to produce BTX, and ethane, propane, butane, and light naphtha are used as ethylene raw materials to produce light olefins, such as being used as steam cracking raw materials to produce ethylene, and propane and butane can also be directly dehydrogenated to produce propylene and butadiene. Among them, light olefins refer to olefins with four or fewer carbon atoms, especially ethylene, propylene, and butadiene.

[0046] Petroleum hydrocarbons have a complex composition, mainly including alkanes, cycloalkanes and aromatics. High-quality ethylene feedstock is small-molecule normal alkanes, and reforming feedstock is monocyclic cycloalkanes and aromatics. Through research, the inventor found that by passing diesel feedstock successively through the shape-selective cracking of straight-chain alkanes, the ring-opening cracking of polycyclic cyclic hydrocarbons, and the selective hydrocracking of long side chains on isoparaffins or cyclic hydrocarbons, while trying to retain monocyclic cyclic hydrocarbons, small-molecule normal alkanes can be generated with high selectivity, so as to achieve the efficient enrichment of small-molecule normal alkanes in the light olefin feedstock, and at the same time retain monocyclic cyclic hydrocarbons in heavy naphtha as much as possible to achieve the efficient enrichment of high-quality reforming feedstock. In this way, the purpose of greatly improving the yields of chemical feedstocks (i.e., light olefin feedstock and reforming feedstock) and the quality of light olefin feedstock and reforming feedstock can be achieved, and thus the present invention is completed.

[0047] Compared with the prior art, the present invention has the following beneficial technical effects:

[0048] (1) In the hydrocracking method for producing chemical feedstocks from diesel oil of the present invention, the diesel feedstock and hydrogen enter the first hydrocracking reaction zone, mainly selectively cracking the normal alkanes in the feedstock and the long straight chains of isoparaffins and cycloalkanes containing long straight chains to generate small-molecule normal alkanes, so that the content of C7 + normal alkanes in the effluent of the first hydrocracking reaction is 1 wt% to 3 wt%. The effluent of the first hydrocracking reaction enters the second hydrocracking reaction zone, mainly to crack the polycyclic cyclic hydrocarbons by ring opening while retaining monocyclic cyclic hydrocarbons and further break the side chains in each hydrocarbon to generate small-molecule hydrocarbons. In this way, a large amount of the linear alkanes in the feedstock can be converted into gas and light naphtha components, that is, enriched in the ethylene feedstock, while the monocyclic cyclic hydrocarbons are retained in the heavy naphtha fraction, that is, enriched in the reforming feedstock. Through simple fractionation, the efficient separation of alkanes and cyclic hydrocarbons can be achieved, increasing the production of high-quality ethylene cracking feed while improving the quality of heavy naphtha as a catalytic reforming feed.

[0049] (2) The content of monocyclic cyclic hydrocarbons in the heavy naphtha obtained by the method of the present invention is high. As the feed for the catalytic reforming unit, the alkane cyclization and dehydrogenation unit in the catalytic reforming unit can be cancelled, which can greatly reduce the investment and energy consumption of the catalytic reforming unit; at the same time, since the hydrocracking reaction follows the positive carbon ion reaction mechanism, the side chain breaking reaction of cyclic hydrocarbons above C9 can be selectively achieved, so that the C6-C8 cyclic hydrocarbons in the product have a high enrichment degree, and the BTX yield can be greatly increased after catalytic reforming and aromatics extraction.

[0050] (3) The present invention selectively converts the alkanes in diesel into small - molecule alkanes. This process consumes a certain amount of hydrogen. However, as a raw material for the ethylene plant, light hydrocarbons also have a high hydrogen production rate, and the lower the carbon number, the higher the hydrogen production rate. Therefore, most of the hydrogen consumed in the hydrogenation process can be recovered after passing through the ethylene plant. At the same time, as an ethylene raw material, light hydrocarbons can significantly increase the yields of ethylene, propylene, and butadiene, and extend the cleaning cycle of the ethylene plant, significantly improving the economic benefits of the plant. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 is a process flow schematic diagram of the process method of the present invention;

[0052] MAIN REFERENCE NUMERAL DESCRIPTION:

[0053] 1 - Diesel, 2 - Hydrogen, 3 - First hydrocracking reaction zone, 4 - First hydrocracking reaction effluent, 5 - Second hydrocracking reaction zone, 6 - Second hydrocracking reaction effluent, 7 - Separator, 8 - Hydrogen - rich gas in the gas - phase stream, 9 - Liquid - phase stream, 10 - Fractionating tower, 11 - Gas fraction, 12 - Light naphtha, 13 - Heavy naphtha, 14 - Tail oil, 15 - Third hydrocracking reaction zone, 16 - Third hydrocracking reaction effluent. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0054] The functions and effects of the present invention will be further illustrated by the following examples, but the following examples do not limit the method of the present invention.

[0055] In the present invention, unless otherwise specified, all percentages, parts, ratios, etc. mentioned in this specification are based on weight, unless it does not conform to the common understanding of those skilled in the art when based on weight.

[0056] In the present invention, the overall volume space velocity in the examples and comparative examples is the ratio of the fresh feed volume to the total volume of the catalyst.

[0057] In the present invention, as Figure 1 shown, it includes: Diesel 1 and hydrogen 2 are mixed and enter the first hydrocracking reaction zone 3 for hydrocracking reaction. The first hydrocracking reaction effluent 4 enters the second hydrocracking reaction zone 5, and the second hydrocracking reaction effluent 6 enters the separator 7. The separated hydrogen - rich gas 8 in the gas - phase stream is recycled. The liquid - phase stream 9 enters the fractionating tower 10, and gas fraction 11, light naphtha 12, heavy naphtha 13, and tail oil 14 are fractionated. Tail oil 14 and hydrogen 2 are mixed and enter the third hydrocracking reaction zone 15, and the third hydrocracking reaction effluent 16 enters the separator 7 for separation and fractionation.

[0058] In the present invention, the first hydrocracking catalyst in each example is represented by Cat-A plus a number, such as Cat-A1, Cat-A2, Cat-A3, and Cat-A4. The first hydrocracking catalyst is prepared by a conventional active metal saturation impregnation method, and the physicochemical properties of the obtained catalyst are shown in Table 1.

[0059] In the present invention, the second hydrocracking catalyst in each example is represented by Cat-B, and the physicochemical properties of the catalyst are shown in Table 2.

[0060] In the present invention, the third hydrocracking catalyst in each example is represented by Cat-C, and the physicochemical properties of the catalyst are shown in Table 2.

[0061] In the present invention, the second hydrocracking catalyst and the third hydrocracking catalyst in each example are prepared by a conventional active metal saturation impregnation method.

[0062] Among them, the properties of the Beta zeolite used in the catalyst Cat-C are as follows: the SiO2 / Al2O3 molar ratio is 30, the specific surface area is 350 m 2 / g, and the pore volume is 0.32 cm 3 / g. The properties of the Y zeolite used in the catalyst Cat-B are as follows: the SiO2 / Al2O3 molar ratio is 15, the specific surface area is 400 m 2 / g, and the pore volume is 0.30 cm 3 / g. The physicochemical properties of the obtained catalyst are shown in Table 2.

[0063] In the present invention, the feedstock oil in each example uses diesel oil as the raw material, and its main properties are shown in Table 3.

[0064] In the present invention, the ethylene feedstock in Table 4 refers to ethane, propane, butane, and light naphtha. It can be used to produce low-carbon olefins.

[0065] In the present invention, the distillation range of light naphtha is the liquid component with a distillation range of less than 60 °C, the distillation range of heavy naphtha is 60 - 175 °C, and the distillation range of the tail oil is the component with a distillation range of >175 °C.

[0066] In the present invention, the yield of the ethylene feedstock refers to the mass ratio of ethane, propane, butane, and light naphtha in the hydrocracking product to the fresh hydrocracking feedstock, and the yield of heavy naphtha refers to the mass ratio of heavy naphtha in the hydrocracking product to the fresh hydrocracking feedstock.

[0067] Examples 1 - 4

[0068] The hydrocracking method described above adopts the following Figure 1 process, including:

[0069] (1) The feedstock oil is mixed with hydrogen and enters the first hydrocracking reaction zone; the first hydrocracking catalyst is loaded in the first hydrocracking reaction zone; in step (1), the content of C7 normal paraffins in the effluent from the first hydrocracking reaction is to be controlled. + The content of normal paraffins.

[0070] [[ID=⑤]](2) The effluent from the first hydrocracking reaction obtained in step (1) enters the second hydrocracking reaction zone, and the second hydrocracking catalyst is loaded in the second hydrocracking reaction zone; a reaction is carried out under the action of the catalyst to obtain the second hydrocracking product. The hydrogen-rich gas obtained after the second hydrocracking product is separated and fractionated is used as recycle hydrogen, and the liquid phase enters the fractionating tower for fractionation to obtain gas, light naphtha, heavy naphtha, and tail oil.

[0071] [[ID=⑧]](3) The tail oil from step (2) enters the third hydrocracking reaction zone, and the third hydrocracking catalyst is loaded in the third hydrocracking reaction zone; the effluent from the third hydrocracking reaction shares a set of separation and fractionation systems with the effluent from the second hydrocracking reaction.

[0072] The process conditions and hydrocracking effects of each example are shown in Table 4.

[0073] Comparative Example 1

[0074] The difference from Example 1 is that: the feedstock oil directly enters the second hydrocracking reaction zone without the first hydrocracking.

[0075] The process conditions and hydrocracking effects in this example are shown in Table 4.

[0076] Comparative Example 2

[0077] The difference from Example 1 is that: in step (1), the content of C7+ normal paraffins in the effluent from the first hydrocracking reaction is controlled to be 4%.

[0078] The process conditions and hydrocracking effects in this example are shown in Table 4.

[0079] Comparative Example 3

[0080] The difference from Example 1 is that: the catalysts in the second and third hydrocracking reaction zones are exchanged. Specifically: the catalyst Cat-C is loaded in the second hydrocracking reaction zone, and the catalyst Cat-B is loaded in the third hydrocracking reaction zone.

[0081] The process conditions and hydrocracking effects in this example are shown in Table 4.

[0082] Comparative Example 4

[0083] The difference from Example 1 is that: the reaction pressure in the first hydrocracking reaction zone is 6 MPa higher than the reaction pressure in the third hydrocracking reaction zone.

[0084] The process conditions and hydrocracking effects in this example are shown in Table 4.

[0085] Table 1 Physical and Chemical Properties of the First Hydrocracking Catalyst

[0086] Catalyst Cat-A1 Cat-A2 Cat-A3 Cat-A4 <![CDATA[Pore volume, cm 3 / g]]> 0.35 0.45 0.25 0.30 <![CDATA[Specific surface area, m 2 / g]]> 300 200 400 350 Content, wt%, based on the weight of the support ZSM-5 58 42 85 75 Aluminum oxide 42 58 15 25 Active metal content in the catalyst, wt% <![CDATA[MoO3]]> 10.0 15.0 5.0 12.5 NiO 3.5 2.0 5.0 4.0 <![CDATA[SiO2 / Al2O3 molar ratio of ZSM-5]]> 40 60 20 50

[0087] Table 2 Physical and Chemical Properties of the Second and Third Hydrocracking Catalysts

[0088] Catalyst properties Cat-C Cat-B <![CDATA[Pore volume, cm 3 / g]]> 0.35 0.35 <![CDATA[Specific surface area, m 2 / g]]> 300 300 Catalyst composition and content Beta, wt% 50 - Y, wt% - 30 <![CDATA[MoO3, wt%]]> 10 20 NiO, wt% 5 5 Aluminum oxide, wt% 35 45

[0089] Table 3 Main Properties of the Feedstock

[0090] Name of feedstock Diesel <![CDATA[Density (20 °C) / kg·m -3 > 836.9 Distillation range / °C (ASTM D86) IBP / 10% 206 / 265 30％ / 50％ 292 / 308 70％ / 90％ 322 / 340 95% / EBP 348 / 353 n-alkane, wt% 26.6 Cyclic hydrocarbon, wt% 56 Nitrogen content, mg / kg 5

[0091] Table 4 Hydrocracking Effect

[0092]

[0093]

[0094] Continued Table 4

[0095]

[0096]

[0097] The specific embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for producing chemical raw materials by hydrocracking of diesel oil, the method comprising: (1) In the presence of hydrogen, the diesel raw material is mixed with hydrogen and enters the first hydrocracking reaction zone for the first hydrocracking, and the mass content of C7 + n-alkanes in the first hydrocracking product is controlled to be in the range of 1 wt% to 3 wt%; (2) The reaction effluent from step (1) enters the second hydrocracking reaction zone to selectively open-loop crack polycyclic hydrocarbons to obtain a second hydrocracking product; The hydrogen-rich gas obtained after the second hydrocracking product is subjected to gas-liquid separation by a separator is used as recycle hydrogen, and the liquid phase enters a fractionation system for fractionation to obtain gas, light naphtha, heavy naphtha and tail oil; (3) The tail oil in step (2) is mixed with hydrogen and enters the third hydrocracking reaction zone to obtain a third hydrocracking product containing monocyclic hydrocarbons, and the third hydrocracking product enters a separation and fractionation system to obtain gas, light naphtha, and heavy naphtha; The reaction pressure in the first hydrocracking reaction zone in step (1) is 0.5 to 5 MPa higher than the reaction pressure in the third hydrocracking reaction zone in step (3); The first hydrocracking reaction zone is filled with a first hydrocracking catalyst; the first hydrocracking catalyst includes an active metal component and a carrier; the carrier includes one or more of ZSM-5 molecular sieve, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35 and ZSM-38 molecular sieves; the active metal component includes at least one of metals of Group VIB and Group VIII; For the first hydrocracking catalyst, based on the weight of the catalyst, the content of the Group VIB metal in terms of oxide is 5.0% to 15.0%, the content of the Group VIII metal in terms of oxide is 2.0% to 5.0%, and the content of the carrier is 80.0% to 93.0%; In the carrier of the first hydrocracking catalyst, based on the weight of the carrier, the content of the molecular sieve is 40% to 92%; The second hydrocracking reaction zone in step (2) is filled with a second hydrocracking catalyst; The third hydrocracking reaction zone in step (3) is filled with a third hydrocracking catalyst; The second hydrocracking catalyst in step (2) and the third hydrocracking catalyst in step (3) include a cracking component, a hydrogenation component and a binder; In the second hydrocracking catalyst in step (2) and / or the third hydrocracking catalyst in step (3), based on the mass of the catalyst, the content of the hydrogenation component in terms of oxide is 5 wt% to 40 wt%; the content of the cracking component is 10 wt% to 80 wt%; the content of the binder is 5 wt% to 85 wt%; The chemical raw materials mainly include ethane, propane, butane, light naphtha and heavy naphtha; among them, heavy naphtha is used as a reforming raw material to produce BTX, and ethane, propane, butane and light naphtha are used as ethylene raw materials to produce light olefins; The cracking component of the second hydrocracking catalyst in step (2) is Y molecular sieve; the cracking component of the third hydrocracking catalyst in step (3) is Beta molecular sieve.

2. The method according to claim 1, wherein The reaction pressure in the first hydrocracking reaction zone in step (1) is 0.5 to 3.0 MPa higher than the reaction pressure in the third hydrocracking reaction zone in step (3).

3. The method according to claim 1, characterized in that, The reaction pressure in the first hydrocracking reaction zone in step (1) is 6 to 13 MPa.

4. The method according to claim 3, wherein In step (1), the reaction pressure in the first hydrocracking reaction zone is 8 to 10 MPa.

5. According to the method described in any one of claims 1-4, characterized in that, The reaction conditions for the first hydrocracking reaction in step (1) are as follows: the average reaction temperature is 250 to 450 °C; and / or, the liquid hourly space velocity is 0.1 to 15.0 h -1 ; and / or, the hydrogen-oil volume ratio is 100:1 to 2500:

1.

6. The method according to claim 5, characterized in that, The reaction conditions of the first hydrocracking reaction in step (1) are as follows: the average reaction temperature is 300~400°C; and / or, the liquid hourly space velocity is 1.0~5.0 h -1 ; and / or, the hydrogen-oil volume ratio is 400:1~2000:

1.

7. The method according to claim 1, wherein In step (2), the reaction pressure in the second hydrocracking reaction zone is 6 to 13 MPa.

8. The method according to claim 7, wherein In step (2), the reaction pressure in the second hydrocracking reaction zone is 8 to 10 MPa.

9. The method according to claim 7 or 1, wherein The reaction conditions in the second hydrocracking reaction zone in step (2) are as follows: the average reaction temperature is 250~450°C; the liquid hourly space velocity is 0.1~15.0 h -1 ; the hydrogen-oil volume ratio is 100:1~2500:

1.

10. The method according to claim 9, characterized in that, The reaction conditions in the second hydrocracking reaction zone in step (2) are as follows: the average reaction temperature is 300 to 400 °C; the liquid hourly space velocity is 1.0 to 5.0 h -1 ; the hydrogen-oil volume ratio is 400:1 to 2000:

1.

11. According to the method described in claim 1, wherein In step (3), the reaction pressure in the third hydrocracking reaction zone is 3 to 10 MPa.

12. The method according to claim 11, wherein In step (3), the reaction pressure in the third hydrocracking reaction zone is 4 to 8 MPa.

13. The method according to claim 1 or 11, characterized in that, In step (3), the reaction conditions in the third hydrocracking reaction zone are as follows: the average reaction temperature is 250~450°C; the liquid hourly space velocity is 0.1~15.0 h -1 ; the hydrogen-oil volume ratio is 100:1~2500:

1.

14. The method according to claim 13, characterized in that, In step (3), the reaction conditions in the third hydrocracking reaction zone are as follows: the average reaction temperature is 300~400°C; the liquid hourly space velocity is 1.0~5.0 h -1 ; the hydrogen-oil volume ratio is 400:1~2000:

1.

15. The method according to claim 1, characterized in that In step (1), the carrier of the first hydrocracking catalyst includes ZSM-5 molecular sieve.

16. The method according to claim 1, wherein In step (1), among the active metal components of the first hydrocracking catalyst, the Group VIB metals are molybdenum and / or tungsten, and the Group VIII metals are cobalt and / or nickel.

17. The method according to claim 1, characterized in that In step (2), the hydrogenation component of the second hydrocracking catalyst and / or in step (3), the hydrogenation component of the third hydrocracking catalyst is at least one of iron, chromium, molybdenum, tungsten, cobalt, and nickel.

18. The method according to claim 1, wherein In the second hydrocracking product of step (2), the content of bicyclic and higher aromatic hydrocarbons is 0.1 wt% to 1 wt%.

19. The method according to claim 18, wherein In the second hydrocracking product of step (2), the content of bicyclic and higher aromatic hydrocarbons is 0.2 wt% to 0.5 wt%.

20. The method according to claim 1, wherein In the third hydrocracking product of step (3), the ratio of the mass of C6-C8 monocyclic cyclic hydrocarbons to the total mass of cyclic hydrocarbons in the feedstock is 0.20 to 0.

40.

21. The method according to claim 20, wherein In the third hydrocracking product of step (3), the ratio of the mass of C6-C8 monocyclic cyclic hydrocarbons to the total mass of cyclic hydrocarbons in the feedstock is 0.30 to 0.37.

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