Complexing dewaxing method and system for separating n-alkanes in hydrocracking tail oil
By directly using solid urea for complexation reaction in hydrocracking tail oil, combined with solid-liquid and oil-water separation technology, the problem of difficult solvent recovery was solved, achieving efficient separation of n-alkanes and purification of isoalkanes, simplifying the process and reducing costs.
Patent Information
- Application Number
- CN202410440478.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-04-12
- Publication Date
- 2025-10-21
AI Technical Summary
Existing technologies for dewaxing hydrocracking tail oil suffer from difficulties in solvent recovery and low separation efficiency, resulting in poor separation of n-alkanes.
Solid urea is directly complexed with liquid hydrocracking tail oil. n-Alkanes are separated through complexation and decomplexation steps, avoiding the use of activators. High-purity n-alkanes and isoalkanes are obtained by using solid-liquid separation and oil-water separation technologies.
It improves the separation efficiency of n-alkanes, simplifies the process flow, reduces the difficulty of solvent recovery, reduces pollution from isoalkanes, and achieves efficient separation of n-alkanes and recovery of urea.
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Abstract
Description
Technical Field
[0001] The present application relates to the technical field of petrochemical industry, and in particular to a complex dewaxing method and system for separating normal alkanes from hydrocracking tail oil. Background Art
[0002] Hydrocracking is one of the most important processing methods in the oil refining industry. The products generated by hydrocracking of raw materials are mainly gas, solvent oil, gasoline components, and middle distillates. Secondly, there is a considerable amount of unconverted oil, also known as hydrocracking tail oil. The hydrocracking tail oil also undergoes good hydrogenation and upgrading during the hydrocracking process, resulting in low aromatic hydrocarbon content, light color, low content of impurities such as sulfur and nitrogen, and high content of cycloalkanes and alkanes. Currently, the application of hydrocracking tail oil is mainly used as a raw material for cracking to produce ethylene, and the second is to return it to the hydrocracking unit for refining to produce automotive fuel, which does not fully realize the value of the hydrocracking tail oil.
[0003] Urea dewaxing technology is one of the oil dewaxing methods. It primarily utilizes the cage-like complexes formed between normal alkanes in the oil and urea. Separating the complexes can lower the pour point of diesel fuel. Alternatively, the complexes can be decomplexed to separate the normal alkanes, resulting in higher levels of these compounds.
[0004] At present, urea dewaxing mainly uses alcohol and ketone solvents as activators to disperse urea in the solvent, which is then mixed with oil products to obtain a solid complex. Finally, the solid complex is separated from the liquid phase to obtain normal alkane products or oil products without normal alkane. Summary of the Invention
[0005] This application proposes a complex dewaxing method and system for separating normal alkanes from hydrocracking tail oil, aiming to solve the problem of difficulty in solvent recovery due to the addition of an active agent during the dewaxing process of hydrocracking tail oil. This application adopts the following technical solutions:
[0006] In a first aspect, the present application discloses a complex dewaxing method for separating normal alkanes from hydrocracking tail oil, comprising:
[0007] Solid urea is added to liquid hydrocracking tail oil to carry out complex reaction to obtain a complex mixture;
[0008] Separating the complex mixture to obtain a complex solid and a liquid component;
[0009] mixing the complex solid with water to perform a decomplexation reaction to obtain a first layered liquid;
[0010] The first layered liquid is separated to obtain a normal alkane oil product and a first urea water product.
[0011] Optionally, the normal alkane content of the normal alkane oil product is 20 wt% to 50 wt% higher than the normal alkane content of the hydrocracking tail oil.
[0012] Optionally, the step of adding solid urea to liquid hydrocracking tail oil to carry out a complex reaction to obtain a complex mixture comprises:
[0013] The temperature range of the hydrocracking tail oil is 60°C to 80°C.
[0014] Optionally, the step of adding solid urea to liquid hydrocracking tail oil to carry out a complex reaction to obtain a complex mixture comprises:
[0015] The mass ratio of the solid urea to the hydrocracking tail oil is in the range of 1:1 to 1:8.
[0016] Optionally, the mixing of the complex solid with water to perform a decomplexation reaction to obtain a first layered liquid comprises:
[0017] The mass ratio of the complex solid to water is in the range of 0.25:1 to 4:1.
[0018] Optionally, the method further includes:
[0019] mixing the liquid phase component with water to obtain a second layered liquid;
[0020] The second layered liquid is separated to obtain an isoparaffin oil product and a second urea water product.
[0021] Optionally, the method further includes:
[0022] The first urea aqueous solution and the second urea aqueous solution are crystallized to obtain recovered urea solid and wastewater.
[0023] Optionally, the step of adding solid urea to liquid hydrocracking tail oil to carry out a complexation reaction comprises:
[0024] Cutting the hydrocracking tail oil to obtain a hydrocracking tail oil fraction with a distillation temperature range of 340-380° C.
[0025] The solid urea is added into the liquid hydrocracking tail oil fraction to carry out a complex reaction.
[0026] Optionally, the temperature for separating the complex mixture, the temperature for separating the first layered liquid, and the temperature for the decomplexation reaction are all consistent with the temperature of the complex reaction.
[0027] In a second aspect, the present application discloses a system for separating normal alkanes from hydrocracking tail oil, wherein the system is used to implement the complex dewaxing method as described in the first aspect;
[0028] The system comprises a complexing reactor, a solid-liquid separator and a first oil-water separator which are connected in sequence.
[0029] In summary, the advantages of this application over the prior art include:
[0030] 1. The complex dewaxing method in the embodiment of the present application is applied to hydrocracking tail oil. Urea is directly added to the liquid hydrocracking tail oil in solid form for complex reaction, replacing the method of dissolving urea in an activator in the related art. After a large number of experiments, it was demonstrated that without adding an activator, the normal alkane content in the normal alkane oil product can still be increased by more than 20% compared with the hydrocracking tail oil. Therefore, the use of the complex dewaxing method in the embodiment of the present application to separate the normal alkanes in the hydrocracking tail oil can achieve the effect of simplifying the normal alkane separation process while maintaining the original separation effect.
[0031] 2. The complexation dewaxing method in the examples of the present application, when compared with related technologies, shows a higher degree of separation of normal paraffins when dewaxing hydrocracked tail oil using the method in the examples of the present application. Therefore, by directly adding urea in solid form to the liquid hydrocracked tail oil for complexation reaction, it is possible to further produce an unexpected effect of promoting the separation of normal paraffins in the hydrocracked tail oil.
[0032] 3. In the complexation dewaxing method in the embodiment of the present application, since no activator is added during the complexation reaction, when the isoparaffins in the liquid phase component are subsequently separated, a relatively pure isoparaffin component can be obtained without performing more filtration-solvent recovery operations, thereby improving the problem of solvent recovery in the liquid phase component.
[0033] 4. The complex dewaxing method in the embodiment of the present application not only achieves the effect of separating normal alkanes and isoalkanes in the hydrocracking tail oil, but also further recovers urea by crystallization and reuses it, thereby reducing the waste of raw materials and lowering costs.
[0034] 5. In the complex dewaxing method of the present invention, the hydrocracked tail oil is pre-cut prior to the complex reaction to obtain fractions with a narrower distillation temperature range. This facilitates concentrating the normal paraffin concentration in the hydrocracked tail oil prior to the complex reaction, shortening the subsequent normal paraffin separation process and yielding an isoparaffin oil product with a lower viscosity index. BRIEF DESCRIPTION OF THE DRAWINGS
[0035] Figure 1This is the first flow chart of complex dewaxing for separating normal paraffins from hydrocracking tail oil in the embodiment of the present application.
[0036] Figure 2 This is the second flow chart of complex dewaxing for separating normal paraffins from hydrocracking tail oil in the embodiment of the present application.
[0037] Figure 3 This is a diagram of a complex dewaxing system for separating normal alkanes from hydrocracking tail oil in an embodiment of the present application.
[0038] Description of reference numerals:
[0039] 1. Complexation reactor; 2. Solid-liquid separator; 3. First oil-water separator; 4. Second oil-water separator; 5. Crystallization reactor;
[0040] 101. Hydrocracking tail oil; 102. Solid urea; 103. Complex mixture; 104. Complex solid; 105. Liquid phase component; 106. Normal paraffin oil product; 107. First urea aqueous product; 108. Isoparaffin oil product; 109. Second urea aqueous product; 110. Recovered urea solid; 111. Wastewater. DETAILED DESCRIPTION
[0041] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.
[0042] Exemplary embodiments will be described in detail herein, with examples illustrated in the accompanying drawings. In the following description, when referring to the drawings, identical numerals in different figures represent identical or similar elements, unless otherwise indicated. The embodiments described in the following exemplary embodiments are not intended to represent all possible embodiments consistent with the present disclosure. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the present disclosure, as detailed in the appended claims.
[0043] Traditional theory holds that when using urea complex dewaxing to separate normal alkanes from oil products, urea usually needs to be dispersed in an activator such as an alcohol or ketone solvent. If no activator is added, the complex reaction usually cannot occur.
[0044] However, the use of an activator inevitably brings about the problem of difficulty in solvent recovery. In addition, in the step of filtration and separation, when the activator in the filtrate is used, part of the urea will be brought into the isoparaffin component, and it is necessary to repeatedly perform multiple filtration-solvent recovery operations to obtain a purer isoparaffin component, and the process is very complicated. For example, patent CN111704526A discloses a solvent recovery system and method for an isopropyl alcohol urea dewaxing process, which mainly recovers isopropyl alcohol through an alcohol concentration tower, an extractive distillation tower, and a solvent recovery tower. The three-tower operation is relatively complex and increases the difficulty of operation.
[0045] After numerous experiments, the inventors discovered that when using urea complex dewaxing to separate normal paraffins from hydrocracking tail oil, the complex reaction can still occur without the addition of an activator, and can produce better separation results. This led the inventors to further research and develop the present invention.
[0046] It should be noted that the hydrocracking tail oil in this application is a heavy hydrocarbon component obtained after the heavy wax oil raw material is hydrogenated. Its distillation range is usually: the initial boiling point is not less than 200°C, the distillation temperature of 50% of the hydrocracking tail oil is 300-400°C, and the distillation temperature of 90% of the hydrocracking tail oil is not less than 450°C. The hydrocracking tail oil mainly includes hydrocarbon compounds with a carbon number distribution of C9-C40, and the main component of the hydrocarbon compound is C17-C30 normal isomers. The normal isomer components of the corresponding hydrocracking tail oil are different due to different crude oil compositions. Generally speaking, the normal alkane content of the hydrocracking tail oil varies in the range of 17-50%. Therefore, the pour point and viscosity of the hydrocracking tail oil are relatively high, usually the pour point is not less than 25°C, the viscosity index is not less than 120, and it is usually solid at room temperature with poor fluidity.
[0047] Based on the above hydrocracking tail oil, in the first aspect, the present application discloses a complex dewaxing method for separating normal alkanes in the hydrocracking tail oil. Figure 1 The method comprises the following steps S1 to S4:
[0048] S1: Add solid urea to liquid hydrocracking tail oil to carry out a complex reaction, and stir to obtain a complex mixture. Specifically, since the hydrocracking tail oil is solid at room temperature, the hydrocracking tail oil should be preheated and melted before adding urea, and the preheating temperature range can be 30-40°C. Then, the preheated hydrocracking tail oil is further heated, and the heating temperature is not less than 50°C, specifically 60-80°C. Thereby, the temperature of the hydrocracking tail oil is increased to 60-80°C to promote the complex reaction and improve the efficiency of the complex reaction.
[0049] In some optional embodiments, the mass ratio of solid urea to hydrocracking tail oil ranges from 1:1 to 1:8. During stirring, the solid urea should be dispersed and thoroughly mixed with the oil to prevent urea agglomeration. Specifically, the stirring time should be no less than 10 minutes, specifically 10-120 minutes, and further preferably 20-60 minutes. This allows for a complete complexation reaction and forms a complex mixture.
[0050] In some optional embodiments, since the carbon number distribution of normal alkanes is primarily C17-C30, in order to further improve the separation efficiency of normal alkanes in the hydrocracked tail oil, the hydrocracked tail oil can be cut before the complexation reaction to obtain a hydrocracked tail oil fraction with a distillation temperature range of 340-380°C. Solid urea is then added to the liquid hydrocracked tail oil fraction to carry out the complexation reaction. This helps to concentrate the normal alkanes in the hydrocracked tail oil before the complexation reaction, thereby reducing the workload of subsequent normal alkanes separation.
[0051] S2: Separate the complex mixture to obtain a complex solid and a liquid phase component. Specifically, after the complex reaction, the normal alkanes in the hydrocracking tail oil enter the complex solid, and other components such as isoalkanes remain in the liquid phase component. The complex solid and liquid phase components can be separated by any method such as filtration and sedimentation for solid-liquid separation. For example, when separating the complex solid and liquid phase components by filtration, a filter element with a pore size of not more than 10 μm can be used to separate the complex solid and liquid phase components. The pore size of the filter element is preferably not more than 5 μm, and more preferably not more than 1 μm. Furthermore, the separation temperature should be consistent with the complex reaction temperature to prevent the liquid phase component from solidifying or the complex solid from decomposing due to temperature changes.
[0052] S3: Mixing the complex solid with water to carry out a decomplexation reaction to obtain a first layered liquid. The upper layer of the first layered liquid is a normal alkane oil product rich in normal alkanes, and the lower layer of the first layered liquid is a first urea water product rich in urea. Specifically, when carrying out the decomplexation reaction, the amount of water added should be sufficient to fully dissolve the complex solid without residual solids. In some optional embodiments, the mass ratio of water to complex solid can be in the range of 1:0.25 to 1:4. It should be noted that the temperature of the decomplexation reaction should also be kept consistent with the complexation reaction temperature to prevent the normal alkane oil product from solidifying after adding water for decomplexation.
[0053] S4: Separate the first layered liquid to obtain a normal alkane oil product and a first urea water product.
[0054] Through the above steps S1 to S4, the separation of normal paraffins in the hydrocracking tail oil is completed.
[0055] Furthermore, in an optional embodiment, after the separation of normal paraffins in the hydrocracking tail oil is completed according to the above method, the isoparaffins in the hydrocracking tail oil can be further separated and the urea can be recovered. Figure 2 , which is specifically achieved through the following steps S5 to S7:
[0056] S5: Mix the liquid components in S1 with water to produce a second layered liquid. The upper layer of the second layered liquid comprises the isoparaffin oil product, while the lower layer comprises the second urea-water product containing less urea. Optionally, the mass ratio of the first urea-water product to water can be in a range of 1:0.25 to 1:4. Similarly, the temperature at which the first urea-water product is mixed with water should be the same as the complexation reaction temperature in S1 to prevent solidification of the isoparaffin-rich isoparaffin oil product.
[0057] S6: Separating the second layered liquid to obtain an isoparaffin oil product and a second urea-water product. Specifically, the second layered liquid can be separated by oil-water separation. Similarly, the separation temperature of the second layered liquid should also be the same as the complexation reaction temperature.
[0058] S7: The first urea water product in S3 and the second urea water product in S5 are crystallized to obtain recovered urea solids. The recovered urea solids can be reused, and the wastewater is sent to a wastewater treatment device for recovery and treatment.
[0059] In the second aspect, the present application also discloses a system for separating normal alkanes in hydrocracking tail oil, referring to Figure 3 The system includes a complexation reactor 1, a solid-liquid separator 2, a first oil-water separator 3, a second oil-water separator 4, and a crystallization reactor 5. The outlet of the complexation reactor 1 is connected to the inlet of the solid-liquid separator 2, the solid phase outlet of the solid-liquid separator 2 is connected to the inlet of the first oil-water separator 3, and the liquid phase outlet of the solid-liquid separator 2 is connected to the inlet of the second oil-water separator 4. The outlets of the first oil-water separator 3 and the second oil-water separator 4 are both connected to the inlet of the crystallization reactor 5.
[0060] Reference Figure 3The working process of the system for separating normal paraffins from hydrocracking tail oil in the embodiment of the present application is as follows: the hydrocracking tail oil 101 is preheated and placed in the complexation reactor 1, and heated to 60-80°C. Then, solid urea 102 is added to the complexation reactor 1 to carry out a complexation reaction to obtain a complex mixture 103. The complexation mixture 103 is transferred to the solid-liquid separator 2 for solid-liquid separation to obtain a complex solid 104 and a liquid phase component 105. The complex solid 104 is transferred to the first oil-water separator 3, water is added, a decomplexation reaction is carried out, and the normal paraffin oil product 106 and the first urea water product 107 are separated by the first oil-water separator 3. At the same time, the liquid phase component 105 is transferred to the second oil-water separator 4, water is added, and the isoparaffin oil product 108 and the second urea water product 109 are separated by the second oil-water separator 4. The normal paraffin oil product 106 and the isoparaffin oil product 108 are discharged from the system, and the first urea water product 107 and the second urea water product 109 are transferred to the crystallization reactor 5 for evaporation and crystallization to obtain recovered urea solid 110 and wastewater 111. The recovered urea solid 110 can be further returned to the complexation reactor 1 for reuse.
[0061] The present application is described in detail below through specific examples and comparative examples:
[0062] Example 1
[0063] In this embodiment, the complex dewaxing method for separating normal paraffins in hydrocracking tail oil mainly includes the following steps:
[0064] (1) The hydrocracking tail oil is preheated and then heated to 80° C. to obtain a liquid hydrocracking tail oil having fluidity.
[0065] (2) Directly placing solid urea into liquid hydrocracking tail oil for complexation reaction, wherein the mass ratio of solid urea to liquid hydrocracking tail oil is 1:1, and stirring for 1 hour to obtain a complexation mixture.
[0066] (3) The complex mixture is subjected to solid-liquid separation to obtain solid and liquid components of the complex.
[0067] (4) adding water to the complex solid to carry out a decomplexation reaction to obtain a first layered liquid, wherein the mass ratio of the complex solid to water is 1:1. The upper layer of the first layered liquid is a normal alkane oil product rich in normal alkanes, and the lower layer of the first layered liquid is a first urea-water product containing urea.
[0068] (5) adding water to the liquid phase component, with the mass ratio of the liquid phase component to water being 1:1. After oil-water separation, an isoparaffin oil product rich in isoparaffins and a second urea-water product containing urea are obtained.
[0069] (6) The first urea aqueous product in (4) and the second urea aqueous product in (5) are evaporated and crystallized to precipitate and recover urea solid.
[0070] The normal alkane and isoalkane contents of the liquid hydrocracking tail oil in (1) and the normal alkane oil product in (4) were tested respectively. The test results are shown in Table 1:
[0071] Table 1 Normal paraffin and isoparaffin contents of liquid hydrocracking tail oil and normal paraffin oil product in Example 1
[0072]
[0073]
[0074] As shown in Table 1, as the complexation reaction proceeds, the normal paraffins in the hydrocracking tail oil enter the complex solid. The normal paraffin content in the normal paraffin-rich product increases from 43.6 wt% to 66.7 wt%.
[0075] Example 2
[0076] The difference between this embodiment and embodiment 1 is that in (1), the hydrocracking tail oil is preheated and then heated to 60° C. to obtain liquid hydrocracking tail oil with fluidity, and the other steps are the same.
[0077] The normal alkane and isoalkane contents of the liquid hydrocracking tail oil and normal alkane oil products were tested. The test results are shown in Table 2:
[0078] Table 2 Normal paraffin and isoparaffin contents of liquid hydrocracking tail oil and normal paraffin oil product in Example 2
[0079]
[0080]
[0081]
[0082] As shown in Table 2, as the complexation reaction proceeds, the normal paraffins in the hydrocracking tail oil enter the complex solid. The normal paraffin content in the normal paraffin-rich product increases from 17.0 wt% to 36.6 wt%.
[0083] Example 3
[0084] The difference between this embodiment and embodiment 1 is that: in (1), the hydrocracking tail oil fraction having a distillation temperature of 340-380°C after cutting is preheated and then heated to 70°C to obtain a fluid hydrocracking tail oil fraction. Solid urea is directly placed in the hydrocracking tail oil fraction to carry out the complexation reaction. In (2), the mass ratio of urea to hydrocracking tail oil fraction is 1:8. In (4), the mass ratio of the complex solid to water is 0.25:1.
[0085] The normal alkane and isoalkane contents of the liquid hydrocracking tail oil and normal alkane oil products were tested. The test results are shown in Table 3:
[0086] Table 3 Normal paraffin and isoparaffin contents of liquid hydrocracking tail oil and normal paraffin oil product in Example 3
[0087]
[0088]
[0089] As shown in Table 3, as the complexation reaction proceeds, the normal paraffins in the hydrocracking tail oil enter the complex solid. The normal paraffin content in the normal paraffin-rich product increases from 16.9 wt% to 68.9 wt%.
[0090] Example 4
[0091] The difference between this embodiment and embodiment 1 is that: in (1), the hydrocracking tail oil fraction having a distillation temperature of 340-380°C after cutting is preheated and then heated to 80°C to obtain a fluid hydrocracking tail oil fraction. Solid urea is directly placed in the hydrocracking tail oil fraction to carry out the complexation reaction. In (2), the mass ratio of solid urea to liquid hydrocracking tail oil fraction is 1:6. In (4), the mass ratio of complex solid to water is 4:1.
[0092] The normal alkane and isoalkane contents of the liquid hydrocracking tail oil and normal alkane oil products were tested. The test results are shown in Table 4:
[0093] Table 4 Normal paraffin and isoparaffin contents of liquid hydrocracking tail oil and normal paraffin oil product in Example 4
[0094]
[0095]
[0096] As shown in Table 4, as the complexation reaction proceeds, the normal paraffins in the hydrocracking tail oil enter the complex solid. The normal paraffin content in the normal paraffin-rich product increases from 33.0 wt% to 75.0 wt%.
[0097] Comparative Example
[0098] The difference between this comparative example and Example 4 is that in (2), urea is dissolved in an ethanol solution, and then the ethanol aqueous solution of urea is added to the liquid hydrocracking tail oil to carry out a complex reaction.
[0099] The normal alkane and isoalkane contents of the liquid hydrocracking tail oil and normal alkane oil products were tested. The test results are shown in Table 5:
[0100] Table 5 Normal paraffin and isoparaffin contents of liquid hydrocracking tail oil and normal paraffin oil products in comparative examples
[0101]
[0102] As shown in Table 5, when urea was dissolved in ethanol solvent and then added to hydrocracking tail oil for urea dewaxing, the normal paraffin content was only increased from 33.0 wt% to 53.2.0 wt% after urea complexation. Compared with the normal paraffin oil product in Example 4, the normal paraffin separation effect of the comparative example was poor.
[0103] The above description includes examples of one or more embodiments. Of course, it is not possible to describe all possible combinations of components or methods for the purpose of describing the above embodiments, but it will be recognized by those skilled in the art that the various embodiments may be further combined and arranged. Therefore, the embodiments described herein are intended to cover all such changes, modifications and variations that fall within the scope of protection of the appended claims. In addition, to the extent that the term "comprising" is used in the specification or claims, the term is intended to be encompassed in a manner similar to the term "including", as explained by the use of "including" as a transitional word in the claims. In addition, any use of the term "or" in the specification of the claims is intended to mean a "non-exclusive or".
Claims
1. A complex dewaxing method for separating normal alkanes from hydrocracking tail oil, characterized in that ,include: Solid urea is added to liquid hydrocracking tail oil to carry out complex reaction to obtain a complex mixture; Separating the complex mixture to obtain a complex solid and a liquid component; mixing the complex solid with water to perform a decomplexation reaction to obtain a first layered liquid; The first layered liquid is separated to obtain a normal alkane oil product and a first urea water product.
2. The complex dewaxing method according to claim 1, wherein The normal alkane content of the normal alkane oil product is 20 wt% to 50 wt% higher than the normal alkane content of the hydrocracking tail oil.
3. The complex dewaxing method according to claim 1, wherein The solid urea is added to the liquid hydrocracking tail oil to carry out a complex reaction to obtain a complex mixture, comprising: The temperature range of the hydrocracking tail oil is 60°C to 80°C.
4. The complex dewaxing method according to claim 1, wherein Solid urea is added to liquid hydrocracking tail oil to carry out complex reaction to obtain a complex mixture, including: The mass ratio of the solid urea to the hydrocracking tail oil is in the range of 1:1 to 1:
8.
5. The complex dewaxing method according to claim 1, wherein The step of mixing the complex solid with water to perform a decomplexation reaction to obtain a first layered liquid comprises: The mass ratio of the complex solid to water is in the range of 0.25:1 to 4:
1.
6. The complex dewaxing method according to claim 1, wherein Also includes: mixing the liquid phase component with water to obtain a second layered liquid; The second layered liquid is separated to obtain an isoparaffin oil product and a second urea water product.
7. The complex dewaxing method according to claim 6, wherein Also includes: The first urea aqueous solution and the second urea aqueous solution are crystallized to obtain recovered urea solid.
8. The complex dewaxing method according to claim 1, wherein The process of adding solid urea to liquid hydrocracking tail oil to carry out a complexation reaction comprises: Cutting the hydrocracking tail oil to obtain a hydrocracking tail oil fraction with a distillation temperature range of 340-380° C. The solid urea is added into the liquid hydrocracking tail oil fraction to carry out a complex reaction.
9. The complex dewaxing method according to claim 1, wherein The temperature for separating the complex mixture, the temperature for separating the first layered liquid, and the temperature for the decomplexation reaction are all consistent with the temperature of the complex reaction.
10. A system for separating normal alkanes from hydrocracking tail oil, characterized in that: The system is used to implement the complex dewaxing method according to any one of claims 1 to 9; The system comprises a complexing reactor, a solid-liquid separator and a first oil-water separator which are connected in sequence.