Method for increasing yield of medium distillate oil through mild hydrogenation of Fischer-Tropsch refined tail oil

Abstract

The present invention provides a Fischer-Tropsch refined tail oil mild hydrogenation yield increasing method, which comprises: (1) introducing Fischer-Tropsch refined tail oil and a hydrogen-containing material flow into a first hydrogenation reactor, carrying out a hydrogenation reaction to obtain a first reaction effluent, and carrying out separation and fractionation on the first reaction effluent to obtain a first gas, light oil, medium distillate oil and heavy oil; (2) introducing the heavy oil and the hydrogen-containing material flow into an enhanced mass transfer mixer, mixing to obtain an emulsion containing microbubbles, carrying out hydrogenation reaction on the emulsion in a second hydrogenation reactor to obtain a second reaction effluent, and separating to obtain a second gas and product oil; wherein the hydrogenation reaction temperature in the first hydrogenation reactor and the second hydrogenation reactor is 290-340 DEG C, the volume space velocity in the first hydrogenation reactor and the second hydrogenation reactor is 0.1-2.0 h <-1 >, and the reaction pressure in the second hydrogenation reactor is 1.5-4.5 MPa; the volume fraction of microbubbles with the particle size being larger than or equal to 1 micron and smaller than 1 mm in the emulsion is larger than or equal to 65 According to the method disclosed by the invention, the medium distillate oil with high yield can be obtained under relatively mild conditions.

Description

Technical Field

[0001] The invention belongs to the technical field of petrochemical industry, and in particular relates to a method for mildly hydrogenating Fischer-Tropsch refined tail oil to produce more middle distillate oil. Background Art

[0002] In the existing hydrocracking process, the reaction system is generally in a high-pressure, hydrogen-exposed state, and there are the following problems: Due to the low molecular weight of hydrogen, it is easy to escape and leak under high pressure, resulting in high investment in high-pressure equipment and high safety risks; the devices all use a high hydrogen-to-oil volume ratio, and the excess hydrogen needs to be circulated and compressed, resulting in high equipment investment and high operating energy consumption; the high operating temperature of the reactor affects the service life of the catalyst. The above problems have brought great troubles to the stable, safe, and long-term operation of the existing hydrocracking process devices.

[0003] CN106350105B discloses a method for processing Fischer-Tropsch synthetic oil, which uses a first and a second isomerization hydrocracking reactor to process refined tail oil, and by limiting the high isomerization activity of the first reactor, limiting the isoparaffin content in the first reaction effluent to not less than 60%, and the second reactor having high cracking activity, the purpose of producing more intermediate distillate oil is achieved. However, the method has high requirements on catalyst performance and catalyst compounding, and increases the interfacial area of ​​each reaction phase by traditional high temperature and high pressure and large hydrogen-oil volume ratio, which easily causes excessive hydrogen to be circulated and compressed while increasing the mass transfer rate, and has problems such as high energy consumption and production cost, high investment intensity, and poor intrinsic safety.

[0004] Therefore, there is an urgent need in the art to find a new method for processing Fischer-Tropsch oil to improve the selectivity of middle distillate oil and obtain a higher yield of middle distillate oil. Summary of the invention

[0005] In order to overcome the deficiencies in the prior art, the present invention provides a method for producing more middle distillate oil under mild reaction conditions.

[0006] In order to achieve the purpose of the present invention, the present invention adopts the following technical solutions:

[0007] The present invention provides a method for mildly hydrogenating Fischer-Tropsch refined tail oil to produce more middle distillate oil, comprising:

[0008] (1) introducing the Fischer-Tropsch refined tail oil and the hydrogen-containing stream into a first hydrogenation reactor for hydrogenation reaction to obtain a first reaction effluent, wherein the first reaction effluent is sequentially separated and fractionated to obtain a first gas, light oil, middle distillate oil and heavy oil;

[0009] (2) the heavy oil and the hydrogen-containing stream are introduced into an enhanced mass transfer mixer and mixed to obtain an emulsion containing microbubbles, the emulsion is subjected to a hydrogenation reaction in a second hydrogenation reactor to obtain a second reaction effluent, the second reaction effluent is separated to obtain a second gas and product oil, and the obtained product oil is returned to the fractionation treatment in step (1);

[0010] The hydrogenation reaction temperature in the first hydrogenation reactor and the second hydrogenation reactor is 290-340°C, and the volume space velocity in the first hydrogenation reactor and the second hydrogenation reactor is 0.1-2.0h -1 ;

[0011] The volume fraction of microbubbles with a particle size of ≥1 μm and <1 mm in the emulsion is ≥65%.

[0012] The researchers of the present invention found that by controlling the conditions of the Fischer-Tropsch refined tail oil in the first hydrogenation reaction, the conversion rate of the first hydrogenation reaction is not higher than 40%, and the mass ratio of light hydrocarbons and light oil in the first reaction effluent to the product oil can be reduced to less than 5%, or even less than 4%. Furthermore, the heavy oil obtained after fractionation treatment mainly undergoes a hydrogenation isomerization reaction in the second hydrogenation reaction to obtain a middle distillate oil with a higher yield.

[0013] In some specific embodiments, the conversion rate of the hydrogenation reaction in the first hydrogenation reactor is not greater than 40%, and the conversion degree of the second hydrogenation reaction in step (2) is controlled to make its conversion rate 40% to 75%, preferably 55 to 65%. The method of the present invention can produce a high yield of middle distillate oil under relatively mild conditions by controlling the conversion rates of the first hydrogenation reaction and the second hydrogenation reaction respectively.

[0014] The method of the present invention adopts an enhanced mass transfer mixer, which is a device that tears the hydrogen-containing flow into microbubbles through the shear force of high-speed flowing heavy oil, including a heavy oil inlet, a hydrogen-containing flow inlet, an emulsion outlet, a membrane element and a shell; wherein the membrane element is a porous material with a pore size greater than or equal to 1μm and less than 1mm, and the porous material can be selected from sintered metal, sintered ceramic, nano-micro ceramic membrane, metal wire mesh, etc. The heavy oil is in shear contact with the hydrogen-containing flow that permeates the membrane element, so that the hydrogen is stably present in the emulsion in the form of micron-scale bubbles. The above-mentioned enhanced mass transfer process efficiently regulates the geometric scale of the gas-liquid and gas-liquid-solid interfaces from the milli-centimeter level to the micron level, which not only greatly improves the hydrogen carrying capacity of the oil product, but also greatly improves the phase interface area and mass-energy transfer efficiency in terms of order of magnitude, and also makes the reaction conditions milder, the efficiency of the chemical production process is doubled, and the energy consumption and material consumption are greatly reduced; at the same time, the pressure and reaction temperature in the second hydrogenation reactor are also reduced, the excessive cracking of the oil product is avoided, and the yield of the middle distillate oil is significantly improved.

[0015] In some specific embodiments, the mass transfer enhancement mixer includes a heavy oil inlet, a hydrogen-containing stream inlet, an emulsion outlet, a membrane element and a shell; the heavy oil and the hydrogen-containing stream passing through the membrane element are shear-contacted and mixed to form an emulsion containing microbubbles. The membrane element is a porous material with a pore size of greater than or equal to 1 μm and less than 1 mm, and the porous material can be specifically selected from sintered metals, sintered ceramics, nano-micro ceramic membranes, metal meshes, etc.

[0016] In some specific embodiments, the second hydrogenation reactor is selected from an upward fixed bed hydrogenation reactor, the feed inlet of which is located at the lower part or bottom of the reactor, and the second reaction effluent outlet is located at the upper part or top of the reactor. In some more specific embodiments, the reaction pressure of the second hydrogenation reactor is 1.5-4.5MPa, for example, 3.0MPa, 2.0MPa; the reaction pressure of the first hydrogenation reactor is 3.0-15.0MPa, for example, 7.0MPa, 8.0MPa; the hydrogen-oil volume ratio is (350-1600): 1, for example, 700:1, 1200:1.

[0017] In the method of the present invention, the first hydrogenation reactor and the second hydrogenation reactor are independently arranged, and catalysts with different catalytic properties are loaded for independent control, so the operation is flexible and the raw material adaptability is wider. The reaction product after being treated by the first hydrogenation reactor is first separated and fractionated, and the light oil and the middle distillate oil are separated out in time to avoid overreaction, and at the same time, the processing capacity of the second hydrogenation reactor is significantly reduced.

[0018] In some specific embodiments of the method of the present invention, the first hydrogenation reactor is filled with a first catalyst having hydrocracking and hydroisomerization activities, and the hydrocracking activity of the hydrogenation catalyst of the first catalyst is higher than its hydroisomerization activity; the second hydrogenation reactor is filled with a second catalyst having hydrocracking and hydroisomerization activities, and the hydroisomerization activity of the hydrogenation catalyst of the second catalyst is higher than its hydrocracking activity. The catalyst with stronger or weaker hydroisomerization or hydrocracking activity mentioned here refers to the catalyst with stronger or weaker activity determined for the same raw material under comparable conditions, i.e., at the same temperature, pressure, volume space velocity and hydrogen partial pressure. Examples of conditions for determining the activity are the conditions in the embodiments.

[0019] In some specific embodiments, the hydroisomerization activity of the catalyst loaded in the second hydrogenation reactor is at least 25% higher than the hydroisomerization activity of the catalyst loaded in the first hydrogenation reactor; the hydrocracking activity of the catalyst loaded in the second hydrogenation reactor is at least 14% lower than the hydrocracking activity of the catalyst loaded in the first hydrogenation reactor. The above-mentioned comparison of hydroisomerization activity or hydrocracking activity refers to the absolute difference between the two activity values.

[0020] In some more specific embodiments, the hydrogenation catalyst loaded in the first hydrogenation reactor is selected from a hydroisomerization cracking catalyst whose carrier is a molecular sieve, and can be a hydroisomerization cracking catalyst containing a molecular sieve that can achieve the corresponding function in the art. Such catalysts can be obtained through commercial channels, such as but not limited to RT-5 and RCF-1 developed by the Petrochemical Research Institute; FC-60, FC16, FC14, FC12, H-06, 3762, 3281 developed by Fushun Petrochemical Research Institute; Haldor TK-943, TK-933, TK-926 developed by our company; HC-215, HC-120, HC-11, HC-14, HC-16, HC-18, HC-24, HC-28, HC-22, HC-33 developed by UOP; ICR-117, ICR-126, ICR-220 developed by Chevron; DHC-39, DHC-41 developed by UOP; ICR-183, ICR-214, ICR-215 developed by LCG.

[0021] In the method of the present invention, the catalyst required for the reaction in the second hydrogenation reactor can be a hydrogenation catalyst that can achieve the corresponding function in the art. As a preferred embodiment, the carrier of the hydrogenation catalyst loaded in the second hydrogenation reactor does not contain a molecular sieve, but amorphous silicon aluminum with weak acidity is selected, so that the generation of aromatics in the multiple cracking process of macromolecular oil can be effectively prevented in the hydrocracking isomerization reaction, which is beneficial to control the content of aromatics in the product oil and improve the yield of the middle distillate oil; for example, the hydrocracking catalyst disclosed in CN110433819A can be used.

[0022] In a specific embodiment of the method of the present invention, the top of the first hydrogenation reactor and the second hydrogenation reactor are loaded with a hydrogenation protection catalyst; loading the hydrogenation protection catalyst to ensure the long-term operation of the hydrogenation unit is well known to those skilled in the art, and the type and loading amount of the hydrogenation protection catalyst agent are conventionally selected, and no further description is given. The hydrogenation protection catalyst includes, for example, but is not limited to: FZC-100, FZC-101, FZC-102, FZC-102A, FZC-102B, FZC-103, FZC-103A, FZC-103B, FZC-105, FZC-106, FZC-204 developed by Fushun Petrochemical Research Institute. The loading amount of the hydrogenation protection catalyst is 10 to 35% of the total amount of the catalyst loaded in the reactor.

[0023] In some specific embodiments, a post-refining agent is loaded at the bottom of the second catalyst bed in the first hydrogenation reactor. The type and loading amount of the post-refining agent are conventionally selected and will not be described in detail.

[0024] In the method of the present invention, the hydrogen-containing logistics refers to logistics that can provide hydrogen, including any one or more of fresh hydrogen, recycled hydrogen, hydrogen-rich gas and other gaseous logistics that can provide hydrogen and liquid logistics that can provide hydrogen. In the present invention, the distillation range of light oil is C5-160°C, and the distillation range of middle distillate oil is 160-365°C.

[0025] In some specific embodiments, the mass ratio of hydrogen to heavy oil in the hydrogen-containing logistics in step (2) is (0.03-0.07):1, preferably (0.035-0.055):1.

[0026] In some specific embodiments, the method of the present invention further comprises: recycling the first gas obtained after the fractionation treatment to step (2) to provide the required hydrogen-containing flow.

[0027] The above technical solution has the following technical effects:

[0028] The method of the present invention uses refined tail oil as a raw material and undergoes a first hydroprocessing with a low conversion rate, so that the mass ratio of light hydrocarbons and light oil in the first reaction effluent to the product oil is less than 5%, or even less than 4%. The heavy oil obtained by fractionation is subjected to a hydroisomerization reaction in the second hydroprocessing process to obtain a high-yield middle distillate oil.

[0029] Compared with traditional downward fixed bed, slurry bed and bubbling bed hydrogenation reactions, the method of the present invention adopts an enhanced mass transfer mixer to allow the hydrogen in the hydrogen-containing logistics to stably exist in the emulsion in the form of micron-sized bubbles, and efficiently regulates the geometric scale of the gas-liquid and gas-liquid-solid interfaces from the milli-centimeter level to the micron level, which not only greatly improves the hydrogen carrying capacity of the oil products and makes the reaction conditions milder, but also the hydrogen contained in the hydrogen microbubbles in the emulsion can meet the needs of the second hydrogenation process, thereby greatly reducing the hydrogen consumption of the second hydrogenation process.

[0030] The method of the present invention can be carried out under relatively mild reaction conditions, which helps to reduce the bed temperature rise, effectively controls the bed temperature of the reactor, prevents the temperature of the isomerization hydrocracking reactor from getting out of control, ensures the stable operation of the device, and prolongs the catalyst life. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A specific flow chart of the method of the present invention is shown in FIG.

[0032] Among them, 1. the first hydrogenation reactor, 2. the separator I, 3. the distillation tower, 4. the preheater, 5. the enhanced mass transfer mixer, 6. the second hydrogenation reactor, 7. the separator II. DETAILED DESCRIPTION

[0033] In order to facilitate the understanding of the present invention, the present invention will be further described below in conjunction with examples. It should be understood that the following examples are only for a better understanding of the present invention and do not mean that the present invention is limited to the following examples.

[0034] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0035] Where specific experimental steps or conditions are not specified in the examples, the corresponding conventional experimental steps or conditions in the art can be used. The reagents or instruments used without specifying the manufacturer are all conventional products that can be purchased commercially.

[0036] The following examples adopt Figure 1 The process method shown is to prepare middle distillate oil by mild hydrogenation of Fischer-Tropsch refining tail oil, as follows:

[0037] (1) introducing the Fischer-Tropsch refined tail oil and a hydrogen-containing stream (hydrogen, hydrogen-rich gas, etc.) into a first hydrogenation reactor 1 for hydrogenation reaction to obtain a reaction effluent; the reaction effluent is subjected to gas-liquid separation in a separator Ⅰ2 to obtain a first gas and other products, the first gas is discharged from the top, and the other products are fractionated in a fractionation tower 3 to obtain light oil, middle distillate oil and heavy oil; wherein the obtained light oil and middle distillate oil are discharged from the top of the tower; in some specific embodiments, the first gas can be circulated as a hydrogen-containing stream to the enhanced mass transfer mixer 5;

[0038] (2) preheating the hydrogen-containing stream (hydrogen) and the heavy oil obtained above in a preheater 4, and introducing them into an enhanced mass transfer mixer 5 for mixing according to a certain mass ratio to obtain an emulsion containing microbubbles; during the mixing process in the enhanced mass transfer mixer 5, the heavy oil and the hydrogen-containing stream passing through the membrane element are in shear contact, and the geometric scale of the gas-liquid and gas-liquid-solid interfaces is efficiently controlled from the milli-centimeter level to the micrometer level, so that the number of microbubbles with a particle size of ≥1μm and <1mm in the emulsion reaches more than 65% of the volume of the bubbles contained in the emulsion;

[0039] The mixed emulsion is fed from the bottom into the second hydrogenation reactor 6 (upward fixed bed reactor) for a second hydrogenation reaction. The second reaction effluent obtained from the top is further separated in the separator II 7 to obtain product oil and a second gas. The product oil is returned from the bottom to the fractionation tower 3 for further fractionation.

[0040] The following examples of the present invention adopt the following detection method:

[0041] 1. Conversion rate = (content of fraction with initial boiling point greater than 365°C in raw materials - content of fraction with initial boiling point greater than 365°C in reaction products × reaction liquid yield) / content of fraction with initial boiling point greater than 365°C in raw materials × 100%;

[0042] Among them, "raw material" for the first hydrogenation reactor refers to the distillate oil (Fischer-Tropsch refined tail oil) used as raw material, and for the second hydrogenation reactor, it refers to the heavy oil with an initial distillation point greater than 365°C entering the reactor, and the reaction liquid yield refers to the mass ratio of the collected liquid product to the raw material.

[0043] 2. The yield of the middle distillate oil = (the content of the distillate with a distillation range of 160-365° C. in the reaction product × the yield of the reaction liquid - the content of the distillate with a distillation range of 160-365° C. in the raw material) / the content of the distillate with a distillation range of 160-365° C. in the raw material × 100%;

[0044] The reaction liquid yield refers to the mass ratio of the collected liquid product to the raw material.

[0045] 3. Microbubble content determination method: Take an in-situ photo of the microbubble image under working conditions, and then count the diameter and number of the bubbles to calculate the proportion of microbubbles with a particle size ≥1μm and <1mm in the emulsion.

[0046] The sources of raw materials used in the following examples and comparative examples of the present invention are as follows:

[0047] The first catalyst RCF-1 loaded in the first hydrogenation reactor: developed by the Petrochemical Research Institute;

[0048] The first catalyst FC14 loaded in the first hydrogenation reactor: Fushun Petrochemical Research Institute;

[0049] The second catalyst loaded in the second hydrogenation reactor was prepared by the method disclosed in CN110433819A; the content of amorphous silicon aluminum in the catalyst was 62wt.%, the pore volume was 1.6mL / g, and the specific surface area was 500m 2 / g, the total weight of aluminum oxide is 21wt.%, the content of tungsten oxide is 15.5wt.%, and the content of nickel oxide is 1.5wt.%.

[0050] The raw oils are all from the Fischer-Tropsch refined tail oil of Ningxia Coal Industry Coal-to-Liquids Company. Its properties are shown in Table 1:

[0051] Table 1

[0052]

[0053] Example 1

[0054] (1) introducing the Fischer-Tropsch refined tail oil and the hydrogen-containing stream (hydrogen) into a first hydrogenation reactor for hydrogenation reaction to obtain a first reaction effluent, and sequentially introducing the first reaction effluent into a separator I for separation, and then fractionating in a fractionation tower to obtain a first gas, light oil, middle distillate oil and heavy oil;

[0055] The first hydrogenation reactor was filled with catalyst RCF-1 (first catalyst), and the hydrogenation reaction conditions were: volume space velocity 1.9h -1 , hydrogen-to-oil volume ratio 1450:1, hydrogen partial pressure 3.0MPa, and reaction temperature 332°C so that the conversion rate of the first hydrogenation reaction is controlled to 40%;

[0056] (2) introducing the hydrogen-containing stream (hydrogen) and the heavy oil obtained above into an enhanced mass transfer mixer at a mass ratio of 0.03:1 and mixing them to obtain an emulsion containing microbubbles, wherein the number of microbubbles with a particle size of ≥1 μm and <1 mm in the emulsion accounts for 72% of the volume of the bubbles contained in the emulsion;

[0057] The emulsion enters the second hydrogenation reactor (upward fixed bed reactor) from the bottom for hydrogenation reaction to obtain a second reaction effluent, the second reaction effluent is further separated in the separator II to obtain a second gas and product oil, and the product oil is returned to the fractionation tower for further fractionation treatment;

[0058] The second hydrogenation reactor is filled with the second catalyst. The reaction conditions of the upward fixed bed reactor are: volume space velocity 1.0h -1 , hydrogen partial pressure 1.5MPa, reaction temperature 340°C was adjusted to make the conversion rate of the second hydrogenation reaction 55%. Under the same process conditions, the hydroisomerization activity of the second catalyst loaded per unit volume in the upward fixed bed reactor was 35% higher than that of the first catalyst, and the hydrocracking activity was 30% lower than that of the first catalyst.

[0059] Example 2

[0060] (1) introducing the Fischer-Tropsch refined tail oil and the hydrogen-containing stream (hydrogen) into a first hydrogenation reactor for hydrogenation reaction to obtain a first reaction effluent, and sequentially separating and fractionating the first reaction effluent to obtain a first gas, light oil, middle distillate oil and heavy oil;

[0061] The conditions for the hydrogenation reaction in the first hydrogenation reactor are: volume space velocity 0.65h -1 , hydrogen-to-oil volume ratio 360:1, hydrogen partial pressure 15.0MPa, and reaction temperature 295°C so that the conversion rate of the first hydrogenation reaction is controlled to 36%;

[0062] (2) introducing the hydrogen-containing stream (hydrogen) and the heavy oil obtained above into an enhanced mass transfer mixer at a mass ratio of 0.055:1 and mixing to obtain an emulsion containing microbubbles, wherein the number of microbubbles with a particle size of ≥1 μm and <1 mm accounts for 65% of the volume of the bubbles contained in the emulsion. The emulsion is fed from the bottom of the upward fixed bed reactor for hydrogenation reaction to obtain a second reaction effluent and product oil, and the product oil is returned to the fractionation treatment in step (1);

[0063] Under the same process conditions, the hydroisomerization activity of the second catalyst loaded in the unit volume of the upward fixed bed reactor (the second hydrogenation reactor) is 26% higher than that of the first catalyst, and the hydrocracking activity is 21% lower than that of the first catalyst; the reaction conditions of the upward fixed bed reactor are: volume space velocity 0.5h -1 , hydrogen partial pressure 2.5 MPa, the reaction temperature was adjusted to 300° C. so that the conversion rate of the second hydrogenation reaction was controlled to 46%.

[0064] Example 3

[0065] (1) introducing the Fischer-Tropsch refined tail oil and the hydrogen-containing stream (hydrogen) into a first hydrogenation reactor for hydrogenation reaction to obtain a first reaction effluent, and sequentially separating and fractionating the first reaction effluent to obtain a first gas, light oil, middle distillate oil and heavy oil;

[0066] The conditions for the hydrogenation reaction in the first hydrogenation reactor are: volume space velocity 0.65h -1 , hydrogen-to-oil volume ratio 360:1, hydrogen partial pressure 15.0MPa, and reaction temperature 295°C so that the conversion rate of the first hydrogenation reaction is controlled to 36%;

[0067] (2) introducing the hydrogen-containing stream (hydrogen) and the heavy oil obtained above into an enhanced mass transfer mixer at a mass ratio of 0.055:1 and mixing to obtain an emulsion containing microbubbles, wherein the number of microbubbles with a particle size of ≥1 μm and <1 mm accounts for 65% of the volume of the bubbles contained in the emulsion. The emulsion is fed from the bottom of the upward fixed bed reactor for hydrogenation reaction to obtain a second reaction effluent and product oil, and the product oil is returned to the fractionation treatment in step (1);

[0068] Under the same process conditions, the hydroisomerization activity of the second catalyst loaded in the unit volume of the upward fixed bed reactor (the second hydrogenation reactor) is 26% higher than that of the first catalyst, and the hydrocracking activity is 21% lower than that of the first catalyst; the reaction conditions of the upward fixed bed reactor are: volume space velocity 2.0h -1 , hydrogen partial pressure 4.5MPa, the reaction temperature was adjusted to 335°C so that the conversion rate of the second hydrogenation reaction was controlled to 64%.

[0069] Comparative Example 1

[0070] The difference between this comparative example and Example 2 is that no mass transfer intensified mixer is used; that is, the hydrogen-containing stream (hydrogen) and heavy oil are preheated and then enter the second hydrogenation reactor from the bottom for hydrogenation reaction.

[0071] The results show that under the same temperature and feed rate, the conversion rate of the second hydrogenation reaction is less than 20%, which is too low and not industrially feasible. The middle distillate oil is not collected and analyzed.

[0072] Comparative Example 2

[0073] The difference between this comparative example and comparative example 1 is that the reaction conditions in the second hydrogenation reactor are such that the conversion rate of the reaction reaches the same as that of Example 2, that is, the conversion rate is 46%.

[0074] The results show that the temperature required in the second hydrogenation reactor is 47° C. higher than that in Example 2. Too high a temperature leads to excessive cracking of the oil product, a low yield of the middle distillate oil, and catalyst coking that seriously affects the service life of the catalyst.

[0075] Comparative Example 3

[0076] The difference between this comparative example and Example 2 is that after mixing in the mass transfer enhanced mixer, in the emulsion containing microbubbles, the number of microbubbles with a particle size of ≥1 μm and <1 mm accounts for 45% of the volume of the bubbles contained in the emulsion.

[0077] The results showed that the conversion rate of the second hydrogenation reaction was only 32%, which was low and had poor process economic benefits.

[0078] The above obtained middle distillate oil was tested, and the performance data are shown in Table 2 below:

[0079] Table 2

[0080]

[0081] It can be seen from the data of Examples 1-3 that the present invention produces middle distillate oil through a relatively mild preparation method with a yield of more than 83%, and meets the requirements of the pour point and flash point of low-freezing diesel.

[0082] It can be seen from the experimental results of Comparative Examples 1 and 2 that, when the enhanced mass transfer mixer is not used, even if the second hydrogenation reactor adopts the same process parameters, the conversion rate is too low, resulting in a large amount of unreacted heavy oil circulation, which is not industrially feasible; or, by increasing the reaction temperature, the conversion rate is increased to the same as that of Example 2, but because the reaction temperature is too high, the catalyst is severely coked and carbonized, which seriously affects the catalyst life.

Claims

1. A method for mildly hydrogenating Fischer-Tropsch refined tail oil to produce more middle distillate oil, characterized in that: include: (1) introducing the Fischer-Tropsch refined tail oil and the hydrogen-containing stream into a first hydrogenation reactor for hydrogenation reaction to obtain a first reaction effluent, wherein the first reaction effluent is sequentially separated and fractionated to obtain a first gas, light oil, middle distillate oil and heavy oil; (2) the heavy oil and the hydrogen-containing stream are introduced into an enhanced mass transfer mixer and mixed to obtain an emulsion containing microbubbles, the emulsion is subjected to a hydrogenation reaction in a second hydrogenation reactor to obtain a second reaction effluent, the second reaction effluent is separated to obtain a second gas and product oil, and the obtained product oil is returned to the fractionation treatment in step (1); The hydrogenation reaction temperature in the first hydrogenation reactor and the second hydrogenation reactor is 290-340°C, and the volume space velocity in the first hydrogenation reactor and the second hydrogenation reactor is 0.1-2.0h -1 ; The volume fraction of microbubbles with a particle size of ≥1 μm and <1 mm in the emulsion is ≥65%.

2. The method according to claim 1, characterized in that The second hydrogenation reactor is selected from an upward fixed bed hydrogenation reactor; the conditions for the hydrogenation reaction in the second hydrogenation reactor are: the reaction pressure is 1.5 to 4.5 MPa; The reaction pressure of the first hydrogenation reactor is 3.0-15.0 MPa, and the volume ratio of hydrogen to oil is (350-1600):

1.

3. The method according to claim 1 or 2, characterized in that: The conversion degree of the first hydrogenation reaction in step (1) is controlled to be no more than 40%; the conversion degree of the second hydrogenation reaction in step (2) is controlled to have a conversion rate of 40-75%, preferably 55-65%.

4. The method according to any one of claims 1 to 3, characterized in that The first hydrogenation reactor is filled with a first catalyst having hydrocracking and hydroisomerization activities, wherein the hydrocracking activity of the hydrogenation catalyst of the first catalyst is higher than its hydroisomerization activity; The second hydrogenation reactor is filled with a second catalyst having hydrocracking and hydroisomerization activities, and the hydroisomerization activity of the second catalyst is higher than its hydrocracking activity.

5. The method according to claim 4, characterized in that The hydroisomerization activity of the second catalyst is at least 25% higher than the hydroisomerization activity of the first catalyst; The hydrocracking activity of the second catalyst is at least 14% lower than the hydrocracking activity of the first catalyst.

6. The method according to claim 5, characterized in that The hydrogenation catalyst loaded in the first hydrogenation reactor is selected from a hydroisomerization cracking catalyst whose carrier is a molecular sieve; The hydrogenation catalyst loaded in the second hydrogenation reactor is selected from a hydroisomerization cracking catalyst whose carrier is amorphous silica-alumina.

7. The method according to any one of claims 1 to 6, characterized in that: The hydrogen-containing stream is selected from fresh hydrogen, recycled hydrogen, and hydrogen-rich gas.

8. The method according to claim 7, characterized in that The mass ratio of hydrogen to heavy oil in the hydrogen-containing logistics in step (2) is (0.03-0.07):

1.

9. The method according to claim 8, characterized in that The mass ratio of hydrogen to heavy oil in the hydrogen-containing logistics in step (2) is (0.035-0.055):

1.

10. The method according to any one of claims 1 to 9, characterized in that: The method further comprises: recycling the first gas obtained after the fractionation treatment to step (2) to provide the required hydrogen-containing flow.

Images