Production method of diesel oil with low freezing point

Abstract

The invention discloses a production method of diesel oil with a low freezing point. The method comprises the following steps: S1, mixing a diesel oil raw material with hydrogen to obtain a mixed feed; s2, enabling the mixed feed obtained in S1 to sequentially pass through at least two hydrogenation reactors which are connected in series, so as to obtain a reaction effluent; and S3, separating and fractionating the reaction effluent obtained in the step S2 to obtain the low-freezing-point diesel oil, wherein a gas removal device is arranged between the two hydrogenation reactors which are connected in series; the two hydrogenation reactors connected in series are respectively a hydrofining reactor and a hydroisomerization pour point depressing reactor. The method for producing the low-freezing-point diesel oil can ensure the yield of the diesel oil, can achieve a better pour point depressing effect, and can meet the requirements of the low-freezing-point diesel oil and increasingly strict environmental protection requirements.

Description

Technical Field

[0001] The invention relates to a production method of low-freezing diesel. Background Art

[0002] As my country's economy continues to grow at a high speed, the demand for light diesel for transportation, which ranks first in diesel consumption, has increased rapidly. In the cold season in the north, in order to improve the low-temperature flow properties of diesel, the diesel pour point needs to be lowered. At present, refineries usually produce low-condensation diesel by lowering the final distillation point of diesel, mixing kerosene into diesel, medium-pressure hydro-modification (MHUG) and catalytic dewaxing. However, the production of low-condensation diesel by lowering the final distillation point of diesel will result in a reduction in the diesel output of the refinery; the addition of kerosene is not economical; although medium-pressure hydro-modification can improve the low-temperature flow properties of diesel, it will cause a decrease in diesel production due to the generation of a large amount of naphtha and gas; catalytic dewaxing is to selectively crack the chain hydrocarbons in the raw materials to reduce the diesel pour point, and its disadvantages are a reduction in diesel yield and a large loss of cetane number. Summary of the invention

[0003] In order to at least partially solve the above-mentioned technical problems existing in the prior art and further increase the selection space of process routes and catalysts for producing low-freezing point diesel, the present invention provides a production method of low-freezing point diesel, which can not only ensure the yield of diesel, but also achieve better degassing effect to meet the demand for low-freezing point diesel and increasingly stringent environmental protection requirements.

[0004] As one aspect of the present invention, it relates to a method for producing low-freezing point diesel, the method comprising the following steps:

[0005] S1, mixing diesel raw material and hydrogen to obtain mixed feed;

[0006] S2, passing the mixed feed obtained in S1 through at least two hydrogenation reactors connected in series in sequence to obtain a reaction effluent;

[0007] S3, separating and fractionating the reaction effluent obtained in S2 to obtain low-condensation diesel;

[0008] Wherein, a gas removal device is arranged between the two hydrogenation reactors connected in series; the two hydrogenation reactors connected in series are respectively a hydrogenation refining reactor and a hydrogenation isomerization decondensation reactor.

[0009] In one or some possible embodiments, the diesel feedstock has a freezing point above 0°C and a nitrogen content below 2000 μg / g; the diesel feedstock is selected from one or more of straight-run diesel, catalytic diesel, coker diesel or secondary processed oil with a distillation range of less than 440°C.

[0010] Preferably, the diesel feedstock has a freezing point above 5°C and a nitrogen content of 50 to 1200 μg / g.

[0011] In one or some possible embodiments, the operating conditions of the hydrotreating reactor and the hydroisomerization decondensation reactor are: reaction pressure 3.0 MPa to 20.0 MPa, hydrogen-to-oil volume ratio 200:1 to 1500:1, volume space velocity 0 to 10.0 h -1 , reaction temperature 270℃~460℃.

[0012] Preferably, the operating conditions of the hydrotreating reactor and the hydroisomerization decondensation reactor are: reaction pressure 4.0-12.0 MPa, hydrogen-oil volume ratio 300:1-1000:1, volume space velocity 0.3-3.0 h -1 , reaction temperature 315℃~400℃.

[0013] In one or some possible embodiments, the hydrotreating reactor is filled with a hydrotreating catalyst, and the hydroisomerization decondensing reactor is filled with a hydroisomerization decondensing catalyst.

[0014] In one or some possible embodiments, the packing volume ratio of the hydrotreating catalyst to the hydroisomerization pour point depressing catalyst is 1:8 to 8:1.

[0015] Preferably, the packing volume ratio of the hydrotreating catalyst to the hydroisomerization pour point depressing catalyst is 1:4 to 4:1.

[0016] In one or some possible embodiments, the hydroisomerization pour point depressing catalyst uses a selective cracking molecular sieve and a binder as a carrier, and uses a Group VI and / or Group VIII metal as a hydrogenation active metal component;

[0017] The selective cracking molecular sieve is a one-dimensional straight pore molecular sieve; the one-dimensional straight pore molecular sieve is selected from one or more of hydrogen-type ZSM-22, ZSM-23, ZSM-35, ZSM-38, SAPO-5, SAPO-11, SAPO-34 and SAPO-41 molecular sieves; the Group VI metal is Cu and / or Pt; the Group VIII metal is Co and / or Ni.

[0018] Preferably, the one-dimensional straight pore molecular sieve is selected from hydrogenated ZSM-23 molecular sieve and / or hydrogenated SAPO-11 molecular sieve.

[0019] In one or some possible embodiments, the silicon-aluminum molar ratio of the type selective cracking molecular sieve is 10-200.

[0020] Preferably, the silicon-aluminum molar ratio of the type-selective cracking molecular sieve is 20-100.

[0021] In one or some possible embodiments, based on the mass of the hydroisomerization depressant catalyst, the mass content of the selective cracking molecular sieve is 20% to 80%; the mass content of the hydrogenation active metal component in terms of oxide is 1% to 10%; and the mass content of the binder is 10% to 70%.

[0022] In one or some possible embodiments, the hydrotreating catalyst comprises a hydrogenation active metal component and a modified alumina carrier component; the hydrogenation active metal component is selected from W, Mo, Co, Ni, and Fe.

[0023] In one or some possible embodiments, based on the mass of the hydrotreating catalyst, the mass content of the hydrogenation active metal component is 15-50%.

[0024] As another aspect of the present invention, it relates to low-freezing point diesel prepared by the above production method, wherein the diesel has a freezing point lower than -35°C, a cold filter point lower than -29°C, and a yield of not less than 90%.

[0025] The production method of low-condensate diesel used in the present invention is that in two hydrogenation reactors connected in series, the diesel raw materials are first passed through the hydrofining reaction zone, and the unsaturated hydrocarbons in the raw materials are partially saturated through the hydrofining reaction, and the sulfur-containing and nitrogen-containing components in the raw materials that are poisonous to the isomerization decondensation catalyst are removed in large quantities; then the hydrogen sulfide and ammonia generated in the hydrofining reaction zone are effectively removed through the gas removal device, which greatly reduces the risk and degree of catalyst poisoning in the subsequent hydroisomerization decondensation reaction zone, thereby ensuring the smooth progress of the hydroisomerization decondensation reaction. The two catalysts are graded and loaded, so that the reaction performance of the decondensation catalyst can be fully utilized, the catalyst isomerization selectivity can be improved, and an ideal reaction effect can be obtained, which can not only ensure the yield of diesel, but also achieve a better decondensation effect.

[0026] The catalyst system used in the present invention can not only achieve a significant reduction in the pour point of diesel, but also has a high reaction activity. In the catalyst system of the present invention, after the molecular sieve material is introduced as a catalyst carrier, the acid distribution tends to be reasonable, the isomerization activity and selectivity are significantly improved, the reaction temperature is reduced, the yield of isomerized products is significantly improved, and the pour point reduction effect is obvious. When producing low pour point diesel at -35°C, the diesel yield reaches more than 90wt%, and the improvement of the cold filter point is also particularly prominent, which has obvious advantages over the traditional hydrogenation pour point reduction.

[0027] The catalyst system used in the present invention has strong aromatic saturation performance. Since the alkane hydrogenation isomerization process will cause a partial loss of cetane number, the traditional hydrodecondensation is usually matched with hydrogenation upgrading to achieve cetane number recovery and improvement. The catalyst system of the hydrorefining / isomerization decondensation combination used in the present invention not only has strong aromatic saturation performance, but also can further achieve aromatic deep saturation during the hydrogenation isomerization reaction, thereby directly ensuring the recovery and improvement of the cetane number.

[0028] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention are realized and obtained by the structures particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The process flow chart of producing low-freezing diesel in Examples 1 to 6 of the present invention;

[0030] Figure 2 This is a process flow chart for producing low-condensation diesel in Comparative Example 1 of the present invention;

[0031] Figure 3 This is a process flow chart for producing low-condensation diesel in Comparative Examples 2 to 3 of the present invention. DETAILED DESCRIPTION

[0032] When the inventors were exploring how to reduce the pour point of diesel while ensuring the yield of diesel without losing the cetane number, they found through reading a large number of documents and conducting corresponding experimental studies:

[0033] The inventors refer to a lubricating oil hydroprocessing catalyst and its preparation method disclosed in CN1552822A. The catalyst adopts a new composite molecular sieve with two structural characteristics of TON and MFI, and the process is as follows: the composite molecular sieve, additives, other inorganic refractory oxides, extrusion aids, water, peptizing agents, etc. are fully kneaded into a plastic paste, extruded into strips, and the catalyst carrier is obtained through post-treatment processes such as drying and roasting; then the active metal components and additives are loaded on the carrier, and the catalyst is obtained by drying and activation. However, the inventors found that: since the composite molecular sieve used has not been modified, it has many surface acid sites, and the proportion of strong acid is relatively large, resulting in side reactions such as cracking. At the same time, since the molecular sieve pores are slightly larger, it is easy to cause the reactants to enter the pores and crack, so its liquid yield still has the potential to be further improved.

[0034] The inventor refers to a method for producing low-sulfur and low-condensation diesel disclosed in CN106675644A, which comprises the following contents: (1) the inferior diesel raw material and the powdered No-Co type hydrorefining catalyst are fully mixed in a mixer to obtain a mixed feed of the catalyst and the raw oil; (2) the mixed feed and hydrogen enter the ebullating bed reactor from the bottom of the reactor equipped with the hydrodecondensation catalyst and the Mo-Ni type hydrorefining catalyst to react; (3) the post-reaction flow containing the powdered No-Co type hydrorefining catalyst is discharged from the top of the ebullating bed reactor and enters the stabilization reactor for supplementary hydrorefining; (4) the material obtained in step (3) is subjected to solid-liquid separation, and the liquid phase enters the fractionation system to obtain a low-sulfur and low-condensation diesel product. The method reasonably combines and utilizes the temperature drop in the hydrodecondensation process and the temperature rise in the hydrogenation process, and while producing low-condensation point and ultra-low sulfur diesel, it reduces the hot spot temperature of the device, prolongs the operation cycle, and saves operating costs; however, the inventor believes that the preparation process is complicated, the operation is difficult, and the decondensation range is limited.

[0035] The inventors refer to a method for producing clean low-freezing-point diesel disclosed in CN103805244A. In this method, diesel is mixed with hydrogen and then passed through at least two series-connected hydrogenation reaction zones in sequence. According to the material flow direction, each hydrogenation reaction zone includes a composite bed of refined decondensation catalysts mixed with hydrodecondensation catalysts and hydrofining catalysts and a bed of hydrogenation reforming catalysts in sequence; the reaction effluent obtained from the last hydrogenation reaction zone is separated and fractionated to obtain a clean low-freezing-point diesel product, as well as a small amount of light naphtha and liquefied gas. This method reasonably combines and utilizes the temperature drop in the hydrodecondensation process with the temperature rise in the hydrofining and reforming processes, while producing low-freezing and low-sulfur diesel, the diesel yield is increased, the hot spot temperature of the device is reduced, and the operation cycle is extended; in addition, the consumption of cold hydrogen or the gas loss of the heating furnace is reduced, and the operating cost is saved. However, the inventors believe that: using this method, the diesel yield loss is large and more light components are generated.

[0036] The inventors refer to a diesel hydrodecondensation method disclosed in CN102051232A. The method adopts a series process of hydrofining and hydrodecondensation, wherein the hydrodecondensation catalyst used is modified by metal additives and silicon, effectively adjusting the acidity and pore shape of the inner and outer surfaces of the shape-selective cracking molecular sieve, which is conducive to the diffusion of wax molecules in the diesel feedstock into the pores of the molecular sieve to carry out shape-selective cracking reaction, has high catalytic activity and selectivity of the target product, and because the acidity of the outer surface of the molecular sieve is weak, secondary cracking and other side reactions are reduced, so that the diesel decondensation effect is good and the diesel fraction yield is high. However, the inventors believe that the diesel produced by this method has a limited decondensation range, a large loss in diesel yield, and no obvious improvement in cold filter point.

[0037] In summary, in view of the fact that the existing technologies are not as good as the inventors' expectations, the inventors have made the present invention through multiple experiments and studies.

[0038] The method of the present invention is further described below in conjunction with the accompanying drawings, but the present invention is not limited thereby.

[0039] like Figure 1 As shown, the production method of low-freezing diesel of the present invention comprises the following steps:

[0040] First, the diesel feedstock and hydrogen are mixed at the inlet of the hydrotreating reactor and then introduced into the hydrotreating reactor to carry out hydrodesulfurization, hydrodenitrogenation, olefin saturation and aromatic saturation reactions to obtain reaction product I; the obtained reaction product I then enters the gas removal device to remove impurity gases such as NH3 and H2S to obtain reaction product II; the reaction product II is then introduced into the hydroisomerization decondensation reactor to carry out hydroisomerization and deep aromatic hydrogenation saturation reactions to obtain reaction product III; then, the reaction product III is successively introduced into the high-pressure separator and the low-pressure separator, and finally introduced into the fractionation tower to obtain the light component product - low-condensation diesel.

[0041] The hydroisomerization pour point depressing catalyst can be selected from various existing commercial catalysts, such as the PHV series hydroisomerization pour point depressing catalyst developed by the PetroChina Petrochemical Research Institute (PRI).

[0042] The hydrotreating catalyst may be selected from various existing commercial catalysts, such as the PHF diesel hydrotreating catalyst series developed by PRI and the PHD bulk high efficiency hydrotreating catalyst series; or a hydrotreating catalyst with similar performance may be prepared and selected according to the common sense in the art as needed.

[0043] The present invention is further described below in conjunction with specific embodiments, and the protection scope of the present invention is not limited by the following embodiments. The materials mainly involved in the embodiments are all conventional commercially available products;

[0044] The main properties of the raw oil used in Examples 1 to 6 are shown in Table 1 below.

[0045] Table 1 Raw oil properties

[0046]

[0047]

[0048] The following are specific examples and comparative examples of the present invention. The operating conditions set in the examples and comparative examples are shown in Table 2. The following hydrotreating catalysts and hydroisomerization pour point depressing catalysts are both from China Petrochemical Research Institute.

[0049] Example 1

[0050] Use Figure 1 The process flow chart shown in the figure produces low-condensate diesel, wherein the loading volume ratio of the hydrotreating catalyst to the hydroisomerization decondensate catalyst is 1:1.

[0051] Example 2

[0052] The difference from Example 1 is that the diesel raw material is coking diesel produced by PetroChina.

[0053] Example 3

[0054] The difference from Example 1 is that the packing volume ratio of the hydrotreating catalyst to the hydroisomerization pour point depressing catalyst is 1:4.

[0055] Example 4

[0056] The difference from Example 1 is that the packing volume ratio of the hydrotreating catalyst to the hydroisomerization pour point depressing catalyst is 1:8.

[0057] Example 5

[0058] The difference from Example 1 is that the packing volume ratio of the hydrotreating catalyst to the hydroisomerization pour point depressing catalyst is 4:1.

[0059] Example 6

[0060] The difference from Example 1 is that the filling volume ratio of the hydrotreating catalyst to the hydroisomerization pour point depressing catalyst is 8:1.

[0061] Comparative Example 1

[0062] Use Figure 2 The process flow chart shown in the figure produces low-freezing diesel. The remaining conditions are the same as those in Example 1.

[0063] Comparative Example 2

[0064] Use Figure 3 The process flow chart shown in the figure produces low-freezing diesel. This comparative example adopts the traditional diesel de-freezing process. The production process of comparative example 1 includes two reactors, the first reactor is filled with a hydrofining catalyst, and the second reactor is filled with a de-freezing catalyst. The filling ratio is the same as that of Example 1. And comparative example 1 and Example 1 produce the same brand of low-freezing diesel.

[0065] Comparative Example 3

[0066] The difference from Comparative Example 1 is that the feedstock oil of Example 2 is used.

[0067] Table 2 Operating conditions

[0068]

[0069]

[0070] After the process operation was completed, the inventors tested the obtained products according to the relevant standards in GB19147-2016, and recorded the test results in the following table.

[0071] Table 3 Performance test results

[0072]

[0073] Through the performance test results in Table 3, combined with Examples 1 to 6 and Comparative Examples 1 to 3, the inventors believe that:

[0074] By adopting the process method of the present invention, low-condensation diesel is produced, and the condensation point and cold filter point of diesel are reduced by more than 40°C, while the diesel yield is maintained at more than 90%, and the aromatic content can also be reduced to 0.3%. While significantly reducing the condensation point and cold filter point of diesel, a very high diesel yield is maintained. At the same time, a significant saturation of aromatics is achieved, thereby compensating for the loss of cetane number caused by the isomerization reaction of diesel fractions, ensuring the recovery and improvement of the cetane number. Compared with Example 1, the condensation point of Comparative Example 1 is only about 30°C, and the cold filter point is difficult to be effectively reduced. At the same time, the diesel yield is only about 85%, the aromatic content is reduced less, and the cetane number loses more than 1 unit.

[0075] The above are only preferred feasible embodiments of the present invention, and the protection scope of the present invention is not limited thereto. Various modifications or applications made according to the above embodiments are within the protection scope of this technical solution.

[0076] Although the specific embodiments of the present invention have been described in detail, it will be understood by those skilled in the art. According to all the teachings disclosed, various modifications and replacements can be made to those details, and these changes are all within the protection scope of the present invention. The full scope of the present invention is given by the attached claims and any equivalents thereof.

Claims

1. A method for producing low-freezing point diesel, characterized in that: The method comprises the following steps: S1, mixing diesel raw material and hydrogen to obtain mixed feed; S2, passing the mixed feed obtained in S1 through at least two hydrogenation reactors connected in series in sequence to obtain a reaction effluent; S3, separating and fractionating the reaction effluent obtained in S2 to obtain low-condensation diesel; Wherein, a gas removal device is arranged between the two hydrogenation reactors connected in series; the two hydrogenation reactors connected in series are respectively a hydrogenation refining reactor and a hydrogenation isomerization decondensation reactor.

2. The method for producing low freezing point diesel according to claim 1, characterized in that: The diesel raw material has a condensation point above 0°C and a nitrogen content below 2000 μg / g; the diesel raw material is selected from one or more of straight-run diesel, catalytic diesel, coker diesel or secondary processed oil with a distillation range of less than 440°C; Preferably, the diesel feedstock has a freezing point above 5°C and a nitrogen content of 50 to 1200 μg / g.

3. The method for producing low-freezing diesel according to claim 1, characterized in that: The operating conditions of the hydrotreating reactor and the hydroisomerization decondensation reactor are: reaction pressure 3.0MPa-20.0MPa, hydrogen-oil volume ratio 200:1-1500:1, volume space velocity 0-10.0h -1 , reaction temperature 270℃~460℃; Preferably, the reaction pressure is 4.0-12.0 MPa, the hydrogen-oil volume ratio is 300:1-1000:1, and the volume space velocity is 0.3-3.0 h -1 , reaction temperature 315℃~400℃.

4. The method for producing low-freezing diesel according to claim 1, characterized in that: The hydrotreating reactor is filled with a hydrotreating catalyst, and the hydroisomerization decondensation reactor is filled with a hydroisomerization decondensation catalyst; The packing volume ratio of the hydrotreating catalyst to the hydroisomerization pour point depressing catalyst is 1:8 to 8:1; Preferably, the packing volume ratio of the hydrotreating catalyst to the hydroisomerization pour point depressing catalyst is 1:4 to 4:

1.

5. The method for producing low-freezing point diesel according to claim 4, characterized in that: The hydroisomerization pour point depressing catalyst uses a selective cracking molecular sieve and a binder as carriers and Group VI and / or Group VIII metals as hydrogenation active metal components; The selective cracking molecular sieve is a one-dimensional straight pore molecular sieve; the one-dimensional straight pore molecular sieve is selected from one or more of hydrogen-type ZSM-22, ZSM-23, ZSM-35, ZSM-38, SAPO-5, SAPO-11, SAPO-34 and SAPO-41 molecular sieves; the Group VI metal is Cu and / or Pt; the Group VIII metal is Co and / or Ni; Preferably, the one-dimensional straight pore molecular sieve is selected from hydrogenated ZSM-23 molecular sieve and / or hydrogenated SAPO-11 molecular sieve.

6. The method for producing low-freezing point diesel according to claim 5, characterized in that: The silicon-aluminum molar ratio of the selective cracking molecular sieve is 10 to 200; Preferably, the silicon-aluminum molar ratio of the type-selective cracking molecular sieve is 20-100.

7. The method for producing low-freezing diesel according to claim 4, characterized in that: Based on the mass of the hydroisomerization depressant catalyst, the mass content of the selective cracking molecular sieve is 20% to 80%; the mass content of the hydrogenation active metal component in terms of oxide is 1% to 10%; and the mass content of the adhesive is 10% to 70%.

8. The method for producing low freezing point diesel according to claim 4, characterized in that: The hydrotreating catalyst comprises a hydrogenation active metal component and a modified alumina carrier component; the hydrogenation active metal component is selected from W, Mo, Co, Ni, and Fe.

9. The method for producing low freezing point diesel according to claim 4, characterized in that: Based on the mass of the hydrotreating catalyst, the mass content of the hydrogenation active metal component is 15-50%.

10. A low freezing point diesel produced by the method according to any one of claims 1 to 9, characterized in that: The diesel has a condensation point lower than -35°C, a cold filter point lower than -29°C, and a yield of not less than 90%.

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