Alkali metal treatment-hydrocracking combined process

Abstract

The present invention discloses a combined alkali metal treatment and hydrocracking process. The process comprises: a coal tar feedstock is sequentially processed through an alkali metal treatment unit and a separation unit, the liquid phase separated out enters the hydrocracking unit, the resulting reaction effluent is fractionated to obtain a hydrocracked tail oil; the hydrocracked tail oil is then mixed with the alkali metal treatment unit reaction effluent and then enters the separation unit. This process efficiently combines alkali metal treatment and hydrocracking technologies to maximize the quality and yield of light oil products, achieve efficient utilization of coal tar resources, and prolong the operation cycle of the processing unit.

Description

Technical Field

[0001] The present invention belongs to the field of coal chemical industry and relates to a method for processing coal tar, in particular to a method for processing coal tar raw materials by combining alkali metal treatment and hydrocracking processes. Background Art

[0002] Coal tar, a black or dark brown viscous liquid with a pungent odor, is one of the primary products of coal thermal processing. Coal tar can be divided into three categories based on its distillation temperature: high-temperature coal tar (900-1000°C), medium-temperature coal tar (700-900°C), and low-temperature coal tar (500-700°C). The comprehensive utilization of coal tar resources can significantly improve economic efficiency and is of great significance to the value-added transformation of my country's coal resources and regional economic development.

[0003] CN115216341A discloses a medium-low temperature coal tar processing system and method. The processing method comprises: (1) hydrogen first enters a mixed hydrogen dissolving unit and then passes upward through a liquid fraction hydrogenation unit, a raw material flash unit, and a gaseous fraction hydrogenation unit in sequence; the raw material flashes into a gaseous fraction and a liquid fraction; (2) the gaseous fraction enters the gaseous fraction hydrogenation unit for shallow hydrogenation, and the gaseous product enters a fractionation unit for separation into triphenyl feedstock and phenol feedstock; the liquid fraction enters the liquid fraction hydrogenation unit for hydrogenation, and the liquid product enters the mixed hydrogen dissolving unit to form a hydrogen dissolving stream for hydrogenation and upgrading.

[0004] CN102851066A discloses a two-stage coal tar hydrogenation combined process method, comprising: (a) coal tar raw material enters a hydrotreatment reaction section for a hydrotreatment reaction; (b) the reaction effluent of the hydrotreatment reaction section is subjected to gas-liquid separation, and the separated liquid phase enters a fractionation device for fractionation into a gasoline fraction, a diesel fraction and a heavy fraction; (c) at least a portion of the heavy fraction obtained in step (b) enters a hydrocracking reaction section for a hydrocracking reaction; (d) the reaction effluent of the hydrocracking reaction section enters a hot high-pressure separator for separation into a gas phase and a liquid phase, and at least a portion of the liquid phase enters the hydrotreatment reaction section of step (a); and (e) the gas phase separated in the hot high-pressure separator in step (d) and the diesel fraction obtained by fractionation in step (b) are mixed and enter the diesel hydroreforming reaction section.

[0005] All of the above technologies utilize hydrogenation processes to deoxygenate, desulfurize, and demetallize coal tar feedstock. However, the water generated by the hydrodeoxygenation reaction can cause the catalyst to break, placing extremely high demands on the water resistance of the coal tar hydrogenation catalyst. In addition, coal tar contains high levels of mechanical impurities and heavy metals, which can easily cause bed blockage and increased bed pressure drop, shortening the unit's operating cycle. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention provides a combined alkali metal treatment and hydrocracking process. This method efficiently combines alkali metal treatment and hydrocracking technologies to maximize the quality and yield of light oil products, achieving efficient utilization of coal tar resources and long-term operation of processing equipment.

[0007] An alkali metal treatment-hydrocracking combined process method comprises the following contents: coal tar raw material is processed in an alkali metal treatment device and a separation device in sequence, the liquid phase material separated out enters the hydrocracking device, the reaction effluent obtained after the processing is fractionated to obtain hydrocracking tail oil; the hydrocracking tail oil is mixed with the reaction effluent of the alkali metal treatment device and then enters the separation device.

[0008] In the method of the present invention, the hydrocracking tail oil is a fraction greater than 320°C, preferably a fraction greater than 340°C; the saturated hydrocarbon content in the hydrocracking tail oil is greater than 75.0 wt.%, preferably greater than 78.0 wt.%.

[0009] A specific method of an alkali metal treatment-hydrocracking combined process comprises the following steps:

[0010] (1) Coal tar and alkali metals are mixed and fed into an alkali metal treatment unit to react in the presence of hydrogen;

[0011] (2) The reaction effluent obtained in step (1) is mixed with the hydrocracking tail oil and then sent to a separation device for treatment to obtain a liquid phase feed stream;

[0012] (3) The liquid phase stream in step (2) enters the hydrocracking unit, undergoes cracking reaction under the action of the hydrocracking catalyst, and is then separated to obtain gas, gasoline, diesel and tail oil, wherein the hydrocracking tail oil repeats the process of step (2).

[0013] In step (1) of the method of the present invention, the coal tar raw material is at least one of low-temperature coal tar, medium-temperature coal tar, and high-temperature coal tar, preferably low-temperature coal tar and / or medium-temperature coal tar. The coal tar raw material has a density of 0.95-1.20 g / ml, a sulfur content of 500-5000 μg / g, a nitrogen content of 4000-10000 μg / g, an oxygen content of 3.0-15.0 wt.%, and a total metal content of 50-350 μg / g.

[0014] In step (1) of the method of the present invention, the coal tar raw material is pretreated and then enters the alkali metal treatment device. The water content of the pretreated coal tar raw material is 0.5wt%-3.0wt%, preferably 1.0wt%-2.5wt%; the solid content is 0.05wt%-0.35wt%, preferably 0.10wt%-0.20wt%.

[0015] In step (1) of the method of the present invention, the alkali metal is at least one of the six metal elements of Group IA of the periodic table except hydrogen, namely lithium, sodium, potassium, rubidium, cesium and francium, preferably lithium, sodium or potassium; and the mass ratio of the alkali metal to the coal tar raw material is (5.0-25.0):100, preferably (10.0-20.0):100.

[0016] In step (1) of the method of the present invention, the reactor used in the alkali metal treatment device is one or more of a kettle reactor, a pipeline reactor and a tower reactor, preferably a kettle reactor or a pipeline reactor.

[0017] In step (1) of the method of the present invention, the operating conditions of the alkali metal treatment device are: reaction temperature 200-400°C, reaction pressure 2.0-20.0 MPa, residence time 0.1-4.0 h, hydrogen to oil volume ratio 500-1800 Nm 3 / m 3 The preferred operating conditions are: reaction temperature 260-360 ° C, reaction pressure 3.0-10.0 MPa, residence time 0.5-1.5h, hydrogen to oil volume ratio 800-1500Nm 3 / m 3 .

[0018] In step (2) of the method of the present invention, the hydrocracking tail oil is a fraction greater than 340°C, preferably a fraction greater than 360°C; and the saturated hydrocarbon content in the hydrocracking tail oil is greater than 75.0 wt.%, preferably greater than 78.0 wt.%.

[0019] In step (2) of the method of the present invention, hydrocracking gasoline is further introduced, and the hydrocracking gasoline is mixed with the reaction effluent and hydrocracking tail oil obtained in step (1) and then enters a separation device for treatment; the hydrocracking gasoline is a fraction with a temperature of less than 220°C in the hydrocracking full fraction product, preferably a fraction with a temperature of less than 200°C; the saturated hydrocarbon content in the hydrocracking gasoline is greater than 70.0wt%, preferably greater than 75.0wt%; the mass ratio of the hydrocracking gasoline to the reaction effluent obtained in step (1) is (5-35):100, preferably (10-20):100.

[0020] In step (2) of the method of the present invention, the solid content of the liquid phase stream obtained by separation treatment is controlled to be 20-200 ppm, preferably 30-100 ppm; the acid value is less than 1.0 mgKOH / g, preferably less than 0.5 mgKOH / g.

[0021] In step (2) of the method of the present invention, the separation process is operated as follows: a first liquid phase stream is obtained by primary separation; the first liquid phase stream is mixed with an acidic auxiliary agent and then subjected to secondary separation to obtain a second liquid phase stream. The solid content of the first liquid phase stream is controlled to be 500-1500 ppm, preferably 500-1000 ppm; the alkalinity is 15-30 mgKOH / g, preferably 11-20 mgKOH / g. The acidic auxiliary agent is one or more of formic acid, hydrochloric acid, sulfuric acid and phosphoric acid, and the acidic auxiliary agent is preferably added under stirring, the stirring rate is 200-1500 r / min, preferably 500-1200 r / min; the mixing temperature is 100-350°C, preferably 150-300°C. The solid content of the second liquid phase stream is controlled to be 20-200 ppm, preferably 30-100 ppm; the acidity is less than 1.0 mgKOH / g, preferably less than 0.5 mgKOH / g.

[0022] In step (3) of the method of the present invention, the hydrocracking unit includes at least one fixed-bed hydrocracking reactor, wherein the hydrocracking reactor is loaded with at least one hydrocracking catalyst; the hydrocracking catalyst includes a carrier and an active metal component, wherein the carrier includes amorphous silica-alumina and / or a molecular sieve, wherein the molecular sieve is a Y-type and / or a β-type molecular sieve; and the active metal component is one or more elements selected from Group VI, Group VII, or Group VIII, preferably one or more selected from molybdenum, tungsten, cobalt, or nickel. The active metal component is present in an amount of 5-40 wt.% as a metal oxide, based on the weight of the catalyst.

[0023] In step (3) of the method of the present invention, the process conditions of the hydrocracking unit are as follows: reaction temperature 320-450°C, reaction pressure 6.0-20.0 MPa, space velocity 0.2-3.0 h -1 , hydrogen-oil volume ratio 100-2500Nm 3 / m 3 Preferably, the reaction temperature is 360-400 ° C, the reaction pressure is 12.0-18.0 MPa, and the space velocity is 0.2-2.0 h -1 , hydrogen-oil volume ratio 800-1500Nm 3 / m 3 .

[0024] During their research, the inventors discovered that the reaction effluent from the coal tar alkali metal treatment unit is rich in alkali metal alkoxides (such as sodium phenoxide), alkali metal sulfides (such as sodium sulfide), and unreacted alkali metals. If these substances enter the hydrocracking unit, they can deactivate the hydrocracking catalyst, necessitating their removal in a separation unit. Analysis revealed that these substances are all highly polar compounds. According to the principle of like dissolves like, solutes composed of polar molecules dissolve readily in solvents composed of polar molecules but not readily in solvents composed of non-polar molecules. Furthermore, the inventors discovered that hydrocracking tail oil is rich in saturated hydrocarbons and constitutes a non-polar material. Therefore, recycling this hydrocracking tail oil to the separation unit and mixing it with the reaction effluent from the alkali metal treatment unit promotes the crystallization of polar substances such as alkali metal alkoxides and alkali metal sulfides, thereby improving separation efficiency. Furthermore, the hydrocracking tail oil fraction has low levels of sulfur, nitrogen, gums, aromatics, and carbon residue, and its group composition is primarily saturated hydrocarbons, making it a high-quality hydrocracking feedstock. Tail oil circulation has a good dilution effect on the feed of the hydrocracking unit, which not only relieves the equipment load but also improves the performance of the hydrogenated products.

[0025] In addition, the present invention also proposes a hydrocracking gasoline recycling technology solution: all or part of the hydrocracking gasoline is mixed with the reaction effluent and hydrocracking tail oil obtained in step (1) and then enters a separation device for treatment. Similarly, hydrocracking gasoline is rich in non-polar molecules such as saturated hydrocarbons, which helps to improve separation efficiency. The difference is that the viscosity of hydrocracking gasoline is significantly lower than that of the tail oil fraction, which can dilute the feed of the hydrocracking unit and improve the reaction effect.

[0026] Compared with the prior art, the method of the present invention has the following advantages:

[0027] 1. The present method efficiently combines alkali metal treatment and hydrocracking processes for coal tar processing. Taking advantage of the fact that hydrocracking tail oil is rich in non-polar substances, the present invention proposes a technical solution for recycling the hydrocracking tail oil to a separation unit. The tail oil fraction is mixed with the reaction effluent from the alkali metal treatment unit and then fed into the separation unit. This promotes the crystallization of polar substances such as alkali metal alkoxides and alkali metal sulfides, improving separation efficiency. This prevents these substances from entering the hydrocracking unit and deactivating the hydrocracking catalyst.

[0028] 2. The present invention further proposes a hydrocracking gasoline recycling technology solution: all or part of the hydrocracking gasoline is mixed with the reaction effluent and hydrocracking tail oil obtained in step (1) and then enters a separation unit for treatment. Similarly, hydrocracking gasoline is rich in non-polar molecules such as saturated hydrocarbons, which helps improve separation efficiency. The difference is that the viscosity of hydrocracking gasoline is significantly lower than that of the tail oil fraction, which can dilute the feed of the hydrocracking unit and improve the reaction effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Attachment Figure 1 This is a schematic diagram of an alkali metal treatment-hydrocracking combined process provided by the present invention.

[0030] Among them, 1-alkali metal treatment reactor, 2-primary separation device, 3-mixing device, 4-secondary separation device, 5-hydrocracking reactor, 6-alkali metal, 7-hydrogen, 8-coal tar feedstock, 9-alkali metal treatment reaction effluent, 10-impurities removed by primary separation, 11-first liquid phase feed stream, 12-gas phase feed stream, 13-liquid phase feed stream obtained by reaction with acidic auxiliary agent, 14-acidic auxiliary agent, 15-second liquid phase feed stream, 16-impurities removed by secondary separation, 17-gas, 18-hydrocracking gasoline, 19-hydrocracking diesel, and 20-hydrocracking tail oil. Implementation Method

[0031] The method provided by the present invention is described below with reference to the accompanying drawings.

[0032] The coal tar raw material from pipeline 8 is mixed with hydrogen from pipeline 7 and alkali metal from pipeline 6 and then enters the alkali metal treatment reactor 1 for reaction. The effluent from the alkali metal treatment reaction is mixed with the hydrocracking tail oil from pipeline 20 through pipeline 9 and enters the primary separation device 2 for separation, wherein the impurities removed by the primary separation are extracted through pipeline 10; the first liquid phase stream obtained by the primary separation enters the mixing device 3 through pipeline 11, reacts with the acidic auxiliary agent from pipeline 14 to obtain a gas phase stream and a liquid phase stream, and the gas phase stream is extracted through pipeline 12; the liquid phase stream enters the secondary separation device 4 through pipeline 13, and the impurities removed by the secondary separation are extracted through pipeline 16; the second liquid phase stream enters the hydrocracking device 5 through pipeline 15 for cracking reaction, and then is fractionated to obtain gas, gasoline, diesel and tail oil fractions, wherein the gas, gasoline and diesel are extracted through pipelines 17, 18 and 19 respectively, and the hydrocracking tail oil is circulated to the primary separation device 2 through pipeline 20.

[0033] The following examples will further illustrate the method provided by the present invention, but are not intended to limit the present invention.

[0034] The alkali metal treatment test in the examples was carried out on an alkali metal treatment pilot plant designed independently in the laboratory. The reactor used was a kettle reactor with a stirring rate of 1200 r / min. Separation and treatment process: a first liquid phase stream was obtained after a primary separation; the first liquid phase stream was mixed with an acidic auxiliary agent under stirring and then subjected to a secondary separation to obtain a second liquid phase stream. The acidic additive used was a mixture of formic acid and hydrochloric acid, with a mass ratio of formic acid to hydrochloric acid of 1:1. The stirring rate was 1200 r / min; the mixing temperature was 150°C. The hydrorefining and hydrocracking tests in the examples and comparative examples were carried out on a fixed-bed hydrogenation unit. The hydrorefining catalyst used was a 3936 hydrorefining catalyst, and the hydrocracking catalyst was a commercial brand FC-32 hydrocracking catalyst. The above catalysts were all developed by Sinopec Fushun Petrochemical Research Institute.

[0035] Example 1

[0036] (1) Coal tar and alkali metals are mixed and fed into an alkali metal treatment unit to react in the presence of hydrogen;

[0037] (2) The reaction effluent obtained in step (1) is mixed with the hydrocracking tail oil and then sent to a separation device for treatment to obtain a liquid phase feed stream;

[0038] (3) The liquid phase stream in step (2) enters the hydrocracking unit, undergoes cracking reaction under the action of the hydrocracking catalyst, and is then separated to obtain gas, gasoline, diesel and tail oil, wherein the hydrocracking tail oil repeats the process of step (2).

[0039] Example 2

[0040] The process flow of this embodiment is the same as that of embodiment 1.

[0041] Example 3

[0042] The process flow of this embodiment is the same as that of embodiment 1.

[0043] Example 4

[0044] (1) Coal tar and alkali metals are mixed and fed into an alkali metal treatment unit to react in the presence of hydrogen;

[0045] (2) The reaction effluent obtained in step (1) is mixed with hydrocracking gasoline and hydrocracking tail oil and then enters a separation device for treatment to obtain a liquid phase feed stream;

[0046] (3) The liquid phase stream in step (2) enters the hydrocracking unit, undergoes cracking reaction under the action of the hydrocracking catalyst, and is then separated to obtain gas, gasoline, diesel and tail oil, wherein the hydrocracking gasoline and hydrocracking tail oil repeat the process of step (2).

[0047] Example 5

[0048] The process flow of this embodiment is the same as that of Example 4.

[0049] Example 6

[0050] The process flow of this embodiment is the same as that of Example 4.

[0051] The raw material used in the Examples and Comparative Examples was medium-low temperature coal tar, the properties of which are shown in Table 1. The hydrocracking distillate recycling scheme is shown in Table 2, the operating conditions of the alkali metal treatment unit and the hydrocracking unit are shown in Table 3, and the product properties after 450 hours of operation are shown in Table 4.

[0052] Table 1 Coal tar raw material properties

[0053]

[0054] Table 2 Hydrocracking distillate oil circulation scheme

[0055]

[0056] Table 3 Operating conditions of alkali metal treatment unit and hydrocracking unit

[0057]

[0058] Table 4 Product properties

[0059]

[0060] Comparative Example 1

[0061] The coal tar feedstock first enters the hydrorefining reaction zone for reaction. The resulting reaction effluent enters the hydrocracking reaction zone for hydrocracking, where it is separated into gas, gasoline, diesel, and tail oil. Operating conditions and reaction results are shown in Table 5.

[0062] Table 5 Operating conditions and reaction results of Comparative Example 1

[0063]

Claims

1. An alkali metal treatment-hydrocracking combined process, characterized in that: The method comprises the following steps: (1) Coal tar and alkali metals are mixed and fed into an alkali metal treatment unit to react in the presence of hydrogen; (2) The reaction effluent obtained in step (1) is mixed with the hydrocracking tail oil and then sent to a separation device for treatment to obtain a liquid phase feed stream; (3) The liquid phase stream in step (2) enters the hydrocracking unit, undergoes cracking reaction under the action of the hydrocracking catalyst, and is then separated to obtain gas, hydrocracking gasoline, diesel and hydrocracking tail oil, wherein the process of step (2) is repeated for the hydrocracking tail oil; The alkali metal is at least one of lithium, sodium, and potassium; the mass ratio of the alkali metal to the coal tar raw material is (5.0-25.0):100; The hydrocracking tail oil is a fraction with a temperature greater than 340° C.; the saturated hydrocarbon content in the hydrocracking tail oil is greater than 75.0 wt.%; The operation of the separation device for treatment is as follows: the reaction effluent obtained in step (1) is mixed with the hydrocracking tail oil and then subjected to a primary separation, a first liquid phase stream is obtained by the primary separation, and then mixed with the acidic auxiliary agent and then subjected to a secondary separation to obtain a second liquid phase stream, and the second liquid phase stream enters the hydrocracking device; The acidic auxiliary agent is one or more of formic acid, hydrochloric acid, sulfuric acid and phosphoric acid.

2. The method according to claim 1, wherein: In step (1), the coal tar raw material has a density of 0.95-1.20 g / mL, a sulfur content of 500-5000 μg / g, a nitrogen content of 4000-10000 μg / g, an oxygen content of 3.0-15.0 wt.%, and a total metal content of 50-350 μg / g.

3. The method according to claim 2, wherein: In step (1), the coal tar raw material is pretreated and then enters the alkali metal treatment device. The water content of the pretreated coal tar raw material is 0.5wt%-3.0wt%; and the solid content is 0.05wt%-0.35wt%.

4. The method according to claim 3, wherein: In step (1), the coal tar raw material is pretreated and then enters the alkali metal treatment device. The water content of the pretreated coal tar raw material is 1.0wt%-2.5wt%; and the solid content is 0.10wt%-0.20wt%.

5. The method according to claim 1, wherein: In step (1), the mass ratio of the alkali metal to the coal tar raw material is (10.0-20.0):

100.

6. The method according to claim 1, wherein: The reactor used in the alkali metal treatment device is one or more of a kettle reactor, a pipeline reactor and a tower reactor.

7. The method according to claim 6, characterized in that: The reactor used in the alkali metal treatment device is one or more of a kettle reactor and a pipeline reactor.

8. The method according to claim 1, wherein: The operating conditions of the alkali metal treatment device are: reaction temperature 200-400°C, reaction pressure 2.0-20.0 MPa, residence time 0.1-4.0 h, hydrogen to oil volume ratio 500-1800 Nm 3 / m 3 .

9. The method according to claim 8, characterized in that: The operating conditions of the alkali metal treatment device are: reaction temperature 260-360°C, reaction pressure 3.0-10.0 MPa, residence time 0.5-1.5h, hydrogen-to-oil volume ratio 800-1500 Nm 3 / m 3 .

10. The method according to claim 1, wherein: In step (2), the hydrocracking tail oil is a fraction having a temperature of >360°C; and the saturated hydrocarbon content in the hydrocracking tail oil is >78.0 wt.%.

11. The method according to claim 1, wherein: In step (2), hydrocracking gasoline is also introduced, and the hydrocracking gasoline is mixed with the reaction effluent and hydrocracking tail oil obtained in step (1) and then enters the separation device for treatment.

12. The method according to claim 11, wherein: In step (2), the hydrocracking gasoline is a fraction with a temperature below 220° C. in the hydrocracking full fraction product; the saturated hydrocarbon content in the hydrocracking gasoline is greater than 70.0 wt %; and the mass ratio of the hydrocracking gasoline to the reaction effluent obtained in step (1) is (5-35):

100.

13. The method according to claim 12, wherein: In step (2), the hydrocracking gasoline is the fraction with a temperature below 200° C. in the hydrocracking full fraction product; the saturated hydrocarbon content in the hydrocracking gasoline is greater than 75.0 wt %; and the mass ratio of the hydrocracking gasoline to the reaction effluent obtained in step (1) is (10-20):

100.

14. The method according to claim 1, wherein: In step (3), the hydrocracking unit includes at least one fixed-bed hydrocracking reactor, and the fixed-bed hydrocracking reactor is filled with at least one hydrocracking catalyst; the hydrocracking catalyst includes a carrier and an active metal component, the carrier includes amorphous silica-alumina and / or molecular sieve, and the molecular sieve is a Y-type and / or β-type molecular sieve; the active metal component is one or more of the elements of Group VIB and Group VIII.

15. The method according to claim 14, characterized in that: In step (3), the active metal component is one or more of molybdenum, tungsten, cobalt and nickel.

16. The method according to claim 1, wherein: In step (3), the process conditions of the hydrocracking unit are as follows: reaction temperature 320-450°C, reaction pressure 6.0-20.0 MPa, space velocity 0.2-3.0 h -1 , hydrogen-oil volume ratio 100-2500Nm 3 / m 3 .

17. The method according to claim 16, wherein: In step (3), the process conditions of the hydrocracking unit are as follows: reaction temperature 360-400 ° C, reaction pressure 12.0-18.0 MPa, space velocity 0.2-2.0h -1 , hydrogen-oil volume ratio 800-1500Nm 3 / m 3 .

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