A process for catalytic diesel hydrogenation

Abstract

A catalytic diesel hydrogenation process comprises the following steps: under hydrogenation reaction conditions, catalytic diesel feedstock and hydrogen are sequentially passed through two fixed-bed reactors connected in series, wherein the first reactor is loaded with a polycyclic aromatic hydrocarbon selective hydrogenation catalyst. The first stage of the process utilizes a specific polycyclic aromatic hydrocarbon selective hydrogenation catalyst, which first undergoes polycyclic aromatic hydrocarbon saturation, followed by a second stage of hydrodesulfurization. The catalyst in the first stage has high polycyclic aromatic hydrocarbon hydrogenation activity, reducing monocyclic aromatic hydrocarbon losses. Desulfurization is completed in the second stage, resulting in a qualified product in both steps.

Description

Technical Field

[0001] The present invention relates to the technical field of oil hydrogenation, and in particular to a process for catalytic diesel hydrogenation. Background Art

[0002] With the demands of economic development, refineries need to flexibly produce refined oil products or chemical feedstocks in response to market demand. The catalytic diesel fuel produced by refineries has a high aromatic content and can be processed as a diesel product or converted into high-value-added BTX products. Catalytic diesel fuel undergoes hydrorefining to saturate polycyclic aromatic hydrocarbons to monocyclic aromatic hydrocarbons. This can be used to produce diesel products through hydrodesulfurization or BTX products through catalytic cracking. Regardless of the route, the activity and selectivity of the catalytic diesel fuel in saturating polycyclic aromatic hydrocarbons must be improved.

[0003] CN202110919784.8 discloses a method for producing light aromatics, comprising: (1) introducing catalytic diesel feedstock into a reactive distillation tower, with the lighter components entering the distillation section to obtain a first liquid phase stream; the heavier components are hydrorefined in the stripping section to obtain a second liquid phase stream; (2) the second liquid phase stream is introduced into the first hydrocracking reaction zone to obtain a third liquid phase stream; (3) the third liquid phase stream and the first liquid phase stream are introduced into the second hydrocracking reaction zone to react to obtain a fourth liquid phase stream; (4) the fourth liquid phase stream is fractionated to obtain a naphtha fraction and a diesel fraction rich in BTX; (5) at least a portion of the diesel fraction is recycled back to step (1). The method of the present invention improves the feed hydrocarbon composition of each reaction zone of catalytic diesel by hydrorefining / hydrocracking, can effectively improve the yield of LCO catalytically converted to BTX, and realizes the high value utilization of LCO.

[0004] CN202011620206.6 discloses a catalyst-graded catalytic diesel hydroconversion method. The catalytic diesel feedstock and hydrogen enter the hydrorefining reaction zone and sequentially contact and react with two or more hydrorefining catalyst beds; the hydrorefining effluent enters the hydrocracking reaction zone and sequentially passes through two or more hydrocracking catalyst beds to undergo a hydroconversion reaction; in the hydrorefining reaction zone, along the logistics direction, the downstream bed has a lower nickel oxide mass fraction, an increased cobalt oxide mass fraction, an increased molybdenum oxide mass fraction, and an increased total active metal mass fraction in the hydrorefining catalyst compared to the adjacent upstream bed. The present invention achieves the purpose of retaining the maximum amount of monocyclic aromatic hydrocarbons in the refined oil and improving the octane number of the gasoline product by grading the hydrorefining catalysts in different reaction zones of the catalytic diesel hydroconversion.

[0005] However, the above existing technologies still have many deficiencies in removing aromatics from catalytic diesel, an oil product with a high aromatic content. For example, the process route is relatively complicated, or multiple catalyst gradations are required, which invisibly increases the difficulty of the process. Summary of the Invention

[0006] In response to the shortcomings of the existing technology, the present invention discloses a process for catalytic diesel hydrogenation, which uses a specially prepared polycyclic aromatic hydrocarbon selective hydrogenation catalyst and adopts a two-stage reaction method to effectively improve the hydrogenation effect of polycyclic aromatic hydrocarbons in catalytic diesel and reduce the loss rate of monocyclic aromatic hydrocarbons.

[0007] In the context of this specification, the pyridine adsorption infrared acid property characterization method is used to analyze the acid properties of the support and catalyst. The test conditions of the pyridine adsorption infrared acid property characterization method include: the sample is purified in a reaction tube at 500°C and 60mPa for 4 hours, cooled to room temperature, and vacuumed to 0.1mPa to adsorb pyridine, and the surface acid properties of the sample are measured.

[0008] In order to achieve the above technical objectives, the technical solutions of the present invention are as follows:

[0009] The technical purpose of the first aspect of the present invention is to provide a process for catalytic diesel hydrogenation, comprising the following steps: under hydrogenation reaction conditions, catalytic diesel feedstock and hydrogen are sequentially passed through two fixed-bed reactors connected in series, wherein the first reactor is filled with a polycyclic aromatic hydrocarbon selective hydrogenation catalyst and the second reactor is filled with a hydrodesulfurization catalyst, and a qualified diesel product is obtained from the outlet of the second reactor; wherein the polycyclic aromatic hydrocarbon selective hydrogenation catalyst is supported by alkali-modified alumina, on which an inorganic acid and an active component are supported, and the active component is a Group VIB metal sulfide and a Group VIII metal sulfide; based on the total weight of the catalyst, the alkali accounts for 0.1-5.0%, preferably 0.3-3.0%; the inorganic acid accounts for 1-12wt%, preferably 1.5-8wt%, and more preferably 2-6wt%; the active component is distributed from the catalyst surface to a catalyst surface layer no thicker than 1 / 3 of the catalyst radius; and the inorganic acid is supported on the outer surface of the catalyst.

[0010] Furthermore, after the catalytic diesel feedstock passes through the first reactor, the polycyclic aromatic hydrocarbon saturation rate is 70-90%, preferably 80-90%, the monocyclic aromatic hydrocarbon saturation rate is 5-30%, and the desulfurization rate is less than 50%, preferably 20-40%. After passing through the second reactor, the desulfurization rate is above 99%.

[0011] Furthermore, the inlet temperature of the raw material to the first reactor is 150-350°C, preferably 200-300°C, most preferably 200-270°C; the inlet temperature of the second reactor is 250-350°C, preferably 280-330°C.

[0012] Furthermore, other process conditions of the first reactor are: pressure 4.0-12.0 MPa, preferably 6.0-10.0 MPa; volume space velocity 0.1-8.0 h -1 , preferably 0.5 to 4.0 hours -1; The volume ratio of hydrogen to oil is 10:1 to 800:1, preferably 300:1 to 500:1.

[0013] Furthermore, the second reactor is used for hydrodesulfurization reaction, and the process conditions of the hydrodesulfurization reaction are: pressure 4.0-12.0 MPa, preferably 6.0-10.0 MPa; volume space velocity 0.1-4.0 h -1 , preferably 0.5 to 2.0 hours -1 The hydrogen-to-oil volume ratio is 10:1 to 800:1, preferably 300:1 to 500:1. The hydrodesulfurization catalyst is well known in the art, preferably a Mo-Ni and / or Mo-Co type diesel hydrogenation catalyst, such as the FHUDS series diesel hydrogenation catalyst developed by FRIPP.

[0014] Furthermore, in the polycyclic aromatic hydrocarbon selective hydrogenation catalyst, based on the total weight of the catalyst, the Group VIB metal sulfide accounts for 10-30%, preferably 15-28%, and the Group VIII metal sulfide accounts for 2-10%, preferably 4-8%.

[0015] Furthermore, in the polycyclic aromatic hydrocarbon selective hydrogenation catalyst, the inorganic acid is selected from at least one of phosphoric acid, boric acid, hydrofluoric acid, hydrochloric acid and sulfuric acid.

[0016] Furthermore, in the polycyclic aromatic hydrocarbon selective hydrogenation catalyst, the inorganic acid loaded on the outer surface of the catalyst is loaded on a Group VIB metal sulfide, and / or loaded on a Group VIII metal sulfide, and / or loaded on an alumina carrier.

[0017] Furthermore, in the polycyclic aromatic hydrocarbon selective hydrogenation catalyst, the active component is preferably distributed from the catalyst surface to the catalyst surface layer that is no more than 1 / 4 of the catalyst radius thickness, more preferably no more than 1 / 5 of the catalyst radius thickness. The concentration distribution of the active metal component in the radial direction of the catalyst can be measured by an electron probe. In the technical solution of the present invention, having an active component distribution means that from the outside to the inside in the radial direction of the catalyst particle, when the active component content is reduced to less than 30% of the content of the component in the outermost layer of the catalyst particle, it is considered that there is no active component distribution from the current catalyst layer to the catalyst center, and there is an active component distribution from the catalyst layer to the catalyst surface. The determination of the active component content in a certain catalyst layer is to randomly select 10 points in the catalyst layer with the same radius of the catalyst, use an electron probe to determine the element content, and perform arithmetic averaging on the measured values.

[0018] It should be understood by those skilled in the art that, for spherical catalysts, the radius is easy to determine, while for cylindrical, strip-shaped and other special-shaped catalysts, the catalyst radius referred to in the present invention refers to the radius of the circumscribed circle of the catalyst cross section.

[0019] Furthermore, in the polycyclic aromatic hydrocarbon selective hydrogenation catalyst, the Group VIB metal sulfide is molybdenum sulfide and / or tungsten sulfide, and the Group VIII metal sulfide is nickel sulfide and / or cobalt sulfide.

[0020] Furthermore, in the polycyclic aromatic hydrocarbon selective hydrogenation catalyst, the Br acid content of the base-modified alumina is 0.01-0.04 mmol / g, and the L acid content is 0.01-0.1 mmol / g; the Br acid content of the catalyst is 0.05-0.2 mmol / g, and the L acid content is 0.3-1.0 mmol / g.

[0021] Furthermore, in the polycyclic aromatic hydrocarbon selective hydrogenation catalyst, the alkali-modified alumina is obtained by impregnating alumina with an alkali solution and drying the alkali solution. The alkali solution is selected from at least one of sodium hydroxide, potassium hydroxide, and ammonia.

[0022] Furthermore, the polycyclic aromatic hydrocarbon selective hydrogenation catalyst is prepared by the following method:

[0023] (1) impregnating an alumina support with an alkaline solution and drying the alumina support to obtain a pretreated support;

[0024] (2) impregnating the pretreated support of step (1) with an impregnation solution containing a Group VIB metal salt and a Group VIII metal salt, wherein the volume of the impregnation solution is less than 70% of the saturated water absorption capacity of the alumina support, and drying and sulfurizing the support to obtain a catalyst precursor;

[0025] (3) impregnating the catalyst precursor of step (2) with an inorganic acid solution, and drying in an inert atmosphere to obtain the polycyclic aromatic hydrocarbon selective hydrogenation catalyst.

[0026] Furthermore, in the above preparation method, the alkaline solution described in step (1) is selected from at least one of sodium hydroxide, potassium hydroxide and ammonia solution, and the solute concentration in the alkaline solution is 0.01 g / mL-0.1 g / mL.

[0027] Furthermore, in the above preparation method, preferably, the volume amount of the alkaline solution is 70%-110%, preferably 80%-100%, of the saturated water absorption capacity of the alumina support.

[0028] Furthermore, in the above preparation method, the drying temperature in step (1) is 90-200° C., and the drying time is 3-6 hours.

[0029] Furthermore, in the above preparation method, the volume of the impregnation solution in step (2) is preferably 5-55% of the saturated water absorption capacity of the alumina support, and more preferably 25%-50%.

[0030] In the impregnation process of step (2), due to the high active metal content, complete dissolution of the active metal cannot be guaranteed when the volume of the impregnation solution is low. Therefore, the active metal can be loaded onto the support by impregnation in batches multiple times. Each impregnation is carried out according to the agreed volume of impregnation solution. After each impregnation, it is dried and calcined before the next impregnation. This ensures that the active components are distributed in the agreed catalyst layer. The calcination conditions are: temperature of 300-500°C and time of 3-6 hours.

[0031] Furthermore, in the above preparation method, in step (2), the impregnation solution containing the Group VIB metal salt is a phosphate or ammonium salt solution of the Group VIB metal, and its preparation method is well known to those skilled in the art. The Group VIB metal is preferably Mo and / or W.

[0032] Furthermore, in the above preparation method, in step (2), the impregnation solution containing a Group VIII metal salt is a solution of a nitrate, acetate, or sulfate of a Group VIII metal, and its preparation method is well known to those skilled in the art. The Group VIII metal is Ni and / or Co. The drying temperature is 90-200°C, and the drying time is 3-6 hours.

[0033] Furthermore, in the above preparation method, the vulcanization treatment in step (2) is dry vulcanization or wet vulcanization. The dry vulcanizing agent is hydrogen sulfide, and the wet vulcanizing agent is one or two of carbon disulfide, dimethyl disulfide, methyl sulfide, and n-butyl sulfide; the vulcanization pressure is 3.2-6.4 MPa, the vulcanization temperature is 250-400°C, and the vulcanization time is 4-12 hours.

[0034] Furthermore, in the above preparation method, the inorganic acid in step (3) is selected from at least one of phosphoric acid, boric acid, hydrofluoric acid, hydrochloric acid, and sulfuric acid. The concentration of the inorganic acid solution is 0.01 g / mL to 0.1 g / mL. The volume of the inorganic acid solution used is 10% to 40%, preferably 10% to 30%, of the saturated water absorption of the catalyst precursor prepared in step (1).

[0035] Furthermore, in the above preparation method, the inert atmosphere in step (3) is one or more of N2 and an inert gas; the drying temperature in step (3) is 20-90°C, and the drying time is 4-16 hours.

[0036] It should be understood by those skilled in the art that when the alkaline solution, active component and inorganic acid are impregnated with an impregnation solution lower than the saturated water absorption capacity of the support, appropriate operations should be taken to ensure that the catalyst surface is in contact with the impregnation solution as evenly as possible, such as using an impregnation method in a rotating drum or a spray impregnation method.

[0037] Compared with the prior art, the catalyst of the present invention has the following advantages:

[0038] (1) In the process method of the present invention, a specific polycyclic aromatic hydrocarbon selective hydrogenation catalyst is used in the first stage reaction to first carry out a polycyclic aromatic hydrocarbon saturation reaction, and then a hydrodesulfurization reaction is carried out in the second stage reaction. The catalyst in the first stage reaction has a high polycyclic aromatic hydrocarbon hydrogenation activity, which reduces the loss of monocyclic aromatic hydrocarbons. The desulfurization is completed in the second stage, and qualified products are obtained in the two-step reaction.

[0039] (2) The process of the present invention preferably makes the saturation rate of polycyclic aromatic hydrocarbons in the first stage reaction reach 70-90%, and the desulfurization rate is controlled below 50%. As one of the specific implementation methods, the polycyclic aromatic hydrocarbons saturation reaction can be carried out at a low temperature environment first, and then the hydrodesulfurization reaction can be carried out at a high temperature environment. On the one hand, it can prevent the hydrogenation saturation of polycyclic aromatic hydrocarbons from being limited by thermodynamic equilibrium, thereby improving the saturation rate of polycyclic aromatic hydrocarbons; on the other hand, it can hydrogenate and saturate the benzene rings of the sulfides containing polycyclic aromatic hydrocarbons, thereby improving the desulfurization activity of large molecular sulfides.

[0040] (3) The polycyclic aromatic hydrocarbon selective hydrogenation catalyst used in the present invention is pretreated with an alkaline solution on the carrier and then loaded with the active component. On the one hand, the alkaline solution can weaken the acidic properties of the carrier surface, which is conducive to the distribution of active metals to the outer surface of the catalyst; on the other hand, the alkalinity inside the carrier can weaken the acidity of the catalyst. During the reaction, even if the aromatic hydrocarbons diffuse into the interior of the carrier, excessive hydrogenation reaction will not occur, which can achieve the purpose of improving the hydrogenation activity of polycyclic aromatic hydrocarbons and reducing the loss of monocyclic aromatic hydrocarbons.

[0041] (3) Inorganic acid is added to the polycyclic aromatic hydrocarbon selective hydrogenation catalyst used in the present invention, and the inorganic acid is loaded on the outer layer of the catalyst instead of being mixed with the carrier or loaded into the carrier. On the one hand, it is beneficial to increase the contact surface between the acid and the active metal, and at the same time, it is beneficial to load the acid on the active site of the active metal, giving full play to the ability of the acid to provide H protons, and improving the hydrogenation activity of the catalyst; on the other hand, the acid will corrode the surface of the catalyst, increase the specific surface area and pore size of the catalyst, and improve the polycyclic aromatic hydrocarbon hydrogenation saturation activity of the catalyst.

[0042] (4) The active metal is impregnated onto the support in a manner lower than the saturated water absorption of the support, so that as much active metal as possible is distributed within a certain thickness of the catalyst surface. This can improve the hydrogenation saturation activity of polycyclic active metals and prevent the diffusion of polycyclic metals into the catalyst, which causes the polycyclic aromatic hydrocarbons to be hydrogenated into monocyclic aromatic hydrocarbons and then further hydrogenated to saturate.

[0043] (5) After the catalyst is prepared, it is treated with inorganic acid to improve the surface acid properties of the catalyst and enhance the hydrogenation capacity.

[0044] Other features and advantages of the present invention will be described in detail in the following detailed description. DETAILED DESCRIPTION

[0045] The following non-limiting examples may enable those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0046] In the context of this specification, the acid properties of the catalyst are analyzed by the pyridine adsorption infrared acid property characterization method. The test conditions of the pyridine adsorption infrared acid property characterization method include: the sample is purified in a reaction tube at 500°C and 60mPa for 4 hours, cooled to room temperature, and vacuumed to 0.1mPa to adsorb pyridine, and the surface acid properties of the sample are measured.

[0047] In the technical solution of the present invention, "active component distribution" means that, when the active component content decreases to less than 30% of the content of the component in the outermost layer of the catalyst particle, the active component is considered to be absent from the current catalyst layer to the center of the catalyst, but to be present from the current catalyst layer to the catalyst surface. The active component content in a catalyst layer is determined by measuring the elemental content using an electron probe at 10 randomly selected points within the catalyst layer with the same radius, and the measured values ​​are arithmetic averaged.

[0048] Example 1

[0049] (1) The alumina support was impregnated with 0.04 g / mL sodium hydroxide solution by equal volume impregnation method and then dried at 150 °C for 4 hours to obtain a pretreated support;

[0050] (2) An impregnation solution containing ammonium heptamolybdate and nickel nitrate was prepared according to 50% of the saturated water absorption capacity of the alumina carrier, and the pretreated carrier was impregnated by the rotating drum impregnation method. After impregnation, it was dried at 110°C for 3 hours, and then sulfurized with hydrogen containing 1.5% H2S. The sulfurization temperature was 330°C, the sulfurization pressure was 3.2 MPa, and the sulfurization time was 5 hours. Then, it was cooled to room temperature in a N2 atmosphere to obtain a catalyst precursor B.

[0051] (3) According to 20% of the saturated water absorption of catalyst precursor B, a corresponding volume of 0.02 g / mL phosphoric acid solution was taken as the impregnation liquid, and the catalyst precursor B prepared in step (2) was impregnated by spray impregnation, and then dried at 80°C in a nitrogen atmosphere for 5 h to obtain catalyst C-1.

[0052] The weight percentages of the components in catalyst C-1 are: MoS2 20%, NiS 4.2%, phosphoric acid 4.0%, sodium hydroxide 1.0%, and the rest is alumina support.

[0053] Example 2

[0054] (1) The alumina support was impregnated with 0.05 g / mL sodium hydroxide solution by equal volume impregnation method and then dried at 130 °C for 4 hours to obtain a pretreated support;

[0055] (2) An impregnation solution containing ammonium heptamolybdate and nickel nitrate was prepared according to 58% of the saturated water absorption capacity of the alumina carrier, and the pretreated carrier was impregnated by the rotating drum impregnation method. After impregnation, it was dried at 120°C for 3 hours, and then sulfurized with hydrogen containing 1.5% H2S. The sulfurization temperature was 360°C, the sulfurization pressure was 3.2 MPa, and the sulfurization time was 6 hours. Then, it was cooled to room temperature in a N2 atmosphere to obtain a catalyst precursor B.

[0056] (3) According to 30% of the saturated water absorption of catalyst precursor B, a corresponding volume of 0.03 g / mL boric acid solution was taken as the impregnation liquid, and the catalyst precursor B prepared in step (2) was impregnated by spray impregnation, and then dried at 80°C in a nitrogen atmosphere for 5 h to obtain catalyst C-2.

[0057] The weight percentages of the components in catalyst C-2 are: MoS2 18.6%, NiS 4.2%, boric acid 3.0%, sodium hydroxide 0.8%, and the rest is alumina support.

[0058] Example 3

[0059] (1) The alumina support was impregnated with 0.03 g / mL potassium hydroxide solution by equal volume impregnation method and then dried at 130 °C for 4 hours to obtain a pretreated support;

[0060] (2) An impregnation solution containing ammonium heptamolybdate and cobalt nitrate was prepared according to 69% of the saturated water absorption capacity of the alumina carrier, and the pretreated carrier was impregnated by the rotating drum impregnation method. After impregnation, it was dried at 120°C for 3 hours, and then sulfurized with hydrogen containing 1.5% H2S. The sulfurization temperature was 360°C, the sulfurization pressure was 6.0 MPa, and the sulfurization time was 4 hours. Then, it was cooled to room temperature in a N2 atmosphere to obtain a catalyst precursor B.

[0061] (3) According to 30% of the saturated water absorption of catalyst precursor B, a corresponding volume of 0.03 g / mL hydrofluoric acid solution was taken as the impregnation liquid, and the catalyst precursor B prepared in step (2) was impregnated by the rotating drum impregnation method, and then dried at 80°C in a nitrogen atmosphere for 5 h to obtain catalyst C-3.

[0062] The weight percentages of the components in catalyst C-3 are: MoS2 is 19.7%, CoS is 4.6%, hydrofluoric acid is 3.2%, potassium hydroxide is 1.2%, and the rest is alumina support.

[0063] Example 4

[0064] (1) The alumina support was impregnated with 0.05 g / mL sodium hydroxide solution by equal volume impregnation method and then dried at 120 °C for 4 hours to obtain a pretreated support;

[0065] (2) The active component is impregnated by a secondary impregnation method: according to the agreed active metal content, half of the active metal is taken, and an impregnation solution containing ammonium heptamolybdate and cobalt nitrate is prepared according to 25% of the saturated water absorption capacity of the alumina carrier. The pretreated carrier is impregnated by a spray impregnation method, dried at 120°C for 3 hours, and calcined at 320°C for 3 hours. The remaining active metal is prepared into a solution according to 25% of the saturated water absorption capacity of the alumina carrier, spray impregnation is performed, and dried at 120°C for 3 hours. Then, hydrogen containing 1.5% H2S is used for sulfurization treatment. The sulfurization temperature is 380°C, the sulfurization pressure is 4.8MPa, and the sulfurization time is 6h. Then, the temperature is cooled to room temperature in a N2 atmosphere to obtain catalyst precursor B.

[0066] (3) According to 20% of the saturated water absorption of catalyst precursor B, a corresponding volume of 0.05 g / mL boric acid solution was taken as the impregnation liquid, and the catalyst precursor B prepared in step (2) was impregnated by spray impregnation, and then dried at 80°C in a nitrogen atmosphere for 5 h to obtain catalyst C-4.

[0067] The weight percentages of the components in catalyst C-4 are: MoS2 22.5%, CoS 4.6%, boric acid 3.2%, sodium hydroxide 0.5%, and the rest is alumina support.

[0068] Example 5

[0069] (1) The alumina support was impregnated with 0.05 g / mL potassium hydroxide solution by equal volume impregnation method and then dried at 120 °C for 4 hours to obtain a pretreated support;

[0070] (2) An impregnation solution containing ammonium metatungstate and cobalt nitrate was prepared according to 50% of the saturated water absorption capacity of the alumina carrier, and the pretreated carrier was impregnated by the rotating drum impregnation method. After impregnation, it was dried at 120°C for 3 hours, and then sulfurized with hydrogen containing 1.5% H2S. The sulfurization temperature was 380°C, the sulfurization pressure was 4.8 MPa, and the sulfurization time was 6 hours. Then, it was cooled to room temperature in a N2 atmosphere to obtain a catalyst precursor B.

[0071] (3) According to 30% of the saturated water absorption of catalyst precursor B, a corresponding volume of 0.05 g / mL phosphoric acid solution was taken as the impregnation liquid, and the catalyst precursor B prepared in step (2) was impregnated by spray impregnation, and then dried at 80°C in a nitrogen atmosphere for 5 h to obtain catalyst C-5.

[0072] The weight percentages of the components in catalyst C-5 are: WS2 is 23.5%, CoS is 4.6%, phosphoric acid is 3.8%, potassium hydroxide is 0.5%, and the rest is alumina support.

[0073] Example 6

[0074] (1) The alumina support was impregnated with 0.05 g / mL sodium hydroxide solution by equal volume impregnation method and then dried at 120 °C for 4 hours to obtain a pretreated support;

[0075] (2) An impregnation solution containing ammonium metatungstate and nickel nitrate was prepared according to 50% of the saturated water absorption capacity of the alumina carrier, and the pretreated carrier was impregnated by the rotating drum impregnation method. After impregnation, it was dried at 120°C for 3 hours, and then sulfurized with hydrogen containing 1.5% H2S. The sulfurization temperature was 360°C, the sulfurization pressure was 4.8 MPa, and the sulfurization time was 6 hours. Then, it was cooled to room temperature in a N2 atmosphere to obtain a catalyst precursor B.

[0076] (3) According to 30% of the saturated water absorption of catalyst precursor B, a corresponding volume of 0.05 g / mL boric acid solution was taken as the impregnation liquid, and the catalyst precursor B prepared in step (2) was impregnated by spray impregnation, and then dried at 80°C in a nitrogen atmosphere for 5 h to obtain catalyst C-6.

[0077] The weight percentages of the components in catalyst C-6 are: WS2 is 22.5%, NiS is 4.6%, boric acid is 3.2%, sodium hydroxide is 0.5%, and the rest is alumina support.

[0078] Comparative Example 1

[0079] Except that the active component was impregnated in an equal volume impregnation manner in step (2), the other operations were the same as in Example 1 to obtain comparative catalyst DC-1.

[0080] The weight percentages of the components in the comparative catalyst DC-1 are: MoS2 20%, NiS 4.2%, phosphoric acid 4.0%, sodium hydroxide 1.0%, and the rest is alumina support.

[0081] Comparative Example 2

[0082] The equal volume impregnation method was adopted, with alumina as the carrier, impregnated with the impregnation solution of ammonium heptamolybdate and nickel nitrate, dried at 110°C for 3 hours, and then sulfurized with hydrogen containing 1.5% H2S. The sulfurization temperature was 330°C, the sulfurization pressure was 3.2MPa, and the sulfurization time was 5h. Then, it was cooled to room temperature in a N2 atmosphere to obtain the comparative catalyst DC-2.

[0083] The weight percentages of the components in the comparative catalyst DC-2 are: MoS2 is 20%, NiS is 4.2%, and the rest is alumina support.

[0084] The acid properties and active metal distribution (ratio of radial thickness of active component to catalyst radius) of the catalysts C-1 to C-6 prepared in the above examples and the catalysts DC-1 to DC-2 prepared in the comparative examples were analyzed. The analysis results are shown in Table 1.

[0085] Table 1.

[0086]

[0087] Example 7

[0088] This example illustrates the hydrogenation performance of the catalytic diesel hydrogenation process provided by the present invention.

[0089] The raw oil used for evaluation is a catalytic diesel feedstock provided by a refinery of Sinopec, and its main properties are as follows: distillation range 200-370°C, sulfur content of 1.6wt%, nitrogen content of 890μg / g, monocyclic aromatic hydrocarbon content of 18%, and polycyclic aromatic hydrocarbon content of 35%. The catalytic diesel feedstock and hydrogen are sequentially passed through two fixed-bed reactors connected in series, wherein the first reactor is filled with polycyclic aromatic hydrocarbon selective hydrogenation catalysts of C-1 to C-6 and comparative examples DC-1 to DC-2, respectively, and the second reactor is filled with Mo-Ni type hydrodesulfurization catalyst (with MoS2 content of 22% and NiS content of 4%). The process conditions of the first reactor are pressure 7.0MPa; volume space velocity 0.8h -1 The hydrogen-oil volume ratio was 500:1, the inlet temperature was 260°C, and the process conditions of the second reactor were a pressure of 7.0 MPa and a volume space velocity of 1.5 h -1 The hydrogen-to-oil volume ratio was 500:1 and the inlet temperature was 320°C. The evaluation results are shown in Table 2.

[0090] Table 2.

[0091]

[0092]

[0093] As can be seen from Table 2, the catalytic diesel hydrogenation process and the specific polycyclic aromatic hydrocarbon selective hydrogenation catalyst of the present invention can effectively improve the hydrogenation effect of polycyclic aromatic hydrocarbons in catalytic diesel and reduce the loss rate of monocyclic aromatic hydrocarbons.

Claims

1. A process for catalytic diesel hydrogenation, comprising the following steps: under hydrogenation reaction conditions, catalytically transferring a diesel feedstock and hydrogen to two fixed-bed reactors connected in series, wherein a polycyclic aromatic hydrocarbon selective hydrogenation catalyst is loaded in the first reactor and a hydrodesulfurization catalyst is loaded in the second reactor, and a qualified diesel product is obtained from the outlet of the second reactor; wherein the polycyclic aromatic hydrocarbon selective hydrogenation catalyst is supported on an alkali-modified alumina carrier on which an inorganic acid and an active component are supported, wherein the active component is a Group VIB metal sulfide and a Group VIII metal sulfide, and based on the total weight of the catalyst, the alkali accounts for 0.1-5.0%, the inorganic acid accounts for 1-12 wt%, the Group VIB metal sulfide accounts for 10-30%, and the Group VIII metal sulfide accounts for 2-10%, the catalyst has a B acid content of 0.05-0.2 mmol / g and an L acid content of 0.3-1.0 mmol / g, the active component is distributed from the catalyst surface to a catalyst surface layer no greater than 1 / 3 the catalyst radius thickness, and the inorganic acid is supported on the catalyst outer surface; in, The distribution of active components refers to the distribution from the outside to the inside of the catalyst particle in the radial direction. When the content of the active component drops to less than 30% of the content of the component in the outermost layer of the catalyst particle, it is considered that there is no active component distribution from the current catalyst layer to the center of the catalyst, but there is an active component distribution from the catalyst layer to the catalyst surface; the determination of the active component content in a certain catalyst layer is to randomly select 10 points in the catalyst layer with the same radius of the catalyst, use an electron probe to determine the element content, and perform arithmetic averaging on the measured values.

2. The process according to claim 1, characterized in that: In the polycyclic aromatic hydrocarbon selective hydrogenation catalyst, based on the total weight of the catalyst, the base accounts for 0.3-3.0% and the inorganic acid accounts for 1.5-8wt%.

3. The process according to claim 2, characterized in that: In the polycyclic aromatic hydrocarbon selective hydrogenation catalyst, the inorganic acid accounts for 2-6 wt % based on the total weight of the catalyst.

4. The process according to claim 1, characterized in that: After the catalytic diesel raw material passes through the first reactor, the polycyclic aromatic hydrocarbon saturation rate is 70-90% and the desulfurization rate is less than 50%.

5. The process according to claim 1, characterized in that: The inlet temperature of the raw material to the first reactor is 150-350°C, and the inlet temperature to the second reactor is 250-350°C.

6. The process according to claim 5, characterized in that: The inlet temperature of the raw material to the first reactor is 200-300°C, and the inlet temperature to the second reactor is 280-330°C.

7. The process according to claim 6, characterized in that: The raw material inlet temperature of the first reactor is 200-270°C.

8. The process according to claim 1, characterized in that: In the polycyclic aromatic hydrocarbon selective hydrogenation catalyst, the inorganic acid is selected from at least one of phosphoric acid, boric acid, hydrofluoric acid, hydrochloric acid and sulfuric acid, and the inorganic acid is loaded on the outer surface of the catalyst, namely, the inorganic acid is loaded on a Group VIB metal sulfide, and / or, on a Group VIII metal sulfide, and / or, on an alkali-modified alumina carrier.

9. The process according to claim 1, characterized in that: In the polycyclic aromatic hydrocarbon selective hydrogenation catalyst, the alkali-modified alumina has a B acid content of 0.01-0.04 mmol / g and a L acid content of 0.01-0.1 mmol / g.

10. The process according to claim 1, characterized in that: In the polycyclic aromatic hydrocarbon selective hydrogenation catalyst, the alkali-modified alumina is obtained by impregnating alumina with alkali solution and drying; the alkali is selected from at least one of sodium hydroxide, potassium hydroxide and ammonia.

11. The process according to claim 1, characterized in that: The polycyclic aromatic hydrocarbon selective hydrogenation catalyst is prepared by the following method: (1) impregnating an alumina support with an alkaline solution and drying the support to obtain a pretreated support; (2) impregnating the pretreated support of step (1) with an impregnation solution containing a Group VIB metal salt and a Group VIII metal salt, wherein the volume of the impregnation solution is less than 70% of the saturated water absorption capacity of the alumina support, and performing drying and sulfurization treatment to obtain a catalyst precursor; (3) Impregnating the catalyst precursor of step (2) with an inorganic acid solution, and drying in an inert atmosphere to obtain the polycyclic aromatic hydrocarbon selective hydrogenation catalyst.

12. The process according to claim 11, characterized in that: The alkaline solution in step (1) is selected from at least one of sodium hydroxide, potassium hydroxide and ammonia solution, and the solute concentration in the alkaline solution is 0.01 g / mL-0.1 g / mL; the volume amount of the alkaline solution is 70%-110% of the saturated water absorption capacity of the alumina support.

13. The process according to claim 11, characterized in that: The drying temperature in step (1) is 90-200° C., and the drying time is 3-6 hours.

14. The process according to claim 11, characterized in that: The volume of the impregnation solution in step (2) is 5-55% of the saturated water absorption capacity of the alumina support.

15. The process according to claim 14, characterized in that: The volume of the impregnation solution in step (2) is 25%-50% of the saturated water absorption capacity of the alumina support.

16. The process according to claim 11, characterized in that: The inorganic acid in step (3) is selected from at least one of phosphoric acid, boric acid, hydrofluoric acid, hydrochloric acid and sulfuric acid; the concentration of the inorganic acid solution is 0.01 g / mL-0.1 g / mL; the volume of the inorganic acid solution is 10%-40% of the saturated water absorption of the catalyst precursor prepared in step (2).

17. The process according to claim 11, characterized in that: The drying temperature of step (3) is 20-90°C, and the drying time is 4-16 hours.

18. The process according to claim 1, characterized in that: Other process conditions of the first reactor are: pressure 4.0~12.0MPa, volume space velocity 0.1~8.0h -1 , hydrogen-oil volume ratio 10:1~800:1; the process conditions of the second reactor are: pressure 4.0~12.0Mpa, volume space velocity 0.1~4.0h -1 , hydrogen-oil volume ratio 10:1~800:

1.

19. The process according to claim 1, characterized in that: The catalyst in the second reactor is a Mo-Ni and / or Mo-Co type diesel hydrodesulfurization catalyst.

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