A catalyst for preparing n-pentene by hydrogenation of piperylene and a preparation method and application thereof

Abstract

The application discloses a catalyst for preparing n-pentene by hydrogenation of piperylene, which comprises a carrier alpha-Al2O3 modified by a metal M, an active noble metal and a Lewis acid supported on the carrier alpha-Al2O3, wherein the active noble metal is Pd; the mass percentage of the metal M in the catalyst is 0.8-2% according to 100%, the metal M is at least one metal selected from W, V or Ga, the mass percentage of the active noble metal Pd is 0.05-0.08%, the mass percentage of the Lewis acid is 0.06-0.3%, and the rest is the carrier. In addition, the application also discloses a preparation method of the catalyst and application of the catalyst in production of n-pentene; and the catalyst can keep high catalytic activity and n-pentene selectivity in a long-time reaction process.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of catalytic selective hydrogenation, and particularly relates to a composite structure noble metal catalyst and a method for continuously producing n-pentene by using the catalyst. BACKGROUND

[0002] N-pentene is a colorless transparent volatile liquid, soluble in ethanol and insoluble in water, and is a high-value fine chemical intermediate. As an important product in the carbon five fraction by-produced in the process of steam cracking of naphtha to produce ethylene, n-pentene is widely used in the fields of daily chemicals, agricultural chemicals, perfumes, oil additives and petrochemical standard gases. Its main industrial use is to produce antibacterial moisturizing agent 1,2-pentanediol and intermediates such as n-hexanal, n-hexanol and n-hexanoic acid through carbonylation reaction, and it is also used as a modifier of ethylene and propylene copolymer materials to improve the ductility and other properties of the copolymer. As an oil additive, it can improve the octane number of oil and enhance the anti-knock performance of oil. Nowadays, fine chemical products are further developing towards high-grade, fine, composite and functional directions, and small molecule basic chemical raw materials have a long life and are one of the key supported fields of the country. High content, low moisture, no sulfur and chlorine and other reaction impurities are key performance indicators for measuring fine chemicals, and have been one of the goals pursued in the production of fine chemicals. Therefore, the current research on the preparation of n-pentene is particularly necessary.

[0003] Patent CN201310314859.5 discloses a method for preparing n-pentene, which emphasizes more on the rectification and purification method of n-pentene, and less on the preparation and design of the catalyst. In addition, the content of noble metal Pd in the catalyst is high, the cost is large, the fixed bed hydrogenation reaction pressure is high, and the energy consumption is large. SUMMARY

[0004] The present application is aimed at the defects of low efficiency, high energy consumption and high catalytic cost in the prior art of selectively hydrogenating piperylene to n-pentene, and provides a catalyst for preparing n-pentene by hydrogenating piperylene, which can efficiently, continuously, low-cost and large-scale produce n-pentene.

[0005] One of the purposes of the present application is to provide a catalyst for preparing n-pentene by hydrogenating piperylene, which comprises a carrier alpha-Al2O3 modified by a metal M, Pd and Lewis acid supported on the carrier alpha-Al2O3; in the catalyst, the mass percentage of the metal M is 0.8-2%, the mass percentage of Pd is 0.01-0.08%, and the mass percentage of Lewis acid is 0.06-0.3%, according to 100%; the metal M is at least one of W, V or Ga, and the particle size of the alpha-Al2O3 is 1.8mm-3mm.

[0006] Preferably, the Lewis acid is any one of SnCl2, ZnCl2, AlCl3, MgCl2, CeCl3.

[0007] Preferably, the mass percentage of metal M in the catalyst is 0.8-1.4%, the mass percentage of Pd is 0.01-0.05%, and the mass percentage of Lewis acid is 0.06-0.16%.

[0008] Preferably, the mass percentage of metal M in the catalyst is 1%, the mass percentage of Pd is 0.03%, and the mass percentage of Lewis acid is 0.12%.

[0009] Another object of the present application is to provide a preparation method of the aforementioned catalyst, comprising the following steps:

[0010] Step one, activate α-Al2O3 by raising the temperature to 250-450℃ at a rate of 1℃ / min for 4-8h to obtain activated α-Al2O3:

[0011] Step two, dissolve a metal M soluble salt in dilute nitric acid to obtain solution M1, immerse the activated α-Al2O3 in solution M1, filter, and stand for 12-36h, then freeze-dry in a freeze dryer, and then calcine at 500℃ for 2h, and naturally cool to room temperature to obtain α-Al2O3 with a special structure modified by metal M, wherein the metal M soluble salt is ammonium metatungstate, sodium metavanadate, or gallium nitrate;

[0012] Step three, load Pd and Lewis acid onto the α-Al2O3 with a special structure modified by metal M obtained in step two by a stepwise loading method, which comprises a first step loading and a second step loading, wherein the first step loading comprises: dissolving a Pd precursor in dilute nitric acid to obtain a Pd precursor solution, while spraying the obtained Pd precursor solution onto the α-Al2O3 with a special structure modified by metal M obtained in step two or immersing the α-Al2O3 with a special structure modified by metal M in the Pd precursor solution, standing for 12-36h, and then freeze-drying in a freeze dryer to obtain a precursor A; the second step loading comprises: dissolving a Lewis acid in pure water to obtain solution B, spraying solution B onto the precursor A obtained in the first step or immersing the precursor A in solution B, immersing, standing for 12-36h, and then freeze-drying in a freeze dryer to obtain a precursor C;

[0013] Step four, place the precursor C in a muffle furnace and calcine at 450-600℃ for 2-6h to obtain catalyst precursor D;

[0014] Step five, the catalyst precursor D obtained in step four is reduced by hydrogen to obtain the catalyst.

[0015] Preferably, the mass concentration of dilute nitric acid in step two or step three is 0.8-3.0wt%

[0016] Preferably, the reduction treatment in step five is specifically: heating the catalyst precursor D to 300-450℃ at a temperature rising rate of 1-2℃ / min under hydrogen condition, keeping for 3-6h and then naturally cooling.

[0017] Preferably, the impregnation in step two or step three adopts rotary evaporation impregnation method, and the specific conditions are: impregnation temperature 30-55℃, impregnation vacuum degree -0.01~-0.04MPa, and impregnation time until the material is in non-flow state

[0018] Preferably, the temperature of the spraying in step three is 40-65℃, the spraying rate is 0.4-2.8mL / s, and the mass of the infiltrating used for spraying is 0.6-0.85 times of the mass of the precursor.

[0019] The purpose of the present application is also to provide a method for continuously producing n-pentene by hydrogenation of piperylene, which comprises the following steps:

[0020] (1) The aforementioned catalyst and inert porcelain balls with a particle size of 1.8-2.4mm are alternately and layer by layer filled in a fixed bed reactor

[0021] , and then nitrogen is introduced until the air in the fixed bed reactor is completely discharged; wherein the volume ratio of the catalyst to the inert porcelain balls is 2:1;

[0022] (2) Hydrogen is introduced into the fixed bed reactor, and under the condition that the hydrogen flow L satisfies 15mL / min≤L≤45mL / min, the gas pressure in the fixed bed reactor reaches a slight positive pressure of 0.5-2.5bar, the molar ratio of hydrogen to piperylene is (0.6-0.8):1, and selective hydrogenation is selected, so that the amount of hydrogen is slightly insufficient to prevent excessive hydrogenation. After the catalyst is heated to 40-60℃ at a heating rate of 1℃ / min, the hydrogen and piperylene raw material liquid are preheated to the reaction temperature, and then introduced into the fixed bed reactor, and the hydrogenation reaction is carried out at the reaction temperature and pressure.

[0023] (3) The reaction liquid obtained in step (2) is sent into a gas-liquid separator for separation, and the tail gas hydrogen is recycled by a hydrogen compressor.

[0024] Preferably, in step (2), the molar ratio of hydrogen to piperylene is (0.6-0.8):1, and the mass space velocity of piperylene is 3.6-8.6g / gcat / hr.

[0025] Preferably, the fixed bed reactor is a fixed bed reactor in tubes, the inner diameter of the reaction tube in the fixed bed reactor in tubes is 14-26 mm, and the filling height of the reaction tube is 2.25-3.6 m.

[0026] The present application has the following excellent effects:

[0027] 1. The Lewis acid and the noble metal Pd are cooperatively loaded on the alpha-Al2O3 carrier modified by the metal M, the Lewis acid can enhance the desorption of n-pentene on the surface of the catalyst, and inhibit excessive hydrogenation, the strong desorption of the Lewis acid to n-pentene and the activation of Pd to hydrogen cooperatively promote the reaction of the hydrogenation of piperyline to generate n-pentene, in addition, the active area of the carrier modified by the metal M is more narrow and specific, and the special catalyst structure greatly improves the activity and selectivity of the catalyst;

[0028] 2. The spraying or the impregnation through the rotary evaporator can improve the dispersion of the active metal, on the one hand, the Pd and the Lewis acid on the surface of the carrier can reach a stable state, and the agglomeration is reduced, on the other hand, the impurities remaining in the internal pores of the carrier can be completely adsorbed, and the mass transfer is increased, which is beneficial to improve the selectivity of the catalyst;

[0029] 3. By using the synergistic effect of the metal M and the Lewis acid, the amount of the active metal Pd can be greatly reduced, the cost is saved, and the industrial scale production is easy to realize;

[0030] 4. The catalyst provided by the present application is used for the continuous preparation of n-pentene from piperyline, and the fixed bed reactor is used to realize the continuous production of n-pentene, under the mild conditions of the reaction pressure of 0.5-2.5 bar and the reaction temperature of 40-60℃, the high-selectivity continuous long-period production of n-pentene can be realized, the operation is simple, the control is easy, the hydrogen recycling is used, the energy consumption is reduced, and the discharge of the three wastes is less. DETAILED DESCRIPTION

[0031] The raw materials involved in the embodiments of the present application, such as no special description, can be obtained from commercial sources or synthesized by using commercially available starting materials and reagents by conventional methods in the art.

[0032] Example 1

[0033] The catalyst of the present embodiment comprises the carrier alpha-Al2O3 modified by the metal M, the Pd and the Lewis acid loaded on the carrier alpha-Al2O3, according to 100%, the mass percentage of the metal M in the catalyst is 1%, the mass percentage of the Pd is 0.03%, and the mass percentage of the Lewis acid is 0.12%, the metal M is W, the particle size of the alpha-Al2O3 is 2 mm, and the Lewis acid is AlCl3;

[0034] The preparation method of the catalyst is as follows:

[0035] Step one, activate α-Al2O3 to 350℃ at 1℃ / min for 6h, to obtain activated α-Al2O3;

[0036] Step two, dissolve ammonium metatungstate in 1.6wt% dilute nitric acid to obtain solution M1, dip the activated α-Al2O3 in solution M1, filter, stand for 24h, then freeze-dry in a freeze dryer, and then calcine at 500℃ for 2h, naturally cool to room temperature, to obtain α-Al2O3 with special structure modified by metal W;

[0037] Step three, load Pd and Lewis acid on the α-Al2O3 with special structure modified by metal W in step two by a step-by-step loading method, which includes first step loading and second step loading, the first step loading includes: dissolve hydrochloride of Pd in 1.6wt% dilute nitric acid to obtain Pd active group solution, put the modified activated α-Al2O3 carrier in step two into a sugar-coating machine, turn on the rotation and heating switches, and spray the Pd active group solution on the rotating carrier in the kettle at a temperature of 60℃, the mass of the Pd active group solution is 0.7 times the mass of the modified α-Al2O3 in step two, and the spraying rate is 2mL / s; after spraying, stand for 24h, then freeze-dry in a freeze dryer, to obtain precursor A; the second step loading includes: dissolve Lewis acid with pure water to obtain solution B, and then use the same spraying and drying steps as above to obtain precursor C.

[0038] Step four, put precursor C into a muffle furnace and calcine at 500℃ for 4h, to obtain catalyst precursor D;

[0039] Step five, reduce catalyst precursor D obtained in step four by hydrogen at 1℃ / min to 350℃ for 4.5h, to obtain the catalyst, which is recorded as Cat.1.

[0040] Example 2

[0041] Replace the metal on the modified carrier α-Al2O3 with equal mass of V, use the precursor of metal V, sodium metavanadate, in step two, and other steps are the same as example 1, the preparation method is the same as example 1, and the obtained catalyst is recorded as Cat.2.

[0042] Example 3

[0043] Replace the metal on the modified carrier α-Al2O3 with equal mass of Ga, use the precursor of metal Ga, gallium nitrate, in step two, and other steps are the same as example 1, the preparation method is the same as example 1, and the obtained catalyst is recorded as Cat.3.

[0044] Example 4

[0045] The Lewis acid is replaced by equal mass of ZnCl2, and other conditions are the same as in Example 1, and the catalyst obtained is denoted as Cat. 4.

[0046] Example 5

[0047] The Lewis acid is replaced by equal mass of CeCl2, and other conditions are the same as in Example 1, and the catalyst obtained is denoted as Cat. 5.

[0048] Example 6

[0049] The mass percentage of the Lewis acid AlCl3 is 0.18%, and other conditions are the same as in Example 1, and the catalyst obtained is denoted as Cat. 6.

[0050] Example 7

[0051] The mass percentage of the metal W is 0.8%, and other conditions are the same as in Example 1, and the catalyst obtained is denoted as Cat. 7.

[0052] Example 8

[0053] The mass percentage of the metal Pd is 0.04%, and other conditions are the same as in Example 1, and the catalyst obtained is denoted as Cat. 8.

[0054] Example 9

[0055] The catalyst of the present example comprises a carrier α-Al2O3 modified by a metal M, Pd supported on the carrier α-Al2O3, and a Lewis acid, wherein the mass percentage of the metal M in the catalyst is 2%, the mass percentage of Pd is 0.01%, and the mass percentage of the Lewis acid is 0.06%, the metal M is W, the particle size of the α-Al2O3 is 1.8 mm, and the Lewis acid is SnCl2.

[0056] The catalyst is prepared as follows:

[0057] Step one, activate the α-Al2O3 by heating at 1 ℃ / min to 250 ℃ for 8 h to obtain activated α-Al2O3;

[0058] Step two, dissolve ammonium metatungstate in 0.8 wt% dilute nitric acid to obtain solution M1, and immerse the activated α-Al2O3 in the solution M1, filter, and then place it in a freeze dryer for freeze-drying treatment after standing for 12 h, and then calcine it at 500 ℃ for 2 h, and then naturally cool it to room temperature to obtain the α-Al2O3 modified by the metal W and having a special structure.

[0059] Step three, loading Pd and Lewis acid onto the metal W modified α-Al2O3 in step two by a stepwise loading method, the stepwise loading method comprising a first step loading and a second step loading, the first step loading comprising: dissolving hydrochloride salt of Pd in 0.8wt% dilute nitric acid to obtain a Pd active group solution, placing the modified activated α-Al2O3 carrier in step two into a sugar-coating machine, turning on the rotation and heating switches, and spraying the Pd active group solution onto the rotating carrier in the kettle at a temperature of 40℃, the volume of the mixed solution being 0.6 times the mass of precursor A, and the spraying rate being 0.4mL / s; after the spraying is completed, after standing for 12h, placing in a freeze dryer for freeze drying treatment to obtain precursor A; the second step loading comprising: dissolving Lewis acid in pure water to obtain solution B, and then using the same spraying and drying steps as described above to obtain precursor C;

[0060] Step four, placing precursor C into a muffle furnace for calcination treatment at 450℃ for 6h to obtain catalyst precursor D;

[0061] Step five, reducing catalyst precursor D obtained in step four by hydrogen gas at a temperature increasing rate of 1℃ / min to 300℃ for 6h to obtain the catalyst, which is recorded as Cat.9.

[0062] Example 10

[0063] The catalyst of the present example comprises a carrier α-Al2O3 modified by metal M, Pd and Lewis acid loaded on the carrier α-Al2O3, in the catalyst, the mass percentage content of metal M is 1.4%, the mass percentage content of Pd is 0.08%, and the mass percentage content of Lewis acid is 0.3% according to 100%, the metal M is W, the particle size of the α-Al2O3 is 3mm, and the Lewis acid is MgCl2;

[0064] The preparation method of the catalyst is as follows:

[0065] Step one, activating α-Al2O3 at a temperature increasing rate of 1℃ / min to 450℃ for 4h to obtain activated α-Al2O3;

[0066] Step two, dissolving ammonium metatungstate in 3.0wt% dilute nitric acid to obtain solution M1, placing the activated α-Al2O3 in solution M1 for impregnation, filtering, and after standing for 36h, placing in a freeze dryer for freeze drying treatment, and then calcining at 500℃ for 2h, and naturally cooling to room temperature to obtain α-Al2O3 modified by metal W and having a special structure;

[0067] Step three, loading Pd and Lewis acid on the metal W modified α-Al2O3 in step two by a step-by-step loading method, the step-by-step loading method comprising a first step loading and a second step loading, the first step loading comprising: dissolving a hydrochloride salt of Pd in 3.0 wt% dilute nitric acid to obtain a Pd active group solution, placing the modified activated α-Al2O3 carrier in step two in a sugar-coating machine, turning on the rotation and heating switches, and spraying the Pd active group solution on the rotating carrier in the kettle at a temperature of 65°C, the volume of the mixed solution being 0.85 times the mass of precursor A, and the spraying rate being 2.8 mL / s; after the spraying is completed, after standing for 36 h, placing it in a freeze dryer for freeze-drying treatment to obtain precursor A; the second step loading comprising: dissolving the Lewis acid in pure water to obtain solution B, and then using the same spraying and drying steps as described above to obtain precursor C;

[0068] Step four, placing precursor C in a muffle furnace for calcination treatment at 600°C for 2 h to obtain catalyst precursor D;

[0069] Step five, reducing catalyst precursor D obtained in step four by hydrogen gas at a temperature increase rate of 2°C / min to 450°C for 3 h to obtain the catalyst, which is denoted as Cat.10.

[0070] Example 11

[0071] The catalyst of the present example comprises a carrier α-Al2O3 modified by a metal M, Pd and a Lewis acid supported on the carrier α-Al2O3, the mass percentage content of the metal M in the catalyst being 1.4%, the mass percentage content of Pd being 0.05%, and the mass percentage content of the Lewis acid being 0.15% according to 100%, the metal M being W, the particle size of the α-Al2O3 being 2.4 mm, and the Lewis acid being AlCl3;

[0072] The preparation method of the catalyst is as follows:

[0073] Step one, activating α-Al2O3 at a temperature increase rate of 1°C / min to 420°C for 4.8 h to obtain activated α-Al2O3;

[0074] Step two, dissolving ammonium metatungstate in 2.4 wt% dilute nitric acid to obtain solution M1, placing the activated α-Al2O3 in solution M1 for impregnation, filtering, standing for 20 h, and then placing it in a freeze dryer for freeze-drying treatment, followed by calcination at 500°C for 2 h, and naturally cooling to room temperature to obtain α-Al2O3 modified by a metal W and having a special structure;

[0075] Step three, loading Pd and Lewis acid on the metal W modified α-Al2O3 in step two by a step-by-step loading method, the step-by-step loading method comprising a first step loading and a second step loading, the first step loading comprising: dissolving a hydrochloride salt of Pd in 2.4wt% dilute nitric acid to obtain a Pd active group solution, placing the modified activated α-Al2O3 carrier in step two in a sugar-coating machine, turning on the rotation and heating switches, and spraying the Pd active group solution on the rotating carrier in the kettle at a temperature of 55°C, the volume of the mixed solution being 0.75 times the mass of precursor A, and the spraying rate being 1.8mL / s; after the spraying is completed, after standing for 20h, placing in a freeze dryer for freeze drying treatment to obtain precursor A; the second step loading comprising: dissolving Lewis acid in pure water to obtain solution B, and then using the same spraying and drying steps as described above to obtain precursor C;

[0076] Step four, placing precursor C in a muffle furnace for calcination treatment at 550°C for 3.5h to obtain catalyst precursor D;

[0077] Step five, reducing catalyst precursor D obtained in step four by hydrogen gas at a temperature increase rate of 1.5°C / min to 380°C for 4.5h to obtain the catalyst, denoted as Cat.11;

[0078] Example 12

[0079] The catalyst of this example comprises a carrier α-Al2O3 modified by metal M, Pd and Lewis acid loaded on the carrier α-Al2O3, in the catalyst, the mass percentage content of metal M is 1%, the mass percentage content of Pd is 0.03%, and the mass percentage content of Lewis acid is 0.12% according to 100%, the metal M is W, the particle size of the α-Al2O3 is 2mm, and the Lewis acid is AlCl3;

[0080] The preparation method of the catalyst is as follows:

[0081] Step one, activating α-Al2O3 at a temperature increase rate of 1°C / min to 400°C for 5h to obtain activated α-Al2O3;

[0082] Step two, dissolving ammonium metatungstate in 1.2wt% dilute nitric acid to obtain solution M1, placing the activated α-Al2O3 in solution M1 for impregnation, filtering, standing for 30h, taking out and placing in a freeze dryer for freeze drying treatment, and then calcining at 500°C for 2h, and naturally cooling to room temperature to obtain α-Al2O3 modified by metal W and having a special structure;

[0083] Step 3: Load Pd and Lewis acid onto the metal W-modified α-Al₂O₃ described in Step 2 using a stepwise loading method. This stepwise loading method includes a first loading step and a second loading step. The first loading step involves dissolving Pd hydrochloride in 1.2 wt% dilute nitric acid, impregnating the precursor from Step 2 using a rotary evaporation impregnation method at 45°C and a vacuum of -0.03 MPa, and rotating the impregnator until the material becomes non-fluid. After standing for 30 hours, the material is removed and freeze-dried to obtain precursor A. The second loading step involves dissolving the Lewis acid in pure water to obtain solution B, and then performing the same impregnation and drying steps as described above to obtain precursor C.

[0084] Step 4: Place precursor C in a muffle furnace and calcine at 450-600℃ for 2-6 hours to obtain catalyst precursor D;

[0085] Step 5: The catalyst precursor D obtained in Step 4 is reduced by heating it to 400°C with hydrogen at a rate of 1.2°C / min for 4 hours to obtain the catalyst, denoted as Cat.12.

[0086] Comparative Example 1

[0087] The α-Al2O3 support was not modified with metal M. Step 2 was omitted from the catalyst preparation steps in Example 1. The rest was the same as in Example 1. The resulting catalyst was denoted as DCat.1.

[0088] Comparative Example 2

[0089] It does not contain Lewis acid, and except that the preparation method does not contain the second loading in step three, it is the same as in Example 1. The resulting catalyst is denoted as DCat.2.

[0090] The above catalyst is used in the selective and continuous production of n-pentene from isoprene, and the application is as follows:

[0091] (1) The catalyst and inert ceramic balls with a particle size of 1.8-2.4 mm are alternately packed layer by layer into a fixed bed reactor, and then nitrogen is introduced until the air in the fixed bed reactor is exhausted; wherein, the volume ratio of the catalyst to the inert ceramic balls is 2:1; the fixed bed reactor is a tubular fixed bed reactor, the inner diameter of the reaction tubes in the tubular fixed bed reactor is 14-26 mm, and the packing height of the reaction tubes is 2.25-3.6 m.

[0092] (2) hydrogen gas is introduced into the fixed bed reactor, the hydrogen gas flow L satisfies 15 mL / min≤L≤45 mL / min, the gas pressure in the fixed bed reactor reaches 0.5-2.5 bar, the molar ratio of hydrogen gas to piperylene is (0.6-0.8):1, selective hydrogenation is selected, so the hydrogen gas amount is slightly insufficient to prevent over hydrogenation. After the catalyst is heated to 40-60℃ at a heating rate of 1℃ / min and kept, the hydrogen gas and the piperylene raw material liquid are preheated to the reaction temperature, then introduced into the fixed bed reactor, the hydrogenation reaction is carried out at the reaction temperature and pressure, the piperylene mass space velocity is 3.6-8.6 g / gcat / hr.

[0093] (3) the reaction liquid obtained in step (2) is sent into a gas-liquid separator for separation, the tail gas hydrogen is recycled through a hydrogen compressor. The specific reaction conditions and reaction results are shown in Table 1

[0094] Table 1 hydrogenation reaction conditions and results

[0095]

[0096]

[0097] Note: the above evaluation results are the average results in each running time.

[0098] The above shows and describes the basic principles, main features and advantages of the present application. It should be understood by those skilled in the art that the present application is not limited by the above examples, the above examples and descriptions in the specification are only to illustrate the principles of the present application, without departing from the spirit and scope of the present application, the present application can have various changes and improvements, these changes and improvements all fall within the scope of the present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a catalyst for the hydrogenation of isoprene to n-pentene, characterized in that, The catalyst for the hydrogenation of isoprene to prepare n-pentene comprises a metal M-modified α-Al₂O₃ support, Pd supported on the α-Al₂O₃ support, and a Lewis acid; the catalyst comprises, by 100%, a metal M mass percentage of 0.8-2%, a Pd mass percentage of 0.01-0.08%, and a Lewis acid mass percentage of 0.06-0.3%; the metal M is W, V, or Ga; the α-Al₂O₃ particle size is 1.8 mm-3 mm; the Lewis acid is any one of SnCl₂, ZnCl₂, AlCl₃, MgCl₂, and CeCl₃; the method comprises the following steps: Step 1: Activate α-Al2O3 by heating it to 250-450℃ at 1℃ / min for 4-8 hours to obtain activated α-Al2O3; Step 2: Dissolve the soluble salt of metal M in dilute nitric acid to obtain solution M1. Immerse the activated α-Al2O3 in solution M1 and let it stand for 12-36 hours. Then, freeze-dry it in a freeze dryer and calcine it at 500°C for 2 hours. After naturally cooling to room temperature, α-Al2O3 with a special structure modified by metal M is obtained. The soluble salt of metal M is ammonium metatungstate, sodium metavanadate, or gallium nitrate. Step 3: Load Pd and Lewis acid onto the metal-modified α-Al2O3 obtained in Step 2 using a stepwise loading method. The stepwise loading method includes a first-step loading and a second-step loading. The first-step loading includes: dissolving the Pd precursor in dilute nitric acid to obtain a Pd precursor solution; simultaneously, spraying the obtained Pd precursor solution onto the metal-modified α-Al2O3 obtained in Step 2, or immersing the metal-modified α-Al2O3 in the Pd precursor solution; after standing for 12-36 hours, freeze-drying in a freeze dryer to obtain precursor A. The second-step loading includes: dissolving the Lewis acid in pure water to obtain solution B; spraying solution B onto precursor A obtained in Step 1, or immersing precursor A in solution B; after standing for 12-36 hours, freeze-drying in a freeze dryer to obtain precursor C. Step 4: Place precursor C in a muffle furnace and calcine at 450-600℃ for 2-6 hours to obtain catalyst precursor D; Step 5: Reduce the catalyst precursor D obtained in step 4 with hydrogen to obtain the catalyst.

2. The method for preparing a catalyst for the hydrogenation of isoprene to n-pentene according to claim 1, characterized in that, The catalyst contains 0.8-1.4% by mass of metal M, 0.01-0.05% by mass of Pd, and 0.06-0.16% by mass of Lewis acid.

3. The method for preparing a catalyst for the hydrogenation of isoprene to n-pentene according to claim 2, characterized in that, The catalyst contains 1% by mass of metal M, 0.03% by mass of Pd, and 0.12% by mass of Lewis acid.

4. The method for preparing a catalyst for the hydrogenation of isoprene to n-pentene according to any one of claims 1-3, characterized in that, The reduction treatment described in step five is as follows: the catalyst precursor D is heated to 300-450℃ in a hydrogen-exposed state at a heating rate of 1-2℃ / min, held for 3-6 hours, and then naturally cooled.

5. The method for preparing a catalyst for the hydrogenation of isoprene to n-pentene according to claim 4, characterized in that, In step three, the spraying temperature is 40-65℃, the spraying rate is 0.4-2.8mL / s, and the mass of the solution used for spraying is 0.6-0.85 times the mass of the precursor.

6. The method for preparing a catalyst for the hydrogenation of isoprene to n-pentene according to claim 4, characterized in that, The mass concentration of the dilute nitric acid mentioned in step two or three is 0.8-3.0 wt%.

7. A method for the continuous production of n-pentene by hydrogenation of isoprene using a catalyst prepared according to any one of claims 1-6, characterized in that, The method includes the following steps: (1) The catalyst prepared by any one of claims 1-6 and inert ceramic balls with a particle size of 1.8-2.4 mm are alternately packed layer by layer into a fixed bed reactor, and then nitrogen is introduced until the air in the fixed bed reactor is exhausted; wherein the volume ratio of the catalyst to the inert ceramic balls is 2:

1. (2) Hydrogen gas is introduced into the fixed bed reactor. Under the condition that the hydrogen flow rate L meets 15 mL / min ≤ L ≤ 45 mL / min, the gas pressure in the fixed bed reactor reaches a slight positive pressure of 0.5-2.5 bar. The catalyst is heated to 40-60°C at a heating rate of 1°C / min and then kept at that temperature. The hydrogen gas and isoprene feed liquid are preheated to the reaction temperature and then introduced into the fixed bed reactor. The hydrogenation reaction is carried out under the reaction temperature and pressure. (3) The reaction liquid obtained in step (2) is sent to a gas-liquid separator for separation, and the resulting tail gas hydrogen is recycled by a hydrogen compressor.

8. The method as described in claim 7, characterized in that, In step (2), the molar ratio of hydrogen to isoprene is (0.6-0.8):1, the mass hourly space velocity of isoprene is 3.6-8.6 g / gcat / hr, the fixed bed reactor is a tubular fixed bed reactor, the inner diameter of the reaction tubes in the tubular fixed bed reactor is 14-26 mm, and the packing height of the reaction tubes is 24-36 cm.

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