Process method for continuously preparing pyrrolidine from 1, 4-butanediol

Abstract

The invention discloses a technological method for continuously preparing pyrrolidine, and belongs to the technical field of organic chemical industry. A fixed bed reactor is filled with a nickel and yttrium loaded solid-phase catalyst, a hydroamination reaction of 1, 4-butanediol and ammonia is continuously catalyzed, no solvent participates, nickel valence distribution and carrier acid sites are optimized through the synergistic effect of double metals, and carbon deposition is inhibited. According to the method, the 100% conversion rate of 1, 4-butanediol and the pyrrolidine selectivity larger than or equal to 93.7% are achieved under the mesoporous confinement effect, and the method is simple in technological process, low in cost and easy to operate; the catalyst is easy to prepare and low in price; the method has the advantages of high raw material conversion rate and good product selectivity, is suitable for continuous preparation of industrial production, and provides a new thought for the design of a heterogeneous catalytic system.

Description

Technical Field

[0001] The present invention belongs to the fields of organic chemical industry and industrial catalysis, and relates to a process for continuously preparing pyrrolidine suitable for industrial production. Background Art

[0002] According to statistics, among the top 200 drugs sold globally currently, about 60% contain nitrogen heterocyclic functional groups. Research shows that the introduction of nitrogen heterocycles can improve the physicochemical properties of candidate drugs, endowing them with better pharmacokinetic properties and low toxicity and side effects, and enhancing drug-likeness. The pyrrolidine skeleton widely exists in natural products (NPs), especially alkaloids, and has structural and biological activity diversity. For example, nicotine (1, antioxidant, anti-inflammatory, anti-hyperglycemic), scalusamides A (2), and (R)-bgugaine (3, antibacterial, antifungal), 1,4-dideoxy-1,4-imino-D-ribitol (4), and aegyptolidine A (5, anti-cancer) all contain pyrrolidine structural units. Pyrrolidine is the most common five-membered non-aromatic nitrogen heterocycle among the drugs approved by the US Food and Drug Administration (FDA) and is highly favored in the fields of pharmaceutical science and drug design. Moreover, pyrrolidine and its derivatives are widely used as transition metal ligands and organic catalysts in asymmetric synthesis to highly selectively control the stereoconfiguration. The broad application prospects of pyrrolidine have prompted chemists to continuously explore new synthetic methods for it.

[0003]

[0004] Moreover, pyrrolidine can also be used as an intermediate and reagent in the production of fuel additives, surfactants, pharmaceutical and crop protection compositions, epoxy resin hardeners, catalysts for polyurethanes, as well as an intermediate and reagent in the production of quaternary ammonium compounds, plasticizers, and corrosion inhibitors, and is used as synthetic resins, ion exchangers, textile auxiliaries, dyes, vulcanization accelerators, and emulsifiers. Therefore, pyrrolidine also plays a crucial role in chemical production.

[0005] Currently, there are mainly the following three heterogeneous catalytic methods that are more suitable for industrial production of pyrrolidine: 1) Hydrogenation of pyrrole to produce pyrrolidine under the catalysis of a metal. In 2018, the Kobayashi research group developed a catalyst with rhodium and platinum simultaneously loaded on alumina, realizing the hydrogenation reaction of various aromatic substrates, including the hydrogenation of pyrrole to produce pyrrolidine; in 2020, the Narani research group used pine needle ash as a carrier to load ruthenium oxide, achieving complete hydrogenation of pyrrole in a reaction time of 15 - 24 h, but this method has problems such as long reaction time and high raw material price; 2) Using aminobutanol as a raw material, also under the catalysis of a metal, hydrocyclization to produce pyrrolidine. In 2012, the Li Yang research group at Tianjin University developed a catalyst with copper, chromium, and lanthanum triple metals loaded on alumina, realizing the intramolecular amination of aminobutanol to produce pyrrolidine, with high conversion but low selectivity, and the aminobutanol raw material is expensive; 3) Changing to the reaction of butanediol with ammonia, amination to produce pyrrolidine under a metal-catalyzed hydrogen environment. As early as 2002, the Kulkarni research group developed a catalyst with acidic ZSM-5 as a carrier. It was found that when using metal copper loading, pyrrolidine could be obtained in a relatively high yield, but this method requires the participation of water and the reaction temperature is as high as 250 °C; in 2016, the Bazanov research group developed a catalyst with nickel and copper loaded on chromium oxide. Compared with the patent of BASF, the conversion rate and selectivity decreased, and ammonia was more excessive; in 2018, the Milstein research group used a complex of ruthenium and phosphine ligands to realize the synthesis of N-substituted pyrrole from butanediol and primary alcohol in an ammonia atmosphere, with good results but the reaction time was as long as 24 h. Therefore, this method generally has problems such as complex catalysts, high system pressure, and serious ammonia excess.

[0006] In 2009 and 2015, the patents WO2009 / 080508Al (BASF SE) and CN104470907A successively reported two catalysts, lead-bismuth-tin loaded on alumina and nickel-cobalt-copper-tin loaded on alumina, both of which realized the amination of butanediol to prepare pyrrolidine, with relatively high conversion rates but low selectivity, and the required metal elements are redundant, the metal loading is large, at the same time the system pressure is as high as 20 MPa, and ammonia is severely excessive, leaving great room for improvement. Although patent CN117177957A has improvements on this basis, there are still problems such as large metal loading and high reaction temperature. At the same time, the existing processes are difficult to achieve co-production of products, with low raw material utilization rate, which is contrary to the concept of green chemistry. There is an urgent need for a new method suitable for industrial production to continuously prepare pyrrolidine from 1,4-butanediol. Summary of the Invention

[0007] To solve the above series of problems, the present invention provides a method for continuously preparing pyrrolidine from 1,4-butanediol, which has a simple process flow, low cost, and is easy to operate; the catalyst is easy to prepare and has a low price; the raw material conversion rate is high, the product selectivity is good, and it is suitable for industrial production.

[0008] A process for continuously preparing pyrrolidine from 1,4-butanediol according to the present invention; the technical solution is as follows: Pyrrolidine of formula I is prepared by reacting 1,4-butanediol (BDO) of formula II with ammonia in the presence of hydrogen and a metal-loaded alumina catalyst.

[0009]

[0010] A process for continuously preparing pyrrolidine from 1,4-butanediol, the specific steps are as follows:

[0011] (1) Charge an unactivated metal-loaded alumina catalyst into a fixed-bed reactor and reduce it under a hydrogen atmosphere; wherein, the metal-loaded alumina catalyst contains nickel and rare-earth metal dual active components; further, it is a bimetal-loaded γ-alumina catalyst; the active components are a dual-component of transition metal nickel and rare-earth metal yttrium. In the present invention, the concepts of the metal-loaded alumina catalyst and the catalyst are equivalent to each other;

[0012] The metal precursor refers to a metal salt used to be loaded on an alumina support, including but not limited to nitrates, acetates, etc., and in the present invention, it refers to a transition metal salt and a rare-earth metal salt; the wet impregnation method is used to load nickel and yttrium precursors to prepare a catalyst precursor.

[0013] The metal precursor is loaded on the support and calcined to obtain a catalyst precursor, which is diluted to obtain an unactivated catalyst, and is reduced to form an activated catalyst;

[0014] (2) Mix the raw materials 1,4-butanediol and ammonia at a molar ratio of 1:5 to 10, then enter the reactor and carry out continuous hydroamination reaction, while introducing hydrogen and maintaining a certain pressure;

[0015] (3) Separate the reaction solution to obtain pyrrolidine; that is, the reaction solution enters a gas-liquid separator, and a liquid-phase sample is taken for gas chromatography analysis.

[0016] In a further preferred embodiment, the metal-loaded alumina catalyst in step (1) is selected from nickel and rare-earth metal-loaded alumina catalysts; the more preferred rare-earth metal is yttrium.

[0017] In a further preferred embodiment, after the unactivated catalyst in step (1) is reduced with hydrogen, the mass ratio of nickel to yttrium is greater than 3:1; more preferably 3 to 15:1, still more preferably the mass ratio of nickel to yttrium is 6 to 10:1, and most preferably 10:1.

[0018] In a further preferred embodiment, the nickel loading in step (1) is 15 to 30 wt%, preferably 20 to 30 wt%.

[0019] In a further preferred embodiment, the yttrium loading in step (1) is 2 to 5 wt%, preferably 2 to 3 wt%.

[0020] In a further preferred embodiment, the alumina in the metal-loaded alumina catalyst in step (1) is selected from amorphous alumina, γ-alumina, α-alumina or basic alumina, preferably γ-alumina.

[0021] In a further preferred embodiment, the calcined catalyst precursor in step (1) is diluted with silica, and the volume of the original catalyst precursor accounts for 30% to 70% of the total volume after dilution, preferably 40% to 60%. The catalyst precursor dilution operation is carried out by the mechanical mixing method, and the calcined catalyst precursor particles and quartz sand (particle size 40 - 70 mesh) are uniformly mixed and filled according to the volume ratio of (1 - 2):1. Example: In Example 1, the catalyst precursor and quartz sand are diluted at a volume ratio of 1:1, which accounts for 50%.

[0022] In a further preferred embodiment, the metal-loaded alumina catalyst precursor in step (1) is prepared by the wet impregnation method. Alumina support is added to the aqueous solution of the metal precursor, and stirred and aged at 80 - 120 °C for 1 - 4 h, preferably stirred and aged at 90 - 110 °C for 2 - 3 h, and then dried and calcined to obtain the metal-loaded alumina catalyst precursor, which is in the oxidized state.

[0023] In a further preferred embodiment, the metal precursor in step (1) is at least one of nitrate and acetate. More preferably, the transition metal salt is nitrate and the rare earth metal salt is nitrate; more preferably, it is a mixed aqueous solution of nickel nitrate hexahydrate and yttrium nitrate hexahydrate, and the mass concentration of the solution based on nickel is 16.6 - 37.5 mg / mL.

[0024] In a further preferred embodiment, the calcination procedure is to rise to 200 °C in 30 min, and then rise to 300 - 500 °C at a rate of 2 °C / min, preferably 350 - 450 °C, and hold for 3 - 6 h, preferably 4 - 5 h.

[0025] In a further preferred embodiment, the drying is carried out at 100 - 140 °C for 10 h, preferably at 110 - 130 °C for 10 h.

[0026] In a further preferred embodiment, in the step (1), the reduction procedure is to rise from room temperature to 100 °C in 0.5 h, then rise to 300 - 500 °C at a rate of 1 °C / min and hold for 3 - 6 h, and the hydrogen GHSV (gas hourly space velocity) is 300 - 700 h -1 .

[0027] In a further preferred embodiment, the unactivated catalyst is used after being reduced and activated by hydrogen in a fixed bed reactor. The reduction procedure is to rise from room temperature to 100 °C in 30 min, then rise to 300 - 500 °C, preferably 350 - 450 °C, at a rate of 1 °C / min and hold for 3 - 6 h, preferably 4 - 5 h. The GHSV of the used hydrogen is 300 - 700 h -1 , preferably 480 - 600 h -1 .

[0028] In a further preferred embodiment, for unactivated catalysts with different filling amounts, the GHSV of the above hydrogen remains unchanged, so the actual flow rate should change. For example, the GHSV of the hydrogen used in the step (1) is calculated based on the filling volume of the unactivated catalyst. The calculation formula is GHSV = hydrogen volume flow rate (L / h) / filling volume of the unactivated catalyst (L). Adjust the hydrogen volume flow rate according to different catalyst filling amounts to keep the GHSV within 480 - 600 h -1 .

[0029] In a further preferred embodiment, the specific surface area of the catalyst > 210 m 2 / g, and the pore diameter is 2 - 10 nm

[0030] In a further preferred embodiment, the amount of the unactivated catalyst used in the step (1) accounts for 30 - 70% of the total volume of the reactor, preferably 40 - 60%

[0031] In a further preferred embodiment, the aging temperature in the step (1) is preferably 90 - 110 °C; the drying temperature is preferably 110 - 130 °C

[0032] In a further preferred embodiment, the reaction is carried out under solvent - free conditions, and the solvent - free conditions mean that no organic solvent or water is added as a solvent to the reaction system

[0033] In a further preferred embodiment, the molar ratio of 1,4 - butanediol to ammonia in the step (2) is 1:8 - 10

[0034] In a further preferred embodiment, the reaction temperature in the step (2) is 170 - 190 °C, further preferably 175 - 185 °C. The pressure is 1.5 - 2.5 MPa; the LHSV of the raw material 1,4 - butanediol is 0.17 - 1 h -1, further preferably 0.17 - 0.5 h -1 The GHSV of hydrogen is 5.81 - 19.36 h -1 , preferably 12.91 - 18.07 h -1 LHSV refers to the ratio of the liquid volume flow rate (L / h) of raw material 1,4 - butanediol to the volume (L) of the unactivated catalyst, with the unit of h -1

[0035] In the method described above, the conversion rate of 1,4 - butanediol is 100%, and the pyrrolidine selectivity ≥ 93.7%.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The nickel - and - yttrium - loaded alumina catalyst not only has a simple preparation method but also requires only two metal elements, overcoming the drawback that traditional catalytic amination reactions require the synergistic action of multiple metal elements. The introduction of rare - earth metal Y not only regulates the valence state distribution of nickel through the electronic effect but also modulates the surface acidic sites of the alumina support, forming a more stable strong metal - support interaction; this synergistic effect significantly improves the conversion rate and selectivity; supported by the mesoporous structure (pore diameter of about 4 nm) and high specific surface area (> 210 m 2 / g), the reaction mass transfer efficiency is optimized.

[0038] Under certain operating conditions, this process method co - produces 4 - amino - 1 - butanol while continuously preparing pyrrolidine. Thanks to the confinement effect of the ordered mesoporous channels on the intermediate products, the side - reaction path is effectively inhibited, improving the raw material utilization rate and having good economy. Under the optimal conditions, the conversion rate of 1,4 - butanediol is 100%, and the selectivity of pyrrolidine is 96.4%.

[0039] This method has low cost, is green and environmentally friendly, easy to operate, and suitable for industrial continuous production. Its support design concept can be extended to fields such as dry reforming of methane and CO2 hydrogenation, providing a new paradigm for the development of heterogeneous catalysts. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a schematic diagram of the fixed - bed reaction device of the present invention.

[0041] In the figure: 1) 1,4 - butanediol raw material bottle; 2) inverted liquid ammonia tank; 3) one - way valve; 4) double - plunger micro - pump; 5) ball valve; 6) three - way valve; 7) pressure gauge; 8) reaction tube and heating jacket; 9) gas - liquid separator; 10) liquid - taking tank; 11) back - pressure valve; 12) nitrogen gas cylinder; 13) hydrogen gas cylinder. DETAILED DESCRIPTION OF THE INVENTION

[0042] The present invention will be described in detail below with specific embodiments. Unless otherwise specifically stated, the chemical reagents and catalyst carriers involved in the embodiments and comparative examples of the present invention are all conventional commercially available products in the art; the experimental equipment (including reactors, constant flow pumps, temperature control devices, etc.) are all general industrial equipment in the art; for raw materials or process steps for which the preparation methods are not described in detail, they are all implemented according to the conventional industrial standards in the technical field to which they belong.

[0043] Example 1

[0044] Catalyst preparation: The catalyst was prepared using the wet impregnation method. Prepare 6.5 g of γ-alumina support, then weigh 14.95 g of nickel nitrate hexahydrate and 2.15 g of yttrium nitrate hexahydrate, dissolve them in 100 mL of deionized water, add the prepared γ-alumina support, stir and age at 100 °C for 2 h, then stir and dry at 120 °C for 12 h. After cooling to room temperature, transfer it to a muffle furnace for calcination. The calcination procedure is to rise from room temperature to 200 °C in 0.5 h, and then rise to 400 °C at a rate of 2 °C / min and hold for 4 h to obtain a metal-loaded alumina catalyst precursor. Dilute the obtained catalyst precursor with quartz sand to twice the volume to obtain the unactivated Ni30Y5 catalyst.

[0045] Catalyst performance evaluation: First, fill the lower section of a heating tubular reactor with an inner diameter of 10 mm, equipped with a thermocouple in the center and a total volume of 39.75 mL, with a quartz sand layer, then fill 15.7 mL of the unactivated Ni30Y5 catalyst on top of it, and finally fill the remaining section with quartz sand again. Second, before the reaction, reduce the unactivated Ni30Y5 catalyst under atmospheric pressure with a hydrogen GHSV of 575 h -1 The reduction procedure is to rise from room temperature to 100 °C in 0.5 h, then rise to 400 °C at a rate of 1 °C / min and hold for 4 h. After the reduction is completed, a Ni30Y5 catalyst with a nickel loading of 30 wt% and a yttrium loading of 5 wt% is obtained. Third, use two double-plunger micro-pumps to pump raw materials 1,4-butanediol and ammonia into the mixing section of the reactor for mixing and reaction at a molar ratio of 1:10. The liquid hourly space velocity of BDO is 0.25 h -1 , control the temperature at 180 °C, the pressure at 1.5 MPa, maintain the reaction pressure with hydrogen, and the hydrogen GHSV is 12.91 h -1 . Then the reaction liquid enters the gas-liquid separation receiver, and a liquid phase sample is taken for gas chromatography analysis. After the entire reaction device runs continuously and stably for 2 hours, the conversion rate of 1,4-butanediol is 100%, and the selectivity of pyrrolidine is 93.7%.

[0046] Example 1 uses a Ni30Y5 / γ-Al2O3 catalyst (nickel loading 30 wt%, yttrium 5 wt%), at 1.5 MPa, 180 °C, and a BDO liquid hourly space velocity of 0.25 h -1Under these conditions, 100% conversion of 1,4-butanediol and 93.7% selectivity of pyrrolidine were achieved. Its success is attributed to: ① Bimetallic synergy (yttrium enhances nickel dispersion and inhibits carbon deposition); ② Quartz sand dilution (50% by volume) optimizes mass transfer and prevents local overheating; ③ Hydrogen space velocity (GHSV 12.91 h -1 ) is matched with the pressure to maintain an active hydrogen environment.

[0047] Examples 2 to 10

[0048] The experimental results can be found in Table I below. Except for the parameters marked in the table, the remaining parameters are the same as those in Example 1.

[0049] Table I

[0050]

[0051]

[0052] Temperature: 180 °C

[0053] Catalyst: Described in the same way as the catalyst code in Example 1

[0054] Molar ratio: Molar ratio of BDO to ammonia

[0055] BDO LHSV: Liquid hourly space velocity LHSV based on BDO, h -1

[0056] Hydrogen pressure: Pressure provided by hydrogen during the reaction, MPa

[0057] Hydrogen GHSV: Gas hourly space velocity GHSV of hydrogen during the reaction, h -1

[0058] BDO conversion: Conversion of butanediol, %

[0059] Pyrrolidine selectivity: Selectivity of pyrrolidine, %

[0060] 4-Amino-1-butanol selectivity: Selectivity of 4-amino-1-butanol, %

[0061] The data in Table 1 show that when using Ni-Y bimetallic catalysts (such as Ni20Y2, Ni30Y5), at a hydrogen pressure of 2.0 MPa (Example 7), a BDO liquid hourly space velocity of 0.17 h -1 (Example 4) and an ammonia ratio of 1:10 (Examples 2 - 6), the highest pyrrolidine selectivity reached 96.4% (Example 7), and the BDO conversion rate reached 100% in all cases, significantly superior to other rare earth metals (such as Ni30Ce5) or multi-metal catalysts (Example 3). In addition, the hydrogen space velocity (GHSV) increased to 25.82 h-1 At this time (Example 10), it selectively drops to 88.6%, indicating that the hydrogen hourly space velocity needs to be controlled at 12.91 - 18.07 h -1 to balance activity and selectivity. The core innovation lies in: through the synergistic effect of Ni - Y bimetals (yttrium loading of 2 - 5 wt%) combined with the optimization of key process parameters (pressure, space velocity, dilution ratio), the coexistence of high conversion rate and high selectivity is achieved, breaking through the limitations of traditional multi - metal catalysts (Comparative Example 1).

[0062] Comparative Example 1

[0063] In Comparative Example 1, the Ni - Co - Cu - Sn / Al2O3 four - metal catalyst (CN104470907A) of the existing patent was used. Under the same reaction conditions (1.5 MPa, 180 °C), the conversion rate of 1,4 - butanediol was only 33.9%, the selectivity of pyrrolidine was as low as 5.8%, and the selectivity of the by - product 4 - amino - 1 - butanol reached 8.4%. In contrast, the Ni - Y bimetal catalyst of the present invention (Example 4) achieved 100% conversion rate and 96.3% pyrrolidine selectivity under the same pressure and temperature, and there were no by - products. The core difference is that the active sites of the multi - metal system in the prior art are chaotic and the loading is high (total metal loading of 47.6%), resulting in many side reactions and low efficiency; while the present invention simplifies the catalyst structure and precisely regulates the active center through the synergism of Ni - Y bimetals (total loading of 22 - 35%), significantly improving selectivity and reaction efficiency.

[0064] Comparative Example 2

[0065] First, the lower section of a heated tubular reactor with an inner diameter of 10 mm, equipped with a thermocouple in the center and a total volume of 39.75 mL, was filled with a quartz sand layer, and on top of this, 23.55 mL of the unactivated Ni20Y2 catalyst obtained in Example 2 was filled, and finally the remaining section was filled with quartz sand again. Secondly, before the reaction, the unactivated Ni20Y2 catalyst was reduced at atmospheric pressure with a hydrogen GHSV of 575 h -1 under the following conditions: heated from room temperature to 100 °C in 0.5 h, then heated to 400 °C at a rate of 1 °C / min and held for 4 h. After the reduction, the Ni20Y2 catalyst with a nickel loading of 20 wt% and a yttrium loading of 2 wt% was obtained. Thirdly, two double - plunger micro - pumps were used to pump the raw materials 1,4 - butanediol and ammonia into the mixing section of the reactor at a molar ratio of 1:10 for mixing and reaction. The liquid hourly space velocity was 0.17 h -1 , the temperature was controlled at 160 °C, the pressure was 1.5 MPa, and the reaction pressure was maintained by hydrogen. The hydrogen LHSV was 12.91 h -1After that, the reaction solution enters the gas-liquid separation receiver, and the liquid-phase sample is taken for gas chromatography analysis. After the entire reaction device has been continuously operating stably for 6 hours, the conversion rate of 1,4-butanediol is 11%, and there is no target product.

[0066] In Comparative Example 2, the Ni20Y2 catalyst of the present invention was used, but the reaction temperature was lowered to 160 °C (180 °C in Example 4). As a result, the conversion rate of 1,4-butanediol dropped sharply to 11%, and no target product was formed. This result shows that temperature is a key limiting factor for reaction activity: below 180 °C, the activity of the catalyst is not fully excited, and the amination reaction cannot proceed forward. In Example 4, a 100% conversion rate and 96.3% selectivity were achieved at 180 °C, verifying the precise regulation effect of the temperature parameter (180-200 °C) of the present invention on the reaction path, ensuring the efficient completion of the dehydrogenation-cyclization step, and avoiding the accumulation of intermediates or side reactions.

[0067] In summary, compared with Comparative Example 1 (conversion rate of 33.9%) and Comparative Example 2 (conversion rate of 11%), Example 1 achieved the unification of high conversion rate and high selectivity under the continuous process for the first time through the systematic optimization of catalyst components, dilution process, and reaction parameters, laying the core competitiveness of the technical solution.

[0068] Comparative Examples 3-5

[0069] The experimental results can be found in Table II below. Except for the parameters marked in the table, the remaining parameters are the same as those in Comparative Example 2 of the examples:

[0070] Table II

[0071]

[0072] Hydrogen pressure: 2.0 MPa

[0073] Hydrogen GHSV: 12.91 h -1

[0074] Catalyst: The description method is the same as the catalyst code in Example 1

[0075] Molar ratio: Molar ratio of BDO to ammonia

[0076] BDO LHSV: Liquid hourly space velocity LHSV in terms of BDO, h -1

[0077] BDO conversion rate: Conversion rate of butanediol, %

[0078] Pyrrolidine selectivity: Selectivity of pyrrolidine, %

[0079] 4-Amino-1-butanol selectivity: Selectivity of 4-amino-1-butanol, %

[0080] The comparative examples in Table II show that for the prior-art multi-metal catalyst (Comparative Example 1), the conversion rate is only 33.9% and the selectivity is 5.8%. In contrast, for the Ni-Y catalyst of the present invention (Comparative Example 4), the conversion rate reaches 68.4% and the selectivity is 30.7% under the same conditions. Moreover, when the catalyst contains only one metal, nickel or yttrium (Comparative Examples 4 and 5), or when the temperature deviates from 180 °C (Comparative Examples 2 and 3), the performance drops sharply. For example, for the single-nickel catalyst (Comparative Example 4), the selectivity is only 30.7%, and the single-yttrium catalyst (Comparative Example 5) has almost no activity. When the temperature rises to 200 °C (Comparative Example 3), the side reactions increase and the selectivity drops to 14.6%. The core comparative advantage lies in the unique combination of Ni-Y bimetals (yttrium as an additive enhances the dispersion and stability of nickel) and the coupling of process parameters (synergistic regulation of temperature, space velocity, and pressure), which solves the problems of low activity and many by-products of traditional catalysts, verifying the irreplaceability of the catalyst and process of the present invention.

[0081] As described above, the above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art can easily conceive of changes or substitutions within the technical scope disclosed by the present invention, and all of them should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A process for continuously preparing pyrrolidine using 1,4-butanediol as a raw material, characterized in that: It includes the following steps: (1) Charge the unactivated nickel and yttrium bimetal-loaded γ-alumina catalyst into a fixed-bed reactor and reduce it under a hydrogen atmosphere; the unactivated catalyst forms an activated catalyst after reduction; (2) Mix 1,4-butanediol and ammonia in a molar ratio of 1:5 - 10 and then feed them into the reactor, and conduct a continuous hydroamination reaction in the presence of hydrogen. The reaction temperature is 170 - 190 °C, and the pressure is 1.5 - 2.5 MPa; the liquid hourly space velocity of 1,4-butanediol is 0.17 - 0.5 h-1; (3) Separate the reaction solution to obtain pyrrolidine.

2. The method according to claim 1, wherein: After the unactivated catalyst is reduced, the nickel loading is 15 - 30 wt%, the yttrium loading is 2 - 5 wt%, and the mass ratio of nickel to yttrium is 6 - 10:

1.

3. The method according to claim 1, wherein: The catalyst precursor is prepared by the wet impregnation method, and the metal precursors are nickel nitrate and yttrium nitrate.

4. The method according to claim 1, wherein: The preparation method of the catalyst includes the following steps: a) Add an alumina support to an aqueous solution of the metal precursor, stir and age at 80 - 120 °C for 1 - 4 h, and then dry; the metal precursor is at least one of nitrates and acetates; the alumina is selected from amorphous alumina, γ-alumina, α-alumina or basic alumina; b) After drying, heat it to 350 - 450 °C at a rate of 2 °C / min and calcine for 4 - 5 h; c) Reduce the calcined catalyst precursor in hydrogen. The reduction temperature is 300 - 500 °C, and the hydrogen GHSV is 300 - 700 h-1.

5. The method according to claim 1, characterized in that: The calcined catalyst precursor is mixed and diluted with quartz sand in a volume ratio of (1 - 2):

1. The diluted catalyst precursor is the unactivated catalyst, and its volume accounts for 30 - 70% of the reactor loading volume.

6. The method according to claim 1, wherein: The specific surface area of the catalyst > 210 m 2 / g, and the pore size is 2 - 10 nm.

7. The method according to claim 1, wherein: During the reaction process, the hydrogen GHSV is 5.81 - 19.36 h-1.

8. The method according to claim 1, characterized in that: The reaction is carried out under solvent-free conditions.

9. The method according to claim 1, characterized in that: In the step (2), the molar ratio of 1,4-butanediol to ammonia is 1:8 - 10.

10. The method according to claim 1, wherein: The LHSV of the raw material 1,4-butanediol is 0.17 to 1 h -1 .

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