Process for the synthesis of piperazines from ethylenediamine

Abstract

This invention relates to a method for synthesizing piperazine by amination of ethylene glycol. The method involves the amination of ethylene glycol in a system of ethylene glycol, ammonia, hydrogen, and a solvent, under the action of a nickel-copper-cerium-aluminum composite catalyst. According to the method of this invention, the conversion rate of ethylene glycol can reach over 86%, the selectivity of piperazine can reach over 80%, and the overall selectivity of piperazine + ethylenediamine can reach over 90%. The production of piperazine using this invention has advantages such as a simple process flow, mild reaction conditions, environmental friendliness, and low production cost, making it a novel method easily achievable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of chemical technology, specifically relating to a method for synthesizing piperazine by amination of ethylene glycol. Background Technology

[0002] Piperazine (PIP), an important nitrogen-containing heterocyclic compound, has a wide range of applications. In the pharmaceutical industry, it is mainly used to produce anthelmintic, anti-tuberculosis, and antibacterial drugs. In other fields, it is a key intermediate in the synthesis of textile dye auxiliaries, rubber vulcanization accelerators, corrosion inhibitors, antioxidants, stabilizers, surfactants, and polyurethane additives. It also plays an important role in organic synthesis and the daily chemical industry. Currently, PIP production methods mainly rely on heterogeneous catalytic synthesis processes. The main heterogeneous catalytic production routes of PIP include the gas-phase cyclization of ethylenediamine (EDA), the dehydration cyclization of ethanolamine (MEA), the reductive amination of MEA, and the cyclization of diethylenetriamine. Among these, the reductive amination route of MEA is the main process currently under research globally. This process uses MEA and ammonia as raw materials, typically employing solid acids or modified H-ZSM-5 zeolite as catalysts. At a reaction temperature of 300-350°C, MEA undergoes dehydration and condensation to form PIP. However, this method has several drawbacks, including low PIP selectivity, high separation costs, and harsh reaction conditions that usually require increased temperature or pressure.

[0003] Ethylene glycol (EG), the simplest vicinal glycol, is an important basic chemical widely used in solvents, antifreeze, surfactants, and plastics. In recent years, significant breakthroughs in coal-to-ethylene glycol technology and the widespread adoption of coal-based pathways have led to a global oversupply of ethylene glycol. Therefore, converting ethylene glycol into other high-value-added chemicals is of great significance. This conversion not only promotes structural optimization of the EG industry but also contributes to achieving carbon neutrality goals. Currently, many studies report that metal catalysts exhibit high efficiency in the reductive amination of alcohols containing at least one primary hydroxyl group, such as aliphatic primary monools and glycols. Similarly, EG and ammonia can undergo reductive amination via a similar hydrogen transfer mechanism. Under a hydrogen atmosphere, EG first dehydrogenates to form 2-hydroxyacetaldehyde (A). Subsequently, this intermediate reacts with ammonia via condensation amination to give an imine intermediate (B), which is then hydrogenated to prepare MEA. MEA further undergoes a series of steps including hydroxyl dehydrogenation, amination, and hydrogenation to form a series of high-value-added amine products (MHS Hamid, PA Slatford, JM Williams. Borrowing hydrogen in the activation of alcohols. Advanced Synthesis & Catalysis. 2007, 349:1555-1575. http: / / doi.org / 10.1002 / adsc.200600638). It is noteworthy that this reaction pathway theoretically produces only water as a byproduct, representing a more direct, environmentally friendly, and economically feasible approach. Based on currently reported EG reductive amination reaction networks, PIP has been identified as an important product (K. Li, D. Zhang, H. Guo, X. Yang, C. Liang, X. Wu, Q. Wang, D. Li, L. Jia. Insight into crystal-plane-dependent of cobalt catalysts for ethylene glycol amination. Molecular Catalysis. 2025, 570: 114655. http: / / doi.org / 10.1016 / j.mcat.2024.114655).Lorentz et al. demonstrated (LL Lorentz‐Petersen, LU Nordstrøm, R. Madsen. Iridium‐catalyzed condensation of amines and vicinal diols to substituted piperazines. European Journal of Organic Chemistry. 2012, 2012:6752-6759. http: / / doi.org / 10.1002 / ejoc.201201099) that EDA and EG can be converted to PIP under the influence of the iridium active component in toluene / aqueous solution, with water being the only byproduct, further confirming the feasibility of this method. In summary, compared with the traditional MEA reductive amination method, the synthesis of PIP via the reductive amination of EG offers a more promising approach, characterized by mild reaction conditions and superior atom economy. However, compared with simple monools, the reductive amination pathway of EG is more complex. Products such as PIP and EDA can further undergo amination reactions with EG and MEA, forming more complex reaction networks, thereby reducing the selectivity for the desired target product. Therefore, developing a catalyst capable of achieving high selectivity for PIP in the reductive amination of EG is a critical challenge that urgently needs to be addressed.

[0004] For example, CN103664649A discloses a method for preparing monoethanolamine from ethylene glycol. The reaction system consists of ethylene glycol, liquid ammonia, and hydrogen. Ethylenediamine and liquid ammonia are converted into monoethanolamine under the action of a catalyst, and ethylenediamine and piperazine are produced in co-production. Under reaction conditions of 3-18 MPa and 200-350℃, the conversion rate of ethylene glycol is 75%, the highest yield of ethanolamine is 53%, and the selectivity of ethanolamine is 70.6%. This method has disadvantages such as harsh reaction conditions, high catalyst cost, and low selectivity of ethylenediamine and piperazine.

[0005] CN119684128 A discloses a method for preparing ethylenediamine and piperazine from ethylene glycol. Co is used as the active component, and components such as Ru, Ni, and Pt are added. At 200℃, 5MPa, and 10-14h, the total selectivity of ethylenediamine and piperazine reaches 85.5%, and the selectivity of piperazine reaches the highest 73.3%.

[0006] CN 1340503 A discloses a gas-solid phase catalytic synthesis method for piperazine from ethylenediamine and ethylene glycol. The catalyst contains Cu, Zn, and Al components. The synthesis of piperazine from ethylenediamine and ethylene glycol via gas-solid phase catalysis is carried out with an ethylenediamine:ethylene glycol:ammonia ratio of 1:1~5:1~10 (mol), a bed temperature of 250~300℃, a pressure of 5.0~10MPa, a liquid hourly space velocity of 0.5~1.0 ml / ml (catalyst)·h, an ethylenediamine conversion rate of 76.34%, and a piperazine selectivity of 71.38%.

[0007] Therefore, in the existing technology, there are relatively few methods for directly synthesizing piperazine using ethylene glycol, ammonia, and hydrogen as raw materials, or the selectivity of piperazine is not high enough. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of existing technologies, such as high pressure, high temperature, long reaction time, and poor operational safety, and to propose a method for synthesizing piperazine by ethylene glycol amination, and to develop a catalyst that can achieve high selectivity for PIP in the reductive amination of EG.

[0009] Technical solution to achieve the purpose of this invention: Ethylene glycol, ammonia, and hydrogen are reacted in a high-pressure reactor solvent. The reaction process is shown in (1): (1) The inventors discovered that the introduction of cerium improves the dispersion of nickel and copper species on an alumina support, promoting the formation of Ni-Cu particles with a size between 4 and 5 nanometers. H2-TPR and XPS results show that cerium exists in a mixed +3 / +4 valence state, significantly enhancing the reducibility of nickel and copper species on the alumina support. This promotes an increase in the surface NiO ratio and oxygen vacancy concentration, considered a key factor in achieving high PIP selectivity. Simultaneously, it reduces reaction conditions and significantly improves catalyst stability.

[0010] This invention is achieved through the following technical solutions: A method for synthesizing piperazine by amination of ethylene glycol involves the synthesis of piperazine by amination of ethylene glycol in a system containing ethylene glycol, ammonia, hydrogen, and a solvent, under the action of a nickel-copper-cerium-aluminum composite catalyst.

[0011] The solvent includes one or more of the following: ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropyl ether, ethylene glycol dibutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol dipropyl ether, and propylene glycol dibutyl ether.

[0012] The nickel, copper, cerium, and aluminum composite catalyst is prepared by co-precipitation and calcination using one or more of nitrates, sulfates, or chlorides.

[0013] The molar percentage of nickel, copper, and cerium in metallic nickel, copper, cerium, and aluminum is 10% to 50%.

[0014] The molar ratio of nickel, copper, and cerium is 5~10:1~4:0.5~2.5.

[0015] The nickel, copper, cerium, and aluminum composite catalyst accounts for 1-5% of the mass concentration of the reaction system.

[0016] The concentration of ethylene glycol in the reaction system is 0.01~0.5 g / ml, and the molar ratio of ammonia, hydrogen and ethylene glycol is 50~110:30~60:1~10.

[0017] In the system, the reaction temperature is 160-200℃, the reaction pressure is 4-6MPa, and the reaction time is 4-10 hours.

[0018] Using the above technical solution, the conversion rate of ethylene glycol can reach over 86%, the selectivity of piperazine can reach over 80%, and the total selectivity of piperazine + ethylenediamine can reach over 90%. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described below through embodiments. However, these embodiments do not limit the scope of protection of this invention. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementations obtained by those skilled in the art without creative effort are within the scope of protection of this invention. Example 1

[0020] Catalyst preparation All catalysts were prepared via conventional co-precipitation. Taking the preparation of Ni9Cu1Ce1AlOx (with a molar ratio of Ni to Cu and Ce of 9:1:1) as an example, 18 mmol of Ni(NO3)2·6H2O, 2 mmol of Cu(NO3)2·3H2O, 2 mmol of Ce(NO3)3·6H2O, and 36 mmol of Al(NO3)3·9H2O were dissolved in 150 ml of deionized water (the amount of aluminum nitrate added can be adjusted according to the Al2O3 content in the catalyst) to prepare solution A. Then, 85 mmol of Na2CO3 was dissolved in 60 ml of deionized water to prepare solution B. Solution B was slowly added dropwise to solution A, controlling the precipitation endpoint pH to 7-9. The mixture was aged at room temperature for 2-10 hours, filtered, and washed with deionized water until the pH of the supernatant reached 7. The resulting green solid was dried overnight in an oven at 100 °C and then calcined in a muffle furnace at 500 °C for 4 hours. The obtained solid was ground into powder and reduced at 450 °C for 2 h under H2 atmosphere. The resulting black powder sample was denoted as Ni9Cu1Ce1AlOx, with the subscript indicating the molar ratio of each component. Example 2

[0021] The reductive amination of ethylene glycol (EG) was carried out in a 50 mL autoclave. 100 mg of Ni9Cu1Ce1AlOx catalyst, 2 mmol of ethylene glycol, and 7 mL of diethylene glycol monomethyl ether (DEM) were charged into the reactor. The reactor was sealed and purged three times with nitrogen to ensure an inert atmosphere. The reactor was then cooled by immersion in an ice-water bath at 0 °C. A predetermined amount of ammonia (NH3) was then introduced into the system. Next, a predetermined amount of hydrogen (H2) was introduced into the reactor. The reactor was then heated from room temperature to the desired reaction temperature and held for a specified time. The reaction conditions were as follows: temperature 160 °C, reaction time 5 h, ammonia to ethylene glycol molar ratio of 60:1, and hydrogen pressure of 1.5 MPa. After the reaction, the autoclave was allowed to cool naturally to room temperature. The catalyst was recovered by filtration and thoroughly washed with ethanol for further analysis.

[0022] The product was removed and weighed, and the sample was quantitatively analyzed by gas chromatography. The conversion rate of ethylene glycol was 88.2%, the selectivity of piperazine was 82.5%, and the selectivity of ethylenediamine was 11.3%.

[0023] Example 3

[0024] The catalyst was changed to 120 mg Ni8Cu2Ce1AlO x The reaction conditions were as follows: temperature 170℃, reaction time 4 hours, ammonia to ethylene glycol molar ratio of 70:1, hydrogen pressure of 1.5 MPa, and other conditions were the same as in Example 2. The conversion rate of ethylene glycol was 91.2%, the selectivity of piperazine was 85.3%, and the selectivity of ethylenediamine was 10.1%.

[0025] Example 4

[0026] The catalyst was changed to 150 mg Ni8Cu2Ce2AlO x The reaction conditions were as follows: temperature 180℃, reaction time 6 hours, ammonia to ethylene glycol molar ratio of 80:1, and hydrogen pressure of 1.5 MPa. Other conditions were the same as in Example 2. The conversion rate of ethylene glycol was 93.5%, the selectivity of piperazine was 86.1%, and the selectivity of ethylenediamine was 10.7%.

[0027] Example 5

[0028] The catalyst was changed to 200 mg Ni5Cu5Ce1AlOx, and the reaction conditions were as follows: temperature 170℃, reaction time 6 hours, ammonia to ethylene glycol molar ratio of 65:1, and hydrogen pressure of 1.5 MPa. Other conditions were the same as in Example 2. The conversion rate of ethylene glycol was 86.5%, the selectivity of piperazine was 80.5%, and the selectivity of ethylenediamine was 10.4%.

[0029] Example 6

[0030] The catalyst is 120 mg Ni8Cu2Ce1AlO x The solvent used was ethylene glycol dimethyl ether, 6 ml. The reaction conditions were as follows: temperature 170℃, reaction time 5 hours, ammonia to ethylene glycol molar ratio 70:1, hydrogen pressure 1.5 MPa, and other conditions the same as in Example 2. The conversion rate of ethylene glycol was 92.6%, the selectivity of piperazine was 87.1%, and the selectivity of ethylenediamine was 9.8%.

[0031] Example 7

[0032] The catalyst is 120 mg Ni8Cu2Ce1AlO x The solvent used was propylene glycol monomethyl ether, 6 ml. The reaction conditions were as follows: temperature 170℃, reaction time 5 hours, ammonia to ethylene glycol molar ratio 70:1, hydrogen pressure 1.5 MPa, and other conditions the same as in Example 2. The conversion rate of ethylene glycol was 92.3%, the selectivity of piperazine was 86.2%, and the selectivity of ethylenediamine was 10.2%.

[0033] Example 8

[0034] The catalyst is 120 mg Ni8Cu2Ce1AlO x The solvent used was a mixture of 3 ml of ethylene glycol monomethyl ether and 3 ml of ethylene glycol dimethyl ether. The reaction conditions were as follows: temperature 170℃, reaction time 5 hours, ammonia to ethylene glycol molar ratio of 70:1, hydrogen pressure 1.5 MPa, and other conditions the same as in Example 2. The conversion rate of ethylene glycol was 92.8%, the selectivity of piperazine was 86.9%, and the selectivity of ethylenediamine was 10.6%.

[0035] Comparative Example 1 The catalyst was changed to 120 mg Ni8Cu2AlO x The reaction conditions were as follows: temperature 170℃, reaction time 4 hours, ammonia to ethylene glycol molar ratio of 70:1, hydrogen pressure of 1.5 MPa, and other conditions were the same as in Example 1. The conversion rate of ethylene glycol was 89.4%, the selectivity of piperazine was 54.5%, and the selectivity of ethylenediamine was 9.3%.

Claims

1. A method for synthesizing piperazine by amination of ethylene glycol, characterized in that: In a system containing ethylene glycol, ammonia, hydrogen, and solvent, ethylene glycol undergoes an amination reaction to synthesize piperazine under the action of a nickel-copper-cerium-aluminum composite catalyst.

2. The method as described in claim 1, characterized in that, The solvent includes one or more of the following: ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropyl ether, ethylene glycol dibutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol dipropyl ether, and propylene glycol dibutyl ether.

3. The method as described in claim 1, characterized in that, The nickel, copper, cerium, and aluminum composite catalyst is prepared by co-precipitation and calcination using one or more of nitrates, sulfates, or chlorides.

4. The method as described in claims 1 and 3, characterized in that, The molar percentage of nickel, copper, and cerium in metallic nickel, copper, cerium, and aluminum is 10% to 50%.

5. The method as described in claims 1, 3, and 4, characterized in that, The molar ratio of nickel, copper, and cerium is 5~10:1~4:0.5~2.

5.

6. The method as described in claim 1, characterized in that, The nickel, copper, cerium, and aluminum composite catalyst accounts for 1-5% of the mass concentration of the reaction system.

7. The method as described in claim 1, characterized in that, The concentration of ethylene glycol in the reaction system is 0.01~0.5 g / ml, and the molar ratio of ammonia, hydrogen and ethylene glycol is 50~110:30~60:1~10.

8. The method as described in claim 1, characterized in that, In the system, the reaction temperature is 160-200℃, the reaction pressure is 4-6MPa, and the reaction time is 4-10 hours.