Piperazine refining and purifying process

Abstract

The invention discloses a piperazine refining and purifying process, which is used for purifying piperazine in a crude piperazine mixed solution containing a small amount of 2-ethylpyrazine, and comprises the following steps: preheating the crude piperazine mixed solution containing 2-ethylpyrazine and piperazine and hydrogen, and feeding the preheated crude piperazine mixed solution and hydrogen into a hydrogenation reactor filled with a nickel-based catalyst for hydrogenation reaction, 2-ethylpyrazine is subjected to hydro-conversion into 2-ethylpiperazine, a reaction product is subjected to cooling and flash evaporation to remove non-condensable gas, a liquid phase is pumped into a piperazine refining rectifying tower by a pump for rectification separation, and piperazine with the purity of 99.5% or above is obtained at the tower top. According to the present invention, with the combination of the catalytic hydrogenation reaction and the rectification separation, the high-purity and high-recovery purification of the piperazine is achieved, and the method has advantages of continuous process, automatic control, high piperazine purity, stable and controllable quality and the like, and can be used for the synthesis of the triethylene diamine and the coproduction of the piperazine.

Description

Technical Field

[0001] The invention belongs to the technical field of separation and purification of fine chemicals, and specifically relates to a piperazine refining and purification process, and in particular to a process for refining piperazine from a crude piperazine mixed liquid by co-producing piperazine and triethylenediamine using ethylenediamine as a raw material. Background Art

[0002] Piperazine, also known as hexahydropyrazine, p-diazohexane, etc., is a white or light yellow flake solid with strong hygroscopicity and typical amine odor. It is strongly alkaline and can absorb moisture and CO2 in the air to generate non-volatile carbonates. Piperazine is an important fine organic chemical intermediate in nitrogen heterocyclic fine chemicals. Piperazine and its derivatives can be used as pharmaceutical intermediates for the production of ofloxacin, enrofloxacin, lomefloxacin, piperazol acid, theophylline acetate piperazine, piperazine amino alcohol, norfloxacin, pipemidic acid, chlorazinic acid, piperazine phosphate, piperazine citrate, as well as fluphenazine, chlorpheniramine, rifampicin, etc.; piperazine and its derivatives are also widely used as copolymerizers, stabilizers, curing agents, emulsifiers and dispersants, vulcanization accelerators, antioxidants and preservatives for polymers such as surfactants, synthetic rubbers, synthetic fibers, and synthetic resins. The quality standard of piperazine requires that the purity of Type I high-end applications is ≥99.5% (w%), and the purity of Type II most common applications is ≥99.0% (w%).

[0003] The current methods for synthesizing piperazine at home and abroad include (1) using monoethanolamine as a raw material for dehydration condensation reaction, which requires high pressure catalytic synthesis of piperazine in a hydrogen and ammonia atmosphere, and this method has a low yield; (2) using N-β-hydroxyethylethylenediamine as a raw material for catalytic intramolecular alcohol amination reaction, which requires a hydrogen atmosphere and ethanol or THF as a solvent, and the raw materials are expensive and the reaction pressure is high; (3) using diethylenetriamine as a raw material for cyclization reaction with ammonia, which has expensive raw materials and high equipment requirements and is difficult to separate; (4) using ethylene oxide and ethylenediamine as raw materials for addition reaction and catalytic dehydration cyclization to prepare piperazine, which is highly dangerous, has a complex process and high pressure; (5) using ethylenediamine (EDA) solution as a raw material for catalytic synthesis of piperazine at atmospheric pressure and simultaneous co-production of triethylenediamine, which has cheap and easy-to-obtain raw materials, high atmospheric pressure reaction yield, and good economic efficiency for co-production of triethylenediamine. The process route of using ethylenediamine as a raw material for atmospheric pressure gas-solid phase one-step synthesis of piperazine and co-production of triethylenediamine has obvious technical and economic advantages. The conversion rate of ethylenediamine in this process is close to 100%, the selectivity of piperazine is greater than 60%, and the selectivity of triethylenediamine is above 40%.

[0004] In recent years, the synthetic process for producing piperazine and triethylenediamine using ethylenediamine as raw material has been developed. The reaction products contain ammonia, water, pyrazine, 2-methylpyrazine, 2-ethylpyrazine, methylethylpyrazine and other substances. After successively removing the by-products of each reaction, triethylenediamine and piperazine can be obtained. This process involves the separation and purification of triethylenediamine and piperazine. In the crude piperazine mixture, since 2-ethylpyrazine (bp; 152-152℃) has a similar relative volatility to piperazine (bp: 148.5℃), the removal of 2-ethylpyrazine is one of the difficulties in the triethylenediamine co-production of piperazine process during the purification of piperazine. Ensuring that the purity of piperazine in the final piperazine product can meet the quality standard and realizing the efficient separation of piperazine and 2-ethylpyrazine is one of the keys to the implementation of the triethylenediamine co-production of piperazine process. At present, there are no relevant literature or patent reports on the separation of piperazine and 2-ethylpyrazine system. Summary of the invention

[0005] The purpose of the present invention is to provide a piperazine refining and purification process which is continuous and automatically controllable and combines catalytic hydrogenation reaction with distillation separation in order to achieve the high-purity separation requirement of piperazine.

[0006] The technical solution of the present invention is as follows:

[0007] The invention provides a high-purity piperazine refining and purification process. The process comprises the following steps: purifying a crude piperazine mixed liquid obtained in a synthesis process for co-producing piperazine and triethylenediamine using ethylenediamine as a raw material, and obtaining high-purity piperazine through catalytic hydrogenation reaction-rectification separation. The process comprises the following steps: preheating a crude piperazine mixed liquid containing 2-ethylpyrazine and piperazine and hydrogen gas and entering a hydrogenation reactor equipped with a nickel-based catalyst for hydrogenation reaction, hydrogenating 2-ethylpyrazine into 2-ethylpiperazine, cooling the reaction product, flashing to remove non-condensable gas, pumping the liquid phase into a piperazine refining and rectification tower by a pump for rectification separation, and obtaining piperazine with a purity of more than 99.5% (other trace impurities are byproducts such as 2-ethylpyrazine and 2-ethylpiperazine) at the top of the tower.

[0008] The high-purity piperazine refining and purification process specifically comprises the following steps:

[0009] Step 1, the crude piperazine mixed liquid enters the raw material buffer tank, is pressurized and transported by a liquid pressure pump, is heated to about 150-230° C. in a liquid heater, and enters the hydrogen / liquid mixer;

[0010] Step 2: The hydrogen after decompression in the hydrogen cylinder is heated to about 150-230° C. by a hydrogen heater and also enters a hydrogen / liquid mixer, and after being fully mixed with the heated liquid in step 1, enters a catalytic hydrogenation reactor for catalytic hydrogenation reaction;

[0011] Step 3: After the catalytic hydrogenation reaction, the material is cooled in a reaction discharge cooler, and after decompression, it is flash-evaporated in a reaction discharge separator to remove non-condensable gas, and the non-condensable gas is recycled or discharged through tail gas treatment;

[0012] Step 4, the liquid after flash evaporation to remove non-condensable gas is transported to the piperazine refining distillation tower by the reaction liquid delivery pump for distillation separation, the condensate at the top of the distillation tower is collected in the high-purity piperazine collection tank at the top of the tower, and the bottom liquid of the distillation tower is collected in the bottom liquid collection tank.

[0013] The nickel-based catalyst is a supported nickel-based catalyst, and the carrier is one or more of aluminum oxide, zirconium oxide, titanium oxide and carbon material; the nickel loading in the supported nickel-based catalyst is 10-50wt%.

[0014] The content of 2-ethylpyrazine in the crude piperazine mixture is 1-10 wt %.

[0015] The catalytic hydrogenation reaction temperature is 150-300° C.; the catalytic hydrogenation reaction pressure is 1-5 MPa.

[0016] The molar flow ratio of the hydrogen gas to the crude piperazine mixed liquid feed is hydrogen gas:crude piperazine mixed liquid=20-300:1.

[0017] The above molar flow ratio is hydrogen molar flow mol / hr: crude piperazine mixture molar flow mol / hr; molar flow is the molar amount of flowing fluid per unit time; molar flow of the mixture = mass flow of the mixture / molecular weight of the mixture.

[0018] The mass space velocity of the crude piperazine mixed liquid feed is 0.1-10 g piperazine / (g catalyst·hour).

[0019] The hydrogenation reactor is a catalytic hydrogenation fixed bed reactor.

[0020] A liquid atomizing device is arranged on the upper part of the hydrogen / liquid mixer, and the crude piperazine mixed liquid enters the hydrogen / liquid mixer through the liquid atomizing device, so that the crude piperazine mixed liquid is fully mixed with hydrogen.

[0021] A branch pipe is arranged on the connecting pipeline between the bottom of the distillation tower and the bottom liquid collecting tank, and is connected to the piperazine refining distillation tower through the piperazine refining distillation tower kettle reboiler.

[0022] After the catalytic hydrogenation reaction, the content of 2-ethylpyrazine in the hydrogenated piperazine mixed solution is 0.05-0.5wt%; the content of 2-ethylpiperazine in the hydrogenated piperazine mixed solution is 1-6wt%.

[0023] The top temperature of the distillation tower is 140-175℃; the bottom temperature of the distillation tower is 150-185℃.

[0024] The pressure at the top of the distillation tower is 0.1-0.2MPa; the pressure at the bottom of the distillation tower is 0.1-0.2MPa.

[0025] After distillation and purification, the content of piperazine in the top liquid of the distillation tower is greater than 99.5wt%; the content of 2-ethylpyrazine is less than 0.5wt%; and the content of 2-ethylpiperazine is less than 0.05wt%.

[0026] The beneficial effects of the present invention are as follows:

[0027] The present invention adopts a process combining catalytic hydrogenation reaction and distillation separation to convert 2-ethylpyrazine, which is difficult to be separated from piperazine by distillation in a crude piperazine mixed liquid, into 2-ethylpiperazine, which is easy to be separated from piperazine by distillation, so as to achieve a better piperazine refining effect and effectively improve the piperazine purity. The content of piperazine in the distillation tower top liquid is greater than 99.5wt%, and the piperazine purity is guaranteed to meet the requirements of the quality standard. However, in the process of non-hydrogenation-solely distillation separation, since the boiling point of 2-ethylpyrazine is similar to that of piperazine, on the one hand, the number of distillation tower plates is greatly increased, the equipment investment is increased, and the energy consumption of the tower bottom reboiler and the tower top condenser is also significantly increased; on the other hand, it is impossible to ensure that the piperazine purity always meets the high purity requirements of the quality standard, thereby increasing the equipment investment and energy consumption of rework processing.

[0028] The innovative advantage of the present invention is that, for two substances with very close boiling points, 2-ethylpyrazine, which is difficult to separate from piperazine by distillation, is converted into 2-ethylpiperazine, which is easy to separate from piperazine by distillation through a catalytic hydrogenation reaction-distillation separation process, thereby achieving a better piperazine refining effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The equipment and flow chart of the refining process of high-purity piperazine are obtained by catalytic hydrogenation reaction and distillation separation; wherein 1 is a liquid raw material buffer tank, 2 is a liquid pressure pump, 3 is a liquid heater, 4 is a hydrogen cylinder, 5 is a hydrogen heater, 6 is a hydrogen / liquid mixer, 7 is a catalytic hydrogenation reactor, 8 is a reaction discharge cooler, 9 is a reaction discharge separator, 10 is a reaction liquid delivery pump, 11 is a piperazine refining distillation tower kettle reboiler, 12 is a piperazine refining distillation tower, 13 is a tower top condenser, 14 is a tower top high-purity piperazine collecting tank, and 15 is a tower bottom liquid collecting tank. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present invention will be described clearly and completely below in combination with the embodiments of the present invention and the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] The equipment and process of the refining process of high-purity piperazine obtained by catalytic hydrogenation reaction and distillation separation are introduced as follows:

[0032] like Figure 1 As shown, a piperazine refining and purification device comprises a raw material buffer tank 1, the outlet of the raw material buffer tank 1 is connected to the liquid atomizing device of the hydrogen / liquid mixer 6 through a pipeline in sequence through a liquid pressure pump 2 and a liquid heater 3, a hydrogen cylinder 4 is connected to the hydrogen / liquid mixer 6 through a hydrogen heater 5, the outlet of the hydrogen / liquid mixer 6 is connected to the inlet of a catalytic hydrogenation reactor 7, the outlet of the catalytic hydrogenation reactor 7 is connected to the inlet of a reaction discharge separator 9 through a reaction discharge cooler 8, the liquid phase outlet of the reaction discharge separator 9 is connected to a piperazine refining distillation tower 12 through a reaction liquid delivery pump 10, the top of the piperazine refining distillation tower 12 is connected to a high-purity piperazine collecting tank 14 at the top of the tower through a tower top condenser 13, and the bottom of the piperazine refining distillation tower 12 is connected to a bottom liquid collecting tank 15.

[0033] A branch pipe is provided on the connecting pipeline between the bottom of the piperazine refining distillation tower 12 and the bottom liquid collecting tank 15 , and is connected to the piperazine refining distillation tower 12 via the piperazine refining distillation tower kettle reboiler 11 .

[0034] The specific steps of the piperazine refining and purification process, i.e., the piperazine hydrogenation-distillation separation and refining process, are as follows:

[0035] The crude piperazine mixed liquid obtained in the synthesis process of co-producing piperazine and triethylenediamine with ethylenediamine as raw materials enters the liquid raw material buffer tank 1, is pressurized and transported by the liquid pressure pump 2, is heated and heated in the liquid heater 3, and enters the hydrogen / liquid mixer 6; the hydrogen in the hydrogen cylinder 4 is decompressed, heated and heated by the hydrogen heater 5, and also enters the hydrogen / liquid mixer 6, and the two are mixed and enter the catalytic hydrogenation reactor 7 to carry out catalytic hydrogenation reaction; the material after the catalytic hydrogenation reaction is cooled by the reaction discharge cooler 8, and the non-condensable gas is flashed in the reaction discharge separator 9, and the non-condensable gas is discharged after tail gas treatment; the liquid after the non-condensable gas is flashed and removed is used as the hydrogenation reaction liquid, and is transported by the reaction liquid delivery pump 10 to the piperazine refining distillation tower 12 for distillation separation. The condensate from the top of the piperazine refining distillation tower 12 is collected in a high-purity piperazine collecting tank 14 at the top of the tower, and the bottom liquid from the piperazine refining distillation tower 12 is temporarily stored in a bottom liquid collecting tank 15 .

[0036] The catalytic hydrogenation reactor 7 is a catalytic hydrogenation fixed bed reactor.

[0037] The catalyst used is not particularly limited and may be a commercially available product or may be prepared according to methods well known to those skilled in the art.

[0038] Example 1

[0039] The crude piperazine mixed liquid obtained in the synthesis process of co-producing piperazine and triethylenediamine using ethylenediamine as raw material is put into the liquid raw material buffer tank 1, pressurized to 2MPa by the liquid pressure pump 2, heated to about 150°C in the liquid heater 3, and enters the hydrogen / liquid mixer 6; the hydrogen in the hydrogen cylinder 4 is depressurized to 2MPa, heated to 150°C by the hydrogen heater 5, and also enters the hydrogen / liquid mixer 6. After the two are mixed, they enter the catalytic hydrogenation reactor 7 for catalytic hydrogenation reaction. The catalyst used is 30% Ni / Al2O3, the molar flow ratio of hydrogen to the crude piperazine mixed liquid is controlled at 130:1, the mass space velocity of the piperazine mixed liquid feed is 5g piperazine / (g catalyst·hour), the catalytic hydrogenation reaction temperature is controlled at 150°C, and the catalytic reaction pressure is controlled at 2MPa. The liquid composition before and after the catalytic hydrogenation reaction is shown in Table 1.

[0040] Table 1 Liquid composition before and after catalytic hydrogenation reaction

[0041]

[0042] After the hydrogenation reaction, the material is cooled to 140°C by the reaction discharge cooler 8, and the non-condensable gas is removed by flash evaporation in the reaction discharge separator 9, and the non-condensable gas is discharged after tail gas treatment; the liquid after flash evaporation to remove the non-condensable gas is used as the hydrogenation reaction liquid, and is transported by the reaction liquid delivery pump 10 to the piperazine refining distillation tower 12 for atmospheric distillation separation. The top temperature of the piperazine refining distillation tower 12 is controlled at 146°C, the top condensate is collected in the top piperazine collection tank 14, the bottom temperature of the piperazine refining distillation tower 12 is controlled at 158°C, and the bottom liquid is temporarily stored in the bottom liquid collection tank 15. The composition of the inlet and outlet materials of the distillation tower is shown in Table 2.

[0043] Table 2 Composition of inlet and outlet materials of distillation tower

[0044] Distillation tower feed Top discharge Tower bottom discharge Mass fraction Mass fraction Mass fraction Piperazine 0.9869 0.9976 0.4762 2-Ethylpyrazine 0.0025 0.0023 0.0095 2-Ethylpiperazine 0.0106 - 0.5143

[0045] Example 2

[0046] The crude piperazine mixed liquid obtained in the synthesis process of co-producing piperazine and triethylenediamine using ethylenediamine as raw material is put into the liquid raw material buffer tank 1, pressurized to 3MPa by the liquid pressure pump 2, heated to 180℃ in the liquid heater 3, and enters the hydrogen / liquid mixer 6; the hydrogen in the hydrogen cylinder 4 is decompressed to 3MPa, heated to 180℃ by the hydrogen heater 5, and also enters the hydrogen / liquid mixer 6. After the two are mixed, they enter the catalytic hydrogenation reactor 7 for catalytic hydrogenation reaction; the catalyst used is 50% Ni / activated carbon, the molar flow ratio of hydrogen to the crude piperazine mixed liquid is controlled at 140:1, the mass space velocity of the piperazine mixed liquid feed is 10g piperazine / (g catalyst·hour), the catalytic hydrogenation reaction temperature is controlled at 180℃, and the catalytic reaction pressure is controlled at 3MPa. The liquid composition before and after the hydrogenation reaction is shown in Table 3.

[0047] Table 3 Liquid composition before and after catalytic hydrogenation reaction

[0048]

[0049] The material after hydrogenation reaction is cooled to 140°C by reaction discharge cooler 8, and non-condensable gas is removed by flash evaporation in reaction discharge separator 9, and the non-condensable gas is discharged after tail gas treatment; the liquid after flash evaporation to remove non-condensable gas is used as hydrogenation reaction liquid, and is transported to piperazine refining distillation tower 12 by reaction liquid delivery pump 10 for atmospheric distillation separation. The top temperature of piperazine refining distillation tower 12 is controlled at 146°C, the top condensate is collected in the top piperazine collection tank 14, the bottom temperature of piperazine refining distillation tower 12 is controlled at 158°C, and the bottom liquid is temporarily stored in the bottom liquid collection tank 15. The composition of the inlet and outlet materials of the distillation tower is shown in Table 4.

[0050] Table 4 Composition of inlet and outlet materials of distillation tower

[0051]

[0052]

[0053] Example 3

[0054] The crude piperazine mixed liquid obtained in the synthesis process of co-producing piperazine and triethylenediamine using ethylenediamine as raw material is put into the liquid raw material buffer tank 1, pressurized to 3.5MPa by the liquid pressure pump 2, heated to 230℃ in the liquid heater 3, and enters the hydrogen / liquid mixer 6; the hydrogen in the hydrogen cylinder 4 is decompressed to 3.5MPa, heated to 230℃ by the hydrogen heater 5, and also enters the hydrogen / liquid mixer 6. After the two are mixed, they enter the catalytic hydrogenation reactor 7 for catalytic hydrogenation reaction; the catalyst used is 50% Ni / activated carbon, the molar flow ratio of hydrogen to the crude piperazine mixed liquid is controlled at 200:1, the mass space velocity of the piperazine mixed liquid feed is 8g piperazine / (g catalyst·hour), the catalytic hydrogenation reaction temperature is controlled at 230℃, and the catalytic reaction pressure is controlled at 3.5MPa. The liquid composition before and after the hydrogenation reaction is shown in Table 3.

[0055] Table 3 Liquid composition before and after catalytic hydrogenation reaction

[0056]

[0057] The material after hydrogenation reaction is cooled to 140°C by reaction discharge cooler 8, and non-condensable gas is removed by flash evaporation in reaction discharge separator 9, and the non-condensable gas is discharged after tail gas treatment; the liquid after flash evaporation to remove non-condensable gas is used as hydrogenation reaction liquid, and is transported to piperazine refining distillation tower 12 by reaction liquid delivery pump 10 for atmospheric distillation separation. The top temperature of piperazine refining distillation tower 12 is controlled at 146°C, the top condensate is collected in the top piperazine collection tank 14, the bottom temperature of piperazine refining distillation tower 12 is controlled at 158°C, and the bottom liquid is temporarily stored in the bottom liquid collection tank 15. The composition of the inlet and outlet materials of the distillation tower is shown in Table 4.

[0058] Table 4 Composition of inlet and outlet materials of distillation tower

[0059] Distillation tower feed Top discharge Tower bottom discharge Mass fraction Mass fraction Mass fraction Piperazine 0.9594 0.9976 0.1528 2-Ethylpyrazine 0.0017 0.0018 0.0035 2-Ethylpiperazine 0.0387 0.0004 0.8455

[0060] Example 4

[0061] The crude piperazine mixed liquid obtained in the synthesis process of co-producing piperazine and triethylenediamine using ethylenediamine as raw material is put into the liquid raw material buffer tank 1, pressurized to 2MPa by the liquid pressure pump 2, heated to 180℃ in the liquid heater 3, and enters the hydrogen / liquid mixer 6; the hydrogen in the hydrogen cylinder 4 is decompressed to 2MPa, heated to 180℃ by the hydrogen heater 5, and also enters the hydrogen / liquid mixer 6. After the two are mixed, they enter the catalytic hydrogenation reactor 7 for catalytic hydrogenation reaction; the catalyst used is 10% Ni / ZrO2-Al2O3, the molar flow ratio of hydrogen to piperazine mixed liquid is controlled at 135:1, the mass space velocity of piperazine mixed liquid feed is 1g piperazine / (g catalyst·hour), the catalytic hydrogenation reaction temperature is controlled at 180℃, and the catalytic reaction pressure is controlled at 2MPa. The liquid composition before and after the catalytic hydrogenation reaction is shown in Table 5.

[0062] Table 5 Liquid composition before and after hydrogenation reaction

[0063]

[0064] After the hydrogenation reaction, the material is cooled to 140°C by the reaction discharge cooler 8, and the non-condensable gas is removed by flash evaporation in the reaction discharge separator 9, and the non-condensable gas is discharged after tail gas treatment; the liquid after flash evaporation to remove the non-condensable gas is used as the hydrogenation reaction liquid, and is transported by the reaction liquid delivery pump 10 to the piperazine refining distillation tower 12 for atmospheric distillation separation. The top temperature of the piperazine refining distillation tower 12 is controlled at 146°C, the top condensate is collected in the top piperazine collection tank 14, the bottom temperature of the piperazine refining distillation tower 12 is controlled at 158°C, and the bottom liquid is temporarily stored in the bottom liquid collection tank 15. The composition of the inlet and outlet materials of the distillation tower is shown in Table 6.

[0065] Table 6 Composition of inlet and outlet materials of distillation tower

[0066] Distillation tower feed Top discharge Tower bottom discharge Mass fraction Mass fraction Mass fraction Piperazine 0.9872 0.9989 0.4618 2-Ethylpyrazine 0.0006 0.0005 0.0024 2-Ethylpiperazine 0.0113 - 0.5205 Triethylenediamine 0.0007 0.0005 0.0118 2-Methylpyrazine 0.0001 0.0001 -- Methylethylpyrazine 0.0001 0.0001 0.0036

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. A person skilled in the art can still refer to the detailed description of the present invention in the above embodiments, modify or replace the specific implementation methods of the present invention, and any modification or replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A piperazine refining and purification process, which comprises purifying piperazine from a crude piperazine mixture obtained in a synthesis process of co-producing piperazine and triethylenediamine using ethylenediamine as a raw material, Features: High-purity piperazine is obtained by catalytic hydrogenation reaction-distillation separation, which includes preheating a crude piperazine mixed liquid containing 2-ethylpyrazine and piperazine and hydrogen into a catalytic hydrogenation reactor equipped with a nickel-based catalyst for hydrogenation reaction, hydrogenating 2-ethylpyrazine into 2-ethylpiperazine, cooling the reaction product, flashing to remove non-condensable gas, pumping the liquid phase into a piperazine refining distillation tower for distillation separation, and obtaining piperazine with a purity of more than 99.5% at the top of the tower.

2. A piperazine refining and purification process as claimed in claim 1, Features: The specific steps include: Step 1, the crude piperazine mixed liquid enters the raw material buffer tank (1), is pressurized and transported by the liquid pressure pump (2), is heated to 150-230° C. in the liquid heater (3), and enters the hydrogen / liquid mixer (6); Step 2, the hydrogen after decompression in the hydrogen cylinder is heated to 150-230° C. by a hydrogen heater (5), enters a hydrogen / liquid mixer (6), is fully mixed with the heated liquid in step 1, and then enters a catalytic hydrogenation reactor (7) to perform a catalytic hydrogenation reaction; Step 3, the material after the catalytic hydrogenation reaction is cooled in a reaction discharge cooler (8), and after decompression, flash evaporation is performed in a reaction discharge separator (9) to remove non-condensable gas, and the non-condensable gas is circulated or discharged through tail gas treatment; In step 4, the liquid after flash evaporation to remove the non-condensable gas is transported to the piperazine refining distillation tower (12) by the reaction liquid delivery pump (10) for distillation separation. The condensate at the top of the distillation tower is collected in the high-purity piperazine collection tank (14) at the top of the tower, and the bottom liquid of the distillation tower is collected in the bottom liquid collection tank (15).

3. A piperazine refining and purification process as claimed in claim 1 or 2, Features: The nickel-based catalyst is a supported nickel-based catalyst, and the carrier is one or more of aluminum oxide, zirconium oxide, titanium oxide and carbon material; the nickel loading in the supported nickel-based catalyst is 10-50wt%.

4. A process for refining and purifying piperazine according to claim 1 or 2, Features: The content of 2-ethylpyrazine in the crude piperazine mixed solution is 1-10 wt %.

5. A process for refining and purifying piperazine according to claim 1 or 2, Features: The catalytic hydrogenation reaction temperature is 150-300° C.; the catalytic hydrogenation reaction pressure is 1-5 MPa.

6. A piperazine refining and purification process as claimed in claim 1 or 2, Features: The molar ratio of hydrogen to crude piperazine mixed liquid feed flow is hydrogen: crude piperazine mixed liquid = 20-300:1; the mass space velocity of the crude piperazine mixed liquid feed is 0.1-10 g piperazine / (g catalyst·hour).

7. The process for refining and purifying piperazine according to claim 1 or 2, Features: The temperature at the top of the distillation tower is controlled at 140-175°C; the temperature at the bottom of the distillation tower is controlled at 150-185°C; the pressure at the top of the distillation tower is controlled at 0.1-0.2MPa; and the pressure at the bottom of the distillation tower is controlled at 0.1-0.2MPa.

8. The process for refining and purifying piperazine according to claim 1 or 2, Features: The catalytic hydrogenation reactor (7) is a catalytic hydrogenation fixed bed reactor.

9. The process for refining and purifying piperazine according to claim 2, Features: A liquid atomizing device is provided on the upper part of the hydrogen / liquid mixer (5), and the crude piperazine mixed liquid enters the hydrogen / liquid mixer (6) through the liquid atomizing device.

10. The process for refining and purifying piperazine according to claim 2, Features: A branch pipe is provided on the connecting pipeline between the bottom of the distillation tower and the bottom liquid collecting tank (15), and is connected to the piperazine refining distillation tower (12) via the piperazine refining distillation tower kettle reboiler (11).

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