Process for continuously separating tar from p-nitrophenol

Abstract

The invention discloses a process for continuously separating tar from p-nitrophenol, and relates to the technical field of p-nitrophenol, which comprises the following steps: adding nitrobenzene and a sodium hydroxide solution into a microwave reactor in proportion, hydrolyzing at a certain temperature and pressure under the assistance of ultrasonic waves, and filtering to obtain a filtrate; performing counter-current extraction on the obtained hydrolysate through an alkaline water phase, a polar organic solvent phase and an ionic liquid phase in sequence, then performing rotary evaporation under the conditions that the vacuum degree is (-0.08)-(-0.095) MPa and the temperature is 50-70 DEG C, and collecting fractions; the temperature of the upper section of the spiral packing layer is 40-50 DEG C, the temperature of the middle section of the spiral packing layer is 60-70 DEG C, the temperature of the lower section of the spiral packing layer is 80-90 DEG C, and finally high-purity p-nitrophenol is obtained. In the process, the conversion rate of nitrobenzene is higher, and the prepared p-nitrophenol has higher purity.

Description

Technical Field

[0001] The present invention relates to the technical field of p-nitrophenol, and particularly relates to a process for continuously separating tar in p-nitrophenol. Background Art

[0002] As an important organic compound, p-nitrophenol has a wide range of applications in the fields of chemical industry, medicine, dyes, etc. Its pure substance is a yellow crystalline solid with a slight phenolic odor, and its physical properties such as melting point, boiling point, and density are stable. P-nitrophenol can undergo acid-base reactions of phenolic hydroxyl groups and reduction reactions of nitro groups, etc., and is a key intermediate in many organic synthesis reactions. Especially in pesticide production, it can be used as an important intermediate for synthesizing insecticides and herbicides; in the dye industry, it is commonly used as a raw material for producing azo dyes and nitro dyes; in the pharmaceutical industry, p-nitrophenol is used to synthesize a variety of drugs, including antipyretic analgesics, antibacterial drugs, etc.

[0003] However, in the production process of p-nitrophenol, especially when prepared by methods such as nitration reaction, a large amount of tarry by-products are often generated. These tarry substances not only reduce the purity of p-nitrophenol, but also pose great challenges to subsequent separation and purification work. Therefore, it is particularly important to develop an efficient and continuous process for separating tar in p-nitrophenol.

[0004] Currently, for the separation of tar in p-nitrophenol, a variety of methods have been studied and applied. Among them, the alkali washing method is a relatively common method. Due to the weak acidity of the hydroxyl group of phenolic compounds, it can undergo an acid-base neutralization reaction with sodium hydroxide solution to form water-soluble phenolate salts, thereby separating from neutral oil and alkaline oil. However, when the alkali washing method is used to treat a complex tar system, there may be problems such as low separation efficiency and low product purity.

[0005] In addition, the coal tar vacuum continuous distillation technology has also been widely used in the separation of tar components. This technology continuously heats coal tar and distills it under negative pressure conditions, which can reduce the boiling points of the contained components, avoid or reduce the decomposition and coking of high-boiling substances, and improve the relative volatility of each component. However, directly applying the coal tar vacuum continuous distillation technology to the tar in p-nitrophenol production may result in poor separation effects due to the complex tar composition, leading to low purity of p-nitrophenol. Summary of the Invention

[0006] The purpose of the present invention is to provide a process for continuously separating tar in p-nitrophenol to solve the following technical problems:

[0007] How to improve the purity of p-nitrophenol products.

[0008] The purpose of the present invention can be achieved through the following technical solutions:

[0009] A process for continuous separation of tar in p-nitrophenol, comprising the following steps:

[0010] Step 1: Put nitrobenzene and sodium hydroxide solution into a microwave reactor in proportion, and hydrolyze it in an ultrasonic environment at 80 - 120 °C, 0.3 - 0.8 MPa, and 10 - 50 kHz to obtain a hydrolysis product; under the action of ultrasonic waves, cavitation bubbles will be generated in the sodium hydroxide solution, and high-energy microjets will be released when the bubbles crack, destroying the mass transfer resistance between the nitrobenzene and sodium hydroxide interfaces, increasing their contact area, and thus enhancing the reaction rate;

[0011] Step 2: Subject the hydrolysis product to countercurrent extraction successively through an alkaline aqueous phase, a polar organic solvent phase, and an ionic liquid phase;

[0012] Step 3: Rotate and evaporate the extracted organic phase under the conditions of a vacuum degree of (-0.08) - (-0.095) MPa and a temperature of 50 - 70 °C, and collect the distillate;

[0013] Step 4: Transfer the distillate into a separation tower equipped with a three-stage spiral packing layer and separate it from top to bottom. Among them, the temperature of the upper section of the spiral packing layer is 40 - 50 °C, the middle section is 60 - 70 °C, and the lower section is 80 - 90 °C; among them, p-nitrophenol droplets in the cold condensate gas phase are captured by wetting the packing surface, the liquid product fluidity is maintained in the medium temperature zone to promote the sedimentation of tar particles, and the liquid phase viscosity is reduced in the high temperature zone to prevent tar adhesion; finally, high-purity p-nitrophenol is obtained.

[0014] Furthermore, in Step 1, the molar ratio of nitrobenzene to sodium hydroxide is 1:(2.5 - 3.5); the mass fraction of the sodium hydroxide solution is 20 - 30%.

[0015] Furthermore, in Step 1, the power density of the microwave reactor is 2 - 5 W / g; microwave pulses can avoid local overheating of the reaction system and make the reaction temperature more balanced.

[0016] Furthermore, in Step 1, a composite catalyst is also added to the microwave reactor, and the addition amount of the composite catalyst is 0.5 - 2 wt% of the weight of nitrobenzene.

[0017] Furthermore, the composite catalyst is a mixture composed of titanium nitride and zirconium oxide in a weight ratio of 1:1; the addition of this mixture can reduce the activation energy of the reaction system, shorten the reaction time, and thus reduce the reaction energy consumption.

[0018] Furthermore, in Step 2, the alkaline aqueous phase is an aqueous solution containing 0.1 - 0.3 wt% dodecylbenzenesulfonic acid (SDBS), and its pH value is 9 - 11. Under alkaline conditions, p-nitrophenol dissociates into phenoxide anions (C6H5O- ) It forms micelles with the added SDBS through electrostatic interaction, solubilizes hydrophobic tar components, and thus realizes primary separation.

[0019] Furthermore, in step two, the polar organic solvent phase is a mixed solvent composed of acetone and ethyl acetate in a volume ratio of 3:7; the dielectric constant of this mixed solvent matches that of medium-polar components in the tar, such as nitrobenzene dimers, etc., and it selectively dissolves through the principle of like dissolves like, while also retaining the high solubility of p-nitrophenol in the organic phase.

[0020] Furthermore, in step two, the ionic liquid phase is a 1-ethyl-3-methylimidazolium hexafluorophosphate (EMIM) solution containing 10 - 15 wt% acetate anions; the acetate anions (OAc - ) in the ionic liquid form hydrogen bonds with polar groups in the tar, such as -OH, -NO2, etc., and the aromatic ring of the imidazolium cation adsorbs polycyclic aromatic hydrocarbons through π-π stacking, which can achieve deep purification.

[0021] Furthermore, the ionic liquid phase is subjected to countercurrent extraction in a pulsating injection manner under the conditions of a frequency of 2 - 5 Hz and an amplitude of 3 - 5 mm. This injection method is conducive to forming a dynamic turbulent cross-section, promoting the reaction to proceed, improving the reaction efficiency, and thus increasing the removal rate of the tar.

[0022] Furthermore, in step four, a vortex type demister is provided at the top of the separation tower, and the blade inclination angle of the vortex type demister is 45 - 60 °C, which can induce the airflow to rotate and separate aerosol tar particles through centrifugal force.

[0023] Advantages of the present invention:

[0024] 1. In the process of continuous separation of tar in p-nitrophenol of the present invention, during the hydrolysis reaction, through the combination of a microwave reactor and ultrasonic assistance, and at the same time in combination with a composite catalyst; microwave pulses can avoid local overheating of the reaction system and make the reaction temperature more balanced; under the action of ultrasonic waves, cavitation bubbles will be generated in the sodium hydroxide solution, and high-energy microjets will be released when the bubbles rupture, breaking the mass transfer resistance between the nitrobenzene and sodium hydroxide interfaces, increasing their contact area, and thus increasing the reaction rate; the addition of the composite catalyst can reduce the activation energy of the reaction system, shorten the reaction time, and thus reduce the reaction energy consumption, thereby increasing the reaction rate and the conversion rate of nitrobenzene.

[0025] 2. In the process of continuous separation of tar in p-nitrophenol of the present invention, the hydrolysis product is subjected to countercurrent extraction successively through an alkaline aqueous phase, an organic solvent, and an organic ionic liquid phase. Under the alkaline condition of the alkaline aqueous phase, p-nitrophenol dissociates into C6H5O -, it forms micelles with the added SDBS through electrostatic interaction, solubilizes the hydrophobic tar components, and thus realizes primary separation; the dielectric constant of the organic solvent matches that of the medium-polarity components in the tar, such as nitrobenzene dimers, and selectively dissolves through the principle of like dissolves like. At the same time, the high solubility of p-nitrophenol in the organic phase can be retained; OAc in the ionic liquid phase - forms hydrogen bonds with the polar groups in the tar, such as -OH, -NO2, etc. The aromatic ring of the imidazole cation adsorbs polycyclic aromatic hydrocarbons through π-π stacking, which can achieve deep purification, and then carry out multi-stage removal of the tar to improve the purity of p-nitrophenol.

[0026] In the process of continuous separation of tar in p-nitrophenol of the present invention, the fraction is transferred into a separation tower equipped with a three-stage spiral packing layer and separated from top to bottom. The temperatures of the upper, middle, and lower sections of the spiral packing layer gradually increase; among them, the p-nitrophenol droplets in the condensed gas phase in the low-temperature zone are captured by wetting the surface of the packing, the liquid product fluidity is maintained in the medium-temperature zone to promote the sedimentation of tar particles, and the liquid-phase viscosity is reduced in the high-temperature zone to prevent tar adhesion; finally, high-purity p-nitrophenol can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be further described below with reference to the accompanying drawings.

[0028] Figure 1 is the process flow diagram of the continuous separation of tar in p-nitrophenol of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0030] The present invention discloses a process for continuous separation of tar in p-nitrophenol. Please refer to Figure 1 , including the following steps:

[0031] Step 1: Put nitrobenzene and a sodium hydroxide solution with a mass fraction of 20-30% into a microwave reactor with a power density of 2-5 W / g according to the molar ratio of nitrobenzene to sodium hydroxide of 1:(2.5-3.5), and then add a composite catalyst (a mixture composed of titanium nitride and zirconia in a weight ratio of 1:1) accounting for 0.5-2 wt% of the weight of nitrobenzene, and hydrolyze at 80-120 °C, 0.3-0.8 MPa, and 10-50 kHz to obtain a hydrolysis product;

[0032] Step 2: Prepare an aqueous solution containing 0.1 - 0.3 wt% dodecylbenzenesulfonic acid with a pH of 9 - 11 as the basic aqueous phase; prepare a mixed solution composed of acetone and ethyl acetate with a volume ratio of 3:7 as the organic solvent; prepare an EMIM solution containing 10 - 15 wt% acetate anions as the ionic liquid phase; the prepared volume of the basic aqueous phase, organic solvent, and ionic liquid phase is 3 times the volume of the hydrolysis product; subject the hydrolysis product to countercurrent extraction successively through the basic aqueous phase, organic solvent, and organic ionic liquid phase. Among them, the ionic liquid phase is subjected to countercurrent extraction in a pulsating injection manner under the conditions of a frequency of 2 - 5 Hz and an amplitude of 3 - 5 mm, and finally obtain the organic phase;

[0033] Step 3: Rotate and evaporate the extracted organic phase under the conditions of a vacuum degree of (-0.08) - (-0.095) MPa and a temperature of 50 - 70 °C, and collect the distillate;

[0034] Step 4: Transfer the distillate into a separation tower equipped with a three-stage spiral packing layer and separate it from top to bottom. A vortex type demister with a blade inclination angle of 45 - 60 °C is provided at the top of the separation tower; among them, the temperature of the upper section of the spiral packing layer is 40 - 50 °C, the middle section is 60 - 70 °C, and the lower section is 80 - 90 °C, and finally obtain high-purity p-nitrophenol.

[0035] The experimental methods in the following examples are all conventional methods unless otherwise specified, and are carried out according to the techniques or conditions described in the literature in this field or according to the product instructions. The materials, reagents, etc. used in the following examples can be obtained from commercial channels unless otherwise specified.

[0036] Example 1

[0037] Step 1: Add nitrobenzene and a 25% sodium hydroxide solution with a molar ratio of nitrobenzene to sodium hydroxide of 1:3 into a microwave reactor with a power density of 3 W / g, then add 0.5 wt% titanium oxide and 0.5 wt% zirconium oxide based on the weight of nitrobenzene, adjust the temperature to 100 °C and the pressure to 0.5 MPa, and then apply ultrasonic assistance at 30 kHz to carry out the hydrolysis reaction. After reacting for 2 h, obtain the hydrolysis product;

[0038] Step 2: Prepare an aqueous solution containing 0.2 wt% dodecylbenzenesulfonic acid with a pH of 10 as the basic aqueous phase; prepare a mixed solution composed of acetone and ethyl acetate with a volume ratio of 3:7 as the organic solvent; prepare an EMIM solution containing 12 wt% acetate anions as the ionic liquid phase; the prepared volumes of the basic aqueous phase, the organic solvent, and the ionic liquid phase are all 3 times the volume of the hydrolysis product; sequentially pass the hydrolysis product through the basic aqueous phase, the organic solvent, and the organic ionic liquid phase for countercurrent extraction. Among them, the ionic liquid phase is subjected to countercurrent extraction in a pulsating injection manner under the conditions of a frequency of 3 Hz and an amplitude of 4 mm to obtain an organic phase;

[0039] Step 3: Rotate and evaporate the organic phase under a vacuum of -0.09 MPa and a temperature of 60 °C, and collect the distillate;

[0040] Step 4: Transfer the distillate into a separation tower equipped with a three-stage spiral packing layer and separate it from top to bottom. A vortex type demister with a blade inclination angle of 50 °C is arranged at the top of the separation tower; among them, the temperature of the upper section of the spiral packing layer is 45 °C, the middle section is 65 °C, and the lower section is 85 °C. The passing time for each section is 20 min, and high-purity p-nitrophenol can be finally obtained.

[0041] Example 2

[0042] Step 1: Add nitrobenzene and a 30% by mass sodium hydroxide solution to a microwave reactor with a power density of 2 W / g according to a molar ratio of nitrobenzene to sodium hydroxide of 1:2.5. Then add 0.25 wt% titanium oxide and 0.25 wt% zirconium oxide based on the weight of nitrobenzene. Adjust the temperature to 80 °C and the pressure to 0.3 MPa, and then apply ultrasonic assistance at 50 kHz to carry out the hydrolysis reaction. After reacting for 2.5 h, a hydrolysis product is obtained;

[0043] Step 2: Prepare an aqueous solution containing 0.2 wt% dodecylbenzenesulfonic acid with a pH of 10 as the basic aqueous phase; prepare a mixed solution composed of acetone and ethyl acetate with a volume ratio of 3:7 as the organic solvent; prepare an EMIM solution containing 12 wt% acetate anions as the ionic liquid phase; the prepared volumes of the basic aqueous phase, the organic solvent, and the ionic liquid phase are all 3 times the volume of the hydrolysis product; sequentially pass the hydrolysis product through the basic aqueous phase, the organic solvent, and the organic ionic liquid phase for countercurrent extraction. Among them, the ionic liquid phase is subjected to countercurrent extraction in a pulsating injection manner under the conditions of a frequency of 3 Hz and an amplitude of 4 mm to obtain an organic phase;

[0044] Step 3: Rotate and evaporate the organic phase under a vacuum of -0.08 MPa and a temperature of 60 °C, and collect the distillate;

[0045] Step 4: Transfer the fraction into a separation column equipped with a three-stage spiral packing layer and separate it from top to bottom. A vortex type demister with a blade inclination angle of 50°C is provided at the top of the separation column. Among them, the temperature of the upper section of the spiral packing layer is 40°C, the middle section is 60°C, and the lower section is 80°C. The passing time for each section is 20 min, and finally, high-purity p-nitrophenol is obtained.

[0046] Example 3

[0047] Step 1: Add nitrobenzene and a sodium hydroxide solution with a mass fraction of 30% into a microwave reactor with a power density of 3 W / g according to a molar ratio of nitrobenzene to sodium hydroxide of 1:3.5. Then add 1 wt% of titanium oxide and 1 wt% of zirconium oxide based on the weight of nitrobenzene. Adjust the temperature to 120°C and the pressure to 0.8 MPa, and then apply ultrasonic assistance at 10 kHz to carry out the hydrolysis reaction. After reacting for 2 h, a hydrolysis product is obtained.

[0048] Step 2: Prepare an aqueous solution containing 0.2 wt% of dodecylbenzenesulfonic acid and with a pH of 10 as the basic aqueous phase; prepare a mixed solution composed of acetone and ethyl acetate with a volume ratio of 3:7 as the organic solvent; prepare an EMIM solution containing 12 wt% of acetate anions as the ionic liquid phase. The prepared volume amounts of the basic aqueous phase, the organic solvent, and the ionic liquid phase are all 3 times the volume of the hydrolysis product. Sequentially pass the hydrolysis product through the basic aqueous phase, the organic solvent, and the organic ionic liquid phase for countercurrent extraction. Among them, the ionic liquid phase is subjected to countercurrent extraction in a pulsating injection manner under the conditions of a frequency of 3 Hz and an amplitude of 4 mm to obtain an organic phase.

[0049] Step 3: Rotate and evaporate the organic phase under a vacuum of -0.095 MPa and a temperature of 60°C, and collect the fraction.

[0050] Step 4: Transfer the fraction into a separation column equipped with a three-stage spiral packing layer and separate it from top to bottom. A vortex type demister with a blade inclination angle of 50°C is provided at the top of the separation column. Among them, the temperature of the upper section of the spiral packing layer is 50°C, the middle section is 70°C, and the lower section is 90°C. The passing time for each section is 20 min, and finally, high-purity p-nitrophenol is obtained.

[0051] Example 4

[0052] Step 1: Add nitrobenzene and a sodium hydroxide solution with a mass fraction of 25% into a microwave reactor with a power density of 3 W / g according to a molar ratio of nitrobenzene to sodium hydroxide of 1:3. Then add 0.5 wt% of titanium oxide and 0.5 wt% of zirconium oxide based on the weight of nitrobenzene. Adjust the temperature to 100°C and the pressure to 0.5 MPa, and then apply ultrasonic assistance at 30 kHz to carry out the hydrolysis reaction. After reacting for 2 h, a hydrolysis product is obtained.

[0053] Step 2: Prepare an aqueous solution containing 0.1 wt% dodecylbenzenesulfonic acid with a pH of 9 as the basic aqueous phase; prepare a mixed solution composed of acetone and ethyl acetate with a volume ratio of 3:7 as the organic solvent; prepare an EMIM solution containing 10 wt% acetate anions as the ionic liquid phase; the prepared volume of the basic aqueous phase, organic solvent, and ionic liquid phase is 3 times the volume of the hydrolysis product; subject the hydrolysis product to countercurrent extraction successively through the basic aqueous phase, organic solvent, and organic ionic liquid phase. Among them, the ionic liquid phase is subjected to countercurrent extraction in a pulsating injection manner under the conditions of a frequency of 3 Hz and an amplitude of 4 mm to obtain an organic phase;

[0054] Step 3: Rotate and evaporate the organic phase under a vacuum of -0.09 MPa and a temperature of 60 °C, and collect the distillate;

[0055] Step 4: Transfer the distillate into a separation tower equipped with a three-stage spiral packing layer and separate it from top to bottom. A vortex type demister with a blade inclination angle of 50 °C is provided at the top of the separation tower; among them, the temperature of the upper section of the spiral packing layer is 45 °C, the middle section is 65 °C, and the lower section is 85 °C. The passing time for each section is 20 min, and finally, high-purity p-nitrophenol is obtained.

[0056] Example 5

[0057] Step 1: Add nitrobenzene and a 25% by mass sodium hydroxide solution to a microwave reactor with a power density of 3 W / g according to a molar ratio of nitrobenzene to sodium hydroxide of 1:3. Then add 0.5 wt% titanium oxide and 0.5 wt% zirconium oxide based on the weight of nitrobenzene. Adjust the temperature to 100 °C and the pressure to 0.5 MPa, and then apply ultrasonic assistance at 30 kHz to carry out the hydrolysis reaction. After reacting for 2 h, a hydrolysis product is obtained;

[0058] Step 2: Prepare an aqueous solution containing 0.3 wt% dodecylbenzenesulfonic acid with a pH of 11 as the basic aqueous phase; prepare a mixed solution composed of acetone and ethyl acetate with a volume ratio of 3:7 as the organic solvent; prepare an EMIM solution containing 15 wt% acetate anions as the ionic liquid phase; the prepared volume of the basic aqueous phase, organic solvent, and ionic liquid phase is 3 times the volume of the hydrolysis product; subject the hydrolysis product to countercurrent extraction successively through the basic aqueous phase, organic solvent, and organic ionic liquid phase. Among them, the ionic liquid phase is subjected to countercurrent extraction in a pulsating injection manner under the conditions of a frequency of 3 Hz and an amplitude of 4 mm to obtain an organic phase;

[0059] Step 3: Rotate and evaporate the organic phase under a vacuum of -0.09 MPa and a temperature of 60 °C, and collect the distillate;

[0060] Step 4: Transfer the fraction into a separation column equipped with a three-stage spiral packing layer and separate it from top to bottom. A vortex demister with a blade inclination angle of 50°C is provided at the top of the separation column. Among them, the temperature of the upper section of the spiral packing layer is 45°C, the middle section is 65°C, and the lower section is 85°C. The passing time for each section is 20 minutes, and finally, high-purity p-nitrophenol is obtained.

[0061] Comparative Example 1

[0062] Compared with Example 1, the only difference is that in Step 1, the microwave reactor is replaced with a stirring kettle, and ultrasonic assistance is cancelled at the same time. Other steps and conditions remain the same, and finally, p-nitrophenol is obtained.

[0063] Comparative Example 2

[0064] Compared with Example 1, the only difference is that in Step 2, the hydrolysis product is not subjected to countercurrent extraction through the ionic liquid phase. Other steps and conditions remain the same, and finally, p-nitrophenol is obtained.

[0065] Comparative Example 3

[0066] Compared with Example 1, the only difference is that in Step 4, the temperatures of the upper, middle, and lower sections of the spiral packing layer are all set to 65°C. Other steps and conditions remain the same, and finally, p-nitrophenol is obtained.

[0067] The conversion rate of nitrobenzene and the purity of the obtained p-nitrophenol in Examples 1-5 and Comparative Examples 1-3 were detected, and the detection results are listed in Table 1 as follows:

[0068] Table 1

[0069] Conversion rate of nitrobenzene / 100% Purity of p-nitrophenol / 100% Example 1 99.7 99.97 Example 2 99.5 99.96 Example 3 99.5 99.96 Example 4 99.6 99.95 Example 5 99.5 99.95 Comparative Example 1 99.1 99.52 Comparative Example 2 99.2 99.51 Comparative Example 3 92.3 99.48

[0070] By analyzing the data in Table 1, it can be known that compared with Comparative Examples 1-3, the conversion rate of nitrobenzene in Examples 1-5 is significantly higher, all reaching more than 99.5%; at the same time, the purity of the p-nitrophenol prepared in Examples 1-5 is also significantly higher, all reaching more than 99.95%. This shows that the production efficiency and product quality of the process for continuous separation of tar in p-nitrophenol of the present invention have been significantly improved compared with the prior art.

[0071] The above has described a detailed description of an embodiment of the present invention, but the content described is only the preferred embodiment of the present invention and cannot be considered as limiting the scope of implementation of the present invention. All equivalent changes and improvements made according to the scope of the present invention application should still fall within the scope covered by the patent of the present invention.

Claims

1. A process for continuous separation of tar in p-nitrophenol, characterized in that, It includes the following steps: Step 1: Put nitrobenzene and sodium hydroxide solution into a microwave reactor in proportion, and hydrolyze at 80 - 120 °C, 0.3 - 0.8 MPa, and 10 - 50 kHz to obtain a hydrolysis product; Step 2: Subject the hydrolysis product to countercurrent extraction successively through an alkaline aqueous phase, a polar organic solvent phase, and an ionic liquid phase; Step 3: Rotate and evaporate the extracted organic phase under the conditions of a vacuum degree of (-0.08) - (-0.095) MPa and a temperature of 50 - 70 °C, and collect the distillate; Step 4: Transfer the distillate into a separation tower equipped with a three-stage spiral packing layer and separate it from top to bottom. Among them, the temperature of the upper section of the spiral packing layer is 40 - 50 °C, the middle section is 60 - 70 °C, and the lower section is 80 - 90 °C, and finally obtain high-purity p-nitrophenol.

2. The process for continuous separation of tar from p-nitrophenol according to claim 1, characterized in that, In Step 1, the molar ratio of nitrobenzene to sodium hydroxide is 1:(2.5 - 3.5); the mass fraction of the sodium hydroxide solution is 20 - 30%.

3. The process for continuous separation of tar from p-nitrophenol according to claim 1, characterized in that, In Step 1, the power density of the microwave reactor is 2 - 5 W / g.

4. The process for continuous separation of tar in p-nitrophenol according to claim 1, characterized in that, In Step 1, a composite catalyst is also added to the microwave reactor, and the addition amount of the composite catalyst is 0.5 - 2 wt% of the weight of nitrobenzene.

5. The process for continuous separation of tar in p-nitrophenol according to claim 4, characterized in that, The composite catalyst is a mixture composed of titanium nitride and zirconium oxide in a weight ratio of 1:

1.

6. The process for continuous separation of tar in p-nitrophenol according to claim 1, characterized in that, In Step 2, the alkaline aqueous phase is an aqueous solution containing 0.1 - 0.3 wt% of dodecylbenzenesulfonic acid, and its pH value is 9 - 11.

7. The process for continuous separation of tar in p-nitrophenol according to claim 1, characterized in that, In Step 2, the polar organic solvent phase is a mixed solvent composed of acetone and ethyl acetate in a volume ratio of 3:

7.

8. The process for continuous separation of tar from p-nitrophenol according to claim 1, characterized in that, In Step 2, the ionic liquid phase is a 1-ethyl-3-methylimidazolium hexafluorophosphate solution containing 10 - 15 wt% of acetate anions.

9. The process for continuous separation of tar in p-nitrophenol according to claim 8, characterized in that, The ionic liquid phase performs countercurrent extraction in a pulsating injection manner under the conditions of a frequency of 2 - 5 Hz and an amplitude of 3 - 5 mm.

10. The process for continuous separation of tar in p-nitrophenol according to claim 1, characterized in that, In Step 4, a vortex type demister is arranged at the top of the separation tower, and the blade inclination angle of the vortex type demister is 45 - 60 °C.

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