Method for high-value utilization of phenolic tar

Abstract

The invention belongs to the technical field of high-value utilization of organic wastes, and particularly relates to a method for high-value utilization of phenolic tar. According to the method, the phenol tar is subjected to alcoholysis, alkylation, steam stripping, rectification, melt crystallization purification and other procedures to obtain high-added-value fine chemical products such as p-xylylene ether and anisole, and the residual tar after steam stripping can be continuously used as fuel to be incinerated to produce steam. According to the method disclosed by the invention, the hydroquinone in the phenol tar can be reacted and converted, the phenol tar with low polymerization degree can be alcoholyzed into phenol, hydroquinone and a small amount of catechol, part of phenolic compounds can be etherified with methanol and then converted into p-xylylene ether and anisole through alkylation, and according to measurement and calculation, the content of the p-xylylene ether in the phenol tar can be measured and calculated, and the content of the p-xylylene ether in the phenol tar can be measured and calculated. According to hydroquinone corresponding to the generated p-xylylene ether, the phenol tar can be converted into hydroquinone with the weight being 10% or above of the weight of tar through alcoholysis by deducting the original hydroquinone amount in the phenol tar, and therefore high-value utilization of the phenol tar is achieved.

Description

Technical Field

[0001] This invention belongs to the field of high-value utilization technology of organic waste, specifically relating to a method for high-value utilization of phenol tar, and more particularly to a comprehensive utilization method for by-product tar from the production of hydroquinone by phenol hydroxylation. Background Technology

[0002] The method for synthesizing hydroquinone by hydrogen peroxide hydroxylation of phenol, developed in the 1970s, uses phenol as a raw material and reacts it with hydrogen peroxide under the action of TS-1 titanium-silicon molecular sieve catalyst to produce hydroquinone and catechol. Compared with the aniline oxidation method and the diisopropylbenzene method, this method has the advantages of abundant and inexpensive raw materials, simple catalytic reaction process, excellent product quality, and is conducive to large-scale industrialization. This method is considered to be one of the most promising "green" process routes in the 21st century, and domestic hydroquinone production enterprises with a capacity of more than 10,000 tons all adopt this process.

[0003] While the above-mentioned process has certain advantages, it produces a relatively large amount of tar byproducts. To ensure the fluidity of the tar, a portion of the product is often discarded as a solvent to dissolve the tar. The tar contains hydroquinone, which has high economic value. According to sampling tests, the hydroquinone content (mass fraction) in the tar is 8.0-25.0%, the catechol content (mass fraction) is 0.0-3.0%, the phosphoric acid content (mass fraction) is 0.1-3.0%, and other substances include phenol, as well as complex etherifications of catechol and hydroquinone, and trace metal impurities.

[0004] Currently, production enterprises treat tar by crushing and incinerating it or dissolving it in solvents before incinerating it, and then using it to generate electricity or steam, but the economic utilization rate is low.

[0005] To improve the economic utilization value of tar, this invention provides a method for obtaining high-value fine chemical products such as anisole and diphenyl ether through processes such as alcoholysis and alkylation, followed by stripping and distillation. The tar residue after this process can still be used as fuel for incineration, thus realizing the comprehensive utilization of tar. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for the high-value utilization of phenolic tar. The phenolic tar is a byproduct of the synthesis of hydroquinone via the hydroxylation of phenol. The method involves processing the phenolic tar through alcoholysis, alkylation, stripping, distillation, and melt crystallization purification to obtain high-value-added fine chemical products such as dimethyl phthalate and anisole. The residual tar after stripping can be used as fuel to produce steam, thus achieving high-value utilization of phenolic tar. The method described in this invention has advantages such as simple process flow, significant economic benefits, and suitability for industrialization.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides a method for the high-value utilization of phenolic tar, comprising the following steps:

[0009] 1) Alcohololysis: Phenolic tar is added to a small molecule alcohol and stirred until the phenolic tar is completely dissolved. If necessary, heating can be carried out. Then, an acid catalyst is added and the mixture is stirred and mixed evenly. Alcohololysis is carried out under closed conditions. After cooling to room temperature, reaction solution I (i.e., alcoholysis solution) is obtained.

[0010] 2) Alkylation: The reaction solution I (i.e., the alcoholysis solution) obtained from the alcoholysis step is subjected to an alkylation reaction to obtain reaction solution II (i.e., the alkylation solution);

[0011] 3) Separation and purification (stripping): After the reaction liquid II (i.e. alkylation liquid) is processed in a rotary evaporator, the residual material is transferred to a stripping tower, where steam is introduced for stripping. The gas phase stripped material is cooled and then separated in a layering tank. The upper oil phase is then subjected to distillation, sintering and melting crystallization to obtain products such as anisole and diphenyl ether.

[0012] Specifically, in step 1) of this invention, the phenolic tar contains substances with the following structures:

[0013]

[0014] Among them, R1, R2, R3, R4 = H, Ph or Ph-OH.

[0015] The by-product tar from the synthesis of hydroquinone via the hydroxylation of phenol, as described in this invention, contains 8.0–25.0% hydroquinone (mass fraction), 0.0–3.0% catechol (mass fraction), and 0.1–3.0% phosphoric acid (mass fraction). Other substances include complex etherifications of phenol, catechol, and hydroquinone, as well as trace amounts of metallic impurities. This tar originates from the process of producing hydroquinone via the hydroxylation of phenol using a scraped-film evaporator and is a viscous liquid at temperatures above 180°C.

[0016] As a preferred technical solution, the alcoholysis steps are as follows: Phenolic tar is ground into powder and added to reaction vessel I along with small molecule alcohols. The mixture is stirred until completely dissolved. If necessary, it can be heated to 45-55°C. Then, an acid catalyst is added, reaction vessel I is sealed, and nitrogen gas at 0.3-0.5 MPa is used to purge the mixture three times. The mixture is heated to the alcoholysis temperature with stirring and reacted for a certain time. Stirring is continued and the mixture is cooled to room temperature. Excess gas in reaction vessel I is then discharged to obtain reaction liquid I.

[0017] Specifically, in the alcoholysis step, the amount of small molecule alcohol should be sufficient to completely dissolve the phenolic tar, and the mass ratio of small molecule alcohol to phenolic tar is (0.3-10):1, preferably (1-3):1; the small molecule alcohol is selected from C1-C5 alcohols, such as pure methanol, pure ethanol, propylene glycol, glycerol, etc., preferably pure methanol.

[0018] Specifically, in the alcoholysis step, the added acid catalyst accounts for 0.1 to 10% of the total mass of the small molecule alcohol and tar, preferably 2 to 5%.

[0019] Specifically, in the alcoholysis step, the acid catalyst is an inorganic acid, such as one or more selected from phosphoric acid, sulfuric acid, halogenated acids and Lewis acids (such as BF3). Considering equipment corrosion and environmental protection, phosphoric acid is preferred.

[0020] Specifically, the alcoholysis temperature is 100–300℃, preferably 120–200℃; the alcoholysis time is 0.5–24h, preferably 3–10h.

[0021] As a preferred technical solution, the alkylation steps are as follows:

[0022] The reaction solution I (i.e., the alcoholysis solution) obtained from the alcoholysis step was transferred into reaction vessel II. A certain amount of dimethyl carbonate and polyethylene glycol (PEG-400) were added, the vessel was sealed, and nitrogen was purged three times. The mixture was heated to the reaction temperature under stirring to carry out the alkylation reaction. During the reaction, the reaction pressure was kept below 2 MPa. When the pressure exceeded 2.0 MPa, the vent valve was opened to release the gas in the vessel. After the reaction was completed, the mixture was slowly cooled to room temperature to obtain reaction solution II.

[0023] Specifically, in the alkylation step, dimethyl carbonate should be added in excess, meaning that dimethyl carbonate can still be separated from the reaction solution after the reaction is completed, to ensure that the reaction proceeds fully; the molar amount of dimethyl carbonate added is 1.2 to 20 times the amount of hydroquinone detected in the phenol tar, preferably 2 to 5 times.

[0024] Specifically, the amount of polyethylene glycol (PEG-400) is 0.5% to 30% of the total mass of the alcoholysis solution and dimethyl carbonate, preferably 3% to 15%, and more preferably 5% to 10%.

[0025] Specifically, the alkylation reaction temperature is 150–200°C; the alkylation reaction time is 0.5–10 h, preferably 2–5 h.

[0026] Specifically, in the method of the present invention, through alcoholysis, some low molecular weight ethers in tar can be converted into phenol, catechol, hydroquinone and a small amount of their ethers. Through alkylation, the generated phenol, catechol, hydroquinone and a small amount of their methyl ethers can be further alkylated to their corresponding methyl ethers. Then, they are stripped out by taking advantage of the azeotropic properties of anisole and dimethyl ether with water.

[0027] As a preferred technical solution, the separation and purification (stripping) steps are as follows:

[0028] Stripping is carried out in a stripping tower (positive pressure tower) with a design pressure ≥5MPa;

[0029] Before vaporization, reaction solution II is first introduced into a rotary evaporator and kept in a water bath at a temperature of 40-60°C. The vacuum is gradually increased to a maximum of -0.090 MPa to remove methanol, residual dimethyl carbonate, and water generated in the reaction. Methanol is then recovered for reuse.

[0030] During stripping, the reactants processed by the rotary evaporator are transferred to a stripping tower, and steam at 1.5–3.5 MPa is introduced until the vapor temperature at the top of the stripping tower exceeds 213°C. Stripping is then carried out. The stripped vapor is cooled and separated in a separator. The upper oil phase is fed into a distillation column for negative pressure distillation to obtain anisole. After distillation, the residue is transferred to a distillation column to distill off a mixture of o-phenylenediamine and p-phenylenediamine, which is then transferred to a melt crystallizer for further processing to finally obtain anisole, p-phenylenediamine, and other products. The process parameters for distillation, distillation, and melt crystallization can be designed based on the material composition or simulated by technicians based on experience or data.

[0031] Specifically, reaction liquid II (i.e., alkylation liquid) is transferred to a rotary evaporator and kept in a water bath at 40–60°C. The vacuum is gradually increased to a maximum of -0.095 MPa to remove methanol, residual dimethyl carbonate, and the water generated in the reaction. The remaining material is transferred to a stripping column, where steam at 1.5–3.5 MPa is introduced for stripping. The vapor stripped from the top of the column is cooled by a condenser and then enters a separator for separation. The upper oil phase is separated from the water phase and sent to a batch distillation column, first at 40–60°C and -0.1–... Water in the oil phase is distilled off under a pressure of -0.08 MPa. Then, anisole is distilled off under a vacuum of -0.1 to -0.095 MPa and a temperature of approximately 110 to 130 °C. When no more fractions are distilled off, the distillation is stopped, and the residue in the distillation vessel is transferred to a distillation vessel. Distillation is carried out under a vacuum of -0.1 to -0.095 MPa and a temperature of 160 to 190 °C to obtain a mixture of diphenyl ether and o-phenylene ether. This mixture is then transferred to a melt crystallizer for further processing to finally obtain products such as anisole and diphenyl ether.

[0032] Specifically, the melting crystallization process parameters are: cooling rate 0.5~0.7℃ / min, final temperature 53~57℃, and sweating temperature 50~54℃.

[0033] Furthermore, the lower layer of water is fed into the subsequent wastewater treatment system;

[0034] The residual liquid at the bottom of the stripping tower is discharged through a bottom pump and incinerated.

[0035] The purity of the anisole and diphenyl ether obtained by liquid chromatography with external standard method was ≥99.0%, which both meet the requirements of downstream applications.

[0036] Specifically, the stripped phenolic tar remains fluid at high temperatures, making it easy to transfer and spray into the incinerator for combustion.

[0037] The method of this invention is simple to process, suitable for industrialization, introduces fewer impurities, and makes full use of the valuable components in the by-product tar.

[0038] Compared with the prior art, the advantages of the present invention are:

[0039] 1. The phenolic tar described in this invention is a by-product tar of hydroquinone synthesis via the hydroxylation of phenol. The method of this invention involves purifying the phenolic tar through steps such as alcoholysis, alkylation, stripping, distillation, and melt crystallization to obtain high-value-added fine chemical products such as dimethyl phthalate and anisole. The residual tar after stripping can continue to be burned as fuel to produce steam, thereby realizing the high-value utilization of phenolic tar.

[0040] 2. The present invention is characterized by the ability to react and convert hydroquinone and catechol present in phenolic tar, and also to alcoholyze low-polymerization-degree phenolic tar into phenol, catechol, and hydroquinone. Some phenols can be etherified with methanol, and then converted into dimethyl phthalate, dimethyl phthalate, and anisole through alkylation. The azeotropic properties of anisole and dimethyl phthalate with water are utilized to separate them from the residual tar. Calculations show that, based on the hydroquinone corresponding to the generated dimethyl phthalate, and after deducting the original amount of hydroquinone in the phenolic tar, phenolic tar can be converted into more than 10% hydroquinone by weight through alcoholysis.

[0041] 3. In summary, the method described in this invention has the advantages of simple process flow, significant economic benefits and suitability for industrialization. Detailed Implementation

[0042] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. However, those skilled in the art should understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] In the following embodiments, the instruments and equipment used in the reaction process include reaction kettles, rotary evaporators, stripping towers, condensers, distillation towers, distillation apparatuses, and melt crystallizers, all of which are common equipment in the prior art. The specific usage methods adopt conventional usage methods in the prior art and are not the inventive point of this invention, so they will not be described in detail.

[0044] In the following examples and comparative examples, room temperature or normal temperature refers to 25±5℃.

[0045] Unless otherwise specified, the experimental methods in the following examples are generally carried out under conventional conditions or as recommended by the manufacturer. Unless otherwise specified, the raw materials and reagents used are all commercially available products.

[0046] The methanol, phosphoric acid, and other raw materials used in the examples are conventional reagents. The phenolic tar was provided by the industrial-scale test equipment of Henan Shengrun New Material Technology Co., Ltd. The content of hydroquinone (mass fraction) in the phenolic tar was 15.3% and the content of catechol (mass fraction) was 0.25% by liquid chromatography with external standard method.

[0047] Example 1

[0048] A method for high-value utilization of phenolic tar, the specific steps of which are as follows:

[0049] S101 alcoholysis steps: Take 500.0g of phenol tar, grind it into powder, and add it together with 500.0g of pure methanol into reactor I. Stir until it is completely dissolved. If necessary, heat it to 50℃. Then add 30.0g of 98% (mass fraction) phosphoric acid, seal reactor I, and replace it with nitrogen gas at 0.3-0.5MPa three times. Heat it to 150℃ with stirring and keep it at that temperature for 5h. Continue stirring and cool it down to room temperature. Remove the excess gas in reactor I. A total of 1025.7g of reaction liquid I is obtained.

[0050] Sampling was performed using the external standard method in liquid chromatography, and the detection method was in accordance with the national standard GB / T 23959-2009. The results showed that the content (mass fraction) of each component in reaction solution I was as follows: hydroquinone 11.18%, p-hydroxyanisole 1.15%, p-phenylenediamine 0.26%, phenol 2.28%, anisole 0.38%, catechol 0.58%, o-hydroxyanisole 0.17%, and o-phenylenediamine 0.03%.

[0051] S102 Alkylation Step: 1000.0g of reaction solution I (i.e., alcoholysis solution) obtained from the alcoholysis step was transferred to reactor II (i.e., high-pressure reactor). 150.0g of dimethyl carbonate (DMC) and 60.0g of polyethylene glycol (PEG-400) were added. Reactor II was sealed, and nitrogen gas was purged three times at 0.3-0.5MPa. The temperature was raised to 180℃ under stirring for alkylation reaction for 3 hours. During the reaction, the reaction pressure was kept below 2.0MPa. When the pressure exceeded 2.0MPa, the vent valve was opened to release the gas. After the reaction was completed, the temperature was slowly lowered to room temperature, yielding a total of 1138.5g of reaction solution II.

[0052] Sampling was performed using the external standard method in liquid chromatography, and the detection method was in accordance with the national standard GB / T 23959-2009. The results showed that the content (mass fraction) of each component in reaction solution II was as follows: p-phenylenediamine 11.93%, p-hydroxyanisole 1.56%, anisole 2.66%, o-phenylenediamine 0.65%, and o-hydroxyanisole 0.05%.

[0053] S103 Separation and Purification (Stripping) Steps: 1000.0g of reaction liquid II (i.e., alkylation liquid) is transferred to a rotary evaporator. A water bath is maintained at 50℃, and the vacuum is gradually increased to a maximum of -0.095MPa to remove methanol, residual DMC, and the water generated during the reaction. The remaining material is transferred to a stripping tower, where 2.0MPa steam is introduced for stripping. The stripped vapor from the top of the tower is cooled by a condenser and then enters a separation tank for separation. The upper oil phase is separated from the water phase and sent to a batch distillation tower. The batch distillation tower is a packed tower using 4mm*4mm triangular spiral packing with a packing height of 40cm. The oil phase is first separated at 50℃ and -0.090MPa. Water was distilled off, and then anisole was distilled off under a vacuum of -0.098 MPa and a temperature of approximately 120°C. When no more fractions were distilled off, the distillation was stopped, and the residue in the distillation vessel was transferred to a distillation vessel. Distillation was carried out under a vacuum of -0.098 MPa and a temperature of 160-190°C to obtain a mixture of p-phenylenediamine and o-phenylenediamine. This mixture was then transferred to a melt crystallizer for processing. The melt crystallization process parameters were: cooling rate 0.7°C / min, final temperature 54°C, and evaporation temperature 52°C. 18.62 g of anisole with a purity of 99.4% and 89.48 g of p-phenylenediamine with a purity of 99.6% were obtained, respectively. The purity was determined by liquid chromatography with external standard method.

[0054] The lower layer of water is fed into the subsequent wastewater treatment system;

[0055] The residual liquid at the bottom of the stripping tower is discharged through a bottom pump and incinerated.

[0056] After melting and crystallization, the resulting mother liquor can be reused or returned to the stripping tower to improve the overall yield.

[0057] Calculations show that, based on hydroquinone, this method can achieve an alcoholysis rate of 10.15% for phenolic tar. The calculation method is as follows:

[0058]

[0059] Where M is the weight of tar; M1 is the weight of the resulting alcoholysis solution; a% is the hydroquinone content in the alcoholysis solution; b% is the p-hydroxyanisole content in the alcoholysis solution; and c% is the p-phenylenediamine content in the alcoholysis solution.

[0060] Based on the weight of tar, the yield of qualified diphenyl ether products obtained by this method is 25.85%, and there is still room for improvement by reusing the mother liquor from melt crystallization.

[0061] Comparative Example 1

[0062] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 did not undergo alcoholysis, but only dissolved the phenolic tar in the corresponding amount of methanol, and then carried out alkylation, separation and purification. The conditions and methods for alkylation and separation and purification were the same as in Example 1, and 71.99 g of terephthalic ether with a purity of 99.7% was obtained. The by-product anisole was too small (less than 3 g) to obtain a qualified product. Based on the amount of tar, the yield of terephthalic ether was 14.40%.

[0063] The reaction results from the examples and comparative examples show that alcoholysis plays a key role in the treatment of phenolic tar. Through alcoholysis, alkylation, and separation and purification, the mass yield of the main products, anisole and diphenyl ether, can be significantly improved.

[0064] Based on the unit prices of 45,000 yuan / ton for dimethyl phthalate and 17,000 yuan / ton for anisole, the method of this invention can generate an economic benefit of more than 10,000 yuan per ton of phenolic tar, and after deducting processing costs, there is still a profit of more than 3,000 yuan per ton.

[0065] This invention describes specific process methods, but it should be understood that the terms used herein are descriptive and explanatory, not limiting. Modifications and revisions can be made to this invention within the scope of the claims, as well as without departing from the scope and spirit of the invention. Although the invention described herein relates to specific methods, materials, and embodiments, it does not imply that the invention is limited to the specific examples disclosed herein; rather, the invention can be extended to all other methods and applications with the same function.

[0066] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for the high-value utilization of phenolic tar, characterized in that, Includes the following steps: 1) Alcohololysis: Phenolic tar is added to a small molecule alcohol and stirred until the phenolic tar is completely dissolved. Heating may be necessary. Then an acid catalyst is added and the mixture is stirred and mixed evenly. Alcohololysis is carried out under closed conditions. After cooling to room temperature, reaction solution I is obtained. 2) Alkylation: The reaction solution I obtained from the alcoholysis step is subjected to an alkylation reaction to obtain reaction solution II; 3) Separation and purification (stripping): After the reaction liquid II is transferred to a rotary evaporator for processing, the residual material is transferred to a stripping tower, where steam is introduced for stripping. The gas phase stripped material is cooled and then enters a separation tank for separation. The upper oil phase is then subjected to steps such as rectification, distillation, and melt crystallization to obtain products such as anisole and diphenyl ether.

2. The method according to claim 1, characterized in that, In step 1), the phenolic tar contains substances with the following structures: Among them, R1, R2, R3, R4 = H, Ph or Ph-OH.

3. The method according to claim 1, characterized in that, The phenolic tar contains the following components: hydroquinone (mass fraction) 8.0–25.0%, catechol (mass fraction) 0.0–3.0%, phosphoric acid (mass fraction) 0.1–3.0%, and other substances include complex etherifications of phenol, catechol, and hydroquinone, as well as trace metal impurities.

4. The method according to claim 1, characterized in that, The steps of alcoholysis are as follows: Phenolic tar is ground into powder and added to reactor I along with small molecule alcohol. The mixture is stirred until it is completely dissolved. Then, an acid catalyst is added, reactor I is sealed, and nitrogen gas at 0.3-0.5 MPa is used to purge the mixture three times. The mixture is heated to the alcoholysis temperature with stirring and reacted for a certain time. Stirring is continued and the mixture is cooled to room temperature. Excess gas in reactor I is then discharged to obtain reaction solution I.

5. The method according to claim 1, characterized in that, In the alcoholysis step, the amount of small molecule alcohol should be sufficient to completely dissolve the phenolic tar. The mass ratio of small molecule alcohol to phenolic tar is (0.3-10):

1. The small molecule alcohol is selected from C1-C5 alcohols. In the alcoholysis step, the acid catalyst is one or more of phosphoric acid, sulfuric acid, halogen acid, and Lewis acid.

6. The method according to claim 1, characterized in that, In the alcoholysis step, the added acid catalyst accounts for 0.1% to 10% of the total mass of the small molecule alcohol and tar. The alcoholysis temperature is 100–300℃; the alcoholysis time is 0.5–24 h.

7. The method according to claim 1, characterized in that, The alkylation steps are as follows: The reaction solution I obtained from the alcoholysis step was transferred into reaction vessel II. A certain amount of dimethyl carbonate and polyethylene glycol PEG-400 were added, the vessel was sealed, and nitrogen was purged three times. The mixture was heated to the reaction temperature under stirring to carry out the alkylation reaction. During the reaction, the reaction pressure was kept below 2 MPa. When the pressure exceeded 2.0 MPa, the vent valve was opened to release the gas in the vessel. After the reaction was completed, the mixture was slowly cooled to room temperature to obtain reaction solution II.

8. The method according to claim 1, characterized in that, In the alkylation step, the molar amount of dimethyl carbonate added is 1.2 to 20 times the amount of hydroquinone detected in the phenol tar, preferably 2 to 5 times; In the alkylation step, the amount of polyethylene glycol PEG-400 is 0.5% to 30% of the total mass of the alcoholysis solution and dimethyl carbonate.

9. The method according to claim 1, characterized in that, The alkylation reaction temperature is 150–200℃; the alkylation reaction time is 0.5–10 h.

10. The method according to claim 1, characterized in that, The steps for separation and purification (stripping) are as follows: Before vaporization, reaction solution II is first placed into a rotary evaporator and kept in a water bath at a temperature of 40-60°C. The vacuum degree is gradually increased to a maximum of -0.090 MPa to evaporate methanol, residual dimethyl carbonate, and water generated in the reaction. During stripping, the reactants processed by the rotary evaporator are transferred into the stripping tower, and steam at 1.5–3.5 MPa is introduced into the stripping tower until the vapor temperature at the top of the stripping tower exceeds 213°C. After cooling, the stripped material enters a separation tank for separation. The upper oil phase is fed into a distillation tower for negative pressure distillation to obtain anisole. After distillation, the residue is transferred to a distillation tower to distill off a mixture of o-phenylenediamine and p-phenylenediamine, which is then transferred to a melt crystallizer for further processing to finally obtain products such as anisole and p-phenylenediamine. The lower layer of water is fed into the subsequent wastewater treatment system.

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