阅读说明：本技术 一种苯醚甲环唑废弃中间体回收利用方法 (Recycling method of difenoconazole waste intermediate ) 是由 冯魏 陈华 贾利华 陈石秀 徐武亮 邢燕 于 2021-09-13 设计创作，主要内容包括：本发明公开了一种苯醚甲环唑废弃中间体回收利用方法,该方法将由原料3,4'-二氯二苯醚经酰化、精制制备苯醚甲环唑中间体1-(2-氯-4-(4-氯苯氧基)苯基)乙酮的精制母液回收,与水合肼在碱性条件下反应生成腙的衍生物,高温下蒸出过量水合肼的同时腙衍生物分解为1-(2-氯-4-(4-氯苯氧基)苯基)乙烷和1-(4-氯-2-(4-氯苯氧基)苯基)乙烷混合物,混合物在路易斯酸存在下发生傅克去烷基化反应,逸出乙烷,得3,4'-二氯二苯醚粗品,精馏得3,4'-二氯二苯醚精品。整个工艺操作简单、所用设备均为常规设备,变废为宝,解决了现有精制母液残渣处理难的问题。(The invention discloses a method for recycling a difenoconazole waste intermediate, which comprises the steps of recovering refined mother liquor for preparing a difenoconazole intermediate 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethanone by acylating and refining raw material 3,4 '-dichlorodiphenyl ether, reacting the refined mother liquor with hydrazine hydrate under an alkaline condition to generate a hydrazone derivative, distilling out excessive hydrazine hydrate at high temperature, decomposing the hydrazone derivative into a mixture of 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethane and 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethane, carrying out Friedel-crafts dealkylation on the mixture in the presence of Lewis acid, escaping ethane to obtain a 3,4' -dichlorodiphenyl ether crude product, and rectifying to obtain 3,4' -dichlorodiphenyl ether refined product. The whole process is simple to operate, the used equipment is conventional equipment, waste is changed into valuable, and the problem that the existing refined mother liquor residue is difficult to treat is solved.)

1. A method for recycling a difenoconazole waste intermediate, wherein the difenoconazole waste intermediate is a refined mother liquor residue obtained after refining a difenoconazole intermediate 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethanone, and is characterized in that:

the refined mother liquor residue reacts with hydrazine hydrate under the alkaline condition to produce hydrazone derivatives, the hydrazone derivatives are decomposed into a mixture of 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethane and 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethane at high temperature, the mixture undergoes inverse Friedel-crafts dealkylation reaction in the presence of Lewis acid to obtain crude 3,4 '-dichlorodiphenyl ether, and the crude 3,4' -dichlorodiphenyl ether is obtained by rectification.

2. The method for recycling the difenoconazole waste intermediate as claimed in claim 1, which is characterized in that: the reaction equation for preparing the crude product of 3,4' -dichlorodiphenyl ether by the reaction of the refined mother liquor residue is as follows:

。

3. the method for recycling the difenoconazole waste intermediate as claimed in claim 2, which is characterized in that: the method comprises the following specific steps:

s1: adding the refined mother liquor residue, diethylene glycol and hydrazine hydrate into a reaction vessel, heating to 115-125 ℃, and carrying out reflux reaction for 4-8 h;

s2: reacting until the sum of the mass contents of the 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethanone and the 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethanone is less than or equal to 1 percent, adding alkali to remove hydrazine hydrate, heating to 160-;

s3: reaction to formulae II and II^，When the sum of the mass contents of the compounds is less than or equal to 1%, cooling to 40-70 ℃, adding cyclohexane, stirring for 0.5-1h under heat preservation, carrying out phase separation, wherein the lower layer is a diethylene glycol layer, applying the diethylene glycol layer to the next batch, the upper layer is a cyclohexane layer, and removing cyclohexane;

s4: adding nitrobenzene and AlCl₃Then, cooling to 20-40 ℃, introducing dry HCl gas, keeping the temperature at 20-40 ℃, preserving heat for 2-3h, then heating to 40-60 ℃, and preserving heat for 2-3 h;

s5: reacting until the sum of the mass contents of the 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethane and the 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethane is less than or equal to 5 percent, heating to 90-110 ℃, and preserving heat for 4-6 hours;

s6: reacting until the sum of the mass contents of the 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethane and the 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethane is less than or equal to 1 percent, cooling to 30-50 ℃, adding water for washing, and carrying out phase separation to obtain a crude product of the 3,4' -dichlorodiphenyl ether;

s7: the denitration radical benzene is switched into a rectifying still for rectification after the temperature is between 125 and 130 ℃ under the negative pressure of-0.098 MPa;

s8: under the negative pressure of-0.098 MPa, the mixture is refluxed until the temperature of the top of the column is stable, namely the mixture is not changed within 30min, then the fraction is collected, the temperature is front distillation at the temperature of less than 135 ℃, middle distillation at the temperature of 135-137 ℃, back distillation at the temperature of 137-142 ℃, and the temperature of the rectification residue in the kettle is reduced to 100-120 ℃, and nitrogen is vented for deslagging; the middle distillate is refined 3,4' -dichlorodiphenyl ether, the front distillate is mixed with nitrobenzene and applied to the next batch, and the back distillate is collected and subjected to secondary rectification after being concentrated.

4. The method for recycling the difenoconazole waste intermediate as claimed in claim 3, which is characterized in that: in the step S1, the molar ratio of the added hydrazine hydrate to the total amount of the 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethanone and the 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethanone in the refined mother liquor residue is 1.2-1.6: 1.

5. the method for recycling the difenoconazole waste intermediate as claimed in claim 3, which is characterized in that: in the step S1, the added weight of the diethylene glycol is 0.6 to 0.7 times of the weight of the refined mother liquor residue.

6. The method for recycling the difenoconazole waste intermediate as claimed in claim 3, which is characterized in that: in the step S2, the alkali is potassium hydroxide, and the molar ratio of the added amount of the potassium hydroxide to the total amount of the 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethanone and the 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethanone in the refined mother liquor residue is 1.7-2.3: 1.

7. The method for recycling the difenoconazole waste intermediate as claimed in claim 3, which is characterized in that: in the step S2, the ratio of the weight of cyclohexane to the weight of the residue to the weight of the purified mother liquor residue was 1: 1.

8. The method for recycling the difenoconazole waste intermediate as claimed in claim 3, which is characterized in that: in the step S4, the molar ratio of the added amount of HCl to the total amount of 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethanone and 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethanone in the refined mother liquor residue is 1.5-2.5: 1; AlCl₃The amount of the compound (c) is equal to the total amount of the 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethanone and the 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethanone in the residue of the mother liquorThe molar ratio of (A) to (B) is 0.01-0.03: 1; the weight ratio of nitrobenzene to residue to refined mother liquor residue was 1: 1.

Technical Field

The invention relates to a method for recovering refined mother liquor, in particular to a method for recycling a difenoconazole waste intermediate.

Background

The common process for preparing the difenoconazole intermediate 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethanone is prepared by acylating and refining 3,4' -dichlorodiphenyl ether serving as a raw material, and the reaction equation is as follows:

the prior art can generate about 10 percent of isomer (1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethanone) in the process of preparing the difenoconazole intermediate 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethanone. The isomer is usually removed by recrystallization, and 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethanone containing 90% per 1 ton is purified to obtain about 700Kg of 99% 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethanone and about 300Kg of 67% waste intermediate (purified mother liquor residue).

Most enterprises have difficulty in treating the waste intermediates, and can only entrust a third party to carry out high-temperature incineration treatment, so that the treatment cost is high, and the environment is not protected. For this purpose. A new technical solution is needed to solve the above technical problems.

Disclosure of Invention

The invention aims to provide a method for recycling 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethanone refined mother liquor residues, which changes the refined mother liquor residues into valuables, recycles the refined mother liquor residues, lightens the environmental protection pressure for production enterprises, reduces the production cost and increases the market competitiveness of the enterprises.

The technical scheme adopted by the invention for solving the technical problems is as follows:

a method for recycling a difenoconazole waste intermediate is characterized in that the difenoconazole waste intermediate is refined mother liquor residue obtained after refining a difenoconazole intermediate 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethanone, the refined mother liquor residue is reacted with hydrazine hydrate under an alkaline condition to produce a hydrazone derivative, the hydrazone derivative is decomposed into a mixture of 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethane and 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethane at a high temperature, the mixture is subjected to inverse Friedel-crafts dealkylation reaction in the presence of Lewis acid to obtain a 3,4 '-dichlorodiphenyl ether crude product, and the 3,4' -dichlorodiphenyl ether refined product is obtained through rectification.

The reaction equation is as follows:

the method comprises the following specific steps:

s1: adding the refined mother liquor residue, diethylene glycol and hydrazine hydrate into a reaction vessel, heating to 115-125 ℃, and carrying out reflux reaction for 4-8 h;

s2: reacting until the sum of the mass contents of the 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethanone and the 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethanone is less than or equal to 1 percent, adding alkali to remove hydrazine hydrate, heating to 160-;

s3: reaction to formulae II and II^，When the sum of the mass contents of the compounds is less than or equal to 1%, cooling to 40-70 ℃, adding cyclohexane, stirring for 0.5-1h under heat preservation, carrying out phase separation, wherein the lower layer is a diethylene glycol layer, applying the diethylene glycol layer to the next batch, the upper layer is a cyclohexane layer, and removing cyclohexane;

s4: adding nitrobenzene and AlCl₃Then, cooling to 20-40 ℃, introducing dry HCl gas, keeping the temperature at 20-40 ℃, preserving heat for 2-3h, then heating to 40-60 ℃, and preserving heat for 2-3 h;

s5: reacting until the sum of the mass contents of the 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethane and the 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethane is less than or equal to 5 percent, heating to 90-110 ℃, and preserving heat for 4-6 hours;

s6: reacting until the sum of the mass contents of the 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethane and the 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethane is less than or equal to 1 percent, cooling to 30-50 ℃, adding water for washing, and carrying out phase separation to obtain a crude product of the 3,4' -dichlorodiphenyl ether;

s7: the denitration radical benzene is switched into a rectifying still for rectification after the temperature is between 125 and 130 ℃ under the negative pressure of-0.098 MPa;

s8: under the negative pressure of-0.098 MPa, the mixture is refluxed until the temperature of the top of the column is stable, namely the mixture is not changed within 30min, then the fraction is collected, the temperature is front distillation at the temperature of less than 135 ℃, middle distillation at the temperature of 135-137 ℃, back distillation at the temperature of 137-142 ℃, and the temperature of the rectification residue in the kettle is reduced to 100-120 ℃, and nitrogen is vented for deslagging; the middle distillate is refined 3,4' -dichlorodiphenyl ether, the front distillate is mixed with nitrobenzene and applied to the next batch, and the back distillate is collected and subjected to secondary rectification after being concentrated.

Further, in the step S1, the molar ratio of the added amount of hydrazine hydrate to the total amount of 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethanone and 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethanone in the purification mother liquor residue is 1.2 to 1.6: 1.

further, in the step S1, the added weight of the diethylene glycol is 0.6 to 0.7 times of the weight of the residue of the purified mother liquor.

Further, in the step S2, the alkali is potassium hydroxide, and the molar ratio of the added amount of the potassium hydroxide to the total amount of the 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethanone and the 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethanone in the refined mother liquor residue is 1.7-2.3: 1.

Further, in the step S2, the ratio of the weight of cyclohexane to the weight of the residue in the purification mother liquor was 1: 1.

Further, in the step S4, the molar ratio of the amount of HCl added to the total amount of 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethanone and 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethanone in the refined mother liquor residue is 1.5-2.5: 1; AlCl₃The molar ratio of the added amount of the (1) ethyl ketone and the total amount of the 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethyl ketone and the 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethyl ketone in the refined mother liquor residue is 0.01-0.03: 1; the weight ratio of nitrobenzene to residue to refined mother liquor residue was 1: 1.

The invention recovers refined mother liquor of 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethanone which is a difenoconazole intermediate prepared by acylating and refining raw material 3,4' -dichlorodiphenyl ether, reacts with hydrazine hydrate under the alkaline condition to generate hydrazone derivatives, the hydrazone derivatives are decomposed into a mixture of 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethane and 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethane while excessive hydrazine hydrate is distilled out at high temperature, Friedel-crafts alkylation reaction is carried out on the mixture in the presence of Lewis acid, ethane escapes, crude 3,4' -dichlorodiphenyl ether is obtained, and refined 3,4' -dichlorodiphenyl ether is obtained by rectification. The whole process is simple to operate, the used equipment is conventional equipment, waste is changed into valuable, and the problem that the existing refined mother liquor residue is difficult to treat is solved.

The method adopts Wolff-Kishner-Huang Minlon (reduction) reaction to reduce 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethanone and 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethanone in refined mother liquor slag into 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethane and 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethane, has novel process steps, and has high recovery rate of 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethanone and 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethanone.

Detailed Description

In order to make the objects, technical solutions and advantages of the technical solutions of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the specific embodiments of the present invention.

It should be noted that the described embodiments of the invention are only preferred ways of implementing the invention, and that all obvious modifications, which are within the scope of the invention, are all included in the present general inventive concept.

Example 1

Adding 300g of refined mother liquor residue (the sum of the mass contents of 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethanone and 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethanone is 93.7 percent), 180g of diethylene glycol and 75g of hydrazine hydrate with the mass content of 80 percent into a reaction kettle, heating to 125 ℃ for 115 ℃ and carrying out reflux reaction for 4-8h until the sum of the mass contents of 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethanone and 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethanone is less than or equal to 1 percent, cooling to 80-95 ℃, adding 180g of water, heating to the water-hydrazine hydrate, removing the hydrazine hydrate through azeotropy, wherein the content of the hydrazine hydrate is less than or equal to 0.5 percent, cooling to 50-80 ℃, adding 103.5g of 92 percent potassium hydroxide, heating to 160-180 ℃ within 2-4h,evaporating water in the temperature rising process, keeping the temperature of 160-^，When the sum of the contents is less than or equal to 1 percent, cooling to 40-70 ℃, adding 300g of cyclohexane, keeping the temperature of 40-70 ℃ and stirring for 0.5h, separating a lower diethylene glycol layer, extracting for 2 times by using 60g of cyclohexane, mechanically applying the separated diethylene glycol to the next batch, combining cyclohexane layers, heating to remove cyclohexane completely, adding 300g of nitrobenzene, cooling to 20-40 ℃, introducing dry HCl gas until the weight of materials in the kettle is increased by 55g, adding 1.3g of anhydrous aluminum trichloride, reacting for 2-3h at 20-40 ℃, reacting for 2-3h at 40-60 ℃, heating to 90-110 ℃, keeping the temperature for 4-6h, wherein the sum of the contents of 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethane and 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethane is less than or equal to 5 percent, the sum of the contents of the 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethane and the 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethane is less than or equal to 1 percent, the temperature is reduced to 30-50 ℃, 60g of water is added for washing for 2 times, phase separation is carried out, nitrobenzene is distilled under the condition of negative pressure of-0.098 MPa to the temperature of 125-. The middle distillate is refined 3,4' -dichlorodiphenyl ether 225.5g with the content of 99.5 percent, the yield is 93.9 percent, the front distillate is mixed with nitrobenzene to cover the next batch, and the back distillate is collected and is subjected to secondary rectification after being concentrated by a certain amount.

Thus, 225.5g of refined 3,4' -dichlorodiphenyl ether is recovered from 300g of refined mother liquor residue, and the recovery rate is more than 75%.

Example 2

Adding 298g of refined mother liquor residue (the sum of the contents of 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethanone and 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethanone is 94.3 percent), 208.6g of diethylene glycol and 100g of 80 percent hydrazine hydrate into a reaction kettle, heating to 125 ℃ for 115 ℃ and carrying out reflux reaction for 4-8h until the sum of the contents of 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethanone and 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethanone is less than or equal to 1 percent, cooling to 80-95 ℃, adding 208.6g of water, heating to carry out azeotropic distillation with water-hydrazine hydrate, removing hydrazine hydrate to the extent that the hydrazine hydrate content is less than or equal to 0.5 percent, cooling to 50-80 ℃, adding 140g of 92 percent potassium hydroxide, heating to 180 ℃ at 160 ℃ within 2-4h, evaporating water in the heating process, and keeping the temperature at 180 ℃ at 160-Should last for 8-12h, II and II^，The sum of the contents is less than or equal to 1 percent, the temperature is reduced to 40 to 70 ℃, 298g of cyclohexane is added, the temperature is kept between 40 and 70 ℃, the stirring is carried out for 0.5h, a lower diethylene glycol layer is separated, 119.2g of cyclohexane is used for extraction for 2 times, the diethylene glycol is applied to the next batch, the cyclohexane layers are combined, the temperature is raised to remove cyclohexane, 298g of nitrobenzene is added, the temperature is increased to 20 to 40 ℃, dried HCl gas is introduced until the weight of materials in the kettle is increased to 91.3g, 4.0g of anhydrous aluminum trichloride is added, the reaction is carried out for 2 to 3h at the temperature of between 20 and 40 ℃, the reaction is carried out for 2 to 3h at the temperature of between 40 and 60 ℃, the sum of the contents of 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethane and 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethane is less than or equal to 5 percent, the temperature is raised to 90 to 110 ℃, the temperature is kept for 4 to 6h, the sum of the contents of the 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethane and the 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethane is less than or equal to 1 percent, the temperature is reduced to 30-50 ℃, 119.2g of water is added for washing for 2 times, phase separation is carried out, nitrobenzene is distilled under the condition of negative pressure of-0.098 MPa to the temperature of 125 ℃ and 130 ℃, and then a rectification system is transferred, after the column top reflux temperature is stable, the temperature of < 135 ℃ is collected as front distillation, the temperature of 135 ℃ and 137 ℃ are middle distillation, the temperature of 137 ℃ and 142 ℃ is collected as back distillation, and the rectification residue in the kettle is cooled to 100 ℃ and 120 ℃ and nitrogen is vented for deslagging. The middle distillate is refined 3,4' -dichlorodiphenyl ether with the content of 226.1g and the content of 99.6 percent, the front distillate is mixed with nitrobenzene to cover the next batch, and the back distillate is collected and is subjected to secondary rectification after being concentrated by a certain amount.

The recovery rate of the refined mother liquor residue is over 75 percent.

Example 3

Adding 301g of refined mother liquor residue (the sum of the contents of 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethanone and 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethanone is 93.4 percent), 200g of diethylene glycol and 87.5g of 80 percent hydrazine hydrate into a reaction kettle, heating to 125 ℃ for 115 ℃ and carrying out reflux reaction for 4-8h until the sum of the contents of 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethanone and 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethanone is less than or equal to 1 percent, cooling to 80-95 ℃, adding 200g of water, heating the water-hydrazine hydrate, removing the hydrazine hydrate through azeotropy, wherein the content of the hydrazine hydrate is less than or equal to 0.5 percent, cooling to 50-80 ℃, adding 115g of 92 percent potassium hydroxide, heating to 160-180 ℃ within 2-4h, evaporating water in the heating process, and reacting at 160-180 ℃ for 8-12h, II and II^，The sum of the contents is less than or equal to 1 percent, the temperature is reduced to 40 to 70 ℃, 301g of cyclohexane is added, the temperature is kept at 40 to 70 ℃, the stirring is carried out for 0.5h, and the lower layer of diethylene glycol is separatedExtracting a glycol layer for 2 times by using 80g of cyclohexane, using diethylene glycol to apply to the next batch, combining the cyclohexane layers, heating to remove cyclohexane, adding 301g of nitrobenzene, cooling to 20-40 ℃, introducing dry HCl gas until the weight of materials in the kettle is increased by 81g, adding 2g of anhydrous aluminum trichloride, reacting for 2-3h at 20-40 ℃, reacting for 2-3h at 40-60 ℃, keeping the sum of the contents of 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethane and 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethane less than or equal to 5%, heating to 90-110 ℃, keeping the temperature for 4-6h, keeping the sum of the contents of 1- (2-chloro-4- (4-chlorophenoxy) phenyl) ethane and 1- (4-chloro-2- (4-chlorophenoxy) phenyl) ethane less than or equal to 1%, cooling to 30-50 ℃, adding 80g of water, washing for 2 times, splitting phases, distilling nitrobenzene to 125-130 ℃ under the condition of negative pressure of-0.098 MPa, then transferring to a rectification system, collecting < 135 ℃ as front distillation, 135-137 ℃ as middle distillation, 137-142 ℃ as back distillation after the temperature of the top of the column is stable (no change in 30 min), cooling the rectification residues in the kettle to 100-120 ℃ and discharging residues by nitrogen venting. The middle distillate is refined 3,4' -dichlorodiphenyl ether with the content of 226.7g being 99.5 percent, the front distillate is mixed with nitrobenzene to cover the next batch, and the back distillate is collected to be concentrated for a certain amount and then is subjected to secondary rectification.

The recovery rate of the refined mother liquor residue is over 75 percent.