阅读说明：本技术 一种从混合二硝基苯中分离纯化间二硝基苯的工艺 (Process for separating and purifying m-dinitrobenzene from mixed dinitrobenzene ) 是由 冯刚 张平 姜能 向勇 黄清武 于 2020-07-17 设计创作，主要内容包括：本发明涉及间二硝基苯技术领域,公开了一种从混合二硝基苯中分离纯化间二硝基苯的工艺,包括如下步骤,向结晶釜中加入二硝基苯同分异构体,升温至全部融化后,边搅拌边对结晶釜进行一次逐级降温处理,得到一次结晶物料；将一次结晶物料分离得到一次结晶固体和一次结晶滤液；将一次结晶固体加入结晶釜中,升温至全部融化后,边搅拌边对结晶釜进行二次逐级降温处理,得到二次结晶物料；将二次结晶固体分离得到二次结晶固体和二次结晶滤液,二次结晶固体即为高纯度的间二硝基苯产品。本申请在分离过程中无需消耗原料、不产生废水,不会造成伤害,且邻(对)二硝基苯和间二硝基苯不会出现损耗,在后续的加工过程中,不会有影响产品的自身性能。(The invention relates to the technical field of m-dinitrobenzene, and discloses a process for separating and purifying m-dinitrobenzene from mixed dinitrobenzene, which comprises the following steps of adding dinitrobenzene isomerides into a crystallization kettle, heating until the dinitrobenzene isomerides and is completely melted, and carrying out primary step-by-step temperature reduction treatment on the crystallization kettle while stirring to obtain a primary crystallization material; separating the primary crystallized material to obtain a primary crystallized solid and a primary crystallized filtrate; adding the primary crystalline solid into a crystallization kettle, heating until the primary crystalline solid is completely melted, and carrying out secondary step-by-step cooling treatment on the crystallization kettle while stirring to obtain a secondary crystalline material; and separating the secondary crystallized solid to obtain a secondary crystallized solid and a secondary crystallized filtrate, wherein the secondary crystallized solid is a high-purity m-dinitrobenzene product. The method does not need to consume raw materials, does not produce waste water and does not cause damage in the separation process, and the loss of the ortho-dinitrobenzene and the meta-dinitrobenzene does not occur, so that the self performance of the product cannot be influenced in the subsequent processing process.)

1. A process for separating and purifying m-dinitrobenzene from mixed dinitrobenzene is characterized by comprising the following steps,

(1) primary crystallization: adding dinitrobenzene isomerides into a crystallization kettle, introducing nitrogen for protection, heating until the dinitrobenzene isomerides are completely melted, and carrying out primary step-by-step cooling treatment on the crystallization kettle while stirring to obtain a primary crystallization material;

(2) primary separation: conveying the primary crystallization material to a centrifuge, performing hot air protection, and separating to obtain a primary crystallization solid and a primary crystallization filtrate;

(3) secondary crystallization: adding the primary crystalline solid into a crystallization kettle, introducing nitrogen for protection, heating until the primary crystalline solid is completely melted, and carrying out secondary step-by-step cooling treatment on the crystallization kettle while stirring to obtain a secondary crystalline material;

(4) and (3) secondary separation: and conveying the secondary crystallized solid to a centrifugal machine, carrying out hot air protection, and separating to obtain a secondary crystallized solid and a secondary crystallized filtrate, wherein the secondary crystallized solid is a high-purity m-dinitrobenzene product.

2. The process for separating and purifying m-dinitrobenzene from mixed dinitrobenzene according to claim 1, wherein in the step (1), the temperature is gradually reduced from 80 ℃ to 60 ℃ in the process of one step-by-step temperature reduction treatment, the temperature is kept for 1 to 3 hours in each step of temperature reduction, and the temperature reduction times are 3 to 4 times.

3. The process for separating and purifying m-dinitrobenzene from mixed dinitrobenzene according to claim 1 or 2, wherein in the step (3), the process parameters of the secondary stepwise temperature reduction treatment are that the temperature is gradually reduced from 90 ℃ to 80 ℃, the temperature is kept for 1h to 3h during each temperature reduction, and the temperature reduction times are 3 to 5.

4. The process of claim 1, wherein the dinitrobenzene isomer is a dinitrobenzene isomer mixture obtained by dinitration of benzene as a starting material.

5. The process for separating and purifying m-dinitrobenzene from mixed dinitrobenzene according to claim 2, wherein in the step (2), the temperature of hot air is 70 ℃ and the centrifugal time is 3-8 min.

6. The process for separating and purifying m-dinitrobenzene from mixed dinitrobenzene according to claim 3, wherein in the step (4), the temperature of hot air is 85 ℃ and the centrifugal time is 3-8 min.

7. The process of claim 1, wherein the crystallization kettle is provided with a jacket, the jacket is heated by introducing steam, and the jacket is cooled by introducing hot water.

8. The process of claim 1 wherein the secondary crystallization filtrate from (4) and the dinitrobenzene isomer are added to a crystallization kettle and the operations from (1) to (4) are repeated.

9. The process for separating and purifying m-dinitrobenzene from mixed dinitrobenzene according to claim 1, wherein the primary crystallization filtrate from (2) is used as a feed for the production of phenylenediamine by means of hydrogenation rectification.

Technical Field

The invention belongs to the technical field of m-dinitrobenzene purification, and particularly relates to a process for separating and purifying m-dinitrobenzene from mixed dinitrobenzene.

Background

M-dinitrobenzene is an important intermediate for organic synthesis and is also used as a polymerization inhibitor for polymerization reactions and the like. At present, the preparation method of m-dinitrobenzene is to carry out dinitration reaction by taking benzene as a raw material, the generated nitration product is a dinitrobenzene isomer mixture, wherein the m-dinitrobenzene content is 85 percent, and the o-dinitrobenzene content and the p-dinitrobenzene content are 15 percent, and then the dinitrobenzene isomer mixture is separated and purified to obtain high-purity m-dinitrobenzene.

One separation method currently known is to perform sulfonation reaction on a benzene nitration product obtained by separation and washing and a sodium sulfite solution to enable o-dinitrobenzene and p-dinitrobenzene to form sodium o- (p) -nitrobenzenesulfonate to enter a water phase, and then separate and wash to obtain high-purity m-dinitrobenzene. The improvement mode of the production method is that a phase transfer catalyst is added during the sulfonation reaction, so that the effects of saving energy, reducing consumption and improving the purity of the m-dinitrobenzene product can be achieved, and sodium o (p) -nitrobenzenesulfonate wastewater is generated in the separation and washing process after the sulfonation reaction. However, the wastewater treatment difficulty is high, the treatment cost is high, the large-scale production of the m-dinitrobenzene is restricted, and part of the m-dinitrobenzene participates in the reaction of sodium sulfite, so that the m-dinitrobenzene is consumed.

Another separation method currently known is to dissolve the dinitrobenzene isomer mixture in a solvent (lower alcohol or acetate), cool it, crystallize it, filter it, wash and dry the crystals to obtain m-dinitrobenzene. The m-dinitrobenzene separated by the method has low crystallization and filtration temperature and is convenient to operate. However, the solvent has low flash point, is easy to burn and volatilize, has safety risk and occupational health injury, and simultaneously needs distillation to recover the solvent in the crystallization mother liquor, and has solvent loss and high energy consumption in post-treatment operation.

Disclosure of Invention

Through a large amount of researches, we find that m-dinitrobenzene with higher purity can be obtained by carrying out twice melt crystallization and hot air protection separation on a dinitrobenzene isomer mixture, raw materials are not consumed in the separation process, waste water is not generated, no harm is caused, no loss occurs to o- (p-) dinitrobenzene and m-dinitrobenzene, and the self performance of products is not influenced in the subsequent processing process.

It is therefore an object of the present invention to provide a process for separating purified m-dinitrobenzene from mixed dinitrobenzene comprising the steps of,

(1) primary crystallization: adding dinitrobenzene isomerides into a crystallization kettle, introducing nitrogen for protection, heating until the dinitrobenzene isomerides are completely melted, and carrying out primary step-by-step cooling treatment on the crystallization kettle while stirring to obtain a primary crystallization material;

(2) primary separation: conveying the primary crystallization material to a centrifuge, performing hot air protection, and separating to obtain a primary crystallization solid and a primary crystallization filtrate;

(3) secondary crystallization: adding the primary crystalline solid into a crystallization kettle, introducing nitrogen for protection, heating until the primary crystalline solid is completely melted, and carrying out secondary step-by-step cooling treatment on the crystallization kettle while stirring to obtain a secondary crystalline material;

(4) and (3) secondary separation: and conveying the secondary crystallized solid to a centrifugal machine, carrying out hot air protection, and separating to obtain a secondary crystallized solid and a secondary crystallized filtrate, wherein the secondary crystallized solid is a high-purity m-dinitrobenzene product.

The application adopts a melt crystallization process for separating and purifying m-dinitrobenzene isomer mixture to prepare m-dinitrobenzene. In a mixture taking m-dinitrobenzene as a main component, in the gradual and slow cooling crystallization process, m-dinitrobenzene crystals are firstly separated out, primary crystallization solid and primary crystallization filtrate are obtained by controlling the temperature of a cooling end point, and a small amount of crystallization filtrate is adsorbed on the surface of the separated primary crystallization solid. Returning the primary crystallized solid to the crystallizing kettle for further melting crystallization and separation, wherein the purity of the intermediate dinitrobenzene in the primary crystallized solid is higher than that of the m-dinitrobenzene before the primary crystallization, so that the m-dinitrobenzene product with higher purity can be obtained by melting crystallization again.

The beneficial effects of the invention are as follows:

raw materials are not consumed in the separation process, no waste water is generated, no harm is caused, no loss occurs to the ortho-dinitrobenzene and the meta-dinitrobenzene, and the self performance of the product is not influenced in the subsequent processing process.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

The invention provides a process for separating and purifying m-dinitrobenzene from mixed dinitrobenzene, which comprises the following steps,

(1) primary crystallization: adding dinitrobenzene isomerides into a crystallization kettle, introducing nitrogen for protection, heating until the dinitrobenzene isomerides are completely melted, and carrying out primary step-by-step cooling treatment on the crystallization kettle while stirring to obtain a primary crystallization material;

(2) primary separation: conveying the primary crystallization material to a centrifuge, performing hot air protection, and separating to obtain a primary crystallization solid and a primary crystallization filtrate;

(3) secondary crystallization: adding the primary crystalline solid into a crystallization kettle, introducing nitrogen for protection, heating until the primary crystalline solid is completely melted, and carrying out secondary step-by-step cooling treatment on the crystallization kettle while stirring to obtain a secondary crystalline material;

(4) and (3) secondary separation: and conveying the secondary crystallized solid to a centrifugal machine, carrying out hot air protection, and separating to obtain a secondary crystallized solid and a secondary crystallized filtrate, wherein the secondary crystallized solid is a high-purity m-dinitrobenzene product.

In the invention, in the step-by-step cooling treatment in the step (1), the temperature is gradually reduced from 80 ℃ to 60 ℃, the temperature is kept for 1-3 h during each cooling, and the cooling frequency is 3-4 times. Through the crystallization mode of slow cooling, just can crystallize m-dinitrobenzene from the mixture out, at the in-process of the crystal that gradually forms, through control cooling rate and every cooling crystallization temperature, guarantee can not hide the crystallization mother liquor in the crystal, and then promote the purity of m-dinitrobenzene crystal. If the temperature for cooling and crystallizing is too low, the isomer mixture is completely solidified, the purity of the crystallized product is low, and if the temperature for cooling and crystallizing is too high, the crystallized product is less and the energy consumption is high. If the cooling speed is too fast, the formed crystal has low compactness, and the crystallization mother liquor is easy to be entrained into the crystal in the process of forming the crystal, so that the purity of the product is low.

In the step (3), the process parameters of the secondary stepwise cooling treatment are that the temperature is gradually reduced from 90 ℃ to 80 ℃, the temperature is kept for 1-3 h during each cooling, and the cooling frequency is 3-5 times. The primary crystallization solid contains higher-purity m-dinitrobenzene, so that the temperature-reduced crystallization temperature is higher than that in the primary crystallization, and more m-dinitrobenzene can be precipitated by crystallization. And then, by controlling the cooling speed and the temperature of each cooling crystallization, the crystallization mother liquor can not be occluded in the crystals, and the purity of the m-dinitrobenzene crystals is further improved.

In the invention, the dinitrobenzene isomer mixture is obtained by carrying out dinitration reaction on benzene as a raw material, the intermediate dinitrobenzene content of the nitration product is 85 percent, and the ortho-dinitrobenzene content and the para-dinitrobenzene content are 15 percent, so that the m-dinitrobenzene is separated by taking the dinitrobenzene as the raw material, and the purity of the m-dinitrobenzene is further improved.

In the invention, in the step (2), the hot air temperature is 70 ℃, and the centrifugation time is 3-8 min, or 3-5 min or 5-8 min.

In the step (4), the hot air temperature is 85 ℃, and the centrifugation time is 3-8 min, or 3-5 min or 5-8 min. In the separation step carried out at a temperature higher than the temperature-lowering crystallization end point, the crystallization mother liquor adhering to the surface of the crystalline solid can be removed, and the crystalline solid containing the crystallization mother liquor can be separated from the crystalline solid to further improve the purity of the intermediate dinitrobenzene as the crystalline solid.

In the invention, a jacket is arranged in the crystallization kettle, steam is introduced into the jacket for heating, and hot water is introduced into the jacket for cooling.

In the invention, the temperature in the primary stepwise cooling treatment and the secondary stepwise cooling treatment refers to the temperature of hot water in the jacket.

In the invention, the secondary crystallization filtrate in the step (4) and dinitrobenzene isomer are added into a crystallization kettle, the operations from the step (1) to the step (4) are repeated, the secondary crystallization filtrate is recycled, and compared with the same crystallization mother liquor, the content of m-dinitrobenzene is high, so that the waste of the secondary crystallization mother liquor can not be caused when the m-dinitrobenzene is mixed with the dinitrobenzene isomer.

In the invention, the primary crystallization filtrate in the step (2) is used as a raw material for producing phenylenediamine by hydrogenation rectification, and the primary crystallization mother liquor contains high-concentration o-dinitrobenzene and p-dinitrobenzene which are used as the raw material of phenylenediamine for further advanced utilization.