CN115819245A - A Novel Coupling Process Method for Mononitrotoluene Distillation and Melt Crystallization - Google Patents

Abstract

The present invention is a novel coupled process method for mononitrotoluene rectification and melt crystallization, comprising the following steps: (1) the mononitrotoluene crude product from the nitration process enters the rectification tower system; (2) the rectification tower top The ortho-nitrate raw material mainly containing ortho-nitrate and meta-nitrate is mined, and the crude crystallization raw material of 88.00%-99.50% para-nitrate is extracted from the tower kettle; (3) the crude para-nitrate crystallization raw material is transported to the crystallizer, crystallized, sweated, melted (4) After the crystallization, the unsolidified mother liquor and sweat produced by sweating are all returned to the rectification system, mixed with the crude product of mononitrotoluene, and then enter the rectification tower system. The invention combines rectification and crystallization process, reduces energy consumption while shortening the production cycle, and optimizes the crystallization and sweating process to further reduce energy consumption and increase crystal yield.

Description

A Novel Coupling Process Method for Mononitrotoluene Distillation and Melt Crystallization

technical field

The invention relates to the technical field of chemical production, in particular to a novel coupled process method for mononitrotoluene rectification and melt crystallization.

Background technique

Mononitrotoluene includes three isomers of o-nitrotoluene (commonly known as o-nitrotoluene), m-nitrotoluene (commonly known as m-nitrotoluene), and p-nitrotoluene (commonly known as p-nitrotoluene), which are used in medicine, pesticides, dyes, Rubber additives, new materials and other industries have a wide range of applications. Mononitrotoluene needs to be separated and purified before use. Rectification is a process widely used in the separation of organic matter, but the traditional method (negative pressure rectification separation) is difficult to separate and requires a rectification tower with high separation efficiency. To obtain products that meet market requirements through high reflux ratio, the quality is unstable and the energy consumption is large. Therefore, after rectification, the melt crystallization process is generally used to supplement, reduce the difficulty of separation, improve product quality, and can make up for the negative pressure rectification method to the greatest extent. defects in workmanship and operation. However, the separate crystallization process and intermittent production have defects such as long production cycle, low production capacity, and complicated equipment.

The existing Chinese patent document with the publication number CN102126958B records "a device and method for preparing high-purity m-(p) nitrotoluene coupled with rectification and crystallization", which is prepared by a separation method coupled with a vacuum rectification tower and a crystallizer High-purity m-(p)nitrotoluene can easily obtain p-nitrotoluene and m-nitrotoluene with a purity content of more than 99.9%, and the mother liquor is recycled with almost no loss. However, in actual production, although the purity of the separated product is as high as 99.9%, the crystallization efficiency is low, and the crystal yield is only about 75%, that is to say, about 25% will flow back with the mother liquor and the sweat produced by sweating. In the rectification tower, this will produce a large amount of energy consumption for the rectification and crystallization process, and the energy consumption is relatively large.

Contents of the invention

In order to solve the technical problems of low crystallization efficiency and high energy consumption in the prior art, the present invention provides a novel coupled process method for mononitrotoluene rectification and melt crystallization. The specific technical scheme of the present invention is as follows.

The present invention is a novel coupled process method for mononitrotoluene rectification and melt crystallization, comprising the following steps:

(1) The mononitrotoluene crude product from the nitration process enters the rectifying tower system;

(2) The ortho-nitrate raw material mainly containing ortho-nitrate and meta-nitrate is mined from the top of the rectifying tower, and the crude crystalline raw material of 88.00%～99.50% para-nitrate is extracted from the tower still;

(3) The crude paranitrate crystallization raw material is transported to the crystallizer, and the high-purity paranitrate finished product is produced through process control such as crystallization, sweating, and melting;

(4) After the crystallization is completed, the unsolidified mother liquor and the sweat produced by sweating are all returned to the rectification system, mixed with the mononitrotoluene crude product and then entered into the rectification tower system;

Wherein, in the step (3), there are tubes inside the crystallizer, and the process of crystallization, sweating, and melting is indirectly controlled by controlling the temperature of the heat exchange medium, and the heat exchange medium is kept circulating by using a large-flow, low-lift circulation pump, and the circulation pump A heat exchanger is installed at the outlet to exchange heat with the heat exchange medium. The crystallization cooling process is operated by gradient cooling, constant temperature, and then rapid cooling. The sweating process is operated by rapid heating, constant temperature, gradient heating, and heat preservation.

As a further technical solution, in the crystallization process in the step (3), the cooling rate of the heat exchange medium is controlled to not exceed 1° C./h.

As a further technical solution, in the step (3), when crystallization occurs in the crystallizer, keep the temperature constant for 2h-4h, and then quickly cool down the heat exchange medium to (30-35)°C after constant temperature, and discharge the unsolidified material Line e returns to the rectification system.

As a further technical solution, when crystallization occurs in the crystallizer in the step (3), keep the temperature constant for 3 hours.

As a further technical solution, the sweating process in the step (3) heats up the heat exchanger 4, indirectly heats the heat exchange medium of the crystallizer, and rapidly raises the temperature of the crystallizer to a constant temperature for 2 hours to 4 hours, and then controls the temperature exchange The heating rate of the heat medium does not exceed 1°C/h, and the temperature is raised to 51°C for 2 hours.

As a further technical solution, the temperature is kept constant for 3 hours during the sweating process in the step (3).

The beneficial effect of the present invention is that the present invention combines the rectification and crystallization process through the new coupling process of mononitrotoluene rectification and melt crystallization, which reduces energy consumption while shortening the production cycle. The crystallizer crystallization of the present invention, The process of sweating and melting is indirect heat exchange by controlling the temperature of the heat exchange medium. The crystallization cooling process is operated in the manner of gradient cooling, constant temperature, and then rapid cooling. rate, further reducing energy consumption.

Description of drawings

Fig. 1 is the used device system structural representation of the present invention;

In the figure: 1-rectification tower; 2-delivery pump; 3-crystallizer; 4-heat exchanger; 5-circulation pump; a-mononitrotoluene raw material feed line; Conveying pipeline; d-conveying pipeline for finished nitrate; e-discharging pipeline.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. The content disclosed in the present invention can be improved from the materials, methods and reaction conditions at the same time, and all these improvements should fall within the conception and protection scope of the present invention. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

As shown in Fig. 1, a kind of device system that the present invention is used for the novel coupling process method of mononitrotoluene rectification and melting crystallization comprises 5 parts: rectification column 1, conveying pump 2, crystallizer 3, changing Heater 4 and circulation pump 5, described rectification column 1 is connected with mononitrotoluene crude product feed line a in the middle, and transfer pump 2 is arranged on the pipeline of the tower kettle, and a part of the kettle is refluxed, and a part is connected to the crystallizer 3 inlet , the outlet of the crystallizer 3 is provided with two pipelines, one is connected with the mononitrotoluene crude product feed pipeline a, and the other is used to transport the finished product of nitrotoluene, the internal heat exchange tube of the crystallizer 3 is equipped with a circulation pipeline, and a circulation pump is installed on the pipeline 5. Heat exchanger 4 is installed on the outlet pipeline of circulation pump 5 .

The present invention is a novel coupled process method for mononitrotoluene rectification and melt crystallization, comprising the following steps:

(1) The mononitrotoluene crude product from the nitration process enters the rectifying tower system;

(2) The ortho-nitrate raw material mainly containing ortho-nitrate and meta-nitrate is extracted from the top of the rectifying tower, and the crystallization raw material of 88.00%～99.50% para-nitrate is extracted from the tower still;

(3) The crude paranitrate crystallization raw material is transported to the crystallizer, and the high-purity paranitrate finished product is produced through process control such as crystallization, sweating, and melting; The process involves indirect heat exchange by controlling the temperature of the heat exchange medium. A large-flow, low-lift circulation pump is used to maintain circulation of the heat exchange medium. A heat exchanger is installed at the outlet of the circulation pump to exchange heat for the heat exchange medium. The crystallization cooling process uses gradient cooling, constant temperature, Then operate in the way of rapid cooling, and the sweating process is operated in the way of rapid heating, constant temperature, gradient heating, and heat preservation;

(4) After the crystallization is completed, the unsolidified mother liquor and the sweat produced by sweating are all returned to the rectification system, mixed with the crude mononitrotoluene, and then entered into the rectification tower system.

Further illustrate below in conjunction with specific embodiment:

Example 1:

The rectification tower 1 transports the mononitrotoluene crude product to the rectification tower through the mononitrotoluene raw material feed line a, and the tower top is taken out and enters the next process through the ortho-nitrate raw material pipeline b, and the para-nitrotoluene content is controlled in the tower reactor It is 88.00%-99.50% crude paranitrate crystallization raw material, and the crystallization raw material enters the crystallizer 3 through the delivery pump 2 and the delivery pipeline c.

After the crystallizer 3 is full, the temperature of the heat exchanger 4 is lowered to indirectly cool the heat exchange medium of the crystallizer, and the cooling rate of the heat exchange medium is controlled to not exceed 1° C./h. When crystallization occurs in the crystallizer, keep the temperature constant for 2 hours, then quickly cool down the heat exchange medium to (30-35)°C, and return the unsolidified material to the rectification system through the discharge pipeline e. Then heat the heat exchanger 4, indirectly heat the heat exchange medium of the crystallizer, rapidly raise the temperature of the crystallizer to a constant temperature, and keep the temperature constant for 2 hours, then control the temperature increase rate of the heat exchange medium to not exceed 1°C/h, and raise the temperature to 51°C for heat preservation 2h. During the period, the sweat continues to return to the rectification system through the discharge pipeline e, and then melts the material in the crystallizer, and transports the finished nitrate product through the finished nitrate delivery pipeline.

After detection and analysis, in Example 1, the product purity is 99.9%, and the crystal yield is 90.5%. Compared with the prior art, the product purity is consistent with 99.9%, and the crystal yield is greater than 75% of the prior art.

Example 2:

The rectification tower 1 transports the mononitrotoluene crude product to the rectification tower through the mononitrotoluene raw material feed line a, and the tower top is taken out and enters the next process through the ortho-nitrate raw material pipeline b, and the para-nitrotoluene content is controlled in the tower reactor It is 88.00%-99.50% crude paranitrate crystallization raw material, and the crystallization raw material enters the crystallizer 3 through the delivery pump 2 and the delivery pipeline c.

After the crystallizer 3 is full, the temperature of the heat exchanger 4 is lowered to indirectly cool the heat exchange medium of the crystallizer, and the cooling rate of the heat exchange medium is controlled to not exceed 1° C./h. When crystallization occurs in the crystallizer, keep the temperature constant for 3 hours, then quickly cool down the heat exchange medium to (30-35)°C, and return the unsolidified material to the rectification system through the discharge pipeline e. Then heat the heat exchanger 4, indirectly heat the heat exchange medium of the crystallizer, and rapidly raise the temperature of the crystallizer to a constant temperature for 3 hours, then control the temperature increase rate of the heat exchange medium to not exceed 1°C/h, and raise the temperature to 51°C for heat preservation 2h. During the period, the sweat continues to return to the rectification system through the discharge pipeline e, and then melts the material in the crystallizer, and transports the finished nitrate product through the finished nitrate delivery pipeline.

After detection and analysis, in Example 2, the purity is 99.9%, and the crystal yield is 93%. Compared with the prior art, the product purity is consistent with 99.9%, and the crystal yield is greater than 75% of the prior art.

Example 3:

The rectification tower 1 transports the mononitrotoluene crude product to the rectification tower through the mononitrotoluene raw material feed line a, and the tower top is taken out and enters the next process through the ortho-nitrate raw material pipeline b, and the para-nitrotoluene content is controlled in the tower reactor It is 88.00%-99.50% crude paranitrate crystallization raw material, and the crystallization raw material enters the crystallizer 3 through the delivery pump 2 and the delivery pipeline c.

After the crystallizer 3 is full, the temperature of the heat exchanger 4 is lowered to indirectly cool the heat exchange medium of the crystallizer, and the cooling rate of the heat exchange medium is controlled to not exceed 1° C./h. When crystallization occurs in the crystallizer, keep the temperature constant for 4 hours, then quickly cool down the heat exchange medium to (30-35)°C, and return the unsolidified material to the rectification system through the discharge pipeline e. Then heat the heat exchanger 4, indirectly heat the heat exchange medium of the crystallizer, rapidly raise the temperature of the crystallizer to a constant temperature for 4 hours, then control the temperature rise rate of the heat exchange medium to no more than 1°C/h, and raise the temperature to 51°C for heat preservation 2h. During the period, the sweat continues to return to the rectification system through the discharge pipeline e, and then melts the material in the crystallizer, and transports the finished nitrate product through the finished nitrate delivery pipeline.

After detection and analysis, in Example 3, the purity is 99.9%, and the crystal yield is 92%. Compared with the prior art, the product purity is consistent with 99.9%, and the crystal yield is greater than 75% of the prior art.

It can be seen from the above-mentioned new coupling process method and examples that the process of crystallization, sweating and melting of the crystallizer of the present invention is controlled by controlling the temperature of the heat exchange medium for indirect heat exchange. The operation of rapid heating, constant temperature, gradient heating and heat preservation has improved the crystal yield, which is as high as 90%, which is greatly improved compared with the crystal yield of 75% in the prior art. While reducing the circulation of raw materials, Further reduce energy consumption.

The preferred specific implementations and examples of the present invention have been described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned implementations and examples. Various changes or equivalent replacements are made under the premise of the inventive concept. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of the application belong to the protection of the present invention In the range.

Claims (6)

1. A novel coupling process method for rectifying mononitrotoluene and melting crystallization comprises the following steps:

(1) Introducing a mononitrotoluene crude product from a nitration process into a rectifying tower system;

(2) The top of the rectifying tower collects the raw material of o-nitre mainly containing o-nitre and m-nitre, and the bottom of the rectifying tower collects the raw material of crude crystallization of 88.00-99.50% of p-nitre;

(3) Conveying the crude paranitre crystallization raw material to a crystallizer, and controlling the processes of crystallization, sweating, melting and the like to produce a high-purity paranitre finished product;

(4) After crystallization is finished, the unsolidified mother liquor and sweat generated by sweating are all returned to the rectification system, and are mixed with the crude mononitrotoluene and then enter a rectification tower system;

the method is characterized in that: the crystallizer in the step (3) is internally provided with a tube array, the crystallization, sweating and melting processes are indirectly subjected to heat exchange by controlling the temperature of a heat exchange medium, a large-flow and low-lift circulating pump is used for keeping circulation of the heat exchange medium, a heat exchanger is arranged at the outlet of the circulating pump for exchanging heat with the heat exchange medium, the crystallization and cooling process is operated in a gradient cooling, constant temperature and rapid cooling manner, and the sweating process is operated in a rapid heating, constant temperature, gradient heating and heat preservation manner.

2. The novel coupled process method for rectification and melt crystallization of mononitrotoluene according to claim 1, characterized in that: and (4) controlling the cooling rate of the heat exchange medium to be not more than 1 ℃/h in the crystallization process in the step (3).

3. The novel coupled process method for rectification and melt crystallization of mononitrotoluene according to claim 2, characterized in that: and (3) when crystals are separated out from the crystallizer in the step (3), keeping the temperature for 2-4 h, quickly cooling the heat exchange medium to (30-35) DEG C after keeping the temperature constant, and returning the non-solidified material to the rectification system through a discharge pipeline e.

4. The novel coupled process method for rectification and melt crystallization of mononitrotoluene according to claim 3, characterized in that: and (4) keeping the temperature for 3h when crystals are separated out from the crystallizer in the step (3).

5. The novel coupled process method for rectification and melt crystallization of mononitrotoluene according to claim 3, characterized in that: and (3) heating the heat exchanger 4 in the sweating process in the step (3), indirectly heating the heat exchange medium of the crystallizer, rapidly heating the temperature of the crystallizer to a constant temperature for 2-4 h, controlling the heating rate of the heat exchange medium not to exceed 1 ℃/h, and heating to 51 ℃ for 2h.

6. The novel coupled process method for rectification and melt crystallization of mononitrotoluene according to claim 5, characterized in that: and (4) keeping the temperature for 3 hours in the sweating process in the step (3).

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