CN103012161A - Cleaning and dehydrating method of toluenediamine - Google Patents

Abstract

The invention belongs to the technical field of chemical distillation, separation and dehydration, and relates to a method for cleaning and dehydrating toluenediamine. First, dehydration is carried out in a double-tower dehydration device, so that the crude TDA enters the lower part of the dehydration tower, and the gas phase at the top of the dehydration tower enters the top of the tower for condensation. The liquid-phase process water is continuously extracted from the side line of the dehydration tower, which is cooled by the waste water cooler and then enters the waste water storage tank for biochemical treatment of waste water; the bottom material of the dehydration tower enters the bottom reboiler through the bottom circulating pump The tower bottom material of dehydration tower enters the tower top of stripper, and the tower bottom of stripper feeds nitrogen, carries out nitrogen stripping in stripper, and the tower top gas phase of stripper enters the tower bottom of dehydration tower, steam The liquid phase at the bottom of the extraction column enters the subsequent vacuum distillation system; the process principle is reliable, the equipment structure is simple, the assembly and operation are convenient, the dehydration effect is good, the dehydration rate is high, resources and raw materials are saved, and the environment is friendly.

Description

A kind of cleaning dehydration method of toluenediamine

Technical field:

The invention belongs to the technical field of chemical distillation, separation and dehydration, and relates to a new process for distilling and removing water from a reaction mixture of toluenediamine, in particular to a method for cleaning and dehydrating toluenediamine.

Background technique:

Toluene diamine (TDA) is the main raw material for the production of toluene diisocyanate (TDI), which is widely used in the synthesis of polyurethane flexible foams, elastomers and coatings due to its excellent performance; currently, TDA is usually hydrogenated with dinitrotoluene The reaction is obtained, except that the target product TDA is contained in the reaction mixture, and by-products such as water and ortho-toluenediamine generated by the reaction, as well as high-boiling impurity tar and low-boiling impurity toluidine and cyclohexyl compounds are contained in the reaction mixture; the reaction mixture is usually passed through A series of rectification processes remove water, o-toluenediamine, and tar to obtain the final product TDA, so removing water from the TDA mixture is an important step in TDA rectification. In the prior art method of removing water from the reaction mixture, a large amount of water is removed by atmospheric distillation. Since the atmospheric boiling point of TDA is about 284°C, the atmospheric process can only reduce the water content. to 3000-7000ppm. The literature with Chinese patent number 200810018118.1 uses negative pressure to remove a small amount of water. Chinese patent ZL200580002158.1 directly performs vacuum distillation on crude TDA containing trace water. The former adds a new vacuum device to remove trace water. The latter rectifies TDA under vacuum conditions, and the existence of trace water will inevitably increase the load of vacuum equipment, and will also cause the water content in the product TDA to exceed the standard; Chinese patent CN101848885A adopts a two-stage vacuum double-tower dehydration process, which is suitable for TDA products Separation from water, but does not consider the removal method of low boiling point components in the mixture. Although the water content of TDA can be reduced to less than 200ppm or even lower, the COD content in the discharged wastewater is usually 3000mg/L or higher , which will inevitably increase the difficulty and cost of subsequent wastewater treatment.

Invention content:

The purpose of the present invention is to overcome the shortcoming that prior art exists, seek to design a kind of clean dehydration method of toluenediamine of new process, TDA in the reaction mixture is dehydrated, make the water content in the tower bottom TDA below 200ppm, to reduce the follow-up refining The vacuum load of the distillation system; at the same time, the waste water at the top of the dehydration tower is treated to reduce the content of low boiling point components and meet the requirements of subsequent biochemical treatment.

In order to achieve the above object, the present invention adopts a double-tower dehydration device and a process thereof composed of an atmospheric rectification tower and a nitrogen stripping tower to dehydrate TDA, first select and install a double-tower dehydration device, and dehydrate in the device, so that The crude TDA mixture enters the lower part of the dehydration tower through the TDA inlet, the top gas phase of the dehydration tower enters the top condenser for condensation, the condensed liquid phase enters the reflux tank, and the low boiling point components enter the peripheral exhaust gas destruction system along with the non-condensable gas. An ordinary glass liquid level gauge is installed on the reflux tank, and total reflux is usually used to facilitate the enrichment of low boiling point components. Collected as a by-product; the side line part of the dehydration tower continuously extracts liquid-phase process water, which is cooled by the waste water cooler and enters the waste water storage tank for the next step of waste water biochemical treatment; the bottom material of the dehydration tower enters the bottom of the tower through the bottom circulating pump Reboiler, a part returns to the dehydration tower for vaporization, and the other part enters the top of the stripping tower as the bottom discharge; the bottom temperature of the dehydration tower is 190-220°C, preferably 200-210°C, the bottom of the dehydration tower The water content is 4000-10000ppm, preferably 5000-8000ppm; the top reflux temperature of the dehydration tower is 40-80°C, preferably 50-70°C; the number of dehydration trays arranged up and down in the dehydration tower is 8-25 , preferably 12-20 pieces; the side line extraction position is at the 3rd-8th plate from top to bottom, preferably the 4th-6th plate; the bottom material of the dehydration tower enters the top of the stripping tower, and the stripping The bottom of the tower is fed with heated nitrogen gas at a temperature higher than 100°C from the nitrogen tank, and nitrogen stripping is carried out in the stripping tower. The gas phase at the top of the stripping tower enters the bottom of the dehydration tower, and the bottom liquid of the stripping tower The phase enters the subsequent vacuum distillation system; the ratio of nitrogen flow rate to feed water mass is 2-6.

The main structure of the double-tower dehydration device involved in the present invention includes a dehydration tower, a tower top condenser, a reflux tank, a tower bottom circulation pump, a tower bottom reboiler, a stripper, a waste water cooler, a tail gas destruction system, and a light component storage system. tank, waste water storage tank, nitrogen tank, vacuum rectification system, TDA inlet, dehydration tray and stripping tray; the bottom of the dehydration tower is connected with the tower bottom circulation pump and the tower bottom reboiler through pipelines respectively to form a circulation loop , the connecting pipe between the bottom circulating pump and the bottom reboiler is connected with a pipe to communicate with the top of the stripping tower; There is a TDA inlet for crude TDA to enter the dehydration tower; 8-25 dehydration trays are arranged evenly distributed up and down in the inner cavity of the dehydration tower; the upper side of the middle part of the dehydration tower is equipped with a pipeline-connected waste water cooler and waste water Storage tank; the top and top side of the dehydration tower are respectively connected with the top condenser and the reflux tank through pipes to form a loop structure. The tower top condenser is connected with the tail gas destruction system, and the reflux tank is connected with the light component storage tank; conventional structure The bottom of the stripper is communicated with the vacuum rectification system, and the side of the bottom is communicated with the nitrogen tank.

Compared with the prior art, the present invention adopts a double-tower dehydration process, conventional rectification in the front tower removes a large amount of water, nitrogen stripping in the rear tower removes trace water, and returns the gas phase carrying trace water to the front tower to ensure that the rear tower The water content in the TDA at the bottom of the tower is low, which reduces the subsequent vacuum load; the presence of nitrogen is more conducive to the removal of low-boiling components at the top of the front tower, ensuring that there are lower light component impurities in the side stream wastewater in the tower, The COD content in the waste water is reduced; since the process water is extracted from the side line, the low boilers are enriched and extracted at the top of the tower, realizing the continuous separation of water and low boilers through the theoretical plate between the side line and the top of the tower, ensuring that the side line The lower COD in the process water is recovered, and the low boiling point substances are recovered; the process principle is reliable, the equipment structure is simple, the assembly and operation are convenient, the dehydration effect is good, the dehydration rate is high, resources and raw materials are saved, and the environment is friendly.

Description of drawings:

Fig. 1 is a schematic diagram of the structure and principle of the double-tower dehydration device of the present invention.

Detailed ways:

Further description will be given below through the embodiments and in conjunction with the accompanying drawings.

In this embodiment, a double-tower dehydration device composed of an atmospheric rectification tower and a nitrogen stripping tower and its process are used to dehydrate TDA. The TDA inlet 13 enters the lower part of the dehydration tower 1, the top gas phase of the dehydration tower 1 enters the tower top condenser 2 for condensation, and the condensed liquid phase enters the reflux tank 3, and the low boiling point components enter the tail gas destruction system of the peripheral equipment along with the non-condensable gas 8. An ordinary glass liquid level gauge is installed on the reflux tank 3, and total reflux is usually used to facilitate the enrichment of low boiling point components. The liquid phase is collected in the light components storage tank 9 as a by-product; the side line part of the dehydration tower 1 continuously extracts the liquid phase process water, and after being cooled by the waste water cooler 7, it enters the waste water storage tank 10 and performs the next step of waste water biochemical treatment; The bottom material of the dehydration tower 1 enters the bottom reboiler 5 through the tower bottom circulation pump 4, a part returns to the dehydration tower 1 for vaporization, and the other part enters the top of the stripping tower 6 as the bottom discharge; the dehydration tower 1 The temperature at the bottom of the tower is 190-220°C, preferably 200-210°C, and the water content at the bottom of the dehydration tower 1 is 4000-10000ppm, preferably 5000-8000ppm; the top reflux temperature of the dehydration tower 1 is 40-80°C, preferably 50- 70°C; the number of dehydration trays 14 arranged up and down in the dehydration tower 1 is 8-25, preferably 12-20; the side line extraction position is at the 3rd-8th plate from top to bottom, preferably At the 4th to 6th plates; the bottom material of the dehydration tower 1 enters the top of the stripper 6, and the bottom of the stripper 6 is fed with nitrogen gas with a temperature higher than 100°C after being heated by the nitrogen tank 11. Nitrogen stripping is carried out in tower 6, and the tower top gas phase of stripping tower 6 enters the tower bottom of dehydration tower 1, and the tower bottom liquid phase of stripping tower 6 enters follow-up vacuum rectification system 12; The nitrogen flow rate and feed water mass ratio are 2-6.

The main structure of the double-tower dehydration device involved in this embodiment includes a dehydration tower 1, a top condenser 2, a reflux tank 3, a bottom circulation pump 4, a bottom reboiler 5, a stripping tower 6, a waste water cooler 7, Exhaust gas destruction system 8, light component storage tank 9, waste water storage tank 10, nitrogen tank 11, vacuum rectification system 12, TDA inlet 13, dehydration tray 14 and stripping tray 15; The pipeline communicates with the tower bottom circulation pump 4 and the tower bottom reboiler 5 and forms a circulation loop, and the connecting pipeline between the tower bottom circulation pump 4 and the tower bottom reboiler 5 is connected with a pipeline to communicate with the top of the stripping tower 6; the dehydration tower The bottom side of 1 is connected with the top of stripping tower 6 through pipelines, and a TDA inlet 13 is formed on the upper side of the bottom of dehydration tower 1 for crude TDA to enter dehydration tower 1; the inner cavity of dehydration tower 1 is evenly distributed and arranged up and down 8-25 dehydration trays 14 are respectively formed; the upper side of the middle part of the dehydration tower 1 is formed with a pipe-connected waste water cooler 7 and a waste water storage tank 10; Condenser 2 and reflux tank 3 are communicated to form a loop structure, tower top condenser 2 is communicated with tail gas destruction system 8, reflux tank 3 is communicated with light component storage tank 9; The system 12 communicates with the nitrogen tank 11 on the bottom side.

Example;

In this embodiment, the flow rate of the crude TDA mixture is selected to be 1000 kg/h, the condensation temperature at the top of the dehydration tower 1 is 50° C., the temperature at the bottom of the tower is 190° C., and nitrogen gas with a flow rate of 150° C. at 8 kg/h is introduced into the stripping tower 6; The diameter of the dehydration tower 1 is 400mm, the quantity of the dehydration tray 14 is 20, the position of the TDA inlet 13 is at the 17th tray, and the side line extraction position is the 4th; the diameter of the stripper 6 is 250mm, and the stripper The number of trays 15 is 10; after the continuous and stable operation of the double-tower dehydration device, the water content of the outlet of the dehydration tower 1 is between 4000-4500ppm, and the water content in the TDA after stripping is stable at 110-180ppm, and the side line is extracted The COD value of the wastewater is 600-900 mg/L. After 24 hours of continuous operation, 10.5 kg of low-boiling point organic matter is extracted from the reflux tank; the extraction position of the side line described in this embodiment is the extraction water collection point.

Claims (2)

1. a clean dehydration method of toluenediamine is characterized in that the double tower dehydration device and technology thereof that adopt atmospheric rectification tower and nitrogen stripping tower to form are combined to carry out dehydration to TDA, first select and install double tower dehydration device, And carry out dehydration in the device, so that the crude TDA mixture enters the lower part of the dehydration tower through the TDA inlet, the gas phase at the top of the dehydration tower enters the top condenser for condensation, and the condensed liquid phase enters the reflux tank, and the low boiling point components follow the non-condensable gas Entering the tail gas destruction system of the peripheral equipment, the reflux tank is equipped with an ordinary glass liquid level gauge, and the total reflux is usually used to facilitate the enrichment of low boiling point components. The liquid phase above the interface is extracted and collected as a by-product; the liquid phase process water is continuously extracted from the side line of the dehydration tower, and after being cooled by the wastewater cooler, it enters the wastewater storage tank and undergoes the next step of wastewater biochemical treatment; the bottom material of the dehydration tower It enters the reboiler at the bottom of the tower through the circulation pump at the bottom of the tower, and part of it returns to the dehydration tower for vaporization, and the other part enters the top of the stripping tower as the discharge from the bottom of the tower; the bottom temperature of the dehydration tower is 190-220°C, and the The water content at the bottom of the tower is 4000-10000ppm; the top reflux temperature of the dehydration tower is 40-80°C; the number of dehydration trays arranged up and down in the dehydration tower is 8-25; the side line extraction position is from top to bottom The bottom of the dehydration tower enters the top of the stripping tower, and the bottom of the stripping tower is fed with nitrogen gas with a temperature higher than 100 ° C from the nitrogen tank. Nitrogen stripping is carried out, the gas phase at the top of the stripping tower enters the bottom of the dehydration tower, and the liquid phase at the bottom of the stripping tower enters the subsequent vacuum rectification system; the mass ratio of nitrogen flow to feed water is 2-6. 2. The cleaning and dehydration method of toluenediamine according to claim 1 is characterized in that the main structure of the double tower dehydration device involved comprises a dehydration tower, a tower top condenser, a reflux tank, a bottom circulation pump, a bottom reboiler device, stripper, waste water cooler, tail gas destruction system, light component storage tank, waste water storage tank, nitrogen tank, vacuum rectification system, TDA inlet, dehydration tray and stripping tray; the bottom of the dehydration tower is respectively The pipeline is connected with the tower bottom circulation pump and the tower bottom reboiler to form a circulation loop. The connection pipeline between the tower bottom circulation pump and the tower bottom reboiler is connected with a pipeline to communicate with the top of the stripping tower; on the bottom side of the dehydration tower It is connected with the top of the stripping tower through the pipe, and there is a TDA inlet on the upper side of the bottom of the dehydration tower for crude TDA to enter the dehydration tower; the inner chamber of the dehydration tower is evenly distributed and arranged up and down, and 8-25 dehydration trays are respectively made. ; The upper side of the middle part of the dehydration tower is equipped with a pipeline-connected waste water cooler and a waste water storage tank; the top and top side of the dehydration tower are respectively connected with the tower top condenser and the reflux tank through pipes to form a loop structure, and the tower top condenser It is connected with the tail gas destruction system, and the reflux tank is connected with the light component storage tank; the bottom end of the stripper with conventional structure is connected with the vacuum rectification system, and the bottom side is connected with the nitrogen tank.

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