CN111574423A - Recovery method of NMP solvent in the process of producing acetylene by partial oxidation of natural gas - Google Patents

Abstract

The invention belongs to the technical field of separation by making a thin layer of liquid contact a heated surface, and particularly relates to a method for recovering NMP solvent in a process for producing acetylene by partial oxidation of natural gas. The method comprises the following steps: heating the NMP solvent to 80-99° C. through a preheater, and then placing the NMP solvent in a thin-film evaporator to realize the separation of the gas-phase NMP solvent and the solid retort residue. The method can realize the recovery of NMP solvent containing easy-to-crystallize and heat-sensitive components, and improve the recovery rate; it can avoid the blockage caused by crystallization and coke formation; it can effectively control the problem of excessive VOCs scattered discharge on the production site, without causing Environmental pollution and occupational health hazards; and no manual slag cleaning is required, which improves the automation level of the NMP solvent recovery device.

Description

Recovery method of NMP solvent in the process of producing acetylene by partial oxidation of natural gas

technical field

The invention belongs to the technical field of separation by making a thin layer of liquid contact a heated surface by evaporation, and in particular relates to a method for recovering NMP solvent in a process for producing acetylene by partial oxidation of natural gas.

Background technique

Acetylene is a very important organic chemical raw material, widely used in metal processing, welding, cutting and other fields, as well as ethylene, vinyl chloride, trichloroethylene, vinyl acetate, acrylonitrile, polyacrylonitrile, 1,4-butanediol Preparation of other chemical products ("A discussion on the new progress of acetylene in organic synthetic chemistry", Bu Zhaosheng, China Chemical Industry Trade, Vol. 7, No. 22, 2015, p. 103, published on December 31, 2015; "Hot Research progress of plasma cracking of low-carbon alkanes to acetylene”, Su Baogen et al., Chemical Reaction Engineering and Technology, 2013, Vol. 29, No. 3, pp. 230-236, published on June 30, 2013). The preparation methods of acetylene mainly include non-catalytic partial oxidation method, electric arc method and plasma method, among which the arc method has been eliminated due to high energy consumption, and the plasma method is still in the experimental stage ("Research Status and Thinking of Natural Gas Acetylene Technology", An Jie, Vinyl Communication, Vol. 33, No. 2, 2013, pp. 15-20, published on December 31, 2013), and high power consumption and strict equipment requirements, it is difficult to popularize and apply so far. The non-catalytic partial oxidation method is The main method of acetylene production.

In the prior art, the main structure and main production process of the production device used in the process of producing acetylene by non-catalytic partial oxidation of natural gas are as follows: the natural gas pipeline and the oxygen pipeline are respectively connected to the gas heater first, and the natural gas and the oxygen are respectively connected first. After preheating to 600-650 ℃, first connect the natural gas to the acetylene reaction furnace. When the temperature of the natural gas reaches the set value, open the auxiliary oxygen regulating valve of the reaction furnace, and operate the ignition gun to ignite; Oxygen is injected, and the reaction gas composed of natural gas and oxygen undergoes partial oxidation reaction in the reaction chamber of the acetylene furnace. After a few milliseconds of reaction, it is cooled to end the reaction, and the hydrocarbon is partially oxidized and cracked into groups including acetylene, carbon monoxide, carbon dioxide, hydrogen and carbon black. The split cracked gas mixture; the cracked gas mixture from the acetylene reaction furnace passes through the lower section of the cooling tower, the electrostatic precipitator, and the upper section of the cooling tower, further cools and washes the carbon black in it, and then enters the concentration system through the compressor to obtain the product Acetylene and syngas. The water containing carbon black discharged from the bottom of the acetylene furnace, cooling tower and electrostatic precipitator enters the collection pipe, and then passes through a primary sieve plate degassing tank to flash off a small amount of gas, and then enters the open carbon black The water tank is used to separate carbon black and water, and part of the obtained clean water is returned to the acetylene furnace as quenching water, and part of the clean water is sent to the cooling tower for cooling and then sent to the cooling tower, electrostatic precipitator and concentration device for spray cooling water (such as shown in Figure 1).

In the process of partial oxidation of natural gas to acetylene, N-methylpyrrolidone (NMP for short) solvent is widely used in the enrichment process of its cracked gas. Under the condition of absolute pressure of 0.8-1.0MPa, the cracked gas is in countercurrent contact with the NMP sprayed in stages, wherein the easily soluble components such as higher alkynes and acetylenes are absorbed by NMP. The carrier gas NMP uses a constant pressure column and a vacuum column to analyze the acetylene components and higher acetylene components respectively. During the process of NMP absorption and analysis, some benzene, naphthalene, advanced alkynes and other easily crystallized and easily polymerized components continuously accumulate in NMP. On the one hand, it affects the absorption capacity of the circulating solvent. Lines and packing. In the prior art, part of the circulating solvent is taken out to be preliminarily concentrated in a continuous flash tank, and the NMP solvent at the bottom is separated by a suspension separator to obtain a concentrated NMP solvent containing a polymer. The concentrated NMP solvent enters the solvent storage tank, and then is added to the dry distillation tank in batches from the storage tank, and clean recovered NMP solvent is obtained after dry distillation. The heavy fraction dry distillation residue is manually taken out from the dry distillation tank and transferred to the storage tank. The dry distillation residue contains a small amount of NMP solvent, and the NMP solvent in the dry distillation residue needs to be recovered, otherwise a large amount of NMP solvent will be lost.

The existing batch dry distillation system (as shown in FIG. 2 ) has low thermal efficiency and long distillation time. Because the retort tank is heated by coils, the thermal efficiency of the retort equipment is about 55%, the thermal efficiency is relatively low, the distillation time is as long as 22 hours per tank, and the operation period is long. The heating temperature of the tank bottom and tank wall cannot be accurately controlled, the local heating is uneven, and the dry distillation slag is easy to coke into a block, which requires manual slag cleaning. Manual slag cleaning is not only labor-intensive, but also emits a large amount of foul VOCs, which pollutes the environment and easily causes serious occupational health hazards. In addition, the dry distillation residue contains about 29% (mass content) of NMP solvent, and it is necessary to recycle the NMP solvent in the dry distillation residue, otherwise it will cause a large loss of NMP solvent. The Chinese patent document with publication number CN1044474780A discloses a method for continuous recovery of NMP solvent of a polyphenylene sulfide production device. The concentrated still liquid is forcedly circulated by a centrifugal pump, and part of the solid product is dehydrated by a centrifuge and then discharged out of the boundary area. The supernatant mother liquor is pumped into the top of the rectification tower C-102 to separate p-dichlorobenzene, and the tower still liquid enters the rectification tower. C-103, after the NMP solvent evaporated at the top of the tower exchanges heat with the feed liquid, it is further cooled and extracted, and the chlorinated salt solution of the NMP solvent is extracted from the bottom of the tower through a forced circulation pump. The method makes the separation of the components in the raw material more refined, the separation purity of the product is higher, and the operability is better. However, for NMP materials containing a large number of heat-sensitive components and easy-to-crystallize components, only part of the NMP solvent can be separated. As the feed port of the rectifying tower is below, the amount of NMP gradually decreases, and the solubility of substances with low relative volatility is relatively increasing. This will make it easier for crystallizers to precipitate out. With the increase of the high polymer concentration and the increase of the bottom temperature, the high polymer is also easier to polymerize, and some of these polymers will adhere to the inner wall of the column and the surface of the packing, causing the polymer to block the packing and pipeline. Acetylene concentration has been confirmed in the production and operation practice; while another part of the crystals and polymers are discharged through the bottom of the column as a suspended liquid, because it contains a large amount of NMP solvent, the NMP recovery rate is obviously low, and will result in greater follow-up disposal. cost. Advanced acetylene is the main cause of pipeline blockage in the acetylene concentration system of the natural gas to acetylene unit. In the presence of unsaturated bonds of components, free radical polymerization is easy to occur under a certain temperature and pressure and the presence of trace oxygen, peroxides, etc. in the system, and the generated free radicals undergo the process of chain initiation, chain growth and chain termination. Macromolecular polymers are generated, and a large amount of polymers are easily deposited and polluted in the advanced acetylene pipeline, blocking the equipment pipeline, thus affecting the safe, stable and long-term operation of the enrichment system ("The cause of blockage of the advanced acetylene pipeline of the acetylene enrichment device is shallow. Analysis”, Xie Quanbing, Natural Gas Chemical Industry, Vol. 36, 2011, pp. 34-37, published on December 31, 2011).

For NMP solvents containing heat-sensitive components, how to realize automatic continuous production during the treatment process, how to improve the thermal efficiency of the dry distillation process, how to prevent large coking of residues and realize automatic slag discharge, for the performance of the solvent recovery system of the natural gas to acetylene concentration device. Energy consumption, automation upgrades, and the disposal of industrial solid waste are of great significance.

SUMMARY OF THE INVENTION

In view of this, the object of the present invention is to provide a kind of recovery method of NMP solvent, this method can realize the recovery of the NMP solvent containing easy crystallization, heat-sensitive component, improve the recovery rate, and can avoid crystallization, coke formation. At the same time, it effectively solves the heavy manual labor caused by manual slag cleaning and the excessive VOCs emission and occupational health hazards caused by this.

For achieving the above object, the technical scheme of the present invention is:

The method for recovering NMP solvent includes the following steps: heating the NMP solvent to 80-99° C. through a preheater, and then placing it in a thin-film evaporator for evaporative separation.

The method can realize the recovery of the NMP solvent containing easy-to-crystallize and heat-sensitive components, and improves the recovery rate.

The method can avoid the clogging problems caused by crystallization and coking, realize automatic slag discharge, and improve the automation level of the dry distillation device.

The method does not require manual slag cleaning, and will not cause environmental pollution and occupational health hazards.

In order to further improve the recovery rate of NMP solvent, the preheater is a tubular preheater, and the inner wall of the preheater is polished.

In order to further improve the recovery rate of NMP solvent, the heating medium is steam or heat transfer oil.

In order to further improve the recovery rate of NMP solvent, a flow regulating valve 10 is provided on the liquid phase inlet line of the preheater 1 .

In order to further improve the recovery rate of NMP solvent, the thin-film evaporator is a wiped-blade thin-film evaporator.

In order to further improve the recovery rate of NMP solvent, the scraper of the thin film evaporator is a movable scraper.

In order to further improve the recovery rate of NMP solvent, the temperature of the thin film evaporator is 120-170°C, and the absolute pressure is 1-5KPa.

In order to further improve the recovery rate of NMP solvent, the following steps are also included: the gas phase NMP coming out of the thin film evaporator is condensed into a liquid phase by a condenser.

In order to further improve the recovery rate of NMP solvent, the condenser 2 is a vertical shell and tube condenser.

In order to further improve the recovery rate of the NMP solvent, the bottom of the condenser 2 is provided with a liquid discharge port, and the liquid discharge port is connected with the solvent recovery tank 6 through the downcomer, and the NMP solvent condensed into the liquid phase is discharged through the downcomer. into the solvent recovery tank 6.

In order to further improve the recovery rate of the NMP solvent, the solvent recovery tank 6 is provided with a vertically arranged separator, and the separator divides the tank cavity into a storage area and a drop zone, and there is a space between the top of the separator and the top of the tank. gap.

In order to further improve the recovery rate of NMP solvent, one end of the downcomer is connected to the liquid outlet of the condenser 2, and the other end is immersed in the solvent recovery tank 6 below the liquid level of the downcomer area, and the vertical distance between the two ends of the downcomer is 10m or more.

In order to further improve the recovery rate of NMP solvent, the bottom of the thin film evaporator 3 is provided with a slag discharge port, and the slag discharge port is connected with a dry distillation slag collection tank 4 through a slag discharge pipe, and the dry distillation slag collection tank 4 is arranged in the thin film evaporator. Below 3, the bottom of the dry distillation residue collection tank 4 is connected to the dry distillation residue storage tank 5 through a slag discharge pipe, and the dry distillation residue storage tank 5 is below the dry distillation residue collection tank.

In order to further improve the recovery rate of NMP solvent, the condenser 2 and the dry distillation residue collection tank 4 are respectively connected with the vacuum pump 7 through pipelines.

In order to further improve the recovery rate of NMP solvent, a vacuum control valve 8 is provided on the pipeline connecting the vacuum pump 7 and the dry distillation residue collection tank 4 .

In order to further improve the recovery rate of NMP solvent, a nitrogen flow regulating valve 13 is provided at the bottom of the dry distillation residue collection tank 4 .

In order to further improve the recovery rate of NMP solvent, the slag discharge pipe is provided with a slag discharge valve 11, and the slag discharge pipe is provided with a slag discharge valve 12.

The NMP solvent enters the preheater 1 from the liquid inlet of the preheater 1. The liquid inlet is provided with a control valve. The preheater 1 is heated by heat transfer oil or steam. The preheater 1 is a tubular preheater. And the inner wall of the preheater 1 is polished. The NMP solvent is heated by the preheater 1 and then enters the thin-film evaporator 3, which is a wiper-type thin-film evaporator, and the wiper of the wiper-type thin-film evaporator 3 is a movable wiper. In the thin film evaporator 3, the heated NMP solvent realizes the separation of the gas phase NMP solvent and the solid phase dry distillation residue.

The gas-phase NMP solvent enters the condenser 2 through the pipeline arranged at the top of the thin-film evaporator 3, and the condenser 2 is a vertical shell-and-tube condenser, and the bottom of the condenser 2 is provided with a drain port, which is The downcomer is connected to the solvent recovery tank 6 .

The condensed liquid-phase NMP solvent falls into the descending area of the solvent recovery tank 6 by gravity through the downcomer (the solvent recovery tank 6 is provided with a vertically arranged baffle plate, and the baffle plate separates the tank inner cavity into a storage area. and drop zone, there is a gap between the top of the baffle and the top of the tank).

One end of the downcomer is connected to the liquid discharge port of the condenser 2, and the other end is immersed below the liquid level in the downcomer area of the solvent recovery tank 6, and the vertical distance between the two ends of the downcomer is more than 10m.

The bottom of the thin film evaporator 3 is provided with a slag discharge port, which is connected to the dry distillation slag collection tank 4 through a slag discharge pipe, and the dry distillation slag collection tank 4 is arranged below the thin film evaporator 3 . The bottom of the dry distillation residue collection tank 4 is communicated with the dry distillation residue storage tank 5 through a slag discharge pipe, and the dry distillation residue storage tank 5 is arranged below the dry distillation residue collection tank 4 . The slag discharge pipe is provided with a slag discharge valve 11, and the slag discharge pipe is provided with a slag discharge valve 12.

The vacuum pump 7 is respectively connected with the vertical tube gas condenser 2 and the dry distillation slag collection tank 4 through the pipeline, and a vacuum control valve 8 is provided on the pipeline connecting the vacuum pump 7 and the dry distillation slag collection tank 4, and the vacuum pump 7 is connected with the vertical gas condenser. 2 is provided with a pressure regulating valve 9 on the pipeline.

The liquid inlet line of the preheater 1 is provided with an NMP flow regulating valve 10, the bottom of the thin film evaporator 3 and the dry distillation residue collection tank 4 is provided with a solenoid valve that cooperates with each other, and the bottom of the dry distillation residue collection tank 4 is provided with There is a nitrogen flow regulating valve 13 .

The nitrogen flow regulating valve 13 is connected with the nitrogen pipe network through pipelines. During slag discharge, the slag discharge valve 11 on the slag discharge pipe is closed, the vacuum control valve 8 is closed, the nitrogen flow regulating valve 13 is opened, the positive pressure of the retort slag collection tank is restored, and the slag discharge valve 12 on the slag discharge pipe is opened. Gravity discharge into dry distillation residue storage tank 5. After the dry distillation slag is discharged, the slag discharge valve 11 on the slag discharge pipe is closed, the nitrogen flow regulating valve 13 is closed, and the vacuum control valve 8 is opened. When the pressure reaches the pressure of the thin film evaporator 3, the vacuum control valve 8 is closed, and the slag discharge pipe The slag discharge valve 11 completes a slag discharge process. Through the above settings, the automatic slag discharge function under continuous operation is realized.

The beneficial effects of the present invention are:

The method of the invention can realize the recovery of the NMP solvent containing easy-to-crystallize and heat-sensitive components, thereby improving the recovery rate.

The method of the present invention can avoid the clogging problems caused by crystallization and coke formation.

The method of the invention does not need manual slag cleaning, and improves the automation level of the NMP recovery device.

The method of the invention can effectively control the problem of excessive VOCs scattered emission at the production site, and will not cause environmental pollution and occupational health hazards.

Description of drawings

Fig. 1 is the flow chart of acetylene enrichment system;

Fig. 2 is batch dry distillation system;

Fig. 3 is the thin film evaporator system of Example 1, wherein 1 is a preheater, 2 is a condenser, 3 is a thin film evaporator, 31 is a thin film evaporator motor, 4 is a retorting slag collection tank, and 5 is a retorting slag storage tank tank, 6 is a solvent recovery tank, 7 is a vacuum pump, 71 is a vacuum pump motor, 8 is a vacuum control valve, 9 is a pressure regulating valve, 10 is an NMP flow regulating valve, 11 is a slag discharge valve, 12 is a slag discharge valve, and 13 is Nitrogen flow control valve, NO.5 is nitrogen with a pressure of 0.5MPa, Iw33 is circulating cooling water, S1.0 is heat transfer oil or steam with a pressure of 1MPa, NMP is NMP stock solution, S0.6 is heat transfer oil or a pressure of 0.6MPa steam, C0.6 is condensate.

Detailed ways

The cited embodiments are used to better illustrate the content of the present invention, but the content of the present invention is not limited to the cited embodiments. Therefore, those skilled in the art make non-essential improvements and adjustments to the embodiments according to the above-mentioned contents of the invention, which still belong to the protection scope of the present invention.

Example 1

Get NMP stoste (from natural gas partial oxidation to make acetylene process in the enrichment process) and carry out component detection, the results are as shown in Table 1;

Among them, the NMP content is detected in accordance with the "GB/T 614-2006 General Method for the Determination of the Shading Rate of Chemical Reagents";

The detection method of the total content of heat-sensitive polymers is the gravimetric method, specifically: heating and evaporating a solvent with a mass of M under gas inert conditions to measure (mass is N), then the total content of heat-sensitive polymers is N/M*100% ;

The water content is tested according to "GB/T 6283-2008 Determination of Moisture Content in Chemical Products";

The content of acetylene, methylacetylene, butadiyne, vinylacetylene, divinylacetylene and benzene was detected by conventional chromatography.

The NMP stock solution is processed by the system shown in FIG. 3 . The system includes a preheater 1 , a condenser 2 , a thin film evaporator 3 , a dry distillation slag collection tank 4 , a dry distillation slag storage tank 5 , a solvent recovery tank 6 and a vacuum pump 7 . The preheater 1 is a tubular preheater, the condenser 2 is a vertical shell and tube condenser, and the thin film evaporator 3 is a wiper film evaporator. The scraper is a movable scraper.

The NMP solvent enters the preheater 1 from the liquid inlet of the preheater 1, the liquid inlet is provided with a control valve, the preheater 1 is heated by heat transfer oil or steam, and the inner wall of the preheater 1 is polished. The NMP solvent is heated by the preheater 1 and then enters the thin-film evaporator 3. In the thin-film evaporator 3, the heated NMP solvent realizes the separation of the gas-phase NMP solvent and the solid-phase dry distillation residue.

The gas phase NMP solvent enters the condenser 2 through the pipeline arranged at the top of the thin film evaporator 3, and the bottom of the condenser 2 is provided with a liquid discharge port, which is connected to the solvent recovery tank 6 through the downcomer.

The condensed liquid phase NMP solvent falls into the descending area of the solvent recovery tank 6 by gravity through the downcomer (the solvent recovery tank 6 is provided with a vertically arranged baffle, and the baffle divides the tank cavity into a storage area and a In the drop zone, there is a gap between the top of the baffle and the top of the tank).

One end of the downcomer is connected to the liquid discharge port of the condenser 2, and the other end is immersed below the liquid level in the downcomer area of the solvent recovery tank 6, and the vertical distance between the two ends of the downcomer is more than 10m.

The bottom of the thin-film evaporator 3 is provided with a slag discharge port, and the slag discharge port is connected to a dry distillation slag collection tank 4 through a slag discharge pipe, and the dry distillation slag collection tank 4 is arranged below the thin film evaporator 3 . The bottom of the dry distillation residue collection tank 4 is communicated with the dry distillation residue storage tank 5 through a slag discharge pipe, and the dry distillation residue storage tank 5 is arranged below the dry distillation residue collection tank 4 . The slag discharge pipe is provided with a slag discharge valve 11, and the slag discharge pipe is provided with a slag discharge valve 12.

The vacuum pump 7 is respectively connected with the condenser 2 and the dry distillation slag collection tank 4 through the pipeline, the vacuum control valve 8 is provided on the pipeline connecting the vacuum pump 7 and the dry distillation slag collection tank 4, and the pipeline connecting the vacuum pump 7 and the condenser 2 is provided with There is a pressure regulating valve 9.

The liquid inlet line of the preheater 1 is provided with an NMP flow regulating valve 10, the bottom of the thin film evaporator 3 and the dry distillation residue collection tank 4 is provided with a solenoid valve that cooperates with each other, and the bottom of the dry distillation residue collection tank 4 is provided with There is a nitrogen flow regulating valve 13 .

The nitrogen flow regulating valve 13 is connected with the nitrogen pipe network through pipelines. During slag discharge, the slag discharge valve 11 on the slag discharge pipe is closed, the vacuum control valve 8 is closed, the nitrogen flow regulating valve 13 is opened, the positive pressure of the retort slag collection tank is restored, and the slag discharge valve 12 on the slag discharge pipe is opened. Gravity discharge into dry distillation residue storage tank 5. After the dry distillation slag is discharged, the slag discharge valve 12 on the slag discharge pipe is closed, the nitrogen flow regulating valve 13 is closed, and the vacuum control valve 8 is opened. When the pressure reaches the pressure of the thin film evaporator, the vacuum control valve 8 is closed, and the slag discharge on the slag discharge pipe The valve 11 is opened to complete a slag discharge process. Through the above settings, the automatic slag discharge function under the continuous operation of the thin film evaporator is realized.

The specific process is: adding the NMP stock solution to the storage tank in front of the pump, adjusting the control valve on the preheater 1, the feed rate is 0.3 m ³ /h, and preheating the preheater 1 to 99 ℃ and then introducing it into the thin film evaporator 3 ( Before starting the thin-film evaporator 3, replenish the NMP solvent to the down-liquid area of the solvent recovery tank 6 to overflow). Adjust the temperature of the thin film evaporator 3 at 170° C. and the pressure of the pressure regulating valve 9 at 1.1-1.2 Pa (absolute pressure). The slag discharge valve 11 on the slag discharge pipe is opened, the slag discharge valve 12 on the slag discharge pipe is closed, and the nitrogen flow valve 13 is closed. The solvent recovery tank 6 is filled with liquid to overflow. After 60 minutes, the dry distillation collection tank is discharged. The dry distillation slag collection tank 4 starts slag discharge, the slag discharge valve 11 is closed, the vacuum control valve 8 is automatically closed, and the system is filled with low-pressure nitrogen through the nitrogen flow control valve 13 to restore the positive pressure of the dry distillation slag collection tank 4, and the slag discharge on the slag discharge pipe The valve 12 is automatically opened, and the dry distillation residue material at the bottom is discharged into the closed dry distillation residue storage tank 5 . After the dry distillation slag is discharged, the slag discharge valve 12 on the slag discharge pipe is automatically closed, the nitrogen flow regulating valve 13 is closed, the pressure regulating valve 8 slowly opens the valve position, and the vacuum degree of the dry distillation slag collection tank 4 is adjusted. When the vacuum degree reaches the thin film evaporator system When the pressure is high, the vacuum control valve 8 is closed, and the slag discharge valve 11 on the slag discharge pipe is automatically opened to complete a slag discharge process.

Table 1 Test results of NMP stock solution components

Test items Test results NMP 96% (quality) heat sensitive polymer 2.01% (mass) water 0.77% (mass) Acetylene 8mg/L methyl acetylene 20mg/L Diacetylene 25mg/L vinyl acetylene 15mg/L Divinylacetylene 27mg/L benzene 1.9mg/L

Example 1, Example 2 and Comparative Example 1

Except for the parameters shown in Table 2, other parameter settings in Example 2 are the same as those in Example 1.

Table 2 Example 2 and Comparative Example 1

Comparative Example 1

The dry distillation system shown in Figure 2 is used to process the NMP stock solution (the composition is the same as that of Example 1), specifically:

Put 4m ³ of NMP stock solution into the dry distillation tank, turn on the 1MPa heat tracing steam and the temperature rises to 170°C, start the vacuum system, control the pressure at 1.1-1.2Kpa.A, dry distillation for 22 hours, and manually remove the slag.

Performance testing

Detect the residual rate of NMP, the state of the dry distillation residue and the content of volatile organic compounds (VOCs) in the surrounding air in the dry distillation residue obtained by the methods described in Examples 1-2 and Comparative Example 1, and the results are shown in Table 3;

Among them, the NMP content in the retort residue is detected according to the "GB/T 614-2006 General Method for the Determination of the Shading Rate of Chemical Reagents";

The detection method of the state of dry distillation residue is visual observation;

The detection method of VOCs content in the surrounding air is to use a portable VOCs detector to detect on-site.

Table 3 Performance test results

source NMP survival rate/% Dry distillation residue state Dry distillation slag removal state VOCs content/ppm Example 1 12.5 into flakes Automatic slag <5 Example 2 23.4 into flakes Automatic slag <5 Comparative Example 1 29 coke into a pie Manual slag removal 1200

It can be seen from Table 1 and Table 3 that the method of Example 1-2 can avoid the clogging problem of crystallization and coke formation, and can realize the recovery of NMP solvent containing easy-to-crystallize and heat-sensitive components, and improve the recovery rate.

It can be seen from Tables 1 and 3 that, compared with Comparative Example 1, the dry distillation slag treated in Examples 1 and 2 did not agglomerate, and the dry distillation slag was automatically discharged smoothly. This proves that the method of the present invention can avoid the clogging problems caused by crystallization and coke formation, and effectively improve the automation degree of the dry distillation device.

It can be seen from Table 1 and Table 3 that compared with Comparative Example 1, the residual rate of NMP in the dry distillation residue treated in Example 1-2 was significantly reduced; and the VOCs content in the surrounding air was significantly reduced. Therefore, it is proved that the method of the present invention can effectively recover the NMP solvent, and can effectively control the problem of excessive VOCs scattered emission at the production site, and solve the occupational health hazard existing in the manual slag removal process.

In addition, it should be understood that although this specification is described in terms of embodiments, not each embodiment only includes an independent technical solution, and this description in the specification is only for the sake of clarity, and those skilled in the art should take the specification as a whole , the technical solutions in each embodiment can also be appropriately combined to form other implementations that can be understood by those skilled in the art.

Claims (17)

1. the recovery method of NMP solvent, is characterized in that, comprises the following steps: NMP solvent is heated to 80-99 ℃ through preheater 1, then is placed in thin film evaporator 3 to realize the separation of gas phase NMP solvent and solid distillation residue. 2 . The method for recovering NMP solvent according to claim 1 , wherein the preheater 1 is a tubular preheater, and the inner wall of the preheater is polished. 3 . 3. The recovery method of NMP solvent according to claim 1 or 2, wherein the heating medium of the preheater 1 is steam or heat-conducting oil. 4. The recovery method of NMP solvent according to claim 1, 2 or 3, characterized in that, a flow regulating valve 10 is provided on the liquid phase inlet line of the preheater 1. 5. The method for recovering NMP solvent according to claim 1, 2, 3 or 4, wherein the thin film evaporator 3 is a wiper type thin film evaporator. 6 . The method for recovering NMP solvent according to claim 5 , wherein the scraper of the thin film evaporator is a movable scraper. 7 . 7. The recovery method of NMP solvent according to claim 1, 2, 3, 4, 5 or 6, wherein the temperature of the thin film evaporator is 120-170°C, and the absolute pressure is 1-5KPa. 8. the recovery method of NMP solvent according to claim 1,2,3,4,5,6 or 7, is characterized in that, also comprises the following steps: the gas phase NMP that comes out from thin film evaporator is condensed into through condenser 2 into liquid phase. 9. The recovery method of NMP solvent according to claim 8, wherein the condenser 2 is a vertical shell and tube condenser. 10. the recovery method of NMP solvent according to claim 8 or 9, is characterized in that, described condenser 2 bottom is provided with liquid discharge port, and this liquid discharge port is connected with solvent recovery tank 6 through downcomer, condensation. The NMP solvent in the liquid phase falls into the solvent recovery tank 6 through the downcomer. 11. the recovery method of NMP solvent according to claim 10, is characterized in that, described solvent recovery tank 6 is provided with the clapboard that is arranged vertically, and the clapboard divides the tank inner cavity into storage area and descending liquid area, every There is a gap between the top of the plate and the top of the tank. 12. the recovery method of NMP solvent according to claim 10 or 11, is characterized in that, one end of described downcomer is connected with the drain port of condenser 2, and the other end is immersed in solvent recovery tank 6 below the liquid level of the downcomer zone , the vertical distance between the two ends of the downcomer is more than 10m. 13. The recovery method of the NMP solvent according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12, wherein the bottom of the thin film evaporator 3 is provided with There is a slag discharge port, and the slag discharge port is connected with a dry distillation slag collection tank 4 through a slag discharge pipe. The dry distillation slag collection tank 4 is arranged below the thin film evaporator 3. The dry distillation residue storage tank 5 is communicated, and the dry distillation residue storage tank 5 is below the dry distillation residue collection tank. 14. The recovery method of NMP solvent according to claim 13, is characterized in that, described condenser 2 and dry distillation residue collection tank 4 are respectively connected with vacuum pump 7 through pipeline. 15 . The method for recovering NMP solvent according to claim 14 , wherein a vacuum control valve 8 is provided on the pipeline connecting the vacuum pump 7 and the dry distillation residue collection tank 4 . 16 . 16. The method for recovering NMP solvent according to claim 13, 14 or 15, wherein a nitrogen flow regulating valve 13 is provided at the bottom of the dry distillation residue collection tank 4. 17. The method for recovering NMP solvent according to claim 13, 14, 15 or 16, wherein the slag discharge pipe is provided with a slag discharge valve 11, and the slag discharge pipe is provided with a slag discharge valve 12.

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