Process for the cooling crystallization of thiram and vacuum continuous crystallization system

Abstract

The application provides a method for cooling and crystallizing thiram and a vacuum continuous crystallization system. A thiram solution is sequentially subjected to first flash evaporation, second flash evaporation and third flash evaporation to obtain thiram crystal slurry. The concentration of the thiram solution is 65% to 75%, and the temperature of the thiram solution is 80 to 90 DEG C. The first flash evaporation is carried out under a vacuum pressure of -0.075 to -0.085 MPa, and the second flash evaporation is carried out under a vacuum pressure of -0.8 to -0.9 MPa. The third flash evaporation is carried out under a vacuum pressure of -0.09 to -0.098 MPa. The process is safe and environmentally friendly, has high automation degree, can obtain thiram crystal slurry with large and uniform crystal morphology, and the obtained thiram product has uniform particle size and high purity.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of fine chemical product production, and particularly relates to a method for cooling and crystallizing sodium dimethyldithiocarbamate and a vacuum continuous crystallization system. BACKGROUND

[0002] Sodium dimethyldithiocarbamate has a chemical name of sodium dimethyldithiocarbamate (English name sodium dimethyldithiocarbamate), and is also known as N, N-dimethyl dithiocarbamic acid sodium. The pure product of sodium dimethyldithiocarbamate is white crystal, and is extremely soluble in water. The crystal obtained by using a crystallization method contains 2.5 crystal waters, loses two molecules of crystal water when heated to 115 DEG C, and completely loses the crystal water at 130 DEG C. The industrial intermediate is a 15% aqueous solution, and is a yellowish or grass green transparent liquid.

[0003] The commonly used method for preparing sodium dimethyldithiocarbamate at home includes the following steps: 32% NaOH solution and 40% dimethylamine solution are added into a reaction kettle, the temperature is controlled below 25 DEG C, carbon disulfide is continuously added into the reaction kettle under continuous stirring, the temperature is controlled below 35 DEG C, the reaction kettle is stirred for another half an hour after the addition of carbon disulfide is completed, the reaction liquid is dehydrated and concentrated, and the concentrated liquid is put into a crystallization tank for cooling and crystallization after being concentrated to a certain extent. After sodium dimethyldithiocarbamate is cooled and crystallized, the product is subjected to a centrifugal process.

[0004] However, the product of sodium dimethyldithiocarbamate prepared by using the above-mentioned common technology has fine and weak crystal grains, small particle size, and poor product quality. SUMMARY

[0005] In order to solve the technical problems of fine and weak crystal grains, small particle size and poor product quality of sodium dimethyldithiocarbamate in the above-mentioned common technology, the present application provides a method for cooling and crystallizing sodium dimethyldithiocarbamate. The sodium dimethyldithiocarbamate solution is sequentially subjected to first flash evaporation, second flash evaporation and third flash evaporation, and sodium dimethyldithiocarbamate crystal slurry is obtained.

[0006] The concentration of the sodium dimethyldithiocarbamate solution is 65% to 75%, and the temperature of the sodium dimethyldithiocarbamate solution is 90 to 95 DEG C. The first flash evaporation is carried out under a vacuum pressure of-0.075 to-0.085 MPa, and the second flash evaporation is carried out under a vacuum pressure of-0.8 to-0.9 MPa. The third flash evaporation is carried out under a vacuum pressure of-0.09 to-0.098 MPa.

[0007] Further, the first flash evaporation is carried out under a vacuum pressure of-0.08 MPa, the second flash evaporation is carried out under a vacuum pressure of-0.85 MPa, and the third flash evaporation is carried out under a vacuum pressure of-0.098 MPa.

[0008] Further, the first flash evaporation includes that the sodium dimethyldithiocarbamate solution is subjected to first flash evaporation to obtain first flash evaporation liquid, and the temperature of the first flash evaporation liquid is 68 to 72 DEG C.

[0009] Further, the second flash evaporation includes: the first flash evaporation liquid is subjected to second flash evaporation to obtain a second flash evaporation liquid, and the temperature of the second flash evaporation liquid is 58-62 DEG C.

[0010] Further, the third flash evaporation includes: the second flash evaporation liquid is subjected to third flash evaporation to obtain the thiram crystal slurry, the temperature of the thiram crystal slurry is 45-50 DEG C, the mother liquor concentration of the thiram crystal slurry is 60%-65%, and the solid content in the thiram crystal slurry is 40%-45%.

[0011] The application further provides a vacuum continuous crystallization system, which is applied to the method for cooling and crystallizing thiram as described in any one of the above embodiments, and comprises a raw material tank, a flash evaporation group and a slurry tank; wherein the raw material tank, the flash evaporation group and the slurry tank are fixedly connected in sequence through pipelines, the number of the flash evaporation group is at least one, and the flash evaporation group is used for sequentially performing first flash evaporation, second flash evaporation and third flash evaporation on the thiram solution.

[0012] Further, the flash evaporation group comprises:

[0013] a vacuum crystallizer;

[0014] a condensing part, which is fixedly installed at the top of the vacuum crystallizer and communicates with the vacuum crystallizer, so as to condense the flash evaporation steam;

[0015] a vacuum part, which communicates with the condensing part, so as to provide a vacuum environment for flash evaporation.

[0016] Further, the number of the flash evaporation group is three, and the three flash evaporation groups are sequentially communicated, so as to respectively process the first flash evaporation, the second flash evaporation and the third flash evaporation.

[0017] Further, the condensing part comprises a condenser, a condensing water storage tank and a condensing water pump which are sequentially connected; wherein the condensing water storage tank is connected with the vacuum part, and the vacuum part comprises a vacuum pump.

[0018] Further, it further comprises an agitating part, which is fixedly installed at the bottom of the vacuum crystallizer, so as to agitate the fluid in the vacuum crystallizer; wherein the agitating part comprises an axial flow pump.

[0019] Compared with the prior art, the application at least has the following advantages:

[0020] The application utilizes step-by-step flash evaporation to control the temperature of the thiram solution in stages. Since the boiling point of the thiram solution is related to the vacuum pressure, the smaller the vacuum pressure is, the smaller the boiling point of the thiram solution is. With the continuous reduction of the vacuum pressure, the water vaporized in the flash evaporation carries heat, so that the temperature of the thiram solution is continuously reduced, and the thiram crystals are gradually precipitated, so that the thiram crystal slurry with large particles is finally obtained.

[0021] Compared with the prior art, the method of the present application concentrates the thiram solution and then places it in a crystallization tank for rapid and static cooling crystallization. On the one hand, the present application utilizes gradual slow temperature drop to allow the thiram crystals in the thiram solution to have sufficient time for growth, thereby inhibiting nucleation and allowing the thiram crystals in the thiram slurry to be large and uniform in morphology.

[0022] On the other hand, the present application does not provide a concentration step, but instead integrates concentration and crystallization in the flash evaporation process. This saves energy and reduces costs, and also reduces the solid content in the thiram solution after the first flash evaporation. Since the first flash evaporation is a nucleation process, if too much nucleation occurs during the first flash evaporation, the crystal particle size in the thiram slurry will be limited according to the AL law of crystal growth. The present application controls the feed concentration of the thiram solution and thereby controls the solid content of the thiram after the first flash evaporation, effectively ensuring the crystal size in the subsequent thiram slurry.

[0023] Finally, since the present application is carried out in a vacuum and closed environment, harmful gases such as carbon disulfide and dimethylamine that escape from the thiram solution after flash evaporation will not disperse into the air, but will be efficiently collected in the closed environment, thereby solving the long-standing environmental threat in the preparation of thiram. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained according to the structures shown in these drawings without creative labor for those skilled in the art.

[0025] Figure 1 Figure 1 is a structural schematic diagram of a vacuum continuous crystallization system according to an embodiment of the present application.

[0026] In the figure, 1 is a raw material tank, 2 is a feed pump, 3 is a first-stage axial flow pump, 4 is a first-stage delivery pump, 5 is a second-stage axial flow pump, 6 is a second-stage delivery pump, 7 is a third-stage axial flow pump, 8 is a third-stage delivery pump, 9 is a slurry tank, 10 is a first-stage vacuum crystallizer, 11 is a first-stage condenser, 12 is a first-stage vacuum pump, 13 is a second-stage vacuum crystallizer, 14 is a second-stage condenser, 15 is a second-stage vacuum pump, 16 is a third-stage vacuum crystallizer, 17 is a third-stage condenser, 18 is a third-stage vacuum pump, 19 is a total condensate tank, 20 is a total condensate pump, 21 is a first-stage condensate tank, 22 is a first-stage condensate pump, 23 is a second-stage condensate tank, 24 is a second-stage condensate pump, 25 is a third-stage condensate tank, and 26 is a third-stage condensate pump. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative effort shall fall within the protection scope of the present application.

[0028] In addition, the technical solutions among the various embodiments of the present application can be combined with each other, but it must be based on the fact that a person of ordinary skill in the art can realize the combination, and when the combination of the technical solutions appears to be contradictory or unachievable, it shall be considered that the combination of the technical solutions does not exist and is not within the protection scope of the present application.

[0029] When the embodiments give numerical ranges, it should be understood that, unless otherwise specified by the present application, both endpoints of each numerical range and any number between the two endpoints can be selected. Unless otherwise defined, all the technical and scientific terms used in the present application are consistent with the mastery of the prior art by the person of ordinary skill in the art and the description of the present application, and any method, equipment and material of the prior art similar or equivalent to the method, equipment and material described in the embodiments of the present application can be used to realize the present application.

[0030] A method for cooling and crystallizing sodium dimethyldithiocarbamate, a sodium dimethyldithiocarbamate solution is subjected to first flash evaporation, second flash evaporation and third flash evaporation in sequence to obtain a sodium dimethyldithiocarbamate crystal slurry.

[0031] In some embodiments, the preparation process of sodium dimethyldithiocarbamate can be as follows: 50% NaOH solution and 99% dimethylamine are added into a high-pressure reaction kettle, carbon disulfide is dropped into the reaction kettle under constant stirring, and the reaction is carried out under the condition of nitrogen protection, the temperature is controlled below 90-95°C, after the addition of carbon disulfide is completed, the reaction kettle is stirred for another half an hour, and after the reaction is completed, the sodium dimethyldithiocarbamate solution in the present application is obtained.

[0032] For example, the concentration of the sodium dimethyldithiocarbamate solution can be 65%-75%, and the temperature of the sodium dimethyldithiocarbamate solution can be 90-95°C.

[0033] Preferably, the first flash evaporation is carried out under a vacuum pressure of-0.075 to-0.085 MPa, the second flash evaporation is carried out under a vacuum pressure of-0.8 to-0.9 MPa, and the third flash evaporation is carried out under a vacuum pressure of-0.09 to-0.098 MPa.

[0034] Further preferably, the first flash evaporation is carried out under a vacuum pressure of-0.08 MPa, the second flash evaporation is carried out under a vacuum pressure of-0.85 MPa, and the third flash evaporation is carried out under a vacuum pressure of-0.098 MPa.

[0035] Flash evaporation is a phenomenon that a part of liquid is converted into steam under the pressure of a container when the liquid enters the container from a high pressure environment. The conversion of the liquid into steam is mainly due to the fact that the boiling point of a substance decreases with the decrease of pressure, and the lower the pressure, the lower the boiling point. Since the temperature of the fluid entering the low pressure environment is higher than the boiling point of the fluid under the pressure, the fluid is rapidly boiled and vaporized in the flash tank, and two-phase separation is carried out. At the same time, the vaporized part of the fluid carries away a certain amount of heat, realizing the temperature drop of the fluid.

[0036] In the above, after the first flash evaporation of the thiram solution under-0.075-0.085 MPa, the temperature is reduced to 68-72℃, no crystal is precipitated, and the first flash evaporation liquid containing a large number of crystal nuclei is formed. The vacuum condition is set to-0.075-0.085 MPa, so that the water in the thiram solution is evaporated at the same time and all is in liquid phase.

[0037] The thiram saturated solution and the precipitated crystal enter the second flash evaporation, the temperature is reduced to 58-62℃, and part of the crystal begins to precipitate, and the second flash evaporation liquid (including mother liquor and precipitated crystal) is obtained. The vacuum condition is set to-0.8-0.9 MPa, so that after the first flash evaporation liquid enters the second flash evaporator, flash evaporation and concentration continue, and crystal nuclei are formed and grow.

[0038] The second flash evaporation liquid enters the third flash evaporation, and the temperature is reduced to 45-50℃ under the vacuum pressure of-0.09-0.098 MPa, and the thiram crystal slurry (including crystal and mother liquor) is obtained, wherein the crystal particle size can reach 1-2 mm, and the concentration of the mother liquor is 60-65%.

[0039] In some embodiments, the obtained thiram crystal slurry can be centrifuged and dried to obtain thiram product. The mother liquor after centrifugation can continue to participate in the synthesis reaction to realize recycling.

[0040] Specifically, the above flash evaporation can be carried out in three flash tanks arranged in sequence.

[0041] Compared with the prior art, the present application at least has the following advantages:

[0042] The present application utilizes stepwise flash evaporation to grade the temperature control of thiram solution. Since the boiling point of thiram solution is related to vacuum pressure, the smaller the vacuum pressure, the lower the boiling point of thiram solution. With the continuous decrease of vacuum pressure, the water evaporated by flash evaporation carries heat, so that the temperature of thiram solution is continuously reduced, and thiram crystals are precipitated step by step, and finally large-particle thiram crystal slurry is obtained.

[0043] Compared with the prior art, the method of the present application is to concentrate the thiram solution and then place it in a crystallization tank for rapid and static cooling crystallization. On the one hand, the present application utilizes gradual and slow temperature drop to allow the thiram crystals in the thiram solution to have sufficient time for growth, thereby inhibiting nucleation and allowing the thiram crystals in the thiram crystal slurry to be large and uniform in morphology.

[0044] On the other hand, the present application does not provide a concentration step, but integrates the concentration and crystallization in the flash evaporation process, thereby saving energy and reducing costs, and reducing the solid content in the thiram solution after the first flash evaporation. Since the first flash evaporation is a nucleation process, if too many nucleations occur during the first flash evaporation, the crystal particle size in the thiram crystal slurry will be limited according to the AL law of crystal growth. The present application controls the feed concentration of the thiram solution and thereby controls the solid content of the thiram after the first flash evaporation, thereby effectively ensuring the crystal size in the subsequent thiram crystal slurry.

[0045] Finally, since the present application is carried out in a vacuum and closed environment, the harmful gases such as carbon disulfide and dimethylamine released after the flash evaporation of the thiram solution will not disperse into the air, but will be efficiently collected in the closed environment, thereby solving the long-standing environmental threat in the preparation of thiram.

[0046] The present application also provides a vacuum continuous crystallization system, which is applied to the method for cooling and crystallizing thiram according to any one of the above embodiments, and comprises a raw material tank 1, a flash evaporation group, and a slurry tank 9; wherein the raw material tank 1, the flash evaporation group, and the slurry tank 9 are sequentially fixedly connected through pipelines.

[0047] In some embodiments, a feeding pump 2 can be arranged in the pipeline between the raw material tank 1 and the flash evaporation part to uniformly feed the flash evaporation part.

[0048] In other embodiments, the flash evaporation group comprises:

[0049] a vacuum crystallizer;

[0050] For example, the vacuum crystallizer can be a vertical tank, and the cross-sectional area of the two ends can be smaller than the cross-sectional area of the middle part.

[0051] a condensing part fixedly installed on the top of the vacuum crystallizer and in communication with the vacuum crystallizer to condense the flash evaporation vapor.

[0052] For example, the condensing part can comprise a condenser, a condensate water storage tank, and a condensate water pump sequentially connected through pipelines.

[0053] a vacuum part in communication with the condensing part to provide a vacuum environment for flash evaporation.

[0054] For example, the vacuum part can be connected with the condensate water storage tank through a pipeline, and the vacuum part can comprise a vacuum pump.

[0055] The stirring part is fixedly installed at the bottom of the vacuum crystallizer to stir the liquid in the vacuum crystallizer and prevent the crystals from depositing at the bottom to block the equipment and pipelines.

[0056] For example, the stirring part can include an axial flow pump. Compared with the stirring paddle used as the stirring device in the prior art, the axial flow pump used in the present application has obvious advantages. On the one hand, the axial flow pump can promote the stirring of the fluid, and at the same time, due to the faster settling velocity of large particles, the large particles enter the next stage crystallizer with the mother liquor from the lower part of the crystallizer, and the fine and weak crystals enter the circulation, further optimizing the product quality and eliminating the weak crystals. On the other hand, compared with the violent stirring of the stirring paddle, the axial flow pump is more uniform in strength, and will not break the crystals due to the physical collision between the paddle and the fluid during stirring, thereby playing a role in protecting the crystals, promoting the growth of the crystals, and protecting the product quality.

[0057] In some embodiments, the number of flash groups is three groups, and the three groups of flash groups are sequentially connected to process the first flash, the second flash, and the third flash, respectively.

[0058] Specifically, as shown in Figure 1 The flash part can include a first flash part, a second flash part, and a third flash part.

[0059] The first flash part includes a first-stage vacuum crystallizer 10, a first-stage condensing part, a first-stage vacuum part, and a first-stage stirring part.

[0060] The first-stage vacuum crystallizer 10 is a vertical tank with a cross-sectional area smaller than that of the middle part;

[0061] The first-stage condensing part is fixedly installed at the top of the first-stage vacuum crystallizer 10 to condense the flash steam after the first flash; and includes a first-stage condenser 11, a first-stage condensing water storage tank 21, and a first-stage condensing water pump 22 connected by pipelines.

[0062] The first-stage vacuum part is connected to the first-stage condensing part by pipelines to provide a vacuum environment for the first flash; and includes a first-stage vacuum pump 12.

[0063] The first-stage stirring part is fixedly installed at the bottom of the first-stage vacuum crystallizer 10 to stir the liquid in the vacuum crystallizer, and includes a first-stage axial flow pump 3.

[0064] The second flash part includes:

[0065] The second-stage vacuum crystallizer 13 is a vertical tank with a cross-sectional area smaller than that of the middle part;

[0066] A second condensing section is fixedly installed on the top of the first vacuum crystallizer 10 to condense the flash steam after the second flash; and includes a second condenser 14, a second condensing water storage tank 23 and a second condensing water pump 24 connected by pipelines.

[0067] A second vacuum section is connected by pipelines with the second condensing section to provide a vacuum environment for the second flash; and includes a second vacuum pump 15.

[0068] A second stirring section is fixedly installed on the bottom of the second vacuum crystallizer 13 to stir the fluid in the second vacuum crystallizer 13, and can include a second axial flow pump 5.

[0069] The third flash section includes:

[0070] A third vacuum crystallizer 16 in the shape of a vertical tank with the cross-sectional area of the two ends smaller than that of the middle part;

[0071] A third condensing section is fixedly installed on the top of the third vacuum crystallizer 16 to condense the flash steam after the third flash; and includes a third condenser 17, a third condensing water storage tank 25 and a third condensing water pump 26 connected by pipelines.

[0072] A third vacuum section is connected by pipelines with the third condensing section to provide a vacuum environment for the third flash; and includes a third vacuum pump 18.

[0073] A third stirring section is fixedly installed on the bottom of the first vacuum crystallizer 10 to stir the fluid in the vacuum crystallizer, and includes a third axial flow pump 7.

[0074] In some embodiments, the specific operations can include the following steps:

[0075] S1. Preparation process: confirm that the control system and the field instruments are in normal operation, and confirm that the states of the valves are normal;

[0076] Confirm that each device is in normal operation;

[0077] Confirm that all mechanical seal cooling valves are opened, and confirm that the condensing water pressure is ≥0.25 MPa;

[0078] Check the settings of the parameters of the control system such as vacuum degree, liquid level, etc., and set appropriate parameters.

[0079] The control system can be a DCS system.

[0080] S2. First flash: start the feed pump 2, and when the liquid level of the first vacuum crystallizer 10 reaches the L1 liquid level, start the first axial flow pump 3.

[0081] For example, the L1 liquid level can be located at a position of 50% of the height of the crystallizer to prevent the liquid level from being too low to cause equipment failure due to failure to circulate.

[0082] When the liquid level of the first-stage vacuum crystallizer 10 reaches the set liquid level L1, the first-stage vacuum pump 12 is turned on and the pressure of the first-stage vacuum pump 12 is set to -0.08MPa.

[0083] When the liquid level in the primary vacuum crystallizer 10 reaches the discharge level, the primary transfer pump 4 is started to feed the material into the secondary vacuum crystallizer 13.

[0084] For example, the discharge level can be located at 70% of the crystallizer.

[0085] S3. Second flash evaporation: When the liquid level in the secondary vacuum crystallizer 13 reaches the L1 level, the secondary axial flow pump 5 is started.

[0086] When the liquid level in the secondary vacuum crystallizer 13 reaches the set liquid level, the secondary vacuum pump 15 is turned on and the pressure of the secondary vacuum pump 15 is set to -0.85MPa.

[0087] When the liquid level in the secondary vacuum crystallizer 13 reaches the discharge level, the secondary transfer pump 6 is started to feed the material into the tertiary vacuum crystallizer 16.

[0088] S4. Third flash evaporation: Start the feed pump 2. When the liquid level of the three-stage vacuum crystallizer 16 reaches the L1 liquid level, start the three-stage axial flow pump 7.

[0089] When the liquid level in the three-stage vacuum crystallizer 16 reaches the set liquid level, the three-stage vacuum pump 18 is turned on and the pressure of the three-stage vacuum pump 18 is set to -0.098MPa.

[0090] When the liquid level in the three-stage vacuum crystallizer 16 reaches the discharge liquid level, the three-stage transfer pump 8 is started to discharge the slurry into the slurry tank 9.

[0091] It should be noted that when the liquid level in the vacuum tank reaches the set value, the condensate in the vacuum tank will be pumped out.

[0092] When the liquid level in slurry tank 9 reaches the set value, the slurry enters the next process.

[0093] The present invention also has the following advantages:

[0094] All processes in this technology are continuous operations with a high degree of automation, low energy consumption, and produce products with uniform particle size, stable quality, and high purity.

[0095] In this invention, the raw material for the crystallization process is the product of a synthesis reaction, and the temperature is 90–95°C. After crystallization, the temperature of the material is approximately 45–50°C, and this heat is utilized in the crystallization process. Throughout the crystallization process, under vacuum conditions, water evaporation continuously carries away heat, and the material temperature continuously decreases. Evaporation and concentration through heating are unnecessary. The process is highly automated, reducing manual labor intensity and improving the working environment.

[0096] Compared with the traditional crystallization method, the material needs to be heated and concentrated, and after concentration, it is discharged while hot, which is easy to cause the volatilization of pollutants. After being put into the crystallization tank, it needs to be cooled for a long time, occupying the equipment for a long time and reducing the equipment utilization rate. In the cooling process, cooling water is also needed to cool down, causing waste of energy.

[0097] Embodiment 1

[0098] A method for cooling and crystallizing thiophanate-methyl.

[0099] The method comprises the following steps:

[0100] S1. First flash evaporation: start the feed pump 2, and the thiophanate-methyl solution with a temperature of 93 DEG C and a concentration of 71% is fed into the first-stage vacuum crystallizer 10. When the liquid level of the thiophanate-methyl solution reaches the L1 liquid level, start the first-stage axial flow pump 3.

[0101] When the liquid level of the first-stage vacuum crystallizer 10 reaches the set liquid level, start the first-stage vacuum pump 12, and set the pressure of the first-stage vacuum pump 12 to -0.08 MPa.

[0102] When the liquid level of the first-stage vacuum crystallizer 10 reaches the discharge liquid level, start the first-stage delivery pump 4 to feed the second-stage vacuum crystallizer 13.

[0103] The first flash evaporation obtains a first flash evaporation liquid, and the temperature of the first flash evaporation liquid is 69 DEG C.

[0104] S2. Second flash evaporation: when the liquid level of the second-stage vacuum crystallizer 13 reaches the L1 liquid level, start the second-stage axial flow pump 5.

[0105] When the liquid level of the second-stage vacuum crystallizer 13 reaches the set liquid level, start the second-stage vacuum pump 15, and set the pressure of the second-stage vacuum pump 15 to -0.85 MPa.

[0106] When the liquid level of the second-stage vacuum crystallizer 13 reaches the discharge liquid level, start the second-stage delivery pump 6 to feed the third-stage vacuum crystallizer 16.

[0107] The second flash evaporation obtains a second flash evaporation liquid, and the temperature of the second flash evaporation liquid is 60 DEG C.

[0108] S3. Third flash evaporation: start the feed pump 2, and when the liquid level of the third-stage vacuum crystallizer 16 reaches the L1 liquid level, start the third-stage axial flow pump 7.

[0109] When the liquid level of the third-stage vacuum crystallizer 16 reaches the set liquid level, start the third-stage vacuum pump 18, and set the pressure of the third-stage vacuum pump 18 to -0.096 MPa.

[0110] When the liquid level of the third-stage vacuum crystallizer 16 reaches the discharge liquid level, start the third-stage delivery pump 8 to discharge the slurry tank 9.

[0111] The third flash gets the thiram crystal slurry, the temperature of the thiram crystal slurry is 48℃, the mother liquor concentration of the thiram crystal slurry is 60.2%, and the solid content of the thiram crystal slurry is 41.8%.

[0112] Example 2

[0113] A thiram cooling crystallization method.

[0114] The method comprises the steps of:

[0115] S1. First flash: start the feed pump 2, and the thiram solution with a temperature of 95℃ and a concentration of 73% enters the first-stage vacuum crystallizer 10; when the liquid level of the thiram solution reaches the L1 liquid level, start the first-stage axial flow pump 3.

[0116] When the liquid level of the first-stage vacuum crystallizer 10 reaches the set liquid level, start the first-stage vacuum pump 12, and set the pressure of the first-stage vacuum pump 12 to -0.08 MPa.

[0117] When the liquid level of the first-stage vacuum crystallizer 10 reaches the discharge liquid level, start the first-stage conveying pump 4 to feed the second-stage vacuum crystallizer 13.

[0118] The first flash gets the first flash liquid, and the temperature of the first flash liquid is 69.6℃.

[0119] S2. Second flash: when the liquid level of the second-stage vacuum crystallizer 13 reaches the L1 liquid level, start the second-stage axial flow pump 5.

[0120] When the liquid level of the second-stage vacuum crystallizer 13 reaches the set liquid level, start the second-stage vacuum pump 15, and set the pressure of the second-stage vacuum pump 15 to -0.85 MPa;

[0121] When the liquid level of the second-stage vacuum crystallizer 13 reaches the discharge liquid level, start the second-stage conveying pump 6 to feed the third-stage vacuum crystallizer 16.

[0122] The second flash gets the second flash liquid, and the temperature of the second flash liquid is 60.3℃.

[0123] S3. Third flash: start the feed pump 2, and when the liquid level of the third-stage vacuum crystallizer 16 reaches the L1 liquid level, start the third-stage axial flow pump 7;

[0124] When the liquid level of the third-stage vacuum crystallizer 16 reaches the set liquid level, start the third-stage vacuum pump 18, and set the pressure of the third-stage vacuum pump 18 to -0.095 MPa;

[0125] When the liquid level of the third-stage vacuum crystallizer 16 reaches the discharge liquid level, start the third-stage conveying pump 8 to discharge to the slurry tank 9.

[0126] The third flash gets the thiram crystal slurry, the temperature of the thiram crystal slurry is 49.2℃, the mother liquor concentration of the thiram crystal slurry is 61.5%, and the solid content of the thiram crystal slurry is 43.5%.

[0127] Example 3

[0128] A thiram cooling crystallization method.

[0129] The method comprises the steps of:

[0130] S1. First flash: start the feed pump 2, and the thiram solution with a temperature of 95℃ and a concentration of 72% enters the first-stage vacuum crystallizer 10; when the thiram solution liquid level reaches the L1 liquid level, start the first-stage axial flow pump 3.

[0131] When the liquid level of the first-stage vacuum crystallizer 10 reaches the set liquid level, start the first-stage vacuum pump 12, and set the pressure of the first-stage vacuum pump 12 to -0.08 MPa.

[0132] When the liquid level of the first-stage vacuum crystallizer 10 reaches the discharge liquid level, start the first-stage conveying pump 4 to feed the second-stage vacuum crystallizer 13.

[0133] The first flash gets the first flash liquid, and the temperature of the first flash liquid is 69.3℃.

[0134] S2. Second flash: when the liquid level of the second-stage vacuum crystallizer 13 reaches the L1 liquid level, start the second-stage axial flow pump 5.

[0135] When the liquid level of the second-stage vacuum crystallizer 13 reaches the set liquid level, start the second-stage vacuum pump 15, and set the pressure of the second-stage vacuum pump 15 to -0.85 MPa;

[0136] When the liquid level of the second-stage vacuum crystallizer 13 reaches the discharge liquid level, start the second-stage conveying pump 6 to feed the third-stage vacuum crystallizer 16.

[0137] The second flash gets the second flash liquid, and the temperature of the second flash liquid is 59.7℃.

[0138] S3. Third flash: start the feed pump 2, and when the liquid level of the third-stage vacuum crystallizer 16 reaches the L1 liquid level, start the third-stage axial flow pump 7;

[0139] When the liquid level of the third-stage vacuum crystallizer 16 reaches the set liquid level, start the third-stage vacuum pump 18, and set the pressure of the third-stage vacuum pump 18 to -0.096 MPa;

[0140] When the liquid level of the third-stage vacuum crystallizer 16 reaches the discharge liquid level, start the third-stage conveying pump 8 to discharge to the slurry tank 9.

[0141] The third flash sodium thiocarbamate crystal slurry has a temperature of 49.6°C, a mother liquor concentration of 60.4%, and a solid content of 42.3%.

[0142] Comparative Example 1

[0143] A sodium thiocarbamate cooling crystallization method.

[0144] The method comprises the following steps:

[0145] S1. First flash: start the feed pump 2, and a sodium thiocarbamate solution with a temperature of 95°C and a concentration of 72% is fed into the first-stage vacuum crystallizer 10. When the liquid level of the sodium thiocarbamate solution reaches the L1 liquid level, start the first-stage axial flow pump 3.

[0146] When the liquid level of the first-stage vacuum crystallizer 10 reaches the set liquid level, start the first-stage vacuum pump 12, and set the pressure of the first-stage vacuum pump 12 to -0.07 MPa.

[0147] When the liquid level of the first-stage vacuum crystallizer 10 reaches the discharge liquid level, start the first-stage delivery pump 4 to feed into the second-stage vacuum crystallizer 13.

[0148] The first flash obtains a first flash liquid, and the first flash liquid has a temperature of 76.4°C.

[0149] S2. Second flash: when the liquid level of the second-stage vacuum crystallizer 13 reaches the L1 liquid level, start the second-stage axial flow pump 5.

[0150] When the liquid level of the second-stage vacuum crystallizer 13 reaches the set liquid level, start the second-stage vacuum pump 15, and set the pressure of the second-stage vacuum pump 15 to -0.75 MPa.

[0151] When the liquid level of the second-stage vacuum crystallizer 13 reaches the discharge liquid level, start the second-stage delivery pump 6 to feed into the third-stage vacuum crystallizer 16.

[0152] The second flash obtains a second flash liquid, and the second flash liquid has a temperature of 64.3°C.

[0153] S3. Third flash: start the feed pump 2, and when the liquid level of the third-stage vacuum crystallizer 16 reaches the L1 liquid level, start the third-stage axial flow pump 7.

[0154] When the liquid level of the third-stage vacuum crystallizer 16 reaches the set liquid level, start the third-stage vacuum pump 18, and set the pressure of the third-stage vacuum pump 18 to -0.09 MPa.

[0155] When the liquid level of the third-stage vacuum crystallizer 16 reaches the discharge liquid level, start the third-stage delivery pump 8 to discharge into the slurry tank 9.

[0156] The third flash distillation is carried out on the sodium thiocarbamate crystal slurry, the temperature of the sodium thiocarbamate crystal slurry is 56.2℃, the mother liquor concentration of the sodium thiocarbamate crystal slurry is 65.1%, and the solid content of the sodium thiocarbamate crystal slurry is 32.9%.

[0157] In the above technical solution of the present application, the above is only the preferred embodiment of the present application, and does not limit the patent scope of the present application. Any equivalent structural transformation, direct / indirect application in other related technical fields, or the like made under the technical concept of the present application, using the content of the present application specification and drawings, is included in the patent protection scope of the present application.

Claims

1. A process for the cooling crystallization of furametpyraze, characterized in that, The sodium dimethyldithiocarbamate solution is sequentially subjected to first flash evaporation, second flash evaporation and third flash evaporation to obtain sodium dimethyldithiocarbamate crystal slurry. The concentration of the sodium dimethyldithiocarbamate solution is 65-75%, and the temperature of the sodium dimethyldithiocarbamate solution is 90-95 ℃. The sodium dimethyldithiocarbamate solution is subjected to the first flash evaporation to obtain first flash evaporation liquid, the first flash evaporation is carried out under a vacuum pressure of-0.075 to-0.085 MPa, and the temperature of the first flash evaporation liquid is 68-72 ℃. The first flash evaporation liquid is subjected to the second flash evaporation to obtain second flash evaporation liquid, the second flash evaporation is carried out under a vacuum pressure of-0.8 to-0.9 MPa, and the temperature of the second flash evaporation liquid is 58-62 ℃. The second flash evaporation liquid is subjected to the third flash evaporation to obtain the sodium dimethyldithiocarbamate crystal slurry, the third flash evaporation is carried out under a vacuum pressure of-0.09 to-0.098 MPa, and the temperature of the sodium dimethyldithiocarbamate crystal slurry is 45-50 ℃.

2. The process for the cooling crystallization of thiamicarb according to claim 1, characterized in that, The first flash evaporation is carried out under a vacuum pressure of-0.08 MPa, the second flash evaporation is carried out under a vacuum pressure of-0.85 MPa, and the third flash evaporation is carried out under a vacuum pressure of-0.098 MPa.

3. The process for the cooling crystallization of thiamicarb according to claim 1, characterized in that, The mother liquor concentration of the sodium dimethyldithiocarbamate crystal slurry is 60-65%, and the solid content in the sodium dimethyldithiocarbamate crystal slurry is 40-45%.

4. The method for cooling crystallization of thiram according to any one of claims 1 to 3, characterized in that, The vacuum continuous crystallization system is applied to the method for cooling and crystallizing sodium dimethyldithiocarbamate, and comprises a raw material tank, a flash evaporation group and a slurry tank.

5. The vacuum continuous crystallization system of claim 4, wherein, The flash evaporation group comprises: a vacuum crystallizer; a condensation part fixedly installed at the top of the vacuum crystallizer and in communication with the vacuum crystallizer to condense flash evaporation vapor; a vacuum part in communication with the condensation part to provide a vacuum environment for flash evaporation.

6. The vacuum continuous crystallization system of claim 5, wherein, The number of the flash evaporation groups is three, and the three flash evaporation groups are sequentially in communication to process the first flash evaporation, the second flash evaporation and the third flash evaporation, respectively.

7. The vacuum continuous crystallization system of claim 5, wherein, The condensation part comprises a condenser, a condensation water storage tank and a condensation water pump connected in sequence; the condensation water storage tank is connected with the vacuum part, and the vacuum part comprises a vacuum pump.

8. The vacuum continuous crystallization system of claim 5, wherein, The vacuum continuous crystallization system further comprises an agitation part fixedly installed at the bottom of the vacuum crystallizer to agitate fluid in the vacuum crystallizer; the agitation part comprises an axial flow pump.

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