A crystallization apparatus and method for continuous production of 2,4-dichlorophenoxyacetic acid

Abstract

A kind of crystallization device of continuous production 2,4-dichlorophenoxyacetic acid, comprising: premix unit is equipped with 2,4-dichlorophenoxyacetic acid methyl ester import, catalyst aqueous solution import and premix outlet;With the hydrolysis unit of premix outlet connection, it includes several groups of series hydrolysis rectification device;Hydrolysis rectification device is equipped with pump, rectification column and hydrolysis kettle in turn along the direction of feed;Hydrolysis unit is equipped with material outlet;Through hydrolysis kettle transfer pump and material outlet connection, rectification unit is equipped with water import and hydrolysis liquid outlet;With the crystallization unit of hydrolysis liquid outlet connection, it includes several groups of series crystallization kettle;Crystallization unit is equipped with crystallization material outlet;With centrifugal filtration unit of crystallization material outlet connection.The present application is with 2,4-dichlorophenoxyacetic acid ester as raw material, through hydrolysis reaction rectification continuous and gradient crystallization continuous, realize the overall better interaction, can continuous production 2,4-dichlorophenoxyacetic acid;Production efficiency is high, product stability is good, and device floor area is small.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of organic synthesis, and more particularly to a crystallization device and method for continuously producing 2,4-dichlorophenoxyacetic acid. BACKGROUND

[0002] 2,4-D, namely 2,4-dichlorophenoxyacetic acid, is also known as 2,4-dichlorophenoxyacetic acid in Chinese, 2,4-D acid in English, and has a molecular formula of C8H6Cl2O3 and a structural formula of:

[0003] ;

[0004] In 1941, R. Pocony, an American, published a synthesis method of 2,4-D, and in 1942, P.W. Zimmelman and A.E. Hitchcock first reported that 2,4-D was used as a plant growth regulator. In 1944, the U.S. Department of Agriculture reported the herbicidal effect of 2,4-D. Due to its low dosage and low cost, 2,4-D has been one of the world's major herbicides. The product has high efficiency and low toxicity, has internal absorption and transmission effects, belongs to a selective hormone type herbicide, and is commonly used in crop fields such as rice, wheat, and corn to prevent broadleaf weeds; it can also prevent flower and fruit drop, and is used as a plant growth regulator to stimulate crop growth and promote early maturity. Nowadays, 2,4-D is rarely used, but is often processed into sodium salt, ammonium salt, and ester. Among them, the physiological activity of the ester is the highest, and the efficacy of the ester is 2-3 times higher than that of the sodium salt according to the equivalent amount of 2,4-D.

[0005] The Chinese patent with publication number CN108467343A discloses a synthesis scheme of 2,4-dichlorophenoxyacetic acid, and the technical scheme is as follows: chloroacetic acid and 2,4-dichlorophenol are respectively salified with liquid alkali, a 2,4-dichlorophenoxyacetic acid sodium solution is obtained after reaction, 2,4-dichlorophenoxyacetic acid wet material is obtained after acidification and filtration, and 2,4-dichlorophenoxyacetic acid is obtained after drying. The Chinese patent with publication number CN106278862A discloses a new synthesis scheme of 2,4-dichlorophenoxyacetic acid, and the technical scheme is as follows: 2,4-dichlorophenol and chloroacetic acid are used as raw materials, step one (1) is that 2,4-dichlorophenol is refluxed with an aqueous solution of inorganic alkali to obtain a 2,4-dichlorophenol salt anhydrous system; (2) after the reaction liquid of step (1) is cooled, chloroacetic acid methyl ester is added dropwise, and reflux reaction is carried out to obtain 2,4-dichlorophenoxyacetic acid methyl ester; (3) separation, purification and desolventization; (4) 2,4-dichlorophenoxyacetic acid methyl ester is hydrolyzed under the action of a solid acid catalyst to prepare 2,4-dichlorophenoxyacetic acid. The above two technical schemes are mainstream production processes in the market at present, but most of them are intermittent or semi-continuous production, and neither of them describes the production mode and device. Based on the existing generation technology, further optimization and innovation are carried out, and a continuous production mode is adopted, which has more cost advantages.

[0006] In summary, the existing production processes of 2,4-dichlorophenoxyacetic acid all adopt an intermittent production mode, and there are many shortcomings, including a long production cycle, high energy consumption, complex operation, large labor intensity, and poor crystalline particle size of the produced product, powder, dust, and slow centrifugal filtration speed. SUMMARY

[0007] Therefore, the purpose of the present application is to provide a crystallization device and method for continuously producing 2,4-dichlorophenoxyacetic acid, which has high production efficiency, good product stability, small device area, continuous reaction rectification, high concentration of methanol fraction, reduced energy consumption, continuous gradient crystallization, good product particle size, and fast suction filtration speed.

[0008] The present application provides a crystallization device for continuously producing 2,4-dichlorophenoxyacetic acid, which comprises:

[0009] a premixing unit, wherein the premixing unit is provided with a 2,4-dichlorophenoxyacetic acid methyl ester inlet, a catalyst aqueous solution inlet and a premixing material outlet;

[0010] a hydrolysis unit connected with the premixing material outlet, wherein the hydrolysis unit comprises a plurality of groups of series-connected hydrolysis rectification devices, the hydrolysis rectification devices are sequentially provided with a pump, a rectification column and a hydrolysis kettle along the feeding direction, and the hydrolysis unit is provided with a material outlet;

[0011] a rectification unit connected with the material outlet through a hydrolysis kettle transfer pump, wherein the rectification unit is provided with a water inlet and a hydrolysis liquid outlet;

[0012] a crystallization unit connected to the hydrolysate outlet; the crystallization unit comprises several groups of series-connected crystallization kettles; the crystallization unit is provided with a crystallization material outlet;

[0013] a centrifugal filtration unit connected to the crystallization material outlet.

[0014] Preferably, the premixing unit is a premixing kettle; the premixing material outlet of the premixing unit is connected to the first-stage rectification column via a premixing kettle transfer pump; the first-stage rectification column is provided with a premixing material inlet in the middle, a catalyst aqueous solution inlet in the upper part, a first rectification material outlet in the bottom, and a first gas phase outlet in the top.

[0015] Preferably, the crystallization device for continuously producing 2,4-dichlorophenoxyacetic acid further comprises:

[0016] a post-treatment unit connected to the first gas phase outlet; the post-treatment unit comprises:

[0017] a fraction receiving tank; the fraction receiving tank is provided with a feed inlet, a tail gas outlet, and a condensed liquid outlet; the tail gas outlet is connected to a tail gas treatment unit; the condensed liquid outlet is connected to a fraction transfer pump to take out condensed liquid;

[0018] a condenser connected to the feed inlet; the condenser is provided with a gas phase inlet connected to the first gas phase outlet.

[0019] Preferably, the hydrolysis unit comprises four groups of series-connected hydrolysis rectification devices; which comprise, in sequence, a hydrolysis first-stage kettle, a hydrolysis second-stage kettle, a hydrolysis third-stage kettle, and a hydrolysis fourth-stage kettle, and, in sequence, a fourth-stage rectification column, a third-stage rectification column, a second-stage rectification column, and a first-stage rectification column; the gas phase inlet of the fourth-stage rectification column is connected to the gas phase outlet of the rectification unit.

[0020] Preferably, the hydrolysis second-stage kettle is connected to the second-stage rectification column via a second circulating pump; the hydrolysis third-stage kettle is connected to the third-stage rectification column via a third circulating pump; and the hydrolysis fourth-stage kettle is connected to the fourth-stage rectification column via a fourth circulating pump.

[0021] Preferably, the rectification unit is a rectification column; the rectification unit is provided with a reboiler; one way of the hydrolysate outlet is connected to the crystallization unit via a rectification column transfer pump, and the other way is connected to the reboiler via a first circulating pump.

[0022] Preferably, the crystallization unit comprises four groups of series-connected crystallization kettles; which comprise, in sequence, a first-stage crystallization kettle, a second-stage crystallization kettle, a third-stage crystallization kettle, and a fourth-stage crystallization kettle; the feed inlet of the first-stage crystallization kettle is connected to the hydrolysate outlet; and the transfer outlet of the fourth-stage crystallization kettle is connected to the centrifugal filtration unit.

[0023] The application further provides a crystallization method for continuously producing 2,4-dichlorophenoxyacetic acid, which adopts the crystallization device for continuously producing 2,4-dichlorophenoxyacetic acid described in the above technical scheme and comprises the following steps:

[0024] a) continuously feeding a water solution of methyl 2,4-dichlorophenoxyacetate and a catalyst into a premixing unit for premixing reaction, pumping into a hydrolysis unit for continuous rectification hydrolysis reaction after reaching reaction equilibrium, and obtaining a hydrolysis liquid through rectification;

[0025] b) continuously gradient crystallizing the hydrolysis liquid obtained in step a), and obtaining 2,4-dichlorophenoxyacetic acid through suction filtration.

[0026] Preferably, the mass ratio of the catalyst, the water solution of the catalyst and the water in the water solution of methyl 2,4-dichlorophenoxyacetate and the catalyst in step a) is 1: (0.12-0.55): (0.48-1.28).

[0027] The temperature of the premixing reaction is 90-130 DEG C, and the time is 1-5 h.

[0028] Preferably, the process of the continuous gradient crystallization in step b) is specifically as follows:

[0029] The hydrolysis liquid is fed into a first-stage crystallization kettle, the temperature of the first-stage crystallization kettle is controlled to be 80-95 DEG C, then the hydrolysis liquid is fed into a second-stage crystallization kettle, the temperature of the second-stage crystallization kettle is controlled to be 60-75 DEG C, then the hydrolysis liquid is fed into a third-stage crystallization kettle, the temperature of the third-stage crystallization kettle is controlled to be 40-55 DEG C, and then the hydrolysis liquid is fed into a fourth-stage crystallization kettle, the temperature of the fourth-stage crystallization kettle is controlled to be 20-35 DEG C.

[0030] This invention provides a crystallization apparatus and method for the continuous production of 2,4-dichlorophenoxyacetic acid; the apparatus includes: a premixing unit; the premixing unit having an inlet for methyl 2,4-dichlorophenoxyacetic acid, an inlet for an aqueous solution of catalyst, and a premix outlet; a hydrolysis unit connected to the premix outlet; the hydrolysis unit including several sets of hydrolysis distillation devices connected in series; the hydrolysis distillation devices having a pump, a distillation column, and a hydrolysis kettle sequentially arranged along the feed direction; the hydrolysis unit having a material outlet; a distillation unit connected to the material outlet via a hydrolysis kettle transfer pump; the distillation unit having a water inlet and a hydrolysate outlet; a crystallization unit connected to the hydrolysate outlet; the crystallization unit including several sets of crystallization kettles connected in series; the crystallization unit having a crystallized material outlet; and a centrifugal filtration unit connected to the crystallized material outlet. Compared with existing technologies, the crystallization apparatus and method for continuous production of 2,4-dichlorophenoxyacetic acid provided by this invention uses 2,4-dichlorophenoxyacetic acid ester as raw material. Through continuous hydrolysis reaction distillation and continuous gradient crystallization, a better overall interaction is achieved, enabling continuous production of 2,4-dichlorophenoxyacetic acid. It has high production efficiency, good product stability, and a small footprint. Furthermore, continuous reaction distillation increases the concentration of methanol in the distillate and reduces energy consumption; continuous gradient crystallization results in good product particle size and fast filtration speed. Attached Figure Description

[0031] Figure 1 A schematic diagram of the structure of a crystallization apparatus for continuous production of 2,4-dichlorophenoxyacetic acid provided in an embodiment of the present invention;

[0032] Figure 2 A process flow diagram of a continuous crystallization method for producing 2,4-dichlorophenoxyacetic acid provided in an embodiment of the present invention. Detailed Implementation

[0033] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0034] This invention provides a crystallization apparatus for the continuous production of 2,4-dichlorophenoxyacetic acid, comprising:

[0035] The premixing unit is equipped with a 2,4-dichlorophenoxyacetic acid methyl ester inlet, a catalyst aqueous solution inlet, and a premix outlet.

[0036] A hydrolysis unit connected to the premix outlet; the hydrolysis unit comprises several groups of hydrolysis rectification devices connected in series; the hydrolysis rectification devices are provided with a pump, a rectification column and a hydrolysis kettle in sequence along the feeding direction; the hydrolysis unit is provided with a material outlet;

[0037] A rectification unit connected to the material outlet through a hydrolysis kettle transfer pump; the rectification unit is provided with a water inlet and a hydrolysis liquid outlet;

[0038] A crystallization unit connected to the hydrolysis liquid outlet; the crystallization unit comprises several groups of crystallization kettles connected in series; the crystallization unit is provided with a crystallization material outlet;

[0039] A centrifugal filtration unit connected to the crystallization material outlet.

[0040] Please refer to Figure 1 , Figure 1 A structure schematic diagram of the crystallization device for continuously producing 2,4-dichlorophenoxyacetic acid provided by the embodiment of the present application; wherein, 1 is a premix kettle, 2 is a premix kettle transfer pump, 3 is a first-stage hydrolysis kettle, 4 is a second-stage hydrolysis kettle, 5 is a third-stage hydrolysis kettle, 6 is a fourth-stage hydrolysis kettle, 7, 8 and 9 are circulation pumps between the kettle and the rectification column, 10 is a first-stage rectification column, 11 is a second-stage rectification column, 12 is a third-stage rectification column, 13 is a fourth-stage rectification column, 14 is a fourth-stage hydrolysis kettle transfer pump, 15 is a rectification column, 16 is a reboiler, 17 is a circulation pump, 18 is a rectification column discharge pump, 19 is a condenser, 20 is a fraction receiving tank, 21 is a fraction transfer pump, 22 is a first-stage crystallization kettle, 23 is a second-stage crystallization kettle, 24 is a third-stage crystallization kettle, and 25 is a fourth-stage crystallization kettle.

[0041] In the present application, the crystallization device for continuously producing 2,4-dichlorophenoxyacetic acid mainly comprises a premix unit, a hydrolysis unit, a rectification unit, a crystallization unit and a centrifugal filtration unit.

[0042] In the present application, the premix unit is used to make the methyl 2,4-dichlorophenoxyacetate and water reach the reaction equilibrium under the action of the catalyst p-toluenesulfonic acid. In the present application, the premix unit is provided with a methyl 2,4-dichlorophenoxyacetate inlet, a water-soluble catalyst inlet and a premix outlet.

[0043] In the present application, the premix unit is preferably a premix kettle, which is provided with a jacket outside the kettle and can be heated by steam.

[0044] In the present application, the premix outlet of the premix unit is preferably connected to the first-stage rectification column through a premix kettle transfer pump; the first-stage rectification column is provided with a premix inlet in the middle, a water-soluble catalyst inlet in the upper part, a first rectification material outlet in the bottom and a first gas phase outlet in the top.

[0045] In the present application, the crystallization device for continuously producing 2,4-dichlorophenoxyacetic acid preferably further comprises:

[0046] a post-processing unit connected with the first gas phase outlet; the post-processing unit comprises:

[0047] a fraction receiving tank; the fraction receiving tank is provided with a feed inlet, a tail gas outlet and a condensate outlet; the tail gas outlet is connected with a tail gas processing unit; the condensate outlet discharges condensate through a fraction transfer pump;

[0048] a condenser connected with the feed inlet; the condenser is provided with a gas phase inlet connected with the first gas phase outlet.

[0049] In the present application, the hydrolysis unit is connected with the premix outlet; the hydrolysis unit comprises several groups of hydrolysis rectification devices connected in series; the hydrolysis rectification devices are sequentially provided with a pump, a rectification column and a hydrolysis kettle along the feed direction; the hydrolysis unit is provided with a material outlet.

[0050] In the preferred embodiment of the present application, the hydrolysis unit preferably comprises four groups of hydrolysis rectification devices connected in series (which can be increased according to the number of hydrolysis kettles and rectification columns); which comprises a hydrolysis first-stage kettle, a hydrolysis second-stage kettle, a hydrolysis third-stage kettle and a hydrolysis fourth-stage kettle connected in series, a fourth-stage rectification column, a third-stage rectification column, a second-stage rectification column and a first-stage rectification column connected in series for rectifying methanol to improve the concentration of methanol, and a water solution of a catalyst is additionally added to the upper part of the first-stage rectification column to prevent 2,4-dichlorophenoxy methyl acetate from entering the fraction; the gas phase inlet of the fourth-stage rectification column is connected with the gas phase outlet of the rectification unit.

[0051] In the present application, the above-mentioned hydrolysis first-stage kettle, hydrolysis second-stage kettle, hydrolysis third-stage kettle and hydrolysis fourth-stage kettle provide heat source, residence time, and continue to react 2,4-dichlorophenoxy methyl acetate and water to generate 2,4-dichlorophenoxyacetic acid and methanol; at the same time, the liquid inlets and outlets of the hydrolysis second-stage kettle and the hydrolysis third-stage kettle are both low-in and high-out, and can also be high-in and low-out, but a device for preventing gas from being mixed must be added to the pipeline.

[0052] In the present application, the hydrolysis second-stage kettle is preferably connected with the second-stage rectification column through a second circulating pump; the hydrolysis third-stage kettle is preferably connected with the third-stage rectification column through a third circulating pump; and the hydrolysis fourth-stage kettle is preferably connected with the fourth-stage rectification column through a fourth circulating pump. In the present application, the second circulating pump, the third circulating pump and the fourth circulating pump are all circulating pumps between the kettle and the rectification column, which fully contact the hydrolysis liquid in the hydrolysis kettle with the gas in the rectification column through the above-mentioned circulating pumps, so that the newly generated methanol in the hydrolysis liquid enters the gas phase, the concentration of methanol in the hydrolysis liquid is maintained constant, and the concentration of methanol in the gas is improved.

[0053] In the present application, the distillation unit is connected with the material outlet through a hydrolysis kettle transfer pump; the distillation unit is provided with a water inlet and a hydrolysis liquid outlet.

[0054] In the present application, the distillation unit is preferably a distillation column, which continues to react the unreacted 2,4-dichlorophenoxyacetic acid methyl ester to qualified products, and the column kettle is supplemented with water to maintain the constant concentration of p-toluenesulfonic acid in the device; the distillation unit is preferably provided with a reboiler to provide a heat source and a residence time; one way of the hydrolysis liquid outlet is connected with the crystallization unit through a distillation column discharge pump, and the other way is connected with the reboiler through a first circulating pump.

[0055] In the present application, the crystallization unit is connected with the hydrolysis liquid outlet; the crystallization unit includes a plurality of groups of series-connected crystallization kettles; the crystallization unit is provided with a crystallization material outlet.

[0056] In the preferred embodiment of the present application, the crystallization unit preferably includes 4 groups of series-connected crystallization kettles (the number of crystallization kettles can be increased as needed); which includes a first-stage crystallization kettle, a second-stage crystallization kettle, a third-stage crystallization kettle and a fourth-stage crystallization kettle connected in sequence; the feed inlet of the first-stage crystallization kettle is connected with the hydrolysis liquid outlet; and the discharge outlet of the fourth-stage crystallization kettle is connected with a centrifugal filtration unit. In the present application, the first-stage crystallization kettle, the second-stage crystallization kettle, the third-stage crystallization kettle and the fourth-stage crystallization kettle all need to be controlled at a constant temperature to realize gradient crystallization and continuous production.

[0057] In the present application, the centrifugal filtration unit is connected with the crystallization material outlet.

[0058] The present application also provides a crystallization method for continuously producing 2,4-dichlorophenoxyacetic acid, which uses the crystallization device for continuously producing 2,4-dichlorophenoxyacetic acid described in the above technical solution, and includes the following steps:

[0059] a) continuously feeding the aqueous solution of 2,4-dichlorophenoxyacetic acid methyl ester and catalyst into the premixing unit for premixing reaction, pumping into the hydrolysis unit for continuous rectification hydrolysis reaction after reaching reaction equilibrium, and then performing rectification to obtain a hydrolysis liquid;

[0060] b) continuously gradient crystallizing the hydrolysis liquid obtained in step a), and then performing suction filtration to obtain 2,4-dichlorophenoxyacetic acid.

[0061] In the present application, the product is obtained by continuous hydrolysis of ester, and the specific reaction equation is as follows:

[0062] .

[0063] The application firstly continuously feeds the aqueous solution of methyl 2,4-dichlorophenoxyacetate and catalyst into a premixing unit for premixing reaction, and after the reaction reaches equilibrium, pumps into a hydrolysis unit for continuous rectification hydrolysis reaction, and then through rectification, the hydrolysate is obtained.

[0064] In the application, the catalyst is preferably an acidic compound, preferably selected from one or more of alkyl benzene sulfonic acid, alkyl naphthalene sulfonic acid, m-toluene sulfonic acid, p-toluene sulfonic acid, and more preferably p-toluene sulfonic acid. The application does not have special restrictions on the source of the catalyst, and commercially available products known to those skilled in the art can be used.

[0065] In the application, the step a) is a continuous process of rectification hydrolysis, preferably comprising the following steps:

[0066] Firstly, the aqueous solution of methyl 2,4-dichlorophenoxyacetate and p-toluene sulfonic acid is fed into a premixing kettle, and the reaction reaches equilibrium in the premixing kettle; then, the material in the premixing kettle that reaches equilibrium is continuously fed into the first-stage rectification column, and part of the aqueous solution of p-toluene sulfonic acid is fed into the first-stage rectification column, and the material is fed from the first-stage rectification column into the first-stage hydrolysis kettle, and the liquid phase is overflowed into the next-stage hydrolysis kettle for continuous reaction, and the material in the hydrolysis kettle is re-fed into the corresponding rectification column from the bottom thereof for separation, and the methanol formed in the hydrolysis kettle is fed into the upper-stage rectification column through a gas phase pipeline, and the liquid phase in the upper-stage hydrolysis kettle is overflowed into the next-stage hydrolysis kettle for continuous reaction; at the same time, the feed inlet of the hydrolysis kettle is lower than the feed outlet, or there is an anti-gas phase cross-gas device in the overflow pipeline, and then the liquid phase is fed into the rectification column for continuous reaction, and in order to maintain the concentration of p-toluene sulfonic acid, the rectification column kettle is supplemented with water generated by reaction and water taken out by distillation, and the kettle of the rectification column obtains the hydrolysate with qualified conversion rate; finally, the methanol formed by reaction in the rectification column and the hydrolysis kettle is finally discharged from the first-stage rectification column, and the methanol aqueous solution is obtained through condensation.

[0067] In the application, the mass ratio of the aqueous solution of methyl 2,4-dichlorophenoxyacetate, the catalyst in the aqueous solution of catalyst, and the water in the aqueous solution of catalyst is preferably 1: (0.12-0.55): (0.48-1.28), and more preferably 1: (0.24-0.35): (0.96-1.12).

[0068] In the application, the temperature of the premixing reaction is preferably 90-130℃, and more preferably 100-110℃, and the time is preferably 1-5h, and more preferably 2-3h.

[0069] After obtaining the hydrolysate, the application continuously performs gradient crystallization on the obtained hydrolysate, and then through suction filtration, 2,4-dichlorophenoxyacetic acid is obtained.

[0070] In the application, the step b) is a continuous process of gradient crystallization, preferably comprising the following steps:

[0071] The hydrolysate with qualified conversion rate enters a first-stage crystallization kettle, and overflows into a next-stage crystallization kettle, and the material after crystallization is completed is sampled and detected for particle size, filtered, washed with water, and dried to obtain 2,4-dichlorophenoxyacetic acid.

[0072] In the present application, the process of the continuous gradient crystallization is preferably specifically as follows:

[0073] The hydrolysate enters a first-stage crystallization kettle, the temperature of the first-stage crystallization kettle is controlled to be 80-95 DEG C, preferably 85-90 DEG C, then enters a second-stage crystallization kettle, the temperature of the second-stage crystallization kettle is controlled to be 60-75 DEG C, preferably 65-70 DEG C, then enters a third-stage crystallization kettle, the temperature of the third-stage crystallization kettle is controlled to be 40-55 DEG C, preferably 45-50 DEG C, and then enters a fourth-stage crystallization kettle, the temperature of the fourth-stage crystallization kettle is controlled to be 20-35 DEG C, preferably 25-30 DEG C.

[0074] The present application provides a crystallization device and method for continuously producing 2,4-dichlorophenoxyacetic acid, compared with batch hydrolysis, the hydrolysis process adopts continuous hydrolysis and reaction rectification, which reduces the energy consumption for removing methanol; at the same time, the crystallization process adopts the way of multi-kettle series continuous gradient cooling crystallization, which has large crystallization particle size, solves the problem of slow filtration speed, and the like; and the continuous production mode reduces the number of on-site equipment and the volume of production equipment, optimizes the production space layout, has high automation degree, reduces labor cost, has stable product quality, is green and environmentally friendly, and the like.

[0075] The present application provides a crystallization device and method for continuously producing 2,4-dichlorophenoxyacetic acid; the device comprises: a premixing unit, the premixing unit is provided with a 2,4-dichlorophenoxyacetic acid methyl ester inlet, a water solution of catalyst inlet and a premixing material outlet, a hydrolysis unit connected with the premixing material outlet, the hydrolysis unit comprises a plurality of groups of series-connected hydrolysis rectification devices, the hydrolysis rectification devices are sequentially provided with a pump, a rectification column and a hydrolysis kettle along the feeding direction, the hydrolysis unit is provided with a material outlet, a rectification unit connected with the material outlet through a hydrolysis kettle transfer pump, the rectification unit is provided with a water inlet and a hydrolysis liquid outlet, a crystallization unit connected with the hydrolysis liquid outlet, the crystallization unit comprises a plurality of groups of series-connected crystallization kettles, the crystallization unit is provided with a crystallization material outlet, and a centrifugal filtration unit connected with the crystallization material outlet. Compared with the prior art, the crystallization device and method for continuously producing 2,4-dichlorophenoxyacetic acid provided by the present application takes 2,4-dichlorophenoxyacetic acid ester as a raw material, realizes hydrolysis reaction rectification continuous and gradient crystallization continuous, realizes good interaction as a whole, can continuously produce 2,4-dichlorophenoxyacetic acid, has high production efficiency and good product stability, at the same time, the device has small floor area; the reaction rectification continuous improves the concentration of distillate methanol, reduces energy consumption; the gradient crystallization continuous has good product particle size and fast filtration speed.

[0076] In order to further illustrate the present application, the following examples are described in detail below.

[0077] Examples

[0078] The crystallization device for continuously producing 2,4-dichlorophenoxyacetic acid in the embodiment of the present application adopts the technical scheme described above, and a structural schematic diagram is shown in Figure 1 The crystallization device for continuously producing 2,4-dichlorophenoxyacetic acid in the embodiment of the present application adopts the technical scheme described above, and a structural schematic diagram is shown in

[0079] The specific working process of the crystallization device for continuously producing 2,4-dichlorophenoxyacetic acid described above is as follows:

[0080] (1) Hydrolysis:

[0081] 1) The 2,4-dichlorophenoxyacetic acid methyl ester and the water solution containing the catalyst p-toluenesulfonic acid are transferred into the 1 pre-mixer, the materials reach the reaction equilibrium, the liquid phase is transferred into the middle of the 10 first-stage rectifying column through the 2 pre-mixer transfer pump, and enters the 3 first-stage hydrolysis kettle.

[0082] 2) At the same time, part of the material B p-toluenesulfonic acid water solution is transferred into the upper part of the 10 first-stage rectifying column and enters the 3 first-stage hydrolysis kettle.

[0083] 3) The gas phase of the 3 first-stage hydrolysis kettle and the gas phase of the 11 second-stage rectifying column enter the lower part of the 10 first-stage rectifying column, the upward gas phase in the rectifying column exchanges with the downward liquid phase, and finally the gas phase is condensed through the 19 condenser and enters the 20 fraction receiving tank; the liquid phase of the 3 first-stage hydrolysis kettle enters the 4 second-stage hydrolysis kettle through the overflow pipeline; at the same time, the feed inlet of the hydrolysis kettle is lower than the discharge outlet or there is an anti-gas phase cross-gas device in the overflow pipeline.

[0084] 4) Part of the liquid phase from the 4 hydrolysis secondary reactor enters the upper part of the 11 second-stage distillation column through the 7 second circulation pump, and then enters the 4 hydrolysis secondary reactor; part of the liquid phase overflows into the 5 hydrolysis tertiary reactor, and the gas phase from the 4 hydrolysis secondary reactor and the 12 third-stage distillation column enter the lower part of the 11 second-stage distillation column. After the upward gas phase and the downward liquid phase in the distillation column exchange gas and liquid, the gas phase enters the lower part of the 10 first-stage distillation column.

[0085] 5) Part of the liquid phase from the 5th hydrolysis tertiary reactor enters the upper part of the 12th stage distillation column through the 8th third circulation pump, and then enters the 5th hydrolysis tertiary reactor; part of the liquid phase overflows into the 6th hydrolysis quaternary reactor. The gas phase from the 5th hydrolysis tertiary reactor and the gas phase from the 13th stage distillation column enter the lower part of the 12th stage distillation column. After the upward gas phase and the downward liquid phase in the distillation column exchange gas and liquid, the gas phase enters the lower part of the 11th stage distillation column.

[0086] 6) Part of the liquid phase from the 6th hydrolysis stage IV reactor enters the upper part of the 13th stage distillation column through the 9th fourth circulation pump, and then enters the 6th hydrolysis stage IV reactor; part of the liquid phase enters the upper part of the 15th distillation column through the transfer pump 14; the gas phase from the 6th hydrolysis stage IV reactor and the 15th distillation column enters the lower part of the 13th stage distillation column; after the upward gas phase and the downward liquid phase exchange gas and liquid in the distillation column, the gas phase enters the lower part of the 12th stage distillation column.

[0087] 7) The liquid in the upper part of the 15 distillation column enters the lower part of the distillation column, and the water enters the lower part of the distillation column. Part of the liquid in the lower part of the distillation column is transferred to the crystallizer through the 18 distillation column discharge pump; part of the liquid enters the reboiler through the 17 first circulation pump to generate a gas phase. The upward gas phase and the downward liquid phase in the distillation column exchange gas and liquid, and the gas phase enters the lower part of the 13 distillation column.

[0088] 8) Finally, the methanol-water solution is obtained from the condenser, and the hydrolysate with qualified conversion rate is obtained from the bottom of the distillation column.

[0089] (2) Crystallization:

[0090] The qualified hydrolysate enters the primary crystallizer (22) and is controlled at temperature T1; it overflows into the secondary crystallizer (23) and is controlled at temperature T2; it overflows into the tertiary crystallizer (24) and is controlled at temperature T3; it overflows into the quaternary crystallizer (25) and is controlled at temperature T4; the material is then transferred out to obtain a qualified crystalline mixture; finally, it is continuously produced by filtration, washing, and drying.

[0091] See Figure 2 As shown, Figure 2 A process flow diagram of a continuous crystallization method for producing 2,4-dichlorophenoxyacetic acid provided in an embodiment of the present invention.

[0092] The specific experimental data are as follows:

[0093] (1) 2,4-dichlorophenoxyacetic acid methyl ester (content 99%) mass flow 235.06 g / h, 25% p-toluene sulfonic acid aqueous solution (p-toluene sulfonic acid is a catalyst) mass flow 282.07 g / h continuously into the premix kettle, stirred and mixed at 97 ℃ for 2-3 h, the reaction reaches equilibrium, the premix kettle liquid level is maintained stable, transferred to the middle of the first rectification column by pump, at the same time 25% p-toluene sulfonic acid aqueous solution is added into the upper part of the first rectification column at a flow rate of 23.51 g / h, the temperature of the hydrolysis first kettle is controlled at 99 ℃, the temperature of the hydrolysis second kettle is controlled at 101 ℃, the temperature of the hydrolysis third kettle is controlled at 102 ℃, the temperature of the hydrolysis fourth kettle is controlled at 103 ℃, the hydrolysis fourth kettle liquid level is maintained stable, transferred into the rectification column by pump, water is added into the column kettle at a mass flow of 210.14 g / h, the column kettle temperature is controlled at 104 ℃, the column kettle liquid level is maintained stable, the qualified hydrolysis liquid is output by pump; detection shows that the conversion rate of 2,4-dichlorophenoxyacetic acid methyl ester is 99.8% (≥99.5%), the C10 content in the hydrolysis liquid is 41.45%, and the distillate obtained at the top of the column contains ≥15% methanol.

[0094] (2) the qualified hydrolysis liquid is added into the first crystallization kettle, the temperature of the first crystallization kettle is controlled at 85-90 ℃, the temperature of the second crystallization kettle is controlled at 65-70 ℃, the temperature of the third crystallization kettle is controlled at 45-50 ℃, the temperature of the fourth crystallization kettle is controlled at 25-30 ℃, the material obtained from the fourth kettle is measured for particle size, and is filtered, the filtration speed is 8000 Kg / (m³*h), and after washing and drying, 2,4-dichlorophenoxyacetic acid is continuously produced.

[0095] The particle size distribution detection results are shown in the following Table 1.

[0096] Table 1

[0097]

[0098] Comparative Example

[0099] The conventional operation mode is adopted, and the operation steps are as follows:

[0100] (1) 2,4-dichlorophenoxyacetic acid methyl ester and p-toluene sulfonic acid aqueous solution are respectively added into a flask, 2,4-dichlorophenoxyacetic acid methyl ester (content 99%) mass 235.06 g, p-toluene sulfonic acid aqueous solution (p-toluene sulfonic acid content 25%) mass 305.58 g, start heating and distillation, control the reaction temperature at 103-105 ℃, and add water to maintain the concentration of p-toluene sulfonic acid during the distillation process; the conversion rate of 2,4-dichlorophenoxyacetic acid methyl ester is detected by sampling the column kettle, the conversion rate is 99.7% (≥99.5%) qualified, and 616.65 g of water is added during the process, and the content of the distillate methanol is about 5.0%.

[0101] (2) The qualified hydrolysis liquid is directly cooled to 25-30 DEG C with cold water, and kept for 30 min, and the particle size is detected, and the same way is used for suction filtration, the suction filtration speed is 5000 Kg / (m3*h), and 2,4-dichlorophenoxyacetic acid is produced after washing with water and drying.

[0102] The particle size distribution detection result is shown in the following table 2.

[0103] Table 2

[0104]

[0105] Compared with the above examples and the comparative examples, it can be seen that the content of the methanol fraction in the examples is close to 3 times, the energy consumption is obviously reduced, and the overall particle size of the gradient crystallization in the examples is larger than that of the comparative examples, and the suction filtration speed of the comparative examples is more intuitive.

[0106] In summary, the crystallization device and method for continuously producing 2,4-dichlorophenoxyacetic acid provided by the application have the following beneficial effects:

[0107] (1) The whole process is continuously produced, and has the following advantages: ① High production efficiency: continuous production can realize the continuity of the production process, reduce the intervention of production workers, and the production efficiency is higher; ② Good product stability: continuous production can ensure the stability of various parameters in the production process, and ensure the stability of the particle size, while the stability of different batches in batch crystallization is poor, and the stability of the product cannot be guaranteed; ③ Small occupied area: the volume of the batch crystallization equipment is too large, the investment is high, and the space is high, while the continuous production can complete the production process in a smaller space, and reduce the land occupation of the production plant.

[0108] (2) The reaction rectification is continuously produced, the concentration of the methanol fraction is improved, and the energy consumption is reduced, and the higher the concentration of methanol is, the lower the energy consumption is.

[0109] (3) The gradient crystallization is continuously produced, the suction filtration speed is fast, and the particle size and the suction filtration speed are used to judge.

[0110] The above description of the disclosed embodiments enables a person skilled in the art to implement or use the application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the application. Therefore, the application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A crystallization apparatus for the continuous production of 2,4-dichlorophenoxyacetic acid, characterized in that, It comprises: a premixing unit; the premixing unit is provided with a methyl 2,4-dichlorophenoxyacetate inlet, a catalyst aqueous solution inlet and a premixing material outlet; the premixing unit is a premixing kettle; the premixing material outlet of the premixing unit is connected with the first-stage rectification column through a premixing kettle transfer pump; the first-stage rectification column is provided with a premixing material inlet in the middle, a catalyst aqueous solution inlet in the upper part, a first-stage rectification material outlet in the bottom and a first-stage gas phase outlet in the top; a hydrolysis unit connected with the premixing material outlet; the hydrolysis unit comprises four groups of hydrolysis rectification devices connected in series; which comprises a hydrolysis first-stage kettle, a hydrolysis second-stage kettle, a hydrolysis third-stage kettle and a hydrolysis fourth-stage kettle connected in series, a fourth-stage rectification column, a third-stage rectification column, a second-stage rectification column and a first-stage rectification column connected in series; the gas phase inlet of the fourth-stage rectification column is connected with the gas phase outlet of the rectification unit; the hydrolysis rectification devices are provided with a pump, a rectification column and a hydrolysis kettle in sequence along the feeding direction; the hydrolysis unit is provided with a material outlet; a rectification unit connected with the material outlet through a hydrolysis kettle transfer pump; the rectification unit is provided with a water inlet, a hydrolysis liquid outlet and a reboiler; the rectification unit is a rectification column; the hydrolysis liquid outlet is connected with the crystallization unit through a rectification column discharge pump in one way and connected with the reboiler through a first circulating pump in another way; a crystallization unit connected with the hydrolysis liquid outlet; the crystallization unit comprises four groups of crystallization kettles connected in series; which comprises a first-stage crystallization kettle, a second-stage crystallization kettle, a third-stage crystallization kettle and a fourth-stage crystallization kettle connected in sequence; the feeding inlet of the first-stage crystallization kettle is connected with the hydrolysis liquid outlet; the discharge outlet of the fourth-stage crystallization kettle is connected with a centrifugal filtration unit; the crystallization unit is provided with a crystallization material outlet; a centrifugal filtration unit connected with the crystallization material outlet.

2. The crystallization apparatus for the continuous production of 2,4-dichlorophenoxyacetic acid according to claim 1, characterized in that The crystallization device for continuously producing 2,4-dichlorophenoxyacetic acid also comprises: a post-treatment unit connected with the first-stage gas phase outlet; the post-treatment unit comprises: a fraction receiving tank; the fraction receiving tank is provided with a feeding inlet, a tail gas outlet and a condensed liquid outlet; the tail gas outlet is connected with a tail gas treatment unit; the condensed liquid outlet is used to take out condensed liquid through a fraction transfer pump; a condenser connected with the feeding inlet; the condenser is provided with a gas phase inlet connected with the first-stage gas phase outlet.

3. The crystallization apparatus for the continuous production of 2,4-dichlorophenoxyacetic acid according to claim 1, characterized in that The hydrolysis second-stage kettle is connected with the second-stage rectification column through a second circulating pump; the hydrolysis third-stage kettle is connected with the third-stage rectification column through a third circulating pump; the hydrolysis fourth-stage kettle is connected with the fourth-stage rectification column through a fourth circulating pump.

4. A crystallization process for the continuous production of 2,4-dichlorophenoxyacetic acid, characterized in that, The crystallization device for continuously producing 2,4-dichlorophenoxyacetic acid according to any one of claims 1-3 comprises the following steps: a) continuously feeding methyl 2,4-dichlorophenoxyacetate and a catalyst aqueous solution into the premixing unit for premixing reaction, after reaching reaction equilibrium, pumping into the hydrolysis unit for continuous rectification hydrolysis reaction, and then rectifying to obtain a hydrolysis liquid; b) continuously gradient crystallizing the hydrolysis liquid obtained in step a), and then suction filtering to obtain 2,4-dichlorophenoxyacetic acid.

5. The continuous crystallization process for producing 2,4-dichlorophenoxyacetic acid according to claim 4, characterized in that, The mass ratio of the methyl 2,4-dichlorophenoxyacetate in step a), the catalyst in the aqueous solution of the catalyst, and water in the aqueous solution of the catalyst is 1:(0.12-0.55):(0.48-1.28). The temperature of the premixed reaction is 90-130 DEG C, and the time is 1-5 h.

6. The continuous crystallization process for producing 2,4-dichlorophenoxyacetic acid according to claim 4, characterized in that, The process of the continuous gradient crystallization in step b) is specifically as follows: The hydrolysis liquid enters a first-stage crystallization kettle, the temperature of which is controlled to be 80-95 DEG C, then enters a second-stage crystallization kettle, the temperature of which is controlled to be 60-75 DEG C, then enters a third-stage crystallization kettle, the temperature of which is controlled to be 40-55 DEG C, and then enters a fourth-stage crystallization kettle, the temperature of which is controlled to be 20-35 DEG C.

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