Crystallization device and method for continuously producing 2, 4-dichlorophenoxyacetic acid

Abstract

A crystallization device for continuously producing 2, 4-dichlorphenoxyacetic acid comprises a premixing unit provided with a methyl 2, 4-dichlorphenoxyacetate inlet, a catalyst aqueous solution inlet and a premix outlet; the hydrolysis unit is connected with the premix outlet and comprises a plurality of groups of hydrolysis rectification devices which are connected in series; the hydrolysis rectification device is 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; the rectification unit is connected with the material outlet through a hydrolysis kettle transfer pump and is provided with a water inlet and a hydrolysate outlet; the crystallization unit is connected with the hydrolysate outlet and comprises a plurality of groups of crystallization kettles which are connected in series; the crystallization unit is provided with a crystallized material outlet; and the centrifugal filtering unit is connected with the crystallized material outlet. According to the invention, 2, 4-dichlorophenoxyacetic acid ester is used as a raw material, and through hydrolysis reaction rectification continuity and gradient crystallization continuity, overall good interaction is realized, and 2, 4-dichlorophenoxyacetic acid can be continuously produced; the device is high in production efficiency, good in product stability and small in occupied area.

Description

Technical Field

[0001] The invention relates to the technical field of organic synthesis, and more specifically to a crystallization device and method for continuously producing 2,4-dichlorophenoxyacetic acid. Background Art

[0002] 2,4-D, namely 2,4-dichlorophenoxyacetic acid, is also known as 2,4-dichlorophenoxyacetic acid and 2,4-D acid in Chinese. Its common English name is 2,4-Dichlorophenoxyacetic acid. Its molecular formula is C8H6Cl2O3 and its structural formula is:

[0003] ;

[0004] In 1941, American R. Poconi published the synthesis method of 2,4-D. In 1942, PW Zimmerman and AE Hitchcock first reported the use of 2,4-D as a plant growth regulator. In 1944, the U.S. Department of Agriculture reported the weed-killing effect of 2,4-D. Later, it has been one of the main herbicide varieties in the world because of its low dosage and low cost. This product has high efficacy, low toxicity, internal absorption and conduction effects, and is a selective hormone-type herbicide. It is often used to control broadleaf weeds in rice, wheat, corn and other crop fields; it can also prevent flower and fruit drop, and as a plant growth regulator, it stimulates crop growth and promotes early maturity. Nowadays, 2,4-D is rarely used, but is mostly processed into sodium salt, ammonium salt and ester. Among them, esters have the highest physiological activity. According to the equivalent amount of 2,4-D, the efficacy of esters is 2 to 3 times higher than that of sodium salts.

[0005] Chinese patent publication number CN108467343A discloses a synthesis scheme for 2,4-dichlorophenoxyacetic acid, and its technical scheme is as follows: chloroacetic acid and 2,4-dichlorophenol are respectively salified with liquid alkali, and after salification, a sodium 2,4-dichlorophenoxyacetic acid solution is obtained by reaction, and 2,4-dichlorophenoxyacetic acid wet material is obtained by acidification and filtration, and 2,4-dichlorophenoxyacetic acid is obtained by drying. The Chinese patent with publication number CN106278862A discloses a new synthesis scheme of 2,4-dichlorophenoxyacetic acid, and its technical scheme is as follows: 2,4-dichlorophenol and chloroacetic acid are used as raw materials, step 1 (1) 2,4-dichlorophenol and an aqueous solution of an inorganic base are refluxed with water to react to obtain an anhydrous system of 2,4-dichlorophenol salt; (2) after the reaction solution of step (1) is cooled, methyl chloroacetate is added dropwise, refluxed to react, and methyl 2,4-dichlorophenoxyacetate is obtained; (3) separation, purification and desolventization; (4) methyl 2,4-dichlorophenoxyacetate is hydrolyzed in the presence of a solid acid catalyst to prepare 2,4-dichlorophenoxyacetic acid. The above two technical schemes are the mainstream production processes on the market, but most of them are intermittent or semi-continuous production, and neither of them describes the production method and device. Further optimization and innovation based on the existing generation technology and the adoption of a continuous production method have more cost advantages.

[0006] In summary, the existing processes for producing 2,4-dichlorophenoxyacetic acid all adopt an intermittent production method, which has many disadvantages including a long production cycle, high energy consumption, complex operation, and a large amount of manual labor; and the product produced has a poor crystal particle size, is powdery, generates dust, and has a slow centrifugal filtration speed. Summary of the invention

[0007] In view of this, the object of the present invention is to provide a crystallization device and method for continuously producing 2,4-dichlorophenoxyacetic acid, which has high production efficiency, good product stability, and a small footprint; and the reaction distillation is continuous, the concentration of methanol in the fraction is increased, and the energy consumption is reduced; the gradient crystallization is continuous, the product particle size is good, and the filtration speed is fast.

[0008] The present invention provides a crystallization device for continuously producing 2,4-dichlorophenoxyacetic acid, comprising:

[0009] Premixing unit; the premixing unit is provided with an inlet for methyl 2,4-dichlorophenoxyacetate, an inlet for an aqueous solution of a catalyst and an outlet for a premix;

[0010] A hydrolysis unit connected to the premix outlet; the hydrolysis unit comprises a plurality of groups of hydrolysis and distillation devices connected in series; the hydrolysis and distillation devices are provided with a pump, a distillation column and a hydrolysis kettle in sequence along the feed direction; the hydrolysis unit is provided with a material outlet;

[0011] A distillation unit connected to the material outlet via a hydrolysis kettle transfer pump; the distillation unit is provided with a water inlet and a hydrolyzate outlet;

[0012] A crystallization unit connected to the hydrolyzate outlet; the crystallization unit comprises a plurality of series-connected crystallization kettles; the crystallization unit is provided with a crystallization material outlet;

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

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

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

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

[0017] The distillate receiving tank is provided with a feed inlet, an exhaust gas outlet and a condensate outlet; the exhaust gas outlet is connected to the exhaust gas treatment unit; the condensate outlet is pumped out through a distillate transfer pump;

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

[0019] Preferably, the hydrolysis unit comprises 4 groups of hydrolysis and distillation devices connected in series, including a first-stage hydrolysis kettle, a second-stage hydrolysis kettle, a third-stage hydrolysis kettle and a fourth-stage hydrolysis kettle connected in sequence, and a fourth-stage distillation column, a third-stage distillation column, a second-stage distillation column and a first-stage distillation column connected in sequence; the gas phase inlet of the fourth-stage distillation column is connected to the gas phase outlet of the distillation unit.

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

[0021] Preferably, the distillation unit is a distillation tower; the distillation unit is provided with a reboiler; one path of the hydrolyzate outlet is connected to the crystallization unit via a distillation tower discharge pump, and the other path is connected to the reboiler via a first circulation pump.

[0022] Preferably, the crystallization unit comprises 4 groups of crystallization kettles connected in series, including a primary crystallization kettle, a secondary crystallization kettle, a tertiary crystallization kettle and a quaternary crystallization kettle connected in sequence; the feed port of the primary crystallization kettle is connected to the outlet of the hydrolyzate; and the discharge port of the quaternary crystallization kettle is connected to the centrifugal filtration unit.

[0023] The present invention 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, comprising the following steps:

[0024] a) 2,4-dichlorophenoxyacetic acid methyl ester and an aqueous solution of a catalyst are continuously introduced into a premixing unit for premixing reaction, and after reaching reaction equilibrium, are pumped into a hydrolysis unit for continuous rectification and hydrolysis reaction, and then rectified to obtain a hydrolyzate;

[0025] b) subjecting the hydrolyzate obtained in step a) to continuous gradient crystallization, and then filtering to obtain 2,4-dichlorophenoxyacetic acid.

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

[0027] The premix reaction is carried out at a temperature of 90° C. to 130° C. and for a time of 1 h to 5 h.

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

[0029] The hydrolyzate enters the first crystallization kettle, the temperature of which is controlled at 80°C-95°C, then enters the second crystallization kettle, the temperature of which is controlled at 60°C-75°C, then enters the third crystallization kettle, the temperature of which is controlled at 40°C-55°C, then enters the fourth crystallization kettle, the temperature of which is controlled at 20°C-35°C.

[0030] The invention 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 catalyst aqueous solution inlet and a premix outlet; a hydrolysis unit connected to the premix outlet; the hydrolysis unit comprises a plurality of groups of hydrolysis and distillation devices connected in series; the hydrolysis and distillation devices are provided with a pump, a distillation column and a hydrolysis kettle in sequence along a feed direction; the hydrolysis unit is provided with a material outlet; a distillation unit connected to the material outlet via a hydrolysis kettle transfer pump; the distillation unit is provided with a water inlet and a hydrolyzate outlet; a crystallization unit connected to the hydrolyzate outlet; the crystallization unit comprises a plurality of groups of crystallization kettles connected in series; the crystallization unit is provided with a crystallization material outlet; and a centrifugal filtration unit connected to 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 invention use 2,4-dichlorophenoxyacetic acid ester as a raw material, achieve overall good interaction through continuous hydrolysis reaction distillation and continuous gradient crystallization, and can continuously produce 2,4-dichlorophenoxyacetic acid; the production efficiency is high, the product stability is good, and the device occupies a small area; and the continuous reaction distillation increases the concentration of methanol in the fraction and reduces energy consumption; the continuous gradient crystallization has a good product particle size and a fast filtration speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A schematic structural diagram of a crystallization device for continuously producing 2,4-dichlorophenoxyacetic acid provided in an embodiment of the present invention;

[0032] Figure 2 A process flow chart of a crystallization method for continuously producing 2,4-dichlorophenoxyacetic acid provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0033] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] The present invention provides a crystallization device for continuously producing 2,4-dichlorophenoxyacetic acid, comprising:

[0035] Premixing unit; the premixing unit is provided with an inlet for methyl 2,4-dichlorophenoxyacetate, an inlet for an aqueous solution of a catalyst and an outlet for a premix;

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

[0037] A distillation unit connected to the material outlet via a hydrolysis kettle transfer pump; the distillation unit is provided with a water inlet and a hydrolyzate outlet;

[0038] A crystallization unit connected to the hydrolyzate outlet; the crystallization unit comprises a plurality of series-connected crystallization kettles; the crystallization unit is provided with a crystallization material outlet;

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

[0040] See also Figure 1 , Figure 1 A schematic structural diagram of a crystallization device for continuously producing 2,4-dichlorophenoxyacetic acid provided in an embodiment of the present invention; wherein 1 is a premixing kettle, 2 is a premixing kettle transfer pump, 3 is a hydrolysis first kettle, 4 is a hydrolysis second kettle, 5 is a hydrolysis third kettle, 6 is a hydrolysis fourth kettle, 7, 8, and 9 are circulating pumps between the tower kettle and the distillation column, 10 is a first-stage distillation column, 11 is a second-stage distillation column, 12 is a third-stage distillation column, 13 is a fourth-stage distillation column, 14 is a fourth-stage hydrolysis kettle transfer pump, 15 is a distillation tower, 16 is a reboiler, 17 is a circulating pump, 18 is a distillation tower 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 invention, the crystallization device for continuously producing 2,4-dichlorophenoxyacetic acid mainly comprises: a premixing unit, a hydrolysis unit, a distillation unit, a crystallization unit and a centrifugal filtration unit.

[0042] In the present invention, the function of the premixing unit is to achieve reaction equilibrium between 2,4-dichlorophenoxyacetic acid methyl ester and water under the action of p-toluenesulfonic acid catalyst. In the present invention, the premixing unit is provided with a 2,4-dichlorophenoxyacetic acid methyl ester inlet, a catalyst aqueous solution inlet and a premix outlet.

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

[0044] In the present invention, the premix outlet of the premixing unit is preferably connected to the first-stage distillation column via a premixing kettle transfer pump; the first-stage distillation column is provided with a premix inlet in the middle, an aqueous catalyst inlet at the top, a first distillation material outlet at the bottom, and a first gas phase outlet at the top.

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

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

[0047] The distillate receiving tank is provided with a feed inlet, an exhaust gas outlet and a condensate outlet; the exhaust gas outlet is connected to the exhaust gas treatment unit; the condensate outlet is pumped out through a distillate transfer pump;

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

[0049] In the present invention, the hydrolysis unit is connected to the premix outlet; the hydrolysis unit includes several groups of hydrolysis and distillation devices connected in series; the hydrolysis and distillation devices are provided with pumps, distillation columns and hydrolysis kettles in sequence along the feed direction; the hydrolysis unit is provided with a material outlet.

[0050] In a preferred embodiment of the present invention, the hydrolysis unit preferably includes 4 groups of hydrolysis and distillation devices connected in series (which can be increased accordingly according to the number of hydrolysis kettles and distillation columns required); including a hydrolysis first kettle, a hydrolysis second kettle, a hydrolysis third kettle and a hydrolysis fourth kettle connected in sequence, a fourth distillation column, a third distillation column, a second distillation column and a first distillation column connected in sequence, which are used to distill methanol and increase the concentration of methanol. At the same time, an aqueous solution of a catalyst is added to the upper part of the first distillation column to prevent methyl 2,4-dichlorophenoxyacetate from entering the distillate; the gas phase inlet of the fourth distillation column is connected to the gas phase outlet of the distillation unit.

[0051] In the present invention, the functions of the above-mentioned hydrolysis first-stage kettle, hydrolysis second-stage kettle, hydrolysis third-stage kettle and hydrolysis fourth-stage kettle are to provide heat source, residence time, and 2,4-dichlorophenoxyacetic acid methyl ester and water continue to react to generate 2,4-dichlorophenoxyacetic acid and methanol; at the same time, the liquid inlet and outlet 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 bottom-out, but an anti-gas cross-talk device must be added to the pipeline.

[0052] In the present invention, the second hydrolysis kettle is preferably connected to the second distillation column via the second circulation pump; the third hydrolysis kettle is preferably connected to the third distillation column via the third circulation pump; the fourth hydrolysis kettle is preferably connected to the fourth distillation column via the fourth circulation pump. In the present invention, the second circulation pump, the third circulation pump and the fourth circulation pump are all circulation pumps between the tower kettle and the distillation column. The hydrolyzate in the hydrolysis kettle is fully contacted with the gas in the distillation column through the above circulation pumps, and the newly generated methanol in the hydrolyzate enters the gas phase, the methanol concentration in the hydrolyzate is maintained constant, and the methanol concentration in the gas is increased.

[0053] In the present invention, the distillation unit is connected to the material outlet via a hydrolysis kettle material transfer pump; the distillation unit is provided with a water inlet and a hydrolyzate outlet.

[0054] In the present invention, the distillation unit is preferably a distillation tower, which is used to continue to react the unreacted 2,4-dichlorophenoxyacetic acid methyl ester to a qualified state, and at the same time, the bottom of the tower is replenished with water to maintain a constant concentration of toluenesulfonic acid in the device; the distillation unit is preferably provided with a reboiler, which provides a heat source and a residence time; the hydrolyzate outlet is connected to the crystallization unit through a distillation tower discharge pump in one way, and is connected to the reboiler through a first circulation pump in the other way.

[0055] In the present invention, the crystallization unit is connected to the hydrolyzate outlet; the crystallization unit comprises a plurality of groups of crystallization kettles connected in series; and the crystallization unit is provided with a crystallization material outlet.

[0056] In a preferred embodiment of the present invention, the crystallization unit preferably includes 4 groups of crystallization kettles connected in series (the number of crystallization kettles can be increased as needed); including 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 port of the first-stage crystallization kettle is connected to the outlet of the hydrolyzate; the discharge port of the fourth-stage crystallization kettle is connected to the centrifugal filtration unit. In the present invention, 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 kept at a temperature controlled to achieve continuous gradient crystallization.

[0057] In the present invention, the centrifugal filtration unit is connected to the crystallized material outlet.

[0058] The present invention 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, comprising the following steps:

[0059] a) 2,4-dichlorophenoxyacetic acid methyl ester and an aqueous solution of a catalyst are continuously introduced into a premixing unit for premixing reaction, and after reaching reaction equilibrium, are pumped into a hydrolysis unit for continuous rectification and hydrolysis reaction, and then rectified to obtain a hydrolyzate;

[0060] b) subjecting the hydrolyzate obtained in step a) to continuous gradient crystallization, and then filtering to obtain 2,4-dichlorophenoxyacetic acid.

[0061] The present invention obtains the product by continuous hydrolysis of the ester, and the specific reaction equation is as follows:

[0062] .

[0063] The invention firstly continuously feeds methyl 2,4-dichlorophenoxyacetate and an aqueous solution of a catalyst into a premixing unit for premixing reaction, and after reaching reaction equilibrium, pumps the solution into a hydrolysis unit for continuous rectification and hydrolysis reaction, and then performs rectification to obtain a hydrolyzate.

[0064] In the present invention, the catalyst is preferably an acidic compound, preferably selected from one or more of alkylbenzenesulfonic acid, alkylnaphthalenesulfonic acid, m-toluenesulfonic acid, and p-toluenesulfonic acid, and more preferably p-toluenesulfonic acid. The present invention has no particular limitation on the source of the catalyst, and commercially available products known to those skilled in the art can be used.

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

[0066] First, the aqueous solution of methyl 2,4-dichlorophenoxyacetate and p-toluenesulfonic acid enters the premixing kettle, and reaches reaction equilibrium in the premixing kettle; then, the materials that have reached reaction equilibrium in the premixing kettle continuously enter the first-stage distillation column, and at the same time, part of the p-toluenesulfonic acid aqueous solution enters the first-stage distillation column, and the materials enter the first-stage hydrolysis kettle from the first-stage distillation column, and the liquid phase enters the next-stage hydrolysis kettle through overflow to continue the reaction, and the materials in the hydrolysis kettle re-enter the corresponding distillation column from the bottom thereof for separation, and the methanol formed in the hydrolysis kettle enters the upper stage through the gas phase pipeline. The liquid phase in the upper hydrolysis kettle overflows into the next hydrolysis kettle to continue the reaction; at the same time, the feed port of the hydrolysis kettle should be lower than the discharge port or there should be a device to prevent gas phase cross-gas in the overflow pipeline, and then the liquid phase enters the distillation tower to continue the reaction. At the same time, in order to maintain the concentration of p-toluenesulfonic acid, the distillation tower kettle is supplemented with water generated by the reaction and water brought out by the distillate, and the tower kettle obtains a hydrolyzate with qualified conversion rate; finally, the methanol formed by the reaction in the distillation tower and the hydrolysis kettle is finally discharged from the first distillation column, and a methanol aqueous solution is obtained after condensation.

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

[0068] In the present invention, the temperature of the premix reaction is preferably 90° C. to 130° C., more preferably 100° C. to 110° C., and the time is preferably 1 h to 5 h, more preferably 2 h to 3 h.

[0069] After obtaining the hydrolyzate, the present invention performs continuous gradient crystallization on the obtained hydrolyzate, and then performs suction filtration to obtain 2,4-dichlorophenoxyacetic acid.

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

[0071] The hydrolyzate with qualified conversion rate enters the first-stage crystallization kettle and enters the next-stage crystallization kettle through overflow. After the crystallization, the material is sampled to detect the particle size, filtered, washed with water and dried to obtain 2,4-dichlorophenoxyacetic acid.

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

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

[0074] The invention provides a crystallization device and method for continuously producing 2,4-dichlorophenoxyacetic acid. Compared with intermittent hydrolysis, the hydrolysis process adopts a continuous hydrolysis and reactive distillation mode to reduce the energy consumption of removing methanol. Meanwhile, the crystallization process adopts a multi-reactor series continuous crystallization gradient cooling mode, which has the advantages of large crystal particle size and solves the problems of slow filtration speed. In addition, the continuous production mode reduces the number of on-site equipment and the volume of production equipment, optimizes the layout of production space, has the advantages of high automation, reduced labor cost, stable product quality, green environmental protection, etc.

[0075] The invention 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 catalyst aqueous solution inlet and a premix outlet; a hydrolysis unit connected to the premix outlet; the hydrolysis unit comprises a plurality of groups of hydrolysis and distillation devices connected in series; the hydrolysis and distillation devices are provided with a pump, a distillation column and a hydrolysis kettle in sequence along a feed direction; the hydrolysis unit is provided with a material outlet; a distillation unit connected to the material outlet via a hydrolysis kettle transfer pump; the distillation unit is provided with a water inlet and a hydrolyzate outlet; a crystallization unit connected to the hydrolyzate outlet; the crystallization unit comprises a plurality of groups of crystallization kettles connected in series; the crystallization unit is provided with a crystallization material outlet; and a centrifugal filtration unit connected to 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 invention use 2,4-dichlorophenoxyacetic acid ester as a raw material, achieve overall good interaction through continuous hydrolysis reaction distillation and continuous gradient crystallization, and can continuously produce 2,4-dichlorophenoxyacetic acid; the production efficiency is high, the product stability is good, and the device occupies a small area; and the continuous reaction distillation increases the concentration of methanol in the fraction and reduces energy consumption; the continuous gradient crystallization has a good product particle size and a fast filtration speed.

[0076] In order to further illustrate the present invention, the following examples are provided for detailed description.

[0077] Example

[0078] The embodiment of the present invention adopts the crystallization device for continuous production of 2,4-dichlorophenoxyacetic acid described in the above technical solution, and the structural schematic diagram is shown in Figure 1 As shown; wherein 1 is a premixing kettle, 2 is a premixing kettle transfer pump, 3 is a hydrolysis first kettle, 4 is a hydrolysis second kettle, 5 is a hydrolysis third kettle, 6 is a hydrolysis fourth kettle, 7, 8, 9 are circulating pumps between the tower kettle and the distillation column, 10 is a first-stage distillation column, 11 is a second-stage distillation column, 12 is a third-stage distillation column, 13 is a fourth-stage distillation column, 14 is a fourth-stage hydrolysis kettle transfer pump, 15 is a distillation tower, 16 is a reboiler, 17 is a circulating pump, 18 is a distillation tower The discharge pump is 19, the condenser is 20, the fraction receiving tank is 21, the fraction transfer pump is 22, the first-stage crystallization kettle is 23, the second-stage crystallization kettle is 24, the third-stage crystallization kettle is 25, the fourth-stage crystallization kettle is; the material A comes from the methyl 2,4-dichlorophenoxyacetate raw material tank; the material B comes from the aqueous solution raw material tank of a certain concentration of p-toluenesulfonic acid (catalyst); the material C comes from the water tank, which is used to supplement the water consumed in the reaction and the water brought out by the fraction to maintain a constant concentration of p-toluenesulfonic acid.

[0079] The specific working process of the above-mentioned crystallization device for continuous production of 2,4-dichlorophenoxyacetic acid is as follows:

[0080] (1) Hydrolysis:

[0081] 1) methyl 2,4-dichlorophenoxyacetate and an aqueous solution containing a catalyst of p-toluenesulfonic acid are transferred into a premixing kettle 1, the materials reach a reaction equilibrium, and the liquid phase is transferred into the middle of the first-stage distillation column 10 through a premixing kettle transfer pump 2, and enters a hydrolysis first-stage kettle 3.

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

[0083] 3) The gas phase of the first-stage hydrolysis kettle 3 and the gas phase of the second-stage distillation column 11 enter the lower part of the first-stage distillation column 10. After the upward gas phase and the downward liquid phase in the distillation column are exchanged, the gas phase is finally condensed by the condenser 19 and enters the fraction receiving tank 20; the liquid phase of the first-stage hydrolysis kettle 3 enters the second-stage hydrolysis kettle 4 through the overflow pipeline; at the same time, the feed port of the hydrolysis kettle must be lower than the discharge port or there must be a device to prevent gas-phase cross-talk in the overflow pipeline.

[0084] 4) A portion of the liquid phase of the second-stage hydrolysis kettle 4 enters the upper part of the second-stage distillation column 11 through the second circulation pump 7, and then enters the second-stage hydrolysis kettle 4; a portion of the liquid phase enters the third-stage hydrolysis kettle 5 through overflow, and the gas phase of the second-stage hydrolysis kettle 4 and the gas phase of the third-stage distillation column 12 enter the lower part of the second-stage distillation column 11. After the upward gas phase and the downward liquid phase in the distillation column undergo gas-liquid exchange, the gas phase enters the lower part of the first-stage distillation column 10.

[0085] 5) A part of the liquid phase of the 3rd-stage hydrolysis kettle 5 enters the upper part of the 3rd-stage distillation column 12 through the 3rd circulation pump 8, and then enters the 3rd-stage hydrolysis kettle 5; a part of the liquid phase enters the 4th-stage hydrolysis kettle 6 through overflow, and the gas phase of the 3rd-stage hydrolysis kettle 5 and the gas phase of the 4th-stage distillation column 13 enter the lower part of the 3rd-stage distillation column 12. After the upward gas phase in the distillation column exchanges gas and liquid with the downward liquid phase, the gas phase enters the lower part of the 2nd-stage distillation column 11.

[0086] 6) A portion of the liquid phase of the 6 hydrolysis fourth-stage kettle enters the upper part of the 13 fourth-stage distillation column through the 9 fourth circulation pump, and then enters the 6 hydrolysis fourth-stage kettle; a portion of the liquid phase enters the upper part of the 15 distillation tower through the transfer pump 14, and the gas phase of the 6 hydrolysis fourth-stage kettle and the gas phase of the 15 distillation tower enter the lower part of the 13 fourth-stage distillation column. After the upward gas phase and the downward liquid phase in the distillation column undergo gas-liquid exchange, the gas phase enters the lower part of the 12 third-stage distillation column.

[0087] 7) The liquid in the upper part of the distillation tower 15 enters the lower part of the distillation tower, water enters the lower part of the distillation tower, part of the liquid in the lower part of the distillation tower is transferred to the crystallization kettle through the distillation tower discharge pump 18; part of the liquid enters the reboiler through the first circulation pump 17 to produce a gas phase, and the upward gas phase and the downward liquid phase in the distillation column are exchanged through gas-liquid, and the gas phase enters the lower part of the distillation column 13.

[0088] 8) The methanol-water solution is finally obtained in the condenser, and the hydrolyzate with qualified conversion rate is obtained at the bottom of the distillation tower.

[0089] (2) Crystallization:

[0090] The qualified hydrolyzate enters the first-level crystallization kettle 22 and is controlled at a temperature of T1; it enters the second-level crystallization kettle 23 through overflow and is controlled at a temperature of T2; it enters the third-level crystallization kettle 24 through overflow and is controlled at a temperature of T3; it enters the fourth-level crystallization kettle 25 through overflow and is controlled at a temperature of T4; the material is transferred out to obtain a qualified crystallization mixed liquid; finally, it is filtered, washed with water, and dried in sequence to continuously produce 2,4-dichlorophenoxyacetic acid.

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

[0092] The corresponding specific experimental data are as follows:

[0093] (1) 2,4-dichlorophenoxyacetic acid methyl ester (content 99%) at a mass flow rate of 235.06 g / h and 25% p-toluenesulfonic acid aqueous solution (p-toluenesulfonic acid is a catalyst) at a mass flow rate of 282.07 g / h were continuously introduced into the premixing kettle, stirred and mixed at 97°C for 2-3 hours, and the reaction reached equilibrium. The liquid level in the premixing kettle was kept stable and transferred to the middle of the primary distillation column by a pump. At the same time, 25% p-toluenesulfonic acid aqueous solution was introduced into the upper part of the primary distillation column at a flow rate of 23.51 g / h. The temperature of the first hydrolysis kettle was controlled at 99°C. The temperature of the second hydrolysis kettle was controlled at 99°C. The temperature of the first kettle is 101°C, the temperature of the third-stage hydrolysis kettle is controlled at 102°C, the temperature of the fourth-stage hydrolysis kettle is controlled at 103°C, the liquid level of the fourth-stage hydrolysis kettle is maintained stable, and it is transferred to the distillation tower through a pump. The water mass flow rate enters the distillation tower kettle at 210.14g / h, the tower kettle temperature is controlled at 104°C, the liquid level of the distillation tower kettle is controlled stable, and the hydrolyzate with qualified conversion rate is output through a pump; after testing, the conversion rate of 2,4-dichlorophenoxyacetic acid methyl ester is 99.8% (≥99.5%), the C10 content in the hydrolyzate is 41.45%, and the methanol content of the distillate obtained at the top of the tower is ≥15%.

[0094] (2) The qualified hydrolyzate enters the first-stage crystallization kettle, and the temperature of the first-stage crystallization kettle is controlled at 85-90°C, the temperature of the second-stage crystallization kettle is controlled at 65-70°C, the temperature of the third-stage crystallization kettle is controlled at 45-50°C, and the temperature of the fourth-stage crystallization kettle is controlled at 25-30°C. The particle size of the material obtained from the fourth-stage kettle is measured and filtered at a rate of 8000Kg / (m³*h). After washing and drying, 2,4-dichlorophenoxyacetic acid is continuously produced.

[0095] The particle size distribution test results are shown in Table 1 below.

[0096] Table 1

[0097]

[0098] Comparative Example

[0099] Use the conventional operation method, the steps are as follows:

[0100] (1) Add methyl 2,4-dichlorophenoxyacetate and aqueous solutions of p-toluenesulfonic acid into flasks respectively. The mass of methyl 2,4-dichlorophenoxyacetate (content 99%) is 235.06 g, and the mass of aqueous p-toluenesulfonic acid solution (p-toluenesulfonic acid content 25%) is 305.58 g. Start heating and distillation. Control the reaction temperature at 103-105°C. In order to maintain the concentration of p-toluenesulfonic acid during the distillation process, add water according to the mass of the distilled fraction. Take samples from the bottom of the tower to detect the conversion rate of methyl 2,4-dichlorophenoxyacetate. The conversion rate is 99.7% (≥99.5%), which is acceptable. During the process, 616.65 g of water is added. The methanol content of the distillate is about 5.0%.

[0101] (2) The qualified hydrolyzate is directly cooled to 25-30°C with cold water and kept warm for 30 minutes. Samples are taken to detect the particle size and filtered in the same manner at a filtration rate of 5000 kg / (m³*h). After washing and drying, 2,4-dichlorophenoxyacetic acid is produced.

[0102] The particle size distribution test results are shown in Table 2 below.

[0103] Table 2

[0104]

[0105] By comparing the above embodiment with the comparative example, it can be seen that the methanol content of the fraction in the embodiment differs by nearly 3 times, and the energy consumption is significantly reduced; and the overall particle size of the particle size using gradient crystallization in the embodiment is larger than that in the comparative example, and the filtration speed of the comparative example is more intuitive.

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

[0107] (1) Full-process continuous production has the following advantages: ① High production efficiency: Continuous production can achieve the continuity of the production process, reduce the intervention of production workers, and improve production efficiency; ② Good product stability: Continuous production can ensure the stability of various parameters in the production process and the stability of particle size, while intermittent crystallization has poor stability in different batches and cannot guarantee product stability; ③ Small footprint: Intermittent crystallization equipment is too large, requires high investment, and occupies a lot of space, while continuous production can complete the production process in a smaller space, reducing the footprint of the production plant.

[0108] (2) Continuous reactive distillation increases the concentration of methanol in the fraction and reduces energy consumption. The higher the methanol concentration, the lower the energy consumption.

[0109] (3) Gradient crystallization is continuous and the filtration speed is fast, which can be judged by the particle size and filtration speed.

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

Claims

1. A crystallization device for continuously producing 2,4-dichlorophenoxyacetic acid, characterized in that: include: Premixing unit; the premixing unit is provided with an inlet for methyl 2,4-dichlorophenoxyacetate, an inlet for an aqueous solution of a catalyst and an outlet for a premix; A hydrolysis unit connected to the premix outlet; the hydrolysis unit comprises a plurality of groups of hydrolysis and distillation devices connected in series; the hydrolysis and distillation devices are provided with a pump, a distillation column and a hydrolysis kettle in sequence along the feed direction; the hydrolysis unit is provided with a material outlet; A distillation unit connected to the material outlet via a hydrolysis kettle transfer pump; the distillation unit is provided with a water inlet and a hydrolyzate outlet; A crystallization unit connected to the hydrolyzate outlet; the crystallization unit comprises a plurality of series-connected crystallization kettles; the crystallization unit is provided with a crystallization material outlet; A centrifugal filtration unit is connected to the crystallization material outlet.

2. The crystallization device for continuous production of 2,4-dichlorophenoxyacetic acid according to claim 1, characterized in that: The premixing unit is a premixing kettle; the premix outlet of the premixing unit is connected to the first-stage distillation column via a premixing kettle transfer pump; the first-stage distillation column is provided with a premix inlet in the middle, a catalyst aqueous solution inlet at the top, a first distillation material outlet at the bottom, and a first gas phase outlet at the top.

3. The crystallization device for continuous production of 2,4-dichlorophenoxyacetic acid according to claim 2, characterized in that: The crystallization device for continuously producing 2,4-dichlorophenoxyacetic acid also includes: A post-processing unit connected to the first gas phase outlet; the post-processing unit comprises: The distillate receiving tank is provided with a feed inlet, an exhaust gas outlet and a condensate outlet; the exhaust gas outlet is connected to the exhaust gas treatment unit; the condensate outlet is pumped out through a distillate transfer pump; A condenser connected to the feed port; the condenser is provided with a gas phase inlet connected to the first gas phase outlet.

4. The crystallization device for continuous production of 2,4-dichlorophenoxyacetic acid according to claim 1, characterized in that: The hydrolysis unit comprises 4 groups of hydrolysis and distillation devices connected in series, including a first-stage hydrolysis kettle, a second-stage hydrolysis kettle, a third-stage hydrolysis kettle and a fourth-stage hydrolysis kettle connected in sequence, and a fourth-stage distillation column, a third-stage distillation column, a second-stage distillation column and a first-stage distillation column connected in sequence; the gas phase inlet of the fourth-stage distillation column is connected to the gas phase outlet of the distillation unit.

5. The crystallization device for continuous production of 2,4-dichlorophenoxyacetic acid according to claim 4, characterized in that: The second-stage hydrolysis kettle is connected to the second-stage distillation column via the second circulation pump; the third-stage hydrolysis kettle is connected to the third-stage distillation column via the third circulation pump; the fourth-stage hydrolysis kettle is connected to the fourth-stage distillation column via the fourth circulation pump.

6. The crystallization device for continuous production of 2,4-dichlorophenoxyacetic acid according to claim 1, characterized in that: The distillation unit is a distillation tower; the distillation unit is provided with a reboiler; one path of the hydrolyzate outlet is connected to the crystallization unit via a distillation tower discharge pump, and the other path is connected to the reboiler via a first circulation pump.

7. The crystallization device for continuous production of 2,4-dichlorophenoxyacetic acid according to claim 1, characterized in that: The crystallization unit comprises 4 groups of crystallization kettles connected in series, including a primary crystallization kettle, a secondary crystallization kettle, a tertiary crystallization kettle and a quaternary crystallization kettle connected in sequence; the feed port of the primary crystallization kettle is connected to the outlet of the hydrolyzate; the discharge port of the quaternary crystallization kettle is connected to the centrifugal filtration unit.

8. A crystallization method for continuously producing 2,4-dichlorophenoxyacetic acid, characterized in that: The crystallization device for continuously producing 2,4-dichlorophenoxyacetic acid according to any one of claims 1 to 7 comprises the following steps: a) 2,4-dichlorophenoxyacetic acid methyl ester and an aqueous solution of a catalyst are continuously introduced into a premixing unit for premixing reaction, and after reaching reaction equilibrium, are pumped into a hydrolysis unit for continuous rectification and hydrolysis reaction, and then rectified to obtain a hydrolyzate; b) subjecting the hydrolyzate obtained in step a) to continuous gradient crystallization, and then filtering to obtain 2,4-dichlorophenoxyacetic acid.

9. The crystallization method for continuous production of 2,4-dichlorophenoxyacetic acid according to claim 8, characterized in that: The mass ratio of 2,4-dichlorophenoxyacetic acid methyl ester, the catalyst in the aqueous solution of the catalyst, and the water in the aqueous solution of the catalyst in step a) is 1: (0.12-0.55): (0.48-1.28); The premix reaction is carried out at a temperature of 90° C. to 130° C. and for a time of 1 h to 5 h.

10. The crystallization method for continuous production of 2,4-dichlorophenoxyacetic acid according to claim 8, characterized in that: The process of continuous gradient crystallization in step b) is specifically as follows: The hydrolyzate enters the first crystallization kettle, the temperature of which is controlled at 80°C-95°C, then enters the second crystallization kettle, the temperature of which is controlled at 60°C-75°C, then enters the third crystallization kettle, the temperature of which is controlled at 40°C-55°C, then enters the fourth crystallization kettle, the temperature of which is controlled at 20°C-35°C.

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