A kind of synthetic method of diquat dichloride

Abstract

The present invention relates to the technical field of herbicide synthesis, and discloses a method for synthesizing diquat dichloride, including (i) mixing raw materials, mixing a catalyst and a substrate 2,2-bipyridine, and dichloroethane to obtain a mixed raw material; (ii) cyclization reaction, pumping the mixed raw material into a reactor, and obtaining a condensed mixed liquid by condensation after the reaction; (iii) post-treatment, the condensed mixed liquid is placed in a static layer to obtain an aqueous phase and an organic phase, and the aqueous phase is concentrated to obtain a diquat dichloride product; the catalyst is any one of DMAP, potassium iodide, tetraethylammonium bromide, tetrabutylammonium chloride, and dodecyltrimethylammonium chloride. This scheme has low cost, simple equipment, and less process flow when synthesizing diquat, and the reactants have no by-products, which not only effectively improves the product yield, but also can realize the continuous production of diquat by continuous feeding and discharging, thereby improving the product production efficiency.

Description

Technical Field

[0001] The invention relates to the technical field of herbicide synthesis, and in particular to a method for synthesizing diquat dichloride. Background Art

[0002] As a powerful herbicide, Diquat is an ideal substitute for Paraquat Aqueous since its sale was banned in China. Its weed control effect is similar to that of Paraquat, but its toxicity is lower, and it has more advantages in crop withering and seed treatment. However, the high cost is an important factor restricting the promotion and use of Diquat. If the production cost can be reduced and the cost of pesticides for farmers can be reduced, it will help to further release the market potential of Diquat.

[0003] At present, the production of diquat is mainly to prepare diquat dibromide by reacting 2,2'-bipyridine with dibromoethane; however, bromine is a precious resource, and diquat dibromide, as a herbicide, will bring bromine into the soil environment during use, resulting in a waste of bromine. Therefore, in terms of atomic economy, diquat dichloride is more economical than diquat dibromide, but due to the low activity of dichloroethane, the preparation of diquat dichloride using a method similar to that of diquat dibromide requires very high pressure and temperature, causing serious corrosion to the equipment, and cannot be achieved in industrial production.

[0004] In order to solve the above problems, the prior art CN113214258A discloses a method and device for synthesizing diquat dichloride, wherein a mixture of dichloroethane, a metal catalyst, nitrobenzene and 2,2-bipyridine is pumped into a slurry bed reactor through a first centrifugal pump, and after the reaction, diquat and an organic phase are obtained by filtration and extraction, and the organic phase includes dichloroethane and 2,2-bipyridine and can enter the reaction again. However, the prior art still has the following disadvantages: 1) The preparation process of the metal catalyst in the prior art is cumbersome and costly, and the reaction easily causes the physical and chemical properties of the metal catalyst to change and become inactivated, thereby increasing the use cost of the metal catalyst; 2) The prior art is completed on a slurry bed reactor, and the slurry bed reactor has a high demand for metal catalysts, further increasing the production cost. Therefore, the development of a method for synthesizing diquat dichloride with a simple process, lower cost and continuous production not only effectively makes up for the shortcomings of the existing diquat dichloride production process, but also has important significance for achieving continuous production and reducing production costs. Summary of the invention

[0005] The present invention aims to provide a method for synthesizing diquat dichloride salt, so as to solve the technical problem that the synthesis of existing diquat dichloride salt has high production cost due to the use of metal catalyst.

[0006] To achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a method for synthesizing diquat dichloride, comprising: (i) mixing raw materials, mixing a catalyst and a substrate 2,2-bipyridine and dichloroethane to obtain a mixed raw material; (ii) a cyclization reaction, pumping the mixed raw material into a reactor, and obtaining a condensed mixed liquid by condensation after the reaction; (iii) post-treatment, allowing the condensed mixed liquid to stand for stratification to obtain an aqueous phase and an organic phase, and concentrating the aqueous phase to obtain a diquat dichloride product; the catalyst is any one of DMAP, potassium iodide, tetraethylammonium bromide, tetrabutylammonium chloride, and dodecyltrimethylammonium chloride.

[0007] The principle and advantages of this scheme are: compared with the prior art that uses metal catalysts to cause high production costs of diquat, this scheme can synthesize diquat using conventional catalysts, effectively reducing the synthesis cost of diquat; and the catalyst in this scheme does not change its physical and chemical properties during the reaction, and can be recycled and reused in production, further reducing the production cost of diquat and improving the diquat production efficiency of the enterprise. In addition, this scheme uses simple equipment and fewer process flows when synthesizing diquat, and no by-products are produced by the reactants, which not only effectively improves the product yield, but also realizes continuous production of diquat through continuous feeding and discharging, thereby improving product production efficiency.

[0008] Preferably, the mass ratio of the substrate 2,2-bipyridine to dichloroethane is 1:3-4.

[0009] Beneficial effects: The organic phase in this scheme is a mixture of substrates 2,2-bipyridine and dichloroethane, which can be used again for the reaction; this scheme limits the amount of substrate raw materials used, so that the substrate can react as completely as possible under the action of the catalyst, thereby reducing the waste of substrate raw materials; in addition, optimizing the substrate dosage ratio can effectively avoid the imbalance of the substrate amount in the mixture caused by multiple recycling of the organic phase, thereby effectively balancing the amount of reaction substrates, and then ensuring that the production of the organic phase and diquat can proceed continuously.

[0010] Preferably, the reactor is a tubular reactor, and the amount of the catalyst is 5-11‰ of the total amount of the substrate.

[0011] Beneficial effect: Compared with the prior art which uses a large amount of metal catalyst when using a slurry bed reactor or a fixed bed reactor, the present solution adopts a U-shaped tubular reactor, which not only prolongs the reaction time, but also has a high volumetric efficiency (production capacity per unit volume) due to its small amount of back-mixing of the reaction solution; it not only facilitates the continuous feeding and discharging of the reactor to improve production efficiency; it can also effectively reduce the amount of catalyst used and reduce production costs.

[0012] Preferably, the reaction temperature of the cyclization reaction is 170-250° C. and the reaction pressure is 0.5-1.5 MPa.

[0013] Beneficial effects: In this scheme, the reaction is carried out in a tubular reactor, and the reaction can be carried out quickly by controlling the reaction temperature. The applicant has found through experiments that when a lower reaction temperature and pressure are used, the substrate conversion rate and the yield of low-grade products are likely to be low; when a higher reaction temperature is used, the substrate is likely to generate impurities such as tar under the action of high temperature, reducing the product concentration.

[0014] Preferably, the flow rate of the mixed raw material pumped into the tubular reactor is 15 to 40 ml / min, and the reaction time of the mixed raw material in the tubular reactor is 20 to 40 min.

[0015] Beneficial effect: In this scheme, the tubular reactor can be continuously fed, and the feed flow rate of the mixed raw materials can be controlled according to the time required for the reaction and the capacity of the tubular reactor, so that the reaction can be continuously carried out while meeting a high product yield, effectively making full use of the equipment and improving the product production efficiency. The applicant has found through research that when the feed speed is too slow and the raw materials stay in the tubular reactor for too long, the product yield will still be reduced. The reason is that the product is prone to generate tar under high temperature for a long time, which reduces the product yield.

[0016] Preferably, the mixed raw material is preheated before entering the tubular reactor, and the preheating temperature is 80-120°C.

[0017] Beneficial effect: This solution can effectively shorten the time for the mixed raw materials to be heated to the reaction temperature by preheating the mixed raw materials before entering the tubular reactor, thereby shortening the time required for the reaction and improving production efficiency. The applicant has found through research that when the preheating temperature is too low, it takes a long time for the raw materials to be heated to the reaction temperature when entering the tubular reactor, and the raw materials will not react completely in the limited reaction time of continuous feeding, thereby reducing the product yield.

[0018] Preferably, the condensed mixed liquid further comprises pH adjustment and filtration before standing and stratification, and the pH adjustment is to adjust the pH of the condensed mixed liquid to 7-8.

[0019] Beneficial effects: This solution can precipitate the catalyst in the form of salt by adjusting the pH of the condensed mixed liquid before standing and stratification, and can achieve catalyst recovery by filtering after pH adjustment, which not only effectively reduces the cost of the catalyst, but also effectively prevents the catalyst from entering the diquat dichloride salt product as an impurity to reduce the product quality; in addition, adjusting the pH of the condensed mixed liquid can also help improve the solubility of the product in the aqueous phase, help separate the substrate and the product, and thus improve the purity and yield of the product.

[0020] Preferably, the organic phase is a mixed solution of 2,2-bipyridine and ethylene dichloride, and the ethylene dichloride and 2,2-bipyridine recovered from the organic phase after dehydration by an evaporator are mixed with the catalyst again to form a mixed raw material.

[0021] Beneficial effect: This solution effectively avoids the waste of raw materials by recycling the substrate in the organic phase and formulating the substrate with wastewater after the reaction is completed. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The schematic diagram of the process structure of synthesizing diquat dichloride in the embodiment of the present invention is shown in FIG. DETAILED DESCRIPTION

[0023] The reference numerals in the drawings of the specification include: a configuration kettle 1, a tubular reactor 2, a cooler 3, a static kettle 4, a concentration kettle 5, and a falling film evaporator 6.

[0024] The following is further described in detail through specific implementation methods, but the implementation methods of the present invention are not limited thereto. Unless otherwise specified, the technical means used in the following examples are conventional means well known to those skilled in the art; the experimental methods used are all conventional methods; the materials and reagents used can all be obtained from commercial channels. A method for synthesizing diquat dichloride is shown in a specific example.

[0025] Example 1

[0026] This embodiment is basically Figure 1 As shown: A method for synthesizing diquat dichloride salt includes (i) mixing raw materials, mixing a catalyst and a substrate 2,2-bipyridine and dichloroethane to obtain a mixed raw material; (ii) cyclization reaction, pumping the mixed raw material into a reactor, adding water after the reaction and condensing to obtain a condensed mixed liquid; (iii) post-treatment, allowing the condensed mixed liquid to stand and separate to obtain an aqueous phase and an organic phase, and concentrating the aqueous phase to obtain a diquat dichloride salt product. Specifically, it includes the following steps:

[0027] (I) Mixing raw materials stage

[0028] The catalyst and substrate 2,2-bipyridine and dichloroethane are added to the configuration kettle 1 and mixed to obtain a mixed raw material, wherein the mass ratio of 2,2-bipyridine to dichloroethane is 1:3-4 (specifically 1:3 in this embodiment), and the amount of the catalyst is 5-11‰ of the total amount of the substrate (specifically 5‰ in this embodiment); the catalyst is any one of DMAP, potassium iodide, tetraethylammonium bromide, tetrabutylammonium chloride, and dodecyltrimethylammonium chloride, and in this embodiment it is specifically tetrabutylammonium chloride.

[0029] Subsequently, the mixed raw materials in the preparation kettle are heated to 60-100° C. for insulation preheating. Specifically, in this embodiment, the mixed raw materials are heated to 80° C. for insulation preheating.

[0030] (II) Cyclization reaction stage

[0031] The mixed raw materials in the configuration kettle 1 are pumped into the tubular reactor 2 (the tubular reactor 2 in the present embodiment has a tube length of 2 m and a tube diameter of 2 cm) through a centrifugal pump at a speed of 15 to 40 ml / min (specifically 15 ml / min in the present embodiment), and reacted at a reaction temperature of 170 to 250 ° C. and a reaction pressure of 0.5 to 1.5 MPa for 20 to 40 min (specifically 40 min at 200 ° C. and 1 MPa in the present embodiment); the reaction mixture obtained by the reaction enters the condenser for condensation to obtain a condensed mixed liquid.

[0032] (III) Post-processing stage

[0033] The condensed mixed liquid enters the static kettle, and the pH of the condensed mixed liquid is adjusted to 7-8 (specifically 8 in this embodiment) by alkali (any one of liquid alkali, ammonia water, and soda ash). At this time, the catalyst is precipitated in the form of salt, and the condensed mixed liquid is filtered to obtain the catalyst and the filtered mixed liquid. The filtered mixed liquid is automatically statically layered during the feeding process through a laminated filter to obtain an upper aqueous phase and a lower organic phase.

[0034] The aqueous phase is an aqueous solution of diquat dichloride salt, and the aqueous phase enters the concentration kettle for concentration to obtain the diquat dichloride salt product. During the concentration process, the concentration amount is determined according to the concentration of diquat dichloride salt in different products. For example, the production of diquat dichloride salt solution requires the concentration of diquat dichloride salt in the product to be quantitatively concentrated to 42%.

[0035] The organic phase is a mixed liquid of 2,2-bipyridine and ethylene dichloride. The organic phase enters a falling film evaporator for dehydration. The dehydrated ethylene dichloride and 2,2-bipyridine are mixed with a catalyst again to form a mixed raw material.

[0036] The difference from Example 1 is that Examples 2 to 10 show the synthesis of diquat dichloride salt with different parameter combinations within the scope of this scheme, and Comparative Examples 1 to 10 show the synthesis of diquat dichloride salt with different parameter combinations outside the scope of this scheme. The raw material dosage, condition differences and product yields of the synthesis of diquat dichloride salt in Examples 2 to 10 and Comparative Examples 1 to 10 are detailed in Table 1.

[0037]

[0038] Experimental data show that this scheme can synthesize diquat dichloride by using conventional catalysts and Tubular reactors, and the product yield is higher than 93%. Among them, this scheme adopts Tubular reactors, which not only facilitates the continuous feeding and discharging of the reactor to improve production efficiency, but also has a high volumetric efficiency (unit volume production capacity) due to its small amount of back-mixing of the reaction solution, and can effectively reduce the amount of catalyst used and reduce production costs. Specifically, compared with the prior art CN113214258A using a slurry bed reactor, the required catalyst is 1.5-4.5% of the reaction substrate, which is significantly higher than 5-11‰ in this scheme; and compared with the prior art that requires the use of metal catalysts with complex preparation and recovery activation processes, the use of conventional catalysts in this scheme can effectively improve the reaction efficiency and further reduce the cost of catalyst raw materials.

[0039] In addition, this scheme limits the feed rate of the mixed raw materials so that the raw materials stay in the tubular reactor 2 for a sufficient time, so that the substrate can fully react under the action of the catalyst, effectively improve the product yield and reduce the waste of raw materials. On the one hand, the raw material ratio significantly affects the product yield during continuous production. As shown in Example 2 and Comparative Examples 2 to 3, the optimal mass ratio of the substrate raw materials 2,2-bipyridine and dichloroethane in this scheme is 1:3 to 4; if it exceeds this range, one of the substrates will not be able to react completely during the reaction process, thereby reducing the product yield; and the unreacted substrates in this scheme will be recycled and re-entered into the reaction system. The mismatched substrate mass ratio will gradually increase the impact after a period of continuous reaction, which will seriously reduce the product yield and cause waste of production energy. On the other hand, the raw material feed rate seriously affects the product yield. For example, the product yield in Comparative Example 6 is only 84.5%, indicating that the feed rate is too slow, which will cause the raw material to stay for too long and reduce production efficiency; and the raw material stays for too long, even at a suitable temperature, it is easy to produce tar and reduce the product yield.

[0040] Furthermore, this solution can effectively shorten the time for the mixed raw materials to be heated to the reaction temperature by preheating the mixed raw materials before entering the tubular reactor, thereby shortening the time required for the reaction and improving production efficiency. For example, when the raw materials were preheated to 40°C in Comparative Example 5, the product yield was only 87.4%, indicating that the too low preheating temperature caused the raw materials to take a long time to be heated to the reaction temperature when entering the tubular reactor, and the raw materials were not completely reacted in the limited reaction time of continuous feeding, thereby reducing the product yield.

[0041] Then, by adjusting the pH of the condensed mixed solution before standing and stratifying, the present solution can not only precipitate the catalyst in the form of salt for recovery, but also help to improve the solubility of the product in the aqueous phase, help to separate the substrate and the product, and thus improve the purity and yield of the product. For example, when the pH is adjusted to 5.5 in Comparative Example 10, the product yield is only 87.8%, indicating that under this pH condition, part of the product is mixed in the raw material and enters the organic phase, resulting in a decrease in the product yield.

[0042] Finally, in this scheme, too short a reaction time (such as the product yield in Comparative Example 1 is 89.4%), too low a reaction temperature (such as the product yield in Comparative Example 8 is only 79.4%), and too high a reaction temperature (such as the product yield in Comparative Example 9 is 85.5%) will all reduce the product yield; the reason is that when the reaction time is too short and the reaction temperature is too low, more substrates are not converted, resulting in a lower product yield; and when the reaction temperature is too high, tar will be produced, resulting in a lower product yield.

[0043] In summary, this solution can effectively improve the volumetric efficiency (unit volume production capacity) of the equipment by using a tubular reactor, so that a higher product yield can be obtained by catalytic production even when the catalyst dosage is changed; and the catalyst requirements are also reduced, and the reaction efficiency can be improved by using conventional catalysts, thereby significantly reducing production costs. In addition, by optimizing the raw material ratio, preheating temperature, and reaction feed-related conditions of the reaction, the product yield can also be improved, and the continuous production of diquat dichloride can be achieved.

[0044] The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical solutions and / or characteristics in the solution is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for synthesizing diquat dichloride, characterized in that: The steps include: (i) mixing raw materials, mixing the catalyst and the substrate 2,2'-bipyridine and dichloroethane to obtain a mixed raw material; the mass ratio of the substrate 2,2'-bipyridine to dichloroethane is 1:3-4; The catalyst is any one of DMAP, potassium iodide, tetrabutylammonium chloride, and dodecyltrimethylammonium chloride; the amount of the catalyst is 5-11‰ of the total amount of the substrate; (ii) cyclization reaction, preheating the mixed raw material to 80-120° C. and then pumping it into a tubular reactor at a flow rate of 15-40 mL / min, and carrying out cyclization reaction for 20-40 min at a temperature of 170-250° C. and a pressure of 0.5-1.5 MPa; after the reaction, condensing to obtain a condensed mixed liquid; (iii) post-treatment, allowing the condensed mixed liquid to stand for stratification to obtain an aqueous phase and an organic phase, and concentrating the aqueous phase to obtain the diquat dichloride product.

2. The method for synthesizing diquat dichloride according to claim 1, characterized in that: The condensed mixed liquid further comprises pH adjustment and filtration before being allowed to stand for stratification, wherein the pH adjustment is to adjust the pH of the condensed mixed liquid to 7-8.

3. The method for synthesizing diquat dichloride according to claim 2, characterized in that: The organic phase is a mixed liquid of 2,2'-bipyridine and dichloroethane. The dichloroethane and 2,2'-bipyridine are recovered through an evaporator. The recovered dichloroethane and 2,2'-bipyridine are mixed with a catalyst again to form a mixed raw material.

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