Continuous synthesis process of low energy diuron

Abstract

This invention discloses a low-energy-consumption continuous synthesis process for diuron, comprising: S1, continuously feeding a mixture of dimethylamine aqueous solution, a co-solvent, and a wetting agent into a primary continuous reactor; S2, adding a 20-40% (w / w) toluene solution of 3,4-dichlorophenyl isocyanate to the primary, secondary, and tertiary continuous reactors in batches at specific proportions; after the reaction, filtering, washing, and drying to obtain diuron. Testing shows that the diuron prepared by this method, using a lower concentration of toluene than existing technologies, produces crystals that meet the requirements of continuous production, yielding qualified diuron products and increasing the D50 to 80 μm, enabling continuous production at higher concentrations. The final product yield is over 98%, the product purity is over 98%, and the steam consumption for dehydration and recrystallization is reduced by 2 tons / ton.

Description

Technical Field

[0001] This invention relates to the field of diuron technology, specifically a low-energy continuous synthesis process for diuron. Background Technology

[0002] Diuron (CAS: 330-54-1) is a classic substituted urea systemic herbicide. It was first developed and introduced by DuPont in the 1950s. Its mechanism of action is primarily through absorption by plant roots and leaves, specifically inhibiting electron transport in photosynthesis (PSII inhibitor), leading to weed death due to energy depletion. Diuron is broad-spectrum and highly effective, widely used in cotton, sugarcane, orchards, and non-arable land for controlling annual grasses and broadleaf weeds.

[0003] From a physicochemical perspective, pure diuron is a white crystalline solid with a melting point of 158-159℃. However, impurities significantly affect its melting point, causing it to soften and melt at 120-150℃. Diuron is sparingly soluble in water (approximately 42 mg / L at 25℃), slightly soluble in toluene, but readily soluble in organic solvents such as acetone. It is stable at room temperature, resistant to rain washout, and has a long-lasting efficacy, making it an important basic herbicide in agricultural applications.

[0004] In the production process of diuron, the intermediate 3,4-dichlorophenyl isocyanate produced by esterification of 3,4-dichloroaniline and phosgene contains a large amount of solvent toluene. When used in the addition reaction, it undergoes a heterogeneous reaction with dimethylamine aqueous solution. Moreover, the solubility of the product diuron in both phases is very small. Therefore, it is easy to generate explosive crystallization at the reaction interface to form a paste, which affects product quality and production efficiency.

[0005] To address these issues, existing technologies typically involve diluting the reaction concentration with toluene, and then using the azeotropic properties of toluene after the addition reaction to perform distillation and reflux dehydration. Ultimately, diuron is softened, dissolved, and recrystallized in a single phase of toluene to obtain a better diuron solid.

[0006] However, existing technologies have the following technical problems: First, excessive toluene content in the isocyanate or the addition of too much toluene leads to low reaction concentrations and high energy consumption in subsequent dehydration recrystallization and solvent toluene recovery. Second, explosive crystallization makes continuous production difficult. To solve these problems:

[0007] Patent CN102746194B discloses a continuous method for the addition reaction of diuron. This method employs a multi-reactor series reactor, continuously feeding the reactants isocyanate and dimethylamine as diluted solutions into the reactors, with the materials discharged via overflow. The collected reactants are directly centrifuged, washed, and dried to obtain diuron. This method overcomes the shortcomings of batch reaction equipment, achieving higher yields and product quality. However, this method uses a large amount of toluene to dilute the reactants, increasing the energy consumption for solvent recovery. The toluene solution of 3,4-dichlorophenyl isocyanate in patent CN102746194B has a mass concentration of 10-13%. That is, every 100 grams of the mixed solution contains 10 to 13 grams of pure 3,4-dichlorophenyl isocyanate, with the remaining 87 to 90 grams being toluene and small amounts of impurities; therefore, the amount of toluene remains high.

[0008] In their paper "Research on the Synthesis Process of Diuron" published in Volume 45, Issue 13 of Guangdong Chemical Industry, Ma Yong et al. studied a three-stage addition continuous reaction. In order to solve the problem of material overflow, the concentration of isocyanate toluene solution was controlled at 10%, but the amount of toluene was still very high.

[0009] The addition method of diuron disclosed in patent CN108863852B uses a reaction vessel divided into an upper constant temperature zone and a lower constant temperature zone, which control the reaction temperature to below 20°C and 45-100°C respectively. It still requires the addition of additional toluene as a solvent to the dimethylamine aqueous solution, which also has the disadvantage of using a high amount of toluene.

[0010] Patent CN118530448A discloses a process for synthesizing diuron, in which modified polyethylene glycol is added to an isocyanate-toluene solution, increasing the weight ratio of isocyanate to toluene in the addition reaction to 15:100. After synthesis, diuron is obtained directly through centrifugation, washing, and drying. The amount of toluene used is still relatively high.

[0011] Therefore, it is urgent to solve the problem of how to prepare better crystals without using excessively high concentrations of toluene, to meet the needs of continuous production, to obtain qualified diuron products, and to save on the thermal addition dehydration, softening, dissolution and recrystallization processes, as well as the consumption of steam for dehydration and recrystallization. Summary of the Invention

[0012] This invention provides a low-energy continuous synthesis process for diuron, which can produce good crystals without using excessively high concentrations of toluene, meeting the needs of continuous production and obtaining qualified diuron products. It also saves the thermal addition dehydration, softening, dissolution and recrystallization processes, and saves steam consumption for dehydration and recrystallization.

[0013] This invention provides the following technical solution: a low-energy-consumption continuous synthesis process for diuron, comprising: S1, continuously feeding a mixture of dimethylamine aqueous solution, a co-solvent, and a wetting agent into a primary continuous reactor; S2, adding a 20-40% (w / w) toluene solution of 3,4-dichlorophenyl isocyanate to the primary, secondary, and tertiary continuous reactors in batches according to a certain proportion, and after the reaction, filtering, washing, and drying to obtain diuron. Testing shows that the diuron prepared by this method, using a lower concentration of toluene than existing technologies, produces crystals that meet the requirements of continuous production, yielding qualified diuron products, increasing the D50 to 80 μm, and enabling continuous production at higher concentrations. The final product yield is over 98%, the product purity is over 98%, and the steam consumption for dehydration and recrystallization is reduced by 2 tons / ton.

[0014] As an optional scheme for the low-energy continuous synthesis process of diuron described in this invention, the dimethylamine aqueous solution has a mass concentration of 5-40%. The co-solvent is dioxane. The wetting agent includes at least one of alkylnaphthalene sulfonate, alkylbenzene sulfonate, alkyl sulfate, and alkyltrimethylammonium bromide. During the research and development process, it was discovered that the co-solvent and wetting agent can improve the diffusion rate and dispersibility of the raw material isocyanate and the product diuron in the aqueous phase, thereby improving the reaction efficiency with dimethylamine and the crystal growth efficiency. Tests showed that a mixing mass ratio of dimethylamine aqueous solution to dioxane and wetting agent of 100:5-20:0.02-0.5, and a molar ratio of 3,4-dichlorophenyl isocyanate to dimethylamine of 1:1-1.05, achieves better results.

[0015] As an optional scheme of the low-energy continuous synthesis process of diuron described in this invention, in S2, the proportions of the toluene solution of 3,4-dichlorophenyl isocyanate added to the first-stage, second-stage, and third-stage continuous reactors are 5%-10%, 50%-70%, and 20%-45%, respectively. The reaction temperatures of the first-stage, second-stage, and third-stage continuous reactors are controlled at 0-15℃, 0-15℃, and 20-30℃, respectively. The average residence times of the first-stage, second-stage, and third-stage continuous reactors are 0.5-1h, 2-3h, and 2-3h, respectively. Variable frequency stirring is used in all three stages of the continuous reactors to control crystal growth. Testing revealed that by controlling the flow rate in stages, the first-stage reaction initiates crystal nuclei, the second-stage reaction grows crystals, and the third-stage slow crystal growth improves the crystal particle size, increasing D50 to 80μm, thus achieving continuous production with higher concentrations. Combining multi-stage feeding and staged reaction temperatures to control isocyanate hydrolysis improves product yield. Ultimately, the product yield is over 98%, the product purity is over 98%, and the steam consumption for dehydration and recrystallization is reduced by 2 tons per ton.

[0016] The present invention has the following beneficial effects:

[0017] 1. This low-energy continuous synthesis process of diuron improves the diffusion rate and dispersibility of the raw material isocyanate and the product diuron in the aqueous phase by using cosolvents and wetting agents, thereby improving the reaction efficiency with dimethylamine and the crystal growth efficiency.

[0018] 2. This low-energy-consumption diuron continuous synthesis process adopts a three-stage continuous reactor and achieves crystal nucleation through stepwise flow control. The first-stage reaction initiates crystal nuclei, the second-stage reaction grows crystals, and the third-stage slow crystal growth improves the crystal particle size, increasing D50 to 80μm, thus enabling continuous production with higher concentrations.

[0019] 3. This low-energy-consumption continuous synthesis process for diuron uses multi-stage feeding and staged reaction temperatures to control isocyanate hydrolysis, thereby improving product yield. Ultimately, it achieves a product yield of over 98% and a product purity of over 98%, while saving 2 tons / ton of steam consumption for dehydration and recrystallization. Attached Figure Description

[0020] Figure 1 This is a diagram illustrating the particle size distribution of diuron, a crystalline paste that occurred during the development of this invention.

[0021] Figure 2 This is a diagram illustrating the particle size distribution of diuron products produced using existing softening, dissolving, and recrystallizing processes.

[0022] Figure 3 This is a diagram illustrating the particle size distribution of the diuron product obtained in Example 1 of the present invention. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] First, the process and problems encountered in this application will be explained. This application aims to solve the problem of preparing better crystals without using excessively high concentrations of toluene, meeting the needs of continuous production, obtaining qualified diuron products, and saving the thermal addition dehydration, softening, dissolution and recrystallization processes, thus saving steam consumption for dehydration and recrystallization.

[0025] Based on this, this application controls the mass concentration of the toluene solution of 3,4-dichlorophenyl isocyanate at 20-40%, but this mass concentration may result in... Figure 1The explosive crystallization shown was a technical problem that the applicant continuously experimented with, ultimately discovering that using a co-solvent and wetting agent could improve the diffusion rate and dispersibility of the raw material isocyanate and the product diuron in the aqueous phase, thereby increasing the reaction efficiency with dimethylamine and the crystal growth efficiency. Simultaneously, a three-stage continuous reactor was employed, with stepwise flow control to achieve crystal nucleation in the first stage, crystal growth in the second stage, and slow crystal growth in the third stage to improve crystal particle size. Combined with the use of co-solvents and wetting agents, and specific reaction parameter adjustments, explosive crystallization can be avoided. Figure 3 As shown, D50 can be increased to 80μm, achieving the following: Figure 2 The quality level of the existing technology shown is such that continuous production at higher concentrations can be achieved.

[0026] The specific preparation process is as follows: Dimethylamine aqueous solution is mixed with a co-solvent and a wetting agent and continuously fed into a primary continuous reactor. Then, a 20-40% (w / w) toluene solution of 3,4-dichlorophenyl isocyanate is added to the primary, secondary, and tertiary continuous reactors in different proportions. The reacted solution is finally fed into a centrifuge intermediate tank, then filtered, washed, and dried by a centrifuge to obtain the diuron product. The mother liquor after filtration is used to recover toluene and dioxane through distillation.

[0027] The following examples illustrate the above scheme. The method steps in Examples 1-8 include: preparing a mixture of dimethylamine aqueous solution, co-solvent dioxane, and wetting agent into a required ratio, and continuously feeding it into a 3000L primary continuous reactor at a flow rate of 3000L / h; then continuously adding a toluene solution of 3,4-dichlorophenyl isocyanate into the 3000L primary continuous reactor, the 6000L secondary continuous reactor, and the 6000L secondary continuous reactor respectively in different proportions; finally, the reacted liquid enters a 6000L centrifugal intermediate tank, and is then filtered, washed, and dried by a centrifuge to obtain the diuron product.

[0028] The specific components and parameters of Examples 1-8 are shown in Table 1.

[0029] Table 1:

[0030]

[0031] like Figure 3 The figure shows the particle size distribution of the diuron product in Example 1. A comparison of Examples 1-8 shows that the absence of a co-solvent or wetting agent significantly impacts the crystallization state during the continuous reaction process, leading to difficulty in slurry flow, severe peritectic formation, a sharp decrease in product content, and a reduction in product yield. Continuous production is impossible if both the co-solvent and wetting agent are lacking.

[0032] To better explain the scheme of this application, the method steps of Examples 9-14 include: preparing a mixture of dimethylamine aqueous solution, co-solvent dioxane, and wetting agent into a required ratio, and continuously feeding it into a 1500L primary continuous reactor at a flow rate of 3000L / h; then continuously adding a toluene solution of 3,4-dichlorophenyl isocyanate into the 1500L primary continuous reactor, the 6000L secondary continuous reactor, and the 6000L secondary continuous reactor respectively in different proportions; finally, the reacted liquid enters a 6000L centrifugal intermediate tank, and is then filtered, washed, and dried by a centrifuge to obtain the diuron product.

[0033] The specific components and parameters of Examples 9-16 are shown in Table 2.

[0034] Table 2:

[0035]

[0036] It should be noted that the difference between Example 15 and Example 9 is that a single-stage fully mixed reaction was used without graded control. It was found that the single-stage fully mixed reaction, which completes the continuous reaction, cannot control the reaction concentration and ensure complete reaction, thus having a certain impact on the yield and a significant impact on crystallization and product quality.

[0037] The three-stage temperature control in Example 16 is the same, which has a slight effect on the reaction yield.

[0038] In summary, the low-energy continuous synthesis process for diuron in this application, while controlling the amount of toluene used, avoids the problem of explosive crystallization caused by controlling the amount of toluene by using a combination of co-solvents and wetting agents in a stepwise flow control manner, thereby increasing the D50 to 80μm and enabling continuous production at high concentrations. Combining multi-stage feeding and staged reaction temperatures to control isocyanate hydrolysis improves product yield. Ultimately, a product yield of over 98% and a product purity of over 98% are achieved, saving 2 tons / ton of steam consumption for dehydration and recrystallization.

[0039] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0040] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A low-energy-consumption continuous synthesis process for diuron, characterized in that, include: S1. Dimethylamine aqueous solution is mixed with cosolvent and wetting agent and then continuously fed into a primary continuous reactor; S2. A toluene solution of 3,4-dichlorophenyl isocyanate with a mass concentration of 20-40% was added in batches to the first-stage, second-stage, and third-stage continuous reactors in a certain proportion. After the reaction was completed, the solution was filtered, washed, and dried to obtain diuron.

2. The low-energy continuous synthesis process for diuron according to claim 1, characterized in that: The mass concentration of dimethylamine aqueous solution is 5-40%.

3. The low-energy continuous synthesis process for diuron according to claim 1 or 2, characterized in that: The cosolvent used is dioxane.

4. The low-energy continuous synthesis process for diuron according to claim 1 or 2, characterized in that: The wetting agent includes at least one of alkylnaphthalene sulfonate, alkylbenzene sulfonate, alkyl sulfate and alkyltrimethylammonium bromide.

5. The low-energy continuous synthesis process for diuron according to claim 3, characterized in that: The mass ratio of dimethylamine aqueous solution to dioxane and wetting agent is 100:5-20:0.02-0.

5.

6. The low-energy continuous synthesis process for diuron according to claim 1 or 2, characterized in that: The molar ratio of 3,4-dichlorophenyl isocyanate to dimethylamine is 1:1-1.

05.

7. The low-energy continuous synthesis process for diuron according to claim 1 or 2, characterized in that: In S2, the toluene solution of 3,4-dichlorophenyl isocyanate is added to the first-stage, second-stage, and third-stage continuous reactors in proportions of 5%-10%, 50%-70%, and 20%-45%, respectively.

8. The low-energy continuous synthesis process for diuron according to claim 1 or 2, characterized in that: The reaction temperatures of the primary, secondary, and tertiary continuous reactors are controlled at 0-15℃, 0-15℃, and 20-30℃, respectively.

9. The low-energy continuous synthesis process for diuron according to claim 1 or 2, characterized in that: The average residence times for the primary, secondary, and tertiary continuous reactors are 0.5-1 h, 2-3 h, and 2-3 h, respectively.

10. The low-energy continuous synthesis process for diuron according to claim 1 or 2, characterized in that: The primary, secondary, and tertiary continuous reactors all use variable frequency stirring to control crystal growth.

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