A process for the preparation of iminodiacetonitrile IDAN

Abstract

The application provides a method for preparing imino diacetonitrile by using hydroxyacetonitrile as raw material, and introducing a catalyst and a stabilizer by using the raw material hydroxyacetonitrile and ammonia, optimizing the synthesis process of imino diacetonitrile, improving the stability and conversion rate of the raw material hydroxyacetonitrile, improving the selectivity of imino diacetonitrile in the reaction solution, and reducing the production amount of other by-products and polymers in the imino diacetonitrile reaction solution. Through the optimization of the post-treatment purification scheme, the organic solvent dissolution separation is adopted, combined with the recrystallization purification, the mother liquor is used, and other technical schemes, the high-quality IDAN product meeting the downstream market is prepared.

Description

Technical Field

[0001] This invention relates to the field of organic chemical engineering, specifically to iminodiacetonitrile, and more specifically to a method for preparing high-purity iminodiacetonitrile using hydroxyacetonitrile, ammonia, sulfuric acid, organic solvents, etc. Background Technology

[0002] Imidodiacetonitrile (IDAN) is an important fine chemical intermediate. Currently, industrial-grade products comply with the quality standard GB / T 23958-2009 Industrial Imidodiacetonitrile. Over 95% of its applications are in the synthesis of glyphosate herbicides. It also has uses in dyes, rubber, fertilizers, electroplating, pharmaceuticals, building materials, water treatment, food processing, synthetic resins, and electronics.

[0003] Currently, there are two main industrial synthesis processes for IDAN: the hydrogen cyanide-hexamethylenetetramine method and the direct synthesis method of hydroxyacetonitrile. Research on the preparation of IDAN using hydrogen cyanide and hexamethylenetetramine was reported as early as 1894. In 1921, it was reported that IDAN could be prepared from an aqueous solution of hexamethylenetetramine and hydrogen cyanide. First, a portion of hydrogen cyanide and hexamethylenetetramine were reacted to generate hydroxyacetonitrile. Then, a mixed aqueous solution of hydroxyacetonitrile, hydrogen cyanide, and hexamethylenetetramine was passed through a tubular reactor to obtain IDAN. Later, with improvements, IDAN was directly synthesized from a mixture of hydrogen cyanide, formaldehyde solution, and hexamethylenetetramine through a tubular reactor.

[0004] Hydrogen cyanide-hexamethylenetetramine method: Monsanto uses this method abroad. While the Guangxi Chemical Industry Research Institute and the Sichuan Natural Gas Chemical Industry Research Institute in China have conducted research on hydrogen cyanide-hexamethylenetetramine, there are no industrial-scale application manufacturers. Numerous related patents have been reported in recent decades, with typical patents including US2794044, US3167580, US3412137, US3886198, US3988360, US3904668, US4307037, US4895971, and US4661614. Each of these methods has various drawbacks, such as the additional burden of forming complex starting reactants, low yield, and harsh reaction conditions. The yield and purity of the prepared IDAN products also vary significantly. This technical route industrially utilizes hydrogen cyanide, a byproduct of acrylonitrile production, or prepares hydrogen cyanide gas and liquid using the Angle process. The byproduct hydrogen cyanide route requires co-production with acrylonitrile, which limits its application. The disadvantages of this process are low yield, the need for high concentrations of hydrogen cyanide, high safety requirements, and harsh operating conditions (pressure approximately 1.4 MPa, temperature 130-140℃, close to the boiling point of hydrogen cyanide).

[0005] Direct synthesis of hydroxyacetonitrile: Domestic industrial enterprises directly use hydrogen cyanide, a byproduct of the natural gas ammonia oxidation process or the acrylonitrile process, to prepare hydroxyacetonitrile as a raw material. Sichuan Provincial Natural Gas Chemical Research Institute, Chongqing Ziguang, and others have developed batch and continuous methods using formaldehyde and gaseous hydrogen cyanide (methane method) as raw materials to prepare a hydroxyacetonitrile solution (40-50% aqueous solution). Ammonia and the hydroxyacetonitrile solution are mixed in a specific ratio and continuously fed into a tubular reactor to obtain an IDAN product solution. The solution is then rapidly cooled at the outlet, acidified, cooled to crystallize, and centrifuged to obtain the IDAN product. Some petrochemical enterprises (Shandong Qitai, Liaoning Fushun, etc.) use liquid hydrogen cyanide, a byproduct of the acrylonitrile unit, to react with formaldehyde to synthesize a hydroxyacetonitrile solution. IDAN synthesis in this process involves mixing an ammonia source and the hydroxyacetonitrile solution in a specific ratio, continuously feeding it into a tubular reactor to obtain a product solution, rapidly cooling at the outlet, acidifying, cooling to crystallize, and centrifuging to obtain the product. However, the purity of IDAN prepared by this process is only 92-95%, and the product appearance is brown or yellow.

[0006] US5187301 discloses two methods for preparing IDAN from hydroxyacetonitrile and an ammonia source: a continuous method and a batch method. This method is a significant improvement over previous patents. It uses a stable intermediate to produce IDAN without the need to store volatile and unstable HCN. The conversion rate of hydroxyacetonitrile does not exceed 95%, and the IDAN yield is up to 81.7%.

[0007] CN1594281A discloses a method for preparing IDAN by hydroxyacetonitrile and ammonia, followed by hydrolysis to prepare iminodiacetic acid (IDA). The IDAN synthesis process involves a catalyst and an ammonia buffer solution to adjust the pH value to 2-7. The catalyst is a reaction product of substituted phenol and ferric trihalide, and the buffer solution is an ammonium sulfate-ammonia water system. The single-pass IDAN synthesis yield is 85%. However, this method has drawbacks such as unstable operation due to batch processing, low production capacity, and excessive ammonium sulfate consumption.

[0008] CN1331844C discloses a method for preparing IDAN by preheating hydroxyacetonitrile and ammonia water separately, then mixing them and feeding them into a tubular reactor. Stabilizers and antioxidants are added during the reaction process to optimize and increase the IDAN content to approximately 98%, with a maximum yield of approximately 91%. However, this method suffers from drawbacks such as significant waste, the presence of stabilizers and antioxidants in the product and mother liquor, impacting downstream applications, and difficulties in waste treatment.

[0009] CN100422144C discloses a method for preparing IDAN using hydroxyacetonitrile and high-concentration liquid ammonia. In this method, a polymerization inhibitor and ammonium salt are added to the raw material hydroxyacetonitrile, the pH value of the system is stabilized by liquid acid, liquid ammonia is used instead of ammonia water to reduce the amount of post-treatment wastewater, and the yield of IDAN is 85-92%.

[0010] CN101591267B discloses a clean production method for preparing IDAN using hydroxyacetonitrile as a raw material. The reaction is characterized by recycling the reaction mother liquor and the catalyst ammonium salt 7 to 8 times, increasing the overall yield after recycling to about 92%. This process uses intermittent recycling of part of the mother liquor and treatment of part of the concentrated water. There is a risk of fluctuation in the content of the product after recycling, and the presence of ammonium chloride salt affects downstream applications.

[0011] CN101914037B discloses a process for continuously synthesizing iminodiacetonitrile using hydroxyacetonitrile and ammonia, and further producing high-purity 99% IDAN. This process employs purification steps for the IDAN reaction solution (nanofiltration, adsorption, flocculation, ion exchange, and other decolorization and impurity removal steps) and three-stage concentration and three-stage crystallization processes. It also includes waste treatment processes. The overall process steps are complex, and a large number of equipment are selected, which is unfavorable from an industrial investment perspective. At the same time, the channels of the membrane system and ion exchange equipment are easily blocked by polymers generated during the IDAN synthesis process. The waste generated during cleaning and replacement costs are high, the service life is short, and the overall yield reaches 86-92% across multiple stages.

[0012] Patents CN105315173B, CN105272881B, CN105315173B, CN105001121B, and CN105315174B disclose an optimization direction: a decolorization method and a clean production method for iminodiacetonitrile; a resource utilization method and apparatus for iminodiacetonitrile production mother liquor; and the application of sulfurous acid as a formaldehyde blocking agent and decolorizing agent. These patents utilize sulfur dioxide, sulfurous acid and its sulfites, hydrogen cyanide, and other substances to reduce formaldehyde in the IDAN reaction solution and crude product. By blocking formaldehyde, they aim to reduce impurities in the product. Under different technical conditions, the overall optimized IDAN content is >97.0%, impurities <3%, IDAN content is at most 99.0%–99.3%, and the impurity MBIDAN content is 0.08%–0.21%. Other impurities are partially reduced, while sulfurous acid and other substances achieve a decolorization effect, improving the gray value of the product to obtain white IDAN.

[0013] In summary, the traditional hydroxyacetonitrile method for direct synthesis of IDAN suffers from numerous side reactions, complex reaction products, and low product purity. The national standard for industrial-grade IDAN using this method has a main content of 92-95%. There are limitations imposed by chemical equilibrium; the conversion rate of the raw material hydroxyacetonitrile is generally only about 95%, meaning that approximately 5% hydroxyacetonitrile remains in the reaction solution. Both the raw material hydroxyacetonitrile and the product iminodiacetonitrile are unstable under alkaline or weakly acidic conditions, self-polymerizing into dimers, trimers, or polymers, as well as polymerizing with each other to form brownish polymers that adhere to the product surface, affecting both appearance and downstream applications. Furthermore, hydroxyacetonitrile contains residual formaldehyde, which reacts with ammonia in alkaline conditions to form hexamethylenetetramine. Before IDAN crystallization, acid (such as sulfuric acid) must be added to adjust the reaction solution to acidity to ensure the stability of both hydroxyacetonitrile and IDAN. However, the addition of sulfuric acid causes the hexamethylenetetramine produced during the reaction to decompose into ammonium sulfate and formaldehyde. Formaldehyde then reacts with IDAN to produce the impurity methylenediiminodiacetonitrile (MBIDAN), affecting product quality and limiting its application range. This is especially true for downstream applications with more stringent requirements, such as the synthesis of diethylenetriamine (DETA) from IDAN through hydrogenation. Some impurities or byproducts in the IDAN raw material have a serious impact on the catalyst in the subsequent hydrogenation process.

[0014] To expand the applications of IDAN products, one of the potential directions for improving the aforementioned IDAN synthesis process using hydroxyacetonitrile as a raw material is to increase the purity of IDAN products, control and limit by-products, polymers, and key impurities in IDAN products, reduce the cost of purifying IDAN, improve the yield of high-quality IDAN preparation, stabilize the preparation process of high-quality IDAN products, and reduce the amount of waste to be treated. These are all potential optimization points. Summary of the Invention

[0015] In view of this, the present invention provides a method for preparing iminodiacetonitrile from hydroxyacetonitrile. Using hydroxyacetonitrile and ammonia as raw materials, the method optimizes the iminodiacetonitrile synthesis process by introducing catalysts and stabilizers, thereby improving the stability and conversion rate of the hydroxyacetonitrile raw material, increasing the selectivity of iminodiacetonitrile in the reaction solution, and simultaneously reducing the generation of other byproducts and polymers in the iminodiacetonitrile reaction solution. Through optimized post-treatment purification schemes, including organic solvent dissolution and separation, combined with recrystallization purification and mother liquor reuse, the method optimizes the preparation of high-quality IDAN products that meet the needs of the downstream market.

[0016] To solve the above technical problems, the present invention provides the following technical solution:

[0017] A method for preparing an iminodiacetonitrile (IDAN) solid product includes the following steps:

[0018] (1) Add stabilizer and catalyst to hydroxyacetonitrile solution, and preheat hydroxyacetonitrile solution and ammonia solution respectively;

[0019] (2) Mix the preheated hydroxyacetonitrile solution and ammonia solution thoroughly in proportion, and pump them into a tubular reactor to prepare iminodiacetonitrile (IDAN) reaction solution.

[0020] (3) Adjust the pH of the IDAN solution obtained from the reactor outlet in step (2) to 2-4, stir and cool, cool and crystallize to obtain crude IDAN solid (a);

[0021] (4) Add the crude IDAN solid (a) obtained in step (3) to an organic solvent, heat it to dissolve it into a mixed solution containing some undissolved substances, and after adsorption decolorization, separate the organic solution and solid residue of IDAN.

[0022] (5) The IDAN organic solution obtained in step (4) is cooled and crystallized to obtain solid IDAN primary crystallization product (b). After solid-liquid separation, the solid primary crystallization IDAN (b) enters the subsequent recrystallization and purification step (6).

[0023] (6) The solid IDAN (b) obtained in step (5) is added to pure water and heated to dissolve. Then, the solid IDAN is cooled down to crystallize and precipitate the recrystallized product. After solid-liquid separation, the solid IDAN is dried under low temperature and reduced pressure to obtain qualified IDAN product (c).

[0024] In one specific implementation, the stabilizer used in step (1) is one or a mixture of two of zinc oxide and silicon dioxide, and the amount of stabilizer added is 0.5 to 2.0 wt% of the weight of the raw material hydroxyacetonitrile.

[0025] In one specific implementation, the catalyst used in step (1) is one or a mixture of two of ammonium citrate, ammonium malate, and ammonium tartrate, and the amount of catalyst added is 0.2 to 1.0 wt% of the weight of the raw material hydroxyacetonitrile.

[0026] In one specific implementation, the concentration of the hydroxyacetonitrile solution in step (1) is 40.0 to 50.0 wt%, and the pH of the hydroxyacetonitrile solution is preferably pre-adjusted to 2.0 to 3.0 by acid; and / or, the preheating temperature of the hydroxyacetonitrile solution is 50 to 100°C, so that the raw material can be produced and used immediately after preheating.

[0027] In one specific implementation, the mass concentration of the ammonia solution in step (1) is 20.0–30.0 wt%, and the preheating temperature is 80–120 °C.

[0028] In one specific implementation, in step (2), the molar ratio of hydroxyacetonitrile solution to ammonia solution is 1.9 to 2.1:1. The preheated hydroxyacetonitrile solution and ammonia solution are simultaneously pumped into a mixer according to the ratio. After being mixed evenly, they are directly pumped into a reactor for reaction. Preferably, the reaction is carried out in a tubular reactor with continuous feeding. The reaction temperature in the reactor is 120 to 160°C, the reaction pressure is 0.5 to 1.0 MPa, and the reaction time is 1 to 4 minutes.

[0029] In one specific implementation, in step (3), after the reactor outlet material is directly depressurized, the temperature of the reaction liquid is reduced to 40-60°C through a heat exchanger. After adding acid to adjust the pH of the reaction liquid to acidic 2-4, the temperature of cooling crystallization is 15-25°C, and the crude IDAN solid (a) is grayish-white or light brown.

[0030] In one specific implementation, in step (4), the organic solvent used to dissolve the crude IDAN solid (a) is selected from one or two of the following: alcohols such as methanol, ethanol, and isopropanol; aromatics such as benzene, toluene, and xylene; esters such as methyl formate, ethyl acetate, and ethyl benzoate; tetrahydrofuran (THF), dimethylformamide (DMF), dimethylacetamide (DMAC), dimethyl carbonate (DMC), and 1,4-dioxane.

[0031] In one specific implementation, in step (4), the temperature at which the crude IDAN solid (a) is dissolved is 40–60°C. The mass ratio of the organic solvent to the crude solid (a) is 1.2–2.3:1, and the mass concentration of IDAN in the organic solution is 30.0–45.0 wt%.

[0032] In one specific implementation, in step (4), the dissolved IDAN solution is yellow or brownish-black. The appearance of the crystalline product is improved by adsorption and decolorization. Colored impurities and polymers are adsorbed. The adsorbent is selected from one or more of powdered activated carbon (>100 mesh, methylene blue 185mg / g), granular activated carbon, diatomaceous earth, zeolite containing acidic alumina, silica, and silicates. The adsorption temperature is 40-60℃ and the adsorption time is 0.5-1h. The organic solution after separation is basically colorless or slightly yellow.

[0033] In one specific implementation, in step (5), the cooling crystallization temperature is 10–20°C, and the crystallization time is 2–4 hours. The IDAN crystalline solid and the organic solution are separated by centrifugation or vacuum filtration.

[0034] In one specific implementation, in step (6), the temperature of the pure water used to dissolve the white solid primary crystal IDAN(b) is 50-60°C, and the mass ratio of the pure water to the primary crystal IDAN(b) is 1-1.8:1.

[0035] In one specific implementation, in step (6), the recrystallization cooling temperature is 10–20°C, and the crystallization time is 2–4 h. The IDAN crystalline solid and aqueous solution are separated by centrifugation or vacuum filtration. After separation, IDAN is vacuum dried at a temperature of 30–50°C, a vacuum degree of <-0.1 MPa, and for 4–6 h.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] Looking at the entire IDAN synthesis process, firstly, the raw materials hydroxyacetonitrile and ammonia are used. By introducing catalysts and stabilizers, the synthesis process of iminodiacetonitrile is optimized, improving the stability and conversion rate of the raw material hydroxyacetonitrile and increasing the selectivity of iminodiacetonitrile in the reaction solution, while reducing the generation of other by-products and polymers in the iminodiacetonitrile reaction solution. Secondly, the post-treatment purification scheme is optimized. An organic solvent dissolution and separation method is used to remove undissolved polymers and most of the by-products in the reaction system through adsorption decolorization. Then, a second purification is carried out by recrystallization to prepare high-quality IDAN products. The main content and key impurity indicators of the product meet the requirements of the downstream high-end market.

[0038] The method and process of this invention are more efficient, and the qualified IDAN product (c) prepared is a white crystalline solid with an iminodiacetonitrile IDAN content ≥99.5%, a methylenebisiminodiacetonitrile MBIDAN content ≤0.01%, an acid value of 0.001~0.02mgKOH / g, and a sulfur content ≤0.02%. Attached Figure Description

[0039] Figure 1 This is a process flow diagram of the IDAN preparation process of the present invention;

[0040] Among them, A is a preheated hydroxyacetonitrile mixed solution; B is an ammonia solution; C is a mixed ammonia and hydroxyacetonitrile solution; D is a sulfuric acid solution; E is the IDAN reaction solution in a tubular reactor; F is the mother liquor from the IDAN reaction after crystallization and separation; G is an organic solvent; H is crude IDAN solid (a); I is IDAN organic solvent; J is IDAN organic solvent mother liquor; K is pure water; L is solid IDAN primary crystallization (b); M is IDAN aqueous solution; N is IDAN aqueous solution recrystallization mother liquor; O is solid IDAN recrystallized wet product; P is qualified IDAN product (c). Detailed Implementation

[0041] The following examples will further illustrate the preparation process and its application provided by the present invention, but the present invention is not limited to the listed examples and should also include any other known modifications within the scope of the claims of the present invention.

[0042] This invention provides a method for preparing iminodiacetonitrile (IDAN) solid products. The method optimizes the process by improving the parameters of the iminodiacetonitrile reaction solution, thereby optimizing the parameters and yield of the crude IDAN crystals and improving the synthesis process from the source. Traditional industrial-grade IDAN synthesis typically employs a two-stage concentration process, resulting in low purity of the crystallized product. The national standard method for industrial-grade IDAN analysis shows a main content of 92-95%. Literature and related patents report that liquid chromatography analysis of solid IDAN products shows even lower main content, with significant fluctuations between different preparation processes, ranging from 88-94%. One major reason for this is that the national standard method GB / T 23958-2009 for industrial iminodiacetonitrile uses sodium nitrite titration. The principle involves the reaction of aliphatic secondary amines with sodium nitrite and hydrochloric acid to generate N-nitrosoamines. This may lead to the analysis of some byproduct MBIDAN, which is then included in the main content of IDAN.

[0043] For downstream market applications, excessively high MBIDAN content in products can negatively impact the synthesis and purification of subsequent products. From the source, it's necessary to improve the purity of the raw IDAN product and control byproducts and key impurities. Although conventional primary crystallization or recrystallization processes can remove some impurities from IDAN by dissolving industrial-grade solid IDAN in secondary water, increasing the main IDAN content to 98%–99%, they cannot completely reduce MBIDAN residue and acid value. Some polymers or byproducts remain in the IDAN, making it difficult to achieve a product purity of ≥99.5%.

[0044] The specific synthesis method steps of the technical solution provided by the present invention are further described in detail below:

[0045] In a specific implementation scheme, the concentration of the hydroxyacetonitrile aqueous solution in step (1) is 40.0–50.0 wt%, for example, including but not limited to 40.0 wt%, 42.0 wt%, 44.5 wt%, 46.0 wt%, 48.5 wt%, and 50.0 wt%. Hydroxyacetonitrile is a mature industrial technology. It can be synthesized from liquid hydrogen cyanide and formaldehyde solution obtained as a byproduct of the acrylonitrile process, or from gaseous hydrogen cyanide and formaldehyde solution obtained through the Angle process, or from other sources. This invention does not impose specific restrictions on the raw material hydroxyacetonitrile, nor does it have any other special indicator requirements. The hydroxyacetonitrile solution only needs to meet known industry standards. Each enterprise can choose the most suitable technical route based on its own technological advantages, local resource advantages, cost differences, and other comprehensive factors.

[0046] In a specific implementation plan, in step (1), due to the high toxicity and instability of hydroxyacetonitrile, the factory generally has its own hydroxyacetonitrile production unit, which is transported through pipelines and temporarily stored in tanks. The pH of the hydroxyacetonitrile solution is adjusted to 2.0 to 3.0 by acid, and the temporary storage temperature of the solution is 15 to 25°C.

[0047] Before feeding, stabilizers and catalysts are added, and the material is rapidly preheated to 50-100°C. This preheating process ensures the material is used quickly to prevent the unstable decomposition of hydroxyacetonitrile into hydrogen cyanide and formaldehyde, and also to prevent the polymerization side reaction of cyanide in hydroxyacetonitrile.

[0048] In one specific implementation, the stabilizer used in step (1) is one or a mixture of two of zinc oxide and silicon dioxide, and the amount of stabilizer added is 0.5 to 2.0 wt% of the weight of the raw material hydroxyacetonitrile. The solid zinc oxide and silicon dioxide are derived from commercially available products, and the stabilizer can be in powder form (100 to 200 mesh) or in fine granular form (8 to 50 mesh).

[0049] In one specific implementation, the catalyst used in step (1) is one or a mixture of two of ammonium citrate, ammonium malate, and ammonium tartrate, and the amount of catalyst added is 0.2 to 1.0 wt% of the weight of the raw material hydroxyacetonitrile.

[0050] The catalysts ammonium citrate, ammonium malate, and ammonium tartrate can be added in solid or aqueous solution form. During the preheating of hydroxyacetonitrile and the synthesis of MBIDAN, they act as a pH buffer and lower the system pH. The catalysts contain ammonium, and the released ammonia can participate in the reaction system. This also avoids the potential negative effects of uneven dispersion due to contact between high-concentration ammonia water and preheated hydroxyacetonitrile. The catalysts also improve the stability of the raw material hydroxyacetonitrile, increasing its conversion rate and preventing the formation of byproducts, especially cyano polymers under high-temperature neutral or alkaline conditions. Simultaneously, the presence of synergistic stabilizers further enhances the conversion rate of hydroxyacetonitrile, reducing residual hydroxyacetonitrile in the system and preventing excessive residual formaldehyde and hydrogen cyanide from self-decomposition, while also reducing the possibility of MBIDAN impurity formation.

[0051] In one specific implementation, the concentration of the ammonia solution in step (1) is 20.0–30.0 wt%, for example, including but not limited to 20.0 wt%, 22.0 wt%, 25.0 wt%, 26.0 wt%, 27.0 wt%, 28.5 wt%, 29.0 wt%, and 30.0 wt%. The ammonia solution used in this invention is either commercially available industrial-grade ammonia solution or ammonia solution of different concentrations prepared from liquid ammonia. From a production economic perspective, this can also coordinate the industrial chain to recover ammonia gas generated from cyanide synthesis and hydrolysis, and prepare recovered ammonia solution through water absorption and concentration. The ammonia solution index only needs to meet the industrial-grade ammonia solution index. The ammonia solution is transported through pipelines and buffered in temporary storage tanks. The preheating temperature of the ammonia solution is 80–120°C.

[0052] In one specific implementation, in step (2), the preheated hydroxyacetonitrile solution and ammonia solution are pumped into a mixer and thoroughly mixed according to a ratio of 1.9–2.1:1.0, for example, including but not limited to 1.90:1.0, 1.95:1.0, 2.0:1.0, 2.05:1.0, and 2.10:1.0. After the preheated raw materials are mixed evenly, they are directly pumped into a tubular reactor for continuous feeding. The reaction temperature in the tubular reactor is 120–160°C, the reaction pressure is 0.5–1.0 MPa, and the reaction time is 1–4 minutes.

[0053] In a specific implementation, after the reactor outlet material is directly depressurized in step (3), the temperature of the reaction liquid is rapidly reduced to 40-60°C through equipment such as plate heat exchangers. At the same time, sulfuric acid is added to adjust the pH of the reaction liquid to acidic 2-4. Due to the reduction in temperature and pressure of the reaction outlet solution, the IDAN reaction liquid is alkaline and the outlet reaction liquid is a yellow to brownish solution. The catalyst and stabilizer added in step (1) can more effectively improve the overall yield of the IDAN reaction liquid and reduce the polymerization of raw materials such as hydroxyacetonitrile. At the same time, hydroxyacetonitrile, iminodiacetonitrile, aminoacetonitrile, hyponitrotriacetonitrile, hydrogen cyanide, formaldehyde, cyano polymers, etc. can also remain stable. Through the cooling crystallization process in step (3), the temperature is cooled to 15-25°C for crystallization and separation, and the crude IDAN solid (a) is grayish-white or light brown.

[0054] In one specific implementation, in step (4), the crude IDAN solid (a) separated in step (3) is directly dissolved in an organic solvent without drying. The organic solvent is heated to 40-60°C and stirred until most of the crude solid dissolves in the organic solvent. The mass ratio of the organic solvent to the crude solid (a) is 1.2-2.3:1.0, for example, including but not limited to using organic solvent to crude solid (a) mass ratios of 1.2:1.0, 1.35:1.0, 1.45:1.0, 1.5:1.0, 1.65:1.0, 1.8:1.0, 2.0:1.0, and 2.3:1.0. Meanwhile, different organic solvents and dissolution temperatures are used, and the mass concentration of IDAN in the organic solution is 30.0 to 45.0 wt%, for example, including but not limited to 30.0 wt%, 33.0 wt%, 36.0 wt%, 38.0 wt%, 40.0 wt%, 42.0 wt%, 43.5 wt%, and 45.0 wt%.

[0055] The organic solvent for dissolving crude IDAN solid (a) is selected from alcohols such as methanol, ethanol, and isopropanol; aromatics such as benzene, toluene, and xylene; esters such as methyl formate, ethyl acetate, and ethyl benzoate; and one or two of tetrahydrofuran (THF), dimethylformamide (DMF), dimethylacetamide (DMAC), dimethyl carbonate (DMC), and 1,4-dioxane.

[0056] The selection of different polar and non-polar solvents needs to be considered comprehensively. A key advantage is that the solvent can fully dissolve IDAN in the solution system, while simultaneously preventing polymers, inorganic salts, byproducts, mechanical impurities, and colored impurities in the crude IDAN from dissolving in the organic phase, and allowing them to dissolve in trace amounts in the aqueous phase. Through simple layering or subsequent adsorption decolorization, most byproduct impurities can be removed, while minimizing the loss of the main product in the solution and ensuring minimal quality loss of the IDAN product. The preferred organic solvent is one with a boiling point >50℃ to ensure sufficient solubility during the IDAN dissolution process.

[0057] In a specific implementation, in step (4), after the IDAN solution is heated after dissolution, the color increases to varying degrees, and the overall color is yellow or brownish-black. The suitable decolorization adsorption process is beneficial to improving the appearance of the crystallized product and adsorbing colored impurities and polymers. The adsorbent can be selected from powdered activated carbon (>100 mesh, methylene blue 185mg / g), granular activated carbon, diatomaceous earth, zeolite containing acidic alumina, silica, silicates, etc. The amount of adsorbent is 0.5 to 1.0 wt% of the total mass of crude IDAN. The adsorbent is added to the fully dissolved IDAN organic solvent, and the adsorption temperature is maintained at 40 to 60°C. The adsorption time is 0.5 to 1 hour. The organic solution and solid residue of IDAN are obtained by hot separation. The organic solution after separation is basically colorless or slightly yellow, and the solid residue is directly treated as environmentally friendly hazardous waste for incineration.

[0058] In a specific implementation scheme, in step (5), a more economical approach is to use the mother liquor after the IDAN solution obtained after decolorization is subsequently used to prepare purified IDAN products. Since IDAN is dissolved in an organic solvent, the mass of the solid IDAN product (b) crystallized from the solution in a single crystallization process can only account for 70-95 wt% of the total mass of the crude IDAN solid (a). After drying, the main content of the IDAN product is about 99.0%, which means that there will be 2-5 wt% dissolved residue in the IDAN organic solvent. If a product with a main content of >99.5% is obtained in a single crystallization process, the crystallization rate needs to be reduced. The total mass of the IDAN product obtained in a single crystallization is only 40-70%, which is relatively less economical for obtaining high-quality products over a long period of time.

[0059] This invention takes into account various factors to achieve a higher yield of IDAN solid in an organic solution. In a specific implementation, step (5) involves cooling the IDAN organic solution obtained in step (4) to crystallize it, resulting in a white solid IDAN primary crystallization product (b). The cooling crystallization temperature is 10–20°C, and the crystallization time is 2–4 hours. After solid-liquid separation, the primary crystallized IDAN (b) proceeds to the subsequent recrystallization purification step (6). The remaining IDAN organic solution is reused in the next batch of step (4) to redissolve the crude IDAN solid (a). This method achieves a higher yield of IDAN while simultaneously separating and purifying the organic solvent and aqueous phase through two crystallization processes, thus separating impurities from the crude IDAN product and obtaining a high-quality IDAN product.

[0060] In one specific implementation, in step (6), the temperature of the pure water used to dissolve the white solid, primary crystallized IDAN(b), is 50–60°C. The mass ratio of the pure water to the primary crystallized IDAN(b) is 1–1.8:1, for example, including but not limited to pure water to primary crystallized IDAN(b) mass ratios of 1.0:1.0, 1.2:1.0, 1.4:1.0, 1.5:1.0, 1.6:1.0, 1.65:1.0, 1.7:1.0, 1.75:1.0, and 1.8:1.0. The mass concentration of IDAN in the aqueous solution is 35.0–50.0 wt%, for example, including but not limited to 35.0 wt%, 38.5 wt%, 40.0 wt%, 42.5 wt%, 45.0 wt%, 47.0 wt%, 48.5 wt%, and 50.0 wt%.

[0061] In one specific implementation, in step (6), the recrystallization cooling crystallization temperature is 10-20°C, the crystallization time is 2-4 hours, the solid IDAN is separated, and the IDAN qualified product (c) is obtained after low temperature and vacuum drying. The separated IDAN aqueous solution is reused in the next batch of step (5) to redissolve the solid IDAN for primary crystallization (b).

[0062] Generally, the solubility of solid IDAN in water increases significantly above 40°C and increases rapidly with increasing temperature, with IDAN mass concentration >20wt% and even as high as 80wt%. During the cooling process, the solubility of IDAN decreases significantly. Below 20°C, the overall IDAN mass concentration is <5wt%. As a secondary recrystallization process in step (6), it can efficiently and with high yield fully purify the solid obtained in step (5) by primary crystallization of IDAN(b), and can maintain a single crystallization yield >90%. Furthermore, the aqueous solution after crystallization can be directly used as the solvent for the next batch, realizing the recycling of the mother liquor.

[0063] In summary, the intermediate products containing IDAN and MBIDAN, such as the IDAN solution, crude IDAN crystals, IDAN organic solution, IDAN aqueous solution, organic solvent mother liquor, and aqueous solution mother liquor prepared in each step, can be monitored for changes in their content components. Due to the inevitable residues or inclusion of impurities and polymers in the crude IDAN during crystallization and dissolution-recrystallization processes, the indicators such as MBIDAN, acid value, and sulfur content in the product and mother liquor will change. Impurities in the organic solvent and aqueous solution systems may accumulate to a certain extent, affecting the dissolution process. For the IDAN organic solvent mother liquor in step (5), after a certain stage of dissolution, some organic solvent can be extracted for incineration, or the organic solvent can be recovered by distillation / rectification, and the remaining small amount of heavy components can be incinerated to reduce the amount of impurities remaining in the system. For the secondary crystallization water system of IDAN dissolved in step (6), there is also the problem that after being used dozens of times, impurities accumulate. In this case, some of the aqueous solution can be extracted and incinerated to reduce the amount of impurities remaining in the system. In the whole process of recycling, the amount of wastewater and waste liquid extracted accounts for less than 1 wt% of the total system mass, which has little impact on the overall product yield.

[0064] The inventors of this invention discovered that combining steps (5) and (6) of the IDAN product can achieve lower control over acid value and impurity MBIDAN and sulfur content, comprehensively improving IDAN yield and product quality. By combining the use of both organic solvent and pure water mother liquor in the process, the IDAN solid product achieves a white crystalline appearance, with an iminodiacetonitrile IDAN content ≥99.5%, MBIDAN content ≤0.01%, an acid value of 0.001–0.02 mg KOH / g, and a sulfur content ≤0.02%. Further optimization yields a high-quality IDAN product with a main content >99.5%, an acid value of 0.001–0.005 mg KOH / g, an MBIDAN content of 0–0.003%, and a sulfur content of 0–0.003%.

[0065] The analytical method used in this invention is further described in detail below:

[0066] IDAN crude solid and IDAN reaction solution, IDAN mother liquor: The main contents, moisture, sulfate and other indicators were tested by chemical titration using the method described in industrial grade iminodiacetonitrile (GB / T 23958-2009).

[0067] IDAN and MBIDAN content in solid IDAN and IDAN solution: High-performance liquid chromatography (HPLC) was used, a method widely recognized in the industry. The typical test method is as follows: Agilent SB-C18 column (4.6 x 150 mm) 5 μm, mobile phase A: water: B: acetonitrile = 80:20 (volume ratio, buffer solution pH = 5), detection wavelength 205 nm, flow rate 1.0 mL / min, column temperature 40 °C, injection volume 10 μL, quantification using external standard method based on IDAN and MBIDAN standards.

[0068] Acid value content in solid IDAN: The potentiometric titration method was used. The typical test method is as follows: Prepare an automatic potentiometric titrator (Metrohm 905Titrando) equipped with a non-aqueous acid electrode. Weigh 4.0g of the sample, accurate to 0.1mg, add 100ml of methanol, pre-add 2ml of 0.01mol / L HCl, and titrate with 0.01mol / L sodium hydroxide standard solution on the potentiometric titrator until the potential jumps. Perform a blank experiment under the same conditions.

[0069] Sulfur content: The trace content was determined by inductively coupled plasma atomic emission spectrometry (ICP-OES).

[0070] The determination of methanol, aminoacetonitrile, hydroxyacetonitrile, iminodiacetonitrile, and hypozonyltriacetonitrile content in IDAN reaction solution and crude IDAN solid was performed using gas chromatography (GC) with an Agilent 7890B instrument and a flame ionization detector (FID). The recommended column was an HP-VOC capillary column with a stationary phase of 6% cyanopropyl-phenyl-polymethylsiloxane, an inner diameter of 0.32 mm, and a length of 60 m. The carrier gas N2 was 1.5 mL / min. The column temperature was initially 50 °C and held for 2 min, then increased to 80 °C at 5 °C / min, and then to 250 °C at 15 °C / min, held for 10 min. The vaporization chamber temperature was 150 °C, and the detector temperature was 260 °C. The injection volume was 1 μL, the split ratio was 10:1, the hydrogen flow rate was 30 mL / min, the air flow rate was 400 mL / min, and the make-up gas flow rate was 25 mL / min. The methanol content standard curve was established by gas chromatography external standard method. For hydroxyacetonitrile, iminodiacetonitrile, aminoacetonitrile, hyponitrotriacetonitrile, etc., industrial grade or standard samples were used to establish standard curves of 100 to 1000 mg / kg. The samples were pre-diluted 5 to 50 times with acetonitrile solution according to the content.

[0071] The main raw material sources in the embodiments and comparative examples of this invention are as follows; unless otherwise specified, all other raw materials are obtained from ordinary commercial channels or through factory self-production:

[0072] Liquid hydrogen cyanide (>99%): Wanhua Chemical

[0073] Formaldehyde solution (37%): Comio

[0074] Ammonia solution (20-30%): Prepare aqueous solutions of different concentrations using reagent-grade methyl methacrylate and ammonia gas.

[0075] Hydroxyacetonitrile (40-50%): Synthesized using formaldehyde solution and liquid hydrogen cyanide, Wanhua Chemical.

[0076] Zinc oxide, acidic aluminum oxide, silicon dioxide: granules or powder, Aladdin

[0077] Ammonium citrate, ammonium malate, ammonium tartrate: reagent grade, 99%, Aladdin

[0078] Powdered activated carbon (>100 mesh, methylene blue 185 mg / g), granular activated carbon, diatomaceous earth, etc.: Aladdin

[0079] Organic solvents: alcohols, aromatics, esters, tetrahydrofuran (THF), dimethylformamide (DMF), dimethylacetamide (DMAC), dimethyl carbonate (DMC), 1,4-dioxane: Aladdin

[0080] IAN (Industrial Grade, National Standard Method > 92%): Guang'an Chengxin Chemical Co., Ltd.

[0081] Example 1

[0082] Preparation of crude solid (a) iminodiacetonitrile (IDAN) (stabilizer zinc oxide and catalyst ammonium citrate)

[0083] Solid zinc oxide was added to a 40 wt% aqueous solution of hydroxyacetonitrile at a concentration of 0.5 wt% of the hydroxyacetonitrile solution mass. Then, ammonium citrate catalyst was added at the same concentration. The mixture was preheated to 80°C, while 30 wt% ammonia was preheated to 100°C. The mixture was then pumped into a mixer using a metering pump at a hydroxyacetonitrile:ammonia molar ratio of 2:1. After mixing, the mixture was continuously pumped into a tubular reactor, with a residence time of 4 minutes. The reaction temperature was controlled at 130–140°C, and the reaction outlet was rapidly cooled to 40°C. The pH of the system was adjusted to 3 using sulfuric acid. The IDAN reaction solution was collected for at least 8 hours. The conversion rate of the raw material in the outlet mixture was >98.0%. The reaction solution was continuously transferred to a crystallizer and cooled to 25°C. After crystallization, the crude IDAN solid (a) was obtained. It was light brown. After low-temperature drying, the IDAN main content was 98.3% by the national standard method and 97.8% by the liquid phase method. The MBIDAN content was 0.9%, the acid value was 3.5 mg KOH / g, the moisture content was 0.9%, the sulfate content was 0.2%, the water-insoluble matter content was 0.2%, and the yield of crude IDAN was 92.5% (based on hydroxyacetonitrile).

[0084] Example 2

[0085] Preparation of crude solid (a) iminodiacetonitrile (IDAN) (stabilizers: zinc oxide and silica, catalyst: ammonium malate)

[0086] Solid zinc oxide and silicon dioxide were added to a 45 wt% aqueous solution of hydroxyacetonitrile at amounts of 0.25 wt% and 0.75 wt% of the hydroxyacetonitrile solution, respectively. Then, ammonium malate catalyst was added at an amount of 0.8 wt% of the hydroxyacetonitrile solution. The mixed solution was preheated to 90°C, while 26.5 wt% ammonia was preheated to 110°C. The mixture was then pumped into a mixer using a metering pump at a hydroxyacetonitrile:ammonia molar ratio of 2.05:1. After mixing, the mixture was continuously pumped into a tubular reactor, with a residence time of 3 minutes. The reaction temperature was controlled at 140–150°C, and the reaction outlet was rapidly cooled to 50°C. Sulfur was then used for the reaction. The pH of the acid-adjusted system was 2. The IDAN reaction solution was continuously collected for at least 8 hours. The conversion rate of the raw material in the mixed solution at the outlet of the reaction solution was >98.5%. The reaction solution was continuously transferred to a crystallizer and cooled to 20°C. After crystallization, the crude IDAN solid (a) was obtained. It was light brown. After sampling and low-temperature drying, the main content of IDAN was 97.9% by the national standard method and 97.5% by the liquid phase method. The content of MBIDAN was 1.1%, the acid value was 4.0 mg KOH / g, the moisture content was 0.5%, the sulfate content was 0.3%, the water-insoluble matter was 0.3%, and the yield of crude IDAN was 93.6% (based on hydroxyacetonitrile).

[0087] Example 3

[0088] Preparation of crude solid iminodiacetonitrile (IDAN) (a) (stabilizers: zinc oxide and silica, catalyst: ammonium citrate)

[0089] Solid zinc oxide and silicon dioxide were added to a 50 wt% aqueous solution of hydroxyacetonitrile at amounts of 0.50 wt% and 1.5 wt% of the hydroxyacetonitrile solution, respectively. Then, ammonium citrate catalyst was added at an amount of 0.2 wt% of the hydroxyacetonitrile solution. The mixture was preheated to 100°C, while 25 wt% ammonia was preheated to 80°C. The mixture was then pumped into a mixer using a metering pump at a hydroxyacetonitrile:ammonia molar ratio of 2.1:1. After mixing, the mixture was continuously pumped into a tubular reactor, with a residence time of 2 minutes. The reaction temperature was controlled at 120–130°C, and the reaction outlet was rapidly cooled to 60°C. The mixture was then adjusted with sulfuric acid. The system pH was set at 4, and the IDAN reaction solution was continuously collected for at least 8 hours. The conversion rate of the raw material in the mixed solution at the outlet of the reaction solution was >98.0%. The reaction solution was continuously transferred to a crystallizer and cooled to 15°C. After crystallization, the crude IDAN solid (a) was obtained. It was light brown. After sampling and low-temperature drying, the main content of IDAN was 98.5% by the national standard method and 98.0% by the liquid phase method. The content of MBIDAN was 0.7%, the acid value was 4.8 mg KOH / g, the moisture content was 0.6%, the sulfate content was 0.5%, the water-insoluble matter was 0.5%, and the yield of crude IDAN was 93.2% (based on hydroxyacetonitrile).

[0090] Example 4

[0091] Preparation of crude solid (a) iminodiacetonitrile (IDAN) (stabilizer: silica and catalyst: ammonium tartrate)

[0092] Solid silica was added to a 50 wt% aqueous solution of hydroxyacetonitrile at a concentration of 1.50 wt% of the hydroxyacetonitrile solution mass. Then, ammonium tartrate catalyst was added at a concentration of 1.0 wt% of the hydroxyacetonitrile solution mass. The mixture was preheated to 50°C, while 20 wt% ammonia was preheated to 120°C. The mixture was then pumped into a mixer using a metering pump at a hydroxyacetonitrile:ammonia molar ratio of 2.1:1. The mixture was continuously pumped into a tubular reactor, with a residence time of 1 minute. The reaction temperature was controlled at 150–160°C, and the reaction outlet was rapidly cooled to 40°C. The pH of the system was adjusted using sulfuric acid. 2. Continuously collect the IDAN reaction solution for at least 8 hours. The raw material conversion rate of the mixed solution at the outlet of the reaction solution is >99.0%. Continuously transfer the reaction solution into the crystallizer and cool it to 20℃. After crystallization, the crude IDAN solid (a) is light brown. After sampling and analysis, the IDAN main content is 97.7% by the national standard method and 97.2% by the liquid phase method. The MBIDAN content is 1.3%, the acid value is 4.2 mgKOH / g, the moisture content is 0.4%, the sulfate content is 0.3%, the water-insoluble matter is 0.3%, and the yield of crude IDAN is 92.9% (calculated as hydroxyacetonitrile).

[0093] Example 5

[0094] Preparation of IDAN(b) by solid-state one-time crystallization of iminodiacetonitrile (with different organic solvents)

[0095] To compare the differences in the preparation processes of different stabilizers and catalysts, and to compare the effects of different types of solvents on the purification of IDAN, the reaction liquid from the tubular reactor outlet prepared in Examples 1-4 was acidified, cooled, and crystallized to separate crude IDAN solid (a) raw material. The crude solid (a) was directly crystallized and dissolved without the need for a low-temperature drying step. After centrifugation, the water content of the crude product was 5-10 wt%. 200 g (wet weight) of the crude solid prepared in Examples 1-4 was quantitatively weighed, dissolved and decolorized in an organic solvent, and then separated and crystallized to prepare solid primary crystallized IDAN (b). The data are summarized in Table 1 below.

[0096] Table 1. Preparation of iminodiacetonitrile solid primary crystallization IDAN(b) (organic solvent)

[0097]

[0098]

[0099] As can be seen from the data in Table 1 above, the crude IDAN prepared by Examples 1-4, after being dissolved and decolorized by different solvents in Example 5, and then cooled and crystallized to obtain the primary crystalline solid (b), showed that the overall liquid phase analysis of the solid content increased from 97.5-98% to 98.7-99.2%. Since some IDAN would remain in the organic solvent mother liquor of the single crystallization, the single product extraction rate from crude IDAN (a) to primary crystalline solid (b) was 72.5%-89.0%.

[0100] Example 6

[0101] Preparation of IDAN(b) by solid-state one-time crystallization of iminodiacetonitrile (organic solvent reuse process)

[0102] To further improve the overall product yield, the process of using the organic solvent mother liquor to dissolve the crude product in the next batch (a) was adopted. Using some batches of Example 5, the same implementation scheme and operating conditions were carried out. The organic solution was used in different batches of experiments, and the changes in product indicators and the total product yield were monitored after the use. The data are summarized in Table 2 below.

[0103] Table 2. Preparation of iminodiacetonitrile solid primary crystallization IDAN(b) (organic solvent application process)

[0104]

[0105] As can be seen from the data in Table 2 above, the crude IDAN prepared through Examples 1-4, after being dissolved and decolorized by different solvents in Example 5 and after being recycled with the organic solvent mother liquor in Example 6, was crystallized at low temperature to obtain a single-crystallized solid (b). The main content of the solid in the liquid phase analysis fluctuated from 98.7% to 99.2% to 98.5% to 99.0%. Since some IDAN and MBIDAN remain in the organic solvent mother liquor of the single crystallization, and some by-products and colored impurities are enriched to a certain extent, the total product extraction rate from crude IDAN (a) to single-crystallized solid (b) after recycling is 87.8% to 93.6%. That is to say, in the process of recycling the organic solvent mother liquor for crystallization, the total mass of IDAN product can be extracted on average >90%, and the highest extraction rate can reach 93.6% after 15 cycles. Theoretically, the highest total extraction rate can reach close to 95%.

[0106] Example 7

[0107] Preparation of solid qualified IDAN product (c) (recrystallization from pure water and recycling)

[0108] To obtain high-quality IDAN qualified products and control the content of main components and other impurities, ensuring that the acid value and sulfur content of the products meet downstream requirements, the solid primary crystallized IDAN (b) from some batches of Examples 5 and 6 was recrystallized in a secondary pure water system. After separation and drying, solid qualified IDAN products (c) were prepared. To further improve the overall product yield, the process of using the recrystallization aqueous solution mother liquor to dissolve the primary crystallized solid (b) in the next batch was adopted. Using some batches of Example 7, the same implementation scheme and operating conditions were carried out. Different batches of the crystallization aqueous solution were used for the reuse experiment. At the same time, the changes in product indicators and the total product yield were monitored. The data are summarized in Table 3 below.

[0109] Table 3. Preparation of solid qualified IDAN product (c) (pure water and recycled recrystallization)

[0110]

[0111]

[0112] As can be seen from the data in Table 3 above, the primary crystalline solid (b) obtained by cooling and crystallization after dissolution and adsorption decolorization in different solvents in Examples 5 and 6 can be significantly improved in quality by recrystallization through a single aqueous solution. The control level of key impurities reaches the optimal level. The main content of the solid in the qualified product (c) increases from 98.7-99.2% to 99.5-99.7% in liquid phase analysis. At the same time, the acid value is 0.003-0.014 mgKOH / g, the MBIDAN content is 0-0.008%, the sulfur content is 0.001-0.012%, and the single recrystallization extraction rate is 85.4-93.7% under different process conditions. After being reused in aqueous solution, the overall crystallization rate of the synthesized product (c) can be stabilized at 92-94%. After 15 reuses, the product quality still meets the requirements.

[0113] Based on Examples 1-4, the optimized preparation process of iminodiacetonitrile adopted in this invention can improve the conversion rate of the IDAN reaction solution to >98%, achieving a stable crude IDAN yield of approximately 93%, which is an improvement over previous processes. Simultaneously, it reduces the conversion rate and selectivity of byproducts. Under the same crystallization conditions, the crude IDAN content of the crystallized product from the tubular reactor outlet is >97.0% (both national standard method and liquid phase method), with a maximum content reaching 98.5%. Compared with existing processes, the content of commercially available products is 92-95%, representing a significant improvement.

[0114] Based on Examples 5 and 6, the purified product achieves a purity of over 99%. Single-phase and cyclical use of organic solvents effectively removes byproducts, resulting in a product purity >99%. The average total crystallization rate is >90%, with an optimal rate of 93.6%. In other words, the process yield for preparing 99% pure iminodiacetonitrile from hydroxyacetonitrile raw materials is 84-87%. Based on Example 7, through aqueous phase recrystallization and recrystallization cycles, the product purity prepared from hydroxyacetonitrile raw materials is ≥99.5%, meeting specific performance requirements. From the initial hydroxyacetonitrile, the overall product yield is >80%, reaching a maximum of 81.8%.

[0115] Comparative Example 1

[0116] Comparative Example 1: Preparation of crude solid (a) of iminodiacetonitrile (IDAN) (using aluminum oxide as a substitute for other stabilizers and ammonium citrate as a catalyst).

[0117] Solid aluminum oxide was added to a 40wt% aqueous solution of hydroxyacetonitrile at a concentration of 0.5wt% of the hydroxyacetonitrile solution mass. Other operations were the same as in Comparative Example 1. The conversion rate of the raw material in the reaction mixture outlet was 97.1%. The reaction mixture was continuously transferred to a crystallizer and cooled to 25°C. After crystallization, crude IDAN solid (a) was obtained, which was light brown. After low-temperature drying, the IDAN content was 96.8% by the national standard method and 96.1% by the liquid phase method. The MBIDAN content was 1.8%, the acid value was 5.2 mg KOH / g, the moisture content was 0.8%, the sulfate content was 0.6%, the water-insoluble matter was 0.6%, and the crude IDAN yield was 90.3% (based on hydroxyacetonitrile).

[0118] Comparative Example 2

[0119] In Comparative Example 1, the preparation of crude IDAN solid (a) was carried out (without a stabilizer, and ammonium citrate was used as the catalyst). Other operations were the same as in Comparative Example 1. The conversion rate of the raw material in the reaction mixture outlet was 96.6%. The reaction mixture was continuously transferred to a crystallizer and cooled to 25°C. After crystallization, the crude IDAN solid (a) was obtained, which was light brown. After sampling and low-temperature drying, the main IDAN content was 95.3% by the national standard method and 94.5% by the liquid phase method. The MBIDAN content was 2.2%, the acid value was 5.5 mg KOH / g, the moisture content was 0.7%, the sulfate content was 0.5%, the water-insoluble matter was 0.6%, and the yield of crude IDAN was 89.2% (based on hydroxyacetonitrile).

[0120] Comparative Example 3

[0121] In Comparative Example 2, the preparation of crude IDAN solid (a) (stabilizers: zinc oxide and silica, no catalyst) was carried out without adding a catalyst. Other operations were the same as in Comparative Example 2. The conversion rate of the raw material in the reaction mixture outlet was 95.5%. The reaction mixture was continuously transferred to a crystallizer and cooled to 20°C. After crystallization, the crude IDAN solid (a) was obtained, which was light brown. After sampling and low-temperature drying, the main IDAN content was 96.2% by the national standard method and 95.5% by the liquid phase method. The MBIDAN content was 1.4%, the acid value was 5.1 mg KOH / g, the moisture content was 0.6%, the sulfate content was 0.4%, the water-insoluble matter was 0.5%, and the yield of crude IDAN was 88.1% (based on hydroxyacetonitrile).

[0122] Comparative Example 4

[0123] In Comparative Example 2, the preparation of crude IDAN solid (a) was carried out (the amounts of stabilizers zinc oxide and silica and catalyst ammonium malate were insufficient). Other operations were the same as in Comparative Example 2, except that ammonium malate catalyst was added at 0.05 wt% of the mass of the hydroxyacetonitrile solution. The conversion rate of the raw material in the mixed solution at the outlet of the reaction liquid was 97.3%. The reaction liquid was continuously transferred to a crystallizer and cooled to 20°C. After crystallization, the crude IDAN solid (a) obtained was light brown. After sampling and low-temperature drying, the main IDAN content was 97.1% by the national standard method and 96.3% by the liquid phase method. The MBIDAN content was 1.5%, the acid value was 4.9 mg KOH / g, the moisture content was 0.5%, the sulfate content was 0.4%, the water-insoluble matter was 0.5%, and the yield of crude IDAN was 90.5% (based on hydroxyacetonitrile).

[0124] Comparative Example 5

[0125] Compared with existing patented processes, this method uses aluminum oxide as a stabilizer and eliminates the need for a catalyst. Following the conditions of Example 3 in patent CN1331844C, a process was simulated where 0.1% of the total amount of hydroxyacetonitrile was added to 20 wt% hydroxyacetonitrile as a stabilizer (aluminum oxide). The mixture was preheated to 60°C, and then preheated to 170°C with 25% ammonia. The mixture was simultaneously pumped into a tubular reactor using a metering pump at a theoretical molar ratio of 2:1. The residence time was 3 minutes, and the reaction temperature was controlled between 120°C and 140°C. The reaction outlet was rapidly cooled to room temperature, and the pH of the system was adjusted to 2 with sulfuric acid to prepare an iminodiacetonitrile solution. The resulting solid IDAN product was then crystallized from this solution. The IDAN reaction solution was continuously collected for at least 8 hours. The conversion rate of the raw material in the mixture at the outlet of the reaction solution was 94.8%. The reaction solution was continuously transferred to a crystallizer and cooled to 15°C. After crystallization, the crude IDAN solid (a) was obtained. It was light brown. After low-temperature drying, the IDAN main content was 94.9% by the national standard method and 93.7% by the liquid phase method. The MBIDAN content was 2.9%, the acid value was 5.8 mg KOH / g, the moisture content was 2.5%, the sulfate content was 0.5%, the water-insoluble matter was 0.5%, and the yield of crude IDAN was 84.5% (based on hydroxyacetonitrile).

Claims

1. A method for preparing iminodiacetonitrile (IDAN) solid product, comprising the following steps: (1) adding a stabilizer and a catalyst to a hydroxyacetonitrile solution, and preheating the hydroxyacetonitrile solution and an ammonia solution separately; the stabilizer is one or a mixture of both of zinc oxide and silicon dioxide; the catalyst is one or a mixture of both of ammonium citrate, ammonium malate and ammonium tartrate; (2) mixing the preheated hydroxyacetonitrile solution and the ammonia solution according to a ratio to make an IDAN reaction solution; (3) adjusting the pH of the IDAN solution obtained from the outlet of the reactor in step (2) to 2-4, stirring and cooling to crystallize, and separating to obtain a crude IDAN solid (a); (4) adding the crude IDAN solid (a) obtained in step (3) to an organic solvent, dissolving at a high temperature to obtain a mixed solution containing part of insoluble substances, and separating to obtain an organic IDAN solution and solid residues after adsorption and decolorization; (5) cooling the organic IDAN solution obtained in step (4) to crystallize to obtain a solid IDAN primary crystallization product (b), and separating the solid primary crystallization IDAN (b) to enter a subsequent recrystallization purification step (6); (6) adding the solid primary crystallization IDAN (b) obtained in step (5) to pure water to dissolve at a high temperature, and then recrystallizing to obtain a recrystallization product, and separating the solid IDAN to obtain a qualified IDAN product (c) after drying at a low temperature and under reduced pressure.

2. The production method according to claim 1, wherein The amount of the stabilizer added in step (1) is 0.5-2.0 wt% of the weight of the raw material hydroxyacetonitrile; and / or, the amount of the catalyst added in step (1) is 0.2-1.0 wt% of the weight of the raw material hydroxyacetonitrile.

3. The production method according to claim 1, wherein The concentration of the hydroxyacetonitrile solution in step (1) is 40.0-50.0 wt%, the pH of the hydroxyacetonitrile solution is adjusted to 2.0-3.0 by acid, and / or the preheating temperature of the hydroxyacetonitrile solution is 50-100℃; and / or, the mass concentration of the ammonia solution in step (1) is 20.0-30.0 wt%, and the preheating temperature is 80-120℃.

4. The production method according to any one of claims 1 to 3, wherein In step (2), the molar ratio of the hydroxyacetonitrile solution to the ammonia solution is 1.9-2.1:1; and / or, the reaction temperature in the reactor is 120-160℃, the reaction pressure is 0.5-1.0 MPa, and the reaction time is 1-4 minutes.

5. The production method according to any one of claims 1 to 3, wherein In step (3), the temperature of the reaction solution is reduced to 40-60℃ by a heat exchanger after the material at the outlet of the reactor is directly depressurized, the pH of the reaction solution is adjusted to 2-4 by adding acid, and the temperature for cooling and crystallization is 15-25℃.

6. The production method according to any one of claims 1 to 3, wherein In step (4), the organic solvent for dissolving the IDAN crude solid (a) is selected from one or more of the following solvents: (1) alcohols; (2) aromatic hydrocarbons; (3) esters; (4) tetrahydrofuran (THF), dimethylformamide (DMF), dimethylacetamide (DMAC), dimethyl carbonate (DMC), 1,4-dioxane; and / or, the temperature for heating the IDAN crude solid (a) is 40-60℃; and / or, the mass ratio of the organic solvent to the mass of the crude solid (a) is 1.2-2.3:1, and the mass concentration of IDAN in the organic solution is 30.0-45.0 wt%.

7. The production method according to claim 6, wherein In step (4), the alcohols in the organic solvent for dissolving the IDAN crude solid (a) are selected from methanol, ethanol, isopropyl alcohol; the aromatic hydrocarbons are selected from benzene, toluene, xylene; and the esters are selected from methyl formate, ethyl acetate, ethyl benzoate.

8. The production method according to any one of claims 1 to 3, wherein In step (4), the adsorbent is selected from one or more of powdered activated carbon, granular activated carbon, diatomite, zeolite containing acidic alumina, silicon dioxide, and silicates, the adsorption temperature is 40-60℃, and the adsorption time is 0.5-1h.

9. The production method according to any one of claims 1 to 3, wherein In step (5), the temperature for cooling and crystallization is 10-20℃, and the crystallization time is 2-4h; and the IDAN crystalline solid and the organic solution are separated by centrifugation or vacuum filtration.

10. The production method according to any one of claims 1 to 3, wherein In step (6), the temperature for dissolving the white solid in water is 50-60℃, and the mass ratio of the water to the first crystallized IDAN (b) is 1-1.8:

1.

11. The production method according to any one of claims 1 to 3, wherein In step (6), the temperature for cooling and crystallization is 10-20℃, and the crystallization time is 2-4h; and / or, the IDAN crystalline solid and the aqueous solution are separated by centrifugation or vacuum filtration, and the separated IDAN is vacuum dried at a temperature of 30-50℃, a vacuum degree of < -0.1 MPa, and for a time of 4-6h.

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