A process for the production of methioninimethylcyanide catalyzed by tbab

Abstract

This invention proposes a TBAB-catalyzed process for the production of methyleneaminoacetonitrile, comprising the following steps: S1. Preparation of an aqueous buffer system: Ammonium chloride, acetic acid, and deionized water are added to a glass-lined reactor and stirred until completely dissolved. The pH of the system is adjusted to 4.5–6.0 with 10% dilute ammonia or glacial acetic acid to obtain a weakly acidic acetic acid-ammonium acetate buffer system; S2. Generation of methyleneamine intermediate: A 37% formaldehyde aqueous solution is added dropwise to the buffer system at a constant rate, controlling the dropping temperature at 20–30°C and the dropping time at 1–2 h. After the dropping is completed, the reaction is maintained at this temperature for 0.5–1 h to generate the methyleneamine intermediate. This invention solves the two-phase mass transfer bottleneck, increasing the main reaction selectivity from 75% to over 95%, and the reaction yield from 62%–70% to a stable increase of 82%–88%, with a maximum of 89%.

Description

Technical Field

[0001] This invention relates to the field of chemical intermediate synthesis technology, and in particular to a TBAB-catalyzed process for the production of methyleneaminoacetonitrile. Background Technology

[0002] The industrial synthesis route of methyleneaminoacetonitrile is mainly based on Mannich-type addition reactions: formaldehyde reacts with ammonium chloride under weakly acidic conditions to generate a methyleneamine intermediate, which then undergoes nucleophilic addition with a cyanide ion to close the ring and yield the target product. Existing processes generally suffer from the following technical defects: 1. Low yield due to two-phase mass transfer barrier: The reaction system is a heterogeneous system consisting of an aqueous phase (ammonium chloride, acetic acid, inorganic salts) and an organic product suspension microphase. The cyanide ion (CN) concentration is high. - Its strong hydrophilicity causes more than 95% of it to be trapped in the aqueous phase, making it unable to fully contact the methylene amine intermediate in the organic phase. The main reaction rate constant is only 1 / 50 to 1 / 100 of that of the homogeneous reaction, and the yield of conventional non-catalytic processes is low.

[0003] 2. Severe hydrolysis of cyanide ions leads to significant raw material loss: In a weakly acidic environment with an aqueous phase pH of 4.5–6.0, free CN... - It readily undergoes hydrolysis, further generating byproducts such as formic acid, formamide, and polymeric tar. Traditional processes require an excess of 15%–20% sodium cyanide to compensate for hydrolysis losses, resulting in high raw material consumption and high costs for treating cyanide-containing waste.

[0004] 3. Poor crystallization performance and complex post-processing: The product precipitates in the form of fine microcrystals with a particle size of 5-10μm, resulting in high filtration resistance, a large amount of mother liquor impurities, low purity of crude product, and the need for several water washing and refining processes to meet downstream requirements, and high product water solubility loss rate.

[0005] 4. Stringent process conditions and limited production capacity: In order to suppress cyanide hydrolysis and methyleneamine decomposition, the reaction temperature must be strictly controlled between 0 and 5°C (requiring -10°C frozen brine for cooling), and the sodium cyanide addition time must be as long as 6 hours or more. The single-reactor production cycle exceeds 12 hours, resulting in low equipment capacity.

[0006] 5. Poor system stability and large batch fluctuations: Fluctuations in the acidity of acetic acid or uneven addition can easily lead to local pH < 4.0, triggering the protonation decomposition of methylene amine and the polymerization of formaldehyde to generate paraformaldehyde impurities. The yield of different batches fluctuates greatly, and the product quality is unstable. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the defects of the existing technology. The present invention proposes a TBAB-catalyzed process for the production of methylene aminoacetonitrile.

[0008] To solve the aforementioned technical problems, the technical solution adopted by the present invention is as follows: A TBAB-catalyzed process for producing methyleneaminoacetonitrile includes the following steps: S1. Preparation of aqueous buffer system: Ammonium chloride, acetic acid and deionized water are added to a glass-lined reactor and stirred until completely dissolved. The pH of the system is adjusted to 4.5-6.0 with glacial acetic acid to obtain an acetic acid-ammonium acetate weakly acidic buffer system. S2. Formation of methyleneamine intermediate: 37% formaldehyde aqueous solution is added dropwise to the buffer system at a constant rate, the dropping temperature is controlled at 20-30℃, the dropping time is 1-2h, and after the dropping is completed, the reaction is kept at the temperature for 0.5-1h to generate methyleneamine intermediate; S3. Phase transfer catalytic addition reaction: Add the phase transfer catalyst tetrabutylammonium bromide (TBAB) pre-dissolved in deionized water to the reaction system and stir for 10 min to make it uniformly dispersed; then add 30% sodium cyanide aqueous solution dropwise at a constant rate, control the reaction temperature at 5-15℃, and the temperature fluctuation during the dropwise addition is less than or equal to ±1℃. After the dropwise addition is completed, continue to keep the reaction at the temperature for 1-2 h. The molar ratio of raw materials is formaldehyde:ammonium chloride:sodium cyanide = 1:(1.05~1.1):(1.0~1.05); S4. Crystallization separation and post-processing: After the reaction is completed, the temperature is lowered to 0-5℃ at a rate of 1-2℃ / min, and crystallization is maintained at this temperature for 1.5-2h. After vacuum filtration, the filter cake is washed with deionized water at 0-5℃ and then dried under vacuum to obtain the finished product, methylene aminoacetonitrile.

[0009] Preferably, the amount of TBAB added is 0.5% to 2 mol of formaldehyde or sodium cyanide.

[0010] Preferably, in step S1, the pH of the system is adjusted to 4.8-5.5, and the stirring speed is controlled at 60-80 rpm.

[0011] Preferably, in step S2, the formaldehyde aqueous solution is added at a rate of 40-60 kg / h (500L reactor size), and the stirring speed for the heat preservation reaction is 60-80 rpm.

[0012] Preferably, in step S3, the dropping rate of the sodium cyanide aqueous solution is 10-20 kg / h (500L reactor size), the total dropping and heat preservation time is 4-6.5 h, and the stirring speed during the reaction stage is 80-100 rpm.

[0013] Preferably, the stirring speed during the crystallization process in step S4 is 30-40 rpm; the vacuum filtration uses a polypropylene filter cloth with a pore size of 5-10 μm and a vacuum degree of -0.085 to -0.095 MPa.

[0014] Preferably, in step S4, the filter cake is washed twice with deionized water at 0-5°C, with the amount of water used each time being 0.3-0.5 times the theoretical mass of the product, until the pH of the filtrate is 6-7.

[0015] Preferably, the vacuum drying temperature in step S4 is 40-45°C, the vacuum degree is -0.08 to -0.095 MPa, and the drying time is 4-6 hours, until the moisture content of the finished product is less than or equal to 0.5%.

[0016] The core innovation of this invention lies in the phase transfer catalysis of TBAB, and its catalytic cycle mechanism is as follows: 1. Ion exchange stage: TBAB in the aqueous phase dissociates into... , and free Ion exchange occurs to produce lipophilic substances. Ion pairs; 2. Phase transition stage: It crosses the water-oil interface and enters the organic microphase, releasing highly active substances. ; 3. Addition reaction stage: It undergoes a rapid nucleophilic addition reaction with a methyleneamine intermediate to generate methyleneaminoacetonitrile; 4. Catalyst regeneration stage: The catalyst generated after the reaction It returns to the aqueous phase to participate in the next round of ion exchange, thus completing the catalytic cycle.

[0017] Through the above cycle, TBAB will be able to exist in the aqueous phase, which was originally the only possible form of TBAB. The continuous supply to the organic reaction sites increased the main reaction rate by 10 to 20 times, while significantly reducing the aqueous phase. Concentration fundamentally inhibits hydrolysis side reactions.

[0018] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention solves the bottleneck of two-phase mass transfer, increases the selectivity of the main reaction from 75% to over 95%, and steadily increases the reaction yield from 62% to 70% to 82% to 88%, with a maximum of 89%.

[0019] 2. In this invention, the cyanide hydrolysis rate is reduced from 25% to 30% to 5% to 8%, the sodium cyanide excess coefficient is reduced from 1.15 to 1.2 to 1.0 to 1.05, the total amount of raw material cyanide is reduced by 8% to 12%, the formaldehyde conversion rate is increased from 88% to over 94%, and the residual formaldehyde in the mother liquor is reduced by 40% to 50%.

[0020] 3. In this invention, TBAB is used as a crystal growth regulator to increase the average particle size of the product from 5-10 μm to 20-50 μm, forming well-formed rod-shaped crystals. The filtration speed is increased by 60%-75%, the purity of the crude product is increased from 92% to over 96%, and only one water wash is needed to meet downstream requirements. The product water loss rate is reduced to below 2%.

[0021] 4. The reaction temperature of this invention is widened from 0-5℃ to 5-15℃, and 7-10℃ circulating cooling water can be used to replace -10℃ frozen brine, reducing refrigeration energy consumption by 30%-40%; the total reaction time is shortened by 25%-35%, the single-reactor production cycle is shortened from 12h to 7-8h, and the equipment capacity is increased by more than 50%.

[0022] 5. The weak cationic buffering effect of TBAB in this invention, combined with the acetate-ammonium acetate system, effectively suppresses local pH fluctuations. The yield fluctuation range of different batches is ≤±1.5%, and the product quality is stable and controllable. At the same time, by-products are reduced by more than 30%, and the cost of waste treatment is reduced. Attached Figure Description

[0023] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts. Wherein: Figure 1 This is a flowchart of the production process steps for methyleneaminoacetonitrile of the present invention. Detailed Implementation

[0024] It is readily understood that, based on the technical solution of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of the invention. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solution of this invention.

[0025] The present invention will be further described in detail below with reference to comparative examples, embodiments, and industrial scale-up experiments.

[0026] General experimental conditions: Reaction equipment: 500L glass-lined reactor (equipped with anchor-type stirrer, online pH monitoring, and low-temperature cooling circulation system) Raw material specifications: Ammonium chloride (industrial grade, ≥99.5%), glacial acetic acid (industrial grade, ≥99%), 37% formaldehyde aqueous solution (industrial grade, methanol content ≤1%), 30% sodium cyanide aqueous solution (industrial grade, free alkali ≤0.5%), TBAB (industrial grade, ≥99%) Analytical methods: Product purity was determined by gas chromatography (GC-2014, FID detector), moisture content was determined by Karl Fischer method, formaldehyde residue in mother liquor was determined by acetylacetone spectrophotometry, and cyanide residue was determined by silver nitrate titration.

[0027] Safety Precautions: All operations involving sodium cyanide must be carried out in a fume hood, and operators must wear gas masks and acid and alkali resistant protective equipment; cyanide-containing wastewater must be treated with sodium hypochlorite oxidation (pH 10-11, reaction time 30 min) to meet the standards before being discharged.

[0028] Comparative Example 1 (Traditional non-catalytic process) Feeding quantities: 150 kg deionized water, 61.5 kg ammonium chloride (1.15 kmol), 12 kg glacial acetic acid, 81.1 kg 37% formaldehyde aqueous solution (1.0 kmol), 187.8 kg 30% sodium cyanide aqueous solution (1.15 kmol, 15% excess). Process conditions: No TBAB is added, the reaction temperature is strictly controlled between 0 and 5℃, the formaldehyde dropping time is 1.5h, the sodium cyanide dropping time is 6h, the reaction is kept at the temperature for 2h; the temperature is lowered to 0℃ for crystallization for 2h, after filtration, it is washed 3 times with 100kg of deionized water, and then vacuum dried at 45℃ for 6h.

[0029] Experimental results: 46.4 kg of methylene aminoacetonitrile was obtained, with a yield of 68.2% (based on formaldehyde), a crude product purity of 91.8%, a product moisture content of 0.62%, sodium cyanide consumption of 1.214 kg / kg, a filtration time of 32 min, a mother liquor formaldehyde residue of 0.82%, and a mother liquor cyanide residue of 0.35%.

[0030] Comparative Example 2 (TBAB overdose) Feeding amount: Same as in Example 2, the amount of TBAB added is 3 mol% (9.67 kg) of the formaldehyde molar amount. Process conditions: reaction temperature 10℃, sodium cyanide addition time 4h, and reaction temperature holding time 1.5h; the rest are the same as the general method.

[0031] Experimental results: 57.0 kg of finished product was obtained, with a yield of 83.7%, a crude product purity of 94.2%, a product moisture content of 0.48%, a sodium cyanide consumption of 0.894 kg / kg, and a filtration time of 15 min. TBAB residue was detected in the mother liquor (HPLC method, content 0.21%). The product purity after water washing was only 95.1%, requiring secondary purification to meet the standard, which increased the post-processing cost.

[0032] Please see Figure 1 Example 1 (TBAB addition amount 0.5 mol%) Feed quantities: 150 kg deionized water, 58.8 kg ammonium chloride (1.1 kmol), 12 kg glacial acetic acid, 81.1 kg 37% formaldehyde aqueous solution (1.0 kmol), 170.0 kg 30% sodium cyanide aqueous solution (1.04 kmol, 4% excess), 1.61 kg TBAB (0.5 mol%, calculated as formaldehyde). Process conditions: Adjust pH to 5.0, methyleneamine formation temperature 25℃, keep warm for 0.5h; addition reaction temperature 5~10℃, sodium cyanide dropwise time 4.5h, keep warm for 2h; cool to 2℃ for crystallization for 1.5h, wash twice with 40kg of 0℃ deionized water, and vacuum dry at 40℃ for 5h.

[0033] Experimental results: 56.0 kg of finished product was obtained, with a yield of 82.2%, a crude product purity of 96.1%, a finished product moisture content of 0.35%, a sodium cyanide consumption of 0.910 kg / kg, a filtration time of 12 min, a mother liquor formaldehyde residue of 0.47%, and a mother liquor cyanide residue of 0.13%.

[0034] Example 2 (TBAB addition amount 1.0 mol%) Feeding amount: TBAB addition amount is 3.22 kg (1.0 mol%), the rest is the same as in Example 1. Process conditions: addition reaction temperature 10℃, sodium cyanide addition time 4h, and heat preservation reaction for 1.5h; the rest are the same as in Example 1.

[0035] Experimental results: 58.3 kg of finished product was obtained, with a yield of 85.6%, a crude product purity of 96.8%, a finished product moisture content of 0.32%, sodium cyanide consumption of 0.874 kg / kg, a filtration time of 9 min, a mother liquor formaldehyde residue of 0.41%, and a mother liquor cyanide residue of 0.10%.

[0036] Example 3 (TBAB addition amount 1.5 mol%) Feeding amount: 4.84 kg (1.5 mol%) of TBAB was added, and the rest was the same as in Example 1. Process conditions: addition reaction temperature 10-15℃, sodium cyanide addition time 3.5h, and heat preservation reaction for 1.2h; the rest is the same as in Example 1.

[0037] Experimental results: 59.4 kg of finished product was obtained, with a yield of 87.2%, a crude product purity of 96.5%, a finished product moisture content of 0.30%, a sodium cyanide consumption of 0.858 kg / kg, a filtration time of 8 min, a mother liquor formaldehyde residue of 0.39%, and a mother liquor cyanide residue of 0.09%.

[0038] Example 4 (TBAB addition amount 2.0 mol%) Feeding amount: 6.45 kg (2.0 mol%) of TBAB was added, and the rest was the same as in Example 1. Process conditions: addition reaction temperature 15℃, sodium cyanide addition time 3h, and holding reaction for 1h; the rest are the same as in Example 1.

[0039] Experimental results: 58.8 kg of finished product was obtained, with a yield of 86.3%, a crude product purity of 96.3%, a finished product moisture content of 0.33%, a sodium cyanide consumption of 0.867 kg / kg, a filtration time of 10 min, a mother liquor formaldehyde residue of 0.43%, and a mother liquor cyanide residue of 0.11%.

[0040] Example 5 (10x Industrial Scale-up Verification) Feed quantities: 1500 kg deionized water, 588 kg ammonium chloride (11 kmol), 120 kg glacial acetic acid, 811 kg 37% formaldehyde aqueous solution (10 kmol), 1700 kg 30% sodium cyanide aqueous solution (10.4 kmol), 32.2 kg TBAB (1.0 mol%) Process conditions: A 5000L glass-lined reactor was used, with a stirring speed of 70-90 rpm, an addition reaction temperature of 10±1℃, a sodium cyanide dropping time of 4h, and a holding reaction time of 1.5h; the crystallization cooling rate was 1.5℃ / min, and the rest were the same as in Example 2.

[0041] Experimental results: After 10 consecutive batches, the average yield of the finished product was 579.0 kg, with an average yield of 85.0%, a crude product purity of 96.6%, a finished product moisture content of 0.31%, a sodium cyanide consumption of 0.879 kg / kg, a filtration time of 11 min, a mother liquor formaldehyde residue of 0.42%, and a mother liquor cyanide residue of 0.10%. The yield of all batches fluctuated between 84.2% and 85.7%, and the purity fluctuated between 96.3% and 96.9%, showing good stability.

[0042] Comprehensive comparative analysis of examples and comparative cases The key technical indicators of each experimental group were compared, and the results are shown in the table below: Comparison conclusion: 1. Compared with traditional processes, the yield of the present invention is increased by 14 to 19 percentage points, the purity of crude product is increased by 4.3 to 5 percentage points, the sodium cyanide consumption is reduced by 25% to 29% (total feed amount is reduced by 9.6%), the filtration time is shortened by 62.5% to 75%, and the refrigeration energy consumption is reduced by 35% to 45%, demonstrating significant comprehensive advantages.

[0043] 2. When the amount of TBAB added is in the range of 0.5% to 2 mol%, the yield first increases and then decreases with the increase of the amount added, reaching a peak of 87.2% at 1.5 mol%. When the amount added exceeds 2 mol%, the yield decreases slightly and the purity of the crude product decreases, and TBAB residue appears in the mother liquor, which verifies the scientific nature of the dosage range of the present invention.

[0044] 3. The results of the industrial scale-up experiment are highly consistent with the laboratory pilot test data, and the batch stability is good, proving that this process is easy to promote industrially and can be applied to the technical transformation of existing production lines.

[0045] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. A TBAB-catalyzed process for producing methyleneaminoacetonitrile, characterized in that, Includes the following steps: S1. Preparation of aqueous buffer system: Ammonium chloride, acetic acid and deionized water are added to a glass-lined reactor and stirred until completely dissolved. The pH of the system is adjusted to 4.5-6.0 with glacial acetic acid to obtain an acetic acid-ammonium acetate weakly acidic buffer system. S2. Formation of methyleneamine intermediate: 37% formaldehyde aqueous solution is added dropwise to the buffer system at a constant rate, the dropping temperature is controlled at 20-30℃, the dropping time is 1-2h, and after the dropping is completed, the reaction is kept at the temperature for 0.5-1h to generate methyleneamine intermediate; S3. Phase transfer catalytic addition reaction: Add the phase transfer catalyst tetrabutylammonium bromide (TBAB) pre-dissolved in deionized water to the reaction system and stir for 10 min to make it uniformly dispersed; then add 30% sodium cyanide aqueous solution dropwise at a constant rate, control the reaction temperature at 5-15℃, and the temperature fluctuation during the dropwise addition is less than or equal to ±1℃. After the dropwise addition is completed, continue to keep the reaction at the temperature for 1-2 h. The molar ratio of raw materials is formaldehyde:ammonium chloride:sodium cyanide = 1:(1.05~1.1):(1.0~1.05); S4. Crystallization separation and post-processing: After the reaction is completed, the temperature is lowered to 0-5℃ at a rate of 1-2℃ / min, and crystallization is maintained at this temperature for 1.5-2h. After vacuum filtration, the filter cake is washed with deionized water at 0-5℃ and then dried under vacuum to obtain the finished product, methylene aminoacetonitrile.

2. The TBAB-catalyzed process for producing methyleneaminoacetonitrile according to claim 1, characterized in that, The amount of TBAB added is 0.5% to 2 mol of the molar amount of formaldehyde or sodium cyanide.

3. The TBAB-catalyzed process for producing methyleneaminoacetonitrile according to claim 1, characterized in that, In step S1, adjust the pH of the system to 4.8-5.5 and control the stirring speed at 60-80 rpm.

4. The TBAB-catalyzed process for producing methyleneaminoacetonitrile according to claim 1, characterized in that, In step S2, the formaldehyde aqueous solution is added at a rate of 40–60 kg / h (500 L reactor size), and the stirring speed for the heat preservation reaction is 60–80 rpm.

5. The TBAB-catalyzed process for producing methyleneaminoacetonitrile according to claim 1, characterized in that, In step S3, the sodium cyanide aqueous solution is added at a rate of 10–20 kg / h (for a 500 L reactor), and the total time for adding and maintaining the temperature is 4–6.5 h. The stirring speed during the reaction stage is 80–100 rpm.

6. The TBAB-catalyzed process for producing methyleneaminoacetonitrile according to claim 1, characterized in that, In step S4, the stirring speed during the crystallization process is 30-40 rpm; the vacuum filtration uses a polypropylene filter cloth with a pore size of 5-10 μm and a vacuum degree of -0.085 to -0.095 MPa.

7. The TBAB-catalyzed process for producing methyleneaminoacetonitrile according to claim 1, characterized in that, The washing process in step S4 involves washing the filter cake twice with deionized water at 0–5°C, using 0.3–0.5 times the theoretical mass of the product each time, until the pH of the filtrate reaches 6–7.

8. The TBAB-catalyzed process for producing methyleneaminoacetonitrile according to claim 1, characterized in that, The vacuum drying temperature in step S4 is 40-45℃, the vacuum degree is -0.08 to -0.095MPa, and the drying time is 4-6h, until the moisture content of the finished product is less than or equal to 0.5%.

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