A method for preparing methacrolein by Mannich reaction

Abstract

The invention discloses a method for preparing methacrolein by using Mannich reaction, wherein dibutylamine acetate catalyst is used to catalyze formaldehyde and propionaldehyde to synthesize methacrolein under mild reaction conditions. By controlling the ratio of each reactant, reaction time and reaction temperature, the process method is used, and the conversion rate of propionaldehyde is higher than 99%, and the selectivity of methacrolein is higher than 98%.

Description

Technical Field

[0001] The invention relates to a catalyst used for preparing methacrolein through Mannich reaction of formaldehyde and propionaldehyde, and relates to the field of organic synthesis. Background Art

[0002] Methacrolein (MAL) is also called isobutylene aldehyde. The molecular formula is C4H6O. Methacrolein is an important organic compound and an important intermediate product in the production of methyl methacrylate by the ethylene carbonylation process. Methyl methacrylate is mainly used to produce an important thermoplastic polymethyl methacrylate (PMMA), which has good chemical stability and wear resistance and is widely used in automotive glass, building consumables and other industries. In addition, methacrolein is also used in the production of fine chemicals such as coatings, adhesives, PVC modifiers, paints, textile slurries, and advanced ester oil additives.

[0003] Formaldehyde and propionaldehyde can synthesize methacrolein through the following two pathways, one is direct aldol condensation reaction, and the other is Mannich reaction. The preparation of methacrolein by direct aldol condensation in liquid phase has limitations. Inorganic bases such as NaOH are efficient aldehyde condensation catalysts, but mainly produce 2-methyl-2-pentenal. NaOH as a strong base is conducive to the homopolymerization of propionaldehyde, but not inclined to the cross-condensation reaction of propionaldehyde and formaldehyde. Therefore, the direct aldol condensation of formaldehyde and propionaldehyde is not conducive to the synthesis of methacrolein. Patent US4408079 uses molten methylamine hydrochloride as a catalyst, formaldehyde and propionaldehyde as reaction raw materials, and prepares methacrolein at a temperature of 140-160°C, proposing a new reaction path for the generation of methacrolein. This reaction path uses secondary amine salts as catalysts, and can effectively synthesize methacrolein through the Mannich reaction. The conversion rate of raw materials and the yield of formaldehyde acrolein are further improved. Patents US2639295, US2848499, JP4173762, JP3069420, JP4173757, US4496770, JP4173757 etc. utilize formaldehyde and propionaldehyde to prepare methacrolein. However, the reaction temperature is high, and aldehydes are easily polymerized at high temperature, resulting in a polymerization reaction of a part of propionaldehyde, and the generated methacrolein is also easily polymerized. Meanwhile, impurities and organic bases can enter the product, which is unfavorable for subsequent separation. Therefore, the process of synthesizing methacrolein using formaldehyde and propionaldehyde needs to be further improved, and secondary amine catalyst plays an important role in the process of synthesizing methacrolein from formaldehyde and propionaldehyde. CN110882722, CN104557490 etc. utilize different secondary amine catalysts to prepare methacrolein, but the conversion rate of propionaldehyde and the selectivity of methacrolein cannot reach a good level, and the catalyst cycle number is not good, and the production efficiency is not high.

[0004] Therefore, there is still a need to develop a secondary amine salt catalyst that can efficiently prepare methacrolein. Summary of the invention

[0005] The object of the present invention is to provide a catalyst for preparing methacrolein from formaldehyde and propionaldehyde through Mannich reaction. The catalyst used is a dibutylamine acetate catalyst. The catalyst can realize the preparation of methacrolein from formaldehyde and propionaldehyde under mild reaction conditions, and the conversion rate of propionaldehyde can reach more than 99%, the selectivity of methacrolein can reach up to more than 98%, and the number of cycles can reach more than 50 times.

[0006] The dibutylamine acetate catalyst can be prepared by the following steps: first, the circulating water of the jacketed reactor is opened, and the dibutylamine and deionized water required for the reaction are added into the reactor, and the measured acetic acid is added dropwise thereto under stirring, and the reaction temperature is maintained at 0 to 40° C. After the addition is completed, the reaction is carried out for 30 to 120 minutes, thereby obtaining the dibutylamine acetate catalyst.

[0007] In a specific embodiment, in the above method, based on the molar amount of the reactant formaldehyde, the amount of dibutylamine used can be 0.01 to 2 times the molar amount of formaldehyde, preferably 0.1 to 1.6 times, and optimally 0.5 to 1.2 times.

[0008] In a specific embodiment, in the above method, the molar ratio of dibutylamine to acetic acid can be 1:0.5-3.5, preferably 1:0.9-2, and optimally 1:1.1-1.5.

[0009] In a specific embodiment, in the above method, the reaction temperature during the dropwise addition of acetic acid can be 0-40°C, preferably 10-30°C, and optimally 15-20°C.

[0010] In a specific embodiment, in the above method, the reaction time after the dropwise addition of acetic acid is completed is 30 to 120 min, preferably 45 to 105 min, and optimally 60 to 90 min.

[0011] In a specific embodiment, in the above method, a certain amount of deionized water can be added during the reaction, and the content of water in the system is 0 to 80%, preferably 0 to 60%, and most preferably 0 to 30%.

[0012] The synthesis method of methacrolein is as follows: take an appropriate amount of the above-prepared dibutylamine acetate catalyst and add it to the reactor, turn on the circulating water to raise the temperature of the catalyst solution to 20-70°C. Then, the formaldehyde solution and propionaldehyde required for the experiment are mixed evenly and added to the constant pressure dropping funnel, the constant pressure dropping funnel is opened, and the mixed solution of formaldehyde and propionaldehyde is slowly added to the reactor, and the dropping speed is controlled so that the temperature in the entire reaction system does not exceed 20-70°C, and the formaldehyde and propionaldehyde mixed solution is added dropwise within 20 minutes. Then, the temperature is kept constant and the system is reacted for 5-60 minutes. After the reaction is completed, the condensation circulating water is turned on to allow the reaction system to cool down rapidly. After the temperature drops to 15°C, the liquid after the reaction is completed is distilled, and the separated oil phase is methacrolein, and the remaining part can be used as a catalyst for recycling.

[0013] In a specific embodiment, the formaldehyde can be provided in the form of formalin or paraformaldehyde.

[0014] In a specific embodiment, in the above method, based on the molar amount of the reactants, the ratio of the amount of formaldehyde to propionaldehyde used is 0.5 to 1.5:1, preferably 0.8 to 1.2:1, and optimally 1 to 1.1:1.

[0015] In a specific embodiment, in the above method, the temperature in the entire reaction system is between 20 and 70°C, preferably between 35 and 55°C, and most preferably between 40 and 50°C.

[0016] In a specific embodiment, in the above method, the reaction time can be 5 to 60 min, preferably 15 to 50 min, and optimally 20 to 45 min.

[0017] In a specific embodiment, in the above method, the reaction pressure may be normal pressure.

[0018] In a specific embodiment, in the above method, a tank reactor may be used.

[0019] Compared with the prior art, the present application is described in detail as follows: the technical scheme of the application adopts the condensation reaction of formaldehyde and propionaldehyde under the catalysis of dibutylamine acetate catalyst, using the Mannich reaction as the pathway. The catalyst dibutylamine acetate used has good catalytic activity, and can further improve the reaction performance of formaldehyde and propionaldehyde in synthesizing methacrolein. When the dibutylamine acetate catalyst of the present invention is used to prepare methacrolein, the conversion rate of the raw material propionaldehyde can reach more than 99%, the raw material reacts completely, and the subsequent separation process is simplified; the selectivity of methacrolein can reach more than 98%, and the raw material is almost converted into a product with high economic value. Moreover, the catalyst also shows high stability, and the catalytic effect remains stable after more than 50 cycles. At the same time, the synthesis of methacrolein from formaldehyde and propionaldehyde using the dibutylamine acetate catalyst is carried out at near normal temperature and pressure, and the reaction conditions are mild, which is conducive to continuous production. DETAILED DESCRIPTION

[0020] the term

[0021] In the following examples, the reaction effect analysis method is as follows: after the reaction, the system is sampled and analyzed by GC

[0022]

[0023]

[0024] Example 1

[0025] 39.16 g of dibutylamine and 34.02 g of deionized water were added to a 250 mL three-necked flask equipped with a thermometer, a condenser, a stirrer and a constant pressure dropping funnel, and stirring was started. After the temperature of the mixed solution of dibutylamine and water reached 20°C, 19.83 g of glacial acetic acid was added dropwise thereto. After the addition was completed, the mixture was reacted for 30 minutes to obtain a dibutylamine acetate catalyst.

[0026] Take the above-prepared dibutylamine acetate catalyst and add it to the reactor, open the circulating water to raise the catalyst solution temperature to 40 ° C. Afterwards, 25.03g of 37% formaldehyde aqueous solution and 17.96g propionaldehyde are mixed evenly and added to the constant pressure dropping funnel, the constant pressure dropping funnel is opened, the mixed solution of formaldehyde and propionaldehyde is slowly added to the reactor, the dropping speed is controlled so that the temperature in the whole reaction system does not exceed 40 ° C, and the formaldehyde and propionaldehyde mixed solution are added dropwise within 20min. Afterwards, keep the temperature unchanged and react the system for 20min. After the reaction is completed, open the condensation circulating water so that the reaction system is cooled rapidly. After the temperature is reduced to 15 ° C, the liquid at the end of the reaction is distilled, and the separated oil phase is methacrolein, and the remaining part can be used as the next catalyst for recycling. According to gas chromatographic analysis, the conversion rate of propionaldehyde is 99%, and the selectivity of methacrolein is 98%.

[0027] Example 2

[0028] 124.84 g of dibutylamine and 39.9 g of deionized water were added to a 500 mL three-necked flask equipped with a thermometer, a condenser, a stirrer and a constant pressure dropping funnel, and stirring was started. After the temperature of the mixed solution of dibutylamine and water reached 20° C., 63.5 g of glacial acetic acid was added dropwise thereto. After the addition was completed, the mixture was reacted for 30 minutes to obtain a dibutylamine / acetic acid catalyst.

[0029] Take the above-prepared dibutylamine acetate catalyst and add it to the reactor, turn on the circulating water to raise the catalyst solution temperature to 50°C. After that, 27.53g of 37% formaldehyde aqueous solution and 17.96g propionaldehyde are mixed evenly and added to the constant pressure constant liquid funnel, the constant pressure dropping funnel is opened, and the mixed solution of formaldehyde and propionaldehyde is slowly added to the reactor, and the dropping speed is controlled so that the temperature in the whole reaction system does not exceed 50°C, and the formaldehyde and propionaldehyde mixed solution are added dropwise within 20min. After that, keep the temperature unchanged and react the system for 30min. After the reaction is completed, turn on the condensation circulating water so that the reaction system is cooled rapidly. After the temperature drops to 15°C, the liquid at the end of the reaction is distilled, and the separated oil phase is methacrolein, and the remaining part can be used as the next catalyst for recycling. According to gas chromatography analysis, the conversion rate of propionaldehyde is 99%, and the selectivity of methacrolein is 99%.

[0030] Example 3

[0031] Methacrolein was synthesized by the synthesis process of Example 1. Five control examples were set, in which the temperature of the reaction system was 20-30°C, 30-40°C, 40-50°C, 50-60°C, and 60-70°C, respectively. The methacrolein synthesized at different reaction temperatures was numbered Ⅰ, Ⅱ, Ⅲ, Ⅳ, and Ⅴ, respectively. The products obtained after the reaction were sampled and detected by gas chromatography to obtain the conversion rate of propionaldehyde and the selectivity of methacrolein. The experimental data are shown in Table 1.

[0032] Table 1 Conversion rate of propionaldehyde and selectivity of methacrolein at different reaction temperatures in Example 3

[0033] Serial number Conversion rate of propionaldehyde / % Methacrolein selectivity / % Ⅰ 99 62 Ⅱ 99 94 Ⅲ 99 98 Ⅳ 99 96 Ⅴ 99 94

[0034] Example 4

[0035] Methacrolein was synthesized by the synthesis process of Example 1. Six control examples were set, and the reaction times were 0-10 min, 10-20 min, 20-30 min, 30-40 min, 40-50 min, and 50-60 min, respectively. The methacrolein synthesized at different reaction times was numbered as ①, ②, ③, ④, ⑤, and ⑥, respectively. The products obtained after the reaction were sampled and detected by gas chromatography to obtain the conversion rate of propionaldehyde and the selectivity of methacrolein. The experimental data are shown in Table 2.

[0036] Table 2 Conversion rate of propionaldehyde and selectivity of methacrolein at different reaction times in Example 4

[0037] Serial number Conversion rate of propionaldehyde / % Selectivity of methacrolein / % ① 99 87 ② 99 96 ③ 99 99 ④ 99 97 ⑤ 99 97 ⑥ 99 96

Claims

1. A method for preparing methacrolein by Mannich reaction, characterized in that: Dibutylamine acetate catalyst is used to catalyze formaldehyde and propionaldehyde to synthesize methacrolein through Mannich reaction. The preparation process of the dibutylamine acetate catalyst is as follows: a. Add a certain amount of dibutylamine and deionized water into the reactor, with the mass fraction of water being 0-80%; b. Slowly add acetic acid to the reactor, and keep the reaction temperature at 0~40℃ during the addition; c. After the addition is complete, react for 30 to 120 minutes to obtain the dibutylamine acetate catalyst; The dibutylamine acetate catalyst is used to catalyze formaldehyde and propionaldehyde to synthesize methacrolein through a Mannich reaction. The molar ratio of the reaction raw materials to the catalyst is: formaldehyde: propionaldehyde: catalyst is 0.5~1.5:1:0.01~2. The specific steps are: a. Add the aqueous solution of dibutylamine acetate catalyst into the reactor and keep the catalyst solution temperature at 40~60°C; b. Add the mixed raw materials of formaldehyde and propionaldehyde into the reactor, and control the temperature in the reaction system not to exceed 40~60℃; c. Under stirring conditions, maintain the reaction temperature at 40-60°C and react for 10-60 min; d. After the reaction is completed, the materials in the reactor are distilled to separate methacrolein and unreacted materials, and the separated catalyst is continuously recycled.

2. The method for synthesizing methacrolein according to claim 1, characterized in that: The temperature was maintained at 40~60°C during the reaction.

3. The method for synthesizing methacrolein according to claim 1, characterized in that: The reaction time can be 10~60min.

4. The method for synthesizing methacrolein according to claim 1, characterized in that: The formaldehyde may be provided by formalin or paraformaldehyde.

5. The method for synthesizing methacrolein according to claim 1, characterized in that: The composition of the dibutylamine acetate catalyst is that the molar ratio of dibutylamine to acetic acid is 1:0.5-3.

5.

6. The method for synthesizing methacrolein according to claim 1, characterized in that: The water content in the dibutylamine acetate catalyst is 0~80%.

7. The method for synthesizing methacrolein according to claim 1, characterized in that: The molar ratio of the reaction raw materials to the catalyst is: formaldehyde: propionaldehyde: catalyst is 0.5~1.5:1:0.01~2; the temperature is maintained at 40~50°C during the reaction process; the reaction time is 20~30min; the composition of the dibutylamine acetate catalyst is the molar ratio of dibutylamine to acetic acid is 1:1.1~1.5; the water content in the dibutylamine acetate catalyst is 30~40%.

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