CN114956980B - Method for synthesizing crotonic acid - Google Patents

Abstract

The invention discloses a method for synthesizing crotonic acid, which comprises the following steps: the crotonaldehyde and oxygen-containing gas are subjected to a first-stage high-temperature high-pressure reaction in a micro-reactor, and the obtained reaction liquid is subjected to gas-liquid separation and then enters a tubular reactor to realize the process of converting the peracid intermediate into crotonic acid at a lower temperature, namely a second-stage reaction. The synthesis and resolution of the crotonic acid are divided into two reaction stages, and the mixing and reaction of gas-liquid two phases in the gas oxidation process are enhanced through the characteristics of the microreactor, so that the reaction efficiency and the safety are improved; and secondly, through tubular reaction, the reaction temperature is reduced, the residence time is prolonged, and the conversion selectivity of the peracid serving as a reaction intermediate is improved, so that the generation of byproducts is obviously reduced. The continuous crotonic acid synthesis process effectively solves the problems of difficult control of reaction temperature, low production efficiency, unstable products and the like in the existing kettle type process, has the advantages of short production period, high selectivity and intrinsic safety, and is suitable for industrial production.

Description

A kind of method of synthetic crotonic acid

technical field

The invention belongs to the technical field of synthesis of fine chemical raw materials, and in particular relates to a method for synthesizing crotonic acid.

Background technique

Crotonic acid (CAS No.: 107-93-7) is an unsaturated fatty acid, which has a wide range of uses in industry, mainly used in the synthesis of various resins, surface coatings, etc., and is also an important pharmaceutical intermediate and pesticide intermediate .

The preparation methods of crotonic acid reported in the literature mainly include oxygen oxidation, metal oxide oxidation and peroxide oxidation. Oxygen, as a green and environmentally friendly oxidant, has the advantages of low cost, simple post-treatment, and easy separation. People such as Zhang Yong (progress in fine petrochemical industry, 2007, volume number: 22-24) are catalyzer with aluminum oxide, pass into oxygen and oxidize crotonaldehyde by electrochemical method, although this method reaches 80% productive rate, but The equipment is expensive and inefficient, making it difficult to industrialize. Cheng Shaoguo et al. (CN1415594A) selected precious metal silver as catalyst, oxidized crotonaldehyde with air in oxidation tower, and the yield was 75%, but the catalyst cost of this process was higher, the operation steps were more loaded down with trivial details, and the reaction cycle was longer. Lin Jing et al. (Journal of Xiamen University: Natural Science Edition; 1993, Volume No.: 745-748) tested respectively the Schiff base complexes of active manganese dioxide, copper acetate-cobalt acetate and cobalt as catalysts, and oxygen Or the effect of air oxidation of crotonaldehyde to prepare crotonic acid. The results show that active manganese dioxide and copper acetate-acetic acid will aggravate the polymerization side reaction of raw material crotonaldehyde and seriously reduce the reaction selectivity.

The mechanism of crotonaldehyde being oxidized to crotonic acid by oxygen is that crotonaldehyde first combines with one molecule of oxygen to form peroxycrotonic acid intermediate, and then the peroxycrotonic acid intermediate reacts with one molecule of crotonaldehyde to generate two molecules of crotonic acid.

The existing production process of crotonic acid by gas oxidation method is mainly kettle-type. When the kettle-type reaction equipment is used for the oxidation of crotonaldehyde, the actual operation is difficult, the safety factor is low, the process controllability is poor, and the reaction selectivity is low. Microreactor has outstanding advantages in gas-liquid reaction mass transfer and heat transfer. The development of crotonaldehyde oxidation micro-reaction process can well solve many problems existing in the kettle process, so as to realize process intensification. Based on the full understanding of the oxidation mechanism of crotonic acid, the present invention proposes a novel micro-chemical continuous oxidation process, which enhances the mixing of gas-liquid two-phase through the characteristics of micro-reaction equipment, and improves the reaction efficiency and safety; through two-stage reaction , improve the reaction selectivity; no catalyst is used in the reaction process, which is green and environmentally friendly.

Contents of the invention

The purpose of the present invention is to provide a method for continuously preparing crotonic acid, which can effectively improve production efficiency and reaction selectivity, reduce the pressure of waste treatment, ensure process controllability and safety, and realize process strengthening.

Technical scheme of the present invention is as follows:

A method for continuously preparing crotonic acid, comprising the following steps:

(1) The material A containing crotonaldehyde and the material B containing oxygen are continuously passed into the microreactor to carry out the first-stage reaction to obtain the reaction liquid C.

(2) The reaction liquid C coming out of the microreactor enters the gas-liquid separation unit after depressurization, and the residual oxygen in the liquid is removed by continuously blowing nitrogen into the unit, and the obtained liquid D is directly introduced into the tubular reactor for the second step. Two-stage reaction to obtain reaction solution E.

(3) The reaction liquid E flowing out of the tubular reactor enters the evaporator, and the unreacted raw materials and solvent are separated from the product through the evaporator, and then recycled after rectification, and the crude material liquid F is obtained at the bottom of the evaporator.

(4) The crude product feed liquid F obtained in step (3) is refined after post-treatment to obtain the product crotonic acid.

The material A in the step (1) is pure crotonaldehyde or an organic solution containing crotonaldehyde, and the organic solvent in the organic solution is a hydrocarbon solvent, preferably a C ₅ -C ₁₀ alkane solvent, a C ₅ -C ₁₀ cycloalkane Solvent, C ₆ -C ₁₀ aromatic hydrocarbon solvent; more preferably inert solvents such as toluene, cyclohexane, n-hexane, n-heptane, and most preferably toluene.

Preferably, the volume ratio of the crotonaldehyde to the organic solvent is 1:1-4.

The material B in the step (1) is pure oxygen or a mixed gas of nitrogen and oxygen.

In the step (1), the molar ratio of the crotonaldehyde contained in the material A and the oxygen contained in the material B passed into the microreactor is 1: (0.3-2.0).

The diameter of the microreactor channel in the step (1) is 0.5～4.0mm, preferably 0.5～2.0mm, more preferably 1.5～2.0mm; the reaction temperature is 50～100°C, further preferably 50～70°C; The time is 30-180s, and the reaction pressure is 1-3MPa.

The reaction temperature of the tubular reactor in the step (2) is 20-50° C., and the residence time of the reaction liquid D in the reactor is 10-60 min.

The evaporator in the step (3) is a thin film evaporator or a rectification tower.

The post-treatment process of step (4) includes activated carbon decolorization and recrystallization, and the post-treatment can be carried out according to the existing process.

Compared with the prior art, the present invention has the following advantages and outstanding technical effects:

In the present invention, by introducing a micro-reactor, the gas-liquid two-phase efficient mixing and reaction of crotonaldehyde and oxygen is realized, and the problem of low gas-liquid reaction efficiency in the traditional kettle reaction process is solved. The continuous process divides the reaction into two stages of high temperature and high pressure and low temperature and normal pressure, and basically separates the two reaction stages of the formation and conversion of peracid in the crotonaldehyde oxidation process, which not only ensures the efficiency of gas oxidation, but also improves the efficiency of peracid production. Transformation selectivity. In addition, a gas-liquid separation unit is added between the two reaction stages, which effectively relieves the pressure of the gas on the second-stage reactor volume, reduces equipment costs, and improves process safety. The whole process uses oxygen as the oxidant, which has a high atom utilization rate and is environmentally friendly, and the first-stage reaction in which oxygen participates is carried out in a microreactor, which is safe and controllable. Since the reaction selectivity will decrease with the increase of the conversion rate of crotonaldehyde, by accurately controlling the reaction time and reaction temperature of each stage, the appropriate conversion rate of crotonaldehyde can be effectively guaranteed and the stability of the process can be improved.

Description of drawings

Fig. 1 is the process flow sheet of the present invention's synthetic crotonic acid.

Detailed ways

The present invention provides a kind of method for continuously preparing crotonic acid, and Fig. 1 is a process flow diagram of the present invention, specifically comprises:

The material A containing crotonaldehyde and the material B containing oxygen are continuously fed into the microreactor for the first-stage reaction, and the obtained reaction liquid C enters the gas-liquid separation unit after pressure relief, and the liquid is removed by continuously blowing nitrogen into the unit Oxygen remaining in the liquid, the obtained liquid D is directly introduced into the tubular reactor for the second-stage reaction, and the obtained reaction liquid E enters the evaporator, and the unreacted raw materials and solvents are separated from the product through the evaporator, and are subsequently recycled by the rectification unit. The crude feed liquid F is obtained at the bottom of the evaporator, and the product crotonic acid is obtained through post-processing and refining.

The present invention will be further described below in conjunction with embodiment.

Example 1

Weigh 300g of crotonaldehyde, dissolve it in n-hexane and set the volume to 800mL as material A; the oxygen from the oxygen cylinder without any treatment is used as material B. Material A and material B were transported to a microchannel reactor (Shenshi, model TMC-01, internal size 1.6mm, material 316L, total channel volume 20mL) using a high-pressure advection pump and a gas mass flow controller, respectively. The temperature is 70°C, the pressure is 2MPa, the flow rate of material A is 5mL/min, and the flow rate of material B is 0.2-0.4SLM (standard liter per minute). The pressure is released through the pressure relief valve, and the liquid obtained after gas-liquid separation is passed into a 316L reaction coil (outer diameter 3mm inner diameter 2mm, total length 50m, normal pressure) at a flow rate of 5mL/min, and the temperature of the water bath outside the coil is 40°C. The reaction solution flowing out from the coil was distilled under reduced pressure to separate the reaction solution from the raw material and the solvent, and the external standard calculation by gas chromatography contained 140 g of crotonaldehyde in the separation solution, and the reaction conversion rate was 53%. The remaining crude product liquid was decolorized and recrystallized by activated carbon to obtain 160 g of pure crotonic acid with a GC purity of >99%. The yield was 81.4% based on the consumed crotonaldehyde.

Example 2

Weigh 300g of crotonaldehyde, dissolve it in n-hexane and set the volume to 800mL as material A; the air coming out of the air cylinder without any treatment is used as material B. Material A and material B are transported to a microchannel reactor (Shenshi, model TMC-02, internal size 2mm, material 316L, total channel volume is 90mL) using a high-pressure advection pump and a gas mass flow controller, respectively. The temperature is 70°C, the pressure is 2.5MPa, the flow rate of material A is 5mL/min, and the flow rate of material B is 1.3～1.5SLM. The pressure is released through the pressure relief valve, and the liquid obtained after gas-liquid separation is passed into a 316L reaction coil (outer diameter 3mm inner diameter 2mm, total length 50m, normal pressure) at a flow rate of 5mL/min, and the temperature of the water bath outside the coil is 40°C. The reaction liquid flowing out of the coil tube is separated from the raw material and the solvent by distillation under reduced pressure, and the external standard calculation by gas chromatography contains 150 g of crotonaldehyde in the separated liquid, and the reaction conversion rate is 50%. The remaining crude product liquid was decolorized by activated carbon and recrystallized to obtain 155 g of crotonic acid pure product with a GC purity of >99%. The yield was 84.1% based on the consumed crotonaldehyde.

Example 3

Take by weighing 300g crotonaldehyde, do not add any solvent as material A; The air that comes out in the air cylinder is not processed in any way, as material B. Material A and material B are transported to a microchannel reactor (Shenshi, model TMC-02, internal size 2mm, material 316L, total channel volume is 90mL) using a high-pressure advection pump and a gas mass flow controller, respectively. The temperature is 70°C, the pressure is 2MPa, the flow rate of material A is 5mL/min, and the flow rate of material B is 1.3～1.5SLM. The pressure is released through the pressure relief valve, and the liquid obtained after gas-liquid separation is passed into a 316L reaction coil (outer diameter 3mm inner diameter 2mm, total length 50m, normal pressure) at a flow rate of 5mL/min, and the temperature of the water bath outside the coil is 40°C. The reaction solution flowing out of the coil was distilled under reduced pressure to separate the reaction solution from the raw material and the solvent, and the external standard calculation by gas chromatography contained 130 g of crotonaldehyde in the separation solution, and the reaction conversion rate was 57%. The remaining crude product liquid was decolorized and recrystallized by activated carbon to obtain 158 g of pure crotonic acid with a GC purity of >99%. The yield was 75.7% based on the consumed crotonaldehyde.

Example 4

Weigh 300g of crotonaldehyde, dissolve it in toluene and set the volume to 800mL as material A; the air coming out of the air cylinder without any treatment is used as material B. Material A and material B were delivered to a microchannel reactor (Shenshi, TMC-02, internal size 2mm, material 316L, total channel volume 90mL) using a high-pressure advection pump and a gas mass flow controller, respectively, and the reactor temperature was 70°C, pressure 2MPa, material A flow rate 5mL/min, material B flow rate 1.3-1.5SLM. The pressure is released through the pressure relief valve, and the liquid obtained after gas-liquid separation is passed into a 316L reaction coil (outer diameter 3mm inner diameter 2mm, total length 50m, normal pressure) at a flow rate of 5mL/min, and the temperature of the water bath outside the coil is 40°C. The reaction solution flowing out of the coil tube is separated from the raw material and the solvent by distillation under reduced pressure, and the external standard calculation by gas chromatography contains 145g of crotonaldehyde in the separation solution, and the reaction conversion rate is 52%. After decolorization and recrystallization of the remaining crude product liquid by activated carbon, 173 g of pure crotonic acid was obtained, the GC purity was >99%, and the yield was 90.1% based on the consumed crotonaldehyde.

Example 5

Weigh 300g of crotonaldehyde, dissolve it in toluene and set the volume to 800mL as material A; the air coming out of the air cylinder without any treatment is used as material B. Material A and material B were delivered to a microchannel reactor (Shenshi, TMC-02, internal size 2mm, material 316L, total channel volume 90mL) using a high-pressure advection pump and a gas mass flow controller, respectively, and the reactor temperature was 60°C, pressure 2MPa, material A flow rate 5mL/min, material B flow rate 1.3-1.5SLM. The pressure is released through the pressure relief valve, and the liquid obtained after gas-liquid separation is passed into a 316L reaction coil (outer diameter 3mm inner diameter 2mm, total length 50m, normal pressure) at a flow rate of 5mL/min, and the temperature of the water bath outside the coil is 30°C. The reaction solution flowing out from the coil was distilled under reduced pressure to separate the reaction solution from the raw material and the solvent, and the external standard calculation by gas chromatography contained 210 g of crotonaldehyde in the separation solution, and the reaction conversion rate was 30%. The remaining crude product liquid was decolorized and recrystallized by activated carbon to obtain 106 g of crotonic acid pure product, with a GC purity of >99%. The yield was 95.9% based on the consumed crotonaldehyde.

Example 6

Take by weighing 150g of the crotonaldehyde recovered by the process of embodiment 4 and 5, dissolve it in toluene and settle to 400mL, as material A; the air coming out of the air cylinder without any treatment, as material B. Material A and material B were delivered to a microchannel reactor (Shenshi, TMC-02, internal size 2mm, material 316L, total channel volume 90mL) using a high-pressure advection pump and a gas mass flow controller, respectively, and the reactor temperature was 60°C, pressure 2MPa, material A flow rate 5mL/min, material B flow rate 1.3-1.5SLM. The pressure is released through the pressure relief valve, and the liquid obtained after gas-liquid separation is passed into a 316L reaction coil (outer diameter 3mm inner diameter 2mm, total length 50m, normal pressure) at a flow rate of 5mL/min, and the temperature of the water bath outside the coil is 30°C. The reaction solution flowing out from the coil was distilled under reduced pressure to separate the reaction solution from the raw material and the solvent, and the separated solution contained 102 g of crotonaldehyde through gas chromatography analysis and external standard calculation, and the reaction conversion rate was 32%. After decolorization and recrystallization of the remaining crude product liquid by activated carbon, 55 g of pure crotonic acid was obtained, with a GC purity of >99%. The yield was 93.3% based on the consumed crotonaldehyde.

Comparative example 1

Weigh 300g of crotonaldehyde, dissolve it in n-hexane and set the volume to 800mL as material A; the oxygen from the oxygen cylinder without any treatment is used as material B. Material A and material B were transported to a microchannel reactor (Shenshi, model TMC-01, internal size 1.6mm, material 316L, total channel volume 90mL) using a high-pressure advection pump and a gas mass flow controller, respectively. The temperature is 70°C, the pressure is 2MPa, the flow rate of material A is 2mL/min, and the flow rate of material B is 0.1～0.15SLM. Pressure release through the pressure relief valve, the reaction liquid after the gas-liquid separation is separated from the raw material and the solvent by distillation under reduced pressure, and the external standard calculation through gas chromatography contains 120g of crotonaldehyde in the separation liquid, and the reaction conversion rate is 60%. The remaining crude product liquid was decolorized and recrystallized by activated carbon to obtain 160 g of pure crotonic acid with a GC purity of >99%, and the yield of consumed crotonaldehyde was 72.3%.

Comparative example 2

Weigh 300g of crotonaldehyde, dissolve it in n-hexane and set the volume to 700mL, put it into a three-necked flask, place it in a water bath at 40°C, turn on magnetic stirring, blow air into it at a flow rate of 0.05SLM, and react for 48h. After the reaction was finished, the reaction liquid was separated from the raw material and the solvent by distillation under reduced pressure, and the external standard was analyzed by gas chromatography to calculate that the separated liquid contained 180 g of crotonaldehyde, and the reaction conversion rate was 40%. The remaining crude product liquid was decolorized and recrystallized by activated carbon to obtain 96 g of pure crotonic acid with a GC purity of >99%, and the yield of consumed crotonaldehyde was 65.1%.

Claims (5)

1. a method for synthesizing crotonic acid, is characterized in that, comprises the following steps: (1) Continuously feed material A containing crotonaldehyde and material B containing oxygen into the microreactor for the first-stage reaction to obtain reaction liquid C; The material A is an organic solution containing crotonaldehyde, and the organic solvent in the organic solution is a hydrocarbon solvent; Step (1) The channel diameter of the microreactor is 0.5~4.0 mm, the reaction temperature is 50~100°C; the residence time is 30~180s, and the reaction pressure is 1~3 MPa; (2) The reaction liquid C coming out of the microreactor enters the gas-liquid separation unit after the pressure is released, and the residual oxygen in the liquid is removed by continuously blowing nitrogen into the unit, and the obtained liquid D is directly introduced into the tubular reactor for the second stage. Two-stage reaction to obtain reaction solution E; The reaction temperature of the tubular reactor in step (2) is 20-50°C, and the residence time of the reaction liquid D in the reactor is 10-60min; (3) The reaction liquid E flowing out of the tubular reactor enters the evaporator, and the unreacted raw materials and solvent are separated from the product through the evaporator, and then recycled through the rectification unit, and the crude material liquid F is obtained at the bottom of the evaporator; (4) The crude product liquid F obtained in step (3) is refined after post-treatment to obtain the product crotonic acid The organic solvent is one or more of toluene, cyclohexane, n-hexane, and n-heptane; In step (1), the material B is pure oxygen or a mixed gas of nitrogen and oxygen. 2. The method according to claim 1, characterized in that the volume ratio of the crotonaldehyde to the organic solvent is 1:1~4. 3. The method according to claim 1, characterized in that the molar ratio of the crotonaldehyde contained in the material A and the oxygen contained in the material B passed into the microreactor in step (1) is 1: (0.3-2.0). 4. The method according to claim 1, characterized in that the evaporator in step (3) is a thin film evaporator or a rectification tower. 5. The method according to claim 1, characterized in that, in step (4), the post-treatment process includes activated carbon decolorization and recrystallization.