A process for the production of crotonaldehyde

Abstract

The application relates to the field of crotonal production synthesis, and particularly discloses a production process of crotonal. The production process adopts calcium-based hydrotalcite solid alkali as a catalyst to make acetaldehyde generate butanol aldehyde through condensation reaction, then makes the butanol aldehyde generate crude crotonal through dehydration reaction under the action of acetic acid, and finally processes the crude crotonal through primary distillation and rectification to obtain crotonal products. The production method has the advantages of high yield and high purity of crotonal products, small corrosion to equipment, simple process steps, mild reaction conditions, reusable catalyst, low production cost and suitability for large-scale industrial production.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of production and synthesis of crotonaldehyde, more particularly, it relates to a production process of crotonaldehyde based on solid base as a condensation catalyst. BACKGROUND

[0002] Crotonaldehyde, also known as butenal, is an organic compound with cis and trans double bond isomers. Since the cis isomer is unstable, the general crotonaldehyde refers to the trans isomer. As an important organic synthesis intermediate, crotonaldehyde is mainly used for the preparation of n-butanol, n-butyraldehyde, rubber vulcanization accelerator, alcohol modifier and leather softener, etc.

[0003] At present, acetaldehyde is used as raw material to generate butanol aldehyde in a condensation tower through condensation reaction, then butanol aldehyde is sent to a dehydration tower to generate butenal crude product through dehydration, and then butenal crude product is processed through primary distillation tower and rectification tower in sequence to obtain crotonaldehyde product, which is a conventional industrialized route for synthesizing crotonaldehyde.

[0004] The existing Chinese patent with publication number CN 1394840A discloses an improved butenal production process. In this process, liquid alkali (dilute sodium hydroxide) is used as a catalyst for condensation reaction, and by improving the equipment structure, the conversion rate of acetaldehyde is increased to 65%, and the yield of butenal is increased to 97%. However, this method uses liquid alkali as a catalyst for condensation reaction, which not only causes corrosion to the equipment to a certain extent, but also has problems such as the catalyst cannot be recovered, the generated liquid needs to be neutralized, the production process is complex, and a large amount of wastewater is generated. SUMMARY

[0005] In order to solve the above problems, the present application provides a production process of crotonaldehyde.

[0006] The production process of crotonaldehyde provided by the present application adopts the following technical scheme:

[0007] A production process of crotonaldehyde, comprising the following steps:

[0008] The solid alkali catalyst is used to make acetaldehyde undergo condensation reaction to generate butanol aldehyde, then butanol aldehyde is allowed to undergo dehydration reaction under the action of acetic acid to generate crotonaldehyde crude product, and then the crotonaldehyde crude product is processed through primary distillation and rectification to obtain crotonaldehyde product.

[0009] The solid alkali catalyst is calcium-based hydrotalcite solid alkali catalyst, and the weight ratio of calcium-based hydrotalcite solid alkali catalyst to acetaldehyde is (0.04-0.06):1.

[0010] By adopting the technical scheme, the acetaldehyde is subjected to condensation reaction under the catalysis of the solid alkali catalyst to obtain an intermediate product of butanol aldehyde, then the butanol aldehyde is subjected to dehydration in an acidic environment provided by acetic acid to generate a crude product of crotonaldehyde, and the crude product of crotonaldehyde is purified to finally obtain a finished product of crotonaldehyde, and the whole production process is simple and easy to operate, and is suitable for large-scale industrial production.

[0011] The calcium-based hydrotalcite solid alkali catalyst is used to replace the liquid alkali catalyst in the traditional process, and the calcium-based hydrotalcite solid alkali catalyst has higher selectivity for the condensation reaction than the liquid alkali catalyst, reduces by-products, improves the conversion rate of acetaldehyde in the condensation reaction, and thus improves the yield of the finished product of crotonaldehyde. In addition, the calcium-based hydrotalcite solid alkali catalyst is easy to separate from the reaction system, can be repeatedly used and regenerated, reduces the production cost, and meets the requirements of green production. In addition, since the calcium-based hydrotalcite solid alkali catalyst is used, the acid-base neutralization reaction process is omitted, the wastewater amount in the production process is greatly reduced, and the energy consumption required for subsequent separation and recovery is reduced.

[0012] Preferably, the preparation method of the calcium-based hydrotalcite solid alkali catalyst comprises the following steps:

[0013] S1. Mixing Ca(NO3)2·4H2O, Al(NO3)3·9H2O and water to obtain a solution a with a cation concentration of 1 mol / L, wherein the molar ratio of Ca 2+ and Al 3+ is (2-4):1; solution b is a NaOH solution with a concentration of 2 mol / L;

[0014] S2. Mixing the solution a and the solution b at room temperature, continuously controlling the pH value of the mixed solution to be between 8-10, stirring and crystallizing for 10-12 hours, then filtering, washing to obtain a filter cake, and drying the filter cake at a temperature of 80-100℃ for 10-12 hours.

[0015] By adopting the technical scheme, the calcium-based hydrotalcite solid alkali catalyst is prepared by using a salt solution of Ca(NO3)2·4H2O and Al(NO3)3·9H2O as a source of metal cations and NaOH as a precipitating agent by a coprecipitation method. The calcium-based hydrotalcite solid alkali catalyst has strong basicity and high catalytic activity, and can improve the conversion rate of acetaldehyde in the condensation reaction.

[0016] Preferably, the preparation method of the calcium-based hydrotalcite solid alkali catalyst further comprises:

[0017] S3. The resulting product of step S2 is calcined at a temperature of 450-500℃ for 4-8h, then ground to obtain a composite oxide powder, which is dispersed in a NaOH solution under the protection of an inert gas, the mass-volume ratio of the composite oxide powder to the NaOH solution is 0.01-0.012g / mL, and stirring is continued for 1-2h, then the product is filtered, washed, and dried at a temperature of 80-100℃ for 10-12h.

[0018] By adopting the technical scheme, the calcium-based hydrotalcite solid base catalyst is first decomposed and converted into a mixed metal oxide by heating, and then rehydrated in a NaOH aqueous solution, so that the layered structure is restored according to the memory effect of the hydrotalcite structure, and the reconstructed calcium-based hydrotalcite solid base catalyst has more basic sites, higher catalytic activity and stability for the condensation reaction, and can further improve the conversion rate of acetaldehyde in the condensation reaction.

[0019] Preferably, the calcium-based hydrotalcite solid base catalyst is doped and modified by a metal element.

[0020] Preferably, the metal element includes Ga, In and Zn.

[0021] Preferably, the metal element is doped and modified to the calcium-based hydrotalcite solid base catalyst in the following manner: Ga(NO3)3·6H2O, In(NO3)3·6H2O and Zn(NO3)2·6H2O are added to solution a, wherein n(Ga 3+ + In 3+ + Zn 2 + The ratio of n(Ga 3+ ) to n(Al 3+ ) is 1:(1.5-9).

[0022] By adopting the technical scheme, the salt solution of Ga(NO3)3·6H2O, In(NO3)3·6H2O and Zn(NO3)2·6H2O is used as the metal cation source of elements Ga, In and Zn to dope and modify the calcium-based hydrotalcite solid base catalyst, which increases the specific surface area of the calcium-based hydrotalcite solid base catalyst and improves the total alkali content, thereby providing more active sites for the condensation reaction of acetaldehyde, and thus improving the catalytic activity of the calcium-based hydrotalcite solid base catalyst and the conversion rate of acetaldehyde in the condensation reaction.

[0023] Preferably, the ratio of n(Ga 3+ + In 3+ + Zn 2+ ) to n(Al 3+ ) is 1:(1.5-2.3).

[0024] By adopting the above technical solution, the doping-modified metal cations and Al are optimized. 3+ The ratio between these parameters can increase the conversion rate of acetaldehyde in the condensation reaction by 1.5%-1.7%, and ultimately increase the yield of crotonaldehyde by 0.39%-0.41%, further improving the doping effect of metal elements on the reconstructed calcium-based hydrotalcite solid base catalyst.

[0025] Preferably, the Ga 3+ In 3+ Zn 2+ The molar ratio is 1:1:(1.2-1.4).

[0026] By adopting the above technical solution, Ga is optimized. 3+ In 3+ and Zn 2+ The appropriate ratio can increase the conversion rate of acetaldehyde in the condensation reaction by 0.3%-0.4%, and ultimately increase the yield of crotonaldehyde by 0.05%-0.07%, fully leveraging the synergistic effect among the three metal elements, thereby further enhancing the catalytic performance of the calcium-based hydrotalcite solid base catalyst.

[0027] Preferably, the condensation reaction is carried out at a temperature of 45°C-47°C and a pressure of 0.05MPa-0.1MPa.

[0028] Preferably, the temperature of the dehydration reaction is 139℃-141℃ and the pressure is 0.25MPa-0.3MPa.

[0029] In summary, this application has the following beneficial technical effects:

[0030] 1. The production process of this application has a high conversion rate of acetaldehyde, a high yield of crotonaldehyde product, and the finished product has high purity.

[0031] 2. The production process of this application causes less corrosion to the equipment, which improves the service life of the equipment, and the amount of wastewater generated during the production process is low, which reduces the energy consumption required for subsequent separation and recycling;

[0032] 3. The production process of this application is simple, the reaction conditions are mild, and the catalyst can be reused, resulting in low production costs and making it suitable for large-scale industrial production. Detailed Implementation

[0033] The present application will be further described in detail below with reference to embodiments and comparative examples.

[0034] The Ca(NO3)2·4H2O, Al(NO3)3·9H2O, Ga(NO3)3·6H2O, In(NO3)3·6H2O, Zn(NO3)2·6H2O in the present application are all detected for the intramolecular water content before actual use.

[0035] Preparation Example 1

[0036] The preparation method of the calcium-based hydrotalcite solid base catalyst comprises the following steps:

[0037] S1. Ca(NO3)2·4H2O, Al(NO3)3·9H2O and water are mixed to obtain a solution a with a cation concentration of 1 mol / L, wherein the molar ratio of Ca 2+ and Al 3+ is 2:1; NaOH and water are mixed to obtain a solution b with a NaOH concentration of 2 mo / L; S2. At room temperature, solution a and solution b are simultaneously and slowly added into a container for mixing, magnetic stirring is adopted, and the pH value of the mixed solution is continuously controlled between 8-10 during the mixing process. After the addition is completed, the slurry is formed by stirring and crystallization for 10 h, and then the filter cake is obtained after suction filtration and washing. The filter cake is dried at 80℃ for 12 h to obtain the calcium-based hydrotalcite solid base catalyst.

[0038] Preparation Example 2

[0039] The preparation method of the calcium-based hydrotalcite solid base catalyst comprises the following steps:

[0040] S1. Ca(NO3)2·4H2O, Al(NO3)3·9H2O and water are mixed to obtain a solution a with a cation concentration of 1 mol / L, wherein the molar ratio of Ca 2+ and Al 3+ is 3:1; NaOH and water are mixed to obtain a solution b with a NaOH concentration of 2 mo / L; S2. At room temperature, solution a and solution b are simultaneously and slowly added into a container for mixing, magnetic stirring is adopted, and the pH value of the mixed solution is continuously controlled between 8-10 during the mixing process. After the addition is completed, the slurry is formed by stirring and crystallization for 11 h, and then the filter cake is obtained after suction filtration and washing. The filter cake is dried at 90℃ for 11 h to obtain the calcium-based hydrotalcite solid base catalyst.

[0041] Preparation Example 3

[0042] The preparation method of the calcium-based hydrotalcite solid base catalyst comprises the following steps:

[0043] S1. Ca(NO3)2·4H2O, Al(NO3)3·9H2O and water are mixed to obtain a solution a with a cation concentration of 1 mol / L, wherein the molar ratio of Ca 2+ and Al 3+The molar ratio of NaOH to water is 4:1; NaOH and water are mixed to obtain a solution b with a NaOH concentration of 2 mol / L; S2. At room temperature, solutions a and b are simultaneously and slowly added dropwise to a container for mixing, using magnetic stirring, and the pH value of the mixed solution is continuously controlled between 8 and 10 during the mixing process. After the addition is complete, the mixture is stirred and crystallized for 12 hours to form a slurry. After filtration and washing, a filter cake is obtained. The filter cake is dried at 100℃ for 10 hours to obtain a calcium-based hydrotalcite solid base catalyst.

[0044] Preparation Example 4

[0045] The preparation method of the calcium-based hydrotalcite solid base catalyst differs from that in Preparation Example 3 in that it also includes:

[0046] S3. The calcium-based hydrotalcite solid base catalyst prepared in Preparation Example 3 was calcined in a muffle furnace for 8 hours at 450℃. After cooling, a composite oxide was obtained. The composite oxide was then ground to obtain composite oxide powder. The composite oxide powder was dispersed in NaOH solution while stirring. The mass-to-volume ratio of the composite oxide powder to the NaOH solution was 0.01 g / mL. The mixture was stirred for 2 hours under Ar protection. After filtration and washing, the mixture was dried at 80℃ for 12 hours to obtain the reconstructed calcium-based hydrotalcite solid base catalyst.

[0047] Preparation Example 5

[0048] The preparation method of the calcium-based hydrotalcite solid base catalyst differs from that in Preparation Example 3 in that it also includes:

[0049] S3. The calcium-based hydrotalcite solid base catalyst prepared in Preparation Example 3 was calcined in a muffle furnace for 4 hours at 500℃. After cooling, a composite oxide was obtained. The composite oxide was then ground to obtain composite oxide powder. The composite oxide powder was dispersed in NaOH solution while stirring. The mass-to-volume ratio of the composite oxide powder to the NaOH solution was 0.012 g / mL. The mixture was stirred for 1 hour under Ar protection. After filtration and washing, the mixture was dried at 100℃ for 10 hours to obtain the reconstructed calcium-based hydrotalcite solid base catalyst.

[0050] Preparation Example 6

[0051] The preparation method of the calcium-based hydrotalcite solid base catalyst differs from that of Preparation Example 5 in that: Ga(NO3)3·6H2O, In(NO3)3·6H2O, Zn(NO3)2·6H2O are mixed with Ca(NO3)2·4H2O, Al(NO3)3·9H2O, and water to prepare solution a, wherein n(Ga 3+ +In 3+ +Zn 2+ ):n(Al 3+The ratio is 1:4, n(Ga) 3+ ):n(In 3+ ):n(Zn 2+ The ratio is 1:1:0.8.

[0052] Preparation Example 7

[0053] The preparation method of the calcium-based hydrotalcite solid base catalyst differs from that of Preparation Example 5 in that: Ga(NO3)3·6H2O, In(NO3)3·6H2O, Zn(NO3)2·6H2O are mixed with Ca(NO3)2·4H2O, Al(NO3)3·9H2O, and water to prepare solution a, wherein n(Ga 3+ +In 3+ +Zn 2+ ):n(Al 3+ The ratio is 1:9, n(Ga) 3+ ):n(In 3+ ):n(Zn 2+ The ratio is 1:1:1.6.

[0054] Preparation Example 8

[0055] The preparation method of the calcium-based hydrotalcite solid base catalyst differs from that of Preparation Example 7 in that: in the mixed solution a, n(Ga 3+ +In 3+ +Zn 2+ ):n(Al 3+ The ratio is 1:1.5.

[0056] Preparation Example 9

[0057] The preparation method of the calcium-based hydrotalcite solid base catalyst differs from that of Preparation Example 7 in that: in the mixed solution a, n(Ga 3+ +In 3+ +Zn 2+ ):n(Al 3+ The ratio is 1:2.3.

[0058] Preparation Example 10

[0059] The preparation method of the calcium-based hydrotalcite solid base catalyst differs from that of Preparation Example 9 in that: in solution a, n(Ga 3 + ):n(In 3+ ):n(Zn 2+ The ratio is 1:1:1.2.

[0060] Preparation Example 11

[0061] The preparation method of the calcium-based hydrotalcite solid base catalyst differs from that of Preparation Example 9 in that: in solution a, n(Ga 3+ ):n(In 3+ ):n(Zn 2+ The ratio is 1:1:1.4.

[0062] Preparation Example 12

[0063] The preparation method of the calcium-based hydrotalcite solid base catalyst differs from that of Preparation Example 5 in that: Ga(NO3)3·6H2O, In(NO3)3·6H2O, Zn(NO3)2·6H2O are mixed with Ca(NO3)2·4H2O, Al(NO3)3·9H2O, and water to prepare solution a, wherein n(Ga 3+ +In 3+ +Zn 2+ ):n(Al 3+ The ratio is 1:1, n(Ga) 3+ ):n(In 3+ ):n(Zn 2+ The ratio is 1:1:1.6.

[0064] Preparation Example 13

[0065] The preparation method of the calcium-based hydrotalcite solid base catalyst differs from that of Preparation Example 5 in that: Ga(NO3)3·6H2O, In(NO3)3·6H2O, Zn(NO3)2·6H2O are mixed with Ca(NO3)2·4H2O, Al(NO3)3·9H2O, and water to prepare solution a, wherein n(Ga 3+ +In 3+ +Zn 2+ ):n(Al 3+ The ratio is 1:12, n(Ga) 3+ ):n(In 3+ ):n(Zn 2+ The ratio is 1:1:1.6.

[0066] Preparation Example 14

[0067] The preparation method of the calcium-based hydrotalcite solid base catalyst differs from that of Preparation Example 5 in that only element Ga is used for doping modification. Specifically, Ga(NO3)3·6H2O is mixed with Ca(NO3)2·4H2O, Al(NO3)3·9H2O, and water to prepare solution a, wherein n(Ga 3+ ):n(Al 3+ The ratio is 1:9.

[0068] Preparation Example 15

[0069] The preparation method of the calcium-based hydrotalcite solid base catalyst differs from that of Preparation Example 5 in that only element In is used for doping modification. Specifically, In(NO3)3·6H2O is mixed with Ca(NO3)2·4H2O, Al(NO3)3·9H2O, and water to prepare solution a, wherein n(In 3+ ):n(Al 3+ The ratio is 1:9.

[0070] Preparation Example 16

[0071] The preparation method of the calcium-based hydrotalcite solid base catalyst differs from that of Preparation Example 5 in that only elemental Zn is used for doping modification. Specifically, Zn(NO3)2·6H2O is mixed with Ca(NO3)2·4H2O, Al(NO3)3·9H2O, and water to prepare solution a, wherein n(Zn) 2+ ):n(Al 3+ The ratio is 1:9.

[0072] Preparation Example 17

[0073] The preparation method of the calcium-based hydrotalcite solid base catalyst differs from that of Preparation Example 5 in that: doping modification is performed using elements Ga, In, and Mn. Specifically, Ga(NO3)3·6H2O, In(NO3)3·6H2O, Mn(NO3)2·4H2O are mixed with Ca(NO3)2·4H2O, Al(NO3)3·9H2O, and water to prepare solution a, wherein n(Ga 3+ +In 3+ +Mn 2+ ):n(Al 3+ The ratio is 1:9, n(Ga) 3+ ):n(In 3+ ):n(Mn 2+ The ratio is 1:1:1.6.

[0074] Example 1

[0075] A process for producing crotonaldehyde includes the following steps:

[0076] (1) Condensation reaction: First, 4 kg of the calcium-based hydrotalcite solid base catalyst prepared in Example 1 was filled into the reaction section of the condensation tower. Then, 100 kg of acetaldehyde with a content of ≥99% was introduced into the condensation tower, and N2 was introduced into the condensation tower to make the system pressure 0.05 MPa-0.1 MPa. Acetaldehyde was sent into the reaction section of the condensation tower by means of N2 pressure. At the same time, demineralized water was introduced above the reaction section of the condensation tower to maintain the temperature of the reaction section of the condensation tower at 45℃-47℃. Acetaldehyde under the catalysis of the calcium-based hydrotalcite solid base catalyst underwent a condensation reaction to generate butanol aldehyde. The temperature of the bottom of the tower was controlled at 76℃-78℃. The gaseous acetaldehyde was distilled off from the top of the condensation tower and refluxed to the top of the tower after circulating cooling. The butanol aldehyde generated by the condensation reaction was pumped from the bottom of the condensation tower to the dehydration tower.

[0077] (2) Dehydration reaction: The top temperature of the dehydration tower is controlled at 116℃±4℃, the bottom temperature is controlled at 139℃-141℃, and the system pressure is controlled at 0.25MPa-0.3MPa. Butyl alcohol is dehydrated in the presence of acetic acid with a concentration of 400g / L to produce crude crotonaldehyde. The crude crotonaldehyde is discharged from the top of the dehydration tower. After condensation, the liquid phase is refluxed back to the dehydration tower, and the rest and the gas phase enter the primary distillation tower.

[0078] (3) Preliminary distillation: The system pressure of the primary distillation column is 0.25MPa-0.3MPa, the bottom temperature is 137℃-139℃, and the top temperature is 50℃-55℃. The acetaldehyde distilled from the top of the primary distillation column is returned to the condensation column for recycling. The material discharged from the middle of the primary distillation column is cooled and separated to obtain water and crotonaldehyde primary product with a purity of 85.5%.

[0079] (4) Distillation treatment: The feed is fed into the distillation column under N2 pressure. The bottom temperature of the distillation column is 106℃-110℃. The product of crotonaldehyde with a purity greater than 99.5% is obtained by further distillation in the distillation column.

[0080] Example 2

[0081] A process for producing crotonaldehyde includes the following steps:

[0082] (1) Condensation reaction: First, 5 kg of the calcium-based hydrotalcite solid base catalyst prepared in Example 2 was filled into the reaction section of the condensation tower. Then, 100 kg of acetaldehyde with a content of ≥99% was introduced into the condensation tower, and N2 was introduced into the condensation tower to make the system pressure 0.05 MPa-0.1 MPa. Acetaldehyde was sent into the reaction section of the condensation tower by means of N2 pressure. At the same time, demineralized water was introduced above the reaction section of the condensation tower to maintain the temperature of the reaction section of the condensation tower at 45℃-47℃. Acetaldehyde under the catalysis of the calcium-based hydrotalcite solid base catalyst underwent a condensation reaction to generate butanol aldehyde. The temperature of the tower bottom was controlled at 76℃-78℃. The gaseous acetaldehyde was distilled off from the top of the condensation tower and refluxed to the top of the tower after circulating cooling. The butanol aldehyde generated by the condensation reaction was pumped from the bottom of the condensation tower to the dehydration tower.

[0083] (2) Dehydration reaction: The top temperature of the dehydration tower is controlled at 116℃±4℃, the bottom temperature is controlled at 139℃-141℃, and the system pressure is controlled at 0.25MPa-0.3MPa. Butyl alcohol is dehydrated in the presence of acetic acid with a concentration of 400g / L to produce crude crotonaldehyde. The crude crotonaldehyde is discharged from the top of the dehydration tower. After condensation, the liquid phase is refluxed back to the dehydration tower, and the rest and the gas phase enter the primary distillation tower.

[0084] (3) Preliminary distillation: The system pressure of the primary distillation column is 0.25MPa-0.3MPa, the bottom temperature is 137℃-139℃, and the top temperature is 50℃-55℃. The acetaldehyde distilled from the top of the primary distillation column is returned to the condensation column for recycling. The material discharged from the middle of the primary distillation column is cooled and separated to obtain water and crotonaldehyde primary product with a purity of 86.5%.

[0085] (4) Distillation treatment: The feed is fed into the distillation column under N2 pressure. The bottom temperature of the distillation column is 106℃-110℃. The product of crotonaldehyde with a purity greater than 99.5% is obtained by further distillation in the distillation column.

[0086] Example 3

[0087] A process for producing crotonaldehyde includes the following steps:

[0088] (1) Condensation reaction: First, 6 kg of the calcium-based hydrotalcite solid base catalyst prepared in Example 3 was filled into the reaction section of the condensation tower. Then, 100 kg of acetaldehyde with a content of ≥99% was introduced into the condensation tower, and N2 was introduced into the condensation tower to make the system pressure 0.05 MPa-0.1 MPa. Acetaldehyde was sent into the reaction section of the condensation tower by means of N2 pressure. At the same time, demineralized water was introduced above the reaction section of the condensation tower to maintain the temperature of the reaction section of the condensation tower at 45℃-47℃. Acetaldehyde under the catalysis of the calcium-based hydrotalcite solid base catalyst underwent a condensation reaction to generate butanol aldehyde. The temperature of the tower bottom was controlled at 76℃-78℃. The gaseous acetaldehyde was distilled off from the top of the condensation tower and refluxed to the top of the tower after circulating cooling. The butanol aldehyde generated by the condensation reaction was pumped from the bottom of the condensation tower to the dehydration tower.

[0089] (2) Dehydration reaction: The top temperature of the dehydration tower is controlled at 116℃±4℃, the bottom temperature is controlled at 139℃-141℃, and the system pressure is controlled at 0.25MPa-0.3MPa. Butyl alcohol is dehydrated in the presence of acetic acid with a concentration of 400g / L to produce crude crotonaldehyde. The crude crotonaldehyde is discharged from the top of the dehydration tower. After condensation, the liquid phase is refluxed back to the dehydration tower, and the rest and the gas phase enter the primary distillation tower.

[0090] (3) Preliminary distillation: The system pressure of the primary distillation column is 0.25MPa-0.3MPa, the bottom temperature is 137℃-139℃, and the top temperature is 50℃-55℃. The acetaldehyde distilled from the top of the primary distillation column is returned to the condensation column for recycling. The material discharged from the middle of the primary distillation column is cooled and separated to obtain water and crotonaldehyde primary product with a purity of 86%.

[0091] (4) Distillation treatment: The feed is fed into the distillation column under N2 pressure. The bottom temperature of the distillation column is 106℃-110℃. The product of crotonaldehyde with a purity greater than 99.5% is obtained by further distillation in the distillation column.

[0092] Example 4-17

[0093] A process for producing crotonaldehyde differs from Example 3 in that: in step (1) the dehydration reaction, the calcium-based hydrotalcite solid base catalyst is the calcium-based hydrotalcite solid base catalyst prepared in Examples 4-17.

[0094] Example 18

[0095] A production process for crotonaldehyde differs from that in Example 3 in that: in step (1) the condensation reaction, the calcium-based hydrotalcite solid base catalyst is the calcium-based hydrotalcite solid base catalyst that has been recycled 5 times according to the production process of Example 3.

[0096] Comparative Example 1

[0097] The difference from Example 3 is that in step (1) the dehydration reaction, NaOH with a concentration of 50 g / L is used as a catalyst.

[0098] Comparative Example 2

[0099] The difference from Example 3 is that in step (1) the dehydration reaction, the calcium-based hydrotalcite solid base catalyst is 1 kg.

[0100] Comparative Example 3

[0101] The difference from Example 3 is that in step (1) the dehydration reaction, the calcium-based hydrotalcite solid base catalyst is 10 kg.

[0102] Performance testing

[0103] The yields of crotonaldehyde products obtained by the production methods of Examples 1-18 and Comparative Examples 1-3 and the conversion rate of acetaldehyde in the condensation reaction of step (1) were tested and calculated respectively. The yield of crotonaldehyde products = weight of crotonaldehyde products / weight of acetaldehyde introduced × 100%, and the conversion rate of acetaldehyde = weight of butanol aldehyde / weight of acetaldehyde introduced × 100%. The results are shown in Table 1.

[0104] Table 1 Performance Test Results

[0105]

[0106]

[0107] As can be seen from Table 1, the conversion rate of acetaldehyde in step (1) of the condensation reaction in Examples 1-3 of this application reaches more than 80%, and the final yield of crotonaldehyde product reaches more than 97%. This indicates that the calcium-based hydrotalcite solid alkali catalyst is used to catalyze the condensation reaction of acetaldehyde in the production method of Examples 1-3 of this application, which results in a high conversion rate of acetaldehyde in the condensation reaction and a high yield of the final crotonaldehyde product.

[0108] The difference between Examples 4-5 and Example 3 is that the calcium-based hydrotalcite solid catalyst prepared by the co-precipitation method was reconstructed. As can be seen from Table 1, compared with Example 3, the conversion rate of acetaldehyde in Examples 4-5 increased by 7.4%-7.9%, and the yield of crotonaldehyde product increased by 0.87%-0.94%. The experimental data show that the reconstructed calcium-based hydrotalcite solid base catalyst has stronger catalytic activity and better catalytic effect on the acetaldehyde condensation reaction.

[0109] The difference between Examples 6-7 and Example 5 is that the reconstructed calcium-based hydrotalcite solid base catalyst was modified by doping with metal elements. As shown in Table 1, compared with Example 5, the conversion rate of acetaldehyde in Examples 6-7 increased by 4.72%-4.84%, and the yield of crotonaldehyde product increased by 0.47%-0.53%. The experimental data show that the catalytic effect can be further improved by doping the reconstructed calcium-based hydrotalcite solid base catalyst with metal elements.

[0110] The difference between Examples 8-9 and Example 7 lies in the further control of the doping metal element and Al. 3+ As shown in Table 1, compared with Example 7, the conversion rate of acetaldehyde in Examples 8-9 increased by 1.5%-1.7%, and the yield of crotonaldehyde product increased by 0.39%-0.41%. Experimental data indicate that further control of the doped metal elements and Al... 3+ The appropriate ratio can further improve the doping effect of metal elements on the reconstructed calcium-based hydrotalcite solid alkali catalyst, thereby further enhancing its catalytic performance.

[0111] The difference between Examples 10-11 and Example 9 is that the ratio of the three doped metal elements is further controlled. As can be seen from Table 1, the conversion rate of acetaldehyde in Examples 10-11 is increased by 0.3%-0.4% and the yield of crotonaldehyde product is increased by 0.05%-0.07% compared with Example 9. The experimental data show that further controlling the ratio of the three doped metal elements can further enhance the synergistic effect between the three metal elements, thereby further improving its catalytic performance.

[0112] By comparing the data from Examples 12-13 with those from Examples 5 and 7, it can be seen that the doped metal elements and Al 3+ If the ratio is not within the scope of this application, it will reduce the doping effect of metal elements on calcium-based layered double hydroxide solid base catalyst, thereby reducing the catalytic performance of calcium-based layered double hydroxide solid base catalyst.

[0113] By comparing the data from Examples 14-17 with those from Examples 5 and 7, it can be seen that the combined use of the metal elements Ga, In, and Zn can fully leverage their synergistic effects. Using only one of them or replacing it with another metal element will reduce the doping effect of the metal elements on the calcium-based layered double hydroxide solid base catalyst, thereby reducing the catalytic performance of the calcium-based layered double hydroxide solid base catalyst.

[0114] By comparing the data from Example 18 and Example 3, it can be seen that the calcium-based solid base catalyst of this application still has a strong catalytic effect after being recycled 5 times, and has good recycling performance.

[0115] The difference between Comparative Example 1 and Example 3 is that liquid alkali was used as the catalyst. As can be seen from Table 1, the conversion rate of acetaldehyde in Comparative Example 1 was only 67.5%, and the final yield of crotonaldehyde was only 78.5%. The experimental data show that the calcium-based solid alkali catalyst has better catalytic performance than liquid alkali and has a stronger catalytic effect on the acetaldehyde condensation reaction.

[0116] The difference between Comparative Examples 2-3 and Example 3 is that the amount of calcium-based solid base catalyst used is not within the range of this application. As can be seen from Table 1, if the amount of calcium-based solid base catalyst used is lower than the range of this application, the best catalytic effect cannot be achieved. If the amount of calcium-based solid base catalyst used is higher than the range of this application, not only will the catalytic performance not be further improved, but it will also be slightly reduced, and the catalyst will be wasted, increasing the production cost.

[0117] The embodiments described in this specific implementation are preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A process for producing crotonaldehyde, characterized in that, Includes the following steps: Acetaldehyde is condensed to form butanol using a solid base catalyst. Butanol is then dehydrated in acetic acid to produce crude crotonaldehyde. The crude crotonaldehyde is then subjected to primary distillation and rectification to obtain the crotonaldehyde product. The solid base catalyst is a calcium-based hydrotalcite solid base catalyst, and the weight ratio of the calcium-based hydrotalcite solid base catalyst to acetaldehyde is 0.06:

1. The preparation method of the calcium-based hydrotalcite solid base catalyst includes the following steps: S1. A solution a with a cation concentration of 1 mol / L is obtained by mixing Ca(NO3)2·4H2O, Al(NO3)3·9H2O, and water. 2+ and A1 3+ The molar ratio of the substances is (2-4):1; solution b is a 2 mol / L NaOH solution; S2. Mix solutions a and b at room temperature and continuously control the pH of the mixed solution between 8 and 10. After stirring and crystallizing for 10-12 hours, filter the mixture and wash it to obtain a filter cake. Dry the filter cake at 80℃-100℃ for 10-12 hours. S3. The product obtained in step S2 is calcined at 450℃-500℃ for 4h-8h and then ground to obtain composite oxide powder. Under the protection of inert gas, the composite oxide powder is dispersed in NaOH solution with a mass-to-volume ratio of composite oxide powder to NaOH solution of 0.01g / mL-0.012g / mL. After stirring continuously for 1h-2h, the product is filtered, washed, and then dried at 80℃-100℃ for 10h-12h. The calcium-based hydrotalcite solid base catalyst is modified by doping with metal elements, including Ga, In and Zn. The metal elements are used to dope and modify the calcium-based hydrotalcite solid alkali catalyst in the following manner: Ga(NO3)3·6H2O, In(NO3)3·6H2O and Zn(NO3)2·6H2O are added to solution a, wherein n(Ga 3+ +In 3+ +Zn 2+ ) and n(A1 3+ The ratio of Ga to Ga is 1:(1.5-2.3). 3+ In 3+ Zn 2+ The molar ratio is 1:1:(1.2-1.4).

2. The production process of crotonaldehyde according to claim 1, characterized in that, The condensation reaction is carried out at a temperature of 45℃-47℃ and a pressure of 0.05MPa-0.1MPa.

3. The production process of crotonaldehyde according to claim 1, characterized in that, The dehydration reaction was carried out at a temperature of 139℃-141℃ and a pressure of 0.25MPa-0.3MPa.

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