A method for synthesizing 2-heptanone

Abstract

This invention discloses a method for synthesizing 2-heptanone, comprising continuously feeding n-butyraldehyde into an alkaline reaction system. The reaction system includes activated acetone and a hydrogenation catalyst, with acetone in excess relative to n-butyraldehyde. In this invention, n-butyraldehyde is continuously fed into an alkaline reaction system comprising a hydrogenation catalyst and activated acetone in a high-pressure reactor under a hydrogen atmosphere. By controlling the feeding rate of n-butyraldehyde, it is rapidly diluted to reduce self-polymerization and the generation of byproducts, especially high-boiling-point substances, thereby improving the selectivity of MAK (methyl ethyl ether). By controlling the total amount of n-butyraldehyde added, the reaction system is kept in excess of acetone to improve the conversion rate of n-butyraldehyde. This invention achieves a one-step synthesis of 2-heptanone in a reactor, with high reaction efficiency, short reaction time, high MAK selectivity, easy purification, easy material recovery and reuse, low energy consumption, and ease of industrialization.

Description

Technical Field

[0001] This invention relates to the field of chemical synthesis technology, and in particular to a method for synthesizing 2-heptanone. Background Technology

[0002] 2-Hepanotone (MAK) has the characteristics of strong solubility, low volatility, low density, low surface tension and high boiling point, making it an excellent industrial solvent, especially suitable for use as a solvent for high solids content, low viscosity and high-grade coatings.

[0003] In the prior art, the main methods for preparing 2-heptanone include: 1) Ethyl acetoacetate method: This is a common synthesis method in China. The synthesis steps include first condensing ethyl acetoacetate with n-butyl bromide to generate ethyl n-butyl acetoacetate, and then obtaining 2-heptanone through a decarboxylation reaction. However, this method requires multiple separation and purification processes, resulting in high energy consumption. It also uses strong bases and strong acids, making post-processing difficult. Furthermore, the reaction releases a large amount of carbon dioxide, which is not conducive to low-carbon and environmental protection.

[0004] 2) One-step aldol condensation method: This method involves the condensation and hydrogenation of acetone and n-butyraldehyde under alkaline conditions to obtain 2-heptanone. A large amount of cyclohexane is used as a solvent to reduce the self-polymerization of n-butyraldehyde. However, this method suffers from low product selectivity due to the large amount of cyclohexane used, which affects the reaction conversion rate and fails to effectively suppress byproducts. Furthermore, subsequent separation is difficult and energy-intensive.

[0005] 3) Two-step aldol condensation method: The raw materials are the same as in the one-step aldol condensation method, still acetone and n-butyraldehyde, but the process is divided into two steps. First, the acetone is activated by heating, and then the acetone and n-butyraldehyde are condensed under alkaline conditions to obtain an intermediate. The purified or crude intermediate is then hydrogenated to obtain 2-heptanone. This preparation method involves multiple material reactions, resulting in a long overall reaction time, low efficiency, and potentially multiple purification processes, increasing material loss and energy consumption. The yield is low, leading to low economic benefits.

[0006] 4) Oxidation method: 2-Heptanol is used as a raw material to produce 2-heptanone through dehydrogenation. However, the raw materials for preparing 2-heptanol are expensive and difficult to obtain, resulting in high costs for this method and making it unsuitable for industrial application. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a method for synthesizing 2-heptanone, which can achieve the one-step synthesis of 2-heptanone while avoiding the use of a large amount of solvent, effectively reducing the self-polymerization of n-butyraldehyde, effectively suppressing high-boiling substances, having high MAK selectivity, high reaction efficiency, short time, readily available raw materials, low cost, and is suitable for industrial application.

[0008] To address the aforementioned technical problems, this invention provides a method for synthesizing 2-heptanone, comprising adding n-butyraldehyde to an alkaline reaction system via continuous injection. The reaction system includes activated acetone and a hydrogenation catalyst, wherein acetone is in excess relative to n-butyraldehyde.

[0009] In this invention, conventional n-butyraldehyde and acetone are used as raw materials. Under alkaline conditions, n-butyraldehyde is continuously injected into the reaction system. By controlling the rate of addition, the n-butyraldehyde entering the reaction system is rapidly diluted, effectively preventing self-polymerization of n-butyraldehyde under alkaline conditions and reducing the formation of by-products. In particular, it effectively suppresses high-boiling substances and improves the selectivity of MAK. Furthermore, an excess of acetone relative to n-butyraldehyde not only increases the conversion rate of n-butyraldehyde but also inhibits its self-polymerization to some extent. In this invention, alkaline conditions refer to, for example, adding alkaline solutions such as NaOH or KOH to the reaction system to increase the hydroxide ion concentration, thus maintaining an alkaline state. In this invention, the conversion rate of n-butyraldehyde reaches over 98%, and the detected content of n-butyraldehyde self-polymers is no higher than 0.38%. Simultaneously, the selectivity of 2-heptanone is higher than 92%, with few by-products. After purification, the product of this invention recovers acetone, catalyst, and alkaline solution for adjusting hydroxide ion concentration, respectively. The reflux process is simple, and the recovered product can be directly reused. It should be noted that, in this invention, activated acetone refers to acetone heated to the required reaction temperature.

[0010] In one specific embodiment, the total molar amount of n-butyraldehyde added to the reaction system does not exceed 19% of the total molar amount of acetone at the start of the reaction, preferably not exceeding 17% and not less than 12%. In this invention, acetone is in excess relative to n-butyraldehyde. Understandably, the higher the molar amount of acetone relative to n-butyraldehyde in the reaction system, the more beneficial it is to improving the conversion rate of n-butyraldehyde and to inhibiting the self-polymerization of n-butyraldehyde.

[0011] In one specific embodiment, the molar amount of n-butyraldehyde added to the reaction system per minute does not exceed 0.8% or 0.6% of the total molar amount of acetone in the reaction system at the start of the reaction. In this invention, the slow addition of n-butyraldehyde to the reaction system facilitates rapid and sufficient dilution of n-butyraldehyde, effectively reducing its self-polymerization and the generation of byproducts.

[0012] In one specific scheme, after all n-butyraldehyde is added, the reaction continues for 10-200 minutes. Understandably, continuing the reaction after the n-butyraldehyde is completely added is beneficial for the full reaction between acetone and n-butyraldehyde, as well as for the catalytic hydrogenation.

[0013] In one specific scheme, the reaction system is kept in a hydrogen atmosphere before n-butyraldehyde is injected. Specifically, before n-butyraldehyde is injected, acetone and hydrogenation catalyst are mixed, and an alkaline solution is added to make the mixture alkaline, resulting in an alkaline reaction system. Then, hydrogen gas is introduced to make the alkaline reaction system in a hydrogen atmosphere, and then the acetone is activated by heating the reaction system to 80°C-95°C. Alternatively, it is preferable to make the alkaline reaction system under a pressure of 0.5-4.0 MPa by introducing hydrogen gas before n-butyraldehyde is injected.

[0014] In one specific embodiment, an alkaline solution is added to the system to form an alkaline reaction system. The mass of the added alkaline solution is 1 / 5 to 1 / 10 of the total mass of n-butyraldehyde and acetone, and the hydroxide ion concentration in the alkaline solution is 0.25-0.75 mol / L. It should be noted that, for this invention, the reaction can only occur in the presence of hydroxide ions. Hydroxide ions are used to consume hydrogen. When the amount of hydroxide ions in the reaction system is too low (e.g., the hydroxide ion concentration in the aqueous phase is below 0.25 mol / L), the reaction cannot continue because the system cannot effectively consume hydrogen. Furthermore, while a higher concentration of hydroxide ions in the reaction system is beneficial for accelerating the reaction process, excessive hydroxide ions can easily lead to the formation of more impurities. Therefore, it is preferable that the hydroxide ion concentration of the alkaline solution does not exceed 0.75 mol / L.

[0015] In one specific scheme, the reaction system is placed in a hydrogenation reactor. During the reaction, hydrogen gas is continuously introduced into the hydrogenation reactor to maintain the pressure inside the reactor at 0.5-4.0 MPa. During the reaction, the temperature of the reaction system is 80-95℃.

[0016] In one specific embodiment, the hydrogenation catalyst includes one or two of Raney nickel catalyst and palladium on carbon catalyst; preferably, the amount of hydrogenation catalyst is 2%-6% of the total mass of n-butyraldehyde.

[0017] This invention involves continuously feeding n-butyraldehyde into an alkaline reaction system comprising a hydrogenation catalyst and activated acetone in a high-pressure reactor under a hydrogen atmosphere. By controlling the feeding rate of n-butyraldehyde, it is rapidly diluted to reduce its self-polymerization and the generation of byproducts, especially high-boiling-point substances, thereby improving the selectivity of MAK. By controlling the total amount of n-butyraldehyde fed, the reaction system is kept in excess of acetone to improve the conversion rate of n-butyraldehyde. This invention achieves a one-step synthesis of 2-heptanone in a reactor, with high reaction efficiency, short reaction time, high MAK selectivity, easy purification, easy material recovery and reuse, low energy consumption, and easy industrialization. Attached Figure Description

[0018] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is the gas chromatogram of Example 1; Figure 2 This is the gas chromatogram of Example 2; Figure 3 This is the gas chromatogram of Example 3; Figure 4 This is the gas chromatogram of Example 4; Figure 5 This is the gas chromatogram of Example 5; Figure 6 This is the gas chromatogram of Comparative Example 1; Figure 7 This is the gas chromatogram of Comparative Example 2. Detailed Implementation

[0020] The technical solutions of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] In the embodiments of the present invention, the purity of acetone is not less than 99%, the purity of n-butyraldehyde is not less than 98%, NaOH solution is used to increase the hydroxide ions in the reaction system, and the hydrogenation catalyst is a palladium-on-carbon catalyst. All these materials are commercially available or can be recycled. The reaction is carried out in a hydrogenation reactor. The results are detected by gas chromatography, and the chromatographic conditions are shown in Table 1. Table 1 carrier gas Nitrogen Column carrier gas flow rate, mL / min 1.0 Hydrogen flow rate, mL / min 30 Air flow rate, mL / min 300 Make-up gas flow rate, mL / min 25 Flow split ratio 80：1 Vaporization chamber temperature, °C 250 Detector temperature, °C 250 Column temperature, °C The initial temperature was 60℃, which was increased to 200℃ at a rate of 5℃ / min and held for 2 minutes. Injection volume, μL 1 Example 1

[0022] In a 1000mL hydrogenation reactor, 400g of acetone, 50g of 2% NaOH solution, and 4g of palladium-on-carbon catalyst were added. After sealing the reactor, hydrogen was used to purge the acetone. The reactor temperature was then set to 90℃ to activate the acetone, and stirring was started. By adding hydrogen, the pressure inside the reactor was adjusted to 2MPa. The liquid phase feed valve was opened, and n-butyraldehyde was continuously fed at a rate of 3ml / min, maintaining the reactor temperature below 95℃ and the pressure at approximately 2MPa. After 30 minutes of continuous feeding, the feed valve was closed, and the feeding was stopped. The reaction was maintained under pressure and temperature conditions for 40 minutes, with the pressure maintained by introducing hydrogen. After the reaction was completed, the temperature was lowered, and samples were taken for analysis. The results showed that the acetone content was 66.80%, n-butyraldehyde was 0.15%, MIBK and intermediates were 1.06%, MAK content was 29.14%, MAK intermediates were 0.1%, n-butyraldehyde self-polymer was 0.07%, and high-boiling-point substances were 2.36%. The chromatogram is shown below. Figure 1 As shown, 3.61 min is acetone, 3.934 min is n-butyraldehyde, and 8.375 min is MAK.

[0023] The reaction system is post-processed as follows: for example, the reaction system is first filtered to obtain the palladium-on-carbon catalyst, which is then recovered; then, the system is heated to the boiling point of acetone at atmospheric pressure using a distillation column to distill off and recover the acetone; the reaction system after acetone recovery is phase-separated, the aqueous phase is a sodium hydroxide solution, which is recovered, and the oil phase is subjected to secondary distillation using a distillation column. First, low-boiling-point impurities are separated at an appropriate temperature with a pressure of -0.045 MPa and a certain reflux ratio, and then high-boiling-point impurities are separated at an appropriate temperature with a pressure of -0.088 MPa and a certain reflux ratio, and MAK is distilled off to obtain MAK. Example 2

[0024] In a 1000mL hydrogenation reactor, 350g of acetone, 50g of 2% NaOH solution, and 4g of palladium-on-carbon catalyst were added. After sealing the reactor, hydrogen was used to purge the acetone. The reactor temperature was then set to 90℃ to activate the acetone, and stirring was started. By adding hydrogen, the pressure inside the reactor was adjusted to 2MPa. The liquid phase feed valve was opened, and n-butyraldehyde was continuously fed at a rate of 3ml / min, maintaining the reactor temperature below 95℃ and the pressure at approximately 2MPa. After 30 minutes of continuous feeding, the feed valve was closed, and the feeding was stopped. The reaction was maintained under pressure and temperature conditions for 40 minutes, with the pressure maintained by introducing hydrogen. After the reaction was completed, the temperature was lowered, and samples were taken for analysis. The results showed that the acetone content was 65.58%, n-butyraldehyde 0.5%, MIBK and intermediates 1.78%, MAK content 25.62%, MAK intermediates 0.15%, n-butyraldehyde self-polymer 0.38%, and high-boiling-point compounds 5.53%. The chromatogram is shown below. Figure 2 As shown, 3.548 min is acetone, 3.934 min is n-butyraldehyde, and 8.287 min is MAK. The post-processing is the same as in Example 1. Example 3

[0025] In a 1000mL hydrogenation reactor, 400g of acetone, 100g of 2% NaOH solution, and 4g of palladium-on-carbon catalyst were added. After sealing the reactor, hydrogen was used to purge the acetone. The reactor temperature was then set to 90℃ to activate the acetone, and stirring was started. By adding hydrogen, the pressure inside the reactor was adjusted to 2MPa. The liquid phase feed valve was opened, and n-butyraldehyde was continuously fed at a rate of 3ml / min, maintaining the reactor temperature below 95℃ and the pressure at approximately 2MPa. After 30 minutes of continuous feeding, the feed valve was closed, and the feeding was stopped. The reaction was maintained under pressure and temperature conditions for 40 minutes, with the pressure maintained by introducing hydrogen. After the reaction was completed, the temperature was lowered, and samples were taken for analysis. The results showed that the acetone content was 65.79%, n-butyraldehyde was 0.13%, MIBK and intermediates were 2.86%, MAK content was 27.7%, MAK intermediates were 0.08%, n-butyraldehyde self-polymer was 0.14%, and high-boiling-point substances were 3.08%. The chromatogram is shown below. Figure 3 As shown, 3.607 min is acetone, 3.992 min is n-butyraldehyde, and 8.367 min is MAK. The post-processing is the same as in Example 1. Example 4

[0026] In a 1000mL hydrogenation reactor, 400g of acetone, 50g of 4% NaOH solution, and 4g of palladium-on-carbon catalyst were added. After sealing the reactor, hydrogen was used to purge the acetone. The reactor temperature was then set to 90℃ to activate the acetone, and stirring was started. By adding hydrogen, the pressure inside the reactor was adjusted to 2MPa. The liquid phase feed valve was opened, and n-butyraldehyde was continuously fed at a rate of 3ml / min. The reactor temperature was maintained below 95℃, and the pressure was maintained at approximately 2MPa. After feeding for 30 minutes, the feed valve was closed, and feeding was stopped. The reaction was maintained under pressure and temperature conditions for 40 minutes. The pressure was maintained by introducing hydrogen. After the reaction was completed, the temperature was lowered, and samples were taken for analysis. The results showed that the acetone content was 65.77%, n-butyraldehyde was 0.1%, MIBK and intermediates were 1.2%, MAK content was 28.17%, MAK intermediates were 0.16%, n-butyraldehyde self-polymer was 0.09%, and high-boiling-point substances were 4.15%. The chromatogram is shown below. Figure 4 As shown, 3.548 min is acetone, 3.934 min is n-butyraldehyde, and 8.287 min is MAK. The post-processing is the same as in Example 1. Example 5

[0027] In a 1000mL hydrogenation reactor, 400g of recovered acetone, 50g of recovered NaOH solution, and 4g of recovered palladium-on-carbon catalyst were added. After sealing the reactor, hydrogen was used to purge the acetone. The reactor temperature was then set to 90℃ to activate the acetone, and stirring was started. The pressure inside the reactor was adjusted to 2MPa by adding hydrogen. The liquid phase feed valve was opened, and n-butyraldehyde was continuously fed at a rate of 3ml / min. The reactor temperature was maintained below 95℃, and the pressure was maintained at approximately 2MPa. After feeding for 30 minutes, the feed valve was closed, and feeding was stopped. The reaction was maintained under pressure and temperature conditions for 40 minutes. The pressure was maintained by introducing hydrogen. After the reaction was completed, the temperature was lowered, and samples were taken for analysis. The results showed that the acetone content was 66.19%, n-butyraldehyde was 0.17%, MIBK and intermediates were 1.37%, MAK content was 28.94%, MAK intermediates were 0.15%, n-butyraldehyde self-polymer was 0.16%, and high-boiling-point substances were 2.78%. The chromatogram is shown below. Figure 5 As shown, 3.593 min is acetone, 3.948 min is n-butyraldehyde, and 8.332 min is MAK. The post-processing is the same as in Example 1.

[0028] Comparative Example 1 In a 1000mL hydrogenation reactor, 300g of acetone, 100g of 3% NaOH solution, and 4g of palladium-on-carbon catalyst were added. After sealing the reactor, hydrogen was used to purge the acetone. The reactor temperature was then set to 80℃ to activate the acetone, and stirring was started. The pressure inside the reactor was adjusted to 1MPa by adding hydrogen. The liquid phase feed valve was opened, and n-butyraldehyde was continuously fed at a rate of 4.5ml / min. The reactor temperature was maintained below 85℃, and the pressure was maintained at approximately 2MPa. After feeding for 20 minutes, the feed valve was closed, and feeding was stopped. The reaction was maintained under pressure and temperature conditions for 40 minutes. The pressure was maintained by introducing hydrogen. After the reaction was completed, the temperature was lowered, and samples were taken for analysis. The results showed that the acetone content was 28.91%, n-butyraldehyde was 0.79%, MIBK and intermediates were 0.95%, MAK content was 55.73%, MAK intermediates were 0.31%, n-butyraldehyde self-polymer was 1.8%, and high-boiling-point substances were 11.36%. The chromatogram is shown below. Figure 6 As shown, 3.517 min is acetone, 3.886 min is n-butyraldehyde, and 8.304 min is MAK. Comparative Example 2 In a 1000mL hydrogenation reactor, 300g of acetone, 100g of 3% NaOH solution, and 4g of palladium-on-carbon catalyst were added. After sealing the reactor, hydrogen was used to purge the acetone. The reactor temperature was then set to 80℃ to activate the acetone, and stirring was started. By adding hydrogen, the pressure inside the reactor was adjusted to 1MPa. The liquid phase feed valve was opened, and n-butyraldehyde was continuously fed at a rate of 6ml / min, maintaining the reactor temperature below 85℃ and the pressure at approximately 2MPa. After 15 minutes of continuous feeding, the feed valve was closed, and the feeding was stopped. The reaction was maintained under pressure and temperature conditions for 40 minutes, with the pressure maintained by introducing hydrogen. After the reaction was completed, the temperature was lowered, and samples were taken for analysis. The results showed that the acetone content was 41.19%, n-butyraldehyde was 0.11%, MIBK and intermediates were 1.21%, MAK content was 40.38%, MAK intermediates were 0.04%, n-butyraldehyde self-polymer was 1.19%, and high-boiling-point substances were 11.86%. The chromatogram is shown below. Figure 7 As shown, 3.582 min is acetone, 3.944 min is n-butyraldehyde, and 8.474 min is MAK.

[0029] Comparing Examples 1 to 5 with Comparative Examples 1 and 2, it can be seen that the total molar amount of n-butyraldehyde exceeds 25% of acetone, and the feed molar amount per minute exceeds 0.8% of the total molar amount of acetone. This not only leads to an increase in the content of n-butyraldehyde self-polymers, but also to a significant increase in the content of high-boiling-point substances in the product. This increases the difficulty of post-processing and is not conducive to obtaining high-purity MAK products. Furthermore, the increase in high-boiling-point substances represents a decrease in the selectivity of MAK, which will increase the product consumption per unit and reduce the downgrading benefits.

[0030] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for synthesizing 2-heptanone, characterized in that, This involves adding n-butyraldehyde to an alkaline reaction system via continuous injection. The reaction system includes activated acetone and a hydrogenation catalyst, with acetone in excess relative to n-butyraldehyde.

2. The method for synthesizing 2-heptanone as described in claim 1, characterized in that, In the reaction system, the total molar amount of n-butyraldehyde added does not exceed 19% of the total molar amount of acetone at the start of the reaction.

3. The method for synthesizing 2-heptanone as described in claim 1, characterized in that, The molar amount of n-butyraldehyde added to the reaction system per minute shall not exceed 0.8% of the total molar amount of acetone in the reaction system at the start of the reaction.

4. The method for synthesizing 2-heptanone as described in claim 3, characterized in that, After all the n-butyraldehyde has been added, continue the reaction for 10-200 minutes.

5. The method for synthesizing 2-heptanone as described in claim 1, characterized in that, Before injecting n-butyraldehyde, maintain the reaction system in a hydrogen atmosphere.

6. The method for synthesizing 2-heptanone as described in claim 1, characterized in that, An alkaline solution is added to the system to form an alkaline reaction system. The mass of the alkaline solution added is 1 / 5 to 1 / 10 of the total mass of n-butyraldehyde and acetone. The concentration of hydroxide ions in the alkaline solution is 0.25-0.75 mol / L.

7. The method for synthesizing 2-heptanone as described in claim 1, characterized in that, Alkaline solutions include sodium hydroxide solution and potassium hydroxide solution.

8. The method for synthesizing 2-heptanone as described in claim 1, characterized in that, The reaction system is placed in a hydrogenation reactor. During the reaction, hydrogen gas is continuously introduced into the hydrogenation reactor to maintain the pressure inside the reactor at 0.5-4.0 MPa. During the reaction, the temperature of the reaction system is 80-95℃.

9. The method for synthesizing 2-heptanone as described in claim 1, characterized in that, Hydrogenation catalysts include one or both of Raney nickel catalysts and palladium on carbon catalysts.

10. The method for synthesizing 2-heptanone according to claim 1, characterized in that, The amount of hydrogenation catalyst is 2%-6% of the total mass of n-butyraldehyde.

Images