Method for preparing ketene by microwave-promoted acetic acid cracking dehydration

Abstract

The invention discloses a method for preparing ketene by promoting cracking dehydration of acetic acid through microwaves. The method comprises the following steps: S1, mixing acetic acid and a polymerization inhibitor, and carrying out vaporization treatment to obtain raw material gas; s2, introducing the raw material gas into a microwave reaction device filled with a catalyst, and carrying out microwave cracking reaction to obtain ketene; wherein the time of the microwave cracking reaction is 5-20 seconds, and the microwave frequency of the microwave cracking reaction is 100-200 MHZ. The method provided by the invention has the characteristics of low energy consumption, high reaction speed, high selectivity, difficulty in side reaction, simple and convenient process flow and small occupied area of equipment when being used for preparing the key raw material ketene of sorbic acid.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical synthesis, and in particular relates to a method for preparing ketene by dehydration of acetic acid promoted by microwave. Background Art

[0002] As an efficient and safe food preservative, sorbic acid is widely used in food preservation around the world. The most common method for producing sorbic acid is to condense crotonaldehyde with highly chemically active ketene in the presence of an inhibitor. Crotonaldehyde is formed by condensing abundant acetaldehyde under alkaline conditions. It is liquid at room temperature, easy to transport and store, and easy to obtain. In contrast, ketene is obtained by high-temperature cracking of acetic acid. Ketene is liquid at room temperature and has extremely high chemical activity. It is easy to self-polymerize into diketene, so ketene cannot be transported and stored and can only be prepared on site.

[0003] Chinese patent CN103570519A discloses an improved method for preparing ethylene ketone by dehydration of acetic acid, which specifically includes: mixing acetic acid and an inhibitor according to a certain mass, then vaporizing in an acetic acid evaporator at 120-140°C, and preheating to 300-400°C before entering a fixed bed reactor, and then contacting with a catalyst at 650-700°C to undergo a dehydration reaction for 3-10 seconds to generate ethylene ketone gas. In order to cool the ethylene ketone gas, it is necessary to first reduce its temperature to 110-160°C through a heat exchanger, and then use a brine cooler to further cool it down to recover the ethylene ketone product. It can be seen that this method requires extremely high temperatures to promote the dehydration reaction, and also requires complex cooling steps. The conditions for heating and cooling are relatively harsh, the energy consumption is large, and the equipment requirements are also high; in addition, side reactions may also occur in the process, leading to the generation of methane.

[0004] Therefore, there is an urgent need for a method for preparing ketene by microwave-promoted acetic acid decomposition and dehydration to solve the shortcomings of the existing technical problems. Summary of the invention

[0005] In view of the above problems, the purpose of the present invention is to provide a method for preparing ketene by microwave-promoted acetic acid decomposition and dehydration. The method provided by the present invention has the characteristics of low energy consumption, fast reaction speed, high selectivity, low occurrence of side reactions, simple process flow and small equipment footprint when preparing ketene, a key raw material of sorbic acid.

[0006] To achieve the above object, the present invention provides a method for preparing ketene by microwave-assisted acetic acid decomposition and dehydration, the steps comprising:

[0007] S1, mixing acetic acid and a polymerization inhibitor and then vaporizing them to obtain a raw gas;

[0008] S2. Feed the raw material gas into a microwave reaction device equipped with a catalyst for microwave cracking reaction to obtain ketene; wherein the time of the microwave cracking reaction is 5 - 20 s, and the microwave frequency of the microwave cracking reaction is 100 - 200 MHz.

[0009] Compared with the prior art, the present invention utilizes microwaves to intensify the local vibration of polar groups within molecules, generating a local high-temperature thermal effect to promote the occurrence of the reaction, thereby achieving an efficient cracking reaction within a short time (5 - 20 seconds); compared with the traditional high-temperature thermal cracking process, the method of the present invention greatly shortens the reaction time and improves the production efficiency. At the same time, the present invention can control the conversion rate and selectivity of the reaction only by precisely controlling the microwave frequency (100 - 200 MHz) and the reaction time (5 - 20 seconds), and can also reduce the occurrence of unnecessary side reactions, significantly improving the purity of the target product ketene. In addition, the microwave energy is concentrated at the key points of the reaction, resulting in a low overall temperature rise of the reactants but a high local temperature in the reaction area, which not only improves the energy utilization rate but also greatly reduces the energy consumption, realizing a green and environmentally friendly production process. Furthermore, the method of the present invention can obtain ketene only by performing a microwave cracking reaction in a microwave reaction device. The process flow is simple, reducing the complex configuration required by the traditional high-temperature thermal cracking process, reducing the floor area of the equipment, and at the same time simplifying the operation process, facilitating large-scale industrial application. Therefore, when using the method provided by the present invention to prepare ketene, the key raw material of sorbic acid, it has the characteristics of low energy consumption, fast reaction speed, high selectivity, difficult occurrence of side reactions, simple process flow, and small floor area of the equipment.

[0010] Further, the mass ratio of acetic acid to the inhibitor in the present invention is 1:0.001 - 0.03.

[0011] Further, the inhibitor in the present invention is at least one of hydroquinone, butylated hydroxytoluene (BHT), and tert-butylhydroquinone (TBHQ).

[0012] Further, the catalyst in the present invention is an HND-34 solid superacid catalyst.

[0013] Further, the vaporization temperature in step S1 of the present invention is 120 - 140 °C.

[0014] Further, the time of the microwave cracking reaction in the present invention is 10 s, and the microwave frequency of the microwave cracking reaction is 150 MHz.

[0015] Further, the microwave reaction device of the present invention includes a microwave reactor, a plurality of waveguide tubes, and a plurality of microwave generators. A reaction tube is provided inside the microwave reactor. The plurality of waveguide tubes are uniformly inserted into the microwave reactor along the length direction of the reaction tube and are in contact with the reaction tube. Each microwave generator is correspondingly connected to one end of each waveguide tube away from the reaction tube. The waveguide tubes are used to guide the microwave generated by the microwave generator into the reaction tube.

[0016] Further, the reaction tube of the present invention is in the shape of a rectangular prism.

[0017] Further, the plurality of waveguide tubes of the present invention are symmetrically distributed at the upper and lower ends of the reaction tube.

[0018] Further, an inlet flow controller is provided at the front end of the reaction tube of the present invention, and an outlet flow controller is provided at the rear end of the reaction tube. Description of the Drawings

[0019] Figure 1 It is a schematic structural diagram of the microwave reaction device used in the method of the present invention. Detailed Embodiments

[0020] To better illustrate the purpose, technical solution, and beneficial effects of the present invention, the present invention will be further described below in conjunction with embodiments and drawings. It should be noted that the scope of protection required by the present invention is not limited to the scope described in the embodiments.

[0021] The present invention provides a method for promoting the cracking and dehydration of acetic acid to prepare ketene by microwave, and the steps include:

[0022] S1. Mix acetic acid and an inhibitor and then perform vaporization treatment to obtain a raw material gas;

[0023] S2. Pass the raw material gas into a microwave reaction device equipped with a catalyst and perform a microwave cracking reaction to obtain ketene;

[0024] Among them, the time of the microwave cracking reaction is 5 - 20 s, and the microwave frequency of the microwave cracking reaction is 100 - 200 MHz. By precisely controlling only the microwave frequency (100 - 200 MHz) and the reaction time (5 - 20 seconds), the conversion rate and selectivity of the reaction can be controlled, and unnecessary side reactions can be reduced, resulting in a significant increase in the purity of the target product ketene. Preferably, when the time of the microwave cracking reaction is set to 10 seconds and the microwave frequency is 150 MHz, the purity of the target product ketene can reach the optimal level.

[0025] Among them, the mass ratio of acetic acid to the inhibitor in the present invention is 1:0.001 - 0.03. For example, the mass ratio of acetic acid to the inhibitor can be but is not limited to 1:0.001, 1:0.005, 1:0.01, 1:0.02, 1:0.03.

[0026] Among them, the polymerization inhibitor of the present invention is at least one of hydroquinone, butylated hydroxytoluene (BHT), and tert-butylhydroquinone (TBHQ). These polymerization inhibitors can effectively inhibit the occurrence of side reactions and improve the selectivity and purity of the target product ketene.

[0027] Among them, the catalyst of the present invention is the HND-34 solid superacid catalyst. Specifically, this catalyst is purchased from Jiangyin Nanda Synthetic Chemistry Co., Ltd.

[0028] Among them, the temperature of vaporization in step S1 is 120-140 °C. Specifically, the vaporization treatment can be carried out in an acetic acid evaporator.

[0029] Among them, please refer to Figure 1 , the microwave reaction device used in the method of the present invention includes a microwave reactor 1, a plurality of waveguide tubes 4, and a plurality of microwave generators 5. A reaction tube 2 is provided in the microwave reactor 1. A plurality of waveguide tubes 4 are uniformly inserted into the microwave reactor 1 along the length direction of the reaction tube 2 and are in contact with the reaction tube 2. Each microwave generator 5 is connected to one end of each waveguide tube 4 away from the reaction tube 2. The waveguide tube 4 is used to guide the microwave generated by the microwave generator 5 into the reaction tube 2. Specifically, the reaction tube 2 is in the shape of a rectangular prism. A plurality of waveguide tubes 4 are symmetrically distributed at the upper and lower ends of the reaction tube 2. More specifically, the microwave generator 5 is used to be connected to a microwave power source. The design of the microwave reaction device enables the microwave energy to be concentrated at the key points of the reaction, the local temperature rises, the energy utilization rate is improved, the energy consumption is reduced, and a green and environmentally friendly production process is realized. More specifically, the catalyst is filled in the reaction tube 2.

[0030] Among them, please continue to refer to Figure 1 , an inlet flow controller 3 is provided at the front end of the reaction tube 2 of the present invention, and an outlet flow controller 6 is provided at the rear end of the reaction tube 2. Specifically, by adjusting the inlet flow controller 3 and the outlet flow controller 6, it can be ensured that the raw material gas enters the reaction tube 2 at a set speed and the generated ketene is discharged from the reaction tube 2 at a set speed, thereby indirectly controlling the residence time of the raw material gas in the reaction tube 2, that is, the time of the microwave cracking reaction can be accurately controlled; therefore, by adjusting the inlet flow controller 3 and the outlet flow controller 6, the stability of the reaction conditions can be ensured. More specifically, the generated ketene enters a heat exchanger after being discharged from the outlet flow controller 6 to be cooled to the temperature required for sorbic acid synthesis, and then is introduced into the crotonaldehyde liquid of the sorbic acid synthesis device to produce sorbic acid polyester, and sorbic acid is obtained after depolymerization.

[0031] In order to illustrate the technical content and achieved technical effects of the present invention in detail, the following further description is made in conjunction with specific embodiments.

[0032] The catalysts in the examples and comparative examples were HND-34 solid superacid catalysts, which were purchased from Jiangyin Nanda Synthetic Chemistry Co., Ltd. The structures of the microwave reaction devices used in Examples 1 to 5 and Comparative Examples 1 to 3 were exactly the same. Specifically, as Figure 1 shown, the microwave reaction device includes a microwave reactor, eight waveguide tubes, and eight microwave generators.

[0033] Example 1

[0034] This example provides a method for preparing ketene by microwave-promoted acetic acid cracking and dehydration. The steps include:

[0035] S1. Mix acetic acid (content ≥ 99.0%) and hydroquinone in a mass ratio of 1:0.01, then enter the acetic acid evaporator and perform vaporization treatment at 128 - 132 °C to obtain the raw material gas;

[0036] S2. Pass the raw material gas into the reaction tube in the microwave reaction device. The reaction tube is filled with a catalyst. Start the microwave generator, set the microwave frequency to 150 MHz, and adjust the inlet flow controller and outlet flow controller to make the raw material gas stay in the reaction tube for 10 seconds, and then take out the sample from the outlet flow controller.

[0037] Example 2

[0038] This example provides a method for preparing ketene by microwave-promoted acetic acid cracking and dehydration. The steps include:

[0039] S1. Mix acetic acid (content ≥ 99.0%) and hydroquinone in a mass ratio of 1:0.01, then enter the acetic acid evaporator and perform vaporization treatment at 128 - 132 °C to obtain the raw material gas;

[0040] S2. Pass the raw material gas into the reaction tube in the microwave reaction device. The reaction tube is filled with a catalyst. Start the microwave generator, set the microwave frequency to 150 MHz, and adjust the inlet flow controller and outlet flow controller to make the raw material gas stay in the reaction tube for 15 seconds, and then take out the sample from the outlet flow controller.

[0041] Example 3

[0042] This example provides a method for preparing ketene by microwave-promoted acetic acid cracking and dehydration. The steps include:

[0043] S1. Mix acetic acid (content ≥ 99.0%) and hydroquinone in a mass ratio of 1:0.01, then enter the acetic acid evaporator and perform vaporization treatment at 128 - 132 °C to obtain the raw material gas;

[0044] S2. Feed the raw material gas into the reaction tube in the microwave reaction device. The reaction tube is filled with a catalyst. Start the microwave generator, set the microwave frequency to 150 MHz, and adjust the inlet flow controller and the outlet flow controller to make the raw material gas stay in the reaction tube for 6 seconds, and then take out the sample from the outlet flow controller.

[0045] Example 4

[0046] This example provides a method for preparing ketene by microwave - promoted acetic acid cracking and dehydration, and the steps include:

[0047] S1. Mix acetic acid (content ≥ 99.0%) and hydroquinone in a mass ratio of 1:0.01, then enter the acetic acid evaporator and perform vaporization treatment at 128 - 132 °C to obtain the raw material gas;

[0048] S2. Feed the raw material gas into the reaction tube in the microwave reaction device. The reaction tube is filled with a catalyst. Start the microwave generator, set the microwave frequency to 100 MHz, and adjust the inlet flow controller and the outlet flow controller to make the raw material gas stay in the reaction tube for 20 seconds, and then take out the sample from the outlet flow controller.

[0049] Example 5

[0050] This example provides a method for preparing ketene by microwave - promoted acetic acid cracking and dehydration, and the steps include:

[0051] S1. Mix acetic acid (content ≥ 99.0%) and hydroquinone in a mass ratio of 1:0.01, then enter the acetic acid evaporator and perform vaporization treatment at 128 - 132 °C to obtain the raw material gas;

[0052] S2. Feed the raw material gas into the reaction tube in the microwave reaction device. The reaction tube is filled with a catalyst. Start the microwave generator, set the microwave frequency to 200 MHz, and adjust the inlet flow controller and the outlet flow controller to make the raw material gas stay in the reaction tube for 6 seconds, and then take out the sample from the outlet flow controller.

[0053] Comparative Example 1

[0054] This comparative example provides a method for preparing ketene by microwave - promoted acetic acid cracking and dehydration, and the steps include:

[0055] S1. Mix acetic acid (content ≥ 99.0%) and hydroquinone in a mass ratio of 1:0.01, then enter the acetic acid evaporator and perform vaporization treatment at 128 - 132 °C to obtain the raw material gas;

[0056] S2. Feed the raw material gas into the reaction tube in the microwave reaction device. The reaction tube is filled with a catalyst. Start the microwave generator, set the microwave frequency to 250 MHz, and adjust the inlet flow controller and the outlet flow controller to make the raw material gas stay in the reaction tube for 6 seconds, and then take out the sample from the outlet flow controller.

[0057] Comparative Example 2

[0058] This comparative example provides a method for preparing ketene by microwave-promoted acetic acid cracking and dehydration, and the steps include:

[0059] S1. Mix acetic acid (content ≥ 99.0%) and hydroquinone in a mass ratio of 1:0.01, then feed them into an acetic acid evaporator and perform vaporization treatment at 128 - 132 °C to obtain the raw material gas;

[0060] S2. Feed the raw material gas into the reaction tube in the microwave reaction device. The reaction tube is filled with a catalyst. Start the microwave generator, set the microwave frequency to 50 MHz, and adjust the inlet flow controller and the outlet flow controller to make the raw material gas stay in the reaction tube for 20 seconds, and then take out the sample from the outlet flow controller.

[0061] Comparative Example 3

[0062] This comparative example provides a method for preparing ketene by microwave-promoted acetic acid cracking and dehydration, and the steps include:

[0063] S1. Mix acetic acid (content ≥ 99.0%) and hydroquinone in a mass ratio of 1:0.01, then feed them into an acetic acid evaporator and perform vaporization treatment at 128 - 132 °C to obtain the raw material gas;

[0064] S2. Feed the raw material gas into the reaction tube in the microwave reaction device. The reaction tube is filled with a catalyst. Start the microwave generator, set the microwave frequency to 150 MHz, and adjust the inlet flow controller and the outlet flow controller to make the raw material gas stay in the reaction tube for 30 seconds, and then take out the sample from the outlet flow controller.

[0065] Measure the total mass M of the samples taken from the outlet flow controllers in Examples 1 - 5 and Comparative Examples 1 - 3 respectively, and then measure the mass M 1 of acetic acid and the mass M 2 of ketene in the taken samples by gas chromatography method. Then, the acetic acid conversion rate = (M - M 1 ) / M × 100%; the ketene purity = M 2 / M × 100%. The measurement results of the acetic acid conversion rate and ketene purity in the samples taken from Examples 1 - 5 and Comparative Examples 1 - 3 are shown in Table 1.

[0066] Table 1

[0067]

[0068]

[0069] As can be seen from Table 1, the acetic acid conversion rates of the methods provided in Examples 1 to 5 are generally high, ranging from 96.1% to 99.3%; at the same time, the ketene purity is also high, ranging from 93.7% to 96.3%. This indicates that the present invention can control the conversion rate and selectivity of the reaction only by precisely controlling the microwave frequency (100 - 200 MHz) and the reaction time (5 - 20 seconds), and can also reduce the occurrence of unnecessary side reactions, thereby being able to efficiently promote the cracking of acetic acid and generate high-purity ketene.

[0070] By comparing Examples 1 - 5 with Comparative Examples 1 - 3, it is found that the acetic acid conversion rates of Comparative Example 1 and Comparative Example 3 are very high, but their ketene purities are significantly lower than those of the examples; while the acetic acid conversion rate and ketene purity of Comparative Example 2 are both significantly lower than those of the examples. This indicates that when the microwave frequency is not within the range of 100 - 200 MHz and the reaction time is not within the range of 5 - 20 seconds, it will affect the conversion rate and selectivity of the reaction and also result in more by-products.

[0071] In summary, the method for preparing ketene by microwave-promoted acetic acid cracking and dehydration provided by the present invention significantly improves the purity of ketene while increasing the acetic acid conversion rate, and has significant technical advantages and application prospects.

[0072] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention and not to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, it is not limited to only those listed in the examples. Those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing ketene by microwave-assisted acetic acid decomposition and dehydration, characterized in that the steps include: S1, mixing acetic acid and a polymerization inhibitor and then vaporizing them to obtain a raw gas; S2, passing the raw gas into a microwave reaction device equipped with a catalyst to carry out microwave cracking reaction to obtain ethylene ketone; wherein the time of the microwave cracking reaction is 5 to 20 seconds, and the microwave frequency of the microwave cracking reaction is 100 to 200 MHZ.

2. The method for preparing ketene by microwave-assisted acetic acid decomposition and dehydration as claimed in claim 1, characterized in that: The mass ratio of the acetic acid to the polymerization inhibitor is 1:0.001-0.

03.

3. The method for preparing ketene by microwave-assisted acetic acid decomposition and dehydration as claimed in claim 1, characterized in that: The polymerization inhibitor is at least one of hydroquinone, butylated hydroxytoluene and tert-butylhydroquinone.

4. The method for preparing ketene by microwave-assisted acetic acid decomposition and dehydration as claimed in claim 1, characterized in that: The catalyst is HND-34 solid super acid catalyst.

5. The method for preparing ketene by microwave-assisted acetic acid decomposition and dehydration as claimed in claim 1, characterized in that: The temperature of the vaporization treatment in step S1 is 120-140°C.

6. The method for preparing ketene by microwave-assisted acetic acid decomposition and dehydration as claimed in claim 1, characterized in that: The time of the microwave cracking reaction is 10 s, and the microwave frequency of the microwave cracking reaction is 150 MHZ.

7. The method for preparing ketene by microwave-assisted acetic acid decomposition and dehydration as claimed in claim 1, characterized in that: The microwave reaction device comprises a microwave reactor, a plurality of waveguides and a plurality of microwave generators. A reaction tube is arranged in the microwave reactor. The plurality of waveguides are uniformly inserted into the microwave reactor along the length direction of the reaction tube and abut against the reaction tube. Each microwave generator is connected to one end of each waveguide away from the reaction tube in a one-to-one correspondence. The waveguide is used to guide the microwave generated by the microwave generator to be conducted into the reaction tube.

8. The method for preparing ketene by microwave-assisted acetic acid decomposition and dehydration as claimed in claim 7, characterized in that: The reaction tube is in the shape of a rectangular column.

9. The method for preparing ketene by microwave-assisted acetic acid decomposition and dehydration as claimed in claim 8, characterized in that: A plurality of waveguides are symmetrically distributed at the upper and lower ends of the reaction tube.

10. The method for preparing ketene by microwave-assisted acetic acid decomposition and dehydration as claimed in claim 7, characterized in that: An inlet flow controller is arranged at the front end of the reaction tube, and an outlet flow controller is arranged at the rear end of the reaction tube.

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