Synthesis process of metaldehyde

Abstract

The invention discloses a synthesis process of metaldehyde, which belongs to the technical field of organic synthesis, and comprises the following steps: S1, adding acetaldehyde into a polymerization kettle, and pre-cooling the polymerization kettle to be less than or equal to-15 DEG C; s2, adding a catalyst into the polymerization kettle in batches, and carrying out polymerization reaction; s3, after the catalyst is added, controlling the temperature of the kettle at 4-6 DEG C, keeping the temperature for 1-2 hours to obtain a mixture, performing centrifugal filtration on the mixture, and cleaning and drying a solid material to obtain metaldehyde; wherein in the polymerization reaction process, the polymerization kettle adopts an external heat exchanger to take away heat generated by the reaction so as to control the temperature of the polymerization kettle. According to the invention, the external heat exchanger is adopted to take away the heat generated by the reaction in the reaction process, so that the reaction temperature can be accurately controlled, the reaction time is shortened, and the production efficiency is improved; meanwhile, by adding the catalyst in batches, the catalyst can continuously play a role in the reaction process, so that the reaction efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of organic synthesis, and particularly relates to a synthesis process of metaldehyde. Background Art

[0002] Metaldehyde is a white needle-shaped crystal with the characteristics of high combustion temperature, stable flame, non-volatility, and insolubility in water. It is known as solid alcohol and can be used to make firecrackers, fireworks, and colored candles. It can replace silver iodide as an artificial rainmaking agent. It can also be used to kill snails, slugs and other lung-type soft-bodied pests and snails that are parasitic on blood-sucking worms.

[0003] In the prior art, the synthesis method of metaldehyde mostly uses hydrochloric acid as a catalyst and a chilled water circulation pump for cooling. Under low temperature conditions, acetaldehyde is polymerized to generate metaldehyde. This method has a long reaction time, is difficult to control the temperature, and causes serious equipment corrosion. Therefore, it needs to be improved. Summary of the invention

[0004] In view of the above situation, in order to overcome at least part of the defects of the above prior art, the present invention provides a synthesis process of metaldehyde.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows: The present invention provides a synthesis process of metaldehyde, comprising the following steps: S1. Add acetaldehyde into the polymerization kettle and pre-cool the polymerization kettle to ≦-15°C; S2, adding catalyst into the polymerization kettle in batches to carry out polymerization reaction; S3. After the catalyst is added, the kettle temperature is controlled at 4°C-6°C and kept warm for 1-2 hours to obtain a mixture, the mixture is centrifuged and filtered, and the solid material is washed and dried to obtain tetraacetaldehyde; During the polymerization reaction, the polymerization kettle uses an external heat exchanger to take away the heat generated by the reaction to control the temperature of the polymerization kettle.

[0006] In some embodiments, the specific step of adding the catalyst in step S2 is: Add the catalyst into the polymerization kettle and control the temperature of the polymerization kettle not to exceed 0°C; When the temperature in the polymerization kettle drops to ≦-10°C, add the catalyst into the polymerization kettle and control the temperature of the polymerization kettle not to exceed 5°C; When the temperature in the polymerization kettle drops to ≤-5°C, add the catalyst into the polymerization kettle and control the temperature of the polymerization kettle not to exceed 10°C.

[0007] In some embodiments, the time from the start of adding the catalyst to the completion of adding the catalyst is 6 hours to 9 hours.

[0008] In some embodiments, the catalyst is added in an amount of 0.5%-3% by mass of acetaldehyde.

[0009] In some embodiments, the amount of the catalyst added is increased sequentially.

[0010] In some embodiments, the catalyst is activated carbon-supported phosphotungstic acid, and the preparation method of activated carbon-supported phosphotungstic acid comprises the following steps: Take the activated carbon, wash it with distilled water and dry it, dissolve the phosphotungstic acid in ether, add the activated carbon under stirring, soak for 2 hours to 4 hours, filter after the soaking, and dry to obtain the activated carbon loaded with phosphotungstic acid.

[0011] In some embodiments, the mass ratio of the activated carbon to phosphotungstic acid is (3-5):(1-2).

[0012] In some embodiments, the drying is constant temperature drying at a temperature of 60° C. for a time of 2 hours to 4 hours.

[0013] In some embodiments, the synthesis process of metaldehyde further comprises: The filtrate obtained by centrifugal filtration is sent to a depolymerization kettle, a depolymerization catalyst is added, and the mixture is heated to 45°C-70°C to depolymerize trimeraldehyde into acetaldehyde, which is then recovered by distillation.

[0014] In some embodiments, the depolymerization catalyst is sulfuric acid.

[0015] The beneficial effects achieved by the present invention are as follows: During the reaction process, an external heat exchanger is used to remove the heat generated by the reaction, so that the reaction temperature can be controlled more accurately, thereby shortening the reaction time and improving production efficiency; By adding the catalyst in batches, the catalyst can continue to work during the reaction, thereby improving the reaction efficiency; Activated carbon-loaded phosphotungstic acid is used instead of hydrochloric acid as a catalyst. Compared with hydrochloric acid, the phosphotungstic acid catalyst does not produce corrosive gases or waste, is more environmentally friendly, and can also reduce equipment corrosion and increase the service life of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The graph is a result of the yield of tetraacetaldehyde in Examples 1-6 of the present invention and Comparative Examples 1 and 2.

[0017] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0019] Unless otherwise defined, all professional and scientific terms used herein have the same meanings as those familiar to those skilled in the art. In addition, any methods and materials similar or equivalent to those described herein may be applied to the present invention. The preferred implementation methods and materials described herein are for demonstration purposes only and are not intended to limit the content of this application.

[0020] In view of the deficiencies in the prior art mentioned in the background technology, the present invention proposes a synthesis process of tetraacetaldehyde, comprising the following steps: S1. Add acetaldehyde into the polymerization kettle and pre-cool the polymerization kettle to ≦-15°C; S2, adding catalyst into the polymerization kettle in batches to carry out polymerization reaction; S3. After the catalyst is added, the kettle temperature is controlled at 4°C-6°C and kept warm for 1-2 hours to obtain a mixture, the mixture is centrifuged and filtered, and the solid material is washed and dried to obtain tetraacetaldehyde; During the polymerization reaction, the polymerization kettle uses an external heat exchanger to take away the heat generated by the reaction to control the temperature of the polymerization kettle.

[0021] Since acetaldehyde releases a large amount of heat during its polymerization reaction, if the heat generated by the reaction cannot be removed in time, the reaction temperature will be too high and a large amount of by-products will be produced. The external heat exchanger has good heat transfer performance. The heat generated by the reaction can be removed in time through the external heat exchanger, which can greatly shorten the reaction time and improve production efficiency. At the same time, by adding the catalyst in batches, the catalyst can continue to play a role in the reaction process, thereby improving the reaction efficiency.

[0022] In some embodiments, the specific step of adding the catalyst in step S2 is: Add the catalyst into the polymerization kettle and control the temperature of the polymerization kettle not to exceed 0°C; When the temperature in the polymerization kettle drops to ≦-10°C, add the catalyst into the polymerization kettle and control the temperature of the polymerization kettle not to exceed 5°C; When the temperature in the polymerization kettle drops to ≤-5°C, add the catalyst into the polymerization kettle and control the temperature of the polymerization kettle not to exceed 10°C.

[0023] In some embodiments, the time from the start of adding the catalyst to the completion of adding the catalyst is 6 hours to 9 hours. By controlling the time of adding the catalyst, it is possible to avoid the catalyst being added too short, resulting in a runaway reaction, and at the same time, it is possible to avoid the catalyst being added too long, resulting in an insufficient reaction, thereby improving the controllability of the reaction and making the reaction sufficient.

[0024] In some embodiments, the catalyst is added in an amount of 0.5%-3% by mass of acetaldehyde.

[0025] In some embodiments, the amount of the catalyst added is increased in sequence, thereby gradually accelerating the reaction process and improving the reaction efficiency.

[0026] In some embodiments, the catalyst is activated carbon-supported phosphotungstic acid, and the preparation method of activated carbon-supported phosphotungstic acid comprises the following steps: Take the activated carbon, wash it with distilled water and dry it, dissolve the phosphotungstic acid in ether, add the activated carbon under stirring, soak for 2 hours to 4 hours, filter after the soaking, and dry to obtain the activated carbon loaded with phosphotungstic acid.

[0027] Among them, phosphotungstic acid has good catalytic activity. Compared with hydrochloric acid phosphotungstic acid catalyst, it does not produce corrosive gas or waste, is more environmentally friendly, and can reduce equipment corrosion and increase the service life of equipment. Loading phosphotungstic acid on activated carbon can improve the stability of phosphotungstic acid and increase the active sites on the surface of phosphotungstic acid, thereby improving the catalytic activity of phosphotungstic acid.

[0028] In some embodiments, the mass ratio of the activated carbon to phosphotungstic acid is (3-5):(1-2). Excessive activated carbon will reduce the catalytic activity of the catalyst, and excessive phosphotungstic acid will cause the activated carbon to be unable to be fully loaded, resulting in waste.

[0029] In some embodiments, the drying is constant temperature drying at a temperature of 60° C. for a time of 2 hours to 4 hours.

[0030] In some embodiments, the synthesis process of metaldehyde further comprises: The filtrate obtained by centrifugal filtration is sent to a depolymerization kettle, a depolymerization catalyst is added, and the mixture is heated to 45°C-70°C to depolymerize trimeraldehyde into acetaldehyde, which is then recovered by distillation.

[0031] Among them, the recovered acetaldehyde can be directly used in the next polymerization reaction.

[0032] In some embodiments, the depolymerization catalyst is sulfuric acid.

[0033] The present invention will be further described below by way of specific embodiments.

[0034] The experimental methods in the following examples are conventional methods unless otherwise specified; the experimental materials used in the following examples are purchased from commercial channels unless otherwise specified.

[0035] Example 1 Preparation of catalyst: Take the activated carbon, wash it with distilled water and then dry it, dissolve 50g of phosphotungstic acid in ether, add activated carbon under stirring, the mass ratio of activated carbon to phosphotungstic acid is 3:1, soak for 2 hours, filter after soaking, dry at 60℃ for 2 hours, and obtain activated carbon loaded with phosphotungstic acid.

[0036] Polymerization reaction: S1. Add 1000g of acetaldehyde into the polymerization kettle and pre-cool the polymerization kettle to ≦-15°C; S2, add 5g of catalyst into the polymerization kettle, and control the temperature of the polymerization kettle not to exceed 0°C; When the temperature in the polymerization kettle drops to ≦-10°C, add 15g of catalyst into the polymerization kettle, and control the temperature of the polymerization kettle not to exceed 5°C; When the temperature in the polymerization kettle drops to ≤-5°C, add 30g of catalyst into the polymerization kettle, and control the temperature of the polymerization kettle not to exceed 10°C; S3. After the catalyst is added, the kettle temperature is controlled at 4°C and kept warm for 1 hour to obtain a mixture, the mixture is centrifuged and filtered, and the solid material is washed and dried to obtain tetraacetaldehyde; S4, sending the filtrate obtained by centrifugal filtration to a depolymerization kettle, adding sulfuric acid as a depolymerization catalyst, heating to 45° C., depolymerizing the trimeraldehyde into acetaldehyde, and recovering the acetaldehyde by distillation; During the polymerization reaction, the polymerization kettle uses an external heat exchanger to take away the heat generated by the reaction to control the temperature of the polymerization kettle.

[0037] Example 2 Preparation of catalyst: Take the activated carbon, wash it with distilled water and then dry it, dissolve 50g of phosphotungstic acid in ether, add activated carbon under stirring, the mass ratio of activated carbon to phosphotungstic acid is 3:2, soak for 3 hours, filter after soaking, dry at 60℃ for 3 hours, and obtain activated carbon loaded with phosphotungstic acid.

[0038] Polymerization reaction: S1. Add 1000g of acetaldehyde into the polymerization kettle and pre-cool the polymerization kettle to ≦-15°C; S2, add 5g of catalyst into the polymerization kettle, and control the temperature of the polymerization kettle not to exceed 0°C; When the temperature in the polymerization kettle drops to ≦-10°C, add 20g of catalyst into the polymerization kettle, and control the temperature of the polymerization kettle not to exceed 5°C; When the temperature in the polymerization kettle drops to ≤-5°C, add 30g of catalyst into the polymerization kettle, and control the temperature of the polymerization kettle not to exceed 10°C; S3. After the catalyst is added, the kettle temperature is controlled at 4°C and kept warm for 2 hours to obtain a mixture, the mixture is centrifuged and filtered, and the solid material is washed and dried to obtain tetraacetaldehyde; S4, sending the filtrate obtained by centrifugal filtration to a depolymerization kettle, adding sulfuric acid as a depolymerization catalyst, heating to 70° C., depolymerizing the trimeraldehyde into acetaldehyde, and recovering the acetaldehyde by distillation; During the polymerization reaction, the polymerization kettle uses an external heat exchanger to take away the heat generated by the reaction to control the temperature of the polymerization kettle.

[0039] Example 3 Preparation of catalyst: Take the activated carbon, wash it with distilled water and then dry it, dissolve 50g of phosphotungstic acid in ether, add activated carbon under stirring, the mass ratio of activated carbon to phosphotungstic acid is 5:2, soak for 2 hours, filter after soaking, dry at 60℃ for 2 hours, and obtain activated carbon loaded with phosphotungstic acid.

[0040] Polymerization reaction: S1. Add 1000g of acetaldehyde into the polymerization kettle and pre-cool the polymerization kettle to ≦-15°C; S2, add 10g of catalyst into the polymerization kettle, and control the temperature of the polymerization kettle not to exceed 0°C; When the temperature in the polymerization kettle drops to ≦-10°C, add 15g of catalyst into the polymerization kettle, and control the temperature of the polymerization kettle not to exceed 5°C; When the temperature in the polymerization kettle drops to ≤-5°C, add 30g of catalyst into the polymerization kettle, and control the temperature of the polymerization kettle not to exceed 10°C; S3. After the catalyst is added, the kettle temperature is controlled at 6°C and kept warm for 1 hour to obtain a mixture, the mixture is centrifuged and filtered, and the solid material is washed and dried to obtain tetraacetaldehyde; S4, sending the filtrate obtained by centrifugal filtration to a depolymerization kettle, adding sulfuric acid as a depolymerization catalyst, heating to 50° C., depolymerizing trimeraldehyde into acetaldehyde, and recovering the acetaldehyde by distillation; During the polymerization reaction, the polymerization kettle uses an external heat exchanger to take away the heat generated by the reaction to control the temperature of the polymerization kettle.

[0041] Example 4 Preparation of catalyst: Take the activated carbon, wash it with distilled water and then dry it, dissolve 50g of phosphotungstic acid in ether, add activated carbon under stirring, the mass ratio of activated carbon to phosphotungstic acid is 5:1, soak for 4 hours, filter after soaking, dry at 60℃ for 4 hours, and obtain activated carbon loaded with phosphotungstic acid.

[0042] Polymerization reaction: S1. Add 1000g of acetaldehyde into the polymerization kettle and pre-cool the polymerization kettle to ≦-15°C; S2, add 10g of catalyst into the polymerization kettle, and control the temperature of the polymerization kettle not to exceed 0°C; When the temperature in the polymerization kettle drops to ≦-10°C, add 20g of catalyst into the polymerization kettle, and control the temperature of the polymerization kettle not to exceed 5°C; When the temperature in the polymerization kettle drops to ≤-5°C, add 30g of catalyst into the polymerization kettle, and control the temperature of the polymerization kettle not to exceed 10°C; S3. After the catalyst is added, the kettle temperature is controlled at 6°C and kept warm for 2 hours to obtain a mixture, the mixture is centrifuged and filtered, and the solid material is washed and dried to obtain tetraacetaldehyde; S4, sending the filtrate obtained by centrifugal filtration to a depolymerization kettle, adding sulfuric acid as a depolymerization catalyst, heating to 60° C., depolymerizing the trimeraldehyde into acetaldehyde, and recovering the acetaldehyde by distillation; During the polymerization reaction, the polymerization kettle uses an external heat exchanger to take away the heat generated by the reaction to control the temperature of the polymerization kettle.

[0043] Example 5 Preparation of catalyst: Take the activated carbon, wash it with distilled water and then dry it, dissolve 50g of phosphotungstic acid in ether, add activated carbon under stirring, the mass ratio of activated carbon to phosphotungstic acid is 4:1, soak for 4 hours, filter after soaking, dry at 60℃ for 4 hours, and obtain activated carbon loaded with phosphotungstic acid.

[0044] Polymerization reaction: S1. Add 1000g of acetaldehyde into the polymerization kettle and pre-cool the polymerization kettle to ≦-15°C; S2, add 5g of catalyst into the polymerization kettle, and control the temperature of the polymerization kettle not to exceed 0°C; When the temperature in the polymerization kettle drops to ≦-10°C, add 10g of catalyst into the polymerization kettle, and control the temperature of the polymerization kettle not to exceed 5°C; When the temperature in the polymerization kettle drops to ≤-5°C, add 20g of catalyst into the polymerization kettle, and control the temperature of the polymerization kettle not to exceed 10°C; S3. After the catalyst is added, the kettle temperature is controlled at 5°C and kept warm for 1 hour to obtain a mixture, the mixture is centrifuged and filtered, and the solid material is washed and dried to obtain tetraacetaldehyde; S4, sending the filtrate obtained by centrifugal filtration to a depolymerization kettle, adding sulfuric acid as a depolymerization catalyst, heating to 65° C., depolymerizing the trimeraldehyde into acetaldehyde, and recovering the acetaldehyde by distillation; During the polymerization reaction, the polymerization kettle uses an external heat exchanger to take away the heat generated by the reaction to control the temperature of the polymerization kettle.

[0045] Example 6 Preparation of catalyst: Take the activated carbon, wash it with distilled water and then dry it, dissolve 50g of phosphotungstic acid in ether, add activated carbon under stirring, the mass ratio of activated carbon to phosphotungstic acid is 4:2, soak for 3 hours, filter after soaking, dry at 60℃ for 3 hours, and obtain activated carbon loaded with phosphotungstic acid.

[0046] Polymerization reaction: S1. Add 1000g of acetaldehyde into the polymerization kettle and pre-cool the polymerization kettle to ≦-15°C; S2, add 5g of catalyst into the polymerization kettle, and control the temperature of the polymerization kettle not to exceed 0°C; When the temperature in the polymerization kettle drops to ≦-10°C, add 15g of catalyst into the polymerization kettle, and control the temperature of the polymerization kettle not to exceed 5°C; When the temperature in the polymerization kettle drops to ≤-5°C, add 20g of catalyst into the polymerization kettle, and control the temperature of the polymerization kettle not to exceed 10°C; S3. After the catalyst is added, the kettle temperature is controlled at 5°C and kept warm for 2 hours to obtain a mixture, which is centrifuged and filtered, and the solid material is washed and dried to obtain tetraacetaldehyde; S4, sending the filtrate obtained by centrifugal filtration to a depolymerization kettle, adding sulfuric acid as a depolymerization catalyst, heating to 55° C., depolymerizing the trimeraldehyde into acetaldehyde, and recovering the acetaldehyde by distillation; During the polymerization reaction, the polymerization kettle uses an external heat exchanger to take away the heat generated by the reaction to control the temperature of the polymerization kettle.

[0047] Comparative Example 1 The difference between this comparative example and Example 1 is that hydrochloric acid is used instead of activated carbon-supported phosphotungstic acid as the catalyst, and the steps of the polymerization reaction are the same as those in Example 1.

[0048] Comparative Example 2 The difference between this comparative example and Example 1 is that a chilled water circulation pump is used instead of the external heat exchanger, and the steps of the polymerization reaction are the same as those in Example 1.

[0049] Figure 1 The yields of tetraacetaldehyde in Examples 1-6 and Comparative Examples 1 and 2 are shown in the figure. The yields of Comparative Examples 1 and 2 are both lower than that of Example 1.

[0050] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should be included in the protection scope of the present invention.

Claims

1. A synthesis process of metaldehyde, characterized in that: The steps include: S1. Add acetaldehyde into the polymerization kettle and pre-cool the polymerization kettle to ≦-15°C; S2, adding catalyst into the polymerization kettle in batches to carry out polymerization reaction; S3. After the catalyst is added, the kettle temperature is controlled at 4°C-6°C and kept warm for 1-2 hours to obtain a mixture, the mixture is centrifuged and filtered, and the solid material is washed and dried to obtain tetraacetaldehyde; During the polymerization reaction, the polymerization kettle uses an external heat exchanger to take away the heat generated by the reaction to control the temperature of the polymerization kettle.

2. The synthesis process of metaldehyde according to claim 1, characterized in that: The specific steps of adding the catalyst in step S2 are: Add the catalyst into the polymerization kettle and control the temperature of the polymerization kettle not to exceed 0°C; When the temperature in the polymerization kettle drops to ≦-10°C, add the catalyst into the polymerization kettle and control the temperature of the polymerization kettle not to exceed 5°C; When the temperature in the polymerization kettle drops to ≤-5°C, add the catalyst into the polymerization kettle and control the temperature of the polymerization kettle not to exceed 10°C.

3. The synthesis process of metaldehyde according to claim 2, characterized in that: The time from the start of adding the catalyst to the completion of adding the catalyst is 6 hours to 9 hours.

4. The synthesis process of metaldehyde according to claim 2, characterized in that: The amount of the catalyst added is 0.5%-3% of the mass of acetaldehyde.

5. The synthesis process of metaldehyde according to claim 4, characterized in that: The amount of the catalyst added increases gradually.

6. The synthesis process of metaldehyde according to claim 1, characterized in that: The catalyst is activated carbon-supported phosphotungstic acid, and the preparation method of activated carbon-supported phosphotungstic acid comprises the following steps: Take the activated carbon, wash it with distilled water and dry it, dissolve the phosphotungstic acid in ether, add the activated carbon under stirring, soak for 2 hours to 4 hours, filter after the soaking, and dry to obtain the activated carbon loaded with phosphotungstic acid.

7. The synthesis process of metaldehyde according to claim 6, characterized in that: The mass ratio of the activated carbon to phosphotungstic acid is (3-5):(1-2).

8. The synthesis process of metaldehyde according to claim 6, characterized in that: The drying is constant temperature drying, the temperature is 60° C., and the time is 2 hours to 4 hours.

9. The synthesis process of metaldehyde according to claim 1, characterized in that: Also includes: The filtrate obtained by centrifugal filtration is sent to a depolymerization kettle, a depolymerization catalyst is added, and the mixture is heated to 45°C-70°C to depolymerize trimeraldehyde into acetaldehyde, which is then recovered by distillation.

10. The synthesis process of metaldehyde according to claim 9, characterized in that: The depolymerization catalyst is sulfuric acid.

Images