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2021-06-16
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Preparation methods and precautions of acetic anhydride
- Categories:Idustry News
- Time of issue:2021-06-15
- Views:924
Preparation methods and precautions of acetic anhydride
- Categories:Idustry News
- Time of issue:2021-06-15
- Views:924
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Acetic anhydride can be produced by artificial synthesis and bacterial fermentation. Biosynthesis, that is, bacterial fermentation, accounts for only 10% of the world's production, but it is still an important method to produce acetic anhydride, especially acetic acid, because many food safety regulations stipulate that vinegar in food must be prepared by biological method, and fermentation method can be divided into aerobic fermentation method and anaerobic fermentation method. 1. Aerobic fermentation
With sufficient oxygen, Acetobacter can produce acetic anhydride from alcoholic food. Usually used is cider or wine mixed with grains, malt, rice or potato mashed fermentation. The specific method is to inoculate the Acetobacter bacteria in the diluted alcohol solution and keep the temperature, and place it in a ventilated position. Within a few months, it can be fermented to produce acetic anhydride products. The method of industrial production of vinegar accelerates the reaction process by providing sufficient oxygen. This method has been used in commercial production, also known as "fast method" or "German method". It is named after its successful application in Germany in 1823. In this method, fermentation is carried out in a tower filled with sawdust or charcoal. The raw material containing alcohol drips in from the top of the tower, and the fresh air naturally enters or is forced to convection from the bottom. This process can be completed in a few weeks due to the enhanced air volume, which greatly shortens the vinegar making time.
2. Anaerobic fermentation
Some anaerobic bacteria, including some members of Clostridium, can convert sugars directly to acetic acid without using ethanol as an intermediate. Because Clostridium has the ability to react with sugars, it reduces the cost, which means that these bacteria have the potential to produce acetic acid more efficiently than Acetobacter. However, Clostridium is less acid tolerant than Acetobacter. Clostridium with high acid resistance can only produce less than 10% acetic acid, while some acetic anhydride bacteria can produce 20% acetic acid. It is still more economical to concentrate vinegar with acetic acid bacteria than with Clostridium bacteria. Therefore, although Clostridium has been found as early as 1940, its industrial application is narrow.
3. Acetaldehyde oxidation
Before the commercial production of Monsanto method, most acetic acid was prepared by oxidation of acetaldehyde. Although it can not be compared with methyl carbonylation, this method is still the second industrial method to produce acetic acid. Acetaldehyde can be prepared by oxidation of butane or light naphtha, or by hydration of ethylene.
4. Liquid phase oxidation of low carbon alkanes
Using n-butane as raw material, acetic anhydride as solvent, air as oxidant was used at 170 ℃ - 180 ℃, 5.5 MPa and cobalt acetate as catalyst. At the same time, LPG or light oil can also be used as raw materials. The raw material cost of this method is low, but the process flow is long, the corrosion is serious, and the yield of acetic anhydride is not high. It is only used in the areas where the cheap isobutane or LPG raw materials are easily available. The reaction can be carried out at high temperature and pressure to keep butane liquid. The by-products include butanone, ethyl acetate, formic acid and propionic acid. Because some by-products have economic value, the reaction conditions can be adjusted to produce more by-products, but the separation of acetic acid and by-products increases the cost of the reaction. Under similar conditions, acetic anhydride can be oxidized to acetic acid by oxygen in air. More than 95% yield of acetic acid can be obtained by using new catalyst. The main by-products are ethyl acetate, formic acid and formaldehyde. Because the boiling point of by-products is lower than that of acetic acid, they can be easily removed by distillation.
5. Ethylene oxidation process
It is formed by the reaction of ethylene with oxygen in the presence of catalyst. This reaction can be regarded as the first oxidation of ethylene to acetaldehyde, and then by acetaldehyde oxidation.
6. Topso method
Topso process uses natural gas or coal as raw material. Step 1: the synthesis gas generates methanol and dimethyl ether under the catalyst; The second part: methanol and dimethyl ether (both do not need purification) and co carbonylation to produce acetic acid, this method is also called two-step method.
With sufficient oxygen, Acetobacter can produce acetic anhydride from alcoholic food. Usually used is cider or wine mixed with grains, malt, rice or potato mashed fermentation. The specific method is to inoculate the Acetobacter bacteria in the diluted alcohol solution and keep the temperature, and place it in a ventilated position. Within a few months, it can be fermented to produce acetic anhydride products. The method of industrial production of vinegar accelerates the reaction process by providing sufficient oxygen. This method has been used in commercial production, also known as "fast method" or "German method". It is named after its successful application in Germany in 1823. In this method, fermentation is carried out in a tower filled with sawdust or charcoal. The raw material containing alcohol drips in from the top of the tower, and the fresh air naturally enters or is forced to convection from the bottom. This process can be completed in a few weeks due to the enhanced air volume, which greatly shortens the vinegar making time.
2. Anaerobic fermentation
Some anaerobic bacteria, including some members of Clostridium, can convert sugars directly to acetic acid without using ethanol as an intermediate. Because Clostridium has the ability to react with sugars, it reduces the cost, which means that these bacteria have the potential to produce acetic acid more efficiently than Acetobacter. However, Clostridium is less acid tolerant than Acetobacter. Clostridium with high acid resistance can only produce less than 10% acetic acid, while some acetic anhydride bacteria can produce 20% acetic acid. It is still more economical to concentrate vinegar with acetic acid bacteria than with Clostridium bacteria. Therefore, although Clostridium has been found as early as 1940, its industrial application is narrow.
3. Acetaldehyde oxidation
Before the commercial production of Monsanto method, most acetic acid was prepared by oxidation of acetaldehyde. Although it can not be compared with methyl carbonylation, this method is still the second industrial method to produce acetic acid. Acetaldehyde can be prepared by oxidation of butane or light naphtha, or by hydration of ethylene.
4. Liquid phase oxidation of low carbon alkanes
Using n-butane as raw material, acetic anhydride as solvent, air as oxidant was used at 170 ℃ - 180 ℃, 5.5 MPa and cobalt acetate as catalyst. At the same time, LPG or light oil can also be used as raw materials. The raw material cost of this method is low, but the process flow is long, the corrosion is serious, and the yield of acetic anhydride is not high. It is only used in the areas where the cheap isobutane or LPG raw materials are easily available. The reaction can be carried out at high temperature and pressure to keep butane liquid. The by-products include butanone, ethyl acetate, formic acid and propionic acid. Because some by-products have economic value, the reaction conditions can be adjusted to produce more by-products, but the separation of acetic acid and by-products increases the cost of the reaction. Under similar conditions, acetic anhydride can be oxidized to acetic acid by oxygen in air. More than 95% yield of acetic acid can be obtained by using new catalyst. The main by-products are ethyl acetate, formic acid and formaldehyde. Because the boiling point of by-products is lower than that of acetic acid, they can be easily removed by distillation.
5. Ethylene oxidation process
It is formed by the reaction of ethylene with oxygen in the presence of catalyst. This reaction can be regarded as the first oxidation of ethylene to acetaldehyde, and then by acetaldehyde oxidation.
6. Topso method
Topso process uses natural gas or coal as raw material. Step 1: the synthesis gas generates methanol and dimethyl ether under the catalyst; The second part: methanol and dimethyl ether (both do not need purification) and co carbonylation to produce acetic acid, this method is also called two-step method.
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