c？ H5OH + O？ →CH？ COOH + H？ O
The specific method is to inoculate acetic acid bacteria into diluted alcohol solution, keep a certain temperature, put it in a ventilated place, ferment within a few months, and finally produce vinegar. The method of industrial production of vinegar accelerates the reaction process by providing sufficient oxygen. This method has been adopted in commercial production, and it is also called "quick method" or "German law", which is named after the first successful application of 1823 in Germany. In this method, fermentation is carried out in a tower filled with sawdust or charcoal. Alcohol-containing raw materials are dripped from the top of the tower, and fresh air naturally enters from the bottom or forced convection. The enhanced air volume enables this process to be completed in a few weeks, greatly shortening the time for vinegar making.
Otto Hromatka and Heinrich Ebner first proposed to prepare vinegar with liquid bacterial culture medium in 1949. In this method, alcohol is fermented into acetic acid under continuous stirring, and air is filled into the solution in the form of bubbles. By this method, vinegar containing 15% acetic acid can be prepared within two to three days. Some anaerobic bacteria, including some members of Clostridium, can directly convert sugar into acetic acid without ethanol as an intermediate. The overall reaction equation is as follows:
C6H 12O6==3 CH3COOH
In addition, many bacteria can produce acetic acid from compounds containing only one carbon, such as methanol, carbon monoxide or a mixture of carbon dioxide and hydrogen.
CO2+TetraH2 → Acetic acid+DiH2O
2 CO + 2 H2 →CH3COOH
Clostridium can reduce the cost because it can react with sugar, which means that these bacteria have the potential to produce acetic acid more effectively than Acetobacter. But the acid resistance of Clostridium is not as good as that of Acetobacter. Clostridium bacteria with the greatest acid tolerance can only produce less than 10% acetic acid, while some acetic acid bacteria can produce 20% acetic acid. Making vinegar with Acetobacter is still more economical than concentrating vinegar with Clostridium. Therefore, although Clostridium was discovered as early as 1940, its industrial application is narrow.
In addition to the above biological methods, industrial acetic acid is mostly synthesized by the following methods: acetic acid is mostly synthesized by methyl carbonylation. In this reaction, methanol and carbon monoxide react to produce acetic acid, and the equation is as follows.
CH3OH + CO →CH3COOH
The process is completed in three steps, the intermediate is methyl iodide, and the catalyst with multi-metal components is needed (the second step).
⑴ CH？ Oh+hi →CH? I + H？ O
⑵ CH？ I + CO →CH？ Central news agency
⑶ CH？ COI + H？ O →CH？ COOH + HI
Acetic anhydride can also be produced by the same reaction by controlling the reaction conditions. Because carbon monoxide and methanol are commonly used chemical raw materials, methyl carbonylation has always been favored. As early as 1925, Celanese Company of the United Kingdom developed the first pilot plant for methyl carbonylation to acetic acid. However, due to the lack of high pressure (200atm or higher) and corrosion-resistant containers, the application of this method is limited. 1963, BASF Chemical Company of Germany developed the first process for industrial production of acetic acid with cobalt as catalyst. In 1968, rhodium catalyst greatly reduced the reaction difficulty. Using the catalyst system composed of rhodium carbonyl compound and iodide, methanol and carbon monoxide react in water-acetic acid medium at 65438 075℃ and pressure less than 3 MPa, and acetic acid products can be obtained. Due to the high activity and selectivity of the catalyst, there are almost no by-products in the reaction. Low pressure carbonylation of methanol to acetic acid has the advantages of cheap raw materials, mild operating conditions, high acetic acid yield, good product quality and simple process flow, but the reaction medium is seriously corrosive and requires special corrosion-resistant materials. 1970 Monsanto Company of the United States has built a device adopting this process, so rhodium-catalyzed methyl carbonylation to acetic acid has gradually become the dominant method of Monsanto Company. At the end of 1990s, BP successfully commercialized Cativa catalytic process, which used ruthenium catalyst and ([Ir(CO)? Me? ]), which is greener and more efficient than Monsanto method. Before commercial production by Monsanto method, most acetic acid was produced by oxidation of acetaldehyde. Although it cannot be compared with methyl carbonylation, this method is still the second industrial method to produce acetic acid, and the reaction equation is as follows:
2CH？ CHO+O？ →2CH？ Wow!
Acetaldehyde can be produced by oxidation of butane or light naphtha or hydration of ethylene. Using n-butane as raw material, acetic acid as solvent, air as oxidant and cobalt acetate as catalyst, the reaction temperature was 170℃- 180℃ and the pressure was 5.5 MPa. At the same time, this method can also use liquefied petroleum gas or light oil as raw materials. This method has the advantages of low raw material cost, long process flow, serious corrosion and low acetic acid yield, and is only used in areas where cheap isobutane or liquefied petroleum gas raw materials are easily available.
2 C？ H + 5 O？ →4 CH？ COOH + 2 H？ O
The reaction can be carried out at the highest temperature and pressure that can keep butane liquid, and the by-products include butanone, ethyl acetate, formic acid and propionic acid. Because some by-products also have economic value, more by-products can be produced by adjusting the reaction conditions, but the separation of acetic acid and by-products increases the cost of the reaction.
Under similar conditions, acetaldehyde can be oxidized by oxygen in the air to produce acetic acid by using the above catalyst:
2 CH？ CHO + O？ →2 CH？ Wow!
It can also be oxidized by copper hydroxide suspension;
2Cu (oh)? +CH？ CHO→CH？ COOH+Cu？ O↓+2H？ O
Using the new catalyst, the yield of acetic acid can reach over 95%. 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. Celanese is also one of the largest producers of acetic acid in the world. During the period of 1978, Hearst Celanese Company (now Celanese Company) was put into industrial production in Monsanto acetic acid plant in Lake Clare, Texas, USA. 1980, Celanese applied for the patent of AOPlus process, which greatly improved Monsanto process.
Adding high concentration inorganic iodine (mainly lithium iodide) in AOPlus process improves the stability of rhodium catalyst. After adding lithium iodide and methyl iodide, the water concentration in the reactor decreased to 4% ~ 5%, but the carbonylation reaction rate remained at a high level, thus greatly reducing the separation cost of the device. The change of catalyst composition makes the reactor run at low water concentration (4% ~ 5%), which improves the yield and separation and purification ability of carbonylation reaction. Acetic acid is a large chemical product and one of the most important organic acids. Mainly used in the production of vinyl acetate, acetic anhydride, acetate and cellulose acetate. Polyvinyl acetate can be used to prepare films and adhesives, and it is also the raw material of synthetic fiber vinylon. Cellulose acetate can be used to make rayon and films. Acetate is an excellent solvent, which is widely used in industry. Acetic acid can also be used to synthesize acetic anhydride, diethyl malonate, ethyl acetoacetate and halogenated acetic acid. It can also be used to make medicines such as aspirin and acetate. Widely used in pesticides, medicine and dyes, photographic medicine manufacturing, fabric printing and dyeing and rubber industry.
In food industry, acetic acid is used as acidulant, flavoring agent and spice. When making vinegar, the acetic acid is diluted to 4-5% with water, and various flavoring agents are added to make edible vinegar. As a sour agent, it can be used to make drinks and canned foods, such as canned foods such as tomatoes, asparagus, baby food, sardines and squid, soft drinks, cold drinks, sweets, baked goods, puddings, gum sugar, condiments and so on.
Acetic acid acts as a preservative. 1.5% has obvious bacteriostatic effect. In the range of 3%, the pulp color turning green and black caused by mildew spots can be avoided.