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What is adipic acid used for?

What is adipic acid used for?

Adipic acid or adipic acid is an organic compound having the formula (CH 2) 4 (COOH) 2. From an industrial point of view, it is the most important dicarboxylic acid: about 2.5 billion kilograms of this white crystalline powder are produced annually, mainly as a precursor for nylon production. Otherwise, adipic acid rarely occurs in nature, but it is called the artificial E value food additive E355.

This passage is going to talk about the followings of adipic acid:

(1) Definition of adipic acid

(2) Production and preparation method of adipic acid

(3) Applications of adipic acid


(1) Definition of adipic acid

Adipic acid, also known as fatty acid, is an important organic dibasic acid with a molecular formula of C6H10O4. It can undergo salt formation, esterification, amidation, etc., and can interact with diamines or diamines. Polycondensation of alcohol into high molecular polymers and so on. Adipic acid is a dicarboxylic acid of great industrial significance. It plays an important role in chemical production, organic synthesis industry, medicine, lubricant manufacturing, etc. Its output ranks second among all dicarboxylic acids.

The functional group of adipic acid is a carboxyl group, so it has the properties of a carboxyl group, such as salt formation reaction, esterification reaction, amidation reaction and so on. At the same time as a dicarboxylic acid, it can also be polycondensed with diamine or glycol to form high molecular polymers.


(2) Production and preparation method of adipic acid

In 1937, the American DuPont Company used nitric acid to oxidize cyclohexanol (prepared by hydrogenation of phenol), and first realized the industrial production of adipic acid. In the 1960s, the industry gradually changed to the cyclohexane oxidation method, that is, the intermediate product cyclohexanone and cyclohexanol mixture (ie ketone alcohol oil, also known as KA oil) was prepared from cyclohexane, and then the KA oil was processed. Nitric acid or air oxidation.

Cyclohexane one-step oxidation method:

Using cyclohexane as raw material, acetic acid as solvent, cobalt and bromide as catalyst, at 2MP. React with 90℃ for 10-13h. The yield was 75%.

Cyclohexane stepwise oxidation method:

The preparation of KA oil can be directly oxidized with air at 1.0~2.5MPa and 145~180℃, with a yield of 70%~75%. Metaboric acid can also be used as a catalyst. Air oxidation can be carried out at 1.0~2.0MPa and 165℃, the yield can reach 90%, and the ratio of alcohol to ketone is 10:1; the reactants can be treated with hot water to hydrolyze and separate the ester. The layer recovers boric acid and is dehydrated into metaboric acid for recycling; the organic layer is saponified with caustic soda to saponify the organic ester, and the acid is removed, and the cyclohexane is recovered by distillation to obtain a mixture of alcohol and ketone.

Oxidation of KA oil The KA oil is oxidized in a two-stage series reactor with an excess of 50%-60% nitric acid at 60-80°C and 0.1-0.4MPa. The catalyst is a copper-vanadium system (copper 0.1% to 0.5%, vanadium 0.1% to 0.2%), and the yield is 92% to 96% of the theoretical value. After the reactant is distilled out of nitric acid, high-purity adipic acid can be obtained after two crystallizations and refining.


(3) Applications of adipic acid

Of the 2.5 billion kilograms of adipic acid produced annually, about 60% are used as monomers for the production of nylon, which forms nylon 66 through polycondensation with hexamethylene diamine. Other major applications involve polymers. It is a monomer for the production of polyurethane, and its ester is a plasticizer, especially in PVC.

In medicine, adipic acid has been incorporated into controlled-release preparation matrix tablets to obtain pH-dependent release of weakly alkaline and weakly acidic drugs. It has also been incorporated into the polymer coating of the hydrophilic overall system to adjust the pH within the gel, resulting in zero-order release of hydrophilic drugs. It is reported that when adipic acid is used as a pore-forming agent, the disintegration of enteric polymer shellac at intestinal pH is improved without affecting its release in acidic media. Other controlled-release preparations include adipic acid, the purpose is to obtain the release profile after the burst.

In food, a small but large amount of adipic acid is used as a food ingredient, as a flavoring agent and a gelling aid. Adipic acid is used in some calcium carbonate antacids to make it sour. As an acidulant in baking powder, it avoids the undesirable hygroscopic properties of tartaric acid. Naturally rare adipic acid does occur naturally in sugar beets, but compared with industrial synthesis, it is not a commercial economic source.




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