Preparation and application of glacial acetic acid

Acetic acid, also called acetic acid, glacial acetic acid, chemical formula CH3COOH, is an organic monic acid and short-chain saturated fatty acid, which is the source of acid and pungent odor in vinegar. Under normal circumstances, it is called "acetic acid", but pure and nearly anhydrous acetic acid (less than 1% water content) is called "glacial acetic acid", which is a colorless hygroscopic solid with a freezing point of 16 to 17 ° C (62 ° F), and after solidification, it is colorless crystal. Although acetic acid is a weak acid, it is corrosive, its vapors are irritating to the eyes and nose, and it smells pungent and sour.

history

The annual worldwide demand for acetic acid is about 6.5 million tons. Of this, about 1.5 million tons are recycled and the remaining 5 million tons are produced directly from petrochemical feedstocks or through biological fermentation.

The glacial acetic acid fermenting bacteria (Acetobacter) can be found in every corner of the world, and every nation inevitably finds vinegar when making wine - it is the natural product of these alcoholic beverages exposed to air. For example, in China, there is a saying that Du Kang's son, Black Tower, got vinegar because he made wine for too long.

The use of glacial acetic acid in chemistry dates back to very ancient times. In the 3rd century BC, the Greek philosopher Theophrastus described in detail how acetic acid reacts with metals to produce pigments used in art, including white lead (lead carbonate) and patina (a mixture of copper salts including copper acetate). The ancient Romans boiled sour wine in lead containers to produce a high-sweetness syrup called sapa. sapa was rich in a sweet-smelling lead sugar, lead acetate, which caused lead poisoning among Roman nobles. In the 8th century, the Persian alchemist Jaber concentrated the acetic acid in vinegar by distillation.

In 1847, German scientist Adolf Wilhelm Hermann Kolbe synthesized acetic acid from inorganic raw materials for the first time. The process of this reaction is the first carbon disulfide through chlorination into carbon tetrachloride, followed by the high-temperature decomposition of tetrachloroethylene after hydrolysis, and chlorination, thus producing trichloroacetic acid, the last step by electrolytic reduction to produce acetic acid.

In 1910, most of the glacial acetic acid was extracted from coal tar from retorted wood. First, coal tar is treated with calcium hydroxide, and then the formed calcium acetate is acidified with sulfuric acid to obtain acetic acid in it. About 10,000 tons of glacial acetic acid were produced in Germany during this period, 30% of which was used to make indigo dye.

preparation

Glacial acetic acid can be prepared by artificial synthesis and bacterial fermentation. Today, biosynthesis, the use of bacterial fermentation, accounts for only 10% of the world's total production, but is still the most important method of producing vinegar, because food safety regulations in many countries require that vinegar in food be biologically prepared. 75% of acetic acid for industrial use is produced by carbonylation of methanol. The vacant parts are synthesized by other methods.

use

Glacial acetic acid is a simple carboxylic acid, consisting of one methyl group and one carboxylic group, and is an important chemical reagent. In the chemical industry, it is used to make polyethylene terephthalate, the main component of beverage bottles. Glacial acetic acid is also used to make cellulose acetate for film and polyvinyl acetate for wood adhesives, as well as many synthetic fibers and fabrics. In the home, dilute solution of glacial acetic acid is often used as a descaling agent. In the food industry, acetic acid is specified as an acidity regulator in the food additives list E260.

Glacial acetic acid is the basic chemical reagent used in the preparation of many compounds. The single use of acetic acid is the preparation of vinyl acetate monomer, followed by the preparation of acetic anhydride and other esters. The acetic acid in vinegar is only a small fraction of all glacial acetic acid.

Diluted acetic acid solution is also often used as a rust removal agent because of its mild acidity. Its acidity is also used to treat stings caused by Cubomedusae and, if used in time, can prevent serious injury or even death by disabling the jellyfish's stinging cells. It can also be used to prepare for the treatment of otitis externa with Vosol. Acetic acid is also used as a spray preservative to inhibit the growth of bacteria and fungi.