Lactic Acid

Brief Overview
Lactic acid is an important organic chemical compound with a global production of 275.000 tonnes per year and is naturally available in humans and animals. Lactic acid is also known as milk acid and is primarily found in milk products. Lactic acid played an important role in biochemical processes and was first isolated in 1780 by the Swedish chemist Carl Wilhelm Scheele. Lactic acid is a carboxylic acid formed by the muscle cells' exertion of glycogen in the human body. In 1856, Louis Paster found that the microorganism Lactobacillus plays an important role in manufacturing Lactic acid. Lactic acid fermentation is considered one of the important mechanisms in the food industry for its sour taste, improved microbiological stability and safety of food.
Manufacturing Process
Lactic acid is produced on an industrial scale by fermentation or a synthetic method.
1. Fermentation Method
The fermentation method requires carbohydrates, nutrients, and a microorganism to produce lactic acid via fermentation. The carbohydrates used in fermentation consist mainly of hexoses or compounds which can be easily split into hexoses, e.g. glucose and sugar. The required nutrients include soluble peptides, amino acids, phosphates and ammonium salts, and vitamins. Fermentation occurs between 5.0 and 6.5 pH. Lime, calcium carbonate, ammonium hydroxide, and sodium hydroxide are typically used to neutralize the lactic acid produced to maintain constant pH. Thus, calcium lactate, ammonium lactate, or sodium lactate salts are formed in the fermentation broth. Lactic acid yields are between 85 and 95% based on fermentable sugars. After fermentation, the lactic acid broth needs to be purified for its intended use.
2. Synthetic Method
The commercial process is based on lactonitrile. It involves the base-catalyzed addition of hydrogen cyanide to acetaldehyde to produce lactonitrile. This is a liquid-phase reaction and occurs at atmospheric pressure. The crude lactonitrile is then recovered and purified by distillation and is hydrolyzed to lactic acid using either concentrated hydrochloric or sulfuric acid, producing the corresponding ammonium salt as a by-product. This crude lactic acid is esterified with methanol, producing methyl lactate. The latter is recovered and purified by distillation and hydrolyzed by water under acid catalysts to produce lactic acid, which is further concentrated, purified, and shipped under different product classifications, and methanol, which is recycled.