Lactic Acid Preparation Lab Report

Process selection

Two possibilities for the synthesis of Lactic acid are chemical synthesis and fermentation of solution that contains carbohydrate.

Chemical synthesis

Hydrogen cyanide is added to acetaldehyde in the presence of a base to produce lactonitrile. This process occurs in liquid phase at high pressures. The crude lactonitrile is recovered and purified by distillation. It is then hydrolyzed to lactic acid, either by conc. HCl or by H2SO4 to produce corresponding ammonium salt and lactic acid. Lactic acid is then esterified with methanol to produce methyl lactate, which is removed and purified by distillation and hydrolyzed by water under acid catalyst to produce lactic acid and methanol, which is recycled [1].

Lactic acid fermentation

It can be described by the reactions [2]. The broth containing calcium lactate is filtered to remove cells, carbon treated, evaporated and acidified with sulphuric acid to get lactic acid and calcium sulphate. The insoluble calcium sulphate is removed by filtration [3]; lactic acid is obtained by hydrolysis, esterification, distillation and hydrolysis [4]. There are two main types of fermentation described below

Homofermentative lactate fermentation

Homofermentative Lactic acid bacteria produce pure or almost pure (90%) lactate. They metabolize glucose via the fructose-bis phosphate pathway and produce one molecule of Lactate from one molecule of glucose [5]. Used bacteria examples are: Lactococcus lactis, Streptococci, Enterococcus faecclis

Heterofermentative lactate

97 w/w % H2SO4 solution is reacted to convert calcium lactate to lactic acid. The reaction is performed at 403 K° and 1 bar pressure and the experimental conversion of calcium lactate is 90%. CaSO4 (Gypsum) is produced as side product and have a very low solubility of 2.4 g L-1 in water at 293 K° and is separated with 99% purity through filtration process.

[〖2(CH_3 CHOCOO)〗^- ] Ca^(2+)+H_2 SO_4 〖→CH〗_3 CHOHCOOH+CaSO_4 Esterification of lactic acid to methyl lactate and methyl lactate recovery by distillation process

For further purification of lactic acid product is done by heat treatment process of distillation. Lactic acid cannot sustain much higher temperatures so initially it is converted to methyl lactate which is more thermally stable and can sustain much higher temperatures. Although vacuum distillation can be used for distillation of lactic acid at lower temperatures but it is not suitable economically. So methyl lactate is formed by reacting methanol with lactic acid with conversion of 88%. Reaction is performed at 353 K° temperature and 1 bar pressure.

CHOHCOOH+CH_3 OH→CH_3 CHOHCOOCH_3+H_2 O Hydrolysis of methyl lactate to lactic