Direct production of pure concentrated tartaric acid from its salts by electromembrane processes

Abstract

A concentrated tartaric acid solution is directly produced from oenological wastes by a double decomposition in electrochemical reactors fitted with ion exchange membranes. In the classical route of production of tartaric acid, a first set of neutralization-separations is used with a view to precipitating calcium tartrate. Then, the acid is produced by metathesis with an aqueous solution of sulfuric acid. The final solution obtained is generally a diluted mixture of tartaric and sulfuric acids which must be separated. In the first step of the process described here, the wasted tartaric salts are treated with a base, in such a way that a soluble neutral salt is formed in an aqueous solution. Then, the solution is fed into an electromembrane reactor where the metathesis of the neutral salt gives tartaric acid, and the corresponding salt or the neutralizing base according to the type of reaction used. In the case of an electrometathesis reactor, the reaction involved can be written as:<br> <p> Potassium tartrate + <em>sulfuric ucid → tartaric acid+ potassium sulfate</em><br /><br /> In the case of an electrohydrolysis reactor, the reaction is:<br /><br /> <em>Potassium tartrate </em>+ <em>water → tartaric acid </em>+ <em>potassium h</em><em>y</em><em>droxide</em><br /><br /> In each case, the use of an electromembrane reactor allows one to obtain a pure solution of each of the products, tartaric acid, potassium sulfate or potassium hydroxide.<br><br> For each kind of stack assembly involved, the influence of the DC voltage applied to the outer electrodes, the concentration of the feeding solutions to each of the four cells and the velocity of the four streams have been studied. The results obtained allow the process to be modelised. According to the operating conditions. a more or less concentrated tartaric acid solution is produced in the concentrating cells.