Process of producing citric acid

Claim 1

IN A PROCESS OF RECOVERING CITRIC ACID FROM STRONGLY CONTAMINATED CITRIC ACID SOLUTIONS OBTAINED ON FERMENTATION OF SUGAR-CONTAINING SOLUTIONS BY MEANS OF ASPERGILLUS NIGER, THE STEPS WHICH COMPRISE CONCENTRATING BY EVAPORATION IN A VACUUM THE FERMENTATION CITRIC ACID SOLUTION TO A CITRIC ACID CONCENTRATION BETWEEN ABOUT 40% AND ABOUT 85%, ADDING TO THE CONCENTRATED CITRIC ACID SOLUTION AN ALKALI METAL COMPOUND SELECTED FROM THE GROUP CONSISTING OF AN ALKALI METAL HYDROXIDE, AN ALKALI METAL CARBONATE, AND AN ALKALI METAL BICARBONATE IN AN AMOUNT SUFFICIENT TO FORM THE MONO-ALKALI METAL DIHYDROGEN CITRATE, ALLOWING THE RESULTING CITRATE SOLUTION TO STAND UNTIL CRYSTALLIZATION IS COMPLETED, SEPARATING THE PRECIPITATED CRYSTALLINE MONO-ALKALI METAL DI-HYDROGEN CITRATE FROM THE MOTHER LIQUOR, WASHING SAID MONO-ALKALI METAL DI-HYDROGEN CITRATE WITH WATER, COMBINING THE MOTHER LIQUOR AND THE WASH WATER, ADDING TO SAID COMBINED MOTHER LIQUOR AND WASH WATER A CALCIUM COMPOUND SELECTED FROM THE GROUP CONSISTING OF CALCIUM HYDROXIDE, CALCIUM CARBONATE, AND CALCIUM CHLORIDE, IN AN AMOUNT CORRESPONDING TO ONE MOLE OF CALCIUM FOR ONE MOLE OF CALCULATED CITRIC ACID PRESENT IN THE MOTHER LIQUOR, FILTERING OFF THE PRECIPITATED MONO-ALKALI METAL CALCIUM CITRATE, SUSPENDING SAID MONO-ALKALI METAL CALCIUM CITRATE IN WATER, ADDING THERETO THE STOICHIOMETRIC AMOUNT OF SULFURIC ACID TO REACT WITH AND PRECIPITATE SUBSTANTIALLY ALL THE CALCIUM PRESENT IN SAID MONO-ALKALI METAL CALCIUM CITRATE, FILTERING OFF THE PECIPITATE GYPSUM, AND CONVERTING THE RESULTING MONO-ALKALI METAL DI-HYDROGEN CITRATE INTO SUBSTANTIALLY PURE CITRIC ACID BY ELECTRODIALYSIS.