Effect of Ammonium Sulfate on the Solubility of α-Form and β-Form l-Glutamic Acid in Water and Actual Fermentation Mother Liquor from 278.15 to 333.15 K

Abstract

The solubility of α-form and β-form L-glutamic acid (L-GA) in aqueous (NH 4 ) 2 SO 4 solutions with 0−1.50 molal (NH 4 ) 2 SO 4 was determined at 288.15 K. And the solubility in aqueous solutions and actual L-GA fermentation mother liquor (GAFML) without and with 0.75 molal (NH 4 ) 2 SO 4 was determined at temperatures ranging from 278.15 to 333.15 K. The results showed that for all the cases (NH 4 ) 2 SO 4 exhibited salting-in effects on L-GA, and the solubility of stable β-form was lower than that of metastable α-form. The other coexisting solutes together with (NH 4 ) 2 SO 4 in the GAFML jointly increased the L-GA solubility. Specifically, 0.75 molal (NH 4 ) 2 SO 4 aroused 19.0− 83.0% of total solubility increment at the temperature range and polymorph studied. Based on the data obtained, the dissolution enthalpy and the entropy of L-GA were estimated by Van't Hoff correlation. The solubility data were correlated using empirical three parameter Van't Hoff equation. The model demonstrated good fitting with the experimental data.