Automated measurement of pH-dependent solid-liquid equilibria of itaconic acid and protocatechuic acid

Abstract

Crystallization is a highly selective unit operation capable of separating target molecules from complex media. Its design requires precise solid-liquid equilibrium (SLE) data. The SLE of platform chemicals like carboxylic acids in complex aqueous media depends on temperature, pH value as well as on present side components, but predominantly, only the solubility for different temperatures is reported. This work presents a novel automated method for the determination of the pH- and temperature-dependent SLE in complex media using readily available laboratory equipment. Taking the example of itaconic acid, the pH-dependent solubility for different temperatures is measured and validated with results obtained from the classic excess solid method along with literature data. Using the automated setup, the influence of different loadings of sodium chloride on the SLE of itaconic acid is investigated and a correlation between solubility and concentration of the electrolyte is derived. The SLE data acquired for protocatechuic acid in fermentation medium demonstrates the applicability of the method for the determination of comprehensive SLE in multicomponent mixtures without the requirement of specific analytical methods for the target compound. The resulting SLE data can be used for a more precise design and techno-economic evaluation of crystallization processes in biotechnological production routes.