Experimental study and modeling of citric acid solubility in alcohol mixtures

Citric acid is a weak organic acid widely used in food industries. The study of this solid's behavior in different solutions is required for the development of separation processes and new applications. Studies on the solubility of citric acid in solutions are still little explored and the information regarding solubility in pure components is imprecise. The objective of this work, therefore, was to study the solubility of citric acid in binary liquid solutions formed by methyl, ethyl and isopropyl alcohol at temperatures of 293.15 K, 303.15 K, 313.15 K and 323.15 K. The solubility results were applied in the determination of the activity coefficient of the solubilized solid. The Jouyban-Acree, NRTL and UNIQUAC models were used in the correlation of the data, and the mUNIFAC model was applied in its prediction. Citric acid had a high solubility in the pure components with the values decreasing from methyl to ethyl and isopropyl alcohol. For the solubility in the binary solutions, the solubility revealed intermediate values. The results for the activity coefficient showed a linear behavior as a function of temperature, and they decreased with increasing solubility. The employed models were able to correlate or predict the experimental data.