Determination, correlation, and thermodynamic analysis of solubility of D-psicose in four binary solvents

D-psicose is a naturally occurring six‑carbon ketose with moderate sweetness and low calories. In this work, the solubility of D-psicose in four binary solvents, including methanol + n-propanol, methanol + isopropanol, methanol + acetone, methanol + acetonitrile, was determined by gravimetric method at 283.15 K to 323.15 K. The solubility of D-psicose in these mixed solvents increases with rising temperature. At the same temperature, the solubility increases with increased methanol content in the solvent mixtures. The modified Apelblat model, van't Hoff model, λ h model, the nonrandom two-liquid (NRTL) model and the Apelblat-Jouyban-Acree model were used to correlate the solubility data. The results show that the modified Apelblat model has the best fitting performance. The thermodynamic dissolution functions of D-psicose in the solvent mixtures were calculated using the van't Hoff equation and enthalpic-entropic compensation was discussed. The thermodynamic parameters of the mixing process were also calculated by the NRTL model. Furthermore, the preferential solvation of D-psicose by methanol was analyzed using the inverse Kirkwood-Buff integrals method. Some crystallization experiments were also carried out, and the crystalline products grown from the four mixed solvents exhibited different morphology. The molecular structure of dominant crystal faces was presented and powder properties of D-psicose crystals were also measured. This study provides thermodynamic data and predictive models for D-psicose, which enable design and optimization of the crystallization process.