Abstract
The solubility of β-Lactose (β-L) in 15 pure solvents (methanol, isopentanol, 1-hexanol, ethanol, isopropanol, 2-butanol, 1-heptanol, 1-propanol, cyclohexanone, propionic acid, isobutanol, 1-butanol, 1-pentanol, 1-octanol and acetonitrile) was studied by static equilibrium gravimetric method from 273.55 K to 323.05 K under atmospheric pressure in this work. The crystal form and stability of β-L have been confirmed by XRD and DSC. Overall, the solubility of β-L in the measured solvents increased non-linearly with increasing temperature. The sequence of the mole-fraction solubility values of β-L is: methanol > isopentanol > 1-hexanol > ethanol > isopropanol > 2-butanol > 1-heptanol > 1-propanol > cyclohexanone > propionic acid > isobutanol > 1-butanol > 1-pentanol > 1-octanol > acetonitrile. Four mathematical models such as the modified Apelblat model, λh model, Wilson model and NRTL model are applied to correlate the solubility of β-L. The fitted values of four models are in good accordance with the experimental solubility, and the obtained root-mean-square deviation (RMSD) and relative average deviation (RAD) were less than 0.441 % and 0.23 × 106, respectively; but the NRTL model provided the best fitting results. In addition, for twoalcohol-watersolutions such as methanol/water and ethanol/water in which thevolumefractionof wateris morethan20 %, β-L can be completely converted to α-lactose (α-L). The polarity of solvent and solute–solvent interactions is an important factor affecting the solubility of β-L in the pure and mixed solvents. The sequence of β-L solubility in selected solvents was analyzed with the Hansen solubility parameter and the solvent interaction through correlating β-L solubility based on KAT-LSER model.Finally, the thermodynamic properties of ΔdisG, ΔdisH and ΔdisS of β-L in different solvents were calculated based on the measured solubility data and Wilson model. The results indicated that the dissolution process of β-L was an endothermic, entropy-driven and spontaneous process.
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