Study On Solubility Of Poly (Vinylpyrrolidone) In Subcritical Or Supercritical Fluids

As an environmentally friendly technology, supercritical fluid technology (SFT) has been widely applied in the field of pharmaceutical, food processing, polymer preparation and so on. In recent decades, the (sub)supercritical fluid impregnation technology represented an emerging technology to prepare and process drug-polymer mixture has attracted widespread attention. In this process, the solubility of crystalline drugs, which exhibit poor water solubility in aqueous solution, could be enhanced by dispersing crystalline drugs into the water-soluble polymer carrier using (sub)supercritical fluids. In this way, the drug is more convenient for people to absorb. Supercritical carbon dioxide (SCCO2) and subcritical 1,1,1,2-tetrafluoroethane (R134a) are widely used in the (sub)supercritical fluid impregnation technology to prepare drug-polymer mixture due to its properties.The phase equilibrium of polymer in (sub)supercritical fluids is the basis to design the (sub)supercritical impregnation technology. Poly(vinylpyrrolidone) (PVP) is widely used as one of the most popular polymeric carrier. In this work, the equilibrium solubility of PVP with molecular weight 10000,24000 and 58000 were measured in SCCO2 and subcritical R134a. The specific contents are as follows:The solubility of PVP with different molecular weight 10000,24000, 58000 in SCCO2 was measured at temperatures from 313 K to 343 K and at pressures from 9.0 MPa to 18.0 MPa by the dynamic method; The solubility of the same solute in subcritical R134a was measured in the pressure from 5.0 MPa to 18.0 MPa and at temperatures from 313 K to 333 K using the static method. Total 123 solubility data points were obtained. In addition, the effects of pressure, temperature and molecular weight of polymer on solubility were analyzed from the view of solvent density, solute vapor pressure and interactions between solute and fluid molecules. The solubility enhancement factor (δ) of PVP in different fluids was also calculated and analyzed.Chrastil model, Mendez-Santiago and Teja(M-S-T) model, Kumar and Johnston(K-J) model, Sung and Shim(S-S) model and Adachi and Lu(A-L) model, which were commonly used in fluid phase equilibrium, were applied to calculate the experimental solubility of PVP with different molecular weight in SCCO2 and subcritical R134a. The correlated precision for models were compared from the view of numbers of model parameters and model expressions, and the average absolute relative deviation (AARD) was also calculated.In this work, a modified M-S-T model was proposed by improving the accuracy of function description of solvent density by the foundation of M-S-T model. The modified M-S-T model was verified by 123 solubility data of this work and 744 solubility data from literature, and the resullts indicated that the correlated precision for the modified M-S-T model was improved campared with the M-S-T model. The modified M-S-T model can be applied to calculate the solubility of solute in (sub)supcritical fluids.