Phase equilibria of the vitamins D2, D3 and K3 in binary systems with CO2 and propane

Solubilities of the fat-soluble vitamins K3, D3 and D2 in CO2 and propane were measured at temperatures 30, 40, 60 and 80°C and over a pressure range of 80–300 bar for CO2 and 10–110 bar for propane using a static-analytic method. In order to verify weather, the solubility isotherm crosses the three-phase S–L–V line, solid–liquid (S–L) phase transitions of vitamins K3, D3 and D2 under the pressure of gas were determined with modified capillary method. For all vitamins under the pressure of CO2, propane and dimethylether, a negative dP/dT slope of the S–L–V curve was found. For K3 under the pressure of inert gas (argon and nitrogen), the S–L–V-curve had a positive dP/dT slope. The solubilities of vitamins D in dense CO2 under the conditions investigated were in the range 0.04×10−3–1.45×10−3 mole fraction. For vitamin K3 the solubility in CO2 was higher and was in the range 0.16×10−3–4.07×10−3 mole fraction. The solubilities of vitamins D in propane were approximately up to 10 times higher as in CO2 and in the range from 0.15×10−3 to 12.40×10−3 mole fraction. Opposite, the solubility of vitamin K3 in propane was lower than in CO2 and was in the range from 0.03×10−3 to 2.99×10−3 mole fraction. The experimental S–L–V data were correlated using Peng-Robinson equation of state and binary iteration parameters obtained from best fit were used for solubility calculation. The fit of S–L–V lines showed good results in the case of vitamin K3 and the order of magnitude of the solid solubilities were well represented.