Phase equilibria of the vitamins D-2, D-3 and K-3 in binary systems with CO2 and propane

Solubilities of the fat-soluble vitamins K-3, D-2 and D-2 in CO2 and propan e were measured at temperatures 30, 40, 60 and 80 degreesC and over a press ure range of 80-300 bar for CO2 and 10-110 bar for propane using a static-a nalytic method. In order to verify weather, the solubility isotherm crosses the three-phase S-L-V line, solid-liquid (S-L) phase transitions of vitami ns K-3, D-2 and D-2 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 K, 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 th e conditions investigated were in the range 0.04 x 10(-3)-1.45 x 10(-3) mol e fraction. For vitamin K-3 the solubility in CO2 was higher and was in the range 0.16 x 10(-3)-4.07 x 10(-3) mole fraction. The solubilities of vitam ins D in propane were approximately up to 10 times higher as in CO2 and in the range from 0.15 x 10(-3) to 12.40 x 10(-3) mole fraction. Opposite, the solubility of vitamin K-3 in propane was lower than in CO2 and was in the range from 0.03 x 10(-3) to 2.99 x 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 calcul ation. The fit of S-L-V lines showed good results in the case of vitamin K- 3 and the order of magnitude of the solid solubilities were well represente d. (C) 2001 Elsevier Science B.V. All rights reserved.