Doctoral Dissertations

Date of Award

12-1997

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Biosystems Engineering

Major Professor

Luther R. Wilhelm

Committee Members

Greg Hulbert, Hank Cochran, F. Ann Draughon

Abstract

Lipids that contain polyunsaturated fatty acids (PUFA) have therapeutic value. Supercritical carbon dioxide extraction of PUFA from the lower fungi, Pythium irregulare was attempted for freeze-dried material in the presence of an aqueous phase. Extraction showed some success at moisture contents up to 30% (wb) and with the addition of a novel CO2 -philic surfactant. Equilibrium and kinetic data are presented. Equilibrium data were taken for the fungal oil in a flow-through apparatus at a low flow rate for two isotherms (40 and 60°C) over a pressure range of 13.7 to 27.5 MPa. Equilibrium data were also taken for pure naphthalene at 40°C to test the system. The compressed-gas model utilizing the Peng-Robinson equation of state was then applied to the data. The kinetic data portrayed three types of mass transfer behavior including an initial surface-film regime where pseudo steady-state conditions prevailed, a diffusion-controlled regime where unsteady-state conditions were evident and a temporary transition region. For tests with extraction times of 5 to 6 hours, data for the diffusion-controlled region were modeled with an analytical solution to Fick's Second Law assuming the particles were spherical shaped. The models worked well for both equilibrium and kinetic data, however the physical property values for the equilibrium data were altered substantially to obtain a reasonable fit with the compressed-gas model.

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