44C-32 |
Steady state analysis of juice aroma transport in the boundary layer of a pervaporation membrane channel |
M. PENG, SR. and S. X. Liu. Dept. of Food Science, Rutgers, The State Univ. of New Jersey, Cook Campus, 65 Dudley Rd., New Brunswick, NJ 08901-8520 Pervaporation (PV) is a membrane process used for the purification or separation of liquid mixtures. When components in the liquid feed are brought to the upstream surface of membrane the difference in their affinities to the membrane leads to different mass transfer rates through the membrane. The operation is usually finalized at the downstream of membrane by condensing the evaporating vapor, which has a much higher concentration of preferentially permeating component in the permeate than it is in the feed mixture. Pervaporation (PV) is a very promising separation technology in food industry for aroma recovery during juice condensation. The feature of extracting and separating compounds in very low concentration with reasonable operation costs is the primary advantage of this technology over other membrane operations. In the process of juice aroma recovery by PV operation the concentration polarization may have serious negative influence on the practical process. The ideal performance of PV will not be attained if these factors are not understood and controlled effectively. In this paper a mathematical model is developed to predict concentration polarization in PV operation of fruit juice aroma recovery. Mathematical analysis and numerical verification is made for changes occurring during PV separation of aroma ingredients to build a model incorporating physical modeling for mass transfer, resistance-in-series theory laminar hydrodynamics, and the boundary layer theory into an easy-to-use correlation. The concentration polarization index (CPI) was used to describe the extent of polarization and characterize resistance. The result from the model indicates that trans-membrane mass flux during aroma recovery decreases when either CPI or boundary layer thickness increases. At low CPI value, the effect of boundary thickness on trans-membrane mass flux is not large and has a negative linear relationship. However, when CPI value is over 0.5 the decrease of trans-membrane mass flux is exponentially decreasing with the increasing of boundary thickness. The adverse influences from boundary thickness and CPI can be controlled by adjusting the velocity feeding material, changing PV configuration, etc. Also these two parameters are inter linked two factors, and the adjustment of one factors usually lead to the change of the other. The model allows the analysis of the impact of flow velocity, feed concentration, and concentration polarization index (CPI) upon the trans-membrane flux and the longitudinal mass flow.
Session 44C, Fruit & Vegetable Products: Chemistry
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