15D-19 |
Significance of fluid rheological properties on the pressure drop during ultrafiltration of xanthan fermentation broth |
M. HUANG1, L. M. Dietrich2, and Y. M. Lo1. (1) Dept. of Animal & Food Sciences, Univ. of Delaware, 040 Townsend Hall, 531 S. College Ave., Newark, DE 19717-1303, (2) Dept. of Chemical Engineering, Univ. of Delaware, Colburn Lab., Newark, DE 19711 Xanthan gum is a microbial polysaccharide with extensive industrial applications because of its unique rheological properties. The low xanthan productivity limited by high broth viscosity, however, results in high production costs due to excessive amount of alcohol needed for product recovery. We have developed an ultrafiltration (UF) system as an alternative to alcohol precipitation for xanthan recovery from dilute fermentation broth. Directly related to overall process energy consumption, the variations of pressure drop during xanthan UF needs to be characterized, especially when both power-law constants, n and K, are dependent on the xanthan concentration in solution. Our objective was to characterize the pressure drop during UF of xanthan fermentation broth with respect to its rheological characteristics. Differential equations for the pipe flow of shear-thinning xanthan broth were solved with boundary conditions. Assuming steady state with negligible external forces and entrance effect, the average velocity for shear thinning xanthan flow in the UF as a function of pressure drop was established. Experimental data from hollow fiber UF of xanthan broth were used to verify the prediction. The liquid flow in the hollow fiber UF tubing was found to be laminar with Reynolds number less than 10 for incompressible xanthan broth. The pressure drop was found to increase with increasing xanthan concentration. The effects of xanthan concentration on the apparent solution viscosity and thus the pumping pressure drop are significant when the concentration is lower than 50 g/L. More power input is required to maintain the same flow rate as the xanthan concentration increases. The predictions from the model fit the experimental data well (p < 0.05). The model developed to predict dynamic pressure drop in xanthan UF provides a solid foundation for scale up consideration. Results obtained from this study are essential for process economic analysis.
Session 15D, Food Engineering: Processing Technologies
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