Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Chemical and Biological Engineering


The kinetics of isolectric precipitation of soy protein in a turbulent stirred tank reactor was studied. The effects of protein feed concentration, pH of precipitation, mean residence time, ionic strength, mixing speed, and order of addition of salt were investigated;The particle size distribution (PSD) of the solid phase was determined using a Coulter Counter Model TAII equipped with a 70 (mu)m diameter aperture tube. Protein recoveries after centrifugation and/or filtration were determined using the Kjeldahl procedure;The kinetics of solid phase formation were modelled and the results compared with the experimental PSD. The model includes growth, breakage, and outflow from the continuous reactor;Aggregate growth was described as proceeding by addition of submicron particles to a growing aggregate as a result of both Brownian and turbulent motion. The frequency of collision of colloidal particles in a turbulent fluid was combined with the definition of a linear growth rate to obtain alternative growth rate expressions dependent on particle diameter, volume fraction of primary particles, and mixer power input;Possible hydrodynamic mechanisms for particle disruption in a turbulent fluid were examined. It was shown that for the size and density of these protein aggregates the local shear mechanism predominates over the usually considered turbulent pressure fluctuations and surface erosion (due to relative motion). The aggregates breakage rate was shown to be a function of aggregate concentration and of a dimensionless Force Number (forces acting on the aggregate/forces binding the aggregate). Breakage was described as a 'thorough' process with daughter fragments smaller than the aggregate nuclei;Good fit was obtained using the proposed model and most aspects of the variation of kinetic parameters with pH, mixing speed, ionic strength, and feed concentration agreed qualitatively with the proposed mechanisms. In addition, growth rate could be related to (zeta)-potential.



Digital Repository @ Iowa State University,

Copyright Owner

Maria Angela de A. Meireles Petenate



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86 pages