Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Conventional techniques of measuring diffusivity (D{dollar}\sb{lcub}\rm e{rcub}{dollar}) in gel entrapment matrices are not practical due to the poor mechanical stability of such solids. A novel apparatus was therefore designed to measure D{dollar}\sb {lcub}\rm e{rcub}{dollar} and partition coefficient (K{dollar}\sb{lcub}\rm p{rcub}){dollar} of glucose in alginate gels using radiotracer techniques. In this method, a specially prepared, large, spherical alginate bead was mounted to a stainless-steel rod and the sphere immersed in a liquid phase of limited volume. By rotating the bead at high angular velocities, the rate of C{dollar}\sp{lcub}14{rcub}{dollar}-glucose uptake or release was measured using a scintillation spectrometer, under conditions of near ideal mixing and negligible film mass transfer resistance. A model equation describing unsteady-state mass transfer in a sphere immersed in a liquid phase of limited volume was used to evaluate D{dollar}\sb{lcub}\rm e{rcub}{dollar}.;When the initial glucose concentration in the liquid phase was increased from 3 to 300 kg.m{dollar}\sp{lcub}-3{rcub}{dollar}, an exponential increase in D{dollar}\sb{lcub}\rm e{rcub}{dollar} values was observed. However, at all concentrations the ratio D{dollar}\sb{lcub}\rm e{rcub}{dollar}/D was constant at 0.91 where D is the free-phase diffusivity of glucose in water. The temperature dependence of D{dollar}\sb{lcub}\rm e{rcub}{dollar} obeyed the Arrhenius relationship and the activation energy for diffusion of glucose in cell-free and cell-occupied (118 kg dry weight/m{dollar}\sp 3{dollar} of gel) Ca-alginate beads was found to be 21.3 and 20.1 kJ.mol{dollar}\sp{lcub}-1{rcub}{dollar}, respectively.;Increase in the concentration of either Ca-alginate, chelating agent (CaCl{dollar}\sb 2{dollar} or BaCl{dollar}\sb 2{dollar}), or entrapped yeast cells, all caused significant reductions in the values of D{dollar}\sb{lcub}\rm e{rcub}{dollar}.;Attempts were made to develop appropriate correlations for predicting D{dollar}\sb{lcub}\rm e{rcub}{dollar} and suitable literature correlations tested whenever possible. The significance of the data reported in this study was assessed in terms of the stability characteristics of the alginate gel matrix and the reported kinetic properties of entrapped cells.



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