Effects of kinetics of adsorption and coalescence on continuous foam concentration of proteins
Abstract
Foam concentration is an adsorptive bubble separation technique in which soluble surface active substances can be concentrated from dilute solution by preferential adsorption at the gas-liquid interface generated by a rising ensemble of bubbles. It was possible to concentrate BSA and $\beta$-casein from 0.01-0.1 wt% and 0.01-0.05 wt% respectively in a continuous foam column because of their surface activity. Enrichments ranged from 1.5-10 and recoveries from 10-30%. The effects of kinetics of adsorption of protein, feed concentration, gas velocity, bubble size, foam height, coalescence, pH and ionic strength on the performance of a foam concentration column were investigated. Gas velocity was varied between 0.13-0.26 cm/s, bubble size between 0.08-0.12 cm, foam height ranged from 7-32 cm, pool height between 2-40 cm, pH from 3-7 and ionic strength from 0.002-0.1 M. Protein enrichment was higher for larger bubble sizes, larger foam heights, lower feed concentrations and smaller gas velocities. A minimum enrichment was found at an intermediate pool height because of opposing effects of kinetics of adsorption and coalescence. Bubble size was minimum at pI of BSA leading to minimum enrichment. Enrichments were insensitive to ionic strength in the range of 0.002-0.1 M. A model for the hydrodynamics of the foam bed was developed accounting for the kinetics of adsorption as well as coalescence. Kinetics of adsorption of proteins was described in terms of surface hydrophobicity, surface pressure and electrostatic interactions. A surface equation of state for globular protein was developed to predict the variation of surface pressure with surface concentration. Coalescence frequencies were evaluated from the experimental measurements of mean bubble size versus foam height using image analysis. Model predicted an upper bound for protein enrichment when only coalescence was accounted for; whereas model predictions accounting only for kinetics of adsorption provided lower bound. Combined effects of coalescence and kinetics of adsorption resulted in a minimum enrichment at an intermediate pool height. Model predictions of protein enrichment at a feed concentration of 0.1 wt% compared well with the experimental data for different pool heights, bubble sizes, gas velocities, foam heights and pH excepting at very low pool heights.
Degree
Ph.D.
Advisors
Narsimhan, Purdue University.
Subject Area
Agricultural engineering
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