Introduction

Foam concentration/fractionation is a separation technique in which surface-active solutes are either concentrated from a dilute solution or separated from a mixture by preferential adsorption at a gas-liquid interface created by sparging an inert gas through the solution. These gas bubbles entrain the surfactant solution and form a stable foam with a large gas-liquid interfacial area. As the foam moves through the column, the surfactant solution tends to drain due to gravity and capillary forces. This results in a decrease in the amount of liquid in the foam. The reduction in the entrained liquid is first associated with the bubbles forming the closest spherical packing, after which they will deform to a dodecahedral shape and then possibly coalesce. Consequently, there is an increase in the gas-liquid interfacial area per unit volume of the liquid. The surfactant tends to adsorb preferentially at the gas-liquid interface. At the top of the column, the foam is sent to a foam breaker where the foam is broken either mechanically or chemically. This results in either enrichment or concentration of more surface-active protein because of the recovery of adsorbed protein from the gas-liquid interface into the bulk entrained liquid. In the case of a dilute solution of a single protein, the extent of enrichment would depend upon the relative amount of adsorbed protein compared to that in the bulk entrained liquid. In the case of a mixture of proteins in solution, the separation of a protein from the mixture would depend upon the extent of preferential adsorption of that protein at the gas-liquid interface. Since the adsorption isotherm usually leads to a much higher proportion of adsorbed protein at very low bulk concentrations, foam concentration is very effective for extremely dilute solutions.

Because of the presence of hydrophilic and hydro-phobic functional groups, proteins are surface active. Therefore, foam-based separations are viable for concentration/separation of protein solutions. Foam-based separation has been applied to various proteins and enzymes. Experimental investigation has been summarized in Table 1. This review highlights the theoretical aspects of prediction of enrichment and separation of proteins and enzymes in a foam frac-tionation column.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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