Liquid foam fractionation

Liquid foam fractionation Bubble fractionation Liquid Rising air bubbles sometimes also complexing surfactants... 

The droplet analogs to the adsubble methods have been termed the adsoplet methods (from adsorptive droplet separation methods) [LeiTilich, Adsorptive Bubble Separation Methods, Ind. E/ig. Chem., 60(10), 16 (1968)]. They are omitted from Fig. 22-41, since they involve adsorption or attachment at liquid-liquid interfaces. Among them are emulsion fractionation [Eldib, Foam and Emulsion Fractionation, in Kobe and McKetta (eds.). Advances in Petroleum Chemistry and Refining, vol. 7, Interscience, New York, 1963, p. 66], which is the analog of foam fractionation and droplet fractionation [Lemlich, loc. cit. and Strain, J. Phys. Chem., 57, 638... 

Conditions sometimes exist that may make separations by distillation difficult or impractical or may require special techniques. Natural products such as petroleum or products derived from vegetable or animal matter are mixtures of very many chemically unidentified substances. Thermal instability sometimes is a problem. In other cases, vapor-liquid phase equilibria are unfavorable. It is true that distillations have been practiced successfully in some natural product industries, notably petroleum, long before a scientific basis was established, but the designs based on empirical rules are being improved by modern calculation techniques. Even unfavorable vapor-liquid equilibria sometimes can be ameliorated by changes of operating conditions or by chemical additives. Still, it must be recognized that there may be superior separation techniques in some cases, for instance, crystallization, liquid-liquid extraction, supercritical extraction, foam fractionation, dialysis, reverse osmosis, membrane separation, and others. The special distillations exemplified in this section are petroleum, azeotropic, extractive, and molecular distillations. 

A 100-mg/L glucosidase solution was used throughout this part of the experiment. Ten milliliters of this solution was poured into the foam fractionation column. The air velocity was then set at 10 cc/min and the pH at 5.4 (the unadjusted solution pH). A 1-mL sample was taken from the liquid phase at several different times 0, 1, 1.5, 2, 3, 4, 5, 7, and 10 min. The experiment was repeated with 100-mg/L of glucosidase solution for more acidic and basic conditions, at pH 2.4 and 11.6, respectively. 

The foam expansion ratio or its reciprocal value the foam liquid volume fraction, called also relative or volume density of a foam, is used as a basic parameter characterizing the liquid to gas ratio in the foam. 

When h r a the contribution of vertexes to the liquid volume fraction of a foam estimated from Eq. (4.4) is smaller compared to that of films, Eq. (4.2) and borders, Eq. (4.3). The relative contribution of borders and films depends on capillary and disjoining pressures. In a foam with thin (black) films at capillary pressures up to 5.103 Pa the border volume is... 

Sharovamikov and Tsap [66] have proposed another way to measure the liquid distribution in a foam based on the evaluation of the geometric coefficient B. The dependence of the film liquid volume fraction on the total foam liquid volume (ft = cp/( +(p) can be expressed by two almost equivalent formulae (see Section 8.3.)... 

In the process of foam evaporation the films on the exterior protect those in the interior from rupturing until they themselves reach the exterior. That is why the rate of foam column destruction vh caused by evaporation would depend on the rate of film evaporation and the liquid volume fraction in films tp /, i. e. 

Mobility of the gas phase is reduced in two ways when a foam is used. First, liquid lamallae become trapped and block off a portion of the porous media. This results in a stationary foam fraction that can be nearly unity at low flow rates. Also lamellae present in the flowing foam fraction create an additional resistance to flow. The apparent viscosity of foam can be several orders of magnitude larger than the gas viscosity. 

The experiment was initiated by introducing nitrogen gas from the gas feed line at the head of the rotating column. Then, a 2.5-L volume of the BC solution was continuously introduced into the coil from the sample feed line at 1.5 mL/min. The hydrophobic components produced a thick foam which was carried with the gas stream and collected from the foam collection line at the tail other components stayed in the liquid stream and eluted from the liquid collection line at the head. High-performance liquid chromatographic analysis of the foam fraction revealed that the degree of enrichment increased with the hydrophobidty of the components. These results clearly indicate that the present method will be quite effective for the detection and isolation of small amounts of natural products present in a large volume of aqueous solution. 

After the experiment, fractions from the foam and liquid outlets are collected and analyzed. The elution curve of bacitracin components from the foam outlet shows three major peaks, and the one from the liquid outlet. The HPLC analysis of fractions clearly indicate that the bacitracin components are separated in the order of hydrophobicity of the molecule in the foam fractions and in increasing order of their hydrophiUcity in the liquid fractions. 

According to the collection procedure for the enriched gas-liquid and/or gas-solid interfaces, adsorptive bubble separation processes or techniques can also be divided into two large categories (a) foam separation, which involves the production of foam in the process, and (b) nonfoaming adsorptive bubble separation, which involves no production of foam. Foam separation can be further subdivide into foam fractionation and flotation. Nonfoaming adsorptive bubble separation, however, can be further subdivided into bubble fractionation, solvent sublation, and noirfoaming flotation. Lemlich (84) and Wang (1,75) provided the definitions of these technical terms in their books. 

Type of flow pattern(s) involved in an adsorptive bubble separation system depends on the type of process used. For example, bubble fractionation involves two-phase (gas-phase and liquid-phase) bubble flow, while solvent sublation involves multiphase bubble flow in their vertical bubble cells. Foam fractionation involves a two-phase bubble flow in the bottom bubble cell, and a two-phase froth flow in the top foam cell. However, all froth flotation processes (i.e., precipitate flotation, ion flotation, molecular flotation, ore flotation, microflotation, adsorption flotation, macroflotation, and adsorbing colloid flotation) involve multiphase bubble flow and multiphase froth flow. 

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