Foam fractionation, separations using

The adsorption at the water-air interface is used in separation and concentration processes (foam separation and flotation extraction) [87]. To remove the traces of metals that are present in the anionic form, the method of foam fractionation is used. (The foam is formed during air bubbhng through the water solution of hexade-cyltrimethylammonium bromide) [88]. In this process the selectivity coefficients are determined by the anion hydration energies. 

Foams have a wide variety of appHcations that exploit their different physical properties. The low density, or high volume fraction of gas, enable foams to float on top of other fluids and to fiU large volumes with relatively Httle fluid material. These features are of particular importance in their use for fire fighting. The very high internal surface area of foams makes them useful in many separation processes. The unique rheology of foams also results in a wide variety of uses, as a foam can behave as a soHd, while stiH being able to flow once its yield stress is exceeded. 

A very low gas rate in a column several feet tall with internal reflux can sometimes be used to effect difficult multicomponent separations in batch operation [Lemlich, Principles of Foam Fractionation, in Periy (ed.). Progress in Separation and Purification, vol. 1, Inter-science, New York, 1968, chap. 1]. 

Foam can also be broken with a rotating perforated basket [Lem-lich, Principles of Foam Fractionation, in Periy (ed.), Progre.ss in Separation and Purification, vol. 1, Interscience, New York, 1968, chap. 1]. If the foamate is aqueous (as it usually is), the operation can be improved by discharging onto Teflon instead of glass [Haas and Johnson, Am. In.st. Chem. Fng. J., II, 319 (1965)]. A turbine can be used to break foam [Ng, Mueller, and Walden, Can. J. Chem. Fng., 55, 439 (1977)]. Foam which is not overly stable has been broken by running foamate onto it [Brunner and Stephan, Ind. Fng. Chem., 57(5), 40 (1965)]. Foam can also be broken by sound or ultrasound, a rotating disk, and other means [Ohkawa, Sakagama, Sakai, Futai, and Takahara,y. Ferment. Technol, 56,428, 532 (1978)]. 

By using an anionic collector and external reflux in a combined (enriching and stripping) column of 3.8-cm (1.5-in) diameter with a feed rate of 1.63 ni/n [40 gal/(h ft )] based on column cross section, D/F was reduced to 0.00027 with C JCp for Sr below 0.001 [Shou-feld and Kibbey, Nucl. AppL, 3, 353 (1967)]. Reports of the adsubble separation of 29 heavy metals, radioactive and otheiwise, have been tabulated [Lemlich, The Adsorptive Bubble Separation Techniques, in Sabadell (ed.), Froc. Conf. Traces Heavy Met. Water, 211-223, Princeton University, 1973, EPA 902/9-74-001, U.S. EPA, Reg. 11, 1974). Some separation of N from by foam fractionation has been reported [Hitchcock, Ph.D. dissertation. University of Missouri, RoUa, 1982]. 

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. 

Foam fractionation. Section 4.14, uses differences in surface activity to effect the separation. 

Foam fractionation and flotation are the terms given to the separation processes by which inorganic and organic ions, molecules, colloidal particles, and suspended solids are floated from aqueous solutions with a rising stream of bubbles. Flotation is sometimes used to mean the removal of particulate materials by bubbling, whereas foam fractionation indicates the foaming off of dissolved materials by adsorption on bubble surfaces. Overlap and inconsistency in terminology are often encountered. 

WIPAG Polymertechnik, of Germany, has developed proprietary separation processes for plastics, some of which are based on physical hardness. The technology is being used for recovering plastic from automobile bumpers and for sorting automobile instrument panels into hard flake, soft flake, and foam fractions. The company is involved in Joint ventures with American Commodities in FUnL MI, and with PPR in Kent, England. ... 

As mentioned before, the basis of bioseparation and unit operation is based on the differences of physicochemical properties of the materials (Figure 2.2). Chromatography methods are not always the best option due to variable yield losses and high costs. ° Therefore, various attempts have been made to find new separation processes focusing on cost reduction. Among these options, a versatile and promising technique is that of the foam fractionation (Figure 2.2), an adsorptive bubble separation technique in which the principle of separation is based on the differences in the surface activity of molecules. It has been used to separate proteins, but it can also be used for other purposes [e.g. the concentration of plant secondary metabolites). ... 

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