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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Continuous foam separation | 3/3 | https://en.wikipedia.org/wiki/Continuous_foam_separation | reference | science, encyclopedia | 2026-05-05T10:46:52.712893+00:00 | kb-cron |
Recovery is how efficiently the protein is removed from the solution into the foam state, the higher the percentage, the better the process is at recovering protein from solute into the foam state. Foam hydrodynamics as well as many of the variables that affect the success of foaming have limited understanding. This complicates using mathematical calculations to predict protein recovery by foaming. However some trends have been determined; high recovery rates have been linked to high concentrations of protein in the initial solution, high gas flow rates, and high feed flow rates. Enrichment is also known to increase when foaming is performed using shallow pools. Using pools with low heights allows for only a small amount of protein to adsorb from the solution to the surface of the bubbles in the foam resulting in lower surface viscosity. This leads to coalescence of the unstable foam higher up in the column causing an increase in the bubble size and an increase in the reflux of the protein in the foam. However, an increased velocity of the gas being pumped into the system has been shown to lead to a decrease in the enrichment ratio. Since these calculations are difficult to predict, bench and then pilot scale experiments are often performed in order to determine if foaming is a viable technique for extraction on an industrial scale.
=== Bacterial cell extraction === Separation of cells is typically done using centrifugation, however foam separation has also been used as a more energy efficient technique. This method has been used on many species of bacteria cells such as Hansenula polymorph, Saccharomyces carlsbergensis, Bacillus polymyxa, Escherichia coli, and Bacillus subtilis, being most effective on cells that have hydrophobic surfaces.
=== Current and Future Directions === Continuous foam extraction was initially used in regard to wastewater treatment in the 1960s. Since then there has not been a lot of research in foaming as an extraction technique. However, in recent years foaming for protein and pharmaceutical extraction has gained increased interest for researchers. Purification of products is the most expensive part of product production in biotechnology, foaming offers an alternative method that is less expensive than some current techniques.
== Separation equipment ==
=== Foaming apparatus ===
Continuous foam separation is one of two major modes of foam separation with the other being batch foam separation. The difference between the two modes is that in continuous mode, surfactant solution is continuously fed through a feed into the foam column and a solution, extracted of surfactant, is also continuously exiting the bottom of the apparatus. The figure to the right shows a diagram of a basic continuous foam separator. The process is stationary (or in steady state) as long as the volume of liquid is constant as a function of time. As long as the process is in steady state, the liquid will not overflow into the foaming column. Depending on the design of the foam separator, the location of the feed flowing in can vary from atop of the liquid solution to the top of the foam column. The creation of the foam starts with the flow of gas into the bottom of the liquid column. The amount of gas flow into the apparatus is measured and maintained through a flow meter. As the foam rises and becomes drained of the liquid, it gets diverted into a separate container to collect the foamate. The height of the foam column is dependent on the application. The diverted foam is liquefied by collapsing the foam bubbles. This can usually be achieved by mechanical means or by lowering the pressure in the foamate collecting vessel. Foam separators for different types of applications use the basic set up shown in the diagram, but can vary with placements and addition of equipment.
=== Design considerations === Additional equipment on the basic form of a foam separator apparatus can be used to achieve other desired effects that suit the type of application, but the underlying process of separation remains the same. The addition of equipment is used to optimize the parameters, enrichment E, or recovery R. Typically, enrichment and recovery are opposing parameters, but there have been some recent studies showing the ability to simultaneously optimize both parameters. The variation of flow rates on the gas input as well as other equipment settings has effects on the optimization of the parameters. The table compares foam separation to other techniques used to separate the protein, α-lactalbumin, from a whey protein solution.
==== pH ==== pH is an important factor in foaming because it will determine if a surfactant will be able to move into the foam phase from bulk liquid phase. The isoelectric point is one factor that must be taken into consideration, when surfactants have neutral charges they are more favorable for adsorption to the liquid-gas interface. pH offers a unique problem for proteins due to the fact that they will denature in pHs that are too high or low. While the isoelectric point is ideal for surfactant adsorption, it has been found that foam is most stable at a pH of 4 and that the foam volume is maximized at pH 10.
==== Surfactants ==== The chain length of non polar parts of surfactants will determine how easily the molecules can adsorb to the foam, and will therefore determine how effective the separation of the surfactant from the solution will be. Longer chains surfactants tend to associate into micelles at the solid-liquid surface. The concentration of the surfactant also plays a factor in the percent removal of the surfactant.
==== Other ==== Some other factors that affect the effectiveness of foaming include the flow rate of the gas, the bubble size and distribution, the temperature of the solution, and the agitation of the solution. Detergents are known to affect foaming. They increase the ability of the solution to foam, increasing the amount of protein recovered in the foamate. Some detergents act as stabilizers for the foam, such as cetyltrimethylammonium bromide (CTAB).
== External links == Biosurfactant Foam Separation Metal Foam Creation Video Collapsing Metal Foam Video
== References ==