Chemical separations, foams

Separations. Foams have important uses in separations, both physical and chemical (51,52). These processes take advantage of several different properties of foams. The buoyancy and mechanical rigidity of foam is exploited to physically separate some materials. The large volume of vapor in a foam can be exploited to filter gases. The large surface area of a foam can also be exploited in the separation of chemicals with different surface activities. 

Surfactant enhanced chemical separations are obtained through coacervation, liquid membranes, ultrafiltration, foams and/or other interactions with phospholipids, proteins and biomolecules. All these topics were deliberately excluded. They are well exposed in the literature [1-3]. 

The chemical equilibrium in a multiphase system and the corresponding species concentrations in chemical separations are altered when chemical reactions take place. We will illustrate this now for gas-liquid equilibrium (as in gas absorption), vapor-liquid equilibrium (as in distillation), liquid-liquid equilibrium (as in solvent extraction), stationary phase-liquid equilibrium (as in ion exchange, chromatography and crystallization), surface adsorption equilibrium (as in foam fractionation) and Donnan equilibrium. 

Chemical additives for gas-based drilling fluids are limited to surfactants (qv), certain polymers, and occasionally salts such as sodium or potassium chloride. An aqueous solution of the additives is iajected iato the air or gas flow to generate a mist or foam. No additives are used ia dry air or gas drilling operations. Gas-based fluids are not recirculated and materials are added continuously. As the fluid exits the well, air or water vapor escapes to the atmosphere, gas and oil are burned, and water and formation soflds are collected into a pit for later disposal. Stable foams must be destabili2ed to separate the air from the Hquid phase for disposal. 

While the ambient-temperature operation of membrane processes reduces scaling, membranes are much more susceptible not only to minute amounts of scaling or even dirt, but also to the presence of certain salts and other compounds that reduce their ability to separate salt from water. To reduce corrosion, scaling, and other problems, the water to be desalted is pretreated. The pretreatment consists of filtration, and may include removal of air (deaeration), removal of CO2 (decarbonation), and selective removal of scale-forming salts (softening). It also includes the addition of chemicals that allow operation without scale deposition, or which retard scale deposition or cause the precipitation of scale which does not adhere to soHd surfaces, and that prevent foam formation during the desalination process. 

The second type is a stable dispersion, or foam. Separation can be extremely difficult in some cases. A pure two-component system of gas and liquid cannot produce dispersions of the second type. Stable foams can oe produced only when an additional substance is adsorbed at the liquid-surface interface. The substance adsorbed may be in true solution but with a chemical tendency to concentrate in the interface such as that of a surface-active agent, or it may be a finely divided sohd which concentrates in the interface because it is only poorly wetted by the liquid. Surfactants and proteins are examples of soluble materials, while dust particles and extraneous dirt including traces of nonmisci-ble liquids can be examples of poorly wetted materials. 

Systems Separated Some of the various separations reported in the literature are listed in Rubin and Gaden, Foam Separation, in Schoen (ed.). New Chemical Engineering Separation Techniques, Interscience, New York, 1962, chap. 5 Lemlich, Ind. Eng. Chem., 60(10), 16 (1968) Pushkarev, Egorov, and Khrustalev, Clarification andDeactiva-tion of Waste Waters by Frothing Flotation, in Russian, Atomizdat, Moscow, 1969 Kuskin and Golman, Flotation of Ions and Molecules, in Russian, Nedra, Moscow, 1971 Lemlich (ed.), Adsorptive Bubble... 

Chemically, the preparation of a "stable" foam or emulsion requires the use of a surfactant to aid in dispersion of the internal phase and prevent the collapse of the foam (or emulsion) into separate bulk phases. The selection of a surfactant is made on the basis of severity of conditions to be encountered, the gas to be entrained (N2, C02, LPG, CH, or air), the continuous phase liquid (water, alcohol, or oil), and half-life of foam stability desired. 

Wallace Jr GT, Wilson DF (1969) Foam separations as a tool in chemical oceanography. Report no. 6958. US Naval Research Laboratory, p 1... 

Although adsorption has been used as a physical-chemical process for many years, it is only over the last four decades that the process has developed to a stage where it is now a major industrial separation technique. In adsorption, molecules distribute themselves between two phases, one of which is a solid whilst the other may be a liquid or a gas. The only exception is in adsorption on to foams, a topic which is not considered in this chapter. 

It is our intention to present strategies based on chemically induced phase separation (CIPS), which allow one to prepare porous thermosets with controlled size and distribution in the low pm-range. According to lUPAC nomenclature, porous materials with pore sizes greater than 50 nm should be termed macroporous [1]. Based on this terminology, porous materials with pore diameters lower than 2 nm are called microporous. The nomination mesoporous is reserved for materials with intermediate pore sizes. In this introductory section, we will classify and explain the different approaches to prepare porous polymers and to check their feasibility to achieve macroporous thermosets. A summary of the technologically most important techniques to prepare polymeric foams can be found in [2,3]. 

The foam produced with Aqueous Film Forming Foam (AFFF) concentrate is dry-chemical compatible. Protein and fluoroprotein foam concentrates and AFFF concentrates are incompatible and should not be mixed although foams separately generated with these concentrates are compatible and can be applied to a fire in sequence or simultaneously. AFFF is available in various liquid concentrate percentages. 

This means if one, through foam bubbles, collected the foam continuously, then more and more surface-active substances will be removed. Such a method of bubble foam separation has been used to purify wastewater from surface-active substances. It is especially useful when very minute amounts of surface-active substances (dyes in the printing industry pollutants in wastewater). The method is economical to use and is free of any chemicals or filters. In fact, if the pollutant is very expensive or poisonous, then this method can have many advantages over the other methods. 

A cross-linked polyolefin foam sheet is produced by two methods using chemical cross-linking and by two methods of radiation cross-linking. The two well-established manufacturing processes for polyolefin foams using radiation cross-linking are the Sekisui process and Toray process. The differences between these two manufacturing methods are mainly in the expansion step, which is almost always done separately. However, the... 

While we will discuss the control of the various properties presented in the last section, the composition of a device must represent an optimum of all the properties. As we have shown, the quality of a foam is achieved by a complex combination of chemical and physical effects. No unifying model combines them in a sufficiently precise way as to minimize the work involved. Thus, as we discuss ways to control compressive and tensile strength, we must be aware that these properties will affect the foaming process. The design process is made somewhat easier by using composite techniques. In this way, one can separate the physical requirements of a device... 

The foaming problem at Suliom Voc terminal was overcome by the development of a novel anti-foam chemical that is effective in breaking down ihe very stable foams generated by g3s release from live crude Foam detection equipment on separators has proved an invaluable as set in aiding foam control... 

Investigation of foaming characteristics of crudes and effectiveness of anti-foam chemicals should he conducted at an early stage of the design of gas/oil separators to assess the economics of extra residence time (larger separation vessels) vs. anti-foam chemical injection as the means of preventing foam... 

Cas-o l separators ran be plagued by solids buildups, especially il solids are a known problem This may be particularly so i( the demulsifier is injected prior to the separator resulting in release of the solids from the emulsion. A suitable demulsifier will break foam and release the gas but if excessive foam is a problem and the chemical does not readily break the emulsion to release the gas at this potni, it is possible for loam to build up and carry emulsion out the gas outlet. The lack of adequate gas removal will cause undesirable agitation at points downstream. It can cause some rolling of fluids ui vessels at atmospheric pressure or in pressure vessels where operating pressures are exceeded. 

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