Foam separation, defined

Olefins or alkenes are defined as unsaturated aliphatic hydrocarbons. Ethylene and propylene are the main monomers for polyolefin foams, but dienes such as polyisoprene should also be included. The copolymers of ethylene and propylene (PP) will be included, but not polyvinyl chloride (PVC), which is usually treated as a separate polymer class. The majority of these foams have densities <100 kg m, and their microstructure consists of closed, polygonal cells with thin faces (Figure la). The review will not consider structural foam injection mouldings of PP, which have solid skins and cores of density in the range 400 to 700 kg m, and have distinct production methods and properties (456). The microstructure of these foams consists of isolated gas bubbles, often elongated by the flow of thermoplastic. However, elastomeric and microcellular foams of relative density in the range 0.3 to 0.5, which also have isolated spherical bubbles (Figure lb), will be included. The relative density of a foam is defined as the foam density divided by the polymer density. It is the inverse of the expansion ratio . 

Flotation has been used for more than 100 years to separate sulphides, oxides and other salts from ores, as well as to obtain phosphates, barite, chromite and other materials. Up to 90% of copper, lead, nickel, zinc are extracted using flotation in the USA [152 - 153]. In Russia, flotation is widely used to additionally obtain apatite, barite and phosphates. Flotation of iron oxides is not used in practise yet, but the number of experiments carried out in this direction is rather large. The main physicochemical principles of flotation have been discussed above [59 -74]. Here, only some practical problems will be discussed. In [153], requirements are pointed out which apply to three-phase flotation foams, and the main components of the process are defined, i.e. surfactant - collector surfactant - frother activator, depressants, colligend, gangue. The peculiarities of flotation and foam separation in batch and continuous modes are outlined as well as the structure and properties of the main types of flotation agents described. As surfaces of the majority of mineral particles are hydrophilic in nature, hydrophobisation of particles is necessary for a selective separation. 

A foam is defined as a coarse dispersion of a gas in a liquid, where the volume fraction of gas is greater than that of the liquid. Solid foams (for example foam rubber or polystyrene foam) are also possible, but here we focus on more common liquid foams. These are always formed by mixtures of liquids (usually containing a soap or surfactant) and never by a pure liquid. If the volume fraction of gas is not too high, the bubbles in the foam are spherical, but at higher gas volume fractions the domains are deformed into polyhedral cells, separated by thin films of liquid (Fig. 3.12). Typically the gas bubbles are between 0.1 and 3 mm in diameter. 

Connectivity may be defined as the maximal number of particles (branches, cell walls, and so on) that may be cut without separating the structure. For several porous foods, such as foamed chocolate bar, honeycomb chocolate bar, chocolate muffin, marshmallow, and strawberry mousse, air cell connectivity was defined as a measure of the relative convexity or concavity of the total slid surface (Lim and Barigou, 2004). Concavity indicates connectivity, whereas convexity indicates isolated disconnected structures. Through the image analysis, authors compare the solid area and perimeter before and after an image dilation operation and calculate the index of connectivity as the following ... 

Nanoparticles are frequently used as a suspension in some kind of solvent. This is a two phase mixture of suspended solid and liquid solvent and is thus an example of a colloid. The solid doesn t separate out as a precipitate partially because the nanoparticles are so small and partially because they are stabilised by coating groups that prevent their aggregation into a precipitate and enhance their solubility. Colloidal gold, which has a typical red colour for particles of less than 100 nm, has been known since ancient times as a means of staining glass. Colloid science is a mature discipline that is much wider than the relatively recent field of nanoparticle research. Strictly a colloid can be defined as a stable system of small particles dispersed in a different medium. It represents a multi-phase system in which one dimension of a dispersed phase is of colloidal size. Thus, for example, a foam is a gas dispersed in a liquid or solid. A liquid aerosol is a liquid dispersed in gas, whereas a solid aerosol (or smoke) is a solid dispersed in a gas. An emulsion is a liquid dispersed in a liquid, a gel is liquid dispersed in a solid and a soils a solid dispersed in a liquid or solid. We saw in Section 14.7 the distinction between sol and gel in the sol gel process. 

Foam exhibits higher apparent viscosity and lower mobility within permeable media than do its separate constituents.(1-3) This lower mobility can be attained by the presence of less than 0.1% surfactant in the aqueous fluid being injected.(4) The foaming properties of surfactants and other properties relevant to surfactant performance in enhanced oil recovery (EOR) processes are dependent upon surfactant chemical structure. Alcohol ethoxylates and alcohol ethoxylate derivatives were chosen to study techniques of relating surfactant performance parameters to chemical structure. These classes of surfactants have been evaluated as mobility control agents in laboratory studies (see references 5 and 6 and references therein). One member of this class of surfactants has been used in three field trials.(7-9) These particular surfactants have well defined structures and chemical structure variables can be assigned numerical values. Commercial products can be manufactured in relatively high purity. 

A dispersion Is a system made of discrete objects separated by a homogeneous medium In colloidal dispersions the objects are very small In at least one dimension. Colloidal sizes range from 1 to 100 nm however these limits are somewhat arbitrary, and It Is more useful to define colloids as dispersions where surface forces are large compared to bulk forces. Here we are concerned with systems where the dispersion medium Is a liquid examples are droplets In emulsions or mlcroemulslons (oll/water or water/oll), aggregates of amphiphilic molecules (surfactant micelles), foams, and all the dispersions of solid particles which are used as Intermediates In the manufacture of ceramics. At this stage we are not too concerned with the nature of the constituents, but rather with the structures which they form this Is a geometrical problem, where the system Is characterized by Its surface area A, by the shapes of Its Interfaces (curvatures - b ), and by the distances between opposing surfaces (d — concentration parameter). 

Perhaps the most important variable in the description of foam flow through porous rock is the mobility of the foam, the flow achieved for a given pressure drop. This quantity is defined as the simple ratio of the combined superficial flow rate to the imposed pressure gradient. This ratio is indicated in the first part of equation 2, in which the mobility, A, is given in terms of the combined flow rate, Q, the cross-sectional area of the sample, A, the pressure drop, AP, across the sample, and its length, L. As is well known, in the flow of an ordinary fluid through porous media, the mobility can be separated into two factors one has to do primarily with the properties of the rock, and the other, with the properties of the fluid. By using Darcy s relation, the mobility for the ordinary fluid is computed to be the ratio of effective rock permeability, k, to the fluid viscosity, n. 

The denominator in equation 6 is the sum of the mobilities of dense C02 and of brine that does not contain surfactant when the two are flowing simultaneously. In those circumstances when the flow of C02 can conveniently be measured separately, a resistance factor, Rp can also be defined, as in equation 7, as the ratio of the mobility of the C02 when it is flowing simultaneously with surfactant-free brine to the mobility of the C02 portion of foam. 

Examples of industrial relevance for the first two phase combinations are the adsorption of pollutants from waste air or water onto activated carbon. Combinations three and four are relevant, for example, related to foam formation and stabilization in the presence of surfactants on water/air interfaces or at the interface of two immiscible liquids (e.g., oil and water). This book deals mainly with the case most typical for preparative chromatographic separations, that is, the exploitation of solid surfaces, liquid mobile phases, and dissolved feed mixtures. The following definitions are made The solid onto which adsorption occurs is defined as the adsorbent. The adsorbed molecule is defined in its free state as the adsorptive and in its adsorbed state as the adsorpt. There are typically different solutes, which are often called components (for example, A and B, Figure 2.1). 

The process performance was characterized by the protein enrichment (E), the protein separation (S), as well as by the protein recovery (R), i. e. the partition of protein between the foam liquid and residue liquid. Protein enrichment (E) is defined as ... 

As is the case in most discussions of interfacial systems and their applications, definitions and nomenclature can play a significant role in the way the material is presented. The definition of an emulsion to be followed here is that they are heterogeneous mixtures of at least one immiscible liquid dispersed in another in the form of droplets, the diameters of which are, in general, greater than 0.1 (.m. Such systems possess a minimal stability, generally defined rather arbitrarily by the application of some relevant reference system such as time to phase separation or some related phenomenon. Stability may be, and usually is, enhanced by the inclusion of additives such as surfactants, finely divided solids, and polymers. Such a definition excludes foams and sols from classification as emulsions, although it is possible that systems prepared as emulsions may, at some subsequent time, become dispersions of solid particles or foams. 

Uquid feed line at the tail and collected from the liquid collection line at the head. Nitrogen gas is fed from the gas feed line at the head and discharged through the foam collection line at the tail, while the sample solution is introduced through the sample feed line in the middle portion of the coil. The head-tail relationship of the rotating coil is conventionally defined by an Archimedean screw force, where all objects of different density are driven toward the head. Liquid feed rate and sample injection rate are each separately regulated with a needle valve, while the foam collection line is left open to the air. 

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