Foaming properties of surfactants

The purpose of the one atmosphere experiment described herein is to determine the relative not the absolute foaming properties of surfactants and to determine the best candidates for evaluation under realistic reservoir conditions. Therefore, the dependence of foam volumes on the experiment design are not of concern as long as the one atmosphere experiments are performed in a reproducible manner and the test design is such as to distinguish between poor, mediocre, and good candidates for testing under reservoir conditions. ... 

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. 

Lachaise, J., Breul, T., Graciaa, A., Marion, G., Monsalve, A. and Salager, J.L. (1990) Foaming properties of surfactant-oil-water systems in the neighbourhood of optimum formulation. /. Dispersion Sci. Technol., 11,443 453. 

Because the core of an aqueous micelle is extremely hydrophobic, it has the abiHty to solubiHze oil within it, as weU as to stabilize a dispersion. These solubilization and suspension properties of surfactants are the basis for the cleansing abiHty of soaps and other surfactants. Furthermore, the abiHty of surfactants to stabilize interfacial regions, particularly the air—water interface, is the basis for lathering, foaming, and sudsing. 

Glasl [149] reported the foaming properties of several alcohol sulfates and alcohol ether sulfates using the perforated disk method as described in the DIN standard 53902. All values were obtained at 0.28 g/L surfactant concentration, both in distilled water and in water of 16°dH hardness at 20, 40, and 60°C. The results are shown in Figs. 15-17. 

Due to the good lime soap dispersing properties it is possible to improve the foaming properties of hard water-susceptible surfactants. Improvement of the formulation of a fatty acid soap by laureth-17 carboxylic acid, sodium salt [57,62], and an amidether carboxylate [62] has been described. 

Figure 32. Foam properties of propylene oxide adduct of secondary alcohol ethoxylate compared with those of others. Test conditions method—Ross-Miles (JIS-K-3362) surfactant concentration—1.0 wt % water temperature—25°C. ((- -) Cn.H SAE (7EO) + (4.5PO) (-1-) CI2 + Ii PAE (7EO) + (4.5PO) (-U-) HPE (8EO) + (4.5PO))...

The foam properties of products are mainly governed by the surfactant system and the use of anti-foams discussed below. Besides this the chemical composition of the product or the washing liquor, for example electrolyte content and soil, strongly influences the foam properties. Physical parameters such as temperature and pH value or mechanical input in the system additionally have to be taken into account. 

Foam stabilising properties of surfactants determined by Foam Pressure... 

These two examples with the homologous series of alkylsulphonates and alkylsulphates indicate the undoubted advantages of Foam Pressure Drop Technique for determining the foam stabilising properties of surfactants. This technique allows to distinguish small differences in the foam stabilising ability of surfactants. 

Mast, in a pioneering 1972 paper, reported visual observations of foam flow in etched glass micromodels (37 ) His observations showed that some of the conflicting claims about the properties of foam flow in porous media were probably due simply to the dominance of different mechanisms under the various conditions employed by the separate researchers (37). Mast observed most of the various mechanisms of dispersion formation, flow, and breakdown that are now believed to control the sweep control properties of surfactant-based mobility control (37,39-41). 

An early attempt to correlate the physical properties of surfactant solutions and their foams with oil recoveries was performed by Deming in 1964 (50). Deming concluded that high foaming ability favored high displacement efficiency, but that high foam stability were not required for high displacement efficiency. Bernard and Holm found that oil substantially decreased the abilities of most surfactants to reduce aqueous permeabilities, but that some surfactants remained effective even in the presence of oil (52,53). 

Figure 4. Effect of number of ethoxy groups on foaming properties of sulfonate surfactants at 1 atmosphere and at 2500 psig.

Correlation equations relating surfactant chemical structure to performance characteristics and physical properties have been established. One atmosphere foaming properties of alcohol ethoxyl-ates and alcohol ethoxylate derivatives have been related to surfactant hydrophobe carbon chain length, ethylene oxide content, aqueous phase salinity, and temperature. Similar correlations have been established for critical micelle concentration, surfactant cloud point, and surfactant adsorption. 

The foaming properties of a large number of alcohol ethoxylates have been reported in the literature(13) (Table 3). No oil phase was present in these tests. Surfactants were obtained from two different suppliers. 

Table I shows various surface and microscopic properties such as surface tension, surface viscosity, foaminess (i.e. foam volume generated in a given time) and bubble size in foams of the surfactant solutions as a function of chain length compatibility. The results indicate that a minimum in surface tension, a maximum in surface viscosity, a maximum in foaminess and a minimum in bubble size were observed when both the components of the mixed surfactant system have the same chain length. These results clearly show that the molecular packing at air-water interface influences surface properties of the surfactant solutions, which can influence microscopic characteristics of foams. The effect of chain length compatibility on microscopic and surface properties of surfactant solutions can be explained as reported in the previous section.

The viscoelastic properties of the surface layer are important parameters. The most useful technique for studying the viscoelastic properties of surfactant monolayers is surface scattering. When transversal ripples occur, a periodic dilation and compression of the monolayer occurs, and this can be accurately measured, enabling the viscoelastic behaviour of monolayers under equilibrium and nonequilibrium conditions, to be obtained, without disturbing the original sate of the adsorbed layer. Some correlations have been found between surface viscosity and elasticity and foam stability an example of this is the addition of lauryl alcohol to sodium lauryl sulphate, which tends to increase the surface viscosity and elasticity [10]. 

The foaming properties of the nonionic surfactants depend upon the temperature because of their inverse solubility temperature relationship. Above the cloud point they are nonfoamers and some nonionic surfactants may even function as defoamers above their cloud point temperature. Therefore, the nonionic surfactant selected for rinse aid formulations must have a cloud point below the temperature of the rinse water. 

In most cases, when different types of surfactants are purposely mixed, what is sought is synergism, the condition in which the properties of the mixture are better than those attainable with the individual components by themselves. For example, a long-chain amine oxide is often added to a formulation based upon an anionic surfactant because the foaming properties of the mixture are better than those of either surfactant by itself. 

The evaluation of surfactant adsorption is particularly important when foams for high salinity reservoirs, such as many Canadian reservoirs subjected to hydrocarbon-miscible flooding, are considered. This puts stringent requirements on the solubility, foaming, and adsorption properties of surfactants that may be considered for foam applications, and severely limits the types of surfactant that may be used. 

Wang Xianguang, et al. Foam Properties of ABEPS Series Anionic-Nonionic Surfactants[J]. Oilfield Chemistry, 2009, 26(4) 357-361. 

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