Surfactant adsorption minimization

Thus, adding surfactants to minimize the oil-water and solid-water interfacial tensions causes removal to become spontaneous. On the other hand, a mere decrease in the surface tension of the water-air interface, as evidenced, say, by foam formation, is not a direct indication that the surfactant will function well as a detergent. The decrease in yow or ysw implies, through the Gibb s equation (see Section III-5) adsorption of detergent. 

Formulation strategies for stabilization of proteins commonly include additives such as other proteins (e.g., serum albumin), amino acids, and surfactants to minimize adsorption to surfaces. Modification of protein structure to enhance stability by genetic engineering may also be feasible, as well as chemical modification such as formation of a conjugate with polyethylene glycol. 

This chapter reports adsorption data for a number of surfactants suitable for mobility control foams in gas-flooding enhanced oil recovery. Surfactants suitable for foam-flooding in reservoirs containing high salinity and hardness brines are identified. The results of adsorption measurements performed with these surfactants are presented surfactant adsorption mechanisms are reviewed and the dependence of surfactant adsorption on temperature, brine salinity and hardness, surfactant type, rock type, wettability and the presence of an oil phase is discussed. The importance of surfactant adsorption to foam propagation in porous media is pointed out, and methods of minimizing surfactant adsorption are discussed. 

This section has demonstrated that some commercially available surfactants are soluble in brines of extreme salinity and hardness and also form effective mobility control foams under these conditions. The remainder of this chapter is devoted to the development of a better understanding of the adsorption properties of foam-forming surfactants, mainly those for high-salinity conditions. It is hoped that this discussion will contribute to the development of a systematic approach for selecting or formulating surfactants with minimal adsorption levels. 

Surfactant—solid and surfactant—surfactant hydrophobic interactions lead to minimization of solid—water and surfactant-chain—water contact and are energetically favorable. Unlike hydrophilic surfaces, hydrophobic surfaces do not lead to significant structuring of interfacial water, and the interfacial water is displaced from the surface relatively easily by the surfactant molecules. Consequently, surfactant adsorption on hydrophobic surfaces has often been found to be higher than adsorption on the corresponding hydrophilic surfaces (39, 54, 56, 57, 59—62), provided aqueous phase salinity is low. 

This section discusses three approaches that may be used to minimize surfactant adsorption matching surfactant type to specific reservoir rock type based on surfactant ionic character and solid surface charge, application of surfactant mixtures, and sacrificial adsorbates (128). 

Even a cursory look at the consumption of chemicals illustrates the importance of minimizing surfactant adsorption (128). A small section of a densely drilled reservoir typical of older oil reservoirs that are prime... 

Surfactant Mixtures. Another promising approach to minimizing surfactant adsorption is through the formulation of surfactant mixtures. The mechanism of adsorption reduction in surfactant mixtures is based on a unique property of surface active substances the formation of micelles (129—134). 

One of the factors that determines foam propagation and foam-flood economics is surfactant loss in the reservoir, most importantly adsorption at the solid—liquid interface. Adsorption levels of foaming surfactants, mostly those suitable for high salinity conditions, cover a wide range and lead to vastly different distances of foam propagation. Therefore, selection of a surfactant with minimal adsorption levels for the reservoir conditions of interest is crucial. 

The next section describes measurements of interfacial tension and surfactant adsorption. The sections on w/c and o/c microemulsions discuss phase behavior, spectroscopic and scattering studies of polarity, pH, aggregation, droplet size, and protein solubilization. The formation of w/c microemulsions, which has been achieved only recently [19, 20], offers new opportunities in protein and polymer chemistry, separation science, reaction engineering, environmental science for waste minimization and treatment, and materials science. Recently, kinetically stable w/c emulsions have been formed for water volume percentages from 10 to 75, as described below. Stabilization and flocculation of w/c and o/c emulsions are characterized as a function of the surfactant adsorption and the solvation of the C02-philic group of the surfactant. The last two sections describe phase transfer reactions between lipophiles and hydrophiles in w/c microemulsions and emulsions and in situ mechanistic studies of dispersion polymerization. 

Low interfacial tensions and minimal surfactant loss due to interactions with reservoir solids are two of the most important conditions for effective oil recovery by displacement fluids in chemical flooding. These two requirements are, of course, related surfactant adsorption from a microemulsion whose properties have been carefully designed leads to changes in the composition and therefore in the interfacial behavior of the microemulsion. 

The importance of minimizing adsorption has provided the impetus for a number of adsorption studies of both anionic and nonionic surfactants on representative reservoir solids most of these deal with surfactant adsorption from aqueous solution. In general it has been found that the adsorption of petroleum sulfonates on mineral adsorbents increases with decreasing solubility in the solvent. Gale and Sandvik (1) have found that petroleum sulfonate adsorption from brine on clay minerals increased with molecular weight and therefore decreasing solubility in brine. 

Some of the techniques used to minimize surfactant adsorption include mixing of different types of surfactants and the use of sacrificial adsorbent [64], At the low pH environment encountered during acidizing, mutual solvent was found to minimize the loss of surfactant due to adsorption in sandstone reservoirs [65]. 

Fluorinated surfactants have unique properties and are therefore indispensable. A potential effect on the environment can be reduced by (1) using synergism with hydrocarbon-type surfactants to minimize the concentration of fluorinated surfactant where feasible and (2) removing fluorinated surfactants from wastewater at industrial sites by adsorption or converting the surfactant by partial biodegradation to physiologically inert substances. 

Loss of surfactant due to adsorption onto the rock surface can also be minimized by blending the AOS with DPOS. This is shown in Fig. 28 which is a plot of the amount of surfactant adsorbed onto montmorillonite clay vs. the percentage of AOS in the blend. Clearly, when there is more than about 30% DPOS in the blend, total adsorption of surfactant is suppressed. 

Surface Behavior. Most extraction processes deal with several phases. At the boundaries between these phases, an interface exists which can be populated with or depopulated of polymer. Situations in which the polymer should accumulate at the surface of one phase are 1. the flocculation of clays and fines or 2. the formation of foams, while situations in which the polymer should depopulate the surface of the phase boundary are 3 minimizing adsorption in mineral acid leaching or 4. minimizing surface tension with surfactants in oil recovery by miscible flooding.,... 

The slopes of the peaks in the dynamic adsorption experiment is influenced by dispersion. The 1% acidified brine and the surfactant (dissolved in that brine) are miscible. Use of a core sample that is much longer than its diameter is intended to minimize the relative length of the transition zone produced by dispersion because excessive dispersion would make it more difficult to measure peak parameters accurately. Also, the underlying assumption of a simple theory is that adsorption occurs instantly on contact with the rock. The fraction that is classified as "permanent" in the above calculation depends on the flow rate of the experiment. It is the fraction that is not desorbed in the time available. The rest of the adsorption occurs reversibly and equilibrium is effectively maintained with the surfactant in the solution which is in contact with the pore walls. The inlet flow rate is the same as the outlet rate, since the brine and the surfactant are incompressible. Therefore, it can be clearly seen that the dynamic adsorption depends on the concentration, the flow rate, and the rock. The two parameters... 

In application-related problems the question may also be formulated in terms of minimizing the necessary additional work. From knowledge of the interfacial properties of surfactant mixtures the surface activity, tendency to form micelles, adsorption, etc., can be increased. The following effects may pertain ... 

Problems that can arise in the process include the formation of emulsions during extraction from the presence of surface-active impurities in the filtered broth. The effect of these can be minimized by introducing appropriate surfactants that can also reduce the accumulation of solids in the extraction equipment. In addition, other organic impurities are present that can be coextracted with the penicillin. It has been found that a number of these can be removed by adsorption onto active carbon. 

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