Surfactant retention tests

The surfactant retention tests were performed in the porous medium at 43° C in sandpack (Sor = 0) saturated with brine (See composition in Table I). The injection flow rate used in these tests (2 cm3/h) corresponds to a front velocity of 30 to 40 cm/day. 

As a test, surfactant slug flow experiments were performed in clayey sandpacks with and without the injection of a desorbent behind the micellar slug. Results show that a substantial decrease in surfactant retention is obtained in calcic environment by such an additive. Likewise, the ethoxylated cosurfactant in the micellar slug can be remobilized simultaneously with sulfonatewithout any change in its ethylene oxide distribution. The application of the RST to sulfonate/ ethoxylated alkylphenol mixtures explains semi-quantitatively the relationship between their properties and composition. 

Laboratory tests with Alipal CD-128 indicated that a steady-state reciprocal apparent viscosity of 0.2-0.4 cP (about equal to that of the oil) could be obtained and that surfactant retention by the reservoir rock would not be excessive (0.00056 lb surfac-tant/ft of rock permanent adsorption). Eventually, the following injection sequence was planned (1) 15 kg of NH4SCN tracer in 371 bbl of water, followed by a water spacer between the tracer and the subsequent surfactant solution (2) 2,764 bbl of 0.1% surfactant, intended to satisfy the adsorption requirements of the rock ... 

Otherwise, the formula selected is very sensitive to oil content, which is an uncontrollable variable. Note that the representation by Zhao et al. using oil vol.%/surfactant vol.% did not take into account the changes in surfactant concentration as the flood proceeds. In other words, the surfactant concentration was constant, which is true in laboratory test tubes but not in the laboratory corefloods or in the field because of surfactant retention. They also showed that the upper and lower boundaries are straight lines. 

Studies on mechanisms are described by Balzer [192]. In the case of anionics the residual oil in the injection zone is removed via displacement into the adjacent reservoirs ether carboxylates show their good adaptation to differences in temperature and salinity. Further it was found from interfacial tension measurements, adsorption and retention studies, and flooding tests that use of surfactant blends based on ether carboxylates and alkylbenzensulfonates resulted... 

The problem with using surfactant-modified stationary phases in LC is that the surfactant will usually slowly elute (bleed) from the support thus resulting in different retention behavior of solutes with time. This is why most applications are in the area of GC or GLC. An exciting recent advance has been reported by Okahata, et al (181). Namely, a procedure has been developed for immobilizing a stable surfactant vesicle bilayer as the stationary phase in GC. A bilayer polyion complex composed of DODAB vesicles and sodium poly(styrene sulfonate) was deposited on Uniport HP and its properties as a GC stationary phase evaluated. Unlike previous lipid bilayers which exhibited poor physical stability, the DODAB polyion phase was stable. Additionally, the temperature-retention behavior of test solutes exhibited a phase transition inflection point. The work demonstrates that immobilized surfactant vesicle bilayer stationary phases can be employed in GC separations (181). Further work in this direction will likely lead to many such unique gas chromatographic supports and novel separations. 

Uncommon IPRs were tested recently. Polymerized acyl monoglydnate surfactant was found to be as effective as sodium dodecylsulfate for the resolution of organic amines [126]. For the analysis of pyridine-based vitamins in infant formnlas, dioc-tylsulfosuccinate produced a unique retention pattern [133], Among bizarre IPRs, tris(hydroxymethyl)aminomethane was used for the determination of cyclamate in foods. It was selected over different ion-pair reagents such as triethylamine and dibu-tylamine, based on sensitivity and time economies [134]. Hexamethonium bromide, a divalent IPR, was used successfully to separate sulfonates and carboxylates [135]. 

Solubilization equilibrium constants for the ligands were determined at selects values of surfactant concentration, ligand concentration, and pH. These "conditional" equilibrium constants were determined from data obtainwi from SED experiments (31). The test solution initially placed in the retentate compartment contained surfactant and ligand at the desired concentrations and pH. After 24 hours, the concentration of the ligand in the permeate was measured by spectrometric titration... 

Actually, we should separate inverse gas chromatography into inverse gas-liquid chromatography and inverse gas-solid chromatography. The obvious basis of such discrimination is the state of the column content being examined. Polymers and their mixtures, commercial stationary phases, surfactants represent liquids (at the measurement temperature) involving a mixed mechanism of the retention of the test solutes. Modified silicas are examples of solids that have been studied, and, in this case, adsorption effects predominate, while solution partition in graft chains seems to be negligible. These problems will be discussed in details by Papirer and Balard in another chapter of this book. 

Field test data show that a typical amount of surfactant injected in Cs (in %) x injection PV (in %) is about 10 to 12 (see Section 13.8). The minimum chemical mass injected should be just about the retention. The rule of thumb is about 20 to 50% more than the retention. According to the work of Trashenski et al. (1974), to prevent water breakthrough polymer and the polymer breakthrough micellar solution, the polymer volume requirement is about 0.5 PV. 

An extraction solvent/surfactant/contamlnant system was found with these characteristics. The extraction oil or solvent used was heptane. Heptane Is relatively Insoluble In water, when compared with the contaminant, toluene. At 25°C heptane and toluene are soluble In water 2.83 ppm and 515 ppm respectively (16). Gas chromatography was used for analyzing the composition of the aqueous and organic phases. In an actual scaled-up version of this process another cheaper solvent, such as kerosene, might be substituted for heptane. Kerosene Is a blend of so many compounds (76 were Identified by us on a GC scan of one sample), including toluene, that it was not feasible to use It In our tests which required the identification of toluene In the retentate and feed streams. Once the feasibility of the process Is proven we can switch to this cheaper solvent. Ultimate disposal of the kerosene, contaminated with the toluene could be by combustion of a bleed stream from the retentate or the process tank. 

As detailed in Chapter 3 by Terabe, micellar electrokinetic chromatography (MEKC) is a useful technique in the retention analysis of water-soluble compounds. The separation and analysis of lypophilic analytes, however, may be difficult in MEKC due to the strong affinity of lypophilic compounds to the micelle resulting in long separation times and poor resolution. An interesting approach for the simultaneous analysis of water- and fat-soluble vitamins by microemulsion electrokinetic chromatography (MEEKC) was proposed by Sanchez. The separation of both water- and fat-soluble vitamins (Bi, B2, B3, Be, B12, C, A palmitate, D, E acetate, and K) was obtained when the microemulsion was prepared with sodium dodecyl sulfate (SDS) as the surfactant, octane as the nonpolar modifier, butanol as the cosurfactant, and propanol as the second cosurfactant. Complete separation of all vitamins was carried out within 55 min however, this approach was tested only in multivitamin formulation. 

Considering the effect of increasii initial concentration of anionic sur ctant on die cotton fabric (Table 1), the retention appears to consistently increase both as concentration of anionic surfactant increases and as number of washes increases. The difference between the first wash and fifth wash has been statistically tested for significance using a 2 tailed t-test. This has been repeated for each anionic surfactant concentration level. The t-value results and an indication of their significance can be seen in Table 3. 

Selectivity. The retention factors of test solutes were dependant on the Mw/aot molar ratio and the heptane content. Fig. 13.4 shows that the k variations were not monotonous. It was demonstrated that the hydration of the polar unbonded silica surface changed significantly in the 0water adsorbed on the silica surface forming a composite layer so thick that it changed the column permeability and dead volume [7]. The combined effect of stationary phase hydration and adsorbed layer was responsible for the observed retention factor variations (Figure 13.4). The Mw/aot ratio is directly related to the water droplet size so the retention factor of a test solute can be related to the structnre of the L2 microemulsion. 

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