Surfactant concentrations recovery

The quantitative determination of surfactant concentration in solution is an essential part of any experimental work on surfactant adsorption or phase behaviour. In the field of experimental enhanced oil recovery the technique employed should be capable of determining surfactant concentrations in sea water, and in the presence of oil and alcohols, the latter being frequently added as a co-surfactant. 

Crisp et al. [212] has described a method for the determination of non-ionic detergent concentrations between 0.05 and 2 mg/1 in fresh, estuarine, and seawater based on solvent extraction of the detergent-potassium tetrathiocyana-tozincate (II) complex followed by determination of extracted zinc by atomic AAS. A method is described for the determination of non-ionic surfactants in the concentration range 0.05-2 mg/1. Surfactant molecules are extracted into 1,2-dichlorobenzene as a neutral adduct with potassium tetrathiocyanatozin-cate (II), and the determination is completed by AAS. With a 150 ml water sample the limit of detection is 0.03 mg/1 (as Triton X-100). The method is relatively free from interference by anionic surfactants the presence of up to 5 mg/1 of anionic surfactant introduces an error of no more than 0.07 mg/1 (as Triton X-100) in the apparent non-ionic surfactant concentration. The performance of this method in the presence of anionic surfactants is of special importance, since most natural samples which contain non-ionic surfactants also contain anionic surfactants. Soaps, such as sodium stearate, do not interfere with the recovery of Triton X-100 (1 mg/1) when present at the same concentration (i.e., mg/1). Cationic surfactants, however, form extractable nonassociation compounds with the tetrathiocyanatozincate ion and interfere with the method. 

The recovery of M2D-C3-0-(E0)n-CH3 after exposure to various solid media has been investigated by API-MS, high performance liquid chromatography light scattering mass detection (HPLC-LSD) and HPLC-APCI-MS methods [10]. Recoveries with extraction immediately following application were determined (surfactant concentration 0.1%, surfactant/solid lOmgg-1) with complete recoveries obtained on all media other than the clays illite and montmorillonite (Table 5.5.2) [10]. 

Electrophoretic Mobility (I0 5cm2s lv 1) Free Surfactant Concentration (I0 4N) pH Primary Recovery (%)... 

Figure 2. Effect of Superficial velocity on particle recovery for various particle diameter at a surfactant concentration of 1 mM SLS.

Figure 6. Variation of recovery with successive injections of a 357 nm polystyrene latex at a surfactant concentration of 6mM SLS.

In the context of a study of foam flotation of powdered activated carbon (PAC), Zouboulis et al. [143] noted large and different pH effects when an anionic surfactant was used instead of a cationic one. For the cationic surfactant, best recovery (at low surfactant concentration) was achieved at the highest pH, in agreement with electrostatic arguments (see Section IV.B.l) for the anionic surfactant, an intermediate pH was the best. The authors also measured the zeta potential of the carbon in the presence and absence of the surfactants and concluded that the specific chemical nature and the dissociation of each surfactant. 

Chan and Shah (26) proposed a unified theory to explain the ultralow interfacial tension minimum observed in dilute petroleum sulfonate solution/oil systems encountered in tertiary oil recovery processes. For several variables such as the salinity, the oil chain length and the surfactant concentration, the minimum in interfacial tension was found to occur when the equilibrated aqueous phase was at CMC. This interfacial minimum also corresponded to the partition coefficient near unity for surfactant distribution in oil and brine. It was observed that the minimum in ultralow interfacial tension occurs when the concentration of the surfactant monomers in aqueous phase is maximum. 

The phase behavior of surfactant formulations for enhanced oil recovery is also affected by the oil solubilization capacity of the mixed micelles of surfactant and alcohol. For low-surfactant systems, the surfactant concentration in oil phase changes considerably near the phase inversion point. The experimental value of partition coefficient is near unity at the phase inversion point (28). The phase inversion also occurs at the partition coefficient near unity in the high-surfactant concentration systems (31). Similar results were also reported by previous investigators (43) for pure alkyl benzene sulfonate systems. 

Clearly, the relationship between the optimum salinity and surfactant concentration is complex (Salager et al., 1979b) and requires further investigation. The possibility of a shifting optimum salinity has to be taken into account to predict phase behavior during the oil recovery process. 

Experiments by Glover et al. (1979) for a type n(-i-) system showed that much of the surfactant retention could be caused by phase trapping. They also showed that much of this retained surfactant could be remobilized with a low-salinity drive. This view was supported by Hirasaki (1981). He pointed out that in a type II(-i-) environment, in the presence of dispersion, not only did the peak surfactant concentration decrease, but the location lagged behind with increased dispersion. These two factors resulted in a lower oil recovery and delay in oil production. 

For all these cases, the total amount of each chemical was the same. The core flood results are shown in Figure 13.21. We can see that the incremental oil recovery factors over waterflooding in Schemes 2 and 4 were obviously higher than that in Scheme 1. The alkali and surfactant concentration gradients from high to low can overcome the negative effects at the displacement front caused by dilution, alkali consumption, and surfactant adsorption. 

FIGURE 13.21 Effect of alkali and surfactant concentration gradients on oil recovery. Source Yang etal. (2002b). 

Salinity was found to decrease foam stability. The surfactant concentrations in which foaming ability increased with concentration were 0 to 0.5%. The optimum polymer molecular weight for foaming ability was around 17 million. Core flood tests showed that ASPF incremental oil recovery factor over ASP was above 10% because the ASPF sweep efficiency was higher than the ASP efficiency. 

The optimum formulation is a surfactant system with which maximum oil recovery can be achieved. For that purpose, the interfacial tension has to be as low as possible and the oil solubilisation in the microemulsion as large as possible [15,115,121,123,127,140,142-144]. In general, formulation is a concept that tunes the properties of a water-oil-surfactant system such that it can be used for the certain application (see Chapter 3). Extensive studies on the optimum formulation for EOR and various other applications have shown that many variables have to be considered to achieve an ultra-low interfacial tension at relatively low surfactant concentration, or the occurrence of a single-phase bicontinuous microemulsion at high surfactant concentration [15, 143, 144]. 

We have recently reported (6, 7) that those surfactant formulations which yield good oil recovery exhibit both low interfacial tensions and low interfacial viscosities. Our experiments have shown that surfactant formulations which ensure low interfacial viscosity will promote the coalescence of oil droplets and thereby decrease the emulsion stability, thus enhancing the formation of a continuous oil bank. It has been demonstrated that the requirements for emulsion stability are the presence of an interfacial film of high viscosity and a film of considerable thickness. We have observed that the surfactant concentration which minimizes the interfacial tension may not simultaneously minimize the interfacial viscosity. Hence, our results indicate both interfacial tension and interfacial rheology must be considered in selecting surfactant formulations for tertiary oil recovery. 

An extreme dependence on concentration of added ionic surfactant was observed by Somasimdaran Chari (1983) by investigating the flotation of quartz and alumina. Flotation decrease at high surfactant concentrations is also explained by the appearance of the same sign due to recharge processes. Calculated interaction energies correlate well with the observed flotation recovery. 

In SPE, a small amount of organic solvent or surfactant is added to collected samples to prevent adsorption to sample containers. To increase recoveries of ng 1 levels of PAHs in SPE, ACN (40%) or surfactants above their CMC can be added to samples prior to preconcentration. Solid supports, chemically modified with copper phthalocyanine trisulfonic acid derivatives for selective sorption of PAHs, have been investigated. The selective interaction is thought to be with the tt electrons of the PAHs. Brij-35, a neutral polyoxyethylene lauryl ether surfactant was added above the CMC to water samples to prevent sorption on container walls. Before preconcentration by SPE, samples were diluted to reduce the surfactant concentration to just below the CMC. Recoveries of over 90% for SPE on solids containing copper phthalocyanine trisulfonic derivatives were obtained for spiked water samples at low ngl levels, except for NAP, ACE, and FLU. Experiments repeated using a C18 SPE preconcentration sorbent gave >90% recovery for all 16 EPA PAHs, except for ACY. Examples of the use of SDB as an SPE sorbent include the online analysis of seawater from the coast of Catalonia in Spain, where no PAHs above the low ng 1 level were detected, and the analysis of leachate from coal deposits. ... 

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