Surfactant Foam Research Articles

Polysaccharide/Surfactant Complexes at the Air−Water Interface − Effect of the Charge Density on Interfacial and Foaming Behaviors

The binding of a cationic surfactant (hexadecyltrimethylammonium bromide, CTAB) to a negatively charged natural polysaccharide (pectin) at air-solution interfaces was investigated on single interfaces and in foams, versus the linear charge densities of the polysaccharide. Besides classical methods to investigate polymer/surfactant systems, we applied, for the first time concerning these systems, the analogy between the small angle neutron scattering by foams and the neutron reflectivity of films to measure in situ film thicknesses of foams. CTAB/pectin foam films are much thicker than the pure surfactant foam film but similar for high- and low-charged pectin/CTAB systems despite the difference in structure of complexes at interfaces. The improvement of the foam properties of CTAB bound to pectin is shown to be directly related to the formation of pectin-CTAB complexes at the air-water interface. However, in opposition to surface activity, there is no specific behavior for the highly charged pectin: foam properties depend mainly upon the bulk charge concentration, while the interfacial behavior is mainly governed by the charge density of pectin. For the highly charged pectin, specific cooperative effects between neighboring charged sites along the chain are thought to be involved in the higher surface activity of pectin/CTAB complexes. A more general behavior can be obtained at lower charge density either by using a low-charged pectin or by neutralizing the highly charged pectin in decreasing pH.

Remediation of sandy soils using surfactant solutions and foams

Remediation of sandy soils contaminated with diesel oil was investigated in bench-scale experiments. Surfactant solution, regular foams and colloidal gas aphrons were used as remediation fluids. An experimental design technique was used to investigate the effect of relevant process variables on remediation efficiency. Soils prepared with different average particle sizes (0.04–0.12 cm) and contaminated with different diesel oil contents (40–80 g/kg) were used in experiments conducted with remediation fluids. A mathematical model was proposed allowing for the determination of oil removal rate-constant ( k v) and oil content remaining in the soil after remediation ( C of) as well as estimation of the percentage of oil removed. Oil removal efficiencies obtained under the central experimental design conditions were 96%, 88% and 35% for aphrons, regular foams and surfactant solutions, respectively. High removal efficiencies were obtained using regular foams and aphrons, demanding small amounts of surfactant.

Foaming Power and Foam Stability of Several Alkyl Polyglycosides

Abstract The foaming power and foam stability of three commercial alkyl polyglycosides (APG), Glucopon 215, 600 and 650, have been studied using a modified Ross Miles method. The effects of APG concentration (0.1–4.0 g/L) and temperature (30–60°C) on foam level have been analysed, determining the volume of air in the foam and the foaming power at different times (0–300 s). Furthermore, the foaminess was determined over time until 300 s, registering values from 0.95 or 0.96 to 0.98 or 0.99. Finally, different binary mixtures of surfactants have been assayed at 40°C. To prepare these mixtures Glucopon 650 was mixed with one of the following surfactants: two commercial fatty alcohol ethoxylates, Findet 1214N/23 and Findet 10/18, and a control foaming surfactant, Triton CF:32.

Effect of Particle Hydrophobicity on the Properties of Silica Particle Layers at the Air−Water Interface

This article describes a study of fumed silica particle layers adsorbed at the air-water interface. We have performed surface pressure, ellipsometry, and Brewster angle microscopy measurements. These determinations were complemented by surface viscoelasticity studies, using capillary waves to measure the compression moduli and an oscillating disc to measure the shear moduli. Our results show a strong influence of the particle hydrophobicity and surface density on the properties of the layers. Under compression-expansion, the particle layers rearrange quasi-instantaneously, and at high density, they buckle and/or collapse. Shear measurements show a transition from viscous to elastic behavior for particles with contact angles close to 90 degrees. The surface compression moduli are quite small and most likely not related to the stability of the foams made with these particles, in contrast to the case of more common surfactant foams.

A bioactive foam reactor for the removal of volatile organic compounds: system performance and model development

A bioactive foam reactor (BFR), a novel bioreactor operated using surfactant foams and suspended microorganisms for the treatment of gaseous toluene, was investigated to characterize its performance with respect to the mass transfer and biodegradation rates. The BFR system consisted of two reactors in series; a foam column for toluene mass transfer using fine bubbles and a cell reservoir where suspended microorganisms actively biodegraded toluene. In this study, a series of short-term experiments demonstrated that the BFR could achieve stable removal performance and a high elimination capacity (EC) for toluene at 100.3 g/m3/h. A numerical model, combining mass balance equations for the mass transfer and subsequent biodegradation, resulted in reasonable agreement with the experimental findings. At an inlet toluene concentration of 100 ppm v, the toluene concentration in the liquid phase remained extremely low, indicating that the microbial activity was not hindered in the BFR system. However, the experimental and model prediction results showed that the actual mass of toluene transferred into the liquid phase was not closely balanced with the amount of toluene biodegraded in the BFR used in this study. Consequently, methods, such as increasing the effective volume of the foam column or the mass transfer coefficient, need to be implemented to achieve higher toluene EC and better BFR performance.

Experimental study of high-temperature foam for acid diversion

Foam treatments are used worldwide for acid diversion in matrix acid well stimulation. Many field treatments require foam effectiveness at elevated temperature in the presence of both acid and corrosion inhibitor. This study examines four surfactant formulations at room temperature, 104 °C (220 °F) and 204 °C (400 °F), with and without acid and corrosion inhibitor. The surfactants included amphoteric as well as nonionic foaming agents. The acid formulation was a mixture of chelating agent and HCl, with pH about 4. Formulations were tested at all three temperatures for foaming with N 2 gas (80% quality) at back-pressure of 600 psi (4.1 MPa) in sandpacks and for bulk-foam stability in a pressure cell. Foam was created in most cases at 24 °C (75 °F) without acid or corrosion inhibitor. Creating foam with acid and corrosion inhibitor at 204 °C was more difficult, requiring higher injection rates and lower foam quality. Once formed, strong foam had higher mobility at elevated temperatures than at room temperature. Addition of corrosion inhibitor was more adverse to foaming than acid itself. At 204 °C foam propagation was slower, and steady-state pressure gradient was lower, than at 24 °C. The two steady-state strong-foam regimes reported elsewhere were present at 104 °C and in the presence of acid. Pressure gradient at 104 °C was lower in both high-quality and low-quality foam regimes. The bulk-foam stability results agree qualitatively with the sandpack results, but quantitative relationships between the two tests are hard to draw. These results also suggest that these surfactants may degrade over a period of time, for example, a couple of hours at 204 °C. Residence time in the heated sandpack therefore should be properly accounted for in design of experiments. These results are consistent with decreasing foam stability at higher temperature; adverse interactions between foaming surfactant and inhibitor; easier foam generation and propagation at higher velocity and lower foam quality; and greater difficulty in creating foam under conditions that reduce steady-state foam strength. These results can aid design of high-temperature foam-acid diversion treatments.

Foaming Properties of Monoglycerol Fatty Acid Esters in Nonpolar Oil Systems

Foaming properties of monoglycerol fatty acid esters that have different alkyl chain lengths were studied in different nonpolar oils, namely liquid paraffin (LP 70), squalane, and squalene. The effect of the hydrocarbon chain length of the surfactant, the concentration, the nature of the oil, and the temperature on the nonaqueous foam stability was mainly studied. Five weight percent of glycerol alpha-monododecanoate (monolaurin) formed highly stable foams in squalane at 25 degrees C, and the foams were stable for more than 14 h. Foam stability of the monolaurin/LP 70 and the monolaurin/squalene systems are almost similar, and the foams were stable for more than 12 h. Foam stability was decreased as the hydrocarbon chain length of the monoglyceride decreased. In the glycerol alpha-monodecanoate (monocaprin)-oil systems, the foams were stable only for 3-4 h, depending on the nature of the oil. However, the foams formed in the glycerol alpha-monooctanoate (monocaprylin)-oil systems coarsened very quickly, leading to the progressive destruction of foam films, and all of the foams collapsed within a few minutes. Foam stability decreased when the oil was changed from squalane to squalene, in both monocaprin and monolaurin systems. It was observed that, in the dilute regions, these monoglycerides form fine solid dispersions in the aforementioned oils at 25 degrees C. At higher temperatures, the solid melts to isotropic single-liquid or two-liquid phases and the foams formed collapsed within 5 min. Judging from the wide-angle X-ray scattering (WAXS) and the foaming test, it is concluded that the stable foams are mainly caused by the dispersion of the surfactant solids (beta-crystal) and foam stability is largely influenced by the shape and size of the dispersed solid particles.

Force analysis and visualization of NAPL removal during surfactant-related floods in a porous medium

Governing mechanisms of dense non-aqueous phase liquid (DNAPL) removal during surfactant and surfactant-foam (SF) flooding were studied by porous-patterned glass model experiments. Physical forces, viscous forces and capillary forces, acting on trichloroethylene (TCE) blobs were quantified to understand DNAPL removal mechanisms during the floods, simultaneously visualizing the removal mechanisms. The viscous force of the remedial fluid was intimately related to TCE removal from the porous medium. The remedial fluid with a high viscous force displaced more TCE blobs. Displacement of residual TCE by the remedial fluid began as viscous pressure of flooding was closed to the capillary pressure of the porous medium. In the region of viscous pressure less than the capillary pressure, residual TCE was either retained or solubilized, not displaced, implying that TCE solubilization was the dominant TCE removal process. Glass porous model visualization validated a dominance of the capillary forces during a surfactant flush and a dominance of the viscous forces of the displacing fluid during a SF flood.

Differences between protein and surfactant foams: Microscopic properties, stability and coarsening

We report results on foamability, stability and coarsening of foams made either of surfactant (SDS) or of milk protein (casein) solutions. Studies have been performed at the scales of the gas–liquid interface, thin liquid film and bubble size, in order to find the correlations between these different scales, and to elucidate the microscopic origins of the macroscopic features. For both systems, foamability concentration thresholds have been measured, and a bubble size dependence has been found. A clear correlation between the stability of an isolated thin film and the foam stability is always evidenced. However, the mechanism of stability of the casein thin films is different from the surfactant one, and related to the confinement and percolation of casein aggregates. We also report results on coarsening at constant liquid fraction, showing that the protein foams coarsen more slowly than the surfactant ones, and that it is due to differences in thin film thickness.

Protein and surfactant foams: linear rheology and dilatancy effect

We report results on the dependence of foam rheology on the nature of its components (gas, liquid and surfactant). We have varied the liquid bulk properties, the gas–liquid interfacial properties, which implies also different thin liquid films properties, and the gas. Microscopic characterizations are also performed to find correlations between the different length scales, and to interpret the macroscopic rheological behavior (oscillations and creep). We have found that the elastic modulus G′, once normalized by the Laplace pressure, does not depend on the foam components, whereas the loss modulus G″ shows some dependence with the interfacial properties. We show that the gas is an important factor for these moduli because of its role in the foam aging, via coarsening. We have also evidenced a dilatancy effect taking place under continuous shear, by using a special foam sample shape, in which only a foam band is subjected to shear. We have observed and measured an increase of the liquid volume fraction ɛ in that band.

Foam Superstabilization by Polymer Microrods

Few foam systems stabilized by solid particles have been reported, and usually the particles have been used in combination with surfactants. We report how foams can be stabilized solely with a new class of anisotropic particles, hydrophobic polymer microrods of diameter less than 1 mum and length of a few tens of micrometers. The obtained foams were extraordinary stable, retaining a constant volume over many days and even surviving drying of most of the free liquid. The bubbles in these foams were sterically stabilized by dense thick "hairy" layers. The rigid intertwined protective shells around the bubbles did not allow the formation of thin films between them. The lifetime of these foams was orders of magnitude longer than the ones stabilized with typical foaming surfactants such as sodium dodecyl sulfate. The addition of sodium dodecyl sulfate led to hydrophilization of the microrods and suppressed the superstabilization effect. Thus, common foaming agents effectively act as defoamers for the ultrastable foams stabilized by microrods.

An evaluation of surfactant foam technology in remediation of contaminated soil

Soil contamination is notoriously difficult to treat because the contaminants are often tightly bound to the soil particles. Conventional remediation technologies are becoming less popular due to the high treatment costs. This paper gives a comprehensive overview and evaluation of an emerging promising alternative, surfactant foam technology. Different from other approaches, surfactant foam technology may be designed either to remove contaminants or/and simultaneously act as an augmentation for the existing technologies such as pump-and-treat systems and bioremediation processes to improve the contaminant removal efficiency and cost effectiveness. Encouraging results were achieved from laboratory and field demonstrations. However, as an innovative technology, there are many factors to be investigated with the future development. Special attention is paid to the selection of the most appropriate foaming surfactant and surfactant concentration, which are critical to the success of the implementation of the remediation process and have significant effects on the treatment costs. Moreover, development of predictive mathematical models in for future research is helpful to optimize the remediation process.

Evaluation of the use of capillary numbers for quantifying the removal of DNAPL trapped in a porous medium by surfactant and surfactant foam floods

The capillary number is used to quantify the mobilization potential of organic phases trapped within porous media. The capillary number has been defined in three different forms, according to types of flow velocity and viscosity used in its definition. This study evaluated the suitability of the capillary number definitions representing surfactant and surfactant foam floods by constructing capillary number–TCE saturation relationships. The results implied that the capillary number should be correctly employed, according to scale and fluid flow behavior. This study suggests that the pore-scale capillary number should be used only for investigating the organic-phase mobilization at the pore scale because it is defined by the pore velocity and the dynamic viscosity. The Newtonian-fluid capillary number using the Darcy velocity and the dynamic viscosity may be suitable for quantifying flood systems representing Newtonian fluid behavior. For viscous-force modified flood systems such as surfactant-foam floods, the apparent capillary number definition employing macroscopic properties (permeability and potential gradient) may be used to appropriately represent the desaturation of organic phases from porous media.

Remediation with surfactant foam of PCP-contaminated soil

An investigation was made into evaluating the capability of surfactants in the form of foam for removing the contaminant pentachlorophenol (PCP), a highly toxic, wood preservative, from soil. Several surfactants were investigated for their ability to make foam. Two of them, Triton X-100 and JBR425 (a rhamnolipid biosurfactant), generated foam with higher quality (99%) and higher stability than other surfactants. Triton X-100 and JBR425 were then used to investigate the removal efficiency in soils contaminated with pentachlorophenol (PCP). Triton X-100 showed better results in terms of final removal efficiency. Triton X-100 (1%) removed 85% and 84% of PCP from fine sand soil and sandy-silt, respectively, contaminated with 1000 mg/kg PCP. These values were 60% and 61% for JBR425 (1%). Of this, 66% and 57% of the PCP was removed by volatilization by Triton X-100 and 36% and 44% by JBR425. Further experiments with Triton X-100 indicated that 1% Triton X-100 removed more than 0.5% and that PCP removal was approximately the same for 1% Triton X-100 for a higher contaminant level (3000 mg/kg) but more pore volumes of foam were required for fine sand (23 pore volumes compared to 12). For the sandy-silt soil, PCP removal was higher for the higher contaminant level, 84% compared to 76%. More pore volumes were required (35 compared to 21). Comparison of liquid and foam injection of 1% Triton X-100 indicated that the foam removed more than twice as much PCP in all cases than the liquid surfactant solution. The results of this study on a sandy and sandy-silt media, thus, found that the foam can be used as a fluid to enhance soil remediation under low pressures compared to other fluids such as liquid surfactant solutions.

Physical model analysis of foam–TCE displacement in porous media

AbstractA glass micromodel was experimented to study the coupled effects of the apparent viscosity and mobility of surfactant foam (SF) on the displacement of residual trichloroethylene (TCE) during SF flooding. The SF floods operated under moderate interfacial tension (4.9 dyne/cm) of surfactant solution with TCE and pressure gradient (20–200 kPa) conditions showed relatively different foam behaviors to the higher pressure gradient conditions. The apparent viscosity of SF seems to be less affected by changes in surfactant concentration and affected more by the gas fraction in SF or the bubble size of SF. As the total SF flow rate and the gas injection velocity increased, the apparent SF viscosity decreased and the SF mobility increased. The latter characteristic led to an increase in the TCE displacement efficiency although SF under low‐pressure gradients resulted in flow channeling. The experiment results imply that the SF flood for environment application would be affected by operating conditions and distribution of residual contaminants.

A micromodel analysis of factors influencing NAPL removal by surfactant foam flooding

A methodology to study the trichloroethylene (TCE) and dodecane removal in porous media by surfactant foams (SF) was presented by using etched-glass micromodels. The purpose of this work was to systematically evaluate the impact of various physicochemical factors such as gas fraction (GF), surfactant concentration, pore structure and nonaqueous phase liquid (NAPL) types on NAPL removal during SF flooding. The TCE displacement by SF was dependent on the gas fraction of SF. Low GFs (50% and 66%) were more efficient for TCE removal and sweep efficiencies than a high GF (85%). An increase in TCE removal was observed with increasing surfactant concentration at a fixed GF. TCE removal by SF flooding appeared to be dependent more to the value of Capillary number rather than to the concentration of surfactant solution. The effect of the pore heterogeneity was evaluated by employing two different types of micromodels. The Capillary number is an important parameter in the determination of sweep efficiency or gas saturation of SF in a nonhomogeneous porous medium. However, the TCE removal from a nonhomogeneous porous medium may not be associated with sweep efficiency. The initial configuration of residual TCE blobs in a nonhomogeneous porous medium would also be influential in displacing TCE. Sweep efficiencies and pressure responses of two NAPL systems (TCE and dodecane) were monitored to evaluate foam stability when the foam contacts the NAPLs. Stable foam contacting with TCE is implied, while it appears that dodecane cause the SF to collapse. All results indicate that the Capillary number (a ratio of viscous forces to capillary forces) is the most important parameter for TCE removal by SF flooding. Micromodel visualizations of water, surfactant and SF floods were showed and also discussed.

Critical capillary pressure for destruction of single foam films and foam: effect of foam film size

Foams and single foam films stabilised by ionic and amphiphile polymer surfactants are studied with foam pressure drop technique (FPDT) and thin liquid film-pressure balance technique (TLF-PBT). A pressure is reached at which the single foam films rupture and the foams destruct very fast (avalanche-like). For film rupture we named this pressure—critical capillary pressure of film rupture, Pcr,film while for foam destruction, we introduced a new parameter—critical capillary pressure of foam destruction, Pcr,foam. The surfactant kind and foam film type (common thin, common black and Newton black) affect the values of both parameters. When below 20 kPa, Pcr,film and Pcr,foam are close by value, when over 20 kPa, there is a significant difference between them. The Pcr,film versus film size and Pcr,foam versus foam dispersity dependences, indicate that the film size and foam dispersity strongly affects the critical capillary pressure values. Film size distribution histograms reveal that a foam always contains films that are of a larger than the most probable size. They rupture at lower pressures, does initiating the destruction of the whole foam, which can be an explanation why higher than 20 kPa there is a difference between Pcr,film and Pcr,foam values. This parameter, Pcr,foam is considered of significant with respect to foam stability and could find use in industry.

Foam flow in low-permeability Berea Sandstone cores: a laboratory investigation

Foam flow in porous media has been a subject of extensive investigation for the last 37 years because of its application in enhanced oil recovery (EOR) and stimulation operations. In acidizing, foam is used to facilitate the diversion of acid into the low-permeability strata when multiple layers of contrasting permeabilities are present. Very little has been done to investigate the flow behavior of foam in low-permeability rocks (1–10 md), mainly because of equipment limitations caused by the very high pressure gradients encountered when foam is injected. This paper discusses the results of several single-core, constant-quality, steady-state foam flow experiments, using a 9-md fired Berea Sandstone core and a 3500 psi (24 MPa) rated coreflooding unit. Factors, such as surfactant type, foam quality, liquid and gas velocities, were varied to investigate their effect on foam mobility, mobility reduction factors, and pressure gradients. To simulate the post-foam acid stage used in acidizing, brine was injected following foam injection in each experiment and the residual permeability and foam stability were observed. The foam qualities used varied from 55% to 90%, and the injection rates varied from 5 to 25 ft/day (1.5–7.5 m/day). Significant reductions in mobilities were observed for all the cases during steady-state foam injection. A new parameter called the persistency index is proposed to quantify foam stability during the post-foam acid stage, which may prove to be critical to predicting the foam diversion behavior. Also, more consistent results were obtained when dimensionless parameters such as mobility reduction factors rather than mobilities were compared. Finally, low-permeability results were compared with those for the higher permeability to identify uniqueness of foam generation in low-permeability formations.

Vinyl Acetate-Acrylic Acid Copolymer for Enhanced Oil Recovery

This paper pertains to the possible use of newly-synthesized vinyl acetate/acrylic acid (VA/AA) copolymer to help recover trapped crude oil, an important mineral resource. The proposed approach is to use the copolymer as a foaming surfactant (in water or brine), which will be driven by a gas, such as carbon dioxide or nitrogen. Neutralized forms of the copolymer result in an anionic surfactant, which has been found to have minimal adsorption onto the rock matrix. The neutralized VA/AA copolymers synthesized in this study are found to outperform other anionic surfactants and even more adsorbing nonionic surfactants. Due to the long chain nature of the hydrophilic groups of nonionic surfactants, they are found to produce better foams than anionic ones. Since VA/AA copolymers have long chain hydrophilic groups, it is not surprising that they are good foaming agents as well. Optical microscopy of VA/AA emulsions reveal that they form microscopic network surface structures, which are presumably due to liquid crystalline formation in macromolecular scale.

A comparison of CSTR and SBR bioslurry reactor performance

A continuous-flow stirred tank reactor (CSTR) and a soil slurry-sequencing batch reactor (SS-SBR) were maintained in 8 l vessels for 180 days to treat a diesel fuel-contaminated soil. The SS-SBR provided markedly enhanced contaminant degradation relative to the CSTR. Diesel fuel removal efficiency was 96% in the SS-SBR, compared with 75% in the CSTR. Microbial growth was approximately 25% greater in the SS-SBR than the CSTR. However, significant biosurfactant production and foaming occurred in the SS-SBR, whereas none was observed in the CSTR. Surfactants were produced in the SS-SBR at concentrations up to 70 times the critical micelle concentration (CMC), but were biodegraded by the end of the cycle. Reactor operation was reversed after 80 days. The reactor converted from an SS-SBR to a CSTR lost surfactant production and showed reduced diesel fuel degradation. Converting the CSTR to an SS-SBR resulted in surfactant production and enhanced diesel fuel degradation. These results indicate that fill-and-draw operation selected for microbes with a greater ability to produce surfactants and degrade diesel fuel than the CSTR operation. Decreasing the diesel fuel addition rate in the SS-SBR by four times on day 160 reduced the maximum surfactant concentration and foam thickness by more than three times without affecting diesel fuel removal.