Effects of Electrolyte Concentration on Surfactant Adsorption to a QCM Immersed in Surfactant + Electrolyte Solutions

Abstract

Surfactant adsorption from aqueous electrolyte solutions onto metal surfaces was characterized through the use of a Quartz Crystal Microbalance (QCM). The need for a better understanding of the surfactant adsorption process became apparent in previous studies by Morton et al., directed toward the development of a thermodynamically-based model of oil removal from metal surfaces. These modeling efforts utilized existing data on surfactant adsorption data, yet required the estimation of surfactant adsorption phenomena, such as the transition between monolayer adsorption and multi-layer adsorption and the location of the critical micelle concentration (CMC). Experimental techniques utilizing the quartz crystal microbalance (QCM) have been shown to be highly reliable for measuring slight changes, on the order of a nanogram, in the adsorption behavior of surfactants from aqueous solutions. The current study demonstrates that the addition of low concentrations (< 100 mM) of sodium chloride to aqueous solutions of ionic surfactant can have a significant effect on the adsorption of the surfactant to a gold surface. An analysis of the QCM measurements as well as a discussion of the effects of salt addition on various solution properties will be presented. Impacts of the current results to previously published work as well as potential applications will be discussed.     

Equilibrium Extraction and Concentration of Multivalent Metal Ion Solutions by Using Winsor II Microemulsions

Abstract

Experimental results on the selective extraction and concentration of bivalent copper into the aqueous core of a water-in-oil microemulsion in equilibrium with an aqueous phase are presented. We have developed an electrostatic model which describes this phenomenosn as a preferential substitutin of the conthe counterions of the surfactant by the introduced bivalent cations. We have assumed that the adsorption of counterions onto the charged surface of the reverse micelle can be modeled by the Stern double layer model. Comparisons of the theoretical predictions against the experimental results are encouraging. The positive features of the model and its limitations are discussed.     

Flotation Using Microgas Dispersions for the Removal of Pentachlorophenol from Aqueous Solutions

ABSTRACT

Microgas dispersions called colloidal gas aphrons (CGAs) were generated using cationic, anionic, and nonionic surfactants, and were used in an adsorptive bubble flotation process in a semibatch mode to remove pentachlorophenol (PCP) from the aqueous phase. The aqueous solution was maintained at pH values by using buffers. CGAs generated with Tergitol, which is a nonionic surfactant, were found to be the most efficient for the removal of PCP; the efficiency remained nearly independent of pH. In the case of an anionic surfactant, sodium dodecylbenzene sulfonate (DDBS), the efficiency of removal improved from 15 to 36% with a change in pH from 10.1 to 3.0. For a cationic surfactant, hexadecyltrimethylammonium bromide (HTAB), the removal at pH 10.1 was 81%, which decreased to 68.1% at pH 3.0. The charges on the encapsulating film of CGAs may explain the higher percentage of adsorption of PCP on the CGAs generated using HTAB as compared to CGAs generated using DDBS. For all the surfactants, an increase in concentration improved the removal efficiency. These results were compared with the removal efficiencies using conventional flotation techniques used by other researchers. Solvent sublation appears to be effective in the removal of PCP, but even in the presence of a surfactant it required 300% more air volume per volume of liquid when compared with CGA flotation.     

A kinetic model for enzymatic reactions in a reverse micellar system,involving water-insoluble substrate

A kinetic model was proposed for enzymatic reactions in a reverse micellar system, involving a water-insoluble substrate. Though surfactant is one of the main structural components of reverse micelles, an increase in the surfactant concentrations affects the enzyme activity remarkably. A relationship between the enzyme activity and the surfactant concentration is discussed. In this study it was assumed that free substrate in the organic phase was in adsorption equilibrium with the surface of the micellar surfactant, and that the adsorption coefficient and the true K_m value (Michaelis constant) were independent of the surfactant concentration. The validity of this model was verified by data on the hydrolysis of olive oil, catalyzed by Chromobacterium viscosum lipase (Glycerol-ester hydrolase; EC 3.1.1.3) in an AOT/isooctane reverse micellar system. The activity value predicted by the model equation agreed well with the experimental data.     

The Phase Transformation Mechanism of Bentonite-Stabilized and Cetyltrimethylammonium Bromide-Stabilized Emulsions and Application in Reversible Emulsification Oil-Based Drilling Fluids

We obtained a reversible emulsion system induced by bentonite solid particles and surfactant Cetyltrimethylammonium bromide (CTAB, whose critical micelle concentration (CMC) value is 9.21 × 10⁻⁴ mol L⁻¹). In this study, the zeta potential and contact angle were used to characterize surface wettability of bentonite solid particles in the process of phase transmission behavior. The adsorption amount was calculated at different CTAB concentrations, and then the adsorption isotherm of surfactant CTAB at bentonite solid particles was also studied to confirm the adsorption behavior and adsorption layer structure. The electrical conductivity and microscopic analysis were employed to characterize the phase inversion behavior of emulsion. The results show that the wettability of bentonite particles can be reversed by changing the CTAB concentration, and then the two phase transition behavior of bentonite emulsion can be induced. Additionally, the surfactant CTAB can be used in oil-based drilling fluid systems for the inversion of the emulsion type. The research on the performance of the reversible emulsion oil-based drilling fluid system shows that it has a good thermal stability and a small amount of fluid loss, and successfully reduces the damage of the traditional oil-based drilling fluids on oil well completion.     

A Practicable Process for Phenol Removal with Liquid Surfactant Membrane Permeation Column

Abstract

A practicable liquid surfactant membrane process for phenol removal is proposed with a stirred countercurrent column used as the liquid membrane contact equipment. The constituents of liquid membranes, such as internal aqueous phase and surfactant, the type of column, and the operating conditions for efficient and continuous performance of the liquid surfactant membrane process, have been examined. When NaOH solution was used as the internal aqueous phase and ECA4360J was used as the surfactant, the W/O emulsion was stable for the duration of column operation. More than 97% phenol could be removed from the feed solution. Nearly complete demulsification was also achieved by gentle agitation with an electrostatic demulsifier.     

SEPARATION PROCESSES FOR RECOVERING ALLOY STEELS FROM GRINDING SLUDGE: SUPERCRITICAL CARBON DIOXIDE EXTRACTION AND AQUEOUS CLEANING

ABSTRACT

Two separation processes have been developed to remove contaminants (cutting oil with trace phosphorus additive) from high-speed steel grinding sludge. One process uses an aqueous surfactant washing technique, and the second process uses supercritical carbon dioxide (SCCO₂) extraction. Our bench-scale aqueous washings have shown that the required phosphorus removal is easily obtained, but a sufficient oil removal is more difficult. The experimental results also indicate a strong dependence of the aqueous washing efficiency on the choice of a suitable surfactant. A mass transfer model is used to simulate a semi-continuous washing process. SCCO₂ extraction at 80 °C and 340 atm shows that approximately 80% of the oil can be removed from the sludge during a 60-minute process to produce a batch of recyclable steel, and that the phosphorus removal also reaches the required level. A linear desorption model is used to describe the irreversible desorption of oil from the solid phase into the CO₂ phase, and the simulated results agree very well with the experimental data.     

Membrane Aging and Related Phenomena in Liquid Surfactant Membranes Process

Abstract

The membrane aging phenomenon and its influences on the kinetics of cobalt(II) permeation by the liquid surfactant membranes (LSM) process has been studied. The experimental results showed that the emulsion formulated from the internal aqueous phase and the membrane (organic phase) of a certain age has far-reaching consequences on the kinetics of metal extraction and emulsion stability. The investigations have revealed that there exists an optimal age and composition of the membrane in which the highest extraction (synergism) and the lowest emulsion swelling are achieved. Analytical and instrumental examinations of the membrane phase during aging have shown various chemical and physical changes as a result of the surfactant decomposition, reaction products precipitation and self-association, and macroemulsion formation.

     

Electrical Aspects of Adsorbing Colloid Flotation. XVII. Quasi-Chemical Method for Adsorption of Mixed Surfactants

Abstract

The quasi-chemical approximation is applied to the calculation of adsorption isotherms for two-component surfactant systems. No further approximations are necessary. The effects of the relative sizes of the interaction energies of the various nearest neighbor pairs are investigated, and plots of representative adsorption isotherms are given. Some possible applications of the theory to foam flotation and other surface chemical separation techniques are suggested.     

Soil Clean-Up by Surfactant Washing. IV. Modification and Testing of Mathematical Models

Abstract

Three models for the operation of surfactant washing/flushing columns or test beds are developed. These differ in the manner in which hydrophobic contaminant is held in the soil and, therefore, in the nature of mass transfer of contaminant from the stationary phase to the advecting surfactant solution. The fitting of parameters to experimental results is addressed, following which the parameters obtained are used to simulate operation of laboratory columns and a pilot-scale test bed. The results are compared which experimental data from the column and test bed. The air stripping of biphenyl from spent surfactant solution is modeled using a local equilibrium approach to see if air stripping could account for observed losses. The air stripping of toluene from the surfactant solution is modeled using a local equilibrium approach or a lumped parameter method to model diffusion-limited kinetics.     

Cloud Point Foaming Technique for Separation of Nonionic Surfactant from Solution

Abstract

We explored a novel cloud point foaming technique to separate nonionic surfactant from aqueous solutions with a wide range of surfactant concentrations. The phase transformation of nonionic surfactant micelles at the cloud point changes the foaming behavior of surfactant solutions during foaming and results in excellent separation efficiency in terms of the volume reduction ratio compared to foaming at room temperature.     

Experimental Conditions for HPLC Analysis of Ethoxylated Alkyl Phenol Surfactants in Microemulsion Systems. Part I. Isocratic Mode with Mixed Solvents

Abstract

In surfactant–oil–water phase behavior studies, especially those related to enhanced oil recovery, each of the oligomers of commercial polyethoxylated non-ionic surfactants partitions in a different pattern into the two or three phases in equilibrium, and a simple, fast, and accurate method is required to analyze all phases. Up to now, only oil-phase GC was relied upon to determine the partitioning without closing the surfactant inventory. Isocratic normal phase HPLC with a ternary mobile phase (n-heptane–chloroform–methanol 70–10–20) is shown to comply with these requirements to analyze the oligomer distribution in microemulsion, excess oil, and excess water phases of an optimum formulation system.     

Contact angle of surfactant solutions on precipitated surfactant surfaces. III. Effects of subsaturated anionic and nonionic surfactants and NaCl

The contact angles of saturated calcium dodecanoate (CaC₁₂) solutions containing a second subsaturated surfactant on a precipitated CaC₁₂ surface were measured by using the drop shape analysis technique. The subsaturated surfactants used were anionic sodium dodecylsulfate (NaDS), anionic sodium octanoate (NaC₈), and nonionic nonylphenol polyethoxylate (NPE). Comparing at the critical micelle concentration (CMC) for each surfactant, NaC₈ was the best wetting agent, followed by NaDS, with NPE as the poorest wetter (contact angles of 32⁰, 42⁰, and 62⁰, respectively). Surface tension at the CMC increased in the order NaC₈<NPE<NaDS, and subsaturated surfactant adsorption increased in the order NPE≪NaDS (1.4 vs. 84 μmole/g); adsorption of the NaC₈ was not measurable. Interfacial tension (IFT) reduction at the solid-liquid interface due to subsaturated surfactant adsorption is an important contribution to contact angle reduction, in addition to surface tension reduction at the air-water interface. Surfactant adsorption onto the soap scum solid is crucial to solid-liquid IFT reduction and to good wetting. The fatty acid was the best wetting agent of the three surfactants studied, probably because calcium bridging with the carboxylate group synergizes surfactant adsorption onto the solid of the higher molecular weight soap. NaCl added to NaDS surfactant results in depressed CMC, lower surface tension at the CMC, decreased NaDS adsorption onto the solid, and decreased reduction in solid-liquid IFT. The contact angle is not dependent on the NaCl concentration for NaDS. The NaCl causes an increased tendency to form monolayers, which decrease air-water surface tension, but a decreased tendency to form adsorbed aggregates on the solid; the two trends offset each other, so wettability is not affected by added salt. The Zisman equation does not describe the wetting data for these systems well except for NaDS, further emphasizing the danger of ignoring solid-liquid IFT reduction in interpreting wetting data in these systems.     

Effect of Cationic Surfactant on the Adsorption of Arsenites onto Akaganeite Nanocrystals

Abstract

The current research focuses on removal of arsenite ions from aqueous solutions by a new adsorbent, surfactant modified akaganeite (Ak_m), prepared after the adsorption of the cationic surfactant, hexadecyl trimethyl ammonium bromide (N‐Cetyl‐N,N,N‐Trimethylammonium Bromide) onto akaganeite. The new adsorbent was investigated with Fourier transform infrared spectra and X‐ray photoelectron spectroscopy methods for a better understanding of the effects of surface properties on arsenite adsorption. Surfactant modified akaganeite was found to be an effective adsorbent for the removal of arsenite ions from aqueous systems. It presented a significantly higher arsenite adsorption capacity than the pure nanocrystalline akaganeite. Kinetics of adsorption obeys a second‐order rate equation. The maximum adsorption capacity was found to 328.3 mg g^?1 over a wide pH range significantly higher than those of other adsorbents reported.     

Studies in Solvent Extraction Using Polyaphrons. I. Size Distribution,Stability, and Flotation of Polyaphrons

Abstract

Predispersed solvent extraction (PDSE) is a promising technique for the treatment of wastewater containing low solubility, hydrophobic contaminants. A stable predispersed organic solvent in the form of polyaphrons of very small diameter results in high surface areas with a minimum energy requirement for mass transfer of solutes from the aqueous phase to the organic solvent. PDSE should greatly improve the performance of a conventional extraction process. This paper focuses on the characterization and size distributions of polyaphrons. Polyaphrons were generated using different cationic, anionic, and nonionic surfactants in water and an oil-soluble nonionic surfactant. Kerosene was used as the organic solvent to form the polyaphrons. Size distributions were obtained using a particle size analyzer. The optimal instrument parameters (sample quantity, optical parameters, run time, etc.) were identified for these measurements. The size distribution based on volume fraction was found to show a bimodal behavior, with peak size maxima between 1–3 and 10–30 μm for all the polyaphrons. The effects of different surfactant types, surfactant concentrations, and storage times on the size distribution spectrum of polyaphrons were studied. The size distribution of different polyaphrons before and after flotation in an aqueous column using colloidal gas aphrons (CGAs) was also studied. Flotation was deduced to occur as a result of electrostatic forces between the CGAs and polyaphrons.     

Cloud Point Extraction of Acetic Acid from Aqueous Solution

Abstract

A new acetic acid separation method was developed through a successful combination of cloud point extraction and complex extraction technology (CPE-SE), where an acetic acid complex compound formed and was solubilized in a surfactant micelle solution, instead of an organic solvent, and then concentrated into one phase by a phase separation process of the CPE technology. Since no organic solvent diluents were used, the new process was environmentally friendly and with a lower cost; meanwhile, the high selectivity of the complex extraction based on chemical complexation and high efficiency of CPE were also inherited as advantages over conventional solvent extraction process. In consideration of the compatibility and the related CPE characteristics, tributyl phosphate and PEG/PPG-18/18 Dimethicone were selected as complexing agent and surfactant of the CPE-SE system, respectively, and the extraction system was optimized by studying the effect of the main process parameters, including surfactant and complexing agent concentration, temperatures for the stirring and incubation steps, on the recovery and the distribution coefficient. A relative high recovery of 71.4% and a distribution coefficient of 1.4 were achieved simultaneously with the optimized process in the treatment of 0.1 M acetic acid solution. Based on its competitive extractability, high efficiency, low-cost, and environment friendlyness, the CPE-SE process was expected to be a potential separation method for a dilute acetic acid solution.     

Complexation of Surfactant/β‐Cyclodextrin to Inhibit Surfactant Adsorption onto Sand,Kaolin, and Shale for Applications in Enhanced Oil Recovery Processes. Part I: Static Adsorption Analysis

Surfactant adsorption onto solid surfaces is a major issue during surfactant flooding in enhanced oil recovery applications; it decreases the effectiveness of the chemical injection making the process uneconomical. Therefore, it was hypothesized that the adsorption of surfactant onto solid surfaces could be inhibited using a surfactant delivery system based on the complexation between the hydrophobic tail of anionic surfactants and β‐cyclodextrin (β‐CD). Proton nuclear magnetic resonance spectroscopy was used to confirm the complexation of sodium dodecyl sulfate (SDS)/β‐CD. Surface tension analysis was used to establish the stoichiometry of the complexation and the binding constant (K_a). Static adsorption testing was applied to determine the adsorption of surfactant onto different solids (sandstone, shale, and kaolinite). The release of the surfactant from the β‐CD cavity was qualitatively evaluated through bottle testing. The formation of the inclusion complex SDS/β‐CD with a 1:1 stoichiometry was confirmed. The K_a of the complexations increases as salinity and hardness concentration increases. The encapsulation of the surfactant into the β‐CD cavity decreases the adsorption of surfactant onto solid surfaces up to 79 %. Qualitative observations indicate that in the presence of solid adsorbents partially saturated with crude oil, the β‐CD cavity releases surfactant molecules, which migrate towards the oil–water interface.     

Removal of Cadmium from Dilute Solutions by Hydroxyapatite. II. Flotation Studies

Abstract

Dissolved-air flotation has been investigated in the present paper as a suitable solid/liquid separation technique, applied downstream for hydroxyapatite ultrafine particles which were used in a preliminary stage for the removal by sorption of toxic cadmium cations. The main parameters affecting this process were evaluated, including the necessary quantity of sorbent material in the dispersion, the proper pH values of Cd solutions, the type and concentration of supplementary inorganic flocculant agents (ferric chloride and aluminum sulfate), and the presence of additional surfactant added. The results obtained were considered to be promising. Under optimum conditions, over 95% of Cd-loaded hydroxyapatite particles were separated in a very short retention time.     

Mechanism of the odor-adsorption effect of zinc ricinoleate. A molecular dynamics computer simulation

Zinc ricinoleate [Zn(Ri)₂] is widely used in surfactant and detergent mixtures for the adsorption of odor-active compounds. The mechanism of this process is not known. In this initial study, we discuss the results of molecular dynamics computer simulations that were performed to get more information and detailed insights into the interaction mechanism between Zn(Ri)₂ and odor-active substances. The calculations, based on simple molecular mechanics approximations, simulated the dynamic features of the molecular structures of Zn(Ri)₂ in vacuum, in the oil phase, and in aqueous solution. We determined actual molecular conformations and simulated an adduct of ammonia with Zn(Ri)₂. On close inspection, in the vacuum and oil phase structures, the Zn²⁺ ion is almost completely shielded by the oxygen ligands. Calculated structural transitions caused by the interaction of Zn(Ri)₂ with water-solvent molecules resulted in a weakening of the electrostatic shield. Nucleophilic attack of odor-active compounds to the relatively unprotected Zn²⁺ atom is easy to achieve in aqueous solution. Simulation of the addition product of Zn(Ri)₂ with ammonia revealed an elementary structural change, resulting in an increase of the solubility and adsorption activity of Zn(Ri)₂. Molecular dynamics simulations showed that the results coincide with experimental observations.     

Statistical modeling of adsorption isotherm of potassium on aza[7]helicene-coated gold electrode attached to quartz crystal microbalance

ABSTRACT

A chemically coated piezoelectric sensor has been used for the determination in liquid phase of the adsorption isotherm of potassium. A thin film of aza[7]helicene was attached to the surface of a gold electrode of a quartz crystal microbalance using spin coating method.

Statistical physics formalism was applied to elucidate the adsorption mechanism of potassium onto coated electrode by aza[7]helicene. The simulation results showed that a monolayer adsorption occurs with the number of potassium per site about 1 and the adsorption energy is less than 30 kJ.mol^?1, characteristic of physical adsorption.

The statistical model was used to investigate three thermodynamic potentials such as the entropy, the free enthalpy, and the internal energy. It is found that the adsorption took place with releasing energy, such behavior confirms the exothermic character of the adsorption process.