Soil Clean Up by in-situ Surfactant Flushing. III. Laboratory Results

Abstract

Data on the solubilization of p-dichlorobenzene (DCB), naphthalene, and biphenyl in aqueous solutions of sodium dodecylsulfate (SDS) (0-100 mM concentration) indicate increases in effective solubilities of these hydrophobic compounds by factors of roughly 20 to 100. DCB is effectively removed from spiked clay-sand mixtures by leaching with SDS solutions in laboratory columns. Surfactant solutions loaded with DCB are satisfactorily treated by gentle extraction with hexane, and the recovered surfactant solution satisfactorily solubilizes biphenyl. A simple model for predicting the solubilization behavior of surfactants is developed and tested experimentally.     

Hydrocarbon Extraction into Surfactant Phase with Nonionic Surfactants. II. Model

Abstract

The solubilization kinetics of an extraction process of oil with an aqueous micellar solution of a nonionic surfactant has been modeled. The model is directly related to the phase diagram, allowing a simple form which explains the main effects. The theoretical results show the adsorption process of surfactant at the phase interfaces to provide the main resistance to the mass transfer processes. The values of adsorption rates, and of some of the diffusion coefficients obtained, compare well with the earlier experimental results.     

The HLD-NAC Model for Mixtures of Ionic and Nonionic Surfactants

The HLD-NAC model has been used as an “equation of state” to predict the properties of microemulsion (μE) systems formulated with either anionic or nonionic surfactants. The model uses the concept of the hydrophilic-lipophilic difference (HLD) to calculate the chemical potential difference of transferring a surfactant from the oil to the aqueous phase; as a function of formulation variables such as type of surfactant, oil, temperature, electrolyte concentration. The value of HLD is used as a scaling parameter to calculate the net and average curvatures (NAC) of the surfactant at the water/oil interface. These curvatures determine the phase volumes, phase transitions, and solubilization capacity of μEs. In this work, the HLD-NAC model is extended to nonideal surfactant mixtures of anionic and nonionic surfactants. The phase behavior of limonene μEs formulated with binary mixtures of sodium dihexyl sulfosuccinate with nonionic nonylphenol ethoxylates and alcohol ethoxylates was used to determine the deviations of the HLD from the ideal mixing behavior. The deviations were fitted using a 2-parameters Margules equation. The results suggests that the deviations in anionic-rich systems are due to the charge shielding effect of nonionic surfactants, and in nonionic-rich systems, the deviations seem to be explained by the increase in hydration of the surfactant headgroups due to the presence of anionic surfactants. When these corrections were used to predict the curvature of dioctyl sulfosuccinate-dodecyl pentaethylene glycol-heptane μEs, the HLD-NAC model corrected for the nonidealities reproduced not only the trends but also the actual range of values reported in the literature.

Aqueous Hydrotropic Solution as an Efficient Solubilizing Agent for Andrographolide from Andrographis paniculata Leaves

Abstract

An aqueous solution based extraction process for andrographolide from Andrographis paniculata leaves has been developed using alkyl benzene sulfonates and carboxylates as hydrotropes. The plant cells are permeabilized by the hydrotrope solutions followed by solubilization of andrographolide into the solutions. The extraction and solubilization of andrographolide is affected by structure and concentration of hydrotrope, temperature and particle size. Sodium cumene sulfonate (Na‐CS) shows the most efficient solubilization of andrographolide amongst the hydrotropes studied. The solubility of andrographolide increased by two orders of magnitude in Na‐CS aqueous solutions and ～96% andrographolide extraction was achieved in just 20 min.     

Self-Assembly of Polyethylene Glycol Ether Surfactants in Aqueous Solutions: The Effect of Linker between Alkyl and Ethoxylate

The aqueous self-assembly behavior of two homologous series of poly(ethylene oxide) (PEO)-containing nonionic surfactants based on a C₁₀-Guerbet hydrophobe is reported. The two families of surfactants, alkyl ethoxylates and alkyl alkoxylates, are commercially available from BASF under the trade name Lutensol® XP-series and XL-series, respectively. The latter incorporate propylene oxide (PO) units in the surfactant chain. Dye solubilization was used to determine the critical micellization concentration (CMC) of each surfactant at 22 and 50 °C. The PO-containing alkyl alkoxylates displayed lower CMC values, which were also more sensitive to temperature. The Gibbs free energy, enthalpy, and entropy of micellization were computed from the CMC data and used to identify the contribution of each surfactant moiety (alkyl chain, PO unit, and PEO block) in controlling the CMC. The micellization properties are compared with compositionally similar surfactants with linear alkyl chains, yielding information about the effects of the Guerbet alkyl chain on micellization. Isothermal titration calorimetry was also used to characterize the CMC and enthalpy of micellization which generally compare well with the dye solubilization results. Cloud point data reveal nonmonotonic relationships for the Lutensol® surfactants with respect to composition, unlike linear alkyl chain surfactants. Finally, dilute solution viscosity measurements performed on some Lutensol® surfactants show a change in the slope, suggesting a structural change that tends to be more pronounced for surfactants with longer PEO blocks. The data presented herein enhance the understanding of surfactant structure–property relationships required for industrial formulation.     

Cloud Point Extraction of Nitrobenzene using TX-100

Cloud point extraction (CPE) is carried out to extract nitrobenzene (NB) from aqueous solution using TX-100 as a nonionic surfactant. The effects of different operating parameters, like concentration of the feed mixture (both NB and surfactant), pH, temperature, and the presence of mono- and di-valent salts on the extraction of both the NB and surfactant have been studied in detail. The solubilization behavior of the NB in the surfactant micelle has been observed in the temperature range of 75°C to 90°C. Concentrations of surfactant and NB have been considered in the range of 0.03 M to 0.25 M and 100 mg/L to 400 mg/L, respectively. An optimum set of surfactant concentration, temperature, and salt concentration is obtained for the removal of NB from aqueous medium. The effects of temperature and concentrations of surfactants and NB on various thermodynamic parameters, like change in Gibbs-free energy (ΔG ⁰), change in enthalpy (ΔH ⁰), and change in entropy (ΔS ⁰) are observed and explained well. Experimental investigations have also been carried out for the recovery of the surfactant from the dilute phase applying solvent extraction (SE) in batch condition using heptane and hexane as the extracting medium.     

Extraction of Piperine from Piper Nigrum (Black Pepper) by Aqueous Solutions of Surfactant and Surfactant + Hydrotrope Mixtures

Abstract

The effect of combining butyl benzene sulfonate as hydrotrope with a surfactant in aqueous solutions is investigated for isolation of piperine, an alkaloid, from black pepper. The standard free energy change associated with piperine solubilization in the aqueous solutions of surfactant and hydrotrope individually and in their mixtures is determined from the solubility of piperine in these solutions. A combination of sodium dodecyl sulfate (SDS) and the hydrotrope gives increased percentage extraction of piperine as compared to the hydrotrope alone. The piperine purity recovered from aqueous solutions was higher as compared to the purity of piperine recovered using organic solvents. The piperine crystallized from aqueous solutions of surfactants and hydrotrope also showed cleaner surfaces and uniform structures with sharp edges, unlike the particles crystallized from organic solvents.     

Solubilization as a Separation Process

Abstract

In this paper a separation process for hydrocarbon molecules is suggested, based on solubilization in aqueous solutions by surfactant micelles. A molecular thermodynamic approach to solubilization is formulated which relates the extent of solubilization and the selectivity to the structure and properties of the surfactant and of the solubilizate molecules. An evaluation of the solubilization characteristics of benzene and hexane in aqueous solutions of non-ionic octyl glucoside, anionic sodium dodecyl sulfate and cationic cetyl pyridinium chloride is made and solubilization phase diagrams for the above systems are constructed. These diagrams indicate the formation of micelles at concentrations which are lower than the critical micelle concentration of the surfactant alone. The calculations predict, for all three surfactants, preferential solubilization of (aromatic) benzene compared to (aliphatic) n-alkanes. The preferential solubilization of benzene is caused by its smaller molecular volume and lower interfacial tension against water. Preliminary experimental results using cetyl pyridinium chloride as surfactant and an equimolar binary mixture of hexane and benzene as solubilizates indicate a selectivity of over 7 for benzene compared to hexane, and a ratio of about one molecule of benzene solubilized for every surfactant molecule in the micelle.     

Solvent Extraction of DNA with a Hydrolysable Double-chain Surfactant

Abstract

A cationic lipophilic surfactant with two hydrolysable groups, di(1-octadecyloxycarbonylmethyl)dimethylammonium chloride, was synthesized and solvent extraction of deoxyribonucleotide (DNA) into organic solution (isooctane/1-octanol) with it as an extractant was examined. Not only a forward extraction of DNA into the organic phase but also back extraction into the aqueous phase (pH > 9) at room temperature proceeded efficiently. The forward extraction is promoted by electrostatic interactions of the surfactant and DNA and the back extraction is exclusively caused by hydrolysis of the surfactant to a non-surfactant.     

Separation of Palladium and Silver from a Nitric Acid Solution by Liquid Surfactant Membranes

Abstract

The recovery of palladium from a nitric acid solution containing silver has been conducted by application of liquid surfactant membranes (LSMs) containing LIX 860, a β-hydroxyoxime, as a mobile carrier in a stirred tank. The extraction equilibria of palladium and silver using several different extractants were also studied. Palladium was selectively extracted from a silver-containing liquor with LIX 860 while it was also observed that both palladium and silver were extractable with a sulfur-containing extractant. The recovery of palladium with LIX 860 was selectively achieved by using perchloric acid solution as the LSM internal phase dosed with thiourea. In the LSM operation, the effects of several chemical parameters on the selective recovery of palladium were studied. The use of hydrochloric acid as an internal receiving phase prevented the transport of silver into the emulsion due to the formation of silver chloride in the external feed solution. Commercially available Span 80 was found suitable for the selective extraction of palladium as a surfactant in LSM operation. Under optimum conditions, palladium was successfully separated from silver and concentrated into a receiving phase in W/O emulsions.     

Liquid-Liquid Extraction of Low Molecular-Weight Proteins by Selective Solubilization in Reversed Micelles

Abstract

The effects of pH and salt concentration on the solubilization of ribonuclease-a, cytochrome-c and lysozyme in Aerosol OT/isooctane reversed micelle solutions have been studied to explore the potential for employing this solvent system in the large-scale recovery and concentration of proteins using liquid extraction. For pH values below the isoelectric point, pI, of the protein, solubilization was high, probably owing to strong electrostatic-interactions between the positively charged proteins and the anionic surfactant heads forming the inner micelle wall. Above the pI, the proteins could not be solubilized, probably because of unfavorable electrostatic repulsions between the like-charged proteins and surfactants. At low ionic strength and neutral pH, complete solubilization of the proteins was observed. As the ionic strength was increased, there was an abrupt decrease in solubilizing power of the reversed micelle solutions; the salt concentration at which this occurred was different for each protein. A mixture of the three proteins was cleanly resolved using a single extraction step and two stripping steps. The conditions in each step were selected according to the results of the single protein extraction studies.     

Effect of Electrolyte and Temperature on Volatile Organic Compounds Removal from Wastewater Using Aqueous Surfactant Two-Phase System of Cationic and Anionic Surfactant Mixtures

Abstract

Benzene, toluene, ethylbenzene, and xylene are frequently observed contaminants in industrial wastewaters causing concerns about environmental and health effects. An aqueous surfactant two-phase (ASTP) extraction system using mixtures of cationic and anionic surfactants have been shown to be a promising surfactant-based separation technique to concentrate solutes such as proteins and dyes from aqueous solution. A phase separation of a surfactant solution occurs at certain surfactant compositions and concentrations, forming two isotropic phases. One is rich in surfactant aggregates (surfactant-rich phase) and the other is lean in surfactant aggregates (surfactant-dilute phase). Most of the organic contaminants tend to solubilize and concentrate in the surfactant-rich phase, leaving the surfactant-dilute phase containing only small amounts of contaminants as remediated water. The effect of NaCl addition on the critical micelle concentration (CMC) and the extraction ability of ASTP formed by mixtures of cationic surfactant (dodecyltrimethylammonium bromide; DTAB) and anionic surfactant (alkyl diphenyloxide disulfonate; DPDS) at 50 mM total surfactant concentration with a 2:1 molar ratio of DTAB:DPDS was investigated; the CMC of the mixture slightly decreases with increasing NaCl concentration. The extraction and preconcentration of benzene are greatly enhanced by added NaCl. The higher the degree of hydrophobicity of contaminants, the greater the extraction into the surfactant-rich phases. At 1.0 M NaCl addition, about 95% of xylene, 92% of ethylbenzene, 90% of toluene, and 79% of benzene are extracted into the surfactant-rich phase within a single stage extraction and the contaminant partition ratios can be as high as 395 for xylene, 273 for ethylbenzene, 206 for toluene, and 84 for benzene, which are greater than those obtained from the conventional ASTP extraction system using nonionic surfactants.     

Reversible Solubilization of Typical Polycyclic Aromatic Hydrocarbons (PAH) by a Gas Switchable Surfactant

Surfactant‐enhanced remediation (SER) is one of the most effective remediation methods for polycyclic aromatic hydrocarbons (PAH) contaminated soils. However, mass deployment of SER has been restricted due to the shortage of the separation, recycle technology of the surfactant and its operation costs. This research mainly studied the reversibility of 2‐n‐lauryl‐1,1,3,3‐tetramethyl guanidine (DTMG) surfactant and its influence on reversible solubilization of typical PAH. Experimental results showed that the reversibility of the DTMG surfactant is excellent. The critical micellar concentration (CMC), surface tension and pH of DTMG in CO₂/N₂ conditions undergo reversible changes promptly. DTMG·CO₂ shows a strong solubilization capacity for PAH; the apparent solubilities of the selected PAH pyrene, phenanthrene and anthracene in 4 mmol/L of DTMG·CO₂ solution were about 32.4, 17.1 and 14.6 times higher than in water, respectively. The corresponding molar solubilization ratios were 5.4 × 10^?3, 2.80 × 10^?2 and 1.1 × 10^?3, much higher than those with DTMG. More than 50 % of the PAH in surfactant solutions could be released through gas control at each surfactant concentration, and improved release efficiency was achieved at low surfactant concentrations. In brief, such results in this work introduce a facile method to meliorate the SER technology.     

Analysis of nonionic surfactants in bench-scale biotreater samples

The effluents and activated sludges used in benchscale biotreater units have been analyzed for nonionic alcohol ethoxylates and their residues. Separate bench-scale units were fed linear alcohol ethoxylates (AE), highly branched and branched nonylphenol ethoxylates. Effluents and sludges were first pretreated by a foam sublation technique to provide a gross separation of surfactants from the environmental matrix. This step was followed by normal-phase high-performance liquid chromatography (HPLC) with either fluorescence detection (FD) or evaporative light-scattering detection (ESLD). The AEs were derivatized with phenylisocyanate and analyzed by normal-phase HPLC coupled with FD. At extremely low surfactant levels, pretreatment of large sample volumes resulted in interferences on derivatization. Hence, a normal-phase HPLC method with ELSD was developed. Although some interferences do appear using ELSD, this method appears to be a more viable alternative to derivatization/FD for very low levels of AE. HPLC with FD and ELSD detection methods are more quantitative and provide information on the polyoxyethylene chain than is possible with traditional methods like cobalt-thiocyanate active substance. Presented at the 82nd AOCS Annual Meeting & Expo, May 1991, Chicago, Illinois.     

Solubilization of model polycyclic aromatic hydrocarbons by nonionic surfactants

Solubilization of model polycyclic aromatic hydrocarbons (PAHs) by the readily biodegradable nonionic surfactants, Tergitol 15-S-X (X=7,9 and 12), consisting of mixtures of secondary ethoxylated alcohols was investigated at temperatures below their cloud points. Their solubilization capacities for phenanthrene were compared to those of three other commonly used surfactants, e.g. Triton X-100 and Tween 20 as well as Tween 80. Correlation between the micelle-water partition coefficients and the octanol-water partition coefficients in Tergitol 15-S-7 solutions indicated that the hydrophobicity of PAHs, i.e., their octanol-water partition coefficients, could be used in predicting the solubilization efficiency of PAHs by this nonionic surfactant. Effects of temperature and salinity on solubilization capacity of Tergitol 15-S-7 surfactant for phenanthrene were also investigated along with the micellar properties. The change in hydrodynamic radius and aggregation number of micelles with temperature was measured by the dynamic and static laser light scattering techniques. Results showed that increasing aggregation number and micellar size at higher temperature when cloud point is approached gives rise to the higher solubilization capacity of this surfactant. Effect of salinity on the enhancement of phenanthrene solubility was also discussed in terms of conformation changes in the micelles due to the possible coordination of sodium cations and oxygen atoms on the ethylene oxide groups of the surfactant.     

Separation of Cobalt and Nickel by Liquid Surfactant Membranes Containing a Synthesized Cationic Surfactant

ABSTRACT

Separation of cobalt(II) and nickel(II) by using a hydroxyoxime extractant has been investigated both in liquid-liquid extraction and in a liquid surfactant membrane(LSM) system. In the liquid-liquid equilibrium extraction studies, hydroxyoximes showed significant extractability for nickel ions, although LIX 84 was found to have exceptional chelating affinity for nickel ions. In the LSM system functionalized by hydroxyoxime, the cobalt ions were efficiently separated from nickel ions as a result of slower permeation of nickel chelates across the emulsion membrane. More complete cobalt recovery was achieved in the LSMs dosed with LIX 860 than when the same carrier was applied to the liquid-liquid extraction system. Furthermore, cobalt permeation rate was enhanced threefold when a quaternary ammonium type of cationic surfactant was used as an emulsifier due to carrier interaction with surfactant at the reaction interface. The permeation mechanism of ions in LSMs was elucidated by an interfacial reaction model which took into account the adsorption of the carrier and surfactant at the reaction interface.     

The Solvent Extraction of Boron with Synthesized Aliphatic 1,3‐Diols: Stripping and Extraction Behavior of Boron by 2,2,5‐Trimethyl‐1,3‐hexanediol

Abstract

A variety of aliphatic 1,3‐diols (4a–c, 5a–c, 6a–c) was synthesized from β‐hydroxy carbonyl compounds (1–3) for potential use in the solvent extraction of boron. Primary‐secondary and primary‐tertiary alcohol structures of 1,3‐diols substituted with isopropyl, isobutyl, and isopentyl groups have been demonstrated to be very efficient for the solvent extraction of boric acid from aqueous solutions. The extraction ability of 2,2,5‐trimethyl‐1,3‐hexanediol (5b) was investigated as a function of 5b concentration, solution pH, solvent properties, and stripping conditions. Extraction efficiency increased with increasing concentration of 5b, and the best extraction of boron (96.8%) was found to be at an equilibrium pH of 2 with 0.5 M of 5b. Chloroform, toluene, chlorobenzene, 2‐octanol, and n‐amyl alcohol were found to be suitable solvents for the solvent extraction of boron. The boron complex can be recovered from the organic phase by treatment with an aqueous solution of sodium hydroxide. The highest ratio (96.7%) of boron was recovered by 0.1 M of sodium hydroxide solution.     

Recovering phenanthrene from spiked sand by a combined remediation process of micellar solubilization and cloud-point extraction

A remediation process, which combines the micellar solubilization and the cloud-point extraction technique by a nonionic surfactant Tergitol 15-S-7, was used to decontaminate phenanthrene, as a model hydrophobic pollutant, from spiked sand samples. A first-order kinetics model was employed to describe the solubilization behavior of phenanthrene well. It was observed that presence of surfactant decreased the mass-transfer coefficient of phenanthrene from sand surface to surfactant solutions, however, higher solubilization rate was obtained due to enhanced aqueous solubility and, thus, the larger driving force resulted from solublization. Cloud-point extraction was used to concentrate the phenanthrene solubilized in the washing solutions in an attempt to minimize the amount of wastewater. The extraction was carried out, subsequently, at room temperature by adding sodium sulfate to suppress the cloud-point low enough to induce phase-separation of the surfactant-rich phase with a minimal phase volume from the coexisting water phase. Recoveries higher than 93% were achieved in the combined process of micellar solubilization and cloud-point extraction on ultimate removal of immobilized phenanthrene sorbed on sands. The results showed that this combined process is efficient in recovering phenanthrene sorbed and immobilized on sands from contaminated sites, and produces only minimal amount of wastewater, i.e. less than 3% of its original volume.     

Recovery of Phenols Using Liquid Surfactant Membranes Prepared with Newly Synthesized Surfactants

Abstract

Extraction and stripping equilibrium of phenol, p-cresol, and p-chlorophenol were studied with an organic solution containing a newly synthesized surfactant and an aqueous alkaline solution as a stripping phase. A cationic surfactant showed the highest extraction ratio of phenol among several surfactants used in this study. The magnitude of phenol extracted from water was in the order phenol < p- chlorophenol < p-cresol. The stripping of phenol extracted in the organic solution was quantitatively accomplished with an alkaline solution of high concentration except for the case of cationic surfactants. Extraction of phenol and its derivatives by liquid surfactant membranes containing a newly synthesized surfactant as an emulsifier was carried out in a stirred cell. The effects of various parameters (such as a surfactant and alkaline concentration, the kind of surfactant, and the alkali composition) on the extraction efficiency of phenol were examined along with demulsification of W/O emulsions. On the basis of the stability of surfactants against alkaline solutions used as a receiving phase, cationic surfactants which did not involve an ester or amide bond in their molecule appeared to be among the best surfactants available for phenol removal in liquid membrane operations. The efficiency of phenol recovery with sodium hydroxide as a stripping agent was much higher than that with sodium carbonate; however, the demulsification efficiency of the emulsions decreased with an increase in the content of sodium hydroxide in the mixed alkaline solutions of sodium hydroxide and sodium carbonate. In the design of an efficient recovery process of phenols by LSMs, the composition of the alkaline solution was one of the key factors. Under optimal conditions, phenolic derivatives could be recovered in a few minutes.

     

Reverse Micellar Extraction and Backextraction of l-Lysine with Three Dialkyl Sodium Phosphinates in Pentanol/Isooctane Mixtures

Abstract

The effects of pH, salt concentration, and structure of the surfactant head on the reverse micellar extraction and backextraction of l-lysine in pentanol/isooctane mixtures have been comparatively studied. The surfactants used were bis(2,4,4-trimethylpentyl) sodium phosphinate (NaPOO), bis(2,4,4-trimethylpentyl) sodium monothiophosphinate (NaPSO), and bis(2,4,4-trimethylpentyl) sodium dithiophosphinate (NaPSS). Since all three surfactants have the same two hydrocarbon tails and differ only in their polar heads, their comparative study gives some insight into the effect of the surfactant head group on the reverse micellar extraction and backextraction of amino acids. The results show that the nature of the surfactant head, the pH, and the salt concentration have a major effect on the reverse micellar extraction of l-lysine. The percent of l-lysine extracted to the organic phase, at fixed surfactant and pentanol concentrations, decreased in the order NaPSS > NaPSO > NaPOO. The exchange with the three surfactants can be easily reversed for the backextraction of amino acids into a new surfactantfree aqueous solution.