Soil Clean up by in-situ Surfactant Flushing. VI. Reclamation of Surfactant for Recycle

Abstract

Solvent extraction has been studied for use in reclaiming contaminated surfactant solutions for reuse in soil surfactant flushing in the remediation of hazardous waste sites. Hexane was used as the solvent to extract p-dichlorobenzene (DCB), naphthalene, and biphenyl from 25, 50, and 100 nM sodium dodecylsulfate (SDS) solutions in a continuous countercurrent flow column. The contaminant concentration in the aqueous SDS was followed with time, and the removal was modeled using an unsteady-state model which included diffusion kinetics. The mass transfer time constant was approximately 2 hours. The percent removal of DCB increased with increasing hexane flow rate and decreased with both increasing SDS flow rate and increasing SDS concentration. The concentrations of all three contaminants were reduced by about 90% or better. Extraction of contaminated SDS solutions with hexane appears to be an effective method for cleaning up these surfactant solutions for recycle.     

Synergistic Behavior Between Zwitterionic Surfactant α-Decylbetaine and Anionic Surfactant Sodium Dodecyl Sulfate

Here, we present experimental surface tension isotherms of mixed solutions of a zwitterionic surfactant α-decylbetaine (DB) and an anionic surfactant sodium dodecyl sulfate (SDS) in different molar ratios. These mixed solutions show a composition dependency with respect to both surface tension effectiveness and critical micelle concentration. The pseudo-regular solution theory has been used to evaluate the interaction parameters in the micelle, β ^m and at the surface, β ^s. The results revealed that the mixed solutions of DB/SDS behave synergistically in both surface tension reduction effectiveness and mixed micelle formation at all mole fractions investigated. The values of adsorption area per surfactant molecule at air/solution interface were estimated, which provides some useful information on evaluating the interaction between DB and SDS in mixed adsorbed monolayers. The solubilization behaviors of toluene in DB/SDS mixed solutions were also investigated to help in understanding the structure of mixed micelles of DB and SDS.     

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.     

Soil Clean-Up by Surfactant Washing. II. Design and Evaluation of the Components of the Pilot-Scale Surfactant Recycle System

Abstract

The components of a pilot-scale system to recycle and reuse a surfactant solution containing contaminants from remediated soil were designed, fabricated and successfully tested. Use of surfactants in soil washing or flushing can expedite remediation manyfold as the aqueous solubility of hydrophobic compounds is increased. The process is of even greater utility when the contaminants are also nonvolatile and nonbiodegradable. Biphenyl was used to represent nonvolatile contaminants. Not only was 99% biphenyl removal (initial concentration 1000 mg/ kg) from soil achieved in 7 pore volumes of 2.5 wt% sodium dodecyl sulfate (SDS) solution, but there was no decrease in the effectiveness of the recycled solution in removing the biphenyl compared to the virgin solution. Approximately 1 ppm biphenyl remained in the SDS solution after recycle. Toluene was used to represent volatile contaminants. Toluene removal from the soil test bed was 98% when using the same SDS solution. There was approximately 3 ppm toluene in the recycled surfactant solution. Again, the effectiveness of recycled surfactant solution in removing toluene from soil was the same as the virgin material.     

Selective Solubilization of Nitrophenols and Adsorption on Ion Exchange Resins in Nonaqueous Conditions

Abstract

Separation of nitrophenols (NP) has been studied by selective solubilization in organic solvents of different polarities. o‐NP dissolves very well in heptane and toluene while intermolecular hydrogen bonding among p‐NP molecules decreases its solubilization in these solvents. Thus partial separation of o‐/p‐nitrophenols is achieved by selective solubilization of o‐NP in heptane. The trace amounts of p‐NP from the o‐NP solutions are removed by its selective sorption on basic ion exchange resins. The sorption of nitrophenols, individually and in mixtures, is experimentally determined from their solutions in heptane, toluene, and methanol by using weakly basic Indion‐850 and Duolite A‐308 resins and strongly basic Indion‐810 resin. The equilibrium adsorption studies show very selective adsorption of p‐NP from heptane with a high loading capacity on Indion‐850.     

Soil Clean up by in-situ Surfactant Flushing. V. Micellar Solubilization of Some Aromatic Contaminants

Abstract

The solubilities of mixtures of naphthalene, biphenyl, and phenanthrene in 50 and 100 mM aqueous sodium dodecylsulfate solutions at room temperature were determined. There does not appear to be any appreciable tendency for these compounds to form solid solutions with each other, and the solubilities of the mixture components in the micellar surfactant solutions are to a fairly good approximation equal to the solubilities of the individual pure components.     

The effect of micellar lifetime on the rate of solubilization and detergency in sodium dodecyl sulfate solutions

The slow relaxation time (τ₂) of sodium dodecyl sulfate (SDS) micelles, measured by the pressure-jump technique, was maximum at 200 mM concentration at 25°C, indicating that the most stable micelles are formed at this concentration. This is presumably related to the optimum molecular packing in the micelle. The rate of solubilization of benzene and Orange OT dye into SDS solutions was also maximum at 200 mM concentration. The results are explained as follows: The distance between micelles (i.e., intermicellar distance) decreases as the surfactant concentration (or the number of micelles) increases, resulting in a stronger electric repulsion between micelles. Therefore, the micelles become more rigid, due to the compressive force of intermicellar repulsion, as the concentration increases up to 200 mM SDS. With further increase in the SDS concentration, the micellar shape changes from spherical to cylindrical to accommodate more surfactant molecules in the solution and to minimize the free energy of the system. The interior of the tightly packed micelles is more hydrophobic than that of loosely packed micelles and, therefore, the tightly packed micelles induce rapid solubilization of nonpolar molecules (e.g., benzene, Orange OT) into these micelles.     

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.     

Electrochemistry of ferrocene in anionic,cationic and nonionic micellar solutions. Effet of the micelle solubilization of the half-wave potentials

The redox properties of the ferrocene/ferricinium Fc/Fc⁺ couple were studied in aqueous 0.1 M NaCl solution of sodium dodecylsulphate (SDS), N-cetyltrimethylammonium bromide (CTAB) and polyoxyethylene-23 lauryl ether (Brij 35). Solubilities of ferrocene were measured by spectrophotometry and by limiting current measurements in direct current voltammetry. The reversible half-wave potentials were determined by cyclic and differential pulse voltammetry. The results are discussed on the basis of the micelle solubilization equilibrium of both the reductant Fc and the oxidant Fc⁺. Indeed, diffusion coefficient ratios of the oxidant to the reductant, measured by coulometry, show that the micelle solubilization of the electrogenerated ferricinium cation Fc⁺ must also be considered in the nonionic and the anionic micellar solutions. Thus in every solution studied, a standard potential of Fc/Fc⁺ in water may be obtained from the experimental values of the half-wave potentials, the partition coefficients of Fc and Fc⁺ and the ratio of their diffusion coefficients. The behaviour of ferrocene in the SDS solutions and the effect produced by the addition of pentanol seem to confirm that SDS forms micelles with a less ordered structure than the other surfactants studied. The invariance of the half-wave potentials of ferrocene in pure SDS solutions whatever the surfactant and ferrocene concentrations suggests the use of this solute-solvent couple as a reference potential system.     

Solubilization Behavior of Organic Mixtures in Optimum Winsor Type III Microemulsion Systems of Sodium Dodecyl Sulfate

Solubilization selectivity and synergism behavior were investigated for the optimum Winsor type III sodium dodecyl sulfate (SDS) microemulsion systems of organic mixtures. The organic mixtures used include toluene and 1 of the following 3 normal alkanes: n‐octane, n‐heptane, and n‐hexane. Selective solubilization toward toluene was observed in the optimum Winsor type III SDS microemulsion system for the toluene/n‐octane mixture. Toluene selectivity showed a decrease trend with the increase of its content in the excess oil phase, salinity showed little influence on the trend, and increasing of the SDS content leads to lowering of the selectivity. Synergism exists in the solubilization of the 2 organics for all the binary mixtures used in this work. A clear reduction of the n‐butanol content (A*) to obtain the optimum formulation and rise of the optimum solubilization parameter (SP*) were seen with the mixing of 2 single components. Coincident relation between A* and equivalent alkane carbon number (EACN) for organic mixtures of toluene with the 1 or 3 of n‐hexane, n‐hexane, and n‐octane was obtained, which is a parabolic curve with a minimum point. At the same time, all the SP*–EACN data fall in the same kind of parabolic curve with a maximum. The EACN for the minimum A* and maximum SP* are both in the range of 3.0–3.5. The A*–EACN curve shifts vertically with the change of the SDS content or ln S* (S* is salinity of the aqueous phase), while the change of salinity also leads to slight deformation of the curve, which can be omitted in a small range of salinity change.     

Supramolecular Systems Based on Novel Amphiphiles and a Polymer: Aggregation and Selective Solubilization

Supramolecular systems based on novel triazole-containing and pyrimidine-containing amphiphiles bearing OH-groups and a hydrophilic polymer (polyethyleneimine, PEI) were fabricated. Aggregation threshold of individual amphiphile solutions and a surfactant/polymer binary mixture were determined to be equal to 2 and 0.05 mM, respectively, using tensiometry and conductometry techniques. It was found, that PEI addition to surfactant aqueous solutions induces the transition from open to closed association mode accompanying the decrease of mean hydrodynamic diameter of particles (D _H) from 100 nm to D _H ≤ 5 nm. Polymer addition to the system results in the leveling of pH decrease with surfactant concentration and increase of the electrokinetic potential values from 10 mV up to 40 mV. It was established that solubilization capacity of the supramolecular system formed could be increased by transition from surfactant individual solutions to the amphiphile/polymer binary system. The solubilization properties of the system strongly depend on the nature of the hydrophobic guest solubilized and differ by two orders of magnitude for hydrophobic azodye and lipophilic oxime.     

Functional polymers for colloidal applications. VII. Aggregate formation of lipophile-modified polyacrylates in aqueous solutions

Water-soluble copolymers, poly(dodecyl acrylate–coacrylic acid) (PDA), are synthesized by copolymerizing different ratios of dodecyl–acrylate/acrylic acid. Their aqueous solutions are transparent. The plots of I₁/I₃ (the intensity ratio of pyrene emission at 374 nm and 385 nm) and of surface tension as a function of polymer concentrations are combined to verify the existence of the aggregates of PDAs. It is found that the aggregations begin to form at concentrations below that of the polymer transfer to the air–water interface. The plots of I₁/I₃ as a function of polymer concentration shows that the polymers with a higher ratio of dodecyl acrylate form polymer aggregates at lower concentrations. The hydrophobicity of the inner core of polymer aggregates is close to that of sodium dodecyl sulfate (SDS). Polymer solutions of PDA 30, PDA 30L, and PDA 15, show significant solubilization ability to pyrene. (The molar ratio of dodecyl acrylate/total acrylates is 30%, 30%, and 15% for PDA 30, PDA 30L, and PDA 15, respectively. L, low molecular weight.) The solubilization ability increases with the increase in polymer concentration and degree of substitution of dodecylamine. The intensity ratio of the excimer emission to monomer emission of pyrene (I_e/I_m) increases with increasing polymer concentration, roughly parallel to the increase in the amount of pyrene solubilized. However, the I_e/I_m at a fixed pyrene concentration (I_e/I) decreases with increasing polymer concentration. These phenomena are interpreted in terms of the amount of pyrene solubilized and the size and concentration of the polymer aggregates. © 1993 John Wiley & Sons, Inc.     

Changes in phospholipid bilayers caused by sodium dodecyl sulfate/nonionic surfactant mixtures

The interaction of mixtures of sodium dodecyl sulfate (SDS) and oxyethylenated nonylphenol (30 mol of ethylene oxide) [NP(EO)₃₀] with phosphatidylcholine liposomes was investigated. Permeability alterations were detected as a change in 5(6)-carboxyfluorescein (CF) released from the interior of vesicles, and bilayer solubilization was measured as a decrease in the static light scattered by liposome suspensions. Three parameters were described as the effective surfactant/lipid molar ratios (Re) at which the surfactant system: (i) resulted in 50% CF release (Re _50%CF); (ii) saturated the liposomes (Re _SAT); (iii) led to complete solubilization of these structures (Re _SOL). The corresponding surfactant partition coefficients (K _50%CF, K _SAT, and K _SOL) were determined from these parameters. The free surfactant concentrations S _W were lower than the mixed surfactant critical micellar concentration at subsolubilizing levels, whereas they remained similar to these values during saturation and solubilization of bilayers. Although the Re values increased linearly as the mole fraction of the SDS rose (X _SDS), the K parameters showed maximum values at X _SDS 0.6 for K _50%CF and approximately at X _SDS 0.2 for K _SAT and K _SOL, respectively. Thus, the lower the surfactant contribution in the surfactant/lipid system, the higher the X _SDS at which the maximum bilayer/water partitioning of added mixed surfactant systems occurred. As a consequence, the influence of SDS in this partition appears to be more significant at the sublytic level (monomeric effect), whereas the influence of NP(EO)₃₀ seems to be greater during saturation and solubilization of liposomes via formation of mixed micelles.     

Pd@Al2O3‐Catalyzed Hydrogenation of Allylbenzene to Propylbenzene in Methanol and Aqueous Micellar Solutions

The palladium on alumina (Pd@Al₂O₃)‐catalyzed hydrogenation of allylbenzene to propylbenzene was studied in methanol and aqueous micellar solutions of sodium dodecyl sulfate (SDS), decyltrimethylammonium bromide (DTAB), and t‐octylphenoxypolyethoxyethanol (TX‐100). Over Pd@Al₂O₃, propylbenzene was obtained via direct hydrogenation of allylbenzene and isomerization to β‐methylstyrene which was hydrogenated afterwards. In aqueous micellar solutions, the reaction was faster than in pure water, but slower than in methanol due to lower hydrogen solubility. In the H₂O/SDS system, a higher activation energy was obtained than in methanol. For the investigated surfactants, the initial reaction rate in the micellar systems decreased in the order SDS > TX‐100 > DTAB.     

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.     

Solubilization of bituminous and lignite coals by chemically and biologically synthesized surfactants

Tween 80 (polyoxyethylene sorbitan monooleate), Triton X-100 (nonaethylene glycol octylphenol ether), and SDS (sodium dodecyl sulfate) solubilized several components of Mississippi Wilcox lignite and Illinois No. 6 bituminous coal. Tween 80 extraction of alkali-soluble Ugljevik lignite resulted in an increase in hydrogen content and decreases in the nitrogen and sulfur contents of undissolved coal solids. Biosurfactant-containing cell-free extracts of Bacillus licheniformis solubilized a 53 000 Da coal component of Mississippi Wilcox lignite. The results suggest that solubilization of coal organic components by chemically- and biologically-synthesized surfactants has potential in terms of upgrading coals.     

Testing different cohesive law shapes to predict damage growth in bonded joints loaded in pure tension

ABSTRACT

Adhesive bonding is a widely used joining method because of specific advantages compared to the traditional fastening methods. Cohesive zone modelling (CZM) is currently the most widely used technique for strength prediction. CZM supposes the characterization of the CZM laws in tension and shear. This work evaluated the tensile fracture toughness (G_IC) and CZM laws of bonded joints with three adhesives by the double-cantilever beam (DCB) test. The experimental work consisted of the adhesives’ tensile fracture characterization by the J-integral technique. As the main novelty of this work, the precise shape of the cohesive law of adhesives ranging from brittle to highly ductile was defined by the direct method, using a digital image correlation method to evaluate the tensile relative displacement (δ_n) of the adhesive layer at the crack tip and adherends’ rotation at the crack tip (?_o). Moreover, finite element (FE) simulations permitted assessing the accuracy of triangular, trapezoidal and linear-exponential CZM laws in predicting the experimental behaviour of the DCB bonded joints with markedly distinct behaviours. As output of this work, fracture data and information regarding the applicability of these CZM laws to each type of adhesive is provided, allowing the subsequent strength prediction of bonded joints.     

Tert-Butylation of Biphenyl over Mordenites

H-mordenites are very highly shape-selective catalysts in the alkylation of biphenyl with tert-butanol under liquid phase conditions using n-decane as a solvent with a selectivity to 4-(tert-butyl)biphenyl above 98% and to 4,4-di(tert-butyl)biphenyl near 100% to give 24% yield of 4,4-di(tert-butyl)biphenyl using H-MOR(45).     

Chelation and Foam Separation of Metal Ions from Solutions

Abstract

An experimental study was conducted on the chelation and foam separation of trace amounts of cadmium, zinc, and lead from their water solutions. The chelation agents ethylenediaminetetraacetate (sodium salt), sodium diethyl-dithiocarbamate, and citric acid were used with sodium dodecylsulfate (SDS) as a foam-producing agent. The chelation agents did not produce metal complexes that were very surface active. The foam-producing agent produced metal ion complexes that were surface active and resulted in appreciable separation of the metal ions. The use of 100 ppm SDS resulted in separation of 90% of the zinc ions from solution containing 2 to 20 ppm zinc. At concentrations below and above this, the removal efficiency dropped significantly     

Study of alcohol-free microemulsion systems containing fatty acids as cosurfactants

In this study, fatty acids with carbon chains ranging in length from 3 to 8 (propyl to octyl) were used in place of alcohols to form microemulsion systems. The microemulsion systems contained sodium dodecyl sulfate (SDS), hexane, fatty acid, water, and NaCl. The phase behavior of these systems was examined using salinity scans at 25°C. The results showed that propanoic and butanoic acids promoted the formation of clear isotropic microemulsions, whereas the other fatty acids promoted a gel formation. High hexane solubilization was obtained with all of the systems. The optimum solubilization parameter (SP^*) and optimum salinity (S ^*) decreased with increasing SDS concentration. With increasing fatty acid chain length, S ^* decreased but SP^* increased. Conductivity meausrements showed that, during the salinity scan, the conductivity of the systems was relatively unchanged, gradually decreased, or was a maximum at a given value. Interfacial tension (IFT) measurements showed that ultralow IFT were realized between microemulsion and oil phases using the fatty acids and that SP^* and IFT were inversely related. The results of this study confirm that microemulsions can be formulated without alcohols through replacement of the alcohols with the appropriate fatty acids.