Solubilization Ratio Research Articles

Surface activity, micellization and solubilization of cationic gemini surfactant-conventional surfactants mixed systems

In this paper, we have studied the mixed surfactant systems containing a cationic gemini surfactant N,N′-bis(dimethyldodecyl)-1,2-pentanediammonium dibromide (12-5-12) with several differently charged surfactants (cationic/anionic/non-ionic/zwitterionic) by using surface tension, small angle neutron scattering (SANS) under standard condition. All the surfactants have same dodecyl chain but different in polar head group viz. Sodium dodecyl trioxyethylene sulphate (SDES)(anionic), dodecyl trimethyl ammonium bromide (DTAB) (cationic), 3-[dodecyldimethyl ammonio] propane sulphonate (C12-PS)(zwitterionic), hexaethylene glycol monododecyl ether (C12E6)(non-ionic) and dimethyl dodecyl amine oxide (DMDAO) (cationic-non-ionic). The Clint, Rubingh, Maeda and Rosen approaches were employed to determine various parameters like critical micelles concentration (CMC), surface excess concentration (Гmax), surface pressure at CMC (πCMC), minimum area per molecule (Amin) etc. as well as thermodynamic parameters. Solubilization of some polycyclic aromatic hydrocarbons (PAHs) have done in single as well as in mixed surfactant systems. Order of solubilization capacity of PAHs compounds are different in pure/mixed surfactant micelles. The solubilization efficiency towards naphthalene, anthracene, and pyrene were measured and the molar solubilization ratio (MSR), deviation ratio (R) and micelle-water partition coefficient (km) were evaluated for single and mixed systems.

The Use of Bile Salt Micelles for the Prediction of Human Intestinal Absorption

Human intestinal absorption (HIA) will dictate biopharmaceutical performance through its influence on absorption, distribution, metabolism, and elimination and can vary significantly depending upon the nature of the compound under consideration. In this study, an in vitro assay method is proposed for the prediction of HIA through the measurement of drug solubility in an aqueous phase containing micellar bile salt, namely sodium deoxycholate. A series of twenty compounds, displaying a range of physicochemical properties and known HIA values, were analyzed using UV spectroscopy to determine a solubilization ratio for each compound. A micelle/water partition coefficient (Kxm/a) was calculated and then used to develop an equation through simple linear regression; logit HIA = −0.919 + 0.4618 logKxm/a (R2 = 0.85). From this equation, a value for % HIA was determined which compared well with literature. Furthermore, 4 additional drugs were then analyzed using the developed equation and found to match well with literature, confirming the suitability of the method. Using a simple, economic, and robust UV bile salt assay allows prediction of HIA and avoids many of the disadvantages of other techniques, such as animal-based methods.

Robust Flash Calculation Algorithm for Microemulsion Phase Behavior

AbstractThe HLD‐NAC model was recently modified to match and predict microemulsion phase behavior experimental data for Winsor type III regions. Until now, the HLD‐NAC model could not generate realistic phase behavior for type II− and type II+ two‐phase regions, leading to significant saturation and composition discontinuities when catastrophe theory is applied. These discontinuities lead to significant failures in modeling surfactant applications. We modify the HLD‐NAC equations to ensure consistency over the entire composition space including type II− and II+ regions. A robust and efficient algorithm is developed that always converges and provides continuous estimates with any formation variable of tie lines and triangles for all Winsor types. Discontinuities are eliminated and limiting tie lines near critical points are determined analytically. The tuning procedure is demonstrated using several sets of experimental data. Excellent predictability of tie lines and tie triangles, and solubilization ratios are shown.

Difference in inclusion behavior of β-cyclodextrin and hydroxypropyl-β-cyclodextrin with menthol

Volatile oils are important active components in traditional Chinese medicine, but their components are complicated and unstable. It is common to use cyclodextrin inclusion technique to improve the stability of volatile oils and make them easier to be prepared. At present, β-cyclodextrin (β-CD) is the most common inclusion material. The evaluation indicators for inclusion technique usually contain the inclusion rate and the oil content in the inclusion compound. However, the articles about the study on selecting inclusion materials for volatile oils were few. In this paper, menthol, the main active ingredient of mint volatile oil, was used as model drug, while β-CD and hydroxypropyl-β-cyclodextrin (HP-β-CD) were used as the inclusion materials. Inclusion equilibrium constant (K), solubilization ratio were investigated, and the results were combined with IR, DSC and TG to verify the formation of inclusion complexes. It turned out that in the range of 0-15 mmol•L⁻¹, the solubility of menthol was increased linearly with the increase of HP-β-CD concentration, with AL-type phase solubility diagram, K=3 188.62 L•mol⁻¹; in the range of 0-12.5 mmol•L⁻¹, the solubility of menthol was increased linearly with the increase of β-CD concentration, K=818.73 L•mol⁻¹. When the concentration was over 12.5 mmol•L⁻¹, the solubility of menthol appeared to be a negative deviation with the increase of β-CD concentration, with AN-type solubility diagram. The above results showed that the inclusion behavior was different between β-CD and HP-β-CD, laying a foundation for further study on inclusion complexes of volatile oil.

Dimensionless Equation of State to Predict Microemulsion Phase Behavior.

Prediction of microemulsion phase behavior for changing state variables is critical to formulation design of surfactant-oil-brine (SOB) systems. SOB systems find applications in various chemical and petroleum processes, including enhanced oil recovery. A dimensional equation-of-state (EoS) was recently presented by Ghosh and Johns1 that relied on estimation of the surfactant tail length and surface area. We give an algorithm for flash calculations for estimation of three-phase Winsor regions that is more robust, simpler, and noniterative by making the equations dimensionless so that estimates of tail length and surface area are no longer needed. We predict phase behavior as a function temperature, pressure, volume, salinity, oil type, oil-water ratio, and surfactant/alcohol concentration. The dimensionless EoS is based on coupling the HLD-NAC (Hydrophilic Lipophilic Difference-Net Average Curvature) equations with new relationships between optimum salinity and solubility. An updated HLD expression that includes pressure is also used to complete the state description. A significant advantage of the dimensionless form of the EoS over the dimensional version is that salinity scans are tuned based only on one parameter, the interfacial volume ratio. Further, stability conditions are developed in a simplified way to predict whether an overall compositions lies within the single, two-, or three-phase regions. Important new microemulsion relationships are also found, the most important of which is that optimum solubilization ratio is equal to the harmonic mean of the oil and water solubilization ratios in the type III region. Thus, only one experimental measurement is needed in the three-phase zone to estimate the optimum solubilization ratio, a result which can aid experimental design and improve estimates of optimum from noisy data. Predictions with changing state variables are illustrated by comparison to experimental data using standard diagrams including a new type of dimensionless fish plot. The results show that the optimum solubilization ratio and salinity using the tuned dimensionless EoS are within average errors of 2.44% and 1.17% of experimental values for the fluids examined. We then use the dimensionless equations and thermodynamic first-principles to derive the constant in Huh's equation for interfacial tension prediction.

An Equation-of-State Model To Predict Surfactant/Oil/Brine-Phase Behavior

Summary Surfactant/polymer (SP) floods have significant potential to recover waterflood residual oil in shallow oil reservoirs. A thorough understanding of surfactant/oil/brine-phase behavior is critical to design SP-flood processes. Current practices involve repetitive laboratory experiments of dead crude at atmospheric pressure in a salinity scan that aims at finding an “optimum formulation” of chemicals for targeted oil reservoirs. Although considerable progress has been made in developing surfactants and polymers that increase the potential of a chemical enhanced-oil-recovery (EOR) project, very little progress has been made to predict phase behavior as a function of formulation variables such as pressure, temperature, and oil equivalent alkane carbon number (EACN). The empirical Hand (1930) plot is still used today to model the microemulsion-phase behavior with little predictive capability because these and other formulation variables change. Such models could lead to incorrect recovery predictions and improper SP-flood designs. In this research, we develop a new predictive-phase-behavior model and introduce a new factor β to account for pressure changes in the HLD equation. This new HLD equation is coupled with the net-average-curvature (NAC) model to predict phase volumes, solubilization ratios, and microemulsion-phase transitions (Winsor II–, Winsor III, and Winsor II+). The predictions of key parameters are compared with experimental data and are within relative errors of 4% (average 2.35%) for measured optimum salinities and 17% (average 10.55%) for optimum solubilization ratios. This paper is the first to use the HLD/NAC model to predict microemulsion-phase behavior for live crudes, including optimal solubilization ratio and the salinity width of the three-phase Winsor III region at different temperatures and pressures. Although the effect of pressure variations on microemulsion-phase behavior is generally thought to be small compared with temperature-induced changes, we show here that this is not necessarily the case. The predictive approach relies on tuning the model to limited experimental data (such as at atmospheric pressure) similar to what is performed for equation-of-state (EOS) modeling of miscible gasfloods. This new EOS-like model could significantly aid the design of chemical floods where key variables change dynamically, and in screening of potential candidate reservoirs for chemical EOR.

Synergistic solubilization of low-brominated diphenyl ether mixtures in nonionic surfactant micelles

The present study investigated the co-solubilization of three representative low-brominated diphenyl ethers (low-BDEs) in nonionic surfactant micelles. Co-solubilization effects were quantified in terms of molar solubilization ratio (MSR), micelle–water partition coefficient (log Km), extent of synergism/inhibition (RΔMSR), first stepwise association constant (K1), the average number of solute molecules per micelle (SM), excess Gibbs energy (ΔG0 excess), and interaction parameter (ω/RT). The solubilities of low-BDEs during co-solubilization were increased (i.e., synergism) in all of the surfactants tested, relative to their respective solubilities during solubilization. In each surfactant system, synergism was weaker for BDE-15/BDE-28 than that for BDE-15/BDE-47 because BDE-15 and BDE-28 may be partitioned more uniformly in the micelle core than BDE-47, which increased the possibility of their competition. Unexpectedly, BDE-28 and BDE-47 with similar log Kow values demonstrated enhanced co-solubility. This phenomenon was attributed to the positive electrostatic potentials of bromines (computed by Gaussian program) on BDE-28 and BDE-47 which may provide additional attractions to oxygen atoms of the hydrophilic chains. The synergism observed for BDE-15/BDE-28 and BDE-15/BDE-47 was stronger in the Brij35 system than that in Brij58 and Brij78 systems, suggesting that a surfactant with lower aggregation number and/or longer hydrophilic chain length can avoid the competition between solutes for the micelle core. This study may improve the understanding of multi-solutes interactions in surfactant micelles.

Enhanced Soil Remediation via Plant-Based Surfactant Compounds from Acanthophyllum Laxiusculum

Abstract In the present study, an aqueous root-extract of Acanthophyllum laxiusculum (AREAL) was evaluated for phenanthrene removal from two samples of contaminated soil. AREAL showed a linear solubilization enhancement for phenanthrene with a weight solubilization ratio of 0.05. Batch soil washing experiments caused the removal of phenanthrene with efficiencies of 96.7 % and 78 % from soils with 0.78 % and 2.73 % organic carbon, respectively. Desorption kinetics of phenanthrene exhibited a two-phase pattern, namely, a rapid release as the initial phase and a slower removal as a subsequent phase. A two-compartment exponential model could adequately represent the two phases of the kinetic pattern of phenanthrene desorption. The rise of pH from acidic to basic levels, decreased phenanthrene removal due to changes in the micelle number of the surfactant phase. Maximum achievable yield of removal was 82 % phenanthrene in a column experiment at defined operational conditions. High removal efficiencies show the potential application of AREAL for improving the bioremediation of polycyclic aromatic hydrocarbons (PAHs) from contaminated soils.

Solubilization of Polycyclic Aromatic Hydrocarbons by Single and Binary Mixed Rhamnolipid-Sophorolipid Biosurfactants.

Biosurfactants are promising additives for surfactant enhanced remediation (SER) technologies due to their low toxicity and high biodegradability. To develop green and efficient additives for SER, the aqueous solubility enhancements of polycyclic aromatic hydrocarbons (PAHs; naphthalene, phenanthrene, and pyrene) by rhamnolipid (RL) and sophorolipid (SL) biosurfactants were investigated in single and binary mixed systems. The solubilization capacities were quantified in terms of the solubility enhancement factor, molar solubilization ratio (MSR), and micelle-water partition coefficient (). Rughbin's model was applied to evaluate the interaction parameters (β) in the mixed RL-SL micelles. The solubility of the PAHs increased linearly with the glycolipid concentration above the critical micelle concentration (CMC) in both single and mixed systems. Binary RL-SL mixtures exhibited greater solubilization than individual glycolipids. At a SL molar fraction of 0.7 to 0.8, the solubilization capacity was the greatest, and the MSR and reached their maximum values, and β values became positive. These results suggest that the two biosurfactants act synergistically to increase the solubility of the PAHs. The solubilization capacity of the RL-SL mixtures increased with increasing temperature and decreased with increasing salinity. The aqueous solubility of phenanthrene reached a maximum value at pH of 5.5. Moreover, the mixed RL-SL systems exhibited a strong ability to solubilize PAHs, even in the presence of heavy metal ions. These mixed biosurfactant systems have the potential to improve the performance of SER technologies using biosurfactants to solubilize hydrophobic organic contaminants by decreasing the applied biosurfactant concentration, which reduces the costs of remediation.

Synthesis, Characterization and Exploratory Application of Anionic Surfactant Fatty Acid Methyl Ester Sulfonate from Waste Cooking Oil

AbstractThe environmentally friendly anionic surfactant fatty acid methyl ester sulfonate (MES) was prepared by esterification of waste cooking oil (WCO), a low‐cost raw material, followed by sulfonation with chlorosulfonic acid. MES production from WCO (W‐MES) gave yields up to 78 %. Such a value is only slightly lower than the one obtained from soybean oil (S‐MES), 82 %, and almost the same as that from reused cooking oil (R‐MES), 76 %. According to the two‐phase titration results, the content of the active component, α‐MES, in S‐MES, R‐MES and W‐MES was equal to 76.82, 69.19 and 66.60 %, respectively. The disalt, RCH(CO2Na)SO3Na, contents were instead 3.2, 3.8 and 4.7 %, respectively. As proved by the results of the FTIR and NMR characterizations, the chemical structure of W‐MES is almost the same as that of S‐MES and R‐MES. The critical micelle concentration of W‐MES is 5.38 mmol/L and the corresponding surface tension is 32.3 mN/m. The hydrophile‐lipophile balance value of W‐MES is 12.33, which indicates that it can form oil/water emulsions. The three MES demonstrated the same adsorption efficiency, yielding a pC20 value of 3.22, and similar foam stability. Their detergency can be up to 75 % at a concentration of 400 mg/kg and the tolerance to Ca2+ is higher than the one exhibited by linear alkylbenzene sulphonic acid and alpha olefin sulfonate. Additionally, W‐MES shows a considerable solubilization capacity towards polycyclic aromatic hydrocarbon as the molar solubilization ratios to pyrene, phenanthrene and acenaphthene in a 30 mmol/L solution are 1.22 × 10−3, 2.67 × 10−3 and 3.81 × 10−3, respectively.

Enhanced aqueous solubility of polycyclic aromatic hydrocarbons by green diester-linked cationic gemini surfactants and their binary solutions

Three homologues of a novel biodegradable diester-linked cationic gemini surfactant series, CmH2m+1 (CH3)2N+(CH2COOCH2)2N+(CH3)2CmH2m+1.2Cl− (m-E2-m; m = 12, 14, 16), were used for investigation of the solubilization of polycyclic aromatic hydrocarbons (PAHs) such as naphthalene, anthracene and pyrene in single as well as binary surfactant solutions. Physicochemical parameters of the pure/mixed systems were derived by conductivity and surface tension measurements. Dissolution capacity of the equimolar binary surfactant solutions towards the PAHs was studied from the molar solubilization ratio (MSR), micelle–water partition coefficient (Km) and free energy of solubilization (ΔGs0) of the solubilizates. Influence of hydrophobic chain length of the dimeric surfactants on solubilization was characterized. Aqueous solubility of the PAHs was enhanced linearly with concentration of the surfactant in all the pure and mixed gemini–gemini surfactant systems.

Synergistic solubilization of polycyclic aromatic hydrocarbons by mixed micelles composed of a photoresponsive surfactant and a conventional non-ionic surfactant

Abstract Surfactant-enhanced remediation is a powerful technology for soil clean-up. However, some drawbacks, such as its high cost and the secondary contamination caused by flushing agents, have hampered this technology and its commercial application has been largely limited to North American and European countries. The aim of this work is to introduce a novel reversible solubilization system composed of the photoresponsive surfactant 4-butylazobenzene-4′-(oxyethyl)trimethylammonium bromide (AZTMA) and the commercial non-ionic surfactant Tween80 for the solubilization of organic contaminants. The solubilization behavior of the AZTMA/Tween80 surfactant system toward polycyclic aromatic hydrocarbons (PAHs) has been studied. Critical micelle concentration (CMC) values indicate that the mixed system has a synergism in mixed micelle formation, and that the interaction parameter ( β ) is −2.85 when the mole ratio is 2:8. AZTMA is also predicted to be low biologic toxicity by the CMC and surface tension. The synergistic effect on molar solubilization ratio (MSR) and micelle-phase/aqueous-phase partition coefficient K mc values is related to the composition and concentration of the mixed system and follows the order pyrene > phenanthrene > acenaphthene, and these parameters are much higher than those for the single surfactants. After irradiation with UV light, more than 65% of the PAHs could be separated from the mixed micelles, and the cumulative release efficiencies of selected PAHs are consistent with the results of solubilization experiments. All of these features demonstrate that mixed AZTMA/Tween80 should be preferable to single surfactants for soil remediation, avoiding the issues associated with chemical flushing agents and decreasing remediation costs.

EFFECT OF THERMAL PRETREATMENT ON THE SOLUBILIZATION OF ORGANIC MATTERS IN A MIXTURE OF PRIMARY AND WASTE ACTIVATED SLUDGE

The increased demand for advanced techniques in anaerobic digestion over the last few years has led to the employment of various pre-treatment methods prior to anaerobic digestion to increase gas production. These pre-treatment methods alter the physical and chemical properties of sludge in order to make it more readily degradable by anaerobic digestion. Although the thermal pre-treatment presents high energy consumption, the main part of this energy to heat can be recovered from the biogas produced in the anaerobic process. In this research a mixture of primary and waste activated sludge was thermally pretreated at 100, 125, 150, 175 and 200o C in order to determine the effect of thermal pretreatment on improving the solubilization of sludge by increasing the soluble organic fraction (expressed as soluble COD and VFA). Experimental results proved that the solubilization ratio of sludge is depends on the treatment time and the applied temperature and the optimal temperature ranged between 175 and 200o C. The COD solubilization ratio (at 175o C) increased from 11.2% to 15.1% and 25.1% when the time of treatment increased from 60 min to 120 and 240 min respectively. The experimental data could be fitted to obtain an empirical model (Known as the enzyme-kinetic equation) relating the COD solubilization ratio of sludge and VFA concentration to the applied temperature and the heating time.

EFFECT OF THERMAL PRETREATMENT ON THE SOLUBILIZATION OF ORGANIC MATTERS IN A MIXTURE OF PRIMARY AND WASTE ACTIVATED SLUDGE

The increased demand for advanced techniques in anaerobic digestion over the last few years has led to the employment of various pre-treatment methods prior to anaerobic digestion to increase gas production. These pre-treatment methods alter the physical and chemical properties of sludge in order to make it more readily degradable by anaerobic digestion. Although the thermal pre-treatment presents high energy consumption, the main part of this energy to heat can be recovered from the biogas produced in the anaerobic process. In this research a mixture of primary and waste activated sludge was thermally pretreated at 100, 125, 150, 175 and 200o C in order to determine the effect of thermal pretreatment on improving the solubilization of sludge by increasing the soluble organic fraction (expressed as soluble COD and VFA). Experimental results proved that the solubilization ratio of sludge is depends on the treatment time and the applied temperature and the optimal temperature ranged between 175 and 200o C. The COD solubilization ratio (at 175o C) increased from 11.2% to 15.1% and 25.1% when the time of treatment increased from 60 min to 120 and 240 min respectively. The experimental data could be fitted to obtain an empirical model (Known as the enzyme-kinetic equation) relating the COD solubilization ratio of sludge and VFA concentration to the applied temperature and the heating time.

EFFECT OF THERMAL PRETREATMENT ON THE SOLUBILIZATION OF ORGANIC MATTERS IN A MIXTURE OF PRIMARY AND WASTE ACTIVATED SLUDGE

The increased demand for advanced techniques in anaerobic digestion over the last few years has led to the employment of various pre-treatment methods prior to anaerobic digestion to increase gas production. These pre-treatment methods alter the physical and chemical properties of sludge in order to make it more readily degradable by anaerobic digestion. Although the thermal pre-treatment presents high energy consumption, the main part of this energy to heat can be recovered from the biogas produced in the anaerobic process. In this research a mixture of primary and waste activated sludge was thermally pretreated at 100, 125, 150, 175 and 200 o C in order to determine the effect of thermal pretreatment on improving the solubilization of sludge by increasing the soluble organic fraction (expressed as soluble COD and VFA). Experimental results proved that the solubilization ratio of sludge is depends on the treatment time and the applied temperature and the optimal temperature ranged between 175 and 200 o C. The COD solubilization ratio (at 175 o C) increased from 11.2% to 15.1% and 25.1% when the time of treatment increased from 60 min to 120 and 240 min respectively. The experimental data could be fitted to obtain an empirical model (Known as the enzyme-kinetic equation) relating the COD solubilization ratio of sludge and VFA concentration to the applied temperature and the heating time.

Cocrystal Solubilization in Biorelevant Media and its Prediction from Drug Solubilization

This work examines cocrystal solubility in biorelevant media (FeSSIF, fed-state simulated intestinal fluid), and develops a theoretical framework that allows for the simple and quantitative prediction of cocrystal solubilization from drug solubilization. The solubilities of four hydrophobic drugs and seven cocrystals containing these drugs were measured in FeSSIF and in acetate buffer at pH 5.00. In all cases, the cocrystal solubility (Scocrystal ) was higher than the drug solubility (Sdrug ) in both buffer and FeSSIF; however, the solubilization ratio of drug, SRdrug = (SFeSSIF /Sbuffer )drug , was not the same as the solubilization ratio of cocrystal, SRcocrystal = (SFeSSIF /Sbuffer )cocrystal , meaning drug and cocrystal were not solubilized to the same extent in FeSSIF. This highlights the potential risk of anticipating cocrystal behavior in biorelevant media based on solubility studies in water. Predictions of SRcocrystal from simple equations based only on SRdrug were in excellent agreement with measured values. For 1:1 cocrystals, the cocrystal solubilization ratio (SR) can be obtained from the square root of the drug SR. For 2:1 cocrystals, SRcocrystal is found from (SRdrug )(2/3) . The findings in FeSSIF can be generalized to describe cocrystal behavior in other systems involving preferential solubilization of a drug such as surfactants, lipids, and other drug solubilizing media.

Physics based HLD–NAC phase behavior model for surfactant/crude oil/brine systems

Abstract Compositional simulation of surfactant flooding highly depends on accurate modeling of surfactant/oil/brine microemulsion phase behavior. This paper introduces a physics-based Hydrophilic–Lipophilic Difference (HLD) equation and the Net-Average Curvature (NAC) called thereafter HLD–NAC equation of state to model the phase behavior of surfactant/crude oil/brine systems. A non-iterative and physics-based algorithm is developed and validated by modeling the solubilization ratio curves and phase volume fraction of different microemulsion systems. The HLD values are calculated by the natural logarithm of salinity over optimum salinity when lacking of oil hydrophobicity and surfactant Characteristic curvature information. Together with lab measured head area of per surfactant molecule, the HLD–NAC model reproduces the microemulsion phase behavior of various formulations for surfactant flooding with only one fitting parameter, the length constant L, which physically represents the surfactant tail length size. Modeling results show that the fitted parameter increases with the surfactant or surfactant mixture tail length in the formulation. Moreover, the length parameter determined from one system can be readily applied to other systems, indicating the physical significance of the HLD–NAC model, which can to some extent predict the performance of one surfactant in various systems. The fitted length parameter for formulations with alcohol is underestimated because of this paper assuming all alcohol partition on the interface leading to overestimated interfacial area. The effect of cosolvent partitioning on the micelle structure and phase behavior modeling will be demonstrated in future studies. In this paper, the HLD–NAC equation of state is proved to be a simple and robust tool for modeling phase behavior of surfactant/crude oil/brine systems. The HLD–NAC model can shorten the surfactant screening process hence help chemical EOR formulation design and optimization, and can also be used in compositional chemical flooding reservoir simulation to improve the predictability of surfactant floods.

Effect of rhamnolipid biosurfactant on solubilization of polycyclic aromatic hydrocarbons

Rhamnolipid biosurfactant-producing bacteria, Bacillus Lz-2, was isolated from oil polluted water collected from Dongying Shengli oilfield, China. The factors that influence PAH solubilization such as biosurfactant concentration, pH, ionic strength and temperature were discussed. The results showed that the solubilities of naphthalene, phenanthrene and pyrene increased linearly with the rise of rhamnolipid biosurfactant dose above the biosurfactant critical micelle concentration (CMC). Furthermore, the molar solubilization ratio (MSR) values decreased in the following order: naphthalene>phenanthrene>pyrene. However, the solubility percentage increased and followed the opposite order: pyrene>phenanthrene>naphthalene. The solubilities of PAHs in rhamnolipid biosurfactant solution increased with the rise of pH and ionic strength, and reached the maximum values under the conditions of pH11 and NaCl concentration 8g·L−1. The solubility of phenanthrene and pyrene increased with the rise of temperature.

Cosolubilization synergism occurrence in codesorption of PAH mixtures during surfactant-enhanced remediation of contaminated soil.

Surfactant-enhanced remediation (SER) has been widely applied in decontaminating PAH-polluted soil. Most researches focus on evaluating washing efficiency without considering pollutants' mutual interaction. This study aims to investigate cosolubilization effect between phenanthrene (Phe) and pyrene (Pyr) in nonionic surfactant Triton X-100 (TX100) solution on their codesorption performance from soil. Cosolubilization experiment showed that, when cosolubilized, solubility of Phe and Pyr in TX100 increased by 15.38% and 18.19%, respectively, as quantified by the deviation ratio of molar solubilization ratio in single and binary solute solubilization systems. The synergism may be due to the enlarged micelle volume caused by PAHs solubilized in the shell region of the micelle. The cosolubilization effect was further observed in the soil washing process. The strengthened TX100 solubilization capacity towards Phe and Pyr could increase the two PAHs' codesorption efficiency from soil, accompanied by synergistic extent of 6-15%. However, synergism in codesorption was weaker than that observed in the cosolubilization system, which may be related to surfactant loss to soil and PAH partition into soil organic matter and the sorbed surfactants. The improved remediation performance during codesorption of mixed PAHs implies the significance of combining PAHs' mutual interaction into evaluating SER, which may reduce the surfactant washing concentration and save remediation cost.

Solubilization of herbicides by single and mixed commercial surfactants

The solubilization capabilities of micellar solutions of three single surfactants, two alcohol alkoxylates B048 and B266, and the tallow alkyl ethoxylated amine ET15, and their equimolar mixed solutions toward the herbicides flurtamone (FL), metribuzin (MTZ) and mesotrione (MST) were investigated. The solubilization capacity was quantified in terms of the molar solubilization ratio (MSR), critical micellar concentration (CMC), micelle–water partition coefficient (Kmc), binding constant (K1), number of aggregation (Nagg) and Stern–Volmer constant (Ksv). The herbicides were greatly solubilized into different loci of the micelles: FL within the inner hydrophobic core, MST at the micelle/water interface and MTZ in the palisade region. Equimolar binary surfactant mixtures did not improve the solubilization of herbicides over those of single components, with the exception of MTZ by the B266/ET15 system which enhanced solubilization by 10–20%. This enhanced solubilization of MTZ was due to an increased number of micelles that arise from both the intermediate Nagg relative to that of the single surfactants and the lower CMC. The use of Ksv values was a better predictor of the solubilization of polar molecules within binary mixtures of these surfactants than the interaction parameter βM from regular solution theory (RST). The results herein suggest that the use of mixed surfactant systems for the solubilization of polar molecules in environmental remediation technologies may be very limited in scope, without clear advantages over the use of single surfactant systems.