Tohren C. G. Kibbey

High-performance liquid chromatographic analysis of polydisperse ethoxylated non-ionic surfactants in aqueous samples

An adsorption HPLC method using traditionally reversed-phase solvents and a hybrid column/precolumn has been developed for the quantitative separation and analysis of ethoxylated non-ionic surfactants on the basis of the number of ethoxylate (EO) groups per molecule. This method is demonstrated to separate ethoxylated homologues of broadly distributed linear alcohol ethoxylates and alkylphenol ethoxylates, with numbers of EO groups ranging from 3 to 50 or greater. This method presents a significant advance in non-ionic surfactant analysis because it permits direct injection of aqueous samples, eliminating the need for extensive sample preparation. The method discussed here is optimized for use with an evaporative light scattering detector (ELSD), but works equally well with UV absorbance or fluorescence detectors for the analysis of surfactants with chromophores. ELSD and UV detector operating conditions and calibration methods are discussed.

Algae, Canola, or Palm Oils—Diesel Microemulsion Fuels: Phase Behaviors, Viscosity, and Combustion Properties

Vegetable oils are being considered as a renewable energy alternative for diesel. The high viscosity of vegetable oils causes injector fouling and durability problems in compression–ignition engines. Microemulsification can be used to reduce vegetable oil viscosity without complex chemical transformation processes. The goal of our work is to formulate reverse micellar microemulsions of vegetable oils and No. 2 diesel fuel blended with ethanol using different combinations of surfactants and co-surfactants. Ethanol, also a renewable fuel, was used as a viscosity modifier. We studied three vegetable oils (canola, palm, and algae oils) to blend with diesel fuel. The microemulsion fuels were tested for temperature stability, viscosity, water tolerance, and their combustion performance in terms of flame radiation and pollutant (CO, NOx) emissions. With appropriate surfactant and co-surfactant systems, we successfully formulated canola and algae/diesel microemulsions with cloud points and points that satisfy the ASTM standards. Among all formulations, palm/diesel microemulsion fuels solidified at 6–6.5°C due to high saturated triglyceride content. While the formulated microemulsion fuels had approximately 10% lower heating value than diesel fuel, their CO emission and flame radiation were superior to those of diesel fuel. NOx emissions were also lower with the blends containing no nitrate additives, but were higher than with diesel fuel in the presence of nitrate additives. Thus, these results show that microemulsification can produce biofuels with desirable viscosity, fuel properties can be adjusted via formulation variables, and microemulsions can replace chemical processes for producing biofuels.

Effects of soil skeleton deformations on hysteretic soil water characteristic curves: Experiments and simulations

[1] Soil water characteristic curves (SWCCs) represent the relationship between suction and water content in unsaturated soils. The SWCCs exhibit hysteresis during wetting-drying cycles; however, the empirical expressions used to describe SWCCs have typically ignored the hysteresis. Additionally, the shape of the SWCC will vary depending on the void ratio of the soil and changes resulting from soil skeleton deformations, which may also show hysteretic behavior under various loading conditions. Therefore, it is important to investigate, both experimentally and theoretically, the relationship between soil skeleton deformations and the SWCC for different soils. There is limited information in the literature that examines, both experimentally and theoretically, the complex coupling between the soil skeleton deformation and SWCC behavior, and generally, this behavior is not well understood. This paper presents laboratory test results of SWCCs determined under different confining stresses on similarly prepared samples of a silty soil; drying, wetting, second drying, and scanning curves were obtained. The influence of soil skeleton deformations on SWCCs is inferred from the curves measured in an oedometer under different stress conditions. An elastoplastic phenomenological constitutive model based on the bounding surface plasticity theory was utilized to simulate the coupled mechanical-hydraulic behavior of measured results. This research demonstrates that the model is capable of predicting hysteresis in SWCCs and soil skeleton deformation and the coupling between the hydraulic and mechanical behavior of unsaturated soils.

Rapid Pseudo-Static Measurement of Hysteretic Capillary Pressure-Saturation Relationships in Unconsolidated Porous Media

An automated system was developed for a rapid measurement of detailed hysteretic capillary pressure-saturation (Pc-S) relationships, including primary drainage, main imbibition, and scanning loops. The method makes use of a slow-dynamic (pseudo-static) measurement method which is able to duplicate static results while expanding the pressure range over which high permeability capillary barriers can be applied, and increasing the quantity of hysteretic data that can be collected. The method is demonstrated for two sands and three silts for capillary pressures as high as 1000 cm water (98 kPa). For the experiments shown, primary drainage and main imbibition loops were completed within approximately 6.5 h for all materials, with full runs, including multiple scanning curves, completed in less than 20 h. A model for selection of pressure rates needed to duplicate static results is presented and is found to produce results consistent with empirically-determined rates. The model also predicts the effects of system resistance on dynamic response and is found to be in good agreement with experimental results, particularly for slower rates approaching those needed for pseudo-static conditions.

Retention and release of TiO2 nanoparticles in unsaturated porous media during dynamic saturation change

The retention and release of TiO(2) nanoparticles in porous media (packed glass beads) were studied under transient unsaturated conditions as the media were taken through multiple drainage/imbibition (drying/wetting) cycles at three different pH values. The focus of the work was to better understand the role of changing water table levels and rainfall infiltration events on the ultimate mobility of TiO(2) nanoparticles. Results indicate that retention during saturated transport varied considerably, from very strong retention at pH 5 (likely due to electrostatic interactions), to no measurable retention at pH 10. During primary drainage, additional retention (i.e., beyond what was retained during initial saturation) was observed at all pH values. During subsequent imbibition/drainage cycles where nanoparticle-free water was imbibed into the porous medium prior to drainage, the mass of retained TiO(2) remained nearly constant at all three pH values. Final imbibition/drainage and subsequent flushing, both using solution conditions adjusted to favor high mobility, showed very little additional nanoparticle release. These results indicate that the release of TiO(2) nanoparticles following retention by either saturated or unsaturated packed glass beads was difficult to achieve, regardless of the likely initial mechanisms of retention, even when solution conditions were changed to those that should favor high mobility.

Effects of surfactant concentration and sorbent properties on the sorption and transport of ethoxylated nonionic surfactant mixtures

Ethoxylated nonionic surfactants are widely used for industrial applications and have been considered for environmental remediation applications. As a result, an understanding of the sorption and transport of nonionic surfactants is important, both for their efficient use during remediation applications and for understanding their potential fate in the environment. Because ethoxylated nonionic surfactants are typically broadly-distributed mixtures containing a substantial number of components, an understanding of the influence of the surfactant component distribution on the overall mixture behavior is also required. In this paper, the sorption behaviors of linear alcohol ethoxylates and alkylphenol ethoxylates are examined in the presence of three different sorbents, a crushed natural silica, an organic-coated crushed natural silica, and a river sediment. Similar sorption behavior is observed for all surfactants on all three sorbents, although the magnitudes of sorption trends vary with sorbent and surfactant properties. In general, sorbed surfactant is enriched in high-EO surfactant components at low concentrations, and is enriched in low-EO surfactant components at intermediate concentrations. At high concentrations, sorbed and solution surfactant compositions approach the initial surfactant composition. This behavior is attributed to mixed aggregate formation on the solid surface and in solution. The varying magnitudes of observed behavior are attributed to differences in surface site energies and to surface site heterogeneity. Column transport data are presented for a nonionic surfactant mixture, and the results are discussed in terms of mixed sorption behavior. Implications of transport results for the fate and transport of surfactants in the environment are also discussed.

A UV-transparent passive concentrator/spectrum deconvolution method for simultaneous detection of endocrine disrupting chemicals (EDCs) and related contaminants in natural waters.

Suspected endocrine disrupting chemicals (EDCs) have been widely detected in the environment, and are a source of increasing concern. One of the major challenges in assessing the risk associated with EDCs in the environment is that their environmental concentrations are typically extremely low - on the order of ngL(-1) to microgL(-1) - making them difficult to quantify without extensive pre-concentration procedures. Further complicating their detection is the fact that they are present in mixtures, sometimes with tens to hundreds of other compounds (pharmaceuticals, personal care products, detergents, natural organic matter). The objective of the work described here was to develop a method for rapid monitoring and detection of EDCs at trace concentrations in natural waters. The method makes use of a UV-transparent polymer-based concentrator to be used as a passive sampling device. The UV-transparent polymer-based concentrator serves both as a solid phase extraction medium to concentrate EDCs for analysis and exclude many compounds likely to interfere with detection (fines, macromolecules such as organic matter, ionic surfactants), and as an analytical optical cell, allowing rapid EDC quantification without labor-intensive pre-concentration procedures. A full-spectrum deconvolution technique is used to determine EDC concentrations from measured UV absorbance spectra in the polymer. Experiments were conducted to measure partitioning rate behavior and partition coefficients between the selected polymer (a functional polydimethylsiloxane) and water for seven compounds known or suspected of being endocrine disruptors: estrone, progesterone, estradiol, 2,6-di-tert-butyl-1,4-benzoquinone, phenanthrene, triclosan, and 4-nonylphenol. The method was tested for its ability to detect and quantify individual compounds in mixtures containing up to six components. Results show the method to have selectivity suitable for rapid screening applications at many sites where multiple compounds are present.

Surfactant Effects on Residual Water and Oil Saturations in Porous Media

A series of soil column tests was performed to determine surfactant effects on residual water and oil saturations in porous media. In particular, these tests focused on the impact of submicellar surfactant solutions and the potential application of these low concentration systems to light nonaqueous phase liquid (LNAPL) contamination in the vadose zone. One set of tests involved surfactant flushing in soil-filled columns followed by drainage to residual water saturation and LNAPL injection to determine the subsequent residual LNAPL saturation. Another set of tests involved surfactant application to a soil-filled column already holding residual LNAPL saturation to promote the release of the previously trapped LNAPL. Test results showed surfactant systems could reduce both residual water and oil saturations by up to 50%. In addition, submicellar surfactant systems were equally effective as supramicellar solutions in reducing residual water saturations and potentially more effective at reducing residual oil saturations. Submicellar surfactant applications to a medium-grained (0.85–0.425 mm) soil containing residual LNAPL saturations were effective at releasing up to 50% of the previously trapped residual LNAPL. These applications were less successful in a fine-grained soil as full drainage of water and LNAPL was unachievable due to high capillary pressures. Overall, observations suggest low concentration surfactant solutions may have the ability to release significant amounts of previously trapped LNAPL in the vadose zone, potentially increasing free-product recovery rates and lowering LNAPL saturations to levels more favorable for biodegradation. The decrease in overall saturations (both water and oil) in a contaminated vadose zone could also present an increase in air permeability, thus enhancing other vadose zone treatment technologies such as bioventing or soil vapor extraction.

Transport and retention of fullerene (nC60) nanoparticles in unsaturated porous media: Effects of solution chemistry and solid phase coating

The retention and release of aqueous aggregates of fullerene nanoparticles (nC(60)) were studied under dynamic unsaturated conditions. Porous media containing nC(60) were taken through multiple drainage/imbibition (drying/wetting) cycles to explore the effects of solution conditions and solid surface modification on transport and ultimate fate in unsaturated porous media. In experiments conducted with NaCl as the background electrolyte, the retention of nC(60) during drainage was found to be negligibly small over a wide range of ionic strengths (I=0.2 to I=6 mM), significantly lower than the retention of titanium dioxide nanoparticles studied previously under similar conditions. In contrast, experiments conducted with CaCl(2) as the background electrolyte found that retention of nC(60) during drainage was significant at higher ionic strengths, particularly at the highest ionic strength studied (I=6 mM). Experiments examining the influence of dissolved natural organic matter on nC(60) retention in unsaturated media found no measurable impact on the transport. The effects of solid surface modification were examined by creating coatings that modified surface hydrophobicity and charge. Experiments found that a hydrophobic coating had no measurable impact on nC(60) retention, when compared with retention by unmodified media. In contrast, a porous medium with surfaces that were both hydrophobic and positively-charged retained 5-10 times more nC(60) during drainage than an unmodified porous medium. This result suggests that electrostatic interactions play a more important role than hydrophobic interactions in the transport and fate of nC(60) in the unsaturated zone. For all conditions where retention was observed, experiments found very little release or retained nC(60) after subsequent flushing with water, suggesting that once retained, the environmental mobility of nC(60) may be extremely limited.

An Experimental Study of the Factors Influencing Apparent Wetting Phase Residual Saturation in Dynamically Drained Porous Media

When a porous medium drains, the wetting phase saturation in the medium [the fractional volume of wetting phase (often water) in the pores] is typically observed to approach a minimum value, referred to as the wetting phase residual saturation (