Bor-Jier Shiau

Surfactant selection for enhancing ex situ soil washing

Ex situ soil washing is commonly used for treating contaminated soils by separating the most contaminated fraction of the soil for disposal. Surfactant-enhanced soil washing is being considered with increasing frequency to actually achieve soil-contaminant separation. In this research eight anionic and nonionic surfactants were evaluated for the enhanced soil washing of three different soils contaminated with petroleum hydrocarbons. Enhanced soil washing occurred at surfactant concentrations below and above the CMC indicating the occurrence of both soil rollup and solubilization mechanisms. In certain cases the lower CMC of nonionic surfactants made them attractive candidates while in other cases the lower sorption and higher solubilization potential of select anionic surfactants made them the preferred choice. Surfactant-induced foaming and turbidity are operating considerations that can also impact surfactant selection. When selecting a surfactant for a given soil-contaminants system we thus recommend evaluating both anionic and nonionic surfactants at concentrations below and above their CMC, and we suggest that the methodology we describe in this paper is a good approach for making the final surfactant selection.

Properties of food grade (edible) surfactants affecting subsurface remediation of chlorinated solvents.

In this research, several food grade (edible) surfactants are systematically evaluated for various loss mechanisms : precipitation, adsorption, and coacervation (for nonionic surfactants). Cloud points for the polyethoxylate sorbitan (T-MAZ) surfactants are much higher than aquifer temperatures, and the effects on surfactant losses should be minimum. Precipitation boundaries of bis(2-ethylhexyl) sodium sulfosuccinate (AOT) and sodium mono- and dimethylnaphthalene sulfonate (SMDNS) were established. Existing precipitation models successfully predicted precipitation boundaries for SMDNS but showed minor deviations for AOT results. AOT was more susceptible to precipitation than the cosurfactant evaluated, SMDNS. Nonionic polyethoxylate (POE = 20) sorbitan monostearate (T-MAZ-60) and POE(80) sorbitan monolaurate (T-MAZ-28) formed liquid crystal phases at high surfactant concentrations (>0.5 wt %) while POE(20) sorbitan monolaurate (T-MAZ-20) and POE(20) sorbitan monooleate (T-MAZ-80) remained in aqueous solution at concentrations up to 5 wt %. T-MAZ-60 and T-MAZ-28 also showed a continuous increase of adsorption at high surfactant concentrations (likely due to liquid crystal formation). Other surfactants showed Langmuirian-shaped isotherms at high concentration, while the cosurfactant SMDNS experienced negligible adsorption. On a mass basis, the maximum adsorption (q max in μmol/g) was higher for T-MAZ surfactants than for alkylphenol ethoxylates, AOT, and disulfonated surfactants.

Surfactant enhanced remediation of subsurface chromium contamination

Abstract The objective of this research was identification of optimal surfactant systems for remediating chromate-contaminated subsurface environments. Batch and column studies were conducted utilizing chromium contaminated soil obtained from the U.S. Coast Guard Support Center, Elizabeth City, N.C. Results of the batch studies demonstrated that surfactants, when used alone, were able to enhance the extraction of chromate 2.0–2.5 times greater than water. When a complexing agent, diphenyl carbazide, was solubilized by aqueous micelles the system was able to enhance the chromate elution by 9.3 to 12.0 times greater than water (or 3.7–5.7 times greater than surfactant without the complexing agent). Column studies showed that when surfactants are used along with the complexing agent, 213% of Cr(VI) can be removed relative to D.I. water in less than 20 pore volumes, whereas D.I. water took 35 pore volumes to reach the baseline removal. The economics of surfactant enhanced subsurface remediation will be affected by surfactant losses (e.g. precipitation and sorption); batch and column studies were conducted to evaluate the losses of surfactants due to such phenomena. Results of these laboratory studies demonstrated that the surfactant system containing Dowfax 8390 and diphenyl carbazide was most effective in remediation of the chromium contaminated soil.

Formulating Microemulsion Systems for a Weathered Jet Fuel Waste Using Surfactant/Cosurfactant Mixtures

This paper identifies surfactant systems capable of forming middle phase microemulsions with a weathered jet fuel at Hill AFB, Utah. A series of batch studies was conducted to characterize the hydrophobicity of this light nonaqueous phase liquid (LNAPL) and to evaluate microemulsion systems for this LNAPL. The contaminant was found to be more hydrophobic than ordinary jet fuel, thus requiring cosurfactant and electrolyte addition to formulate middle phase microemulsions. Successful salinity (NaCl) and hardness (CaCl2) scans were conducted with one anionic surfactant, Aerosol OT (AOT), and three different cosurfactant systems—one alcohol (isobutanol), one hydrotrope (sodium mono- and dimethyl naphthalene sulfonate or SMDNS), and two nonionic surfactants [POE[20] sorbitan monostearate or T-MAZ 60 and POE[20] sorbitan monooleate or T-MAZ 80]. Of the five systems which successfully microemulsified the LNAPL (versus 10 others evaluated), one was selected for implementation in a subsequent field demonstration.

Characterization of Crude Oil Equivalent Alkane Carbon Number (EACN) for Surfactant Flooding Design

Equivalent alkane carbon number (EACN) of crude oil reflects the hydrophobicity of the crude oils, thus it would be helpful to estimate the EACN of crude oil before fine tuning the surfactant selection for enhanced oil recovery field application. In this study, we used the titration methodology to quantify the EACN values for several crude oil samples retrieved from the targeted mature oil fields. The results showed that the method of using extended surfactant was simpler but reliable to determine the EACN of crude oils. The resulting EACN for these crude oils was found to be in the range of 6.0–11.3. GRAPHICAL ABSTRACT

Surfactant-Enhanced NAPL Remediation: From the Laboratory to the Field

Pump-and-treat remediation has routinely been prescribed for subsurface nonaqueous phase liquid (NAPL) contamination. However, pump-and-treat systems have proven incapable of remediating contaminated aquifers in a timely and economical manner. Cost overruns of 80% and cleanup times as much as three time longer than original estimates are typically reported (Olsen and Kavanaugh 1993). Several factors have been identified that contribute to the inefficiency of pump-and-treat remediation, including: (1) diffusion limitations for contaminants from low conductivity zones to high conductivity zones; (2) hydrodynamic isolation, such as dead end zones; (3) rate-limited desorption of contaminants from solid surfaces; and (4) liquid-liquid dissolution of residual NAPLs (Bouwer et al. 1988; Keely 1989; Mackay and Cherry 1989; Haley et al. 1991; Schmelling et al. 1992; NRC 1994). When residual NAPL is present, subsurface contamination can be categorized into three zones: the source/residual zone, the concentrated plume (center of mass of the groundwater plume), and the dilute groundwater plume. Innovative technologies are necessary for residual phase materials as pump-and-treat alone will be extremely inefficient in this zone.

Performance and chemical stability of a new class of ethoxylated sulfate surfactants in a subsurface remediation application

Abstract The suitability of a surfactant for use in subsurface remediation depends on performance, toxicity and biodegradability. In order to increase the performance of a series of edible, polyethoxylated sorbitol esters, one or two sulfate groups were added to the hydrophilic poly(ethylene oxide) moieties. The solubilization and salt tolerance of these surfactants were good, but they readily formed a mesophase when contacted with a common soil at a high concentration. Crystals, which have the same Maltese-cross patterns as liquid crystals, are also present when the mesophase forms. CMC of these surfactants are reported as well as soil adsorption and chlorinated organic solute solubilization data. These surfactants were found to undergo degradation at moderate temperatures; a proposed mechanism for the breakdown and data on the rate of degradation are presented.

Enhancing foam stability in porous media by applying nanoparticles

ABSTRACT Several new foaming agent formulations (surfactants and polymers) in the presence of multi-walled carbon nanotube (MWCNT) were developed in 3% salinity (NaCl, 2.4 wt%, CaCl2, 0.6 wt%). The dispersion stability of the MWCNT and the viscosity of the solutions were examined as a prerequisite for reservoir applications. Foam was generated in situ and one-dimensional flow-through tests were performed by co-injecting air and foaming solution either in the presence of MWCNT or at particle-free condition. The pressure drop (Δp) across the sand-pack and the nanoparticles breakthrough were closely monitored. The fluid injection rate, gas fraction, and the effect of MWCNT on foams in porous media were investigated. Our results reveal that foams stabilized by the selected nanoparticles are capable of generating stronger foams leading to higher apparent Δp. The Δp profile varies with gas fraction, which largely affects the foam texture and quality. Also, the viscosity of foaming agent solutions influences Δp values. Adding MWCNT to the foaming agent solutions appears beneficial to the flooding as surfactants adsorption onto nanoparticle surfaces, which facilitates surfactants partitioning to the G/L interface. Addition of nanoparticles in the developed foam formulations leads to the formation of high-quality stronger foams in porous media, which could potentially improve the sweep efficiency and increase the oil recovery. GRAPHICAL ABSTRACT