Grantee Research Project Results
Final Report: Hydrodynamic Mixing Effects on Macro- and Micro-Emulsification of Nonaqueous Phase Liquids into Water
EPA Grant Number: R826158Title: Hydrodynamic Mixing Effects on Macro- and Micro-Emulsification of Nonaqueous Phase Liquids into Water
Investigators: Jafvert, Chad T. , Hondzo, Midhat , Lyn, Dennis A.
Institution: Purdue University
EPA Project Officer: Aja, Hayley
Project Period: January 16, 1998 through January 15, 2000
Project Amount: $206,335
RFA: Exploratory Research - Physics (1997) RFA Text | Recipients Lists
Research Category: Water , Air , Safer Chemicals , Land and Waste Management
Objective:
The formation of microemulsions and micelles are of importance in many practical environmental engineering applications, yet have received relatively little systematic study. The primary objective of this study was to investigate the dynamics of nonaqueous phase liquid (NAPL) emulsification in well-defined systems, primarily under conditions where micro-emulsification of oil-in-water occurs, and to investigate interfacial properties that lead to formation of emulsification. Of particular interest was the prediction in the interfacial tension decrease at the NAPL-water interface as a function of surfactant dose and ionic strength. In these investigations, the following specific experimental and theoretical examinations were conducted: (1) experimental and theoretical characterization of the interfacial tension as a function of fluid properties, and (2) experimental determination of the rates of emulsification as a function of fluid properties.
Figure 1.
Interfacial Tension Predictive Algorithms. To evaluate these and other data, models describing the change in the interfacial tension (IFT) with variation in the surfactant and electrolyte concentrations were developed. The model constructs fall under the generic classifications of a ?double layer' and a ?triple layer' model. These models were developed for the surfactant concentration range less than cmc to avoid interference by completing mechanisms during model evaluation. In our approach three general mass action processes are considered. These processes are: (1) adsorption of surfactant at the interface, accounted for by the Boltzmann equation, (2) accumulation of counter-ions within a diffuse double layer within the aqueous phase next to the interface, accounted for by Gouy-Chapman theory, and (3) the effect of surface excess (surfactant at the interface) on the interfacial tension, accounted for with Gibb's adsorption equation. A paper describing these models is in preparation. Initial model results are promising, indicating that changes in surfactant dose and ionic composition predictably affect oil-water interfacial tension.
Microemulsion Design. Investigations on microemulsion formation in the toluene-water-NaDS system were conducted in a series of test tube experiments and in an annular reactor. The critical behavior of the system has been studied extensively by Cazabat et al. (1982) in test tube experiments. The interfacial tensions between the different phases and compositions are well characterized, although no one has previously reported the importance of mixing conditions on microemulsion formation. Mixtures are should in Figure 2 that each contain by weight: 47.25 percent toluene, 1.99 percent SDS, 3.96 percent butanol, and 46.8 percent of one of several NaCl brine solutions (S = 3, 4, 4.5, 5, 6, 6,5 g NaCl/l00 g water) after 2 weeks of equilibration. At equilibrium, tubes at S # 5 are single-phase microemulsions (two phases) despite the fact that the three layers observed in the tubes are stable for several months. Similarly, At equilibrium, tubes at S = 6 and 6.5 are middle phase microemulsions (three phases) despite the fact that four layers are observed in these tubes for months.
| Figure 2. Single phase microemulsions at salinities (3, 4, 4.5, 5, 6, and 6.5 g / 100 g) and component weights reported in the text. Below S = 5%, three, rather than two phases exist for extended periods of time (weeks). |
These results show that formation of single-phase microemulsions in quiescent reactors, under surfactant and salinity compositions likely to be employed in the field, occurs through the development of a transient aqueous ?middle phase', whose formation likely occurs due to buoyancy forces. This work indicates that while spontaneous emulsification occurs, the dynamics of this process are highly dependent on the amount of mixing energy applied to any system. Further, we show that the difference between the densities of the oil and water phases also affect the formation and mixing of emulsion droplets.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
| Other project views: | All 2 publications | 1 publications in selected types | All 1 journal articles |
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Lin CC, Jafvert CT. A triple layer, planar coordinate model for describing counterion association to micelles. Langmuir 2000;16(6):2450-2456. |
R826158 (Final) |
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Supplemental Keywords:
interfacial tension, tensiometer, toluene, TCE, dodecylsulfate., Scientific Discipline, Water, Toxics, HAPS, Environmental Chemistry, Engineering, Chemistry, & Physics, Physics, Environmental Engineering, chemical transport modeling, contaminant transport, environmental monitoring, microemulsion kinetics, Trichloroethylene, chemical composition, chemical detection techniques, hydrodynamic stability theory, environmental contaminants, fate and transport, fluid properties, interfacial phenomena, solvents, NAPLs, chemical kineticsProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.