Emulsion based recovery of multicomponent hydrocarbons using nonionic surfactants.
Remediation of source zones containing non-aqueous phase liquids (NAPL) often involves
aggressive mass removal to reduce mass discharge and create favorable conditions for
follow-on treatments. One option for aggressive mass removal is the use of surfactants.
Surfactants can aid subsurface remediation through three primary mechanisms -
solubilization, mobilization or emulsification.... read moreWhile surfactant selection and flow
field design can promote one mechanism over the others, the three are rarely mutually
exclusive. Solubilization-based approaches rely on increases in apparent solubility of
the contaminant in the surfactant solution due to partitioning of the organic
contaminant into the hydrophobic interiors of surfactant self-assemblies (e.g. micellar
solubilization). Mobilization-based approaches draw on the use of surfactants that
greatly reduce the interfacial tension at the NAPL-water interface, thereby reducing the
capillary forces and freeing entrapped NAPL. Emulsion-based approaches rely on the
mechanical energy associated with the flow-field in combination with more
limited-reductions in interfacial tension to create and stabilize NAPL droplets in
macroemulsions (i.e., oil-in-water emulsions having average droplet diameters in the
range of 1-10 µm). Among these mechanisms, emulsification has been studied far
less, perhaps due to concerns about the mobility of emulsions in porous media. Studies
examining surfactant-based recovery processes largely focus on pure-component NAPLs.
Multicomponent NAPLs, however, increase the complexity of remediation, especially when
treatment technologies preferentially recover certain contaminants from the NAPL. This
sort of preferentially removal, or fractionation of the NAPL, can increase the
recalcitrance of the remaining NAPL. Here emulsification is examined within the context
of LNAPL recovery, specifically a five-component synthetic gasoline. The objective of
this research is to elucidate the physical and chemical nature of the emulsification
process when applied to a multicomponent NAPL. Batch and column experiments were used to
examine emulsification of the synthetic gasoline mixture containing approximately 50% 2,
2, 4-trimethylpentane, 30% 1, 2, 4-trimethylbenzene, 12% m-xylene, 6% toluene and 2%
benzene. The surfactants used to promote emulsification fall within two classes of
non-ionic surfactants currently used in remediation (nonylphenol ethoxylates and alcohol
ethoxylates). The alcohol ethoxylate formulation was designed by the manufacture as a
more environmentally-friendly version of the nonylphenol ethoxylate formulation. The
surfactant formulations have similar hydrophile-lipophile balances and are therefore
anticipated to have similar emulsification behavior with petroleum hydrocarbons. Results
from the batch experiments were used to quantify the potential for preferential
dissolution and/or solubilization of the synthetic gasoline components, as well as
mobilization of the synthetic gasoline mixture -NAPL for each of the surfactant
solutions. Batch experiments also provided important data related to the density and
viscosity of the emulsions formed when the solutions are contacted with synthetic
gasoline mixture. This batch-derived information was then used to interpret the recovery
of the synthetic gasoline mixture from column experiments containing approximately 15%
NAPL saturation entrapped within a medium-to-fine grain Ottawa sand. Results from
experiments conducted with the nonylphenol ethoxylate formulation suggest that
emulsification was responsible for recovery of the synthetic gasoline mixture. In
contrast, results from the experiments conducted with the alcohol ethoxylate suggest
this recovery occurs by both emulsification and mobilization. Mobilization observed with
the alcohol ethoxylate formulation enhanced recovery, suggesting the combination of
mobilization and emulsification could be beneficial when treating multicomponent LNAPLs.
For both formulations, results suggest that emulsion-based recovery of the
multicomponent NAPL used herein was a physical process that limits fractionation of the
synthetic gasoline NAPL. Results also imply that the alcohol ethoxylate formulation is
an effective, more environmentally conscious replacement for the nonylphenol ethoxylate
Thesis (M.S.)--Tufts University, 2015.
Submitted to the Dept. of Civil Engineering.
Advisor: Andrew Ramsburg.
Committee: John Durant, Paul Dombrowski, and Patrick Haskell.
Keyword: Environmental engineering.read less