The research involves a team that will test the efficacy of natural and model surfactants in conditions similar to Deepwater Horizon spill sites. Two types of surfactant systems are investigated: synthetic polymeric surfactants (where chemical functionality and architecture can be precisely controlled) and natural polymeric surfactants. The natural surfactants yield important cues for designing non-toxic dispersants. The research team plans to compare the surfactants' effectiveness to currently used dispersants at the 2010 Deepwater Horizon spill site in the Gulf of Mexico.
Intellectual Merit:
The goal of this RAPID proposal is to advance knowledge between surfactant design and dispersion efficacy in the open sea. Currently, the relationship between the design of dispersants and effectiveness in oil spills is not well understood. Two major outcomes of this research are new in situ experimental methods to study dispersion efficiency under flow as well as a set of design rules for the next generation of non-toxic dispersants that can function over a broad range of oil viscosities.
This work is instrumental in advancing surfactant technology and represents a first step in understanding the design parameters and system variables with respect to dispersion efficiency at the recent Deepwater Horizon Oil Spill in the Gulf of Mexico. Two specific aims of the proposed project are: 1) evaluation of naturally occurring surfactants and understanding their mechanism of action to remediate crude oil in sea water, and 2) the synthesis of polymer surfactants with biologically inspired motifs that can function as dispersants for Deepwater Horizon spill sites.
Broader Impacts:
This research will improve the understanding and effective use of novel, non-toxic dispersants and its intrinsic character to modify interfacial processes in complex water systems. Natural surfactants yield important cues for designing non-toxic dispersants. The important technological applications of such dispersants include their utilization in the remediation of crude oil from salt water. This research also has a strong environmental and societal impact, with its focus on developing non-toxic solutions for oil spill dispersion. This project also provides training to graduate students in the area of self-assembly at interfaces, a far-reaching phenomenon with implications in several important industries, from coatings to healthcare to environmental remediation. This project exposes students to ideas related to environmental impact, sustainability, and green technologies. It is expected that green technologies will grow significantly over the next one to two decades.
The scope: The role of dispersants in emergency situations such as an oil spill is critical. Oil spills can cause significant damage to marine and local beach environments. Dispersants are able to remove oil from surface of the ocean by causing the formation of droplets that can be taken into the bulk water column and degraded efficiently by oil-eating microorganisms. The need for using dispersants with the minimum adverse impact to aquatic life is important for a successful oil-clean-up operation. Intellectual Merit: Our research project involved investigating the use of natural surfactants for forming oil/water dispersions, and to test their efficacy in conditions similar to those undertaken at the 2010 Deepwater Horizon oil spill site in the Gulf of Mexico. We found that extracts from the common cactus plant have the capability of breaking oil films and form stable oil/water (o/w) dispersions, so that the natural process of oil degradation can be efficiently assisted (Figure 1). Three extracts of the Opuntia ficus-indica mucilage (i.e., nopal or prickle pear cactus) were tested as a function of extract concentration, temperature, salt water concentration and at different stirring velocities. We refer as cactus mucilage to the gooey part of the plant. Results: Water solutions of three extracts of cactus mucilage including a Gelling Extract (GE) and Non-Gelling Extract (NE), and combined (Gelling and Non-Gelling Extract) were prepared with concentrations ranging between 1 and 0.006 weight per volume percentage (w/v %). These solutions were then mixed at different velocities into 30:70 % o/w dispersions. We use a light mineral oil to mimic the effect of crude oil. We then measured surface active properties such as surface tension (?), area per molecule, and critical micellar concentration (cmc) as a function of cactus concentration using physicochemical models derived using thermodynamic concepts. The droplet size and droplet size distributions of the dispersions prepared were measured using spectroscopic tools. We found that decreasing the cactus mucilage resulted in increasing droplet size. That is, droplet sizes using minimal concentrations of natural dispersants (0.006 w/v %) produced droplets in the range of 4.5 microns (Figure 1). Smaller concentrations of natural dispersants will have a significant less impact in the environment. When these natural dispersants were tested in salted water, the droplet size decreased slightly. However, the greatest advantage was observed in the stability of the dispersion. Higher stabilities were observed due to the presence of salt in the oil/water dispersion. That said, increasing the salt concentration tends to speed up the dispersant adsorption, which is a phenomenon associated with reducing the interfacial tension; and therefore, preventing droplet breakage. On the other hand, when the effect of flow rate (by inducing different stirring velocities) was tested, we observed that droplet sizes decreased almost linearly as stirring velocities increased. Broader impact: Working with natural dispersants is an advantage over surfactants that are a combination of synthetic chemical products. The concentration of mucilage needed to produce a stable dispersion is significantly less than commercially available dispersants. The solvent for this dispersant is water, which has minimal impact in marine environments. In terms of education, this project supported the creating of a new class involving sustainability with an engineering approach. Students in the class learned how to construct life assessment inventories and assessments. Students also educated to integrate concepts related to materials properties and synthesis, design parameters, zero-waste processes, and sustainability principles. Conclusion: Analysis of the particle size and stability of the dispersion were determined for situations where the oil mimicking the crude oil characteristics and utilizing water salinity and fluid flow as variables of study. We found that cactus mucilage over-performed commercially available dispersants published previous parameters in terms of droplet size, dispersion stability, and flow rates. Undergraduate and graduate students were supported under this award. Two female students working in projects related to this award graduated with their Master’s and Ph.D. degrees. This work resulted in two publications, and three more manuscripts are being prepared for publication. The PIs and students presented 9 oral and poster presentations locally, nationally, and internationally.
