Project Overview

Summary:

In January 2016, Dr. Srinivasa Raghavan at the University of Maryland was awarded an RFP-V grant of $1,369144 to lead the GoMRI project entitled, “Molecular Engineering of Food-Grade Dispersants as Highly Efficient and Safe Materials for the Treatment of Oil Spills” consisted of approximately 13 research team members (including students).

The team behind the current proposal has recently developed a dispersant using commercially available food-grade surfactants and has shown that it is efficient at emulsifying and dispersing crude oil into sea water. Initial work was funded by GoMRI via the Consortium for the Molecular Engineering of Dispersant Systems (C-MEDS), which was headed by a member of the current team, viz. John (Tulane). The current proposal seeks to build on this initial discovery. The goal is to engineer a new class of dispersants that combine environmental safety and high efficiency. By avoiding the synthetic components in current dispersants that are of questionable toxicity, and replacing them with food-grade components, new dispersants will be created that are nontoxic and safe for use in aquatic environments. At the same time, through an improved understanding of the fundamentals of dispersion, high dispersion efficiencies will be achieved that are comparable or higher than with current dispersants i.e., the Corexits.

This proposal is entirely focused on GoMRI Theme 4 (Technology developments for improved response, mitigation, detection, characterization, and remediation associated with oil spills and gas releases.) The use of food-grade dispersants will enable a safer and more environment-friendly approach to the mitigation of crude oil spills, which will help avert issues of public concern regarding dispersant toxicity. Molecular-level insights into dispersant action via innovative experiments will reveal ways to enhance the efficiency of dispersion and also allow for dispersants to be optimized for a variety of complex conditions (such as dispersion of highly viscous or weathered oils).

The project will involve the following five approaches: (1) Optimizing Food-Grade Surfactant Mixtures; (2) Optimizing Solvents and the Overall Dispersant; (3) Optimize Dispersants for Different Conditions (Oil, Water, Temperature); (4) Pilot-Scale Testing; and (5) Biodegradation and Toxicity Testing. In Approach 1, mixtures of food-grade surfactants, specifically mixtures of soy lecithin with nonionic surfactants from the Tween family, will be studied. To guide these studies, the oil/water interfacial tension will be monitored in the presence of these mixtures since it has been shown to correlate with dispersant effectiveness. In Approach 2, the focus will be on the solvent(s) used to solubilize the surfactants, which have been found to significantly impact the dispersion efficiency. An underlying theme here will be to contrast the mechanism for dispersion with that for emulsification. The PIs hypothesize that efficient dispersion is connected to the micellar nanostructure present in the dispersant and in dispersant/oil mixtures. This hypothesis will be critically evaluated via structural characterization at the nanoscale. If proven correct, it could indicate how dispersants could function even with limited extents of shear (i.e., minimal wave action on the open seas). In Approach 3, the insights from (1) and (2) will be applied to guide dispersant design for more difficult cases, such as the dispersion of highly viscous oils, dispersion into fresh or brackish water, and dispersion under cold temperatures.

The concept of food-grade dispersants is one of the truly promising ideas to come out of the work done under C-MEDS. This project seeks to translate the inherent idea into a practical and viable technology. Towards this end, pilot-scale testing of optimized food-grade dispersants (Approach 4) will be conducted using the indoor wave tanks at S. L. Ross Environmental Research. In addition, initial tests on bacterial biodegradation in the presence of food-grade dispersants will be studied (Approach 5). The toxicity of these dispersants to aquatic species will also be studied using commercial assays, and further aspects concerning toxicity and biological effects will be investigated together with collaborators. The team's research efforts will also support outreach and education efforts, particularly in Southeastern Louisiana, as well as to develop web content for GoMRI use.

Research Highlights

As of December 31, 2019, this project’s research resulted in 5 peer-reviewed publications, 17 scientific presentations, and  5 datasets being submitted to the GoMRI Information and Data Cooperative (GRIIDC), which are/will be made available to the public. The project also engaged 2 Masters and 7 PhD level students over its award period.

Significant outcomes of this project’s research are highlighted below. All pertain to Theme 4.  

1.   Efficient Dispersion of Crude-Oil by a Food-Grade Dispersant Demonstrated Using Both Lab-Scale and Large-Scale Tests:

Through careful laboratory studies, the team was able to molecularly engineer each component of their food-grade dispersant for optimal efficiency. The optimal system consisted of the phospholipid lecithin (L), the surfactant Tween80 (T), and a solvent such as octanol or undecanol. Each component in the above mixture is food-grade and biocompatible. The optimal composition of the dispersant was a mixture of L/T at a 60/40 (w/w) ratio, with the total L+T content being 60 to 70 wt% (the remaining 30 to 40% being the solvent). A dispersant of this composition was found to be highly efficient at dispersing crude oil (O) into seawater (W) in lab-scale tests.

In addition, the team also conducted tests on dispersing crude oil in a large tank using their food-grade dispersant. Members of the team made a trip to Ottawa, Canada and conducted the tests at the facilities of a company called S. L. Ross, which has extensive experience with such large-scale tests. The tank was filled with seawater, and a given type and amount of crude oil was placed on the water surface. The dispersant was then added to the oil slick. Next, wave action was simulated within the tank using a proprietary setup; the waves periodically perturbed the oil-covered water for a period of 30 min. Following this period, the fraction of oil that was dispersed into the water column was determined. The above tests were done both with the team’s food-grade dispersant as well as the synthetic dispersant (Corexit) that is the current industry-standard. The efficiency of dispersing crude oil with the food-grade dispersant was found to be comparable to that observed with Corexit. Thus, overall, the results confirmed that the food-grade dispersant was highly effective at dispersing crude oil in a situation that mimicked real-world conditions.  

2.   The Role of Solvent on the Performance of Food-Grade Dispersants:

One aspect studied in detail by Prof. Srinivasa Raghavan’s group was on understanding the role of the solvent in the dispersant. For this, a systematic study was conducted with various solvents, and in each case, the dispersant was used to disperse a model crude oil (O) into seawater (W).

A key insight from the studies was that solvents that are optimal for O/W dispersion efficiency could be identified in a systematic way. This was done using solvent properties called “Hansen Solubility Parameters” (HSPs). In the HSP scale, each solvent is associated with three parameters that characterize its chemical nature, corresponding to dispersion interactions (d_D), polar interactions (d_P) and hydrogen-bonding interactions (d_H). Ignoring dispersion interactions, an HSP plot of d_P vs. d_H could be constructed, with each solvent being a point on this plot. When L/T mixtures in these solvents were used to form O/W dispersions, the solvents corresponding to good dispersion clustered in a specific trend on the d_P vs. d_H plot. Thus, the above HSP plot allowed systematic identification of the optimal solvent for dispersion efficiency. These data are combined with additional information regarding the solvent’s flash point (i.e., its volatility) as well as its biocompatibility (lack of oral and dermal toxicity). Using the combined criteria, solvents such as octanol and undecanol were identified as the best solvents for dispersants. A paper on the above work was published in the journal Langmuir in 2019.  

3.   Studies on the Bacterial Biodegradation of Oil Dispersed by Food-Grade Dispersants:

Two members of our team, Prof. Vijay John and Prof. Geoff Bothun, have been studying systems containing an oil slick on seawater with oil-eating bacteria, such as Alcanivorax borkumensis, present in the seawater. One surprising result that has emerged from this work is that the bacteria on their own, in the presence of sufficient shear (simulated wave action), can disperse a substantial (~ 45%) portion of the oil slick into seawater without the need for any dispersant. The dispersion occurs through bacterial adsorption onto the oil droplets together with the aid of naturally secreted biosurfactants that lower the oil-water interfacial tension by a factor of two. The oil droplets thereby get covered by a bacterial biofilm, wherein the bacterial cells are interconnected by exopolymers secreted by the bacteria. Hexadecane biodegradation by the bacteria was also studied and it was found that about 90% of hexadecane was degraded in the period of 5 days. A paper describing the above results was published in the journal ACS Sustainable Chemistry and Engineering in 2019. 

  Proposal Abstract - RFP-V PI Srinivasa Raghavan