Studies Explore the Roles of Halloysite Clay Particles and Solvents in Oil Dispersion Technologies

– SEPTEMBER 1, 2020

Responders used chemical dispersants during Deepwater Horizon to break up the oil spewing from the riser pipe and the subsequent-forming oil slick into smaller droplets and enhance biodegradation processes. The unprecedented amount of chemical dispersants used in the spill response raised concerns about their potential toxic effects on the environment.

(Click to Enlarge) Tulane University’s Marzhana Omarova (seated) and Igor Mkam Tsengam (standing) along with Jibao He (seated far left, Tulane’s director of electron microcopy) use the Transmission Electron Microscope in their research investigating alternative dispersant technologies. (Photo provided by Vijay John.)

Scientists with the Gulf of Mexico Research Initiative (GoMRI) have been investigating solvent-free formulations to improve the safety and efficiency of dispersant technologies used in oil spill response. One promising area involves halloysite clay nanotubes, which are abundant, natural, and ecologically friendly submicron particles that enable the formation and stabilization of oil emulsions with energy provided by ocean turbulence. The low cost and biocompatibility of halloysite clay and its hollow nanotube structure provides a potential cargo-carrying medium for the slow release of active molecules such as surfactants.

Here are recaps of three studies that provide additional insights into the use of halloysite clay nanotubes for improved oil spill mitigation, including how it promotes oil emulsification and enhances oil biodegradation and a method that helps prevent the halloysite’s premature release of surfactants. A fourth study offers new insights about the role of solvents in oil dispersion.

Building upon earlier investigations that includes a process that increases the hydrophilic nature of halloysite clay particles, researchers demonstrate that the treated particles can emulsify a model alkane (n-Hexadecane) and Macondo oil and that they attract and stimulate the growth of the alkane-degrading bacteria Alcanivorax borkumensis. Compared to controls using pristine clay particles, the treated particles that coat oil droplets generate more stable oil-in-water emulsions and create a rougher droplet surface that is easier for bacteria to latch on to. More bacteria attach to oil droplets covered with treated particles compared to artificial surfactants, and the bacteria’s morphology changes to a more elongated shape that help stabilize the emulsions. The researchers published their findings in Colloids and Surfaces B: Biointerfaces: Bacterial proliferation on clay nanotube Pickering emulsions for oil spill bioremediation. Data are publicly available through the Gulf of Mexico Research Initiative Information and Data Cooperative (GRIIDC) at doi: 10.7266/N72B8WDN.

Researchers developed a method to systematically adjust the hydrophilic nature of halloysite particles (which are attracted to water molecules and dissolve) using polypeptoids with combined hydrophilic and lipophilic qualities. Compared to unaltered halloysite clay particles, particles functionalized with relatively high hydrophobic content contain the smallest oil droplet sizes and are more effective as emulsion stabilizers by reducing oil-water interfacial tension, enhancing the particles’ thermodynamic propensity to partition at the oil-water interface, and increasing the emulsion viscosities that inhibit oil droplet coalescence. Cell cultures reveal that functionalized halloysite clay particles are non-cytotoxic to A. borkumensis and increase the bacteria’s proliferation compared to less hydrophobic or pristine halloysite clay particles, presumably by serving as a nitrogen source. The researchers published their findings in ACS Applied Materials & Interfaces: Investigation of Amphiphilic Polypeptoid-Functionalized Halloysite Nanotubes as Emulsion Stabilizer for Oil Spill Remediation. Data are publicly available through GRIIDC at doi: 10.7266/N7125R29.

Scientists report an improvement to engineering a stimuli-responsive delivery system for surfactant-loaded halloysite nanotubes so that the surfactant release is triggered by contact with oil, preventing the water-soluble surfactant’s premature release. In an earlier study, the researchers used a two-dimensional metal phenolic network to seal surfactant-loaded halloysite nanotubes for oil spill applications, but it has a drawback that requires a pH reduction to begin the stopper breakdown just prior to delivery. In this study, they seal the surfactant (Tween 80, a component of COREXIT 9500EC) inside the nanotubes using a thin coating of high-melting-point paraffin wax, which does not dissolve until it comes in contact with the oil-water interface. The wax-coated clay nanotubes stay on the oil side of the interface as the surfactant releases. Additionally, previous research indicates that the oil-degrading bacteria A. borkumensis can efficiently degrade paraffin wax compounds. The researchers published their findings in ACS Applied Materials & Interfaces: Targeted and Stimulus-Responsive Delivery of Surfactant to the Oil–Water Interface for Applications in Oil Spill Remediation. Data are publicly available through GRIIDC at doi: 10.7266/MDV8KEG6.

Scientists re-examine the role of solvents, typically viewed as a non-active component in dispersant formulations, and systematically assess how they affect the dispersion efficiency of crude oil in formulations containing food-grade surfactants (soy lecithin and Tween 80). After testing 28 solvents, they found that the dispersion efficiency can be altered from poor to excellent simply by varying the solvent while keeping the surfactant blend the same. The most-effective solvents have a strong affinity for crude oil and limited hydrophilicity, allowing the solvent to incorporate into and remain with the oil slick rather than leaching into the water. Additionally, they found eight solvents that do not solubilize one or both of the surfactants at all. These results provide an additional factor when considering different dispersant formulations, which should include component toxicity and properties such as flash point, density, and viscosity. The researchers published their findings in Langmuir: Does the Solvent in a Dispersant Impact the Efficiency of Crude-Oil Dispersion? Data are publicly available through GRIIDC at doi: 10.7266/PTKX4HDT.

These studies demonstrate continued advancements that improve oil dispersant technologies. Building upon previous work that showed surfactant-loaded halloysite clay nanotubes are an effective alternative to traditional chemical dispersants, new investigations provide further insights into their emulsification capabilities and their ability to enhance bacterial degradation of oil. Adjusting the hydrophilic nature of halloysite clay particles further improved the stability of oil emulsions and the proliferation of oil-degrading bacteria. A simple and inexpensive method that sealed surfactant-loaded nanotubes with paraffin wax and created a stimuli-responsive surfactant delivery system also addressed the need for surfactants to be stored and transported as dry materials prior to being typically aerially sprayed during a spill response. Finally, researchers took a new approach to evaluating dispersant formulations, asking if the solvent can be an active component that affects oil dispersion. By combining the optimal solvent with food grade surfactants, they expanded the possibilities of moving toward “greener” oil dispersant formulations.

Here are related studies that examine halloysite clay and other ecofriendly options for oil spill remediation:

• Study Finds Clay Nanotubes Yield More Efficient Oil-Water Emulsions than Spherical Particles
• Study Demonstrates How Natural Clay Particles Enhance Oil Dispersion and Biodegradation
• Studies Show Carbon Black Particles as an Alternative or Supplement for Oil Dispersants
• Study Assesses a New Class of Safer, More Effective Dispersants
• Eco-Friendly Oil Herders Show Promise for Effective Marine Spill Cleanup

By Nilde Maggie Dannreuther and Stephanie Ellis. Contact maggied@ngi.msstate.edu with questions or comments.

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This research was made possible in part by grants from the Gulf of Mexico Research Initiative (GoMRI) to Tulane University for the project The Design of Synergistic Dispersant and Herding Systems using Tubular Clay Structures and Gel Phase Materials and to the University of Maryland for the project Molecular Engineering of Food-Grade Dispersants as Highly Efficient and Safe Materials for the Treatment of Oil Spills. Other support included the State of Louisiana Board of Regents, Nalco-Champion Corporation, and the National Science Foundation (1826146).

The Gulf of Mexico Research Initiative (GoMRI) is a 10-year independent research program established to study the effect, and the potential associated impact, of hydrocarbon releases on the environment and public health, as well as to develop improved spill mitigation, oil detection, characterization and remediation technologies. An independent and academic 20-member Research Board makes the funding and research direction decisions to ensure the intellectual quality, effectiveness and academic independence of the GoMRI research. All research data, findings and publications will be made publicly available. The program was established through a $500 million financial commitment from BP. For more information, visit https://gulfresearchinitiative.org/.

© Copyright 2010-2020 Gulf of Mexico Research Initiative (GoMRI) – All Rights Reserved. Redistribution is encouraged with acknowledgement to the Gulf of Mexico Research Initiative (GoMRI). Please credit images and/or videos as done in each article. Questions? Contact web-content editor Nilde “Maggie” Dannreuther, Northern Gulf Institute, Mississippi State University (maggied@ngi.msstate.edu).