Marine oil spills arise from incidents that cannot be anticipated in time and space, and bring huge disaster to environment. One typical example is the catastrophic explosion and spill that occurred on the Deepwater Horizon drilling platform in the Gulf of Mexico, on April 20, 2010. This devastating incident brought about 1700 kilometers of coastline contaminated. According to a panel of scientist’s commission, an estimated 4,900,000 barrels of oil were spilled. However, the distressing reality is that only about 16% were captured or managed which is also a common level in most oil spill incidents. However, the real disaster to marine animals continued for the following decade, where massive dead animals were floating on the sea or densely packed everywhere on the beach. In those times, the daily routine for coastal residents involved salvaging oil-covered sea turtles stranded on the shore. Even years later, the haunting consequences prevailed, as dolphins continued to get stranded in the polluted areas. These poignant scenes deeply impacted us and served as a catalyst for developing transformative ideas to bring about changes. People were encouraged to find more efficient and sustainable methods for oil spill recovery.
Viscous crude oil accounts for 70% of the world's fossil fuel reserves, and its recovery process can be exceptionally challenging due to the high viscosity. Conventional time-sensitive techniques, including oil absorbents, mechanical skimmers, vacuum suction, and manual removal, encountered difficulties in effectively handling viscous oil due to its low flowability. For example, the oil skimmers with the fixed floating pad may be trapped in the viscous oil and their suction nozzles are vulnerable to being blocked. In the past, the prevailing approach for managing viscous spilled oil was to burn it with the assistance of floating booms, rather than recycling it in a sustainable manner.
Induction heating technique was explored for the first time to resolve the challenge of highly viscous oil. Owing to the rheological behavior, the viscosity of highly viscous oil can be reduced by three orders of magnitude when the temperature was raised from RT to 90°C. Induction heating technique was widely utilized in industrial melting, annealing, welding, and other domestic uses. It plays an essential role as the ultrafast, non-contact, and controllable heating and is feasible in various environments. For example, the induction heating can keep the feed rod freely suspended with no direct physical contact with the surroundings for the floating melt-solid crystallization interface. This inspired us to integrate this technique on the superwetting surfaces to promote the oil-water separation for viscous oil recovery in oil spill accidents.
A holistic design of materials and strategy was developed for the recovery of viscous crude oils based on gel-coated mesh with the reversibly interfacial process. The superhydrophobic and oleophilic filter was made by a gel-coated mesh and then rolled to a closed drum, named gel-coated stainless-steel mesh membrane (GSSM) roller. We employed non-contact induction heating to aid the roller in achieving separation of heating/cooling interfaces, creating a heat gradient while avoiding thermal dissipation. The gel-coated mesh roller on the seawater selectively adhered spilled viscous oil at the interface of cold seawater (on the bottom side of the roller), while effectively separating viscous oil/water mixtures in the heating area (on the top side of the roller). In this heating area, the viscosity of the oil is sufficiently reduced, allowing for oil penetration and recovery. The ultrathin gel-coated mesh filter surpasses absorbent materials in terms of oil recovery throughput. This advantage stems from the system's ability to achieve micron-scale penetration at the interface, whereas other absorption materials rely on a convoluted pathway and bulk penetration length for the oil permeation.
On an actual boat, we constructed an enlarged meter-size oil-collecting device that performed exceptionally well on a wide expanse of water contaminated by viscous motor oil resulting from an accident. In practice, the oil thickness varied in different areas of the water while the device on a boat can efficiently clean up a viscous oil area of over 20 square meters in 1 minute regardless of the environmental disturbances or the oil thickness. The demonstration showcased a successful integration of meticulously designed gel-based coatings, and ultrafast induction heating, to enable a reversibly interfacial process for the practical treatment of viscous oil spills.
The immediate environmental effects of oil spills have been readily identified, however, assessing their long-term impact on the ecological system of an affected area is more challenging. We hope this new high-throughput viscous oil recovery strategy can motivate the applications for a more rapid and time-efficient cleanup of oil spills.