Innovative sponge for offshore oil drilling wastewater cleanup

Credit Kevin Soobrian, University of Toronto

RESEARCHERS at Imperial College London, UK and the University of Toronto (UoT), Canada have developed an innovative surface engineered sponge which could enable offshore oil drilling to clean up wastewater and increase oil recovery.

Drilling and fracking for oil under the sea results in 100bn bbl/y of contaminated wastewater, due to the release of oil microdroplets into surrounding water. Current methods are ineffective for removing these droplets at the variable pH levels common in wastewater.

The sponge developed by the research team can remove 92% of oil microdroplets from wastewater within ten minutes at pH5.6, the optimal pH. Removal increases to 99% after 60 minutes.

Additionally, the researchers discovered that over a wider pH range, microdroplets were removed with 95–99% efficiency in less than 180 minutes. The researchers investigated removal under acidic, neutral, and basic conditions. Wastewater pH ranges from 4–10.

The sponge removes the microdroplets from the water by adsorbing them onto its surface. A saturated sponge contains water droplets within the free volume of its pores as well as the oil adhered to its surface. The water can be released from the pores using mechanical compression. The oil can be removed under ambient conditions by displacement using a solvent. In their study, the researchers used pentane.

Once the oil is removed, the sponge can be reused. In the study, the sponge was reused ten times without degradation in performance. For oil recovery the researchers distilled the crude oil/solvent mixture at 60°C (above the boiling point of pentane).

Pavani Cherukupally, Research Associate at Imperial’s Department of Chemical Engineering, said: “Depending on the type and its quality, we could use the recovered crude oil for various applications, such as petrochemical manufacturing, pesticide manufacturing, or heat energy generation.”

Cherukupally was the lead author of the study, and the recently-developed sponge improves on a previous prototype developed during her PhD at UoT. It was able to remove 95% of microdroplets from oil but this took three hours – too long to be useful to industry. Additionally, the optimal pH for the system was 5.6 and removal reduced significantly at the top end of the pH 4–10 scale, to around 6 or 7%, said Cherukupally.

Together with academics at Imperial and UoT, Cherukupally chemically modified the sponge to enable potential use by industry. The current prototype is a polyester polyurethane sponge, surface modified with nanocrystalline silicon particles. The surface modification improved oil droplet capture and retention.

According to Cherukupally, crude oil composition varies with geography, water chemistry, and age. To further develop the technology, the sponge needs to be tailored to address variation in the surrounding environment.

Currently, the researchers are working to improve the sponge’s material properties to enable oil recovery from marine environments and in cold weather conditions. Additionally, the researchers are looking to scale up the technology.

Cherukupally also wants the sponge to be used to treat contamination from gas, mining, and textile industries and to make it affordable for use in developing countries – primarily for removing organics, metals, and pathogens from rivers.

She said: “Currently, oily wastewater is a new economic opportunity. Due to stringent environmental standards, the demand for reclaiming billions of litres of oil-field wastewater is increasing rapidly. These effluents also contain residual oil.

“Having low-cost solutions like reusable sponges could reduce stress on water resources and improve the yield of oil extraction processes. We need the contribution of more researchers and engineers in addressing this water and environmental challenge across the world.” 

Nature Sustainability: http://doi.org/dmjg