Novel sponge tech collects oil in ultra-cold waters

RESEARCHERS in Canada and the UK have developed a coating for commercially-available sponges that can recover oil droplets from water as cold as 5°C, offering a sustainable and economical method for removing oil from ultracold industrial wastewater and oil spills.

More than 1trn L of oil sands tailings and marine and arctic oil spills are awaiting cleanup. Oil sands tailings are a waste byproduct of oil extraction. Energy efficient recovery of crude oil droplets from ice-cold water in such cases poses a challenge, because at low temperatures saturated wax in the oil crystallises at the surface, increasing viscosity and preventing flow, making it difficult to collect.  

Traditional technologies for removal are either energy intensive, costly, or ineffective for use with micrometre-sized oil droplets. Others can risk further damage to the environment, such as those that reheat the oil to allow for collection, which can cause it to dissolve or evaporate. 

The research team from Imperial College London, UK and the University of Toronto, Canada, developed a sponge with a surface engineered to confer wax-wetting properties. Wax-wetting materials can attach to waxes.   

The sponge is made of polyester polyurethane and coated with nanosilicon capped with paraffin-like, 18-carbon ligands. In cold water, the wax groups at the surface of oil droplets can interact with other materials, and the coating was designed with a similar chemical structure to the oil to create mutual attraction between the surfaces. The wax-like nanomaterials allow droplets to adsorb to the sponge surface “like lego blocks” explained Pavani Cherukupally, Research Associate at Imperial’s Department of Chemical Engineering. It does not require additional energy input.

Researchers tested the sponge’s capabilities for difficult-to-remove dilute emulsions with initial oil concentrations of about 10,000 ppm. They found that in freshwater, at 5, 20, and 40°C, the sponges were able to remove oil droplets with 90–99% efficacy within 180 mins. They exhibited a maximum uptake of 993–1,094 mg/g of sponge across all temperatures.

They also found that the sponge can be regenerated in seconds by rinsing it in a non-toxic solvent, a mixture of heptane and toluene (heptol), with the sponge able to adsorb droplets with the original efficacy for ten cycles. The recovered oil could be used by industry again, contributing to a more circular economy.

In addition to protecting natural resources and offering benefits to the environment, the developed sponge could provide an economically viable option to industry, which is vital to allowing widespread uptake.

According to the researchers, the approach used to design the sponge could revolutionise design of energy-efficient sorbents in reclaiming oil from wastewater. The method could also be used to design materials for separating other viscous organic pollutants from industrial effluents such as petrochemicals, lubricants, and paints.

As well as scaling up the technology and using the sponge to reclaim fracking wastewater, researchers are working to extend its use to killing bacteria in river water for use in resource-limited communities such as in India and Rwanda.

The researchers are confident that the technology could be adapted to meet different needs across many different environmental conditions.

Cherukupally said: “Developing technologies to reclaim wastewater alone is not enough. To solve current industrial challenges, the technologies should have multiple functions, such as reclaiming wastewater, recovering resources from the wastewater, and be reusable/recyclable in addition to being affordable. Such multifunctional solutions could reduce environmental impacts and improve circular economy metrics in meeting UN Sustainable Development Goals and net-zero emission goals.”

Daryl Williams, Chemical Engineering Professor at Imperial and Principal Investigator in this work, commented to a university reporter:  “If we continue treating the environment as we have been for decades, clean water will become increasingly scarce. As such an important global resource, it is vital that society and industry has access to innovative, low-cost methods for water cleanup like those we report in our study.

“Our technology heralds a new approach for global remediation which we hope will be widely utilised before it is too late.”

The work builds on a previous achievement which saw the team develop a sponge with optimised surface characteristics that could stick to oil droplets across a broad range of pH levels.

Science Advances: https://doi.org/fz5w