Taming the black gold

Researchers at Imperial College London and the University of Toronto believe they have developed a sustainable and economical way to recover oil from ultra-cold industrial wastewater and oil spills

What the group say they have developed is a sponge that can remove hard-to-recover oil from Artic waters. At these cold temperatures, some oil can be especially difficult to clean up, especially the portion of heavier compounds that reside within crude oil. This includes the approximately 2.44 percent that is made of paraffin wax. When this kind of material begins to crystallise, it creates larger and stickier regions that are less amenable to capture using traditional oil-spill-cleanup methods.

This latest research builds on previously developed sponge technology to target specific challenges with recovering oil from ultra-cold water.

The findings, published in Science Advances, present an economical and sustainable method of oil recovery which will benefit the environment whilst presenting a cost-effective solution to industry, says the group.

Oil contamination in the Arctic

More specifically, the researchers have developed a special coating for commercially available sponges which can recover oil droplets from water as cold as 5ºC. Oil is more difficult to remove from ultra-cold water because it becomes viscous at low temperatures, reducing its flow and making it harder to collect.

Oil contamination in Arctic waters is a significant issue, with over one trillion litres of oil sands tailings, a waste by-product of oil extraction, marine and Arctic oil spills awaiting clean up.

Traditional technologies used to recover oil from such sites are either energy intensive, costly, or ineffective when faced with micrometre-size oil droplets. Some can even risk causing further environmental damage, such as those that reheat the oil before collection, which can cause it to dissolve or evaporate.

The technology designed by Imperial and University of Toronto addresses these challenges by harnessing the properties of cold-temperature oil to create a low-energy and cost-efficient solution. Not only will this benefit the environment and help to protect natural resources, says the group, it offers an economically viable solution for industry which is vital to ensuring widespread uptake.

Mutual attraction

The team at Imperial engineered a special coating for commercially-available sponges based on the behaviour of oil droplets in cold water.

When oil is below 38ºC, it begins to crystallise and becomes sticky at the edges. Lead author Dr Pavani Cherukupally decided to exploit this effect to design a paraffin-like sponge coating with the same chemical structure as oil that could create a mutual attraction between the two surfaces.

The sponge can be rinsed with a non-toxic solvent which displaces the sticky oil droplets and allows them to be collected, enabling both the sponge and the oil to be reused. The process is known as wax-wetting, where one fluid is used to displace another. In this case, the solvent, known as heptol, is used to displace the oil droplets.

Having established the optimum wax-wetting characteristics, a team of  U of T Chemists synthesised the nanocoating which made it functional and ready to use on a larger scale.

Rigorous testing seemingly shows that the engineered sponge can adsorb oil droplets from water ranging between 5 and 40ºC and remove 90-99% of contaminants within two and a half hours. The recovered oil can be used again by industry, the basis for a further economic benefit, and the sponge can be reused ten times with consistent results.

Next steps

This method of oil recovery holds forth the possibility of significant benefits for both industry and the environment, say the researchers. It has a high success rate for removing oil from ultra-cold water and requires no additional energy input as it uses the material properties of the sponge and oil to generate results, says the group.

Cherukapally explained: “We’ve developed an energy efficient way of reclaiming crude oil which has ecological benefits for the environment and is economically beneficial to industry.

“Our work is significant because it targets a specific issue, oil crystallisation at low temperatures, and addresses it from a materials perspective.”

Principle Investigator Professor Daryl Williams added: “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 clean-up 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.”

Next the team will explore how the sponge can be used to collect range of oils, which each have a different composition and will behave differently at low temperatures. They say they are confident that their sponge technology can be adapted to meet these different needs across many different environmental conditions.