Membranes separate or filter out molecules from mixtures according to differences such as size and shape. If molecules are nearly the same size, separation becomes more challenging. Using a well-known process for bonding nitrogen and carbon atoms, the spiral polymers were made by connecting building blocks with a kinked structure to create disordered materials with built-in voids.
Membranes are already widely used in such applications as seawater desalination, but refining petroleum is complicated and, until now, was not possible with current membranes. To overcome that challenge, the Georgia Tech research team developed a novel spirocyclic (spiral-shaped) polymer and put it on a strong substrate to make membranes. They can be used separate complex hydrocarbon mixtures by applying pressure to filter out what isn’t needed rather than using heat to “steam” away unwanted compounds.
Using heat-based distillation to refine crude oils eats up nearly 1% of the world’s energy, consuming 1,100 terawatt-hours per year (enough to power the entire state of New York for that timeframe). To save energy while still refining oil, engineers at Georgia Institute of Technology, working with others from Imperial College London and ExxonMobil, have developed a membrane that could replace some of the energy-intensive distillation processes.
The team found a way to form the membranes using a simple and scalable process, and they made the membranes more rigid so that some small molecules pass through more easily than others. The research team was then challenged to make the membrane’s structure more flexible so that it could better discriminate among molecules based on size and also make it slightly “sticky” toward certain molecules found in abundance in crude oil.
After designing several new polymers and finding some success in refining a synthetic gasoline, jet fuel and diesel fuel mixture, the team tried to separate a crude oil sample. The researchers were happy to find that the new membrane was effective at recovering gasoline and jet fuel from the complex mixture.
The researchers worked with polymers designed and tested at Georgia Tech, then converted them to 200-nanometer-thick films and incorporated into membrane modules using a roll-to-roll process. Samples were tested at all three organizations, providing multi-lab confirmation of the membrane capabilities.
“We have the foundational experience of bringing organic solvent nanofiltration, a membrane technology becoming widely used in pharmaceuticals and chemicals industries, to market,” says Andrew Livingston, professor of chemical engineering at Imperial. “We worked extensively with ExxonMobil and Georgia Tech to demonstrate the that this technology can be scaled up to the levels needed by the petroleum industry.”
“We brought together basic science and chemistry, applied membrane fabrication fundamentals and engineering analysis of how membranes work,” adds Ryan Lively, associate professor at Georgia Tech’s School of Chemical and Biomolecular Engineering. “We were able to go from milligram-scale powders all the way to prototype membrane modules in commercial form factors.”
ExxonMobil’s relationship with Georgia Tech goes back nearly 15 years and has produced innovations in other separation technologies, including a carbon-based molecular sieve membrane that dramatically reduces the energy required to separate a class of hydrocarbon molecules known as alkyl aromatics.