Separation Membrane Fractionates Crude Oil Using Much Less Energy

Researchers at the Massachusetts Institute of Technology (MIT) have developed a membrane that separates crude oil components by molecular size, potentially reducing the energy required for crude oil fractionation.

The research is published in Science Advances.

Energy demands in crude oil processing

Separating crude oil into products such as gasoline, diesel and heating oil currently relies on distillation, which consumes substantial amounts of energy. This process involves heating crude oil – the main contributor to this energy consumption – to separate its components based on their boiling points. THis process accounts for around 6% of global CO₂ emissions.

In the hunt for an alternative, the MIT team have created a membrane that filters crude oil components according to their molecular size rather than boiling point. This membrane offers an energy-efficient alternative to heat-driven fractionation.

The membrane is a thin film made using a method that is already commonly found in industrial processes, which may facilitate large-scale production. It can efficiently separate lighter and heavier components in crude oil and resists swelling, a common problem in existing hydrocarbon filtration membranes.

Designing the membrane

Previous efforts to create membranes for crude oil separation often used polymers of intrinsic microporosity (PIMs) like PIM-1, which allow hydrocarbons to pass quickly but tend to swell when absorbing certain organic compounds. This swelling reduces their ability to filter by size.

To improve on this, the researchers modified membranes originally designed for reverse osmosis water desalination. These membranes are made from polyamide films formed at the interface between water and an organic solvent using interfacial polymerization, a process that creates thin, durable films.

However, polyamide membranes do not have the right pore sizes or resistance to swelling for crude oil components. To address this, the team replaced the amide bonds in the polymer with imine bonds. The imine bonds are more rigid and hydrophobic, allowing hydrocarbons to pass through without causing swelling.

“The polyimine material has porosity that forms at the interface, and because of the cross-linking chemistry that we have added in, you now have something that doesn’t swell,” said Zachary P. Smith, an associate professor of chemical engineering at MIT and the senior author of the new study. “You make it in the oil phase, react it at the water interface, and with the crosslinks, it’s now immobilized. And so those pores, even when they’re exposed to hydrocarbons, no longer swell like other materials.”

Additionally, the researchers incorporated a molecule called triptycene, which helps create pores of the right size and shape to selectively allow hydrocarbons through.

Separation performance

Testing the membrane with a mixture of toluene and triisopropylbenzene showed the membrane could concentrate toluene to 20 times its original level. When applied to a mixture representative of industrial fuels – naphtha, kerosene and diesel – the membrane successfully separated lighter from heavier hydrocarbons by molecular size.

“You can imagine that with a membrane like this, you could have an initial stage that replaces a crude oil fractionation column. You could partition heavy and light molecules and then you could use different membranes in a cascade to purify complex mixtures to isolate the chemicals that you need,” Smith said.

Because interfacial polymerization is already widely used to produce water desalination membranes, existing manufacturing lines could be adapted to produce the new membranes at scale.

The research was funded, in part, by ExxonMobil through the MIT Energy Initiative. 

Reference: Lee TH, Balcik M, Ali Z, et al. Microporous polyimine membranes for efficient separation of liquid hydrocarbon mixtures. Science. 2025. doi: 10.1126/science.adv6886

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