A new membrane inspired by those used in reverse osmosis water filtration can split crude oil into heavy and lighter molecules.
If scaled up, the technology could reduce the energy footprint of crude oil fractionation, which currently consumes 2.5% of all U.S. energy and 1% of global energy annually. The distillation processes currently in use also contribute 6% of the world’s carbon dioxide emissions each year.
Membrane separation consumes far less energy, but most commercial membranes are made of polymers, which swell and plasticize in the presence of crude oil, explains Zachary Smith, a professor of chemical engineering at the Massachusetts Institute of Technology (MIT). “You have challenges with stability that prevent you from using membranes for applications like hydrocarbon mixtures,” Smith says.
The Trip-TFS solution
Membranes made via cross-linking polyamides are currently used in reverse osmosis and are capable of very selective separation near the thermodynamic minimum, Smith says, but the bond chemistries aren’t suited to hydrocarbons because they cause the pores to shift and swell. To solve this problem, Smith and his team swapped out the flexible amide bonds for more rigid imine bonds. These bonds yield smaller, less polar linkages. They added additional stability by incorporating the shape-persistent monomers triptycene and tetraformylspirobifluorene. They called the membrane Trip-TFS after these components.
The films are manufactured using interfacial polymerization, in which a polymer forms at the interface between two aqueous compounds. Typically, this is done between water and an organic solvent, but the molecules in the modified membrane are insoluble in water. Instead, the researchers used a porous polyacrylonitrile support and soaked it in water containing an acid catalyst. “When the monomers diffuse to the interface, they react together and form a cross-linked structure,” Smith says. “You can now use that for oil-based separations, despite starting with monomers that are soluble in oil.”
Testing and future applications
The researchers then tested the stability of the membranes in toluene, a common organic solvent that occurs naturally in crude oil, and found that the structure was able to preserve its glassy behavior rather than swelling and losing selectivity. Next, they experimented with separating several mixtures, including toluene from triisopropylbenzene and a multicomponent mixture consisting mostly of toluene with small amounts of 11 different hydrocarbons. They also tested a simulated light shale-oil mixture and a crude-oil mixture consisting of naphtha, kerosene, and diesel-grade fuel.
“Our Trip-TFS membrane showed significant enrichment of light hydrocarbons in the permeate, while the commercial membrane (Puramem, Evonik) showed no change,” says Tae Hoon Lee, the study’s first author who is now an assistant professor of future energy engineering at Sungkyunkwan Univ. in South Korea. “We did not observe any noticeable membrane degradation during testing. However, since we used a simulated ‘realistic’ crude oil mixture, future studies should investigate potential long-term effects when working with actual crude oil.”
Just as reverse osmosis membranes are now made in industrial quantities, the new hydrocarbon membrane could also be scaled up to a roll-to-roll manufacturing process, Smith believes. Additional chemical tweaks could also lead to membranes that could separate other complex mixtures, such as biocrude. The researchers are now interested in identifying industry partners to scale up the membrane fabrication process, Lee adds. They also hope to demonstrate the potential of the technology to fossil fuel companies.
“There are many areas where stability is needed in organic and hydrocarbon mixtures where this type of idea could really apply broadly,” Smith says.
Lee, T. H., et al., “Microporous Polyimine Membranes for Efficient Separation of Liquid Hydrocarbon Mixtures,” Science, doi: 10.1126/science.adv6886 (May 22, 2025).
This article originally appeared in the News Update column in the July 2025 issue of CEP. Members have access online to complete issues, including a vast, searchable archive of back-issues found at www.aiche.org/cep.
