A new class of ultrathin polymer membranes, dubbed Polymers of Locked Intrinsic Microporosity (PLIMs), has been developed through a global research collaboration.

These membranes can separate complex hydrocarbon mixtures (like crude oil), potentially transforming the energy-intensive refining process.

Modifying membrane structure

Every single day, standard crude oil refining uses the thermal distillation method. This process boils oil to separate it into useful fractions like gasoline, plastics, and jet fuel. It works well, but it carries an environmental price tag. It consumes a high amount of energy.

Now, a team of international researchers has created a workaround that could take the heat out of the equation entirely.

The Polymers of Locked Intrinsic Microporosity (PLIMs) are ultrathin membranes that can filter out complex hydrocarbon mixtures at a microscopic level without needing a heat source.

“Membranes can, in principle, do the same job as distillation or evaporation, using far less energy,” explained Andrew Livingston, Professor of Chemical Engineering and Vice President Research and Innovation at Queen Mary University of London, and CEO of Exactmer. 

“The problem has been finding materials that are both fast and selective when exposed to real hydrocarbon mixtures,” the lead researcher added.

The study introduces a novel fabrication method that injects a crosslinking agent during membrane formation to create highly efficient separating layers. It combines two features that have eluded scientists for decades: extreme molecular selectivity and incredibly fast transport speeds.

Testing of membrane

Membranes promise a cleaner, low-energy alternative to massive boilers. In this concept, rather than boiling the liquid, it is run through a molecular sieve that catches specific molecules based on their size.

In practice, organic liquids like crude oil ruined everything.

The team focused on highly porous polymers, materials possessing an internal structure like a sub-nanometer sponge. However, these materials have a flaw. When exposed to harsh hydrocarbons, it swells. As the polymer expands, the tiny pores dilate, allowing larger molecules to slip through. The filter becomes useless.

To fix this, the team altered the fabrication process and introduced an in situ crosslinking agent directly into the polymer film during its formation.

“The key was stabilizing the structure before the polymer had a chance to swell,” said Dr Zhiwei Jiang. “This preserves the tiny pores that make molecular separation possible, while still allowing hydrocarbons to flow through very quickly.”

When the researchers tested the membranes against real Arabian Extra Light crude oil, the results defied standard expectations. The PLIM system successfully stripped out 99.8% of heavy hydrocarbons (those with more than 15 carbon atoms). It also slashed corrosive sulfur compounds by 93%. 

This is a massive victory for refineries, as sulfur frequently degrades downstream equipment and catalysts.

The membrane performed just as well on lighter refinery streams, such as virgin naphtha. It sorted out smaller molecules destined for fuel upgrading from heavier components used to manufacture everyday plastics. It did all this while operating at flow rates comparable to those of commercial water desalination systems.

Moreover, this team designed the material with mass manufacturing in mind from day one.

Using standard roll-to-roll processing, PLIM sheets were manufactured over a meter wide. These sheets were wrapped into spiral-wound modules, the exact shape used in existing industrial filtration plants worldwide.

The membranes also proved they have stamina, running continuously for 30 days without a drop in performance.

The results were published in the journal Science on June 18.

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