Despite efforts to pivot toward renewable sources of energy, oil remains the backbone of modern society. It provides fuels for heat and transportation, and chemicals for everything from plastics to pharmaceuticals. But all these uses require separating crude oil into its various components. That separation process—which traditionally relies on heat—takes a tremendous amount of energy and accounts for roughly 1% of global greenhouse gas emissions each year.
Now, chemists say a newly developed material might one day help lighten this significant—if largely invisible—carbon footprint, which consumes some 230 gigawatts annually, equivalent to the total energy consumption of Nevada. Researchers report this week that a novel membrane might, if scaled up, reduce the energy required to separate crude oil by more than half. Such membranes would not only make using crude oil greener, but also cheaper for refineries to produce, as it would save them billions of dollars a year in energy costs.
“The potential savings are pretty impressive,” says Ryan Lively, a chemical engineer at the Georgia Institute of Technology who was not involved in the new work. The new membranes, he adds, must still prove to be durable for months if not years at a time. He and others also caution that conventional oil refineries may be slow to adopt them, because companies have already sunk costs into installing conventional separations systems. However, Lively says, the new membranes could quickly be adopted in new refineries built to separate hydrocarbon mixtures created from biofuels or synthetic fuels made using renewable electricity. “That’s really ripe territory,” Lively says.
Crude oil is a mixture of tens of thousands of chemicals. The first step in petroleum refining is separating that mix through a distillation process. The raw crude oil is heated up to about 500°C. Lighter components, such as those that make up gasoline, vaporize at lower temperatures and are captured. Heavier components, such as home heating oil, vaporize at higher temperatures.
Two years ago, researchers led by Lively and Andrew Livingston, a chemical engineer at Queen Mary University of London, reported in Science that it was possible to separate out these components using membranes rather than distillation. They created membranes with built-in pores that allow small, light hydrocarbons to pass through and keep larger, heavier ones out. But light hydrocarbons passed through the membranes too slowly to make them practical for real-world use.
To get around this, Livingston and his colleagues turned to an industrial approach for making ultrathin water desalination membranes called interfacial polymerization. They hoped thinner membranes would enable the desired hydrocarbons to pass through more quickly. However, Livingston notes, while the membranes typically used for desalination are sturdy in a water-based environment, they quickly fall apart when subjected to hydrocarbons that include industrial solvents.
So, he and colleagues reformed the polymers that make up conventional membranes. First, they made individual polymers, linking a hydrophobic, or oil-like portion, to a hydrophilic, or waterlike strand. When they added these molecules in a mix of oil and water, they spontaneously assembled into tiny bubbles, or vesicles, with the hydrophobic portion facing inward. They then used the interfacial polymerization technique to spread these vesicles into a continuous ultrathin sheet and link all the polymer units together to form a robust membrane.
The approach worked. The hydrophobic cores of the vesicles allowed selected (based on size and other characteristics) hydrocarbons to pass through readily—some 10 times faster than in previous oil-separation membranes, Livingston and his colleagues reported yesterday in Science. The researchers also showed that by tailoring the chemical makeup of the polymers, they could create different membranes that selectively pass through hydrocarbons of different sizes.
According to Neel Rangnekar, a chemical engineer with Exxon and a team member on the new paper, switching from distillation to membrane separation could save up to 50% of the cost of heating the crude oil and 75% of the cost of electricity used in refining, amounting to at least $3.5 billion per year.
“It’s a very exciting result,” says David Sholl, a separations expert at Oak Ridge National Laboratory who was not involved with the study. However, Sholl notes, the novel membranes aren’t yet ready for industrial use. They still need to be scaled up from the size of a piece of writing paper to hundreds of square meters and prove durable for months of continuous use. But Sholl thinks these…