Engineers have developed a new way to separate chemicals that could drastically cut the energy required to make fuels or synthetic polymers.
The process could cut the energy needed in separation stages in half and save $2 billion a year in energy costs in the United States and avert 45 million tons of carbon dioxide emissions around the world annually.
Researchers designed a membrane that could distinguish between very closely related molecules and could survive in conditions that would cause existing membranes to fall apart, opening a whole new suite of applications. They published their findings last week in the journal Science.
Benjamin McCool, a co-author and an advanced research associate at Exxon Mobil Corp., explained that separating chemicals is a longstanding industrial problem and that upward of 10 percent of the world’s energy demand goes to these processes, like removing salt from seawater.
Between 40 and 60 percent of the energy used to make clean water, fuels and industrial chemicals goes toward separation.
In this case, the researchers looked at separating a class of organic compounds called xylenes.
“It’s a separation we have been working on at Exxon Mobil dating back to the 1990s,” McCool said.
Xylenes are precursors for materials like polyesters and are important industrial solvents. However, they come in several varieties that use the same atomic components but attach them differently. This means that they have overlapping traits like mass and boiling points, so conventional separation techniques like distillation aren’t as effective and others require a lot of energy to tell these very similar molecules apart.
“We’re talking very, very small size differences,” McCool said. “They differ in size by a tenth of a nanometer.”
The researchers decided to come up with a method that would work at room temperature, cutting its energy requirement, and build it from off-the-shelf components, reducing its cost.
The process, called reverse osmosis, is the same technique that many desalination plants use to produce potable water from the ocean. These plants use a membrane to allow water and prevent salt from flowing through as pressure is applied to one side.
But these membranes are made of organic polymers, so they would dissolve or swell up if they were used in an organic solution. And separating organic compounds requires much higher pressures than desalination.
“Today’s desalination membranes would not be chemically stable” to separate xylenes, McCool said. “This membrane has to be stronger.”
Instead, the researchers used a synthetic carbon membrane to act as a molecular sieve.
“The way we make the membrane is we start with a commercially available polymer because we want a line of sight towards commercialization,” said co-author Ryan Lively, an assistant professor of chemical and biomolecular engineering at the Georgia Institute of Technology.
The team then spun the polymer into hollow fibers, chemically cross-linked them together and then pyrolized the material to create a carbon fiber membrane.
“The pyrolysis stem influences how close the pore walls are,” Lively said. This could be altered to tune the membrane to serve in different applications.
When deployed at scale, using the membrane to separate organic chemicals could dramatically shrink the carbon footprint of making fuels or plastics. “We’re looking at a 10- to 20-fold reduction in energy intensity,” Lively said.
Right now though, the researchers are still at the bench stage and are looking to scale up their membranes and test them in different applications.
“We’re thinking about tough challenges in water and pharmaceutical production,” Lively said. “We think membranes have a good chance.”
Reprinted from ClimateWire with permission from Environment & Energy Publishing, LLC. E&E provides daily coverage of essential energy and environmental news at www.eenews.net. Click here for the original story.