Natural Sciences

Energy to Burn

Cleaning up natural gas by building a better molecule
Chem Student

The US has a lot of natural gas and keeps finding more. This resource, which burns cleaner than other fossil fuels, is playing an ever-bigger role in our energy portfolio.

But many natural gas reserves are so impure that they aren’t worth tapping.

Nitrogen is a big part of the problem. Natural gas containing more than four percent nitrogen burns poorly, hindering the performance of the machines that run on it.

Ian Rinehart is putting his energy into solving this power problem.

Rinehart, a 2016 chemistry graduate, is part of a team under professor David Tyler that aims to purify natural gas reserves in an efficient and cost-effective way. Their custom-made molecule traps nitrogen, freeing the rest of the fuel for collection; now the goal is making this chemical compound stable over repeated use.

The popular method to remove nitrogen from natural gas is to cool the fuel to extremely cold temperatures—about –259 F. Methane liquefies at that temperature, while nitrogen remains a gas and can be extracted. But this approach is expensive and requires a lot of energy.

Instead of putting natural gas in the big chill, Tyler and his team are creating molecules that essentially suck nitrogen right out of it.

They built a phosphorus and iron molecule to which nitrogen atoms readily bond. When natural gas is exposed to a solution with these manufactured molecules, the nitrogen atoms stick to them, freeing the methane for collection.

Unfortunately, this nitrogen-trapping molecule works only a few times before it breaks down.

Tyler’s team has a solution: They build a “scaffolding” of phosphorus atoms around the iron atom, which gives the molecule durability for the long run.

In practice, the natural gas would be pumped through a solution that contains the iron-phosphorus molecules. The methane would bubble to the surface for collection while the nitrogen remains trapped in the solution.

Now that the team has designed an effective molecule in the lab, they’re working to “scale up” so that their creation will work, time after time, in the large volumes of solution that would be needed by industry.

It will take the right mix of iron and phosphorus atoms, and Rinehart spends his days trying to hit that winning combination. He proposes the chemicals and conditions for “trial” molecules, then tests them out himself.

It takes a highly controlled environment to make the magic happen—an airtight metal and Plexiglas tank about the size of a small sedan, from which all oxygen has been removed.

Using thick rubber gloves that reach into the box, Rinehart mixes solutions and powders in vials and flasks. From the start of planning through completion, each run takes several days.

Rinehart works with small quantities of the test materials—fractions of an ounce—that are added to a solution. When his job is complete, the result is small flakes of the finished product, settling on the bottom of a flask.

Those flakes are then added to a solu.tion and natural gas is pumped in, so the team can measure the amount of nitrogen that is collected. They’re entering final testing and hope to know soon whether they’ve got a product to take to industry.

For Rinehart, it’s satisfying to take his classroom knowledge about the physical properties of substances and test them in the lab.

“It’s been a big challenge,” Rinehart said. “I feel like I’ve learned how to think like a scientist. That doesn’t come up in classes.”

—Jim Murez

Photo caption: Ian Rinehart’s work requires use of a chemical mixing tank—an airtight metal and Plexiglas box with thick rubber gloves attached. The reactions that occur can be breathtaking, “some of the most beautiful colors I’ve ever seen,” he said.

Photo credit: Charlie Litchfield/University Communications