Methane, a greenhouse gas that has been and still is a huge contributor to global warming, can be used in a clean way that will not harm the climate, according to researchers from the University of Pennsylvania.
"Finding ways to use methane besides burning it as a fuel constitutes a practical approach to using this abundant gas," said Daniel Mindiola, a Presidential Professor in Penn's Department of Chemistry in the School of Arts & Sciences. "Our method will hopefully provide inspiration to move away from burning our resources and instead using them more as a carbon building block to prepare more valuable materials."
Mindiola and fellow researchers examined how they could use the composition of methane to their advantage. Methane is made up of one carbon atom that is bonded to four hydrogen atoms. When methane burns, all of the bonds break apart to produce carbon dioxide and water. The researchers reasoned that if they could find a way to control how many bonds are broken, they can potentially use those bonds to create a larger chemical.
"If only one or two hydrogen bonds could be broken efficiently, then it might be possible to connect carbon atoms from two or more methane molecules to make larger hydrocarbons," said researcher Milton R. Smith III from Michigan State University. "For example, gasoline is a mixture of hydrocarbons containing between four and 12 carbon atoms. The polyethylene used to make garbage bags and milk jugs is composed of millions of carbon atoms."
Since breaking up some bonds and not others is very difficult, the researchers decided to try something new. They looked at a chemical reaction called carbon-hydrogen borylation, which was discovered by Smith's team. The process involves using a catalyst, usually a metal, to get a hydrocarbon to react with a compound that has boron. If the hydrocarbon reacts, the process results in a carbon-boron bond that can more easily be used to bond with another chemical than the carbon-hydrogen bond.
After assessing which combinations of compounds and catalysts would work together by using Penn's High Throughput Screening Center, the researchers found that they could borylate methane. The combination involved 500 pound-per-square-inch of methane, the catalyst iridium, which is a metal, and a temperature of 150 degrees Celsius (302 degrees Fahrenheit).
"It turns out methane is not as inert as one would have expected," Mindiola said. "We were able to borylate it using off-the-shelf reagents, which is very convenient."
The researchers are currently trying to find out if other combinations, particularly ones that would be more cost effective, could also borylate methane.
"I think this work is going to inspire a lot of chemistry and get people thinking about methane in a different way," Mindiola said. "That doesn't mean that the natural gas industry is going to borylate all the methane they're extracting -- there is a lot out there and boron is rare -- but it's another valuable option."
The study was published in March 25 issue of the journal Science.