Flaring of natural gas in the Texas oil fields silhouettes an electric oil pump jack.
Burning of natural gas at oil and gas wells, called flaring, is a major waste of fossil fuels and a contributor to climate change. But to date, capturing the flared natural gas, estimated at some 140 billion cubic meters per year by the International Energy Agency, has not been economically feasible.
University of California, Berkeley, chemists have now come up with a simple and green way to convert these gases — primarily methane and ethane — into economically valuable liquids, mostly alcohols like methanol and ethanol. The liquids are also easier to store.
The alcohols can be used as feedstocks for production of numerous other petrochemical products, providing an additional revenue source for oil and gas companies but also lowering carbon dioxide emissions from flaring. Flaring is used to mitigate the more harmful effects of directly venting natural gas — methane is 34 times more potent as a greenhouse gas than carbon dioxide — into the atmosphere.
Details of the process were published Nov. 3 in the journal Science.
Graphic: Detail of the porous MOF (left and inside circle at right) showing the metal reactive site where oxygen and hydrocarbons like ethane (molecules at extreme left) are converted into alcohols, such as ethanol, plus carbon dioxide (molecules at extreme right). The red balls are oxygen atoms; the gray are carbon; orange is iron; light blue is zinc; dark blue is nitrogen; and white is hydrogen.
Jonas Börgel/UC Berkeley
The new process for oxygenating hydrocarbons to alcohols mimics the way plants and animals add oxygen to carbon-hydrogen bonds to produce energy from carbohydrates, fats and proteins. Carbon-hydrogen bonds are equally abundant in the hydrocarbon molecules that comprise fossil fuels.
The natural oxidation processes involve an enzyme centered around a reactive metal — in most cases, iron — that catalyzes the insertion of an oxygen atom between a carbon and hydrogen bond to produce C-O-H, an alcohol group.
Much research has gone into finding variants of these natural enzymes that would convert gaseous hydrocarbons from fossil fuels into liquid alcohols without the energy input and huge infrastructure needed today in the chemical industry. But most of these processes involve artificial enzymes in a liquid solution.
The UC Berkeley innovation incorporates these reactive iron sites into a rigid and porous crystalline structure — a metal-organic framework, or MOF — that stabilizes the iron and allows easy entry of gas and easy exit of liquid alcohols.