Tuesday, February 27, 2007

A Practical Use for Waste Methane

A direct method of converting methane into useful chemical compounds could reduce the release of the potent greenhouse gas at isolated oil fields.

By Prachi Patel-Predd

Burning solution: Natural gas is routinely burned at isolated oil fields and refineries. A simple new way to convert methane, the major component of natural gas, into useful chemical compounds that could be easily transportable might help reduce emissions of the potent greenhouse gas. Credit: Michael Simpson - One Sky

About 100 billion cubic meters of natural gas are burned off or simply vented at remote oil rigs and refineries that are not connected by pipelines. The practice wastes a precious fuel and pumps methane, a potent greenhouse gas, into the atmosphere. Technologies for compressing or liquefying natural gas in order to transport it are expensive and only make sense at large oil fields. So, researchers have been looking for viable technologies to convert the natural gas found at small, isolated oil fields into compounds that are easier to transport and distribute.

A new breakthrough by chemists at the Munich University of Technology, in Germany, and Dow Chemical, in Midland, MI, could lead to a technology for turning methane, the main component of natural gas, into easily transportable and valuable chemicals. Because of its simplicity, the new chemistry could be employed at natural-gas reserves that are in remote locations with no infrastructure to transfer the gas to markets. About half of the world's known natural-gas reserves of 170 trillion cubic meters are in such deposits, according to the U.S. Department of Energy.

Specifically, the researchers found a simple way to convert methane into methyl chloride, which can easily be converted into petrochemicals such as ethylene or propylene, used to make plastics. Ethylene and propylene, says Johannes Lercher, a chemistry professor at the Munich University of Technology, are far easier to transport than methane is.

The current process for making methyl chloride takes a lot of energy and involves multiple steps, including first converting methane into a combination of carbon monoxide and hydrogen. In an online paper in the Journal of the American Chemical Society, the Munich and Dow researchers demonstrate a straightforward technique that uses much less energy. They show that mixing methane, hydrogen chloride, and oxygen in the presence of a lanthanum catalyst yields methyl chloride. "Capital and complexity frequently go hand in hand," says Mark Jones, a plastics and hydrocarbons researcher at Dow. "The general trend is that reducing processing steps is good."

The technique could have one drawback, though: it uses chlorine, a toxic gas. The researchers' plan includes recycling the hydrogen chloride and repeatedly using it for the reaction. "In the vision we're playing with, the chlorine would not ever get on a boat," says Eric Strangland, a chemistry and catalysis researcher at Dow and a coauthor of the paper.

However, companies that are not used to handling chlorine might initially be intimidated by the technique, says Bert Weckhuysen, a chemistry professor at Utrecht University, in the Netherlands. "Dow has a long experience with chloride chemistry, so working with chloride streams is not a big deal [for them]," Weckhuysen says. "Others companies could, at least in the beginning, be scared off due to the requirement of being able to work with chloride compounds. It requires infrastructure."

The process will also face competition. New gas-to-liquids technology, which converts natural gas into synthetic liquid fuels, is starting to become popular as an alternative to liquefied natural gas, and it's garnering the attention of oil giants like Exxon and Shell. It has not yet been widely used, though, because it's expensive to implement: it requires a lot of energy and large facilities. Weckhuysen says that if Dow could develop an affordable commercial process based on it new reaction, it could compete with gas-to-liquids technology.

Another competitor, Gas Reaction Technologies, based in Santa Barbara, CA, is commercializing a technology to directly convert natural gas into liquid fuels and chemicals. The process is very similar to the new Dow process, except it uses bromine instead of chlorine. Gas Reaction Technologies, which is working with several partners, including Cargill, expects to have facilities going within three to five years, says Eric McFarland, the company's CEO.