New Method for Converting Methane Directly to Methanol Developed

Chemists at ETH Zurich and the Paul Scherrer Institute have found a new, direct way to convert gaseous methane into liquid methanol—offering industry the prospect of using the gas, rather than simply burning it off, as is currently practiced.

Methane is an abundant and inexpensive gas. Although it could be a suitable energy source and base material for the chemical industry, huge quantities of it are simply burned off around the world—above all at oil fields and refineries.

“On satellite images of Earth at night, the Middle East is brightly illuminated. This is not because the region has an especially high number of large, brightly lit settlements, but rather because of methane flaring at the oil fields,” says Jeroen van Bokhoven, professor of heterogeneous catalysis at ETH Zurich and head of the Laboratory for Catalysis and Sustainable Chemistry at the Paul Scherrer Institute (PSI).

Another reason for this wasteful approach to methane is that, currently, it is not sufficiently profitable to convert the gas into methanol in liquid form, which is easier to transport and more reactive. On the industrial scale, this conversion is currently performed using an indirect, elaborate and energy-intensive method that involves the production of syngas as an intermediate step.

Theoretically, it is already possible to convert methane into methanol, using crystalline, copper-containing silicon aluminum compounds (zeolites) as catalysts. The process involves activating the catalyst at very high temperatures—up to 450 degrees Celsius. However, the actual reaction between methane and oxygen to form methanol cannot be carried out at temperatures significantly higher than 200 degrees, as any methanol formed would burn off immediately. The reaction vessel must therefore be heated and cooled repeatedly, which is why this approach has never made it out of the research lab and into industry.

However, van Bokhoven and his colleagues have now demonstrated that this reaction cycle can also take place at a constant temperature of 200 degrees. They achieved this through a clever trick, using methane at a far higher pressure: 36 bars instead of under 1 bar, as previously used. “Working at a constant temperature makes this a much easier process to implement in industry,” says Patrick Tomkins, master student in van Bokhoven’s group at PSI.

Through analysis using X-ray absorption spectroscopy, the researchers were also able to show that, at the atomic level, the catalyzed reaction in the new low-temperature/high-pressure method does not take place at the same position as it did in the existing high-temperature method. “As a result of the high pressure, different active centers are utilized in the copper zeolites,” says van Bokhoven.

The new approach opens up a new range of possibilities. “In the past, catalysis scientists focused their research on copper zeolites for this reaction, because these are the most successful option in the high-temperature method," he says. "We also used these copper zeolites for the current study.”

As the high-pressure method is catalyzed differently at the atomic level, it is now worth investigating different catalysts, including those that haven’t been considered so far, says van Bokhoven. These might be even better suited to the high-pressure method.

Follow-up research will concentrate on these catalysts, with a view to developing an easy, direct and efficient process for converting methane into methanol.