Methane represents one of the world's largest sources of greenhouse gas emissions, often as a byproduct of natural gas. As a result, there is a worldwide push to prevent methane from escaping into the atmosphere and to reduce its flaring.
Instead of burning it, an alternative strategy is to convert methane into a more valuable liquid that can be transported. Methanol is one example of such a fuel that can be used in industrial processes, alternative fuel cells and pharmaceuticals. However, the process for making this conversion is fundamentally flawed.
Texas Engineers have developed the most efficient method yet to convert methane to methanol over the distributed scales where it is produced. They discovered a method to break a scaling law that has limited the yield of methanol that can be produced in more conventional single-step approaches. These methods are limited by the tradeoff between methane conversion and methanol selectivity; as one increases, the other falls. Instead, the team has developed an approach that breaks this limit and allows a yield of methanol that is scalable based on the timescale and energy cost of conversion.
"In addition to simplifying the conversion of methane to methanol by allowing it to proceed in a single step at mild conditions, we have demonstrated the highest yield yet, bringing this process to reduce emissions closer to the mainstream," said Thomas Underwood, an assistant professor in the Cockrell School of Engineering's Department of Aerospace Engineering and Engineering Mechanics who led the project.
The Research: As documented in ACS Sustainable Chemistry & Engineering, the researchers achieved a record yield of methanol in a single-step process, converting more than 20% of methane into methanol using electrical energy at atmospheric pressure and near room temperature. The mild conditions, compact design, and integration of electrical energy into their process means this technology can be deployed to locations where methane is emitted or flared without requiring pipelines to store and transmit the methane.
The key to this research is the use of plasmas to excite methane and to trap methanol before they can be converted into CO and CO2. These plasmas form a state of vibrational non-equilibrium within the reactor where reactions can proceed at low gas temperatures. This allows for extraction techniques to be deployed in the same volume where reactions occur, unlike existing industrial processes. Manipulating the transport, reaction, and extraction timescales within the plasma was key to achieving a selective conversion.
Why it Matters: Because of its volatility, methane is emitted at an annual rate in excess of 500 million tons from various processes, including agriculture, wetlands, coal mining, natural gas, and more. While methane is a source of energy, challenges with its compression and transport (e.g., low boiling point, flammability, etc.) make it difficult to utilize over distributed scales. Due to these challenges, methane continues to flare at levels that contribute up to 22% of the global CO2 emissions.
Today's methods for converting methane to methanol involve a two-step process that features a high pressure, temperature and carbon footprint. These features make current industrial processes unsuitable for utilizing methane where it is emitted.
What's Next: Underwood's goal is to use plasma technologies to rethink how fuels are stored, converted, and used within the global energy economy. These efforts aim to reduce the carbon intensity of industrial processes within the energy sector. Underwood and his team are working with UT's Discovery to Impact group to patent the technology as they continue to improve it.
