PNNL researchers create affordable means of converting captured CO2 into methane

Published on September 07, 2021 by Chris Galford

Researchers at the United States Department of Energy’s (DOE) Pacific Northwest National Laboratory (PNNL) have successfully developed a streamlined method of converting captured CO2 into methane, reducing the materials and energy needed, and potentially, the cost.

The result could be more affordable prices for the resulting natural gas — of which methane is a primary component — and for carbon capture in general. The new method achieves this through a PNNL-developed solvent known as EEMPA, which takes CO2 from power plant flue gas and binds it for conversion to useful chemicals. Traditionally, other CO2 conversion methods rely on high temperatures and expensive means.

“Right now a large fraction of the natural gas used in the U.S. has to be pumped out of the ground and demand is expected to increase over time, even under climate change mitigation pathways,” Jotheeswari Kothandaraman, lead author and PNNL chemist, said. “The methane produced by this process — made using waste CO2 and renewably sourced hydrogen — could offer an alternative for utilities and consumers looking for natural gas with a renewable component and a lower carbon footprint.”

Compared to the conventional methods of methane conversion, the EEMPA method requires an initial investment that costs 32 percent less. That cost reduction holds throughout, with operation and maintenance costs also 35 percent cheaper, resulting in the overall selling price of synthetic natural gas being brought down 12 percent, according to PNNL.

EEMPA achieves this because it can make CO2 dissolve more easily, reducing the amount of energy needed to fuel a reaction and less pressure needed to run a conversion. CO2 captured by EEMPA can also be converted to methane on site, reducing the costs of transport and conversion elsewhere. In the actual conversion process, EEMPA can also convert more than 90 percent of captured CO2 to methane, and capture more than 95 percent of CO2 emitted in flue gas. Excess heat and resulting steam generated along the way can then be utilized for power generation, as well.