Researchers at the National Energy Technology Laboratory (NETL) are reporting positive results in development of new pre-combustion solvents that can capture carbon dioxide (CO₂) more effectively and economically than state-of-the-art solvents now in use.

A solvent is a liquid capable of dissolving another substance. For example, water is a solvent for salt.

CO₂ capture and storage from power generation is a critical component of strategies for preventing a further rise in atmospheric CO₂ concentrations. However, current solvent technology could result in a prohibitive rise in the cost of energy production. NETL researchers have been searching for better solvents that can be more effective and economical than solvents now being used to capture CO₂.

The current state-of-the-art pre-combustion CO₂ capture solvent is a polyethylene glycol solvent that is fully miscible with water. A miscible liquid can be mixed with another liquid without separating from it. However, it requires water vapor to be removed by lowering the temperature of the syngas in the carbon capture process. Lowering the temperature, removing the water vapor, and then raising the temperature back is inefficient from both a cost and net electricity perspective.

NETL has been pursuing a strategy to minimize energy and cost penalties by addressing industrial streams in which CO₂ is already at high partial pressures, such as the synthesis gas (syngas) exiting coal gasifiers at integrated gasification and combined cycle (IGCC) power plants, using hydrophobic solvents that repel water. IGCC is a technology that uses a high-pressure gasifier to turn coal and other carbon-based fuels into pressurized syngas. Impurities can then be removed from the syngas prior to the power generation cycle.

Hydrophobic solvents can be operated at higher temperatures, minimizing the energy and cost penalties associated with cooling the syngas and reducing excessive corrosion in plants. NETL recently tested two solvents its researchers developed and determined that they are more effective and economical than the polyethylene glycol solvent that is currently used for pre-combustion carbon capture.

NETL received confirmation of its better-performing solvents when they were tested at the University of North Dakota’s Energy and Environmental Research Center (EERC) using a gasifier with actual syngas. The solvents were tested at two different solvent flow rates and three different temperatures for each solvent.

According to NETL’s David Hopkinson, two proprietary hydrophobic NETL solvents were tested known as PEG-PDMS-3 and CASSH-1. The work was the result of molecular design and optimization done with the assistance of computational chemistry and experimental studies at the lab/bench scale. PEG-PDMS-3 was developed experimentally in the lab and CASSH-1 was identified through computational methods.

“The EERC tests showed that PEG-PDMS-3 had improved CO₂ capacity and CO₂/H2 selectivity compared with the currently used polyethylene glycol solvents on the market, while CASSH-1 showed a dramatic improvement in these properties,” Hopkinson said. “Both NETL solvents have better performance when operated above room temperature while the currently used market solvents must be operated below room temperature.”

He said the next step toward bringing the NETL solvents forward is further testing on a larger scale with a different gasifier at the University of Kentucky while commercial development partners are sought.

The gasifier was operated by a team of engineers led by Joshua Stanisklowski and Michael Swanson, both of UND EERC, and testing conditions for the four solvents were chosen and modeled in AspenPlus by NETL/RIC researcher, Nicholas Siefert, Ph.D., who also attended the testing at the gasifier in North Dakota. The PEG-PDMS-3 solvent was synthesized by a team of NETL/RIC researchers led by Robert Thompson, Ph.D. of Battelle, and the computational-screening effort that led to CASSH-1 was done by NETL/RIC researcher Wei Shi, Ph.D.

NETL Director Brian Anderson, Ph.D., said, “The successful development of advanced CO₂ capture technologies is critical to reducing greenhouse gas emissions and maintaining the cost-effectiveness of fossil energy-based power generation and other industrial processes. The U.S. Department of Energy (DOE) Fossil Energy Program and NETL have adopted a comprehensive, multi-pronged approach to development of advanced CO₂ capture technologies for today’s coal power platforms and for future platforms.”

He added that effective CO₂ capture research will enable cost-effective implementation of technologies throughout the power generation sector and help ensure the United States will continue to have access to safe, reliable and affordable energy from fossil fuels.
NETL develops and commercializes advanced technologies that provide reliable and affordable solutions to America's energy challenges. NETL’s work supports DOE’s mission to advance the national, economic, and energy security of the United States.