Research seeks efficient, inexpensive retrofit for power plant carbon dioxide capture
In light of the Environmental Protection Agency’s (EPA) pending limits on fossil fuel-fired power plant carbon dioxide (CO2) emissions, new electrical utility generating units (EGUs) are incorporating the latest technologies to capture and store excess CO2. Limits for existing power plants are not to be released until 2014. However, it’s a given that those facilities will be looking for the most effective, efficient and inexpensive retrofits.
Sheila Baker, an associate professor of chemical engineering at the University of Missouri, is working to develop just such a solution.
In the United States, a decision by the U.S. Supreme Court in 2007 ruled greenhouse gasses to be air pollutants under the Clean Air Act. They authorized the EPA to determine if the pollutants constituted a threat to public health, which they did in 2009. In June of this year, President Obama issued a Climate Action Plan, which included a directive to the EPA to quickly complete carbon pollution standards.
Carbon dioxide represents nearly three-quarters of all greenhouse gas pollution worldwide. According to the EPA, it constitutes 84 percent of greenhouse gas emissions in this country with EGUs being responsible for over one-third of the total U.S. carbon pollution.
“Currently, most of the operating cost is not in capturing the CO2, but in the next step, a process commonly referred to as regeneration,” said Baker.
“In regeneration, the chemical that binds CO2 is heated to release the CO2 — so it may be sequestered or further processed — and the binding chemical is regenerated so it can be sent back to the flue gas stream to capture more CO2,” Baker said of efforts by the industry to comply with new regulations.
“The only current commercial process uses a chemical dissolved in water and takes a lot of energy to heat for CO2 removal,” she added. “Furthermore, the chemical they are using for CO2 absorption is corrosive and tends to evaporate.”
Baker and her chemical engineering graduate students, Jiangyun “Julie” Zhu and Jing Wang — along with former chemical engineering master’s students Carrie Hofmann and Omar Al-Azzawi — have developed solid materials that she believes are far superior. Baker has applied for a provisional patent for the technology.
“We basically coat seven- to 14-nanometer silica particles with different polymers that contain both parts for CO2 capture and parts that enable easy regeneration. When exhaust flows over the resulting solid, it captures the CO2,” she explained. “You can then pull the CO2 out under vacuum at 45 degrees [Celsius]. People have previously made similar materials, but they can only achieve good regeneration under vacuum at much higher temperatures than ours. The operation temperature of our materials is optimal between 45 to 60 degrees, the same as the flue gas.”
As an undergraduate, Zhu participated in research in which monoethanolamine (MEA) was used for CO2 capture, the current industry-favored solution mentioned by Baker. She, too, described use of the chemical as risky.
“Since ours is a solid, it is not corrosive, and it does not need to be heated,” Zhu said of the benefits of the technology they are testing in Baker’s lab.
Baker said her group intended to use high temperatures to test the regeneration ability of their new materials. However, Hofmann mistakenly put the research through its paces without using increased heat to remove the bound CO2. This turned out to be a very serendipitous mistake as they discovered they could achieve almost 100 percent regeneration without the extra heating required for similar materials, making their CO2 sorbent alternatives much more cost effective. This work resulted in a journal publication in 2012.
Baker’s group also is investigating membranes made from ionic liquids with similar groups for CO2 capture and release. Baker had extensive experience using ionic liquids as she began research with them during her days as a graduate student and during her many years working at Los Alamos and Oak Ridge National Labs prior to coming to MU. She and Wang also have used them in research aimed at pesticide extraction from water, which resulted in a publication earlier this year.
“We polymerize the ionic liquid into a thin membrane for CO2 capture or separation,” Wang said. “We are just starting by doing some characterization on the fabricated membrane. We are working to improve selectivity and permeability before we can test the capacity and selectivity.”
The work is going well and the team’s results have made her optimistic about the future success of the project, though there are still hurdles to overcome.
“There are some issues we will need to tackle when we scale up for both systems,” Baker said of the emerging carbon capture solution.
Baker received the Ralph E. Powe Jr. Faculty Enhancement Award to conduct the early research. This competitive award recognizes assistant professors — within two years of their initial tenure-track appointment — at Oak Ridge Associated University member institutions for their research in science and technology disciplines.
Baker plans to apply for a UM Fast Track funding award if that program is continued next year. Fast Track is focused on development, testing, prototype construction or market analysis of innovative technologies originating on all four UM campuses. The awards have resulted in moving some exciting faculty/researcher technologies forward toward commercialization. Baker is passionate about the project and also intends to seek additional outside funding to continue the promising research.
The research also has opened her eyes to additional innovative possibilities to investigate.
“Novel nanofluids and nanomaterials like those we are using for this work are excellent and tunable candidates for multiple research areas including soil remediation and oil recovery,” Baker said. “They also are particularly well suited as heat transfer fluids for industrial applications, nuclear reactors, transportation, electronics and biomedicine.”