Tetramine modified MOFs remove 90% of CO2 more efficiently and cheaper.
Major advances in carbon capture technology could provide natural gas power plants with an efficient and inexpensive way to remove carbon dioxide from their flue gas emissions, a necessary step in reducing greenhouse gas emissions to slow global warming and climate change.
Developed by researchers in the USA University of California, Berkeley, Lawrence Berkeley National Laboratory and ExxonMobil, the new technique uses a highly porous material called a metal-organic structure or MOF, modified with nitrogen-containing amine molecules, to capture CO2 and low temperature steam to release CO2 for other uses or for sequestration underground.
In experiments, this technique showed six times the capacity to remove CO2 from flue gas as a current technology based on amines and was highly selective and captured more than 90% CO2 issued. This process uses low-temperature steam to regenerate the reusable MOF, which means that less energy is needed to capture the carbon.
“Why2 steam trapping – if you use direct contact with steam to remove CO2 – he was a kind of holy grail for the field. This is rightly considered to be the cheapest way to achieve this, “said Jeffrey Long, a researcher at UC Berkeley Chemistry and Chemical and Biomolecular Engineering and a Berkeley Lab scientist. “These materials, at least from the experiments we’ve done so far, look very promising.”
Because there is a small market in the market with the most captured CO2, power plants would probably pump most of it back to the ground, or sequester it, where it would ideally turn into rock. The cost of scrubbing emissions should be stimulated by government policies such as carbon trading or the carbon tax to stimulate CO2 capture and sequestration, which many countries have already introduced.
The work was funded by ExxonMobil, which works with the Berkeley Group and Long Mosaic Materials Inc. in founding Long to develop, expand and test CO removal processes.2 from emissions.
Long is the lead author of a paper describing a new technique, published on July 24, 2020, the issue of the magazine science.
“We were able to make an initial discovery and, through research and testing, we derived material that showed in laboratory experiments the potential not only to capture CO2 in the extreme conditions present in flue gas emissions from natural gas power plants, but without loss of selectivity, “said co-author Simon Weston, researcher and project manager at ExxonMobil Research and Engineering Co. have shown that these new materials can then be regenerated with reusable low temperature steam, providing a pathway for a viable scale carbon capture solution. “
Carbon dioxide emissions from fossil fuel vehicles, power plants and industry account for about 65% of climate change greenhouse gases, which have already raised the Earth’s average temperature by 1.8 degrees. fahrenheit (1st degree Celsius) from 19th century. Without reducing these emissions, climate scientists are predicting ever-hot temperatures, more uneven and violent storms, rising sea levels by a few feet and subsequent droughts, floods, fires, famines and conflicts.
“In fact, about the things that the Intergovernmental Panel on Climate Change is saying, we need to take action to control global warming, CO2 capture is a big part, “said Long. “We have no use for most of what2 that we must stop emitting, but we must do it. “
Power plants strip CO2 from smoke emissions today by bubbling flue gases through organic amines in water, which bind and extract carbon dioxide. The liquid is then heated to 120-150 ° C to release CO2 gas after which the liquids are reused. The whole process consumes about 30% of the energy produced. Sequestration of captured CO2 The underground costs another, albeit small, part.
Six years ago, Long and his group discovered a chemically modified MOF at the UC Berkeley Gas Separation Center, funded by the US Department of Energy, that easily captures CO2 from the power plant’s concentrated flue gas emissions, potentially halving capture costs. Diamine molecules were added to the magnesium-based MOF to catalyze the formation of CO polymer chains2 which could then be rinsed by washing with a moist stream of carbon dioxide.
Because MOFs are very porous, in this case like a honeycomb, the weight of the paper clip has an inner surface equal to the surface of a football field, all available for gas adsorption.
The main advantage of amine-linked MOFs is that amines can be tuned to capture CO2 at various concentrations, from 12% to 15% of typical emissions from coal-fired power plants to 4% typical of natural gas installations or even much lower concentrations in ambient air. The mosaic materials co-founded and managed by Long were created to make this technology widely available to energy and industrial facilities.
But 180 ° C water and CO2 it is necessary to flush the captured CO2 it eventually removes diamine molecules, shortening the life of the material. The new version uses four molecules of amines – tetraamine – which are much more stable at high temperatures and in the presence of steam.
“Tetraamines are so tightly bound within the MOF that we can use a very concentrated stream of water vapor with zero CO2and if you tried it with previous adsorbents, the steam would start destroying the material, ”said Long.
They have shown that direct contact with steam at 110 – 120 ° C – slightly above the boiling point of water – removes CO well2Steam at this temperature is readily available in natural gas power plants, while at 180 ° C2– the aqueous mixture needed to regenerate the previously modified MOF required heating, which wastes energy.
When Long, Weston, and their colleagues first considered replacing diamines with harder tetraamines, it looked like a long shot. However, the crystal structures of diamine-containing MOFs suggest that there could be ways to join two diamines to form a tetraamine while maintaining the ability of the material to polymerize CO.2When UC Berkeley, graduate student Eugene Kim, the first author of the paper, chemically created MOF with the addition of tetraamine, in the first attempt he overcame MOF with the addition of diamine.
The researchers then studied the structure of the modified MOF using an improved Berkeley Lab light source, which revealed that CO2 the polymers that line the pores of the MOF are actually connected by tetraamines, such as ladders, to tetraamines as partitions. Calculations of functional density theories using density principles using the Cori supercomputer at the Berkeley Lab National Energy Research Center (NERSC), computational resources at Molecular Foundry, and resources provided by Berkeley Research Computing on campus confirmed this remarkable structure that Long’s team had originally envisioned.
“I’ve been doing research at Cal for 23 years, and that’s one of those times when you got what seemed like a crazy idea, and it just worked right away,” Long said.
Reference: “Cooperative Carbon Capture and Steam Regeneration with Metallic-Organic Structures with Added Tetraamine” Eugene J. Kim, Rebecca L. Siegelman, Henry ZH Jiang, Alexander C. Forse, Jung-Hoon Lee, Jeffrey D. Martell, Phillip J Milner , Joseph M. Falkowski, Jeffrey B. Neaton, Jeffrey A. Reimer, Simon C. Weston and Jeffrey R. Long, 24 July 2020, science.
DOI: 10.1126 / science.abb3976
Co-authors Long, Kim and Weston are Joseph Falkowski of ExxonMobil; Rebecca Siegelman, Henry Jiang, Alexander Forse, Jeffrey Martell, Phillip Milner, Jeffrey Reimer and Jeffrey Neaton of UC Berkeley; and Jung-Hoon Lee of Berkeley Lab. Neaton and Reimer are also faculty members at the Berkeley Lab.