Researchers from ISIS Neutron and Muon Source alongside collaborators from University of Texas (El Paso), Washington State University and Pacific Northwest National Laboratory (PNNL) have studied glassification in carbon capture solvents, which causes the failure of carbon capture technologies. This work is the first paper that focuses on glassification and how working above glass transition temperature can minimize clusters and prompt more efficient testing of carbon capture and sequestration technology.
According to the Intergovernmental Panel on Climate Change, carbon capture and sequestration are the ultimate tactics which could minimize Earth warming due to elevated carbon dioxide (CO2) emissions. In the future, the aim is to develop technologies that do not emit greenhouse gases but, until that is a completely viable option, post-combustion capture technologies like solvents, membranes and porous materials are being tested.
Solvent-based technology is the most mature post-combustion carbon capture solvent technology that is undergoing testing. The advantage of using solvent-based technologies is that their formulation can be designed to reduce the amount of water used. These "water-lean" compounds exhibit unique physical and thermodynamic properties that make them more efficient. For example, by using a concentrated CO2-rich solvent, less material is heated during regeneration.
Researchers from ISIS alongside other collaborators have been studying the properties of these concentrated solvents, such as CO2-binding organic liquids (CO2BOLs). These are derived from chemicals known as alkanolguanidines. Their recent study, chosen as a 2020 HOT article in the "Physical Chemistry and Chemical Physics" journal, implements new structural measurements using ISIS instruments NIMROD and Larmor, combined with computational studies, to measure changes in the CO2BOL, 1-IPADM-2-BOL.
They began with viscosity test simulations with ''CO2-rich'' and ''CO2-lean" solvents. The same experiment was repeated with a fresh batch of 1-IPADM-2-BOL and another material with a similar chemical structure. Based on the simulations, they found that the viscosity increases in alkanolguanidine solvents coincide with the glassy state that is driven by changes in the orientation of hydrogen bond in the solution.
To explain the structural changes that were converting the 1-IPADM-2-BOL to a glassy state, the scientists used neutron diffraction on Nimrod, combined with computer simulations, to investigate the molecular and nanoscale interactions within the water-lean solvent, and observe changes in the solvent structure as the temperature was changed. They found that the glassy state is consistent with the CO2-loaded solvent.
Using Larmor to take SANS measurements to outline the behavior and properties of the solvent, they took measurements at temperatures ranging at - 5°C to 40°C. These showed the formation of large aggregates with declining temperature, and the opposite with a temperature increase.
Ultimately, they found that the heating and cooling of these clusters is reversible and temperature-dependent, much like a glass transition. They saw that the alkanolguanidine solvents, such as 1-IPADM-2-BOL, show a first-order phase transition at 40°C, which is near to the absorption temperature for post-combustion CO2 capture processes.
Although further research has to be conducted into this area, the molecular-level understanding of alkanolguanidine-based solvents is crucial in exploiting commercial operations that help lessen carbon emissions.
When asked about the impact of the work Dr David J Heldebrant, from PNNL, explains, "Climate change is a global challenge that will require multinational approaches to solve. This international collaboration between our team and the world-class scientists using cutting edge instrumentation and analytical capabilities at ISIS was paramount to making this study of the behavior of carbon capture solvents a success."
This research is based on work supported by the U.S. Department of Energy, Office of Science Basic Energy Sciences Early Career Research Program FWP 67038 in the Chemical Sciences, Geoscience, and Biosciences (CSGB) Division.
The full publication can be found here: https://doi.org/10.1039/D0CP03503C