Department of Chemical and Biochemical Engineering

Ionic Liquids for CO2 capture

Project funded by: The Danish Council for Strategic Research (DCSR), DONG Energy & Vattenfall

Contact: Associate Professor Kaj Thomsen ()
Coworkers: Erling H. Stenby DTU ChemistryCERE , Kaj Thomsen and Subham Paul - DTU Chemical EngineeringCERE
Rasmus Fehrman, Anders Riisager and Saravanamurugan Shunmugavel - DTU Chemistry - CSC  


Capturing CO2  using ionic liquids

CO2 capture is expected to become an important part of the future power production. Current technology for CO2 capture is very energy demanding. In order to make this process feasible and sustainable new technology must be developed. This project will explore an advanced technology with this potential. One or more new solvents will be identified for post combustion carbon dioxide capture. The new solvents will reduce the energy requirement of the capture process significantly, compared to current methods. Existing concepts of CO2 capture are based on the absorption of CO2 in aqueous solutions of alkanolamines, ammonia, or potassium carbonate. Alkanolamine absorption processes are available as proven technology for CO2 capture, but they are not considered long term solutions primarily due to very large energy consumption. Thus, there is an urgent need to develop smarter technologies for CO2 capture.  

The solvents suggested for CO2 capture in this project belong to a group of compounds called ionic liquids. Ionic liquids are molten salts consisting of anions and cations. Unlike common salts, ionic liquids are liquid even at temperatures below 100 °C. Ionic liquids can be designed to have specific properties, such as hydrophobicity and the ability to dissolve gases, e.g. CO2. Ionic liquids with these properties can be potential solvents for CO2. When CO2 is absorbed in common ionic liquids, CO2 molecules are stored in the cavities between the ions. No chemical process is taking place during the absorption and the amounts of energy exchanged during the absorption and the desorption processes are small compared to the present technology    


Objective of the project

The objective of this project is to find a feasible way to reduce the emission of antropogeneous carbon dioxide. In order to achieve this purpose, we are examining the feasibility of using ionic liquids for CO2 absorption. One or more  ionic liquids that can reduce the energy consumption of the CO2 capture process significantly will be identified, synthesized, and tested. The selected ionic liquids should possess generally acceptable properties concerning health, safety, and environmental impact. For the target compounds synthesis, structural characterization, CO2 absorption capacity, and thermodynamic modeling will be addressed. As these ionic liquids are new compounds, all their properties need to be determined experimentally. The required experimental work will be carried out in this project. Current technologies for CO2 capture typically require 25 % of the energy produced by the power plant. If a new, energy efficient solvent for CO2 capture can be found and a suitable process design be developed for utilizing this solvent, a global market for producing CO2 capture units will be opened.    


Expected main results of the project: 

  • Significant new understanding of the structure - property relationship for ionic liquids. 
  • Identification of potential ionic liquids as solvents for CO2 capture. 
  • Synthesis path for the selected ionic liquids. 
  • Laboratory testing of the solubility of CO2 in the selected ionic liquids. 
  • Experimental data for the thermal properties of the relevant ionic liquids.  Improved tools for modeling the properties of systems with ionic liquids. 
  • Simulation of large scale applications with ionic liquids as solvents for CO2 capture.
  • Proposal for possible process design for large scale CO2 capture.


Initially, the strategy was to synthesize new ionic liquids containing nitrogen-based functional groups which would allow chemical bonding to CO2 of moderate strength. No significant CO2 absorption was found in these ionic liquids. The synthesis strategy was therefore modified to include both a primary amine group together with a sulfonamido group in the same ionic liquid. But eventually, this ionic liquid was also found to be unable to absorb CO2 when tested in the Magnetic Suspension Balance. Finally, amino acid functionalized ionic liquids were synthesized. These were found to have good absorption capacity for CO2. They were also quite viscuous and were therefore tested as Silica Supported Ionic Liquids. After publication of the results, a link to the paper will be posted here.


This was a two year project which started in the summer of 2009 and ended August 31st 2011.


Last updated 24.02.2012