Solvent technology – environmental issues (Task 2)

This Task addresses the challenges related to solvent technology, with a focus on environmental issues.

We work to better understand the degradation of solvents by investigating which factors have the highest impact on the stability of amines (organic compound derived from ammonia), which are used to capture CO2 from various flue gas sources.

The work also helps to reduce operational- and investment cost by indicating amines with higher stability and developing technologies to control and monitor solvent stability. Higher stability of solvent means reduced cost, reduced emissions, improved lifetime of both material and solvent, improved safety for employees and reduced environmental impact.

Results 2021

Solvent management by using degradation mitigation technologies

As solvent degradation leads to increased capture cost and environmental issues, several different mitigation technologies are being studied. In 2021, the technology readiness for the three degradation mitigation technologies has been increased.

For example in 2021, the dissolved oxygen removal apparatus (DORA) was successfully tested at TRL level 4, using TNO's ODIN (Oxygen Depletion Installation) for the dense layer membrane. DORA was tested for both MEA and CESAR 1, and oxygen removal was achieved in both solvents. DORA operates using a porous membrane, and the skid design for testing (skid design and start of construction) at Waste-to-Energy plant in the Netherlands is ready. The skid construction is on-going and the test itself will start in early 2022 (successful testing will result in TRL 7). The results for the dense layer at TRL 4 and porous membrane at TRL 6 were presented in a paper in the International Journal of Greenhouse Gas Control.

Furthermore, the proof-of-concept of in-situ iron removal was also achieved in 2021, and the patent was filled. As iron is believed to have an essential role in accelerating solvents' degradation, removing it could significantly reduce solvent loss.

Finally, the work with the oxidative degradation inhibitor continued in 2021. The results from the small-scale lab experiments performed in 2020 were published in Chemical Engineering Science. The inhibitor was also tested in a circulative solvent degradation rig in order to understand how well the inhibitor performs in more realistic process conditions and raise the concept to TRL-level 3. The test campaign showed slightly less amine loss at standard operating conditions than the non-inhibited campaign. However, the inhibitor influenced the degradation mechanism, reducing the formation of some degradation compounds while others increased. An evaluation will be performed in 2022 to identify any operating windows where the inhibitor performs well. The results from this evaluation will decide if the developed salt concept should be taken to a pilot scale.

Understanding of solvent degradation

This is an ongoing work that resulted in several scientific publications in 2021. The findings related to the impact of the amine's structural feature on oxidative degradation were presented in Industrial & Engineering Chemistry Research. The work showed that steric effects play a large role in stabilising the amines under oxidative conditions, and carbamate formation plays a vital part in the degradation pathway of some solvents.

A review paper on the pilot plant testing of amine solvents for post-combustion CO₂ capture was published in the International Journal of Greenhouse Gas Control 2021 (accepted for publication in 2020). It summarised the lessons learned in different pilot campaigns and provided recommendations on how solvent stability and emissions can be monitored and assessed.

Models to predict solvent degradation are needed in order to understand how different process conditions influence solvent degradation. Furthermore, degradation models could support and, to some extent, replace time-consuming and costly degradation experiments. Literature data was used to develop a thermal degradation model, describing the typical reactions that occur in the desorber for 2-ethanolamine (MEA). The results were presented at PCCC-6 conference.

Impact and innovations from 2021

The solvent technologies developed in Task 2 will positively impact the cost of CO₂ capture and CCS. The developed solvent management technologies (DORA, in-situ iron removal, and stable salts as degradation inhibitors) aim to reduce solvent loss through reduced solvent degradation. Reduced solvent degradation directly reduces operational costs, environmental impact, and the amount of waste produced.

Figure 1: PID and picture of the DORA skid under construction.
Figure 1: PID and picture of the DORA skid under construction.

Results 2020

Solvent management by using degradation mitigation technologies

As solvent degradation leads to increased capture cost and environmental issues, we study several different mitigation technologies. For example, a dissolved oxygen removal apparatus (DORA) was successfully tested at TRL-level 6 at PlantOne in Rotterdam in 2020. Typically, the concentrations of degradation compounds increase with increasing pilot-hours. However, with DORA in use, stable concentrations of degradation compounds were seen. Our preliminary assessment shows that DORA is an economically viable solution for controlling the degradation of CO2 capture solvents in a large-scale plant and could be applied independently or combined with a reclaimer unit, as part of the plant solvent management strategy.

The proof-of-principle of in-situ iron removal was also achieved in 2020. As iron is believed to have an essential role in accelerating solvents' degradation, removing it could significantly reduce solvent loss.

Finally, in 2020 we identified a salt that leads to significant inhibition of oxidative degradation of MEA-solvent when added in small concentrations (~2wt%). Several salts did show increased chemical stability of aqueous MEA under oxidative degradation. The addition of the best performing salt into MEA-solvent did not reduce the solvent's absorption capacity, nor did it increase the solvent viscosity or changed the thermal degradation behaviour. The results suggest that adding a small concentration of specific salt into MEA-solvent can reduce oxidative degradation without deranging neither CO2 solubility nor its mass transfer rates. This is excellent news. In 2020, the idea was taken from TRL0 to TRL3. The results will be shared with the CO2 capture community in a gold-open access journal publication.

In 2021, the work will continue, and the technology is taken to higher TRL-levels. We will run a campaign in the circulative solvent degradation rig to understand how the salt behaves in a circulative, temperature swing process. After that, we are ready to take the salt-concept to a pilot scale.

: Amine conservation (%) as a function of time (days) for oxidative degradation experiments without (red markers - basecase) and with various salts added (yellow, green, blue).
: Amine conservation (%) as a function of time (days) for oxidative degradation experiments without (red markers - basecase) and with various salts added (yellow, green, blue).

Main results 2019

The technology developed in Task 2 will positively impact CCS' already positive effect on the environment and reduce CCS costs through developing more stable solvents with longer lifespans.

Oxygen solubility

Throughout 2019 different factors influencing oxygen solubility have been investigated and several methods to measure oxygen solubility have been evaluated. Oxygen reduces the stability of the solvent and if oxygen solubility could be measured and if a correlation between oxygen solubility and degradation could be identified, a faster method to evaluate chemical stability of new solvents would be available. The limitations and opportunities with online oxygen sensors have been identified and recommendations for their applicability were made. Online oxygen sensors (analytical instrument measuring oxygen concentration) have shown to be very useful for stable solvents, while measurements of oxygen concentration in fast degrading solvents is challenging with all available measurement methods.

DORA - Dissolved oxygen removal apparatus

Oxygen from the flue gas is a contributor to decomposition of amine solvents, the decomposition mechanism is also more difficult to follow since the initial step involves radical reactions. We've performed lab scale experiments to demonstrate Dissolved oxygen removal apparatus' (DORA)  ability to reduce oxygen concentration in the solvent. It was demonstrated that ammonia concentration is reduced when DORA is used, which indicate less decomposition of the solvent. The technology has been qualified for testing at a larger scale pilot campaign (1 kg CO2/hour) for a longer time period to take place in 2020.

Technologies like DORA is an example of both the cost and environment aspect of CCS. Our results thus far show that DORA will reduce solvent loss through mitigating solvent degradation. Less solvent loss means less environmental impact and costs saved, e.g. by not having to handle as much waste and consuming less solvents.

PLS-model validated

The Partial Least Square (PLS) model (statistical method used to evaluate data sets) developed in Task 2 in 2018, was validated in 2019 using samples from pilot projects around the world. It was proved that the PLS-model accurately predicts the concentrations of ethanolamine (MEA) and CO2 in the solvent, these components are important input to daily operation of the pilot plant. It can therefore potentially be used for online solvent analysis using Fourier-transform infrared spectroscopy (FT-IR) technology. Infrared spectroscopy exploits the fact that molecules absorb frequencies that are characteristic of their structure and functional groups give rise to characteristic bands both in terms of intensity and position (frequency). For gas samples, this is a technology that is used to monitor emissions from process industry overall the world.

Illustrating 2019's main results – Score plot from Principal Component Analysis (statistical method to investigate dataset) over different lab experiments (batch and solvent degradation rig- SDR) and Tiller pilot (x-axes-Principal Component 1, y-axes-Principal Component 2). The figure shows that the open batch lab-scale experiments at low O2, in regard to degradation compounds profile, shows highest resemblance to cycled experiment (SDR) and pilot demonstration (Tiller).

Main Results 2018

Main Results

  • Verification of experimental set-up for degradation tests and oxygen solubility.
  • Effect of amine concentration, loading and temperature on O2-solubility studied.
  • Guidelines/lessons learned for evaluating solvent stability presented
  • PLS model tested on real/aged MEA samples from bench scale experiments to large Pilot Plant.
  • Developed techniques for oxygen removal showed good results with removal rate above 80% obtained.
  • Test and scale up study of oxygen removal techniques performed

Impact and innovations

  • Observation from pilot plant operations in several capture plants shows that there is a correlation between the level of dissolved oxygen in the rich absorption liquid and the degradation profile. Reduction /removal of dissolved oxygen can significantly reduce solvent degradation and then reducing operational problems and cost of carbon capture plants using amine technology.
  • Reaction schemes for MEA or other amines are transferable to other amines. Data from pilots, especially, for MEA is currently available and could be used to verify different laboratory set-ups.
Figure illustrating 2018's main results: DORA LL MODE, Sodium Sulphite as scavanger

Results 2017

One of the drawbacks for post-combustion CO2 capture with solvent technology is that absorption capacity of a solvent is reduced because of for example degradation. This mean that unwanted chemical reactions (degradation) occur in addition to the CO2 absorption and desorption reaction.

Different strategies are used to reduce unwanted reactions:

  • Development of mitigation technologies to reduce degradation
  • Development of new experimental methodologies to predict chemicals stability of new solvents at process conditions
  • Gathering of knowledge on relation between amine structure and chemical stability. In addition, online monitoring of the solvent status in the process has been a focus

The main results from 2017:

  • Successful proof-of-principle of the oxygen removal concept (mitigation technology)
  • New methodology has been suggested for evaluation of chemical stability of solvents
  • Several amine structures sensitive to degradation have been identified
  • The existing Partial Least Square (PLS) model used to evaluate solvent status has been improved


See also other NCCS Publications registered in Cristin, the Norwegian Research Information system.

Journal Publications




Conference Publications


  • Impact of Dissolved Oxygen Removal on Solvent Degradation for Post-combustion CO2 Capture - R. V. Figueiredo, T. Srivastava, T. Skaar, N. Warning, P. Gravesteijn, P. van Os, L. Ansaloni, L. Deng, H. K.  Knuutila, J. Monteiro, E. Goetheer. 15th International Conference on Greenhouse Gas Control Technologies, GHGT-15 Abu Dhabi, UAE
  • Experimental assessment of the environmental impact of ethanolamine - V. Buvik, R. Strimbeck, H. K. Knuutila. TCCS-11 conference, Trondheim, Norway
  • Introduction of Potassium Iodide as an inhibitor for oxidative degradation of amines - V. Buvik, S.  Thorstad, R. R. Wanderley, H. K. Knuutila. TCCS-11 conference, Trondheim, Norway
  • Modelling and evaluating carbamate polymerization of monoethanolamine in post-combustion carbon capture - L. Braakhuis, H. K. Knuutila. TCCS-11 conference, Trondheim, Norway
  • Evaluation of results from SDR campaigns and pilot data - S. J. Vevelstad, A. Grimstvedt, G. Haugen, M. Wiig, K. Vernstad. TCCS-11 conference, Trondheim, Norway
  • Techno-economic performance of DORA with MEA and CESAR1 - T. Srivastava, R. V. Figueiredo, T. Skaar, N.  Warning, P. Gravesteijn, J. Monteiro, P. van Os, E. Goetheer. TCCS-11 conference, Trondheim, Norway


  • Oxidative and biological degradability of aqueous amine solvents for CO2 capture - V. Buvik, S. J. Vevelstad, H. K. Knuutila. University of Texas 5th Conference on Carbon Capture and Storage, UTCCS-5


  • De-oxygenation as countermeasure for the reduction of oxidative degradation of CO2 capture solvents - R. V. Figueiredo, D. Bakker, A. Huizinga, J. Monteiro, E. Goetheer. TCCS-10 conference, Trondheim, Norway
  • Short-cut oxidative degradation test for CO2 capture solvents - J. Monteiro, P. Gravesteijn, E. Goetheer. TCCS-10 conference, Trondheim, Norway
  • Comparison of oxidative degradation and biodegradability of aqueous amine solvents for CO2 capture - V. Buvik, S. J. Vevelstad, H. K. Knuutila. TCCS-10 conference, Trondheim, Norway
  • Oxygen solubility of amine solutions - V. Buvik, S. J. Vevelstad, H. K. Knuutila. PCCC-5 conference, Kyoto, Japan


  • O2 solubility and oxidative degradability of aqueous amine solutions for CO2 capture - V. Buvik, S.J. Vevelstad, H.K. Knuutila. GHGT-14, Melbourne
  • Multi-component analysis of liquid samples by FTIR - A. Grimstvedt, M. Wiig, A. Einbu, S.J. Vevelstad. GHGT-14, Melbourne
  • Review of oxidative degradation of 30 wt. % MEA in pilot campaigns- V. Buvik, H.K. Knuutila. University of Texas 4th Conference on Carbon Capture and Storage UTCCS-4

Pop Science Articles


  • When little things have a big impact - V. Buvik, H. K. Knuttila, NTNU TekNat (blog) 2021.02.19


  • Etter-forbrenning fangst (post-combustion) av CO2 - Potensiale og utfordringer - Vevelstad S.J., #SINTEFBlog, 2019.09.12
  • FTIR combined with multivariate analysis for monitoring of solvent composition in CO2 capture plant - Grimstvedt A., #SINTEFBlog, 2019.09.03

Task leader