Oxidative degradation is the main degradation mechanism for amine-based solvents. It is responsible for about 70% of the total amine losses, leading to a decrease in CO₂ absorption capacity of the solvent and limits its lifetime. The costs associated with solvent degradation for solvent make-up, operation of reclaiming systems and waste disposal represent a major contribution to the operational expenses of capture plants. Moreover, degradation products can lead to equipment corrosion and increase the effort for emission mitigation of volatile degradation products of amines, like ammonia.

In the Accelerating CCS Technologies ACT1 project ALIGN-CCUS, the Dutch research organization TNO has developed and patented the Dissolved Oxygen Removal Apparatus (DORA). A membrane contactor, containing a bundle of hollow fibers, is used to remove O₂ that is dissolved from the flue gas in the solvent before the solvent enters the thermal regeneration step in the stripper column (desorber), to prevent degradation and prolong the solvent lifetime. The membrane is operated in liquid-gas mode, meaning that the liquid solvent runs on the shell side of hollow fiber membranes. A sweeping gas – N₂ or CO₂ – in combination with a vacuum is used on the tube side of the membrane to promote oxygen transfer through the membrane. 

The DORA concept is designed to be solvent-independent, but its deployment might be hindered by long-term stability issues associated with the operation of porous membrane contactors.  Therefore, long-term tests are of greatest importance to advance the DORA technology and make it market ready to be applied at different CO₂ capture facilities regardless of the solvent, flue gas or plant size.

The recently started three-year ACT4 project MeDORA will demonstrate long-term operation of the DORA technology using porous membranes and advanced coated membranes aiming at extended lifetime. MeDORA is a collaboration between SINTEF as coordinator, RWE Power AG, TNO and N.V. HVC, the Norwegian University of Science and Technology (NTNU), and Aker Carbon Capture AS. The project aims to reduce oxidative degradation by 90%, resulting in major benefits in terms of operational costs in relation to solvent management and environmental impact of the capture plant. Additionally, it is intended to reduce the oxygen content in the CO₂ product to less than 10 ppm. The promising technology will be validated in 24/7 long-time capture plant tests – in total ca. 20,000 testing hours – using fully representative industrial flue gasses from RWE’s lignite-fired power plant at Niederaussem, Germany and from HVC’s Waste-to-Energy plant in Alkmaar, The Netherlands. The complete solvent flow in the capture plants will be treated by membrane contactors over representative periods.