Decarbonisation Technology - February 2023

capture focuses mainly on IL-water solutions, IL-alkanolamine blends, IL-organic solvents, and IL-IL mixtures (Gomez-Coma, Garea and Irabien, 2016), (Cao, et al., 2017) (Li, et al. 2014), (Yang, et al., 2017). Ionic liquids: recent novel applications Four examples of research paths showing improved CO 2 separation and economics through the use of ionic liquids and their blends with solvents are:  Bernard et al (2021) explore the use of encapsulated RTILs in CO 2 capture and describe the preparation of encapsulated imidazolium- based fluorinated RTILs. Specifically, [Emim][TF 2 N], [Bmim][TF 2 N], and [Hmim][TF 2 N] RTILs were encapsulated in polysulfone (PSF) using an emulsification method and characterised by several techniques. The pressure-decay technique was used to assess the CO 2 sorption capacity and reusability. These encapsulated RTILs showed improved utility for CO 2 capture processes compared with non-encapsulated RTILs, with higher CO 2 sorption capacity and faster CO 2 sorption/desorption. The CO 2 absorption/desorption cycles demonstrated the reusability of all microcapsules under mild conditions. The highest CO 2 sorption capacity was noted for encapsulated [Emim][TF 2 N] (39.5 mg CO 2 g − 1 at 298.15 K and 1 bar; 62.7 mg CO 2 g − 1 at 298.15 K and 10 bar). The encapsulated [Emim][TF 2 N] contained a lower ionic liquid content (37.5. ± 0.6) when compared to other encapsulated samples. Moreover, encapsulated [Emim][TF 2 N] presented a higher CO 2 affinity than the encapsulated ILs previously reported. All the encapsulated RTILs showed high stability and reuse capacity in CO 2 capture processes (Bernard, et a l., 2021).  New porous ionic liquids, based on the ZIF-8 metal-organic framework (MOF) and phosphonium acetate or levulinate salts, show an increased capacity to absorb CO 2 at low pressures. Porous suspensions based on phosphonium levulinate ionic liquid absorb reversibly 103% more CO 2 per mass than pure ZIF-8 at 1 bar and 303 K. The study showed how the rational combination of MOFs with ionic liquids could greatly enhance low-pressure CO 2 absorption, paving the way towards a new generation of high-performance, readily available

liquid materials for effective low-pressure carbon capture (Avila, et al., 2021).  Vadillo and colleagues presented a carbon capture technology strategy based on non- dispersive CO 2 absorption and membrane vacuum regeneration (MVR), comparing two imidazolium ionic liquids with different CO 2 absorption behaviours: chemical absorption with [emim][Ac] and physical absorption with [emim][MS]. Polypropylene hollow fibre membrane contactors were used to conduct continuous absorption-desorption experiments. The chemical IL, [emim][Ac], showed the highest desorption behaviour with an MVR performance efficiency of 92%, 9% more than the physical IL under the same conditions (313 K and 0.04 bar). The MVR technology increased the overall CO 2 capture performance by up to 61% for [emim][Ac] and 21% for [emim][MS]. The authors concluded that these results merit further work on MVR technology with chemical ILs, but additional techno-economic evaluation is needed to ensure the competitiveness of this CO 2 desorption approach for large-scale application (Vadillo, et al., 2022).  Mihaila et al report on the application of deep eutectic solvents (DESs). The CO2 absorption- desorption capacity of two choline chloride- based DES, ethaline (ChCl:EG, 1:2 molar ratio) and reline (ChCl:U,1:2 molar ratio), was studied. The tests showed that ethaline had 3x better CO 2 absorption and desorption capacity than reline, attributed to weaker intermolecular interactions, which lead to a larger free volume and lower density and viscosity than reline. Increasing temperature and pressure increases the absorption capacity of the two eutectics due to physical changes (lower viscosity and density), allowing easier penetration of the CO 2 molecule into the ‘eutectic cage’. Conversely, reducing temperature and pressure induces desorption. This project is at the demonstration stage (Mihaila, et al ., 2021). Cryogenic carbon capture Cryogenic carbon capture (CCC) represents a rapidly developing and highly competitive CCS option. One author considered the CCC process to have the greatest potential of all the carbon capture processes (Herzog, 2018). Low-temperature CO 2 capture technologies