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Abstract
The need to create a new approach to carbon capture processes that are economically viable has led to the design and synthesis of sorbents that selectively capture carbon dioxide by physisorption. Solid Ionic Liquids (SoILs) were targeted because of their tunable properties and solid form under operational conditions. Molecular modelling was used to identify candidate SoILs and a number of materials based on the low cost, environmentally friendly acetate anion were selected. The materials showed excellent selectivity for carbon dioxide over nitrogen and oxygen and moderate sorption capacity. However, the rate of capture was extremely fast, in the order of a few seconds for a complete adsorb-desorb cycle, under pressure swing conditions from 1 to 10 bar. This showed the importance of rate of sorption cycling over capacity and demonstrates that smaller inventories of sorbents and smaller process equipment are required to capture low concentration CO2 streams. Concentrated CO2 was isolated by releasing the pressure back to atmospheric. The low volatility and thermal stability of SoILs mean that both plant costs and materials costs can be reduced and plant size considerably reduced.
Highlights
One of the key challenges facing Carbon Capture and Storage (CCS), and any carbon dioxide emission mitigation strategy, is the separation and puri cation of carbon dioxide from dilute gas streams
When considering physisorption processes for CO2 capture, ionic liquids (ILs) have emerged over the last decade to be prominent as an area of active research. These molecular organic salts (MOSs) show the high selectivity behaviour that is required for effective CO2 separation and are inherently tuneable in their syntheses to allow for task-speci c compounds to be developed.[4]
Because the interaction is between the cation and the oxygen on CO2 there is no distortion of the molecule, suggesting that the cation does not promote CO2 activation but that it does stabilise the ion–gas complex
Summary
One of the key challenges facing Carbon Capture and Storage (CCS), and any carbon dioxide emission mitigation strategy, is the separation and puri cation of carbon dioxide from dilute gas streams. When considering physisorption processes for CO2 capture, ionic liquids (ILs) have emerged over the last decade to be prominent as an area of active research These molecular organic salts (MOSs) show the high selectivity behaviour that is required for effective CO2 separation and are inherently tuneable in their syntheses to allow for task-speci c compounds to be developed.[4] they have the bene t of low vapour pressures at room temperature and show negligible volatility. The anion used was acetate, which has previously been shown to enable a high degree of CO2 solubility in RTILs and minimises cost by avoiding more complex anions such as PF6, BF4 and NTf2, which are typically used to promote low melting points.[21] A preliminary computational simulation was carried out to determine interaction energies between the ILs and CO2 These showed that acetate was a good candidate anion as it gave a moderate binding energy with CO2, indicating reasonable selectivity but with low-energy regenerative desorption of the gas. Desorption rates were measured by on-balance depressurisation timed using a stopwatch
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