Additives, Silica-PEI Preparation and Screening
Solid Adsorbent Optimisation
Silica-PEI formulations prepared at a lab-scale using the candidate silica and PEI samples from WP1 and 2 will be screened using thermogravimetric analysis (TGA) to assess CO2 adsorption capacities and the rate of adsorption and the heats of adsorption. It is hoped to identify mesoporous silicas close to 2 ml/g, which should result in an achievable PEI loading of 50 %.
Antioxidants in the formulation will need to be involatile to prevent any loss during regeneration. Preliminary work has demonstrated that borax (sodium tetraborate decahydrate) and sodium salicylate reduce oxidation rates by ca. 70-80%, with borax also reducing moisture co-adsorption. Other candidates will also be investigated.
Chelating agents for complexing the trace metals, notably Fe and Cu, that catalyse the oxidation of PEI have been found to be effective at reducing the extent of oxidation by over 90% when used in conjunction with alkoxylation of primary amines, (Min et al., 2018).
Surfactants which serve to reduce PEI viscosity and increase CO2 adsorption capacities and the rate of uptake. Surfactants are preferred to polyethylene glycols for this purpose because much lower concentrations are required. The improvements for the optimal silica-PEI formulations will be determined, limiting the concentration of surfactant to no more than 10% of that for PEI.
The economically most effective combination of these additives will be identified and will be used in the larger-scale preparations for pilot-scale testing.