Assessing the environmental impacts of flow and batch syntheses of hypercrosslinked polymers for low-pressure CO2 adsorption

Abstract

The microporosity of hypercrosslinked polymers (HCPs) renders such materials ideal adsorbents for carbon capture. We recently showed that the CO2/N2 selectivity of HCPs synthesised by internal crosslinking of poly-α,α′-dichloro-p-xylene (p-DCX) in continuous flow synthesis was 850 % higher than those produced in batch reactions. We hypothesised that this could potentially reduce the amount of HCP adsorbents required for delivering the same carbon capture performances, hence improving the environmental impacts of carbon capture. This was evaluated here where we analysed the environmental impacts of using both batch- and flow-synthesised HCPs for adsorbing 40 mg of CO2 with the life-cycle assessment method. We also deployed this approach to evaluate HCPs synthesised via post-crosslinking of polystyrene crosslinked with DCX (p-PS-DCX) and externally crosslinking of polystyrene with formaldehyde dimethyl acetal (FDA) crosslinker (p-PS-FDA). Amongst all HCPs studied in this work, the changes in environmental impact of deploying internally crosslinked HCPs for carbon capture were the worst. This was mostly attributed to its low product yield (7 %), which had a larger influence on the environmental impacts than its adsorption performance as verified by sensitivity analysis. To offset the adverse effects of low product yield, the product yield from flow synthesis of HCPs should ideally reach 25 %. By identifying that product yield is key for promoting environmental sustainability in carbon capture using flow-derived HCPs, future work should focus on optimising continuous flow synthesis to deliver ideal product yield. Hypercrosslinked polymers (HCPs) can be deployed adsorbents for carbon capture. Here we hypothesise that one can use HCPs with better CO2/N2 selectivity to deliver the same carbon capture performances, hence improving the environmental impacts of carbon capture. This was evaluated here using batch- and flow-synthesised HCPsvia internal, external and post-crosslinking strategies with the life cycle assessment method. The environmental impacts of internally crosslinked HCPs were worst due to a low product yield of 7 % Sensitivity analyses indicated that this limitation can be overcome when HCP yield from flow synthesis reach 25 %. Future work should focus on optimising continuous flow synthesis to deliver ideal product yield for minimising environmental impacts of deploying HCPs in carbon capture.