Epoxy Cross-Linked Polyamine CO₂ Sorbents Enhanced via Hydrophobic Functionalization

Optimizing sorption capacity and amine efficiency are among the major challenges in developing solid carbon dioxide sorbents. Such materials frequently feature polyamines impregnated onto supports adding weight to the sorbents. This work presents the cross-linking of polyethyleneimine (PEI) by the industrially available epoxy resin, bisphenol-A diglycidyl ether (DER) to form support-free sorbent materials. Prior to cross-linking, the polyamine chain is functionalized with hydrophobic additives; one material modified with the branched chain hydrocarbon 2-ethylhexyl glycidyl ether displays a CO2 uptake of 0.195 g/g, 4.43 mmol CO2/g (1 atm single component CO2, 90 °C). The additive loading affects the cross-linking, with the lesser cross-linked materials showing more favorable sorption capacities and higher amine efficiencies. The type of additive also influences sorption, with the larger, longer and bulkier additives better able to free the amines from their hydrogen bonding network, generally promoting better sorption. In addition to increasing CO2 uptake, the additives also reduce the optimum sorption temperature, offering a handle to tune sorbents for specific working conditions. The best performing material shows high selectivity for CO2 sorption, and under sorption cycles in a 10% CO2/90% N2 mixture, utilizing temperature swing desorption, demonstrates a good working capacity of 9.5% CO2 uptake over the course of 29 cycles. Furthermore, humidity has been found to promote CO2 sorption at lower temperatures with a CO2 uptake of 0.235 g/g, 5.34 mmol/g (1 atm single component CO2, 25 °C) using a prehydrated sample. Overall, these findings confirm the value of our approach where cross-linking emerges as a valid and practical alternative to loading polyamines onto solid supports. This work demonstrates the versatility of these types of materials and their potential for use in large-scale carbon capture systems.