Sequential polymer infusion into solid substrates (SPISS): Impact of processing on sorbent CO2 adsorption properties

Abstract

Solid sorbents made of small amine molecules and polyamines infused into mesoporous substrates are promising materials for CO2 capture technologies. To date, their preparation is mainly based on wet infusion with focus on increasing amine content by varying the structure of the amine sorbent and designing solid substrates of various pore parameters. Less explored in the field are changes in processing to afford efficient CO2 sorbents. In this study, branched poly(ethylenimine) (bPEI, Mw = 800 Da) alone and blends with linear poly(propylenimine) (LPPI, Mn = 6,700 Da) are infused into solid SBA-15 substrates by a method that varies the solution processing called sequential polymer infusion into solid substrates (SPISS). The reference 40 % bPEI-SBA-15 samples are split by two methods: split batch in dry suspension (SBD) and split batch in liquid suspension (SBL). Sequentially, alcoholic 10% of bPEI (non-blends) and 10% of LPPI (blends) solutions are introduced to afford the desired products. Under dry conditions, the resulting 50% bPEI-SBA-15 SBD & SBL sorbents display high CO2 capacities up to 3.47 mmol CO2/gSiO2 for simulated flue gas (10% CO2) and 2.62 mmol CO2/gSiO2 for direct air capture (DAC, 400 ppm CO2). Under humid DAC conditions the CO2 performance is further enhanced with an uptake of 4.62 mmol CO2/gSiO2 and amine efficiency of 0.22 mmol CO2/mmol N. Subjected to extended temperature swing adsorption kinetic cycling (20 cycles), the SPISS samples display stable working capacities and retain over 70% (blends) and over 90% (non-blends) of their initial 12 h adsorption performance. LPPI is demonstrated to be an effective water sorption limiting agent using dynamic vapor sorption measurements. Solid state NMR techniques reveal important insights into the dynamics of the amine polymers confined into SBA-15 pores, as impacted by processing conditions. The results suggest that the conformation of the polymers is different depending on the processing method, displaying relatively tight (SBD) and loose (SBL) packing. The simple solution processing approaches presented here show that processing variations may guide the design of solid amine sorbents with desirable properties relevant for integration into CO2 capture technologies.