Effect of Post-Functionalization Conditions on the Carbon Dioxide Adsorption Properties of Aminosilane-Grafted Zirconia/Titania/Silica-Poly(amide-imide) Composite Hollow Fiber Sorbents

In this study, 3-aminopropyltrimethoxysilane (APS) was used as a grafting agent in three solvents with different polarities for post-functionalization of a ZrO2-TiO2-SiO2/poly(amide-imide) composite hollow fiber sorbent (Zr-Ti-Si/PAI-HF) at ambient temperature. The same fiber at two different states: (i)wet (as-spun) and (ii)dry were used for amine grafting. The influence of the polarity/nature of various solvents such as acetone, ethanol, and toluene on the CO2 sorption characteristics of wet and dry Zr-Ti-Si/PAI-HF fibers was investigated accordingly. Several parameters such as grafting time (1-4h), amine concentration (10-50wt%), and solvent type (acetone, ethanol, and toluene) were systematically varied. The CO2 sorption capacity and breakthrough tests were performed under simulated flue gas conditions for grafted fiber composites. Our results indicate that the CO2 sorption capacity of amine-grafted Zr-Ti-Si/PAI-HF strongly depends on both the type of solvent and the state of the fibers (i.e., dryness or wetness). The APSgrafting of wet fibers performed in toluene led to high amine loading and CO2 capacity (1.40mmolg(-)1), whereas dry fibers gave rise to a relatively low CO2 capacity (0.90mmolg(-)1). In contrast, dry fibers functionalized in either acetone or ethanol exhibited higher CO2 capacity compared to the wet fibers prepared in the same solvent. By using ethanol as a solvent, the solvolysis of the Si-O-Si linkages is much faster than the competitive condensation reaction between the silanol groups (Si-OH) of APS moieties and hydroxyl group (OH) of the ethanol, which leads to the lower siloxane formation. In the case of acetone, a dense polymeric network is formed under condensation reaction between an acetone molecule and the amine moieties, thus reducing the amount of primary amine groups available for interacting with the CO2 molecules.