Evaluation of electrospun nanofibrous mats as materials for CO2 capture: A feasibility study on functionalized poly(acrylonitrile) (PAN)

We fabricated a new type of nanostructured materials for CO2 capture processes, based on poly (acrylonitrile), PAN, a polymer almost impermeable to CO2, but easily functionalizable and spinnable. The preparation involved amine functionalization of PAN powder, electrospinning of the powder to form a nanofibrous mat with a large surface area, and compression of the mat to obtain dense membranes for facilitated transport of humid CO2. The functionalization step was carried out with different routes: amination with hexamethylene diamine or ethylene diamine, and basic hydrolysis. The final amine content in the polymer could be tuned varying the reaction type and conditions, although high functionalization degrees led to crosslinking, which made the powder insoluble. The dry CO2uptake was measured at various stages of the preparation, in order to assess separately the effect of chemical functionalization and surface area enhancement on the material capture ability. Such tests indicated that both chemical and morphological changes of the neat polymer enhanced the dry CO2sorption capacity, although the increase of surface area yielded the largest improvement. CO2permeation tests in humid conditions were carried out on the compacted membranes, indicating that the materials functionalized via direct amination exhibit a behavior compatible with the facilitated transport mechanism, with CO2permeability reaching 83 Barrer, increasing by 17 times with respect to the dry state value, at a relative humidity of 50%. Membranes functionalized via hydrolysis did not show such a behavior, maybe because the amine functionalities were consumed by an unwanted reaction. The procedure can be further improved by optimizing each processing step, or changing the order of the steps. The electrospinning process seemed the key factor of the approach, as the large surface area of electrospun mats allowed to obtain membranes with a higher permeability than the original ones, and a large availability of amine groups useful for humid CO2capture.