Effect of humidity and nanocellulose content on Polyvinylamine-nanocellulose hybrid membranes for CO2 capture

In order to address the need for more efficient technologies for carbon capture applications, a novel type of nanocellulose based hybrid membrane has been successfully prepared by blending the commercial Polyvinylamine solution Lupamin (R) 9095 (BASF) with Nano Fibrillated Cellulose (NFC) to improve its mechanical and separation capabilities. Self-standing films with different nanocellulose loading (from 30 to 70 wt %) have been prepared and characterized at 35 degrees C through water vapor sorption experiments and humid gas permeation tests. As expected, membrane permeability consistently increased with increasing water vapor and a higher presence of Lupamin in the film resulted in an increment of both gas permeability and selectivity. In particular blends with a NFC content of 70 wt% Lupamin reached an ideal selectivity of 135 for the separation of CO2/CH4 and 218 for CO2/N-2, at 60 RH%, while the maximum permeability in the order of 187 Barrer was instead reached at 80% RH. Water vapor solubility was also measured and modeled through Park Model to correlate the gas separation properties with the effective content of water present in the membrane matrix. As expected, a higher content of the hydrophilic polymer resulted in a larger water uptake, which at medium to high humidity appeared to trigger a water clustering phenomenon in the matrix. This fact was accompanied by a substantial relaxation of the polymer network, causing a marked reduction of selectivity, which dropped, at the highest RH investigated, to values in the order of 30 and 80 towards CH4 and N-2 respectively. Despite this loss in performance, most materials tested still showed very interesting properties, well above Robeson's 2008 Upper Bound, making them an interesting alternative for traditional gas separation processes.