Abstract
Facilitated transport membranes obtained by coupling polyvinylamine with highly charged carboxymethylated nanocellulose fibers were studied considering both water sorption and gas permeation experiments. In particular, the effect of the L-arginine as a mobile carrier was investigated to understand possible improvements in CO2 transport across the membranes. The results show that L-arginine addition decreases the water uptake of the membrane, due to the lower polyvinylamine content, but was able to improve the CO2 transport. Tests carried on at 35 °C and high relative humidity indeed showed an increase of both CO2 permeability and selectivity with respect to nitrogen and methane. In particular, the CO2 permeability increased from 160 to about 340 Barrer when arginine loading was increased from 0 to 45 wt%. In the same conditions, selectivity with respect to nitrogen was more than doubled, increasing from 20 to 45. Minor improvements were instead obtained with respect to methane; CO2/CH4 selectivity, indeed, even in presence of the mobile carrier, was limited to about 20.
Highlights
The increased awareness of issues related to global warming has in recent years generated a strong push towards the reduction of greenhouse gas emissions in the atmosphere [1,2]
The results show that L-arginine addition decreases the water uptake of the membrane, due to the lower polyvinylamine content, but was able to improve the CO2 transport
The infrared spectra of the different membranes considered in the present work are reported in Figures 3 and 4, together with those of the materials used for blending, that is, carboxymethylated nanofibrillated cellulose (cNFC), PVAm and L-arginine
Summary
The increased awareness of issues related to global warming has in recent years generated a strong push towards the reduction of greenhouse gas emissions in the atmosphere [1,2]. FTMs rely on the interaction of the target molecules with fixed or mobile carriers, which are able to transport them from one side of the membrane to the other, creating an additional transport mechanism, which can overcome most of the limitations of solution diffusion membranes [12,13,14]. For acidic gases such as carbon dioxide, the considered carriers are often based on alkaline species such as salts, aminated compounds and amino acids [15,16,17,18,19]. Aminated polymers in particular have been used as base materials for a number of membranes due to the possibility of transporting CO2 through different pathways, related to the formation of bicarbonate (II) or carbamate ions (I) [14,20,21]: (I) CO2 + H2O + R–NH2 HCO3− + R–NH3+
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