Facilitated acetylene transfer through membranes composed of sulfonate-containing aromatic polyamides and poly-N-vinylamides involving nanocluster silver

Abstract

Abstract A series of approaches was considered to facilitate acetylene transfer in comparison with methane through membranes based on aromatic polyamides. One of the approaches is variation of composition of the rigid-chain polymer by progressive introduction of bulky sulfonic acid groups in chains. An effect of the polymer structure was found on the internal structure of the films made of sulfonate-containing polyamides. The variation of content of sulfonate-containing fragments results in the formation of channels of different types which provide selective transport of acetylene. There are several compositions of aromatic polyamides which form films with a higher selectivity of transport of acetylene in comparison with methane ( α =4–6). The films made of a mixture of the aromatic polyamide together with another polymer such as poly- N -vinylpyrrolidone or poly- N -vinylcaprolactam with a high local concentration of amide groups do not reveal a marked selective transfer of acetylene relative to methane. In order to facilitate acetylene transfer through the polyamide membranes, their modification by AgNO 3 aqueous solutions was performed. It is interesting to note that the modification effect on acetylene transfer through the films was observed only for films made of a mixture of two polymers: sulfonate-containing aromatic polyamide and poly- N -vinylcaprolactam (PVCL). Both content of sulfonic acid groups in the film-forming polyamide and that of the second PVCL in the mixture affect permeability and selectivity for acetylene in comparison with methane. Unlike methane, the acetylene transfer occurs even at room temperature, whereas the permeability of both acetylene and methane through unmodified films is just realised at higher temperature (140–160°C). The considerable increase of acetylene permeability is explained by formation of silver nanoclusters in the slightly swollen matrix. The presence of macromolecules of PVCL in the mixture is necessary as they are likely to be stabilizers forming metal clusters of a certain size. Metal silver clusters synthesized ‘in situ’ in the presence of the polymers facilitate the transfer of acetylene unlike methane due to an increase of acetylene solubility. We propose that acetylene molecules interact with positive surface charges of silver particles being in channels of such modified films. In addition, the role of water molecules in the acetylene transfer is likely to be essential.