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

A series of approaches was considered to facilitate acetylene transfer in c omparison 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 effec t of the polymer structure was found on the internal structure of the films made of sulfonate-containing polyamides. The variation of content of sulfo nate-containing fragments results in the formation of channels of different types which provide selective transport of acetylene. There are several co mpositions of aromatic polyamides which form films with a higher selectivit y of transport of acetylene in comparison with methane (alpha = 4-6). The f ilms made of a mixture of the aromatic polyamide together with another poly mer such as poly-N-vinylpyrrolidone or poly-N-vinylcaprolactam with a high local concentration of amide groups do not reveal a marked selective transf er of acetylene relative to methane. In order to facilitate acetylene trans fer through the polyamide membranes, their modification by AgNO3 aqueous so lutions was performed. it is interesting to note that the modification effe ct 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 p ermeability and selectivity for acetylene in comparison with methane. Unlik e methane, the acetyltene 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 degreesC). The considerable i ncrease of acetylene permeability is explained by formation of silver nanoc lusters in the slightly swollen matrix. The presence of macromolecules of P VCL in the mixture is necessary as they are likely to be stabilizers formin g metal clusters of a certain size. Metal silver clusters synthesized 'in s itu' in the presence of the polymers facilitate the transfer of acetylene u nlike methane due to an increase of acetylene solubility. We propose that a cetylene molecules interact with positive surface charges of silver particl es being in channels of such modified films. In addition, the role of water molecules in the acetylene transfer is likely to be essential. (C) 2001 El sevier Science B.V. All rights reserved.