Synthesis of cross-linked amides and esters as thin film composite membrane materials yields permeable and selective material for water vapor/gas separation

In this work, 3,5-diaminobenzoic acid (BA) was selected to synthesize polyamide as a selective layer because it is considered desirable to fabricate hydrophilic thin film composite (TFC) membranes for water vapor separation. Cross-linked chains of TFC membranes by interfacial polymerization were suggested, confirmed and discussed by using the compiled results of characterization, such as ATR-FTIR, XPS, FE-SEM, BET surface area, TGA and water contact angle. As a result, the BA-1-10 membrane (1.0 wt% of BA, 0.2 wt% of TMC and 10 min of reaction time) showed the best permeance and separation factor as 2160 GPU and 23, respectively, compared with other TFC membranes prepared under different conditions. It was shown that with a higher concentration of BA containing carboxylic acid a faster diffusion, greater reactivity and the formation of hydrophobic esters are possible. Moreover, the acyl chloride group (-COCl) of TMC was hydrolyzed to COOH and improved the hydrophilicity for a better sorption of water vapor. However, the hydrophobic esters were generated on a selective layer due to the excessive reaction time over 10 min. It was found that the reaction time should be the same as the immersion time of the aqueous monomer to give adequate high performances.