Effect of Synthesis Parameters on Structural Characteristics of Polysulfone Membrane and its Gas Separation Properties

Abstract

In this study the effects of water/solvent mixture as coagulation medium with different solvent content, coagulation bath temperature (CBT) and coagulant type on the performance, morphology and thermal stability of polysulfone membranes were investigated. SEM and TGA techniques were used to characterize the fabricated membranes. Based on the obtained SEM images, decreasing of water/N,N-dimethyl acetamide (DMAc) ratio as coagulation medium from pure water to mixture of 90 vol.% DMAc and 10 vol.% water, resulted in completely disappearing of macrovoids. Gas permeation test results showed that by addition of solvent into the coagulation bath, H2/CH4 and H2/N2 permselectivities) reduced dramatically from 46.3 to 16.1 and 51.0 to 18.5, respectively. By the way, reducing the CBT from 80°C to 5°C led to elimination of macrovoids as well as attaining high thermal stability. As an interesting result, the membrane prepared at the CBT of 25°C showed the best gas separation performance with permselectivities of 46.3 and 51.0 for H2/CH4 and H2/N2 respectively, and H2 permeance of 25 GPU. Using methanol as coagulant resulted in less selective membrane compared with those prepared using ethanol and water. On the other hand, the H2 permeance of the former case was about 3 and 9 times more than those prepared using ethanol and water as coagulant, respectively. Obtained membrane with methanol revealed the lower thermal stability than those of ethanol and water.