Formation of Asymmetric Polysulfone Flat Sheet Membrane for Gas Separation: Rheological Assessment

Abstract

Kajian ini memfokuskan kepada kesan kadar ricih ke atas struktur membran asimetrik polisulfona dan prestasi pemisahan gas. Membran asimetrik kepingan rata dibentukkan dengan mengunakan satu larutan pertigaan yang optima. Membran asimetrik yang mempunyai lapisan kulit bermolekul terhala disediakan melalui satu teknik fasa balikan kering/basah yang ringkas bersertakan olakan paksaan menggunakan sistem tuangan kawalan Pneumatik yang baru dibangunkan. Ujikaji yang dijalankan juga menumpukan kepada perbezaan kelajuan tuangan yang mewakili keadaan reologi yang berlainan. Kelajuan tuangan dibezakan dari 5 saat hingga ke 60 saat, diketahui bahawa pengubahan kelajuan tuangan boleh mengubah kadar ricihan. Halaan molekul teraruh secara reologi atas lapisan kulit membran diukur menggunakan spektroskopi jumlah pantulan terkecil jelmaan fourier (ATR–FTIR) untuk menguji sama ada kadar ricih yang tinggi berupaya mempengaruhkan tak isotropi peringkat molekul pada membran. Keputusan reologikal ini juga dikaitkan kepada prestasi pemisahan gas dengan 4 jenis gas tulen yang berlainan. Keputusan menunjukkan bahawa membran asimetrik ricihan tinggi cenderung mempamerkan penghalaan molekul yang lebih ketara dalam lapisan kulit. Dengan peningkatan kelajuan, kadar ricihan pada lapisan permukaan membran juga ditingkatkan. Keadaan ini telah menyebabkan peningkatan penghalaan molekul yang lebih ketara dalam lapisan kulit. Oleh sebab itu, kememilihan gas O₂/N₂ and CO₂/CH₄ dipertingkatkan dengan peningkatan kadar ricih dan lebih ketara dibandingkan dengan nilai kememilihan hakiki. Kata kunci: Polisulfona, membran asimmetrik, pemisahan gas, reologi, kadar ricih This study was focused on the effect of shear rate on asymmetric polysulfone membrane structure and gas separation performance. Flat sheet asymmetric membranes were formed using an optimized ternary casting solution. The asymmetric membranes with the molecular–oriented skin layer were prepared by a simple dry/wet phase inversion technique with forced convection using a newly developed Pneumatically–controlled casting system. Experimental investigation was conducted focusing on different casting speed, thus representing different rheological conditions. Casting speed was varied from 5s to 60s, as known that varying casting speed would vary shear rate. Rheologically induced molecular orientation on the skin layer of membrane was measured using fourier transform attenuated total reflection spectroscopy (ATR–FTIR) to examine whether higher shear rate may induce anisotropy at the molecular level of the membrane. These rheological results were then correlated to the gas separation performance in four different pure gases. The results indicated that the highly sheared asymmetric membranes tend to exhibit greater molecular orientation in the skin layer. As the casting speed increased, the level of shear experienced on the membrane surface layer also increased, thus this was leading to greater molecular orientation in the skin layer. Hence, the gas selectivities of O₂/N₂ and CO₂/CH₄ significantly increase with an increase in the shear rate and were greater than that of the recognized intrinsic value. Key words: Polysulfone, asymmetric membrane, gas separation, rheological, shear rate